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Proving ?R² Using Chains, a Ruler, and Sixty Seconds
In this brief video, Minute Physics shows a visual proof demonstrating why ?R² gets you the area of a circle. By using various lengths of chain laid into a circular shape, you can make a triangle from the circle -- and from there it's a hop, skip, and a trigonometry jump to proof of your circle's area. Check it:
As Minute Physics explains in the YouTube video description, this video is based on a paper by Russell Jay Hendel of Dowling College: Proof Without Words: Area of a Disk is ?R² (PDF link). | <urn:uuid:cea8c368-52d2-4648-850c-f618deec2348> | 3.25 | 132 | Truncated | Science & Tech. | 68.671028 |
The Universe Revealed by Subaru Telescope Ⅲ
The Milky Way and its Group
Our solar system belongs to a large spiral-shaped group of stars called the Milky Way Galaxy, which is about 100,000 light years across. The next nearest large galactic neighbor is the Andromeda Galaxy (M31), located 2.5 million light-years away. It is spiral also and is similar size as the Milky Way Galaxy. Between Andromeda and the Milky Way galaxies there are dozens of smaller ones. The interactions between members of this galactic group provide us with important clues when we try to understand the mechanism of how galaxies are formed.
The World of Stars in the Andromeda Galaxy
The Andromeda Galaxy (M31) is just bright enough in our sky that it can be recognized with the naked eye. However, since the galaxy is so large and so close, it is difficult to observe the whole region with a large telescope. One of the best features of the Subaru Prime Focus Camera is its wide field of view. The camera succeeded in taking a very clear image of the southwest quadran of M31 (yellow square). From the upper left to the lower right in this image, the colors of the stars range from yellow to blue. What this means is that the older stars, which were formed about a few billion years ago, which characteristically shine with yellow light, are distributed more toward the center of the Andromeda Galaxy. The younger stars, which shine with blue light, are located more toward the outer reaches of the galaxy. This kind of observation allows us to understand more about how spiral galaxies formed.
The Structure of a Dwarf Galaxy
There are many small objects known as dwarf galaxies that populate our local galaxy group. Some of them lie relatively far away from the Milky Way and Andromeda galaxies, and astronomers made a theory that they evolved independently, without much interaction with each other, hence this structures are supposed to be simple. However, the analysis of star distribution in the dwarf galaxy Leo A, as seen in a Subaru Prime Focus Camera image, shows that it has a surprisingly complex structure. There is also a possibility that dwarf galaxies may form when even smaller ones merge together.
The First Stars in the Universe
A comparison between the optical spectra of the Sun versus a star HE1327-2326 with the least heavy elements. The top panel shows the low-dispersion spectrum while the bottom panel is the high dispersion spectrum captured by Subaru Telescope's HDS (High Dispersion Spectrograph). The solar spectrum has many absorption lines that are caused by the heavy elements at its surface. In contrast, the spectrum of HE1327-2326 shows almost no absorption lines due to the lack of heavy elements.
In the Milky Way Galaxy, there survives a type of star that was born very early in the history of the universe. How did it form? Just after the "Big Bang," the universe consisted of only hydrogen and helium. The first stars were thought to contain no heavy elements. Subaru Telescope has discovered such a primordial stars having lowest content of heavy elements known to date. Its chemical composition may hold information that could lead us to a better understanding of what the first stars were like.
Commentary from Dr. Nobuo Arimoto, Professor at NAOJ:
Subaru Telescope excels at extensive imaging, and succeeded in discovering the halo structure of a dwarf galaxy for the first time. Due to this discovery we can understand that even a dwarf galaxy has a complex history of formation. It is expected that in the future, further systematic research of this halo structure will show that it is an attribute of many galaxies that exist in our local group. | <urn:uuid:165dc187-2b42-4695-a026-239367bb4b97> | 3.75 | 741 | Knowledge Article | Science & Tech. | 42.826174 |
Q1 A common feature of all life on Earth is...
Q2 If extraterrestrials had visited Earth at some random time
between the Earth's formation and now, what kind of life forms would they
most likely have found
stone age humans
humans with radio telescopes
dinosaurs and insects
Q3 Which of the following ideas is NOT being discussed as a
possible explanation for the origin of life on Earth?
life originated in a "warm primordial soup" - possibly in tide pools
life originated several kilometers beneath the surface of the Earth
or at the bottom of the oceans near hydro-thermal vents
life on Earth came from Mars
life on Earth originated on the Moon
Q4 The age of the Universe, the age of the Earth and the age
of the earliest evidence for life on Earth are respectively (in billions
1000, 100, 5
50, 10, 4.1
13, 4.5, 3.8
1.1, 0.6, 0.5
Q5 The Earth's atmosphere contains about 80% nitrogen and 20%
oxygen. The oxygen that we breathe...
came from volcanic emission
came from cow digestive tracts
is generated by ozone depletion
is the waste product of blue-green algae
Q6 The bombardment of the early Earth by meteorites can be quantified
meteorologists using a state of the art PC
measuring the number of craters in the lunar maria and highlands
measuring the abundance of volcanic gases in the atmosphere
careful mapping of the holes in the ozone layer
Q7 We may all be martians since...
sequencing of martian DNA shows that it is very similar to DNA on Earth
life could have begun first on Mars and then have been carried to Earth inside of a meteorite
there is good evidence for artificial canals on the martian surface
we are adapted to living on land and there is much less water on Mars than there is on Earth
Q8 Astronomers have been searching for planets around Sun-like
stars. So far...
they haven't found any
about a dozen small Earth-like planets have been found
about 100 large Jupiter-like planets have been found
about 100 Earth-like planets have been found
Q9 Water and organic molecules...
have been found in molecular clouds all over our galaxy
are probably only found on Earth because so far it's the only place
where life has been detected
are only found in living creatures
are only found in plants and animals
Q10 The Drake equation...
tries to estimate the number of advanced civilizations in our galaxy
describes the organic gases from eukaryotic bacteria
quantifies the observation that once a species goes extinct it never comes back
describes how life gets more and more complex as it evolves
Q11 Fermi's paradox is...
if technological civilizations are common in our Galaxy, they should
be here but they aren't
why are plants green? They should be black to absorb light better
the asteroid belt should be a planet but it's not
comets should contain lots of water ice but they don't
Q12 In our class Dr. Butler announced a discovery which made
world wide press the next day. We heard it first! He and his colleagues
had discovered the first stellar system with more than one planet. They
made this discovery by...
the radial velocity or Doppler method (seeing how the velocity of
the star varies with time)
the astrometric method (seeing how the position on the sky of the
star varies with time)
the occulting method (seeing how the apparent luminosity of the star
varies as the planet intersects the line of sight towards us, blocking
out some of the light)
the symbiotic method (seeing how the biogenic atmospheres of the planets
change the spectra of the central star)
Q13 NASA's Terrestrial Planet finder (TPF) is a proposed space-borne
interferometer. TPF will use the technique of `nulling' to locate planets
near stars. The process of `nulling' is...
cancellation of interstellar sound waves
using interference methods to eliminate the light from the bright
star, thereby rendering the fainter planet detectable
shining an intense laser beam from Earth onto the star and surrounding
regions of sky in the hope of illuminating the neighbouring planet so
we can see it by reflected light
using radio receivers to observe the planet and eliminating any possible
radio signals from the bright star by tuning to a different frequency
Q14 Predictions about the future of artificial intelligence
depended on Moore's Law which states that...
computing power doubles every 2 weeks or so
computing power doubles every 2 years or so
exponential growth in the human population means exponential growth
in the number of computers
computers will be smarter than people when a panel of experts cannot
distinguish between the computer's answers and a human's answers to
Q15 The basic idea of the Gaia hypothesis is that...
a supreme being watches over life on Earth
the physical and biological components of the Earth are waging a constant
battle for supremacy
the physical and biological components of the Earth are part of a
single living entity
all the races of humanity are one species
Q16 The Weak Anthropic Principle says that...
the laws of physics we deduce by experiment must be compatible with
our own existence
the laws of physics we deduce by experiment need not be compatible
with anything whatsoever, including our own existence
the laws of physics deduced by experiment are invalid
people invented physics, therefore only people see physical laws in
Q17 If we receive a message from an extraterrestrial inhabiting
a planet orbiting one of the nearest stars, how long ago was the message
a few hours
a few days
a few years
a few millennia
Q18 If we succeed in detecting a signal from an extraterrestrial
civilization there is a protocol which says...
keep it secret
don't reply immediately, inform the press
inform only the military and large corporations
reply immediately to inform the aliens of our coordinates
Q19 Which of the following are regularly reported in the media
as being UFOs?
the planet Venus
all of the above
Q20 The opinion about the existence of extraterrestrials that
most closely represents the opinions of the organisers of this course is...
flying saucers with alien beings have landed on Earth but so far
scientists have been unable to find them
it is probable that alien beings will resemble human beings more
closely than they will resemble bizarre Hollywood creatures
there is much evidence that extraterrestrials visited Earth before
the evolution of humanity but it has been destroyed by plate tectonics
there is a good chance that some kind of alien life exists out there | <urn:uuid:7a9e56ea-9b69-4ba5-be0e-68d862ede046> | 3.15625 | 1,432 | Q&A Forum | Science & Tech. | 47.66488 |
My question is driven by the plot below. We see that acceptable operating range of a motor is between 50-100% of the rated load. Below 40% or so the efficiency of the motor drops off dramatically.
What is the cause of this phenomenon?
First, efficiency of an electric motor is just output power divided by input power. Input power is your electrical input power, which is V*I. Output power is your mechanical output power, which is speed*torque.
Given that, we can see that efficiency for every motor is going to be 0% at no load (i.e., maximum speed at 0 torque). Efficiency will then increase as torque increases until it reaches a maximum and then it will start to drop off until stall torque is reached. At this point, the efficiency is 0% again because the speed will be zero.
The other way to ask your question is why is efficiency low at low loads? Friction is the main cause of inefficiency at low loads. Losses due to friction are essentially constant with respect to load so at low loads, the majority of your input power may be used to overcome friction. As the load increases, friction plays a smaller and smaller roll in the overall efficiency. Granted, other inefficiencies begin to occur at larger loads ($I^2R$ losses, copper losses, stray load losses, etc.) but in a well-designed motor the efficiency will peak in the 80-100% load range. | <urn:uuid:d992cc07-cfe0-4cef-94bf-f0719f8d6f04> | 2.890625 | 299 | Q&A Forum | Science & Tech. | 62.148702 |
As the autumn leaves turn handsomely, I’ve been wondering, why do trees bother? It’s a question scientists have been asking for the past few years, and for the first time, they’ve carried out an experiment to find out.
The color of an autumn leaf can actually take a lot of work. In the fall, the green chlorophyll in a tree fades away, while the tree actively builds new pigments to turn it red or yellow. It’s generally agreed that these colors must serve some function for trees. Otherwise, natural selection would favor drab trees that dropped their leaves without such bother. They could use the energy they didn’t waste on autumn colors to fight diseases, capture more sunlight, or some other essential task.
In 2001, the late biologist William Hamilton made a provocative proposal: he argued that leaves turned colors in the fall to warn off insects. Healthy trees could produce anti-insect toxins and have energy to spare for building red and yellow pigments. The stronger the tree, the brighter the signal. As I described here, Hamilton and Sam Brown of the University of Texas found support for his hypothesis by comparing different species of trees. Species with bright leaves tend to be attacked by more species of aphids in the fall than species with drab leaves. This correlation was consistent the idea that the evolution of bright leaves was driven by feasting bugs.
But skeptics have argued that autumn colors actually serve a different function. They propose that the colors act as a sunscreen. An autumn leaf actually bustles with molecular preparations for the winter. Leaves pump their nutrients into a tree’s branches, where the tree can use them to survive till spring. But the cold, short days of fall play havoc with leaf chemistry. The sun’s UV rays cause more damage to the leaf tissue, as to harmful charged molecules released by photosynthesis. Some scientists argue that autumn pigments absorb these dangerous rays and molecules, allowing the leaf to do its autumnal business. (For more on the debate, see my blog post and the article I wrote for the New York Times.)
Scientists have continued to come up with new ideas about autumn leaves and to make new observations to test them. But no one has carried out a full-blown experiment. It’s easier said than done. Trees, after all, will not be rushed. Scientists must wait patiently for their leaves to turn in the fall. If they haven’t gathered enough observation by winter, they have to wait another year for another chance. It’s also difficult to reduce the glory of an autumn leaf to a precisely controlled variable, in order to measure the strength of its connection to the behavior of insects.
H. Martin Schaefer and Gregor Rolshausen, two scientists at the University of Frieburg, recently put autumn leaves to the test by painting trees. They found a stand of ash trees, and painted the leaves of some of the trees red and some green. If the colors served as a signal to the insects, the paint should make a difference.
Aphids did not alter their attacks on trees after they were painted. Nor did painted trees get attacked at a different rate as unpainted ones. In a paper published today in the journal Biology Letters, Schaefer and Rolshausen argue that their experiment doesn’t support Hamilton’s signal hypothesis.
Interestingly, the scientists found that the aphids did prefer to land on some trees over others. The most heavily attacked trees turned out to be the ones producing the most seeds. It’s possible that the trees that produce lots of seeds have to sacrifice some of their defenses against insects, making them good targets for aphids. The aphids would somehow have to detect the seed-heavy ash trees–either by seeing the seeds themselves or perhaps by smelling some compound given off by the trees. In either case, the aphids don’t care about the color of the leaves.
Schaefer and Rolshausen also tested the various theories for autumn leaves by comparing different populations of ash trees near Frieburg. The scientists found an association with cold weather and both bright colors and few aphids. Their findings, which are in a paper in press at Plant Ecology, may favor the sunscreen hypothesis over the signal hypothesis. But there’s a catch. Some of the trees grew on a mountainside at 1100 meters, and others grew at 360. If leaves need sunscreen to withstand harsh environments, the high-altitude trees might have been brighter. But they weren’t.
So for now, the fall foliage remains a mystery. The slow life of trees will mean we have a long time to wait for a resolution. At least we can enjoy the colors in the meantime.
Aphids do not attend to leaf colour as visual signal, but to the handicap of reproductive investment. H. Martin Schaefer and Gregor Rolshausen. Biology Letters, 2006. DOI:10.1098/rsbl.2006.0548
Do aphids paint the tree red (or yellow)–can herbivore resistance or photoprotection explain colourful leaves in autumn? Gregor Rolshausen H. Martin Schaefer. Plant Ecology in press. DOI: 10.1007/s11258-006-9215-3 | <urn:uuid:36c93807-1fc9-496d-804a-42b70f0b157b> | 3.890625 | 1,103 | Personal Blog | Science & Tech. | 60.361702 |
Academics at the Universities of Bristol, Yale and Calgary have shown that prehistoric birds had a much more primitive version of the wings we see today, with rigid layers of feathers acting as simple airfoils for gliding.
Close examination of the earliest theropod dinosaurs suggests that feathers were initially developed for insulation, arranged in multiple layers to preserve heat, before their shape evolved for display and camouflage.
As evolution changed the configuration of the feathers, their important role in the aerodynamics and mechanics of flight became more apparent. Natural selection over millions of years ultimately modified dinosaurs' forelimbs into highly-efficient, feathered wings that could rapidly change its span, shape and area – a key innovation that allowed dinosaurs to rule the skies.
This basic wing configuration has remained more or less the same for the past 130 million years, with bird wings having a layer of long, asymmetrical flight feathers with short covert feathers on top. They are able to separate and rotate these flight feathers to gain height, change direction and even hover.
This formation allows birds to move in such a way as to produce both lift and thrust simultaneously – a capability that man, with the help of technology, is still trying to successfully imitate.
The research, published today [21 November] in Current Biology, looked at the dinosaur Anchiornis huxleyi and the Jurassic bird Archaeopteryx lithographica. The latter is 155 million years old and widely considered to be the earliest known bird, presenting a combination of dinosaur and bird characteristics.
Their wings differed from modern day birds in being composed of multiple layers of long feathers, appearing to represent early experiments in the evolution of the wing. Although individual feathers were relatively weak due to slender feather shafts, the layering of these wing feathers is likely to have produced a strong airfoil.
The inability to separate feathers suggests that taking off and flying at low speeds may have been limited, meaning that wings were primarily used in high-speed gliding or flapping flight.
Dr Jakob Vinther, from the University of Bristol's Schools of Biological and Earth Sciences, said: "We are starting to get an intricate picture of how feathers and birds evolved from within the dinosaurs. We now seem to see that feathers evolved initially for insulation. Later in evolution, more complex vaned or pinnate feathers evolved for display.
I was under the impression that feathers were for display first and then insulation was the side benefit. Well, this will be one of those fights that's not resolved for years at best. I am hoping its not theory advancement by attrition. | <urn:uuid:39e55209-472b-459e-aadb-ff17a8b1f023> | 4.4375 | 527 | Personal Blog | Science & Tech. | 30.803764 |
Featured Scientist: David G. McGrath, Ph.D. Associate Scientist
Project: Human ecology and management of the Amazon floodplain
The Amazon varzea, the core area of the Amazon floodplain, is one of the largest and most biodiverse tropical wetland systems in the world. Its fertile soils and abundant plant and animal resources supported some of the densest and most politically complex societies in the Amazon basin. Varzea resources have continued to play a central role in the regional economy. In recent decades the rise of commercial fishing, logging and extensive cattle ranching have modified varzea habitat and depleted key resources, leading to conflicts over access to and use of floodplain lakes, forests and grasslands. WHRC scientists are working with floodplain communities, grassroots organizations, key government agencies and other stakeholder groups, to develop a multi-scale comanagement system for reconciling conflicts and sustainably managing varzea resources. The overall objective is to develop the policies, and technical and organizational capacity needed for the co-management of floodplain fisheries and other natural resources and so conserve the ecological integrity and services that major tropoical wetlands like the Amazon provide.
Video: Produced by Research Associate Kathleen Savage.
Image: Igarapé de Costa in Santarém, State of Pará, Brazil. Courtesy of David G. McGrath. Composite design by Development Solutions of New England (DSNE). | <urn:uuid:e114fb30-3aae-4d7a-a28a-70f21b8499d0> | 3.484375 | 290 | Truncated | Science & Tech. | 20.016667 |
¨ is injective if and only if different inputs give different outputs.
¨ is injective if and only if “different elements of A go to different elements of B.”
¨ It is the whole function that is or is not injective.
¨ The articles about most of the example functions state whether they are injective or not. Checking each of these functions to see why it is or is not injective is an excellent way to get a feel for the concept of injectivity.
¨ The doubling function is injective on the real numbers and in fact on the complex numbers. Doubling different numbers gives different numbers.
¨ The squaring function is not injective, because for example . Squaring different numbers might give you the same number.
¨ The cubing function on the reals is injective. It is not injective on the complex numbers, because for example
¨ See Wikipedia for more examples and more discussion.
No information loss
An injective function loses no information. If you have an output from the function, you know it came from exactly one input.
¨ If you got 8 when you cubed a real number, the real number had to be 2. The cubing function is injective on the reals. But if you got 8 when you cubed a complex number, the complex number could be any of three numbers (see above); the cubing function is not injective on the complex numbers.
¨ If you got 4 when you squared something, the something could have been either 2 or 2: You lost some information about the input, namely its sign in this case. The squaring function is not injective.
¨ If you get as an output from the sine blur function, it could have come from any one of an infinite number of inputs. The sin blur function is ridiculously noninjective.
Embeds as a substructure
Some functions preserve some structure. For example, multiplying integers by 2 preserves addition. In other words, if you let be defined by , then (write it out, don’t just believe me!). This makes it a group homomorphism. Because multiplying by 2 is injective, this says that the substructure of the group of integers with addition as operation that consists of the even integers is a copy of the group of integers itself.
Horizontal line crosses the graph only once at most
Let be a real continuous function. Then F is injective if no horizontal line cuts it twice. This is a useful way of thinking about injective continuous functions, but it doesn’t work with arbitrary functions.
a) This is a plot of part of (which is injective) with some horizontal lines
b) On the other hand, is not injective. Note that some horizontal lines cut it more than once, but others cut it only once.
c) Horizontal lines don’t have to cut a function at all. This is part of . Horizontal lines below zero don’t cut its graph because 0 is its minimum. There are horizontal lines that cut it twice, so it is not injective.
A function is surjective if and only if
¨ is surjective if and only if the image of F is the same as the codomain B.
¨ is surjective if and only if “every element of B comes from an element of A.”
¨ Let be the squaring function, so for every real number x. Then F is not surjective, since for any negative number b, there is no real number a such that F(a) = b. (You can’t solve , for example).
¨ But if you define (where denotes the set of nonnegative reals) by , then G is surjective. As you can see, whether a function is surjective or not depends on the codomain you specify for it. Note that “G is surjective” says exactly that every nonnegative real number has a square root.
Another way of saying that is surjective is to say, “F is surjective onto B”, or simply, “F is onto B”. Saying it this way does not depend on whether you use the loose or strict definition for functions.
A function is surjective if every horizontal line crosses its graph (one or more times). Check out the graphs (a) through (c) above: and are surjective onto , but is not surjective onto . H is surjective onto the set of nonnegative real numbers. | <urn:uuid:0945305e-e17b-4cbc-a1e8-190848e4baef> | 3.6875 | 955 | Knowledge Article | Science & Tech. | 56.154743 |
|Auroras can make spectacular sights.
Photographed above last weekend, flowing multi-colored auroras helped
illuminate a busy sky above
spectacular aurora pictured above,
the photographer caught three satellites streaks, one airplane streak, and a
friend trying to
the same sight.
Although auroras might first appear to be moonlit clouds,
they only add light to the sky and do not
block background stars from view.
Called northern lights in the northern hemisphere,
auroras are caused by
charged particles from the
and air molecules high in the Earth's atmosphere.
If viewed from space, auroras can be
seen to glow in
X-ray and ultraviolet light as well.
might occur a few days after a
powerful magnetic event
has been seen on the Sun.
Credit & Copyright:
Ole Christian Salomonsen | <urn:uuid:96be8006-55fa-40d2-9626-aaf880566f45> | 3.34375 | 183 | Knowledge Article | Science & Tech. | 40.131936 |
Bryde's whale, tropical whale
Little is known about Bryde's whales and they are often confused with sei whales.
Possibly two (offshore and inshore), and maybe a third, dwarf subspecies around the Solomon Islands.
Up to 72 years.
Body length: 11.5-14.5m, Weight: 12-20 tonnes.
Bryde's whales are very similar to sei whales, but they have three longitudinal ridges on their head. The skin may be mottled and they are dark above with a light greyish underside. They have a deeply curved dorsal fin.
Bryde's whales live in all oceans, in the tropics and sub-tropics.
They feed on fish and krill.
This species lives singly or in pairs, but congregate loosely to feed.
The 2000 IUCN Red List class Bryde's whales as Data Deficient. They are thought to be locally common with a population of approximately 90,000. | <urn:uuid:4c457cf7-6448-4213-9796-10e37353a09b> | 3.140625 | 211 | Knowledge Article | Science & Tech. | 71.667808 |
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Once you are finished and click submit, your modifications will be sent to our editors for review.
...diameter antenna near Effelsberg, Ger.; the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) 64-metre (210-foot) dish near Parkes; and the 76-metre (250-foot) Lovell Telescope at Jodrell Bank in England. These filled-aperture radio telescopes are used for atomic and molecular spectroscopy over a wide range of frequency and for other galactic and...
Jodrell Bank Observatory
location of one of the world’s largest fully steerable radio telescopes, which has a reflector that measures 76 metres (250 feet) in diameter. The telescope is located with other smaller radio telescopes at Jodrellbank (formerly Jodrell Bank), about 32 kilometres (20 miles) south of Manchester in the county of Cheshire, Eng. Immediately after World War II the British astronomer Alfred Charles...
What made you want to look up "Lovell Telescope"? Please share what surprised you most... | <urn:uuid:644fb2fb-944f-40a0-b7c3-63b1e8f222dc> | 3.203125 | 234 | Truncated | Science & Tech. | 43.767406 |
Global warming news and climate change headlines for March 2008
March 31 - Australia's love affair with cars cranks emissions
The Australian state of Victoria has experienced an overall carbon
emission increase of 12.6% since 1990 with transport associated
emissions being the major contributor, skyrocketing by 26.5% over the
last 20 years. Road transport is the biggest offender, contributing
14.8% of the state's total emissions. Read
March 30 - Global warming already affecting islanders
The Sundarbans are where the Ganges and the Brahmaputra rivers meet. For
many villagers living on islands in this area, the effects of global
warming are very real and they battle for survival. Melting Himalayan
glaciers are raising river and sea levels - rebuilding crude dams
and dikes to try and prevent inundation is a daily task. Read
March 29 - Earth Hour initiative- 8PM - 9PM on March 29
Earth Hour, organized by conservation group WWF is a global climate change initiative which rallies individuals and businesses around the world to turn off their lights for one hour on Saturday March 29 2008 between 8 pm and 9pm. The aim of the campaign is to express that individual action on a mass scale can help change our planet for the better and to get people thinking more about ways of maximizing energy efficiency.
March 28 - Warmer recent winters for Britain and Canada
A study released by the British Meteorological Office has stated that the coldest winter days in Russia and Canada are as much as four degrees Celsius milder since the 1950s.
In Britain, warming was between 0.5 and 2.0 Celsius. Read
March 27 - Major ice shelf in Antarctica collapsing
The Wilkins ice shelf, a 13,000 square kilometre body of floating ice
recently lost 415 square kilometres and a large part of the ice shelf is
now supported by only a thin area of ice. Ted Scambos, a scientist at
the National Snow and Ice Data Centre says the phenomenon has been rare
up until recent times and is due to warm air and wave action. Read
March 25 - Climate change threatens Aussie animals
In Australia, climate change is not only threatening the viability of
some of its unique animal species, but also encouraging the
proliferation of non-native species. The cane toad that has ravaged
parts of the state of Queensland is steadily spreading across the
country and conditions are also benefiting the European fox. Read
March 24 - Power needs accelerating faster than predicted
The activity of developing nations including Africa, Asia and South America has accelerated global warming past official predictions. While the International Energy Authority states yearly growth in the planet's power consumption will be 3.3 per cent until 2015 an Aggreko study commissioned from Oxford Economics states 5 per cent annual growth.
March 23 - Lovelock predicts global disaster
James Lovelock, creator of the Gaia hypothesis which sees all the components
of our planet as a complex interacting system that can be thought of as a single organism, believes that it too late to save the planet from global warming. Lovelock predicts that by 2040, parts of the Sahara desert will have moved into middle Europe, and China will become uninhabitable. Southern Europeans and South-East Asian, will be scrambling into countries such as Canada, Australia and Britain and subsequent ethnic tensions could lead to civil war.
March 22 - US power station emissions increase
The Environmental Integrity Project has released their findings after studying data from the US Environmental Protection Agency from more than 1,000 power plants using coal, oil and natural gas for electricity generation. Their study shows that carbon dioxide emissions grew by nearly three per cent last year, the biggest annual increase in nearly a decade.
March 21 - Forget oil, invest in water
According to the UN, around 20% of humanity lacks access to safe drinking water; while 44 percent of the world's population live in areas affected by high water stress - a figure expected to increase to 47 percent by 2030. Global warming related issues and population increases are beginning to see huge investment in water and waste projects around the world.
March 19 - Adelaide heatwave one in 3,000 years event
Adelaide residents (including me) are breathing a sigh of relief after a
record heatwave finally subsided yesterday. The city experienced
temperatures exceeding 35 degrees Celsius for 15 days in a row, smashing
the capital city record set by Perth in 1988 and ending with
temperatures reaching 40.5 degrees. A climate model created by
atmospheric scientist Dr Warwick Grace indicates that a heatwave of such
intensity is only likely to happen once in 3,000 years. Read
March 17 - Glaciers melting at record rate
Experts been monitoring 30 glaciers around the planet for close to 30 years have found that glaciers are melting faster than at any time since records began. The findings have added to growing concerns about sea levels rising faster than previously predicted.
March 14 - Deforestation emissions increasing
According to the World Wildlife Fund, the current ratio of greenhouse gas contribution is
80/20, the larger figure being energy production and the smaller, deforestation.
The WWF has warned that split may change if deforestation continues. The countries
generating the largest amount of emissions through deforestation are Indonesia with 35 percent, Brazil with 19 percent and Malaysia with 10 percent.
March 13 - Rapid growth in China's CO2 emissions forecast
Previous estimates predicted China's CO2 emission to increase by 2.5 to 5 percent annually between 2004 and 2010, but new research from University of California, Berkeley, and UC San Diego believes the annual growth rate will be at least 11 percent for the same time period - representing an amount greater than the total current emissions produced by Great Britain.
March 12 - Adelaide, Australia breaks temperature records
Adelaide, the capital city of South Australia experienced its 9th
consecutive day of temperatures over 35C (95F) with high temperatures
expected to persist for at least another 6 days. The heatwave has been
particularly unusual given the southern hemisphere is now in Autumn. The
Australian Bureau of Meteorology is confident that the heatwave is
connected to a general warming of the atmosphere. Read
March 11 - Britain goes back to black - coal power
The UK government has sent environmentalists into a spin after showing support for the construction of new so-called clean coal power stations. An aging coal fired plant is to be replaced with two new units using cleaner coal technologies and utilizing controversial carbon sequestration. A further seven coal fired plants are also in the pipeline.
March 10 - Wind power statistics
According to the Earth Policy Institute, wind power capacity will exceed
100,000 megawatts globally this month and 2008 will be the first year
that wind power additions in Europe will have exceeded the additions of
any other power source, including natural gas. The cost wind power has
decreased by more than 80 percent over the last 25 years to
approximately 7 cents per kilowatt-hour at suitable sites. Read
March 9 - European leaders warned of mass migration
European leaders are being warned that due to their closeness to
countries particularly vulnerable to the effects of climate change,
pressure from migration and regional political instability could
increase in the future. In the Middle East, water is becoming
increasingly scarce and major reductions in crop yields are forecast.
Climate change could also have a dramatic impact in South Asia, with
serious consequences. Read
March 8 - Oceanic deserts expanding due to warming
The regions of the ocean where little to no plant life is found have expanded dramatically over the past decade. According to recent research, these biological deserts are growing at roughly 1 to 4 percent annually - an area around the size of Texas every year. Scientist have found that these barren areas are expanding due to
increasing water temperatures. Read
March 7 - OECD warns of 38% global emissions increase
The OECD has warned the global economy could double in size by 2030, largely due to growth in countries including Russia, China and India. Without proper controls, this could create a 38 percent increase in carbon dioxide emissions by 2050. The OECD is urging for carbon taxes to be established for most countries as soon as possible in order to motivate shifts to renewable energy, and low impact design and construction.
March 6 - Reduction in coral growth points to acidic oceans
A study of a section of Australia's Great Barrier Reef has found an
unprecedented 21 per cent decline in the growth rate of finger corals.
This is believed to be a warning sign of ocean acidification - where
massive amounts of carbon dioxide from the atmosphere have dissolved into the ocean, causing it to become more acidic.
March 4 - China's killer dust storms on the move
Schools in Korea have been closed due to a veil of sand and toxic dust from China covering much of the country and other parts of Asia. The yearly yellow dust storms, originating in China's Gobi Desert have been increasing in frequency and toxicity over the years because of China's rapid economic growth . The storms kill scores of people each year and cause billions of dollars in damage.
March 2 - EPA's final ruling rejects Cali. emission standards
The USA Environmental Protection Agency's has rejected California's request to regulate greenhouse gas emissions from vehicles, marking the first time that the EPA denied states the ability to enforce more stringent vehicle emissions standards. The EPA's justification is the Clean Air Act only allows for emission standards for vehicles to address local or regional pollution problems, rather than global ones such as climate change.
March 1 - Finland: warmest winter on record
With average temperatures approximately 5 degrees Celsius (9 Fahrenheit) higher than usual, the warmest winter on record in Finland may increase crop yields due to an extended growing season. Parts of Finland had snow cover for only 20 days, which is over 50 less days than during a usual winter.
March 1 - An ice free Arctic this year?
According to Dr. Olav Orheim, from the Norwegian International Polar Year Secretariat, if Norway's average temperature this summer reaches the same level as 2007,the ice cap in the Arctic will be non-existent. Dr. Orheim and his associates are deeply concerned that the new shipping channels such an event will open up could see irreversible impact on ecological security in the Arctic region.
March 1 - A warmer Arctic could become a battleground
Former U.S. Coast Guard Lt.-Cmdr. Scott Borgerson believes a Canada-U.S. agreement must be formulated on how the Arctic should be handled as global warming opens northern sea lanes and the Arctic's huge economic potential. Territorial disputes could pose threat of "armed brinkmanship". With an ice-free Arctic in the summer being predicted to occur as early as
this year; the complexities of carving up the Arctic among five states with competing claims is sure to become an increasingly pressing diplomatic and political issue very soon.
March 1 - Australia to buy back water from farmers.
The Australian government will be spending $50 million this year to buy back
irrigator water entitlements in order to rescue the Murray-Darling Basin's rivers and wetlands
after 11 consecutive years of dry conditions and six consecutive years
of record low inflow on the Murray River. The Murray-Darling is one of
Australia's longest river systems and is a critical water source for
farming and drinking water for many towns and cities. Read | <urn:uuid:298bd6c7-3314-4b9c-acf7-aa2f30ab4334> | 2.765625 | 2,342 | Content Listing | Science & Tech. | 39.431632 |
I’ve put off writing about Wesley Traub’s paper on the frequency of planets in the habitable zone because I knew Adam Crowl had reservations about Traub’s method. We talked about this at the 100 Year Starship Symposium, which led to Adam’s agreeing to writing this piece for Centauri Dreams. How you define a habitable zone is, of course, a critical matter, especially when you’re dealing with a topic as compelling as extrasolar planets that can support life. Adam places Traub’s work in the context of earlier attempts at defining the habitable zone and finds HZ estimates different from Traub’s, though one is surprisingly similar to a much earlier study.
by Adam Crowl
The recent paper by Wesley Traub [reference below] has estimated the frequency of terrestrial (“Earth-like”) planets in the Habitable Zone (HZ) of their stars based on statistical analysis of the recent Kepler data release, but the frequency computed, of ~34(+/-14)% around FGK stars, is dubious due to the assumption of wide HZ limits. Before I discuss the specifics, let’s look at the modern history of the “Habitable Zone”.
The modern discussion really began with Stephen Dole’s “Habitable Planets for Man”, a RAND commissioned study from the early 1960s, eventually updated in 1970, and popularized with Isaac Asimov. Dole based his HZ limits on the criterion that a significant fraction of a terrestrial planet would experience a “hospitable climate”. He didn’t examine the effect of atmosphere, and derived the HZ limits of 0.725 – 1.25 AU, from just outside the orbit of Venus and a bit closer to the Sun than Mars at its closest. Applying statistical analysis to various features of the known planets, then extrapolating to other stars, Dole found that potentially 645 million Earth-like planets might exist in the Galaxy.
In the mid 1970s Michael Hart developed the first evolutionary models of the atmosphere of an Earth-like planet, finding Earth to be poised on a virtual knife-edge, tipping towards a Runaway Greenhouse if closer than 0.95 AU and Runaway Glaciation if further out from the Sun than 1.01 AU. When this criterion was applied to other stars, the frequency of Earth-like planets was less than 1 in a quarter million stars, or less than 400,000 Earths in a Galaxy of 100 billion stars.
Hart’s limits seemed overly sensitive to climate perturbations, and further work on the evolution of Earth’s atmosphere in the 1980s led to the paper “Habitable Zones Around Main Sequence Stars”, (Kasting, Whitmire & Reynolds, 1993) , which redefined the debate. What James Kasting and colleagues discovered was a powerful feedback loop between the levels of carbon dioxide in the atmosphere, geological weathering and the heat input from the Sun.
This creates a self-regulated surface temperature which can keep water in its liquid range out to a significant distance from the Sun. The chief uncertainty came from the complication of dry-ice clouds. Past 1.37 AU clouds of dry-ice begin forming and by 1.67 AU the cloud cover becomes total, negating the effectiveness of the carbon dioxide greenhouse effect. Some preliminary work on water clouds also suggests the inner radius of the habitable zone, just 0.95 AU, might be extended to closer to Venus.
Traub’s paper has somewhat more generous HZ limits. Traub examined three cases, with the ranges from 0.72-2.0 AU in the best case, a nominal HZ of 0.8-1.8 AU, and a “conservative” 0.95-1.67 AU. Using the observed planetary radii distribution and the orbital radii, Traub was able to compute the frequency of terrestrial planets in these HZ as 34(+/-14)%, with the extremes providing the error bar limits.
Here’s where just what is computed and why is important. The ranges used by Traub for the HZ apply to specifically liquid water compatible planets with extensive greenhouse gas atmospheres. Such worlds, with up to several bars of carbon dioxide for atmosphere, are only distantly “Earth-like”, much like Mars or Venus can be called Earth-like. The Earth we know, with an oxygen rich, carbon dioxide poor, atmosphere is somewhat more sensitive to climatic instability. If more conservative HZ ranges are used a quite different result is obtained.
The HZ, inside of the CO2 cloud limit found by Kasting, et.al., is the more restrictive 0.95-1.37 AU. This gives a frequency of just 13.3%. If we use the Continuously Habitable Zone (0.95-1.15 AU), also from Kasting, et.al., then the frequency drops to a mere 6.3%. Using Hart’s even more restricted range drops the frequency to less than 2%. Another caveat is that the planet frequency estimated is limited to stars in the mass-range 1.13-1.01 solar masses and is yet to be extended into the wider population of stars which make up ~80% of the Galaxy.
The HZ limits derived by Kasting et.al. assumed ocean-dominated terrestrial planets. The broader range of land dominated “desert planets” (Abe et.al., 2011), with water bodies limited to circum-polar lakes/ice-caps, increases the HZ range to 0.75-1.3 AU, and a corresponding frequency of 17.3%. Incidentally this range is equivalent to that derived by Dole’s (1964) ground-breaking study.
So, in conclusion, the high frequency of “Earth-like” planets derived by Traub, is tempered somewhat when a more precise Earth-like Habitable Zone range is used. Planets warm enough for liquid water thanks to multi-bar atmospheres of carbon dioxide, methane or hydrogen, while probably conducive to extremophiles, aren’t “Earth-like” as usually understood, and this caveat should be more widely appreciated when making such estimates.
The paper is Traub, “Terrestrial, Habitable-Zone Exoplanet Frequency from Kepler,” available online as a preprint. Other references:
Y.Abe, A.Abe-Ouchi, N.H.Sleep, and K.J.Zahnle. “Habitable Zone Limits for Dry Planets”, Astrobiology, Volume 11, Issue 5, pp. 443-460 (2011).
S.H. Dole, Habitable Planets for Man, Blaisdell, New York (1964).
M.H. Hart, “Habitable zones about main sequence stars”, Icarus, 37: 351-357 (1978).
J.F. Kasting, D.P. Whitmire and R.T. Reynolds. “Habitable Zones Around Main Sequence Stars” Icarus 101: 108-128 (1993). | <urn:uuid:45670bf4-28f3-406c-8aa2-6346ad57eae2> | 3.1875 | 1,509 | Nonfiction Writing | Science & Tech. | 60.382629 |
This topic deserves special attention because many people from database designers to application developers (sometimes one person does both) do not get it right. A Many-to-Many relationship occurs when each instance from the entity on the left can have many instances from the entity on the right, and vice versa.
Some examples of many-to-many relationships are as follows:
- Each order can contain many items. Each item can also belong to many orders as it can be purchased by different customers.
- Each student can be signed up for many coursers. Each course can be assigned to multiple students.
Incorrect implementation of many-to-many relationships
We see this problem when people are trying to use foreign keys to solve this problem. Let’s illustrate it with the second example listed above as follows:
What we are trying to say here is that each student can take many courses and that each course can be taken by many students. So to implement this we have put a FK to the student table which will point to the course table.
Do you see any problems with this?
- Yes!!! we will have repeated student rows for each different course a student is taking.
- At the moment you do this your database would no longer be in 3NF because we would have repeated groups.
- This issue above can potentially yield to update anomalies.
- This relationship is said to be unresolved.
Correct implementation of many-to-many relationships
In order to correct the many-to-many implementation above we have to resolve relationship. This is done as follows:
- By adding another table between the two entities; this table is called associative entity or intersection table.
- By making the PK of the associative entity a composite key that consist of each of the parent’s PK (We are using Identifying relationship).
- By naming the intersection table as follows (not required by DBMS, but suggested): ENTITYA_ENTITYB. In our case STUDENT_COURSE or STUDENT_COURSE_REL.
- By Changing the cardinality of the parent tables to be One-to-Many to the associative entity.
Let’s see it in action:
What improvements do you see?
- The student is defined once so we avoid duplicate data.
- The courses are defined once and we avoid the same problem as if we would have put the FK in the course table in scenario #1.
- We do not run the risk of update anomalies.
- We can add meaningful fields in the associative entity. Those are called the Fixed Intersection data.
Alert: The FID will become your FACT tables and the parent entities would become your DIMENSION tables in OLAP database structures. Dimensional modeling is a different modeling technique which uses a lot of denormalization so that you can yield better query performance as data is only 1 join away at most. | <urn:uuid:037f6064-e2a0-4c11-be75-7b0f33977b67> | 3.125 | 607 | Personal Blog | Software Dev. | 44.36562 |
When it comes to full-text indexing, we usually think of methods such as inverted indices that break text on word boundaries, consequently requiring search terms to be whole words only. Yet all of us probably have had the experience of searching for not-quite-words C++, VM/CMS, SQL*Plus, 127.0.0.1, <blink>, and the like that were skipped by an inverted index, or broken into less-distinctive pieces. The same goes when you are working with data such as DNA sequences, where you need to quickly find any sequence of symbols.
In this article, I examine an indexing method that lets you find any character sequence in the source text in time only proportional to the sequence length using a structure that can compress the entire source text and index into less space than the text alone. This technique is exceptionally fast at detecting and counting occurrences of any string in the source text. The fact that you can build a string match incrementallyadding one character at a time and seeing the result at each stepgives you the flexibility to explore variable patterns such as regular expressions with maximum effectiveness.
Finding any character sequence in source textand fast!
In Fast String Searching with Suffix Trees (DDJ, August 1996), Mark Nelson addressed full-text indexing using suffix trees; while in Data Compression with the Burrows-Wheeler Transform (DDJ, September 1996), he focused on the use of the Burrows-Wheeler Transform (BWT) for compression. While the BWT is commonly known as a data-compression technique, researchers have found that block-sorted data has a structure that lends itself naturally to search, while using space close to its minimal compressed size. This was first demonstrated in the FM index (see Opportunistic Data Structures with Applications, by Paolo Ferragina and Giovanni Manzini, Proceedings of the 41st IEEE Symposium on Foundations of Computer Science, 2000). In short, the same transformation that yields high-compression ratios, by grouping similar substrings together, also lets you find arbitrary substrings with little overhead.
Block Sorting Reviewed
When block sorting, you construct a list of n blocks consisting of the source text S (usually followed by a special End-of-String character $) of length n, cyclically shifted from zero to n-1 positions. When you sort the blocks, you get a matrix M; see Figure 1(a). The first column of M is called F, and the last, L. F has a simple structure, containing all the characters of S in sorted order, with duplicates. Column L has a more complex structure that contains enough information to reconstruct the original string, and usually forms the basis for BWT compression.
Figure 1(a): Block-sorted text. Start with the source string "abracadabra." Append an end-of-file metacharacter $, with the property that $<a-z. Cyclically shift the string from 0 to n-1 places, and sort the resulting list. Each row is called a "block," containing original text left-shifted 0 to n-1 places. M is the 12×12 block-sorted matrix for string "abracadabra$," F is the first column of the matrix, L is the last column.
In its naive form, M contains n2 characters, but a simple trick represents each block by its first character and a link to the block starting one character to the right; Figures 1(b) and 1(c). To decode a block, you read its first character, follow its link to the next block, read its character and link, and repeat the process until the desired number of characters have been read. This character-and-link representation slashes spatial complexity from O(n2) to O(n).
Figure 1(b): Replacing abracadra$ with "a" and a pointer to bracadabra$a.
Figure 1(c): Twelve blocks replaced with F column and 12 pointers to suffixes.
The links act as a permutation on M, which I call FL because it permutes the orderly F column to the higher entropy L column. FL is the permutation caused by shifting M one column to the left and resorting it; each row i moves to a new position FL[i].
Since the F column is a sorted list of characters, the next space saver is to change from explicitly storing the F column, to simply recording the starting position for each character's range in F, using an array that I call "C"; Figure 1(c). At a given position i in M, you look through C to find the section c of F that contains i. The F() method in bwtindex.cc applies this idea. Also see Figure 1(d).
Figure 1(d): Discard F column and use C to identify characters.
By storing only FL and C, you have a reasonablebut not minimalrepresentation of M, and you can decode successive characters of the source from left to right. The decode method in bwtindex.cc shows how to carry out this iteration. See Figure 1(e).
Figure 1(e): Decoding from any position. Chase pointers and translate each position to char using C. The decode method shows this technique in bwtindex.cc.
Useful Properties of the Permutation
Figure 2 shows how FL is order preserving on blocks that start with the same character. That is, given two blocks i and j that both start with c, lexical comparison implies that if i<j, then FL[i]<FL[j]. This is one of the core elements of the BWT.
Figure 2: This map is called FL because it rearranges the F column into the L column. FL is order-preserving for strings that start with the same character, so each character's section in FL contains an ascending list of integers. Here, you see the "fan-out" for blocks prefixed by "a."
This order-preserving property means that FL consists of sections of integers in ascending order, one section for each character. You can search one of these sections for a target value quickly, using binary search. | <urn:uuid:1c238001-944c-4fd7-8665-f7c369fc648f> | 2.9375 | 1,300 | Academic Writing | Software Dev. | 61.033227 |
Ancient Ecosystem Discovered Beneath Antarctic Glacier
Scientists have found life in an ecosystem trapped underneath a glacier in Antarctica for nearly 2 million years. The microbes, they suggest, are surviving the dark, oxygen-free waters by drawing energy from sulfur and iron. The findings provide insight into how life may have survived "Snowball Earth"--periods when some scientists speculate that the planet was entombed in ice--and hint at the possibility of life in other inhospitable environments, such as Mars and Jupiter's icy moon Europa.
Researchers have found microbial life surviving in the most unusual places: the depths of cold and dark oceans, seething geothermal vents, and the deepest layers of permafrost. And ever since scientists discovered Antarctica's dark and mysterious subglacial lakes in the late 1960s and early 1970s, they've wondered if microbes could make a life for themselves there too. But the challenges of drilling through kilometers of ice and concerns about contaminating these pristine lakes have curtailed previous efforts to find out.
Blood Falls, a small, saltwater outflow from Taylor Glacier's subglacial lake in Antarctica's Dry Valleys, offers an alternative. The lake sits beneath 400 meters of ice and trickles out at the glacier's end, painting an orange stain across the ice as its iron-rich waters rust upon contact with air. The subglacial lake was originally part of a marine fjord system that became trapped as Taylor Glacier enclosed it between 1.5 million and 2 million years ago. Its sporadic outflow allows researchers to explore the lake without drilling or risking contamination of the isolated environment. | <urn:uuid:26e6eff9-5a4e-4c12-8618-d87c95516771> | 3.96875 | 330 | Truncated | Science & Tech. | 32.326272 |
The new Pythagoras
One of mathematics' best known theorems is that which is attributed to Pythagoras.
Pythagoras, however, had a rival, named Pyfudgerous.
He too had a theorem for working out the hypotenuse of
a right-angled triangle from the length of the other two sides.
I am confident that readers will have no difficulty, whatsoever, in working out the hypotenuse of a right-angled triangle, if given measurements of the other two sides. To prove the point, let us say that one of the shorter sides in such a triangle is of length 9 cm and that the other is of length 40 cm. What is the length of the hypotenuse ?
Figure 1 contains the theorem that you probably used, namely:
Figure 1 also features a second theorem that I suspect is new to you. It too is a theorem for working out the length of the hypotenuse of a right-angled triangle from the lengths of the other two sides.
This pythagorean alternative I have named Pyfudgerous because I do not want you to trust it !
Try substituting in A = 9 cm and B = 40 cm to check that it gives H = 41 cm as Pythagoras' theorem just did. In fact, it does give the anticipated answer, but perhaps I have rigged it that way. ( I just might ! ) So try putting in some other Pythagorean integer triples such as 3:4:5 or 5:12:13 or 8:15:17 or 7:24:25. Integer triples are particularly useful here because we want to know it it is working exactly.
A quick spree of button pressing should reveal that the theorem of Pyfudgerous seems to be delivering the goods. In fact, it will always work, as can easily be proved by expanding the brackets and cancelling:
The truth is that the theorem of Pyfudgerous is simply the theorem of Pythagoras in an altered form. This is a sad moment. Something new and intriguing has turned out to be something old in a repackaged form.
The repackaging idea
This repackaging idea is not new. How one chooses to write a quadratic equation depends upon what aspect is to be emphasised. For example, I might rewrite the equation of the curve
in factorised form as
if it is the x-axis crossing points that are of interest or in the completed square form as
when it is the minimum point that is under consideration. Similarly, although the theorem of Pyfudgerous is not a piece of fundamentally new mathematics, it may still be of some significance.
Here is a problem for which Pyfudgerous, rather than Pythagoras, is tailor-made.
What is the length of the hypotenuse of a right-angled triangle in which the difference between the two shorter sides is 97 and the product of the two shorter sides is 1680 ?
( I hope that you are busily working out a solution at this point, before reading on ! )
The Pyfudgerean solution is effortless, for the question, in effect, states that (B - A) = 97 and AB = 1680. So, double the 1680 and add on a squared 97. Now square root and up pops the answer: H = 113. Try out this problem on a friend. I have had many a happy moment watching two simultaneous equations awkwardly being solved from which it transpires that A = 15 and B = 112 and then, via Pythagoras, being informed that H = 113.
In fact, if it is required to find A and B, there is a further clever hop in the spirit of Pyfudgerous using the fact that
to quickly find (B + A) = 127, which can be very easily solved simultaneously with (B - A) = 97 to give the correct solutions.
Figure 2 is an illustration of how the theorem of Pythagoras might have been spotted by looking hard at a tiled floor.
The grey square formed upon the hypotenuse of the black triangle contains the same number of tiles (i.e has the same area as) the two grey squares formed upon the other sides of the black triangle.
Figure 3 is a picture from which it is clear that the total area, (B + A)², is made up from four rectangles of dimension A by B plus a square of side (B - A). This is the previously used Pyfudgerean hop
Likewise, Figure 4 is a visual representation of the theorem of Pyfudgerous.
The large square of side H is of the same area, H², as the four triangles, ½AB each, plus the small square, (B - A)².
One of the interesting features of Figure 4 is the fact that it is a square expressed in terms of a ring of four triangles plus a smaller square. There must be some reduction factor, r, that will shrink Figure 4 into its own central square.
Figure 5 shows one such shrinkage and Figure 6 shows an infinity of such stepped shrinkages.
This is a fascinating picture. It spirals inwards and indefinite zooming in upon the centre reveals an unending, repeating structure. I am going to call Figure 6 the fractile of Pyfudgerous. ( A fractile is a fractal that tiles the plane )
The mathematical principle behind this process is outlined in Box 1.
Notice that it could be applied to any ringed square such as Figure 3, for example. In fact, it can be applied to any ringed shape, as illustrated by Figures 7 and 8. Box 1 reveals that all such diagrams represent the sum to infinity of a geometric progression, a topic tackled early on in all A-level mathematics courses.
Mathematics Review, November 1993, Volume 4, Number 2.
© Philip Allan Publishers Limited. ISSN 0957-1280
The following Figure was submitted with the article but not published.
Bonus Figure not used by the publisher
All images, text and file downloads © 2004 - 2012, The MathMagical Software Company. | <urn:uuid:d549566b-e6e9-4008-8719-66f3335e174c> | 3 | 1,286 | Personal Blog | Science & Tech. | 58.510991 |
Chiricahua National Monument AQRV's
Most surface waters in Chiricahua NM are likely to be well-buffered and, as a result, insensitive to acidic atmospheric deposition because of an abundance of base cations in underlying park soils and rocks. However, studies currently underway have identified certain soils in the park that appear to be very sensitive to acidification; small potholes or other waterbodies on these soils may also be vulnerable to acidification. Small potholes may also be sensitive to nutrient enrichment from nitrogen deposition. Nitrogen enrichment may result in algae blooms and oxygen depletion, but no studies have been done to study these potential effects in the park.
While there have been no systematic studies, there is currently no information indicating that wildlife in Chiricahua NP are being affected by air pollutants.
Dark night skies are considered an important air quality related value at Chiricahua NM, possessing value as a cultural, scenic, natural, and scientific resource. Air pollution and poor quality outdoor lighting degrade night skies, lessening a viewer's ability to see stars and other astronomical objects, and altering the nocturnal scene. Use of high quality lighting that produces very little scattered light can greatly improve the night sky. Reduction of haze from air pollution can also improve the night sky.
Soils in Chiricahua NM may be sensitive to atmospheric deposition of nitrogen compounds. In some areas of the country, elevated nitrogen deposition has been shown to alter soil nutrient cycling.
Several species of vegetation in Chiricahua NM are known to be sensitive to ozone, including Pinus ponderosa (ponderosa pine) and Rhus trilobata (skunkbush). Ozone concentrations and cumulative ozone doses are high enough to induce foliar injury to sensitive vegetation under certain conditions.
- Ozone Sensitive Plant Species Listed by Park
- Ozone Sensitive Plant Species on NPS and U.S. FWS Lands
- Ozone Bioindicators on NPS and U.S. FWS Lands
Visibility is a sensitive AQRV at Chiricahua NM. Visibility monitoring in the park has documented frequent visibility impairment(haze) due to fine particle pollution in the area. | <urn:uuid:587efa52-4661-4d0c-9651-8479bf115231> | 3.53125 | 464 | Knowledge Article | Science & Tech. | 20.830164 |
Generating Graphics With Piddleby Michal Wallace
You probably know by now that Python's flexible data structures make working with complex data a breeze. Did you know Python also makes it a snap to visualize your data in vibrant color?
Thanks to the slew of graphics modules people have built, Python is a handy language for creating graphics on the fly. This article looks at two of those modules and shows how to use them to generate graphics from a Python data structure. The example we'll use is a simple Gantt chart.
Gantt charts, a type of timeline often used in project planning, clearly show how resources are allocated to different tasks over time. A Gantt chart makes it easy to see who's supposed to be doing what, and when they're supposed to be finished. It also shows who's overbooked and who's free to pick up the slack.
I use Gantt charts to help organize my projects so I don't try to take on too much. In this case, the resources I am tracking are really just chunks of my time and energy. If I see less than three boxes in a column, I know I've got some free time coming up. If I see more than that, I try to reschedule things. Here's a recent example:
This chart, reduced in size to fit this page, was generated with just under 100 lines of Python code, using two imaging modules: piddle and PIL.
Piddle stands for Plug In Drawing, Does Little Else. It provides a simple interface for drawing 2D lines, arcs, shapes, and text. It allows you to write your drawings to a variety of file types and to interactive displays generated by Tk or wxWindows.
You can fetch Piddle from SourceForge. You'll notice two packages there: piddle and sping. At the moment, sping (Simple Platform Independent Graphics) is the development branch of piddle, rebundled as a python package and renamed to be a little less offputting. But we'll use piddle for this example.
We'll also need the Python Imaging Library (PIL), which we'll use to save our chart as a JPEG. The PIL homepage offers the complete source as well as precompiled binaries for Windows.
Why two modules? PIL by itself is excellent for general image manipulation. It takes care of the low level details of reading and writing file formats, scaling and rotating images, and dealing with individual pixels. While PIL provides some drawing capabilities, piddle operates at a higher level. It offers more choices for storing and displaying images, and it provides the support I mentioned for interactive drawings (though we won't get into that here).
To install piddle, add the unzipped piddle directory to your Python path. To install PIL on windows, unzip the precompiled binaries to your Python directory. Installing PIL on Unix is a bit trickier; you'll have to follow the installation instructions to compile it yourself.
We'll test the installation by generating a simple, empty graphic. The first step is to define a
Canvas object. A piddle Canvas is a rectangular drawing area similar to a painter's canvas, but composed of pixels.
There is a different
Canvas class for each piddle backend. Since we're working with PIL, we'll use
piddlePIL.PILCanvas. Because we might want to change to another backend later, we'll use python 2.0's
import as syntax to hide the module name:
import piddlePIL as pid c = pid.PILCanvas(size=(250,250)) # .. code to draw graphics goes here .. c.save("gantt", format="jpeg")
If everything is installed correctly, running this code will save a completely blank 250x250 JPEG called gantt.jpeg to the current directory. Note that at the time of this writing, neither piddle nor PIL has been updated for python 2.1. If you're using the latest interpreter you may get some warning messages, however, the code should still run.
Drawing the Background
Now that we've got the basics working, let's draw the simple outline of our chart. A Gantt chart is essentially a set of rows and columns with some colored rectangles drawn on it, so we'll use the
drawLine methods from
PILCanvas to do most of our work.
Before we start drawing, let's define a few variables to control how we draw: things like column titles, cell sizes, and even the size of the image itself. This will make the code a little easier to read, and also make it easier for us to tweak our image later. Replace the canvas definition with the following:
titles = ["apr","may","jun","jul","aug","sep"] cols = len(titles) # number of data columns rows = 6 # number of data rows cellW = 80 # cell width cellH = 20 # cell height lftColW = 100 # width of left column (task names) topRowH = 25 # height top row (month names) # calculate image size and define the canvas: imgW = lftColW + (cellW * cols) imgH = topRowH + (cellH * rows) c = pid.PILCanvas(size=(imgW,imgH))
For the chart's background, we'll draw some shaded boxes on the top and left and use a couple
for loops to draw the lines. In the code below, notice how passing three arguments to Python's
range function lets us define our grid wholly in terms of the variables we created. The arguments tell Python where to start, where to end, and how long to make each step in between. To avoid clutter, we'll multiply
cellH by two in the second loop, skipping every other horizontal line.
## color in the headers: c.drawRect(0,0,imgW,topRowH, fillColor=pid.gainsboro) c.drawRect(0,0,lftColW,imgH, fillColor=pid.gainsboro) # and the area where toprow and lftcol overlap: c.drawRect(0,0,lftColW,topRowH, fillColor=pid.silver) ## draw the grid: for x in range(lftColW, imgW, cellW): c.drawLine(x, 0, x, imgH) for y in range(topRowH, imgH, cellH * 2): c.drawLine(0, y, imgW, y) ## draw outer border c.drawRect(0, 0, imgW-1, imgH-1)
To fill in the labels, we'll call the
method, passing it a string, some x and y coordinates, and a
We need some math to center the labels. The formula for centering
requires taking the width of the string in pixels and subtracting half
from the point around which we're centering. Piddle provides the
stringhWidth method for just this task:
## column titles, centered horizontally and vertically: for i in range(cols): c.drawString(titles[i], lftColW + (cellW * i) + (cellW - c.stringWidth(titles[i]))/2, # left (topRowH + 12)/2, # top pid.Font(face="sansserif",size=12,bold=1))
Pages: 1, 2 | <urn:uuid:a0845093-1ce8-4deb-94e9-53179146b469> | 2.703125 | 1,598 | Documentation | Software Dev. | 63.990474 |
Global fisheries receive billions of dollars in subsidies each year. Although some of this money, such as that to improve fisheries management, can promote sustainable fishing practices, other funding can lead to overfishing in the world’s oceans. Capacity-enhancing subsidies, for example for fuel or boat construction, reduce costs for fishers, enabling them to increase their capacity and catch more fish. The unintended consequence of this kind of assistance is that encouraging fishers to bring in larger catches
contributes to unsustainable fishing practices over the long-term.
Rashid Sumaila of the University of British Columbia and his co-authors improved upon previous estimates of global subsidies using updated data and methodology and calculated global amounts and types of fisheries subsidies for 2003. They found global subsidies totaled roughly $27 billion, 60 percent of which went toward unsustainable capacity-enhancing subsidies. Instead of continuing to invest billions of dollars into activities that aggravate overfishing, the authors suggest directing those funds toward fishery conservation and improved management. This Pew Ocean Science Series report is a summary of the scientists’ findings. | <urn:uuid:9d8b2e5c-c2c0-4092-9b07-b067ce66155d> | 3.21875 | 266 | Knowledge Article | Science & Tech. | 22.01376 |
OPEN cursor_name OPEN cursor_name USING value [, ... ] OPEN cursor_name USING SQL DESCRIPTOR descriptor_name
OPEN opens a cursor and optionally binds actual values to the placeholders in the cursor's declaration. The cursor must previously have been declared with the DECLARE command. The execution of OPEN causes the query to start executing on the server.
The name of the cursor to be opened. This can be an SQL identifier or a host variable.
A value to be bound to a placeholder in the cursor. This can be an SQL constant, a host variable, or a host variable with indicator.
The name of a descriptor containing values to be bound to the placeholders in the cursor. This can be an SQL identifier or a host variable.
EXEC SQL OPEN a; EXEC SQL OPEN d USING 1, 'test'; EXEC SQL OPEN c1 USING SQL DESCRIPTOR mydesc; EXEC SQL OPEN :curname1;
Please use this form to add your own comments regarding your experience with particular features of PostgreSQL, clarifications of the documentation, or hints for other users. Please note, this is not a support forum, and your IP address will be logged. If you have a question or need help, please see the faq, try a mailing list, or join us on IRC. Note that submissions containing URLs or other keywords commonly found in 'spam' comments may be silently discarded. Please contact the webmaster if you think this is happening to you in error.
Proceed to the comment form. | <urn:uuid:69169b99-23f3-4892-9962-e0dd61c245ea> | 2.75 | 325 | Documentation | Software Dev. | 56.121193 |
String replaceAll in java
In this section you will learn about replaceAll() method in java, This will replace each of the sub string with the given replacement. This method will return the resulting string..
Split in java
This section illustrate the use of split in java. Split is used to split the string in the given format..
Convert String into date
In this example we are going to convert String into date. SimpleDateFormat is a concrete class for formatting the dates which is inside package "java.text.*" which have a date format which convert a string into Date format..
Object Class Methods in Java
We are going to discus about Object Class Methods in Java. The java.lang.Object class is the root of the class hierarchy tree in JDE(java development environment). Every Java class extends the java.lang.Object class directly or indirectly. There are many methods defined in java.lang.Object class these are as clone(), equals(), finalize(), notify(), notifyAll(), getClass(), toString(), wait(), etc.
Interface in java with example
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How to delete file in java ?
In this section we will learn how to write a program to delete a file in java. You can delete the file or folder, java File class provide two methods..
Inheritance in Java with example
Here we are going to discuss Inheritance in Java with a simple example. Inheritance is a Object Oriented Programming concepts, which allows to extend a superclass/parentclass to a subclass. Interface in java is used for class inheritance and interface inheritance. extend and implement keywords are used for inheritance in Java..
clone method in Java
clone() method in Java is used to create and return copy of the object. Clone() method is used in class where Cloneable interface is implemented but throws a CloneNotSupportedException where a Cloneable interface is not implemented..
Vector in java
Vector in java implements dynamic array. It is similar to array and the component of vector is accessed by using integer index. Size of vector can grow or shrink as needed, by adding and removing item from vector..
Marker Interface In Java
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Autoboxing in Java
Autoboxing in Java is the automatic transformation of primitive data types ((int, float, double) into their corresponding Wrapper class object (Integer, Float, Double) by Java compiler..
Matrix multiplication in java
In this section we will learn about multiplication of two matrices. In java this is a simple program to multiply two matrices, we have to take two-dimensional array and the result should be saved in third two-dimensional array.
Simple Date Format Example
Following is a simple date format example made using Format class. We have uses a pattern of special characters to date and time format..
Constructor overloading in java
In this section we will discuss about constructor overloading in java. Constructor overloading is not much different from method overloading, in method overloading you have multiple method with same name having different signature but in case of constructor overloading you have multiple constructor with different signature..
String reverse in java
In this section we are going to discuss about how to reverse a sting in java. There are many ways to reverse a string in java. Java API provides StringBuffer and StringBuilder reverse() method which can easily reverse a string..
Difference between GenericServlet and HttpServlet
In this section we will discuss about the difference between GenericServlet and HttpServlet. GenericServlet is an abstract class that extends java.lang.Object while HttpServlet is an abstract class that extends GenericServlet..
Break statement in java
Break statement in java is used to change the normal control flow of compound statement like while, do-while , for. Break statement is used in many languages such C, C++ etc. Sometimes it may happen that we want to come out of the loop in that case break is used..
Thread priority in java
A thread is a part or entity of a process that is scheduled for execution. As we know java is a multithreading language which means JVM allow an application to have multiple thread running concurrently..
In this section we will discuss about the feature of java, they are as follows..
Difference between Encapsulation and Abstraction in Java
In this section we will discuss about the difference between Encapsulation and Abstraction in Java. Encapsulation is a process of hiding all the data and methods within a class from outside world. Abstraction on the other hand displays the essential features but hide the unnecessary features of an object..
Java Queue example
Queue Interface is part of java.util package. Queue generally works on FIFO (First In First Out) in ordering elements. In FIFO, new element is added at the end while in other cases ordering properties has to be specified. Queues are bounded which means that number of elements are restricted in it..
assert In Java
This section describes you how to implement assertion in Java. In this tutorial you will learn about what is assertion, how to express assert keyword in Java, where to use assertion in Java, benefits of implementing assertion in Java..
BufferedReader in Java
BufferedReader in Java is used to to read characters, arrays, lines and File Line by line. It also reads text from a character-input stream. A programmer can change the buffer size or can use default size..
Logger in Java
In this section we will learn how to use the Logger in Java program. Logger in Java is part of java.util.logging are used to log the error and messages into the log file. The name of Logger are dot-separated and should be the package name or class name..
Applets in Java
Applet is a Java program embedded within HTML pages. Java applets is compatible with almost all the web browsers like Mozilla Firefox, Google Chrome, Internet explorer, Netscape navigator and others that are java enabled. Applets make a website more dynamic and are secure..
How to declare String array in Java?
Following example will show you how to declare string array in java. There are many ways to declare an array and initialize them. We can use 'new' keyword to declare an array. However, an array can also be declared without the use of 'new' keyword..
Java Stack Example
In this section you will learn about Stack class in java, how to use Stack in java. Before going into details we should know what is stack class, stack class represent Last In First Out(LIFO) of object..
charAt() method in java
In this section you will get detail about charAt() in java. This method comes in java.lang.String package. charAt() return the character at the given index within the string, index starting from 0. This method return the character at the specified index in the string..
Java XOR Operator
Bitwise XOR (exclusive or) "^" is a Java operator that provides the answer 1 if both of the bits in its operands are different. But if both of the bits are same then the XOR operator gives the result 0..
Quick Sort in Java
Quick sort in Java is used to sort integer values of an array. It is a comparison sort. Quick sort is one of the fastest and simplest sorting algorithm in comparison to other sorting algorithms like bubble sort, insertion sort, heap sort, etc..
Keyword is a reserved word in programming language which is predefined. Because it has a special meaning. keyword cannot be used as name for class, method and function. Keyword cannot be used as a identifier..
Simple Java Programs
In this section we will discuss about the Java programs. This section will describe you the various Java programs that will help you understand how to create Java applications. .
Selection Sort in Java
Selection sort in Java is used to sort the unsorted values in an array. In selection sorting algorithm, the minimum value in an array is swapped to the very first position in that array..
Data type in java
In this section we will tell you about data type in java. A data type is defined as " type of data that can be stored in variable". Java is a statically-typed language that means before using the variable it must be declared..
How to copy a file in java
In this section you will learn about how to copy a content of one file to another file. In java, File API will not provide any direct way to copy a file..
Java bitwise OR "|" operator
In this section you will learn about how to use" |" operator in java. Java provides six types of operators: among them one is Bitwise (OR) "|" operator which can be applied to integer, long, int char short type. Bitwise OR "|" operator work on bit and perform bit by bit operation. .
Heap Sort in Java
Heap Sort in Java is used to sort integer values of an array. Like quicksort, insertion sort, bubble sort and other sorting methods, heap sort is used to sort an unsorted list..
Merge Sort Java
Merge Sort in Java is used to sort integer values of an array. There are many methods to sort Java like bubble sort, insertion sort, selection sort, etc. In Merge sort unsorted values are divided into two equal parts, then they are repeatedly merged till the final list is in sorted order completely..
Why and how to use Integer.parseInt() in java
Integer.parseInt() method is used to convert an string value into integer. JVM reads each element as String and hence we have to convert an entered String value into respective data type.
Array in java
In following example we will discuss about Array in Java. Array is a collection of data of same datatype.We can use it to store Integer, Boolean, String object. We can store only primitive data in array..
Java LinkedList example
The LinkedList implements the List interface.We have stores collections of data in LinkedList.The linked list is a data structure which can change during execution..
Difference between Java and C++
Java is an Object Oriented Programming(OOPs) language, developed by James Gosling 1992. Important feature of java is that it allows the developer to Write Once Run Anywhere (WORA) meaning that the code that run on one platform need not required to compile again on another platform. C++ is a superset of C, because it has many new feature other than that already exist in C language. .
Java "&" operator
In this section you will learn how to use "&" operator in java. Java provide six types of operators: among them one is Bitwise operator which can be applied to integer, long, int char short type. "&" operator comes under type of Bitwise operator in java. Bitwise operator work on bit and perform bit by bit operation. .
What is HashSet in java
In following example we will discuss about HashSet in Java. The HashSet class implements the set interface. We have stored data of collection used for HashSet method.hashSet stored only object HashSet class in java.util package. The HashSet does not accept duplicate value..
Java Create Directory
The following example will show how to Create Directory in Java. Though this can be created by using mkdir() also, the following program has used file object in File class..
Java Calendar Example
The following Java Calendar Example will discuss java.util.Calender class and its methods performing various operations on Date object..
Java error cannot find symbol
Whenever a Compiler does not recognize a class name, Java displays an error ?cannot find symbol?..
Two dimensional array in java
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Command line argument in java
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Difference between throw and throws in java.
Throws and throw both are keywords in java, used for handling the exception. When a method is not able to handle the checked exception, it should declared with throws keyword. Throws can be declared with multiple Exceptions separated with comma. Throw is used within the method to throw exception to the caller.. | <urn:uuid:e91862c5-9c86-4844-8490-e9f2bba14e11> | 3.921875 | 2,710 | Content Listing | Software Dev. | 48.462209 |
Web edition: June 15, 2012
Print edition: June 30, 2012; Vol.181 #13 (p. 26)
Arguably, and it would be a tough argument to win if you took the other side, computers have had a greater impact on civilization than any other machine since the wheel. Sure, there was the steam engine, the automobile and the airplane, the printing press and the mechanical clock. Radios and televisions also made their share of societal waves. But look around. Computers do everything TVs and radios ever did. And computers tell time, control cars and planes, and have rendered printing presses pretty darn near obsolete. Computers have invaded every realm of life, from work to entertainment to medicine to education: Reading, writing and arithmetic are now all computer-centric activities. Every nook and cranny of human culture is controlled, colored or monitored by the digital computer. Even though, merely 100 years ago, no such machine existed. In 1912, the word computer referred to people (typically women) using pencils and paper or adding machines.
Coincidentally, that was the year that Alan Turing was born. If you don’t like the way computers have taken over the world, you could blame him.
No one did more to build the foundation of computer science than Turing. In a paper published in 1936, he described the principle behind all of today’s computing devices, sketching out the theoretical blueprint for a machine able to implement instructions for making any calculation.
Turing didn’t invent the idea of a computer, of course. Charles Babbage had grand plans for a computing machine a century earlier (and even he had precursors). George Boole, not long after Babbage, developed the underlying binary mathematics (originally conceived much earlier by Gottfried Leibniz) that modern digital computers adopted. But it was Turing who combined ideas from abstract mathematical theory and concrete mechanical computation to describe precisely how, in principle, machines could emulate the human brain’s capacity for solving mathematical problems.
“Turing gave a brilliant demonstration that everything that can be reasonably said to be computed by a human computer using a fixed procedure can be computed by … a machine,” computer scientist Paul Vitányi writes in a recent paper (arxiv.org/abs/1201.1223).
Tragically, though, Turing didn’t live to see the computer takeover. He died a victim of prejudice and intolerance. His work lived on, though, and his name remains fixed both to the idealized machine he devised and to a practical test for machine intelligence, a test that foreshadowed powers that today’s computers have begun to attain.
Born in London on June 23, 1912, Turing grew up in an era when mathematics was in turmoil. Topics like the nature of infinity, set theory and the logic of axiomatic systems had recently commandeered the attention of — and confused — both practitioners and philosophers interested in the foundations of mathematics. Constructing an airtight logical basis for proving all mathematical truths had been established as the ultimate goal of mathematical inquiry.
But in 1931, Austrian logician Kurt Gödel dashed that hope, proving that some true statements could not be proved (within any mathematical system sufficiently complex to be good for anything). In other words, no system built on axioms could be both complete and internally consistent — you couldn’t prove all true statements about the system by deductions from its axioms.
A second deep question remained, though. Even if not all true statements can be proved, is there always a way to decide whether a given mathematical statement is provable or not?
Turing showed the answer to be “no.” He wasn’t the first to figure that out; as he was finishing his paper, the American logician Alonzo Church at Princeton published his own proof of such “undecidability.” Turing’s triumph was not in the priority of his claim, but rather in the creative way his proof was constructed. He proved the “no” answer by inventing his computer.
He didn’t actually build that computer (at first, anyway), nor did he seek a patent. He conceived a computational machine in his imagination — and outlined the essential principles by which it would work — to explore the limits of mathematics.
Turing’s machine was deceptive in its conceptual simplicity. Its basic design consisted of three parts: a limitless length of tape, marked off by squares on which symbols could be written; a read-write “head” that could inscribe symbols on the tape and decipher them; and a rule book to tell the machine what to do depending on what symbol the head saw on the tape.
These rules would tell the head both what to do in response to a given symbol and then which rules to use next. Suppose, for instance, the head detects a 1 on the tape. A possible rule might be to move one square to the left and write a 1; or move one square to the right and write a 0; or stay on that square, erase the 1 and leave the square blank. By following well-thought-out rules, such a mechanism could compute any number that could be computed (and write it as a string of 0s and 1s).
One of the prime consequences of Turing’s analysis was his conclusion that some numbers could not be computed. He adopted Gödel’s device of assigning a number to every possible mathematical statement and then showed that this inability to compute all numbers implied that the provability of some statements could not be decided. (And Turing showed that his proof of undecidability was also equivalent to Church’s more complicated proof.) Turing’s result was immediately recognized as exceptional by his professor at the University of Cambridge, who advised Turing to go to Princeton for graduate school and work with Church.
Turing’s imaginary computer (christened by Church the “Turing machine”) offered additional lessons for future computer scientists. Depending on the type of calculation you wanted to perform, you could choose from Turing machines with different sets of instructions. But, as Turing showed, you have no need for a roomful of machines. A portion of one computer’s tape could contain the rules describing the operations needed for carrying out any particular computation. In other words, you can just give that machine a rule book (today, you’d call it a program) that tells it what to do. Such a “universal Turing machine” could then be used to solve any problem that could be solved.
During his time at Princeton, Turing discussed these ideas with the mathematician John von Neumann, who later articulated similar principles in describing the stored program general purpose computer, the model for digital computers ever since. Today’s computers, whether Macs or PCs or teraflop supercomputers, are all Turing machines.
“Von Neumann realized that Turing had achieved the goal of defining the notion of universal computing machine, and went on to think about practical implementations of this theoretical computer,” writes Miguel Angel Martín-Delgado of Universidad Complutense in Madrid in a recent paper (arxiv.org/abs/1110.0271).
Turing’s thoughts about his machine went well beyond the practicality of mixing math and mechanics. He was also entranced by the prospect of machines with minds.
To specify which rule or set of rules to follow, Turing assigned his machine a “state of mind.” More technically, he called that state a “configuration.” After each operation, the rules specified the machine’s configuration; the configuration in turn determined what rule the machine should implement next. For instance, in configuration “B,” if the head is positioned over a blank square, the instruction might be to write a 0 on the square, move one position to the right and then assume configuration C. In configuration C, a head positioned over a blank square might be instructed to write a 1, move one square to the right and then assume configuration A.
When Turing referred to the machine’s configuration as its “state of mind,” he really did consider it analogous to the state of mind of a human computer, using a notepad, pencil and rule book rather than tape, head and program. Turing’s imaginary machine demonstrated that the computing abilities of the person and the mechanical computer were identical. “What he had done,” wrote his biographer, Andrew Hodges, “was to combine … a naïve mechanistic picture of the mind with the precise logic of pure mathematics.”
Turing believed that people were machines — that the brain’s magic was nothing more than physics and chemistry “computing” thoughts and behaviors. Those views emerged explicitly years later, when he devised the now-famous test of artificial intelligence that goes by his name. To analyze whether machines can think, Turing argued, the question must be posed in a way that enables an empirical test. As commonly described, the Turing test involves a human posing questions to an unseen respondent, either another human or a computer programmed to pretend to be human. If the computer succeeds in deceiving the interrogator, then — by Turing’s criteria — it qualifies as intelligent.
Actually, Turing’s proposal was a bit more elaborate. First, the interrogator was to pose questions to two unseen humans — one man, one woman — and attempt to determine which one was which. After several trials, either the man or the woman was to be replaced by a computer, and the game repeated, this time the interrogator attempting to tell which respondent was human. If the interrogator succeeded no more often in this task than when the respondents were both human, then the machine passed the thinking test.
Since Turing’s paper appeared, in 1950, multiple objections to his test have been raised (some of which Turing anticipated and responded to in the paper). But the test nevertheless inspired generations of computer scientists to make their machines smart enough to defeat chess grandmasters and embarrass humans on Jeopardy! Today you can talk to your smartphone and get responses sufficiently humanlike to see that Turing was on to something. He even predicted a scenario similar to something you might see today on a TV commercial. “One day ladies will take their computers for walks in the park and tell each other ‘My little computer said such a funny thing this morning!’ ” he liked to say.
Turing seeded a future in which machines and people interact at a level that is often undeniably personal. But he was not around to participate in the realization of his imaginations. Four years after that paper on artificial intelligence appeared, he was dead.
A surviving vision
During World War II, Turing had been the key scientist in the British government’s code-breaking team. His work on cracking the German Enigma code was, of course, a secret at the time, but later was widely recognized as instrumental in the Allies’ defeat of Germany. After the war, Turing returned to computer science, eventually developing software for a sophisticated (at the time) programmable computer at the University of Manchester.
While in Manchester, he composed his paper on the artificial intelligence test. Later there he encountered the lack of intelligence in the British criminal code. During a police investigation of a break-in at Turing’s home, he acknowledged that he knew the culprit’s accomplice from a homosexual encounter. And so Turing became the criminal, prosecuted for “gross indecency” under a law banning homosexual acts. Upon his conviction, Turing chose the penalty of chemical castration by hormone injection rather than serving a term in prison. His security clearance was revoked.
Two years later, Turing’s housecleaner found him dead in bed, a partly eaten apple at his bedside. It was officially ruled a suicide by cyanide. At the age of 41, the man who played the starring role in saving Western democracy from Hitler became the victim of a more disguised form of evil.
In his tragically truncated life, Turing peered more deeply into reality than most thinkers who had come before him. He saw the profound link between the symbolisms of mathematical abstraction and the concrete physical mechanisms of computations. He saw further how computational mechanisms could mimic the thought and intelligence previously associated only with biology. From his insights sprang an industry that invaded all other industries, and an outlook that today pervades all of society. Science itself is infused with Turing’s information-processing intuitions; computer science is not merely a branch of the scientific enterprise — it’s at the heart of the enterprise. Modern science reflects Turing’s vision. “He was,” wrote Hodges, “the Galileo of a new science.”
A. Hodges. Alan Turing: The Enigma, The Centenary Edition. Princeton University Press, 2012.
Teens take home science gold at Intel ISEF
One of the most abstract fields in math finds application in the 'real' world
Fine-tuning of technique used in other animals could enable personalized medicine
Simulation suggests long-term effect on sea level not as dire as some predictions
Coverage of the 2013 American Association for the Advancement of Science meeting
The Year in Science 2012
Three-part series on the scientific struggle to explain the conscious self
Tables of contents, columns and FAQs on SN Prime for iPad | <urn:uuid:939ee34a-3711-4e56-ae18-216fe2c0cf05> | 3.46875 | 2,804 | Knowledge Article | Science & Tech. | 37.696996 |
Dear Astronomers: […] I've poured through my roughly 200 astronomy books and can't find an answer to this question asked by a boy at one of my recent talks: Why do the outer gas giant planets [generally] rotate faster than the inner planets? I was shocked at first because I realized I should know that! The best I could come up with was that the planet forming gas/dust around the bigger planets just happened to have faster moving eddies of material there than in the inner areas of the forming solar system. But I'm not sure that's it. Any ideas?
What a great question! Here's my thoughts on the subject, I hope they help: So the rotation rates of the terrestrial planets, ice-giants and gas-giant cores are largely determined by the stochastic collisions near the end of the formation process (when the colliding bodies are largest and so impart the most angular momentum). This effect is largely random and so will give a certain average angular momentum but has not inherent preferred direction and so won't lead to huge rotation rates.
Meanwhile the rotation of the gas giants is determined by a combination of the net angular momentum of infalling material during it's runaway growth as well as asymmetric inflow of material during the final stages of growth when the gas giant has largely opened up a gap in the gas disk it's forming in (the same process that generates type-2 migration). Looking at this first effect, the fact that gas giant planets are formed by so much material/mass which starts out relatively far apart will give a fairly large angular momentum depending on the eddy speed as you pointed out. On top of that, the fact that the late stage inflow onto the gas giants is in a single sense (clockwise OR counter-clockwise from the inner AND outer inflows) will spin up the planet's rotation rate significantly.
I hope this helps answer the question to your satisfaction.
University of California, Santa Cruz. | <urn:uuid:4cb4b674-79a5-49c4-bcd8-7d5c9dac6689> | 3.0625 | 401 | Q&A Forum | Science & Tech. | 46.137697 |
All-Wavelengths Galactic Center
In celebration of the International Year of Astronomy 2009, NASA's Great Observatories -- the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory -- have collaborated to produce an unprecedented image of the central region of our Milky Way galaxy.
In this spectacular image, observations using infrared light and X-ray light see through the obscuring dust and reveal the intense activity near the galactic core. Note that the center of the galaxy is located within the bright white region to the right of and just below the middle of the image (labeled Sagitarrius A when you roll your mouse over the above composite image). The entire image width covers about one-half a degree, about the same angular width as the full moon.
Each telescope's contribution is presented in a different color: Yellow represents the near-infrared observations of Hubble. They outline the energetic regions where stars are being born as well as reveal hundreds of thousands of stars. Red represents the infrared observations of Spitzer. The radiation and winds from stars create glowing dust clouds that exhibit complex structures from compact, spherical globules to long, stringy filaments. Blue and violet represents the X-ray observations of Chandra. X-rays are emitted by gas heated to millions of degrees by stellar explosions and by outflows from the supermassive black hole in the galaxy's center. The bright blue blob on the left side of the full field image is emission from a double star system containing either a neutron star or a black hole.
When these views are brought together, this composite image provides one of the most detailed views ever of our galaxy's mysterious core.
Image: X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolovy [high-resolution]
Caption: Chandra space telescope | <urn:uuid:ca158c08-cd95-4f0a-ae10-6adf589306b9> | 3.890625 | 406 | Truncated | Science & Tech. | 41.392778 |
Hop, skip and jumping robots
February 11, 2013 |
Jumping robots powered by a combustion engine? Sounds like something from 1930s sci-fi.
New leaps and bounds in heat-resistant materials mean soft-bodied silicon robots can now use controlled explosions, like those in car engines, to make them jump really high.
An electrode sparks a reaction in the simple robot’s leg. This releases lots of energy downwards, making the robot hop up to 30 cm off the ground.
This jump in innovation could lead to new search-and-rescue robots designed to leap and do cartwheels over obstacles.
This research appears in the 8 February 2013 issue of the journal Nature.
Do you like this story?VN:F [1.9.4_1102]214 people liked this story | <urn:uuid:70bf8da2-e964-443d-91b1-81cabe981f69> | 3.34375 | 169 | Truncated | Science & Tech. | 71.374421 |
Differential Absorption Lidar (DIAL)
Light is absorbed by many of the atmospheric components. Absorption of light by molecules is the basis for DIAL which is used to measure the atmospheric concentrations of gases such as water vapor and ozone.
DIAL Measurements of Water Vapor
As shown in figure (a), water vapor has many discrete absorption lines. In water vapor DIAL, laser pulses are transmitted at two wavelengths, one on a water vapor absorption line, λon, and another off-line, λoff. If the two wavelengths are close together, then for both wavelengths the scattering by molecules and particles is essentially equal. The difference in the returns between the two wavelengths is then due entirely to absorption by water vapor molecules, figure (b). Thus, measurement of the ratio of the backscatter at the two wavelengths as a function of range can be used to calculate the water vapor concentration profile.
DIAL Measurements of Ozone
DIAL measurements of ozone require less precise laser frequency because ozone has a broad (~200 nm) absorption band [see figure] instead of narrow lines lines like water vapor. This requires that the on- and off- wavelengths be chosen with sufficient wavelength separation to ensure a significant difference in their absorption. However, uncertainty in the changes of aerosol scattering and patterning between the wavelengths can introduce error. The difference in aerosol scattering at λon and λoff can be extrapolated from a third measurement taken at a longer wavelength, λa. Therefore, DIAL measurements with three wavelengths can be used to determine ozone concentration profiles to good accuracy. | <urn:uuid:2beebe7c-8aaa-4c3d-80fc-4a5dce1df539> | 4.125 | 330 | Knowledge Article | Science & Tech. | 22.809924 |
Tourmaline is easy to recognize. This Chinese tourmaline specimen, shown about twice life size, displays the typical crystal shape of a nine-sided prism. It also displays the typical striations along the long axis and the glassy luster. Its hardness is 7 to 7.5, its streak is white, and it has poor cleavage. Tourmaline might be mistaken for hornblende, another black glassy mineral that occurs in prisms, but hornblende forms flattened crystals (being an amphibole), is softer (5 to 6), and has a strong cleavage.
Tourmaline is found in coarse-grained granite bodies, especially their late-forming pegmatite cores, and in some metamorphic rocks. In these rocks tourmaline is the principal boron mineral, whereas in sedimentary rocks boron occurs as borates like ulexite.
Clear and colored forms of tourmaline can be attractive gemstones and fancy specimens; their chemical formulas replace Na with Ca and Fe with Mg, Al, or Li; they may also contain fluorine in place of the OH group. But all forms of tourmaline display piezoelectricity, which means that they change their electrical properties in response to pressure. This makes tourmaline useful in certain electrical apparatus. Tourmaline also gains an electric charge upon heating and coolingyou can watch the crystal pick up bits of paper as this happens.
Tourmaline is the state gemstone of Maine. | <urn:uuid:3238a0a1-4857-484a-acf4-631dbb08e1dc> | 3.0625 | 311 | Knowledge Article | Science & Tech. | 36.913313 |
Between the Galaxies
Name: bryan matthewkarp
Date: 1993 - 1999
What if any thing is in between galaxies, besides space?
How much cooler are sunspotsthan the actual surface of the sun?
Why is the sky sometimes green?
How are satellites named?
"empty" space between galaxies (extra-galactic space) actually
contains about one hydrogen atom per cubic meter. Inter-galactic
space contains about one hydrogen atom per cubic cm.
The surface temperature of the sun is 5770 deg. Kelvin; sunspots
are about (?) 1000 degrees cooler. the sun's photosphere (higher
up in the sun's atmosphere) can get to over 10 million degrees!
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:170a9f4e-2399-4901-8b9c-7da60e0ff802> | 3.1875 | 167 | Content Listing | Science & Tech. | 48.927714 |
Odonates as biological indicators of grazing effects on Canadian prairie wetlands
Article first published online: 27 MAY 2005
Volume 30, Issue 3, pages 273–283, June 2005
How to Cite
Lee Foote, A. and Rice Hornung, C. L. (2005), Odonates as biological indicators of grazing effects on Canadian prairie wetlands. Ecological Entomology, 30: 273–283. doi: 10.1111/j.0307-6946.2005.00701.x
- Issue published online: 27 MAY 2005
- Article first published online: 27 MAY 2005
- Accepted 16 December 2004
- Aquatic invertebrates;
- cattle grazing;
Abstract. 1. Aquatic macro-invertebrates have frequently been used as biological indicators in lotic environments but much less commonly so in lentic habitats. Dragonflies and damselflies (Order Odonata) satisfy most selection criteria for lentic bioindicators of grazing impacts.
2. Intensive cattle grazing affects most of the Canadian prairie pothole region but the effects of grazing on wetlands are poorly understood.
3. Here the vegetation structure and invertebrate community composition of 27 prairie potholes in Alberta, Canada were studied and compared. Wetlands were evenly divided into three treatments of different grazing regimes.
4. Removal of emergent vegetation by cattle grazing decreased odonate abundance and reproductive effort. Shorter Scirpus acutus stems resulted in significantly fewer damselflies (Suborder Zygoptera) and lower reproductive efforts.
5. Overall odonate diversity was affected by the height of key plant species, highlighting the importance of the vegetation structure of both emergent vegetation for breeding and adjacent upland vegetation for nocturnal roosts. Wetland vegetation structure was more important than vegetation composition to the life history of odonates.
6. Wetland water quality parameters of nitrogen, phosphorus, total dissolved solids (TDS), and chlorophyll-a concentration did not change due to the presence of grazing cattle at wetlands so water quality influences were rejected as mechanisms of change.
7. Larval odonate diversity and abundance was positively correlated with overall aquatic macro-invertebrate diversity and abundance, hence it was concluded that the larval odonate community can be an accurate bioindicator of intactness and diversity of overall aquatic macro-invertebrate communities in Canadian prairie wetlands. | <urn:uuid:1fe80887-456a-4d0b-8a09-9151ec296f71> | 3.359375 | 510 | Truncated | Science & Tech. | 21.342857 |
(By masak and moritz)
Newcomers to the Perl programming language, version 5, often complain that
they can’t reverse strings. There’s a built-in reverse function, but it doesn’t seem to work at first glance:
$ perl -E "say reverse 'hello'" hello
When such programmers ask more experienced Perl programmers, the solution is quickly found:
reverse has actually two different operation modes. In list context it reverses lists, in scalar context it reverses strings.
$ perl -E "say scalar reverse 'hello'" olleh
Sadly this an exception from Perl’s usual context model. For most operators or functions the operator determines the context, and the data is interpreted in that context. For example
* work on numbers, and
. works on strings (concatenation). So a symbol (or function name, in the case of uc) stands for an operation, and provides context. Not so
In Perl 6, we try to learn from previous mistakes, and get rid of historical inconsistencies. This is why list reversal, string reversal and hash inversion have been split up into separate built-ins:
# string reversal, sorry, flipping: $ perl6 -e 'say flip "hello"' olleh
# reversing lists # perl6 -e 'say join ", ", reverse <ab cd ef>' ef, cd, ab
# hash inversion perl6 -e 'my %capitals = France => "Paris", UK => "London"; say %capitals.invert.perl' ("Paris" => "France", "London" => "UK")
Hash inversion differs from the other two operations in that the result is of a different type than the input. Since hash values need not be unique, inverting a hash and returning the result as a hash would either change the structure (by grouping the keys of non-unique values together somehow), or lose information (by having one value override the other ones).
Instead hash inversion returns a list of pairs, and the user can decide which mode of operation they want for turning the result back into a hash, if that’s necessary at all.
Here’s how you do it if you want the hash inversion operation to be non-destructive:
my %inverse; %inverse.push( %original.invert );
As pairs with already-seen keys get pushed onto the
%inverse hash, the original value isn’t overriden but instead "promoted" to an array. Here’s a small demonstration:
my %h; %h.push('foo' => 1); # foo => 1 %h.push('foo' => 2); # foo => [1, 2] %h.push('foo' => 3); # foo => [1, 2, 3]
All three (flip/reverse/invert) coerce their arguments to the expected type (if possible). For example if you pass a list to
flip, it is coerced into a string and then the string is rever^W flipped. | <urn:uuid:02776515-42d9-4138-8c7f-3fd7de5967da> | 2.890625 | 660 | Personal Blog | Software Dev. | 56.919318 |
Blood clot, coloured scanning electron micrograph (SEM). Red blood cells (erythrocytes) and white blood cells (leucocytes, green) trapped within the fibrin mesh (yellow) of a fresh blood clot. Clots are formed in response to cardiovascular disease or injuries to blood vessels. White blood cells commonly occur in blood clots, fulfilling their immune system role in defending the body from invading bacteria, viruses and foreign substances. Magnification: x2000 when printed 10 centimetres wide. | <urn:uuid:2007721c-ac15-426a-ae42-dcb5ec41808c> | 3.59375 | 104 | Truncated | Science & Tech. | 35.944 |
Editor's note: The following column was co-authored by Alex Johnson, a post-doctoral fellow at Harvard University.
For the past several years--until the credit crisis--investors have flocked toward renewable energy. Their hope is that solar radiation can be harnessed directly and through intermediaries such as the wind and biosphere to power the global economy into perpetuity. This hope is understandable since renewable energy has benefits that range from the environment to geopolitics. Nevertheless, care and scientific rigor should be used to quantify the challenge of converting society to renewable energy.
The maximum theoretical potential of advanced lithium-ion batteries that haven't yet been demonstrated to work is still only about 6 percent of crude oil."
The most significant challenge to renewable energy is competition from fossil carbon--the world's predominant source of primary energy for the past 150 years. Fossil carbon has dominated the energy market for many reasons--not the least of which is its intrinsic mass and volume energy densities. Indeed, 1 kilogram of crude oil contains nearly 50 mega-joules of chemical potential energy, which is enough to lift 1 metric ton to a height of around 5,000 meters. Furthermore, crude oil happens to be liquid at Earth's surface conditions, making it easy to store, transport, and convert.
The energy densities of natural gas and coal, around 55 mega-joules per kilogram and 20-35 mega-joules per kilogram respectively, are similar to those of crude oil. Fossil carbon is packed with chemical energy because carbon and the hydrogen it stabilizes in a condensed form react strongly with oxygen to form carbon dioxide and water. In addition, geologic processes have concentrated large quantities of fossil carbon into relatively small geographic areas such as coal mines and oil fields. Biofuels such as ethanol and biosynthetic diesel can have volume and mass energy densities equal to that of fossil carbon, but since they're regularly harvested, their areal energy densities are substantially lower.
Renewable energy--unlike fossil carbon--is harnessed dynamically from the environment. Therefore, it won't be as useful as fossil carbon until it can be stored and transported with similar ease.
Many companies and scientists are diligently trying to improve energy storage technologies, and we're confident that substantial progress will be made. We can, however, use thermodynamics to calculate the upper limits of what's possible for a variety of technologies. And when we do this, we find that many technologies will never compete with fossil carbon on energy density.
Let's start with batteries. Today's lead acid batteries can store about 0.1 mega-joules per kilogram, or about 500 times less than crude oil. Those batteries, of course, could be improved, but any battery based on the standard lead-oxide/sulfuric acid chemistry is limited by foundational thermodynamics to less than 0.7 mega-joules per kilogram.
Due to the theoretical limits of lead-acid batteries, there has been serious work on other approaches such as lithium-ion batteries, which usually involve the oxidation and reduction of carbon and a transition metal such as cobalt. These batteries have already improved upon the energy density of lead-acid batteries by a factor of about 6 to around 0.5 mega-joules per kilogram--a great improvement. But as currently designed, they have a theoretical energy density limit of about 2 mega-joules per kilogram. And if research regarding the substitution of silicon for carbon in the anodes is realized in a practical way, then the theoretical limit on lithium-ion batteries might break 3 mega-joules per kilogram. Therefore, the maximum theoretical potential of advanced lithium-ion batteries that haven't been demonstrated to work yet is still only about 6 percent of crude oil!
But what about some ultra-advanced lithium battery that uses lighter elements than cobalt and carbon? Without considering the practicality of building such a battery, we can look at the periodic table and pick out the lightest elements with multiple oxidations states that do form compounds. This thought experiment turns up compounds of hydrogen-scandium. Assuming that we could actually make such a battery, its theoretical limit would be around 5 mega-joules per kilogram.
So the best batteries are currently getting 10 percent of a physical upper bound and 25 percent of a demonstrated bound. And given other required materials such as electrolytes, separators, current collectors, and packaging, we're unlikely to improve the energy density by more than about a factor of 2 within about 20 years. This means hydrocarbons--including both fossil carbon and biofuels--are still a factor of 10 better than the physical upper bound, and they're likely to be 25 times better than lithium batteries will ever be.
What about storing energy in electric fields (i.e., capacitors) or magnetic fields (i.e., superconductors)? While the best capacitors today store 20 times less energy than an equal mass of lithium-ion batteries, one company, EEstor, claims a new capacitor capable of 1 mega-joule per kilogram. Whether or not this claim proves valid, it's within about a factor of 2 of the physical limit based on the bandgap of the dielectric material. Electromagnets of high-temperature superconductors could in theory reach about 4 mega-joules per liter similar to our theoretical batteries given a reasonable density; existing magnetic energy storage systems top out around 0.01 mega-joules per kilogram, about equal to existing capacitors. Here again, both the realized technology and its ultimate physical potential are far behind the energy density of common hydrocarbon fuels.
That brings us to the option of storing chemical potential energy as fuel that can be oxidized by atmospheric oxygen. We do it today, but with two differences: We generate this fuel renewably and convert it to work more efficiently than in combustion engines, either by fuel cells or air batteries. Zinc air batteries, which involve the oxidation of zinc metal to zinc hydroxide, could reach about 1.3 mega-joules per kilogram. But if we take elemental zinc all the way to zinc oxide, then we can theoretically beat the best imagined batteries at about 5.3 mega-joules per kilogram. Zinc has proved interesting enough that several writers (not us) have imagined a "zinc economy."
To get really ambitious, we imagine storing energy as elemental aluminum or elemental lithium. Those two highly electro-positive elements yield a theoretical energy density--when oxidized in air--of 32 and 43 mega-joules per kilogram. At least now the theoretical limit is between 60 percent and 80 percent to that of hydrocarbons; we just have to figure out how to extract a large fraction of the energy from that oxidation.
A more promising approach is to use fuel cells with liquid and gaseous fuels. The two obvious choices for such fuels are hydrogen and hydrocarbons; in terms of energy per unit mass, hydrogen beats crude oil and natural gas by a factor of almost 3. Alas, hydrogen is a gas at surface conditions, so its volume density is horrible unless it's compressed to several hundred atmospheres of pressure. At 700 bars, for example, hydrogen has an energy-volume density of around 6 mega-joules per liter, while gasoline at 1 bar has about 34 mega-joules per liter. Both hydrogen and hydro-carbons can be produced from renewable energy sources, though doing so economically and at a global scale remains a challenge.
There is one more energy-storage approach that theoretically beats hydrocarbons. Energy density comparable to lithium-ion batteries has been demonstrated with flywheels, and a theoretical device composed solely of toroidal carbon nanotubes could reach 100 mega-joules per kilogram. But the fabrication and safety challenges inherent in such a device render it unlikely that even a small fraction of this potential will ever be realized.
The bottom line is that nature has given us hydrocarbons in the form of fossil carbon and biomass, and their energy-mass and energy-volume densities are superior to the thermodynamic limits of nearly all conceivable alternatives. Thus, it's quite likely that hydrocarbons of one form or another will be humanity's primary energy storage medium for quite a long time. | <urn:uuid:6b7ba779-60ae-4245-947f-1023736357ef> | 3.59375 | 1,718 | Nonfiction Writing | Science & Tech. | 32.397655 |
Molar heat capacity
From Uncyclopedia, the content-free encyclopedia
Molar heat capacity is a measurable physical quantity that characterizes the ability of a mole to explode (or, in scientific terms, asplode.) It is defined as the rate of change of temperature as heat is added to a mole's body at the given conditions and state of the body (usually its temperature).
In the International System of Units, heat capacity is expressed in units of Julie's per Kelvin. And, as we all know, the average Kelvin likes him some Julie's! It is termed an "expensive quantity" because it is sensitive to the size of the object's wallet. Dividing heat capacity by the moles body's mass yields a specific heat capacity (also called mole-specific heat capacity or more loosely mole in heat), which is an "insensitive quantity," meaning it is no longer dependent on how much the mole likes you, which is good, as you're about to blow him up.
Please review the first paragraph.
edit Explanation of the Formula
Where equals the number of times the cheerleader dumps on Kelvin and where equals Dr. Kelvin's body temperature at maximum embarrassment and where shows that a mole is better than a rat and where is the whole point of the exercise.
is what we solve for, usually by eating the freshly asploded mole.
Dr. Kelvin, renowned temperature scientist discovered Molar Heat Capacity, mostly by accident. It is well understood that Dr. Kelvin discovered Absolute Zero in relation to his studies of cheerleaders and their reactions to him. The hottest of the cheerleaders (in scientific terms, of course) had a pet mole. After rejecting Dr. Kelvin in front of the whole gym class, Dr. Kelvin vowed revenge. After a few days in the cafeteria, he was ready.
edit Dr. Kelvin is Ready
Converting one of the microwave ovens into a portable microwave gun, Dr. Kelvin took careful aim at Julie's pet mole. As a scientist, he was careful to note the settings he used on the rodent. With the gun set to pop popcorn, the mole asploded beautifully. Julie was left covered in mole haggis and Dr. Kelvin was voted Most Likely to Asplode Things.
Word of this discovery spread throughout the scientific research community. Several different organizations used this information.
The CIA, due to an excess of experimentation, came up with several postulates on how mole's explode. Since larger moles have more mass, they require more and more energy, in the form of microwaves, to asplode, However, when large moles are detonated the ensuing asplosion is that much more brilliant and orgasmic.
MI6, being more reserved and British, focused on mole density as a solution. The younger a mole is, the more dense it is, that is because when things get old, the get wrinkly n' stuff, so they take up more space. As a mole gets denser, it becomes more difficult to aspolde, but the asplosion is so much more bloody and satisfying.
With their abundance of Microwaved Meat Technology, KFC is uniquely positioned to take advantage of Molar Heat Capacity research. As yet no findings have been forthcoming from KFC, it is hoped that moles might soon replace chicken on their menu.
edit Home Experiments
Though the average person does not have access to Dr. Kelvin's enormous research grants, his enormous brain, or Julie's enormous research funding, they can perform a few simple experiments with molar heat capacity.
First take an old microwave oven, then bash open the door. Attach a long extension cord, long enough to reach the girl next door. Take your new device over to her house, and call her Julie. She'll probably get mad, unless her name IS Julie. At this point, you must turn it ON. Some people miss this step and get mad. After the micowave has been on for a few minutes, you will hear a series of loud pops coming from behind Julie. Then you know you killed the moles on her back. | <urn:uuid:8e3140d8-ea79-4669-92a0-fd89ded9055b> | 3.5625 | 846 | Knowledge Article | Science & Tech. | 49.293683 |
Thanks to one of the most productive spacecraft ever built, scientists are far better acquainted with the star that lights our world and gives us life. Built for ESA by European industry, the Solar and Heliospheric Observatory (SOHO) went into space on December 2, 1995.
The tenth anniversary of SOHO's launch is a time for celebration for the scientists and engineers in Europe and the USA who conceived, created and still operate this unprecedented solar spacecraft - and who have rescued it from oblivion three times.
Four months after its flawless launch by a NASA rocket, SOHO was at its special vantage point 1.5 million kilometres away from the sunward side of Earth. There it watches the Sun unblinkingly 24 hours every day, and sends home a stream of images of the ceaseless frenzy in the solar atmosphere. Apart from unmasking the Sun, and teaching us how it works, SOHO's pictures give early warning of storms in space that can affect astronauts, satellites and power and communications systems on Earth.
Originally planned for a nominal life of just two years, SOHO has performed so well and delivered such important data that operations are now to set to continue at least until 2007. That corresponds to a full 11-year cycle of magnetic storms on the Sun, and a further extension is under discussion. But the going has not always been easy.
All contact was lost with the spacecraft in June 1998. Dramatic efforts by ESA and NASA engineers, supported by Matra Marconi Space (now Astrium) who built SOHO, restored the spacecraft to full operation in November 1998. Shortly afterwards, the spacecraft's last gyroscope failed, but the teams developed new software that controls the spacecraft without a gyroscope. A third crisis occurred in June 2003, when SOHO's main antenna became stuck. Using the secondary antenna and software for intermittent recording, observations continued.
"I tip my hat to SOHO's engineering and operations teams, whose skills and dedication let us overcome all these challenges," says Bernhard Fleck, ESA's Project Scientist for SOHO.
More than 3200 scientists from around the world have been involved with SOHO, which is a project of international collaboration between ESA and NASA. SOHO's telescopes probe the Sun from deep in its interior and all the way out to Earth's orbit and beyond, where the magnetised solar wind of atomic particles sweeps through interplanetary space.
"It's impossible to overstate the importance of SOHO to the worldwide solar science community," said Dr. Joe Gurman, U.S. project scientist for SOHO at NASA's Goddard Space Flight Center, Greenbelt, Md. "In the last ten years, SOHO has revolutionized our ideas about the solar interior and atmosphere and the acceleration of the solar wind."
Some of SOHO's major scientific accomplishments include:
SOHO data are freely available over the Internet, and people all over the world have used images from the observatory to discover more than 1,000 comets.
- Allowing space weather forecasters to play a lead role in the early warning system for space weather and give up to three days notice of Earth-directed disturbances.
- Supplying the most detailed and precise measurements beneath the surface of the sun.
- Providing the first images of a star's turbulent outer shell (the convection zone) and of the structure of sunspots beneath the solar surface.
- Making the sun transparent by creating images of the sun's far side, including stormy regions there that will turn with the sun and threaten the Earth.
- Discovering a mechanism that releases more than enough energy to heat the sun's atmosphere (corona) to 100 times its surface temperature.
- Discovering that a series of eruptions of ionized gas (coronal mass ejections) from the sun blasts a "highway" through space where solar energetic particles flow. These particles disrupt satellites and are hazardous to astronauts outside the protection of Earth's magnetic field.
- Monitoring the sun's energy output (the "total solar irradiance" or "solar constant") as well as variations in the sun's extreme ultraviolet radiation, both of which are important to understand the impact of solar variability on Earth's climate.
- Identifying the source regions and acceleration mechanisms of the solar wind, a thin stream of ionized gas that constantly flows from the sun and buffets Earth's magnetosphere. | <urn:uuid:88bdc9c8-6693-4e59-a6ec-448c6fc1f0b9> | 3.46875 | 918 | Knowledge Article | Science & Tech. | 38.935324 |
This is another post on open standards, a concept that affects all aspects of the mobile experience, from the processors and operating systems to carriers and devices and finally to the end user. When creating web-based content, XHTML and CSS set standards for open sourced coding structure and help to create a consistent experience from desktop to mobile devices. Standards-compliant Scalable Vector Graphics (with a mobile variation known as the Mobile SVG Profiles – which include SVG Basic and SVG Tiny) is the standard for complex vector-based graphics and animation and are targeted to SVG-enabled third generation mobile phones which were announced in January 2006.
The following are the “languages” currently supported by the W3C and OMA for mobile authoring:
• XHTML (eXtensible HyperText Markup Language) is the official web markup standard, replacing HTML and Wireless Application Protocol (WAP 1.0) for mobile devices. XHTML is compliant with XML to support specific tags and structure. Variations such as XHTML basic and XHTML mobile profile are used extensively in combination with CSS to control web-based presentation, structure and layout.
• CSS (Cascading Style Sheets) controls many of the visual elements on a web page, including font sizes, colors and formatting. Stylesheets are also used to control presentation and layout in conjunction with XHTML for both web and mobile web content. Variations include CSS2, CSS-basic, etc.
• SVG-Tiny (Scalable Vector Graphics) is the standard for interactive and dynamic vector based graphics and animation on mobile devices. Based on XML, SVG-T allows for 2D graphics to be displayed and/or manipulated. Currently, SVG-Tiny is supported by many mobile browsers including Opera, Access, Openwave and Obigo. A current list (last updated in December 2005) is available showing SVG implementations is available (although confusing).
• SMIL (Synchronized Multimedia Integration Language) uses XML to create a timeline describing how graphics, text and sound should be displayed or how they will play together in a sequence. SMIL was developed by REAL when they realized there was a way to add animation and synchronize sound and images without having actual video. SMIL allows for multiple versions (playing on different bandwidths) as well as multiple languages to be displayed. MMS is a stripped down version of SMIL, with very similar capabilities.
For the mobile designer, the topic of open standards using XHTML and CSS is not new, as this initiative has been floating around for several years in the web-development world, highly promoted for accessibility purposes as well as cross browser compatibility. Separation of content from presentation using style sheets goes one step further when creating web-based content for mobile devices. Ideally, the content would remain static on a web page, and a user agent would apply the correct style sheet for either PC-based browsing, or mobile web browsing. However each mobile browser has its own quirks and display habits that cause mobile designers to spend a lot of time tweaking code and testing on various emulators and devices. Mobile designers generally need to determine up front if they are coding for one specific browser type (for example, a demo on a Symbian-based smartphone, such as Sony Ericsson P910a) or if they are creating an experience that needs to work on a number of devices and browser types. Usually, one or more specific browsers and devices are targeted for development, and then ported to other devices.
Obviously, this is all changing so quickly, I cannot keep up. Please feel free to post any updates and/or email me with newer considerations! | <urn:uuid:ea62cf04-657d-469b-ae7e-b9e6bf37daa3> | 3.203125 | 746 | Personal Blog | Software Dev. | 34.963664 |
Translation - of a polygon
From Latin: translatus - "carried over,"
Moving a figure to a new location with no other changes.
Drag any orange dot to reshape the left (yellow) original figure. Drag the image (right, gray) to translate it to a new location.
To translate a figure is to simply slide it somewhere else. But in the move, you may not change the figure in any other way. You cannot rotate
it, resize it, or flip it over. You may only slide it side to side, up and down.
In the diagram above,the original object is the yellow one on the left. By translating it up and to the right, we get the gray object on the right.
This is called the translated "image" of the original. Notice the vertices of the original are labelled A,B etc.
By convention, the corresponding vertices of the image are labelled A' B' etc.
The small dash after the letter is called a 'prime' so the vertices are pronounced "A prime, B prime" and so on.
Properties of translated objects
The original object and its image are
- identical in every respect except for their position.
in the original to the corresponding vertex in the image are
In the diagram above, click on "show distances" and note that the segment AA' is congruent and parallel to BB' etc.
A way to remember
A way to remember what translation means is "tranSLate means SLide"
Things to try
In the diagram above - click 'reset'
In the yellow figure on the left, drag any vertex to reshape it. Note how the translated image on the right changes to match.
The image is merely moved, but otherwise matches the original in every respect.
Drag the gray image on the right. Notice that the image remains an exact copy of the original except for its location on the plane.
Other transformation topics
(C) 2009 Copyright Math Open Reference. All rights reserved | <urn:uuid:cc12f88a-469c-4d09-88f6-0ec821383584> | 3.828125 | 424 | Tutorial | Science & Tech. | 49.786801 |
How Pine Bark Beetles Created an Elaborate and Deadly Mess
By DINA FINE MARON of ClimateWire
Published: October 28, 2010
More News From ClimateWire
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- European Renewables Industry Staggered First by Recession, Now by Budget Cuts
- The Arctic Shifts to a New Climate Pattern in Which 'Normal' Becomes Obsolete
- Coal Looms Large for Democrat in Texas Governor's Race
- Bringing Clean Light to Poor Nations and Moving Beyond Charity
DILLON,Colo. -- Cal Wettstein presides over a sea of dead and dying trees the size of Connecticut.
Across his domain, hillsides blanketed with lodgepole pines are in the final throes -- their needles are turning red, or their trunks are tipping precariously to one side. Others are already rotting on the forest floor.
Voracious bark beetles are known for leaving a formidable trail of destruction in their wake, and at this point, there is nothing that can be done to stop them.
As beetle kill incident commander for the U.S. Forest Service, Wettstein is mounting a triage operation for the 3.6 million acres of trees in northern Colorado and southeastern Wyoming that have been bested by the ant-sized insects in the past 15 years.
There are no known methods for saving the trees once they've been hit by the beetles, and removing the dead wood has been slow going. Wettstein's job is to prioritize which trees need to go first before they hurt somebody or become the fuel for an uncontrollable wildfire.
It's not a small job.
Extreme emergencies usually warrant an incident command. Some examples are wildfires, hurricanes and tornadoes. The damage wrought by waves of beetle crusaders fits in that category because it poses a serious threat to both ecosystems and people, said Wettstein.
More than 3,500 miles of roads, 1,300 miles of trails and more than 600 miles of power lines cut through the area and could be seriously damaged by downed trees or wildfire, according to Forest Service estimates. That same beetle-kill space overlaps the headwaters for rivers that supply water to more than a dozen Western states and is also home to some of the largest ski resorts in the country; lack of tree cover in these places could accelerate problematic evaporation.
"The infrastructure and resources affected are huge. Pulling together exactly what work needs to be done and prioritizing where the mitigation will be is a big part of what my team does," Wettstein said.
The dead trees, along with hotter and drier climate conditions, raise the risk of more frequent and intense wildfires. Current science states that trees that have turned red and the trees that have fallen to the forest floor make for elevated fire risk.
Meanwhile, there is no possible way to clear out all the dead trees -- logistically because much of the area is roadless, and legally because wilderness protection legislation blocks going into the area and chopping down some of these trees. Then there is a financial obstacle because the costs of attempting to remove them all would be staggering.
But each year, the Forest Service continues to chip away at the problem -- signing contracts for thousands of acres of wood removal.
Beetles learn there is free lunch
A confluence of events first gave rise to the beetle issue, and climate change was in the driver's seat.
Warming weather meant more beetles survived the winter. Meanwhile, the results of previous logging and fires caused the area's pine trees all to mature around the same time. Such seasoned trees are the preferred source of food for the beetles. Decades of fire exclusion policy imposed by the Forest Service also created conditions where the tree stands were more dense.
"Evolution is a beautiful thing," Wettstein said, "and these beetles are adapted to their environment."
When a pine beetle lands on the trunk of a tree, it bores a hole in it -- attempting to take root under the bark. A healthy tree can mount an active effort to pitch the pest out -- producing sap that would ooze out of the beetle-dug hole and hopefully take the beetle outside with it. But trees that have suffered from years of drought or are overwhelmed by a phalanx of intruders -- as these have -- lose their power to resist.
While bugs that munch on tree leaves can be felled by spraying pesticide from the air, these beetles attack tree bark, so aerial assaults miss the mark. | <urn:uuid:f487642d-ae0f-4ff5-b301-60380e707bdf> | 2.90625 | 931 | Truncated | Science & Tech. | 45.390027 |
The community wiki for GLIBC
The official and canonical GLIBC website is http://www.gnu.org/software/libc/
Any Unix-like operating system needs a C library: the library which defines the "system calls" and other basic facilities such as fopen, malloc, printf, exit etc.
The GNU C Library is used as the C library in the GNU systems and most systems with the Linux kernel.
1.1. Project Goals
The GNU C Library is primarily designed to be a portable and high performance C library.
It follows all relevant standards including ISO C11 and POSIX.1-2008. It is also internationalized and has one of the most complete internationalization interfaces known.
1.2. Project Features
- POSIX Threading
A History of Threading in GLIBC (todo) - Describes the GLIBC version history of POSIX NPTL as well as mutex and futex constructs.
- ... and more!
The history of Unix and various standards determine much of the interface of the C library. In general the GNU C library supports the ISO C and POSIX standards. We also try to support the features of popular Unix variants (including BSD and System V) when those do not conflict with the standards. Different compatibility modes (selectable when you compile an application) allow the peaceful coexistence of compatibility support for different varieties of Unix.
1.4. Editing the wiki
Owing to automated spammers we have switched to only allowing those people in the EditorGroup to edit the wiki. If you would like to participate in the wiki please email your request to email@example.com or contact one of the editors in EditorGroup and have them vouch for you and add you to the list. We are sorry for the inconvenience. Please help make the world a better place by helping prevent spam.
2. Obtaining the Official Source
The "Download" section of the GLIBC website contains instructions on obtaining the official sources for the latest GLIBC release.
You can obtain official tarballs from the standard location, ftp://ftp.gnu.org/gnu/glibc/.
Source snapshots are available from ftp://sourceware.org/pub/glibc/snapshots/.
The working source tree is located in GIT, look here for instructions.
Consult the GLIBC FAQ for common questions and answers.
If you wish to contribute to glibc please post your idea or patch to firstname.lastname@example.org for initial review.
glibc has maintainers for each architecture. Please CC them on any libc-alpha emails related to the architecture of your interest.
Developers with commit access should follow the committer checklist prior to pushing patches to the upstream source code repository.
4.2.1. Developer Resources
- The IRC channel is on Freenode at #glibc.
4.2.2. Standards and Documentation References
4.3. Release management
4.4. Internals Documentation
PTR_MANGLE & friends: http://udrepper.livejournal.com/13393.html
Namespace control: __-prefixed symbols
Conditional Code: PIC, SHARED, etc.
AddOns: Working with addon dirs
4.5. Issue Tracking
Do you want to help with GLIBC? The GLIBC Bug Triage initiative is a great way to get involved.
If you think the GLIBC bugzilla version selection drop-down is missing a version number, please contact libc-help < email@example.com >.
If you think that bugs aren't being fixed fast enough or that new features aren't being implemented fast enough, please take the time to read this email http://sourceware.org/ml/libc-help/2008-08/msg00009.html
4.8. Tips and Tricks
Another recipe for intercepting syscalls and providing your own version of FOO (instructions specifically for Ubuntu Linux systems).
The Plash project has some hints about GLIBC (mainly about build issues).
rtldi can be used to install multiple versions of GLIBC simultaneously (specifically, multiple versions of the dynamic linker, ld.so).
4.8.1. Project TODO
We have one master TODO list. The links below are pages dedicated to specific entries in the master list.
4.9. Project Wishlist by Developer
If you are looking for a GLIBC project this is the place to start.
4.10. Website Maintenance
The current website maintenance procedure is documented here.
4.11. Project Ports
4.11.2. How to Submit a New Port
Section Porting on http://www.gnu.org/software/libc/development.html
We look forward to your feedback! Please be aware that this wiki uses text captchas to deter spam. If you have any problems answering the text captchas please contact firstname.lastname@example.org. | <urn:uuid:ed48bde2-5e8c-43d0-8af3-ce51e2e47e2b> | 3.140625 | 1,081 | Knowledge Article | Software Dev. | 60.859511 |
The Rain-shadow Effect
Sheltered by mountains
by Philip Eden
"Rain shadow" is a phrase often used by meteorologists in their day-to-day work, and is occasionally mentioned by television weather forecasters. Some may regard it as a solecism, but it well describes the phenomenon whereby much less rain falls on the lee side of a mountain range compared with the windward side. Last week produced one of the best examples of the rain-shadow effect we have seen in the UK in recent years thanks to a persistent southwesterly airflow.
Things are very different on the leeward side of the mountains. The air-mass has now lost much of its moisture, and as the winds descend the lee slope the air becomes denser again, and therefore warmer. As it warms up its capacity to hold moisture increases again, thus it is no longer saturated. The mechanism which produced the persistent rain on the windward slope is now switched off, the rain stops, and the clouds dissipate.
Last week's rain shadow effect (see plot above) was very prominent in the shelter of the Scottish Highlands. During the week ending 0600 on Saturday (Jan 19) almost 100mm of rain was recorded in the Strath of Orchy in Argyllshire and an estimated 150mm fell in the upper parts of nearby Glen Strae and Glen Kinglass. By contrast no measurable rain at all fell at Kinloss in Morayshire, and only 2mm at Aberdeen. The effect was also well illustrated in northern England where Shap in Cumbria recorded 83mm of rain compared with 4mm at Newcastle, and also in Wales and the Midlands with 96mm at Capel Curig in Snowdonia but only 2mm at several sites in the Midlands. | <urn:uuid:8883653a-8aee-43cb-8b53-ebe9bd34cc3a> | 2.859375 | 365 | Nonfiction Writing | Science & Tech. | 48.883738 |
TEXTAREA - Multi-line Text Input
The TEXTAREA element defines a form control for the user to enter multi-line text input. While TEXTAREA is most useful within a FORM, HTML 4.0 allows TEXTAREA in any block-level or inline element other than BUTTON. However, Netscape Navigator will not display any TEXTAREA elements outside of a FORM.
The initial value of the TEXTAREA is provided as the content of the element and must not contain any HTML tags. When a form is submitted, the current value of any TEXTAREA element within the FORM is sent to the server as a name/value pair. The TEXTAREA element's NAME attribute provides the name used.
The required ROWS and COLS attributes specify the number of visible rows and columns, respectively, in a visual browser. These attributes provide a guide for the user rather than a restriction; browsers allow an unlimited amount of text input in theory, though in practice many browsers limit the contents of a TEXTAREA to 32 or 64 kilobytes. Author restrictions on the amount of data entered should be enforced by the CGI script or Java servlet handling the form.
The boolean READONLY attribute, new in HTML 4.0 and poorly supported by current browsers, prevents the user from editing the content of the TEXTAREA. Read-only elements are still submitted with the form. The DISABLED attribute, also poorly supported, disables the TEXTAREA. Disabled elements are read-only elements with the added restrictions that the values are not submitted with the form, the elements cannot receive focus, and the elements are skipped when navigating the document by tabbing.
The ACCESSKEY attribute specifies a single Unicode character as a shortcut key for giving focus to the TEXTAREA. Authors can set the access key on the TEXTAREA element or the LABEL element associated with it. Entities (e.g. é) may be used as the ACCESSKEY value.
The TABINDEX attribute specifies a number between 0 and 32767 to indicate the tabbing order of the element. A TEXTAREA with TABINDEX=0 or no TABINDEX attribute will be visited after any elements with a positive TABINDEX. Among positive TABINDEX values, the lower number receives focus first. In the case of a tie, the element appearing first in the HTML document takes precedence.
The TEXTAREA element also takes a number of attributes to specify client-side scripting actions for various events. In addition to the core events common to most elements, TEXTAREA accepts the following event attributes:
- ONFOCUS, when the element receives focus;
- ONBLUR, when the element loses focus;
- ONSELECT, when text in the element is selected;
- ONCHANGE, when the element loses focus and its value has changed since it received focus.
Copyright © 1998 by Liam Quinn. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/). | <urn:uuid:fbce2fc6-6a88-4729-8221-563495a12ef0> | 2.75 | 656 | Documentation | Software Dev. | 40.277357 |
Tungsten: the essentials
Pure tungsten is a steel-gray to tin-white metal. Tungsten has the highest melting point and lowest vapour pressure of all metals, and at temperatures over 1650°C has the highest tensile strength. The metal oxidises in air and must be protected at elevated temperatures. It has excellent corrosion resistance and is attacked only slightly by most mineral acids.
Tungsten: historical information
Tungsten used to be known as wolfram (from wolframite, said to be named from wolf rahm or spumi lupi, because the ore interfered with the smelting of tin and was supposed to devour the tin). The de Elhuyar brothers found an acid in wolframite in 1783 that they succeeded in reducing to the elemental metal with charcoal.
Tungsten: physical properties
Tungsten: orbital properties
Isolation: coming soon!
WebElements now has a WebElements shop at which you can buy periodic table posters, mugs, T-shirts, games, molecular models, and more. | <urn:uuid:2c0fde25-fe72-4273-8b07-11be50eb012b> | 2.9375 | 228 | Knowledge Article | Science & Tech. | 38.422224 |
FishBaseFishBase is a comprehensive database of information about fish.
As of 2003, it included descriptions of over 27,000 species, over 137,000 common names in hundreds of languages, over 34,000 pictures, and references to over 29,000 works in the scientific literature.
In 1987, Daniel Pauly, inspired by cataloging work of Walter Fischer for the FAO in the 1970s, proposed a standardized database for fish species, originally calling it the "ICLARM Software Project". The following year he began to work with Rainer Froese, who had been working on an expert system to identify fish larvae. After an abortive attempt to build a system using PROLOG, Froese switched to DataEase, a relational database for DOS. In 1989 the project received its first grant.
In 1993 the project switched to Microsoft Access, and 1995 the first CD-ROM was released as "FishBase 100". Its initial reviews in scientific journals admired the scope but criticized the many gaps in coverage. Subsequent CD releases have come annually, with the FishBase 2000 release needing four CDs.
FishBase first appeared on the World Wide Web in August 1996, and hired a webmaster in the following year. Eventually the complete data of the CDs became available online.
As awareness of FishBase has grown among fish specialists, it has attracted several hundred contributors and collaborators. In order to preserve its value as a scientific database, FishBase is not allowed to include original data; all of its content must be based on previously-published material.
Source | Copyright
Webmasters: Add your website here:
Readers: Edit |
Discovery, history and establishment of weather stations on Bouvet Island, South Atlantic Ocean. Includes map of Bouvet
World Factboook: Bouvet Island
Information on the location and size of the Norwegian territory.
Temperature and atmospheric pressure readings from the sea-ice buoy on the island.
FishBase: List of Marine/Brackish Fishes for Bouvet Island
Listing and illustrated entries on species native to the island. Includes detailed information on each species.
Bouvet Island Dxpedition 2000
Describes Dr Chuck Brady's scientific expedition to the island.
Maps of the islands and features in and around Bouvet. | <urn:uuid:e3c0fae9-763b-4561-a5d7-f74cf0608fca> | 2.96875 | 467 | Knowledge Article | Science & Tech. | 36.067357 |
Partial Pressure and Kp
In a mixture of two or more gases, each component gas contributes to the total pressure of the system. For example, the earth's atmosphere is made up of (by mole percent) 78% nitrogen, 21% oxygen, .9% argon, .03% carbon dioxide, and other trace gases. Each gas contributed to the total pressure of 1 atm in accordance with its percent: for example, 78% of the 1 atm total pressure is .78 atm; argon contributes only .009 atm to the mixture.
The pressure each gas contributes to the total mixture is called its partial pressure; the rule governing them is Dalton's Law of Partial Pressures, which states that the total pressure is the sum of the pressures of the component gases. Furthermore, through a proof using the Ideal Gas Law, we can show that the pressure of each component gas is directly proportional to its mole fraction. The mole fraction (symbol: X) is simply the number of moles of the sample gas over the total number of moles. For example, if a box of normal air contains 5 moles of gas and 3.9 moles of nitrogen, the mole fraction of nitrogen would be XN2 = 3.9 mol / 5 mol= 0.78. If the total pressure in the box is 1.5 atm, the partial pressure of nitrogen is 0.78 * 1.5 atm = 1.17 atm.
Since partial pressure is directly related to the number of moles present, a gas' partial pressure can be substituted for its concentration in an equilibrium constant. In this case, the subscript "p" is applied to the equilibrium constant, K, indicating the use of partial pressure instead of concentration in moles per liter. Other than the use of partial pressures in place of molarity, there is no difference in the use of Kp from the other equilibrium constants we have already discussed. | <urn:uuid:439c7842-81ef-46bb-9008-4aae2eac5679> | 3.765625 | 400 | Academic Writing | Science & Tech. | 62.557762 |
2007-10-28 / 19:59 / dave
From the wikipedia entry
Forth parsing is simple, as it has no explicit grammar. The interpreter reads a line of input from the user input device, which is then parsed for a word using spaces as a delimiter; some systems recognise additional whitespace characters. When the interpreter finds a word, it tries to look the word up in the dictionary. If the word is found, the interpreter executes the code associated with the word, and then returns to parse the rest of the input stream. If the word isn’t found, the word is assumed to be a number, and an attempt is made to convert it into a number and push it on the stack; if successful, the interpreter continues parsing the input stream. Otherwise, if both the lookup and number conversion fails, the interpreter prints the word followed by an error message indicating the word is not recognised, flushes the input stream, and waits for new user input.
[Historical note: If the execution model that FORTH uses looks strange from the following paragraphs, then it was motivated entirely by the need to save memory on early computers. This code compression isn't so important now when our machines have more memory in their L1 caches than those early computers had in total, but the execution model still has some useful properties...
One interesting consequence of using a linked list is that you can redefine words, and a newer definition of a word overrides an older one. This is an important concept in FORTH because it means that any word (even "built-in" or "standard" words) can be overridden with a new definition, either to enhance it, to make it faster or even to disable it. However because of the way that FORTH words get compiled, which you'll understand below, words defined using the old definition of a word continue to use the old definition. Only words defined after the new definition use the new definition.
From Jones' Forth file
\\ Now we can use [ and ] to insert literals which are calculated at compile time. (Recall that \\ [ and ] are the FORTH words which switch into and out of immediate mode.) \\ Within definitions, use [ ... ] LITERAL anywhere that ‘…’ is a constant expression which you \\ would rather only compute once (at compile time, rather than calculating it each time your word runs). : ‘:’ [ \\ go into immediate mode (temporarily) CHAR : \\ push the number 58 (ASCII code of colon) on the parameter stack ] \\ go back to compile mode LITERAL \\ compile LIT 58 as the definition of ‘:’ word ;
Forth's design seems driven by efficiency. But as the quote says, that gives it some interesting properties.
The lack of grammer makes parsing trivial but doesn't seem to limit expressiveness.
] words were particularly pretty. They allow Jones' trick--inserting character literals at compile time--and also peeking inside words while you're defining them with something that looks like a syntax. Similar for the
) words for comments.
The uniform syntax and stack based operations also make for compact code. I guess the same can be said for Lisp/Scheme. Also like Lisp, the philosophy of Forth seems to be "here is a small set of orthogonal tools, use them to quickly shape your own universe!"
Implementing the dictionary as a linked list provides an elegant way to allow extension without breaking existing words. The unfortunate downside is that you can't use "virtual" words: have old words call new code. That keeps us from defining a debugging version of a word and watching output then deleting it and reverting to the old definition.
I played around with manually hacking a words memory to change the call from an old word (
MAX) to a new one (
MAXD, max with debugging output added). The memory looked right when
dumped, but the new code didn't seem to be called. But Forth is so low-level I can imagine a Forth hacker could come up with a word--
VIRTUAL?--that would make words late-binding.
Some quick googling turned up a few articles:
- Does Late Binding Really Have To Be Slow?
- Dynamic Binding
- An Assembly Programer's Approach to Object-oriented Forth (not strictly the same thing, but interesting)
But I didn't read any in depth, mostly because for me this is
So Forth is pretty neat but I don't think I'll be using it anytime soon. It's niche seems to be embedded programming or code micro-management. Neither is part of making interactive SVG graphs which is what I'm supposed to be doing.
If I want to do any more, I'd probably take a look at Factor which claims to be heavily influenced by Forth. | <urn:uuid:ed7f545e-027b-453e-a2af-30429432c2f2> | 3.859375 | 1,007 | Personal Blog | Software Dev. | 50.376964 |
At time there are talks about quantum computers and lot of talks and discussion on its exponential speed. But studying in some more details it makes reference to "Heisenberg uncertainty principle", which simply says that either position or momentum can be calculated for any electron. If we already know the limitation, then in which direction this research is going?
Quantum Computers can process information in a different way then classical computers the main isuues is how to use classical input to "convince" the qbit to process what we are asking and then give an answer that we can use in a positive way. Research is progressing towards a quantum level interface that can account for decoherence between the information we give and a understandable answer coming out.
In other words the language barrier between classical people and quantum interpretation. There is no technical limitation to QC's at this time only a limit of our ability to minipulate qbit s the do What we want.
http://www.cra.org/ccc/docs/init/Quantum_Computing.pdf is a PDF document link to the currently imposed limitations of quantum computers. | <urn:uuid:3b8c46d6-1647-4f0e-834f-e8cb5a5226ab> | 2.75 | 230 | Q&A Forum | Science & Tech. | 42.095508 |
Polar coordinatesThe representation of a complex number as a sum of a real and imaginary number, z = x + iy, is called its Cartesian representation.
Recall from trigonometry that if x, y, r are real numbers and r 2 = x 2 + y 2, then there is a unique number θ with 0 ≤ θ < 2π such that
sin(θ) = y / r.
That number is
|θ||=||cos -1(x / r),|
|=||sin -1(y / r)|
|=||tan -1(y / x)|
We can therefore express any complex number z = x + iy as
|z||=||| z | (x / | z | + iy / | z |)|
|=||| z | (cos θ + i sin θ)|
|=||| z | e iθ ,|
where θ = tan -1(y / x). The angle or argument θ is measured in radians, and it is written as arg(z). So we have the polar representation of any complex number z as
The two representations are related by
The values x and y are called the Cartesian coordinates of z, while r and θ are its polar coordinates. Note that r is real and r 3 0.
Note that for any integer K,
This is because
Thus, the polar coordinates (r, θ) and (r, θ + 2Kπ) for any integer K represent the same complex number. Thus, the polar representation is not unique; by convention, a unique polar representation can be obtained by requiring that the angle given by a value of θ satisfying 0 ≤ θ < 2π or -π < θ ≤ π.
|The polar representation of the number 1 is 1 = 1 e i0. Notice that it is also true that 1 = 1 e i2π, because the sine and cosine are periodic with period 2π. The polar representation of the number -1 is -1 = 1 e iπ. Again, it is true that -1 = 1 e i3π, or, in fact, -1 = 1 e iπ + K2π for any integer K.|
ProductsProducts of complex numbers represented in polar coordinates are easy to compute. If zi = ri e iθi , then
Thus, the magnitude of a product is a product of magnitudes, and the angle of a product is the sum of the angles,
arg(z1 z2 ) = arg(z1 ) + arg(z2 )
We can use the polar representation to find the n distinct roots of the
equation z n = 1. Write z = re
iθ, and 1 = e
which gives r = 1 and θ = 2kπ / n, k = 0, 1, ... , n - 1. These are called the n roots of unity.
Figure: The 5 roots of unity. | <urn:uuid:cba335e3-a7f4-4777-8c73-6cfdf2fcd305> | 4.25 | 641 | Tutorial | Science & Tech. | 80.570712 |
Monday, April 4, 2011
Energy: Understanding Nuclear Energy
In light of recent events in Japan, or just in the course or your curriculum, you may be looking for ways to help your students understand nuclear energy.
I just stumbled across this publication, Nuclear Experiments You Can Do, from the Charles Edison Fund..
The pdf file includes simple models/demonstrations for splitting an atom and chain reactions, as well as more
advanced demonstrations related to nuclear energy and radioactivity.
I wanted to pass this your way as quickly as possible, since it is a timely topic. As a result, I haven't looked through the other experiments available, but they could very well be worth taking a look at. | <urn:uuid:c4cb84c7-c861-4daa-be41-e77f7ed18194> | 2.71875 | 146 | Personal Blog | Science & Tech. | 46.351299 |
In the 1950s, the US Air Force was worried about the survival of their pilots if forced to eject at high altitude. Tests with dummies didn’t go so well, so they worked on developing a new parachute design that wasn’t so likely to kill its wearer. But eventually, a human being had to test it. That was Project Excelsior: get Joseph Kittinger to jump from progressively higher balloons. Kittiger’s final jump, in 1960, set records that lasted for decades: a 102,800 feet (31,333 m) descent and falling for 4:36 minutes before opening his parachute. He came close to the speed of sound, but didn’t quite make it (614 miles per hour or 988 km/h). (It’s worth reading the linked references: Kittiger’s jumps were incredibly risky, and nearly failed.)
Several of those records were broken yesterday. Felix Baumgartner stepped out of a balloon at 128,100 feet (39,044 m), and spent 4:20 in free fall (Kittinger still holds the time record). He hit 833.9 miles per hour (1342 kph) on his way down, exceeding the local speed of sound: it gets complicated because the speed of sound varies with altitude, mostly due to changes in atmospheric temperature. Kittinger was part of Baumgartner’s team.
Dr. Jon Clark was also a member of the prep team. Dr. Clark, a former NASA space shuttle crew surgeon, has become increasingly interested in high altitude human survival since his wife Laurel Clark died aboard Columbia in 2003. One of the fascinating things about this high-altitude human descent: nobody knew what would happen to the human body when it exceeded the speed of sound.
Since Baumgartner landed safely, fears that he would be battered to death as parts of him went supersonic or subsonic at different times were apparently unfounded. It will be fascinating to see what kind of new scientific and medical insights come from his telemetry. Even with all we know about human physiology and all the places we’ve sent human beings, from the Moon to the bottom of the ocean, there’s still plenty we don’t know.
“Usually when a doctor shows up to a press conference, we’re having a bad day,” said mission medical director Jonathan Clark. The data from Baumgartner’s jump has yet to be fully analyzed, but Clark said the data collected “is going to break incredible new ground.”
Incidentally, the first human creation to break the sound barrier? The bullwhip.
(Thanks to Micah Joel for the idea for this post.) | <urn:uuid:a9615d07-315d-4ca1-bec2-35e4ee6d4f79> | 2.96875 | 571 | Personal Blog | Science & Tech. | 63.602215 |
Hair color and static
The hypothesis that hair color will not affect the amount of static electricity produced is proven to be correct.
Natural hair is made from keratin which is the same type of protein that is also found on nails and skin. The static charges in our hair are carried by keratin. The proteins that determine the color of hair do not affect the ability of the keratin to carry static. Therefore, the color of hair does not influence the amount of static electricity produced by the hair. However, the physical properties of the hair, such as its thickness, can affect the amount of static charge produced on.
The experiment can also be done using a comb instead of a balloon.
Try to repeat the experiment using different types of hair like curly, wavy and straight.
What if the hair is wet? Do you think the amount of static electricity produced will be greater or less?
Static electricity - http://en.wikipedia.org/wiki/Static_electricity
Static electricity - http://science.howstuffworks.com/vdg1.htm | <urn:uuid:1037c301-9a6c-4727-aeb5-ca2d56588db2> | 3.15625 | 220 | Tutorial | Science & Tech. | 52.602379 |
Science Fair Project Encyclopedia
Complete algebraic variety
- X × Y → Y
is a closed map, i.e. maps closed sets onto closed sets. (NB Here the cartesian product variety does not carry the product topology, in general; the Zariski topology on it will except in very simple cases have more closed sets.)
The most common example of a complete variety is a projective variety, but there do exist complete and non-projective varieties in dimensions 3 and higher. The first example of a non-projective complete variety was given by Heisuke Hironaka. An affine space of dimension > 0 is not complete.
The morphism taking a complete variety to a point is a proper morphism, in the sense of scheme theory. An intuitive justification of 'complete', in the sense of 'no missing points', can be given on the basis of the valuative criterion of properness , which goes back to Claude Chevalley.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:de5b1578-62fc-4074-bc66-68d6ce805ea5> | 3.21875 | 232 | Knowledge Article | Science & Tech. | 41.014242 |
Ever Heard of a Butterfly Farm?
Did you know that some butterflies are as big as dinner plates? That they're talented chemists? That the international butterfly trade is a booming business?
Most of the world's butterflies, and certainly its largest and most beautiful ones, are found in tropical rain forests. Habitat destruction has greatly endangered a number of species, including the spectacular Queen Alexandra's Birdwing. Fortunately, butterflies can be farmed (though not quite like lettuce), providing a small-scale economic alternative to logging or oil palm plantations.
A successful twenty-year-old program in Papua New Guinea uses a method called butterfly ranching, in which wild adults feed and lay eggs in gardens planted on the edge of existing forest. It's ideal from a conservation point of view because the local ranchers become protectors of the forest as the source of their livelihoods. Butterfly farming requires a good grasp of butterfly biology, which was also key to the rescue of the Schaus swallowtail butterfly. | <urn:uuid:22eed861-6c04-4063-ab4e-e48fda5b0975> | 3.65625 | 202 | Knowledge Article | Science & Tech. | 42.236571 |
An air bubble of volume 21 cm3 is at the bottom of a lake 40 m deep where the temperature is 3.0°C. The bubble rises to the surface, which is at a temperature of 25°C. Take the temperature of the bubble to be the same as that of the surrounding water. What is the volume of the bubble just as it reaches the surface?
Answer in cm^3 | <urn:uuid:b03af770-0eff-401e-88e5-e6bbd15874db> | 3.140625 | 82 | Q&A Forum | Science & Tech. | 79.224817 |
Mock-up of the XMM-Newton at the Cité de l'espace, Toulouse
|Launch date||10 December 1999|
|Launched from||Guiana Space Centre, Kourou, French Guiana, South America|
|Launch vehicle||Ariane 5|
|Mission length||13 years, 4 months, and 20 days elapsed|
|Type of orbit||Elliptical|
|Orbit height||7,000 to 114,000 km|
|Orbit period||48 hours|
|Collecting area||4300 cm² (three mirror-assemblies of 1400 cm² each)|
|Focal length||7.5 m|
Originally known as the High Throughput X-ray Spectroscopy Mission it was placed in a very eccentric 48 hour elliptical orbit at 40°; at its apogee it is nearly 114,000 kilometres (71,000 mi) from Earth, while the perigee is only 7,000 kilometres (4,300 mi)
The satellite weighs 3,800 kilograms (8,400 lb), is 10 metres (33 ft) long and 16 metres (52 ft) in span with its solar arrays deployed. It holds three X-ray telescopes, developed by Media Lario of Italy, each of which contains 58 Wolter-type concentric mirrors. The combined collecting area is 4,300 cm². The three European Photon Imaging Cameras (EPIC) are sensitive over the energy range 0.2 keV to 12 keV. Other instruments onboard are two reflection grating spectrometers which are sensitive below ~2 keV, and a 30 centimetres (12 in) diameter Ritchey-Chretien optical/UV telescope.
The mission was proposed in 1984 and approved in 1985; a project team was formed in 1993 and development work began in 1996. The satellite was constructed and tested from March 1997 to September 1999. Launched in Dec 1999, in-orbit commissioning started Jan 2000, and the first images were published Feb 2000. The original mission lifetime was two years, but it has now been extended for further observations until at least 2010, and again until 2012, and technically the observatory could operate until beyond 2018.
Observations are managed and archived at the European Space Astronomy Centre (formerly known as VILSPA) at Villafranca, Spain. Until March 2012 the scientific data placed into the archive and distributed to observers were processed by the XMM-Newton Survey Science Centre led by the University of Leicester, England. After this date, responsibility for data processing transferred to the Science Operations Centre at ESAC.
The European satellite XMM-Newton (X-ray Multi Mirror), built under contract to ESA by a consortium of 35 European companies with Astrium as prime contractor, by far excels its predecessor, the Astrium-built ROSAT satellite.
The observational scope of XMM Newton includes the detection of X-ray emissions from Solar System objects, detailed studies of star-forming regions, investigation of the formation and evolution of galaxy clusters, the environment of supermassive black holes and the mapping of the mysterious "dark matter".
The object SCP 06F6, discovered by the Hubble Space Telescope (HST) in February 2006, was then observed by XMM Newton in early August 2006, and appeared to show an X-ray glow around it two orders of magnitude more luminous than that of supernovae.
In June 2011, a team from the University of Geneva, Switzerland, reported XMM-Newton seeing a flare that lasted four hours at a peak intensity of 10,000 times the normal rate, from an observation of Supergiant Fast X-Ray Transient IGR J18410-0535, where a blue supergiant star shed a plume of matter that was partly ingested by the smaller neutron star with the accompanying X-ray emissions.
Each telescope consists of 58 600 mm-long shells, with diameters from 306 to 700 millimetres, and thickness linearly dependent on the diameter increasing from 470 µm at the small shells to 1070 µm at the large one; the fully assembled telescope has gaps of about one millimetre between the shells. The shells are made by electroforming onto a highly polished aluminium mandrel, starting with a 250 nm layer of vapour-deposited gold that becomes the reflecting surface, then the nickel support; the mandrels are reusable but a different one is needed for each shell. The electroforming deposits nickel at a rate of 10 µm per hour. The mandrels were manufactured at Carl Zeiss, and the electroforming and final assembly performed at Media Lario; Kayser-Threde also played a role.
The shells are glued into grooves in an Inconel spider, which keeps them aligned to within the five-micron tolerance required to get adequate X-ray resolution.
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Thu Jan 08 10:22:22 GMT 2009 by Colin Barras
The fuel cell is similar in some ways to a non-rechargeable battery, but there are important differences. Batteries operate in a sealed environment, whereas fuel cells need to receive oxygen, and release water and/or CO2 depending on the cell type. But according to the paper's authors, the key difference between this (or any) fuel cell and a battery is that it can delivery both high energy and power density simultaneously. Batteries provide either one or the other. For instance a watch battery delivers high energy density for years but works at low power. A car battery can deliver high power - enough to start the engine - but only for a very short amount of time before it burns out, which leaves a lot of unused chemical energy within the battery that can't be accessed. A fuel cell can give high energy and power density until all of the fuel is exhausted.
Colin Barras, online technology reporter | <urn:uuid:974e2630-e6f5-4095-b1a3-bd7d151831c9> | 3.78125 | 208 | Comment Section | Science & Tech. | 38.660172 |
Over the last few years, knowledge about the effects of rising heat and CO2 levels in the atmosphere on coral reefs, those bizarre, multicultural underwater gardens, has proliferated. One of the newest reports, published this past March, predicts that if atmospheric carbon levels reach double what they are now – 750 parts per million – coral reefs will start to grow so slowly that they won’t keep themselves from dissolving.
Coral has already been dubbed a canary in a coalmine, due to its sensitivity to temperature and acidity, which make it a kind of first warning for the environmental changes wrought by rising global temperature and atmospheric carbon. We dive in to that canary-like sensitivity, and the complex life of a reef, in this new PopSci Comic.
Next: Coral (Up Close and Personal)
Next: Coral Needs Carbonate
Next: Disappearing Reefs
Next: The Bright Side
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more. | <urn:uuid:b4f4893c-4d73-42f6-95b6-e8ba9a7f2a17> | 3.578125 | 241 | Truncated | Science & Tech. | 32.240406 |
As Thurston’s article approached its 30th anniversary this year, all but four of the 23 main questions had been settled, including the geometrization conjecture, which the Russian mathematician Grigori Perelman proved in 2002 in one of the signal achievements of modern mathematics. The four unsolved problems, however, stubbornly resisted proof.
“The fact that we couldn’t solve them for so long meant that something deep was going on,” said Yair Minsky, of Yale University.
Finally, in March, Ian Agol, of the University of California at Berkeley, electrified the mathematics community by announcing a proof to “Wise’s conjecture,” which settled the last four of Thurston’s questions in one stroke.
Mathematicians are calling the result the end of an era.
“The vision of three-manifolds that Thurston articulated in his paper, which must have looked quite fantastic at the time, has now been completely realized,” said Danny Calegari, of the California Institute of Technology. “His vision has been remarkably vindicated in every way: every detail has turned out to be correct.”
“I used to feel that there was certain knowledge and certain ways of thinking that were unique to me,” Thurston wrote when he won a Steele mathematics prize this year, just months before he died in August at 65. “It is very satisfying to have arrived at a stage where this is no longer true — lots of people have picked up on my ways of thought, and many people have proven theorems that I once tried and failed to prove.”
Agol’s result means that there is a simple recipe for constructing all compact, hyperbolic three-manifolds — the one type of three-dimensional shape that had not yet been fully explicated.
“In a precise sense, we now understand what all three-manifolds look like,” said Henry Wilton, of University College London. “This is the culmination of a massive success story in mathematics.”
Thurston’s program tried to do for three-dimensional manifolds what mathematicians had successfully done more than a century earlier for two-dimensional manifolds. As a warm-up for understanding three-dimensional manifolds, let’s look under the hood at the classification of “compact, orientable” surfaces (finite surfaces with no punctures or gashes and a consistent sense of orientation).
To tackle this classification problem, mathematicians showed that, given an arbitrary surface, it is possible to progressively simplify it by cutting it open along curves until the surface completely opens out into a flat polygon.
Figure 1. Cutting a torus open along loop A yields a cylinder. Cutting further, along loop B, unfurls the cylinder into a square.
Image: Courtesy of the Simons Foundation
Figure 2. Cutting a double torus along loops A, B, C and D yields an octagon.
Image: Courtesy of the Simons Foundation
It’s easy to see how to do this with, say, a torus: first cut it open along loop A in Figure 1, producing a cylinder. Next, cut along loop B, flattening the cylinder out into a square. It’s a little harder to see, but cutting along the four curves in Figure 2 converts a double torus (a torus with two holes) into an octagon. Similarly, for any n-holed torus, we can cut along 2n loops to flatten out the surface into a 4n-gon.
Given an arbitrary, unidentified surface, we can try to simplify it (and ultimately identify it) by dissecting it in a similar way. Provided that the surface is not a sphere, topologists have shown that it must contain some embedded loops (loops that don’t intersect themselves) that cannot be pulled down to a single point, similar to loops A and B on the torus. Dissecting the surface along one of these loops removes some of the surface’s interesting topological features. Mathematicians have shown that there are only a finite number of times we can cut in this way before we have reduced the surface to a flat polygon.
Once we have simplified our surface down to a polygon, it’s fairly simple to see that when we re-glue the sides to recover our original surface, we must produce a torus, or a double torus, or a triple torus, and so on. After all, the first gluing will turn the polygon into a tunnel-shaped surface, and then each subsequent gluing will either introduce a new tunnel-shaped handle on the surface or simply sew up some open seams. When we’re finished, the result is a torus surface with some number of holes.
This approach does more than just show that the surface is topologically equivalent to a sphere or a torus of some type: it also gives a way to endow the surface with a simple, uniform geometric structure. | <urn:uuid:9d1fe6f9-c61c-4f9c-be94-878581f8de0f> | 2.78125 | 1,068 | Knowledge Article | Science & Tech. | 37.76296 |
In the summer of 2006 Marshall W. Nirenberg chanced on a just published biography of a prominent molecular biologist. It was entitled Francis Crick: Discoverer of the Genetic Code.
“That’s awful!” he thought. “It’s wrong—it’s really and truly wrong!”
Nirenberg himself, along with two other scientists, had received the Nobel Prize in Physiology or Medicine in 1968 “for their interpretation of the genetic code and its function in protein synthesis,” and neither of his co-winners happened to be named Crick. (They were in fact Robert W. Holley and Har Gobind Khorana.)
The incident was testimony to the inconstancy of fame. And it was by no means an isolated example, as Nirenberg knew from the long and bitter experience of seeing similar misattributions elsewhere. The breaking of the genetic code was one of the most important advances in molecular biology, secondary only to the discovery of the double-helical structure of DNA in 1953 by Crick and James D. Watson. But whereas they are household names, Marshall Nirenberg certainly is not.
Nirenberg, 80, is now a laboratory chief at the National Institutes of Health, where he has spent his entire career. His otherwise standard-issue science office is distinguished by framed copies of his lab notebooks tabulating the results of his genetic code work. Many of the original documents and some of the instruments he used in this research are on display on the first floor of the NIH Clinical Center, in the exhibit “Breaking the Genetic Code.”
“People had hypothesized that there was a genetic code in the 1950s,” Nirenberg says. “But nobody knew how proteins were synthesized. Nobody knew how it was done.”
When Nirenberg arrived at the NIH in 1957 as a biochemistry postdoc, cracking the genetic code was not the first item on his agenda. Ambitious as he was, deciphering the language of life seemed too daunting a project—at least initially.
Consider the problem. The information inside a DNA molecule is encoded by the nucleotide bases adenine, thymine, guanine and cytosine (A, T, G and C). The full sequence of those four nucleotides, which run in nearly endless combinations up and down the strands, constitutes a molecular message for building an organism. Each three-letter sequence of nucleotides (or codon) stands for a specific amino acid. GCA, for example, codes for alanine, one of the 20 different amino acids found in animal organisms. Cellular machinery strings together the amino acids to form the proteins that make up a living being. The task of deciphering the genetic code, then, was reduced to the problem of finding out which exact three-letter sequences stood for which precise amino acid.
In 1955 Crick himself tried to solve the problem, not by experimenting but essentially by thinking, just as a cryptanalyst might try to crack a coded message. He got nowhere and abandoned the attempt. (People today may attribute the discovery of the code to Crick because of his theoretical efforts and because in 1966, based on the experiments of others, he drew up one of the first charts of the complete code.)
Nirenberg started work on the code around 1960, but he had to confront a preliminary problem first. “My question was, Is DNA read directly to protein?” DNA, he knew, resided in the cell nucleus, whereas protein synthesis took place in the cytoplasm. Therefore, either DNA itself exited the nucleus, or some intermediate molecule did—what we now know as messenger RNA. “So the question I was asking was, Does messenger RNA exist? And I thought if I made a cell-free protein-synthesizing system from E. coli and added DNA to it, or RNA, then I would see if they stimulated protein synthesis.”
The so-called cell-free system is one of the stranger tools of experimental biology. Also known as cell sap, it is a mass of cells denuded of their membranes, the result being a quantity of free cytoplasm in which the original cellular organelles and other structures remain largely intact and functional. In late 1960 Nirenberg and Heinrich Matthaei, who had joined Nirenberg’s lab, found that putting RNA into the cell-free system caused it to synthesize proteins but that adding DNA did not. | <urn:uuid:5359d1d2-6647-44bd-bb29-7195b9906057> | 2.90625 | 941 | Nonfiction Writing | Science & Tech. | 45.857469 |
The death of radio astronomer Sir Bernard Lovell
The Lovell Telescope at Jodrell Bank, Cheshire, UK on 12 May 1976. Picture Nick Lomb
Sir Bernard Lovell, the man forever associated with the giant 250 foot (76-metre) radio telescope near Manchester UK, has died on 6 August 2012 at the age of 98. At his death he was Emeritus Professor of Radio Astronomy at the University of Manchester.
Born in 1913, Sir Bernard studied at the University of Bristol, but moved in 1936 to the University of Manchester. During the Second World War he did important radar work. After the war he wanted to use his knowledge of radar and surplus equipment to study the trails left behind by cosmic rays. In December 1945 he set up two trailers full of radar apparatus plus a diesel generator in a field in the Cheshire countryside where the university happened to have a botanical outstation. He did receive echoes, but instead of receiving them from cosmic rays they were from the trails left behind by meteors. Henceforth meteors became the main research area of his group.
There were some people in the group though that Sir Bernard directed to the new field of cosmic noise, which later became known as radio astronomy. Amongst these was Robert Hanbury Brown who was to marry Sir Bernard’s niece and later was a professor at the University of Sydney. It was the results of Hanbury Brown and his student Cyril Hazard in radio astronomy that provided the justification for a large steerable radio telescope. Work on the telescope began with laying its foundations in September 1952 and the telescope began operating in August 1957.
The Lovell Telescope in the Cheshire countryside on 12 May 1976. Picture Nick Lomb
Costs for the telescope were larger than expected and at one stage during construction it was found that the project was about a quarter of a million pounds in debt. These financial problems were ongoing even after the completion of the telescope and Sir Bernard as director of the project would have been in serious trouble but for the launch of the first Earth-orbiting satellite Sputnik 1 soon after the telescope was completed. As the telescope could receive signals from the satellite its worth was confirmed to the public and to politicians and the financial problems disappeared.
Astronomers have used the Lovell telescope to make many significant observations that have added to our knowledge of the Universe. Today the giant radio telescope is still one of the largest steerable radio telescopes in the world. Jodrell Bank holds an important place in astronomy as indicated by the fact that later this year the headquarters of the Square Kilometre Telescope, the giant radio telescope that is to be built in South Africa and in Western Australia, is to move there.
As stated in the announcement of his death by the Jodrell Bank Centre for Astrophysics, ‘Sir Bernard’s legacy is immense, extending from his wartime work to his pioneering contributions to radio astronomy and including his dedication to education and public engagement with scientific research. A great man, he will be sorely missed.’
The announcement from the Jodrell Bank Centre for Astrophysics
Boffin: A Personal Story of the Early Days of Radar, Radio Astronomy and Quantum Optics, by R Hanbury Brown, Adam Hilger, Bristol, 1991. | <urn:uuid:df7ec3b8-73c6-4b2d-befe-59edd1335716> | 2.921875 | 669 | Nonfiction Writing | Science & Tech. | 37.963504 |
Satellites don't take videos; they capture still images. But in a new mosaic, 56 stills have been stitched together to present a seamless video flyover of what LDCM saw one day in April 2013. Read more
A field campaign called the Iowa Flood Studies (IFloodS) is taking place in eastern Iowa from May 1 to June 15, 2013. The goal is to evaluate how well rainfall data from the upcoming Global Precipitation Measurement (GPM) mission can be used for flood forecasting. GPM is scheduled for launch in early 2014. Read more
Prescribed fires should prevent blazes from raging out of control in one of Namibia’s most prized wildlife preserves. Read more
NASA scientists return to Greenland, not to investigate the ice but to learn more about the water trapped within the ice. Read more
Extreme storms such as Hurricane Sandy, Snowmageddon, and the tornadoes of 2011 have prompted questions about whether climate change is affecting the intensity of weather. Satellites, statistics, and scientific models are teaching us a lot about what we know and don't know about severe storms. Read more
Satellite images showing how our world— forests, oceans,
cities, even the Sun— has changed in recent decades.
The night side of Earth twinkles with light in these composite global and regional views. | <urn:uuid:5c9f31f7-755b-4e18-bcfc-7ba0c7164b43> | 2.90625 | 280 | Content Listing | Science & Tech. | 48.645758 |
What happens to the delicate larvae of ocean creatures when they’re exposed to increasing acid levels in the ocean? That’s the question marine biologists Steve Palumbi of Stanford and Eric Sanford of UC Davis are trying to answer through experiments with sea urchin larvae off the California and Oregon coasts.
Their theory is that the increased acidity in the oceans—caused in part by increased CO2 levels in the atmosphere—makes it difficult for marine species to grow their shells. In this short documentary, you’ll see the scientists test their theory by designing and building a time machine in their lab, transporting sea urchin babies to the ocean of the future.
This video comes courtesy of our friends Dan Griffin and Robin Garthwait of GG Films and Steve Palumbi of Stanford University. We’ll be featuring more of their great work in the coming months. In the meantime, head over to the GG Films website and Microdocs.org. | <urn:uuid:e21635b5-85d7-4cb0-8c60-95ada76d685b> | 3.6875 | 198 | Truncated | Science & Tech. | 49.787007 |
Mimer SQL Database Objects
This chapter provides a general introduction to the basic concepts of Mimer SQL databases and Mimer SQL objects.
Mimer SQL is a relational database system. This means that the information in the database is presented to the user in the form of tables. The tables represent a logical description of the contents of the database which is independent of, and insulates the user from, the physical storage format of the data.
The Mimer SQL database includes the data dictionary which is a set of tables describing the organization of the database and is used primarily by the database management system itself.
The database, although located on a single server, may be accessed from many distinct clients, linked over a network.
Commands are available for managing the connections to different databases, so the actual database being accessed may change during the course of an SQL session.
At any one time, however, the database may be regarded as one single organized collection of information.
System and Private Objects
Mimer SQL database objects can be divided into the following groups:
- System Objects
- Private Objects
Private objects belong to a schema. Private object names are local to a schema, so two different schemas may contain an object with the same name. It is also possible to have objects with the same name in a schema, if they are of different types.
The private objects in a Mimer SQL database are collations, domains, functions, indexes, methods, modules, precompiled statements, procedures, sequences, synonyms, tables, triggers, user-defined types, and views.
Private objects are usually fully identified by their qualified name, which is the name of the schema to which they belong and the name of the object in the following form: schema.object, see Qualified Object Names.
Functions, procedures, and methods may exist in multiple versions having the same name. See Mimer SQL Programmer's Manual, Parameter Overloading.
Conflicts arising from the use of the same object name in two different schemas are avoided when the qualified name is used. If a private object name is specified without explicit reference to its schema, it is assumed to belong to a schema with the same name as the current ident.
Mimer Information Technology AB
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The waters of the Dead Sea, a landlocked lake between Israel and Jordan, are the saltiest on Earth, inhospitable to all but a few hardy species of bacteria and one species of alga. How do these microbes survive? Researchers in Israel and the United States have now found the secret of at least one of them. Haloarcula marismortui (which means, roughly, salt- loving boxlike bacterium that lives in the Dead Sea) has unique proteins that protect it from the depredations of salt.
To operate normally, proteins must stay in solution, bonded to water molecules. Take away the water, and proteins precipitate, binding instead to one another and forming a whitish, dysfunctional sludge. A high concentration of salts has that effect on most proteins: the salts pull water molecules away from the proteins.
In H. marismortui, though, the proteins win the molecular tug-of- war. Structural biologist Menachem Shoham of Case Western Reserve University and his colleagues at Tel Aviv University and the Weizmann Institute of Science in Israel used X-ray crystallography--in which X-rays are bounced and scattered off protein crystals like the one shown here--to reveal the molecular structure of a common H. marismortui protein, ferredoxin. The protein turned out to be shaped like a coffee mug with a handle spiked all over with glutamic and aspartic acid, two negatively charged amino-acid building blocks with a very strong affinity for water molecules. (Water molecules have a positive charge on one end and a negative charge on the other.) The negatively charged acids snatch water away from the salt, helping to keep the protein in solution.
Shoham’s research team one day hopes to be able to graft similar amino-acid sequences onto other, salt-intolerant proteins, thereby making them soluble in saline water. In countries like Israel, where freshwater is in short supply, such a process could find wide application. For instance, industrial enzymes that are designed to degrade toxins could be dissolved in seawater or even sewage--both of which are plentiful all over the planet. | <urn:uuid:94e1e052-aac4-4844-aa29-90f4430c2a76> | 3.90625 | 442 | Knowledge Article | Science & Tech. | 34.036641 |
On this third day of our research project in the Mojave Desert, we did a series of tests on the biological soil crusts and soil samples we collected yesterday at three sites along Kelbaker Road near Baker, CA.
The laboratory building at the Desert Research Station is set up with standard equipment for chemical and biological tests, including flasks, test tubes, Bunsen burners, sinks, a fume hood, etc. Most of the detailed equipment and supplies was brought by Rakesh Mogul and the other scientists working on this project, including a centrifuge, a spectrometer, pipettes and pumps, and test kits and reagents for the extractions and analyses we’d be doing.
The students and scientists had set up a series of protocols for the tests and a plan of attack for how to identify each sample. First, a group were taking samples of the crusts at each location and extracting the DNA from them. Each time, the scoop was sterilized with a Bunsen burner. The solution was then centrifuged to settle out the non-dissolved portions. Another group was at work using polymerase chain reaction techniques to increase the DNA yield so that the final sequencing could be done in a specialized lab. We’ll have the lab look at the specific species in the crusts, including the cyanobacteria, fungi, lichens, mosses, and archaea present in these symbiotic communities.
Parag Vaishampayan worked with a group to extract ATP (adenosine triphosphate), which will give us a measure of metabolic rate in the crusts at each site. We sampled not only the crust itself but the soil directly underneath each sampled crust, and will look at ATP of the crust compared as a ratio to the ATP in the soil. The hypothesis is that the healthier crust will have a higher ratio.
Meanwhile, the soil itself was analyzed. Mary Beth Wilhelm and Liza Coe used a soil test kit to look for trace elements in the soil, such as aluminum, iron, chlorine, and magnesium. I helped do some of this analysis, since my background is in chemistry and geology. Rosalba Bonaccorsi, Ruben Hovanesian, and Leonard Bacon separated the soils using sieves to find the relative sizes of particles and materials at each site.
A final group of pre-math teachers developed a series of statistical tests to look at results of all these tests, including some ANOVA (analysis of variance) tests, which I vaguely remember from my masters degree program.
We got quite far with the tests today – it helps to have a group of people who are experienced and work well together. Although they come from all over the California State University system, the students are all in their second year in the program and know what to do and what each other’s strengths and weaknesses are. We all helped out where we had experitise. It was fun to see what college students can accomplish. We have one major remaining test for tomorrow: chlorophyll extraction and spectral analysis.
I also talked with Geoff Chu, Paul Mans, and Ryan Piaget from NASA Ames who are developing a prototype rover built from a commercial off-the-shelf RC car, with video camera provided by an Android phone controlled from a laptop over a local network. Motor servos are controlled by an Arduino brick. The point of this rover is to analyze the soil crusts remotely without having 20-odd people stomping around on them. The rover will be equipped with a stereoscopic IR camera that can read 3D depth, along with an RGB camera. My goal is to take the height data from the IR camera and convert it into a grayscale heightmap of the various crust locations, then turn the heightmap into a 3D model in Daz3D Bryce. The RGB photo will be mapped over the top of the model as a texture. Ultimately, the model can be uploaded to an online app where people can rotate and explore the crusts themselves.
We had a preliminary results meeting after supper to look at what we have so far. The ATP analysis was not consistent across sites, possibly because the results changed as the day warmed up, but we’ll send the samples to labs for more accurate results. | <urn:uuid:20d815a6-e920-48f9-a99a-93b147836454> | 2.984375 | 879 | Personal Blog | Science & Tech. | 46.993131 |
Comprehensive DescriptionRead full entry
BiologyInhabits open waters of lakes and medium to large rivers. Forms large aggregations in backwaters and other still waters during winter. Adults occur in shoals near the surface. Larvae live in littoral zone of rivers and lakes while juveniles leave shores and occupy a pelagic habitat, feeding on plankton, drifting insects or invertebrates fallen on the water surface (Ref. 59043). Feeds mainly on plankton, including crustaceans (Ref. 30578) and insects (Ref. 9696). Spawns in shallow riffles or along stony shores of lakes, occasionally above submerged vegetation (Ref. 59043). Excellent as bait for carnivorous fishes. May be captured using the smallest hook and a fly as bait. Its flesh is tasty (Ref. 30578). Of little interest to commercial or sport fisheries in its native range because of its small size (Ref. 1739). Scales were previously utilized in making Essence d"Orient, a coating for artificial pearls (Ref. 59043). | <urn:uuid:c2dfee77-f255-4d44-9a49-fb82780ecf92> | 3.140625 | 218 | Knowledge Article | Science & Tech. | 47.609019 |
See also the
Dr. Math FAQ:
0.9999 = 1
0 to 0 power
n to 0 power
0! = 1
dividing by 0
Browse High School Number Theory
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Infinite number of primes?
Testing for primality.
What is 'mod'?
- Percentages of Prime Numbers [01/31/1999]
Does the percentage of prime numbers at every power of 10 decrease until
it reaches a constant value?
- Perfect Logarithms [06/24/2002]
What can you tell me about the equation log(abc)= log(a+b+c)?
- Perfect Number [7/21/1996]
How can I find a perfect number? What are some reference books about
- Perfect Number Algorithms [03/31/1998]
What is the formula for a computer program that tests whether an integer
is a perfect integer?
- Perfect Numbers [11/10/1997]
Do the sums of the digits of perfect numbers always equal 1?
- Perfect Numbers [06/15/2002]
Please show that any even perfect number ends in 6 or 8.
- Perfect Square [10/26/2001]
If a and b are positive integers such that (1+ab) divides (a^2+b^2), show
that the integer (a^2+b^2)/(1+ab) must be a perfect square.
- Perfect Square [07/23/2001]
If g.c.d.(x, 3) = 1 and g.c.d.(y, 3) = 1, show that x^2 + y^2 cannot be
a perfect square.
- Perfect Square? [02/18/2002]
If we use the digits 1,2,3,4,5,6,7 each only once to form a 7-digit
number, can the resulting number be a perfect square?
- Perfect Square, Cube, Fourth Power [01/25/2002]
Find the least integer greater than 1 that is a perfect square, a perfect
cube, and a perfect fourth power.
- Perfect Square Equation [02/22/2002]
Prove that if n is greater than 1, then nC2 + (n-1)C2 is a perfect
- Perfect Squares and Irrational Numbers [02/13/2002]
Isn't any non-perfect square an irrational number? What is the number
0.49? Its square root is 0.7, which is neither irrational nor an integer.
- Perfect Squares: n+125 and n+201 [01/21/2002]
Find the smallest positive integer n so that n+125 and n+201 are both
- Perfect Squares with Congruences [02/16/2002]
Prove that there is no perfect square a^2 whose last digits are 35.
- Perimeter of Pascal's Triangle [06/05/2001]
Is there a general formula for finding the perimeter of Pascal's triangle
using the number of rows?
- The Phi Function [11/21/1998]
What are the conditions on n,m so that phi(n*m) = phi(n)*phi(m)? What is
- Polynomial Divisible by 7 [11/14/2001]
Prove that 2^(3n+1) + 4^(3n+1) + 1 is divisible by 7.
- Positives and Negatives with Infinity and Zero [10/05/1999]
Are there such things in math as +0, -0, and unsigned 0; and +infinity, -
infinity, and unsigned infinity? Are these different?
- Powers of 2 Proof [03/24/2003]
Prove that any number that is not a power of 2 can be expressed as a
sum of two or more consecutive positive integers, but that this is
not possible for powers of 2.
- p, p+8, p+22 Not Prime [10/16/2001]
Prove that there is no positive integer p such that each of the numbers:
p, p+8, p+22 is prime.
- Prefix for 10^30 Bytes [05/25/2000]
What do you call 1,000,000,000,000,000,000,000,000,000,000 or 10^30
- Primality Test [11/26/2001]
I want to write a program using Pascal that will verify whether a number
- Primality Testing [04/22/1998]
Is there any fomula to find if a number is a prime?
- Primality Testing [12/02/2004]
How can I determine if a given number is prime?
- Prime and Consecutive Numbers [11/16/2001]
Why are 3, 5, and 7 the only numbers that appear to be prime and
- Prime Factor [02/18/2002]
I need to prove that each integer of the form 3n + 2 has a prime
factor of this form.
- Prime Factors, Modular Arithmetic, and Using Pari [08/08/2007]
Suppose we have two positive integers 'a' and 'b'. Is there a method
to find a positive integer 'k', such that a + bk = x^2 for some
integer 'x'? In other words, how can we find a positive integer 'k',
such that 'a + bk' is a square?
- Prime Factors of 4,194,305 [09/20/1999]
How can I find the prime factors of 2^22+1?
- Prime Integer Proof [03/24/2002]
Prove that if p is a prime number greater than or equal to 5, then there
exists an integer k such that p=sqrt(24k+1).
- Prime Number 2001, Sieve of Eratosthenes [01/25/1997]
Is 2001 a prime number?
- Prime Number Formula [11/11/2001]
What formula did Leonhard Euler use to find prime numbers?
- Prime Number Proof: p_2n Greater Than 2*p_n [10/07/2001]
Prove that for n greater than 1, p_2n is greater than 2*p_n, where p_n is
the nth prime number.
- Prime Numbers [07/10/1998]
If you multiply all the prime numbers up to N together, the limit appears
to be exp(N) as N gets large. Is there a simple reason for this?
- Prime Numbers [12/15/2000]
How can I prove that if A = (P1*P2+1)^4 - 1, where P1 and P2 are two
distinct primes; then A is a multiple of three distinct primes?
- Prime Numbers and n^2-n+41 [07/23/2003]
How does n^2-n+41 work to produce a prime number for every integer
value, and why does it it fail when n = 41 ?
- Prime Numbers as the Difference of Two Squares [08/07/2002]
Express the prime numbers 7, 15, and 261 as the difference of two
- Prime Numbers between 1 and 150 [7/30/1996]
How many prime numbers are there between 1 and 150?
- Prime Numbers in Cryptography [08/14/1999]
What are some practical uses of prime numbers?
- Prime Numbers in Different Bases [10/07/1998]
Are all prime numbers the same in all bases? If 21 is a prime, are 10101
(in binary), and 15 (in hexadecimal) also primes?
- Prime Number Tests [11/12/1998]
Is the number 55409243 prime? How can you test to see whether a number is | <urn:uuid:07ad1d7c-316b-4175-b933-3229a4af6ac7> | 2.71875 | 1,727 | Q&A Forum | Science & Tech. | 87.323337 |
Wonder how the Spanish dancer, or Hexabranchus sanguineus, got its common name? When it swims, the frilled edges of its mantle resemble the color and movement of the skirts of a flamenco dancer.
When they're not swimming, Spanish dancers crawl along relatively flat surfaces with the edges of their mantle tucked up close to their bodies (see the picture). They feed on sponges and can produce a toxic chemical to protect themselves from predation.
Today’s Oil Spill Quote of the Day features Elizabeth Griffin Wilson, one of our very own scientists:
From yesterday’s Guardian:
Some 1,020 sea turtles were caught up in the spill, according to figures (pdf) today – an ominous number for an endangered species. Wildlife officials collected 177 sea turtles last week – more than in the first two months of the spill and a sizeable share of the 1,020 captured since the spill began more than three months ago. Some 517 of that total number were dead and 440 were covered in oil, according to figures maintained the Deepwater Horizon response team.
Of the approximately 100 species of cuttlefish, the Australian giant cuttlefish is the largest cuttlefish in the world. They can grow almost five feet long and weigh almost 30 pounds.
The coolest thing about these colossal cephalopods is their ability to change color for a number of reasons, including aggression, excitement, camouflage, or mating. They can change color so effectively that they can become almost entirely invisible when hiding among rocks and in caves. When they want to be noticed, they can put on a brilliant display of colors and flashes, particularly during the winter mating season.
From today's Washington Post:
The government said last week that three-quarters of the spilled oil has been removed or naturally dissipated from the water. But the crab larvae discovery was an ominous sign that crude had already infiltrated the Gulf's vast food web - and could affect it for years to come.
"It would suggest the oil has reached a position where it can start moving up the food chain instead of just hanging in the water," said Bob Thomas, a biologist at Loyola University in New Orleans. "Something likely will eat those oiled larvae ... and then that animal will be eaten by something bigger and so on."
Tiny creatures might take in such low amounts of oil that they could survive, Thomas said. But those at the top of the chain, such as dolphins and tuna, could get fatal "megadoses."
The final FOTD for Shark Week is on the fascinating great white shark, or white shark. Despite their reputation as man-eaters, great white sharks are actually more threatened by humans than vice versa.
From NPR.com today:
"It's actually round two of psychological trauma for these communities, who also in the back of their minds are already worried about hurricanes this season," said [president of the Children’s Health Fund, Dr. Irwin] Redlener, who plans to bring doctors to the Gulf in the next few weeks to provide physical and mental care for the children who are suffering nightmares or other stress, or who have rashes, breathing problems or other physical effects from the spill.
Today’s FOTD is about the beautiful zebra shark. These sharks get their name from the impressive stripes found on the juveniles.
As they grow into adulthood, these stripes change into spots, which is why this shark is occasionally also called the leopard shark. (Taxonomists even originally thought that juvenile zebra sharks were actually a different species than the adult zebra sharks because their markings are so different!)
From yesterday's New York Times:
Federal scientists and coastal residents agree in at least one respect: that the long-term effects of the spill are unknown, and that it is too early to make any conclusions about the true scale of the damage. That uncertainty leads to perhaps the most potent source of skepticism: a deep anxiety about the region’s economic future.
From yesterday’s Washington Post:
BP's well was gushing faster than expected, government experts said. The latest estimate pegs original "flow rate" at 62,000 barrels a day (2.6 million gallons), higher than the last estimate of 35,000 to 60,000 barrels. As the reservoir was depleted, the rate was reduced to 53,000 barrels a day. They calculated the total oil coming from the blown-out well at 4.9 million barrels, more than 18 times the amount of oil that was spilled during the Exxon Valdez disaster.
Today’s FOTD is brought to you by the letter C, which is for cookie…and cookiecutter shark.
Unlike most of the other sharks I’ve written about so far, the cookiecutter shark is a relatively small shark; they only reach about 20 inches in length. Like some other sharks, such as great white sharks, female cookiecutters are larger than their male counterparts.
Despite their small size, these sharks still have quite a bite. They latch onto their prey and create suction with their large lips. Then they use their powerful jaws and many teeth to carve a circular chunk of flesh out of the unlucky victim. (Get it? Like a carnivorous, marine cookiecutter?)
Cookiecutter sharks attack large fish like tuna or even whales and dolphins; the prey usually survives the attack but the telltale round scar remains. They are also bioluminescent; they have a patch on their bellies that glows in the dark, deep waters where they live. They use their bioluminescence to attract potential prey.
See you tomorrow for another shark FOTD and I hope you’re enjoying Shark Week as much as I am!
- What Do Historic CO2 Levels Mean for the Oceans? Posted Tue, May 14, 2013
- U.S. Coast Guard Captures Illegal Fishermen in Texas Posted Tue, May 14, 2013
- Victory! Delaware Becomes Seventh State in U.S. to Ban Shark Fin Trade! Posted Thu, May 16, 2013
- It's Endangered Species Day! Posted Fri, May 17, 2013
- Stocks Show Signs of Recovery, But Still Work to Do Posted Fri, May 17, 2013 | <urn:uuid:d3ca5afe-b66f-400d-ba60-aa22e2afd09c> | 3.3125 | 1,302 | Personal Blog | Science & Tech. | 56.718232 |
Null Hypothesis Testing with Pearson's r
When to Use
This is straightforward. Do this when you have a sample value of Pearson’s r and you want to test the null hypothesis that the value of r in the population is zero. For example, imagine that each of 50 subjects judges the intelligence level of a stimulus person on a 1 to 7 scale and also rates their mood on a 0 to 10 scale. Imagine also that for this sample of 50 subjects, Pearson’s r is +.23. We want to test the null hypothesis that Pearson’s r in the population is actually 0 and that this sample correlation of .23 represents nothing more than sampling error.
The Test Statistic
The test statistic in this case is t. However, this statistic is not usually computed or reported. Instead, we can proceed straight to a table (see below).
The p Value
p is the probability of a value of Pearson’s r as extreme as the one you got if the null hypothesis were true. Again, you do not have to figure out the exact p value. Instead, you can just figure out whether p is lower than your α level (.05). The table at right lists these critical r values for α levels of .10, .05, .02, and .01. Note that it also lists different critical values depending on the degrees of freedom, which is the number of cases minus two (df = N – 2). Again, notice from the table that as the sample size gets smaller, the r value needed to reject the null hypothesis gets larger.
You decide to reject the null hypothesis if your sample r value is more extreme than the critical r value. This means that the probability of getting an r value at least as extreme as yours, if the null hypothesis were true, is less than 5% (or whatever α is). So you decide that the null hypothesis is not true. You fail to reject the null hypothesis if your sample r value is less extreme than the critical t value. This means that the probability of getting an r value at least as extreme as yours, if the null hypothesis were true, is greater than 5%. So you decide that the null hypothesis could be true.
A group of 50 subjects rates the intelligence of a stimulus person and rates their moods. Pearson’s r for the sample is +.23. I can look in the table for 48 degrees of freedom. It is not there, but 50 is pretty close. For an α level of .05, the critical value is .27. So I fail to reject the null hypothesis; the correlation is not statistically significant. In other words, I cannot conclude that my sample correlation reflects anything other than sampling error.
Expressing the Result in Writing
Here is how such a result might be expressed in APA style: “The correlation between intelligence ratings and mood was not statistically significant, r(48) = .23, p > .05.
TABLE: CRITICAL VALUES OF r
Click the link below for a complete table of critical values of r: http://www.gifted.uconn.edu/siegle/research/Correlation/corrchrt.htm | <urn:uuid:37ea1b80-17b4-4caf-b458-d9987c3fe34e> | 4 | 659 | Documentation | Science & Tech. | 72.433404 |
|IODP publications Expeditions Apply to sail Sample requests Site survey data Search|
Backstripping is a proven method for extracting amplitudes of global sea level from passive margin records (e.g., Watts and Steckler, 1979). One-dimensional backstripping is a technique that progressively removes the effects of sediment loading (including the effects of compaction) and paleowater depth from basin subsidence. By modeling thermal subsidence on a passive margin, the tectonic portion of subsidence can be assessed and a eustatic estimate obtained (Kominz et al., 1998, 2008; Van Sickel et al., 2004). Backstripping requires knowing relatively precise ages, paleodepths, and porosities of sediments, and each of these criteria are best obtained from borehole transects. Such transects also allow application of two-dimensional backstripping techniques that account for lithospheric flexural effects, increasing the precision of the eustatic estimates (Steckler et al., 1999; Kominz and Pekar, 2001). The eustatic component obtained from backstripping needs to be verified by comparing sea level records with other margins and those derived from δ18O estimates.
Drilling at Sites MAT-1 to MAT-3 will allow us to make precise late Oligocene to early middle Miocene eustatic estimates using one- and two-dimensional backstripping as described above. One- (Kominz et al., 1998; Van Sickel et al., 2004) and two-dimensional (Kominz and Pekar, 2001) backstripping of onshore New Jersey sites have provided preliminary amplitude estimates of 10–60 m for million year–scale variations, but the estimates are incomplete, particularly for the Miocene, because most lowstand deposits are generally not represented (Miller, Sugarman, Browning, et al., 1998; Miller et al., 2005a, and fig. F2 therein). Amplitude estimates derived from δ18O studies require assumptions about temperature and the sea level/δw calibration; although the uncertainties are large, initial eustatic estimates based on δ18O records are consistent with backstripping results (Fig. F1). Sites MAT-1 to MAT-3 are precisely located to recover as nearly a complete set of late Oligocene–middle Miocene sequences as possible and, through backstripping, provide a much more direct measure of the full range of amplitudes for this time interval.
Once we have obtained precise eustatic estimates from late Oligocene to early middle Miocene records at Sites MAT-1 to MAT-3, we will be able to extend our results to the older and younger records. Middle Miocene through recent sediments record similar clinoform geometries on the New Jersey shelf; by applying calibrations of seismic profiles and facies developed as part of this work, we should be able to derive eustatic estimates for the interval 16–0 Ma. In particular, deriving a firm, independent eustatic estimate from margin sediments will
Whereas both backstripping and δ18O methods make inherently large assumptions, the convergence of the two methods (Fig. F1) suggests that we will be able to produce a testable eustatic model for the past 42 m.y. and perhaps for the older record as well.
Shallow-water records contain unconformities observed in outcrop or in the subsurface at all spatial scales, whether they divide beds or basins. Unconformably bounded sequences are the fundamental building blocks of the shallow-water record (Sloss, 1963; Van Wagoner et al., 1990; Christie-Blick, 1991). Researchers at the Exxon Production Research Company (Vail et al., 1977; Haq et al., 1987; Van Wagoner et al., 1988; Posamentier et al., 1988) claimed that similarities in the ages of stratal unconformities pointed to global sea level (eustasy) as the overriding control. The resulting "eustatic curve" has remained controversial (e.g., Christie-Blick et al., 1990; Miall, 1991), largely because of basic assumptions about the stratigraphic response to eustatic change and because the work relies in part on unpublished data. In response to this controversy, Christie-Blick and Driscoll (1995), among others, pointed out that the fundamental enterprise of interpreting the origin of layered rocks does not really require any assumptions about eustasy. They emphasized that sequence boundaries attest to changes in depositional base level. The timing of many of the Exxon Production Research Company sequence boundaries has been validated onshore New Jersey and correlated to the δ18O proxy of eustatic change (Miller et al., 1998, 2005a), though other sequence boundaries on this and other margins may be tectonically derived. Whether sequence boundaries are caused by changes in eustasy, local tectonism, or sediment supply (Reynolds et al., 1991), disconformable surfaces irrefutably divide the shallow-water record into sequences. Whatever their cause, these stratal breaks are real and they provide an objective means of analyzing the rock record.
Facies between sequence boundaries vary in a coherent fashion, and various facies models have been proposed for shelf sedimentation (e.g., Posamentier et al., 1988; Galloway, 1989). Much work has been done by the exploration and academic communities in testing and applying these models, and much has been learned. For example, flooding surfaces (particularly maximum flooding surfaces) can be used to unravel stratigraphic stacking patterns (e.g., Galloway, 1989), whereas highstand deposits are generally regressive and commonly serve as reservoirs for oil or water resources (e.g., Posamentier et al., 1988; Greenlee et al., 1992; Sugarman and Miller, 1997; Sugarman et al., 2006). Nonetheless, predictions of facies models have not been widely successful because they are the products of many unevaluated processes (Reynolds et al., 1991).
One major reason that models are still poorly constrained is that there has been no publicly available study of continuous cores across a prograding clinoform deposit that constitutes the central element of many facies models. As a result, the water depths in which clinoforms form and the distribution of lithofacies they contain are not well known. It is widely debated whether clinoform tops ever become subaerially exposed during sea level lowstands and whether the shoreline ever retreats to (or perhaps moves seaward of) the clinoform rollover (Fulthorpe and Austin, 1998; Austin et al., 1998; Steckler et al., 1999; Fulthorpe et al., 1999). Settling these controversies will have significant implications on our understanding of how sequence boundaries develop and how much of the facies distribution within clinoforms can be attributed to eustasy. Some workers assume that the shoreline is always located at the clinoform rollover (e.g., Posamentier et al., 1988; Van Wagoner et al., 1990; Lawrence et al., 1990). Others have presented models of basin evolution that suggest the shoreline and the clinoform rollover can move independently of each other (e.g., Steckler et al., 1993, 1999). The sea level estimates of Greenlee and Moore (1988) argue that sea level falls expose an entire continental shelf and that strata onlapping clinoform fronts are coastal plain sediments deposited during the beginning of the subsequent sea level rise. Many researchers (e.g., Steckler et al., 1993) stress that if strata onlapping clinoform fronts were deposited at or near sea level, then the clinoform heights dictate that sea level occasionally fell hundreds of meters in less than a million years; such magnitudes and rates are beyond the reasonable scales of any known mechanism for eustatic change. Extracting the amplitude of sea level fluctuations from sequence architecture is critically dependent on whether the lowest point of onlap onto sequence boundaries is truly coastal or is deeper marine. Determining water depths at the clinoform edge is essential to sequence stratigraphic models and understand this basic element of the dynamic land-sea interface. It can only be established by sampling, such as proposed here. | <urn:uuid:3aee58fa-a54c-4bf1-be5d-98922731a658> | 3.078125 | 1,738 | Academic Writing | Science & Tech. | 35.48036 |
This huge cloud of dust and gas is the orion Nebula. Inside it stars are forming. About 4,600 million years ago the sun and the planets were forming inside a nebula like this.
Most of the scientists believe that the sun and the other planets are formed about 4,600 million years ago from a huge cloud of tiny, solid particles and gases called a NEBULA. The solid particles and some of the gas had been thrown out of earlier stars that had died. The nebula began to shrink and spin, collapsing inwards because of its own gravity. Soon, material near the centre was colliding at tremendous speeds and giving out so much heat that a glowing star, the SUN, was born.
The rest of nebula formed into a ring around the sun and collision inside this ring built up the planets. For a time the planets were very hot, but they never become hot enough to shine like stars. All the planets were bombard by other much smaller bodies, so that their surfaces became covered with crates like the one still seen on the Moon today.
On the earth, however, wind and rain have gradually worn most of the crates away. The earth original atmosphere probably contained large amounts of carbon dioxide . As plants developed on earth they used the carbon dioxide to make food and released the oxygen on which all animal life depends. | <urn:uuid:ca7f2bb5-174a-4f4e-a1da-68ff9de58603> | 4 | 273 | Knowledge Article | Science & Tech. | 56.611782 |
SAVING THE SAND MOUNTAIN BLUE BUTTERFLY
Sand Mountain blue butterflies live in only one place on Earth — within and near the dunes of “Singing” Sand Mountain in Nevada. But over the past three decades, extensive off-road vehicle use on these public lands managed by the Bureau of Land Management has destroyed more than 50 percent of the rare butterfly’s habitat and main food source, leaving the species perched on the edge of extinction.
The Sand Mountain blue butterfly is closely linked to Kearney buckwheat; larvae feed exclusively on the plant, and adult butterflies rely on its nectar as a primary food source. Unfortunately, the Bureau of Land Management has allowed off-road vehicle use to destroy much of the Kearney buckwheat that once thrived on the dunes at Sand Mountain. To ensure that the Sand Mountain blue butterfly will have adequate habitat and protection, the Center submitted a petition to list this rare species as federally endangered in 2004.
In 2006, after the U.S. Fish and Wildlife Service failed to respond to our initial petition, the Center filed another suit against the Service to compel a response. In 2007, the Service denied our petition to list the species despite continued threats from increasing off-road vehicle use at the dunes. The Service is staking the continued existence of the species on a new Conservation Plan that relies on largely voluntary measures to stem the tide of habitat destruction from off-road vehicle use. The Center will continue to advocate for mandatory legal protections for the butterfly and its habitat under the Endangered Species Act.
Contact: Lisa Belenky
|Photo courtesy of Carson City BLM Field Office||HOME / DONATE NOW / SIGN UP FOR E-NETWORK / CONTACT US / PHOTO USE /| | <urn:uuid:5d3dc9c2-c5f5-4f44-802e-07a862657863> | 3.0625 | 364 | Knowledge Article | Science & Tech. | 33.046944 |
development of CO2 emissions
Whilst Eastern Europe/Eurasia`s emissions of CO2 will increase by 43% between 2009 and 2050 under the Reference scenario, under the Energy [R]evolution scenario they will decrease from 2,483 million tonnes in 2009 to 243 million tonnes in 2050. Annual per capita emissions will drop from 7.3 tonnes to 0.7 tonne. In spite of the phasing out of nuclear energy and increasing demand, CO2 emissions will decrease in the electricity sector. In the long run efficiency gains and the increased use of renewable energy in vehicles will reduce emissions in the transport sector. With a share of 43% of CO2, the power sector will be the largest sources of emissions in 2050. By 2050, Eastern Europe/Eurasia’s CO2 emissions are 94% below 1990 levels. | <urn:uuid:79a61f80-c10e-4545-9296-cd167b4f0669> | 2.78125 | 171 | Knowledge Article | Science & Tech. | 57.883004 |
Sharks roamed the oceans before dinosaurs walked the land. They even survived the Permian mass extinction 252 million years ago, when over 90% of all species died off. Today, however, these top predators are disappearing from our oceans. They are in trouble on the Great Barrier Reef, have almost been eliminated from the Atlantic Ocean, and are a regular on the endangered species list. This magnificent animal, which has been around for over 400 million years, is falling victim to overfishing. Sharks are being taken from the oceans before they can replenish their populations.
Many people believe these creatures hold the secret to long life. Reports of sharks with abnormalities are so rare that it's commonly thought they do not get cancer. Sharks have cartilage instead of bones, and lack bone marrow where humans produce immune cells. Sharks produce their immune cells in the spleen, thymus, esophagus and in unique tissues associated with the gonads. Since these immune cells circulate in the bloodstream, they offer a more efficient immune response. In humans, on the other hand, there is a brief lag before immune cells are produced in the bone marrow and mobilized into the bloodstream to fight off invaders.
When a top predator such as the shark disappears, the rest of the ecosystem often spirals out of control. With declining large shark populations, the smaller sharks, skates, and rays increase in numbers and their prey then plummets. Off the coast of South Africa, for example, bony fish are disappearing due to increased smaller inshore sharks. Similarly, off the North Carolina coast, rays are depleting the bay scallop populations. The collapse of the Caribbean coral-reef ecosystem may also have been triggered by the overfishing of sharks.
Millions of sharks are killed each year to supply a growing demand for shark fin soup – one of the most expensive foods available. Shark fins are said to contain the essence of virility, wealth and power. In fact, shark fins may actually be harmful to eat since sharks are often high in mercury. Processing the fins also frequently involves soaking them in industrial grade hydrogen peroxide and ammonia to bleach out their color.
The demand for shark fins is at an all-time high. Shark fin soup is popular at Chinese weddings, celebratory occasions and corporate functions. In China, the rapid rise of a middle-class population with disposable income means more people can afford the expensive soup. If the soup is not served, the host will look cheap and lose face. The fins can cost as much as $275 a kilogram, and millions of sharks are killed for their fins each year. The fish is caught live, the fins removed and the animal thrown back into the water.
While those who consume shark fin soup are contributing to the shark's demise, they are not the only ones. Many people are taking supplements containing shark products in the hope that it will lead to healthier lives or cure their cancer. They often do this without exploring the science behind the myth.
Sharks occasionally attack us, but this is extremely rare: they are actually positively elusive compared with other large animals which have been known to attack humans. Each year, sharks attack between 50 and 100 people, with fewer than 20 fatalities. Most attacks are “hit and run” attacks, where the shark makes a single bite and passes (humans are not an ideal food for a shark—not enough fat). These attacks are rarely life-threatening. Despite all this, shark attacks draw worldwide attention.
Sharks should not be feared. But life without sharks is scary. If sharks continue their rapid decline, the only people who'll need to worry about a shark attack will be those working in zoos and aquariums. | <urn:uuid:e3930070-b1a0-4f91-9ae6-0ef04e6a252a> | 3.625 | 758 | Knowledge Article | Science & Tech. | 49.150598 |
February 28, 2007
GCRIO Program Overview
Our extensive collection of documents.
Archives of the
Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 7, NUMBER 3, MARCH 1994
- OF GENERAL INTEREST: OZONE DEPLETION
Protection of the Ozone Layer," M.K.W. Ko (Atmos. &
Environ. Res. Inc., 840 Memorial Dr., Cambridge MA 02139), N.-D.
Sze, M.J. Prather, Nature, 367(6463), 505-508, Feb.
Because more and more chemicals, such as rocket fuel and
pharmaceuticals, are turning out to be ozone-depleting, a more
refined approach is needed for effective and equitable control.
Makes specific recommendations for ways to extend international
agreements to include chemicals whose applications and
life-cycles are very different from the synthetic halocarbons
already controlled by the Montreal Protocol. The goal is
long-term protection of the ozone layer, based on scientific
understanding of stratospheric ozone and the chemicals in
question, avoiding capricious impacts on technological
related items in Science, 263(5151), Mar. 4, 1994:
"Fires, Atmospheric Chemistry and the Ozone Layer,"
R.J. Cicerone (Earth System Sci., Univ. California, Irvine CA
92717), 1243-1244. Provides a scientific perspective on the
results published in the following article.
"Emission of Methyl Bromide from Biomass Burning,"
S. Manö, M.O. Andreae (M. Planck Inst. Chem., POB 3060, D-55020
Mainz, Ger.), 1255-1257. Because bromine is far more effective
than chlorine at destroying stratospheric ozone, control of the
pesticide methyl bromide is scheduled under the Montreal
Protocol. Estimates based on laboratory measurements show that
biomass burning is a major source of methyl bromide emissions,
comparable to pesticide use and natural oceanic emissions.
Guide to Publishers
Index of Abbreviations | <urn:uuid:cad74500-739c-4b26-9efb-8b7a1b31324c> | 3.0625 | 481 | Content Listing | Science & Tech. | 44.774422 |
Importance of programming languages
As technology evolves, as a driving force in business. In the past, companies were manage by people and processes. These two factors that have led business performance and to determine whether the organization will be successful in achieving important goals. Thus, the need and importance of programming was arose.
Graphical Programming with Python: QT Edition
OpenDocs Publishing is now taking feedback on Graphical Programming with Python: QT Edition. You may view the book online as it develops. The book is being authored by: Boudewijn Rempt.
Python course for beginners?
Is there such a thing? Yes, there are several Python courses for people who have no programming background, but their quality varies widely. Most of the Python manuals and courses aimed at people who already have extensive programming skills and would like to expand the list of programming languages, they are competent in.
Why Python is popular?
Application developers those developing applications for Linux, as a rule, have a huge range of possibilities. It is believed that Linux can be used effectively for almost any sort of job. Linux provides its users with a luxurious choice of language. The developer can find an updated version of virtually any programming language.
Python application development
Python is a dynamic object-oriented programming language that can be compared with Java and Microsoft .NET-based languages, a general-purpose substrate for many types of software.
Connecting access to Python
Access is not really a database, it is a file format. Thus, programs that access it, access the file directly. This has several advantages for small projects, as the file size and speed. Most of the DB to act as a gate keeper between the application and data files. It also makes it impractical for many user environments. | <urn:uuid:73651ab1-1c53-462f-9cec-d9ed5668f096> | 2.84375 | 361 | Knowledge Article | Software Dev. | 36.004824 |
Vectors - Fundamentals and Operations
Need to see it? Study the 6 + 8 = ??? animation from the Multimedia Physics Studios.Walter Fendt Physics Applets: Resultant of Forces (Addition of Vectors)
Add between two and five vectors together with this interactive Java simulation.
Explore nine lessons from a two-week unit on vectors by the Center for Innovation in Science and Engineering Education (CIESE).The Laboratory
Looking for a lab that coordinates with this page? Try the As the Crow Flies Lab from The Laboratory.The Laboratory
Looking for a lab that coordinates with this page? Try the Map Lab from The Laboratory.Treasures from TPF
Need ideas? Need help? Explore The Physics Front's treasure box of catalogued resources on vectors.
The resultant is the vector sum of two or more vectors. It is the result of adding two or more vectors together. If displacement vectors A, B, and C are added together, the result will be vector R. As shown in the diagram, vector R can be determined by the use of an accurately drawn, scaled, vector addition diagram.
To say that vector R is the resultant displacement of displacement vectors A, B, and C is to say that a person who walked with displacements A, then B, and then C would be displaced by the same amount as a person who walked with displacement R. Displacement vector R gives the same result as displacement vectors A + B + C. That is why it can be said that
A + B + C =
The above discussion pertains to the result of adding displacement vectors. When displacement vectors are added, the result is a resultant displacement. But any two vectors can be added as long as they are the same vector quantity. If two or more velocity vectors are added, then the result is a resultant velocity. If two or more force vectors are added, then the result is a resultant force. If two or more momentum vectors are added, then the result is ...
In all such cases, the resultant vector (whether a displacement vector, force vector, velocity vector, etc.) is the result of adding the individual vectors. It is the same thing as adding A + B + C + ... . "To do A + B + C is the same as to do R." As an example, consider a football player who gets hit simultaneously by three players on the opposing team (players A, B, and C). The football player experiences three different applied forces. Each applied force contributes to a total or resulting force. If the three forces are added together using methods of vector addition (discussed earlier), then the resultant vector R can be determined. In this case, to experience the three forces A, B and C is the same as experiencing force R. To be hit by players A, B, and C would result in the same force as being hit by one player applying force R. "To do A + B + C is the same as to do R." Vector R is the same result as vectors A + B + C!!
In summary, the resultant is the vector sum of all the individual vectors. The resultant is the result of combining the individual vectors together. The resultant can be determined by adding the individual forces together using vector addition methods. | <urn:uuid:38790c07-e177-47fa-8857-0f677afe020d> | 4.25 | 673 | Tutorial | Science & Tech. | 61.11956 |
|Oct14-04, 04:49 PM||#1|
Rotational energy levels
Are rotational energy levels of a molecule in general equally spaced or does the spacing increase with energy? How about a diatomic molecule; I have seen a derivation showing that the rotational levels in a diatomic molecule are equally spaced, but when drawn in an energy level diagram they clearly aren't? What is right?
And another thing; in my book the expression for the rotational and vibrational energies of a diatomic molecule is derived in terms of a classical "dumb-bell"-picture? How is this justified taking quantum mechanics into account?
|Oct14-04, 05:58 PM||#2|
No, even in the most simple diatomic molecule rotational levels are not equally spaced. If you look at any rotational spectrum of such molecules you will clearly appreciate it. You will see how the first lines are separated more or less a 2B distance (B is the rotational constant) but they get closer when increasing frequency. But be carefull with this, the energy levels get more separated when you increase J, but the transition frequency values: E(J+1)-E(J) get closer between them when increasing J. This is the real behaviour.
The question is what model do you choose to theoretically calculate those energy levels (and the frequency values). The most simple quantum model is the rigid rotor (exuse me if that isnīt the correct word, Iīm spanish). The energy expression derived from that model is:
E(cm-1)=B J (J+1)
then the frequency expression F=2B (J+1). Frequencies are equally separated. But this is not real. In order to get a better description elastic rotor is used:
[tex] E(cm^-1)=BJ(J+1)-DJ^2 (J+1)^2 [/tex]
This model introduces the "D" constant to allow the variation of bond length (in fact vibration movement). The frequency values obtained get closer between them while increasing J, Itīs more real but It continues being a model. Theese expressions are only for diatomic molecules.
|Oct25-04, 05:12 AM||#3|
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|Rotational energy levels||General Physics||0| | <urn:uuid:915f0cab-1fde-4bcf-934a-376116e6ee70> | 2.71875 | 573 | Comment Section | Science & Tech. | 45.271061 |
This is an issue that is often misunderstood in the public sphere and media, so it is worth spending some time to explain it and clarify it. At least three careful ice core studies have shown that CO2 starts to rise about 800 years (600-1000 years) after Antarctic temperature during glacial terminations. These terminations are pronounced warming periods that mark the ends of the ice ages that happen every 100,000 years or so.
Does this prove that CO2 doesn’t cause global warming? The answer is no.
The reason has to do with the fact that the warmings take about 5000 years to be complete. The lag is only 800 years. All that the lag shows is that CO2 did not cause the first 800 years of warming, out of the 5000 year trend. The other 4200 years of warming could in fact have been caused by CO2, as far as we can tell from this ice core data.
The 4200 years of warming make up about 5/6 of the total warming. So CO2 could have caused the last 5/6 of the warming, but could not have caused the first 1/6 of the warming.
It comes as no surprise that other factors besides CO2 affect climate. Changes in the amount of summer sunshine, due to changes in the Earth’s orbit around the sun that happen every 21,000 years, have long been known to affect the comings and goings of ice ages. Atlantic ocean circulation slowdowns are thought to warm Antarctica, also.
From studying all the available data (not just ice cores), the probable sequence of events at a termination goes something like this. Some (currently unknown) process causes Antarctica and the surrounding ocean to warm. This process also causes CO2 to start rising, about 800 years later. Then CO2 further warms the whole planet, because of its heat-trapping properties. This leads to even further CO2 release. So CO2 during ice ages should be thought of as a “feedback”, much like the feedback that results from putting a microphone too near to a loudspeaker.
In other words, CO2 does not initiate the warmings, but acts as an amplifier once they are underway. From model estimates, CO2 (along with other greenhouse gases CH4 and N2O) causes about half of the full glacial-to-interglacial warming.
So, in summary, the lag of CO2 behind temperature doesn’t tell us much about global warming. [But it may give us a very interesting clue about why CO2 rises at the ends of ice ages. The 800-year lag is about the amount of time required to flush out the deep ocean through natural ocean currents. So CO2 might be stored in the deep ocean during ice ages, and then get released when the climate warms.]
To read more about CO2 and ice cores, see Caillon et al., 2003, Science magazine
Guest Contributor: Jeff Severinghaus
Professor of Geosciences
Scripps Institution of Oceanography
University of California, San Diego.
Update May 2007: We have a fuller exposition of this on a more recent post. | <urn:uuid:28efacbf-3847-488e-947e-46cb72f8526b> | 3.65625 | 653 | Knowledge Article | Science & Tech. | 61.451226 |
In this tutorial, we will see how to create a short array with the help of short buffer.
The java.nio.ShortBuffer class extends java.nio.Buffer class. It provides the following methods:
|static ShortBuffer||allocate( int capacity)||The allocate(..) method allocate a short buffer of given capacity.|
|short||array()||The array() method returns short array based on short buffer.|
|abstract short||get()||The get() method read short value from current position and increment position..|
Capacity of short buffer : 1024
Content in shortbuffer :
Length of short buffer array : 1024
Content in short buffer array :
If you are facing any programming issue, such as compilation errors or not able to find the code you are looking for.
Ask your questions, our development team will try to give answers to your questions. | <urn:uuid:29117fa5-11be-4cce-bc6c-50fb5a6459a6> | 2.75 | 188 | Documentation | Software Dev. | 57.494615 |
Hello, Frank Indiviglio here. Genetic research has revealed that a fairly well-studied frog has been hiding an astonishing secret – pairs form lifelong pair bonds and remain faithful to one another. Equally surprising is the fact that pool size alone (and not morality!) seems responsible for the fidelity shown by Mimic Poison Frog (Ranitomeya imitator) couples. These findings, to be published in an upcoming issue of The American Naturalist, illustrate the second “first” for this species (please see below).
Teamwork in Raising the Young
Inhabiting wet forests in the foothills of the Peruvian Andes, male and female Mimic Poison Frogs must cooperate very closely if their young are to survive. Males transport up to 6 tadpoles to individual pools at the bases of bromeliads (like all Dendrobatids, their eggs are deposited on land) and call to their mates when feeding time arrives. The female then visits the pool and deposits an unfertilized egg, which is consumed by the tadpole.
The Effect of Pool Size
Interestingly, a close relative, the Variable Poison Frog (R. variabilis), does not exhibit mate fidelity despite dwelling in the same habitat and having a seemingly similar lifestyle (and appearance – Mimic Poison Frogs imitate the warning colors of this species).
However, the Variable Poison Frog deposits its tadpoles in large, nutrient-rich pools, where they mature without additional food from the female. Without the unfertilized eggs supplied by the female, Mimic Poison Frog tadpoles would perish in the tiny pools that they inhabit…it seems that the strong bonds exhibited by the parents are essential to the tadpoles’ survival.
Another First – Imitating 3 Species
Monogamy is not the only surprise that this tiny frog has in store for us. It is also the only amphibian known to exhibit “mimetic radiation”. In all other amphibians that mimic the warning colors of other species, only 1 species is copied. However, different populations of Mimic Poison Frogs imitate the warning colors of 3 distinct Poison Frog species.
With the array of complicated breeding strategies exhibited by frogs of the family Dendrobatidae, it’s save to assume that there are more interesting discoveries on the way…please write in with your own observations and theories.
You can learn more about this frog and its relatives on the website of the American Museum of Natural History.
Please see my article Begging in Poison Frog Tadpoles for info on yet another amazing reproductive strategy.
Thanks, until next time,
R. ventrimaculata image referenced from wikipedia and originally posted by Thomas Ruedas | <urn:uuid:aca2f117-bbee-4224-b2c3-c5dafaf79600> | 3.28125 | 564 | Personal Blog | Science & Tech. | 28.644912 |
A macro replaces the original text in the code before the compiler start to process the file. I.e. every single place where you use the macro will get a duplicate of the code.
A function is a complete section of code i.e. no duplication occur.
Consider macros to be evil and stick to using functions instead, at least until you have a LOT of programming experience. There is no end in how many hard to solve issues you can create for yourself with the use of macros...
Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it.
- Brian W. Kernighan
No: From the call alone, it is not possible to know if you are using a macro, a function, or an object's operator().
However, there is a very widespread coding practice that says that macros should be in ALL_CAPS:
DO_SOMETHING(); //Probably a macro
do_something(); //Probably a function
Is your question related to IO?
Read this C++ FAQ LITE article at parashift by Marshall Cline. In particular points 1-6.
It will explain how to correctly deal with IO, how to validate input, and why you shouldn't count on "while(!in.eof())". And it always makes for excellent reading.
Another downside to macros is that they don't obey the C++ scoping rules.
ANYTHING that matches the macro name is replaced by the pre-processor.
Anybody who has named a member function GetMessage when using Windows and MFC will know what I mean.
(The preprocessor will replace ANY GetMessage with GetMessageA or GetMessageW, depending on whether the setup is ASCII or Unicode. The compiler will then complain that your class doesn't contain a definition of one of these! )
"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
Richard P. Feynman | <urn:uuid:b16f546e-1ff8-4914-a5a4-16a8b8c0bde9> | 3.296875 | 445 | Comment Section | Software Dev. | 61.40352 |
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Many images of the solar system do not do justice to how small the planets are relative to the Sun, or how distant they are from the Sun and each other. The solar system is really mostly empty space. The Toilet Roll Solar System activity helps give an idea of the relative distances between the planets. Some other fun things to try include finding your age and weight on other planets. | <urn:uuid:34c1061a-aeab-4f8c-bb27-f33c51722326> | 2.875 | 83 | Truncated | Science & Tech. | 49.725068 |
Vent Communities Under the Galapagos Islands
Vent communities are animals and plants that are found deep in the ocean near hot water or geothermal vents. Vents are found where the tectonic plates crack. Molten lava lies deep within the cracks and heats up the water. This ecosystem is teeming with life. They are rich in biodiversity. There are many species found near the vent communities that are not found anywhere else at the bottom of the ocean. Scientists discovered that these vents have hydrogen sulfide coming out of them. The hydrogen sulfide provides nutrients for the plants and animals. Vent animals have strange characteristics. They are giants. An example is the tube worm which grows to be nearly 3 meters long. They grow at a much faster rate. Vent clams grow five times faster than regular clams.
(click to enlarge) | <urn:uuid:30046acd-23e8-4dc9-9e9e-29081e35b098> | 3.671875 | 171 | Knowledge Article | Science & Tech. | 54.501374 |
Towards the end of every year tropical storm activity moves from the northern hemisphere to the southern hemisphere. The South Indian Ocean has already spawned three tropical storms including the unusually strong early season Cyclone Anais in October. Attention has now switched to the South Pacific Ocean and Cyclone Evan.
Evan formed near Fiji a few days ago and moved north-east as it strengthened. As it reached the equivalent of hurricane intensity (winds near 75 mph) it made landfall over Samoa close to the capital city of Apia. Although winds of this strength are not exceptional for a cyclone, first reports indicate considerable wind damage and flooding from a storm surge of 12-15 feet (3.5-4.5 m). This storm surge is of similar height to that experienced in New York City during ‘Superstorm’ Sandy in October.
Although Samoa lies within the cyclone belt of the South Pacific Ocean, the island nation has been relatively storm free for many years. Cyclone Heta passed close by in 2003, but the last time Samoa received direct strikes from tropical storms was in 1997 and 1998 by storms named Tui and, coincidentally, Evan.
To make matters worse, Cyclone Evan is expected to become slow moving near Samoa and American Samoa, producing large amounts of rainfall, before turning back south-west. Latest forecasts suggest Evan will strengthen some more and could threaten a strike on Fiji early next week.
Regional warnings for Cyclone Evan are produced by the Fiji Meteorological Service. The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance. | <urn:uuid:0ca18714-2557-45f4-bcd5-1ceca5844f67> | 3.125 | 345 | Knowledge Article | Science & Tech. | 39.128947 |
Tag: "microbes" at biology news
Newly Discovered Bacteria Produce Magnetic Material
... "In 1994," Phelps says, "we determined that these microbes
from theTaylorsville Triassic Rift Basin near Fred...ionth of a meter. "We also found evidence that the microbes
can remediate groundwatercontaining chlorocarbon compounds, such as trichloroethylene andtetrachloro...
Researchers Find How Disease-resistant Plants Recognize Bacteria
...stance breaks down. By learning how the plants and microbes
recognize one another, we hope to create crop plants that have broader, more stable resistance." According to Martin, the findings will have wide application. "It turns out that plants resist diverse pathogens -- including bacteria, fungi and viruses...
Ten Years of Progress For Superfund Basic Research Program
...to thegenus Mycobacterium. This group includes the microbes
which causeleprosy and tuberculosis, but the strai...of work isneeded to find the best way to use these microbes
in the fieldwhere they will have to compete with other naturally occurringorganisms. Environmental e...
Munching Microbes Make A Meal Out Of Toxic Substances
...s. "We've known for decades that the soil contains microbes
with the ability to degrade chemicals such as petr...perience." One of Nies' projects involves studying microbes
that eat pentachlorophenol, a chemical used as a wood preservative. "We're investigating a contamina...
Chesapeake Bay Sediment : Home To Pfiesteria-Like Microbes
...sent can be made. The presence of Pfiesteria-like microbes
and their effect on aquatic life is a complicated issue requiring knowledge of fishimmunology, chemical reactions involving nutrients, stream dynamics, sediment loads, the life cycles of Pfiesteria-like microbes,water temperatures, and other factors....
Photocatalytic Air Cleaning System Promises To Help Allergy Sufferers
...he result is oxidation, which attacks and destroys microbes
by disintegrating their DNA. The reaction also kills dust mites and mold. Goswami said that the photocatalytic process is superior to conventional techniques using filters, which must be changed and disposed of. "With this system, co...
Limits Of Life On Earth: Are They The Key To Life On Other Planets?
...lve finding techniques for isolating and culturing microbes
found in extreme environments, developing methods of studying these microbes
in their natural habitats and devising technologies for recovering non-contaminated samples. HIG...
Max-Planck Researchers Unravel The Structure Of The Methane Forming Enzyme
...ly carried out by a group of strictly anaerobic microbes
called methanogens which use the formation of methane for the purpose of cellular energy generation. Within the microbial ecosystem methanogens participate in the final step of anoxic decomposition of complex organic materials thereby pro...
Food Bacteria-Spice Survey Shows Why Some Cultures Like It Hot
...rld where -- before refrigeration -- food-spoilage microbes
were an even more serious threatto human health an...evolutionary race between usand our parasites. The microbes
are competing with us for the same food,"Sherman says. "Everything we do with food -- drying, cooki...
Study Of Microbes May Hone Predictions Of Mining Impact
...-level ecological study of the naturally occurring microbes
that mediate some of the most severe pollution eve...wing precisely where and under what conditions the microbes
thrive in nature can be a powerful new tool to predict the effects of sulfide mining at a given site...
Environmental Technology Breakthroughs Forecast -- Year 2008
...c Northwest includes developing aprocess that uses microbes
to break down sulfur in waste tire rubber, makingtires recyclable; working with other national laboratories and automakers todevelop a cleaner, more efficient automobile; designing a 190-liter-per-second(3,000 gallon-per-minute) jet mixing pump to st...
Poison-Eating Bugs Strike Gold
...th-based mining biotechnology firm, of indigenous microbes
capable of devouring toxic effluent from gold ext...rals have identified several new species of native microbes
able to break down the thiocyanate formed from the cyanide used to extract gold. The project is ...
Do Termites Use
...culates. Another possibleorigin, he says, is that microbes
are making the naphthalene by acting onmaterial in the termite nest, the gut, or on the food. A nonprofit organization with a membership of more than 155,000 chemists andchemical engineers, the American Chemical Society publishes scientific journals,...
Study At UNC-CH Shows Chlorinated Water Dramatically Cuts Strawberry Contamination
...le but efficient method of recovering anyremaining microbes
to determine how effective washing had been. They found theirmethod "highly successful" in eliminating most viruses and bacteria. "Our work is important because it demonstrates for the first time thathepatitis A virus can be inactivated on st...
Can Contaminated Aquifers Restore Themselves?
...e carriedoxygen below the infiltration beds, where microbes
used it to convertammonium to nitrate in a process called nitrification. Biological activityin the aquifer now is high enough to consume most of the oxygen flowing inwith the native ground water and little oxygen is available fornitrification. As a...
Georgia Scientists Study Salt Marsh To Understand Global Warming
...singlyhigh rate of carbon and nutrient turnover by microbes
in one ofGeorgia's coastal salt marshes, a highly productive ecosystem. The team of researchers, all associated with the Georgia Institute ofTechnology, is conducting a long-term study at Sapelo Island, Ga., toexamine the marsh's biogeochemical proce...
EPA And UC Researchers Find Bacteria That Can Destroy Giardia Cysts
...ms and rivers around Greater Cincinnatilooking for microbes
which might be able to feed on the Giardia cysts. "It's always been known that the viabilityof cysts decreases over time in a natural environment. We wereinterested in knowing what kind of biological factors contribute." Rodgers' hunch paid off, and...
Third Annual Awards For Presidential Green Chemistry Challenge Recognize Innovations
...e University, East Lansing):genetically engineered microbes
that can manufacture starting materials fornylon and other products from nontoxic, readily available glucose. Barry M. Trost (Stanford University, Stanford, Calif.): the concept of "atomeconomy," demonstrated by efficient catalytic reactions with wh...
Banking On Safer Drinking Water
...er it is." The work is important because dangerous microbes
and cancer-causing chemicals sometimes slip past traditional watertreatment. "We're worried about resistant pathogens created bythe overuse of antibiotics," says Bouwer, a professor in Hopkins'Department of Geography and Environmental Engineering. "S...
Purdue Golf Course Serves Double Duty As Research Lab
...are caught in the thatch layer of the turf, where microbes
digest them and break them down. Other chemicals in the water in the soil are taken up by the roots of the plants. When these plants die, the plant material, along with the chemicals, is broken down by the microbes. The Purdue Kampen course b...
1 2 3 4 5 6 7 8 9 10 | <urn:uuid:0887eb30-b3d9-4456-bdb8-ec0c6e420fb0> | 2.859375 | 1,558 | Content Listing | Science & Tech. | 34.958807 |
unassimilatible writes "The Harvard-Smithsonian Center for Astrophysics reports 'to impress your favorite lady this Valentine's Day, get her the galaxy's largest diamond.' A newly discovered cosmic diamond is a chunk of crystallized carbon 50 light-years from the Earth in the constellation Centaurus. It is 2,500 miles across and weighs 5 million trillion trillion pounds, which translates to approximately 10 billion trillion trillion carats, or a one followed by 34 zeros. A cheesy, unrealistic simulation is also available. AP has a story as well." | <urn:uuid:c85c2700-6e4e-4b05-917b-2b1db99838be> | 3.1875 | 112 | Comment Section | Science & Tech. | 40.921 |
Once oil has entered the Gulf Stream, it may stay offshore in the Gulf Stream. There is some chance that it could move toward nearshore coastal waters and even reaching the coastlines of South Atlantic states. The amount of oil — if any — that reaches shore depends on several factors, including:
- the amount of oil in the Gulf Stream;
- prevailing winds;
- weather events such as storms or hurricanes;
- effects from additional eddies in the Gulf Stream; and
- influences from currents moving southward from the Mid-Atlantic Bight.
The risk of having oil come ashore would be greatest along the southern portion of Florida's east coast, due to the close proximity of the Florida coast to the Gulf Stream.
A second area in the South Atlantic that would be at higher risk for oil coming ashore is Cape Hatteras, North Carolina and the neighboring Outer Banks beaches, especially in the September through April time frame. Cape Hatteras is vulnerable because of both its proximity to the Gulf Stream and by onshore eddies and currents that may interact with the Gulf Stream near Hatteras.
Shorelines between south Florida and Cape Hatteras also could experience visible oil deposits, such as tar balls or oil pancakes, especially if coastal storms and/or wind patterns push the oil toward shore.
Movement of waters from the Gulf Stream to South Atlantic shorelines can vary greatly. If you frequent these shores, you might notice that some years there might be great amounts of Sargassum seaweed carried onto the beaches, or a flurry of Portuguese man-of-war sightings. But in other years, there might be few of these floating organisms washed ashore. Other floating debris – such as surface oil – would also be subjected to this variable ebb and flow of coastal currents. | <urn:uuid:d5a43cf0-e630-4c37-83f4-4fdb026ba079> | 3.609375 | 367 | Knowledge Article | Science & Tech. | 41.386749 |
Although the highly invasive water hyacinth was introduced into Florida over 30 years ago, the aquatic plant hasn’t been nearly as successful as it has been in other places such as Lake Victoria, South Africa. Despite this, Florida’s weather and conditions are optimal for sufficient growth of water hyacinth. The warm climate, high nutrient and light environment is very conducive to water hyacinth growth. Researchers Volin and Soti from the University of Connecticut and Florida Atlantic University sought to test various nutrient and herbivory levels versus water hyacinth growth to see if the specific amount of nutrients and plant removal found in Florida had a negative impact on the water hyacinth. Soti and Volin found that water hyacinth are able to survive under low amounts of plant removal no matter the nutrient level. This suggests the most effective method of removal of the plant is a high level of herbivory. This research gives great insight into future control of the highly invasive plant.
Biological Control Vol. 54 Issue:1 35-40 July 2010
Researchers A. Bradley and John F. Mustard at Brown University have done research on the dynamics of invasive plant species in order to see if more effective land management can reduce the chance of future invasions. Specifically, they studied Bromus tectorum, better known as cheatgrass. Remote sensing was used to track how likely cheatgrass expansion was in relation to how the land was cultivated, elevation, roads and several other factors. There were positive correlations between cheatgrass invasion and high elevation, close proximity to cultivated land, roads and other areas already occupied by cheatgrass. These relationships were used to create a “risk map” for future cheatgrass invasion that can help change the way land is managed for the better. This study shows the importance of including how land is used in methods to reduce plant invasions.
Ecological Applications, Pages 1132-1147(2006)
Ever since this fish’s release into the Atlantic Ocean in the late 20th century, the lionfish (Pterois volitans) has invaded coastline areas from Belize to Massachusetts. Authors Isabelle M. Cote and Aleksandra Maljkovic in their article “Predation rate of Indo-Pacific lionfish on Bahamian coral reefs” demonstrate how these fish are simply taking over many of the reefs in the Caribbean. After doing several Scuba dives off of New Providence Island, Bahamas, the researchers made several important discoveries about lionfish behavior. They saw how Lionfish in the Atlantic mainly feed during the day, unlike the native pacific population that does so at night. Finally, the authors found that the predation rates of lionfish in the Caribbean are significantly higher than the presumed rate in the eastern pacific. This final observation brought the authors to the conclusion that lionfish could be much more destructive than many scholars think. (Cote 2010) | <urn:uuid:286c4586-712d-4978-ac2a-a17e99544c1e> | 3.546875 | 594 | Academic Writing | Science & Tech. | 32.138458 |
The CGI (Common Gateway Interface) defines a way for a web server to
interact with external content-generating programs, which are often
referred to as CGI programs or CGI scripts.
Within Tomcat, CGI support can be added when you are using Tomcat as your
HTTP server and require CGI support. Typically this is done
during development when you don't want to run a web server like
Tomcat's CGI support is largely compatible with Apache httpd's,
but there are some limitations (e.g., only one cgi-bin directory).
CGI support is implemented using the servlet class
this servlet is mapped to the URL pattern "/cgi-bin/*".
By default CGI support is disabled in Tomcat. | <urn:uuid:91f15aa7-7164-4e02-a672-0a55cb422ca4> | 3.09375 | 156 | Documentation | Software Dev. | 52.904655 |
This post is from Dr John Bissell, a physicist researching tipping points in mathematical systems for the project.
In a conference that had largely focused on `tipping points’ in human society, especially those involving the spread of `buzzwords’, `innovation’ and `trends’, Prof Richard Law‘s talk on ecological dynamics (for those who might not have a clue as to what ecological dynamics means this rather humorous rap might help) acted as an important reminder of the role `tipping points’ might play in natural systems.
Perhaps the most classic–if not defining–example of a `tipping point’ is the fold bifurcation, and Law began his discussion here. Broadly speaking, fold bifurcations occur when changes in a system’s underlying parameters alter the number of its steady-states (solutions to the system that stay constant over time), for example, if the prevailing steady-state is destroyed, then the whole system may need to rapidly reconfigure to a new and often quite different equilibrium. These kinds of catastrophic transitions can be particularly important because they tend to exhibit what’s called hysteresis. Indeed, once `tipped’, large reverse changes to the governing parameters may be needed to return a system to its original steady-state. Law illustrated some transitions of this kind in terms of both desertification of scrubland following grazing by cattle, and the collapse of fish stocks due to over-fishing.
Another `tipping point’ mechanism in ecological systems is the onset of chaos, which Law described using an example taken from the population dynamics of the Colorado potato beetle. In this case, small modifications to the survival rate of beetle larvae can lead to otherwise stable numbers of adult beetles oscillating erratically between relatively small populations and sudden large outbreaks. This kind of chaotic dynamic is notoriously difficult to predict.
From Law’s discussion it seems that ecological systems can not only exhibit `tipping point’ dynamics, but that such behaviour may have significant implications for our understanding of the natural world. However, as Law pointed out in the conclusion to his talk, the evidence for `tipping-points’ is subject to ongoing debate, and warning signals of their onset are difficult to quantify. Nevertheless, areas of scientific uncertainty are often those which best lend themselves to further scrutiny, and I look forward to hearing of, and possibly participating in, future researches on the ecological `tipping-point’ theme. | <urn:uuid:e4bc7cec-7b94-468b-9df3-f54037e70154> | 2.78125 | 518 | Academic Writing | Science & Tech. | 20.614824 |
Authors: Amrit S. Sorli
Penrose describes consciousness as a result of quantum gravity acting on the neurons of the brain. Consciousness is non local; it does not exist exclusively in the brain. Here it is introduced idea that consciousness is a basic frequency of quantum space. Human brains have ability to "connect" and harmonize with consciousness. In scientific experiment consciousness acts as an observer.
Comments: 2 pages
[v1] 12 Oct 2009
Unique-IP document downloads: 187 times
Add your own feedback and questions here: | <urn:uuid:2795051b-f03b-40c8-af60-0f56ed597685> | 2.859375 | 112 | Truncated | Science & Tech. | 47.596429 |
Higgs bosonArticle Free Pass
Higgs boson, also called Higgs particle, hypothetical particle that is postulated to be the carrier particle, or boson, of the Higgs field, a theoretical field that permeates space and endows all elementary subatomic particles with mass through its interactions with them. The field and the particle—named after Peter Higgs of the University of Edinburgh, one of the physicists who first proposed this mechanism—provide a testable hypothesis for the origin of mass in elementary particles. In popular culture, the Higgs boson is often called the “God particle,” after the title of Nobel physicist Leon Lederman’s The God Particle: If the Universe Is the Answer, What Is the Question? (1993), which contained the author’s assertion that the discovery of the particle is crucial to a final understanding of the structure of matter.
The Higgs field is different from other fundamental fields—such as the electromagnetic field—that underlie the basic forces between particles. First, it is a scalar field—i.e., it has magnitude but no direction. This implies that its carrier, the Higgs boson, has an intrinsic angular momentum, or spin, of 0, unlike the carriers of the force fields, which have spin. Second, the Higgs field has the unusual property that its energy is higher when the field is zero than when it is nonzero. The elementary particles therefore acquired their masses through interactions with a nonzero Higgs field only when the universe cooled and became less energetic in the aftermath of the big bang (the hypothetical primal explosion in which the universe originated). The variety of masses characterizing the elementary subatomic particles arises because different particles have different strengths of interaction with the Higgs field.
The Higgs mechanism has a key role in the electroweak theory, which unifies interactions via the weak force and the electromagnetic force. It explains why the carriers of the weak force, the W particles and the Z particles, are heavy while the carrier of the electromagnetic force, the photon, has a mass of zero. Experimental evidence for the Higgs boson would be a direct indication for the existence of the Higgs field. It is also possible that there is more than one type of Higgs boson. Experiments searched for the massive Higgs boson at the highest-energy particle-accelerator colliders, in particular the Tevatron at the Fermi National Accelerator Laboratory and the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research). On July 4, 2012, scientists at the LHC announced that they had detected an interesting signal that was likely from a Higgs boson with a mass of 125–126 gigaelectron volts (billion electron volts; GeV). Further data would be needed to definitively confirm those observations.
What made you want to look up "Higgs boson"? Please share what surprised you most... | <urn:uuid:04e23da0-bef7-4d40-969e-273afae8c3a8> | 3.765625 | 605 | Knowledge Article | Science & Tech. | 34.59825 |
How do macrophyte distribution patterns affect hydraulic resistances?
In eutrophic river systems, macrophytes attain high biomass with reduced drainage and increased flooding risk. To avoid these problems, water managers remove vegetation. Total removal, however, increases wash out of macro-invertebrate communities reducing the ecological value of rivers. Partial vegetation removal reduces this washout and prevents an increase in hydraulic resistance. In this, study the hydraulic performance of three partial vegetation removal patterns was tested. From the results it was seen that hydraulic resistance, expressed as Manning's n, was varying between 0.025 m−1/3 s and 0.050 m−1/3 s. Compared with the empty situation, the different distribution patterns increased resistance between 14 and 23%. Hydraulic resistance of these patterns was also significantly influenced by the species present in the vegetation patches. Three groups of macrophyte plants (emerged, floating leaved and submerged) with significantly different hydraulic resistances were determined. The emerged species Sparganium erectum generated the least resistance with an average friction of 0.03 m−1/3 s. Stuckenia pectinata and Potamogeton natans had slightly higher friction values around 0.4 m−1/3 s. Ranunculus penicillatus and Callitriche platycarpa had average friction values around 0.05 m−1/3 s. The proposed vegetation removal patterns are good alternatives to create a management system, which minimally increases hydraulic resistance but still guarantees the ecological functions. | <urn:uuid:cc282816-aad2-4002-bc37-07c80cc060eb> | 2.84375 | 316 | Academic Writing | Science & Tech. | 29.762071 |
Simple information searches -- name lookups, word searches, etc. -- are often implemented in terms of an exact match criterion. However, given both the diversity of homophonic (pronounced the same) words and names, as well as the propensity for humans to misspell surnames, this simplistic criterion often yields less than desirable results, in the form of reduced result sets, missing records that differ by a misplaced letter or different national spelling.
This article series discusses Lawrence Phillips' Double Metaphone phonetic matching algorithm, and provides several useful implementations, which can be employed in a variety of solutions to create more useful, effective searches of proper names in databases and other collections.
This article series discusses the practical use of the Double Metaphone algorithm to phonetically search name data, using the author's implementations written for C++, COM (Visual Basic, etc.), scripting clients (VBScript, JScript, ASP), SQL, and .NET (C#, VB.NET, and any other .NET language). For a discussion of the Double Metaphone algorithm itself, and Phillips' original code, see Phillips' article in the June 2000 CUJ, available here.
Part I introduces Double Metaphone and describes the author's C++ implementation and its use. Part II discusses the use of the author's COM implementation from within Visual Basic. Part III demonstrates use of the COM implementation from ASP and with VBScript. Part IV shows how to perform phonetic matching within SQL Server using the author's extended stored procedure. Part V demonstrates the author's .NET implementation. Finally, Part VI closes with a survey of phonetic matching alternatives, and pointers to other resources.
Part I of this article series discussed the Double Metaphone algorithm, its origin and use, and the author's C++ implementation. While this section summarizes the key information from that article, readers are encouraged to review the entire article, even if the reader has no C++ experience.
The Double Metaphone algorithm, developed by Lawrence Phillips and published in the June 2000 issue of C/C++ Users Journal, is part of a class of algorithms known as "phonetic matching" or "phonetic encoding" algorithms. These algorithms attempt to detect phonetic ("sounds-like") relationships between words. For example, a phonetic matching algorithm should detect a strong phonetic relationship between "Nelson" and "Nilsen", and no phonetic relationship between "Adam" and "Nelson."
Double Metaphone works by producing one or possibly two phonetic keys, given a word. These keys represent the "sound" of the word. A typical Double Metaphone key is four characters long, as this tends to produce the ideal balance between specificity and generality of results.
The first, or primary, Double Metaphone key represents the American pronunciation of the source word. All words have a primary Double Metaphone key.
The second, or alternate, Double Metaphone key represents an alternate, national pronunciation. For example, many Polish surnames are "Americanized", yielding two possible pronunciations, the original Polish, and the American. For this reason, Double Metaphone computes alternate keys for some words. Note that the vast majority (very roughly, 90%) of words will not yield an alternate key, but when an alternate is computed, it can be pivotal in matching the word.
To compare two words for phonetic similarity, one computes their respective Double Metaphone keys, and then compares each combination:
- Word 1 Primary - Word 2 Primary
- Word 1 Primary - Word 2 Alternate
- Word 1 Alternate - Word 2 Primary
- Word 1 Alternate - Word 2 Alternate
Obviously if the keys in any of these comparisons are not produced for the given words, the comparisons involving those keys are not performed.
Depending upon which of the above comparisons matches, a match strength is computed. If the first comparison matches, the two words have a strong phonetic similarity. If the second or third comparison matches, the two words have a medium phonetic similarity. If the fourth comparison matches, the two words have a minimal phonetic similarity. Depending upon the particular application requirements, one or more match levels may be excluded from match results.
The .NET implementation of Double Metaphone is very similar in design and use to the C++ implementation presented in Part I. To use the .NET implementation, simply add the Metaphone.NET.dll assembly to your project's references in Visual Studio. NET, import the
nullpointer.Metaphone namespace into the source files, and instantiate the
ShortDoubleMetaphone classes, for string and unsigned short Metaphone keys, respectively.
For example, to compute the Metaphone keys for the name "Nelson", code similar to that listed below may be used (C# code listed; the .NET implementation is callable from VB.NET, J#, and all other .NET languages):
DoubleMetaphone mphone = new DoubleMetaphone("Nelson");
Note that the Metaphone keys are obtained via the
As with the C++ implementation, an existing instance of a
ShortDoubleMetaphone class can be used to compute the Metaphone keys for a new word, by calling the
DoubleMetaphone mphone = new DoubleMetaphone();
As with all of the implementations presented in this article series, a sample application—CS Word Lookup--written in C# is presented to demonstrate the use of the .NET implementation. CS Word Lookup uses a
Hashtable collection class to map Metaphone phonetic keys to an
ArrayList class, containing the words which produce the said Metaphone keys.
While the .NET CLR performs reasonably well, it must be stated that the C++ implementation of Double Metaphone will likely perform significantly faster than the .NET version, due primarily to the fact that the C++ version judiciously avoids memory allocation and buffer copies, while the .NET implementation is unable to avoid such constructs. The ambitious reader is encouraged to optimize the .NET implementation, perhaps through the use of the
unsafe keyword, to perform direct memory access, at the expense of CLR compliance.
This brief article introduced the author's .NET implementation of Double Metaphone, including code snippets and a brief discussion of performance issues. Continue to Part VI for a review of alternative phonetic matching techniques, and a list of phonetic matching resources, including links to other Double Metaphone implementations.
- 7-22-03 Initial publication
- 7-31-03 Added hyperlinks between articles in the series
My name is Adam Nelson. I've been a professional programmer since 1996, working on everything from database development, early first-generation web applications, modern n-tier distributed apps, high-performance wireless security tools, to my last job as a Senior Consultant at BearingPoint posted in Baghdad, Iraq training Iraqi developers in the wonders of C# and ASP.NET. I am currently an Engineering Director at Dell.
I have a wide range of skills and interests, including cryptography, image processing, computational linguistics, military history, 3D graphics, database optimization, and mathematics, to name a few. | <urn:uuid:878a76ff-9056-4c2e-ad0c-f0ba2d84ccce> | 3.15625 | 1,491 | Documentation | Software Dev. | 29.884647 |
How Much Potential Energy Do Different Nuts Have?
It seems that at least once a year California has another energy crisis, and almost as often, someone wonders what will happen when California runs out of energy sources. Christopher Crews, knowing that all living things contain energy, set out to prove that different varieties of nuts have energy stores that can be released by burning.
I believe that burning different varieties of nuts will produce energy, and that peanuts will produce the most energy.
Amount of heat produced
- Number of nuts tested
- Amount of water
- Ten each whole, raw, unshelled nuts:
- 32-ounce coffee can
- Two 10-ounce soup cans
- Drill and bits
- Kitchen scale
- Fill large coffee can with water.
- Measure nut.
- Weigh water on kitchen scale.
- Measure and record starting water temperature.
- Drill hole through nut.
- Insert skewer through hole in nut.
- Heat nut with lighter and let the nut burn fully.
- Measure and record ending water temperature.
- Calculate BTU (starting temperature minus ending temperature divided by the weight of the water). BTU stands for British Thermal Unit, the energy necessary to raise the temperature of one pound of water by 1@dgsF. One BTU equals approximately 1,055 joules (or 1,055 watt-seconds).
- Repeat Steps 1 through 9 for each nut.
The average BTU for each type of nut is as follows:
Cashews 15.75 BTU
Almonds 13.76 BTU
Peanuts 10.77 BTU
The hypothesis was that burning different varieties of nuts would produce energy, with peanuts producing the most energy. That’s partially correct because all the nuts produced energy. However, the hypothesis was incorrect because the cashews produced the most energy, and peanuts produced the least.
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety. | <urn:uuid:70991200-cc00-4786-b3cc-22df4b25f76e> | 3.46875 | 469 | Tutorial | Science & Tech. | 46.829936 |
Some operations are difficult or even impossible to obtain with an expression, or the operation could become too complex to achieve. The alternative is to create a function that would take care of performing the operation and supplying the result to the table. Of course, as you may know already, a function is its own object. This means that, after creating it, to use its result in a table, you must call it. For example, you can create a function that returns a value, then call that function and assign its returned value to a column. You can create your own function and use it, or you can use one of the built-in functions of Transact-SQL.
In order to involve a function with your data entry, you must have one. You can create your own function using the techniques we learned already. To make the function easily accessible, you should create it as part of the database that would use it. Here is an example:
-- ============================================= -- Author: FunctionX -- Create date: Saturday 22 December 2007 -- Description: Used to calculate the greatest common divisor -- ============================================= CREATE FUNCTION GCD ( @a int, @b int ) RETURNS int AS BEGIN DECLARE @Remainder int; WHILE @b <> 0 BEGIN SET @Remainder = @a % @b; SET @a = @b; SET @b = @Remainder; } RETURN @a }
When calling the function, follow the normal rules. Here are examples:
INSERT INTO Calculations VALUES(345, 135, dbo.GCD(345, 135)); GO INSERT INTO Calculations VALUES(40, 6, dbo.GCD(40, 6)); GO INSERT INTO Calculations VALUES(16, 28, dbo.GCD(16, 28)); GO
You can use one of the built-in functions of Transact-SQL. Probably the best way to be familiar with the built-in functions is to check the online documentation to find out if the assignment you want to perform is already created. Using a built-in functions would spare you the trouble of creating your own function. For example, imagine you have a database named AutoRepairShop and imagine it has a table used to create repair orders for customers:
CREATE TABLE RepairOrders ( RepairID int Identity(1,1) NOT NULL, CustomerName varchar(50), CustomerPhone varchar(20), RepairDate DateTime ); GO
When performing data entry for this table, you can let the user enter the customer name and phone number. On the other hand, you can assist the user by programmatically entering the current date. To do this, you would call the GETDATE() function. Here are examples:
INSERT INTO RepairOrders(CustomerName, CustomerPhone, RepairDate) VALUES('Annette Berceau', '301-988-4615', GETDATE()); GO INSERT INTO RepairOrders(CustomerPhone, CustomerName, RepairDate) VALUES('(240) 601-3795', 'Paulino Santiago', GETDATE()); GO INSERT INTO RepairOrders(CustomerName, RepairDate, CustomerPhone) VALUES('Alicia Katts', GETDATE(), '(301) 527-3095'); GO INSERT INTO RepairOrders(RepairDate, CustomerPhone, CustomerName) VALUES(GETDATE(), '703-927-4002', 'Bertrand Nguyen'); GO
You can also involve the function in an operation, then use the result as the value to assign to a field. You can also call a function that takes one or more arguments; make sure you respect the rules of passing an argument to a function when calling it.
If none of the Transact-SQL built-in functions satisfies your requirements, you can create your own. | <urn:uuid:c0647975-81bf-4915-9484-30a474c1ec66> | 2.75 | 811 | Tutorial | Software Dev. | 42.359164 |
The module Storable provides most elementary support for marshalling and is part of the language-independent portion of the Foreign Function Interface (FFI) - see also Section 4.13. It provides a class Storable and instances of this class for all primitive types that can be stored in raw memory. The member functions of this class facilitate writing values of primitive types to raw memory (which may have been allocated with the above mentioned routines) and reading values from blocks of raw memory. The class, furthermore, includes support for computing the storage requirements and alignment restrictions of storable types.
Memory addresses are represented as values of type Ptr a, for some a which is an instance of class Storable. The type argument to Ptr helps provide some valuable type safety in FFI code (you can't mix pointers of different types without an explicit cast), while helping the Haskell type system figure out which marshalling method is needed for a given pointer.
All marshalling between Haskell and a foreign language ultimately boils down to translating Haskell data structures into the binary representation of a corresponding data structure of the foreign language and vice versa. To code this marshalling in Haskell, it is necessary to manipulate primtive data types stored in unstructured memory blocks. The class Storable facilitates this manipulation on all types for which it is instantiated, which are the standard basic types of Haskell, the fixed size IntXX (Section 4.18) and WordXX (Section 4.38) types, stable pointers (Section 4.34), all types from CTypes (Section 4.7) and CTypesISO (Section 4.8), as well as Ptrs (Section 4.29)).
class Storable a where sizeOf :: a -> Int alignment :: a -> Int peekElemOff :: Ptr a -> Int -> IO a pokeElemOff :: Ptr a -> Int -> a -> IO () peekByteOff :: Ptr a -> Int -> IO a pokeByteOff :: Ptr a -> Int -> a -> IO () peek :: Ptr a -> IO a poke :: Ptr a -> a -> IO () destruct :: Ptr a -> IO ()
Minimal complete definition: sizeOf, alignment, one of peek, peekElemOff or peekByteOff, and one of poke, pokeElemOff and pokeByteOff. The behaviour of the member functions is as follows:
The function sizeOf computes the storage requirements (in bytes) of the argument, and alignment computes the alignment constraint of the argument. An alignment constraint x is fulfilled by any address divisible by x. Both functions do not evaluate their argument, but compute the result on the basis of the type of the argument alone.
Read a value from a memory area regarded as an array of values of the same kind. The first argument specifies the start address of the array and the second the index into the array (the first element of the array has index 0). The following equality holds,
peekElemOff addr idx = IOExts.fixIO $ \result -> peek (addr `plusPtr` (idx * sizeOf result))
Note that this is only a specification, but not necessarily the concrete implementation of the function.
Write a value to a memory area regarded as an array of values of the same kind. The following equality holds,
pokeElemOff addr idx x = poke (addr `plusPtr` (idx * sizeOf x)) x
Read a value from a memory location given by a base address and offset. The following equality holds,
peekByteOff addr off = peek (addr `plusPtr` off)
Write a value to a memory location given by a base address and offset. The following equality holds,
pokeByteOff addr off x = poke (addr `plusPtr` off) x
Read a value from the given memory location.
Write the given value to the given memory location.
Perform finalization (e.g. free an additional memory associated with the object) if poke does something which needs to be undone. A call to poke followed by destruct should leave resources in the same state as before. The default definition of destruct does nothing, as most types don't need any finalization.
Note that the peek and poke functions might require properly aligned addresses to function correctly. This is architecture dependent; thus, portable code should ensure that when peeking or poking values of some type a, the alignment constraint for a, as given by the function alignment is fulfilled. | <urn:uuid:30ab7895-4b57-4e50-9fba-60eb63276c2b> | 2.71875 | 925 | Documentation | Software Dev. | 42.353662 |
Lava, not water, may have carved the biggest channels on Mars.
Ever since NASA's Mariner 9 spacecraft beamed back the first images of the channels in the 1970s, most people have assumed they were created by massive floods. But David Leverington of Texas Tech University in Lubbock says flowing water would have left behind much more sediment than is seen. There are also few minerals that form in liquid water present.
Lava, however, is known to have carved big channels on the moon. And Leverington points out that some of the channels on Mars start on the flanks of volcanoes and end in large deposits of solidified lava (Geomorphology, DOI: 10.1016/j.geomorph.2011.05.022).
Kelin Whipple of Arizona State University (ASU) in Tempe agrees that lava probably carved the huge channels, such as Kasei Valles (shown). He says the study calls into question the case for huge volumes of water – and possibly an ocean – on ancient Mars.
But Phil Christensen, also at ASU, says clays and fans of sediment still point to the existence of smaller Martian lakes and rivers. These would be better places to search for life, he says, because they would have held water for longer periods than the giant channels, where floods – if there ever were any – would have been fleeting. "Lakes and deltas are probably the places people are going to look for life," he says.
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Plenty Of Water
Mon Aug 22 23:14:35 BST 2011 by Michael Paine
There appears to be sufficient quantities of water (ice) on Mars and climate fluctuations that redistribute this water to account for the formation of most valleys by water on Mars. Volcanoes cause the ice to melt and so it is not suprising that some channels start on the flanks of volcanoes. However it would be wise to assume that both lave and water can carve the canyons. Only geological sampling of the sites will resolve the issue.
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support. | <urn:uuid:3f607ba1-e14d-4a3e-8d9b-55af8ff3041c> | 3.921875 | 560 | Truncated | Science & Tech. | 54.708963 |
Size of 23s and 16s RNA different - (Apr/24/2006 )
I did DNA extraction from B. subtilis sample, but did not use any RNase to remove RNA in my sample. Two distinct bands appear at size 1.2kb and 1.7kb. I am suspecting they are 16s and 23s rRNA. However, I found out the size of 23 and 16s respectively are 2.9kb and 1.5kb.
Does electrophoresis conditions will affect the size of the RNA? I run normal agarose gel by the way, under non-denaturing conditions. Any other factors will affect the size of the RNA from different bacteria?
I'm not very familiar with this topic, but I remember two possibilites:
It is the RNA you mention, but already fragmented. Or second, the RNA is somewhat folded, i.e. having a secondary structure and so appearing to be smaller as expected on the gel.
But this are only guesses.
sizes of rRNAs will depend on percentage of gel, whether you use TBE or TAE.....try a RNase digest to see if you remove them if it is a problem.....?
You can't accurately size RNA under non-denaturing conditions. You should run a formaldehyde gel if you want to do this, with an RNA ladder rather than a DNA ladder | <urn:uuid:2f82beef-5928-42e0-92ec-f90a05ece7ec> | 2.84375 | 292 | Comment Section | Science & Tech. | 75.21229 |
This is a printer version of an UnderwaterTimes.com
To view the article online, visit: http://www.underwatertimes.com/news.php?article_id=86510072139
This graphic shows how the movements of the fish along the lake bed left the trails. Credit: Anthony Martin
ATLANTA, Georgia -- The wavy lines and squiggles etched into a slab of limestone found near Fossil Butte National Monument are prehistoric fish trails, made by Notogoneus osculus as it fed along a lake bottom, says Emory University paleontologist Anthony Martin.
"This is a fish story, about ," Martin says. "And I can tell you that the fish was 18-inches long, based on good evidence."
He led a detailed analysis, published May 5 in PLoS (Public Library of Science) One, that gives new insights into the behavior of the extinct N. osculus, and into the ancient ecology of Wyoming's former Fossil Lake.
"We've got a snapshot of N. osculus interacting with the bottom of a lake that disappeared millions of years ago," Martin says. "It's a fleeting glimpse, but it's an important one."
Fossil Lake, part of a subtropical landscape in the early Eocene Epoch, is now a sagebrush desert in southwestern Wyoming, located in Fossil Butte National Monument and environs. The region is famous for an abundance of exquisitely preserved fossils, especially those of freshwater fish.
Trails left by these fish, however, are relatively rare. The National Park Service had identified about a dozen of them and asked Martin to investigate. Martin specializes in trace fossils, including tracks, trails, burrows and nests made by animals millions of years ago.
One of the fish trace fossils especially intrigued Martin. In addition to apparent fin impressions of two wavy lines, it had squiggles suggesting oval shapes. "The oval impressions stayed roughly in the center of the wavy lines and slightly overlapped one another. I realized that these marks were probably made by the mouth, as the fish fed along the bottom," Martin says.
He then deduced that the trace was likely made by N. osculus - the only species found in the same rock layer whose fossils show a mouth pointing downward.
Martin brought his detailed notes, photos and sketches of the trace fossil back to Atlanta, where he enlisted the aid of disease ecologist Gonzalo Vazquez-Prokopec and geographer Michael Page, two of his colleagues in Emory's Department of Environmental Studies.
Vazquez-Prokopec, who does digital spatial analyses of geographic patterns of diseases and pathogens, applied similar techniques to the trace fossil data. The results showed a mathematical correlation between the trace impressions and the mouth, tail, pelvic and anal fins of an 18-inch N. osculus.
"This provides the first direct evidence of N. osculus bottom feeding," Martin says. "Not only that, the fish was bottom feeding in the deepest part of the lake. Previous research had suggested that the bottom of the lake had such low levels of oxygen that it was hostile to life. Our analysis indicates that, at least seasonally, some fish were living on the lake bottom."
The scientists were also able to calculate how the fish was moving, and the pitch and yaw of its swimming motion. "The trace fossil lines look simple, but they're not so simple," Martin says, explaining that even the gaps in the lines carry information.
Page, an expert in cartography and geographic information systems, created a map of the discovery site, and a Web site that allows viewers to zoom in on different aspects of the fish trace.
"All three of us believe in making scientific data as open and assessable as possible," Martin says, adding that he thinks it may be the first collaboration between a paleontologist, a disease ecologist and a geographer. "This opens up a new technique for studying trace fossils that we hope other people will try and test." | <urn:uuid:af575c11-9d51-4ea7-ab89-3bbc69247eeb> | 3.40625 | 842 | Truncated | Science & Tech. | 44.375777 |