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Not only have multiple independent researchers demonstrated that global temperatures are likely greater than at any period in the last 2000 years, but the data used by researchers are all independent too. Sources as varied as marine sediments, corals, tree rings, stalagmites, boreholes, the length of glacial tongues, ice cores, and lake sediments all independently confirm that modern global temperatures are anomalously high. Independent researchers using independent data and methodologies to reproduce the each other’s results is the ideal for how to conduct good science.
Brian Angliss, from Serious errors and shortcomings void climate letter by 49 former NASA employees
So very good. This is what popular science writing is all about.(via globalspin) | <urn:uuid:2466a9ae-7bae-41fb-bc1b-2888318af9bd> | 3.140625 | 148 | Comment Section | Science & Tech. | 21.646522 |
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Articles, documents and multimedia from ABC Science
Tuesday, 30 April 2013
Proto-dinos Ten million years after the world's largest mass extinction, a lineage of animals thought to have led to dinosaurs took hold in what is now Tanzania and Zambia, according to new research.
Thursday, 7 March 2013
Fencing lions in wildlife reserves could help save them from extinction, says an international team of conservationists. | <urn:uuid:8d8a0249-817e-46bf-adee-cc8cc72d9903> | 2.75 | 92 | Content Listing | Science & Tech. | 31.645 |
Saturday 18 May
Marsh clubmoss (Lycopodiella inundata)
Marsh clubmoss fact file
- Find out more
- Print factsheet
Marsh clubmoss description
Clubmosses are simple plants, related to ferns; their common name is an indication of their resemblance to true mosses, the 'club' referring to the shape of the spore-bearing cones that most produce. Marsh clubmoss is the only British member of its particular genus. In appearance, it resembles another clubmoss, Lycopodium clavatum or stag's-horn clubmoss, not uncommon in the uplands.
Like ferns, clubmosses have two distinct forms; the 'gametophyte', which stays underground and grows in partnership with a fungus, and the form in which most people are likely to see, the 'sporophyte'. This consists of long trailing and rooting stems, which are covered with a coat of tiny leaf-like scales called microphylls with tiny, pale brown spore cases at the tips.Top
Marsh clubmoss biology
The ancestry of clubmosses can be traced back to at least the Carboniferous period, 300 million years ago. Most of the land on the planet was then composed of one huge super-continent called Pangea. A large part formed an extensive area of wetland, populated by the giant clubmosses. These tree-like plants grew to over 35 metres tall extremely quickly, at a rate of several metres a year. It is believed that they only reproduced once, at their maximum height and size, before dying and sinking back into the wet ground. Conditions at the time favoured the formation of vast peatlands and, over the vast periods of geological time, these peats were compressed and formed the extensive coalfields now found over much of the Earth's surface.
The spores of clubmoss are highly inflammable, and have been put to a number of different uses over the centuries. Known as 'Lycopodium powder', they have been used as a dusting powder for infants' sores, in treatment for irritation and spasm of the bladder, and used in pyrotechny in the making of fireworks, and for artificial lightning on the stage. Another use has been dyeing woollen cloth, and as the lubricant on condoms.Top
Marsh clubmoss range
In the UK, this species is mainly found the New Forest, Dorset and Surrey, and in the Republic of Ireland. It is also found in Wales and Scotland. There are a scattering of other sites in Cornwall, Devon, West Sussex and East Sussex. Attempts have been made to re-introduce it to Norfolk in 1999. Its global range includes Europe, where is known to be in decline, North America and Asia.Top
Marsh clubmoss habitat
Marsh clubmoss grows on wet heaths, peaty soil, and other places that are wet for much of the winter, preferably with some disturbance from grazing, peat cutting or where vehicles or cattle have broken up the surface.Top
Marsh clubmoss status
Classified as Nationally Scarce in the UK.Top
Marsh clubmoss threats
Marsh clubmoss was once much more widely spread and was once described as 'common'. Since 1855, loss of habitat by drainage has caused a major decline in its populations. Today, it is principally threatened by neglect and scrub encroachment arising as a result of the decline of sustainable peat-cutting, under-grazing and, possibly, pollution.Top
Marsh clubmoss conservation
Marsh clubmoss is listed in the UK Biodiversity Action Plan (UK BAP), and included in English Nature's Species Recovery Programme. In order to return this species to its former range, a number of re-introduction projects have taken place. In one case, the turves containing the clubmoss specimens were sent by post in a biscuit tin. All of these re-introduced plants have shown some signs of initial success, but over the long-term, they do not seem to be surviving. The reasons for this are not clear at present but the sites are being monitored in order to discover the source of the problem. Conversely, where plants have been introduced to new sites where there is proper management, they seem to have survived much better. However, in the case of the Norfolk site, it is well managed but still the plant does not seem to be responding.Top
Information supplied by English Nature.
- A category used in taxonomy, which is below 'family' and above 'species'. A genus tends to contain species that have characteristics in common. The genus forms the first part of a 'binomial' Latin species name; the second part is the specific name.
- Microscopic particles involved in both dispersal and reproduction. They comprise a single or group of unspecialised cells and do not contain an embryo, as do seeds.
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Structural maintenance of chromosomes (SMC) proteins are critical regulators of chromosome organization and function (1).
This family of chromosomal ATPases is highly conserved from bacteria and archaeal species to vertebrates. There are at least six eukaryotic SMC proteins. The SMC proteins display a common primary architecture that consists of five structural domains.
The five domains include two nucleotide-binding motifs termed the Walker A and Walker B motifs located at the N- and C-terminus, a central “hinge” domain, and two coiled-coil motifs that flank the central “hinge”. The SMC proteins associate in specific dimer pairs and arrange in an anti-parallel, two-armed structure that folds into a V-shape at the “hinge” domain.
Three SMC complexes have been identified and are defined by the SMC subunits which associate to form a heterodimer and their respective associated proteins.
SMC1 and SMC3 are part of the cohesin holocomplex which also includes at least two non-SMC subunits Scc1/mcd1/rad21 and scc3/SAs. The cohesin complex is required for holding together sister chromatids after replication in S-phase and throughout G2 phase.
SMC2 and SMC4 are part of the condensin complex which also includes three non-SMC subunits: CAP-D2, CAP-G, and CAP-H. Condensin plays a critical role in mitotic chromosome condensation during prophase and metaphase and segregation of sister chromatids during anaphase.
and SMC6 are part of a not-yet-named octameric complex (2). The function of this complex is not fully understood; but it appears to be polyfunctional. The SMC5/SMC6 complex displays activities similar to cohesin and condensin, and it appears to be mainly involved in a variety of DNA repair pathways, replication, and recombination.
The necessity of SMC proteins to the chromosome cycle has been well demonstrated, and more studies of these factors are needed for a better understanding of the complex dynamics of chromosome structure and function.
1. T. Hirano, "The ABCs of SMC Proteins: Two-Armed ATPases for Chromosome Condensation, Cohesion, and Repair," Genes Dev. 16, no. 4 (2002): 399-414.
2. G. De Piccoli, J. Torres-Rosell, and L. Aragon, "The Unnamed Complex: What Do We Know About Smc5-Smc6?," Chromosome.Res. 17, no. 2 (2009): 251-263.
Bethyl Laboratories Portfolio
Phospho SMC1 (S957)
Phospho SMC1 (S966)
Phospho SMC3 (S383)
Phospho SMC3 (S1083)
Antibodies to Condensin Complex Proteins ... | <urn:uuid:ad93430c-efa6-44ee-a181-18ab4df5394c> | 2.734375 | 652 | Knowledge Article | Science & Tech. | 53.891527 |
Neural Network is a powerful tool used in modern intelligent systems. Nowadays, many applications that involve pattern recognition, feature mapping, clustering, classification and etc. use Neural Networks as an essential component. In recent decades, several types of neural networks have been developed. Back Error Propagation, Kohonen feature map and Hopfield network are some of basic networks that have been developed and are used in many applications.
In this article general Multi Layer Perceptron or Back Error Propagation is presented. The sample application uses this Multi Layer Perceptron and classifies the blue and red patterns generated by user.
Figure below shows a typical MLP with three layers of weights.
In a typical neural network, these objects exist: layers (usually 3 layers), some neurons in each layer and synapses between layers. Based on these objects, I developed appropriate classes.
Classes used in MLP
Neuron: This is the basic element of network, that has some members such as
static double momentum; static double learningRate; CList<Synapse*> inlinks; CList<Synapse*> outlinks;
double output; double sum; double delta;
Layer: This class has a list of
neurons and some methods for computing errors and weight adjustment.
Layer(CString strLbl,int size);
Neuron* getNeuron(int i);
void computeBackpropDeltas(Samples s); void computeBackpropDeltas(); void computeWeights();
Synapse: This class has its
weight and two pointers to its connected neurons (
double weight; double data;
Perceptron: This is the last class that has some lists of
CList<Samples> inputSamples; CList<Samples> outputSamples;
How to use Sample Application
To use this program follow these steps:
- Clear screen by pressing on the Clear button.
- Define your network structure by putting appropriate values in H1, H2 and H3 edit boxes. These are the number of neurons in hidden layers. If some value was 0, that layer will not be included in network (by default the network has three layers: one input, one hidden and one output).
- Put some blue and red points on screen by clicking on it. (Select color from combo box).
- Now you can press “initialize” network button.
- Set maximum number of iterations and press “learn” as more as the network correctly classifies all points on screen. You can see the error graph by clicking on “Show error graph”. The “smartgraph” component is used in this project and you must download and register it on your computer to see error graph correctly. It is available here.
- Error values can be written into a text file, if you check in “Write errors to file”.
This program is fully object oriented and can be understood easily if you are familiar with Multi Layer Perceptron. At last, I used this class to develop a Farsi OCR application and it was working very well!.
Use and enjoy… | <urn:uuid:a1f0e5ef-5857-4786-a568-99039c8ed098> | 3.328125 | 657 | Documentation | Software Dev. | 45.164796 |
Moisture (in the form of water vapor) is a highly variable - and extremely important - component of Earth's atmosphere. In the spring of 2002, scientists from Europe and the United States collaborated on the International H2O Project, with the ultimate goal of improving the understanding and forecasting of convection. IHOP's duration was approximately six weeks (May 13 - 25 June), and occurred over the Southern Great Plains of the United States.
More information about IHOP (including a list of participants, presentations, etc.) can be found here.
This page is still under construction. Please check back soon for more updates and information. | <urn:uuid:44daca32-9a2e-43a2-8c9c-e331df788467> | 2.953125 | 131 | Knowledge Article | Science & Tech. | 38.904851 |
The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
ULTRAFAST CHEMICAL SEPARATIONS
are totally separated from each other. The peripheral partition walls and the baffle ridges force a zigzag motion for the flowing liquid. There are two collection chambers, one above and one below the separation volume; the light phase is discharged from the upper collection chamber, whereas the heavy phase is discharged from the lower chamber. Different types of pump wheels are used for discharge. The centrifuge was constructed of pure titanium (later models have the titanium pacified with palladium that has been diffused into the titanium surface) and was driven by a pneumatic motor or a variable-speed induction motor. The central bowl volume was 120 mL, and the holdup time was about 3 s. The system gave excellent phase separation.
Figure 29.Sketch of the experimental apparatus used for on-line separationof gallium from zinc and copper activities after these had been transportedto a low-background area with an HeJRT system. [Kos74; reprintedwith permission fromNucl. Instrum. Methods]
Aronsson, Ehn, and Rydberg [Art70] used the H-centrifuge to achieve fast, continuous separation of 116Pd produced by 14-MeV neutron-induced fission of 238U. Figure 30 shows a schematic of the equipment they used. Uranyl nitrate (2M) in 1M nitric acid solution containing acetylacetone (0.1M) passed through the irradiation cell and a delay line and was then mixed with toluene and fed to the first centrifuge. Palladium isotopes formed in fission were complexed by acetylacetone and were extracted by toluene. The toluene phase from the centrifuge was passed through a delay line; 116Pd decayed to 116Ag during the delay. The organic phase was then mixed | <urn:uuid:69dc1b98-420f-457a-a764-f041f4e7a34e> | 2.96875 | 427 | Academic Writing | Science & Tech. | 34.061419 |
Heatwaves aren't just a problem for humans. They can reshape marine ecosystems too. Such extreme weather events will become more common because of climate change. They can ravage land ecosystems, but until now little has been known about their effects in the seas.
Events last year in the sea off Australia's west coast suggest that the impact can be extreme and rapid. For more than ten weeks beginning in January, sea temperatures were between 2 °C and 4 °C warmer than usual along a 2000-kilometre stretch of coast – the area's most extreme warming event since records began.
In November 2011, Daniel Smale at the University of Western Australia in Perth and colleagues surveyed the area, as they have done every year since 2006. The formerly pristine and stable ecosystem had completely changed.
"In less than a year, we can have ecological switches from one kind of habitat to another," Smale says.
The ecosystem had lost complexity. The kelp (Ecklonia radiate) that covered 80 per cent of the area, providing a range of habitats, had declined to cover just 50 per cent. Mats of algal "turf", which create fewer distinct niches, had moved in instead.
Smale will return to the area this November to see whether the changes are permanent – he suspects that some will be.
This is not the first evidence that marine heatwaves can have a devastating impact. The 2003 heatwave that gripped Europe triggered a heatwave in the Mediterranean Sea. Temperatures rose by between 1 °C and 3 °C, and in places 80 per cent of sea fans died (Global Change Biology, DOI: 10.1111/j.1365-2486.2008.01823.x).
We don't yet know whether climate change triggered Australia's marine heatwave, but there is good evidence that it triggered Europe's 2003 heatwave. Models suggest that such events will become more common.
Working out what effect that will have on biodiversity is tricky. "It's a thing we all know is important, but it's very difficult to deal with," says Chris Thomas of the University of York, UK.
Thomas predicts that climate change will commit 15 to 37 per cent of species to extinction by 2050 (Nature, DOI: 10.1038/nature02121). He says the toll may be made worse by more frequent extreme weather events.
It's a concern that the International Union for Conservation of Nature (IUCN) shares. The IUCN Red List of Threatened Species factors in climate change, but a species that may seem stable as temperatures rise gradually might be hit much harder by an extreme event.
"If dramatic ecosystem changes happen, that may be something that takes us by surprise," says Rebecca Miller, programme officer at the IUCN red list unit.
Journal reference: Nature Climate Change, DOI: 10.1038/nclimate1627
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A False Distinction
Fri Jul 27 10:02:08 BST 2012 by Eric Kvaalen
"We don't yet know whether climate change triggered Australia's marine heatwave,..."
That implies that it might have been caused by climate change or it might not have (and that someday we will know!). But actually, climate change simply changes the probabilities for events.
One could take a determinstic point of view, in which case one has to say that anything that happens is a result of whatever happened earlier. That means global warming was part of the cause. Or we can take a probabilistic point of view, in which all we can say is that the heatwave was more probable because of global warming.
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support. | <urn:uuid:126b191b-a6df-4845-a129-3c29958b8001> | 4.15625 | 883 | Truncated | Science & Tech. | 56.687188 |
How do scientists figure out relationships between living things?
Some scientists compare every single feature of every single organism to try to work out their evolutionary relationships. But, another group of scientists has come up with a more efficient, more reliable approach. With this method, called cladistic analysis, you only compare a few carefully selected traits.
For example, how would a scientist figure out evolutionary relationships between sharks, dolphins and wolves? Two fishy-looking animals and a four-legged, furry one.
First we need to find the ancestral line they all came from. For this, we can go to the fossil record. Fish appear in the fossil record before four-legged animals (tetrapods), so the ancestor of this group must be at least as primitive as a fish. The most ancient fish were jawless, and since our whole group has jaws, we can safely choose a jawless fish as a fairly recent ancestor.
Unfortunately, this ancestor is long dead. To compare anything besides bones, we need a living animal for comparison. For this, scientists use something called an "outgroup", a living descendant that still shares many of the ancestor's primitive traits. So we need a living jawless fish, like a lamprey.
Lampreys are jawless fishes that look a lot like sucker-mouthed eels. While lampreys have retained many primitive ancestral traits (like jawlessness and a simple fish-style body), the other descendants of our jawless ancestor branched off more recently, as they evolved new traits. But which traits do we want to compare?
Organisms have only two types of traits: primitive and derived. Primitive traits are those inherited from distant ancestors. Derived traits are those that just appeared (by mutation) in the most recent ancestor -- the one that gave rise to a newly formed branch. Of course, what's primitive or derived is relative to what branch an organism is on.
Now let's compare traits on the lamprey-dolphin-shark-wolf branch.
Dolphins and sharks both have a torpedo-like shape, so are they the closest relatives? Because the lamprey also has this shape, we know this body plan is a primitive trait and we have to ignore it.
Limbs (like those of the wolf) are a derived trait, since lampreys do not have them. If we look inside the front fins of dolphins and sharks, we find--surprise!--that the bones inside the dolphin's front flippers look a lot like wolf leg bones. Dolphins and wolves share this derived trait (and many others), so they are actually out on the same branch together. If we had been fooled by the primitive trait, we would have gotten the relationships all wrong. But why does this matter? | <urn:uuid:300a49a4-9b27-4600-990e-c622d7dd41c8> | 3.875 | 566 | Knowledge Article | Science & Tech. | 49.576127 |
|Nov17-04, 07:09 PM||#1|
Why are orbitals called s, p, d, and f? I know how they work I was just wondering how did they get that specific abbreviation?
|Nov17-04, 07:27 PM||#2|
I asked this in chem. class also. I was wondering why it wasn't a, b, c, d, instead of s, p, d,.. My teacher said,"I don't know!"
**Although, she's not the brightest teacher** Not as an insult, just a opinion.
|Nov17-04, 08:38 PM||#3|
They stand for sharp, prinicpal, diffuse, and fundamental. They arise from an antiquated understanding of emission spectra. Spectroscopists didn't have a good idea of what was happening with the atoms themselves, so they tried to group the spectra they observed. When we got a better understanding of orbitals, the names stuck around.
|Nov20-04, 11:01 AM||#4|
Electrons are attracted to protons, but repell electrons. So, instead of all the electrons being bunched up right next to the nucleas, they orbit around the nucleas in shells. These shells can sometimes contain sub-shells. For example, the first shell contains only one sub-shell. As an electron gets further away from it's atom, it must have more "quantum energy." Electrons want to get as close to the nucleas as possible, but according to quantum physics, no to electrons can have the same "quantum energy." So, they orbit in shells. The electrons orbit in orbitals. The sub-shells have orbitals. For example, the 1 shell has an S orbital. Because it's an s orbital and it's the first shell it's labelled 1S. For 1-First shell-, S-S orbital. An S orbital has the shape of a sphere. An orbital wants to fill it's self. Alright, so why would the atom want to have 8 electrons in it's outer most shell, good question. The second shell has two sub-shells. One sub-shell has an S orbital, and the second has three P orbitals. The reason it has three is because they can arrange themselves according to X,Y,Z. Each orbital has only two electrons, because no two electrons can have the same "quantum energy." So, for the valence shell of an atom with two shells, one S orbital and three P orbitals. Two electrons an orbital adds to...8. Hydogen, on the other hand, only has one shell. So, to fill it's valence shell, it only needs two electrons. It already has one - Hydogen = one proton, one electron - so, it only needs to bond with one atom to fill itself. Carbon, on the other hand, has two shells, so it needs 8 to fill it's valence shell. So....
H C H Methane!!! CH4.
If you were to count it up everyone's filled. The carbon atom has 6 electrons. 2 in it's first shell, and 4 in it's valence shell. It needs 8 in it's valence shell. So, it shares one with hydrogen, and the hydrogen shares one of the carbons. This gives the carbon an extra electron, and the hydrogen it's desired two. The carbon, then, bonds with three more to add to 8.
HOH Water!!! H20. Oxygen has six valence electrons, meaning it needs 2 to gain, which it does with 2 hydrogen molecules.
O=O Oxygen!!! O2.
You're probably wondering, why is there an equals sign between the Oxygen molecules?
This indicated a double bond. Oxygen has six valence electrons, when it bonds with another oxygen, it gets 7. That's not the desired 8. So, it makes a double bond, and they share two electrons each. Which adds to 8.
O O Ozone!!! O3. Each one of these atoms share with each other, making 8.
That's covelant bonding!!!
This "quantum energy I told you about is somewhat true. What's really true is that there are four "quantum numbers" that cannot match.
The first is N.
N is the energy of an electron. For example, an electron in the first shell would have an N of 1. An electron in the second shell would have an N of 2. An electron in the third shell would have an N of 3.
N=1, means it's in the first shell.
The second is L. It's actually a greek cursive L kind of like this. l. Okay. This sign is the orbital. L = N - 1. That's the equasion. So, if N = 1, then, L = 0. 0 is an S orbital.
If N = 2, L can equal either 0 or 1. If it is 1, that's a P orbital. If N = 3, then that can be either 0,1 or 2. An S,P or...a D orbital.
Now, the third quantum number is M. It is the orientation of the orbitals, you know XYZ.
M can equal anything between -L and +L. For example if L is 1, then M can equal -1,0,1.
This is 3 different ways of arranging the P orbital.
Now the final one is Ms. For Spin. The spin of the electron can equal - 1/2 or 1/2.
Okay, so let's look at the possible arrangements of some electrons.
N L M Ms
1 0 0 -1/2
1 0 0 1/2 First shell, only can have two electrons.
2 0 0 -1/2
2 0 0 1/2
2 1 -1 -1/2
2 1 -1 1/2
2 1 0 -1/2
2 1 0 1/2
2 1 1 -1/2
2 1 1 1/2 Second shell, eight electrons, but none of them, nor the one's in the first shell have the same 4 quantum numbers.
HOPE YOU UNDERSTAND. IT TOOK ME A WHILE TO WRITE, I'D HATE TO LOSE IT AT THE LAST MOMENT, LIKE THE POWER SHUT DOWN OR SOMETHING. IF YOU UNDERSTAND THIS, YOU WILL UNDERSTAND THE REST.
HERE'S SOME SITES.
|Nov20-04, 03:54 PM||#5|
Thanks Dual Op Amp, but I think you missed the question. I think most know about quantum numbers and Wolfgang Pauli's exclusion principle and all of the quantum numbers and Heisenburg's Uncertainty Principle and... on and on,
We were just wondering what s,p,d,and all of the other letters stand for, which was answered by movies.
I think you would benefit most in your writings by starting a new thread and putting it in the "Chemistry" or "K-12" homework section as it's own topic.
Thank you, nonetheless,
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Welcome to PhysLink.com - Your physics and astronomy online portal. Stay a while! Check out our extensive library of educational and reference materials. Also, check out our fun section!
Where is mercury found in the world?
Asked by: William
Mercury (atomic symbol Hg) is a liquid at room temperature. Finding large pools of the element is for all purposes impossible, and finding it in its native state is also fairly rare. The mineraloid is usually found in the ore cinnabar (HgS) where it must go through a heating and condensing process to be obtained. Mercury may also occasionally be found with Silver.
Globally, mercury is most commonly 'produced' in Spain, particularly from the Almaden mine which is known for its high quality mercury. It may also be obtained from Yugoslavia, the United States (mainly California), and Italy.
Answered by: Jonathan Lashier, Student at ASU, Tempe, Arizona
Mercury is obtained from an ore called cinnabar or another called calomel. The places cinnabar and calomel can be mined in the world (quoting www.minerals.net) are as follows:
'The locality that yields the most and the finest Native Mercury for collectors is Almadén, Ciudad Real, Spain. There, small blobs are found in the associating Cinnabar. Many small blobs have also come from the mercury mines in Idrija, in former Yugoslavia. In the U.S., Mercury occurs in the Almaden and New Almaden mines in Santa Clara Co., California; the Socrates Mine, Sonoma Co., California; and Idria, San Benito Co., California. Small quantities of Mercury also occur in Arkansas and Texas.'
More fascinating information about this unique metal can be directly found at:
Answered by: Selquan Synfallan, Computer Programmer, Rutland Vermont
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Windmill Generator 4M Kit | <urn:uuid:cd1e2bfb-ce91-4e44-9e2d-248c044b6a19> | 3 | 522 | Q&A Forum | Science & Tech. | 41.173555 |
Many, if not most, modern object oriented languages have support for a concept called accessor methods object methods . Basically, these are simple methods which control access to some or all object internals via some form of indirection.
Most of the languages which support them do not have direct language syntax support for accessors, including the Java code included in the link above, and REBOL. Instead, these languages just use methods with naming conventions that mark them as accessors to the reader, if not the compiler. See JavaBeans for such an example, or the SET-* and GET-* accessors in REBOL 3's GUI.
Some languages have adopted direct syntax support for accessor functions, which enable the programmer to use them without using function call syntax, or even necessarily realizing that they are calling functions. With careful API design this can make it possible to extend the semantics of the language with new behavior, while allowing the syntax to continue to superficially resemble setting/getting values to/from variables or arrays. This is exceedingly helpful for object-oriented languages that don't otherwise have much of a way to not be object-oriented when it's needed (Self), and for formerly procedural languages that have had object-orientation grafted on later, but still have a lot of procedural-style programmers to feed (Delphi and its derivatives). It is also useful for wrapping component-oriented systems in syntax that makes sense within a regular language (Delphi's derivatives made by Microsoft, Vala).
It has been suggested that syntax support for method-based accessors be added to R3's object! semantics, but really, only one accessor would be required: The set accessor. The get accessor is unnecessary because we don't need parentheses to call a function, so all we have to do is assign a function to an appropriate word. None of the other accessors are possible to apply to an object!; we would need user-defined datatypes for those. The only one left standing is having a way to call a function when a set-word or set-path expression is encountered, instead of plain assignment.
- You don't have to understand a naming convention and call functions directly.
- You can type-check assignment, or apply other constraints.
- You can make read-only or write-only variables.
- It's easier to write code that implements the named accessors than it would be to write set-word accessors.
- It isn't necessary, at least since PROTECT/hide was implemented. You can do all that stuff without them. All of the access controls that accessors are supposed to solve are supported in R3 already.
- Code that uses your set accessor code will be incomprehensible at first glance, and will require full reading of your source and docs to understand.
- The overhead of the accessor will be hidden, and look like a simple, efficient assignment when it's really a function call.
- It won't help you at all with wrapping component code; you still have to use user-defined datatypes for those to work in some natural-seeming way.
In their current design, neither REBOL 2 (e.g. R2) nor REBOL 3 (e.g. R3) have any real support for defining or manipulating access to object content or state. As R3 is intent on larger and more structured application development, support for Accessor methods feels like a logical "next step" for object! datatype evolution. Moliad 20:42, 3 May 2010 (EDT)
That is no longer so for R3: There is no declarative syntax support for access control, but plenty of procedural support. Note that since that blog post, the (UN)PROTECT changes have been made (or proposed in some cases), user-defined datatypes were proposed, and an entire GUI system with accessors, was created without any language support for making those accessors look like assignments. The importance of this proposal has lessened accordingly. BrianH 23:24, 3 May 2010 (EDT) | <urn:uuid:260da9e6-884a-402f-959d-82bb2ca9818a> | 3.578125 | 852 | Comment Section | Software Dev. | 44.919537 |
is a standard notation for describing quantum states
in the theory of quantum mechanics
composed of angle brackets
(chevrons) and vertical bars
. It can also be used to denote abstract vectors
and linear functionals
in pure mathematics
. It is so called because the inner product
(or dot product
) of two states is denoted by a bra
, consisting of a left part,
, called the bra
, and a right part,
, called the ket
. The notation was invented by Paul Dirac
, and is also known as Dirac notation
Bras and kets
Most common use: Quantum mechanics
In quantum mechanics
, the state of a physical
system is identified with a ray
in a complex separable Hilbert space
, or, equivalently, by a point in the projective Hilbert space
of the system. Each vector
in the ray is called a "ket
" and written as
, which would be read as "ket psi
". (The ψ
can be replaced by any symbols, letters, numbers, or even words—whatever serves as a convenient label for the ket.)
can be viewed as a column vector and (given a basis for the Hilbert space) written out in components,
when the considered Hilbert space is finite-dimensional. In infinite-dimensional spaces there are infinitely many components and the ket
may be written in complex function notation, by prepending it with a bra
(see below). For example,
Every ket has a dual bra, written as . For example, the bra corresponding to the ket above would be the row vector
This is a continuous linear functional from to the complex numbers , defined by:
- for all kets
where denotes the inner product defined on the Hilbert space. Here an advantage of the bra-ket notation becomes clear: when we drop the parentheses (as is common with linear functionals) and meld the bars together we get , which is common notation for an inner product in a Hilbert space. This combination of a bra with a ket to form a complex number is called a bra-ket or bracket.
The bra is simply the conjugate transpose (also called the Hermitian conjugate) of the ket and vice versa. The notation is justified by the Riesz representation theorem, which states that a Hilbert space and its dual space are isometrically conjugate isomorphic. Thus, each bra corresponds to exactly one ket, and vice versa. More precisely, if is the Riesz isomorphism between and its dual space, then
Note that this only applies to states that are actually vectors in the Hilbert space. Non-normalizable states, such as those whose wavefunctions are Dirac delta functions or infinite plane waves, do not technically belong to the Hilbert space. So if such a state is written as a ket, it will not have a corresponding bra according to the above definition. This problem can be dealt with in either of two ways. First, since all physical quantum states are normalizable, one can carefully avoid non-normalizable states. Alternatively, the underlying theory can be modified and generalized to accommodate such states, as in the Gelfand-Naimark-Segal construction or rigged Hilbert spaces. In fact, physicists routinely use bra-ket notation for non-normalizable states, taking the second approach either implicitly or explicitly.
In quantum mechanics the expression (mathematically: the coefficient for the projection of onto ) is typically interpreted as the probability amplitude for the state to collapse into the state
More general uses
Bra-ket notation can be used even if the vector space is not a Hilbert space. In any Banach space B, the vectors may be notated by kets and the continuous linear functionals by bras. Over any vector space without topology, we may also notate the vectors by kets and the linear functionals by bras. In these more general contexts, the bracket does not have the meaning of an inner product, because the Riesz representation theorem does not apply.
is a linear operator
, we can apply A
to the ket
to obtain the ket
. Linear operators are ubiquitous in the theory of quantum mechanics. For example, observable physical quantities are represented by self-adjoint operators
, such as energy
, whereas transformative processes are represented by unitary
linear operators such as rotation or the progression of time.
Operators can also be viewed as acting on bras from the right hand side. Composing the bra with the operator A results in the bra , defined as a linear functional on H by the rule
This expression is commonly written as
If the same state vector appears on both bra and ket side, this expression gives the expectation value, or mean or average value, of the observable represented by operator A for the physical system in the state , written as
A convenient way to define linear operators on H is given by the outer product: if is a bra and is a ket, the outer product
denotes the rank-one operator that maps the ket to the ket (where is a scalar multiplying the vector ). One of the uses of the outer product is to construct projection operators. Given a ket of norm 1, the orthogonal projection onto the subspace spanned by is
Just as kets and bras can be transformed into each other (making into ) the element from the dual space corresponding with is where A† denotes the Hermitian conjugate of the operator A.
It is usually taken as a postulate or axiom of quantum mechanics, that any operator corresponding to an observable quantity (shortly called observable) is self-adjoint, that is, it satisfies A† = A. Then the identity
holds (for the first equality, use the scalar product's conjugate symmetry
and the conversion rule from the
This implies that expectation values
of observables are real.
Bra-ket notation was designed to facilitate the formal manipulation of linear-algebraic expressions. Some of the properties that allow this manipulation are listed herein. In what follows, c1
denote arbitrary complex numbers
, c* denotes the complex conjugate
of c, A
denote arbitrary linear operators, and these properties are to hold for any choice of bras and kets.
- Since bras are linear functionals,
- By the definition of addition and scalar multiplication of linear functionals in the dual space,
Given any expression involving complex numbers, bras, kets, inner products, outer products, and/or linear operators (but not addition), written in bra-ket notation, the parenthetical groupings do not matter (i.e., the associative property
holds). For example:
and so forth. The expressions can thus be written, unambiguously, with no parentheses whatsoever. Note that the associative property does not
hold for expressions that include non-linear operators, such as the antilinear time reversal operator
Bra-ket notation makes it particularly easy to compute the Hermitian conjugate (also called dagger
, and denoted †) of expressions. The formal rules are:
- The Hermitian conjugate of a bra is the corresponding ket, and vice-versa.
- The Hermitian conjugate of a complex number is its complex conjugate.
- The Hermitian conjugate of the Hermitian conjugate of anything (linear operators, bras, kets, numbers) is itself—i.e.,
- Given any combination of complex numbers, bras, kets, inner products, outer products, and/or linear operators, written in bra-ket notation, its Hermitian conjugate can be computed by reversing the order of the components, and taking the Hermitian conjugate of each.
These rules are sufficient to formally write the Hermitian conjugate of any such expression; some examples are as follows:
left(c_1|psi_1rangle + c_2|psi_2rangleright)^dagger = c_1^* langlepsi_1| + c_2^* langlepsi_2|.
Composite bras and kets
Two Hilbert spaces V
may form a third space
by a tensor product
. In quantum mechanics, this is used for describing composite systems. If a system is composed of two subsystems described in V
respectively, then the Hilbert space of the entire system is the tensor product of the two spaces. (The exception to this is if the subsystems are actually identical particles
. In that case, the situation is a little more complicated.)
If is a ket in V and is a ket in W, the direct product of the two kets is a ket in . This is written variously as
- or or or
Representations in terms of bras and kets
In quantum mechanics, it is often convenient to work with the projections of state vectors onto a particular basis, rather than the vectors themselves. The reason is that the former are simply complex numbers
, and can be formulated in terms of partial differential equations
(see, for example, the derivation of the position-basis Schrödinger equation
). This process is very similar to the use of coordinate vectors
in linear algebra
For instance, the Hilbert space of a zero-spin point particle is spanned by a position basis , where the label x extends over the set of position vectors. Starting from any ket in this Hilbert space, we can define a complex scalar function of x, known as a wavefunction:
It is then customary to define linear operators acting on wavefunctions in terms of linear operators acting on kets, by
For instance, the momentum operator p has the following form:
One occasionally encounters an expression like
This is something of an abuse of notation, though a fairly common one. The differential operator must be understood to be an abstract operator, acting on kets, that has the effect of differentiating wavefunctions once the expression is projected into the position basis:
For further details, see rigged Hilbert space.
The unit operator
Consider a complete orthonormal system (basis), , for a Hilbert space H, with respect to the norm from an inner product . From basic functional analysis we know that any ket can be written as
the inner product on the Hilbert space. From the commutativity of kets with (complex) scalars now follows that
must be the unit operator, which sends each vector to itself. This can be inserted in any expression without affecting its value, for example
where in the last identity Einstein summation convention
has been used.
In quantum mechanics it often occurs that little or no information about the inner product of two arbitrary (state) kets is present, while it is possible to say something about the expansion coefficients and of those vectors with respect to a chosen (orthonormalized) basis. In this case it is particularly useful to insert the unit operator into the bracket one time or more.
Notation used by mathematicians
The object physicists are considering when using the "bra-ket" notation is a Hilbert space
(a complete inner product space).
Let be a Hilbert space and . What physicists would denote as is the vector itself. That is
Let be the dual space of . This is the space of linear functionals on . The isomorphism is defined by where for all we have
are just different notations for expressing an inner product between two elements in a Hilbert space (or for the first three, in any
inner product space). Notational confusion arises when identifying
respectively. This is because of literal symbolic substitutions. Let
. This gives
One ignores the parentheses and removes the double bars. Some properties of this notation are convenient since we are dealing with linear operators and composition acts like a ring multiplication.
References and notes | <urn:uuid:625ff2c5-ff41-44bc-8734-854cfc09291c> | 3.34375 | 2,474 | Knowledge Article | Science & Tech. | 31.990668 |
EDITOR'S CHOICE IN DEVELOPMENTAL BIOLOGY
When a cell hits an obstacle, the actin filaments driving the membrane protrusion must reorganize and create additional branches to resist the pressure. Dan Fletcher at the University of California, Berkeley, and colleagues wanted to understand what effect that force has on the branching of actin filaments. They first glued unbranched actin filaments to a surface, some curved, some straight, and then added the raw materials necessary for the branching: the branch-initiating complex Arp2/3, the nucleation-promoting factor that activates it, and raw actin monomers, which polymerize into two tightly wound strands under the right conditions.
The researchers found that new actin branches were more likely to form on the convex side, or outer side, of curved segments. The questions were why and how the branching was occurring mostly on that side, says Fletcher. He recalled early studies on actin in which researchers noticed that isolated filaments would wiggle and squirm without the addition of any external energy. Though it was impossible to detect the wiggling at the scale of the isolated branching proteins under a microscope, Fletcher and colleagues wondered if the actin fragments they had immobilized still retained their wiggle, creating momentary curvature in certain areas and generating more branching. To test the idea, the team created a mathematical model to predict actin wiggling, and hypothesized that Arp2/3 would only bind when the curvature of the filament was greater than a certain value, and then imposed all the constraints of the experiment: the glue that held a filament down, the addition of Arp2/3, and the overabundance of raw actin proteins. The model fit.
When people think of mechanotransduction, they usually think of adhesion proteins, says Fletcher. But this study shows that “actin itself can be a sensor of its physical state,” and that the “structure that’s bearing the load may help organize the cell.” The results additionally hint at the possibility that some of the other 100 or so actin-binding proteins may also be regulated in part by the curvature of the strand. Curvature may turn out to be a “general mechanism for signaling during migration or other mechanotransduction processes,” says Harvard Medical School’s Jessica Tytell, who was not involved in the research.
V.I. Risca et al., “Actin filament curvature biases branching direction,” PNAS, 109:2913-18, 2012. | <urn:uuid:5e9eb599-807f-44d2-b4cd-2c31996b7add> | 3.453125 | 545 | Truncated | Science & Tech. | 35.368243 |
I’ve never really thought of how much water is on earth, especially compared to the size of the Earth. There’s so much I don’t think anyone can really fathom (har har) such a thing. Well, now you can. The image above is a representation of all the water on earth in sphere form, and it’s absolutely staggering.
This picture shows the size of a sphere that would contain all of Earth’s water in comparison to the size of the Earth. The blue sphere sitting on the United States, reaching from about Salt Lake City, Utah to Topeka, Kansas, has a diameter of about 860 miles (about 1,385 kilometers) , with a volume of about 332,500,000 cubic miles (1,386,000,000 cubic kilometers). The sphere includes all the water in the oceans, seas, ice caps, lakes and rivers as well as groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant. | <urn:uuid:c3b24b09-d35c-4139-a10d-8fbc6a9bcbce> | 2.875 | 210 | Personal Blog | Science & Tech. | 60.192638 |
Technology Research Area:
What is concentrated solar power, and what does it have to do with TVA's mission?
TVA is committed to developing new, clean, efficient sources of power. Solar power is one of the most promising alternatives to fossil fuel. TVA has already added photovoltaic solar generation to its power mix and is interested in expanding its involvement into other solar technologies.
Concentrated solar works by using lenses or mirrors to focus a large amount of solar energy collected from a wide area on a much smaller area, greatly concentrating the power of the sun. The sunlight is either focused on photovoltaic surfaces or used to heat a transfer liquid to run a conventional power plant.
The most developed and commercialized concentrated solar technology is parabolic trough generation, which consists of a straight, ditch-shaped array of mirrors that heats molten salt to drive power generation systems.
Whereas the best photovoltaic cells convert about a quarter of the sun's energy to DC electrical power, concentrated solar systems convert as much as 40 percent.
What is TVA doing about it?
TVA is investigating the use of concentrated solar to generate electricity and to produce steam to augment the steam cycle of power generation at fossil plants.
What are the possibilities for concentrated solar technology?
Concentrated solar systems are best suited for clear skies and low humidity, which explains their use in the desert Southwest. In the TVA region, clear skies and low humidity are much less frequent, so adoption of the technology in the region is still in the earliest stages.
The effects on the environment are minimal during manufacture and operation of the systems. Because the systems shade a large area, the habitat for plants and animals could be affected over time.
Since generation of power takes place some distance from populated areas, power storage or transmission or both are necessary to get the most out of concentrated solar. Solar power still has a long payback period, so state or local subsidies are often needed to make solar work.
However, the drive to limit emissions from power generation, the dropping prices of solar photovoltaic panels and the high output of concentrated photovoltaic solar power will continue to drive its development. | <urn:uuid:97c74e97-a5a6-489e-a473-0de19dac416c> | 3.6875 | 448 | Knowledge Article | Science & Tech. | 30.664143 |
A scientist from the University of London has crowned the world's strongest insect after an experiment using some string, glue and a yoghurt pot.
Dr Rob Knell and the paper's co-writer Professor Leigh Simmons from the University of Western Australia found that Onthophagus Taurus dung beetles could pull 1,141 times their own bodyweight as part of the study that investigated the beetle's walking speed, horn length and testes mass as well as their strength.
To determine the beetles' strength, Knell used glass tubes lined with sandpaper to mimic the tunnels dug by female dung beetles beneath dung pats. In their natural habitat, the male dung beetles guard these tunnels to prevent rival males from mating with the female inside, fighting off any would-be suitors using their large horns and immense strength. Continue reading | <urn:uuid:340e024b-f12c-4eba-aa60-82438e462644> | 3.03125 | 171 | Truncated | Science & Tech. | 38.881736 |
5 Virtual Machines
Note: we refer to pharo, but this applies also to squeak, because the mechanisms are the same. Even their VMs are 100% compatible when not exactly the same.
When you run an instance of pharo, you are actually running a virtual machine, with the specified image passed as an argument. Pharo is made of a VM in the sense that its executable consists of an interpreter, which contains its own instruction set (called its bytecode) to which all smalltalk methods are compiled. When a smalltalk method needs to be executed, the virtual machine looks up the method's bytecodes and interpret them one by one. You can see the bytecodes within the image, try exploring
SmallInteger >> #timesRepeat:
this will show you the instance of CompiledMethod that gets executed when you do something like 20 timesRepeat: aBlock. You can even see the bytecodes there. The term Virtual Machine has been given diverse meanings, as you can see here, so when talking about pharo's virtual machine we may use a term taken from A Tour of the Squeak Object Engine, which is Object Engine (OE) that fits much better and is more appropriate.
The OE you execute each time you run Pharo is programmed half in Smalltalk and half in C. It would be nice to have all of it written in Smalltalk, but for many reasons that's not possible nor desirable today. A not so small amount of the code consists of platform specific support files, so it's easier/better to have them written directly in C. We call this code the handwritten C part (HC). The not-C part of the OE is all written in Smalltalk, and to be more precise it is written in Slang, which is a subset of Smalltalk that can be easily translated to C. We call this the Slang code (SC). This SC is later translated to C by VMMaker and used in conjuntion with HC to make the OE. We call it the automatically generated C code (GenC).
The Slang code is inside VMMaker package, which is explained in the next section. The HC code is hosted at www.squeakvm.org, where you can also get a copy of specific versions of the GenC, in case you don't want to mess with VMMaker.
This compilation generates a native executable file and many libraries (one for each external plugin). This files contain the native executable bits of the primitive parts of the OE. That includes:
- Bytecode interpretation
- Numbered and named primitives
- Plugin primitives
As we said, methods are compiled into CompiledMethod instances in the image which have -among other things- a list of bytecodes. Thus, when a method is activated, its bytecodes have to be interpreted; that's the base of the execution model.
Inside the OE native executable code, this bytecode interpretation consists mainly of managing the OE state, like pushing and poping arguments to and from the stack, and sending messages. If you read carefully, you'll notice that there is an important group of things that is not implemented as bytecodes: primitives. There isn't any bytecode for things like adding two integers, but there is one to send a message, which determines if the method to be activated is a Smalltalk one or if it calls a numbered primitive, a named primitive or even a plugin primitive. Then you also have the actual executable code that got compiled with these groups of primitives. That would roughly make all the executable code you get when you compile.
But then, for all this native code you need to get support from the image. That is, you need methods that make the interpreter call the primitives and objects on which to perform them. For example, for SmallIntegers, you are going to have a lot of methods whicho don't have any Smalltalk code but a reference to the primitive that will do what the method's name says.
^ super + aNumber
Note: code after the <primitive: *> is a kind of fallback code that will be executed if and only if the primitive fails.
The idea is that for each group of primitives you'll have an object model onto which to apply them by sending messages that call primitive code. You may also notice that after compiling the OE you don't need Interpreter and Plugin classes anymore (unless you want to change the primitives and recompile), the only thing you need are the classes that make use of the primitives, and that's the reason why VMMaker isn't included with in the image by default.
Some time ago, Eliot Miranda started to work on a new VM for Squeak (and all its fork, like Pharo). This VM is called CogVM and it has been already released. In fact, is the default VM included in the PharoOneClick 1.1.1 and beyond. Cog VM includes a lot of new features, but in a glance:
- Real and optimized block closure implementation. This is why from the image side blocks are now instances of BlockClosure instead of BlockContext.
- Context-to-stack mapping.
- JIT (just in time compiler) that compiles methods to machine code.
- PIC (polymorphic inline caching).
If you are a little arround Smalltalk you may have heard about Cog VM and Stack VM. What is the big difference? Stack VM implements 1) and 2). And Cog VM is on top of the Stack VM and adds 3) and 4). Finally, there is CogMT VM which is on top of Cog VM and adds multi-threading support for external calls (like FFI for example).
Cog VMs have increased performance arround 4x-10x. In addition, it has improved VMMaker quite a lot.
Useful links for CogVM: | <urn:uuid:1f4e6576-4829-49b7-86a9-0ad2cf72469b> | 2.6875 | 1,235 | Documentation | Software Dev. | 53.07798 |
Phormosoma placenta is a species of sea urchin in the order Echinothurioida. It is a deep water species, seldom being found at depths less than 500 metres (1,600 ft), and occurs on either side of the Atlantic Ocean on the continental slope.
Phormosoma placenta is a yellowish-brown colour and can grow to a diameter of 12 cm (5 in). The flexible test is dome shaped above and flattened beneath. The plates from which the test is made overlap each other and are bound together by a membranous connection. Specimens removed from the water usually collapse into disc shapes. The upper (aboral) surface has few primary tubercles and spines but the lower (oral) surface is densely covered in perforate tubercles from which slender, club-shaped spines project, each one embedded in a membranous sac. These spines articulate with the tubercles and are used to support the animal and also in locomotion. Observations of live individuals on the seabed show that the few spines on the aboral surface are also enclosed in large membranous sacs but these are usually destroyed in bringing the animal to the surface.
Distribution and habitat
Phormosoma placenta is found in the Atlantic Ocean from Iceland and Greenland south to the Caribbean Sea in the west and the Gulf of Guinea in the east. There are three recognised subspecies: P. p. placenta occurs in the northerly part of the range, P. p. sigsbei in the Caribbean and P. p. africana off the coast of Africa. The depth range is normally 500 to 3,700 metres (1,600 to 12,100 ft) but individuals are occasionally found at shallower depths.
Phormosoma placenta is a gregarious species and can sometimes be found aggregating in large groups on sand and coral rubble substrates. It is believed to be an omnivore, primarily eating algal fragments which sink to the seabed or other detritus. Examination of its stomach contents has found 3 mm (0.1 in) pellets of mud bound together by mucus.
Juvenile cusk-eels have been found to associate with Phormosoma placenta, either hiding underneath it or between the long spines on its aboral surface. The fish are believed to receive protection from predators among the spines and may be able to feed in areas where there are few natural refugia.
Like other sea urchins, Phormosoma placenta is gonochoristic, individual animals being either male or female. The eggs contain large yolks and are buoyant. They are fertilised by sperm released by males and rise at the rate of 25 centimetres (9.8 in) per minute, taking two days to ascend from bathyal depths to the surface. They later lose their buoyancy and sink to the seabed. The embryos feed on their yolks and develop directly without a planktonic larval stage. Phormosoma placenta does not seem to be seasonal in its reproductive activities, spawning at any time of year. The aggregation of many individuals in one area increases the chances of fertilisation taking place and the buoyancy of the eggs should aid in their dispersal.
- Kroh, A.; Hansson, H. (2012). "Phormosoma placenta Thomson, 1872". In A. Kroh & R. Mooi. World Echinoidea Database. World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=124343. Retrieved 2012-12-30.
- Serafy, D. Keith; Fell, F. Julian (1985). "Marine Flora and Fauna of the Northeastern United States. Echinodermata: Echinoidea". NOAA Technical Report NMFS 33. http://docs.lib.noaa.gov/noaa_documents/NMFS/TR_NMFS/TR_NMFS_33.pdf. Retrieved 2012-12-30.
- Moore, Jon A.; Auster, Peter J. (2009). "Commensalism between Juvenile Cusk Eels and Pancake Urchins on Western North Atlantic Seamounts". Bulletin of the Peabody Museum of Natural History 50 (2): 381–386. doi:10.3374/014.050.0205.
- Young, Craig M.; Cameron, J. Lane (1987). "Laboratory and in situ flotation rates of lecithotrophic eggs from the bathyal echinoid Phormosoma placenta". Deep Sea Research 34 (9): 1629–1639.
- Tyler, P. A.; Gage, J. D. (1984). "The reproductive biology of echinothuriid and cidarid sea urchins from the deep sea (Rockall Trough, North-East Atlantic Ocean)". Marine Biology 80 (1): 63–74. doi:10.1007/BF00393129. | <urn:uuid:12aed83a-3183-49f3-9fb4-408e9a4bee71> | 3.296875 | 1,087 | Knowledge Article | Science & Tech. | 60.511276 |
because char, signed char and unsigned char are different types and it's implementation defined whether char is signed or not. More specifically, the integer literal 0xff has type int, which is converted to char that, being signed in your compiler implementation, acquires the integer value -1. Then, in the expression "*y==0xff" where you're comparing a char and an int, integer promotion rules kick in and the char is converted to the int -1, giving the observed result.
That would be handy in some cases but also quite confusing since the other integers (short, int...) are signed. There are a lot of pitfalls in C/C++ and integer promotion will create nasty surprises for you in many other cases as well. It's just to get used to it...
Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it.
- Brian W. Kernighan
why doesnt the following program work as expected:
Two guidelines that can help to prevent these kinds of errors are:
- Don't use magic numbers. If you use a const variable for the value 0xff, you make the type of that variable explicit.
- Don't mix signed and unsigned arithmetics. Signed values will get promoted to unsigned, which can cause unexpected results.
Cheers, D Drmmr
Please put [code][/code] tags around your code to preserve indentation and make it more readable.
As long as man ascribes to himself what is merely a posibility, he will not work for the attainment of it. - P. D. Ouspensky | <urn:uuid:c77ca4da-2785-431a-92df-40dcc6e57a32> | 3.859375 | 356 | Comment Section | Software Dev. | 59.610174 |
Section 8: Inflation and the Origin of Structure
Figure 27: While the universe appears approximately uniform, we see varied and beautiful structure on smaller scales.
Source: © NASA, ESA, and F. Paresce (INAPF-AIASF, Bologna, Italy). More info
On the largest cosmological scales, the universe appears to be approximately homogeneous and isotropic. That is, it looks approximately the same in all directions. On smaller scales, however, we see planets, stars, galaxies, clusters of galaxies, superclusters, and so forth. Where did all of this structure come from, if the universe was once a smooth distribution of hot gas with a fixed temperature?
The temperature of the fireball that emerged from the Big Bang must have fluctuated very slightly at different points in space (although far from enough to solve the horizon problem). These tiny fluctuations in the temperature and density of the hot gas from the Big Bang eventually turned into regions of a slight overdensity of mass and energy. Since gravity is attractive, the overdense regions collapsed after an unimaginably long time to form the galaxies, stars, and planets we know today. The dynamics of the baryons, dark matter, and photons all played important and distinct roles in this beautiful, involved process of forming structure. Yet, the important point is that, over eons, gravity amplified initially tiny density fluctuations to produce the clumpy astrophysics of the modern era. From where did these tiny density fluctuations originate? In inflationary theory, the hot gas of the Big Bang arises from the oscillations and decay of the inflaton field itself. Therefore, one must find a source of slight fluctuations or differences in the inflaton's trajectory to its minimum, at different points in space. In our analogy with the ball on the hill, remember that inflation works like a different ball rolling down an identically shaped hill at each point in space. Now, we are saying that the ball must have chosen very slightly different trajectories at different points in space—that is, rolled down the hill in very slightly different ways.
Figure 28: Small fluctuations in density in the far left box collapse into large structures on the right in this computer simulation of the universe.
Source: © Courtesy of V. Springel, Max-Planck-Institute for Astrophysics, Germany. More info
One source of fluctuations is quantum mechanics itself. The roll of the inflaton down its potential hill cannot be the same at all points in space, because small quantum fluctuations will cause tiny differences in the inflaton trajectories at distinct points. But because the inflaton's potential energy dominates the energy density of the universe during inflation, these tiny differences in trajectory will translate to small differences in local energy densities. When the inflaton decays, the different regions will then reheat the Standard Model particles to slightly different temperatures.
Who caused the inflation?
This leaves our present-day understanding of inflation with the feel of a murder mystery. We've found the body—decisive evidence for what has happened through the nearly uniform CMB radiation and numerous other sources. We have an overall framework for what must have caused the events, but we don't know precisely which suspect is guilty; at our present level of knowledge, many candidates had opportunity and were equally well motivated.
Figure 29: Typical string theories or supersymmetric field theories have many candidate scalar field inflatons.
In inflationary theory, we try to develop a watertight case to convict the single inflaton that was relevant for our cosmological patch. However, the suspect list is a long one, and grows every day. Theories of inflation simply require a scalar field with a suitable potential and some good motivation for the existence of that scalar and some rigorous derivation of that potential. At a more refined level, perhaps they should also explain why the initial conditions for the field were just right to engender the explosive inflationary expansion. Modern supersymmetric theories of particle physics, and their more complete embeddings into unified frameworks like string theory, typically provide abundant scalar fields.
While inflationary expansion is simple to explain, it is not simple to derive the theories that produce it. In particular, inflation involves the interplay of a scalar field's energy density with the gravitational field. When one says one wishes for the potential to be flat, or for the region over which it is flat to be large, the mathematical version of those statements involves MPlanck in a crucial way: Both criteria depend on MPlanck2 multiplied by a function of the potential. Normally, we don't need to worry so much about terms in the potential divided by powers of MPlanck because the Planck mass is so large that these terms will be small enough to neglect. However, this is no longer true if we multiply by MPlanck2. Without going into mathematical details, one can see then that even terms in the potential energy suppressed by a few powers of MPlanck can qualitatively change inflation, or even destroy it. In the analogy with the rolling ball on the hill, it is as if we need to make sure that the hilltop is perfectly flat with well-mown grass, and with no gophers or field mice to perturb its flat perfection with minute tunnels or hills, if the ball is to follow the inflation-causing trajectory on the hill that we need it to follow.
Figure 30: The LHC creates the highest-energy collisions on Earth, but these are irrelevant to Planck-scale physics.
Source: © CERN. More info
In particle physics we will probe the physics of the TeV scale at the LHC. There, we will be just barely sensitive to a few terms in the potential suppressed by a few TeV. Terms in the potential that are suppressed by MPlanck are, for the most part, completely irrelevant in particle physics at the TeV scale. If we use the cosmic accelerator provided by the Big Bang, in contrast, we get from inflation a predictive class of theories that are crucially sensitive to quantum gravity or string theory corrections to the dynamics. This is, of course, because cosmic inflation involves the delicate interplay of the inflaton with the gravitational field. | <urn:uuid:341274d2-bd75-49df-b675-2e58feb000e0> | 4.03125 | 1,281 | Academic Writing | Science & Tech. | 34.079726 |
Draw venn diagrams to ilustrate the following, then prove them.
Any help will be much appreciated.
Do you know what the diagrams look like when drawn (not mathematically proven)? If you draw two circles that overlap within your universal set, the parts that are common between the circles corresponding to A and B is A∩B and the part that is common to both circles is everything in both A and B A∪B. You should start off by drawing a diagram of these (even in microsoft paint or some other similar program) and attach them here because this part doesn't need any mathematics at all.
The first one has the definition of A\B = A and B^c, and we know that if complement something twice we get back the original. So (B^c)^c = B which means A\B^c = A and (B^c)^c = A and B.
For the second one, we know that anything plus its complement (like the above) will be the universal set or Omega. So this means that if we have a set X and its complement X' then U\X = X'.
I'm not really sure how much detail you need to go into proving these, so I might get your feedback on that. If you have to go really deep instead of being able to assume a lot of the identities, then what I said above may not be sufficient. | <urn:uuid:df899c27-b16e-48c2-a521-3bd92699a5d7> | 3.0625 | 295 | Q&A Forum | Science & Tech. | 70.832045 |
x:Code XAML Directive Element
Allows placement of procedural code within a XAML page, which is to be compiled by any XAML reader implementation that compiles XAML as opposed to interpreting it.
x:Class Attribute must also be provided on the parent element shown as object in the syntax, and that element must be the root element in a page. The x:Code directive element must be an immediate child element of the object root element.
The code within the x:Code XAML directive element is still interpreted within the XML namespaces provided. Therefore, it is usually necessary to also enclose the code within x:Code inside a CDATA segment.
x:Code is not permitted for all possible deployment mechanisms of a XAML file. Code for WPF must still be compiled, it is not interpreted or used just-in-time. For instance, x:Code is not permitted within a XML Paper Specification (XPS) document, or loose XAML.
The correct language compiler to use for x:Code content is determined by settings and targets of the containing project that is used to compile the application.
Code declared within x:Code has several notable limitations. The code placed within x:Code will be treated by compilation to be within the scope of the partial class that is already being created for that XAML page. Therefore all code you define must be members or variables of that partial class. You cannot define additional classes, other than by nesting a class inside the partial class (that is legal, but uncommon, because nested classes cannot be referenced in XAML). Other namespaces beyond the namespace being used for the existing partial class cannot be defined or added to. References to code entities outside of the partial class namespace must all be fully qualified. If members being declared are overrides to the partial class overridable members, this must be specified with the language-specific override keyword. If members conflict with members of the partial class created out of the XAML page, in such a way that the compiler reports it, the XAML file will fail to be loaded or compiled. | <urn:uuid:844de6d4-a5b5-40bb-b4a1-b8cda3a5f805> | 2.875 | 438 | Documentation | Software Dev. | 38.607549 |
How the cheetah got its stripes—a genetic tale
Feral cats in Northern California have enabled researchers to unlock the biological secret behind a rare, striped cheetah found only in sub-Saharan Africa, according to researchers at the Stanford University ...
Land management options outlined to address cheatgrass invasion
A new study suggests that overgrazing and other factors increase the severity of cheatgrass invasion in sagebrush steppe, one of North America's most endangered ecosystems.
The maternal effect: How mother deer protect their future kings
(Phys.org) —Do mothers invest more care in their sons if they believe their child is destined to be a king, president or a high-powered leader?
In the Eastern US, spring flowers keep pace with warming climate
Using the meticulous phenological records of two iconic American naturalists, Henry David Thoreau and Aldo Leopold, scientists have demonstrated that native plants in the eastern United States are flowering ...
Tigers roar back: Good news for big cats in three key landscapes
The Wildlife Conservation Society (WCS) announced today significant progress for tigers in three key landscapes across the big cat's range due to better law enforcement, protection of additional habitat, ...
126 new species discovered in Greater Mekong, WWF reports
From a devilish-looking bat to a frog that sings like a bird, scientists have identified 126 new species in the Greater Mekong area, the WWF said in a new report detailing discoveries in 2011.
Ancient DNA sheds light on Arctic whale mysteries
Scientists from the Wildlife Conservation Society, the American Museum of Natural History, City University of New York, and other organizations have published the first range-wide genetic analysis of the ...
Biology prof says eyeball may belong to big squid
Word that a giant eyeball washed up on a Florida beach has created a buzz on the Internet and in the marine biology community.
Carson's Silent Spring turns 50
Record-breaking python found in Florida Everglades with 87 eggs
A monster Burmese python captured in the Everglades has broken the state size record, stretching 17 feet, 7 inches, its belly bursting with 87 eggs, the University of Florida announced in August.
Record loss of Arctic ice may trigger extreme weather
Arctic sea ice is shrinking at a rate much faster than scientists ever predicted and its collapse, due to global warming, may well cause extreme weather this winter in North America and Europe, according to climate scientists.
Sanctuary chimps show high rates of drug-resistant staph
(Phys.org) -- Chimpanzees from African sanctuaries carry drug-resistant, human-associated strains of the bacteria Staphlyococcus aureus, a pathogen that the infected chimpanzees could spread to endangered wild a ...
Democracy works for Endangered Species Act, study finds
When it comes to protecting endangered species, the power of the people is key, an analysis of listings under the U.S. Endangered Species Act finds.
Citizen science reveals that protected areas allow wildlife to spread in response to climate change
A new study led by scientists at the University of York has shown how birds, butterflies, other insects and spiders have colonised nature reserves and areas protected for wildlife, as they move north in response ... | <urn:uuid:8bb2b97f-d6cb-477a-b07c-a61c0dd272bd> | 2.75 | 670 | Content Listing | Science & Tech. | 37.215992 |
When you study the motion of a rigid body you have $\vec\omega$, the vector associated to angular velocity. In the case you are using Euler angles and want a quick formula for the rotational kinetic ...
I'm learning about angular velocity, momentum, etc. and how all the equations are parallel to linear equations such as velocity or momentum. However, I'm having trouble comparing angular acceleration ...
Hey so I've just learned about angular velocity and momentum and how torque changes it. Looking at a wheel spinning around an axis, with one end being held up by a rope, what causes the wheel to ... | <urn:uuid:403e117f-96bc-4e05-b532-e3e25fbe5556> | 3.1875 | 125 | Q&A Forum | Science & Tech. | 51.191209 |
Synonyms: Limnobotrya montigena, Ribes lacustre var. molle, Ribes lentum, Ribes molle, Ribes nubigneum
Alpine prickly currant blooming at Indian Springs Campground, Malheur National Forest..............July 1, 2010. Note the glandular upper surface of the leaves which differentiates this species from the similar prickly currant (Ribes lacustre) which has glabrous upper leaf surfaces (and usually larger leaves).
Alpine prickly currant is a a low shrub with straggly branches ranging from 20-100 cm high. It is a densely short-pubescent and glandular species with 1-5 flattened spines at the nodes from 4-6 mm long and a few shorter, slender bristles or spines between the nodes. The leaves are deeply 5-lobed with hear-shaped bases and with the lobes deeply cleft and coarsely toothed. Individual leaves are 1.5-3 cm wide are haired above and covered with numerous stalked glands.
The inflorescences consist of short axillary racemes of 4-10 whitish, pinkish or purplish flowers. The pedicels are 1-5 cm long and jointed. The hypanthium is saucer-shaped rather than tubular , about 5 mm wide and lined with a thin disk. The sepals are yellowish-green to pinkish in color. The stamens are about equal to the petals. The berry is reddish to black, 5-8 mm wide and glandular.
Alpine prickly currant is found on dry, open rocky outcrops or slopes at high elevations above 1800 meters in the mountains.
Alpine prickly currant may be found from the Cascade Mts of British Columbia south to California and east to Idaho, Nevada and Arizona. | <urn:uuid:6b9abaaf-09ed-4eb6-ab90-1f621b3e429a> | 2.71875 | 399 | Knowledge Article | Science & Tech. | 61.199756 |
From: Shynn Chris (email@example.com)
Date: Tue May 01 2001 - 11:47:20 BST
This paper investigates the principals of making a conscious robot and
whether or not making a robot with a singular consciousness is feasible.
It details a project at MIT which was aimed at making not a conscious
robot but a robot which could interact with the real world in a versatile
and robust way. This robot would also be able to provide invaluable
information which would be near impossible to get otherwise.
> It is unlikely, in my opinion, that anyone will ever make a robot that
> is conscious in just the way we human beings are.
I am not sure if I agree with Dennett in this point. I believe it
depends on what people define as the essence of consciousness. If you
believe that that essence is the human soul or spirit then in that case
I agree with Dennett that humans will never be able to make a conscious
robot as we would have to become near gods ourselves and able to bestow
a soul upon a robot. If, however you see that consciousness as just the
correct balance of chemicals and elements in the human brain then I
believe that it is totally possible to make a conscious robot akin to
our own consciousness as we would eventually understand and be able
to replicate that balance.
> Might a conscious robot be "just" a stupendous assembly of more
> elementary artifacts--silicon chips, wires, tiny motors and cameras
> --or would any such assembly, of whatever size and sophistication,
> have to leave out some special ingredient that is requisite for
Cannot a human also be seen in this light ? are we not just a collection
of neural cells, veins, arteries and nerves ? The only thing Dennett
points out here is that many people believe in a 'spark' of
consciousness which is what would be missing in a robot that any human
had constructed. Once again it comes back to a debate of whether or not
the consciousness is some ethereal quality akin to a soul or whether it
can be explained by physical science. If it can be explained by phyisical
science then that balance or ingredient will at some level of
sophistication be replicated.
> The phenomena of consciousness are an admittedly dazzling lot, but I
> suspect that dualism would never be seriously considered if there
> weren't such a strong undercurrent of desire to protect the mind from
> science, by supposing it composed of a stuff that is in principle
> uninvestigatable by the methods of the physical sciences.
Physical scientific methods are advancing all the time and more and more
false conceptions attributed to the supernatural are being proved false
all the time. Yet still the desire to protect the mind by encasing it in
the notion of a transcendant being able to bestow life and a soul must be
enourmous as there are over a billion people in the world that believe in
some form of higher being and of the human spirit. Yet even with these
conceptions of higher powers we strive to create an artificial mind
capable of conscious thought.
> Robots are inorganic (by definition), and consciousness can exist only
> in an organic brain.
Why ? arent both organic and inorganic compounds made up of the same
component materials ? This argument for the impossibility of a conscious
robot is not valid in my opinion as all compounds are created of the same
elements such as carbon and hydrogen so why shouldnt consciousness be able
to reside within an inorganic structure of those elements ?
> So there might be straightforward reasons of engineering that showed
> that any robot that could not make use of organic tissues of one sort or
> another within its fabric would be too ungainly to execute some task
> critical for consciousness.
again I raise the objection that why shouldnt a robot be able to have a
conscious mind using solely inorganic materials as these are the same in
base elements as organic compounds. Once again it comes back to an
argument of a specific required ingredient, the 'spark' of
consciousness. If such a spark is required and can only be attained by the
use of organic compounds then I agree that a robot purely consisting of
inorganic materials could not attain consciousness. Also there is the
problem of interfacing between the organic and inorganic components of the
robot. If these components could not be interfaced efficiently and
properly then the robot could not make use of its organic components and
therefore suffer as a result. But would this deny it consciousness ? I do
not think it would, I believe that the consciousness would still be
present but would be severly limited, akin to limitations placed upon
autistic people who because of a genetic problem are not as versatile as
> Robots are artifacts, and consciousness abhors an artifact; only
> something natural, born not manufactured, could exhibit genuine
I do not agree with this point that Dennet exhibits at all, already human
genetic scientists have cloned sheep and these behave just as normal sheep
would, they have as much consciousness as other sheep yet just because
they were cloned and not born naturally should not exclude them from
having a chance at being catagorised as conscious. I totally agree with
Dennet when later on in the same passage he describes this as origin
chauvinism and should be completly discounted.
> And to take a threadbare philosophical example, an atom-for-atom
> duplicate of a human being, an artifactual counterfeit of you, let us
> say, might not legally be you, and hence might not be entitled to your
> belongings, or deserve your punishments, but the suggestion that such a
> being would not be a feeling, conscious, alive person as genuine as any
> born of woman is preposterous nonsense, all the more deserving of our
> ridicule because if taken seriously it might seem to lend credibility to
> the racist drivel with which it shares a bogus "intuition".
I completely agree with the point Dennett makes here in that what is in
essence a clone of you, although it is not the exact same person as you,
because of what in my opinion is changes in thought patterns due to a
lifetime of experiences, is still alive and should not be discounted out
> it could turn out that any conscious robot had to be, if not born, at
> least the beneficiary of a longish period of infancy. Making a fully-
> equipped conscious adult robot might just be too much work. It might be
> vastly easier to make an initially unconscious or nonconscious
> "infant" robot and let it "grow up" into consciousness, more or less the
> way we all do.
I believe this hypothesis to be correct, all humans start life with a bare
minimum of knowledge and have only their instincts and their capability
for learning to build upon. It is the same with neural nets, they start
out with the bare minimum of base rules and learn from there building
patters and recognising those patterns when they reappear. I believe that
making a fully-adult robot would be too much work as you would have to
program in a lifetimes worth of experiences and rules, whereas an infant
robot would be able to learn those rules for itself just as a human baby
might. It may take longer but I think that this is the only way making a
conscious robot akin to ourselves will ever work.
> Robots will always just be much too simple to be conscious.
The argument that is put foward in the relevant passage to this quote is
in my opinion very close-minded as who knows what technology will be
capable of in the future. If we had decided that tools would always be
much too simple to be usefull we would still be plodding around in the mud
looking for our next meal with a crude club.
> There is no reason at all to believe that some one part of the brain is
> utterly irreplacible by prosthesis, provided we allow that some crudity,
> some loss of function, is to be expected in most substitutions of the
> simple for the complex. An artificial brain is, on the face of it, as
> "possible in principle" as an artificial heart, just much, much harder
> to make and hook up.
As we have been told much of the brain is made up of sensori material and
is used to interpret sensori input. Once part of the brain is incapable of
functioning then if that part is replaced it would undoubtedly affect the
conscious mind of the person. In this matter then, I agree with Dennett
that if a piece of the brain is replaced the consciousness is affected and
although this cannot be proven, until we fully understand the functioning
of the brain and the storing of the huge ammounts of data the brain
contains we will not know how a prosthestic brain would affect the mind.
> A much more interesting tack to explore, in my opinion, is simply to set
> out to make a robot that is theoretically interesting independent of the
> philosophical conundrum about whether it is conscious.
This next section of the paper outlines and comments on the COG project,
which is the project to make an interactive robot at MIT. As stated
previously the aim of COG is not to be conscious, but to be versatile and
interactive with its environment to provide invaluable data to the
> Cog's eyes won't give it visual information exactly like that provided
> to human vision by human eyes (in fact, of course, it will be vastly
> degraded), but the wager is that this will be plenty to give Cog
> the opportunity to perform impressive feats of hand-eye coordination,
> identification, and search. At the outset, Cog will not have color
I agree with Dennett here that, though Cog's eyes will be vastly
downgraded from ourown they will still model sight as well as they need
to. As for the fact that Cog doesnt have colour vision, I dont see that
this would make any difference at the outset as many animals such as dogs
survive with only greyscale vision and even as humans we have the rod
cells in our eyes to provide greyscale vision at night.
> part of the hard-wiring that must be provided in advance is an
> "innate" if rudimentary "pain" or "alarm" system to serve roughly the
> same protective functions as the reflex eye-blink and pain-avoidance
> systems hard-wired into human infants.
I also agree with with Dennett here, but only to a point. Yes human
infants have reflexes and pain-avoidance systems build in but they learn
by trial and error as to what will set off those alarms. Infants are not
in my opinion a good model for this as, though they have the systems, they
are almost unable to make use of them as they have not yet built up an
idea of what will set them off. I believe that this could also be the case
with Cog, in early stages while he is still learning what will set off the
alarms he may damage much equipment in that learning.
> The goal is that Cog will quickly "learn" to keep its funny bones from
> being bumped--if Cog cannot learn this in short order, it will have to
> have this high-priority policy hard-wired in.The same sensitive
> membranes will be used on its fingertips and elsewhere, and, like human
> tactile nerves, the "meaning" of the signals sent along the attached
> wires will depend more on what the central control system "makes of
> them" than on their "intrinsic" characteristics. A gentle touch,
> signalling sought- for contact with an object to be grasped, will not
> differ, as an information packet, from a sharp pain, signalling a need
> for rapid countermeasures.
Here Dennet puts foward the idea of modelling the lower level functions of
the human brain in Cog. These reactions to the data-packets sent by the
membrane will be essential learning material and it would be interesting
to see how Cog will differentiate between a light touch upon an object and
a touch that would break something as according to Dennett they will be
exactly the same data-wise. It would also be interesting to see how
Cogs brain would be organised and what priorities were given to which
alarm signals. Such as would one membrane be more important than another ?
modelling a critical system that needs to be protected.
> DENNETT :
> So even in cases in which we have the best of reasons for thinking that
> human infants actually come innately equipped with pre-designed gear, we
> may choose to try to get Cog to learn the design in question, rather
> than be born with it. In some instances, this is laziness or
> opportunism- -we don't really know what might work well, but maybe Cog
> can train itself up.
I like this view of designing future versions of Cog, it is a view similar
to giving him a set of knowledge then after his lifetime you take all his
accumulated knowledge and pass that on as genetic knowledge if you like to
his offspring. This is a good idea and I think that this will work as
instead of trying to model all of the human mind in one go it will start
out with the very basics and learn what it needs to from there, just like
a human infant does.
> How plausible is the hope that Cog can retrace the steps of millions of
> years of evolution in a few months or years of laboratory exploration?
This hope is unfounded in my opinion as for Cog the environment will be
totally different to the environment that any other creature has evolved
in. In real life there is a balance between predators and prey and
creatures use their sences for survival and the finding of food. In the
laboratory environment Cog will have no need of food and is in no danger
of 'dying' so the whole process is different.
> We are going to try to get Cog to build language the hard way, the way
> our ancestors must have done, over thousands of generations. Cog has
> ears (four, because it's easier to get good localization with four
> microphones than with carefully shaped ears like ours!) and some
> special-purpose signal-analyzing software is being developed to give Cog
> a fairly good chance of discriminating human speech sounds, and probably
> the capacity to distinguish different human voices.
Here Dennett describes what will be designed into Cog to aid him in
picking up the human language, or at least some rudimentary form of
language. But I believe that just to give him this equipment will not be
enough, I think that Cog will also need to have a sort of desire to
imitate its 'mothers' like human infants do when they start to speak for
the first time. I think that if Cog does have this desire and also the
desire to understand what it is imitating then he will be able to pick up
language much as a human infant does. But it is the understanding of the
language it is learning that is the most important, otherwise Cog becomes
just a parrot who has a basic use of language but no understanding of what
that language refers to.
> This is so for many reasons, of course. Cog won't work at all unless it
> has its act together in a daunting number of different regards. It must
> somehow delight in learning, abhor error, strive for novelty, recognize
> progress. It must be vigilant in some regards, curious in others, and
> deeply unwilling to engage in self-destructive activity. While we are at
> it, we might as well try to make it crave human praise and company, and
> even exhibit a sense of humor.
I totally agree with Dennett here, without these desires and needs then
Cog will only ever be a learning machine, learning because it is designed
to, and not as is the case of humans because it wants to.
> I submit that Cog moots the problem of symbol grounding, without having
> to settle its status as a criticism of "strong AI". Anything in Cog that
> might be a candidate for symbolhood will automatically be "grounded" in
> Cog's real predicament, as surely as its counterpart in any child, so
> the issue doesn't arise,
I agree with Dennett here in that all symbols of need in grounding would
be automatically grounded because Cog is modelling an infant to begin
with. I think this because although he will not know the use for objects
such as an Umbrella neither does an infant untill much later in its
development. All either Cog of an inafnt wold have would be the knowledge
that an object exists and it looks like an umbrella although neither of
them know what it is called.
> if Cog develops to the point where it can conduct what appear to be
> robust and well-controlled conversations in something like a natural
> language, it will certainly be in a position to rival its own monitors
> (and the theorists who interpret them) as a source of knowledge about
> what it is doing and feeling, and why.
Here is where Dennett concludes saying that since Cog is designed to
re-design himself as much as possible then it will eventually be Cog who
will be the expert on what is happening to Cog. If he manages to reach a
stage where he is able to converse with his designers he will have
redesigned himself so much then only he will be able to tell the
designers what is happening in him, as they although experts will not have
the current operational knowledge of Cog at any one time.
This archive was generated by hypermail 2.1.4 : Tue Sep 24 2002 - 18:37:30 BST | <urn:uuid:f8291b0c-5c71-4056-8819-af80ffd15999> | 2.78125 | 3,875 | Comment Section | Science & Tech. | 39.0563 |
Learn more physics!
What other experiments follow the same principle as the "Dunking Bird" Experiment?
The Dunking Bird experiment works because the liquid in the bird separates two different areas of gas. Normally, these two areas have the same pressure. When you get the head of the bird wet this water will evaporate, which cools the gas in the head part of the bird, decreasing the pressure there. This "pulls" the liquid up into the head, which makes the bird tip over.
When it tips, two things happen: 1) the head gets wet again since it dips into a glass of water and 2) the liquid runs back into the bottom of the bird causing the bird to stand back up. The water on the head evaporates, and the whole cycle repeats.
A similar experiment is Franklin's Palm Glass (also called the Love Meter). The way this works is that you warm the liquid in the bottom of the tube in your hand. The liquid happens to be very volatile - this means that it evaporates very easily. Your hand is just warm enough to make the liquid in the bottom evaporate. When it does, it fills the bottom bulb with higher-pressure gas that pushes the liquid up into the top part.
Hope this helps!
(published on 10/22/2007)
Follow-up on this answer. | <urn:uuid:34f6712b-a02d-4587-845d-269fc8c6c63d> | 3.6875 | 279 | Q&A Forum | Science & Tech. | 67.262687 |
Experiments were also made with the dregs left after liquefied air had nearly entirely evaporated, and again with the same result; no increase in discharging power is produced by concentration of a possible radioactive constituent of the atmosphere.
We have since found that the radium emanation withstands prolonged sparking with oxygen over alkali, and also, during several hours, the action of a heated mixture of magnesium powder and lime. The discharging power was maintained unaltered after this treatment, and inasmuch as a considerable amount of radium was employed it was possible to use the self-luminosity of the gas as an optical demonstration of its persistence.
In an experiment in which the emanation mixed with oxygen had been sparked for several hours over alkali, a minute fraction of the total mixture was found to discharge an electroscope almost instantly. From the main quantity of the gas the oxygen was withdrawn by ignited phosphorus, and no visible residue was left. When, however, another gas was introduced, so as to come into contact with the top of the tube, and then withdrawn, the emanation was found to be present in it in unaltered amount. It appears, therefore, that phosphorus burning in oxygen and sparking with oxygen have no effect upon the gas so far as can be detected by its radioactive properties.
The experiments with magnesium-lime were more strictly quantitative. The method of testing the gas before and after treatment with the reagent was to take 1/2000th part of the whole mixed with air, and after introducing it into the reservoir of an electroscope to measure the rate of discharge. The magnesium-lime tube glowed brightly when the mixture of emanation and air was admitted, and it was maintained at a red heat for three hours. The gas was then washed out with a little hydrogen, diluted with air and tested as before. It was found that the discharging power of the gas had been quite unaltered by this treatment.
The emanation can be dealt with as a gas; it can be extracted by aid of a Töpler pump; it can be condensed in a U-tube surrounded by liquid air; and when condensed it can be "washed" with another gas which can be pumped off completely, and which then possesses no luminosity and practically no discharging power. The passage of the emanation from place to place through glass tubes can be followed by the eye in a darkened room. On opening a stopcock between a tube containing the emanation and the pump, the slow flow through the capillary tube can be noticed; the rapid passage along the wider tubes; the delay caused by the plug of phosphorus pentoxide, and the sudden diffusion into the reservoir of the pump. When compressed, the luminosity increased, and when the small bubble was expelled through the capillary it was exceedingly luminous. The peculiarities of the excited activity left behind on the glass by the emanation could also be well observed. When the emanation had been left a short time in contact with the glass, the excited activity lasts only for a short time; but after the emanation has been stored a long time the excited activity decays more slowly.
The emanation causes chemical change in a similar manner to the salts of radium themselves. The emanation pumped off from 50 milligrams of radium bromide after dissolving in water, when stored with oxygen in a small glass tube over mercury turns the glass distinctly violet in a single night; if moist the mercury becomes covered with a film of the red oxide, but if dry it appears to remain unattacked. A mixture of the emanation with oxygen produces carbon dioxide when passed through a lubricated stopcock.
The experiment was carefully repeated in apparatus constructed of previously unused glass with 30 milligrams of radium bromide, probably four or five months old, kindly lent us by Professor Rutherford. The gases evolved were passed through a cooled U-tube on their way to the vacuum-tube, which completely prevented the passage of carbon dioxide and the emanation. The spectrum of helium was obtained and practically all the lines were seen, including those at 6677, 5876, 5016, 4932, 4713, and 4472. There were also present three lines of approximate wave-lengths 6180, 5695, 5455, that have not yet been identified.
On two subsequent occasions the gases evolved from both solutions of radium bromide were mixed, after four days' accumulation which amounted to about 2.5 c.c. in each case, and were examined in a similar way. The D3 line of helium could not be detected. It may be well to state the composition found for the gases continuously generated by a solution of radium, for it seemed likely that the large excess of hydrogen over the composition required to form water, shown in the analysis given by Bodländer might be due to the greater solubility of the oxygen. In our analyses the gases were extracted with the pump, and the first gave 28.6, the second 29.2 per cent. of oxygen. The slight excess of hydrogen is doubtless due to the action of the oxygen on the grease of the stop-cocks, which has been already mentioned. The rate of production of these gases is about 0.5 c.c. per day for 50 milligrams of radium bromide, which is over twice as great as that found by Bodländer.
We wish to express our indebtedness to the Research Fund of the Chemical Society for a part of the radium used in this investigation.
Ibid.., 1903, p. 457.
Cf. Giesel, 'Ber.,' 1903, 347.
'Ber.' (loc. cit.). | <urn:uuid:4a8366d3-c331-4a8e-b8cd-703270892f34> | 3.03125 | 1,177 | Academic Writing | Science & Tech. | 46.605484 |
How Do Fossils Form?
A fossil is remains or evidence of previous life preserved in the earth's surface. You have probably seen fossils at one time or another. It may have been a fossil of an ancient fern leaf or perhaps some prehistoric creature. It is exciting to look at something that lived millions of years ago. Though scientists have found many, many fossils, they are not all that common. It takes very special conditions for fossils to form. Here's how you can make a modern day fossil.
What Do I Need?
- Plaster of Paris
- Sea shells
- Petroleum Jelly
How Do I Make the Fossil?
Fossils form a number of ways. We will simulate a type of fossil that forms in mud.
Mix a small amount of water with a handful of plaster of paris, the plaster should be smooth and thick.
Spread the plaster of paris onto the cardboard, making it about an inch thick, and just slightly larger than a leaf.
Coat the leaf with petroleum jelly and place it onto the plaster. Press gently down on the leaf to push it into the plaster.
Allow the plaster to dry in a warm place.
Remove the leaf when the plaster is dry and you have a type of fossil! You can try the same thing using sea shells or even models of animals.
How is This Like real Fossils? How else can Fossils form? | <urn:uuid:5cc831db-8aa1-4ba1-bc7f-7d74368311bf> | 3.90625 | 291 | Tutorial | Science & Tech. | 72.341751 |
Asteroid Fire Drill
“This thing missed, but chances are, at this size, we will one day find an object headed for an impact,” says Binzel, a professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “Depending on where it’s falling, you might need to know whether it’s going to survive passage through the atmosphere, and how many fragments [will make impact]. We’d like to have the capability to deliver those kinds of answers, if we need to.”
Binzel is part of an international team of astronomers who monitor the skies for approaching asteroids. The scientists receive data from the Minor Planet Center (MPC), a clearinghouse for asteroid discoveries at the Smithsonian Astrophysical Observatory. Researchers at the MPC collect observational data from telescopes and satellites around the world, then calculate the orbits of asteroids and comets. Each day, the MPC sends out circulars to astronomers around the world, highlighting new objects discovered in space.
When an object’s orbit appears poised to bring it close to Earth, scientists like Binzel take particular notice. Binzel’s research group routinely reserves time at NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea in Hawaii, operating the telescope remotely from MIT to observe objects of interest. When Binzel receives an MPC circular, he scans the data for objects that may come close to Earth, and that are observable using the NASA scope.
In the case of KT42, the incoming asteroid fit both categories, but the scientists had to act fast: The asteroid was moving at high speed, and would streak past Earth within 24 hours, a small window for scientists to request observing time on the IRTF. Typically, researchers reserve telescope time months in advance, to observe distant planets and stars. In the event of an incoming asteroid, scientists may put in a last-minute proposal to interrupt a previously scheduled project, though these requests are not always guaranteed.
Tracking an asteroid
“I have the capability of doing it from my attic,” Binzel says. “Once everything was set, I just waited until after midnight, then went upstairs.”
At the appointed time, Binzel fired up an array of computer screens, showing Skype sessions with the telescope’s operator, along with a support astronomer and technician in Hilo, Hawaii. Two more screens displayed images from the telescope’s camera, tracking the asteroid in real time, as well as light-intensity data. Over three hours, the researchers took measurements and tracked the asteroid’s incoming path.
“These readiness drills are important, because there’s a process to go through, and we want to make sure it works,” Binzel says. “In the event that we really need to work on short order, we’ll have confidence that we’ll be successful.”
In this case, the team quickly analyzed the data and calculated that the asteroid was about 23 feet wide, and likely made from a crumbly carbon material — a combination unlikely to penetrate Earth’s atmosphere intact. Binzel says in order for an asteroid to make impact, it would have to be much larger, and made from a hardier material, such as silica or iron. He speculates that an object 30 to 60 feet wide might make it through the atmosphere, breaking up into small meteorites before hitting the ground, while an asteroid 150 to 200 feet wide might hit the surface completely intact.
For the most part, these chunks of rock stay within the asteroid belt. But every so often, asteroids escape and travel as far as Earth’s orbit. For 100 years, why this happens remained a mystery.
In the 1980s, Jack Wisdom, a professor of planetary science at MIT, came up with a solution: He discovered that Jupiter’s gravitational field occasionally forces an asteroid out of its orbit, tugging at the asteroid repeatedly and stretching its orbit until, like an overstretched rubber band, the orbit snaps, flinging the asteroid into space.
“Once in a while, Jupiter will nudge things out and send them our way, for better or worse,” Binzel says. “The dinosaurs probably wish it hadn’t.”
Binzel is now looking for ways to improve the asteroid rapid-response program. The May 29 incident, he says, demonstrated a new level of readiness: Scientists were able to quickly gain access to the telescope facility, and the asteroid was the fastest object ever tracked by the telescope. The astronomers were also able to characterize the asteroid’s size and composition in a limited amount of time — observations that would be essential in the event of an actual impact.
In the future, Binzel hopes to improve the telescope’s tracking ability, to observe even faster-approaching objects. The speed of KT42, he says, was at the upper limit of what the telescope could reliably track.
“This one was so close and so fast, it demonstrated a new level of capability of the telescope,” Binzel says. “Now we’re finding ways to improve for the next one.” | <urn:uuid:5a1d7b38-1d40-4cfe-84d2-1e45c19f95a0> | 3.625 | 1,087 | Knowledge Article | Science & Tech. | 40.344348 |
High Power and High Bandwidth in the Oceans
The concept of a regional cabled ocean observatory--a system that would provide continuous high power and interactive real-time high-bandwidth data transfer to and from shore--began to be seriously explored by scientists at the University of Washington in the mid 1990s.
This vision carried with it solutions to some of oceanography’s most difficult challenges: how to study natural phenomena on time scales that range from seconds to decades and on spatial scales from microns to kilometers. The vision provided novel alternatives to science investigations based on limited and uncertain life spans of battery-powered instruments and on the vagaries of northeast Pacific storms that restrict ship-based expeditions to field seasons of only a few months each year.
Exciting exchanges between scientists and engineers led to a plan for a network of distributed sensors in the oceans attached to submarine fiber-optic/power cables connected to land. The fiber would provide continous power to interactive networked instrument arrays that would capture data and immediately send it to shore and onto the Internet. Such a system could encircle an entire tectonic plate and the ocean above it.
In 1998, the National Oceanographic Partnership Program (NOPP) funded the University of Washington to take the lead on a feasibility study for the program that became known as NEPTUNE—Northeast Pacific Time-Series Undersea Networked Experiments. The feasibility study design featured a cable encircling and crossing the Juan de Fuca tectonic plate, which lies off the coasts of Oregon, Washington, and British Columbia. The system would continuously collect an unprecedented diversity of coregistered information in space and time, and would respond to events—the passage of blue whales, an undersea landslide, an increase in the carbon dioxide or ocean acidity, an earthquake in the ocean crust. Thirty study sites were planned. Canada expressed interest in building the infrastructure on the northern third of the plate and also undertook a feasibility study.
In 2000, NEPTUNE feasibility studies for the U.S. and Canada were published and a multi-institutional, international partnership of institutions was established. Led by the University of Washington, members of the NEPTUNE Partnership included Woods Hole Oceanographic Institution, Canada’s Institute for Pacific Ocean Science and Technology, the University of Victoria, the Monterey Bay Aquarium Research Institute, and Caltech's Jet Propulsion Laboratory.
With a combination of U.S. and Canadian Federal, State and Provincial, and private funding, the NEPTUNE Partnership undertook development of a power system, a communications system, a proto-NEPTUNE observatory, and two shallow-water observatories—MARS in Monterey Bay, California, and VENUS off Vancouver Island, British Columbia.
The Ocean Observatories Initiative
The U.S. NEPTUNE cabled observatory effort was made part of the National Science Foundation’s Ocean Observatories Initiative (OOI), which was approved as an NSF Major Research Equipment and Facilities Construction project by the National Science Board in October 2000. NEPTUNE was eventually renamed the Regional Cabled Observatory, subsequently known as the Regional Scale Nodes within the OOI. Canada began development and construction of NEPTUNE Canada on the northern portion of the plate. Numerous science workshops in both countries garnered input from ocean science and education communities for planning experiments.
In 2005, over 175 scientists across the US responded to a Request for Assistance from the National Science Foundation to develop a cabled observatory on the Juan de Fuca Plate. From this, and with additional input from the science community, a network of focused experimental sites was developed that stretched around and across the Juan de Fuca Plate and throughout the water column covering nearshore and deep, blue-water environments 300 miles off the coast.
The NEPTUNE Canada observatory has been installed and is in operation.
The U.S. regional cabled network, or Regional Scale Nodes, component of the Ocean Observatories Initiative funded by the National Science Foundation, will be launched as two main cable segments. One segment extends approximately 300 miles from a shore station in Pacific City, Oregon westward out to the Juan de Fuca Ridge to Axial Volcano--the most robust volcano on the ridge and a site of intense hydrothermal activity. A second cable extends south and east to a major gas hydrate deposit at Hydrate Ridge and to shallow coastal sites. Each site will be densely populated with sensors and there will be four full water-column moorings on the network. The system is scheduled to be operational and commissioned in 2014.
The system is designed to be expandable over its 25-30 years of planned operation, pending availability of funds and Congressional approval. The vision remains to create an observatory that, when complemented by NEPTUNE Canada, will encompass an entire tectonic plate and all the natural phenomena that occur there, whether below the seafloor, on the seafloor, in the ocean, or at the air-sea interface. | <urn:uuid:ed2b184c-eeed-41c7-bc63-f902ca5832ab> | 3.40625 | 1,042 | Knowledge Article | Science & Tech. | 20.821958 |
Magallania (Punta Arenas)
On-line version ISSN 0718-2244
Earthquakes in Magallanes, southern Chile, are associated to the relative motions (smaller than 2 cm./y) of three plates: South-American, Antarctic and Scotia. Thus, the seismicity is low as compared with northern Chile where the Nazca and South-American plates converge at a rate of about 10 cm./y. In Magallanes however, two main historical earthquakes (ML = 7.5) occurred in 1879 and 1949. Recent seismicity, registered in 1997 and 1998, of magnitude smaller than 4.3 is located within the continental crust. Some very shallow earthquakes concentrate around two active volcanoes: Reclus and Burney. Short descriptions of the 2007 seismic cluster in Aysén and the 2008 eruption of the Chaitén volcano are also included.
Keywords : Magallanes; Tectonic plates; Seismicity; Volcanoes. | <urn:uuid:5e2bd80e-7087-4c8b-be5e-1eab7fa17bc9> | 3.265625 | 203 | Knowledge Article | Science & Tech. | 46.212922 |
Propulsion in space is an extremely tricky affair, one that’s centred heavily on trade-offs. The engines we use to get into space are woefully inefficient due to the large amount of propellent that has to be taken along with them. The faster/further you want to go the more propellent you need which makes the rockets increasingly bigger, putting a soft upper limit on what makes for a feasible craft. On the flip side once you’re in space we have engines with efficiencies that are so good that they can achieve incredible speeds with fractions of a percent of the fuel that it takes to get them into orbit. It’s no wonder that these engines were chosen for the Dawn mission to Vesta and Ceres.
There’s also engines that straddle the boundaries of these two like the VASIMR which aren’t capable of getting payloads off the surface of the earth but are quite capable of performing the same tasks as chemical rockets in space with a fraction of the required reaction mass (fuel). The trade off here is that it requires a rather large power source for it to be effective, on the order of hundreds of kilowatts, which means that in order for it to fly you need an ultra dense power source, usually in the form of a nuclear reactor. They’ve also never been flown on an operational mission yet (they have been thoroughly tested and verified however) but we will likely see one aboard the International Space Station within the next 3 years or so.
Barring some technological breakthrough I was pretty sure these engines were going to be the ones powering most of our craft for the next couple decades or so as we’ve got most of the bases covered. However it turns out that there might be a way to improve on the high efficiency/low thrust idea by doing away with the reaction mass completely. Sounds impossible right? I mean what engine can run without any fuel to drive it? As it turns out there’s quite a lot of energy to be derived from the vacuum of space and NASA are investigating how to tap into it:
The lab will first implement a low-thrust torsion pendulum (<1 uN), and commission the facility with an existing Quantum Vacuum Plasma Thruster. To date, the QVPT line of research has produced data suggesting very high specific impulse coupled with high specific force. If the physics and engineering models can be explored and understood in the lab to allow scaling to power levels pertinent for human spaceflight, 400kW SEP human missions to Mars may become a possibility, and at power levels of 2MW, 1-year transit to Neptune may also be possible
Essentially the way a QVPT works is by harnessing the random fluctuating magnetic fields that are present throughout the vacuum of space and using them to propel the craft. This works by polarizing a block magnetoelectric material leading to a force in one direction on the block whilst the field, or more accurately the bosons they’re made up of, are pushed in the other. Technically QVPTs are drives that uses photons as its reaction mass but it doesn’t have to bring them along which is a pretty big distinction between them and ion thrusters.
Much like VASIMR and ion thrusters QVPTs main limitation is the size of the power source that they can bring with them. However unlike their predecessors QVPTs have a far greater upper limit on how long they can run (referred to as specific impulse). These means for long distance missions like those to Mars and beyond there’s great potential to cut much of the transit time off by utilizing a QVPT. To put it into perspective the fastest craft ever launched, New Horizons, will take approximately 9 years to reach Pluto at its current speed. A QVPT powered craft is theoretically capable of getting there in just on a year, almost an order of magnitude faster. Of course this will rely on the effect being experimentally verified but since NASA has dedicated an entire team, dubbed EagleWorks, to verifying the idea I’d say that there’s at least some credence to it.
It’s quite exciting as new ideas like this don’t come along very often and it’s not common for NASA to simply dedicate significant resources to them in order to see if they pan out. This is what they’re good at though and it makes me incredibly happy to see NASA engaging in some good old fashioned envelope pushing. It might be a while before this bears fruit but the potential for unlocking our solar system is just too good to pass up. | <urn:uuid:c9da04bc-c309-4c8b-b7c8-7f95568f5913> | 3.265625 | 954 | Personal Blog | Science & Tech. | 42.359231 |
We are all familiar with Trees, and we assume that pointers are an required evil needed for encoding the structure of a tree. Anyway, why do you need to spend 64bit pointers, when you can represent the structure with just few bits? Those ideas are not just theory, they are used in real implementation of Large Scale Tree data Structures that needs to fit in memory.
Let's start from this example taken from the paper Representing Trees of Higher Degree (E. Demain is one of the authors and his studies about Khipu are fascinating, but this is another story...)
An ordinal tree T can be represented as a bit array. The degree of each tree (number of sons) is encoded with a sequence of 1 terminated by a 0. All the nodes are represented with a level degree visit of T (commas are used just for helping the reader but we don't need to represent them). This representation is known as Level Ordered Unary Degree Sequence (LOUDS). Using auxiliary data structures for Rank and Select operations, LOUDS supports in constant time, finding the parent, the ith child, and the degree of a node.
- The number of 0 in the binary array is the number of node in the three.
- Each node is son of another node and therefore has a 1 representing it (we need to find which 1 is the correct one)
- As a consequence, we need at least a space of 2n, plus something for navigation
Now, we need to introduce two operations which can be computed in constant time with additional 0(n) space (see the paper).
- Rank1(j) returns the # of 1 up and including position j. Rank0(j) is a similar operation for 0
- Select1(j) returns the position of of the j-th 1. Select0(j) is a similar operation for 0
- Compute the degree of a node in position p. This is the number of 1 up to the next 0 and can be computed as Select0(rank0(p)+1) - p
- Compute the parent of a three as in Select1(rank0(p)+1)
- Compute the ith children of a tree;
Another magic representation is based on balanced parenthesis and it is due to Munro and Raman. Suppose you visit the three depth first and open a parenthesis on the way down, and close the parenthesis on the way up. The ordinal tree is encoded again ad a bitvector but now we have the additional benefit that the nodes of a subtree are very close in the bitvector. This is a consequence of the depth first visit. It is possible to navigate the three with Rank & Select operations.
Benoit, Demain, Munro, Raman proposed a variant of LOUDS based on depth first named Depth First Unary Degree Sequence (DFUDS), which preserves locality and still allows tree navigation in terms of Rank & Select. In addition, they proposed further optimization for finding the ith children of a node, if the tree is a trie with k outdegree.
More information about this fascinating word is available in Succinct Trees in Practice, 2010 | <urn:uuid:cb368b56-a2c2-411b-98d9-26d4c80d8137> | 3.421875 | 664 | Personal Blog | Software Dev. | 54.83343 |
According to a British study, wind farms do not pose a serious risk for open-country passerines.
"The message on farmland specifically is that, so far, the evidence we have gathered shows that there is little effect on farmland birds," explained co-author Mark Whittingham, from Newcastle University's School of Biology.Unfortunately this study does not address the potential risks for raptors and possibly waterfowl. It also found some changes in the distribution of pheasants, suggesting that related species may also be affected. Another limitation is that the surveys were conducted during the winter months. Breeding surveys may show a different picture.
The team carried out surveys around two wind farms located in the East Anglian fens, recording almost 3,000 birds from 23 different species.
Their data showed that the presence of the turbines did not affect the distribution of seed-eating birds, corvids or skylarks.
"This is the first evidence suggesting that the present and future location of large numbers of wind turbines on European farmland is unlikely to have detrimental effects on farmland birds," said Dr Whittingham.
That said, surveys like this are still helpful since they help narrow down the list of species we need to worry about, especially if the result holds at other times of year.
For more about wind power in a different environment, see Nick's discussion and excerpts from the DEIS for the Cape Wind project between Cape Cod and Nantucket. | <urn:uuid:40ad23e3-5e37-402e-8808-258aafe4c0da> | 3.265625 | 298 | Personal Blog | Science & Tech. | 41.725074 |
1 When moist, warm air rises to a cooler elevation, water condenses onto microscopic “seeds” like dust, ash, or bacteria. Water + seeds + updraft = clouds.
2 If there’s more water vapor than places for it to condense, already-formed ice crystals can also serve as seeds. As the crystals take on moisture, they may become too heavy for updrafts to support. Time for the umbrella.
3 It makes sense, then, that adding seeds to thin clouds should make them rain out. Believing the theory, 37,000 Chinese peasants shot rockets filled with silver iodide (a widely used seeding agent) into clouds.
4 So much for People Power. After reviewing 40 years of cloud-seeding efforts in an area north of Israel, researchers at Tel Aviv University have concluded that seeding doesn’t actually produce additional precipitation (pdf).
5 Super-seeding: A team led by Stephen Salter of the University of Edinburgh has proposed using 1,500 oceangoing ships to spray saltwater into stratocumulus clouds in order to increase our planet’s cloud cover.
6 They want to accomplish goals set out in 1990 by John Latham of the National Center for Atmospheric Research. He suggested that saturating the air with salt crystal seeds would create a haze of water droplets so small that they would never rain out. The intended result: A permanent, low-hanging cloud cover that would deflect sunlight and, in theory, reverse global warming.
7 But excess cloud cover might actually warm the planet by trapping heat.
8 In fact, a 2009 Stanford University study claims that clouds created by aircraft emissions triggered an overall rise in surface temperatures of 0.03 to 0.06 degree Celsius worldwide. That would account for 4 to 8 percent of the warming that has occurred since record keeping began in 1850.
9 Nacreous clouds, or “mother of pearl” clouds, appear iridescent because of their ultrafine ice crystals, which form 10 to 15 miles up in the stratosphere.
10 Unfortunately, nacreous clouds also support chemical reactions that convert benign chlorine-containing molecules into a form that destroys Earth’s ozone layer.
11 Roll clouds form when updrafts and downdrafts churn clouds into a long, spinning cylinder. They look spectacular, but they often herald an approaching storm front.
12 Highest of them all: 50 miles up, noctilucent, or “night shining,” clouds glow an eerie bluish white. They are invisible by day, but after sunset they catch solar rays shining from far below the horizon.
13 Noctilucent clouds seemed to first appear after the 1883 eruption of Krakatoa and are now a common sight.
14 A June 2010 hailstorm in South Dakota dropped the largest hailstone in U.S. history. It was nearly as large as a soccer ball and weighed two pounds.
15 Bad weather likes workdays. An Israeli-American team correlated 15 years of pollution records with the National Weather Service Storm Prediction Center’s records on storms. They found that hailstorms over the eastern United States peak in the middle of the week, when summertime air pollution is at its worst.
16 Cumulonimbus clouds are the ones that make your flight late. Their winds are so intense and unpredictable that pilots never go through them.
17 Not “through” but sometimes over.
18 In 1959 Lt. Col. William Rankin was flying his F-8 fighter jet over a cumulonimbus when the engine failed. He parachuted out and spent the next 30 minutes bounced around inside the storm. Amazingly, he survived.
19 In 2007 German paragliding champion Ewa Wisnierska experienced “cloud suck.” While gliding under a cumulonimbus, she was pulled upward to 32,000 feet. She blacked out due to lack of oxygen but regained consciousness at roughly 23,000 feet.
20 Referring to the dark clouds on the horizon, Wisnierska said, “Usually there is no problem.”
Rebecca Coffey's blog, The Excuses I'm Going With, is at rebeccacoffey.blogspot.com | <urn:uuid:c0510dd7-c38d-45d6-95a0-b4f6af66a2fc> | 3.734375 | 894 | Listicle | Science & Tech. | 60.256301 |
Complex number, polynomials, matrix, system of equation, Gaussian elimination, vector space, linear transformation, etc. T.M. Aposotol's Calculus Vol. 1 in the calculus sections also introduce topics that is relevant to this area.
A few Americans (exchanged to Sydney) in my third year abstract algebra class told us they couldn't follow because they haven't learnt much complex number. In order to have fun with linear algebra and complex variables in stage 2, it's better to learn complex number now.
- Anton H. and Rorres C. Elementary Linear Algebra - The application version introduced how linear algebra can be applied to Markov Chains, Graph Theory, Games of Strategy, Computer Graphics, Fractals, Chaos, Cryptography, Genetics, etc.
- Axler S. Linear Algebra Done Right - See Axler's page for this.
- Chen W.W.L. Linear Algebra (FREE!) - Read Chapter n's, for all positive integer n<8.
- Chen W.W.L. Miscellaneous Topics in First Year Mathematics (FREE!)
- Dawkins P. Algebra (FREE!)
- Gardner R.B. Linear Algebra (FREE!) - Leave Chapter 6 and 7 to the next stage.
- Joyce D.E. A Short Course on Complex Numbers (FREE!)
- Lang S. Undergraduate Algebra - He's a member of the Bourbaki and wrote many books. Not friendly for beginners, but you should get use to it.
- Lay D.C. Linear Algebra and Its Applications
- Matthews K. Elementary Linear Algebra (FREE!)
- Santos D. Linear Algebra Notes [.pdf] (FREE!)
- Strang G. Linear Algebra and Its Applications
- Wedderburn J.H.M. Lectures on Matrices (FREE!)
- 山东大学数学学院：秦静教授线性代数课件 [.rar] (FREE!) | <urn:uuid:4883e424-8210-47e9-a5a1-b4d4a3e568f8> | 2.890625 | 442 | Personal Blog | Science & Tech. | 69.964269 |
The sunset pictured here may look strange to you and me, but on Mars it's a rather common sight. A bluish hue radiates outward from the setting Sun, fading gradually before taking on a pinkish tinge.
Strangely enough, that's more or less the exact opposite of what you'd expect to see during sunsets here on Earth, which tend to fade from warm, ruddy colors into the bluish purples typical of a late afternoon sky. So why, exactly, are Martian sunsets blue? For that matter, why are they basically inverted versions of what we find here on Earth?
Over on NPR, Ezra Block and Robert Krulwich explain that the answer boils down to airborne dust — more specifically the size of that dust, and the wavelengths of light those dust particles let through.
Martian dust is smaller and more plentiful than the particles you find floating around here on Earth, and it happens to be just the right size that it absorbs blue wavelengths while scattering red ones across the sky. These red wavelengths are what give much of the Martian firmament that pinkish hue. Look directly toward the setting sun, however, and you'll see blue. That's because the beams of light coming from this direction have lost their red waves entirely (they've been filtered out, and scattered by the dust, remember?), so the only wavelengths of light that make it through are those that give the light its blue appearance.
On Earth, our larger atmospheric particles scatter blue wavelenghts instead of red, so the opposite effect is observed. What's interesting is that astronomers think they can use spectral properties like these to gather important details about planets throughout our galaxy — details that could even one day lead us to other habitable planets. [NPR | Nano Patents and Innovations] | <urn:uuid:cb48ff1c-2811-49b6-9b0f-4642b568ecc7> | 4.09375 | 364 | Truncated | Science & Tech. | 49.15789 |
Near Earth Asteroid Rendezvous - Shoemaker
Launch Date: February 17, 1996
Mission Project Home Page - http://near.jhuapl.edu/
The Near Earth Asteroid Rendezvous - Shoemaker (NEAR Shoemaker), named in honor of planetary scientist Gene Shoemaker, was designed to study the near Earth asteroid 433 Eros, one of the largest of the near Earth asteroids, from close orbit over a period of one year. The mission was the first-ever to orbit an asteroid and the first to touch down on the surface of an asteroid. The primary scientific objectives of NEAR were to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution and magnetic field of Eros. Secondary objectives include studies of regolith properties, interactions with the solar wind, possible current activity as indicated by dust or gas, and the asteroid spin state.
The location of NEAR Shoemaker's planned landing site on Eros is shown in this image mosaic taken on December 3, 2000, from an orbital altitude of 200 kilometers (124 miles). In this view, south is to the top and the terminator (the imaginary line dividing day from night) lies near the equator. The landing site (at the tip of the arrow) is near the boundary of two distinctly different provinces, both of which the spacecraft will photograph as it descends.
Image Credit: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland
The spacecraft was equipped with an X-ray/gamma ray spectrometer, a near infrared imaging spectrometer, a multi-spectral camera fitted with a CCD imaging detector, a laser rangefinder, and a magnetometer. A radio science experiment was also performed using the NEAR tracking system to estimate the gravity field of the asteroid and determine its mass and density.
The NEAR mission sought to answer fundamental questions about the nature and origin of the many asteroids and comets close to Earth's orbit. These "near Earth" objects may contain clues about the formation of Earth, and other planets. Eros' pristine surface offers a look at conditions in space when Earth formed more than 4.5 billion years ago.
NEAR Shoemaker collected data completing the most detailed scientific profile ever of a small celestial body. NEAR's portrait of Eros - a solid, undifferentiated, primitive relic from the solar system's formation - has already answered fundamental questions on a common class of asteroid. NEAR's 160,000 images of Eros have shown that asteroids can be incredibly diverse objects: NEAR scientists spotted more than 100,000 craters, about 1 million house-sized (or bigger) boulders, and a layer of debris resulting from a long history of impacts. Scientists were able to determine that Eros is not a “rubble pile” of loosely bound pieces, but rather a consolidated object. Furthermore, the chemical information gleaned from the mission is helping us to understand how asteroids like Eros are linked to meteorite samples recovered on Earth.
This image was taken from a range of just 250 meters (820 feet) during NEAR-Shoemaker’s decent to the surface. The image is 12 meters (39 feet) across.
NEAR launched on February 17, 1996 and entered into orbit around Eros on February 14, 2000. As its mission neared completion, a decision was made to attempt to land on the asteroid, something the spacecraft had not been designed to do. As it descended, NEAR Shoemaker snapped dozens of detailed pictures during the final three miles (five kilometers), the highest resolution images ever obtained of an asteroid. The camera delivered clear pictures from as close as 394 feet (120 meters) showing features as small as a golf ball. The spacecraft touched down at a gentle 4 mph, just outside the asteroid's large saddle-shaped depression, Himeros. Despite being an orbiter that was not designed to land, NEAR Shoemaker continued operating and communicating. The craft's gamma-ray spectrometer operated for two weeks after the landing, gathering unprecedented data on the elemental composition on and just below the asteroid's surface. NEAR Shoemaker made its last call to Earth on Feb. 28, 2001. | <urn:uuid:37c964e8-9815-4121-9e74-02639aaf53a1> | 3.421875 | 861 | Knowledge Article | Science & Tech. | 37.673267 |
Artificial coral growth speeds up post-El Nino recovery
June 16, 2009
In 1998, El
Nino brought excessive and prolonged heat to the Maldives, bleaching and killing
90 per cent of the nation’s corals, and in some atolls, damaging up to 98 per
cent of reefs. The stress of that year’s oscillation left the normally
tropical-coloured marine organisms in a pallid white state, and some scientists
are trying to speed up the recovery process through cutting-edge techniques of
coral propagation, also known as artificial reef growth.
Read the full
.Artificial Reef Program Web
Beach Artificial Reef Assn., Inc.
Dr. Ron Childs, PresidentEmail: | <urn:uuid:a769c28d-9bfc-465e-b423-24c2a3525f5d> | 2.71875 | 157 | Truncated | Science & Tech. | 54.022201 |
Astronaut photograph ISS008-E-5983 was taken November 14, 2003, with a Kodak DCS760 digital camera equipped with an 80 mm lens and provided by the Earth Observations Laboratory, Johnson Space Center. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.
Rio de la Plata is the muddy estuary of the Paraná and Uruguay Rivers, and forms part of the border between Argentina and Uruguay. The rich estuary supports both capital cities of Buenos Aires and Montevideo.
The Paraná is South America’s second longest river, and drains much of the southeastern part of the continent. The extensive delta of the Paraná nearly reaches across the mouth of the Uruguay River. The rivers’ fertile soils support extensive agriculture, including livestock, in the region surrounding the cities.
This image provides a snapshot of the complicated mixing in the Rio de la Plata between the fresh river waters and the water of the South Atlantic. The thick sediment plume of the Paraná and Uruguay Rivers serves as a marker for the fresher water masses. It can be traced far out into the South Atlantic Ocean. The nutrients in the fresh water plume often feed large plankton blooms offshore.
This image originally appeared on the Earth Observatory. Click here to view the full, original record. | <urn:uuid:1afe7373-2fa0-4b19-835e-f5545594354d> | 3.75 | 321 | Knowledge Article | Science & Tech. | 40.585769 |
The United States Wave Height image shows the expected wave height for coastal areas for the current day. Ocean surface waves are surface waves that occur in the upper layer of the ocean. They usually result from wind or geologic effects and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis. There is little actual forward motion of individual water particles in a wave, despite the large amount of energy and momentum it may carry forward.
The great majority of large breakers one sees on an ocean beach result from distant winds. Three factors influence the formation of "wind waves":
- wind speed
- distance of open water that the wind has blown over; called fetch, and
- time duration the wind has blown over a given area.
All of these factors work together to determine the size and shape of ocean waves. The greater each of the variables, the larger the waves. Waves are characterized by:
- Height (from trough to crest),
- Wavelength (from crest to crest),
- Period (time interval between arrival of consecutive crests at a stationary point),
- Wave propagation direction (with respect to north).
Waves in a given area typically have a range of heights. For weather reporting and for scientific analysis of wind wave statistics, their characteristic height over a period of time is usually expressed as significant wave height. This figure represents the average height of the highest one-third of the waves in a given time period (usually chosen somewhere in the range from 20 minutes till twelve hours), or in a specific wave or storm system. Given the variability of wave height, the largest individual waves are likely to be about twice the reported significant wave height for a particular day or storm. | <urn:uuid:a66bd7da-553c-4d12-abb5-e8c156a03211> | 4.5 | 353 | Knowledge Article | Science & Tech. | 37.755975 |
A library is more or less a set of tools meant to help you make games quicker. For example
- reading XML files
- getting access to OpenGL (LWJGL, JOGL)
- handling game objects
- handling game menus and UI
- a full game engine
With a game engine you don't have to code so much since the engine handles most of it. You pretty much only have to code things like game logic. The real work is filling the engine with content (images, menus, textures, 3D models, game logic, game content (items, skills, etc)). A game engine often comes with things like level editors and other editors for creating resources usable by the engine. Usually, the easier an engine is to use the more limitations there are. For example, a 2D game engine can't handle 3D graphics but is obviously simpler to use. Sometimes an engine allows you to work outside it or extend it, for example like how it's possible to do normal OpenGL calls while using Slick2D to do any kind of rendering (3D or 2D) you want.
Making your own complete game engine is a pretty bad idea in my opinion. It's a lot more work than most people think, especially the surrounding tools and deciding which features to implement, and in the end you might realize that it's not exactly what you wanted. You'll also not end up with a complete game, just an engine so the "reward" for your work is pretty much just the ability to make a game (hopefully) quicker than before. The chance that someone else is going to base their game on your engine is also pretty much 0 since not many people are willing to bet on a new unproven game engine.
I'd instead encourage you to write much smaller "libraries" for personal use. In other words write reusable code. I have a voxel renderer which I could easily use/modify to render a Minecraft world file (if I knew how to read a Minecraft save file that is
). I have a threading library I can use to multithread my games. I have a few classes abstracting things like OpenGL textures, tiled images, shaders, 3D cameras, etc. I have a frustum culler that can be used to check if objects actually will end up on the screen. I have a few pathfinding algorithms implemented, a fog-of-war renderer and some GUI stuff using TWL.
Many things can be shared between games that seem to be very different. A 2D strategy game needs pathfinding for the units, but so does a 3D first person shooter for AI controlled players. The same pathfinding "library" can be used in them if they're written correctly or with just slight modifications. Building up a bag of tools will help you make games quicker, but of course don't just make tools all day.
Make them as you make games. Again, just write reusable code. | <urn:uuid:e4f452ef-d244-4807-95e5-f8db2dd32336> | 2.703125 | 612 | Comment Section | Software Dev. | 54.055928 |
|Oracle8i Application Developer's Guide - XML
Release 3 (8.1.7)
Part Number A86030-01
An XML Primer, 8 of 9
Why Use XML?
XML, the internet standard for information exchange is useful for the following reasons:
- Solves Data Interchange Problems. It facilitates efficient data communication where the data:
- Is in many different formats and platforms
- It must be sent to different platforms
- Must appear in different formats and presentations
- Must appear on many different end devices
In short, XML solves application data interchange problems. Businesses can now easily communicate with other businesses and workflow components using XML. See Chapters 2 through 20 for more information and examples of how XML solves data interchange problems.
Web-based applications can be built using XML which helps the interoperation of web, database, networking, and middleware. XML provides a structured format for data transmission.
- Industry-Specific Data Objects are Being Designed Using XML. Organizations such as OAG and XML.org are using XML to standardize data objects on a per-industry basis. This will further facilitate business-to-business data interchange.
- Database-Resident Data is Easily Accessed, Converted, and Stored Using XML. Large amounts of business data resides in relational and object-relational tables as the database provides excellent data queriability, scalability and availability. This data can be converted from XML format and stored in object-relational and pure relational database structures or generated from them back to XML for further processing.
Other Advantages of Using XML
Other advantages of using XML include the following:
- You can make your own tags
- Many tools support XML
- XML is an Open standard
- XML parsers built according to the Open standard are interoperable parsers and avoid vendor lock-in. XML specifications are widely industry approved.
- In XML the presentation of data is separate from the data's structure and content. It is simple to customize the data's presentation. See "Presenting XML Using Stylesheets" and "Customizing Your Data Presentation".
- Universality -- XML enables the representation of data in a manner that can be self-describing and thus universally used
- Persistence -- Through the materialization of data as an XML document this data can persist while still allowing programmatic access and manipulation.
- Platform and application independence | <urn:uuid:6c8580d9-de40-4445-8c21-ff72eec68ffc> | 2.953125 | 496 | Documentation | Software Dev. | 28.310039 |
. "5 Impacts in the Next Few Decades and Coming Centuries." Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia. Washington, DC: The National Academies Press, 2011.
The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia
3,130 km2. Without aid from humans these species are probably not going to be able to persist.
Extinction is irreversible. Choices among stabilization targets can be expected to determine the scope of future extinction (e.g., types of species, geographic regions, etc.) that could be caused by climate change, or alternatively the scale of protective adaptation measures such as species management that could be considered to avoid extinctions.
5.8 BIOLOGICAL OCEAN
Impacts of CO2, pH, and Climate Change in the Ocean’s Biology
Marine ecosystems will be affected by climate change via physical changes in ocean properties and circulation (Sections 4.1, 4.4, and 4.7), ocean acidification via altered seawater chemistry from rising atmospheric CO2 (Section 4.9), and sea-level rise via coastal habitat loss. Some of the key potential impacts will involve changes in the magnitude and geographical patterns of ecological and biogeochemical rates and shifts in the ranges of biological species and community structure (Boyd and Doney, 2002). Impacts are expected to include both direct physiological impacts on organisms through, for example, altered temperature, CO2, and nutrient supply, and indirect effects through altered food-web interactions such as changing seasonal timing (phenology) of phytoplankton blooms or disruptions in predatory-prey interactions.
Primary production by upper-ocean phytoplankton forms the base of the marine food-web and drives ocean biogeochemistry through the export flux of organic matter and calcareous and siliceous biominerals from planktonic shells. Plankton growth rates for individual species are temperature dependent and tend to increase under warming up to some threshold. When viewed in aggregate, plankton community production rates approximately follow an exponential curve in nutrient replete conditions, which would suggest increasing global primary productivity over this century as sea surface temperatures increase (Sarmiento et al., 2004). In most regions of the ocean, however, primary production rates are limited by nutrients such as nitrogen, phosphorus, and iron. Diatoms, a key shell-forming group of phytoplankton, are also limited by silicon. The rates of many other biological processes, such as bacterial respiration and zooplankton growth and respiration, also speed-up as temperature rises, the integrated effect at the ecosystem level is difficult to predict from first principles. Warming also occurs in conjunction | <urn:uuid:66e2fff2-ae20-41d2-ba93-b913cfcb3884> | 3.21875 | 623 | Truncated | Science & Tech. | 23.196364 |
Science highlights from Cassini's 10 years in space
NASA's Cassini spacecraft to Saturn, the most complex spacecraft ever sent to another planet, launched 10 years ago today, on 15 October 1997.
It has had a highly successful mission, together with the European Space Agency's Huygens probe, which landed on Saturn's moon Titan on 14 January, 2005, after separating from Cassini.
Since arriving at Saturn on 1 July 2004, Cassini has returned spectacular images of Saturn and its rings, along with views of its moons showing unprecedented detail. Among its most exciting findings to date is the discovery of plumes of water vapour spewing from the south pole of the icy Saturnian moon, Enceladus. The finding raised hopes that there might be liquid water somewhere below the moon's surface, perhaps providing the right conditions for life.
Cassini's radar instrument has cut through the smoggy atmosphere of Saturn's moon, Titan, to reveal what appears to be a plethora of lakes filled with liquid hydrocarbons pooling on the surface of the frigid moon. Huygens also returned a wealth of data on Titan, including views of what may be drainage channels and a shoreline on the moon's surface related to rains of liquid methane.
In honour of the 10-year launch anniversary, the Cassini team has released a video from the spacecraft's September 2007 flyby of Saturn's walnut-shaped moon, Iapetus (click on the image above to watch it). Just as impressive is a video previously made from Cassini data showing a huge hurricane-like storm at Saturn's south pole. It doesn't get any closer to feeling like you're really flying by Saturn and its moons than this.
Cassini's primary mission is set to end in July of 2008, but that is sure to be extended, since the spacecraft is still healthy, allowing many more observations of Saturn and its rings and moons.
All of these results are exciting, but to me the most fascinating results are those on Titan. Its extreme cold and exotic materials like liquid methane make it so different from Earth ? but its lakes, dunes and rains also make it strangely familiar.
The planets and moons of our solar system are a noisy bunch, as we point out in our feature article Sounds in space. It highlights some of the strange creaks and groans, crackles and pops that many scientists would like to record on these worlds by sending spacecraft there equipped with good old-fashioned microphones.
But if you widen the net and include radio emissions converted to sound, astronomers have already recorded all kinds of space cacophonies. Don Gurnett from the University of Iowa has compiled some of his favourites, including the Jovian chorus, radio emissions from electrons zinging around in Jupiter's radiation belts. Sounds like mass panic in the jungle to me.
The European Space Agency also has a space sounds page, where you can "listen" to magnetic field fluctuations on Saturn's icy moon Enceladus (a flying saucer taking off, perhaps?) and the eerie song of wailing Leonids, meteor trails reflecting high-frequency radio waves from transmitters around the world.
My personal favourites are pulsar recordings from Jodrell Bank Observatory. Pulsars are the collapsed cores of stars that blew themselves to smithereens in supernova explosions. The core can collapse into a rotating magnetised ball of neutrons about 15 kilometres wide, which emits radio beams from its poles. If these beams sweep across Earth as the collapsed star rotates, we see regular radio beeps.
The Crab pulsar (pictured) sits in the middle of the beautiful Crab Nebula, the wreckage of a star seen to explode in the year 1054. It rotates 30 times a second. This one is rotating 642 times a second, so fast the beeps have merged seamlessly into a high-pitched whine ? isn't that bizarre?
Hazel Muir, correspondent (Image: Credit: NASA/HST/CXC/ASU/J Hester et al.)
Alan Shepard teed off from the Moon. Mikhail Tyurin took a swing from the International Space Station. Now, Cassini scientists are giving non-astronauts a chance to see what it would be like to golf from Saturn's moons in their Flash game, Golf Sector 6.
The idea is to see how something like a golf ball would behave in the different gravity environments of these moons. I especially like how you can reset the ball if you accidentally hit it into outer space.
My first shot from Hyperion (seen in image) was definitely out of bounds. I adjusted my stroke for the second shot, and it looked like the ball went about two feet (judging by the inaccurate scale of my golfer).
My third shot, I overshot, but at least I landed on the moon. Shot four ? another foot. Shot five ? another half foot, but into a crater. Shot six ? the ball went on the other side of the hole. Shot seven ? another foot. Shot eight ? another six inches. Getting close! Shots nine and ten ? I'm on the crater rim. Can't quite seem to nudge the ball in. Blasted low gravity. 11 ? I'm in and my rocket-pack takes me to hole #2: Saturn's moon Telesto.
By the time I got to spectacular-looking Phoebe, hole #5, I was already 44 over par. But by that point, it seemed I was getting the hang of the game. I think actually bogeyed on Phoebe. But when I'd finished the front nine, I was still a miserable 72 over par. I improved on the back nine, but not by much.
The Saturn LPGA won't be calling any time soon, I suppose.
To my father's chagrin, I am no better at golf in 1g. I'm also lacking in skills in the video game department, with the exceptions of Dig Dug and Ms. Pac Man.
If you play the Saturn golf game, check out the third hole on the front nine, Enceladus. It is spewing water vapour from its south pole.
Kelly Young, Online reporter (Image: NASA/JPL/Space Science Institute) | <urn:uuid:0bb7d3a6-eb7b-4ba9-906d-de6fe3ef42f4> | 3.3125 | 1,296 | Personal Blog | Science & Tech. | 57.981805 |
Classical optics holds that the extinction cross of particles should be equal to twice their geometric cross section, in the limit where the particles are much larger than the wavelength. It follows that the extinction coefficient of such large scatterers should be independent of wavelength. Snowflakes are much larger than the wavelengths of visible and infrared radiation, yet many investigators have found that the visible and infrared extinction coefficient of falling snow measured with transmissometers is wavelength dependent. This dependency is known to be a result of the scattering contribution to the transmissometer signal. Furthermore, many measurements in the visible and infrared show that extinction values measured simultaneously with two transmissometers are linearly related up to at least 12 km-1. The slope depends on the wavelengths and optical characteristics of the transmissometers. We show that for small values of extinction, the observations can be explained by taking into account single-scattering contributions to transmissometer signals. For high values of extinction, a multiplescattering model gives good agreement with measurements.
© 1992 Optical Society of America
D. L. Hutt, L. R. Bissonnette, D. St. Germain, and J. Oman, "Extinction of visible and infrared beams by falling snow," Appl. Opt. 31, 5121-5132 (1992) | <urn:uuid:abd534af-4d97-4b10-9f76-ce426929dc07> | 2.921875 | 265 | Academic Writing | Science & Tech. | 39.52367 |
Nuclear weapons – largest and most devastating
Nuclear weapons are the most powerful weapons ever invented. The devastating effects from nuclear bombs emanate from the forces that keep atomic nuclei together.
There are two main types of nuclear weapons: Fission bombs, where energy is released through splitting of heavy nuclei (uranium or plutonium); and thermonuclear bombs, or hydrogen bombs, where joining (fusion) of the lightest nuclei (hydrogen) contributes to the release of explosive power, even greater that of fission bombs.
How a fission bomb works
In a fission bomb, energy is released when heavy atom nucleic are hit by slow, so called “thermal”, neutrons and split as a result. During fission, vast quantities of energy are released along with additional neutrons, which can split more nuclei and release more energy in a chain reaction, if conditions are right.
The fission process
The fission bomb is designed to release as much energy as possible before the bomb disintegrates, stopping the chain reaction. The longer a chain reaction lasts, the more powerful the explosion will be. In order to start such a reaction, a “critical mass” is required. The critical mass depends on the properties of the fissile material, its density and geometry. For uranium-235 it is around 25 kg and for plutonium-239 some 5 kg. The nuclei of these elements can be split by thermal neutrons, setting off a chain reaction. The splitting process produces a few hundred different radioactive isotopes such as krypton, barium, iodine-131, cesium-137, and strontium-90.
1. A neutron with a suitable energy level (thermal neutron) hits a nucleaus of U235 (a corresponding sequence is valid for Pu239).
2. The uranium atom is split, which results in release of energy and a number of additional thermal neutrons. These, in turn, may either escape from the material or hit a U238 nucleus so that nothing further happens. But if the neutron hits another U235 nucleus, that one will be split and emit additional neutrons.
3. The number of free thermal neutrons will grow exponentially for the duration of the chain reaction, resulting in release of huge amounts of energy and radioactive fission products as fallout.
The bombs over Hiroshima and Nagasaki
The bombs that were dropped on Hiroshima and Nagasaki were of the fission type. The Hiroshima bomb had a blasting power corresponding to 13 kilotons (kt) of TNT, while the Nagasaki bomb was 21 kt. The Hiroshima bomb had a core of U235; the Nagasaki bomb Pu239.
How a thermonuclear bomb works
A hydrogen bomb is detonated in three steps: first a plutonium bomb, then a fusion bomb, and finally a uranium bomb (U238). The plutonium bomb goes off first and ignites a fusion process in hydrogen gas (tritium), setting off a large number of fast neutrons. These, in turn, start a fission in a shielding – tamper – of U238, which encloses the bomb. The primary yield (explosive energy) of a hydrogen bomb is generated by fission of the tamper. The diagram below shows schematically the design of such a bomb.
The explosion will continue over 600 nanoseconds, with the initial fission taking 550 ns. (one nanosecond relates to a second as a second relates to 30 years).
The explosive power of a hydrogen bomb is, in theory, unlimited, which in not the case for a fission bomb. The largest hydrogen bomb that has been tested had a power corresponding to 58 megatons (Mt), which equals about 4 600 Hiroshima bombs. This test was done in 1961 over Novaja Zemlja, in what was then the Soviet Union. A strategic bomb today has a blasting power of some 200 – 500 kilotons, which is frightful, considering the devastating effects caused by the bombs over Japan, which were less powerful by an order of magnitude.
The fusion process
Fusion occurs when two isotopes of hydrogen combine to form a single nucleus of helium, which releases enormous amounts of energy. In order for this to happen, extreme levels of temperature and pressure are required. Fusion naturally occurs in the interior of stars, which is the source of their energy. On Earth, fusion occurs only in hydrogen bombs or in experiments with nuclear physics (e. g. fusion energy research).
In a hydrogen bomb, two isotopes of hydrogen – deuterium and tritium – are joined to form a nucleus of helium and a neutron is emitted. Fusion of the two isotopes releases large quantities of energy and a shower of fast neutrons.
Material for atomic bombs
The common materials for nuclear weapons are uranium (U) and plutonium (Pu). While uranium occurs as a natural element on Earth, plutonium does not exist in natural form and is therefore created synthetically from U238 through neutron irradiation in nuclear reactors. Natural uranium consists mainly of two different isotopes: U235 and U238. Both of these isotopes have a very long half life, 700 and 4500 million years, respectively. The uranium that occurs in nature has a low content of U235 (0.7%). Fuel for nuclear reactors usually contains 3-4% of U235. For weapons grade uranium, the proportion of U235 needs to be over 90%. Therefore the uranium needs to be enriched, a process performed in plants that separate the two uranium isotopes from each other so that U235 can be concentrated.
Plutonium from nuclear reactors used for energy production can be used to build a nuclear bomb. This process is cumbersome, however, due to dangerous radiation from the plutonium and because there is a mixture of other plutonium isotopes than Pu239, which reduces the power of a bomb and makes it unpredictable. In conventional warfare, depleted uranium (i. el, tailings from enrichment) is used for armor-breaking ammunition and also as reinforcement of the armor shieldind on vehicles. Use of depleted uranium in weapons implies health effects for the population in areas where such weapons are used, since it still is toxic.
A state, that aspires to obtain nuclear weapons, might retrieve irradiated fuel from a research reactor and use it for nuclear bombs after reprocessing (1). This is the road that Israel may have gone down, according to the assumption that it possesses nuclear weapons. If a state has capacity for Uranium enrichment for production of nuclear reactor fuel, it is relatively simple to proceed with the enrichment up to weapons grade material (2) Today there are concerns that for instance Iran might take this path for production of nuclear bombs. An alternative way to obtain material for nuclear explosives is separation of plutonium from (partially) burnt-out nuclear fuel (3). It is likely that North Korea produced material for its nuclear tests in this way in the first decade of this century.
For a nuclear weapon to reach the intended target, some sort of delivery mechanism is required. The most common carriers today are missiles. These may either be ballistic missiles, without control of flight track after launching, or cruise missiles that can adjust the course of flight and even navigate. Depending on range, nuclear weapon systems are divided into three categories: strategic, eurostrategic/regional or tactical.
There is no common definition of these categories and it is not clear where the borders between them should be drawn. The difference between strategic and tactical nuclear weapons may be defined based on size of charge or on range or on planned use. If the type of nuclear weapon is defined based on range, a strategic bomb would be one that is intended for long-range deployment (>5500 km). Tactical nuclear weapons exist as missiles, mines, torpedoes and nuclear artillery.
Hair Trigger Alert
The US and Russian presidents are always accompanied by a case, that is carried by a carefully selected and trained military officer. The case contains a satellite radio along with the codes for launching that country´s nuclear arsenals. This case is often called “the nuclear football”. The “football” was established during the Cold War, when the leaders of the USA and the Soviet Union wanted to be in constant control of the ability to launch a nuclear attack.
The US president has a sovereign last say about deployment of nuclear weapons. After the collapse of the Soviet Union, the president of Russia took over the “football”, but in Russia an order to deploy nuclear weapons may be issued by the president, the minister of defense or the commander in chief of the army.
Nuclear War by Mistake
The large nuclear weapon states have a wide network of satellites and radar stations, which would give early warning about nuclear attacks. The intent is to allow the state under attack to detect incoming missiles early enough for counter-attack before impact of the hostile nuclear missiles.
False alarms are, unfortunately, not uncommon. Such alarms may be caused by fires, research missiles, electronic disturbances, or other spurious events. So even if the nuclear weapon states have no intent to use their nuclear weapons, a risk is always present that nuclear war could break out as a consequence of a system malfunction or through human errors. From the beginning of the nuclear era, there have been concerns about nuclear war by mistake.
If the number of nuclear weapon states increases, the risk for nuclear war will increase significantly, since it can be assumed that new nuclear weapon states would not have the skills and technology to effectively filter out false alarms.
What happens at the bang?
When a nuclear charge goes off, there will be an intense flash of light, like a giant lightning. It blinds and burns everything within a certain radius. There is no chance to take cover, unless there has been prior warning.
Everything within a certain radius from ground zero of the explosion will be smashed and burned. What remains would be smoke, gasses and small particles, which rise up in the sky. A mushroom-shaped cloud will be formed. Simultaneously there will be gamma radiation, which causes radiation sickness, and an electromagnetic pulse that ruins electrical equipment. Both of these effects are invisible. Immediately afterwards the blast wave hits. It is so violent that it smashes buildings and blows people away many kilometers from ground zero. After these immediate effects there will be radioactive fallout, which makes large areas un-inhabitable for a long time into the future.
Page last revised 2012-07-11 | <urn:uuid:22d4c43d-86d2-4adc-95b0-77f64b816cb8> | 4.125 | 2,152 | Knowledge Article | Science & Tech. | 43.486056 |
Science Fair Project Encyclopedia
Placodermi - extinct
Chondrichthyes (cartilaginous fish)
Acanthodii - extinct
Actinopterygii (ray-finned fish)
Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. The bones of the spinal column (or vertebral column) are called vertebrae. Vertebrata is the largest subphylum of chordates, and contains most animals with which people are generally familiar (except insects). Fish (including lampreys but excluding hagfishes), amphibians, reptiles, birds, and mammals (including humans) are vertebrates. Additional characteristics of the subphylum are a muscular system that mostly consists of paired masses, as well as a central nervous system which is partly located inside the backbone.
The internal skeleton which defines vertebrates consists of cartilage or bone, or in some cases both. The skeleton provides support to the organism during the period of growth. For this reason vertebrates can achieve larger sizes than invertebrates, and on average vertebrates are in fact larger. The skeleton of most vertebrates, that is excluding the most primitive ones, consists of a skull, the vertebral column and two pairs of limbs. In some forms of vertebrates, one or both of these pairs of limbs may be absent, such as in snakes or whales. These limbs have been lost in the course of evolution.
The skull is thought to have facilitated the development of intelligence as it protects vital organs such as the brain, the eyes and the ears. The protection of these organs is also thought to have positively influenced the development of high responsiveness to the environment often found in vertebrates.
Both the vertebral column and the limbs support the body of the vertebrate overall. This support facilitates movement. Movement is normally achieved with muscles that are attached directly to the bones or cartilages. The contour of the body of a vertebrate is formed by the muscles. A skin covers the inner parts of a vertebrate's body. The skin sometimes acts as a structure for protective features, such as horny scales or fur. Feathers are also attached to the skin.
The trunk of a vertebrate is hollow and houses the internal organs. The heart and the repiratory organs are protected in the trunk. The heart is located behind the gills, or where there are lungs, in between the lungs.
The central nervous system of a vertebrate consists of the brain and the spinal cord. Both of these are characterized by being hollow. In lower vertebrates the brain mostly controls the functioning of the sense organs. In higher vertebrates the size of the brain relative to the size of the body is larger. This larger brain enables more intensive exchange of information between the different parts of the brain. The nerves from the spinal cord, which lies behind the brain, extend to the skin, the inner organs and the muscles. Some nerves are directly connected to the brain, linking the brain with the ears and lungs.
Vertebrates have been traced back to the ostracoderms of the Silurian Period (444 million to 409 million years ago) and the conodonts, a group of eel-like vertebrates characterized by multiple pairs of bony toothplates.
All vertebrates have: the ability to form bones; paired, specialised sensory organs and a brain.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:86a443e3-b15d-48ed-b291-91f652cdc07e> | 4.1875 | 733 | Knowledge Article | Science & Tech. | 37.944094 |
I am sure that you have come across strange physics or astronomy symbols, or chemical elements, and wondered what they meant? Now you will be able to find the answer more easily thanks to two fantastic new web resources.
Scientists and astronomers use many strange symbols to define various phenomena. To help demystify these symbols for ordinary folk, a team of experts at the University of Nottingham (UK) has produced an easy to understand, fun and informative collection of sixty videos, entitled “Sixty Symbols“. A further sixty videos are in preparation and will be ready in the near future.
For those needing information on a chemical element, another team at the University of Nottingham (UK) has produced an amazing set of videos illustrating the entire 118 chemical elements of The Periodic Table. Some of the videos have even been made available for foreigners, with subtitles in Spanish, Portuguese, Indonesian and Italian.
These two sites are really very cool and fun! We love them! | <urn:uuid:acd5ebe8-c763-4d67-8c1f-9986e7028d60> | 3.15625 | 198 | Personal Blog | Science & Tech. | 30.670627 |
It is quite easy to add new built-in modules to Python, if you know how to program in C. Such extension modules can do two things that can't be done directly in Python: they can implement new built-in object types, and they can call C library functions and system calls.
To support extensions, the Python API (Application Programmers
Interface) defines a set of functions, macros and variables that
provide access to most aspects of the Python run-time system. The
Python API is incorporated in a C source file by including the header
The compilation of an extension module depends on its intended use as well as on your system setup; details are given in later chapters. | <urn:uuid:483a6383-e910-4aaa-8c6d-c3230a5be58f> | 2.84375 | 142 | Documentation | Software Dev. | 40.32 |
Structural Color in the Little Blue Penguin
How do birds get their color? Light absorption by pigments is one way color can be produced. Bird feathers have pigments like melanins and carotenoids – we even have evidence for color in the fossil penguin Inkayacu from fossilized melanin-bearing structures. Color can also be produced by physical interactions between light and biological nanostructures. These colors are called structural colors.
Recently the color of Little Blue Penguins was found to be generated by a new type of structural color. As their name implies, Little Blues are both small and wrapped in bluish feathers. A previously unrecognized nanostructure is responsible for the blue feather barbs of these penguins. Structural color can be generated by several different types of structures, such as tiny spheres or channels. However, researchers were surprised to find a completely unknown nanostructural arrangement in the penguin feathers. At the subcellular level, Little Blue Penguin feather barbs are composed of parallel b-keratin nanofibres organized into densely packed bundles. Essentially, the miniscule structures scatter light waves so as to give off blue color.
This is an important discovery, because learning how birds make color at the nanostructural level may help scientists synthesize artificial colored structures in the lab. Of course, it also has implications for penguin evolution. We are only beginning to understand how the microstructure of feathers affects their function in the air and under water. Exciting research is on the horizon, and future investigations may yield a better understanding of what exactly makes penguin feathers so efficient at insulation and streamlining.
D’Alba L; Sarananthan V; Clarke JA; Vinther JA; Prum RO; Shawkey MD. 2011. Colour-producing β-keratin nanofibres in blue penguin (Eudyptula minor) feathers. Biology Letters. February 9 doi: 10.1098/rsbl.2010.1163: 1 | <urn:uuid:f9dedbf0-8666-489e-9fa5-bff602e16e27> | 4.03125 | 413 | Academic Writing | Science & Tech. | 35.067655 |
The BBC has created a very, very large infographic titled “How Big Is Our Solar System?” Scroll down (which is a little odd) and it will take you from the surface of earth to the far reaches of space.
It’s similar to a couple of other infographics:
Scroll to see the ocean’s deepest depths is an interactive infographic from The BBC. Scroll down the infographic and it not only shows you information about what is happening at that depth of the ocean, it also provides videos and images. “Our Amazing Planet: Top To Bottom,” is another one, but there’s no interactivity and it also covers above the ocean. | <urn:uuid:da710548-2c88-41ac-85d8-a2ba8be76fa3> | 3.296875 | 142 | Personal Blog | Science & Tech. | 52.447946 |
We misspelled a number of elements in the periodic table printed in part VI of the Science Course supplement distributed with the paper on May 1. We meant Iron (not Irone); Praseodymium (not Praseodynium); Neodymium (not Neodynium); Neptunium (not Neptuniam); Americium (not Americum); Seaborgium (not Seoborgium); and Darmstadtium (not Darmstadium).
The Great Beyond goes on to present the first ever Neodymium mis-spelling league. Nature does not do too well, but at least it has never mis-spelled (or mis-spoke) "iron" as "irone".
Nature 148, 114-114 (26 July 1941). Abstract:
THE formulation of Irene as 1: 1: 2: 6-tetra-methyltetralin has recently been established synthetically by Bogert and Apfelbaum. On the basis of this formulation of irene and the production of ββγ-trimethyl pimelic acid by ozonization of irone, structural formulæ have been postulated for this ketone by Ruzicka and his co-workers. Two of the postulated structures contain the chromophoric system C = C – C = C – C = O which should therefore give rise to a characteristic absorption spectrum.
Who said science used to be simple and has only become complex since 1953, and publication of the double-helix structure of DNA? | <urn:uuid:96caf0fb-b3ab-43ab-8515-579ab0971224> | 2.6875 | 322 | Personal Blog | Science & Tech. | 39.740647 |
One of the perplexing questions people ask in the origin of Life is how did such complexity ever evolve from a simple broth of chemicals in the prebiotic world. The first person to ever attempt to try to answer it was Harold Urey and Stanley Miller who created a chemical soup of ammonia (reduced Nitrogen), methane (reduced C), and hydrogen (should be present in a reduced atmosphere) and subjected the soup to electric discharge (simulating lightning and solar radiation). This experiment was performed in the 1950s and was done to simulate early Earth condition. After this electric discharge passed through the soup, simple amino acids and sugars and the raw materials for nucleic acid bases such as adenine were found to be created in this mixture . These are all the raw ingredients for biochemistry to start hence bringing evolution of the origin of life into the realm of experimental science for the first time. Even though, the conditions of early Earth have come into question since then, Urey and Miller deservedly received a Nobel prize for the novel aspect of their work. In fact, the experiments were repeated recently with nitrogen gas instead of ammonia, carbon dioxide instead of methane, and hydrogen or water (currently accepted conditions for early Earth), and the products from the broth were similar in nature to those found in the Urey-Miller experiment.
In the prebiotic world envisioned by most scientists, chemistry would have dominated the changing scenario and landscape found in Earth. Chemistry, unlike biochemistry, is very non-specific and would create a huge pool of chemicals. Under the assumption that there were signs of modern cellular organisms in that pool (and this is a big assumption made out of necessity), then all or most of the biochemical reactions would be a small subset of all the reactions occurring in this pool called protometabolism . Somehow, after the first catalyst were formed (not as efficient as modern enzymes), those catalysts were more specific towards a subset of these reactions and made these reactions occur at a faster rate leading to a feedback mechanism by which these reactions became the dominant reactions leading to the biochemicals or life as we know it now.
One such theory of the origin of life states that an autocatalytic reaction cycle was present in the chemical gemisch in the prebiotic world and by the nature of it being autocatalytic, it started dominating this prebiotic world leading to the first signs of life [3-6]. One such autocatalytic cycle is the tricarboxylic acid cycle (TCA or Krebs or Calvin cycle), which is present in all modern organisms in one form or the other . The TCA cycle is the only route of carbon fixation into biochemicals starting with carbon dioxide as the source of carbon [8,9]. In one form of the cycle, called the reverse TCA cycle (and found in few organisms), the overall reaction can be visualized as 2 molecules of carbon dioxide (found in prebiotic earth) reacting with a molecule of citrate and 6 molecules of hydrogen to form 2 molecules of citrate and 5 molecules of water. The important thing to note is that 2 molecules of citrate were formed from 1 molecule of citrate hence producing more of the reactant. In other words, 2 molecules of citrate can be used as reactant in the next round of the TCA and the cycle is hence called autocatalytic. As it is autocatalytic, once prebiotic conditions existed where this cycle could take place completely (all reactions in it have to take place), this cycle would have taken place much faster after some time and would have slowly dominated the early prebiotic metabolism.
In addition, in modern cells, the TCA or the rTCA cycle is at the center of a cell's metabolism. In other words, the intermediates of the TCA cycle form amino acids, nucleotides, and cofactors for the rest of the cellular machinery. So, after this cycle starts to dominate the prebiotic world, the side reactions would start producing amino acids and nucleotides leading to complexity required for biochemistry to begin . However, the conditions required for this cycle to take place completely have not been found so far. Secondly, the source of energy of these reactions and the compartmentalization of these reactions (to cause insignificantly higher concentration of these biochemicals) is still a matter of speculation and further research.
It was postulated that in early prebiotic conditions, these reactions could have taken place on clay or on metal sulfide surfaces such as FeS. These metals would have themselves been oxidized to ferric sulfide providing energy to take place to completion [3,4]. Another theory is that it may not have been just the TCA cycle but some other cycle like the ribose cycle that could have been at the origin of metabolism . The advantage of the ribose cycle is that unlike the TCA cycle, there are only 1 or 2 reactions in the cycle that do not take place at an appreciable rate without a catalyst and hence only 1 or 2 reactions need the clay or metal surface as a catalyst.
In either case, it is a question whether an autocatalytic cycle should be considered as life. In my opinion it should not, even though it is producing more of itself (chemical form of reproduction) at the end of the day and there is energy conversion in the cycle (metabolism). It is just that life is very specific and driven unlike early chemistry which would have been highly aspecific. But this is certainly a matter of speculation and discussion.
Biochemistry - Stryer.
Singularities - de Duve.
Wechterheuser - Evolution of the first metabolic cycles - PNAS, 87:200-204, 1990.
Wechterheuser - On the chemistry and evolution of the pioneer organism - Chemistry and Biodiversity, 4:584-602, 2007.
Orgel - Self-organizing biochemical cycles - PNAS, 97:12503-12507, 2000.
Smith and Morowitz - Universality in intermediary metabolism - PNAS, 101:13168-13173, 2004.
Wikipedia entry on Citric acid cycle.
Morowitz, Kostelnik, Yang, and Cody - The origin of intermediary metabolism - PNAS, 97:7704-7708, 2000.
Srinivasan and Morowitz - Ancient genes in contemporary persistent microbial pathogens - Biol. Bull., 210:1-9, 2006.
PS: Stanley Miller passed away this year at the age of 77 and this post is dedicated to him. | <urn:uuid:de759799-956e-4261-ae04-08cca4b01cfd> | 3.609375 | 1,359 | Personal Blog | Science & Tech. | 34.428963 |
When 50mL of water are added to 50mL of ethanol in a 100mL graduated cylinder, there are only ~97mL of liquid. Ethanol and water molecules are attracted to each other through hydrogen bonding. The two molecules pack closer together with each other than they do with just themselves.
In this “trash-to-treasure” activity, polystyrene clamshell containers (#6 plastic) are used to make hard plastic art pieces. When polystyrene clamshell containers are produced, the material is heated and stretched into a mold, thus locking the material in an extended state. When this material is heated again, it returns to its unstretched size and shape. This property can be utilized to create a range of crafts, including buttons, key chains, luggage tags and jewelry. If students mass their plastic before and after, this could also be tied to the Law of Conservation of Mass.
In this demonstration, warm water is placed in a plastic syringe, the syringe is sealed, and the plunger is pulled back causing the water to boil. The water boils because the action of pulling back the plunger increases the volume, thus decreasing the pressure. The boiling point of a liquid is dependent on the pressure of the system, so a decrease in pressure leads to a decrease in boiling point.
In this demo, a skewer is pierced through a balloon without popping it. The balloon is made from a rubber polymer. The polymer is made of many long, elastic, overlapping chains, very similar to spaghetti. When a skewer pierces the balloon, these chains are stretched and pushed open to make a hole for the skewer and the balloon does not pop. It is important to pierce the balloon near the bottom & top, where the rubber has the least amount of stress. The polymer is more able to stretch and rearrange, allowing the skewer to pass through.
When a marshmallow is placed in a large capped syringe and the plunger is pushed in, the air in the marshmallow contracts from the pressure. Conversely, if the plunger is pulled back, the pressure decreases causing the air in the marshmallow to expand.
Liquid nitrogen is -196˚C and quickly freezes the ingredients into ice cream. The nitrogen boils out leaving deliciously creamy ice cream. The “fog” that we see is condensed water vapor though, not nitrogen gas.
When a balloon is placed in liquid nitrogen the air inside it is condensed from the cold (-196°C), causing the balloon to shrink. Once the balloon is removed it will regain its size as the air heats up. Liquid nitrogen boils at room temperature. The “fog” that we see is condensed water vapor though, not nitrogen gas.
Sugar solutions that have different concentrations have different densities; the more sugar in a solution the more dense it is. Therefore less dense solutions can be layered on top of denser ones.
Water has a very high surface tension because of the strong hydrogen bonding between water molecules, which allows the pepper to float on top of the water. When a small amount of soap is added it forms a monolayer on the surface. The monolayer spreads away from the point of contact causing the pepper to move to the edges of the dish.
When dry ice is placed in warm water it sublimes very quickly forming a large amount of carbon dioxide gas. When a bubble is placed over this the bubble grows from the pressure.
When M&M’s are placed in water, the outer shell, which is made of sugar, dissolves. The sugar moves from a place of high concentration (the M&M) to a place of low concentration (the water away from the M&M). When the sugar shell dissolves and moves outward, it takes the layer of food dye with it. When more than one M&M is placed into a petri dish the colors do not mix because the concentration of sugar at the interface is approximately the same. Also, around the bottom of the M&M water appears cloudy because the sugar that is dissolved is more dense than the water, so it sinks.
Universal indicator goes from red (pH 4) to violet (pH10) as the pH of a substance changes. Adding NaOH to water starts the solution off at pH 8-9 (blue). When dry ice is added to water it forms carbonic acid, and lowers the pH, which is the reason for the color changes. The “fog” that we see is condensed water vapor though, not carbon dioxide gas.
Diet soda contains artificial sweeteners while regular soda has sugar in it. Artificial sweeteners are so sweet so only a small amount is needed, where as much more sugar is needed to achieve the same sweetness. Because regular soda has more mass in the same size can, it is more dense than the diet soda.
In this demo, food coloring is added to a stirring beaker of water to create a tornado of color. This could be used as an example of a physical change, or to demonstrate the importance of properly mixing solutions.
When a small amount of water is heated inside the can, steam is produced, filling the can. When the can is inverted into cold water, all of the steam condenses quickly causing the can to implode.
CO2 gas from subliming dry ice gets caught in a soapy solution creating a column of bubbles. When the bubbles are popped, the “fog” that we see is condensed water vapor, not carbon dioxide gas.
In this demo, camphor particles are placed in water. They sublime at room temperature which is why camphor’s odor permeates the room so quickly. The gas that forms around the particles propels the particles in random directions. Earwax contains a large percentage of long chain fatty acids which form a monolayer in water, thus ceasing the motion of the camphor particles.
When the balloon is rubbed on a pair of jeans, electrons are wiped from the jeans to the balloon, causing a net negative charge on the balloon. The charged balloon is held near a thin stream of water. Charges in the water rearrange so that the positive charges in the water become attracted to the negatively charged balloon, and the stream of water bends. The rearranging of charges is pronounced because water is a polar molecule. | <urn:uuid:a8f4bf59-7bf7-4576-bd6f-f26e28fdd906> | 3.828125 | 1,310 | Content Listing | Science & Tech. | 54.237539 |
Using The Poster
Click on image to enlarge.
Photocopy the black-and-white poster image and distribute copies to your students. For an enlarged view, download the PDF version of the poster tiled into 6 sections; print the 6 pages of the PDF document on standard letter-sized paper, trim the margins, and tape together in order to form the complete poster.
Then, consider the following activities to help students learn about energy forms, sources, transformations, and uses. Before beginning these activities, review the definition of energy (the ability to do work—e.g., move things, change things, heat them) and discuss the annotated examples to help prepare your students for the activities.
1. Let students study the poster to find examples of potential energy (stored energy) and kinetic energy (the energy of movement).
2. On the chalkboard, draw a chart with six columns–one for each form of energy. Label the columns mechanical, chemical, radiant, nuclear, thermal, and electrical. Help students list and classify examples of each form.
Mechanical Energy: the energy of position and motion.
Chemical Energy: the energy that bonds molecules together. Chemical energy is released from a chemical reaction such as burning wood, coal, or oil. Our digested food releases chemical energy for use by the body.
Radiant Energy: energy that travels in waves, such as sunlight, radio waves, and X rays.
Nuclear Energy: the kind of energy produced when the nuclei of atoms split or join together. Nuclear power plants split the nuclei of uranium atoms in a process called fission. The sun combines the nuclei of hydrogen atoms in a process called fusion. (Note: Other than the sun itself, no examples of nuclear energy are shown in the poster.)
Thermal Energy: heat, the energy of moving and vibrating molecules. Geothermal energy is an example of thermal energy.
Electrical Energy: the energy of moving electrons. Electricity is electrons moving through a wire. Lightning is another example of electrical energy.
3. Let students circle and label examples of different types of energy sources depicted in the poster, such as solar, gas, electric, wind. (Note: Some sources may not actually be shown, but implied, such as the gasoline in the car.)
4. Let students work in small groups to identify examples of energy transformations. Then, have them explain the ones they've found to others in the class. | <urn:uuid:88ba60f8-14b7-4a7b-b6bf-f6d92ec549c3> | 4.625 | 507 | Tutorial | Science & Tech. | 45.298302 |
Image by phil_g via Flickr
People who want to be a website developer and learn the PHP programming language believe that they can just jump into it and learn it right away. The problem is learning PHP programming language is like learning any other type of language and it can be difficult to pick up, especially if you don’t have experience with previous computer programming languages.
If you are considering learning PHP programming language, here are some tips on how to get started.
Start Out Easy
If you don’t have any previous computer programming experience it is a good idea to get the basics down first. Programming experts recommend that you start with something known as VB.NET. This very basic program allows you to learn the basics of programming, design and computer languages.
Learn The Designing and Creating Process
After you have picked up the programming language from the VB.NET you need to start learning the creative and design process behind being a PHP programmer. You can do this by using a program known as SQL Server Express, where you will learn the basics of designing and creating websites and programming languages.
Remember it Takes Times
Learning the PHP language can be difficult and it will take some time. For some people it will be second nature and you will learn it quickly, while others will take time to learn the proper coding, use and language to become a PHP programmer.
Follow these steps and you’ll be able to learn the computer programming language you need to be a computer programmer. | <urn:uuid:71e2605d-6660-47e6-ab3d-95509babb157> | 2.78125 | 305 | Tutorial | Software Dev. | 51.851501 |
Formation of Clouds
Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere. The air is normally cooled by expansion during its upward movement. Upward flow of air in the atmosphere may be caused by convection resulting from intense solar heating of the ground; by a cold wedge of air (cold front) near the ground causing a mass of warm air to be forced aloft; or by a mountain range at an angle to the wind. Clouds are occasionally produced by a reduction of pressure aloft or by the mixing of warmer and cooler air currents.
Sections in this article:
More on cloud Formation of Clouds from Infoplease:
See more Encyclopedia articles on: Weather and Climate: Terms and Concepts | <urn:uuid:d330ad37-d521-4ac1-bf3a-6d08212860fe> | 4.21875 | 176 | Knowledge Article | Science & Tech. | 25.604694 |
How Santa deals with the challenge of the Travelling Salesman Problem
THAT’S MATHS:In the course of a single night, Santa Claus has a billion homes to visit. To ensure that every child gets a gift, he needs to pick a smart route. How does he do it? His challenge is called the Travelling Salesman Problem, or TSP.
Suppose a salesman based in Dublin must visit Waterford, Cork and Derry, and wants the shortest route. He can pick any city to begin, then either of the remaining two, and finally the last one before returning home. So, he has 3 x 2 x 1 = 6 choices. But some routes are much longer than others. Clearly, he will not go first to Cork, then to Derry and then to Waterford.
The salesman can calculate the distance of all six possible routes and choose the shortest. This is the “brute-force” solution of the TSP. But what if there are 10 cities instead of three? Then there are 10 x 9 x 8 x . . . x 3 x 2 x 1 possible routes. The product of the first 10 numbers, called 10 factorial and written 10!, comes to 3,628,800, far too many to check by hand. And for 20 cities it is 20 factorial, which is more than two million million million. The brute force approach is useless: we have to find a smarter way to solve the problem.
The TSP is a “combinatorial optimisation” problem. It is easy to state but difficult to solve effectively. The mathematical structure underlying the problem is called a graph: each city is a vertex, and edges are drawn connecting every two vertices. A round-trip of all the cities is called a Hamiltonian cycle, after William Rowan Hamilton, the outstanding Irish mathematician. Hamilton solved a problem of this type when designing a puzzle called the Icosian Game.
The goal of the TSP is to minimise the total length of the round trip. Various “heuristic solutions” have been devised: for example, the nearest neighbour algorithm, where we pick the closest city not yet chosen. But none of these is optimal in all cases. Cross-overs can be removed so that the best route does not intersect itself but is a simple curve, like a greatly distorted circle with an inside and an outside.
Why should we worry about the TSP? Well, the same problem arises in a large number of practical applications. These include the manufacture of computer circuit boards, calculating DNA sequences in genetic engineering, allocating routes to a fleet of aircraft, designing fibre-optic-cable networks and scheduling material stocks in warehouses.
The TSP is a prototype for the “P versus NP Problem”, one of the trickiest unsolved problems in mathematics. The record number of “cities” for which an optimal solution has been found is 85,900. But Santa’s challenge is vast by comparison, so he must have found a truly excellent algorithm for solving the TSP.
* Peter Lynch is professor of meteorology at University College Dublin. He blogs at thatsmaths.com | <urn:uuid:b77de6fd-f193-4b42-9d5e-672818912935> | 3.515625 | 658 | Nonfiction Writing | Science & Tech. | 61.198632 |
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readability. Many aspects of typography translate only awkwardly to HTML.
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Advancing the Science of Climate Change
modeling, scientists have deduced that the ice ages were initiated by small recurring variations in the Earth’s orbit around the Sun.
GHG Emissions and Concentrations Are Increasing
Human activities have increased the concentration of CO2 and certain other GHGs in the atmosphere. Detailed worldwide records of fossil fuel consumption indicate that fossil fuel burning currently releases over 30 billion tons of CO2 into the atmosphere every year (Figure 2.3, blue curve). Tropical deforestation and other land use changes release an additional 3 to 5 billion tons every year.
Precise measurements of atmospheric composition at many sites around the world indicate that CO2 levels are increasing, currently at a pace of almost 2 parts per million (ppm) per year. We know that this increase is largely the result of human activities because the chemical signature of the excess CO2 in the atmosphere can be linked to the composition of the CO2 in emissions from fossil fuel burning. Moreover, analyses of bubbles trapped in ice cores from Greenland and Antarctica reveal that atmospheric CO2 levels have been rising steadily since the start of the Industrial Revolution (usually taken as 1750; see Figure 2.3, red curve). The current CO2 level (388 ppm as of the end of 2009) is higher than it has been in at least 800,000 years.
FIGURE 2.3 CO2 emissions due to fossil fuel burning (blue line and right axis) from 1800 to 2006 and atmospheric CO2 concentrations (red line and left axis) from 1847 to 2008. For further details see Figures 6.2, 6.3, and 6.4. Based on data from Boden et al. (2009), Keeling et al. (2009), and Neftel et al. (1994). | <urn:uuid:e621ce68-9573-4e1f-be45-30eb1793ad6c> | 3.8125 | 404 | Truncated | Science & Tech. | 52.333597 |
Space as a reference point
Date: 1993 - 1999
I would like to know if the black part is gas and could
be a reference poi for finding objects in motion
By the black part, I mean outer space.
The density of gas in most of nearby space is about one atom or
ion per cubic meter, so it is very low density. We do not need
to have any gas present to measure the motion of objects in space.
One of the current questions about the black part of space is
how much cold and therefore invisible mass there is out there.
Some new experiments are starting to suggest there is much "dark
matter" out there.
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:dcbfed9d-66cd-4609-823a-60ecc1cc410a> | 2.875 | 154 | Audio Transcript | Science & Tech. | 53.820929 |
These energy packets are called photons and its interaction with mass is what we call light, so there is no such thing as light as is, just the interaction of the photons with mass. that effect is broken down into different forms of interaction, and the light we see is only a small part of that.
So my point is this... a photon is light and light is a photon, but its only light when it interacts with mass again, until that, its a packet of energy, not even a particle, not a carrier of light, just pure energy, and its effect becomes clear when it meets another electron, and is bounced/ reflected/ or absorbed etc and we see this energy as light.
So light could be called a energy interaction with mass, from its birth to its final arrival in your eye.
Hey I'm not too clever, this is prob totally incorrect lol.
What do you think?.
You see a photon contains all the energy needed , and its interaction with the mass it reaches shows us this energy in different ways, depending on the electrons it meets, so the so called light streaming from the sun is not light at all, but pure energy, and its collisions with mass is what we call light, photons hitting mass and carrying the info to our eyes, and some going right through and out the back of your head and some not making it to your eye etc.
So there's no light without mass, just energy with nothing to interact with, add mass and things start to light up a little, as the photons start to interact with it.
So light is a photon's interaction with mass, gravity is the displacement of space by mass, so also effects the energy as it passes through or close by this mass space interaction.
Your going to tell me I'm wrong lol, but at the end of the day, that's why I'm here. | <urn:uuid:349b7650-61c7-4b9a-8497-f89a52b230c0> | 2.859375 | 383 | Comment Section | Science & Tech. | 66.10503 |
Explanation: Today's solstice, the astronomical beginning of summer in the north, is at 23:09 UT when the Sun reaches the northernmost declination in its yearly trek through planet Earth's sky. While most in the northern hemisphere will experience the longest day of the year, for some the Sun won't set at all, still standing just above the horizon at midnight as far south as about 66.6 degrees northern latitude. Of course, as summer comes to the north the midnight Sun comes earlier to higher latitudes. Recorded near midnight, this time series from June 6 follows the Sun gliding above a mountainous horizon from a latitude of 69 degrees north. The remarkable scene looks north over the Norwegian Sea from Sortland, Norway. The 2012 transit of Venus is already in progress, with Earth's sister planet in silhouette at the upper left against the bright disk of the midnight Sun.
|<< Previous APOD||This Day in APOD||Next APOD >>| | <urn:uuid:19a20aba-af63-42ce-aa64-274fbcec28e9> | 3.6875 | 197 | Comment Section | Science & Tech. | 54.356111 |
We are at a stage in time where we desperately need to find a viable alternative source of energy to replace our dependence on fossil fuel.
We always read articles regarding the major problems we are facing because of global warming. Many think that alternative energy should be focused on the development of wind and solar energy but when it comes to cold fusion most people and even some scientists think that it is just a waste of time.
Yes, a lot of people do not take cold fusion seriously. They think it is just a fraud or it is impossible to achieve and only the sun can replicate its process. But imagine having limitless sources of energy. Cold fusion will rely on our ocean because the process involves heavy hydrogen, found in oceans, being fused with precious metals and coupled with a jolt of electricity. The result of this combination would be an intense amount of energy that could forever provide us all the energy we need. It is our hope that one day cold fusion will become a reality and replace all the planet’s oil reserves. Scientists and engineers continue harnessing and discovering the missing steps in making this dream a reality. | <urn:uuid:d3d4ffb7-b3d4-4ef3-beac-2df39fcf4742> | 2.9375 | 224 | Personal Blog | Science & Tech. | 42.826524 |
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Your organization might have access to this article on the publisher's site. To check, click on this link:http://dx.doi.org/+10.1063/1.4740512
A diagnostic technique based on the Cherenkov effect is proposed for detection and characterization of fast (super-thermal and runaway) electrons in fusion devices. The detectors of Cherenkov radiation have been specially designed for measurements in the ISTTOK tokamak. Properties of several materials have been studied to determine the most appropriate one to be used as a radiator of Cherenkov emission in the detector. This technique has enabled the detection of energetic electrons (70 keV and higher) and the determination of their spatial and temporal variations in the ISTTOK discharges. Measurement of hard x-ray emission has also been carried out in experiments for validation of the measuring capabilities of the Cherenkov-type detector and a high correlation was found between the data of both diagnostics. A reasonable agreement was found between experimental data and the results of numerical modeling of the runaway electron generation in ISTTOK. | <urn:uuid:e0641cbb-1a57-4b99-bde0-e737abdcc80f> | 2.734375 | 228 | Truncated | Science & Tech. | 34.51832 |
Short Data Type (Visual Basic)
Holds signed 16-bit (2-byte) integers that range in value from -32,768 through 32,767.
Use the Short data type to contain integer values that do not require the full data width of Integer. In some cases, the common language runtime can pack your Short variables closely together and save memory consumption.
The default value of Short is 0.
Widening. The Short data type widens to Integer, Long, Decimal, Single, or Double. This means you can convert Short to any one of these types without encountering a OverflowException error.
Type Characters. Appending the literal type character S to a literal forces it to the Short data type. Short has no identifier type character.
Framework Type. The corresponding type in the .NET Framework is the Int16 structure. | <urn:uuid:e6957085-ebef-4468-9d5f-63e8d63947ed> | 3.4375 | 176 | Documentation | Software Dev. | 53.330468 |
What will they think of next? First, there was the brain-computer interface for controlling Second Life avatars, and yesterday I mentioned a gig in which the music is controlled by the audience’s brainwaves. Now, researchers from Austria and Slovenia have developed a device called Brainloop, which can be used to navigate in Google Earth:
Brainloop is an interactive performance platform that utilizes a Brain Computer Interface (BCI) system which allows a subject to operate devices merely by imagining specific motor commands. These mentally visualized commands may be seen as the rehearsal of a motor act without the overt motor output; a neural synapse occurs but the actual movement is blocked at the corticospinal level. Motor imagery such as “move left hand”, “move right hand” or “move feet” become non-muscular communication and control signals that convey messages and commands to the external world. In Brainloop the performer is able – without physically moving – to investigate urban areas and rural landscapes as he globe-trots around virtual Google Earth. Through motor imagery, he selects locations, camera angles and positions and records these image sequences in a virtual world. In the second half of the performance, he plays back the sequence and uses Brainloop to compose a custom soundtrack by selecting, manipulating and re-locating audio recordings in real time into the physical space.
That’s a very good description of how BCIs work, apart from the bit that says “a neural synapse occurs but the actual movement is blocked at the corticospinal level“.
Presumably, what they mean is that signals generated in the premotor cortex, which contains neurons involved in planning movements, are not transmitted to the primary motor cortex, which contains cells that descend into the spinal cord in the corticospinal tract, and which are involved in executing movements.
Pendantry aside, here’s a film clip of the Brainloop device in use:
[Via Ogle Earth] | <urn:uuid:4761c6ab-698d-4d0d-82de-a85ed3fde2e9> | 2.859375 | 411 | Personal Blog | Science & Tech. | 21.088848 |
- BirdLife. Red Data Book - Threatened Birds of Asia. Accessed July 11th, 2007.
- World Bank. Philippines Environment. Accessed July 11th, 2007.
- WWF. 2004. The Sulu-Sulawesi Marine Ecoregion - Cradle of Life. Accessed July 11th, 2007.
Environmental problems in the Philippines
Saving precious remains
Fishers in the Philippines are increasingly coming home with pitiful catches. Of a number of factors which have led to this situation, one stands out: over-fishing in many areas. According to the Asian Development Bank (ADB), there has been a drop of 90% in the quantity of marine organisms that can be trawled in some traditional fishing areas of the Philippines.
This isn’t just a question of declining fish stocks and biodiversity, but also of social impacts and economic losses. Mismanagement of fisheries resources is estimated to cost US$ 420 million annually in lost revenues.
At the root of the overfishing problem is weak fisheries management, ineffective policies and poor enforcement of fishery laws.
Coastal zone development has been particularly damaging to the Philippines’ marine environment, especially to coral reefs, mangroves, and seagrasses.
As populations have increased, so have their needs for construction materials and living space. Excavation, dredging, and coastal conversion to accommodate coastal development have seen corals being extracted for reclamation and construction, especially in coastal villages.
Mangroves have particularly suffered from coastal development, notably at the hands of the aquaculture industry. In the Philippines, aquaculture has reduced mangrove stands to only 36% of 1900 levels.
After decades of deforestation, which has left about 3% of the original cover, forests continue to be under threat from agriculture and urbanization, illegal logging and forest fires.
Sustained forest loss in the Philippines is causing severe soil erosion, and is threatening the country’s rich biodiversity. This is particularly worrying as many of the Philippines’ species, which depend on these forests, are endemic (they cannot be found anywhere else in the world). For example, of 180 native terrestrial mammal species here, about 61% are endemic.
Inconsistent laws, inadequate regulations, weak enforcement and lack of funding are making forest conservation a major challenge.
Only about 10% of sewage in the Philippines is treated or disposed of in an environmentally sound manner. The rest goes back to nature – usually the sea.
In this context of poor waste treatment and high population growth, water pollution is a growing problem for the country’s groundwater, rivers, lakes, and coastal areas. Polluting industrial material is also found in abandoned mining areas, with mercury pollution affecting water bodies in these areas.
These problems are unfolding in a context of poor planning, and weak management and enforcement of regulations. | <urn:uuid:a29ef4e4-a285-455d-b549-bc3472b9b942> | 3.125 | 592 | Knowledge Article | Science & Tech. | 29.421224 |
Images of an ultracold gas of potassium-40 atoms. Since each atom is composed of an odd number of particles, they are classified as fermions--objects which have values of a quantity known as spin in multiples of 1/2. One of the two types of matter found in nature, fermions have many specific properties. Many of the building blocks of nature, such as electrons, neutrons, and protons, are also fermions.
Ultracold Fermi gases can provide potential insights into the basic properties of such objects as neutron stars, since they are made up of fermions. The gas in the picture is initially trapped in magnetic fields. The images show the gas 15 thousandths of a second (milliseconds) after they are released from the trap. The hotter cloud (left) had 2.5 million potassium-40 atoms at a temperatures of 2.4 microkelvin (millionths of a degree above absolute zero). The colder cloud (right) had approximately 780,000 atoms at 290 nanokelvins (billionths of a degree) above absolute zero--the lowest temperature yet recorded for a gas of fermion atoms.
The images are in false color, with white signifying the highest density regions of atoms and blue/black indicating the lowest density regions. At absolute zero (T) all of the atoms would lie inside the radius marked "Fermi energy" in each cloud.
This illustration contrasts how fermions and bosons occupy levels in an energy well. Bosons all fall into the lowest energy state, forming a Bose Einstein condensate. Fermions, on the other hand, must obey the Pauli exclusion principle, which prohibits two identical particles from occupying the same state.
At a temperature of absolute zero (T=0), fermions stack up in the energy levels, with the energy of the highest-filled state called the Fermi energy (figures courtesy of D.S. Jin, NIST/University of Colorado).
This research is reported by B. DeMarco and D.S. Jin in the 10 September 1999 issue of Science.
Link to related Physics News Update item. | <urn:uuid:946cd66e-1257-4c1e-831a-8d205bc8228b> | 3.828125 | 452 | Knowledge Article | Science & Tech. | 48.939782 |
Puerto Rico is Listening
Puerto Rico Coast.
|The SETI team searches for radio frequencies, using large telescopes such as the Arecibo Observatory,
Credit: David Parker / Science Photo Library
At first glance, Puerto Rico seems a strange place to eye the sky. A tilted block of land guarding the eastern end of the Greater Antilles, this island boasts no soaring mountains on which an optical telescope could perch, nor an unpopulated outback that would suit the signal-sensitive ears of a radio array.
What Puerto Rico does have is geology and location.
Stretching across the islands northern edge from the suburbs of San Juan to the western town of Aguadilla is a bumpy, limestone terrain known as karst. Pockmarked from thousands of millennia of rain, the karst is a jumble of haystack hills and broad sinkholes. One of the latter, about 8 miles south of the coastal city of Arecibo, is a perfect natural dimple to house the worlds biggest single-dish antenna: the Arecibo radio telescope.
Cornell University, which built this instrument in the early 1960s, realized that Puerto Rico offers more than accommodating topography. The islands southern latitude (18 degrees north) ensures that Venus and other members of our solar system pass overhead a big plus for a telescope whose 1,000-foot reflector, aimed at the zenith, is far too large to tilt.
|In a universe brimming with stars, the search is on if life exists elsewhere
Twice a year Spring and Fall we come to Arecibo, to profit from its unrivaled sensitivity in our search for signals from other worlds and other beings. This time, our night-time observing shift will be from 5:00 pm to 8:00 am, somewhat longer than usual. The run lasts 2-1/2 weeks, which is a very healthy allocation on an instrument in constant and widespread demand by astronomers worldwide. Cornell now operates the observatory under a cooperative agreement with the U.S. National Science Foundation, and Arecibo is frequently busy with studies of pulsars, galaxies, and (as Madison Avenue would gush) a whole lot more.
Project Phoenix has been using Arecibo since 1998, and in that time hundreds of nearby star systems have been examined for microwave signals. Unlike other SETI experiments, Phoenix can drill down on its targets to maximize the chances of picking up truly faint emissions.
If an extraterrestrial broadcast breathes as much as 0.00000000000000000001 watts onto Arecibos 18-acre reflector, we could detect it.
That's a billion times fainter than kisses blown across a stadium.
|The Milky Way. Credit: Akira Fujii
I was packed and prepped for April in Arecibo, but my connecting flight to the island is hung up in Dallas. An ornery fuel valve necessitates an extra stop, and many of the passengers are peeved. I try to remain philosophical.
After all, in November, 1493, when Columbus first stumbled upon the island, it had taken him 40 days to bridge the Atlantic from Cadiz to the Caribbean, a distance roughly comparable to the mileage from California. Despite the delays, my trip is still a hundred times faster than his.
Watching the iridescent towns of the Bahamas slide by in the dark waters below, it strikes me how five centuries an eye blink in the history of humanity has changed Puerto Rico from an island awaiting discovery to one from which discovery is made.
The plane bounces onto the tarmac in San Juan, and the windows immediately fog up from the humidity. Once outside, I find the evening air a pleasant 77 F. Soon, I'm stuffed into a rental car with fellow astronomer Mike Davis, his wife Jean, a small dog, and an impressive collection of luggage. We snake our way out of the airport, and ease on to the freeway to the west. It takes just over an hour to reach the small, labyrinthine roads that lead to the observatory.
Somewhat after midnight we pull into the observatory gates, and I collect my cabin key. The coquis thumb-size frogs with watermelon-size throats are out in force, lacing the humid air with their familiar ko-kee calls.
In the near distance, the tracking motors of the telescope grind and groan. I find my way to bed.
The morrow will bring work, yes; but also promise.
Related Web Pages
Allen Telescope Array Capabilities
The Astrophysical Journal (March 2003, v. 145,pp. 181-198): "Target Selection for SETI: I. A Catalog of Nearby Habitable Stellar Systems" (PDF)
How To Find An Extrasolar Planet
SIM (NASA's Space Interferometry Mission
GAIA - The Galactic Census Project
FAME: Full-sky Astrometric Mapping Explorer | <urn:uuid:83d5ecc3-0d01-4d53-8524-704acd301876> | 3.65625 | 1,021 | Personal Blog | Science & Tech. | 47.431575 |
Huge Coral Reefs Discovered off Puerto Rico
A new discovery of thriving coral reefs off the coast of Puerto Rico may offer hope for other shallower reefs. Scuba diving scientists discovered sprawling and diverse coral reefs at 100 to 500 feet (30 to 150 meters) below the ocean surface within a 12-mile (19-kilometer) span off the southwestern coast near La Parguera, Puerto Rico.
With the overall health of shallow coral reefs and the abundance of reef fish in Puerto Rico in decline, this finding brings hope that deeper fish stocks may help to replenish stocks on shallower reefs.
These mesophotic ecosystems — 'meso' for middle and 'photic' for light — are the deepest of the light-dependent coral reefs. Too deep for exploration with traditional scuba gear, these reefs have until recently remained largely unexplored because of the cost and technical difficulty of reaching them. Advances in diving techniques allowed scientists to safely dive and conduct the new survey.
"We had no idea how extensive, vibrant and diverse these mesophotic coral ecosystems are off La Parguera," said Richard Appeldoorn, the study team leader from the University of Puerto Rico, Mayaguez.
"At mesophotic depths in Puerto Rico, scientists are seeing fish species that were once common inhabitants of shallow reefs such as groupers, snappers and reef sharks," said Kimberly Puglise of the National Oceanic and Atmospheric Administration (NOAA), the organization that funded the study. "These reefs stand in stark contrast to declining shallow water reefs in the same area." | <urn:uuid:a924b067-739d-45e9-9f57-30c0888fa3ff> | 3.703125 | 327 | Truncated | Science & Tech. | 30.133853 |
Direct routing allows one task to send messages to another through a TCP link, avoiding the overhead of forwarding through the pvmds. It is implemented entirely in libpvm, using the notify and control message facilities. By default, a task routes messages to its pvmd, which forwards them on. If direct routing is enabled (PvmRouteDirect) when a message (addressed to a task) is passed to mroute(), it attempts to create a direct route if one doesn't already exist. The route may be granted or refused by the destination task, or fail (if the task doesn't exist). The message is then passed to mxfer().
Libpvm maintains a protocol control block (struct ttpcb) for each active or denied connection, in list ttlist. The state diagram for a ttpcb is shown in Figure . To request a connection, mroute() makes a ttpcb and socket, then sends a TC_CONREQ control message to the destination via the default route. At the same time, it sends a TM_NOTIFY message to the pvmd, to be notified if the destination task exits, with closure (message tag) TC_TASKEXIT. Then it puts the ttpcb in state TTCONWAIT, and calls mxfer() in blocking mode repeatedly until the state changes.
When the destination task enters mxfer() (for example, to receive a message), it receives the TC_CONREQ message. The request is granted if its routing policy (pvmrouteopt != PvmDontRoute) and implementation allow a direct connection, it has resources available, and the protocol version (TDPROTOCOL) in the request matches its own. It makes a ttpcb with state TTGRNWAIT, creates and listens on a socket, and then replies with a TC_CONACK message. If the destination denies the connection, it nacks, also with a TC_CONACK message. The originator receives the TC_CONACK message, and either opens the connection (state = TTOPEN) or marks the route denied (state = TTDENY). Then, mroute() passes the original message to mxfer(), which sends it. Denied connections are cached in order to prevent repeated negotiation.
If the destination doesn't exist, the TC_CONACK message never arrives because the TC_CONREQ message is silently dropped. However, the TC_TASKEXIT message generated by the notify system arrives in its place, and the ttpcb state is set to TTDENY.
This connect scheme also works if both ends try to establish a connection at the same time. They both enter TTCONWAIT, and when they receive each other's TC_CONREQ messages, they go directly to the TTOPEN state.
Figure: Task-task connection state diagram | <urn:uuid:09a0a107-ce1a-4f63-a5eb-304f9de6df04> | 3.125 | 608 | Documentation | Software Dev. | 47.67367 |
ALIVE, ALIVE-O! Inverclyde council in Scotland is proud of the bird life to be found in the inner Clyde estuary, which has been designated a site of special scientific interest. The council devotes a page of its website to the birds that live there or pass through. The Clyde, it tells us, is the most northerly of the large west-coast estuaries in the UK that are used by migrating birds.
But there is a puzzle about this otherwise attractive and informative web page. A discussion of the feeding habits of the birds in the area contains this mystifying sentence: "Mussels and *bleep*les, the principal food source for scaup, goldeneye and eider, are found in large concentrations on Mussel Bank and *bleep*le Bank."
It took Liam Anton, who discovered this, a while to work out what is going on here. At last he realised that the council's net censor ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:567ce394-8cba-4656-a917-32169e96d378> | 3.140625 | 230 | Truncated | Science & Tech. | 57.233297 |
HANDS up if you think the "invisibility cloaks" produced recently lack a certain practicality. Then you might be pleased to hear that ideas originally applied to creating them could now have a more down-to-earth application: shielding coastlines from destructive waves.
By scaling up notions from semiconductor physics and so-called metamaterials, the technology behind "invisibility cloaks", it may be possible to create a zone in front of vulnerable coastlines where waves of certain frequencies cannot reach. Such a system could even double up as an energy plant.
Metamaterials were first developed about a decade ago. They typically use arrays of tiny antenna-like resonators to bend and channel electromagnetic waves, leading to exotic behaviour. Most famously, in 2006, an Anglo-American team led by John Pendry of Imperial College London used such a set-up to create an invisibility cloak: a series of resonators that steered light around an object, ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:c0812619-8724-41ba-852b-b8ffc6e4dad8> | 3.171875 | 227 | Truncated | Science & Tech. | 31.6013 |
Amphibians in Winter
Mammals are not the only animals to use hibernation as a way to survive winter. Amphibians, like frogs and salamanders, have evolved with some very unique ways of surviving the cold. Many amphibians will spend the time underwater or, like salamanders, go deep underground in tunnels made by small mammals. Wood frogs and the spring peepers will often spend their winters in deep cracks in logs and rocks or the might bury themselves as far as they can in leaf litter to avoid the frosts. Unfortunately, sometimes even these protected places can freeze, but yet the amphibian doesn't die. This is because of special chemicals in their bodies similar to anti-freeze that allows them to survive nearly frozen during the winter. While their hearts have stopped beating and they are not breathing, these frogs will thaw out when spring arrives, and continue on with their lives, as good as new. | <urn:uuid:cefc8076-0129-4dd6-9244-12a3ac30f334> | 3.59375 | 192 | Knowledge Article | Science & Tech. | 46.270968 |
The specific intensities of nonparallel light in the direction of a stellar source, such as the sun, resulting from multiple scattering and diffuse ground reflection of a unit flux of parallel radiation incident on a plane parallel, Rayleigh atmosphere, equivalent to the Earth’s atmosphere in composition and density, are evaluated following S. Chandrasekhar's extension of the Rayleigh theory. Values are given as a function of direction of the source and normal optical thickness covering the visible and near ultra violet spectrum.
It is shown that the flux resulting from such nonparallel radiation, for a sufficiently small solid angle (10-3 radian) around the source, when the latter is within 50° or less of the vertical, is of the order of 10-5 of the reduced flux of the direct solar beam, for radiation within the visible range. The relative importance of the scattered light increases with normal optical thickness and zenith distance of the source.
It is pointed out that certain observations of apparent atmospheric transmissions of solar radiation in the blue end of the visible spectrum exceed in magnitude significantly the values obtained from the exact Rayleigh scattering theory, and it is suggested that this anomaly may be due to non-Rayleigh particles existing in the high atmosphere, with strong forward scattering characteristics.
DIRAN DEIRMENDJIAN and ZDENĚK SEKERA, "Quantitative Evaluation of Multiply Scattered and Diffusely Reflected Light in the Direction of a Stellar Source in a Rayleigh Atmosphere," J. Opt. Soc. Am. 43, 1158-1165 (1953) | <urn:uuid:2c110de6-c475-41f7-90d9-eef19865d9fc> | 2.8125 | 327 | Academic Writing | Science & Tech. | 30.368729 |
Comments on snowflakes
The earliest preserved illustration of snowflakes is by Olaus Magnus in
1555. Others interested in snowflakes were Descartes (in Discours de
la Methode, 1635) and Leuwenhoek (and there were, and are many more).
It seems that at present there is no accepted explanation why many
snowflakes have a very symmetric hexagonal structure though the details
are quite different for different flakes. In fact, there is still research
going on in this field. The basic structure comes from the properties of
the water molecules, no doubt. The problem is that the aggregation
process from the supercooled steam of the cloud is plausibly a local one.
Hence there is no obvious reason why it should conserve the symmetry of
the growing snowflake.
Some starting points for finding out more.
The standard bible on snowflakes:
Snow crystals, natural and artificial
Harvard UP., Oxford UP 1954
A book on symmetry groups with a few pages on the symmetries of snow
crystals with more references:
Hargittai, I and Hargittai, M
Symmetry through the eyes of a chemist: 2nd ed.
New York: Plenum Press 1995
The picture book of snowflakes:
W.A. Bentley and W. J. Humphreys
New York: Dover 1962
A link to active research on the growth of snow crystals at Caltech,
with more links. | <urn:uuid:caf28e5a-4d11-481c-9703-02173e1296d0> | 3.4375 | 318 | Knowledge Article | Science & Tech. | 55.966483 |
PhysClips: The Foucault Pendulum Relations
Physics Front Related Resources
This is the full set of PhysClip tutorials relating to Newton's Laws and force interactions.
This interactive tutorial explains how a Foucault Pendulum is used to demonstrate the Earth's rotation. It is appropriate for middle school physical science and Physics First courses.
Create a new relation | <urn:uuid:d2216d12-ed7e-421a-9c8e-95012afb6041> | 3.28125 | 76 | Content Listing | Science & Tech. | 33.192105 |
should array index start at 0 or 1?
the eminent computer scientist Edsger W Dijkstra (EWD) thinks it should start at 0. See: 〔Why numbering should start at zero By Edsger W Dijkstra. @ www.cs.utexas.edu…〕. But it's not really convincing.
those starting at 1 include: FORTRAN, SASL, MATLAB, Smalltalk, Lua, Julia, Mathematica.
Seems most number crunching languages start at 1. New interesting one is Julia. Mathematica is a special case. It starts at 1, but actually, 0 refers to the head of expression, so it's all consistent.
Python follows EWD's recommendation to a tee. It start at 0, and the ending index does not include the element. Example:
# -*- coding: utf-8 -*- # python3 a = list(range(1,4)) print(a) # [1, 2, 3]. most annoying. b = ["a", "b", "c"] print(b[0:1]) # ['a']
Python's way is the most painful to work with.
most other langs, even they start at 0, but a ending index usually is inclusive. For example, here's Perl.
# -*- coding: utf-8 -*- # perl use Data::Dumper; @a = ('a','b','c'); @b = @a[0..1]; print Dumper(\@b); # ['a', 'b']
in my view, it should start at 1, and ending index should be inclusive. Because that's just easier to work with. Also, when you have nested array, starting at 1 is much easier to work with. Nested array is heavily used in math, for marix, tensor, tree, no wonder most number crunchers start at 1.
what's your experience? | <urn:uuid:4e0a6183-a7a0-4334-b571-e51726f034ee> | 2.953125 | 417 | Q&A Forum | Software Dev. | 87.32736 |
Science Fair Project Encyclopedia
Jöns Jakob Berzelius
Jöns Jakob Berzelius (August 20, 1779 - August 7, 1848) was a Swedish chemist, who invented modern chemical notation and is considered one of the fathers of modern chemistry (along with John Dalton and Antoine Lavoisier). Berzelius discovered the elements silicon, selenium, thorium, and cerium. He was inducted into the Royal Swedish Academy of Sciences in 1808, and became a member of the Swedish Academy in 1837.
Trained as a medical doctor at the Uppsala University, in 1802 he became a teacher, from 1807 professor, in medicine and surgery at the Stockholm School of Surgery. In 1810 the school became a part of Medico-Kirurgiska institutet, the predecessor to the Karolinska Institute, and Berzelius was appointed professor in chemistry and pharmacy. Not long after arriving to Stockholm he wrote a chemistry textbook for his medical students, from which point a long and fruitful career in chemistry began. While conducting experiments in support of the textbook he discovered the law of constant proportions , which showed that inorganic substances are composed of different elements in constant proportions by weight. From this, by 1828 he compiled a table of the relative atomic weights (with oxygen set to 100) of all elements then known. Taken together, this work was a strong confirmation of the atomic hypothesis ; that inorganic chemical compounds were composed of atoms combining in whole number amounts. In discovering that the atomic weights were also not integer multiples of hydrogen's, Berzelius also disproved Prout's hypothesis that elements were built up from atoms of hydrogen. Berzelius in 1838 discovered proteins.
In order to aid his experiments, he developed a system of chemical notation in which the elements were given simple written labels -- such as O for oxygen, or Fe for iron -- and proportions were noted with numbers. This is the same basic system as is used today, the only difference being that where we would use a subscript number (i.e., H2O), Berzelius would use a superscript.
A biography on Jac. Berzelius - his life and work was written by J. Erik Jorpes and published in 1966 and 1970 (originally in Swedish, first published in 1949).
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:2bf56400-a15e-416a-8fc0-f9c99ca8fcf9> | 3.6875 | 512 | Knowledge Article | Science & Tech. | 38.604419 |
|Home · All Classes · Main Classes · Deprecated|
A gesture is a high-level event that represents a series of user input. Qt and MeeGo Touch support the following gestures:
Press, drag, release
Press (with two fingers), move fingers on surface,
Press, quick drag and release
Tap and hold
As a gesture is merely an interpreted series of input, the application determines what the gesture actually means. For example, a pinch gesture may be used to either rotate or zoom a picture, or both. If combined, gestures may have overlapping interactions, as is the case of swipe and pan. It is up to the application design to make sure there are no overlapping interactions in UI (the result of overlapping interactions is undefined). Typically a swipe gesture would be used in a UI where a flick should be interpreted as "next" or "previous", while a pan gesture implies an event with acceleration such as scrolling a web page.
While all of the above gestures are touch-activated, gestures can potentially use any type of input such as key events or sensor data. You can use the QGestureRecognizer framework to register new custom gesture types.
While gesture events are mainly meant for application consumption, the MeeGo Touch UI design guidelines specify some default actions based on gestures. Unless the application developer overrides the behaviour, gestures may be consumed by the framework itself in the following cases:
While some of the gestures mentioned above (such as pinch) are implemented using multipoint touch events, by itself multipoint touch merely refers to the capability of detecting several fingers on the screen at once. Multipoint touch events are also directly accessible by applications in a low-level form comparable to mouse and key presses and releases, where the actual interpretation of the events is left entirely up to you. Note: Multipoint touch requires special hardware to function, since many touch input devices are not capable of detecting multiple touch points at once.
In Qt, multipoint-touch input is delivered through the QTouchEvent class, through which it is possible to determine all the currently touched screen points.
Note: Since multipoint touch events are not delivered to widgets by default, the delivery must be explicitly enabled with the QGraphicsItem::setAcceptTouchEvents method.
You can simulate the multipoint touch pinch gesture without real multipoint-touch hardware, for example, in a development environment on a standard PC. Simply hold down the <Ctrl> key on the keyboard, then press and drag with the left mouse button.
MeeGo Touch provides several event handlers for gestures:
Gestures are not delivered to widgets by default, gesture delivery is enabled by the QGraphicsObject::grabGesture method.
MeeGo Touch currently replaces some of the default Qt gesture recognizers with versions capable of interpreting regular mouse events in addition to the touch events used by Qt. Pan and swipe are also one-finger gestures in MeeGo Touch, while they are two- and three-finger gestures, respectively, in Qt (as of version 4.7).
The examples/gestures directory of the MeeGo Touch source contains a sample application demonstrating proper use of gestures combined with MeeGo Touch widgets. The example is a gallery application, where pinching zooms and rotates the picture simultaneously, while swiping left or right changes the picture.
The example below illustrates the following:
Below is the example code relevant to the gestures:
|Copyright © 2010 Nokia Corporation||Generated on Thu Feb 24 06:02:51 2011 (PDT) | <urn:uuid:a46cea14-414d-430d-a5b7-f8bc77b80b3d> | 3.046875 | 732 | Documentation | Software Dev. | 23.561396 |
A giant impact from an asteroid or comet can ruin your whole day. Or year. Or, if you’re a dinosaur, your existence.
So astronomers do what they can to understand this menace from space. We look for rocks on orbits that intersect ours, we think about ways of moving them out of the way should we find one, and we also think about the record we do have of past impacts to see what we can learn from them.
There are about 180 impact craters known on our planet, ranging from tens of millennia in age to billions of years. They also vary in size from a few kilometers across to monsters so big they can only be detected from space. Sometimes it’s hard to measure their size (they can have multiple concentric rings, or be underground — covered up due to extreme age — making definite sizes hard to figure out) or hard to get their age. But we do have some statistics on them, and there have been many studies about them.
A big question is: are impacts periodic? That is, do they happen with some repeating period? If so, then there must be some astrophysical cause: a giant planet in the outer solar system, for example, that shakes loose comets every 50 million years, or the Sun passing near another star. This has been studied, and all kinds of periods have been found in the data. I’ve always been a little skeptical of them, since the data are sparse. And now it looks like my thoughts are being supported: a new study finds no such pattern in the ages of craters, and concludes all the periods found previously are probably due to errors in the analyses. | <urn:uuid:aae3c6ad-cb86-45b3-93de-819cbd773f6b> | 4.09375 | 341 | Personal Blog | Science & Tech. | 59.436494 |
1. CJM 2007 (vol 59 pp. 1008)
|Ideas from Zariski Topology in the Study of Cubical Homology |
Cubical sets and their homology have been used in dynamical systems as well as in digital imaging. We take a fresh look at this topic, following Zariski ideas from algebraic geometry. The cubical topology is defined to be a topology in $\R^d$ in which a set is closed if and only if it is cubical. This concept is a convenient frame for describing a variety of important features of cubical sets. Separation axioms which, in general, are not satisfied here, characterize exactly those pairs of points which we want to distinguish. The noetherian property guarantees the correctness of the algorithms. Moreover, maps between cubical sets which are continuous and closed with respect to the cubical topology are precisely those for whom the homology map can be defined and computed without grid subdivisions. A combinatorial version of the Vietoris-Begle theorem is derived. This theorem plays the central role in an algorithm computing homology of maps which are continuous with respect to the Euclidean topology.
Categories:55-04, 52B05, 54C60, 68W05, 68W30, 68U10 | <urn:uuid:cb94b961-48fa-499a-80a5-dec465b18b75> | 2.734375 | 272 | Academic Writing | Science & Tech. | 40.140024 |
Nature has a special issue on Earth monitoring out tonight.
Nearly fifty years ago —things were up and running by March 1958 — Charles Keeling and colleagues began a series of measurements of atmospheric CO2 on Mauna Loa in Hawaii. The results, made graphic in the jagged ‘Keeling curve’ running across this week’s cover, made the world take notice — eventually. The Mauna Loa measurements constitute the longest continuous record of atmospheric CO2 in the world. The steady rise in CO2 that they record now forms the accepted backdrop to today’s climate science and economic and political decision making. As well as being an important resource in itself, the Mauna Loa record highlights the vital importance of Earth monitoring programmes. The fiftieth anniversary of the start of this work is marked in this issue by News Features and other pieces on the Earth monitoring being done today, historical pieces on the Mauna Loa data and more.
I’ve a long futuristic article in the special looking at how close we might be to a totally monitored Earth by 2025: Earth Monitoring: The planetary panopticon
Nature itself has an great editorial — Patching together a world view — which provides a great big picture view, that I’d have struggled to write, so kudos to my colleagues who did such a good job of capturing succintly such a vast topic.
Alex Witze then contrasts my upbeat forecast with the lack of leadership of, and the disarray in, the US’s current Earth monitoring programmes — Earth Observation: Not enough eyes on the prize.
And the journalistic content doesn’t stop there: there are also features on:
Earth Monitoring: Observing the ocean from within
Earth Monitoring: The crucial measurement
And to finish it all off there are two Commentaries by scientists
Earth monitoring: Cinderella science
Earth monitoring: Vigilance is not enough
And an online version of all is here, including a timeline of Earth monitoring.
The UK National Institute for Environmental eScience (NIEeS) recently organized a scientific workshop at Cambridge University on environmental research applications of Google Earth and other virtual globes; some of the presentations are now available online here.
Nature recently published an Editorial “Millennium development holes” on problems with the underlying data used to assess progress to the goals.
Every year, the UN rolls out reports with slick graphics, seemingly noting with precise scientific precision progress towards the goals. But the reports mask the fact that the quality of most of the underlying data sets is far from adequate. Moreover, the indicators often combine very different types of data, making aggregation and analysis of the deficient data even more complicated.
There are decent data for just a handful of indicators, such as child mortality, but for most of the 163 developing countries, many indicators do not even have two data points for the period 1990–2006. And few developing countries have any data for around 1990, the baseline year. It is impossible to estimate progress for most of the indicators over less than five years, and sparse poverty data can only be reliably compared over decades.
Meanwhile, here are links to a few of my recent articles:
Barely a month after Google Earth made the front cover of Nature, computing is back on the cover again. Tomorrow’s issue contains a big special on the future of scientific computing. All the articles are free, thanks to sponsorship from Microsoft; the special was produced in conjunction with the 2020 report published today by an international group of experts convened by Microsoft. The special is, however, of course completely editorially-independent of Microsoft
The special, by journalists and top computing experts, looks at some of the key emerging technologies and concepts that look set to have a major impact on scientific computing by 2020. I’ve a three pager on “sensor webs†– “2020 computing: Everything, everywhere†— in it; there is also a short pop-up box — “Batteries not included” — on the problems of powering these small remote devices. | <urn:uuid:aa2f7bca-2ca3-4c31-baef-32a16aead6ea> | 3.1875 | 853 | Personal Blog | Science & Tech. | 27.098651 |
Boffins have reconstructed how a 47-million-year-old moth fossil looked while alive: a psychedelically-coloured insect whose wings both camouflaged it and warned away predators. fossil_moth An artist's impression of the original colours of the moth. Credit: McNamara, ME et al. PLoS Biology The moth once had yellow, green, …
"The fossil's closest modern-day relatives ... produce hydrogen cyanide."
Thank you, I missed that.
Day Glo helped it warn off predators???
Obviously it did not work out to well if it is extinct now is it?
Ah but it did...
> Obviously it did not work out to well if it is extinct now is it?
Ah but it did. Over the intervening 47m years, that moth has evolved into the day-glo jacketed motorway construction worker.
Thanks for the heads up.
I didn't realise that the day-glo jacketed motorway construction worker was toxic to eat. Guess I'll just have to find something else for lunch.
Just add garlic...
... and even day-glo jacketed motorway construction workers become palatable.
"“Biology is unpredictable. The moths may have been doing what their relatives are doing today, or they may have been doing something totally different,” she said."
Translated means "I'm guessing". Typical nonsense expected of the believer in Evolution. | <urn:uuid:9723b9b1-33a8-408b-911c-0e9bf2bf5c80> | 3.203125 | 299 | Comment Section | Science & Tech. | 62.653554 |
This post assumes familiarity with some basic concepts in abstract algebra, specifically the terminology of field extensions, and the classical results in Galois theory and group theory.
The fundamental theorem of algebra has quite a few number of proofs (enough to fill a book!). In fact, it seems a new tool in mathematics can prove its worth by being able to prove the fundamental theorem in a different way. This series of proofs of the fundamental theorem also highlights how in mathematics there are many many ways to prove a single theorem, and in re-proving an established theorem we introduce new concepts and strategies. And perhaps most of all, we accentuate the unifying beauty of mathematics.
Problem: Let be a non-constant polynomial. Prove has a root in .
Solution: Without loss of generality, we may assume has real coefficients, since if has no roots, then neither does , where the bar represents complex conjugation. In particular, is invariant under complex conjugation, and all such quantities are real.
Let be the splitting field for over , and embed in some algebraic closure of . Consider the extension . We claim is Galois over ; indeed, it is the splitting field of the separable polynomial constructed as the square-free part of , i.e., the product of all linear factors of that polynomial.
Let be the Galois group of this extension over , and note that since , we have an intermediate field , so that the degree of the extension is 2; so 2 divides the degree of , and hence the order of the Galois group (recall for any Galois field extension).
Since , there is a Sylow 2-subgroup , which by Sylow’s theorem has odd index in . By the Galois correspondence, corresponds to an intermediate field extension of odd degree (the degree is equal to the index of the subgroup ). Since every real polynomial of odd degree has a root in (recall the intermediate value theorem), we see that there are no irreducible polynomials of odd degree , and hence there can be no separable extensions of degree (in particular, every such extension is finite and separable, and all such extensions are simple: the minimal polynomial of the singly-adjoined element must be irreducible). Hence, the degree of over must be 1, i.e. is a trivial extension.
Taking this back to the group, since the index by the Galois correspondence, we have , and hence has order for some . We note that since , is a Galois extension of . In particular the automorphism group is a subgroup of , and hence has order for some dividing . We will show that , which occurs precisely when the extension is trivial (again, by virtue of being a Galois extension).
If , then we recall the corollary of Cauchy’s theorem for -groups, that has a subgroup of order for any , and in particular a subgroup of index 2. But such a subgroup corresponds to an intermediate field extension of degree 2. As with the case for odd extensions of , we note that there are no irreducible polynomials of degree 2 over : we have the sing-a-long quadratic formula which constructs the roots in . So , and hence is the splitting field of , and contains all of its roots. | <urn:uuid:efcdf7d2-ef71-4db2-a361-5d5275b467cf> | 2.890625 | 704 | Personal Blog | Science & Tech. | 47.926427 |
Fire’s been part of the Australian ecosystem for probably about 30 million years. It’s been a long time and it’s gone hand in hand in the development of our unique fauna and flora. So our eucalypts, our acacia flora for example, basically started to spread across the continent when fire became more common.
The dry forests of Victoria are largely in foothill sort of country, so the foothills are areas where we get reasonably high rainfalls which means their fairly rich in fauna and flora in those areas. But they also get subjected to seasonal drought conditions and it is in those dry conditions that we tend to get more fires occurring. And one of those things that probably often missed is that fire creates an opportunity for regeneration of particularly the plant species but it needs to be fire with a certain pattern and distribution across the landscape.
Some fires, they’re so intense and so large, that they create a long term structural change to the environment. So large intense fires can be a part of the process but they might be one in a 100 year, one in 200 year type event, where as if they start to occur every 20 years we totally change the structure and even the species composition.
What we’ve been seeing in recent times we’re seeing an increase in the frequency of drought, but we’re also seeing increased moisture in summer but that moisture not resulting in a lot of rain and a lot of run off and a lot of soil wetting, it’s actually increasing the amount of lightening activity we get, and lightening is a natural source of ignition of bushfires. So that’s really quite important because a lot of lightening actually occurs in quite remote areas and whilst lightening fires might only start about a third of the fires they actually burn about three quarters of the area that actually burnt by wildfires.
So when we’re talking about climate change it’s not a gradual process, we actual see a very rapid transition from one state to another, so we’re starting to see more fire, more fire in remote areas, and those fires are tending to be larger because of the drought conditions we’re subjected to. | <urn:uuid:5aa2485d-34ce-4cbd-bd88-b3118726db08> | 3.59375 | 459 | Audio Transcript | Science & Tech. | 36.501739 |
Threats to Sharks
Despite their superior physiology and hunting skills, many shark species are now threatened with extinction due to human fishing. The main threats to sharks are over-fishing and accidental bycatch. In many parts of the world, sharks are in very high demand, for their meat, skin and cartilage, which is used in several medicines. These shark products sell at very high prices, making them an attractive catch to fishermen.
Sharks mate only rarely and have a relatively small number of shark pups at a time. Consequently, they can't replenish their population quickly. Sharks also have fairly long lifespans -- on average, sharks live 25 to 30 years. According to Andy Dehart, Director of Biological Programs at the National Aquarium and shark expert for Discovery Communications, sharks can live up to 60 years, with the spiny dogfish reaching 70 to 100 years. If left alone, a female will mate many times in its life. With this reproductive pattern, the death of every single shark obviously has a significant effect on the shark population.
Over-fishing is actually a problem for both sharks and humans. If humans kill too many sharks in a given amount of time, the population will dwindle and they won't be able to catch many sharks in the future. The only way to maintain profitable shark fishing over time is to allow sharks to continue to reproduce, which means decreasing shark fishing significantly. Sharks are also killed accidentally, primarily by long lines used to catch other fish. Researchers suggest we must ban certain fishing methods, or some shark species will die out at some point in the near future.
One major obstacle to conservation efforts is our ignorance about sharks. We still don't fully understand their behavior, their breeding habits or their migration patterns. For most shark species, we don't even have an idea of their population size. This makes it very difficult to organize effective conservation methods since we can't accurately calculate safe fishing restrictions.
Sharks have persevered for hundreds of millions of years, while thousands of other animals have come and gone. When you consider this incredible history, and the unique physiological characteristics found in sharks, it's clear that it would be a great tragedy to lose any shark species. They are among the most remarkable animals on earth, and there is still so much we don't know about them.
For a summary of what you've read in this article, check out the next page. | <urn:uuid:fc55d62d-3fda-4f0a-8c69-295ba00be188> | 3.546875 | 494 | Knowledge Article | Science & Tech. | 46.200195 |
Learn more physics!
Do (or can) anti-protons form nuclei and has this ever been done. Does (or would) the strong nuclear force hold the anti-protons together?
- Mike Strobach (age 48)
The answer is yes. Anti-deuterons, which consist of an anti-proton and an anti-neutron, were first observed in 1965 by a group from Columbia University. See: http://prl.aps.org/abstract/PRL/v14/i24/p1003_1
. More recently both anti-helium3
have been observed.
(published on 04/18/2011)
Follow-up on this answer. | <urn:uuid:197f0450-0c47-4bdf-87ff-b1e84ee14d8a> | 2.6875 | 151 | Q&A Forum | Science & Tech. | 77.42519 |
New tools to measure carbon caught in windbreak trees
Trees are great! That's pretty much a given in the green world, but scientists haven't - until now, been able to asses how well they work as windbreaks in agriculture, improving yields and storing carbon.
American farmers already use windbreaks. They take up a small amount of land, help to protect both crops and livestock from a battering and keep a check on soil erosion too. Not only that, but trees are great ways of capturing carbon, thus reducing the amount of the greenhouse gas that agriculture pumps into the environment.
While many of the benefits are well-known and common sense, there has been no measurement of the carbon capture they achieve.
James Brandle, a University of Nebraska-Lincoln professor, has examined the problem. He says that trees grown in the narrow windbreak plantations most often used behave differently to natural woodlands and has designed a computer tool to measure their impact.
With fellow scientists from University of Florida, University of Kansas, University of Nebraska and the USDA National Agroforestry Centre (NAC) Brandle publishes the results of his work in the new edition of the Journal of Environmental Quality.
Top Image Credit: © Piotr Sikora | <urn:uuid:20d2905e-ac2e-44c0-9948-f7bf5722d0bf> | 3.734375 | 255 | Truncated | Science & Tech. | 36.800434 |
Purpose: To compare the amount of Carbon Dioxide (CO2) in four different sources of gases.
(Enough for each team of two or four students)
5 vials or test tubes
A graduated cylinder
A funnel straw
A marble-size piece of modeling clay
4 different colored balloons
A narrow-necked bottle (the neck should be narrow enough for a balloon to fit over it)
A dropping bottle of bromthymol blue indicator solution
A dropping bottle of dilute household ammonia (1 part ammonia to 50 parts distilled water)
100 mL vinegar
5 mL baking soda
Safety goggles for wear at all times
Teacher's Lab Notes:
The students will be filling balloons with pure carbon dioxide, exhaled air, and ambient air. For safety reasons, you should fill the balloons with automobile exhaust. You should wear thick gloves to protect your hands from being burned. Fill the balloons in an open area and when a slight breeze is blowing to keep the exhaust gases away from your face. Place a balloon over the narrow end of a metal funnel and place the wide end of the funnel over the exhaust pipe of a running car. When inflated, the balloons should be about 7.5 cm in diameter. It may be easier to overinflate the balloon and then let a little gas escape. Twist and tie the balloon. Repeat the procedure with the same color balloon until you have one for each lab group.
The ambient air solution in vial A will not turn yellow. The level of CO2 in ambient air is too low to affect bromthymol blue.
Students will need around 60 drops of the diluted ammonia to neutralize the solution in vial D (vinegar-baking soda reaction). The other two vials should require between 7 and 40 drops. Caution students to add the drops slowly and shake solutions between drops so they can get a careful record of when the color changes back to the same color blue as the control.
Since the students will have to add a relatively large amount of ammonia to the solution in vial D, the color of this sample may be affected by dilution. To equalize this effect, you can have students add some water to the other samples to make the volume in each sample equal. This is easiest to do if sample D is titrated last.
1. Add 15 mL of water and 10 drops of bromthymol blue indicator solution to each vial or test tube. Label the vials A, B, C, D, and Control.
2. Fill each balloon until it has a 7.5 diameter.
Sample A (Ambient Air) - Use a tire pump to inflate the balloon to the required diameter. Twist the rubber neck of the balloon and fasten it shut with a twist tie. The tie should be at least 1 cm from the opening of the balloon. Record the color of the balloon used for this sample.
Sample B (Human Exhalation) - Have one team member blow up a balloon to the required diameter. Twist and tie the balloon, and record balloon color.
Sample C (Automobile Exhaust) - Your teacher will supply you with this balloon. Record the color.
Sample D (Nearly pure CO2) - Put 100 mL of vinegar in the narrow-necked bottle. Using a funnel, add 5 mL of baking soda. Let the mixture bubble for 3 seconds to drive the air out, then slip the balloon over the neck of the bottle. Inflate the balloon to the proper diameter. Twist, tie, and record the color.
3. Soften the clay and wrap it around one end of the straw to make a small airtight collar that will fit into the neck of a balloon. The collar should look like a cone with the straw in its middle, and should be large enough to plug the neck of the balloon.
4. Pick up Balloon A. Keeping the tie on it, slip the balloon's neck over the clay collar and hold it against the collar to make an airtight seal. Place the other end of the straw into the vial of water and bromthymol blue labelled A. Have another partner remove the tie on the balloon and slowly untwist the balloon. Keeping the neck of the balloon pinched to control the flow of gas, gently squeeze the balloon so the gas slowly bubbles through the solution.
5. Repeat the same procedure with the other balloons and their respective vials. In some cases, the bromthymol blue solution will change color, from blue to yellow, indicating the presence of carbonic acid formed from CO2.
6. Analyze each of the samples by titrating them with drops of dilute ammonia. Ammonia neutralizes the carbonic acid. The bromthymol blue will return to a blue color when all the acid has reacted. Add drops of ammonia to each of the samples that turned yellow, carefully counting the number of drops needed until they are about the same color as your control. Record the results.
Post Lab Discussion:
Make a chart on the board to pool each group's results. Ask the students which samples had the most and the least carbon dioxide. Why didn't the ambient air sample not turn yellow? (The test isn't sensitive enough to detect low concentrations of CO2.) Carbon dioxide is a natural part of our atmosphere, but too much CO2 could make the Earth warmer through an increased greenhouse effect. Why is automobile exhaust a concern? What ways could you reduce the amount of CO2 you create? How could a city reduce the amount of CO2 they emit? What's more important, to develop and adapt cars with a new fuel that's safe for the environment or to improve public transportation systems? What alternative power sources could be used with cars? (Solar, electric, methanol.) Why might it be difficult for the public to start using an alternative source? (Car industry not mass-producing new cars, expense of buying new car, less power/speed than gas- powered car.)
This activity is used with the permission of Climate Protection Institute and the Global Systems Science (GSS) project at Lawrence Hall of Science, University of California, Berkeley. To receive more information about GSS and other activities visit www.lawrencehallofscience.org/gss. This activity originally appeared in The Science Teacher, May 1989. | <urn:uuid:d8da42a5-f267-4efa-b00b-3bb13f631a5b> | 3.75 | 1,312 | Tutorial | Science & Tech. | 64.324402 |
Solar Power from Satellites
The sun powers the biosphere, which is to say that the energy used by almost all plants and animals comes from the sun. So why not use solar energy to power industry, transportation, and the home as well? Well, a principal difficulty with solar power is that the sun doesn't always shine on a particular location: half the time the earth blocks the sun, and for much of the remaining time clouds and fog do. But what if the solar energy were collected by a set of satellites above the earth’s atmosphere? Then we might obtain solar power for 24 hours every day of the year. This is the idea behind solar-power satellites.
A satellite with solar panels to convert light energy into electricity can be put into orbit. Indeed, most satellites in orbit today are powered by solar panels. But how can we get the energy from the satellite back to earth? Clearly it would be impossible to use the electric lines we use for long-distance power transmission on earth. This is where microwaves come in.
This drawing shows how power collected by solar-power satellites might be beamed to a receiving antenna on Earth. The antenna would convert the energy back into electrical current, which would be fed into the power grid. Courtesy: Space Studies Institute.
The idea is that a satellite be equipped with a microwave generator, so that the electrical energy from the solar panels can be converted into a microwave beam. Then the microwave beam can be directed to antennas on the surface of the earth, which would convert the microwaves back to electrical energy. The energy could then either be used at the site of the antenna or injected into the electric-power network.
It was during the late 1960s that the engineer Peter Glaser first had the notion of solar power satellites. The principle of transmitting power by microwaves had already been demonstrated, though not put into practice. (Microwaves in practical devices, such as radar systems and long-distance telephone relays, were used to convey information.) To convey information, the intensity of the received signal need only be less than one nanowatt (one billionth of a watt). Glaser’s idea was to put the solar-power satellites in geosynchronous orbits, so that each would hover over a single location on the earth. This meant, however, that the satellites had to be very high (36,000 kilometers or about 22,000 feet), and this in turn meant that the antenna on the satellite and the receiving antenna on the ground had to be extremely large (a kilometer or more in diameter). The idea did not seem practical, and after some initial funding by the U.S Department of Energy and NASA there was little interest in pursuing the technology.
Today, however, the situation is changed because of the very large number of communications satellites in low orbits. It might be possible to make these satellites dual purpose—solar-energy collectors as well as communications devices. Because of the much lower orbits, the antennas on the satellites and on the ground need not be nearly so large. A drawback however, is that satellites in low-earth orbit circle the earth rapidly (about every 90 minutes) and therefore do not provide a connection for a very long time. There are also other concerns. One is that the transmission down to the ground might be interrupted by clouds and weather. Another is the safety of the people and animals near the receiving antennas who might be exposed to the microwave radiation. Today, the viability of solar-power satellites as a long-term solution to our energy needs is being investigated by government agencies and individual companies in many countries. | <urn:uuid:a548f51f-5a94-42ac-8994-fedef7b3f7a2> | 3.953125 | 737 | Knowledge Article | Science & Tech. | 40.817727 |
The following story is contributed by the Florida Museum of Natural History, one of Natural History magazine’s Museum Partners. Members of any of our partner organizations receive Natural History as a benefit of their museum membership. At the Florida Museum of Natural History, visitors may enjoy hundreds of exotic butterflies in a rainforest setting, witness a South Florida Calusa Indian welcoming ceremony, experience a life-sized limestone cave, and see a mammoth and mastodon from the last Ice Age. Permanent exhibits include Northwest Florida: Waterways & Wildlife; South Florida People & Environments; Florida Fossils: Evolution of Life & Land; and the McGuire Center for Lepidoptera and Biodiversity, which features the screened, outdoor Butterfly Rainforest exhibit with hundreds of live butterflies. Located at the University of Florida, in Gainesville, this is Florida’s state museum of natural history, dedicated to understanding, preserving and interpreting biological diversity and cultural heritage. For further information, visit the Museum’s Web site, www.flmnh.ufl.edu.
The largest snake the world has ever known—as long as a school bus and as heavy as a small car—ruled tropical ecosystems only 6 million years after the demise of the fearsome Tyrannosaurus rex, according to a new discovery published in the journal Nature.
Partial skeletons of a new giant, boa-constrictor-like snake named Titanoboa found in Colombia by an international team of scientists and now at the Florida Museum of Natural History are estimated to be 42 to 45 feet long, the length of the T-rex “Sue” displayed at Chicago’s Field Museum, said Florida Museum of Natural History vertebrate paleontologist assistant curator Jonathan Bloch, who co-led the expedition with Carlos Jaramillo, a paleobotanist from the Smithsonian Tropical Research Institute in Panama.
“Truly enormous snakes really spark people’s imagination, but reality has exceeded the fantasies of Hollywood,” said Bloch, who is studying the snake. “The snake that tried to eat Jennifer Lopez in the movie Anaconda is not as big as the one we found.”
Jason Head, a paleontologist at the University of Toronto in Mississauga and the paper’s senior author, described it this way: “The snake’s body was so wide that if it were moving down the hall and decided to come into my office to eat me, it would literally have to squeeze through the door.”
Besides tipping the scales at an estimated 1.25 tons, the snake lived during the Paleocene Epoch, a 10-million-year period immediately following the extinction of the dinosaurs 65 million years ago, Bloch said.
The scientists also found many skeletons of giant turtles and extinct primitive crocodile relatives that likely were eaten by the snake, he said.
“Prior to our work, there had been no fossil vertebrates found between 65 million and 55 million years ago in tropical South America, leaving us with a very poor understanding of what life was like in the northern Neotropics,” he said. “Now we have a window into the time just after the dinosaurs went extinct and can actually see what the animals replacing them were like.”
Size does matter because the snake’s gigantic dimensions are a sign that temperatures along the equator were once much hotter. That is because snakes and other cold-blooded animals are limited in body size by the ambient temperature of where they live, Bloch said.
“If you look at cold-blooded animals and their distribution on the planet today, the large ones are in the tropics, where it’s hottest, and they become smaller the farther away they are from the equator,” he said.
“Based on the snake’s size, the team was able to calculate the mean annual temperature at equatorial South America 60 million years ago was about 91 degrees Fahrenheit, about 10 degrees warmer than today.” Bloch said.
The presence of outsized snakes and freshwater turtles shows that even 60 million years ago the foundations of the modern Amazonian tropical ecosystem were in place, he said.
Fossil hunting is usually difficult in the forest-covered tropics because of the lack of exposed rock. But excavations in the Cerrejon Coal Mine in Northern Colombia exposed the rock and offered an unparalleled opportunity for discovery, Bloch said.
After the team brought the fossils to the Florida Museum of Natural History, it was UF graduate students Alex Hastings and Jason Bourque who first recognized they belonged to a giant snake, Bloch said. Head, an expert on fossil snakes, worked with David Polly, a paleontologist at the University of Indiana, to estimate the snake’s length and mass by determining the relationship between body size and vertebral—backbone—size in living snakes and using that relationship to figure out body size of the fossil snake based on its vertebrae.
Harry W. Greene, a professor in the department of ecology and evolutionary biology at Cornell University and one of the world’s leading snake experts, said the “colossal” ancient boa researchers found has “important implications for snake biology and our understanding of life in the ancient tropics.”
“The giant Colombian snake is a truly exciting discovery,” said Greene, who wrote the book Snakes: The Evolution of Mystery in Nature. “For decades herpetologists have argued about just how big snakes can get, with debatable estimates of the max somewhat less than 40 feet.” | <urn:uuid:1774e5be-5287-4548-8d0a-6ca69620c90c> | 3.140625 | 1,158 | Truncated | Science & Tech. | 26.52697 |
I'm confused, a negative number with an exponent (exponentiation), will first have the exponent evaluated, and then have the opposite applied, ie. -2^2 = -4
However, if the negative number is enclosed with parentheses, (-2)^2, that indicates (-2) x (-2) = 4
So my question, when finding points for graphing a parabola, it appears from the examples I have studied that any negative values for x^2 always come out positive when evaluated in the quadratic equation, but there are no parentheses enclosing that value.
f(x) = ax^2 + bx + c
f(-2) = -2^2 + 4(-2) + 3 = -9, but all the examples that I study would evaluate this as f(-2) = (-2)^2 + 4(-2) + 3 = -1. But the parentheses are not shown, what rule or concept am I missing?
Thanks in advance. | <urn:uuid:138a3b8c-0e08-4469-bb26-c402c28f464a> | 3.5 | 209 | Q&A Forum | Science & Tech. | 60.363333 |
Deterministic Quantum-State Teleportation Achieved With High Fidelity
Teleportation, the transfer of quantum states between widely separated atoms, was achieved by different research teams in Austria and the United States.
(From Teleportation Setup)
...it has been shown that the entangling properties of quantum mechanics, in combination with classical communication, allow quantum-state teleportation to be performed. Teleportation using pairs of entangled photons has been demonstrated, but such techniques are probabalistic, requiring post-selection of measured photons. Here, we report deterministic quantum-state teleportation between a pair of trapped calcium ions. Following closely the original proposal, we create a highly entangled pair of ions and perform a complete Bell-state measurement involving one ion from this pair and a third source ion. Site reconstruction conditioned on this measurement is then performed on the other half of the entangled pair. The measured fidelity is 75%, demonstrating unequivocally the quantum nature of the process."
(From Deterministic Quantum-State Teleportation With Atoms)
For an early example of sf teleportation, see the transo from Clifford Simak's 1961 novel Time is the Simplest Thing. For an example of wireless communication at a distance (since quantum teleportation is really a transfer of information), see hyperwave relay from Isaac Asimov's classic Foundation, published in 1951.
See the related article The Latest In Quantum-Dot Switches. Read the original article in Nature at Deterministic Quantum-State Teleportation With Atoms and
Deterministic quantum teleportation. Story from BBC at Teleportation breakthrough made.
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diagram on the right is a simplified version of the pathways, transformations,
and chemical species in a marine mat sulfur cycle. Thickness of
the arrow depicts relative abundance.
1) Sulfate that diffuses into a mat is reduced
to hydrogen sulfide (H2S) by sulfate-reducing bacteria (SRB).
2) Some sulfate is assimilated by organisms to form
cell components such as amino acids and cofactors.
3) Upon mineralization, organic sulfur is converted
4) H2S is transformed to elemental sulfur and
5) then to SO42- by sulfide oxidizing bacteria such
as Beggiatoa sp.
6,7) Anoxygenic phototrophic bacteria also convert
H2S to SO42- via elemental sulfur.
8) Elemental sulfur may be transfomred back to H2S
by sulfur reducing bacteria such as Desulfuromonas spp.
9) Some H2S complexes with iron to form black FeS | <urn:uuid:8cd67a53-f7af-40d2-a4a4-36a90e23a819> | 3.421875 | 213 | Knowledge Article | Science & Tech. | 37.657308 |
In 2012, a survey by the Chesapeake Bay Program found the Bay had 48,191 acres of submerged aquatic vegitation (SAV), or underwater grasses,down from the 72,935 acres estimated by data gathered in 2004. This is just 26 percent of the 185,000-acre goal for the Bay and its tidal tributaries, down from 39 percent in 2004. Extreme weather conditions in recent years have contributed to the decrease.
|Bay Grasses Distribution Used to Set the Restoration Goal in 2003
||Bay Grasses (SAV) Restoration Goal Achievement 2010-2012
|Download PDF (1.86 MB)
||Download PDF (1.86 MB)
The Chesapeake Bay Program has created an online mapping tool that shows how the Bay's underwater grasses have changed in location, abundance, and species over the last 30 years. Find the map at http://www.chesapeakebay.net/visualization/baygrasses/
Learn more about Bay grasses | <urn:uuid:d2cfb1ec-5ce8-42aa-b1a9-a7b5f7b22f28> | 3.46875 | 204 | Knowledge Article | Science & Tech. | 64.163642 |
An INSERT statement creates a row or rows and stores them in the named table. The number of values assigned in an INSERT statement must be the same as the number of specified or implied columns.
Whenever you insert into a table which has generated columns, Derby calculates the values of those columns.
INSERT INTO table-Name [ (Simple-column-Name [ , Simple-column-Name]* ) ] Query [ ORDER BY clause ] [ result offset clause ] [ fetch first clause ]
Single-row and multiple-row VALUES expressions can include the keyword DEFAULT. Specifying DEFAULT for a column inserts the column's default value into the column. Another way to insert the default value into the column is to omit the column from the column list and only insert values into other columns in the table. For more information, see VALUES expression.
The DEFAULT literal is the only value which you can directly insert into a generated column.
When you want insertion to happen with a specific ordering (for example, in conjunction with auto-generated keys), it can be useful to specify an ORDER BY clause on the result set to be inserted.
If the Query is a VALUES expression, it cannot contain or be followed by an ORDER BY, result offset, or fetch first clause. However, if the VALUES expression does not contain the DEFAULT keyword, the VALUES clause can be put in a subquery and ordered, as in the following statement:
INSERT INTO t SELECT * FROM (VALUES 'a','c','b') t ORDER BY 1;
For more information about Query, see Query.
INSERT INTO COUNTRIES VALUES ('Taiwan', 'TW', 'Asia') -- Insert a new department into the DEPARTMENT table, -- but do not assign a manager to the new department INSERT INTO DEPARTMENT (DEPTNO, DEPTNAME, ADMRDEPT) VALUES ('E31', 'ARCHITECTURE', 'E01') -- Insert two new departments using one statement -- into the DEPARTMENT table as in the previous example, -- but do not assign a manager to the new department. INSERT INTO DEPARTMENT (DEPTNO, DEPTNAME, ADMRDEPT) VALUES ('B11', 'PURCHASING', 'B01'), ('E41', 'DATABASE ADMINISTRATION', 'E01') -- Create a temporary table MA_EMP_ACT with the -- same columns as the EMP_ACT table. -- Load MA_EMP_ACT with the rows from the EMP_ACT -- table with a project number (PROJNO) -- starting with the letters 'MA'. CREATE TABLE MA_EMP_ACT ( EMPNO CHAR(6) NOT NULL, PROJNO CHAR(6) NOT NULL, ACTNO SMALLINT NOT NULL, EMPTIME DEC(5,2), EMSTDATE DATE, EMENDATE DATE ); INSERT INTO MA_EMP_ACT SELECT * FROM EMP_ACT WHERE SUBSTR(PROJNO, 1, 2) = 'MA'; -- Insert the DEFAULT value for the LOCATION column INSERT INTO DEPARTMENT VALUES ('E31', 'ARCHITECTURE', '00390', 'E01', DEFAULT) -- Create an AIRPORTS table and insert into it -- some of the fields from the CITIES table, with the airport -- codes sorted alphabetically CREATE TABLE AIRPORTS ( AIRPORT_ID INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY PRIMARY KEY, AIRPORT VARCHAR(3), CITY VARCHAR(24) NOT NULL, COUNTRY VARCHAR(26) NOT NULL ); INSERT INTO AIRPORTS (AIRPORT, CITY, COUNTRY) SELECT AIRPORT, CITY_NAME, COUNTRY FROM CITIES ORDER BY AIRPORT;
The INSERT statement depends on the table being inserted into, all of the conglomerates (units of storage such as heaps or indexes) for that table, and any other table named in the statement. Any statement that creates or drops an index or a constraint for the target table of a prepared INSERT statement invalidates the prepared INSERT statement. | <urn:uuid:d42cb93c-77c4-4cc6-b091-453ff7029eac> | 2.734375 | 873 | Documentation | Software Dev. | 27.515431 |