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Just been two smaller ones off cali coast I believe, a 5 and a 6.
The depth where the earthquake begins to rupture. This depth may be relative to mean sea-level or the average elevation of the seismic stations which provided arrival-time data for the earthquake location. The choice of reference depth is dependent on the method used to locate the earthquake. Sometimes when depth is poorly constrained by available seismic data, the location program will set the depth at a fixed value. For example, 33 km is often used as a default depth for earthquakes determined to be shallow, but whose depth is not satisfactorily determined by the data, whereas default depths of 5 or 10 km are often used in mid-continental areas and on mid-ocean ridges since earthquakes in these areas are usually shallower than 33 km. | <urn:uuid:aa478ab7-62af-4638-9ef6-c35c5ad07d20> | 2.859375 | 165 | Comment Section | Science & Tech. | 42.432978 |
ENDANGERED SPECIES ACT PROFILE
PROTECTION STATUS: Not listed
RANGE: McCleary Canyon and Sawmill Canyon in the Santa Rita Mountains; a single population in the Dragoon Mountains
THREATS: Mining, livestock grazing, recreation, drought and global climate change
POPULATION TREND: Only four populations of this orchid were ever known, and one of them no longer exists. The remaining three populations combined have fewer than 200 flowers in any given year. Populations are known to decline in times of drought. | <urn:uuid:9dacac29-b851-44e2-8ec6-4c08ea591123> | 2.75 | 114 | Structured Data | Science & Tech. | 24.767749 |
Chandra Discovers Light Echo from the Milky Way's Black Hole
This set of Chandra images shows evidence for a light echo generated by the Milky Way's supermassive black hole, a.k.a. Sagittarius A* (pronounced "A-star"). Astronomers believe a mass equivalent to the planet Mercury was devoured by the black hole about 50 years earlier, causing an X-ray outburst which then reflected off gas clouds near Sagittarius A*.
The large image shows a Chandra view of the middle of the Milky Way, with Sagittarius A* labeled. The smaller images show close-ups of the region marked with ellipses. Clear changes in the shapes and brightness of the gas clouds are seen between the 3 different observations in 2002, 2004 and 2005. This behavior agrees with theoretical predictions for a light echo produced by Sagittarius A* and helps rule out other interpretations.
While the primary X-rays from the outburst would have reached Earth about 50 years ago, before X-ray observatories were in place to see it, the reflected X-rays took a longer path and arrived in time to be recorded by Chandra.
The clouds of gas featured in the image are glowing by a process called fluorescence. Iron in these clouds has been bombarded either by X-rays from a source that had an outburst in the past or by very energetic electrons. The electrons or photons hit the iron atoms, knocking out electrons close to the nucleus, causing electrons further out to fill the hole, emitting X-rays in the process.
The detection of variability in these fluorescing gas clouds rules out the possibility that they were bombarded by energetic electrons. It also helps rule out other explanations for the X-ray emission, including the possibility that the gas clouds are the remnants of exploded stars or that the light echo came not from Sagittarius A* but from a neutron star or black hole pulling matter away from a binary companion.
Studying this light echo gives a crucial history of activity from Sagittarius A*, and it also illuminates and probes the poorly understood gas clouds near the center of the galaxy. | <urn:uuid:1ba901e4-915c-44d4-bc6a-b5b0fbe127af> | 3.828125 | 435 | Knowledge Article | Science & Tech. | 45.645045 |
Unbeknownst to the Russians, their drill had mingled with the uppermost reaches of one of the largest freshwater lakes in the world; a pristine pocket of liquid whose ecosystem was separated from the rest of the Earth millions of years ago. As for what sort of organisms might lurk in that exotic environment today, no one can really be certain.
In prehistoric times the Antarctic continent was much more temperate, with lush tropical foliage and thriving wildlife. But millions of years ago the Earth's extra-flaky crust caused the landmasses of Australia and South America to gradually peel away from Antarctica, creating a ring of open sea around the southernmost continent. This allowed a massive oceanic current to begin encircling the pole, deflecting warmer northerly currents away from Antarctica's shores. Without warm water to moderate the temperature, a scab of polar ice developed over the formerly forested lands.
Roughly forty million years later, in 1996, the men and women of the Scientific Committee on Antarctic Research (SCAR) urged their Russian colleagues to halt their indiscriminate drilling.
Lake Vostok was found to have approximately the same surface area as the great Lake Ontario in North America, with more than thrice the depth. Separated from sunlight by two miles of solid ice, the subglacial lake is a place of profound darkness and bitter cold. The water temperature is estimated at 3 degrees below zero Celsius, but it maintains a liquid state due to the crushing weight of the polar ice slab; the temperature at which water freezes is significantly lower under such phenomenal pressure. It is also suspected that geothermal heat from the ground below adds some ambient warmth. According to the ice cores extracted by the Vostok Base scientists, the lonely lake has been sealed beneath the ice for at least 500,000 years, but possibly as much as 25 million.
As requested, the Russians temporarily suspended their drilling efforts pending further study. Their borehole-- which was filled with sixty tons of kerosene and freon to prevent re-freezing-- stopped within a mere 300 feet of the lake surface. The anomalous ice they had encountered turned out to be lake water which had long ago frozen to the bottom of the slowly migrating glacier. These ice samples provided a few insights into the lake's anatomy, such as its lack of salt, and its absurd overabundance of oxygen; under extreme pressures oxygen will more readily dissolve in water. If the drilling over Vostok had continued uninterrupted, thereby encroaching upon the liquid portion of the lake, the hapless Russians might have been assaulted by a towering geyser of ancient water and liberated oxygen due to the astonishing pressure of the hidden body of water.
It is not unreasonable to suggest that cold-tolerant creatures could thrive in the waters of Lake Vostok, overcoming the oxygen saturation with extraordinary natural antioxidants. But millions of years of evolutionary isolation in an extreme environment may have created some truly bizarre organisms. This notion is supported by the ice samples drawn from the ice just above Lake Vostok, where some unusual and unidentifiable microbial fossils have been found. But the possibility that they are merely contaminates has not yet been completely ruled out.
At present, a number of researchers are mulling over methods to investigate the lake's unique ecosystem without defiling its pristine nature. The introduction of any organisms or chemicals from the surface could irreversibly pollute its waters, and there is a small but real possibility that the lake's alien organisms could be dangerous to humans. To date, the best candidate seems to be the cryobot, a fittingly phallic penetrating probe designed to gingerly work its way into the virgin lake. Its heated tip would melt a channel straight into the ice as it unspools a power and communications line behind it. The melted water would quickly re-freeze behind the cryobot in temperatures which linger around minus 100 degrees Fahrenheit, and once it finally reached the water it would eject a small submersible hydrobot to capture images and take measurements.
If science seizes the opportunity to properly explore this perplexing pocket of liquid, it would be equally enlightening whether there is a plethora of life or a complete absence thereof. If the lake is found to be sterile, its desolate waters will provide some measure of insight into life's practical limitations. But if living things do indeed lurk beneath the thick Antarctic icecap-- even if only in microbial form-- their presence will demonstrate that life is made up of truly resilient stuff, with scientific implications well beyond the scope of our planet.
Update 06 February 2012: The Russians seem to have penetrated the ice and reached the upper reaches of the subglacial lake. Further penetration is on hold due to international outcry for more precautions. 07 March 2013: "Russian scientists believe they have found a wholly new type of bacteria in the mysterious subglacial Lake Vostok in Antarctica, the RIA Novosti news agency reported on Thursday. The samples obtained from the underground lake in May 2012 contained a bacteria which bore no resemblance to existing types, said Sergei Bulat of the genetics laboratory at the Saint Petersburg Institute of Nuclear Physics." | <urn:uuid:187ddee5-07af-4003-8910-6d407079f00c> | 3.90625 | 1,050 | Nonfiction Writing | Science & Tech. | 26.434348 |
A gas cloud weighing a million times the mass of the Sun is hurtling towards the Milky Way galaxy and is set to trigger stellar fireworks after it collides in 20 to 40 million years. A ring of stars in the Sun's neighbourhood may be the signature of a previous cloud's impact.
The cloud is made mostly of hydrogen gas and is 11,000 light years long and 2500 light years wide, about the size of a dwarf galaxy. It was discovered in 1963, but nothing was known about its motion towards our galaxy until now.
Using the Green Bank Telescope in West Virginia, US, a team led by Felix Lockman of the National Radio Astronomy Observatory has made a detailed radio image of the cloud and measured its velocity.
The new image shows the cloud's comet-like appearance as it ploughs into the gaseous "atmosphere" around our galaxy. The measurements also reveal the cloud is about 8000 light years away and is closing in on the Milky Way at 240 kilometres per second. Exactly when it will impact is unclear because astronomers are not sure how much the drag from our galaxy's envelope of gas will slow it down.
Based on its direction of motion, the cloud is expected to hit a region about a quarter of the way around the galaxy from the Sun, near the Perseus arm of the galaxy.
Astronomers think the results will be spectacular when the cloud does hit the galaxy. "You have all these shock waves that go out - it's just like making a bomb go off in this area," Lockman says. "In the shock waves, you can trigger a ring or region of enhanced star formation. A few million years later, they'll start going off as supernovae."
The impact of the gas cloud itself poses no danger to any inhabited solar systems that might be present at the impact site. Despite its great mass, it is spread out over such a wide area that it would have no direct effect on existing stars and planets. But the supernovae that go off a few million years later could be hazardous to life in solar systems unfortunate enough to be nearby, Lockman says.
A similar collision tens of millions of years ago may explain a ring of stars and gas about 2000 light years across that is slowly expanding in the Sun's neighbourhood. The ring includes most of the bright stars in the constellation Orion as well as the Orion star-forming region.
Although the motions of other hydrogen clouds near our galaxy have not been measured as well, some are probably heading towards the Milky Way as well. Such clouds probably regularly fall into our galaxy and supply it with new material for forming stars, Lockman says. "I think we're seeing now that the Milky Way is under bombardment," he says. "There are still fragments of it coming in that are still arriving on the scene."
If the cloud were visible to the naked eye, it would stretch about 10 to 12 degrees across the sky, about as wide as the constellation Orion.
The object is called Smith's Cloud after Gail Smith, now Gail Bieger, who discovered it 45 years ago as an astronomy student. Lockman recently contacted Bieger, who lives near The Hague in the Netherlands, to tell her about the new results. "She was quite astonished," Lockman says. "She said, 'You have brightened my day'."
The new observations of Smith's Cloud were revealed on Friday at a meeting of the American Astronomical Society in Austin, Texas, US.
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Sat Jan 12 01:47:20 GMT 2008 by Lusia Salazar
With a mass that big will the aftershock effect the earth at any point and time. And will it do very much damage or will it just take out everything on the earth with the aftershock?
Sun Jan 13 21:58:03 GMT 2008 by Fiona
Do you know when or if it will hit earth? I looked at the article and I couldn't find that information, unless I totally missed it.
Mon Jan 14 05:47:24 GMT 2008 by Anonymous
Hi Fiona. Not to worry. It will NOT strike the Earth. It is important to realize just how THIN the gas in the cloud is. Believe it or not, it is thinner than the "vacuum" that the International Space Station and its astronauts orbit through!
Even if such a cloud were to make a bull's eye on our Solar System, the gas in the cloud is so thin that it STILL wouldn't reach the planets. Why? Because the Sun produces a powerful "solar wind" that streams out in every direction. The solar wind would easily force the gas in such a cloud to move around it. Right this moment, the Sun is actually doing this: we are moving through a sea of interstellar gas which is being forced out of the way by its wind. The collision front produces a shock front (like the wave you see in front of a moving boat) that shoves the gas around our system. Most of the gas from interstellar space never reaches our planet.
But do not think that our planet escapes entirely: our planet has its own shock front, and our own Sun is responsible! Most of the particles in the solar wind are charged particles - the Earth's magnetic field deflects most of them. Those that do strike our atmosphere are channeled by the magnetic field to the polar regions, where they light up the sky in the form of wonderfully beautiful aurora displays.
Giant Gas Cloud
Sat Jan 12 03:06:05 GMT 2008 by Sgt_venom
Interesting. I wonder what it would be like to be born before it hits and fel the shock waves radiating out from ground zero at about age 15 or something.
Giant Gas Cloud
Sun Jan 13 21:59:34 GMT 2008 by Fiona
Can you please tell me what a shock wave is? Is it dangerous?
Giant Gas Cloud
Mon Jan 14 05:05:54 GMT 2008 by Anonymous
Hi Fiona. Good question. Basically, a shock wave is any disturbance in a gas or liquid that moves faster than the speed of sound in that medium. Ordinary sound waves in air, for example, propagate by the collisions between molecules. But after a sound wave passes a group of molecules, their basic arrangement remains unchanged. A shock wave moves so fast that the molecules cannot move out of the way quickly enough, so the molecules pile up ahead of it for a time.
Lots of things can produce shock waves, and most of them are not dangerous (except sometimes to one's hearing!). When something moves through the air faster than the speed of sound, for example, it pushes air molecules out of the way faster than the air molecules themselves move. This produces a shock wave. In objects like a fast aircraft, a meteor, and even the tip of a cracking whip, a shock wave is produced which travels faster than sound for a distance until its energy is dissipated into ordinary sound waves, which we call a "sonic boom".
Lightning bolts heat the air so intensely that it explosively expands to produce a shock wave that soon dissipates into the familiar sound of thunder, which is a kind of extended sonic boom. (Thunder can roll on for some time after you see the lightning flash because it takes some time for all the sound waves to reach your ear from every point along the length of the lightning bolt, which can be miles long). You can probably think of other examples.
Sat Jan 12 06:01:02 GMT 2008 by Anonymous
Please re-read the article. The million solar-mass cloud sounds like a very bad cloud, but it's spread out over a vast region of space. The gas in this cloud is therefore actually more rarefied than the best vacuums that can be produced in a laboratory.
Condensed objects like stars as well as the Sun and its family of planets would not be affected any more than they are by countless gusts of interstellar gas they are passing through now and have been passing through throughout their history, including numerous supernova shocks. (Moreover, stars surround themselves with a stellar wind which effectively deflects interstellar gas around them).
The "collision" will be between the gas molecules and atoms in this cloud and those in our galaxy, producing a shock front (still a very good vacuum!) which can locally enhance the density enough to trigger star formation via gravitational collapse over millions of years: the effect would be that we'd simply see more star-forming regions appearing around us. It's undoubtedly happened numerous times in the past (as the article suggests) and will probably happen numerous times in the future. Residents of our galaxy will thus continue to enjoy the beauty and splendor of continued star formation for a long time to come. With that enhanced star formation, one gets supernova explosions, but space is a big place and one would have to go off well within 100 light-years of a life-bearing planet for it to cause much harm.
Incidently, the illustration is a little misleading: by the time the cloud strikes the spot indicated in about 40 million years, our own orbital motion around the galaxy will have brought us to near front-row seats.
Sun Jan 13 00:44:48 GMT 2008 by Whitefang
The illustration may be misleading. But the impact site and the location of the sun isn't. An animation would probably have the galaxy rotated anti clockwise by about 90 degrees and then as the cloud came in, the galaxy would rotoate around with the gas hitting the approx site correctly.
Mon Jan 14 05:27:00 GMT 2008 by Anonymous
Hence the qualifier in the phrase, "a LITTLE misleading". You are wrong: the illustration IS fairly accurate for the CURRENT situation. (Why muddy it up by suggesting that the galaxy be rotated 90 degrees anti-clockwise?). But if you were to run time forward 40 million years you would see our Solar System arriving near the approximate location of the cloud's impact somewhere near what is CURRENTLY the Perseus Arm, which is an outer arm which we do not occupy. We would still be substantially closer to the core than the impact site. (Our orbit, BTW, travels routinely through spiral arms substantially more populated than the outer arm - a region which is treacherous enough as it is. Our Sun is orbiting the galaxy in a period of somewhat under a few hundred million years: in 40 million years we shall have advanced about a quarter of that circuit from our current position). I brought it up as a LITTLE misleading since some readers may have come away with the impression that the cloud's impact site would be as distant from us as the illustration implies. The center of the cloud impact in 40 million years could be roughly as near to us as the Perseus Double Cluster is now, or around 8,000 light-years.
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Ornate Chorus Frog
Scientific Name: Pseudacris ornata
Description: A stout species and the largest chorus frog species in the southeast, reaching a maximum length of 1.6 in. This species displays a variety of background colors including gray, brown, reddish-brown, and even bright green. All individuals exhibit bold dark stripes through the eyes and along the sides, but the pattern along the sides may be broken. The forelimbs and hind limbs are marked with dark bars, and most individuals exhibit a dark triangle on top of the head between the eyes. Dorsal (back) patterns may or may not be present. The groin and thigh areas are bright yellow.
Distribution: Ornate chorus frogs are a Coastal Plain species, ranging from North Carolina, south through North Florida, and west to extreme eastern Louisiana. In Alabama, this species is restricted to the southeast region of the state, extending into Mississippi only along the coast.
Habitat: The ornate chorus frog inhabits ephemeral (temporary) wetlands and surrounding uplands associated with Coastal Plain forest habitats such as sandhills, pine flatwoods, and upland pine forests. Breeding habitats include cypress ponds, wet meadows, Carolina Bays, barrow pits, and roadside ditches. During the nonbreeding season, these frogs hide in burrows or under logs and debris in the adjacent uplands.
Feeding Habits: Feeds primarily on small insects and other invertebrates.
Life History and Ecology: Ornate chorus frogs are most active during the winter months and breeding occurs from December to March with the peak activity depending on rainfall. Males arrive at the breeding ponds before the females, so calls may be heard as early as October and November after significant rain events. Males advertise to females while floating or perched just above the water on aquatic vegetation or floating debris. Their call is a metallic peeping that has been compared to the sound of a hammer hitting a chisel. It is similar to a spring peeper’s call but differs in that is a sharper, shorter note that does not increase in pitch.
Females lay eggs in clumps of 20-100, attaching them to aquatic vegetation. The tadpoles hatch within a few days and will transform into froglets within 3 months. Tadpoles have a high tail fin with two gold stripes usually present on the sides of the back with a dark background. Some individuals have a bicolored tail. Tadpoles can reach a length of 1.75 in. before transforming.
Basis for Classification: Declines of this species are occurring throughout much of its range. Loss of breeding habitat along with destruction and disturbance of the surrounding uplands during industrial pine farming are likely contributors. Ornate chorus frogs live in habitats that are predominantly fire dependent, and lack of fire in these systems can cause dramatic changes in wetland vegetation and water levels. These changes may cause the loss of populations in many areas where frequent (prescribed) fire does not occur. Pine plantation operations along with a restricted range in Alabama make this a potential species of concern for the state.
Dorcas, M. and Gibbons, W. 2008. Frogs & Toads of the Southeast. University of Georgia Press, Athens, GA. 238 pp.
Jensen, J. B., Camp, C. D., Gibbons, W., Elliott, M. J. 2008. Amphibians and Reptiles of Georgia. University of Georgia Press, Athens, GA. 575 pp.
Mount, Robert H. 1975. The Reptiles and Amphibians of Alabama. Auburn Printing Company, Alabama. 347 pp.
Author: Aubrey M. Heupel, Wildlife Biologist, Alabama Partners in Amphibian and Reptile Conservation, January 2011 | <urn:uuid:9db10ac0-7c76-4f35-8400-69febc94a417> | 3.265625 | 781 | Knowledge Article | Science & Tech. | 51.719682 |
|Feb4-13, 10:58 AM||#1|
1. The problem statement, all variables and given/known data
You have two identical tiny conducting spheres: sphere A carries positive charge qA, and sphere B carries negative charge qB. First the spheres are placed distance d = 0.404 m apart, and they attract each other with a force F1 = 0.748 N. Then the spheres are brought together, touch each other, and are brought back to distance 0.404 m apart. Now the spheres are both positive, and they repel each other with force F2 = 0.59 N. Find the original charge on each sphere.
2. Relevant equations
3. The attempt at a solution
after the spheres touch i get qf=(q1+q2)/2
and i solve for the charge on the spheres after they touch and get .1035uC as my answer but im not sure how to find original charge after that my proffesor never did an example like this any help is welcome and appreciated
|Feb4-13, 11:41 AM||#2|
Charge is conserved. Make use of that along with F1.
Besides, this belongs in the introductory physics section.
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|Coulomb's Law||Introductory Physics Homework||8| | <urn:uuid:9d6826f1-e07f-4952-97b1-8de43c9a3911> | 3.5625 | 369 | Comment Section | Science & Tech. | 67.720588 |
GET and POST
When defining the method a web browser should use to send variables to the page specified by your action, you either use GET or POST. Both send variables across to a page, but they do so in different ways.
GET sends its variables in the URL of your visitors' web browsers, which makes it easy to see what was sent. However, it also makes it very easy for visitors to change what was sent, and, moreover, there is usually a fairly low limit on the number of characters that can be sent in a URL - normally fewer than 250. As a result, if you send long variables using GET, you are likely to lose large amounts of it.
POST on the other hand sends its variables hidden to your user, which means it is much harder to mimic, cannot be changed without some effort on your visitors' behalf, and has a much higher limit (usually several megabytes) on the amount of data that can be sent. The downside to using POST is that browsers will not automatically re-send post data if your user clicks their Back button, leading to messages like "The data on this page needs to be resent", which often confuses users. This does not happen with GET, because browsers consider GET URLs the same as any other URL, and so happily re-send data as needed.
You can set how much data PHP should accept by editing the post_max_size entry in your php.ini file - it is usually set to 8M by default, allowing your users to transfer up to 8 megabytes.
Given this new found knowledge, here's the same form again, this time using action and method. It will still look the same as our previous effort, but this time it will use POST to send data to someform.php:
<input type="submit" />
Next chapter: Available elements >>
Previous chapter: Designing a form
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Farnsworth: These are the dark matter engine I invented. They allow my starship to travel between galaxies in mere hours.
Cubert: That's impossible. You can't go faster than the speed of light.
Farnsworth: Of course not. That's why scientists increased the speed of light in 2208.
--Futurama, "A Clone of My Own"
We may not have to wait two centuries. Researchers in Switzerland's Ecole Polytechnique Federale de Lausanne (EPFL) have developed a method of altering the speed of light in an off-the-shelf optical fiber. Their findings were published in the current Applied Physics Letters, and describe being able to reduce the speed of photons in optical fiber to below 71,000 km/s (the speed of light in a vacuum is approximately 300,000 km/s) as well as increasing photons to a speed "well exceeding the speed of light in vacuum." The press release isn't much more forthcoming than the abstract, noting only that "relativity isn't called into question, because only a portion of the signal is affected."
Much more attention is given to the ability to slow light. This is because, counter-intuitive though it may be, slowing down light could lead to significantly faster computers. Slowed-down light would allow for temporary "optical memory," allowing for routing and processing of optical computing signals without having to convert to electricity (which slows down processing considerably). The speed gained by not having to do conversion from light to electricity more than compensates for any speed loss from "slow light."
The attractive aspect of this development is that it uses off-the-shelf technology at room temperature, and doesn't require exotic materials or environmental conditions.
Now if someone can explain (a) how much faster than light they achieved, and (b) why this doesn't violate relativity?
(a) No clue (b) Group Velocity can exceed the speed of light. Cannot send or recieve information with it unfortunately I believe that's why it doesn't invalidate any of Einsteins work. It may happen at a later date but who knows eh.
"Group velocity" is like the spokes in stagecoach wheels in old Western movies. They can appear to move faster or slower than the stagecoach is moving, or even backwards. They don't violate physical laws because the movement is illusory.
Another example would be the point of intersection of the blades of a scissors. The intersection point can move faster than the speed of light, but physics isn't violated because the blades themselves are moving much more slowly.
While the phenomenon is potentially of use in telecommunications, press releases on group velocity findings are traditionally misleading in order to attract attention. Information is not actually moving faster than light, just the point that the information appears to come from.
The faster-than-light speed they claim is 205,000 km/s. The authors point out that the signal is highly distorted in this case, and that not all of the parts of the signal can propagate this fast, so that the information contained in the signal is still limited to the speed of light. I must admit my comprehension of this article is less than 100%, so hopefully I haven't mis-stated anything....
Can someone explain (for non-subscribers) (c) just _how_ this works?
Unfortunately we frequently read in the newspapers about how someone has succeeded in transmitting a wave with a group velocity exceeding c, and we are asked to regard this as an astounding discovery, overturning the principles of relativity, etc. The problem with these stories is that the group velocity corresponds to the actual signal velocity only under conditions of normal dispersion, or, more generally, under conditions when the group velocity is less than the phase velocity. In other circumstances, the group velocity does not necessarily represent the actual propagation speed of any information or energy. For example, in a regime of anomalous dispersion, which means the refractive index decreases with increasing wave number, the preceding formula shows that what we called the group velocity exceeds what we called the phase velocity. In such circumstances the group velocity no longer represents the speed at which information or energy propagates.
Set up say, 1000 domino blocks in a row. Then tip the first one over. Given constant size, weight, spacing of individual blocks, and a horizontal surface, you will observe blocks falling down at a constant rate/speed ('c'). Given that constant rate/speed, tipping over the first block will cause all blocks to fall down, tipping over the last block some time later. Time delay calculates as distance divided by 'c'.
Now, create 'extreme conditions', where the first domino block is down, the last one is still standing, and halfway down the row, blocks are falling, but not quite down on the floor. Then, observe the 'wave front' of falling domino blocks. It will appear to move faster than the previously determined 'c'. How come?
Look more closely: as each block falls down, there's a fixed delay before it hits the next block. But what happens under our 'extreme conditions'? At the exact time a previous block would have hit the next one (under normal circumstances), that next block is already falling down! The time it takes for the 1000 blocks to fall down, is less than what normally would be expected.
Did this 'c' constant get violated? Nope, it still took the same amount of time for each block to fall down. Was the maximum 'c' speed exceeded? Nope. After tipping the first block, it still took the same amount of time before this 'information' was passed on to the next block. With a set of 1000 blocks all standing, the time needed for an initial 'disturbance' to be passed on to the last block, is still limited by 'c'.
So these 'extreme conditions' are like pre-tipping each block, and let you observe something that appeared to move faster than 'c'.
Nice for the lab folks, but other than that, sensationalist journalism. | <urn:uuid:3affdeae-ecde-4920-a643-ee58f53241a3> | 3.625 | 1,254 | Comment Section | Science & Tech. | 51.215729 |
Porites is a genus of stony coral; they are SPS (Small Polyp Stony) corals. They are characterised by a finger-like morphology. Members of this genus have widely spaced calices, a well-developed wall reticulum and are bilaterally symmetrical. Porites, particularly Porites lutea, often form microatolls.Corals of the genus Porites also often serve as hosts for christmas tree worms (Spirobranchus giganteus).
Specimens of Porites are sometimes available for purchase in the aquarium trade. Most Porites that are collected have Christmas tree worms (Spirobranchus giganteus) that bore into the coral, serving as additional aesthetic livestock. These particular Porites specimens are called "christmas tree worm rocks" or "christmas tree worm coral". However, due to the strict water quality, lighting and dietary requirements, keeping Porites in captivity is very difficult.
- WoRMS (2010). "Porites Link, 1807". World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=206485. Retrieved 2011-12-15.
- "ITIS Standard Report Page: Porites". http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=53178. Retrieved 2011-12-15.
- Flora, C.J.; Ely P.S. (2003). "Surface Growth Rings of Porites lutea Microatolls Accurately Track Their Annual Growth". Northwest Science 77 (3): 237–245. http://research.wsulibs.wsu.edu:8080/dspace/bitstream/2376/798/1/v77%20p237%20Flora%20and%20Ely.PDF. Retrieved 2009-10-30.
|This class Anthozoa related article is a stub. You can help Wikipedia by expanding it.| | <urn:uuid:4e29f72b-ca10-4eef-a34a-1914900bdbd0> | 2.8125 | 434 | Knowledge Article | Science & Tech. | 55.171884 |
Ionizing & Non-Ionizing Radiation
Ionizing & Non-Ionizing Radiation
Radiation having a wide range of energies form the electromagnetic spectrum, which is illustrated below. The spectrum has two major divisions:
Radiation that has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons, is referred to as "non-ionizing radiation." Examples of this kind of radiation are sound waves, visible light, and microwaves.
Radiation that falls within the ionizing radiation" range has enough energy to remove tightly bound electrons from atoms, thus creating ions. This is the type of radiation that people usually think of as 'radiation.' We take advantage of its properties to generate electric power, to kill cancer cells, and in many manufacturing processes.
The energy of the radiation shown on the spectrum below increases from left to right as the frequency rises.
|Types of Radiation in the Electromagnetic Spectrum|
|Type of Radiation|
We take advantage of the properties of non-ionizing radiation for common tasks:
- microwave radiation telecommunications and heating food
- infrared radiation infrared lamps to keep food warm in restaurants
- radio waves broadcasting
Non-ionizing radiation ranges from extremely low frequency radiation, shown on the far left through the audible, microwave, and visible portions of the spectrum into the ultraviolet range.
Extremely low-frequency radiation has very long wave lengths (on the order of a million meters or more) and frequencies in the range of 100 Hertz or cycles per second or less. Radio frequencies have wave lengths of between 1 and 100 meters and frequencies in the range of 1 million to 100 million Hertz. Microwaves that we use to heat food have wavelengths that are about 1 hundredth of a meter long and have frequencies of about 2.5 billion Hertz.
Higher frequency ultraviolet radiation begins to have enough energy to break chemical bonds. X-ray and gamma ray radiation, which are at the upper end of magnetic radiation have very high frequency in the range of 100 billion billion Hertz and very short wavelengths 1 million millionth of a meter. Radiation in this range has extremely high energy. It has enough energy to strip off electrons or, in the case of very high-energy radiation, break up the nucleus of atoms.
Ionization is the process in which a charged portion of a molecule (usually an electron) is given enough energy to break away from the atom. This process results in the formation of two charged particles or ions: the molecule with a net positive charge, and the free electron with a negative charge.
Each ionization releases approximately 33 electron volts (eV) of energy. Material surrounding the atom absorbs the energy. Compared to other types of radiation that may be absorbed, ionizing radiation deposits a large amount of energy into a small area. In fact, the 33 eV from one ionization is more than enough energy to disrupt the chemical bond between two carbon atoms. All ionizing radiation is capable, directly or indirectly, of removing electrons from most molecules.
There are three main kinds of ionizing radiation:
- alpha particles, which include two protons and two neutrons
- beta particles, which are essentially electrons
- gamma rays and x-rays, which are pure energy (photons). | <urn:uuid:9c49f8b8-e4a2-4085-916b-5acbbad16bb2> | 3.953125 | 679 | Knowledge Article | Science & Tech. | 31.781358 |
According to the third law of motion, you van't have an mass move in a particular direction unless there is a proportional opposite mass/acceleration ratio in the opposite direction.
No-one has been able to provide a convincing argument otherwise, but the best one to date is Shawyer's EM Drive. He claims some fancy relativistic effects are what allows his engine to work, but I have read some papers which claim he is a fraud.
My question is, why is it impossible to move a mass in a given direction without a proportional change in the opposite direction?
I'm not talking about a perpetual motion machine, or anything. Sure, the device would need to consume at least the amount of energy proportional to the energy required to accelerate the mass.
Here's a highly hypothetical example: Say we either can project a gravity well in front of our vehicle, and/or project a gravity hill behind. In empty space, the effects of the gravity will be near-negligible by the time they reach any other object, however close to the vehicle they will be more significant. The end result would be the vehicle would move in the given direction, and nothing else around would really move at all.
An even cruder example would be to shine a bright torch out the back of your vehicle. Even though the photons have no mass, wouldn't the vehicle move forward? | <urn:uuid:27f23cc4-268f-4370-ba43-e29cbe9f1324> | 3.203125 | 282 | Q&A Forum | Science & Tech. | 42.922355 |
Neutrons and atoms
Neutrons are found in the nuclei of all atoms that are heavier than hydrogen. The chemical behavior of an element is determined by the electronic structure bound to the nucleus, and it is the number of protons in the nucleus that determine the nuclear charge which is balanced, for the atom, by the number of electrons. However, the mass of the nucleus varies with the number of neutrons, differing numbers of neutrons defining different isotopes.
Except for hydrogen-1 (a bare proton) and helium-3 (two protons and one neutron), isotopes of elements with fewer neutrons than protons are not stable. Stable heavier elements have either the same number of neutrons as protons or have more neutrons.
The heaviest fully stable element is lead, with 82 protons, and three stable isotopes with 124 to 126 neutrons.
Free neutrons
Neutrons that are not part of a nucleus are, themselves, unstable. They have a half-life of about 15 minutes, and decay into a proton and an electron.
Because a neutron has no electric charge, it can nuzzle up nice and close to a (positively charged) atomic nucleus without being repelled away. If conditions are right, this nucleus can capture the neutron, adding it to its contents. This results in the nucleus becoming a new isotope of the same element; a carbon-12 nucleus that captures a neutron, for example, would become a carbon-13 nucleus. Unfortunately, depending on the nucleus that did the capturing, the new resulting isotope can be radioactive. If a non-radioactive cobalt-59 nucleus captures a neutron, for example, it becomes radioactive cobalt-60. Nuclear scientists refer to this process as "neutron activation", but most folks call it radioactive contamination.
Neutron radiation
Nuclear fission results in neutron radiation consisting of free neutrons. This radiation is blocked by water, concrete, and paraffin wax.
The speed of emitted neutrons makes a difference as to how often they get captured by the nuclei they run into. Fast neutrons are rarely captured, but the slower thermal neutrons are much more likely to be captured.
See also
- ↑ They can even be found in the nuclei of hydrogen -- the heavy hydrogen isotopes deuterium and tritium contain one and two neutrons per nucleus, respectively. | <urn:uuid:19445782-cb35-40b3-b720-f5eb08f8a48a> | 4.625 | 499 | Knowledge Article | Science & Tech. | 39.482674 |
Juno (space probe)
Juno (also Jupiter polar orbiters) is a planned space probe of NASA, which is to study the giant planet Jupiter from a polar orbit at least one year long. It is after new Horizons the second space probe of the new Frontiers of program of NASA and may thus at the most 700 million US Dollar cost. The probe, not later than to 30. June 2010 to start is (although another starting possibility is likewise considered at present in August 2011), is at present (conditions at the end of of 2005) in the planning phase and is afterwards with Lockheed Martin under direction of the project of the JPL to be built. Contrary to earlier space probes to the planet Jupiter will not possess Juno nuclear power supply, but by particularly efficient solar cells the necessary river to generate. However the use of solar cells is possible only in this special case, since Juno mostly is on a polar orbit favorable for sun power production outside of the strong radiation belts of the Jupiters. A mission to the moons of the Jupiters would be for example further dependent on a nuclear power supply and particularly radiation-resistant electronics.
the start of the probe is to take place either in June 2010 or in August 2011 on board Atlas a V (551 ) in Cape Canaveral. The probe will accomplish two years after the start Swing by - maneuvers at the earth, which it will accelerate toward Jupiter. The entire journey to the Jupiter will take up 5.2 years flying time. There arrived, Juno will occur a polar orbit with a Periapsis of 5000 km and a scan time of eleven days. The primary mission of the probe is to take about one year long and contain 32 of such orbits.
Juno will carry seven instruments and to the following tasks will dedicate themselves:
- Examination of the existence of a firm Jupiterkerns
- determination of the portion of water, ammonia and methane in the atmosphere
- study of convection and production of wind profiles in the atmosphere
- determination of the source of the Jupiter of magnetic field
- investigation of the polar Magnetosphäre.
The probe is equipped with the following instruments:
- Jovian Auroral distribution experiment (JADE)
- JADE will study the Aurora of the Jupiters, by loaded particles, as electrons and ions are measured, along the Magnetfeldlinien of the planet. The instrument is built by the Southwest Research of institutes (SwRI ).
- Juno Ultraviolet Spectrograph (UVS)
- UVS will take photographs of the Aurora in the ultraviolet light and will work at it together with JADE. The instrument is built by the Southwest Research of institutes (SwRI).
- Magnetometer (LIKES)
- a magnetometer to the study that of magnetic field. The instrument is built by the Goddard space Flight center and JPL.
- Microwave radiometer (MWR)
- microwaves a spectrometer for the measurement of ammonia and Wasseranteils in the Jupiteratmosphäre. The instrument is built by the JPL.
- Energetic Particle Detector (EPD)
- the instrument is built by the Applied Physics Labority John Hopkins University.
- the instrument is built by the University OF Iowa.
- a smaller camera, which is to take photographs of Jupiters cloud cover in the visible light. Besides it is possible that the camera will take photographs of jupiternahen moons, like IO or Amalthea. The instrument is built by Malin space Science of system.
Web on the left of
- Juno side at NASA (English)
- The Juno mission ton of Jupiter (English)
- JunoCam - camera of the Juno space probe (English)
see also: List of the unmanned space missions
painted missions: Jupiter Icy Moons orbiter | <urn:uuid:ecfb5889-e5a4-42f5-ae58-085a769a5aa4> | 3.46875 | 802 | Knowledge Article | Science & Tech. | 38.016987 |
Asian Elephants: Threats and Solutions
The Asian elephant once roamed from the Tigris and Euphrates rivers in western Asia as far east as China's Yangtze River. No longer. Now a highly endangered species, it has been eliminated from western Asia completely, from substantial parts of the Indian subcontinent and Southeast Asia, and almost entirely from China. Exceedingly adaptable in diet and behavior, elephants can survive anywhere from grasslands to rain forests, but they must migrate across large areas to find water and suitable food at different times of the year. Such vast ranges have become extremely rare in densely populated, rapidly developing Asia.
Though it's difficult to count elephants in the wild, it's estimated that the wild Asian population, which numbered in the hundreds of thousands at the turn of the 20th century, is now only 37,000 to 48,000 animals. Yet thanks to ancient cultural tradition, about 16,000 Asian elephants are kept in captivity in 11 Asian countries. This situation makes the Asian elephant unique among endangered large mammals. In Thailand there are nearly three times as many elephants in domesticity as in the wild.
Threats to Wild Elephants
• No room to roam: The greatest threat to wild Asian elephants is habitat loss and fragmentation. Throughout the tropics, humans have cleared large areas of forest and have rapidly populated river valleys and plains. Elephants have been pushed into hilly landscapes and less suitable remnants of forest, but even these less accessible habitats are being assaulted by poachers, loggers, and developers.
Once-continuous habitat has become increasingly broken up by dams, tea and coffee plantations, roads, and railway lines. These developments obstruct the seasonal migrations of elephant clans. Habitat fragmentation also divides elephant populations into small, isolated groups, which are then at risk of inbreeding. Some biologists believe that there are no longer any wild Asian elephant populations large enough to avoid genetic deterioration over the long term.
• Conflicts with humans: When elephants stray out of the forest into settled areas, they sometimes destroy property, trample crops, and even kill people. Not infrequently, farmers respond with gunfire or poison.
• Ivory poaching: The international ivory trade has contributed far more to the decline of African elephants than Asian ones over the last few decades. Still, the people of Asia have a 500-year tradition of ivory carving and often hunt males for their tusks.
• Capture of young elephants: Many young elephants are removed from the wild to supply tourist and entertainment industries. In the process, mothers and other females attempting to protect the young are killed. Many calves captured for such purposes are prematurely weaned, socially isolated or otherwise cruelly treated, and die before they reach age five.
Threats to Domestic Elephants
For thousands of years the elephant was part of the fabric of daily life in Asia. They served primarily to transport goods and people. When the 20th century began, elephants were put to use by the timber industry, destroying their own habitat in the process. Except in less-developed Myanmar, the need for elephant labor has steadily declined since World War II, and so has the domesticated Asian elephant population.
With domestic elephants becoming obsolete, the occupation of mahout, or elephant handler, no longer commands the respect it once did. The profession, its specialized knowledge, and the time-honored relationship between man and animal are dying out. Children have little interest in learning the trade. "The skill level of elephant-keeping, the ability to control bulls, is going down very, very rapidly," says Thai elephant expert Richard Lair. "Ten, twenty, fifty years from now, what are we going to be doing with our bull elephants?"
The biggest problem facing domesticated elephants is unemployment. The situation is perhaps most dire in Thailand, where a complete ban on logging in 1989 put several thousand elephants and mahouts out of work. An elephant typically eats about 200 kilograms of food a day, "so unless you're a very wealthy person who likes to keep expensive pets, or unless your elephant is actually working for you and generating some income, it's not easy to keep an elephant in captivity," explains Robert Mather, the country representative for the World Wildlife Fund in Thailand.
And while one person can watch a whole herd of cattle or sheep, each elephant needs one person and sometimes two people to look after it. But with the decline in skilled mahouts, many elephants are now handled by inexperienced people. This leads to elephants that at best are poorly cared for and at worst severely abused. Human keepers are being harmed by elephants more often as well.
New Jobs for Beasts of Burden?
Although well protected from international trade, Asian elephants have little protection under domestic laws. Generally, national wildlife agencies in Asia consider the domesticated elephant to be just another domestic animal (and allow their tusks to be sold), while livestock departments consider it wild and not under their jurisdiction. "So it's in a very curious, halfway position that makes conservation very difficult," explains Lair. Caring for privately owned domesticated Asian elephants often turns out to be the job of an impoverished mahout—or nobody's job at all.
Elephants are now competing for fewer jobs at lower pay, which has forced mahouts to accept undesirable jobs or to overwork their animals. In Thailand, some owners have even started selling their elephants to be slaughtered for meat. Less than 10 years ago, such an act would still have been unthinkable. "Captive elephants in Thailand at the moment would seem to have rather limited options," says Mather bluntly. Possibilities include:
• The tourist industry: Ecotourism is a booming market in many developing countries, and often it's the only viable solution for elephants. In addition to offering protection to some wild herds so that tourists can observe them in their natural habitat, ecotourism has given many domesticated elephants better work opportunities. The elephants that carry tourists safely on treks through the jungle are usually well cared for. "It's not desirable; it's not traditional," Lair points out. "On the other hand, it's relatively harmless, and it's the only form of employment that will make sure that people continue to keep elephants." But not all elephants are temperamentally suited for toting tourists—especially not the large, aggressive male elephants once valued by loggers.
Unfortunately, an increasing number of elephants are also being used in less benign forms of tourism. Performing in shows or serving as special attractions in hotels and tourist centers, they often suffer from lack of social contact with fellow elephants or risk injury doing dangerous and unnatural tricks.
• Logging: Selective logging—in which only certain trees are cut, leaving the forest habitat as a whole intact—would be an optimal choice. Elephants could work in a traditional and legitimate manner, and their use would protect the forest by reducing the need for roads and heavy machinery. Selective logging is rarely employed, however. It is an option only in places where sufficient healthy forest remains, which is not the case in many parts of Asia. And in Thailand, the 1989 ban has made all forms of logging illegal.
The Thai ban sparked a jump in lumber prices, which led to a boom in illegal woodcutting. Elephant labor is essential to this illicit trade, which is thought to employ between 1,000 and 2,000 animals, in northern Thailand in particular. But these animals are poorly cared for.
• Begging in the streets: More and more elephants can be found with their destitute mahouts begging for money in the streets of large Asian cities like Bangkok. These elephants suffer respiratory infections, damage property, and get hit by cars.
Solving the Plight
Fortunately, the elephant has become a flagship species of wildlife conservation in all 13 countries of Asia where it is still found. Efforts are being made on many fronts:
• Reducing the hunting and capture of wild elephants for ivory and tourism.
• Curbing habitat destruction: One solution is to create vegetated corridors between separated habitats. This can be as simple as building a bridge across a canal, but the bridge must be wide, as only bulls are bold enough to cross a narrow bridge. Other ways to improve the quantity or quality of remaining habitat include maintaining a buffer zone of secondary-growth forest and creating waterholes.
• Improving protection of wild herds: This is complicated. Populations must be large enough offset inbreeding and environmental dangers such as droughts and floods. Yet herd size must be controlled to minimize encroachment on human habitats and to foster local support for elephant conservation.
Trenches, electric fences, spotlights, and noisy rockets have all been used to deter elephants from straying onto planted fields, but with varying degrees of success. Other tactics include persuading farmers to grow crops that aren't attractive to elephants and removing troublesome bull elephants. However, the males disproportionately responsible for crop damage and attacks on humans tend to be the most successful breeders, so eliminating them from the population isn't a desirable solution. If existing habitat is inadequate, sometimes elephants are relocated to roomier ones.
• Better care for captive elephants: Another initiative is to establish centers to accommodate unwanted, abused, and confiscated elephants. For example, the Thai Elephant Conservation Center in Lampang provides a home, work, food, and veterinary care to more than 100 elephants. Dangerous animals are confined in a secure area; young working elephants are trained; and the rest roam free and breed, producing young elephants that will be reintroduced to the wild.
• Reintroduction to the wild: "If elephants can't find gainful employment, then instead of having them wandering the streets of Bangkok begging for money from tourists or Thais, let's just put them back in the wild," says Mather. "Send them back into the forest. That's their home." Thailand's Elephant Reintroduction Foundation does such work, releasing domesticated elephants into the wild to generate wild herds.
More About This Resource...
Our innovative Science Bulletins are an online and exhibition program that offers the public a window into the excitement of scientific discovery. This essay was published in July 2007 as part of the Wild at Heart: The Plight of Elephants in Thailand Bio Feature.
- It begins by stating the Asian elephant once roamed from the Tigris and Euphrates rivers in western Asia as far east as China's Yangtze River.
- It then explains that the Asian elephant is now a highly endangered species, with the unique situation of having nearly three times as many elephants in domesticity as in the wild.
- The essay then details the threats faced by wild and domestic elephants, followed by conservation efforts in all 13 countries of Asia where the elephant is still found.
Supplement a study of biology with a classroom activity drawn from this Science Bulletin essay.
- Have students read the essay (either online or a printed copy).
- Working individually or in small groups, have students create an poster that warns of the dangers of either ivory poaching or removing elephants from the wild to supply tourist and entertainment industries. | <urn:uuid:060f83b7-2007-4bc5-8124-965c7d6ad571> | 3.625 | 2,271 | Knowledge Article | Science & Tech. | 35.595211 |
Q: What's wrong with casting malloc's return value?
A: Suppose that you call malloc but forget to #include <stdlib.h>. The compiler is likely to assume that malloc is a function returning int, which is of course incorrect, and will lead to trouble. Now, if your call to malloc is of the form
char *p = malloc(10);the compiler will notice that you're seemingly assigning an integer to a pointer, and will likely emit a warning of the form ``assignment of pointer from integer lacks a cast'' (see question 7.6), which will alert you to the problem. (The problem is of course that you forgot to #include <stdlib.h>, not that you forgot to use a cast.) If, on the other hand, your call to malloc includes a cast:
char *p = (char *)malloc(10);the compiler is likely to assume that you know what you're doing, that you really do want to convert the int returned by malloc to a pointer, and the compiler therefore probably won't warn you. But of course malloc does not return an int, so trying to convert the int that it doesn't return to a pointer is likely to lead to a different kind of trouble, which will be harder to track down.
(Of course, compilers are increasingly likely--especially under C99--to emit warnings whenever functions are called without prototypes in scope, and such a warning would alert you to the lack of <stdlib.h> whether casts were used or not.) | <urn:uuid:8490e35c-2575-4450-a221-35c7de4da8b2> | 3 | 325 | Q&A Forum | Software Dev. | 65.112251 |
An Aerial-Hawking Bat Uses Stealth Echolocation to Counter Moth Hearing
An Aerial-Hawking Bat Uses Stealth Echolocation to Counter Moth HearingAn Aerial-Hawking Bat Uses Stealth Echolocation to Counter Moth Hearing
Current Biology, Volume 20, Issue 17,
Publication Date 19 August 2010
Copyright © 2010 Elsevier Ltd All rights reserved.
Holger R. Goerlitz
Hannah M. ter Hofstede
Matt R.K. Zeale
Marc W. Holderied
School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
These authors contributed equally to this work
► Sequencing fecal DNA revealed that barbastelle bats eat almost exclusively eared moths ► Barbastelle calls are 10–100× lower in amplitude than those of other aerial-hawking bats ► Bats with these “stealth” calls hear moth echoes before moths are likely to react ► Stealth echolocation gives bats an advantage in the arms race with eared moths
Ears evolved in many nocturnal insects, including some moths, to detect bat echolocation calls and evade capture [1,2]. Although there is evidence that some bats emit echolocation calls that are inconspicuous to eared moths, it is difficult to determine whether this was an adaptation to moth hearing or originally evolved for a different purpose [2,3]. Aerial-hawking bats generally emit high-amplitude echolocation calls to maximize detection range [4,5]. Here we present the first example of an echolocation counterstrategy to overcome prey hearing at the cost of reduced detection distance. We combined comparative bat flight-path tracking and moth neurophysiology with fecal DNA analysis to show that the barbastelle, Barbastella barbastellus, emits calls that are 10 to 100 times lower in amplitude than those of other aerial-hawking bats, remains undetected by moths until close, and captures mainly eared moths. Model calculations demonstrate that only bats emitting such low-amplitude calls hear moth echoes before their calls are conspicuous to moths. This stealth echolocation allows the barbastelle to exploit food resources that are difficult to catch for other aerial-hawking bats emitting calls of greater amplitude. | <urn:uuid:210b2a23-c05e-42a6-b5cc-a310f0a6626b> | 3.09375 | 489 | Academic Writing | Science & Tech. | 25.557057 |
What are clouds and why does it rain?
Key Stage 3, Geography, QCA Scheme of work
Unit 10.3 Weather patterns over Europe (Year 8)
At Key Stage 2 students learnt the basic water cycle, this is adding to and building upon this work.
By the end of the lesson:
- All students will know that water moves within the hydrological cycle
- Most students will know that key vocabulary for the hydrological cycle
Get the students to complete the hydrological cycle word search to give them the key vocabulary for the lesson.
Option to demonstrate water cycle in a bowl
- A quick visual refresh of what is going on. Simple demonstration requiring a kettle (to supply steaming water) a mixing bowl, cling film and some ice cubes.
Condensation should form on the cling film and drip (rain) back into the bowl. A slower version of this demo can be found in the primary kids section.
Go through hydrological cycle animation with students.
Clear glass bowl
Kettle for steaming water
PDF document containing printable worksheet of diagram to label. Hydrological cycle worksheet answers
PDF document containing the answers to the above worksheet.
Complete the hydrological cycle crossword to check their understanding of the cycle. Alternatively compile their own crossword using key words. | <urn:uuid:d7fa2e5d-707c-4e9a-b692-fa4d45b78bfe> | 3.765625 | 277 | Tutorial | Science & Tech. | 51.453132 |
Springs and Cedar Trees
Country: United States
Date: July 2008
We recently discovered some natural springs on our land
that we were told by some "old timers" were there. We discovered a
small amounts of water forming at the head of a canyon at some small
holes in the side of the cliff. Rumor is that these springs once ran
fluidly. You can tell by the size of the canyon they must have at
one time. I have heard that if we cleared the cedar off of the land
these springs would run again because the cedar takes so much water.
Is there any truth to that statement and is it possible to find out
how much water is underground? Additional info: this is in Texas
Hill Country, about 400 acres, about 5 miles from one of the largest
cavern attractions in the State/US.
I believe you are right about water flowing in the region in past times.
The Texas hill county sits at the southern end of a huge aquifer that runs
north almost to Canada. Unfortunately, farmers in Kansas, Nebraska, Oklahoma
and even Texas tapped into the aquifer. The aquifer is depleted (hence the
meager flow of water you see today). So much water has been withdrawn that
the aquifer cannot recharge itself.
It may be that cedars are very thirsty trees. But there are not enough of
them to drain the aquifer. Check out the history of the Ogalalah aquifer
Click here to return to the Environmental and Earth Science Archives
Update: June 2012 | <urn:uuid:3f7b466a-aad7-4673-8b52-85afe0e2d6da> | 3.203125 | 328 | Q&A Forum | Science & Tech. | 54.67186 |
Night-time View of Aurora
January 15, 2013
Overnight on October 4-5, 2012, a mass of energetic particles from the atmosphere of the Sun were flung out into space, a phenomenon known as a coronal mass ejection. Three days later, the storm from the Sun stirred up the magnetic field around Earth and produced gorgeous displays of northern lights. NASA satellites track such storms from their origin to their crossing of interplanetary space to their arrival in the atmosphere of Earth. Using the “day-night band” (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS), the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite acquired this view of the aurora borealis early on the morning of October 8, 2012. The northern lights stretch across Canada’s Quebec and Ontario provinces in the image. Auroras typically occur when solar flares and coronal mass ejections—or even an active solar wind stream—disturb and distort the magnetosphere, the cocoon of space protected by Earth’s magnetic field. The collision of solar particles and pressure into our planet’s magnetosphere accelerates particles trapped in the space around Earth (such as in the radiation belts). Those particles are sent crashing down into Earth’s upper atmosphere—at altitudes of 100 to 400 kilometers (60 to 250 miles)—where they excite oxygen and nitrogen molecules and release photons of light. The results are rays, sheets, and curtains of dancing light in the sky.
Topics: Environment, Technology Internet, Astrophysics, Physics, Space plasmas, Magnetosphere, Coronal mass ejection, Solar wind, Aurora, Jets, Planetary science, light sources, Astronomy, Plasma physics | <urn:uuid:bfa6428e-9783-4ba9-86e9-da5fc0641905> | 4 | 360 | Truncated | Science & Tech. | 26.815466 |
In this section, you will learn how to use 'Pointer' function in C.
C provides a special feature of pointer to a function. As you know that every function defined in C language have a base address attached to it. This base address acts as an entering point into that function. This address can be stored in a pointer known as function pointer. The pointer to a function is the declaration of pointer that holds the base address of the function. The declaration of a pointer to a function is:
return_type (* pointer_name) ( variable1_type variable1_name , variable2_type variable2_name , variable3_type variable3_name .................);
You can see in the given example, we have create a function mul to find the product of three numbers. Then we have declared the function pointer for storing the base address of function mul in the following way:
int (*function_pointer) (int,int,int);
Here is the code:
Output will be displayed as:
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:47f1ebb5-69cc-41ec-a4f9-d44f54a32075> | 4.28125 | 253 | Tutorial | Software Dev. | 59.741225 |
versión On-line ISSN 0717-6643
CRISCI, Jorge Víctor. Signs of the times: biodiversity, systematics and education. Gayana Bot. [online]. 2006, vol.63, n.1, pp. 106-114. ISSN 0717-6643. doi: 10.4067/S0717-66432006000100006.
Biodiversity is the variety and variability of living things and of the ecosystem that they constitute. It can be studied at three levels: genes, species, and ecosystems. The most common way to quantify biodiversity is using the species level. Estimates place the number of species in the world at around thirteen million, yet only 1.7 million of these have been identified and described. There is evidence that we are destroying species faster than we are identifying them. This paper is a presentation of the problem of the loss of biodiversity as a sign of our time. Also biological systematics and education are discussed as tools to ameliorate the problem
Palabras clave : Extinction; conservation; classification. | <urn:uuid:3d625fe8-cddd-49e2-8493-6d052236b187> | 2.921875 | 227 | Academic Writing | Science & Tech. | 55.340606 |
A fascinating phenomenon with a forbidding name (parametric down conversion) occurs in certain crystals. A single photon enters, but two emerge. There are myriad pair combinations; but in each case, the sum of the total energy and momentum of the two output photons exactly equals those of the single input photon.
Parametric down conversion is finding a host of uses in physics, from testing the efficiency of high-tech single-photon detectors to cutting-edge experiments in quantum mechanics.
Alan Migdall of the National Institute of Standards and Technology explains and demonstrates how it's done. | <urn:uuid:112d60db-3558-403b-96ff-5056142e0593> | 2.984375 | 118 | Truncated | Science & Tech. | 30.4845 |
Functional Prog: ML
Functions in ML
A function is a computation that maps an input domain to
an ouput range
In math, the function of a line of slope 2 and y-intercept 3 is f(x)
= 2*x + 3
x is an identifier which takes on values in the domain of the
function - we call x a parameter of the function f
For a given value of x, f(x) is the value resulting from
computing its expression with x being replaced by its value --
e.g., if x is 2 , f(x) is 7 -- we also
just simply write f(2)=7
Defining and Using functions
functions are defined using the fun keyword:
fun square(x:real) = x * x;
because ML is strongly typed, we must tell ML the type of value x will
refer to -- hence the need to use the x:real syntax
x is a parameter to the function square -- it is an identifier
that refers to a value that the function will use to compute its result
ML responds by telling us square is a function "fn : real
-> real" -- what this means is that square takes a real value
and results in another real value. The arrow separates the input types
(the domain) of the function from the output type (the range)
The scope of parameters
The definition of a function is done in the fun statement, as
A function is used (we say called, or invoked), when it is
named in an expression, and values are used in place of each parameter
(the values can be existing identifiers, or expressions, but must always
be of the correct type).
The use of a function means that the values are used to evaluate the expression
in the body of the function, and the computed value is returned to the
expression containing the function use.
Some examples are here
When we use x as a parameter to a function, that use of x
only applies to the body of the function
Any other "x" is not affected
Identifier Scopes and Lifetimes
- When an identifier is created and assigned a value to refer to using
the val command, it has a certain area of use and a certain lifetime.
This area is called its scope.
- If we just type in a val statement into ML, that identifier-value
binding has a scope of the rest of the ML session, or until the
identifier is reassigned a different value.
- A parameter of a function has a scope that is just the body of the
function. Its lifetime is just one execution of the function body.
The ML stack of identifiers (and function names)
- Think of an upward growing stack of identifier-value bindings. Each
val statement adds a layer onto this stack.
- A reassignment of an existing identifier does not erase the old one.
It simply adds a new layer to the stack.
- When an indentifier is used in an expression, the stack is searched
from top to bottom. The first occurrence of the identifier is the
one whose value is used in the expression.
- When a function is defined, its name and body is added to the stack
as well. Very importantly, any identifier that is in the body that is not
a parameter is immediately searched for on the stack and located. It
is this identifier-value binding that is used during function execution.
- Parameters are viewed as temporary additions to the identifier stack,
only there during the function execution. When the function begins (is
called), the value passed in as an argument is used to create an identifier-value
binding for that parameter. When the function ends, that entry in the identifier
stack is erased.
- Functions can themselves be redefined! Just like identifiers,
they are simply added to the stack, and the old versions are not removed.
Previously defined functions using that function name refer to the old
binding, because they looked it up immediately when they were defined.
examples found here.
The let...in Statement: Defining temporary identifiers
- Function parameters are one type of temporary identifier-value binding.
- Another is the let..in statement. It allows you to create
temporary identifier-value bindings for use in an expression. Its form
val id1 = value;
val id2 = value;
The identifiers id1, id2, ... are bound to the values
specified (these can be expressions, of course), and then the expression
after in is evaluated, and the resulting value of this expression is the
resulting value of the let...in statement. After that expression
is evaluated the bindings created for id1, id2, ... are
The let statement allows you to break apart a computation into separate
- The examples used used in class are in here,
the file let.sml, and the ML session is here.
- We used functions to break apart the computation as well, but then
the expressions became complex because of the inside-to-out order of evaluation.
The first step would be a function innermost in the expression, then the
next outermost part of the expression, and on until the whole expression
was evaluated. This is shown in the example function circle_area1 in
- The let statement lets us put each of the computation steps
in a separate expression, and assign that intermediate step's value to
a new identifier. So it is more like how we think when we solve the problem,
and it prevents individual expressions from getting too complex. The example
function circle_area2 in the examples uses the let statement to
make this computation clearer.
- the final function in the examples is rect_area, and just
shows another use of the let statement
and ML sessions
ML has a data type that groups sets of values, called a tuple. A
tuple is an ordered set of data values; the values do not have to be the
same type. A tuple with three values is called a three-tuple. In general,
N values makes an N-tuple.
A tuple is strongly typed, just like simple values are. Each value is a
specific type, and the type of the tuple is the ordered types of its values,
with a * in between.
This is the same notation for function types
In ML, a tuple is surround by parentheses, and the values are separated
A point on the Cartesian plane can be represented as a two-tuple of two real numbers, like
(3.4,5.4), where the first number is the x coordinate and the second is
the y coordinate
A function can return a tuple as well -- the body becomes a series of comma-separated
expressions, each computing the value for its place in the returned tuple.
Tuples can act as records of data - ("Doe,","John","123 Any St","Any | <urn:uuid:788681b8-8b18-4726-bd1e-691bb5f34ad2> | 4 | 1,465 | Documentation | Software Dev. | 54.168404 |
Are Hurricanes Becoming Stronger and More Frequent?
Hurricanes can be the deadliest, strongest, and costliest storms in the world and they have been more severe than usual in recent years, causing an amazing amount of damage to coastal towns and cities. In 2004, a record number of hurricanes affected Florida and typhoons struck Japan. A hurricane even formed in the South Atlantic Ocean, off the coast of Brazil, where no one had ever seen a hurricane before. The 2005 Atlantic hurricane season was predicted to be above normal as well and one of those storms, Hurricane Katrina, devastated the gulf coast of the United States as it passed through.
Why are these monster storms becoming even more monstrous? Some scientists have identified that the number of hurricanes probably waxes and wanes with a regular and natural cycle. Other scientists have identified that the strength and length of storms is probably affected by global warming. Both processes might be at work, and reserchers continue their studies so that we can better understand these monsterous storms. Read on to learn more about these theories.
A natural cycle may control the number of storms
There is evidence that the number of storms each year is controlled, at least in part, by a natural 20 to 40-year cycle. For example, the number of hurricanes each year was less than usual from the mid-1960’s to the mid-1990’s. This was the part of the cycle when there were fewer hurricanes. But since 1995 there have been typically more hurricanes than usual each year. This means we are currently in the phase of the cycle when there are more hurricanes than usual. Scientists predict that the number of storms will be higher than normal until about 2015.
Global warming causes stronger storms
As global warming causes oceans to become warmer, and more moisture is held in the atmosphere, the intensity of hurricanes and the amount of rain they produce will likely increase, according to NCAR scientist Kevin Trenberth and others. There is strong evidence that global warming has been increasing the intensity of hurricanes for over the past few decades.
In the past 30 to 50 years the oceans have warmed about 0.1 degree Fahrenheit. This may not seem like much of a temperature change, but it is quite significant. Think about a pot of water heating on a stove. A small pot of water will heat quickly, while a large pot of water will heat very slowly. This is due to a difference in heat capacity. The oceans have an enormous heat capacity because of their large size, thus, they are like an enormous pot of water, and so it takes a great amount of heat to warm them. The fact that they have warmed significantly in 30 to 50 years is remarkable. And this change appears to be causing a remarkable change in the strength and length of hurricanes.
The warming oceans are very likely causing the strength of hurricanes to increase. According to MIT scientist Kerry Emmanuel, hurricanes have become 70-80% more powerful over this time. Hurricanes take heat energy from the oceans and convert it into the energy of the storm. The warmer oceans offer more heat energy to hurricanes. This makes them become stronger storms. | <urn:uuid:415b4782-00bb-48ea-bb79-1d1ca10b127d> | 3.421875 | 635 | Knowledge Article | Science & Tech. | 50.030415 |
Basic Molecular Biology
The Central Dogma
Alright, we’ve described the basic players in molecular biology: DNA, RNA, and proteins. What they do is this:
Here’s what’s going on: You have the Genome which is one or more really big double-stranded DNA molecule within every cell. Every cell has at least one genomic DNA. Humans have 23 pairs of them, so a total of 46 giant DNAs in each cell totaling something like 8 billion base pairs of DNA. E. coli has just one at around 4 million base pairs. Through the process of Replication, the genomic DNA can be copied into another identical molecule (or set of molecules). When cells divide, each daughter cell gets a copy of the genomic DNA. Short regions of the genome called genes (typically 1/1000th of the genome’s total length) get Transcribed into RNA molecules. RNAs then get Translated into protein molecules. Proteins do all the busy work.
The thing that is being preserved during each of these steps is information. The sequence of DNA is transcribed base-per-base using simple rules into RNA. The RNA is translated according to a simple code called the genetic code 3 bases at a time into a sequence of amino acids. Since the number of different genes present in a cell is usually between 500 and 50,000, many different proteins are encoded by a cell. Those proteins go on to be enzymes that catalyze chemical reactions, be structural materials, transport chemicals, and do all sorts of other amazing things. So, how does it work? Well, it’s very complicated, and I will only give you the 30 thousand foot view of what’s going on. These processes of replication, transcription, and translation are themselves performed by proteins, RNA molecules, and a few small molecules like the amino acids and nucleotides. So, one of the roles of the proteins encoded by the genome is to make the machinery that does the central dogma. Additionally, the smorgasbord of chemical reactions that make up primary metabolism are each performed by at least one protein encoded by a gene in the genome.
To really understand what’s going on in the Central Dogma, any basic modern biology, biochemistry, or molecular biology textbook will go through it in great detail. Additionally, there are all sorts of web pages that go through it. I’ll just touch on the basics:
The core molecular machine responsible for replication is the “DNA polymerase”. There are many proteins that together make up the DNA polymerase complexes, but in general they start their work on a specific sequence of DNA on the genome called the “origin”. What the polymerases do is first break apart the two strands of DNA and use deoxynucleotide monomers to polymerize a new strand of DNA complementary to the first. The result of replication is two double-stranded DNAs that are identical to the original.
Additional DNA elements called “promoters” and “terminators” define the boundaries of genes. RNA polymerases are the molecular machines that look for promoter elements in the DNA and initiate the polymerization of ribonucleotides into RNAs complementary to the DNA. Transcription proceeds much like replication. It starts at a promoter (rather than the origin), opens up the double stranded DNA and starts adding NTPs to a growing chain. It stops when it reaches the terminator and releases the free single-stranded RNA molecule which is now called a “messenger RNA” or “mRNA”.
Translation acts up the mRNA molecule product of transcription. It involves amino acids, a large molecular machine composed of protein and RNA molecules called the ribosome, RNA molecules called transfer RNAs or “tRNA”, and assorted other proteins. In general, the ribosome searches the RNA molecule for a specific signal sequence called the ribosome binding site and then initiates polymerization of a peptide chain at the “start codon” which is usually an AUG. It then adds amino acids one at a time by reading the next 3 bases and adding the amino acid corresponding to that 3 base sequence (called a “codon”) according to the genetic code:
The tRNA molecules are the adapters that “read” the RNA and match up each codon with an amino acid. These tRNA molecules have a region called the “anticodon” that base-pairs with the mRNA codons. On one end of the tRNA is a covalently attached amino acid. When the ribosome finds a match between the tRNA and the current codon, it will transfer the covalently-charged amino acid onto the growing chain. The ribosome keeps doing this until it encounters one of the 3 stop codons and then it releases the newly-synthesized protein. That new protein can then fold into its functional form and do whatever biochemical function it can.
The biochemical composition and behavior of a cell is somehow all orchestrated by its genes and biochemical products. To make it all work, the genome is encoding tons of information about the who, what, where, when and how much of the biochemistry of the cell. The qualitative composition of the cell—the who and what—of a cell is determined by the protein sequences encoded by the genes and the biological functions those proteins exert on the cell. So, for example, myosin is the major protein in muscle that has the biological function of converting chemical energy into physical movement. Myosin is transcribed 3 bases at a time into the amino acid sequence that has this biochemical activity. That information is readily apparent in the gene sequence as the rules for encoding DNA sequence into protein is pretty simple. So, the “who” of molecular movement is the Myosin protein molecule, and the “what it does” of molecular movement is a chemical property of the protein molecule itself. The “what it does” is the real magic of biology. It is determined by the amino acid sequence of a protein, but how you go from basic chemical principles to understanding the biochemical behavior of a protein is really complicated. Nevertheless, it is sufficient to appreciate that “what it does” is somehow a function of the amino acid sequence of itself—the molecule knows what it’s supposed to do. Take another example: phosphofructokinase. This is an enzyme that catalyzes the addition of a phosphate moiety from ATP to fructose-6-phosphate. It is one of many protein enzymes involved in the process of extracting the chemical energy from glucose and transferring it to ATP currency in the cell. “Who it is” is a molecule of defined amino acid sequence encoded by its gene. “What it does” is catalyze a chemical reaction involving ATP and fructose-6-phosphate. The ability to do this reaction is an intrinsic property of the protein molecule—no additional information is needed to make the protein molecule do its reaction.
Regulation deals with the where, when, and how much of a biochemical in a cell. There are many distinct environments within a cell. A bacterium has its cytoplasm, membrane, and periplasm. A human cell has organelles such as mitochondria, the endoplasmic reticulum, lysosomes, the nucleus, etc. Cells also are able to send molecules outside of the cell. So, the “where” of a biochemical somehow has to be dictated through regulation. There has to be some sort of information provided in the gene that tells the cell where that molecule is supposed to go. I won’t explain how it works, but suffice it to say that you often have short regions of a protein, often on the ends, that encode the information about where a protein goes. Small molecules tend to exist wherever the enzymes that make them exist.
The “How much” and “when” is where regulation gets complicated. This is where the genetic circuits and regulatory networks come into play. There are many many many mechanisms that cells use to do this type of regulation. You can distinguish the types of control by where they are exerted within the central dogma. For example, many genes are regulated at the level of transcription. By this, we mean that the gene isn’t always being transcribed or it might be transcribed at different levels depending on the internal or external environment of a cell. For example, let’s say there isn’t any glucose present in the environment of a bacterium. The bacterium has no glucose to consume, so why would it bother making the enzymes needed to breakdown glucose? So, you might expect that the gene for phosphofructokinase might be “repressed” in the absence of exogenous glucose. Exactly how that works gets complicated, but in general, somehow the RNA polymerase within the cell would only work on the promoter of the phosphofructokinase gene when external glucose is present. The most famous example of transcriptional control is the lac operon which encodes the genes needed to catabolize the disaccharide lactose in E. coli. Google it—you’ll find tons of pages describing it.
You can also have translational control, though it is not generally as common a mechanism as transcriptional control. Here, some biochemical in the cell is acting upon the mRNA of a gene and preventing the ribosome from translating it. There can be all sorts of mechanisms of posttranslational control, and it is extremely common. Here, biochemicals in the cell act on the protein through protein-protein interactions, small molecule-protein interactions, covalent modifications such as phosphorylation, etc. to alter the protein’s activity or even cause the protein to degrade. Finally, you can have intrinsic regulation that is the property of the protein itself. Product inhibition is one of these mechanisms. Here, an enzyme for a chemical reaction is inhibited by the product of the reaction it catalyzes. The result is that it only makes so much product and then shuts itself down—a simple negative feedback mechanism. This type of behavior is very common and robust, particularly in primary metabolism.
So, regulation is really complicated, and I talk about it here because 1) it’s an incredibly important part of how cells work and interact with each other and their environment, and 2) it’s what most synthetic biology folks are trying to engineer.
How do I learn more?
This pretty much covers the basic principles of molecular biology and biochemistry. Understanding the rest of it is largely a matter of learning all the various details. I highly recommend the textbook “Molecular Biology of the Cell”. One thing to keep in mind is that there are 3 distinct domains of life: prokaryotes (the bacteria), eukaryotes (plants, animals, fungi), and the archaea (funky single-celled things that live in places like hydrothermal vents). The rules for molecular biology are a little different for the 3 different domains. Pretty much everything I’ve said here is universal, but as you build up on this foundation things start diverging. So, as you are reading something, keep in your mind what domain they are talking about and don’t mix up the stories in your mind. | <urn:uuid:1319bb11-c666-4330-a6f4-189302fe2754> | 3.84375 | 2,367 | Tutorial | Science & Tech. | 39.92728 |
When people travel they remember their trip in different ways. Most of us have a camera, some make notes in a journal, while others make entries through social networking venues. If you are a botanical researcher you go one step further and mark your voyage of discovery with pressed plants. Images of the landscapes, copious notes, and the geographical coordinates are part of the collection process, but critical evidence is obtained by taking plants, arranging them between sheets of paper and placing them neatly into a tightly bound stack that squeezes the specimens into two dimensions.
The botanical experts at the Canadian Museum of Nature work on all sorts of plants. They work in the field to discover and document the plants that live in water, ice, dirt, on rocks and just about every kind of habitat imaginable. In general, plants include life forms that are as small as the point of a pin (for example, diatoms) or as tall as a house. And because they aren’t mobile like animals plants often live for generations in one place and are able to tell us a great deal about the past. For example, studying a record of plant life across vast areas over time can reveal the climate history of an area and indicate what changes lie ahead.
So what does a plant field record look like? For larger specimens (visible by eye . . . the ones we’ll talk about), like the flowering plants, mosses, and ferns, field work is done at a time when the best characters of the plant for identification can be seen (usually during summer). Samples are taken of the entire plant intact (roots, leaves, flowers) – minus the dirt – or representative parts for larger plants like trees and shrubs. These are placed between a large sheet of newspaper, one or a few for each species from a single location. A collection of those sheets is spaced between layers of cardboard, which lets air move through the specimens for rapid drying. This stack is book-ended by wooden slats that are the same size as the cardboard and paper, and the entire pile is cinched together with straps, providing even pressure that flattens all the plants. This is a plant press.
Plant presses have been used by botanists for centuries to create dry, preserved specimens for safe transport to the laboratory and long term storage. With some final adjustments and fixing onto a new and heavier paper sheet (usually clean white paper without the daily news printed on it), a pressed plant will last for several hundred years. Have you ever made something that will last several hundred years? This sounds simple, but a team of botanists in the field can collect hundreds of these specimens and the work to preserve them for a scientific collection can take until the next field season (or longer!).
Each of these botanical sheets has the original collection data that makes them so valuable for future study. Any new information acquired about the specimen will also be added to the sheet, as well as to the associated digital record. The museum is full of this kind of scientific data that it lends out (via specimens or as digital data), and uses for study.
Botanists discover and study plant specimens throughout Canada and abroad and have a tradition of taking enough samples for their work and for some of their colleagues. So once they have sorted their lot, there are packages sent far and wide in a global exchange of science data. The newest kind of specimens associated with this work is DNA. For hundreds of years botanists have used plant structures to tell one species from another. They still do this today, and more and more are also using DNA. The plant DNA comes from sub-samples for each pressed plant (usually the leaves) placed into small plastic bags of silica gel for quick drying and optimal DNA results.
A major effort led by the Canadian Museum of Nature in collaboration with many experts, called the Flora of the Arctic, is to discover and make a record and description of all the plants in the Canadian Arctic, a place where plant presses, DNA samples and botanists are moved around by helicopter. This dedication to the natural world is a regular part of scientific work at a museum, and a major contribution to understanding the natural heritage of Canada. | <urn:uuid:fa2655e1-1636-4df6-a552-011eb714c026> | 3.96875 | 859 | Personal Blog | Science & Tech. | 47.326326 |
Instead of a small-scale field test, Cao and Caldeira decided to model iron fertilization using the ocean GCM from Lawrence Livermore National Laboratory. To account for uncertainties, they chose to calculate an upper bound on iron fertilization rather than a most likely scenario. That is, they maxed out phytoplankton growth until something else became the limiting factor – in this case, phosphates. On every single cell of the sea surface, the model phytoplankton were programmed to grow until phosphate concentrations were zero.
A 2008-2100 simulation implementing this method was forced with CO2 emissions data from the A2 scenario. An otherwise identical A2 simulation did not include the ocean fertilization, to act as a control. Geoengineering modelling is strange that way, because there are multiple definitions of “control run”: a non-geoengineered climate that is allowed to warm unabated, as well as preindustrial conditions (the usual definition in climate modelling).
Without any geoengineering, atmospheric CO2 reached 965 ppm by 2100. With the maximum amount of iron fertilization possible, these levels only fell to 833 ppm. The mitigation of ocean acidification was also quite modest: the sea surface pH in 2100 was 7.74 without geoengineering, and 7.80 with. Given the potential side effects of iron fertilization, is such a small improvement worth the trouble?
Unfortunately, the ocean acidification doesn’t end there. Although the problem was lessened somewhat at the surface, deeper layers in the ocean actually became more acidic. There was less CO2 being gradually mixed in from the atmosphere, but another source of dissolved carbon appeared: as the phytoplankton died and sank, they decomposed a little bit and released enough CO2 to cause a net decrease in pH compared to the control run.
In the diagram below, compare the first row (A2 control run) to the second (A2 with iron fertilization). The more red the contours are, the more acidic that layer of the ocean is with respect to preindustrial conditions. The third row contains data from another simulation in which emissions were allowed to increase just enough to offest sequestration by phytoplankton, leading to the same CO2 concentrations as the control run. The general pattern – iron fertilization reduces some acidity at the surface, but increases it at depth – is clear.
The more I read about geoengineering, the more I realize how poor the associated cost-benefit ratios might be. The oft-repeated assertion is true: the easiest way to prevent further climate change is, by a long shot, to simply reduce our emissions. | <urn:uuid:222a326f-3b16-412b-9f5f-db6dee5312a9> | 3.296875 | 553 | Personal Blog | Science & Tech. | 33.206208 |
Date of this Version
Of 14 species of freshwater fishes held in cages in one or more of 13 alkaline lakes and ponds in Nebraska, few species survived more than a month where carbonate alkalinity, mostly as compounds of Na2C03 and KC03, was above 300 mg/liter. Of the 14 species tested, Sacramento perch (Archoplites interruptus), fathead minnow (Pimephales promelas), northern pike (Esox lucius), and the black bullhead (lctalurus melas), were the most tolerant of alkaline environments. Most centrachid fishes except A. interruptusand the green sunfish (Lepomis cyanel!us), did not survive more than a month in alkaline waters greater than 950 mg/liter total alkalinity. A lake classification index for slightly alkaline to strongly alkaline environments is presented, along with suggested fish species for introduction into such waters. | <urn:uuid:5e152803-2f5b-4893-8715-dafb7a9e000d> | 2.765625 | 197 | Academic Writing | Science & Tech. | 26.305523 |
where = last term of the series = .
Let be distinct constants, and be a polynomial of degree less than . Then
and is the -th derivative of (§1.4(iii)).
If are positive integers and , then there exist polynomials , , such that
To find the polynomials , , multiply both sides by the denominator of the left-hand side and equate coefficients. See Chrystal (1959, pp. 151–159).
The arithmetic mean of numbers is
The geometric mean and harmonic mean of positive numbers are given by
If is a nonzero real number, then the weighted mean of nonnegative numbers , and positive numbers with
is defined by
with the exception
For , ,
The last two equations require for all . | <urn:uuid:fecc39ab-951f-4a7d-a130-c1645559a059> | 2.921875 | 164 | Q&A Forum | Science & Tech. | 57.416071 |
Being struck by lightning is a dangerous and scary experience and can even be fatal. Sometimes, the electrical discharge can leave a tattoo-like marking or scar known as a Lichtenberg figure. The patterns created are known to be examples of fractals.
Lichtenberg figures are branching electric discharges that sometimes appear on the surface or the interior of insulating materials. They are named after the German physicist Georg Christoph Lichtenberg, who originally discovered and studied them. When they were first discovered, it was thought that their characteristic shapes might help to reveal the nature of positive and negative electric “fluids”. | <urn:uuid:ec7574c9-e37a-4eff-b876-2934191c682f> | 2.984375 | 127 | Personal Blog | Science & Tech. | 28.332333 |
How to Fight Global Warming
From Larry West, former About.com Guide
8 of 10
Plant a Tree
Every tree you plant pays dividends for years to come.
If you have the means to plant a tree, start digging. During photosynthesis, trees and other plants absorb carbon dioxide and give off oxygen. A single tree will absorb approximately one ton of carbon dioxide during its lifetime.
Trees are an integral part of the natural atmospheric exchange cycle here on Earth, but there are too few of them to fully counter the increases in carbon dioxide caused by automobile traffic, manufacturing and other human activities.
More About Global Warming | <urn:uuid:01558f76-47cb-4d2d-a9b1-9fa0472bb504> | 3.25 | 131 | Tutorial | Science & Tech. | 42.081667 |
February 10, 2006
No evidence that methane releases triggered global warming at end of last ice age
Methane escaping from the sea floor to the atmosphere has been a popular suspect for causing rapid climate changes during and at the end of the last ice age. But new data derived from a Greenland ice core have delivered a killer blow to the idea.
Methane (CH4) is a much stronger greenhouse gas than carbon dioxide. It is usually released from swamps or through biomass burning. But it is also trapped in huge amounts in some ocean-floor sediments, where it lies buried in a strange kind of ice known as 'methane clathrate'. These clathrates are stable only within a certain range of temperatures and pressures; when brought to the surface, they melt rapidly and release burnable gas to the air.
A catastrophic release of trillions of tonnes of methane is thought to have triggered a temperature jump some 55 million years ago in an already warm climate at the Palaeocene/Eocene boundary. But some scientists suspect that similar methane bursts, triggered perhaps by submarine landslides, sea-level drops or changes in water temperature, may also have caused a number of rapid warming episodes during and at the end of the last glacial period.
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Quasar lensing helps to solves astrophysical puzzles in various ways, but one of its most beautiful applications is probably the determination of the Hubble parameter H0.
3.1. The Time-delay Method
In 1964, the Norwegian astronomer Sjur Refsdal proposed an original method (Refsdal 1964) to use gravitational lensing as a tool to measure the size/age of the Universe. When photons propagate from a distant source toward the observer, they are under the effect of the gravity field of lenses along the line of sight. They do not follow a straight line anymore, but their trajectory is curved and longer than the original one. As a consequence, it takes more time for the photons to travel from a lensed source than from an unlensed one. The geometrical difference introduced by the lens between the two, lensed and unlensed paths, introduces a time-lag between the arrival times of the (lensed and unlensed) photons at the position of the observer. This time lag is called the geometrical "time-delay", tgeom. While passing in the immediate vicinity of the gravity field of the lens, the light is affected by a second delay: the gravitational time-delay, tgrav. A "lensed photon" will be seen by an observer with a total time-delay ttot = tgeom + tgrav, with respect to the observation of the same photon if it were not lensed.
The time-delay is a function of image position in projection on the plane of the sky. One can then define an arrival time surface that associates, to each position on the sky, a given a value of the time-delay. Most of this surface is missed by the observer who has only access to the few areas where the lensed images form. When two or more images of the source are observed it is possible to compare the arrival times at the positions of the lensed images and to determine a "relative time-delay". This is in fact the only truly measurable quantity, rather than the actual time-delay between the lensed and unlensed paths to the source, since the unlensed source is never visible.
In practice, time-delays are measured taking advantage of a lensed source with significant photometric variations. Due to the time-delay, the variations will be detected by the observer at different times in the light curves of each image. The shift in time between the light curves is simply the (total) time-delay between the images. Refsdal (1964) proposed to measure time-delays in lensed supernovae, but his method was published just when the first quasars were discovered (Schmidt 1963). Quasars, that later turned out to be very numerous in the sky, rather bright, and photometrically variable, were promising objects to measure time-delays if at least some of them were found to be lensed. They appeared in any case much more promising than rare and transient phenomena such as supernovae. Indeed, thousands of quasars are now known, and several tens of them are lensed. Measured quasar time-delays span over a broad range of values, between days and months. One is larger than a year: Q 0957+561 (e.g., Vanderriest et al. 1989). | <urn:uuid:23df9dcc-3da4-4f5a-89f4-eaf115b95e1b> | 4.0625 | 688 | Academic Writing | Science & Tech. | 43.650682 |
A fascinating article in Livescience reveals the answer to a century-old zoological mystery: what do y-larvae grow up to become? Discovered in 1899, y-larvae are clearly young crustaceans but their adult stage could not be determined. While this in itself was perplexing, the newly discovered answer is even more startling: y-larvae metamorphosize into “simple, pulsing, slug-like masses of cells… far simpler than their larval stage.” In a sense, the creatures revert backwards to forms more commonly seen further down the evolutionary ladder as they mature.
Watch the process
This awesome video shows the transformation from promising young crustacean to parasitic adult slug monster. Would make a great anti-drug commercial.
As Y-larvae do not seem to be in any rush to grow into their adult form naturally (and who can blame them) the researchers used powerful hormones to induce rapid growth. The scientists theorized that adult y-larvae, or ypsigons (rolls right off the tongue…), are parasitic as they have no digestive tract or nervous system. This means that they would need to absorb nutrients from their surroundings. Some species of parasitic barnacles exhibit similar physiological changes during development. | <urn:uuid:77915bf1-cf74-4557-9ca9-96be085b104b> | 3.84375 | 258 | Personal Blog | Science & Tech. | 34.7625 |
Part of twisted.spread.jelly View Source View In Hierarchy
|Method||prepare||(internal) Create a list for persisting an object to. This will allow backreferences to be made internal to the object. (circular references).|
|Method||preserve||(internal) Mark an object's persistent list for later referral.|
|Method||jelly_decimal||Jelly a decimal object.|
|Method||unpersistable||(internal) Returns an sexp: (unpersistable "reason"). Utility method for making note that a particular object could not be serialized.|
|Method||_cook||(internal) Backreference an object.|
|Method||_jellyIterable||Jelly an iterable object.|
(internal) Backreference an object.
Notes on this method for the hapless future maintainer: If I've already gone through the prepare/preserve cycle on the specified object (it is being referenced after the serializer is "done with" it, e.g. this reference is NOT circular), the copy-in-place of aList is relevant, since the list being modified is the actual, pre-existing jelly expression that was returned for that object. If not, it's technically superfluous, since the value in self.preserved didn't need to be set, but the invariant that self.preserved[id(object)] is a list is convenient because that means we don't have to test and create it or not create it here, creating fewer code-paths. that's why self.preserved is always set to a list.Sorry that this code is so hard to follow, but Python objects are tricky to persist correctly. -glyph
(internal) Create a list for persisting an object to. This will allow backreferences to be made internal to the object. (circular references).The reason this needs to happen is that we don't generate an ID for every object, so we won't necessarily know which ID the object will have in the future. When it is 'cooked' ( see _cook ), it will be assigned an ID, and the temporary placeholder list created here will be modified in-place to create an expression that gives this object an ID: [reference id# [object-jelly]].
|Parameters||atom||the identifier atom of the object.
|obj||any iterable object.
|Returns||a generator of jellied data.
|Parameters||d||a decimal object to serialize.
|Returns||jelly for the decimal object. | <urn:uuid:cfcb2509-4548-41ea-801f-3853d14253d0> | 2.890625 | 546 | Documentation | Software Dev. | 46.997903 |
Learn more physics!
what is the stucture of a photon?
- ali (age moeeni)
The photon has no known structure. Maybe at some extremely small distance scale there's some sort of string structure, but that's way past what anybody can measure or even predict theoretically.
What the photon does have is properties:
Boson statistics, energy, momentum, angular momentum, and coupling to electrically charged particles and to particles with magnetic moment.
(published on 02/11/2011)
Follow-up on this answer. | <urn:uuid:e460cd6e-45a1-47eb-8137-e96c8f536f73> | 2.75 | 115 | Q&A Forum | Science & Tech. | 44.821389 |
Science subject and location tags
Articles, documents and multimedia from ABC Science
Monday, 17 October 2011
Climate change is reducing the size of many animal and plant species, according to a new study.
Monday, 26 September 2011
A new study has found circadian rhythms control volatile gas emissions from plants, shedding light on an atmospheric modelling conundrum.
Tuesday, 6 September 2011
A world-leading researcher in photonics, a globetrotting plant biologist and the creator of a popular climate change website are some of the winners announced at tonight's Eureka Prizes held in Sydney.
Wednesday, 24 August 2011
Competition Australia's plants and animals are beautiful even in the coldest months. Congratulations to our photo competition winners and finalists.
Tuesday, 19 July 2011
Australia's native flora maybe more adaptable to climate change than previously thought.
Wednesday, 8 June 2011
Swapping needles for flat leaves allowed members of one conifer family to diversify and compete with flowering plants.
Wednesday, 1 June 2011
Photo gallery Delve deep inside plants to see the tiny cells from which they are built with these stunning images taken by scientists from the ARC Centre of Excellence in Plant Energy Biology.
Wednesday, 11 May 2011
West Australian scientists have identified a smoke-detector gene that triggers dormant plant seeds to germinate after bushfires.
Tuesday, 3 May 2011
Fossil evidence confirms that the first rainforests sprang up around 65 million years ago when flowering plants became photosynthesising powerhouses.
Tuesday, 1 March 2011
An exotic fungus that attacks native plant species including eucalypts, threatens to become endemic after thwarting containment on the NSW central coast and reaching North Queensland this summer.
Tuesday, 22 February 2011
Seaweed sends off a natural chemical response to ward off fungal attack, a process that could help the search for anti-malaria drugs.
Monday, 21 February 2011
Scientists have sequenced the genome of a fungus responsible for destroying canola crops worldwide.
Thursday, 27 January 2011
A bat and a carnivorous plant in Borneo enjoy an unusual mutually beneficial relationship, according to a new paper.
Friday, 15 October 2010
Australian native rice may contain valuable genes that could help buffer the world's rice crop against the damage wrought by rising global temperatures.
Friday, 8 October 2010
When it comes to genomes, size matters - and British scientists say a rare and striking plant native to Japan is in a perilous position. | <urn:uuid:b3055132-023d-4cb1-bdaa-1917fcda8403> | 2.734375 | 513 | Content Listing | Science & Tech. | 33.547038 |
Science subject and location tags
Articles, documents and multimedia from ABC Science
Wednesday, 22 May 2013
The Earth's ever-shifting geology is affecting the diversity of coral reefs across the Indian and Pacific oceans.
Friday, 19 April 2013
Antarctica's abrupt deep freeze around 34 million years ago caused a plankton explosion that transformed Southern Ocean ecosystems, new research has found.
Monday, 15 April 2013
Dugongs in one of Australia's largest populations appear to be getting sick and dying as a result of exposure to cold water, say researchers.
Tuesday, 2 April 2013
Growth rates of coral can override the climate information held in their skeletons, a study of giant corals has found.
Wednesday, 20 March 2013
A new study on the dispersal of fish larvae has reignited a debate on the science behind marine parks.
Wednesday, 20 March 2013
The giant squid has inspired legends about sea monsters, now a new genetic analysis reveals some of the enigmatic creature's secrets.
Friday, 15 March 2013
The first direct evidence of communities of micro-organisms buried deep in the oceanic crust has been discovered during deep sea drilling off the United States Pacific coast.
Wednesday, 30 January 2013
The decline of fish size due to fishing and climate change could make some fish more vulnerable to predators, say researchers.
Wednesday, 16 January 2013
A recent marine heatwave off Western Australia rapidly shrank the distribution range of an ecologically-important seaweed, researchers report.
Thursday, 13 December 2012
Australian box jellyfish can cause deadly cardiac arrest within minutes by punching holes in red blood cells and causing potassium to leak out of them, Hawaiian researchers have found.
Tuesday, 4 December 2012
Photosynthetic seaweed evolved from microscopic creatures cannibalising single-celled algae for their genetic parts, a new analysis has shown.
Wednesday, 28 November 2012
Parasitic crustaceans cause significant drag on reef fish impeding their ability to swim fast and stay safe, researchers have found.
Friday, 16 November 2012
Between 700,000 and one million species live in the world's oceans, according to a thorough new analysis.
Thursday, 2 August 2012
A coral-eating flatworm that is a notorious pest in aquariums has for the first time been found in the wild - on Australia's Great Barrier Reef.
Monday, 23 July 2012
A record-breaking Indian Ocean heatwave off the Western Australian caost has shown how global warming might trigger marine ecosystem change. | <urn:uuid:43e54f0c-1fa4-4fc0-8a43-f80bcf98ecfb> | 2.71875 | 515 | Content Listing | Science & Tech. | 37.235805 |
What Are Stingrays?
What do stingrays look like? How do they behave? What do you need to know about Stingrays?
What do they look like?
Stingrays are flat creatures that to many observers may not even appear to be alive. They typically look like doormats. They are usually fairly large (typically, they reach about three-feet across their bodies and can be more than six-feet long), and they are usually dark gray in appearance. The heads of stingrays is barely noticeable, protruding only slightly from the remainder of its disk-like body. The eyes are found on top of their heads and they have spines running in a fairly straight line back to their tails. Their tails are generally long and somewhat narrow.
How do they behave?
These animals are named for their spines--they produce venom. The scales have glands and passages underneath the skin that allow them to create venom and spit them out their corresponding spines. If they're attacked by a would-be predator, the stingray points its spines at the creature and fires off a potentially lethal dose of toxins.
What else should you know about stingrays?
Some stingrays prefer to live on the bottom of the deepest parts of the sea; others like more shallow waters. Regardless, all stingrays like to live on the bottom of the ocean floor. They particularly like sandy areas in which they can hang out. To the casual observer, they often can be mistaken for a non-threatening animal. | <urn:uuid:c6b170f6-317c-441c-936f-abcc81c1939a> | 3.609375 | 309 | Knowledge Article | Science & Tech. | 59.950136 |
Can large wind farms tweak weather downwind?
(Page 2 of 2)
The short take: After a variety of calculations, they find that large assemblages of 2.5 megawatt land-based turbines in the right regions would meet more than 40 times the world's current electricity needs. And that's with turbines running at no more than 20 percent efficiency. They looked at the US specifically and estimated that wind energy could meet up to 16 times the current US demand for electricity.Skip to next paragraph
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At first blush, the thought of vast collections of wind farms affecting weather patterns seems a bit far-fetched. But scientists have long studied the effects that changes in the roughness of Earth's surface can have on low-level wind patterns. And large, regional collections of wind turbines would rough up the surface. In effect, it's like planting very tall trees (roughly 300 feet high).
But what about the weather?
An early study of the impact that large collections of wind farms might have came out in 2004. A team from the University of Calgary, Carnegie Mellon University, Princeton University, and the National Center for Atmospheric Research explored the effect of what it termed "large amounts of wind power" and found a "non-negligible climatic change on continental scales." In this case, the changes involved atmospheric circulation patterns.
Last year, Mr. Kirk-Davidoff and a colleague, took a more detailed look to figure out how and why the climate changed. They looked at an expanse of wind farms roughly equal to the typical expanse for storm systems that move across North America. Essentially, surface winds and those somewhat higher in the atmosphere slowed as they crossed the region hosting the wind farms. They found that the presence of rougher landscape over large areas introduced "appreciable" changes in wind, temperature, and cloudiness.
How far afield are those changes found? In the study Kirk-Davidoff currently has under review, increased roughness over North America appears to trigger "substantial changes" in the development of storms over the North Atlantic and the tracks they follow. Substantial means that the size of the change is larger than typical weather-forecast uncertainties. The amount of roughness the wind farms present could be controlled by the way operators orient the turbines to the wind.
Still 'pretty speculative'
At the moment, Kirk-Davidoff acknowledges, the work is "pretty speculative." Real-world measurements of wind farms' effect on wind patterns are few and far between. In 2005, scientists in Europe published a study of the effects that large off-shore wind farms had on wind patterns, using satellite-based radar. But no one so far has built collections of wind farms on continental scales.
Yet "the possibility of relying heavily on wind power is not unreasonable," he says – especially in light of wind-energy's potential as outlined in the paper from the Proceedings of the National Academy of Sciences.
For Kirk-Davidoff, his work involves examining potential unintended consequences – at least the ones people can think up – "as the technology ramps up, so hopefully we don't get into really surprising consequences before we have a chance to realize what they might be." | <urn:uuid:d0ee8b5e-86a8-4de5-b87e-39d87593c9f6> | 3.203125 | 660 | Truncated | Science & Tech. | 44.778996 |
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Learn HTML 5 - HTML5 Tutorial
Hypertext Markup Language HTML 5 uses the combined technologies of HTML 4.01, DOC Level 2 HTML, and XHTML to generate web pages. The new language is designed to reduce dependency on proprietary RIA technologies for the generation of animated pictures such as Adobe Flash, Sun JavaFX, and Microsoft Silverlight. The perception of a new HTML was designed in 2004 by Web Hypertext Application Technology Working Group (WHATWG) and World Wide Web Consortium (W3C). The revised version of HTML is in use now but work on HTML 5 has yet to be completed.
Here are some of the major features added in HTML 5.
Some new elements have been added in HTML 5 that provides better support for drawing, images, audio, and video files. New form elements have been added and new input elements are supported by the new version. For formatting a text in a page, header and footer tags have been introduced. There are other options for supporting Chinese characters such as and < rt >. To record time and date, a new tag < time > can be used. Some new elements are designed to differentiate between user and author such as isindex or plaintext.
Here are some of the new elements of HTML 5.
HTML 5 is still in the developmental phase and some attributes have been added to make it simple for the user to author content. Some of the tags in prior version have been modified and a number of elements and attributes have been removed from HTML 5. Most of the presentation elements have been deprecated because presentation of a web page can be handled in CSS. Frames have been removed because it created presentation problems with different browsers. Some tags were obsolete and rarely used so they have been removed and replaced with better options. The elements which have been removed from HTML 5 are
HTML5 has support for global tags and APIs. APIs are required for creating web applications. API can be used for audio or video, and it also supports offline web application. The drag and drop features has been introduced with the “dragable” attribute. The HTMLDocument interface has been added, which enables the user to use classes and objects. For navigation, “allow-top-navigation” has been added which allows the user to navigate embedded content. HTML 5 provides an easy to write script language that can be used for designing an interactive webpage. It’s independent of Third Party web tools.
Check these links to find more information on HTML 5 and HTML5 tutorial.
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A linked list is a dynamic data structure used to hold a linearly arranged (typically unordered) collection of data. The simplest variation will be just a "head" pointer referencing the first node in the list. Nodes are declared to contain a data portion and a "next" pointer to the succeeding node on the list. If the next pointer of a node is NULL (or some equivalent), that node is the last one on the list. Additional pointers can be included to facilitate faster access to specific points in the list; e.g., a "tail" pointer referencing the last node will speed up appending new nodes to the end of the list.
Why were linked lists developed? Won't an array work just as well or better? While a linked list doesn't support random access to any element on the list, it does allow for the insertion, deletion, or relocation of nodes in O(1) time. And there are no limits — other than the amount of memory available on the system — to the number of nodes that can be held in the list. So, with regards to access and data movement restrictions, arrays and linked lists would appear to be complementary. Programmers have learned to use whichever data structure best fits the algorithmic situation they are coding.
Now that we've entered the parallel programming epoch, do linked lists still have a place? Dan Grossman of The University of Washington says, "No." I first heard of this radical idea from a colleague that had done a presentation with Prof. Grossman at a SIGCSE conference. The claim is that a tree can be used anywhere that you might want to use a linked list. (In my visually oriented mind, I see an animated linked list and tree singing "Anything You Can Do" from Annie Get Your Gun. I doubt if either data structure can bake a pie, either.) Is Dr. Grossman's idea heretical or forward-looking? Let me try to convince you of the latter.
A linked list is a sequential data structure that is very well-suited for sequential processing. A tree is the epitome of fork-join parallelism, as I've been expounding throughout my previous three posts. As with a linked list, a tree can dynamically expand and contract. The time needed to add a new leaf node might not be constant, but it can be O(log
n) for a well-organized tree, which is much better than the O(
n) needed for two pointers to chase each other to the end of a list without a tail pointer. What about some of the other operations for which you might use a linked list? Can these be emulated by a tree, especially in parallel? Here are some operations on a linked list and how they can be "simulated" by a tree. | <urn:uuid:8790962d-c4b0-4f47-a219-09ec22103bc0> | 3.359375 | 571 | Personal Blog | Software Dev. | 58.966272 |
The yellowtail damselfish (scientific name: Microspathodon chrysurus) is a member of the damselfish family (Family Pomacentridae) that lives on coral reefs in the Western Atlantic Ocean and the Caribbean Sea.
Yellowtail damselfish. Source: Florent Charpin/www.reefguide.org
Juvenile yellowtail damselfish. Source: Kathy Hoyt/www.quiescence.com
Kingdom: Animalia (Animals)
Adult yellowtail damselfish are small fish (10 to 21 centimeters in length) with an oval shape.Adults have a dark body with a bright yellow tail. Juveniles are dark blue in color and are covered by a number of bright light-blue dots. The iridescence juveniles are sometimes called jewelfish.
Yellowtail damselfish live on coral reefs at depths from zero to 120 meters. Females tend to establish territories near the reef crest while males live in deeper zones in areas of elkhorn coral rubble.
Yellowtail damselfish are primarily herbivores that graze on algae. In addition, they occasionally feed on fire coral polyps and other invertebrate animals. Juveniles occasionally pick parasites from other species of fishes.
Both male and female yellowtail damselfish defend territories that often include the smaller territories of threespot damselfish or dusky damselfish. Unlike many of the other damselfishes, yellowtail damselfish are not particularly aggressive while defending their territories and they appear to rely on the smaller damselfish living in their territories to aggressively defend their algal food source. Small individuals who are unable to defend their own territory become wanderers who are forced to attempt to feed in territories defended by larger individuals.
The peak reproduction periods are in February/March and July/August. Large territorial males prepare nests in seven to eleven meters of water by scraping algae and other organisms off of the substrate. Males attempt to attract mates to their territories by swimming in figure eight patterns ,and may even attempt to herd females to their territories by butting them. Females deposit eggs in nests where they are fertilized by the male. Females may spawn once every three days and males may care for up to five clutches of eggs. Males aggressively defend eggs from potential predators by grunting and chasing. After three to our days, the eggs hatch and the larvae enter the pelagic stage which lasts for 21 to 27 days. Larvae settle on shallow patch reefs and the juveniles tend to live near blades of Fire coral.
Yellowtail damselfish are deemed to be a species that is not at risk.
References and Further Reading
- Microspathodon chrysurus (Cuvier, 1830)
- Humann, P. and N. Deloach (Editor), 1994. Reef Fish Identification: Florida, Caribbean, Bahamas. New World Publications, Inc. Jacksonville, FL. ISBN: 1878348078
- Deloach, N. 1999. Reef Fish Behavior, Florida, Caribbean, Bahamas. New World Publications, Inc. Jacksonville, FL. ISBN: 1878348280 | <urn:uuid:0c199067-d484-441a-99c8-d0a419597df9> | 4.125 | 645 | Knowledge Article | Science & Tech. | 37.460331 |
Homogeneous and stable magnetic nanofluids containing γ-Fe2O3 nanoparticles were prepared using a two-step method, and their thermal transport properties were investigated. Thermal conductivities of the nanofluids were measured to be higher than that of base fluid, and the enhanced values increase with the volume fraction of the nanoparticles. Viscosity measurements showed that the nanofluids demonstrated Newtonian behavior and the viscosity of the nanofluids depended strongly on the tested temperatures and the nanoparticles loadings. Convective heat transfer coefficients tested in a laminar flow showed that the coefficients increased with the augment of Reynolds number and the volume fraction.
Keywords:γ-Fe2O3 nanoparticle; Magnetic nanofluid; Thermal conductivity; Viscosity; Heat transfer coefficient
Nanofluids, which contain nanoparticles dispersed in base fluids, have been proposed as a new kind of heat transfer media because they can improve the heat transport and energy efficiency and may have potential applications in the field of heat transfer enhancement. The thermal conductivity of the nanofluids can be enhanced obviously when nanoparticles, such as CNTs , Fe , Cu , and Al2O3, are dispersed into the base fluids. Viscosity of the fluids also increases with the augment of the nanoparticles concentrations [5,6] when nanoparticles are dispersed into the base fluids as well. At the same time, temperature and nanoparticles size may have effects on the viscosity of the nanofluids. According to the previous studies [7-9], nanofluids can improve the convective heat transfer coefficient considerably comparing to the conventional heat transfer fluids and can be used in thermal devices or systems such as heat exchangers or cooling system to enhance heat transfer.
Magnetic fluids, suspension containing magnetic nanoparticles, show both magnetic and fluid properties and have important applications in industrial [10,11] and biomaterial fields [12-14]. However, seldom experiments and applications on the heat transfer of magnetic fluids have been reported. The conductivity of magnetic nanofluids could be improved through controlling the alignment of nanoparticles by the external magnetic field . What’s more, with the development of the industry and the technology, the performance elevation of the traditional heat transfer medium using mixture of water and ethylene glycol (EG) is necessary. Kulkarni et al. investigated the thermal properties of aluminum oxide nanofluids based on the mixture of EG and water. And they found that the heat transfer was enhanced efficiently.
In the present paper, γ-Fe2O3 nanoparticles were chosen to form nanofluids with mixture base fluid composed of 55 vol% deionized water (DW) and 45 vol% EG. Thermal transport properties including thermal conductivity, viscosity, and convective heat transfer coefficient of the nanofluids were further investigated.
Preparation of Nanofluids
Two-step method was used to prepare nanofluids. Commercial spherical-shaped γ-Fe2O3 nanoparticles with diameter of 20 nm were selected as additives, and the mixture of ethylene glycol and deionized water with volume ratio of 45:55 was selected as a base fluid. In a typical procedure, adequate surfactant (sodium oleate) was dissolved into the mixture at first, and then the nanoparticles were gradually added into the base mixture fluid with violent stirring. Afterward, the suspensions were stirred using disperse mill (7,200 r/min) for 40 min. Nanofluids with different volume fractions (φ, φ = Vnanoparticles/Vbase fluids) of 0.005, 0.01, 0.015, and 0.02 were obtained by intensive ultrasonication for 45 min.
Measurement of Thermal Properties
The size of nanoparticles was observed by means of transmission electron microscope (TEM) (JEOL, JEM-2100F). The sample for TEM observation was prepared in a typical procedure. First, the nanoparticles were dispersed into the ethanol solution. Then, the mixture was ultrasonicated for 10 min to obtain stabilized suspension. Finally, the upper layer of the suspension was carefully selected to drop on a copper mesh.
The thermal conductivity of the nanofluids (knf) as a function of volume fraction of the nanofluids was measured using a transient short hot-wire method. Ethylene glycol was used to calibrate measurement apparatus. The thermal conductivity of ethylene glycol was measured threes times under a temperature at an interval of 5 min. The uncertainty of measurements is estimated to be within ±1.0%.
Viscosity of the base fluids or the nanofluids, η (mPa·s), was measured using a rotary viscometer (Brookfield, DV-II + Pro), which was calibrated using the standard fluid at first. The uncertainty of measurements is estimated to be within ±1.5%. The viscometer contains a sample chamber and a spindle. The fluid or nanofluid was put into the chamber, and the temperature of the sample, ranging from 10 to 60°C in 5°C increments in chamber, was controlled by water bath.
The convective heat transfer coefficient measurement setup shown in Fig. 1 is self-established, the convective heat transfer coefficient, h (W/m2·K), was measured as a function of volume fraction of nanofluids in laminar flow region. The base fluids or the nanofluids was pumped to flow along the tube from reservoir containing fluids and back to the reservoir by a peristaltic pump (MasterFlex L/S, MODEL 77202-50). At the same time, the temperature of the heating bath and the cooling bath was controlled at 60°C and −15°C, respectively, to form a constant wall temperature boundary condition. Four T-Type thermocouples were used to measure the temperature at the outlet of the heating bath (Tw), the entrance of the cooling bath (T1), 25 cm behind the entrance of the cooling bath (T2), and inside the cooling bath, respectively. At last, the convective heat transfer coefficients can be easily determined according to the formula,
where ,Cp, r, and ΔL are the mass flow rates, the specific heat capacity, the radius of tube, and the length of tested region, respectively. Reynolds number, Re, was derived from
where ρ,u, D, and η are the density of the fluid, the flow rate of the fluid, the diameter of the tube, and the viscosity of the fluids, respectively.
Figure 1. Schematic of experimental setup
Results and Discussion
The XRD pattern in Fig. 2 shows peaks at 30.272°, 35.684°, 43.34°, 53.852°, 57.4°, and 63.011°, which are corresponding to the diffraction peaks of γ-Fe2O3 (JCPDS 25-1402), indicating that nanoparticles are single phase with tetragonal structure. Figure 3 shows the TEM micrograph of γ-Fe2O3 nanoparticles. The average size of nanoparticles is estimated to be about 20 nm.
Figure 2. XRD pattern of γ-Fe2O3 nanoparticles
Figure 3. TEM micrograph of the γ-Fe2O3 nanoparticles
Figure 4 shows the particle size distributions in the magnetic nanofluids with and without surfactant, respectively. From Fig. 4, we can see that the average size is about 1,200 nm without surfactant (Fig. 4a) and about 150 nm with surfactant (Fig. 4b), respectively. When sodium oleate, a kind of organic salt, was dissolved into solution, the ionization of C18H33O2− and Na+ happens. One end of C18H33O2− plunges into the solution, and another end was absorbed on the surface of nanoparticles. With the addition of dispersant in the base fluids, the suspensions can keep stability for a long time, while sedimentation happened immediately in the suspensions without surfactant. Sodium oleate is effective for improving the stability of γ-Fe2O3 nanofluids.
Figure 4. Particle size distribution in the nanofluids a without dispersant b with dispersant
Figure 5 represents enhanced ratios (knf − k0)/k0 of the thermal conductivity of the nanofluids as a function of volume fraction (φ). It can be seen from Fig. 5 that the enhanced ratios of the thermal conductivity increase with the volume fraction of the nanoparticles. Unexpectedly, the conductivity of γ-Fe2O3 nanofluids was not so encouraging as previous investigation results for other kind of metal oxide nanofluids. For example, Zhu et al. measured the thermal conductivity of Fe3O4/water nanofluids. They found that the ratios of the thermal conductivity enhanced by more than 15.0% even at the volume fraction of 0.005. Karthikeyan et al. reported that the ratios of the thermal conductivity of CuO/water nanofluid enhancement were 31.6% with 1.0% CuO nanoparticles loading. The species of the dispersant may be the main reason to these differences. Sodium oleate that contains a long carbon-chain could improve the stability of γ-Fe2O3 nanoparticles suspending in the solution; however, it may also reduce the efficiency of heat transfer between the particles.
Figure 5. Dependence of the enhanced ratios of the thermal conductivity on the volume fraction of γ-Fe2O3 nanoparticles
Viscosity is an important parameter in the pipeline flow. Figure 6 presents the results of the viscosity of the nanofluids with different volume fractions as a function of temperature. It is shown that the viscosity of the nanofluids strongly depends on both temperature and volume. We observed that the viscosity of the nanofluids increases with the augment of the volume fraction but decreases with an increase in the temperature. Nguyen et al. measured the viscosity of Al2O3/water nanofluids, which showed the same trend as well. Figure 7 depicts the rheological behaviors of the nanofluids with different particle loadings. The behaviors of the nanofluids from the Fig. 7 are close to the typical Newtonian fluids. Yu et al. measured the viscosity of ZnO/EG nanofluids against shear rate. The results also showed that the viscosity of nanofluids increased with the increasing of particle concentrations and decreased with the augment of temperature. And they observed that the nanofluid demonstrated Newtonian behaviors and non-Newtonian behaviors at lower (φ < 0.02) and higher (φ > 0.03) volume fractions, respectively. Some theoretical predictions of viscosity (Einstein model , Brinkman model ) about the fluid were employed to compare with experiments of the nanofluids in Fig. 8. It is found that the experiment data of the nanofluids is much larger than the theoretical predictions values. The result may ascribe to the specific surface areas of the nanoparticles. The enhancement of viscosity may due to the very large surface area of the nanoparticles in the nanofluids . Furthermore, the reason of the discrepancy may due to the nanoparticles size, which has an important effect on viscosity of nanofluids. When the diameter of the nanoparticles is less then 20 nm, the viscosity of nanofluids will increase rapidly as the diameters decrease .
Figure 6. Viscosity as a function of the volume fraction of γ-Fe2O3 nanoparticles and temperature
Figure 7. Viscosity as a function of shear rate
Figure 8. Comparison of experimental data with theoretical predictions
The convective heat transfer coefficient of the nanofluids with different volume fractions as a function of Reynolds number (Re) was shown in Fig. 9. It is seen that an augmentation of volume fraction or Reynolds number can make the heat transfer coefficient increase. It should be noted that though the conductivity of γ-Fe2O3 nanofluids was not encouraging in our experiment, the convective heat transfer coefficient increases with Reynolds number and volume fraction. The behaviors of convective heat transfer are similar to the base fluids at the volume fraction of 0.005, which may be due to the adhesion of nanoparticles on tube wall. Obviously, from the volume fraction of 0.01, the convective heat transfer coefficient enhanced quickly. For the nanofluid with a volume fraction of 0.02, the convective heat transfer coefficient can be enhanced by more than 60.0% at Reynolds number of 1,000. The viscosity value of the nanofluids in our experiment was nearly close to the base fluid especially at a higher temperature. The higher viscosity of nanofluids may suppress flow turbulence . Furthermore, the nanofluids with homogeneous and stable property may be also a critical factor to this result. Heris et al. reported that the nanoparticles in a fluid changed the flow structure. Heat transfer enhancement of the nanofluids is not only related to the conductivity of nanofluids but also related to chaotic movements, dispersions, and so on.
Figure 9. Heat transfer coefficients versus Reynolds numbers for γ-Fe2O3 nanofluids
We presented a technical route for preparing stable nanofluids composed of γ-Fe2O3 nanoparticles and the mixture of deionized water (DW) and ethylene glycol (EG) (DW-EG) as the base fluid. Sodium oleate was used as surfactant, and it was proved to be beneficial to the dispersion of the nanoparticles in the nanofluids. The viscosity of the γ-Fe2O3 nanofluids fits Newtonian behavior and strongly depends on the temperature and the volume fraction. Thermal conductivities of the nanofluids are higher than that of base fluid, and the enhanced values increase with the volume fraction of the nanoparticles. Though the enhanced ratios of thermal conductivity of the nanofluids are not so encouraging compared with other oxides nanofluids, the convective heat transfer coefficient of the nanofluids has substantial enhancement when compared to that of the base fluid. These results indicate that the enhanced thermal conductivity is not the only mechanism responsible for heat transfer enhancement and other factors such as stability of nanofluids, thermal properties, and viscosity of the nanofluids also should be considered.
This work was supported by the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, the National High Technology Research and Development Program of China (No. 2006AA05Z232), and Shanghai Nanotechnology Promotion Center (0852nm03200).
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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COI number [1:CAS:528:DC%2BD38XmsVamt7s%3D] | <urn:uuid:d493a4ca-59e9-4947-8764-d1ce6f6cc27e> | 2.8125 | 4,214 | Academic Writing | Science & Tech. | 55.232792 |
|Jan17-09, 12:40 PM||#1|
Fluid Dynamics: Using Bernoulli's equation and Volume Flow Rate
1. The problem statement, all variables and given/known data
Water flowing out of a 15.0mm -diameter faucet fills a 1.50 L bottle in 5.00s. At what distance below the faucet has the water stream narrowed to 10 mm in diameter?
2. Relevant equations
Bernoulli's equation: P_1+pgh+1/2pv^2=constant
Q(volume flow rate)=vA
Continuity Equation: A_1(V_1)=A_2(V_2)
3. The attempt at a solution
Finding the intial velocity of the fluid:
A_1=pi(0.0075m^2)= 1.77*10^-4 m^2
Q=1.5L/5.00s=0.3L/s --->Q=vA (Rearrange the equation)--> v_1=Q/A_1= 0.0003m^3/s / 1.77*10^-4m^2 = 1.69765..m/s
Finding the final velocity of the fluid:
v_2=Q/A_2= 0.0003/7.85*10^-5 m^2 =3.81971...
Finding the height:
h=(1/2*p*v_1^2)-(1/2*p*v_2^2)/pg---> (p cancels out)
But, I feel that I must have done something wrong in my calculations. I don't know if my answer makes sense.
|bernoulli's equation, continuity equation, volume flow rate|
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by Shauna, 10th Grade, Coastal Studies for Girls
Recently, the students of Coastal Studies for Girls, our marine science teacher, and one of our resident assistants visited the Bowdoin College Marine Laboratory
. Upon walking through the doors of the little building hidden in the woods, we were greeted with multiple touch tanks containing so many sea creatures. There were sea stars, sea squirts, hermit crabs, sea anemones, sea cucumbers, and brittle stars, just to name a few. We were allowed to ask questions about the marine life, as well as to pick them up and feel them.
Dr. Amy Johnson
, a Biology professor and director of the Marine lab, and Tamara Perreault, who is an undergraduate student there. Tamara was working on her very cool experiments on Harmothoe imbricara
-- more commonly known as the fifteen-scaled worm -- which glow and flash their own light when threatened.
The two women who were there were
One of my personal favorite species in the touch tanks was the Skeleton Shrimp, or Caprella sp. From a distance, they look like little pieces of grass, but once you get closer, they look to me like those little worm aliens from the first Men in Black movie.
With my hands in the tank, I placed a couple of Caprella on my fingers and they began clinging to me right away, swaying back and forth with the water. They were in huge packs of perhaps a couple hundred or more. There were so many together that they looked almost like one large organism.
In the video above, a skeleton shrimp female oxygenates her eggs in her red polka-dotted marsupium.
There are several species of skeleton shrimp in the coast of Maine, and even more around the world. We think the species we observed belonged to the genus Caprella. Despite their name, the skeleton shrimp aren’t exactly “shrimp”. The skeleton shrimp and your average cocktail shrimp are both crustaceans, but the skeleton shrimp are classified in a different order than the shrimp we eat.
Skeleton shrimp are invertebrates, meaning they don’t have a spine, and they can grow to be up to 4 cm in length. They can be found in the low intertidal zone and subtidal waters in bays. Skeleton Shrimp eat microscopic plants and filtered food particles.
Skeleton shrimp are pretty odd creatures. Sometimes after mating, the female will kill the male, although the reason is still unknown. They move by bending and straightening their bodies, propelling themselves through the water in small, jerky movements. | <urn:uuid:a2a43947-67b5-499d-8734-23c8083c3dfc> | 3.078125 | 546 | Personal Blog | Science & Tech. | 51.28826 |
MATERIAL METAMORPHOSIS: When heated, biodegradable shape-memory polymer transforms from a temporary shape (top) to its parent shape (bottom) within 20 seconds. Image: © 2001 National Academy of Sciences, U.S.A.
Special plastic materials able to change shape in response to temperature may soon find applications in a variety of extreme climes¿from the warm, moist environs of human blood vessels to cold, wet and windy mountaintops. These plastics have a "memory" that allows them to be deformed into a temporary configuration and then be restored to the original parent geometry by applying heat. Shrink-wrap is perhaps the most familiar example of a shape-memory polymer (SMP). But since the mid-1980s chemists, materials scientists and engineers have been working to develop SMPs as a kind of "smart" material¿a substance that can respond to environmental changes as desired.
Shape-memory substances are not new: certain metallic compounds exhibited the effect in the 1930s, and alloys such as nickel-titanium (Nitinol) have since found use in actuators and medical devices such as dental braces and endovascular implants. These metals switch from a temporary to a parent shape above a certain transition temperature. Below that temperature, the shape-memory alloy (SMA) can be bent into various configurations. | <urn:uuid:7cebaafc-f543-4e9f-a427-1545185c86fa> | 3.734375 | 289 | Knowledge Article | Science & Tech. | 29.569328 |
Modern Day Heroes: Conservationists can preserve diversity of life on Earth by applying up-to-date scientific knowledge to help solve environmental problems. Here’s how: they work to protect ecosystems, plants and animals, and they promote efficient use of renewable resources to reduce pollution. There are many different ways that conservationists can achieve these goals, and anything method works is valuable:
1) Understand: Advancing wildlife research and knowledge.
2) Protect: Protecting whole ecosystems (including plant and animal populations).
3) Waste Not, Want Not: Promoting efficient use of renewable resources.
Conservation efforts increase knowledge of new species so habitats are not destroyed before humans know that their inhabitants exist.For example, conservationists discovered 52 new species of animal and plants in the south-east Asian island Borneo between 2005 and 2006, including 30 species of fish, 2 new tree frogs, and 16 unusual species of ginger!
The remote forests of Borneo are among the most important centers of biodiversity on Earth. Thanks to recent discoveries, conservationists have more knowledge of Borneo's animal inhabitants and how to protect them.
In addition, conservationists must understand the large economic, political, natural, and cultural forces that influence animals and the environment. By increasing the world's knowledge base, conservationists increase the odds that we'll figure out how to address the problems facing endangered animals! | <urn:uuid:c96c2826-e16b-49ad-b70f-9ff18085bba9> | 4.0625 | 284 | Knowledge Article | Science & Tech. | 23.247752 |
Sea level rise. Desertification. Ocean acidification. Climategate. Permafrost. Greenland ice sheet. Hockey stick. The language of global climate change can be overwhelming. Every year, as we learn more about the ways that human activity fundamentally alter global processes, the subject becomes even broader and more complicated. Fortunately, world renowned oceanographer Orrin Pilkey and his son, Keith Pilkey, have produced a comprehensive and readable primer on global climate change. The strength of Global Climate Change: A Primer can be broken into three sections – the content, the conflict, and the illustrations. | <urn:uuid:860247b5-974a-4bfa-af4c-97f9496a55f9> | 2.765625 | 120 | Truncated | Science & Tech. | 22.768795 |
| Olivine, more commonly known as peridot, is a beautiful green mineral. Most of the time olivine is used by jewelers. Occasionally it is ground into a dust and is used to cover the inside of iron molds to keep the liquid metal hot. It is also the birth stone for the month of August. Olivine is a silicate meaning it is partly composed of silicon and oxygen. On Mohs scale it’s hardness ranks about a 7. Over 3,000 years ago the world thought that peridot had special healing powers. At one time in ancient history it was worth more than diamonds. The stone didn’t just heal you physically but emotionally as well. Doctors would use it to heal the sick and when physiologists would use it they combined the treatment with amethyst in order to heal the broken-hearted and a troubled mind because it helped connect you to your inner self. They thought olivine could do all of this because its olive color never left it. In fact Olivine is one of the only minerals that exist in one color. It has been mined for over 3,500 years! Coal is a very common mineral that is formed when dead plant remains are compressed in swamps. The first stage of coal is called peat and is a very light brown. As coal goes through each stage it becomes darker and harder to burn. The last stage of coal is diamond and is the hardest mineral known. |
Earthquakes are caused by plate tectonics. Plate tectonics weren’t considered factual until the late 1960’s! The plates beneath the earth are constantly moving. This movment causes earthquakes, volcanoes, ridges, and mountain chains. There are 15 plates known.
Plate Techtonics can cause volcanos. A volcano is an opening in the crust of the Earth through which molten rock and gases from the interior of the Earth build up and are released. The largest volcano on earth is Mauna Loa on Hawai'i Big Island. The most active volcano is Kilauea in Hawaii. The eruption of Kîlauea Volcano began in 1983 and still continues to erupt today. Kîlauea is is said to be the home of Pele, the Hawaiian volcano goddess.
The final frontier
Outside of Earth's atmosphere lies a vacuum larger than everything but immagination. We call this vacuum space! In space lie wonderous things like nebulas, stars, and moons. The first person to walk on earth's moon is Neil Armstrong. The first person ever to exit Earth's atmosphere and enter space was a man named Yuri Gagarin. Earth is located in a galaxy called The Milky Way. Don't get it confused with the candy bar. The Milky Way is a spiral galaxy. All together there are three types of galaxies... spiral, eliptical, and irregular. | <urn:uuid:8f5fbcfc-eef9-4ba4-a5a5-3733ea2ef66c> | 3.359375 | 591 | Knowledge Article | Science & Tech. | 62.96875 |
Paper chromatography is one method for testing the purity
of compounds and identifying substances. Paper chromatography
is a useful technique because it is relatively quick and requires
small quantities of material.
A paper chromatography experiment.
Separations in paper chromatography involve the same principles as those in thin layer chromatography. In paper chromatography, like thin layer chromatography, substances are distributed between a stationary phase and a mobile
phase. The stationary phase is usually a piece of high quality
filter paper. The mobile phase is a developing solution that
travels up the stationary phase, carrying the samples with it.
Components of the sample will separate on the stationary phase
according to how strongly they adsorb to the stationary phase versus
how much they dissolve in the mobile phase.
Video: Chromatography process (same as TLC Process video) ( 5.83 M )
Preparing the Chamber
Choose a developing chamber that can be sealed well. The chamber
should be large enough to hold the paper that is to be
The chamber should be clean and dry before use.
Add the mobile phase to the chamber so that it is about 2
cm deep. Seal the chamber tightly and let the chamber stand overnight
if possible. Why? The larger the chamber,
the longer it should stand.
What is wrong with this student's paper chromatography chamber
Preparing the Stationary Phase
Cut a square piece of high-quality filter paper to fit into your development chamber.
With a pencil, draw a straight line about 3 cm from the bottom edge of the paper.
Video: Prepare the paper ( 4.61 M )
Spotting the Samples
First, each sample should be dissolved in an appropriate solvent
to make about a one percent solution (0.01 g sample/1 g solvent). Less than one milliliter
of solution will be needed for the experiment. Then the dissolved
samples may be spotted to the paper.
Video: Spotting the samples ( 3.13 M ) Text description
If a larger quantity of sample is needed for the experiment than is
provided by one application, the solution may be re-spotted.
Video: Re-spotting ( 1.12 M ) Text description
All spots on the chromatogram should be 2 to 2.5 cm away from
the edges of the paper and from each other.
Developing the Chromatograms
After preparing the chamber and spotting the samples, the
paper is ready for development. Be careful to handle the paper
only by its edges, and try to leave the development chamber uncovered
for as little time as possible.
Initially, the chromatogram should be suspended in the chamber without touching the solvent. To suspend the chromatogram, to the top of the paper and thread a piece of string throught the paper clip. Then tape the string to the outside of the chamber to hold the chromatogram in place. The paper should hang in the development chamber overnight, if possible.
Video: Hanging the chromatogram ( 5.41 M )
After the chromatogram has hung in the chamber, immerse the paper's
bottom edge into the developing solvent.
Video: Immerse the chromatogram ( 5.83 M ) Text description
Allow the chromatogram to dry in a well-ventilated area.
A student has developed a chromatogram as shown in the picture above.
Will this chromatogram yield good results?
A student removed this chromatogram from the development chamber and allowed the solvent to dry. What did he forget to do?
Identifying the Spots
If the spots can be seen, outline them with a pencil.
If the spots are not obvious, the most common visualization
technique is to hold the paper under an ultraviolet lamp. (Caution:
Do not look directly into the lamp!) Many organic compounds can
be seen using this technique. Outline the spots with a pencil.
Interpreting the Data
The Rf value for each spot should be calculated. Rf stands
for "ratio of fronts" and is characteristic for any
given compound. Hence, known Rf values can be compared to those
of unknown substances to aid in their identifications.
(Note: Rf values often depend on the temperature, solvent, and type
of paper used in the experiment; the most effective way to identify a
compound is to spot known substances next to unknown substances on the
In addition, the purity of a sample may be estimated from
the chromatogram. An impure sample will often develop as two or
more spots, while a pure sample will show
only one spot.
Copyright © 1995-1996 NT Curriculum Project, UW-Madison | <urn:uuid:ed0afbf9-3eed-48b5-b603-275c67c5b266> | 3.65625 | 987 | Tutorial | Science & Tech. | 50.804345 |
This picture illustrates the concepts "atomic mass" and "atomic number". The carbon atom (14C) nucleus on the top has 6 protons plus 8 neutrons, giving it an atomic number of 6 (the number of protons) and an atomic mass (protons plus neutrons) of 14. Tritium (3H), an isotope of hydrogen, is shown on the bottom. It has 1 proton plus 2 neutrons in its nucleus, giving it an atomic number of 1 and an atomic mass of 3.
Original artwork by Windows to the Universe staff (Randy Russell). | <urn:uuid:0a5633bf-40bd-49a8-aa4f-de15692d5c79> | 3.1875 | 122 | Truncated | Science & Tech. | 63.993727 |
Coming out of the Dark Ages, man believed the Earth was flat, and that the heavens revolved around the Earth. Evidence that contradicted these assumptions was ignored until the weight of evidence became so heavy that the comfortable assumption was eroded. How could such a theory as the flat Earth even evolve? To man today, this theory seems laughable, but when it evolved, the edges of the horizon always seemed at the edge of a flat plane, so this was the newborn child's first conclusion. But did not the fact that the stars moved about the heavens in a manner that lined up with a solar system model not move him to question? The toddler assumes the world revolves around him, and is loath to let this go. The alternate explanation, that the heavens were dancing for his amusement, fit his mind-set. Did not the Sun rise when he felt refreshed, and set when he was weary? All to serve his needs, he had no doubt.
Elaborate mathematical descriptions of trajectories and orbits were drawn up in an age when man had not peeked beyond the Solar System with high powered telescopes floating above the atmosphere, and when slow motion video was unheard of. The only complete orbits known were those of the planets which hugged the Sun, and as the math was drawn up to fit these orbits, the orbits fit the math. The explanation for comets either fit the model or they didn't. When they fit the model they were assumed to have the orbit, when out of view, that the model dictated. If they didn't fit the model then they were dressed up in mathematical curves, parabolas or hyperbolas, which came close enough to let everyone go home at the end of the day feeling smug. As concepts tend to solidify as time passes, the young taking as absolutes what their elders preach, the Earth was now no longer flat, and the heavens no long revolved around the Earth, but most certainly all orbits were elliptical.
When slow motion video demonstrated that trajectories do not, in fact, mirror the downward side to the upward side, the facts did not change the precepts taught to the young. Why change a handy tool that works for everyday applications? Close enough, and change would require reprinting all those books! The fact that the downward side of the trajectory marries the forward thrust to the gravity drop was noted by those who think deeply about such matters, and is a known but not extensively taught fact. For most, the Earth is still flat, as they have not been told otherwise and are not inclined to question. Where the trajectory precept stands inviolate to most, the precepts of elliptical orbits have even fewer challenges. Man sees the dance of stars, but there are so many variables that come into play, about which he is uncertain at best, that the arrows of doubt seldom get launched. Yet the arrows exists.
Where orbits are snug about their center of gravity, there is little contradiction between these and what mankind calls their laws of gravity and motion. These are not laws, of course, but elaborate descriptions of what they observe. The flaws in the laws, however, were always present. If gravity diminishes with distance, but distance is attained with speed, then an object in a snug elliptical orbit seems to logically be adhering to the laws of gravity and motion. Speed up during the approach, sling past, and the speed carries the body outward where the diminishing gravity pull slows the body down so that its curve sidewards takes predominance. The theory fit what man observed, and thus was not questioned until his powers of observation increased. Tiny comets, seen by man in the past only when they gave their brilliant displays while going around the Sun, have only recently been observed in great detail during this passage.
Repeating comets are not slinging past, as in a passing body. They are in orbit, doing the better part of a circle about the Sun. Unlike the planets, whose center of gravity is just that, at the center, the comet does not behave as though the Sun is its center of gravity. The elliptical orbit of planets is such that if one were to examine the distance from the Sun, the difference at any given point would be slight. It is more circular than not. Comets, however, are at the other extreme. They appear to be a fan, rather than an eye. For the laws of gravity and motion to fit, the comet must be increasing its speed as it leaves the Sun, thus explaining its increasing distance. However, careful studies have shown this not to be the case. The comet is going its fastest when closest to the Sun, and has slowed down when it begins to leave what is assumed to be its gravitational master. The slowing precedes the exit, thus throwing the smug assumptions of man into consternation.
In addition, the distance comets travel outward, and the curvature of their exit are now able to be examined where in the past they were an unknown. They go essentially straight away, not the curve anticipated. Thus the distance from the Sun wherein they would have to complete an elliptical curve is extreme, challenging the laws of gravity and motion. The distance where the elliptical curve would reinstate is too far, and the curve during the straight away too slight. Rather than deal with this new information, the majority of scientists prefer their comfort factor over new knowledge. Change is resisted, and for many the Earth is still flat. | <urn:uuid:1a745ceb-8a31-4fd3-80a9-ad33c1780b4a> | 3.203125 | 1,110 | Personal Blog | Science & Tech. | 51.756375 |
Science Fair Project Encyclopedia
- For other uses of this word, see Quartz (disambiguation).
|Chemical formula (or Composition)||Silica (silicon dioxide, SiO2)|
|Color||Clear (if no impurities); also see Varieties|
|Crystal habit||6-sided prism ending in 6-sided pyramid (typical)|
|Mohs Scale hardness||7 - lower in impure varieties|
|Refractive index||1.544-1.553 - DR +0.009 (B-G interval)|
|Pleochroism||Most varieties weak; definite in smoky quartz|
|Specific gravity||2.65 constant; variable in impure varieties|
|Chalcedony||Any cryptocrystalline quartz, although generally only used for white or lightly coloured material. Otherwise more specific names are used.|
|Agate||Banded Chalcedony, translucent|
|Onyx||Agate where the bands are staight, parallel and consistent in size.|
|Jasper||Opaque chalcedony, impure|
|Aventurine||Translucent chalcedony with small inclusions (usually mica) that shimmer.|
|Tiger's eye||Fibrous quartz, exhibiting chatoyancy.|
|Rock Crystal||Clear, colourless|
|Citrine||Yellow to reddish orange, greenish yellow|
|Rose quartz||Pink, translucent, may display diasterism|
|Milk quartz, or snow quartz||White, translucent to opaque, may display diasterism|
|Smoky quartz||Brown, transparent|
|Carnelian||Reddish orange chalcedony, translucent|
Quartz is the second most abundant mineral in the Earth's crust. It has a hexagonal crystal structure made of trigonal crystallized silica (silicon dioxide, SiO2), with a hardness of 7 on the Mohs scale. Density is 2.6g/cm³. The typical shape is a six-sided prism that ends in six-sided pyramids, although these are often distorted, or so massive that only part of the shape is apparent from a mined specimen. Additionally a bed is a common form, particularly for varieties such as amethyst, where the crystals grow up from a matrix and thus only one termination pyramid is present. A quartz geode consists of a hollow rock (usually with an approximately spherical shape) with a core lined with a bed of crystals.
Quartz is one of the world's most common crustal minerals and goes by a bewildering array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.
Although many of the varietal names historically arose from the colour of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Colour is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. This does not always hold true.
Not all varieties of quartz are naturally occurring. Prasiolite , an olive coloured material, is produced by heat treatment. Although citrine occurs naturally, the majority is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its colour.
Because natural quartz is so often twinned , much quartz used in industry is synthesized. Large, flawless and untwinned crystals are produced in an autoclave via the hydrothermal process: emeralds are also synthesized in this fashion.
Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several metres in length and weigh hundreds of kilograms. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."
The name "quartz" comes from the Greek word Krystallos, meaning "ice". Roman naturalist Pliny the Elder believed quartz to be permanently frozen ice. He supported this idea by saying that quartz is found near glaciers in the Alps and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of ability of quartz to split light into a spectrum. And it was Nicolas Steno's study of Quartz that paved the way for modern crystallography, he discovered that no matter how distorted a quartz crystal the long prism faces always made a perfect 60 degree angle.
Quartz is also a type of piezoelectric crystal that creates electricity through a process called piezoelectricity when mechanical stress is put upon it. One of the earliest uses for a quartz crystal was a phonograph pickup. Today, one of the most ubiquitous piezoelectric uses of quartz is as a crystal oscillator -- in fact these oscillators are often simply called "quartzes".
References and external links
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0471805807
- Quartz group - Mineral Galleries
- Quartz - Mineral Galleries
- Quartz - Mineral.net
- Arkansas quartz
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:6749b975-2a64-461a-8ab2-90d7670f400e> | 3.203125 | 1,173 | Knowledge Article | Science & Tech. | 32.046711 |
Mike Breen and Annette Emerson
Public Awareness Officers
paoffice at ams.org
"We are in the midst of math all the time."
This from Dr. Kathy Mann Koepke of the National Institutes of Health. She's quoted by Lauran Neergaard, an Associated Press medical writer, in a March 26, 2013 AP release about the importance of very young children learning to understand how to use numbers to count and to measure. Neergaard also spoke with Dr. David Geary, who is leading an NIH-funded study of children's mathematical progress K-12. Geary terms this understanding "number system knowledge" (to be distinguished from the ability to estimate numbers without counting, which is innate in "young babies and a variety of animals.") As Neergaard explains it,
"What's involved? Understanding that numbers represent different quantities -- that three dots is the same as the numeral "3" or the word "three." Grasping magnitude -- that 23 is bigger than 17. Getting the concept that numbers can be broken into parts -- that 5 is the same as 2 and 3, or 4 and 1. Showing on a number line that the difference between 10 and 12 is the same as the difference between 20 and 22."
Children who lacked this fluency in first grade ended up in seventh grade lagging "behind their peers in a test of core math skills needed to function as adults," even correcting for IQ and attention span. "They're not catching up," according to Geary. And the defecits persist. Leergaard: "About 1 in 5 adults in the U.S. lacks the math competence expected of a middle-schooler, meaning they have trouble with those ordinary tasks and aren't qualified for many of today's jobs." As Mann Koepke puts it: "It's not just, can you do well in school? It's how well can you do in your life. We are in the midst of math all the time." Her advice to parents: integrate numbers meaningfully into what you say to your children, from the very beginning. Count things, measure things. This AP release was picked up by The Denver Post and USA Today.
Great Scientist $\neq$ Good at Math?
Without the question mark, this was the heading on an April 5 2013 Wall Street Journal piece by the eminent Harvard biologist E. O. Wilson, printed the next day in the paper. "During my decades of teaching biology at Harvard, I watched sadly as bright undergraduates turned away from the possibility of a scientific career, fearing that, without strong math skills, they would fail. This mistaken assumption has deprived science of an immeasurable amount of sorely needed talent. It has created a hemorrhage of brain power we need to stanch." Wilson argues that
"exceptional mathematical fluency is required in only a few disciplines, such as particle physics, astrophysics and information theory. Far more important throughout the rest of science is the ability to form concepts, during which the researcher conjures images and processes by intuition."
The math can be outsourced, later: "When something new is encountered, the follow-up steps usually require mathematical and statistical methods to move the analysis forward. If that step proves too technically difficult for the person who made the discovery, a mathematician or statistician can be added as a collaborator."
Starting with math is not a good idea: "The annals of theoretical biology are clogged with mathematical models that either can be safely ignored or, when tested, fail."
Wilson's dicta were sharply challenged by Edward Frenkel, the Berkeley Math Professor, in an April 9 posting on Slate, "Don't Listen to E.O. Wilson." Frenkel addresses Wilson's lament about bright students driven from science by their fear of math. "Turns out he actually believes not only that the fear is justified, but that most scientists don't need math. 'I got by, and so can you' is his attitude. Sadly, it's clear from the article that the reason Wilson makes these errors is that, based on his own limited experience, he does not understand what mathematics is and how it is used in science." Frenkel quotes Galileo ("The laws of Nature are written in the language of mathematics.") and explains the power of mathematics in organizing our perception of the world. He concludes: "It would be fine if Wilson restricted the article to his personal experience, a career path that is obsolete for a modern student of biology. We could then discuss the real question, which is how to improve our math education and to eradicate the fear of mathematics that he is talking about. Instead, trading on that fear, Wilson gives a misinformed advice to the next generation, and in particular to future scientists, to eschew mathematics. This is not just misguided and counterproductive; coming from a leading scientist like him, it is a disgrace." (See Frenkel's Multivariate Calculus lectures.)
"Mary, Queen of Maths"
On March 8, 2013, BBC News Magazine ran "A point of View: Mary, Queen of Maths," by Lisa Jardine (University College, London). The "Mary" is Mary Cartwright (1900-1998), an expert in differential equations, whose prominence in British science (elected to the Royal Society in 1947, President of the London Mathematical Society from 1961 to 1963, Dame Commander of the British Empire in 1969) was equaled by her personal modesty. Jardine quotes Freeman Dyson: "Only Cartwright understood the importance of her work as the foundation of chaos theory, and she is not a person who likes to blow her own trumpet." Dyson refers to work Cartwright did with J. E. Littlewood, starting in 1938. They investigated "a tricky type of equation," related to the then-secret development of radar: "Engineers working on the project were having difficulty with the erratic behaviour of high-frequency radio waves." As Dyson explains it: "The whole development of radar in World War Two depended on high power amplifiers, and it was a matter of life and death to have amplifiers that did what they were supposed to do. The soldiers were plagued with amplifiers that misbehaved, and blamed the manufacturers for their erratic behaviour. Cartwright and Littlewood discovered that the manufacturers were not to blame. The equation itself was to blame." Jardine tells us that this very early identification of chaotic behavior in a mathematical system went "largely overlooked for almost 20 years." But now: "The results unexpectedly obtained from the equations predicting the oscillations of radio waves are part of the foundation for the modern theory that accounts for the unpredictable behaviour of all manner of physical phenomena, from swinging pendulums and fluid flow, to the stock market."
Stony Brook University
tony at math.sunysb.edu
Math Digest Summaries posted May 2013:
Crinkly curves; Twitter; fighting disease...
Recent articles on mathematics used--or not used--in other sciences and in certain kinds of jobs:
"Great Scientists ≠ Good at Math," by E.O. Wilson. The Wall Street Journal, 5 April 2013.
In this editorial, which is thought-provoking, insightful and mostly sensible, renowned evolutionary biologist E.O. Wilson makes the case that success as a scientist does not require a high level of mathematical proficiency. Wilson's goal here is to stem "a hemorrhage of brain power"--namely, the loss (to science) of students who see their perceived mathematical illiteracy as an insurmountable obstacle to pursuing a scientific career. To this end, he offers reassurances that will ring bells for many mathematicians... Offering his experience picking up calculus as a tenured professor at age 32, Wilson suggests that excellence can be achieved by researchers at any level of mathematical competence, and that it is easy to find mathematicians and statisticians to collaborate with when investigations lead into quantitative territory. All well and good. Unfortunately, while making these points, Wilson overgeneralizes his experiences as a biologist somewhat, making statements that account for the 243 sometimes contentious comments following the article. Read more...
--- Ben Polletta
"Here's How Little Math Americans Actually Use at Work," by Jordan Weissmann. The Atlantic, 24 April 2013.
Based on data by Michael Handel, "What Do People Do at Work? A Profile of U.S. Jobs from the Survey of Workplace Skills, Technology and Management Practices (STAMP)," Weissmann reports "less than a quarter of employees do any calculations more complicated than basic fractions, and blue-collar workers generally do more advanced math than their white-collar friends." Jobs are broken down into upper and lower level white and blue collar categories, and one chart shows the percentage of people in those job categories who use "Any advanced math," "Algebra (basic)," "Geometry/trig," "Statistics," "Algebra (complex)," and "Calculus." Read more...
--- Annette Emerson
Citations for reviews of books, plays, movies and television shows that are related to mathematics (but are not aimed solely at the professional mathematician). The alphabetical list includes links to the sources of reviews posted online, and covers reviews published in magazines, science journals and newspapers since 1996. | <urn:uuid:0f086491-e34f-4008-81a0-6d1f5ad1fe96> | 3.171875 | 1,904 | Content Listing | Science & Tech. | 47.177534 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2004 July 18
Explanation: Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about two million years for light to reach us from there. Although visible without aid, the above image of M31 is a digital mosaic of 20 frames taken with a small telescope. Much about M31 remains unknown, including how the center acquired two nuclei.
Authors & editors:
NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U. | <urn:uuid:1faeaa81-8409-4ac8-9e19-6a32c4ec6310> | 3.75 | 249 | Knowledge Article | Science & Tech. | 49.251745 |
The Delegation Pattern is a technique where an object's behavior (public methods) is implemented by delegating responsibility to one or more associated objects.
Groovy allows the traditional style of applying the delegation pattern, e.g. see Replace Inheritance with Delegation.
Implement Delegation Pattern using ExpandoMetaClass
The ExpandoMetaClass allows usage of this pattern to be encapsulated in a library. This allows Groovy to emulate similar libraries available for the Ruby language.
Consider the following library class:
With this in your classpath, you can now apply the delegation pattern dynamically as shown in the following examples. First, consider we have the following classes:
We can now use the delegator to automatically borrow methods from the lender object to extend the Person class. We can borrow the methods as is or with a rename:
The first line above, adds the borrowFor method to the Person class by delegating to the lender object. The second line adds a getMoney method to the Person class by delegating to the lender object's borrowAmount method.
Alternatively, we could borrow multiple methods like this:
Which adds these two methods to the Person class.
Or if we want all the methods, like this:
Which will make all the methods in the delegate object available in the Person class.
Alternatively, we can use a map notation to rename multiple methods:
Implement Delegation Pattern using @Delegate annotation
Since version 1.6 you can use the built-in delegation mechanism which is based on AST transformation.
This make delegation even easier: | <urn:uuid:88b373fb-523a-4ed9-8443-f36cdde4351c> | 3.359375 | 327 | Documentation | Software Dev. | 27.526743 |
THE fgets AND fputs STATEMENTS
These are useful for reading and writing entire lines of data to/from a file. If buffer is a pointer to a character array and n is the maximum number of characters to be stored, then
fgets (buffer, n, input_file);
will read an entire line of text (max chars = n) into buffer until the newline character or n=max, whichever occurs first. The function places a NULL character after the last character in the buffer. The function will be equal to a NULL if no more data exists.
fputs (buffer, output_file);
writes the characters in buffer until a NULL is found. The NULL character is not written to the output_file.
NOTE: fgets does not store the newline into the buffer, fputs will append a newline to the line written to the output file.
ęCopyright B Brown. 1984-1999. All rights reserved. | <urn:uuid:38204260-6e26-406b-8a72-4d3cbee1816b> | 4.15625 | 203 | Documentation | Software Dev. | 61.639288 |
Major Section: PROGRAMMING
See binary-* for multiplication and see unary-/ for reciprocal.
/ represents division as follows:
(/ x y)represents the same term as
(* x (/ y))which is really
(binary-* x (unary-/ y)).Also note that
/represents reciprocal as follows:
(/ x)expands to
/is a Common Lisp macro. See any Common Lisp documentation for more information. | <urn:uuid:a4896f13-e3ed-41a9-9927-a856cbe52437> | 3.140625 | 99 | Documentation | Software Dev. | 39.060568 |
Inertia-dominated deltas are considered to be an uncommon dominance for deltas. They are associated with high flow velocities and large amounts of turbulence. As shown in the figure above, sediments are deposited close to the main flow of the channel as it enters the basin. In other words, the deposition of sediments in inertia dominated deltas does not have a large lateral component.
Learn more about delta systems by linking to the following:
Wednesday, April 03, 2013 | <urn:uuid:d6db405c-0643-462f-9937-9a8b393b0930> | 2.890625 | 102 | Knowledge Article | Science & Tech. | 28.688654 |
Sometimes, as the Earth orbits the Sun, it comes between the Sun and the
Moon. When this happens, the Earth throws a dark shadow across the Moon.
This is known as an eclipse of the Moon, or a lunar eclipse.|
Sometimes, the Moon passes between the Earth and the Sun. The Moon blocks
the light of the Sun and a shadow of the Moon is cast on the Earth's
surface. This is an eclipse of the Sun, or a solar eclipse.
A total solar eclipse can only occur when two events happen at the same time. The first event is a new Moon. This phase of the Moon occurs when the Sun is almost directly behind the Moon, and we see only a sliver of the Sun's light reflected by the Moon. During this time the Moon and the Sun appear close together. The second event that must occur is that the Moon must be in the right position, directly in the line of sight between the Earth and the Sun. These two events occur at the same time about once every year and a half. A total solar eclipse will be visible from Europe and Asia on 11 August 1999.Help me understand how the Sun and Moon can appear to be the same size
Help me understand why eclipses happen
Show me what I'd see in a total solar eclipse
The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/ GSFC.
StarChild Authors: The StarChild Team
StarChild Graphics & Music: Acknowledgments
StarChild Project Leader: Dr. Laura A. Whitlock
Responsible NASA Official:
If you have comments or questions about the StarChild site, please send them to us. | <urn:uuid:c307931a-06e2-47a1-9db3-302c0109946d> | 3.921875 | 374 | Knowledge Article | Science & Tech. | 65.118359 |
In analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
, a calibration curve
is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. A calibration curve is one approach to the problem of instrument calibration; other approaches may mix the standard into the unknown, giving an internal standard
An internal standard in analytical chemistry is a chemical substance that is added in a constant amount to samples, the blank and calibration standards in a chemical analysis. This substance can then be used for calibration by plotting the ratio of the analyte signal to the internal standard signal...
The calibration curve is a plot of how the instrumental response, the so-called analytical signal
, changes with the concentration of the analyte
An analyte, or component , is a substance or chemical constituent that is of interest in an analytical procedure. Grammatically, it is important to note that experiments always seek to measure properties of analytes—and that analytes themselves can never be measured. For instance, one cannot...
(the substance to be measured). The operator prepares a series of standards across a range of concentrations near the expected concentration of analyte in the unknown. The concentrations of the standards must lie within the working range of the technique (instrumentation) they are using (see figure). Analyzing each of these standards using the chosen technique will produce a series of measurements. For most analyses a plot of instrument response vs. analyte concentration will show a linear relationship. The operator can measure the response of the unknown and, using the calibration curve, can interpolate
to find the concentration of analyte.
In more general use, a calibration curve is a curve
In mathematics, the graph of a function f is the collection of all ordered pairs . In particular, if x is a real number, graph means the graphical representation of this collection, in the form of a curve on a Cartesian plane, together with Cartesian axes, etc. Graphing on a Cartesian plane is...
A table is a means of arranging data in rows and columns.Production % of goalNorth 4087102%South 4093110% The use of tables is pervasive throughout all communication, research and data analysis. Tables appear in print media, handwritten notes, computer software, architectural...
for a measuring instrument
In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...
which measures some parameter indirectly, giving values for the desired quantity as a function of values of sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
output. For example, a calibration curve can be made for a particular pressure transducer to determine applied pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
output (a voltage). Such a curve is typically used when an instrument uses a sensor whose calibration varies from one sample to another, or changes with time or use; if sensor output is consistent the instrument would be marked directly in terms of the measured unit.
The data - the concentrations of the analyte and the instrument response for each standard - can be fit to a straight line, using linear regression
In statistics, linear regression is an approach to modeling the relationship between a scalar variable y and one or more explanatory variables denoted X. The case of one explanatory variable is called simple regression...
analysis. This yields a model described by the equation y = mx + y0
, where y
is the instrument response, m
represents the sensitivity, and y0
is a constant that describes the background. The analyte concentration (x
) of unknown samples may be calculated from this equation.
Many different variables can be used as the analytical signal. For instance, chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
(III) might be measured using a chemiluminescence method, in an instrument that contains a photomultiplier tube (PMT) as the detector. The detector converts the light produced by the sample into a voltage, which increases with intensity of light. The amount of light measured is the analytical signal.
Most analytical techniques use a calibration curve. There are a number of advantages to this approach. First, the calibration curve provides a reliable way to calculate the uncertainty of the concentration calculated from the calibration curve (using the statistics of the least squares
The method of least squares is a standard approach to the approximate solution of overdetermined systems, i.e., sets of equations in which there are more equations than unknowns. "Least squares" means that the overall solution minimizes the sum of the squares of the errors made in solving every...
line fit to the data).
Second, the calibration curve provides data on an empirical relationship. The mechanism for the instrument's response to the analyte may be predicted or understood according to some theoretical model, but most such models have limited value for real samples. (Instrumental response is usually highly dependent on the condition of the analyte, solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s used and impurities it may contain; it could also be affected by external factors such as pressure and temperature.)
Many theoretical relationships, such as fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
, require the determination of an instrumental constant anyway, by analysis of one or more reference standards; a calibration curve is a convenient extension of this approach. The calibration curve for a particular analyte in a particular (type of) sample provides the empirical relationship needed for those particular measurements.
The chief disadvantages are (1) that the standards require a supply of the analyte material, preferably of high purity and in known concentration, and (2) that the standards and the unknown are in the same matrix. Some analytes - e.g., particular proteins - are extremely difficult to obtain pure in sufficient quantity. Other analytes are often in complex matrices, e.g., heavy metals in pond water. In this case, the matrix may interfere with or attenuate the signal of the analyte. Therefore a comparison between the standards (which contain no interfering compounds) and the unknown is not possible. The method of standard addition
The method of standard addition is used in instrumental analysis to determine concentration of a substance in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve...
is a way to handle such a situation.
Error in calibration curve results
As expected, the concentration of the unknown will have some error which can be calculated from the formula below. This formula assumes that a linear relationship is observed for all the standards. It is important to note that the error in the concentration will be minimal if the signal from the unknown lies in the middle of the signals of all the standards (the term
goes to zero if
- is the standard deviation in the residuals
- is the slope of the line
- is the y-intercept of the line
- is the number standards
- is the number of replicate unknowns
- is the measurement of the unknown
- is the average measurement of the standards
- are the concentrations of the standards
- is the average concentration of the standards
- Analysis of concentration
- Verifying the proper functioning of an analytical instrument or a sensor device such as an ion selective electrode
An ion-selective electrode , also known as a specific ion electrode , is a transducer that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or pH meter. The voltage is theoretically dependent on the logarithm of the...
- Determining the basic effects of a control treatment (such as a dose-survival curve in clonogenic assay
A clonogenic assay is a microbiology technique for studying the effectiveness of specific agents on the survival and proliferation of cells. It is frequently used in cancer research laboratories to determine the effect of drugs or radiation on proliferating tumor cells as well as for titration of... | <urn:uuid:dd08a69d-7967-434b-9d44-a49cc1c373d7> | 3.34375 | 1,986 | Knowledge Article | Science & Tech. | 31.465304 |
Free online HTML tutorial about how to code an image for your Web page with examples of image codes. The picture (image) codes are useful for gif images, jpg images, bitmap images and others.
[Web Images, Introduction to Images
[Related Links and Image Maps
Images are ignored by non-graphical
. An image "tag" is used in HTML
to code an image or a photograph onto a Web page and the image will be displayed
by graphical browsers recognizing that particular filename. If the browser does
not recognize an image it may put up very empty squares onto the Web
page instead of the image. To limit the size of the non-image squares you can
code the HEIGHT="" and WIDTH="" attributes of your image inside the image tag,
as discussed below. Images which are very large take a long time to download on
the Web, even with DSL connections, and users trying to view your page will probably leave before your large
images have completely downloaded. Keep your image files small (reduce file size in PhotoShop using File, Save for Web); use them only when they have a specific purpose and text
will not suffice, and study Web graphics because there are techniques to get smaller
image file sizes and to get the image to start loading onto the Web page sooner.
Software programs useful in Web design include
Paint Shop Pro
, or Adobe Illustrator, and others. See Introduction to Graphics Software
PhotoShop is especially useful in being able to slice an image into sections. Some Web sites have huge images in the banner section at the top of their page. Click on View, Source in Internet Explorer to view the code for such a page. Notice that several images make up the one larger image. This is done to facilitate faster loading of the Web page by the browser. Again, slowly loading Web pages lose Web visitors.
Cute little drawings and animations are .gif file images.
Photographs are usually .jpg file images. Many logos are .jpg images.
Only the .gif images can have a transparent background. An icon with a transparent
background will not have a white,
black, or colored block that appears on a textured web page behind the image.
See the article Web Images, Introduction to Images
many types of image files. I have gotten .bmp images to appear on a web site but
the two images most supported by the graphic browsers are the .gif and .jpg (JPEG)
Make a separate folder on your Web site to hold the images. If the folder is named images, you will need to reference the folder name when placing a link on a Web page.
<IMG SRC="images/stocking2.gif" ALT="stocking image">
Let the Coding Begin
Do you know where to find online images? Do you know how to download online images which are in the public domain? Always obtain permission before using someone else's images from their own Web page unless they say that the images may be downloaded and used.
To begin coding an image you will start with the <IMG> "tag". There is no
end tag for the image code. Inside the "tag" (the image element) you will want to
of the IMG element and give the attributes the values of your own choice.
To do this, first look at three simple examples, before I discuss the
attributes of the IMG element.
You have to state the location of the image file in relation to your Web document file, using
the SRC attribute <IMG SRC="[path][filename]">.
If you have an image called flower5.gif
and it is in a folder called graphics, you would call the image by its folder name,
a slash, and its file name: graphics/flower5.gif. If the web page and the image
are in the SAME LOCATION, just call the image "flower5.gif". The SRC attribute
of the image tag is set equal to the path of the image from the web page. Take a look
at the following examples.
<IMG SRC="flower5.gif" BORDER="0" ALT="This is a rose">
This is for images in the same location as the Web document file. The BORDER attribute
has been set to "0" (BORDER="0") because I did not want a border around the image.
I used the ALT attribute so the user would get a message by holding the mouse pointer over
the image, and also in case the image does not appear on the Web page (the message
would still appear).
The Web page here, is in the same folder as the index.html (main web page), but a
folder called graphics holds the file, "flower5.gif":
<IMG SRC="graphics/flower5.gif" BORDER="0" ALT="This is a rose.">
If the Web page is in a folder called html and the image is in a folder called
graphics and both folders are in the main folder where the index.html (main page) resides:
Code as follows, <IMG SRC="../graphics/flower5.gif" BORDER="0" ALT="This is a rose.">
This is what "flower5.gif" looks like, from my own graphics file...
Notice that the image in the paragraph automatically aligned to the left side.
Old way to center an image
If you want to center an image, using HTML 3.2, code all of the <IMG> information
between <CENTER> and </CENTER>. This is what happens in the paragraph:
No text appears on either side of
an image centered using the <CENTER></CENTER> tags.
Trying a TABLE to center an image
When you learn to create tables using HTML you can make
a table having 3 table cells across the page, put the image in the middle and have text on
either side but positioning and centering of images is limited if just using coding tags
and the older HTML 3.2.
Center Tag is Tossed Out
Note: The CENTER tag was deprecated (phased out) of HTML 4.0 and later on, browsers will stop supporting this CENTER tag.
New Way to Center Something
Use <DIV ALIGN="center"> to create a division of centered objects, then close it with </DIV>.
Using the ALT attribute of the <IMG> tag
Stop for a moment and hold your mouse pointer over one of the images above. See the
pop-up message. What the message will say, is whatever you have coded into the ALT=""
attribute as a value. This string message of the ALT attribute is displayed if the user
has disabled images or if a browser is not able to display images.
Now I'd like to change to a different image and right align it
in a paragraph. I have found an image
named "xmastree3.gif" in my image file. <IMG SRC="../images/xmastree3.gif"
ALIGN="right" ALT="A little Christmas tree .gif file" BORDER="0">
This works. The image is now right aligned in
the paragraph and the text is flowing to the left of the image. The attributes of the image may be
in any order inside the IMG "tag". The SRC attribute is required or the browser will not
know where to find the image. There are attributes of the IMG element that can control white
space above and below the image. In the next section you will learn more about the IMG attributes.
More About Image Attributes
This is a .jpg image file for which I specified a width of "70" (use quotations for values). I did not specify alignment such as ALIGN="right", so the default was to
be left-aligned. I gave it a border width of "2" (BORDER="2"). A value of "3" is thicker
and a value of "1" is a thinner border. If I had used BORDER="0" the image would still
have the white background because that is the way this .jpg image was made. (Remember that
only .gif images can have a transparent background like the image of the rose seen earlier.)
: Besides the SRC attribute, Netscape provides for the LOWSRC attribute which can be a link
to a much smaller image. When the browser sees the LOWSRC attribute it will load the smaller
image, the rest of the Web page, then go back and load the larger SRC image, so the user gets
to start reading the Web page while the other image is loading. Other browsers have not
supported the LOWSRC attribute and ignore it, just loading the SRC image.
ALIGN: The ALIGN attribute has been mentioned above. We know that we can specify
ALIGN="left|center|right" and that there is not text to either side of the image with
center alignment. Netscape, Microsoft Internet Explorer 4.x and 5.x and WebTV support the
additional values of "absbottom|absmiddle|absbaseline|texttop" to align an image in
respect to the text in a line of text.
BORDER: Border width can be anything you specify but only some of the smaller
values are resonable. Values of "5" or more begin to displace surrounding objects.
The default is "1" so if you DO NOT WANT A BORDER, you must specify BORDER="0".
DYNSRC: This is a special attribute not supported by all browsers but currently
supported by Microsoft and WebTV to specify the location (URL) of a movie file. When
DYNSRC is used, SRC is not used.
HEIGHT: The height in pixels of the image.
WIDTH: The width in pixels of the image.
HSPACE: The horizontal space in pixels, above and below the image -- the space
horizontally between the image and the surrounding text.
VSPACE: The vertical space in pixels, on both sides of the image -- the space
situated vertically between the image and the surrounding text.
ID: An identifying reference string for the image, used for stylesheets (CSS1, CSS2)
and absolute positioning. These are topics not in the realm of the new HTML student but
part of the technologies of Dynamic HTML.
How to Use An Image As A Link
You may have already seen links to other pages using the <A HREF=""></A> link
element. The only difference here in making an image link is that in the middle of the link
element you will place your image element and attributes, just prior to the </A>. I will
explain two examples, below.
Examples of Image Links
Navigating With a Button Image
In this first example I am going to use a navigation button (image) to navigate away this page to the page about "Introduction to Graphics Software". Use the Back button of the browser to return to this page. Note that button images may either be a .JPG file or a .GIF file.
The name of the image file is "bu_rainNext60.jpg". It has a width
of 60 pixels. In the image tag I will use WIDTH="60". I want text to appear if someone mouses over the image and holds the cursor on the image. In the image tag I will use ALT="Next button navigates to another related page." I will have to next the image tag within the navigation set of <A HREF="[insert location and path of path of image]"> and </A>. See the button in the middle and try to navigate to another page, then use the back button of the browser to return to this page. Here, the image is located in another folder named images.
Click on the image button to navigate to a page about "Introduction to Graphics Software".
The code is as follows:
<A HREF="graphics.html"><IMG SRC="images/bu_rainNext60.jpg" WIDTH="60"
ALT="Next button navigates to another related page."></A>
Navigating With a Book Image, .JPG File
<IMG SRC="../images/dhtmlref.gif" ALT="http://www.oreilly.com/catalog/dhtmlref2/; Dynamic HTML The Definitive Reference"
BORDER="2" ALIGN="left" VALIGN="top" HSPACE="20"></A>
The <A HREF=""> part is where the image is linking to.
It is the target of the hyperlink, or the location on the Web where you will
go to if you click on the image link.
The <IMG SRC=""> refers to the location where you keep that particular
image file -- the path to the file from your document.
Notice that in my example I had to begin with ../ because
I was inside another folder which I had to exit in order to
access the graphics folder. If you are inside a folder within
a folder you will need to begin the path to the graphics
file with "../../graphics/filename.extension".
This type of reference to the location of the image file is
called a relative reference
. The other type which includes your full
domain name and then the folder and file is called an absolute reference
The ALT attribute was explained above. For images that are acting as
hyperlinks the BORDER attribute is coded with a positive value of 1 or 2
depending upon your own choice and the color of the image border will be
the same color as your other hyperlinks on the Web page.
You cannot alter the border color of an image that is a link. You want the border width to show, so that users know that that particular image is a link. My blue border will become purple once the link has been visited by you, until the Browsing History in your browser is deleted, then the border will be blue again, as if you had not yet visited the link.
I coded ALIGN="left" to place the image to the left side of the page. I coded VALIGN="top" to that the text would begin at the top of the image and lastly the HSPACE was coded to allow for 20 pixels horizontally between the image and the text.
If you want to widen space above or below the image you would code a value for the VSPACE attribute, for the vertical space separation.
Navigating With a Photograph, .JPG File
Even though the photograph has no border, it is possible to click on the picture to move to the home page of hitmill.com. Use the browser back button to return to this page. It would be clearer to the user had you set a BORDER value of 1 instead of zero inside the image tag when coding this link. Without a border it does not look like something to click on.
The ALIGN attribute of the image tag may have values of left, right, middle, which are the standard attributes as well as browser specific attributes such as absbottom, abstop, absmiddle, center.
When you play with the non-standard values (browser-specific values)of the ALIGN attribute be sure to test your pages in 2 or 3 different browsers to get a feel of how your pages will look. You may wish to only use the standard values which have wider browser support.
The code for the above photograph (which will link to the domain's home page) is as follows:
<A HREF="../index.htm"><IMG SRC="../images/inpool.jpg" HEIGHT="180" ALIGN="left" ALT="baby" VSPACE="20" HSPACE="25" BORDER="0"></A>
Notice now that the value for HSPACE is not the same value of the VSPACE yet on the Web page, the horizontal and vertical free space around the image appears to be very similar. I think the reason is due to the shape of a pixel which is not square. Pixels are the default unit of measurement for HSPACE and VSPACE.
Now go have fun practicing. Make a small page using your text editor such as NotePad for Windows machines) and save each
change that you code in your editor as well as remembering to "Refresh" or "Reload" your browser window after each "Save" in the text editor. | <urn:uuid:be12329f-28d8-4399-bbb2-c069749b10f6> | 2.9375 | 3,515 | Tutorial | Software Dev. | 58.684372 |
Saltcedar (Tamarix spp.) has impacted many native plant communities in the western United States and has become a significant problem on many national wildlife refuges including the Kern and Pixley National Wildlife Refuges. The Kern Refuge has a significant infestation of saltcedar with approximately thirty percent of the refuge covered with this invasive plant. The Pixley Refuge has only a minor infestation which is isolated to spots within the 950 acre wetland unit.
A variety of techniques have been developed for the treatment of the saltcedar. The best technique for the control or eradication of this plant can be site sensitive and vary depending upon objectives and habitat needs. These techniques include fire, mechanical removal with bulldozers, root rakes or root plows, and chemical treatment as well as a combination of these techniques. In many situations, when the use of heavy equipment or fire would do more harm than good or when the infestation is small or sparsely spread, the cut-stump treatment, although time consuming, may be the best alternative. This is the case in the riparian unit on the Kern National Wildlife Refuge where saltcedar is interspersed with desirable riparian trees such as cottonwoods and willows and in the wetland unit on the Pixley National Wildlife Refuge where trees are found in isolated locations.
The cut-stump technique used on the Kern Complex involves cutting saltcedar trees and shrubs to ground level and spraying stumps with the herbicide Garlon 4. Methods of removal include chain saws, brush cutters, lopping shears and other hand tools. Stumps are then sprayed using hand-held spray bottles. The herbicide must be applied to the stump immediately following cutting in order to reach full effectiveness. The herbicide is most effective while the tree is actively growing and translocating nutrients. The treatment should be applied after the plant has bloomed and prior to dormancy. Cutting the tree outside of this time frame is effective in removing the bulk of the biomass but the resprouts will need to be treated with chemical the following year to in order to kill the plant. Many saltcedar plants grow in a bush or multiple stem tree. To help insure all stumps or stems are covered with herbicide it is useful to add a dye to the chemical mixture which tags each stump when sprayed allowing the applicator to see the amount of coverage and which stumps have been sprayed. The most efficient procedure is to have the crew work in groups of three to five people. Generally, one person to cut the tree, one or two people to pull trees as they are cut and one or two people to spray the stump as soon as access is available. This technique is time consuming and not recommended for extremely large infestations.
One concern that is discussed when controlling exotic plants is the effects on non-target species and possible effects to endangered or sensitive species. Many techniques such as burning, widespread mechanical treatment or broadcast spraying of herbicides can have some impact on non-target plants and animals. When using the cut-stump treatment for saltcedar many of these concerns can be set aside. In many cases the saltcedar out competes all native vegetation in the local vicinity reducing the risk of impacting non-target plants. In addition, this methods utilizes a pesticide delivery method which reduces if not eliminates non-target effects. Individual saltcedar plants are selected and the herbicide is sprayed at a range that limits drift to non-target plants.
Most national wildlife refuges do not have the personnel available that the cut-stump method requires unless the saltcedar problem is small. Therefore, it is important to locate an alternative source of labor to conduct this work. Over the past six years, alternative labor sources such as volunteers and prison labor have been used on both Kern and Pixley Refuges to cut saltcedar. The Corcoran prison crew was used in 1990 to cut and treat saltcedar in a wetland unit on Kern. Volunteers from the Tulare Audubon Society have been used on Pixley. A third labor source available to the Kern Complex is the state supported California Conservation Corps (CCC).
The CCC is a state department which was established in 1976 to protect and restore California's natural resources by employing California residents between the ages of 18 and 23. A portion of their funding is generated by sponsor partnerships for specific work projects. Starting in 1993 the CCC began cutting saltcedar in the Riparian Unit on the Kern Refuge as part of a Riparian Restoration and Rehabilitation Project. Phase 2 of the project deals with saltcedar control within the 320 acre riparian unit. This plan will ultimately lead to defined water management goals for riparian habitats, increased acreage of native riparian vegetation, potential reintroduction of native species and preservation of habitat for giant slough thistle.
The control techniques outlined in the plan are being conducted by the CCC under the guidance and training of refuge staff. The use of the CCC on the Kern Refuge has been successful thus far. They have effectively controlled the saltcedar adjacent to the main riparian channel for approximately mile. The CCC has been working this area for four consecutive years (1993-1996). Their time commitment ranges from two to four weeks per year which is dependent upon their work load and funding availability.
The first three years the refuge received non-base funding (non-game and challenge-cost share monies) to support the CCC work. The fourth year no funding was available but the CCC volunteered one week of time to the project. The non-game funding provided in 1993 purchased one week of labor from a twelve person CCC crew with the CCC donating an additional three weeks of labor. In 1994 Challenge Cost Share money was provided to continue the funding of this project. The U.S. Fish and Wildlife Service paid CCC $5,000.00 for the first week to cut and treat saltcedar; the CCC donated the labor for the second week. The work was continued in 1995 with the same funding source. In 1996 no money was available to fund the CCC although they did donate several days in the spring.
The cut-stump treatment can be a useful tool in the fight against saltcedar but its effectiveness is dependent upon the quality and reliability of the workforce. Three sources of hand labor have been used on the Kern Complex, volunteers, prison crews, and the California Conservation Corps crews. Individual crews have their strengths and weaknesses. Many times a volunteer work force will be more effective because they may have a greater motivation to kill the plant and improve the habitat than a prison crew. Depending upon the location, volunteers to do this type of high intensity labor may be difficult to find. Therefore, a prison crew or an organization such as the California Conservation Corp may provide a more dependable labor source for projects which will span longer periods of time.
When working with volunteers or groups which may only work occasionally, it is important to keep the crew motivated. If the project is so large that it is overwhelming, keeping the crew motivated will be difficult. Breaking a large project into smaller projects which can be easily completed provides the crew with a sense of accomplishment and a willingness to return and do more work.
When working with prison crews or organizations such as the CCC effectiveness of the treatment is directly related to the crew leader and the work attitude of the crew. To help ensure proper treatment it is critical that the herbicide be applied within seconds of the tree being cut. Some crews are more diligent than other at applying the herbicide which relates directly to the percent kill. Overall the Kern refuge has had good success using CCC crews with the exception of 1996. The 1996 crew was pulled by the CCC crew leader from the complex three days into the project and did not return. The crew members were slow and lackadaisical about their work and very little of the work was completed. This crew has been the exception rather than the rule for the quality of crews working on the refuge complex. Overall the quality of work the CCC provides has been good.
Prior to utilizing the alternative labor sources for saltcedar control, an evaluation of cost effectiveness for the specific project should be undertaken. These expenses will vary based upon available labor, equipment needs, and availability of herbicide selected. Expenses include costs for labor, herbicides, tools, fuel for powered equipment, safety equipment, and miscellaneous expenses for equipment maintenance.
Labor sources can range from free to approximately $1,000.00 or more per week. In addition to the crew labor, staff time to oversee, supervise and train the crew must also be considered. Some crews will need greater amount of staff supervision than others. Groups such as the CCC are able to provide a competent crew leader which can reduce the amount of staff time needed to oversee the project. Volunteer groups will require staff involvement to supervise the crew for the duration of the project unless a volunteer is sufficiently knowledgeable about saltcedar control. The cost of herbicides also needs to be considered. Garlon 4, which is the herbicide used on the Kern Complex, costs approximately $85.00/gallon. Cost effectiveness will vary based upon the cost and quality of labor. If a good, hard working crew is obtained, this can be a relatively cost effective method for dealing with some saltcedar problems.
In closing, the use of alternative labor force can be successfully utilized in the control of saltcedar if the time is taken to research and plan the project.
Return to Workshop Home Page or continue on to the next paper " Saltcedar Biological Control: Methodology, Exploration, Laboratory Trials, Proposals for Field Releases, and Ecological Effects."
For information on the outcome of this workshop or integrated weed management in the Pacific Region (Region 1), U.S. Fish and Wildlife Service, Portland, OR, contact: Scott_Stenquist@fws.gov
Conference proceedings hosted by the National Invasive Species Information Center | <urn:uuid:5438045a-f150-4cdf-88cd-c5aa7b37c42e> | 3.46875 | 2,048 | Knowledge Article | Science & Tech. | 41.463517 |
This experiment is designed to measure the adsorption characteristics of nitrogen molecules on activated charcoal particles maintained at liquid nitrogen temperature. The basic outline and theory of this experiment can be found in Experiment 26 of Garland and Shoemaker.
This experiment also incorporates a specific web-based module designed to help students come to grips with the underlying physical nature of adsorption. The web-site can found at http://www.jhu.edu/~chem/fairbr/teach/BET/isot.html.
The essence of this experiment involves a series of volume expansions, ultimately to determine the adsorption properties of nitrogen on activated charcoal. A pictorial representation of the experimental set-up can also be found at http://www.jhu.edu/~chem/fairbr/teach/BET/betexptl.pdf
The pre-lab is constructed as a series of questions – answers to these questions should constitute a working knowledge of adsorption and enable you to carry out the experiment.
Basis for Pre-Lab:
- What is the pressure-to-volume relationship for an ideal gas expansion between two vessels with volumes V1, V2 and initial pressures P1 and P2? After expansion the pressures can be written P1` and P2`.
- What is the fundamental chemical concept underlying the pressure-to-volume relationship; conservation of mass, energy, number of moles or volume? Show how this leads to the relationship used in (a)
- Answer the following question: If gas at 500 Torr is expanded into another container, initially under high vacuum (i.e. P2 = O Torr) having four times the volume of the initial container what will the final pressure of the overall system be? Show your working clearly and carefully.
- How would the volume expansion relationship be modified in the case of adsorption? Explain either in words or using an equation how volume expansions be used to determine adsorption characteristics?
- Why do we out gas the carbon prior to adsorption experiments?
- What the liquid nitrogen is used for (2 reasons)?
- The Langmuir adsorption isotherm (see web page) is a simplified version of the BET isotherm that gives the same qualitative form of the variation in adsorption as function of external pressure at low gas pressures. Using the Langmuir isotherm explain in words how the number of moles adsorbed on the activated charcoal should vary as a function of the external pressure. (e.g. number of moles of gas adsorbed is constant as a function of the applied pressure)
- Also from the animated gifs provided on the webpage explain at a molecular level how adsorption is effected by external parameters such as temperature and pressure?
- Give some examples of practical everyday situations where adsorption is important.
- Identify likely sources of error in the experiment?
(A) Preparation of "activated" charcoal:
- Carefully remove the sidearm flask from the glass line
- Measure approximately 2 grams of activated carbon and transfer into the sidearm flask without contaminating the glass wool filter inside the sidearm flask
- Reattach the sidearm flask to the glass line, and begin pumping through the sidearm valve to reestablish the vacuum
- Attach the heating tape to the flask so that as much of the carbon is covered without overlaying the heating tape on itself. Power the heating tape at 100/140 on the Variac (Heat for 30 minutes)
- Remove heating tape from flask and allow to cool for 15 minutes
- Once cool, slowly open the valve connecting the sidearm flask to the glass line making sure that the vacuum in the glass line does not disturb the carbon in the flask
Close the valve and repeat the helium expansion from above, making sure that when you evacuate the side arm flask the you do it through the sidearm or else you may lose some of your now activated carbon
(B) Helium Expansion into glassware to determine the volume of the line and the volume of the sidearm vessel containing the charcoal:
- check to make sure that all relevant stop cocks are open for initial pumping
- start the Alcatel mech. pump and pump the glass line and both gas line to the regulators, (both the Helium and Nitrogen) – MAKE SURE THAT THE NEEDLE VALVES ON BOTH NITROGEN AND HELIUM TANKS ARE CLOSED.
- fill the 1025 mL round bottom flask with a known pressure of He (200-800 Torr in »
100 Torr increment). Throughout all experiments pressure should be read off the Baratron Digital Pressure Gauge.
- Pump the line and side arm flask back to base pressure (< 5 Torr)
- (a) Expand the gas from the round bottom flask into the line, recording the pressure drop.
- Then expand the round bottom and line pressure in the sidearm flask containing the characoal, again recording the pressure drop.
- Fill the round bottom to another known pressure, evacuate the line and sidearm flask and repeat 5(a) and (b) until a total of 7 data points have been acquired.
Once all helium expansions are complete, evacuate the helium line and open the nitrogen line.
(C) Determine the adsorption characteristics of nitrogen in contact with the activated charcoal:
- Immerse the activated carbon in liquid nitrogen.
- Fill the round bottom flask and the line with a known pressure of nitrogen (starting low, »
10-20 Torr and going to higher pressures »
700-800 Torr), open the sidearm flask and watch pressure drop stabilize. It will typically take 5-10 minutes for the pressure to stabilize as the system comes to equilibrium.
- Close the stopcock between the sidearm flask and the main glass line
- Refill the glass line and round bottom to next higher pressure as in 2) and carry our successive expansions into the sidearm.
Make sure to watch the liquid nitrogen level does not fall below the level of charcoal in the sidearm vessel as the experiment continues.
Once done bring line back to atmosphere before removing the liquid nitrogen for the charcoal, ensuring that the gas has a place to escape. | <urn:uuid:4e4670c3-574c-4e5c-a9fd-e610151f3112> | 3.921875 | 1,311 | Tutorial | Science & Tech. | 40.864704 |
chem ! help!
.A balloon is filled with 14 L of gas at 302 K. What is its temperature in Kelvin when the volume expands to 20 L? Round to the nearest whole number. Don't forget the units. my teacher explained it but im still lost please help
please help Solve for h in U= mgh. Please show steps.
find the LCM of 15ef and 12e^4 (12e to the power of 4) Please show the steps. I do not understand how to do this.
Oh and the Ksp values for AgCl and PbCl2 is 1.8x10^-10 and 1.7x10^-5, respectively.
A solution contains 0.022 M Ag and 0.033 M Pb2 . If you add Cl, AgCl and PbCl2 will begin to precipitate. What is the concentration of Cl required, in molarity, when A. AgCl precipitation begins? B. AgCl precipitation is 99.99% complete? C. PbCl2 precipitation begi...
find the verticle, horizontal, and oblique asymptotes, if any, for the given rational function: g(x)=x^4-81/3x^2-9x I feel like such a dork becaue i have no clue how to do this, can someone please help me????
3). The shaded region is bounded by the y-axis and the graphs of y=1+√x, y=2. Find the volume of the solid obtained by rotating this region around the x-axis. Answer choices: 7/6pi, 4/3pi, 11/6pi, 5/3pi, 13/6pi, 5/6pi 4). Find the area of the region bounded by y=x^2-6x+7...
5). Find the volume of the solid of revolution generated by rotating the graph of y=8 lnx about the y-axis between y=0 and y=16 Answer choices: 238.39pi, 246.39pi, 230.39pi, 214.39pi, 222.39pi 7). Find the area of the region bounded by y=√x-2, y=9, y=0, x=0
10). Find the area of the region bounded by the graph of f(x)=4lnx/x, y=0, x=5.8 11). Find the area of the region bounded by x=y^2-1y, x=0
8). Part 1 of 2: In the solid the base is a circle x^2+y^2=16 and the cross-section perpendicular to the y-axis is a square. Set up a definite integral expressing the volume of the solid. Answer choices: integral from -4 to 4 of 4(16-y^2)dy, integral from -4 to 4 of (16+y^2)dy...
For Further Reading | <urn:uuid:9f522be0-4f75-44fb-a57e-81d3ad7d247c> | 2.6875 | 630 | Q&A Forum | Science & Tech. | 104.247472 |
A designator is an object that denotes another object.
Where a parameter of an operator is described as a designator, the description of the operator is written in a way that assumes that the value of the parameter is the denoted object; that is, that the parameter is already of the denoted type. (The specific nature of the object denoted by a ``<<type>> designator'' or a ``designator for a <<type>>'' can be found in the Glossary entry for ``<<type>> designator.'')
For example, ``nil'' and ``the value of *standard-output*'' are operationally indistinguishable as stream designators. Similarly, the symbol foo and the string "FOO" are operationally indistinguishable as string designators.
Except as otherwise noted, in a situation where the denoted object might be used multiple times, it is implementation-dependent whether the object is coerced only once or whether the coercion occurs each time the object must be used.
For example, mapcar receives a function designator as an argument, and its description is written as if this were simply a function. In fact, it is implementation-dependent whether the function designator is coerced right away or whether it is carried around internally in the form that it was given as an argument and re-coerced each time it is needed. In most cases, conforming programs cannot detect the distinction, but there are some pathological situations (particularly those involving self-redefining or mutually-redefining functions) which do conform and which can detect this difference. The following program is a conforming program, but might or might not have portably correct results, depending on whether its correctness depends on one or the other of the results:
(defun add-some (x) (defun add-some (x) (+ x 2)) (+ x 1)) => ADD-SOME (mapcar 'add-some '(1 2 3 4)) => (2 3 4 5) OR=> (2 4 5 6)
In a few rare situations, there may be a need in a dictionary entry to refer to the object that was the original designator for a parameter. Since naming the parameter would refer to the denoted object, the phrase ``the <<parameter-name>> designator'' can be used to refer to the designator which was the argument from which the value of <<parameter-name>> was computed. | <urn:uuid:c5aa95a8-0143-43d7-92f9-d3e7fd5e3073> | 3.25 | 499 | Documentation | Software Dev. | 25.128756 |
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Microbes generate electricity while cleaning up nuclear waste
Researchers at Michigan State University have unraveled the mystery of how microbes generate electricity while cleaning up nuclear waste and other toxic metals.Details of the process, which can be improved and patented, are published in the current issue of the Proceedings of the National Academy of Sciences. The implications could eventually benefit sites forever changed by nuclear contamination, said Gemma Reguera, MSU microbiologist.
"Geobacter bacteria are tiny micro-organisms that can play a major role in cleaning up polluted sites around the world," said Reguera, who is an MSU AgBioResearch scientist. "Uranium contamination can be produced at any step in the production of nuclear fuel, and this process safely prevents its mobility and the hazard for exposure."
The ability of Geobacter to immobilize uranium has been well documented. However, identifying the Geobacters' conductive pili or nanowires as doing the yeoman's share of the work is a new revelation. Nanowires, hair-like appendages found on the outside of Geobacters, are the managers of electrical activity during a cleanup."Our findings clearly identify nanowires as being the primary catalyst for uranium reduction," Reguera said. "They are essentially performing nature's version of electroplating with uranium, effectively immobilizing the radioactive material and preventing it from leaching into groundwater."
The nanowires also shield Geobacter and allow the bacteria to thrive in a toxic environment, she added.Their effectiveness was proven during a cleanup in a uranium mill tailings site in Rifle, Colo. Researchers injected acetate into contaminated groundwater. Since this is Geobacters' preferred food, it stimulated the growth of the Geobacter community already in the soil, which in turn, worked to remove the uranium, Reguera said.
Reguera and her team of researchers were able to genetically engineer a Geobacter strain with enhanced nanowire production. The modified version improved the efficiency of the bacteria's ability to immobilize uranium proportionally to the number of nanowires while subsequently improving its viability as a catalytic cell.
Reguera has filed patents to build on her research, which could lead to the development of microbial fuel cells capable of generating electricity while cleaning up after environmental disasters.
Source : Michigan State University
|cleaning , electricity , generate , microbes , nuclear , waste|
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Mechanics: Momentum and Collisions
Momentum and Collisions: Audio Guided Solution
Cassie has just finished her session on the trampoline during PE. As she prepares to exit the trampoline, her vertical momentum is reduced by a series of three resistive impulses with the bounce mat. Just prior to this series of impulses, her 48.5-kg body is moving downward at 8.20 m/s. On the first impulse, Cassie experiences an average upward force of 230 N for 0.65 seconds. The second impulse of 112 N•s lasts for 0.41 seconds. The last impulse involves an average upward force of 116 N which cases a 84 kg•m/s momentum change. What vertical velocity does Cassie have after these three impulses?
Audio Guided Solution
Click to show or hide the answer!
Habits of an Effective Problem Solver
- Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
- Identify the known and unknown quantities in an organized manner. Equate given values to the symbols used to represent the corresponding quantity - e.g., m = 1.50 kg, vi = 2.68 m/s, F = 4.98 N, t = 0.133 s, vf = ???.
- Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
- Identify the appropriate formula(s) to use.
- Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.
Read About It!
Get more information on the topic of Momentum and Collisions at The Physics Classroom Tutorial.
Return to Problem Set
Return to Overview | <urn:uuid:5dba4595-5b35-4c86-939a-278c1efb6135> | 3.265625 | 371 | Tutorial | Science & Tech. | 62.026667 |
QNX Developer Support
Count the bytes in a UTF-8 character
#include <utf8.h> int utf8len( const char *s, size_t n );
- A pointer to a UTF-8 character.
- The maximum number of bytes to count.
The utf8str() function counts the number of bytes in the UTF-8 character pointed to by s, to a maximum of n bytes, if n is nonzero.
This function is similar to mblen(), except that:
- utf8str() isn't affected by the current locale.
- The s argument isn't allowed to be NULL.
- You can pass 0 for n if you know that s points to a null-terminated string (i.e. 0 is equivalent to, but more efficient than, strlen(s)).
- utf8str() returns -1 if s points to an invalid byte sequence. If n is nonzero and the n bytes pointed to by s look like an incomplete but potentially valid character, the function returns the negative total length of that (complete) character (this is in the range from -2 to -UTF8_LEN_MAX).
- s points to the null character.
- > 0
- The number of bytes that comprise the multibyte character (if the next n or fewer bytes form a valid multibyte character).
- The n-byte sequence that s points to isn't a valid (beginning of a) UTF-8-encoded character.
- Other negative value
- The n bytes pointed to by s could be the initial bytes of a valid UTF-8 sequence.
Unicode Multilingual Support in the Photon Programmer's Guide
mblen() in the QNX Neutrino Library Reference | <urn:uuid:5742037e-60e7-4f04-8919-7d4f4c86c27d> | 2.96875 | 382 | Documentation | Software Dev. | 68.849073 |
The Antarctic ice sheets drain from the continent interior to the ocean via fast flowing ice streams. As the ice within these streams moves, it erodes and modifies the bed over which it travels. Some of the eroded material is trapped within the ice as mineral and rock fragments and transported into the ocean as icebergs.
As the icebergs melt, the minerals and rock fragments sink to the ocean floor as ice rafted debris. This study uniquely links lead isotope geochemistry of recently deposited ice rafted feldspars with geophysical observations over the glacial catchments and ice streams from where the feldspars originated.
The findings presented by M.J. Flowerdew and colleagues indicate that subglacial erosion of bedrock is restricted to regions where ice velocity, basal shear stresses, and bed roughness are high. Changes in the age and isotope composition of ice-rafted debris are commonly taken as evidence for the collapse or disintegration of parts of the ice sheet.
This study shows that significant variations in the chemistry and age of the ice rafted materials can instead result from changing the loci of subglacial erosion and do not necessarily correspond with episodes of major ice sheet instability.
Paper: M.J. Flowerdew et al., doi: 10.1130/G33644.1 | <urn:uuid:d14df512-d6e8-4836-8fbe-73a7626bcbda> | 3.765625 | 269 | Knowledge Article | Science & Tech. | 41.863218 |
Geothermal power is the use of geothermal heat for electricity generation.
It is often referred to as a form of renewable energy, but because the heat at any location can eventually be depleted it technically may not be strictly renewable.
For more information about the topic Geothermal power, read the full article at Wikipedia.org, or see the following related articles:
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Quantum mechanics permits the existence of unique correlations, or entanglement, between individual particles. For a pair of entangled photons, this means that performing a measurement on one photon appears to affect the state of the other. The ability of entangled particles to act in concert is preserved even when they are separated by large distances and serves as a resource for numerous applications. For example, distributing entangled photon pairs over fiber-optic cables enables secure communication between two remote parties or could offer the possibility of interconnecting quantum computers. The vast transparency band of the installed global fiber-optic network, consisting of over a Gigameter of optical fiber cables, presents a particularly attractive opportunity for this task. The bond between entangled photons is, however, very fragile and could be lost. How far could one send entangled photons while still maintaining the connection between them?
We investigate, theoretically and experimentally, how inherent defects and miniscule imperfections in fiber-optic cables degrade entanglement between two photons transmitted over fibers. We show that the loss of entanglement could be either gradual or surprisingly abrupt. We describe relation between local and non-local effects and suggest a novel non-local way to compensate for adverse effects that occur during propagation in fibers. The richness of the observed phenomena suggests that fiber-based entanglement distribution systems could serve as natural laboratories for studying entanglement decoherence.
A brief introduction to the topic of the talk is available on the front page of AT&T Labs website: www.research.att.com
Location: Physics Bldg., Room 401 | <urn:uuid:ea5f7915-61e5-4540-bbe0-03180c1cc70d> | 2.9375 | 322 | Academic Writing | Science & Tech. | 21.089256 |
Online annual reports (since 1999) documenting hydrologic data for Pennsylvania gathered from USGS surface water and ground water data-collection networks and information on ordering paper copies of previous years.
Congress asked us (in the Energy Independence and Security Act of 2007) to figure out how to assess the effects of carbon storage, sequestration, and greenhouse gas fluxes in our ecosystems. Here's how we plan to do that.
Site for a USGS project under the U.S. Global Change Research Program for a national assessment of the impacts of climate variability and change on resources with links to impacts in Alaska, western U.S., public lands, and water resources.
Using ground-water geochemical analyses, and mathematical models, the factors affecting the quality of public water supply were identified as pumping schedule, screened interval, past land use within the recharge area, and natural geochemical conditions.
Using ground-water geochemical analyses and mathematical models, the factors affecting the quality of public water supply were identified as mixing of very recent recharge with older water, karst features, natural geochemical processes, and pumping.
Explains the natural and human-affected factors that determine the concentration of contaminants in groundwater, especially where the concentration is different at the surface than at depth, and where pumping varies with time. | <urn:uuid:22144703-3c3e-424b-8232-b553b893e81a> | 2.859375 | 265 | Content Listing | Science & Tech. | 21.95274 |
This is a drawing of the interior of Jupiter's moon Ganymede.
Click on image for full size
How do we know what the inside of a Planet or Moon is like?
You may wonder how it is that scientists know what the inside of a planet is like.
The interior of a moon or planet can be closely determined from spacecraft navigation data when a spacecraft passes by or goes into orbit around a planet or moon.
When a spacecraft goes into orbit, the planet or moon's gravity helps to pull it into a certain trajectory around the body. The trajectory of the spacecraft helps scientists determine the mass of the planet or moon through a law of physics known as Kepler's 3rd law.
The way the mass of a body is distributed inside the body affects how the body spins in space. If the body has a large core, it will spin with a certain speed, if it has no core it will spin at another rate of speed. By studying the rate of spin of a body, as well as determining the mass of the body, scientists use another law of physics known as the Moment of Intertia to figure out if the body must have a core and how large that core must be.
The picture shown here is that of Jupiter's moon Ganymede, and illustrates that spacecraft measurements were able to determine that the moon has at least two layers inside, besides the surface crust (scientists think that there are really three layers). Scientists must still use theories to estimate exactly what the layers are made of.
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The diagram to the left shows a cutaway of the possible interior structure of Ganymede, based on recent measurements by the Galileo spacecraft. It shows a small core of metal, overlain with some rocky...more
Unlike the Earth, which has a protective shield around it called the magnetosphere, the surface of the moon is not protected from the solar wind. This picture shows the magnetosphere surrounding the Earth,...more
Mars Global Surveyor (MGS) is conducting mapping operations at Mars more than 30 years after America's first reconnaissance missions reached the mysterious red planet. Here are some of the instruments...more
The Viking I and Viking 2 missions were designed to both orbit Mars and land and make exploratory observations on the planet's surface. At this stage in the history of the exploration of Mars, scientists...more
AU stands for Astronomical Units. Distances in space are too large to measure in Earth standards like miles or kilometers. For distances too large to measue in AU, we use light years. A light year is the...more
The solar wind is formed as the Sun's topmost layer blows off into space carrying with it magnetic fields still attached to the Sun. Gusts and disturbances form in the solar wind associated with violent...more
For a planet to be affected by a blob of material being ejected by the sun, the planet must be in the path of the blob, as shown in this picture. The Earth and its magnetosphere are shown in the bottom...more | <urn:uuid:8e017730-5049-4b8b-87b4-6038e32995d9> | 4.1875 | 658 | Knowledge Article | Science & Tech. | 58.676109 |
Honey bees (or honeybees) are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis. Currently, there are only seven recognised species of honey bee with a total of 44 subspecies, though historically, anywhere from six to eleven species have been recognised. Honey bees represent only a small fraction of the approximately 20,000 known species of bees. Some other types of related bees produce and store honey, but only members of the genus Apis are true honey bees.
Honeybees are extraordinary animals, and for years scientists have looked at them for inspiration to develop new technologies from artificial hive mind computers to explosive detectors. Bees have been truly gifted by nature, and we’re only starting to unravel the many abilities these fantastic insects possess. Recently, researchers at Newcastle University have found that bees enjoy [...]
Elections in the States are currently topping headlines all over the world, as people debate over their favorite candidate and the direction this country is heading towards. Still, as always, elections seemed to be plagued by scandals, lies or manipulation. Yes, democracy is far from being perfect, the alternatives aren’t any better either. I don’t [...]
Honeybees are one of the most crucial members of the ecosystem, pollinating crops and plant cultures all around the world. Various studies conducted in the past couple of years have shown an alarming dwindling of the world bee population, with some locations being hit more aggressively than others. The main factor linked to this bee genocide seems to be pesticides [...]
We’ve reported in the past about the frightening, ever growing cases of honeybee population dye-offs of the past few years, and while no immediate or long term plan has been effective thus far, it seems at least that scientists are identifying the causes. It’s been known for some time that some classes of pesticides are [...]
HYDERABAD (South India): Believe it or not. Paper cups disposed off by coffee and fruit juice bars have become ‘death traps’ for honey bees which account for 80 per cent of pollination of crops in India. The bees, in their pursuit for honey in flowers, get attracted to the sugar residue in the cups and [...] | <urn:uuid:6d7d79a0-b556-4fc7-ac27-05b348231db0> | 2.71875 | 485 | Content Listing | Science & Tech. | 46.186628 |
Introduction to Recombinant Genetics- Biology 350
Chapter Review - Phage isolation
Background on bacteriophages
Bacteriophages can serve as a source of cloned DNA.
Two types of bacteriophages are commonly used, the lambda phage and the M13 family of phages.
The lambda phage can exist as a prophage (integrated into bacterial genome, lysogenic) or as an independent genetic element (lytic). The lambda phage is a linear double-stranded bacteriophage when packaged in the phage protein coat. The lambda DNA has 13 unpaired complementary bases at each end of the linear DNA and upon infection of a cell it circularizes.
The M13 phage enters the bacteria through pili and mature phage buds from the cell without lysing the bacteria. M13 is a single-stranded DNA phage which produces a double-stranded replicative form. The double-stranded replicatitive form of the M13 phage can be isolated from the bacteria by standard plasmid isolation proceedures.
Many Phages can be detected by plating them on a bacterial lawn and looking for cleared regions (plaques) where the bacteria have been lysed (clear plaques, lambda) or the bacterial grown has been slowed (cloudy plaques, M13).
Isolation of DNA from bacteriophages
Isolation of DNA from bacteriophages begins by separating the phage from the cellular components. Since active production of phage results in the release of phage particles into the media, phage particles can be separated from cells by centrifugation. Phages are small and will be retained in the supernatant while cells and cellular debris will be pelleted.
Phages can be isolated from the supernatant with the addition of PEG (polyethylene glycol) and NaCl. The PEG absorbs water and causes the phage to aggregate and precipitate. After centrifugation the precipitated phage is in the pellet.
Phage can be further purified in a CsCl gradient (NO Ethidium Bromide). The phage can easily be visualized in the gradient by shining a flashlight on the gradient in a darkened room and looking for the light scatter created by the phage particles.
Since both lambda and the M13 phages are isolated with their protein coat, you must remove the protein coat in order to purify the DNA.
|© 2005 by CA Rinehart||Index • Syllabus • CourseInfo LogIn • References • Assignment • Next|
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November 2012 Weather and Its Impacts on Missouri
Commercial Agriculture/University of Missouri Extension
Seasonable temperatures and dry weather prevailed across the Show Me State in November. Preliminary data indicates the average statewide temperature was just shy of 45°F, or less than one degree above normal for the month. Regionally, northwestern sections averaged 1-2 degrees above normal for the month, whereas southeastern portions averaged 1-2.5 degrees below normal. The majority of days witnessed high temperatures in the 50's and 60's and low temperatures in the 30's and 40's. Coldest temperatures occurred for a few days after Thanksgiving, when minimum temperatures dropped to the teens and lower 20's across many locations. Lowest monthly temperatures in the Bootheel dropped only to the mid 20's.
Precipitation was limited statewide, and rain events were few and far between during the month. Preliminary data indicate an average statewide total of 1.65 inches, or about 1.25 inches below normal. Heaviest monthly totals were confined to southeastern Missouri where 2-2.5 inches were common. A 100-mile wide corridor of lighter monthly totals, less than 1-inch, were reported from around Springfield, MO, in southwestern sections, to northwest of St. Louis, in east central Missouri. A CoCoRaHS observer residing near Vienna, MO, in Maries County, reported only 0.13" for the month.
There was one widespread and significant rain event to affect the state, occurring on the 11th of the month. Most locations received 0.75-1.50 inches of rain during the event.
Drought continued to impact Missouri by the end of November, with more than 95% of the state experiencing moderate to severe drought according to the Drought Monitor map, Figure 1. Surface water and ground water supplies were still running well below normal despite some improvement in September and October. January through November precipitation deficits exceeded 10 inches in many Missouri locations, and it ranked as the driest January through November period in more than 30 years, or since 1980, Figure 2.
Winter is typically the dry season in Missouri and it is unlikely surface and ground water supplies will fully recover for the start of next year's growing season, especially across northern and central sections. The highest likelihood for hydrological drought to carry over into next year exists across northwestern Missouri, where year-end precipitation deficits exceed a foot and only 3-4 inches generally falls between December and February. Better chances for drought recovery will exist over southern sections where 7-12 inches typically fall from December to February. | <urn:uuid:42cd5e4a-d7b4-4e84-842f-d00edac2da31> | 2.78125 | 524 | Knowledge Article | Science & Tech. | 42.827952 |
Clients of the X Window System specify the visual attributes of graphical output primitives by using graphics contexts. A graphics context is a set of graphical attribute values such as foreground color, font, line style, and so forth. Like a window, a graphics context is another kind of X server resource which is created and maintained at the request of a client program. The client program, which may use several different graphics contexts at different times, is responsible for specifying a graphics context to use with each graphical output function.
CLX represents a graphics context by an object of type gcontext and defines functions to create, modify, and manipulate gcontext objects. By default, CLX also records the contents of graphics contexts in a cache associated with each display. This local caching of graphics contexts has two important advantages:
Caching graphics contexts can result in a synchronization problem if more than one client program modifies a graphics context. However, this problem is unusual. Sharing a graphics context among several clients, while possible, is not expected to be useful and is not very easy to do. At any rate, a client program can choose to not cache a gcontext when it is created.
Each client program must determine its own policy for creating and using graphics contexts. Depending on the display hardware and the server implementation, creating a new graphics context can be more or less expensive than modifying an existing one. In general, some amount of graphics context information can be cached in the display hardware, in which case modifying the hardware cache is faster than replacing it. Typical display hardware can cache only a small number of graphics contexts. Graphics output is fastest when only a few graphics contexts are used without heavy modifications.
This section explains the CLX functions used to: | <urn:uuid:3af729ea-8aed-4fd0-8df9-2dd309a85481> | 2.703125 | 349 | Documentation | Software Dev. | 38.489733 |
[March 24, 11:10 p.m.: Apologies for the blog silence and slow comment moderation. I'm camped on a beach with Pace University students making a film about efforts to balance fishing with marine conservation. ]
The seasonal rains called monsoons matter enormously to human affairs, from the Indian subcontinent to the American Southwest. Getting a better understanding of the forces that will shape these features of the climate system in coming decades is a big research priority, but also a very tough challenge given the many factors in play.
In a study published in this week’s Proceedings of the National Academy of Sciences, researchers analyzing monsoon patterns around the Northern Hemisphere since the 1970s conclude that there has been a substantial intensification of summer monsoon rainfall and circulation. The researchers say natural variations in the Pacific and Atlantic Oceans appear to be the main force behind the shift. Climate models have tended to project a different result.
I asked a variety of scientists working on these questions to evaluate the paper and related materials in an e-mail discussion including one of the authors, Peter Webster, a Georgia Institute of Technology climate scientist.
I distributed the abstract and a news release from the University of Hawaii, where the lead author, Bin Wang, is chairman of the department of meteorology.
Here’s an excerpt from the release:
Current theory predicts that the Northern Hemisphere summer monsoon circulation should weaken under anthropogenic global warming.
Wang and his colleagues, however, found that over the past 30 years, the summer monsoon circulation, as well as the Hadley and Walker circulations, have all substantially intensified. [Explore this Real Climate post to see how much this finding conflicts with what had been conventional wisdom.]
This intensification has resulted in significantly greater global summer monsoon rainfall in the Northern Hemisphere than predicted from greenhouse-gas-induced warming alone: namely a 9.5% increase, compared to the anthropogenic predicted contribution of 2.6% per degree of global warming.
Most of the recent intensification is attributable to a cooling of the eastern Pacific that began in 1998. This cooling is the result of natural long-term swings in ocean surface temperatures, particularly swings in the Interdecadal Pacific Oscillation or mega-El Niño-Southern Oscillation, which has lately been in a mega-La Niña or cool phase. Another natural climate swing, called the Atlantic Multidecadal Oscillation, also contributes to the intensification of monsoon rainfall.
Here’s a link to the paper and the abstract, followed by the discussion so far: Read more… | <urn:uuid:5693569e-8580-437f-8cbe-c39e334e7768> | 3 | 533 | Personal Blog | Science & Tech. | 29.08634 |
Odin is a Swedish satellite working in two disciplines; astrophysics and aeronomy, and it was named after god Odin. Within the field of astrophysics, Odin is used in the study of star formation. When used for aeronomical observations, it is the ozone layer depletion and effects of global warming that are explored.
Odin was developed by the Space Systems Division of Swedish Space Corporation (now OHB Sweden) as part of an international project involving the space agencies of Finland (funded by TEKES), Canada (CSA) and France (CNES). Odin was launched on a START-1 rocket on February 20, 2001 from Svobodny, Russia.
In April 2007, astronomers announced that Odin had discovered the existence of interstellar clouds of molecular oxygen for the first time.
- Molecular Oxygen Detected For The First Time In The Interstellar Medium ScienceDaily, April 17, 2007
- Odin information at Swedish National Space Board
- Odin information at OHB Sweden
- ESA Third Party Missions Overview
|This article about one or more spacecraft of Sweden is a stub. You can help Wikipedia by expanding it.| | <urn:uuid:8c796f5c-7f4c-4965-9c26-05654d0b0117> | 3.65625 | 230 | Knowledge Article | Science & Tech. | 29.172543 |
Gopinathan, C P (1971) Seasonal abundance of phytoplankton in the Cochin backwater. Journal of the Marine Biological Association of India, 14 (2). pp. 568-577.
Qualitative and quantitative studies on phytoplankton of the Cochin Backwater showed that about 120 species of phytoplankters (excluding nanoplankton) commonly occur in the estuary. Of the 88 species of diatoms, 74 occur regularly and the rest are rare. These 14, have been recorded for the first time from the Indian waters. Two peaks of abundance were observed—one during the monsoon months (May to July) and the other in the post-monsoon period (October to December). In the Backwater the enrichment of water with nutrients largely occurs during the monsoon months. This seems to be the most important feature governing the quantitative abundance of the species.
|Uncontrolled Keywords:||diatoms; Cochin Backwater|
|Subjects:||Marine Biology > Phytoplanktons|
|Divisions:||CMFRI-Cochin > Fishery Environment|
|Deposited By:||Geetha P Mrs|
|Deposited On:||26 Jul 2010 17:42|
|Last Modified:||26 Jul 2010 17:42|
Repository Staff Only: item control page | <urn:uuid:2d0f7a62-7639-49b1-864f-cd1b915567f6> | 3.03125 | 295 | Academic Writing | Science & Tech. | 39.788235 |
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Poyang Lake, which has a high level of biomass, is the largest freshwater lake in China with an area of about 3,000km2. Its wetland ecosystem has a significant impact on China's environment change. In order to investigate the biomass information of Poyang Lake wetland plants, the characteristics of wetland plants must be researched firstly. The MIMICS (Michigan Microwave Canopy Scattering) forest backscattering model was modified to accommodate the two scattering components of wetland plants. Using GoogleEarth as one of the references, a reasonable field sampling route was planned and carried out during from 2007-3-29 to 2007-4-3. Thus we can calculate the backscattering coefficient in MIMICS model using surveyed data. By analyzing of the output, it is found that height, gravimetric moisture content and leaf number density are the main three factors dominating the backscattering coefficients, in other words, the major scattering is from crown directly. At last, ANN (Artificial Neural Networks) method was used to retrieve the biomass information of Poyang Lake wetland. The biomass is 1.06 times 109kg in April, 2007.
Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008. IEEE International (Volume:1 )
Date of Conference: 7-11 July 2008 | <urn:uuid:532996ae-ce7d-43c3-af40-fdca415a002f> | 2.890625 | 281 | Academic Writing | Science & Tech. | 45.259068 |
Ada is a modern programming language designed for large, long-lived applications – and embedded systems in particular – where reliability and efficiency are essential.
The WG9 committee, after discussions with the ARG and with members of the Ada community, has instructed the ARG to complete the Amendment to Ada 2005 so that ISO standardization of the new version can be completed by 2012. Read More »
See an overview of the evolution of the major features of the Ada programming language: Programming Structure, Modularity, Object Oriented Programming, Concurrency, Scientific Computing, Standard Libraries, and Character Support. Read More »
Ada has a set of unique technical features that make it highly effective for use in large, complex and safety-critical projects. But the benefits don’t stop there. We’ll explain how these same technical strengths can also translate into long-term business benefits. Read More »
Learn about the key new language features introduced with Ada 2005. Read More »
Ada is a modern programming language designed for large, long-lived applications – and embedded systems in particular – where reliability and efficiency are essential. It was originally developed in the early 1980s (this version is generally known as Ada 83) by a team led by Dr. Jean Ichbiah at CII-Honeywell-Bull in France. The language was revised and enhanced in an upward compatible fashion in the early 1990s, under the leadership of Mr. Tucker Taft from Intermetrics in the U.S. The resulting language, Ada 95, was the first internationally standardized (ISO) Object-Oriented Language. Read More »
Thanks to its rich support for object-orientation, concurrency and pre/post conditions, Ada is an excellent target language for automatic code generation from UML models. The following modeling environments offer industrial-strenght solutions for Ada code generation. Read More » | <urn:uuid:e87b32d9-2f6e-42e9-a8ef-01d6fdc5a9fe> | 3.125 | 388 | Content Listing | Software Dev. | 28.961935 |
Atlantic Lobsters, Homarus americanus
Taxonomy Animalia Arthropoda Malacostraca Decapoda Nephropidae Homarus americanus
Description & Behavior
Of the 30-odd types of clawed lobsters worldwide, Atlantic lobsters, Homarus americanus (H. Milne Edwards, 1837), most closely resembles Homarus gammarus, a related European species with slightly less robust claws, or chelae. Both have asymmetrical claws formed from the first of five pairs of legs, with the larger one used for crushing and the smaller one for cutting or seizing prey. (The other major type of lobsters, the spiny lobsters, do not have asymmetrical claws.) The Atlantic lobster's other four pairs of legs are used to crawl, rather than swim. Underneath the abdomen are six pairs of swimmerets (also called pleopods). The first pair of swimmerets, closest to the head, are hard and bonelike in the male, but soft and featherlike in the female. The last of the pairs is enlarged and forms what we usually think of as the tail.
Lobsters have compound eyes, each made up of as many as 14,000 individual units, that are located on the end of short stalks. They can detect movement, though they may not be able to detect different colors.
Live Atlantic lobsters are usually olive green or greenish brown, though they may dusky orange or even bright blue, depending on factors including diet, heredity, and exposure to light. Lobsters turn bright red when cooked because the major pigment in their shell, astaxanthin, is red only when it is not bonded to other chemicals. In life, the pigment is bonded to proteins; cooking breaks those bonds.
Atlantic lobsters usually reach about two feet in length and two or more pounds, although the Guinness Book of World Records lists a giant and presumably very old specimen at 20.14 kg and 1.06 meters from the end of the tail-fan to the tip of the largest claw. Adults molt three or four times a year, the only way they can increase their size. In preparation for molting, the lobster lays down a new, soft shell underneath its old hard carapace, then seeks out a rocky crevice for protection from predators during this extremely vulnerable stage of life. (Not only is a newly molted lobster soft—it can barely move.) Then the lobster rolls onto its side, bends into a V shape, shrinks its extremities by drawing fluids from them, and withdraws from its old shell. If it finds itself unable to squirm out of the old shell, the lobster may self-amputate a leg or claw to release itself—a skill that may also help it escape a predator, as seen in some small land lizards. Over several hours after molting, the lobster regains its larger size and the new shell begins to harden. If it has self-amputated, the missing leg or claw will begin to regenerate.
Scientists estimate that Atlantic lobsters may live as long as 100 years, but no one has yet figured out a way to accurately tell a lobster's age.
World Range & Habitat
Atlantic lobsters, Homarus americanus, are by far most abundant off the coast of Maine, but the species can be found from the Canadian Maritimes down to Cape Hatteras, North Carolina. They may range from the intertidal zone to about 480 meters, but are most common from four to fifty meters. Lobsters that live close to shore tend to stay in one small area, seldom moving more than a mile or so. Deep water lobsters farther out on the continental shelf, however, migrate shoreward in the summer, returning to the shelf as temperatures cool in the autumn. The record travel so far is 362 kilometers covered by a lobster tagged off the continental shelf and recovered at Port Jefferson, Long Island, New York.
Feeding Behavior (Ecology)
Atlantic lobsters eat mainly live food—fish, small crustaceans, and mollusks—though they will scavenge when necessary. Their diet typically consists of crabs, clams, mussels, worms, an occasional sea urchin or flounder, and even a few plants. Lobsters have been observed eating all manner of organisms—gnawing on the tails of skates, burying crabs in the sand for extended snacking over a period of days, even eating other lobsters when kept in captivity (however, cannibalism has not been observed in the wild). Scientists have found lobster skin in the guts of wild lobsters, but this is not likely evidence of cannibalism, because lobsters eat their own molts in order to replenish their calcium reserves after their molting process.
Atlantic lobsters can mate only when the females are soft, shortly after molting. At this time females release a pheromone, and the mating pair begin a courtship dance with their claws held closed. Males then insert their first pair of pleopods into the female's seminal receptacle and deposit their sperm packets there, where they stay until the female produces eggs—sometimes as long as 15 months after mating. Once the eggs are released from the female's oviducts into the seminal receptacle and fertilized by the stored sperm, they are cemented to the swimmerets, where they remain for 10 to 11 months before hatching. The transparent, "bug-eyed" larvae then molt four times over 10 to 20 days, depending on water temperature, and congregate near the surface of the water, mixing with other types of plankton. They are extremely vulnerable to predation, and only about one-tenth of one percent of the larvae survive to young adulthood, when they sink to the rocky ocean bottom, safer from predators. In the first year of its adult life, a young lobster will molt about 10 times and reaching a length of 2.5 to 3.8 centimeters. As lobsters grow older, they molt less and less frequently. It takes about six years for a lobster to reach a weight of half a kilogram.
Conservation Status & Comments
Atlantic lobsters are intensely fished all along the northeast Atlantic Coast of Canada and the United States as far south as New England, and particularly in Maine—but the demand for lobsters still exceeds the supply. Aquaculture is apparently a possibility, but more expensive pound for pound than traditional fishing methods.
References & Further Research
Holthuis, L.B., FAO species catalogue. Vol. 13. Marine lobsters of the world. An annotated and illustrated catalogue of species of interest to fisheries known to date, FAO Fisheries Synopsis. No. 125, Vol. 13. Rome, FAO. 1991. 292 p.
The American Lobster, Rhode Island Sea Grant Fact Sheets
The Lobster Conservancy
All About Lobsters, Gulf of Maine Aquarium
Research Homarus americanus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SCIRIS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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Help us continue to share the wonders of the ocean with the world, raise awareness of marine conservation issues and their solutions, and support marine conservation scientists and students involved in the marine life sciences. Join the MarineBio Conservation Society or make a donation today. We would like to sincerely thank all of our members, donors, and sponsors, we simply could not have achieved what we have without you and we look forward to doing even more. | <urn:uuid:471e8214-7e34-4022-a288-406004af6ab5> | 3.78125 | 1,679 | Knowledge Article | Science & Tech. | 45.034497 |
Sighting in a Rifle
Library Home || Primary || Math Fundamentals || Pre-Algebra ||
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|Geometry, difficulty level 3. Analyze the given target of four shots, and tell me how far to move the scope on my rifle so that the group of shots will be centered around the bull's-eye.|
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I'm new here and I'm soooo happy I found this forum where people can help me!
I'm in 12th grade and I'm a pre-calc student.
There are two problems that are due tomorrow before 8:30 AM.
I have wasted maybe 5 pieces of paper trying to figure out the first problem.
Here it goes, and I pray someone is here to guide me!!
The lengths of the sides of a triangle are 13, 13, 10. The sides of a second triangle are 13, 13 and x, where x is not equal to 10. If the two triangles have equal areas, what is the value of x?
I started off by finding out the area of triangle one, by the pythagorean theorem. The area is 60.
Can anyone guide me on how to find the value of x?
The second question is:
Find the missing coordinate for the given info
P (x, -3) ; Q (9,6) and the slope between P and Q is 3.
I did it with the slope formula y1-y0 divided by x1-x0 equals slope which has to be 3. It gave me x=6.
So, please, can you help my poor mathematics soul? haha thanks in advance!! | <urn:uuid:7eaaf6fa-5125-4ba3-be82-6ce893885d13> | 3.234375 | 269 | Comment Section | Science & Tech. | 90.983034 |
This article for the young and old talks about the origins of our number system and the important role zero has to play in it.
Using balancing scales what is the least number of weights needed
to weigh all integer masses from 1 to 1000? Placing some of the
weights in the same pan as the object how many are needed?
This article looks at how models support mathematical thinking about numbers and the number system
This article for teachers describes how number arrays can be a
useful reprentation for many number concepts.
Dotty Six is a simple dice game that you can adapt in many ways.
This article for teachers describes how modelling number properties
involving multiplication using an array of objects not only allows
children to represent their thinking with concrete materials,. . . .
First or two articles about Fibonacci, written for students. | <urn:uuid:6936ac26-3e3e-4775-ac49-2ee8e350fbc0> | 3.53125 | 175 | Content Listing | Science & Tech. | 50.926094 |
Introduction to My Submarine Ocean Explorer
Welcome to My Submarine Ocean Explorer! Come see exciting creatures and features found in the ocean. You will see videos from NOAA Office of Ocean Exploration and Research (NOAA OER) expeditions and you can find more information about the creatures and features in text and photos. Check out the maps and charts from NOAA explorations that show where the creatures and features were located. You can use the depth indicator to find out the depth where the creatures and features are typically found. You will observe the change in the darkness of the water through the sub window as the sub goes lower or higher. Listen to scientists talk about their ocean explorations and scientific research by clicking on the speaker phone on the sub console. You can even send an email postcard to a friend about your favorite creature. Have fun exploring!
For parents and teachers: Look for guides to each creature and feature that provide more details about NOAA OER expeditions and links to related educational materials and resources. Notice the ocean literacy brochure on the bottom left of the console screen, which describes essential ocean literacy principles and fundamental concepts that are important for everyone to know about the ocean. Thank you to NOAA Office of Ocean Exploration and Research for funding the project. | <urn:uuid:2ccfcec4-4e80-4f65-a7ba-a89416b4e5c6> | 3.015625 | 252 | Tutorial | Science & Tech. | 38.120899 |
A home from home: Five planets that could host life
It's one of the big questions: Are we alone on this blue marble or is there life elsewhere in the cosmos? To shed some light, astronomers are searching for habitable worlds circling far-off stars.
A team has now published updated evidence for a planet that could be the most Earth-like yet. According to the US Planetary Habitability Laboratory, it would be the fifth potentially habitable world known outside our Solar System.
So what do we know about these five Earth-like planets, and how likely is it that they could support life?
- Similarity to Earth (ESI): 0.92
- Minimum mass: 2.2 times that of Earth
- Distance: 20.3 light-years
The discovery of Gliese 581g was announced in September 2010 by a US-led team. But as soon as they made the announcement, doubts began to surface. The team at the Geneva observatory which had discovered all four other planets around the star Gliese 581 failed to detect it in their own data. However, the original discoverers of 581g have now published an analysis using a greater amount of data to provide more promising evidence for its existence.
This would be significant because the Earth Similarity Index (ESI), devised by a team including Dirk Schulze-Makuch from Washington State University and Abel Mendez from the University of Puerto Rico (UPR) in Arecibo, shows that Gliese 581g is the most Earth-like planet discovered to date. The ESI measures characteristics of exoplanets on a scale from zero to one, with one being identical to Earth. Accordingly, the online Habitable Exoplanets Catalog, based at UPR, has decided to include it in their list of the most promising worlds to support life.
Like the other worlds in the catalogue, Gliese 581g orbits in a "sweet spot" around its star - the habitable zone, or Goldilocks zone - that is neither too hot nor too cold to allow for liquid water. It is just over twice the mass of Earth and, although the planet is closer to its parent star than is Earth, it receives about the same light flux (a measure of the star's apparent brightness) as our planet because Gliese 581 is a red dwarf star and therefore dimmer than our own Sun. Steven Vogt, from University of California, Santa Cruz, US, one of original discoverers, said Gliese 581g orbits "squarely in the star's Habitable Zone at 0.13 AU, where liquid water on planetary surfaces is a distinct possibility". But it remains to be seen whether the new evidence will convince the doubters.
New kid on the block
- Similarity to Earth (ESI): 0.85
- Minimum mass: 4.5 times that of Earth
- Distance: 22 light-years
Announced in February 2012 by a team from the US Carnegie Insitution and Germany's Goettingen University, Gliese 667Cc belongs to a class of planets known as Super Earths - a class of planet with a size in between that of rocky worlds like Earth and Mars and the gas giants like Jupiter and Saturn.
Roughly 4.5 times the mass of Earth, Gliese 667Cc takes 28 days to complete a single orbit of its star, which is located just 22 light-years away.
The exoplanet absorbs about as much energy from its star as Earth does from the Sun, which means surface temperatures could be similar to Earth's. This would allow for the presence on the planet's surface of liquid water - one of the pre-requisites for life.
However, astronomers say this cannot be confirmed without further information on the planet's atmosphere. Nevertheless, co-discoverer Guillem Anglada-Escude has said of 667Cc: "This planet is the new best candidate to support liquid water and, perhaps, life as we know it."
- Similarity to Earth (ESI): 0.81
- Mass: Up to 40 times that of Earth (upper limit), but could be closer to six
- Distance: 620 light-years
Since it was launched in March 2009, Nasa's Kepler Space Telescope has detected more than 2,300 candidate exoplanets. Of these, Kepler 22b is the only confirmed world in the habitable zone around its parent star, which is the same class - a G-type - as our Sun (though slightly cooler and smaller).
With a radius 2.1 times that of Earth, Kepler 22b is bigger than some others in the list of five. But its orbit of 290 days around a Sun-like star resembles that of our own planet.
Astronomers do not yet know for sure whether it has a predominantly gaseous, rocky or liquid composition. But to some, its size suggests a composition closer to the gaseous Neptune than to Earth. At the time of its discovery, exoplanet hunter Geoff Marcy, from the University of California, Berkeley, told the AP news agency that he would "bet my telescope that there is no hard, rocky surface to walk on".
But this is not necessarily bad for its prospects for hosting biology: mission scientist Natalie Batalha said that if Kepler 22b were mostly ocean with a small rocky core, "it's not beyond the realm of possibility that life could exist in such an ocean".
- Similarity to Earth (ESI): 0.77
- Minimum mass: 3.6 times that of Earth
- Distance: 35 light-years
Another Super-Earth, with a mass 3.6 times that of our planet, HD85512b orbits on the inner margins of its habitable zone. This means it is closer to Venus than Earth in the amount of energy it absorbs from its star. However, that would not necessarily preclude the possibility of life.
How hospitable the planet is may depend on how much cloud cover it has, since clouds reflect solar radiation. Its discoverers calculate that if HD85512b were to have more than 50% cloud cover (on the same order as Earth), it could offset the planet's proximity to its star enough for water to stay liquid at the surface.
However, any life forms on HD85512b will have to be suited to very balmy conditions, "It's going to be really muggy, just think about the muggiest day you can think of," co-discoverer Lisa Kaltenegger, from the Max Planck Institute in Germany, said at the time of its discovery. "We're not saying it's habitable for you and me."
- Similarity to Earth (ESI): 0.72
- Minimum mass: 5.6 times that of Earth
- Distance: 20.3 light-years
Discovered in 2007 by a team at the Geneva Observatory using the HARPS planet-finding instrument in Chile, Gliese 581d is probably too large to be formed entirely of rocky material. Instead, it is a serious candidate for an ocean planet, according to one of its discoverers, Stephane Udry.
One of a system of five planets, it is the immediate neighbour of Gliese 581g. However, Gliese 581d orbits at a greater distance from its parent star, on the colder, outer fringe of the habitable zone. As a result, sunlight on Gliese 581d has about 35% the intensity that is does on Mars.
But computer simulations of the exoplanet's atmosphere suggest that under some scenarios, greenhouse gases would allow surface temperatures to remain above 0C, allowing water to stay liquid. Indeed, says Dr Udry, the planet "could even be covered by a large and deep ocean".
Since it is located only 20.3 light-years away - in the Constellation Libra - astronomers should be able to resolve some of these questions in the future, with direct spectroscopic observations of the planet's atmosphere. | <urn:uuid:352909c7-b0e3-46fe-8b47-07b17ff0b1a2> | 2.921875 | 1,668 | Content Listing | Science & Tech. | 51.64821 |
Common Lisp the Language, 2nd Edition
There are several variables whose values are streams used by many functions in the Lisp system. These variables and their uses are listed here. By convention, variables that are expected to hold a stream capable of input have names ending with -input, and variables that are expected to hold a stream capable of output have names ending with -output. Variables expected to hold a bidirectional stream have names ending with -io.
In the normal Lisp top-level loop, input is read from *standard-input* (that is, whatever stream is the value of the global variable *standard-input*). Many input functions, including read and read-char, take a stream argument that defaults to *standard-input*.
In the normal Lisp top-level loop, output is sent to *standard-output* (that is, whatever stream is the value of the global variable *standard-output*). Many output functions, including print and write-char, take a stream argument that defaults to *standard-output*.
The value of *error-output* is a stream to which error messages should be sent. Normally this is the same as *standard-output*, but *standard-output* might be bound to a file and *error-output* left going to the terminal or to a separate file of error messages.
The value of *query-io* is a stream to be used when asking questions of the user. The question should be output to this stream, and the answer read from it. When the normal input to a program may be coming from a file, questions such as ``Do you really want to delete all of the files in your directory?'' should nevertheless be sent directly to the user; and the answer should come from the user, not from the data file. For such purposes *query-io* should be used instead of *standard-input* and *standard-output*. *query-io* is used by such functions as yes-or-no-p.
The value of *debug-io* is a stream to be used for interactive debugging purposes. This is often the same as the value of *query-io*, but need not be.
The value of *terminal-io* is ordinarily the stream that connects to the user's console. Typically, writing to this stream would cause the output to appear on a display screen, for example, and reading from the stream would accept input from a keyboard.
It is intended that standard input functions such as read and read-char, when used with this stream, would cause ``echoing'' of the input into the output side of the stream. (The means by which this is accomplished are of course highly implementation-dependent.)
The value of *trace-output* is the stream on which the trace function prints its output.
The variables *standard-input*, *standard-output*, *error-output*, *trace-output*, *query-io*, and *debug-io* are initially bound to synonym streams that pass all operations on to the stream that is the value of *terminal-io*. (See make-synonym-stream.) Thus any operations performed on those streams will go to the terminal.
X3J13 voted in January 1989 (STANDARD-INPUT-INITIAL-BINDING) to replace the requirements of the preceding paragraph with the following new requirements:
The seven standard stream variables, *standard-input*, *standard-output*, *query-io*, *debug-io*, *terminal-io*, *error-output*, and *trace-output*, are initially bound to open streams. (These will be called the standard initial streams.)
The streams that are the initial values of *standard-input*, *query-io*, *debug-io*, and *terminal-io* must support input.
The streams that are the initial values of *standard-output*, *error-output*, *trace-output*, *query-io*, *debug-io*, and *terminal-io* must support output.
None of the standard initial streams (including the one to which *terminal-io* is initially bound) may be a synonym, either directly or indirectly, for any of the standard stream variables except *terminal-io*. For example, the initial value of *trace-output* may be a synonym stream for *terminal-io* but not a synonym stream for *standard-output* or *query-io*. (These are examples of direct synonyms.) As another example, *query-io* may be a two-way stream or echo stream whose input component is a synonym for *terminal-io*, but its input component may not be a synonym for *standard-input* or *debug-io*. (These are examples of indirect synonyms.)
Any or all of the standard initial streams may be direct or indirect synonyms for one or more common implementation-dependent streams. For example, the standard initial streams might all be synonym streams (or two-way or echo streams whose components are synonym streams) to a pair of hidden terminal input and output streams maintained by the implementation.
Part of the intent of these rules is to ensure that it is always safe
to bind any standard stream variable to the value of any other
standard stream variable (that is, unworkable circularities are
avoided) without unduly restricting implementation flexibility.
No user program should ever change the value of *terminal-io*. A program that wants (for example) to divert output to a file should do so by binding the value of *standard-output*; that way error messages sent to *error-output* can still get to the user by going through *terminal-io*, which is usually what is desired. | <urn:uuid:2c01ba96-55f9-421b-b432-d136d86bb7c7> | 3.296875 | 1,210 | Documentation | Software Dev. | 46.783656 |
The images from cameras and sensors on the latest satellite watching the sun are a dramatic reminder of the awesome power of the star that warms our planet. They show clouds of magnetized gas big enough to engulf the Earth breaking away from the outermost layer of the sun’s atmosphere. These coronal mass ejections (CMEs), which are usually accompanied by solar flares with the explosive force of millions of atomic bombs, can last for several hours and travel through space at over 1 million kilometers per hour. Yet the sun has been in one of its quietest recorded phases for a century. The sun’s activity ebbs and flows in a cycle that averages about 11 years.
Sunspots, vast dark areas on the sun created by strong magnetic fields beneath its surface, provide a visual guide to the evolution of the solar cycle, appearing in large numbers at the time of maximum activity and all but disappearing during the minimum.
NASA launched its Solar Dynamics Observatory satellite in February not just to gain a better understanding of how the sun behaves and why, but also to keep a closer watch on space weather.
Since the spacecraft and its instruments were officially commissioned on May 14, more than 5 million images have poured in. If there are no malfunctions, they will keep coming at a rate of about 70,000 each day for at least the next five years.
The satellite has shown that it can check the sun’s activity faster and in greater depth and detail than any previous observatories on land or in space. This is breaking barriers of timeliness and clarity that have long blocked progress in forecasting dangerous solar storms.
CMEs usually take about three days reach Earth, but very fast ones can arrive in under a day. The charged particles and magnetic forces emit radiation across the electromagnetic spectrum, from low-energy radio waves through to high-energy gamma rays, as they penetrate the outermost layer of Earth’s atmosphere, the ionosphere.
If the geomagnetic storm is violent enough, it can interfere with high- technology networks on which Japan and other advanced economies increasingly depend. Electricity supply grids, satellite navigation, air travel, financial services and radio communications, including mobile-phone networks, could all be disrupted for hours or even days.
A major solar storm in 1989 shut the Quebec power grid in Canada for nine hours. Another storm in 2003 caused satellite problems around the world.
A 2008 report by the U.S. National Academy of Sciences warned that a once-in-a-century space storm striking network-dependent America today could cause 20 times more economic damage than Hurricane Katrina in 2005.
Now that solar activity appears to be on the rise again, scientists are trying to work out when the next peak will occur, how severe it will be, and how long it will last. The U.S. National Oceanic and Atmospheric Administration said last year that the next solar maximum was expected to occur in May 2013 and that the whole cycle would be below average in intensity. But there is considerable uncertainty attached to such predictions.
Since the space age began in the 1950s, solar activity has generally been high. Five of the 10 most intense solar cycles on record have occurred in the last 50 years. Researchers will use the new solar images and data from the NASA satellite and several other spacecraft due to be launched later this year to try to determine the extent to which the sun may be heating or cooling the Earth, and thus contributing to climate change.
This is a controversial issue. For more than two centuries, scientists have wondered how much heat and light the sun expels, and whether this energy varies enough to change Earth’s climate. Since NASA launched its first satellite carrying a radiometer in 1978 to measure the amount of sunlight striking the top of Earth’s atmosphere, researchers have realized that this total irradiance fluctuates. It is not constant, as was previously thought.
Measurements collected in the 1980s and 1990s provided evidence that irradiance is a balance between darkening from sunspots and brightening from hotter regions called faculae, a Latin word meaning “bright torch.”
Sunspots appear dark because they are cooler than surrounding areas. They are footprints of magnetic restraining loops pushing through the solar surface and holding the hot plasma below. When solar activity increases, both sunspots and faculae become more numerous. But during the peak of the cycle, the faculae brighten the sun more than sunspots dim it.
However, the recorded variations in solar irradiance are small, prompting many scientists to conclude that only the emission of rapidly rising amounts of greenhouse gases from human activity in recent decades could have been largely responsible for global warming.
A study published in March concluded that the average world sea and land surface temperature was likely to rise by between 3.7 and 4.5 degrees Celsius by 2100 if fossil-fuel burning and deforestation continue. The increase in greenhouse gas emissions driving this warming trend would be far greater than the impact of any known shifts in solar energy output.
Michael Richardson is a visiting senior research fellow at the Institute of Southeast Asian Studies in Singapore. | <urn:uuid:4fadbacb-adc4-4c8c-8ae5-abfc85eca44d> | 3.765625 | 1,048 | Truncated | Science & Tech. | 41.134194 |
Modern web pages are written in a language known as Extended Hypertext Markup Language or XHTML. Pages written only for older browsers are written in HTML or Hypertext Markup Language. The XHTML and HTML languages are almost identical but have slight syntax differences, as noted below. Both XHTML and HTML are "markup languages", meaning they allow one to mark up text with special instructions to browsers so browsers can format the document. The text itself is not changed.
In this web site, web pages are referred to as HTML pages, while the markup language is referred to as XHTML.
There are two kinds of XHTML elements.
|Non-empty elements: Non-empty elements enclose content such as text and/or graphics. The elements consist of two parts, a start tag and a close tag. An example of a non-empty element is the paragraph tag.|
<p>text, graphics, etc.</b>
|The start tag is <p> and consists of the name of the tag (p) enclosed in angle brackets (<>). The start tag could also contain attributes in addition to the name of the tag.|
|The content of the paragraph (text, graphics, etc.) could span several lines.|
The content is enclosed by the start and end tags.
|The close tag is </p>. It has the same name as the start tag except there is a slash (/) before the name of the tag.|
Differences between XHTML and XTML
Modern browsers will accept either language, but you should write in XHTML to insure future compatibility with newer browsers.
|XHTML empty elements must be closed with " />" HTML does not require the slash.|
|XHTML element names and attributes must be in lower case. In HTML, they can be in either case.|
|In XHTML all non-empty elements must have end tags.|
XHTML Elements that are Used with CSS
Begin learning XHTML by becoming familiar with the following lists of elements.
|There are four elements that must be in each page. These elements form a skeleton of the page.|
|There are two parts to the page, the header and the body. The header contains information that is not visible to your visitors but is used by the browser and other software that reads the page. The body contains the information that is seen by your visitors.|
|Notice that the required elements are closed elements: <element name> and </element name> The <element name> begins information spanned by that element, and the </element name> ends that information. The following table gives the four required elements.|
|<html>||XHTML start tag. First element in the page.|
|<head>||Header start tag. Always follows the XHTML element. Second element in the page.|
|<title> < /title>||Title, title-end tags. Begins and ends a title for the browser title bar & bookmark. Must be inside the header.|
|</head>||Header-end tag. Ends the header element.|
|<body>||Body start tag. Begins the body or visible part of your page. Follows the header.|
|</body>||Body-end tag. Ends the body.|
|</html>||HTML-end tag, Ends the html page. Last tag in the page|
The elements that go in the header portion of the page are known as meta elements and are explained in the meta tags page.
The following table gives the major elements that can be placed in the body of the text.
|<h1> </h1>||Header 1 start tag, header 1 end tag. Can also be header 2, header 3, header 4, header 5, header 6 tags. Defines a header block in the text. CSS rules specify the characteristics of each header type.|
|<p> </p>||Paragraph element with start tag and end tag. Creates a paragraph block. CSS rules specify the characteristics of paragraphs. Paragraphs can not contain other block elements.|
|Blockquote start and end tag. Identifies a block of paragraphs; leave the paragraph start/end tags around the paragraphs. CSS rules define the characteristics of the blocks. |
|<em> </em>||Emphasis start tag, emphasis end tag. Begins/ends text to be emphasized. CSS rules define the nature of "emphasis".|
|<strong> </strong>||Strong emphasis start tag, strong emphasis end tag. Begins/ends text to be made strong. CSS rules define the nature of "strong".|
|<q> </q>||Quote start tag, quote end tag. Begins/ends short text to be quoted. CSS rules define the nature of "quoted". Use blockquote for longer quotations.|
|<cite> </cite>||Citation of a published work. The title goes in the cite element. CSS rules define the nature of "cite".|
|<div> </div>||Generic block element. The block is not inline with other text. CSS rules define the nature of the block through use of the class= attribute.|
|<span> </span>||Generic inline block element. The block is inline with other text. CSS rules define the nature of the block through use of the class= attribute.|
Don't Mix Elements
Suppose you mix the head and title elements. The XHTML code might look like the following example, which violates the container concept of element structure discussed in another page.
In contrast, the XHTML code should look like this.
Notice that in the correct code, the end tags are in reverse order from the start tags. That is, the title start tag, title text, and title end tag occur before the head end tag. To avoid this problem, it is common practice for the designer to put the full title element, including start and end tags, on one line, while the head element is on multiple lines, as shown in the table given above. If you mix elements, it is unpredictable what the browsers will do, depending on the browser and on the version of browser. To read more about this, go to
Reading Other Pages
Finally, study pages written by other people to see how they used XHTML. You can do this, because web browsers give you the ability to see the XHTML code for any web page. Open the View menu, select the Page Source (Netscape or Mozilla Firefox) or Source (Internet Explorer) entry, and a window will appear containing the XHTML code for that page. You can then study the code. This ability to learn XHTML from reading other pages is an important way to learn XHTML. Keep in mind that if you're studying an older page, you may see the syntax of HTML instead of the syntax for XHTML.
.[ Site Map ] [ Distance Learning ][ Home ] [ Up ] [ Intro to CSS ] [ Type Selectors ] [ Inheritance ] [ Learning XHTML ]
© Copyright 1998, 2011 Allen Leigh | <urn:uuid:cbd9aea4-b8dc-46c1-8362-9494579c4579> | 4.53125 | 1,480 | Tutorial | Software Dev. | 65.189791 |
Earth was so hot 2,000 years ago that the Romans grew grapes in Northern England.
How did the Romans grow grapes in northern England? Perhaps because it was warmer than we thought.
A study suggests the Britain of 2,000 years ago experienced a lengthy period of hotter summers than today.
German researchers used data from tree rings – a key indicator of past climate – to claim the world has been on a ‘long-term cooling trend’ for two millennia until the global warming of the twentieth century.
This cooling was punctuated by a couple of warm spells.
These are the Medieval Warm Period, which is well known, but also a period during the toga-wearing Roman times when temperatures were apparently 1 deg C warmer than now.
They say the very warm period during the years 21 to 50AD has been underestimated by climate scientists.
Lead author Professor Dr Jan Esper of Johannes Gutenberg University in Mainz said: ‘We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low.
‘This figure we calculated may not seem particularly significant, however it is not negligible when compared to global warming, which up to now has been less than 1 deg C.’
In general the scientists found a slow cooling of 0.6C over 2,000 years, which they attributed to changes in the Earth’s orbit which took it further away from the Sun.
The study is published in Nature Climate Change.
It is based on measurements stretching back to 138 BC.
In so doing, the researchers have been able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling.
Professor Esper said: ‘Such findings are also significant with regard to climate policy, as they will influence the way today’s climate changes are seen in context of historical warm periods.’
The annual growth rings in trees are the most important witnesses over the past 1,000 to 2,000 years as they indicate how warm and cool past climate conditions were.
Researchers from Germany, Finland, Scotland, and Switzerland examined tree-ring density profiles.
In the cold environment of Finnish Lapland, trees often collapse into one of the numerous lakes, where they remain well preserved for thousands of years.
The density measurements correlate closely with the summer temperatures in this area on the edge of the Nordic taiga; the researchers were thus able to create a temperature reconstruction of unprecedented quality.
The reconstruction provides a high-resolution representation of temperature patterns in the Roman and Medieval Warm periods, but also shows the cold phases that occurred during the Migration Period and the later Little Ice Age.
In addition to the cold and warm phases, the new climate curve also exhibits a phenomenon that was not expected in this form.
Should we tell Al Gore about this? | <urn:uuid:170aa5a8-38e2-42c3-aac9-3c8a3bf11d5a> | 4.0625 | 585 | Personal Blog | Science & Tech. | 46.583079 |
MVC1 was a first generation approach that used JSP pages and the JavaBeans component architecture to implement the MVC architecture for the Web. HTTP requests are sent to a JSP page that implements Controller logic and calls out to the Model for data to update the View. This approach combines Controller and View functionality within a JSP page and therefore breaks the MVC paradigm. MVC1 is appropriate for simple development and prototyping. It is not, however, recommended for serious development.
MVC2 is a term invented by Sun to describe an MVC architecture for Web-based applications in which HTTP requests are passed from the client to a Controller servlet which updates the Model and then invokes the appropriate View renderer-for example, JSP technology, which in turn renders the View from the updated Model.
The hallmark of the MVC2 approach is the separation of Controller code from
content. (Implementations of presentation frameworks such as Struts, adhere to the MVC2 approach).
If you want to read a more detailed doc: | <urn:uuid:4534d0fa-733c-446a-b714-1ea4398eea1e> | 3.296875 | 216 | Q&A Forum | Software Dev. | 43.725669 |
Researchers in Japan are trying to get a rise out of viewers with an experimental chair that makes your arm hairs stand on end.Read More
Ramesh Raskar presents femto-photography, a new type of imaging so fast it visualizes the world one trillion frames per second, so detailed it shows light itself in motion. This technology may someday be used to build cameras that can look “around” corners or see inside the body without X-rays.Read More
“The Amazing Spider-Man” has some real and interesting science behind Peter Parker and his webs. University of Minnesota professor Jim Kakalios served as the science consultant on the new film, giving the filmmakers a factual perspective on the physics of wall crawling and the tensile strength of spider’s webbing. In addition, Kakalios contributed an equation called the Decay Rate Algorithm, which is at the center of a few major plot points throughout the film.
Pictures of atoms have been physically impossible to take because they are smaller than the wavelengths of visible light. But that hasn’t stopped researches in Ohio, who devised a unique way of coaxing atoms to reveal themselves.Read More
Charles Limb performs cochlear implantation, a surgery that treats hearing loss and can restore the ability to hear speech. But as a musician too, Limb thinks about what the implants lack: They don’t let you fully experience music yet. At TEDMED, Limb reviews the state of the art and the way forward.
MIT Media Lab researchers have created a new imaging system that can acquire visual data at a rate of one trillion frames per second. That’s fast enough to produce a slow-motion video of light traveling through objects.
This True 3D display technology, developed by Burton, uses a laser to creates luminous points of light at desired locations in air or underwater. It works by focusing laser light, to produce plasma excitation from the oxygen and nitrogen in the air.Read More
In this final episode of Stephen Fry’s BBC documentary about language, Planet Word, he celebrates the power and glory of storytelling. It has been with us as long as language itself and as a species, we love to tell our stories. This desire to both entertain and explain has resulted in the flowering of language to describe every aspect of the human condition.Read More | <urn:uuid:17b906da-b735-4752-ba80-8bf9991e9d7e> | 2.8125 | 487 | Content Listing | Science & Tech. | 44.016873 |
Type: New Feature
Resolution: Won't Fix
Affects Version/s: 2.1.M0, 2.4-M2
Fix Version/s: 2.7-M3
NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. The netCDF software was developed at the Unidata Program Center in Boulder, Colorado.
More detail can be found at:
A LGPL Java library already exists at:
NOTE Added 6/25/2005 by Bryce:
A review of the current form of the netCDF java library, as well as reviewing the direction in which netCDF is heading reveals:
- Java is the prototype language for which the new features in NetCDF4 are tested.
- NetCDF4 implements a "Common Data Model" (CDM) which is the result of generalizing the NetCDF3, HDF5, and OpenDAP data models.
- The NetCDF-Java library automatically recognizes many of the common ways of storing geographic information in netCDF files and abstracts to the "GeoGrid" object.
- The NetCDF-Java library is a 100% java library which can read/write NetCDF3 files, and can read a number of other formats (HDF5, GRIB, etc.)
This should alleviate some of the concerns expressed in the comments below and suggests the following:
- GeoTools should provide an adapter from the GeoGrid abstraction to the GeoAPI framework.
- NetCDF conventions should be added to the netCDF-java library. | <urn:uuid:7619d274-111f-409f-b897-1e7b3b747e1f> | 3.03125 | 388 | Comment Section | Software Dev. | 48.236429 |
From Math Images
Basic DescriptionThe method was first used to approximate π by Georges-Louis Leclerc, the Comte de Buffon, in 1777. Buffon posed the Buffon's Needle problem and offered the first experiment where he threw breadsticks over his shoulder and counted how often the crossed lines on his tiled floor.
Subsequent mathematicians have used the method with needles instead of bread sticks, or with computer simulations. In the case where the distance between the lines is equal the length of the needle, we will show that an approximation of π can be calculated using the equation
A More Mathematical Explanation
Will the Needle Intersect a Line?
To prove that the Buffon's Needle experiment will give an approximation of π, we can consider which positions of the needle will cause an intersection. Since the needle drops are random, there is no reason why the needle should be more likely to intersect one line than another. As a result, we can simplify our proof by focusing on a particular strip of the paper bounded by two horizontal lines.
The variable θ is the acute angle made by the needle and an imaginary line parallel to the ones on the paper. Finally, d is the distance between the center of the needle and the nearest line.
We can extend line segments from the center and tip of the needle to meet at a right angle. A needle will cut a line if the green arrow, d, is shorter than the leg opposite θ. More precisely, it will intersect when
See case 1, where the needle falls at a relatively small angle with respect to the lines. Because of the small angle, the center of the needle would have to fall very close. In case 2, the needle intersects even though the center of the needle is far from both lines because the angle is so large.
The Probability of an Intersection
In order to show that the Buffon's experiment gives an approximation for π, we need to show that there is a relationship between the probability of an intersection and the value of π. If we graph the outcomes of θ along the X axis and d along the Y, we have the sample space for the trials. In the diagram below, the sample space is contained by the dashed lines.
The sample space is useful in this type of simulation because it gives a visual representation of all the possible ways the needle can fall. Each point on the graph represents some combination of an angle and distance that a needle might occupy. We divide the area that contains combinations that represent an intersection by the total possible positions to calculate the probability of an intersection.
There will be an intersection if , which is represented by the blue region. The area under this curve represents all the combinations of distances and angles that will cause the needle to intersect a line. The area under the blue curve, which is equal to in this case, can found by evaluating the integral
Then, the area of the sample space can be found by multiplying the length of the rectangle by the height.
The probability of a hit can be calculated by taking the number of total ways an intersection can occur over the total number possible outcomes (the number of trials). For needle drops, the probability is proportional to the ratio of the two areas in this case because each possible value of θ and d is equally probable. The probability of an intersection is
Using Random Samples to Approximate Pi
The original goal of the Buffon's needle method, approximating π, can be achieved by using probability to solve for π. If a large number of trials is conducted, the proportion of times a needle intersects a line will be close to the probability of an intersection. That is, the number of line hits divided by the number of drops will equal approximately the probability of hitting the line.
Therefore, we can solve for π:
Watch a Simulation
Why It's Interesting
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The Number Pi. Eymard, Lafon, and Wilson.
Monte Carlo Methods Volume I: Basics. Kalos and Whitlock.
Heart of Mathematics. Burger and Starbird
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Loosely speaking, a number describing the ability of a transparent material such as glass, plastic, liquid or crystal, to bend (refract) light. More technically, the ratio of the velocity of light in a vacuum compared to the velocity of light in a given medium.
The refractive index of a vacuum is 1 (by definition) and the refractive index of air is very close to 1. Ordinary glass, however, has a refractive index around 1.5. Water has a refractive index of about 1.3.
Different types of glass and crystal have differing refractive indices, which is useful for lens designers, who can use different types of glass to correct different forms of aberration. ED and UD glass and fluorite crystals are common examples of this.
cf. ED, element, fluorite, refractive index, lens, optical glass, refraction, Snells law, transparent.
Entry last updated 2002-05-09. Term 1022 of 1487.
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