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|Feb3-08, 12:04 PM||#1|
What is Heat?
Written by Hootenanny. Edited by berkeman and Kurdt. Feel free to contact me with any questions, comments or corrections.
What is Heat?
One of the most frustrating misconceptions in Thermodynamics centres on the actual definition of heat. Many science/engineering students often refer to a body as to be possessing heat, but as we shall see, to do so is completely nonsensical.
We start by examining the first law and defining each of it’s terms. The first law is simply a statement of the principle of conservation of energy and is often stated thus;
[tex]\Delta U = Q + W[/tex]
Where [itex]\Delta U[/itex] is the change in internal energy, Q is the heat added to the system and W is the work done on the system. So what do all these terms actually mean?
We define the internal energy as the energy associated with the microscopic energies of system, that is with the energy associated with the random motion of the molecules within a system. So for a general fluid, the internal energy of a system is the sum of the translational kinetic energies, the rotational kinetic energies, the vibrational kinetic energies and the potential energies of all the molecules in that system. The internal energy of a system is often erroneously referred to as the heat of a system and we shall see why this is incorrect later. One important point to note here is that the internal energy is a state variable, that is, the change in internal energy between any two states is independent of the path taken.Work
Well, if you're reading this I assume that you know the definition of work; in thermodynamics work is usually associated with a transfer of energy into or out of a system. An example of work specific to thermodynamics would be the application of a force to a piston, which would then compress the gas within the cylinder, thus doing work on the gas. Since work is being done on the gas the W term in our expression would be positive. If we assume that the walls of the cylinder are adiabatic (no heat transfer) then all the work done would be converted to internal energy. Suppose that after we have compressed the piston, we release it. Intuitively, we would expect the piston to recoil back, and this is exactly what happens; the gas expands and does [an equal amount of] work on the piston against atmospheric pressure. In this case, since it is the gas that is doing work, our W term would be negative.Heat
So we have defined the internal energy of a system and we can quantify the work done on the system, but what about heat? First let us examine temperature. One useful definition of temperature is often called kinetic temperature and is derived from kinetic theory. Using kinetic theory the temperature of a system is taken to be a measure of the average translational kinetic energy associated with the random motion of the molecules with the system. It should be noted that although related to internal energy, temperature is not directly proportional to internal energy since internal energy also involves the rotational and vibrational kinetic energies and the potential energies of the constituent molecules.A note about Thermal Energy
Some texts make use of the term "thermal energy" when discussing the "translational kinetic energy" of the molecules, I personally find that the term "thermal energy" only serves to confuse discussions further.Further Reading
Thermal Physics, 2nd Edition, C.B.P. Finn
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Research Highlights : Physics
Smaller, cheaper and better
31 October 2008 (Volume 3 Issue 10)
A new design for compact free-electron lasers leads the way towards exploiting extremely short wavelengths
Figure 1: A view at the beam hall of the FEL test facility. The electron gun is contained in the grey box on the left.enlarge image
Physicists are greatly interested in free-electron lasers (FEL) because they are capable of generating high-intensity laser radiation across a very broad wavelength spectrum, even down to the extreme ultraviolet rays and x-rays. Worldwide, several multi-billion-dollar efforts are underway to build next-generation free-electron lasers at x-ray wavelengths. As part of these efforts, a compact and efficient design has been realized by researchers from the RIKEN XFEL Project Head Office, collaborating with the Japan Synchrotron Radiation Research Institute (JASRI). They report on the superior properties of extreme ultraviolet FEL laser radiation from a first-test system in Nature Photonics1.
Free-electron lasers consist of two fundamental components: an accelerator that produces high-energy electrons, and so-called ‘undulators’ that send these electrons on a periodically curved path. The wiggling of the electrons along the path causes the emission of high-energy laser radiation through electro-magnetic interaction between the electrons and the radiation field.
Currently, x-ray FELs require large-scale electron accelerators of a few kilometers in length. It is important to reduce this length to enable the fabrication of cheaper FEL systems. The project team’s compact FEL design of 55 m has produced a high-quality laser beam at the RIKEN Harima Institute.
To achieve this significant reduction in accelerator length, the team used special undulators with a shorter electron oscillation period, which allows the generation of x-rays with lower energy electrons. However, for this novel scheme to work effectively, “a stable and high-quality electron beam is needed, where all electrons propagate nearly parallel and with high density,” comments Hitoshi Tanaka from the team. To attain such good beam properties, the team used a 'thermionic electron gun' (Fig. 1), which has a CeB6 single crystal cathode. This type of cathode is commonly used as an electron emitter in the electron microscope.
The full system presently being constructed next to the SPring-8 storage ring will reach a total length of about 700 m, which is less than a third of the length of competing designs. This shorter length reduces the construction cost, which is estimated at 370 billion yen, compared to 750 and 1,500 billion yen, respectively, for international competitors.
A future aim of the researchers is to also realize FELs at much shorter wavelengths, down to the x-ray region at around 0.1 nm, which will enable new research applications. Indeed, Makina Yabashi from the research team is convinced that this can be achieved and that “the compactness of our design will considerably expand the opportunities for engineering and medical research.”
- Shintake, T., Tanaka, H., Hara, T., Tanaka, T., Togawa, K., Yabashi, M., Otake, Y., Asano, Y., Bizen, T., Fukui, T. et al. A compact free-electron laser for generating coherent radiation in the extreme ultraviolet region. Nature Photonics 2, 555–559 (2008). | article |
The corresponding authors for this highlight are based at the RIKEN XFEL Project Head Office | <urn:uuid:d5f2568d-8a66-4238-8d4f-150710cb7935> | 3.703125 | 752 | Academic Writing | Science & Tech. | 41.673701 |
Carbon is the sixth element on the periodic table, having six protons in its nucleus. The most common number of neutrons in its nucleus is also six and the Carbon-12 isotope is the basis for atomic weights, with the mass of the proton being defined as 1/12 of the mass of the Carbon nucleus.
The next most common isotopoe is Carbon-14 with 8 neutrons in the nucleus. C-14 is the isotope famous for its use in carbon radiometric dating techniques.
Carbon has two elemental forms, the more common of which is black graphite. Less common but probably far more well known is the diamond.
Carbon can form up to four covalent bonds with other elements. This property makes it highly suited for building long chains of atoms together. It is these chains that form the building blocks of life, primarily carbohydrates, lipids, proteins, nucleic acids and so forth.
Atomic mass: 12.0107 g/mol
Chemical symbol: C | <urn:uuid:c900371b-19dd-4269-a480-d1f9ab5476bc> | 3.90625 | 210 | Knowledge Article | Science & Tech. | 63.330767 |
Cirripedes (barnacles) are known for their sessility – it’s their defining characteristic. They count as one of the first model organisms of evolutionary biology, having been comparatively studied by Darwin for over 8 years (one would think they’re his favourite animals – although this letter says otherwise!). The 4 resulting monographs (two for Recent, two for fossil) are still some of the best examples of systematic biology done right (cf. Newman, 1987), and his experience working on them was extremely influential in setting his ideas on adaptation straight; among other things, it led to him stressing the importance of embryology for identification of possible homologies, laying the foundation for Haeckel’s expansion of that idea.
While they may be seen as a mindfuck taxon, it was actually recognised fairly early on, by surgeon J. Vaughan Thomson in 1830, that they were crustaceans, since they have a naupliar larva. This hasn’t been doubted since.
Systematically, cirripedes are a member of the Thecostraca, along with the Facetotecta and the Ascothoracida. Autapomorphic for the thecostracans is a second larval stage, the cypridoid, which comes between the nauplius and the adult. However, keep in mind that we currently have no clue where the Thecostraca fit in the crustacean system (Regier et al., 2005)
Cirripedes have several autapomorphies identifying them as a monophylum. These are taken and translated from the seminal Ax (1999). Cirripedes have three stages to their life cycle: the naupliar larva is planktonic and serves for dispersal, turning into a cypris larva that looks for a suitable substrate (with the help of compund eyes!) and attaches itself to it before metamorphosing into the adult (Høeg & Møller, 2006); each of these stages has its own set of autapomorphies.
Cuticular frontolateral horns, with glands at the tips. These are unique and allow immediate identification of a cirripede larva. Darwin (1854) wrongly suggested that they are homologous to other crustaceans’ primary antennae; this is false. They’re labelled as “fh” in the above SEMs, taken from the gorgeous Semmler et al. (2009) paper.
- Univalved dorsal carapace.
- First antenna modified to an attachment organ, with cement glands.
- Thoracomeres 6 and 7 fused. A penis attachment structure is found on the 6th thoracical segment, even though it should be on the 7th. Therefore, there was a fusion of the 6th and 7th segments. They’re followed by 2 abdominal segments and the telson with a furca.
- No feeding apparatus.
- Two segments visible from the outside: the capitulum (“head”) and peduncle (the attachment shaft), instead of seeing the actual body of the creature. Keep in mind that the capitulum includes part of the thorax, not just the head.
- Carapace fused ventrally into a sac. Only a slit remains for the cirri (feeding) and the penis.
- Calcareous plates. The standard is to have five plates: a dorsal carina, paired scuta and paired terga, but this can be modified.
- Thoracopods 1-6 modified to cirri, for filter-feeding.
- Thoracopod 7 modified into penis. It’s long and freely moveable.
- Reduced abdomen, most often to the point of complete absence.
Basically, to recognise the cirripedes by look is easy: if it’s sessile, enclosed in a house-like carapace, with feathery appendages sticking out of the top (cirri), it’s a cirripede. The lack of an abdomen is also unique, but not visible without dissection. The name-giving cirri develop from the cypris’s thoracopods and are recognisable as multisegmented hairy appendages. The setae are there to filter whatever is flowing in the current (organic particles, plankton).
Neuroanatomically, cirripedes are pretty interesting. The naupliar larva is standard and doesn’t have major differences from other crustaceans: there’s a tripartite brain, with a central protocerebrum, a deuterocerebrum controlling the primary antennae and a tritocerebrum for the antennules. The only divergence has to do with the innervation of the autapomorphic frontolateral horns, which are sensory structures – what they sense is still anyone’s guess though.
The cypris larva’s brain is pretty complex, befitting an animal with complex behaviour. Being the stage at which the cirriped chooses its final living space, it has to have multiple sensory systems to detect suitable sites. Harrison & Sandeman (1999) showed that they have the neural substrate needed to achieve this.
The interesting part comes with the metamorphosis to the adult, where the brain gets reduced (Gwilliam & Cole, 1979), a change undoubteably related to the sessile way of life (brain simplification is a trend observed in all suspension-feeders).
Cirripedes colonise hard substrates. These may be immobile (sea floor, rocks), or mobile – they’re known to foul ship hulls, or they can colonise the skin of wales (Coronula diadema) or the shells of marine turtles (Chelonibia testudinaria); back in the Cretaceous, some lived on ammonites (Ifrim et al., 2011). It doesn’t matter, as long as they can anchor themselves. Except for the parasitic Rhizocephala, all cirripedes are suspension-feeders.
We split the cirripedes into three groups: the Acrothroacica, the Thoracica and the Rhizocephala.
The Rhizocephala are the parasitics, mostly on decapods, but can also occur on stomatopods, peracarids and even other cirripedes. As is always the case with parasitism, these forms are even more derived than the already highly-derived cirripedian body plan (only the pentastomids rival them as the weirdest crustaceans). The adult is nothing more than a bag of reproductive organs anchored into the host by a system of roots – all organs, body structures, etc. are reduced. However, the presence of a naupliar larva confirms they are crustaceans, and the frontolateral horns on this larva confirms they are cirripedes.
The most well-known rhizocephalan is Sacculina carcini, a crab parasite. When the naupliar larva finds its host crab, it attaches on a joint and metamorphoses into the cypris, drilling through the crab’s cuticle and into the haemocoel. Here, it metamorphoses again into the vermigon, which is what the adult is called. From this point on, any resemblance to a cirripede disappears: the vermigon is a wormish thing that can swim, has no appendages, segments or organs (it only has four cell types!); it basically consists of only a thin epidermis and a ball of ovaries. The vermigon, swims to a specific site where it will stick out of the host crab to reproduce (Høeg, 1995).
The poorly-known Acrothoracica are unique in that they are plate-less, instead burrowing into living corals or inhabited gastropod shells. They are also suspension-feeders, and do not count as ectoparasites.
However, the bulk of the cirripedes are the regular Thoracica; if you’ve ever seen a cirripede (in tidal pools, on whales or ships, or as fossils are the most accessible ways to see them), it was most likely a thoracican.
If you’re lucky, you might catch them mating, which is an interesting act in itself. At reproduction time, the males stick out their penis, made really really long by turgor pressure, out over the substrate and move it around until they find a female. To help them out, the penis is equipped with many sensory structures and setae (see Klepal et al. (1972) for any details you want on their penis). Then they ejaculate. The human equivalent is to run blindly around and masturbate on the first woman you touch. (Don’t try this at home, you might hit your mother and you’ll end up a bunch of diseased inbreds like the British Royal Family. Do it in public just to be safe.)
Here’s a video of this. If you look closely, you’ll see that at several points, one of the cirri is longer than the rest. It goes beyond the crown, searching randomly and eventually going into other barnacles. That’s the penis, and every time that happens, it ejaculates.
And really, once that’s said, there’s nothing I can say to make cirripedes more interesting.
Ax P. 1999. Das System der Metazoa II.
Darwin C. 1854. A Monograph on the subclass Cirripedia, with figures of all the species.
Gwilliam GF & Cole ES. 1979. The morphology of the central nervous system of the barnacle, Semibalanus cariosus (Pallas). Journal of Morphology 159, 297-310.
Harrison PJH & Sandeman DC. 1999. Morphology of the Nervous System of the Barnacle Cypris Larva (Balanus amphitrite Darwin) Revealed by Light and Electron Microscopy. The Biological Bulletin 197, 144-158.
Høeg JT. 1995. The biology and life cycle of the Rhizocephala (Cirripedia). Journal of the Marine Biological Association of the United Kingdom 75, 517-550.
Høeg JT & Møller OS. 2006. When similar beginnings lead to different ends: Constraints and diversity in cirripede larval development. Invertebrate Reproduction & Development 49, 125-142.
Ifrim C, Vega FJ & Stinnesbeck W. 2011. Epizoic Stramentid Cirripedes on Ammonites from Late Cretaceous Platy Limestones in Mexico. Journal of Paleontology 85, 524-536.
Klepal W, Barnes H & Munn EA. 1972. The morphology and histology of the cirripede penis. Journal of Experimental Marine Biology and Ecology 10, 243-265.
Newman WA. 1987. Evolution of Cirripedes and their major groups. In: Southward AJ (ed.). Barnacle Biology.
Regier JC, Schultz JW & Kambic RE. 2005. Pancrustacean phylogeny: hexapods are terrestrial crustaceans and maxillopods are not monophyletic. Proc. R. Soc. B 272, 395-401.
Semmler H, Høeg JT, Scholtz G & Wanninger A. 2009. Three-dimensional reconstruction of the naupliar musculature and a scanning electron microscopy atlas of nauplius development of Balanus improvisus (Crustacea: Cirripedia: Thoracica). Arthropod Structure & Development 38, 135-145.
Thomson JV. 1830. On the cirripedes or barnacles. Zoological Research 1, 69-85.
Research Blogging necessities :)
Høeg, J. (1995). The biology and life cycle of the Rhizocephala (Cirripedia) Journal of the Marine Biological Association of the United Kingdom, 75 (03) DOI: 10.1017/S0025315400038996 | <urn:uuid:c72621f5-7611-41a7-962f-eb7b93b72030> | 3.203125 | 2,593 | Personal Blog | Science & Tech. | 46.294744 |
Melting polar ice has a worrisome list of consequences—methane gas release, rising sea levels, and the liberation of long frozen 750,000-year-old microbes. While melting glaciers probably aren’t going to turn into Jurassic Park, scientists are understandably concerned how they might affect the environment. Scientific American has a new feature on the impact of these liberated microbes on ocean life:
More likely is [the] prospect that thawing ice sheets will allow ancient microbial genes to mix with modern ones, flooding the oceans with never-before-seen types of organisms. Rogers [an evolutionary biology] believes this is already taking place. “What we think is happening is that things are melting out all the time and you’re getting mixing of these old and new genotypes,” he said. | <urn:uuid:90e1a725-a414-4fa9-947c-746939ab7e1f> | 3.59375 | 166 | Truncated | Science & Tech. | 30.117308 |
The .Net framework defines operator overloads for the + and - operators on the Delegate data type. The + operator effectively combines delegates so that a multiple delegates are called within one. The - operator, on the other hand, attempts to remove the delegate invocation list from a delegate.
The list discinction is important here: what this implies is that subtraction of a delegate effectively implies a subtraction of lists. For example, in the code below, removing the A and C delegates from the ABC invocation list via the expression s - (a + c) has no effect whatsoever, because AC is not a sublist of ABC.
It’s also worth noting that sublist removal happens from the end of the list. For example:
Since the above mechanics can lead to unpredictable results, ReSharper issues a warning whenever it encounters a delegate subtraction operator. | <urn:uuid:0cf96bb3-2788-4bd0-bfb8-87c84a02cd79> | 2.71875 | 177 | Documentation | Software Dev. | 29.934946 |
suppress is equivalent to
In the format string
zis a format modifier that turns off all translate rules,
his a format modifier that turns off all line-breaking rules, and
%is the parse continuation operator.
The following sample code demonstrates the use of
suppress in a simple SGML program. The program prints
all of the titles in a document whose doctype is
process do sgml-parse document scan #main-input output "%c" done element "doc" suppress element "title" put #main-output "%c%n" element #implied output "%c"
If there are subelements in
title, they will be processed by the
element #implied rule.
output "%c" is used instead of
suppress to process the content of these subelements. This
ensures that the content of the subelement is sent to the same destination as the content of the parent element.
If the subelement is within a
title, its content will be sent to
#main-output in its proper
place within the title. Otherwise, it will be sent to | <urn:uuid:0a319ea4-dc09-4a1a-a596-8013bc4a9bcc> | 2.875 | 235 | Documentation | Software Dev. | 41.511591 |
Equilateral Triangle Areas
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The Math Forum is a research and educational enterprise of the Drexel University School of Education. | <urn:uuid:b045e1c6-b9a9-4228-b853-7766254023e9> | 2.84375 | 174 | Content Listing | Science & Tech. | 30.026542 |
I found these clocks in the Arts Centre at the University of
Warwick intriguing - do they really need four clocks and what times
would be ambiguous with only two or three of them?
A bicycle passes along a path and leaves some tracks. Is it
possible to say which track was made by the front wheel and which
by the back wheel?
This task depends on groups working collaboratively, discussing and
reasoning to agree a final product.
Glarsynost lives on a planet whose shape is that of a perfect
regular dodecahedron. Can you describe the shortest journey she can
make to ensure that she will see every part of the planet?
A game for 2 people. Take turns joining two dots, until your opponent is unable to move.
A visualisation problem in which you search for vectors which sum
to zero from a jumble of arrows. Will your eyes be quicker than
A cube is made from smaller cubes, 5 by 5 by 5, then some of those
cubes are removed. Can you make the specified shapes, and what is
the most and least number of cubes required ?
What can you see? What do you notice? What questions can you ask?
This is a simple version of an ancient game played all over the world. It is also called Mancala. What tactics will increase your chances of winning?
Two boats travel up and down a lake. Can you picture where they
will cross if you know how fast each boat is travelling?
Discover a way to sum square numbers by building cuboids from small
cubes. Can you picture how the sequence will grow?
This is an interactive net of a Rubik's cube. Twists of the 3D cube become mixes of the squares on the 2D net. Have a play and see how many scrambles you can undo!
A square of area 3 square units cannot be drawn on a 2D grid so that each of its vertices have integer coordinates, but can it be drawn on a 3D grid? Investigate squares that can be drawn.
In a three-dimensional version of noughts and crosses, how many winning lines can you make?
A and C are the opposite vertices of a square ABCD, and have
coordinates (a,b) and (c,d), respectively. What are the coordinates
of the vertices B and D? What is the area of the square?
Two angles ABC and PQR are floating in a box so that AB//PQ and BC//QR. Prove that the two angles are equal.
A cheap and simple toy with lots of mathematics. Can you interpret
the images that are produced? Can you predict the pattern that will
be produced using different wheels?
A rectangular field has two posts with a ring on top of each post.
There are two quarrelsome goats and plenty of ropes which you can
tie to their collars. How can you secure them so they can't. . . .
Imagine you are suspending a cube from one vertex (corner) and
allowing it to hang freely. Now imagine you are lowering it into
water until it is exactly half submerged. What shape does the
surface. . . .
The whole set of tiles is used to make a square. This has a green and blue border. There are no green or blue tiles anywhere in the square except on this border. How many tiles are there in the set?
Bilbo goes on an adventure, before arriving back home. Using the
information given about his journey, can you work out where Bilbo
A 10x10x10 cube is made from 27 2x2 cubes with corridors between
them. Find the shortest route from one corner to the opposite
A right-angled isosceles triangle is rotated about the centre point
of a square. What can you say about the area of the part of the
square covered by the triangle as it rotates?
Find all the ways to cut out a 'net' of six squares that can be
folded into a cube.
What is the shape of wrapping paper that you would need to completely wrap this model?
Can you make sense of the charts and diagrams that are created and used by sports competitors, trainers and statisticians?
Find the ratio of the outer shaded area to the inner area for a six
pointed star and an eight pointed star.
Watch these videos to see how Phoebe, Alice and Luke chose to draw 7 squares. How would they draw 100?
We're excited about this new program for drawing beautiful mathematical designs. Can you work out how we made our first few pictures and, even better, share your most elegant solutions with us?
A spider is sitting in the middle of one of the smallest walls in a
room and a fly is resting beside the window. What is the shortest
distance the spider would have to crawl to catch the fly?
Blue Flibbins are so jealous of their red partners that they will
not leave them on their own with any other bue Flibbin. What is the
quickest way of getting the five pairs of Flibbins safely to. . . .
A tilted square is a square with no horizontal sides. Can you
devise a general instruction for the construction of a square when
you are given just one of its sides?
Can you recreate these designs? What are the basic units? What
movement is required between each unit? Some elegant use of
procedures will help - variables not essential.
How many moves does it take to swap over some red and blue frogs? Do you have a method?
Use a single sheet of A4 paper and make a cylinder having the greatest possible volume. The cylinder must be closed off by a circle at each end.
Start with a large square, join the midpoints of its sides, you'll see four right angled triangles. Remove these triangles, a second square is left. Repeat the operation. What happens?
A game for 2 players. Can be played online. One player has 1 red
counter, the other has 4 blue. The red counter needs to reach the
other side, and the blue needs to trap the red.
A half-cube is cut into two pieces by a plane through the long diagonal and at right angles to it. Can you draw a net of these pieces? Are they identical?
A ribbon runs around a box so that it makes a complete loop with two parallel pieces of ribbon on the top. How long will the ribbon be?
Mathematics is the study of patterns. Studying pattern is an
opportunity to observe, hypothesise, experiment, discover and
An irregular tetrahedron has two opposite sides the same length a
and the line joining their midpoints is perpendicular to these two
edges and is of length b. What is the volume of the tetrahedron?
Show that among the interior angles of a convex polygon there
cannot be more than three acute angles.
In how many ways can you fit all three pieces together to make
shapes with line symmetry?
The triangle OMN has vertices on the axes with whole number co-ordinates. How many points with whole number coordinates are there on the hypotenuse MN?
There are 27 small cubes in a 3 x 3 x 3 cube, 54 faces being
visible at any one time. Is it possible to reorganise these cubes
so that by dipping the large cube into a pot of paint three times
you. . . .
A Hamiltonian circuit is a continuous path in a graph that passes through each of the vertices exactly once and returns to the start.
How many Hamiltonian circuits can you find in these graphs?
Use the interactivity to listen to the bells ringing a pattern. Now
it's your turn! Play one of the bells yourself. How do you know
when it is your turn to ring?
Slide the pieces to move Khun Phaen past all the guards into the position on the right from which he can escape to freedom.
Four rods, two of length a and two of length b, are linked to form
a kite. The linkage is moveable so that the angles change. What is
the maximum area of the kite? | <urn:uuid:ffbc4a17-8db6-43b3-a57e-9c29c7a4fb52> | 3.234375 | 1,733 | Content Listing | Science & Tech. | 69.117218 |
In mathematics, a rational number is a number which can be expressed as a ratio of two integers. Non-integer rational numbers (commonly called fractions) are usually written as the vulgar fraction a / b, where b is not zero. a is called the numerator, and b the denominator.
Each rational number can be written in infinitely many forms, such as 3 / 6 = 2 / 4 = 1 / 2, but it is said to be in simplest form when a and b have no common divisors except 1 (i.e., they are coprime). Every non-zero rational number has exactly one simplest form of this type with a positive denominator. A fraction in this simplest form is said to be an irreducible fraction, or a fraction in reduced form.
The decimal expansion of a rational number is eventually periodic (in the case of a finite expansion the zeroes which implicitly follow it form the periodic part). The same is true for any other integral base above one, and is also true when rational numbers are considered to be p-adic numbers rather than real numbers. Conversely, if the expansion of a number for one base is periodic, it is periodic for all bases and the number is rational. A real number that is not a rational number is called an irrational number.
where denotes the set of integers.
In mathematics, an irrational number is any real number that is not a rational number — that is, it is a number which cannot be expressed as a fraction m/n, where m and n are integers, with n non-zero. Informally, this means numbers that cannot be represented as simple fractions. It can be deduced that they also cannot be represented as terminating or repeating decimals, but the idea is more profound than that. While it may seem strange at first hearing, almost all real numbers are irrational, in a sense which is defined more precisely below. Perhaps the most well known irrational numbers are π and .
\ denotes the irrational numbers.
Having read the above recap on rational and irrational numbers, try answering the following multiple choice question which I had in a test today:
Which of the following is the first false statement?
(a) Between two different rational numbers, we can always find another rational number.
(b) Between two different rational numbers, we can always find an irrational number.
(c) Between two different irrational numbers, we can always find a rational number.
(d) Between two different irrational numbers, we can always find another irrational number.
(e) 0 = 1. | <urn:uuid:27ecf364-e2dc-402b-bfd9-dfac1efe9e4e> | 4.03125 | 530 | Personal Blog | Science & Tech. | 48.155034 |
Climate change explained
The Earth’s climate is driven by a continuous flow of energy from the sun.
Heat energy from the sun passes through the Earth’s atmosphere and warms the Earth’s surface.
As the temperature increases, the Earth sends heat energy (infrared radiation) back into the atmosphere.
Some of this heat is absorbed by gases in the atmosphere, such as carbon dioxide (CO2) , water vapour, methane, nitrous oxide, ozone and halocarbons.
Watch this video from National Geographic for a short visual explanation of climate change.
The greenhouse effect
4 billion years ago its concentration in the atmosphere was much higher than today - 80% compared to today's 0.03%. But most of it was removed through photosynthesis over time. All this carbon dioxide became locked in organisms and then minerals such as oil, coal and petroleum inside the Earth's crust.
A natural carbon dioxide cycle keeps the amount of CO2 in our atmosphere in balance. Decaying plants, volcanic eruptions and the respiration of animals release natural CO2 into the atmosphere, where it stays for about 100 years. It is removed again from the atmosphere by photosynthesis in plants and by dissolution in water (for instance in the oceans).
The amount of naturally produced CO2 is almost perfectly balanced by the amount naturally removed. But even small changes caused by human activities can have a significant impact on this balance. | <urn:uuid:e46cfa52-be0a-4fe4-b378-8609dd43662e> | 4.03125 | 294 | Knowledge Article | Science & Tech. | 40.712457 |
|South of Antares, in the tail of
the nebula-rich constellation
Scorpius, lies emission nebula
Nearby hot, massive stars, millions of years young,
nebula with invisible ultraviolet light, stripping electrons
The electrons eventually recombine with the atoms to produce the visible
dominated by the red emission of hydrogen.
At an estimated distance of 6,000 light-years, the region shown
is about 250 light-years across, spanning an area equivalent to
four full moons on the sky.
The nebula is also
cataloged as Gum 56 for Australian
astronomer Colin Stanley Gum,
but seafood-loving astronomers might
this cosmic cloud as
The Prawn Nebula. | <urn:uuid:8a68c7b8-0c27-4765-a0d0-d7268ebe990d> | 3.34375 | 151 | Knowledge Article | Science & Tech. | 24.142006 |
the Full Moon will
planet Earth's shadow in a
The entire eclipse sequence,
including 51 minutes of totality,
will be visible from Asia and Australia,
but moonwatchers in
Europe and Africa will miss out on the beginning partial phases
because for them, the eclipse will start before
In central and western North America
the earlier phases of the eclipse
will be in progress as the Moon sets.
In fact, while those in the east will miss out,
North Americans far enough west could see a scene very
much like this one, with a mostly eclipsed Moon
low and near the western
horizon during morning twilght.
morning twilight view of another lunar eclipse approaching
its total phase at moonset was captured in 2008 on February 21, from
the Zagros Mountains of Iran.
Credit & Copyright: | <urn:uuid:efcb2c90-ca77-4d59-b6cb-f28f246ae62b> | 2.796875 | 176 | Knowledge Article | Science & Tech. | 25.128184 |
- Recorder Online - http://www.berthoudrecorder.com -
Earthsky Tonight—May 7, See the legendary green flash
Posted By Gary Wamsley On May 6, 2010 @ 10:53 pm In Earth & Sky | Comments Disabled
Courtesy of EarthSky
A Clear Voice for Science
Our image today was taken by Mike Baird . It is a classic image of a detached green flash, seen at sunset. Used with permission.
You can see green flashes with the eye, sometimes, if you are looking toward a very clear horizon. You must be looking just at sunset, at the last moment before the sun disappears below the horizon. In addition, you have to be careful not to look too soon. Wait until just the thinnest rim of the sun appears above the horizon. If you look too soon, the light of the sunset will dazzle (or damage) your eyes, and you will miss that day’s green flash.
There are many different types of green flash. Some describe a streak or ray of the color green . . . like a green flame shooting up from the sunrise or sunset horizon. The most common green flash which many people describe, is a flash of the color green seen when the sun is nearly entirely below the horizon.
You need a distant horizon to see any of these phenomena, and you need a distinct edge to the horizon. Therefore, these green flashes, streaks and rays are often seen over the ocean, but you can see them over land, too, if your horizon is far enough away. Pollution or haze on the horizon will hide this instantaneous flash of the color green.
Here is another good article about the green flash by Peter Michaud.
Here is a rather subtle green flash video . I had to watch it several times to convince myself I saw any green.
Written by Deborah Byrd
CHANDRA Photo Album
StarDate Online
Sky and Telescope
National Geographic
Space Com
Amazing Space
Scope City
Article printed from Recorder Online: http://www.berthoudrecorder.com
URL to article: http://www.berthoudrecorder.com/2010/05/06/earthsky-tonight%e2%80%94may-7-see-the-legendary-green-flash/
URLs in this post:
www.EarthSky.org: http://www.EarthSky.org
Image: http://www.berthoudrecorder.com/wp-content/uploads/2010/05/phase07.gif
Image: http://www.berthoudrecorder.com/wp-content/uploads/2010/05/greenflash_4301.jpg
Mike Baird: http://www.flickr.com/photos/mikebaird/298481228/
ray: http://mintaka.sdsu.edu/GF/observing/greenray.html
green flash: http://mintaka.sdsu.edu/GF/
Andrew Young’s green flash page: http://mintaka.sdsu.edu/GF/index.html
picture of green flashes: http://mintaka.sdsu.edu/GF/pictures.html
green flash: http://www.bishopmuseum.org/planetarium/greenflash.html
green flash video: http://www.well.com/user/pk/waterfront/photo-of-the-week/GreenFlashVideo.avi
Astronomy Picture of the Day from NASA/JPL: http://antwrp.gsfc.nasa.gov/apod/
CHANDRA Photo Album: http://chandra.harvard.edu/photo/
U.S. Naval Observator Astronomical Information cente: http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/astronomical-information-center
StarDate Online: http://stardate.org/
Sky and Telescope: http://www.skyandtelescope.com/observing/ataglance/
National Geographic: http://news.nationalgeographic.com/news/
Space Com: http://www.space.com/nightsky/
Amazing Space: http://amazing-space.stsci.edu/tonights_sky/
The York County Astronomical Society: http://www.ycas.org/tonights_sky.htm
Scope City: http://www.scopecity.net/
Copyright © 2010 Berthoud Recorder. All rights reserved. | <urn:uuid:cce7d55d-e6e7-44f3-9c64-9db4b106213c> | 2.828125 | 982 | Truncated | Science & Tech. | 68.817593 |
The log of a molecule's molecular weight is proportional
to the distance that molecule has migrated. Therefore, the first step is
to generate a standard curve using molecules of know size (the molecular
When using semilog paper (see the next page), the molecular weights (in bp for DNA and kiloDaltons, kDa, for proteins) is plotted on the Y-axis and the distance the molecule migrated is plotted on the X-axis. When generating a standard curve, you will obtain a straight line (use a best-fit line).
Once your standard curve is ready, measure the distance traveled by your molecule of interest. Find that distance on the X-axis, and go up until you intersect with your standard curve. Move over to the Y-axis and that will indicate the molecular weight of the molecule you are studying.
Use the graph paper below and the DNA gel shown to the right to determine the molecular weight of the unknown band indicated with an arrow.
Distance Migrated (mm)
Lab Schedule Outlined
Lab Schedule In Context of Research Project
Molecular Biology Main Page
Biology Main Page | <urn:uuid:9a407e85-a9ba-4682-a534-320587392f5b> | 3.671875 | 234 | Tutorial | Science & Tech. | 35.046757 |
2 min 20 sec
Today, about one in four molecules of carbon dioxide in the atmosphere come from human activity, mainly burning fossil fuels. We also know that carbon dioxide, or CO2, is a "greenhouse gas" — it traps extra energy from the sun and warms the earth. Carbon dioxide levels in the air have been increasing every year, and usually faster each year, as we burn more and more coal, oil and gas. These are scientific facts beyond any dispute. But before Charles David Keeling started daily measurements of atmospheric CO2 in 1958, from near the top of Mauna Loa volcano on Hawaii's Big Island, no one knew for sure about this growth.
Keeling's measurements showed not only an increase in carbon dioxide, but also a human fingerprint. The instrument he used — a spectrometer — is able to chemically tell apart the kind of carbon found in fossil fuels, from the kind normally found in the air and water today. And the numbers add up: the increase of CO2 since the start of the Industrial Revolution has mostly been from burning fossil fuels. The remainder has come mainly from clearing and burning forest, which spectrometers can also detect (Spectrometers can tell apart different isotopes, or sizes, of carbon. CO2 from different sources has different mixes of carbon isotopes; so with a little accounting, scientists have been able to learn a lot about the sources of CO2 in our atmosphere).
In one more twist, Keeling's record showed that the planet "breathes" each year. Every spring and summer, carbon dioxide levels drop slightly in the northern hemisphere, as plants grow and take in CO2. Every fall and winter, levels increase again, as leaves fall and plants decay, releasing carbon back into the air. When Keeling's work revealed this subtle pattern, it provided even more confidence in the sensitivity and accuracy of his measurements.
ACTIVITY DESCRIPTION AND TEACHING MATERIALS
Watch >> What We Know For Sure
TEACHING NOTES / CONTEXT FOR USE
This is a short video that gives a convincing case for human-caused carbon increase and, therefore, cliamte change.
Assessment is at the discretion of the educator as to how the video is applied and the expectations after viewing it.
REFERENCES AND RESOURCES | <urn:uuid:f6b86a2a-1b18-4517-bf15-8085b3db962f> | 3.9375 | 481 | Truncated | Science & Tech. | 40.963161 |
The Document Object Model: an Introduction
Published on May 14, 2001
Definition of a Document Object Model
A Document Object Model is a model of how the various HTML elements in a page (paragraphs, images, form fields, etc.) are related to each other and to the topmost structure: the document itself. So the document is represented as a kind of tree, in which each HTML element is a branch or leaf, and has a name.
I see the use of the DOM as a kind of naming magic. If you call on an HTML element using its proper name, you are granted access and you can influence the element, forcing the browser to react to your arcane incantations. Of course, like in fairy tales, if you use a wrong name or try to influence the wrong property, terrible things may start to happen.
Therefore it is very important that you know the proper incantations (plural, because sometimes you need to know several names for the same element).
For instance, when you write a rollover script you access a certain image in the page by using its correct name:
When you are granted access, you can change its src property. As soon as you do that, the browser reacts to your "spell" by loading another image in the place of the first. If the image you try to name doesn't exist, however, or if you misspelled the name, the browser gives error messages and your magic won't work.
Level 0 DOM
Netscape undersood this need quite well, devised the Level 0 DOM, and built it into Netscape 2. It was still very simple, you could only access forms, links and (in Netscape 3) images, but web developers were enthousiastic about it. They could check what people had filled in in forms! They could create the famous rollover effect! It seemed like living in Paradise.
Therefore Microsoft also started using the Level 0 DOM and the same names gave access to the same elements in Netscape 3 and Explorer 3.
But not quite. People quickly found out that Explorer 3 didn't give access to the images on a page, so that the mouseovers wouldn't work. Even worse, when you tried calling an image by its proper DOM name, Explorer 3 would produce errors because it didn't understand what you were talking about. So web developers were forced to take compatibility questions into account. Don't start calling document.images immediately - check first, to ensure that it's supported by that visitor's browser. This was the beginning of support detection:
// do something with document.images, for instance:
document.images['thename'].src = 'the_new_image.gif';
...So first check if the browser supports document.images at all, and only when it does, call the image by its proper name and change its properties.
DHTML was supposed to give web developers the opportunity of changing a web page on the fly, for instance by adjusting the position of a layer. Since more HTML elements needed to be accessible, the DOM had to be extended. In view of their increasing competition it is not surprising that Netscape and Microsoft decided to implement their own proprietary DOMs, document.layers for Netscape and document.all for Explorer. These were the two Intermediate DOMs.
The Intermediate DOMs offered access to what are popularly known as layers: independent parts of the page that could be moved or hidden1. In addition, the Explorer 4 DOM also offered access to most other HTML elements (paragraphs,
<td>'s), though actually changing the properties of these elements sometimes didn't work quite properly.
Web developers groaned and moaned and wrote more complicated scripts to make sure both browsers could handle their DHTML. For instance, to adjust the position of the layer with
document.layers['layername'].top = 200;
else if (document.all)
document.all['layername'].style.top = 200;
The document.layers bit was executed in Netscape 4, the document.all bit in Explorer 4. So far so bad - the browser-specific coding was not what developers had in mind for writing simple web pages, but it could be handled.
A worse problem was that Netscape 4 offered far less access than Explorer 4. In Explorer you could change the colour or the margin of a paragraph, in Netscape you couldn't. This difference was partly balanced by the fact that Netscape was released slightly earlier and had far better and more accessible documentation.
On the other hand Netscape's DOM was far more complex than Microsoft's. Netscape insisted on making each layer a separate document, so that if you want to access an image inside a layer you'd have to write your code like this:
The image is inside the document that's inside the layer. Although it isn't entirely illogical this model quickly becomes too verbose. In contrast, for Explorer you could still use the familiar
reference, because Explorer didn't put separate documents inside the layer. Therefore, the Microsoft DOM was easier to learn and use.
For reasons of backward compatibility, the Version 4 browsers still supported the Level 0 DOM, so that the old form validation scripts and mouseovers still functioned. The number of DOMs now had reached three, the old Level 0 DOM for the old effects and the two Intermediate DOMs for DHTML.
Level 1 DOM
Meanwhile the World Wide Web Consortium had started working on the specifications for the XML DOM, also called the Level 1 DOM. The objective of the new DOM was to provide access to each and every part of an XML document, including comments and processing instructions. It was meant to work for any programming language that could parse and manipulate XML documents.
This standard was adopted by Microsoft and the Mozilla Project (the development team that developed Netscape 6.x) as a result of developer support mobilized by the Web Standards Project from 1998 onward.
There are other browsers that provide support for this standard as well, most notably Opera and Konqueror. However, Opera only supports the subset of the DOM that makes possible simple DTHML effects, while all of the other browsers mentioned have attempted to support the entire standard.
Microsoft has (quite rightly) decided that Explorer 5 should continue to support the document.all DOM, thus providing backward compatibility for the many scripts that were written to work in IE4.. Despite this, the Windows and Macintosh versions of Internet Explorer differ considerably, so you cannot be certain that scripts developed on one platform will work properly on the other.
The Mozilla Project took a completely different approach with their decision to remove completely the complicated and buggy
document.layers DOM. Their reason for doing this was that they were going to rewrite Netscape from scratch anyway - so why build in something that's horrendously complicated? The drawback is, of course, that the scripts written to work in Netscape 4.x will fail in Netscape 6.x. Netscape 6.x and Mozilla don't provide native support for the document.all DOM, either.
That's what all the hubbub is about: you have to rewrite your scripts to make them work in Netscape 6. I don't think that this is such a bad thing, because it becomes necessary to learn the basics of the W3C DOM if you're going write DHTML that works in Netscape. It may seem like something of a trial, but since the Level 1 DOM is (supposed to be) a lasting standard, you can learn it with the confidence that you'll be acquiring knowledge of lasting value.
The Level 1 DOM is supported at least in part across a wide range of recent browsers, and is comprehensive in its methods for accessing the elements of a Web document. Simple scripts will work without difficulty in all of these browsers, though attempts at more sophisticated effects may be difficult, in part because certain browser vendors have also added their own proprietary extensions.
As said before, the goal of the Level 1 DOM is to provide access to each part of an XML (or HTML) document. This means there are also methods and properties for reading out and even changing the comments in your page. Although this may be quite useful when editing XML documents, I don't think web developers would be much interested in this functionality. I also doubt that DocumentFragments, NamedNodeMaps and ProcessingInstructions will play a significant role in web development.
In a way this is fortunate. To start using the new DOM you only have to know a few simple things, and when you want to write very complex scripts with lots of browser incompatibilities you can turn to my compatibility table and look up the specific things you need.
The document tree
In the Level 1 DOM all HTML elements are part of the document tree. This tree starts with the document itself and then goes down to the level of individual
br's. Take this example document
<title>An example of a document tree</title>
<h3>The document tree</h3>
<p>This makes a document tree.</p>
<p>It contains <BR> several paragrahps.</p>
<p>It is, like, totally awesome.</p>
The document has two children,
head has one child,
body has four children: one
h3 and three
p's. In addition, the
h3 and two of the
p's have one child: the text node that contains the actual text. The second
p has even three children: one text node, then a
br, then another text node.
You can walk through the entire tree, saying, for instance, "Go to the child of fourth child of the second child of the document and change its value to 'Foo-Bar'": document.childNodes.childNodes.firstChild.nodeValue = 'Foo-Bar', which "magically" changes the text of the last paragraph to 'Foo-Bar'. You could even say "Append the same node to the first child of
document.childNodes.childNodes.appendChild(document.childNodes.childNodes) which - in the context of our example document - transfers the entire
p into the
However, this code will change the structure of the document tree. If you try to execute the same code again, you'll get an error message. After all, the
body doesn't have a fourth child any more, you just moved it to another position. So going through the entire DOM tree is not the best way to access an element. It's far better to use its ID, its unique name.
<p id="the_unique_element">It is, like, totally awesome.</p>
By giving our
id we can call it by its name:
document.getElementById('the_unique_element') and it will respond, regardless of its location in the document. This makes your elements easier to find, and makes possible a much more robust script.
Conclusion: The promise of DHTML
The promise of DHTML has only really come true now that the Version 5/6 browsers are here. Now you can rewrite your pages on the fly. Do you want to sort a large table by product color instead of product name? No problem. Access the correct
td's, read out the values of their text nodes, sort them alphabetically, completely rewrite the table, and display the new sorting order. No more round-trips to the server are necessary.
When you're ready for the real work, check out these sites. They'll give you interesting tips and tricks about various aspects of the DOM:
- Mozilla - Traversing a Table. Simple example script that messes with a table.
- J. David Eisenberg's excellent series of articles in A List Apart:
Meet the DOM: About the DOM in general and the differences with the earlier browser specific DOMs.
DOM Design Tricks 1: About the display style declaration.
DOM Design Tricks 2: About event capturing in Netscape 6.
DOM Design Tricks 3: About the changing of texts in a document. About nodes.
- PBWizard. Interesting examples of and articles about the W3C DOM and related standards.
Footnotes1 The term 'layers' was coined by Netscape and it was also the name of its Intermediate DOM. Since in the beginning of DHTML the Netscape model was considered the standard and Microsoft's only a strange extension, the Netscape name has become the standard term.
Back to content | <urn:uuid:0efb1a5f-c2cc-4cfa-ab88-79bef0289544> | 3.5 | 2,600 | Knowledge Article | Software Dev. | 57.010283 |
- Sir Bernard Lovell
- Planck First Results
- Lovell Telescope
- SKA Telescope
- New Discovery Centre
- ALMA Fringes
- Active Galaxies
- The Sun
- PhD Studentships
- Night Sky
- Behind the Scenes
- Sounds of Space
- Meteor Detector
It is with regret that we announce that Sir Bernard Lovell OBE FRS died on the 6th August 2012 at the age of 98.
Planck unveils wonders of the Universe
The first results from ESA's Planck satellite have been released, looking at the coolest objects within our Universe.
Radio eye on the universe
The 76-m Lovell Telescope is the world's third largest, fully-steerable radio telescope and has stood proudly over the plains of Cheshire since 1957.
This dramatic image is the first to be produced by e-MERLIN, a powerful new array of radio telescopes linked across the UK.
An International radiotelescope for the 21st century
Jodrell Bank Centre for Astrophysics hosts the global headquarters of the world's next generation radio telescope, the €1.5bn Square Kilometre Array (SKA).
The Northwest Regional Development Agency (NWDA) and the Northwest European Regional Development Fund (ERDF) today confirmed funding of £3.1 million to kick-start the development of a new Science Discovery Centre.
We study the chemical elements found in molecular gas clouds.
A team of astronomers and engineers at the Atacama Large Millimeter Array have made the first observations linking radio signals from two telescopes in the array.
Formed in supernova explosions following the collapse of massive evolved stars, pulsars make superb cosmic clocks which are used to study some of the most extreme physics in the universe.
The hunt for Earth-2
This is an artists impression of OGLE-2005-BLG-390, a 5 Earth mass planet discovered using the microlensing effect. Find out more about our research on extra-solar planets
Active Galaxies are like normal galaxies except their central region is very bright over some or all of the electromagnetic spectrum.
At Jodrell Bank Centre for Astrophysics we study fluctuations in the cosmic microwave background, allowing us to probe the Universe at early times and make deductions about fundamental processes in cosmology.
Our nearest star may be a familiar sight in the daytime sky but it still holds many mysteries. At Jodrell Bank we study the complex interactions between plasma and magnetic fields in the solar corona.
Engineers at Jodrell Bank Observatory needed more than just a jack and a brace when a steel tyre on the famous Lovell radio telescope cracked.
We have fully funded STFC fellowships to support PhD students in any area of astrophysics research starting in September. Students interested in being considered for one of these fellowships should apply as soon as possible.
Having trouble finding the Andromeda Galaxy? Wondering where Jupiter is? Ian Morison describes what you can see in the UK night sky this month.
The Control Room is where the duty controller takes responsibility for the giant 76m Lovell Telescope and our other telescopes. Take a virtual behind-the-scenes tour of the observatory.
A twice-monthly podcast covering all aspects of astronomy including the latest news, what you can see in the current night sky, and interviews with astronomers.
In space nobody can hear you scream but that doesn't mean it is totally quiet. As mentioned on BBC Radio 4's Today Programme, Jodrell Bank's Dr Tim O'Brien explored the sounds of the cosmos on an episode of the Jodcast.
Come down to Earth from space and enjoy the Jodrell Bank nature experience. The 35 acre arboretum at the Visitor Centre will open your eyes to the environment and the world of trees. | <urn:uuid:d6f195a6-71bc-4eb0-8c2f-0c9e6b634144> | 2.75 | 788 | Content Listing | Science & Tech. | 41.298555 |
returns a pointer to a string containing the name of
the user logged in on the controlling terminal of the process, or a
null pointer if this information cannot be determined.
The string is
statically allocated and might be overwritten on subsequent calls to
this function or to
returns this same username in the array
returns a pointer to a string containing a username
associated with the effective user ID of the process.
is not a null pointer, it should be an array that can hold at least
L_cuserid characters; the string is returned in this array.
Otherwise, a pointer to a string in a static area is returned.
string is statically allocated and might be overwritten on subsequent
calls to this function or to
The macro L_cuserid is an integer constant that indicates how
long an array you might need to store a username.
L_cuserid is declared in <stdio.h>.
These functions let your program identify positively the user who is
or the user who logged in this session
(These can differ when set-user-ID programs are involved.)
For most purposes, it is more useful to use the environment variable
LOGNAME to find out who the user is.
This is more flexible
precisely because the user can set LOGNAME arbitrarily.
returns a pointer to the username when successful,
and NULL on failure.
returns 0 when successful, and nonzero on failure.
The calling process already has the maximum allowed number of open files.
The system already has the maximum allowed number of open files.
The calling process has no controlling tty.
The length of the username, including the terminating null byte,
is larger than
Linux/glibc also has
There was no corresponding entry in the utmp-file.
Insufficient memory to allocate passwd structure.
Standard input didn't refer to a terminal.
password database file
some libc versions used /var/adm/utmp)
specified in POSIX.1-2001.
System V has a
function which uses the real
user ID rather than the effective user ID.
was included in the 1988 version of POSIX,
but removed from the 1990 version.
It was present in SUSv2, but removed in POSIX.1-2001.
and a username
associated with a session, even if it has no controlling tty.
Unfortunately, it is often rather easy to fool
Sometimes it does not work at all, because some program messed up
the utmp file.
Often, it gives only the first 8 characters of
the login name.
The user currently logged in on the controlling tty
of our program need not be the user who started it.
for security-related purposes.
Note that glibc does not follow the POSIX specification and uses
(Other recent systems, like SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8
all return the login name also when
Nobody knows precisely what
does; avoid it in portable programs.
Or avoid it altogether: use
instead, if that is
what you meant.
Do not usecuserid(). | <urn:uuid:8d94ef6a-3fbe-4b2c-a3e9-646b709cbd15> | 2.6875 | 675 | Documentation | Software Dev. | 52.34264 |
But is the increase in shark sightings due to the Gulf of Mexico oil spill? Perhaps not, explains George Burgess, director of Florida program for shark research at the University of Florida
"It may be a situation where there's more people out there looking for things than there were before," he said.
Warmer temperatures may also play a role, if indeed more sharks are swimming in shallow waters, Burgess added.
"This time of year, the water's warmer and shark sightings are normally up along the northeast Gulf Coast," he said.
If the oil spill is to blame, scientist won't know for sure until an ecological study is done to determine the spill's affect.
"The oil does make you wonder," Burgess said. "It's hard to say what's going on at this point, but it's safe to suggest that a large mobile predator like a shark is more easily able to escape from an area that's inhospitable." | <urn:uuid:3d7d6bdf-6ffa-4199-98d6-ba234381187b> | 2.734375 | 192 | Truncated | Science & Tech. | 54.483436 |
Australian cows are doing what they do best - ruminating and burping - for scientists who last month began an experiment to measure the contribution cattle make to the greenhouse effect.
Cud-chewing animals such as cows, sheep and goats produce methane as they digest their food. This is thought to represent an estimated 3 per cent of the greenhouse gases generated by all human activities. But the precise quantity of methane released by ruminants is 'one of the big unknowns', says Tom Denmead of the Centre for Environmental Mechanics in Canberra, part of Australia's government research organisation CSIRO.
Present estimates are based on measurements of the amount of methane belched out by cattle that have been confined in a sealed chamber. But the animals' behaviour in the chambers differs from that out of doors, so the amount of methane they produce may also be different, says Lowry Harper of the ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:f076ce8b-1de5-491b-bfd7-268d6b4902f0> | 3.5 | 206 | Truncated | Science & Tech. | 42.276471 |
HYDROGEN is the darling of alternative fuel proponents. But Olah, a Nobel laureate, Prakash and Goeppert argue that methanol is better, despite its higher toxicity. It is a liquid, so it is easier to ship and store. Today it can be created from natural gas. The authors' real dream is of a future in which nuclear or renewable power is harnessed to make methanol from carbon dioxide and water - mitigating global warming by reusing carbon dioxide. A bit dry but, aside from some of the chemistry, it is mostly non-technical and a potentially important work.
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:130a6e55-05a0-42e5-a4a7-87e80a2f0ea6> | 3.515625 | 153 | Truncated | Science & Tech. | 44.0675 |
In 1931 Kurt Gödel wrote an important paper in which he showed that an axiomatic system which contained the axiom of infinity could not be proved to be consistent or complete. The trouble does not exist, however, for finite systems. As a result, one might be tempted to confine their research interests to solely finite phenomena, but there are difficulties even there.
For instance, if one is going to study, say, finite abelian groups, the fundamental theorem of arithmetic plays an important part in the development of that theory, and the fundamental theorem of arithmetic is a theorem about the natural numbers, which, as currently formulated, depend upon the axiom of infinity for their existence. Is it possible to prove the fundamental theorem of arithmetic without the axiom of infinity?
Of course it is. The fundamental theorem of arithmetic goes back thousands of years. The axiom of infinity, which states that the collection of all natural numbers forms a set, goes back only to the development of set theory which is much more recent.
The most important thing that is lost when you throw out the axiom of infinity is the closure property of natural numbers under addition and multiplication. Any set of non zero natural numbers that is closed under addition must be infinite. However, any computation that can be practically performed will require only a finite number of operations and a finite number of numbers.
All that is required is a slight shift in philosophy. Instead of developing a set that will contain the results of any possible computation, we can deal with any practical application by starting with the application and merely developing a set of numbers that will suffice for that particular application.
In particular, the fundamental theorem of arithmetic states that given a natural number greater than one, it is possible to break it up into a product of primes in a unique manner. So we start with a natural number greater than one, and at that point everything we need could take place in the set of all natural numbers less than our given number, which is a finite set.
What is required is to start with a basic axiomatization and prove everything we need to get to the fundamental theorem of arithmetic to make sure that it can be done without the axiom of infinity.
We use just four axioms. The first three are that subsets, unions, and power sets of known sets are sets, and the fourth is that the empty set is a set. Intersections and Cartesian products can be obtained using subsets and power sets.
Without the axiom of infinity, we can depend only on sets that can be developed from the empty set in a finite number of steps using these operations. Any individual natural number can be obtained in the standard manner in a finite number of steps, and so any finite collection of natural numbers will form a set.
The more one thinks about it, less reasonable the axiom of infinity becomes. The conveniences that it provides turn out to be nice but unnecessary luxuries.
The material is organized into definitions, axioms, and theorems. They are ordered so that each one is stated before it is used.. The material is organized into eight sections. Each section has a title which usually accurately reflects the material covered in the section.
Web pages offer unique opportunities for presenting mathematical material. The definitions, axioms, and the statements of the theorems in each section are stated in a single web page. The theorem numbers are links to the proofs of the theorems. In the proofs of the theorems, if a definition, axiom, or previous theorem are invoked, there is a link to it. The links to previous theorems go to the proof of the theorem, but since the definitions and axioms do not have proofs, the links form them go to their statements in the main web page for the section in which they are found. At the bottom of the main web pages for each section is a link to the next section. The title, "Finite Mathematics", in each section is a link to the table of contents, and any place you see my name in this web site is a link to my home page. Enjoy.
Table of Contents
1. Definitions and Axioms | <urn:uuid:e60ffe22-2498-49c0-ad81-ccbd36f8273d> | 3.578125 | 859 | Academic Writing | Science & Tech. | 43.013698 |
Giant Tree Lobsters Rediscovered
Eighty years after they disappeared, tree lobsters have been rediscovered, living near an old volcano in Australia. And no, they’re not actually “lobsters,” but special six-legged insects that were thought to be extinct decades ago. The rare “tree lobsters,” otherwise commonly known as Lord Howe Island walking sticks (Dryococelus australis), were thought to be decimated in 1918 when a British ship ran aground on Lord Howe Island, the creatures’ native home. On board were a few black rats, which invaded the island and wrought havoc to the natural ecosystem. By 1960, everyone had assumed the creepy crawler had gone the way of the dodo. But two Australian scientists made the leap to Balls Pyramid, just 13 miles southeast of their original home, on a hunch to hunt for the tree lobsters. There in 2001, they discovered a small, surviving population, hovered around a single plant. | <urn:uuid:c6e25a0f-fab4-4bf4-899f-ef6c1716f30d> | 3.34375 | 209 | Truncated | Science & Tech. | 43.753245 |
How is freezing rain different than sleet?
Published: Jul 27 2011 10:34:13 AM EDT
Freezing rain is rain which freezes on impact with a cold surface (below 32 degrees creating a glaze).
Sleet occurs when raindrops freeze as small ice pellets BEFORE they hit the surface of the earth.
» More Homework Help Questions | <urn:uuid:dc01f85d-067c-455e-b3a8-524f39864693> | 3.15625 | 74 | Q&A Forum | Science & Tech. | 71.324848 |
Note: This project has been replaced by the BEC project.
An Optical lattice (OL) is an array of periodic light-shift potentials formed due to interference of two or more laser beams. Atoms are cooled and localized in the potential minima.
OL demonstrate many of the characteristics associated with solid state lattices, with the important difference that they have significantly longer coherence times - which facilitates observation of coherent phenonema such as tunneling, Bloch oscillations, and Wannier-Stark ladders.
The shape of the OL can be easily tailored by varying the parameters of the light field or applying an external magnetic field.
Learn more about Optical Lattices | <urn:uuid:d853670d-8cb1-4b1b-8f33-d1f1be18894a> | 2.953125 | 142 | Knowledge Article | Science & Tech. | 20.905679 |
Database Server System Requirements
From the point of view of the operating system, a database server requires the system resources described in the following sections.
The amount of physical memory used by the database server process is determined by parameters in the local database definition, see The Local Database, whose initial default values are determined by looking at the amount of installed memory.
VMS: For a database server running on an OpenVMS node the amount of physical memory used by the database server process will vary between the OpenVMS process parameters WSQUOTA and WSEXTENT.
The WSQUOTA parameter is calculated by MIMCONTROL and is set large enough to include the bufferpool, communication buffers, code, and stack data.
The WSEXTENT parameter is taken from the parameter with the same name in the MULTIDEFS file, see The MULTIDEFS Parameter File. The default value for WSEXTENT is the SYSGEN parameter WSMAX (the maximum amount of physical memory a single process may have).
The amount of virtual memory that the database server process can use is limited by the operating system.
VMS: The MIMCONTROL command sets the paging file quota of the database server so that it is large enough to contain all memory areas, including the bufferpool and an SQLPOOL that has grown to MaxSQLPool kilobytes.
VMS: The database server creates a global section for its communication buffers. This global section resides on the page file. The amount of memory a global section may take from a page file is generally controlled by an operating system parameter. If this limit set by the operating system is exceeded, the MIMCONTROL/START command will fail with the message:
Upright Database Technology AB
Voice: +46 18 780 92 00
Fax: +46 18 780 92 40 | <urn:uuid:e76d44d2-526d-42f0-a883-f21e4a6646df> | 2.703125 | 383 | Documentation | Software Dev. | 25.454205 |
Garbage collection (GC) reclaims the heap space previously allocated to objects no longer needed. The process of locating and removing the dead objects can stall any application and consume as much as 25 percent throughput.
Almost all Java Runtime Environments come with a generational object memory system and sophisticated GC algorithms. A generational memory system divides the heap into a few carefully sized partitions called generations. The efficiency of a generational memory system is based on the observation that most of the objects are short lived. As these objects accumulate, a low memory condition occurs forcing GC to take place.
The heap space is divided into the old and the new generation. The new generation includes the new object space (eden), and two survivor spaces. The JVM allocates new objects in the eden space, and moves longer lived objects from the new generation to the old generation.
The young generation uses a fast copying garbage collector which employs two semi-spaces (survivor spaces) in the eden, copying surviving objects from one survivor space to the second. Objects that survive multiple young space collections are tenured, meaning they are copied to the tenured generation. The tenured generation is larger and fills up less quickly. So, it is garbage collected less frequently; and each collection takes longer than a young space only collection. Collecting the tenured space is also referred to as doing a full generation collection.
The frequent young space collections are quick (a few milliseconds), while the full generation collection takes a longer (tens of milliseconds to a few seconds, depending upon the heap size).
Other GC algorithms, such as the Concurrent Mark Sweep (CMS) algorithm, are incremental. They divide the full GC into several incremental pieces. This provides a high probability of small pauses. This process comes with an overhead and is not required for enterprise web applications.
When the new generation fills up, it triggers a minor collection in which the surviving objects are moved to the old generation. When the old generation fills up, it triggers a major collection which involves the entire object heap.
Both HotSpot and Solaris JDK use thread local object allocation pools for lock-free, fast, and scalable object allocation. So, custom object pooling is not often required. Consider pooling only if object construction cost is high and significantly affects execution profiles.
Pauses during a full GC of more than four seconds can cause intermittent failures in persisting session data into HADB.
While GC is going on, the Application Server isn’t running. If the pause is long enough, the HADB times out the existing connections. Then, when the application server resumes its activities, the HADB generates errors when the application server attempts to use those connections to persist session data. It generates errors like, “Failed to store session data,” “Transaction Aborted,” or “Failed to connect to HADB server.”
To prevent that problem, use the CMS collector as the GC algorithm. This collector can cause a drop in throughput for heavily utilized systems, because it is running more or less constantly. But it prevents the long pauses that can occur when the garbage collector runs infrequently.
Make sure that the system is not using 100 percent of its CPU.
Configure HADB timeouts, as described in the Administration Guide.
Configure the CMS collector in the server instance.
To do this, add the following JVM options:
Use the jvmstat utility to monitor HotSpot garbage collection. (See Further Information
For detailed information on tuning the garbage collector, see Tuning Garbage Collection with the 5.0 Java Virtual Machine. | <urn:uuid:9f6e84e5-b1e5-4eca-a60e-2ede302a97cb> | 3.203125 | 749 | Documentation | Software Dev. | 37.113247 |
Black Hole Eats Star, Beams Signal to Earth
On March 28, 2011, NASA's Swift detected intense X-ray flares thought to be caused by a black hole devouring a star. In one model, illustrated here, a sun-like star on an eccentric orbit plunges too close to its galaxy's central black hole. About half of the star's mass feeds an accretion disk around the black hole, which in turn powers a particle jet that beams radiation toward Earth.
Awesome, one of natures amazing phenomenons | <urn:uuid:17b4a822-422c-473d-8c11-278f98fdc626> | 3.15625 | 108 | Personal Blog | Science & Tech. | 50.013793 |
This data set consists of exposure ages for glacial deposits on nunataks and ice-free areas adjacent to Scott Glacier, Transantarctic Mountains. Most samples are glacially transported clasts deposited during the last glacial period or exposed by subsequent retreat of the glacier, ca. 16,000 yr B.P. to present. These ages are based on concentrations of the cosmic-ray-produced nuclide Be-10. There ... are also data from bedrock samples on Mt Rigby, which have longer and more complicated exposure histories. For these samples, concentrations of the cosmogenic nuclides Al-26 and Be-10, and associated "ages" are the result of repeated exposure punctuated with periods of ice cover and may have been affected by glacial erosion. Apparent ages for the bedrock samples should not be taken as indicative of prolonged single-stage exposure. The primary data are sample locations and exposure ages. Ages are calculated using currently accepted nuclide production rates and correction factors, as described in the footnotes. The data set also contains chemical and isotopic data needed to re-compute exposure ages if nuclide production rates or correction factors are revised in future. | <urn:uuid:118d1755-e553-46e8-8fb0-643b4773dcf4> | 2.96875 | 243 | Academic Writing | Science & Tech. | 31.76743 |
There are several types of indexes are available in MySQL:
- B-Tree Indexes:
- Normal Indexes – Normal indexes are the most basic indexes, and have no restraints such as uniqueness. It can contain duplicate value.
- Unique Indexes – Unique indexes are the same as “Normal” indexes with one difference: all values of the indexed column(s) must be unique. You can not add duplicate value in this column but you can add null.
- Primary keys – Primary keys are unique indexes+Not Null. All values of the index column must be unique and not null. Generally, people uses AUTO_INCREMENT with this.These indexes are almost always added when creating the table. Note that you may only have one primary key per table.
- Full-text Indexes – Full-text indexes are used by MySQL in full-text searches. Generally, this index is used for search engine kind of utility where you want to search some specific keyword from the Text column.
A B-tree index can be used for column comparisons in expressions like =, >, >=, <, <=, or BETWEEN operators. The index also can be used for LIKE, IN, IS NULL comparisons. Here, there some scenarios where MySQL will not use index (i.e NOT IN, IS NOT NULL, LIKE ‘%sql%’ etc).
- Spacial Indexes (R-tree) – Spacial index is supported by only MyISAM storage engine. Its just like B-tree but the index follow any order not just left to right. This index used for only specific purpose. (I.e MySQL GIS functions)
- Hash Indexes – Hash index supported only by Memory Storage Engine.
Hash indexes are completely different than B-tree indexes. Here, we can use only equality comparisons where we can use = or != operators and it will be very fast. Unfortunately, we can not use other comparison operators like <, >, <=, >= and that’s why some of the queries which needs range search, will not use these indexes. In the equality comparison also, we need to use whole key for compare and search row while In B-tree index, any leftmost prefix of the key can be used for searching rows.
More details are here: http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html | <urn:uuid:2552a711-fb49-4d38-a3b0-076468a37864> | 3 | 504 | Documentation | Software Dev. | 51.099413 |
Spotted Garden Eel Heteroconger hassi
These eels spend their lives swaying gracefully to and fro with their heads up in the water and their tails in their sandy burrows. Several hundred fish live together in a colony, or “garden,” looking like evenly spaced plants blowing in the breeze. Garden eels are much slimmer than their close relatives, the conger eels. They are only about in (14 mm) in diameter and have very small pectoral fins. The spotted garden eel usually has two large dark spots behind the head as well as many tiny ones all over the body. It has an upturned mouth that is designed to pick tiny planktonic animals from the water as the current flows by. Colonies of these eels occur only on sandy slopes that are exposed to currents but sheltered from waves. When danger threatens, the eels sink back down into their burrows, using their tails as an anchor until only their small heads and eyes are visible. They are very difficult to photograph underwater because they are able to detect the vibrations from a scuba diver’s air bubbles and will disappear when they are approached.
Spotted garden eels stay in their burrows even when spawning. Neighboring males and females reach across and entwine their bodies before releasing eggs and sperm. Mixed colonies of spotted and whitespotted garden eels sometimes occur.
- Order Anguilliformes
- Length Up to 16 in (40 cm)
- Weight Not recorded
- Depth 23–150 ft (7–45 m)
- Distribution Red Sea and tropical waters of Indian Ocean and western Pacific | <urn:uuid:3030cbb8-6431-46a4-96b4-718feabd6578> | 3.421875 | 340 | Knowledge Article | Science & Tech. | 49.586919 |
Part of twisted.flow.stage View Source View In Hierarchy
Merges two or more Stages results into a single streamFor example:
source = flow.Zip([1,flow.Cooperate(),2,3],["one","two"]) printFlow(source)
|Method||_yield||executed during a yield statement by previous stage|
Inherited from Stage:
|Method||next||return current result|
executed during a yield statement by previous stageThis method is private within the scope of the flow module, it is used by one stage in the flow to ask a subsequent stage to produce its value. The result of the yield is then stored in self.result and is an instance of Failure if a problem occurred. | <urn:uuid:8a322a80-9b8a-4023-be53-93d1abec77ed> | 2.84375 | 158 | Documentation | Software Dev. | 51.741667 |
According to the rock record, until about a million years ago the climate followed a neat 41,000-year cycle of ups and downs. Then, abruptly, that cycle stopped operating, and another one — 100,000 years long — took over. Why? Some scientists speculated that a cosmic catastrophe had reset the climatic clock. Others simply shrugged. Now two paleoclimatologists — Steven Clemens, at Brown University in Rhode Island, and Ralf Tiedemann, at the University of Kiel, Germany — have shown that people have been asking the wrong question. The 100,000-year cycle was there, unnoticed, all along; the real mystery is not where it came from, but what turned up the volume.
The 41,000-year cycle was no mystery at all. That’s the time it takes the tilt of Earth’s axis to wobble from 22 degrees to 25 degrees from the vertical and back again. Those changes in tilt, or obliquity, affect the amount of sun each region of the planet gets, especially near the poles. And that, in turn, affects the climate.
The 100,000-year climate cycle was harder to explain. Astrophysicists had found three orbital cycles — 95,000 years, 124,000 years, and 404,000 years long — which, in combination, cause Earth’s orbit to stretch from nearly circular to slightly elliptical and back again about every 100,000 years. The shape of the orbit (which physicists call, charmingly, “eccentricity”) determines how close Earth gets to the sun. In principle, that could affect the climate. But while cycles such as the 41,000-year rhythm change the amount of radiation from the sun by several percent, the eccentricity cycle changes it less than a tenth of a percent — too little, climatologists thought, to have much effect.
Clemens and Tiedemann’s results may change that view. The pair studied a 460-foot-long cylinder of mud bored from the ocean floor near the Cape Verde Islands, off the northwest coast of Africa. The mud was deposited continuously between 5.2 million and 1.2 million years ago. Much of it was made up of the remains of foraminifera — tiny one-celled organisms whose heaped-up shells record the vagaries of Earth’s changing climate.
It works like this: The shells are made of calcium carbonate, which is made, in part, of oxygen atoms absorbed from seawater. A normal oxygen atom has 16 particles in its nucleus. But a small proportion of oxygen atoms have 18. Water with O-16 is lighter than water with O-18, so it evaporates more easily. Usually the O-16 water rains back down and returns to the ocean. But when the climate turns cold, a lot of the water gets trapped on land as ice and snow, leaving the O-18 water in the ocean. And when there’s a lot of O-18 in the ocean, there’s a lot of O-18 in the forams’ shells.
Clemens and Tiedemann measured the O-18 in foram skeletons to see how it varied over the 4-million-year time span of the sediment core. To tease apart the several climate patterns that might show up in the core, they used a mathematical tool known as a Fourier transform. Just as a prism splits a beam of light into different colors, a Fourier transform takes a jumble of cycles and splits it into bands representing the underlying time periods The researchers found highs and lows that, as expected, matched well-known orbital shifts, including the 41,000-year cycle. But three other patterns showed up as well. They were at 95,000 years, 124,000 years, and 404,000 years — just the ones predicted by eccentricity cycles.
They came through loud and clear, even though the core spanned a time before the mysterious climate switchover. The tiny 0.1-percent difference in solar radiation seems to have made a difference after all. The 100,000-year cycle was ticking away much more than a million years ago; it was just too faint to be detected.
Why it got stronger is anybody’s guess. Rich Muller, a physicist at Lawrence Berkeley National Laboratory in California, thinks that orbital change is too feeble to do the job and that Clemens and Tiedemann’s evidence is an artifact of data processing. “The 100,000-year cycle of the ice ages could not possibly be explained by eccentricity,” Muller says. Instead, he believes that a million years ago, two asteroids collided, creating a large dust cloud. The 100,000-year climate cycle is caused by the Earth’s periodic passage into and out of that dust cloud.
Most other scientists reject Muller’s theory, but no one yet has convincingly explained why the 100,000-year eccentricity cycle suddenly grew powerful enough to overwhelm the 41,000-year obliquity cycle. “The thing that Muller’s right about is that we don’t know how eccentricity works,” says David Thomson, a mathematician at Bell Labs in Murray Hill, New Jersey, who has worked extensively with ocean sediment cores. “The few explanations I’ve heard seem contrived.” | <urn:uuid:804a1137-0277-4f39-af58-147847c6fdfe> | 4 | 1,128 | Nonfiction Writing | Science & Tech. | 60.354634 |
The fossil was originally described (Radoičić, 1959) as minute thick-walled cylindrical bags closed at one end, ca 500 to 780 µm long, with 32 to 80 µm external and 10 to 24 µm internal diameters. It was ascribed to the genus Aeolisaccus Elliott, 1958, under the name A. kotori Radoičić, 1959. A supplementary description with photomicrographs was published later (Radoičić, 1972) showing calcareous tubes with thick walls composed of a series of inserted conical units. De Castro (1975) examined and measured large populations of this fossil in shallow-water Senonian carbonates from the Apenninic Carbonate Platform. He recognized that the the peculiar architecture of the walls was comparable to that of modern scytonematacean cyanobacteria and deduced that this fossil was an ancient cyanobacterium.
When observed in petrographic thin sections under transmitted light the fossils appear as cylindrical tubules, each characterized by a dark wall and a clear lumen. The walls are cylindrical and smooth internally, but uneven externally (Fig. 3A). They are composed of funnels that diverge outward, and often have thin and undulating margins (Fig. 3B). This unique architecture can be examined by optical sectioning, or reconstructed from numerous transverse, oblique and longitudinal cuts through the fossils in thin section. The three-dimensional aspect of the series of inserted funnels is deducible from transitions between saggital and tangential sections (Figs. 3C-E). The fossil tubules, of different lengths and randomly oriented, are scattered in the sediment in densities ranging up to 100 tubules mm3. Such a distribution suggests that they were deposited as fragments, possibly after some transportation. They were never seen in growth position.
Longer tubules are sometimes branched, that is the clear central core (lumen) along with the inner layers of the wall penetrates laterally through the outer wall to form a branch. Several cases of this unusual 'inside out' branching pattern were seen and illustrated by De Castro (1975, Pl. 5, figs. 1-9), who recognized them as false branching of the type characteristic of the filaments in the family Scytonemataceae. | <urn:uuid:0c2496ba-68fb-4d5d-8f89-1ba0ac19a6c8> | 3.234375 | 489 | Knowledge Article | Science & Tech. | 35.495 |
We can use what we know of arithmetic sequences to understand arithmetic series. An arithmetic series is a series or summation that sums the terms of an arithmetic sequence. There are methods and formulas we can use to find the value of an arithmetic series. Understanding arithmetic series can help to understand geometric series, and both concepts will be used when learning more complex Calculus topics.
We're now going to talk about the partial sums for an arithmetic series. So basically what partial sums means is you are summing up a portion of a sequence. Okay? So remember that the sum of a sequence is called the series. So when we add up a portion of the sequence we just get what is called a partial sum, okay? So we're just adding up sum of the terms in the sequence. And we actually have a formula for the sum of an arithmetic sequence. And how it works is s of n, so this is the sum of the first n terms in this series is equal to n over 2. So that's the number of terms and then it's the s of 1 the first term plus s of n being the last term. Okay? So this is a really good formula for you to remember.
There is actually another way to write this as well, and you can either remember it which I tend not to. I have a really bad memory. Or you can derive it which is the way that I do it. Okay? So s of n is the nth term. We have an equation for that though. We have the general term which is s of n is equal to s of 1 plus n-1 times d, okay? So using substitution we could sub this right in and rewrite this equation another way.
s of n is equal to, n over 2 stays the same and what we end up with now is s of 1 plus s of 1, so we end up with 2 s of 1 plus n-1 times d. Okay? So 2 different equations to find the partial sums for an arithmetic sequence.
Kind of key things to note about which one is good for what, okay? They both need to know the number of terms you're adding up. This one is really handy when you know the first and the last term because then you can just plug it in. If you don't know the last term though and you know the difference instead this bottom one is a convenient way to use it because you don't don't have this, you can use this instead. So they're both great but they come in at different times depending on what you have available to you, okay? You could always just remember one but then you're going to have to figure things out along the way. So two different equations for summing a arithmetic series. | <urn:uuid:235bb47c-afed-4554-88f3-f83973a21e40> | 3.9375 | 559 | Tutorial | Science & Tech. | 78.223216 |
The visible satellite imagery is essentially a snapshot of what the satellite sees, unlike Infrared (IR) satellite imagery, which depicts the temperature of the clouds. As the sun approaches midday over a given area, clouds will appear as bright white, as opposed to gray at sunrise and sunset. This is due to more sunlight being reflected as the sun moves overhead. Bodies of water, including lakes and rivers, absorb more sunlight and appear as black, with landmasses displaying as dark gray. It is also important to note that Visible imagery is only updated between sunrise and sunset, when each satellite's 'flashbulb' (a.k.a. the sun) is available.
A weather satellite
is a type of satellite that is primarily used to monitor the weather
of the Earth. These meteorological satellites, however, see more than clouds
and cloud systems
. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover
, ice mapping, boundaries of ocean
currents, energy flows, etc., are other types of environmental information collected using weather satellites.
Weather satellite images helped in monitoring the volcanic ash cloud from Mount St. Helens and activity from other volcanoes such as Mount Etna. Smoke from fires in the western United States such as Colorado and Utah have also been monitored.
Other environmental satellites can detect changes in the Earth's vegetation, sea
color, and ice fields. For example, the 2002 oil spill off the northwest coast of Spain was watched carefully by the European ENVISAT, which, though not a weather satellite, flies an instrument (ASAR) which can see changes in the sea surface
El Niño and its effects on weather are monitored daily from satellite images. The Antarctic ozone hole is mapped from weather satellite data. Collectively, weather satellites flown by the U.S., Europe, India, China, Russia, and Japan provide nearly continuous observations
for a global weather | <urn:uuid:c6f86b3c-8c2d-4079-95bb-5eadb6f47a05> | 4.25 | 396 | Knowledge Article | Science & Tech. | 35.368784 |
Sometimes mathematicians play "fast and loose" with definitions. We probably will not find total
agreement about what a "polynomial" is. Some books will define "a polynomial in x" as opposed
to just a polynomial. And what about a "polynomial in two variables?" If y=2+x is x+y a binomial?
And what does "quotient" refer to? If we consider 7÷2 as a fraction, is 7/2 a quotient? Or is it
3.5? Or is the quotient 3 (with remainder 1)?
And what is a fraction? Which among the following are fractions?
x, 2/x, x/y, 2/3, 2÷3, x÷y, 2*(1/x), x/1, x/3, xy where y=1/z, z where z=1/y, etc.
Let x=1/y, y=1/3 and z=1/x. Which are fractions? x, y, 1/x, 1/y, y/3, xy, xz, yz, 1/yz, etc.
What is an arithmetic fraction, an algebraic fraction, etc.?
And in geometry is an equilateral triangle also isoseles? There has been disagreement on whether
to make the set of equilateral triangles a subclass of isoseles triangles or a separate category of
The best we find at times is a "local" definition where an author defines a term precisely for his
following discussion. And often other mathematicians may find fault with this.
Mathematics is a LANGUAGE and has not been (nor ever is likely to be) "nailed down" so as to be
without ambiguity or disagreement even for the most common and "simple" concepts.
Sometimes we just have to "roll with the punches" and at times ask for clarification of what the
author intends (as is often the case in this forum).
Often pushing for the exact meaning of all the terms we encounter may result in returning to the
undefined terms of a system. But then the expression we obtain for a "higher level" concept's
definition may be so long and involved with the elementary undefined terms as to be basically
As an example consider the "Sheffer stroke" or "Dagger" in T/F two valued logic. Each of these
can be used to define the usual AND, OR, if..then, if and only if, NOT, exclusive OR. But the
expressions for some of these are quite long and complicated using just the one stroke or dagger.
It is interesting that one "operation" can be used to define all the usual stuff, but it is way too
unwieldly to want to use it. As humans we work better with the AND, OR, etc.
As another example consider binary vs hexadecimal. Working with hexadecimal is much easier
for us humans than working with binary, especially when numbers are fairly large. The strings
of 1's and 0's just get too long and difficult to deal with. | <urn:uuid:c12fa179-bffc-48f0-a379-cad89290ead3> | 3.296875 | 668 | Comment Section | Science & Tech. | 69.888537 |
How to Spot The Comet This Week
Two comets visible in the Chilean night sky, March 2013. PANSTARRS is seen in the lower right. Credit: Juri Beletsky, Observatorio de Las Campanas, Chile.
The first of two great comets expected to be visible to the naked eye in 2013 makes its flyby this weekend.
Comet PANSTARRS will be closest to the sun on March 10th, but for those of us in the northern hemisphere, it will start to appear to the west just after sunset tonight, March 8. But for the first couple of days it's going to be close to the western horizon and dim, so you'll need a pair of binoculars and quick reflexes to spot it.
The best viewing will be on March 12th, when we'll have a thin, dim crescent moon to guide youthe comet will be passing very close to it, from our perspective. Even on the 12th and 13th, though (Tuesday and Wednesday), keep a pair of binocs handy if you have them. Although the comet might well be visible to the naked eye, the binoculars will give you a better chance to catch it.
PANSTARRS, first spotted in June 2011 by Hawaii's Panoramic Survey Telescope and Rapid Response project (from which it takes its name), initially had an expected magnitude of 19 (the higher the number, the dimmer the comet). That magnitude would have made it too dim to see without a telescope, but later, scientists revised their rating to a 13.5 and it's been dropping ever since then. Now, it's expected to be a 1 or 2plenty bright enough to spot in the night sky.
To make the event even more exciting, PANSTARRS is a non-periodic comet, meaning it's not like Halley's Comet, which swings by our planet every 86 years or so. Its orbit won't bring it back to our sun for hundreds, if not millions, of years, if it ever returns. | <urn:uuid:d79eef91-1470-4acc-80a8-1036edf016c3> | 3.125 | 421 | Tutorial | Science & Tech. | 66.866336 |
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Posted Sunday, March 10, 2013, at 8:00 AM
I worked with Hubble Space Telescope (HST) for many years. First it was with early data (taken weeks after launch) for my PhD research, and then several years helping to build and calibrate a camera on board called STIS. Working with HST (as those of us in the know call it) and doing as much outreach as I do, I learned quickly that there are a lot of misconceptions about the orbiting observatory.
One of the most frequent is that it can’t observe the Moon, because our natural satellite is too bright. Trying to snap a shot of it would damage Hubble’s detectors.
That’s not true. Well, not totally true. Some cameras on HST are very sensitive, and could be damaged if pointed to a bright source. The ultraviolet camera I worked on was so sensitive it would fry if it looked some kinds of stars too faint to even see with the naked eye!
But other cameras are just fine with bright sources, and that includes the Advanced Camera for Surveys. On Jan. 11, 2012, it took this pretty amazing picture of the Moon:
That’s the crater Tycho, arguably the most famous on the Moon. First, it’s pretty easy to spot near Full Moon with just binoculars; plumes of material that splashed out when the crater formed over 100 million years ago fell back to the surface, creating long streamers called rays that radiate out from the crater. They’re bright and obvious, and delightful through a small telescope. You can see a hint of them in the Hubble picture.
Also, Tycho was where the Monolith was found, buried 4 million years ago by extremely advanced aliens. So there’s that.
Tycho is actually quite round. It only looks elliptical in the Hubble image because the telescope saw the crater at an angle. Judging from the short axis to long axis ratio, it was pretty close to 45°. Notice that the craters around it are similarly distorted. For proof, here’s a picture of Tycho taken by the Lunar Reconnaissance Orbiter, looking straight down on the massive impact site:
Image credit: NASA/Goddard/Arizona State University
See? Round. And mind you, what you’re seeing is huge: Tycho is more than 85 kilometers (53 miles) across! If whatever hit the Moon to form Tycho had instead hit the Earth, we wouldn’t be here to talk about it. That asteroid was probably bigger than any mountain on Earth.
I’ll note that this is a wide-angle image from LRO. It also has a camera that has more magnification, and it took this, one of my favorite pictures of the Moon of all time, showing the mountains in the very center of Tycho:
Image credit: NASA Goddard/Arizona State University
So there you go. The Moon is not too bright for Hubble. Funny though, it is hard to observe by HST, but that’s actually because it’s moving too fast in the sky. Hubble isn’t designed to track that quickly, so what they do to observe it is put it in “ambush mode”: Aim Hubble in the sky where the Moon will soon be, then wait. When the Moon moves in, Hubble grabs the snapshot. This has been done many times, actually (like in 1999 and 2005).
In this case, the shot of Tycho was taken as preparation for the transit of Venus last year. I know, it sounds weird, but the idea was that when Venus passed in front of the Sun, sunlight would be transmitted through the atmosphere of Venus. The different molecules in the planet’s air would then selectively absorb very discrete colors of sunlight. Astronomers hoped that fingerprint would be visible in their observations of the Moon, lit by that same Venusian-filtered sunlight. In this way, they might be able to make similar observations when exoplanets (alien worlds) transit their own stars as seen from Earth, possibly leading to a detection of those planets’ atmospheric constituents. It’s a clever idea.
And, I’ll note, it was done using STIS, the camera I worked on! So it’s neat to see this go full circle. | <urn:uuid:264f443d-b4df-4e8b-9921-455ff9a68cb4> | 3.375 | 910 | Personal Blog | Science & Tech. | 62.407683 |
Bring Back Project Pilot
Most people have never heard of Project Pilot, the U.S. Navy’s maverick air-launched orbital booster program of 1958. Those who have call it an interesting failure. The project probably put one satellite in orbit in six launch attempts. It had minimal effect on the future: The designer of today’s only air-launched booster, the Pegasus, was unaware it existed.
I propose that we bring it back.
Bring all of it back: the shoestring budget, the small team and the lack of structure, reporting and paperwork. If we can’t do all the things in the outlandish concept I’m about to lay out, then let’s at least talk about which parts we can do. We know that no effort since 1958 has given us a cheap responsive launcher, so let’s consider something so crazy it just might work.
For the new Project Pilot, the Department of Defense or NASA would assemble a team of maybe two dozen engineers and technicians. (A couple might be retirees, since end-to-end, hands-on rocket building is out of fashion at best.) Give them access to stored or surplus stages, a test site and machine shop support. Tell them they have a year to put a 5-kilogram payload in orbit. Require short weekly progress reports. Ban PowerPoint and waive all other reporting. Above all, leave them alone.
The original program was started at the Naval Ordnance Test Station (NOTS) in California, now the Naval Air Weapons Station China Lake, when some of their people watched Sputnik 1 pass overhead and said, “We can do that.” They launched Project Pilot, or NOTSNIK. Working initially without official sanction, and with no budget until the last few months, they designed a five-stage all-solid rocket built of surplus and locally made stages. They called their approach “Tinkertoy engineering” — bolting things together to see what worked, fashioning a 1-kilogram satellite and hanging the results on an F4D Skyray fighter to be lofted over the Pacific.
Since then, the utility of nanosatellites has exploded: Missions undreamed of in 1958 can be accomplished with cubesat-based designs. The current nanosat launch approach, ride-sharing, is affordable, but everything depends on the schedule and orbit of the primary payload. Being able to pick the time and orbit is of special concern to the military, though scientific satellites would also benefit. “NOTSNIK 2” would aim to provide users the flexibility of air launch, a recurring cost far below any current launcher, and a response time measured in hours. The chief scientist at U.S. Air Force Space Command has put forth the challenge of a tenfold reduction in launch costs. Let’s do it.
The Project Pilot approach of try-and-fly design and minimal oversight is anathema in the modern age, and didn’t always work in 1958. Of six launches, one achieved at least a short-lived orbit, one may have orbited, and four were definite failures. One Navy report even called Project Pilot an illustration of how not to run a program. And yet it came so close that doing it again, with modern rocket technology, microelectronics (NOTSNIK lacked a flight computer for accurate orbital injection) and personal computer-based design and trajectory programs, should have a high probability of success. While the 1-kilogram NOTSNIK satellites carried a radio transmitter and sometimes a radiation counter, aiming for a 5-kilogram payload today will allow for sophisticated military and scientific missions. If it can evolve to 10 or 15 kilograms, we can start carrying medium-resolution imagers.
I know it wouldn’t be this simple. It would take considerable time and effort just to apply for the waivers needed. Fighter planes and test pilots may not always be available. The payload environment will be harsh. We’d need some expertise Project Pilot didn’t have, such as software skills. To say this can’t work, though, is to say our people are not as good as the Navy team of 1958, when surely they are. NOTSNIK veterans have told me the key was the freedom to try anything without going through channels or being micromanaged. They told me, “You couldn’t do this today.” Well, actually, we can, if we have the will. Physics and orbital mechanics haven’t changed.
How do we do it? Accept risk and development failures. Scrap rules on space-qualified parts. Follow safety rules for aircraft flight and ordnance handling, but waive the 24-month Universal Documentation System process for launch vehicles: If experienced space and missile engineers can’t build something like this safely, we’ve hired the wrong people. Don’t fly from Cape Canaveral Air Force Station in Florida or Vandenberg Air Force Base in California — the no-risk approach to mission assurance (logical when flying billion-dollar satellites) is too entrenched there. China Lake might still be optimal: It has machine shops, launch aircraft, missile stages and quick ocean access. Operate without radar tracking — use GPS only. Since use of a launch range would cost more than the rocket itself, don’t use one: Fly to open ocean where there’s no reporting except for the minimum required by treaty, such as a Notice to Airmen.
U.S. government efforts to build cheap small launchers have struggled in part because they were traditional programs with traditional staff and overhead, and thus had unpalatable cost numbers. Project Pilot spent about $4 million ($29 million today), not counting the contributions of people using their spare time and grabbing surplus parts. The total cost of NOTSNIK 2 should be considerably less than a single Minotaur launch, and would result in an operational launch system at the end that accommodates the desire (in the military’s case, often the necessity) to get the most out of nanosats by launching them exactly when and where needed. Forgo the overhead of return on investment and business case analysis. No one asks about return on investment or break-even for a tactical missile program: They just aim at performing the mission as affordably as possible.
The concept of Project Pilot was sound. Its failures were due to insufficient time and money for testing. (More tests would have revealed they needed to strengthen the fin mounts and thicken the solid rocket motor casings.) They tried to do the whole thing, except for preliminary design work, in about five months. A year is more than enough time to do it right if we accept that the modern mindset about maximizing the payload and minimizing the risk has been carried too far. (It’s also short enough that the leadership would not rotate, an event that can devastate a small, innovative program.) Given the advancements in propellant and materials since 1958, modern stages should allow something akin to NOTSNIK (which weighed 950 kilograms and was only 4.4 meters long) to build in adequate margins rather than requiring precise trajectory shaping and bleeding-edge mass fractions. NOTSNIK had zero moving parts: A launcher with the same philosophy would be orders of magnitude simpler than, say, a Standoff Land Attack Missile Expanded Response (SLAM-ER) missile, which costs $500,000, and should cost less despite the missile’s advantage of mass production.
There are current programs for more affordable small launch. Great — keep them going. But if we want a true paradigm-smasher — reviving the NOTSNIK concept of a launcher as a “munitions-quality round” stored and used as much like a tactical missile as possible — then let’s turn our best people loose with maximum freedom and trust them to succeed.
If we take what worked from Project Pilot and combine it with today’s cheap commercial-off-the-shelf electronics and guidance, add the advantages of modern software and computers, and structure it in a mini-Skunk Works, we can do what they almost did in 1958: create a truly cheap, responsive nanosatellite launch system. The future will thank us for it.
Matt Bille is a freelance space writer and historian in Colorado Springs, Colo. | <urn:uuid:53fc970e-e3ea-4d08-ae3c-cb97b778f7ba> | 2.75 | 1,729 | Personal Blog | Science & Tech. | 50.134333 |
HYPERSPHERE VISUALISATION AND LENSING.
This paper provides a method of visualising the four dimensional hypersphere as a perspective construction in three dimensions, and it also shows how the curvature of hyperspherical space will distort images from distant galaxies and supernovae.
Figure 1. Any attempt to project the surface of the Earth onto a flat surface necessarily leads to some kind of distortion. In addition to the usual Mercator projection that distorts distances towards the poles, we can also make a polar projection by cutting through the equator and then "photographing" each hemisphere from above the poles. Such a projection gives a good representation of distances near the poles but it leads to progressive distortions as we near the equator. Cartographers normally place the two halves of the polar projection in contact at some point, to remind us that all points around the equator of one hemisphere actually touch a corresponding point on the other hemisphere.
Similarly we can represent the 3-sphere or hypersphere as two spheres in which every point on the surface of one of the spheres corresponds to a point on the other sphere, despite that we can only represent them with a single point of contact. Now when we make a polar projection of the Earth's surface, convention dictates that we centre the projection on the poles, but we could chose any two opposite points and cut the sphere across a great circle other than the equator. An egomaniac might delight in a projection with his house at the very centre of the projection, but it would remain a valid projection.
Thus an observer A, in an hypersphere can define her map of it with herself at the centre of one of the spheres. This then defines a second point B, as her hyperspherical antipode, analogous to the point furthest away from her on the surface of the world. In a hypersphere it represents the furthest point you can travel to without starting to come back to where you started from.
Figure 2 . An observer looking into the deep space of an hypersphere could in theory see an abject at her antipode point B, by looking in any direction, analogous to the way in which all routes from the North Pole lead to the South Pole on the Earth. Note that lines of sight curve within an hypersphere, in a way analogous to the way in which meridians curve around the surface of the Earth. Light follows geodesics in space, so if space curves, light has to follow the curvature. Theoretically our observer could see right past her antipode and catch sight of the back of her own head In practice light from near the antipode becomes so red-shifted by the time it gets to A, that A cannot even see quite as far as the antipode.
VHC argues that the curvature of the universe also causes the progressive red-shift of light travelling across it, and that conventional cosmology has mistaken this for recession velocity, an hypothesis which implies an expanding universe. This paper will attempt to show that the supposed acceleration of that expansion arises from the lensing effect of hyperspherical space.
Figure 3. Imagine that we take the polar projection of the Earth and then roll the equator of the Southern Hemisphere around that of the Northern one. This will have the effect of stretching out Antarctica so that it goes all the way around the circumference of the whole map. We would then have a circular and highly topological map of the world with huge distance distortions towards the South Pole which itself now stretches around the entire edge. With a little effort at visualisation we can do something analogous with the two sphere map of the hypersphere, by rolling one sphere all over the entire surface of the other so that all corresponding points come into contact. This will result in the antipode point becoming spread out over the entire surface of the resulting sphere. Astronomers who assume a "flat" Euclidean universe will have effectively and unwittingly distorted their view of the universe in exactly this way if it does in fact have an hyperspherical geometry.
Figure 4. Astronomers who assume a flat universe with no curvature will assume that they can see in straight lines. If they look out into the apparent sphere of space that surrounds them, they will actually see along geodesics which curve relative to the assumed flat space of their maps.
Figure 5. This shows the lensing effects of the hyperspherical curvature.
Objects around the halfway to antipode distance will appear magnified whilst objects well past that point will appear diminished, for an observer located at the origin.
Observers who assume flat space will and measure red-shifts along the linear sight line will also overestimate the distance of objects. VHC calculates the distance to the antipode at about 11 billion light years, whilst current estimates based on flat space give the universe an horizon at about 13.4 billion light years.
Now if hyperspherical lensing diminishes the apparent magnitude of very distant objects it explains why the red-shifts of type 1A supernovae do not match their apparent magnitudes. These supernovae which act as standard candles appear dimmer than they should for their measured red-shifts.
In the VHC model, red-shift still gives a fairly accurate measure of distance, (it does not mean recession velocity), and hyperspherical lensing means that far objects will appear dimmer than expected in flat space. | <urn:uuid:78a5879f-93c6-43d3-a4af-3215a1527fe3> | 3.421875 | 1,117 | Academic Writing | Science & Tech. | 37.519932 |
In this interactive activity adapted from NOVA Online, learn how a typical photovoltaic cell converts solar energy into electricity. Explore the components of a photovoltaic cell, including the silicon layers, metal backing, antireflective coating, and metal conductor strips. Using animations, investigate why the silicon layers are doped with phosphorous and boron, and how an electric field is used to generate electricity from sunlight.
Many solar technologies have been, and continue to be, developed to harness energy from the Sun, an essentially unlimited source of free and environmentally friendly energy. One such technology—photovoltaic (PV) cells—converts sunlight into electricity without producing the harmful emissions that are a by-product of burning fossil fuels in traditional power plants. Typical PV cells are composed of several layers: two different layers of silicon, a metal backing, an antireflective coating, and metal conductor strips. As solar radiation hits the silicon, the energy knocks electrons loose from the silicon atoms; the free electrons then flow out of the cell along the metal conductor strips as electrical current.
PV cells are usually packaged in modules or panels, which are then connected to one another in arrays. PV cells have a variety of applications, from personal electronic devices (such as calculators, cell phone chargers, and bicycle lights) to utility-scale electricity generation at a power plant. Spacecraft and satellites also utilize PV cells to supply energy while in space. Other common uses on the ground include powering road signs, emergency telephones, streetlamps, and driveway lights. PV panels can also be installed to produce environmentally friendly electricity for homes and buildings. Homeowners who install PV systems in homes that are grid connected can sell their excess power to the grid. In addition, PV systems can provide electricity to rural areas that do not have access to the electrical grid.
The materials and manufacturing techniques used to make PV systems are expensive. High production costs, then, have kept the technology from becoming widely implemented. Despite incentives such as subsidies and tax credits, homeowners still have to pay significant initial costs. However, even though there may be higher initial costs to purchase and install a PV system, the system may pay for itself through fuel savings over the lifetime of its use. Furthermore, alternative materials and new technologies are being developed with the aim to reduce costs. For example, thin-film solar cells use less materials than traditional solar cells. These solar cells consist of a thin layer of semiconductor material applied to a supporting material such as glass, plastic, or metal. The reduction in materials needed to make these cells results in a reduction of cost. Researchers are also working on developing nanoparticles that can convert sunlight to electricity. This technology could possibly be used in something like a "solar paint."
Another limiting factor for PV systems is efficiency. Conventional PV cells convert into electricity only about 15 percent of the light that strikes them. At low efficiencies, larger arrays are needed to generate an adequate amount of electricity, and that means higher cost. Advances in PV technology aim to improve efficiency while also keeping production costs low.
Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment. | <urn:uuid:9c5833f4-68a6-4f39-aabf-7e65f7df9344> | 4.46875 | 760 | Knowledge Article | Science & Tech. | 25.841538 |
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A mass driver is a proposed device for propelling objects by using electromagnets. It was first conceptualized in the 1970′s as a possible method to launch rockets into space but still has to come into fruition. Think of it as a linear accelerator directed to the cosmos which, instead of propelling subatomic particles, can shoot large objects.
A typical mass driver will launch an object at very high velocities. After leaving the mass driver, the object will then act as a freely falling body. That is, aside from air resistance, the only substantial force acting on it will be that of gravity. Therefore, in order for it not to be pulled back to the ground, its launch velocity should really be extremely high.
This is one of the reasons why mass drivers are deemed unsuitable for earth-based launches. The rocket, as well as everything inside it, will be subjected to very high g’s. Thus, the trip can end in a disaster before the rocket can even reach its destination. High g’s can be hazardous to human passengers and damaging to sensitive equipment.
Such problems are not present in low-gravity conditions though. Therefore, moon-based or spacecraft-based launches can make use of these contraptions more successfully. All you’ll need is a considerable source of energy, like a nuclear reactor.
Talking about spacecraft-based mass drivers, you can actually use these contraptions to work the other way around. Alright here’s the basic idea: recall Newton’s 3rd Law a.k.a. the action-reaction law. If we take a closer look at any launch scenario or even the manner by which rockets or jet planes move forward, we can easily recognize the action-reaction law at work.
That is, a rocket is propelled forward by pushing some reaction mass backward, much like what happens when you throw a really heavy rock – you get pushed back slightly. If you are somehow able to duplicate that feat in outer space, the absence of friction will allow you to be pushed back much easier.
Thus, if we can attach mass drivers to asteroids, we can slowly change their trajectories by shooting out reaction masses into space. Where to get the reaction masses? Why, the asteroid itself can be your source. Chip off huge chunks of the asteroid and load them into your device.
Think Armageddon and Deep Impact. With this technology, you’ll have an alternative plan to simply just blowing up the asteroid or comet. Of course, that will prevent Bruce Willis wannabes to perform their heroic deeds and a dramatic ending.
We’ve got a few articles that touch on mass driver here in Universe Today. Here are two of them:
NASA also has some more related articles:
Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste: | <urn:uuid:665f3263-de5a-4cef-bf70-159fad1f0b9d> | 3.78125 | 618 | Truncated | Science & Tech. | 54.984736 |
Manipulate directed acyclic graphs
Date/Time of Processing: Tuesday 24 May 1994 12:53:46Pm Overall Assessment of System: OK Classification of System: B Basis of Classification -- Syntax Errors PASS Completeness PASS Independence from External Libraries FAIL Independence from a Specific Ada Compiler PASS Explanations for failures -- System withs non-standard library units that are not provided Number of ... Files 2 Library Units 2 Lines 1761 Statements 500 Comments 581 Unidentified Withed Units -- 3 unidentified withed units
languages/ada/asr/abstractions/dag: File Name Size --------- ---- dag.zip 10,348 Totals ============== ============== 1 Files 10,348
This generic package provides the DAG, or Directed Acyclic Graph, abstract data type. A directed graph is a set of nodes and a set of directed edges connecting pairs of nodes. A directed graph, G, is acyclic iff for each node, N, in G, there is no sequence of edges in G that leads to N. This package maintains acyclicity. The nodes consist of labels and their associated values. Both types are generic formals. There are no explicit bounds on the size of DAGs, as they are implemented on the heap. A DAG is denoted by a labels/edges pair. The following is a list of operations: Constructors: Create: Create an empty DAG Add_Node, Add_Edge: Add a node or an edge to a DAG Set_Value: Set the value of a label of a DAG Copy: Make a copy of a DAG Query Operations: Is_Empty: Return TRUE if a DAG has not been initialized (Create) Is_Root, Is_Leaf: Return TRUE if there is no edge in a DAG such that equal(1,12) or equal(1,11) Is_Successor, Is_Descendent: Return TRUE if (11,12) is an edge or if there is a sequence of edges beginning at 11 and ending at 12 Get_Value: Return the value of a label Root_Count, Node_Count, Edge_Count, Pred_Count, Succ_Count: Counts Put_Image: Output a literal form of a DAG into a file Iterators: Make_Nodes_Iter, More, Next (2) Make_Edges_Iter, More, Next Make_Roots_Iter, More, Next (2) Make_Leaves_Iter, More, Next (2) Make_Preds_Iter, More, Next (2) Make_Succs_Iter, More, Next (2) Make_Preorder_Iter (2), More, Next (2) Make_Postorder_Iter (2), More, Next (2) Heap Management: Destroy_DAG Destroy_DAG_and_Labels Destroy_DAG_and_Values Destroy_DAG_and_Nodes ABSTRACTIONS is used by NOSC/WIS tools 5.1.1, 5.1.2, 6.1.2, and 6.2. See also NEW_ABSTRACTIONS.
DATE VERSION AUTHOR HISTORY 03/85 1.0 Bill Toscano Initial Release
This prologue must be included in all copies of this software. This software is copyright by the author. This software is released to the Ada community. This software is released to the Public Domain (note: software released to the Public Domain is not subject to copyright protection). Restrictions on use or distribution: NONE
This software and its documentation are provided "AS IS" and without any expressed or implied warranties whatsoever. No warranties as to performance, merchantability, or fitness for a particular purpose exist. The user is advised to test the software thoroughly before relying on it. The user must assume the entire risk and liability of using this software. In no event shall any person or organization of people be held responsible for any direct, indirect, consequential or inconsequential damages or lost profits. | <urn:uuid:efd65254-f16e-4128-8924-6a3317f8aa2a> | 2.765625 | 850 | Documentation | Software Dev. | 41.716341 |
Published March 17, 2010
Amphipods , Hemipterans (True Bugs) , Isopods (Pill Bugs) , Uncategorized
Tags: Antarctica, Aphids, Biofuel, Genomics, Limnoria, Limnoriids, Lyssianasids
Quick blurbs about arthropod research and news:
- NASA climate researchers have discovered animal life deep below the Pine Island Glacier Ice Shelf in Antarctica. The researchers drilled a hole six-hundred feet deep and eight inches wide into the glacial ice sheet about twelve miles from the open ocean. When they lowered a camera below the ice sheet, the scientists were surprised to see a Lyssianasid amphipod crustacean swim up and park on the cable. The researchers were only expecting to find microbial life under the ice sheet this far in from the open ocean. It is unknown what the primary energy source for animals living here could be. The presence of a three-inch amphipod, however, suggests a much more elaborate and dynamic ecosystem than hypothesized in this poorly understood habitat. (DSN has a video of the amphipod)
- Limnoriid isopods, commonly called gribble worms for some reason (they neither are, nor resemble worms), have a ravenous appetite for wood. This is not unusual among arthropods; many diverse groups including termites, millipedes, and squat lobsters are capable of digesting woody plant matter. However, all these creatures process the wood with the aid of gut-dwelling symbiotic bacteria. A new study finds that the Limnoriid isopod, Limnoria quadripunctata is special in that it doesn’t rely on bacteria-produced catalysts to break down wood, but rather has the necessary glycosyl hydrolase enzymes incorporated into its genome. These enzymes are evolutionarily related to similar proteins found in arthropods, but their derived function for wood digestion in Limnoriid isopods is completely novel. The researchers, or their over-excitable university PR department, think the study of these enzymes could aid in bio fuel synthesis.
- The gemone of the pea aphid, Acyrthosiphon pisum, has been sequenced. This is the first Hemipteran (true bug) genome and will provide clues about the evolutionary history of certain hexapod groups. This new genome could also help agriculturalists develop new techniques to control aphid pests and the spread of aphid-borne plant viruses. Researchers are also interested in the pea aphid’s, apparently, scaled down immune response system and their ability to easily switch specialization from one plant species to another.
The BBC is presenting an article and series of films from a recent University of Aberdeen research expedition. The films are shot between 5.5 kilometers and 10 kilometers in depth and feature snailfish, decapod shrimp, isopods, and amphipods as they scavenge on a bait bag. The videos are narrated by Dr. Alan Jamieson, and he shares some neat insights about deep sea life.
I am personally surprised at the ridiculous swarms of amphipods in the 9 km and 10 km videos. I did not think deep sea life was that dense except around vents and seeps. They don’t say how long the bait bag was there before the film starts, and it could have been down there for hours attracting every amphipod in a 100 m radius. However, a quick check of the literature reveals that these near-bottom deep-sea amphipod swarms have been observed near vents as well as in open abyssal plains. Pelagic swarming is not typically a characteristic attributed to deep sea crustaceans and its ecological significance is unknown.
A swarm of undescribed paradaliscid amphipods, photographed from the submersible Alvin near a deep sea vent in the East Pacific Rise (Dover et al., 1992).
Dover, C.L.V. et al., 1992. Deep-sea amphipod swarms. Nature, 358(6381), 25-26.
Published December 10, 2009
There is an interesting anecdote which claims that the amphipod crustacean genus, Phronima, served as the inspiration for the alien queen first seen in James Cameron’s, “Aliens.”
Photo: Pål Abrahamsen
The story seems to originate from David Attenborough’s narration in the “Blue Planet” documentary (Skip to 3:25 in this video for the scene in question). Some people around the web rebut this, stating that the original alien design was based on a painting by artist H. R. Giger. This seems to be the case as far as the original “soldier” alien morph seen in “Alien” (1979) is concerned. It is much more likely that Phronima actually influenced the design of the queen alien morph, seen in “Aliens” (1986).
I’ve tried to contact someone at the special effects company, Stan Winston Studios, but they seem to be hard to get a hold of if you are not the producer of a multi-hundred-million dollar blockbuster. Instead, lets talk a little about Phronima, which is an awesome animal regardless of whether or not it was the inspiration for the alien queen.
Continue reading ‘Did Phronima inspire the design of the Alien Queen?’
Published December 3, 2009
Amphipods , Photography
Photo: Torben Riehl, University of Hamburg
The antarctic oceans holds a surprising diversity of marine life, including this pointy amphipod crustacean. See other amphipods from the antarctic, here. | <urn:uuid:d6ea4499-f398-4811-ba55-b43aba4cd63d> | 3.3125 | 1,207 | Personal Blog | Science & Tech. | 41.013423 |
The total eclipse of 1999 August 11 is the twenty-first member of Saros series 145 (Table 37), as defined by van den Bergh . All eclipses in the series occur at the Moon's ascending node and gamma1 decreases with each member in the family. The series is a young one which began with a minuscule partial eclipse at high northern hemisphere latitudes on 1639 Jan 04. After fourteen partial eclipses each of increasing magnitude, the first central eclipse occurred on 1891 Jun 06. The event was a six second annular eclipse with a path sweeping through eastern Siberia and the Arctic Ocean. Although the vertex of the umbral shadow fell just short of Earth's surface, the Moon's distance was gradually decreasing with each subsequent eclipse in the series. In fact, the very next eclipse was a hybrid or annular/total eclipse on 1909 Jun 17. Greatest eclipse occurred in the Arctic Ocean and lasted 24 seconds.
The third central eclipse of Saros 145 occurred on 1927 Jun 29. It was the first total eclipse of the family and coincidentally passed through England in addition to Scandinavia and Siberia. On 1945 Jul 09, the path of totality began in Idaho and quickly swept northeast through Montana, Saskatchewan and Manitoba. After crossing Hudson Bay, Greenland and the North Atlantic, the umbra returned to Scandinavia and Siberia. The fifth central eclipse occurred on 1963 Jul 20 and is well known to many eclipse observers. Its path crossed Alaska, central and eastern Canada and Maine. The event drew a great deal of media attention and a beautiful article about the eclipse appeared months later in the pages of National Geographic [November 1963]. In fact, one of the authors (Espenak) has fond memories of watching the partial phases of this eclipse as a boy from his grandmother's home in Long Island.
The most recent eclipse of the series took place on 1981 Jul 31 and its path crossed central Siberia, Sakhalin Island and the Pacific Ocean where it ended north of Hawaii. After 1999, the following member occurs on 2017 Aug 21. This is the first total solar eclipse visible from the continental United States since 1979 Feb 26. The path of totality stretches from Oregon through Idaho, Wyoming, Nebraska, Missouri, Illinois, Kentucky, Tennessee and the Carolinas and has a greatest duration of 2m 40s (Map of Eclipses in North America - 2001 - 2050).
During the 21st through 24th centuries, Saros 145 continues to produce total solar eclipses of increasing duration as the path of each event shifts southward. By the time the midpoint of the series is reached (2324 Feb 25), the duration of totality exceeds four minutes. The duration continues to increase into the 25th and 26th centuries. The maximum duration of totality peaks at 7m 12s on 2522 Jun 25. In the remaining six umbral eclipses, the duration rapidly drops but still lasts almost three minutes during the final total eclipse on 2648 Sep 09.
For the next three and a half centuries, twenty partial eclipses of progressively decreasing magnitude occur. The final event takes place on 3009 Apr 17 from the polar regions of the Southern Hemisphere. A detailed list of eclipses in Saros series 145 appears in Table 37.
In summary, Saros series 145 includes 77 eclipses with the following distribution:
Saros 145 Partial Annular Ann/Total Total Non-Central 34 0 0 0 Central - 1 1 41
1 Minimum distance of the Moon's shadow axis from Earth's center in units of equatorial Earth radii.
Gamma defines the instant of greatest eclipse and takes on negative values south of the Earth's center.
Adapted from NASA RP 1398 "Total Solar Eclipse of 1999 August 11".
WebMaster: Fred Espenak
Planetary Systems Branch - Code 693
NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771 USA | <urn:uuid:1aaedd37-213e-4aab-9eea-d1494f1792d2> | 2.953125 | 789 | Knowledge Article | Science & Tech. | 51.84024 |
Previous Next Edit Rename Undo Refresh Search Administration
Static Sub IndexMask ( Mask As Integer )
the writing of individual bits in the color index buffers.
Specifies a bit mask to enable and disable the writing of individual bits
in the color index buffers.
Initially, the mask is all 1's.
controls the writing of individual bits in the color index buffers.
The least significant
bits of mask
is the number of bits in a color index buffer,
specify a mask.
Where a 1 (one) appears in the mask,
it's possible to write to the corresponding bit in the color index
buffer (or buffers).
Where a 0 (zero) appears,
the corresponding bit is write-protected.
This mask is used only in color index mode,
and it affects only the buffers currently selected for writing
Initially, all bits are enabled for writing.
Gl.INVALID_OPERATION is generated if Gl.IndexMask
is executed between the execution of Gl.Begin
and the corresponding execution of Gl.End.
with argument Gl.INDEX_WRITEMASK
See original documentation on OpenGL website | <urn:uuid:f3de3e5d-0343-4886-b6a3-e412261b1eb9> | 2.9375 | 242 | Documentation | Software Dev. | 46.80686 |
What is Phase?
As a sinoidal signal in the time domain can be defined as
The signal phase describes an 'offset' of the signal along the time axis and defines the 'zero crossing' of the signal. An sinoid signal is periodic, therefore usually only phase values from +/-180deg (or +/-Pi) are used.
You see here an sinoidal signal with a frequency of 1kHz and an amplitude of 2 Volts. Time scale is -1msec..+1msec. The signal is shown with 3 different phases, from left to right:
- -60 degree
- 0 degree
- +60 degree
Please have a look at the zero crossings! In the left picture the crossings are shifted to the right, in the right picture to the left hand side.
Note: the phase can be either expressed as +/-Pi or +/-180deg. The signal itself can be described as cosine or sine, both is equivalent and up to you depending where you define the time t = 0. | <urn:uuid:facf3f3e-fc6b-4983-b3ac-997e4f762fc3> | 3.25 | 211 | Knowledge Article | Science & Tech. | 64.998147 |
Value Types and Reference Types
A data type is a value type if it holds the data within its own memory allocation. A reference type contains a pointer to another memory location that holds the data.
Reference types include the following:
All arrays, even if their elements are value types
Class types, such as Form
You can assign either a reference type or a value type to a variable of the Object data type. An Object variable always holds a pointer to the data, never the data itself. However, if you assign a value type to an Object variable, it behaves as if it holds its own data. For more information, see Object Data Type.
You can find out whether an Object variable is acting as a reference type or a value type by passing it to the IsReference method on the Information class in the Microsoft.VisualBasic namespace. Information.IsReference returns True if the content of the Object variable represents a reference type. | <urn:uuid:6965d1fa-d93e-4736-8096-40969a3b34b0> | 3.640625 | 190 | Documentation | Software Dev. | 37.496317 |
Computer Simulations of the Martian Atmosphere Interacting with the Solar Wind
Tom Bridgman, Marte Newcombe, Cindy Starr, Naoki Terada, Hiroyuki Shinagawa, NASA GSFC Scientific Visualization Studio, NASA GSFC Scientific Visualization Studio, NASA GSFC Scientific Visualization Studio, Solar-Terrestrial Environment Laboratory; Nagoya
University; Japan, Solar-Terrestrial Environment
Laboratory; Nagoya University; Japan
Mars possesses no significant intrinsic magnetic field. The absence of magnetic
protection allows the supersonic solar wind flow to directly interact with the
Martian ionosphere (an almost fully ionized region of the Mars upper
atmosphere). When the velocity of the solar wind increases,
the Martian ionosphere is compressed and the ionopause (a boundary layer
between the ionosphere and the solar wind) is displaced to lower altitudes.
The ions of planetary origin such as O+ and O2+ escape from the upper
atmosphere of Mars due to solar wind induced scavenging processes. Many more
planetary ions are scavenged when the solar wind velocity increases because a
much larger part of the planetary atmosphere is exposed to the solar wind as
the ionopause is pushed inwards towards the planetary surface.
There are some indications that the solar wind flow, as well as the Suns x-ray
and extreme ultraviolet radiation, were much more intense early in solar system
history. It is thought that some 3.5 billion years ago, these extreme
interplanetary conditions may have caused a much larger rate of water loss from
the Martian atmosphere. We estimate that the solar wind scavenging pictured
here under the extreme conditions in the early solar system would have caused
the loss of a 10 meter global equivalent ocean layer from Mars over the last
3.5 billion years. This loss is less than one tenth of the 156 m global
equivalent ocean layer estimated to have existed on early Mars using the Mars
Global Surveyor observations.
Arrows represent the flow of the ions of planetary origin. The colors represent the density of the
Martian ionosphere, with red as high and blue as low.
This description of a site outside SERC has not been vetted by SERC staff and may be incomplete or incorrect. If you
have information we can use to flesh out or correct this record let us know. | <urn:uuid:68f0f781-98fc-4640-8362-77042167a7cc> | 3.140625 | 490 | Knowledge Article | Science & Tech. | 24.19523 |
Investigate how this pattern of squares continues. You could
measure lengths, areas and angles.
A man paved a square courtyard and then decided that it was too
small. He took up the tiles, bought 100 more and used them to pave
another square courtyard. How many tiles did he use altogether?
Can you work out the area of the inner square and give an
explanation of how you did it?
A $2$ by $3$ rectangle contains $8$ squares. Can you see how?
A $3$ by $4$ rectangle contains $20$ squares. Can you see how?
A $4$ by $6$ rectangle contains $50$ squares. Can you see how?
What size rectangle contains exactly $100$ squares?
Is there more than one?
Can you find them all?
Can you prove that there are no more?
Click here for a poster of this problem. | <urn:uuid:305853ed-76a2-4383-9b63-f7a97de40ea6> | 2.890625 | 196 | Tutorial | Science & Tech. | 79.852429 |
The extent of adsorption of a gas on the surface of a solid depends on the following factors:
(a) Nature of gas
(b) Nature of solid
(c) Specific area of solid
(d) Pressure of gas
(f) Activation of solid
(i) Nature of gas:
Since physical adsorption is non-specific in nature, any gas will be adsorbed on the surface of a solid to some extent or other. However, under any given conditions of temperature and pressure, easily liquefiable gases such as NH3, CH4HCI, CI2, SO2, CO etc. are adsorbed more than permanent gases like H2, O2, N2 etc. Chemisorption is specific in nature. Therefore, only those gases will be adsorbed which form chemical bonds with it.
(ii) Nature of solid:
Activated charcoal is the most common adsorbent for easily liquefiable gases. Poisonous gases such as CH4 and CO fall in this group. Therefore, it is used in gas masks. Other gases such as O2, H2 and N2 adsorb more on metals such as Ni, Pt and Pd.
(iii) Specific area of solid:
Specific area of an adsorbent is the surface area available for adsorption per gm of adsorbent. Greater the specific area of an adsorbent, greater will be the adsorption. The specific area of an adsorbent can be increased by making the surface rough. The pores must be large enough to allow penetrations of gas molecules. | <urn:uuid:059228dc-7946-4343-81ae-cfd49d904ac0> | 3.4375 | 336 | Knowledge Article | Science & Tech. | 47.6905 |
An infinitely long, thin conducting sheet defined over the space \(0<=x <= \infty\) and \(-\infty <= y <=\infty\) is carrying a current with a uniform surface current density \(J_s=a_y5\) .
(a) write down R
(b) what is the direction of dI x R? Note that I is the current vector
(c) Calculate B (note you may need to preform lengthy algebra). | <urn:uuid:ac3b2d8d-854b-47d3-b334-b3515a88f855> | 3.125 | 101 | Q&A Forum | Science & Tech. | 62.455 |
public member function
explicit binomial_distribution ( result_type t = 1, double p = 0.5 );
explicit binomial_distribution ( const param_type& parm );
Construct binomial distribution
Constructs a binomial_distribution object, adopting the distribution parameters specified either by t and p or by object parm.
- The upper bound of the range ([0,t]) of possible values the distribution can generate.
This represents the number of independent Bernoulli-distributed experiments each generated value is said to simulate.
result_type is a member type that represents the type of the random numbers generated on each call to operator(). It is defined as an alias of the first class template parameter (IntType).
- Probability of success.
This represents the probability of success on each of the independent Bernoulli-distributed experiments each generated value is said to simulate.
This shall be a value between 0.0 and 1.0 (both included).
- An object representing the distribution's parameters, obtained by a call to member function param.
param_type is a member type.
// binomial_distribution example
// construct a trivial random generator engine from a time-based seed:
unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
std::default_random_engine generator (seed);
std::binomial_distribution<int> distribution (10,0.5);
std::cout << "some binomial results (t=10,p=0.5): ";
for (int i=0; i<10; ++i)
std::cout << distribution(generator) << " ";
std::cout << std::endl;
some binomial results (t=10,p=0.5): 5 5 4 5 4 5 6 4 5 4 | <urn:uuid:6ffd3978-fec0-4bbd-98b2-e6bd40fd6bac> | 3.171875 | 406 | Documentation | Software Dev. | 44.466346 |
The phosphatases are enzymes which catalyse the transfer of the phosphate radical (PO4) between the inorganic ionic state, as in sodium phosphate, and attachment to an organic radical, as in glucose 6-phosphate. There are numerous kinds of phosphatase in the body. One of these, red-cell acid phosphatase, is present in red cells and is most active under acid conditions. It has several genetic variants, distinguished by their electric charges, and hence by their speeds of migration during electrophoresis. They also differ somewhat in the strength of their enzymic activity.
The variants Pa, Pb, and PC are present in most populations with greatly varying frequencies, while Pr is found almost solely in southern Africans, and especially in the Khoisan peoples.() | <urn:uuid:46b5ff44-2fd5-4065-b3b9-204fa2d52c37> | 3.09375 | 164 | Knowledge Article | Science & Tech. | 31.149304 |
On December 25, 1999, another "Chesapeake Bay" effect snow event occured within the Wakefield CWA. As in the November 30, 1999 case, very cold 850 MB temperatures were indicated across the area. 850 MB temperatures were in the -10C to -15C range across the area where the "bay effect" plume was generated. Bay water temperatures were around 4C. This yielded an 850 MB - Bay surface temperature difference on the order of 14-19C, in excess of the 13C temperature difference required to generate "Bay effect" or "Lake effect" snow.
Wind direction is also critical for the generation of a "Bay effect" snow
event. Surface winds must be between 340 degrees and
010 degrees. 360 degrees is optimal. The direction of wind is oriented along the length of the Bay to provide the maximum over water trajectory conducive to the development of "Bay effect" snow bands.
Enhanced IR satellite imagery from 1615 UTC December 25, 1999 shows a plume of low clouds (indicated by the blue enhancement) across the southern Chesapeake Bay extending across portions of Norfolk and Virginia Beach. The Wakefield WSR-88D was in clear ir mode at the time. The 0.5 degree base reflectivity image from 1600 UTC December 25, 1999 shows the plume of low clouds and "Bay effect" snow quite clearly. Some reflectivity values were in the 16-21 dBz range. Light to locally moderate snow was occuring over portions of Norfolk, Chesapeake and Virginia Beach at the time. Temperatures were in the Middle and Upper 20s at the time.
The following is a sequence of surface observations from Norfolk
International Airport - Times are in EST
|05:51||26.6° F 12.2° F 30.33 in 10.0 mi 340/12 Mostly Cloudy|
|06:51||26.6° F 12.2° F 30.39 in 10.0 mi 350/13 Mostly Cloudy|
|07:51||26.6° F 14.0° F 30.39 in 10.0 mi 350/14 Mostly Cloudy|
|08:51||26.6° F 15.8° F 30.42 in 10.0 mi 360/10 Snow/Light Snow|
|09:51||26.6° F 17.6° F 30.42 in 7.0 mi 350/13 Snow/Light Snow|
|10:51||28.4° F 12.2° F 30.42 in 10.0 mi 340/12 Scattered Clouds|
|11:51||30.2° F 10.4° F 30.39 in 10.0 mi 330/14 Partly Cloudy|
|12:51||30.2° F 12.2° F 30.39 in 10.0 mi 330/12 Partly Cloudy| | <urn:uuid:a05f9589-ef58-480a-b90a-a3a34371cbfe> | 3 | 602 | Knowledge Article | Science & Tech. | 97.592727 |
Given three disjoint circles A, B and
C of unequal radii situated entirely in each other's exterior,
the common internal tangents of circles A and C meet in Y, the
common internal tangents of circles A and B meet in Z and the
common external tangents of circles B and C meet in X. Then the
points X, Y and Z are collinear.
Instructions: Dynamic Geometry
(Requires Java 1.3 or higher and Java enable browser)
You can alter the figure above
dynamically in order to test and prove (or disproved)
conjectures and gain mathematical insight that is less readily
available with static drawings by hand. To explore this
theorem use the replay buttons above to move step by step
(1-2-3-4-5) through the geometric construction:
the Start (Step 1),
to next break (Step 2-3-4-5),
To the end.
Manipulate the dynamic circles
by dragging the points
at any step.
The cursor keys (left, right,
up, down) move the picture. To give the keyboard focus to
the applet, click into it.
The + and - key change the size
This page contains a
C.a.R. interactive geometry applet by R. Grothmann. Please be
patient while the applet loads on your computer. If you are
using a dial-up connection, it may take a couple minutes. If you
get a warning-security asking 'Do you want to trust the
signed applet distributed by "Rene Grothmann"?'. Please
click 'Always', and you will not be troubled again.
If you can't see the presentation above, check a more recent
version of your browser. Alternately, it may be that your
browser supports Java, but that it’s currently set to disable
Java applets. Dynamic Geometry applet requires a Java Plug-in
1.3 or higher (More details at: | <urn:uuid:0fad43f9-b9d4-4487-87db-5942470fc679> | 3.125 | 432 | Tutorial | Science & Tech. | 65.341862 |
Maintained by W-W
There are two main reasons for studying the Sun. First, there is the practical need to understand how changes at the Sun's surface affect the flow of energy and of dangerous radiation to Earth. Second, the Sun is the only star that is close enough to study its surface in detail. What we learn about sunspots and flares on the Sun can be applied to billions of other stars in the Galaxy.
IfA scientists are participating in a project to design and develop the next-generation solar research telescope called the Advanced Technology Solar Telescope (ATST). This instrument represents the largest single advance in ground-based solar observing since the time of Galileo! The project is being funded by the National Science Foundation (NSF).
The Science Working Group of the ATST project have recommended Haleakala as the future site of the world's largest optical solar telescope, with a final decision to be made in December 2004 based on logistical and other issues.
The main instrument used at Mees Observatory is the imaging vector magnetograph, which allows astronomers to measure the electric currents passing through selected regions of the Sun's surface. Electric currents are closely tied with magnetic fields on the Sun and are a key to understanding what goes on both below and above the visible surface of the Sun.The Imaging Vector Magnetograph measures the circular and linear polarization of the Zeeman components of a neutral iron absorption line in the spectrum of the Sun. These data are used to make a three-dimensional map of the magnetic field at the Sun's surface; the electric current through the surface is obtained by calculating the 'curl' of the magnetic field and applying Maxwell's equations.
Measurements of sunspots with the imaging vector magnetograph show that magnetic fields emerge at the solar surface already carrying electric currents and that the direction of currents' flow is systematic over space and time. This work has caused us to think of solar electric currents in a different way: as probes of the solar interior and of the magnetic dynamo that drives the 11-year sunspot cycle.
A fundamental mystery of the Sun is why it varies with a semi-regular period of 11 years. These changes have been detected from acoustic wave observations (helioseismology) and by sensitive measurements of the Sun's brightness. While the ultimate engine that drives these changes is almost surely magnetic, we are beginning to learn how global solar properties, like the Sun's brightness are affected by cyclical changes in the deep solar interior.
Jeffrey Kuhn is working to understand the physical mechanisms of the solar cycle. He uses data from a world network of telescopes he designed with Haosheng Lin and R. Coulter, and a space satellite experiment called the Solar Oscillations Investigator which is a part of the SOHO experiment package at the Earth-Sun Lagrange point. Much of this work involves modeling and understanding small oscillations in the Sun's shape and brightness.
Eruptive flares on the Sun's surface generate high-energy particles that reach Earth in a few days. These particles can disrupt radio communication, trigger the aurorae, and produce dangerous levels of radiation at high altitudes. Observations at Mees indicate that the emergence of electric currents at the Sun's surface is likely to be important to the driving of solar flares because previously existing magnetic structures suddenly can be energized. This is analogous to turning on a light bulb: It is much faster to connect it to a current-carrying system than to start a generator. To test this idea, magnetic data from Mees are being compared with images of the solar corona taken by spacecraft such as the Japanese satellite Yohkoh and the European satellite SOHO.
The solar corona is the highest layer in the Sun's atmosphere and the place where the solar wind originates. The distribution of gas in the corona, as revealed by X-ray images taken from satellites, is strongly affected by solar magnetic fields, but the coronal fields themselves cannot be measured directly. By extrapolating the magnetic field and current data at the Sun's surface, however, it is possible to calculate the magnetic fields in the corona and relate these to the structure, temperatures, pressures, and other physical properties of the corona observed in the spacecraft images.
Jeffrey Kuhn is working on new ideas for telescopes which can see faint objects near the bright glare of, for example, the Sun. Such a prototype telescope for solar coronal observing, called SOLARC, will soon be working on Haleakala. He is also involved with the SPHERIS satellite project to measure solar brightness, shape and radius properties with unprecedented precision: surface temperature variations of 0.1K, shape oscillations which affect the limb at the level of 1 microarcsecond, and radius changes of smaller than a milliarcsecond | <urn:uuid:17990261-88f2-4e94-854a-0cf855572326> | 3.828125 | 978 | Knowledge Article | Science & Tech. | 30.15747 |
Why is 30 the “Magic Number” for Sample Size?
It seems like whenever people learn about statistical problem solving, the sample size question comes up. Invariably, the number 30 is bandied about as a sweet spot that should get the job done. Astute learners generally want to understand why 30 seems to work. Read on to find out why.
The answer really hinges on an understanding of how confidence intervals for the standard deviation are created, and how they rely on the sample size for their accuracy: the larger the sample size, the better the accuracy of the standard deviation estimate. Here’s the formula for the upper and lower confidence limits on standard deviation:
Rather than go into a lengthy explanation of chi-squared distributions and how the formula is derived, it’s easier to visualize what’s going on. Imagine that we’re taking samples of the melting point of blue candles, and after each sample, we calculate the mean, standard deviation, and the confidence limits for the range of where the standard deviation could be at the 95% confidence level. For the sake of argument, let’s assume that we know from previous experience that the mean melting point is 100F, with a standard deviation of 3. If we start taking samples and calculating as we go, we get something like this:
With only one sample, we can’t calculate much in terms of standard deviation, but look at what happens to our best guess of the standard deviation (s) as we take each sample. It starts at 1.7, moves down to 1.3, and then jumps up to 1.9. Furthermore, look at the limits. While the lower limit isn’t changing much, the upper limit is certainly bouncing around. How long do we have to continue taking samples until the standard deviation and limits stop bouncing around?
The best way to see is to create a graph of the standard deviation and limits, calculated at each sample. Here’s the graph:
Notice how the confidence limits tend to bounce around a lot at the beginning, then they tend to calm down after awhile? This is why 30 samples is usually deemed sufficient: if we recreate our chart with some new measurements, here’s what we get:
In this case, we didn’t get so much bouncing as the first time, so we’re more confident more early on. However, it’s very hard to know beforehand how much bouncing around you’ll get, so most people stick with 30 samples, just to be sure.
But don’t just take my word for it. I’ve made an Excel Demo that you can play with. Just input your parameters, and it will calculate a sampling scenario. Pressing ‘F9′ will force Excel to choose new samples and recalculate the graph. If you’re curious about the Math and the Excel functions, just unlock the worksheet and have at look (there’s no password required–I locked the worksheet to make it simpler).
Looking for a way to calculate how many samples you need? Take a look at the software page, and see if Stats Helper is right for you. | <urn:uuid:20a08ff6-ecef-4808-9cb4-c877adddf5b0> | 3.296875 | 665 | Personal Blog | Science & Tech. | 61.010561 |
THE future of biofuels just got brighter. Yields from farm-scale plantings of the switchgrass Panicum virgatum suggest that producing ethanol from the cellulose in these crops will be about twice as energy-efficient as previously estimated.
Researchers led by Ken Vogel of the US Agricultural Research Service in Lincoln, Nebraska, paid farmers in Nebraska, North Dakota and South Dakota to grow switchgrass for five years in plots ranging from 3 to 9 hectares. They measured the energy needed to grow the crops, including that used to make fertilisers and the diesel consumed by farmers' vehicles.
From the biomass of grasses harvested, they calculated that ethanol derived from them should yield 5.4 times as much energy as all these inputs combined (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0704767105).
Vogel's results will not please ecologists who want to restore prairie ecosystems by growing mixtures of grasses without ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:9d1499ed-f1b5-433b-874e-dd7ebe220911> | 3.21875 | 231 | Truncated | Science & Tech. | 47.600525 |
Uses of linear programming
Name: nick j wilwert
Date: Around 1995
Could you list some ways in which linear programming is used in real life?
There is a journal called "The Journal of Operations Research" that
contains articles by people who apply linear programming to everyday
problems. One of the classic applications is by railroads that own freight
cars that have to be sent to all parts of the country. At any given moment,
where are the best places to put all the railroad cars so that the custo-
mer's needs can be met in the shortest time and with the least expense.
And of course in general in economics, linear programming tells you what
arrangement of activities will maximize your profits (or whatever you are
trying to maximize). Of course things are seldom linear in real life, so
extensions of linear programming techniques, rather than linear programming
itself, is probably more important these days.
Click here to return to the Mathematics Archives
Update: June 2012 | <urn:uuid:b64563d8-92e8-49ba-a122-841926378bba> | 2.734375 | 213 | Knowledge Article | Science & Tech. | 39.272789 |
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A useful introduction to a range of modern quantum mechanics principles with many animations and examples of everyday situations.
This applet enables the user to show how a quantum wave packet develops with time.
A complex mathematical description of the essential non-classical nature of quantum entanglement
The new world of quantum computers promises amazing breakthrough and find out how computers hope to achieve this.
This site is about Quantum Atomica, a free program developed to specifically visualise the hydrogen orbitals in a variety of ways.
The Leidenfrost effect explains why water sometimes 'rolls' off a hot plate or frying pan, and how some experts can dip their hands into liquid nitrogen or even molten lead without hurting themselves
Description of the Mossbauer effect and absorption in Ir-191, with application to gravitational red shift.
An experiment to show the Coanda effect along with a short explanation of why and how aeroplanes fly.
A video about the electrowetting effect, which change the shape of a liquid droplet.
Having it both ways is part of quantum mechanics, our best guess at understanding how the universe works at its deepest level. It’s thoroughly weird and contradictory, and computers are preparing ...
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The best way to predict the future is to create it.
The researchers used high-speed light sheet microscopy to image the activity of 80% of the neurons in the brain (which is composed of ~100,000 neurons) of a fish larva at 0.8 Hz (an image every 1.3 seconds), with single-cell resolution.
This represents the first technology that achieves whole brain imaging of a vertebrate brain at cellular resolution with speeds that approximate neural activity patterns and behavior, as Nature Methods methagora blog noted.
The authors saw correlated activity patterns at the cellular level that spanned large areas of the brain — pointing to the existence of broadly distributed functional circuits.
The next steps will be to determine the causal role that these circuits play in behavior — something that will require improvements in the methods for 3D optogenetics, the blog said. Obtaining the detailed anatomical map of these circuits will also be key to understand the brain’s organization at its deepest level. | <urn:uuid:8df48799-85c2-4ab3-92f3-42cb2a698846> | 3.34375 | 216 | Truncated | Science & Tech. | 42.781566 |
This PEP has been withdrawn in favor of PEP 3141.
Today, Python's numerical model is similar to the C numeric model:
there are several unrelated numerical types, and when operations
between numerical types are requested, coercions happen. While
the C rationale for the numerical model is that it is very similar
to what happens at the hardware level, that rationale does not
apply to Python. So, while it is acceptable to C programmers that
2/3 == 0, it is surprising to many Python programmers.
NOTE: in the light of recent discussions in the newsgroup, the
motivation in this PEP (and details) need to be extended.
In usability studies, one of the least usable aspect of Python was
the fact that integer division returns the floor of the division.
This makes it hard to program correctly, requiring casts to
float() in various parts through the code. Python's numerical
model stems from C, while an model that might be easier to work with
can be based on the mathematical understanding of numbers.
Other Numerical Models
Perl's numerical model is that there is one type of numbers --
floating point numbers. While it is consistent and superficially
non-surprising, it tends to have subtle gotchas. One of these is
that printing numbers is very tricky, and requires correct
rounding. In Perl, there is also a mode where all numbers are
integers. This mode also has its share of problems, which arise
from the fact that there is not even an approximate way of
dividing numbers and getting meaningful answers.
Suggested Interface For Python's Numerical Model
While coercion rules will remain for add-on types and classes, the
built in type system will have exactly one Python type -- a
number. There are several things which can be considered "number
Obviously, a number which answers true to a question from 1 to 5, will
also answer true to any following question. If "isexact()" is not true,
then any answer might be wrong.
(But not horribly wrong: it's close to the truth.)
Now, there is two thing the models promises for the field operations
(+, -, /, *):
- If both operands satisfy isexact(), the result satisfies
- All field rules are true, except that for not-isexact() numbers,
they might be only approximately true.
One consequence of these two rules is that all exact calcutions
are done as (complex) rationals: since the field laws must hold,
(a/b)*b == a
There is built-in function, inexact() which takes a number
and returns an inexact number which is a good approximation.
Inexact numbers must be as least as accurate as if they were
Several of the classical Python functions will return exact numbers
even when given inexact numbers: e.g, int().
The number type does not define nb_coerce
Any numeric operation slot, when receiving something other then PyNumber,
refuses to implement it.
The functions in the "math" module will be allowed to return
inexact results for exact values. However, they will never return
a non-real number. The functions in the "cmath" module are also
allowed to return an inexact result for an exact argument, and are
furthermore allowed to return a complex result for a real
Numerical Python Issues
People who use Numerical Python do so for high-performance vector
operations. Therefore, NumPy should keep its hardware based
Which number literals will be exact, and which inexact?
How do we deal with IEEE 754 operations? (probably, isnan/isinf should
On 64-bit machines, comparisons between ints and floats may be
broken when the comparison involves conversion to float. Ditto
for comparisons between longs and floats. This can be dealt with
by avoiding the conversion to float. (Due to Andrew Koenig.)
This document has been placed in the public domain. | <urn:uuid:aca8af98-4d77-4ea0-8125-a3bdcc8201c1> | 3.328125 | 864 | Documentation | Software Dev. | 44.836484 |
The process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance from the targeted area. Remote sensing is used in this thesaurus to refer to methods that are solely or primarily deployed through air or space. Included in this concept are studies of biological populations using remote imaging techniques. Related methods which are used most frequently on the ground (e.g. photography), whether underwater, from airplanes or satellites, are not included in the term remote sensing.
We combine long-term records from aerial photographs, detailed mapping using survey-grade GPS, and ground-based lidar with meteorological monitoring. Sand dune migration rates are currently about 35 meters per year.
Georeferenced high-resolution mapping of bathymetry of the West Florida Shelf, Gulf of Mexico of areas suspected to be critical benthic habitats for fisheries. Includes links to images, data, metadata, and TIFF image files.
The National Assessment of Coastal Change Hazards is a multi-year undertaking to identify and quantify the vulnerability of U.S. shorelines to coastal change hazards such as the effects of severe storms, sea-level rise, and shoreline erosion and retreat.
The Coastal and Marine Geology Program of the U.S. Geological Survey (USGS) is conducting an analysis of historical shoreline changes along open-ocean sandy shores of the conterminous United States and parts of Alaska and Hawaii.
Links to standards prepared under the National Mapping Program to produce and maintain top quality mapping and geospatial data products. Documents may be viewed and downloaded in PDF and HTML formats with links to related information.
USGS Archive for preservation and access for satellite remote sensing data and imagery (Landsat and AVHRR). Links to locating and ordering imagery, international collaborators, advisory committee, and Earthshots (satellite photos.). | <urn:uuid:64fb5c34-eeac-402b-9191-144f92ab13ad> | 3.40625 | 383 | Content Listing | Science & Tech. | 25.273939 |
www.windaction.orgfacts, analysis, exposure of wind energy's real impactsWindactionhttp://www.windaction.org/articles/c38+111?theme=atomXarayar2006-06-12T02:16:27ZWind turbine pressure change kills bats, research may help prevent future deaths.364212012-10-30T10:27:36Z2012-10-30T10:27:36ZMiles away, wind turbines sat motionless in the windless night. Their spinning blades can be deadly to bats, bursting capillaries in their lungs before the blades hit their tiny bodies. Three Wyoming bats are particularly susceptible when they migrate from summer to winter ranges.
Keinath and Abernethy were looking for bats to tell them which, if any, species called the area home.
Migratory bats hardest hit by wind turbines .364202012-10-30T10:24:50Z2012-10-30T10:24:50ZOf Wyoming's 15 resident bat species, three of them are most susceptible to the deadly effects of wind turbines: the hoary bat, the silver-haired bat and the eastern red bat.
They are Wyoming's only tree-roosting bats, said Douglas Keinath, senior zoologist with the Wyoming Natural Diversity Database.
Wyoming researchers study impact of wind farms on antelope, elk.340332012-01-08T00:47:32Z2012-01-08T00:47:32ZHard winters usually limit animals to certain areas where wind blows snow away and food is available. If those are the same places where turbines exist, and elk or antelope avoid turbines, it could hurt the winter survival rate of the herds, Beck said.
"It is an area of research that we don't have a lot of information on.Study: Energy boom hurting deer, antelope herds.325492011-07-21T13:41:30Z2011-07-21T13:41:30ZAfter reviewing population trends, hunter-harvest reports and licenses sales from the two states over the last 30 years, wildlife biologists concluded that oil and gas drilling, wind farms, agricultural practices and other human encroachments are slicing and dicing critical habitat the animals have historically relied upon to survive.Wyoming G&F approves wildlife guidelines for wind power .269452010-04-24T13:03:07Z2010-04-24T13:03:07ZWyoming will monitor the wind energy industry's effects on wildlife through guidelines unanimously approved by the Game and Fish Commission on Friday.
The commission resisted calls from some landowners and some industry representatives who wanted to delay approval of the 65-page document because of technical issues and concerns about private property rights.
Wyoming wind project offers grouse conservation plan.267772010-04-18T17:36:55Z2010-04-18T17:36:55ZThe developer of a proposed southern Wyoming wind farm is seeking federal approval of a conservation deal that could help the project move forward in an area that's also home to sage grouse.
The Power Company of Wyoming wants to build a 1,000-turbine wind farm on part of a 486-square-mile cattle ranch near Rawlins. Denver-based Anschutz Corp. owns the Power Company and the ranch, which is a mixture of private and federal lands.
Wyo. wind project offers grouse conservation plan .266312010-04-11T18:50:35Z2010-04-11T18:50:35ZThe Power Company of Wyoming, an affiliate of Denver-based Anschutz (AN'-shoots) Corp., wants to build a 1,000-turbine wind farm on a ranch near Rawlins. But the company faces the challenge of building the project in an area that overlaps with sage grouse habitat.Wyoming mulls wildlife guidelines for wind developers.265242010-04-04T18:22:07Z2010-04-04T18:22:07ZThe Wyoming Game and Fish Department wants to discourage the construction of wind turbines close to water, forests and other wildlife habitat, but the agency's latest draft recommendations offer developers a bit more flexibility depending on the specifics of a site.
The department recently released a new draft of wildlife protection recommendations for wind developers.Sage grouse stability opens door to wind farms.260042010-03-06T13:38:36Z2010-03-06T13:38:36ZThe finding shows the government is willing to protect sage grouse but not willing to do what's necessary, said Jon Marvel, executive director of the Hailey, Idaho-based Western Watersheds Project.
"None of the actions proposed to date are mandatory, and that undermines the commitment for improving conditions for sage grouse," Marvel said.
'Warranted but precluded'; Decision offers encouragement, concerns for industry, conservationists.259682010-03-06T07:21:15Z2010-03-06T07:21:15ZWildlife conservationists and energy developers alike found some encouragement in Friday's announcement that the sage grouse won't be listed as a threatened or endangered species.
Many agreed that such a listing would have had a chilling effect on the agriculture and minerals industries, which are the foundation of Wyoming's economy.
U.S. to protect bird, oil drilling likely restricted .259642010-03-06T06:57:30Z2010-03-06T06:57:30ZThe iconic sage grouse that once roamed the western U.S. plains in great numbers ...will not be listed under the Endangered Species Act, but the department will put special emphasis on preserving the chicken-sized bird on lands where oil companies want to drill and wind companies want to erect their massive turbines.No endangered status for plains bird .259612010-03-06T06:41:52Z2010-03-06T06:41:52ZThe Interior Department said Friday that the greater sage grouse, a dweller of the high plains of the American West, was facing extinction but would not be designated an endangered species for now.
Yet the decision in essence reverses a 2004 determination by the Bush administration that the sage grouse did not need protection, a decision that a federal court later ruled was tainted by political tampering with the Interior Department's scientific conclusions.
Much at stake as grouse endangered finding nears .257392010-02-21T20:37:33Z2010-02-21T20:37:33ZA lot of Westerners are watching whether the U.S. Fish and Wildlife Service is about to pursue Endangered Species Act protection for the greater sage grouse.
A finding is expected by week's end and the oil and gas, livestock and wind energy industries _ to name the bigger interests concerned _ all have an enormous stake in whatever the agency decides.
Idaho deal urges landowners to protect sage grouse.256102010-02-13T14:22:02Z2010-02-13T14:22:02ZIdaho and the federal government have signed an agreement that offers incentive and protection for ranchers and landowners who voluntarily take conservation steps to improve the plight of the sage grouse. ...Todd Tucci, attorney for Advocates for the West, said the bigger challenge is dealing with sage grouse habitat on public land, where wind energy development, oil and natural gas drilling and cattle grazing pose thornier policy questions.
U.S. bird listing to hit energy, wind industries.249702010-01-06T02:12:10Z2010-01-06T02:12:10ZEfforts to protect an iconic bird could disrupt oil, natural gas and wind energy development in the U.S. West and add to the Democratic Party's green woes ahead of the 2010 congressional elections.
The U.S. Fish and Wildlife Service has until Feb. 26 to decide whether or not to list the greater sage-grouse under the Endangered Species Act. This may prove politically charged as it comes in the face of opposition from energy interests and state governments who fear it will hurt economic development.
Wyoming BLM issues sage grouse guidelines.249402010-01-05T12:51:58Z2010-01-05T12:51:58ZThe U.S. Bureau of Land Management is directing its Wyoming offices to consider certain restrictions for oil and gas drilling, new wind turbines and other types of development in sage grouse habitat.
In many cases, the BLM could limit drilling to one well pad per square mile. Also, the BLM will prohibit many activities during sage grouse breeding season each spring.
New rules to limit wind power in Wyoming.249352010-01-05T03:22:18Z2010-01-05T03:22:18ZWind energy development is "functionally precluded" in about 20 percent of Wyoming under new Bureau of Land Management guidelines laid out on Monday to protect a threatened bird, the governor's office said. ...the reality going forward will be that new developments will have to be relegated to the one oil pad per square mile."BLM: Mark fences for sage grouse .246462009-12-17T07:43:26Z2009-12-17T07:43:26ZThe U.S. Bureau of Land Management is telling its field offices to mark certain fences and guy wires to make them more visible to sage grouse, sharp-tailed grouse and lesser prairie chickens.
Studies have shown that barbed-wire fences can be deadly when these bird species fly into the fences without seeing them
Sage grouse effort yields slow results.229262009-08-31T02:05:40Z2009-08-31T02:05:40ZNot much is certain about the future of sage grouse in Wyoming - including the birds' undecided status as a potentially endangered species and their possible role in curbing oil, gas and even wind energy development.
But based on a number of sage grouse habitat improvement projects in development across the Bighorn Basin, one thing is certain: Boosting the bird's prospects is a slow and painstaking process.
Nesting uncomfortably? G&F schedules study of golden eagle population .229092009-08-30T03:03:32Z2009-08-30T03:03:32ZBrian Rutledge, executive director of Audubon Wyoming out of Laramie, said golden eagles, along with other raptors, are struggling in light of the energy development around the state. Power poles are being erected in areas of the sagebrush sea ...and now raptors can perch there and pick off sage grouse. ...He said a rise in wind energy also threatens the bird. | <urn:uuid:f30e544d-1211-4a4d-a221-b77def976840> | 2.953125 | 2,278 | Content Listing | Science & Tech. | 59.251224 |
Mars Student Imaging Project
The Mars Student Imaging Project (MSIP, sometimes called Mars Student Imaging Program) is a collaboration between NASA and Arizona State University's Mars Education Program that gives United States grade school students the opportunity to participate in Mars research. Students from grade 5 through college sophomore level work with THEMIS scientists at ASU’s Mars Space Flight Facility to take images of sites on Mars using the visible wavelength camera on the Mars Odyssey spacecraft.
After students frame a research question, they help direct the Mars Odyssey to take images that will answer their question. In June, 2010, 7th grade science students at Evergreen Middle School in Cottonwood, California helped researchers discover a new series of lava tubes, including one with a pit crater. The students were looking for the most common sites for lava tubes on Mars, asking whether they are more prevalent near the volcano's summit, its flanks, or in the plains surrounding the volcano. The pit crater they discovered is in the form of a skylight above a lava tube, on the slope of the Pavonis Mons volcano.
The pit crater is only the second one discovered on Pavonis Mons, and is estimated to be approximately 190 meters wide and 115 meters deep. | <urn:uuid:d3f01d17-6604-43d3-b3eb-fd07e16e39e0> | 3.3125 | 247 | Knowledge Article | Science & Tech. | 26.686445 |
Comprehensive DescriptionRead full entry
BiologyNear shore and in bays. Very common, has been successfully introduced to Lakes Kava, Kariba and Carbora Bass (Ref. 4967). A lacustrine species, preferring open water (Ref. 13337). Forms large schools. Mainly nocturnal and feeds on plankton (especially atyid shrimps, also copepods, prawns), but larger individuals take larval Stolothrissa. Cannibalism does occur (Ref. 13337). Breeds close to shore throughout the rainy seasons, but with peaks in May to June and December to January. Fire is used to attract the fish and caught by means of scoop nets (Ref. 36900). | <urn:uuid:ec460111-d7bb-4e0c-987a-e68544b1ba2a> | 2.90625 | 153 | Knowledge Article | Science & Tech. | 52.510685 |
Energy and Magnitude of the Sliding Block
The following unit definitions are from: http://www.unc.edu/~rowlett/units/index.html
newton (N) the SI unit of force.
A force of one newton will accelerate a mass of one kilogram at the rate of one meter per second per second. The corresponding unit in the CGS system is the dyne; there are 105 dynes in one newton. In traditional English terms, one newton is about 0.224 809 pounds of force. Nineteenth-century engineers created another English unit of force, the poundal; there are approximately 7.233 01 poundals in a newton. The newton is named for Isaac Newton (1642-1727), the British mathematician, physicist, and natural philosopher. He was the first person to understand clearly the relationship between force (F), mass (m), and acceleration (a), expressed by the formula F = ma.
newton meter (N m) the SI unit of torque.
Torque, the tendency of a force to cause a rotation, is the product of the force and the distance from the center of rotation to the point where the force is applied. Torque has the same units as work or energy, but it is a different physical concept. To stress the difference, scientists measure torque in newton meters rather than in joules, the SI unit of work. One newton meter is approximately 0.7376 pound foot.
joule (J) the SI unit of work or energy, defined to be the work done by a force of one newton acting to move an object through a distance of one meter in the direction in which the force is applied. Equivalently, since kinetic energy is one half the mass times the square of the velocity, one joule is the kinetic energy of a mass of two kilograms moving at a velocity of 1 m/sec. This is the same as 107 ergs in the CGS system, or approximately 0.737 562 foot-pound in the traditional English system. In other energy units, one joule equals about 9.478 170 x 10-4 Btu, 0.238 846 (small) calories, or 2.777 778 x 10-4 watt hour. The joule is named for the British physicist James Prescott Joule (1818-1889), who demonstrated the equivalence of mechanical and thermal energy in a famous experiment in 1843. Although Joule pronounced his name "jowl", the unit is usually pronounced "jew'l".
If we assume that the wooden block slips at about 5 newtons force, then if the displacement is x cm or x/100 meters, then the energy is 5*x/100, or x/20 joules.
The magnitude of an earthquake, M, is given by
M = (log E - 4.8)/1.5 where E is measured in joules.
Substituting x/20 for E we have:
M = (log x/20 - 4.8)/1.5 = (log x - log20 -4.8)/1.5
M = (log x - 1.3 - 4.8)/1.5 = (log x - 6.1)/1.5
Or, solving for x, log x = 1.5 M + 6.1
x = 10**(1.5 M + 6.1) (meaning, 10 raised to the power (1.5M + 6.1)
Using this equation, we can compute the value of x for a series of values of M:
These limits could be used to assign each slip event to a specific magnitude range. The number of events in each bin could then be plotted versus the magnitude to see the magnitude distribution of the slip events. This distribution can be compared with the distribution observed for the world's earthquakes. | <urn:uuid:08424691-251f-4a68-917a-80f3fa064a49> | 3.96875 | 819 | Knowledge Article | Science & Tech. | 77.458934 |
This post is about the LHCb – the motivations and science behind the experiment, and what scientists hope to discover there.
The LHCb is one of four experiments at the Large Hadron Collider (LHC) at CERN in Geneva. It will study the decays of particles known as B mesons in the hope of discovering the answer to a problem known as matter-antimatter asymmetry.
The problem is this: at the big bang, matter and antimatter should have been, and in all likelihood were, created in equal amounts. However, according to what we currently know, if they had been created in equal amounts, then I wouldn’t be here to write this and you wouldn’t be here to read it either. We exist due to a tiny imbalance in the ratio of matter to antimatter at the beginning of time. This tiny imbalance meant that when most of the stuff created in the big bang was annihilated (when matter meets antimatter both are destroyed and lots of energy is released) a tiny amount of matter was left over, and this tiny amount makes up all the matter we see in the Universe today, including us.
To investigate the matter-antimatter asymmetry, physicists are looking at B mesons. These particles are so called because they each contain a b, or bottom, quark. After its discovery in 1977 there were some attempts to change the bottom quark’s name to “beauty”, but the original name stuck. Incidentally, the “b” in LHCb does stand for “beauty” as opposed to “bottom”.
Decays involving B mesons may hold the key to the matter-antimatter asymmetry problem because they exhibit a property known as CP violation. CP stands for “charge parity” and is used to describe the combination of two symmetries called charge conjugation symmetry and parity symmetry. If these symmetries were obeyed, the laws of physics would treat matter and antimatter exactly the same. CP violation occurs when matter and antimatter are treated differently, and as such might be able to explain why we live in a matter dominated Universe today.
It is the weak force that is responsible for the decay of B mesons, and it is the only one out of nature’s four fundamental forces that is known to violate CP. CP violation has been seen at experiments BaBar and Belle, which are located at the Stanford Linear Accelerator Centre (SLAC) in the US and the KEK laboratory in Japan respectively. However, the weak force alone is not enough to explain all the CP violation we see.
Scientists at the LHCb will search for rare decays of B mesons in order to try and find new physics to explain the asymmetry. They will be looking for new particles that have never been seen before as well as new physical phenomena. This new source of CP violation could be found in quarks, or it could be found in some other particle. If the Higgs boson is discovered, maybe it will point us in the right direction. We don’t yet know exactly where the answer lies, but there’s only one way to find out…
For more information see the LHCb website.
Images: US / LHC webpage | <urn:uuid:c90d6131-c1a0-4887-93d5-47b2f94823bc> | 3.703125 | 688 | Personal Blog | Science & Tech. | 48.347458 |
The father of genetics, Gregory Mendel, discovered that pea plants passed certain traits on to their offspring. Once we began to explore genetics, we found a complex system of proteins that make up every living thing on Earth. This complex system, DNA, is so difficult to decode that even though the entire human genome was published in 2001, we've yet to really understand what most of it means.
This video explains the brief history of genetics, and the exciting future that is just around the corner. Take a look… via The Guardian | <urn:uuid:9596c6df-7d05-4ef6-a748-0b61eafd8d14> | 3 | 108 | Truncated | Science & Tech. | 48.603992 |
A game that tests your understanding of remainders.
In a square in which the houses are evenly spaced, numbers 3 and 10
are opposite each other. What is the smallest and what is the
largest possible number of houses in the square?
In this article for teachers, Bernard Bagnall describes how to find
digital roots and suggests that they can be worth exploring when
confronted by a sequence of numbers.
When Charlie asked his grandmother how old she is, he didn't get a
straightforward reply! Can you work out how old she is?
Look on the back of any modern book and you will find an ISBN code. Take this code and calculate this sum in the way shown. Can you see what the answers always have in common?
Can you order the digits from 1-6 to make a number which is
divisible by 6 so when the last digit is removed it becomes a
5-figure number divisible by 5, and so on?
Yasmin and Zach have some bears to share. Which numbers of bears
can they share so that there are none left over? | <urn:uuid:7ba1ecb6-528a-4daf-8ec1-032eb34a6962> | 3 | 231 | Content Listing | Science & Tech. | 69.883333 |
I’ve heard from the likes of Brian Cox that what we see of the sun during a sunset and sun rise is actually the mirage of the sun. The Sun has actually set/risen and we see it due to the way light is bent across the atmosphere. Apparently due to coincidence of the size and distance of the sun, its exactly the same size - so if we see 50% of the sun, the sun is 50% below the horizon. So, I understand all this, so here is my question :
If this is the case, then when we read things like what time sun sets and rises on websites, books, calendars, other official times, et al… does that mean when we see for example ‘sun set at 18:35’ is the time denoting the actual sun set taking into account of the mirage or what is visible to us. If I were to know the time and watched the sun against an accurate clock, would the sun not be visible before the actual sun set time?
I would also like to know how this affects things like iphone apps that tells us what time sun sets are and where it is in relation to the horizon at a given time. So is the set/rise time taking into account of the mirage and the time is recalculated to give us when it has ‘actually’ set/risen or when the mirage has set/risen. | <urn:uuid:ca9fe890-69ff-469d-a352-f420d5ac0ac0> | 2.796875 | 294 | Q&A Forum | Science & Tech. | 51.142705 |
Analysis confronts model of universe’s formation
Nov 16, 2007 2 comments
Tiny temperature variations found in maps of the cosmic microwave background are commonly thought to be proof that stars, galaxies and other large-scale structures grew from density perturbations in the early universe. But one physicist in the US is controversially claiming that these observed variations are in fact caused by hydrogen atoms in our own galaxy. If he is right, cosmologists will have to drastically rethink their models of the universe’s evolution.
In the early universe’s hot plasma, light left over from the Big Bang could not travel far without being scattered by electrons. But by the time the universe was some 380,000 years old, it had cooled enough to let electrons and protons combine and form hydrogen atoms. Photons could then travel freely over long distances without being scattered, stretching in wavelength as the universe expanded to become the cosmic microwave background (CMB) — a map of the early universe’s structure frozen in time.
Data taken by the COBE satellite in 1993, and to a greater extent by the Wilkinson Microwave Anisotropy Probe (WMAP) in 2003, showed that tiny temperature variations permeated the CMB. These proved that the early universe was not an even distribution of mass, but had dense regions that — as cosmologists’ models suggest — were to seed the galaxies and other structures we see today.
Gerrit Verschuur, a physicist from the University of Memphis in the US, disagrees. He has noticed that the temperature variations recorded by WMAP tend to coincide with radio emissions from neutral hydrogen in the Milky Way. In other words, the fluctuations may not be part of the CMB at all (Astro. J. in publication; preprint available at arXiv.org:0704.1125v2).
My approach now is to determine what I can learn about interstellar physics in studying these cases, and not to worry about statistical arguments
Verschuur made his discovery while studying the Leiden-Argentina-Bonn (LAB) survey, a map of radio emissions from neutral hydrogen in the Milky Way that was completed for the entire sky in 2005. “So many data are daunting and users of the all-sky LAB survey still tend to extract only the data for the small area they are interested in,” he told physicsworld.com. “I had been working with the data over a large area.” In his paper Verschuur notes six areas where he has found visual correlations between the LAB and WMAP surveys, though he says that he has since found around 200 more correlated areas.
If his analysis is correct, it would undermine the widely established “cold dark matter” model of the universe’s evolution, which says that large-scale structure grew from small density perturbations in the early universe. According to studies of the WMAP survey, normal matter makes up just 4% of the universe, with mysterious dark matter and dark energy accounting for 24% and 72%, respectively. Although WMAP scientists had to carefully subtract known contributions from physical processes in the Milky Way, Verschuur points out that the correlating hydrogen emissions could be originating from an unidentified process.
Not everyone agrees with the US physicist’s inferences, however. Kate Land at the University of Oxford in the UK and Anže Slosar at the University of Ljubljana in Slovenia compared various maps from the LAB and WMAP surveys at different frequency bands and scales using computer “Monte Carlo” techniques, but found no statistically significant correlations (Phys. Rev. D 76 087301).
The results are somewhat anecdotal
As for the reliability of visual inspections, Land and Slosar recall the urban myth that a certain point in the WMAP survey contains Stephen Hawking’s initials. “Correlations by eye are very misleading,” they conclude.
Even so, Verschuur is keen to continue his analyses. “My approach now is to determine what I can learn about interstellar physics in studying these cases, and not to worry about statistical arguments,” he said.
But Gary Hinshaw, a physicist on the WMAP mission team at NASA’s Goddard Space Flight Centre, also disputes Verschuur’s conclusions. “My impression is that it is primarily based on a visual comparison of the maps and not on a rigorous statistical analysis, so the results are somewhat anecdotal,” he told physicsworld.com. Referring to the study by Land and Slosar, he added: “I think this paper really puts the claim to rest.”
About the author
Jon Cartwright is a reporter for physicsworld.com | <urn:uuid:80b68605-b116-4fcb-a5e5-d97b546ed7ce> | 3 | 987 | Truncated | Science & Tech. | 40.483836 |
Some people love washing their cars, but many folks would appreciate having the fresh-from-the-showroom look without all of the effort. And don't forget the environmental impact of car washing, which drains water reserves and spills pollutants into endangered wetlands. If only our cars would clean themselves.
Thanks to some researchers at the Eindhoven University of Technology in the Netherlands, we may be closer to a perpetually polished Prius. The scientists didn't invent a brand-new nanotechnology. Instead, they took an existing water-resistant product, already in use on some vehicles, and made it better. The original coating worked because it came embedded with nanocapsules in its surface. Those tiny capsules both repelled water and contained cleaning agents or paint droplets so that when they were ruptured, say by a key scratch, they released their contents and "healed" the blemish. Unfortunately, the capsules had a limited shelf life. To extend the self-cleaning/healing properties of the coating, the Dutch scientists have redesigned its nanostructure so that the capsules reside on stalks. When one capsule/stalk combination gets disturbed, another underlying stalk rises up and orients itself at the surface to restore the factory finish.
Cars armed with this new coating will require little more than a good rain to wash away dirt and grime. And bird droppings splashed across your door or hood may be a thing of the past. | <urn:uuid:d1c8f675-5484-42f3-9afb-eb620ac74ae5> | 3.25 | 297 | Listicle | Science & Tech. | 42.686923 |
Calculate ionospheric equivalent currents (1D)
From ground magnetometer data the ionospheric equivalent currents can be calculated. These are currents that flow only within the ionospheric plane (assumed at 100 km altitude) and cause the same magnetic field on the ground as the actual ionospheric current system (which may be three-dimensional). So please note: Ionospheric equivalent currents are not necessarily equal to the actual currents!
For the technique used here, we assume for simplicity that the currents are only varying in north-south direction, but not in east-west direction (electrojet-type situation). Only the east-west component of equivalent current is calculated.
The results are displayed as colour plots that show the time evolution of the equivalent currents along a north-south profile. Red colours (positive numbers) mean eastward equivalent currents, blue colours (negative numbers) mean westward currents. Four plots are displayed:
- Ionospheric equivalent currents
- Ionospheric equivalent currents, only eastward component
- Ionospheric equivalent currents, only westward component
- Integrated ionospheric equivalent current, separately for eastward and westward components
To scale the magnetic data, you need to give a baseline period, i.e. magnetically quiet period close to the event you are going to analyse. To find one, use the IMAGE IL index plots.
More info may be found from 1D upward continuation page under "analysis methods".
Event selection form
NOTE: The script cannot handle midnight crossings so the event start and event end days must be same.
(calculation will take a few seconds) | <urn:uuid:1a6f41f2-9b9d-4562-893a-96551ddd62ec> | 3.109375 | 338 | Tutorial | Science & Tech. | 22.491937 |
What's the point of a triploid tissue?
koning at ECSUC.CTSTATEU.EDU
Thu Feb 27 09:32:05 EST 1997
At 7:16 AM -0000 2/27/97, John Hewitson wrote:
>My students ask "What's the point of a triploid tissue?"
>The thinking goes like this:-
>* Triploid tissue is unique to angiosperms. True?
>* Natural selection does not support a structure unless it confers some
>* The fact that triploid tissue exists suggests that there is some
>advantage. What is the advantage of a TRIPLOID endosperm?
>* Does a study of angiosperms suggest that the most recent members use this
>tissue less, OR do they make greater use? What is the direction that
>evolution seems to be taking?
Not every endosperm IS triploid; most are, but some are even more
polyploid. Books teach triploid because of its common status.
There are other embryo sac types.
There is an old hypothesis that polyploidy of certain tissues
diverts nutrients from diploid tissues. This helps explain the
accumulation of nutrients by endosperm tissue at the expense
of the maternal tissues without a concomittant investment in the
diploid embryo. Until the endosperm starts making enzymes to
degrade its own tissues at seed germination, or until the embryo
does the same to transfer nutrients to itself (in species with
limited/no endosperm) the endosperm holds these aggrandized
nutrients. I haven't read any of the supporting papers from the
old days, and so I'm not sure if this is much more than an hypothesis.
If you want a human analog, there is a parallel evolution of fetal
hemoglobin and a relationship between maternal hemoglobin, maternal
myoglobin, and fetal hemoglobin for oxygen. These are VERY different
solutions to a similar problem of nutrient balances.
There certainly is STRONG evidence that polyploidy of normal tissues
results in larger plants, flowers, and fruits. Use of colchicine to
induce polyploidy was one of the initial thrusts for crop yield. So
there is a very practical side to polyploidy. Parallel improvements
by natural means are also evident. Increased competitiveness would
certainly be adaptive.
Another interesting, related topic is allopolyploidy. This is both
a natural and artificial phenomenon. Among ferns and oaks, there
are huge hybrid swarms among natural populations. Many "natural"
species are, in fact, allopolyploid hybrids. These occur when
matings between "incompatible" species occur. Each gamete brings
a unique chromosome set to the syngamy. The unmatching sets would
render the resulting progeny sterile. By as yet incompletely understood
mechanisms, the progeny can double the chromosomes to generate an
allo-tetraploid. This organism has two double-sets of chromosomes
and therefore is usually fertile. If mating with other allotetraploids
of the same kind, the "species" reproduces stably which is why they
are sometimes listed as a species of their own. Cytogenetics though
reveals they are just allopolyploid hybrids. The point is: polyploidy
provides the advantage of complex hybridization of species, improving
the genetic diversity of the gene pools by making "impossible"
recombinations a reality.
Hope this gives you and your students some ideas to consider.
Ross Koning | koning at ecsu.ctstateu.edu
Biology Department | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA | fax: 860-465-4479
More information about the Plant-ed | <urn:uuid:521cfe75-97c5-4f64-9d64-84ce88e4fbcd> | 3.03125 | 860 | Comment Section | Science & Tech. | 40.980427 |
Glen Paul: G'day and welcome to CSIROpod, I'm Glen Paul.
You're probably familiar with the East Australian current, if from nothing more than the 2003 animated film Finding Nemo, where the current is portrayed as a super-highway for marine life to travel down the East Coast of Australia. In a recent paper published in the journal Nature Climate Change scientists have found that riding the current could now take Nemo further south than he might like to travel. Oceanographers have identified a series of ocean hotspots around the world generated by strengthening wind systems that have driven Oceanic currents, including the East Australian current, pole wards beyond their known boundaries.
The study, which involved an international scientist team, found that the hotspots are formed alongside ocean currents that wash the East Coast of the major continents and their warming is far exceeding the rate of Average Ocean surface warming. Co-authors of the paper, CSIRO's Dr Wen Ju Cai and visiting scientist Dr Mike McPhadden from the United States National Oceanic and Atmospheric Administration, worked together on the project and join me on the phone.
Firstly, Wen Ju, what actually prompted an international effort?
Cai: The initiation of this project was a study that we had done years ago, looking at the Tasman Sea warming. We have shown that over the past 50 years the Tasman Sea warming rate is actually faster than the global oceanic average, two to three times faster and it could link to the climate change ocean factors such as ozone depletion and perhaps also greenhouse warming but we were not sure. We'd like to see, if this is caused by climate change then we should have other evidence in other oceanic current systems.
Glen Paul: Right. So with evidence in mind how do you measure this accurately? Do you, for example, have reliable records to fall back on to make comparisons?
McPhadden: In fact, there are only a few of these ocean currents, Wen Ju mentioned the East Australian current, and we've seen this warming signal now in other currents around the world, for example, the Gulf Stream off the East Coast of the US, the Kuroshio current off the East Coast of Asia. These currents are very strong so it's difficult to make direct measurements of the current flows in these regions for sustained periods of time.
What we relied on for this study was a long history of occasional measurements plus a computer model that represented the dynamics of these currents and we basically blended the two, the sparse data and the computer model code for how these currents should respond to wind forcing. From that analysis we derived indications that the currents have undergone a systematic change over the last 50 to 100 years.
Glen Paul: Right, and these are as a result of these strengthening wind systems. Where does the cause of that lay?
McPhadden: The fingerprint of climate change is on this because we know from other studies, independent studies that the tropical zone is expanding, the trade wind system is moving northward and that links into all the other wind and current systems of the oceans. The fact that the global tropics are expanding, the fact that we see this warming in all the mid latitude currents like the East Australian current, Gulf Stream and Kuroshio current off of East Asia tell us that the likely culprit here is climate change.
Glen Paul: I see. Wen Ju, how sure are you that this is the result of climate change and not just natural changes that would otherwise occur in oceans over time?
Cai: Natural changes do occur but we have a lot of other evidence and, as Mike just pointed out, over Southern Australia as an example, this study pointed out that the current is moving forward but we also have the weather system that has been moving forward. Southern Australia, as you know, has just been through a long drought and that is associated with weather systems moving poleward.
In Perth, for example, that kind of drought condition has been persisting for more than 35 years. When you put all this evidence together we could say that there is at least a part that is driven by climate change.
Glen Paul: OK. Aside from these local ecological implications then what other impacts does a change in these currents bring?
Cai: There are some ecological impacts. We had a bit of observation showing that the boundaries of marine bio-diversity have been changing, the biotas has been changing and a lot of species have been moving further poleward, for example, the New South Wales Sea Urchin has been seen in Tasmania and while they are in Tasmania they are eating those giant kelp. Now kelp is a shelter for a lot of other species so it has quite a bit of knock on effect.
They also have implications for aquaculture as we know that Tasmania is a farm ground for salmon and farming salmon need a good temperature range and so the food that is produced for salmon also need to have a good temperature range. We could also quite a lot of other introduced species, in Victoria waters, for example, is the shore crab. We are now seeing them further and further south in Tasmanian waters. There is quite a bit of impact on ecosystems.
Glen Paul: Right. So, bringing all this together, what's the upshot?
Will this situation worsen and, if so, how quickly do you think?
Mcphadden: There is a trend for these currents, they appear to be moving forward over the past hundred years by a couple of hundred kilometres and in some cases they appear to be strengthening. These changes are related to changes in the wind field that we suspect strongly are related to climate change. The likelihood is, if we're to take these pieces of evidence and project into the future that these kinds of trends will continue. What the impacts are … are a little bit uncertain because there are so many feedbacks in the climate system that may either amplify or dampen some of these trends.
There are issues we should be concerned about because, for example, if you take the Gulf Stream which flows off the East Coast of the US then it carries a hundred times more water from the Equatorial Region to the pole, a hundred times more water in this current than all the Worlds Rivers combined. It's a huge, massive flow and that's just one of these current systems. They are transporting a tremendous amount of heat and water pole ward and the reason, for example, that Western Europe has a milder winter than the Eastern US is in part because of this transport of warm water from the tropics to the pole region and so if these currents are shifting northward it implies changes in the climates of Europe, North America, Australia and other regions of the globe.
It's a trend that we've noted, we're very interested in following up on this study about what some of the more detailed climate implications may be and already, as Wen Ju has mentioned, we can see the implications for marine ecosystems in the East Australia current region.
Glen Paul: So you as a representative of the Northern Hemisphere, what's the most important message then for policy makers to come from this research?
McPhadden: Well, this research is pointing to another manifestation of human impact on climate, one of many manifestations. It's yet another reason why we should be concerned about how our activities are affecting the world in which we live. From that point of view, as with all climate changes, there will be winners and losers depending on what the impacts are but it's real, it's happening and it's something that we should be concerned about.
Glen Paul: Wen Ju, your thoughts?
Cai: Yes, I would echo Mike's concern. A lot of implications we don't quite understand of yet so, for example, you have solid warming and that warming covers a great depth from surface to a thousand metres. That is going to do to our sea level rise locally faster than the global average and that would have its own set of impacts as well. I think we need to take this kind of change seriously.
Glen Paul: Absolutely. Well, if they ever decide to do a second Finding Nemo movie there are some serious plot lines there, that's for sure. Thank you both for talking to me about it today.
McPhadden: Thank you, Glen.
Cai: Thank you, Glen.
Glen Paul: Drs Wen Ju Cai and Mike McPhadden. For more information you can find us online at www.csiro.au, you can like us on Facebook or follow us o | <urn:uuid:a9c8f088-6e4a-497c-a05f-1dbe0a33d4bd> | 3.15625 | 1,752 | Audio Transcript | Science & Tech. | 49.343105 |
You already know how to link XML documents together with XLink, and isolate specific nodes or node collections with XPath. Now uncover the third and final piece of the XML linking jigsaw - XPointer, an experimental technology from the W3C, which allows you to create XML links to specific points or ranges within an XML document.
To the various node types defined in the XPath specification, XPointer adds two more: points and ranges.
A point is defined as the address of a specific location within an XML document. It is identified by two characteristics: a container node and an index number. The container node is the node which encloses the point, while the index number is an integer which indicates the relative position of the point among the children of the container node.
There are two types of points: node-points, which refer to XML elements, and character-points, which refer to the text contained within XML elements.
The index number within a point definition differs in meaning depending on whether the point is a node-point or a character-point. In the case of a node-point, the index number references a specific child node or nested XML element; in the case of a character-point, it references a particular character of the text string.
Points are defined with XPointer's start-point() and end-point() functions, both of which accept a location path (or collection of location paths) as argument.
A range, defined as the area between two points, is created with the range() function, which returns a collection containing all the elements within the specified range.
An example might help to make this clearer. Consider the following XML document:
<movie id="67" genre="sci-fi">
Jackman, Patrick Stewart and Ian McKellen</cast>
Now, the XPointer
would return a range covering the / element (the document element) and all those
within it - in other words, a range covering the entire document.
The start and end points of this range would be accessible via the XPointers
and would point to the beginning and end of the document respectively.
In a similar manner, the XPointer
would identify the range
while the XPointer
would point to the location immediately preceding the "director" element. | <urn:uuid:1666b97e-5b3e-4de2-b83f-deb8a83b3059> | 3.40625 | 477 | Documentation | Software Dev. | 42.094009 |
In NIU's Math Education Lab, brightly colored Macintosh computers sit all in a row.
Hundreds of Tupperware containers line the shelves on the wall, each containing a different material used in demonstrating math concepts, such as pattern blocks, geoboards and base blocks.
The shelves on both sides of the room are filled with math journals and books.
About 20 students began to pile into DuSable Hall, Room 306, for Math 402, Methods of Instruction for Math, K-9. This class is different in that the students become the teachers.
Students are required to demonstrate how to complete a problem. They were given a sample problem involving Auntie Mae, a candy store owner who received an order for 432 pieces of candy. She got a call asking her to mail the candy in three separate equal packages. How much candy will be in each package?
Students used base boards to simulate how the candy would be divided. The boards consist of flats, which are 10-by-10, or 100 squares; rods, which are 10 squares long and units, which are single squares.
The students first divided the flats into three groups, then the rods and the individual units. Exchanges were made if necessary.
They determined that 144 pieces of candy would be in each package.
The students then watched a video in which this same procedure was used with actual children. The children responded well to this method and showed an understanding of division.
NIU math professors feel that the lab, which is used for all the math methods courses, contains many useful resources for the students, including hundreds of current teaching books and journals.
Helen Khoury, a math professor, said students understand something best when they have to teach it to someone else.
"The math education lab contains a remarkable collection of materials for prospective teachers," said Mary Shafer, a math professor.
Shafer said many of the materials aid in developing students' understanding of place value, fractions and decimals, and concepts in geometry and measurement. | <urn:uuid:6d19804e-676f-4301-ac70-90313a71eccc> | 3.765625 | 414 | Knowledge Article | Science & Tech. | 52.559786 |
On January 30, 2012, the Schmidt Ocean Institute ship Lone Ranger returns to the Sargasso Sea for a third time with Ken Smith and Alana Sherman aboard to continue their study on the effects of climate variation on the sea-surface communities and deep-sea ecosystems. This third Sargasso Sea research expedition is a collaborative effort of MBARI, the Marine Science and Technology Foundation, and the Schmidt Ocean Institute. Smith and Sherman first journeyed to the western North Atlantic Ocean to begin their time-series study in February 2011, returning in August of that year to collect samples from the surface and the seafloor. Follow this latest endeavor as daily updates are posted on this website with images and information about the research as it happens.
Day 14: Arriving in Freeport, Bahamas
February 12, 2012
Winds gusted to 45 knots on a cold and blustery morning as we approached Freeport, Bahamas.Read more...
Day 13: Steaming to Bahamas
February 11, 2012
We began the 40-hour journey toward the Bahamas late last night and will arrive early tomorrow morning, one day ahead of schedule. Read more...
Day 12: Sargassum surveys from space and sea
February 10, 2012
The Sargasso Sea expedition is using remote sensing at multiple scales to help understand Sargassum dynamics.Read more...
Day 11: Deploying the observatory
February 9, 2012
In addition to recording animal life, the time-lapse camera on the Sargasso deep-sea observatory has provided a window into physical dynamics on the seafloor. Read more...
Day 10: Drifting through Sargassum
February 8, 2012
The winds and waves also seemed ideal for Sargassum as we passed several large aggregations. We saw the most extensive raft today in the late afternoon, an extensive windrow with patches nearly half the size of the Lone Ranger. Read more...
Day 9: Views from the observatory
February 7, 2012
With the Sargasso deep-sea observatory safely secured on the ship, the science team began the job of processing the data and samples and servicing the instruments for another deployment.Read more...
Day 8: Recovering the deep-sea observatory
February 6, 2012
The deep sea is cold, dark, and under tremendous pressure, yet it is the largest habitat on planet Earth and home to many kinds of life. For deep-sea scientists, much of the challenge is getting instruments into this remote habitat.Read more...
Day 7: Sampling at Station 6
February 5, 2012
The winds reduced enough through the night for us to return to sampling today, even though the ocean swell remained substantial. But first we had to find Sargassum. Read more...
Day 6: Rough Seas
February 4, 2012
The winds increased through the night as we approached our next sampling location. When we prepared to launch the tender boat in the morning, it became clear that the weather was just too rough to continue. Read more...
Day 5: Sampling Station 5
February 3, 2012
With stormy weather approaching, the science team focused on collecting and processing Sargassum samples as quickly as possible during the morning while conditions were still adequate for operating the tender boat. Read more...
Day 4: Calm winds and kytoons
February 2, 2012
Light winds and calm seas contributed to a smooth transit during the day. The conditions were also just right for the KAI team to deploy a specially-designed kite balloon, also called a kytoon.Read more...
Day 3: Sargassum at Station 3
February 1, 2012
Today’s experience highlighted the efforts of the Kite Assist Institute (KAI) team to provide supporting imagery of Sargassum and its distribution patterns for the science team. Read more...
Day 2: Life in the Sargassum
January 31, 2012
The science team completed sampling at Station 1 today, processing nearly 13 liters of Sargassum material. This was well above the targeted 10 liter objective, a sometimes challenging goal at several stations last February and August when Sargassum coverage was more sparse.Read more...
Day 1: Leaving Bermuda
January 30, 2012
Today the Schmidt Ocean Institute ship the Lone Ranger departed from Bermuda to begin the third segment of the Sargasso Sea research project. Read more.
The western North Atlantic Ocean is a unique ocean habitat. Known as the Sargasso Sea, it is named for the free-floating brown algae, Sargassum—also called “gulf weed”—and their associated community of plankton, invertebrates, and fish, many of which are found only there. Over a period of two years, Smith and his team will conduct four research cruises in the area in order to observe how this community has been altered by warmer surface waters and increased acidity. They will also study how the effects of climate variation on the surface life ultimately affect the food supply of the area's deep-sea ecosystems.
On their first cruise in February 2011, Smith and his team spent three weeks in the Sargasso Sea on board the Schmidt Ocean Institute research vessel, Lone Ranger. During that cruise, the research team collected samples from within the Sargassum and the surrounding surface waters, and deployed a deep-sea observatory to photograph the seafloor and collect particles of debris that drift down from the surface. The data collected by this observatory will contribute to the global effort to monitor the effects of warming ocean waters on both surface and deep-sea ecosystems.
During their second cruise from July 27 to August 10, 2011, Smith’s research team collected additional samples from the surface waters, and recovered and redeployed the deep-sea observatory they left on the seafloor in February 2011.
During this third cruise of the time series, the researchers will again sample the surface waters of the Sargasso Sea, collect data from the deep-sea observatory, and perform a final deployment of the observatory, which will be retrieved later this year. One additional resource the team will have at their disposal on this cruise is the Kite Assist System. Just as it sounds, this system consists of kites of varying sizes to suit varying weather conditions, sea states, and wind speeds. The kites will be fitted with cameras and launched from the ship, providing an aerial platform from which video, stills, and a live feed can be captured to assist in locating Sargassum for local collections from the ship and ground-truthing for remote satellite (MERIS) data. | <urn:uuid:f7cf381b-a7d7-4bed-826c-c85c951ba7d6> | 2.78125 | 1,376 | Content Listing | Science & Tech. | 53.661689 |
the quantity of electric charge that, passed though an ionic solution, will cause electrolysis of one equivalent of ions; it is equal to about 96,490 coulombs. The number of univalent metal ions (such as silver in a silver nitrate solution) which would be deposited as free metal by such a current is Avogadro's number, 6.023 x 1023.
a unit of electric charge equal to that on 1 mole of electrons.
a constant representing the charge of one mole of electrons; 96,485 coulombs
The charge on one mole of electrons: 96485 C.
an outmoded unit of charge, which we would now define as the charge of a mole of protons, 96 406 coulombs
the charge carried by one mole of electrons or 96,485 C.
In physics, the faraday (not to be confused with the farad) is a unit of electrical charge; one faraday is equal to the charge of 6.02 × 1023 electrons (one mole). The faraday is no longer in general use and has been replaced by the SI unit coulomb; one faraday is approximately equivalent to 96485.3415 coulombs. | <urn:uuid:987763bf-62c7-48be-97f4-e77672b17d4a> | 3.453125 | 253 | Structured Data | Science & Tech. | 57.72777 |
Photograph courtesy Beth Shapiro
Beth Shapiro travels through time—observing mammoths, dodos, and other extinct animals; witnessing the last ice age and arrival of humans in North America; watching genetic diversity shrink in one species while blossoming in another.
Her journey is made possible by ancient DNA samples and statistical models that give science a whole new view of our tumultuous past.
This very new field uses genetic information gleaned from ancient animals and plants to discover how evolution happens over time and territory. By analyzing DNA samples from species at not just one, but many moments in time, researchers can trace changes in populations, and overlay those changes with concurrent environmental events. The precision this allows is unprecedented.
“We can pinpoint when a species’ genetic diversity changed.” Shapiro says. “We can see if that change may have been influenced by a specific event such as a new predator or shift in climate. By sampling populations across time, we can actually see diversity being lost or gained as animals evolve and migrate.”
“There have been many hypotheses about why populations maintain or lose diversity.” she explains, “Now, for the first time, ancient DNA lets us explicitly test those hypotheses and propose new ones. Answering these questions can help form strategies to protect and conserve species today. We can look at prehistoric analogs to modern populations and see who was in trouble, when, and why. We can measure which environmental or habitat factors were most important in determining the fate of different species, and how those factors influenced each other. For example, if we identify a time when horses were doing particularly well, we can extract ancient plant DNA from the soil and scrutinize vegetation they grazed on.”
Already, ancient DNA has proved several long-standing assumptions wrong. “It was commonly accepted that the reason bison have no diversity today is that almost all of them were killed by human hunters in North America 200 years ago,” Shapiro notes.
Instead, her ancient DNA analysis proved that even when there were millions of bison, they had no genetic diversity. In fact, their decline began not 200, but 35,000 years ago as climate changed and they passed through the peak of the last ice age.
Ancient DNA also sheds new light on the decades-old debate over what caused the mass extinctions of mammoths, saber-toothed cats, mastodons, and other distinctive species about 10,000 years ago. Some scientists argue that the arrival of humans and overhunting triggered the extinctions; others attribute the event to major changes in vegetation and climate.
Surprising new ancient DNA findings reveal that the true beginning of this massive extinction was well before human intervention or the peak of the last ice age. As Shapiro notes, “Suddenly we realize that all the species we have data on began declining 35,000 to 50,000 years ago. Understanding that period has never been a scientific priority. But now we see that something very important was happening at that time which ultimately determined the outcome of many different animals.”
If analyzing ancient DNA is an adventure, so is gathering it. Shapiro has scoured remote landscapes in Alaska, Kenya, Siberia, and Canada to collect small samples from bones, teeth, skulls, and tusks that will be brought back to the lab, ground up, dissolved, altered and "cooked" so DNA can be extracted.
Shapiro’s ongoing expeditions to gold fields in Canada’s Yukon Territory have proved especially fruitful. Good relationships with numerous mining companies there permit her team to gather bone samples exposed as miner’s high-pressure hoses wash permafrost away. What makes these samples especially valuable is the ability to date them to earlier periods than traditional radiocarbon methods allow.
“Radiocarbon dates,” she explains, “can only go back about 40,000 to 50,000 years. But these Yukon sites give us a unique chance to establish the age of samples as far back as 130,000 years.”
How? For millennia, layers of volcanic ash have settled in sites being mined today. These layers can be linked to specific eruptions that occurred prior to the time registered by radiocarbon dating. “Let’s say we know an eruption happened about 80,000 years ago. If we find bones associated with that volcanic ash layer, we know they’re that old too," she says. "This lets us push back population genetics estimates to older and older time periods than ever before.”
What does the future hold for a scientist who spends her days peering into the past? “We’re now able to look not only at particular genes, but at how whole genomes—the entirety of a species’ genetics—evolved. We can go beyond mitochondrial DNA to nuclear DNA, which gives us an entirely new set of evolutionary information. We can see how genetic traits changed through time and how natural selection happened in real populations. I think we’re on the brink of the most exciting time ever in this field.”
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When the Leonid meteor storm hits the Earth on 17 November, the Hubble Space Telescope will be turned away from the onslaught to protect its delicate optics. But the time will be put to good use. Teams from the University of New South Wales in Sydney, NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Alabama in Tuscaloosa have won a competition among astronomers to use the space telescope while it is looking "the other way". They will study a quasar called PKS2200-238 and smaller galaxies that occupy the part of the sky the telescope will be fixed on.
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In the Solar System, the region beyond Neptune. It includes more than 70,000 small objects, a number up to asteroidal size. It is located from 30 to 50 A.U.'s and was discovered in 1992. The Kuiper belt may be the source of the short-period comets (like Halley's comet). The Kuiper belt was named for the Dutch-American astronomer Gerard P. Kuiper, who predicted its existence in 1951. In general, any belt beyond the outermost large planet of a solar system, consisting of mainly icy objects (ice dwarfs and ice planetisimals). | <urn:uuid:9b781256-8429-451d-8c35-28ee19aa6042> | 3.71875 | 128 | Knowledge Article | Science & Tech. | 65.213743 |
(often represented by the generic formula HA
]) is traditionally considered any chemical compound
that, when dissolved in water
, gives a solution with a hydrogen ion activity
greater than in pure water, i.e. a pH
less than 7.0. That approximates the modern definition of Johannes Nicolaus Brønsted
and Martin Lowry
, who independently defined an acid as a compound which donates a hydrogen ion
) to another compound (called a base
). Common examples include acetic acid
) and sulfuric acid
(used in car batteries
). Acid/base systems are different from redox
reactions in that there is no change in oxidation state
The word "acid" comes from the Latin acidus
meaning "sour," but in chemistry
the term acid has a more specific meaning. There are four common ways to define an acid:
- Arrhenius: According to this definition developed by the Swedish chemist Svante Arrhenius, an acid is a substance that increases the concentration of hydrogen ions (H+), which are carried as hydronium ions (H3O+) when dissolved in water, while bases are substances that increase the concentration of hydroxide ions (OH-). This definition limits acids and bases to substances that can dissolve in water. Around 1800, many French chemists, including Antoine Lavoisier, incorrectly believed that all acids contained oxygen. Indeed the modern German word for oxygen is Sauerstoff (lit. sour substance), as is the Afrikaans word for oxygen suurstof, with the same meaning. English chemists, including Sir Humphry Davy, at the same time believed all acids contained hydrogen. Arrhenius used this belief to develop this definition of acid.
- Brønsted-Lowry: According to this definition, an acid is a proton (hydrogen nucleus) donor and a base is a proton acceptor. The acid is said to be dissociated after the proton is donated. An acid and the corresponding base are referred to as conjugate acid-base pairs. Brønsted and Lowry independently formulated this definition, which includes water-insoluble substances not in the Arrhenius definition. Acids according to this definition are variously referred to as Brønsted acids, Brønsted-Lowry acids, proton acids, protic acids, or protonic acids.
- Solvent-system definition: According to this definition, an acid is a substance that, when dissolved in an autodissociating solvent, increases the concentration of the solvonium cations, such as H3O+ in water, NH4+ in liquid ammonia, NO+ in liquid N2O4, SbCl2+ in SbCl3, etc. Base is defined as the substance that increases the concentration of the solvate anions, respectively OH-, NH2-, NO3-, or SbCl4-. This definition extends acid-base reactions to non-aqueous systems and even some aprotic systems, where no hydrogen nuclei are involved in the reactions. This definition is not absolute, a compound acting as acid in one solvent may act as a base in another.
- Lewis: According to this definition developed by Gilbert N. Lewis, an acid is an electron-pair acceptor and a base is an electron-pair donor. (These are frequently referred to as "Lewis acids" and "Lewis bases," and are electrophiles and nucleophiles, respectively, in organic chemistry; Lewis bases are also ligands in coordination chemistry.) Lewis acids include substances with no transferable protons (ie H+ hydrogen ions), such as iron(III) chloride, and hence the Lewis definition of an acid has wider application than the Brønsted-Lowry definition. In fact, the term Lewis acid is often used to exclude protic (Brønsted-Lowry) acids. The Lewis definition can also be explained with molecular orbital theory. In general, an acid can receive an electron pair in its lowest unoccupied orbital (LUMO) from the highest occupied orbital (HOMO) of a base. That is, the HOMO from the base and the LUMO from the acid combine to a bonding molecular orbital.
Although not the most general theory, the Brønsted-Lowry definition is the most widely used definition. The strength of an acid may be understood by this definition by the stability of hydronium and the solvated conjugate base upon dissociation. Increasing or decreasing stability of the conjugate base will increase or decrease the acidity of a compound. This concept of acidity is used frequently for organic acids such as carboxylic acid. The molecular orbital description, where the unfilled proton orbital overlaps with a lone pair, is connected to the Lewis definition.
- Are generally sour in taste
- Strong or concentrated acids often produce a stinging feeling on mucous membranes
- Change the color of pH indicators as follows: turn blue litmus and methyl orange red, turn phenolphthalein colorless
- React with metals to produce a metal salt and hydrogen
- React with metal carbonates to produce water, CO2 and a salt
- React with a base to produce a salt and water
- React with a metal oxide to produce water and a salt
- Conduct electricity, depending on the degree of dissociation
- Produce solvonium ions, such as oxonium (H3O+) ions in water
Acids are/can be gases, liquids, or solids. Respective examples (at 20 °C and 1 atm) are hydrogen chloride, sulfuric acid and citric acid. Solutions of acids in water are liquids, such as hydrochloric acid - an aqueous solution of hydrogen chloride. At 20 °C and 1 atm, linear carboxylic acids are liquids up to nonanoic acid (nine carbon atoms) and solids beginning from decanoic acid (ten carbon atoms). Aromatic carboxylic acids, the simplest being benzoic acid, are solids.
Strong acids and many concentrated acids, being corrosive, can be dangerous; causing severe burns for even minor contact. Generally, acid burns on the skin are treated by rinsing the affected area abundantly with running water, followed up with immediate medical attention. In the case of highly concentrated mineral acids such as sulfuric acid or nitric acid, the acid should first be wiped off, otherwise the exothermic mixing of the acid and the water could cause thermal burns. Particular acids may also be dangerous for reasons not related to their acidity. Material Safety Data Sheets (MSDS) can be consulted for detailed information on dangers and handling instructions.
In the classical naming system, acids are named according to their anions
. That ionic suffix is dropped and replaced with a new suffix (and sometimes prefix), according to the table below. For example, HCl has chloride
as its anion, so the -ide suffix makes it take the form hydrochloric acid
. In the IUPAC
naming system, "aqueous" is simply added to the name of the ionic compound. Thus, for hydrogen chloride, the IUPAC name would be aqueous hydrogen chloride. The prefix "hydro-" is added only if the acid is made up of just hydrogen and one other element.
Classical naming system:
In water the following equilibrium
occurs between a weak acid (HA) and water, which acts as a base:
HA(aq) + H2O ⇌ H3O+(aq) + A-(aq)
The acidity constant (or acid dissociation constant) is the equilibrium constant for the reaction of HA with water:
Strong acids have large Ka values (i.e. the reaction equilibrium lies far to the right; the acid is almost completely dissociated to H3O+ and A-). Strong acids include the heavier hydrohalic acids: hydrochloric acid (HCl), hydrobromic acid (HBr), and hydroiodic acid (HI). (However, hydrofluoric acid, HF, is relatively weak.) For example, the Ka value for hydrochloric acid (HCl) is 107.
Weak acids have small Ka values (i.e. at equilibrium significant amounts of HA and A− exist together in solution; modest levels of H3O+ are present; the acid is only partially dissociated). For example, the Ka value for acetic acid is 1.8 x 10-5. Most organic acids are weak acids. Oxoacids, which tend to contain central atoms in high oxidation states surrounded by oxygen may be quite strong or weak. Nitric acid, sulfuric acid, and perchloric acid are all strong acids, whereas nitrous acid, sulfurous acid and hypochlorous acid are all weak.
Note on terms used:
- The terms "hydrogen ion" and "proton" are used interchangeably; both refer to H+.
- In aqueous solution, the water is protonated to form hydronium ion, H3O+(aq). This is often abbreviated as H+(aq) even though the symbol is not chemically correct.
- The strength of an acid is measured by its acid dissociation constant (Ka) or equivalently its pKa (pKa= - log(Ka)).
- The pH of a solution is a measurement of the concentration of hydronium. This will depend on the concentration and nature of acids and bases in solution.
are those acids that are able to donate one proton
per molecule during the process of dissociation
(sometimes called ionization) as shown below (symbolized by HA):
- HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq) Ka
Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO3). On the other hand, for organic acids the term mainly indicates the presence of one carboxyl group and sometimes these acids are known as monocarboxylic acid. Examples in organic acids include formic acid (HCOOH), acetic acid (CH3COOH) and benzoic acid (C6H5COOH).
Polyprotic acids are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic acid
(two potential protons to donate) and triprotic acid
(three potential protons to donate).
A diprotic acid (here symbolized by H2A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, Ka1 and Ka2.
- H2A(aq) + H2O(l) ⇌ H3O+(aq) + HA−(aq) Ka1
- HA−(aq) + H2O(l) ⇌ H3O+(aq) + A2−(aq) Ka2
The first dissociation constant is typically greater than the second; i.e., Ka1 > Ka2 . For example, sulfuric acid (H2SO4) can donate one proton to form the bisulfate anion (HSO4−), for which Ka1 is very large; then it can donate a second proton to form the sulfate anion (SO42−), wherein the Ka2 is intermediate strength. The large Ka1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid (H2CO3) can lose one proton to form bicarbonate anion (HCO3−) and lose a second to form carbonate anion (CO32−). Both Ka values are small, but Ka1 > Ka2 .
A triprotic acid (H3A) can undergo one, two, or three dissociations and has three dissociation constants, where Ka1 > Ka2 > Ka3 .
- H3A(aq) + H2O(l) ⇌ H3O+(aq) + H2A−(aq) Ka1
- H2A−(aq) + H2O(l) ⇌ H3O+(aq) + HA2−(aq) Ka2
- HA2−(aq) + H2O(l) ⇌ H3O+(aq) + A3−(aq) Ka3
An inorganic example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid. All three protons can be successively lost to yield H2PO4−, then HPO42−, and finally PO43− , the orthophosphate ion, usually just called phosphate. An organic example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion. Even though the positions of the protons on the original molecule may be equivalent, the successive Ka values will differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged.
Neutralization is the reaction between an acid and a base, producing a salt and neutralized base; for example, hydrochloric acid and sodium hydroxide form sodium chloride and water:
- HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
Neutralization is the basis of titration, where a pH indicator shows equivalence point when the equivalent number of moles of a base have been added to an acid. It is often wrongly assumed that neutralization should result in a solution with pH 7.0, which is only the case with similar acid and base strengths during a reaction.
Neutralization with a base weaker than the acid results in a weakly acidic salt. An example is the weakly acidic ammonium chloride, which is produced from the strong acid hydrogen chloride and the weak base ammonia. Conversely, neutralizing a weak acid with a strong base gives a weakly basic salt, e.g. sodium fluoride from hydrogen fluoride and sodium hydroxide.
Weak acid/weak base equilibria
In order to lose a proton, it is necessary that the pH of the system rise above the pKa
of the protonated acid. The decreased concentration of H+
in that basic solution shifts the equilibrium towards the conjugate base form (the deprotonated form of the acid). In lower-pH (more acidic) solutions, there is a high enough H+
concentration in the solution to cause the acid to remain in its protonated form, or to protonate its conjugate base (the deprotonated form).
Solutions of weak acids and salts of their conjugate bases form buffer solutions.
Applications of acids
There are numerous uses for acids. Acids are often used to remove rust and other corrosion from metals in a process known as pickling. They may be used as an electrolyte in a wet cell battery, such as sulfuric acid in a car battery.
Strong acids, sulfuric acid in particular, are widely used in mineral processing. For example, phosphate minerals react with sulfuric acid to produce phosphoric acid for the production of phosphate fertilizers, and zinc is produced by dissolving zinc oxide into sulfuric acid, purifying the solution and electrowinning.
In the chemical industry, acids react in neutralization reactions to produce salts. For example, nitric acid reacts with ammonia to produce ammonium nitrate, a fertilizer. Additionally, carboxylic acids can be esterified with alcohols, to produce esters.
Acids are used as catalysts; for example, sulfuric acid is used in very large quantities in the alkylation process to produce gasoline. Strong acids, such as sulfuric, phosphoric and hydrochloric acids also effect dehydration and condensation reactions.
Acids are used as additives to drinks and foods, as they alter their taste and serve as preservatives. Phosphoric acid, for example, is a component of cola drinks.
In humans and many other animals, hydrochloric acid
is a part of the gastric acid
secreted within the stomach
to help hydrolyze proteins
, as well as converting the inactive pro-enzyme, pepsinogen
into the enzyme, pepsin
. Some organisms produce acids for defense; for example, ants produce formic acid
- Methanesulfonic acid (aka mesylic acid) (MeSO3H)
- Ethanesulfonic acid (aka esylic acid) (EtSO3H)
- Benzenesulfonic acid (aka besylic acid) (PhSO3H)
- Toluenesulfonic acid (aka tosylic acid, or (C6H4(CH3) (SO3H)) | <urn:uuid:1dcb69cf-5d80-440e-a735-44f64f2823eb> | 3.859375 | 3,598 | Knowledge Article | Science & Tech. | 31.914795 |
C2 Epstein Diagrams
The dogma reads: Everybody is always and everywhere moving at the speed of light c in 4D space-time. Everyone calls the direction in which they move their time and the directions orthogonal to it form their space. One second of time therefore corresponds to 299,792,458 m (≈ 300,000 km) of space (that one did not notice this earlier can be explained as a consequence of the ‘disproportionateness’…).
If we want to plot this movement in 4D space-time then we have the same problem as everyone else who attempts to draw a four-dimensional representation. One must be happy when a three-dimensional picture is clearly understood on a flat sheet of paper. In our case however these difficulties are easily eliminated: We represent only one direction in space, the one in which the two reference systems move relative to each other! Anyway, nothing exciting happens in the other two spatial directions according to our formulas of B3!
We will always use a black coordinate system with origin A and a red one with origin B, like the one shown above in B3. B moves with velocity v along the x-axis of black and A moves with velocity -v along the x'-axis of red. A and B met at O and at that point both set their clocks to zero. In addition, everyone tells time with the clocks of their respective system which have been synchronized respective to the master clocks of their system. A and B are each spatially at rest in their own system and move (in their own system) only through time. Our first attempt:
In order to avoid complications with causality we must forbid that red, which had an interaction at O with A, can ever influence the temporal past of black before point O. This means that the angle φ may not be larger than 90º. Otherwise red would be able to ignite its engine after some time, return to point O and arrive there at a time before the interaction between A and B, which already took place. We adhere emphatically to the following:
For systems, which can interact with one another, the angle φ between the two time axes (that is, the directions of the journey through 4D space-time) may not be larger than 90º.
It is important that the segments OA and OB are equal: In a given interval of time both cover the same distance in space-time! That is Epstein’s dogma. What is the meaning of the angle between the time axes? We depict the direction of the x-axis of black and mark the place, which B has reached in this x-direction, while black has just aged by the segment OA:
Thus OA = OB. OA is for black simply the time, which elapsed since the meeting with B at O. B has in this time, from the point of view of black, traversed the segment OX. This yields
since in the right triangle OXB angle φ occurs again at vertex B. We obtain B’s position in the coordinate system of A simply by projecting the space-time position of B perpendicularly onto the space-axis of A. In so doing we are being rather cavalier with our mix of units: OA, OB and OX are segments in space-time. When reducing to pure times and distances we must consider that 1 second of time corresponds to a distance of 1 light-second, or about 300,000 km! If we clean up the units of measurement in the above equation it looks as follows:
The unit-free number sin(φ) corresponds in the Epstein diagram to the ratio v to c! So far we have taken the point of view of black. That is unnecessary since Epstein diagrams have (unlike Minkowski diagrams!) the beautiful characteristic that they display symmetrical relationships symmetrically. Thus, we draw the above diagram again with the addition of a space-axis for B:
From the point of view of B: During the time OB, A traverses OX’.
The two triangles OXB and OX'A are congruent. The same absolute value for the relative velocity v arises in both coordinate systems. Because of the selected orientation of the axes we obtain however different signs for v: For red A moves in negative x'-direction, while for black B moves in positive x-direction. Thus we are in complete agreement with the presentation in B3.
Perhaps you are surprised that the time axes are not indicated with t or t’ (Note: in the diagrams the German word 'Zeit' stands for 'time', where as 'Raum' stands for 'space'). We reveal the reason for this in the next section. First we want to do another small calculation, which yields a very important result. For acute angles φ we have
The radical which appears in the calculation of time dilation and length contraction, has a simple geometrical meaning in the Epstein diagram! Spoken as black: sin(φ) projects OB on my space-axis, cos(φ) projects OB on my time-axis. We would like to exploit that immediately. | <urn:uuid:edd63c97-af05-428c-92a9-14f716a430ba> | 3.203125 | 1,071 | Academic Writing | Science & Tech. | 54.976264 |
The word synoptic means "view together" or "view at a common point". Therefore, synoptic meteorology is primarily concerned with viewing the weather at a common point -- time.
Also known as large scale or cyclonic scale, the size of weather patterns we are looking at range upwards from about 620 miles (1,000 kilometers) across to about 1,500 miles (2,500 kilometers).
When different parameters of the earth's atmosphere are viewed together at the synoptic scale then large-scale weather patterns emerge, such as extratropical cyclones and their associated fronts.
The forecast weather map (right) is an example of the use of synoptic meteorology. It shows the positions of high and low pressure systems as well as locations of weather fronts.
But before this map will provide any relevant information, one of the primary things a good meteorologist will check is the "time" these various weather elements were observed. We will begin by learning about synoptic times displayed on weather maps and text products issued by the National Weather Service. | <urn:uuid:dfb85734-9ed4-4c85-8f5c-69609bd6deb7> | 3.796875 | 220 | Knowledge Article | Science & Tech. | 36.223586 |
Common Names in English:
'The Nymphalidae are members
of the Superfamily
Papilionoidea, the true butterflies. Distributed worldwide, butterflies of this family
are especially rich in the tropics. They are highly variable, and there are more species in this family than in any other. Adults
vary in size from small to large, and their front legs
are reduced, unable to be used for walking. Wing
is also highly variable: some species have irregular margins
(anglewings and commas), and others have long taillike projections (daggerwings). Browns, oranges, yellows, and blacks are frequent colors, while iridescent
colors such as purples and blues are rare. Adults of some groups are the longest-lived butterflies, surviving 6-11 months. Adult feeding behavior depends on the species, where some groups primarily seek flower nectar while others only feed
, rotting fruit, dung, or animal carcasses. Males exhibit
behaviors when seeking mates. Egg-laying
varies widely, as some species lay eggs
in clustsers, others in columns, and others singly. Caterpillar appearance
and behavior vary widely. Brushfoots overwinter
as larvae or adults.
Brushfoots are the most prevalent members of the Family Nymphalinae. Distributed worldwide, this is a diverse group that contains several tribes , each with somewhat different structural and biological features. Adults of North American species are predominantly orange, brown, and black. Wing shape and mating systems are variable. Most checkerspots and crescentspots patrol for mates, while the remainder of groups exhibit either perching or perching and patrolling . Migration varies widely; some strong migrants are found in the lady butterflies, tortoiseshells, and anglewings, while other species are local in occurrence. Most species limit their host plants to a few species, but the Painted Lady has one of the widest host palettes of all butterflies. Eggs are laid singly or clustered in groups, and caterpillars be found feeding alone or communally. Brushfoots overwinter as young caterpillars or hibernating adults.
Species Phyciodes orseis
Upperside is dark brown with orange-brown markings in distinct bands . Underside is yellow-orange with scattered reddish brown markings. (ref. 105921)
Wing span : 1 1/4 - 1 5/8 inches (3.2 - 4.2 cm). (ref. 105921)
Mountain valleys, meadows, stream canyons . (ref. 105921)
- Whittaker & Margulis,1978
- C. Linnaeus, 1758
- (Hatschek, 1888) Cavalier-Smith, 1983
- Grobben, 1908
- A.M.A. Aguinaldo et al., 1997 ex T. Cavalier-Smith, 1998
- Latreille, 1829
- Snodgrass, 1938
- Heymons, 1901
- C. Linnaeus, 1758
- Butterflies and Moths
- Infraorder: Heteroneura ()
- Order: Lepidoptera () - C. Linnaeus, 1758 - Butterflies and Moths
- Superorder: Panorpida ()
- Cohort: Myoglossata ()
- Infraclass: Pterygota ()
- Subclass: Dicondylia ()
- Epiclass: Hexapoda ()
- Superclass: Panhexapoda ()
- Infraphylum: Atelocerata () - Heymons, 1901
- Subphylum: Mandibulata () - Snodgrass, 1938
- Phylum: Arthropoda () - Latreille, 1829 - Arthropods
- Superphylum: Panarthropoda () - Cuvier
- Infrakingdom: Ecdysozoa () - A.M.A. Aguinaldo et al., 1997 ex T. Cavalier-Smith, 1998
- Branch: Protostomia () - Grobben, 1908
- Subkingdom: Bilateria () - (Hatschek, 1888) Cavalier-Smith, 1983
- Kingdom: Animalia () - C. Linnaeus, 1758 - animals
Name Status: Accepted Name .
Members of the genus Phyciodes
ZipcodeZoo has pages for 37 species and subspecies in this genus:
P. argentea (Chestnut Crescent) · P. batesii (Tawny Crescent) · P. batesii anasazi (Canyon Crescent) · P. batesii batesii (Tawny Crescent) · P. batesii lakota (Lakota Crescent) · P. batesii maconensis (Appalachian Crescent) · P. cocyta (Northern Crescent) · P. cocyta arenacolor (Steptoe Valley Checkerspot) · P. frisia (Cuban Crescent) · P. graphica (Graphic Crescent) · P. graphica vesta (Vesta Crescent) · P. incognitus (Mimic Crescent) · P. mylitta (Mylitta Crescent) · P. mylitta mexicana (Mylitta Crescent) · P. orseis (California Crescent) · P. orseis herlani (Orseis Crescent) · P. orseis orseis (Orseis Crescent) · P. pallescens (Mexican Crescent) · P. pallida (Pale Crescent) · P. pallida barnesi (Barnes' Crescent) · P. pallidus (Pallid Crescentspot) · P. phaon (Phaon Crescent) · P. picta (Painted Crescent) · P. picta canace (Painted Crescent) · P. pratensis (Field Crescent) · P. pulchella (Field Crescent) · P. pulchella camillus (Camillus Crescent) · P. pulchella pulchella (Field Crescent) · P. pulchella shoshoni (Field Crescent) · P. pulchella totchone (Field Crescent) · P. texana (Texan Crescent) · P. tharos (Arctic White) · P. tharos arctica (Pearl Crescent) · P. tharos riocolorado (Northern Pearl Crescent) · P. tharos tharos (Pearl Crescent) · P. tulcis (Pale-Banded Crescent) · P. vesta (Vesta Crescent)
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- A manual of North American butterflies by Charles J. Maynard. Boston: De Wolfe, Fiske, 1891. url .
- Bibliography (Lepidoptera: Rhopalocera) / Charles A. Bridges. Urbana, Ill.: C.A. Bridges, c1993. url p. 374.
- Bulletin of the British Museum (Natural History). London: BM(NH) url p. 179, p. 197, p. 85, p. 87, p. 90.
- Entomological news. [Philadelphia]American Entomological Society, 1925- url p. 135.
- Occasional papers of the California Academy of Sciences. San Francisco: California Academy of Sciences, url p. 23.
- The Macrolepidoptera of the world; a systematic description of the hitherto known Macrolepidoptera, ed. in collaboration with well-known specialists. Stuttgart: Seitz'schen (Kernen), 1906- url p. 436.
- The butterfly book a popular guide to a knowledge of the butterflies of North America / by W.J. Holland. Toronto: W. Briggs, 1898. url .
- The butterfly book: a popular guide to a knowledge of the butterflies of North America / by W.J. Holland. Garden City, N.Y.: Doubleday, 1910. url p. 154, p. 155.
- The butterfly book; a popular guide to a knowledge of the butterflies of North America. With 48 plates in color-photography, reproductions of butterflies in the author's collection, and many text illustrations presenting 1922 Garden City, N.Y., Doubleday, Page, 1922 [c1898] url p. 154, p. 155, explanation of plate XVII.
- Brands, S.J. (comp.) 1989-present. The Taxonomicon. Universal Taxonomic Services, Zwaag, The Netherlands. Accessed January 10, 2012.
Accessed through GBIF Data Portal November 06, 2007:
- Avian Knowledge Network, Hawk Migration Association of North America - HawkCount
- Institute of Marine and Coastal Sciences, Rutgers University, South African Institute for Aquatic Biodiversity - Fish Collection
- Museum of Southwestern Biology, Division of Amphibians and Reptiles, Museum of Southwestern Biology, Division of Amphibians and Reptiles database
- Biodiversity Heritage Library NamebankID: 2631024
- Catalogue of Life Accepted Name Code: Lep-156562.0
- Natural Heritage Network Species Identifier: IILEPK3070
- Zipcode Zoo Species Identifier: 171750 | <urn:uuid:81c4eabe-ac3d-4a3f-904f-997a2d75a400> | 4.03125 | 2,063 | Knowledge Article | Science & Tech. | 44.29857 |
Not many of you will believe that hagfish, also called snot-eels, are fascinating creatures, but they truly are. You will only be able to believe me after reading this post. I still persist saying that I am not falling in love with them but some of my colleagues start worrying about my desire to always know more on their behaviour. Another step in this direction, I just published with colleagues from Te Papa, Massey University and the University of Western Australia a paper describing new extraordinary behaviours of my current favourites.
Hagfish are deep-sea primitive fishes which have been living on Earth for at least 300 millions years, almost unchanged. They are like living fossils and scientists wonder how it is possible that they could survive for such a long time on Earth. To give you an idea of how long 300 millions years is, keep in mind that the dinosaurs appeared on Earth about 230 millions years and went extinct about 65 millions ago. With this research, we reveal a few more clues on what make hagfishes so special.
Hagfish were thought to fulfil primarily the ecological niche of scavengers in the deep ocean, i.e. we thought they were feeding on dead animals only. Reviewing video footage taken in New Zealand waters, we now know that they are also able to hunt for live preys such as fishes. During a video deployment off Great Barrier Island at 97 m depth, one hagfish species was successfully observed predating on a red bandfish.
But there is more. After carefully reviewing over 1000 hours of underwater video footage, I realized that not a single shark or other large fish could bite and feed on hagfish. Hagfish versus sharks and co: 1-0! What happens is that every time a large fish tries to attack, the hagfish produce large amount of slime at incredible speed. This slime then clogs the gills of those would-be predators which start choking, unable to breathe. Amazingly, not a single attack resulted in successful predation! This is an extremely effective defence mechanism, totally unique.
The paper describing those two newly observed behaviours can be downloaded here from the journal Scientific Reports. | <urn:uuid:ce125a3b-66d6-486d-af0c-46b2b4766f93> | 2.921875 | 441 | Personal Blog | Science & Tech. | 49.402934 |
Carlo Zapponi created Bolides, a fantastic animated visualization of meteorites that have been seen hitting the Earth. The data source is the Nomenclature Committee of the Meteoritical Society's Meteorite Bulletin. "The word bolide comes from Greek βολίς bolis, which means missile. Astronomers tend to use bolide to identify an exceptionally bright fireball, particularly one that explodes." Bolides
Here is Heritage Auctions' description for the Gibeon Mask -- "an incomparable iron meteorite"
Closing out the Gibeon section is arguably the most aesthetic iron meteorite known to exist. In 1992, indigenous tribesmen in Namibia's Kalahari recovered this matchless specimen with the aid of a metal detector. It is extremely rare for meteorites to have naturally formed holes, and rarer still when the holes are positioned in the matrix in such a way as to yield a magnificent aesthetic specimen-let alone the highly zoomorphic example seen here. Defined by the two adjacent hollows that perforate its mass and separated by perfectly sculpted ridges, there is an exquisite asymmetric balance between this meteorite's two sides: the outward flanging of one side is offset by the larger hollow and more prominent opposing crest.
In addition to the mechanisms involved in the shaping of aesthetic iron meteorites described in the previous lot, there is one other critical detail that was of particular significance to the current example: the moment of extraction from beneath the Earth's surface. If removed several hundred years earlier, this specimen would not have been the perfectly singular zoomorphic evocation before us. If removed several hundred years later, the holes would be far too large and outsized. Adorned with a sumptuous natural patina from its stay in the Kalahari and accompanied by a custom armature and Lucite dome, this is an incomparable meteorite from the finest collection of aesthetic iron meteorites in the world. 195 x 212 x 177mm (7.66 x 8.33 x 7 inches) and 9.37 kilograms (20.66 pounds)
Provenance: The Macovich Collection, New York City. Estimate: $140,000 - $160,000.
This is a very cool, behind-the-scenes peek at how researchers at the Smithsonian deal with the problem of studying meteorites without contaminating said meteorites.
This is a big issue. We study meteorites to learn things about what has happened and is happening outside our own planetary system. If, in the process of that, we end up covering the samples with the detritus of Earth, then the message gets muddled. If you're studying a meteorite, you want to be reasonably sure that you're not accidentally studying dust or bacteria from this planet. Clean rooms like the one in this video make it easier to examine these samples in a way that is less destructive. | <urn:uuid:f8ceb47e-ed2c-41eb-ba7d-72ac9aacab27> | 2.796875 | 596 | Personal Blog | Science & Tech. | 36.32357 |
I don't really get how the authors came up with their three models:
- the "Paleolithic" model assumes beginning of expansion at 21 kBP; as this was unsupported under any mutation rate, I won't bother with it further.
- the "Neolithic" models had expansion beginning at 10.5kBP, that is about 2k prior to the known earliest colonization of Europe from Anatolia, that occurred around 6,700 years BC.
- the "recent" model has the expansion starting at 3kBP, but already at 3kBP R1b1b2 makes its earliest appearance at Lichtenstein in Germany, and indeed 3kBP takes us to the Iron Age, a period extremely unlikely to have been one of major dispersals into Europe, dispersals that could not have gone unnoticed by the literate civilizations of the time.
Here is what the authors have to say:
Our results show that an expansion in Neolithic or Mesolithic times (350 generations ago or 10 ky) leads to a lower sum of squared errors than post-glacial re-expansion started 700 generations ago (21 ky ago), regardless of assuming a GMR or EMR model (Figure 2 and Table 2). Using GMRs, simulations of recent (100 generations ago) and rapid expansions from three distinct origins provided a better fit to the geographical distribution of microsatellite diversity than did models with expansion started 350 generations ago. Although models of recent origins using GMRs provided poorer fit than a model of Neolithic expansion using the EMR (Figure 2 and Table 2), the small observed difference makes them however difficult to discriminate (odd ratio = 1.7; Figure 3).So, basically the "evolutionary" rate stands its own against the "germline" rate assuming that the Neolithic expansion started 2,000 years before it did, and using the "germline" rate for an expansion at a much later time than anyone would believe.
Not directly related to the paper, I looked at the ongoing Dodecad v3 results to possibly correlate the spread of R-M269 to Western Europe with the autosomal evidence. It appears that the "West European" autosomal component shows a stronger relationship to the "West Asian" one than the "East European" one. This is consistent with an episode of gene flow into Europe from West Asia that affected Western more than Eastern Europe, which parallels the R-M269 distribution in Europe.
More interestingly, I had previously traced a peculiar "Dagestan component" in Europe that, counter-intuitively, seemed to be maximized in the Northwest. Looking at the recent Caucasus Y-chromosome paper, I notice the presence of R-M269 in the Lezgins of Dagestan (~29.6%), as well as the Abkhaz (12.1%). Looking at my Dodecad v3 results, I obtain a value of 24.3% of the "West European" component in the Lezgins, and a value of 15.7% in the Adygei, who are linguistically related to the Abkhaz. By contrast, other R1b-rich populations (namely Armenians and Turks) from West Asia show no substantial evidence of the "West European" component.
PLoS ONE 6(6): e21592. doi:10.1371/journal.pone.0021592
Wave-of-Advance Models of the Diffusion of the Y Chromosome Haplogroup R1b1b2 in Europe
Per Sjödin1, Olivier François
Whether or not the spread of agriculture in Europe was accompanied by movements of people is a long-standing question in archeology and anthropology, which has been frequently addressed with the help of population genetic data. Estimates on dates of expansion and geographic origins obtained from genetic data are however sensitive to the calibration of mutation rates and to the mathematical models used to perform inference. For instance, recent data on the Y chromosome haplogroup R1b1b2 (M269) have either suggested a Neolithic origin for European paternal lineages or a more ancient Paleolithic origin depending on the calibration of Y-STR mutation rates. Here we examine the date of expansion and the geographic origin of hgR1b1b2 considering two current estimates of mutation rates in a total of fourteen realistic wave-of-advance models. We report that a range expansion dating to the Paleolithic is unlikely to explain the observed geographical distribution of microsatellite diversity, and that whether the data is informative with respect to the spread of agriculture in Europe depends on the mutation rate assumption in a critical way. | <urn:uuid:fe4c5f09-8eed-4c86-b3b3-7c6d75fb1a0e> | 2.828125 | 962 | Personal Blog | Science & Tech. | 33.318143 |
Tuesday, April 17, 2012 - 14:00 in Biology & Nature
Lobes of fat connecting to their ears may allow baleen whales to hear underwater.
- Researchers find first genetic evidence for loss of teeth in the common ancestor of baleen whalesWed, 29 Sep 2010, 17:23:24 EDT
- Scientists use marine robots to detect endangered whalesWed, 9 Jan 2013, 19:05:12 EST
- Genetic analysis disputes increase in Antarctic minke whalesFri, 15 Jan 2010, 9:57:20 EST
- Dwarf whale survived well into Ice AgeThu, 4 Apr 2013, 14:05:36 EDT
- Story of 4.5 million-year-old whale unveiled in HuelvaTue, 15 Dec 2009, 10:21:33 EST | <urn:uuid:84fc445d-720f-4ace-843a-e156363375a4> | 2.96875 | 162 | Content Listing | Science & Tech. | 39.225 |
Spring Pygmy Sunfish, One of Alabama's Rare Fishes
Keith B. Floyd
Alabama is blessed with an abundance of streams and rivers. This large amount of fresh water provides a home to over 306 native freshwater species. Alabama is second only to Tennessee in the number of freshwater fish species found in a state. These diverse aquatic habitats also support thirteen species of fish that only occur within the state of Alabama. These unique species are found in limited areas of river basins, particular watersheds, or springs. One of the fish species that is unique to Alabama is the spring pygmy sunfish.
The spring pygmy sunfish is found only in two locations, both in the Tennessee Valley region of north Alabama. The Beaverdam Creek watershed that drains into Wheeler Reservoir contains spring pygmy sunfish, and Pryor Spring contains a re-established population of the species. Biologists stocked the fish in Pryor Spring during the 1980s, and the spring pygmy sunfish are doing well. Both of these populations are in Limestone County. The first spring pygmy sunfish was discovered in Cave Spring, Lauderdale County. Spring pygmy sunfish were feared to be extinct after Pickwick Reservoir filled and changed the habitat.
The Fisheries Section of the Division of Wildlife and Freshwater Fisheries studied the spring pygmy sunfish for several years during the early 1990s. Unlike some rare species that are difficult to find even in their preferred habitat, spring pygmy sunfish are often abundant. Their preferred habitat consists of thick concentrations of aquatic vegetation such as parrot’s feather and coontail. Often 10 spring pygmy sunfish can be collected from a vegetated area the size of a basketball net. High densities of these unique fish also occur in shallow, heavily vegetated margins of the spring run below a lake on Beaverdam Creek. Recent sampling efforts extended the known range downstream in Beaverdam Creek to the impounded section of Wheeler Reservoir. These populations are spotty and restricted to dense vegetation.
The close association to vegetation serves two purposes. Vegetation provides a ready source of food -- insect larvae and tiny crustaceans such as copepods and daphnia. The vegetation also acts as a refuge from predators. Spring pygmy sunfish in aquaria experiments lose their association with vegetation in the absence of predators.
Spring pygmy sunfish rarely grow larger than an inch. Males and females of the spring pygmy sunfish exhibit substantially different color patterns, a condition known as sexual dimorphism. Breeding males are generally dark brown with five to seven narrow silver or gold vertical bars along their sides. The dorsal and anal fins have darkened areas. Females are brown on the back, mottled brown and white on the sides, and white on the bottom. The spring pygmy sunfish is also unusual in that it lives little more than a year. Spawning occurs in March and April with eggs being laid on vegetation. Few adults are seen after spring.
The spring pygmy sunfish is one of Alabama’s unique fish. Agreements with Limestone County landowners have been successful in preserving and extending the finite habitat for this special fish. Knowledge and awareness of rare species and their preferred habitats assist in conserving this fish for many more years.
Photographs by Doug Darr
Date Published: November 1999 | <urn:uuid:3fb30fd6-e19f-46d1-9dcd-42c0edbcc2aa> | 3.515625 | 691 | Knowledge Article | Science & Tech. | 40.242118 |
(Submitted February 16, 1998)
I just heard the term 'hypernova'. Do hypernovae really exist? Is it true
that there was a recently discovered one? How does a hypernova form, in
contrast to supernovae & black holes?
A hypernova is a possible explanation for gamma-ray bursts. It can
be thought of as a "failed supernova" -- a massive star whose core
collapses but which doesn't quite blow itself apart. The idea is that the
star's core collapses because it has run out of fuel and can no longer
produce enough pressure to withstand gravity. The central part of the
star collapses, forming either a neutron star or a black hole. In a
supernova the resulting shockwave blows off the outer parts of the star.
In the case of a hypernova the shock wave doesn't blow off the outer
layers of the star. The material of the outer layers falls onto the
central black hole or neutron star converting its gravitational potential
energy to heat and radiation. This can result in a much higher luminosity
than a supernova. This is why hypernovae were proposed as a possible
explanation for gamma-ray bursts. The X-ray afterglow from a gamma-ray
burst has been found to be more luminous than a supernova. Whether
hypernovae actually exist is still an open question.
for Ask an Astrophysicist | <urn:uuid:232add54-1ad1-4d84-a993-32c130d8de98> | 3.96875 | 303 | Q&A Forum | Science & Tech. | 53.824988 |
Questions, Suggestions, & References
Back to Franklin Square
QuestionsHere are some ideas for questions:
Is it possible to make a Franklin Cube with some or all of the properties of the square? Which properties?
Can some of the observations be combined to discover new magical or half-magical shapes?
Can the construction algorithm and some observations be used to say more about the value of specific cells on the square?
Can Observation 17 be changed into an if, only if, statement regarding where on-their-side Vs must be located in order to be magic? Can you prove it?
Can the locations of the median value cells in each column be predicted? If so, can the prediction be proven?
What is the mean value of the range of all of the columns of a Franklin Square?
Which columns of a Franklin Square have the least range? How can Observation 13 be extended?
Devise a proof for observation 2.
Spreadsheet Suggestions:If you are an experienced user of spreadsheets, you can probably devise a way of easily generating Franklin Squares. If you aren't, this might be helpful.
After placing the values in the seed columns manually, use logical tests in the formula for a cell's value to determine the odd/even value of the column and of the row it is in. Based upon that information, you can devise an expression using both the row's seed value and the value of the previous cell to determines the cell's value.
Spreadsheets expedite the testing of conjectures. Say a student suspects that some checkerboard-like pattern of n cells is magical. He or she can select a cell well off the square, click on auto-sum, and then select cells falling into that pattern on the sheet using the Control key with the Windows version of Excel (your spreadsheet may differ), then press Enter when done. If the sum is the magic constant, he or she can then reselect the cell and drag the mouse so that many other cells are selected and use the Edit Fill command to obtain the values of the same shaped groups of cells on the square which are in the same positions relative to the initial group of cells as the cells just filled are relative to the initial off-square cell. One caution in this is that some of the new groups evaluated may include empty cells, but students would probably recognize this if it occurred.
Home || The Math Library || Quick Reference || Search || Help | <urn:uuid:04b28713-6a6e-4e6d-8353-e286ef46b999> | 3.0625 | 501 | Q&A Forum | Science & Tech. | 53.658638 |
If b>0 prove that limn->infinity 1/1+nb=0 using the limit definition.
I can't seem to make any headway in choosing my delta to make progress in this exercise.
what we need to do is show that for ANY ε > 0 (even, or perhaps especially the very tiny ones), we can find SOME positive integer N, such that:
for ALL n > N:
note we're not using "delta" because n isn't tending to a certain definite real number (|x - ∞| < δ doesn't make any sense). instead, we're using the idea that "close to infinity" means "really big".
we expect that if ε is very small, N should be quite large.
(since we can insist n > 0 (we are, after all, going "all the way positive to infinity") and we know that b > 0).
if we want:
, then we want:
this suggests we pick , or N = 1 (just to keep N positive).
so, if we choose:
, we have for all n > N:
, as desired.
let's see how this works for a specific ε, and a specific b (we'll actually find the N that works).
suppose b = 2, and ε = 0.1 or 1/10.
according to what we did above, the integer N we want is:
N > (1/2)(9/10)(10) = 9/2, so we should pick N = 5.
note that 1/(1 + 2*4) = 1/9 > 1/10, so N = 4 doesn't work.
now if n ≥ 5:
1/(1 + 2n) < 1/11 < 1/10. | <urn:uuid:ee85ce25-af1b-4d47-badd-311788ad1447> | 3.25 | 383 | Q&A Forum | Science & Tech. | 96.492441 |
(a) AB = 8, BC = 6 in rectangle ABCD. Find the lengths of all segments shown in the diagram above.
Specifically: BD, CF,DE, BE, FE, CE
Comments: This is another in a series of rectangle investigations. To deepen student understanding of triangle relationships and to provide considerable practice with these ideas, the question asks for more than just one result. Students should be encouraged to first draw ALL of the triangles in the diagram separately and recognize why they are all similar! Using ratios, students should be able to find all the segments efficiently. One could also demonstrate the altitude on hypotenuse theorems as well!
(b) In case, students need a bit more of a challenge, have them derive expressions for all of the above segments given that AB = b and BC = a. To make life easier, assume b > a. This should keep your stronger students rather busy! This algebraic connection is powerful stuff. We want our students to appreciate that algebra is the language of generalization. | <urn:uuid:e8f8627a-3de6-4022-b40f-b49d380cd8aa> | 4.1875 | 211 | Comment Section | Science & Tech. | 50.865272 |