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+44 1803 865913
By: Antoinette M Mannion(Author)
387 pages, illustrations, tables
Unmodified reprint of a second edition that was published in 1997. For this second edition, the text has been extensively revised and rewritten to reflect the growth in environmental research during the last decade. Human-induced environmental change is occurring at such a rapid rate that, inevitably, the fundamental processes involved in biogeochemical cycling are being altered.
Global Environmental Change considers alterations to the biogeochemical cycles of carbon, nitrogen, sulphur and other elements as a result of industrial/technological development and agriculture, which have significantly altered the natural environment. Global Environmental Change adopts a temporal and spatial approach to environmental change, beginning with the natural environmental change of the Quaternery period and continuing with the culturally-induced change since the inception of agriculture 10,000 years ago.
Preface to second edition
1. Nature, culture and environmental change
2. Quaternary geology and climatic change
3. Environmental change in the late and post-glacial periods
4. Prehistoric communities as agents of environmental change
5. Environmental change in the historic period
6. Environmental change due to post-1700 industrialisation
7. The environmental impact of agriculture in the developed world
8. The environmental impact of agriculture in the developing world
9. Other agents of change: forestry, recreation and tourism, biotechnology
10. Conclusion and prospect
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The asteroid in question, dubbed 2010 WC9, was first discovered in 2010 by astronomers using the Catalina Sky Survey in Arizona.
But shortly after it was discovered experts lost track of the huge space rock.
2010 WC9 was spotted again earlier this month and scientists now say that it is heading towards Earth and will just miss us.
The asteroid will fly by Earth at a distance of 126,000 miles – just half the distance between the Earth and the Moon – at 11.05PM on May 15.
Anything that comes closer than 4,650,000 miles of Earth is classified by NASA as a “near-Earth object” (NEO).
NASA said the event is the closest 2010 WC9 will be to Earth within the next 300 years.
At 130 metres, the asteroid would not destroy life on Earth, but would be more than six times the size of the space rock that almost wiped out Chelyabinsk.
In 2013, a 20 metre meteor exploded over the Russian city which smashed windows and caused injuries to more than 1,000 people.
And if 2010 WC9 were to hit Earth, it could easily wipe out a major city or a small country.
People will have to opportunity to watch the flyby life courtesy of a live stream from the Northolt Branch Observatories in London.
Guy Wells, of the observatory, said: “We are planning to broadcast this asteroid live to our Facebook page if the weather forecast remains positive.
“The broadcast will be less than 25 minutes in duration, as the asteroid will cross our field of view within that period of time.
“The asteroid will be moving quite rapidly (30 arc seconds per minute).
“Our display will update every five seconds. We are of course collecting astrometric data whilst this is happening, but the motion of the asteroid will be apparent every five seconds.” | <urn:uuid:a89ba45c-8ebe-4a0b-b658-cbb35331b784> | 3.21875 | 389 | News Article | Science & Tech. | 63.27131 | 95,480,312 |
- Open Access
The phytochrome red/far-red photoreceptor superfamily
© BioMed Central Ltd 2008
Published: 28 August 2008
Proteins of the phytochrome superfamily of red/far-red light receptors have a variety of biological roles in plants, algae, bacteria and fungi and demonstrate a diversity of spectral sensitivities and output signaling mechanisms. Over the past few years the first three-dimensional structures of phytochrome light-sensing domains from bacteria have been determined.
Light is an important environmental factor in most ecosystems. Photosynthetic organisms in particular must sense and respond to light cues to optimize their growth and metabolism. The quantity, direction and spectral make-up (the color or 'quality') of the light sensed by an organism conveys information regarding the abiotic and biotic environment and can be used to control adaptive responses. One superfamily of photosensory receptors comprises the phytochromes ('plant color'), which absorb in the red/far-red part of the spectrum . These receptors were first discovered in plants in the 1950s , but have more recently been identified in a broad spectrum of eukaryotic and prokaryotic phyla. In this brief overview I shall focus on recent advances relating principally to the understanding of phytochrome diversity and structure.
The absorption spectra of Pr and Pfr overlap to some extent and in the light an equilibrium between Pr and Pfr is established that reflects ambient light conditions. This equilibrium responds rapidly to changes in the ratio of red to far-red light, making phytochromes useful as sensors of critical changes in light quality. The physiological and developmental responses regulated by phytochromes in plants and algae are very diverse, including seed germination, photomorphogenesis and chloroplast movement, shade avoidance, and photoperiodic time measurement . In most cases, responses are induced by red light and cancelled by far-red, leading to the idea that Pfr is the active conformation and Pr is inactive. Phytochrome function in other organisms is less well understood, but it has been implicated in light regulation of motility and pigment synthesis in bacteria and sexual development and secondary metabolism in fungi.
The diversity of the phytochrome superfamily
Generalized properties of major groups of phytochromes
Approximate MW (kDa)
Pr λmax (nm)
Pfr λmax (nm)
Plants and green algae
The carboxy-terminal modules of plant phytochromes contain two predicted PAS domains followed by a sequence with apparent homology to two-component histidine kinases (TC-HKs) - the effector proteins in the 'two-component' environmental sensing systems common in bacteria, plants and fungi . (Two-component systems typically comprise a receptor histidine kinase that receives the signal and relays it to a 'response regulator' protein that elicits the cellular response.) However, in the plant phytochromes, amino acids critical to histidine kinase catalytic function are not conserved, and so these histidine kinase related domains (HKRDs) do not function via a typical TC-HK mechanism (Figure 2b). As we shall see later, bacterial and fungal phytochromes do contain functional histidine kinase domains and act via a two-component mechanism.
Exceptions to the conserved domain organization shown in Figure 2b for the plant phytochromes have been described in green algae and ferns, in which 'neochrome' photoreceptors combine a Phy-like PLD-GAF-PHY red/far-red sensing module with a flavin-binding LOV (light/oxygen/voltage) domain characteristic of cryptochrome and phototropin blue-light receptors .
In the late 1990s, phytochromes were discovered in cyanobacteria and other eubacteria. Genetic analysis of light-induced changes in the composition of phycobilisomes (large photosynthetic antenna complexes of phycobiliproteins anchored to thylakoid membranes) in Fremyella and the genome sequencing of Synechocystis first revealed the existence of prokaryotic cyanobacterial phytochromes (termed Cph to distinguish them from the plant Phy proteins) [8–10]. Cyanobacterial genomes contain small families of one to five Cph genes. The amino-terminal regions of Cph proteins contain Phy-related PLD-GAF-PHY regions but the carboxy-terminal sequences lack the tandem PAS and HKRD domains of Phy proteins and instead contain a prototypical TC-HK domain with characteristic amino acid motifs and the substrate histidine residue that is autocatalytically phosphorylated on activation of the kinase (Figure 2b).
Synechocystis Cph1 uses phycocyanobilin (PCB) rather than PΦB as its chromophore, and autocatalytically attaches the chromophore to the GAF domain as in the Phy proteins . Cph1 undergoes reversible photoconversion, but with Pr and Pfr absorption spectra shifted towards the blue end of the spectrum compared with the plant phytochromes (Table 1). Most notably, recombinant Synechocystis Cph1 shows red/far-red differential histidine kinase autophosphorylation, with Pr more active than Pfr, and histidine-to-aspartate phosphorelay to a Synechocystis response regulator protein . This demonstration that Cphs are light-regulated two-component histidine kinases led to a reassessment of phytochrome function and evolution, and moved the evolutionary context of the origin of bilin-containing photosensing pigments back many hundreds of millions of years. It also encouraged searches for Phy-related gene sequences in the genome databases of diverse organisms.
Phy-related coding sequences have now been found in the genomes of nonphotosynthetic bacteria, including Deinococcus, Pseudomonas and Agrobacterium, the purple photosynthetic bacterium Rhodospirillum, and the symbiotic photosynthetic bacterium Bradyrhizobium [11–15]. These genomes contain from one to six eubacterial phytochrome (Bph) genes. Bph proteins attach biliverdin (BV), the precursor to PΦB and PCB, as their chromophore and, like other phytochromes, have photoreversible Pr and Pfr conformations. Attachment of BV occurs autocatalytically via a thioether linkage to a cysteine side chain near the Bph amino terminus, rather than in the GAF domain (Figure 2b), and the absorbance maxima of Bph Pr and Pfr forms are red-shifted relative to Phys and Cphs (Table 1). Bph proteins have canonical TC-HK domains at their carboxyl termini and function as red/far-red light-regulated histidine kinases . The fact that diverse heterotrophic nonphotosynthetic bacteria contain phytochromes raises many questions about the possible roles of red and far-red light as environmental signals in these organisms, but the biological functions of most of the Bph proteins are not yet known.
The genome sequences of the filamentous fungi Neurospora and Aspergillus also revealed coding sequences for PLD-GAF-PHY-HKD proteins [16, 17] (Figure 2b). Like Bphs, these fungal phytochromes (Fphs) attach a BV chromophore at the amino-terminal end of their PLD domains and their red/far-red conformations are spectrally red-shifted (Table 1). From one to several Fph sequences have also been identified in the genomes of other ascomycete and basidiomycete fungi, but not in those of yeasts such as Saccharomyces or Candida. The carboxy-terminal output modules of the Fphs so far characterized also carry a response regulator domain, forming a 'hybrid' TC-HK structure in which autophosphorylation of the substrate histidine residue is followed by intramolecular phosphotransfer to an aspartate in the response regulator region. Hybrid TC-HK architectures are also found among a small number of Cphs and Bphs (Figure 2b).
Comparison of phytochrome function in different organisms
In green plants, phytochromes have very diverse regulatory functions throughout the entire life cycle, mediating light effects on seed germination, the switch from nonphotosynthetic growth in dark-grown seedlings to photoautotrophy, neighbor sensing, and timing of flowering. In seedlings, for example, phytochrome activation regulates approximately 10% of plant genes , and controls cell growth and division, chloroplast development, and circadian rhythms . Plant Phys assembled as Pr in the dark are localized to the cytoplasm, but undergo red/far-red light-regulated translocation to the nucleus, where they accumulate in sub-nuclear foci . Although a complete signal transduction pathway for a plant phytochrome response has not yet been described, both cytosolic and nuclear mechanisms are implicated. There is evidence that plant Phys have serine/threonine kinase activity . In addition, upon movement to the nucleus, they bind to a subfamily of plant basic helix-loop-helix (bHLH) transcription factors . Several bHLH proteins are rapidly phosphorylated and degraded following their interaction with phytochrome, suggesting that one major rapid Phy signaling mechanism involves targeted turnover of transcriptional regulators .
In cyanobacteria and eubacteria, phytochromes function in the regulation of phototaxis, pigmentation, and synthesis of the photosynthetic apparatus [1, 22]. In fungi, Fph phytochromes have roles in the control of sexual development and mycotoxin production. In contrast to plant Phy proteins, fungal phytochromes were initially observed to localize exclusively to the cytosol, irrespective of light conditions [16, 17]. This conclusion has been challenged recently by the finding that Aspergillus FphA binds to and forms a complex in the nucleus with the LreA and LreB proteins, homologs of the Neurospora zinc-finger transcription factors WC-1 and WC-2 . WC-1 functions as both a flavin-containing blue-light photoreceptor and a DNA-binding transcription factor, and a WC-1/WC-2 protein complex is involved in setting the Neurospora circadian clock. Direct physical interaction between Aspergillus Fph and the blue-light photosensing/response proteins opens up new and exciting possibilities for crosstalk in light signal transduction in fungi.
More structurally divergent phytochrome-related proteins have been identified in prokaryote sequence databases. These contain recognizable bilin-binding GAF domains but lack PLD and/or PHY domains, have various non-HK-related carboxy-terminal signaling domains, or lack cysteine residues at either of the typical locations for chromophore attachment . It was suggested that these proteins be grouped as 'phytochrome-like' gene products. Moreover, among the more structurally typical Bph receptors, some are unusual with respect to classical concepts of phytochrome activity and function. The 'bathyphytochromes' identified in Bradyrhizobium and Agrobacterium adopt a Pfr conformation rather than Pr as their ground state in the absence of light and work 'backwards', in that it is the Pr conformation that induces biological responses, such as the synthesis of the photosynthetic apparatus, and conversion to Pfr that cancels them [15, 24]. Some Bphs of Rhodopseudomonas and Bradyrhizobium photoconvert between Pr and a near-red 'Pnr' or orange 'Po' conformation [25, 26]. A distantly related phytochrome-like GAF domain from the cyanobacterium Anabaena reversibly photoconverts between a relatively standard Pr form and a green-light-absorbing (Pg543) form . Finally, a chromophore-less achromo-Bph found in some Rhodopseudomonas strains is postulated to function as a redox sensor rather than a light sensor . It appears that, since its very early origins, the bilin-binding GAF domain has been spectrally and biologically highly adaptable and in the world of non-plant phytochromes many of the old expectations must be put aside.
The three-dimensional structures of bacteriophytochrome photosensory modules
Photoconversion between the Pr and Pfr conformations differentially affects the enzymatic activities of Cphs and Bphs [8, 11], while the plant phytochromes function by interacting with a large number of proteins, including bHLH transcription factors, substrates for phytochrome-associated serine/threonine kinase activity, cryptochrome blue light receptors, and other proteins, which bind differentially to the Pr and Pfr forms . Hence, a molecular understanding of the three-dimensional structures of phytochromes and of the very rapid photochemical and slower protein conformational changes that occur upon red or far-red photoconversion will be crucial to understanding their mechanisms of action. Attempts to crystallize plant phytochromes or their truncated domains have not been successful. The prokaryotic phytochromes have, however, proved more amenable.
Wagner et al. [29, 30] crystallized the PLD-GAF chromo-phore-binding domain (see Figure 2c) of Deinococcus Bph in the Pr conformation and determined its three-dimensional structure by X-ray analysis at 2.2 Å and 1.45 Å resolution, while Yang et al. determined the structure of a similar region of Rhodopseudomonas BphP3. These fragments assemble with chromophore and fold into a Pr conformation but are not capable of photoconverting to Pfr. Nevertheless, this work provided critical three-dimensional structural information and resolved several longstanding questions. As expected for PAS-related domains, PLD and GAF in these proteins fold into five- or six-stranded antiparallel β-sheets, flanked by bundled α-helices. The BV chromophore, in the C5-Z,syn/C10-Z,syn/C15-Z,anti configuration, sits in a hydrophobic pocket formed from GAF domain elements. The chromophore A, B and C rings are nearly co-planar and the D ring is 40-45° out of that plane. This structure is consistent with the Z-to-E isomerization of the C15 = C16 double bond and rotation of the D ring that is proposed to be the initial photoreaction induced by absorption of red light . Surprisingly, the refined 1.45 Å structure of the Deinococcus Bph chromophore-binding domain indicates that, on linkage to the apoprotein, the BV chromophore adopts a configuration more similar to PCB and PΦB than previously thought . Whether this chemistry is characteristic of other BV-containing Bphs and Fphs will need to be resolved. The crystal structures also confirm that the chromophore in the Pr conformation is completely protonated and that photoconversion between Pr and Pfr probably involves a deprotonation/reprotonation cycle .
All currently characterized phytochromes act as dimers. Plant Phy proteins form homo- or heterodimers as a result of interactions between their carboxy-terminal ends [32, 33]. This is in line with the fact that prototypical TC-HKs are homo- or heterodimers, an interaction mediated by α-helices in their HisKA domains , although it is not known whether the HisKA-related sequences in plant Phys play a similar role. It has been noted that the Bph and BphP3 PLD-GAF crystal structures contain buried contact surfaces between monomer symmetry mates and that these surfaces may represent biologically relevant subunit-interaction sites . However, in vivo expression of truncated Phy proteins shows that the PLD-GAF-PHY regions do not dimerize . Further analysis of phytochrome quaternary structure determinants will resolve this point and determine what functional role, if any, dimerization plays in regulating photosensing activity.
In summary, the phytochrome 'light switch' has been revealed in many of its details over the past few years and much more information is on the way. References to unpublished crystal structures for the Pr forms of larger regions of Bph and Cph sensory modules, including the full PLD-GAF-PHY domains (Figure 2c), have appeared [35, 36]. These structures will show how the three domains surrounding the chromophore-binding pocket interact in Pr and may suggest roles for the PHY domain in photoconversion and conformational stability. This new and exciting atomic-level picture of phytochrome structure and function is poised to be rapidly expanded by the application of solution structure methods such as small-angle X-ray scattering, nuclear magnetic resonance (NMR), and resonance Raman spectroscopy [36, 37]. For example, the isolated GAF domain from a thermostable Synechococcus Cph, lacking both PLD and PHY sequences, photoconverts between Pr and Pfr conformations and is small enough for NMR analysis . These approaches will be particularly relevant to determining structural changes associated with the phytochrome phototransformation cycle. The roles of individual amino-acid residues in bilin binding, spectral integrity and photoconversion can then be probed by structurally guided site-directed mutagenesis [25, 39].
Origins and evolution
The expanded phylogenetic distribution of phytochromes clearly has implications for understanding their origins and evolution. Bilin-binding photosensor proteins in eubacteria, cyanobacteria and fungi are of ancient origin and have adopted diverse functions in regulating motility, sexual development, metabolic adaptation and probably many other behaviors. Published phylogenetic trees, based on alignments of GAF, PLD-GAF, or PHY domain sequences, lack sufficient information to develop strong hypotheses for the relationships among prokaryotic and eukaryotic phytochromes, although the Phy, Cph, Bph, Fph and Phy-like sequences form five distinct clusters in these analyses [22, 26].
The advent of the blue-shifted Cph and Phy forms, which use PCB or PΦB rather than BV as chromophore and a GAF domain attachment site rather than a more amino-terminal site, gave rise to photoreceptor systems better tuned to detecting the red wavelengths that efficiently drive chlorophyll and phycobiliprotein-mediated photosynthesis. Plant and algal phytochromes, with their unique carboxy-terminal PAS-PAS-HKRD modules, may have arisen via transfer of a Cph gene from an endosymbiotic cyanobacterium and subsequent divergence from the typical Cph structure . Interestingly, Jaubert et al. observed that a genomic island encoding PCB chromophore synthesis enzymes and a novel Bph phytochrome that binds PCB rather than BV as its chromophore has been acquired by the genome of the plant symbiont Bradyrhizobium via lateral gene transfer. Alternatively, it has been argued from phylogenetic analysis that the plant Phy proteins are more likely to have evolved from a progenitor PHY gene that existed in the ancestral eukaryotic cell before endosymbiosis of a photosynthetic cyanobacterium . Further study of phytochrome lineages will be useful in resolving these questions. It is notable that sequences encoding phytochrome-related bilin-binding GAF domain proteins have not been found in many groups of organisms for which there are extensive genomic databases, including animals and yeasts, although there is one preliminary finding of a possible archeal PLD-GAF protein .
The signature phytochrome GAF bilin-binding domain has been fused to and regulates many different output protein modules with many biological roles. Analysis of these output mechanisms in experimentally accessible prokaryotes and fungi should help to elucidate their transduction pathways. Indeed, a TC-HK mechanism for Bph regulation of photosynthetic gene transcription in Rhodopseudomonas and Fph interaction with well known fungal transcription factors have been reported. However, plant Phys evolved as proteins with a conserved and unique carboxy-terminal domain structure that does not immediately suggest a signaling mechanism and has not been readily dissected by genetic and molecular approaches. Many questions downstream of the recent elegant analyses of phytochrome structure and photochemistry remain.
This work was supported by grant IBN-0348913 to RAS from the National Science Foundation.
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Deciphering Plant Immunity Against Parasites
Mary Wang´ombe and Badou Mendy from the Department of Molecular Phytomedicine at the University of Bonn. (c) Photo: Molecular Phytomedicine/University of Bonn
Nematodes are a huge threat to agriculture since they parasitize important crops such as wheat, soybean, and banana; but plants can defend themselves. Researchers at Bonn University, together with collaborators from the Sainsbury Laboratory in Norwich, identified a protein that allows plants to recognize a chemical signal from the worm and initiate immune responses against the invaders. This discovery will help to develop crop plants that feature enhanced protection against this type of parasites. The work is published in the current issue of PLoS Pathogens.
Plant-parasitic nematodes are microscopic worms that parasitize their host plants to withdraw water and nutrients. The feeding process seriously damages the host plant. Nematode infection distorts root and shoot structure, compromises the plant´s ability to absorb nutrients from soil, and eventually reduces crop yield. Yearly losses exceed ten percent in important crops such as wheat, soybean, and banana. In addition to causing direct damage, nematode infection also provides an opportunity for other pathogens to invade and attack the host plants.
Until now, near to nothing was known about the general innate immune response of plants against nematodes. A team of researchers at the University of Bonn, in cooperation with scientists from the Sainsbury Laboratory in Norwich, has now identified a gene in thale cress (Arabidopsis thaliana), called NILR1, that helps plants sense nematodes. “The NILR1 is the genetic code for a receptor protein that is localized to the surface of plant cells and is able to bind and recognize other molecules,” says Prof. Florian Grundler, chair at the Department of Molecular Phytomedicine at the University of Bonn. “NILR1 most probably recognizes a molecule from nematodes, upon which, it becomes activated and immune responses of plants are unleashed.”
NILR1 recognizes a broad spectrum of nematodes
Although a few receptors, so-called resistance genes, providing protection against specific types of plant-parasitic nematodes have already been identified, NILR1 recognizes rather a broader spectrum of nematodes. “The nice thing about NILR1 is that it seems to be conserved among various crop plants and that it provides protection against many nematode species,” says group leader Dr. Shahid Siddique. “The discovery of NILR1 also raises questions about the nematode derived molecule, whose recognition is thought to be integral to this process.” Now that an important receptor is discovered, the scientists are working to find the molecule which binds to NILR1 to switch on the immune responses. The two first authors, PhD students at the department share tasks in the project. Whereas Mary Wang´ombe focuses on the receptor protein and its function, Badou Mendy concentrates on isolating the signal molecule released by the nematodes.
New options for breeding resistant crop plants
The findings of the University Bonn Scientists open new perspectives in making crops more resistant against nematodes. They could already show that important crop plants such as tomato and sugar beet also possess a functional homologue of NILR1 – an excellent basis for further specific breeding. Once the nematode signal is characterized, a new generation of natural compounds will be available that is able to induce defense responses
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- Open Access
Hybridization and speciation in angiosperms: a role for pollinator shifts?
© Chase et al; licensee BioMed Central Ltd. 2010
Received: 13 April 2010
Accepted: 21 April 2010
Published: 21 April 2010
The majority of convincingly documented cases of hybridization in angiosperms has involved genetic introgression between the parental species or formation of a hybrid species with increased ploidy; however, homoploid (diploid) hybridization may be just as common. Recent studies, including one in BMC Evolutionary Biology, show that pollinator shifts can play a role in both mechanisms of hybrid speciation.
See research article http://www.biomedcentral.com/1471-2148/10/103
Hybridization as a mechanism of speciation in angiosperms
Species dynamics are often molded by gene flow between existing species due to interbreeding. Occasional interbreeding between species may have three main long-term outcomes: 1, genetic introgression into one or both of the hybridizing species, in some cases leading to assimilation of one species by the other; 2, formation of a new species without a change in ploidy (homoploid hybrid speciation); or 3, formation of a new species with a shift in ploidy (allopolyploidy). However, gene flow will most often have no long-term result, due to various isolation mechanisms that act to keep parental species apart either at the stage of hybrid formation or, later, at establishment of new hybrid derivatives . Hybridization involving a change in ploidy has long been known to play a role in angiosperm evolution . Successful establishment as independent species of such hybrid polyploid progeny easily succeeds because allopolyploids are immediately isolated from further interactions with parental taxa due to high levels of sterility in their progeny (due to uneven numbers of chromosome complements). Recently in an assessment of genetic distances between parents of hybrid species, it was shown that parental species of allopolyploids are significantly more genetically divergent than those of homoploid hybrid species . Such a relationship seems mainly reinforced by fertility selection, resulting from the inability of homoploid hybrids to undergo normal meiosis if the parental chromosome complements have experienced too many rearrangements since they last shared a common ancestor. There appear to be genetic limits having to do with physical rearrangements of parental chromosomes (presumably caused by non-disjunction at meiosis) that make polyploidy more likely when the parental species are distantly related. Of course, documenting allopolyploidy is relatively easy and involves demonstrating that the hybrids have twice as many chromosomes (or more) as the parental species and that they retain fixed polymorphisms at protein-coding loci as documented by either protein studies, which were common in the 1980 and 1990s, or DNA sequencing/fingerprinting, which are the current methods of choice.
Documenting homoploid speciation is difficult without large data sets
In contrast to allopolypoidy, documenting homoploid hybrid speciation is notoriously difficult. We wish to make clear that we are referring here to established hybrids that have become genetically isolated from their parents and are functioning as distinct evolutionary units, as bona fide species. Hybrid individuals form often , but in general are ephemeral, either dying off or being reabsorbed into one of their parental taxa, which leads to introgression between the parents but not increased species diversity. Introgression occurs frequently when the parental taxa have 'porous genomes', that is, genomes that are still arranged similarly enough for there to be few if any barriers to hybridization .
There are two principal ways to detect the presence of homoploid hybrid species: 1, looking for incongruence (genes that give different information about species relationships, that is, reveal different signals or evolutionary histories; shown by methods such as split decomposition ) in phylogenetic studies involving multiple independent loci; and 2, documenting linkage disequilibrium, markers closely linked being more likely to originate from the same parent and give the same ideas about relatedness than those further separated on the chromosome or on different chromosomes. The second method, which relies upon the assumption that hybrid speciation involves recombination and homogenization of parental homologues, is by far the most powerful, but it also requires DNA sequences from a large number of loci and knowledge of their chromosome positions. The first method can often lead to confusing interpretations caused by other populational and stochastic processes (mainly persistent ancestral polymorphisms or gene duplications), and thus it too requires data from a large number of loci, becoming more powerful as the number of loci analyzed increases . Therefore, for the great majority of plant groups, proving that a species has had a homoploid hybrid origin is difficult.
Thus far, fewer than 50 cases of homoploid hybridization have been documented in the angiosperms [1, 8], but as more plant genomes are sequenced we are sure that this number will increase dramatically. Cases in which homoploid hybrid species have been documented thus far have often involved analyses of morphometric data or data that document the mixed morphological traits of the hybrids, with relatively small amounts of genetic data that fortuitously demonstrate the incongruence expected when loci have been derived from different parents. Congruence of morphological and genetic data compatible with homoploid hybridization is powerful enough to make convincing arguments, whereas evidence from either data type alone can easily be attributed to other populational and stochastic phenomena .
Hybridization does not guarantee reproductive isolation
Once formed, hybrids, both allopolyploid and homoploid, face similar ecological challenges. As mentioned above, allopolyploids benefit from immediate genetic barriers to backcrossing onto their parents that do not exist for homoploid hybrids, facilitating their genetic isolation from the parental taxa. Homoploid hybrids, in contrast, must face further genetic interactions with their parents, which often result in their reabsorption into a parental gene pool and introgression in that parent. When they do become established, there are several potential reasons why they succeed: 1, they exhibit transgressive traits (novel mixtures of those exhibited by their parents ) that facilitate their existence in habitats in which neither of their parents can grow, conferring the isolation needed to prevent their reabsorption into the gene pool of one of their parents; or 2, their intermediacy in some morphological traits or ecological preferences enables them to exploit a novel niche, again delivering a degree of genetic isolation from both of their parents. The degree to which the latter mechanism is feasible has been widely debated. Often such hybrids can only exploit the ecological transition zone between those of their parents, which places them near one or both parents and which may be so limited in area that they cannot form viable populations. Such intermediates are unlikely to form viable species in their own right.
Pollinator shifts as a mechanism of reproductive isolation hybrids
Hybridization leads to rapid genomic alterations, including chromosomal rearrangements and gene expression changes, some of which are mediated by transposable elements [10, 11]. These genomic changes often result in novel phenotypes, some that are intermediate between parentals, some that represent novel combinations of parental features, and, finally, others that are extreme or transgressive compared to those of the parental species. Homoploids with flowers intermediate between their parents in morphology or that produce a complex mixture of floral fragrances from both parents are likely to be ineffective in attracting the pollinator of either parent, so there is likely to be strong selection to conform to the morphology of one or the other parent. This affects both homoploids and allopolyploids equally.
Hybrid invasion of an alternative niche is likely to be successful if it parallels the reproductive isolation of its parents and thus subjects the hybrids to different selection pressures. Penstemon clevelandii, a homoploid hybrid of P. centranthifolius (red-flowered, hummingbird-pollinated) and P. spectabilis (lavender-flowered, wasp-pollinated) has established reproductive isolation by selection for a divergent pollination syndrome (magenta-flowered, bee- and hummingbird-pollinated) .
Overall, recent evidence has demonstrated the power of hybridization in creating new combinations of traits and genes responsible for niche divergence, both ecological and reproductive. As more examples of homoploid hybridization are identified, we predict that the frequency of successful niche novelties will also increase.
- Paun O, Forest F, Fay MF, Chase MW: Hybrid speciation in angiosperms: parental divergence drives ploidy. New Phytol. 2009, 182: 507-518. 10.1111/j.1469-8137.2009.02767.x.PubMed CentralView ArticlePubMedGoogle Scholar
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- Whittall JB, Hodges SA: Pollinator shifts drive increasingly long nectar spurs in columbine flowers. Nature. 2007, 447: 706-709. 10.1038/nature05857.View ArticlePubMedGoogle Scholar
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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. | <urn:uuid:7872235b-e59a-4fcc-a26c-9e818e351669> | 2.890625 | 2,617 | Academic Writing | Science & Tech. | 27.977265 | 95,480,391 |
Researchers from the UK and Malaysia have detected a human fingerprint deep in the Borneo rainforest in Southeast Asia. Cold winds blowing from the north carry industrial pollutants from East Asia to the equator, with implications for air quality in the region. Once there, the pollutants can travel higher into the atmosphere and impact the ozone layer. The research is published today in Atmospheric Chemistry and Physics, an open access journal of the European Geosciences Union (EGU).
Rainforests are often associated with pure, unpolluted air, but in Borneo air quality is very much dependent on which way the wind blows. “On several occasions during northern-hemisphere winter, pockets of cold air can move quickly southwards across Asia towards south China and onward into the South China Sea,” says Matthew Ashfold, Assistant Professor at the University of Nottingham Malaysia Campus.
In a new study, Ashfold and his team show that these ‘cold surges’ can very quickly transport polluted air from countries such as China to remote parts of equatorial Southeast Asia. “The pollution travels about 1000 km per day, crossing the South China Sea in just a couple of days,” states Ashfold, who was based at the University of Cambridge, UK, when he conducted parts of the study.
The researchers were initially looking for chemical compounds of natural origin: they wanted to test whether the oceans around Borneo were a source of bromine and chlorine. They designed their experiments to measure these gases, but also detected another gas called perchloroethene, or perc, in the air samples they collected from two locations in the Borneo rainforest. “This gas is a common ‘marker’ for pollution because it does not have natural sources,” says Ashfold.
The team wanted to find out where the man-made gas came from, and where it might go. “We used a UK Met Office computer model of atmospheric transport to look back in time, at where the air samples we collected had travelled from.” Their experiments suggested the high levels of perc in the air samples were influenced by East Asian pollution, as reported in the Atmospheric Chemistry and Physics study.
Perc is produced in a number of industrial and commercial activities, such as dry cleaning and metal degreasing, and exposure to large amounts (above about 100 parts per million) can affect human health. While global emissions of perc have declined in the past 20 years or so, it is not clear whether this has been the case in East Asia, where air pollution has increased over the past couple of decades.
The researchers say the levels of perc measured in Borneo are low, at a few parts per trillion. But because the gas does not occur naturally, even small concentrations are a sign that other more common pollutants, such as carbon monoxide and ozone, could be present. Ozone, for example, can damage forests when in high concentrations, as it reduces plant growth.
Indeed, the team’s measurements showed the amounts of perc varied strongly over the course of about a week, and models they analysed indicated this variation to be related to similar changes in carbon monoxide and ozone. “During the one ‘cold surge’ event we studied in detail, levels of these pollutants over Borneo appeared to be double typical levels,” Ashfold points out.
But diminished air quality in the remote rainforest is not the only way East Asia pollution affects the tropics. “The atmosphere over Southeast Asia and the Western Pacific is home to unusually strong and deep thunderstorms during the northern hemisphere winter. Because of this, the region is an important source of air for the stratosphere,” says Ashfold.
In their study the researchers show that, once in the deep tropics, the polluted air is lifted towards the upper atmosphere. “This can introduce a range of industrial chemicals with atmospheric lifetimes of just a few months to the stratosphere, which could have a potentially negative impact on the ozone layer.”
# # #
Please mention the name of the publication (Atmospheric Chemistry and Physics) if reporting on this story and, if reporting online, include a link to the paper (TBA) or to the journal website (http://www.atmospheric-chemistry-and-physics.net/).
This research is presented in the paper ‘Rapid transport of East Asian pollution to the deep tropics’ to appear in the EGU open access journal Atmospheric Chemistry and Physics on 31 March 2015.
The scientific article is available online, free of charge, from the publication date onwards, at http://www.atmos-chem-phys.net/recent_papers.html. A pre-print version of the paper is available for download at http://www.egu.eu/news/150/travelling-pollution-east-asian-human-activities-affe....
The team is composed of M. J. Ashfold (Department of Chemistry, University of Cambridge, UK [Ch. Cam.], now at School of Biosciences, University of Nottingham Malaysia Campus, Semenyih, Malaysia), J. A. Pyle (Ch. Cam. and National Centre for Atmospheric Sciences, UK), A. D. Robinson (Ch. Cam.), E. Meneguz (UK Met Office, Exeter, UK), M. S. M. Nadzir (Universiti Kebangsaan Malaysia, Bangi, Malaysia and Institute of Ocean and Earth Sciences, University of Malaysia, Kuala Lumpur [IOES]), S. M. Phang and A. A. Samah (IOES), S. Ong and H. E. Ung (Global Satria Life Sciences Lab, Tawau, Malaysia), L. K. Peng and S. E. Yong (Malaysian Meteorological Department, Lahad Datu, Malaysia), and N. R. P. Harris (Ch. Cam.).
The European Geosciences Union (EGU) is Europe’s premier geosciences union, dedicated to the pursuit of excellence in the Earth, planetary, and space sciences for the benefit of humanity, worldwide. It is a non-profit interdisciplinary learned association of scientists founded in 2002. The EGU has a current portfolio of 17 diverse scientific journals, which use an innovative open access format, and organises a number of topical meetings, and education and outreach activities. Its annual General Assembly is the largest and most prominent European geosciences event, attracting over 11,000 scientists from all over the world. The meeting’s sessions cover a wide range of topics, including volcanology, planetary exploration, the Earth’s internal structure and atmosphere, climate, energy, and resources. The EGU 2015 General Assembly is taking place in Vienna, Austria, from 12 to 17 April 2015. For information about meeting and press registration, please check http://media.egu.eu or follow the EGU on Twitter (https://twitter.com/EuroGeosciences) and Facebook (http://www.facebook.com/EuropeanGeosciencesUnion).
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http://www.egu.eu/news/150/travelling-pollution-east-asian-human-activities-affe... – release on the EGU website
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Dr. Bárbara Ferreira | European Geosciences Union
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Crewed missions to Mars remain an essential goal for NASA, but scientists are only now beginning to understand and characterize the radiation hazards that could make such ventures risky, concludes a new paper by University of New Hampshire scientists.
In a paper published online in the journal Space Weather, associate professor Nathan Schwadron of the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and the department of physics says that due to a highly abnormal and extended lack of solar activity, the solar wind is exhibiting extremely low densities and magnetic field strengths, which causes dangerous levels of hazardous radiation to pervade the space environment.
"The behavior of the sun has recently changed and is now in a state not observed for almost 100 years," says Schwadron, lead author of the paper and principal investigator for the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on NASA's Lunar Reconnaissance Orbiter (LRO). He notes that throughout most of the space age, the sun's activity has shown a clockwork 11-year cycle, with approximately six- to eight-year lulls in activity (solar minimum) followed by two- to three-year periods when the sun is more active. "However, starting in about 2006, we observed the longest solar minimum and weakest solar activity observed in the space age."
These conditions brought about the highest intensities of galactic cosmic rays seen since the beginning of the space age, which have created worsening radiation hazards that potentially threaten future deep-space astronaut missions.
"While these conditions are not necessarily a showstopper for long-duration missions to the moon, an asteroid, or even Mars, galactic cosmic ray radiation in particular remains a significant and worsening factor that limits mission durations," says Schwadron.
The study is the capstone article in the Space Weather CRaTER Special Issue, which provides comprehensive findings on space-based radiation as measured by the UNH-led detector. The data provide critical information on the radiation hazards that will be faced by astronauts on extended missions to deep space such as those to Mars. The papers can be viewed here: http://onlinelibrary.wiley.com/10.1002/(ISSN)1542-7390/specialsection/CRATER1
"These data are a fundamental reference for the radiation hazards in near Earth 'geospace' out to Mars and other regions of our sun's vast heliosphere," says Schwadron.
At the heart of CRaTER is material called "tissue equivalent plastic"—a stand-in for human muscle capable of gauging radiation dosage. Ionizing radiation from galactic cosmic rays and solar energetic particles remains a significant challenge to long-duration crewed missions to deep space. Human beings face a variety of consequences ranging from acute effects (radiation sickness) to long-term effects including cancer induction and damage to organs including the heart and brain.
The high radiation levels seen during the sun's last minimum cycle limits the allowable days for typical astronauts behind spacecraft shielding. Given the trend of reducing solar output, the allowable days in space for astronauts is dropping and estimated to be 20 percent lower in the coming solar minimum cycle as compared to the last minimum cycle.
UNH coauthors on the capstone paper titled "Does the worsening radiation environment preclude future manned deep-space exploration?" include Colin Joyce, Marty Quinn, Charles Smith, Sonya Smith, Harlan Spence, and Jody Wilson.
The CRaTER investigation is a collaboration with team members at UNH, the University of Tennessee at Knoxville, Southwest Research Institute, Harvard-Smithsonian Center for Astrophysics, The Aerospace Corporation, the University of Michigan, and NASA Goddard Spaceflight Center. For more information on the CRaTER instrument and the LRO mission, visit http://crater.unh.edu.
Support for this research comes from NASA's LRO/CRaTER mission, and NASA'S Earth-Moon-Mars Radiation Environment Module and Corona-Solar Wind Energetic Particle Acceleration projects. Additional support is provided by the National Science Foundation's Frontiers in Earth-System Dynamics program, which funds the UNH-led "Sun-to-Ice" project that uses theory and modeling results to inform the analysis of current space-based NASA measurements of the radiation environment.
The NASA Goddard Space Flight Center in Greenbelt, Md. developed and manages the LRO mission. LRO's current science mission is implemented for NASA's Science Mission Directorate. NASA's Exploration Systems Mission Directorate sponsored LRO's initial one-year exploration mission that concluded in September 2010.
The University of New Hampshire, founded in 1866, is a world-class public research university with the feel of a New England liberal arts college. A land, sea, and space-grant university, UNH is the state's flagship public institution, enrolling 12,300 undergraduate and 2,200 graduate students.
Images to download: http://www.eos.unh.edu/Spheres_1012/graphics/fall12_pics/prediccs2_lg.jpg
Caption: Solar flare observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager and associated coronal mass ejection observed by the Solar and Heliospheric Observatory spacecraft. Solar energetic particles from these events can easily penetrate typical shielding and damage spacecraft electronics and biological cells. Image courtesy of Nathan Schwadron, UNH-EOS.
Caption: Artist's rendition of the Lunar Reconnaissance Orbiter at the moon. The CRaTER telescope is seen pointing out at the bottom right center of the LRO spacecraft. Illustration by Chris Meaney/NASA.
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“Galaxies going through an intensive phase of star formation show a certain distinctive and characteristic gradation in their spectral energy distribution. We can detect this gradation by observing a galaxy through a telescope with different filters“, states Dr. Adi Zitrin, who is part of Prof. Bartelmann’s work group. However, the gradation shifts in just as characteristic a manner depending on how far away the galaxy is. In the case of MACS1149-JD1 this shift, known as redshift, has a value of 9.6. According to the Heidelberg scientists, this puts the galaxy at a distance which light has covered within 13.2 billion years.Essential clues that led to the discovery of MACS1149-JD1 were provided by a method of analysis also developed at the ZAH. This method has scientists measuring the distortion of the telescope images of galaxies located far behind the galaxy clusters, a distortion that is caused by the large amount of invisible dark matter in the clusters. In the case of MACS1149+22, the researchers detected a total of seven background galaxies whose image was enhanced, distorted and split into 23 multiple images by the gravitational effect of the galaxy cluster. This enabled the team to predict the location of a light-enhanced galaxy at a redshift of 9.6. The scientists concluded that the galaxy must have formed as early as 490 million years after the Big Bang.
Marietta Fuhrmann-Koch | idw
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Materials Sciences
19.07.2018 | Earth Sciences
19.07.2018 | Life Sciences | <urn:uuid:e63c789a-5d13-461f-bc37-50678fc696ed> | 3.03125 | 944 | Content Listing | Science & Tech. | 44.610824 | 95,480,413 |
Jupiter Now Reveals 'Great Cold Spot' in Thermosphere
The cool dark patch stretches up to 24,000 km across and 12,000 km wide, and it is in the gas giant's thin high-altitude thermosphere which is much cooler than the surrounding atmosphere.
'Great Cold Spot' has been discovered on Jupiter which is created by the powerful energies exerted by the planet's polar aurorae. (Image: NASA)
Jupiter is best known for the Great Red Spot, a long-lived storm roughly the diameter of Earth. But astronomers have now discovered another such Great Spot, dubbed 'Great Cold Spot', created by the powerful energies exerted by the great planet's polar aurorae.
The cool dark patch stretches up to 24,000 km across and 12,000 km wide, and it is in the gas giant's thin high-altitude thermosphere which is much cooler than the surrounding atmosphere, said a study in the Geophysical Research Letters.
"This is the first time any weather feature in Jupiter's upper atmosphere has been observed away from the planet's bright aurorae," said lead author of the study Tom Stallard, Associate Professor in Planetary Astronomy at the University of Leicester in Britain.
The phenomenon, only recently observed, may have existed for thousands of years.
"The Great Cold Spot is much more volatile than the slowly changing Great Red Spot, changing dramatically in shape and size over only a few days and weeks, but it has re-appeared for as long as we have data to search for it, for over 15 years," Stallard said.
"That suggests that it continually reforms itself, and as a result, it might be as old as the aurorae that form it - perhaps many thousands of years old," Stallard added.
The Great Cold Spot was first discovered on Jupiter using observations taken of Jupiter's auroral region by the CRIRES instrument on European Southern Observatory's Very Large Telescope in Chile.
The researchers then compared the data with thousands of images from NASA's InfraRed Telescope Facility in Hawaii.
The analysis confirmed the presence of the Great Cold Spot.
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Concepts and Elementary Results
Part of the Ergebnisse der Mathematik und ihrer Grenzgebiete book series (MATHE2, volume 80)
Throughout this book the symbol F will be used to denote a field that is either the real field ℝ or the complex field ℂ.
KeywordsBanach Algebra Unit Element Left Ideal Normed Linear Space Elementary Result
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Unable to display preview. Download preview PDF.
© Springer-Verlag Berlin Heidelberg 1973 | <urn:uuid:7a348197-cfd8-41e1-bbe4-155804e445d5> | 2.84375 | 137 | Truncated | Science & Tech. | 40.109 | 95,480,419 |
The subtle variations reveal themselves as a minuscule ripple in the overall movement of the solar surface. Astronomers have been searching for ripples of this kind since the 1970s, when they first detected that the solar surface was oscillating in and out.
The so-called ‘g-modes’ are driven by gravity and provide information about the deep interior of the Sun. They are thought to occur when gas churning below the solar surface plunges even deeper into our star and collides with denser material, sending ripples propagating through the Sun’s interior and up to the surface. It is the equivalent of dropping a stone in a pond.
Unfortunately for observers, these waves are badly degraded during their passage to the solar surface. By the time g-modes reach the exterior, they are little more than ripples a few metres high. To make matters more difficult, the g-modes take between two and seven hours to oscillate just once. So, astronomers are faced with having to detect a swell on the surface that rises a metre or two over several hours.
Now, however, astronomers using the Global Oscillation at Low Frequency (GOLF) instrument on SOHO think they may have caught glimpses of this behaviour. Instead of looking for an individual oscillation, they looked for the signature of the cumulative effect of a large number of these oscillations.
By analogy, imagine that the Sun was an enormous piano playing all the notes simultaneously. Instead of looking for a particular note (middle C for instance) it would be easier to search for all the ‘C’s, from all the octaves together.
In the piano their frequencies are related to each other just as on the Sun, one class of g modes are separated by about 24 minutes.
“So that’s what we looked for, the cumulative effect of several g modes,” says Rafael A. García, DSM/DAPNIA/Service d’Astrophysique, France. They combined ten years of data from GOLF and then searched for any hint of the signal at 24 minutes. They found it.
“We must be cautious but if this detection is confirmed, it will open a brand new way to study the Sun’s core,” says García.
Until now, the rotation rate of the solar core was uncertain. If the GOLF detection is confirmed, it will show that the solar core is definitely rotating faster than the surface.
The rotation speed of the solar core is an important constraint for investigating how the entire Solar System formed, because it represents the hub of rotation for the interstellar cloud that eventually formed the Sun and all the bodies around it. The next step for the team is to refine the data to increase their confidence in the detection. To do this, they plan to incorporate data from other instruments, both on SOHO and at ground-based observatories.
“By combining data from space (VIRGO and MDI, on SOHO) and ground (GONG and BiSON) instruments, we hope to improve this detection and open up a new branch of solar science,” says García.
Bernhard Fleck | alfa
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
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20.07.2018 | Materials Sciences | <urn:uuid:303ab396-b179-4647-a88e-520998aab898> | 3.765625 | 1,245 | Content Listing | Science & Tech. | 44.070521 | 95,480,444 |
The polar oceans are not biological deserts after all.A marine census released Monday documented 7,500 species in the Antarctic and 5,500 in the Arctic, including several hundred that researchers believe could be new to science."The textbooks have said there is less diversity at the poles than the tropics, but we found astonishing richness of marine life in the Antarctic and Arctic oceans," said Victoria Wadley, a researcher from the Australian Antarctic Division who took part in the Antarctic survey. "We are rewriting the textbooks."In one of the biggest surprises, researchers said they discovered dozens of species common to both polar seas — separated by nearly 7,000 miles (11,000 kilometers). Now they have to figure out how they separated."We probably know more about deep space than we do about the deep polar oceans in our own backyard," said Gilly Llewellyn, leader of the oceans program for the environmental group WWF-Australia. She did not take part in the survey. "This critical research is helping reveal the amazing biodiversity of the polar regions."Most of the new discoveries were simpler life forms known as invertebrates, or animals without backbones.Researchers found scores of sea spider species that were as big as a human hand, and tiny, shrimp-like crustaceans in the Arctic basin that live at a depth of 9,850 feet (3,000 meters).The survey is one of several projects of the Census of Marine Life, an international effort to catalog all life in the oceans. The 10-year census, scheduled for final publication in 2010, is supported by governments, divisions of the United Nations and private conservation organizations.The survey — which included over 500 polar researchers from 25 countries — took place during International Polar Year which ran in 2007-2008.Researchers endured up to 48-foot (16-meter) waves on their trip to the Antarctic, while their colleagues in the Arctic worked under the watchful eye of a security guard hired to protect them from polar bears.New technology also helped make the expeditions more efficient and productive than in the past. Researchers used cell-phone-like tracking devices to record the Arctic migration of narwhals, a whale with a long twisted tooth, and remotely operated submersibles to reach several miles (kilometers) down into the oceans to study delicate marine animals that are impossible to collect.As many as 235 species were found in both polar seas, including five whale species, six sea birds and nearly 100 species of crustaceans."We think of the Arctic and Antarctic as similar habitats but they are separated by great distances," said University of Alaska Fairbanks plankton ecologist Russ Hopcroft, who took part in the Arctic survey."So finding species at both ends of the Earth — some of which don't have a known connection in between — raises a whole bunch of evolutionary questions," he said.Hopcroft and other polar researchers will now try to determine how long these species have been separated and whether they have drifted apart genetically.David Barnes, of the British Antarctic Survey, said there a number of possibilities to explain how similar species live so far apart.Some may have traveled along the deep-sea currents that link the poles or may have thrived during the height of the last ice age about 20,000 years ago when the polar environment was expanded and the two habitats were closer.Hopcroft and Barnes cautioned that more work needs to be done to confirm whether the 235 species are indeed the same or differ genetically. "Painstaking work by geneticists investigating both nuclear and mitochondrial genes will only be able to confirm this," Barnes said in an e-mail interview. "It may be they separated sometime ago but similar selective pressures have meant they have not changed much." | <urn:uuid:005e937d-7c2c-47ea-b9de-95ceea3ac31f> | 3.625 | 746 | News Article | Science & Tech. | 37.971051 | 95,480,469 |
Artist’s depiction of a black hole eating a nearby star In 2005, astronomers detected a burst of infrared light coming from the heart of a galaxy nearly 150 million light-years from Earth. They had been studying the night sky for supernovae, the glittering explosions that mark the deaths of stars, but this seemed different. Intrigued, they decided to keep an eye on it.
After years of observations, the astronomers have determined the source of this burst was indeed the death of a star. But the star hasn’t exploded. It’s being eaten.
The star drifted too close to a supermassive black hole, the vacuum cleaner of the universe. The black hole’s fierce gravity dragged the star toward its invisible mouth, toward a point from which nothing, not even light, can return. The tugging stretched and shredded the star, producing a bright tail of light that could be detected by powerful telescopes on Earth.
An international team of astronomers—led by Seppo Mattila of the University of Turku in Finland and Miguel Pérez-Torres of the Astrophysical Institute of Andalusia in Spain—tracked this event over the course of a decade. Six years into their monitoring, the glow of light began to change shape and lengthen—a tell-tale sign that this wasn’t a one-off star explosion.
Their observations produced a ghostly image of this violent cosmic meal. The discovery, described in a paper published Thursday in Science , marks the first time that astronomers have directly imaged the formation and shape-shifting expansion of the jet of stellar material that forms when black holes devour stars.
The stellar debris grows brightly as it swirls around the black hole, emitting light across many different wavelengths. This interaction occurred at the site of another cosmic mashup: in one of the galaxies that makes up a pair of colliding galaxies known as Arp 299, and their colleagues first spotted the light from the black hole’s dinner with the William Herschel Telescope in the Canary Islands […]
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Bohr’s Atomic Model:
Thomson’s atomic model and Rutherford’s atomic model failed to answer many questions related to the energy of an atom and its stability. In the year 1913, Niels Bohr proposed an atomic structure model, describing an atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the positively charged nucleus as planets around the sun in our solar system, with attraction provided by electrostatic forces, popularly known as Bohr’s atomic model.It was basically an improved version of Rutherford’s atomic model overcoming its limitations. On most of the points, he is in agreement with him, like concepts of nucleus and electrons orbiting it. Salient features of Bohr’s atomic model are:
- Electrons revolve around the nucleus in stable orbits without emission of radiant energy. Each orbit has a definite energy and is called energy shell or energy level.
- An orbit or energy level is designated as K, L, M, N shells. When the electron is in the lowest energy level, it is said to be in the ground state.
- An electron emits or absorbs energy when it jumps from one orbit or energy level to another. When it jumps from higher energy level to lower energy level it emits energy while it absorbs energy when it jumps from lower energy level to higher energy level.
- The energy absorbed or emitted is equal to the difference between the energies of the two energy levels (E1, E2) and is determined by Plank’s equation.
ΔE = energy absorbed or emitted
h= Plank’s constant
v= frequency of electromagnetic radiation emitted or absorbed
- Angular momentum of an electron revolving in energy shells is given by:
n= number of corresponding energy shell; 1, 2, 3 …..
me= mass of the electron
h= Plank’s constant
Limitations of Bohr Atomic Model Theory:
- It violates the Heisenberg Uncertainty Principle. The Bohr atomic model theory considers electrons to have both a known radius and orbit i.e. known position and momentum at the same time, which is impossible according to Heisenberg.
- The Bohr atomic model theory made correct predictions for smaller sized atoms like hydrogen, but poor spectral predictions are obtained when larger atoms are considered.
- It failed to explain the Zeeman effect when the spectral line is split into several components in the presence of a magnetic field.
- It failed to explain the Stark effect when the spectral line gets split up into fine lines in the presence of electric field.
To learn more on Rutherford and Thomson’s atomic structure model, please visit Byjus.
Practise This Question | <urn:uuid:3b6cc4c6-55c9-45d2-a136-1b21945e90da> | 3.8125 | 565 | Knowledge Article | Science & Tech. | 36.830916 | 95,480,473 |
Neonicotinoids, the most important new class of synthetic insecticides of the past three decades, are used to control sucking insects both on plants and on companion animals. Imidacloprid (the principal example), nitenpyram, acetamiprid, thiacloprid, thiamethoxam, and others act as agonists at the insect nicotinic acetyl- choline receptor (nAChR). The botanical insecticide nicotine acts at the same target without the neonicotinoid level of effectiveness or safety. Fundamental differences between the nAChRs of insects and mammals confer remarkable selectivity for the neonicotinoids. Whereas ionized nicotine binds at an anionic subsite in the mam- malian nAChR, the negatively tipped (“magic” nitro or cyano) neonicotinoids interact with a proposed unique subsite consisting of cationic amino acid residue(s) in the in- sect nAChR. Knowledge reviewed here of the functional architecture and molecular aspects of the insect and mammalian nAChRs and their neonicotinoid-binding site lays the foundation for continued development and use of this new class of safe and effective insecticides.
Mendeley saves you time finding and organizing research
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How Small Is It - 04 - Elementary Particles (1080p)
Text at http://howfarawayisit.com/documents/
Music free version https://www.youtube.com/playli....st?list=PLpH1IDQEoE8
In this segment of our “How small is it” video book, we introduce elementary particles.
We start with a description of cosmic rays and gamma rays. They collide with atoms in the atmosphere to create a wide variety of particles. We cover how cloud chambers work to ‘see’ these new particles. That includes taking a look at the tracks for electrons and protons. We then take a look at the new particles we found on mountain tops and up in balloons: positrons, electron-positron pair creation, muons; pions; kaons; and particle decay timing and signatures.
We then cover the hard to find neutrino, starting with the Ellis - Wooster experiment to measure the energy of radium decay into polonium that lead to Wolfgang Pauli’s 1927 prediction that the existence of the neutrino. We then take a look at the 1970 bubble chamber track that first detected it.
Next we probe the proton using scattering experiments like the ones used by Rutherford to probe the nucleus. This time we use electrons instead of alpha particles. We cover how this was done at the Stanford Linear Accelerator Center (SLAC) in 1969. We show how particle acceleration is accomplished, and how particle detection is done with hodoscopes and calorimeters. We also examine the test results, explaining the idea of ‘cross section’ measurements as a way to identify scattering target sizes. We end with the results that showed that the proton has 3 parts: now called quarks.
We then cover how quarks form hadrons (baryons and mesons) with their predicted spin, charge and mass. With these predictions, the hunt for these particles went into high gear. We cover the discovery of the lambda, xi, and omega particles that show that the quark theory was correct.
We end with a review of particle sizes we’ve seen so far from the atom to the neutrino. We also show how this large array of new particles begins to fit into a model organized around particle masses (leptons and hadrons) and particle spins (fermions and bosons) along with their different statistical behaviors in a group. | <urn:uuid:33fa8731-6b21-42a3-90c5-049e43291dde> | 4.3125 | 514 | Truncated | Science & Tech. | 55.366314 | 95,480,489 |
Extreme weather events fuelled by unusually strong El Ninos, such as the 1983 heatwave that led to the Ash Wednesday bushfires in Australia, are likely to double in number as our planet warms.
An international team of scientists from organisations including the ARC Centre of Excellence for Climate System Science (CoECSS), the US National Oceanic and Atmospheric Administration and CSIRO, published their findings in the journal Nature Climate Change.
"We currently experience an unusually strong El Niño event every 20 years. Our research shows this will double to one event every 10 years," said co-author, Dr Agus Santoso of CoECSS.
"El Nino events are a multi-dimensional problem, and only now are we starting to understand better how they respond to global warming," said Dr Santoso. Extreme El Niño events develop differently from standard El Ninos, which first appear in the western Pacific. Extreme El Nino's occur when sea surface temperatures exceeding 28°C develop in the normally cold and dry eastern equatorial Pacific Ocean. This different location for the origin of the temperature increase causes massive changes in global rainfall patterns.
"The question of how global warming will change the frequency of extreme El Niño events has challenged scientists for more than 20 years," said co-author Dr Mike McPhaden of US National Oceanic and Atmospheric Administration.
"This research is the first comprehensive examination of the issue to produce robust and convincing results," said Dr McPhaden.
The impacts of extreme El Niño events extend to every continent across the globe.
The 1997-98 event alone caused $35 US billion in damage and claimed an estimated 23,000 human lives worldwide.
"During an extreme El Niño event countries in the western Pacific, such as Australia and Indonesia, experienced devastating droughts and wild fires, while catastrophic floods occurred in the eastern equatorial region of Ecuador and northern Peru," said lead author, CSIRO's Dr Wenju Cai
In Australia, the drought and dry conditions induced by the 1982-83 extreme El Niño preconditioned the Ash Wednesday Bushfire in southeast Australia, leading to 75 fatalities.
To achieve their results, the team examined 20 climate models that consistently simulate major rainfall reorganization during extreme El Niño events. They found a substantial increase in events from the present-day through the next 100 years as the eastern Pacific Ocean warmed in response to global warming.
"This latest research based on rainfall patterns, suggests that extreme El Niño events are likely to double in frequency as the world warms leading to direct impacts on extreme weather events worldwide."
"For Australia, this could mean summer heat waves, like that recently experienced in the south-east of the country, could get an additional boost if they coincide with extreme El Ninos," said co-author, Professor Matthew England from CoECSS.
Alvin Stone | EurekAlert!
New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz
Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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We see things every day, from the moment we get up in the morning until we go to sleep at night. We look at everything around us using light. We appreciate kids' crayon drawings, fine oil paintings, swirling computer graphics, gorgeous sunsets, a blue sky, shooting stars and rainbows. We rely on mirrors to make ourselves presentable, and sparkling gemstones to show affection. But did you ever stop to think that when we see any of these things, we are not directly connected to it? We are, in fact, seeing light -- light that somehow left objects far or near and reached our eyes. Light is all our eyes can really see.
The other way that we encounter light is in devices that produce light -- incandescent bulbs, fluorescent bulbs, lasers, lightning bugs, the sun. Each one uses a different technique to generate photons.
In this edition of HowStuffWorks, we will look at light from many different angles to show you exactly how it works!
Ways of Thinking About Light
You have probably heard two different ways of talking about light:
From the time of the ancient Greeks, people have thought of light as a stream of tiny particles. After all, light travels in straight lines and bounces off a mirror much like a ball bouncing off a wall. No one had actually seen particles of light, but even now it's easy to explain why that might be. The particles could be too small, or moving too fast, to be seen, or perhaps our eyes see right through them.
- There is the "particle" theory, expressed in part by the word photon.
- There is the "wave" theory, expressed by the term light wave.
The idea of the light wave came from Christian Huygens, who proposed in the late 1600s that light acted like a wave instead of a stream of particles. In 1807, Thomas Young backed up Huygens' theory by showing that when light passes through a very narrow opening, it can spread out, and interfere with light passing through another opening. Young shined a light through a very narrow slit. What he saw was a bright bar of light that corresponded to the slit. But that was not all he saw. Young also perceived additional light, not as bright, in the areas around the bar. If light were a stream of particles, this additional light would not have been there. This experiment suggested that light spread out like a wave. In fact, a beam of light radiates outward at all times.
Albert Einstein advanced the theory of light further in 1905. Einstein considered the photoelectric effect, in which ultraviolet light hits a surface and causes electrons to be emitted from the surface. Einstein's explanation for this was that light was made up of a stream of energy packets called photons.
Modern physicists believe that light can behave as both a particle and a wave, but they also recognize that either view is a simple explanation for something more complex. In this article, we will talk about light as waves, because this provides the best explanation for most of the phenomena our eyes can see.
What is Light?
Why is it that a beam of light radiates outward, as Young proved? What is really going on? To understand light waves, it helps to start by discussing a more familiar kind of wave -- the one we see in the water. One key point to keep in mind about the water wave is that it is not made up of water: The wave is made up of energy traveling through the water. If a wave moves across a pool from left to right, this does not mean that the water on the left side of the pool is moving to the right side of the pool. The water has actually stayed about where it was. It is the wave that has moved. When you move your hand through a filled bathtub, you make a wave, because you are putting your energy into the water. The energy travels through the water in the form of the wave.
All waves are traveling energy, and they are usually moving through some medium, such as water. You can see a diagram of a water wave in Figure 1. A water wave consists of water molecules that vibrate up and down at right angles to the direction of motion of the wave. This type of wave is called a transverse wave.
Light waves are a little more complicated, and they do not need a medium to travel through. They can travel through a vacuum. A light wave consists of energy in the form of electric and magnetic fields. The fields vibrate at right angles to the direction of movement of the wave, and at right angles to each other. Because light has both electric and magnetic fields, it is also referred to as electromagnetic radiation.
Light waves come in many sizes. The size of a wave is measured as its wavelength, which is the distance between any two corresponding points on successive waves, usually peak-to-peak or trough-to-trough (Figure 1). The wavelengths of the light we can see range from 400 to 700 billionths of a meter. But the full range of wavelengths included in the definition of electromagnetic radiation extends from one billionth of a meter, as in gamma rays, to centimeters and meters, as in radio waves. Light is one small part of the spectrum.
Light waves also come in many frequencies. The frequency is the number of waves that pass a point in space during any time interval, usually one second. It is measured in units of cycles (waves) per second, or Hertz (Hz). The frequency of visible light is referred to as color, and ranges from 430 trillion Hz, seen as red, to 750 trillion Hz, seen as violet. Again, the full range of frequencies extends beyond the visible spectrum, from less than one billion Hz, as in radio waves, to greater than 3 billion billion Hz, as in gamma rays.
As noted above, light waves are waves of energy. The amount of energy in a light wave is proportionally related to its frequency: High frequency light has high energy; low frequency light has low energy. Thus gamma rays have the most energy, and radio waves have the least. Of visible light, violet has the most energy and red the least.
Light not only vibrates at different frequencies, it also travels at different speeds. Light waves move through a vacuum at their maximum speed, 300,000 kilometers per second or 186,000 miles per second, which makes light the fastest phenomenon in the universe. Light waves slow down when they travel inside substances, such as air, water, glass or a diamond. The way different substances affect the speed at which light travels is key to understanding the bending of light, or refraction, which we will discuss later.
So light waves come in a continuous variety of sizes, frequencies and energies. We refer to this continuum as the electromagnetic spectrum (Figure 2). Figure 2 is not drawn to scale, in that visible light occupies only one-thousandth of a percent of the spectrum.
Producing a Photon
Any light that you see is made up of a collection of one or more photons propagating through space as electromagnetic waves. In total darkness, our eyes are actually able to sense single photons, but generally what we see in our daily lives comes to us in the form of zillions of photons produced by light sources and reflected off objects. If you look around you right now, there is probably a light source in the room producing photons, and objects in the room that reflect those photons. Your eyes absorb some of the photons flowing through the room, and that is how you see.
There are many different ways to produce photons, but all of them use the same mechanism inside an atom to do it. This mechanism involves the energizing of electrons orbiting each atom's nucleus. How Nuclear Radiation Works describes protons, neutrons and electrons in some detail. For example, hydrogen atoms have one electron orbiting the nucleus. Helium atoms have two electrons orbiting the nucleus. Aluminum atoms have 13 electrons orbiting the nucleus. Each atom has a preferred number of electrons orbiting its nucleus.
Electrons circle the nucleus in fixed orbits -- a simplified way to think about it is to imagine how satellites orbit the Earth. There's a huge amount of theory around electron orbitals, but to understand light there is just one key fact to understand: An electron has a natural orbit that it occupies, but if you energize an atom you can move its electrons to higher orbitals. A photon of light is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit. During the fall from high-energy to normal-energy, the electron emits a photon -- a packet of energy -- with very specific characteristics. The photon has a frequency, or color, that exactly matches the distance the electron falls.
There are cases where you can see this phenomenon quite clearly. For example, in lots of factories and parking lots you see sodium vapor lights. You can tell a sodium vapor light because it is very yellow when you look at it. A sodium vapor light energizes sodium atoms to generate photons. A sodium atom has 11 electrons, and because of the way they are stacked in orbitals one of those electrons is most likely to accept and emit energy (this electron is called the 3s electron, and is explained on this page). The energy packets that this electron is most likely to emit fall right around a wavelength of 590 nanometers. This wavelength corresponds to yellow light. If you run sodium light through a prism, you do not see a rainbow -- you see a pair of yellow lines.
Probably the most common way to energize atoms is with heat, and this is the basis of incandescence. If you heat up a horseshoe with a blowtorch, it will eventually get red hot, and if you heat it enough it gets white hot. Red is the lowest-energy visible light, so in a red-hot object the atoms are just getting enough energy to begin emitting light that we can see. Once you apply enough heat to cause white light, you are energizing so many different electrons in so many different ways that all of the colors are being generated -- they all mix together to look white, as explained in one of the sections below.
Heat is the most common way we see light being generated -- a normal 75-watt incandescent bulb is generating light by using electricity to create heat. However, there are lots of other ways to generate light, some of which are listed below:
The thing to note from this list is that anything that produces light does it by energizing atoms in some way.
- Halogen lamps - Halogen lamps use electricity to generate heat, but benefit from a technique that lets the filament run hotter.
- Gas lanterns - A gas lantern uses a fuel like natural gas or kerosene as the source of heat.
- Fluorescent lights - Fluorescent lights use electricity to directly energize atoms rather than requiring heat.
- Lasers - Lasers use energy to "pump" a lasing medium, and all of the energized atoms are made to dump their energy at the exact same wavelength and phase.
- Glow-in-the-dark toys - In a glow-in-the-dark toy, the electrons are energized but fall back to lower-energy orbitals over a long period of time, so the toy can glow for half an hour.
- Indiglo watches - In Indiglo watches, voltage energizes phosphor atoms.
- Chemical light sticks - A chemical light stick and, for that matter, fireflies, use a chemical reaction to energize atoms.
Visible light is light that can be perceived by the human eye. When you look at the visible light of the sun, it appears to be colorless, which we call white. And although we can see this light, white is not considered to be part of the visible spectrum (Figure 2). This is because white light is not the light of a single color, or frequency. Instead, it is made up of many color frequencies. When sunlight passes through a glass of water to land on a wall, we see a rainbow on the wall. This would not happen unless white light were a mixture of all of the colors of the visible spectrum. Isaac Newton was the first person to demonstrate this. Newton passed sunlight through a glass prism to separate the colors into a rainbow spectrum. He then passed sunlight through a second glass prism and combined the two rainbows. The combination produced white light. This proved conclusively that white light is a mixture of colors, or a mixture of light of different frequencies. The combination of every color in the visible spectrum produces a light that is colorless, or white.
- Colors by Addition - You can do a similar experiment with three flashlights and three different colors of cellophane -- red, green and blue (commonly referred to as RGB). Cover one flashlight with one to two layers of red cellophane and fasten the cellophane with a rubber band (do not use too many layers or you will block the light from the flashlight). Cover another flashlight with blue cellophane and a third flashlight with green cellophane. Go into a darkened room, turn the flashlights on and shine them against a wall so that the beams overlap, as shown in Figure 3. Where red and blue light overlap, you will see magenta. Where red and green light overlap, you will see yellow. Where green and blue light overlap, you will see cyan. You will notice that white light can be made by various combinations, such as yellow with blue, magenta with green, cyan with red, and by mixing all of the colors together.
By adding various combinations of red, green and blue light, you can make all the colors of the visible spectrum. This is how computer monitors (RGB monitors) produce colors.
- Colors by Subtraction - Another way to make colors is to absorb some of the frequencies of light, and thus remove them from the white light combination. The absorbed colors are the ones you will not see -- you see only the colors that come bouncing back to your eye. This is what happens with paints and dyes. The paint or dye molecules absorb specific frequencies and bounce back, or reflect, other frequencies to your eye. The reflected frequency (or frequencies) are what you see as the color of the object. For example, the leaves of green plants contain a pigment called chlorophyll, which absorbs the blue and red colors of the spectrum and reflects the green.
Here is an absorption experiment that you can try at home: Take a banana and the blue cellophane-covered flashlight you made earlier. Go into a dark room, and shine the blue light on the banana. What color do you think it should be? What color is it? If you shine blue light on a yellow banana, the yellow should absorb the blue frequency; and, because the room is dark, there is no yellow light reflected back to your eye. Therefore, the banana appears black.
So, if you had three paints or pigments in magenta, cyan and yellow, and you drew three overlapping circles with those colors, as shown in Figure 4, you would see that where you have combined magenta with yellow, the result is red. Mixing cyan with yellow produces green, and mixing cyan with magenta creates blue. Black is the special case in which all of the colors are absorbed. You can make black by combining yellow with blue, cyan with red or magenta with green. These particular combinations ensure that no frequencies of visible light can bounce back to your eyes.
But the color scheme demonstrated in Figure 4 appears to go against what your art teacher told you about mixing colors, right? If you mix yellow and blue crayons, you get green, not black. This is because artificial pigments, such as crayons, are not perfect absorbers -- they do not absorb all colors except one. A "yellow" crayon can absorb blue and violet while reflecting red, orange and green. A "blue" crayon can absorb red, orange and yellow while reflecting blue, violet and green. So when you combine the two crayons, all of the colors are absorbed except for green. Therefore, you see the mixture as green, instead of the black demonstrated in Figure 4.
So there are two basic ways by which we can see colors. Either an object can directly emit light waves in the frequency of the observed color, or an object can absorb all other frequencies, reflecting back to your eye only the light wave, or combination of light waves, that appears as the observed color. For example, to see a yellow object, either the object is directly emitting light waves in the yellow frequency, or it is absorbing the blue part of the spectrum and reflecting the red and green parts back to your eye, which perceives the combined frequencies as yellow.
When Light Hits an Object
When a light wave hits an object, what happens to it depends on the energy of the light wave, the natural frequency at which electrons vibrate in the material and the strength with which the atoms in the material hold on to their electrons. Based on these three factors, four different things can happen when light hits an object:
And more than one of these possibilities can happen at once. The following five illustrations show these possibilities, with reflection and scattering illustrated separately.
- The waves can be reflected or scattered off the object.
- The waves can be absorbed by the object.
- The waves can be refracted through the object.
- The waves can pass through the object with no effect.
- Transmission - If the frequency or energy of the incoming light wave is much higher or much lower than the frequency needed to make the electrons in the material vibrate, then the electrons will not capture the energy of the light, and the wave will pass through the material unchanged. As a result, the material will be transparent to that frequency of light.
Most materials are transparent to some frequencies, but not to others. For example, high frequency light, such as gamma rays and X-rays, will pass through ordinary glass, but lower frequency ultraviolet and infrared light will not.
You can read more about what makes glass transparent on this page.
- Absorption - In absorption, the frequency of the incoming light wave is at or near the vibration frequency of the electrons in the material. The electrons take in the energy of the light wave and start to vibrate. What happens next depends upon how tightly the atoms hold on to their electrons. Absorption occurs when the electrons are held tightly, and they pass the vibrations along to the nuclei of the atoms. This makes the atoms speed up, collide with other atoms in the material, and then give up as heat the energy they acquired from the vibrations.
The absorption of light makes an object dark or opaque to the frequency of the incoming wave. Wood is opaque to visible light. Some materials are opaque to some frequencies of light, but transparent to others. Glass is opaque to ultraviolet light, but transparent to visible light.
- Reflection and Scattering: The atoms in some materials hold on to their electrons loosely. In other words, the materials contain many free electrons that can jump readily from one atom to another within the material. When the electrons in this type of material absorb energy from an incoming light wave, they do not pass that energy on to other atoms. The energized electrons merely vibrate and then send the energy back out of the object as a light wave with the same frequency as the incoming wave. The overall effect is that the light wave does not penetrate deeply into the material.
In most metals, electrons are held loosely, and are free to move around, so these metals reflect visible light and appear to be shiny. The electrons in glass have some freedom, though not as much as in metals. To a lesser degree, glass reflects light and appears to be shiny, as well.
A reflected wave always comes off the surface of a material at an angle equal to the angle at which the incoming wave hit the surface. In physics, this is called the Law of Reflectance. You have probably heard the Law of Reflectance stated as "the angle of incidence equals the angle of reflection."
You can see for yourself that reflected light has the same frequency as the incoming wave. Just look at yourself in a mirror. The colors you see in the mirror's image are the same as those you see when you look down at yourself. The colors of your shirt and hair are the same as reflected in the mirror as they are on you. If this were not true, we would have to rely entirely on other people to tell us what we look like!
Scattering is merely reflection off a rough surface. Incoming light waves get reflected at all sorts of angles, because the surface is uneven. The surface of paper is a good example. You can see just how rough it is if you look at it under a microscope. When light hits paper, the waves are reflected in all directions. This is what makes paper so incredibly useful -- you can read the words on a printed page regardless of the angle at which your eyes view the surface.
Another interesting rough surface is Earth's atmosphere. You probably don't think of the atmosphere as a surface, but it nonetheless is "rough" to incoming white light. The atmosphere contains molecules of many different sizes, including nitrogen, oxygen, water vapor and various pollutants. This assortment scatters the higher energy light waves, the ones we see as blue light. This is why the sky looks blue.
- Refraction - Refraction occurs when the energy of an incoming light wave matches the natural vibration frequency of the electrons in a material. The light wave penetrates deeply into the material, and causes small vibrations in the electrons. The electrons pass these vibrations on to the atoms in the material, and they send out light waves of the same frequency as the incoming wave. But this all takes time. The part of the wave inside the material slows down, while the part of the wave outside the object maintains its original frequency. This has the effect of bending the portion of the wave inside the object toward what is called the normal line, an imaginary straight line that runs perpendicular to the surface of the object. The deviation from the normal line of the light inside the object will be less than the deviation of the light before it entered the object.
The amount of bending, or angle of refraction, of the light wave depends on how much the material slows down the light. Diamonds would not be so glittery if they did not slow down incoming light much more than, say, water does. Diamonds have a higher index of refraction than water, which is to say that they slow down light to a greater degree.
One interesting note about refraction is that light of different frequencies, or energies, will bend at slightly different angles. Let's compare violet light and red light when they enter a glass prism. Because violet light has more energy, it takes longer to interact with the glass. As such, it is slowed down to a greater extent than a wave of red light, and will be bent to a greater degree. This accounts for the order of the colors that we see in a rainbow. It is also what gives a diamond the rainbow fringes that make it so pleasing to the eye.
Rainbows in Soap Bubbles
Have you ever wondered why soap bubbles are rainbow colored, or why an oil spill on a wet road has rainbow colors in it? This is what happens when light waves pass through an object with two reflective surfaces. When two incoming light waves of the same frequency strike a thin film of soap, as seen in Figure 5 below, parts of the light waves are reflected from the top surface, while other parts of the light pass through the film and are reflected from the bottom surface. Because the parts of the waves that penetrate the film interact with the film longer, they get knocked out of sync with the parts of the waves reflected by the top surface. Physicists refer to this state as being out of phase. When the two sets of waves strike the photoreceptors in your eyes, they interfere with each other; interference occurs when waves add together or subtract from each other and so form a new wave of a different frequency, or color.
Basically, when white light, which is a mixture of different colors, shines on a film with two reflective surfaces, the various reflected waves interfere with each other to form rainbow fringes. The fringes change colors when you change the angle at which you look at the film, because you are changing the path by which the light must travel to reach your eye. If you decrease the angle at which you look at the film, you increase the amount of film the light must travel through for you to see it. This causes greater interference.
Everything we see is a product of, and is affected by, the nature of light. Light is a form of energy that travels in waves. Our eyes are attuned only to those wave frequencies that we call visible light. Intricacies in the wave nature of light explain the origin of color, how light travels, and what happens to light when it encounters different kinds of materials.
- Hewitt, Paul G., (1999) Conceptual Physics, Third Edition, Scott-Foresman-Addison-Wesley, Inc., Menlo Park, Calif.
- Serway, Raymond A, and Jerry S. Faughn, (1999) Holt Physics, Holt, Rinehart, and Winston, Austin, Texas
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Ten Important Types of Overlap in General HomoDinuclear M.O.’s
Are there any other possibilities that have gone unmentioned?
Five s+px s+py px+py px+pz py+pz
Five s-px s-py px-py px-pz py-pz
Q. What about these? A. They are zero overlap
Due to the three different types of atomic orbitals depicted below, we also have three different types of M.O.’s*
*These three types of a.o.’s can combine with one another to give m.o.’s that have zero ( σ ), one (π), or two (δ) nodal planes σ, π, δ bonding σ, π*, δ* antibonding
Examples of Diatomic M.O. Treatment (1) F2 Molecule: F is 22s22p5 valence electrons Buried, next to nucleus does not participate in bonding Remember effective nuclear charge increases left → right in periodic table (adding protons to atoms whose electrons are going into the same shell) F- effective Nuclear Charge is high → 2s/2p orbital energies are therefore quite different (p orbitals are more shielded than s orbitals) 1s – very low in energy 2s – still very low in energy 2p – higher energy due to being more shielded from nuclear charge so their relative I.E. is less
σ4* π2* 2p
2p' π1 σ3
E σ2* 2s
2s' F atomic orbitals
F atomic orbitals
Fill the diagram with the 14 valence electrons (7 from each F)
F2 Electronic Configuration is : σ12 σ2*2 σ32 π14 π2*4 (σ levels are non degenerate) (π levels are doubly degenerate) Net bonding is: σ12 σ2*2 σ32 π14 π2*4 one σ bond based on the 2pz….2pz overlap
Bond order in MO theory is: (#of bonding electrons - # of antibonding electrons)/2 2e- per bond Example 2 Li2 Main difference between Li2 and F2 is that the 2s and 2p separation is much lesser in Li2 Li 1s22s12p0 Need to understand why σ3 goes up
The electronic configuration is σ12 based only on s…s overlap. It is a weak bond because s…s overlap is poor (compared say to s-p σ overlap)
Li2 (σ) Weak s…s bond looks like this in terms of the electron density contour. Each new contour line as you go in from perimeter is a double of e- density
Note: this bond doesn’t depend on any of the higher energy M.O.’s
The difference in the separation of 2s and 2p lead to different energy orderings for Li2 → F2 *Crossing of π, and σ3 occurs at O2 when mixing becomes unimportant.
What are the bond order for the series? Li2 σ12 B.O. = 2/2 = 1 Be2 σ12 σ2*2 B.O. = 0 B2 σ12 σ2*2π12 B.O. = 1 C2 σ12 σ2*2π14 B.O. = 2 N2 σ12 σ2*2π14 σ32 B.O. = 3 O2 σ12 σ2*2 σ32 π14 π2*2 B.O. = 2 F2 σ12 σ2*2 σ32 π14 π2*4 B.O. = 1 - N2 has highest bond order (:N≡N:), the shortest, and the strongest bond - O2 is a double bond and a paramagnetic molecule because the last two electrons go in the π set unpaired * O2 Lewis Structure is correct, but it does not predict two unpaired electrons.
Q. What about Ne2? A. This is an unstable molecule: σ12 σ2*2 σ32 π14 π2*4 π4*2 16 valence electrons (B.O. =0) Heteronuclear Diatomic Molecules AB rather than A2 means that the atomic orbitals no longer begin at the same energies.
Contrast M.O. Diagram for CO with N2:
10 valence electrons: σ12 σ2*2 π14 σ32 (B.O. =3.0)
M.O. Diagrams for the Isoelectronic N2 and CO molecules are very different. They help explain the different reactivites of N2 vs CO in a way that Lewis Diagrams never could (or formal charges!) CO N2 (1) Highest e- are in a (1) Highest e- are in a strongly bonding slightly antibonding orbital σ12σ1*2π14σ32, orbital σ12σ1*2π14σ3*2 (higher in energy pz-pz σ orbital than the starting (2) As a consequence N2 a.o.’s) is very stable, + -eN2 →N 2 weakens the (2) As a consequence CO is not as stable, N-N bond. I.E. is CO →CO+ actually very high leads to a strong C≡O bond!
What does ionization of N2 versus CO have to do with their activation? (meaning destroying the molecule or even attaching it as a “ligand” to metals through lone pair) A. Lewis basicity of CO is much higher than N2 :C≡O: This end binds to Lewis acids such as M+ ions very easily. The highest energy l.p. is σ*3 which is primarily C-based.
:N≡N: Very difficult to get this lone pair to donate (buried in energy!)
Extrapolation of M.O. Theory Diatomic to Polyatomic Linear Triatonics like BeH2 which can form only σ orbitals
1) In each bonding orbitals, B, The e- density is continuous over adjacent atoms, in antibonding orbitals, A, there is a node. 2) In each bonding orbital, the electron pair is spread out (delocalized) over entire molecule.
BeH2 M.O. Diagram
Two H atoms
Two equal energy One 2s and three 1s orbitals are 2p orbitals lie at placed in the much higher diagram. energy than H 1s They are low in and they are close energy due to together due to higher effective lower effective nuclear charge. nuclear charge Bonding in H-Be-H σ12σ22 = 4 Bonding electrons Distributed over two Be-H bonds. So two single bonds.
Trigonal Planar Molecules AB3 BF3 , CO32- , NO3Recall, we invoked π- bonding in CO32- and NO3- as part of “resonance” structures like these:
Q. But how does M.O. theory account for πbonding? More to the point: Can M.O. theory explain the one π bond in the above structure needing to be in 3 places at the same time? A. YES!!!
M.O. Treatment of AB3 planar molecules. For example BF3, NO3-, CO32Requires two different groups of atomic orbitals to be considered. 1) Hybrid Orbitals on central atom, A, and on B that will be used to make σ- bonds (A-B bonds) and used to house lone pairs (in plane) 2) Group Orbitals on outer atoms, B, that are made of pz orbitals (out-of-plane) that can overlap with the pz orbital on central atom A. BF3
3e- + 3(7e-) = 24e-
4e- + 3(6e-) + 2e- = 24e-
5e- + 3(6e-) + 1e- = 24e-
The xy plane is the plane of molecule The z axis comes out of paper
Diagrams showing how π- bonding and π- antibonding M.O.’s arise from overlap of G.O.3 with the pz Orbital of A.
BF3 Only 6 valence CO32- electrons are pz NO3 available for π- orbital on A bonding. The 18ebefore this are involved in σ interactions (24enon-bonding systems).
pz orbitals on B make up these three
The part of the M.O. Diagram that depicts the π- bonding is:
if BF3 then: each of these is a single bond based on sp2 overlap
there is 1/3 of a π bond (1 π bond over 3 atoms)
Note, we did not draw a complete M.O. diagram here with all of the orbitals and interactions. It is too complicated to try and get the relative energies of the starting orbitals and M.O.’s correct. Nevertheless, we succeeded in developing a qualitative picture of the bonding that holds true for these types of molecules.
Multi-Center Bonding in Electron Deficient Molecules This happens when you don’t have enough electrons to have a two-electron bond between all adjacent atoms. Examples (classic ones) *
There are eight adjacent pairs of atoms in these molecules but count electrons… 2B 6e- (3 each) H 6e12e-
You need 16e- to make 8 bonds but you have only 12e- which is only enough for 6 bonds
*These are not planar (note that BH3 and Al(CH3)3 are not really the way the formulae indicate)
Consider these two resonance forms (canonical forms)
This implies that in each bridge, that one electron pair is shared between (or distributed over) two B•••H bonds. This would lead to a bond order of ½ for each B•••H bridge bond but still result in the other two
bonds being normal 2e- bonds.
Q. Doesn’t this seem a little artificial to you? A. Yes. There is a better way to think about this with M.O. theory B has sp3 hybridization for tetrahedral Boron - BH2 has two ordinary bonds made from two of the four sp3 hybrids and the H 1s orbitals.
These BH2 fragments are coplanar - the remaining two sp3 hybrids overlap in a perpendicular orientation with the bridging H atoms
Formation of three-center two-electron Bonds in B2H6
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In response to the need for localized efforts to protect and recover the surviving populations of the threatened staghorn coral, Diego Lirman, Ph.D., and James Herlan, researchers from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science (RSMAS) have established an underwater nursery dedicated to the propagation of staghorn corals.
The goals of the coral nursery are to develop effective coral fragmentation and propagation methodologies, and to evaluate the role of coral genetics on the resilience of this species to disturbance. A total of 250 fragments of staghorn coral have been collected to date, and placed on cement platforms where they are individually measured at monthly intervals to assess growth and mortality patterns. It is expected that the staghorn fragments kept in the nursery will provide an expanding coral stock to be used in future reef restoration, as well as in scientific experiments.
Until recently, branching Elkhorn (Acropora palmata) and Staghorn (Acropora cervicornis) corals were among the most abundant reef-building corals in Caribbean and Florida reefs. However, in the last few decades a drastic regional decline of this genus has been recorded due mainly to elevated temperatures, coral diseases, and the impact of hurricanes. This region-wide decline, which has resulted in losses of up to 95 percent of colonies at several locations, has prompted the listing of these species as “threatened” under the U.S. Endangered Species Act in 2006.
“The fast growth rate of this particular coral species (up to 15 cm per year) makes it an ideal candidate for reef restoration programs,” said Dr. Lirman, RSMAS assistant research professor and director of the coral nursery. “Faced with declining coral populations worldwide, we have to explore all available options to protect and expand surviving populations of these resources which are vital to the overall health of our reef systems. Coral nurseries provide a unique opportunity to learn about coral growth and survivorship patterns, as well as how to stabilize corals damaged by natural physical disturbances or through human activity.”
The new underwater nursery, located in the waters of Biscayne National Park, is part of a network of Acropora nurseries established with support from The Nature Conservancy, NOAA, and the National Park Service. Additional staghorn nurseries are presently located in Broward County, and in the Upper and Middle Florida Keys.
Barbra Gonzalez | EurekAlert!
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Materials Sciences
19.07.2018 | Earth Sciences
19.07.2018 | Life Sciences | <urn:uuid:bcba9f41-5e9f-4356-a689-a69671c88204> | 3.453125 | 1,167 | Content Listing | Science & Tech. | 35.289433 | 95,480,536 |
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.
Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.
Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure, extending from the central bulge, at the ends of which the spiral arms begin. The proportion of barred spirals relative to their barless cousins has likely changed over the history of the Universe, with only about 10% containing bars about 8 billion years ago, to roughly a quarter 2.5 billion years ago, until present, where over two-thirds of the galaxies in the visible universe (Hubble volume) have bars.
In the 1970s, our own Milky Way was confirmed to be a barred spiral, although the bar itself is difficult to observe from the Earth's current position within the galactic disc. The most convincing evidence for the stars forming a bar in the galactic center comes from several recent surveys, including the Spitzer Space Telescope.
Together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in today's universe. They are mostly found in low-density regions and are rare in the centers of galaxy clusters.
Spiral galaxies may consist of several distinct components:
The relative importance, in terms of mass, brightness and size, of the different components varies from galaxy to galaxy.
Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name. Naturally, different classifications of spiral galaxies have distinct arm-structures. Sc and SBc galaxies, for instance, have very "loose" arms, whereas Sa and SBa galaxies have tightly wrapped arms (with reference to the Hubble sequence). Either way, spiral arms contain many young, blue stars (due to the high mass density and the high rate of star formation), which make the arms so bright.
A bulge is a huge, tightly packed group of stars. The term refers to the central group of stars found in most spiral galaxies, often defined as the excess of stellar light above the inward extrapolation of the outer (exponential) disk light.
Using the Hubble classification, the bulge of Sa galaxies is usually composed of Population II stars, that are old, red stars with low metal content. Further, the bulge of Sa and SBa galaxies tends to be large. In contrast, the bulges of Sc and SBc galaxies are much smaller and are composed of young, blue Population I stars. Some bulges have similar properties to those of elliptical galaxies (scaled down to lower mass and luminosity); others simply appear as higher density centers of disks, with properties similar to disk galaxies.
Many bulges are thought to host a supermassive black hole at their centers. Such black holes have never been directly observed, but many indirect proofs exist. In our own galaxy, for instance, the object called Sagittarius A* is believed to be a supermassive black hole.
Bar-shaped elongations of stars are observed in roughly two-thirds of all spiral galaxies. Their presence may be either strong or weak. In edge-on spiral (and lenticular) galaxies, the presence of the bar can sometimes be discerned by the out-of-plane X-shaped or (peanut shell)-shaped structures which typically have a maximum visibility at half the length of the in-plane bar.
The bulk of the stars in a spiral galaxy are located either close to a single plane (the galactic plane) in more or less conventional circular orbits around the center of the galaxy (the Galactic Center), or in a spheroidal galactic bulge around the galactic core.
However, some stars inhabit a spheroidal halo or galactic spheroid, a type of galactic halo. The orbital behaviour of these stars is disputed, but they may describe retrograde and/or highly inclined orbits, or not move in regular orbits at all. Halo stars may be acquired from small galaxies which fall into and merge with the spiral galaxy—for example, the Sagittarius Dwarf Spheroidal Galaxy is in the process of merging with the Milky Way and observations show that some stars in the halo of the Milky Way have been acquired from it.
Unlike the galactic disc, the halo seems to be free of dust, and in further contrast, stars in the galactic halo are of Population II, much older and with much lower metallicity than their Population I cousins in the galactic disc (but similar to those in the galactic bulge). The galactic halo also contains many globular clusters.
The motion of halo stars does bring them through the disc on occasion, and a number of small red dwarfs close to the Sun are thought to belong to the galactic halo, for example Kapteyn's Star and Groombridge 1830. Due to their irregular movement around the center of the galaxy, these stars often display unusually high proper motion.
The oldest spiral galaxy on file is BX442. At eleven billion years old, it is more than two billion years older than any previous discovery. Researchers think the galaxy’s shape is caused by the gravitational influence of a companion dwarf galaxy. Computer models based on that assumption indicate that BX442's spiral structure will last about 100 million years.
The pioneer of studies of the rotation of the Galaxy and the formation of the spiral arms was Bertil Lindblad in 1925. He realized that the idea of stars arranged permanently in a spiral shape was untenable. Since the angular speed of rotation of the galactic disk varies with distance from the centre of the galaxy (via a standard solar system type of gravitational model), a radial arm (like a spoke) would quickly become curved as the galaxy rotates. The arm would, after a few galactic rotations, become increasingly curved and wind around the galaxy ever tighter. This is called the winding problem. Measurements in the late 1960s showed that the orbital velocity of stars in spiral galaxies with respect to their distance from the galactic center is indeed higher than expected from Newtonian dynamics but still cannot explain the stability of the spiral structure.
Since the 1970s, there have been two leading hypotheses or models for the spiral structures of galaxies:
These different hypotheses are not mutually exclusive, as they may explain different types of spiral arms.
Bertil Lindblad proposed that the arms represent regions of enhanced density (density waves) that rotate more slowly than the galaxy’s stars and gas. As gas enters a density wave, it gets squeezed and makes new stars, some of which are short-lived blue stars that light the arms.
The first acceptable theory for the spiral structure was devised by C. C. Lin and Frank Shu in 1964, attempting to explain the large-scale structure of spirals in terms of a small-amplitude wave propagating with fixed angular velocity, that revolves around the galaxy at a speed different from that of the galaxy's gas and stars. They suggested that the spiral arms were manifestations of spiral density waves - they assumed that the stars travel in slightly elliptical orbits, and that the orientations of their orbits is correlated i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic center. This is illustrated in the diagram to the right. It is clear that the elliptical orbits come close together in certain areas to give the effect of arms. Stars therefore do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.
The following hypotheses exist for star formation caused by density waves:
The arms appear brighter because there are more young stars (hence more massive, bright stars). These massive, bright stars also die out quickly, which would leave just the darker background stellar distribution behind the waves, hence making the waves visible.
While stars, therefore, do not remain forever in the position that we now see them in, they also do not follow the arms. The arms simply appear to pass through the stars as the stars travel in their orbits.
Charles Francis and Erik Anderson showed from observations of motions of over 20,000 local stars (within 300 parsecs) that stars do move along spiral arms, and described how mutual gravity between stars causes orbits to align on logarithmic spirals. When the theory is applied to gas, collisions between gas clouds generate the molecular clouds in which new stars form, and evolution towards grand-design bisymmetric spirals is explained.
with being the disk scale-length; is the central value; it is useful to define: as the size of the stellar disk, whose luminosity is
The spiral galaxies light profiles, in terms of the coordinate , do not depend on galaxy luminosity.
"Spiral nebula" was a term used to describe galaxies with a visible spiral structure, such as the Whirlpool Galaxy, before it was understood that these objects existed outside our Milky Way galaxy. The question of whether such objects were separate galaxies independent of the Milky Way, or a type of nebula existing within our own galaxy, was the subject of the Great Debate of 1920, between Heber Curtis of Lick Observatory and Harlow Shapley of Mt. Wilson Observatory. Beginning in 1923, Edwin Hubble observed Cepheid variables in several spiral nebulae, including the so-called "Andromeda Nebula", proving that they are, in fact, entire galaxies outside our own. The term "spiral nebula" has since fallen into disuse.
The Milky Way was once considered an ordinary spiral galaxy. Astronomers first began to suspect that the Milky Way is a barred spiral galaxy in the 1960s. Their suspicions were confirmed by Spitzer Space Telescope observations in 2005, which showed that the Milky Way's central bar is larger than was previously suspected.
Lin and Shu showed that this spiral pattern would persist more or less for ever, even though individual stars and gas clouds are always drifting into the arms and out again. | <urn:uuid:be2e6010-6fdf-415e-af0b-0a8cc1fcc907> | 4.125 | 2,175 | Knowledge Article | Science & Tech. | 39.582901 | 95,480,546 |
The Remote Sensing Toolkit will help grow the number of users who put NASA's free and open data archive to work for people.
Calculations based on CMB observations indicate the universe contains five per cent normal matter protons, neutrons and other subatomic particles, 25 per cent dark matter, and 70 per cent dark energy.
Researchers from Ecole Polytechnique Federale de Lausanne (EPFL) showed that piloting a drone using torso movements is more effective than using the long-established joystick
The wire, which is threaded into a vein, attracts special magnetic nanoparticles engineered to glom onto tumour cells that may be roaming the bloodstream if you have a tumour somewhere in your body.
The study suggests that the parent star, located about 450 light years from Earth, is now in the process of devouring the planetary debris resulting from collision of infant planetary bodies.
The results showed that beaches in Australia and Africa are experiencing more erosion than growth, a process scientists call accretion.
Astronomers have now spotted 12 new moons orbiting around Jupiter, that brings the number of natural satellites up to 79.
The Meghalayan, the youngest stage, runs from 4,200 years ago to 1950. It began with a destructive drought, whose effects lasted two centuries, and severely disrupted civilisations.
The UK is a “geographically strategic location for launch” with its northern latitudes, and well-placed to reach polar and near-polar orbits.
In September ISRO will fly a PSLV rocket with two foreign satellites, earning revenue for the country.
Total Lunar Eclipse on 27-28 July 2018: Here is why this month's Blood Moon and lunar eclipse will be the most unique one of the century.
The Vikas Engine is the workhorse liquid rocket engine used to power the second stage of the ISRO's trusted Polar Satellite Launch Vehicle (PSLV).
Scientists have discovered a new volcano on Io, a moon of Jupiter. The observations were made from data collected by NASA's Juno spacecraft
The frozen corpse of a 5,300-year-old hunter could provide evidence of the meals that ancient man ate.
The findings detailed in the journal Science marked the detection of the source of such a particle for the first time.
The observations revealed two distinct lobes, but the asteroid's orientation was such that scientists could not see if the two bodies were separate or joined.
The brighter Mars will remain very close to the eclipsed Moon in the sky on July 27-28 and can be spotted very easily with the naked eye,” according to a statement from the ministry.
A Blue Origin employee with first-hand knowledge of the pricing plan said the company will start selling tickets in the range of about $200,000 to $300,000.
Surya Grahan or Solar Eclipse 2018 Dates and Time in India: A partial solar eclipse will take place on July 13 in 44 years. The eclipse will last for about an hour and 13 minutes.
NASA does not have a contingency plan for ensuring uninterrupted US access to the International Space Station. | <urn:uuid:0ac25cf6-ed09-4815-8214-d9fe2e151c51> | 2.796875 | 637 | Content Listing | Science & Tech. | 42.134818 | 95,480,547 |
One of the most basic yet least understood processes in our bodies is how cells crawl along tissues. This behavior is essential to the formation of an embryo and other processes, but it must be tightly controlled. A disturbance can lead to the spread of cancer cells or diseases like Spina bifida and Lissencephaly, in which cells fail to reach their proper destinations. Scientists from the European Molecular Biology Laboratory (EMBL) in Monterotondo have now made a significant step forward in understanding cell motility.
The researchers discovered that a molecule called n-cofilin is critical for regulating cell movement. Most cells in the body are normally locked to their neighbors, tightly embedded in a tissue. Their connections to their neighbors depend on fibers built from long chains of a protein called actin. For an embryo to form properly, certain types of cells have to immigrate to new locations, where they help to form the face, muscles, and skin.
Before cells “set sail”, the actin fibers that bind them to their neighbors are untied and recycled. This not only allows the cells to move, but also changes their form, because actin fibers give the cell its basic shape. Cells carefully regulate the breakdown and assembly of actin fibers because if they are cast off at the wrong time and place, for example in a tumor, cancerous cells may spread throughout the body and form metastases.
Trista Dawson | alfa
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences | <urn:uuid:97f0d7d6-80b6-4485-abf9-8c7f89f71221> | 3.671875 | 876 | Content Listing | Science & Tech. | 40.178433 | 95,480,563 |
Everything You Need to Know About API Testing
Everything You Need to Know About API Testing
APIs are essential for applications to communicate, especially in the cloud and IoT. Learn about the importance and methods for testing them continuously.
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API testing, a.k.a. Application Programming Interface testing, is the term which has garnered growing attention in the past five years. It is a staple of any internet based product testing team, used for small stuff like image loading to huge stuff like payment processing.
An API, or application programming interface, is a set of tools, protocols, and programs that glues all of our digital worlds altogether. If you are able to login to Medium, Quora, and other popular sites websites using "Login with Google," the main hero behind that is an API.
How APIs Made Our Lives Easier
Remember the Trivago guy? Aggregator websites like Trivago bring you offer prices of various hotels from multiple sources like Expedia, Hotels.com, Goibibo, etc, all in a single platform. A user can book a hotel and take an offer rolled out by Expedia, without even logging into Expedia!
So, how does this happen? The simple answer to your question turns out to be APIs.
So, with the help of APIs, your application can communicate with third-party applications without any human intervention, acting as a communication bridge.
API Testing: What Led to the Growth?
Verifying that all the API endpoints act as expected without any breaks in between is the main aim of API Testing. It is one of the most important aspects of a testing process because of:
1. Agile Practices
Organizations are lovingly embracing agile development, calling for dramatically changed ways of automated testing. Continuous builds ask for continuous feedback and improvements, and GUI tests tend to take longer to run. Since API tests do not lean on the UI to be done, they match the frequency to keep pace with Agile development.
2. Internet of Things
IoT is no doubt gaining speed and various sources predict that devices connected to IoT will keep growing, and by the end of 2020, will be at 20 billion. Devices connected to the cloud are highly backed by APIs. You won’t be launching satellites or developing google again to connect the devices in cloud, all we’ll be using will be API. So, it’s incumbent to make sure that the connected devices stay connected.
Where API Testing Stands in Services-Based Architecture
Types of API Testing
Integration testing, security testing, performance testing, and usability testing are some terms that you might be aware of. API testing holds all these terms under a single umbrella. When you perform API testing, you make sure that your API passes the following tests:
Functional Testing: To make sure that all the API endpoints are up and working and doing what exactly they are supposed to so.
Reliability Testing: Making sure that the API works when connecting to various devices and doesn’t get disconnected.
Load Testing: When various servers send a request to an API, it is necessary to make sure that the API responds to all of them.
Stress Testing: When more than a set number of requests is received by the API, how does it behave? Does it send a message? It's mandatory to check whether it works as intended.
Security Testing: While giving authentication, it is important to make sure that no security breaches happen in between and that no more than the required data is shared. Have appropriate authentications, permissions, and access controls.
Integration Testing: Ensures that all the APIs connected to each other must communicate properly and the addition of features in the API does not cause bugs in other API modules.
Usability Testing: The API is functional, and on top of it, user-friendly.
The Test Pyramid: Pumping Up API Testing
Coupled with some major use cases like authentication, saving from the pain of writing the already written code, there are certain features that add up to the need of API Testing.
One of them was well explained by Mike Cohn in his book Succeeding with Agile: Software Development Using Scrum with the help of the test pyramid. According to which, automation test strategy calls for automating the different levels:
The need for automating the tests increases from top to bottom. Unit tests forming the base of the pyramid calls to be automated first and the GUI tests forming the top are the ones required to be the least automated. But we are concerned about the ones in the middle: Service/API layer tests. Their proportion describes their relevance to be automated.
Furthermore, API automated testing takes far much less time than automated UI tests. In some cases, it takes less than 1 second to run a single end-to-end API test, thus blending with CI protocols.
The bottom line is, when you are developing an application, smooth communication with various other apps must be at the top of your checklist, and API testing helps you complete that checklist.
Published at DZone with permission of Deeksha Agarwal . See the original article here.
Opinions expressed by DZone contributors are their own. | <urn:uuid:b1235fbb-6f8c-43b0-b2a3-f111310c093f> | 2.578125 | 1,126 | Truncated | Software Dev. | 44.465039 | 95,480,574 |
According to a study in Geographical Research published by Wiley-Blackwell, the droughts are related to the solar magnetic phases and not the greenhouse effect.
The study titled “Exploratory Analysis of Similarities in Solar Cycle Magnetic Phases with Southern Oscillation Index Fluctuation in Eastern Australia” uses data from 1876 to the present to examine the correlation between solar cycles and the extreme rainfall in Australia.
It finds that the Southern Oscillation Index (SOI) – the basic tool for forecasting variations in global and oceanic patterns – and rainfall fluctuations recorded over the last decade are similar to those in 1914 -1924.
Author Professor Robert G. V. Baker from the School of Environmental Studies, University of New England, Australia, says, “The interaction between the directionality in the Sun’s and Earth’s magnetic fields, the incidence of ultraviolet radiation over the tropical Pacific, and changes in sea surface temperatures with cloud cover – could all contribute to an explanation of substantial changes in the SOI from solar cycle fluctuations. If solar cycles continue to show relational values to climate patterns, there is the potential for more accurate forecasting through to 2010 and possibly beyond.”
The SOI-solar association has been investigated recently due to increasing interest in the relationship between the sun’s cycles and the climate. The solar application offers the potential for the long-range prediction of SOI behavior and associated rainfall variations, since quasi-periodicity in solar activity results in an expected cycle of situations and phases that are not random events.
Professor Baker adds, “This discovery could substantially advance forecasting from months to decades. It should result in much better long-term management of agricultural production and water resources, in areas where rainfall is correlated to SOI and El Niño (ENSO) events.”
Alina Boey | alfa
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences | <urn:uuid:9787caa7-763d-48c3-bfe4-10ea8824b7be> | 3.171875 | 980 | Content Listing | Science & Tech. | 32.79 | 95,480,579 |
Microbes are well-known for their ability to grow in demanding and nutritionally poor environments, which has allowed them to colonise some of the most remote places on the planet. Bacteria living in theoretically nutrient-rich environments like the mammalian intestine face similar challenges due to intense competition between bacterial species in the intestine for the finite amount of available food.
Researchers led by Dr Gavin Thomas in the University’s Department of Biology discovered that a protein present in the intestinal bacterium Escherichia coli was a unique sugar transporter.
Common sugars like glucose form a cyclic structure called a ‘pyranose’ when dissolved in water. All transporters for glucose recognise the pyranose form. But, for sugars such as galactose, which is commonly found in dairy produce, around 10 per cent is found in a different ring form called a ‘furanose’.
Initial work on the unknown E. coli transporter by Dr Thomas’s team suggested that it was a galactose transporter. The researchers knew that E. coli has a galactopyranose transporter already, so why should the bacterium have evolved another system to do exactly the same thing?
The answer to the problem was discovered when researchers led by Professor Keith Wilson in the York Structural Biology Laboratory solved the 3D structure of the protein, revealing that it was bound to the rarer furanose form of galactose. Experiments by Dr Jennifer Potts in the University’s Centre for Magnetic Resonance confirmed that the transporter was the first biological example to recognise furanose over pyranose forms.
Dr Thomas said: “The picture that emerges is that bacteria have evolved many related transporters to allow them to exploit every possible potential source of nutrient in their environment. Being able to use the extra 10 per cent of galactose available in the gut appears a trivial adaptation. But it is exactly the small change required to allow E. coli to grow a little bit faster when galactose is present in the gut, and so persist at the expense of other species of bacteria.”
The work was funded through a Biotechnology and Biological Sciences Research Council quota studentship to Dr Richard Horler in the laboratory of Dr Thomas. The research involved Dr Axel Muller, from the laboratory of Professor Wilson, and NMR expertise from David Williamson and Dr Potts. The work was published in the Journal of Biological Chemistry.
David Garner | EurekAlert!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
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20.07.2018 | Power and Electrical Engineering
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Consider a projectile of mass m which is shot vertically upward from the surface of the earth with initial velocity V. Assume that the gravitational force acts downward at a constant acceleration g while the force of air resistance has a magnitude proportional to the square of the velocity with proportionality constant k>0 and acts to resist motion. Let x=x(t) denote the height of the projectile at time t and v(t) = dx/dt(t) , its velocity.
a) Explain why the governing equation of motion is given by:
mdv/dt = -kv^2 - mg v > 0 For t > 0 (1)
mdv/dt = kv^2 - mg v < 0
x(0) = 0 and v(0) = Vo
b) Solve this system as follows: Introduce V(x) = v[t(x)]. Then define V1(x) = V^2(x) for V(x) >0 and V2(x) = V^2(x) for V(x) < 0. Show that V1 and V2 satisfy
dV1/dx + 2k/m V1 = -2g , V1(0) = Vo^2
dV2/dx - 2k/m V1 = -2g , V2(Xm) = 0
Where Xm is defined implicitly by V1(Xm) = 0. Demonstrate that V2(0) < Vo^2.© BrainMass Inc. brainmass.com July 15, 2018, 3:25 pm ad1c9bdddf
Following is the text part of the solution. Please see the attached file for complete solution. Equations, diagrams, graphs and special characters will not appear correctly here. Thank you for using Brainmass.
v > 0 denotes the motion of the projectile upward. During the upward motion, forces on the projectile are: Downward gravitational force (mg) and the downward force of air resistance (kv^2).
Using Newton's second law in the upward direction,
m d^x/dt^2 = -kv^2 - mg
But, dx/dt = v
Hence, d^x/dt^2 = dv/dt
m dv/dt = -kv^2 - mg ------------- (1)
v < 0 denotes the ...
This 4-page word document is full of explanations and detailed answer to the question of finding the equations of motion for an object shot vertically upward considering the effects of air resistance. This document also contains the solution process of the first order differential equation using a substitution. Equations are typed using the equation editor. Answer is very well formulated and presented. | <urn:uuid:12dd907e-d4a2-460c-b63b-6ed3399f9a5c> | 3.984375 | 575 | Truncated | Science & Tech. | 85.693857 | 95,480,597 |
We see it almost every night of our lives. For thousands of years, the greatest philosophers and astronomers alike have watched its face change and wondered why.
Step outside and observe the moon every day for a month and you will notice something fascinating. Over the course of the entire month, the moon will go through an entire cycle of phases—no more, no less.
The phases of the moon are something I’ve talked about before, but I wanted to spend some time on a few common misconceptions this time around and show you the truth behind the lunar phases. Continue reading
When you hear about “space-time,” it’s just a way to say that space is related to time. And the curvature of space-time, as Albert Einstein predicted, is the way space and time alike literally bend around a mass such as the Earth or the sun.
That’s what’s diagramed above. This is a three-dimensional concept diagram of the way space sort of “clings” to an object. Notice the way it sort of tightens up when you get close to Earth? And because time is part of this whole equation…time sort of tightens up, too.
I assume that explains the “twin paradox,” as it’s called. That’s where the space-traveling twin returns home to Earth younger than their Earth bound twin.
Why? Seems to me it’s because time was tighter and passed faster on Earth, while it spread out and passed a bit slower for the traveler. (Don’t quote me on that, I just guessed that from this diagram.)
Einstein figured all this out. But scientists need evidence. Trusting Einstein’s genius wasn’t enough for them. How did they accept relativity as fact? Continue reading
Thales and Pythagoras suggested that the natural world could be understood. Aristotle dared to imagine what was beyond the Earth. Plato encouraged thought about the universe, even if he did take astronomy one step forward and two steps backward.
Copernicus followed in Ptolemy’s wake, devising the revolutionary heliocentric (sun-centric) model of the universe. Tycho Brahe may have (incorrectly) rejected that model, but he did make some of the most detailed night sky observations yet.
What’s more, by Johannes Kepler’s time, Tycho had cast doubt on the idea of uniform circular motion that had plagued astronomy for centuries.
At last, the world was ready for a more mathematical take on a question that had confounded philosophers, mathematicians, and classical astronomers alike: how do the planets truly move through space?
By standing on the shoulders of giants, Johannes Kepler was finally able to devise his three laws of planetary motion, which are still the leading mathematical theory today. Continue reading
Nicolaus Copernicus lived from 1473-1543, a time when rebellion against the Church was at its height. And unfortunately for the astronomy of the time, it had gotten inextricably tied up with Christian teachings.
In that time, heaven and hell weren’t just parts of our personal religions and beliefs—the Church held some of the highest authority over the land, and questioning heaven and hell just wasn’t done.
The way astronomers of the time pictured the universe fell right in sync with the heaven and hell geometry—Earth was the imperfect center of the universe, with hell nested deep below. Heaven was a place of perfection, and it was where all the heavenly bodies—the moon, sun, planets and stars—all moved.
Problem was, the Ptolemaic model of the universe really couldn’t explain detailed observations. It used epicycles to explain why the planets moved backwards sometimes. And no matter what people tried, they couldn’t get it to be accurate…
But then along came Copernicus, who would be the first to challenge the Ptolemaic universe and be believed. Continue reading
Claudius Ptolemy lived about five centuries after the Greek philosopher Aristotle’s time. Aristotle’s model for the universe—the first geocentric model, with Earth at the center—was still widely accepted, and Ptolemy sought to improve it.
Ptolemy was one of the first of the ancient Greeks to be a true astronomer and mathematician, rather than a philosopher.
Where Aristotle, Plato, Thales, and Pythagoras before him had tried to use “pure thought” to understand the nature of the heavens, Ptolemy set about to perfect the geocentric model mathematically.
This was a huge step forward for science as a whole, as science today relies heavily on mathematics.
In Ptolemy’s time, science didn’t really exist yet. The Greeks preferred to just think through problems logically and reasonably, and if the logic they used was based on untrue assumptions…well, no one was the wiser.
But Ptolemy came up with the wonderful idea to line up observations of the sky with mathematics. And even though Aristotle’s view of the universe shackled him, he moved science forward with great strides. Continue reading
You may have heard of a common pseudoscience—astrology. Astrology is a pseudoscience because it’s a set of beliefs that seem to be based on scientific ideas, but really, it fails to obey even the most basic rules of science.
What are the basic rules of science, then? Continue reading
The ecliptic, as astronomers call it, is the apparent path of the sun against the background of the stars in the sky.
It’s useful because it tells us how to find the planets in the sky. They can be hard to spot if you don’t know where to look, but they will always be somewhere along one imaginary line that arcs across the sky—the ecliptic.
This pattern never changes. The planets don’t follow the ecliptic exactly, but it’s useful for getting an idea of where they should be.
But why does it work—and what exactly does it mean, when it’s obvious we can’t see the sun among the stars of the night sky? Continue reading
In the 4th century B. C. E. (Before Common Era), scientists believed the Earth was the center of the universe. Before that, they were convinced the Earth was flat.
Now, if anyone so much as mentions that the Earth is the center of the universe, they are quickly corrected. The very idea is absurd. (Although there are in fact online “societies” for people who believe the Earth is flat.)
We now know that not only is the Earth not the center of the universe, but neither is the sun, which is undeniably the center of the solar system. Were we to zoom out much further and take a look at our galaxy, the Milky Way, we would find that the sun is not even near the center of its own galaxy.
In fact, it’s located in a small “spur” of stars just off one of the spiraling arms of the galaxy. Since the current theory states our universe is infinite, there can’t even be a center, and thus our galaxy is not the center of everything. How wrong those early astronomers were!
But what does all this mean? Where exactly are we in the universe? | <urn:uuid:071bf7b9-66d7-4f15-9343-19e83cb08093> | 3.1875 | 1,572 | Content Listing | Science & Tech. | 53.924108 | 95,480,642 |
International conference on particle detectors
Leading experts on gaseous ionizing particle detectors meet at TUM’s IAS
2017-06-18 – News from the Physics Department
The conference deals with detectors for particles whose kinetic energy is sufficiently high to ionize gas molecules or atoms. The resulting ions cause a current flow which can be measured. The oldest and arguably best known example of such a “gaseous ionizing particle detector” is the Geiger counter, invented more than 100 years ago.
Today, gaseous ionisation detectors form an important group of instruments used for radiation detection and measurement and are used in a range of different fields. These include particle and astro-particle physics as well as nuclear physics and their applications in biology and medicine. They are indispensable in radiation protection. Some gaseous ionization detectors – like dosimeters – are optimized for low levels of radiation to be observed over long periods of time, others can measure very fast and with a high spatial resolution.
Modern developments include so-called micro-pattern gas detectors (MPGD). These utilize advances in photolithography and other microprocessing techniques developed for semiconductor electronics to build particle detectors with high radiation resistance and excellent resolution in time and space.
The meeting covers recent and future developments in the field. One day will be fully dedicated to a topical workshop on protection of MPGDs against electrical discharges. This is particularly important for the safe operation of such detectors in harsh radiation environments, like at CERN’s large hadron collider (LHC).
About the RD51 collaboration
RD51 is the technical name of a worldwide collaboration established at CERN, the European research organization that operates the largest particle physics laboratory in the world in Geneva. The LHC, operated at CERN, is also the world’s largest and most powerful particle accelerator and collider.
The RD51 collaboration works on the development and application of advanced gaseous detector technologies and associated electronic readout systems. It serves as a global platform for the scientific community – for sharing know-how and results and working on common projects and infrastructure. The RD51 collaboration involves 90 universities and research laboratories from 25 countries in Europe, North and South America, Asia and Africa.
About the local organizers
The topics of Prof. Laura Fabbietti’s research group at TUM’s Physics Department include the development and application of gaseous particle detectors for basic research. The group is currently involved in the ALICE TPC upgrade project at CERN’s LHC. ALICE is one of the largest particle detectors in the world and the time projection chamber is at the heart of ALICE, recording the 3d paths of the ejected particles after a collision.
The Fabbietti group built all full-size prototypes for the detectors, ran a dedicated R&D program and are now actively involved in the production of readout chamber elements and the coordination of the project. In parallel to the ALICE activities, the group continues its research on improving the stability of micro-pattern gaseous detectors against electrical discharges and on optimization of their high-voltage systems.
The organization of the meeting is supported by:
- RD51 Collaboration, CERN
- TUM Excellence Cluster ‘Universe’, Garching
- TUM Institute for Advanced Study, Garching
Local Organizing Committee
Prof. Dr. Laura Fabbietti (co-chair), Dr. Piotr Gasik (chair), Bernhard Hohlweger, Thomas Klemenz, Lukas Lautner, Andreas Mathis and Petra Zweckinger (secretary)
- RD51 Collaboration: Development of Micro-Pattern Gas Detectors Technologies
- Research group Fabbietti
- ALICE Experiment at the Large Hadron Collider
- Wikipedia article about the ALICE experiment
- Dr. Johannes Wiedersich | <urn:uuid:778d8191-d559-4562-8473-0e19f808b7f0> | 2.734375 | 809 | News (Org.) | Science & Tech. | 19.725201 | 95,480,674 |
Téorema Bayes mangrupa hasil dina
In the context of Bayesian probability theory and
As a mathematical theorem, Bayes' théorem is valid regardless of whether one adopts a frequentist or a Bayesian interpretation of probability. However, there is disagreement as to what kinds of variables can be substituted for A and B in the théorem; this topic is tréated at gréater length in the articles on Bayesian probability and frequentist probability.
Bayes' théorem is named after the Reverend Thomas Bayes (1702–61). Bayes worked on the problem of computing a distribution for the paraméter of a binomial distribution (to use modérn terminology); his work was edited and presented posthumously (1763) by his friend Richard Price, in An Essay towards solving a Problem in the Doctrine of Chances. Bayes' results were replicated and extended by Laplace in an essay of 1774, who apparently was not aware of Bayes' work.
One of Bayes' results (Proposition 5) gives a simple description of conditional probability, and shows that it does not depend on the order in which things occur:
The main result (Proposition 9 in the essay) derived by Bayes is the following: assuming a uniform distribution for the prior distribution of the binomial paraméter p, the probability that p is between two values a and b is
where m is the number of observed successes and n the number of observed failures. His preliminary results, in particular Propositions 3, 4, and 5, imply the result now called Bayes' Théorem (as described below), but it does not appéar that Bayes himself emphasized or focused on that result.
What is "Bayesian" about Proposition 9 is that Bayes presented it as a probability for the paraméter p. That is, not only can one compute probabilities for experimental outcomes, but also for the paraméter which governs them, and the same algebra is used to maké inferences of either kind. Interestingly, Bayes actually states his question in a way that might maké the idéa of assigning a probability distribution to a paraméter palatable to a frequentist. He supposes that a billiard ball is thrown at random onto a billiard table, and that the probabilities p and q are the probabilities that subsequent billiard balls will fall above or below the first ball. By making the binomial paraméter p depend on a random event, he cleverly escapes a philosophical quagmire that he most likely was not even aware was an issue. | <urn:uuid:1123eaf5-e768-4ac4-9bf8-49de3008e704> | 3.609375 | 545 | Knowledge Article | Science & Tech. | 26.080176 | 95,480,677 |
The project, led by Stuart Harrop, Professor of Wildlife Management Law at DICE and Deputy Head of Kent’s Department of Anthropology, and Matthew Linkie, a researcher at DICE, also aims to improve local livelihoods through sustainable natural resource use in forest-edge communities and to develop an innovative model for Indonesian community-based conservation.
The Indonesian archipelago contains about 10% of the world’s tropical rainforest, which plays a critical role in regional watershed protection, as well as in global efforts to conserve biodiversity and to sequester carbon. However, Indonesia currently experiences one of the highest rates of deforestation in the world and the multiple threats that biodiversity faces in Indonesia show little sign of waning.
Indonesia, with its diversity of traditional culture, also supports the world’s largest population of Muslims whose religion has a strong influence on their daily life. Islamic philosophies underpin biodiversity conservation in a number of ways principally through the doctrine of Khalifa (stewardship). Furthermore other traditional belief systems similarly hold a wealth of practices and beliefs that further conservation strategies. Taken together there is much scope for enhancing positive community attitudes for effective natural resource conservation.
Professor Harrop said: ‘This project presents a unique opportunity to work with Indonesian Islamic leaders in national Islamic religious institutes and their subsidiary colleges in rural areas, who have been prominent in promoting Islamic ideas and teachings. Working with communities in this capacity provides an ideal opportunity to increase their support for biodiversity conservation through integrating key religious concepts and traditional conservation approaches into conventional management plans and conservation strategies.’
Matthew Linkie said: ‘The project will take place around Sumatra’s Kerinci Seblat National Park, a UNESCO World Heritage Site that is vital to biodiversity conservation. Kerinci Seblat is surrounded by farming communities who live in close proximity to wildlife, and suffer losses from human-wildlife conflicts, such as crop-raiding or livestock depredation incidents. These conflicts reduce local tolerance towards wildlife and local support for biodiversity conservation. So the Department of Forestry, in partnership with local and international NGOs, has implemented a human-wildlife conflict management strategy for Kerinci, but no formal project, as of yet, has attempted to forge strong links with the local communities. So there is an urgent need to work more closely with the forest-edge communities to improve both local livelihoods and biodiversity conservation prospects.’
Their local partners include GreenLaw Indonesia, an NGO that has run community conservation and development projects in Sumatra and elsewhere in Indonesia since 2003. The project is funded by a Darwin Initiative and a Rufford Small Grant for Nature Conservation.
Karen Baxter | alfa
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
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New Zealand plants are unique! New Zealand has some of the oldest primeval forests in the world, the largest type of moss and some of the largest tree ferns found anywhere. Many of the species are very similar to those growing on Earth in the time of the dinosaurs – and even earlier.
Aotearoa separated from Gondwanaland approximately 85 million years ago. The separation from Australia left New Zealand at least 2,000 km away 55 million years ago. This isolation from other land masses meant that, until humans arrived, plants were not replaced or competed with by other species from elsewhere. They continued to evolve alone – in this unique environment.
Many plant varieties are related to plants found elsewhere – both in the northern and southern hemispheres. Fossil records also show that many of New Zealand’s plants are similar to those that were living on Gondwanaland.
However, our indigenous flora and fauna have also had time to evolve into unique species: 82% of New Zealand plants are endemic – they are not found anywhere else in the world.
Geological processes such as tectonic activity, erosion and glaciation as well as climate change and sea level changes have altered the coastline of New Zealand in the past. As a result, over millions of years, New Zealand has been a series of islands, a larger landmass, largely underwater or under ice.
The changes to the land forced a process called speciation: animals and plants with useful adaptations survived. Eventually, these animals and plants become so different from their ancestors that they were no longer able to reproduce with the ancestral species. They had become new species.
Aotearoa New Zealand also has many examples of regional endemism – where animal or plant varieties are found only in restricted locations.
Some specific adaptations of New Zealand plants
Many native shrubs have a characteristic growth form called divarication. This is where the plant grows in a tangled way, with interlaced stems and small leaves. There are several ideas about why this is useful, but the dominant theory is that divarication may be a protective mechanism. The leaves are tucked inside and therefore less accessible for browsing animals and less prone to damage from frost or snow.
Many flowers are small and white. New Zealand has a more limited range of pollinators compared to the rest of the world. Plants have evolved with animals, and the flowers have become specifically adapted to particular pollinators. Many of our pollinators are moths, small native bees, lizards and crawling insects that are not attracted by colour but by scent – so having showy flowers is unnecessary.
Most trees are evergreen. New Zealand did not undergo the extreme ice ages of the northern hemisphere, and as a result, not many of our trees are cold tolerant. They don’t have the protective adaptation of losing leaves in the winter as many northern hemisphere trees do. Only 11 species of New Zealand plants are deciduous – losing their leaves over winter.
Many of our trees are dioecious. This means they have flowers on separate male and female trees. A much higher proportion (12–13%) of New Zealand tree species are dioecious compared with other parts of the world (less than 5% in the UK). There is increased possibility of genetic variation carried in the seeds of dioecious plants. Genetic variability provides more likelihood of survival in a changing environment. The disadvantage of having separate male and female trees is that, if they are too far apart, it is more difficult for the pollen to be carried from the male to the female, reducing the likelihood of seeds forming.
Many of our plants are highly variable in their form. This often makes identification difficult. Some have slightly different forms depending on the environment they are growing in – this is called heterophylly. Hybridism is also common – where plants of different species in a family cross-pollinate, creating new varieties. Many New Zealand plant families such as the Veronica genus (formerly Hebe) now include many species.
Many plants have very different juvenile and adult forms. This is called heteroblasty, and the different form at each stage of the plant’s life provides an advantage, for example while it is growing.
Animals and plants evolved together within the environment, and over time, unique and finely tuned ecosystems developed in New Zealand. In many of our ecosystems, the organisms became so interdependent – relying on each other for food, habitats and life processes such as pollination – that any changes could be detrimental. These changes are easier to see with iconic species of animals but may be less obvious in the plant world. However, many of our plants are now endangered. Deforestation caused a huge reduction in habitats, as did the introduction of other organisms into the New Zealand environment.
Many introduced plant species have become weeds, which can either outcompete native plants for habitat (wilding pines) or have a direct negative impact on the plants themselves (old man’s beard). Predators and other introduced wildlife can destroy pollinators such as birds or lizards or successfully compete with them (stoats and possums) or impact negatively on the plants themselves (mice eating native seeds).
Nature of science
This article highlights the ‘Understanding science’ aspect of the Nature of science – it illustrates how scientists use evidence to create theories about why New Zealand plants are so unique.
There is a range of useful resources for further reading about native plants. These include books by authors such as Andrew Crowe, John Salmon, John Dawson and Tony Foster. Websites such as Manaaki Whenua – Landcare Research, Department of Conservation and Bushmansfriend all provide detailed information about New Zealand native plants.
The Department of Conservation has recently produced a report on our endangered plant species – New plant status report shows increased threats – and kauri has now been reclassified as a threatened species, mainly due to kauri dieback disease. | <urn:uuid:cd250256-f4b6-4d15-a61a-0a2f10a99df0> | 4.15625 | 1,217 | Knowledge Article | Science & Tech. | 33.887892 | 95,480,712 |
Specific Heat of Four Rare-Earth Compounds Between 0.4° and 5°K
We have measured the specific heat of lanthanum and holmium ethylsulfate (LaES and HoES) and of lutetium and gadolinium iron garnet (LuIG and GdIG) by means of a cryostat using liquid 3He or 4He. The sample, in the form of single crystals or a sintered block, is attached to a support which is made up of a quartz frame and thin copper strips in order to have a low specific heat. This support can be brought in contact with the helium refrigerator by means of a heat switch. Two carbon resistors are used: a Speer 450-Ω resistor covers the region from 0.35° to 0.9 °K, and a 40-Ω (math)W Allen-Bradley is used at higher temperatures. The resistor operating below 0.9°K is calibrated by means of the vapor pressure of liquid 3He and the susceptibility of three single crystals of cerium magnesium nitrate which obeys Curie’s law in this temperature region. The samples are cooled from room temperature entirely by means of the heat switch and without any helium exchange gas. This is to prevent adsorption of the gas on the specimen, in particular on the sintered samples, which have been found to be porous.
KeywordsHeat Switch Helium Refrigerator Cerium Magnesium Nitrate Total Specific Heat Gadolinium Iron
Unable to display preview. Download preview PDF. | <urn:uuid:517e91ea-c3f5-4c4e-869f-380ca4a6ce2a> | 2.5625 | 325 | Truncated | Science & Tech. | 56.366923 | 95,480,746 |
What are the historical origins of the $f(x)$ notation used for functions? That is when did people start to use this notation instead of just thinking in terms of two different variables one being dependent on the other?
Any references would be appreciated.
The authoritative reference for these matters is the book
Florian Cajori, A History of Mathematical Notations (1929), reprinted by Dover.
On page 268 of volume II, Cajori says that the notation $f(x)$ was first used by Euler in 1734:
According to this wiki article (search for “function”), this goes back to the first half of 17th century, so long before Euler (as it should be, since Newton already use the dot over the function symbol for derivative).
Take a look at Earliest uses of symbols.
It has a good historical information. | <urn:uuid:fe0e10a7-8122-48bf-b32f-b4f46016e913> | 3 | 185 | Q&A Forum | Science & Tech. | 47.151765 | 95,480,753 |
(For brevity's sake, hereafter I will refer to the parent isotope as ).In addition, it requires that these measurements be taken from several different objects which all formed at the same time from a common pool of materials.When objects of the Old Kingdom and Middle Kingdom of Egypt yielded carbon dates that appeared roughly comparable with the historical dates, Libby made his method known.With initial large margin of error and anything that did not square with expectation, judged as contaminated, the method appeared to work and was hailed as completely reliablejust as the atomic clock is reliableand this nobody doubted.The Oxalic acid standard was made from a crop of 1955 sugar beet. The isotopic ratio of HOx I is -19.3 per mille with respect to (wrt) the PBD standard belemnite (Mann, 1983). T designation SRM 4990 C) was made from a crop of 1977 French beet molasses.
In centuries to come a body of a man or animal who lived and died in the 20th century would appear paradoxically of greater age since death than the body of a man or animal of the 19th century, and if the process of industrial use of fossil, therefore dead, carbon continues to increase, as it is expected will be the case, the paradox will continue into the forthcoming centuries.
The carbon-14 atoms that cosmic rays create combine with oxygen to form carbon dioxide, which plants absorb naturally and incorporate into plant fibers by photosynthesis.
Animals and people eat plants and take in carbon-14 as well.
Cosmic rays enter the earth's atmosphere in large numbers every day.
For example, every person is hit by about half a million cosmic rays every hour. | <urn:uuid:a4ddb7fb-479b-4bd7-80be-726c48c47a05> | 3.125 | 351 | Spam / Ads | Science & Tech. | 44.999049 | 95,480,756 |
Using electron microscopy techniques (SEM, LTSEM) coupled with analytical methods (XRD and EDS) the role of phosphorus has been assessed in the formation of freshwater calcite deposits (tufa) in a small pond of the Ruidera Lakes (Spain). Differences between the cell walls and sheaths of bacteria and eukaryotic algae as well as the existence of additional layers of extracellular polymeric substances (EPS) were features that lead to differences in the process of induced calcite biomineralization. Phosphorus has influence in the biornineralization of the EPS, sheaths and cell walls of cyanobacteria allowing for fossil preservation whereas does not participate in the calcite precipitation around algae and mosses. This variability may explain the different positive or negative roles played by natural or artificial inputs of phosphorus in hard water lakes and the different morphological features of calcite precipitates associated with eukaryotic and cyanobacteria picoplankton found in natural environments. The biomineralization observed is in agreement with the isotopic composition of the tufa layers that reflect the variations in environmental conditions around biological communities.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below | <urn:uuid:f1850814-adff-4179-9164-9a88dd5e8ff1> | 2.90625 | 257 | Academic Writing | Science & Tech. | -10.58429 | 95,480,784 |
A long-standing question in astrophysics is: how and when did supermassive black holes appear and grow in the early universe? New research using NASA's Chandra X-ray Observatory and the Sloan Digital Sky Survey (SDSS) suggests that an answer to this question lies with the intermittent way giant black holes may consume material in the first billion years after the Big Bang.
Astronomers have determined the Big Bang occurred about 13.8 billion years ago and have evidence from the SDSS that supermassive black holes with masses of about a billion times that of the sun existed by about 12.8 billion years ago. This implies that supermassive black holes grew rapidly in the first billion years after the Big Bang. Yet, scientists have struggled to find signs of these growing giant black holes.
"Supermassive black holes are not spontaneously born—they need to ingest vast amounts of material and that takes time," said lead author Edwige Pezzulli, PhD student of the University of Rome in Italy and member of the project "FIRST", funded by the European Research Council. "We are trying to figure out how they have done this without giving off many telltale signs of this growth."
When material is falling toward a black hole, it becomes heated, and produces large amounts of electromagnetic radiation, including copious X-ray emission. Rapidly growing black holes in the very early Universe should be detectable with Chandra. However, these growing supermassive black holes have proved to be elusive, with only a few, yet to be confirmed candidates found in very long Chandra observations such as the Chandra Deep Field-South, the deepest X-ray image ever taken.
To address this conundrum, Pezzulli and her colleagues examined different theoretical models and tested them against optical data from the SDSS and X-ray data from Chandra. Their findings indicate that black hole feeding during this era may turn on abruptly and last for short periods of time, which means this growth may be difficult to spot.
"In our model only about a third of black holes were actively consuming material and growing 13 billion years ago" said co-author Rosa Valiante of the National Institute for Astrophysics (INAF) in Italy and member of the FIRST team. "About 200 million years earlier only 3% of the black holes were actively eating. Timing, it appears, may be everything."
The researchers reached their conclusions after testing multiple hypotheses, all of which assumed that the black hole growth could exceed the so-called Eddington limit, where the outward pressure of radiation from the hot gas balances the inward pull of the gravity of the black hole.
The authors' results argued against the possibility that only a small fraction of galaxies during the first billion years after the Big Bang contain supermassive black holes. Also, although these early black holes were likely obscured by thick clouds of material, the authors found that most of the X-rays would have been able to penetrate these clouds.
The study is based on the idea that when they were born, the first black holes weighed only about a hundred suns. "These "light" black holes seeds could be the remnants of the first generation of massive stars formed only a few hundred million years after the Big Bang" said co-author Maria Orofino, PhD student of the Scuola Normale Superiore in Italy.
The researchers, a team of female scientists, including Simona Gallerani of Scuola Normale Superiore in Pisa and Tullia Sbarrato of Bicocca University of Milan, in Italy, found that black holes can bulk up so much in their relatively rare bursts of intense growth that light seeds can reach a billion times the mass of the Sun when the universe is only a billion years old.
"In order to know if we are ultimately correct, we will need to look at larger swaths of the sky in X-rays to see if we can find the early, feasting black holes that our models have predicted," said Raffaella Schneider, of Sapienza University in Italy and leader of the ERC project FIRST. "Our results certainly show promise."
Explore further: Hubble finds clues to the birth of supermassive black holes
Edwige Pezzulli et al. Faint progenitors of luminous ∼ 6 quasars: Why do not we see them?, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stw3243 , https://arxiv.org/abs/1612.04188 | <urn:uuid:fedbcf66-5dac-475e-8e1a-9f6c9d4bd5eb> | 4.1875 | 938 | Knowledge Article | Science & Tech. | 43.989595 | 95,480,797 |
Authors: Wei Fan
We have always believed that stationary charges generate an electrostatic field. A moving charge generates a current and a magnetic field. A changing magnetic field produces electromagnetic radiation. Frictional electrification is the generation of electrostatic charge and an electrostatic field through friction. The charge does not move. It has no current, magnetic field and Electromagnetic radiation. However, in the latest experiments we found that a rubbed rule can cause small magnetic needle deflection and electromagnetic radiation. This shows that the rubbed ruler can produce current, magnetic field and electromagnetic radiation. This can lead us to rethink traditional electrostatics.
Comments: 2 Pages.
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Short-Period Ocean Bottom Seismometers detect vibrations from small earthquakes ranging from 0.1 Hz to 100 Hz. These earthquakes are caused by local phenomena, such as melt movement beneath volcanoes and upward flow of hydrothermal fluids in the conduits that feed black smoker chimneys. These instruments enable imaging of the seismic energy traveling through the seafloor.
All instruments are streaming data live to IRIS (Incorporated Research Institutions for Seismology), and are available to the public. Daily and hourly updates on the number of earthquakes occurring at Axial Seamount can be accessed through Dr. William Wilcock’s website, one of several Community Tools that users have created.
This instrument measures the following data products. Select a data product's name to learn more.
|Short Period Ground Velocity||SGRDVEL||DPS|
The algorithm code used to generate data products for this instrument is also available in the ion-functions GitHub repository.Algorithm Code
Instrument Models & Deployed Locations
The OOI includes the following instrument makes and models for this instrument type. Follow the links below to find out where in the OOI this instrument has been deployed. You'll also find quick links for each instrument to Data portal, where you can plot and access data. | <urn:uuid:4da40e88-e32b-4bc5-905a-c2ca03cc6bbe> | 2.953125 | 268 | Knowledge Article | Science & Tech. | 40.955828 | 95,480,821 |
By Julian Lowell Coolidge
Read Online or Download A History of Geometrical Methods (Dover Books on Mathematics) PDF
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Extra resources for A History of Geometrical Methods (Dover Books on Mathematics)
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Found most commonly in these habitats: 3 times found in Coega Bontveld, 7 times found in rainforest, 1 times found in Savanna, 2 times found in coastal lowland rainforest, 1 times found in mature forest edge, 2 times found in pondoland coastal plateau, 1 times found in Primary forest, 1 times found in Aghulas Sand Fynbos, 1 times found in Algoa Dune Strandveld / Southern Cape Dune Fynbos mozaic, 1 times found in tropical wet forest, ...
Found most commonly in these microhabitats: 2 times sifted litter (leaf mold, rotten wood), 2 times sour grassland, 1 times nest in soil, 1 times forest margin in large clearing, 1 times summit ridge, 1 times sifted leaf litter.
Collected most commonly using these methods: 6 times Hand collected, 4 times Pitfall trap, 3 times EC31 yellow pan trap, 3 times Malaise trap, 2 times MW 50 sample transect, 5m, 1 times search, 1 times EC32 sweeping, 1 times Malaise, 1 times pitfall trap, PF bucket, 1 times Pitfalls, 1 times Winkler sifter, ...
Elevations: collected from 14 - 1500 meters, 371 meters average
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ESAs Proba satellite here shows a winding segment of the 7240-km long Great Wall of China situated just northeast of Beijing. The Great Walls relative visibility or otherwise from orbit has inspired much recent debate.
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The 21 hours spent in space last October by Yang Liwei - Chinas first ever space traveller - were a proud achievement for his nation. The only disappointment came as Liwei informed his countrymen he had not spotted their single greatest national symbol from orbit.
"The Earth looked very beautiful from space, but I did not see our Great Wall," Liwei told reporters after his return.
Frédéric Le Gall | ESA
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
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PL/SQL programs normally are used to manipulate database information. You commonly do this by declaring variables and data structures in your programs, and then working with that PL/SQL-specific data.
A variable is a named instantiation of a data structure declared in a PL/SQL block (either locally or in a package). Unless you declare a variable as a CONSTANT, its value can be changed at any time in your program.
The following table summarizes the different types of program data.
Variables made up of a single value, such as a number, date, or Boolean.
Variables made up of multiple values, such as a record, collection, or instance of a user-defined object type. See the sections "Records in PL/SQL," "Collections in PL/SQL," and "Object-Oriented Features."
Logical pointers to values or cursors.
Variables containing large object (LOB) locators.
Scalar datatypes divide into four families: number, character, datetime, and Boolean. Subtypes further define a base datatype by restricting the values or size of the base datatype.
Numeric datatypes represent real numbers, integers, and floating-point numbers. They are stored as NUMBER, PLS_INTEGER, and IEEE floating-point storage types.
Decimal numeric datatypes store fixed and floating-point numbers of just about any size. They include the subtypes NUMBER, DEC, DECIMAL, NUMERIC, FLOAT, REAL, and DOUBLE PRECISION. The maximum precision of a variable ... | <urn:uuid:15a664bb-8abd-4a38-b61c-702bdc02647d> | 3.53125 | 340 | Documentation | Software Dev. | 39.151263 | 95,480,879 |
Construct a library Time that contains the time-conversion functions (given a number of seconds, returns the equivalent number of minutes; given the number of minutes, returns the equivalent number of hours; given the number of hours, returns the equivalent number of days; given the number of seconds, returns the equivalent number of days). Write a driver program to test your library.© BrainMass Inc. brainmass.com July 19, 2018, 9:24 pm ad1c9bdddf
First compile the library file
gcc -c myTime.c
this will create myTime.o
then simply do
gcc -o test testTime.c myTime.o
remember that the header file myTime.h containing the signatures of the functions should be included in your test driver file
Here is the code file
/* To compile the functions into a library ...
Three source code files will show you how to write appropriate functions to convert different time scales/metrics. This can be useful in
a) code to write software clock or watch
b) understanding of how to use multiple files for a single project
c) understanding of the use of header files
This will show how to compile multiple files into one executable file. | <urn:uuid:7dc2e5ee-2a61-4d3f-b6fb-00dd00618193> | 2.59375 | 255 | Tutorial | Software Dev. | 53.449754 | 95,480,890 |
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A larva (plural: larvae //) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The larva's appearance is generally very different from the adult form (e.g. caterpillars and butterflies) including different unique structures and organs that do not occur in the adult form. Their diet may also be considerably different.
Larvae are frequently adapted to environments separate from adults. For example, some larvae such as tadpoles live almost exclusively in aquatic environments, but can live outside water as adult frogs. By living in a distinct environment, larvae may be given shelter from predators and reduce competition for resources with the adult population.
Animals in the larval stage will consume food to fuel their transition into the adult form. In some species like barnacles, adults are immobile but their larvae are mobile, and use their mobile larval form to distribute themselves.
Some larvae are dependent on adults to feed them. In many eusocial Hymenoptera species, the larvae are fed by female workers. In Ropalidia marginata (a paper wasp) the males are also capable of feeding larvae but they are much less efficient, spending more time and getting less food to the larvae.
It is a misunderstanding that the larval form always reflects the group's evolutionary history. This could be the case, but often the larval stage has evolved secondarily, as in insects. In these cases the larval form may differ more than the adult form from the group's common origin.
Selected types of larvaeEdit
|Animal||Name of larvae|
|Porifera (sponges)||coeloblastula (= blastula, amphiblastula), parenchymula (= parenchymella, stereogastrula)|
|Cnidarians||planula (= stereogastrula), actinula|
|Platyhelminthes||Turbellaria: Müller's larva, Götte’s larva;|
Trematoda: miracidium, sporocyst, redia, cercaria;
Cestoda: cysticercus, cysticercoid, oncosphere (or hexacanth), coracidium, plerocercoid
|Nematoda||Dauer larva, microfilaria|
|Ectoprocta||cyphonautes, vesiculariform larvae|
|Cycliophora||pandora, chordoid larva|
|Nemertea||pilidium, Iwata larva, Desor larva|
|Certain molluscs, annelids, nemerteans and sipunculids||trochophore|
|Mollusca: freshwater Bivalvia (mussels)||glochidium|
|Arthropoda: †Trilobita||protaspis (unjointed), meraspis (increasing number of joints, but 1 less than the holaspis), holaspis (=adult)|
|Arthropoda: Xiphosura||euproöps larva ("trilobite larva")|
|Crustaceans||General: nauplius, metanauplius, protozoea, antizoea, pseudozoea, zoea, postlarva, cypris, primary larva, mysis|
|Insecta: Lepidoptera (butterflies and moths)||caterpillar|
|Insecta: Flies, Bees, Wasps||maggot|
|Deuterostomes||dipleurula (hypothetical larva)|
|Echinodermata||bipinnaria, vitellaria, brachiollaria, pluteus, ophiopluteus, echinopluteus, auricularia|
|Urochordata||tadpole (does not feed, technically a "swimming embryo")|
|Fish: Petromyzontiformes (lamprey)||ammocoete|
|Fish: Anguilliformes (eels)||leptocephalus|
Within Insects, only Endopterygotes show different types of larvae. Several classifications have been suggested by many entomologists, and following classification is based on Antonio Berlese classification in 1913. There are four main types of endopterygote larvae types:
- Apodous larvae – no legs at all and are poorly sclerotized. Based on sclerotization, three apodous forms are recognized.
- Protopod larvae – larva have many different forms and often unlike a normal insect form. They hatch from eggs which contains very little yolk. Ex. first instar larvae of parasitic hymenoptera.
- Polypod larvae – also known as eruciform larvae, these larva have abdominal prolegs, in addition to usual thoracic legs. They poorly sclerotized and relatively inactive. They live in close contact with the food. Best example is caterpillars of lepidopterans.
- Oligopod larvae – have well developed head capsule and mouthparts are similar to the adult, but without compound eyes. They have six legs. No abdominal prolegs. Two types can be seen:
- Campodeiform – well sclerotized, dorso-ventrally flattened body. Usually long legged predators with prognathos mouthparts. (lacewing, trichopterans, mayflies and some coleopterans).
- Scarabeiform – poorly sclerotized, flat thorax and abdomen. Usually short legged and inactive burrowing forms. (Scarabaeoidea and other coleopterans).
- Crustacean larvae
- Spawn (biology)
- Non-larval animal juvenile (immature) stages and other life cycle stages:
- In Porifera: olynthus, gemmule
- In Cnidaria: ephyra, scyphistoma, strobila, gonangium, hydranth, polyp, medusa
- In Mollusca: paralarva, young cephalopods
- In Platyhelminthes: hydatid cyst
- In Bryozoa: avicularium
- In Acanthocephala: cystacanth
- In Insecta:
- Protozoan life cycle stages
- Algal life cycle stages:
- Marine larval ecology
- Sen, R; Gadagkar, R (2006). "Males of the social wasp Ropalidia marginata can feed larvae, given an opportunity". Animal Behaviour. 71: 345–350. doi:10.1016/j.anbehav.2005.04.022.
- Williamson, Donald I. (2006). "Hybridization in the evolution of animal form and life-cycle". Zoological Journal of the Linnean Society. 148: 585–602.
- Moore, R.C. (1959). Arthropoda I – Arthropoda General Features, Proarthropoda, Euarthropoda General Features, Trilobitomorpha. Treatise on Invertebrate Paleontology. Part O. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. O121, O122, O125. ISBN 0-8137-3015-5.
- "Recognizing Insect Larval Types". University of Kentucky. Retrieved 28 April 2016.
- "Insect Larval Forms". About.com. Retrieved 28 April 2016.
- "Types of Insect Larva". Agri info. Retrieved 28 April 2016.
|Wikisource has the text of the 1911 Encyclopædia Britannica article Larval Forms.|
- Media related to Larva at Wikimedia Commons
- The dictionary definition of larva at Wiktionary
- Arenas-Mena, C. (2010) Indirect development, transdifferentiation and the macroregulatory evolution of metazoans. Philosophical Transactions of the Royal Society B: Biological Sciences. Feb 27, 2010 Vol.365 no.1540 653-669
- Brusca, R. C. & Brusca, G. J. (2003). Invertebrates (2nd ed.). Sunderland, Mass. : Sinauer Associates.
- Hall, B. K. & Wake, M. H., eds. (1999). The Origin and Evolution of Larval Forms. San Diego: Academic Press.
- Leis, J. M. & Carson-Ewart, B. M., eds. (2000). The Larvae of Indo-Pacific Coastal Fishes. An Identification Guide to Marine Fish Larvae. Fauna Malesiana handbooks, vol. 2. Brill, Leiden.
- Minelli, A. (2009). The larva. In: Perspectives in Animal Phylogeny and Evolution. Oxford University Press. p. 160-170. link.
- Shanks, A. L. (2001). An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Oregon State University Press, Corvallis. 256 pp.
- Smith, D. & Johnson, K. B. (1977). A Guide to Marine Coastal Plankton and Marine Invertebrate Larvae. Kendall/Hunt Plublishing Company.
- Stanwell-Smith, D., Hood, A. & Peck, L. S. (1997). A field guide to the pelagic invertebrates larvae of the maritime Antarctic. British Antarctic Survey, Cambridge.
- Thyssen, P.J. (2010). Keys for Identification of Immature Insects. In: Amendt, J. et al. (ed.). Current Concepts in Forensic Entomology, chapter 2, pp. 25–42. Springer: Dordrecht, . | <urn:uuid:64a6f4d8-3a32-49c7-91b1-f666acf386c2> | 4.09375 | 2,174 | Knowledge Article | Science & Tech. | 26.267999 | 95,480,897 |
Concept: Marine pollution
Ocean plastic can persist in sea surface waters, eventually accumulating in remote areas of the world’s oceans. Here we characterise and quantify a major ocean plastic accumulation zone formed in subtropical waters between California and Hawaii: The Great Pacific Garbage Patch (GPGP). Our model, calibrated with data from multi-vessel and aircraft surveys, predicted at least 79 (45-129) thousand tonnes of ocean plastic are floating inside an area of 1.6 million km2; a figure four to sixteen times higher than previously reported. We explain this difference through the use of more robust methods to quantify larger debris. Over three-quarters of the GPGP mass was carried by debris larger than 5 cm and at least 46% was comprised of fishing nets. Microplastics accounted for 8% of the total mass but 94% of the estimated 1.8 (1.1-3.6) trillion pieces floating in the area. Plastic collected during our study has specific characteristics such as small surface-to-volume ratio, indicating that only certain types of debris have the capacity to persist and accumulate at the surface of the GPGP. Finally, our results suggest that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than in surrounding waters.
Imidacloprid is one of the most widely used insecticides in the world. Its concentration in surface water exceeds the water quality norms in many parts of the Netherlands. Several studies have demonstrated harmful effects of this neonicotinoid to a wide range of non-target species. Therefore we expected that surface water pollution with imidacloprid would negatively impact aquatic ecosystems. Availability of extensive monitoring data on the abundance of aquatic macro-invertebrate species, and on imidacloprid concentrations in surface water in the Netherlands enabled us to test this hypothesis. Our regression analysis showed a significant negative relationship (P<0.001) between macro-invertebrate abundance and imidacloprid concentration for all species pooled. A significant negative relationship was also found for the orders Amphipoda, Basommatophora, Diptera, Ephemeroptera and Isopoda, and for several species separately. The order Odonata had a negative relationship very close to the significance threshold of 0.05 (P = 0.051). However, in accordance with previous research, a positive relationship was found for the order Actinedida. We used the monitoring field data to test whether the existing three water quality norms for imidacloprid in the Netherlands are protective in real conditions. Our data show that macrofauna abundance drops sharply between 13 and 67 ng l(-1). For aquatic ecosystem protection, two of the norms are not protective at all while the strictest norm of 13 ng l(-1) (MTR) seems somewhat protective. In addition to the existing experimental evidence on the negative effects of imidacloprid on invertebrate life, our study, based on data from large-scale field monitoring during multiple years, shows that serious concern about the far-reaching consequences of the abundant use of imidacloprid for aquatic ecosystems is justified.
Environmental pollutants such as dioxins and PCBs, heavy metals, and organochlorine pesticides are a global threat to food safety. In particular, the aquatic biota can bioaccumulate many of these contaminants potentially making seafood of concern for chronic exposure to humans.
Environmental pollution by pharmaceuticals is increasingly recognized as a major threat to aquatic ecosystems worldwide. A variety of pharmaceuticals enter waterways by way of treated wastewater effluents and remain biochemically active in aquatic systems. Several ecotoxicological studies have been done, but generally, little is known about the ecological effects of pharmaceuticals. Here we show that a benzodiazepine anxiolytic drug (oxazepam) alters behavior and feeding rate of wild European perch (Perca fluviatilis) at concentrations encountered in effluent-influenced surface waters. Individuals exposed to water with dilute drug concentrations (1.8 micrograms liter(-1)) exhibited increased activity, reduced sociality, and higher feeding rate. As such, our results show that anxiolytic drugs in surface waters alter animal behaviors that are known to have ecological and evolutionary consequences.
The past uranium/polymetallic mining activities in the Sudety (SW Poland) left abandoned mines, pits, and dumps of waste rocks with trace elements and radionuclides which may erode or leach out and create a potential risk for the aquatic ecosystem, among others. In the present work four rivers affected by effluents from such mines were selected to evaluate the application of aquatic mosses for the bioindication of 56 elements. Naturally growing F. antipyretica and P. riparioides were compared with transplanted samples of the same species. The results demonstrate serious pollution of the examined rivers, especially with As, Ba, Fe, Mn, Pb, Ti, U and Zn, reaching extremely high concentrations in native moss samples. In the most polluted rivers native F. antipyretica and P. riparioides samples showed significantly higher concentrations of As, Ba, Cu, Fe, La, Nd, Ni, Pb, U and Zn than corresponding transplanted samples, whereas at less polluted sites a reverse situation was sometimes observed. Transplanted moss moved from clean to extremely polluted rivers probably protects itself against the accumulation of toxic elements by reducing their uptake. Selection of native or transplanted F. antipyretica and P. riparioides depended on the pollution load.
Microplastics are present in aquatic ecosystems the world over and may influence the feeding, growth, reproduction, and survival of freshwater and marine biota; however, the extent and magnitude of potential effects of microplastics on aquatic organisms is poorly understood. In the current study, we conducted a meta-analysis of published literature to examine impacts of exposure to microplastics on consumption (and feeding), growth, reproduction, and survival of fish and aquatic invertebrates. While we did observe within-taxa negative effects for all four categories of responses, many of the effects summarized in our study were neutral, indicating that the effects of exposure to microplastics are highly variable across taxa. The most consistent effect was a reduction in consumption of natural prey when microplastics were present. For some taxa, negative effects on growth, reproduction and even survival were also evident. Organisms that serve as prey to larger predators, e.g., zooplankton, may be particularly susceptible to negative impacts of exposure to microplastic pollution, with potential for ramifications throughout the food web. Future work should focus on whether microplastics may be affecting aquatic organisms more subtly, e.g., by influencing exposure to contaminants and pathogens, or by acting at a molecular level.
River ecosystems are among the most affected habitats globally by human activities, such as the release of chemical pollutants. However, it remains largely unknown how and to what extent many communities such as zooplankton are affected by these environmental stressors in river ecosystems. Here, we aim to determine major factors responsible for shaping community structure of zooplankton in heavily polluted river ecosystems. Specially, we use rotifers in the Haihe River Basin (HRB) in North China as a case study to test the hypothesis that species sorting (i.e. species are “filtered” by environmental factors and occur at environmental suitable sites) plays a key role in determining community structure at the basin level. Based on an analysis of 94 sites across the plain region of HRB, we found evidence that both local and regional factors could affect rotifer community structure. Interestingly, further analyses indicated that local factors played a more important role in determining community structure. Thus, our results support the species sorting hypothesis in highly polluted rivers, suggesting that local environmental constraints, such as environmental pollution caused by human activities, can be stronger than dispersal limitation caused by regional factors to shape local community structure of zooplankton at the basin level.
Marine plastic pollution has been a growing concern for decades. Single-use plastics (plastic bags and microbeads) are a significant source of this pollution. Although research outlining environmental, social, and economic impacts of marine plastic pollution is growing, few studies have examined policy and legislative tools to reduce plastic pollution, particularly single-use plastics (plastic bags and microbeads). This paper reviews current international market-based strategies and policies to reduce plastic bags and microbeads. While policies to reduce microbeads began in 2014, interventions for plastic bags began much earlier in 1991. However, few studies have documented or measured the effectiveness of these reduction strategies. Recommendations to further reduce single-use plastic marine pollution include: (i) research to evaluate effectiveness of bans and levies to ensure policies are having positive impacts on marine environments; and (ii) education and outreach to reduce consumption of plastic bags and microbeads at source.
Many microbial ecology studies have demonstrated profound changes in community composition caused by environmental pollution, as well as adaptation processes allowing survival of microbes in polluted ecosystems. Soil microbial communities in polluted areas with a long-term history of contamination have been shown to maintain their function by developing metal-tolerance mechanisms. In the present work, we review recent experiments, with specific emphasis on studies that have been conducted in polluted areas with a long-term history of contamination that also applied DNA-based approaches. We evaluate how the “costs” of adaptation to metals affect the responses of metal-tolerant communities to other stress factors (“stress-on-stress”). We discuss recent studies on the stability of microbial communities, in terms of resistance and resilience to additional stressors, focusing on metal pollution as the initial stress, and discuss possible factors influencing the functional and structural stability of microbial communities towards secondary stressors. There is increasing evidence that the history of environmental conditions and disturbance regimes play central roles in responses of microbial communities towards secondary stressors.
The demethylation potential of environmental pollutants is possibly an innate part of their comprehensive health risk. This paper develops a novel method called TDQ to quantify the demethylation epigenetic toxicity, termed the 5-AZA-CdR demethylation toxic equivalency, of aquatic samples from the heavily polluted Bohai Bay using Hep G2 cell lines transiently transfected with the pEGFP-C3 plasmid containing a methylated promoter of the EGFP reporter gene inserted artificially in vitro. | <urn:uuid:c98990ae-927f-4bf6-9519-0a711835b9d7> | 3.203125 | 2,172 | Academic Writing | Science & Tech. | 15.451462 | 95,480,908 |
Discovery (observation)(Redirected from Scientific discovery)
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Discovery is the act of detecting something new, or something "old" that had been unrecognized as meaningful. With reference to sciences and academic disciplines, discovery is the observation of new phenomena, new actions, or new events and providing new reasoning to explain the knowledge gathered through such observations with previously acquired knowledge from abstract thought and everyday experiences. A discovery may sometimes be based on earlier discoveries, collaborations, or ideas. Some discoveries represent a radical breakthrough in knowledge or technology.
New discoveries are acquired through various senses and are usually assimilated, merging with pre-existing knowledge and actions. Questioning is a major form of human thought and interpersonal communication, and plays a key role in discovery. Discoveries are often made due to questions. Some discoveries lead to the invention of objects, processes, or techniques. A discovery may sometimes be based on earlier discoveries, collaborations or ideas, and the process of discovery requires at least the awareness that an existing concept or method can be modified or transformed. However, some discoveries also represent a radical breakthrough in knowledge.
Within scientific disciplines, discovery is the observation of new phenomena, actions, or events which helps explain knowledge gathered through previously acquired scientific evidence. In science, exploration is one of three purposes of research, the other two being description and explanation. Discovery is made by providing observational evidence and attempts to develop an initial, rough understanding of some phenomenon.
Discovery within the field of particle physics has an accepted definition for what constitutes a discovery: a five-sigma level of certainty. Such a level defines statistically how unlikely it is that an experimental result is due to chance. The combination of a five-sigma level of certainty, and independent confirmation by other experiments, turns findings into accepted discoveries.
Discovery can also be used to describe the first incursions of peoples from one culture into the geographical and cultural environment of others. Western culture has used the term "discovery" in their histories to subtly emphasize the importance of "exploration" in the history of the world, such as in the "Age of Exploration".
- Bold hypothesis
- Creativity techniques
- List of multiple discoveries
- Multiple discovery
- USSR' state registry of discoveries
- Role of chance in scientific discoveries
- Scientific priority
- Timeline of scientific discoveries
- List of German inventors and discoverers
- Category:Lists of inventions or discoveries
This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (December 2011) (Learn how and when to remove this template message)
- General references
- B Barber (1 September 1961). "Resistance by scientists to scientific discovery". Science. 134 (3479): 596–602. doi:10.1126/science.134.3479.596. PMID 13686762.
- Merton, Robert K. (December 1957). "Priorities in scientific discovery: a chapter in the sociology of science". American Sociological Review. 22 (6): 635–659. doi:10.2307/2089193. ISSN 0003-1224. JSTOR 2089193.
- Carnegie Mellon University Artificial Intelligence and Psychology Project; Yulin Qin, Herbert A Simon (1990). "Laboratory replication of scientific discovery processes". Cognitive Science. 14 (2): 281–312. doi:10.1016/0364-0213(90)90005-H. OCLC 832091458. (preprint)
- A Silberschatz; A Tuzhilin (December 1996). "What makes patterns interesting in knowledge discovery systems". IEEE Transactions on Knowledge and Data Engineering. 8 (6): 970–974. doi:10.1109/69.553165.
- Tomasz Imielinski, Heikki Mannila (November 1996). "A database perspective on knowledge discovery". Communications of the ACM. 39 (11): 58–64. doi:10.1145/240455.240472.
- Specific references
- Rincon, Paul (12 December 2011). "Higgs boson: Excitement builds over 'glimpses' at LHC". BBC News. Retrieved 2011-12-12. | <urn:uuid:94492f6e-7bfe-42ea-b837-d7761d910d99> | 2.9375 | 906 | Knowledge Article | Science & Tech. | 32.929537 | 95,480,914 |
Earthwatch provides citizens with the opportunity to work alongside leading scientists to combat some of the planet’s most pressing environmental issues. With Earthwatch, you'll experience hands-on science in some of the most astounding locations in the world. You'll meet a community of like-minded travelers and return home with stories filled with adventure.
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What can we learn about Italy’s ancient people from the ruins they left along the coast of Tuscany? Help us dust off clues. | <urn:uuid:7fd446fa-1ca7-408c-85b0-e0f06e54c4ae> | 2.703125 | 602 | Content Listing | Science & Tech. | 55.502912 | 95,480,922 |
NASA gave GPM the green light to proceed to the mission implementation phase in a review meeting chaired by NASA’s Associate Administrator Christopher Scolese.
Building on the success of the Tropical Rainfall Measuring Mission (TRMM), a joint project between NASA and the Japan Aerospace Exploration Agency (JAXA), GPM will usher in a new generation of space-based observations of global precipitation, a key element of the Earth’s climate and also the primary source of freshwater. GPM is an international collaboration that currently includes NASA and JAXA, with anticipated contributions from additional international partners.
"This joint NASA/JAXA mission is scientifically important and stands as a prime example of the power of international cooperation in Earth observations," said NASA’s Earth Science Division director Michael Freilich. "GPM's global precipitation measurements will advance our abilities to monitor and accurately predict precipitation on a global basis. GPM builds on the strong scientific and technical collaborations developed between NASA and JAXA. GPM instruments will also provide key calibration references to allow measurements from a wide variety of other satellite missions, including those from other U.S. and international organizations, to be combined to provide accurate predictions and global data sets."
The heart of the GPM mission is a spaceborne Core Observatory that serves as a reference standard to unify and advance measurements from a constellation of multinational research and operational satellites carrying microwave sensors. GPM will provide uniformly calibrated precipitation measurements globally every 2-4 hours for scientific research and societal applications. The GPM Core Observatory sensor measurements will for the first time make quantitative observations of precipitation particle size distribution, which is key to improving the accuracy of precipitation estimates by microwave radiometers and radars.
The GPM Core Observatory will carry a Dual-frequency Precipitation Radar (DPR) and a multi-channel GPM Microwave Imager (GMI). DPR will have greater measurement sensitivity to light rain and snowfall compared to the TRMM radar. GMI uses a set of frequencies to retrieve heavy, moderate, and light precipitation from emission and scattering signals of water droplets and ice particles.
GPM is the cornerstone of the multinational Committee on Earth Observation Satellites Precipitation Constellation that addresses one of the key observations of the Global Earth Observation System of Systems.
NASA is responsible for the GPM Core Observatory spacecraft bus, the GMI carried on it, the Core Observatory integration, launch site processing, mission operation and science data processing and distribution. NASA is also responsible for the development of a second GMI to be flown on a partner-provided Low-Inclination Observatory (LIO) and the Instrument Operational Center for the LIO. The GPM Core Observatory is scheduled for launch in July 2013 from JAXA’s Tanegashima launch site on an H-IIA rocket.
NASA’s Goddard Space Flight Center in Greenbelt, Md., manages the GPM mission on behalf of the Earth Science Division of the Science Mission Directorate at NASA Headquarters. Goddard oversees the in-house Core Observatory development and the GMI acquisition from Ball Aerospace & Technologies Corporation of Boulder, Colo. The GPM project life cycle cost is $978 million.
Sarah DeWitt | EurekAlert!
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
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20.07.2018 | Materials Sciences | <urn:uuid:a44d2c82-89a3-4402-bd71-4632290b31de> | 2.859375 | 1,243 | Content Listing | Science & Tech. | 27.744894 | 95,480,928 |
Want to find the magnitude of a vector?
You quite simply have to know that:
And that if:
Firstly, look at the image below:
Also know that:
From the image, you’ll be able to see that:
Firstly, look at the image below.
You should know that, if and are perpendicular .
You should also know these rules:
Knowing these rules, we can say that:
*Click on the proof above to see it in full.
Don’t waste time memorising two sets of formulas that are simply the same.
Use the formulas you’d use to calculate the area of a triangle. See the magic emerge. | <urn:uuid:d295acf0-1e7f-4faf-acc1-bf6cef4a4260> | 3.59375 | 144 | Tutorial | Science & Tech. | 65.918571 | 95,480,934 |
a. show that every subfield of complex numbers contains rational numbers
b. show that the prime field of real numbers is rational numbers
c. show that the prime field of complex numbers is rational numbers
a. Let R be a domain. Prove that the polynomial f(x) is a unit in R[x] if and only if f(x) is a nonzero constant which is a unit in R.
b. Show that (x + )^2 = in (integers modulo 4)[x] Conclude that the statement in part (a) may be false for the commutative rings that are not domains. [ An element z element of R is called a nilpoint if z^m = 0 for some integer m greater than or equal to one. For any commutative ring R, it can be proved that a polynomial f(x) = a(sub 0) + a(sub 1)x +...+a(sub n)x^n element R[x] is a unit in R[x] if and only if a(sub 0) is a unit in R and a(sub i) is nilpoint for all I greater than or equal to 1.]© BrainMass Inc. brainmass.com July 16, 2018, 12:55 am ad1c9bdddf
(1) By definition, the prime subfield of a field F is smallest subfield of F containing 1; in other words, the prime subfield is contained in every subfield of F containing 1. Moreover, if F is a ...
This provides examples of proofs regarding subfields and prime fields, polynomial in a domain, and commutative rings. | <urn:uuid:2a4b758c-9751-4b80-8e1e-40bfbba0d2f6> | 2.796875 | 357 | Tutorial | Science & Tech. | 86.793355 | 95,480,939 |
|Scientific Name:||Anolis granuliceps Boulenger, 1898|
Anolis breviceps Boulenger, 1913
Norops granuliceps (Boulenger, 1898)
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Castro, F. & Mayer, G.C.|
|Reviewer(s):||Böhm, M., Collen, B. & Ram, M.|
|Contributor(s):||Hedges, B., Powell, R., De Silva, R., Milligan, H.T., Wearn, O.R., Wren, S., Zamin, T., Sears, J., Wilson, P., Lewis, S., Lintott, P. & Powney, G.|
Anolis granuliceps has been assessed as Least Concern owing to its large distribution. While no major widespread threats are thought to be impacting this species, it is a lowland forest-dependent species, in a region which is being impacted by habitat loss and degradation. Monitoring of this species and its habitat should occur due to the localized threats that exist within its range.
|Range Description:||This species is known from the western slopes of the Andes, from the state of Choco in Colombia south to northwestern Ecuador. This species is found up to 550 m above sea level.|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||There is no population information available for this species.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||This species is found in lowland moist forest habitat.|
|Major Threat(s):||This species may be locally threatened by deforestation associated with an expanding human population.|
|Conservation Actions:||There are no known species-specific conservation measures in place for this species. Monitoring of populations and habitat trends is required to ensure that localized threats do not become more widespread across this species' range.|
Castro, F. 2007. pers. comm. Red List Assessment.
IUCN. 2011. IUCN Red List of Threatened Species (ver. 2011.1). Available at: http://www.iucnredlist.org. (Accessed: 30 June 2017).
Mayer, G.C. 2007. pers. comm. Red List Assessment.
Miyata, K. 1985. A new Anolis of the lionotus group from northwestern Ecuador and southwestern Colombia (Sauria: Iguanidae). Breviora 481: 1-11.
Peters, J.A. and Donoso-Barros, R. 1986. Catalogue of the Neotropical Squamata. Smithsonian Institution Press, Washington DC.
Williams, E.E. 1986. Anolis vicarius, new species, related to A. granuliceps. Caldasia 15(71/75): 452-459.
|Citation:||Castro, F. & Mayer, G.C. 2011. Anolis granuliceps. The IUCN Red List of Threatened Species 2011: e.T178231A7503093.Downloaded on 17 July 2018.|
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By: Brendan Gallagher and Peter Bond
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Presented in the same style as existing Jane's Recognition Guides, this exciting new book contains a selection of over 500 satellites, spacecraft and launch vehicles (rockets), with information on purpose, operations, specifications, and a brief type history. The entries (each with a colour picture) are split into: * Historic Missions (to include Sputnik, Apollo, Mir and Voyager) * Historic Launchers * Space Organisations (to include NASA, ESA and JAXA) * Launchers * Current Spacecraft Programmes * Manned Spaceflight * Futures * This is a most comprehensive guide and a stunning tribute to the exploration of space.
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Despite their diminutive sizes, dwarf galaxies play a crucial role in cosmic evolution. Astronomers think they were the first galaxies to form, and they provided the building blocks for larger galaxies. They are by far the most numerous galaxies in our Universe, and are an important tracer of the large-scale structure of the cosmos. Computer simulations of cosmic evolution suggest that high-density regions of the Universe, such as giant clusters, should contain significantly more dwarf galaxies than astronomers have observed to date.
A team led by Leigh Jenkins and Ann Hornschemeier, both at NASA Goddard Space Flight Center in Greenbelt, Md., used Spitzer to study the Coma cluster, an enormous congregation of galaxies 320 million light-years away in the constellation Coma. The cluster contains hundreds of previously known galaxies that span a volume 20 million light-years across.
Jenkins, Hornschemeier, and their collaborators used data from Spitzer's Infrared Array Camera (IRAC) to study galaxies at the cluster's center. They also targeted an outlying region with the goal of comparing the galaxy populations in the different locations to see how environmental variations influence the evolution of galaxies. They stitched together 288 individual Spitzer exposures, each lasting 70 to 90 seconds, into a large mosaic covering 1.3 square degrees of sky.
The team found almost 30,000 objects, whose catalog will be made available to the astronomical community. Some of these are galaxies in the Coma cluster, but the team realized that a large fraction had to be background galaxies. Using data taken with the 4-meter (13 foot) William Herschel Telescope on the Canary island of La Palma, team member Bahram Mobasher of the Space Telescope Science Institute, in Baltimore, Md., measured distances to hundreds of galaxies in these fields to estimate what fraction are cluster members.
A surprising number turned out to be Coma galaxies. They appear to be comparable or even smaller in mass to the Small Magellanic Cloud, the Milky Way's second largest satellite galaxy. Jenkins estimates that about 1,200 of the 30,000 faint objects are dwarf galaxies in Coma, many more than have been identified in the past. Given that the observations only cover a portion of the cluster, the results imply a total dwarf galaxy population of at least 4,000.
Spitzer made these discoveries possible because it can survey large areas of sky very effectively. Even better, infrared observations in space can probe more deeply than ground-based near-infrared surveys because the sky background is up to 10,000 times darker.
"With Spitzer's superb capabilities, we have suddenly been able to detect thousands of faint galaxies that weren't seen before," says Jenkins. She is presenting these results on Monday at the American Astronomical Society meeting in Honolulu, Hawaii. The discovery paper will also appear in the Astrophysical Journal.
"We're blowing away previous infrared surveys of nearby clusters," adds Hornschemeier. "Thanks to Spitzer, we can observe nearby clusters such as Coma very deeply in a short amount of time. The total observing time is comparable to just a few nights at a ground-based observatory."
Additional Coma dwarf galaxies might be lurking in the Spitzer data, but more follow-up work is needed to determine how many. Hornschemeier and other astronomers are currently making deeper spectroscopic measurements with the 6.5-meter (21 foot) telescope of the MMT Observatory in Arizona, and the 10-meter (32 foot) Keck telescope in Hawaii, to find out how many of the faintest objects belong to the Coma cluster.
Bob Naeye | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
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Before life emerged on earth, either a primitive kind of metabolism or an RNA-like duplicating machinery must have set the stage – so experts believe. But what preceded these pre-life steps?
A pair of UCSF scientists has developed a model explaining how simple chemical and physical processes may have laid the foundation for life. Like all useful models, theirs can be tested, and they describe how this can be done. Their model is based on simple, well-known chemical and physical laws.
The work appears online this week in The Proceedings of the National Academy of Sciences.
The basic idea is that simple principles of chemical interactions allow for a kind of natural selection on a micro scale: enzymes can cooperate and compete with each other in simple ways, leading to arrangements that can become stable, or “locked in,” says Ken Dill, PhD, senior author of the paper and professor of pharmaceutical chemistry at UCSF.
The scientists compare this chemical process of “search, selection, and memory” to another well-studied process: different rates of neuron firing in the brain lead to new connections between neurons and ultimately to the mature wiring pattern of the brain. Similarly, social ants first search randomly, then discover food, and finally build a short-term memory for the entire colony using chemical trails.
They also compare the chemical steps to Darwin’s principles of evolution: random selection of traits in different organisms, selection of the most adaptive traits, and then the inheritance of the traits best suited to the environment (and presumably the disappearance of those with less adaptive traits).
Like these more obvious processes, the chemical interactions in the model involve competition, cooperation, innovation and a preference for consistency, they say.
The model focuses on enzymes that function as catalysts – compounds that greatly speed up a reaction without themselves being changed in the process. Catalysts are very common in living systems as well as industrial processes. Many researchers believe the first primitive catalysts on earth were nothing more complicated than the surfaces of clays or other minerals.
In its simplest form, the model shows how two catalysts in a solution, A and B, each acting to catalyze a different reaction, could end up forming what the scientists call a complex, AB. The deciding factor is the relative concentration of their desired partners. The process could go like this: Catalyst A produces a chemical that catalyst B uses. Now, since B normally seeks out this chemical, sometimes B will be attracted to A -- if its desired chemical is not otherwise available nearby. As a result, A and B will come into proximity, forming a complex.
The word “complex” is key because it shows how simple chemical interactions, with few players, and following basic chemical laws, can lead to a novel combination of molecules of greater complexity. The emergence of complexity – whether in neuronal systems, social systems, or the evolution of life, or of the entire universe -- has long been a major puzzle, particularly in efforts to determine how life emerged.
Dill calls the chemical interactions “stochastic innovation” – suggesting that it involves both random (stochastic) interactions and the emergence of novel arrangements.
“A major question about life’s origins is how chemicals, which have no self-interest, became ‘biological’ -- driven to evolve by natural selection,” he says. “This simple model shows a plausible route to this type of complexity.” Dill is also a professor of biophysics and associate dean of research in the UCSF School of Pharmacy. He is a faculty affiliate at QB3, the California Institute for Quantitative Biomedical Research, headquartered at UCSF.
Source: University of California - San Francisco
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PHP can be considered more as a revolution in the web development arena. Beginning with scripting of simple web pages, PHP today has evolved into a language that powers almost 60% of the web. Well, it has been extensively modified to develop frameworks and content management systems to ease the tasks of developers. Essentially, frameworks have some pre-coded functionalities that developers require on a regular basis and content management systems are built with the end user in mind.
We assume that Core PHP means solving a Mathematical problem by using paper and pen. Frame work means solving Mathematical problem by using a calculator.
Core PHP-Solving Mathematical Problem
Only some students can achieve results by using paper and pen as same as in PHP. Only a few of the developers can write the code in an easy way and reliable format.
Core PHP uses the PHP script in its purest form. A developer needs to know the language thoroughly in order to write a clear and concise code using core PHP. Only the experts can write flawless and reliable code using its core form.
Framework – Solving Mathematical problem
Everyone can achieve the result by using the calculator as same as in PHP. Even beginners can write the code in easy way and reliable format.
Frameworks are basically time savers. They have a rich set of functionalities available so that the developer does not have to embed the same code again and again. These frameworks generally have a fixed set of rules and hence the code can be passed on from one developer to another without any hassles.
In core PHP one developer may not be able to read another developer’s code that easily. Frameworks on the other hand provide consistency in the code and are big time savers when the project needs to be handled by several developers at the same time. Frameworks rarely allow you to write bad code. This ensures less time in debugging and helps you deliver your project faster.
- Framework introduces an extra layer to wrap your business code which in turn provides better manageability and easily workability in teams. If you take an example of any MVC( Model-View-Controller)framework; you can understand that the teams can separately work on Model, Views and controller part. ORM (Object-relational mapping) provides easy scalability.
- A framework gives you some tools and function to make it easier for yourself. For example the database seeds, the form request classes, the migrations, and so on.
- In framework everything come as set of predefined codes, helpers, libraries. So, you don’t have to write your own pagination, security code or integrate someone else’s pagination, security scripts. Framework follow specific standard which makes the codes more organized. Besides, frameworks have organized MVC pattern that separate your code into 3 categories, excluding the probability of code.
- Framework is better because almost everything is provided, you need to write less code and there is less to worry about.
- Frameworks usually have security classes in the core. Some methods of Input class have flags to clean XSS from _POST or other global array.
- You need to learn more as there is a specific learning curve for specific frameworks.
- Frameworks are slower than core PHP code.
Core PHP code Advantages:
- Core PHP offers you a lot of freedom a lot of space for imagination and invention.
- If code is small; going with procedural PHP/Core PHP is good idea.
- You need to write lots of code that may already be written.
- There is more to consider about, like security (SQL Injection, XSS), organization of code, separation of business logic, view etc., (that frameworks already do it for you).
Everyone wants to move into sophisticated technologies. If any website or web applications have developed in Core PHP, it is difficult to enhance the website components, but if website or web applications has developed in Frame Work PHP, it is very easy to enhance the features.
Lets see some of the widely used PHP Frameworks:
According to Sitepoint’s recent online survey it is the most popular framework among developers. Laravel has a huge ecosystem with an instant hosting and deployment platform, and its official website offers many screencast tutorials called Laracasts.
Laravel has many features that make rapid application development possible. Laravel has its own light-weight templating engine called “Blade”, elegant syntax that facilitates tasks you frequently need to do, such as authentication, sessions, queueing, caching and RESTful routing. Laravel also includes a local development environment called Homestead that is a packaged Vagrant box.
Symfony is a flexible, scalable yet powerful PHP frameworks for MVC application. There are plenty of reusable PHP components that can can be used like Security, Templating, Translation, Validator, Form Config and more. Like Laravel, it’s alss modularize with Composer. Its goal is to make your web application creation and maintenance faster with less repetitive coding.
CodeIgniter is a lightweight PHP framework that is initially released in 2006. CodeIgniter has a very straightforward installation process that requires only a minimal configuration, so it can save you a lot of hassle. It’s also an ideal choice if you want to avoid PHP version conflict, as it works nicely on almost all shared and dedicated hosting platforms.
CodeIgniter is not strictly based on the MVC development pattern. Using Controller classes is a must, but Models and Views are optional, and you can use your own coding and naming conventions, evidence that CodeIgniter gives great freedom to developers. If you download it, you’ll see it’s only about 2MB, so it’s a lean framework, but it allows you to add third-party plugins if you need more complicated functionalities.
CakePHP is a PHP framework that support version 4 and above. It is easy to learn with fast and flexible templating. The integrated CRUD (create, read, update and delete) is a handy feature in CakePHP for your database interaction. It also has various built-in feature for security, email, session, cookie and request handling.
Yii is a generic Web programming framework, meaning that it can be used for developing all kinds of Web applications using PHP. Because of its component-based architecture and sophisticated caching support, it is especially suitable for developing large-scale applications such as portals, forums, content management systems (CMS), e-commerce projects, RESTful Web services, and so on.
Yii is a full-stack framework providing many proven and ready-to-use features: query builders and ActiveRecord for both relational and NoSQL databases; RESTful API development support; multi-tier caching support; and more.
The Phalcon framework was released in 2012, and it quickly gained popularity among PHP developers. Phalcon is said to be fast as a falcon, because it was written in C and C++ to reach the highest level of performance optimization possible. Good news is that you don’t have to learn the C language, as the functionality is exposed as PHP classes that are ready to use for any application.
As Phalcon is delivered as a C-extension, its architecture is optimized at low levels which significantly reduces the overhead typical of MVC-based apps. Phalcon not only boosts execution speeds, but also decreases resource usage. Phalcon is also packed with many cool features such as a universal auto-loader, asset management, security, translation, caching, and many others. As it’s a well-documented and easy-to-use framework.
Slim is a lightweight micro-framework for PHP inspired by Sinatra, a Ruby framework. It has a tiny size without overkill learning curve. It’s built with incredible routing system and focuses on RESTful API with all HTTP methods (GET, POST, PUT, DELETE) supports. To use it, you need at least has a PHP version of 5.2+.
Zend Framework is a scalable and full featured object-oriented PHP framework.It has an online training and certification which make it popular and used by plenty of enterprise organizations. With its OOP (object-oriented programming) and design patterns consistency, you can easily extend custom classes and use only what you need.
The Nette Framework is another player in the world of php web application frameworks – but like most others, it has its right to be here. It comes with great and powerful features, and makes life easier for web developers. Nette uses revolutionary technology that eliminates security holes and their misuse, such as XSS, CSRF, session hijacking, session fixation, etc.
Nette is modern php framework which supports AJAX / AJAJ, Dependency Injection, SEO, DRY, KISS , MVC, Web 2.0, cool URL | <urn:uuid:c5b97927-59d3-4596-a139-b63943a04985> | 3 | 1,844 | Listicle | Software Dev. | 37.544632 | 95,481,033 |
By Laila Kearney
(Reuters) – Fierce solar blasts that could have badly damaged electrical grids and disabled satellites in space narrowly missed Earth in 2012, U.S. researchers said on Wednesday.
The bursts would have wreaked havoc on the Earth’s magnetic field, matching the severity of the 1859 Carrington event, the largest solar magnetic storm ever reported on the planet. That blast knocked out the telegraph system across the United States, according to University of California, Berkeley research physicist Janet Luhmann.
“Had it hit Earth, it probably would have been like the big one in 1859, but the effect today, with our modern technologies, would have been tremendous,” Luhmann said in a statement.
A 2013 study estimated that a solar storm like the Carrington Event could take a $2.6 trillion bite out of the current global economy.
Massive bursts of solar wind and magnetic fields, shot into space on July 23, 2012, would have been aimed directly at Earth if they had happened nine days earlier, Luhmann said.
The bursts from the sun, called coronal mass ejections, carried southward magnetic fields and would have clashed with Earth’s northward field, causing a shift in electrical currents that could have caused electrical transformers to burst into flames, Luhmann said. The fields also would have interfered with global positioning system satellites.
The event, detected by NASA’s STEREO A spacecraft, is the focus of a paper that was released in the journal Nature Communications on Tuesday by Luhmann, China’s State Key Laboratory of Space Weather professor Ying Liu and their colleagues.
Although coronal mass injections can happen several times a day during the sun’s most active 11-year cycle, the blasts are usually small or weak compared to the 2012 and 1859 events, she said.
Luhmann said that by studying images captured by the sun-observing spacecraft, scientists can better understand coronal mass injections and predict solar magnetic storms in the future.
“We have the opportunity to really look closely at one of these events in all of its glory and look at why in this instance was so extreme,” Luhmann said.
(Editing by Scott Malone and David Gregorio) | <urn:uuid:c67ad1cf-7795-4c5c-bf52-89cb82d6d9f5> | 2.96875 | 474 | News Article | Science & Tech. | 41.005 | 95,481,051 |
A simple formula for calculating porosity of magma in volcanic conduits during dome-forming eruptions
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We present a simple formula for analyzing factors that govern porosity of magma in dome-forming eruptions. The formula is based on a 1-dimensional steady conduit flow model with vertical gas escape, and provides the value of the porosity as a function of magma flow rate, magma properties (viscosity and permeability), and pressure. The porosity for a given pressure depends on two non-dimensional numbers ε and θ. The parameter ε represents the ratio of wall friction force to liquid-gas interaction force, and is proportional to the magma viscosity. The parameter θ represents the ratio of gravitational load to liquid-gas interaction force and is inversely proportional to the magma flow rate. Gas escape is promoted and porosity decreases with increasing ε or θ. From the possible ranges of ε and θ for typical magmatic conditions, it is inferred that the porosity is primarily determined by ε at the atmospheric pressure (near the surface), and by θ at higher pressures (in the subsurface region inside the conduit). The porosity near the surface approaches 0 owing to high magma viscosity regardless of the magnitude of the magma flow rate, whereas the subsurface porosity increases to more than 0.5 with increasing magma flow rate.
Key wordsConduit flow dome-forming eruptions magma porosity gas escape from magma
As silicic volatile-rich magma ascends to the surface and decompresses in volcanic conduits, the magma vesiculates and its porosity (i.e., gas volume fraction) increases. The porosity changes with depth owing to the competition between the vesiculation and escape of gas from the magma. When gas escape occurs efficiently, the porosity decreases, which may lead to an effusion of a lava dome with a low porosity (Eichelberger et al., 1986; Jaupart and Allegre, 1991; Woods and Koyaguchi, 1994). Recent numerical studies have revealed that the porosity critically depends on magma properties such as viscosity and permeability in dome-forming eruptions and that complex porosity profiles may result as viscosity, permeability, or both change with depth; the porosity increases in the subsurface region, and then decreases near the surface (e.g., Melnik and Sparks, 1999; Diller et al., 2006). However, the relationships between porosity and viscosity and between porosity and permeability are still unclear, which makes it difficult to understand the mechanism through which the complex porosity profiles are formed.
In this study, we derive a simple formula for calculating the porosity in dome-forming eruptions as a function of the magma properties and geological conditions. This formula is based on a 1-dimensional steady conduit flow model that considers vertical gas escape from magma. This formula enables us to systematically investigate how porosity changes in response to changes in viscosity and permeability during magma ascent and also to identify the essential effects controlling the porosity profile in the conduit.
2. A Formula for Calculating Porosity
Equations (1) and (2) describe the mass conservations of the liquid and the gas respectively, and Eqs. (3) and (4) the momentum conservations of the liquid and the gas respectively. Equation (5) is the equation of state for the gas phase, and Eq. (6) represents the mass-flow-rate fraction of the gas when equilibrium gas exsolution on the basis of the solubility curve of H2O in a magma (Burnham and Davis, 1974) is assumed. We also assume that temperature change due to expansion is negligible because of the large heat capacity of the liquid magma; therefore, the energy equation is not solved.
In the 1-dimensional steady conduit flow models, the porosity of magma is determined by solving the differential equations (i.e., Eqs. (1)–(8)) as a two-point boundary value problem (referred to as “DE-2BV”). The boundary condition at the bottom end of the conduit is that the pressure is equal to the pressure at the magma chamber and ug = u l , and the boundary condition at the vent is that the pressure is equal to the atmospheric pressure. The variations of physical quantities such as Φ, ul, ug and P with depth throughout the conduit and the value of the mass flow rate q are obtained such that the boundary conditions are satisfied. On the other hand, Eq. (10) provides an algebraic expression of Φ for a given ε, θ, and P. This formula cannot determine the value of q as DE-2BV does, but determines the relationships among Φ, µ, and k at a given pressure when the value of q is somehow known. Because Eq. (10) is valid for general forms of µ and k, it is useful for studying how Φ varies as µ and k change with depth in a complex way. In this section, we demonstrate that Eq. (10) can correctly estimate the porosity as a function of P for realistic forms of µ and k when the value of q is given as a parameter.
The above results show that if the value of q is known, Eq. (10) can correctly determine the porosity as a function of P for realistic forms of β and k. In actual eruptions, the value of q can be estimated from field observations. In addition, we know that P at the surface is atmospheric and that P in the subsurface region is greater than atmospheric. Therefore, we can evaluate how the porosity at the surface or in the subsurface region is controlled by the variations of β and k on the basis of Eq. (10).
4. Geological Implications
During dome-forming eruptions, magma porosity changes through the competing effects of the magma vesiculation and the gas escape from magma. According to field observations, the porosity of lava domes typically ranges from 0 to 0.5 (e.g., Melnik and Sparks, 2002; Kueppers et al., 2005; Mueller et al., 2005). On the other hand, Clarke et al.(2007) showed that the porosity in the subsurface region where the pressure is higher than about 10 MPa can be as large as 0.5–0.7, as was the case for the pre-explosion (dome growth) state of the 1997 events in Soufriere Hills Volcano, Montserrat (SHV). We discuss the mechanism for these observed porosity distributions to be generated on the basis of our simple formula, Eq. (10).
Figure 2 describes how the porosity near the surface (P = 0.1 MPa) and that in the subsurface region (P = 10 MPa) depend on ε and θ on the basis of Eq. (10). In this diagram, possible ranges of ε and θ estimated from the typical values of β, k, rc and q for actual dome-forming eruptions are shown. Generally, the value of ε increases dramatically with decreasing P in response to the increase in β (Fig. 3(c)). This effect is taken into consideration for the possible range of ε in Fig. 2. At pressures near the surface (P = 0.1 MPa), the porosity depends on ε and is unaffected by θ (Fig. 2(a)). On the other hand, at pressures in the subsurface region (P = 10 MPa), the porosity depends on θ rather than on ε (Fig. 2(b)).
The above results show that the increase in the magma viscosity plays an important role in explaining the low porosity (close to zero) near the surface observed in lava domes. The porosity near the surface decreases with increasing ε (Fig. 2(a)). Considering that the permeability decreases with decreasing porosity (e.g., Mueller et al., 2005) and that there is not a large variation of rc, the increase in ε is ascribed to the increase in the magma viscosity (see Eq. (11)). The viscosity drastically increases in the region near the surface because of volatile exsolution and crystallization. As a result, the ascent of the liquid is suppressed owing to large wall friction force, whereas the gas ascends easily (i.e., efficient gas escape). For example, when the viscosity near the surface increases up to 1014 Pa s, ε can become larger than 103, which leads to a porosity smaller than 0.2 (Fig. 2(a)). The porosity near the surface remains low even when the mass flow rate is high, because the porosity in this region is insensitive to θ (Fig. 2(a)).
In contrast, the porosity in the subsurface region is sensitive to θ (Fig. 2(b)). This indicates that the increase in the mass flow rate plays a major role in explaining the high porosity in the subsurface region estimated for SHV (0.5∓ 0.7). Considering again the permeability-porosity relationship, the increase in mass flow rate results in a decrease in θ (see Eq. (12)), which in turn leads to an increase in subsurface porosity (see Fig. 2(b)). For the possible ranges of ε and θ in Fig. 2(b), the porosity Φ is larger than 0.5 when θ is smaller than about 1. In the case of k ∼ 10-12 m2 (the value for SHV when Φ = 0.5–0.7; Melnik and Sparks, 2002), the mass flow rate q must exceed 5 kg m-2 s-1 for θ< 1. (e.g., compare Fig. 3(a–c) with Fig. 3(d–f)). This estimation is consistent with the observation that q at the pre-explosion state of the 1997 events in SHV reached about 28 kg m-2 s-1 (Sparks et al., 1998). We suggest that the high flow rate immediately prior to the explosive activity induced the increase in the subsurface porosity.
In conclusion, we have derived a simple formula for calculating the porosity of magma in dome-forming eruptions as a function of mass flow rate, magma properties such as the viscosity and the permeability, and pressure. On the basis of this formula, we have shown that the increase in the magma viscosity due to volatile exsolution and crystallization near the surface plays a key role in the formation of a porosity distribution in dome-forming eruptions. The porosity near the surface approaches 0 owing to the high magma viscosity regardless of the magnitude of the mass flow rate, whereas the subsurface porosity increases to more than 0.5 with increasing mass flow rate. In order to understand the mechanism of the porosity change in dome-forming eruptions, we need to quantitatively evaluate complex effects of the magma properties such as degassing-induced crystallization (e.g., Melnik and Sparks, 2005), non-Newtonian rheology of crystal-bearing magma (e.g., Caricchi et al., 2007), and various relationships between permeability and porosity (e.g., Eichelberger et al., 1986; Takeuchi et al., 2005). The simple formula obtained in this paper (Eq. (10)) will be useful for systematically analyzing the relationship between these complex effects of the magma properties and the conduit flow dynamics.
We thank Sebastian Mueller and Wim Degruyter for insightful comments in improving an earlier version of the manuscript. We are grateful to Alain Burgisser and Shigeo Yoshida for helpful reviews and suggestions that greatly improved the manuscript. This work was supported by Grant-in-Aid for Scientific Research (B) (No. 18340130, 21340123) and for Young Scientist (B) (No. 21740322) from MEXT, and the Earthquake Research Institute cooperative research program.
- Hess, K. U. and D. B. Dingwell, Viscosities of hydrous leucogranitic melts: A non-Arrhenian model, Am. Mineral., 81, 1297–1300, 1996.Google Scholar
- Melnik, O. and R. Sparks, Dynamics of magma ascent and lava extrusion at Soufrière Hills Volcano, Montserrat, in The Eruption of Soufrière Hills Volcano, Montserrat, from 1995 to 1999, edited by T. H. Druitt and B. P. Kokelaar, 645 pp, Geological Society, London, Memoirs, 21, 153–171, 2002.Google Scholar
- Melnik, O. and R. Sparks, Controls on conduit magma flow dynamics during lava dome building eruptions, J. Geophys. Res., 110, B02209, 2005.Google Scholar
- Sparks, R., S. Young, J. Barclay, E. Calder, P. Cole, B. Darroux, M. Davies, T. Druitt, C. Harford, R. Herd, and others, Magma production and growth of the lava dome of the Soufrière Hills Volcano, Montserrat, West Indies: November 1995 to December 1997, Geophys. Res. Lett., 25, 3421–3424, 1998.CrossRefGoogle Scholar | <urn:uuid:825d058b-c981-45ac-97d8-d905206d9d38> | 3.265625 | 2,881 | Academic Writing | Science & Tech. | 57.819628 | 95,481,064 |
In your book THE C++ TRAINING GUIDE, you create a string class as an example. In describing, in chapter 8, why we needed to use a reference argument to the operator = instead of a value argument, you state that the compiler - generated copy constructor will wipe out the caller's pointed-to-data when the temporary is destroyed at the end of its scope.(posted 7010 days ago)
While this is true, and certainly a danger, isn't this entirely obviated by the fact that we have a perfectly good copy constructor provided in the previous chapter? One that doesn't just copy the pointer itself but also the refered-to-data? I don't see how there would be any danger in that at all as long as a well thought out copy constructor is available. Or would this not be used to create the temporary? Or are you just trying to get us into good programming habits? Or did I just demonstrate that I've missed half the book? I don't fully follow. Please help.
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Usually software is a solutions for certain problems. Nowadays software is not only can be used locally on a machine but also work on the cloud as subsciption basis. Software is important piece of technology that drives the nation forward.
Now, people want to create a software to solve problem and of course making money, which is good. But people sometime don't understand the process and the steps required to make software, which is bad. And people think with just idea, and some sketch they can might a great software build for them from a software developer.
No you are wrong. But in small cases you might get lucky.
Software for people is what they can see on the screen. Which is the visual design / user interface.
What software can make people feel is the user experience design.
Visual design is usally done by graphic designer. A good graphic designer understand the concept of the platform they want to build, they have experience on various of available software and they can emulate it to become good software.
So here come the software architect. From Wiki, software architect is a software expert who makes high-level design choices and dictates technical standards, including coding standards, tools and platforms.
Usually software architect don't do the visual design, they deal with technical stack. But they might need to use UML, graph, model, structure diagrams or so. It can be a tough job.
iReka Soft Software Architect
Here is what we want to define Software Architect as for ourselves. We are small team, and the projects are not humungous. So Software Architect term to my mind to suit the business what it should do for smaller software development.
The deliverable of software architect is not yet the final product or software but a documents with visual designs, architecture, diagrams and specifications.
iReka Soft Software Architect should combine visual design and software architecture.
Which means he/she can do the concept of the software in visual perspective with using the right user interface for particular platform.
He knows what to looking for for a particular solutions, mark it as a module. And how other modules can be interacts.
Why We need to have Software Architect
The whole idea of having a software architect is for plan. It's so intimidating to jump right into the development, but yes when we get older and more experience, we know sometime the development can be just done, but of course there are a lot more stuff we haven't yet done, but we know where to find it. So by having proper plan, master plan we hope that it will not make the development stuck in the middle of development. Which meetings can be a cure; putting more ideas and changes, thus sometime make the software development ineffective.
Having too much plan is not good as well, but having too little plan is also not good.
So we need to having a good balance of planning of software. It's true on our own software development and also for clients.
I cannot stress enough that for client project wireframing is important. If don't have let's make it have it. Because we will be...
Pada tanggal 30 Januari 2016, saya telah menghadiri program Seminar My Documents dengan tagline 'Urus bisnes gaya korporat' yang di ...
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Menjelang tahun 2016 ini mungkin ada ramai lagi orang nak masuk dalam pembangunan perisian/ software/ perisian mudah alih. Saya telah bermul... | <urn:uuid:d6073150-ba3f-4f15-8a72-1729835ebbc9> | 2.9375 | 777 | Personal Blog | Software Dev. | 53.493959 | 95,481,083 |
What makes the high atmosphere, or corona, so hot – over a million degrees, compared to the sun surface's 10,000 degrees Fahrenheit -- remains a poorly understood aspect of the sun's complicated space weather system. That weather system can reach Earth, causing auroral lights and, if strong enough, disrupting Earth's communications and power systems. Understanding such phenomena, therefore, is an important step towards better protecting our satellites and power grids.
"The traditional view is that all the heating happens higher up in the corona," says Dean Pesnell, who is SDO's project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "The suggestion in this paper is that cool gas is being ejected from the sun's surface in spicules and getting heated on its way to the corona."
Spicules were first named in the 1940s, but were hard to study in detail until recently, says Bart De Pontieu of Lockheed Martin's Solar and Astrophysics Laboratory, Palo Alto, Calif. who is the lead author on a paper on this subject in the January 7, 2011 issue of Science magazine.
In visible light, spicules can be seen to send large masses of so-called plasma – the electromagnetic gas that surrounds the sun – up through the lower solar atmosphere or photosphere. The amount of material sent up is stunning, some 100 times as much as streams away from the sun in the solar wind towards the edges of the solar system. But nobody knew if they contained hot gas.
"Heating of spicules to the necessary hot temperatures has never been observed, so their role in coronal heating had been dismissed as unlikely," says De Pontieu.
Now, De Pontieu's team -- which included researchers at Lockheed Martin, the High Altitude Observatory of the National Center for Atmospheric Research (NCAR) in Colorado and the University of Oslo, Norway -- was able to combine images from SDO and Hinode to produce a more complete picture of the gas inside these gigantic fountains.
The scientists found that a large fraction of the gas is heated to a hundred thousand degrees, while a small fraction is heated to millions of degrees. Time-lapsed images show that this material spews up into the corona, with most falling back down towards the surface of the sun. However, the small fraction of the gas that is heated to millions of degrees does not immediately return to the surface. Given the large number of spicules on the Sun, and the amount of material in the spicules, the scientists believe that if even some of that super hot plasma stays aloft it would make a contribution to coronal heating.
Astrophysicist Jonathan Cirtain, who is the U.S. project scientist for Hinode at NASA's Marshall Space Flight Center, Huntsville, Ala., says that incorporating such new information helps address an important question that reaches far beyond the sun. "This breakthrough in our understanding of the mechanisms which transfer energy from the solar photosphere to the corona addresses one of the most compelling questions in stellar astrophysics: How is the atmosphere of a star heated?" he says. "This is a fantastic discovery, and demonstrates the muscle of the NASA Heliophysics System Observatory, comprised of numerous instruments on multiple observatories."
Hinode is the second mission in NASA's Solar Terrestrial Probes program, the goal of which is to improve understanding of fundamental solar and space physics processes. The mission is led by the Japan Aerospace Exploration Agency (JAXA) and the National Astronomical Observatory of Japan (NAOJ). The collaborative mission includes the U.S., the United Kingdom, Norway and Europe. NASA Marshall manages Hinode U.S. science operations and oversaw development of the scientific instrumentation provided for the mission by NASA, academia and industry. The Lockheed Martin Advanced Technology Center is the lead U.S. investigator for the Solar Optical Telescope on Hinode.
SDO is the first mission in a NASA science program called Living With a Star, the goal of which is to develop the scientific understanding necessary to address those aspects of the sun-Earth system that directly affect our lives and society. NASA Goddard built, operates, and manages the SDO spacecraft for NASA's Science Mission Directorate in Washington.
Susan Hendrix | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
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This book covers the physics, technology and applications of short pulse laser sources that generate pulses with durations of only a few optical cycles. The basic design considerations for the different systems such as lasers, parametric amplifiers and external compression techniques which have emerged over the last decade are discussed to give researchers and graduate students a thorough introduction to this field. The existence of these sources has opened many new fields of research that were not possible before. These are UV and EUV generation from table-top systems using high-harmonic generation, frequency metrology enabling optical frequency counting, high-resolution optical coherence tomography, strong-field ultrafast solid-state processes and ultrafast spectroscopy, to mention only a few. Many new applications will follow. The book attempts to give a comprehensive, while not excessive, introduction to this exciting new field that serves both experienced researchers and graduate students entering the field. The first half of the book covers the current physical principles, processes and design guidelines to generate pulses in the optical range comprising only a few cycles of light. Such as the generation of relatively low energy pulses at high repetition rates directly from the laser, parametric generation of medium energy pulses and high-energy pulses at low repetition rates using external compression in hollow fibers. The applications cover the revolution in frequency metrology and high-resolution laser spectroscopy to electric field synthesis in the optical range as well as the emerging field of high-harmonic generation and attosecond science, high-resolution optical imaging and novel ultrafast dynamics in semiconductors. These fields benefit from the strong electric fields accompanying these pulses in solids and gases during events comprising only a few cycles of light.
Few-Cycle Laser Pulse Generation and Its Applications
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For every cucumber project there is a single directory at the root of the project named "features". This is where all of your cucumber features will reside. In this directory you will find additional directories, which is step_definition and support directories
What is "Feature File"?
Feature File consist of following components -
- Feature: A feature would describe the current test script which has to be executed.
- Scenario: Scenario describes the steps and expected outcome for a particular test case.
- Scenario Outline: Same scenario can be executed for multiple sets of data using scenario outline. The data is provided by a tabular structure separated by (I I).
- Given: It specifies the context of the text to be executed. By using datatables "Given", step can also be parameterized.
- When: "When" specifies the test action that has to performed
- Then: The expected outcome of the test can be represented by "Then"
Feature: Visit career guide page in career.guru99.com
Scenario : Visit career.guru99.com
Given: I am on career.guru99.com
When: I click on career guide menu
Then: I should see career guide page
What is "Step Definition"
Step definition maps the Test Case Steps in the feature files(introduced by Given/When/Then) to code. It will execute the steps on Application Under Test and checks the outcomes against expected results. For a step definition to be executed, it must match the given compoent in a feature. Step definition is defined in ruby files under "features/step_definitions/*_steps.rb".
Example for Step Definition: Here we will above example of browsing career.guru99.com do We will use features like "When, Then, Given "
Step 1: Given (/^ I am on career.guru99.com$/) do Browser.goto "http://career.guru99.com" -This will visit career.guru99 on browser end Step 2: When (/^ click on career guide menu$/) do Browser.text (:name, " career guide" ).click – This will click "career guide menu" end Step 3: Then (/^ I should see career guide page$/) do Browser.goto "http://career.guru99.com/category/career-guide/" - It will visit "career guide page" end
- You need 2 Files – Features and Step Definition to execute a Cucmber test scenario
- Features file contain high level description of the Test Scenario in simple language
- Steps Definition file contains the actual code to execute the Test Scenario in the Features file. | <urn:uuid:64439a0a-aec3-4152-ab1f-4b15343ca96e> | 2.796875 | 570 | Documentation | Software Dev. | 46.713837 | 95,481,111 |
Induced by global warming, regions of oxygen-poor water - so-called oxgen minimum zones - are expanding in the world's oceans. That has significant consequences on the marine habitat and fisheries, as higher organisms avoid these regions.
The global elemental cycles of carbon and nitrogen are closely linked to oxgen minimum zones. Therefore, detailed knowledge of these cycles is essential for predicting the effects of climate change on the oceans as well as possible feedback mechanisms. A study by an international group of scientists around Phyllis Lam from the Max-Planck-Institute for Marine Microbiolgy in Bremen, Germany, published in the journal "PNAS", brings us a big step closer to this understanding.
The scientists concentrated on the nitrogen cycle of the Peruvian oxgen minimum zone in the eastern Tropical South Pacific. This region is one out of three regoins in the world's oceans where nitrogen escapes from seawater. "For a long time, this loss was attributed to denitrification, which transforms nitrate to gaseous nitrogen, which can then escape to the atmosphere", Lam explains. "This picture is changing: Apparently, the so-called anammox-bacteria are responsible for the major part of the lost nitrogen. However, up to now it has been unclear where the anammox-bacteria obtain their resources for this transformation." Moreover, the lack of denitrification strongly questions our understanding of the closely-linked carbon cycle - if not by denitrification, how else is organic matter degraded in these oxygen-depleted waters?
Lam's results shake the previous assumptions about the nitrogen cycle in the Peruvian oxygen minimum zone. Experiments as well as molecular analyses show that several processes (presenting the layman with quite some technical terms) are involved: The major proportion of nitrogen is indeed lost through Anammox. It is directly coupled to nitrate reduction and aerobic ammonia oxidation (the first step of nitrification) for sources of NO2-.
The NH4+ required by anammox originates from dissimilatory nitrate reduction (DNRA) and remineralization of organic matter via nitrate reduction and likely microaerobic respiration. The importance of the single processes varies between shelf and open ocean settings as well as the depth layers of the OMZ. Besides, the finding of DNRA itself is also surprising, because up till now, it has generally been considered insignificant in the open ocean.
Therewith, Lam and her colleagues challenge the prevailing opinion that nitrate from the deep sea is responsible for all the nitrogen losses from the Ocean. Its fraction sums up to only about 50 percent, while the remaining losses were attributed to remineralized nitrogen (originating from organic material).
Hitherto existing calculations of nitrogen losses, relying only on measurements of the nitrate deficit, may therefore have substantially underestimated the effective losses from the Ocean - particularly if the same applies to the other OMZs in the world. "Especially the role of remineralized nitrogen needs to be reconsidered". Lam points out, "That is the only way to enable reliable predictions about the future role of the oceans for global climate."
Background 1: The marine nitrogen cycle
All lives on Earth depend on nitrogen, as it is essential for the making of cell components such as proteins and DNA. However, organisms can't use all forms of nitrogen, therefore only a part of the nitrogen present in the ocean determines the productivity of the whole ecosystem. The conversion of different forms of nitrogen is carried out by specialized microorganisms.
In the ocean, nitrogen in the form of ammonium (NH4+) is mainly set free by the degradation of organic matter. In a central step known as nitrification, ammonium is being transferred to nitrite (NO2-) and subsequently to nitrate (NO3-). This process consumes oxygen. With several intermediate steps, the nitrate is subsequently transformed to elemental nitrogen (gaseous nitrogen, N2) in the absence of oxygen. This reaction is termed denitrification. All transformations are mediated by microorganisms. The gaseous N2 bubbles up and leaves the ocean. A few years ago, scientists at the Max Planck Institute in Bremen discovered the process of anaerobic oxidation of ammonium (ANAMMOX) in the oceans. In this process, anammox-bacteria transform ammonium directly with nitrite to gaseous nitrogen (N2) under oxygen-free conditions.
Background 2: Oxygen Minimum Zones
The Oxgen Minimum Zone (OMZ) is an oxygen-depleted layer of water, usually in 200 to 1000 m water depth. Although oxygen minimum zone waters constitute only about 0.1% of the total ocean volume in the world, 20-40% of total oceanic nitrogen loss is estimated to occur therein.
Background 3: The methods
For their analyses, Lam and her colleagues used the stable isotope of nitrogen (15N), allowing them to trace single transformations in high detail. Furthermore, they analysed the parallel gene expression - that is, when organisms are signalling their cell machineries to build the required enzymes.
Fanni AspetsbergerFor further information please contact:
Dr. Fanni Aspetsberger | Max-Planck-Gesellschaft
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Materials Sciences
19.07.2018 | Earth Sciences
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|PORIFERA : POECILOSCLERIDA : Hymedesmiidae||SPONGES|
Description: This sponge grows as a thin sheet or cushion in patches 10-15cm across. It is normally pale orange/pink in colour but occasionally it is bright red. The surface is covered in shallow, circular, non-contractile depressions of varying diameters. The rims of these depressions are usually lighter coloured than the rest of the body. The depressions contain the inhalant pores, and are covered by a fine, gauze-like mesh.
Habitat: A common species in areas with silt free, infralittoral bedrock and boulders. Apparently not found in harbours.
Distribution: Recently known from scattered localities all around the British Isles, but currently not recorded from North Sea coasts.
Similar Species: Provided the colour is pale orange-pink and the rims of the depressions are of a lighter colour, the identification stands a good chance of being correct, but in case of doubt microscopic examination is essential. Several other genera contain species which have depressions with rims which are the same colour as the general surface (see e.g. Phorbas fictitius and Hymedesmia pauperatus.
Key Identification Features:
Distribution Map from NBN: Interactive map : National Biodiversity Network mapping facility, data for UK.
WoRMS: Species record : World Register of Marine Species.
|Picton, B.E. & Morrow, C.C. (2016). Hemimycale columella (Bowerbank, 1874). [In] Encyclopedia of Marine Life of Britain and Ireland. |
http://www.habitas.org.uk/marinelife/species.asp?item=C7750 Accessed on 2018-07-16
|Copyright © National Museums of Northern Ireland, 2002-2015| | <urn:uuid:f44dc551-d98a-4ef7-99d9-945496838e48> | 3.234375 | 402 | Knowledge Article | Science & Tech. | 40.412026 | 95,481,156 |
Straight lines are actually intersected at a point in the plane due to their non-parallelism. In other words, if two straight lines do not maintain equidistance at all their opposite points, they are non-parallel lines and surely get intersected at a point in the plane. Therefore, the two straight lines are known as intersecting lines geometrically.
There are two possibilities for the lines to get intersected at a point in the plane. One case is, straight lines are intersected at a point in the plane directly. The second case is, the straight lines have a chance to get intersected at a point in the plane.
and are two straight lines. These two straight lines do not maintain equidistance separation in the plane and they intersected at a point . Now, the straight lines and are called as intersecting lines geometrically.
and are two other straight lines and they do not maintain equal distance between them. It seems they do not intersect each other but they surely intersect at a point at somewhere in the plane if they are extended. Let us say the chance of intersection is at point in the plane.
List of most recently solved mathematics problems.
Learn how to solve easy to difficult mathematics problems of all topics in various methods with step by step process and also maths questions for practising. | <urn:uuid:18f0cc54-1311-4797-9b0d-1a217c9173ef> | 3.90625 | 276 | Tutorial | Science & Tech. | 49.325221 | 95,481,157 |
The system uses extremely short pulses of low-energy laser light to stimulate the emission of ultrasonic acoustic waves from the tissue area being examined. These waves are then converted into high-resolution 3D images of tissue structure.
This method can be used to reveal disease in types of tissue that are more difficult to image using techniques based on x-rays or conventional ultrasound. For example, the new system is better at imaging small blood vessels, which may not be picked up at all using ultrasound. This is important in the detection of tumours, which are characterised by an increased density of blood vessels growing into the tissue.
The technique, which is completely safe, will help doctors diagnose, monitor and treat a wide range of soft-tissue conditions more effectively.
The first of its kind in the world, the prototype system has been developed by medical physics and bioengineering experts at University College London, with funding from the Engineering and Physical Sciences Research Council (EPSRC). It is soon to undergo trials in clinical applications, with routine deployment in the healthcare sector envisaged within around 5 years.
The emission of an acoustic wave when matter absorbs light is known as the photoacoustic effect. Harnessing this basic principle, the new system makes use of the variations in the sound waves that are produced by different types of soft human tissue to identify and map features that other imaging methods cannot distinguish so well.
By appropriate selection of the wavelength of the laser pulses, the light can be controlled to penetrate up to depths of several centimetres. The technique therefore has important potential for the better imaging of conditions that go deep into human tissue, such as breast tumours, and for contributing to the diagnosis and treatment of vascular disease.
The prototype instrument, however, has been specifically designed to image very small blood vessels (with diameters measured in tens or hundreds of microns) that are relatively close to the surface. Information generated about the distribution and density of these microvessels can in turn provide valuable data about skin tumours, vascular lesions, burns, other soft tissue damage, and even how well an area of tissue has responded to plastic surgery following an operation.
The development process has included theoretical and experimental investigations of photoacoustic interactions with soft tissue, development of appropriate computer image-reconstruction algorithms, and construction of a prototype imaging instrument incorporating the new technique.
“This new system offers the prospect of safe, non-invasive medical imaging of unprecedented quality,” says Dr Paul Beard who leads UCL’s Photoacoustic Imaging Group. “It also has the potential to be an extremely versatile, relatively inexpensive and even portable imaging option.”
Natasha Richardson | alfa
Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication
16.07.2018 | Chinese Academy of Sciences Headquarters
Theorists publish highest-precision prediction of muon magnetic anomaly
16.07.2018 | DOE/Brookhaven National Laboratory
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
16.07.2018 | Physics and Astronomy
16.07.2018 | Transportation and Logistics
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Essential minerals are phenocrysts and glomerocrysts of anorthoclase, sanidine up to 1,5 cm and anorthoclase-mantled plagioclase; accessory minerals are red biotite, and hastingsite while trace minerals are augite, zircon, sphene and magnetite.
Accessory and trace minerals are corroded and oxidized hastingsite (Figure 6), euhedral zircon and euhedral sphene.
In the glassy matrix there were identified finer crystals of anorthoclase, hastingsite, oxihornblende and sphene.
there was no chemical and no physical equilibrium between plagioclase and hastingsite crystals and the melt, as suggested by dissolution texture, reabsortion and reaction borders (Figures 6A, 613, 6E, 14D).
It is interesting to note that analytical data exist in the literature for at least two amphiboles which fall into the hastingsite field and which are chlorine-dominant; one of these is almost completely characterized but the data for the other consists only of chemical analytical data.
Hastingsite, [Mathematical Expression Omitted], mon.
forms a series with Hastingsite, Amphibole group, Can. | <urn:uuid:6798681f-34a5-480e-96d0-2a0d01ee5baa> | 2.6875 | 266 | Knowledge Article | Science & Tech. | 1.514839 | 95,481,203 |
A distant planet 430 light years from Earth has clear skies and an atmosphere almost entirely composed of hydrogen and helium, scientists have discovered.
Conditions on the “warm Neptune” – similar in size to Neptune but much closer its parent star – shine a light on how solar systems are born and evolve.
The primitive atmosphere suggests that the planet either formed near its host star or relatively late in its solar system’s development.
In contrast, Neptune and Uranus in our own solar system are thought to have been created towards the edge of the disc of dust and gas that swirled around the immature sun.
Professor David Sing, from the University of Exeter, whose team carried out a detailed study of the planet together with scientists from the US space agency Nasa, said: “This exciting new discovery shows that there is a lot more diversity in the atmospheres of these exoplanets than we have previously thought.
“This ‘warm Neptune’ is a much smaller planet than those we have been able to characterise in depth, so this new discovery about its atmosphere feels like a big breakthrough in our pursuit to learn more about how solar systems are formed, and how it compares to our own.”
The scientists analysed data from Nasa’s Hubble and Spitzer space telescopes to measure light filtering through the planet’s atmosphere as it passed in front of its host star.
MOST READ IN TECH AND SCIENCE
20,000 TREES UNDER THE SEAMysterious ancient underwater forest offers a chilling glimpse of Earth's grim future, scientists say
The findings, published in the journal Science, provide enough detail to show that the planet, named HAT-P-26P, has skies relatively clear of clouds and a strong water signature.
Co-author Dr Hanna Wakeford, from Nasa’s Goddard Space Flight Center in Greenbelt, Maryland, said: “Astronomers have just begun to investigate the atmospheres of these distant Neptune-mass planets, and almost right away, we found an example that goes against the trend in our solar system.” | <urn:uuid:fb5247d9-61ca-47a0-889a-b80746d0aca4> | 3.640625 | 432 | Truncated | Science & Tech. | 28.049839 | 95,481,213 |
from the National Geographic Daily News of June 8:
"Solar Flare Sparks Biggest Eruption Ever Seen on Sun"
Enormous ejection of particles into space shocks scientists.
A mushroom of cooled plasma popped like a pimple and rained onto the surface
of the sun yesterday—shooting perhaps the largest amount of solar material
into space ever seen, scientists say.
The solar flare — an unusually bright spot on the sun — wasn't surprising as
"moderate" event. Space observatories in the past year recorded about 70
such solar flares, each roughly ten times weaker than "extreme" flares, of
which only two have occurred since 2007.
Instead, what shocked scientists was the unusual amount of material that
lofted up, expanded, and fell back down over roughly half the surface area
of the sun. The event's simultaneous launch of particles into space is
called a coronal mass ejection (CME).
"This totally caught us by surprise. There wasn't much going on with this
spot, but as it came from behind the sun, all of the sudden there was a
flare and huge ejection of particles," said astrophysicist Phillip
Chamberlin of NASA's Solar Dynamics Observatory (SDO), one of several
spacecraft that recorded the event.
"We've never seen a CME this enormous."
Solar Flares May Threaten Power Grids.
Chamberlin said it will take some time to calculate the energy and mass of
electrons and protons blasted into space. But he noted the volume occupied a
space hundreds of times bigger than a single Earth.
The ejection of particles burst from the right limb of the sun and sprayed
into space, so the blast will miss Earth—though the explosion may brighten
auroras near Earth's poles, Chamberlin said.
But he warned space-weather experts are concerned about future solar events.
The sun's 11-year cycle of activity, driven by tangled surface magnetic
fields, will hit its maximum in late 2013 or early 2014. Magnetic messiness
will peak around that time and prompt nasty solar storms.
"We'll probably see [extreme] flares every couple of months instead of
years," Chamberlin said.
If one of these powerful flares—and its coronal mass ejection—faces Earth,
the particles will pound satellite components with charged particles, short
some out, and potentially cripple them.
On the planet's surface, extra currents of solar particles drive extra
electric current through power lines and heat them up.
Power companies distribute loads to avoid such a disaster, but energetic
solar storms could still blow transformers and lead to power outages,
especially during heat waves like the one sweeping the eastern U.S. this
"Despite great countermeasures, the power grid is still vulnerable. We could
be in for some serious problems," Chamberlin said. (end)
So no problems for the inhabitants of Earth, at least this time!
Regards from Melbourne! | <urn:uuid:aeab66ec-88ba-479d-bb6a-bf52d221e471> | 3.328125 | 630 | Personal Blog | Science & Tech. | 47.116342 | 95,481,218 |
Presentation on theme: "This quiz reviews you about the fundamental SI units."— Presentation transcript:
1 This quiz reviews you about the fundamental SI units. SI Units QuizThis quiz reviews you about the fundamental SI units.
2 Instructions for QuizIf you have sound, you can click on the sound icon by the choice to see if your answer is correct.If you do not have sound, write your answers on a piece of paper and check your results on the last slide.Click anywhere in the slide to go to the next slide.
3 Question 1 What is the SI unit for length? A. kilogramC. gramB. kilometerD. meter
4 Question 2 What is the SI unit for temperature? A. Degrees kelvinC. Degrees centigradeB. Degrees CelsiusD. kelvins
5 Question 3 What is the SI unit for mass? A. poundsC. gramsB. kilogramsD. mole
6 Question 4 What is the SI unit for time? A. secondsC. light yearB. minutesD. There is no SI unit for time.
7 Question 5 What is the SI unit for amount of a substance? A. gramC. kilogramB. moleD. liter
8 Question 6 What is the SI unit for electric current? A. voltC. ohmB. coulombD. ampere
9 Question 7 What is the SI unit for luminous intensity? A. light yearsC. candelasB. caloriesD. foot candles
10 Bonus Question One liter is always defined as xxx. A. a mass of one gramC. the volume of one cubic decimeterB. a mass of one kilogramD. the volume of one cubic meter
11 End of quizIf you did not get sound with this presentation, the answers are on the next page.Measurements like milliliters, cubic centimeters, and Celsius are used for convenience, but they are not SI units.If you need help with this topic, see your teacher or your text.
12 Key1) D2) D3) B4) A5) B6) D7) CIf you answered all of these questions correctly, congratulations!If you still need some review, see your teacher or your text.You may also want to practice conversions.Any comments, questions, or problems, please me. | <urn:uuid:d052ac79-7d31-4c22-a350-40a47e1673e8> | 3.765625 | 493 | Truncated | Science & Tech. | 75.185179 | 95,481,262 |
Monday, July 25, 2016
Links and References
1. The Future of Ocean Nuclear Synfuel Production
2. Will Russia and China Dominate Ocean Nuclear Technology?
3. Nuclear Navy's Synfuel from Seawater Program: An interview with Kathy Lewis of the U.S. Naval Research Laboratory
Monday, July 11, 2016
Substantially Enhancing the Capability of the SLS Architecture by Utilizing EUS Derived Propellant Depots and Reusable Orbital Transfer Vehicles
|Left: Orion space capsule with hypergolic fueled Service Module; right: notional Orion spacecraft with a reusable EUS derived orbital transfer vehicle.|
At minimum, an interplanetary round trip to the Red Planet would require several hundred tons of water for drinking, washing, food preparation, radiation shielding, the production of air, and for the production of liquid oxygen (LOX) and liquid (LH2) for rocket propellant.
Supplying the water needed for an interplanetary spacecraft parked at LEO would require a delta-v ranging from 9.3 km/s to 10 km/s from the Earth's surface. Minimum energy launch windows during the 2030s would require an additional delta-v ranging from 3.59 km/s to 4.81 km/s for Trans Mars Injections (TMI) that could send humans to Mars in less than a year.
But at different locations within cis-lunar space, substantially lower levels of delta-v could be taken advantage of in order to launch cargo and crew into a Trans Mars Injection. And these interplanetary launch points within cis-lunar space are most easily accessible from the lunar surface rather than from within the Earth's deep gravity well. So utilizing lunar ice resources could greatly reduce the cost and the complexity of sending humans to Mars.
Delta-v to important destinations within cis-lunar space
Earth surface to LEO - 9.3 km/s to 10 km/s
LEO to EML1 - 3.77 km/s (~3 days)
LEO to EML1 - 4.5 km/s (~2 days)
LEO to EML2 - 3.43 km/s (~8 days)
LEO to EML2 - 3.95 km/s (~4 days)
Lunar surface to EML1 - 2.52 km/s (~3 days)
Lunar surface to EML2 - 2.53 km/s (~3 days)
Delta-v from cis-lunar space to Trans Mars Injection
LEO to TMI (2030s) - 3.59 km/s to 4.81 km/s
EML1 to TMI (2030s) - 1.04 km/s to 1.3 km/s
Because of its shorter travel times from Earth orbit, EML1 would appear to be the optimal region for locating Deep Space Habitats (DSH), reusable lunar shuttles, propellant manufacturing water depots that receive water from the lunar surface and for launching cargoes and crew on interplanetary journeys to the orbits of Mars and Venus.
A delta-v of 3.77 can transport crews to EML1 in approximately 4 days. It would require 3.95 km/s to travel to EML2 in 4 days but 8 days of travel and radiation exposure would be required to take advantage of a lower delta-v to EML2 at 3.43 km/s. A delta-v of 2.52 km/s would be required for a 3 day journey between EML1 to the lunar surface. 2.53 km/s would be required for a similar journey between EML-2 and the lunar surface. The significant presence of habitats and depots and reusable vehicles at EML-2 could also interfere with future radio astronomy on the back side of the Moon.
Taking full advantage of polar ice resources on the Moon would require a space architecture that utilizes orbiting depots to supply water and propellant to reusable interplanetary spacecraft and landing vehicles. Some space advocates have argued that propellant depots make heavy lift vehicle's an unnecessary expense. However, heavy lift vehicles would make it possible to easily deploy propellant manufacturing water depots to EML1 for crewed interplanetary journeys to the orbits of Mars and Venus.
Similar depots located at LEO could also enable large payloads originally deployed to LEO by heavy lift vehicles to be later deployed by reusable orbital transfer vehicles practically anywhere within cis-lunar space.
|Expendable EUS for SLS launch vehicle (Credit: NASA)|
In 2018, NASA will launch the first SLS heavy lift vehicle with an unmanned Orion space capsule and a hypergolic fueled Service Module and an interim upper stage. But NASA currently envisions crewed SLS launches in the 2020s to include an Orion space capsule with a hypergolic fueled Service Module and a large LOX/LH2 fueled Exploratory Upper Stage (EUS).
But two of the principal companies (Boeing and Lockheed Martin) currently developing the SLS/Orion architecture are also-- privately developing-- an alternate space architecture through their joint company, the ULA (the United Launch Alliance). In this alternate architecture, the ULA will utilize their emerging IVF (Integrated Vehicle Fluids ) technology to deploy a reusable ACES upper stage that could eventually utilize LOX/LH2 propellant depots for travel within cis-lunar space during the 2020s. IVF technology allows a spacecraft to utilize hydrogen and oxygen ullage gases for attitude control, power production, and for autogenously pressurizing propellant tanks, eliminating the need for hydrazine and liquid helium.
NASA could greatly enhance the capability, efficiency, and the safety of the SLS/Orion architecture by taking full advantage of the ULA’s emerging IVF technology. While there's no reason to stop Boeing from developing the EUS as an expendable upper stage for the SLS, it would still be technologically advantageous for NASA to commission the ULA to use its IVF technology to convert some EUS vehicles into reusable orbital transfer vehicles and others into propellant depots.
|EUS derived propellant manufacturing water depot and reusable Orion orbital transfer vehicle.|
An SLS/Orion architecture utilizing EUS derived Orbital Transfer Vehicles (OTV-125) and EUS derived propellant producing water depots (WPD-OTV-125) would no longer require the expense and the enhanced risk of launching astronauts on top of a super heavy lift vehicle. So for beyond LEO missions in the 2020s, under this scenario, astronauts would simply be transported to LEO by Commercial Crew vehicles that would have already been in operational service since 2018.
Once in orbit, the commercial crew capsule would dock directly with the Orion-OTV-125 reusable spacecraft, transferring its crew aboard the Orion for its beyond LEO mission. Alternatively, a crew capsule could dock at the port of a space station where the Orion-OTV-125 would also be docked at a different port. Both scenarios would mean that the ATV based hypergolic Service Module being manufactured by the Europeans would not be required for crewed beyond LEO missions, and would only be used once during the 2018 test mission. So only the domestically manufactured Orion capsule being developed by Lockheed Martin would be preserved in this architecture.
A single SLS Block I cargo launch could be used to deploy two WPD-OTV-125 depots to LEO plus a two 1 MWe solar arrays. With at least 35 tonnes of propellant, one of the water/propellant depots could self deploy itself to EML1 along with its 1.4 to 2.8 MWe solar array. Another basic SLS Block I cargo launch could be used to deploy two reusable Orion-OTV-125 vehicles to LEO. But once this reusable depot based extraterrestrial architecture is deployed by the SLS, private commercial launch vehicles will only be required to conduct crewed beyond LEO missions. This will allow the SLS to be used exclusively as a cargo launcher for the deployment of large and heavy spacecraft and habitats and other large and heavy structures.
|Notional lunar water ice extraction, storage, and LOX/LH2 manufacturing facility.|
Water for the propellant manufacturing orbital depots could be regularly supplied to LEO and to EML1 from commercial launch vehicles (Atlas V, Delta IV heavy, Falcon 9, and the future Falcon Heavy, Vulcan, and Vulcan Heavy vehicles). However, once water is being manufactured on the lunar surface, water transported to EML1 would be supplied exclusively from the lunar surface.
Since the Orion-OTV-125 would derived from the EUS, it would be capable of accommodating up to 125 tonnes of propellant. But less than 35 tonnes of propellant would be required for an Orion-OTV-125 to transport its crew to EML1. And an equal amount of fuel would be needed to return astronauts to LEO. No aerobraking would be required.
A reusable Extraterrestrial Landing Vehicle (ETLV) would transport astronauts from EML1 to the surface of the Moon and back to EML1 with a single fueling of LOX/LH2. A single SLS Block I cargo launch could deploy three ten tonne ETVL-2 vehicles to LEO, each with enough propellant to travel to EML1. The ETLV-2 could also serve as an back up OTV in case one or both of the Orion-OTV-125 vehicles becomes inoperable.
Until new RS-25 engines are in production, perhaps by 2021 to 2023, NASA will only be able to launch four SLS vehicles. And one of those launches will be an unmanned test launch in 2018. So after 2018, only three SLS launches will be possible before the RS-25 engines go into production.
|Notional EUS derived propellant manufacturing water depot @ EML1 after refueling a reusable Extraterrestrial Landing Vehicle.|
But just three basic SLS Block I cargo launches would be required to deploy a reusable EUS derived cis-lunar transport architecture (WPD-OTV-125, Orion-OTV-125, and the ETLV-2) capable of transporting humans to EML1 and to the lunar surface and back.
However, the deployment of the lunar landing vehicles could be delayed until the new RS-25 engines are in production. This would allow NASA to use their last four Space Shuttle Main Engines to be used to launch a DHS (Deep Space Hab) to EML1. An SLS propellant tank derived habitat with over 510 cubic meters of pressurized habitable volume would have a dry weight of 22.4 tonnes. So in theory, a single SLS Block I cargo launch could be used to deploy two or three pressurized habitats to LEO. A partially fueled Orion-OTV-125 could then be used to transport one of the pressurized habitats to EML1.
|SLS propellant tank derived habitat (Credit: NASA).|
This would leave one or two pressurized habitats at LEO with a combined pressurized habitable volume exceeding that of the ISS! All of that would be achieved with a single SLS launch and a reusable propellant producing water depot architecture routinely and sustainably supplied with water from commercial launch vehicles.
Moon first, then Mars? Congress moves to shift space priorities
The return to the moon, Lori Garver, and the price of ambition
Lori Garver Questioned Astronauts about NASA's Next Destination?
Seeing the end of Obama’s space doctrine, a bipartisan Congress moves in
What about Mr. Oberth
Human Lunar exploration architectures
Earth Departure Options for Human Missions to Mars
A Study of CPS Stages for Missions beyond LEO
Deep Space Habitats
First Human Voyages to the Martian Moons Using SLS and IVF Derived Technologies
Congress Requires NASA to Develop a Deep Space Habitat
UltraFlex Solar Array Systems
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Nuclear Synfuel Economy The Methanol Economy Gasoline from Air & Water
Notional MADV on the surface of Mars (Credit: Lockheed Martin) by Marcel F. Williams At the 68th International Astronautical Congress...
Nuclear Navy's Synfuel from Seawater Program: An interview with Kathy Lewis of the U.S. Naval Research LaboratoryLinks The feasibility and current estimated capital costs of producing jet fuel at sea using carbon dioxide and hydrogen Navy S...
Chinese floating nuclear power station (Credit: China General Nuclear Corporation) by Marcel F. Williams T oday, more than 180 small...
Computer illustration of Near Rectilinear Orbits between EML1 and EML2 (Credit: NASA). N ASA appears to have settled on a Near Rectil...
by Marcel F. Williams Tuscany is renowned for its beautiful cities of Florence and Siena, and is historically famous as the birthplace ...
by Marcel F. Williams Congress has now made it clear that they want the immediate development of a heavy lift vehicle and a crew explorat...
Links and References Bell V-280 Valor Watch the Army's futuristic V-280 helicopter flying in cruise mode for the first tim... | <urn:uuid:3b044378-df4c-4362-bf01-7bcd8e38aa7f> | 2.515625 | 2,828 | Content Listing | Science & Tech. | 51.012906 | 95,481,271 |
Excluding a handful of astronauts, all of humanity lives on a little spinning marble hurtling through the almost uninterrupted void of cosmic emptiness, protected by the warm, comforting envelope of our atmosphere.
But where does that atmosphere end and the edge of space begin?
Scientists aren’t exactly sure. There’s even a debate over whether we should determine where Earth ceases and space begins — the UN and the US State Department believe we shouldn’t make anything official.
We do have some general boundaries though.
Above Earth’s surface, our atmosphere is divided into five layers, the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
Chances are, unless you’ve spent time as a fighter pilot, you’ve never gone beyond the troposphere. And all humans except for the 24 astronauts who have visited the moon have ever ventured beyond the thermosphere.
When you reach 50 miles of altitude, near the border between the mesosphere and the thermosphere, that’s where aerodynamic control surfaces stop working (you’ll need rockets to steer).
And for record-keeping and giving out astronaut wings, the Kármán Line, located around 62 miles (100 km) above the surface of the Earth, serves as a rough space border: this is where a craft begins to escape the grip of our planet’s gravity.
As you fly higher into the atmosphere, the air gets thinner, and this means a plane needs more speed for its wings to generate the lift needed to keep it aloft.
The Kármán Line is the point where the speed needed to maintain altitude is equal to escape velocity: the speed at which a craft ceases to follow the curvature of the Earth, and the craft begins to enter space.
NASA and the Fédération Aéronautique Internationale, the organization for international aeronautical and astronautical record-keeping, recognize this line as the point where space begins — if you’ve gone above the Karman Line, your aeronautics become astronautics and you’re considered an astronaut.
But the atmosphere doesn’t stop there — it continues on, gradually thinning out for thousands of miles.
The final layer of the atmosphere, the enormous exosphere, continues until around 6,700 miles (10,000 km) above the surface of our planet (and some say even further). At that point, the moon is still hundreds of thousands of miles away.
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From a quarter to half of Earth's vegetated lands has shown significant greening over the last 35 years largely due to rising levels of atmospheric carbon dioxide, according to a new study published in the journal Nature Climate Change on April 25.
An international team of 32 authors from 24 institutions in eight countries led the effort, which involved using satellite data from NASA's Moderate Resolution Imaging Spectrometer and the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer instruments to help determine the leaf area index, or amount of leaf cover, over the planet's vegetated regions. The greening represents an increase in leaves on plants and trees equivalent in area to two times the continental United States.
Green leaves use energy from sunlight through photosynthesis to chemically combine carbon dioxide drawn in from the air with water and nutrients tapped from the ground to produce sugars, which are the main source of food, fiber and fuel for life on Earth. Studies have shown that increased concentrations of carbon dioxide increase photosynthesis, spurring plant growth.
However, carbon dioxide fertilization isn't the only cause of increased plant growth--nitrogen, land cover change and climate change by way of global temperature, precipitation and sunlight changes all contribute to the greening effect.
To determine the extent of carbon dioxide's contribution, researchers ran the data for carbon dioxide and each of the other variables in isolation through several computer models that mimic the plant growth observed in the satellite data.
Results showed that carbon dioxide fertilization explains 70 percent of the greening effect, said co-author Ranga Myneni, a professor in the Department of Earth and Environment at Boston University. "The second most important driver is nitrogen, at 9 percent. So we see what an outsized role CO2 plays in this process."
About 85 percent of Earth's ice-free lands is covered by vegetation. The area covered by all the green leaves on Earth is equal to, on average, 32 percent of Earth's total surface area - oceans, lands and permanent ice sheets combined. The extent of the greening over the past 35 years "has the ability to fundamentally change the cycling of water and carbon in the climate system," said lead author Zaichun Zhu, a researcher from Peking University, China, who did the first half of this study with Myneni as a visiting scholar at Boston University.
Every year, about half of the 10 billion tons of carbon emitted into the atmosphere from human activities remains temporarily stored, in about equal parts, in the oceans and plants. "While our study did not address the connection between greening and carbon storage in plants, other studies have reported an increasing carbon sink on land since the 1980s, which is entirely consistent with the idea of a greening Earth," said co-author Shilong Piao of the College of Urban and Environmental Sciences at Peking University.
While rising carbon dioxide concentrations in the air can be beneficial for plants, it is also the chief culprit of climate change. The gas, which traps heat in Earth's atmosphere, has been increasing since the industrial age due to the burning of oil, gas, coal and wood for energy and is continuing to reach concentrations not seen in at least 500,000 years. The impacts of climate change include global warming, rising sea levels, melting glaciers and sea ice as well as more severe weather events.
The beneficial impacts of carbon dioxide on plants may also be limited, said co-author Dr. Philippe Ciais, associate director of the Laboratory of Climate and Environmental Sciences, Gif-suv-Yvette, France. "Studies have shown that plants acclimatize, or adjust, to rising carbon dioxide concentration and the fertilization effect diminishes over time."
"While the detection of greening is based on data, the attribution to various drivers is based on models," said co-author Josep Canadell of the Oceans and Atmosphere Division in the Commonwealth Scientific and Industrial Research Organisation in Canberra, Australia. Canadell added that while the models represent the best possible simulation of Earth system components, they are continually being improved.
Read the paper at Nature Climate Change.
For more information about NASA's Earth science activities, visit:
Ellen Gray | EurekAlert!
New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz
Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
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Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
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Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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A reprint of a classical work in the Princeton Legacy Library, originally published in 1994.
Ecological Genetics represents work by five distinguished ecological geneticists, offering an up-to-date source for theoretical concepts and experiments in an exciting field. Combining ecological fieldwork and laboratory genetics, ecological genetics examines the adjustments and adaptations of wild populations to their environments. Articles focus on important interactions between genetics and population ecology, delving into issues like gene flow and migration, population differentiation, the maintenance of genetic variation, and the demographic and spatial structure of populations. The contributors – Janis Antonovics, Michael Lynch, Montgomery Slatkin, Joseph Travis, and Sara Via – emphasize the importance of population size and structure, interaction between local selection and genetic drift, and an expanded phenotype including quantitative as well as qualitative characters. This new form of ecological genetics focuses on large-scale geographic variation in demographic and genetic dynamics among small, partially isolated populations and will prove extremely valuable in natural resource management and in rare or endangered species conservation.
"The five contributors are all exciting and accomplished researchers in ecological and population genetics [...] Each contribution expresses a unique and powerful viewpoint on topics of considerable interest."
List of Contributors
Introduction: Current Directions in Ecological Genetics
1 Gene Flow and Population Structure 3
2 Cladistic Analysis of DNA Sequence Data from Subdivided Populations 18
3 The Evolution of Phenotypic Plasticity: What Do We Really Know? 35
4 Population Structure and Local Adaptation in a Clonal Herbivore 58
5 Neutral Models of Phenotypic Evolution 86
6 Evolutionary Genetics of Daphnia 109
7 The Interplay of Numerical and Gene-Frequency Dynamics in Host-Pathogen Systems 129
8 Ecological Genetics of Metapopulations: The Silene-Ustilago Plant-Pathogen System 146
9 Ecological Genetics of Life-History Traits: Variation and Its Evolutionary Significance 171
10 Evolution in the Sailfin Molly: The Interplay of Life-History Variation and Sexual Selection 205
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By: Matts Roos
The Third Edition of the hugely successful Introduction to Cosmology provides a concise, authoritative study of cosmology at an introductory level. Starting from elementary principles and the history of cosmology, the text carefully guides the student on to curved spacetimes, general relativity, black holes, cosmological models, particles and symmetries, and phase transitions. Extensively revised, this latest edition includes broader and updated coverage of distance measures, gravitational lensing and waves, dark energy and quintessence, the thermal history of the Universe, inflation, large scale structure formation, and the 'cosmological coincidence'problem.* Illustrated throughout and comprehensively referenced with problems at the end of each chapter.* Includes more material on observational astrophysics and expanded sections on astrophysical phenomena.* Latest observational results from the WMAP satellite and the 2 degree Field Galaxy Redshift Survey.
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Species Detail - Golden Spindles (Clavulinopsis fusiformis) - Species information displayed is based on all datasets.
Terrestrial Map - 10kmDistribution of the number of records recorded within each 10km grid square (ITM).
Marine Map - 50kmDistribution of the number of records recorded within each 50km grid square (WGS84).
Clavaria ceranoides, Clavaria fusiformis, Clavaria fusiformis var. ceranoides, Ramaria ceranoides
13 September (recorded in 1997)
6 November (recorded in 2007)
National Biodiversity Data Centre, Ireland, Golden Spindles (Clavulinopsis fusiformis), accessed 22 July 2018, <https://maps.biodiversityireland.ie/Species/158152> | <urn:uuid:39eb4a94-0f6e-4919-aa9a-2668d097b1a1> | 2.609375 | 177 | Structured Data | Science & Tech. | 16.459227 | 95,481,359 |
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured this natural-color image on June 23, 2012. Red outlines approximate the locations of actively burning fires. The High Park and Weber Fires produced the largest plumes of smoke.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image on June 23, 2012. Red outlines approximate the locations of actively burning fires. The High Park and Weber Fires produced the largest plumes of smoke.
Credit: NASA Earth Observatory image by Jesse Allen using data obtained from the Land Atmosphere Near real-time Capability for EOS (LANCE).
The High Park Fire continued to burn west of Fort Collins. Started by lightning on June 9, 2012, this blaze had consumed 83,205 acres (33,672 hectares), making it the second-largest fire in Colorado history, after the Hayman Fire that burned in 2002. As of June 25, more than 2,000 people were fighting the High Park Fire, and firefighters had it 45 percent contained, according to InciWeb. Nevertheless, The Denver Post reported that the fire had destroyed 248 homes, making it the most destructive in Colorado history, even if it was not the largest.
In the opposite corner of the state, the Weber Fire started around 4:15 p.m. on June 22. As of June 25, the fire had burned approximately 8,300 acres (3,400 hectares) and was being fought by 164 personnel. The cause was under investigation. The fire had high growth potential because of possible wind gusts from thunderstorms, InciWeb reported. On the other side of Durango, the Little Sand Fire had been burning for weeks after being started by a lightning strike on May 13. As of June 25, that fire had burned 21,616 acres (8,748 hectares), was being fought by nearly 200 people, and was 31 percent contained.
West of Colorado Springs, the Waldo Canyon Fire forced 11,000 people from their homes, many of them compelled to evacuate in the middle of the night on June 23. The fire started around noon on June 23, and by June 25 it had grown to 3,446 acres (1,395 hectares). InciWeb stated that 450 firefighters were battling the blaze, which retained the potential for rapid growth.
The Woodland Heights Fire just west of Estes Park was small but very destructive, consuming 27 acres (11 hectares) and destroying 22 homes, Denver's Channel 7 News reported. That fire was completely contained by the evening of June 24.
As fires burned, Colorado also coped with extreme heat. The Denver Post reported that Denver endured triple-digit temperatures June 22 through 24, and the National Weather Service forecast temperatures of at least 100 degrees Fahrenheit (38 degrees Celsius) for June 25 and 26, with temperatures in the upper 90s through June 29.
Colorado's fires have followed a dry spring. Although the state experienced unusually heavy snow in February, little snow followed in March and April, part of a larger pattern of low snowfall. By June 19, 2012, conditions throughout the state ranged from unusually dry to extreme drought, according to the U.S. Drought Monitor.
On June 25, 2012, Tim Mathewson, a fire meteorologist with the Rocky Mountain Area Coordination Center, remarked: "Current conditions are comparable to 2002 fire season, which was the worst in Colorado history. Fires haven't burned as many acres at this point, but the drought conditions and fuel conditions are right up there with the 2002 season, if not worse."For a non-labeled, high resolution image, visit: http://eoimages.gsfc.nasa.gov/images/imagerecords/78000/78367/colorado
Rob Gutro | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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For the full story see the NASA Hubble site: NASA/ESA managed to combine the powerful Hubble Space Telescope with the incredible sling-shot magnification of gravitational lensing to produce what appears to be mankind’s first visible-light image of an accretion disk. .
[quote]An international team of astronomers has used a new technique to study the bright disc of matter surrounding a faraway black hole. Using the NASA/ESA Hubble Space Telescope, combined with the gravitational lensing effect of stars in a distant galaxy , the team measured the disc’s size and studied the colours (and hence the temperatures) of different parts of the disc. These observations show a level of precision equivalent to spotting individual grains of sand on the surface of the Moon.[/quote]
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How do you provide clean drinking water to some of the places in the world that need it the most? Figure out a way to filter it that costs very little and that uses natural resources found in abundance where these people live.
That’s exactly what 18-year-old Meghan Shea did with bamboo and a plant called the moringa seed, and it earned her an Innovator Award from Popular Mechanics. It was one of 10 such prizes the magazine gave out as part of its ninth annual Breakthrough Awards in New York City Tuesday, along with 10 product honors. Peter Diamandis, founder of the XPrize Foundation, earned the Leadership Award.
“Innovators can create the future,” Diamandis said during his keynote address. “I don’t see anything that’s impossible.”
To that end, Diamandis announced three new Ocean XPRIZEs by 2020. Those come on top of the one already in existence, a $2 million motivation to push inventors to create what the XPRIZE Foundation calls “accurate, affordable ocean pH sensors” to help advance the scientific community’s understanding of ocean acidification and how to reverse it.
“The lungs of planet Earth are becoming acidified,” Diamandis said. The new prizes will hopefully answer the question, what else can we be doing to help, he added. The idea is to crowd source to come to the best conclusion.
Other honorees from the Breakthrough Awards included a liquid repellent that, once sprayed on something, protects it from all manner of liquid, as well as drones that fly on their own, the doctors who created a 3-D tracheal splint (and successfully used it on a patient) and the Mars Curiosity Rover team. | <urn:uuid:63821792-a0f1-4501-8c6e-53387ea750cd> | 2.890625 | 381 | News Article | Science & Tech. | 49.009176 | 95,481,437 |
Suppose we live on a Latitude of L degrees (The Gold Coast is at a latitude of about 28 degrees South of the equator... it is also on Earth). A "Latitude" on the surface of a planet is a circle on its surface where a radius from every point on it to the centre makes an angle of L degrees with the equatorial plane of the planet... sort of a parallel circle to the equator:
Figure 1 shows a cross section of a planet of radius R (6,400 km for Earth) with some algebra relevant to latitude L ...well one of the latitude L's, our L is the "downunder" one called South and rather unfairly "minus" on Earth. The "Solar Axis" is the axis perpendicular to the sun's (the planets star's) light, the planet actually rotates about an axis which is T degrees different from this and that axis is conveniently directly behind the "Solar Axis" in figure 1. Therefore in this diagram T is the same as A but as mentioned before this is only the case on a special occasion.
Another fact to note in figure 1 is that for latitudes bigger than a certain value, called P for "Polar" in figure 1, the latitude is either entirely in the dark (the Southern Hemisphere in figure 1) or entirely in the light (the Northern Hemisphere in figure 1) so we need to remember that +P and -P degrees are boundaries inside which the following Maths works and outside which it doesn't, much the same as the limitation that the latitudes can only lie between outside +90 and -90 degrees and still be on the planet!
There is a neat relationship between A degrees and P degrees and it is pretty easy to work out. Note that the triangle formed with base equal to the latitude P (either one, but the Northern one is drawn in in figure 1) and the centre of the circle, the arms of the triangle are both the same (equal to R the radius of the planet) and that the central angle of this (isoceles) triangle is 90-P+A degrees, the base angles are both P degrees (because of the isocelesnessosity!) of the triangle and all three add up to 180 degrees. Therefore
i.e. P + P + (90-P+A) = 180 so 90 + P + A = 180 so P + A = 90 so P = 90 - AThis means that P and A are complimentary angles. For Earth, the special case where the axial Tilt T = A (= 23.5 degrees) P will be the polar circles at 66.5 degrees, the limit of the 24 hour day in summer and 24 hour night in winter:
At this stage I am going to introduce some "preemptive retrospection", this is my term for discovering a problem in the derivation later on and then tracing it back to, in this case, around about here, and inserting the fix in such a way as to pretend that it is obvious to consider such things a priori... I have a hypothesis that the greater the haughtiness or "this is obvious..ness" of the justification the greater the actual mollification the author experienced when he she or it realised the blunder.
Ahemm... it is clearly obvious to any carbon based life form that the angle "A" can be negative as well as positive, as it will range from -T to +T degrees throughout the year, figures 3 and 4 (will) illustrate this. "A" will be positive when it leans the same way as the axial tilt and negative when it leans the other away. This means that the above representation of P is a special case where A is positive and P = 90-A, if A is negative then P would be 90+A to put these two exigencies together we use the modulus of A, written as |A| which is technically defined as +A for A >0 and -A for A < 0 so the general relationship between P and A is
|P| = 90 - |A|
The second clearly obvious thing is that the Latitude L is negative in the diagrams because it resides in the Southern Hemisphere. This is not important at this stage, but later, if L is considered positive, then the seasons are reversed! and indeed the formula generated needs to be measured, not from te Southern Winter Solstice, but the Summer one.
Figure 2 shows perspective of latitude L with the results form figure 1 incorporated in even more Algebra (remember this maths only applies for latitudes between +P and -P degrees). The purpose of both these pictures and the calculations is to figure out how much sunshine there is in proportion to darkness at latitude L
Following on from the calculation box in figure 2... to figure out the angle C we need to "un cosine" it, the is called "arc cos" or "inverse cos", it is a standard function on calculators and computers.
C = arc Cos(Tan(L)Tan(A))The angle defining the "Sector of sunshine" is actually 2 C. Now there are 360 degrees in a circle and if a day is H hours long (H=24 for Earth) then the number of sunshine hours is
2C.H C.H ---- = --- 360 180therefore
Sunshine Hours = (H/180) arc Cos(Tan(L)Tan(A)) (EQ 1)
but remember it is only when |L| < P
Figure 3 shows the planet at several times during the year (dates are for Earth!). Also note the parochial naming of the equinoxes by the Northerners ("up overs" ... I think they would like to call themselves). The IMPORTANT thing to note is how the axis of rotation (arrowed line) changes its orientation relative to the sunlight. I have defined the "Day Angle", DA for short, which relates to the number of days since the Southern Winter Solstice:
If the number of days per year is DY (365.25 for Earth) and the Day of the year D days since the Southern Winter Solstice then the "day angle" DA representing this day is given by
DA D --- = --- and so DA = D.360/DY (EQ 2) 360 DY
Figure 4 shows a detailed schematic view of figure 3 from above, the axial tilt angle is projected onto (a line through) the direction of the sun, this projection is directly related to the "Shadow Axis angle" A which is used above. Recall that A is the effective angle required in the "sunshine" calculation for any particular day. Figure 5, which is a perspective of a particular (but not special) day shows this relationship.
A = arc Tan(Tan(T).Cos(360.D/Y))Now recall the formula for Sunlight Hours (EQ 1), we can now substitute for A, the "Shadow axis angle"
Sunshine = (H/180) arc Cos(Tan(L)Tan(A)) (EQ 3)This is an important point in the derivation, because it is where we leave the angle A. Recall that the limit of applicability of the formula I am generating is +/- P = +/- (90 - |A|). However I will return to it to make the final formula into several slightly less terrifying parts. For the meantime...
we get a really horrible looking formula when we substitute for A
Sunshine = (H/180) arc Cos(Tan(L)Tan(arc Tan(Cos(360 D/Y)Tan(T)))Note however that we are tan-ing then immediately un tan-ing something to no net effect, so the formula can be "de taned" to become
Sunshine = (H/180) arc Cos(Tan(L)Cos(360 D/Y)Tan(T))You may find it neater, given that the limitations of the equations (|L| < 90-|A|) involve the shadow axis angle "A", to retain "A" in the final representation (that is EQ 3).
Given that A = arc Tan(Tan(T)Cos(360.D/Y)) Sunshine = (H/180) arc Cos(Tan(L)Tan(A)) when |A|-90 < L < 90-|A|
|L|=90-|A| which is the same as L = 90-|A| and L= |A| - 90
Sunshine = (H/180) arc Cos(Tan(90-|A|)Tan(A)) when 90-|A| < L < 90 and (H/180) arc Cos(Tan(|A|-90)Tan(A)) when -90 < L < -90+|A|At this point it useful to note that
Given that A = arc Tan(Tan(T)Cos(360.D/Y)) Sunshine... = (H/180) arc Cos(Tan(L)Tan(T)Cos(360.D/Y)) when A-90 < L < 90-A = 0 when L > 0 and H when L < 0 when 90-A < L < 90 = H when L > 0 and 0 when L > 0 when -90 < L < A-90
|H||Hours per day||24|
|D||Days since the Southern Winter solstice||22 June|
|DY||Days in a Year||365.25|
|T||Tilt of axis of rotation||23.5|
figure 6 shows a three dimensional view of the sunshine function.
You've read the proof now see the movie: see the "Mexican wave" of sunshine hours varying horizontally with latitude and vertically with number of hours, the particular values used in this movie are brought to you by the planet Earth: The action covers the year depicted in figure 6 which has drawn on it, at the start of the year, the curve of figure 7. The scene opens on the Southern Summer Solstice. Note that on this day, the duration reaches 24 hours at -66.5 degrees, from there to the South pole any traveller will have 24 hour sunshine (on this day). Similar Northern polar bound persons will have 24 hours of dark. Only the curve within the bounds of |P| is drawn. Equatorial Earthlings experience the same 12 hours of sunshine each and every day. Click the picture to see and hear what happens next!
The movie is a quicktime movie, so if you are using a Windows computer (but for God's sake why?) then you will need to Download and add (as usual) yet another set of meaningless file names to your system for MPLAYER.EXE to show it thankfully this is small. Or install Quicktime. and the QTVR player for windows which is large.
Sunshine= (H/pi) arc Cos(Tan(L)Tan(T)Cos(2pi.D/DY))A good exercise is to make up a spreadsheet with this formula in it use references to other cells for the variables and don't forget to use the radians version because that is what spreadsheets use for angle measure.
Here is a formula for a spreadsheet, all angle measures in degrees.
|B1||Hours per day|
|B2||Latitude of place|
|B3||Days since Southern Summer Solstice|
|B4||Days per year|
By the way
The other big consideration is the fuzzy bit about the planet, the atmosphere refracts light to the extent that when you see the sun's lower rim touching the horizon, it is actually below the horizon. | <urn:uuid:32f1abf4-2b89-4876-8ff1-5fdd6aace9a9> | 4.0625 | 2,431 | Personal Blog | Science & Tech. | 69.265191 | 95,481,449 |
Inscrit le: 07 Oct 2017
|Posté le: Sam 16 Déc - 09:08 (2017) Sujet du message: Scientists find teeth of early human ancestor
Scientists have come to believe that modern placental mammals – from whales to bats, and yes, humans too – descended from small furry mammals that lived during the age of the dinosaurs.
On November, scientists announced the discovery of two fossil teeth from these ancient creatures, the earliest fossils of these creatures known so far, in rocks from the coast of Dorset in England. The teeth date back to 145 million years ago. The scientists’ statement said.
Steve Sweetman at the University of Portsmouth is the paper’s main author. He’s an expert in small vertebrates that lived during the Cretaceous period. In his team’s statement, he recounted how an undergraduate at the university, Grant Smith, made the extraordinary discovery of two unusual fossil teeth.
Sweetman believes, were probably nocturnal. To an expert’s eye, a single tooth can reveal a lot about an animal. One of the fossil teeth may have belonged to a ground burrower that probably ate insects. The other tooth may have belonged to a creature that also ate plants.
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The electron is a subatomic particle, symbol
, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. As it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.
Hydrogen atom orbitals at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.
|Interactions||Gravity, electromagnetic, weak|
|Antiparticle||Positron (also called antielectron)|
Richard Laming (1838–1851),|
G. Johnstone Stoney (1874) and others.
|Discovered||J. J. Thomson (1897)|
[822.8884845(14)]−1 u 1[note 1]
|Mean lifetime||stable ( > ×1028 yr6.6)|
e−1 [note 2]|
|Magnetic moment||−1.00115965218091(26) μB|
|Weak isospin||LH: −1/, RH: 0|
|Weak hypercharge||LH: -1, RH: −2|
Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry and thermal conductivity, and they also participate in gravitational, electromagnetic and weak interactions. Since an electron has charge, it has a surrounding electric field, and if that electron is moving relative to an observer, it will generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors and particle accelerators.
Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms. Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge 'electron' in 1891, and J. J. Thomson and his team of British physicists identified it as a particle in 1897. Electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. The antiparticle of the electron is called the positron; it is identical to the electron except that it carries electrical and other charges of the opposite sign. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons.
Discovery of effect of electric forceEdit
The ancient Greeks noticed that amber attracted small objects when rubbed with fur. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, to refer to this property of attracting small objects after being rubbed. Both electric and electricity are derived from the Latin ēlectrum (also the root of the alloy of the same name), which came from the Greek word for amber, ἤλεκτρον (ēlektron).
Discovery of two kinds of chargesEdit
In the early 1700s, Francis Hauksbee and French chemist Charles François du Fay independently discovered what they believed were two kinds of frictional electricity—one generated from rubbing glass, the other from rubbing resin. From this, du Fay theorized that electricity consists of two electrical fluids, vitreous and resinous, that are separated by friction, and that neutralize each other when combined. American scientist Ebenezer Kinnersley later also independently reached the same conclusion.:118 A decade later Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess (+) or deficit (-). He gave them the modern charge nomenclature of positive and negative respectively. Franklin thought of the charge carrier as being positive, but he did not correctly identify which situation was a surplus of the charge carrier, and which situation was a deficit.
Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges. Beginning in 1846, German physicist William Weber theorized that electricity was composed of positively and negatively charged fluids, and their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion. He was able to estimate the value of this elementary charge e by means of Faraday's laws of electrolysis. However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".
Stoney initially coined the term electrolion in 1881. Ten years later, he switched to electron to describe these elementary charges, writing in 1894: "... an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron". A 1906 proposal to change to electrion failed because Hendrik Lorentz preferred to keep electron. The word electron is a combination of the words electric and ion. The suffix -on which is now used to designate other subatomic particles, such as a proton or neutron, is in turn derived from electron.
Discovery of free electrons outside matterEdit
The German physicist Johann Wilhelm Hittorf studied electrical conductivity in rarefied gases: in 1869, he discovered a glow emitted from the cathode that increased in size with decrease in gas pressure. In 1876, the German physicist Eugen Goldstein showed that the rays from this glow cast a shadow, and he dubbed the rays cathode rays. During the 1870s, the English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside. He then showed that the luminescence rays appearing within the tube carried energy and moved from the cathode to the anode. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged. In 1879, he proposed that these properties could be explained by what he termed 'radiant matter'. He suggested that this was a fourth state of matter, consisting of negatively charged molecules that were being projected with high velocity from the cathode.
The German-born British physicist Arthur Schuster expanded upon Crookes' experiments by placing metal plates parallel to the cathode rays and applying an electric potential between the plates. The field deflected the rays toward the positively charged plate, providing further evidence that the rays carried negative charge. By measuring the amount of deflection for a given level of current, in 1890 Schuster was able to estimate the charge-to-mass ratio of the ray components. However, this produced a value that was more than a thousand times greater than what was expected, so little credence was given to his calculations at the time.
In 1896, the British physicist J. J. Thomson, with his colleagues John S. Townsend and H. A. Wilson, performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier. Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles," had perhaps one thousandth of the mass of the least massive ion known: hydrogen. He showed that their charge-to-mass ratio, e/m, was independent of cathode material. He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal. The name electron was again proposed for these particles by the Irish physicist George Johnstone Stoney, and the name has since gained universal acceptance.
While studying naturally fluorescing minerals in 1896, the French physicist Henri Becquerel discovered that they emitted radiation without any exposure to an external energy source. These radioactive materials became the subject of much interest by scientists, including the New Zealand physicist Ernest Rutherford who discovered they emitted particles. He designated these particles alpha and beta, on the basis of their ability to penetrate matter. In 1900, Becquerel showed that the beta rays emitted by radium could be deflected by an electric field, and that their mass-to-charge ratio was the same as for cathode rays. This evidence strengthened the view that electrons existed as components of atoms.
The electron's charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil-drop experiment of 1909, the results of which were published in 1911. This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity. This device could measure the electric charge from as few as 1–150 ions with an error margin of less than 0.3%. Comparable experiments had been done earlier by Thomson's team, using clouds of charged water droplets generated by electrolysis, and in 1911 by Abram Ioffe, who independently obtained the same result as Millikan using charged microparticles of metals, then published his results in 1913. However, oil drops were more stable than water drops because of their slower evaporation rate, and thus more suited to precise experimentation over longer periods of time.
Around the beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of supersaturated water vapor along its path. In 1911, Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles, such as fast-moving electrons.
By 1914, experiments by physicists Ernest Rutherford, Henry Moseley, James Franck and Gustav Hertz had largely established the structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons. In 1913, Danish physicist Niels Bohr postulated that electrons resided in quantized energy states, with their energies determined by the angular momentum of the electron's orbit about the nucleus. The electrons could move between those states, or orbits, by the emission or absorption of photons of specific frequencies. By means of these quantized orbits, he accurately explained the spectral lines of the hydrogen atom. However, Bohr's model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atoms.
Chemical bonds between atoms were explained by Gilbert Newton Lewis, who in 1916 proposed that a covalent bond between two atoms is maintained by a pair of electrons shared between them. Later, in 1927, Walter Heitler and Fritz London gave the full explanation of the electron-pair formation and chemical bonding in terms of quantum mechanics. In 1919, the American chemist Irving Langmuir elaborated on the Lewis' static model of the atom and suggested that all electrons were distributed in successive "concentric (nearly) spherical shells, all of equal thickness". In turn, he divided the shells into a number of cells each of which contained one pair of electrons. With this model Langmuir was able to qualitatively explain the chemical properties of all elements in the periodic table, which were known to largely repeat themselves according to the periodic law.
In 1924, Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state, as long as each state was occupied by no more than a single electron. This prohibition against more than one electron occupying the same quantum energy state became known as the Pauli exclusion principle. The physical mechanism to explain the fourth parameter, which had two distinct possible values, was provided by the Dutch physicists Samuel Goudsmit and George Uhlenbeck. In 1925, they suggested that an electron, in addition to the angular momentum of its orbit, possesses an intrinsic angular momentum and magnetic dipole moment. This is analogous to the rotation of the Earth on its axis as it orbits the Sun. The intrinsic angular momentum became known as spin, and explained the previously mysterious splitting of spectral lines observed with a high-resolution spectrograph; this phenomenon is known as fine structure splitting.
In his 1924 dissertation Recherches sur la théorie des quanta (Research on Quantum Theory), French physicist Louis de Broglie hypothesized that all matter can be represented as a de Broglie wave in the manner of light. That is, under the appropriate conditions, electrons and other matter would show properties of either particles or waves. The corpuscular properties of a particle are demonstrated when it is shown to have a localized position in space along its trajectory at any given moment. The wave-like nature of light is displayed, for example, when a beam of light is passed through parallel slits thereby creating interference patterns. In 1927 George Paget Thomson, discovered the interference effect was produced when a beam of electrons was passed through thin metal foils and by American physicists Clinton Davisson and Lester Germer by the reflection of electrons from a crystal of nickel.
De Broglie's prediction of a wave nature for electrons led Erwin Schrödinger to postulate a wave equation for electrons moving under the influence of the nucleus in the atom. In 1926, this equation, the Schrödinger equation, successfully described how electron waves propagated. Rather than yielding a solution that determined the location of an electron over time, this wave equation also could be used to predict the probability of finding an electron near a position, especially a position near where the electron was bound in space, for which the electron wave equations did not change in time. This approach led to a second formulation of quantum mechanics (the first by Heisenberg in 1925), and solutions of Schrödinger's equation, like Heisenberg's, provided derivations of the energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in 1913, and that were known to reproduce the hydrogen spectrum. Once spin and the interaction between multiple electrons were describable, quantum mechanics made it possible to predict the configuration of electrons in atoms with atomic numbers greater than hydrogen.
In 1928, building on Wolfgang Pauli's work, Paul Dirac produced a model of the electron – the Dirac equation, consistent with relativity theory, by applying relativistic and symmetry considerations to the hamiltonian formulation of the quantum mechanics of the electro-magnetic field. In order to resolve some problems within his relativistic equation, Dirac developed in 1930 a model of the vacuum as an infinite sea of particles with negative energy, later dubbed the Dirac sea. This led him to predict the existence of a positron, the antimatter counterpart of the electron. This particle was discovered in 1932 by Carl Anderson, who proposed calling standard electrons negatons and using electron as a generic term to describe both the positively and negatively charged variants.
In 1947 Willis Lamb, working in collaboration with graduate student Robert Retherford, found that certain quantum states of the hydrogen atom, which should have the same energy, were shifted in relation to each other, the difference came to be called the Lamb shift. About the same time, Polykarp Kusch, working with Henry M. Foley, discovered the magnetic moment of the electron is slightly larger than predicted by Dirac's theory. This small difference was later called anomalous magnetic dipole moment of the electron. This difference was later explained by the theory of quantum electrodynamics, developed by Sin-Itiro Tomonaga, Julian Schwinger and Richard Feynman in the late 1940s.
With the development of the particle accelerator during the first half of the twentieth century, physicists began to delve deeper into the properties of subatomic particles. The first successful attempt to accelerate electrons using electromagnetic induction was made in 1942 by Donald Kerst. His initial betatron reached energies of 2.3 MeV, while subsequent betatrons achieved 300 MeV. In 1947, synchrotron radiation was discovered with a 70 MeV electron synchrotron at General Electric. This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light.
With a beam energy of 1.5 GeV, the first high-energy particle collider was ADONE, which began operations in 1968. This device accelerated electrons and positrons in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron. The Large Electron–Positron Collider (LEP) at CERN, which was operational from 1989 to 2000, achieved collision energies of 209 GeV and made important measurements for the Standard Model of particle physics.
Confinement of individual electronsEdit
Individual electrons can now be easily confined in ultra small (L = 20 nm, W = 20 nm) CMOS transistors operated at cryogenic temperature over a range of −269 °C (4 K) to about −258 °C (15 K). The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the effective mass tensor.
In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be fundamental or elementary particles. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-generation of fundamental particles. The second and third generation contain charged leptons, the muon and the tau, which are identical to the electron in charge, spin and interactions, but are more massive. Leptons differ from the other basic constituent of matter, the quarks, by their lack of strong interaction. All members of the lepton group are fermions, because they all have half-odd integer spin; the electron has spin 1/.
The invariant mass of an electron is approximately ×10−319.109 kilograms, or ×10−4 5.489atomic mass units. On the basis of Einstein's principle of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV. The ratio between the mass of a proton and that of an electron is about 1836. Astronomical measurements show that the proton-to-electron mass ratio has held the same value, as is predicted by the Standard Model, for at least half the age of the universe.
Electrons have an electric charge of ×10−19 −1.602coulombs, which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge. This elementary charge has a relative standard uncertainty of ×10−8. 2.2 Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. As the symbol e is used for the elementary charge, the electron is commonly symbolized by
, where the minus sign indicates the negative charge. The positron is symbolized by
because it has the same properties as the electron but with a positive rather than negative charge.
The electron has an intrinsic angular momentum or spin of 1/. This property is usually stated by referring to the electron as a spin-1/ particle. For such particles the spin magnitude is √/ ħ.[note 3] while the result of the measurement of a projection of the spin on any axis can only be ±ħ/. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis. It is approximately equal to one Bohr magneton,[note 4] which is a physical constant equal to 00915(23)×10−24 joules per tesla. 9.274 The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity.
The electron has no known substructure and it is assumed to be a point particle with a point charge and no spatial extent. In classical physics, the angular momentum and magnetic moment of an object depend upon its physical dimensions. Hence, the concept of a dimensionless electron possessing these properties contrasts to experimental observations in Penning traps which point to finite non-zero radius of the electron. A possible explanation of this paradoxical situation is given below in the "Virtual particles" subsection by taking into consideration the Foldy-Wouthuysen transformation.
The issue of the radius of the electron is a challenging problem of the modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the self-energy of the electron tending to infinity.
Observation of a single electron in a Penning trap suggests the upper limit of the particle's radius to be 10−22 meters. The upper bound of the electron radius of 10−18 meters can be derived using the uncertainty relation in energy.
There is also a physical constant called the "classical electron radius", with the much larger value of ×10−15 m, greater than the radius of the proton. However, the terminology comes from a simplistic calculation that ignores the effects of 2.8179quantum mechanics; in reality, the so-called classical electron radius has little to do with the true fundamental structure of the electron.[note 5]
There are elementary particles that spontaneously decay into less massive particles. An example is the muon, with a mean lifetime of ×10−6 seconds, which decays into an electron, a muon 2.2neutrino and an electron antineutrino. The electron, on the other hand, is thought to be stable on theoretical grounds: the electron is the least massive particle with non-zero electric charge, so its decay would violate charge conservation. The experimental lower bound for the electron's mean lifetime is ×1028 years, at a 90% 6.6confidence level.
The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle. In quantum mechanics, the wave-like property of one particle can be described mathematically as a complex-valued function, the wave function, commonly denoted by the Greek letter psi (ψ). When the absolute value of this function is squared, it gives the probability that a particle will be observed near a location—a probability density.:162–218
Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties. In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system. The wave function of fermions, including electrons, is antisymmetric, meaning that it changes sign when two electrons are swapped; that is, ψ(r1, r2) = −ψ(r2, r1), where the variables r1 and r2 correspond to the first and second electrons, respectively. Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. Bosons, such as the photon, have symmetric wave functions instead.:162–218
In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state. This is responsible for the Pauli exclusion principle, which precludes any two electrons from occupying the same quantum state. This principle explains many of the properties of electrons. For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in the same orbit.:162–218
In a simplified picture, every photon spends some time as a combination of a virtual electron plus its antiparticle, the virtual positron, which rapidly annihilate each other shortly thereafter. The combination of the energy variation needed to create these particles, and the time during which they exist, fall under the threshold of detectability expressed by the Heisenberg uncertainty relation, ΔE · Δt ≥ ħ. In effect, the energy needed to create these virtual particles, ΔE, can be "borrowed" from the vacuum for a period of time, Δt, so that their product is no more than the reduced Planck constant, ħ ≈ ×10−16 eV·s6.6. Thus, for a virtual electron, Δt is at most ×10−21 s. 1.3
While an electron–positron virtual pair is in existence, the coulomb force from the ambient electric field surrounding an electron causes a created positron to be attracted to the original electron, while a created electron experiences a repulsion. This causes what is called vacuum polarization. In effect, the vacuum behaves like a medium having a dielectric permittivity more than unity. Thus the effective charge of an electron is actually smaller than its true value, and the charge decreases with increasing distance from the electron. This polarization was confirmed experimentally in 1997 using the Japanese TRISTAN particle accelerator. Virtual particles cause a comparable shielding effect for the mass of the electron.
The interaction with virtual particles also explains the small (about 0.1%) deviation of the intrinsic magnetic moment of the electron from the Bohr magneton (the anomalous magnetic moment). The extraordinarily precise agreement of this predicted difference with the experimentally determined value is viewed as one of the great achievements of quantum electrodynamics.
The apparent paradox (mentioned above in the properties subsection) of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of virtual photons in the electric field generated by the electron. These photons cause the electron to shift about in a jittery fashion (known as zitterbewegung), which results in a net circular motion with precession. This motion produces both the spin and the magnetic moment of the electron. In atoms, this creation of virtual photons explains the Lamb shift observed in spectral lines.
An electron generates an electric field that exerts an attractive force on a particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge. The strength of this force in nonrelativistic approximation is determined by Coulomb's inverse square law.:58–61 When an electron is in motion, it generates a magnetic field.:140 The Ampère-Maxwell law relates the magnetic field to the mass motion of electrons (the current) with respect to an observer. This property of induction supplies the magnetic field that drives an electric motor. The electromagnetic field of an arbitrary moving charged particle is expressed by the Liénard–Wiechert potentials, which are valid even when the particle's speed is close to that of light (relativistic).:429–434
When an electron is moving through a magnetic field, it is subject to the Lorentz force that acts perpendicularly to the plane defined by the magnetic field and the electron velocity. This centripetal force causes the electron to follow a helical trajectory through the field at a radius called the gyroradius. The acceleration from this curving motion induces the electron to radiate energy in the form of synchrotron radiation.:160[note 6] The energy emission in turn causes a recoil of the electron, known as the Abraham–Lorentz–Dirac Force, which creates a friction that slows the electron. This force is caused by a back-reaction of the electron's own field upon itself.
Photons mediate electromagnetic interactions between particles in quantum electrodynamics. An isolated electron at a constant velocity cannot emit or absorb a real photon; doing so would violate conservation of energy and momentum. Instead, virtual photons can transfer momentum between two charged particles. This exchange of virtual photons, for example, generates the Coulomb force. Energy emission can occur when a moving electron is deflected by a charged particle, such as a proton. The acceleration of the electron results in the emission of Bremsstrahlung radiation.
An inelastic collision between a photon (light) and a solitary (free) electron is called Compton scattering. This collision results in a transfer of momentum and energy between the particles, which modifies the wavelength of the photon by an amount called the Compton shift.[note 7] The maximum magnitude of this wavelength shift is h/mec, which is known as the Compton wavelength. For an electron, it has a value of ×10−12 m. 2.43 When the wavelength of the light is long (for instance, the wavelength of the visible light is 0.4–0.7 μm) the wavelength shift becomes negligible. Such interaction between the light and free electrons is called Thomson scattering or linear Thomson scattering.
The relative strength of the electromagnetic interaction between two charged particles, such as an electron and a proton, is given by the fine-structure constant. This value is a dimensionless quantity formed by the ratio of two energies: the electrostatic energy of attraction (or repulsion) at a separation of one Compton wavelength, and the rest energy of the charge. It is given by α ≈ 353×10−3, which is approximately equal to 7.2971/.
When electrons and positrons collide, they annihilate each other, giving rise to two or more gamma ray photons. If the electron and positron have negligible momentum, a positronium atom can form before annihilation results in two or three gamma ray photons totalling 1.022 MeV. On the other hand, a high-energy photon can transform into an electron and a positron by a process called pair production, but only in the presence of a nearby charged particle, such as a nucleus.
In the theory of electroweak interaction, the left-handed component of electron's wavefunction forms a weak isospin doublet with the electron neutrino. This means that during weak interactions, electron neutrinos behave like electrons. Either member of this doublet can undergo a charged current interaction by emitting or absorbing a
and be converted into the other member. Charge is conserved during this reaction because the W boson also carries a charge, canceling out any net change during the transmutation. Charged current interactions are responsible for the phenomenon of beta decay in a radioactive atom. Both the electron and electron neutrino can undergo a neutral current interaction via a
exchange, and this is responsible for neutrino-electron elastic scattering.
Atoms and moleculesEdit
An electron can be bound to the nucleus of an atom by the attractive Coulomb force. A system of one or more electrons bound to a nucleus is called an atom. If the number of electrons is different from the nucleus' electrical charge, such an atom is called an ion. The wave-like behavior of a bound electron is described by a function called an atomic orbital. Each orbital has its own set of quantum numbers such as energy, angular momentum and projection of angular momentum, and only a discrete set of these orbitals exist around the nucleus. According to the Pauli exclusion principle each orbital can be occupied by up to two electrons, which must differ in their spin quantum number.
Electrons can transfer between different orbitals by the emission or absorption of photons with an energy that matches the difference in potential. Other methods of orbital transfer include collisions with particles, such as electrons, and the Auger effect. To escape the atom, the energy of the electron must be increased above its binding energy to the atom. This occurs, for example, with the photoelectric effect, where an incident photon exceeding the atom's ionization energy is absorbed by the electron.
The orbital angular momentum of electrons is quantized. Because the electron is charged, it produces an orbital magnetic moment that is proportional to the angular momentum. The net magnetic moment of an atom is equal to the vector sum of orbital and spin magnetic moments of all electrons and the nucleus. The magnetic moment of the nucleus is negligible compared with that of the electrons. The magnetic moments of the electrons that occupy the same orbital (so called, paired electrons) cancel each other out.
The chemical bond between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechanics. The strongest bonds are formed by the sharing or transfer of electrons between atoms, allowing the formation of molecules. Within a molecule, electrons move under the influence of several nuclei, and occupy molecular orbitals; much as they can occupy atomic orbitals in isolated atoms. A fundamental factor in these molecular structures is the existence of electron pairs. These are electrons with opposed spins, allowing them to occupy the same molecular orbital without violating the Pauli exclusion principle (much like in atoms). Different molecular orbitals have different spatial distribution of the electron density. For instance, in bonded pairs (i.e. in the pairs that actually bind atoms together) electrons can be found with the maximal probability in a relatively small volume between the nuclei. By contrast, in non-bonded pairs electrons are distributed in a large volume around nuclei.
If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has a net electric charge. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than the number of protons in nuclei, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can develop an electric charge through rubbing, by the triboelectric effect.
Independent electrons moving in vacuum are termed free electrons. Electrons in metals also behave as if they were free. In reality the particles that are commonly termed electrons in metals and other solids are quasi-electrons—quasiparticles, which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass. When free electrons—both in vacuum and metals—move, they produce a net flow of charge called an electric current, which generates a magnetic field. Likewise a current can be created by a changing magnetic field. These interactions are described mathematically by Maxwell's equations.
At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied. Examples of good conductors include metals such as copper and gold, whereas glass and Teflon are poor conductors. In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator. Most semiconductors have a variable level of conductivity that lies between the extremes of conduction and insulation. On the other hand, metals have an electronic band structure containing partially filled electronic bands. The presence of such bands allows electrons in metals to behave as if they were free or delocalized electrons. These electrons are not associated with specific atoms, so when an electric field is applied, they are free to move like a gas (called Fermi gas) through the material much like free electrons.
Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimeters per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the velocity of propagation, is typically about 75% of light speed. This occurs because electrical signals propagate as a wave, with the velocity dependent on the dielectric constant of the material.
Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature. This is expressed mathematically by the Wiedemann–Franz law, which states that the ratio of thermal conductivity to the electrical conductivity is proportional to the temperature. The thermal disorder in the metallic lattice increases the electrical resistivity of the material, producing a temperature dependence for electric current.
When cooled below a point called the critical temperature, materials can undergo a phase transition in which they lose all resistivity to electric current, in a process known as superconductivity. In BCS theory, this behavior is modeled by pairs of electrons entering a quantum state known as a Bose–Einstein condensate. These Cooper pairs have their motion coupled to nearby matter via lattice vibrations called phonons, thereby avoiding the collisions with atoms that normally create electrical resistance. (Cooper pairs have a radius of roughly 100 nm, so they can overlap each other.) However, the mechanism by which higher temperature superconductors operate remains uncertain.
Electrons inside conducting solids, which are quasi-particles themselves, when tightly confined at temperatures close to absolute zero, behave as though they had split into three other quasiparticles: spinons, orbitons and holons. The former carries spin and magnetic moment, the next carries its orbital location while the latter electrical charge.
Motion and energyEdit
According to Einstein's theory of special relativity, as an electron's speed approaches the speed of light, from an observer's point of view its relativistic mass increases, thereby making it more and more difficult to accelerate it from within the observer's frame of reference. The speed of an electron can approach, but never reach, the speed of light in a vacuum, c. However, when relativistic electrons—that is, electrons moving at a speed close to c—are injected into a dielectric medium such as water, where the local speed of light is significantly less than c, the electrons temporarily travel faster than light in the medium. As they interact with the medium, they generate a faint light called Cherenkov radiation.
The effects of special relativity are based on a quantity known as the Lorentz factor, defined as where v is the speed of the particle. The kinetic energy Ke of an electron moving with velocity v is:
where me is the mass of electron. For example, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV. Since an electron behaves as a wave, at a given velocity it has a characteristic de Broglie wavelength. This is given by λe = h/p where h is the Planck constant and p is the momentum. For the 51 GeV electron above, the wavelength is about ×10−17 m, small enough to explore structures well below the size of an atomic nucleus. 2.4
The Big Bang theory is the most widely accepted scientific theory to explain the early stages in the evolution of the Universe. For the first millisecond of the Big Bang, the temperatures were over 10 billion kelvins and photons had mean energies over a million electronvolts. These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons. Likewise, positron-electron pairs annihilated each other and emitted energetic photons:
An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of the Universe. After 15 seconds had passed, however, the temperature of the universe dropped below the threshold where electron-positron formation could occur. Most of the surviving electrons and positrons annihilated each other, releasing gamma radiation that briefly reheated the universe.
For reasons that remain uncertain, during the annihilation process there was an excess in the number of particles over antiparticles. Hence, about one electron for every billion electron-positron pairs survived. This excess matched the excess of protons over antiprotons, in a condition known as baryon asymmetry, resulting in a net charge of zero for the universe. The surviving protons and neutrons began to participate in reactions with each other—in the process known as nucleosynthesis, forming isotopes of hydrogen and helium, with trace amounts of lithium. This process peaked after about five minutes. Any leftover neutrons underwent negative beta decay with a half-life of about a thousand seconds, releasing a proton and electron in the process,
For about the next 000– 300000 years, the excess electrons remained too energetic to bind with 400atomic nuclei. What followed is a period known as recombination, when neutral atoms were formed and the expanding universe became transparent to radiation.
Roughly one million years after the big bang, the first generation of stars began to form. Within a star, stellar nucleosynthesis results in the production of positrons from the fusion of atomic nuclei. These antimatter particles immediately annihilate with electrons, releasing gamma rays. The net result is a steady reduction in the number of electrons, and a matching increase in the number of neutrons. However, the process of stellar evolution can result in the synthesis of radioactive isotopes. Selected isotopes can subsequently undergo negative beta decay, emitting an electron and antineutrino from the nucleus. An example is the cobalt-60 (60Co) isotope, which decays to form nickel-60 (60
At the end of its lifetime, a star with more than about 20 solar masses can undergo gravitational collapse to form a black hole. According to classical physics, these massive stellar objects exert a gravitational attraction that is strong enough to prevent anything, even electromagnetic radiation, from escaping past the Schwarzschild radius. However, quantum mechanical effects are believed to potentially allow the emission of Hawking radiation at this distance. Electrons (and positrons) are thought to be created at the event horizon of these stellar remnants.
When a pair of virtual particles (such as an electron and positron) is created in the vicinity of the event horizon, random spatial positioning might result in one of them to appear on the exterior; this process is called quantum tunnelling. The gravitational potential of the black hole can then supply the energy that transforms this virtual particle into a real particle, allowing it to radiate away into space. In exchange, the other member of the pair is given negative energy, which results in a net loss of mass-energy by the black hole. The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes.
Cosmic rays are particles traveling through space with high energies. Energy events as high as ×1020 eV have been recorded. 3.0 When these particles collide with nucleons in the Earth's atmosphere, a shower of particles is generated, including pions. More than half of the cosmic radiation observed from the Earth's surface consists of muons. The particle called a muon is a lepton produced in the upper atmosphere by the decay of a pion.
A muon, in turn, can decay to form an electron or positron.
Remote observation of electrons requires detection of their radiated energy. For example, in high-energy environments such as the corona of a star, free electrons form a plasma that radiates energy due to Bremsstrahlung radiation. Electron gas can undergo plasma oscillation, which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by using radio telescopes.
The frequency of a photon is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies. For instance, when atoms are irradiated by a source with a broad spectrum, distinct absorption lines appear in the spectrum of transmitted radiation. Each element or molecule displays a characteristic set of spectral lines, such as the hydrogen spectral series. Spectroscopic measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.
In laboratory conditions, the interactions of individual electrons can be observed by means of particle detectors, which allow measurement of specific properties such as energy, spin and charge. The development of the Paul trap and Penning trap allows charged particles to be contained within a small region for long durations. This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months. The magnetic moment of the electron was measured to a precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.
The first video images of an electron's energy distribution were captured by a team at Lund University in Sweden, February 2008. The scientists used extremely short flashes of light, called attosecond pulses, which allowed an electron's motion to be observed for the first time.
The distribution of the electrons in solid materials can be visualized by angle-resolved photoemission spectroscopy (ARPES). This technique employs the photoelectric effect to measure the reciprocal space—a mathematical representation of periodic structures that is used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the material.
Electron beams are used in welding. They allow energy densities up to across a narrow focus diameter of 107 W·cm−20.1–1.3 mm and usually require no filler material. This welding technique must be performed in a vacuum to prevent the electrons from interacting with the gas before reaching their target, and it can be used to join conductive materials that would otherwise be considered unsuitable for welding.
Electron-beam lithography (EBL) is a method of etching semiconductors at resolutions smaller than a micrometer. This technique is limited by high costs, slow performance, the need to operate the beam in the vacuum and the tendency of the electrons to scatter in solids. The last problem limits the resolution to about 10 nm. For this reason, EBL is primarily used for the production of small numbers of specialized integrated circuits.
Electron beam processing is used to irradiate materials in order to change their physical properties or sterilize medical and food products. Electron beams fluidise or quasi-melt glasses without significant increase of temperature on intensive irradiation: e.g. intensive electron radiation causes a many orders of magnitude decrease of viscosity and stepwise decrease of its activation energy.
Linear particle accelerators generate electron beams for treatment of superficial tumors in radiation therapy. Electron therapy can treat such skin lesions as basal-cell carcinomas because an electron beam only penetrates to a limited depth before being absorbed, typically up to 5 cm for electron energies in the range 5–20 MeV. An electron beam can be used to supplement the treatment of areas that have been irradiated by X-rays.
Particle accelerators use electric fields to propel electrons and their antiparticles to high energies. These particles emit synchrotron radiation as they pass through magnetic fields. The dependency of the intensity of this radiation upon spin polarizes the electron beam—a process known as the Sokolov–Ternov effect.[note 8] Polarized electron beams can be useful for various experiments. Synchrotron radiation can also cool the electron beams to reduce the momentum spread of the particles. Electron and positron beams are collided upon the particles' accelerating to the required energies; particle detectors observe the resulting energy emissions, which particle physics studies .
Low-energy electron diffraction (LEED) is a method of bombarding a crystalline material with a collimated beam of electrons and then observing the resulting diffraction patterns to determine the structure of the material. The required energy of the electrons is typically in the range 20–200 eV. The reflection high-energy electron diffraction (RHEED) technique uses the reflection of a beam of electrons fired at various low angles to characterize the surface of crystalline materials. The beam energy is typically in the range 8–20 keV and the angle of incidence is 1–4°.
The electron microscope directs a focused beam of electrons at a specimen. Some electrons change their properties, such as movement direction, angle, and relative phase and energy as the beam interacts with the material. Microscopists can record these changes in the electron beam to produce atomically resolved images of the material. In blue light, conventional optical microscopes have a diffraction-limited resolution of about 200 nm. By comparison, electron microscopes are limited by the de Broglie wavelength of the electron. This wavelength, for example, is equal to 0.0037 nm for electrons accelerated across a 100,000-volt potential. The Transmission Electron Aberration-Corrected Microscope is capable of sub-0.05 nm resolution, which is more than enough to resolve individual atoms. This capability makes the electron microscope a useful laboratory instrument for high resolution imaging. However, electron microscopes are expensive instruments that are costly to maintain.
Two main types of electron microscopes exist: transmission and scanning. Transmission electron microscopes function like overhead projectors, with a beam of electrons passing through a slice of material then being projected by lenses on a photographic slide or a charge-coupled device. Scanning electron microscopes rasteri a finely focused electron beam, as in a TV set, across the studied sample to produce the image. Magnifications range from 100× to 1,000,000× or higher for both microscope types. The scanning tunneling microscope uses quantum tunneling of electrons from a sharp metal tip into the studied material and can produce atomically resolved images of its surface.
In the free-electron laser (FEL), a relativistic electron beam passes through a pair of undulators that contain arrays of dipole magnets whose fields point in alternating directions. The electrons emit synchrotron radiation that coherently interacts with the same electrons to strongly amplify the radiation field at the resonance frequency. FEL can emit a coherent high-brilliance electromagnetic radiation with a wide range of frequencies, from microwaves to soft X-rays. These devices are used in manufacturing, communication, and in medical applications, such as soft tissue surgery.
Electrons are important in cathode ray tubes, which have been extensively used as display devices in laboratory instruments, computer monitors and television sets. In a photomultiplier tube, every photon striking the photocathode initiates an avalanche of electrons that produces a detectable current pulse. Vacuum tubes use the flow of electrons to manipulate electrical signals, and they played a critical role in the development of electronics technology. However, they have been largely supplanted by solid-state devices such as the transistor.
- The fractional version's denominator is the inverse of the decimal value (along with its relative standard uncertainty of ×10−13 u). 4.2
- The electron's charge is the negative of elementary charge, which has a positive value for the proton.
- This magnitude is obtained from the spin quantum number as
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- Bohr magneton:
- The classical electron radius is derived as follows. Assume that the electron's charge is spread uniformly throughout a spherical volume. Since one part of the sphere would repel the other parts, the sphere contains electrostatic potential energy. This energy is assumed to equal the electron's rest energy, defined by special relativity (E = mc2).
From electrostatics theory, the potential energy of a sphere with radius r and charge e is given by:
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- Radiation from non-relativistic electrons is sometimes termed cyclotron radiation.
- The change in wavelength, Δλ, depends on the angle of the recoil, θ, as follows,
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- Freund, H.P.; Antonsen, T. (1996). Principles of Free-Electron Lasers. Springer. pp. 1–30. ISBN 0-412-72540-1.
- Kitzmiller, J.W. (1995). Television Picture Tubes and Other Cathode-Ray Tubes: Industry and Trade Summary. DIANE Publishing. pp. 3–5. ISBN 0-7881-2100-6.
- Sclater, N. (1999). Electronic Technology Handbook. McGraw-Hill Professional. pp. 227–228. ISBN 0-07-058048-0.
- Staff (2008). "The History of the Integrated Circuit". The Nobel Foundation. Retrieved 2008-10-18.
|Wikiquote has quotations related to: Electron|
|Wikisource has the text of the 1911 Encyclopædia Britannica article Electron.|
|Wikimedia Commons has media related to Electrons.|
- "The Discovery of the Electron". American Institute of Physics, Center for History of Physics.
- "Particle Data Group". University of California.
- Bock, R.K.; Vasilescu, A. (1998). The Particle Detector BriefBook (14th ed.). Springer. ISBN 3-540-64120-3.
- Copeland, Ed. "Spherical Electron". Sixty Symbols. Brady Haran for the University of Nottingham. | <urn:uuid:e19165e4-a013-491e-91c1-8b6e21fb7980> | 3.859375 | 21,154 | Knowledge Article | Science & Tech. | 62.555837 | 95,481,460 |
Experiments show that the friction between two surfaces depends on their history of contact and that this “memory” is reminiscent of the behavior of glasses.
Contrary to what you may have learned in high school, friction between two surfaces is not constant. For a wide range...Read More »
Everybody knows that sliding on ice or snow, is much easier than sliding on most other surfaces. But why is the ice surface slippery? This question has engaged scientists for more than a century and continues to be subject of debate. Researchers from AMOLF, the University of Amsterdam...Read More »
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But once in a while, under just the right conditions, you get something entirely new: a futuristic alloy called metallic...Read More »
In contact mechanics and tribology it is frequently needed to calculate the contact area between rough surfaces to estimate possible slip, friction, electric conductivity, etc. In this tutorial, it will be shown how to perform this calculation using a freely available software – Tribology Simulator....Read More »
How can flies walk on the window glass upside down? How can geckos climb walls and trees? It looks like a simple question, but it is hard to answer. The secret is that flies and geckos, and many other living species can control the ability to stick to surfaces, ability to adhere. Adhesion has...Read More »
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Sandia National Laboratories is developing specialized computer modeling and simulation methods to better understand how blasts on a battlefield could lead to traumatic brain injury and injuries to vital organs, like the heart and lungs.
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By M.Ciavarella, A. Papangelo. Politecnico di BARI, Italy.
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Simple equation predicts force needed to push objects through granular and pasty materials.
For those of you who take sandcastle building very seriously, listen up: MIT engineers now say you can trust a very simple equation to calculate the force required to push a shovel — and any other “intruder”— through...Read More »
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Forty years ago, MIT emeritus professor of mechanical engineering Ernest Rabinowicz calculated that 6 percent of the annual U.S. gross domestic product was lost through mechanical wear. His assertion gained enough traction that it became known as the “Rabinowicz Law.”
“Even so, the mechanism by which mechanical wear happens is one...Read More »
The Contact-Mechanics Challenge completed
In late 2015 we posed the Contact-Mechanics Challenge. This has now been completed and the winner is—the field of tribology.
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Temporal range: Cambrian–Recent
|A coral outcrop on the Great Barrier Reef, Australia|
|Extant subclasses and orders|
Corals are marine invertebrates in the class Anthozoa of phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.
A coral "group" is a colony of myriad genetically identical polyps. Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in length. A set of tentacles surround a central mouth opening. An exoskeleton is excreted near the base. Over many generations, the colony thus creates a large skeleton characteristic of the species. Individual heads grow by asexual reproduction of polyps. Corals also breed sexually by spawning: polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon.
Although some corals are able to catch small fish and plankton using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues. These are commonly known as zooxanthellae. Such corals require sunlight and grow in clear, shallow water, typically at depths less than 60 metres (200 ft). Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia.
Other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,300 metres (10,800 ft). Some have been found on the Darwin Mounds, north-west of Cape Wrath, Scotland, and others as far north as off the coast of Washington State and the Aleutian Islands.
- 1 Taxonomy
- 2 Anatomy
- 3 Ecology
- 4 Reproduction
- 5 Reefs
- 6 Evolutionary history
- 7 Status
- 8 Relation to humans
- 9 Gallery
- 10 References
- 11 Sources
- 12 External links
|Phylogeny of Anthozoa, relationships of the orders still undefined|
Aristotle's pupil Theophrastus described the red coral, korallion in his book on stones, implying it was a mineral; but he described it as a deep-sea plant in his Enquiries on Plants, where he also mentions large stony plants that reveal bright flowers when under water in the Gulf of Heroes. Pliny the Elder stated boldly that several sea creatures including sea nettles and sponges "are neither animals nor plants, but are possessed of a third nature (tertius natura)". Petrus Gyllius copied Pliny, introducing the term zoophyta for this third group in his 1535 book On the French and Latin Names of the Fishes of the Marseilles Region; it is popularly but wrongly supposed that Aristotle created the term. Gyllius further noted, following Aristotle, how hard it was to define what was a plant and what was an animal.
The Persian polymath Al-Biruni (d. 1048) classified sponges and corals as animals, arguing that they respond to touch. Nevertheless, people believed corals to be plants until the eighteenth century, when William Herschel used a microscope to establish that coral had the characteristic thin cell membranes of an animal.
The phylogeny of Anthozoans is not clearly understood and a number of different models have been proposed. Within the Hexacorallia, the sea anemones, coral anemones and stony corals may constitute a monophyletic grouping united by their six-fold symmetry and cnidocyte trait. The Octocorallia appears to be monophyletic, and primitive members of this group may have been stolonate. The cladogram presented here comes from a 2014 study by Stampar et al. which was based on the divergence of mitochondrial DNA within the group and on nuclear markers.
Corals are classified in the class Anthozoa of the phylum Cnidaria. They are divided into three subclasses, Hexacorallia, Octocorallia, and Ceriantharia. The Hexacorallia include the stony corals, the sea anemones and the zoanthids. These groups have polyps that generally have 6-fold symmetry. The Octocorallia include blue coral, soft corals, sea pens, and gorgonians (sea fans and sea whips). These groups have polyps with 8-fold symmetry, each polyp having eight tentacles and eight mesenteries. Ceriantharia are the tube-dwelling anemones.
Corals are sessile animals in the class Anthozoa and differ from most other cnidarians in not having a medusa stage in their life cycle. The body unit of the animal is a polyp. Most corals are colonial, the initial polyp budding to produce another and the colony gradually developing from this small start. In stony corals, also known as hard corals, the polyps produce a skeleton composed of calcium carbonate to strengthen and protect the organism. This is deposited by the polyps and by the coenosarc, the living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as corallites. Colonies of stony coral are very variable in appearance; a single species may adopt an encrusting, plate-like, bushy, columnar or massive solid structure, the various forms often being linked to different types of habitat, with variations in light level and water movement being significant.
In soft corals, there is no stony skeleton but the tissues are often toughened by the presence of tiny skeletal elements known as sclerites, which are made from calcium carbonate. Soft corals are very variable in form and most are colonial. A few soft corals are stolonate, but the polyps of most are connected by sheets of coenosarc. In some species this is thick and the polyps are deeply embedded. Some soft corals are encrusting or form lobes. Others are tree-like or whip-like and have a central axial skeleton embedded in the tissue matrix. This is composed either of a fibrous protein called gorgonin or of a calcified material. In both stony and soft corals, the polyps can be retracted, with stony corals relying on their hard skeleton and cnidocytes for defence against predators, and soft corals generally relying on chemical defences in the form of toxic substances present in the tissues known as terpenoids.
The polyps of stony corals have six-fold symmetry while those of soft corals have eight. The mouth of each polyp is surrounded by a ring of tentacles. In stony corals these are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species these are reduced to mere stubs and in some they are fused to give a paddle-like appearance. In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow water species of both stony and soft corals can be zooxanthellate, the corals supplementing their plankton diet with the products of photosynthesis produced by these symbionts. The polyps interconnect by a complex and well-developed system of gastrovascular canals, allowing significant sharing of nutrients and symbionts.
Polyps feed on a variety of small organisms, from microscopic zooplankton to small fish. The polyp's tentacles immobilize or kill prey using their nematocysts. These cells carry venom which they rapidly release in response to contact with another organism. A dormant nematocyst discharges in response to nearby prey touching the trigger (cnidocil). A flap (operculum) opens and its stinging apparatus fires the barb into the prey. The venom is injected through the hollow filament to immobilise the prey; the tentacles then manoeuvre the prey to the mouth.
The tentacles then contract to bring the prey into the stomach. Once the prey is digested, the stomach reopens, allowing the elimination of waste products and the beginning of the next hunting cycle. They can scavenge drifting organic molecules and dissolved organic molecules.:24
Many corals, as well as other cnidarian groups such as Aiptasia (a sea anemone) form a symbiotic relationship with a class of dinoflagellate algae, zooxanthellae of the genus Symbiodinium.:24 Aiptasia, a familiar pest among coral reef aquarium hobbyists, serves as a valuable model organism in the study of cnidarian-algal symbiosis. Typically, each polyp harbors one species of algae, and coral species show a preference for Symbiodinium. Young corals are not born with zooxanthellae, but acquire the algae from the surrounding environment, including the water column and local sediment. Via photosynthesis, these provide energy for the coral, and aid in calcification. The main benefit of the zooxanthellae is their ability to photosynthesize. By using this technique, zooxanthellae are able to supply corals with the products of photosynthesis, including glucose, glycerol, and amino acids, which the corals can use for energy. As much as 30% of the tissue of a polyp may be algal material.:23 Zooxanthellae also benefit corals by aiding in waste removal.
The algae benefit from a safe place to live and consume the polyp's carbon dioxide and nitrogenous waste. Due to the strain the algae can put on the polyp, stress on the coral often drives them to eject the algae. Mass ejections are known as coral bleaching, because the algae contribute to coral's brown coloration; other colors, however, are due to host coral pigments, such as green fluorescent proteins (GFPs). Ejection increases the polyp's chance of surviving short-term stress—they can regain algae, possibly of a different species at a later time. If the stressful conditions persist, the polyp eventually dies. Zooxanthellae are located within the corals' cytoplasm and due to the algae's photosynthetic activity, the internal pH of the coral can be raised; this behavior indicates that the zooxanthellae are responsible to some extent for the metabolism of their host corals
Corals can be both gonochoristic (unisexual) and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows coral to settle in new areas. Reproduction is coordinated by chemical communication.
About 75% of all hermatypic corals "broadcast spawn" by releasing gametes—eggs and sperm—into the water to spread offspring. The gametes fuse during fertilization to form a microscopic larva called a planula, typically pink and elliptical in shape. A typical coral colony forms several thousand larvae per year to overcome the odds against formation of a new colony.
Synchronous spawning is very typical on the coral reef, and often, even when multiple species are present, all corals spawn on the same night. This synchrony is essential so male and female gametes can meet. Corals rely on environmental cues, varying from species to species, to determine the proper time to release gametes into the water. The cues involve temperature change, lunar cycle, day length, and possibly chemical signalling. Synchronous spawning may form hybrids and is perhaps involved in coral speciation. The immediate cue is most often sunset, which cues the release. The spawning event can be visually dramatic, clouding the usually clear water with gametes.
Brooding species are most often ahermatypic (not reef-building) in areas of high current or wave action. Brooders release only sperm, which is negatively buoyant, sinking on to the waiting egg carriers who harbor unfertilized eggs for weeks. Synchronous spawning events sometimes occurs even with these species. After fertilization, the corals release planula that are ready to settle.
Planula larvae exhibit positive phototaxis, swimming towards light to reach surface waters, where they drift and grow before descending to seek a hard surface to which they can attach and begin a new colony. They also exhibit positive sonotaxis, moving towards sounds that emanate from the reef and away from open water. High failure rates afflict many stages of this process, and even though millions of gametes are released by each colony, few new colonies form. The time from spawning to settling is usually two to three days, but can be up to two months. The larva grows into a polyp and eventually becomes a coral head by asexual budding and growth.
Budding involves splitting a smaller polyp from an adult. As the new polyp grows, it forms its body parts. The distance between the new and adult polyps grows, and with it, the coenosarc (the common body of the colony). Budding can be intratentacular, from its oral discs, producing same-sized polyps within the ring of tentacles, or extratentacular, from its base, producing a smaller polyp.
Division forms two polyps that each become as large as the original. Longitudinal division begins when a polyp broadens and then divides its coelenteron (body), effectively splitting along its length. The mouth divides and new tentacles form. The two polyps thus created then generate their missing body parts and exoskeleton. Transversal division occurs when polyps and the exoskeleton divide transversally into two parts. This means one has the basal disc (bottom) and the other has the oral disc (top); the new polyps must separately generate the missing pieces.
Asexual reproduction offers the benefits of high reproductive rate, delaying senescence, and replacement of dead modules, as well as geographical distribution.
Whole colonies can reproduce asexually, forming two colonies with the same genotype. The possible mechanisms include fission, bailout and fragmentation. Fission occurs in some corals, especially among the family Fungiidae, where the colony splits into two or more colonies during early developmental stages. Bailout occurs when a single polyp abandons the colony and settles on a different substrate to create a new colony. Fragmentation involves individuals broken from the colony during storms or other disruptions. The separated individuals can start new colonies.
Many corals in the order Scleractinia are hermatypic, meaning that they are involved in building reefs. Most such corals obtain some of their energy from zooxanthellae in the genus Symbiodinium. These are symbiotic photosynthetic dinoflagellates which require sunlight; reef-forming corals are therefore found mainly in shallow water. They secrete calcium carbonate to form hard skeletons that become the framework of the reef. However, not all reef-building corals in shallow water contain zooxanthellae, and some deep water species, living at depths to which light cannot penetrate, form reefs but do not harbour the symbionts.
There are various types of shallow-water coral reef, including fringing reefs, barrier reefs and atolls; most occur in tropical and subtropical seas. They are very slow-growing, adding perhaps one centimetre (0.4 in) in height each year. The Great Barrier Reef is thought to have been laid down about two million years ago. Over time, corals fragment and die, sand and rubble accumulates between the corals, and the shells of clams and other molluscs decay to form a gradually evolving calcium carbonate structure. Coral reefs are extremely diverse marine ecosystems hosting over 4,000 species of fish, massive numbers of cnidarians, molluscs, crustaceans, and many other animals.
Although corals first appeared in the Cambrian period, some , fossils are extremely rare until the Ordovician period, 100 million years later, when rugose and tabulate corals became widespread. Paleozoic corals often contained numerous endobiotic symbionts.
Tabulate corals occur in limestones and calcareous shales of the Ordovician and Silurian periods, and often form low cushions or branching masses of calcite alongside rugose corals. Their numbers began to decline during the middle of the Silurian period, and they became extinct at the end of the Permian period, .
Rugose or horn corals became dominant by the middle of the Silurian period, and became extinct early in the Triassic period. The rugose corals existed in solitary and colonial forms, and were also composed of calcite.
The scleractinian corals filled the niche vacated by the extinct rugose and tabulate species. Their fossils may be found in small numbers in rocks from the Triassic period, and became common in the Jurassic and later periods. Scleractinian skeletons are composed of a form of calcium carbonate known as aragonite. Although they are geologically younger than the tabulate and rugose corals, the aragonite of their skeletons is less readily preserved, and their fossil record is accordingly less complete.
At certain times in the geological past, corals were very abundant. Like modern corals, these ancestors built reefs, some of which ended as great structures in sedimentary rocks. Fossils of fellow reef-dwellers algae, sponges, and the remains of many echinoids, brachiopods, bivalves, gastropods, and trilobites appear along with coral fossils. This makes some corals useful index fossils. Coral fossils are not restricted to reef remnants, and many solitary fossils may be found elsewhere, such as Cyclocyathus, which occurs in England's Gault clay formation.
Coral reefs are under stress around the world. In particular, coral mining, agricultural and urban runoff, pollution (organic and inorganic), overfishing, blast fishing, disease, and the digging of canals and access into islands and bays are localized threats to coral ecosystems. Broader threats are sea temperature rise, sea level rise and pH changes from ocean acidification, all associated with greenhouse gas emissions. In 1998, 16% of the world's reefs died as a result of increased water temperature.
Approximately 10% of the world's coral reefs are dead. About 60% of the world's reefs are at risk due to human-related activities. The threat to reef health is particularly strong in Southeast Asia, where 80% of reefs are endangered. Over 50% of the world's coral reefs may be destroyed by 2030; as a result, most nations protect them through environmental laws.
In the Caribbean and tropical Pacific, direct contact between ~40–70% of common seaweeds and coral causes bleaching and death to the coral via transfer of lipid-soluble metabolites. Seaweed and algae proliferate given adequate nutrients and limited grazing by herbivores such as parrotfish.
Water temperature changes of more than 1–2 °C (1.8–3.6 °F) or salinity changes can kill some species of coral. Under such environmental stresses, corals expel their Symbiodinium; without them coral tissues reveal the white of their skeletons, an event known as coral bleaching.
Submarine springs found along the coast of Mexico's Yucatán Peninsula produce water with a naturally low pH (relatively high acidity) providing conditions similar to those expected to become widespread as the oceans absorb carbon dioxide. Surveys discovered multiple species of live coral that appeared to tolerate the acidity. The colonies were small and patchily distributed, and had not formed structurally complex reefs such as those that compose the nearby Mesoamerican Barrier Reef System.
Many governments now prohibit removal of coral from reefs, and inform coastal residents about reef protection and ecology. While local action such as habitat restoration and herbivore protection can reduce local damage, the longer-term threats of acidification, temperature change and sea-level rise remain a challenge.
Relation to humans
Local economies near major coral reefs benefit from an abundance of fish and other marine creatures as a food source. Reefs also provide recreational scuba diving and snorkeling tourism. These activities can damage coral but international projects such as Green Fins that encourage dive and snorkel centres to follow a Code of Conduct have been proven to mitigate these risks.
Corals' many colors give it appeal for necklaces and other jewelry. Intensely red coral is prized as a gemstone. Sometimes called fire coral, it is not the same as fire coral. Red coral is very rare because of overharvesting.
Always considered a precious mineral, "the Chinese have long associated red coral with auspiciousness and longevity because of its color and its resemblance to deer antlers (so by association, virtue, long life, and high rank". It reached its height of popularity during the Manchu or Qing Dynasty (1644-1911) when it was almost exclusively reserved for the emperor's use either in the form of coral beads (often combined with pearls) for court jewelry or as decorative Penjing (decorative miniature mineral trees). Coral was known as shanhu in Chinese. The "early-modern 'coral network' [began in] the Mediterranean Sea [and found its way] to Qing China via the English East India Company". There were strict rules regarding its use in a code established by the Qianlong Emperor in 1759.
In medicine, chemical compounds from corals are used to treat cancer, AIDS and pain, and for other uses. Coral skeletons, e.g. Isididae are also used for bone grafting in humans. Coral Calx, known as Praval Bhasma in Sanskrit, is widely used in traditional system of Indian medicine as a supplement in the treatment of a variety of bone metabolic disorders associated with calcium deficiency. In classical times ingestion of pulverized coral, which consists mainly of the weak base calcium carbonate, was recommended for calming stomach ulcers by Galen and Dioscorides.
Coral reefs in places such as the East African coast are used as a source of building material. Ancient (fossil) coral limestone, notably including the Coral Rag Formation of the hills around Oxford (England), was once used as a building stone, and can be seen in some of the oldest buildings in that city including the Saxon tower of St Michael at the Northgate, St. George's Tower of Oxford Castle, and the mediaeval walls of the city.
Annual growth bands in some corals, such as the deep sea bamboo corals (Isididae), may be among the first signs of the effects of ocean acidification on marine life. The growth rings allow geologists to construct year-by-year chronologies, a form of incremental dating, which underlie high-resolution records of past climatic and environmental changes using geochemical techniques.
Certain species form communities called microatolls, which are colonies whose top is dead and mostly above the water line, but whose perimeter is mostly submerged and alive. Average tide level limits their height. By analyzing the various growth morphologies, microatolls offer a low resolution record of sea level change. Fossilized microatolls can also be dated using Radiocarbon dating. Such methods can help to reconstruct Holocene sea levels.
Increasing sea temperatures in tropical regions (~1 degree C) the last century have caused major coral bleaching, death, and therefore shrinking coral populations since although they are able to adapt and acclimate, it is uncertain if this evolutionary process will happen quickly enough to prevent major reduction of their numbers.
Though coral have large sexually-reproducing populations, their evolution can be slowed by abundant asexual reproduction. Gene flow is variable among coral species. According to the biogeography of coral species gene flow cannot be counted on as a dependable source of adaptation as they are very stationary organisms. Also, coral longevity might factor into their adaptivity.
However, adaptation to climate change has been demonstrated in many cases. These are usually due to a shift in coral and zooxanthellae genotypes. These shifts in allele frequency have progressed toward more tolerant types of zooxanthellae. Scientists found that a certain scleractinian zooxanthella is becoming more common where sea temperature is high. Symbionts able to tolerate warmer water seem to photosynthesise more slowly, implying an evolutionary trade-off.
In the Gulf of Mexico, where sea temperatures are rising, cold-sensitive staghorn and elkhorn coral have shifted in location. Not only have the symbionts and specific species been shown to shift, but there seems to be a certain growth rate favorable to selection. Slower-growing but more heat-tolerant corals have become more common. The changes in temperature and acclimation are complex. Some reefs in current shadows represent a refugium location that will help them adjust to the disparity in the environment even if eventually the temperatures may rise more quickly there than in other locations. This separation of populations by climatic barriers causes a realized niche to shrink greatly in comparison to the old fundamental niche.
Corals are shallow, colonial organisms that integrate δ18O and trace elements into their skeletal aragonite (polymorph of calcite) crystalline structures, as they grow. Geochemistry anomalies within the crystalline structures of corals represent functions of temperature, salinity and oxygen isotopic composition. Such geochemical analysis can help with climate modeling.
Strontium/calcium ratio anomaly
Oxygen isotope anomaly
The comparison of coral strontium/calcium minimums with sea surface temperature maximums, data recorded from NINO 3.4 SSTA, time can be correlated to coral strontium/calcium and δ18O variations. To confirm accuracy of the annual relationship between Sr/Ca and δ18O variations, a perceptible association to annual coral growth rings confirms the age conversion. Geochronology is established by the blending of Sr/Ca data, growth rings, and stable isotope data. El Nino-Southern Oscillation (ENSO) is directly related to climate fluctuations that influence coral δ18O ratio from local salinity variations associated with the position of the South Pacific convergence zone (SPCZ) and can be used for ENSO modeling.
Sea surface temperature and sea surface salinity
The global moisture budget is primarily being influenced by tropical sea surface temperatures from the position of the Intertropical Convergence Zone (ITCZ). The Southern Hemisphere has a unique meteorological feature positioned in the southwestern Pacific Basin called the South Pacific Convergence Zone (SPCZ), which contains a perennial position within the Southern Hemisphere. During ENSO warm periods, the SPCZ reverses orientation extending from the equator down south through Solomon Islands, Vanuatu, Fiji and towards the French Polynesian Islands; and due east towards South America affecting geochemistry of corals in tropical regions.
Geochemical analysis of skeletal coral can be linked to sea surface salinity (SSS) and sea surface temperature (SST), from El Nino 3.4 SSTA data, of tropical oceans to seawater δ18O ratio anomalies from corals. ENSO phenomenon can be related to variations in sea surface salinity (SSS) and sea surface temperature (SST) that can help model tropical climate activities.
Limited climate research on current species
Climate research on live coral species is limited to a few studied species. Studying Porites coral provides a stable foundation for geochemical interpretations that is much simpler to physically extract data in comparison to Platygyra species where the complexity of Platygyra species skeletal structure creates difficulty when physically sampled, which happens to be one of the only multidecadal living coral records used for coral paleoclimate modeling.
The saltwater fishkeeping hobby has expanded, over recent years, to include reef tanks, fish tanks that include large amounts of live rock on which coral is allowed to grow and spread. These tanks are either kept in a natural-like state, with algae (sometimes in the form of an algae scrubber) and a deep sand bed providing filtration, or as "show tanks", with the rock kept largely bare of the algae and microfauna that would normally populate it, in order to appear neat and clean.
The most popular kind of coral kept is soft coral, especially zoanthids and mushroom corals, which are especially easy to grow and propagate in a wide variety of conditions, because they originate in enclosed parts of reefs where water conditions vary and lighting may be less reliable and direct. More serious fishkeepers may keep small polyp stony coral, which is from open, brightly lit reef conditions and therefore much more demanding, while large polyp stony coral is a sort of compromise between the two.
Coral aquaculture, also known as coral farming or coral gardening, is the cultivation of corals for commercial purposes or coral reef restoration. Aquaculture is showing promise as a potentially effective tool for restoring coral reefs, which have been declining around the world. The process bypasses the early growth stages of corals when they are most at risk of dying. Coral fragments known as "seeds" are grown in nurseries then replanted on the reef. Coral is farmed by coral farmers who live locally to the reefs and farm for reef conservation or for income. It is also farmed by scientists for research, by businesses for the supply of the live and ornamental coral trade and by private aquarium hobbyists.
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Predators play important roles in maintaining diverse and stable ecosystems. Climate change can push species to move in order to stay in their climatic comfort zones, potentially altering where species live and how they interact, which could fundamentally transform current ecosystems.
A symposium focusing on climate's effects on predators—causing cascading effects on whole ecosystems -- will take place on Tuesday, August 12th during the Ecological Society of America's 99th Annual Meeting, held this year in Sacramento, California.
There will be "winners" and "losers" as species adapt to a changing climate. Ecologists are just beginning to understand why different competitors may be favored by climate change and how consumer-resource interactions are modified. Impacts on one species can affect many organisms in an ecosystem.
Because predator species are animals that survive by preying on other organisms, they send ripples throughout the food web, regulating the effects other animals have on that ecosystem. This cause and effect process is called a "trophic cascade," or the progression of direct and indirect effects predators have across lower levels in a food chain.
Sea otter populations provide a historical example of this phenomenon. The fur trade spanning the late 1700s to early 1900s decimated their numbers across their range, from Alaska to Baja California, Mexico. Populations went from an estimated several hundred-thousand to more than a million down to 1,000. Today, there are estimated to be just over 106,000 worldwide, with just under 3,000 in California. Now sea otters and other important predator species face the challenges of a changing climate.
"The near extinction of sea otters is one of the most dramatic examples of human-induced impacts to the structure and functioning of temperate nearshore marine ecosystems," said Rebecca G. Martone, of the Center for Ocean Solutions at Stanford University.
In the U.S., there are two distinct sea otter subspecies, the Northern sea otter (Enhydra lutris kenyoni) and the Southern sea otter (Enhydra lutris nereis). Northern sea otters are found in the Aleutian Islands, Southern Alaska, British Columbia, and Washington. Southern sea otters, also known as California sea otters, live in the waters along the California coastline and range from San Mateo County in the north to Santa Barbara County in the south.
Sea otters live offshore in forests of kelp—huge, yellow-brown, rubbery seaweed reaching from the sea floor to the surface, like tall trees. In coastal North America, sea otters help maintain healthy kelp forests, which benefits other marine species dependent on this habitat.
Sea otters must eat about 25% of their body weight daily to maintain their body temperature since unlike other marine mammals they rely solely on their fur rather than an extra layer of blubber to stay warm—it's like a 120-pound human eating 30 pounds of food per day. Some of otters' favorites are abalone, clams, crabs, mussels, shrimp, and sea urchins. Few predators can crack the globe-shaped spiny urchins, which in unchecked hordes will chew through the holdfasts of the kelp, leaving vast barrens in place of the vibrant forests. The otter is a "keystone predator" whose presence has an outsized effect on its kelp forest habitat.
Without sea otters, the undersea sea urchins they prey on would devour the kelp forests, resulting in dense areas called sea urchin barrens that have lower biodiversity due to the loss of kelp that provide 3-dimensional habitat and a food source for many species. Researchers found that when sea otters arrive in an area from which they have been absent, they begin feasting on urchins. As a result, the kelp forest begins to grow back, changing the structure of kelp forest communities.
Many fish, marine mammals and birds are also found in kelp forest communities, including rockfish, seals, sea lions, whales, gulls, terns, snowy egrets as well as some shore birds. Otters might also offer a defense against climate change because healthy kelp forests can grow rapidly and store large amounts of carbon.
Dr. Martone's analyses of the effects of sea otters on kelp forest ecosystems can help shape predictions of how climate change and trophic cascades, in concert with other drivers, affect coastal ecosystems. The ecological impacts of a changing climate are evident, from terrestrial polar regions to tropical marine environments. Ecologists' research into the tropic cascading effects of predators will assist decision makers by providing important scientific findings to prepare for the impacts of climate change occurring now and into the future. Speakers for the symposia include marine, freshwater and terrestrial experimental ecologists who will present their research and offer insights from different approaches used to studying consumer-resource interactions.
Ecological Society of America's 99th Annual Meeting, August 10th, 2014, in Sacramento, Cal.
Symposium 9: From Oceans to Mountains: Using Abiotic Gradients to Investigate the Effects of Climate on the Cascading Effects of Predators
Tuesday, August 12, 2014; 1:30 PM; Magnolia, Sheraton Hotel
Organizer: William L. Harrower
Co-organizer: Mary I. O'Connor
Angélica L. González, University of British Columbia; Rana W. El-Sabaawi, University of Victoria
Daniel Boyce, Queen's University and The Bedford Institute of Oceanography; William Leggett, Queens University; Brian Petrie, Bedford Institute of Oceanography; Boris Worm, Dalhousie University; Kenneth T. Frank, Department of Fisheries and Oceans
Celia C. Symons, University of California- San Diego; Jonathan B. Shurin, University of California- San Diego
John M. Fryxell, University of Guelph; Tal Avgar, University of Alberta; Anna Mosser, University of Minnesota; Andrew Kittle, University of Guelph; Garrett Street, University of Guelph; Madeleine Mcgreer, University of Guelph; Erin Mallon, University of Guelph; Ian D. Thompson, Canadian Forest Service; Arthur R. Rodgers, Ontario Ministry of Natural Resources; Brent Patterson, Ontario Ministry of Natural Resources; Glen S. Brown, Ontario Ministry of Natural Resources; Doug Reid, Ontario Ministry of Natural Resources; Merritt R. Turetsky, University of Guelph
Rebecca G. Martone, Stanford University; Russell W. Markel, University of British Columbia; Gerald Singh, University of British Columbia
William L. Harrower, University of British Columbia; Lauchlan H. Fraser, Thompson Rivers University; Roy Turkington, University of British Columbia
The Ecological Society of America is the world's largest community of professional ecologists and a trusted source of ecological knowledge. ESA is committed to advancing the understanding of life on Earth. The 10,000 member Society publishes five journals, convenes an annual scientific conference, and broadly shares ecological information through policy and media outreach and education initiatives. Visit the ESA website at http://www.esa.org.
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A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
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- Open Access
Origin of resistivity in reconnection
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2001
Received: 5 June 2000
Accepted: 16 October 2000
Published: 26 June 2014
Resistivity is believed to play an important role in reconnection leading to the distinction between resistive and collisionless reconnection. The former is treated in the Sweet-Parker model of long current sheets, and the Petschek model of a small resistive region. Both models in spite of their different dynamics attribute to the violation of the frozen-in condition in their diffusion regions due to the action of resistivity. In collisionless reconnection there is little consensus about the processes breaking the frozen-in condition. The question is whether anomalous processes generate sufficient resistivity or whether other processes free the particles from slavery by the magnetic field. In the present paper we review processes that may cause anomalous resistivity in collisionless current sheets. Our general conclusion is that in space plasma boundaries accessible to in situ spacecraft, wave levels have always been found to be high enough to explain the existence of large enough local diffusivity for igniting local reconnection. However, other processes might take place as well. Non-resistive reconnection can be caused by inertia or diamagnetism. | <urn:uuid:23a6929c-4155-4753-a168-5d65cae500f4> | 2.59375 | 306 | Truncated | Science & Tech. | 15.235105 | 95,481,528 |
Temporal range: Early Permian–Recent
|Tau emerald (Hemicordulia tau) dragonfly|
Dragonflies are generally larger, and perch with their wings held out to the sides; damselflies have slender bodies, and hold their wings over the body at rest.
Etymology and terminology
The word dragonfly is also sometimes used to refer to all Odonata, but odonate is a more correct English name for the group as a whole. Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or simply Anisopteran, when referring to just the Anisoptera. The term Warriorfly has also been proposed. Some 5,900 species have been described in this order.
Systematics and taxonomy
This order has traditionally been grouped together with the mayflies and several extinct orders in a group called the "Paleoptera", but this grouping might be paraphyletic. What they do share with mayflies is the nature of how the wings are articulated and held in rest (see insect flight for a detailed discussion).
In some treatments, the Odonata are understood in an expanded sense, essentially synonymous with the superorder Odonatoptera but not including the prehistoric Protodonata. In this approach, instead of Odonatoptera, the term Odonatoidea is used. The systematics of the "Palaeoptera" are by no means resolved; what can be said however is that regardless of whether they are called "Odonatoidea" or "Odonatoptera", the Odonata and their extinct relatives do form a clade.
The Anisoptera was long treated as a suborder, with a third suborder, the "Anisozygoptera" (ancient dragonflies). However, the combined suborder Epiprocta (in which Anisoptera is an infraorder) was proposed when it was found that the "Anisozygoptera" was paraphyletic, composed of mostly extinct offshoots of dragonfly evolution. The four living species placed in that group are (in this treatment) in the infraorder Epiophlebioptera, whereas the fossil taxa that were formerly there are now dispersed about the Odonatoptera (or Odonata sensu lato).
The phylogenetic tree of the orders and suborders of odonates according to Bechly (2002):
The largest living odonate is the giant Central American helicopter damselfly Megaloprepus coerulatus (Zygoptera: Pseudostigmatidae) with a wing span of 191 mm. The heaviest living odonates are Tetracanthagyna plagiata (Anisoptera: Aeshnidae) with a wing span of 165 mm, and Petalura ingentissima (Anisoptera: Petaluridae) with a body length of 117 mm (some sources 125 mm) and wing span of 160 mm. The longest extant odonate is the Neotropical helicopter damselfly Mecistogaster linearis (Zygoptera: Pseudostigmatidae) with a body length of 135 mm. Sometimes the giant Hawaiian darner Anax strenuus (Anisoptera: Aeshnidae) is claimed to be the largest living odonate with an alleged wing span of 190 mm, but this seems to be rather a myth as only 152 mm are scientifically documented.
The fossil Paleozoic "giant dragonflies" like Meganeuropsis permiana from the Permian of North America with up to 71 cm wing span and 43 cm body length have been the largest insects of all times and belonged to the order Meganisoptera, the griffinflies, related to odonates but not part of the modern order Odonata in the restricted sense.
The smallest living dragonfly is Nannophya pygmaea (Anisoptera: Libellulidae) from east Asia, which a body length of 15 mm and a wing span of 20 mm, and the smallest damselflies (and smallest odonates of all times) are species of the genus Agriocnemis (Zygoptera: Coenagrionidae) with a wing span of only 17–18 mm.
These insects characteristically have large rounded heads covered mostly by well-developed, compound eyes, legs that facilitate catching prey (other insects) in flight, two pairs of long, transparent wings that move independently, and elongated abdomens. They have three ocelli and short antennae. The mouthparts are on the underside of the head and include simple chewing mandibles in the adult.
In most families there is a structure on the leading edge near the tip of the wing called the pterostigma. This is a thickened, hemolymph–filled and often colorful area bounded by veins. The functions of the pterostigma are not fully known, but it most probably has an aerodynamic effect and may also have a visual function. More mass at the end of the wing may also reduce the energy needed to move the wings up and down. The right combination of wing stiffness and wing mass could reduce the energy consumption of flying. A pterostigma is also found among other insects, such as bees.
The nymphs have stockier, shorter, bodies than the adults. In addition to lacking wings, their eyes are smaller, their antennae longer, and their heads are less mobile than in the adult. Their mouthparts are modified, with the labium being adapted into a unique prehensile organ for grasping prey. Damselfly nymphs breathe through external gills on the abdomen, while dragonfly nymphs respire through an organ in their rectum.
Although generally fairly similar, dragonflies differ from damselflies in several, easily recognizable traits. Dragonflies are strong fliers with fairly robust bodies and at rest hold their wings either out to the side or out and downward (or even somewhat forward). Damselflies tend to be less robust, even rather weak appearing in flight, and when at rest most species hold their wings folded back over the abdomen (see photograph below, left). Dragonfly eyes occupy much of the animal's head, touching (or nearly touching) each other across the face. In damselflies, there is typically a gap in between the eyes.
Ecology and life cycle
Odonates are aquatic or semi-aquatic as juveniles. Thus, adults are most often seen near bodies of water and are frequently described as aquatic insects. However, many species range far from water. They are carnivorous throughout their life, mostly feeding on smaller insects.
Male Odonata have complex genitalia, different from those found in other insects. These include grasping cerci for holding the female and a secondary set of copulatory organs on the abdomen in which the sperm are held after being produced by the primary genitals. To mate, the male grasps the female by the thorax or head and bends her abdomen so that her own genitalia can be grasped by the copulatory organs holding the sperm. Male odonates have a copulatory organ on the ventral side of abdominal segment 2 in which they store spermatozoa; they mate by holding the female's head (Anisoptera) or thorax (Zygoptera) with claspers located at the tip of the male abdomen; the female bends her abdomen forward to touch the male organ and receive sperm. This is called the "wheel" position.
Eggs are laid in water or on vegetation near water or wet places, and hatch to produce pronymphs which live off the nutrients that were in the egg. They then develop into instars with approximately 9–14 molts that are (in most species) voracious predators on other aquatic organisms, including small fishes. The nymphs grow and molt, usually in dusk or dawn, into the flying teneral immature adults, whose color is not yet developed. These insects later transform into reproductive adults.
Odonates can act as bioindicators of water quality in rivers because they rely on high quality water for proper development in early life. Since their diet consists entirely of insects, odonate density is directly proportional to the population of prey, and their abundance indicates the abundance of prey in the examined ecosystem. Species richness of vascular plants has also been positively correlated with the species richness of dragonflies in a given habitat. This means that in a location such as a lake, if one finds a wide variety of odonates, then a similarly wide variety of plants should also be present. This correlation is not common to all bioindicators, as some may act as indicators for a different environmental factor, such as the pool frog acting as a bioindicator of water quality due to its high quantity of time spent in and around water.
- Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed. Oxford University Press. p. 320. ISBN 0-19-510033-6.
- Fabricius, Johann Christian (1793). Entomologia Systematica Emendata et Aucta. Secundum, Classes, Ordines, Genera, Species, adjectis synonimis, locis, observationibus, descriptionibus (in Latin). Hafniae : impensis Christ. Gottl. Proft. pp. 519 . doi:10.3931/e-rara-26792 – via e-rara.ch.
- Mickel, Clarence E. (1934). "The significance of the dragonfly name "Odonata"". Annals of the Entomological Society of America. 27 (3): 411–414. doi:10.1093/aesa/27.3.411.
- "Odonate". Merriam-Webster Dictionary.
- Field guide to lower aquarium animals. Cranbrook Institute of Science. 1939.
- Orr, A. G. Dragonflies of Peninsular Malaysia and Singapore. ISBN 983-812-103-7.
- Philip S. Corbet & Stephen J. Brook (2008). Dragonflies. London: Collins. ISBN 978-0-00-715169-1.
- Zhang, Z.-Q. (2011). "Phylum Arthropoda von Siebold, 1848 In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness" (PDF). Zootaxa. 3148: 99–103.
- E.g. Trueman & Rowe (2008)
- Trueman
- Lohmann (1996), Rehn (2003)
- Bechly, G. (2002): Phylogenetic Systematics of Odonata. in Schorr, M. & Lindeboom, M., eds, (2003): Dragonfly Research 1.2003. Zerf – Tübingen. ISSN 1438-034X (CD-ROM)
- Dragonfly – The largest complete insect wing ever found
- Mitchell, F.L. and Lasswell, J. (2005): A dazzle of dragonflies Texas A&M University Press, 224 pages: page 47
- Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed. Oxford University Press. pp. 355–358. ISBN 0-19-510033-6.
- Norberg, R. Åke. "The pterostigma of insect wings an inertial regulator of wing pitch". Journal of Comparative Physiology A. 81 (1): 9–22. doi:10.1007/BF00693547.
- Golfieri, B., Hardersen, S., Maiolini, B., & Surian, N. (2016). Odonates as indicators of the ecological integrity of the river corridor: Development and application of the Odonate River Index (ORI) in northern Italy. Ecological Indicators, 61, 234-247.
- Sahlén, Göran; Ekestubbe, Katarina (16 May 2000). "Identification of dragonflies (Odonata) as indicators of general species richness in boreal forest lakes". Biodiversity and Conservation. 10 (5): 673–690. doi:10.1023/A:1016681524097.
|Wikimedia Commons has media related to Odonata.|
|Wikispecies has information related to Odonata|
|The Wikibook Dichotomous Key has a page on the topic of: Odonata|
- Anatomy of Odonata
- Worldwide Dragonfly Association
- IORI species list, photos, social media links
- dragonflies and damselflies on the UF / IFAS Featured Creatures Web site
- World Odonata List
- Dragonflies and Damselflies (Odonata) of the United States – USGS state-by-state listing with distribution maps, images
- Journal of the Entomological Research Society | <urn:uuid:3ec997ae-322c-47d0-8e0f-675d22fa30aa> | 3.828125 | 2,793 | Knowledge Article | Science & Tech. | 46.046719 | 95,481,549 |
While this experiment involved clouds of lithium atoms, cooled to near absolute zero, the findings could also help explain the behavior of similar systems such as neutron stars, high-temperature superconductors, and quark-gluon plasma, the hot soup of elementary particles that formed immediately after the Big Bang. A paper describing the work will appear in the April 14 issue of Nature.
The researchers, led by MIT assistant professor of physics Martin Zwierlein, carried out their experiment with an isotope of lithium that belongs to a class of particles called fermions. All building blocks of matter — electrons, protons, neutrons and quarks — are fermions.
Different states of fermionic matter are distinguished by their mobility. For example, electrons can be mobile, as in a metal; immobile, as in an insulator; or flow without resistance, as in a superconductor. However, for many types of material, including high-temperature superconductors, it is not known what circumstances induce fermions to form a given state of matter. This is especially true of materials with strongly interacting fermions, meaning they are more likely to collide with each other (also called scattering).
In this study, the researchers set out to model strongly interacting systems, using lithium gas atoms to stand in for electrons. By tuning the lithium atoms' energy states with a magnetic field, they made the atoms interact with each other as strongly as the laws of nature allow, meaning that they scatter every time they encounter another atom.
To eliminate any effects of heat energy, the researchers cooled the gas to about 50 billionths of one Kelvin, close to absolute zero (-273 degrees Celsius). They used magnetic forces to separate the gas into two clouds, labeled "spin up" and "spin down, then made the clouds collide in a trap formed by laser light. Instead of passing through each other, as gases would normally do, the clouds repelled in dramatic fashion.
"When we saw that these ultra dilute puffs of gas bounce off each other, we were completely amazed," says graduate student Ariel Sommer, lead author of the Nature paper.
The gas clouds did eventually diffuse into each other, but in several cases it took an entire second or more — an extremely long time for events occurring at microscopic scales.
The research, conducted at the MIT-Harvard Center for Ultracold Atoms, is part of a program aimed at using ultracold atoms as easily controllable model systems to study the properties of complex materials, such as high-temperature superconductors and novel magnetic materials that have applications in data storage and improving energy efficiency.
In future work, the researchers plan to confine the lithium gases to two-dimensions, which will allow them to simulate the two-dimensional state in which electrons exist in high-temperature superconductors.
Their work can also be used to model the behavior of other strongly interacting systems, such as high-density neutron stars, which are only a few tens of kilometers in diameter but more massive than our sun.
Another substance that interacts as strongly as the atoms in the ultracold lithium gas clouds created at MIT is quark-gluon plasma, which existed at the universe's formation and has been recreated in particle colliders by colliding atomic nuclei at energies corresponding to a trillion degrees.
Written by Anne Trafton, MIT News Office
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The Atmospheric Infrared Sounder or AIRS instrument flies aboard NASA's Aqua satellite. AIRS captured an infrared image of Tropical Storm Flossie on July 25 at 10:05 UTC (6:05 a.m. EDT). Infrared data helps determine temperature, such as the cloud top and sea surface temperatures.
The AIRS instrument aboard NASA's Aqua satellite captured this infrared image of Tropical Storm Flossie on July 25. Strongest storms and heaviest rains are around the center and in a fragmented band of thunderstorms south of the center with cloud top temperatures near -63F/-52C (purple).
Image Credit: NASA JPL/Ed Olsen
AIRS data revealed that Flossie's strongest storms and heaviest rains were around its center and in a fragmented band of thunderstorms south of the center. Those areas had cloud top temperatures near -63F/-52C, indicating very high thunderstorms.
The National Hurricane Center or NHC noted that at 8 a.m. PDT (11 a.m. EDT) the center of Tropical Storm Flossie was near latitude 15.3 north and longitude 125.6 west. Flossie is moving toward the west near 16 mph (26 kph) and is expected to continue in that direction for the next couple of days. Flossie's maximum sustained winds remain near 40 mph (65 kph) and NHC expects some strengthening during the next 48 hours. The estimated minimum central pressure is 1003 millibars.
The NHC's current forecast track takes Flossie toward Hawaii as a depression by Tuesday, July 30.Text credit: Rob Gutro
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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The 3D ocean map that could reveal exactly what effect global warming is having on rainfall
Nasa is planning to create a 3D map of the ocean that could reveal exactly what effect global warming is having on rainfall.
The expedition is set to sail to the North Atlantic's saltiest spot to get a detailed, 3D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet.
The research voyage is part of a multi-year mission, dubbed the Salinity Processes in the Upper Ocean Regional Study (SPURS), which will deploy multiple instruments in different regions of the ocean.
Nasa's mission will study salt levels in the north Atlantic and create the first 3D map of salt levels as they flow around the ocean
The new data also will help calibrate the salinity measurements NASA's Aquarius instrument has been collecting from space since August 2011.
Scientists above the vessel Neurr are already heading for a spot known as the Atlantic surface salinity maximum, located halfway between the Bahamas and the western coast of North Africa.
The researchers will spend about three weeks on site deploying instruments and taking salinity, temperature and other measurements.
They aim to return with new data to aid in understanding one biggest effects of climate change, the acceleration of Earth's water cycle.
As global temperatures go up, evaporation increases, altering the frequency, strength, and distribution of rainfall around the planet, with far-reaching implications for life on Earth.
How it will work: Nasa plans to employ a variety of sensors and underwater floats to collect data for the project
'What if the drought in the U.S. Midwest became permanent? To understand whether that could happen we must understand the water cycle and how it will change as the climate continues to warm's said Raymond Schmitt, a physical oceanographer at Woods Hole and principal investigator for SPURS.
'Getting that right is going to involve understanding the ocean, because the ocean is the source of most of the water.'
Oceanographers believe the ocean retains a better record of changes in precipitation than land, and translates these changes into variations in the salt concentration of its surface waters.
Scientists studying the salinity records of the past 50 years say they already see the footprint of an increase in the speed of the water cycle.
The places in the ocean where evaporation has increased and rain has become scarcer have turned saltier over time, while the spots that now receive more rain have become fresher.
This acceleration may exacerbate droughts and floods around the planet, researchers believe.
Some climate models, however, predict less dramatic changes in the global water cycle, and researchers hope to find out what is really occuring.
'With Spurs we hope to find out why these climate models do not track our observations of changing salinities," said Eric Lindstrom, physical oceanography program scientist at Nasa.
'We will investigate to what extent the observed salinity trends are a signature of a change in evaporation and precipitation over the ocean versus the ocean's own processes, such as the mixing of salty surface waters with deeper and fresher waters or the sideways transport of salt.'
Current maps of salinity levels are not as accurate as the new 3D version
Researchers will deploy an array of instruments and platforms, including autonomous gliders, sensor-laden buoys and unmanned underwater vehicles.
Some will be collected before the research vessel heads to the Azores, but others will remain in place for a year or more, providing scientists with data on seasonal variations of salinity.
The Knorr research vessel will deploy a range of sensors to create a 3D map of ocean's saltiest area.
'We'll be able to look at lots of different scales of salinity variability in the ocean, some of which can be seen from space, from a sensor like Aquarius,' said David Fratantoni, a physical oceanographer with Woods Hole and a member of the expedition.
'But we're also trying to see variations in the ocean that can't be resolved by current satellite technology.'
A second expedition in 2015 will investigate low-salinity regions where there is a high input of fresh water, such as the mouth of a large river or the rainy belts near the equator.
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- Piglets brutally killed by having their heads slammed on floor
- Drowned woman and child found next to survivor clinging to wreck
- The terrifying moment a plane comes crashing down in South Africa
- Comedian is forced to move her scooter from disability space on train
- Trump's daughter grasps her Secret Service agent's hand
- 'I won't go anywhere near children': Sir Cliff Richard
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+44 1803 865913
By: Minoru Ozima and Frank A Podosek
286 pages, 82 figs, 42 tabs
Noble Gas Geochemistry discusses the fundamental concepts of using noble gases to solve problems in the earth and planetary sciences. The discipline offers a powerful and unique tool in resolving problems such as the origin of the solar system, evolution of the planets, earth formation, mantle evolution and dynamics, atmospheric degassing and evolution, ocean circulation, dynamics of aquifer systems, and numerous applications to other geological problems. This book gives a comprehensive description of the physical chemistry and cosmochemistry of noble gases, before leading on to applications for problem-solving in the earth and planetary sciences. There have been many developments in the use of the noble gases since publication of the first edition of this book in 1983. This second edition has been fully revised and updated. The book will be invaluable to graduate students and researchers in the earth and planetary sciences who use noble gas geochemistry techniques.
' ! likely to remain a highly relevant introductory text for years to come ! lucid and easy style of presentation: there is a great deal of useful, accessible reference data ! invaluable to geochemists and will find wide use as an introduction to the subject for a range of non-specialists at both the undergraduate and graduate level.' R. K. O'Nions, Nature 'The book led to my discovery or rediscovery of many interesting facts about the geochemistry of the rare gases and strongly tempts me to teach a graduate seminar on the subject.' John T. Wasson, American Scientist '! an excellent book, both as an introduction to its subject, and as a review of research in the field. ! Anyone interested in the development of the earth and its atmosphere will find this an interesting overview.' William R. Green, Geophysics '! certainly recommended to anyone involved in, or who feels that they ought to be involved in, noble gas studies !' Geological Magazine '! Ozima and Podosek are to be commended for bringing together the rather disparate aspects of noble gas research in a successful fashion. They have produced a clear text amply illustrated with diagrams and tables. The informal and lucid style of writing has led to an easily read text ! suitable as a textbook for a graduate course ! heartily recommended to students and professional geoscientists.' Kenneth A. Foland, Chemical Geology
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A. W. 2000. Vegetation modification and resource competition in grazing ungulates. – Oikos 89: 501 – 508. The prevalence of interspecific competition in animal communities is the subject of a long-running debate, chiefly because the underlying processes of resource exploitation and resource supply are often poorly understood. To provide some insight into these processes within a guild of grazing herbivores, two hypothetical mechanisms of exploitation competition were tested by measuring food intake of topi (Damaliscus lunatus) and wildebeest (Connochaetes taurinus) when foraging on different sward structures in the Serengeti National Park. According to our bite quantity hypothesis, wildebeest, which have relatively wide mouths, can graze down vegetative swards to a height below that which can be tolerated by topi; and according to our bite quality hypothesis, the narrower-mouthed topi can reduce the leafy component of differenti-ated swards (i.e. swards in which seed-bearing stems have developed) through selective feeding to a level below that which can be tolerated by wildebeest. On differentiated swards with erect growth form, the topi selected 20% more green leaf in their diet, as measured by a calibrated visual technique, and also obtained higher short-term intake rates. Greater selectivity alone provided topi with a metabolisable energy intake estimated to be 16% higher than that of wildebeest. On vegetative swards, it was estimated that wildebeest could maintain positive energy balance on 2-cm swards, 1 cm shorter than the threshold height for topi. Our findings indicate the conditions under which each ungulate species may limit the other's use of natural pastures through interspecific competition: bite quantity competition may apply on short grazing lawns; bite quality competition is expected on differentiated swards with a limited supply of green leaf. We suggest that herbivory by one species can modify the vegetation in a way that makes it less profitable to competing species. In effect the vegetation is 'captured' as a resource by one species. Thus modification of vegetation is argued to be a critical component of resource competition in herbivores.
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Resources of Near-Earth Space
by J. S. Lewis, M. S. Matthews
Publisher: University of Arizona Press 1993
Number of pages: 977
The parts of the solar system that are most accessible from Earth (the Moon, the near-Earth asteroids, and Mars and its moons) are rich in materials of great potential value to humanity. Immediate uses of these resources to manufacture propellants, structural metals, refractories, life-support fluids and glass can support future large-scale space activities. In the longterm, non-terrestrial sources of rare materials and energy may be of great importance here on Earth.
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Download or read it online for free here:
by James Schombert - University of Oregon
The purpose of this course is to educate you on the basic science behind our exploration of the Solar System so you may make informed choices as future/current voters on issues of our environment and the future of science in this country.
- National Aeronautics and Space Administration
Passing by Jupiter in 1979, the Voyager spacecraft have collected an enormous amount of data that may prove to be a keystone in understanding our solar system. This publication provides an early look at the Jovian planetary system ...
by Thomas P. Hansen - NASA
The 1964 Lunar Orbiter program consisted of the investigation of the Moon by five unmanned spacecraft. Its objective was to obtain detailed photographs of the Moon. This document presents information on the location and coverage of all photographs.
- National Academy of Sciences
This book surveys the current state of knowledge of the solar system and recommends a suite of planetary science flagship missions for the decade 2013-2022 that could provide a steady stream of important new discoveries about the solar system. | <urn:uuid:980bd8e8-2f76-428a-afd4-9bf9b799df2c> | 3.53125 | 358 | Content Listing | Science & Tech. | 38.77537 | 95,481,645 |
The craters feature a thin-layered outer deposit that extends well beyond the typical range of ejecta, said Nadine Barlow, professor of physics and astronomy at Northern Arizona University.
A low-aspect-ratio layered ejecta crater on Mars.
She has given them a name—Low-Aspect-Ratio Layered Ejecta Craters—and presented the findings this week at the American Astronomical Society Division for Planetary Sciences in Denver.
Barlow found the LARLE craters while poring over high-resolution images to update her highly popular catalog of Martian craters.
“I had to ask, ‘What is going on here?’ “ Barlow said.
Delving into “explosion literature,” Barlow said she and her collaborators learned more about a phenomenon known as base surge. After a large explosion, fine-grain material forms a cloud and moves out along the surface. The cloud erodes the surface and picks up more material, creating an extensive outer deposit.
By adjusting equations from volcano research for Martian conditions, Barlow said, the researchers, including Joe Boyce, an NAU alum from the University of Hawaii, could accurately explain the “thin, sinuous, almost flame-like deposits.”
“So we think we’re on to something,” Barlow said.
The craters are found primarily at higher latitudes, a location that correlates with thick, fine-grained sedimentary deposits rich with subsurface ice. “The combination helps vaporize the materials and create a base flow surge,” Barlow said. The low aspect ratio refers to how thin the deposits are relative to the area they cover.
Barlow, Boyce and Lionel Wilson, of Lancaster University, relied on the stream of data that continues to flow from ongoing surveillance of Mars. Older data from the Mars Odyssey Orbiter was used for a global survey, but more detailed studies referred to high-resolution images from the Mars Reconnaissance Orbiter—about six meters per pixel.
“We’re looking in more detail at these deposits to find out what their characteristics are,” Barlow said. “We can see dune-like structures and the hollows that occur in the outer deposit.”
Barlow said she hopes to complete the revision of her catalog within a year, and welcomes surprises such as the LARLE finding along the way.
“That’s part of the fun of science, to see something and say, ‘Whoa, what’s that?’ ” she said. “Projects like this end up leading to proposals.”
Eric Dieterle | EurekAlert!
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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20.07.2018 | Materials Sciences | <urn:uuid:56a3fcf2-d0a2-4cfd-b403-31f131720b0f> | 3.203125 | 1,149 | Content Listing | Science & Tech. | 38.086292 | 95,481,744 |
Glutathione S-transferases (GSTs) are a major family of detoxification enzymes which possess a wide range of substrate specificities. Most organisms possess many GSTs belonging to multiple classes. Interest in GSTs in insects is focused on their role in insecticide resistance; many resistant insects have elevated levels of GST activity. In the malaria vector Anopheles gambiae, elevated GST levels are associated with resistance to the organochlorine insecticide DDT [1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane]. This mosquito is the source of an insect GST, agGSTd1-6, which metabolizes DDT and is inhibited by a number of pyrethroid insecticides. The crystal structure of agGSTd1-6 in complex with its inhibitor S-hexyl glutathione has been determined and refined at 2.0 A resolution. The structure adopts a classical GST fold and is similar to those of other insect delta-class GSTs, implying a common conjugation mechanism. A structure-based model for the binding of DDT to agGSTd1-6 reveals two subpockets in the hydrophobic binding site (H-site), each accommodating one planar p-chlorophenyl ring.
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What if one of the largest volcanic eruptions in recent history happened today? A new study suggests that a blast akin to the Laki eruption that devastated Iceland in the 1780s would waft noxious gases southwestward and kill tens of thousands of people in Europe. And in a modern world that is intimately connected by air traffic and international trade, economic activity across much of Europe, including the production and import of food, could plummet. At least four Laki-sized eruptions have occurred in Iceland in the past 1,150 years.
From June of 1783 until February of 1784, the Laki volcano in south-central Iceland erupted, spewing an estimated 122 million metric tons of sulfur dioxide gas into the sky — a volume slightly higher than human industrial activity today produces in the course of a year, according to Anja Schmidt, an atmospheric scientist at the University of Leeds reported online in the Proceedings of the National Academy of Sciences.
Two years after the Laki eruption, approximately 10,000 Icelanders died --about one-fifth of the population, along with nearly three-quarters of the island’s livestock. Parish records in England reveal that in the summer of 1783, when the event began, death rates were between 10 percent and 20 percent above normal.
To assess how such an eruption might affect the densely populated Europe of today, Schmidt created a computer simulation using weather models to estimate where sulfur dioxide emissions from an 8-month-long eruption that began in June would effect. They also estimated the resulting increases in the concentrations of airborne particles smaller than 2.5 micrometers across, the size of aerosols that are most easily drawn into human lungs and that cause cardiopulmonary distress. They also used modern medical data to estimate how many people those aerosols would kill.
In the first 3 months after the hypothetical eruption began, the average aerosol concentration over Europe would increase by 120 percent. The number of days during the eruption in which aerosol concentrations exceed air-quality standards would rise to 74, when a normal period that length typically includes only 38. Not surprisingly, the air would become thickest with dangerous particles in areas downwind of the eruption, such as Iceland and northwestern Europe, where aerosol concentrations would more than triple. But aerosol concentrations in southern Europe would also increase dramatically, rising by 60 percent.
In the year after the hypothetical eruption commences, the increased air pollution swept from Iceland to Europe would cause massive amounts of heart and lung disease, killing an estimated 142,000 people. Fewer than half that number of Europeans die from seasonal flu each year.
The Daily Galaxy via ScienceNOW and newscientist.com
Image credit: Ulrich Latzenhofer on Flickr
Image: Laki volcanic region, Iceland. (R.M.C. Lopes/NASA) | <urn:uuid:98ee7113-b241-4cc6-8f6f-12babb7ef496> | 3.5625 | 577 | News Article | Science & Tech. | 33.283526 | 95,481,799 |
It is a fact: we just entered in the Big Data era. More sensors, more
computers, and being more evenly distributed throughout space and time
than ever, are forcing data analyists to navigate through oceans of
data before getting insights on what this data means.
Tables are a very handy and spreadly used data structure to store
datasets so as to perform data analysis (filters, groupings, sortings,
alignments...). However, the actual table implementation, and
especially, whether data in tables is stored row-wise or column-wise,
whether the data is chunked or sequential, whether data is compressed or not,
among other factors, can make a lot of difference depending on the
analytic operations to be done.
My talk will provide an overview of different libraries/systems in the
Python ecosystem that are designed to cope with tabular data, and how
the different implementations perform for different operations. The
libraries or systems discussed are designed to operate either with
on-disk data ([PyTables] , [relational databases] , [BLZ] ,
[Blaze] ...) as well as in-memory data containers ([NumPy] ,
[DyND] , [Pandas] , [BLZ] , [Blaze] ...).
A special emphasis will be put in the on-disk (also called
out-of-core) databases, which are the most commonly used ones for
handling extremely large tables.
The hope is that, after this lecture, the audience will get a better
insight and a more informed opinion on the different solutions for
handling tabular data in the Python world, and most especially, which
ones adapts better to their needs.
AbstractTables are a very handy data structure to store
datasets to perform data analysis (filters, groupings, sortings,
But it turns out that *how the tables are actually implemented* makes a large impact on how they perform.
Learn what you can expect from the current tabular offerings in the Python ecosystem. | <urn:uuid:684877b3-ba43-4d8f-a0f7-aa24f3a020db> | 2.671875 | 440 | News (Org.) | Software Dev. | 35.726523 | 95,481,802 |