text large_stringlengths 148 17k | id large_stringlengths 47 47 | score float64 2.69 5.31 | tokens int64 36 7.79k | format large_stringclasses 13 values | topic large_stringclasses 2 values | fr_ease float64 20 157 |
|---|---|---|---|---|---|---|
Investigate the number of faces you can see when you arrange three cubes in different ways.
Investigate the area of 'slices' cut off this cube of cheese. What
would happen if you had different-sized block of cheese to start
Choose a box and work out the smallest rectangle of paper needed to
wrap it so that it is completely covered. | <urn:uuid:21615f5b-e97e-4c21-ba15-f2ee7aa539bd> | 3.171875 | 75 | Content Listing | Science & Tech. | 53.055683 |
High school chemistry students the world over know the work of Russian scientist Dmitri Mendeleev — he’s one of the inventors of the periodic table of the elements. But Mendeleev’s interests went far beyond what he could see in the laboratory — and he was willing to risk his neck to pursue them.
125 years ago today he rose through the clouds in a hot air balloon to watch a total solar eclipse. Even though he was his own pilot, he didn’t know how to land a balloon. In fact, he’d never even been in one.
Solar eclipses were prized scientific events. Among other things, they offered the only chance to study the Sun’s hot outer atmosphere, the corona, which is too faint to see through the daytime sky.
Mendeleev took off from a village in western Russia, and climbed to an altitude of more than two miles. He recorded detailed observations of the eclipse, then turned his attention to how to get down. He figured it out and soon landed safely — his valuable eclipse notes in hand.
He left his post with Saint Petersburg University a few years later. But he continued to pursue his diverse interests — helping set up Russia’s first oil refinery, for example, and establishing a national standard for vodka.
Decades after his death, scientists named an element that was created in the laboratory in his honor. Mendelevium is the 101st element on the periodic table — one of the many legacies of a scientist who climbed to meet the Sun.
Script by Damond Benningfield, Copyright 2012
For more skywatching tips, astronomy news, and much more, read StarDate magazine. | <urn:uuid:2582e4e6-c052-478d-8201-aad9976061e5> | 3.6875 | 351 | Truncated | Science & Tech. | 54.209 |
In response to recommendations from the National Research Council (NRC) Decadal Survey (2003), and NASA’s Solar System Exploration (SSE) Roadmap (2006), over the past year NASA has funded a mission concept study to better understand the science goals and technology requirements for a future Venus Flagship-class mission.
The study was guided by a NASA appointed Venus Science and Technology Definition Team (STDT) – which comprised of an international group of scientists and engineers from the United States, the Russian Federation, France, Germany, the Netherlands, and Japan – with support from JPL through a dedicated engineering core team, and the Advanced Project Design Team, also known as Team X.
This study group assessed science goals and investigations, and identified a suitable mission architecture – including a notional instrument payload, subsystems and technologies – to achieve mission objectives. Based on NASA guidelines for the study, this mission concept targeted a launch opportunity between 2020 and 2025, and a cost cap between $3B and $4B. It is also expected that a future Venus Flagship mission will be built on international partnerships. Such a mission would revolutionize our understanding of the climate of terrestrial planets, including the coupling between volcanism, tectonism, the interior, and the atmosphere; and the habitability of extrasolar terrestrial planets. It could also contribute to resolving the geologic history of Venus, including the existence of a past ocean. The chosen mission architecture pointed to specific technology development needs, such as sample acquisition and handling; aerial mobility; and high temperature tolerant components (e.g., sensors, electronics, mechanisms, instruments, and power storage).
Findings from the report will be used in NASA’s program planning activities and will provide important input to the ongoing NRC Decadal Survey update.
All graphics are artist’s renderings. | <urn:uuid:9171b576-229c-4ac7-b851-8d7fe3845838> | 3.375 | 376 | Knowledge Article | Science & Tech. | 20.61875 |
Never Before Seen: Two Supermassive Black Holes in Same Galaxy
The Chandra image of NGC 6240, a butterfly-shaped galaxy that is the product of the collision of two smaller galaxies, revealed that the central region of the galaxy (inset) contains not one, but two active giant black holes.
Previous X-ray observatories had shown that the central region was an X-ray source, but astronomers did not know what was producing the X-rays. Radio, infrared, and optical observations had detected two bright nuclei, but their exact nature also remained a mystery.
Chandra was able to show that the X-rays were coming from the two nuclei, and determine their X-ray spectra. These cosmic fingerprints revealed features that are characteristic of supermassive black holes - an excess of high-energy photons from gas swirling around a black hole, and X-rays from fluorescing iron atoms in gas near black holes.
Over the course of the next few hundred million years, the two supermassive black holes, which are about 3000 light years apart, will drift toward one another and merge to form one larger supermassive black hole. This detection of a binary black hole supports the idea that black holes grow to enormous masses in the centers of galaxies by merging with other black holes.
NGC 6240 is a prime example of a "starburst" galaxy in which stars are forming, evolving, and exploding at an exceptionally rapid rate due to a relatively recent merger (30 million years ago). Heat generated by this activity created the extensive multimillion degree Celsius gas seen in this image.
Note on Cosmic Look-Back Time: The finite speed of light means that we must always be out of date, no matter how hard we strive to keep up with the times. Thus, the seemingly simple question - what is happening right now on the Sun? - cannot be answered by an observer on Earth, because it takes light 8 minutes to reach Earth from the Sun. For distant galaxies, the light travel times are even longer, so our information about the galaxy NGC 6240, which is 400 million light years away, is 400 million years out of date! One consolation is that if astronomers on NGC 6240 are observing our Milky Way galaxy, they are likewise 400 million years behind the times - our times, that is. As Albert Einstein said, "The past, present and future are only illusions, even if stubborn ones." more | <urn:uuid:cabfdf7d-801e-4c31-9334-f9219410d3ed> | 4.125 | 497 | Knowledge Article | Science & Tech. | 42.668737 |
Basically it means: Cast/Convert an array of chars into an enumerable array of strings.
IEnumerable is a collection class which is the base class for almost all the collection classes. In other words, almost all collection classes inherit functionalities from IEnumerable class.
One of the thing that IEnumerable class provides is that you can use foreach loop to iterate over all the elements in an array or list or any other collection that inherits from IEnumerable.
Anyway, I just tested the above code and it doesn't even work. The exception is thrown in runtime saying the it is not able to cast from char to string.
But the above explanation of IEnumerable class is still correct :-) | <urn:uuid:3a91f20a-8dff-479a-a24b-946006288ea9> | 2.734375 | 149 | Q&A Forum | Software Dev. | 42.049605 |
--- TRINET'S SHAKEMAP ---
-- A Broadcaster's Guide to Reporting Earthquake Intensity --
Earthquake Information Summary:
Date: MAY 17 2012
Time: 08:12:01 AM GMT
Location: N31.90 W94.33: EASTERN TEXAS
Name: Unnamed Earthquake (Event ID b0009rtk)
ShakeMap on the world-wide web: http://www.trinet.org/shake
INSTRUMENTAL INTENSITY SCALE:
ESTIMATED INTENSITY PERCEIVED SHAKING POTENTIAL DAMAGE
------------------- ----------------- ---------------
I Not Felt None
II-III Weak None
IV Light None
V Moderate Very Light
VI Strong Light
VII Very Strong Moderate
VIII Severe Moderate/Heavy
IX Violent Heavy
X Extreme Very Heavy
------------------- ----------------- ----------------
TRINET is the seismic network in southern California operated
United States Geological Survey (USGS)
California Institute of Technology (Caltech)
California Division of Mines and Geology (CDMG)
Dr. David Wald, USGS, Pasadena
Dr. Bruce Worden, USGS, Pasadena
Mr. James Goltz, Caltech
What is earthquake intensity? How does ShakeMap display intensity?
ShakeMap is a geographic representation of the ground shaking produced by
an earthquake. Intensity is one of the ways that ground shaking is
expressed, along with more quantitative measures like velocity and
acceleration. The information ShakeMap presents is different from the
earthquake magnitude. Magnitude is the number (for example, 7.1) that
represents the energy released in an earthquake; a single number
representing magnitude is assigned to each earthquake. Intensity, on the
other hand, is a measure of how the ground shook at a particular site. So,
while an earthquake has one magnitude and one epicenter, it produces a
range of ground shaking levels at sites throughout the region. These
different intensities depend on distance from the earthquake, the rock and
soil conditions at geographical sites, and variations in the propagation
of seismic waves from the earthquake due to complexities in the structure
of the Earth's crust. ShakeMap focuses on the ground shaking produced by
the earthquake, rather than the characteristics of the earthquake source.
How are earthquake intensities expressed?
Intensities portray the effects of an earthquake in a particular
location. These effects include potential damage, perception of shaking
and permanent changes in topography. Whether there was damage, and the
severity of observed damage, is one element of intensity. Intensity scales
also take into account how the earthquake was perceived by persons in a
geographic location ranging from "not felt" to "unable to stand." The
impact of the earthquake shaking on the ground, whether, for example,
cracks or displacements occurred, or in some cases of severe shaking,
landslides, is also a feature of measured intensity.
The most popular intensity scale used in the United States is the Modified
Mercalli Scale (MMI) first developed in 1931. This scale uses Roman
Numerals to represent progressively greater shaking from MMI I in which
"people do not feel any earth movement" to MMI X in which "most buildings
and their foundations are destroyed, bridges and dams are severely damaged
and large landslides occur." Historically, intensities were derived in
the months following an earthquake through questionnaires sent to Post
Offices in the impacted area. Postal officials were asked to report the
effects of shaking in their district and their observations were combined
with those of scientists and engineers. When all the questionnaires and
observations were combined, they were used to construct an intensity map
of the earthquake.
With the development of the new seismic network under the TriNet project,
intensity (ShakeMaps) maps can be generated automatically from measured
ground acceleration and velocity. These "instrumental intensities" are
calculated and mapped within 5 minutes of the earthquake and are thus
termed "real-time" maps. To the extent possible, shaking expressed as
intensity in ShakeMap correspond to the observed intensity of the older
Modified Mercalli scale. To provide news broadcasters guidance in the
interpretation of intensities reported in ShakeMap, we have provided below
the ten intensity levels and the human perception, damage and topographic
change associated with each level.
It is important to note in reporting intensity information contained in
ShakeMap that shaking and damage vary considerably from location to
location, and only some structures may exhibit the effects noted below in
an area assigned a particular intensity.
MODIFIED MERCALLI INTENSITY SCALE
Value Full Description
I People do not feel any earth movement.
II Felt by persons at rest, on upper floors of tall buildings
III Felt by people indoors. Hanging objects swing back and forth.
Vibration from the earthquake may seem like the passing of light
trucks. May not be recognized as an earthquake.
IV Hanging objects swing. Vibration may seem like the passing of heavy
trucks or a jolt, like a heavy ball striking the walls. Parked
vehicles may rock noticeably. Windows, dishes, doors may rattle and
glasses clink. In the upper range of IV, walls of wood frame
buildings may creak.
V Almost everyone feels movement whether inside or outdoors. Sleeping
people are awakened. Liquids in containers are disturbed; some are
spilled. Small unstable objects are displaced or overturned. Doors
swing, close, or open. Shutters, pictures on the wall move.
VI Felt by all; some are frightened and take cover. People have
difficulty walking due to motion. Objects fall from shelves and
dishes, glassware and ceramics may be broken. Pictures fall off
walls. Furniture moves or is overturned. Weak plaster and masonry
cracked. Damage slight in poorly constructed buildings. Trees, bushes
shaken visibly or are heard rustling.
VII People have difficulty standing. Drivers on the road feel their cars
shaking. Furniture may be overturned and broken. Loose bricks fall
from buildings and masonry walls and cracks in plaster and masonry
may appear. Weak chimneys may break at the roofline. Damage is slight
to moderate in well-built structures; considerable in poorly
constructed buildings and facilities.
VIII Drivers have trouble steering. Tall structures such as towers,
monuments and chimneys may twist and fall. Wood frame houses that
are not bolted to their foundations may shift and sustain serious
damage. Damage is slight to moderate in well-constructed buildings,
considerable in poorly constructed buildings. Branches are broken and
fall from trees. Changes occur in flow or temperature of springs and
wells. Cracks appear in wet ground and on steep slopes.
IX Masonry structures and poorly constructed buildings suffer serious
damage or collapse. Frame structures, if not bolted, shift off
foundations. Serious damage to reservoirs. Underground pipes broken.
Conspicuous cracks in the ground. In alluvial areas, sand and mud
ejected and sand craters are formed.
X Most masonry and frame structures destroyed along with their
foundations. Some well-built wooden structures and bridges are
destroyed. Serious damage to dams, dikes, and embankments. Large
landslides occur. Water thrown on the banks of canals, rivers and
lakes. Sand and mud shift horizontally on beaches and flat land.
Earthquake Planning Scenarios
In addition to post-earthquake shaking maps, we can estimate and display
intensities and ground motions for "Earthquake Scenarios". These are events
on faults that have ruptured in the past or have a likelihood of rupturing
in the future. The primary purpose is for emergency response exercises and
planning as well as for understanding the potential consequences of future
These earthquake scenarios are not earthquake predictions. No one knows in
advance when an earthquake will occur or how large it will be. However, if
we make assumptions about the size and location of a hypothetical
earthquake, we can make a reasonable prediction of the effects of that
earthquake, particularly the way in which the ground will shake. This
knowledge of the potential shaking effects is the main benefit of the
earthquake scenario for planning and preparedness purposes.
Please read more about scenario earthquakes at | <urn:uuid:fae3808a-d7b7-4171-b71f-645cfb0a5179> | 3.046875 | 1,805 | Comment Section | Science & Tech. | 35.62096 |
This sequence shows a parabolic encounter and subsequent merger between two disk galaxies with a 3:1 mass ratio. The galaxies orbit each other in a clockwise direction, and the orbit plane is viewed face-on. The larger disk lies in the orbit plane but spins in a counter-clockwise direction, while the smaller disk is inclined at an angle of 71 degrees.
Each frame shows the dark matter in red, the disk stars in blue, and the bulge stars in yellow. The nominal time-span between frames is 250 million years, or roughly one galactic rotation period.
The main result of this and similar calculations is that disk galaxies can sometimes accrete smaller (1/3-mass) companions without being totally disrupted, in contrast to the outcome of equal-mass mergers. Here the large disk survives because it does not couple strongly to a retrograde perturber.
Computer simulation performed at the Maui High-Performance Computing Center (MHPCC).
Last modified: September 28, 1995 | <urn:uuid:fc0de0c1-bdbf-4c27-9627-5337ac433465> | 3.296875 | 205 | Knowledge Article | Science & Tech. | 47.370139 |
Ocean Margins (LINK)
Ocean margins (where the deep oceans meet continental shelves) include the sites of some of the world's largest accumulations of sediments which may provide the source of significant reserves of oil and gas.
The multidisciplinary Ocean Margins (LINK) programme aimed to develop a clear knowledge of the structure, composition and evolution of ocean margins and provided clearer scientific understanding, that will be critical to the wealth and well being of many coastal nations, including the UK. More about the Ocean Margins programme
14 Feb 2007
The UK oil industry is benefiting from the knowledge that science can provide. Science strikes oil
24 Nov 2006
The final scientific meeting of the Ocean Margins LINK Programme took place at the Geological Society, London 15-16 November 2006. Ocean Margins (LINK) programme: end of programme conference | <urn:uuid:72925013-0183-4325-8edb-2d6437c79cc0> | 2.703125 | 173 | Content Listing | Science & Tech. | 22.631834 |
Will Penguins Become Extinct?
Penguins and Global Warming
The earth has a bipolar disorder. Global warming threatens the wildlife of both the north and south polar regions. In the north, the polar bears are dying off because the ice shelves they depend on to reach their prey have been melting. In the south, melting ice and snow create huge cracks and caverns which trap penguins and make it difficult for them to travel to breeding and feeding areas.
by Fred E. Foldvary, Senior Editor
Skeptics of global warming can point to areas such as the center of Antarctica where there has been no warming, but the evidence is clear now that average global temperatures are rising, and the visual evidence of melting glaciers is there for anyone to see. In the U.S.A., Glacier National Park will have to be renamed Park Meltdown.
In 1998 I wrote on the threats to the survival of the penguins. At that time, oil spills, pollution, and predators were killing many penguins. Now warming is the main problem, as it could destroy the habitat of the penguins in Antarctica.
The various types of birds are classified as “orders,” and the penguin order is called Sphenisciformes. This order contains aquatic flightless birds which live in the Southern Hemisphere. As only penguins are in that order, penguins are quite different from all other birds in walking upright and in some of them being able to live in extremely cold climates.
Penguins are dying throughout the Southern Hemisphere. In the Prince Edward Islands by South Africa in the Indian Ocean, penguin populations are shrinking. As the oceans warm up, the prey eaten by penguins move south to cooler waters.
The 900-mile-long Antarctic Peninsula which sticks out from the main continent is warming up at a greater pace than the world average. There the ice is melting rapidly, and huge chucks of ice sheets are braking off. The Adelie penguins there have to swim ever longer distances to get food, and there is also less food, especially krill, small shrimp-like animals that depend on the sea ice. If the warming continues, they will be unable to survive there.
In the Ross Sea by Antarctica, two huge ice sheets have broken away from the ice sheet and block the passage that penguins use from feeding to breeding areas. They have to walk 30 miles (50 kilometers) more to get to the feeding waters. This creates an extreme hardship for penguins as they waddle on land at only one mile per hour. The population of the impressive emperor penguins in Antarctica has been cut in half during the past 50 years.
The penguin order is not overall threatened with extinction, as some species can live in warmer climates. Nevertheless, penguins everywhere are under pressure, as while there are no predators on Antarctica, penguins further north are threatened by predators such as cats, dogs, and rats.
The warming of the Antarctic Peninsula and decline of the penguins there is a warning to humanity about the looming global threat for humanity. Many people world-wide have viewed the documentary film by former U.S. Vice President Al Gore, “An Inconvenient Truth.” It is unfortunate that this persuasive film dwells almost entirely on the problem, with very little on solutions. It’s fine to replace old light bulbs with new ones that are more energy efficient, but there is no good substitute for economic policies that make people pay the social cost when they do damage to the planet.
In a speech at the New York University School of Law on September 18, 2006, Al Gore, proposed replacing payroll taxes with a tax on carbon dioxide emissions. Gore has advocated “the elimination of all payroll taxes -- including those for social security and unemployment compensation - and the replacement of that revenue in the form of pollution taxes -- principally on CO2. The overall level of taxation would remain exactly the same. It would be, in other words, a revenue neutral tax swap. But, instead of discouraging businesses from hiring more employees, it would discourage business from producing more pollution.”
Some Green parties and environmentalists and geoists (Georgists) have gone further and propose a complete green tax shift that would replace all punitive taxes with levies on pollution and land value. By shifting public revenue to land rent or land value along with pollution, the shift to efficiency taxes would benefit both the economy and the environment, as it would eliminate the deadweight loss of the punitive taxation of wages, profits, and trade.
A rapid green tax shift would stop the human contribution to global warming and help save both the penguins and human beings from the looming damage of rising temperatures. The bonus is that there is a great economic benefit from this shift even if human activity is contributing little to global warming.
In cost-benefit analysis, the probability of an outcome has to be multiplied by its estimated cost. The potential cost of runaway global warming, of reaching a tipping point followed by an exponential increase in global heat, is colossal, so even a small probability warrants quick action. So Al Gore and those properly alarmed by global warming should focus on the green tax shift. Anything else, whether greener light bulbs or pollution permits, will only help a little. Regulations and permits impose economic costs, while the green tax shift provides big benefits. Only a global green tax shift will save the penguins, humanity, and the planet from a possible global catastrophe.
-- Fred Foldvary
Copyright 2007 by Fred E. Foldvary. All rights reserved. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechanical, which includes but is not limited to facsimile transmission, photocopying, recording, rekeying, or using any information storage or retrieval system, without giving full credit to Fred Foldvary and The Progress Report.
Foldvary's Earlier Classic: Save the Penguins
We All Know How to Stop Global Warming
The Geo Way to Reduce Global Warming
Email this article Sign up for free Progress Report updates via email
What are your views? Share your opinions with The Progress Report:
Page One Page Two Archive Discussion Room Letters What's Geoism? | <urn:uuid:3371980d-eb1f-417f-a8e0-ffef8eca316d> | 3.53125 | 1,274 | Nonfiction Writing | Science & Tech. | 44.086614 |
Erwin Schrödinger and Louis de Broglie
Paul Dirac has offered the opinion that his fellow theorists are guided not only by their hopes, but just as importantly, by their fears. Theoretical researchers find it hard, he says, to ignore fears that their work contains hidden, possibly disastrous, flaws; and their thoughts, influenced by this worry, are not so logical as they might be: “You might think a good research worker would review the situation quite calmly and unemotionally and with a completely logical mind, and proceed to develop whatever ideas he has in an entirely rational way. This is far from being the case. The research worker is only human and, if he has great hopes, he also has great fears…. As a result, his course of action is very much disturbed. He is not able to fix his attention on the correct line of development.”
If there was a fundamental fear threatening the development of quantum theory during its first two decades, it was the concept of wave-particle duality, demanded because light can appear to be wavelike in certain experiments and particle-like in others. Einstein was among the first to face the duality mystery. In spite of long-established experimental and theoretical evidence for light as waves, Einstein proposed a particle theory of light to explain puzzling features of the photoelectric effect. Einstein's equation E = hv for the energy E of a light particle or photon casually introduces the duality theme: the equation combines E, a property of light as a particle, with the frequency v, a property of light as a wave.
From the logical viewpoint, this was a paradox, which hardly any theoretician but Einstein had the courage to confront. How could light be two essentially different things, wave and particle, at the same time? The duality seemed to be a threat, a “fundamental blemish” that might, if pushed too far, bring the entire theoretical edifice crashing down.
Questia, a part of Gale, Cengage Learning. www.questia.com
Publication information: Book title: Great Physicists:The Life and Times of Leading Physicists from Galileo to Hawking. Contributors: William H. Cropper - Author. Publisher: Oxford University Press. Place of publication: New York. Publication year: 2001. Page number: 275.
This material is protected by copyright and, with the exception of fair use, may not be further copied, distributed or transmitted in any form or by any means. | <urn:uuid:d2555d5d-b34e-4472-9ac2-12a79095e668> | 2.9375 | 520 | Truncated | Science & Tech. | 45.356114 |
Yukon Glossarymeteoroid -- a tiny space rock (usually a speck of debris from a comet or asteroid) while it is in space or flying through Earth's atmosphere
meteor -- a streak of light in the sky caused by a disintegrating meteoroid
meteorite -- a rock from space that hit the ground because it did not burn up entirely in the atmosphere.
C-type -- includes more than 75% of known asteroids: extremely dark (albedo 0.03); similar to carbonaceous chondrite meteorites; approximately the same chemical composition as the Sun minus hydrogen and helium.
S-type -- 17% of all main-belt asteroids: relatively bright (albedo .10-.22); metallic nickel-iron mixed with iron- and magnesium-silicates;
M-type -- most of the rest: bright (albedo .10-.18); pure nickel-iron. There are also a dozen or so other rare types. | <urn:uuid:4a82988c-1ba6-43a2-816f-482d6160f1f1> | 3.40625 | 201 | Structured Data | Science & Tech. | 46.85 |
If you asked us to explain how a nuclear reaction works, chances are we'd throw our hands up in the air and change the subject to that funny video of a begging cat instead.
Realising this, some clever chaps at St. Mary's University in Halifax have put together a nifty vid to explain it all in easy-to-understand and, more importantly, really fun to watch fashion.
As workers at the Fukushima Daiichi power plant bravely battle to prevent the reignition of nuclear chain reactions in damaged reactors, it's useful to know exactly what this means.
This video utilises plastic golf balls and mousetraps to simulate what a chain reaction actually looks like. Take a gander for an explanation and also to see loads of mousetraps go off. | <urn:uuid:615df644-02b2-41b6-9d65-ec0b3261e115> | 2.765625 | 164 | Truncated | Science & Tech. | 50.993251 |
In the second of two articles, the authors describe how to develop business patterns based on business functions, data, and business components, and show how these can be used to engineer software systems.
Data models and data profiling are complementary techniques. Although data models do not tell us the whole truth, profiling the database does not provide the whole truth either. In fact, both may be misleading. However, used together, they can provide better insight into the data.
XML is a perfectly good vehicle for describing data to be transmitted from one place to another. It is not so good for describing the semantics – the nature of – the underlying data. It cannot replace data modeling and sound database design. XML, data modeling, and database design are all ways to structure data. Each has its place. Unfortunately, our industry is somewhat confused as to what those places are. This article attempts to sort that out.
There has been much discussion about “atomic” data, but what about “molecular” data? This concept encompasses not only more concrete data specifications, but also more abstract function specifications, than conventional application development techniques. | <urn:uuid:8b1f78d5-c5db-4936-9659-9e5e6c3b819c> | 2.75 | 231 | Content Listing | Software Dev. | 32.673222 |
Written By TheVBProgramer.
A cryptogram is a coded message where each letter in the cryptogram puzzle stands for a different letter of the alphabet. The coded message is often a famous quotation, proverb, or maxim. The objective of the game is to decode the message. Write a VB application that will present a cryptogram puzzle to the user and provide a way for them to enter the solution.
Below is a screenshot showing my implementation:
Following is information from the help file written for the application, which will be displayed when the user clicks the "Instructions" button. It can also provide a guideline for how you might go about designing this application. Bear in mind that this applies to my implementation; you may have an entirely different vision of how this might be done. Feel free to use all, any, or none of the ideas presented here for your own implementation. As with the Calculator program, you will need to look into the KeyUp and KeyDown events as well as the KeyPreview property.
When you start the game, a new puzzle is displayed on the interface as black letters on gray tiles, with space separating each word in the puzzle. Above each gray tile is a black box in which you type the letter that the coded letter below it represents. The letters you type in the black boxes will be displayed in green.
Whatever letter you type for a coded letter will automatically be propagated throughout the puzzle. For example, if you type an "A" above an "X" tile, then the letter "A" will appear over ALL "X" tiles.
Whenever you type a letter in a black box, the cursor will automatically move forward to the next unused black box. To move forward to any black box, use the <right arrow> key, the <Tab> key, or click it with the mouse. To move backward to any black box, use the <left arrow> key, the <Shift-Tab> key combination or click it with the mouse. To move up or down a line, use the <up arrow> and <down arrow> keys. To go directly to the beginning of a line, use the <Home> key; to go directly to the end of a line, use the <End> key.
To delete a character in a black box, press the <Delete> key if the insertion point appears to the left of the letter, or press <Backspace> if the insertion point appears to the right of the letter.
Only letters may be entered into a black box; input of any other character is inhibited. Also, input of any letter you have already used will be inhibited. If you wish to change a coded letter to a letter you have already used, you must first delete the original occurrence of the letter.
Command Button Options
Displays the help screen.
This option checks your solution and temporarily changes the color of any incorrect letters to red (if you have not completed the puzzle, only the letters you have entered so far will be checked). Once you type a new letter or click another command button, all letters will turn back to green.
If you have completed the puzzle and your solution is correct, you will be asked if you want to play another game. If so, a new puzzle will be presented; otherwise, the program will end.
If your solution is incomplete or incorrect as this point, you will first be asked if you are sure you want to see the answer. If you choose Yes, the game board will temporarily freeze as the answer is revealed. At that point, you can either start a new game or exit.
If your solution is correct, you will be asked if you want to play another game. If so, a new puzzle will be presented; otherwise, the program will end.
This option starts a new puzzle. If you already have a game in progress, your solution will be checked to see if it is incomplete or incorrect, and if so, you will be asked if you want to abandon the game before moving on.
If you abandon the game, the solution for the abandoned game will be shown to you, then the new game will start.
Download the solution for this project here. | <urn:uuid:960bc8c1-611b-4e68-a264-b8c7b1ae34a3> | 3.375 | 860 | Documentation | Software Dev. | 55.887214 |
Towering Cumulus cloud (cumulus congestus)
Click on image for full size
Image courtesy of Gary Anthes/UCAR
Cumulus Congestus Clouds
Cumulus clouds can be associated with good or bad weather. Cumulus congestus clouds, also called towering cumulus, are in the last stage of development before becoming cumulonimbus clouds. The tops of cumulus congestus clouds look like cauliflower, and sometimes light rain can fall from them. Once they become cumulonimbus clouds, thunderstorms with rain, hail, thunder and lightning can occur.
Cumulus humilis clouds are smaller and are associated with good weather.
Shop Windows to the Universe Science Store!
The Fall 2009 issue of The Earth Scientist
, which includes articles on student research into building design for earthquakes and a classroom lab on the composition of the Earth’s ancient atmosphere, is available in our online store
You might also be interested in:
Cumulus (weather symbol - Cu) clouds belong to the Clouds with Vertical Growth group. They are puffy white or light gray clouds that look like floating cotton balls. Cumulus clouds have sharp outlines...more
Cumulonimbus (weather symbol - Cb) clouds belong to the Clouds with Vertical Growth group. They are generally known as thunderstorm clouds. A cumulonimbus cloud can grow to such heights that it actually...more
Rain is precipitation that falls to the Earth in drops of 5mm or greater in diameter according to the US National Weather Service. Virga is rain that evaporates before reaching the ground. Raindrops form...more
Thunderstorms are one of the most thrilling and dangerous types of weather phenomena. Over 40,000 thunderstorms occur throughout the world each day. Thunderstorms form when very warm, moist air rises into...more
Lightning is the most spectacular element of a thunderstorm. In fact it is how thunderstorms got their name. Wait a minute, what does thunder have to do with lightning? Well, lightning causes thunder....more
Cumulus clouds can be associated with good or bad weather. Cumulus humilis clouds are common in the summer and are associated with fair weather. They are usually widely spaced in the sky, have a flat base...more
Altocumulus clouds (weather symbol - Ac), are made primarily of liquid water and have a thickness of 1 km. They are part of the Middle Cloud group (2000-7000m up). They are grayish-white with one part...more | <urn:uuid:706582ea-35e9-46d4-8acb-e3ed2e89acbe> | 3.59375 | 525 | Content Listing | Science & Tech. | 53.865144 |
Doing calculations only seems difficult. If you break it into small steps you will find that none of the steps requires anything difficult.
Here is a step-by-step guide to evaluation of the relationship for the period of a simple pendulum, as used in lab 5.
When performing any multi-step calculation, write down the appropriate expression at each and every step with the calculated values substituted. It may seem like extra work, but it will keep your thoughts organized. It is easier to enter the numbers into the calculator when they are written down!.
Suppose your length is L = 48.291 cm. Then your relationship would look like this:
For L = 48.291 cm. it would look like this: .
It would look like this:
The number should already be on the calculator display. If it is, simply press the key on the calculator.
If the number has been erased from the calculator display, reenter it, then press the key.
is a number that appears in calculations from time to time. It is the ratio of circumference to diameter of a circle, but it 'pops up' in unexpected places.
There is a key on most calculators. Press the key when you want to enter . If there is not a key, enter the value, 3.14 for .
With the number 0.2219831 still on the calculator display, press the X key, the key, the X key again, then 2, then = .
The result is 1.3947614, which rounds to 1.3948. The unit is seconds.
The calculated result was rounded to the same number of significant figures as the measurement of L. (There are 5 significant figures in 48.291 cm.)
T = 1.3948 sec. when L = 48.291 cm | <urn:uuid:cf4a21d5-6624-4454-a4f8-b11511b46822> | 3.59375 | 375 | Tutorial | Science & Tech. | 79.388967 |
In communications, a code is a rule for converting a piece of information (for example, a letter, word, or phrase) into another object or action, not necessarily of the same sort. One reason for this is to enable communication in places where ordinary spoken or written language is difficult or impossible. For example, a cable code replaces words (eg, ship, invoice, ...) into shorter words, allowing the same information to be sent with fewer characters, more quickly, and most important, less expensively. Another example is the use of semaphore flags, where the configuration of flags held by a signaller or the arms of a semaphore tower encodes parts of the message, typically individual letters and numbers. Another person standing a great distance away can interpret the flags and reproduce the words sent.
- For other meanings of the word code see Code (disambiguation)
Cryptography: codes versus ciphers
Codes have long been used in cryptography. Codes are used to transform the content or meaning of a message into something else, preventing those not in on the secret from understanding what is actually transmitted. The usual method is to use a "codebook" with a list of common phrases/words matched with different phrases/words, so that people without the codebook who might intercept the message get nothing but a message referring to something else altogether, or alternatively, complete gibberish. A cable code would be one such.
In general usage, the term code is very often confused with the term cipher, but in cryptography they refer to different concepts. They can be distinguished best by the scope of the differing transformations: A code is a set of rules which result in a change in the representation of meaningful information to some other form -- this need not include secrecy. Most cable codes are examples in which secrecy isn't the purpose. Cable codes were developed to lower transmission costs by reducing message length. Codes work at the level of meaning; that is, words or phrases are converted into something else; for a cable code the something else had fewer letters. But, when the information should not be known to anyone but the intended recipient, the transformation must not be reversible by just anyone. There must be some secret information required to successfully reverse the transformation.
A code which requires such secret knowledge is a cryptographic code, and the secret information and rules to use it is a codebook.
A cipher by contrast, does not work at the level of meaningful information. While a code might transform "attack" into "FRGPL" or "mincemeat pie", a cipher transforms elements below the semantic level, ie, below the level of meaning. The "a" in attack might be converted to "Q", the first "t" to "f", the second "t" to "3", and so on. Cyphers are more convenient than codes in some situations, there being no need for a codebook.
Codes on the other hand, were long believed to be more secure than cyphers, there being (if one's codebook constructor did a good job) no 'pattern of transformation' which can be discovered. With the advent of automatic processors (ie, in recent times the electronic computer), cyphers have come to dominate cryptography.
Codes in communication used for brevity
Code can be used for brevity. When telegraph messages were the state of the art in rapid long distance communication, elaborate commercial codes which encoded complete phrases into single words (commonly five-letter groups) were developed, so that telegraphers became conversant with such "words" as BYOXO ("Are you trying to weasel out of our deal?"), LIOUY ("Why do you not answer my question?"), BMULD ("You're a skunk!"), or AYYLU ("Not clearly coded, repeat more clearly."). Code words were chosen for various reasons: length, pronouncability, etc. Meanings were chosen to fit perceived needs: commercial negotiations, military terms for military codes, diplomatic terms for diplomatic codes, any and all of the preceding for espionage codes, ... Codebooks and codebook publishers proliferated, inlcuding one run as a front for the American Black Chamber run by Herbert Yardley between WWI and WWII. The purpose of most of these codes was to save on cable costs.
In the computer era since World War II, there are also "codes" for data compression, e.g. Huffman coding, which uses short codes for frequent symbols and longer codes for seldom used symbols - the same principle is used in the Morse code. It and the Baudot code which uses the same length representation for all symbols and characters, both go back to telegraph days. The later was a primary ancestor of the ASCII character code widely used in computers.
An example: the ASCII code
Probably the most widely known data communications code (aka character representation) in use today is ASCII. In one or another (somewhat compatible) version, it is used by nearly all personal computers, terminalss, printerss, and other communication equipment. Its original version represents 128 characters with seven-bit binary numbers--that is, as a string of seven 1s and 0s.
In ASCII a lowercase "a" is always 1100001, an uppercase "A" always 1000001, and so on.
Extensions to ASCII have included 8-bit characters (for letters of European languages and such thingsas card suit symbols), and in fullest flowering have included glyphs from essentially all of the world's writing systems (see Unicode and Bob Bemer).
Codes to detect or correct errors (e.g., in storage or transmission)
Codes may also be used to represent data in a way more resistant
to errors in transmission or storage. Such a "code" is
called an Error-correcting code, and works by including carefully crafted redundancy with the stored (or transmitted) data. Examples include Hamming codes, Reed-Solomon, Reed-Muller, Bose-Chaudhuri-Hochquenghem, Turbo, Golay, Goppa, and Gallager Low-density parity-check codes.
Codes and acronyms
Acronyms and abbreviations can be considered codes, and in a sense all languages and writing systems are codes for human thought. Occasionally a code word achieves an independent existence (and meaning) while the original equivalent
phrase is forgotten or at least no longer has the precise meaning attributed to the code word. For example, the number "86" was once used as a code word in restaurants meaning "We're out of the requested item". It is now commonly used to mean the removal or destruction of something. '30' was widely used in journalism to mean "end of story", and it is sometimes used in other contexts to signify "the end".
- See also: Glossary of coding terms.
Source | Copyright
Webmasters: Add your website here:
Readers: Edit |
SIGS Conferences and Publications
Pertinent, informative and resource-packed magazines, conferences and exhibitions for the application development marketplace.
A collection of news, resources, and tools for software engineering, computer programming, and information technology management.
Binoj's Home Page
Large list online books and online compilers. Other programmer helpers.
Online site for programmers with thousands of links and files to explore. Everything from Assembler to Visual Basic can be found here.
The community of computer experts. Get expert answers to your computer questions, read articles, download software, find a book, or get a new job.
The Programmer's Lair
Offers programs, source codes, forums, tutorials, newsletters and more for C++, Visual Basic and Delphi.
An on-line resource for programmers to learn new programming languages, find job sites and programmer web resources.
Lee's Programming Source Site
Source Code for: C, C++, Java, MIPS and Motorola Assembly, Ada, Verilog, VHDL, and ABEL. Links and helpful hints.
Source Code Corner
Articles, forum, tips and tricks.
Programming site reviews posted by users.
BrilliaNeT's Programming Section
Utilities, turorials, and source-codes which deal with many programming languages (including Pascal, C, Assembly, Java) and issues(including Protected-Mode, OS Programming).
A resource for software developers, containing articles about Netbeans, Java and Lotus Domino.
European Source for C, C++ and Java development tools.
Tutorials and source code for VB, ASP, PHP, XML, SQL Server, C#, C++, Perl developers. ActiveX controls, reviews, discussion forum.
Articles and tutorials for web developers and programmers. Also forums, resources.
Hundreds of reviewed components, samples, applications for Delphi, Visual Basic, Visaul C++ developers. Also free downloads, top lists, tools, forums.
A database of useful information from Decatomb's Community and Discussion forums. Also archive of the technical papers and articles.
TILISOFT Developer Resources
A directory to developer resources. It also has code archive and download collections, forum, and chat and direct messaging.
The Peon's Guide To Secure System Development
A short, hard-hitting paper which puts forth and argues for various basic principles which must be understood by all programmers in order to make systems secure.
MetalShell - Source Code Examples
A growing archive of source code examples for different languages and platforms. All code is written for the purpose of helping others learn to program. C, C++, Perl, Python, HTML sources. Shell scripts.
Programming resources, tutorilas and FAQs. Also geometric formulas. Microsoft OS and program tutorials.
Programming information and tutorials for Delphi, Pascal, C, C++, Java, HTML, Assembly.
An online collection of tutorials, sample code, standards, and other resources provided experts at IBM to assist software developers using open standards and cross-platform technologies.
An archive of development resources relating to web development with PHP and ASP, software development with Delphi and Visual Basic, GIS development.
The Fellowship of Hobbyist Programmers
A community for coders interested in collaboration, education, and fun.
Resources such as reviews of freely available programming tutorials for C, C++, Visual Basic. Also included are software drivers for BeOS, Linux, Windows 95/98/NT/2000, and a font gallery.
Online developer repository, allowing developers to share and access their own personal code libraries from anywhere in the world.
Sources (Pascal, Delphi, C, Java), games (Java,C).
Cataloged Collection of Annotated Examples
A free-to-use comparitive resource, for programmers and non-programmers, containing complete sample code, well commented, for many different languages.
For Windows developers, covering COM, COM+, XML, ASP and Visual Basic with articles, breaking news, discussion groups, training courses, FAQs, humour.
Tips, articles and examples for Microsoft Access and visual basic. Programming of graph objects, graphical shareware and wizard downloads are also featured.
Yet Another Society
A non-profit corporation for the advancement of collaborative efforts in computer and information sciences. News, events, projects, and contact details.
Zen Spider Website
Information and tools for language writers and programmers.
Microsoft Developer Network
Provides articles, whitepapers, interviews, and sample code for software developers using Microsoft products.
Coder's Guild Mailing List Archive
Once a highly frequented programmer community, this archive contains four years of discussions about many programming problems for all languages.
Tom's Programmers Resource
Languages and other development tools that are available for the MS Windows 98/ME/XP platforms.
Tutorials on several languages (Assembly, C/C++, Java, Perl, PHP, Visual Basic), discussion forums on each, general forum, news, survey, holds quarterly programming contests. In English, despite .sk domain.
Ideas, tips, useful information on programming, graphics, games via C++, Flash, HTML, Java, PHP, Turing, Visual Basic. Links to tutorials, other interesting sites.
Code-Source: The Source for Code
Source code repository. Algorithms with various language versions of code. Open source, free for all.
Teen Programmers Unite
Organization that aims to help teen programmers learn and exchange ideas.
CodingCake - Articles
Include code examples library (including ASP, Java, VC++, database related) and coding toolkit (such as backup project, count source code, execute SQL).
Programming related articles, C/C++, Visual Basic, Pascal code examples.
The Programmers Corner
Programming resource website containing articles, tips, downloads, standards and source code in several popular programming languages, such as: VB, VB.Net, C#, C++, Java and PHP.
Aim to establish a single destination for software porting professionals, enabling community interaction and establishment of porting as a separate discipline with its own body of knowledge.
Geared toward teenage programmers, but everyone is welcome. General, PHP, MySQL, HTML, Delphi, Visual Basic tutorials. C++, Perl, PHP downloads. Forums.
Vyom Source Codes Directory
Contains categorised source codes in different programming languages - C, C++, Java, Pascal and COBOL.
Collections code snippets for XML, Java, VB, ASP, SQL, C#.
Contains PHP and C source code and resources for programmers. Offers tools for free download.
Computer technology, programming, 3D animation: tutorials, tools.
MediaDev - Software Development Portal
Recent news and events with specific market studies and resources for software developers. Localised for the UK, France, Spain, Italy and Germany.
Programming languages, web development, computer science resources.
The Code Project
C++, C# and .NET (including VB.NET) articles, code snippets, discussions.
Erix World of Programming
Source code, and forums to find help with programming.
Tutorials, articles and scripts for ASP, PHP, C++, HTML.
Source code and tips for Java, PHP, VB, VBScript and other programming languages.
E-books available in pdf format on .Net, ASP, XML and C#.
Various information for developers on windows printing.
Forums and web based access to many programming usenet newsgroups.
Sun Developer's Network - The Source
Resources for software developers using Java, web services, C, C++, and Fortran.
DevJunkies.com - developer resource
Development articles, news, code snippets and a community forum to answer questions.
Programming examples and tutorials for developers
Provides information and tutorials for developers.
Offers forum, articles and news section.
A resource for free compilers, SDKs, source code, and drivers.
Tutorials covering ranging from beginner to advanced levels with forums for extra support if needed while researching.
Resources, tutorials, forums and code samples for new and student programmers.
Programming portal and search tool. Plus a wide range of examples, tutorials and industry news.
Source Code Online
Visual Basic, ASP, VBScript and Access source code. Many products, certification questions, polls, books.
Dr. Dobb's Programmers Vault
Programming tutorials, FAQs, downloads, and hints and tips.
Grk's home page
This home page contains useful documents, texts, sources, and links for computer programmers, and tutorials for the beginners.
Programming Tutorials - justPhukit.com
A resource of tutorials and articles for programmers and developers.
A community site for open source developers. Articles covers several languages as well as important stuff like regular expressions and community building.
Youth Tech Coding Microsphere
A programming site for teens, by teens. A members showcase, programming challenges, resources, and information on most programming languages.
News, articles and reference resource for developers interested in core technology topics.
Planet Source Code
Lets programmers submit code for review by other programmers; many source code samples to help educate beginners on many concepts; contests where programmers vote for the most efficient, useful code recently submitted.
Free version of very low cost 4 CD-ROM set for computer science students. Has libraries, compilers, tutorials, extensive reference material for over 24 languages, 13,000+ entry computing dictionary, a Linux distribution.
Programming Links Page
Long page with many links to a wide variety of computer programming information.
Categorized source library. By programming languages and topics.
Free online computer books, documentations and references. All which can be viewed, copied and printed at no charge for private use.
Information on Open Source software movement. Also provides a collection of links to Linux, programming languages, databases, and networking.
VoiceCode Programming by Voice Toolbox
For many programmers with computer related injuries such as Repetitive Strain Injury (RSI), programming via voice is the only way they can exercise their talents in their chosen profession. Yet, programming-by-voice using off the shelf speech recognition systems is now awkward because programming languages were never meant to be spoken.
Resources, source code, tips for professional developers. | <urn:uuid:77f86156-497e-4025-8f51-232fb647740c> | 3.75 | 3,618 | Content Listing | Software Dev. | 34.457483 |
Rogers DW and Greig D (2009) Experimental evolution of a sexually selected display in yeast. Proc Biol Sci 276(1656):543-9
Abstract: The fundamental principle underlying sexual selection theory is that an allele conferring an advantage in the competition for mates will spread through a population. Remarkably, this has never been demonstrated empirically. We have developed an experimental system using yeast for testing genetic models of sexual selection. Yeast signal to potential partners by producing an attractive pheromone; stronger signallers are preferred as mates. We tested the effect of high and low levels of sexual selection on the evolution of a gene determining the strength of this signal. Under high sexual selection, an allele encoding a stronger signal was able to invade a population of weak signallers, and we observed a corresponding increase in the amount of pheromone produced. By contrast, the strong signalling allele failed to invade under low sexual selection. Our results demonstrate, for the first time, the spread of a sexually selected allele through a population, confirming the central assumption of sexual selection theory. Our yeast system is a powerful tool for investigating the genetics of sexual selection.
|Status: Published||Type: Journal Article||PubMed ID: 18842545|
Topics addressed in this paper
Number of different genes curated to this paper: 2
- To find other papers on a gene and topic, click on the colored ball in the appropriate box.
- displays other papers with information about that topic for that gene.
- displays other papers in SGD that are associated with that topic.
The topic is addressed in these papers but does not describe a specific gene or chromosomal feature.
- To go to the Locus page for a gene, click on the gene name. | <urn:uuid:c95d4f13-c7b3-4dde-851d-d00a917480f4> | 2.875 | 363 | Academic Writing | Science & Tech. | 33.785789 |
Credit: ESA/K. Dennerl/B. Aschenbach
A Snowball's Chance
Comets are sometimes called "dirty snowballs" since that's what they
resemble - they are composed of ice, snow, dust and rocks. Surprisingly
these "snowballs" are surrounded by a halo of X-ray producing gas. Since
X-rays usually imply extremely high temperatures, it may be that comets
simultaneously represent some of the coldest and some of the hottest
material in the solar system. These surprising cometary X-ray "halos" were
detected by ROSAT, while a Chandra
observation of X-rays around the comet C/1999 S4 (LINEAR) suggested
that the emission was produced by the capture of free electrons in the
solar wind. Now an
X-ray halo around the comet McNaught-Hartley has been observed by the
XMM-Newton X-ray observatory. The XMM-Newton image (shown above) and the
measured spectrum of the X-ray emission provide another piece of the
puzzling mechanism by which these frozen "snowballs" produce X-rays.
Last Week *
HEA Dictionary * Archive
* Search HEAPOW
Each week the HEASARC
brings you new, exciting and beautiful images from X-ray and Gamma ray
astronomy. Check back each week and be sure to check out the HEAPOW archive!
Page Author: Dr. Michael F.
Last modified April 16, 2001 | <urn:uuid:6aac5d5b-e9b6-426b-9e5b-4a7aa9a23469> | 3.640625 | 333 | Knowledge Article | Science & Tech. | 53.06659 |
At a conference made up of speakers and participants, there were 20% more men than women. The ratio of mae speakers to female speakers was 8:5. There was an equal number of male and female participants.
(a) Find the ratio of male speakers to male participants at the conference
(b) Halfway, 40 male participants left the conference and another 60 female participants joined the conference. In the end, there were 3/4 as many male participants as female participants remaining behind. How many speakers were at the conference? | <urn:uuid:6959d23c-3a68-4a6e-80da-c5478e53ecea> | 3.109375 | 109 | Q&A Forum | Science & Tech. | 42.540964 |
Olivia Judson on the influence of science and biology on modern life.
Here’s a problem: evolution never stops.
Imagine you’re a wild fruit fly, of the species Drosophila melanogaster. You’re happily feasting on some yeast that’s growing on rotting fruit when, whoomf, you get sucked into a bottle and taken to a laboratory. From now on, this is your home.
Life in a bottle — or cage — is different from life in the wild. In nature, for example, fruit flies reproduce throughout their adult lives. Often, in the laboratory, they do not: flies grown in bottles may only be allowed to reproduce for the first five or six days after emerging from the pupa. (Wild flies can live for more than 80 days.) In nature, flies choose their mates. Often, in the laboratory, they do not: they are often assigned to one, and that one may be a close relative. On top of that, the food is different; infectious diseases are rare; predators are absent.
In short, the pressures of daily life have been transformed — and traits that were an advantage Out There may no longer be so Inside. Similarly, traits that would have killed you in the wild may help you get along inside a bottle.
If, for example, older flies are never allowed to reproduce, the ability to lay eggs later in life becomes irrelevant, so there’s nothing to prevent the appearance of mutations that interfere with that ability. Indeed, if those mutations increase early fertility, they may even be favored: the most fecund young flies are likely to leave the most descendants.
Thus, the switch from the wild to the laboratory immediately alters the evolutionary trajectory of a population — and sure enough, within a few generations, laboratory-bred life-forms become noticeably different from their wild cousins.
Exactly what happens depends on how the organisms are kept — different rearing methods create different evolutionary forces. But in general, laboratory Drosophila melanogaster evolve shorter lifespans than wild flies; they become less able to cope with stresses like starvation or desiccation; and their pattern of fertility changes. As you’d expect, females reared in bottles evolve to be hugely fecund as young flies but much less so when they are older.
Also as you’d expect, laboratory evolution is not unique to Drosophila melanogaster. In the wasp Nasonia vitripennis, females descended from a long line of laboratory wasps evolve to be more prone to promiscuous sexual behavior than wild wasps. In the Mediterranean fruit fly, Ceratitis capitata, laboratory-reared females evolve to be less fussy about who they mate with, and male sexiness changes. Wild female medflies don’t find laboratory-reared males as attractive as they find wild males. Mexican fruit flies, Anastrepha ludens, have the same problem: laboratory males have evolved in such a way that they are less popular with wild females.
Mice show a host of changes, too. Compared to their wild relations, laboratory mice are typically bigger, more docile, reach sexual maturity earlier and die younger. Some of these changes can appear quickly: one study found that the ability to reproduce later in life declined within 10 generations of the mice being bred in the laboratory.
Intriguingly, laboratory mice also have longer telomeres than wild mice. (Telomeres are the segments of DNA at the ends of chromosomes; they are thought to play a role in aging and cancer.) Since no one is deliberately breeding mice for extra-long telomeres, this must arise as some consequence of laboratory life. But what?
That’s not clear. One possibility is that it’s due to inbreeding — for lab mice are often highly inbred. Consistent with this, one study of white-footed mice, Peromyscus leucopus, found that, when animals were forced to inbreed, telomeres lengthened substantially in fewer than 30 generations — although why this should be so is entirely mysterious.
All of which is fascinating. But does it matter?
That depends. For some scientific problems, the fact that laboratory life-forms evolve substantial differences from their wild relatives is irrelevant. For others, however, it matters a lot.
Let me give you two examples. Adaptation to the laboratory — or to captivity more generally — can make it much more difficult for organisms to thrive if they are later released to the wild. This has important implications for the conservation of endangered animals and for the control of pests. Captive breeding programs have been important tools for re-establishing wild populations of species such as the California condor; but not all programs are successful. Genetic changes in captivity may be one reason. Similarly, many pest control programs depend on the “sterile male technique,” whereby males are bred in the laboratory, sterilized, then released into nature to mate with wild females. For this to work, the wild females must find the laboratory males attractive. Changes in mating behavior like the ones I mentioned earlier can, therefore, quickly reduce the effectiveness of the approach.
A second area where laboratory evolution can be a serious problem is in the study of subjects like the evolution of aging, and the diseases associated with it. For example, the study of laboratory populations may give a misleading impression of how easy it is to extend lifespans: since laboratory organisms tend to have unnaturally short lifespans, discovering ways to make them live longer may not be especially informative. We may simply be reversing the unnatural shortening that we created in the first place, a view supported by the fact that selection to increase lifespan in laboratory populations often simply restores it to levels seen in the wild.
Such realizations have led an increasing number of scientists to argue that long-established laboratory populations are “suspect starting material” for understanding aging, and that comparisons with wild populations “support the pessimistic interpretation that laboratory-adapted stocks of rodents may be particularly inappropriate for the analysis of the genetic and physiological factors that regulate aging in mammals.”
For some subjects, it’s better to go wild.
For an interesting overview of evolution in the laboratory, see Artamonova, V. S. and Makhrov, A. A. 2006. “Unintentional genetic processes in artificially maintained populations: proving the leading role of selection in evolution.” Russian Journal of Genetics 42: 234-246.
A large number of studies have found evidence of evolution to laboratory conditions. For Drosophila melanogaster, I drew, in part, on Sgrò, C. M. and Partridge, L. 2000. “Evolutionary responses of the life history of wild-caught Drosophila melanogaster to two standard methods of laboratory culture.” American Naturalist 156: 341-353. This paper shows how differences in laboratory rearing methods can affect evolutionary trajectories, and also shows how truncating the reproductive life of adult flies rapidly leads to flies evolving to reproduce more earlier; compared to wild flies, laboratory flies had shorter lives. For laboratory populations being “suspect starting material” for aging studies, see page 351 of this paper.
For the lifespan of wild flies compared to laboratory flies, see Linnen, C., Tatar, M. and Promislow, D. 2001. “Cultural artifacts: a comparison of senescence in natural, laboratory-adapted and artificially selected lines of Drosophila melanogaster.” Evolutionary Ecology Research 3: 877-888. These authors show that wild flies live longer than standard laboratory flies, and that lines of flies that have been bred specifically to have long lifespans do not live longer than wild flies.
For laboratory rearing leading to loss of resistance to desiccation and starvation, see Hoffmann, A. A. et al. 2001. “Rapid loss of stress resistance in Drosophila melanogaster under adaptation to laboratory culture.” Evolution 55: 436-438. For promiscuous laboratory wasps, see Burton-Chellew, M. N. et al. 2007. “Laboratory evolution of polyandry in the parasitoid wasp Nasonia vitripennis.” Animal Behaviour 74: 1147-1154.
For evolution in the mating behavior of laboratory populations of medflies, see Rodriguero, M. S. et al. 2002. “Sexual selection on multivariate phenotype in wild and mass-reared Ceratitis capitata (Diptera: Tephritidae).” Heredity 89: 480-487. For the same phenomenon in Mexican fruit flies, see Rull, J., Brunel, O. and Mendez, M. E. 2005. “Mass rearing history negatively affects mating success of male Anastrepha ludens (Diptera: Tephritidae) reared for sterile insect technique programs.” Journal of Economic Entomology 98: 1510-1516. These papers also discuss the problems that laboratory evolution pose for pest control. An additional analysis of this is provided by Hendrichs, J. et al. 2002. “Medfly areawide sterile insect technique programmes for prevention, suppression, or eradication: the importance of mating behavior studies.” Florida Entomologist 85: 1-13.
For an overview of evolutionary changes in laboratory mice, see Miller, R. A. et al. 2002. “Longer life spans and delayed maturation in wild-derived mice.” Experimental Biology and Medicine 227: 500-508. This paper shows that wild-caught mice live much longer than most laboratory mice, and reach sexual maturity later. These authors are also responsible for the “pessimistic interpretation” quotation; see page 507.
For the study showing that the ability to reproduce later in life can decline within 10 generations of laboratory residence, see Flurkey, K. et al. 2007. “PohnB6F1: a cross of wild and domestic mice that is a new model of extended female reproductive life span.” Journal of Gerontology, Biological Sciences 62A: 1187-1198.
For laboratory mice having weirdly long telomeres, see Hemann, M. T. and Greider, C. W. 2000. “Wild-derived inbred mouse strains have short telomeres.” Nucleic Acids Research 28: 4474-4478. For inbreeding producing long telomeres in white-footed mice, see Manning, E. L. et al. 2002. “Influences of inbreeding and genetics on telomere length in mice.” Mammalian Genome 13: 234-238.
For the possibility that evolution in captivity may pose a potential problem for captive breeding programs, see Woodworth, L. M. et al. 2002. “Rapid genetic deterioration in captive populations: causes and consequences.” Conservation Genetics 3: 277-288; and Williams, S. E. and Hoffman, E. A. 2009. “Minimizing genetic adaptation in captive breeding programs: a review.” Biological Conservation 142: 2388-2400.
The problem of laboratory mice in aging research has been discussed extensively by some authors. In addition to the papers I have already mentioned, see Harper, J. M. 2008. “Wild-derived mouse stocks: an underappreciated tool for aging research.” Age 30: 135-145; and Miller, R. A. et al. 1999. “Exotic mice as models for aging research: polemic and prospectus.” Neurobiology of Aging 20: 217-231.
Many thanks to Bret Weinstein for drawing my attention to the fact of long telomeres in laboratory mice, and for discussions about some of the implications this may have. Many thanks also to Nicholas Judson and Jonathan Swire for insights, comments and suggestions. | <urn:uuid:cb1397e0-9c8a-46d9-83b0-ed5536d13d34> | 3.421875 | 2,523 | Personal Blog | Science & Tech. | 37.9001 |
My text says that Aristarchus (310 BC – ~230 BC) measured the "angle subtended by the Earth-Moon distance at the Sun" ($\theta$ in the figure below) to establish the relative Earth-Moon and Earth-Sun distances.
I understand that he must, in fact have used the Moon-Earth-Sun angle, and then subtracted that from 90° to arrive at $\theta$; but how did he establish the Moon-Earth-Sun angle? The reference points for all three objects is their centers, yet what Aristarchus must have in fact measured was the angle between the Moon and the Sun at the surface of the Earth.
Did Aristarchus take this discrepancy into account in his calculations? If so, how? | <urn:uuid:e3d6c0fd-40d7-443d-92df-89b2c98bcfe9> | 3.734375 | 158 | Q&A Forum | Science & Tech. | 57.845621 |
On Sunday May 20th, 2012 a solar eclipse will sweep across east Asia, over the northern Pacific Ocean, and then into the southwestern United States. The eclipse will span from 4:14pm to 6:36pm PST and will be total for 4 minutes and 40 seconds with the maximum eclipse of the sun at 5:30pm PST.
The periodicity and recurrence of solar eclipses is governed by the Saros cycle, a period of approximately 6,585.3 days (18 years 11 days 8 hours). Saros cycle 128 is a solar eclipse that repeats every 18 years and encompasses 73 events. The series started with a partial solar eclipse on August 29, 984 AD and progresses into annular eclipses from August 11, 1561 through July 25, 2120.
In 2012 the eclipse will cover 96.7% of the sun leaving a thin fiery ring of sunlight around the black disc of the moon. | <urn:uuid:16e86636-182f-4727-92d6-093ee69c437d> | 2.859375 | 188 | Knowledge Article | Science & Tech. | 73.9431 |
Is it possible or practical to predict vog? The Vog Measurement and Prediction Project (VMAP) is a feasibility study in which scientists will evaluate [are evaluating] whether vog forecasts are achievable and useful. Project collaborators are making the feasibility study available to the public through this Web site, but as an ongoing investigation, VMAP currently provides limited service and reliability. Thus, VMAP users should have no expectation of accuracy or timeliness, and project data should not be used for decision making purposes at this time. Comments and inquiries can be directed to the appropriate contact.
Vog is primarily a mixture of sulfur dioxide (SO2) gas and sulfate (SO4) aerosol. SO2 (invisible) reacts with oxygen and moisture in the air to produce SO4 aerosol (visible). SO2 is expected to be the main problem in areas near the vent (Hawai`i Volcanoes National Park, Pahala, Na`alehu, Hawaiian Ocean View Estates) and SO4 aerosol is expected to be the main problem at locations far from the vent (Kona and farther north and west).
The model output animation and accompanying forecast table is generated using the HYSPLIT numerical dispersion model. The model uses estimates of volcano emissions along with forecast winds to predict the concentrations of sulfur dioxide gas (SO2) and sulfate aerosol particles (SO4) downwind of the ongoing Kilauea eruption. This is a research effort that is in progress.
For emissions updates click here
[ Top of this page ]Select Region: Island of Hawaii | Hawaiian Islands
[ Top of this page ]
The location of the sites in the table below are shown on the map linked here.
|Fri, May 17, 2013||0400||0||0||0||0||0||0||0||0||0||0||0|
|Fri, May 17, 2013||0700||0||0||0||0||0||0||0||0||0||0||0|
|Fri, May 17, 2013||1000||0||0||0||0||9||0||0||0||0||0||0|
|Fri, May 17, 2013||1300||0||0||0||0||1||0||0||0||0||21||0|
|Fri, May 17, 2013||1600||0||0||0||0||0||0||0||0||0||1||0|
|Fri, May 17, 2013||1900||0||0||0||0||0||0||0||0||0||4||0|
|Fri, May 17, 2013||2200||0||0||0||0||0||0||0||0||0||3||0|
|Sat, May 18, 2013||0100||0||0||0||0||9||0||1||0||0||0||0|
|Sat, May 18, 2013||0400||0||0||0||0||5||0||19||0||0||0||0|
|Sat, May 18, 2013||0700||0||0||0||0||2||0||0||0||0||1||0|
|Sat, May 18, 2013||1000||0||0||0||0||2||0||1||0||0||2||0|
|Sat, May 18, 2013||1300||0||0||8||0||0||0||6||0||0||0||0|
|Sat, May 18, 2013||1600||0||0||9||4||0||0||0||0||0||28||0|
|Sat, May 18, 2013||1900||0||0||7||2||0||0||0||0||0||0||0|
|Sat, May 18, 2013||2200||0||0||0||0||8||0||0||0||0||0||0|
|Sun, May 19, 2013||0100||0||0||22||3||6||0||0||0||0||0||0|
|Sun, May 19, 2013||0400||17||9||23||28||15||0||0||0||0||13||0|
|Sun, May 19, 2013||0700||18||1||5||10||32||0||0||0||0||1||0|
|Sun, May 19, 2013||1000||9||8||21||15||6||0||11||0||0||10||0|
|Sun, May 19, 2013||1200||7||3||0||2||0||0||5||0||0||0||0|
Daily discussion of vog concentrations over the Hawaiian Islands as a result of the interaction of the volcanic emissions and the current and forecast weather. | <urn:uuid:a659cdb6-21d1-41d2-b522-30a843fc4294> | 3.234375 | 1,050 | Knowledge Article | Science & Tech. | 79.773441 |
- C. Characteristic Groups Containing Carbon, Hydrogen, Oxygen, Nitrogen, Halogen, Sulfur, Selenium, and/or Tellurium
- C-0. Nomenclature Systems
- 0.0 General Principles
0.1 Substitutive Nomenclature
0.2 Radicofunctional Nomenclature
0.3 Additive Nomenclature
0.4 Subtractive Nomenclature
0.5 Conjuctive Nomenclature
0.6 Replacement Nomenclature
0.7 Nomenclature of Assemblies of Identical Units
0.8 Free Radicals, Ions, and Radical Ions
This HTML reproduction of Sections A, B and C of IUPAC "Blue Book" is as close as possible to the
published version [see Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H, Pergamon Press, Oxford, 1979.
Copyright 1979 IUPAC.] If you need to cite these rules please quote this reference as their source.
Published with permission of the IUPAC by Advanced Chemistry Development, Inc., www.acdlabs.com, +1(416)368-3435 tel, +1(416)368-5596 fax. For comments or suggestions please contact email@example.com | <urn:uuid:ac923aed-28b1-4c3c-8fec-6697638041c5> | 2.875 | 294 | Documentation | Science & Tech. | 56.230789 |
The impossibility of energy for free is enshrined in one of the most fundamental
and important laws of physics: the First Law of Thermodynamics or the Law of
Conservation of Energy, which states that energy can neither be created nor destroyed,
but can only change its form.
In 1847, a 26-year-old German medical doctor, Hermann Helmholtz, gave a
presentation to the Physical Society of Berlin that would change the course of history.
He presented the original formulation of what
is now known as the First Law of Thermodynamics, beginning with the axiomatic
statement that a Perpetual Motion Machine is impossible.
Axiom - A statement or proposition that is accepted as true without proof.
No one had ever succeeded, he wrote, in building a Perpetual Motion Machine that
worked. Therefore, such machines must be impossible. If they are impossible it must
be because of some natural law preventing their construction. This law, he said,
could only be the Conservation of Energy.
But a profound reversal of reasoning has occurred in the last century. Helmholtz
originally said "Because a Perpetual Motion Machine is impossible, therefore the
First Law of Thermodynamics;" while in any physics text book today one will
find the statement that "Because of the First Law of Thermodynamics, a
Perpetual Motion Machine is impossible."
Skeptics are quick to cite the Laws of Thermodynamics to disprove Bessler's claims.
In fact, the argument is circular. The Laws of Thermodynamics do not prove that
Bessler's machine is impossible. On the contrary, they are deduced
from the "leap of faith" of first presuming it is impossible. | <urn:uuid:dc1f3d1c-ef3a-426d-9e67-0e23b9ec1564> | 3.671875 | 366 | Knowledge Article | Science & Tech. | 35.980991 |
For those that don't know, the with statement allows you to use an object inside a new context. You can't just use any only Python object, like a string or a dictionary. Any object used in a with statement needs a context manager. For more on using context managers (and the with statement in general), see Fredrik Lundh's guide.
The additional piece of with magic I've been playing with is returning data from inside a with statement. For example, consider the following getcount() function that returns that line count of a file...
def getcount(fobj): with fobj as f: return len(f.readlines()) fobj = open('tmp.txt') print getcount(fobj) print fobj.closed
This example is quite simple — open a file object and print the number of lines. The getcount() function uses the with statement to open and close the file. But wait a minute, how was the file object closed if we returned from the function inside the with statement? This is the beauty of the context manager — it is guaranteed to carry out all clean-up tasks no matter what. This is why we're printing out fobj.closed — to verify that this did indeed work.
The same methodology can be used with lock context managers. For example...
import time from threading import Thread, Lock class MyThread(Thread): lock = Lock() def __init__(self): super(MyThread, self).__init__() def set_name(self): with self.lock: self.name = 'MyName' time.sleep(2) def get_name(self): print 'Waiting for name...' with self.lock: return self.name def run(self): self.set_name() tobj = MyThread() tobj.start() print tobj.get_name()
Here we're explicitly making set_name() take longer than it should — causing the lock object to block. The return statement in get_name() is paused until the name is set, since it's inside the with. Cool stuff. | <urn:uuid:18ab416b-e850-4781-8f9d-9df1f662d7f4> | 3.28125 | 437 | Documentation | Software Dev. | 69.76367 |
at the Carnegie Institution's Department of Global Ecology are
looking to optimize climate change reduction by injecting
sulfates into the stratosphere. George
Ban-Weiss, lead author of the study, along with his team of Carnegie
scientists, have studied how the injection of aerosols of sulfate
into the stratosphere will affect Earth's chemistry and climate, and
which aerosol distribution pattern will bring them closest to their
do this, Ban-Weiss and his team used a global climate
model with different sulfate aerosol concentrations
depending on latitude to run five simulations. They then determined
what distribution of sulfates would bring them closest to climate
goals by using the results from the simulations in an optimization
model. These distributions were then tested in the global climate
model to see how close they came to these goals.
know that sulfate can cool
the Earth because we have observed global temperature
decreases following volcanic eruptions," said Ban-Weiss. "Past
computer model simulations have shown that injecting sulfate
uniformly into the stratosphere could reduce the surface temperature
of the Earth, but the equator would be over cooled and the poles
under cooled. You would also make the Earth drier, and decrease
surface water runoff."
Ban-Weiss' results from his climate models showed that more sulfate
poles rather than tropical regions would result in a
low-carbon climate. But when sulfates were distributed uniformly,
changes in the water cycle were "most effectively diminished."
If the right amount of uniformly distributed aerosols were injected
into the stratosphere, the consequence of climate change could be
decreased by 90 percent and the change in runoff would be decreased
by two-thirds. But when aerosols are distributed latitudinally as a
parabola, temperature change decreased by 94 percent while runoff
changes were only cut in half.
in temperature and the hydrological cycle cannot be simultaneously
minimized because the hydrological cycle is more sensitive to changes
radiation than are surface air temperatures," said
Caldeira, co-author of the study, added that the study was mainly
aimed to develop "a new methodology" for observing the
current climate change problem, and that their model does not include
all process that are essential in reality. Their results are strictly
illustrative and not yet ready to provide a basis for policy
decisions. But he also mentioned that the models of course worked.
optimization model worked well because the complex climate models
indicate that much of the climate system operates as a very linear
system," said Caldeira. "This is surprising when you hear
all the talk of tipping points."
study was published in Environmental
Research Letters this
quote: New research on global warming is contradicting research from 3 months ago (I pulled that out of my ass, but you get the point)
quote: Let's assume that you're someone who accepts that humans are causing a catastrophic global warming. Then let's assume that you're also not a complete idiot:
quote: Pulling CO2 out of the air is too energy intensive to be useful, putting safe particulates into the upper atmosphere seems like an idea worth pursuing.
quote: Ken Caldeira, co-author of the study, added that the study was mainly aimed to develop "a new methodology" for observing the current climate change problem, and that their model does not include all process that are essential in reality . Their results are strictly illustrative and not yet ready to provide a basis for policy decisions. But he also mentioned that the models of course worked .
quote: CO2 is only 3% of the atmosphere
quote: closest to their climate goals
quote: This here says it all. WHAT CLIMATE GOALS? And what about MY climate goals? Maybe they are totally different.
quote: They're going to call it Global Climate Disruption now instead.
quote: Their results are strictly illustrative and not yet ready to provide a basis for policy decisions. | <urn:uuid:35cb016f-c9c3-4062-80a7-89ab57e5046e> | 3.828125 | 839 | Comment Section | Science & Tech. | 27.014751 |
Critical Loads (CL) approach as a tool to evaluate harmful effects of nitrogen and sulfur deposition to forests
Critical Loads Meeting Series
The PSW Research Station hosted the third in a series of critical loads meetings. These are a collaboration between US and European scientists to examine implementing a Critical
Loads (CL) approach for evaluating ecological effects of sulfur
& nitrogen deposition and acidity on the U.S. federal lands.
The Station will continue to host a CL Meetings website to share results and ongoing efforts.
There is a need for tighter air pollution controls and monitoring to protect sensitive the U.S. forests and other ecosystems (National Research Council, 2004). Standards based on air pollutant concentrations are inappropriate for biological resources at risk from nitrogen (N) and sulfur (S)deposition. Therefore the Critical Loads (CL) approach has been suggested as a tool for evaluating ecological effects of N & S deposition in the United States. Critical Loads for N and S deposition is a level of deposition of these two elements below which no harmful effects occur in an ecosystem.
The CL approach has been used in Europe since late 1980s by the International Cooperative Programs under the auspices of the UN Economic Commission for Europe (US and Canada area also members of those programs). The CL approach has allowed for developing risk probability maps from N and S deposition for forest and other ecosystems in entire Europe. A similar approach, at a smaller scale has been used in SE Canada and New England.
The National Research Council also recommends development of a secondary (biologically based) standard for ozone since negative effects on plants can develop before human effects occur. In that regard a concept of an effective flux of ozone on vegetations is being developed in Europe and in the future could also be used in the United States.
These new concepts may have important effects on how U.S. ecosystems are managed and protected from harmful effects of N & S deposition and ozone.
Research conducted by: | <urn:uuid:d518245f-1aa2-4ca2-a98f-11056cf4697f> | 2.859375 | 400 | Knowledge Article | Science & Tech. | 34.192343 |
- The Rho Ophiuchi dark cloud, a nearby star-forming region.
- Messier 62, a globular cluster also known as NGC 6266.
- The Cat's Paw Nebula, NGC 6334, is a complex emission nebula that hosts massive star formation.
- Messier 20, the Trifid Nebula
- Messier 6, a young open cluster in the Scorpion.
- The Pipe Nebula, a dark cloud obscuring the background stars.
- Messier 4, one of the nearest globular clusters, it hosts stars almost as old as the Universe itself.
- Antares, a star whose diameter is 800 times larger than the Sun's.
- Messier 7, Ptolemy's Cluster
- Messier 8, the Lagoon Nebula
- NGC 6302, the Bug Nebula
- NGC 6400, an open cluster
- The Snake Nebula, a dark cloud
- The Galactic Centre
- NGC 6357, an emission nebula | <urn:uuid:954dfe10-ca84-4eca-908b-8c3d9645d39a> | 3.046875 | 210 | Listicle | Science & Tech. | 67.036429 |
@part: Groups of Chapters
The final sectioning command is
@part, to mark a part of
a manual, that is, a group of chapters or (rarely) appendices. This
behaves quite differently from the other sectioning commands, to fit
with the way such “parts” are conventionally used in books.
@node command is associated with
@part. Just write
the command on a line by itself, including the part title, at the
place in the document you want to mark off as starting that part. For
@part Part I:@* The beginning
As can be inferred from this example, no automatic numbering or
labeling of the
@part text is done. The text is taken as-is.
Because parts are not associated with nodes, no general text can
@part line. To produce the intended output, it
must be followed by a chapter-level command (including its node).
Thus, to continue the example:
@part Part I:@* The beginning @node Introduction @chapter Introduction ...
In the TeX output, the
@part text is included in both the
normal and short tables of contents (see Contents), without a page
number (since that is the normal convention). In addition, a “part
page” is output in the body of the document, with just the
@part text. In the example above, the
@* causes a
line break on the part page (but is replaced with a space in the
tables of contents). This part page is always forced to be on an odd
(right-hand) page, regardless of the chapter pagination
In the HTML output, the
@part text is similarly included in
the tables of contents, and a heading is included in the main document
text, as part of the following chapter or appendix node.
In the XML and Docbook output, the
<part> element includes all
the following chapters, up to the next
containing chapters is also closed at an appendix.
In the Info and plain text output,
@part has no effect.
@part is ignored when raising or lowering sections (see next
section). That is, it is never lowered and nothing can be raised to it. | <urn:uuid:5e37e37c-4407-4e4b-8a62-ce2480d496de> | 2.890625 | 479 | Documentation | Software Dev. | 57.624873 |
A plasmid is double-stranded DNA not native to the regular chromosomal DNA of the organism. They are hoop-shaped, which is largely why the cell does not eliminate them. Most of the time, plasmids are found in bacteria. They are fairly short, from 1 to 400 kilobase pairs, and may be found in one copy or hundreds of copies in any given cell. Plasmid DNA is replicated separate from nuclear DNA, and is usually passed on to daughter cells.
Plasmids can confer several advantages onto their hosts. For instance, bacteria may take up plasmids from other bacteria or from a host that confers antibiotic resistance.
Episomes are a type of plasmid that integrates into the chromosomal DNA of its host. This creates a new modified bacteria that can consistently pass down traits like antibiotic resistance to its daughter cells.
Often, plasmids are used by genetic engineers as vectors to transfer genes from one organism to another. They can also be used to make many copies of desired genes for later use, or for the creation of large quantities of desired proteins.
Plasmids are found primarily in prokaryotes like bacteria, but are sometimes found in eukaryotic organisms; they are double-stranded DNA molecules separate from the cell's chromosomal DNA, and are typically circular in shape. Plasmids can be made up of from one to four hundred kilobase pairs. You'll find them alone, or you may find hundreds of copies of the same plasmid in a single cell. When the cell divides, the plasmids are duplicated to both daughter cells.
Plasmids provide a variety of advantages for the bacteria. The most commonly studied is antibiotic resistance; in addition, a resistant plasmid, once developed, can be passed to other bacteria as well. Some related plasmids are incompatible, and one must be eliminated from the cell line.
Episomes are a type of plasmid that can integrate itself into the chromosomal DNA of the host organism. Plasmids that are used in genetic engineering are called vectors; they transfer genes into the bacteria, and generally contain a genetic marker that can be selected for or against in the final resulting organism. Once genes have been transferred into a bacteria, genetic tests can be performed, or the bacteria can be used in different ways such as the mass-production of a specific protein.
Functions of plasmids include fertility, resistance, colicines (or proteins that kill other bacteria), degrative, or unusual digestive, properties, and virulence. Any given plasmid may belong to more than one of these groups.
Web Resources On Plasmid
Recombinant DNA and Gene Cloning
Book Resources On Plasmid
Plasmid Biology by Funnell & Phillips
The Biology of Plasmids by Summers | <urn:uuid:2a16e951-21a7-4105-aa89-fe990ef5532a> | 4.28125 | 590 | Knowledge Article | Science & Tech. | 33.396058 |
The Hertzsprung-Russell Diagram
One of the most significant discoveries was that by Ejnar Hertzsprung and H. N. Russell. These two astronomers, each acting independently, observed each star in the Pleiades with a photometer. This device provides an electical current proportional to the amount of light coming from the star. This current is measured and the brightness of the star, in magnitudes, computed.
Hertzsprung and Russell had each chosen the Pleiades for study because as an open cluster, all the stars in the Pleiades are of the same distance, since they were all formed out of the same gas cloud a mere 4.2 million years ago. This meant that the brightness differences between the stars of the Pleiades must be caused by an intrinsic property of each star rather than by the stars being at different distances.
This "discovery" was not particulaly new, but a confirmation that different stars had different intrinsic brightnesses. Hertzsprung and Russell felt that if the brightness of a star was a property of that star, then there may be some other properties of the starlight that would shed light on the nature of stars.
Light is the only property of a star that can be measured directly, so Hertzsprung and Russell went back to the telescope and re-measured the brightnesses of the different stars. This time they took two measurements of each star. The first was through a filter that allowed only blue light to reach the photometer. This measurement was called the B(lue) magnitude of the star. The second measurement was through a yellow filter that closely matches the spectral response of the eye. This measurement was called the V(isual) magnitude of the star. Comparing these two magnitudes, we can measure the color of the star.
The difference between the B-magnitude and the V-magnitude is called the color index of the star and indicates it's color. If the star was really "white", then the star would have the same brightness in the blue part of the spectrum (B-magnitude) as in the visual (yellow or V-magnitude). The difference of the B-magnitude minus the V-magnitude, written B-V, would be zero. Note that this difference is a constant regardless of the magnitude of the star or it's distance. What can affect the color index is interstellar dust, which causes a "reddening" of the star.
If the star is bluish, then the B-magnitude will be brighter, meaning it will be numerically smaller (remember that first magnitude stars are brighter than second magnitude stars). This makes the difference B-V negative for bluish stars. The more negative B-V, the bluer the star. Reddish stars have smaller V-magnitudes, making the difference B-V positive. The more positive B-V, the redder the star.
Our sun has a color index of +0.63, making it somehat yellowish. Betelgeuse, in Orion, has a color index of +1.87, indicating a very red star: a red giant. Achernar (Alpha Eridani) is a blue giant, and has a color index of -0.16. Vega with a color index of 0.00 is a white star.
Hertzsprung and Russell completed their color index measurements on the Pleiades and then plotted the magnitude of each star on the y-axis and it's color index on the x-axis. The resulting diagram showed an amazing correlation between the color index and the magnitude!
This diagram reproduced here is called a Hertzsprung-Russell diagram (or H-R diagram for short). It shows that most of the stars can exist only with certain color indices and brightnesses. The main line of stars from the upper left to the lower right is called the main sequence (this chart shows primarily the main sequence). The stars in it are called main sequence stars.
The stars (not shown here) that are not on the main sequence are either dwarf stars (lower left) or giant stars (upper right) that are either near the beginning or the end of their life cycle.
Magnitude and color measurements of nearby stars whose distance is known from trignometric parallax allow the H-R diagram to be calibrated in absolute magnitude. Absolute magnitude is the brightness of a star as it would be measured from a distance of ten parsecs from the star.
The H-R diagram can then tell us the actual brightness of a star based on it's color index and the knowledge that it is a main sequence star. This was a tremendous step forward in understanding the nature of stars. It led to an understanding of the evolution of stars from dwarf to main sequence to giant and then back to dwarf.
The truly amazing thing about the H-R diagram is the large variety of labels that can be put on the axes of the H-R diagram. For example, the same diagram that plots magnitude vs color index also plots absolute magnitude vs surface temperature, and absolute magnitude vs spectral classification. This lead to relating color index, spectral classification, and stellar temperature. Thus, Hertzsprung and Russell discovered a starting point for the science of Cosmology and stellar evolution, on which all astrophysics has been built.Published in the August 1996 issue of the NightTimes | <urn:uuid:89f91ab0-39e6-4037-98d9-b805d637cf98> | 4.40625 | 1,122 | Knowledge Article | Science & Tech. | 56.893759 |
Hexadecimal colour values
This little trick avoids having to write a function to do the conversion.
The decimal system
The numbering scheme in everyday use is the decimal (or denary) system and numbers are represented by 10 digits i.e. the numbers 0 to 9.
Counting starts at zero, (see counting wheels below). Rotating the wheel anticlockwise adds 1 to the current count until the number reaches 9 whereupon the count is reset to 0.
Radians and degrees (or angular measure)
When measuring angles we usually
measure them in degrees. There are 360 degrees in a circle.
I.e. a degree simply divides a circle into 360 segments.
An alternative radial measure is known as a radian. A radian is the angle formed by measuring the radius around the circumference of a circle as show by the diagram. 1 radian is approximately 57.32 degrees.
The most common operators are mathematical operators; +, -, /, * (add, subtract, divide, multiply) for example. Operators can be split into two groups, comparison operators and assignment or 'action' operators. Comparison operators test to see if two variables relate to each other in the specified way, for example, one variable is a higher number than the other. Other operators perform an action on a variable, such as increasing it by one.
With decimal numbers, 12e+4 may be used to replace 12x104 and 12e-4 may be used to replace 12x10-4 etc.
The String object is used to manipulate a stored piece of text. String objects are created with new String().
A string literal is 0 or more characters enclosed in either double, or single quotes. For example
"Hello World" 'Sun wind and rain' "123"
Strings are a fundamental to any programming language and as well as all the comparison operators strings may be concatenated (joined) together using the concatenation operator, the plus symbol ( + ). for example
Ternary if statement
This provides a shorthand way to assign different values to a variable, depending on a condition.
var myVariable = document.getElementById("color").value myVariable == "red" ? 1 : 0;
This is identical to:
The following function performs the same test using the switch case statement. As you can see it is much more compact and consequently easier to read. | <urn:uuid:41e5e5dc-6552-4fea-b14f-428bbc600992> | 3.984375 | 501 | Tutorial | Software Dev. | 48.173464 |
|SEVERE STORM STRUCTURE:|
METEOROLOGIST JEFF HABY
The core of the updraft has the strongest
convective upward vertical velocity. This core of rapidly rising air
will only slow down and stop when it encounters a very stable layer in the atmosphere. This very stable layer
tropopause. Air will rise as long as it is less dense and therefore more buoyant than surrounding air.
The faster air rises the longer it takes generally to slow down and stop once it encounters a
very stable layer.
This occurs because a moving object has momentum. That part of the updraft that has the greatest momentum
will form the overshooting top on a
severe thunderstorm. The diagram below shows the overshooting top at | <urn:uuid:1082397a-3313-4088-9bd4-c6a841844b29> | 3.53125 | 162 | Knowledge Article | Science & Tech. | 47.052119 |
The Oceans tides, waves and currents have the potential to provide us with enough renewable energy to power billions of homes worldwide. But how? Can this be achieved in a manner that's affordable?
British inventor; Alvin Smith of Dartmouth Wave Energy Ltd believes he can, by utilizing his invention called the "Searaser".
"The "Searaser" is a wave energy converter that harnesses the power of the ocean and has the potential to provide renewable energy on demand."
- Alvin Smith
The "Searaser" works via a center piston in conjunction with two floats; the larger float sits on the oceans surface and the other is held underwater at a fixed depth by an anchor chain. When the top float bobs up and down on the swells, seawater is pumped in both directions creating water pressure. This water pressure then forces seawater through an underground pipe that leads several meters above sea-level, where it can be stored in a holding tank. From the holding tank or reservoir the seawater can be released back down through a hydro electric turbine to produce renewable electricity, before returning to the ocean.
Mr. Smith claims 1 Large scale "SEARASER 1200" could:
- Pump 1.6 cubic meters of seawater per second
- Pump 136,000 cubic meters per day
- Produce 1 MW of electricity
- Power 1720 homes
- Cost 2 cents per kWh to produce
With Great numbers like this; Why isn't the "Searaser" in full operation right now? Whats the delay?
According to this article; "Football scores a goal in mastery of wave power" It's due to a lack of government support. This is unfortunate because the "Searaser" has great potential, and among it's competitors, the "Searaser" may also be the least expensive to build.
Here's an example of the "Searaser's" Potential! The World's 1st "Seawater Pumped Storage Hydro Power Plant" in Okinawa Japan. (How Pumped Storage Hydro Electricity works)
Presently it runs on coal to power it's generators, but there's a better option; the "Searaser" could completely replace the facilities use of coal. Significantly decrease it's environmental impact, reduce cost and increase efficiency to produce up to 30 MW of electricity per day.
The image above is a concept that suggests how combining the "Searaser" and "Okinawa's Seawater Pumped Storage Power Station" could be transformed into a "Multi Purpose Seawater Power Station". It may sound too good to be true; But is it? Perhaps the real question isn't; Can we make this Happen? Perhaps it's more about; Does the Will to make this Happen Exist?
The information and data on Dartmouth Wave Energy's website regarding the "Searaser" and the "Multi Purpose Seawater Power Station" sounds feasible.
My conclusion is that "Harnessing the Power of the Ocean" is a:
- Viable, sustainable solution.
- Could power millions of homes worldwide.
- Help diversify the worlds renewable energy resources.
- Decrease our dependence on fossil fuels & nuclear energy.
- Help protect our health and environment
At the moment, our ability to utilize such a vast renewable energy resource is only limited by a lack of funding and corporate willpower. It's not due to a lack of innovation or inventions that could harness the power of the ocean. It's not due to a lack of forward thinking people. It's about those controlling the energy industry delaying progress for the sake of profit. In essence, It's about greed.
For instance; there is no other reason why countries like Japan shouldn't be utilizing the power of the ocean to generate their electricity right now! Not 30 or 50 years from now.
Inventions and concepts like those Alvin Smith presents, appear to be more than viable solutions, I believe it's a step in the right direction. With sufficient funding, government support, and corporate willpower. Inventions like the "Searaser" and "Multi Purpose Seawater Power Station's" could become a reality. Reduce our dependence on fossil fuels, nuclear energy and power millions of homes.
(Searaser images, diagrams provided by: Dartmouth Wave Energy Ltd.) | <urn:uuid:c34cf49d-6596-4737-84b4-3160266a20ab> | 3.546875 | 894 | Personal Blog | Science & Tech. | 46.768714 |
Fig. 1 Seaweed, Sargassum species. A single branch illustrating the leaflike structures and air bladders growing from a central stem.
Fig. 2 Seaweed, Turbinaria species. Note the pyramidal, trumpet shaped reproductive bodies at the ends of the stems (arrow). Very common in the rough areas of the reef, brown in colour and washes up extensively on the beach.
Fig. 3 Seaweed, Turbinaria species.
Fig. 4 Goniolithon species. Note the extensive system of branches. This specimen is dead and only the white skeleton remains, but is red when alive. Very noticeable as components of the sand.
Fig. 5 A large star coral head (Montastraea) at Mexico Rocks. Note the cauliflower like appearance of the surface. Divers and snorklers will readily notice this massive round, brown coral. It is the major active coral of the Belize Barrier Reef and grows from shallow water to the deep drop off. In the shallower water they are more round and in the deeper water they tend to become flatter. It is everywhere in the deep canyons (grooves) and ridges (spurs) off the front of the reef. The environment of Mexico Rocks is a typical example of large viable Montastraea patches opposite the reef breaks. One should observe in some of these shallower patches the concave, hollow, upper surface of the large coral heads. These areas of the coral head are dead and silted in, probably due to the shallow water covering them which allows more sunlight and thus more colonization by algae. These dead coral area are colonized by sponges, algae, colonial anemones, urchins etc.
Fig. 6 Close up of a star coral showing the individual living chambers of the coral animal and the rays that give this coral its name. This is a good example of the individual polyps which form the large skeletal mass. These polyps secrete copious quantities of mucus that are very evident upon death. Brilliantly Feather Duster worms often invade the chamber area and encrust part of the coral.
Fig. 7 Chenille coral (Manicina), up to 4" long. These colonies are found primarily in the Thalassia sand flats. They are weakly attached to the substrate, and are often seen washed up on the beach. (Chenille is a tufted cloth used a lot for bedspreads)
Fig. 8 Two separate coral colonies, one a star coral on left and a brain coral (Diploria) on the right. These are typical of the massive, boulder like types of coral, unlike the more delicate varieties. | <urn:uuid:d9f453cc-1635-4ab3-ab88-f97888902723> | 3.578125 | 557 | Knowledge Article | Science & Tech. | 51.974044 |
Striding buoyantly across the low-gravity surface of the moon, there may someday be strange new men — part human, part machine — like the ones above. They will have a strange name: CYBORGS (for CYBernetic ORGanisms). Cyborgs, according to the daring new idea, will be men whose body organs and systems are automatically adjusted for life in unearthly environments by artificial organs and senses. Some of these devices will be attached, others actually implanted by surgery. With their aid cyborgs can dispense with clumsy, easy-to-puncture space suits in which earth conditions are recreated. Instead they can move about safely wearing not much more than they would at home.
The artificial senses of cyborgs will measure changes inside the body and outside in the environment. They will signal artificial glands telling them what to secrete for regulating normal body functions. Then body temperature may fall to that of a fish in ice, or the pulse may quicken like a robin’s in flight, but the human organism will survive. Fantastic as the idea sounds, its originators (see next page) think that it is feasible and that much of the knowledge needed already exists. | <urn:uuid:84f2394f-c9ed-44c4-adc1-ea94f0f5ecf3> | 2.953125 | 248 | Personal Blog | Science & Tech. | 37.770889 |
The objective of this experiment is to determine the molar ratio, or stoichiometry, between the reactants of a chemical reaction. By holding the number of moles of reactant A constant and varying the moles of reactant B, you will determine the number of moles of B required to react completely with the amount of A present so that neither reagent is limiting or in excess.
In Part I of this lab, you will look at the reaction between hydrogen peroxide (H2O2) and bleach (NaOCl). When these two chemicals are mixed, oxygen gas (O2) is produced and the volume of gas produced is measured as a function of the amount of hydrogen peroxide added to a fixed amount of bleach.
? H2O2(aq) + ? NaOCl (aq) —› O2(g) + other products
In Part II of this lab, you will work with a reaction that produces a colored species. You will add an iron (Fe2+) solution to 1,10-phenanthroline and measure the intensity of the colored product as a function of the amount of Fe2+ added to a fixed amount of 1,10-phenanthroline solution.
Fe2+ (aq) + n (1,10-phenanthroline) (aq) —› Fe(1,10-phenanthroline)n (aq) | <urn:uuid:88ffcf5c-1025-4008-bf08-9f6e3187583f> | 4.0625 | 293 | Tutorial | Science & Tech. | 51.83259 |
A sequence is a database object that provides a series of integer values.
A sequence has a start value, an increment step value and a minimum value and a maximum value defined when it is created (by using the
A sequence can be specified as having a certain data type which will determine the span of possible values for the sequence. The possible data types are
A sequence with
CYCLEoption will generate its series of values repeatedly.
A sequence with
NO CYCLEbecomes exhausted when the end value has been used, and can not be used any more. (An exhausted sequence can be reset using the
A sequence is created with an undefined value initially.
To generate the next value in the integer series of a sequence the
NEXT VALUEfunction is used, see NEXT VALUE. When this expression is used for the first time after the sequence has been created, it establishes the initial value for the sequence. Subsequent uses will establish the next value in the series of integer values of the sequence as the current value of the sequence.
It is also possible to get the current value of a sequence by using the
CURRENT VALUEfunction, see CURRENT VALUE. This function can not be used until the initial value has been established for the sequence (by using
NEXT VALUEfor the first time).
If a sequence is dropped with the
CASCADEoption in effect, column defaults referencing the sequence will be removed, but the columns will still exist. Similarly domain defaults referencing the sequence will be removed, but the domains will still exist. Other objects referencing the sequence will be dropped.
Mimer Information Technology AB
Voice: +46 18 780 92 00
Fax: +46 18 780 92 40 | <urn:uuid:068fbbb1-22ca-4c5a-bcec-41492334518a> | 3.0625 | 354 | Documentation | Software Dev. | 39.856748 |
Molecular 'amplifier' boosts DNA computing
DNA-based computing just got a big boost. A method of amplifying weak chemical signals in a way that can be tailored to specific molecules has brought DNA-based circuits closer to practical applications.
Machine made of electricity and microbes
MECs are modified versions of microbial fuel cells, which are used to harvest electrons produced by metabolising microbes as they feed to generate electricity. The electrochemical reactions are balanced when the used electrons are combined oxygen and hydrogen ions also released by the microbes to form water.
Logan's MECs are like microbial fuel cells in reverse. Instead of charge being drawn out, it is pumped in, and the hydrogen ions combine with electrons alone to form hydrogen gas. Applying roughly 0.5 volts provides enough energy to drive thermodynamically unlikely chemical reactions that break down the dead-end products that limited previous attempts to ferment hydrogen.
Water-gathering machine based on spider webs
A portable dew-harvesting kit inspired by a spider's web is being developed by Israeli architects for use in areas where clean and safe water is scarce.
Reading mind of paralyzed guy
Electrodes have been implanted in the brain of Eric Ramsay, who has been "locked in" - conscious but paralysed - since a car crash eight years ago.
These have been recording pulses in areas of the brain involved in speech.
Now, New Scientist magazine reports, they are to use the signals he generates to drive speech software.
Scientists designing reality wormholes
[They] came up with the idea by building on the mathematical theory that gave us the invisibility cloak - a device that was realized for microwaves last year. Whereas in an invisibility cloak rays of light are guided around a cylindrical or spherical volume like water flowing around a stone, a wormhole would have light guided around a more elaborate, tubular shape. | <urn:uuid:ef46070d-8f62-495d-a257-9a5626778f5c> | 3.546875 | 390 | Content Listing | Science & Tech. | 27.759231 |
Photo: rofanator (Flickr)
Here’s a neat question you may have never thought to ask. How far away is the horizon?
Think about it. The Earth seems flat from our viewpoint, and if you are in a desert or out at sea you get a sense that the earth extends indefinitely in every direction. This isn’t correct, though; the planet is round, so at some point the ground must drop away. When it drops below your angle of vision, you can’t see it any more, and that’s what we call the horizon.
So how far can you see before the planet curves away? If you’re six feet tall, the answer is about three miles. Surprised? You aren’t alone. Try asking a friend next time you’re at the beach on a clear day to guess how far out across the ocean you are looking. She’s more likely to say twenty or fifty miles than just three.
Where Is The Horizon Line?
Now that we’re thinking about horizons, here’s another cool thing to think about. The horizon is three miles away on earth. But elsewhere in the solar system it’s closer or farther, depending on the size of the body you’re standing on!
Take the moon. The moon is two thousand, one hundred and sixty miles in diameter, only about one quarter the size of the earth.
So the curvature at its surface is much more noticeable, and the horizon is much closer. It’s only about 1.5 miles away.
One cool result? The surface bends so quickly on the moon that it’s possible to stand inside some of the largest impact craters and not know you’re in one. The walls of the crater are below the horizon on all sides! | <urn:uuid:5264a4c5-8a24-4787-b16d-68f9e1917e88> | 3.828125 | 387 | Knowledge Article | Science & Tech. | 73.961219 |
I have been trying to find an acceptable definition of the "sum" of two natural numbers. Wikipedia has come close to what I am looking for. They begin by saying:
Let n' be the successor of n, that is the number following n in the natural numbers, so 0'=1, 1'=2. Define a+0=a.
I get all the above. They then continue by saying:
Define the general sum recursively by a + (b') = (a+b )'. Hence 1+1=1+0' = (1+ 0)'=1'=2.
I see the truth in everything that they are saying in the immediately preceding. However, I fail to see how that gives us a general definition for the sum of two natural numbers. I was really expecting something more along the lines of, "c is the sum of the natural numbers a and b if and only if blah blah blah." Anyway, can someone please tell me how I interpret the above as the definition of two natural numbers?
Thanks for any input. | <urn:uuid:26d62115-ed5d-4d1d-9526-fc6378df24d0> | 2.71875 | 225 | Q&A Forum | Science & Tech. | 72.775 |
This Week: Ancient water = ancient habitat?
In the News: Methane on the menu in the Gulf of Mexico?
Coming Thursday: Roaches: A lot smarter than you thought!
Synopsis: To view neutrinos from distant explosions, astrophysicists have set up thousands of detectors in pure ice at the South Pole. What are neutrinos, and what do these scientists hope to learning from them? Find the article: Chasing Neutrinos at the South Pole Illustration: The Why Files IceCube sees both cosmic rays and neutrinos from [...]
Synopsis: Native American agriculture was often a sophisticated response to a challenging environment. What were the secrets of permaculture, companion cropping and corn farming? Could these techniques contribute to modern farming? Find the article: Farming: Native American style Courtesy Eve Emshwiller, University of Wisconsin-Madison A woman in Peru’s highlands harvests oca, the white tubers in [...]
Synopsis: Hurricanes, the most powerful and dangerous storms of all, get their energy from the difference in temperature between a warm ocean and a cooler atmosphere. A century ago, hurricanes blew in with almost no warning; now they are tracked from the sky and space, and every year, warnings get a bit more useful. How [...]
How do hurricanes form? How do we predict their paths? How can we improve predictions?
Finally, an A-to-Z encyclopedia of ionizing radiation — but one that omits key topics.
“Yes, but…” is the word from the frontiers of physics. The world’s largest atom smasher has blasted protons against each other with such enormous energy that they have — apparently — appeared in the debris of decaying particles. At last, matter can have mass!
Classroom Activity Page: Hydraulic fracturing, or fracking, is a high-pressure technique for cracking rocks and allowing natural gas to reach wells. Amid a boom in U.S. natural gas production, industry promises that fracking will bring Americans jobs and low-cost energy for decades. Opponents warn that the drilling-and-fracking process threatens to pollute air, surface water, and most importantly, groundwater. Will these concerns stymie an ongoing boom in natural gas production? Should they?
The ocean’s most valuable fish are caught in a vise. Areas known as dead zones are encroaching on their living zones and pinning them closer to the surface, where they are more vulnerable to becoming the day’s catch. The predicament is yet another side effect of climate change.
For 15 years, we’ve presented the science behind the news. The Why Files are accurate, engaging, entertaining and educational. Check our links from national science teaching standards to specific Why Files — all 750 of them! Whether it’s geology or archaeology, weather or human behavior, The Why Files has it covered.
Experiment finds Earth “dragging” spacetime, as Einstein predicted. Einstein knew his physics. Bending light, gravity lenses, shifting spacetime, spinning neutron stars: he called them all.
Earth’s orbit subtly changes over thousands of years, in complex cycles that affect the timing and delivery of sunlight to various regions of the globe. Climatologists have said that when this “Milankovitch cycle” warms the Arctic, it somehow warms the Antarctic. A new study finds that the cycle acts more directly.
High-speed movies of popping bubbles show a ring of “daughter” bubbles forming around the edge. A close look reveals a third generation of “granddaughter” bubbles. How does this happen? Does this matter to real-world medicine and climatology? And can we get paid to play with bubbles?
Adding nanotubes makes a stronger plastic, but adding several nano-structures greatly increases the benefit, according to a new study from India. Read about the frontier of material science.
Underground nuclear tests have been the biggest roadblock to a comprehensive test ban. How are these explosions detected, and how reliably? | <urn:uuid:cb3c50dd-df5c-452f-9115-a85c9e461750> | 2.734375 | 848 | Content Listing | Science & Tech. | 47.479633 |
The Sixth Extinction
Il Sole 24 (Italy), January 13, 2008
Last fall, the organizers of the Rome Science Festival asked me to come give a lecture about mass extinctions--about how our planet has experienced huge die-offs in the past, and whether it may be on the verge of another die-off today. Only after I began to prepare my talk did I realize how fitting it was to speak of such matters in Italy. For it is in Italy that some of the most important advances in understanding extinctions have taken place.
The first advance was the most simple and yet the most profound: the realization that rocks store a record of life’s history. In 1666 two fisherman caught a giant shark near Livorno. It was so extraordinary that it was delivered to Florence to be dissected by the great anatomist Nicholas Steno. As Steno cut apart the enormous fish, he was struck by how much its teeth resembled mysterious objects known as tongue stones. Tongue stones were triangular pieces of rock that had been known for centuries. They were generally thought to be “sports of nature.” Geometrical forms somehow impressed themselves on rocks, producing both the repeating structures of mineral crystals as well coils, stripes, or--in the case of tongue stones--triangles.
But Steno had a different idea. He wondered if the tongue stones were petrified teeth of long-dead sharks. In the twenty-first century, this seems like an inevitably obvious conclusion. But in the seventeenth century it was nothing of the sort. The journey from a shark’s mouth in the ocean to a rock on dry land was hard for most of Steno’s contemporaries to imagine. Fortunately, Steno lived during the scientific revolution, when some alchemists and natural philosophers were beginning to argue that matter was made up of invisible corpuscles--what we would call molecules and atoms. Steno argued that after animals died their teeth, bones, and shells could be transformed, corpuscle after corpuscle, into stone. As animal remains slowly fossilized, they were incorporated into rocks.
Steno traveled through the Italian countryside to ponder how this might happen. Gazing at cliffs and hillsides, he concluded that all rocks and minerals were originally fluid. Floating on the surface of the planet long ago, they gradually settled out of the ocean and formed horizontal layers, with new layers forming on top of older ones. Molten rock sometimes intruded into the rocks, spreading out on the surface of the Earth to form new layers of their own. As these rocks formed, they buried animal remains, allowing them to be transformed to fossils. Thus Steno could explain how, for example, a sea shell could end up on top of a mountain.
Later generations learned how to read those rock layers, to discover their relative ages, and to use the fossils they contained to create a history of life. And they were astonished to discover that some fossils belonged to species that no longer existed. In Italy, for example, fossils of elephant-like creatures were discovered in the eighteenth century. Georges Cuvier, the founder of modern paleontology, pointed out that elephant fossils were found in many places where no elephant lives today. Cuvier was also famous for being able to distinguish species based on subtle features. He demonstrated that the teeth of fossil elephants found in places like Italy were different from the teeth of elephants today. In fact, they were different enough to belong to a different species--a species, he claimed, that no longer exists. It had, Cuvier declared, become extinct.
Extinction, nineteenth-century paleontologists realized, was a dominant feature of the history of life. The fossil record is made up of mostly species that emerge and then disappear. Many of those species were nothing like any creature alive today. Scientists could divide the history of life into eras based on how emergence and disappearance of species. The Mesozoic Era, for example, stretched from 250 million years ago to 65 million years ago. The end of the era was marked by the extinction of giant dinosaurs, marine reptiles, and other strange creatures we don’t see around us today. Their place was taken by mammals, including our own primate ancestors.
Up until 30 years ago, most scientists believed these transformations were unimaginably slow. Extinction rates rose over the course of many millions of years and then subsided again. But the rocks of Italy once again revealed an important clue to the nature of mass extinctions: they can happen very quickly.
Walter Alvarez, a geologist at the University of California at Berkeley, found that a gorge near the town of Gubbio contained rocks that had formed precisely at the end of the Mesozoic Era. When he and his colleagues analyzed the chemistry of the rocks, they were surprised to find it loaded with a rare element called iridium. Alvarez proposed that an iridium-rich comet or asteroid had crashed into Earth 65 million years ago, and the impact showered iridium-laced dust around the planet.
Alvarez inspired a generation of geologists and paleontologists to search for evidence of the impact. We know now exactly where the impact took place--along the coast of the Yucatan. We now know that the impact triggered tidal waves, global forest fires, and environmental havoc. And most experts generally now agree that the impact was at least partly responsible--or perhaps entirely so--for the mass extinctions at the end of the Mesozoic Era. In a geological instant, half of all species on Earth became extinct.
The discovery of a dinosaur-killing impact prompted scientists to take a fresh look at how rapid environmental changes can cause biodiversity to collapse. Today, the most intriguing of these mass extinctions is the one that struck 250 million years ago, ending the previous era, known as the Mesozoic. It’s sometimes called the Great Die-Off, because it claimed over 90 percent of all marine animals and over 70 percent of species on land.
While many sites around the world preserve rocks from this age, some of the best-studied are, once more, in Italy--in particulary, in Butterloch Canyon in the Dolomites. These rocks record an epic of unparalleled ecological collapse. On land, for example, huge forests disappeared, replaced by vast expanses of weedy plants called club mosses that dominated ecosystems for millions of years.
In 2003, a team of scientists claimed to have found evidence that another impact coinciding with the Great Die-Off. But since then, other researchers have not been able to confirm the finding, and in general they remain skeptical. They don’t know exactly what caused the mass extinctions, but the strongest candidate is a colossal flow of lava that covered much of Siberia. It released heat-trapping gases, such as carbon dioxide and methane that may have created a stifling climate. The warmth then caused the oceans to become starved of oxygen.
Some researchers argue that these conditions triggered an explosion of a certain type of bacteria, known as sulfate-reducers. These microbes live today in swamps and ocean muck; they produce hydrogen sulfide, which creates the noxious odor of rotten eggs. Hydrogen sulfide also highly toxic. It’s possible that this gas killed or at least seriously harmed marine organisms. The gas that escaped the ocean may have harmed life on land directly. Or it may have wreaked havoc by helping to destroy the ozone layer. In the Dolomites, as well as in other places in Europe, Asia, Africa, and North America, paleontologists have found a huge number of deformed fern spores coinciding with the Great Die-Off. It’s possible that they mutated because the ozone layer had disappeared, allowing cosmic rays to reach the surface of the Earth.
This research has deep implications for the future of life on Earth. For the first time in the history of life, a single species is driving many others extinct. Humans are hunting species to oblivion, decimating them with pollution, and destroying their habitats. Scientists estimate that the current rate of extinctions is a thousand times higher than the ordinary rate of extinctions recorded by fossils. Some projects foresee the rate reaching ten thousand times higher.
Missing from many of these projections is the effect of global warming. We are now playing the part of volcanoes, putting heat-trapping gases into the atmosphere at a rapid rate. As temperatures rise, biologists are finding that the ranges of species are shifting. In some cases, the ranges may shrink, leaving species more vulnerable to extinctions. Estimating how many extinctions will occur thanks to climate-driven range shifts is difficult, as scientists are hobbled by many uncertainties. But the Intergovernmental Panel on Climate Change estimates that twenty to thirty percent will likely be at high risk of extinction if the global mean temperature rises 2 to 3 degrees C. That toll would come on top of the one we’re already inflicting by other means.
But the fossil record shows that to understand the full impact of what we’re doing to life on Earth, we must think on a bigger scale. Changing the Earth’s climate isn’t a simple matter of adjusting a thermostat. Many unexpected things can come from warming the planet. In ten thousand years, will our descendants have to defend themselves from a planetary miasma of sewer gas? Will we trigger another Great Die-Off? We can’t say, but we also can’t eliminate the possibility. It’s easy to ignore these possible long-term effects of what we do today. Politicians are not thrown out of office for what will happen in a thousand years. Indeed, the problem is neurological: our brains are not well-adapted to think more than a few years into the future.
But if Steno could look at the hills of Italy and begin to understand that how shark teeth could be turned to stone in the past, then we can at least try to understand that our impacts on life will linger long after we are dead.
Copyright 2008 Carl Zimmer | <urn:uuid:21685371-161d-499b-8504-bf9146563b1a> | 2.9375 | 2,071 | Nonfiction Writing | Science & Tech. | 43.994835 |
The history of the Universe divides roughly into three regimes which reflect the status of our current understanding:
The standard cosmology is the most reliably elucidated epoch spanning the epoch from about one hundredth of a second after the Big Bang through to the present day. The standard model for the evolution of the Universe in this epoch have faced many stringent observational tests.
Particle cosmology builds a picture of the universe prior to this at temperature regimes which still lie within known physics. For example, high energy particle acclerators at CERN and Fermilab allow us to test physical models for processes which would occur only 0.00000000001 seconds after the Big Bang. This area of cosmology is more speculative, as it involves at least some extrapolation, and often faces intractable calculational difficulties. Many cosmologists argue that reasonable extrapolations can be made to times as early as a grand unification phase transition.
Quantum cosmology considers questions about the origin of the Universe itself. This endeavours to describe quantum processes at the earliest times that we can conceive of a classical space-time, that is, the Planck epoch at 0.0000000000000000000000000000000000000000001 seconds. Given that we as yet do not have a fully self-consistent theory of quantum gravity, this area of cosmology is more speculative.
The following diagram illustrates the main events occurring in the history of our Universe. The vertical time axis is not linear in order to show early events on a reasonable scale. The temperature rises as we go backwards in time towards the Big Bang and physical processes happen more rapidly. Many of the transitions and events may be unfamiliar to newcomers; we shall explain these in subsequent pages.
The timescales and temperatures indicated on this diagram span an enormous range. A cosmologist has first to get the order of magnitude (or the power of ten) correct. Quantities which are given as 10 to some power 6 (say) are simply 1 followed by 6 zeros, that is, in this case 1,000,000 (one million). Quantities which are given as 10 to some minus power -6 (say) have 1 in the 6th place after the decimal point, that is, 0.000001 (one millionth). At extremely high temperatures we tend to use gigaelectron volts (GeV) instead of degrees Kelvin. One GeV is equivalent to about 10,000,000,000,000K.
[Back][Hot big bang][Galaxies][Relic radiation][Cosmic strings][Inflation][Cosmology][Next] | <urn:uuid:fc6278d3-205a-4846-bb3c-9f25bd3f90ea> | 3.5625 | 523 | Knowledge Article | Science & Tech. | 39.517691 |
Contact: Dr. Hanno Teeling
Caption: Flavobacteria (green) occur both free living and attached to microalgae in the North Sea. In this image some flavobacterial cells accumulated around a microalgae cell (chloroplasts in red). All other cells are shown in blue. The technique of Fluorescence in situ Hybridization that was used in this image allows for the staining and visualization of bacteria in the intact sample without the need of prior cultivation.
Credit: P. Gomez-Perreira/B. Fuchs
Usage Restrictions: None
Related news release: Nutrient supply after algal bloom determines the succession of the bacterial population | <urn:uuid:8575352a-4b26-4ed1-bfa9-df38b445c631> | 3.3125 | 138 | Truncated | Science & Tech. | 34.546316 |
50 years - Our future
Global warming is an issue that will have to be solved sooner rather than later. Between 2031 and 2060, the annual average temperature in Europe will raise (in a best case scenario) up to 2° Celsius – in southern Austria and souther Europe even up to 2,5° C. The result will be heat waves (which will take its toll on temperature sensitive people) and dry periods, the lack of rain making it harder for crops and plants to grow. There might be shortages on bread and other products made of wheat and other crops. 2° C does not sound much? Will animals like cows, sheeps and horses that do not get enough to eat and have to starve agree to that? Will people that are going to be affected by floods agree with that? Will people not affected by floods but by drinking water shortages agree to that? Probably not. Peasants will have to react and cultivate millet instead of wheat, which is more temperature resistent. Forest rangers will have to change the types of trees in their forests. While European beeches will be able to withstand higher temperatures, European spruces – according to experts - will not be.
Animals that are already on the Red List of endangered creatures will probably be extinct by the year 2060 if the climate change is not stopped and the protection of those animals not amplified. In Austria, the Red List contains animals such as the crested newt, the Eurasian spadefoot toad, the European green lizard, common wall lizard and the dice snake. On the brink of extinction in Austria is the European Terrapin, the sand viper and the meadow viper. Do you really want to loose these precious animals?
The deforestation that is happening all over the world it not helping to stop climate change either. If we continue cutting them down at the same rate we do now, in 2050, 230 million hectar will disappear (and that is a size of 460 million soccer fields!!!). Trees are not only important to absorb carbon dioxide, they also give living environment to a lot of different kind of animals, like birds, monkeys, tigers and many more. Speaking of tigers. Did you know that in 2010, only 3,200 tigers still existed in the wild? Only 100 years ago, there were more than 100,000. If no action is taken to save them, in 2060 no more tigers will live on this planet. They will not even make it to the next year of the tiger in 2022.
But not only the raise of the atmospheric temperature will be an issue, the rise of the water temperature is also going to be a problem.
Already, the North Pole has lost 10 % of its pack ice surface within the last 30 years. Until the end of the 21st century, its surface might loose up to 50 %, with it reducing the living space of polar bears, different penguin and seal species. The melting of not only the Arctic (North Pole) but also the Antarctica (South Pole) might result in an increase of the water level up to 8 meters (if both North and South Pole were to melt entirely the water level would rise up to 64 meters!). Islands would disappear, countries would become smaller and decrease the living environment of animals and humans. The atmospheric temperature would rise even more, since the (melted) ice will no longer be able to reflect the sun.
And that is not all. Not only will the Antarctic krill – which is the staple diet of many fish an wales who would loose their food – be a victim of higher water temperatures, also corals will suffer severely from the rise.
The crisp pillow coral and the elegance coral, as well as other tropical coral reefs, might be extinct by 2050 according to experts of the London Zoo, if the water temperature is continuing to increase. Why are these underwater ecosystems so important you might ask? For one, they are a natural protection against surf. If it were not for coral reefs, villages close to the beach could not exist for the waves would destroy them. Furthermore, islands and beaches would be denuded faster than they are.
Coral reefs are also the habitat and the spawning ground of many different kind of fish, mussels and shellfish. The reason why so many organisms can survive there is the fact that coral reefs absorb carbon dioxide, not only from the water but from the air as well.
Another important fact is that coral reefs are also the source for many important medications and experts even put high hopes into coral organisms to produce substances that slow the impact of aids and cancer.
These are only a few reasons why coral reefs are so important and why they need to be protected. In 2010, Australia complained that the climate change is responsible for the bleaching of its coral reef around the Lord-Howe-islands. The bleaching of corals is the first sign that a coral reef is not intact and that action has to be taken or it will be lost forever.
You ask yourself what else can happen within the next 50 years?
Aside from the impacts of global warming and climate change, there is also to mention the fact that the oil in place is getting smaller and smaller. Some experts say the reserves will last only 20 more years, other experts say they will last another 40 to 50 years. But what will happen, when there is no more oil to drill? Where will we get our energy from? How will we warm up our houses and appartements? How will we drive our cars?
Do you want to live in a scenario as mentioned above? Do you want your children to face such a future? Sure, it might sound farfetched and drastic at times and who really knows how our planet adjusts (or does not adjust) to these changes? The fact remains though that if things do not change, the future – if not in 50 years, then maybe in 80 or 100 years – will be a grim one.
Instead of burying your head in the sand now, let me tell you that it is not too late to change something. Alternatives for crude oil exist, renewable energies are and will further be explored and applied. Massive deforestation has to stop and reforestation has to be encouraged by governments all over the world. Many societies, ecological groups and businesses work on saving and reforesting the rain forest and other forests. They will create new habitats for crawling creatures, repitles, endangered birds and orangutans. Not to forget the tigers, of course. The WWF's goal is to double the number of tigers to 6,400 until 2022.
And each and every one of us can do something – starting with saving energy, recycling and using renewable energies – to make this world a better place. To guarantee that we and our children and our children's children will have a great life 50 years from now. And to ensure that in 50 years, the crested newt and the sand viper will still live in Austrian lakes and forest.
Article by Nathalie W. | <urn:uuid:a4dbe7e7-46e4-4344-82d6-27d20041c0e0> | 3.140625 | 1,433 | Personal Blog | Science & Tech. | 59.994118 |
Guile classifies Scheme objects into two kinds: those that fit entirely
SCM, and those that require heap storage.
The former class are called immediates. The class of immediates includes small integers, characters, boolean values, the empty list, the mysterious end-of-file object, and some others.
The remaining types are called, not surprisingly, non-immediates.
They include pairs, procedures, strings, vectors, and all other data
types in Guile. For non-immediates, the
SCM word contains a
pointer to data on the heap, with further information about the object
in question is stored in that data.
This section describes how the
SCM type is actually represented
and used at the C level. Interested readers should see
libguile/tags.h for an exposition of how Guile stores type
In fact, there are two basic C data types to represent objects in
|• Relationship between SCM and scm_t_bits:|
|• Immediate objects:|
|• Non-immediate objects:|
|• Allocating Cells:|
|• Heap Cell Type Information:|
|• Accessing Cell Entries:| | <urn:uuid:ae0b7834-1dc3-4de5-b071-5172a5fd359e> | 2.71875 | 259 | Documentation | Software Dev. | 37.400142 |
When you compare the Earth’s magnetic fields with those of Mars you begin to understand why our planet is truly such a magic place. Life could be prolific in our universe but it takes a very special set of circumstances for it to thrive. In order for life to not just exist but to thrive some of the things it needs include right temperature, a source of food, energy, water, air, and the protection from radiation and solar winds that our magnetic field provides. You cannot underestimate how important this protection is. Our planets atmosphere is reliant on the electric dynamo that lives at the center of our planet. The spinning iron core generates a huge electric current which in turn creates our magnetic shield. Without it the solar winds would slowly scour our atmosphere away until there was nothing left. Taking our water with it. If you look at Mars you can see the end result. At one time Mars was more than a little Earth like. It had large amounts of liquid water, [...]
Home / Posts tagged 'water'
History Repeats itself….sigh NASA held a news conference today to reveal what one of the program scientists said was an announcement “for the history books”. Well……..if the history books are about how history repeats itself then they are right. NASA announced the findings in this NASA Press Release that they have found The lander found water and one-carbon organics. The water seen by SAM does not mean the drift was wet. Water molecules bound to grains of sand or dust are not unusual, but the quantity seen was higher than anticipated. SAM tentatively identified the oxygen and chlorine compound perchlorate. This is a reactive chemical previously found in arctic Martian soil by NASA’s Phoenix Lander. Reactions with other chemicals heated in SAM formed chlorinated methane compounds — one-carbon organics that were detected by the instrument. The chlorine is of Martian origin, but it is possible the carbon may be of Earth origin, carried by Curiosity and detected by SAM’s high sensitivity design For those of you old enough you may remember Viking also found signs of organics/life in it’s [...]
Smallest Recorded Amount of Summer Arctic Ice Ever Still don’t think global warming is real? The Arctic Ocean appears to have reached its annual summertime minimum ice extent and broken a new record low on Sept. 16, as reported by the National Snow and Ice Data Center. NASA and the NASA-supported NSIDC analysis of satellite data at the University of Colorado in Boulder showed that the sea ice extent shrunk to 1.32 million square miles (3.41 million square kilometers). The new record minimum measures almost 300,000 square miles less than the previous lowest extent in the satellite record, set in mid-September 2007, of 1.61 million square miles (4.17 million square kilometers). For comparison, the state of Texas measures around 268,600 square miles. NSIDC cautioned that, although Sept. 16 seems to be the annual minimum, there’s still time for winds to change and compact the ice floes, potentially reducing the sea ice extent further. NASA and NSIDC will release a complete analysis of the 2012 melt season next month, once all data for September are available. | <urn:uuid:e04e9be8-ee70-4d07-b3d3-f44db47843f1> | 2.8125 | 660 | Content Listing | Science & Tech. | 54.054101 |
|Ivars Peterson's MathTrek|
September 27, 1999
If each tile consists not of a single square but of a certain number of squares joined together along their edges to form a unit, the problem of determining whether you can use such tiles to cover a rectangular floor flawlessly gets more complicated.
Indeed, mathematicians have proved that the general question of whether it's possible to cover the plane (or even a smaller region, such as a rectangle) with identical copies of a given finite set of tiles (or even a single geometric figure) is, in principle, computationally undecidable. In other words, there's no cookbook recipe or handbook procedure that you can routinely apply to indicate whether you can fit together copies of an arbitrary shape to form a rectangle.
Mathematicians, however, have solved a variety of special cases of the tiling problem in two dimensions, particularly those that involve shapes known as polyominoes--forms that cover connected squares on a checkerboard. The term polyomino was coined in 1953 by mathematician Solomon W. Golomb, now at the University of Southern California in Los Angeles.
There is only one type of monomino (the unit square by itself) and one domino (two squares stuck together along one edge). There are two distinct trominoes (three squares) and five different tetrominoes (four squares). As the number of connected squares increases, the number of different possible configurations grows rapidly.
Polyominoes are the basis of thousands of mathematical puzzles. Cristopher Moore of the Santa Fe Institute in New Mexico has focused on the problem of determining how many different tilings of rectangles of various widths are possible using a given type of polyomino. In a recent preprint (http://xxx.lanl.gov/abs/math.CO/9905012), he calculates the number of ways a rectangle 4 units wide and n units long can be tiled with right trominoes.
Suppose you have a 4 x n rectangle, where n is a multiple of 3. It turns out that you need to consider only three types of interfaces when fitting right trominoes together into a strip of the required width and length. For example, two trominoes fit together to form a 2 x 3 rectangle, and two such rectangles stacked one on top of the other produce a 4 x 3 rectangle. There are four ways to do the stacking. These configurations all result from what Moore describes as a "straight" interface for building rectangular strips.
Two other interfaces are also possible: deep jog and shallow jog.
Examples of interfaces with a deep jog (left) and a shallow jog (right).
Because the number of possible interfaces is limited to three, Moore could derive a formula that gives the number of different ways to tile rectangles of different sizes. There are four ways to produce a 4 x 3 rectangle (see above), 18 ways to produce a 4 x 6 rectangle, 88 ways to produce a 4 x 9 rectangle, and 468 ways to produce a 4 x 12 rectangle. By definition, there is only one way to build a 4 x 0 rectangle.
[Technical details: The number of ways of tiling a m x n rectangle with any finite collection of shapes, where m is fixed, can be found by calculating the nth power of a matrix whose rows and columns correspond to the various interface shapes a partial tiling may have, Moore says. For the three interfaces possible for right trominoes, he solves a system of linear equations to obtain the formula, or generating function, G (z) = (1 - 6z)/(1 - 10z + 22z2 + 4z3). The terms of the Taylor expansion of G give the number of ways to tile rectangles of size 4 x 0, 4 x 3, 4 x 6, and so on: 1, 4, 18, 88, 468, 2672, 16072, . . ..]
Moore also worked out formulas giving the number of different ways to tile rectangles of width 5 with right trominoes and rectangles of width 4 with L tetrominoes and T tetrominoes.
You can prove that T tetrominoes cannot tile any rectangles of width 5, 6, or 7. Indeed, a rectangle can be tiled with T tetrominoes only if its length and width are both multiples of 4.
Nonetheless, that still leaves a lot of different patterns you can try out when tiling your bathroom floor with polyominoes.
Copyright 1999 by Ivars Peterson
Gardner, M. 1988. Polyominoes. In Hexaflexagons and Other Mathematical Diversions: The First Scientific American Book of Mathematical Puzzles and Games. Chicago: University of Chicago Press.
Golomb, S.W. 1994. Polyominoes: Puzzles Patterns, Problems, and Packings, 2nd. ed. Princeton, N.J.: Princeton University Press.
Klarner, D.A. 1998. My life among the polyominoes. In Mathematical Recreations: A Collection in Honor of Martin Gardner, D.A. Klarner, ed. Mineola, N.Y.: Dover.
Moore, C. Preprint. Some polyomino tilings of the plane. Available at http://xxx.lanl.gov/abs/math.CO/9905012.
Peterson, I. 1990. Beyond chaos: Ultimate unpredictability. Science News 137(May 26):327.
______. 1990.Islands of Truth: A Mathematical Mystery Cruise. New York: W.H. Freeman.
______. 1987. Pieces of a polyomino puzzle. Science News 132(Nov. 14):310.
______. 1986. Games mathematicians play. Science News 130(Sept. 20):186.
Cristopher Moore has a Web page at http://www.santafe.edu/~moore/.
Additional information about polyomino tiling can be found at http://www.treasure-troves.com/math/PolyominoTiling.html, http://www.ics.uci.edu/~eppstein/junkyard/polyomino.html, and http://www.cwi.nl/~jankok/etc/Polyomino.html.
Comments are welcome. Please send messages to Ivars Peterson at email@example.com. | <urn:uuid:b7eb3eb2-839f-4812-a6c5-22623d7a6898> | 3.453125 | 1,350 | Nonfiction Writing | Science & Tech. | 62.546886 |
Freshwater fish in salt water
What would actually happen if a fresh water fish had to live in salt water?
For most fish, they would die. But some, like eels and salmon, can move
freely between the two at certain stages of their lives. To do this they have special
mechanisms of excretion and absorption of salt and water.
If you put a freshwater fish into saltwater, most fish would lose weight
(from losing water from its body) and eventually die. Approximately 2% of all 21000
species of fish actually move from freshwater to saltwater or from salt to fresh at some
point in their lives, the move would kill any other fish. But even with these special
varieties of fish, the move must be gradual so their bodies can adjust, or they too,
will die from the change. If you want to learn more about why the freshwater fish will
lose water, (or why a saltwater fish in freshwater would gain water), look up the words
"diffusion" and "osmosis".
Tom F Ihde
Click here to return to the Biology Archives
Update: June 2012 | <urn:uuid:94d400b1-5d24-4a24-8037-fb3751a20ea3> | 3.390625 | 242 | Knowledge Article | Science & Tech. | 58.42913 |
Atoms and Substrate Images
Date: March 2009
Back in 1989, scientists at the IBM Research Center in San
Jose, California conducted an interesting activity using atoms. The
scientists manipulated 35 atoms of the gas xenon on a nickel
substrate, to write the letters, IBM.
Why are none of the nickel substrate atoms visible? I have seen
other images, since then, with much the same issue: Where are the
atoms of the substrate? It always looks smooth! Please help me
explain this to my students.
Imaging at atomic scale is quite different than how people see things at our
scale. Nanoscale imaging, unlike our eyes, doesn't use light, lenses and
detectors, and that means the results may seem counter-intuitive compared to
how human eyes work. However, with a little understanding of how nano
imaging works, the images produced will make more intuitive sense.
In the famous IBM image, a type of instrument called an STM (scanning
tunneling microscope) was used. The principle of operation of an STM is that
a very small pointy tip is moved very close to a surface, and when it gets
close enough, a small electrical change can be detected. When you move the
tip across a surface and measure the height at which the change occurs, you
can map out a series of heights associated with different coordinates. Think
of it as an atomic topographic map. You can then use software to create an
image of the heights and coordinates that "looks like" a photograph.
In this case, the instrument was set up to image the xenon atoms, but not to
reach all the way down to the nickel surface between the nickel atoms. The
purpose was to emphasize the xenon atoms, not the nickel substrate. That's
why they got the image they did. However, they could have imaged the nickel
had they so desired. If you Google for STM images, you can see lots of
examples of flat planes of atoms being imaged by STM.
Hope this helps,
The way the "atoms" are imaged is through a process called Atomic Force Microscopy
(AFM). As you know, all atoms exhibit a repulsive force (Van der Waal) as though
the atom were acting like solid object. AFM uses a technique whereby an atom thin
stylus (like in those old style phonographs for vinyl records) that is dragged
through the surface of a substrate and the "bumps" produced by individual atoms
through their Van der Waal's radius, causes the stylus to deflect. The deflection
is measured as a force and converted to an image. The stronger the deflection, the
stronger the force, the higher the mound depicted in the computer generated image.
There are two reasons the substrate does not appear to have any bumps (and therefore
the atoms in the substrate do not get imaged), is (1) a very uniform patch of the
substrate is used so that the bumps are regularly spaced and predictable (usually
densely packed silicon crystals), and (2) since the image is essentially computer
generated from data, the substrate data -which is very uniform and predictable- can
be deleted so that the added information (such as the IBM letters) becomes clearly
visible in relief.
Greg (Roberto Gregorius)
Once you understand what the Scanning Tunneling Microscope (STM) is
doing, the answer becomes more clear. The STM uses a probe that has
been sharpened to an incredibly sharp point... a point only one or two
atoms at its tip. This probe is "hovered" very accurately over the
xenon atoms. In fact, it passes much less than one atom's diameter
over the xenon atoms (which, by the way, are much larger than nickel
atoms). Using the quantum tunneling effect, the STM (operating via its
probe) electrically senses the presence of the Xenon atoms as the
probe passes over, and hence a 3D map can be made of their presence
(which is in essence what you are seeing). Note that you are not
seeing a photo, but only a map of the electric charge.
Whereas the probe passes (and can sense) the xenon atoms at a distance
much smaller than an atom's diameter, the probe is too far away from
the nickel substrate atoms below, to be able to sense the individual
nickel atoms themselves. In a way, it is as if the nickel background
is blurred out of focus and all the STM can "see" is a blurred
background plane that underlies the xenon atoms.
This is not unlike what happens with a closeup shot using a normal
camera. Suppose you were trying to take a shot of an object that was
positioned some distance in front of very fine black and white
checkerboard pattern. If you focused on the object, it would be very
clear, but the background may be so badly out of focus, it might
appear as a solid, featureless grey background.
Click here to return to the Material Science Archives
Update: June 2012 | <urn:uuid:41356877-a77b-4ffa-b71c-d7eaa54dd115> | 3.875 | 1,100 | Knowledge Article | Science & Tech. | 47.517115 |
Planetary Construction Zone?
Astronomers detect the beginnings of planet formation in a dusty disk surrounding a nearby star
July 5, 2007
The constellation Hydra is named for a twisting snake that, according to Greek mythology, was rejected by the god Apollo and cast up into the sky. For astronomers, however, this region of space is becoming a straight pathway to understanding how the universe works. One of the constellation's star systems, TW Hydrae,* has been the subject of much recent study due to its proximity to our solar system. The star is located 180 light-years away from Earth, close enough to call it a neighbor.
Powerful radio and optical telescopes are providing a better look at TW Hydrae, as well as other regions of the universe. Astronomers have discovered new "dwarf planets" within our solar system, and nearly 200 extra-solar planets orbiting stars quite like our own.
But until recent years, no astronomer had observed planet formation from its early stages of infancy. In 2005, David Wilner, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, discovered that the gaseous disk surrounding TW Hydrae holds vast swaths of pebbles extending outward for at least one billion miles.
The pebbles could be the stuff that future planets will be made of. The planet formation process, according to common theory, begins when dust grains in a disk collide and accrete to form larger and larger clumps. Eventually, after millions of years of colliding and combining, the clumps form planets.
Wilner and his colleagues used the National Science Foundation (NSF)-funded Very Large Array (VLA) radio telescope to measure the strength of radio waves emitted by TW Hydrae. Based on the relationship between wavelength and particle size, they determined the grainy materials surrounding the star to be centimeter-sized.
According to Wilner, the team's discovery came almost by accident and with a good dose of irony. One of the collaborators, Mark Claussen of the National Radio Astronomy Observatory, thought the strong and variable emissions detected from TW Hydrae in previous x-ray detections indicated magnetic activity common in young stars. Claussen thought that if they monitored TW Hydrae at radio wavelengths for a period of a few months, they could determine if the emissions might be strong enough to image at a much higher resolution with the NSF-funded Very Long Baseline Array and study this activity. To their surprise, they found that the radio emissions did not vary significantly.
"Frankly, it was a puzzle," said Wilner. "I had it on my desk for about a year with no idea what to do with it."
He decided to revisit the VLA. The observatory's twenty-seven operating antennae are spread throughout the plains of San Agustin, N.M., and arranged in one of four configurations that are changed every few months. In their closest configuration, the antennas cover about 0.6 miles (1 kilometer), while in the largest configuration, they span up to 22 miles (36 kilometers) across. At its highest frequency, the telescope has a resolution of .04 arc seconds. To put it in perspective, if Tiger Woods' eyes had this same capacity, the champion golfer would be able to spot a golf ball 100 miles away!
Wilner found his pebbles using a larger configuration and higher angular resolution of the VLA. He enlisted the help of Nuria Calvet, a colleague at the Center for Astrophysics, who created a computer model of the disk surrounding TW Hydrae using previously published data.
"For the first time, you could see dust emissions of grains that had evolved into such a large size," said Wilner. "This is a crucial step in the formation of planets." Wilner published his research in the June 20, 2005, issue of the Astrophysical Journal Letters.
Wilner's examination of TW Hydrae began in the late 1990s, enabled by the new capabilities of telescopes. "TW Hydrae is an important young stellar system and unique in being nearby," he said.
It is only 5 to 10 million years-old, a mere toddler compared to our 5 billion-year-old Sun. The younger star is four-fifths the size of the Sun, and its surrounding disk has a radius equal to about 200 times the distance from Earth to the Sun.
Wilner believes the current project to enhance the VLA will allow him and others to explore star systems beyond TW Hydrae.
NSF is currently refurbishing and updating the telescope's receivers to allow increased data sensitivity, more efficient transmission of data, and fine-tuned estimates of how emissions vary with frequency. Half a dozen receivers have been outfitted so far and the project will be completed in 2011.
"The VLA is a tremendous facility," said Wilner. "The upgrades will make everything ten times faster."
Using the VLA and other advanced instruments, Wilner and his colleagues hope they will be able to better understand how solar systems evolve. Just recently, Wilner collaborated with his graduate student, Meredith Hughes, and several other colleagues to identify a hole in TW Hydrae's dusty disk. Wilner says that the hole was probably created when a Jupiter-sized planet cleared that gap of much of its rocky material. This latest research was accepted for publication by the Astrophysical Journal in April 2007.
He expects future research involving planet and star formation will be enhanced by the NSF-funded Atacama Large Millimeter/submillimeter Array (ALMA), which promises to be the world's most sensitive, highest resolution, millimeter-wavelength telescope. In addition to the improved sensitivity and resolution, the new telescope affords another advantage, according to Wilner. TW Hydrae is located in the southern sky, so the ALMA site in the mountains of Chile will allow more detailed imaging of the star.
* WhyTW Hydrae? It comes from a system devised by astronomers to describe a star's brightness. The convention was to start with A, B, C, etc., in order of descending brightness. After all the single letters are gone, they use double letters, such as AA, AB, AC... BA, BB, BC, etc. TW indicates a pretty faint star. But in a cluster with many hundreds of stars, it would be easy to reach that letter combination. (Return to the story.)
Harvard-Smithsonian Center for Astrophysics
Associated Universities Inc/National Radio Astronomy Observatory
#0226933 NRAO Management, Operations and Maintenance
#0223851 Cooperative Agreement for the Management, Operation of the National Radio Astronomy Observatory and Support of Other Scientific Activities
National Radio Astronomy Observatory: www.nrao.edu
Harvard-Smithsonian Center for Astrophysics: http://cfa-www.harvard.edu/ | <urn:uuid:e4ce2df7-d4fb-4720-845b-79fd25357cdb> | 3.640625 | 1,416 | Knowledge Article | Science & Tech. | 44.364323 |
12 November 2010
Posted in NatureWorks
Being a carnivorous animal, an Eastern Indigo Snake’s diet consists of turtles, fish, birds, small alligators and other snakes, venomous and non-venomous. Primiarily found in Central and South Florida, Eastern Indigo Snakes frequent flatwoods, dry glades and sandy soils. Humans are the biggest known threat to these snakes because of highway fatalities, pet trade and habitat destruction. These creatures are enlisted as an endangered species and if you happen to see one in your yard, please contact the Florida Fish & Wildlife Conservation Commission 1-888-404-3922. | <urn:uuid:6d00e7bd-43ea-477f-ac38-ec92df8d743f> | 3.21875 | 129 | Knowledge Article | Science & Tech. | 34.010855 |
Aspecies is the basic unit of biodiversity.
A species is a group of organisms that can interbreed in nature to produce a fertile offspring.
For more information about the topic Species, read the full article at Wikipedia.org, or see the following related articles:
Recommend this page on Facebook, Twitter,
and Google +1:
Other bookmarking and sharing tools: | <urn:uuid:989cad8e-7ce5-4a11-888f-0c63019f3164> | 3.046875 | 79 | Knowledge Article | Science & Tech. | 32.597874 |
Long before the discovery of the first planet beyond our solar system, astronomer Laurance Doyle began theorizing about the habitability of planets around other stars, clarifying the conditions needed for a planet to bear life. Relying on his expertise in signal processing, he now looks for patterns in astronomical data, searching for extrasolar planets.
Recently, Doyle has begun using these same statistical tools to look for patterns in animal communication. Drawing on central concepts of information theory, he and colleagues from the University of California at Davis have precisely measured the complexity of the songs of humpback whales, comparing them with communication in other species—including humans. In the future, he plans to expand this innovative line of research, moving to the next level of understanding animal communication. Not content to understand how much an animal can communicate, he seeks to understand the meaning of the vocalizations of other species.
(Excerpt from an Interview with Laurance Doyle)
QUESTION: How will you know if the planet is habitable?
For a planet to have the potential to be inhabited, it must be the right distance from the star so it will receive the right amount of light. The temperature of a habitable planet should allow liquid water to exist on the surface for long periods of time.
Based on the best available ground- and space-based data, I expected there would be about 350 eclipsing binaries in the Kepler data. Actually, there turned out to be more like 3,000 to 4,000 eclipsing binaries that Kepler sees. Just in our first year, we had to look at tens of thousands of light curves to pick out these eclipsing binaries.
QUESTION: Why should the public care about your research?
This work is important for two reasons. If we don’t find a habitable planet, that means earths are rare. It puts the earth in perspective as a somewhat isolated spaceship. That knowledge may allow us to convey the concept that we need to take care of our own planet, and that would be a good thing. People think about moving to Mars, but Mars’ land surface area is only equal to earth’s (since three-fourths of earth is covered with water). With earth’s population currently doubling every 54 years, moving to Mars would only buy us another half century. So earth is it for now.
If we do find another earth, whether it’s around a circumbinary “earth” or a regular single sun-like star, I think people’s thoughts are going to transition to becoming less self-centered. Finding another earth might also make us think more positively about finding other beings in the universe. We have a very real shot at finding other earths with the Kepler Mission. We could detect a potentially habitable extrasolar planet within the next three years. Kepler is hugely important for the question of life in the universe. This is a key time in history. | <urn:uuid:93b7476e-7be2-4b0a-8c57-2b05bcfbe0db> | 3.875 | 596 | Audio Transcript | Science & Tech. | 45.768321 |
Neutron scattering at ISIS and ILL is being used to develop our understanding of the Earth’s geology and natural environment. You can find out more about ISIS’s natural world research here (link opens in a new window)
Neutron scattering is playing a key role in discovering how silk can be made artificially.
Spider-silk is five times as strong as steel and absorbs three times more energy than the material used in bullet-proof vests. The strength and elasticity of silk could be harnessed for new plastics and biomedical implants if it could be made artificially.
Spiders spin silk from a mix of water and proteins stored as a gel in specialised silk glands inside their bodies. As the gel is pulled through their spinning glands it becomes a very resilient solid that could have many potential uses in the industrial world.
Research teams are using neutron beams tuned for studying biological materials to shine a light on the atomic scale structural changes as the gel transforms into solid fibre. Experiments have unlocked some answers, but more of nature’s secrets remain.
“We are asking how nature makes such amazing materials. Neutron scattering is an excellent technique for understanding the spider’s magic tricks”
Dr Chris Holland, Oxford University Silk Group
Find out more:
Food storage, fertility treatment and transporting medicines could benefit from a new understanding of how lizards survive at low temperatures.
Cold-blooded lizards have only limited ability to regulate their own body temperature. When temperatures fall in winter, so does their body temperature, putting tissues and cells at risk of irreparable damage from internal ice.
To prevent lethal ice crystals forming in and between cells in their body, lizards use chemical compounds such as glycerol to reduce the freezing temperature of water. During prolonged exposure to sub-zero temperatures, cell activity is paused until temperatures rise again and normal activity can safely resume.
Molecular structure data collected with neutron scattering shows how mixing glycerol with water prevents rigid ice networks from forming. This new fundamental understanding of the role of glycerol will be helpful in a range of applications.
“Improving our fundamental knowledge of lizard cryopreservation may lead to improved storage and recovery of tissue for fertility treatment, better storage of drugs in the pharmaceutical industry and transport of organs for surgery, and better storage of food in the agricultural industry.”
Dr Lorna Dougan, University of Leeds
Find out more:
Anti-microbial plant defence proteins could be used in transgenic crop species to increase disease resistance and food yield
Food security is becoming a major concern in the UK and across the world, as harvest yields are challenged by climate change, pests, diseases and the demands of a rising world population.
A quarter of the world’s crops are lost to pests and disease. Understanding how plants defend themselves could be one way to reduce losses.
Common crops like rye, barley, oats, and wheat make antimicrobial proteins to defend themselves against disease, fungi and bacteria. In wheat, the defence proteins play an additional role in giving the endosperm texture, an economically important quality that determines the milling characteristics of the wheat.
Food scientists are using neutron scattering to learn about the molecular action of defence proteins and their interaction with the cell membranes of invaders. They can watch defence proteins punch their way through a cell membrane to kill hostile bacteria or strip vital components from its surface.
As regional climates change, this knowledge will help farmers and breeders to adapt plants to counteract shifting weather patterns.
Find out more:
Geologists have developed novel high-pressure neutron scattering experiments to model the Earth’s interior or predict the geology of the icy moons of the Solar System.
Satellite missions to the giant gas planets Jupiter and Saturn have revealed that our Solar System displays a rich variety of bodies, each with a complex and diverse evolutionary history.
Understanding the evolution of the planets and moons presents one of the major challenges in Earth and planetary sciences
Unique equipment developed by university groups in the UK and France for neutron scattering instruments can squeeze rocks and other materials to very high pressures.
These high pressures reproduce the conditions found inside Titan, Saturn’s largest moon, or inside the mantle of the Earth at depths of up to 700 km.
The precise data derived from neutron scattering experiments allows planetary scientists to better interpret the geology seen in surface images taken from spacecraft, or create robust interpretations of seismic data recorded on Earth.
Find out more: | <urn:uuid:43cb5dd9-f869-45e4-b589-8d492ff4c9d7> | 3.703125 | 921 | Content Listing | Science & Tech. | 25.279561 |
Figure 43–5. open (GENERIC)
PROCEDURE open (PRODUCES POINTER(textFile) f;
PRODUCES OPTIONAL STRING msg);
PROCEDURE open (PRODUCES POINTER(dataFile) f;
PRODUCES OPTIONAL STRING msg);
open is used to open a file, i.e., to make the file available for input and/or output. The predeclared CLASSes textFile and dataFile are explained in Section 22.2.
A file with the name fileName is opened in accordance with the bits specified in openBits. If the file is successfully opened, a POINTER to the file is produced in f (which is used for later access to the file) and the open PROCEDURE returns TRUE. If the file is not successfully opened (and errorOK is set), f is set to NULLPOINTER, msg is set to be an error message, and the PROCEDURE returns FALSE.
43.5.1. File Names
It is an error if fileName is the null STRING
(unless the prompt bit is set in openBits).
The names of files passed to open may be surrounded by double quote characters. This simplifies the processing of quoted file names parsed from command lines (see Section 42.12).
The double quote character is not special unless it occurs at the beginning of the file name. An error message is issued if a file name starts with an unmatched double quote, or if extraneous text follows a closing quote. For example:
|File Name Passed to open||File Name Used|
|abc def||abc def|
|"abc def"||abc def|
Note that it is not necessary to quote a file name just because it contains blank characters.
MAINSAIL does not handle files whose real names (e.g., as known
to the operating system) contain a double quote character; the
treatment of such files is undefined.
For a description of the treatment of carriage returns in
a text file, see Section 39.1.1.
If random is specified, but neither
input nor output, then both input
and output are assumed. If output
is specified, but not random, then
create is assumed. That is, a
sequential file opened for output has to
be a file that does not already exist; specifying create would
be redundant information.
The permissible combinations of input, output,
random, and create
(after the default rules have been applied) are:
The BITS constants below
are valid for openBits:
Create a new file. If this bit is not set, it is an error
if the file does not already exist.
Allow random access. If this bit is not set, it is an error
to attempt to call relPos or setPos for the file.
This bit should also be set if the same file is to be closed
and reopened for random access in the future.
Allow read access.
Allow write access.
fileName is really a prompt to be written to logFile.
After writing the prompt, read the real file name from
Each implementation has a null character that is
normally discarded when read from a text file. On many
systems, carriage return is also discarded by default.
keepNul means do not discard any null characters or
carriage returns from this file. delete
Delete the file when it is closed.
Permission is normally requested from cmdFile
when an existing file is deleted or altered.
alterOK suppresses the request for permission
and performs the operation silently (unless an
error occurs and errorOK is not set).
If the operating system is unable to carry out
the open as requested, an error message is by
default written to logFile and a new file name
read from cmdFile. If errorOK is set, the error
message is suppressed, f is set to NULLPOINTER,
and open returns FALSE.
Do not allocate a buffer for the file (this bit
may be ignored for some file types, e.g., memory
files, which are necessarily buffered). Input
and output must be performed by means of
$pageRead, $pageWrite, $storageUnitRead,
$characterWrite, fldRead (textFile form only)
and the MAINSAIL Structure Blaster. The
PROCEDUREs setPos, getPos, relPos,
and close may
also be called for an unbuffered file, but the
use of other I/O PROCEDUREs (e.g., read, write,
scan, etc.) generates an error. If large
amounts of data are to be read or written at
once, the use of the $unbuffered bit may result
in a substantial speed increase for I/O. If the
file is being created, the random bit should be
set if the $unbuffered bit is set to ensure that
unbuffered I/O can be performed on the file.
Open the file for PDF I/O.
PDF I/O is described in detail in Chapter 26.
Do not look up logical names or use a
searchpath; use the file name specified.
create output (sequential)
create random output
random input and output
create random input and output
43.5.3. Error Behavior
If errorOK is not set and the file cannot be opened,
an error message is issued and the user may type either:
For a description of the treatment of carriage returns in a text file, see Section 39.1.1.
If random is specified, but neither input nor output, then both input and output are assumed. If output is specified, but not random, then create is assumed. That is, a sequential file opened for output has to be a file that does not already exist; specifying create would be redundant information.
The permissible combinations of input, output, random, and create (after the default rules have been applied) are:
Example 43–6. Use of open
Open the file named notes for text input (it must already exist). Use f for subsequent references to the file.
The prompt is written to logFile, and then a file name is read from cmdFile. A new file is created for random text output. Only write access is allowed. If creation of the new file requires that an existing file be deleted, permission must be obtained before proceeding.
If errorOK is set and the file cannot be opened, open returns FALSE and sets the msg parameter to a STRING that describes the error. The first line of the error STRING is one of the STRINGs in Table 43–7. The error STRING may contain additional lines that give more detailed information about why the open failed.
An identifier is defined for the text of each possible first line of msg. When testing for one of these STRINGs, always use the predefined identifiers, since the text of the STRINGs is subject to change.
Note: XIDAK reserves the right to add new values to this list.
Note: The value of the msg parameter is undefined when open returns successfully.
|Temporary feature: subject to change|
In MAINSAIL Version 12.16 and earlier, although MAINSAIL expanded operating system environment variables that appeared within file names, MAINSAIL did not record the result of that expansion in the name field of the file record. Thus, after the call:
f.name was $MYDIR/myfile.msl. Starting with MAINSAIL Version 14.10, however, the name field of the file record reflects the expansion of environment variables, so that if MYDIR is defined as /usr/foo, f.name would be "/usr/foo/myfile.msl".
When the MAINSAIL compiler produces an intmod, it records the name of each source file that contributed to the intmod in the intmod itself. The name recorded comes from the name field of the file record. This is also the name of the source file that MAINDEBUG tries to open when it uses an intmod.
Thus, under Version 12.16, if you compiled $MYDIR/myfile.msl debuggable, the debugger later opened the file $MYDIR/myfile.msl. If you wanted to move your source directory, say, from /usr/foo to /usr/bar, you could just do:
setenv MYDIR /usr/bar
and the debugger would continue to find your source files.
In Version 14.10 and later, however, if you compile $MYDIR/myfile.msl debuggable, the name recorded in the intmod is expanded to /usr/foo/myfile.msl. If you moved your sources to /usr/bar and changed MYDIR as above, the debugger would still be unable to find your source files. You could get around this by issuing the MAINEX subcommand:
SEARCHPATH /usr/foo/* /usr/bar/*
However, some users find the 12.16 behavior more convenient. XIDAK has introduced a temporary feature to make the current version of MAINSAIL behave like Version 12.16 in its treatment of environment variables in file names.
If the STRING global symbol saveUnexpandedFileNames has the value "TRUE" when a file is opened, any operating-system-dependent transformations of the file name (such as the expansion of environment variables, or on UNIX, of the ~userName shorthand for a user's home directory) are not reflected in the name field of the file record. Thus, you can set this symbol (e.g., with:
GLOBALSYMBOL saveUnexpandedFileNames TRUE
in the site.cmd file on the MAINSAIL directory) when compiling MODULEs debuggable to ensure that the debugger follows Version 12.16 rules to find source files.
If saveUnexpandedFileNames is not defined or is defined to be a STRING other than "TRUE", MAINSAIL records operating-system-dependent changes to a file name in the file's name field.
In a future version of MAINSAIL, this mechanism is likely to be replaced by more general mechanisms for specifying how the debugger is to search for source files. | <urn:uuid:28f15c7a-357e-48a3-a1c2-06ffaa832db9> | 3.515625 | 2,196 | Documentation | Software Dev. | 53.720095 |
|« Main Page | Index|
The TextView Widget
GTK+ has an extremely powerful framework for multi-line text editing. The primary objects involved in the process are TextBuffer, which represents the text being edited, and TextView, a widget which can display a TextBuffer. Each buffer can be displayed by any number of views.
One of the important things to remember about text in GTK+ is that it's in the UTF-8 encoding. This means that one character can be encoded as multiple bytes. Character counts are usually referred to as offsets, while byte counts are called indexes. If you confuse these two, things will work fine with ASCII, but as soon as your buffer contains multi-byte characters, bad things will happen.
You can create a TextView widget using the following constructors:
The first constructor creates a text view widget with an empty default buffer. The second constructor creates a text view widget initialized with the specified 'buffer'.
You can set and/or retrieve the text buffer using these TextView methods:
Text in a buffer can be marked with tags. A tag is an attribute that can be applied to some range of text. Tags can have names, which is convenient sometimes (for example, you can name your tag that makes text bold "bold"), but they can also be anonymous (which is convenient if you're creating tags on-the-fly). Tags don't have to affect appearance. They can instead affect the behavior of mouse and key presses, 'lock' a range of text so the user can't edit it, or countless other things. A tag is represented by a TextTag object. One TextTag can be applied to any number of text ranges in any number of buffers.
Each tag is stored in a TextTagTable. A tag table defines a set of tags that can be used together. Each buffer has one tag table associated with it; only tags from that tag table can be used with the buffer. A useful optimization is to create a TextTagTable in advance, and reuse the same tag table for all the buffers with the same tag set, instead of creating new copies of the same tags for every buffer. Tags are assigned default priorities in order of addition to the tag table. That is, tags created later that affect the same text property affected by an earlier tag will override the earlier tag.
You can create a new tag with one of these constructors:
The first constructor creates an anonymous tag and the second constructor creates a tag with the specified name. Anonymous tags are convenient if you are creating tags on-the-fly, otherwise tags should have a name. After creating a tag you need to add it to the buffer's tag table before you can apply it to any text in the buffer.
The following TextBuffer method returns a buffer's tag table:
To create a "Bold" tag and add it to a text buffer's tag table, you would do something like this:
In the second line the tag's 'weight' property is set to Pango::WEIGHT_BOLD. This is how you manipulate text tags, through properties not getter and setter functions. There are 62 properties that can be set on a text tag.
There is an easier way to create and add a text tag to a text buffer; call one of the TextBuffer create methods which creates a new tag and adds it to its tag table:
Like the TextTag constructors, the first create_tag() method creates an anonymous tag and the second creates a tag with the specified name. Note, the returned tag is owned by the buffer's tag table, so the reference count will be equal to one.
Now we can simplify creating a "Bold" tag and adding it to a buffer's tag table:
Most text manipulation is accomplished with iterators, represented by a TextIter object. An iterator represents a position between two characters in a text buffer. TextIter is a class designed to be allocated on the stack; it's guaranteed to be copyable by value and never contain any heap-allocated data. Iterators are not valid indefinitely; whenever the buffer is modified in a way that affects the number of characters in the buffer, all outstanding iterators become invalid. (Note that deleting 5 characters and then reinserting 5 still invalidates iterators, though you end up with the same number of characters you pass through a state with a different number).
After adding a tag to a buffer's tag table you can apply the tag to some range of text in the buffer. This can be done by calling one of the TextBuffer apply methods, or by calling one of the insert methods which will apply the tag to the text the method inserts.
Here is one of the TextBuffer apply methods:
The 'tag' argument is the tag (that must be in the buffer's tag table) whose properties should be applied to the text in the range 'start' to 'end'.
Here is one of the TextBuffer insert methods:
The 'iter' argument is an iterator to a position in the buffer, 'text' is the text string to insert at this position and 'tag' is the text tag to apply to the text. There are other insert methods that can insert text without specifying a tag, insert text at the current cursor position or insert pixbufs. You should have a look at the TextBuffer and TextTag API reference. The functions are all well documentated.
Iterators can't be used to preserve positions across buffer modifications. To preserve a position you need to use a TextMark object. You can think of a mark as an invisible cursor or insertion point; it floats in the buffer, saving a position. If the text surrounding the mark is deleted, the mark remains in the position the text once occupied; if text is inserted at the mark, the mark ends up either to the left or to the right of the new text, depending on its gravity. The standard text cursor in left-to-right languages is a mark with right gravity, because it stays to the right of inserted text.
Like tags, marks can be either named or anonymous. There are two marks built-in to TextBuffer; these are named "insert" and "selection_bound" and refer to the insertion point and the boundary of the selection which is not the insertion point, respectively. If no text is selected, these two marks will be in the same position. You can manipulate what is selected and where the cursor appears by moving these marks around.
Unlike tags, you can't construct a mark. The only way to create a mark is the call the TextBuffer create_mark() method:
The 'mark_name' argument is the name for the mark, 'where' is the position in the buffer to place the mark, and 'left_gravity' specifies whether the mark should have left or right gravity. If mark_name is null, the mark is anonymous. If a mark has left gravity, and text is inserted at the mark's current location, the mark will be moved to the left of the newly-inserted text. If the mark has right gravity (left_gravity = false), the mark will end up on the right of newly-inserted text. The standard left-to-right cursor is a mark with right gravity (when you type, the cursor stays on the right side of the text you're typing). The caller of this method does not own a reference to the returned TextMark, so you can ignore the return value if you like. Marks are owned by the buffer and go away when the buffer does.
An anchor is a spot in a TextBuffer where child widgets can be anchored, inserted inline, as if they were characters. An anchor, represented by TextChildAnchor, can have multiple widgets anchored, to allow for multiple views.
The easiest way to create an anchor it to call the TextBuffer create_child_anchor() method:
The 'iter' argument is the position in the buffer to place the anchor. The new anchor is owned by the buffer so no reference count is returned to the caller. Have a look at the TextView demo program in <demos/xfc-demo/textview.cc>. It displays a text buffer that has several widgets anchored.
The one thing not covered yet is creating a text buffer. That's easy, but as you saw at the start, if you don't specify a text buffer when you create a TextView widget, the widget creates an default buffer for you.
You can create a text buffer by calling the following constructor:
You could create your own buffer when you want to reuse one TexTagTable, or when you want to display one buffer in multiple text views. Text buffers always contain at least one line, but may be empty (that is, buffers can contain zero characters). The last line in the text buffer never ends in a line separator (such as newline); the other lines in the buffer always end in a line separator. Line separators count as characters when computing character counts and character offsets. Note that some Unicode line separators are represented with multiple bytes in UTF-8, and the two-character sequence "\r\n" is also considered a line separator.
One TextBuffer method worth mentioning is place_cursor():
This method lets you place the cursor in response to a user action, moving both "insert" and "selection_bound" marks simultaneously without causing a temporary selection (moving one mark then the other temporarily selects the range in between the old and new positions). The 'where' argument is the position in the buffer to place the cursor.
The header file for this TextView example is <textview.hh>
and the source file is textview.cc
If you compiled and installed XFC yourself, you will find the source
code for TextView in the
<examples/howto/textview> source directory along with a Makefile. If
XFC came pre-installed, or you installed it from an RPM package, you
find the source code in the
</usr/share/doc/xfcui-X.X/examples/howto/textview> subdirectory. In
this case you will have to create the Makefile yourself (replace X.X
version number of the libXFCui library you have installed).
|Copyright © 2004-2005 The XFC Development Team||Top | <urn:uuid:967ed8e5-98ea-4835-9a99-3051aba05d42> | 3.390625 | 2,152 | Documentation | Software Dev. | 52.762448 |
Integrity Rules are imperative to a good database design. Most RDBMS have these rules automatically, but it is safer to just make sure that the rules are already applied in the design. There are two types of integrity mentioned in integrity rules, entity and reference. Two additional rules that aren't necessarily included in integrity rules but are pertinent to database designs are business rules and domain rules.
Entity integrity exists when each primary key within a table has a value that is unique. this ensures that each row is uniquely identified by the primary key.One requirement for entity integrity is that a primary key cannot have a null value. The purpose of this integrity is to have each row to have a unique identity, and foreign key values can properly reference primary key values.
Reference integrity exists when a foreign contains a value that value refers to an exiting tuple/row in another relation. The purpose of reference integrity is to make it impossible to delete a row in one table whose primary key has mandatory matching foreign key values in another table.
Business rules are constraints or defintions created by some aspect of a business. They can apply to almost all aspects of a business and are meant to describte operations of a business. An example of a business rule might be no credit check is to be performed on return customers. This example would change a database design for a car company.
Domain rules or integrity specify that al columns in a database must be declared upon a defined domain. A domain is a set values of the same value type.
Other integrity rules include not null and unique constraints. The not null constraint can be placed on a column to ensure that every row in the table has a value for that column. The unique constraint is restriction placed on a column to ensure that no duplicate values exist for that column. | <urn:uuid:d679b701-a8fa-4478-98e3-0eb2116d600d> | 3.546875 | 361 | Knowledge Article | Software Dev. | 32.067233 |
|file[, mode[, compression[, allowZip64]]])|
'r'to read an existing file,
'w'to truncate and write a new file, or
'a'to append to an existing file. For mode is
'a'and file refers to an existing ZIP file, then additional files are added to it. If file does not refer to a ZIP file, then a new ZIP archive is appended to the file. This is meant for adding a ZIP archive to another file, such as python.exe. Using
cat myzip.zip >> python.exe
also works, and at least WinZip can read such files.
compression is the ZIP compression method to use when writing
the archive, and should be ZIP_STORED or
ZIP_DEFLATED; unrecognized values will cause
RuntimeError to be raised. If ZIP_DEFLATED
is specified but the zlib module is not available,
RuntimeError is also raised. The default is
If allowZip64 is
True zipfile will create ZIP files that use
the ZIP64 extensions when the zipfile is larger than 2 GB. If it is
false (the default) zipfile will raise an exception when the
ZIP file would require ZIP64 extensions. ZIP64 extensions are disabled by
default because the default zip and unzip commands on
Unix (the InfoZIP utilities) don't support these extensions.
|filename[, arcname[, compress_type]])|
Note: There is no official file name encoding for ZIP files. If you have unicode file names, please convert them to byte strings in your desired encoding before passing them to write(). WinZip interprets all file names as encoded in CP437, also known as DOS Latin.
Note: Archive names should be relative to the archive root, that is, they should not start with a path separator.
The following data attribute is also available:
0(the default, no output) to
3(the most output). Debugging information is written to
See About this document... for information on suggesting changes. | <urn:uuid:d30768f9-8d2b-45f9-b14e-54ca626c6867> | 2.859375 | 443 | Documentation | Software Dev. | 49.063603 |
1818 - 1889
Born in Salford,
England. A physicist, he shared in discovering the law of
the conservation of energy. Two German physicists, Hermann
von Helmholtz and Julius von Mayer, and Irish/Scottish physicist
Lord Kelvin, also worked on the law of physics. The law
states that energy used up in one form reappears in another
and is never lost.
In 1840, he stated a law, now called
Joule's Law, that heat is produced in an electrical
conductor. The International unit of energy, the joule, is
named in his honor.
Other Places to Visit...
James Joule Website (Michigan State University)
Answers.COM Web Page on Joule | <urn:uuid:0fb50cca-3963-4bd6-96ff-ac9145e30b95> | 3.078125 | 158 | Knowledge Article | Science & Tech. | 56.406189 |
Sat Jul 28 03:47:24 CEST 2007
Chad Wilson wrote:
> I have programmed my first function in Erlang!
> It just had to get that off my chest. I felt it was an accomplishment
> worth drinking a Pepsi for because I remembered that capitalization
> part. Speaking of which, why case sensitive language parts? Does it
> make designing the parser and compiler easier? Reading the code?
> Something else?
It may partly be a inheritance from the orginal erlang implementation,
that was based on Prolog.
Prolog uses upper case to mark something as a varibale.
It is also probably a parser/complier issue, it might otherwise be hard
to distinguish variables from atoms, as well as differentiate a regular
function call like foo(...) from the function call Foo(...) (where Foo
is a fun()).
Other languages like bash (and PHP ?) that have no or only rarely used
constructs to declare variables, also act in a similar manner - bash for
example requires $VarName to get the value of a varible rather than just
the string VarName.
More information about the erlang-questions | <urn:uuid:25f5688e-dcff-4614-acbf-36a8a65b793f> | 2.78125 | 251 | Comment Section | Software Dev. | 55.639351 |
LISA Will Listen for Gravitational Waves ESAThe NASA/ESA LISA project aims to measure gravitational waves with giant lasers and floating cubes of gold CERN's Large Hadron Collider is currently the biggest science experiment in operation, but it may have to pass that mantle on soon enough. A collaboration between NASA and the ESA plans to launch three spacecraft into orbit around the sun 3 million miles apart, then have them shoot lasers at each other, all in the name of proving the existence of gravitational waves, the last piece of Einstein's relativity theory that is as yet unproved. Einstein's general relativity predicts several things, such as gravity's ability to bend time light and the constant speed at which gravity travels. But a means to prove the existence of gravitational waves -- huge ripples in time and space that flow outwards from the collision of huge celestial bodies like black...
- Atom interferometer provides most precise test yet of Einstein's gravitational redshiftWed, 17 Feb 2010, 13:32:39 EST
- LISA gravitational-wave mission strongly endorsed by National Research CouncilWed, 18 Aug 2010, 13:17:46 EDT
- LIGO listens for gravitational echoes of the birth of the universeWed, 19 Aug 2009, 13:51:48 EDT
- Scientist instils new hope of detecting gravitational wavesFri, 27 May 2011, 9:33:55 EDT
- LIGO observations probe the dynamics of the crab pulsarMon, 2 Jun 2008, 12:42:22 EDT | <urn:uuid:c2eb0ffe-061a-4727-98b4-59b5097e7c06> | 3.5 | 305 | Content Listing | Science & Tech. | 28.654006 |
Variables are just boxes to store a value in (this works nicely with 'simple' data like integers. For objects, it gets a bit more complicated). You have variables (boxes) of different sizes, see http://java.sun.com/docs/books/jls/seco ... s.doc.html
section 4.2.1. A byte-sized variable can store values -128 to 127, etc.
This is especially important if you have not so much room (eg in an embedded device), or if you have storage requirements eg in a file.
In general, you should not care very deeply about the sizes, and just use 'int' for everything, unless -2147483648 to 2147483647 is not large enough :)
Byte code is something different entirely. It is Java program code, translated for your computer (JVM (Java Virtual Machine), to be precise), so it can run the program. Not something you should care much about when still learning about variables. | <urn:uuid:6a353d41-ebbe-46ec-98b2-305b692f81bc> | 3.03125 | 210 | Q&A Forum | Software Dev. | 65.903118 |
The Planck hangs out close to a million miles (1.5 million kilometers) from Earth and always points away from the sun, in order to get clearer measurements. Its operating temp is a bit lower than -273° C, just above absolute zero and a few degrees warmer than the average American bed when the anniversary gift and flowers are purchased at the nearby convenience store because it's still open 10 minutes before midnight.
It scans the sky in a sort of one swath at a time back and forth mode, the way my dad wanted me to mow the yard even though concentric squares took less time. Ahem. Anyway, as the story notes, it builds a strip-by-strip (some might say "Planck-by-Planck," but we would harm them if they did) view of the sky.
Scientists have detected radiation that comes from a mere 380,000 years after the initial singularity or Big Bang that is theorized as the beginning of the universe. Prior to that, conditions in the universe were too hot to differentiate between actual substance and emitted radiation. Again, insert your own favorite elected official/government functionary joke here.
The best guess age estimate of the universe is about 15 billion years, which means the Planck is taking pictures of the universe the way it looked when it was about 2½ percent as old as it is now. If the average human lifespan is about 75 years, then this is like a picture of us taken when we were about 22½ months old. Evidently the universe holds still for the camera better than we did -- I hesitate to imagine what God used for a squeaky toy to get its attention otherwise. | <urn:uuid:a6d3866b-25ca-4c44-baa9-eef61d7faad5> | 2.84375 | 340 | Personal Blog | Science & Tech. | 49.321953 |
Packed vectors : use these whenever possible. The generic vector type is is represented at run-time by a linked list of boxed values. Packed types, however, store the vector components sequentially in memory. Vector operations can be defined using the generic types, and the compiler will inline and specialize these definitions for the packed types, avoiding any list cells or unnecessary heap allocations.
Packed vectors are related to their unpacked representations by way of an
associated type. An instance of class
a packed representation, and the type of that is
. The packed
constructors are named
VecNT where N is 2, 3 or 4 and T is
Double. So the expression
Vec3D x y z
constructs a packed 3-vector of Doubles, the type of which is
Double). The constructor name is also a synonym for the packed type name,
type Vec3D = Packed (Vec3 Double), so the packed type acts as if it
had been declared
data Vec3D = Vec3D x y z.
ZipWith instances are
provided for packed vectors, so some operations do not require pack/unpack.
does not require pack/unpack because it is defined in
and most others are recursive, and so you'll still need to
use pack/unpack with these. This goes for
as well because it
. Some functions, like
, do not need their
arguments to be unpacked, but the result is a polymorphic vector
you will need to pack it again. I admit that this is awkward.
- class PackedVec v where
- type Vec2I = Packed (Vec2 Int)
- type Vec3I = Packed (Vec3 Int)
- type Vec4I = Packed (Vec4 Int)
- type Vec2F = Packed (Vec2 Float)
- type Vec3F = Packed (Vec3 Float)
- type Vec4F = Packed (Vec4 Float)
- type Vec2D = Packed (Vec2 Double)
- type Vec3D = Packed (Vec3 Double)
- type Vec4D = Packed (Vec4 Double)
- type Mat22D = Vec2 Vec2D
- type Mat23D = Vec2 Vec3D
- type Mat24D = Vec2 Vec4D
- type Mat33D = Vec3 Vec3D
- type Mat34D = Vec3 Vec4D
- type Mat44D = Vec4 Vec4D
- packMat :: (Map row (Packed row) mat packedMat, PackedVec row) => mat -> packedMat
- unpackMat :: (Map (Packed row) row packedMat mat, PackedVec row) => packedMat -> mat
PackedVec class : relates a vector type to its space-optimized representation.
Construct a semi-packed matrix, one whose rows are packed. | <urn:uuid:8e078067-8239-4f88-bbf7-979001884c71> | 3.203125 | 637 | Documentation | Software Dev. | 45.794535 |
Tag: "surfaces" at biology news
Researchers find color sensitive atomic switch in bacteria
...rogram bumps up against a membrane." Cell membrane surfaces
and their exposed proteins are the most accessible targets to treat human tissue or destroy infectious microbes, he said. More than 60 percent of medications target membrane proteins on human cells and many antibiotics target membranes on pathogens....
Study reveals why eyes in some paintings seem to follow viewers
...e was viewed from, Todd said. "When observing real surfaces
in the natural environment the visual information that specifies near and far points varies when we change viewing direction," he said. "When we observe a picture on the wall, on the other hand, the visual information that defines near and far points...
Green, leafy spinach may soon power cellphones and laptops
...multiple layers of PSI or assembling them on rough surfaces
or 3-D surfaces, like skyscrapers that concentrate a huge amount of surface area within a relatively small space. ...
Popular Science announces Third Annual 'Brilliant 10'
...ing. His ability to translate the play of light on surfaces
into digital code has not only secured his status as an academic computer scientist, it has taken him on a red carpet ride, earning him credits on films such as Terminator 3 and Shrek 2. In February, he earned an Academy Award for Technical Achieveme...
First glimpse of DNA binding to viral enzyme
...at allows structural information on the contacting surfaces
of biological molecules to be precisely mapped. These contact points are regions providing critical communication in the cell," Chance explained. "In this study the footprinting approach provided information on the DNA binding region of the adenoviru...
Disease diagnosis, drug development focus of UH prof's biochip research
...derstanding the fundamental principles of how hard surfaces
affect softer biological components like proteins and DNA. DNA chips, a type of biochip, have DNA molecules attached to a high-tech chip surface and have applications in genetic screening, disease diagnosis and drug development. "The design of bi...
Protein fishing in America: The movie
...heory holds. The repeated weak slapping of protein surfaces
against one-another is the critical first step in a chain of events that rule all subsequent cellular behavior. But this vital exchange between single molecules has defied direct observation because that line-flicking and message-passing happen rando...
Meteorites supplied Earth life with phosphorus
...howed that phosphorus became concentrated at metal surfaces
that corroded in the early solar system. "This natural mechanism of phosphorus concentration in the presence of a known organic catalyst (such as iron-based metal) made me think that aqueous corrosion of meteoritic minerals could lead to the formati...
UV light, coatings reduce bacterial adhesion up to 50 percent
...also may offer a 'green' approach to keeping glass surfaces
free of contamination." Li described her res...s. The Penn State researcher exposed flat glass surfaces
(silica dioxide) coated with thin layers of silicon dioxide, titanium dioxide or tin dioxide to eigh...
Researchers show how to assemble building blocks for nanotechnology
...nth. The results of the simulations showed that if surfaces
of particles could be patterned with patches of molecules, they could make the particles assemble into different shapes. The trick, according to the researchers, is using patches that are strongly directional and attract and repel specific parts of o...
Sweet success in targeting sugar molecules to cells in living animals
... with chemically unique functional groups onto the surfaces
of cells in living animals without altering the an... glycosylation patterns of sugar molecules on cell surfaces
can influence their interaction with other cells. "Glycobiologists have known that cancer cells, for...
The first engineering of cell surfaces in living animals
... Berkeley, introduced a new way of engineering the surfaces
of cells, by arming cell-surface sugars to take pa...eled cells of living mice. The ability to tag cell surfaces
in living beings may someday allow the targeting of specific kinds of cells for noninvasive imaging,...
Urban heat islands make cities greener
...ntrations of buildings, roads and other artificial surfaces
retain heat, creating urban heat islands. Satellite data reveal that urban heat islands increase surface temperatures compared to rural surroundings. Using information from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument o...
'Search and destroy' protein turns tables on HIV
...d in some HIV-resistant people, in which the outer surfaces
of their cells no longer offer footholds for the virus to attach and begin the process of infection." Here's how the APOBEC proteins are thought to work. When the core of an HIV particle enters a cell, it contains single-stranded RNA as its genetic m...
Physicists reveal first 'nanoflowers'
...wn that as a coating water droplets roll off these surfaces
when they are tilted at angles as small as 5 degre... consequence of the ability of such nanostructured surfaces
to strongly repel water". Dr Paul Danielsen, director of communications at the Institute of Physics,...
Biocompatibility to widen scope of biomaterial applications
...ion and adhesion of blood platelets to biomaterial surfaces
as well as fibrous-tissue encapsulation of biomaterials that are implanted in soft tissues are two challenging issues for researchers in quest of biocompatibility," says Technical Insights Analyst Dr. James Smith. Biocompatibility assumes greater sig...
Medical implants work better when you rough them up, study finds
... to joint replacements may work better when their surfaces
are on the rough side, new research suggests. Implants often have surfaces
that soft tissue, such as skin and connective tissue, cannot attach to, said Andreas von Recum, the ...
Microbes found in Mayan ruins may deteriorate stone from inside out
...ed bacterial communities on the inside and outside surfaces
of the stone. Photosynthetic microorganisms, mainly proteobacteria, were found to populate the surface whereas Actinobacteria was the dominate population on the interior where no photosynthetic organisms were detected. Additional tests on the inter...
Study suggests double punch could more efficiently kill viruses
...all pieces of viral protein presented on the pAPCs surfaces
can be generated when the infected protein is made by pAPC. Alternately, the other pathway, known as cross-priming, involves transfer of some form of protein, previously thought to be peptides, to the pAPC where it can be presented to T cells. "Altho...
Innovative 'self healing' bandage to help diabetics
...t the University has focused on the development of surfaces
that human cells will not only grow on but also transfer from to the patient's wound. It is also developing new approaches to culturing human skin cells without using animal derived products such as bovine serum. The new bandages could take some pr...
1 2 3 4 5 6 7 8 9 10 | <urn:uuid:0795bab6-33cc-4388-a054-968cf30aa8e4> | 2.703125 | 1,458 | Content Listing | Science & Tech. | 45.10169 |
Electromagnetic and Weak Theory
Name: Nick L.
What was the main link between electromagnetism and weak
theories to create the electroweak theory? Does it have to do with beta
Originally, weak interactions were thought to be separate from
electromagnetic forces. Eventually, three fairly massive particles were
discovered: W+, W-, Z. The weak force is an electromagnetic interaction
producing one of these particles. The particle travels then is absorbed
through electromagnetic interactions with another particle. Although the
Z-particle has no electric charge, it does have a spin. It can interact
with magnetic force. Standard electromagnetic force is transmitted by
photons of light. Weak force is transmitted by these "weak" particles.
Still the actual interactions are the based on the same force.
Dr. Ken Mellendorf
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:95e48c0e-0c8a-41f7-9528-918be97590d8> | 3.078125 | 187 | Knowledge Article | Science & Tech. | 34.989583 |
In less than a decade, the Indo-Pacific lionfish (Pterois volitans) has become widely established along the Southeast U.S. and Caribbean. Lionfish are capable of permanently impacting economically important species (e.g., snapper and grouper) and may hamper coral reef conservation measures.
Invasive species can harm both the natural resources in an ecosystem as well as threaten human use of these resources. An invasive species can be introduced to a new area via the ballast water of oceangoing ships, intentional and accidental releases of aquaculture species, aquarium specimens or bait, and other means.
Invasive species are capable of causing extinctions of native plants and animals, reducing biodiversity, competing with native organisms for limited resources, and altering habitats. This can result in huge economic impacts and fundamental disruptions of coastal and Great Lakes ecosystems.
For more information:
Learn more about invasive lionfish from NOAA's Center for Coastal Fisheries and Habitat Research
National Centers for Coastal Ocean Science
Episode 14 (Making Waves podcast, 1.30.09)
Aquatic Invasive Species | <urn:uuid:bd0ec68a-eb21-4e30-992d-de0d5c7e0dc7> | 3.625 | 226 | Knowledge Article | Science & Tech. | 22.339233 |
A regular expression in python is a special module that helps filter sequence of strings, characters and symbols using specialized syntax written in a particular pattern. Like any other programming language, regular expression module ‘re’ in python allows you to process unlimited amount of strings that passes regular expression requirements. If you want to process large amount of text data with some conditions then regular expression is your best bet. There are many other reasons to use regular expressions in your programs.
Why Regular Expressions?
- Search and Replace : It’s easy to extract specific strings from large documents. You can use it as a search and replace feature to correct grammatical errors or to add/remove strings in document. It is also possible to use the regular expressions for the purpose search the occurrence of strings, as purely for search purpose.
- Splitting String: You can split the strings if occurrence of a character or symbol is found. Likewise there are many ways to approach splitting your document as per regex matches.
- Validation: You can validate your document for certain requirements. This is one good feature if you’re testing some web based standards or company specific standards in your code.
Let’s take a look at some of the examples of regular expression so that you can feel comfortable writing your own as per your needs. In these examples we’re using a one simple string and using the regex for performing replace, search, split, match and to check the occurrences operations.
If you want to replace particular word in your statement or block of text then you have to use sub() method. This method ensures that you substitute new text in the place of pattern. This method takes 4 arguments sub(pattern,rep,string,count).
Check this example:
import re st=”big black fox jumps over lazy blue fox”; st_new=re.sub(‘fox’,’beever’,’big black fox jumps over lazy blue fox’,1);
You can also write this code by using the name of the string st instead of writing it down. If you’re not declaring any string separately then you have to explicitly use it in the method.
import re st=”big black fox jumps over lazy blue fox”; st_new=re.sub(‘fox’,’beever’,st,1);
You can split a particular string or word from the block of text. It is possible to do that using split() method. It takes three arguments and you get a choice to replace the text upto particular count. For example,
import re st=”big black fox jumps over lazy blue fox”; st=re.split(‘fox’,st,2)
Here, we have word fox 2 times in the string and we have placed the maxcount at 2, so it only splits the string for ‘fox’ word twice. If you have that word for more than two times then you need to set the maxcount for higher number as per your requirement.
Occurrence of Word in Strings
As you can see in previous example, we are repeating word “fox” for more than once. You can find the number of occurrence of that word in the string and get it in output.
import re st=”big black wolf jumps over the lazy blue wolf’; print ‘wolf’ in st, re.findall(‘wolf’,st);
This will print out the number of occurrences of word “wolf” in string. If you’re using the word joint with another word like wolfstream or wolfram then you have to set the boundary using r’\b’ for the exact match in your stream. This way you’re limited to exact match.
import re st=”big black wolf jumps over the lazy wolf but there is no wolfpack here to see”; print ‘wolf’ in st, re.findall(r’\bwolf\b’,st);
If you see the output of the following program you’ll notice that it only prints the wolf occurrence count as two.
Search() and Match() method
Search() method checks for the match of a particular word in the string and shows the success message if it finds specific word in string. In case of match(), python checks the exact match from the beginning of the string and usually returns none or no match message if the beginning of the string doesn’t match the queried word.
import re st=”big black wolf jumps over the lazy wolf but there is no wolfpack here to see”; print re.search(‘wolf’,st); print re.match(‘wolf’,st);
Possible Errors and Solutions
While writing regular expression programs you’ll find some errors in your program. Make sure you read the error thrown by the python interpreter. I’m going to save your time by pointing to some common errors.
- method() and argument related errors : Some methods in re needs exact arguments before you can process them. Some methods may not have that compulsion and you’ll be able to execute the code without adding additional arguments in these methods. Check each method carefully and see if it requires you to type all arguments.
- Failed to import re: If you failed to import re module then all the methods called in your program for regex are going to throw an error.
- Coma and semicolon: Check if you’re using coma in methods and not semicolon. This is often possible if you’re migrating from another language.
This completes our simple tutorial on regular expressions in python. Hope this tutorial helped you to understand how to use regex in python. There are many other things which are not covered in this tutorial and we expect you to learn these things on your own and share it with others on the internet. Regular expressions can save a lot of your time so I suggest you to learn them and use it in code and benefit from the usefulness of it. If you have any questions or suggestions to improve this tutorial, feel free to send tweet to @maheshkale. | <urn:uuid:59a80441-c002-4439-a0d9-a34514911e36> | 3.9375 | 1,307 | Tutorial | Software Dev. | 60.633748 |
When a lithium ion battery reaches the point at which it can no longer be used in an electric car, it still has the potential to be used in other applications. But exactly what are the best uses for them?
The U.S. government is backing a comprehensive study to determine just that, the National Renewable Energy Laboratory (NREL) announced Tuesday.
"To date, no one has comprehensively studied the feasibility, durability, and value of Li-ion batteries for second-use applications," NREL said in a statement.
The California Center for Sustainable Energy (CCSE) will lead the research project which will … Read more | <urn:uuid:3ca817f4-0fda-4cfe-a5fe-f32b20885000> | 2.859375 | 130 | Truncated | Science & Tech. | 37.797647 |
Perhaps you remember Heroes, a popular American television show, whose tagline during its first season was “Save the cheerleader—save the world.” Well, I don’t know about cheerleaders, but I do know that we need to save the data to save our world.
Those of us involved in the burgeoning arena of data-intensive science sometimes think that we invented the collection and curation of the numbers that so preoccupy us. Fortunately, that isn’t true, as I was recently reminded while serving as a member of the Task Force on Data and Visualization of the National Science Foundation’s Office of Cyberinfrastructure. As is recounted the Task Force report, 200-year-old data from ships’ logs are helping to us understand climate change. The British navy has carefully recorded and maintained information on wind speed, temperature, and pressure for over two centuries—a truly unique collection of climate data.
Of course much of our data about climate change is of a more recent vintage, the result of numerous field and satellite observations. As the report section entitled Preserving Data to Preserve the Planet discusses, our understanding of chlorofluorocarbons’ destructive impact on the ozone layer stems from laboratory experiments, measurements in the field, and copious satellite data. The collection, curation, and analysis of these data led to the Montreal Protocol, the 1980s treaty (since revised several times) that has phased out ozone-depleting compounds and led to hopeful signs of recovery in stratospheric ozone.
As the NFS-OCI report makes clear, such data-intensive science is critical to understanding climate change and to unraveling the natural cycles of our planet. It’s not hyperbole to say—as the report does—that a robust data service infrastructure is required for the breakthrough science that will help us preserve Mother Earth.
The overall report challenges the NSF to “create a sustainable data infrastructure fit to support world-class research and innovation.” This particular section of the report offers several recommendations, all worth repeating.
The key recommendation is that we recognize and appropriately fund data infrastructure and services as essential research assets. Governments (in this case, the U.S. government) must provide adequate budgets to establish and maintain data sets and create the requisite cyberinfrastructure for their access and manipulation.
To achieve this overarching goal, the Task Force makes three supporting recommendations:
- Key research domains should identify the essential data for retention and archival. The Task Force suggests adopting a 20- to 30-year outlook, asking what data collected today will be needed two or three decades down the road.
- There needs to be an open call for large-scale data services that cut across disciplines and embrace a range of data types. This will lead to economies of scale and should include incentives for service providers to develop cost-effective methods of data access and curation.
- The entire scientific research community should be engaged to evangelize open access to these data services.
We should make no mistake about it: the collection, curation, and storage of data are essential to modern science, as are the access to and sharing of these data stores. It’s wonderful that the British navy had the foresight to gather and preserve valuable meteorological information. We need to take a page from their log book and ensure that we are building the cyberinfrastructure to support research in the years ahead. So, at the risk of being a cheerleader myself, let me just say “Save the data—save the world.” | <urn:uuid:392e396b-0752-47d3-a5a6-57793bf7ea3a> | 3.03125 | 735 | Personal Blog | Science & Tech. | 28.14245 |
Moorings are autonomous systems, which remain in the ocean for several years to measure a variety of oceanographic properties at a distinct location with high temporal resolution. By this means it is possible to obtain measurements to detect the exact course of temporal variations even if there is no ship in the area.
A mooring consists of the ground weight, a wire, and floats which keep the wire upright in the water column. On the wire instruments are fixed to measure e.g. temperature, salinity current speed and velocity, sea ice thickness and underwater sound. All data are recorded internally. After the end of the observation period, the wire is released from the ground weight by means of an acoustic signal from Polarstern’s Posidonia system and the floats tow the wire with the instruments to the surface. This ascend can be surveyed as well by the Posidonia system. At the sea surface a satellite transmitter is activated and one can receive the signal of it on board. If the mooring cannot be spotted by eye, the satellite signals helps to detect it. In case of reception problems on board, the position is obtained by email from Bremerhaven.
In open water normally no problems occur, however if there is fog even recovery in open water can be a challenge. In the ice, either the floats find their way through the floes up to the surface or one has to locate them by acoustic means under the ice and break them free. Then the ship must approach the mooring very carefully not to crash them between the floes. The last few meters are made the mammy chair, from which the connection to the ship is achieved by a rope.
However, even in open water the recovery of a mooring can be a challenge if the wind is blowing as strong as it happens frequently in higher latitudes. Then, high skill is required from the ship’s officers to bring the huge ship very smoothly to the relatively small mooring without damaging it.
In Fram Strait moorings were maintained since August 1997 in the context of the VEINS, ASOF-N, DAMOCLES and ACOBAR projects. Mainly current meters have been used which also record temperature. Moorings are exchanged every year during the summer season. Since 1989 time long-term measurements are performed in the Atlantic sector of the Southern Ocean in the Weddell Sea and since 1996 along the meridian of Greenwich between 53°S and the continental slope. After a recording period of two to three years these moorings are exchanged during southern summer. Adittionally moorings with sound sources are deployed in the Weddell Sea for acoustically tracking the RAFOS floats. | <urn:uuid:7024c9e3-77a2-4629-978c-ed673f1e8d00> | 3.734375 | 551 | Knowledge Article | Science & Tech. | 47.474104 |
A wide variety of missions of exploration seek to explain the Universe's unanswered questions. Many are exceedingly expensive and are funded by the taxpayers. However, amateurs with relatively small telescopes or binoculars still make important contributions to astronomy.
This section features some of the most famous attempts to explore the night sky.
Image: Astronauts repair the Hubble Space Telescope from the space shuttle in 1993 (credit: NASA)
The AAO hunts exoplanets.
This space telescope measures the Universe's high energy objects.
Compton tracks gamma ray bursts from orbit.
A satellite finds important evidence supporting the Big Bang.
Herschel is the largest telescope ever launched into space.
This device was used to discover the cosmic microwave background radiation.
This famous telescope makes beautiful images of the Universe.
This facility is home to one of the world's largest radio telescopes.
A mission hunts for exoplanets similar to the Earth.
Kitt Peak is the national observatory of the United States.
The LHC investigates the first moments after the Big Bang.
19th century astronomers use a great telescope to study spiral galaxies.
Key discoveries have been made here.
This satellite captured a stunning image of light from the early Universe.
This project produces 3D maps of the Universe.
Spitzer studies the infrared Universe.
Swift aims to discover more about gamma ray bursts.
Astronomy's most important tool continues to evolve.
There are twin telescopes on Mauna Kea, Hawaii.
An underground lab is part of the dark matter search.
UKIRT observes the infrared sky.
This powerful telescope is located in Chile.
This European telescope is located on La Palma.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so. | <urn:uuid:be7da9fe-f861-4017-97a1-55371ca85245> | 3.984375 | 422 | Content Listing | Science & Tech. | 40.723642 |
you had two charges in a line (q1 = +7µC and q2 =
0.5µC) separated by 0.9m. You found a point between them
where the electric field is 0 (about 0.71m from q1).
a. Is the electric potential equal to 0 at that point? Calculate
b. Change the problem so that the electric potential is 0 at 0.71m
from q1. Now, is the electric field equal to 0? | <urn:uuid:d2353b21-f7c7-43d9-a580-5fad75fc0c72> | 3.09375 | 107 | Q&A Forum | Science & Tech. | 104.898766 |
Sloths are medium-sized South American mammals belonging to the families Megalonychidae and Bradypodidae, part of the order Pilosa. Most scientists call these two families the Folivora suborder, while some call it Phyllophaga. Sloths are herbivores, eating very little other than leaves.
Sloths have made extraordinary adaptations to an arboreal browsing lifestyle. Leaves, their main food source, provide very little energy or nutrition and do not digest easily: sloths have very large, specialized, slow-acting stomachs with multiple compartments in which symbiotic bacteria break down the tough leaves. Sloths may also eat insects and small lizards and carrion.
As much as two-thirds of a well-fed sloth's body-weight consists of the contents of its stomach, and the digestive process can take as long as a month or more to complete. Even so, leaves provide little energy, and sloths deal with this by a range of economy measures: they have very low metabolic rates (less than half of that expected for a creature of their size), and maintain low body temperatures when active (30 to 34 degrees Celsius), and still lower temperatures when resting.
Until geologically recent times, large ground-dwelling sloths such as Megatherium lived in North America, but along with many other species they became extinct immediately after the arrival of humans on the continent.
Much evidence suggests that the extinction of the American megafauna, like that of Australia, far northern Asia, and New Zealand, resulted from human activity. However, simultaneous climate change that came with the end of the last Ice Age probably played a role as well.
10,000 years ago humans had reached the very southern tip of South America, where in present day Chilean Patagonia they shared a cavern with the giant sloth whose bones Charles Darwin discovered in the 1830's. The creatures portrayed there may have been giant sloth.
Seven thousand years later the giant sloth and most other large animal species in the Americas were extinct, but the first beginnings of complex human societies were taking shape, around 3000 BCE.
Many of the large mammals (e.g., the mammoth, the saber-tooth tiger) that inhabited the Americas, some even after the end of the last ice age, became extinct, in an episode known as the late Pleistocene die off. Significant climatic change is most often cited as the reason but some anthropologists argue that the entrance of humans, first on to the North American plains east of the Canadian Rockies, then southward, could have had a dramatic impact, out of all proportions to their numbers, on the big animals at the top of the food chain. Only the small tree sloth survives today.
15,000-year-old ground sloth footprints found in Argentina PhysOrg - January 31, 2007
Explorer Charles Darwin reported in his journal of travel aboard the Beagle finding in 1832 a scelidotherium fossil in Punta Alta near Bahia Blanca, south of Buenos Aires. Another Briton, Richard Owen, identified the scelidotherium in 1839 based on Darwin's find. Argentine experts have set to the task of making casts of the footprints with polyester resin, which will allow them to make molds that can be displayed in the museum. "We can work on the prints about four hours a day, because they are covered by the tide the rest of the time," Di Martino said. The same beach yielded 7,000-year-old human footprints in the 1990s.
June 20, 2000 - University of Florida News
Bones of a newly discovered ground sloth that is the oldest of its kind ever found in North America have been uncovered by a University of Florida research team. Weighing more than five tons and able to reach as high as 17 feet, the 2.2 million-year-old prehistoric creature was larger than today's African bull elephants, said UF paleontologist David Webb. "This is a great, wonderful animal unlike anything in existence whose huge size is almost reminiscent of the dinosaurs," Webb said.
Eremotherium eomigrans, as named in a recent academic journal article, was the earliest of the giant sloths known as megatheres to have migrated from South America north across the Panamanian Land Bridge, Webb said. Before the Ice Age, these slothful plant-eaters lumbered across the Florida peninsula like herds of elephants, using their fearsome claws to strip leaves from branches and entwine them in their long tongues, he said. Unlike other large-bodied ground sloths, the new species had an extra claw, representing a surprisingly primitive stage of evolution, Webb said. While all other giant sloths had four fingers with only two or three claws, this one had five fingers, four of them with large claws, the biggest being nearly a foot long, he said."The existence of such sloths would have been expected at a much earlier time, and in South America, not Florida," he said. This evolutionary pattern of a reduction in the number of fingers and claws over time continued into the present with its modern-day descendant, the much smaller three-toed sloth, which lives in the tropical forests of Central and South America, he said. A university geology student found the ground sloth bones in 1986 during a class field trip at the Haile limestone quarry west of Gainesville. Over the years, a dozen other ground sloths were found, some completely articulated skeletons, and were brought to UF's Florida Museum of Natural History.
In 1989, Webb invited two of the world's leading specialists on such animals to examine the bones. Castor Cartelle, a zoologist from the University of Belo Horizonte in Brazil, and Gerardo De Iuliis, a zoologist from the University of Toronto in Canada, studied the bones for a decade before concluding this was a new, huge find. The findings were published as a 20-page paper in the December issue of the Zoological Journal of the Linnean Society of London. The fossil deposit was unusual in that it was found in what was a quiet pond, which allowed for excellent preservation, Webb said. Most fossil collections in Florida are found in small sinkholes or in stream deposits, where the bones are stirred up, he said.
"To get every bone in a hand perfectly articulated in a stream deposit would be very rare," he said. "Because bones are usually scattered, you would probably never know for sure how many claws an animal had, as we were able to determine with this ground sloth." The bones of one of the largest, most complete individuals will be assembled at the Natural History Exhibit Hall in Livingston, Mont. Matt Smith, a professional fossil preparator, was in Gainesville last week to collect the bones and will mount the skeleton. He said visitors to nearby Yellowstone National Park can stop and see him work through a picture window. The skeleton is to be posed in an upright position, as if stripping branches from a tree, and the finished product will be returned to the UF museum in 18 months for display in UF's Powell Hall. Giant ground sloths also fascinated President Thomas Jefferson, an amateur palentologist who brought their bones to the White House. "My favorite piece of history is when he instructed Meriwether Lewis, of the Lewis and Clark expedition, to keep an eye out for ground sloths," Webb said. "He was hoping they would find some living in the Western range."
ANCIENT AND LOST CIVILIZATIONS
PHYSICAL SCIENCES INDEX
ALPHABETICAL INDEX OF ALL FILES
CRYSTALINKS HOME PAGE
PSYCHIC READING WITH ELLIE
2012 THE ALCHEMY OF TIME | <urn:uuid:dee8df9f-a552-48a1-a87d-d308796379f6> | 3.96875 | 1,610 | Knowledge Article | Science & Tech. | 39.248154 |
New theoretical modeling by Carnegie's Alan Boss provides clues to how the gas giant planets in our solar system—Jupiter and Saturn—might have formed and evolved. New stars are surrounded by rotating gas disks during the early stages of their lives. Gas giant planets are thought to form in the presence of these disks.
Observations of young stars that still have these gas disks demonstrate that sun-like stars undergo periodic outbursts, lasting about 100 years, which transfer mass from the disk onto the young star, increasing its luminosity. It is thought that these short bursts of mass accretion are driven by marginal gravitational instability in the gas disk.
"Gas giant planets, once formed, can be hard to destroy," said Boss, "even during the energetic outbursts that young stars experience."
Boss developed highly detailed, three dimensional models demonstrating that regardless of how gas giant planets form, they should have been able to survive periodic outbursts of mass transfer from the gas disk onto the young star.
One model similar to our own Solar System was stable for more than 1,000 years, while another model containing planets similar to our Jupiter and Saturn was stable for more than 3,800 years. The models showed that these planets were able to avoid being forced to migrate inward to be swallowed by the growing proto-sun, or being tossed completely out of the planetary system by close encounters with each other.
Given that searches for extrasolar gas giant planets have found them to be present around about 20% of sun-like stars, this is a reassuring outcome. It suggests that our improved theoretical understanding of the formation and orbital evolution of gas giants is on the right track.
This research was supported in part by the NASA Origins of Solar Systems Program and contributed to in part to the NASA Astrobiology Institute. The calculations were performed on the Carnegie Alpha Cluster, the purchase of which was partially supported by a NSF Major Research Instrumentation grant.
The study was published recently by the Astrophysical Journal.
The Daily Galaxy via Carnegie Institution for Science
The image at the top of the page is an ALMA observation of the disc and gas streams around HD 142527. Credit: ALMA (ESO/NAOJ/NRAO), S. Casassus et al. | <urn:uuid:dafc7ff3-7243-41b5-a0c1-d994e11fbfa1> | 4.03125 | 464 | Knowledge Article | Science & Tech. | 43.174997 |
Beyond The Requirements
Most security vulnerabilities aren't requirements violations; rather, they come from incomplete requirements. For example, a simple requirement takes the form of "when a user applies input x, the software should produce output y." It's easy to test such requirements: Apply input x, then look for y.
Verifying requirements is critical, but security testing looks beyond intended behaviors set out in requirements. Behind those may be a lot of unspecified assumptions and constraints. For example, if the input or output is sensitive (say, a credit card number), storing it even temporarily in an insecure place is a bad idea. Developers may overlook this and make design and implementation choices that leave the software at risk. To instill security quality into a project, testers use fuzzing and similar techniques to look beyond stated requirements and get answers to questions like:
- What isn't the system supposed to do?
- How should inputs, functionality, and data be restricted?
- Are security features correct and is functional code secure?
Vulnerabilities can be introduced at any stage of development. A key security requirement might be poorly defined or missing. An architectural weakness could get introduced during design. Developers may use a vulnerable function to process user input. Security testing tools can check for these vulnerabilities, but there are limitations.
Over the past few years, several classes of security testing tools have emerged. Essentially, these tools, some of which incorporate fuzz testing, have taken over the security aspects of testing. While they tend to find certain classes of vulnerabilities, they miss many others. They aren't substitutes for security testing, but instead, like a pair of pliers, they extend your reach when testing software. Bottom line, it's people thinking creatively about how to misuse or abuse software who drive security testing. For example, a source-code scanner or security-aware compiler can look for functions and constructs that commonly result in vulnerabilities. They can alert you that the code may have a weakness even when the syntax is essentially correct. While these tools can be useful during development and testing, they see only part of the picture.
Most applications are highly interconnected and have lots of interaction with other software. Statically scanning the code of one application or module doesn't give a complete view of how a running application will respond to hostile input. Some dynamic security tools exist to help bridge the gap. Application scanners primarily focusing on Web apps create input strings that can reveal potential vulnerabilities; they also look for symptoms of failure. These tools can be good at finding low-hanging fruit and tend to focus on some of the more common vulnerabilities.
We were about 13 sodas into our discount scheme when we discovered another design choice that would make the soda machine flaw far worse -- when the machine ran out of sodas and a little red "Empty" light came on. Not willing to take a loss on the 40 cents we'd just invested, we pressed the "Coin Return" button. We assumed the machine would give us back the four Bahamian 10-cent pieces. However, pressing the button returned four U.S. quarters -- a 150% return on our investment! This was a definite upgrade over free sodas.
On its own, the coin-return design was likely a good one based on mechanics and convenience. The developer relied on the assumption that the rest of the system worked as intended, including that it correctly identified objects as quarters. The coin return design choice by itself wasn't a security vulnerability, but it severely increased the impact of the machine's existing problem, mixing up U.S. quarters and Bahamian 10-cent pieces. To have a good approach to systems security, you have to practice the principle of defense-in-depth, which forces design choices that create a safety net around potential problems. Problems like this speak to the need of a more holistic approach to security testing.
Software security quality should be woven throughout the development process. It begins in requirements and design, is propagated through development and testing, and continues into deployment and support. The good news is that there are lots of resources. Microsoft has made many of its processes and tools available from its Security Development Lifecycle, a process that provides security and privacy throughout the development process. Likewise, SAFECode is synthesizing and distributing security best practices from some of the world's largest software makers.
The various secure development methodologies have some common themes, with the need for education perhaps being the biggest. The term "education" isn't exactly right -- what's really needed is re-education so developers understand that security isn't a natural outcome of traditional qualityassurance processes. Building secure software takes focused work and a different mind-set. In a few years, if all goes well, perhaps we'll be beyond worrying about security quality because security will be woven into software in the same way that reliability is. But until that happens, I still have a few more sodas to buy. | <urn:uuid:6785d522-ca27-472f-bd8a-4e16dc011f02> | 2.921875 | 1,000 | Personal Blog | Software Dev. | 34.792997 |
joule (jōl, joul) [key], abbr. J, unit of work or energy in the mks system of units, which is based on the metric system; it is the work done or energy expended by a force of 1 newton acting through a distance of 1 meter. The joule is named for James P. Joule.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
More on joule from Fact Monster:
See more Encyclopedia articles on: Physics | <urn:uuid:26a1e971-62ae-4a88-bcf2-9392b7c71fdf> | 2.84375 | 116 | Structured Data | Science & Tech. | 61.519241 |
How do I use the java.util.Formatter class to format output?
John Zukowski There are at least three ways to generate formatted output:
- Use the format() method of an instance of Formatter.
- Use the format()/printf method of an OutputStream, as in System.out.format("The time is %tT.", Calendar.getInstance());
- Use the format() method of String, as in String.format("Today is %1$tm %1$te,%1$tY", Calendar.getInstance()); | <urn:uuid:0ddb6f5f-527d-45bc-952b-4520814cb4eb> | 3.234375 | 118 | Q&A Forum | Software Dev. | 65.577 |
"OFTEN in error but never in doubt." This accusation has sometimes been levelled against cosmologists - and justifiably so. They have frequently embraced poorly grounded speculations with irrational fervour, and been led by wishful thinking to read too much into vague and tentative evidence.
However, although this still happens, even the more cautious among us are confident that we now know some of the key cosmic numbers, and are grasping at least the outlines of how stars and galaxies emerged. Astronomers can trace the evolutionary story back long before our solar system formed 4.5 billion years ago; we can now observe galaxies that are so far away that their light set out 12 billion years ago.
We also have precise measurements of the microwaves that are, we believe, an afterglow of an intensely hot "genesis event" about 14 billion years ago. The first microsecond is still shrouded in mystery, but ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:43eeaeb5-8298-4a87-b81b-0d2aa253c4c6> | 3.546875 | 215 | Truncated | Science & Tech. | 42.664069 |
A pest is considered an animal or plant species which, in high numbers, is detrimental to park resources. When managing pests, our goals are to preserve the natural and cultural resources of the park, and to assist the agricultural cooperators with keeping the historic scene.
A prominent, but surprising, pest is the White-tailed Deer. Many parks within the National Park Service have had to address the issues associated with increasing deer populations. Deer pose a problem because, in high concentrations, they can prevent forest regeneration by eating all of the young vegetation and removing the forest understory. The battlefield also has an active agricultural lease program and the deer have affected farming practices. Fields that were traditionally planted with wheat, corn or soybeans are no longer profitable due to deer browsing.
Another pest is the Ground Hog, which is affecting the park’s cultural resources by destroying the foundations to many of our historic buildings. Their large system of burrows can also damage crops and farm equipment.
The Gypsy Moth is an exotic insect species which, in high numbers, can cause considerable defoliation of native trees. Defoliation can cause habitat changes such as decreased food for wildlife, increased sunlight which creates good habitat for invasive plants, an increase in the amount of dead timber, and changes in water quality. Last year Gypsy Moths were found in high concentrations in an area of the Brooks Hill forest. In cooperation with the U.S. Forest Service, a 40 acre block of the forest was sprayed to reduce insect populations and prevent significant defoliation. This summer park staff will be monitoring the population to determine how effective those actions were.
Did You Know?
Amphibians play an important role in the stability and diversity of the park's ecosystem. The American Toad is one of the many different types of amphibians that can be found while hiking some of the streamside trails at the park. More... | <urn:uuid:e8091664-5eae-43ad-806d-4c9bffd45d2a> | 3.65625 | 386 | Knowledge Article | Science & Tech. | 42.376917 |
In this chapter we discuss the design and implementation of a client/server
system with Java. Our simple web server provides hypertext (HTTP) pages
to the clients. We create both the server and client programs from Java,
relying heavily on classes from the java.net
package in the core language.
- Web Servers and Java - overview
of Web servers and Java is used to build them
- Design of Server -
designing a server with Java
- the tool used to monitor for and connect with clients
- Thread Workers for Clients
- assign thread process to server each individual client
- Client Socket Streams
- the I/O streams used for communications between clients and the server
via a socket.
- HTTP Protocol - basics
of the standard hypertext protocol and a method in the server for interpreting
the HTTP from the client and returning a file to the client.
- Run Server -
instructions for running the demonstration server application.
- Security Problems
- possible security roadblocks and creating a more secure version of
the demo server.
- More about Security
- more about setting up the policy file, using the policytool
program, and checking permissions inside a program.
- A Client Application
- we create a client program to interact with our Web server.
- Server Apps - example
applications of custom designed servers.
- Servlets - brief discussion
of Java programs run by application servers
Latest update: Dec. 9, 2003 | <urn:uuid:65e5c100-66fb-4588-953c-c7f050a34a22> | 3.3125 | 312 | Content Listing | Software Dev. | 44.389932 |
RENO, NEV.--The Chicxulub Crater, sprawled across the Gulf of Mexico and the Yucat¿n Peninsula, is an approximately 180-kilometer-wide remnant of the impact of a 10-kilometer-wide meteorite. It has been called the smoking gun in the extinction of the dinosaurs between the Cretaceous and Tertiary periods 65 million years ago. Some geologists, though, are starting to believe the meteorite didn't act alone. Volcanic phenomena known as superplumes may have been accomplices in that and other mass extinctions. "The general idea is that plumes are strengthened by impacts," says Dallas Abbott, a researcher at Columbia University's Lamont-Doherty Earth Observatory. At the Geological Society of America meeting in Reno last November, she showed a correlation between the timing of purported superplumes and large impact events--and their possible association with mass extinctions.
A plume can be visualized as a rising glob of liquid in a slowly warming lava lamp: material hotter than the surrounding rock of the earth's mantle pushes toward the surface in a concentrated stream. The funnel ends below the earth's outer crust, where the plume material spreads and ponds. If the molten rock erupts through the earth's surface, it releases gas and particulates into the air and produces lava flows. A superplume may be a gathering of small plumes, the size of those under the Hawaiian Island chain and Iceland, or one very large plume.
This article was originally published with the title Volcanic Accomplice. | <urn:uuid:69ff9dba-0507-4f9f-bdbd-cb23a7fa2a9c> | 3.8125 | 327 | Truncated | Science & Tech. | 34.895953 |
We learned of the existence of bacteria over 300 years ago, and we have far more of them in our bodies than human cells, but it was less than 40 years ago when we first realized how they swim. With the discovery of the rotary motor of E. coli in 1973, a motor just 45 nanometers in diameter, some claimed this incredible mechanism as evidence of God, though it is really just a step along the path of evolution. Now we can actually build nanorobots that swim similar to bacteria like E. coli. We’re working to use these to deliver drugs to specific locations in the body. E. coli itself is a kind of robot, it has sensors (chemoreceptors), motors, communication along protein guided pathways, and software (DNA). When you look at a bacterium from this perspective, it seems like a machine, one that we will be hopefully able to duplicate someday. So if bacteria are really just machines, then what are we?
Brad Nelson is the Professor of Robotics and Intelligent Systems at ETH Zürich, where his primary research focus is on microrobotics and nanorobotics with an emphasis on applications in biology and medicine. He studied mechanical engineering at the University of Illinois at Urbana-Champaign and the University of Minnesota and robotics at Carnegie Mellon University. He has worked at Honeywell and Motorola and served as a United States Peace Corps Volunteer in Botswana, Africa. He was a professor at the University of Illiois at Chicago and the University of Minnesota before joining ETH in 2002.
Prof. Nelson was named to the 2005 “Scientific American 50,” Scientific American magazine’s annual list recognizing fifty outstanding acts of leadership in science and technology from the past year for his efforts in nanotube manufacturing. His lab won the 2007 and 2009 RoboCup Nanogram Competition, both times the event has been held, in which micrometer size robots competed in soccer. His lab appears in the 2012 Guinness Book of World Records for the “Most Advanced Mini Robot for Medical Use.” He serves on the editorial boards of several journals, has chaired several international workshops and conferences, has served as the head of the ETH Department of Mechanical and Process Engineering, the Chairman of the ETH Electron Microscopy Center (EMEZ), and is a member of the Research Council of the Swiss National Science Foundation.
More about this speaker
His favourite TED Talk | <urn:uuid:a2486b45-f1fb-4b01-b954-17b8968eea24> | 2.875 | 498 | Audio Transcript | Science & Tech. | 35.411662 |
New findings suggest that biodiversity increases during warm periods, which may imply that global warming is actually good for the origination of species. The problem is that the process usually takes between thousands and millions of years, while current global warming is happening at a much faster pace.
The paper, published in the Proceedings of the National Academy of Sciences, is based on analysis of fossils and sea-surface temperatures over the last 540 million years.
‘The improved data give us a more secure picture of the impact of warmer temperatures on marine biodiversity and they show that, as before, there is more extinction and origination in warm geological periods,’ says lead author Dr Peter Mayhew of the University of York. ‘But, overall, warm climates seem to boost biodiversity in the very long run, rather than reducing it.’
The benefits, then, may be in the long term. ‘Our results seem to show that temperature improves biodiversity through time as well as across space,’ says co-author Professor Tim Benton of the University of Leeds. ‘However, they do not suggest that current global warming is good for existing species. Increases in global diversity take millions of years, and in the meantime we expect extinctions to occur.’
Mayhew, P. J., Bell, M. A., Benton, T. G., & McGowan, A. J (2012). Biodiversity tracks temperature over time Proceedings of the National Academy of Sciences
Louise I. Gerdes | <urn:uuid:fd556fcc-9977-4ff9-8139-9df92425f4d0> | 3.546875 | 307 | Knowledge Article | Science & Tech. | 45.555616 |
NAVGEM (Navy Global Environmental Model) is a global numerical weather prediction computer model run by NOAA. It replaced NOGAPS as the prime model in the middle of February 2013 at the FNMOC Weather model synoptic site. NOGAPS: Global weather forecast model from the "Fleet Numerical Meteorology and Oceanography Center" (USA)
|Updated:||2 times per day, from 10:00 and 23:00 GMT|
|Greenwich Mean Time:||12:00 GMT = 12:00 GMT|
|Resolution:||1.0° x 1.0°|
|Parameter:||Sea Level Pressure in hPa|
|Description:||The surface chart (also known as surface synoptic chart) presents the distribution of the atmospheric pressure observed at any given station on the earth's surface reduced to sea level. You can read the positions of the controlling weather features (highs, lows, ridges or troughs) from the distribution of the isobars (lines of equal sea level pressure). The isobars define the pressure field. The pressure field is the dominating player in the weather system. Additionally, this map helps you to identify synoptic-scale waves and gives you a first estimate on meso-scale fronts.|
|NWP||Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to predict the weather. Although the first efforts to accomplish this were done in the 1920s, it wasn't until the advent of the computer and computer simulation that it was feasible to do in real-time. Manipulating the huge datasets and performing the complex calculations necessary to do this on a resolution fine enough to make the results useful requires the use of some of the most powerful supercomputers in the world. A number of forecast models, both global and regional in scale, are run to help create forecasts for nations worldwide. Use of model ensemble forecasts helps to define the forecast uncertainty and extend weather forecasting farther into the future than would otherwise be possible.|
Wikipedia, Numerical weather prediction, http://en.wikipedia.org/wiki/Numerical_weather_prediction(as of Feb. 9, 2010, 20:50 GMT). | <urn:uuid:f3f44620-ebab-4a3d-a33a-cce6069ac387> | 3.484375 | 462 | Knowledge Article | Science & Tech. | 39.140198 |
- Define meteorology. Explain how the weather affects farmers, sailors, aviators, and the
outdoors construction industry. Tell why weather forecasts are important to each of these
- Name five dangerous weather-related conditions. Give the safety rules for each when
outdoors and explain the difference between a severe weather watch and a warning. Discuss
the safety rules with your family.
- Explain the difference between high and low pressure systems in the
atmosphere. Tell which is related to good and to poor weather. Draw cross
sections of a cold front and a warm front, showing the location and movements
of the cold and warm air, the frontal slope, the location and types of clouds
associated with each type of front, and the location of precipitation.
- Tell what causes wind, why it rains, and how lightning and hail are
- Identify and describe clouds in the low, middle, and upper levels of the atmosphere.
Relate these to specific types of weather.
- Draw a diagram of the water cycle and label its major processes. Explain the water cycle
to your counselor.
- Define acid rain. Identify which human activities pollute the atmosphere as well as the
effects such pollution can have on people.
- Do ONE of the following:
- Make one of the following instruments: wind vane, anemometer, rain gauge, hygrometer.
Keep a daily weather log for 1 week using information from this instrument as well as from
other sources such as local radio and television stations or NOAA Weather Radio. The
following information should be recorded at the same time every day: wind direction and
speed, temperature, precipitation, and types of clouds. Be sure to make a note of any
morning dew or frost. In the log, also list the weather forecasts from radio or television
at the same time each day and show how the weather really turned out.
- Visit a National Weather Service office or talk with a local radio or television
weathercaster, private meteorologist, local agricultural Extension service office, or
university meteorology instructor. Find out what type of weather is most dangerous or
damaging to your community. Determine how severe weather and flood warnings reach the
homes in your community.
- Do ONE of the following:
- Give a talk of more than five minutes to your unit explaining the camping safety rules in
the event of lightning, flash floods, and tornadoes. Before your talk, show your outline
to your counselor for approval.
- Read several articles about acid rain and give a prepared talk of more than
about the articles to your unit. Before your talk, show your outline to your counselor for
- Find out about a weather-related career opportunity that interests you.
Discuss with and explain to your counselor what training and education are
required for such a position, and the responsibilities required of such a | <urn:uuid:7a20d56d-bdc9-4ce8-b364-77508bcc6644> | 3.84375 | 601 | Tutorial | Science & Tech. | 38.643387 |
Modern techniques in genetics
Increasingly scientists are using new molecular techniques to investigate the structure and function of DNA. Whole genes and parts of genes can be extracted from chromosomes, linked to other DNA molecules to form recombinant DNA and introduced into living cells.
In a process known as gene cloning, the host cell's biochemical processes are used to make many copies of the inserted gene and the protein it codes for.
These technologies have produced transgenic plants and animals; where a gene from one species is introduced into another species. Transgenics have brought the possibility of specific gene therapies for human diseases such as diabetes.
Genomics attempts to understand the genome of a species as a whole, including mapping the complete nucleotide sequence for every gene. The most ambitious of these projects is the Human Genome Project, which has mapped every gene on every chromosome in the human genome.
This work is licensed under a Creative Commons Licence. | <urn:uuid:e42c26b4-ff63-49b0-a627-1d28660c8623> | 3.71875 | 188 | Knowledge Article | Science & Tech. | 22.6225 |
BATS DO IT TOO: Bats emit a series of ultrasonic pulses that bounce off objects in their environment. How long it takes for the sound to be reflected back to the bat indicates how close (or far) a given object might be, enabling the bat to orient itself as it flies, and detect food. Modern sonar technology is based on the same principle. The more feedback the bat receives, in terms of incoming reflections, the more accurately it can pinpoint a given object's location That's why the rate of the ultrasonic calls increases as the bat nears its prey, climaxing into a "feeding buzz" as the bat locks in on its target and prepares to strike. In contrast, whales appear to use sounds (or "songs") to communicate, emitting a complex sequence of low moans, high squeals and clicking noises that can last as long as 30 minutes. The songs appear to be related to mating cycles.
ABOUT SOUND: Sound waves are pressure waves: the result of a vibrating object that creates a disturbance in the surrounding air. For instance, when the telephone rings, the ringer vibrates very quickly, sending energy radiating outward through the air. These vibrations disturb the molecules that make up the air. The air molecules push closer together as the object moves one way - an effect known as compression -- and then create a space between themselves and the vibrating object as it moves the other way, called rarefaction. The motion disturbs the neighboring molecules in turn, creating an outward ripple effect, much like a stone cast in a quiet pond will cause waves to ripple outward from the spot where the stone hit.
The Acoustical Society of America contributed to the information contained in the TV portion of this report. | <urn:uuid:ea5d911f-9ff8-47bc-9cfd-881bfcb6a4b8> | 3.953125 | 358 | Knowledge Article | Science & Tech. | 43.65512 |
Physicists in Switzerland just reported they are closing in on the “Higgs boson,” a hypothesized ultra-small unit that may be the building block of subatomic particles. Let’s hope they are right, so European taxpayers get a return on the $10 billion complex built to look for the Higgs boson.
Whether this particle is found will not affect your life in any way. But the search for abstract knowledge is part of the human quest.
Last year as the holidays approached, I reviewed the state of understanding of the size and age of the cosmos. This year for the holidays, the topic is what science knows (or thinks it knows) about some fundamental questions of nature.
* What is matter? When the atom was shown to contain neutrons, protons and electrons, these were assumed to be the basic components of matter. Then such particles were shown to be made up of quarks. Now it turns out quarks — well, you can fill in the sentence. The closer researchers look at matter, the less seems to be there. A baseball is solid at the macro scale: at the subatomic scale, it seems to be made of rapidly spinning packets of nothingness.
The Higgs boson, from which quarks may be made, is conceptualized not so much as a solid entity, rather, as a fluctuation in a mysterious field that some researchers think permeates the cosmos. What is the mysterious field? Your guess is as good as the next Nobel Prize winner’s. | <urn:uuid:30bb4982-e30b-453c-a32e-d0a4f0e206c2> | 2.875 | 315 | Personal Blog | Science & Tech. | 61.557084 |
This video from Russia is called White Orca.
Here is another version of that video.
This story is, ironically, by Richard Black, Environment correspondent, BBC News:
23 April 2012 Last updated at 01:19 GMT
White killer whale adult spotted for first time in wild
The adult male, which they have nicknamed Iceberg, was spotted off the coast of Kamchatka in eastern Russia.
It appears to be healthy and leading a normal life in its pod.
White whales of various species are occasionally seen; but the only known white orcas have been young, including one with a rare genetic condition that died in a Canadian aquarium in 1972.
The sightings were made during a research cruise off Kamchatka by a group of Russian scientists and students, co-led by Erich Hoyt, the long-time orca scientist, conservationist and author who is now a senior research fellow with the Whale and Dolphin Conservation Society (WDCS).
“We’ve seen another two white orcas in Russia but they’ve been young, whereas this is the first time we’ve seen a mature adult,” he told BBC News.
“It has the full two-metre-high dorsal fin of a mature male, which means it’s at least 16 years old – in fact the fin is somewhat ragged, so it might be a bit older.”
Orcas mature around the age of 15, and males can live to 50 or 60 years old, though 30 is more commonplace.
“Iceberg seems to be fully socialised; we know that these fish-eating orcas stay with their mothers for life, and as far as we can see he’s right behind his mother with presumably his brothers next to him,” said Dr Hoyt.
The cause of his unusual pigmentation is not known. The captive white orca, Chima, suffered from Chediak-Higashi syndrome, a genetic condition that causes partial albinism as well as a number of medical complications.
It is possible that an attempt may be made to take a biopsy from Iceberg; but with researchers reluctant to do so unless there is a compelling conservation reason, they are hoping instead for closer observations including a detection of eye colour.
The project Dr Hoyt co-leads, the Far East Russia Orca Project, has pioneered visual and acoustic monitoring in the inhospitable Kamchatka seas, and has produced a number of papers on the communication of killer whales.
This may lead to improved understanding of the animals’ complex social structure, which includes matrilineal family clans, pods consisting of several families, and much larger “super-pods”.
A related project aims to study and conserve habitat for all whales and dolphins around the Russian coast.
The most famous white whale, though, is the fictional sperm whale that drove Captain Ahab to his eventually fatal fury in Moby Dick.
4 white Southern Right whale calves spotted off South Australia: here.
The Acrobatic Humpbacks of Baja (Mexico): here.
April 2012. The International Jojoba Export Council (IJEC) has signed an historic agreement with conservation group, the Whale and Dolphin Conservation Society (WDCS), at Europe’s premier trade show for cosmetic ingredients (In-Cosmetics®) in order to promote the benefits of using jojoba as a green and renewable alternative to oil taken from whales killed in cruel hunts, and also to highlight the fact that, despite international bans, the use of whale-derived ingredients in cosmetic products still occurs: here.
April 2012. Conservation and animal welfare groups have expressed concern over news that Iceland’s hunt of endangered Fin whales will resume this summer: here. | <urn:uuid:24112824-4359-4b11-9dc2-eb49be23b77b> | 2.6875 | 782 | Personal Blog | Science & Tech. | 41.27558 |
Anthropogenic climate warming is leading to consideration of options for geoengineering to offset rising carbon dioxide levels. One potential technique involves injecting artificial sea spray into the atmosphere. The sea salt particles would affect Earth's radiation budget directly, by scattering incoming solar radiation, and indirectly, by acting as cloud condensation nuclei, which could lead to whiter clouds that reflect more radiation.
- Geoengineering: A whiter skyFri, 1 Jun 2012, 16:02:22 EDT
- Geoengineering by coalitionThu, 21 Feb 2013, 15:34:16 EST
- Symposium to discuss geoengineering to fight climate change at the ESA Annual MeetingThu, 6 Aug 2009, 2:56:35 EDT
- Biological activity alters the ability of sea spray to seed cloudsTue, 23 Apr 2013, 6:22:24 EDT
- Whiter clouds could mean wetter landMon, 28 Jun 2010, 12:09:46 EDT | <urn:uuid:72c1d656-6435-43cc-8ee3-9bdbe9dc748d> | 3.421875 | 190 | Content Listing | Science & Tech. | 27.653557 |
Well, I'd have figured my definition would be in here already, but it's not, so I'll take a stab at this.
The best definition for infinity that I know of is
inf = lim ___
where n is any positive real number, and |x| approaches downward to zero (as noted by Professor Pi). I prefer to actually set n to 1 when I define infinity, because certain math problems arise where the limits of two functions f(x) and g(x) both approach infinity, but for any x g(x) is not the same value as f(x). For example, g(x) might be defined as twice f(x). In these cases, the limit of f(x) would be infinity, and the limit of g(x) would be 2 · infinity. To me, defining infinity as the limit of 1 divided by x as x approaches zero is easiest on my brain as it clears any ambiguity. I just use the above definition with n=1 and I know how large any infinite value is relative to any other. When you factor in the fact that you can have negative infinite values, well, I think it just makes sense.
Personally, I do think this definition makes the most sense because it can rearranged as a definition of zero:
zero = lim ___
In my mind, n in this case is not so important since any number times zero is zero, but still, I prefer n to be one (at least, when dealing w/ limits). So there you have it. Well, my take on it at least.
The proper name for the symbol is actually infinity and it looks like an 8 rotated 90°. Supposedly, some browsers (supporting HTML 4.0) should be able to display infinity as ∞ or ∞ (but mine doesn't). In case yours does, the HTML for it is (or should be) ∞ or ∞ To use the former, your browser must support HTML 4. Ability to use the latter of course depends upon your system being able to display the ISO 10646 character set. My browser/OS combination doesn't allow either, but I've included it just in case yours does.
As for the name of the symbol, it is simply "infinity." It has no other fancy name, and in fact has no "official" name. Some do refer to it as lazy eight, and some call it lemniscate. As far as lemniscate goes, it is actually the name of a mathematical system that just looks like the symbol for infinity. The symbol itself was introduced by mathmetician John Wallis in 1655 when he wrote "De sectionibus conicis." The symbol was supposedly borrowed from a Roman symbol for 1 000 and was declared to represent infinity.
Now Txikwa tells me (in addition to the correct spelling of Wallis' treatise on conic sections)
"Probably the thousand symbol mentioned is not ordinary M but an old alternative way of writing it: CID where the D is a backwards C. (And half of that gave normal D for 500.)" Sounds reasonable to me.
Ken "Dr." Math. Ask Dr. Math - Infinity Symbol. The Math Forum. <http://forum.swarthmore.edu/dr.math/problems/lazy8.html>
W3C. Character entity references in HTML 4. <http://www.w3.org/TR/REC-html40/sgml/entities.html> | <urn:uuid:1e1fffa3-c11d-4787-9049-c10706d04884> | 2.75 | 729 | Comment Section | Science & Tech. | 70.660887 |
This brochure was prepared by researchers
at Carnegie Mellon University to explain
the issue of global warming and climate change. The key points are covered
in the three parts that follow:
The issue at a glance...
- Burning coal, oil and natural gas releases carbon dioxide gas into
the atmosphere. On average, this may warm the earth and change the climate
in other ways. For example, it might change the severity and duration
of storms or droughts.
- Other human activities, such as cutting down forests, and growing
rice, and raising cattle, may have the same effect, but are less important.
- If the climate changes heating, cooling, water use, and sea level
will be affected. In wealthy countries, the average cost would probably
be small, although some people and regions might have high costs and
others might receive large benefits. In some poor countries, the cost
could be very high.
- A large or fast change in climate will have a big effect on plants
and animals in the natural environment.
- Very rapid climate change is unlikely, but could be disastrous, even
for wealthy countries.
- We could reduce the rate at which we add carbon dioxide to the atmosphere
by burning less coal, oil and natural gas.
- If climate changes, we could adapt by changing agriculture and other
human activities. Many plants and animals in the natural environment
might be unable to adapt.
- If warming is large and costly, some people might want to make changes
to the atmosphere or oceans in order to cool the earth. This is very
The three sections linked from this summary tell you more about the climate
change issue. You can find even more information in the "details booklets"
found via the links in each section. A glossary, that defines words, and a list of additional
readings are in the back of Details Booklet Part 3.
This brochure was written by a group in the Department of Engineering and Public Policy at
Carnegie Mellon University. More information about the authors.
To obtain one or more print copies of the Brochure
Carnegie Mellon University
All orders must be prepaid. Make check payable to Carnegie Mellon University
and send to the address indicated above. Thank you.
Department of Engineering and Public Policy
Pittsburgh, PA 15213
ATTN: Climate Brochure
$6.00/copy quantities less than 10
$5.50/copy quantities greater than 10
$5.00/copy quantities greater than 100
Copyright 1994. This material may be reproduced
for free distribution. It may not be reproduced for sale in any form without
the written permission of the authors. | <urn:uuid:19c4a1c1-b552-47ed-8b35-abb3a3c07411> | 3.53125 | 559 | Knowledge Article | Science & Tech. | 50.401266 |
Functions may have polymorphic arguments, subject to three restrictions:
- Such functions must have explicit type signatures, using forall to bind polymorphic type variables, e.g.
g :: (forall a. a -> a) -> (Bool, Char)
- In the definition of the function, polymorphic arguments
- must be matched on the left-hand side, and
- can only be matched by a variable or wildcard (_) pattern. The variable then has the polymorphic type of the corresponding argument, e.g.
g f = (f True, f 'a')
- When such a function is used, it must be applied to at least as many arguments to include the polymorphic ones (so it's a good idea to put those first). Each expression must have a generalized type at least as general as that declared for the corresponding argument, e.g.
g id g undefined
The more general RankNTypes relax restrictions 2(1) and 3.
- PolymorphicComponents do the same thing for data constructors.
- add RankNTypes or Rank2Types
- simple type inference
- offered by GHC and Hugs for years
- enables runST and similar devices
- used in cheap deforestation
- useful with non-regular (or nested) types
- useful with PolymorphicComponents
- functions with rank-2 types are not first class
- can be awkward in comparison with RankNTypes | <urn:uuid:9879eafe-2dde-408e-8793-7fc8c3f37aba> | 3.15625 | 306 | Documentation | Software Dev. | 46.867286 |
This image of comet 55P/Tempel-Tuttle was obtained as part of a research effort at the Pic du Midi Observatory in France by a team of observers, including L. Jorda (Max Planck Institute for Aeronomie), J. Lecacheux (Meudon Observatory), F. Colas (Bureau des Longitudes, Paris), E. Frappa (Planetarium de Saint-Etienne, France) and P. Laques (Bagneres-de-Bigorre, France). The image was obtained with a 105cm telescope and a Thomson 7863 CCD camera and a broadband filter 530-900 nm. The image is the sum of 40 exposures of 240 seconds. The comet was 1.09 AU form the Sun and 0.59 AU from Earth. The left image shows the unprocessed result. By applying a median selection algorithm to the full set of images, the observers were able to efficiently remove all things that did not share the comet motion (middle image). After removing a radial 1/rho profile, a dust jet is visible (left image).
The extend of the jet structure is shown in these images. These images were obtained after a radial profile substraction and a rotational gradient. The reduction of many observation nights allowed the observers to find two possible spin periods for the comet. This informations was published in the IAU Circular 6816 on 1998, January 30th. In their posting of February 2nd, Jean Lecacheux, Eric Frappa and Francois Colas report that the rotation period of the nucleus is: 15.33 +/- 0.02 hours. | <urn:uuid:63f19525-4f76-4f74-a0da-d000703c6c45> | 3 | 337 | Knowledge Article | Science & Tech. | 60.2275 |
The rapid increase in carbon dioxide (CO₂) in the atmosphere since the industrial revolution is heating the earth and decreased the ocean’s pH level. Sea temperature is predicted to rise by between 2 to 4 °C and ocean pH is predicted to decrease 0.2-0.4 units by the end of this century. These changes, along with associated changes in the carbonate chemistry of seawater, are predicted to disrupt calcification and affect the physiology of many marine organisms. While the effects of ocean acidification (OA) on adult scleractinian corals have been extensively studied, until very recently, the effects of OA on the ecology of the early life history stages of corals remained largely unexplored. Similarly, while the effects of temperature on adults and early life history stages of corals are well known, the possible synergistic effects of temperature and OA have not been examined. It is important to assess the effect of OA on the early life stages of corals in order to predict the likely effects on population dynamics. In addition, such research will provide useful guidance for managing coral reefs. To address these critical knowledge gaps, I explored the effect of OA and temperature on fertilization, development, survivorship and metamorphosis using gametes and larvae of a number of abundant scleractinian corals from the Great Barrier Reef. In the first series of experiments, I used four treatment levels of pCO2 corresponding to current levels of atmospheric CO2 (approximately 380 ppm), and three projected values within this century (550, 750 and 1000 ppm), to test whether fertilization, embryonic development, larval survivorship or metamorphosis was affected by OA. None of these variables were consistently affected by pCO₂ suggesting that there will be no direct ecological effects of OA on the pre-settlement stages of reef corals, at least in the near future. In a second series of experiments, I tested the effect of OA in combination with elevated temperature on the response variables mentioned above. We used four treatments: control, elevated temperature (+2°C), decreased pH (600-700 ppm) and a combination of elevated temperature and acidity. There were no consistent effects of OA on fertilization, development, survivorship or metamorphosis either alone, or acting synergistically with temperature. In contrast, temperature consistently increased rates of development, but otherwise had little effect. I conclude that temperature is more likely to affect the ecology of the early life history stages of corals in the near future, mostly by speeding up rates of development and therefore altering patterns of connectivity among reefs. In the third set of experiments, I compared the effects of ocean acidification on the larval metamorphosis of a spawning coral Goniastrea retiformis and a brooding coral Leptastrea cf transversa in Guam. Again, metamorphosis was not consistently affected by pCO₂ in either species. These results suggest that the mode of reproduction does not affect the larval response to pCO₂ and furthermore, there will be no direct effects of ocean acidification on settlement rates of reef corals, at least in the near future. In the final set of experiments, I tested the effect of ocean acidification on its own and in combination with elevated temperature on the growth of juveniles of Acropora millepora and Acropora tenuis using the treatment levels described above. Neither OA nor temperature had any significant effect on growth or the pattern of skeleton formation in these species. I concluded ocean acidification is not a threat to the early life history stages of corals in the foreseeable future.
Chua, C.-M., 2012. The effects of ocean acidification and warming on the early life history stages of corals. PhD thesis, James Cook University, 109 p. Thesis. | <urn:uuid:78e92f99-054e-4cbc-a1d4-5d818ef29664> | 2.828125 | 786 | Academic Writing | Science & Tech. | 23.12599 |