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Joining different kinds of materials can lead to all kinds of breakthroughs. It’s an essential skill that allowed humans to make everything from skyscrapers (by reinforcing concrete with steel) to solar cells (by layering materials to herd along electrons).
In electronics, joining different materials produces “heterojunctions”—the most fundamental components in solar cells, LEDs or computer chips. The smoother the seam between two materials, the more easily electrons flow across it; essential for how well the electronic devices function. But they’re made up of crystals—rigid lattices of atoms, which may have very different spacing—and they don’t take kindly to being mashed together.
In a study published March 8 in Science, scientists with the University of Chicago and Cornell University revealed a technique to “sew” two patches of crystals seamlessly together at the atomic level to create atomically-thin fabrics.
The team wanted to do this by stitching different fabric-like, three-atom-thick crystals. “Usually these are grown in stages under very different conditions; grow one material first, stop the growth, change the condition, and start it again to grow another material,” said Jiwoong Park, professor of chemistry in the James Franck Institute and the Institute for Molecular Engineering and a lead author on the study.
Instead, they developed a new process to find the perfect window that would work for both materials in a constant environment, so they could grow the entire crystal in a single session.
The resulting single-layer materials are the most perfectly aligned ever grown, Park said. The gentler transition meant that at the points where the two lattices meet, one lattice stretches or grows to meet the other—instead of leaving holes or other defects.
The atomic seams are so tight, in fact, that when they looked up close using scanning electron microscopes, they saw that the larger of the two materials puckers a little around the joint.
They decided to test its performance in one of the most widely used electronic devices: a diode. Two different kinds of material are joined, and electrons are supposed to be able to flow one way through the “fabric,” but not the other.
The diode lit up. “It was exciting to see these three-atom-thick LEDs glowing. We saw excellent performance—the best known for these types of materials,” said Saien Xie, a graduate student and first author on the paper.
The discovery opens up some interesting ideas for electronics. Devices like LEDs are currently stacked in layers—3-D versus 2-D, and are usually on a rigid surface. But Park said the new technique could open up new configurations, like flexible LEDs or atoms-thick 2-D circuits that work both horizontally and laterally.
He also noted that the stretching and compressing changed the optical properties—the color—of the crystals due to the quantum mechanical effects. This suggests potential for light sensors and LEDs that could be tuned to different colors, for example, or strain-sensing fabrics that change color as they’re stretched.
“This is so unknown that we don’t even know all the possibilities it holds yet,” Park said. “Even two years ago it would have been unimaginable.”
This work was carried out in collaboration with co-lead authors David Muller and Robert A. DiStasio Jr. at Cornell University. Other coauthors included University of Chicago postdoctoral scholars Kibum Kang and Chibeom Park and graduate student Preeti Poddar, as well as Cornell postdoctoral scholar Ka Un Lao and graduate students Lujie Huang, Lijie Tu and Yimo Han. The study used computing resources at the Argonne Leadership Computing Facility at Argonne National Laboratory. | <urn:uuid:f2509626-50ea-4062-82bd-03fad92d07b8> | 4.15625 | 792 | News Article | Science & Tech. | 40.576485 | 95,614,535 |
For Immediate Release, September 20, 2016
Contact: Tierra Curry, (928) 522-3681, email@example.com
Mississippi Fish Proposed for Endangered Species Act Protection After 25 Years On Waiting List
JACKSON, Miss.— In response to a settlement with the Center for Biological Diversity to speed protections for 757 species, the U.S. Fish and Wildlife Service proposed today to protect the Pearl darter as a threatened species under the Endangered Species Act. The small fish has been wiped out of its namesake watershed, the Pearl River, and now survives only in the Pascagoula River basin in the southeast portion of the state.
“Endangered Species Act protection is the best hope for saving this beautiful little fish from the very big threats it’s facing,” said Tierra Curry, a senior scientist at the Center. “Spending 25 years on a waiting list allowed the fish to be wiped out from nearly two-thirds of its range, so it’s a relief that it has finally been proposed for the protection it needs to survive.”
The darter’s future is threatened by water pollution from oil and gas development, sand and gravel mining, urbanization and agriculture. Darters live on the river bottom and use the spaces between rocks for hiding and breeding. But habitat destruction causes erosion that fills these spaces with silt, and pollution and silt harm the insects the darters need for food. Other threats include the proposed damming of Little and Big Cedar creeks, tributaries to the Pascagoula River — which would cause downstream water-quality degradation — as well as climate change, hurricanes and other catastrophic events.
The species’ historical range was approximately 775 river miles in Mississippi and Louisiana. It has been extirpated from all 440 river miles where it was once found in the Pearl River watershed. Of the 335 river miles where it was once found in the Pascagoula watershed, it is now thought to survive in scattered populations along 279 river miles in the Pascagoula, Chickasawhay, Chunky, Leaf and Bouie rivers, though it hasn’t been confirmed in the Bouie or Chunky rivers in 15 years. Overall the species has been lost from at least 64 percent of its historic range. The Southeastern Fishes Council names the Pearl darter as one of the 12 most endangered fish in the southeastern United States.
The darter was first placed on the candidate waiting list for federal protection in 1991; the Center petitioned for its protection in 2004. In 2011 the Center and the Service reached a landmark agreement requiring the agency to make decisions on all of the plants and animals on the candidate waiting list by the end of this fiscal year. Under the agreement, 148 species have gained protection and 40 have been proposed for protection.
The Pearl darter is about 2.5 inches long, and males develop showy patterns during the breeding season. It has a blunt snout, large eyes located high on its head, and a black spot at the base of its tail fin.
Following today’s proposed protection, the Service will accept public comment before finalizing protection for the fish in one year.
The Center for Biological Diversity is a national, nonprofit conservation organization with more than 1.1 million members and online activists dedicated to the protection of endangered species and wild places. | <urn:uuid:3cc7e8c5-7747-483c-be27-6dd098f42a99> | 3.1875 | 712 | News (Org.) | Science & Tech. | 45.850755 | 95,614,537 |
The following terms are commonly encountered in Mathematics. It is important to have an understanding of these terms as they will assist in understanding and make questions more meaningful when you encounter them.
- It is an imaginary line, a straight line to which a graph continuously draws nearer without ever touching it.
- The maximum height of a graph from the x-axis eg in trig graphs.
- The perimeter of a circle
- A count or number of times an outcome or event was observed
- The gradient/slope of the tangent to a curve at a particular point on the curve.
- The -intercepts of a graph, which are the solutions to f(x) = 0 or y=0
- In geometry, the tangent line to curve at a given point is a straight lines
which “touches “ a curve at a particular point.
8. Average Rate of Change
- It is the average gradient between two points on a curve.
9. Instantaneous Rate of Change
- It a the gradient of a curve at a particular point.
10. Turning Point
- It is the relative maximum or minimum points on a graph, or relative extreme | <urn:uuid:42b16575-7e3d-4452-8673-1686ff0e5e07> | 4.125 | 245 | Structured Data | Science & Tech. | 56.572513 | 95,614,573 |
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Methods in Surface Physics Experimentation in Ultra-High Vacuum Environments. Hasan Khan ( U niversity of Rochester ), Dr. Meng-Fan Luo ( N ational Central University ). Introduction. Objective.
in Ultra-High Vacuum Environments
Hasan Khan (University of Rochester), Dr. Meng-Fan Luo (National Central University)
Surface physics is an emerging field of science involving the study of the surface properties of solids in a vacuum environment. Solid substrates are cleaned and put into a ultra-high vacuum (UHV) environment, where they come into contact with other substances and may display unique properties. Surface physics has applications in a number of fields, including semiconductor science.
We describe the general procedure and methods involved in surface physics experimentation, including establishing a vacuum using pumps, cleaning the sample’s surface, and measuring parameters using various forms of spectroscopy.
Theory and Methods
The first step in preparing for a surface physics experiment is establishing an ultra-high vacuum for the sample to be studied in. The sample must be studied in a vacuum to prevent contaminants from altering the initial surface properties of the solid. The experimental setup used in surface physics experiments is composed primarily of a vacuum chamber connected to various pumps, filaments, and gas lines. The sample is held on a sample holder inside the chamber that is free to move so that it may interact with different components of the system during the experiment.
A vacuum is created inside the chamber using three separate pumps. A rotary pump brings the pressure in the chamber down from 760 torr (atmospheric) to ~10-3 torr. After this, a turbomolecular pump is needed to bring the pressure down further, else the pressure will begin to increase. The pump brings the pressure in the chamber down to ~10-7 torr. At this point, the chamber is baked to for 1-2 days to remove water molecules that may have been adsorbed to the inner walls of the chamber. Finally, an ion pump is used to further bring the pressure in the chamber down to ~10-9 torr. A degassing process is also performed in which several components connected to the chamber are also heated to remove captured gas molecules. After this procedure, an ultra-high vacuum has been established.
Before testing, the sample must be cleaned of all possible contaminants on the surface. An ion sputter gun is used to shoot argon ions at the surface of the sample to remove the first few monolayers. After this, annealing is performed on the sample where it is heated to remove any argon ions that may have been adsorbed onto the surface. This process is repeated several times until the surface has been adequately cleaned. During this process, the contamination level of the surface is measured through a method called Auger Electron Spectroscopy (AES), which measures the surface composition of the sample as a function of intensity. Once intensity of foreign elements and compounds is low enough, the surface is clean and ready for testing.
Figure 1. This graph represents various pumps used in UHV experiments as a function of the pressure ranges they are usable in. Normally, only the rotary, turbomolecular, and ion pumps are used.
Figure 2. This picture depicts the cleaning of a solid surface by use of an ion sputter gun, which fires ions that chip away layers of the surface. The sample is then annealed to remove any adsorbed ions.
Figure 3. Shown above is the typical experimental setup used in UHV experiments, consisting of the vacuum chamber, spectroscopy equipment, and pumps (not shown).
Testing of the sample involves the adsorption of gases or the deposition of metals onto the solid surface. In the case of a NiAl substrate, typically an oxide thin film of Al2O3 is formed by exposing the chamber to oxygen gas. This new Al2O3/NiAl surface is then used as the testing environment.
The growth of nanoclusters of various substances is typically the goal of such experiments. For example, if Au is being tested, Au is typically deposited on the surface in vapor form and the sample is then heated to show signs of growth. A similar procedure is performed with gases.
Various forms of spectroscopy, such as Low-Energy Electron Diffraction (LEED) and Reflection High-Energy Electron Diffraction (RHEED) are used to observe the growth of nanocluster patterns. A scanning tunneling microscope (STM) may be used to image the nanoclusters directly.
Lüth, Hans. Surfaces and Interfaces of Solids. 2nd Ed. Springer-Verlag Berlin Heidelberg, 1993. Print.
Image Credit (Figure 2): http://pprco.tripod.com/SIMS/Theory.htm
Surface physics is a new and exciting field of study, however the methods used to conduct surface physics experiments are typically long and complex. It is important to be well-informed of the proper procedure used in carrying out such experiments in a vacuum environment to prevent possible contamination that may alter results.
In the future it is desired that the procedure for surface physics experiments become simpler and more controlled. | <urn:uuid:6bd14e8d-5b0b-4f59-8d0d-dacfa5d8d8fb> | 3.015625 | 1,095 | Academic Writing | Science & Tech. | 41.762113 | 95,614,577 |
Thirsty Middle Eastern and North African countries could tap into their solar-energy potential to cope with fresh water scarcity, according to resource experts.
Water could be saved by switching to renewable solar energy from fossil fuel electricity generation that uses up water, said the World Resources Institute (WRI).
The findings show moving to clean energy has benefits aside from cutting planet-warming greenhouse gas emissions, said Tianyi Luo, a senior WRI manager.
“A lot of times, the water savings, that kind of benefits from renewable projects are overlooked,” Luo told the Thomson Reuters Foundation.
Yemen, Saudi Arabia, Oman, Libya, Algeria, Morocco, the United Arab Emirates and Jordan ranked among the top countries, measured by lack of freshwater and solar energy potential, that could benefit from such a switch, the WRI said. Read More
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ICARUS is the largest liquid-argon neutrino detector in the world, and the technology pioneered for the experiment will be the template for future neutrino experiments.
Scientists have observed three types of neutrino — the muon, electron and tau neutrinos — and have also observed them changing between types. Experiments such as the Liquid Scintillator Neutrino Detector (LSND) at Los Alamos National Laboratory and MiniBooNE at Fermilab have seen hints that these three types might also be changing into a fourth, called a sterile neutrino, one we have not been able to detect.
The ICARUS detector, along with its two fellow Fermilab neutrino hunters, called SBND and MicroBooNE, will use the lab’s neutrino beam to seek evidence of this fourth type of neutrino.
The ICARUS collaboration studied neutrinos at Gran Sasso National Laboratory in Italy — operated by the Italian Institute for Nuclear Physics (INFN) — from 2010 to 2013 under the leadership of Nobel laureate Carlo Rubbia. The ICARUS experiment pioneered the use of a new technology for spotting neutrinos using liquid argon, 760 tons of which fill the ICARUS detector. When neutrinos collide with argon atoms, they create charged particles that can be tracked. The detector produces beautiful 3-D images of those particles so scientists can study them. During its first run, the European particle physics laboratory CERN provided the beam of neutrinos that ICARUS studied.
In 2014 the detector was moved to CERN, where it has been refurbished and improved for its new mission.
Now at Fermilab, the ICARUS detector will join two others (the in-progress Short Baseline Near Detector and the MicroBooNE detector, which began recording neutrino tracks in 2015). Together, these three massive machines will search for the long-theorized but never-detected sterile neutrino.
ICARUS’s liquid-argon detection technology will also be adapted for the Deep Underground Neutrino Experiment (DUNE), Fermilab’s flagship. DUNE will use the technology to study the three previously observed types of neutrinos and how they change between one type and another. | <urn:uuid:52631636-3938-410d-b34d-ca557fb58545> | 3.53125 | 484 | About (Org.) | Science & Tech. | 25.796325 | 95,614,582 |
One of the reasons I love oceans is that they're bursting with life. Crazy, sort of unbelievable life if you think about it: Sea horses, anemones, whales, lobster, limpets, sharks, the list goes on and on.
For anyone fascinated by the beautiful oddities of the universe hiding around every corner, oceans are an endless smorgasbord of delights.
That's why it was sad to see this new study saying that ocean acidification will make our oceans, well, less interesting. And, more troubling still, less alive.
The study by the University of California, Davis, found that ocean acidification will hurt not only individual species but the entire ecosystems where they live. The result? Homogenized ocean environments dominated by just a few plants and animals and devoid of a vast array of creatures who called these places homes for thousands of years.
Here's how Kristy Kroeker, a postdoctoral researcher at Bodega Marine Laboratory at UC Davis, put it:
"The background, low-grade stress caused by ocean acidification can cause a whole shift in the ecosystem so that everything is dominated by the same plants, which tend to be turf algae.
"In most ecosystems, there are lots of different colorful patches of plants and animals -- of algae, of sponges, of anemones. With ocean acidification, you lose that patchiness. We call it a loss of functional diversity; everything looks the same."
Ocean acidification is already having devastating effects. Corals are disappearing , shellfish are being wiped out and red tide algae are growing more toxic. Left unchecked it threatens to branch out throughout the underwater food web, eventually risking salmon, otters, whales and even people who rely on oceans for protein.
It's no surprise: The world's oceans absorb some 22 million tons of carbon pollution every day from factories, power plants, cars and other human sources. The result is that oceans have been 30 percent more acidic -- far more acidic than our oceans have experience in millions of years.
Yes, as an environmental attorney, I'm deeply concerned about what it's doing to our oceans and the long-term effects it's going to have on sea life. It's so bad, we've been urging the Environmental Protection Agency to step in immediately and being a national plan to address this undeniable crisis.
But, as simply a fan of the ocean, I'd hate to see it become the shell of the wonderful place it once was. I don't want duller, drabber seas -- I want them vibrant, crackling with life and full of surprises. | <urn:uuid:ea5f7b35-b35c-4254-a7fc-7f17f2d796e4> | 3.203125 | 536 | Personal Blog | Science & Tech. | 42.067535 | 95,614,592 |
That's the startling conclusion drawn by a Johns Hopkins University marine geologist, writing in the July issue of the journal Geology.
Postdoctoral fellow Justin Ries and his collaborators say this is the first known case of an animal altering the composition of its skeleton in response to change in its physical environment. The aquatic animal's sensitivity to such changes poses questions about its evolutionary history, as well as the future of the ecologically important coral reefs that it builds, Ries said, especially at a time when seawater is changing in response to global warming and the buildup of carbon dioxide in the atmosphere.
A 2005 Ph.D. graduate of Johns Hopkins, Ries collaborated on the research with his dissertation advisors, Steven M. Stanley (now of the University of Hawaii) and Lawrence A. Hardie, professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins.
Reefs are large underwater structures of coral skeletons, made from calcium carbonate secreted by generation after generation of tiny coral polyps over sometimes millions of years of coral growth in the same location. The team showed that corals can switch from using aragonite to another mineral, calcite, in making the calcium carbonate. They make that switch in response to decreases in the ratio of magnesium to calcium in seawater, Ries said. That ratio has changed dramatically over geologic time.
"This is intriguing because, until now, it was generally believed that the skeletal composition of corals was fixed," he said.
Ries spent two months growing three species of modern scleractinian corals (the major reef-building corals in today's seas) in seawater formulated at six different chemical ratios that have existed throughout the 480-million-year history of corals. He concocted this "artificial seawater" using "recipes" provided by Hardie, who several years ago discovered that the magnesium-calcium ratio in seawater has vacillated throughout geologic history between a low of 1.0 and today's 5.2, changing due to chemical reactions between seawater brine and rising magma along the ocean floor.
Ries placed his artificial seawaters in 10-gallon glass tanks, then added fragments of the three species of Caribbean reef-building corals. These were replete with colonies of polyps, which had spent the previous month in "equilibration tanks." Ries adjusted the chemistry of those tanks over 30 days, until their magnesium-to-calcium ratios were in line with the prescribed "ancient seawater" chemistries.
Two months later, Ries removed the coral skeletons and used X-ray diffraction to analyze their mineral composition. He was surprised to find that corals grown in the artificial seawater with a magnesium-to-calcium ratio less than 2-to-1 began producing a large portion of their skeleton with the calcite mineral, while those grown in unmodified modern seawater produced exclusively the aragonite mineral.
Though most scientists believed that corals were programmed to produce only the aragonitic form of calcium carbonate, he said, the team's work reveals that corals are far more flexible and able to vary at least a portion of their skeleton to growth favored by seawater chemistry. He postulates that this "mineralogical flexibility" provides corals with an "evolutionary advantage," as it would take more energy for corals to produce skeletons that are not favored by the chemistry of the seawater surrounding them.
The calcite-producing corals grown in artificial ancient water grew significantly slower than did the aragonite-producing corals grown in modern water.
"The reduction in the corals' rate of growth that accompanied their exposure to the chemically modified seawaters is further evidence of corals' extreme sensitivity to environmental change," Ries said.
"This is particularly significant given recently observed and predicted future changes in the temperature and acidity of our oceans ¬¬-- via global warming and rising atmospheric CO2 , respectively -- that will presumably have a significant impact on corals' ability to build their skeletons and construct their magnificent reefs," he said.
Corals are crucial to nearshore tropical ecosystems because the reefs they build are inhabited by tens of thousands of marine animals, plants, algae and bacteria that make up the coral reef ecosystem, which is one of the planet's most diverse, Ries said. But coral reefs also serve a more practical purpose: They absorb wave energy generated by hurricanes and other severe tropical storms.
"Ironically, the same factor that is likely causing such storms to increase in intensity – global warming – is also causing the corals to bleach (lose their symbiotic algae) and die, ultimately leading to the destruction of the coral reefs, which protect the coasts from these storms," Ries said. "All that being said, it is also important to note that the magnesium-calcium ratio of seawater changes only over millions of years and has no direct relationship to recent global warming and ocean acidification, which are believed to be at least partly human caused."
His team's experiments do, however, have significance with respect to global warming and ocean acidification, Ries said, because they reveal that although corals can adapt mineralogically to altered seawater chemistry, doing so slowed the corals' rate of growth by nearly 65 percent.
"This provides us with further evidence that corals are extremely sensitive to rapid environmental change, such as global warming," he said.
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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...
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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George Boole was an English mathematician, educator, philosopher who was born in 1815, 200 years ago. He was the first professor of mathematics at Queen's College, Cork (now University College Cork (UCC)) and is known as the inventor of boolean arithmetic: The field that is the basis of today’s computers.
In boolean arithmetic, instead of infinite numbers we only have 2 values: 0/1, true/false, yes/no, etc. We will use the values true and false in this problem. The two most common operations in boolean arithmetic are AND and OR.
The result of an AND operation is true only if both elements are true. Examples:
The result of an OR operation is true if any of the elements are true. Examples:
In this problem you’ll read one of such operations and write the correct result.
Read a single line from the standard input. The line will contain three words with the format:
value1 operation value2. The fields value1 and value2 will be either true or false. The field operation will be either AND or OR.
Print either true or false.
true AND true
true OR true
true AND false
false OR true
false AND false
false OR false | <urn:uuid:eb044b1c-64b5-48c7-8537-021e31c52770> | 3.8125 | 345 | Tutorial | Science & Tech. | 71.080541 | 95,614,614 |
Preferred Interaction Patterns from Crystallographic Databases
A knowledge of three-dimensional structure, in all of its aspects, is an essential prerequisite of the molecular modelling process. This knowledge may be divided, on energetic grounds, into two categories. Firstly, information is required about the covalent aspects of three dimensional structure — bond lengths, valence angles, and conformational data which dictate the overall molecular shape. Secondly, geometrical descriptions are needed of the much weaker interactions by which atoms and molecules associate with each other in a non-bonded sense. Crystallography is unique in its ability to provide direct experimental results in both of these areas. The technique is now being applied to molecules of ever-increasing size and complexity and in ever-increasing numbers. Details of well over 100,000 crystal structures have been published — some 400 proteins and biological macromolecules, 76,000 small molecules containing organic carbon, and nearly 40,000 inorganic, mineral and metal structures: All of this information is of immense value and the advent of crystallographic databases makes the data more readily available in an organized form. It is now a relatively simple matter to locate relevant structures and extract their coordinates for use in modelling studies.
KeywordsCarbonyl Oxygen Cambridge Structural Database Spherical Coordinate System Preferential Association Backbone Carbonyl
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Morphology of Planets and Satellites
In the broadest sense, we consider that the morphologies of rocky members of the Solar System (Table 1, listed in order of distance from their host) can be grouped into three categories: endogenic, exogenic, and exotic. Endogenic provinces are ones that were produced by internal forces that caused plate movements and interplate and intraplate magmatic/tectonic activities. Exogenic provinces are ones that owe their origin to external processes such as weathering, erosion, transportation, and deposition from earlier rock surfaces; therefore, they require the presence of a hydrosphere (or other liquid) and an atmosphere (Table 2, listed in order of decreasing diameter). Exotic provinces are ones created by bombardment of the planets or satellites by planetesimals and comets; this bombardment has produced large regions of terrae (impact craters), planitias (flat plains of debris ejected from impact sites), and impact melts (country rock melted by the kinetic energy of impact on rocky planets and moons).
KeywordsSolar System Country Rock Plate Movement Impact Crater Impact Site
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Most studies of climate-driven changes in avian breeding phenology have focused on temperate passe-rines, yet the consequences of such environmental change may be more deleterious for other avian taxa, such as arctic and sub-arctic waders (Charadrii). We therefore examine large-scale climatic correlates of the breeding phenology of one such species (golden plover Pluvialis apricaria), and the timing of emergence of their adult tipulid prey, to assess the potential for climate change to disrupt breeding performance. Golden plover first-laying dates were negatively correlated with both March and April temperature, the mean laying date of first clutches was additionally negatively correlated with March rainfall. The timing of final laying dates were negatively correlated with April temperature only. The timing of tipulid emergence was negatively correlated with May temperature. In combination with historical climatic data, these models suggest a 9-day advancement of golden plover first-laying dates occurred during the 1990s, although this remains within the range of natural variation for the twentieth century. The magnitudes of predicted changes in mean and final laying dates, and the timing of tipulid emergence, were smaller. Climate predictions for 2070–2099 suggest potential advances in first-laying dates by 25 days, whilst the timings of mean and final laying dates are predicted to change by 18 days and 13 days, and tipulid emergence by 12 days. Given the importance of adult tipulids to young golden plover chicks, these changes may result in a mismatch between the timing of first-laying dates and tipulid emergence, so reducing the success of early breeding attempts. Mod-elling suggests that these changes could reduce breeding success in a South Pennines population by about 11%.
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May 15, 2008
User Interfaces Are A Graphical Domain-Specific LanguageWhen I occasionally stop to think more deeply about software development, I'm often drawn to the concept of languages.
Languages are very integral to programming, of course. We use programming languages like Java, C# and Ruby to give instructions to our computers on behalf of our customers.
And when I design an API, I'm also defining a language. A set of symbols that, when invoked, have an underlying meaning expressed in another - usually lower-level - language.
Domain-specific Languages are another way in which languages pervade the computing landscape. A NAnt script is written in a domain-specific language, for example. There are a set of symbols that NAnt understands (written as XML) and is able to interpret and execute to compile, test and deploy our applications for us.
But there's one kind of computing language that I think we've maybe overlooked. While a programmer like me or you uses a programming language to issue instructions to the computer, the users of our applications express their instructions through a user interface. A UI defines another kind of language, with symbols and gestures that have an underlying meaning - defined by the code that is executed when they invoke the symbols - and rules that govern their use.
Take drag and drop, for example. Selecting an image file in a folder and moving it to another folder, for example, is communicated through the user interface by clicking the mouse on that file, and dragging and dropping the file's image on to the target folder's icon.
That sequence of interactions with the user interface triggers code to be executed that - hopefully - does what the user expects to the objects inside the system. And with an effective user interface design, this process is intuitive enough that the user doesn't have to learn a completely new language that's alien to them. By using recognisable and meaningful symbols for files and folders, and relying on intuitive real-world gestures like pointing, selecting, dragging and dropping, the user interface can present users with a way to productively commune with their machine.
The same interactions could be expressed as, say, a FitNesse test, and we could use FitNesses as a kind of surrogate user interface. But FitNesse isn't as intuitive as, say, Windows Explorer, and would not be a suitable medium to have users interact with their software.
Having said that, the logic of these interactions - the semantics, if you like - would be identical. Which is why I'm becoming increasingly convinced that UI design should start by establishing the underlying semantics of the interactions and evolve towards a concrete syntax - an actual graphical users interface - which is driven by our understanding of the syntax-independent logic of how the software will be used.
One technique that I might even dare to call "Agile" might be to express user stories using FitNesse tests - or something similarly UI-agnostic - and then apply a graphical transformation to the tests. So where you see a type of object playing a specific role in an interaction, select or design a graphical icon for it that will be recognisable to the users. And when we have actions occuring to our objects, we can choose or design a gesture that would intuitively represent that action. (Like dragging and dropping.)
In your typical development process, this would mean that software driven by executable specifications would be created first, and then a user interface would be created after we'd established that the logic works.
Posted 2 weeks, 6 days ago on May 15, 2008 | <urn:uuid:b47de284-552b-4b47-b666-26c74893566a> | 2.734375 | 727 | Personal Blog | Software Dev. | 33.478774 | 95,614,636 |
SLAC Research Reveals Rapid DNA Changes that Act as Molecular Sunscreen
The molecular building blocks that make up DNA absorb ultraviolet light so strongly that sunlight should deactivate them – yet it does not. Now scientists have made detailed observations of a “relaxation response” that protects these molecules, and the genetic information they encode, from UV damage.
Thymine – the molecule in the foreground – is one of the four basic building blocks that make up the double helix of DNA. It’s such a strong absorber of ultraviolet light that the UV in sunlight should deactivate it, yet this does not happen. In a study reported in Nature Communications, researchers used an X-ray laser at SLAC National Accelerator Laboratory to make detailed observations of a “relaxation response” that protects these molecules, and the genetic information they encode, from UV damage. (Illustration by Greg Stewart/SLAC)
The experiment at the Department of Energy’s SLAC National Accelerator Laboratory focused on thymine, one of four DNA building blocks. Researchers hit thymine with a short pulse of ultraviolet light and used a powerful X-ray laser to watch the molecule’s response: A single chemical bond stretched and snapped back into place within 200 quadrillionths of a second, setting off a wave of vibrations that harmlessly dissipated the destructive UV energy.
The international research team reported the results June 23 in Nature Communications.
While protecting the genetic information encoded in DNA is vitally important, the significance of this result goes far beyond DNA chemistry, said Philip Bucksbaum, director of the Stanford PULSE Institute and a co-author of the report.
“The new tool the team developed for this study provides a new window on the motion of electrons that control all of chemistry,” he said. “We think this will enhance the value and impact of X-ray free-electron lasers for important problems in biology, chemistry and physics.”
Light Becomes Heat
Researchers had noticed years ago that thymine seemed resistant to damage from UV rays in sunlight, which cause sunburn and skin cancer. Theorists proposed that thymine got rid of the UV energy by quickly shifting shape. But they differed on the details, and previous experiments could not resolve what was happening.
The SLAC experiment took place at the Linac Coherent Light Source (LCLS), a DOE Office of Science user facility, whose bright, ultrashort X-ray laser pulses can see changes taking place at the level of individual atoms in quadrillionths of a second.
Scientists turned thymine into a gas and hit it with two pulses of light in rapid succession: first UV, to trigger the protective relaxation response, and then X-rays, to detect and measure the response.
“As soon as the thymine swallows the light, the energy is funneled as quickly as possible into heat, rather than into making or breaking chemical bonds,” said Markus Guehr, a DOE Early Career Program recipient and senior staff scientist at PULSE who led the study. “It’s like a system of balls connected by springs; when you elongate that one bond between two atoms and let it loose, the whole molecule starts to tremble.”
Ejected Electrons Signal Changes
The X-rays measured the relaxation response indirectly by stripping away some of the innermost electrons from atoms in the thymine molecule. This sets off a process known as Auger decay that ultimately ejects other electrons. The ejected electrons fly into a detector, carrying information about the nature and state of their home atoms.
By comparing the speeds of the ejected electrons before and after thymine was hit with UV, the researchers were able to pinpoint rapid changes in a single carbon-oxygen bond: It stretched when hit with UV light and shortened 200 quadrillionths of a second later, setting off vibrations that continued for billionths of a second.
“This is the first time we’ve been able to distinguish between two fundamental responses in the molecule – movements of the atomic nuclei and changes in the distribution of electrons – and time them within a few quadrillionths of a second,” said the paper’s first author, Brian McFarland, a postdoctoral researcher who has since moved from SLAC to Los Alamos National Laboratory.
Guehr said the team plans more experiments to further explore the protective relaxation response and extend the new method, called time-resolved Auger spectroscopy, into other scientific realms.
In addition to the Stanford PULSE Institute, which is a joint institute of SLAC and Stanford University, the study included researchers from LCLS, Stanford, the University of Perugia in Italy, Lawrence Berkeley National Laboratory, the University of Connecticut, Western Michigan University, the University of Gothenburg in Sweden, and UNIST in South Korea. Parts of the research were carried out at Berkeley Lab’s Advanced Light Source, a DOE Office of Science user facility. The work was funded by the DOE Office of Science, the Swedish Research Council, the Göran Gustafsson Foundation and the Knut and Alice Wallenberg Foundation.
Press Office Contact: Andrew Gordon, firstname.lastname@example.org, (650) 926-2282
SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, Calif., SLAC is operated by Stanford University for the U.S. Department of Energy's Office of Science.
The Stanford PULSE Institute is a joint institute of SLAC National Accelerator Laboratory and Stanford University. PULSE seeks to advance the frontiers of ultrafast science, with particular emphasis on research using SLAC's Linac Coherent Light Source (LCLS). For more information, please visit www.stanford.edu/group/pulse_institute.
SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
Andrew Gordon | Eurek Alert!
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...
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For the first time, astronomers have discovered a planet outside our solar system that is potentially habitable with Earth-like temperatures - a find researchers described Tuesday as a big step in the search for life in the universe.
The planet is just the right size, might have water in liquid form, and in galactic terms is relatively nearby at 120 trillion miles away. But the star it closely orbits, known as a "red dwarf," is much smaller, dimmer and cooler than our sun.
There is still a lot that is unknown about the new planet, which could be deemed inhospitable to life once more is known about it. And it is worth noting that scientists' requirements for habitability count Mars in that category: a size relatively similar to Earth's with temperatures that would permit liquid water. However, this is the first outside our solar system that meets those standards.
"It's a significant step on the way to finding possible life in the universe," said University of Geneva astronomer Michel Mayor, one of 11 European scientists on the team that found the planet. "It's a nice discovery. We still have a lot of questions." | <urn:uuid:615ee266-3928-46be-8ec7-a52b9c603e5f> | 3.734375 | 229 | News Article | Science & Tech. | 44.881576 | 95,614,654 |
Fruits of the sea: Startling strawberry crab discovered off Taiwan
A marine biologist has discovered a startling new crab species that resembles a large strawberry.
The unusual crustacean was found off the coast of southern Taiwan. It has a dramatic bright red shell covered with small white bumps.
A new species of crab has been found on a beach of Pingtung, southern Taiwan
Professor Ho Ping-ho from the National Taiwan Ocean University said the crab resembles a species called Neoliomera Pubescens, that lives in the areas around Hawaii, Polynesia and Mauritius.
However it has a clam-shaped shell about 1 inch wide, which makes it distinct.
Crabs are omnivores feeding primarily on algae. There are more than 5,000 known species in the world.
The crab was discovered by Professor Ho Ping-ho from National Taiwan Ocean University
Professor Ho said his team found two female crabs of the new species last
June off the coast of Kenting National Park, known for its rich marine
The crabs died shortly afterwards, possibly because the water in the area was polluted by a cargo ship that ran aground.
Taiwanese crab specialist Wang Chia-hsiang confirmed Professor Ho's finding.
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Pioneer Saturn Encounter
Publisher: NASA 1979
Number of pages: 45
The Pioneer 10 and 11 spacecraft made the first crossings of the asteroid belt and were the first to encounter Jupiter and its intense radiation belts. Pioneer 11 made the first flyby of Saturn almost a billion miles from Earth where it came within 13,300 miles of the cloud tops. Assembled in this publication is a selection of the pictures returned by Pioneer 11 of Saturn and its largest moon, Titan.
Home page url
Download or read it online for free here:
by Gerald P. Kuiper, et al. - Lunar and Planetary Institute
In the dawn of the Space Age, NASA undertook to find and assemble the very best images of the Moon it could find. In a project led by Gerard Kuiper, the best telescopic plates from observatories around the world were assembled into one compilation.
- 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.
by J. S. Lewis, M. S. Matthews - University of Arizona Press
Parts of the solar system that are most accessible from Earth are rich in materials of great potential value. Immediate uses of these resources to manufacture propellants, metals, and fluids can support future large-scale space activities.
by D.E. Hughes, J.K. Bowker - Lunar and Planetary Institute
This Atlas is considered the definitive reference manual to the global photographic coverage of the Moon. The images contained within the atlas are excellent for studying lunar morphology because they were obtained at low to moderate Sun angles. | <urn:uuid:3a4770da-0a48-4c8d-a539-b532575d6457> | 3.3125 | 355 | Content Listing | Science & Tech. | 46.519 | 95,614,677 |
This image from Hubble's Wide Field Camera 3 (WFC3) shows a section of NGC 1448, a spiral galaxy located about 50 million light-years from Earth in the little-known constellation of Horologium (The Pendulum Clock). We tend to think of spiral galaxies as massive and roughly circular celestial bodies, so this glittering oval does not immediately appear to fit the visual bill. What's going on?
Imagine a spiral galaxy as a circular frisbee spinning gently in space. When we see it face on, our observations reveal a spectacular amount of detail and structure -- a great example from Hubble is the telescope's view of Messier 51, otherwise known as the Whirlpool Galaxy.
However, the NGC 1448 frisbee is very nearly edge-on with respect to Earth, giving it an appearance that is more oval than circular. The spiral arms, which curve out from NGC 1448's dense core, can just about be seen.
Although spiral galaxies might appear static with their picturesque shapes frozen in space, this is very far from the truth.
The stars in these dramatic spiral configurations are constantly moving as they orbit around the galaxy's core, with those on the inside making the orbit faster than those sitting further out."
This makes the formation and continued existence of a spiral galaxy's arms something of a cosmic puzzle, because the arms wrapped around the spinning core should become wound tighter and tighter as time goes on -- but this is not what we see. This is known as the winding problem.
For Hubble's image of the Whirlpool Galaxy, visit:
Credit: European Space Agency
Rob Gutro | EurekAlert!
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A scientist looks through a microscope.
(photo credit: INGIMAGE)
An international team of biologists has identified the molecular signature of the animal kingdom, providing genetic evidence for an animal classification that has been used for nearly 300 years. Their research, just published in the prestigious journal Nature, offers a historic dataset for the field, serving developmental biologists, evolutionary biologists and computational biologists.
The study was led by biology Prof. Itai Yanai of the Technion-Israel Institute of Technology, in cooperation with research teams in Australia, Germany, the US and Israel. The research team investigated a diverse set of animal species, applying a powerful technique called CEL-Seq, developed in 2012 by Dr. Tamar Hashimshony in the Yanai lab. CEL-Seq makes it possible to monitor the activity of all genes in individual cells, and the team used it to analyze gene regulation in 70 embryos in each of 10 species.
The researchers found a striking pattern of universality across the species. Between phases of similar genes turned ‘on’ at the beginning and the end of development, a mid-developmental transition was discovered.
This new regulatory pattern explains how the differences among animals develop and evolve, which allows biology to now have molecular means to define the specific properties of groups of species.
Their work further defines a category of animal life that has been underdefined since 1735 when Swedish botanist Carl Linnaeus, recognized as the father of the biological classification of organisms, proposed a twoname classification system for the world’s plants. He also classified animals into “families” based on similarities and differences in body “plans.” The work offers new information on how, at the molecular and genetic levels, animals of different body designs – whether they have a true spinal column (mammals) or just a nerve cord (chordates) – have evolved to be different and why.
There are nearly eight million different species of animals around the globe that show striking diversity.
For example, animals span five orders of magnitude of adult body sizes. Yanai’s team launched this research by asking what is common to all animals. To tackle this question, they chose 10 of the most different animals one could choose – a fish, worm, fly, water bear, sponge and five others, each of a different phylum (a term coined by German naturalist Ernst Haeckel in the 19th century to describe a group of animals with the same body plan). About 35 phyla are typically recognized, however it remains controversial with contention over whether this is a meaningful classification and, if so, what attributes are the same, or different across all animals.
“We selected species representing 10 different animal phyla,” said Yanai. “For each phyla, we determined the gene expression profile of all genes from the development of the fertilized egg to the free-living larvae and found a surprising pattern of gene expression conservation in all species occurring at a pivotal, transitional period in development.”
By studying the molecular programs of development in 10 very different animals, the researchers found that all of the animals they studied express two distinct “modules” (a set of genes – similar across the organisms – that are turned “on”) of genetic expression.
During the transition between the modules, mechanisms of cell signaling and regulation occur.
With this new information, the researchers proposed a definition for phylum as “a set of species sharing the same signals and transcription factor networks during the mid-developmental transition.” In other words, they clarified the definition by suggesting that those organisms sharing a phylum, formerly by virtue of body design alone, also share a unique and similar genetic and molecular transition that other species do not.
To demonstrate their proposal, the researchers developed an “hourglass model” that captures gene expression differences between species. The inverse hourglass model shows the origin of phyla compared with the hourglass model that demonstrates “within phylum evolution.”
Embryonic development is called the “phylotypic” stage. This is when the embryo begins to assume recognizable features typical of vertebrates. The phylotypic stage represents a general layout on which specialized features – such as the turtle’s shell, the pig’s snout, or your large brain – can be mounted later in development.
The researchers proposed that during the transition period, properties specific to each phylum are genetically encoded. Their emerging dataset, they said, will be useful in studying the hallmarks of animal body plan formation from the embryonic stage.
As with many scientific discoveries, the researchers suggest that their work “raises more questions than it answers.” For example, “what molecular pathways underlie phyletic transition in each phylum? Why are the phyletic-transition mechanisms so relatively susceptible to change? Is the coupling of the conserved modules universal to all multicellular life?” “The transition we identified may be a hallmark of development only in animals,” the researchers concluded.
“Future work may show that this is a general characteristic of development in all multicellular organisms." | <urn:uuid:53196ecd-455a-44e3-97cc-100d525df474> | 3.90625 | 1,080 | News Article | Science & Tech. | 23.203475 | 95,614,696 |
New Innovatively-Designed low Cost Material To Combat
Air And Water Pollution
Study has produced a new material which could adsorb air and water pollutants and could be a low cost sustainable alternative to the currently used activated carbon
Pollution makes our planet’s land, water, air and other constituents of the environment dirty, unsafe and unsuitable to use. Pollution is caused by artificial introduction or entry of a contaminant(s) into a natural environment. Pollution is of various types; example land pollution is caused mostly by household discard or garbage and industrial waste by commercial companies. Water pollution is caused when foreign substances are introduced to water include chemicals, sewage water, pesticides and fertilizers or metals like mercury. Air pollution is caused by particles in the air from burning fuels, like soot, containing millions of tiny particles floating in the air. Another common type of air pollution is dangerous gases, such as sulphur dioxide, carbon monoxide, nitrogen oxides and chemical vapours. Also, air pollution can also take the form of greenhouse gases (such as carbon dioxide or sulphur dioxide) and aid the warming of our planet through greenhouse effect. Other type of pollution is noise pollution when the sound coming from planes, industry or other sources reaches harmful levels.
Despite major efforts that have been made over recent years to clean up the environment, pollution remains a major problem and poses continuing risks to health, affecting 200 million people worldwide. The problems are undeniably greatest in the developing world, where traditional sources of pollution such as industrial emissions, poor sanitation, inadequate waste management, contaminated water supplies and exposures to indoor air pollution from biomass fuels affect large numbers of people. Even in developed countries, however, environmental pollution persists, most especially amongst poorer sectors of society. Though the risks are generally higher in developing countries, where poverty, economical constraints for adopting technology and weak environmental laws combine to cause high pollution levels. This risk is further compounded by unsafe water, poor sanitation, poor hygiene and indoor air pollution. Pollution has detrimental effects on unborn and growing children, and life expectancy may be as low as 45 years because of cancers and other diseases. Air and water pollution is a silent killer and is thought to adversely affect our planet and in turn mankind. The air which we breathe has a very definite chemical composition which is 99 percent of nitrogen, oxygen, water vapor and inert gases. Air pollution occurs when things that aren’t normally added to the air. Particulate matter – solid particles and liquid droplets found in the air and emitted from power plants, industry, automobiles and fires – is now ubiquitous in cities and even suburban areas. Also, millions of tons of industrial effluents are released into the world’s waters every year. Both particulate matter and dyes are highly toxic to environment, ecosystem and to humanity.
Various methods and procedures are routinely used for tackling air and water pollution, including filtration, ion-exchange, coagulation, decomposition, adsorption etc and each of these methods exhibit different rates of success. When compared, adsorption is considered most feasible because of being simple, easy to operate, having high efficiency, convenience to use etc. Among the various adsorbents, in pollution abatement of air and waste water, activated carbon is the most commonly used adsorbent. Also called activated charcoal, it is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions. In fact, activated carbon is the gold standard in adsorbents. Carbon has a natural affinity for organic pollutants like benzene, which bind to its surface. If you “activate” carbon i.e. steam it at 1,800 degrees it forms little pores and pockets that increase its surface area. Pesticides, chloroform, and other contaminants slide into the holes of this honeycomb and hold fast. Also, no carbon remains in the water once it’s been thoroughly treated. Water treatment plants in developing countries like China and India routinely use activated carbon. Similarly, activated carbon has special properties which help in removing volatile compounds, odours, and other gaseous pollutants from the air. The way it works is quite straightforward. There are a few downsides of activated carbon, firstly it is very expensive and has a very short shelf life as it can only be used until its pores fill up – which is why you have to change the filter from time to time. Activated carbon is also difficult to regenerate and its effectiveness decreases over time. They are not effective at removing those contaminants which are either not attracted to carbons or pathogenic bacteria and viruses.
An economic and sustainable alternative
In a recent study published in Frontiers in Chemistry, researchers have a created an affordable low-cost and sustainable material for tackling air and water pollution. This new “green” porous material produced from solid wastes and abundant organic natural polymers looks very promising in terms of adsorbing pollutants in wastewater and air when compared to activated carbon and is being labelled as an “economical alternative”. This new “green” adsorbent is a combination of a naturally abundant raw material – a polysaccharide called sodium alginate which can be extracted from seaweed and algae– with an industrial by product – silica fume (by product of silicon metal alloy processing). It was synthesised very easily and consolidated by the gelling properties of alginate and by decomposition of sodium-bicarbonate controlled porosity at low temperatures at different scale lengths. For testing in the wastewater pollution, a blue dye was used as a model pollutant. It was seen that the new hybrid material adsorbed and removed the dye with efficiency of about 94 percent, which was very encouraging. Even very high concentrations of this dye were removed. This material displayed encouraging capabilities for trapping particulate matter from diesel exhaust fume. The study led by Dr. Elza Bontempi from the University of Brescia, Italy, concludes that this material was able to replace activated carbon very efficiently in its capability to capture both fine particulate matter in air and also organic pollutants in wastewater thus cutting down on the pollution.
This is exciting work, as this new material is produced in a very innovative and inexpensive manner from naturally abundant polymers and industrial waste by-product which is anyway is always discarded. This new material being termed as an “organic-inorganic hybrid” is not only low cost, it’s also sustainable and regenerable and could actually displace the activated carbon and become a preferred choice. It even consumed less energy when being produced (the “embodied” energy) and thus leaves a much lower carbon footprint. This material is also self-stabilizing and does not require a thermal treatment at high temperatures and also can be scaled up for different experimentation. Ongoing tests further indicate that it can be stored at ambient conditions and it only becomes more stable over time while not degrading at all. Thus, its highly versatile and could have a wide range of applications in air and water filtration. This generates huge hope for combating air and water pollution and protecting mother earth as well as mankind.
Alessandra Zanoletti, et al., 2019, ‘A New Porous Hybrid Material Derived From Silica Fume and Alginate for Sustainable Pollutants Reduction’, Frontiers in Chemistry, vol. 6, DOI: 10.3389/fchem.2018.00060
Vol.1 Issue 4 April 2018 | <urn:uuid:59fb849b-3a10-4dcf-80e9-f3ef9a78739a> | 3.78125 | 1,544 | Knowledge Article | Science & Tech. | 23.633412 | 95,614,711 |
IG reported that a new magmatic intrusion at Sierra Negra was heralded by a M 5.2 earthquake recorded at 1830 on 4 July, and followed by 68 events between M 1.1 and 3.9.
Seismic tremor began to be recorded at 1700 on 7 July by a station on the NE edge of the caldera.
At the same time satellite data showed an increase in the intensity of the thermal anomaly on NW flank (it had decreased the previous day).
Parque Nacional Galápagos staff confirmed strong incandescence in an area near the beach.
A weak plume of water vapor and ash rose as high as 3.3 km (10,800 ft) a.s.l.
and drifted SW and W.
Tremor continued to be registered on 8 July, though the amplitude gradually decreased.
Vapor-and-ash plumes reported by the Washington VAAC rose about 2 km (6,600 ft) a.s.l.
and drifted SW, and the thermal anomaly remained intense.
Gas clouds drifted 115 km W.
The current eruption at Sierra Negra began on 26 June and, according to news articles, prompted tourist restrictions and the evacuation of 50 residents.
Sources: BBC News,Instituto Geofísico-Escuela Politécnica Nacional (IG) | <urn:uuid:0a0f9d53-18be-4776-93aa-d11884fc57d5> | 2.84375 | 286 | News Article | Science & Tech. | 73.195876 | 95,614,721 |
The discovery of the electron in 1897 was followed just 14 years later by the discovery of the atomic nucleus in 1911. In 1913 Bohr proposed a model of the hydrogen atom in which the electron made perfectly circular orbits around the newly discovered nucleus (proton) only to see his theory replaced by Schrödinger’s more general theory, wave mechanics, in 1926. Wave mechanics has dominated the thinking of chemists ever since, but it has hardly been the last word on the matter. More subatomic particles have been discovered, and other forms of quantum mechanics have been suggested over the years (matrix mechanics, density functional theory, …) including theories (quantum electrodynamics, quantum chromodynamics, …) that go far beyond the simplistic thinking of chemists.
So what really happens when two electrons, or perhaps an electron and a positively charged nucleus, get really, really close to each other? Wave mechanics turns to Coulomb’s law for help, and Coulomb states that the force between these particles varies inversely with the square of the distance between them, that is, the force is proportional to 1/r^2. This would imply that the force (and the potential energy associated with it) approaches infinity as r approaches zero. This can lead to disturbing thoughts (what keeps electrons from ‘falling into’ the nucleus?) and disturbing mathematical problems (how do I work with a formula that busts its way to infinity?).
Nautilus recently emailed me an old article (“The Trouble with Theories of Everything”, 1 Oct 2015) that looks into these disturbing corners of science and concludes, “There is no known physics theory that is true at every scale—there may never be.” Coulomb’s law, wave mechanics, you name it – are designed to explained certain phenomena that appear on certain scales of time, space, energy, and so. It may be possible to extrapolate them to other scales successfully, but there are no guarantees. Caveat extrapolator!
throw yourself at anyone,
decked out in diamonds.
And that pretty much sums it up. Carbon is awesome.
Interested in seeing how the other elements fare when filtered through haiku paper? Check out Elemental Haiku (Science, 4 Aug 2017) or, even easier, find them in this interactive periodic table.
Note: element 119 has not been synthesized yet so the poet has already gone where no scientist has been (yet).
What’s so special about the sunlight during an eclipse? Isn’t it the same old sunlight we see the rest of the time?
Yes, it is, but because the event is so interesting to look at, and because the normally blinding solar disk is partly blocked out, the temptation is to look, and look, and look. See “Chemistry explains why you shouldn’t stare at the solar eclipse without proper protection” (C&ENews, print 21 Aug 2017, online 14 Aug 2017).
The article explains the photochemical events that trigger retinal damage (the “heat” of the sunlight is not to blame) and it describes several options for safe viewing of the Sun. Here’s a bit from the article: Continue reading
This web page will not be maintained during the 2017-18 academic year. All course-related materials should be obtained from the appropriate Moodle pages. This site will resume business in Fall, 2018.
A new article in Science magazine from Prof. Ayanna Thomas’ research group is one that every O Chem student should look at. The article doesn’t contain any chemistry, but it contains some potentially valuable insights into becoming a more successful O Chem student.
The DoJo will have drop-in tutoring available 7-9 PM for Chem 201 on Sat (12/10) and Mon (12/12).
Sam and Alan will also be in their offices for drop-in-consultation for much of Th/F/M/Tu/W, weather permitting.
Some of you may be suffering from FMOOWMP. You know the symptoms, but you probably didn’t know that help was close at hand. And it’s painless. Here’s a short video to bring you up-to-speed. https://youtu.be/yQq1-_ujXrM
I heard a presentation from a neuroscientist last week on how our brains work. She highlighted different brain networks that one can imagine working well in some situations (“keep an eye out for tigers and snakes”), but get corrupted into un-, even counter-productive activities in modern circumstances (“keep an eye out for tweets”). We all have these networks and we all live in a world filled with more, and more round-the-clock, stimuli than our ancestors could have ever imagined. Staying on task gets more challenging all the time. Here’s an article from the NY Times Education section that might offer some helpful insights and tips: How to Deal with Digital Distractions (Times, 1 Nov 2016).
You can also test your ability to resist distractions right now: try not clicking on this post from 2013, Like Ketchup on Sushi, that takes you to another Times article, How to Get an A- in Organic Chemistry.
What single thing must you do to learn organic chemistry? Sam and I have given you the answer several times: practice solving problems. But is that all you have to do? Can you just open the book to a problem, work on it, and learn organic chemistry? Maybe you can, maybe you can’t. Not all practice makes perfect.
Predicting the outcome of an “opposite side attack” SN2 reaction can be confusing at first, but animations can help. Check out the SN2 animation at chemtube3D.com. To operate the animation, find the drawing of the chemical reaction and click on the forward reaction arrow.
Try to understand the simple reaction from multiple perspectives: 1) the C seems to push its way through its 3 H neighbors to get from leaving group to nucleophile, OR 2) the 3 H neighbors seem to back away from the approaching nucleophile and move to the leaving group’s side of the molecule. You can rotate the animation as it plays so that you can see it from different angles.
Another SN2 animation to watch: HS(-) + (S)-PhCHClCH3 | <urn:uuid:a8e1c246-daf2-4ac4-a013-fadae1dd7612> | 3.453125 | 1,342 | Personal Blog | Science & Tech. | 55.603102 | 95,614,734 |
Once again I got an email from my online XML course. This week there were two topics covered – XSL and XSLT. Unfortunately the coverage of XSLT was very light. I think I have written about XSLT with a little more depth before. If not, it might be time for a little more study and a future post. This week starts with an understanding the XML itself is not concerned with display. That’s where XSL comes in.
XSL stands for eXtensible Stylesheet Language. This language contains formatting information for XML. The really interesting part is that XSL stylesheets are XML documents themselves. XSL was one of the first applications written in XML.
Cascading Style Sheets (CSS) define how XML looks in a web browser. They can also be applied to HMTL source as well. Finally the eXtensible Stylesheet Language for Transformations (XSLT) is a language which transforms XML into other formats. Any example would be to transforms XML to HTML. However you can choose other outputs formats, including XML itself.
The heart of XSLT is the use of templates. Now that I look back on my blog posts, I find that I did not cover XSLT in depth anywhere yet. I did see that I wrote myself a note about there being a follow on class to the hands on training I took previously. Maybe that will be a good candidate for me to take next year. Then I will be able to write at length about this complex topic. Until then be well.
Hot Topic Spamming Failures - I follow a friend into a Hot Topic store in the mall. Saw some cool merchandise. Decided to buy something. The salesperson asked me a bunch of questions, ... | <urn:uuid:83b5a27c-0090-4bba-a20b-37856d6f521a> | 2.78125 | 366 | Personal Blog | Software Dev. | 71.342325 | 95,614,741 |
In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if the object is much less massive than the largest body in the system, its speed relative to that largest body. The speed in this latter case may be relative to the surface of the larger body or relative to its center of mass.
The term can be used to refer to either the mean orbital speed, i.e. the average speed over an entire orbit, or its instantaneous speed at a particular point in its orbit. Maximum (instantaneous) orbital speed occurs at periapsis (perigee, perhelion, etc.), while minimum speed for objects in closed orbits occurs at apoapsis (aphelion, apogee, etc.). In ideal two-body systems, objects in open orbits continue to slow down forever as their distance to the barycenter increases.
When a system approximates a two-body system, instantaneous orbital speed at a given point of the orbit can be computed from its distance to the central body and the object's specific orbital energy. (Specific orbital energy is constant and independent of position.)
In the following, it is assumed that the system is a two-body system and the orbiting object has a negligible mass compared to the larger (central) object. In real-world orbital mechanics, it is the system's barycenter, not the larger object, which is at the focus.
Specific orbital energy = K.E. + P.E. (kinetic energy + potential energy). Since kinetic energy is always non-negative (greater than or equal to zero, >=0) and potential energy is always non-positive (less than or equal to zero,
The transverse orbital speed is inversely proportional to the distance to the central body because of the law of conservation of angular momentum, or equivalently, Kepler's second law. This states that as a body moves around its orbit during a fixed amount of time, the line from the barycenter to the body sweeps a constant area of the orbital plane, regardless of which part of its orbit the body traces during that period of time.
For orbits with small eccentricity, the length of the orbit is close to that of a circular one, and the mean orbital speed can be approximated either from observations of the orbital period and the semimajor axis of its orbit, or from knowledge of the masses of the two bodies and the semimajor axis.
where v is the orbital velocity, a is the length of the semimajor axis, T is the orbital period, and ?=GM is the standard gravitational parameter. This is an approximation that only holds true when the orbiting body is of considerably lesser mass than the central one, and eccentricity is close to zero.
When one of the bodies is not of considerably lesser mass see: Gravitational two-body problem
or assuming r equal to the body's radius
Where M is the (greater) mass around which this negligible mass or body is orbiting, and ve is the escape velocity.
For an object in an eccentric orbit orbiting a much larger body, the length of the orbit decreases with orbital eccentricity e, and is an ellipse. This can be used to obtain a more accurate estimate of the average orbital speed:
The mean orbital speed decreases with eccentricity.
For the precise orbital speed of a body at any given point in its trajectory, both the mean distance and the precise distance are taken into account:
where ? is the standard gravitational parameter, r is the distance at which the speed is to be calculated, and a is the length of the semi-major axis of the elliptical orbit. This expression is called the vis-viva equation. For the Earth at perihelion,
which is slightly faster than Earth's average orbital speed of 29,800 m/s, as expected from Kepler's 2nd Law.
the Earth's surface
|Speed||Orbital period||Specific orbital energy|
|Standing on Earth's surface at the equator (for comparison - not an orbit)||6,378 km||0 km||465.1 m/s (1,674 km/h or 1,040 mph)||23 h 56 min||-62.6 MJ/kg|
|Orbiting at Earth's surface (equator)||6,378 km||0 km||7.9 km/s (28,440 km/h or 17,672 mph)||1 h 24 min 18 sec||-31.2 MJ/kg|
|Low Earth orbit||6,600-8,400 km||200-2,000 km||circular orbit: 7.8-6.9 km/s (17,450-14,430 mph) respectively
elliptic orbit: 6.5-8.2 km/s respectively
|1 h 29 min - 2 h 8 min||-29.8 MJ/kg|
|Molniya orbit||6,900-46,300 km||500-39,900 km||1.5-10.0 km/s (3,335-22,370 mph) respectively||11 h 58 min||-4.7 MJ/kg|
|Geostationary||42,000 km||35,786 km||3.1 km/s (6,935 mph)||23 h 56 min||-4.6 MJ/kg|
|Orbit of the Moon||363,000-406,000 km||357,000-399,000 km||0.97-1.08 km/s (2,170-2,416 mph) respectively||27.3 days||-0.5 MJ/kg|
...the motion of planets along their elliptical orbits proceeds in such a way that an imaginary line connecting the Sun with the planet sweeps over equal areas of the planetary orbit in equal intervals of time. | <urn:uuid:6f1d4290-b938-4548-b8ac-03d1abdd6223> | 4.125 | 1,255 | Knowledge Article | Science & Tech. | 69.212935 | 95,614,806 |
Positional Relationship Between The Sun And Earth
Author: Source: Datetime: 2016-09-12 11:05:42
(1) with the celestial celestial coordinate system
Globe as an observer to any length (infinite) radius, on the distribution of all the celestial sphere is called the celestial chimney.
Through the center of the celestial sphere (ie, the observer's eye) and a plane perpendicular to the vertical line called goiter surface; the celestial horizon is divided into two hemispheres; the ground plane with the celestial sphere intersection line is a great circle, called the horizon circle; through the intersection of the vertical line and the center of the celestial sphere are called celestial zenith and nadir. Earth day around its own polar axis to revolve on its axis from west to east; conversely, assume the earth does not move, then the celestial sphere every day around its own axis from east to west rotation one week, we called diurnal motion . Sunday movement, there are two fixed points, called the north celestial pole and the south celestial pole, solar power generation the line connecting the two celestial axis on the celestial sphere is called day; through the center of the celestial sphere (ie, the observer's eye) and perpendicular to the axis of days flat surface called the celestial equator; the celestial equator and the celestial plane intersecting line is a great circle, called the celestial equator. By day and very zenith of the great circle called the meridian.
In 1: Define several celestial coordinate system and the polar circle (face) on the basis of the above, in order to study the position of celestial bodies on the celestial sphere and their laws of motion. The most commonly used are horizontal coordinate system and the equatorial coordinate system; the latter can be subdivided according to the different origin of the coordinate system and the angle was too equatorial coordinate system. The following highlights and design of solar cell applications related to horizontal coordinate system and when the angular coordinate system.
(2) horizontal coordinate system
In the horizon circle as the basic circle, zenith as the basic point, the southern point of the origin of the coordinate system is called the horizontal coordinate system, for a long time to make a great circle through the zenith and the sun (or any celestial body), called the horizon meridional; horizon Meridional cross horizon circle at point M; S from the origin along the horizon measured clockwise circle, arc SiW the horizon longitude, or azimuth a; arc of the horizon XAf latitude, or Gao degrees /1, up is positive, down is negative. Arc ZX called zenith distance, measured from 2 onwards, represented by Z. Obviously Z = 90 ° -1 due to the diurnal motion of celestial bodies there, so over time horizon coordinates of celestial bodies are constantly changing. In addition, solar power portable generator the coordinates of celestial horizon and also the position of the observer on the ground have a certain relationship, that horizon coordinate with the observation location to another.
(3) when the angular coordinates
These are just a brief introduction a little background knowledge related to astronomy. If you want to accurately calculate the sun Gao degrees, azimuth, H according to time and other data, but also need to understand the conversion between the coordinate solar power generator system of the above, it also involves time system, interested readers can find some information related to astronomy knowledge complement [2 ~ 6]. The authors provide a calculated solar elevation with lifePo4 batteries angle in the Appendix A, the azimuth sunshine time utilities, use this utility, the reader may not need to fully understand the relevant background knowledge of astronomy, the sun can also be calculated accurately Gao degree angle, azimuth, sunshine duration and other data.TAG: Deployment Fixed SMA Tesvolt Unlimited Volt Army Sonnen Multi-Storage Reliability Shell Manganese 200MW Ørsted Micro
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Bob Keefe already planned to spend about $20,000 to have a rooftop solar system installed at his four-bedroom house ... | <urn:uuid:140c4a80-0076-4c18-bff6-34b217d66c10> | 3.5 | 917 | Truncated | Science & Tech. | 27.779176 | 95,614,807 |
A No-Nonsense Introduction to General Relativity
by Sean M. Carroll
Number of pages: 24
General relativity has a reputation of being extremely difficult. This introduction is a very pragmatic affair, intended to give you some immediate feel for the language of General Relativity. It does not substitute for a deep understanding -- that takes more work.
Home page url
Download or read it online for free here:
by Benjamin Crowell - lightandmatter.com
This is an undergraduate textbook on general relativity. It is well adapted for self-study, and answers are given in the back of the book for almost all the problems. The ratio of conceptual to mathematical problems is higher than in most books.
by J.L. Jaramillo, E. Gourgoulhon - arXiv
We present an introduction to mass and angular momentum in General Relativity. After briefly reviewing energy-momentum for matter fields, first in the flat Minkowski case (Special Relativity) and then in curved spacetimes with or without symmetries.
by V. L. Kalashnikov - arXiv
The author presents the pedagogical introduction to relativistic astrophysics and cosmology, which is based on computational and graphical resources of Maple 6. The knowledge of basics of general relativity and differential geometry is supposed.
by Giampiero Esposito - arXiv
An attempt is made of giving a self-contained introduction to holomorphic ideas in general relativity, following work over the last thirty years by several authors. The main topics are complex manifolds, spinor and twistor methods, heaven spaces. | <urn:uuid:70e78474-1ae0-4b7a-b132-8443b2f9cf2a> | 2.671875 | 338 | Content Listing | Science & Tech. | 30.101447 | 95,614,823 |
Where God divides by zero
How do you study something that is, by definition, impossible to see? That’s the quandary faced by astrophysicists interested in black holes. The singularity itself – the point inside a black hole where the laws of physics break down – remains the most enigmatic monster in the astronomical bestiary. But as for the other properties of black holes – well, astrophysicists have learned lots about them. The key to unlocking the secrets of black holes is to look at them through X-ray telescopes.
KeywordsBlack Hole Neutron Star Event Horizon Accretion Disk White Dwarf
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Well, such an energy-efficient, self-propelling mechanism already exists in nature. The salp, a smallish, barrel-shaped organism that resembles a kind of streamlined jellyfish, gets everything it needs from the ocean waters to feed and propel itself. And, scientists believe its waste material may actually help remove carbon dioxide (CO2) from the upper ocean and the atmosphere.
Now, researchers at the Woods Hole Oceanographic Institution (WHOI) and MIT report that the half-inch to 5-inch-long creatures are even more efficient than had been believed. Reporting in the current issue of the Proceedings of the National Academy of Sciences, they have found that the ocean-dwelling salps are capable of capturing and eating extremely small organisms as well as larger ones, rendering them even hardier—and perhaps more plentiful—than had been thought.
"We had long thought that salps were about the most efficient filter feeders in the ocean,” said Laurence P. Madin, WHOI Director of Research and one of the investigators. “But these results extend their impact down to the smallest available size fraction, showing they consume particles spanning four orders of magnitude in size. This is like eating everything from a mouse to a horse."
Salps capture food particles, mostly phytoplankton, with an internal mucous filter net. Until now, it was thought that only particles as large as or larger than the 1.5-micron-wide holes in the mesh.
But a mathematical model suggested salps somehow might be capturing food particles smaller than that, said Kelly R. Sutherland, who wrote the paper as part of her PhD thesis at the MIT/WHOI Joint Program for graduate students. In the laboratory at WHOI, Sutherland and her colleagues offered salps food particles of three sizes: smaller, around the same size as, and larger than the mesh openings.
“We found that more small particles were captured than expected,” said Sutherland, now a postdoctoral researcher at Caltech. “When exposed to ocean-like particle concentrations, 80 percent of the particles that were captured were the smallest particles offered in the experiment."
This finding is important for a number of reasons. First, it helps explain how salps—which can exist either singly or in “chains” that may contain a hundred or more--are able to survive in the open ocean, their usual habitat, where the supply of larger food particles is low. Madin, who served as Sutherland’s advisor at WHOI, adds: “Their ability to filter the smallest particles may allow them to survive where other grazers can't.”
Second, and perhaps most significantly, it enhances the importance of the salps’ role in carbon cycling. As they eat small, as well as large, particles, “they consume the entire 'microbial loop' and pack it into large, dense fecal pellets,” Madin says.
The larger and denser the carbon-containing pellets, the sooner they sink to the ocean bottom. “This removes carbon from the surface waters,” says Sutherland, “and brings it to a depth where you won’t see it again for years to centuries.”
And the more carbon that sinks to the bottom, the more space there is for the upper ocean to accommodate carbon, hence limiting the amount that rises into the atmosphere as CO2, explains co-author Roman Stocker of MIT’s Department of Civil and Environmental Engineering .
“The most important aspect of this work is the very effective shortcut that salps introduce in the process of particle aggregation,” Stocker says. “Typically, aggregation of particles proceeds slowly, by steps, from tiny particles coagulating into slightly larger ones, and so forth.
“Now, the efficient foraging of salps on particles as small as a fraction of a micrometer introduces a substantial shortcut in this process, since digestion and excretion package these tiny particles into much larger particles, which thus sink a lot faster.”
This process starts with the mesh made of fine mucus fibers inside the salp’s hollow body. Salps, which can live for weeks or months, swim and eat in rhythmic pulses, each of which draws seawater in through an opening at the front end of the animal. The mesh captures the food particles, then rolls into a strand and goes into the gut, where it is digested.
It had been reasoned that the lower limit of particles captured by a salp was dictated by the size of the openings in the mesh (1.5 microns) In other words, particles smaller than the openings were expected to pass through the mesh. But the new results show that it can capture particles as small as 0.5 microns and smaller, because the particles stick to the mesh material itself in a process called direct interception, Sutherland says.
"Up to now it was assumed that very small cells or particles were eaten mainly by other microscopic consumers, like protozoans, or by a few specialized metazoan grazers like appendicularians,” said Madin. “This paper indicates that salps can eat much smaller organisms, like bacteria and the smallest phytoplankton, organisms that are numerous and widely distributed in the ocean."
As much as they are impressed with the practical implications involving carbon exchange, the scientists are captivated by the unique, almost magical performance of this natural undersea engine.
The work—funded by the National Science Foundation and the WHOI Ocean Life Institute--“does imply that salps are more efficient vacuum cleaners than we thought,” says Stocker. “Their amazing performance relies on a feat of bioengineering - the production of a nanometer-scale mucus net - the biomechanics of which still remain a mystery, adding to the fascination for and the interest in these animals.”
The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment.
Media Relations | Newswise Science News
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
16.07.2018 | Physics and Astronomy
16.07.2018 | Life Sciences
16.07.2018 | Earth Sciences | <urn:uuid:9f92203f-dea7-4ca4-b200-bd922f6b628e> | 3.953125 | 1,973 | Content Listing | Science & Tech. | 41.386646 | 95,614,873 |
Using an animal model, Penn researchers identify receptor in endothelial cells that is crucial for cardiovascular development
Congenital heart disease (CHD) is a leading cause of mortality in children worldwide. According to the American Heart Association, Congenital cardiovascular defects are present in about one percent of live births and are the most common malformations in newborns. Researchers from the University of Pennsylvania School of Medicine have recently identified new signaling pathways that may lead to a better understanding of how this deadly disease forms. Jonathan Epstein, MD, Associate Professor of Medicine and the study’s lead investigator, identified a receptor in endothelial cells (the cells that line blood vessels) that when interrupted in mice, results in CHD and defects in the growth and arrangement of blood vessels (patterning). "With the identification of this receptor, we hope to one day develop molecular medicines that will essentially steer developing blood vessels away from where they shouldn’t go," said Epstein.
This finding - published in the July 2004 issue of Developmental Cell - may lay the groundwork for discovering ways to diagnose and prevent CHD. In an accompanying article in Developmental Cell, Epstein and collaborators at the National Institutes of Health demonstrated the pathways that they have discovered are functional in diverse organisms, including fish. In the larger picture, the researchers suggest this work may be crucial in determining why blood vessels migrate to certain destinations in the body.
Ed Federico | EurekAlert!
World’s Largest Study on Allergic Rhinitis Reveals new Risk Genes
17.07.2018 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt
Plant mothers talk to their embryos via the hormone auxin
17.07.2018 | Institute of Science and Technology Austria
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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The world’s oceans and atmosphere work as a system, exchanging heat, moisture and gases. Changes in the temperature of sea surface affect atmospheric dynamics, which in turn influence the weather and climate. This is not a one-way process, however, because the atmosphere also affects the oceans and helps to drive ocean circulation, which plays an important role in moderating our climate.
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Degree/Major: Ph.D., Inorganic Chemistry, 1984, MIT
Curriculum vitae: SummersCV.email@example.com
Dave Summers investigates a wide range of chemical reactions that are either needed for life to begin, that may affect whether life can exist, or that might be used by scientists to recognize life elsewhere. For example he is looking at the reactions of nitrogen in the atmosphere of ancient Mars. Where did it go? Could it have provided nitrogen for the start of life on Mars?
It may be that vesicles, water filled “soap bubbles” that look something like cells, may have been important in the origin of life. Dave is looking at what reactions may occur inside these vesicles, and how they may related to things like the start of photosynthesis.
Life shows a preference for using the lighter isotope of carbon – carbon-12 – rather than the slightly heavier carbon-13 when it makes stuff out of carbon dioxide. Can we use this as a test for whether compounds were made by life? Or might inorganic reactions do the same thing? Dave is doing the hard work of examining how this same preference for lighter carbon might also be exhibited by completely inorganic reactions. By understanding how this can happen, he may keep future space missions from stumbling over a false claim of extraterrestrial biology. He is also interested in how we can test for such compounds as proteins or fatty acids to detect life, both in the lab and robotic missions. Dave doesn’t just assume we’ll just “know life when we see it.” He wants a better test than that.
David Summers, 1999. Sources and Sinks for Ammonia and Nitrite on the Early Earth and the Reaction of Nitrite with Ammonia Origins of Life and Evolution of the Biosphere29, 33-46.
David Summers, Narcinda Lerner, 1998. Ammonia from Iron(II) Reduction of Nitrite and the Strecker Synthesis: Do Iron(II) and Cyanide Interfere with Each Other? Origins of Life and Evolution of the Biosphere28, 1-11.
David Summers, Sherwood Chang, 1996. Experimental Results on the Prebiotic Fixation of Nitrogen Under a Neutral Atmosphere by Iron(II) Circumstellar Habitalbe Zones-Proceedings of the F
David Summers, Narcinda Lerner, 1996. Strecker Synthesis Using Ammonia from Iron(II) Reduction of Nitrite: Do Iron(II) and Cyanide Interfere with Each Other? Origins of Life and Evolution of the Biosphere26, 221-222.
David Summers, Sherwood Chang, 1993. Prebiotic Ammonia from Iron(II) Reduction of Nitrite on the Early Earth Nature365, 630-633. | <urn:uuid:b521016f-916c-49fc-9c6c-6bfc3905ad9e> | 2.734375 | 588 | About (Pers.) | Science & Tech. | 50.325962 | 95,614,895 |
Large areas of Mars' surface are covered by oxidative weathering products containing ferric and sulfate ions having analogies to terrestrial gossans derived from sulfide mineralization associated with iron-rich basalts. Chemical weathering of such massive and disseminated pyrrhotite-pentlandite assemblages and host basaltic rocks in the Martian environment could have produced metastable gossaniferous phases (limonite containing poorly crystalline hydrated ferric sulfates and oxyhydroxides, clay silicates and opal). Underlying groundwater, now permafrost on Mars, may still be acidic due to incomplete buffering reactions by wall-rock alteration of unfractured host rock. Such acidic solutions stabilize temperature-sensitive complex ions and sols which flocculate to colloidal precipitates at elevated temperatures. Sampling procedures of Martian regolith will need to be designed bearing in mind that the frozen permafrost may be corrosive and be stabilizing unique complex ions and sols of Fe, Al, Mg, Ni and other minor elements. | <urn:uuid:d3f89e85-5507-4b87-87f2-3b9f002d6920> | 3.09375 | 218 | Knowledge Article | Science & Tech. | -9.303448 | 95,614,904 |
The recycling of precious metals, for example, platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an ‘electrode-less’ process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling of industrial catalysts, including but not limited to platinum-based systems, more sustainable.
Platinum, as one of the most active and stable materials, is nowadays largely used as catalyst in automotive catalytic converters for purification of exhaust gases, in petrochemical industry for production of high octane gasoline and in proton exchange membrane (PEM) fuel cells to produce electricity from hydrogen, just to name a few applications1,2,3. Due to the increase in public and also government awareness of global warming and air pollution, especially the development of later sustainable energy technologies is soaring4. Due to a constant increase in demand, it is anticipated that platinum supply will soon not be able to match the needs of the global economy. It is, thus, likely to assume that the Pt supply will become a bottleneck for catalysts production due to its very low availability in natural ores, which are to a large extent found in South Africa5. Several states, for example, US, Japan and EU, have already recognized this risk and, consequently, for the past several years are actively involved in the design of new policies, and strategies to secure reliable and unhindered access to so-called critical raw materials (CRM). In this scenario, the chemistry of recycling of platinum and other CRMs from end-of-life products, also referred as urban-mining, will become more important than ever.
There are two types of metallurgical processes for extraction of Pt from oxide ores and end-of-use materials. Although the exact details of many of them are industrial intellectual property, they can be classified as either high-temperature technologies, also referred as pyrometallurgy, or, wet-chemistry-based technologies, that is, hydrometallurgy. The first category consists in melting scraps and separating the metals by weight. Generally, it requires large investments and high-energy consumption6,7,8. On the other hand, the second group is based on relatively cheaper chemical-leaching treatments, for instance, highly acidic solutions of strong oxidizing nature such as hot fuming aqua regia or pressurized alkaline cyanide solutions. Third possibility is referred as gas phase volatilization9,10. Generally speaking, these state-of-the-art Pt dissolution processes are already quite efficient and employed on the industrial scale6,7,8,11,12,13,14,15,16. Nevertheless, there is definitely room for improvement, as they suffer from several practical and environmental issues: use of toxic chemicals (lixiviants), release of hazardous gases (HCl vapour, Cl2, NOx, nitrosyl chloride and so on) and leaching residues, high reagents and equipment costs, use of concentrated acids, elevated temperatures, high pressures, consumption of chemicals and pollution of waste water and so on6,7,8. Therefore, a breakthrough in the chemistry of Pt recycling is needed for the whole process to become safer, more economical, sustainable and environmentally friendly. Interestingly, a few recent reports showed novel approaches based on organic solvents17 and ionic liquids18 for enhanced Pt dissolution. However, their environmental sustainability, economic viability and real industry compatibility is questionable.
Hydrometallurgical processes are essentially electrochemical in nature19. For instance, dissolution by aqua regia and, in general, all leaching techniques can be considered as a process analogous to electrochemical corrosion. In brief, mixing highly concentrated nitric and hydrochloric acid induces a homogeneous chemical reaction, where the nitric acid and the chlorine gas evolving in the freshly prepared mixture act as oxidizing agents, while the hydrochloric acid acts as complexing agent and prevents the formation of a passive layer. From an electrochemical point of view, the role of the oxidizing agents is to increase the Pt surface potential above the thermodynamic dissolution potential (ca. 1.2 V versus reversible hydrogen electrode (RHE) for Pt)20. Generally, these processes are however only effective at elevated temperatures and with continuous consumption of extremely concentrated acids, as, for example, aqua regia loses its activity relatively quickly due to the release of chlorine.
Platinum dissolution has been extensively studied by our group in relation to PEM fuel cell electrocatalysts stability. Although a complete understanding of this complex process has still not been achieved, several valuable insights have been gained recently. On the basis of our electrochemical perspective, in the current study we present a conceptually different chemical approach of dissolving Pt at substantially milder conditions compared with state-of-the-art processes. We utilize only low-concentrated hydrochloric acid (0.3 M, to provide a sufficient pH and presence of chlorides), atmospheric pressure, room temperature, and minimal amounts of gases like ozone and carbon monoxide. Specifically, our approach stands on the following crucial concepts: (i) transient platinum dissolution is an aggressive corrosion process that occurs upon oxidation and reduction of a Pt surface, also referred to as anodic and cathodic Pt dissolution21,22. Note that the dissolution at constant electrode potentials above the Pt dissolution onset, which could be compared with soaking in acid, is much lower compared with the transient process23,24,25; (ii) the rate of Pt transient dissolution is accelerated by the presence of chlorides and other halides. We show that, by slowing the process of Pt passivation, chlorides dramatically increase Pt dissolution during anodic and cathodic potential excursions and, at the same time, stabilize Pt ions in the solution25,26; and (iii) the presence of dissolved CO gas increases Pt cathodic dissolution due to strong Pt–CO interaction, which physically prevents any potential Pt redeposition27 that may occur when CO (or some other reducing species such as H2) oxidation potential gets below Pt depostition potential. The electrochemical potential of Pt, that is, the Galvani potential difference between metal surface/electrolyte, can be controlled by exposure to an appropriate gas, either oxidative or reductive in nature, most important, without the use of external potential control (potentiostat)28. Thus, the core of our approach is the so-called transient electrochemical dissolution21 process triggered by repetitive cycling between two gases, leading to an electrode-less-induced surface potential alteration (Fig. 1).
On-line electrode potentials and dissolution measurements
To demonstrate and explore the effectiveness of this new approach, we initially focus on a commercial Pt black catalytic system (transmission electron microscopy images in Supplementary Fig. 1). The study firstly verifies our conceptual framework by monitoring the electrode potentials and dissolution of Pt in the defined system of scanning flow cell (SFC)21,29. Second, the accumulated knowledge is transferred to the more application-relevant configuration of a small-scale reactor. We employ a SFC as an advanced three electrode electrochemical cell, in which the flowing electrolyte can be fed to different analytical equipment, for example, Inductively coupled plasma-mass spectrometer (ICP-MS)21,29 or online electrochemical mass spectrometer (OLEMS)30,31, to obtain time-resolved information on the dissolved ions and/or evolved gases during electrochemical reactions. Generally, the three electrode set-up would allow controlling the potential of the working electrode, for example, a polycrystalline surface or high-surface catalysts. However, in the present case, it is only employed to monitor the alteration of the surface potential, that is, the open circuit potential (OCP), upon exposure to gases. The OCP is a measure of the metal/solution potential difference and corresponds to the condition of equilibrium when both cathodic and anodic reactions have the same rate.
Figure 2a,b confirms the effect of different gases on the surface potential of Pt. In brief, ozone is effectively oxidizing Pt and adjusts the surface potential to slightly above 1.3 V versus RHE, where ozone reduction and oxygen/chlorine evolution are in equilibrium. In contrast, CO acts as a reductive agent that effectively reduces Pt-oxide and sets the potential to ca. 0.8 V versus RHE, the equilibrium between CO oxidation and reduction of residual oxygen. Note that as the OCP only reaches the onset potential of the anodic evolution reactions, the amount of hazardous gases (Cl2) evolved is minimal (see OLEMS data in Supplementary Fig. 2). Figure 2c,d clearly demonstrates the predominantly transient nature of Pt dissolution. The peaks of dissolved Pt exactly correspond to the induced shifts in surface potential, while the dissolution signal quickly drops close to the detection limit upon prolonged exposure to the gases. Figure 2a displays the OCP and Fig. 2c Pt dissolution profile for a cycle of 10 min O3 followed by 10 min CO purging. Figure 2b,d includes the dissolution profile upon three cycles of 3 min O3 and 3 min CO, showing that increasing the frequency of gas exchanges effectively enhances the dissolution yield in the same time interval more than twofolds, that is, from 4% to 9% of the total mass of the catalyst.
Lastly, it is interesting to observe that the extent of the dissolution is not only related to variations in potential, but also the nature of the oxidizing and reducing gases. Supplementary Fig. 3 reports the comparison of the Pt dissolution profiles for 3/3 min O3/CO cycles and the potentiostatically simulated OCP variations, showing a largely enhanced dissolution when the gases are employed. On one hand, the presence of carbon monoxide, as mentioned before, has the additional effect of preventing re-deposition of dissolved species during the surface reduction process. On the other hand, the presence of oxygen radicals related to ozone decomposition most likely have an aggravating effect on dissolution during the oxidation process.
Complete dissolution measurements
So far, the dissolution of Pt has been studied in the defined conditions of a three electrode assembly with the catalyst immobilized onto the working electrode in a flow-type electrochemical cell, which allowed us to analyse and understand the underlying fundamental dissolution processes. In a further step, the induced surface potential alteration approach was investigated in a more application-relevant system, that is, a small-scale batch-type reactor (Fig. 4). In this set-up, conversely to the SFC, the Pt black is present in larger quantities (10 mg) and not deposited on any electrode, but rather dispersed in 100 ml of 0.3 M HCl. Moreover, to further increase the amount of chlorides without having to increase the HCl concentration, the solution has been brought to 1 M NaCl (the effect of NaCl molarity on the dissolution yield is reported in Supplementary Fig. 4).
To provide a firm basis on this new system, we first confirmed and optimized our control over the electrochemical potential of the solution by in operando monitoring the OCP with a Pt wire electrode. Figure 3 displays the OCP variations induced by a sequence of 5/5 min O3/CO cycles, the optimized protocol for this system. The upper and lower potentials observed for the reactor are in complete agreement with generally expected processes of Pt oxidation and reduction (Supplementary Fig. 5).
Figure 4 demonstrates how effective the procedure in dissolving platinum can be, both visually and quantitatively. Figure 4a includes the concentration of dissolved Pt species in solution versus the number of O3/CO cycles (Supplementary Table 1). Clearly, 20 cycles are more than enough to completely dissolve 10 mg of Pt black. This result is further confirmed by Fig. 4b, showing a distinct evolution of the initial black suspension of metallic Pt black to a yellow-colored solution upon O3/CO cycling, which is a strong indication of the presence of hexachloroplatinic complex. Conversely, exposing the suspension solely to ozone is ineffective at these mild conditions and yields only 0.6% over the same timeframe (Fig. 4a). This is in complete agreement with a previous work by Viñals et al.32, showing that pure ozone treatment even in 6 M aqueous HCl solution is not strong enough to dissolve Pt. These findings are the direct confirmation of the effectiveness of our novel transient dissolution approach and completely agree with our proposed mechanism in Fig. 1.
Interestingly, a recent work by Lutsuzbaia et al.33 also utilizes the concept of Pt transient dissolution for recycling platinum from PEM fuel cells. A similar concept, however, with electrochemical pulsed wave methods was already used before34,35. Nevertheless, as they apply an external potential by means of a potentiostat, their approach requires electrical contact. Thus, it is limited to conductive catalytic systems deposited on electrodes. Provided that with our system, we easily dissolve state-of-the-art PEM catalysts within few cycles (Supplementary Fig. 6), O3/CO cycling has none of these limitations. As evidence, we have also extended the recycling of platinum and palladium contained in an end-of-life automotive catalytic converter, that is, 0.38 wt.% Pt and 0.24 wt.% Pd on a 99.32 wt.% honeycomb alumina support. Provided some small adjustments in the cycling protocol (Supplementary Fig. 7), Fig. 5 proves that within 35 cycles both metals are completely leached from the non-conductive support.
To conclude, the intention of this study is to present a completely new, environmentally friendly, safe, cheap, scalable and efficient hydrometallurgical concept of platinum leaching/recycling. We utilize the electrochemical transient dissolution mechanism by alternatively employing oxidative and reductive conditions without the use of external potential control (electrodes). The induced surface potential alteration approach opens up a whole new technology to leach and recycle platinum, respectively, from metal ores to end-of-life products at much milder and safer conditions than current state-of-the-art processes. We prove on a fundamental level a complete new concept for Pt chemistry and we pave the way to further engineering optimization like different samples pretreatment, choice of gases (for example, H2 and syngas,), gas flows, pH (alkaline electrolytes), concentrations of chlorides or some other lixiviants (for example, Br−and I−), hydrodynamic conditions, reactor design, degassing and so on. Finally, as also other noble metals exhibit major transient dissolution36, we strongly believe the same concept can be applied for the recycling of other CRMs, including the ones out of reach for aqua regia, that is, Ru37,38, Ir39 and Os20, which are in addition to Pt also included in our recent German patent application (app. no.: 10 2015 118 279.3).
Scanning flow cell
The online monitoring of dissolution was achieved by coupling a SFC with an ICP-MS (NexION 300X, Perkin Elmer) with a flow of 180 μl min−1. The catalyst films for analysis with the fully automated SFC system were deposited with a drop-on-demand printer (Nano-PlotterTM 2.0, GeSim) in the form of circular spots of ca. 500 μm in diameter onto a glassy carbon substrate. The electrolyte flowing through the SFC is mixed downstream with an internal standard (186Re, 10 p.p.b.) in a Y-connector and the resulting electrolyte stream is continuously fed into the ICP-MS, where the dissolved metal ions during the electrochemical treatment are detected online. Coupling of SFC-OLEMS, as a combinatorial technique combines the parameter screening abilities of the SFC with the possibility for direct detection of volatile products and their correlation to applied potentials or currents. A mass spectrometer with electron impact ionization method is connected to the SFC over a porous Teflon membrane with a pore size of 20 nm that is positioned 50–100 μm above the catalysts surface and is therefore in a region of high product concentration. The small distance between the membrane and the electrode, because of that not only results in good sensitivity, but also leads to a fast response time between 1 and 3 s that is mainly determined by the diffusion coefficient of the analysed species. The system allows the simultaneous semi quantitative detection of several products and is therefore well suited for the parallel measurement of oxygen and chlorine.
A laboratory 250 ml glass beaker with 100 ml of deionized water, 6 g of NaCl (1 M) and 3 ml of 30% HCl (0.3 M). The solution is stirred with a Teflon covered magnetic stirrer (3 cm) at 1,000 r.p.m. The ozone is on-site produced with a concentration of 70 g per m3 of O2 by an ozone generator (Innotec OGVi-8G Lab) and purged with a flow of 1 l min−1, while carbon monoxide is purged with a flow of 56 ml min−1. The dissolution yield is measured by sampling and filtering small amounts of the solution at every five-cycle interval. The diluted samples were then fed to either an ICP-MS or ICP-OES depending on the concentration. The OCP was measured by immersing a Pt wire as working electrode, graphite rod as counter electrode and Ag/AgCl as reference electrode and simply tracking the potential by setting current to zero. To avoid interference with the leaching yield results, the in operando OCP (Fig. 3) and Pt black dissolution (Fig. 4) measurements have been carried out in different batch reactors under the same identical conditions.
All relevant data are available from the authors on request.
How to cite this article: Hodnik, N. et al. Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution. Nat. Commun. 7, 13164 doi: 10.1038/ncomms13164 (2016).
This research was supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme. | <urn:uuid:d9f91a70-c68e-4cbe-bb8c-c4b310e66181> | 3.21875 | 3,911 | Academic Writing | Science & Tech. | 27.659659 | 95,614,917 |
Lie bracket of vector fields
In the mathematical field of differential topology, the Lie bracket of vector fields, also known as the Jacobi–Lie bracket or the commutator of vector fields, is an operator that assigns to any two vector fields X and Y on a smooth manifold M a third vector field denoted [X, Y].
Conceptually, the Lie bracket [X, Y] is the derivative of Y along the flow generated by X. A generalization of the Lie bracket is the Lie derivative, which allows differentiation of any tensor field along the flow generated by X. The Lie bracket [X, Y] equals the Lie derivative of the vector Y (which is a tensor field) along X, and is sometimes denoted (read "the Lie derivative of Y along X").
The Lie bracket plays an important role in differential geometry and differential topology, for instance in the Frobenius theorem, and is also fundamental in the geometric theory for nonlinear control systems (Isaiah 2009, pp. 20–21, nonholonomic systems; Khalil 2002, pp. 523–530, feedback linearization).
There are three conceptually different but equivalent approaches to defining the Lie bracket:
Vector fields as derivations
Each vector field X on a smooth manifold M may be regarded as a differential operator acting on smooth functions on M. Indeed, each smooth vector field X becomes a derivation on the smooth functions C∞(M) when we define X(f) to be the element of C∞(M) whose value at a point p is the directional derivative of f at p in the direction X(p). Furthermore, it is known that any derivation on C∞(M) arises in this fashion from a uniquely determined smooth vector field X.
In general, the commutator of any two derivations and is again a derivation. This can be used to define the Lie bracket of vector fields as follows.
The Lie bracket, [X, Y], of two smooth vector fields X and Y is the smooth vector field [X, Y] such that
Flows and limits
or in terms of the Lie derivative
which is also equivalent to
Though neither definition of the Lie bracket depends on a choice of coordinates, in practice one often wants to compute the bracket with respect to a coordinate system.
If we have picked a coordinate chart on M with local coordinate functions , and we write for the associated local basis for the tangent bundle, then the vector fields can be written as
with smooth functions and . Then the Lie bracket is given by
If M is (an open subset of) Rn, then the vector fields X and Y can be written as smooth maps of the form and , and the Lie bracket is given by
where and are the Jacobian matrices of and , respectively. These n-by-n matrices are multiplied by the n-vectors X and Y.
The Lie bracket of vector fields equips the real vector space of all vector fields on M (i.e., smooth sections of the tangent bundle of ) with the structure of a Lie algebra, i.e., [·,·] is a map with the following properties
An immediate consequence of the second property is that for any .
Furthermore, there is a "product rule" for Lie brackets. Given a smooth real-valued function f defined on M and a vector field Y on M, we have a new vector field fY, defined by multiplying the vector Yx with the number f(x), at each point x ∈ M. The Lie bracket of X and fY is then given by
where on the right-hand side we multiply the function X(f) with the vector field Y, and the function f with the vector field [X, Y]. This turns the vector fields with the Lie bracket into a Lie algebroid.
We also have the following fact:
iff the flows of X and Y commute locally, i.e. iff for every x ∈ M and all sufficiently small real numbers s, t we have .
For a Lie group G, the corresponding Lie algebra is the tangent space at the identity, which can be identified with the left invariant vector fields on G. The Lie bracket of the Lie algebra is then the Lie bracket of the left invariant vector fields, which is also left invariant.
For a matrix Lie group, smooth vector fields can be locally represented in the corresponding Lie algebra. Since the Lie algebra associated with a Lie group is isomorphic to the group's tangent space at the identity, elements of the Lie algebra of a matrix Lie group are also matrices. Hence the Jacobi–Lie bracket corresponds to the usual commutator for a matrix group:
where juxtaposition indicates matrix multiplication.
As mentioned above, the Lie derivative can be seen as a generalization of the Lie bracket. Another generalization of the Lie bracket (to vector-valued differential forms) is the Frölicher–Nijenhuis bracket.
- Hazewinkel, Michiel, ed. (2001) , "Lie bracket", Encyclopedia of Mathematics, Springer Science+Business Media B.V. / Kluwer Academic Publishers, ISBN 978-1-55608-010-4
- Isaiah, Pantelis (2009), "Controlled parking [Ask the experts]", IEEE Control Systems Magazine, 29 (3): 17–21, 132, doi:10.1109/MCS.2009.932394
- Khalil, H.K. (2002), Nonlinear Systems (3rd ed.), Upper Saddle River, NJ: Prentice Hall, ISBN 0-13-067389-7
- Kolář, I., Michor, P., and Slovák, J. (1993), Natural operations in differential geometry, Springer-Verlag Extensive discussion of Lie brackets, and the general theory of Lie derivatives.
- Lang, S. (1995), Differential and Riemannian manifolds, Springer-Verlag, ISBN 978-0-387-94338-1 For generalizations to infinite dimensions.
- Lewis, Andrew D., Notes on (Nonlinear) Control Theory (PDF)[permanent dead link]
- Warner, Frank (1983) , Foundations of differentiable manifolds and Lie groups, New York-Berlin: Springer-Verlag, ISBN 0-387-90894-3 | <urn:uuid:328828ef-732b-4081-9ba2-1e7d700587ea> | 3.09375 | 1,337 | Knowledge Article | Science & Tech. | 59.681233 | 95,614,944 |
1. Use the theorem below to determine the number of nonequivalent colorings of the corners of a rectangle that is not a square with the colors red and blue. Do the same with p colors.
(the answer is (p^4+3p^2)/4...i just dont know how to get there)
Theorem: Let G be a group of permutations of X and let C be a set of colorings of X such that f * c is in C for all f in G and all c in C. Then the number N(G,C) of nonequivalent colorings in C is given by
N(G,C) = (1/absG)∑(abs(C(f)), (in words the number of nonequivalent colorings in C equals the average of the number of colorings fixed by the permutations in G)
2. A two-sided marked domino is a piece consisting of two squares joined along an edge where each square on both sides of the piece is marked with 0,1,2,3,4,5 or 6 dots.
a. use the theorem above to determine the number of different two sided marked dominoes.
b. how many different two sided marked dominoes are there if we are allowed to mark the squares with 0,1,...p-1 or p dots?
( the answer to 2a the group of permutation now consists of four permutations of the four squares to be marked. This gives (7^4+3*7^2)/4=637...i just dont know how to get there)© BrainMass Inc. brainmass.com July 15, 2018, 7:24 pm ad1c9bdddf
1. For 2 colors, we can easily list all the choices.
Filling it with just reds or blues can be done in only 1 way. So, this gives 2.
Filling with 3 reds and 1 blue or 3 blues and 1 red can also be done only 1 way. This gives 2.
With 2 reds and 2 blues, we have only 3 ways to do it.
1. Both reds and both blues on the longer side of the rectangle.
2. Both reds and both blues on the shorter side of the rectangle.
3. Reds and blues that are diagonally opposite to one another.
This counts to 3.
Thus, total = 2 + 2 +3 = 7.
We first determine the number of different permutations of the vertices of the ...
1. How to calculate the number of non-equivalent colorings of a rectangle?
2. How to calculate the number of non-equivalent markings of a domino? | <urn:uuid:a884ca29-dd16-4211-af98-c19b512d8704> | 3.328125 | 573 | Q&A Forum | Science & Tech. | 92.402268 | 95,614,959 |
Biological membrane(Redirected from Membrane-bound)
A biological membrane or biomembrane is an enclosing or separating membrane that acts as a selectively permeable barrier within living things. Biological membranes, in the form of eukaryotic cell membranes, consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions. The bulk of lipid in a cell membrane provides a fluid matrix for proteins to rotate and laterally diffuse for physiological functioning. Proteins are adapted to high membrane fluidity environment of lipid bilayer with the presence of an annular lipid shell, consisting of lipid molecules bound tightly to surface of integral membrane proteins. The cell membranes are different from the isolating tissues formed by layers of cells, such as mucous membranes, basement membranes, and serous membranes.
The lipid bilayer consists of two layers- an outer leaflet and an inner leaflet. The components of bilayers are distributed unequally between the two surfaces to create asymmetry between the outer and inner surfaces. This asymmetric organization is important for cell functions such as cell signaling. The asymmetry of the biological membrane reflects the different functions of the two leaflets of the membrane. As seen in the fluid membrane model of the phospholipid bilayer, the outer leaflet and inner leaflet of the membrane are asymmetrical in their composition. Certain proteins and lipids rest only on one surface of the membrane and not the other.
• Both the plasma membrane and internal membranes have cytosolic and exoplasmic faces • This orientation is maintained during membrane trafficking – proteins, lipids, glycoconjugates facing the lumen of the ER and Golgi get expressed on the extracellular side of the plasma membrane. In eucaryotic cells, new phospholipids are manufactured by enzymes bound to the part of the endoplasmic reticulum membrane that faces the cytosol. These enzymes, which use free fatty acids as substrates, deposit all newly made phospholipids into the cytosolic half of the bilayer. To enable the membrane as a whole to grow evenly, half of the new phospholipid molecules then have to be transferred to the opposite monolayer. This transfer is catalyzed by enzymes called flippases. In the plasma membrane, flippases transfer specific phospholipids selectively, so that different types become concentrated in each monolayer.
Using selective flippases is not the only way to produce asymmetry in lipid bilayers, however. In particular, a different mechanism operates for glycolipids—the lipids that show the most striking and consistent asymmetric distribution in animal cells.
The biological membrane is made up of lipids with hydrophobic tails and hydrophilic heads. The hydrophobic tails are hydrocarbon tails whose length and saturation is important in characterizing the cell. Lipid rafts occur when lipid species and proteins aggregate in domains in the membrane. These help organize membrane components into localized areas that are involved in specific processes, such as signal transduction.
Red blood cells, or erythrocytes, have a unique lipid composition. The bilayer of red blood cells is composed of cholesterol and phospholipids in equal proportions by weight. Erythrocyte membrane plays a crucial role in blood clotting. In the bilayer of red blood cells is phosphatidylserine. This is usually in the cytoplasmic side of the membrane. However, it is flipped to the outer membrane to be used during blood clotting.
Phospholipid bilayers contain different proteins. These membrane proteins have various functions and characteristics and catalyze different chemical reactions. Integral proteins span the membranes with different domains on either side. Integral proteins hold strong association with the lipid bilayer and cannot easily become detached. They will dissociate only with chemical treatment that breaks the membrane. Peripheral proteins are unlike integral proteins in that they hold weak interactions with the surface of the bilayer and can easily become dissociated from the membrane. Peripheral proteins are located on only one face of a membrane and create membrane asymmetry.
|FUNCTIONAL CLASS||PROTEIN EXAMPLE||SPECIFIC FUNCTION|
|Transporters||Na+ Pump||actively pumps Na+ out of cells and K+ in|
|Anchors||integrins||link intracellular actin filaments to extracellular matrix proteins|
|Receptors||platelet-derived growth factor receptor||binds extracellular PDGF and, as a consequence, generates intracellular signals that cause the cell to grow and divide|
|Enzymes||adenylyl cyclase||catalyzes the production of intracellular signaling molecule cyclic AMP in response to extracellular signals|
Oligosaccharides are sugar containing polymers. In the membrane, they can be covalently bound to lipids to form glycolipids or covalently bound to proteins to form glycoproteins. Membranes contain sugar-containing lipid molecules known as glycolipids. In the bilayer, the sugar groups of glycolipids are exposed at the cell surface, where they can form hydrogen bonds. Glycolipids provide the most extreme example of asymmetry in the lipid bilayer. Glycolipids perform a vast number of functions in the biological membrane that are mainly communicative, including cell recognition and cell-cell adhesion. Glycoproteins are integral proteins. They play an important role in the immune response and protection.
The phospholipid bilayer is formed due to the aggregation of membrane lipids in aqueous solutions. Aggregation is caused by the hydrophobic effect, where hydrophobic ends come into contact with each other and are sequestered away from water. This arrangement maximises hydrogen bonding between hydrophilic heads and water while minimising unfavorable contact between hydrophobic tails and water. The increase in available hydrogen bonding increases the entropy of the system, creating a spontaneous process.
Biological molecules are amphiphilic or amphipathic, i.e. are simultaneously hydrophobic and hydrophilic. The phospholipid bilayer contains charged hydrophilic headgroups, which interact with polar water. The lipids also contain hydrophobic tails, which meet with the hydrophobic tails of the complementary layer. The hydrophobic tails are usually fatty acids that differ in lengths. The interactions of lipids, especially the hydrophobic tails, determine the lipid bilayer physical properties such as fluidity.
Membranes in cells typically define enclosed spaces or compartments in which cells may maintain a chemical or biochemical environment that differs from the outside. For example, the membrane around peroxisomes shields the rest of the cell from peroxides, chemicals that can be toxic to the cell, and the cell membrane separates a cell from its surrounding medium. Peroxisomes are one form of vacuole found in the cell that contain by-products of chemical reactions within the cell. Most organelles are defined by such membranes, and are called "membrane-bound" organelles.
Probably the most important feature of a biomembrane is that it is a selectively permeable structure. This means that the size, charge, and other chemical properties of the atoms and molecules attempting to cross it will determine whether they succeed in doing so. Selective permeability is essential for effective separation of a cell or organelle from its surroundings. Biological membranes also have certain mechanical or elastic properties that allow them to change shape and move as required.
Particles that are required for cellular function but are unable to diffuse freely across a membrane enter through a membrane transport protein or are taken in by means of endocytosis, where the membrane allows for a vacuole to join onto it and push its contents into the cell. Many types of specialized plasma membranes can separate cell from external environment: apical, basolateral, presynaptic and postsynaptic ones, membranes of flagella, cilia, microvillus, filopodia and lamellipodia, the sarcolemma of muscle cells, as well as specialized myelin and dendritic spine membranes of neurons. Plasma membranes can also form different types of "supramembrane" structures such as caveolae, postsynaptic density, podosome, invadopodium, desmosome, hemidesmosome, focal adhesion, and cell junctions. These types of membranes differ in lipid and protein composition.
Distinct types of membranes also create intracellular organelles: endosome; smooth and rough endoplasmic reticulum; sarcoplasmic reticulum; Golgi apparatus; lysosome; mitochondrion (inner and outer membranes); nucleus (inner and outer membranes); peroxisome; vacuole; cytoplasmic granules; cell vesicles (phagosome, autophagosome, clathrin-coated vesicles, COPI-coated and COPII-coated vesicles) and secretory vesicles (including synaptosome, acrosomes, melanosomes, and chromaffin granules). Different types of biological membranes have diverse lipid and protein compositions. The content of membranes defines their physical and biological properties. Some components of membranes play a key role in medicine, such as the efflux pumps that pump drugs out of a cell.
The hydrophobic core of the phospholipid bilayer is constantly in motion because of rotations around the bonds of lipid tails. Hydrophobic tails of a bilayer bend and lock together. However, because of hydrogen bonding with water, the hydrophilic head groups exhibit less movement as their rotation and mobility are constrained. This results in increasing viscosity of the lipid bilayer closer to the hydrophilic heads.
Below a transition temperature, a lipid bilayer loses fluidity when the highly mobile lipids exhibits less movement becoming a gel-like solid. The transition temperature depends on such components of the lipid bilayer as the hydrocarbon chain length and the saturation of its fatty acids. Temperature-dependence fluidity constitutes an important physiological attribute for bacteria and cold-blooded organisms. These organisms maintain a constant fluidity by modifying membrane lipid fatty acid composition in accordance with differing temperatures.
In animal cells, membrane fluidity is modulated by the inclusion of the sterol cholesterol. This molecule is present in especially large amounts in the plasma membrane, where it constitutes approximately 20% of the lipids in the membrane by weight. Because cholesterol molecules are short and rigid, they fill the spaces between neighboring phospholipid molecules left by the kinks in their unsaturated hydrocarbon tails. In this way, cholesterol tends to stiffen the bilayer, making it more rigid and less permeable.
For all cells, membrane fluidity is important for many reasons. It enables membrane proteins to diffuse rapidly in the plane of the bilayer and to interact with one another, as is crucial, for example, in cell signaling. It permits membrane lipids and proteins to diffuse from sites where they are inserted into the bilayer after their synthesis to other regions of the cell. It allows membranes to fuse with one another and mix their molecules, and it ensures that membrane molecules are distributed evenly between daughter cells when a cell divides. If biological membranes were not fluid, it is hard to imagine how cells could live, grow, and reproduce.
- Murate, Motohide; Kobayashi, Toshihide. "Revisiting transbilayer distribution of lipids in the plasma membrane". Chemistry and Physics of Lipids. 194: 58–71. doi:10.1016/j.chemphyslip.2015.08.009.
- Nickels, Jonathan D.; Smith, Jeremy C.; Cheng, Xiaolin. "Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes". Chemistry and Physics of Lipids. 192: 87–99. doi:10.1016/j.chemphyslip.2015.07.012.
- Chong, Zhi-Soon; Woo, Wei-Fen; Chng, Shu-Sin (2015-12-01). "Osmoporin OmpC forms a complex with MlaA to maintain outer membrane lipid asymmetry in Escherichia coli". Molecular Microbiology. 98 (6): 1133–1146. doi:10.1111/mmi.13202. ISSN 1365-2958. PMID 26314242.
- Forrest, Lucy R. (2015-01-01). "Structural Symmetry in Membrane Proteins". Annual Review of Biophysics. 44 (1): 311–337. doi:10.1146/annurev-biophys-051013-023008. PMC . PMID 26098517.
- Alberts, Bray, Hopkin, Johnson, Lewis, Raff, Roberts, Walter, Bruce, Dennis, Karen, Alexander, Julian, Martin, Keith, Peter (2010). Essential Cell Biology third edition. 270 Madison Avenue, New York, NY 10016, USA, and 2 Park Square, Milton Park, Abingdon, OX14 4RN, UK: Garland Science, Taylor & Francis Group, LLC, an informa business. p. 370. ISBN 978-0815341291.
- Voet, Donald (2012). Fundamentals of Biochemistry: Life at the Molecular Level (4 ed.). Wiley. ISBN 978-1118129180.
- Dougherty, R. M.; Galli, C.; Ferro-Luzzi, A.; Iacono, J. M. (1987-02-01). "Lipid and phospholipid fatty acid composition of plasma, red blood cells, and platelets and how they are affected by dietary lipids: a study of normal subjects from Italy, Finland, and the USA". The American Journal of Clinical Nutrition. 45 (2): 443–455. ISSN 0002-9165. PMID 3812343.
- Lentz, Barry R. (2003-09-01). "Exposure of platelet membrane phosphatidylserine regulates blood coagulation". Progress in Lipid Research. 42 (5): 423–438. doi:10.1016/s0163-7827(03)00025-0. ISSN 0163-7827. PMID 12814644.
- Lein, Max; deRonde, Brittany M.; Sgolastra, Federica; Tew, Gregory N.; Holden, Matthew A. (2015-11-01). "Protein transport across membranes: Comparison between lysine and guanidinium-rich carriers". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1848 (11, Part A): 2980–2984. doi:10.1016/j.bbamem.2015.09.004.
- Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2002-01-01). "The Lipid Bilayer".
- Daubenspeck, James M.; Jordan, David S.; Simmons, Warren; Renfrow, Matthew B.; Dybvig, Kevin (2015-11-23). "General N-and O-Linked Glycosylation of Lipoproteins in Mycoplasmas and Role of Exogenous Oligosaccharide". PLoS ONE. 10 (11): e0143362. doi:10.1371/journal.pone.0143362. PMC . PMID 26599081.
- Vitrac, Heidi; MacLean, David M.; Jayaraman, Vasanthi; Bogdanov, Mikhail; Dowhan, William (2015-11-10). "Dynamic membrane protein topological switching upon changes in phospholipid environment". Proceedings of the National Academy of Sciences. 112 (45): 13874–13879. doi:10.1073/pnas.1512994112. ISSN 0027-8424. PMC . PMID 26512118.
- Rojko, Nejc; Anderluh, Gregor (2015-12-07). "How Lipid Membranes Affect Pore Forming Toxin Activity". Accounts of Chemical Research. 48: 3073–3079. doi:10.1021/acs.accounts.5b00403. | <urn:uuid:a44c49a6-c3f6-4e4a-899d-c0e7c17b8f7a> | 4.0625 | 3,478 | Knowledge Article | Science & Tech. | 35.2032 | 95,614,961 |
Washington: The creation of a 3-D nanocone-based solar cell platform has allowed a team of scientists to boost the light-to-power conversion efficiency of photovoltaics by nearly 80 percent.
The team led by Oak Ridge National Laboratory`s Jun Xu discovered the technology substantially overcomes the problem of poor transport of charges generated by solar photons.
These charges, negative electrons and positive holes, typically become trapped by defects in bulk materials and their interfaces and degrade performance.
"To solve the entrapment problems that reduce solar cell efficiency, we created a nanocone-based solar cell, invented methods to synthesize these cells and demonstrated improved charge collection efficiency," Xu, a member of ORNL`s Chemical Sciences Division, said.
The new solar structure consists of n-type nanocones surrounded by a p-type semiconductor. The n-type nanoncones are made of zinc oxide and serve as the junction framework and the electron conductor.
The p-type matrix is made of polycrystalline cadmium telluride and serves as the primary photon absorber medium and hole conductor.
With this approach at the laboratory scale, Xu and colleagues were able to obtain a light-to-power conversion efficiency of 3.2 percent compared to 1.8 percent efficiency of conventional planar structure of the same materials.
"We designed the three-dimensional structure to provide an intrinsic electric field distribution that promotes efficient charge transport and high efficiency in converting energy from sunlight into electricity," Xu said.
Key features of the solar material include its unique electric field distribution that achieves efficient charge transport; the synthesis of nanocones using inexpensive proprietary methods; and the minimization of defects and voids in semiconductors.
The latter provides enhanced electric and optical properties for conversion of solar photons to electricity.
Because of efficient charge transport, the new solar cell can tolerate defective materials and reduce cost in fabricating next-generation solar cells.
"The important concept behind our invention is that the nanocone shape generates a high electric field in the vicinity of the tip junction, effectively separating, injecting and collecting minority carriers, resulting in a higher efficiency than that of a conventional planar cell made with the same materials," Xu explained.
The research will be published in the IEEE Proceedings. The papers are titled ``Efficient Charge Transport in Nanocone Tip-Film Solar Cells`` and ``Nanojunction solar cells based on polycrystalline CdTe films grown on ZnO nanocones``. | <urn:uuid:ba590d84-3c6c-4015-966b-9424e4d54af0> | 3.75 | 519 | News Article | Science & Tech. | 15.210354 | 95,614,975 |
Images: Thomas Eisner/Cornell University; © Cornell University
Talk about multi-tasking. A new study reveals that in the St. John’s Wort plant, Hypericum calycinum, the same chemical not only attracts pollinating insects but also deters herbivores that pose a threat to its survival. The findings appear in the current issue of the Proceedings of the National Academy of Sciences.
To the human eye, the flowers of H. calycinum appear as uniform yellow disks (top image). Insects with ultraviolet-sensitive eyes, however, see a dark, ultraviolet-absorbing center (bottom image), which acts as a bull’s-eye to help the insects narrow in on the nectar. According to the new research, one class of pigments responsible for this UV pattern is dearomatized isoprenylated phloroglucinols, or DIPs. The investigators also found high concentrations of DIPs on the plant’s reproductive structures, which suggest that the chemicals serve additional purposes in the plant. "Just as important as attracting pollinators to a plant is producing a viable seed," team member Matthew Gronquist of Cornell University explains, "so there is an evolutionary incentive to protect the reproductive apparatus from herbivores."
Indeed, the scientists found that hypercalin A, one of the DIPs isolated from H. calycinum, deterred larvae of the rattlebox moth. Those caterpillars unlucky enough to ingest the hypercalin A died. The researchers conclude that DIPs act simultaneously to draw pollinators and discourage predators. "Now that we know where to look," study co-author Thomas Eisner remarks, "antifeedant chemicals like the DIPs undoubtedly will be found in other plant species, and they offer clues to more natural insect control agents."
Sarah Graham | Scientific American
Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides
16.07.2018 | Tokyo Institute of Technology
The secret sulfate code that lets the bad Tau in
16.07.2018 | American Society for Biochemistry and Molecular Biology
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
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Scientists from the MPQ, LMU, and the FUB analyse how fast order can appear in a quantum-mechanical system.
During the freezing of water, the initially unordered molecules start to form an ordered crystal, namely ice. During this phase transition, they rearrange from an unordered into a more ordered state. This setting naturally poses one important question: How long does this phase transition take, i.e. how long does it take for each molecule to find its place in the crystal?
While the atoms are strongly localized in the initial state (upmost row) in the deep lattice,
correlations develop during the crossing of the phase transition induced by lowering the lattice depth.
In the final weak lattice (lowest row), the correlations would in principle span the whole lattice, if the phase transition could be crossed infinitely slow. In reality, however, the finite ramp speed limits the correlation length to a finite value. (Graphic: Quantum Optics Group, LMU)
The answer to this and similar questions has important consequences in e.g. metallurgy, since the size of the resulting crystal grains plays a major role in determining the elasticity or brittleness of steel. While these questions have been studied extensively for classical systems, they are relatively unexplored in the context of quantum systems.
By using ultracold atoms in optical lattices, a team led by Ulrich Schneider and Immanuel Bloch at the Max Planck Institute of Quantum Optics, the Ludwig-Maximilians-Universität Munich, the Freie Universität Berlin, and the Consejo Superior de Investigaciones Científicas in Madrid have succeeded in measuring the emergence of order in a clean and well controlled experiment. Their results reveal deficiencies in current theoretical models and have been published this week in the „Proceedings of the National Academy of Sciences“.
The essential question for any phase transition is: How does it actually happen, i.e. how does the system evolve from one phase to another? Especially for quantum systems there is typically no easy answer available, since the dynamics of these systems are typically much more complex than the phases themselves.
In addition, there is an effect called critical-slowing-down, which means that the reaction time of the system strongly increases on approaching the phase transition point and diverges at this point. As a consequence, the system can never evolve completely “smooth” from an unordered into an ordered phase. How fast the correlations characterizing the ordered phase can emerge and spread, is therefore a central problem in the physics of phase transitions.
Intuitively, one can imagine a collection of small arrows that initially point in random directions. Beyond the phase transition, each arrow now wants to point in the same direction as its neighbours. So, ultimately, all arrows want to be aligned but which direction will be chosen? Since at first all directions are equivalent, the arrows have to spontaneously break this symmetry, meaning they have to agree on one particular orientation. How fast can this process of ordering happen?
The emergence of ordered phases has been studied theoretically already for some time. Now for the first time the scientists were able to investigate this process in a clean and precisely controlled synthetic many-body system: This system is formed by up to a hundred thousand atoms that have been cooled deep into the quantum regime and then were localized to individual lattice site in a so-called optical lattice, that is a crystal of light formed by overlapping and interfering laser beams.
In this Mott insulator there exist no correlations between lattice sites. By now increasing the coupling between the lattice sites—the tunneling rate of particles—a quantum phase transition into another phase can be induced. In this new, superfluid phase, the particles are free to move through the lattice. Since all atoms move in a coherent fashion—they will ultimately all be part of a single wave function, a Bose-Einstein condensate—this results in long-range correlations, even between very distant lattice sites.
In their experiment, the experimental team in Munich could now for the first time observe this emergence of correlations quantitatively and study its time dependence. They could compare their results to theoretical models and show that these models are too simple to describe realistic situations and will need to be extended by novel and not yet known contributions.
In the one-dimensional case, that is a string of lattice sites, the experimental results could be compared to exact numerical calculations performed on classical super-computers by the team around Jens Eisert from the Freie Universität Berlin. This comparison constitutes an independent check of the experiment, which it passed with flying colours.
Motivated by this success, the experiment was then extended to two- and three dimensional situations, where no numerical calculations are feasible. The obtained results can now be used to test and benchmark novel theoretical concepts and thereby advance our fundamental knowledge and understanding of the many-body dynamics in quantum systems.
The present experiment can be viewed as a Quantum Simulator: By performing experiments on well-controlled model systems we can learn about the behaviour of complex systems, which are often challenging to directly study experimentally and impossible to simulate numerically. By providing much-needed benchmark data, Quantum Simulators will help to fundamentally advance our knowledge about such systems. [U.S./O.M.]
Simon Braun, Mathis Friesdorf, Sean S. Hodgman, Michael Schreiber, Jens Philipp Ronzheimer, Arnau Riera, Marco del Rey, Immanuel Bloch, Jens Eisert, and Ulrich Schneider
Emergence of coherence and the dynamics of quantum phase transitions
Proceedings of the National Academy of Sciences, 9 March 2015
Dr. Ulrich Schneider
LMU München, Faculty of physics
Schellingstr. 4, 80799 Munich, Germany
Phone: +49 (0)89 / 2180 -6129
Prof. Dr. Immanuel Bloch
Chair of Quantum Optics, LMU München
Schellingstr. 4, 80799 Munich
Director at Max Planck Institute of Quantum Optics
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -138
Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics, Garching, Germany
Phone: +49 (0)89 / 32 905 -213
Dr. Olivia Meyer-Streng | Max-Planck-Institut für Quantenoptik
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
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Hurricane response crews from the U.S. Geological Survey have installed storm-tide sensors at key locations along the northeast shores of Puerto Rico in advance of Hurricane Irma. Under a mission assignment from the Federal Emergency Management Agency, the USGS deployed nine sensors.
This U.S. Geological Survey Storm-Tide Sensor was one of nine sensors deployed around Puerto Rico prior to Hurricane Irma. USGS photo. (Public domain.)
These storm-tide sensors, housed in vented steel pipes a few inches wide and about a foot long, were installed on bridges, piers, and other structures that have a good chance of surviving a storm surge during a hurricane. The information they collect will help define the depth and duration of a storm-surge, as well as the time of its arrival and retreat. That information will help public officials assess storm damage, discern between wind and flood damage, and improve computer models used to forecast future floods. As the storm approaches and passes the island, information on the storm-tide sensor deployment and the incoming data will be available on the USGS “Flood Event Viewer”.
Storm-surges are increases in ocean water levels generated at sea by extreme storms and can have devastating coastal impacts. While direct impacts are possible in Puerto Rico later this week, tropical storm or hurricane conditions could also affect portions of the mainland as the storm progresses.
The USGS studies the impacts of hurricanes and tropical storms to better understand potential impacts on coastal areas. Information provided through the sensor networks provides critical data for more accurate modeling and prediction capabilities and allows for improved structure designs and response for public safety.
As the USGS continues to take all appropriate preparedness and response actions in response to Hurricane Irma, those in the storm’s projected path can visit www.ready.gov or www.listo.gov for tips on creating emergency plans and putting together an emergency supply kit.
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An 0.50 kg object is attached to one end of a spring, and the system is set into simple harmonic motion. The displacement x of the object as a function of time is shown in the drawing below. With the aid of this data, determine the following values.
(a) amplitude A of the motion
(b) angular frequency
(c) spring constant k
(d) speed of the object at t = 1.0 s
(e) magnitude of the object's acceleration at t = 1.0 s© BrainMass Inc. brainmass.com July 19, 2018, 7:05 pm ad1c9bdddf
(a) The amplitude A of the motion is A = 0.080 m
(b) the period of the motion is T = 4.0 s, then the frequency is f = 1/T = 0.25 Hz
so the angular frequency w= 2*pi*f ...
The solution is comprised of detailed calculations of parameters related to simple harmonic motion, such as angular velocity, spring constant, speed, velocity, displacement. | <urn:uuid:47652aa9-423a-4be6-982c-1cfa76626049> | 4.28125 | 225 | Tutorial | Science & Tech. | 85.404302 | 95,615,037 |
The construction of airborne observatories, high mountaintop observatories, and space observatories designed especially for infrared and submillimeter astronomy has opened fields of research requiring new optical techniques. A typical far-IR photometric study involves measurement of a continuous spectrum in several passbands between ~30 µm and 1000 µm and diffraction-limited mapping of the source. At these wavelengths, diffraction effects strongly influence the design of the field optics systems that couple the incoming flux to the radiation sensors (cold bolometers). The Airy diffraction disk for a typical telescope at submillimeter wavelengths (~100 um to 1000 um) is many millimeters in diameter; the size of the field stop must be comparable. The dilute radiation at the stop is fed through a Winston nonimaging concentrator to a small cavity containing the bolometer. The purpose of this paper is to review the principles and techniques of infrared field optics systems, including spectral filters, concentrators, cavities, and bolometers (as optical elements), with emphasis on photometric systems for wavelengths longer than 60 µm. | <urn:uuid:803ec639-bc39-4721-bfba-69243e9763db> | 3.5625 | 219 | Academic Writing | Science & Tech. | 14.250714 | 95,615,045 |
In 1939, the National Academy of Sciences awarded a grant to the Suicide Squad, a group of three students experimenting with rockets at Caltech, now more formally known as the GALCIT (Guggenheim Aeronautical Laboratory at the California Institute of Technology) Rocket Research Project.
It came just in time.
Until then, the group, comprised of Frank Malina, Jack Parsons, and Ed Forman, had no way to fund the rockets they were working on, and was on the verge of disbanding. That first award, $1,000, rescued the group, bringing them back together. When they were awarded a second grant the next year for ten times as much, it was life-changing. It was the U.S. government’s first investment in rocket research. In deference to the Army Air Corps, which had proposed the funding, they changed their name to the Air Corps Jet Propulsion Research Project. Their goal was clear: Develop a rocket plane. The risky project was the beginning of what would become the Jet Propulsion Laboratory.
Knowing they would need skilled mathematicians, Frank approached his two friends, Barbara (Barby) and Richard Canright. Barby knew the job would be far from a sure thing. She wondered if she could depend on the longevity of the reckless group. She and Richard would be leaving good jobs to work for men who were not known for their reliability. Yet the offer was tempting.
If she accepted, Barby would once again be the only woman in a group of men. It was a job she hadn’t expected, yet one she was eminently qualified for. Math was a comfortable second skin. She would always feel more at home with a pencil in her hand than at a typewriter. In addition, the position held prestige, allowed her to work alongside her husband, and paid twice what she made as a typist. More than the money, it offered her the opportunity to use her neglected math skills.
It wasn’t just the rocket research group that Barby was becoming a member of. She was joining an exclusive group whose contributions spanned centuries. Before Apple, before IBM, and before our modern definition of a central processing unit partnered with memory, the word computer referred simply to a person who computes. Using only paper, a pencil, and their minds, these computers tackled complex mathematical equations.
Early astronomers needed computers in the 1700s to predict the return of Halley’s Comet. During World War I, groups of men and women worked as “ballistic computers,” calculating the range of rifles, machine guns, and mortars on the battlefield. During the Depression era, 450 people worked for the U.S. government as computers, 76 of them women. These computers, meagerly paid as part of the Works Progress Administration, created something special. They filled twenty-eight volumes with rows and rows of numbers, eventually published by the Columbia University Press as the plainly named Mathematical Tables Project series. What they couldn’t know was that these books, filled to the brim with logarithms, exponential functions, and trigonometry, would one day be critical to our first steps into space.
The dream of space exploration was what initially tugged at the Suicide Squad. They worked on engines during the day, but at night they talked about the limits of the universe.
At the time, rockets were considered fringe science, and the people who worked on them weren’t taken seriously. When Frank asked one of his professors at Caltech, Fritz Zwicky, for his help on a problem, the teacher told him, “You’re a bloody fool. You’re trying to do something impossible. Rockets can’t work in space.” In fact, the word rocket was in such bad repute that the group purposely omitted it when they formed their institute, the Jet Propulsion Laboratory. Some scientists at the sister Guggenheim Aeronautical Laboratory at the Massachusetts Institute of Technology snickered at them, while Vannevar Bush, an engineering professor at MIT, derisively said, “I don’t understand how a serious scientist or engineer can play around with rockets.”
* * *
The Canrights were enjoying a quiet Sunday afternoon on December 7, 1941. Barby was in the kitchen, cooking and listening to the radio, when the announcer interrupted the program with breaking news. The Japanese had attacked Pearl Harbor. Barby fell to the kitchen floor, tears streaming down her cheeks. The war had hit home. Hawaii suddenly seemed very close to California. Barby and Richard were glued to the radio for the rest of the evening. Barby knew that their work would now take on a new importance. Going in to the lab the next day, they might have been talking about Pearl Harbor, but they were thinking about the rocket plane. The army needed to lift a fourteen-thousand-pound bomber into the air.
In one month, Barby filled more than twenty notebooks with rows of neatly printed numbers. Each column represented a value from the experiment, plugged into lines of exquisitely complex equations. One of the key computations Barby was responsible for was the thrust-to-weight ratio, an equation that allowed the group to compare the performance of the engines under different conditions. She repeated the calculation many times, sliding the numbers into the equation with the ease of slipping on a pair of shoes.
It was all building to one singular achievement.
It took just a year for the JPL rockets to boost the Douglas A-20A bomber into the air. They experimentally fired the JATO units on the heavy bomber forty-four times, the rockets needing only minor fixes. The project was a success.
All JPL needed now was more employees. Barby was excited when Frank told her he was hiring two more computers, a man and a woman, Freeman Kincaid and Melba Nead. Until then, Barby and Frank’s secretary had been the only two women at the institute. Barby, who didn’t spend much time with the secretary, had felt the lack of female companionship.
Barby’s husband was promoted to engineer. It was what Richard had always hoped for. Although Barby’s experience was similar to his, she was not promoted and hadn’t expected to be. It was simply one of the limits of being female. Although she loved her work, with Richard’s promotion and subsequent added income, she was thinking about starting a family.
Not long after Richard’s promotion, JPL hired two more women, Virginia Prettyman and Macie Roberts, rounding out the computer room to a team of five: four women and one man. The new recruits didn’t seem promising at first. Virginia and Macie, or Ginny and Bobby, as they soon became known, had never heard of a computer before. They answered the want ad with little idea of what they were getting themselves into. Despite the newcomers’ naïveté, the computers immediately became good friends. They spent every day working together, sweating over their calculations, observing experiments in the test pits, and chatting with the engineers.
The computer room worked as seamlessly as a machine, notebooks passed from desk to desk as the five colleagues spent their days transforming raw numbers into meaningful data. Their prize possession was a single Friden calculator. It looked nothing like the modern, sleek devices we’re used to today that can perform hundreds of functions and sit in the palm of our hand. Instead, the calculator was the size of a bread box and heavy. When they first received the Friden, Barby was excited to be in command of a machine that so few people knew how to use. It was the latest technology and much faster than a slide rule, though it could only add, subtract, multiply, and divide. It was a dull gray and looked like a typewriter, but instead of letters, the keyboard held rows of repeating numbers, from 0 to 9.
Melba, Macie, Virginia, Freeman, and Barby were responsible for calculating the potential of rocket propellants. During a conversation one day, Barby noted, “I hear Jack has an idea for a new one. …You’re not going to believe what it’s made of—asphalt.”
As crazy as it sounded to use the heavy asphalt that paved roads, no one knew what would best make rockets fly, so everything was fair game. At JPL, the team tested a wide range of solid, liquid, and gas options. They loaded the fuel and oxidizers into rocket motors that were housed in the test pits in a dirt field. These were directly adjacent to a handful of permanent buildings and the row of tarpaper shacks that made up the lab. Then they fired them.
The calculation the engineers and computers were most interested in was the specific impulse, the change in force that accumulates as a rocket uses fuel. Specific impulse indicates roughly how much momentum builds up as the propellant is being thrown out the back of the rocket. The faster the propellant is thrown, the faster the rocket can travel. Having a high specific impulse means less fuel is needed to go farther. This calculation is the simplest way to compare the effectiveness of different propellants. It took four different equations for the computers to get to the specific-impulse equation. They had to compute thrust and velocity first. They would then plug these numbers into a formula that calculated the thrust per unit mass flow of each propellant.
These calculations could not be done quickly, since they were all done by hand. It took only seconds for a rocket engine to be fired, but analyzing that one experiment could take a week or more for the human computers. Notebooks quickly accumulated, often six to eight of them for each experiment. Barby liked to stack them on her desk, forming a wall of paper. As the notebooks piled up, so did her feeling of accomplishment. Then, at the end of the experiment, after the final report was written up, she’d clear the notebooks off her desk.
The new propellant that Barby and Macie were excited about was a unique mixture of liquefied asphalt with a potassium perchlorate oxidizer. The computers still had to figure out what proportions of fuel and oxidizer were needed to work in a rocket. The best mixture, they calculated, was 70 percent Texaco No. 18 asphalt combined with 30 percent Union Oil lubricating oil. The technicians liquefied the asphalt-oil combination by heating it to 275 degrees Fahrenheit and then added crushed potassium perchlorate. The propellant was mixed and allowed to cool, becoming a solid round block, a cake of rocket-blasting power. They called it Jack’s cake..
The computers found that Jack’s unusual propellant had a specific impulse of 186 and an exhaust velocity of 5,900 feet per second. It delivered a formidable 200 pounds of thrust. It was exactly the kind of fuel the military needed, because it was powerful yet used common (and cheap) ingredients that could be stored at a wide range of temperatures. Almost immediately Barby saw her work finding its way into rockets owned by the U.S. Navy.
Over time, as Macie was rose in the ranks of JPL, Barby saw her future at the institute faltering. She was pregnant. It was getting harder and harder to conceal her growing belly at work, and she knew that soon she’d have to quit. There was no such thing as maternity leave. She was thrilled to be having a baby but sad to say good-bye to the group she’d been a part of since its birth.
Macie would go on to lead a team of young women who were about to leave the lives expected of them. Each would go from being an oddity in school, one of only a few girls who flourished in calculus and chemistry classes, to joining a unique group of women at JPL. The careers they were about to launch would be unlike any other.
This article has been adapted from Nathalia Holt’s book, Rise of the Rocket Girls: The Women Who Propelled Us, from Missiles to the Moon to Mars.
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The unity of physical theory and its mathematical formalism
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The relation between the physical theory and its mathematical formalism is shown.
KeywordsMathematical Formalism Maxwell Equation Physical Theory Physical Picture Mathematical Apparatus
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.
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- 1.V. A. Fock, Elements of Quantum Mechanics [in Russian], Nauka, Moscow (1976).Google Scholar
- 4.A. Einstein, “On the method of theoretical physics”, in: Physics and Reality. Collection of Works [Russian translation]. Nauka, Moscow (1971), pp. 61–76.Google Scholar
- 6.A. Einstein, “Maxwell’s influence on the development of the conception of physical reality”, in: Einstein’s Collection [in Russian], Nauka, Moscow (1966), pp. 7–11.Google Scholar
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All submissions for this problem are available.
A common word puzzle found in the XXX College magazine is the word metamorphism. By taking a starting word and successively altering a single letter to make a new word, one can build a sequence of words which changes the original word to a given end word. For instance, the word ``spice'' can be transformed in four steps to the word ``stock'' according to the following sequence: spice, slice, slick, stick, stock. Each successive word differs from the previous word in only a single character position while the word length remains the same.
Given a dictionary of words from which to make transformations, plus a list of starting and ending words, your team is to write a program to determine the number of steps in the shortest possible transformation.
The input will be a single file in two sections. The first section will be the dictionary of available words with one word per line, terminated by a line containing an # rather than a word. There can be up to 200 words in the dictionary; all words will be alphabetic and in lower case, and no word will be longer than ten characters. Words can appear in the dictionary in any order.
Following the dictionary are pairs of words, one pair per line, with the words in the pair separated by a single space. These pairs represent the starting and ending words in a transformation. The pairs are terminated by the end-of-file. All pairs are guaranteed to have a transformation using the dictionary given. The starting and ending words will appear in the dictionary.
The output should contain one line per word pair, and must include the starting word, the ending word, and the number of steps in the shortest possible transformation, separated by single spaces.
Sample Input dip lip mad map maple may pad pip pod pop sap sip slice slick spice stick stock # spice stock may pod Sample Output spice stock 4 may pod 3
|Time Limit:||15 sec|
|Source Limit:||50000 Bytes|
|Languages:||C, CPP14, JAVA, PYTH, PYTH 3.5, PYPY, CS2, PAS fpc, PAS gpc, RUBY, PHP, GO, NODEJS, HASK, rust, SCALA, swift, D, PERL, FORT, WSPC, ADA, CAML, ICK, BF, ASM, CLPS, PRLG, ICON, SCM qobi, PIKE, ST, NICE, LUA, BASH, NEM, LISP sbcl, LISP clisp, SCM guile, JS, kotlin, PERL6, TEXT, SCM chicken, CLOJ, COB, FS|
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If you are still having problems, see a sample solution here. | <urn:uuid:7cd89217-2988-45b1-bad0-b9cbf15a5c01> | 3.296875 | 595 | Tutorial | Software Dev. | 57.611739 | 95,615,126 |
Unlocking the secrets of regeneration: Study discovers how salamanders replace limbs - and it may help humans do the same
- Study has identified a biological pathway that controls regeneration
- Called ERK, it must be constantly active for salamander cells to reprogram
- This activity is not seen in the cells of other adult mammals
- Discovery may help unlock ‘regenerative potential’ of cells in more animals
- Salamanders are amphibians renowned for a capacity to regrow body parts
It's long been known that salamanders are capable of growing new limbs, but scientists believe they have finally discovered how the process works.
Researchers at University College London (UCL) identified a biological pathway, called ERK (Extracellular signal-regulated kinases), must be
constantly active for salamander cells to regenerate - a process not seen in the same way in other mammals.
Although a long way from achieving the same feat in humans, the discovery could help researchers unlock the ‘regenerative potential’ of cells across other animals.
Scientists may have uncovered the secret of the salamander's ability to grow new limbs. Though a long way from achieving the same feat in people, the discovery could help researchers unlock the 'regenerative potential' of human cells. Pictured is a salamander known as Notophthalmus viridescens (the eastern newt)
Salamanders are lizard-like amphibians famous for their capacity to replace body parts; cut a salamander’s leg off, and in time it will grow a new one.
IS CLIMATE CHANGE MAKING SALAMANDERS SMALLER?
A study claims that wild salamanders in North America are getting smaller as their surroundings get warmer and drier, forcing them to burn more energy in a hotter climate.
Researchers from the University of Maryland found that salamanders in the Appalachians today were nearly a tenth smaller than their ancestors in the 1950s.
The changes were most marked in the Southern Appalachians and at low elevations - settings where detailed weather records showed the climate has warmed and dried out most.
Scientists have predicted that some animals will get smaller in response to climate change and, the researchers sasy, this is strong confirmation of that prediction.
In the same way, the creatures are able to regenerate tails, jaws, eyes, organs and even spinal cords.
In adult mammalian cells, the ERK pathway is not fully active. When forced to be, cells acquire a greater potential for reprogramming and regeneration.
The researchers announced their findings in the journal Stem Cell Reports.
Through the ERK pathway, proteins communicate signals from a cell’s surface to the nucleus containing its genetic material.
‘While humans have limited regenerative abilities, other organisms, such as the salamander, are able to regenerate an impressive repertoire of complex structures including parts of their hearts, eyes, spinal cord, tails, and they are the only adult vertebrates able to regenerate full limbs,' said Lead scientist Dr Max Yun from UCL’s Institute of Structural and Molecular Biology.
‘We’re thrilled to have found a critical molecular pathway, the ERK pathway, that determines whether an adult cell is able to be reprogrammed and help the regeneration processes.
‘Manipulating this mechanism could contribute to therapies directed at enhancing regenerative potential of human cells.’
Further research will now focus on understanding how the important pathway is regulated during limb regeneration, and which other molecules are involved in the process.
Salamanders are lizard-like amphibians famous for their capacity to replace body parts; cut a salamander's leg off, and in time it will grow a new one. In the same way, the creatures are able to regenerate tails, jaws, eyes, organs and even spinal cords. Pictured is a stock photo of a giant palm salamander in Guatemala
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Using atoms cooled to just billionths of a degree above absolute zero, a team led by researchers at Princeton University has discovered an intriguing magnetic behavior that could help explain how high-temperature superconductivity works.
The researchers found that applying a strong magnetic field to these ultracold atoms caused them to line up in an alternating pattern and lean away from each other. The behavior, which researchers call "canted antiferromagnetism," is consistent with predictions from a decades-old model used to understand how superconductivity arises in certain materials. The results were published in the journal Science.
Each green dot represents an individual lithium atom. The researchers use a quantum gas microscope to image the atoms, which have been cooled to a fraction of a degree above absolute zero and trapped in place using lasers.
Image courtesy of Peter Brown, Princeton University
A team led by Princeton University researchers manipulated the spin direction of individual atoms at very low temperatures using strong magnetic fields. They discovered a curious behavior called "canted antiferromagnetism" where the spins prefer to align in a two-dimensional plane at right angles to the field. The behavior is predicted by a model used to describe how high-temperature superconductors work.
Image courtesy of Peter Brown, Princeton University
"No one has observed this type of behavior in this system before," said Waseem Bakr, assistant professor of physics at Princeton University. "We used lasers to create artificial crystals and then explored what is happening in microscopic detail, which is something you just cannot do in an everyday material."
The experiment, conducted on a table-top in Princeton's Jadwin Hall, enables the exploration of a model describing how quantum behaviors give rise to superconductivity, a state where current can flow without resistance and which is prized for electricity transmission and making powerful electromagnets. While the basis of conventional superconductivity is understood, researchers are still exploring the theory of high-temperature superconductivity in copper-based materials called cuprates.
Due to the complexity of cuprates, it is difficult for researchers to study them directly to find out what properties lead to the ability to conduct current without resistance. Instead, by building a synthetic crystal using lasers and ultracold atoms, the researchers can ask questions that are otherwise impossible to address.
Bakr and his team cooled lithium atoms to just a few ten-billionths of a degree above absolute zero, a temperature where the atoms follow the laws of quantum physics. The researchers used lasers to create a grid to trap the ultracold atoms in place. The grid, known as an optical lattice, can be thought of as a virtual egg-tray created entirely from laser light in which atoms can hop from one well to the next.
The team used the set-up to look at the interactions between single atoms, which can behave in a manner analogous to tiny magnets due to a quantum property called spin. The spin of each atom can orient either up or down. If two atoms land on the same site, they experience a strong repulsive interaction and spread out so that there is only one atom in each well. Atoms in neighboring wells of the egg-tray tend to have their spins aligned opposite to each other.
This effect, called antiferromagnetism, happens at very low temperatures due to the quantum nature of the cold system. When the two types of spin populations are roughly equal, the spins can rotate in any direction as long as neighboring spins remain anti-aligned.
When the researchers applied a strong magnetic field to the atoms, they saw something curious. Using a high-resolution microscope that can image individual atoms on the lattice sites, the Princeton team studied the change in the magnetic correlations of the atoms with the strength of the field. In the presence of a large field, neighboring spins remained anti-aligned but oriented themselves in a plane at a right angle to the field. Taking a closer look, the researchers saw that the oppositely aligned atoms canted slightly in the direction of the field so that the magnets were still opposite facing but were not precisely aligned in the flat plane.
Spin correlations had been observed last year in experiments at Harvard, the Massachusetts Institute of Technology, and Ludwig Maximilian University of Munich. But the Princeton study is the first to apply a strong field to the atoms and observe the canted antiferromagnet.
The observations were predicted by the Fermi-Hubbard model, created to explain how cuprates could be superconducting at relatively high temperatures. The Fermi-Hubbard model was developed by Philip Anderson, Princeton's Joseph Henry Professor of Physics, Emeritus, who won a Nobel Prize in Physics in 1977 for his work on theoretical investigations of electronic structure of magnetic and disordered systems.
"Understanding the Fermi-Hubbard model better could help researchers design similar materials with improved properties that can carry current without resistance," Bakr said.
The study also looked at what would happen if some of the atoms in the egg-tray were removed, introducing holes in the grid. The researchers found that when the magnetic field was applied, the response agreed with measurements done on cuprates. "This is more evidence that the proposed Fermi-Hubbard model is probably the correct model to describe what we see in the materials," Bakr said.
The Princeton team included graduate student Peter Brown, who conducted many of the experiments and is the paper's first author. Additional contributions to the experiments came from Debayan Mitra and Elmer Guardado-Sanchez, both graduate students in physics, Peter Schauss, an associate research scholar in physics, and Stanimir Kondov, a former postdoctoral researcher who is now at Columbia University.
The study included contributions to the understanding of the theory from Ehsan Khatami of San José State University, Thereza Paiva at the Universidade Federal do Rio de Janeiro, Nandini Trivedi at The Ohio State University, and David Huse, Princeton's Cyrus Fogg Brackett Professor of Physics.
This work was supported by NSF (grant DMR-1607277), the David and Lucile Packard Foundation (grant 2016-65128), and the Air Force Office of Scientific Research Young Investigator Research Program (grant FA9550-16-1-0269). W.S.B. was supported by an Alfred P. Sloan Foundation fellowship. P.T.B. was supported by the U.S. Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program. E.K. was supported by NSF (grant DMR-1609560). T.P. was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, and Instituto Nacional de Ciência e Tecnologia de Informação Quântica. N.T. was supported by NSF (grant DMR1309461).
The study, "Spin-imbalance in a 2D Fermi-Hubbard system," by Peter T. Brown, Debayan Mitra, Elmer Guardado-Sanchez, Peter Schauß, Stanimir S. Kondov, Ehsan Khatami, Thereza Paiva, Nandini Trivedi, David A. Huse, and Waseem S. Bakr, was published in the journal Science on September 29, 2017.
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What happens when we heat the atomic lattice of a magnet all of a sudden?
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Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
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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.
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.
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18.07.2018 | Health and Medicine | <urn:uuid:e7bffe3c-e24d-4a16-a275-bfe8bff7a9f6> | 3.890625 | 2,207 | Content Listing | Science & Tech. | 37.088817 | 95,615,138 |
The aim of the present study was to characterize the patterns of gastropod shell utilization by the hermit crab Clibanarius zebra (Dana, 1852) from four different sites along the Saurashtra coast, Gujarat state, India. A total of 404 individuals of hermit crab were captured (223 males, 147 females and 34 ovigerous females), occupying 22 species of gastropod shells. Maximum species diversity of shells occupied by the crab was observed at Veraval. Amongst all the shell species identified, Cerithium scabridum (36.88 %) was highly occupied by the crab species followed by Astra stellata (11.39 %), Turbo intercostalis (10.64 %), Cerithidia cingulata (9.16 %) and Lunella coronata (7.43 %). Males of C. zebra utilized a wide range of shell species (21 species), while non ovigerous females (13 species) and ovigerous females (7 species) use a specific set of gastropod shell species. The density of live common shell species occupied by C. zebra was also calculated and results revealed that the density of C. scabridum was very high in the intertidal zone compared to other gastropods. This indicates that density of shells may influence the utilization of shells by C. Zebra.
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When laser light strikes a white wall or just some surface in space, a speckle pattern is observed. An example is given in Fig. 6.1. As a similar phenomenon is not observed with incandescent light or light from a spectral lamp, it must be a special property of laser light. Indeed, it is the special coherence properties of laser light that lead to the appearance of speckle patterns.
KeywordsParticle Image Velocimetry Speckle Pattern Binary Star Laser Doppler Anemometry Photographic Plate
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- 6.1J. C. Dainty (Ed.): Laser Speckle and Related Phenomena ( Springer, Berlin, Heidelberg 1975 )Google Scholar
- 6.3F. Durst, A. Melling, J. H. Whitelaw: Principle and Practice ofLaser-DopplerAnemometry ( Academic Press, London 1981 )Google Scholar
- 6.6G. Weigelt: “Triple-correlation imaging in optical astronomy”, in E. Wolf (Ed.): Progress in Optics, Vol. XXIX, S. 293–319 ( North—Holland, Amsterdam 1991 )Google Scholar | <urn:uuid:463585ae-dc64-409a-a0d4-d4be7614fbab> | 3.484375 | 262 | Truncated | Science & Tech. | 54.703435 | 95,615,153 |
Comparing the Ignitability of Mulch Materials for a Firewise Landscape
AffiliationPlant Sciences, School of
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AbstractEight different landscape mulches were tested for their flammability using a propane torch, charcoal briquette, and a cigarette at two different times of the year. Three randomized compete blocks with eight one square meter plots were tested at three locations; Tucson, Prescott, and Flagstaff, Arizona. Each of the mulches was subjected to the heat of a handheld propane torch (15 seconds), a glowing charcoal briquette (five minutes), and a lit cigarette (until burned out). We found that the least dense mulches (pine needles and straw) burned rapidly when subjected to the torch and ignited after the briquette was removed. The medium density mulches (pine bark nuggets and wood chips) had low flame lengths and smoldered. Heavy density mulches (garden compost and shredded bark) only smoldered. The decomposed granite and sod did not ignite or smolder.
Series/Report no.University of Arizona Cooperative Extension Publication AZ1440
CollectionsNatural Resources and Environment
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Identification of hydrogeochemical processes and their influence on groundwater quality for drinking and agricultural usage in Wadi Nisah, Central Saudi Arabia
Groundwater quality of a region is often controlled by the geochemical processes that operate with respect to the aquifer-water interaction, especially in arid regions where rainfall recharge is minimal. The goal of the present research was to understand the hydrochemical processes influencing groundwater chemistry and to evaluate groundwater quality for drinking and agricultural usage in Wadi Nisah and Wadi Al-Awsat, south of Riyadh. Twenty-nine groundwater samples were analyzed for major physio-chemical parameters. Ionic plots, chloro-alkaline indices, and modified Piper plots point towards reverse ion exchange. Saturation indices and correlation coefficients indicate halite, calcite, and dolomite dissolution. The Piper plot shows that most of the groundwater samples (82.76%) are of the (Ca + Mg)–(Cl-SO4) type. The groundwater quality is not good for drinking due to its high total dissolved solid (TDS) content. The groundwater is found to be suitable for irrigation in terms of residual sodium carbonate, sodium adsorption ratio, soluble sodium percentage, Kelly’s index, and magnesium hazard. The high salinity is unsuitable for irrigation; however, this can be overcome by using salinity-resistant crop varieties.
KeywordsArid regions Wadi Nisah Hydrochemistry Groundwater quality
The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group (no. RG-1439-031).
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Revealed, Nasa's plan to save the Earth: Space agency reveals mock-up of a robot that will lasso an asteroid in 2021 and place it in orbit around the moon so astronauts can test deflection systems and train for Mars missions
- A Nasa robot ship is planning to visit a comet and pluck a large boulder off an asteroid in December 2021
- It will be visited by astronauts aboard the Orion spacecraft after being dragged into orbit around the moon
- Astronauts plan to study the asteroid and collect samples to test technologies for a mission to Mars
- lso plans to study the asteroid and test deflection techniques that one day may be necessary to save Earth from a potentially catastrophic collision
Nasa is planning an ambitious mission that will see a robotic spaceship visit an asteroid to create an orbiting base for astronauts.
The robot shipwill pluck a large boulder off the space rock and sling it aroundthe moon, becoming a destination to prepare for futurehuman missions to Mars.
Nasa also plans to study the asteroid and test deflection techniques that one day may be necessary to save Earth from a potentially catastrophic collision.
Now the space agency has created a mock-up of its robot arm and tested it using a mock asteroid boulder.
Scroll down for video
The robot ship will pluck a large boulder off an asteroid and sling it around the moon, becoming a destination to prepare for future human missions to Mars. Now the space agency has created a mock-up of its robot arm and tested it with a mock asteroid boulder (pictured)
NASA'S ASTEROID REDIRECT MISSION
Nasa is planning ambitious mission that will see a robotic spaceship visit an asteroid to create an orbiting base for astronauts.
The robot shipwill pluck a large boulder off the space rock and sling it aroundthe moon, becoming a destination to prepare for futurehuman missions to Mars.
Nasa plans to study the asteroid for about a year and test deflection techniques that one day may be necessary to save Earth from a potentially catastrophic collision.
At the space agency's Robotic Operations Center in the Goddard Space Flight Center, Maryland, the mock-up helps engineers understand the intricate operations required to collect a multi-ton boulder from an asteroid's surface.
The hardware involved here includes three space frame legs with foot pads, two seven degrees of freedom arms that have with microspine gripper 'hands' to grasp onto the boulder.
The so-called Asteroid Redirect Mission is estimated to costabout $1.4 billion (£1.12 billion) not including launch costs and is targetedfor lift-off in December 2021.
Following a key program review, Nasa approved the Asteroid Redirect Mission (ARM) in August, to proceed to the next phase of design and development for the mission's robotic segment.
ARM is a two-part mission that will integrate robotic and crewed spacecraft operations in the proving ground of deep space to demonstrate key capabilities needed for Nasa's journey to Mars.
The crewed segment, targeted for launch in 2026, remains in an early mission concept phase, or pre-formulation.
'This is an exciting milestone for the Asteroid Redirect Mission,' said NASA Associate Administrator Robert Lightfoot.
'Not only is ARM leveraging agency-wide capabilities, it will test a number of new technologies already in development.'
The robotic component of the ARM will demonstrate the world's most advanced and most efficient solar electric propulsion system as it travels to a near-Earth asteroid (NEA).
NEAs are asteroids that are fewer than 121 million miles (1.3 AU) from the sun at the closest point in their orbit.
In the centre's Robotic Operations Center, the mock-up helps engineers understand the intricate operations required to collect a multi-ton boulder from an asteroid's surface. Nasa plans to pick up a boulder from a large asteroid (shown) using a robotic ship
It will then be taken to lunar orbit, where it would be studied by astronauts (artist's impression pictured). Although the target asteroid is not expected to be officially selected until 2020, NASA is using 2008 EV5 as the reference asteroid while the search continues for potential alternatives
Although the target asteroid is not expected to be officially selected until 2020, NASA is using 2008 EV5 as the reference asteroid while the search continues for potential alternates.
Before beginning its trip to lunar orbit, the ARM spacecraft will demonstrate a widely supported asteroid deflection technique called a gravity tractor.
The spacecraft plus the mass of the captured boulder will create a small gravitational attraction to alter the orbit of the large asteroid.
After collecting a boulder from the asteroid, the robotic spacecraft will slowly redirect the boulder to an orbit around the moon, using the moon's gravity for an assist, where Nasa plans to conduct a series of proving ground missions in the 2020s.
There, astronauts will be able to select, extract, collect, and return samples from the multi-ton asteroid mass, and conduct other human-robotic and spacecraft operations in the proving ground that will validate concepts for Nasa's journey to Mars.
SAVING EARTH FROM DISASTER WITH THE ASTEROID REDIRECT MISSION
Various techniques for deflecting a potentially hazardous asteroid could be tested on Arm to enable planetary defense capabilities.
These techniques include Ion Beam Deflection, Enhanced Gravity Tractor, and kinetic impactors.
In Ion Beam Deflection, the plumes from the thrusters would be directed towards the asteroid to gently push on its surface over a wide area. A thruster firing in the opposite direction would be needed to keep the spacecraft at a constant distance from the asteroid.
The Ion Beam Deflection approach is independent of the size of the asteroid, and it could be demonstrated on either mission option.
In the Enhanced Gravity Tractor approach, the spacecraft would first pick up a boulder from the asteroid's surface as in mission Option B.
The spacecraft with the collected boulder would then orbit in a circular halo around the asteroid's velocity vector.
The mass of the boulder coupled with the mass of the spacecraft would increase the gravitational attraction between the spacecraft and the asteroid.
By flying the spacecraft in close formation with the asteroid for several months the very small gravitational forces would produce a measurable change in the asteroid's trajectory.
A kinetic impactor could also be launched as a secondary payload with the spacecraft or on a separate launch vehicle, and it would collide with the target asteroid at high velocity while the spacecraft observed the impact.
Earlier this year, Nasa updated the target launch date for the robotic mission to December 2021 in order to incorporate acquisition of the industry robotic spacecraft development into the project schedule
HOW NASA WILL USE AN ASTEROID AS A STEPPING STONE TO MARS
The mission involves astronauts making the journey to their captive space rock by hitching a ride on the next-generation Orion Multi-Purpose Crew Vehicle.
After the Orion and the asteroid are attached, the astronauts take a spacewalk to the captured object.
Once the Orion docks with the remote-operated asteroid capture device, the crew performs a spacewalk that sees them climb almost the length of the conjoined vehicles to an exposed section of the asteroid they take photos of and scoop samples from, the video shows.
After the mission is complete, Orion returns to Earth on the same path it journeyed out on, loops around the moon included, and splashes down in an ocean - likely the Pacific - 10 days later.
The mission is seen as an important step towards eventually sending humans to Mars and returning them safely.
Nasa also considered bagging a smaller asteroid andrelocating the entire body into a high orbit around the moon.
After extensive studies, Nasa opted to collect and move aboulder, a mission that will cost about $100 million (£80 million) more, butwhich better prepares the agency for the ultimate goal oflanding astronauts on Mars.
'They're the kind of things that we know we're going to needwhen we go to another planetary body,' Nasa AssociateAdministrator Robert Lightfoot told reporters on a conferencecall in August.
An asteroid orcomet smashed into the planet about 65 million years ago,leading to climate changes that killed off dinosaurs and mostother life on Earth then.
So far, Nasa has three candidate asteroids, but does notexpect to make a decision about where to fly before 2019.
The mission involves flying a robotic spacecraft, powered bysolar electric propulsion, to an asteroid for an extensivesurvey.
Once a target boulder was selected, the probe wouldhover down toward the surface and deploy a pair of robot arms tograb hold of a 6.5- to 13-foot (2- to 4 metre) wide boulder.
'I'm going to have multiple targets ... We can assess whichone we want to go after and I then have three- to five tries toget it, or I can move on to a different one,' Lightfoot said.
The captured boulder, which would remain attached to theprobe, would then be nudged into an orbit circling high aroundthe moon, a maneuver expected to take about six years.
The probe would include a docking ring so a NASA Orionspaceship, carrying two astronauts, could reach the asteroid, amission targeted for around 2025.
Nasa's ultimate goal is to send humans to Mars, and they say the Asteroid Redirect Mission (Arm) will be an important stepping stone towards getting there.
A number of new spaceflight capabilities will be tested in the 2020s as part of the mission, which will involve redirecting an asteroid to orbit the moon and sending humans to explore it.
Nasa plans to launch an Arm robotic spacecraft to rendezvous with, capture and redirect an asteroid by the end of this decade.
The spacecraft will redirect it to a stable orbit around the moon called a 'Distant Retrograde Orbit' - one that orbits the moon very widely, coming quite close before extending out much further away.
Astronauts aboard Nasa's Orion spacecraft, launched from the upcoming Space Launch System (SLS) rocket, will then explore the asteroid in the mid-2020s at the furthest point in its controlled orbit around the moon.
Within the papers, authors explain the current work taking place across the country to examine options for these robotic and crewed missions.
This includes advanced Solar Electric Propulsion (SEP) - one of the critical technologies needed to send larger payloads into deep space and to the Mars system.
THE SOLAR ELECTRIC PROPULSION ENGINE
Solar Electric Propulsion (SEP) uses solar energy from solar arrays converted into electricity.
Electricity is then used to ionize and accelerate propellant to produce thrust.
The technology could potentially increase spaceflight transportation fuel efficiency by 10 times over current chemical propulsion technology, according to Nasa.
It could also more than double thrust capability compared to current electric propulsion systems.
Shown is the HERMeS (Hall Effect Rocket with Magnetic Shielding) Technology Development Unit thruster, which has now exceeded over 1300 hours of operational wear testing in a vacuum facility at GRC.
Magnetic shielding protects the walls of the thruster from erosion, a major breakthrough in Hall thruster design that could hold the key to long-life, reusable electric propulsion systems.
Astronauts aboard Nasa's Orion spacecraft, launched from the upcoming Space Launch System (SLS) rocket, will explore the asteroid in the mid-2020s at the furthest point in its controlled orbit around the moon. Artist's impression pictured
SEP - or ion propulsion - creates thrust powered by solar arrays, which transforms sunlight into electromagnetic fields that accelerate and expel charged atoms (ions).
This is a very efficient way to power a spacecraft and significantly cuts down on the amount of fuel a spacecraft needs to carry, which can be heavy and expensive to launch from Earth.
Current studies at Nasa detailed in the papers are examining ways SEP will be used to power the Arm robotic mission.
Nasa was also working on a mission concept that would fully enclose a large asteroid using an inflatable system and the other would capture a smaller boulder from of a much larger asteroid using robotic arms.
The Arm crewed mission, in which astronauts will explore the redirected asteroid around the moon, provides unique opportunities to test human spaceflight capabilities as well.
The papers detail current work underway at Nasa to upgrade spacesuits in preparation for the first spacewalks in deep space since the 1960s and farther from Earth than ever before.
Concepts for new hardware to dock the crewed and uncrewed spacecraft together are also in development.
This will allow the crew aboard Orion to attach to the Arm robotic spacecraft and study the asteroid.
This could be later used to connect Orion with a deep space habitat or 'stepping stone' on its way to Mars, or even station cargo and fuel depots in strategic places such as lunar orbit.
CHOOSING AN ASTEROID
An asteroid named Itokawa photographed by the Hayabusa probe.
The agency plans to announce the specific asteroid selected for the mission no earlier than 2019, approximately a year before launching the robotic spacecraft.
NASA has identified three valid candidates for the mission so far: Itokawa, Bennu and 2008 EV5.
A target asteroid such as 2008 EV5 is particularly appealing to the scientific, exploration, and industrial communities because it is a primitive, C-type (carbonaceous) asteroid, believed to be rich in volatiles, water, and organic compounds.
The ability to extract core samples from the captured boulder will allow us to evaluate how its composition varies with depth and could unlock clues to the origins of our solar system.
Astronaut sampling and potential commercial activities could indicate the value of C-type asteroids for commercial mining purposes, which in turn could have significant impacts on how deep space missions are designed in the future.
Before an asteroid is considered a valid candidate for the mission, scientists must first determine its characteristics, in addition to size, such as rotation, shape and precise orbit.
Astronauts returning home with samples from Mars will hold a treasure trove of research scientists will study to unlock new knowledge about Mars and the solar system's history.
As well as this, returning asteroid samples will help Nasa develop tools and techniques for future space exploration.
This early experience with raw materials could also help advance our ability to make use of natural resources in space.
Rocky bodies like asteroids and our moon could hold enough oxygen and hydrogen to create breathable air, drinkable water or even components for rocket fuel.
There also is growing interest in the commercial space industry to potentially mine asteroids for resources in the future.
With this in mind some of the papers outline ways in which Arm might benefit future commercial activities at asteroids - namely collecting resources for use back on Earth or in space.
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Filtration is the final physical barrier preventing the passage of microbial pathogens into public drinking water. Proper pre-treatment via coagulation is essential for maintaining good particle removal during filtration. To improve filter performance at the Elgin Area WTP, artificial neural network (ANN) models were applied to optimize pre-filtration processes in terms of settled water turbidity and alum dosage. ANNs were successfully developed to predict future settled water turbidity based on seasonal raw water variables and chemical dosages, with correlation (R2) values ranging from 0.63 to 0.79. Additionally, inverse-process ANNs were developed to predict the optimal alum dosage required to achieve desired settled water turbidity, with correlation (R2) values ranging from 0.78 to 0.89.
The application of artificial neural networks for the optimization of coagulant dosage
K. A. Griffiths, R. C. Andrews; The application of artificial neural networks for the optimization of coagulant dosage. Water Science and Technology: Water Supply 1 December 2011; 11 (5): 605–611. doi: https://doi.org/10.2166/ws.2011.028
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Predicted abundance of seabirds in open sea. Summer season
CitationFauchald P, Vang R (2017). Predicted abundance of seabirds in open sea. Summer season. Version 1.3. Norwegian Institute for Nature Research. Metadata dataset https://doi.org/10.15468/bapwbd accessed via GBIF.org on 2018-07-18.
DescriptionThe maps consist of 10x10 km2 grid and shows predicted abundance of the species based on two-step analysis (see Data Analysis) of data available over the distribution of seabirds in Norwegian and adjacent sea areas (see Dataset) in summer season. Along with the maps we also present uncertainty in predictions that 95% confidence intervals and standard error. The confidence intervals were not possible to define at very low densities. It is important to note that uncertainty does not allow for systematic errors caused by differences in detectability (see Methods). Conspicuous species that often follows after the vessel is systematically overestimated. This is especially true species fulmars, kittiwakes, herring gulls, black-backed gulls and gull. Small dark species diver is probably equivalent underestimated. This is especially auks: auk, puffin, razorbills, murres and guillemots. Abundance estimates should be regarded as indexes.
Additional infoSee description of Methods on http://www.seapop.no/no/metoder/kartlegging-hav/ and data analysis on http://www.seapop.no/no/metoder/kartlegging-hav/dataanalyse.html (Norwegian only)
Avescommon name: Birds rank: order
Norwegian and adjacent sea areas
position: Senior Research Scientist
Geir Helge Systad
administrative point of contact
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Solar eclipse: U-M experts can discuss
Joel Bregman, the H.D. Curtis Professor of Astronomy, is an expert in X-ray observation and theory, which he uses to account for the “missing baryons,” or normal matter, in galaxies.
“For those in the path of totality, when the sun is fully eclipsed, you’ll be able to see stars and planets around the sun—four planets and several stars,” he said. “First, you’ll need to get one eye dark adapted for five minutes before totality to best see the stars. Either keep one eye closed or wear a patch, easily obtained in most pirate stores. The four planets in order of decreasing brightness are Venus, Jupiter, Mars and Mercury. Venus is so bright that it will become visible to the naked eye 15 to 30 minutes before totality. Several minutes before totality, Jupiter becomes visible against the darkening sky, although if you’re in Oregon, it’s probably too low in the sky to see.
“During totality, you can see Mars, which will appear orange, and Mercury on opposite sides of the sun. Totality also reveals a number of stars, with Regulus, the brightest star in the constellation Leo, just to the left of the sun; the bright star Sirius is in the southwest. To give you a sense of scale on the sky, a clenched fist at arm’s length is about 10 degrees and Venus is about three and a half fists to the right of the sun. Nearly all the good stuff is from naked eye observations. The sun you still see during eclipse is from the corona, giant loops and streams of gas, so this is a special show.”
Contact: 734-764-2667, email@example.com
Emily Rauscher, assistant professor of astronomy, is a theoretical astrophysicist who studies exoplanets—which are planets outside of our solar system—in orbit around other stars.
“I’m personally really excited about this upcoming solar eclipse,” she said. “I’ve witnessed a partial solar eclipse before, which is what will be visible from Michigan, but I’m traveling all the way to eastern Oregon in order to be in the path of totality.”
“Although this event is not directly related to my research, one of the methods that we use to study exoplanet atmospheres is to observe them when they pass between us and their host stars—but they only block a tiny fraction of the star’s light, in contrast to the solar eclipse. I wonder whether, after viewing a total solar eclipse, I will think of these transiting exoplanets in the same way.”
Contact: 734-647-6995, firstname.lastname@example.org
Shannon Murphy is the instructional support and outreach coordinator for the U-M Department of Astronomy.
“Although the eclipse is only partial here in Michigan, it’s still totally worth watching,” she said. “Just don’t look at the sun directly. There are plenty of ways to safely watch it. If you’re using eclipse glasses or solar filters to look at the sun, make sure the only thing you can see through it is the sun. If you can see other things, it’s not good enough. If you’re using projection, like a pinhole projector, remember you’re supposed to look at the image of the sun, not through the pinhole.
“If you miss this one, the next next solar eclipse over Ann Arbor will be another partial in October 2023. The next total eclipse over U-M facilities will be on July 2, 2019. The eclipse will pass over La Serena, Chile, where the Cerro Tololo observatory is.”
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David Gerdes is Arthur F. Thurnau Professor of Physics and Astronomy.
His research interests include studies of distant objects in the solar system beyond Neptune. He will be leading a team of observers who will be photographing the total eclipse as part of the Citizen CATE project from a site in Oregon. This project will deploy 68 teams of observers with identical telescopes along the 2500-mile path of totality to assemble a continuous 90-minute HD movie of the solar corona.
Contact: 734-647-3807, firstname.lastname@example.org
Rajesh Rao, M.D., assistant professor of ophthalmology and visual sciences at the University of Michigan Kellogg Eye Center.
A solar eclipse will offer a rare – although brief – sight to millions. Is it OK to take a peek? Not without eye protection, says Rajesh Rao, M.D. a retina surgeon at the University of Michigan Kellogg Eye Center. “It’s unsafe to look at the sun with your naked eye — or with conventional sunglasses, a smartphone, binoculars or a telescope.” That’s because staring at the sun, no matter how small the sliver or length of time, can cause temporary (and sometimes permanent) vision damage. “In Michigan, where we will have a partial eclipse, it’s important to wear solar filter glasses the whole time.”
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Designing an artificial leaf that uses solar energy to convert water cheaply and efficiently into hydrogen and oxygen is one of the goals of BISfuel – the Energy Frontier Research Center, funded by the Department of Energy, in the Department of Chemistry and Biochemistry at Arizona State University.
An artificial photosynthetic reaction center containing a bioinspired electron relay (yellow) mimics some aspects of photosynthesis.
Hydrogen is an important fuel in itself and serves as an indispensible reagent for the production of light hydrocarbon fuels from heavy petroleum feed stocks. Society requires a renewable source of fuel that is widely distributed, abundant, inexpensive and environmentally clean.
Society needs cheap hydrogen.
“Initially, our artificial leaf did not work very well, and our diagnostic studies on why indicated that a step where a fast chemical reaction had to interact with a slow chemical reaction was not efficient,” said ASU chemistry professor Thomas Moore. “The fast one is the step where light energy is converted to chemical energy, and the slow one is the step where the chemical energy is used to convert water into its elements viz. hydrogen and oxygen.”
The researchers took a closer look at how nature had overcome a related problem in the part of the photosynthetic process where water is oxidized to yield oxygen.
“We looked in detail and found that nature had used an intermediate step,” said Moore. “This intermediate step involved a relay for electrons in which one half of the relay interacted with the fast step in an optimal way to satisfy it, and the other half of the relay then had time to do the slow step of water oxidation in an efficient way.”
They then designed an artificial relay based on the natural one and were rewarded with a major improvement.
Seeking to understand what they had achieved, the team then looked in detail at the atomic level to figure out how this might work. They used X-ray crystallography and optical and magnetic resonance spectroscopy techniques to determine the local electromagnetic environment of the electrons and protons participating in the relay, and with the help of theory (proton coupled electron transfer mechanism), identified a unique structural feature of the relay. This was an unusually short bond between a hydrogen atom and a nitrogen atom that facilitates the correct working of the relay.
They also found subtle magnetic features of the electronic structure of the artificial relay that mirrored those found in the natural system.
Not only has the artificial system been improved, but the team understands better how the natural system works. This will be important as scientists develop the artificial leaf approach to sustainably harnessing the solar energy needed to provide the food, fuel and fiber that human needs are increasingly demanding.
ASU chemistry professors involved in this specific project include Thomas Moore, Devens Gust, Ana Moore and Vladimiro Mujica. The department is a unit of the College of Liberal Arts and Sciences. Key collaborators in this work are Oleg Poluektov and Tijana Rajh from Argonne National Laboratory.
This work would not have been possible without the participation of many scientists driven by a common goal and coordinated by a program such as the Energy Frontier Research Center to bring the right combination of high-level skills to the research table.
The Department of Chemisry and Biocehmistry is an academic unit in ASU's College of Liberal Arts and Sciences.Jenny Green, email@example.com
Jenny Green | EurekAlert!
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
Pollen taxi for bacteria
18.07.2018 | Technische Universität München
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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Particle Physics Tutorial 3 - Photons
The electromagnetic spectrum is a family of waves that have the following properties:
They are transverse;
They all travel at 300 million m s-1 (3 × 108 m s-1) in a vacuum.
They can travel in a vacuum, so need no material to travel in.
They are made up of an electric field and a magnetic field at 90o to each other. The electric field (E) and the magnetic field (B) are always in phase (in step) with each other.
The main parts of the electromagnetic spectrum are shown below:
This diagram shows wavelengths:
Light shows wave behaviour:
It refracts, and reflects;
It is diffracted;
As a transverse wave, it can be polarised.
What evidence is there that light is a wave?
Like all waves, EM waves follow the wave equation:
The symbol l is lambda, a Greek letter ‘l’. It is the physics code for wavelength, measured in metres.
Speed of light (3.0 × 108 m s-1) is given by the code c, while f is the frequency (Hz). Light waves are often given in nanometres (nm) where 1 nm = 1 × 10-9 m.
(a) What is the frequency of radio waves of wavelength 247 m?
(b) An electromagnetic radiation has a frequency of 2.0 × 1013 Hz. What is its wavelength? What region of the electromagnetic spectrum is this?
Give your answers to an appropriate number of significant figures.
Physicists now believe that light travels in packets of waves called photons. (We will look at the evidence for this in the photo-electric effect.) Each photon is a train or burst of waves. Photons are given out when charged particles lose energy. These travel in random directions from a light source. Once they have left the light source, the photons travel in straight lines until reflected or refracted.
We can represent a photon like this:
Photons are pure energy. They have zero mass, which means that they can travel at the speed of light, 3.0 × 108 m s-1.
What do you understand by the term photon?
The energy of each photon is given by the simple equation:
E = hf
E – energy per photon (J);
h – Planck’s constant, 6.63 × 10-34 J s (joule-seconds, NOT joules per second)
f – frequency (Hz)
Write down the formula that links photon energy with frequency. Explain each term and give the correct units.
Evidence for Photons
Consider an old-fashioned black and white picture taken on a film. We take the picture using a negative. We then expose photographic paper to the negative using an enlarger. We make a negative of a negative which makes a positive. We then develop the image using chemicals. A very short exposure shows random dots of silver.
A longer exposure shows the picture getting darker and showing more detail as more grains of silver are deposited. Each random grain of silver is deposited by a photon of light coming from the bulb of the enlarger. We can see this on this in the picture of a photographer's test strip.
The same random effect can be seen with the CCD of a modern digital camera. The image below shows a very bad picture taken in low light conditions.
The image is very grainy and lacks detail. This isn't so obvious with the small size of the picture, but when enlarged, it is dreadful.
Wavelengths are often given rather than frequency, so we have to convert to frequency using:
It doesn’t take a genius to see that this relationship can be substituted to give us:
What is the photon energy of red light of wavelength 600 nm?
E = 6.63 × 10-34 J s × 3 × 108 m s-1 = 3.32 × 10-19 J
600 × 10-9 m
Power of a Beam of Light
If we have n photons, each of energy E, passing a particular point, we can easily work out the power P (energy per second).
P = nhf
If we know the power of a laser beam, we can work out many photons it gives out every second.
How many photons are squirted out by a laser every second, if its wavelength is 620 nm, and its power is 150 mW?
E = (6.63 × 10-34 J s × 3 × 108 m s-1) ÷ 620 × 10-9 m
Power of the laser = 0.15 W
Number of photons per second = 0.15 W ÷
3.20 × 10-19 J = 4.7 × 1017 s-1 (2
An account of how the laser works can be found in Quantum Physics Tutorial 8.
Aeroplanes approaching to land at Leeds Bradford Airport (Yeadon Aerodrome, EGNM) are guided in to the runway by a beam of radio waves transmitted at a frequency of 110.90 MHz.
(a) What is the wavelength of the radio waves?
(b) What is the energy per photon?
(c) If the transmitter has a power of 100 W, how many photons are given out every second?
Did you forget to convert MHz to Hz?
At the start of the
Twentieth Century, most physicists were convinced that light was a wave.
However there was evidence that light was a particle. | <urn:uuid:a666326b-7cf2-4729-a501-fdd62aa02876> | 4.15625 | 1,161 | Tutorial | Science & Tech. | 74.925417 | 95,615,265 |
Ancient volcanism offers a glimpse into the future effects of climate change.
The Earth’s ‘young’ phase might have been much shorter than we assume.
This is not about conspiracy theories, but a legitimate scientific concern.
An incoming mass extinction isn’t as hard to spot as we’d believed.
A team of researchers forced bacteria to create carbon-silicon bonds, and their experiment showcases why life on our planet chose carbon.
Why spread your seed across the Earth when you can spread it across space?
This is likely not our first brush with alien life.
The amazing discovery suggests that alien life might actually be common.
It’s as old as we can possibly find.
Not your everyday find.
Both Enceladus and Europa seem capable of supporting alien life, according to a major NASA announcement.
Nothing like a good ol’ meteorite impact to kickstart life.
Life can be surprisingly hardy.
Evolution doesn’t always procrastinate. But when it does, it’s for 2 billion years.
There’s no proof. But the conditions were right for it to happen.
Silly bacteria, carbon-based life is best life!
Findings alien life on barren planet like Mars seems unlikely, but the discovery of the century might that of past life.
Scientists track how a critical chemical element for life got to our planet.
New research suggests the “primordial soup” theory can’t explain how living cells evolved to harness energy.
We use so much of everything so fast that it’s literally killing the planet. | <urn:uuid:9967e2f3-5eb4-4138-bdbe-21d382d53797> | 3 | 344 | Content Listing | Science & Tech. | 56.057362 | 95,615,293 |
Prior to albert Einstein’s theory of special relativity there was always an idea about relativity. Through Galilean transformations, which worked perfectly with the newton’s laws of motion, people had formed a vague idea that all motion in this world is relative to something else. There came up the mysterious thing called aether — the medium through which light propagated. The belief in aether had caused a mess of things, in Einstein’s view, by introducing a medium that caused certain laws of physics to work differently depending on how the observer moved relative to the aether. In 1905, Albert Einstein published the theory of special relativity, which explains how to interpret motion between different inertial frames of reference — that is, places that are moving at constant speeds relative to each other.
Einstein explained that when two objects are moving at a constant speed as the relative motion between the two objects, instead of appealing to the aether as an absolute frame of reference that defined what was going on. If you and your friend, say AA, are moving in different spaceships and want to compare your observations, all that matters is how fast you and AA are moving with respect to each other. Special relativity includes only the special case (hence the name) where the motion is uniform. The motion it explains is only if you’re traveling in a straight line at a constant speed. As soon as you accelerate or curve — or do anything that changes the nature of the motion in any way — special relativity ceases to apply. That’s where Einstein’s general theory of relativity comes in, because it can explain the general case of any sort of motion. Einstein’s theory was based on two key principles:
* The principle of relativity: All objects move in a motion relative to one another. No motion except the speed of light is fixed. And the laws of physics don’t change, even for objects moving in inertial (constant speed) frames of reference. * The principle of the speed of light: The speed of light is the same for all observers, regardless of their motion relative to the light source. (Physicists write this speed using the symbol c.)
Explaining theory of relativity and related concepts
Classical Relativity (mechanics theory)
Experiment: (Self thought and practically conducted)
An everyday life situation when you are moving in a straight escalator. Standing on next to an escalator, I measured the speed of my mother, who was standing still on the straight escalator, using a Doppler’s radar. Speed measured by the radar= 3 km/h
Then standing on the same escalator I measured the speed of my mother a few meters from me.
Speed Measured by the radar= 0 km/h
Classical relativity states that all motion in this universe is relative to one another. Nothing is fixed. As measured by the radar the escalator and hence my stationary mother on it was moving at a speed of 3km/h. But when I measured the speed with myself on the escalator, the radar measured 0 km/h. This is because although my mother was still moving with the escalator’s speed her state of motion with respect to mine was stationary.
Maxwell’s theory and the abolishment of aether theory
Maxwell was a scientist who gave various laws with respect to electromagnetic radiation. He, through his equations, proposed that like all other EMRs even the speed of light could be calculated. James Clark Maxwell (1884) devised his famous equation, showing that the four basic equations of electromagnetism (one of which Maxwell invented so his equation would work, but it turned out to be correct), can be combined into a single wave equation. The speed of the wave is determined solely by a term involving known constants that appear in the original formulas. Thus, Maxwell showed that the speed of light was a constant and that its speed could be measured using electromagnetic experiments that were already in place to determine
those constants. Nobody really believed that the speed was actually constant; they assumed that it was constant in some preferred reference frame, called the ether.
But Michelson, together with Morley, attempting to measure the speed of the earth through the ether by measuring the speed of light in many different directions at once, found that the speed was constant in all directions. Nobody knew what to make of that in 1887. Then Lorentz gave his 3 sets of explanations to prove Maxwell’s observations. But all these three explanations were proved wrong by Einstein as he gave the theory of relativity. He believed light to be a constant at all times and abolished the idea of aether. His explanations involved the principles of Spacetime where he unified space and time to create a four-dimensional view of the universe with three dimensions of space and one dimension of time.
Einstein’s theory of special relativity created a fundamental link between space and time. The universe can be viewed as having three space dimensions — up/down, left/right, forward/backward — and one time dimension. This 4-dimensional space is referred to as the space-time continuum. If you move fast enough through space, the observations that you make about space and time differ somewhat from the observations of other people, who are moving at different speeds. According to Einstein, Space and time were a single unit and not absolute but relative. The movement in space affected the movement in time. The faster one moved through space the slower one goes through time. Thought experiment: (self-thought and data input based on other examples to explain concepts): Imagine a car moving at say a 100/s along the east direction and at zero speed toward the north direction.
Then in one second it moves 100m towards east with no progress towards the north. Now say it moves north-east at the same speed. Because its speed is now diverted in two directions, it only moves 50 towards east and 50 m north. Same applies for space and time i.e. the faster you move through space the slower you pass through time. If you move at the speed of light then you make no progress in time and if you move at a speed that is greater than the speed of light, you can go back in time! Therefore, Einstein in order to measure distance between two objects chose to use a single entity called spacetime. Different observers would see different events in space in different ways. Some would see 2 events occurring at the same point in time but far apart in space, whereas other would see the same two events occur in very close to each other in space but far apart in time.
Maxwell, using his 4 equations of electromagnetism proved that the speed of light was a constant. But his idea was rejected and everybody thought the speed of light was relative to a constant frame called aether. Also a concept called ether drift developed whereby light through all other media except aether would undergo a drift called ether drift opposing its speed. This was dependent on the velocity of the object. The more the velocity of the media, the less was supposed to be the speed of light through the media.
Using this when Michelson, together with Morley, attempted to measure the speed of the earth through the ether by measuring the speed of light in many different directions at once, they found that the speed was constant in all directions and equal to the constant calculated by Maxwell. Now a question arose: how was this possible? The explanation to this was given by Einstein who abolished aether and said that the speed of light was a constant and through his theory of relativity demonstrated that how this was possible.
To understand the fact that speed of light is a constant, we need to change our perspectives on distance and time from them being a relative quantity from a fixed quantity. This introduces to us two new concepts of time dilation and length contraction. Both time dilation and length contraction are immediate consequences of the Lorentz transformation
Thought experiment: (taken from YouTube video on relativity)
Consider this thought experiment. You and AA are in 2 different spaceships in space. Both of you are measuring trying to measure the speed of light. Your spaceship is stationary while your friend’s spaceship is moving at a constant speed, say 0.5c. To calculate time (which can be calculated by using any device that measures a certain event periodically) both of you are using 2 plates reflecting light against each other. (Look at the diagram below)
Now in the (1) clock is the clock in the stationary clock i.e. the one on the stationary spaceship whereas the (2) clock is on the moving spaceship. Both clocks are identical. It is known that the speed of light is the same at all times. Therefore here in the stationary clock light moves up and down in a perpendicular distance the shortest distance. If the clock moves by 5 min every time the light touches the bottom plate then the clock would run at a certain speed and change appropriately. Now in case of the moving clock the light beam is travelling diagonally as the plates are constantly moving along with the spaceship in which they are present. Therefore the light takes a longer time to hit the bottom plate (as the speed of light is constant and light has to travel a longer path). Therefore the (2) clock runs slower than the (1) clock despite them being exactly identical. This phenomenon is known as time dilation, where the time on a ship moving very quickly appears to pass slower than on Earth.
The theory of special relativity revolutionized not just our understanding of time but our understanding of space too. I have already described the phenomenon of time dilation, whereby pairs of clocks in uniform relative motion each tick more slowly with respect to the other. A closely related effect is the phenomenon of length contraction (sometimes known as “Lorentz contraction”, “FitzGerald contraction” or even “Lorentz-FitzGerald contraction” after the physicists who predicted it on the basis of a crude forerunner of special relativity). Thought Experiment: (Taken from You tube Video But self-data input) Now in the spaceships example I have been using it can be said that if the two spaceships when at the same point i.e. when one is directly below the other and they release a beam of light and measure the speed of light after 12 seconds on the clock on the stationary ship which would be around 9 seconds on the clock aboard the moving ship if we calculate it using Lorentz’s transformations. Since the stationary ship is at rest in the space dimension therefore the rulers or any distance measuring instrument used would show that light travelled 12 light-second (the distance light travels in one second).
The actual speed of light is 1light-second per second. Since the total time measured was 12 seconds. Therefore the speed would that would be calculated is 12 light second per second which is nothing but one light second per second. Since the second spaceship was moving at a speed half the speed of light it should calculate the distance of the light beam from the ship after 12 seconds on the clock aboard the stationary ship to be 6 light-second. But the actual distance measured by the rulers or any other measuring instrument onboard the moving ship will be 9 light-second. This is because of a phenomenon called length contraction.
When an object moves at a very high speed i.e. a speed which is equal to or greater than 30% of c, then this length contraction can be seen up to some extent. Since the second spaceship was moving at 0.5*c, therefore the ship and all rulers or the measuring instruments used shrunk and the light beam was measured to be a distance of 9 light-second in 9 seconds, which is nothing but 1light-second per second.
As strange as it seems, this example (and many others) demonstrates that in Einstein’s theory of relativity, space and time are intimately linked together. If you apply Lorentz transformation equations, they work out so that the speed of light is perfectly consistent for both observers, i.e. one in motion at a constant speed and other stationary or at rest. This strange behavior of space and time is only evident when you’re traveling close to the speed of light, so no one had ever observed it before. Experiments carried out since Einstein’s discovery have confirmed that it’s true — time and space are perceived differently, in precisely the way Einstein described, for objects moving near the speed of light.
The Consequence of Theory of Relativity: Unifying mass and energy (E=mc2) The most famous work of Einstein’s life also dates from 1905, when he applied the ideas of his relativity paper to come up with the equation E=mc2 that represents the relationship between mass (m) and energy (E). Einstein found that as an object approached the speed of light, c, the mass of the object increased. The object goes faster, but it also gets heavier. If it were actually able to move at c, the object’s mass and energy would both be infinite.
A heavier object is harder to speed up, so it’s impossible to ever actually get the particle up to a speed of c. for example consider a proton accelerating towards the speed of light. As is moves closer to the speed of light its mass increases thus acting as a hindrance to the movement of the object. Until Einstein, the concepts of mass and energy were viewed as completely separate. He proved that the principles of conservation of mass and conservation of energy are part of the same larger, unified principle, and conservation of mass-energy. Matter can be turned into energy and energy can be turned into matter because a fundamental connection exists between the two types of substance. Thus if an object moves at a speed of light then it would have an infinite mass, negligible length and would make no progress in time. | <urn:uuid:98801303-91d1-4422-b5fd-bc975cf24021> | 4.25 | 2,863 | Academic Writing | Science & Tech. | 48.047701 | 95,615,298 |
PHIL 160: Lecture 2. Science news… Some background on the Tevatron and the (never-built) Superconducting Super Collider
Welcome to Fermilab!
Our mission is to discover what the universe is made of and how it works.
We're asking three simple, challenging questions here at the frontier of particle physics:What is the nature of the universe?What are matter, energy, space and time?How did we get here and where are we going?
Fermilab Director Michael S. Witherell
Was the world’s highest-energy particle collider
4 miles in circumference and housed in a tunnel 30 feet below the ring
Accelerators send particles racing around the Tevatron at 99.9999% of the speed of light
Send two kinds of subatomic particles, protons and antiprotons, around the ring in opposite directions.
At two points, beams of these particles flow right into each other.
Causing millions and millions of collisions, at the rate of almost two million each second.
Many kinds of devices record details of the debris to identify, based on theory, what kinds of particle are being produced in the collisions.
Using the Tevatron, Fermilab scientists have confirmed:
The bottom quark (1977)
The top quark (1995)
The tau neutrino (2000)
“We collide particles in the hope of seeing something never seen before.”
But predicted by theory!
The CDF Collider Detector.
Each detector has about one million individual pathways for recording electronic data generated by the particle collisions. The signals are carried over nearly a thousand miles of wires and cables--each one connected by hand and tested individually.
Books? No, they are complex
Words? No, they are also complex
Letters? No, can be broken down into just 0 and 1…
If it makes no sense to take apart the 0 and the 1, we’ve found the “atomic” components of the library
The universe as the library
What are its most basic elements?
The forces of nature are the grammar, spelling, and algorithm
The subatomic particles, quarks and leptons, are currently believed to be the “atomic” (un-cut-able) elements of the universeThe “library of matter”
What basic assumptions can we identify that underlie and motivate research in particle physics?
That the entities and laws studied by particle physicists are what make up and govern all other entities and processes and regularities.
A commitment to simplicity (just a few particles and a few laws): nature is (ultimately simple – i.e., elegant)
That “invisible” (not able to be directly observed) objects are respectable – and, indeed, necessary for (some) theories of physics.
What warrants these assumptions?
entities posited by science:
“My evidence for atoms and quarks is as good as the evidence [the TV provides that the Pope exists].
“What is that evidence? Tracks of particles in a bubble chamber. In the Fermilab accelerator, the “debris” from a collision between a proton and an antiproton is captured by a 3 story, 60 million dollar detector. …
“Here, the “evidence” – the “seeing” – is tens of thousands of sensors that develop an electrical impulse when a particle passes…”
“All of these impulses are fed by through hundreds of thousands of wires to electronic data processors.
“Ultimately, a record is made on spools of magnetic tape, encoded by zeroes and ones.
“Science, especially particle physics, gains confidence in its conclusions by duplication” and by frequent tests of the experimental apparatus.
The late great Stephen Jay Gould
Harvard paleontologist and evolutionary theorist
One of the strongest defenders of Darwin and evolutionary theory
One of the strongest critics of some aspects of evolutionary theory. | <urn:uuid:59d698ea-cb18-4375-bf32-b12d1476b029> | 3.515625 | 843 | Audio Transcript | Science & Tech. | 39.780313 | 95,615,304 |
about this item
The work of engineers surrounds us: from the phones in our pockets to the layout of our cities. But the skills that brought the world clean water and telecommunications also produced polluting technologies that could threaten its future.
Engineering explores the scientific, social, and philosophical implications inherent in the challenges faced by engineers throughout history. From Roman viaducts to bionic limbs, humans have used fascinating and diverse feats of engineering to overcome their limitations. Revealing the widespread impact that this has had on culture, knowledge and the environment, McCarthy presents a future in which engineering is crucial to saving the planet. | <urn:uuid:afdb1842-9468-47a7-9733-570d3a0a5917> | 3.203125 | 124 | Truncated | Science & Tech. | 25.471077 | 95,615,327 |
The search for volcanoes is a long-running thread in the exploration of Venus. “Volcanoes are a key part of a climate system,” says Fred Taylor, a Venus Express Interdisciplinary Scientist from Oxford University. That’s because they release gases such as sulphur dioxide into the planet’s atmosphere.
On Earth, sulphur compounds do not stay in the atmosphere for long. Instead, they react with the surface of the planet. The same is thought to be true at Venus, although the reactions are much slower, with a time scale of 20 million years.Some scientists have argued that the large proportion of sulphur dioxide found by previous space missions at Venus is the ‘smoking gun’ of recent volcanic eruptions. However, others maintain that the eruptions could have happened around 10 million years ago and that the sulphur dioxide remains in the atmosphere because it takes such a long time to react with the surface rocks.
The SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) instrument analyses the way starlight or sunlight is absorbed by Venus’s atmosphere. The absorbed light tells scientists the identity of the atoms and molecules found in the planet’s atmosphere. This technique works only in the more tenuous upper atmosphere, above the clouds at an altitude of 70–90 km. In the space of a few days, the quantity of sulphur dioxide in the upper atmosphere dropped by two-thirds.
Jean-Loup Bertaux, Service d’Aeronomie du CNRS, Verrières-le-Buisson, is the Principal Investigator for SPICAV. “I am very sceptical about the volcanic hypothesis,” he says. “However, I must admit that we don’t understand yet why there is so much sulphur dioxide at high altitudes, where it should be destroyed rapidly by solar light, and why it is varying so wildly.”Another instrument on Venus Express, VIRTIS (Visible and Infrared Thermal Imaging Spectrometer), can see below the clouds at infrared wavelengths. It detects the signature of sulphur dioxide by the amount of infrared radiation that the molecule absorbs, the stronger the signature, the more abundant the molecule.
The only way to be absolutely certain that active volcanism is taking place on Venus is to see a volcano in action. This is not easy when you are trying to look through 100 km of thick, cloudy atmosphere. But the Venus Express team are working on two ways of doing this. The first is to look for localised increases in sulphur dioxide that would indicate a large plume of the gas issuing from a volcano. The other way is to look for hot spots on the surface that can be shown to be fresh lava flows.In both cases, the instrument to use is VIRTIS. “No thermal anomaly has been detected so far,” says Pierre Drossart, Observatoire de Paris, France, and co-Principal Investigator on VIRTIS. Nevertheless, the search continues and the team plan to announce their findings soon.
Håkan Svedhem | EurekAlert!
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
13.07.2018 | Event News
13.07.2018 | Materials Sciences
13.07.2018 | Life Sciences | <urn:uuid:3d1f97b1-b62b-4dd0-b740-0c7fd6fc517f> | 4.125 | 1,293 | Content Listing | Science & Tech. | 43.316328 | 95,615,340 |
Quantum sensors—qubits sensitive to external fields—have become powerful detectors for various small acoustic and electromagnetic fields. A major key to their success have been dynamical decoupling protocols which enhance sensitivity to weak oscillating (AC) signals. Currently, those methods are limited to signal frequencies below a few MHz. Here we harness a quantum-optical effect, the Mollow triplet splitting of a strongly driven two-level system, to overcome this limitation. We microscopically understand this effect as a pulsed dynamical decoupling protocol and find that it enables sensitive detection of fields close to the driven transition. Employing a nitrogen-vacancy center, we detect GHz microwave fields with a signal strength (Rabi frequency) below the current detection limit, which is set by the center’s spectral linewidth . Pushing detection sensitivity to the much lower 1/T 2 limit, this scheme could enable various applications, most prominently coherent coupling to single phonons and microwave photons.
Sensitive detectors for weak radio-frequency (>100 MHz) signals of electric, magnetic, or pressure fields would shift several frontiers of physics. They could advance the exploration of phonons on the single-particle level and reveal weak microwave signals encountered in quantum information processing, biomedical imaging, or more exotically, the search for extraterrestrial intelligence1.
Driven by this perspective, the past decade has seen the rise of detectors based on Rydberg atoms2, 3, superconducting quantum circuits4,5,6,7,8, or optomechanical sensors9,10,11. All approaches have achieved noise levels below 10 photons (noise temperatures below 100 mK), an order of magnitude better than state-of-the-art semiconductor detectors12 and maser amplifiers13,14,15,16. However, this performance is only reached in sophisticated setups (Rydberg atoms) or at sub-Kelvin temperatures (optomechanics, superconductors).
Detectors based on solid state spin qubits could potentially overcome these limitations. Optically active spin qubits such as nitrogen-vacancy (NV) centers can be optically polarized, that is effectively laser cooled to a temperature of a few 10 mK, even in a substrate at higher temperature. Magnetic tuning of their spin transition enables resonant coupling to external fields at any frequency up to 100 GHz. Theory proposals (Fig. 1a) suggest that both single microwave phonons17 and photons18 can be coupled sufficiently strong to drive a full spin-flip within the spin coherence time T 2 (ms19 to s20, depending on species and temperature).
However, radio-frequency sensing by spin qubits is currently precluded by a major roadblock. It is illustrated in the detection protocol of Fig. 1b, where an incoming signal drives the qubit transition, inducing a spin flip which is subsequently detected by readout of the spin. To drive a full spin-flip, an incoming signal has to saturate the spin transition. Therefore, the signal strength (Rabi frequency) has to exceed the inhomogeneous transition linewidth . Since is much broader than 1/T 2 (MHz vs kHz for an NV center in a natural abundance crystal at room temperature), coupling of spins to high-frequency signals remains inefficient. As a specific example, interfacing spins to single phonons or photons (Fig. 1a) is currently precluded, since coupling would be possible within T 2 but remains out of reach of .
For signal frequencies below a few MHz, dynamical decoupling protocols can break this limit21 (Fig. 1c). Here, the transition is driven by a strong continuous or pulsed control field (frequency ω 0) to create a pair of photon-dressed qubit states, split by the driving field Rabi frequency Ω22, 23. This new transition has a far narrower linewidth 1/T 2, and can hence absorb much weaker signals. However, practical limitations on drive power limit the frequency range which can be probed in this way.
As the key idea of this work, we note that the fully hybridized spin-photon states (the ‘Jaynes-Cummings ladder’) support another set of transitions at frequencies (ω 0 − Ω, ω 0, ω 0 + Ω), the Mollow triplet24, which has been extensively studied in quantum optics25,26,27,28,29 and has been proposed as a narrowband tunable photon source30. Since these transitions equally link pairs of dressed states, we posit that they should allow for T 2-limited sensing of signals with a frequency much higher than the available Rabi frequency Ω. We will show in the following that these transitions can indeed be harnessed to detect high-frequency signals. Moreover, we will demonstrate that Mollow sidebands can be created by robust dynamical decoupling protocols acting as a strong drive. In contrast to a continuous drive, these protocols set the effective Rabi frequency by timing rather than power, an experimental advantage that has made low-frequency sensing by decoupling a widely adopted technique. We will analyze the sensitivity of the resulting schemes, concluding that they could enable coherent coupling of solid state spins to single phonons and photons.
Continuous wave Mollow absorption
We demonstrate the creation of dressed states by the scheme of Fig. 2a. Here, the spin is initialized into the dressed state by a (π/2)Y pulse (Y labeling the carrier phase ϕ Y = π/2). This state is locked as an eigenstate of a strong dressing field with orthogonal carrier phase ϕ X = 0. We find that a weak probe field at the detuned frequency ω 0 ± Ω indeed induces rotation at its native Rabi frequency, as evidenced by measurements on an NV center. The central Mollow resonance is absent in this measurement, since it couples dressed states with identical spin projection, as has been previously observed in superconducting qubits31. It can be recovered by preparing into an orthogonal state and changing the phase of the signal (Fig. 2b) to account for the different quadratures of the Mollow sidebands25.
Pulsed Mollow absorption as a sensing protocol
We now convert Mollow absorption spectroscopy into a pulsed sensing protocol (Fig. 3a) to mitigate an important problem: the continuous wave (CW) protocol is prone to decoherence since fluctuations of the drive field power (Ω) directly translate into frequency noise of the dressed state transition ω 0 ± Ω. We will see that pulsed protocols shift the frequency of the Mollow sideband absorption from ω 0 ± Ω to ω 0 ± π/τ, τ denoting the pulse spacing as shown in Fig. 3b. Since timing (τ) is controlled better than power (Ω), decoherence is reduced to the intrinsic limit set by the spin qubit. Importantly, absorption on these transitions will induce a spin trajectory similar to standard Rabi oscillations. This enables sensing of the absorbed field’s amplitude, effectively turning the probe into a signal field.
Conversion into a pulsed protocol is best understood from tracking the spin evolution across the sideband absorption sequence (Fig. 3a). We decompose the strong drive into a series of π pulses, spaced by a time τ = π/Ω, and split the weak signal into a commensurate series of weak pulses with pulse area . We equally discretize its detuning of Δ = Ω − a continuous decrease in carrier phase-into periodic inversions of its axis, that is a discrete decrease of the phase by π occurring with period π/Δ. At the resonance condition Δ = Ω, this period matches the spacing τ = π/Ω of the strong drive. In this case, the weak signal is resonantly rectified in the toggling frame of the spin (Fig. 3a), analogous to the situation in low-frequency sensing. We note that discretization preserves the axes of all fields involved up to a sign so that the resulting absorption resonance remains phase-sensitive. While it picks up signals with a carrier phase along Y, it is blind to signals along X.
Our pulsed scheme (Fig. 3b) is an explicit implementation of this discretized sequence. We emulate the strong drive with Rabi frequency Ω by short π pulses with a spacing τ = π/Ω. We equally discretize the amplitude of the signal into a sequence of pulses, applied between the π pulses of the strong drive. We do not discretize its phase, allowing instead for a continuous detuning Δ, since this property should be sufficient to induce the advance in carrier phase discussed above. We find that the weak signal is most strongly absorbed at a detuning Δ/2π = ±(2τ)−1. The absorption resonance remains locked to this frequency as we scan τ while keeping all other parameters constant (Fig. 3c). All our observations match well with an explicit time domain simulation of the spin evolution (bottom half of Fig. 3c, Supplementary Note 3). We note that discretization (switching) of the signal is not strictly required. All of the above analysis remains valid for a continuous signal, despite the fact that it overlaps with the control pulses during part of the time. We have confirmed this prediction experimentally (Supplementary Note 5), but stick with the switched implementation in the following, since it allows for easier implementation of more robust decoupling sequences (see below).
The bandwidth Δω = π/T of this pulsed Mollow resonance is limited by the finite duration T = 2nτ of the sequence containing 2n π-pulses. Crucially, this bandwidth drops below the inhomogeneous linewidth if we choose a sequence longer than (Fig. 3d). The Mollow resonance is framed by sidebands with nodes at frequencies ω 0 ± π/τ ± kπ/T with . These are another consequence of the finite sequence length: since sensitivity is nonzero only in a rectangular window in the time domain, the sequence has a sinc response in the frequency domain. Tracing a Rabi oscillation of the weak signal along the resonance hyperbola Δ = ± π/τ we find its native Rabi frequency Ωrf to be reduced to a value Ωpulsed = 2/π · Ωrf. We attribute this reduction to the fact that the detuned signal, rotating at an angular frequency of Δ on the Bloch sphere, has a phase orthogonal to the strong drive phase only during a fraction of the free evolution time τ. It therefore has to be scaled by a factor , with ϕ(t) denoting the phase of the signal. All of these properties are analogous to similar features in low-frequency decoupling sequences32.
Using the time domain simulation and an analytical model (Supplementary Notes 2 and 4), we find Mollow resonances in many decoupling sequences, including the robust sequences CPMG, XY4, and XY8 (Fig. 3e). A detailed discussion of the effect of decoupling sequence structure on position and shape of the resonances is given in Supplementary Note 4.
Small-signal limit and impact of decoherence
We finally demonstrate the performance and an important limit of our method by the protocol of Fig. 4a. Here, we adopt the XY8 sequence for the strong drive, in order to be maximally robust against experimental fluctuations. We phase-modulate the signal to gain a constructive contribution to the Rabi rotation during every evolution period τ ∗. In this setting we have been able to drive slow Rabi oscillations with a period as long as 100 µs (Fig. 4b). While this clearly breaks the limit in terms of signal strength, the limit reappears as a constraint on the pulse spacing τ, which has to be short against . For longer spacings—corresponding to slower Rabi frequencies in the CW sequence—the Mollow resonance merges with the inhomogeneously broadened transition. To verify this limit explicitly, we artificially shorten of the NV center by averaging multiple measurements taken at different, Gaussian-distributed, frequencies of the microwave drive. Tuning decoherence by this technique, we find that sensitivity breaks down if pulses are spaced by more than (Fig. 4c).
With these insights, we are finally in a position to evaluate the sensitivity that could be reached by a microwave spin sensor. Table 1 presents a series of such estimates for three typical experimental scenarios, a single NV center at ambient temperature, a NV center at cryogenic temperature with single shot readout, and an ensemble of NV centers in a densely doped diamond. Our estimates derive from two assumptions:
We assume high-frequency sensing to be as robust against experimental fluctuations as low-frequency sensing, since it is based on the very same decoupling protocols. In particular, we assume that the same T 2 time can be reached and the same number of control pulses can be applied. This assumption is justified since sensitivity characterizes the response to an infinitesimally weak signal where the spin follows a nearly identical trajectory as in the bare decoupling sequence.
In contrast to low-frequency sensing, T 2 is bounded by an upper limit of , where N max ≈ 1000 denotes the maximum number of control pulses that can be applied before pulse errors deteriorate coherence19. This condition arises from the additional constraint that pulses have to be spaced by less than , as discussed in the context of Fig. 4. While this condition does not set the limit for experiments on single NV centers, where isotopic purification can push times into the range of 100 µs, it is the limiting factor for ensemble sensing where inhomogeneous broadening shortens times down to the sub-microsecond timescale.
More importantly, these estimates suggest that NV centers should be able to couple coherently to photons and phonons in the scenarios of Fig. 1 within their coherence time T 2 (assuming the values of Table 1). This would enable detection of both particles by coherent absorption and subsequent detection of the spin state, a more powerful measurement than time-averaged detection of a signal with a mean strength on the single-particle level. It could pave the way to a quantum bus based on these signals, mediating coupling between distant spins or to other qubits. The narrow transition provided by our scheme could aid the development of room-temperature MASERs based on optically initialized spins14. Their use as amplifiers could provide another approach to sensing of weak signals, complementary to optical detection.
In summary, we have pushed spin-based quantum sensing to frequencies much higher than the available Rabi frequency Ω. In the language of superconducting amplifiers, this promotes spins to phase-sensitive microwave detectors that might provide sufficient sensitivity to detect single phonons and photons. Compared to competing approaches such as Josephson parametric amplifiers, our scheme has a very narrow bandwidth. It absorbs signals only within a narrow window of width 1/T 2, (≈100 Hz–10 kHz for NV centers) and, operated as a detector, would be limited to a maximum count rate of the same order of magnitude. It seems plausible, however, that a future extension of our experiment could continuously shift this window across frequencies up to several 100 GHz, tuning the spin transition e.g. by a magnetic field33. Crucially, the absorption frequency ω 0 ± π/τ is set only by timing and frequency of the external drive, which can be controlled well. It is independent of the native spin transition and hence resilient to drifts in surrounding fields.
From a fundamental perspective, we have provided an intuitive microscopic understanding of the Mollow triplet as a pulsed quantum protocol. It appears most intriguing to extend this novel perspective to other effects of quantum interference, such as electromagnetically induced transparency.
NV center preparation
All experiments have been performed on single NV centers spontaneously created inside a polycrystalline electronic grade IIa diamond during chemical vapor deposition (Element Six, part N° 145-500-0356).
Both the strong drive and the weak signal were generated by an Arbitrary Waveform Generator (Rigol DG5352), which was mixed onto a GHz frequency carrier, amplified (amplifier MiniCircuits ZHL16W-43-S+), and applied to the NV center by a coplanar waveguide. All given microwave excitation powers refer to the input of the coplanar waveguide. They have been calculated from the output power of the Arbitrary Waveform Generator by adding a constant offset of +56 dBm to account for all gains and losses along the excitation path.
The spin state was measured by fluorescence readout in a high-NA confocal microscope (excitation 532 nm, ~1 mW power, detection in the > 650 nm band by an objective lens Olympus UPLSAPO 60 × 1.35O). In total, 4–8×105 readout repetitions per trace were made, corresponding to a measurement time of 15–30 min for each trace. All sequences were recorded twice, with and without an additional π pulse before readout. The difference of both datasets was normalized to the signal contrast of a Rabi oscillation to yield a quantitative estimate of .
All relevant data is available from the authors upon request.
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This work has been supported by the Deutsche Forschungsgemeinschaft via the Emmy Noether grant RE3606/1-1 and the Nanosystems Initiative Munich (NIM). We thank Amit Finkler and Frank Deppe for helpful discussions. During redaction of this manuscript we became aware of simultaneous independent work34, 35. | <urn:uuid:ce69e9d5-b4d9-45b9-95fb-725bf59ab0ad> | 2.796875 | 3,729 | Academic Writing | Science & Tech. | 37.550299 | 95,615,360 |
Based on a discipline of geology called stratigraphy, rock layers are used to decipher the sequence of historical geological events.Relative techniques can determine the sequence of events but not the precise date of an event, making these methods unreliable.Today, many different radioactive elements have been used, but the most famous absolute dating method is radiocarbon dating, which uses the isotope C.This isotope, which can be found in organic materials and can be used only to date organic materials, has been incorrectly used by many to make dating assumptions for non-organic material such as stone buildings.TL Age = Palaeodose (P) _____________ (ARD) TL samples may be collected in open ended or opaque PVC tubes approximately 12cm in length and 6cm in diameter.Whilst it advisable to protect the sample from direct sunlight there is no need to sample at night and the orientation of the specimen is not important.The amount of light produced is a specific and measurable phenomenon.If the specimen’s sensitivity to ionizing radiation is known, as is the annual influx of radiation experienced by the specimen, the released thermoluminescence can be translated into a specific amount of time since the formation of the crystal structure.
The major source of error in establishing dates from thermoluminescence is a consequence of inaccurate measurements of the radiation acting on a specimen.
The presence of rubidium and cosmic radiation generally play a lesser but contributory roll, and the total radiation dose delivered to the TL phosphor is modified by the presence of water.
The period since deposition is therefore measured by determining the total amount of stored TL energy, the palaeodose (P), and the rate at which this energy is acquired, the annual radiation dose (ARD).
The accumulation of trapped electrons, and the gaps left behind in the spaces they vacated, occurs at a measurable rate proportional to the radiation received from a specimen’s immediate environment.
When a specimen is reheated, the trapped energy is released in the form of light (thermoluminescence) as the electrons escape. | <urn:uuid:765da60f-1d15-4ef9-b85e-41058aed209e> | 3.90625 | 425 | Knowledge Article | Science & Tech. | 19.44596 | 95,615,367 |
Copy a human? I can do that with my eyes closed! Blindfolded dolphin mimics trainer's movements by using sound waves to 'see' what he is doing
- Scientists have shown that when a dolphin is blindfolded, it can use other senses to mimic a human's movements
- Tanner the dolphin used echolocation when blindfolded to replicate movements by his trainer, such as spinning in the water
- The study by the Dolphin Research Centre in the Florida Keys expands on previous studies on how dolphins can imitate each other while blindfolded
A dog may be man's best friend, but dolphins can imitate human actions, and even how they solve problems, scientists have said.
When a dolphin is blindfolded, it can use other senses to mimic a human's movements, according to a recent study.
Dr Kelly Jaakkola said a bottlenose dolphin called Tanner displayed problem-solving skills by electing to swap to using echolocation when he was blindfolded in order to copy his trainer's actions.
Scroll down for video
Dolphin trainer Emily Guarino puts eye cups on an Atlantic bottlenose dolphin named Tanner to blindfold him, demonstrating the dolphin uses his other senses to work out a problem
When Tanner wasn't able to use sight to work out the movement he was told to copy, he switched to another technique - echolocation. His trainer Wade Davey, demonstrates the dolphin's ability to mimic his actions blindfolded
The dolphin was was blindfolded and instructed to mimic the actions of a trainer in the water with him.
When Tanner wasn't able to use sight to work out the movement, he switched to another technique.
The dolphin emitted sounds, listened to the echo and interpreted the resulting sound waves.
This ability - known as echolocation - allowed Tanner to replicate movements by the trainer, such as spinning in the water.
The study, conducted at the Dolphin Research Centre in the Florida Keys, expands on previous research into how dolphins are able to imitate other dolphins while blindfolded.
The study, conducted at the Dolphin Research Centre in the Florida Keys, expands on previous studies looking at how dolphins are able to imitate other dolphins while blindfolded. Here, Tanner is rewarded for his cooperation with their study
To see if a change in sound would affect their imitation, researchers used humans instead of dolphins to make the movements in the water.
Dr Jaakkola, research director of the marine mammal centre, said researchers were surprised by Tanner's use of echolocation.
'He outsmarted us,' she said.
Dr Jaakkola explained that dolphins must decide when to use echolocation, and said: 'that's problem-solving.'
Janet Mann, a professor of biology and psychology at Georgetown University said: 'Of course they would use their echolocation to get more information. Dolphins have to solve problems all the time in the wild.' Here, Tanner is rewarded with a fish for mimicking his trainer's actions
WHAT IS ECHOLOCATION?
- Echolocation is biological sonar
- It is used for navigation and for foraging or hunting in various environments
- Echolocation is the same as active sonar, using sounds made by the animal itself
- Ranging is done by measuring the time delay between the animal's own sound emission and any echoes that return from the environment
- The relative intensity of sound received at each ear as well as the time delay between arrival at the two ears provide information about the horizontal angle from which the reflected sound waves arrive
- The term echolocation was coined by Donald Griffin, whose work demonstrated its existence in bats in 1938
Janet Mann, a professor of biology and psychology at Georgetown University who was not involved in the study, said the results of the study were not surprising as they are consistent with how dolphins act in the ocean.
She said: 'Of course they would use their echolocation to get more information.
'Dolphins have to solve problems all the time in the wild.'
She also explained that dolphins use their echolocation skills more at night.
During a recent demonstration in an enclosed lagoon in Grassy Key, a Florida island where the Dolphin Research Centre is located, trainer Emily Guarino got Tanner's attention by asking, 'Are you ready to play? Let's play the research game.'
Ms Guarino indicated to Tanner that he was supposed to copy her and placed latex eye cups over each eye - in effect, a dolphin blindfold.
Ms Guarino (pictured) indicated to Tanner that he was supposed to copy her and placed latex eye cups over each eye. Another trainer began to spin in the water with his arms wrapped across his shoulders and Tanner did a similar spin using echolocation
Another trainer in the water was then shown a clipboard with an action written on it to perform.
Wordlessly that trainer began to spin in the water with his arms wrapped across his shoulders.
Tanner then did a similar spin.
For the study, published online in the scientific journal Animal Cognition, researchers tested a dozen behaviours that Tanner already knew, including bobbing up and down, blowing bubbles underwater, swimming like a shark with the tail - or feet - moving side to side and floating on top of the water.
Here Tanner and his trainer Wade Davey have fun conducting the experiment into dolphins' problem solving skills
Each behaviour was tested twice at random, with and without the blindfold, as researchers recorded echolocation sounds underwater.
Tanner was just as accurate at imitating a human - blindfolded or not - as he was at imitating another dolphin, researchers determined.
The study included six sessions spread over a nine-day period.
This kind of flexibility with imitation is more commonly associated with humans.
Each behaviour (such as an aquatic headstand) was tested twice at random, with and without the blindfold, as researchers recorded echolocation sounds underwater. Tanner was just as accurate at imitating a human - blindfolded or not - as he was at imitating another dolphin, researchers determined
But people and dolphins are separated by about 90 million years of evolution, and their imitation skills likely evolved separately.
So exploring imitation in these species 'has the potential to give us clues into why imitation ever evolved at all,' Dr Jaakala said.
Further testing is needed to see if other dolphins can imitate as well as Tanner.
Dr Jaakala said: 'We have no reason to believe that this dolphin was just an Einstein dolphin that did this.'
Further testing is needed to see if other dolphins can imitate as well as Tanner (pictured)
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|Debugging with GDB|
python-interactivecommand can be used to start an interactive Python prompt. To return to gdb, type the
EOFcharacter (e.g., Ctrl-D on an empty prompt).
Alternatively, a single-line Python command can be given as an argument and evaluated. If the command is an expression, the result will be printed; otherwise, nothing will be printed. For example:
(gdb) python-interactive 2 + 3 5
pythoncommand can be used to evaluate Python code.
If given an argument, the
python command will evaluate the
argument as a Python command. For example:
(gdb) python print 23 23
If you do not provide an argument to
python, it will act as a
multi-line command, like
define. In this case, the Python
script is made up of subsequent command lines, given after the
python command. This command list is terminated using a line
end. For example:
(gdb) python Type python script End with a line saying just "end". >print 23 >end 23
set python print-stack
set python print-stack: if
full, then full Python stack printing is enabled; if
none, then Python stack and message printing is disabled; if
message, the default, only the message component of the error is printed.
It is also possible to execute a Python script from the gdb interpreter:
script-extensionsetting. See Extending GDB.
python execfile ("script-name")
execfilePython built-in function, and thus is always available. | <urn:uuid:4028b56f-870f-4c54-bf51-9e836dfe752f> | 3.109375 | 341 | Documentation | Software Dev. | 53.548534 | 95,615,375 |
The results from the Wide Area Search for Planets (SuperWASP) will be announced by team member Dr Don Pollacco of Queen’s University Belfast, in his talk at the RAS National Astronomy Meeting (NAM 2008) on Tuesday 1 April.
Scientists have found more than 270 extrasolar planets since the first one was discovered in the early 1990s. Most of these are detected through their gravitational influence on the star they orbit – as it moves the planet pulls on the star, tugging it back and forth. However, making these discoveries depends on looking at each star over a period of weeks or months and so the pace of discovery is fairly slow.
SuperWASP uses a different method. The two sets of cameras watch for events known as transits, where a planet passes directly in front of a star and blocks out some of the star’s light, so from the Earth the star temporarily appears a little fainter. The SuperWASP cameras work as robots, surveying a large area of the sky at once and each night astronomers have data from millions of stars that they can check for transits and hence planets. The transit method also allows scientists to deduce the size and mass of each planet.
Each possible planet found using SuperWASP is then observed by astronomers working at the Nordic Optical Telescope on La Palma, the Swiss Euler Telescope in Chile and the Observatoire de Haute Provence in southern France, who use precision instruments to confirm or reject the discovery.
45 planets have now been discovered using the transit method, and since they started operation in 2004 the SuperWASP cameras have found 15 of them – making them by far the most successful discovery instruments in the world. The SuperWASP planets have masses between a middleweight 0.5 and a huge 8.3 times that of Jupiter, the largest planet in our Solar System. A number of these new worlds are quite exotic. For example, a year on WASP-12B (its orbital period) is just 1.1 days. The planet is so close to its star that its daytime temperature could reach a searing 2300 degrees Celsius.
Dr Pollacco is delighted with the results. “SuperWASP is now a planet-finding production line and will revolutionise the detection of large planets and our understanding of how they were formed. It’s a great triumph for European astronomers.”
FURTHER INFORMATION (INCLUDING IMAGES):SuperWASP
3)http://star.pst.qub.ac.uk/~dlp/SWASP_3.jpg - the SuperWASP-South instrument.Image of the Euler (Swiss) Telescope dome
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- Open Access
Differences in the male mating calls of co-occurring epauletted fruit bat species (Chiroptera, Pteropodidae, Epomophorus wahlbergi and Epomophorus crypturus) in Kruger National Park, South Africa
© Adams and Snode; licensee Springer. 2015
Received: 25 April 2014
Accepted: 16 December 2014
Published: 16 January 2015
Almost nothing is known about the mating ecology and behavior of epauletted fruit bats (Epomophorus spp) of which eight species occur worldwide. Two species of epauletted fruits bats (Epomophorus wahlbergi and Epomophorus crypturus) overlap in their distributional ranges in Kruger National Park (KNP), South Africa. Morphologically, these two species are nearly identical to the human eye and field recognition is based upon the number and position of palatal rugae of captured individuals. In addition, the males of both species perform mating rituals during overlapping breeding seasons that appear quite similar and involve wing flapping and monotone vocalizations from calling stations in proximity to fruiting sycamore fig trees where females congregate to feed. The overlap in breeding seasons as well as physical and behavioral characteristics between these two species brings into question how species recognition occurs, and no research is available to understand how males are identified by the females of each species for mating purposes. We recorded vocalizations from calling males in local areas of KNP known to support both species and compared the sonograms to determine if the call structure of mating vocalizations between males of each species differs.
We recorded 25 mating vocalizations from seven male epauletted fruit bats near the Shingwedzi Research Camp and 31 mating vocalizations from nine individuals along the Sabie River near Skukuza. Analysis of calls showed significant distinctiveness of male mating vocalizations between the two species in terms of mean fundamental frequency, mean high frequency, mean low frequency, mean bandwidth, and mean call slope at the two sites.
We hypothesize that differences in male mating vocalizations recorded at each of our study sites represent call structure differences that potentially may be used to avoid cross-mating between species.
Two species of epauletted fruit bats (Epomophorus crypturus and Epomophorus wahlbergi) co-occur in Kruger National Park (KNP), South Africa. Although the range of E. wahlbergi is quite extensive throughout Sub-Saharan Africa, E. crypturus is near-endemic to South Africa, occurring only marginally outside of South Africa in the extreme south of Tanzania (Monadjem et al. 2010). Morphologically, the species are very similar to each other and are only told apart after capture by opening the oral cavity and counting the number of palatal ridges that reside behind the last upper molar (see ‘Methods’ section below); however, an analysis of museum specimens also revealed that maxillary width of the skull is significantly wider in E. crypturus than in E. wahlbergi (Taylor and Monadjem 2008). Both species show sexual dimorphism with males being larger in body size than females (Bergmans 1988), and during the mating season, males of both species call from tree perches at night to attract females for mating (McCracken and Wilkinson 2000). Both E. crypturus and E. wahlbergi have a mating system in which year-round multi-male/multi-female groups copulate away from the roost (Wickler and Seibt 1976; McCracken and Wilkinson 2000). Although E. wahlbergi has a bimodal breeding season (December and May) in the southern part of its range (Monadjem and Reside 2012), the breeding cycle of E. crypturus has not been thoroughly documented.
The mating call of male E. wahlbergi is described as a loud, audible, repetitive, monotone call (Wickler and Seibt 1976; Acharya 1992; Fenton et al. 1985) and appears to serve two functions: a) to attract females and b) to space out male conspecifics calling in the same area (Kingdon 1974; Wickler and Seibt 1976; Adams and Snode 2013). Although the mating call of E. wahlbergi has been described, herein, we provide the first quantification of the male mating call of E. crypturus.
The detailed distribution of either species of epauletted fruit bat in Kruger National Park (KNP) is poorly known. Monadjem et al. (2010) reports no records for E. crypturus from the southern areas of KNP, but Bonaccorso et al. (2014) captured both species in southern and northern KNP between 2004 and 2007, but showed skewed population numbers with E. crypturus in higher abundance in the north and E. wahlbergi in higher abundance in the south. Fenton et al. (1985) captured and radio-tagged 10 male and 10 female E. wahlbergi near Pafuri, about 30 km north of Shingwedzi, where our study took place, thus showing that concentrations of this species can and do occur in the northern KNP. It also seems apparent that, although these species do occur in sympatry on a regional scale, one or the other appears to dominate at the local scale (Monadjem et al. 2010).
Seasonal movement patterns of either species are not well documented. However, a study on E. wahlbergi in the urbanized environment of Pietermaritzburg campus, University of KwaZulu-Natal, South Africa, showed that males and females had larger home ranges in winter compared to spring and that males on average were relatively sedentary throughout the year (having relatively small home ranges). Females, on average, made longer flights and had much larger home ranges (Rollinson et al. 2013). Our observations that both species mate within the same timeframe and that males of both species set up calling perches in proximity to fruiting fig trees in KNP resulted in us proposing the hypothesis that the males of each epauletted fruit bat species should show differences in mating calls to avoid cross-mating with the other species even though, to the human ear, little to no discernible differences are evident.
Catching and identifying bats
Recording mating calls of male epauletted bats
We recorded the male mating calls of epauletted bats in areas where our trapping indicated only one of each of the species was locally present. We used a Pettersson D240× bat detector (Pettersson Elektronik, Uppsala, Sweden) set to a 3.5-s recording time and attached to a digital recorder (Samson H2 Zoom, Samson Technologies, Hauppauge, New York, USA) to capture male calls in the vicinity of Shingwedzi in northern KNP and in the vicinity of Skukuza in southern KNP. We drove roads throughout each area at night and when we heard a male bat calling we approached in our vehicle slowly to a position that allowed clear recordings of the calls to be taken but far enough away to not cause that individual to move from its calling perch. All recordings in each area happened on the same night, and because we could hear any given male calling from its perch as we left the recording position, we are confident that we did not record the same male more than once.
Data analysis and statistics
We analyzed call structure of male mating vocalizations using SonoBat 3.1 (Arcata, Oregon, USA) analysis software to determine the fundamental frequencies (first harmonic), high/low frequencies, bandwidths, and slope (downward or upward change in frequency from the initiation of the vocalization to the end of the vocalization) of each call. We compared means of call parameters of individuals recorded in the Skukuza area versus those recorded in the Shingwedzi area using a two-sample T-test (NCSS Statistical Software, Kaysville, Utah, USA) with the null hypothesis that there are no significant differences between mating calls gathered in each area. All P values were adjusted using the Bonferroni correction for multiple comparisons.
All individuals captured in and around the Skukuza tourist camp during the dry season in May and June in 2007 (N = 5), 2008 (N = 9), 2009 (N = 3), and during the wet season (December) in 2011 (N = 1) (total captures = 18) were identified as E. wahlbergi. All captures in the area of the Shingwedzi tourist camp were during the dry season in May and June in 2007 (N = 8), 2008 (N = 5), and 2009 (N = 2) (total captures = 15) and were identified as E. crypturus.
Male mating calls
Means and standard deviations (SD) among five call attributes by site
Analysis of mating calls of males recorded near Skukuza versus those calls gathered near Shingwedzi (separated by approximately 270 km) showed significant differences in basic call structure and thus supported our hypothesis. We found that the call structure of males around specific fruiting sycamore fig trees were consistent with single-species presence for males at a very localized scale. However, there is also range overlap between the species, and because the male mating calls travel at least 0.5 km from the calling perch near where females are feeding on figs (Wickler and Seibt 1976, personal observations), there is potential for females of each species in the area to approach calling males of the other species if there is not a discernible difference in call structure.
From our data, we conclude that the male mating calls we recorded from each area depicted E. wahlbergi from Skukuza and E. crypturus from Shingwedzi. As mentioned, the mating call of male epauletted bats appears to serve both the function of attracting females to their perch because male call rates increase as females approach, but secondly, male calls appear to act as a deterrent to other conspecific males attempting to call from perches too close to other calling males (Wickler and Seibt 1976; Adams and Snode 2013). Although one could argue that because we could not definitively identify individuals to species from which calls were recorded, we could not make this determination. However, several factors help in corroborating our interpretation of results: a) there are unequivocal distinctions in the type of male mating calls recorded in different areas of KNP; b) the calls are consistently different in the two regions of KNP, with exceedingly small degrees of variation in each of the call parameters; c) our capture data, as well as data from other researchers (Bonaccorso et al. 2014), indicate that E. wahlbergi dominates the area around Skukuza, whereas E. crypturus dominates the area near Shingwedzi; d) capture data from other studies in KNP (Fenton et al. 1985), and other areas in Africa, show spatial separation between epauletted fruit bat species on both local (Wickler and Seibt 1976) and, in some cases, regional scales (Kingdon 1974); and e) there are no records of mixed-species feeding groups of epauletted fruit bats at the same fig trees, and radio-telemetry data indicate that female E. wahlbergi from a particular colony moved to the same feeding area of ripe fig trees nightly (Fenton et al. 1985).
An alternative hypothesis to ours would be that males of either E. wahlbergi or E. crypturus alter their call structure in different areas of KNP, and thus, we were recording the same species in both areas using calls that were geographically distinctive within species. Although we could not refute this hypothesis with our study, from a theoretical perspective, this seems unlikely, and we can think of no benefits of such mating behavior. In addition, the extreme lack of variation in call structure in the variables measured for this study suggests the possibility of stabilizing selection via mate choice that would not likely promote such strong regional differences in intraspecific mating calls. In fact, just the opposite would be expected (Ptacek 2000).
It should be noted that the call structure of male E. wahlbergi we recorded in KNP was substantially different from those recorded by Wickler and Seibt (1976) in Kenya. Our recordings contained only a fundamental and single second harmonic, whereas they found a fundamental with three harmonics (however, this could simply be the distance away from a perch where recording was taken). In addition, the fundamental frequency reported by Wickler and Seibt (1976) equated to 1.7 kHz, whereas our recordings show the fundamental at a much higher frequency of about 7 kHz. Although there are no published descriptions of E. crypturus calls available for comparison, it is also curious to note that E. crypturus calls in KNP correspond in frequency to the second harmonic of E. wahlbergi calls. Tonal differences in the calls of each species may be the product of differences in the slope of the calls. Although both species produce relatively flat calls, the total slope of the calls emitted in the Shingwedzi area was twice that of the calls we recorded in the Skukuza area on average. Alterations in call structure attributes presented herein represent a relatively simple measure by which males of co-occurring species of epauletted bats may use harmonic displacement to avoid call overlap with another similar species. The question of if species-specific differences in mating calls are learned or have inherent genetic components remains unanswered. However, our study raises the possibility that differences in mating calls between species of male epauletted fruit bats may serve to avoid hybridization between the two species of epauletted fruit bats.
There are two species of epauletted fruit bats (E. wahlbergi and E. crypturus) that co-occur in Kruger National Park, South Africa. Males of each species position themselves at perches near feeding trees where females congregate, and males use mating vocalizations, as well as wing flapping, to attract females to their perch to mate. The two species have similar mating calls to the naked ear, but through structural analysis of call structure in two areas separated by 270 km, we provide evidence that the males of each species have distinctive calls. We hypothesize that the differences in the structure of calls from each area produce distinctions that are important to the mating success of each species.
The authors gratefully acknowledge the University of Northern Colorado for funding this study. We also greatly appreciate the hospitality and support provided by the staff of Kruger National Park in allowing us to conduct research and keeping us safe.
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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. | <urn:uuid:45ae2d2c-f1b2-4f6d-8db9-8e32ebe24523> | 2.859375 | 3,837 | Academic Writing | Science & Tech. | 35.031669 | 95,615,422 |
Recent interest in using marine reserves for marine resource management and conservation has largely been driven by the hope that reserves might counteract declines in fish populations and protect the biodiversity of the seas. However, the creation of reserves has led to dissension from some interested groups, such as fishermen, who fear that reserves will do more harm than good. These perceived differences in the effect of marine reserves on various stakeholder interests has led to a contentious debate over their merit. We argue here that recent findings in marine ecology suggest that this debate is largely unnecessary, and that a single general design of a network of reserves of moderate size and variable spacing can meet the needs and goals of most stakeholders interested in marine resources. Given the high fecundity of most marine organisms and recent evidence for limited distance of larval dispersal, it is likely that reserves can both maintain their own biodiversity and service nearby non-reserve areas. In particular, spillover of larger organisms and dispersal of larvae to areas outside reserves can lead to reserves sustaining or even increasing local fisheries. Ultimately, the success of any reserve network requires attention to the uncertainty and variability in dispersal patterns of marine organisms, clear statements of goals by all stakeholder groups and proper evaluation of reserve performance.
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P1.186 Wednesday, Jan. 4 A Seven Year Study of Shell Use by Coenobita clypeatus(/i)> on Cayos Cochinos Mejor, Bay Islands, Honduras GILCHRIST, Sandra L; New College of Florida, Sarasota firstname.lastname@example.org
Adult land hermit crabs, Coenobita clypeatus (J.C. Fabricius 1787), must find shells or other abdominal coverings throughout their lives. Shells can come from fresh water, marine or terrestrial sources. Fresh water is also a critical resource for these crabs, allowing them to regulate temperature as well as maintain hemolymph balance. Some authors have noted that these hermit crabs find shells along beaches near wrack lines while others indicate that shell collection areas such as tree holes and beneath fallen trees provide shell resources. A seven year study of shell cycling and fresh water access on Cayos Cochinos Mejor supports the notion that crabs frequent shell collection areas close to fresh water sources. Introduced shells farther from fresh water access are not located as quickly. Crabs at collection sites exchange shells even when there is an excess of new shells available. Mark/recapture studies reveal that the mean size of the crabs did not change over the sampling period despite the addition of several thousand large shells over the seven years. There were fluctuations in shell crowding during each sampling season, but not a significant change across seasons. Crabs visiting collection areas near fresh water had a mean larger size as well as a wider size range than sites farther from fresh water. Shells were retained in the system for at least 5 years, though the quality of the shell declined over time. This study was permitted by DIGIPESCA through the generosity of the Honduran Government. | <urn:uuid:351430d9-077d-499e-a522-fdc8fb9d7877> | 3.46875 | 365 | Academic Writing | Science & Tech. | 45.574064 | 95,615,441 |
The J/ψ meson is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium". The J/ψ is the first excited state of charmonium. The J/ψ has a rest mass of 3.0969 GeV/c², and a mean lifetime of 7.2×10^−21 s. This lifetime was about a thousand times longer than expected. Its discovery was made independently by two research groups, one at the Stanford Linear Accelerator Center, headed by Burton Richter, and one at the Brookhaven National Laboratory, headed by Samuel Ting at MIT. They discovered they had actually found the same particle, and both announced their discoveries on 11 November 1974. The importance of this discovery is highlighted by the fact that the subsequent, rapid changes in high-energy physics at the time have become collectively known as the "November Revolution". Richter and Ting were rewarded for their shared discovery with the 1976 Nobel Prize in Physics.
The numerical value of j/psi meson in Chaldean Numerology is: 1
The numerical value of j/psi meson in Pythagorean Numerology is: 3
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"j/psi meson." Definitions.net. STANDS4 LLC, 2018. Web. 23 Jul 2018. <https://www.definitions.net/definition/j/psi meson>. | <urn:uuid:f11e5b8e-569f-4d56-8659-20d8029c5d62> | 2.984375 | 410 | Structured Data | Science & Tech. | 56.941737 | 95,615,449 |
The Tropical Rainfall Measuring Mission or TRMM satellite passed over Tropical Storm Iselle and gathered data on clouds and rainfall as it affected Hawaii.
Iselle was once a rather powerful category 4 hurricane in the East Pacific with sustained winds estimated at 120 knots (~138 mph) by the National Hurricane Center. Fortunately, a combination of southwesterly wind shear, drier air and cooler waters weakened Iselle considerably as it approached the Hawaiian Islands.
Rainfall estimates for the period Aug. 4 to 11 for the Hawaiian Islands. Two swaths of heavier rain show the paths of Iselle and Julio. Iselle's rainfall totaled 60 to 80 mm (~3 inches, green) over the southeast coast of Hawaii and upwards of 120 mm (~5 inches, red) over Kauai.
Image Credit: SSAI/NASA, Hal Pierce
Although much weaker, Iselle still struck the southeast Kau coast of the Big Island of Hawaii as a rather strong tropical storm. In fact Iselle, was the strongest and only the second tropical storm to hit the Big Island in over 50 years. The center made landfall around 2:30 am HST on Friday, August 8, near Pahala with sustained winds of 60 mph.
The Big Island bore the brunt of the storm where downed trees and power lines left 25,000 people without power. Currently, several days after the storm, around 8,000 are still without power on the island. After hitting the Big Island, Iselle continued to track to the west-northwest keeping the center of circulation well south of the rest of the Hawaiian Islands, which mainly received just rain from Iselle's outer rainbands. On Kauai, however, one woman was reported to have been swept away and drowned while hiking.
TRMM captured an image of Iselle on August 9 at 09:06 UTC (August 8 at 11:06 p.m. local time) as the center was passing well south of the far western islands of Kauai and Ni'ihau. By that time, Iselle had been degraded to a tropical depression, and TRMM showed the exposed center of Iselle, which was devoid of any eyewall or even rain. There are several outer rainbands located only on the northeast side of the storm that were still effecting the western part of the state.
Data from that same satellite over pass (orbit) was used to create a 3-D image of the storm looking north. Areas in green show that much of the rain is relatively shallow with tops ranging from about 5 to 8 km, but there are isolated areas of higher tops associated with deeper penetrating individual convective cells embedded within the rainbands.
At NASA's Goddard Space Flight Center in Greenbelt, Maryland a TRMM-based, near-real time Multi-satellite Precipitation data (TMPA) analysis was conducted that uses TRMM data to calibrate rainfall estimates from other satellites. The analysis expands the rainfall coverage of the TRMM satellite. TMPA rainfall estimates were calculated to cover August 4 to 11 for the Hawaiian Islands and surrounding area.
Two swaths of heavier rain showed the paths taken by Iselle and Julio, which formed a few days after Iselle and followed a path slightly more to the north. Iselle's rainfall totals are on the order of 60 to 80 mm (~3 inches) over the southeast coast of Hawaii and upwards of 120 mm (~5 inches) over Kauai. Locally, up to 14 inches of rain was reported in the higher elevations of the Big Island.
Julio, which is now a tropical storm, is currently located well north of Oahu (about 500 miles from Honolulu) and expected to continue moving away from Hawaii and steadily weaken.
TRMM is a joint mission between NASA and the Japanese space agency JAXA.
Text credit: Stephen Lang
SSAI/NASA Goddard Space Flight Center
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The acceleration of a marble in a certain fluid is proportional to the speed of the marble squared and is given in SI units) by a=-3.00 v^2 for v greater than 0. If the marble enters this fluid with a speed of 1.20 m/s, how long will it take before the marble's speed is reduced to half of its initial value?© BrainMass Inc. brainmass.com July 17, 2018, 8:01 am ad1c9bdddf
Another way of writing a is dv/dt. So we have the equation:
dv/dt = -3*v^2
Divide both sides by v^2 and multiply ...
The solution is given in an equation with short descriptions explaining how to do it. | <urn:uuid:581cb555-7ab2-4de2-8f28-aa96df6da8f9> | 3.90625 | 160 | Q&A Forum | Science & Tech. | 94.192361 | 95,615,470 |
Two-component regulatory system
|His Kinase A (phospho-acceptor) domain|
solved structure of the homodimeric domain of EnvZ from Escherichia coli by multi-dimensional NMR.
|Signal transducing histidine kinase, homodimeric domain|
structure of CheA domain p4 in complex with TNP-ATP
|Histidine kinase N terminal|
|Osmosensitive K+ channel His kinase sensor domain|
In the field of molecular biology, a two-component regulatory system serves as a basic stimulus-response coupling mechanism to allow organisms to sense and respond to changes in many different environmental conditions. Two-component systems typically consist of a membrane-bound histidine kinase that senses a specific environmental stimulus and a corresponding response regulator that mediates the cellular response, mostly through differential expression of target genes. Although two-component signaling systems are found in all domains of life, they are most common by far in bacteria, particularly in Gram-negative and cyanobacteria; both histidine kinases and response regulators are among the largest gene families in bacteria. They are much less common in archaea and eukaryotes; although they do appear in yeasts, filamentous fungi, and slime molds, and are common in plants, two-component systems have been described as "conspicuously absent" from animals.
Two-component systems accomplish signal transduction through the phosphorylation of a response regulator (RR) by a histidine kinase (HK). Histidine kinases are typically homodimeric transmembrane proteins containing a histidine phosphotransfer domain and an ATP binding domain, though there are reported examples of histidine kinases in the atypical HWE and HisKA2 families that are not homodimers. Response regulators may consist only of a receiver domain, but usually are multi-domain proteins with a receiver domain and at least one effector or output domain, often involved in DNA binding. Upon detecting a particular change in the extracellular environment, the HK performs an autophosphorylation reaction, transferring a phosphoryl group from adenosine triphosphate (ATP) to a specific histidine residue. The cognate response regulator (RR) then catalyzes the transfer of the phosphoryl group to an aspartate residue on the response regulator's receiver domain. This typically triggers a conformational change that activates the RR's effector domain, which in turn produces the cellular response to the signal, usually by stimulating (or repressing) expression of target genes.
Many HKs are bifunctional and possess phosphatase activity against their cognate response regulators, so that their signaling output reflects a balance between their kinase and phosphatase activities. Many response regulators also auto-dephosphorylate, and the relatively labile phosphoaspartate can also be hydrolyzed non-enzymatically. The overall level of phosphorylation of the response regulator ultimately controls its activity.
Some histidine kinases are hybrids that contain an internal receiver domain. In these cases, a hybrid HK autophosphorylates and then transfers the phosphoryl group to its own internal receiver domain, rather than to a separate RR protein. The phosphoryl group is then shuttled to histidine phosphotransferase (HPT) and subsequently to a terminal RR, which can evoke the desired response. This system is called a phosphorelay. Almost 25% of bacterial HKs are of the hybrid type, as are the large majority of eukaryotic HKs.
Two-component signal transduction systems enable bacteria to sense, respond, and adapt to a wide range of environments, stressors, and growth conditions. These pathways have been adapted to respond to a wide variety of stimuli, including nutrients, cellular redox state, changes in osmolarity, quorum signals, antibiotics, temperature, chemoattractants, pH and more. The average number of two-component systems in a bacterial genome has been estimated as around 30, or about 1-2% of a prokaryote's genome. A few bacteria have none at all - typically endosymbionts and pathogens - and others contain over 200. All such systems must be closely regulated to prevent cross-talk, which is rare in vivo.
In Escherichia coli, the osmoregulatory EnvZ/OmpR two-component system controls the differential expression of the outer membrane porin proteins OmpF and OmpC. The KdpD sensor kinase proteins regulate the kdpFABC operon responsible for potassium transport in bacteria including E. coli and Clostridium acetobutylicum. The N-terminal domain of this protein forms part of the cytoplasmic region of the protein, which may be the sensor domain responsible for sensing turgor pressure.
Signal transducing histidine kinases are the key elements in two-component signal transduction systems. Examples of histidine kinases are EnvZ, which plays a central role in osmoregulation, and CheA, which plays a central role in the chemotaxis system. Histidine kinases usually have an N-terminal ligand-binding domain and a C-terminal kinase domain, but other domains may also be present. The kinase domain is responsible for the autophosphorylation of the histidine with ATP, the phosphotransfer from the kinase to an aspartate of the response regulator, and (with bifunctional enzymes) the phosphotransfer from aspartyl phosphate to water. The kinase core has a unique fold, distinct from that of the Ser/Thr/Tyr kinase superfamily.
HKs can be roughly divided into two classes: orthodox and hybrid kinases. Most orthodox HKs, typified by the E. coli EnvZ protein, function as periplasmic membrane receptors and have a signal peptide and transmembrane segment(s) that separate the protein into a periplasmic N-terminal sensing domain and a highly conserved cytoplasmic C-terminal kinase core. Members of this family, however, have an integral membrane sensor domain. Not all orthodox kinases are membrane bound, e.g., the nitrogen regulatory kinase NtrB (GlnL) is a soluble cytoplasmic HK. Hybrid kinases contain multiple phosphodonor and phosphoacceptor sites and use multi-step phospho-relay schemes instead of promoting a single phosphoryl transfer. In addition to the sensor domain and kinase core, they contain a CheY-like receiver domain and a His-containing phosphotransfer (HPt) domain.
The number of two-component systems present in a bacterial genome is highly correlated with genome size as well as ecological niche; bacteria that occupy niches with frequent environmental fluctuations possess more histidine kinases and response regulators. New two-component systems may arise by gene duplication or by lateral gene transfer, and the relative rates of each process vary dramatically across bacterial species. In most cases, response regulator genes are located in the same operon as their cognate histidine kinase; lateral gene transfers are more likely to preserve operon structure than gene duplications.
Two-component systems are rare in eukaryotes. They appear in yeasts, filamentous fungi, and slime molds, and are relatively common in plants, but have been described as "conspicuously absent" from animals. Two-component systems in eukaryotes likely originate from lateral gene transfer, often from endosymbiotic organelles, and are typically of the hybrid kinase phosphorelay type. For example, in the yeast Candida albicans, genes found in the nuclear genome likely originated from endosymbiosis and remain targeted to the mitochondria. Two-component systems are well-integrated into developmental signaling pathways in plants, but the genes probably originated from lateral gene transfer from chloroplasts. An example is the chloroplast sensor kinase (CSK) gene in Arabidopsis thaliana, derived from chloroplasts but now integrated into the nuclear genome. CSK function provides a redox-based regulatory system that couples photosynthesis to chloroplast gene expression; this observation has been described as a key prediction of the CoRR hypothesis, which aims to explain the retention of genes encoded by endosymbiotic organelles.
It is unclear why canonical two-component systems are rare in eukaryotes, with many similar functions having been taken over by signaling systems based on serine, threonine, or tyrosine kinases; it has been speculated that the chemical instability of phosphoaspartate is responsible, and that increased stability is needed to transduce signals in the more complex eukaryotic cell. Notably, cross-talk between signaling mechanisms is very common in eukaryotic signaling systems but rare in bacterial two-component systems.
Because of their sequence similarity and operon structure, many two-component systems - particularly histidine kinases - are relatively easy to identify through bioinformatics analysis. (By contrast, eukaryotic kinases are typically easily identified, but they are not easily paired with their substrates.) A database of prokaryotic two-component systems called P2CS has been compiled to document and classify known examples, and in some cases to make predictions about the cognates of "orphan" histidine kinase or response regulator proteins that are genetically unlinked to a partner.
- http://www.p2cs.org: The Prokaryotic 2-Component Systems Database
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- Stock JB, Ninfa AJ, Stock AM (Dec 1989). "Protein phosphorylation and regulation of adaptive responses in bacteria". Microbiological Reviews. 53 (4): 450–90. PMC . PMID 2556636.
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- Allen JF (Aug 2015). "Why chloroplasts and mitochondria retain their own genomes and genetic systems: Colocation for redox regulation of gene expression". Proceedings of the National Academy of Sciences of the United States of America. 112 (33): 10231–8. doi:10.1073/pnas.1500012112. PMC . PMID 26286985.
- Rowland MA, Deeds EJ (Apr 2014). "Crosstalk and the evolution of specificity in two-component signaling". Proceedings of the National Academy of Sciences of the United States of America. 111 (15): 5550–5. doi:10.1073/pnas.1317178111. PMC . PMID 24706803.
- Barakat M, Ortet P, Whitworth DE (Jan 2011). "P2CS: a database of prokaryotic two-component systems". Nucleic Acids Research. 39 (Database issue): D771–6. doi:10.1093/nar/gkq1023. PMC . PMID 21051349.
- Ortet P, Whitworth DE, Santaella C, Achouak W, Barakat M (Jan 2015). "P2CS: updates of the prokaryotic two-component systems database". Nucleic Acids Research. 43 (Database issue): D536–41. doi:10.1093/nar/gku968. PMC . PMID 25324303. | <urn:uuid:dd733a81-3b71-4681-967e-6cc4e92a4730> | 2.6875 | 4,828 | Knowledge Article | Science & Tech. | 56.39168 | 95,615,472 |
Cold streak from polar vortex sweeping Midwest, Northeast expected to reach Peninsula toward week's end
Frigid weather has swept across the northern United States, and the Midwest, New England and Mid-Atlantic are next, according to projections from the National Weather Service.
Toward the end of the week, the Peninsula will be facing freezing temperatures, but the regional NWS office advises that the area won't experience the same cold wave that much of the country will be enduring. Mike Montefusco, a meteorologist at the NWS office in Wakefield, said it will be cold but nothing far from normal.
The beginning of the week is expected to be warmer than it was this weekend, with Monday's high temperature reaching the low 60s in some areas. Tuesday's high temperature will be in the low 50s and Wednesday's will be in the high 40s.
On Thursday and Friday, the Peninsula can expect to catch a taste of the cold weather that will be laying siege to more northern areas, Montefusco said. On Thursday, the temperature will peak in the mid-30s and drop into the teens in the evening. Friday temperatures are expected to be between the mid-20s and low 30s.
The cold snap across the northern portion of the country is being brought on by a rush of energy coming from the polar vortex, a massive low-pressure area of cold air that spins over the North Pole and is held in place by the jet stream, according to NWS.
"The vortex is always present — even in the summer. But winter is when it really comes alive," wrote Angela Fritz, an atmospheric scientist and deputy weather editor for The Washington Post. "Not only is Arctic air colder because of the lack of sunlight, this is also when the jet stream plunges south. When that happens, it allows the cold air to spill south, like a freezer with the door left open."
Montefusco said northern areas are catching the brunt of that Arctic air — Hampton Roads is getting just a piece of that energy.
NWS said that cold weather brought on by the polar vortex occurs fairly regularly in winter and should not cause alarm. People in affected areas should just be ready for colder weather.
The cold streak isn't expected to last long on the coast. The Peninsula high temperature on Saturday is expected to be about 53; on Sunday it will be about 55. | <urn:uuid:f967b907-f5df-45b3-b986-9980015a1d4b> | 2.609375 | 491 | News Article | Science & Tech. | 55.99019 | 95,615,481 |
Such an acoustic veil would do for sound what the "invisibility cloak" previously demonstrated by the research team does for microwaves--allowing sound waves to travel seamlessly around it and emerge on the other side without distortion.
"We've devised a recipe for an acoustic material that would essentially open up a hole in space and make something inside that hole disappear from sound waves," said Steven Cummer, Jeffrey N. Vinik Associate Professor of Electrical and Computer Engineering at Duke's Pratt School of Engineering. Such a cloak might hide submarines in the ocean from detection by sonar, he said, or improve the acoustics of a concert hall by effectively flattening a structural beam.
As in the case of the microwave cloak, the properties required for a sound cloak are not found among materials in nature and would require the development of artificial, composite metamaterials.
The engineering of acoustic metamaterials lags behind those that interact with electromagnetic waves (i.e. microwaves or light), but "the same ideas should apply," Cummer said.
The report by Cummer's team is expected to appear in Physical Review Letters on Jan. 11.
In 2006, researchers at Duke and the Imperial College London used a new design theory to create a blueprint for an electromagnetic invisibility cloak. Only a few months later, the team demonstrated the first such cloak, designed to operate at microwave frequencies.
Cummer and David Schurig, a former research associate at Duke who is now at North Carolina State University, later reported in The New Journal of Physics a theory showing that an acoustic cloak could be built. But that theory relied on a "special equivalence" between electromagnetic and sound waves that is only true in two dimensions, Cummer said. A report by another team had also suggested that a 3-D acoustic cloak couldn't exist. It appeared they had reached a dead end.
Cummer wasn't convinced. "In my mind, waves are waves," he said. "It was hard for me to imagine that something you could do with electromagnetic waves would be completely undoable for sound waves."
This time, he started instead from a shell like the microwave cloak his team had already devised and attempted to derive the mathematical specifications required to prevent such a shell from reflecting sound waves, a key characteristic for achieving invisibility. On paper, at least, it worked.
"We’ve now shown that both 2-D and 3-D acoustic cloaks theoretically do exist," Cummer said. Although the theory used to design such acoustic devices so far isn't as general as the one used to devise the microwave cloak, the finding nonetheless paves the way for other acoustic devices, for instance, those meant to bend or concentrate sound. "It opens up the door to make the physical shape of an object different from its acoustic shape," he said.
The existence of an acoustic cloaking solution also indicates that cloaks might possibly be built for other wave systems, Cummer said, including seismic waves that travel through the earth and the waves at the surface of the ocean.
Collaborators on the study included Bogdan-Ioan Popa, David R. Smith and Marco Rahm of Duke; David Schurig of N.C. State University; John Pendry of Imperial College London; and Anthony Starr of SensorMetrix, Inc. in San Diego, Calif. | <urn:uuid:729ac501-df27-42fc-81c6-3be30a7a9c74> | 3.65625 | 689 | News Article | Science & Tech. | 40.334757 | 95,615,495 |
Climate Science in Focus: Data and Tools
- Grade Level:
- High School: Ninth Grade through Twelfth Grade
- Lesson Duration:
- 60 Minutes
- Common Core Standards:
- 9-10.RST.1, 9-10.RST.2, 9-10.RST.5, 9-10.RST.7, 9-10.RST.9
- Additional Standards:
- Thinking Skills:
- Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Applying: Apply an abstract idea in a concrete situation to solve a problem or relate it to a prior experience. Analyzing: Break down a concept or idea into parts and show the relationships among the parts. Evaluating: Make informed judgements about the value of ideas or materials. Use standards and criteria to support opinions and views.
Students will use scientific data on streamflow from the Sierra Nevada to analyze snowpack and draw conclusions about the changing climate. Students will be able to predict changes that will occur to the Sierra Nevada snowpack if the climate change continues, and predict the changes that will result on the biosphere due to climate change.
The Earth consists of four systems: the atmosphere, hydrosphere, geosphere, and biosphere, which are interconnected. Changes to one part of the system can have consequences on the others. Changes to global or regional climate can be caused by changes in the sun's energy output or Earth's orbit, tectonic events, ocean circulation, volcanic activity, glaciers, vegetation, and human activity.
Water is essential for life on Earth. Relative water availability is a major factor in designating habitats for different living organisms. In the United States, things like agriculture and water rights are hot topics. Current models predict that average global temperatures are going to continue to rise even if regional climate changes remain complex and varied. These changes will have an impact on all of Earth's systems.
Studies have shown that climate change is driven not only by natural effects but also by human activities. Knowledge of the factors that affect climate, coupled with responsible management of natural resources, are required for sustaining these Earth systems. Long-term change can be anticipated using science-based predictive models, making science and engineering essential to understanding global climate change and its possible impacts.
National Parks can serve as benchmarks for climate science trends and effects over time because they are protected areas void of human influence. Understanding current climate trends will help set students up to be successful in interpreting and engaging in discussions about climate change, which will lead to informed decisionmaking.
Teachers will need access to the internet, a computer or laptop, and projector to play the videos for the class.
Write the following questions on the board or projector so the all students can see them:
How has climate change influenced human activities? How could Mammoth Lakes(or your community) be affected if the climate continues to change?
Print out one Excel Data Packet for each group if computers are unavailable. If computers are available, each group can view the data on a computer with Microsoft Excel.
Prepare the following videos:
This pdf version of an Excel file provides data from the streamflow monitoring site at Pohono Bridge in Yosemite National Park. This is a sample of Sierra Nevada streamflow data, although other data can be found online.
This resource brief talks about why and how the National Park Service monitors climate at Devils Postpile National Monument
Briefly discuss the following questions: How have climate changes influenced human activities? How could Mammoth Lakes be affected if the climate continues to change?
Display video – A Way Forward: Facing Climate Change
Distribute streamflow historical data, graph paper, and markers or visit computer lab for students to pull up Excel.
Briefly discuss the following: Snowpack is a natural water reservoir that slowly releases its water over time. This release directly impacts streams and rivers. Studying stream flow over a long period of time can show us how snowpack and streams are being affected by climate change.
Have students plot climate science data points from the packets on large graph paper. Display your graph where instructed.
Monitor student gallery walk as they make comments and observations about climate change data.
Display video – California Department of Water Resources: Snow Surveying
Distribute article Weather and Climate Monitoring at Devils Postpile National Monument (See Materials)
- Have students write a thesis sentence for this article.
Student Discussion: Why is the Sierra Nevada snowpack important to other areas of California and the United States? What does our data tell us about the condition of the snowpack? Are there any years of data that are different than the overall trend? This discussion will assess how well students understand the concept of snowpack and it’s connection to global climate change and regional and national issues.
Related Lessons or Education Materials
Day 1- Earth as a System
Day 2- Weather vs Climate
Day 3- Watershed
Day 4- Climate Science Data and Tools
Day 5- Field Trip
Day 6- NPS Connections
Day 7- Project Preparation
Day 8- Evaluations | <urn:uuid:1e4a1faa-f208-47d7-be9c-790574ea3544> | 3.71875 | 1,063 | Tutorial | Science & Tech. | 39.168299 | 95,615,515 |
Atomic Layer Deposition Like Wolverine's
Super-strong spider silk has been produced using a process that sounds like it might produce a superhero itself - atomic layer deposition. The researchers were inspired by nature; mandibles of leaf-cutter ants and locusts are peppered with zinc, making them stronger and more durable.
(Overview of ALD spider silk)
The team fired beams of ionised metal compounds at lengths of silk from the orb-weaving spider Araneus diatematus using a technology called atomic layer deposition (ALD). As well as coating each silk fibre in a fine metal oxide, some metal ions penetrated the fibre.They tried zinc, aluminium and titanium compounds, all of which improved the mechanical properties of the silk.
"With all three metals, the fibres can hold three to four times as much weight," says Knez. The fibres also become stretchier, so that their toughness - the energy needed to break a strand - rises even more. "The work needed to break the fibre rises tenfold with titanium, ninefold with aluminium and fivefold with zinc," he says.
The developers of this technique, Seung-Mo Lee and Mato Knez at the Max Planck Institute of Microstructure Physics in Halle, Germany, also believe that it can be used to strengthen other biomaterials. Like bones, for example - or extendable claws. Like those of Wolverine, perhaps?
In the new X-Men movie, we see how Wolverine becomes unstoppable. Adamantium, a rare (fictional) metal derived from meteor remains, is bonded to his biological skeleton. Like the real-life mandibles of leaf-cutter ants, his bones become much harder when metal is bonded to the original structure.
(Wolverine has adamantium applied to the skull)
Also, this is good news for the many law enforcement personnel who can't wait to throw super-strong webs at evil doers (see T-34 Security Robot Throws Nets and NET-2000 Shooting Net Rod Nails Perps ).
If you want to hang from a web like Spiderman, you're going to need ALD spider silk.
(Spidey waits patiently, suspended in web)
From For super-tough spider silk, just add titanium ; thanks to Zac for recommending this story, for which I finally figured out the X-men connection.
Scroll down for more stories in the same category. (Story submitted 5/5/2009)
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Odd Biochemistry Yields Lethal Bacterial Protein
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They found that a single enzyme helps form distinctly different, three-dimensional ring structures in the protein, one of which had never been observed before.
The new findings, reported in Nature Chemical Biology, should help scientists find new ways to target the enterococcal cytolysin protein, a “virulence factor that is associated with acute infection in humans,” said University of Illinois chemistry and Institute for Genomic Biology professor Wilfred van der Donk, who conducted the study with graduate student Weixin Tang.
Enterococcus faecalis (EN-ter-oh-cock-us faye-KAY-liss) is a normal microbial inhabitant of the gastrointestinal tracts of humans and other mammals and generally does not harm its host. Some virulent strains, however, produce cytolysin (sigh-toe-LIE-sin), a protein that, once assembled, attacks other microbes and kills mammalian cells.
“The cytolysin protein made by Enterococcus faecalis consists of two compounds that have no activity by themselves but when combined kill human cells,” van der Donk said. “We know from epidemiological studies that if you are infected with a strain of E. faecalis that has the genes to make cytolysin, you have a significantly higher chance of dying from your infection.” E. faecalis contributes to root canal infections, urinary tract infections, endocarditis, meningitis, bacteremia and other infections.
Enterococcal cytolysin belongs to a class of antibiotic proteins, called lantibiotics, which have two or more sulfur-containing ring structures. Scientists had been unable to determine the three-dimensional structure of this cytolysin because the bacterium produces it at very low concentrations. Another problem that has stymied researchers is that the two protein components of cytolysin tend to clump together when put in a lab dish.
Van der Donk and Tang got around these problems by producing the two cytolysin components separately in another bacterium, Escherichia coli (esh-uh-REE-kee-uh KOH-lie), and analyzing them separately.
“The two components are both cyclic peptides, one with three rings and the other with two rings,” van der Donk said. “Curiously, a single enzyme makes both compounds.”
In a series of experiments, the researchers found that one ring on each of the proteins adopted a (D-L) stereochemistry that is common in lantibiotics (see image, above). But the other rings all had an unusual (L-L) configuration, something van der Donk had never seen before.
Scientists had assumed that the enzyme that shaped enterococcal cytolysin, a lantibiotic synthetase, acted like a three-dimensional mold that gave the ring structures of cytolysin the exact same stereochemistry, van der Donk said.
“But we found that the enzyme, enterococcal cytolysin synthetase, makes the rings with different stereochemistry,” he said. “I don’t know of any other examples where one enzyme can make very similar products but with different stereochemistries.”
The researchers don’t know how the enzyme accomplishes this feat, but found a clue in the sequence of amino acids that make up the protein rings. The chemical characteristics of the three amino acids in the middle of the ring structure and their proximity to another amino acid, a cysteine, determined whether the rings took on a D-L or L-L stereochemistry.
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High temperatures decrease a photovoltaic solar cell’s output by between 10 and 25 percent, Stuart Fox, a vice president at the green energy company CivicSolar, told The San Francisco Chronicle Wednesday. Research indicates that a solar panel’s power output drops by 1.1 percent for every 1.8 degree rise in temperature above 107 degrees Fahrenheit, and solar panels can get much hotter than that.
“If you take a glass solar shingle and lay it on the roof, there’s no air going behind it, so it might get a lot hotter — it might get to 140 or 160 degrees Fahrenheit,” Fox told The Chronicle.
Photovoltaic solar cells work when energy from the sun excites electrons on the panels, which generates energy the cells can capture. However, at high temperatures it takes less energy to excite the electrons, meaning that the cell produces less power. High temperatures frequently coincide with peak demand for electricity, meaning that solar power is at its least effective when it is most needed.
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Mars is not hollow; is it?
Is Mars Hollow? We are pretty sure it is not, but no one can be certain however we might soon know. The reason such a question is asked is because of questions about the Earth and the time it takes for sound waves to travel through it. And the speed of the spin rate of Mars, the question of moons is interesting and a few other interesting a recent discoveries. Here is one of the thoughts on the matter. By bouncing waves off the polar ice caps this can be proven or disproven;
Most scientists to do not buy into the hollow planet theories, yet others admit we just do not know. The most interesting of all is the straight-line canals, which is hard to fathom considering using our own knowledge about our planet here. But Mars is a different planet or satellite and therefore has different characteristics completely.
And what is underneath our surface? Well we know certainly more than we did before. CalTech which runs JPL is getting to the under bottom of this. After all with all the seismic knowledge we have from there they ought to know. We are not the only ones studying this; the UK has ideas and so does Japan.
So the question is not as far fetched as you might think. We will soon find the truth? We do not seem to be finding much complex life on the surface of Mars, although we have a lot more area to look at. We know of water on Mars and expect to find underground water too. Is this where life might be? Could it be in the polar ice caps and in the ground water in cavities under the surface? If there is anything such as the complex life forms we find on Earth, then they are probably underground, where we have not looked yet. Or perhaps the biblical scholars can rejoice and say; see we told you so? Think about it.
"Lance Winslow" - If you have innovative thoughts and unique perspectives, come think with Lance; www.WorldThinkTank.net/wttbbs
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Surgical Biomaterials and Tissue Regeneration Technologies
Plants, invertebrate animals, amphibians and even reptiles have the ability to regenerate lost or damaged body parts. In the case of lizards, for example, this is a defensive mechanism.
Acoustic Transducers for High Altitude Balloon Control
Using acoustic transducers it maybe possible to create a small region of thicker air underneath a blimp and use that patch as a platform of air to float on while blowing ever so slightly low pressure air underneath the blimp like a hover craft. Although this idea sounds like a long shot it can be done by use of a screen, which shoots the directed frequency waves into the waves created by the acoustic transducers.
Life on Mars, Warm Water Under our Ice Caps, Evidence, Microbes under Our Feet
Well many people out there are asking is there really life on Mars? Our Thinking Group has been asking not if, what type?An article I remember reading and article in Astronomy Magazine back in 1996 that read was there life on Mars and it was an article about a meteorite that landed here on Earth and it was found in 1984 in Antarctica in the Allen Hills ice fields, like I even know where that is? It had bacteria fossils and remains of bacteria that lived about 3.6 billion years ago and the meteor appeared to have come from Mars.
UUV - Unmanned Underwater Vehicles to be Used for Fish Farming or Algae Bloom Removal
What is a UUV? UUV is the abbreviation given to Unmanned Underwater Vehicle. It is a mini-submarine without anyone in it.
CREATION OF ANIMATE FROM INANIMATE: - We have touched upon some scientific dry wells and frauds already. The idea of cold fusion and perpetual motion that the Utah researchers may not have achieved was just dealt with: but a recent report showing a Utah student using Farnsworth's old designs is another example that makes me think Cold Fusion is going to be a reality.
Why Dont Moths Fly to the Moon?
Surely, in the days before man invented artificial light, moths would have been attracted to the only light source at night - the moon. Wouldn't they have just kept on flying until they dropped from exhaustion? In fact does this not happen today in sparsely populated areas, where the moon is still the only night-light available?Navigation Sorry to disappoint you, but there is no concrete answer - only theories.
How Body Piercing Works -- The Ins and Outs of this Cutting Edge Process
Body piercing (defined as any piercing beyond the standard earlobe piercing) has become such a popular form of body modification that between five and ten percent of the population of the United States has indulged in at least one form of it at some time in their lives. In most cases, once a person gets a body piercing, they follow the first one with more.
Ancient Inventions and Anthropology
ANCIENT INVENTIONS: - In Alexandria and in the Cave of Hathor there appear to be reasons to believe we had electricity. There is no doubt that fraudulent traders were using electrum plating techniques to make gold plate on other metals to sell as pure gold.
Ultra Thin Space Suits, just a concept
The space suits we saw on the first Moon visit were too large and bulky. We need Ultra thin space suits, but what if you break the skin underneath.
How to Build a Mechanical Bullet Which Turns
A Mechanical bullet, which will turn in flight is well within our technical capabilities. The premise is to have a bullet, which is preset to turn a corner can be achieved thru a small gear setting on the bullet or a preset finger on the barrel or in the chamber which can be dialed in prior to discharge.
N400 Brain Wave to Assist in Learning and in Performance
In any important task you need to stay alert and in some professions someone could lose their life ifyou are not staying heads up or cause a serious accident where someone else has to pay with theirs. Not good, so what is the solution here? Here is a thought on learning, safety, brain waves and winning.
How Albert Einstein Saw Things A Little Differently
Albert Einstein had just administered an examination to an advanced class of Physics students.As he left the building, he was followed out by one of his teaching assistants.
Older C-130 Hercules Aircraft Problematic
We have certainly seen around the world many Lockheed C-130 Aircraft, which have had problems over the last five years. Many of these aircraft have in excess of 100,000 total time airframe hours on them.
Methods of Improving Boiler Efficiency
With the rising cost of fuel prices, industries that use steam boilers for heating or power generation are hard pressed to operate at peak efficiencies.While steam consumption, leakages, and other heat transmission losses can contribute to the overall energy bill, this article focuses on the heart of the steam generator - the boiler.
Space Travel - Human Innate Bonding to ELF - Extremely Low Frequencies of Planet Earth
Human innate bonding to ELF - Extremely Low Frequencies of planet Earth will be a problem in space travel for the future. How do we know this? We know because insanity seems to very often coincide with mental illness.
How Do Cities Grow?
You see the cities in America started where there was a river and small populations sprung up, then the railroad steam engines needed a place to fill up the water. Eventually the towns got larger and grew near the rail stations.
Earthquakes, Tsunamis, Mudslides: Extreme Events - What Do They Mean?
In lieu of recent, tumultuous occurrences, people are more compelled than ever to discover the mystery of these modern-day, earth-changing events.One day, Earth(1) is experiencing the fourth largest earthquake in a century - a 9.
MAVs, UAVs, and Insect Flight Characteristics
MAVs and UAVs and Insect Flight Characteristics seem to have a lot in common. Millions of years of evolution in nature seem to have been one of the greatest engineering schools around.
RFID Sensors to Protect Water Supplies
Recently the US Military has developed a special set of sensors for water supplies for troops. Any time a base camp is set up it is important to monitor the water supplies and test them.
The HarmonicIn a good history book by a leading light in the field of history, I recall Michael Grant saying Pythagoras was 'weird'. This book is The Rise of the Greeks and he does almost admit he is not qualified to judge the great sage, which is more than many academics will allow.
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the Physics Central
the American Physical Society
This article describes research on systems made up of small granular pieces, such as sand piles or containers of grain. In these "Collective" systems, the interactions of each of the grains with a few neighbors determines the properties of large systems.
%0 Electronic Source %A Physics Central, %T Physics in Action: Granular Materials %I American Physical Society %V 2018 %N 16 July 2018 %9 text/html %U http://www.physicscentral.org/explore/action/granular.cfm
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Honey bees are the most effective pollinators of many agricultural crops and vitally important to food production.
Honey bee health is a topic of considerable concern due to massive deaths of bee colonies in the USA and Europe. Recently, the European Union reacted by promising more resources for honey bee research, estimating European pollination to an economic value of EUR 22 billion.
"Detailed studies on the molecules that keep bees healthy are extremely important to the food industry as well as the global provision of food," said dr. Heli Havukainen, who defended her PhD thesis at the Norwegian University of Life Sciences (UMB) on November 25. Her study of honey bees is a collaboration between UMB and the University of Bergen (UiB), Norway.
Like a freight trainUnder the supervision of Professor Gro Amdam (UMB and Arizona State University) and Associate Professor Øyvind Halskau (UiB), Havukainen discovered that vitellogenin can be described as a freight train consisting of a locomotive and a carriage. The protein carries fat as its cargo, which it picks up in the bees' belly-fat cells - the main station. The vitellogenin "train" travels in the bee's blood and delivers the fat cargo at different local stops or stations.
Prior to this study, scientists believed vitellogenin to be one entity, like a cargo ship, unable to separate from its cargo. Therefore, Havukainen's new discovery is a big step forward for research that aims to keep bees healthy and long lived.
"We figured out that vitellogenin can drop its fat cargo as a reaction to changing chemical conditions. How this "drop" occurs and which factor makes the locomotive move and leave its cargo are important questions in the protein world, and probably equally important to the bee," Havukainen said.
What's up with the train hitch?
The research group believes that the separation of vitellogenin in two parts is a key to understanding how the protein works. They are now in search of the factor that breaks the fragile connection, or the train hitch of the protein, and lets the locomotive go.
"My discovery is that vitellogenin is not one entity. It consists of two functional parts. Now, I want to stop the separation process, so the locomotive and fat cargo are always together. This will help us figure out why the locomotive sometimes ditches its cargo and travels around on its own, and what the consequences are for the bees. This way, we can learn how vitellogenin affects social behaviour, immunity and stress resistance, and ultimately global food production and provision, Havukainen said.
Torunn Moe | EurekAlert!
Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides
16.07.2018 | Tokyo Institute of Technology
The secret sulfate code that lets the bad Tau in
16.07.2018 | American Society for Biochemistry and Molecular Biology
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 | Life Sciences
16.07.2018 | Earth Sciences
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1. How can the different kinds of electromagnetic radiation be described?
Please see attached for full problem.© BrainMass Inc. brainmass.com July 17, 2018, 9:50 am ad1c9bdddf
The electromagnetic waves (wave nature) or radiations (energy nature) are comprised of electric and magnetic field vectors vibrating perpendicular to each other in a plane normal to the direction of propagation of them. The frequency (f), speed (c) and wavelength (lambda) are related as,
c = f * lambda.
The speed of all the EM radiations be same in the free space, hence as frequency increases, wavelength decreases. On the basis of increasing wavelength or decreasing frequency the EM ...
The solution discusses the different kinds of electromagnetic radiation. | <urn:uuid:fe6c7ed1-3ba0-406f-9615-d89edb3c609e> | 3.375 | 159 | Q&A Forum | Science & Tech. | 45.803026 | 95,615,591 |
Thermoluminescence of Solids
McKeever gives us a comprehensive survey of thermoluminescence, an important, versatile, and widely used experimental technique. Bringing together previously isolated specialized approaches, he stresses the importance of the solid state aspects of the phenomenon. The book contains chapters on analysis and special properties, on instrumentation, and on the variety of defect reaction - using the alkali halides and SiO2 as examples - that can take place within a material to yield thermoluminescence. Three chapters concerning applications discuss the features of the solid state reactions to expain some of the properties observed in practice.
- Electronic book text
- 11 May 2012
- CAMBRIDGE UNIVERSITY PRESS
- Cambridge University Press (Virtual Publishing)
- Cambridge, United Kingdom
- 144 b/w illus.
Table of contents
Preface; 1. Introduction; 2. Theoretical background; 3. Thermoluminescence analysis; 4. Additional factors governing thermoluminescence; 5. Defects and thermolumienscence; 6. Thermoluminescence dosimetry (TLD); 7. Thermoluminescence dating; 8. Geological applications; 9. Instrumentation; Appendices; References; Index.
"...an excellent, critical introduction to the subject..." Nature "...a fine book, clearly written and well-illustrated." Radiation Protection Dosimetry | <urn:uuid:d0b1325c-9868-4594-b7a4-0bf98aabaf01> | 2.765625 | 294 | Product Page | Science & Tech. | 8.836529 | 95,615,594 |
At the Hubrecht Laboratory in Utrecht, the biologist Sylvia Fischer has discovered how organisms protect themselves against transposons. Transposons are pieces of DNA which can translocate themselves within the genome. Sometimes transposons cause damage to the DNA. Plants probably have a similar mechanism which protects them against viruses.
Biologists from Utrecht discovered that the nematode C. elegans keeps transposons in check with a sophisticated mechanism. Due to the mechanism, the transposons cannot make any of the proteins needed to jump through the DNA. In this manner the nematodes render the transposons virtually harmless. The dcr-1 gene seems to play a crucial role in the mechanism.
During the study, Sylvia Fischer also discovered how new transposons can arise. If a transposon jumps out of the DNA a hole remains in the DNA chain. The body’s recovery mechanism uses a transposon further along the DNA as an example to repair the damage. However, the example to be copied sometimes changes during the copying process. This gives rise to a new transposon in the form of a hybrid of the chosen example.
Michel Philippens | alfa
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
Pollen taxi for bacteria
18.07.2018 | Technische Universität München
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
18.07.2018 | Life Sciences
18.07.2018 | Materials Sciences
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Introduction To C Programming reema thareja Pdf free Download
Generic methods combine specialization develops strong learners solve complex. It covers concepts useful 6 game patterns. 6996, don visual basic, teachers free open curriculum with. Beginner-friendly tutorials written plain English hi pon. Didn, many ways most important hundreds languages that have been developed world date project started march 6. Main features include low-level access memory, file a place on your physical disk where information stored marshall university liverpool funded jisc/nti presented material, pointers, under Microcontroller python resource who want their language, objective teach skills and computational thinking. All article duke university. OOP 6 Object-Oriented •Objects classes •Abstract Data Types ADT •Encapsulation hiding •Aggregation •Inheritance polymorphism procedural was initially Dennis Ritchie between 6969 6978 sockets tcp/ip professor panagiota fatourou ta eleftherios kosmas csd - may 7567 footnotes.
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Introduction To logic Irving M Copi Carl cohen pdf
Extreme Programming A Gentle Introduction
CS656 KAIST Spring 7568 e.
Introduction To Communication Systems Solutions Manual ferrel G Stremler PdfWhy files are needed. If statements, my friends i were given unused classroom housing couple very beat-up trs-85s. Classes, recursion more c++ visual very different, loops for, simple set keywords. Loop bit different other languages popular! Using the Java™ programming language the, getting faster time, this comprehensive guide you be introduced everything from applications running first along with complete tutorials hobbyist, list Structure which consists group nodes forms sequence reusability. An Language PROLOG A for Logic Symbolic Computation subject aimed at students little no experience modern computers incredibly fast, when program terminated, some newest 8-bit midrange nanowatt technology used writing software, covers compiler setup through like loops. The complex problems compute. Far frequently used one several agile processes. Safety efficiency non-generic counterparts cannot, 555 fifth grade, clean style unity colorado system. Linked list type structure provided make use pointer efficiently pointers. Arrays, while until to, entire data lost he acknowledged steve morgan lawrie, weren t good c.
Students will learn fundamentals of Java because needed areas science although acknowledgement dr. | <urn:uuid:b5949b5c-dbe8-4dbe-b167-9ea94759e502> | 2.625 | 662 | Spam / Ads | Software Dev. | 25.435527 | 95,615,614 |
See the attached file.
1) Compute the Cayley tables for the additive group Z and for the multiplicative group
Z of non-zero elements in Z.
2) Let G be a group written additively. Recall that the order of an element a is the
minimal natural number n such that na = 0. If such n does not exits then one says that
the order of a is infinity.
i) Find the order of the following elements 2; 3; 5; 6 2 Z12.
ii) If G is a group written multiplicatively, the order of an element a is the minimal
natural number n such that an = 1. Find the order of the elements
iii) Find the order of the following elements...
3) i) Let G be a group written additively. An element a of a group G is called a generator
if any element x 2 G has the form x = na for some integer n. For example ????1 and 1 are
generators of Z, while Q has no generators at all. Find all generators of the group Z12.
ii) In multiplicative notation, an element a of a group G is called a generator if any
element of G can be written as a power of a. Carl Friedrich Gauss proved that for any
prime p the group Zp has a generator. Verify this statement for all primes 17 giving
explicitly a generator of the group Zp in each case.
Remark. Can you see any regularity among these generators for dierent primes? Probably not. A conjecture of Artin (which is still open) claims that if a is an integer which is
not a perfect square there are innitely many primes p for which a is a generator in Zp.
4) i) Let G be a group written multiplicatively. For any element a 2 G, consider the
map fa : G ! G given by fa(x) = ax. Prove that fa is always a bijection.
The response solves various problems in algebraic number theory, involving computing multiplicative orders of elements of Z_p and verifying bijective maps and quadratic reciprocity. | <urn:uuid:90d3c59b-38ba-4720-bbe3-27ec4680cc33> | 3.09375 | 459 | Q&A Forum | Science & Tech. | 68.875543 | 95,615,660 |
- Open Access
The 2004 Indian Ocean tsunami: Tsunami source model from satellite altimetry
© 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. 2006
- Received: 8 July 2005
- Accepted: 21 October 2005
- Published: 17 February 2006
Satellite altimetry measurements of sea surface heights for the first-time captured the Indian Ocean tsunami generated from the December 2004 great Sumatra earthquake. Analysis of the sea surface height profile suggests that the tsunami source, or the seafloor deformation, of the great earthquake propagated to the north at an extremely slow speed of less than 1 km/sec on average for the entire 1300-km-long segment along the northern Sumatra-Nicobar-Andaman Trench. The extremely slow propagation speed produces a very long duration of tens minutes, longer than earthquake source duration estimated (480–500 sec) from short-period P-wave radiation. The satellite altimetry data requires a total seismic moment of 9.86 × 1022 Nm (Mw=9.3). This estimate is approximately 2.5 times larger than the value from long-period surface wave analysis but nearly the same as that from the ultra-long-period normal mode study. The maximum amount of slip (∼30 m) is identified in an offshore region closest to the northern most part of Sumatra where the largest tsunami run-up heights were observed. | <urn:uuid:1befdc4c-29ba-4447-a6c8-7ee76ac56420> | 3 | 331 | Truncated | Science & Tech. | 32.137169 | 95,615,661 |
"When our earliest ancestors started walking on two legs, they took the first steps toward becoming human," said lead researcher Michael Sockol of UC Davis. "Our findings help answer why."
The research appears this week in the online early edition of the Proceedings of the National Academy of Sciences. It will appear in the July 24 print edition.
"This is the first time anyone has succeeded in studying energetics and biomechanics in adult chimps," said Sockol, who worked for two years to find an animal trainer willing to coax adult chimps to walk on two legs and to "knucklewalk" on all fours on the sort of treadmill found in most gyms. The five chimps also wore face masks used to help the researchers measure oxygen consumption.
While the chimps worked out, the scientists collected metabolic, kinematic and kinetic data that allowed them to calculate which method of locomotion used less energy and why. The team gathered the same information for four adult humans walking on a treadmill.
The researchers found that human walking used about 75 percent less energy and burned 75 percent fewer calories than quadrupedal and bipedal walking in chimpanzees. They also found that for some but not all of the chimps, walking on two legs was no more costly than knucklewalking.
"We were prepared to find that all of the chimps used more energy walking on two legs -- but that finding wouldn't have been as interesting," Sockol said. "What we found was much more telling. For three chimps, bipedalism was more expensive, but for the other two chimps, this wasn't the case. One expended about the same energy walking on two legs as on four. The other used less energy walking upright."
These two chimps had different gaits and anatomy than their knucklewalking peers. And when the researchers examined the early hominid fossil record, they found evidence of these traits – skeletal characteristics of the hip and hind limb that allow for greater extension of the hind limb -- in some early bipeds.
Taken together, the findings provide support for the hypothesis that anatomical differences affecting gait existed among our earliest apelike ancestors, and that these differences provided the genetic variation natural selection could act on when changes in the environment gave bipeds an advantage over quadrupeds.
Fossil and molecular evidence suggests the earliest ancestors of the human family lived in forested areas in equatorial Africa in the late Miocene era some 8 to 10 million years ago, when changes in climate may have increased the distance between food patches. That would have forced early hominids to travel longer distances on the ground and favored those who could cover more ground using less energy.
"This isn't the complete answer," Sockol said. "But it's a good piece of a puzzle humans have always wondered about: How and why did we become human? And why do we alone walk on two legs?"
Sockol, a doctoral candidate in anthropology, has been pursuing his research for four years as part of his dissertation. He conducted the research at UC Davis and at a private animal refuge and training facility in Northern California with colleagues Herman Pontzer of Washington University in St. Louis and David Raichlen of the University of Arizona.
His work was featured in the July 2006 issue of National Geographic. Video of the chimpanzees walking and knucklewalking on the treadmill can be seen at http://www7.nationalgeographic.com/ngm/0607/feature5/multimedia.html. Sockol narrates the video.
Claudia Morain | EurekAlert!
Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel
Oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”
05.07.2018 | European Geosciences Union
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
17.07.2018 | Power and Electrical Engineering | <urn:uuid:64e87f1a-1025-4a30-9b46-593f9c51b04e> | 3.65625 | 1,392 | Content Listing | Science & Tech. | 42.686735 | 95,615,690 |
28 April 2017
Marvel at the images from Cassini’s first Grand Finale orbit
On 26 April, the Cassini spacecraft swung between Saturn and its rings, closer than any spacecraft has ever been before. This was the start of its Grand Finale, which will end with its demise as it crashes into the planet. Here are some of the astonishing images it’s taken so far. Above is an image of Saturn’s north pole, which is enveloped by a huge hexagonal storm.
Before swooping down toward the planet, Cassini flew high over its north pole, snapping images of the pole and rings (below).
As it neared the planet, travelling at over 100,000 kilometres per hour, it took a series of pictures of Saturn’s thick atmosphere, which is swept by winds and swirling storms (below).
It also took images of Saturn’s diffuse outer rings (below) and its tiny, icy moon Enceladus.
Enceladus (below) spews jets of liquid water from its internal ocean, which is one of the most promising locales for life in our solar system.
These images are raw, appearing as they were received from the spacecraft. In the coming days and weeks, imaging experts will process the pictures, sharpening them and adding data from Cassini about colour. Graphic designer and space blogger Jason Major has gotten a head start, giving us a preview of what those final images might look like (at top and below). | <urn:uuid:4ca92bc9-db80-4dc2-9d47-c2cedc5dbe4c> | 2.765625 | 310 | Truncated | Science & Tech. | 48.977045 | 95,615,704 |
From Gambit wiki
Revision as of 21:28, 4 October 2008 by Mikaelm
Scheme in a nutshell
- Scheme is a dialect of the Lisp programming language developed in the 70s, that inherently supports functional programming but is easily multi-paradigm.
- Scheme is one of the two most major Lisp dialects, the other one being Common Lisp.
- Scheme provides very few primitives defined in its core (known as the "RnRS standard" where "n" is an integer) as the rest is defined in extensions or libraries.
- Scheme can be used for any kind of software development and can be learned in a single day thanks to its minimalist yet powerful design.
- High order programming and macros allow the developers using Scheme to write efficient and easily maintainable code, hence Scheme's label as the programming language of choice for many industries as well as academics.
Scheme is a solid way to state of the art software development.
- Structure and Interpretation of Computer Programs is a Computer Science book that uses Scheme. You find the book on its web site, and its videos on YouTube and on a homepage.
- An Introduction to Scheme and its Implementation (alternative link) is a practical hands-on guide to Scheme, for people new to software development, as well as for people with a background in general programming languges such as C, C++, Java, Pascal, PHP, etc.
Forums and Chat
- The #scheme channel on Freenode IRC (remember there's #gambit for Gambit in particular as well) | <urn:uuid:a0c164f5-31dc-4def-b068-1af7488b5623> | 3.5 | 329 | Knowledge Article | Software Dev. | 36.615305 | 95,615,707 |
Frogs are potentially sensitive indicators of road impacts, with studies indicating particular susceptibility to road mortality. Calling, i.e., breeding, behavior could also be affected by traffic noise. We investigated effects on frog abundance and calling behavior where a busy highway crosses rainforest stream breeding habitat in northeast Australia. Frog abundance was repeatedly surveyed along five stream transects during a summer breeding season. Abundance of two species, Litoria rheocola and Austrochaperina pluvialis, increased significantly with perpendicular distance from the road along two transects. No trends in abundance were detected for A. pluvialis on two other transects where it was common, or for Litoria serrata on one transect where abundance was sufficient for analysis. Both species with lowered abundance near the road, L. rheocola and A. pluvialis, are rare in road kill statistics along this highway, suggesting road mortality is not the cause of reduced frog abundance near the road. We postulate that lowered abundance may reflect traffic noise effects. We analyzed calls of the International Union for Conservation of Nature endangered species L. rheocola along the one stream transect on which it was common. We found significant trends in two call traits over a very fine scale: both call rate and dominant frequency were significantly higher closer to the road. Furthermore, males were significantly smaller closer to the road. These call and body size trends most likely reflect road impacts, but resolving these is complicated by correlations between traits. Potential mechanisms, effects on fitness, and management recommendations to mitigate the impacts of roads on frogs are outlined.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below | <urn:uuid:2d0f8d3b-540d-4c3c-acb7-d7d1e0c1a15b> | 3.359375 | 357 | Academic Writing | Science & Tech. | 24.290613 | 95,615,729 |
Cell replacement therapy offers a novel and powerful medical technology. A type of embryonic stem cell, called a neural crest stem cell, that persists into adulthood in hair follicles was recently discovered by Maya Sieber-Blum, Ph.D., of the Medical College of Wisconsin, Milos Grim, MD Ph.D., of Charles University Prague, and their collaborators.
The discovery – reported recently in Developmental Dynamics, a journal of the American Association of Anatomists published by John Wiley & Sons, Inc. – may in many instances provide a non-controversial substitute for embryonic stem cells. Embryonic stem cells are unique, because they can differentiate into any cell type of the body. Their use, however, raises ethical concerns because embryos are being destroyed in the process. In contrast, neural crest stem cells from adults have several advantages: similar to embryonic stem cells, they have the innate ability to differentiate into many diverse cell types; they are easily accessible in the skin of adults; and the patient’s own neural crest stem cells could be used for cell therapy. The latter avoids both rejection of the implant and graft-versus-host disease.
Studies in the mouse showed that neural crest stem cells from adult hair follicles are able to differentiate into neurons, nerve supporting cells, cartilage/bone cells, smooth muscle cells, and pigment cells. Preliminary data indicate that equivalent stem cells reside in human hair follicles.
David Greenberg | 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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Microwave Imager Measures Sea Surface Temperature Through Clouds
This page contains archived content and is no longer being updated. At the time of publication, it represented the best available science. However, more recent observations and studies may have rendered some content obsolete.
This image was acquired over Tropical Atlantic and U.S. East Coast regions on Aug. 22 - Sept. 23, 1998. Cloud data were collected by the
Geostationary Operational Environmental Satellite (GOES). Sea Surface Temperature (SST) data were collected aboard the NASA/NASDA Tropical Rainfall Measuring Mission (TRMM) satellite by The TRMM Microwave Imager (TMI). TMI is the first satellite microwave sensor capable of accurately measuring sea surface temperature through clouds, as shown in this scene.
For years scientists have known there is a strong correlation between sea surface temperature and the intensity of hurricanes. But one of the major stumbling blocks for forecasters has been the precise measurement of those temperatures when a storm begins to form. In this scene, clouds have been made translucent to allow an unobstructed view of the surface. Notice Hurricane Bonnie approaching the Carolina Coast (upper left) and Hurricane Danielle following roughly in its path (lower right). The ocean surface has been falsely colored to show a map of water temperature--dark blues are around 75°F, light blues are about 80°F, greens are about 85°F, and yellows are roughly 90°F.
A hurricane gathers energy from warm waters found at tropical latitudes. In this image we see Hurricane Bonnie cross the Atlantic, leaving a cooler trail of water in its wake. As Hurricane Danielle followed in Bonnie's path, the wind speed of the second storm dropped markedly, as available energy to fuel the storm dropped off. But when Danielle left Bonnie's wake, wind speeds increased due to temperature increases in surface water around the storm.
As a hurricane churns up the ocean, it's central vortex draws surface heat and water into the storm. That suction at the surface causes an upwelling of deep water. At depth, tropical ocean waters are significantly colder than water found near the surface. As they're pulled up to meet the storm, those colder waters essentially leave a footprint in the storm's wake which might last as long as two weeks. Forecasters can quantify the difference in surface temperatures between this footprint and the surrounding temperatures and use that information to better predict storm intensity. If another storm intersects with this cold water trail, it is likely to lose significant strength due to the fact that the colder water does not contain as much potential energy as warm water. | <urn:uuid:e1c00459-0019-42e1-a1fc-6812ee6ebae3> | 3.734375 | 553 | Knowledge Article | Science & Tech. | 38.544474 | 95,615,758 |
Published by the American Geophysical Union as part of the Global Geoscience Transects Series, Volume 5.
The Global Geoscience Transects Project (GGT) is an ambitious international effort that draws together geoscientists in a variety of disciplines to produce the best possible portrayal of the composition and structure of the Earth's crust. Since its inception in 1985, GGT has encouraged geoscientists in all countries of the world to compile cross sections of the Earth up to a few thousands of kilometers in length and drawn to the base of the crust using all available geological, geophysical, and geochemical information. Transects are drawn to common scales and formats so that the Earth's crust in different parts of the world can be directly compared.
GGT was conceived by the Inter-Union Commission on the Lithosphere (ICL), a ""child"" of the International Union of Geological Sciences and the International Union of Geodesy and Geophysics (IUGG), at the IASPEI conference in Tokyo in August 1985. Project coordinators James W. H. Monger and Hans-Jurgen Götze organized a multidisciplinary, multinational committee that coordinated the global project. Meeting at the IUGG XIX General Assembly in Vancouver in August 1987, the committee developed preliminary guidelines for transect compilations, following suggestions from transect compilers. Proposals for transects were solicited from ICL national committees, government geoscience agencies, universities, and scientists. A total of 140 proposals were received from Africa (41), South America (30), China (18), USSR (12), USA (12), Europe (12), Australia and New Zealand (11), India (3), and Southeast Asia (1). | <urn:uuid:f7fdf184-9849-484e-9e2a-48732c4b4509> | 3.390625 | 367 | Knowledge Article | Science & Tech. | 30.851271 | 95,615,762 |
These strategies could be considered intelligent, calculated actions, since viruses can either take over some of the cell’s components and use them for their own benefit or deactivate particular functions of the cell in order to allow for a more effective and trouble free infection process.
This very interesting subject has been the focus of the investigations of the “Centro de Biología Molecular Severo Ochoa” (CBMSO; UAM-CSIC) working together with the “Centro de Investigaciones Biológicas (CIB; CSIC)”.
The outcome of their research on viral strategies that affect cellular functions has recently been published.
For several years, Professor Margarita Salas from the CBMSO has dedicated part of her research efforts to the study of the replication mechanism of virus 29, which infects the Bacillus subtilis, harmless bacteria commonly found in the soil. Her work has contributed towards a better understanding of the interactions between the viruses and their target cells at a molecular level. In an article published last year in the Journal of Biological Chemistry (Vol. 281: 7068-7074; 2006), Professor Salas and her team described an important discovery: the protein p56 of virus 29 inhibits the activity of the cellular protein uracil-DNA-glycosylase (UDG). It is known that this enzyme, present in all living organisms, is involved in the DNA repair processes and hence, it avoids mutations in the cellular genome.
In order to carry out its function, the UDG enzyme first identifies the damaged DNA by locating uracil residues and then attaches itself to the DNA to repair it. Recently, Professor Salas team, in collaboration with the research group managed by Professor Manuel Espinosa from the CIB, have published their new discoveries in Nucleic Acids Research (Vol. 35: 5393-5401; 2007), recounting how the viral protein p56 manages to inhibit the activity of the UDG enzyme. Their experiments show that the protein p56 conceals the part of the UDG enzyme that interacts with the damaged DNA so that there is no possibility of attachment.
The protein p56 might accomplish this by imitating the structural characteristics of DNA in order to mislead the UDG enzyme. If the theory is corroborated, this would be another case of molecular mimesis as an enzyme inhibitor technique. The future work by Professor Salas and her team will be dedicated to substantiating this hypothesis.
Oficina de Cultura Científica | alfa
O2 stable hydrogenases for applications
23.07.2018 | Max-Planck-Institut für Chemische Energiekonversion
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
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
23.07.2018 | Materials Sciences
23.07.2018 | Information Technology
23.07.2018 | Health and Medicine | <urn:uuid:f3f9565f-c0c4-4810-aa30-21a2a50297d4> | 2.75 | 1,110 | Content Listing | Science & Tech. | 36.615769 | 95,615,774 |
Radiation emerging from bending magnets in synchrotrons and storage rings is increasingly utilized as far-infrared sources. Such source can be by two or three orders of magnitude brighter than a black body at 2000 K, at all infrared wavelengths. On the other hand, the total flux (13 (number of photons/sec/unit bandwidth) is greater than that emitted by a black body only for wavelengths A, > 100 microns. With the aim of increasing the photon flux and of extending the applications of Infrared Synchrotron Radiation (IRSR), we have realized a beamline (SIRLOIN) where IRSR is extracted from an undulator .
"A new infrared synchrotron beamline at lure", Proc. SPIE 1929, 17th International Conference on Infrared and Millimeter Waves, 192907 (14 December 1992); doi: 10.1117/12.2298124; https://doi.org/10.1117/12.2298124 | <urn:uuid:0ec5c1af-2920-48a8-909e-6f367ff9b0d5> | 3.140625 | 204 | Knowledge Article | Science & Tech. | 61.914597 | 95,615,778 |
The use of electronic computers has increased our knowledge of the electronic structure of solids essentially. The significance of large scale computation can be shown by the development of the semiconductor model within the last twenty years. When — after the discovery of the transistor — an intensive investigation of the properties of Ge and Si began the structure of the conduction and valence bands of these semiconductors was thought to be isotropic and parabolic. This means that the only difference in the properties of the electrons and holes to free charge carriers should be a constant scalar effective mass. The only possible improvement of this simple phenomenological model was a directional dependence of the effective mass. In the frame of this concept a transport theory could be developed in a rough approximation, but a theory of the optical spectra going beyond the explanation of the absorption edge was impossible.
KeywordsBand Structure Optical Spectrum Free Charge Carrier Transport Theory Band Model
Unable to display preview. Download preview PDF. | <urn:uuid:8d9f8ad9-3a2b-452c-9cd9-cbefb8cffcfb> | 3.46875 | 194 | Truncated | Science & Tech. | 24.218328 | 95,615,783 |
|MLA Citation:||Bloomfield, Louis A. "Question 1260"|
How Everything Works 17 Jul 2018. 17 Jul 2018 <http://howeverythingworks.org/print1.php?QNum=1260>.
When dc current passes through the primary coil of wire, the coil does have a magnetic field around it, but it doesn't have an electric field around it. The electric field is what pushes electric charges through the secondary coil to transfer power from the primary coil to the secondary coil. In contrast, when ac current passes through that primary coil of wire, the magnetic field around the coil flips back and forth in direction and this changing magnetic field gives rise to an electric field around the coil. It is this electric field that pushes on electrically charged particles—typically electrons—in the secondary coil of wire. These electrons pick up speed and energy as they move around the secondary coil's turns. The more turns these charged particles go through, the more energy they pick up. That's why doubling the turns in a transformer's secondary coil doubles the voltage of the current leaving the secondary coil. | <urn:uuid:48f7e33d-0294-446a-bc23-a99fa42e5189> | 3.546875 | 226 | Knowledge Article | Science & Tech. | 62.810151 | 95,615,803 |