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Landing a space vehicle on a celestial body devoid of atmosphere, such as the moon, presents special technical problems of braking the vehicle’s descent and accurately controlling the braking action. The conditions of entry are different from those presented by a major planet enveloped in a relatively dense atmosphere. For a moon landing the entire kinetic energy of the vehicle must be braked by a counteracting thrust developed by rockets.
On arrival in the vicinity of the moon, the spacecraft is first slowed down by firing its retro-rocket motors, so that it goes into a circular parking orbit round the moon. This applies more particularly to a manned spacecraft such as the Apollo which the Americans have used for landing men on the moon. In the case of the Apollo XI project the actual descent onto the moon’s surface was made by two astronauts in a special mooncraft, the “lunar (excursion) module” (abbreviated as “LEM” or “LM”), which was detached from the orbiting spacecraft, in which one astronaut remained awaiting the return of the mooncraft.
The entire procedure of releasing the mooncraft, landing it at a predetermined site on the moon and then linking it once again to the spacecraft is one which requires precise control of the direction and velocity of both vehicles. When the spacecraft is accurately in orbit and in the correct position on its orbit to ensure a landing in the desired area, the mooncraft briefly fires its rocket motor so that it moves away from the spacecraft and goes into an elliptical orbit whose point nearest the moon is located some 10 to 20 miles before and six or seven miles above the planned landing area. The periodic time of the mooncraft in this elliptical orbit must be the same as that of the spacecraft in its circular parking orbit. This particular requirement is for the astronauts’ safety; should the landing rockets fail to fire, the mooncraft will simply continue in orbit and automatically encounter the spacecraft; the latter can then be maneuvered into a docking position with the mooncraft, so that the two astronauts in it can return to the spacecraft that will take them back to earth.
When the mooncraft is in the correct position in its orbit, the actual landing maneuver can commence. The landing rocket motor of the mooncraft must be able to develop a thrust that can be suitably varied, because at the start of the landing operation the craft still carries its full load of rocket fuel, and its speed has to be slowed down from about 5000 mph to zero. In doing this, fuel corresponding to about two-thirds of the mooncraft’s initial total weight (with full tanks) is consumed. The power and direction of the thrust developed by the motor are so controlled that the craft lands at a predetermined point and at a predetermined speed. If the orbit in which the mooncraft is moving around the moon deviates a little from the specified orbit, corrections can be made by means of small steering rocket jets. In this way the horizontal and the vertical speed in relation to the landing area are reduced. When the horizontal speed has diminished to zero, the mooncraft will slowly sink towards the surface, the actual speed being kept under control by means of retroactive rocket motor thrust. By this time the astronauts have taken over manual control of the mooncraft. Scanning the lunar surface from an altitude of several hundred feet, they select a zone free from boulders, deep cracks or other hazards and then bring their craft gently down. The final operation calls for very accurate control of the thrust so that it almost exactly balances the mooncraft’s weight. When the feet of the craft touch the surface, the motors are shut off.
On completion of their exploration of the lunar surface, the astronauts return to their mooncraft. The lower half of the craft serves as a launching pad for the upper half, which is provided with a second, smaller rocket motor just under the crew cabin. This motor propels the ascent stage of the mooncraft back to the spacecraft, which will rendezvous and dock with it. The lunar astronauts then transfer to the spacecraft and jettison the mooncraft; the return flight to earth then begins.
The sequence of operations for the Apollo XI moon landing project was as follows:
1. Saturn rocket is launched, carrying the Apollo spacecraft with the mooncraft
enclosed within it.
2. First stage of the rocket is jettisoned, second stage is fired.
3. Second rocket stage is jettisoned, third stage goes into orbit around the earth (1 ½ revolutions).
4. Third stage is fired, thereby increasing the speed from 17,500 mph to the so-called “escape velocity” of almost 25,000 mph.
5. Third stage burns out. Apollo spacecraft is released. Mooncraft (LEM) and command module are now docked together nose to nose by a complex maneuver. They then reconnect with the third stage and continue the flight. Third stage is then finally jettisoned, and Apollo spacecraft starts up its own rocket motors. Apollo comprises the command module (i.e., the crew capsule), the service module, and the mooncraft.
6. Braking rockets are fired; spacecraft goes into orbit around the moon at an altitude of about 70 miles.
7. Two astronauts enter moon craft, which is now detached from the spacecraft.
8. Mooncraft goes into its own orbit bringing it over the landing area.
9. Main braking rocket motor of moon craft is fired. Telescopic legs of mooncraft are extended and it lands on the lunar surface.
10. Ascent stage of mooncraft launched for return flight to orbiting spacecraft.
11. Rendezvous with spacecraft. Lunar astronauts transfer themselves from mooncraft to spacecraft.
12. Mooncraft is jettisoned.
13. Spacecraft starts return flight to earth.
14. Command module is detached from service module.
15. Command module is maneuvered so that the heat shield is facing forward on entering the earth’s atmosphere.
16. Final parachute descent to earth. | <urn:uuid:febbb094-0f0c-413c-8664-7bd833078b09> | 4.0625 | 1,243 | Tutorial | Science & Tech. | 53.111057 |
Division of Energy
Wind Energy Resources
- Small Wind Energy Systems, Fact Sheet--PUB2313 (02/09)
- Net Metering and the Easy Connection Act, Fact Sheet--PUB2238 (02/08)
- Wind Energy Public Forums (2008 forums)
- Missouri Wind Energy Workgroup
- Wind Energy Internet Resources
- Missouri Anemometer Loan Project Initial Results (Graphs and Data Files)
Wind Speed Maps
The final wind speed maps show the predicted mean wind speed in Missouri at heights of 30 meters, 50 meters, 70 meters, and 100 meters, respectively, above the effective ground level. As of 2005, typical tower height for the current generation of large utility-scale wind turbines of 750 KW (kilowatt) to 2 MW (megawatt) rated capacity is 70 meters. A typical height for small turbines of up to 50 KW rated capacity is 30 meters, which is consistent with on-farm or residential use.
|Wind Speed 30 Meters||High Res 3.9 MB||Low Res 717 KB|
|Wind Speed 50 Meters||High Res 2.8 MB||Low Res 783 KB|
|Wind Speed 70 Meters||High Res 3.2 MB||Low Res 726 KB|
|Wind Speed 100 Meters||High Res 3.1 MB||Low Res 733 KB|
Wind Power Density Maps
The 50-meter wind power density map shows the predicted mean wind power density (amount of wind energy) at 50-meter height in the National Renewable Energy Laboratory's (NREL) standard wind resource classes.The 100-meter wind power density map shows the predicted mean wind power density at 100-meter height. When compared to the 50-meter wind density map, this indicates a substantial increase in wind energy as the distance from the ground increases.
|Wind Power Density 50 Meters||High Res 2.5 MB||Low Res 814 KB|
|Wind Power Density 100 Meters||High Res 2.4 MB||Low Res 725 KB|
The mean speed and power describe different aspects of the wind resource, and both can be useful in different ways. The mean speed is the easiest for most people to relate to. Some experts regard the mean wind power, which depends on the air density and the cube of the wind speed, as a more accurate indicator of the wind resource when assessing wind project sites.
Generally speaking, utility-scale wind power projects using large turbines that service the electrical grid require an average wind speed of at least 7 meters per second (15.7 miles per hour) or average power of at least 400 Watts per square meter (NREL class 4). Small-scale turbines such as those used by farmers and homeowners are often used in locations with lower average annual wind speeds.
Persons interested in evaluating the financial aspects of an investment in a wind energy project are encouraged to become familiar with one or more of the free wind energy financial calculators that can be found on the internet at:
- Windustry: http://www.windustry.com/calculator/default.htm
- Wind Powering America (U.S. Department of Energy): http://analysis.nrel.gov/windfinance/login.asp
- Canada's Renewable Energy Decision Support Center's "RETScreen International": http://www.retscreen.net/ang/g_win.php
These maps are final work products of AWS Truewind Solutions prepared under contract with the Missouri Department of Natural Resources, with financial support from the U.S. Department of Energy's Wind Powering America.
Validation of the map was conducted by the National Renewable Energy Lab and consulting meteorologists. After reviewing the validation results, NREL recommended moderate adjustments in speed and power to one region of the state. The speed was increased by 5 percent in eastern Missouri in the counties of St. Charles and St. Louis, and the power was increased by about 30 percent. For your convenience we have kept the INTERIM wind maps online.
Note that while it is believed that these maps represent an accurate overall picture of Missouri's wind energy resource, estimates at any location should be confirmed by additional wind measurements taken at the specific site.
Portions of the preceding description were adapted from the final report submitted by AWS Truewind as part of their preparation of these maps. For more information see AWS Truewind's Final Report .
30 meter average annual wind speed - County level maps
All of the following counties are predicted to have some areas with an average-annual wind speed (measured at 30 meters, 100 feet above ground level) of 6.0 meters per second (13.4 miles per hour) or greater.
Click below to view a county level version of the 30-meter wind speed map for the listed counties. State and county roads are displayed in red.
Note: * Indicates counties that are predicted to have some areas with average annual wind speeds between 6.5 and 7.0 meters per second (14.5 and 15.7 miles per hour) at 30 meters above ground level.
Counties not included in the list below are predicted to have very little area, or no area, with an average-annual wind speed of 6.0 meters per second (13.4 miles per hour) or greater.
Missouri Wind Energy Resources CD-ROM
- An interactive version of the wind maps, that includes ArcReader 8.3 Geographic Information System map viewing software is available on CD-ROM. According to the company that created ArcReader 8.3, the software will work on a PC-Intel system with:
- Windows NT 4.0 with service pack 6a,
- Windows 2000 or
- Windows XP operating systems
- It will not work on Windows ME, 98 or earlier.
- The CD-ROM will also include a variety of wind energy publications, presentations, and links to internet websites.
You can request a free copy of this CD-ROM by filling out our online form. It is expected that the initial mailing of the CD-ROM will be during September 2005. | <urn:uuid:01ee7460-aca1-4437-8f41-388b1e52af9d> | 3.09375 | 1,270 | Knowledge Article | Science & Tech. | 59.956723 |
Albert Einstein (1879 - 1955) was a theoretical physicist, philosopher and author who is
widely regarded as one of the most influential and best known scientists and intellectuals of all time. He is often
regarded as the father of modern physics. He received the1921 Nobel Prize in Physics "for his services to
Theoretical Physics, and especially for his discovery of the law of the photoelectric effect". The latter was pivotal
in establishing quantum theory within physics.
Near the beginning of his career, Einstein thought that Newtonian mechanics was no longer enough to reconcile the laws of classical mechanics with the laws of the electromagnetic field. This led to the development of his special theory of relativity. He realized, however, that the principle of relativity could also be extended to gravitational fields, and with his subsequent theory of gravitation in 1916, he published a paper on the general theory of relativity. (from wikipedia.org)
|Einstein (History Channel)|
|This is a 2010 History Channel documentary that provides a glimpse of Einstein's life and his scientific achievements, featuring his decades-long battle to prove his theory of general relativity.|
Einstein Revealed is a science documentary film chronicling Albert Einstein's life and scientific achievements from his birth to his death.
|Film||Albert Einstein: How I See the World
This is a PBS documentary exploring Einstein's life, work and legacy. Albert Einstein is considered one of the greatest scientific thinkers of all time.
This is a 1979 BBC documentary hosted by Peter Ustinov, which is based on the book Einstein's Universe by Nigel Calder. It provides demonstrations to illustrate the concepts of Einstein's relativity.
|Film||E=mc2: Einstein's most famous equation
Based on David Bodanis's best selling book E=mc2: A Biography of the World's Most Famous Equation, Einstein's Big Idea tells the story behind how the equation E=mc2 could be invented.
|Book.||Einstein His Life And Times
Author: Philipp Frank, Translated from a German manuscript by George Rosen, Edited and revised by Shuichi Kusaka. Publisher: Alfred A. Knopf. Book Contributor: Universal Digital Library.
|Book||From Newton to Einstein; changing conceptions of the universe
Author: Benjamin Harrow, 1888-1970. Subject: Isaac Newton, 1642-1727; Albert Einstein, 1879-1955; Gravitation; Relativity (physics); Ether (of space). Publisher: New York, D. Van Nostrand company.
|Book||An introduction to the theory of relativity
Author: Lyndon Bolton. Subject: Relativity (physics). Publisher: New York, E. P. Dutton. Language: English. Book Contributor: University of California Libraries.
|Book||The principle of relativity; original papers
Author: A. Einstein and H. Minkowski. Translated into English by M.N. Saha and S.N. Bose. Subject: Relativity (physics). Publisher: [Calcutta] The University of Calcutta. Book Contributor: MIT Libraries.
|Book||Relativity; the special and general theory
Author: Albert Einstein, 1879-1955; Translated by Robert Lawson. Subject: Relativity (physics). Publisher: New York, H. Holt and company. Book Contributor: Cornell University Library.
|Book||The meaning of relativity : four lectures delivered at Princeton University, May, 1921
Author: Albert Einstein, 1879-1955. Subject: Relativity (Physics); Physicists. Publisher: Princeton : Princeton University Press. Book Contributor: Northeastern University, Snell Library.
|Book||The Evolution Of Physics
Author: Albert Einstein and Leopold Infeld. Subject: Natural Sciences; Physics; General mechanics. Publisher: The Scientific Book Club And Company Limited. Book Contributor: Osmania University. | <urn:uuid:72bfe07d-350c-45be-91a3-375e332e8a97> | 3.515625 | 817 | Content Listing | Science & Tech. | 38.520259 |
The swallow-tailed kite is a graceful raptor with a seemingly effortless soaring ability, making it a favorite among birder-watchers. March to September is the optimum time to spot a swallow-tailed kite in the Southeastern U.S.
The kite leaves its wintering habitat in northern South America, taking various migration routes – either over the Gulf of Mexico or around the Gulf through Central America and Mexico.
Final destination: the wooded wetlands and major river systems of Alabama, the Florida peninsula, Georgia, Louisiana, Mississippi, South Carolina and Texas. The greatest breeding numbers, however, are found in Florida.
In Mississippi, the Pascagoula and the lower Pearl rivers are known to attract populations of the swallow-tailed kite each spring and summer. In 2005, 27 nesting pairs were seen soaring above the expansive bottomland forests and healthy marshes of the lower Pearl River.
Scientists estimate that the swallow-tailed kite only inhabits about 5 percent of its historic range. Prior to the early 1900s, kites were abundant and known to nest in 21 states, including most of Florida, the southeastern U.S. coastal region and throughout the Mississippi Valley as far north as Wisconsin.
Today, the global population of swallow-tailed kites is estimated to be 150,000. Considered a species of conservation concern in Mississippi, the swallow-tailed is one of the most threatened land birds currently without federal protection under the Endangered Species Act of 1973.
Populations of the swallow-tailed kite declined rapidly in the last century. Widespread habitat loss and the on-going conversion of bottomland forests for agriculture and development purposes continue to threaten the recovery of this species. Other activities such as the collection of eggs and the shooting of adults also contributed to population losses.
The Conservancy and its partners are working along the Pascagoula and lower Pearl rivers to protect the forests, swamps and marshes essential to the survival of swallow-tailed kites, an on-going effort since the 1970s.
Today, nearly 70,000 acres of bottomland forests and swamps are protected along the Pascagoula River, the nation’s largest unaltered river system. In 2001, the Conservancy helped establish the Pascagoula River Basin Alliance, a coalition of public, private and individual stakeholders who use research, communication and action to ensure the Pascagoula remains one of the nation’s best preserved river systems.
The Conservancy owns and manages five preserve in the lower Pearl River Basin, totaling more than 6,400 acres, and helped secure 13,206 acres for the Old River Wildlife Management Area managed by the Mississippi Department of Wildlife, Fisheries, and Parks.
The Conservancy also helped purchase 22,765 acres in the lower Pearl basin for the Bogue Chitto National Wildlife Refuge, creating a vital wildlife corridor by connecting the land to the Pearl River Wildlife Management Area in Louisiana.
The Conservancy’s Mississippi and Louisiana programs, in collaboration with the state agencies, created the Lower Pearl Partnership in 2002. The Lower Pearl Partnership is working with public and private stakeholders to restore and protect ecologically significant areas on the Pearl River and its tributaries.
February 14, 2011 | <urn:uuid:67c8ccaa-4c7e-4e5a-92ab-27c57afe12e9> | 3.609375 | 671 | Knowledge Article | Science & Tech. | 29.352027 |
Algae and Pond Maintenance
From WikiAlgae thrive during the spring season and the dog days of summer. Algae can be revealed in several shapes and pigments. Green algae are the most typical kind of pond algae. They are ancient plants similarly analogous to fungi. They don’t have any real leaves, stems, or roots. They multiply by way of spores, by cells dividing, or by breaking down into fragments. Algae require light from the sun to grow and flourish from a superabundant supply of vitamins and minerals in the water.
Planktonic algae are tiny and almost undetectable plants, typically dangling from the topmost feet of water. I used to swim in the ponds at my grandparents campsite and my mother would have a fit and insist that I take a bath when I got out. I could never understand why, I thought I was super clean. When I was older I went back to the same ponds and understood exactly why my mother made me bathe. The algae in the ponds gave it a vivid green appearance. Large numbers of fish can perish on account of not getting enough oxygen. A few varieties have been discovered to be poisonous to farm animals and animals in the wild.
If you look at the top of the water you will notice green colored masses. This kind of algae normally starts its threadlike, filamentous, development adjacent to the borders or base of the pond and will sooner or later usurp the whole bottom. The filaments are created from cells fastened end to end giving it the illusion of threads. Some of the most widely known types of algae are Pithophora or Filamentous and Spirogyra.
Spirogyra is a threadlike form of algae and can be encountered in virtually all ponds and ditches. Chloroplasts in this algae are spiral structures, hence the origin of the name. It reproduces at a speedy rate and could possibly grow throughout the whole pond, smothering it.
Pithophora is filamentous algae that is a deep shade of green and is typically called cotton ball or horsehair algae. It normally cultivates in unrefined clusters of interwoven filaments looking like little globes of cotton. An over abundant amount of branches are seen in single pieces of filament. Maturation is extremely fast on account of cells reproducing.The next type of algae is Macro Algae and bares resemblance to a plant blossoming with flowers because this algae appears to be grounded when they are really only fastened to the surface area. As with Spirogyra and Pithophora, this too is generates at a fast rate.
The last type of algae this article will touch upon is Chara. It is referred to as musk grass on account of its stagnant garlicky aroma. Chara, being comprised of many cells, is also green and is a lot of times mistaken as underwater plants baring flowers. It is affixed to the bottom but is not grounded. Chara normally exhibits black balls referred to as sporangia that can be seen throughout the regeneration stage.
Most algae infestation can be controlled by applying copper based type product to the area either in a granular form for spot treatment or a liquid form for larger areas. Bacterial products are generally used as a sludge digester, restoring the natural balance to an aquatic environment after harsh chemicals are used for algae removal.
By: Bradley Skierkowski | <urn:uuid:14dcebc6-708a-4caf-931a-cb78751e0d00> | 3.0625 | 704 | Knowledge Article | Science & Tech. | 46.823886 |
Water conservation involves the reduction in usage of water as well as the recycling of waste water for various purposes, including cleaning, manufacturing, and agricultural irrigation. A major issue for both consumers and industry alike, water conservation is increasingly important in a world with a rapidly growing population, particularly in urban areas.
As people push against the limits of what nature freely offers us in terms of fresh water, climate stability and more, how can we use our resources to achieve the greatest return for society?
3 | April 1, 2013 3:00am |
PARIS -- Part 2 in a two-part series: Fusion could be the future of cleaner energy, but many in France and beyond oppose the cost and uncertainy of the ITER project.
10 | March 29, 2013 3:00am |
Thanks to ambitions of humans going to Mars one day, technology that turns wastewater into drinking water is improving.
February 14, 2013 7:27am |
Nowhere is the challenge of the energy-water nexus so acute as in the Middle East. Here's what Abu Dhabi plans to do about it.
26 | February 6, 2013 3:00am |
The author and Audubon Medal-winner talks about transforming cities into "incubators of biodiversity" and tackling Nature-Deficit Disorder.
1 | December 10, 2012 4:15am |
Taking an optimistic approach to ecological preservation and resilience theory, versus a gloomy one, could push conservation in exciting directions, says Peter Kareiva of the Nature Conservancy.
November 21, 2012 8:34am |
The World Bank president Jim Yong Kim has called for urgent measures to combat the "devastating" consequences of climate change.
20 | November 19, 2012 5:45am |
HYDERABAD -- India walks a tightrope between development and conservation.
2 | October 22, 2012 12:00am |
Chicago's Department of Transportation just might have accomplished its mission to create the "greenest street in America."
13 | October 21, 2012 3:04pm |
The air is fresh and clean, and the "pebbles" have a certain sheen. Check out this photo essay to see what we mean. Learn what happens a century after you use your beach as the city dump.
4 | September 10, 2012 2:28am |
The energy policies of President Obama and Mitt Romney offer two radically different directions into the future. Which one would take us into prosperity?
95 | September 5, 2012 1:48am |
Scientists have discovered how furry creatures shake off water, which has practical uses, plus gives us this adorable video.
1 | August 24, 2012 3:03am |
When a sprawling urban city like New York's drainage system can be overwhelmed with the smallest amount of rain, what can be done?
1 | August 21, 2012 5:47am |
Scientists created an ocean health index to judge how oceans are faring in providing us with food, jobs and carbon storage. The U.S. scored just above average, at 63.
4 | August 21, 2012 3:01am |
A Boston start-up says that the energy solutions market has a goldilocks problem that it can solve by making collecting and analyzing data cost effective for the small commercial sector.
1 | August 5, 2012 6:19pm |
First the Queen did it on the River Thames near Windsor Castle. Now a London park heads to the river to turn the ancient Archimedes screw upside down and generate electricity. Watch videos.
5 | July 19, 2012 8:50am |
Take some cues from Integral Group, an over-achieving building engineering company that has designed the most world�s most energy-efficient office space.
5 | July 16, 2012 3:00am |
Can you imagine a "harmless" building? That's the impetus behind a Passive House, a new or retrofitted building with the singular goal of minimizing energy consumption.
11 | July 16, 2012 2:35am |
Smart grid technologies are just years away from being installed throughout municipal water systems to reduce waste, detect contaminants, and raise awareness about how much of this resource so...
July 12, 2012 6:00pm |
The giant beverage company figures it could save close to 26.4 billion gallons of water annually across its global bottling operations.
5 | July 11, 2012 4:12am | | <urn:uuid:eab4bebb-2495-4698-ba1c-605a99bcea73> | 3.34375 | 919 | Content Listing | Science & Tech. | 52.893429 |
These images show thermal infrared radiation from Jupiter at different wavelengths which are diagnostic of physical phenomena The 7.85-micron image in the upper left shows stratospheric temperatures which are elevated in the region of the A fragment impact (to the left of bottom). Temperatures deeper in the atmosphere near 150-mbar are shown by the 17.2-micron image in the upper right. There is a small elevation of temperatures at this depth, indicated by the arrow, and confirmed by other measurements near this wavelength. This indicates that the influence of the impact of fragment A on the troposphere has been minimal. The two images in the bottom row show no readily apparent perturbation of the ammmonia condensate cloud field near 600 mbar, as diagnosed by 8.57-micron radiation, and deeper cloud layers which are diagnosed by 5-micron radiation.
Images, Images, Images | <urn:uuid:4f4fbc49-35b9-4b75-a181-2b9d088399fa> | 2.734375 | 184 | Knowledge Article | Science & Tech. | 39.971524 |
Binary tree in C++
Simple, may not be the best implementation there is. Contains functions for inserting, deleting, finding the next and previous values, checking if a node is a leaf, printing, searching, counting the number of nodes, etc.
Also contains a main with examples. Nice for beginners.by cohenman on 29 May 110536 downloads0
Doubly linked list in C++. A simple implementation that includes a few simple features:
Adding a node, erasing a node, searching a node, counting the number of nodes in the list, printing the list by a recursive function, printing the list iteratively and printing the list in reverse order.
The nodes hold only integers as data but this can be generalized easily.by Mr on 12 May 110550 downloads0
Graph is a data structure used in many algorithms. It's vertices are represented by a separate class, Vertex. There is a data (Object type) field in vertex class, which can be used to store any data. Vertex class can be modified to hold any information (e.g. Student, Account, etc.) by using the example.by javadream on 09 Apr 110450 downloads0
Binary heap is a tree type data structure. It has all the properties of binary search trees including the following ones-
1) All the levels of the binary tree must be filled except the last one. Levels are filled from left to right order. This property is known as shape property.
2) Each node's value must be less than or equal to all it's child nodes values [for min-heap]. Or, Each node's value must be greater than or equal to all it's child nodes values [for max-heap]. This property is known as heap property.by javadream on 12 Nov 100465 downloads0
Binary search tree is a tree type data structure. Each node can have at most two immediate children. Binary search tree (BST) also have some special properties- 1) For any node, the node value will be greater than the values of all the nodes of the left subtree (if any). 2) For any node, the node value will be less than (or equal to) the values of all the nodes of the right subtree (if any). 3) For any node, it's left and right subtrees (if any) will also be binary search trees.
Here is an implementation example of BST in Java.by javadream on 08 Nov 100391 downloads0
Queue is a FIFO (First In First Out) type data structure. The first item to enter queue always comes out of the queue first. In queue, data is inserted (enqueue) in its "rear" and extracted (dequeue) from its "front".
Here is an implementation of queue using Java. It stores integer type data. It's simple and easy to understand.by javadream on 08 Nov 100369 downloads0
Singly linked list (also known as, linked list) is a data structure that serves the purpose of a dynamic array. Every item in that list contains two parts- data, and pointer to next item. The first item is pointed by a pointer known as "head". And, the last item has "null" to its next, which means the end of list.
There can various of methods in a linked list, such as- goFirst(), insert(), remove(), etc. Here is an implementation of linked list in Java with basic functionality. It can hold integer type data.0342 downloads0
Stack is a LIFO (Last In First Out) type data structure. The last item to enter stack always comes out of the stack first. This data structure is very useful in implementing many algorithms.
Here is an implementation of stack using Java. It stores integer type data so it's a very simple implementation. Good as a tutorial for data structures 101.0339 downloads0
Doubly linked list is a data structure that serves the purpose of a dynamic array. Every item in that list contains three parts- data, pointer to next item and pointer to previous item. The first and last items are pointed by pointers known as "head" and "tail" respectively. The last item has "null" to its next, which means the end of list. Similarly, the first item has "null" to its previous, which means starting of the list. Unlike singly linked list, this list is able to move in both forward and backward direction.0490 downloads0 | <urn:uuid:7925921b-30ee-4b37-b959-8d7b3b4cd1a7> | 3.5625 | 940 | Content Listing | Software Dev. | 64.945003 |
Add a wee bit of science to your St. Patrick's Day pranks and celebration with these fun chemistry projects.
1. Green Fire
Wasn't there green fire in Disney's 1959 movie "Darby O'Gill and the Little People"? If not, there should have been. Eldritch green fire screams Irish and St. Patrick's Day.
2. Dye Beer Green
Use food coloring, not some weird chemical reaction. If you drink enough green beer, it could cause your urine to turn green. I imagine you might see even see leprechauns, though that would be from the alcohol, not the coloring.
3. Gold Pennies
Use chemistry to make your very own pot of gold by changing the color of pennies from copper to silver and finally to gold! Some say leprechaun gold vanishes before you can spend it. You can't spend this gold either, but that doesn't make the project any less fun.
4. Green Eggs
Eat fried green eggs for breakfast. They look a little strange, but most people would prefer it to cabbage and corned beef. Actually, this project uses cabbage juice to turn the eggs green, so it's highly appropriate.
Make green slime and set it someplace tricky to try to catch a leprechaun! It's like a humane glue trap, right? Personally, I'll be highly surprised if you manage to catch a leprechaun using green slime, but it's worth a try.
If you put green food coloring in a white flower's water, you can get a pretty green flower. It's also possible to apply a little chemistry know-how to make a glowing green flower for St. Pats. | <urn:uuid:323da947-8c6c-4d92-8a27-1fd86ecd6954> | 2.890625 | 353 | Listicle | Science & Tech. | 78.386329 |
The Rise and Full of the Space Shuttle
JANUARY 28, 1986 proved to be the blackest day in the history of human adventure into outer space. On this cragic'day^all the seven crew mertibers perished in the 25th space shuttle mission (Mission S\ -L) and the 10th flight of the space shuttle Challenger. This single accident left as many dead as the total dead in all the previous space travel accidents.
The explosion was indeed a disaster for the entire humanity. What adds to its tragic dimensions is that millions of children, watching on TV a school teacher Chnsta McAuliffe lift off into space, saw everything end up in a fireball. A unique experiment was in the offing in which the teacher in outer space was to give lessons to her students on the planet Earth. In restrospect her words : "If the teacher in space doesn^t come back to teach, something is wrong", holds an irony that no one can ignore. Her words were meant to assure her students that the newly acquired space fame would not keep her away from her students.
Space ventures have always had an element of uncertainty and risk. However, humanity had taken pride in this endeavor and had come to believe that every fors»eeable risk had been eliminated, every conceivable safety system incorporated and every possible accident scenario anticipated and eliminated. At least, that was the case till militarisation and commercialisation got the upper hand in space missions.
It is now left to the ashes of the shuttle crew to tell the tragic consequence of rapid militarisation and commercialisation of outer ^space. Hidden behind the triumphant story ofshutde flights, an all-time record of two dozen flights since 1981, is the not so widely known history of a space programme ridden with serious problems from its very outset. The manipulation by the powerful l6bby of Aerospace industry and the US Space Administration ensured that those facts never got much attention in the mass media. But as one ofthe investigative reports put it, "the question was not whether a major disaster could befall the shuttle programme but of when."
The first launch of space shuttle—the Columbia mission of April 12, 1981—came after a series of delays, causing severe anxiety to the US Space Administration. However, the delay did not lead to an early reappraisal of the programme. This launch took place after the computer monitoring the launch stopped the launch several rimes.
Delhi Science Forum, New'Ddhi. | <urn:uuid:28f7c17b-b2b1-4092-b697-2e82a6e9d8a6> | 3 | 507 | Knowledge Article | Science & Tech. | 42.138277 |
Comprehensive data on the chemical element Fluorine is provided on this page; including scores of properties, element names in many languages, most known nuclides of Fluorine. Common chemical compounds are also provided for many elements. In addition technical terms are linked to their definitions and the menu contains links to related articles that are a great aid in one's studies.
A list of reference sources used to compile the data provided on our periodic table of elements can be found on the main periodic table page.
If you need to cite this page, you can copy this text:
Kenneth Barbalace. Periodic Table of Elements - Fluorine - F. EnvironmentalChemistry.com. 1995 - 2013. Accessed on-line: 5/22/2013 | <urn:uuid:71121a48-1a96-4b2f-b59c-07a9f60622eb> | 3.046875 | 156 | Structured Data | Science & Tech. | 41.070769 |
The following completion functions have nothing in themselves to do with minibuffers. We describe them here to keep them near the higher-level completion features that do use the minibuffer.
This function returns the longest common substring of all possible completions of string in collection. The value of collection must be a list of strings or symbols, an alist, an obarray, a hash table, or a completion function (see Programmed Completion).
Completion compares string against each of the permissible completions specified by collection. If no permissible completions match,
nil. If there is just one matching completion, and the match is exact, it returns
t. Otherwise, it returns the longest initial sequence common to all possible matching completions.
If collection is an alist (see Association Lists), the permissible completions are the elements of the alist that are either strings, symbols, or conses whose car is a string or symbol. Symbols are converted to strings using
symbol-name. Other elements of the alist are ignored. (Remember that in Emacs Lisp, the elements of alists do not have to be conses.) In particular, a list of strings or symbols is allowed, even though we usually do not think of such lists as alists.
If collection is an obarray (see Creating Symbols), the names of all symbols in the obarray form the set of permissible completions. The global variable
obarrayholds an obarray containing the names of all interned Lisp symbols.
Note that the only valid way to make a new obarray is to create it empty and then add symbols to it one by one using
intern. Also, you cannot intern a given symbol in more than one obarray.
If collection is a hash table, then the keys that are strings are the possible completions. Other keys are ignored.
You can also use a symbol that is a function as collection. Then the function is solely responsible for performing completion;
try-completionreturns whatever this function returns. The function is called with three arguments: string, predicate and
nil(the reason for the third argument is so that the same function can be used in
all-completionsand do the appropriate thing in either case). See Programmed Completion.
If the argument predicate is non-
nil, then it must be a function of one argument, unless collection is a hash table, in which case it should be a function of two arguments. It is used to test each possible match, and the match is accepted only if predicate returns non-
nil. The argument given to predicate is either a string or a cons cell (the car of which is a string) from the alist, or a symbol (not a symbol name) from the obarray. If collection is a hash table, predicate is called with two arguments, the string key and the associated value.
In addition, to be acceptable, a completion must also match all the regular expressions in
completion-regexp-list. (Unless collection is a function, in which case that function has to handle
In the first of the following examples, the string ‘foo’ is matched by three of the alist cars. All of the matches begin with the characters ‘fooba’, so that is the result. In the second example, there is only one possible match, and it is exact, so the value is
t.(try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))) ⇒ "fooba" (try-completion "foo" '(("barfoo" 2) ("foo" 3))) ⇒ t
In the following example, numerous symbols begin with the characters ‘forw’, and all of them begin with the word ‘forward’. In most of the symbols, this is followed with a ‘-’, but not in all, so no more than ‘forward’ can be completed.(try-completion "forw" obarray) ⇒ "forward"
Finally, in the following example, only two of the three possible matches pass the predicate
test(the string ‘foobaz’ is too short). Both of those begin with the string ‘foobar’.(defun test (s) (> (length (car s)) 6)) ⇒ test (try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) ⇒ "foobar"
This function returns a list of all possible completions of string. The arguments to this function (aside from nospace) are the same as those of
try-completion. Also, this function uses
completion-regexp-listin the same way that
The optional argument nospace is obsolete. If it is non-
nil, completions that start with a space are ignored unless string starts with a space.
If collection is a function, it is called with three arguments: string, predicate and
all-completionsreturns whatever the function returns. See Programmed Completion.
Here is an example, using the function
testshown in the example for
try-completion:(defun test (s) (> (length (car s)) 6)) ⇒ test (all-completions "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) ⇒ ("foobar1" "foobar2")
This function returns non-
nilif string is a valid completion possibility specified by collection and predicate. The arguments are the same as in
try-completion. For instance, if collection is a list of strings, this is true if string appears in the list and predicate is satisfied.
This function uses
completion-regexp-listin the same way that
If predicate is non-
niland if collection contains several strings that are equal to each other, as determined by
completion-ignore-case, then predicate should accept either all or none of them. Otherwise, the return value of
test-completionis essentially unpredictable.
If collection is a function, it is called with three arguments, the values string, predicate and
lambda; whatever it returns,
test-completionreturns in turn.
This function returns the boundaries of the field on which collection will operate, assuming that string holds the text before point and suffix holds the text after point.
Normally completion operates on the whole string, so for all normal collections, this will always return
(0 . (lengthsuffix
)). But more complex completion such as completion on files is done one field at a time. For example, completion of
"/usr/sh"will not include
"share/". So if string is
"/usr/sh"and suffix is
(5 . 1)which tells us that the collection will only return completion information that pertains to the area after
If you store a completion alist in a variable, you should mark the
variable as “risky” with a non-
risky-local-variable property. See File Local Variables.
If the value of this variable is non-
nil, Emacs does not consider case significant in completion. Note, however, that this variable is overridden by
read-file-name(see Reading File Names), and by
read-buffer(see High-Level Completion).
This is a list of regular expressions. The completion functions only consider a completion acceptable if it matches all regular expressions in this list, with
case-fold-search(see Searching and Case) bound to the value of
This macro provides a way to initialize the variable var as a collection for completion in a lazy way, not computing its actual contents until they are first needed. You use this macro to produce a value that you store in var. The actual computation of the proper value is done the first time you do completion using var. It is done by calling fun with no arguments. The value fun returns becomes the permanent value of var.
Here is an example of use:(defvar foo (lazy-completion-table foo make-my-alist))
completion-in-region provides a convenient way to
perform completion on an arbitrary stretch of text in an Emacs buffer:
This function completes the text in the current buffer between the positions start and end, using collection. The argument collection has the same meaning as in
try-completion(see Basic Completion).
This function inserts the completion text directly into the current buffer. Unlike
completing-read(see Minibuffer Completion), it does not activate the minibuffer.
For this function to work, point must be somewhere between start and end. | <urn:uuid:fcfa693d-ed38-4799-9fe6-6e18eb694aa7> | 2.6875 | 1,877 | Documentation | Software Dev. | 48.890526 |
The answer would be actually much simpler if the collapse produced a black hole. It can be easily shown to have entropy vastly exceeding the entropy of any gas of the same mass.
Concerning your main question, the answer is, of course, that any system with many degrees of freedom - both in classical physics as well as quantum physics - always satisfies the second law of thermodynamics. The second law may always be proved - quite generally. The proofs are the proofs of the H-theorem or its generalization for any physical system you consider.
Just think about the "balls" in the phase space - any phase space - how it gets deformed via the time evolution. The "smoothened" version of this evolved "spaghetti" has a higher volume whose logarithm represents the entropy increase.
If you didn't allow the molecules to emit photons when they collide, they wouldn't ever shrink spontaneously by obeying the laws of gravity. The probability that a molecule slows down (or gets closer) under the gravitational influence of the other molecules would be equal to the probability that it speeds up (or gets further) - in average. If you introduce some objects and terms in the Hamiltonian that allow inelastic collisions, these inelastic collisions will selectively slow down the molecules that happened to be closer to each other, which is the mechanism that will be reducing the average distance between the molecules (the actual rate will depend on the gravitational attraction, too).
I wrote photons because, obviously, the probability of the emission of a photon is much higher for real-world gases because most of their interactions are electromagnetic interactions. Because a photon carries as much entropy as a graviton would, but you produce many more photons by random collisions, the entropy increase is stored in the photons. The entropy carried by gravitons is smaller by dozens of orders of magnitude. | <urn:uuid:e04de9e8-7334-4092-adf8-2aa18a9908f3> | 3 | 380 | Q&A Forum | Science & Tech. | 30.086538 |
Sakurajima in Japan erupting in 2000.
Sometimes, it is the volcanoes that erupt out of the blue that get all the attention, leaving the ones that are constant producers to be ignored by the fawning media. Sakurajima in Japan is just one of those constant erupting volcanoes that doesn’t get its just due. Well, over the weekend, Sakurajima broke its own record as it produced its 549th explosive event this year – in June no less – marking the most explosions (video) in a single year at the volcano on record. The previous record for most explosive eruptions in a single year at Sakurajima was 548 set all of last year (2009). The eruptions of Sakurajima so far in 2010 tend are believe to have released over 3 million tonnes of ash – however, the volcano observatory near Sakurajima doesn’t think that this activity is leading to a large explosive eruption – instead they just warn “watch out for large rocky ash falling in surrounding areas.” Good advice!
Sakurajima is one of the most active (unsurprisingly) volcanoes in Japan, just off shore from Kagoshima City, and is actually a series of overlapping cones making up an andesitic volcanic complex – all part of the Aira caldera. The current eruptive period at the volcano started in 1955 and have produced the equivalent of a VEI 3 eruption (albeit over half a century), but it has produced VEI 1-2 eruptions frequently over the few hundred years. In 1914 and 1779, Sakurajima did have larger explosive events – VEI 4 eruptions – so the potential for bigger eruptions is there. However, right now you can watch Sakurajima put on its explosive show via its webcam … so enjoy the record year at the Japanese volcano. | <urn:uuid:6369f140-58df-44d1-9d88-39819f731987> | 2.78125 | 394 | Personal Blog | Science & Tech. | 36.208476 |
How do you decide what to call a variable? Many conflicting constraints come to bear on this question. I want to communicate my intent fully through my names, which often suggests long names. I’d like the names to be short to simplify code formatting. Names will be read many times for each time they are typed, so the names should be optimized for readability, not ease of typing. Both the way the data in the variable is used and the role that data plays in the computation need to be expressed.
There are several pieces of information I need when I am trying to understand a variable. What is its purpose in the computation? How is the object referred to by the variable used? What is the scope and lifetime of the variable? How widely is the variable referenced?
Many variable naming schemes include type information in the names. Mine doesn’t. What is the point of telling the compiler the types of variables over and over if I have to turn around and embed that same information again in the variable names? I can see including type information in variable names in languages that don’t do much to prevent type errors, like C. Java provides ample support for avoiding type errors.
If I want to know the type of one of my variables, my IDE gives me quick feedback about it. Using short, composed methods also provides a quick reference to the most commonly used variables, locals and parameters.
Another facet of variables that readers need to understand is the scope of variables. Some variable naming practices encode the scope as a prefix to the name so
fCount is a field and
lCount is a local. Again, by composing relatively short methods I find that I am seldom confused by the scope of a variable. If I can’t see a declaration of the variable here in this method, it is most likely a field (I use other techniques to avoid most static fields).
This leaves the role of the variable as the primary piece of information I try to communicate with my variable names, generally leading to short, clear names. If I have to struggle to find a name, it is generally because I don’t understand the computation very well.
There are a few variable names that recur in my code:
- result — stores the object that will be returned from a function
- each — stores the individual elements of a collection while iterating (although I am becoming fond of using the singular form of the collection’s name, for example for (
Node child: getChildren())).
- count — stores counts
If I have multiple variables that I would like to give the same name, I qualify the name:
I am sometimes tempted to abbreviate words in variable names. This optimizes typing at the expense of reading. Since variables are read many times for each time they are written, this is a false economy. Sometimes I am tempted to use several words for a variable, which makes the variable too long for comfortable typing. When this happens I look at the surrounding context. Why do I need so many words to distinguish this variable’s role from the role of other variables? Often this leads me to simplify the design, allowing me to again write short variable names in good conscience.
To summarize, I communicate the role a variable plays through its name. Everything else important about the variable—its lifetime, scope, and type—can generally be communicated through context.
|This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License| | <urn:uuid:6a7be0a1-2998-4609-8c7b-52b6e62609ce> | 2.78125 | 723 | Documentation | Software Dev. | 44.840567 |
Statistics and Probability Dictionary
Select a term from the dropdown text box. The online statistics
glossary will display a definition, plus links to other
related web pages.
Statisticians distinguish between two broad categories of
Probability sampling. With probability sampling, every element
of the population has a known probability of being included in the sample.
Non-probability sampling. With non-probability sampling, we
cannot specify the probability that each element will be included in the
Probability samples allow us to make probability statements about sample
statistics. We can estimate the extent to which a sample
is likely to differ from a population
. The bulk of this web site focuses on probability sampling. | <urn:uuid:3b74db44-8647-4ad0-b3fc-3a940516850c> | 2.984375 | 152 | Structured Data | Science & Tech. | 20.503226 |
|Did Lacis et al try to turn the control knob up to 12 out of 10?|
The links for the article are http://www.tswj.com/2012/761473/ and the journal itself - http://www.tswj.com/contents/
Emeritus Faculty, Australian National University, Canberra, ACT 0200, Australia
Academic Editor: Donald H. Stedman
Copyright © 2012 Timothy Curtin. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper tests various propositions underlying claims that observed global temperature change is mostly attributable to anthropogenic noncondensing greenhouse gases, and that although water vapour is recognized to be a dominant contributor to the overall greenhouse gas (GHG) effect, that effect is merely a “feedback” from rising temperatures initially resulting only from “non-condensing” GHGs and not at all from variations in preexisting naturally caused atmospheric water vapour (i.e., [H2O]). However, this paper shows that “initial radiative forcing” is not exclusively attributable to forcings from noncondensing GHG, both because atmospheric water vapour existed before there were any significant increases in GHG concentrations or temperatures and also because there is no evidence that such increases have produced measurably higher [H2O]. The paper distinguishes between forcing and feedback impacts of water vapour and contends that it is the primary forcing agent, at much more than 50% of the total GHG gas effect.
Read More at Scientific World Journal...That means that controlling atmospheric carbon dioxide is unlikely to be an effective “control knob” as claimed by Lacis et al. (2010). | <urn:uuid:8df44685-07eb-468c-baac-39810e8dba4b> | 2.71875 | 376 | Truncated | Science & Tech. | 33.002879 |
Texas Leafcutting Ant (Atta texana)
Anonymous. 1989. Insects and Diseases of Trees in the South. USDA Forest Service. Protrotection Report R8-PR16. 98 pp.
The Texas leafcutting ant, or town ant, is a serious pest of pine regeneration in the upland areas of west central Louisiana and east Texas. It does not occur in other forested areas across the South.
Identifying the Insect
Leafcutting ants are rust colored with large heads. They live in large colonies. The queen is 3/4 inch (18 mm) long, and lives in an underground chamber. The worker ants are most numerous and range in size from 1/10 to 1/2 inches (3 to 12 mm) long. Ant nests consist of numerous crescent-shaped mounds on the surface and extensive underground passageways and chambers. The mounds may be restricted to a small area or extend over an acre or more. Foraging trails cleared of vegetation are often present around the central town area.
Identifying the injury
Leafcutting ants will attack hundreds of plant species. They damage all species of southern yellow pine by removing the needles, buds, and bark of seedlings during the winter and early spring when other green vegetation is unavailable. This is when large acreages of pine regeneration can be killed around leafcutting ant colonies. Once the seedlings have reached the height of 2 to 3 feet, they are rarely killed by leafcutting ants.
The ants have a mating flight in May or June. After mating, the females establish nests beneath the soil and become the queens of the colonies. Worker ants carry the cut foliage and other vegetative material back to the nest, where it is used to culture the fungus that is their primary food.
There are few natural enemies. Control can be attained by fumigating the nest. | <urn:uuid:9a498d3c-7f7b-410d-8f1a-ca64d3f64965> | 3.390625 | 381 | Knowledge Article | Science & Tech. | 58.094139 |
Hydrogen produced from water using aluminium and gallium
Jerry Woodall describes a method of producing hydrogen using water, aluminium and gallium.
Robyn Williams: A couple of weeks ago we brought you research at the University of Queensland using algae to produce hydrogen. Now another promising means using aluminium. Here's Peter Pockley with the swashbuckling Professor Jerry Woodall at Perdue University in Indiana USA.
Jerry Woodall: We have learned how to split water with a material that normally won't do it because of a passivating oxide that covers it, that material is aluminium, and I figured out a way of disrupting this passivating A oxide so that the water that comes in contact will react with the aluminium forming hydrogen, aluminium oxide and heat. The hydrogen part is a highly volatile gas that is hard to store, transport and use safely. No one has yet figured out how to provide hydrogen to tens of millions of motorists without great risk. What I hope to show you today is I have found a way to get around those risks for hydrogen, and the bottom line is I can make hydrogen when you want it, or hydrogen on demand.
Okay, so what we're going to use is aluminium now. Aluminium is not thought of as a fuel but if you were a thermochemist and you were asking the question of the energy content of aluminium...suppose I compare it to oil. So I take some aluminium and take it to its oxide, namely aluminium oxide, compare that energy that's released to oil, and it turns out that a pound of oil will give you 19,000 BTUs, British Thermal Units. Well, aluminium will give you 14,000 BTUs per pound. So aluminium, even though you don't think of it this way, is a very high energy density material, and the amount of energy released when it goes from aluminium to aluminium oxide is a lot, just like when you burn oil, that's a lot too.
Peter Pockley: We're with Professor Jerry Woodall and we've now just moved into the laboratory at Perdue.
Jerry Woodall: Okay, we're going to show you an alloy pellet.
Peter Pockley: That's 50% aluminium and 50% gallium.
Jerry Woodall: Right. So this is a little chunk of that and we're going to add water to it.
Peter Pockley: And Jeffrey you're a...
Jeffrey: I'm a PhD student in the electrical and computer engineering department here at Perdue University.
Peter Pockley: And in your gloved hand is a pellet of this magical material.
Peter Pockley: Okay, what are we going to see?
Jeffrey: You can expect to see that pretty much on the instant it comes into contact with water, you will see particles being dispersed in the water from the reaction and you will see bubbles, and those bubbles are indicative of hydrogen production. So you can see the pellet in there, it weighs probably roughly three or four grams, and here goes some water.
Peter Pockley: Yes, quite rapidly some very small bubbles, the kind of thing you see in a soft-drink when the pressure is released. And how long will this fizzing process go on for?
Jeffrey: You can expect to see noticeable reaction for up to three or four minutes after the initial contact with water.
Peter Pockley: And what turns it off?
Jeffrey: Either removing the water from contact with the alloy or using up all the aluminium that's present in the alloy.
Peter Pockley: So it's bubbling away at quite a rate now. Is it fairly constant, that it goes at a predictable rate using this kind of material?
Jeffrey: Yes, some start up faster than others, but you can pretty much expect to see the same thing happening each time you conduct an experiment like you see here.
Peter Pockley: And if you test the gas which is coming off, it's quite evidently hydrogen?
Jeffrey: Yes, we've done several tests already and we've gotten up to around 88% hydrogen. We expect that the rest are just contaminants from our measuring equipment and stuff. We expect that if we do it right we can get 99% purity hydrogen or higher.
Jerry Woodall: Turning out grey like it usually does.
Peter Pockley: Is that the pellet beginning to disintegrate with the release of the...
Jeffrey: That's right.
Peter Pockley: Is that a factor that's going to be something you've got to take account of in a commercial process?
Jerry Woodall: No because we'll use the aluminium up and then reclaim the aluminium oxide, the water, and we'll reprocess it. It's all mechanical separation after that.
Jeffrey: You can expect to see a power such as this after the reaction has gone to completion and you evaporate off the water.
Peter Pockley: A sort of a granular light-grey powdery material, which is aluminium oxide.
Jeffrey: Yes, aluminium oxide with a little bit of the gallium compound that we put in there.
Peter Pockley: It looks deceptively simple.
Jerry Woodall: I'm not smart enough to do complicated things, Peter.
Peter Pockley: Was it simple to get to this point, though?
Jerry Woodall: It was a discovery, you know. What can I tell you? I was working on something complicated, as I told you, in my office to make crystals, that was complicated, but this is not. And in hindsight it's very obvious that it should work.
Peter Pockley: So we could be looking at this very simple beaker which is common in a chemistry laboratory at any school, that built into there could be a solution or one of the solutions to the world's energy problems. You're not taking it too far in making that claim, are you?
Jerry Woodall: No. I mean, look, this is scalable easily. If you could imagine scaling this thing into a steam ship, a submarine or anything. But I'm not going to claim that that's been done, it's got to be done.
Peter Pockley: Well done to Perdue, and thank you very much for the demonstration.
Jerry Woodall: Okay.
Peter Pockley: Energy galore.
Robyn Williams: Peter Pockley at Perdue and his full report on that approach and its potential is in the current addition of the Australasian Science magazine.
- Jerry M. Woodall
- Professor of Electrical and Computer Engineering
West Lafayette, Indiana USA
- Peter Pockley
- Science writer
- Robyn Williams
- David Fisher | <urn:uuid:97e17ba5-0bda-4db4-93c9-c868b77d6bff> | 3.390625 | 1,409 | Audio Transcript | Science & Tech. | 57.593308 |
Glycolipids are carbohydrate-attached lipids. Their role is to provide energy and also serve as markers for cellular recognition.
They occur where a carbohydrate chain is associated with phospholipids in the cell surface membrane. The carbohydrates are found on the outer surface of all Eukaryotic cell membranes.
They extend from the phospholipid bilayer into the aqueous environment outside the cell where it acts as a recognition site for specific chemicals as well as helping to maintain the stability of the membrane and attaching cells to one another to form tissues. | <urn:uuid:d5f170db-420d-403b-bc95-db94ea59aab0> | 3.34375 | 116 | Knowledge Article | Science & Tech. | 22.185 |
The general steps to creating a widget in GTK are:
gtk_*_new() - one of various functions to create a new widget. These are all detailed in this section.
Connect all signals and events we wish to use to the appropriate handlers.
Set the attributes of the widget.
Pack the widget into a container using the appropriate call such as gtk_container_add() or gtk_box_pack_start().
gtk_widget_show() the widget.
gtk_widget_show() lets GTK know that we are done setting the attributes of the widget, and it is ready to be displayed. You may also use gtk_widget_hide to make it disappear again. The order in which you show the widgets is not important, but I suggest showing the window last so the whole window pops up at once rather than seeing the individual widgets come up on the screen as they're formed. The children of a widget (a window is a widget too) will not be displayed until the window itself is shown using the gtk_widget_show() function.
You'll notice as you go on that GTK uses a type casting system. This is always done using macros that both test the ability to cast the given item, and perform the cast. Some common ones you will see are:
G_OBJECT (object) GTK_WIDGET (widget) GTK_OBJECT (object) GTK_SIGNAL_FUNC (function) GTK_CONTAINER (container) GTK_WINDOW (window) GTK_BOX (box)
These are all used to cast arguments in functions. You'll see them in the examples, and can usually tell when to use them simply by looking at the function's declaration.
As you can see below in the class hierarchy, all GtkWidgets are derived from the GObject base class. This means you can use a widget in any place the function asks for an object - simply use the G_OBJECT() macro.
g_signal_connect( G_OBJECT (button), "clicked", G_CALLBACK (callback_function), callback_data);
This casts the button into an object, and provides a cast for the function pointer to the callback.
Many widgets are also containers. If you look in the class hierarchy below, you'll notice that many widgets derive from the Container class. Any one of these widgets may be used with the GTK_CONTAINER macro to pass them to functions that ask for containers.
Unfortunately, these macros are not extensively covered in the tutorial, but I recommend taking a look through the GTK header files or the GTK API reference manual. It can be very educational. In fact, it's not difficult to learn how a widget works just by looking at the function declarations. | <urn:uuid:1cbee8df-fc09-44a7-ae35-605ba7b6da1f> | 3.140625 | 592 | Tutorial | Software Dev. | 54.54262 |
Explanation: Comet Halley was photographed superposed in front of the disk of our Milky Way Galaxy in 1986 by the Kuiper Airborne Observatory. Comet Halley is the bright white streak near this photograph's center. Comet Halley is the most famous comet in history, and returns to the inner Solar System every 76 years. Stars visible in our Milky Way Galaxy typically lie millions of times further in the distance and orbit the Galactic center every 250 million years. Billions of comets are thought to orbit our Sun but most do not get close enough for us to see. Similarly, billions of stars orbit our Milky Way's center but do not get close enough for us to see. | <urn:uuid:0213db70-2957-4ecd-948e-7f19d711e212> | 4.03125 | 139 | Knowledge Article | Science & Tech. | 53.050385 |
While refining their novel method for making nanoscale wires, chemists at the National Institute of Standards and Technology (NIST) discovered an unexpected bonus—a new way to create nanowires that produce light similar to that from light-emitting diodes (LEDs). These "nano-LEDs" may one day have their light-emission abilities put to work serving miniature devices such as nanogenerators or lab-on-a-chip systems.
"Measurement of Fast Electron Spin Relaxation Times with Atomic Resolution").
Solar energy could be a central alternative to petroleum-based energy production. However, current solar-cell technology often does not produce the same energy yield and is more expensive to mass-produce. In addition, information on the total effect of solar energy production on the environment is incomplete, experts say.
At the 25th European Photovoltaic Solar Energy Conference (Valencia, Spain), imec presents several large-area silicon solar cells with a conversion efficiency above 19%.
Dynasil Corporation of America has announced that the U.S. Department of Energy (DOE) has approved seven of its Phase-II SBIR projects for awards, ranging from $750,000 to $1,000,000 each. The awards, totaling $6.2 million, are being made to its wholly owned subsidiary, Radiation Monitoring Devices, Inc ("RMD"), to develop its state of the art nuclear sensors and instruments.
NanoEngineers at the University of California, San Diego are designing new types of lithium-ion (Li-ion) batteries that could be used in a variety of NASA space exploration projects – and in a wide range of transportation and consumer applications. NEI Corporation and UC San Diego recently won a Phase II Small Business Technology Transfer contract from NASA to develop and implement high energy density cathode materials for lithium batteries.
Electronic products pollute our environment with a number of heavy metals before, during and after they're used. In the U.S. alone, an estimated 70% of heavy metals in landfill come from discarded electronics. With flat screen TVs getting bigger and cheaper every year, environmental costs continue to mount.
Inorganic chalcogenide (WS2) nanotubes have shown revolutionary chemical and physical properties that offer a broad range of applications. They are ultra-strong impact-resistant materials. This makes them excellent candidates for producing bullet proof vests, helmets, car bumpers, high strength glues and binders, and other safety equipment. The unique nanotubes are up to four to five times stronger than steel and about six times stronger than Kevlar, the nowadays most popular material used for bullet proof vests.
Imec has fabricated tandem organic solar cells with peak conversion efficiencies of 5.15%. This was achieved by stacking two different planar heterojunction devices, each with a high open-circuit voltage (Voc). The universal nature of the interconnection scheme makes it easy to incorporate new promising materials in the tandem configuration. The screening of candidate materials is ongoing at imec, with the focus on materials with absorption spectra extended to higher wavelengths. The goal is to combine these new materials with the current tandem set, creating a stack of 3 or more cells that will result in an even broader coverage of the solar spectrum and in higher efficiencies.
An international team of researchers has succeeded in producing nanocrystals that build conductive two-dimensional nanostructures trough self-organisation ("Ultrathin PbS Sheets by Two-Dimensional Oriented Attachment").
Photovoltaic cells made from organic compounds, rather than silicon wafers, are set to transform the solar energy industry. Because organic solar cells are made using solution processes, they can be spread onto flexible substrates, like films or fabrics, in the same manner as inks or paints. These properties open the way for intriguing new applications, such as light-harvesting clothes and window coatings — but only if scientists can find organic materials that combine high solar conversion efficiency with favorable behaviour in solutions.
Harnessing darkness for practical use, researchers at the National Institute of Standards and Technology (NIST) have developed a laser power detector coated with the world's darkest material—a forest of carbon nanotubes that reflects almost no light across the visible and part of the infrared spectrum. | <urn:uuid:fa4a1afe-18bb-47c6-a3ef-0b76286235c5> | 3.15625 | 900 | Content Listing | Science & Tech. | 25.964471 |
The impact of biological invasions on the food web of the Wadden Sea (INFOWEB)
09 / 2011 - unknown
To demonstrate the impact of invasive species on the food web of the Wadden Sea three characteristic areas with a different degree of invasive impact will be analysed with respect to the food web, the status of the system and its interaction with human activities. In contrast to the bulk of monitoring data and long term series for the different parts of the Wadden Sea, there hardly exists a synthesized and integrated view of the food web of the area that could indicate the influence of the changing environment on the complex interactions within the biota of the Wadden Sea. In recent years the data on biotic and abiotic components have been synthesized for the Sylt-Rømø Bight, Northern Wadden Sea, resulting in a food web model based on network analysis for the total bay as well as for the dominant intertidal communities (Baird, Asmus, Asmus 2004, 2007, 2008, 2011). This food web describes carbon flow as well as nitrogen and phosphorus cycling within a larger geographic unit based on the data material of the mid nineties representing a snapshot of this tidal basin before the major alterations occurred due to the invasion of neophytic and neozoic species. We therefore plan an update of the model including new communities such as Pacific oyster beds, Sargassum muticum- forests, and American razor clam beds. We also have to include new species such as Mnemiopsis leydii and Caprella mutica and investigate their probable place in the food web and their role as predators and prey. For the established communities we have to consider alterations in species composition and in energy flow rates due to altered seasonal temperatures. Using the already existing model as a background we plan to establish the food web of the Sylt-Rømø Bight as a reference food web for the Northern German and Danish part of the Wadden Sea. We would like to initiate an adaptation of this idea to the Trilateral strategy of the Wadden Sea, by installing two additional areas for research, as in the Central Wadden Sea the Jade Bay that is more directly influenced by the large estuaries of the rivers Elbe, Weser and Ems and the Balgzand area in the Southern Wadden Sea in order to cover the whole area. These reference food webs will be compared and will deliver scenarios of the changing environment of the Wadden Sea, especially due to biotic invasions and temperature. They will be helpful tools for the management of the area and will be especially helpful in detecting indirect effects between components and trophic cascades of the area. The multiple factors that are changing in the Wadden Sea require their integration at the ecosystem level. Finally, this ecosystem approach can be used as a start of an ecosystem based management. Especially the future trends in the development of populations of invertebrates, fishes, birds and mammals could be proven from a trophic perspective and the influence of mussel, shrimp as well as flatfish fishery could be evaluated by an ecosystem based management concept. | <urn:uuid:5243c6fd-d3dd-41fb-97b8-7d2b65e2170a> | 2.984375 | 635 | Academic Writing | Science & Tech. | 21.621425 |
The major species groups, habitats and processes detailed below were selected for analysis in the assessment because they play critical roles in supporting diverse marine life. Within the species groups, specific species or habitat types were identified to represent the ecosystem of the Northwest Atlantic.
There are several ways to access the data:
The full report is also available for download. Please note: this PDF is 55MB. Download the full report.
This section provides important context for the assessment: acknowledgements of our contributors, an introduction to the assessment, an overview of human uses of marine resources in the region and potential next steps for conservation.
Seafloor (or benthic) habitats of the Northwest Atlantic support a wide range of organisms that live on the ocean floor. Cold water corals prefer rocky areas, while sponges and sand dollars dominate sandy zones and marine worms dominate fine-grained muds. Conservation of all seafloor habitat types is necessary to maintain their roles in fueling the food web and recycling nutrients.
The fringing ribbons of habitats where land meets sea provide crucial support for offshore marine diversity. Hundreds of productive estuaries along the Northwest Atlantic’s coastline provide juvenile nursery and spawning grounds for fish, mollusks, seabirds and crabs. Dense beds of oysters, clams, scallops and mussels also provide a wide array of ecological services such as filtering water and protecting coastal communities from sea level rise and storm surge.
Groundfish or “demersal” fish are characterized by their close association with the seafloor for feeding, spawning and juvenile nursery areas. As dominant predators, they influence the abundance of many other species. Fisheries for cod, haddock, halibut and hake attracted and sustained European settlement in North America some 500 years ago, and they are still economically important in many parts of the region.
Diadromous fish are species that utilize both freshwater and saltwater habitats during their life cycles. Their abundance played an important role in the settlement patterns of early colonists, and they provide an important energy link between freshwater, estuarine and marine food webs.
Small pelagic fish such as menhaden, herring and mackerel are the primary food source for top marine predators like marine mammals, sea birds and larger fish. Because of their migration patterns and life histories, some of these species transfer energy and biomass seasonally from coastal bays to offshore habitats, providing a significant link between coastal and pelagic systems.
Marine mammals use this region primarily in spring and summer when there is an abundance of food associated with the region’s cool nutrient-rich waters. As predators, cetaceans such as dolphins, porpoises and whales are major consumers in the system.
Sea turtles utilize and link oceanic, estuarine and terrestrial ecosystems, traversing thousands of miles through productive ocean habitats to forage in seagrass meadows and bury their eggs on sandy beaches. Their highly migratory and long-lived life histories present unique challenges to their continued protection and recovery.
Large pelagic fish such as tunas, sharks and swordfish are highly migratory fish species that live in the water column. They play a key ecological role as predators that regulate their prey communities and structure marine food webs. When they die, their carcasses add important nutrients to sea floor habitats.
The physical characteristics of the ocean play a critical role in supporting the area’s diverse marine life. To help explain and predict distribution patterns of marine mammals, sea turtles and pelagic fish, this assessment compiled regional datasets on sea surface temperature, stratification, seafloor complexity, chlorophyll a and zooplankton biomass.
Sea birds spend the majority of their life at sea, but return to coastal areas to breed, while shorebirds spend their lives on the coastal land edge, but forage in marine environments. Worldwide, a higher percentage of seabird species are at risk of extinction than any other bird group.
This section contains all of the species groups, specific species and habitat types to allow for cross target comparison. This section contains a lot of data, so please be patient with loading and downloading.
If you are interested in a copy of the complete report data, please contact email@example.com. | <urn:uuid:d3a4b31e-6bbc-4ea3-bbf7-d6ebbed08771> | 4 | 882 | Knowledge Article | Science & Tech. | 26.201502 |
4. METHOD OF SOLUTION
The code is run interactively and the user examines the output and chooses what he feels to be the best values for the number of resonances to be considered and for D noting for example that at the higher energies resources may have been missed through lack of resolution, which leads to a steady increase in successive values of D.
The program goes on to calculate the value of the level density parameter which corresponds to the chosen value of D, using a back- shifted Fermi-gas model, and to calculate the values of D for dif- ferent spin states of the compound nucleus. Finally the observed resonance energies are compared with an energy ladder whose rungs are uniformly spaced; the deviations of the resonance from the lad- der energies are tabulated, and their standard deviation. This com- parative table indicates roughly just where resonances may have been missed, supposing the value of D well-chosen. Most probable values are given for the energies of the top bound resonances, these are estimated by use of Dyson's Coulomb gas model.
For materials such as iron the resolved resonances extend nearly to 1 MeV, and over so wide a range D must be expected to decrease steadily by a factor of two. If the resonance energies are input in keV units, DEEBAR uses the level density formalism to allow for the expected energy dependence, both in calculation of D values for zero neutron energy and in the energy ladder. | <urn:uuid:b2a5b824-28c6-48db-a504-5f7e9596200b> | 3 | 302 | Documentation | Science & Tech. | 27.819643 |
Hi I'm Dave Thurlow and this is The Weather Notebook. As the summer fire season draws to a close, listener Eileen Williams of Grand Haven Michigan has a question about the cause of some of the worst forest fires in history. She listens to the Weather Notebook on Michigan Public Radio from Ann Arbor-Grand Rapids. Here's what she writes.
There are so many fires out west this year and we keep hearing that a lot of them are being started by "dry lightning." Could you please explain to those of us that live in a wet Great Lakes area what exactly "dry lightning" is and what the difference is to the lightning that we experience in a thunder storm with rain?
Well, that's precisely the difference. A thunderstorm with rain produces "wet" lightning I guess you could call it. A thunderstorm without rain produces dry lightning. A thunderstorm without rain actually does have rain; it's just that the rain dries up before it reaches the ground. This type of storm is common in the west where the air is considerably drier than it is generally east of the Mississippi.
Because it's so dry in the west, thunderstorms form much higher in the sky, so high that when the rain falls it often evaporates before reaching the ground. But the lightning generated in the storm, the same way it does in any storm east or west, CAN reach the dry land below, even if the base of storm itself is two, three or more miles high. When lightning does strike, a fire is sparked but there's no rain falling to douse the flames. And this summer the unremitting heat dried the forests to the point were any spark, especially from dry lightning, could turn to a blaze in seconds.
We appreciate weather questions, please call us with yours. The number is 1-888-RAIN-001. That's 1-888-RAIN-001. | <urn:uuid:1985f759-7675-4d70-8eb6-64d30a7df2b1> | 3.375 | 391 | Audio Transcript | Science & Tech. | 67.57565 |
More Images of Cepheus B
Labeled Image of Cepheus B
A new study suggests that star formation in Cepheus B is mainly triggered by radiation from one bright, massive star (HD 217086) outside the molecular cloud. According to the particular model of triggered star formation that was tested -- called the radiation-driven implosion (RDI) model -- radiation from this massive star drives a compression wave into the cloud triggering star formation in the interior, while evaporating the cloud's outer layers. This labeled version of the image shows important regions in and around Cepheus B. The "inner layer" shows the Cepheus B region itself, where the stars are mostly about one million years old and about 70-80% of them have protoplanetary disks. The "intermediate layer" shows the area immediately next to Cepheus B, where the stars are two to three million years old and about 60% of them have disks, while in the "outer layer" the stars are about three to five million years old and about 30% of them have disks. This increase in age as the stars are further away from Cepheus B is exactly what is predicted from the RDI model of triggered star formation.
X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.))
Chandra X-ray and Spitzer Infrared Images of Cepheus B
X-rays from Chandra and infrared data from Spitzer reveals a beautiful scene of star formation within our Galaxy. There are hundreds of very young stars inside and around the cloud -- ranging from a few millions years old outside the cloud to less than a million in the interior -- making it an important testing ground for star formation. By combining the data from these two observatories, researchers have shown that radiation from massive stars may trigger the formation of many more stars than previously thought..
(Credit: X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.))
Return to Cepheus B (August 12, 2009)
Cepheus B with Scale Bar
(Credit: X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.) | <urn:uuid:ebbf8119-fe2b-4d81-835b-18d0bb477184> | 3.671875 | 529 | Knowledge Article | Science & Tech. | 63.865645 |
Transmutation and Radioactivity
Transmutation of one elementA substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means. into another requires a change in the structures of the nuclei of the atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. involved. For example, the first step in the spontaneousCapable of proceeding without an outside source of energy; refers to a reaction in which the products are thermodynamically favored (product-favored reaction). radioactiveDescribes a substance that gives off radiation‐alpha particles, beta particles, or gamma rays‐by the disintegration of its nucleus. decay of uranium is emission of an α particle, 42He2+, from the nucleusThe collection of protons and neutrons at the center of an atom that contains nearly all of the atoms's mass. 23892U. Since the α particle consists of two protons and two neutrons, the atomic numberThe number of protons in the nucleus of an atom; used to define the position of an element in the periodic table; represented by the letter Z. must be reduced by 2 and the mass numberThe sum of the numbers of protons and neutrons in an atom; these two kinds of particles contain almost all of the mass of an atom. by 4. The productA substance produced by a chemical reaction. of this nuclear reaction is therefore 23490Th. In other words, loss of an α particle changes (transmutes) uranium into thorium. In the equation for the decay, the sum of the atomic numbers on the left and right are equal, as is the sum of the massA measure of the force required to impart unit acceleration to an object; mass is proportional to chemical amount, which represents the quantity of matter in an object. numbers on the left and right:
Alpha decay is typical for large nuclei, because it reduces their size rapidly. Every element above Z = 83 (Bi) is radioactive, apparently because no number of neutrons can stabilize the nucleus against the repulsions between large numbers of protons.
Loss of a β particle (electronA negatively charged, sub-atomic particle with charge of 1.602 x 10-19 coulombs and mass of9.109 x 1023 kilograms; electrons have both wave and particle properties; electrons occupy most of the volume of an atom but represent only a tiny fraction of an atom's mass.) from an atomic nucleus leaves the nucleus with an extra unitA particular measure of a physical quantity that is used to express the magnitude of the physical quantity; for example, the meter is the unit of the physical quantity, length. of positive charge, that is, an extra proton. This increases the atomic number by 1 and also changes one element to another. For example, the 23490Th mentioned above emits β particles. Its atomic number increases by 1, but its mass number remains the same. (The β particle is an electron and has a very small mass.) In effect one neutron is converted to a proton and an electron. Thus the thorium transmutes to protactinium 23491Pa. (Note carefully that the β particle is an electron emitted from the nucleus of the thorium atom, not one of the electrons from outside the nucleus.) Using the standard symbol
Beta decay increases the number of protons, so it occurs when a nucleus has a high n/p ratio, compared to the stable nuclei of that element. If the nucleus has a low n/p ratio, it can reduce the number of protons by "positronA positively charged particle having the same mass and magnitude of charge as an electron." emission:
Positrons ( ) are the basis of medical "PET (Positron Emission Tomography) Scans", in which they annihilate their antiparticle, the beta:
The two gammas leave in opposite directions from the point of the annihilation, so the PET machine can "trace" their origin to create an image.
A gamma rayHigh energy electromagnetic radiation emitted during radioactive decay. is not a particle, and so its emission from a nucleus does not involve a change in atomic number or mass number. Rather it involves a change in the way the same protons and neutrons are packed together in the nucleus. In equation (1) above, the product Th is shown with an asterisk, indicating that the decay leaves it in an excited state. It releases its extra energyA system's capacity to do work. in the form of a gamma:
It is important to note, however, that radioactivityThe release of particles and/or energy from an unstable nucleus. and transmutation both involve changes within the atomic nucleus. Such nuclear reactions will be discussed in more detail in the section devoted to Nuclear Chemistry. Because protons and neutrons are held tightly in the nucleus, nuclear reactions are much less common in everyday life than chemical reactions. The latter involve electrons surrounding the nucleus, and these are much less rigidly held. | <urn:uuid:00cff7ac-3994-4a56-9260-e0dfd1b431e2> | 4 | 1,054 | Knowledge Article | Science & Tech. | 38.241028 |
The challenge is to write an interpreter for the untyped lambda calculus in as few characters as possible. We define the untyped lambda calculus as follows:
There are the following three kinds of expressions:
A lambda expression has the form
(λ x. e)where
xcould be any legal variable name and
eany legal expression. Here
xis called the parameter and
eis called the function body.
For simplicity's sake we add the further restriction that there must not be a variable with the same name as
xcurrently in scope. A variable starts to be in scope when its name appears between
.and stops to be in scope at the corresponding
- Function application has the form
aare legal expressions. Here
fis called the function and
ais called the argument.
- A variable has the form
xis a legal variable name.
A function is applied by replacing each occurrence of the parameter in the functions body with its argument. More formally an expression of the form
((λ x. e) a), where
x is a variable name and
a are expressions, evaluates (or reduces) to the expression
e' is the result of replacing each occurrence of
A normal form is an expression which can not be evaluated further.
Your mission, should you choose to accept it, is to write an interpreter which takes as its input an expression of the untyped lambda calculus containing no free variables and produces as its output the expression's normal form (or an expression alpha-congruent to it). If the expression has no normal form or it is not a valid expression, the behaviour is undefined.
The solution with the smallest number of characters wins.
A couple of notes:
- Input may either be read from stdin or from a filename given as a command line argument (you only need to implement one or the other - not both). Output goes to stdout.
- Alternatively you may define a function which takes the input as a string and returns the output as a string.
- If non-ASCII characters are problematic for you, you may use the backslash (
\) character instead of λ.
- We count the number of characters, not bytes, so even if your source file is encoded as unicode λ counts as one character.
- Legal variable names consist of one or more lower case letters, i.e. characters between a and z (no need to support alphanumeric names, upper case letters or non-latin letters - though doing so will not invalidate your solution, of course).
- As far as this challenge is concerned, no parentheses are optional. Each lambda expression and each function application will be surrounded by exactly one pair of parentheses. No variable name will be surrounded by parentheses.
- Syntactic sugar like writing
(λ x y. e)for
(λ x. (λ y. e))does not need to be supported.
- If a recursion depth of more than 100 is required to evaluate a function, the behaviour is undefined. That should be more than low enough to be implemented without optimization in all languages and still large enough to be able to execute most expressions.
- You may also assume that spacing will be as in the examples, i.e. no spaces at the beginning and end of the input or before a
.and exactly one space after a
.and between a function and its argument and after a
Sample Input and Output
((λ x. x) (λ y. (λ z. z)))
(λ y. (λ z. z))
(λ x. ((λ y. y) x))
(λ x. x)
((λ x. (λ y. x)) (λ a. a))
(λ y. (λ a. a))
(((λ x. (λ y. x)) (λ a. a)) (λ b. b))
(λ a. a)
((λ x. (λ y. y)) (λ a. a))
(λ y. y)
(((λ x. (λ y. y)) (λ a. a)) (λ b. b))
(λ b. b)
((λx. (x x)) (λx. (x x)))
Output: anything (This is an example of an expression that has no normal form)
(((λ x. (λ y. x)) (λ a. a)) ((λx. (x x)) (λx. (x x))))
(λ a. a)(This is an example of an expression which does not normalize if you evaluate the arguments before the function call, and sadly an example for which my attempted solution fails)
((λ a. (λ b. (a (a (a b))))) (λ c. (λ d. (c (c d)))))
`(λ a. (λ b. (a (a (a (a (a (a (a (a b))))))))))This computes 2^3 in Church numerals. | <urn:uuid:57d0928e-7251-472e-9879-f0623e72a271> | 3.4375 | 1,061 | Documentation | Software Dev. | 77.139358 |
Lessons and tutorials in the Programming Language C.
Branching Statements (if, else, switch) :
The if statement :
The if statement allows you to control if a program enters a section of code or not based on whether a given condition is true or false.
An if statement includes the keyword if followed by a logical expression, which is an expression that evaluates to either true or false. follow the parentheses with the statement that you want executed if the logical expression is true.
- An if statement has the form :
- In this example the program tells you if the number you entered is an odd number or an even number.
The switch statement
A switch statement is used in place of many if statements.
- The switch statement has the form:
- The example above represents a calculator. | <urn:uuid:f0384579-5fb8-4363-8ab5-301b81dcf678> | 4.375 | 167 | Tutorial | Software Dev. | 47.246791 |
Although we still haven’t found any biological activity elsewhere, it’s hardly inconceivable that before your car gets its next oil change, robot spacecraft could discover a horde of microbes hidden beneath the Martian sands. Or maybe a few years down the road, some astrobiology experiment will stumble across alien pond scum floating in Titan’s rime-frosted lakes, or pick up a radio signal beamed earthward from the star system Gliese 581.
The impact of such news would be significant and, at this point, largely unknown. So to get a better grip on how astrobiological discoveries would play out, the SETI Institute and the NASA Astrobiology Institute recently held a three-day workshop to bring together scientists, ethicists, historians, lawyers, anthropologists, and the media to consider the societal consequences of this type of research.
It seems that everyone is jumping on the “find the alien” bandwagon this week, even Uncle Seth in his ultra-conservative, micro-organism, beamed radio signal kind of way.
Does that mean for sure the unwashed masses are being prepared for the “we are not alone” speech?
Speaking of Martian water and possible microbial life:
NASA’s Phoenix lander may have captured the first images of liquid water on Mars – droplets that apparently splashed onto the spacecraft’s leg during landing, according to some members of the Phoenix team.
The controversial observation could be explained by the mission’s previous discovery of perchlorate salts in the soil, since the salts can keep water liquid at sub-zero temperatures. Researchers say this antifreeze effect makes it possible for liquid water to be widespread just below the surface of Mars, but point out that even if it is there, it may be too salty to support life as we know it.
A few days after Phoenix landed on 25 May 2008, it sent back an image showing mysterious splotches of material attached to one of its legs. Strangely, the splotches grew in size over the next few weeks, and Phoenix scientists have been debating the origin of the objects ever since.
If NASA insists on just sending robot probes to explore planets, please, please let the next Martian mission have a real biological testing lab?
Water seems to be the choice which decided future outer solar system missions also, according to the European Space Agency and NASA:
The proposal could be the agencies’ next “flagship” endeavour, to follow on from the successful Cassini-Huygens mission to the Saturn system.
Officials had been considering the Jupiter mission along with a venture to Saturn’s moons Titan and Enceladus.
But they will target an earlier flight opportunity for the Europa mission.
A Saturnian return will have to wait until later in the century, agency chiefs say.
Must be that ol’ H2O-centric idea of biology, since it’s worked so well here.
At this rate, I sure as hell hope there’s going to be a Technological Singularity, if not, I’ll be long dead before humans even step foot back on the Moon! | <urn:uuid:0969d2b5-81d7-406c-b629-44a3e5ceff71> | 3.046875 | 664 | Personal Blog | Science & Tech. | 36.689179 |
Arctic Blog: A Place for Wildlife
By Steve Zack, Wildlife Conservation Society
In the National Petroleum Reserve
26 Jul 2011
During my four-night stay at our remote Ikpikpuk camp, we were serenaded virtually nonstop by a Smith’s longspur, a songbird usually found in the Brooks Range and adjacent foothills, some 60 miles to the south. He had come to settle where there were no others of his kind. His message was urgent, yet ignored by the Lapland longspurs, savannah sparrows, and other wildlife busy with their lives.
of the Wildlife Conservation Society blogs from the Arctic for Yale Environment 360
. The third in a series
. Read the previous entry
When contemplating our conservation efforts in Arctic Alaska, I can relate to “Mr. Smith,” as our field assistants called him. Imagine singing the praises of the biggest public landscape in the United States, though there are few people aware or listening. Imagine that this landscape encompasses the world’s largest Arctic wetland — nearly 200 miles long east to west, 100 miles deep north to south — and that this wetland is home to the most spectacular gathering of migratory birds from all over the world, numbering in the millions. Imagine, as well, that a vast predator/prey spectacle — gizzly bears, wolves, and wolverines pursuing caribou — plays out annually in its foothills. And then imagine that this immense region, about the size of Indiana and bigger than 11 individual U.S. states, will likely have its future decided, its balance of development and wildlife protection, within a year.
This place is called the National Petroleum Reserve — Alaska, or NPR-A. Never heard of it? Most people have not. It is public land, administered by the U.S. Bureau of Land Management (BLM), and as its name implies, it contains a large quantity of oil and gas (although a recent study by the U.S. Geological Survey indicated that it contains only 10 percent of the oil previously assumed).
The BLM is expected to rule within a year which of the NPR-A’s 23 million acres can be developed, and which (if any) should be set aside for conservation. The Wildlife Conservation Society (for which I work) and other environmental groups are advocating for a balance of energy development and wildlife protection. We especially want to make sure that the three large “special areas,” delineated by the federal government in the 1970s, remain protected.
A wetland within the National Petroleum Reserve — Alaska.
For the past several years, my colleagues and I have been traveling through this vast, Arctic landscape of tundra, meandering rivers, and wetlands to assess key wildlife habitats. Our core emphasis has been on the Teshekpuk Lake Special Area, centered in the coastal plain amid millions of breeding migratory birds and tens of thousands of caribou.
Our standing and leverage in this debate rest on our science, which involves assessing the quantity and variety of the wildlife around Teshekpuk Lake, particularly migratory birds. This often involves finding and monitoring nests. Depending on the day, our seven-person field team is either rope-dragging a plot — using a 50 meter rope to rouse incubating birds off their nests — or walking in a systematic manner to watch for nesting behavior.
Semipalmated and pectoral sandpipers are perhaps the easiest species to locate. When you are close, the birds try to lure you away from their nests with behaviors that suggest they are injured and vulnerable. But if they fly from a nest we are trying to find, and we can’t pinpoint it right away, we must withdraw and sit with binoculars, awaiting their return and furtive walk back to the nest. It is then that you can find the nest, invariably of four eggs, covered with sedge leaves.
Long-billed dowitchers can be the hardest, as they are the most wary and most reluctant to return to their nests. It can be a long wait.
We use tongue depressors, compasses, GPS devices, and our plot stakes to help us “mark” nests and monitor them. Finding most of the nests in our one-kilometer by 100-meter plots gives us a measure of total density. The breeding success of the birds gives us an estimate of nest productivity.
Collecting these data across years has given us a sufficient sample size to compare and contrast with other Arctic areas, and we have published those results in a scientific, peer-reviewed journal. To date, our studies near Teshekpuk have revealed high densities and high productivity for birds in comparison to studies by us at Prudhoe Bay and elsewhere in Arctic Alaska. Those data, in turn, help to highlight the unique wildlife attributes in the Teshekpuk Lake Special Area.
We use our data, and other information on wildlife, to assert that the wildlife values in this and the other “special areas” are reason to protect them from development. Our overall position is that balanced development in the NPR-A can be achieved by protecting these areas (and a few other key places) with responsible development outside them.
The Teshekpuk Lake Special Area surrounds that lake and contains the most important and diverse migratory bird populations in Arctic Alaska. In addition, the caribou herd that spends its year around the lake is the most important to the Inupiat Eskimos for subsistence. In the northeast corner of this area, geese from Siberia, Alaska, and Canada aggregate in the fall to undergo their flightless molt, the most vulnerable part of their life cycle.
Click to enlarge
Alaska Center for the Environment
The “special areas” of the National Petroleum Reserve
The two other large special areas of the NPR-A have different wildlife values. The Colville River Special Area contains the highest densities of breeding birds of prey — species such as peregrine falcon, gyrfalcon, golden eagle, and rough-legged hawk. The other, and very dramatic area, is the Utukok River Upland Special Area. It is here that the largest caribou herd in Alaska, the Western Arctic Herd, roams. Nearly three-quarter of a million caribou move through this system with their young in the spring, surrounded by grizzly bears, wolves, and the highest densities of wolverine known on earth. It is our own Serengeti of predator and prey, and yet virtually unknown to the outside world.
I have been fortunate to have rafted through these latter two special areas — the Colville in 2005 and down the Utukok River last year. My impressions of the Utukok remain vivid: rolling and distinct syncline hills surrounding the meandering Utukok, whose sandy beaches hold the footprints of the myriads of caribou as well as wolf and grizzly tracks. We saw but the tail end of the massive caribou migration (as well as wolves and grizzlies), and yet did get to see a wolverine — the great phantom of the north.
Few have been in the NPR-A, fewer yet in the special areas. Raising the awareness of these places, through science and outreach, is vital as, with the arrival of oil and gas development, this remote part of the world is about to become far less remote.
12 July 2011: Unraveling the Mysteries of Migration
19 July 2011: Tracking the Impact of Oil Development on Wildlife
2 August 2011: As Climate Warms, a Shifting Landscape for Wildlife | <urn:uuid:518ad9ce-b236-44be-92ce-0f06d904d298> | 2.75 | 1,593 | Personal Blog | Science & Tech. | 44.305274 |
ANSI Common Lisp 21 Streams 21.2 Dictionary of Streams
sequence stream &key start end
sequence - a sequence.
stream - an output stream.
start, end - bounding index designators of
sequence. The defaults for start and end are 0 and nil, respectively.
write-sequence writes the elements of the subsequence
of sequence bounded by start and end to
(write-sequence "bookworms" *standard-output* :end 4)
- Side Effects:
- Exceptional Situations:
Should be prepared to signal an error of type type-error if sequence is not a proper sequence.
Should signal an error of type type-error if start is not a non-negative integer.
Should signal an error of type type-error if end is not a non-negative integer or nil.
Might signal an error of type type-error if an element of the
bounded sequence is not a member of the
stream element type of the stream.
- See Also:
Section 3.2.1 Compiler Terminology,
write-sequence is identical in effect to iterating over the indicated
subsequence and writing one element at a time to stream, but
may be more efficient than the equivalent loop. An efficient implementation
is more likely to exist for the case where the sequence is a
vector with the same element type as the stream.
- Allegro CL Implementation Details: | <urn:uuid:6afa6b70-7009-49a9-9e44-b13eb41f1e1f> | 2.6875 | 299 | Documentation | Software Dev. | 46.424334 |
See also the
Dr. Math FAQ:
Browse High School Higher-Dimensional Geometry
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Do cones or cylinders have edges?
Latitude and longitude.
MaximizIng the volume of a cylinder.
- Relative Motion on Face of Earth [05/06/2007]
If I am traveling along the earth's surface at the same rate of speed
that the earth is rotating in the opposite direction then would I
appear to not be moving if you watched me from space?
- Resolving Pitch and Yaw [02/10/2003]
Is there an equation to find the resultant of pitch and yaw?
- Resources on 3D Surface Plots [9/12/1995]
I would appreciate it if you would let me know of any databases or
handbooks on the Internet for 3D surface plots of equations z=f(x,y,...).
- Rhumb Lines and Great Circle Routes [09/24/1998]
Can you explain great circles and rhumb lines and how they relate to
shortest distances in geometry?
- The Role of Postulates [03/29/2003]
Who decided what were postulates and what were theorems? Why is it
okay that postulates aren't proven?
- Roll of Paper [06/15/2003]
I am getting a paper rewinder that runs 6,000 ft a minute, and the
roll is 50' high above the floor. How many miles and feet are there in
this roll of paper and how long will it take to run?
- Same Surface Area and Volume [03/28/2001]
How can I find two objects of the same type of shape with the same
surface area but different volumes? For example, two rectangular prisms
or two cylinders?
- The Second Octant [04/03/2002]
Where is the second octant? No one seems to know how to count the next
octants after the first.
- Segment of an Ellipse [09/06/2001]
We often use horizontal oval tanks for storing drinking water and fuel,
and we would like to be able to calculate the contents.
- Setting Sun [5/19/1995]
A fellow Naval retiree and I have been discussing whether the sun appears
to set faster at the horizon near the equator than it does in the
- Shared Points on Concentric Circles [03/11/2004]
Can two concentric circles share only a few points? If they are
concentric and they have the same radius, they would share all of
their points, and if they don't have the same radius they will share
no points. It seems like it's all or none.
- Shortest Distance between Points [01/17/1998]
I am doing a project on the shortest distance between two points via
another plane. I need help with my theorems.
- Similar Pyramids and Measurement Ratios [08/10/2002]
The volumes of two similar pyramids are 27 and 64. If the smaller has
lateral surface area of 18, how would I find the lateral surface area
of the larger one?
- Sketching a Plane in Three Dimensional Space [11/15/2005]
I know that an equation like 2x + y + z = 3 represents a plane in
three dimensions. How can I sketch that plane on the xyz axes? Also,
how can I sketch a system of such equations to find the solution
- Small Section of a Sphere [01/10/2002]
Find the volume and the areas of each of the surfaces/faces of a small
section of a sphere with "dimensions" delta r, delta theta, delta phi, in
- Spaces Formed by Intersecting Planes [07/19/1998]
Do you know of a proof that would be used to show how many spaces can be
formed by the intersecting of five planes in space? n spaces?
- Sphere Equation Variables [08/21/2001]
In the standard equation: r^2 = (x-h)^2 + (y-K0^2 + (z-l)^2 ...what do
the points h, k, and l represent?
- Sphere Eversion [8/11/1996]
How do you mathematically turn a sphere inside out?
- Sphere Formulas [03/26/1997]
What are the formulas for area and volume of a sphere?
- A Sphere in a Cube [3/23/1996]
I have a cube of 200x200x200 and a sphere with a radius of 100 is inside
it. I want to be able to put in x and y and using a formula get z.
- A Sphere's Surface Area and Volume [12/17/1998]
What is the relation between a sphere's surface area and its volume? How
does their ratio change?
- Sphere Surface Area Precision [04/22/2003]
How can the formula 4*pi*r^2 for the surface area of a sphere be
- Spherical Triangles [10/26/1996]
Why can't you use the Pythagorean formula to measure the distance between
two points on Earth?
- Surface Area and Volume: Cubes and Prisms [05/27/1998]
What is the definition of surface area and volume? What are the
differences and similarities between surface area and volume?
- Surface Area and Volume Derivative [10/30/2000]
For what 3D figures is the derivative of the volume formula equal to the
formula for surface area? With respect to which variable would you need
- Surface Area and Volume of a Sphere [08/30/1999]
Besides using integration, is there an intuitive way of seeing why the
surface area of a sphere = 4(pi)r^2 and the volume = (4/3)(pi)r^3?
- Surface Area and Volume of a Sphere [05/16/2000]
Without using calculus, how can I show why the coefficient in the formula
for the surface area of a sphere is 4, and why 4/3 is the coefficient in
the formula for the volume of a sphere?
- Surface Area and Volume of Cylinders [05/25/2001]
How do you find the surface area and volume of a cylinder?
- Surface Area of a Cone [06/18/1998]
What is the formula for the surface area of a cone?
- Surface Area of a Cylinder [9/25/1995]
What is the formula to calculate the surface of a cylinder with 25cm
diameter and 20cm height?
- Surface Area of an Egg [02/28/2001]
How do you find the surface area of an egg?
- Surface Area of an Egg [07/20/2002]
How do I find the surface area of an egg?
- Surface Area of an n-dimensional Sphere [07/28/1997]
I was wondering how to calculate the surface area of a sphere in n
- Surface Area of a Rectangular Solid [09/21/1999]
Can you find the surface area of a cube or other 3D rectangular object by
calculating the area of the sides you can see and multiplying by 2?
- Surface Area of a Right Circular Cone [9/5/1995]
Could you please tell me the formula for finding the surface area of a
right circular cone?
- Surface Area of a Right Cylinder [08/21/2001]
The problem in my book asked me to find the surface area of a right
cylinder in centimeters with the dimensions given in meters.
- Surface Area of a Sphere [10/03/1997]
How is the surface area of a sphere calculated, and why?
- Surface Area of a Sphere [04/10/1998]
Can you derive the formula for the surface area of a sphere?
- Surface Area of a Sphere [03/25/1999]
How do I calculate the surface area of a sphere?
- Surface Area of Blocks Glued Together [09/09/2001]
Three cubes whose edges are 2, 6, and 8 centimeters long are glued
together at their faces. Compute the minimum surface area possible for
the resulting figure. | <urn:uuid:aaf01d32-81a9-4dea-bc6c-6514bd29c826> | 3.46875 | 1,800 | Q&A Forum | Science & Tech. | 66.546636 |
Copyright © University of Cambridge. All rights reserved.
A large container holds 14 litres of a solution that is 25% antifreeze, the remainder being water. How many litres of antifreeze must be added to the container to make a solution that is 30% antifreeze?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
This problem is taken from the UKMT Mathematical Challenges.View the previous week's solution | <urn:uuid:e98f76e1-caf7-4543-acdc-9ce087219c70> | 3.015625 | 102 | Tutorial | Science & Tech. | 47.041491 |
Scientists have been using small variations in the Earth’s gravity to identify trouble spots around the globe where people are making unsustainable demands on groundwater, one of the planet’s main sources of fresh water.
They found problems in places as disparate as North Africa, northern India, northeastern China and the Sacramento-San Joaquin Valley in California, heartland of that state’s $30 billion agricultural industry.
Jay S. Famiglietti, director of the University of California’s Center for Hydrologic Modeling here, said the center’s Gravity Recovery and Climate Experiment, known as Grace, relies on the interplay of two nine-year-old twin satellites that monitor each other while orbiting the Earth, thereby producing some of the most precise data ever on the planet’s gravitational variations. The results are redefining the field of hydrology, which itself has grown more critical as climate change and population growth draw down the world’s fresh water supplies.
However, as the article notes, lawmakers don't really want to know about this, because the solutions are expensive and politically sensitive. I'm sure you know the old adage that the two things that are hardest to get out of water are salt and politics... | <urn:uuid:668ba6dd-2241-47db-8996-861c75dad937> | 3.09375 | 255 | Personal Blog | Science & Tech. | 32.8628 |
Earth's biodiversity is mostly in the tropics, and most tropical species can survive within only a narrow temperature range. That's because the environment they're adapted to is fairly constant year-round.
As global temperature warms, tropical animals are likely to feel the effects in unpredictable ways. Perhaps most at risk are species with small habitats in the tropical mountains. Some are moving to higher ground in search of cooler conditions--but those already living near summits may find themselves with nowhere to go.
Out of room
The chameleon on display in the exhibit, Calumma tsaratanense, is found nowhere on Earth but the island of Madagascar, off the southeast coast of Africa (map). And on that island, they are found nowhere but the remote Tsaratanana massif, the highest peak in Madagascar.
But even there, the chameleons aren't safe. Warming trends in Madagascar equal or exceed global averages. And scientists studying reptile and amphibian species found an average uphill migration that almost exactly matched what the animals needed to offset that temperature increase. The researchers predict that a 1.7oC (3oF) rise would be enough to drive to extinction endemic species living within 300 meters (1,000 feet) of summits all over the island.
On Borrowed Time?
The spotted lined gecko (Phelsuma lineata punctulata) lives only within 600 meters of Madagascar's highest peak. Like many mountain-dwelling tropical animals, it is vulnerable to habitat loss caused by projected warming.
In the past, protecting species has meant protecting habitat from development. But even a protected habitat like this region in northeastern Madagascar may be lost for inhabitants that cannot adapt to climate change. | <urn:uuid:67a4b9e5-1f35-4a44-83c5-498a3c877407> | 4.25 | 356 | Knowledge Article | Science & Tech. | 37.212973 |
How small insects survive the rain
Scientists have found that mosquito’s tiny, low-weight body, is the key to its ability to survive flying in the rain.
This showed that their bodies put up so little resistance that, rather than the drop of water stopping in a sudden, catastrophic splash, the mosquito simply combined with the drop and the two continued to fall together.
The team reports their findings in PNAS.
As well as helping explain how the insects thrive in damp, humid environments, the research could ultimately help researchers to design tiny, flying robots that are just as impervious to the elements.
“I hope this will make people think a little bit differently about rain,” said lead researcher David Hu.
“If you’re small, it can be very dangerous. But it seems that these mosquitoes are so small that they’re safe.”
Dr. David Hu is interested in understanding completely the “tricks” that insects use to survive being so small.
After repeated attempts at what he described as the most difficult game of darts ever, he and his colleagues managed to hit flying mosquitoes with drops of water and capture footage of the result.
Each droplet was between two and 50 times the weight of a mosquito, so what they saw surprised them.
Describing the results, Dr. David Hu cited the Chinese martial art of Tai chi.
“There is a philosophy that if you don’t resist the force of your opponent, you won’t feel it,” he explained.
“That’s why they don’t feel the force; they simply join the drop, become one item and travel together.”
When a moving object crashes into another, it is the sudden halt that produces a damage-causing force. For example, when a car hits a wall at 30 mph, the stationary wall and the car have to absorb all of the energy carried by that moving car, causing a great deal of damage.
The trick for a mosquito is that it hardly slows the raindrop down at all, and absorbs very little of its energy.
Surviving the collision though, is not the end of the drama for a tiny insect. It has to escape from its watery cocoon before the droplet smashes the insect into the ground at more than 20 mph.
This is where the insect’s body, which is covered in water-repellent hairs, seems to give it another crucial survival technique.
Every mosquito studied in this experiment managed to separate itself from the water drop before it hit the ground.
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Short URL: http://www.bellenews.com/?p=20097 | <urn:uuid:c0ade91a-c8c1-4c41-ac11-b0023005fbf3> | 3.375 | 989 | Truncated | Science & Tech. | 57.052684 |
Concept 21 RNA is an intermediary between DNA and protein.
Francis Crick describes RNA and its role and Paul Zamecnick explains protein synthesis.
Hello, I'm Francis Crick. The story of DNA does not end with Watson and me solving its three-dimensional structure. Because DNA is the hereditary molecule of the cell, we reasoned that the sequence of nucleotides in the molecule must function as a code, able to direct the synthesis of proteins. One puzzle we had to figure out was how DNA, which is found mainly in the cell's nucleus, can direct the synthesis of proteins that are made exclusively in the cell's cytoplasm. I proposed the "Central Dogma" where information flows from DNA to protein via a carrier molecule. A candidate for this information carrier was ribonucleic acid — RNA. RNA is a nucleic acid found mostly in the cell's cytoplasm. Like DNA, RNA has a sugar-phosphate backbone. However, RNA uses the sugar ribose instead of deoxyribose. DNA and RNA use the same nitrogenous bases except that DNA uses the nucleotide base thymine, whereas RNA uses uracil. Uracil can hydrogen bond with adenine just like thymine. DNA, as you know, is usually a double-stranded molecule. RNA, however, is usually single-stranded. After proposing the Central Dogma — where information flows from DNA to RNA to protein — I realized there was another problem. How did the amino acids interact with the carrier RNA? There must be adaptor molecules; in fact there must be 20 different adaptors, one for each amino acid. Hi, I'm Paul Zamecnik and I was interested in protein synthesis. In the 50's, I didn't know about Crick's Central Dogma or his adaptor hypothesis, and I approached the problem from a biochemical point of view. I made an extract using rat liver cells; it was basically a water-based solution that contained all the parts from a culture of cells. In 1953, I showed that this extract had everything needed to make proteins in a test tube. Remember that a protein is a polypeptide chain of amino acids linked to one another by peptide bonds. To follow protein construction, I added radiolabeled amino acids to the cell-free extract. After incubating the reaction at body temperature, I then centrifuged the tube. I expected that the newly-made polypeptides, being heavier, would pellet at the bottom of the tube. Unincorporated amino acids, being lighter, would remain in the supernatant. Sure enough, the radiolabel was present in the pellet, showing that new polypeptides had been synthesized. Mingled with the labeled polypeptides in the pellet, I identified a large cellular structure, later named the ribosome. It seemed clear the ribosome is the cytoplasmic organelle where protein assembly occurs. Ribosomes are constructed of both RNA and proteins. While the RNA part of the ribosome (rRNA) is involved in protein synthesis, its role was unclear. However, Mahlon Hoagland and I identified another RNA molecule associated with the unincorporated amino acids in the supernatant. Hi, I'm Mahlon Hoagland. I started working in Paul's lab in 1953, focusing on how amino acids were activated, or energized, prior to their incorporation into proteins. This is done by enzymes that I found, later known as aminoacylt RNA synthetases, in the soluble fraction of the cell. In 1955, Paul, Mary Stephensen and I found, to our surprise, that amino acids were first attached to a low molecular weight ("soluble") RNA in this same soluble fraction, and those amino acids were subsequently transferred to proteins in ribosomes. We named these intermediary carrier molecules "soluble" RNA. On a visit to our lab, Jim Watson recognized that soluble RNA met the requirements of Crick's adaptor hypothesis. Each of the soluble RNAs could pair to its partner amino acid and ferry the amino acid to the ribosome for protein synthesis. Soluble RNA was later renamed transfer RNA (tRNA) to better reflect its role. But, still, there was no answer to the problem of how the genetic code instructed cytoplasmic tRNAs and amino acids to make proteins. While some thought rRNA was the "template" on which proteins were built, it was becoming clear that rRNA did not have the right properties. So, now the hunt was on for the "information" molecule. But, still, there was no answer to the problem of how the genetic code instructed cytoplasmic tRNAs and amino acids to make proteins. While some thought rRNA was the "template" on which proteins were built, it was becoming clear that rRNA did not have the right properties. So, now the hunt was on for the "information" molecule. But, still, there was no answer to the problem of how the genetic code instructed cytoplasmic tRNAs and amino acids to make proteins. While some thought rRNA was the "template" on which proteins were built, it was becoming clear that rRNA did not have the right properties. So, now the hunt was on for the "information" molecule. Hello, I'm Sydney Brenner. With my colleagues, François Jacob and Matthew Meselson, I showed that rRNA was not the template for building proteins. There was a third type of RNA — an unstable intermediate — that carries the DNA message to the ribosome. We did this by using phage-infected bacteria. We started by growing bacteria in "heavy" isotopes of carbon and nitrogen to radiolabel all of the bacterial RNA and proteins. We then infected this bacterial culture with phage... …and immediately transferred the infected bacteria to media that lacked the heavy isotopes but contained radioactive 32P. We stopped phage growth before the bacteria were lysed and extracted RNA and ribosomes from the bacteria. We spun the bacterial extract in a density gradient in a centrifuge. This separated the various components and I was able to analyze the distribution of heavy and light isotopes in the bacterial ribosomes, and the incorporation of 32P in newly-made phage RNA. First, let's look at the ribosomes. One ribosome is made up of two subunits. In a density gradient, ribosomes can separate into two bands. The heavier band consists of whole ribosomes; the lighter band consists of dissociated subunits. I reasoned that if the rRNA in the ribosomes were the template for building new phage proteins, then new ribosomes with phage rRNA would have to be made after phage infection. As I suspected, this was not the case. All the ribosomes were made with heavy isotopes. Then I looked at where 32P had been incorporated in the production of new phage RNA. I found that 32P associated with the whole ribosome band and there was also 32P at the bottom of the tube. This turned out to be a new type of RNA. It was associated with the ribosomes so it must have a role in protein synthesis. However, it must be a large molecule since some of it was found in the sediment at the bottom of the tube. This was the information carrier envisioned by Crick in his Central Dogma, and I named it messenger RNA (mRNA).
tRNAs had been isolated prior to Hoagland and Zamecnik's experiments. No one thought they were important because tRNAs were so small. Some scientists even thought tRNAs were the degradation products of larger RNAs and thus "junk."
There are 20 different types of tRNA adapters, one for each amino acid. How do the tRNA molecules recognize their amino acid partners? | <urn:uuid:81257009-efe2-4ae0-8cd3-e4d866607c39> | 3.5625 | 1,636 | Knowledge Article | Science & Tech. | 44.764535 |
New Zealand has 3,820 lakes over one hectare in size and many more that are smaller. Less than 40 lakes are greater than 1,000 hectares in size. [Based on the database of lakes produced by NIWA for developing a lake classification system.] The largest lake in New Zealand is Lake Taupo with an area of about 62,000 hectares and maximum depth of 163 metres. The next largest North Island lake is Lake Wairarapa with an area of almost 8,000 hectares and a maximum depth of less than three metres. The deepest North Island lake is Waikaremoana, at 248 metres deep, formed when a landslide blocked a valley 200 years ago (Spigel and Viner 1991, MfE 1997).
The South Island's largest lakes are Lake Te Anau, with an area of around 35,000 hectares and a maximum depth of 417 metres, and Lake Wakatipu with an area of 29,000 hectares and a maximum depth of 380 metres. The third largest South Island lake is Ellesmere (or Waihora) with an area of 18,000 hectares and a maximum depth of less than three metres. The deepest lake in New Zealand is Lake Hauroko in Southland with a maximum depth of 462 metres (Spigel and Viner 1991, MfE 1997).
Several broad categories of lakes can be identified that reflect formation processes. Volcanic eruptions created many of the North Island's larger lakes. Glacial ice gouged out the basins for many of the South Island lakes. Dune lakes are common in Northland and on the west coast of the North Island. Peat lakes are a distinctive feature of the Waikato region; they typically have slightly acidic and humic-stained water. Riverine lakes are formed when rivers change their course. Landslides blocking valleys can form large lakes. Lagoons are created by the movement of sandbars - they often have brackish water and are occasionally open to the sea. Finally, we create artificial lakes or reservoirs for hydro-power stations (Spigel and Viner 1991, MfE 1997).
NIWA is currently developing a classification system for New Zealand lakes for the Department of Conservation. This is a multivariate classification system based on lake variables (eg, physical attributes of area, depth, fetch etc) and catchment attributes (eg, proportion of catchment in beach forest, glaciers, peat, pasture, geology with high phosphorus etc). It is designed to discriminate the variation in the natural and existing character of New Zealand's lakes.
Lakes are intimately linked to their catchments. Land-use activities in a catchment affect the amount of water, nutrients, sediment and other contaminants that enter a lake. These inputs affect the water quality and the functioning of the lake's ecosystem. This is called eutrophication. Typically, an increase in nutrients to a lake stimulates growth of phytoplankton which reduces water clarity. At high nutrient levels algae blooms may occur, often of potentially toxic cyanobacteria species, causing surface scums and a decline in dissolved oxygen as the bloom decomposes. In very bad situations fish may die from the low dissolved oxygen levels. The state of the water quality and degree of nutrient enrichment is described by trophic state, with oligotrophic, mesotrophic and eutrophic lakes having progressively more nutrients, more algae biomass and poorer water clarity.
Although we report water quality in simple terms such as trophic state, the factors affecting lake water quality can be very complex. Some of the key factors that interact to affect lake water quality are: sediment resuspension and release of nutrients, grazing of phytoplankton, phytoplankton community composition, macrophytes and fish.
Wind has a strong influence on lakes; it can mix the water and resuspend bottom sediments - particularly in shallow lakes. This can increase the nutrients available for algae growth, at the same time the more turbid water can inhibit algae and macrophyte growth by reducing the amount of light available.
Lake Coleridge is a deep glacial lake in the South Island. In 1993, an earthquake triggered a large release of suspended sediments into the lake, reducing the water clarity. Over the next two years a die-off of native aquatic macrophytes (characean algae) occurred in the deep water so that the depth of macrophyte growth reduced from 30 metres to 20 metres. The depth of macrophyte growth has recently extended back down to 30 metres as the water has cleared (Elliot and Sorrell 2002).
The growth of aquatic macrophytes also has strong interactions with lake water quality. A collapse in the coverage of aquatic macrophytes has been observed in many shallow lakes around New Zealand - always with a corresponding decline in water quality, eg, Lake Rotokauri in 1996/97, Lake Rotomanuka 1996/97, Lake Rotoroa 1989/90, Lake Whangape in 1987 (in the Waikato), and Lake Omapere since 2000 (in Northland).
A crash in the macrophyte population can occur very quickly and be triggered by a storm, grazing by swans or fish, an increase in nutrient inputs or lowering of the water level. Following a die-off, the macrophytes decompose, releasing nutrients into the water which stimulates the growth of aquatic algae resulting in a decline in water clarity. Without the macrophyte cover, the lake sediments are more prone to resuspension - further increasing the turbidity of the water and the availability of nutrients. This turbid, phytoplankton-dominated state can last a long time and the macrophytes recover only slowly. When they do recover, as recently found in Lake Rotoroa (Hamilton), there is generally a corresponding increase in water quality.
Grazing by swan, fish or koura (native freshwater crayfish) has a very strong impact on the growth of aquatic macrophytes. In the North Island, koura (Parenephrops planifrons) reduce the density of charophytes in deeper water where the light is also limited. Introduced fish such as Japanese koi have a much larger impact on macrophytes and can completely destroy populations and prevent regeneration. A recent improvement in water quality in Lake Wainamu, near Bethels Beach in Auckland, has been partially attributed to the trapping and removal of coarse fish (eg, perch, goldfish, rudd) by the Auckland Regional Council and the local community (more information can be found on the ARC website www.arc.govt.nz).
For further information on factors affecting lake water quality refer to the Lake Managers Handbook (Vant 1987) and the updated version on Land-Water Interactions (Elliot and Sorrell 2002). | <urn:uuid:879367d1-790a-4269-97cf-746935e66393> | 3.828125 | 1,411 | Knowledge Article | Science & Tech. | 36.117053 |
COULD sulphur traces on Jupiter's moon Europa be a sign of alien life? The compounds look like waste products rising from bacterial colonies living beneath the surface.
The Galileo space probe first spotted the sulphur compounds, as well as revealing that the moon almost certainly has a volcanically heated and potentially habitable ocean hiding beneath the surface layer of ice. Some scientists say the sulphur may have come from the nearby moon Io, where the compound is abundant. Or volcanic eruptions in the moon's core may have brought the sulphur to the surface.
But Aranya Bhattacherjee of the University of Pisa, Italy, and Julian Chela-Flores of the International Centre for Theoretical Physics in Trieste say the sulphur could be biological in origin. They base their idea on an Earth-based analogue of Europa - the dry valley lakes of Antarctica. The icy surface of these lakes also contains traces of sulphur ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:f680816b-d1fc-4bc8-89fc-8131c4a0b00a> | 3.921875 | 216 | Truncated | Science & Tech. | 41.095725 |
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Water From Where?
Sat Nov 21 20:58:38 GMT 2009 by anonymous
Part 1 of 2
Wondering: Great question!
Consider what water is composed of: each water molecule is made up of 2 hydrogen atoms attached to an oxygen atom.
The hydrogen atoms part is easy: they were formed directly out of the big bang as the soup of hot gas of particles cooled: the simplest of atoms, hydrogen is comprised of a single proton in the nucleus orbited by a single electron (which is why a hydrogen atom is electrically neutral).
As the universe cooled during its formative expansion within the first several hundred thousand years following the big bang, free electrons were captured by free protons to produce the hydrogen atoms in great abundance. 13.7 billion years later, hydrogen remains the most abundant atom of matter in the universe. Helium - which is almost completely inert and does not readily chemically combine with other atoms to create molecules - was also synthesized during that formative epoch in the early universe, but most of the left-over nuclei and electrons went into the synthesis of hydrogen by roughly a ratio of 4:1.
(You may note that the word "hydrogen" actually takes its name from the ancient Greek word for "water". By itself, it has nothing to do with water, per se, but that is how it was first identified, and as the chief constituent atom in the universe, it was, together with the 27% of helium atoms that were formed (and a very tiny trace contamination of primordially-synthesized atoms like lithium) those were ALL the main ingredients available in the recipe for making stars that formed later...
Oxygen was not formed in such primordial processes, but by the nucleosynthesis ("atomic nucleus-making activity") within early generations of massive stars that subsequently blew up and cast their heavier atomic nuclei products back into the interstellar medium. In fact, ALL the chemical element nuclei heavier than hydrogen, helium and some of the lithium were ALL synthesized within the fierce pressure-cooker furnaces at the interior cores of massive stars. Everything up to and heavier than iron. A lot of it was rebroadcast out into interstellar space over many stellar generations, gradually contaminating it with those additional heavier elements. But hydrogen and helium remain the main consituents.
That interstellar medium, polluted by those heavier elements in what we would ordinarily consider "trace amounts", continued to spawn additional generations of stars, as it still does in galaxies like our own Milky Way to this day, and once those oxygen nuclei had the opportunity to cool and acquire their complement of electrons, they were able to grab onto other species of atoms...including the always-abundant hydrogen.
When late-generation stars like our Sun formed, gravity compressed the (now cold) interstellar gas and dust (being comprised of rocky and metallic elements such as carbon and silicon and iron and nickel, likewise synthesized in the interiors of massive stars) and formed "accretion disks" around the newly-forming stars where atoms and molecules of volatile and refractory materials can combine to form compounds bigger than molecules. (A "compound" is simply a collection of molecules that stick together because its cold enough for them to keep in touch without getting knocked apart). But the process is cumuluative and can "condense" out objectsw that in turn stick together and form objects that become the building blocks of planets orbiting those stars.
Oxygen atoms happen to be quite "reactive" and will combine with many other atomic species. It's called "oxidation", but since there is plenty of hydrogen commonly available, it will "oxidize" the hydrogen quite readily - that is, grab them to make "water"..."H2O" is made by an atom of oxygen that has captured two hydrogen atoms in order to render the resulting molecule - H2O. | <urn:uuid:30b772e6-e75a-4b19-8158-fff9448e065e> | 2.96875 | 805 | Comment Section | Science & Tech. | 33.944619 |
“Impossible colors,” or “forbidden colors,” are hues that cannot be seen by the human eye in ordinary viewing conditions. These are actually simpler to describe than one might think.
In our color wheel, we have colors like “red-orange” or “blue-green.” These colors exist because they are right next to each other on the color wheel. An “impossible color” is a color such as “green-purple,” or any two colors put together that are not next to each other on the color wheel. Though the idea of mixing green and purple makes most people think of a brown color, this is actually referring to a color that would be similar to both purple and green.
Other colors outside of our range of color perception are also included in this. Included is an image of two colors that are dissimilar. Some people who stare at the image with crossed eyes so that the pluses align may be able to see “yellow-blue.” Try it yourself! | <urn:uuid:d60fd8e3-fd6e-4219-bda0-9151d38059d8> | 3.296875 | 221 | Knowledge Article | Science & Tech. | 55.752955 |
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Five space-filling polyhedra
The main text of this article is reproduced by kind permission from:
The Mathematical Gazette 80, November 1996, p.p. 466-475.
Some changes have been made from the original as follows:
10 January 2010. Links to Maurice Starck's page updated.
18 October 2006. Printable nets & link to Maurice Starck's page added.
7 October 2006. Correction to errors introduced at last update. Preface added. Minor tidy-up.
8 January 2006. Corrections and updates to original.
10 June 2007. More corrections to corrections, etc.
Solid shapes which pack together to fill space cover a large and varied range. I recently found five such polyhedra which I have not seen described elsewhere. The names which I have used for them here are rather ferocious I am afraid, but that just happens to be the way the names of polyhedra work.
Nets and coordinates for the polyhedra are given in Appendix A and Appendix B respectively.
The bisymmetric hendecahedra
A polyhedron with eleven faces is called a hendecahedron, from the Greek for eleven. The one shown in Figure 1 has two planes of symmetry, i.e. it is bisymmetric. This hendecahedron also has eleven vertices; polyhedra with the same number of faces as vertices are not very common. It has 2 large rhombic faces, a small rhombic face (which in the proportions used here is square), 4 congruent iscosceles triangular faces which meet along edges at right angles, and 4 congruent kite-shaped faces. (see Appendix B for coordinates.)
Figures 2 and 3 shows how four hendecahedra together form a kind of hexagonal boat shape which will stack in interlocking layers. This boat shape is also a 'translation unit' - it can be regularly stacked in a lattice to fill space, without any rotation or reflection. This lattice is similar to the body-centred cubic, but scaled vertically by a factor which is here one-half (but see below). In Figure 4 the way the hendecahedra themselves stack together to form a space-filling 'honeycomb' can be seen.
The particular polyhedron described here has an arbitrary height (chosen for convenience of its coordinates): it can be distorted vertically by stretching, to give an infinite series of shapes which are all space-fillers. In Figure 4, vertical lines can be seen running through the stack. Figure 2 shows how these lines are made from the edges where two triangular faces meet. In Figure 3, the lines are viewed end-on and appear as the corners where four hendecahedra from each layer meet. It is obvious from this that the angle between two triangular faces must be a right angle, but what should the other angles seen in Figure 3 be? These other angles can be varied by rotating the triangular faces together about their vertical edges, whilst maintaining the right angles and the overall symmetry of the shapes, up to the points at which faces merge or disappear. This rotation generates space-filling hendecahedra varying continuously from ones with broad front rhombs and blunt backs to ones with narrow front rhombs and sharper backs. The two distortions together yield a doubly-varying range of space-fillers.
By cutting a hendecahedron in half horizontally and inserting a (pentagonal) prismatic centre section, an elongated bisymmetric hendecahedron is formed (Figure 5). The square face has become hexagonal, and the triangles are now trapezia (the term trapezium has two quite different interpretations - I use the term to describe a quadrilateral with one pair of parallel sides). The new solid has fourteen vertices with coordinates obtained from the original solid as described in Appendix B.
The shape fills space in a similar way to the unstretched variant. It may be distorted vertically in two independent zones: one being the prismatic centre zone and the other the tapering top and bottom ends corresponding to an unelongated shape. Together with rotation of the trapezoidal faces, this yields a threefold range of distortions which still fill space.
The sphenoid hendecahedra
'Sphenoid' means wedge-shaped, which is an apt description for the hendecahedron shown in Figure 6. This also has eleven vertices, but it has only one plane of symmetry: top and bottom halves have reflective symmetry, but left and right halves are different, as can be seen in the end views. The sphenoid hendecahedron has three sizes of kite-shaped face and two types of isosceles triangle, all coming in pairs. In the proportions used here, the rhombic face is square. Unexpectedly the numbers of 3- and 4- sided faces are the same as for the bisymmetric variant, and indeed both hendecahedra have the same topology - they can be simply distorted into one another.
Figure 7 shows how six units pack like flower petals to form a 'floret'. A second floret fits up to it from below and is the other way up. The two florets form a translation unit which packs in a simple hexagonal lattice, here with a height equal to the unit length.
Florets will stack in layers, alternate ways up, to form faceted columns. In Figure 8, one floret is laid upon another, and in Figure 9 it can be seen how the florets also fit together side by side to form a layer. The layer is not quite symmetrical, alternate layers being right- and left-handed about the junction of three florets. Perhaps a little harder to visualise is the way the whole structure of layers and columns interlocks with no gaps, as illustrated in Figure 10.
A new polyhedron can also be made by elongation (Figure 11): in the elongated sphenoid hendecahedron, the square face again becomes a hexagon and the triangles become trapezia. It also has fourteen vertices, with coordinates obtained from the original solid as described in Appendix B, and fills space in a similar way to its unstretched cousin.
The two sphenoid shapes can be distorted vertically in the same way as the bisymmetric ones, but have no analogue of the rotational distortion.
The rhombic dodecahemioctahedron
There are a number of solids with faces which pass through their centre, so that the face has no inside or outside but can be seen from both sides in different places. These central faces are typically parallel to the faces of some normal convex polyhedron, but number half as many. Figure 12 shows two of the four hexagonal face planes corresponding to half an octahedron which make this solid 'hemi-octa.' The hemi faces are the visible parts of the hexagons, and comprise 'butterfly' cross-quadrilaterals. Neither the hexagons nor the octahedron are regular, the octahedron being slightly flattened or 'oblate'. The solid also has 4 rhombic faces and 8 (isosceles) triangular ones, making in all 12 ordinary faces. Hence the name rhombic dodecahemioctahedron.
Figures 13 and 14 illustrate two other ways of deriving its shape: Figure 13 as a cube cut into six square pyramids meeting at the centre, with two opposing pyramids removed and four new pyramids stuck onto the square bases of the remaining ones, and Figure 14 as four oblate octahedra joined face to face around a central vertex. It can also be thought of as a rhombic dodecahedron with two oblate octahedra removed leaving dimples behind.
The corner of one rhombic dodecahemioctahedron exactly fits the dimple of another (Figure 15). A series of units can be fitted together in two basic ways, as in Figure 16. In various combinations, these give rise to several different packings which fill space. These packings are not true lattices, since they have 'false' edges, where the edge of one or more units lies across the face of another.
The most regular packing I have found is shown in Figure 17. The units form layers, each of which has alternate rows of peaks and dimples. The packing does not have full cubic symmetry, since the rows of peaks and dimples give each layer a directional 'grain'. But there is no distinction between the three main axes. Another packing, shown in Figure 18, forms distinct layers of peaks alternating with layers of dimples. This pattern is only seen in one plane, so the packing has a definite way up or orientation.
The rhombic dodecahemioctahedron is pristine, which means it cannot be distorted in any way and still fill space.
Postscript on duality
The reciprocal or dual of a polyhedron is a kind of anti-twin. It has vertices corresponding to the faces of the original, and faces to the vertices. It has the same number of edges as the original, but at right-angles to them. The relationship is reciprocal, which means that the dual of a dual is the original shape.
Self-dual polyhedra are possible: the regular tetrahedron is an example. Such a shape must have the same number of vertices as faces, and without going into detail the pattern, or topology, of edges around every face must corresond exactly to the pattern of edges meeting at every vertex. The two unelongated hendecahedra described share the same topology, which fulfils this requirement. But neither meets more subtle requirements for the angles of faces, etc. A self-dual hendecahedron does exist - it is the canonical form of this topology and is not a space-filler.
The rhombic dodecahemioctahedron does not have a finite dual. The dual feature corresponding to a face through the centre would be a vertex at infinity, in both opposing directions orthogonal to the face, therefore joining finite edges to it is not possible.
The 3-D views of polyhedra were created by WimpPoly and Polydraw software for the RISC OS (Acorn) operating system, from Fortran Friends, PO Box 64, Didcot, Oxon OX11 0TH. I am indebted to the author K. M. Crennell for advice, enthusiasm and pre-release software.
Appendix A: Nets
The elongated hendecahedra have slightly different z scalings from the given coordinates, but this should not matter for most purposes. Click to download printable copies.
Appendix B: Coordinates
For an elongated version add ½ to the z ordinates of points A,B,C,D,E,F and G and subtract ½ from the z ordinates of points E,F,G,H,J,K and L, thus creating three additional vertices.
|A:||13 / 7||3√3 / 7||1|
|D:||2.5||√3 / 2||0|
|E:||2.25||√3 / 4||0.5|
|J:||2.25||√3 / 4||-0.5|
|L:||13 / 7||3√3 / 7||-1|
For an elongated version add ½ to the z ordinates of points A,B,C,D,E,F and G and subtract ½ from the z ordinates of points B,D,F,H,J,K and L, thus creating three additional vertices.
Park View, Queenhill, Upton-upon-Severn, Worcs WR8 0RE, England | <urn:uuid:00c239e4-abb3-4fd3-8156-38cf1dc6367e> | 2.875 | 2,519 | Academic Writing | Science & Tech. | 48.266676 |
"Mammals could be in for a stormy ride and face a greater risk of extinction due to predicted increases in extreme weather conditions, according to a paper published today by the Zoological Society of London (ZSL).
Scientists have mapped out land mammal populations and combined this with their knowledge of where droughts and cyclones are most likely to occur around the globe."
"In particular, primates, our closest relatives - which are already among the most endangered mammals in the world - are thought to be especially at risk.
Over 90 per cent of black howler monkey (Alouatta pigra) and Yucatan spider monkey (Ateles geoffroyi yucatanensis) known habitats have been damaged by cyclones in the past, and studies have documented ways they are able to adapt to the detrimental effects of these natural disasters."
Full Article: http://www.dailymail...opulations.html
From the article; "In Madagascar, entire known populations of the western woolly lemur (Avahi occidentalis) and the golden bamboo lemur (Hapalemur aureus) have been exposed to both cyclones and drought
Hmm, I think I know why these mammals are exposed, over 90% of Madagascar has been deforested in the last 100 years (see Haiti). This is not caused by extreme weather or global climate change, it was caused by humans with a lack of foresight. | <urn:uuid:3bff5b37-1982-48ae-9f00-0c29d6fcb42a> | 3.25 | 296 | Comment Section | Science & Tech. | 37.045698 |
What kind of telescopes are used to look farthest into space? Is it radio telescopes?
Radio waves are electromagnetic radiation, according to Wikipedia. Does that mean that radio waves fall under the domain of quantum physics?
That's what I wish to know for now.
Both optical and radio -- as well as ultraviolet, x-ray, and gamma ray telescopes are used in cosmology. Because of conditions in the early universe the most distant sources are radio-sources. So radio telescopes see father into space.
Yes quantum mechanics deals with radio waves. QM explains every force except gravity.
I have NO idea what the other posters are talking about.
Maybe because not all things emit gamma waves?
Thanks for the link.
I ask because I had a rather intuitive thought the other day. According to big bang theory, we look back in time towards the origin of the universe. This explanation has proven problematical, since it raises the question of pre-big bang conditions.
Quantum mechanics has no such thing as a linear timeline. How then can sub-atomic waves registered with a radio telescope give us an impression of a progression that follows a linear timeline?
Radio waves are part of the EM spectrum just as visible light is. All sensing equipment "sees" only what arrives at it. If the sources don't emit, then the receivers don't receive (there is nothing to receive if it was never emitted).
The microwave background radiation is the "softest" signal the Universe emits, and it is also the most distant time wise. The WMAP equipment gives the best image of earliest heat in the Universe.
WMAP detects the background heat from the Universe. It does not detect nor resolve galaxies at all. The WMAP pictures show the asymmetry of heat distribution in the early universe. That asymmetry eventually resulted in the super galactic threading structures and to the giant voids (bubbles) that form the basic filament structure of the Universe.
so WMAP is not based on microwave radiation ? | <urn:uuid:460c0ffe-5634-4706-8e45-9a1f093575ef> | 3.515625 | 413 | Q&A Forum | Science & Tech. | 48.115714 |
Summary: The orientation and sedimentary structure of sand dunes depend on the strength and direction of the prevailing winds, so ancient dunes should contain important clues to paleoatmospheric circulation patterns--if their ages can actually be determined. Preusser et al. (p. 2018) used difficult luminescence techniques to construct a 160,000-year record of dune formation in Oman. Their results indicate that models of past atmospheric circulation over southern Arabia during times of high-latitude glaciation, which assume that the intensity of the prevailing westerly winds strengthens during these periods, need to be revised. The dominant wind direction was from South to North, and general atmospheric circulation was not very different from present conditions.
- A 160,000-Year Record of Dune Development and Atmospheric Circulation in Southern Arabia, Preusser, Frank, Radies, Dirk, Matter, Albert, Science 2002 296: 2018-2020 | <urn:uuid:b43b0daf-2e0f-4bd9-a59c-275189055a37> | 3.1875 | 189 | Truncated | Science & Tech. | 28.119394 |
It is related to volume fraction by dividing by 100%.
A solution consists of a solvent, which is commonly a liquid, and a solute, which may be any substance that dissolves in the solvent. For example, if salt water (a solution) is distilled, water (the solvent) passes over into the receiver and salt (the solute) remains in the still.
In the case of a mixture of ethanol and water, which are miscible in all proportions, the designation of solvent and solute is arbitrary. The volume of such a mixture is slightly less than the sum of the volumes of the components. Thus, by the above definition, the term "40% alcohol by volume" refers to a mixture of 40 volume units of ethanol with enough water to make a final volume of 100 units, rather than a mixture of 40 units of ethanol with 60 units of water.
|Look up Volume percent in Wiktionary, the free dictionary.|
||This article needs additional citations for verification. (August 2007)|
|This chemistry-related article is a stub. You can help Wikipedia by expanding it.| | <urn:uuid:af7e3f08-a9ff-4401-bcf9-e4a2d0b8859c> | 3.609375 | 229 | Knowledge Article | Science & Tech. | 44.988288 |
Home Effects Global Warming Preventions Diversity Collaboration Works Cited
What Causes Global Warming?
Global Warming- an increase in the Earth's average surface temperature.
Our earth is heated by the rays of the sun. As the sun shines down on us, energy from the heat reflects off of the earth, into space. Gases from the atmosphere take this energy and reheat the earth. This is called the "greenhouse gas" effect. This is caused by water vapor and carbon dioxide, with the rest heated by other gases.
http://www.r10net-seo-yarismasi.com/resimler/Global-Warming.jpg; (information) http://ngm.nationalgeographic.com/ngm/0409/feature1/index.html?fs=www7.nationalgeographic.com; (also information) http://environment.nationalgeographic.com/environment/global-warming/gw-impacts-interactive.html
Thank you for reading my web page about the causes of global warming!!!
~ Renee!!! :) | <urn:uuid:9d48c669-48d5-4a61-bb06-2d399a186f44> | 3.25 | 230 | Knowledge Article | Science & Tech. | 57.391048 |
In the x direction: 160 N + 250*0.96 = 400 N
In the y direction: 370 N - 250*0.28 = 300 N
Unfortunately he/she didn't add them correctly and got the wrong components.
To finish the problem from here we are looking for a vector R such that x + y + R = 0. (Note carefully what direction R is in!)
As far as the angle 97.1, the angle the 250 N force is pointed in is acs(0.96) = 16.26 degrees below the x axis. So that number is wrong. (That may be why he/she got the components wrong.) | <urn:uuid:dafb3002-6750-4994-9f89-44e88182ce20> | 3.015625 | 138 | Q&A Forum | Science & Tech. | 108.624113 |
Figure 3 summarizes our description of reradiation from gas and dust in the host galaxy of a quasar. Provided quasars are located in galaxies like those of their lower luminosity cousins, it is hard to imagine how thermal reradiation can fail to make a significant contribution to the infrared luminosity of quasars. As we have outlined above, assuming that this dominates provides attractively natural explanations for the shape of the far infrared and submillimeter spectrum, for the high-frequency radio emission, for the ``3 - 5 µm'' bump, and for the universal minimum in L at = 1014.5 Hz. Some support for the latter can be adduced from the elegant observations of near-infrared variability in Fairall 9 by Clavel et al. (1989). The general absence of variability at longer infrared wavelengths (Neugebauer et al. 1989) is at least consistent with a thermal interpretation. Still, objections can be raised: e.g., the general absence of emission features associated with polycyclic aromatic hydrocarbons and silicates (Moorwood 1989). Nonthermal models can be contrived (and the author must confess to some involvement!) to explain many of the same features, though perhaps less naturally.
This debate will ultimately be resolved by a measurement of the brightness temperatures. Nonthermal models of the submillimeter spectrum (de Kool & Begelman 1989) require brightness temperatures TB > 1010 K, while thermal models require TB < 103 K. The two models thus predict angular sizes for the emitting region differing by a factor 104. A submillimeter interferometer with a few kilometers baseline would determine the nature of the emission. Continued monitoring of infrared variability will also discriminate between thermal and non-thermal models (though one should beware of sources like 3C273, where a weak Blazar component seems occasionally to wobble into the line of sight). The model outlined above predicts hysteresis in the near infrared flux: when the central source increases in brightness, the near infrared flux can rise with it (with only a mean light-travel time delay). But the rise will sublimate the dust in a larger area than before, and if the central luminosity subsequently falls faster than grains can reform and grow, the dust-free ``hole'' will produce a large dip in the near infrared L, at the frequencies corresponding to the missing temperatures. If the emitting dust grains are aligned by shear or a globally anisotropic magnetic field, their thermal radiation could be significantly polarized.
Figure 3. Cartoon illustrating the state of and frequencies of reradiation from gas in a quasar's host galaxy. Note the sudden transition in the gas temperature at ~ 1018 cm caused by the drop in opacity when dust sublimates.
It is devoutly to be hoped that we will soon be freed from our embarrassing ignorance (after 20 years of observations and theoretical activity) of whether the infrared emission from quasars arises from a source 1014 cm across, or from one 1022 cm across.
ACKNOWLEDGEMENTS. I thank: Liz for typing, Gerry Neugebauer, Dave Sanders, Tom Soifer and Ski Antonucci for making this subject impossible to ignore, and the Irvine Foundation, the Boeing Corporation, and the NSF for support under Presidential Young Investigator grant AST 84-51725. | <urn:uuid:e5477d5b-c8bd-4c7f-816f-4c5ea4a40bd7> | 2.96875 | 687 | Academic Writing | Science & Tech. | 33.570287 |
Rendering Microsoft Tags in .tag Format
Rendering a Microsoft Tag in the .tag file format provides a hexadecimal code that you can use to programmatically generate the Tag in other applications. This documentation explains how to interpret the hexadecimal encoding of a Tag and how to generate a scannable graphic.
Download a .pdf version of this information.
Microsoft Tags are available in a four-color version (using pure versions of cyan, magenta, yellow, and black) and in a larger black-and-white version. Each Tag includes:
The symbols within a standard Tag are triangles. However, for custom Tags, the symbols can be dots. The symbol rows are separated from the frame and from one another by row spacers. The black frame is enclosed in a white border; the width of the white border is equal to the height of the bottom black bar.
The number of symbol rows depends on the Tag type. Standard color Tags have five symbol rows, whereas standard black-and-white Tags have seven. Regardless of type, Tags always have twice as many symbols per row as they have rows. For example, standard, five-row color Tags will always have 10 symbols per row. Standard black-and-white Tags will always have 14 symbols per row.
Getting Started with the Tag Web Services API
Microsoft Tags are represented in hexadecimal format that can be stored in the .tag file format. They can also be retrieved from the Microsoft Tag API. Each .tag file can contain one or more hexadecimal encodings of a given Tag to allow the Tag graphic to be created in different formats. Different formats will be separated by a semicolon and a space.
Note: The encoding for a color Tag inside a .tag file cannot be converted to a black-and-white Tag. To interpret the hexadecimal code for a Tag, use the following guidelines:
1. The first character in the series indicates the Tag type. Currently, the only possible values are zero (black-and-white) or one (color). The interpretation of the rest of the characters in the encoding is determined by the Tag type.
2. For both color and black-and-white Tag types, the second character in the series indicates the number of rows that make up the Tag. While standard black-and-white Tags are made up of seven rows each and standard color Tags are made up of five rows each, Tags created in the future can consist of as few as four rows and as many as 15 rows.
3. For both of these Tag types, the third and subsequent characters specify the color of each symbol within the Tag. The Tag symbols are encoded left to right, starting with the first row. For color Tags, each character contains two symbols. For black-and-white Tags, each character represents four symbols. If the number of symbols in a Tag does not divide evenly by two (for a color Tag) or four (for a black-and-white Tag), the last character will be padded with zero-valued symbols as necessary.
Each symbol within a black-and-white Tag corresponds to a one-bit value. Each symbol within a color Tag corresponds to a two-bit value.
The color values used for the symbols in a Tag are shown in the following table.
|Color Tags (2-bit values) ||Black and White Tags (1-bit values) |
|00Yellow ||0Black |
|01Magenta ||1White |
|10Black || |
|11Cyan || |
For example, let’s look at the hexadecimal values for both a color Tag and a black-and-white Tag that, when scanned, will open the Microsoft Tag website at http://tag.microsoft.com.
The color Tag for this URL looks like this:
The hexadecimal code for this Tag, when rendered in the .tag format is:
The initial character, 1, indicates that this is a color tag. The second character, 5, indicates the number of rows in the Tag – this Tag has five rows. The third value, C, indicates the first two symbols in the row. Each subsequent hexadecimal character represents two symbols in a symbol row. Translated from the hexadecimal, C becomes “1100,” which designates a cyan symbol followed by a yellow symbol, as you can see in the Tag itself. The rest of the hexadecimal characters are interpreted in the same way.
In contrast, let’s look at the image and coding for the black-and-white Tag that opens the same website.
The black-and-white Tag for this URL looks like this:
The hexadecimal code for this Tag is:
In the above example, each hexadecimal character represents four symbols in a symbol row. The initial character, 0, indicates that this is a black-and-white Tag. The second character, 7, indicates the number of rows in the Tag – this Tag has seven rows. When converted from hexadecimal, the third character, A, gives us 1010. Because this is a black-and-white Tag, 1010 here designates four symbols: white black white black.
To design a Tag, you must calculate its basic unit size. (In these guidelines, “unit” refers to any unit of measure upon which the Tag is based.)
Use the following rules to calculate the size of the Tag:
The following table shows how to calculate the dimensions of sample color and black-and-white Tags.
|Tag Dimension ||Color Tags ||Black/White Tags |
|No of Rows ||5 ||7 |
|Bar Code Height (in Units)
- 7 for the top white border
- 3 for the top frame
- 7 for the bottom black frame
- 7 for the bottom white border
- 2 between rows and between rows and frames 7+3+7+7+7*Rows+2*(Rows+1)=26+9*Rows
|26+9*5 = 71 ||26+9*7 = 89 |
|Symbols Per Row Note: This number is always equal to 2*Rows. ||10 ||14 |
|Row Width (in Units):
- 7 for the left white border
- 5 for the left black frame
- 5 for the right black frame
- 7 for the bottom white border
- 7 for the right white border
|71-24 = 47 ||89-24 = 65 |
|Symbols Widths Per Row The symbols are laid out in a triangle pattern. So, the actual triangle widths that fit into a particular row are equal to one-half the number of symbols plus half of the symbol. |
Base Width = Symbols Per Row / 2 + ½
|10/2 + ½ = 5½ ||14/2 + ½ = 7½ |
|Symbol Width (in Units) The width of the triangle symbol is calculated by dividing the row width by the width of symbols. ||47/5.5 = 8.545 ||65/7.5 = 8.533 |
Drawing the Symbols
All shapes are drawn based on the actual size of the bar code and the calculated unit size. For example, if you are publishing a Tag in a magazine, you may choose to create a Tag that is one-inch square. A five-line, one-inch bar code has 71 units, so each unit is 0.014085 inches. The bottom black frame is seven units tall, so it works out to 7/71*1 inches tall, or 0.098592 inches. If, instead of publishing a one-inch Tag in a magazine, you plan to create a Tag that will be displayed on a billboard, you will have to calculate much larger units to ensure that your Tag can be scanned from a distance.
The following table shows the relative size of each type of Tag.
Example: Standard Tag
Between the black frame and the first triangle in a row of symbols is a half-triangle that is black. The first full triangle in the row is drawn next to the black half-triangle, base-side up. The last triangle of a row is drawn base-side down, followed by a black half-triangle between it and the black frame on the right of the Tag.
Example: Custom Tag
When drawing a very basic custom Tag, the symbols are drawn as dots instead of triangles and a barcode background – in this case, the blue field – shows through the space between the frames. The first and last row spacers are white, as are the remaining row spacers that overlap the frame sides. The background should show through the row-spacers that are between the rows and between the frames. In addition, the background shows through the parts of each triangular symbol that is not taken up by the dots and the additional half-triangle spaces at the beginning and the end of each row. In other words, the background shows through every position inside the frame except where the dots and the top and bottom row spacers appear.
Dots are drawn with a diameter that is one-third of the width of the triangles. The dots must be horizontally aligned at the center of each triangle and vertically aligned one-third of the way toward the center of the triangle as measured from the triangle’s base.
Rendering Microsoft Tags Sample Code
Rendering a Microsoft Tag in the .tag file format provides a hexadecimal code that you can use to programmatically generate the Tag. The above information explains how to interpret the hexadecimal encoding of a Tag, and how to generate a scannable graphic. The following sample code demonstrates generating a PNG image of a Tag in C#.
private static Image RenderTag(string tagCode, int sizeInPixels)
// check the arguments
if (string.IsNullOrEmpty(tagCode) || !tagCode.StartsWith("15"))
throw new ArgumentException("Only tag codes for 5-row color
tags are supported.");
// constants: tag layout
const int rows = 5;
const int symbolsPerRow = 10;
// constants: dimensions of inner tag components, in "units"
const int whiteBorderThickness = 7;
const int blackFrameTopThickness = 3;
const int blackFrameBottomThickness = 7;
const int blackFrameHorizThickness = 5;
const int rowHeight = 7;
const int rowSpacerHeight = 2;
const int rowSpacerHang = 2;
const int rowsAreaHeight = rows * rowHeight
+ (rows + 1) * rowSpacerHeight;
const int blackFrameSize = blackFrameTopThickness
+ rowsAreaHeight + blackFrameBottomThickness;
const int rowsAreaWidth = blackFrameSize - 2
const int whiteBorderSize = 2 * whiteBorderThickness
const float halfSymbolWidth = ((float)rowsAreaWidth)
/ (symbolsPerRow + 1);
// areas surrounding the inner tag components
Rectangle whiteBorderRect = new Rectangle(0, 0,
Rectangle blackFrameRect = new Rectangle(whiteBorderThickness,
whiteBorderThickness, blackFrameSize, blackFrameSize);
Rectangle rowsAreaRect = new Rectangle(blackFrameRect.Left
+ blackFrameHorizThickness, blackFrameRect.Top
+ blackFrameTopThickness, rowsAreaWidth, rowsAreaHeight);
// brushes for the colors used
Brush whiteBrush = new SolidBrush(Color.White);
Brush blackBrush = new SolidBrush(Color.Black);
Brush brushes = new Brush
new SolidBrush(Color.Yellow), // 00
new SolidBrush(Color.Magenta), // 01
blackBrush, // 10
new SolidBrush(Color.Cyan), // 11
// render the tag to a bitmap
Bitmap bitmap = new Bitmap(sizeInPixels, sizeInPixels,
using (Graphics g = Graphics.FromImage(bitmap))
// scale all graphics dimensions to use tag units
Matrix matrix = new Matrix();
float scaleFactor = ((float)sizeInPixels) / whiteBorderSize;
g.Transform = matrix;
// fill the white border and black frame
// fill the row spacers in white
for (int row = 0; row <= rows; ++row)
rowsAreaRect.Left - rowSpacerHang,
rowsAreaRect.Top + row * (rowSpacerHeight + rowHeight),
rowsAreaRect.Width + 2 * rowSpacerHang,
// fill the triangular symbols; the first two characters in
// the tag code indicate the tag color scheme and row count,
// and are skipped.
for (int i = 2; i < tagCode.Length; ++i)
// read the next hex digit
int hexDigit = int.Parse(tagCode.Substring(i, 1),
int firstSymbolCode = (hexDigit >> 2) & 0x03;
int secondSymbolCode = hexDigit & 0x03;
// find out the row and column for the two symbols needed
// to represent the hex digit
int row = (i - 2) / (symbolsPerRow / 2);
int col = ((i - 2) % (symbolsPerRow / 2)) * 2;
// compute the position of the symbols, in units
float left = rowsAreaRect.Left + col * halfSymbolWidth;
float top = rowsAreaRect.Top + rowSpacerHeight
+ row * (rowSpacerHeight + rowHeight);
float bottom = top + rowHeight;
// fill the triangular symbols
new PointF(left + 0 * halfSymbolWidth, top),
new PointF(left + 1 * halfSymbolWidth, bottom),
new PointF(left + 2 * halfSymbolWidth, top)
new PointF(left + 1 * halfSymbolWidth, bottom),
new PointF(left + 2 * halfSymbolWidth, top),
new PointF(left + 3 * halfSymbolWidth, bottom)
static void Main(string args) | <urn:uuid:1c386670-a388-4bf5-b55a-d57ef4ac5676> | 2.953125 | 3,041 | Documentation | Software Dev. | 57.267628 |
More abstractly, a charge is any generator of a continuous symmetry of the physical system under study. When a physical system has a symmetry of some sort, Noether's theorem implies the existence of a conserved current. The thing that "flows" in the current is the "charge", the charge is the generator of the (local) symmetry group. This charge is sometimes called the Noether charge.
Thus, for example, the electric charge is the generator of the U(1) symmetry of electromagnetism. The conserved current is the electric current.
In the case of local, dynamical symmetries, associated with every charge is a gauge field; when quantized, the gauge field becomes a gauge boson. The charges of the theory "radiate" the gauge field. Thus, for example, the gauge field of electromagnetism is the electromagnetic field; and the gauge boson is the photon.
Sometimes, the word "charge" is used as a synonym for "generator" in referring to the generator of the symmetry. More precisely, when the symmetry group is a Lie group, then the charges are understood to correspond to the root system of the Lie group; the discreteness of the root system accounting for the quantization of the charge.
* Various charge quantum numbers have been introduced by theories of particle physics. These include the charges of the Standard Model:
* The color charge of quarks. The color charge generates the SU(3) color symmetry of quantum chromodynamics.
* The weak isospin quantum numbers of the electroweak interaction. It generates the SU(2) part of the electroweak SU(2) × U(1) symmetry.
* Weak isospin is a local symmetry, whose gauge bosons are the W and Z bosons.
* The electric charge for electromagnetic interactions.
Charges of approximate symmetries:
* The strong isospin charges. The symmetry groups is SU(2) flavor symmetry; the gauge bosons are the pions. The pions are not fundamental particles, and the symmetry is only approximate. It is a special case of flavor symmetry.
* Particle flavor charges, such as strangeness or charm. These generate the global SU(6) flavor symmetry of the fundamental particles; this symmetry is badly broken by the masses of the heavy quarks.
* Hypothetical charges of extensions to the Standard Model:
The magnetic charge, another charge in the theory of electromagnetism. Magnetic charges are not seen experimentally in laboratory experiments, but would be present for theories including magnetic monopoles. | <urn:uuid:b248d5f5-db76-41e3-a97a-0ad44aaaab04> | 3.453125 | 537 | Knowledge Article | Science & Tech. | 37.314881 |
|More About JUDGING HAZARDS
Lava flows from andesitic and rhyolitic magmas rarely
cover more than a few square kilometers because of their
high viscosity. More viscous lava comes to the surface
fairly slowly, so lava flows don't travel very far before
cooling and slowing. If large quantities of lava are
extruded quickly, then areas of up to a few hundred
square kilometers can be covered. The most hazardous lava
flows, then, are not from andesitic or rhyolitic magmas,
but from more fluid basaltic eruptions.
|A helicopter lands
near Mt. St. Helens.
Volcanic ash blanketed the
area after the
erupted in 1980.
Tephra deposits cause damage in a variety of ways. Large
fragments of tephra can cause significant damage on
impact, colliding with structures or setting things on
fire. Accumulations of tephra do their damage by burial:
roofs collapse, for example, or crops are killed.
Very fine particles of tephra cause breathing
difficulties and interfere with machinery. Thin layers of
very fine tephra can accumulate thousands of kilometers
from the source. Heavier layers of several centimeters or
more can cover tens of thousands of square kilometers.
Pyroclastic flows cause damage by burial and by
incineration, and because of their speed and gas content
can also cause impact damage and asphyxiation. These
flows are common at stratovolcanoes, since they are
associated with andesitic and rhyolitic magmas.
Pyroclastic flows can travel at speeds of up to 200
meters per second and can extend as far as 200 kilometers
from their source. The heat of the flows can reach
several hundred degrees Celsius. With the capacity to
sweep over barriers as high as a hundred meters or more,
they are a serious danger.
Debris flows can be triggered by a volcanic eruption, by
the normal rumblings and small emissions leading up to an
eruption, by volcanic earthquakes, or simply by gravity
acting on a weakened and overly steep part of the
volcano. Some types of volcanic debris flows are very
similar to rock avalanches. These rarely extend farther
than 100 kilometers from the volcano but can spread
debris over an area of 1,000 square kilometers.
Another common type of debris flow is a lahar, or
volcanic mudflow. This mixture of mud (mainly volcanic
ash from tephra deposits) and water flows quickly down
stream valleys that drain the volcano's slopes. Large
lahars can travel hundreds of kilometers down valleys.
Because of their high density, these mudflows can cause
[Back to JUDGING HAZARDS] [Next: Forecasting] | <urn:uuid:b00ac2f3-20b2-4d0f-8c68-349b567583a4> | 4.375 | 612 | Knowledge Article | Science & Tech. | 40.209742 |
A depiction of the vast "Fermi Bubbles" of gamma-ray emitting magnetic fields emanating from above and below the center of our Milky Way galaxy. / NASA's Goddard Space Flight Center
Vast radiation-emitting "bubbles" erupting from the center of the Milky Way spring from rapid star formation there over the last 10 million years, astronomers report.
Discovered in 2010 by NASA's Fermi Gamma-ray Space Telescope, the so-called radiation-emitting Fermi bubbles emanating from the center of the galaxy are each 25,000 light years (147,000 trillion miles) tall. Visible to gamma-ray telescopes, the bubbles jut from the top and bottom of our spiral-shaped galaxy like doorknobs on both side of a door.
In a new study of these in the journal Nature led by Ettore Carretti of Australia's CSIRO Astronomy and Space Science, astronomers report that the magnetic field of these structures springs from a region of star formation at the center of the galaxy that blasts outward all the way to an outer halo of stars.
"The energy involved is of the order of a million supernova explosions. That is a lot!" Carretti says, by e-mail. A supernova is the explosive blasting-apart of a star, typically releasing as much energy in a single burst as our sun will release in its lifetime.
Most intriguingly, ridges discovered in the Fermi bubble's magnetic field serve as a "phonographic" record of star births in the center of the galaxy over the last 10 million years, the study suggests. Essentially, the height of each ridge tells when outbursts of star creation started in the galactic center. "Each ridge requires some 400 (to) 1,000 supernovae to be generated," Carretti says.
Copyright 2013 USATODAY.com
Read the original story: Astronomy: Galactic radiation records star creation | <urn:uuid:eb8c7f04-8e5f-4c58-9af4-3a5fc9f04f0a> | 3.984375 | 405 | Truncated | Science & Tech. | 42.629279 |
When Google went public, the founders Sergey Brin and Lawrence Page suddenly joined the ranks of the world's wealthiest men.
Anyone wishing to imitate their success would first have to get hold of a gigantic computer and then create a catalog of all the world's websites. There are currently ...
This is an article from the book "Five-minute mathematics" by Ehrhard Behrends which was published in 2008 by the American Mathematical Society (AMS). It is reproduced here with the kind permission of the AMS.
When Google went public, the founders Sergey Brin and Lawrence Page suddenly joined the ranks of the world's wealthiest men. Anyone wishing to imitate their success would first have to get hold of a gigantic computer and then create a catalog of all the world's websites. There are currently about twenty billion web pages. (To get an idea of the size of this number, note that the distance along the Earth's surface from the North Pole to the South Pole is about 20 billion millimeters. For each page, one has to create an index of all terms of interest. That is surely a time-consuming task, but for a team of talented programmers, it is no insuperable challenge. Of course, all the really hard work is left to the computer!
Suppose that all these tasks have been satisfactorily completed. Unfortunately for you, you are still in no position to offer a competitive search engine. The reason is the enormous size of the Internet. Given a particular query, such as all sites containing both ``USA'' and ``hurricane,'' it is not difficult to produce all the web pages with the two search terms. The problem is how to present the results, since typically a search returns from hundreds of thousands to millions of hits. No one has the time or patience to sift through all those pages. One would like to have the most important pages presented first.
Those who have done much ``googling'' know that Google has done a surprisingly good job of solving this problem, for generally one finds what one is looking for among the first dozen or so pages. The secret is in the correct definition of ``important.'' Google's great idea was to consider a web page important if many important web pages refer to it. If one thinks of a web page as a point, with two points connected by an arrow if the page at the arrow's tail has a link to the page at the arrow's head, then the Internet can be pictured as a network of about two billion points connected by many more billions of arrows.
Pages at which many arrows terminate are ``important,'' particularly if the arrows emanate from ``important'' web pages. If we number the web pages 1,2,... and assign a weight Wi to page i as a measure of its importance, there should be a relationship among these numbers. For example, if page 2 is linked to from page 5, and page 5 is linked to by three pages altogether, then page 2 ``inherits'' one-third of the importance of page 5.
Perhaps page 7 also links to page 2 and has ten outgoing links altogether. Then page 2 inherits one-tenth of W7. Suppose that is all: no other pages link to page 2. That leads to the equation
Most web sites are connected in complex ways, and altogether, we end up with twenty billion equations in the twenty billion unknowns W1, W2. ....
The math you learned in school is not going to be of much help here. For most readers, two equations in two unknowns is the most they ever had to deal with. But even for professional mathematicians this number is too large to be handled by the standard methods, even given that some optimization problems with several hundred thousand or even several million variables can be solved.
Another path leads to the goal: one takes a ``random walk.'' Imagine an Internet addict, let us call her Isabella, who starts at, say, the web page ams.org. Isabella then searches the page at random for a link to another page and clicks on it. Arriving at that page, she sees another set of links, and randomly clicks on one. Thus a random walk through the worldwide web has begun, in which out of logical necessity, the ``more important'' pages are visited more frequently than the ``less important'' ones. It is a remarkable fact that the relative frequencies of the visits satisfy the system of equations described above. In short, the importance of a page can be determined by measuring the percentage of time that a surfer is to be found there. However, doing these calculations doesn't seem any easier than solving the initial problem. And if an exact solution is required, that is indeed the case. However, an approximate solution (in which, say, you would be satisfied with five decimal places of accuracy) can be had in several hours. Now the search engine is fully functional, since once you have the levels of importance, the rest falls into place: simply search for all pages with ``USA'' and ``hurricane'' and return them in order of importance.
That is a first approximation to Google's methodology. The details and refinements are complex and as secret as the formula for Coca Cola. As an example of a necessary refinement, we might mention that our random surfer Isabella would have a problem if she arrived at a site without any further links. To avoid such a scenario, at each step in the search, the links on a page are ignored with a certain probabilityp and one goes instead to a randomly selected web page somewhere in the Internet. (That may not be easy for Isabella, but with a directory of all web pages it is no problem.) It is rumored that Google uses the probability p=0.15, which seems to be a good value, based on experience.
Google is also constantly working to minimize the effects of ``Google bombing,'' which is a strategy of puffing up the importance of one's web site by artificially increasing the number of links to one's own pages. Google's competitors have also not been asleep at the switch. There is constant work underway at developing new approaches and calculational techniques for evaluating the ``importance'' of websites. For different users and different combinations of search terms, ``important'' can mean something quite different. But adding in such complexity then leads to the problem of whether - as with Google - the results of a search can be returned within a fraction of a second. | <urn:uuid:8bf00d08-26d4-4a84-afd6-d878f1eafe79> | 2.9375 | 1,318 | Truncated | Science & Tech. | 52.563104 |
The mexican jumping death spider is a very peculiar kind of spider indeed. The name is misleading, as this spider is native to the Waterloo region. The rest of its name comes from the fact that as a direct result of the spider jumping, it dies.
The mexican jumping death spider will only die if it intends to jump, and makes it to the apex of that jump. If you were to attach some metal to this spider and place an electromagnet nearby such that the spider moves as if it were jumping, it would not die. Also, if you were to somehow force its legs to go through the motions of jumping, it would not die. Again, if there was a wall directly in front of the maximum height the spider would reach in its jump, it would not die. The mexican jumping death spider will only die from jumping if it consciously makes the decision to jump and succeeds in doing so. The spider will jump, and when it reaches the peak of the jump, it dies. Mexican jumping death spiders always land on their back. Mexican jumping death spiders do know that they will die when they jump, it is when they are startled that they jump to hide, then they die. It is not possible to kill a mexican jumping death spider in any way other than making it want to jump.
It would seem that there would not be very many of these spiders in the region, but the jumping actually increases their numbers. In the same way that the mexican jumping death spider dies as a result of jumping, a male spider of this species must jump to mate. After some time, the female will have a huge urge to jump. She will jump, die and hundreds of baby mexican jumping death spiders will emerge. Only a few of these spiders actually survive, because most of them try to jump away. If the female did not give birth in this fashion, she would not be able to have as many children.
Please note that since the only way to kill a mexican jumping death spider is to make it jump successfully, they can effectively be grant temporary immortality by amputating their legs. However since it is a spider, the legs will grow back over time.
A common misconception about the mexican jumping death spider is that since they must jump to die, they do not need to eat/sleep/brush their teeth. This is not true. If a spider of this species neglects to get sufficient nourishment/rest/oral hygiene, it shall be overcome with the urge to jump; and it shall die.
Mexican jumping death spiders are incredibly good jumpers. They can cover large distances in a single bound; they will simply not live to see their great feat. As a point of interest, a Mexican jumping death spider thrown into a fire will usually jump. Intelligence in a mexican jumping death spider consists purely of a commitment to NOT JUMPING.
The Mexican jumping death spider is a rare sight to see in Waterloo, and chances are if you see one, it will die trying to hide from you. Please, for the sake of the species, do not look for them; they are an endangered species. | <urn:uuid:da4c8f4c-1c03-49a0-be9d-c563f5a15cc0> | 2.953125 | 649 | Knowledge Article | Science & Tech. | 61.880362 |
Dinoflagellates are an important group of phytoplankton that produce oxygen in marine and freshwater. Some species form symbiotic relationships with larger animals, including corals (zooxanthellae), jellyfish, sea anemones, nudibranchs and others. Sometimes dinoflagellates grow out of control, to more than a million cells per milliliter, causing an algae bloom or red tide. Because some dinoflagellates produce toxins, when there are too many in the water, they can creep up the food chain, killing animals and making people sick. Learn more about red tides. | <urn:uuid:6d41f949-cfa4-490d-9795-a68d0c8d2a17> | 3.453125 | 133 | Knowledge Article | Science & Tech. | 20.786 |
2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements
The alkali metals are a series of elements comprising Group 1 ( IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). (Hydrogen, although nominally also a member of Group 1, very rarely exhibits behavior comparable to the alkali metals). The alkali metals provide one of the best examples of group trends in properties in the periodic table, with well characterized homologous behaviour down the group.
The alkali metals are all highly reactive and are rarely found in elemental form in nature. As a result, in the laboratory they are stored under mineral oil. They also tarnish easily and have low melting points and densities. Potassium and rubidium possess a weak radioactive characteristic (harmless) due to the presence of long duration radioactive isotopes.
The alkali metals are silver-colored (cesium has a golden tinge), soft, low- density metals, which react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to form a singly charged positive ion, or cation.
Hydrogen, with a solitary electron, is usually placed at the top of Group 1 of the periodic table, but it is not considered an alkali metal; rather it exists naturally as a diatomic gas. Removal of its single electron requires considerably more energy than removal of the outer electron for the alkali metals. As in the halogens, only one additional electron is required to fill in the outermost shell of the hydrogen atom, so hydrogen can in some circumstances behave like a halogen, forming the negative hydride ion. Binary compounds of hydride with the alkali metals and some transition metals have been prepared. Under extremely high pressure, such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal; see metallic hydrogen.
Alkali metals have the lowest ionization potentials in their respective periods, as removing the single electron from the outermost shell gives them the stable inert gas configuration. Their second ionization potentials are very high, as removing an electron from a species having a noble gas configuration is very difficult.
Alkali metals are famous for their vigorous reactions with water, and these reactions become increasingly violent as one moves down the group. The reaction with water is as follows:
Alkali metal + water → Alkali metal hydroxide + hydrogen gas
With potassium as an example:
- 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
Reaction in ammonia
Alkali metals dissolve in liquid ammonia to give blue solutions that are paramagnetic. As the solution approaches saturation, it becomes deep purple, then metallic.
Because the solution contains free electrons, it occupies more space than the sum of the volumes of the metal and ammonia. The presence of free electrons also makes these solutions very good reducing agents and good electrical conductors. Since they are easier to handle than the metals themselves they are sometimes used as substitutes.
The solution is not stable over long periods, and the dissolved alkali metal will react to form the corresponding amide. This reaction, when accelerated with a catalyst (usually iron(III) nitrate), is used for the production of sodium amide:
The amide can be extracted, or it can be converted to sodium azide by bubbling nitrous oxide through the ammonia solution:
The alkali metals show a number of trends when moving down the group - for instance, decreasing electronegativity, increasing reactivity, and decreasing melting and boiling point. Density generally increases, with the notable exception of potassium being less dense than sodium, and the possible exception of francium being less dense than caesium.
|Alkali metal||Standard Atomic Weight ( u)||Melting Point ( K)||Boiling Point ( K)||Density ( g· cm−3)||Electronegativity ( Pauling)|
|Francium||(223)||? 295||? 950||? 1.87||0.7|
- The metal lithium is not essential for any biological functions, but was found to exist in extremely tiny quantities in umbilical cord blood. This was found during a study by taking blood samples of newborns from both the umbilical cord and the mother at the time of birth, and subjecting the samples to a number of tests. They found that there was 7 times the amount of lithium in blood than previously believed. (Krachler and Rossipal 488) While it is considered a non-essential trace element (an element needed in extremely tiny amounts for proper growth), lithium also has medicinal uses. A double-blind, placebo-controlled, two-week long study conducted by a group of doctors on severely depressed patients proved that lithium is a key component in the treatment of severe depression. (Joffe, Levitt, and Sokolov, 791) It has also been proven to play a role in the treatment of other mental disorders. (Bildik et al. 277) One recorded instance was the case of a girl who developed a condition known as Neuroleptic malignant syndrome, who was given an antipsychotic drug (a tranquilizing drug that induces a state of relative calm). She quickly developed the symptoms of NMS, and was quickly hospitalized. There, doctors began treating her for the disorder, and in the final stage of her treatment, lithium was administered to her to help stabilize her mental functions. Weeks later, she was released and was in good physical health, but retained her previous diagnosis of Bipolar Disorder (a mental disorder that encompasses periods of mania and depression interspersed by periods of normal behaviour). (Bildik et al. 278)
- Sodium and potassium are very common alkali metals. These elements are essential for the existence of all known life. They are found in the cytoplasm (organic fluid, mainly water) of all living cells, and they are critical to everyday cell operation and regulation. (Chang and Tsong 587) Also, a common sodium salt, sodium chloride (table salt), has been identified many times as a contributor to hypertension in humans. (Sharp 727) A double-blind, two-month study was conducted on a group of elderly adults by modestly cutting their salt intake, to find if cutting salt intake would lower blood pressure. Some in the group were given half the salt that others were given for the duration of the study. The findings indicated that those who were given only half the amount of salt experienced a drop in blood pressure of up to 7.2 mm Hg (millimeters Mercury). (Cappacio and Markandu 850)
- Rubidium is not required for any known biological functions, but is known to be an unnecessary and toxic trace-element in humans. (Krachler and Rossipal 488) A recent study conducted on rubidium levels in freshwater ecosystems from Lake Erie and two Arctic lakes indicate that this element biomagnifies (the concentration grows as you move higher in the food chain) in marine food chains. This was found by collecting samples of fish, birds and plankton, and conducting tests on them. They found that the predatory animals (the small-mouth bass, for example) had higher rubidium concentrations than animals commonly considered to be prey. (Campbell et al. 1163)
- Caesium (also spelled cesium) is not typically found in any biological systems. However, caesium salt (caesium chloride) is a popular medicinal supplement taken to counteract the effects of damaged or diseased cells on the body. (Ackerman et al. 1011) Furthermore, this supplement has been shown to be toxic to human physiology, and has caused very serious side effects in people, and potentially can be deadly if not taken carefully. (Ackerman et al. 1011)
- Francium is an extremely rare element, and its chemical and physical properties have not been characterized to the same extent as the other alkali metals. It is known to have the same chemistry as caesium and is primarily an exotic curiosity in the world of physics. At any one moment in time, less than one ounce of francium is believed to exist on Earth, and its most stable isotope has a half life of a little less than 23 minutes.("Physics update" 9) This makes working with the element dangerous and difficult and radiochemistry techniques must be used to characterize its chemical properties. It has not been found to exist in any biological systems, and while there is no direct evidence of this, it is assumed to be true due to the rarity and instability of the element. | <urn:uuid:10d49e97-7a24-42a8-ad4a-227de4c49b1b> | 3.953125 | 1,863 | Knowledge Article | Science & Tech. | 33.759138 |
Scientific Name:Ascidiella aspersa
Common Name:Euorpean sea squirt (others: dirty sea squirt, solitary ascidian)
Established Range:On the East Coast, from the Bay of Fundy to Cape Hatteras
Established in Rhode Island?Yes, throughout Narragansett Bay
Date and Location of Introduction:1970's, New England
Method of Introduction:Unknown, but likely through hull fouling or ballast water
Habitat:A. aspersa can be found in protected subtidal areas, attached to rocks, boulders, and artificial structures such as pilings, boat hulls, bouys, and floating docks. This tunicate can can tolerate a wide range of temperatures, and can survive in salinities between 18 and 40 parts per thousand. Prefers shallow waters and can only be found at depths less than 90 meters.
Diet:A. aspersa is a filter feeder that eats zooplankton, phytoplankton, and detritus.
Average Life Span:Approximately 18 months
Breeding:A. aspersa is hermaphroditic and breeds by broadcast spawning from March to October in the New England region.
Concerns:All invasive tunicates, including A. aspersa, pose the same problems. These tunicates are notorious fouling organisms, and can completely cover submerged boat hulls, aquaculture cages, and just about any other surface that they are capable of living on. As a result, they can slow down boats and have negative impacts on the local environment. Invasive tunicates have been known to smother shellfish and other sessile organisms, and will outcompete native filter feeders for food and space.
Control:There are no known effective control methods at this time. Copper-based anti-foulants have little effect.
Identification Card:Courtesy of Salem Sound Coastwatch
- Currently, there are no documents for this species
Works Cited:ISSG. 2010. Ecology of Ascidiella aspersa. The Global Invasive Species Database, http://www.issg.org/database/species
NIMPIS. 2010. Ascidiella aspersa (soliatary ascidian). National Introduced Marine Pest Information System, http://www.marinepests.gov.au/nimpis. | <urn:uuid:e0419b97-6ccb-40ad-8476-01cb0c228794> | 3.640625 | 507 | Knowledge Article | Science & Tech. | 36.00957 |
Rhizomes of mangrove swamps are unique in the sense that they can deal with water as well as drought. They can adapt to low levels of oxygen as well as limit their intake of salt. Furthermore, mangroves protect coastlines from erosion by waves.
Adaptation is really the word of the day concerning mangroves.
3 Responses to “Biological coastline protection”
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The Spitzer Space Telescope is a technological marvel, featuring many innovations never before used on a space mission. It stands about 4 meters (13 feet) tall, and weighs approximately 865 kilograms (1,906 pounds).
Since Spitzer is designed to detect infrared radiation, or heat - its detectors and telescope must be cooled to only about 5 degrees above absolute zero (-450 degrees Fahrenheit, or -268 degrees Celsius). This will ensure that the observatory's "body heat" does not interfere with its observations of relatively cold cosmic objects.
While parts of Spitzer must be kept cold to function properly, other electronics onboard the spacecraft need to operate near room temperature. To achieve this balance of warm and cold, the telescope is compartmentalized into two components:
The Cryogenic Telescope Assembly - houses Spitzer's cold components, including the 0.85-meter telescope and three scientific instruments.
The Spacecraft - contains the relatively warm components, including solar panels, telescope controls and tools to communicate scientific information with Earth.
Innovations - other creative ways scientists and engineers achieved this temperature balance. | <urn:uuid:7bcf8f2b-27c0-4325-99cd-dd767ebc5f91> | 4 | 223 | Knowledge Article | Science & Tech. | 22.036583 |
Data from Venus - On Dec. 14, 1962, NASA's Mariner 2 spacecraft sailed close to the shrouded planet Venus, marking the first time any spacecraft had ever successfully made a close-up study of another planet. It flew by Venus as planned at a range of 34,762 km (21,600 miles), scanning the planet's atmosphere and surface for 42 minutes.
The spacecraft showed that surface temperature on Venus was at least 425°C (797°F) on both the day and night sides, hot enough to melt lead. It also showed that Venus rotates in the opposite direction from most planets in our solar system, has an atmosphere mostly of carbon dioxide with very high pressure at the planet's surface, continuous cloud cover and no detectable magnetic field. It also found the solar wind streams continuously and that the density of cosmic dust between planets is much lower than it is near Earth. | <urn:uuid:fe73cd02-7b30-45ee-aa8d-265586e4f1dc> | 3.796875 | 180 | Truncated | Science & Tech. | 51.803844 |
The concept of global warming is compelling, but how can last year's cold winter fit into that pattern?
—Bill Price, Madison, Wis.
First, short-term cooling (a few years) does not contradict the concept of global warming — longer-term trends are what count; and second, one must consider the planet as a whole. Last year's harsh winter was a regional event affecting mainly the eastern U.S., whereas most of the Northern Hemisphere experienced a mild winter. Last winter, the average temperature range between the middle and high latitudes of the Northern Hemisphere was less than usual because of pronounced warming in the Arctic. This weakened the pattern of Northern Hemisphere jet streams, which draw their energy from zones of great temperature contrast, thereby allowing a greater-than-usual southward penetration of polar air. | <urn:uuid:9a1e50fd-78c0-4e1f-b5a2-e208f0544c7f> | 3.234375 | 165 | Q&A Forum | Science & Tech. | 48.994706 |
Here's our next installation in our occasional series on the Chandra blog called "The Unexpected." These posts will take a look at some of the biggest surprises (and expected discoveries) made by Chandra so far in its mission. Today's topic is "normal stars," which is what astronomers call stars that are similar to our Sun.
Expected and Detected:
X-ray emission from the outer atmospheres, or coronas, of stars of almost every type: young and old, large and small.
William Blair is an astrophysicist and research professor at The Johns Hopkins University in Baltimore, Md. He penned this blog post to help explain the excitement -- and challenges -- involved with getting a handle on the mysterious ULX (ultraluminous X-ray source) he and his colleagues discovered in the spiral galaxy M83.
The spiral galaxy M83, also known as the Southern Pinwheel Galaxy, is an amazing gift of nature. At 15 million light years away, it is actually one of the closer galaxies (only 7-8 times more distant than the Andromeda galaxy), but it appears as almost exactly face-on, giving earthlings a fantastic view of its beautiful spiral arms and active star-forming nucleus. M83 has generated six observed supernovas since 1923, but the last one seen was in 1983. We are overdue for a new supernova!
Because of all the star formation and supernova activity in M83, we also expect there to be a lot of X-ray binary stars and supernova remnants—the expanding leftovers from old supernovas that stay visible for several tens of thousands of years after the supernova fades. By tying multiwavelength observations of M83 together, my colleagues and I hope to learn a lot about the interplay between the stars and the gas, and how they impact the entire galaxy.
This morning, the Space Shuttle Discovery touched down from its final flight – a journey from the Kennedy Space Center in Florida to Washington, DC. Discovery will eventually be on display at the Smithsonian's Udvar-Hazy Center near the Dulles airport.
Chandra's own Roger Brissenden was on hand in Washington, DC, for today's event. Chandra has connections to this event on both the NASA and the Smithsonian sides.
To celebrate its 22nd anniversary in orbit, the Hubble Space Telescope has released a dramatic new image of the star-forming region 30 Doradus, also known as the Tarantula Nebula because its glowing filaments resemble spider legs. A new image from all three of NASA's Great Observatories - Chandra, Hubble, and Spitzer - has also been created to mark the event.
Astronomy can generate a large amount of attention from the public, but the number of working astronomers is smaller than the number of researchers in many other academic fields. So, when people get over their surprise at meeting a real astronomer, they often ask "How did you end up working in this field?". There are many different answers, but an interesting one is provided here by Will Dawson from the University of California, Davis, who kindly explains his career change from engineering to astronomy. We were very satisfied to hear that part of his motivation for this big change came from the publicity generated by the Bullet Cluster in 2006.
Will is the first author of a recent paper describing the discovery of the Musket Ball Cluster.
What field did you work in before astronomy?
After graduating with my bachelor of science degree in Maritime Systems Engineering from Texas A&M at Galveston in 2002, I went to work in the offshore engineering industry at Technip. During my four years with Technip I was primarily involved with the design and analysis of Spars, which are floating offshore oil production platforms (essentially stiffened steel cylinders roughly 90 feet in diameter, 550 feet long and 25,000 tons).
What inspired you to change fields?
Using a combination of powerful observatories in space and on the ground, astronomers have observed a violent collision between two galaxy clusters in which so-called normal matter has been wrenched apart from dark matter through a violent collision between two galaxy clusters.
The newly discovered galaxy cluster is called DLSCL J0916.2+2951. It is similar to the Bullet Cluster, the first system in which the separation of dark and normal matter was observed, but with some important differences. The newly discovered system has been nicknamed the "Musket Ball Cluster" because the cluster collision is older and slower than the Bullet Cluster.
Continuing our interest in poetry, here is a poem inspired by Chandra's image from August 11th 2011 of VV340 , in which two colliding galaxies look like a 'Cosmic Exclamation Point.' The author was fascinated by the image and the metaphor used to encapsulate it – by, that is, the whole notion of 'cosmic punctuation' – so he decided to explore these ideas further in a poem.
Every two years or so, NASA's Astrophysics Division (part of NASA's Science Mission Directorate) conducts what is called its Senior Review. During this process, an outside panel of experts looks at a variety of things about operating missions in astrophysics that are in their "extended phase." This includes Chandra.
Most of us appreciate a bit of a break in our day. Even a brief moment away can help us stay focused on the usual tasks of work, home life, or whatever occupies our time.
Sometimes, astronomy can supply that step away from the every day. It can provide an opportunity to consider big picture questions about our place in the Universe, think about exotic and fascinating phenomena, or even just relax and enjoy beautiful imagery.
We can only imagine how much more important it is to have that chance for a momentary escape if you have a dangerous and important job such as being a soldier.
Please note this is a moderated blog. No pornography, spam, profanity or discriminatory remarks are allowed. No personal attacks are allowed. Users should stay on topic to keep it relevant for the readers.
Read the privacy statement | <urn:uuid:b317bc38-2cf5-403b-94fa-ad3fdb8df3a9> | 3.3125 | 1,235 | Personal Blog | Science & Tech. | 40.941168 |
In languages like C or C++, the programmer is responsible for dynamic allocation and deallocation of memory on the heap. In C, this is done using the functions malloc() and free(). In C++, the operators new and delete are used with essentially the same meaning; they are actually implemented using malloc() and free(), so we'll restrict the following discussion to the latter.
Every block of memory allocated with malloc() should eventually be returned to the pool of available memory by exactly one call to free(). It is important to call free() at the right time. If a block's address is forgotten but free() is not called for it, the memory it occupies cannot be reused until the program terminates. This is called a memory leak. On the other hand, if a program calls free() for a block and then continues to use the block, it creates a conflict with re-use of the block through another malloc() call. This is called using freed memory. It has the same bad consequences as referencing uninitialized data -- core dumps, wrong results, mysterious crashes.
Common causes of memory leaks are unusual paths through the code. For instance, a function may allocate a block of memory, do some calculation, and then free the block again. Now a change in the requirements for the function may add a test to the calculation that detects an error condition and can return prematurely from the function. It's easy to forget to free the allocated memory block when taking this premature exit, especially when it is added later to the code. Such leaks, once introduced, often go undetected for a long time: the error exit is taken only in a small fraction of all calls, and most modern machines have plenty of virtual memory, so the leak only becomes apparent in a long-running process that uses the leaking function frequently. Therefore, it's important to prevent leaks from happening by having a coding convention or strategy that minimizes this kind of errors.
Since Python makes heavy use of malloc() and free(), it needs a strategy to avoid memory leaks as well as the use of freed memory. The chosen method is called reference counting. The principle is simple: every object contains a counter, which is incremented when a reference to the object is stored somewhere, and which is decremented when a reference to it is deleted. When the counter reaches zero, the last reference to the object has been deleted and the object is freed.
An alternative strategy is called automatic garbage collection. (Sometimes, reference counting is also referred to as a garbage collection strategy, hence my use of ``automatic'' to distinguish the two.) The big advantage of automatic garbage collection is that the user doesn't need to call free() explicitly. (Another claimed advantage is an improvement in speed or memory usage -- this is no hard fact however.) The disadvantage is that for C, there is no truly portable automatic garbage collector, while reference counting can be implemented portably (as long as the functions malloc() and free() are available -- which the C Standard guarantees). Maybe some day a sufficiently portable automatic garbage collector will be available for C. Until then, we'll have to live with reference counts. | <urn:uuid:31b50666-7c3e-47f9-be08-06838571a219> | 3.640625 | 643 | Documentation | Software Dev. | 39.578747 |
This module provides an interface to the mechanisms used to implement the import statement. It defines the following constants and functions:
(suffix, mode, type), where suffix is a string to be appended to the module name to form the filename to search for, mode is the mode string to pass to the built-in open() function to open the file (this can be
'r'for text files or
'rb'for binary files), and type is the file type, which has one of the values PY_SOURCE, PY_COMPILED, or C_EXTENSION, described below.
None, the list of directory names given by
sys.pathis searched, but first it searches a few special places: it tries to find a built-in module with the given name (C_BUILTIN), then a frozen module (PY_FROZEN), and on some systems some other places are looked in as well (on the Mac, it looks for a resource (PY_RESOURCE); on Windows, it looks in the registry which may point to a specific file).
If search is successful, the return value is a triple
(file, pathname, description) where
file is an open file object positioned at the beginning,
pathname is the pathname of the
file found, and description is a triple as contained in the list
returned by get_suffixes() describing the kind of module found.
If the module does not live in a file, the returned file is
None, filename is the empty string, and the
description tuple contains empty strings for its suffix and
mode; the module type is as indicate in parentheses above. If the
search is unsuccessful, ImportError is raised. Other
exceptions indicate problems with the arguments or environment.
This function does not handle hierarchical module names (names
containing dots). In order to find P.M, that is, submodule
M of package P, use find_module() and
load_module() to find and load package P, and then use
find_module() with the path argument set to
P.__path__. When P itself has a dotted name, apply
this recipe recursively.
|name, file, filename, description)|
'', respectively, when the module is not being loaded from a file. The description argument is a tuple, as would be returned by get_suffixes(), describing what kind of module must be loaded.
If the load is successful, the return value is the module object; otherwise, an exception (usually ImportError) is raised.
Important: the caller is responsible for closing the
file argument, if it was not
None, even when an exception
is raised. This is best done using a try
... finally statement.
Trueif the import lock is currently held, else
False. On platforms without threads, always return
On platforms with threads, a thread executing an import holds an internal lock until the import is complete. This lock blocks other threads from doing an import until the original import completes, which in turn prevents other threads from seeing incomplete module objects constructed by the original thread while in the process of completing its import (and the imports, if any, triggered by that).
The following constants with integer values, defined in this module, are used to indicate the search result of find_module().
The following constant and functions are obsolete; their functionality is available through find_module() or load_module(). They are kept around for backward compatibility:
Noneis returned. (Frozen modules are modules written in Python whose compiled byte-code object is incorporated into a custom-built Python interpreter by Python's freeze utility. See Tools/freeze/ for now.)
1if there is a built-in module called name which can be initialized again. Return
-1if there is a built-in module called name which cannot be initialized again (see init_builtin()). Return
0if there is no built-in module called name.
Trueif there is a frozen module (see init_frozen()) called name, or
Falseif there is no such module.
|name, pathname, file)|
|name, pathname[, file])|
|name, pathname, file)| | <urn:uuid:fbb7bb7a-e2a6-4996-903e-36af912bd3e9> | 2.859375 | 899 | Documentation | Software Dev. | 39.072013 |
Actin and myosin
- Study guide:
- Wikipedia article: Myosin
Myosins are mechanochemical enzymes and motor proteins that function through ATP hydrolysis.
Myosin Structure
Myosin is composed of heavy chains and light chains. The heavy chains have head, neck and tail domains. The head domain binds actin and has ATPase activity. The neck domain provides an attachment point for regulatory and essential lightchains such as calmodulin. The tail domain differs between myosins and determines the specific properties of each myosin.
Myosin II
Myosin II has a long α-helix tail which forms a dimer with another Myosin to create a coiled-coil dimer. The tails also mediate polymerization into bipolar thick filaments.
Myosin I
Myosin I has a short tail which does not assemble into filaments. Some Myosin I proteins have membrane binding sites and can move organelles into the cell.
Myosin Motility and ATP hydrolysis
Myosin motility is coupled to ATP hydrolysis. Most myosins move toward the (+) end of the filament. Myosin VI, however, moves towards the (-) end.
Myosin Cross-bridge Cycle
(1) Rigor: The ATP binding site is empty and myosin is tightly bound to actin
(2) ATP binding: The ATP binding cleft closes upon ATP binding and the actin binding cleft opens, which weakens the actin-myosin bond.
(3) ATP hydrolysis: The ATP molecule is hydrolyzed to ADP and Pi and the myosin head moves to a new position.
(4) Pi release: This step is also referred to as the power stroke. The actin fliament is moved relative to the myosin filament
(5) ADP release: myosin is restored to original rigor state.
Muscle Cell and Sarcomere Structure
Skeletal muscle have a regular internal structure and the muscle fivers of skeletal muscle (myofibers) are enormous cells that contain multiple nuclei. Muscle fibers are composed of individual contractile bundles called myofibrils. Each myofibril consists of small contractile units called sarcomeres.
Thin filaments are composed of actin filaments, CapZ, tropomodulin, tropomyosin, troponin, and nebulin. Thick filaments are composed of myosin II. Protease can cut myosin into the S1 and tail (motor) domains. The isolated tails can make filaments alone. Thick filaments are bipolar. They are 5 main parts to these CapZ and a-actinin mediate binding of the (+) end of actin to the Z disk.
The (-) ends of actin are capped by tropomodulin.
Nebulin wraps along the length of the filament.
Titin connects the ends of myosin thick filaments to the Z-disk and extends along the filaments to the M-line (½ the length of the sarcomere).
The Sliding Filament Model of Contraction
The sarcomere shortening caused by myosin filaments sliding past actin filaments with no change in the length of either filament. Because the myosin filament is bipolar, it pulls the thin filaments and Z-disk towards the center of the sarcomere, causing sarcomere shortening.
External Links
- http://www.sci.sdsu.edu/movies/actin_myosin_gif.html (3D Animation: Myosin Crossbridge Cycle) | <urn:uuid:eb9a902b-5b7b-49d2-88d3-a2c49f8a6133> | 3.40625 | 793 | Knowledge Article | Science & Tech. | 42.92625 |
Displaying 21 - 30 of 30 resources in Wildlife and Publications:
21. Nature Essays by Robert Winkler
Columns by Robert Winkler about his encounters with birds and other wildlife in the "suburban wilderness" of New England. ...
22. Nature's Holism - the coevolutionary mechanism
Stanger, kzn, South Africa
Nature's Holism explores the coevolution of long-associated species arriving at a holistic view of nature where the compatibility between species within an ecosystem is significant. ...
Narragansett, RI, USA
Nor'easter magazine is a collaborative project of the Northeast regional Sea Grant college programs, part of the National Sea Grant College Program. This publication opens ...
24. Notes from the Field
Articles on various wildlife issues ...
25. Rally Cry, Defending Headwaters Forest
Resources is RFF`s quarterly newsletter containing news of economic research and policy analysis regarding natural resources and the environment. ...
27. Restoring Borders Woodland: Conference Proceedings
Complete proceedings of the 1993 conference held at the Dryburgh Abbey Hotel, Jedburgh, Scottish Borders ...
28. Too Wild to Drill by The Wilderness Society
The Wilderness Society released a report highlighting wild lands that are currently being threatened by the Bush administration's energy plan. In this report, The Wilderness ...
29. World Watch in Spanish
Madrid, Madrid, Spain
World watch in Spanish is a magazine and editorial that monitor climate, water, sustainable future, energy, forest, food, population, biodiversity and other trends. ...
30. Yearbook of International Co-operation on Environment and Development
Presents comprehensive information on international environmental treaties, IGOs and international NGOs working within the environmental field, in addition to country profiles ...
Displaying 21 - 30 of 30 | <urn:uuid:180362a6-bf3b-43f6-b881-0a6ebc5c649b> | 2.75 | 369 | Content Listing | Science & Tech. | 35.387452 |
It is known that the area of the largest equilateral triangular
section of a cube is 140sq cm. What is the side length of the cube?
The distances between the centres of two adjacent faces of another
cube is 8cms. What is the side length of this cube? Another cube
has an edge length of 12cm. At each vertex a tetrahedron with three
mutually perpendicular edges of length 4cm is sliced away. What is
the surface area and volume of the remaining solid?
The builders have dug a hole in the ground to be filled with concrete for the foundations of our garage. How many cubic metres of ready-mix concrete should the builders order to fill this hole to make the concrete raft for the foundations?
What is the volume of the solid formed by rotating this right
angled triangle about the hypotenuse? | <urn:uuid:f56fd6ba-4e6d-4824-af3b-cd2734b710d9> | 2.71875 | 175 | Tutorial | Science & Tech. | 60.0315 |
What mechanisms exist for generating lift on a static object? Condition is: Other than propellers I know that generating lift on a static object in a sense of anti-gravity for e.g. drone is not ...
This air plane just caught my eye. Two contrails apparently are flowing backward, slightly off-centered and then ultimately converge, giving the overall shape of a very narrow rhomboid parallelogram, ...
The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly. ...
I was reading in the papers how some-airline-or-the-other increased their prices for extra luggage, citing increased fuel costs. Now I'm a bit skeptical. Using the (wrong) Bernoulli-effect ...
I'm watching an episode of Mythbusters where they show aircraft saving 3-5% fuel when flying in a tight V formation. Interestingly, this also applies for the lead airplane. How is that possible for ...
Say that the airplane is going in 1000 km/h. On the side of the airplane, there is a 10x10 cm window. How much friction would this window cause. For the sake of the calculation, imagine that the ...
I've noticed that an airplane appears to have more lift when it's almost touching the ground then it has 100 feet or more in the air. What causes this to occur? | <urn:uuid:e1975562-da4d-45e0-be8a-ac8eaa2c7da7> | 3.484375 | 300 | Q&A Forum | Science & Tech. | 70.579559 |
Short note: This made some big headlines recently. Scientists have been able to encode digital information into DNA molecules. Here are four headlines that all report on the same paper from Science, but with a few different details each. They’re all great articles.
Headline from Science:
“DNA: The Ultimate Hard Drive”
Headline from io9:
“Soon you’ll be backing up your hard drive using DNA”
Headline from The Guardian:
“Book written in DNA code
Scientists who encoded the book say it could soon be cheaper to store information in DNA than in conventional digital devices”
Headline from Discover Magazine:
“Want to Get 70 Billion Copies of Your Book In Print? Print It In DNA”
DNA can store digital information. Your hard drive could someday be a DNA molecule.
One milligram of DNA could encode the complete text of every book in the Library of Congress, with plenty of room left over. A gram of the stuff can hold a billion gigabytes. I don’t even know what that’s called – a billion gigabytes – I guess it’s 950 petabytes (if that helps any).
A team led by George Church at Harvard Medical just encoded 5 MB – including illustrations – into a sequence of DNA.
“Wow,” one may say. “How did they do that? Did they take dog DNA and mix it with turtle DNA and then splice it and dice it and recombine it somehow?”
Not exactly. As a matter of fact, not at all.
Let’s break this down. Two technologies made this possible: 1) DNA synthesis, and 2) DNA sequencing.
1) DNA Synthesis – (my definition) – building DNA piece by piece from scratch. DNA has that twisted ladder shape, right? So imagine that I throw you a bunch of rungs and said, “Build a ladder.” That’s synthetic DNA (except with nucleobases instead of wooden rods). Trick is to make a ladder that won’t break my neck – that is, the pieces fit together, stay together, and remain stable.
Now imagine that the rungs I threw you each have a label on them – keep it simple: a “1” or a “2”. Then I said, “Two 1’s in a row is an ‘A’; a 1 followed by 2 is a ‘B’…” and so on. And the goal was to transcribe a book into ladder rungs – each and every letter of each and every word represented by the order of the rungs.
You’d have a damn long ladder, but it could certainly be done.
Researchers can do this now with DNA. (Here’s a longer science-y post I wrote about it)
2) DNA Sequencing – no biggie here – this is the ability to “read” DNA. You have a DNA strand and you want to know the order of the nucleobases (the rungs). This was a long and costly process, but the technology is getting better. It’s already reliable; it just needs to be cheaper and faster to make it mainstream.
So that’s basically what the researchers did – they used the four nucleobases of DNA (A, C, G, T) to code the letters of the words of the book, and then built their DNA ladder.
As soon as synthesis and sequencing become cheap, effective, and contained (like small tabletop units), then we could see a lot more of this.
I don’t know though – forget hard drives – code up the Library of Congress and inject it right into my brain. Bypass the middle-man.
The Fiction 1/2
Pick what you want to know. Encode it into DNA. Wrap it with a mutational algorithm, and stick the needle into your brain. The DNA will mutate your synaptic pathways and you’ll instantly be smarter.
Knowledge is all about pathways in the brain. These pathways form through experience – the more you do something, the stronger the synaptic pathways. Now we can hard-code these pathways.
Anyone want to take a trip to Mars and free the mutants?
The Fiction 2/2
Researchers have been transferring digital files into strands of DNA for decades now. But DNA is the blueprint of life, and recently researchers have begun to bring digital information to life.
In an advancement that’s sure to delight some and scare the $h!t out of others, researchers have added arms, legs, faces, ears, hearts, lungs, and everything else to make your browsing history a real-life pet.
The ultimate look and personality of your pet is directly related to the digital information in its DNA.
So be careful what you look at when no one’s watching. | <urn:uuid:83067ef4-c44c-4f45-84f3-90299012c400> | 3.046875 | 1,039 | Personal Blog | Science & Tech. | 67.543862 |
Modern programming practices and computer languages (like .NET) tend to dynamically create and destroy objects at run-time, but how does it correlate with multi-core-enabled programming? A parallel program may need to synchronize both lifetime of- and access to- an object in shared memory.
Known methods suffer from either limitation of scalability or additional synchronization overhead. For example, the most popular implementation for erasing an item from a concurrent container is to exclusively lock the item before or after cutting it out from a list. So, no one can see (find) and access it anymore thus it’s safe to destroy it completely. It involves fairly small overhead if there is no contention but otherwise it leads to blocking of a thread destroying the object and so imposes scalability degradation. And in some situations, it can cause a deadlock.
To unlock scalability and to enable multiple references, a reference counter is usually used in combination with mutual exclusion. Each owner thread increments the counter to acquire access. To release the rights or to remove the object, the counter is decremented. The thread which reaches zero destroys the object. This method involves overhead of two (!) additional atomic operations (per turn) modifying the counter.
The new algorithm was developed (but not yet released) to overcome described issues while combining theirs strengths in concurrent_hash_map container distributed within Intel® Threading Building Blocks. But it is general enough to be used widely in similar situations and with any other container or collection of objects that accessed and destroyed concurrently.
Usually, a mutual exclusion and a reference counter are represented by separate synchronization objects because their functions are considered as orthogonal. It means separate synchronization. But used in combination, all status fields can be read at once without explicit synchronization and some joint operations can be optimized to only one atomic RMW operation which performs synchronization only once reducing the overhead.
The algorithm enables this optimization by combining spin lock and reference counter inside one machine word of one synchronization object. It which provides the same functionality as its parts while also enabling extra functionality such as full and recurrent lifetime cycle of a dynamic object with stages of construction and destruction, which are protected by mutual exclusion. Of course, recycling is useful only for user objects that are not deallocated after destruction.
Separate operations that don’t benefit from the combination can still be executed separately by addressing only necessary parts of the synchronization object and thus reducing the synchronization effort.
Another optimization which becomes possible due to one atomic read of all fields is considering the acquired mutex to be a reference to the object without an explicit increment of the reference counter. In other words, the lock operation does not touch the reference counter at all, while still keeping the object marked as “in use”. There are also other tricks improving scalability and fail-safety guarantees that may be interesting to experts.
However, users interested in improving scalability and performance of theirs synchronization may need some new high-level usage model to apply this synchronization algorithm. A prototype of such an interface may be like std::shared_ptr but with some additional semantics to manage also access rights to an object.
If you are interested in this idea, I will probably provide more details in the next blog. And perhaps then, your feedback will help us to finally release the code (which already 2 years waits its turn) as part of TBB.
Update: Thanks for comments! Let me clarify the purpose of this technique. It is a small-sized synchronization primitive that is suitable to individually protect each object from a swarm of similar objects. And so, it is *not* supposed to handle heavy contended case with a lot of threads trying to lock/attach to the same object nor to support thousands of references (yes, 16 bit ref counter is enough, otherwise it is not the primitive you need). Here, under scalability I meant that it allows to unlock a list (bucket) which contains up to several objects while desired object is locked by a busy thread. Thus, many threads accessing many different objects which can share the same list finally meet less contention - it is what reference counter is about. It is probably a subject for separate blog where I can show the use case in pseudo-code. | <urn:uuid:c50597e7-2f10-4159-94b3-d2e47a0576e4> | 2.9375 | 859 | Documentation | Software Dev. | 26.960892 |
I figure that since I’m going to Dartmouth on Monday (my title and abstract aren’t posted, unfortunately), I should finally say something about what I do. Rather than dive right in, I’ll just talk about knots.
A knot is a mathematical idealization of a tangled-up loop of string in space. Formally, it’s a (smooth) path in space that closes up at the end. The thing you tie in your shoelaces is not a not, since it has two loose ends. If you actually used a knot, you couldn’t ever untie them!
Speaking of untying knots, it seems intuitively obvious that if we pick up a loop of string, move it around, and never break the loop, we still have “the same” knot as we started with. So we have to adjust the previous definition a bit: knots are smooth closed paths in space, but if we can deform two such paths into each other (for some suitable definition of “deform”) then they’re really the same knot. What we want to know is, “how can we tell if two knots are the same or different?” and, “what different knots are there, anyway?”
First of all, there are a lot of them. Dror Bar-Natan has posted up a table of knots up to ten crossings, and each one links to a page of information about the knot. When we say a knot has “n crossings”, we mean that there’s a way I can arrange it on the table so one strand crosses over another one n times, and no such arrangement for fewer than n crossings. There are some more technical points about the knots on this table, but for now it’s nice to just look and see a bunch of them, and know that they’re just the tip of the iceberg.
Okay, so how can we tell if two knots are the same? Say we’ve got two actual loops of string to fidget with. We can sit there all day and not make them look the same, but we still don’t know that if we played with them just a little longer we wouldn’t hit on something. We need some more powerful tool.
Enter invariants. An invariant is a way of assigning some value to each knot — like a number, or a polynomial, or even a group — to each knot. We want to be sure that if we move the knot around the value of the function won’t change. That is, we want it to be invariant when we deform the knot. A lot of the bits of information on the page for each knot in Bar-Natan’s table are the values various invariants have for that knot.
So here’s how an invariant helps us: if two knots are the same they’ll get the same value for the invariant. That means that if we have two knots that get different values, they can’t be the same! We know that no matter how long we play with the knot we’re not going to turn one into the other, just as surely as we’re not going to turn 1 into 0.
Unfortunately that’s not quite good enough. We can tell when knots are different, but we still can’t be sure when knots are the same. There isn’t yet known a knot invariant that’s an injection, which would assign every knot a different value. Well, strictly speaking that’s not true. There’s one that’s known to essentially be an injection, but it’s also known that it’s impossible to tell when two values are the same or not, so in practice it’s still not helpful. Weird.
It seems there are two ways to get invariants. The older way uses a lot of heavy topology and/or geometry, while the newer way uses a lot of combinatorial fiddling with diagrams — pictures of knots like you see on that table. The topological style really is fascinating once you get into it, and it’s bound up with all sorts of other areas of mathematics. It’s a little hard to get into without building up a lot of machinery first, though.
The combinatorial style, on the other hand, is a great on-ramp for playing with knots. There were some combinatorial calculations of invariants in the past, but they usually had some topology hiding behind them. The real explosion in this style came with Vaughn Jones’ discovery of what’s now called the “Jones polynomial”. It’s really straightforward to calculate it, but the definition came completely out of left field, and took pretty much everyone by surprise back in the early ’80s. It’s still uncertain what the geometric or topological meaning behind it is, but everyone’s sure there’s something there. I have some thoughts in this direction, but I’ll leave those until I’ve laid out some more of knot theory in general and my own research program in particular. | <urn:uuid:9205d4c9-b993-4c76-8334-acda268cce23> | 2.71875 | 1,099 | Personal Blog | Science & Tech. | 66.923978 |
Sunspots are dark spots that migrate across the surface of the sun. Astronomers believe that the spots on the sun are actually electrical and magnetic. Sunspots appear to be whirlwinds of electrified matter bursting out from the sun's interior. They shoot beams of negatively charged electrons into space, some of which enter the earth's atmosphere. This can cause electromagnetic effects, such as the northern lights, or disrupt radio transmissions.
Sunspots are cooler than the rest of the sun's surface because less new, hot gas is brought to the surface in those areas. That's why they appear dark. They are roughly circular and have a dark center called the umbra. The less dark outer region is called the penumbra. There is also a region called a plage that is slightly brighter than the rest of the region. The plage emits cosmic rays, ultraviolet light, and X-rays, which are all related to visible light, but are much stronger.
Sunspots form within a few days, and usually disappear within a few weeks. They can vary in size, from small specks on the sun's surface, to regions as much as 90,000 miles long and 200,000 miles in length. They can even be larger across than the Earth is.
Sunspots follow a recurring 11-year cycle. Over this time, sunspots and solar flares get more frequent, then rarer. These times are called the solar maximum and the solar minimum.
Sunspots are visible on most clear days, but you should never look at the sun directly with the naked eye, or even through dark glasses. This can damage vision. To look for sunspots or other features on the sun, use a shaded telescope or specially designed eyewear to protect your eyes. | <urn:uuid:335bc4e5-9414-48a4-8b44-6a5369052d9b> | 4.375 | 366 | Knowledge Article | Science & Tech. | 61.456035 |
Gators Breathe Like Birds
Did Dinosaur's Ancestors Inhale their Way to Dominance?
Before and until about 20 million years after the extinction - called "the Great Dying" or the Permian-Triassic extinction - mammal-like reptiles known as synapsids were the largest land animals on Earth.
The extinction killed 70 percent of land life and 96 percent of sea life. As the planet recovered during the next 20 million years, archosaurs (Greek for "ruling lizards") became Earth's dominant land animals. They evolved into two major branches on the tree of life: crocodilians, or ancestors of crocodiles and alligators, and a branch that produced flying pterosaurs, dinosaurs and eventually birds, which technically are archosaurs.
By demonstrating one-way or "unidirectional" airflow within the lungs of alligators, the new study - published in the Jan. 15 issue of the journal Science - means that such a breathing pattern likely evolved before 246 million years ago, when crocodilians split from the branch of the archosaur family tree that led to pterosaurs, dinosaurs and birds.
That, in turn, means one-way airflow evolved in archosaurs earlier than once thought, and may explain why those animals came to dominance in the Early Triassic Period, after the extinction and when the recovering ecosystem was warm and dry, with oxygen levels perhaps as low as 12 percent of the air compared with 21 percent today.
"The real importance of this air-flow discovery in gators is it may explain the turnover in fauna between the Permian and the Triassic, with the synapsids losing their dominance and being supplanted by these archosaurs," says C.G. Farmer, the study's principal author and an assistant professor of biology at the University of Utah. "That's the major reason this is important scientifically."
Even with much less oxygen in the atmosphere, "many archosaurs, such as pterosaurs, apparently were capable of sustaining vigorous exercise," she adds. "Lung design may have played a key role in this capacity because the lung is the first step in the cascade of oxygen from the atmosphere to the animal's tissues, where it is used to burn fuel for energy."
Farmer emphasized the discovery does not explain why dinosaurs, which first arose roughly 230 million years ago, eventually outcompeted other archosaurs.
Farmer conducted the study - funded by the National Science Foundation - with Kent Sanders, an associate professor of radiology at the University of Utah School of Medicine. They performed CT scans of a 4-foot-long, 24-pound alligator.
'The Great Dying' - Decline of the Synapsids, Rise of the Archosaurs
"Some got up to be bear-sized," says Farmer. Some were meat-eaters, others ate plants. They were four-footed and had features suggesting they were endurance runners. Their limbs were directly under their body instead of sprawling outward like a lizard's legs. There is evidence they cared for their young.
The cause of the mass extinction 251 million years ago is unknown; theories include massive volcanism, an asteroid hitting Earth and upwelling of methane gas that had been frozen in seafloor ice.
"A few of the synapsids survived the mass extinction to re-establish their dominance in the early Triassic, and the lineage eventually gave rise to mammals in the Late Triassic," says Farmer. "However, the recovery of life in the aftermath of the extinction involved a gradual turnover of the dominant terrestrial vertebrate lineage, with the archosaurs supplanting the synapsids by the Late Triassic."
From then until the dinosaurs died out 65 million years ago, any land animal longer than about 3 feet was an archosaur, says Farmer, while mammal-like synapsid survivors "were teeny little things hiding in cracks. It was not until the die-off of the large dinosaurs 65 million years ago that mammals made a comeback and started occupying body sizes larger than an opossum."
No one knows much about the archosaur that was the common ancestor of crocodilians and of pterosaurs, dinosaurs and birds, Farmer says.
It probably was "a small, relatively agile, insect-eating animal," Farmer says. Illustrations of early archosaurs look like large lizards.
"Our data provide evidence that unidirectional flow [of air in the lungs] predates the origin of pterosaurs, dinosaurs and birds, and evolved in the common ancestor of the crocodilian and bird [and pterosaur and dinosaur] lineages," Farmer says.
Cul-de-sacs or Loops for Airflow
In the lungs of humans and other mammals, airflow is like the tides. When we inhale, the air moves through numerous tiers of progressively smaller, branching airways, or bronchi, until dead-ending in the smallest chambers, cul-de-sacs named alveoli, where oxygen enters the blood and carbon dioxide moves from the blood into the lungs.
In modern birds, the lungs' gas exchange units are not alveoli, but tubes known as "parabronchi," through which air flows in one direction before exiting the lung. Farmer says this lung design helps birds fly at altitudes that would "render mammals comatose."
Some researchers have argued that unidirectional airflow evolved after crocodilians split from the archosaur family tree, arising among pterosaurs and theropod dinosaurs, the primarily meat-eating group that included Tyrannosaurus rex. Others have argued it arose only among coelurosaurs, a group of dinosaurs that also includes T. rex and feathered dinosaurs.
Unidirectional air flow in birds long has been attributed to air sacs in the lungs. But Farmer disagrees, since gators don't have air sacs, and says it's due to aerodynamic "valves" within the lungs. She believes air sacs help birds redistribute weight to control their pitch and roll during flight. Farmer says many scientists simply assume air sacs are needed for unidirectional airflow, and have pooh-poohed assertions to the contrary.
"They cannot argue with this data," she says. "I have three lines of evidence. If they don't believe it, they need to get an alligator and make their own measurements."
Assessing Airflow in Alligators
Farmer did three experiments to demonstrate one-way airflow in alligators' lungs:
How does air loop through an alligator's multichambered lungs?
Inhaled air enters the trachea, or windpipe, and then flows into two primary bronchi, or airways. Each of those primary bronchi enters a lung. From those primary airways, the bronchi then branch into a second tier of narrower airways. Inflowing air jets past or bypasses the first branch in each lung because the branch makes a hairpin turn away from the direction of airflow, creating an aerodynamic valve. Instead, the air flows into other second-tier bronchi and then into numerous, tiny, third-tier airways named parabronchi, where oxygen enters the blood and carbon dioxide leaves it.
The air, still moving in one direction, then flows from the parabronchi into the bypassed second-tier bronchi and back to the first-tier bronchi, completing a one-way loop through the lungs before being exhaled through the windpipe. | <urn:uuid:cbc8c4e2-aeaf-4ff2-9893-4624d9612529> | 3.59375 | 1,554 | Knowledge Article | Science & Tech. | 38.730817 |
On a dry winter day, if you scuff your feet
across a carpet, you build up a charge and get
a shock when you touch a metal doorknob.
In a dark room you can actually see a spark
about 2 cm long. Air breaks down at a field
strength of 3 × 106 N/C.
Assume that just before the spark occurs,
all the charge is in your finger, drawn there by
induction due to the proximity of the door-
knob. Approximate your fingertip as a sphere
of diameter 1.44 cm, and assume that there is
an equal amount of charge on the doorknob
2 cm away.
How much charge have you built up?
Answer in units of C. | <urn:uuid:80dbb581-b0f7-411a-a65b-5b873653a199> | 3.140625 | 161 | Q&A Forum | Science & Tech. | 85.09822 |
During our recent study of chemistry, I had my eighth grade students create a comic strip of a rather complicated experimental method. They drew this comic strip across the white board at the front of the room. Each class contributed a section of the comic, and also improved on sections previously created. By the end of the last class we had an incredible, student-generated resource to support the experiment we were going to do the next day. As an unplanned bonus, this process also unearthed a rather comical misunderstanding. Check out the images below.
Students working in collaborative groups on different sections of the comic.
A section of the comic showing a filtration set up.
A drawing showing that the experimenter needs to find the mass of a funnel by placing the funnel inside a weighing boat, and placing both on an electronic balance.
This is what an actual weighing boat look like:
Thank goodness the artist took a risk and sketched out her version of a weighing boat. It was only then I realized I hadn’t actually pre-taught what this piece of equipment was. I definitely think I’ll try this strategy again. We’ve done a lot of chemistry experiments this year. Now I’m left wondering how else I’ve completely baffled them. | <urn:uuid:bc96257a-3c3d-426f-b685-b909cb058151> | 3.171875 | 263 | Personal Blog | Science & Tech. | 55.752021 |
Actinopterygii (ray-finned fishes) > Perciformes
(Perch-likes) > Pomacentridae
(Damselfishes) > Pomacentrinae
Etymology: Pomachromis: Greek, poma, -atos = cover, operculum + Greek, chromis = a fish, perhaps a perch (Ref. 45335).
Environment / Climate / Range
Marine; reef-associated; non-migratory; depth range 3 - 12 m (Ref. 7247). Tropical; 12°N - 6°N
Size / Weight / Age
Maturity: Lm ? range ? - ? cm
Max length : 5.0 cm SL male/unsexed; (Ref. 7247)
Western Central Pacific: known only from the Marshall Islands and Caroline Islands.
Adults inhabit lagoon and seaward reefs. A planktivorous species (Ref. 1602). Oviparous, distinct pairing during breeding (Ref. 205). Eggs are demersal and adhere to the substrate (Ref. 205). Males guard and aerate the eggs (Ref. 205).
Allen, G.R., 1991. Damselfishes of the world. Mergus Publishers, Melle, Germany. 271 p.
IUCN Red List Status (Ref. 90363)
Threat to humans
ReferencesAquacultureAquaculture profileStrainsGeneticsAllele frequenciesHeritabilityDiseasesProcessingMass conversion
Estimates of some properties based on empirical models
Phylogenetic diversity index (Ref. 82805
= 0.5625 [Uniqueness, from 0.5 = low to 2.0 = high].
Bayesian length-weight: a=0.01516 (-0.15937 - 0.18968), b=2.99 (2.90 - 3.09), based on LWR estimates for this family-BS (Ref. 93245
Trophic Level (Ref. 69278
): 3.4 ±0.45 se; Based on food items.
Resilience (Ref. 69278
): High, minimum population doubling time less than 15 months (Preliminary K or Fecundity.).
Vulnerability (Ref. 59153
): Low vulnerability (12 of 100) . | <urn:uuid:627b6710-2b17-4262-a5fe-f0646135945f> | 3.046875 | 492 | Knowledge Article | Science & Tech. | 61.203919 |
"Tags" are a listing of code objects in a group of files, together with their precise location, often used by text editors to quickly jump around in a program. ctags (for C) was the first tag-generation program.
There are currently a number of different ways to generate tags with Haskell.
This page should be used to collect information on tag-generation for Haskell, including information on how to use tags with common editors and what benefits they can give you.
2 Haskell tag generators
Chris Ryder and Simon Thompson give a tag generator's source in a paper
echo ":ctags" | ghci -v0 Main.hs
echo ":etags" | ghci -v0 Main.hs
utils/hasktags from GHC.
The tags file generated in ctags format can be used in (amongst others) vim, BBEdit and NEdit. The one in etags format can be used in at least Emacs. Note that the default names for the file in ctags format and the file in etags format are 'tags' and 'TAGS' respectively. These names clash on case-insensitive filesystems, such as Mac OS's HFS and HFS+ in the default configuration.
In vi, one jumps to a tag using either
or by using control-] with the cursor on the tag to jump to. Using control-T returns to the previous position.
4 Random other bits
insert-mode tag completion]
Chapter 14 of the BBEdit manual | <urn:uuid:233d6682-e9d6-4573-8df8-804cefd275ab> | 2.703125 | 315 | Documentation | Software Dev. | 58.91521 |
What would the gravitational potential energy be if the bucket were raised six times as high?
If you do 110 J of work to elevate a bucket of water, how much energy did you add to the gravitational field?
A boulder is raised above the ground so that the gravitational potential energy relative to the ground is 360 J. Then it is dropped. What is its kinetic energy just before it hits the ground?
Calculate the work done when a 18 N force pushes a cart 2.5 m.
What is the pH of a 0.77M solution of methylamin at 25 degree C? CH3NH2, Kb= 4.4X10-4? How do I set this up to get the answer?
find the first 3 terms in the expansion of (x+4)(1+3x)^-2 as a series in ascending powers. I expanded the second bracket using binomial expansion and got 1 -6x +27x^2 -108x^3 how do I combine (x+4) with the expansion? Any help would be appreciated.
X= log base 3 1/27
What is the momentum of a 50 kg carton that slides at 2 m/s across an icy surface? The sliding carton skids onto a rough surface and stops in 3 s. Calculate the force of friction it encounters.
A car with a mass of 700 kg moves at 18 m/s. What braking force is needed to bring the car to a halt in 10 s?
In terms of impulse and momentum, why are airbags in automobiles a good idea? A.)Airbags actually do not help if a car is in an accident. B.)They increase the amount of force involved in a collision. C.)They decrease the amount of time for a collision to happen. D.)They increa...
For Further Reading | <urn:uuid:8033ad54-9a0d-40f7-b3cd-2f464e83e9d6> | 2.921875 | 385 | Content Listing | Science & Tech. | 88.063138 |
Catarina Hits Brazil
image (328 Kb)
2004, only two tropical cyclones had ever been noted in the South
Atlantic Basin, and no hurricanes. In late March 2004, a circulation
center well off the coast of southern Brazil developed tropical
cyclone characteristics and continued to intensify as it moved westward.
The system developed an eye and apparently reached hurricane strength
on Friday, March 28, before eventually making landfall late the
The crew of
the International Space Station was notified of the cyclone and
acquired these excellent oblique photos of the storm just as it
made landfall on the southern Brazilian state of Catarina. The storm
has been unofficially dubbed "Hurricane Catarina." Note the
clockwise circulation of Southern Hemisphere cyclones, the well-defined
banding features and the eyewall of at least a Category 1 system.
The coastline is visible under the clouds in the upper right corner
of the image.
was provided by the Earth Sciences and Image Analysis Laboratory
at Johnson Space Center. The International
Space Station Program supports the laboratory to help astronauts
take pictures of Earth that will be of the greatest value to scientists
and the public, and to make those images freely available on the
Internet. Additional images taken by astronauts and cosmonauts can
be viewed at the NASA/JSC Gateway
to Astronaut Photography of Earth. | <urn:uuid:e5ab71e7-55dc-4976-b865-f88e704af866> | 3.53125 | 289 | Truncated | Science & Tech. | 23.753105 |
THE "green flash" sky that watchers sometimes report at sunset is often all in the mind, a scientist from California reported last week. While some green flashes are true mirages, he says, others are probably caused by the effect of bright light on our colour vision.
As the Sun sinks below the horizon, observers sometimes see its top turn bright green for a few seconds. True green flashes happen because if land or water are very warm, they can create a warm layer of air that bends light of different colours by different amounts, says Andrew Young, an astronomer at San Diego State University. This can make the rim of the Sun look green for a moment. If the land is cool and the air hot, a cool layer of air can cause a similar effect.
At last week's meeting of the American Astronomical Society in San Diego, however, Young ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:70cfdfaa-6f5b-435c-ac28-e166a786442a> | 3.265625 | 202 | Truncated | Science & Tech. | 59.9511 |
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Measuring times of the eclipses of Jupiter's moons when Earth and Jupiter were in various positions gave evidence for light traveling at a finite speed. Includes a list of measurements of c made ...
Diagram showing forces of attraction with planet alignment.
In 1676, Ole Roemer made the first accurate measurement of the speed of light using Jupiter's moons. His estimate was 140,000 miles/second.
Details of how large planets have been detected around three other solar type stars. Understanding Doppler wobble aided by an exercise.
Roemer's observations of the periods of Jupiter's moon allowed the first estimate of the speed of light. A good site relevant to all college students.
A site containing details of the Galileo project and the results received in this mission to study the atmosphere of Jupiter.
Java animation showing the motion of the planets of the solar system, moons of Jupiter and two comets. | <urn:uuid:7a05acf1-854f-4d53-8369-b0a5f365aa67> | 3.328125 | 280 | Content Listing | Science & Tech. | 56.493123 |
PostNatural Organism of the Month:
Sterile Male Screwworm
During the late 1950's a large-scale public works program was initiated to eradicate the live-flesh-eating screwworm plaguing cattle ranches across the American south. The screwworm is the larval stage of the fly, Cochliomyia hominivorax. Full-scale fly factories were produced in Florida and Texas capable of producing 500 billion sterile male flies per week.
The factories were optimized to expedite each stage of the fly's life and to sort them by gender prior to their emergence from the pupae. Male screwworms, at the age of 5 ½ days, were loaded into metal tubes and carried by a lone worker to the irradiation facility where they were exposed to a radioactive sample of Cobalt 60, permanently ending their reproductive capacity. Following maturation into adult flies, they were released from airplanes 1,000 ft above America's cattle growing regions where the now impotent males would attempt unsuccessfully to mate with the typically monogamous females.
Previous PostNatural Organisms of the Month: | <urn:uuid:b3c9db41-c12e-4282-81c5-396b88383008> | 3.015625 | 231 | Knowledge Article | Science & Tech. | 22.310426 |
Solar System with Snug Suns
This artist's concept depicts a faraway solar system like our own except for one big difference. Planets and asteroids circle around not one, but two suns. NASA's Spitzer Space Telescope found evidence that such solar systems might be common in the Universe.
Spitzer did not see any planets directly, but it detected dust that is kicked up from disks of asteroids and comets like the one depicted here. The disks were spotted circling all the way around several double, or binary, stars, some of which were closer together than Earth is to our sun. In fact, Spitzer found more disks in orbit around close-knit binary stars than single stars. This could mean that planets prefer two parent stars to one, but more research is needed to figure out exactly what's going on. | <urn:uuid:c5cc5157-0da7-43e6-beaf-89ff05ff1d34> | 3.5 | 166 | Knowledge Article | Science & Tech. | 52.59 |
The biggest physics experiment ever, CERN’s Large Hadron Collider (LHC), goes live this summer. The international project, whose design was approved in 1994, cost over $6 billion. Thousands of powerful magnets, cooled by tons of liquid helium to 1.9 Kelvin (just above absolute zero), will guide two beams of protons as they travel in opposite directions around a 27-kilometer tunnel at close to the speed of light; then magnets at two locations will pull the beams together for the highest-energy particle collisions ever achieved. By identifying the products of these collisions, physicists hope to test the standard model of physics and discover new subatomic particles. (Read Nobel laureate Jerome Friedman’s thoughts on the LHC.)
Precision Before Collision
The compact muon solenoid (CMS), one of the LHC’s main detectors, is made up of 11 conjoined pieces; each has layers of detectors tuned to find different particles that might result from proton collisions, including muons and electrons. This piece weighs 1,270 metric tons and was lowered from above ground to the bottom of the tunnel, 90 meters below, with mere centimeters of clearance. It took 11 hours. | <urn:uuid:f592b26e-9e47-425b-8952-b7218fc20c64> | 4.0625 | 248 | Truncated | Science & Tech. | 46.825417 |
U.S. Water News Online
GLOUCESTER, Mass. -- After cleaning the bottom of his boat
in the Annisquam River last September, Brad Chase dove a few feet
deeper to look at the bed of the salt water estuary, expecting a view
more like a moonscape than a seascape.
What he found surprised, awed, and disturbed him. Chase, a marine
biologist, saw a cascade of color in green crabs, blue mussels,
orange tunicates, and flat, browning European oysters. "The contrast
in colors and textures as the sunlight filtered through the running
tide was mesmerizing," he said. "It took a few minutes before I
realized that these creatures were not supposed to be here. Almost
every creature catching my eye was not native to our waters."
Chase said he began wondering about the future of coastal waters
from Boston Harbor to the Gulf of Maine. He is not alone. Bruce
Carlisle and Christian Krahforst at the state's Office of Coastal
Zone Management have a focus on the health of wetlands between the
sea and shore. Others, including April Ridlon, a biology researcher
at the Massachusetts Audubon Society's North Shore office in Wenham,
and Sal Genovese, education coordinator at Northeastern University's
Marine Science Center in Nahant, also research the coastline and
Their views on the region's coastline offer hope, pessimism, a
large dose of caution, and as many questions as answers about the
next decade and beyond.
Chase, a researcher at the state Division of Marine Fisheries
Laboratory in Gloucester, said the invasion of non-native species
such as the European oyster, along with the destruction of natural
habitats and watershed buffers, are threatening a variety of marine
With him, colleague Jeff Plouff, a lab analyst and field support
technician at the state's Annisquam Station, examined the flat shells
of European oysters, whose population has exploded in Salem and more
recently in Gloucester, including the Annisquam River. They are not
as meaty as American oysters, which they tend to crowd out.
"Influences from stormwater inputs and watershed development are
quickly degrading the spawning habitats of river herring, smelt, and
their cousins," he said.
Fish such as smelt come in from the ocean to lay their eggs in
estuaries where salt and fresh water meet. As a result of human
development of that habitat, "these sea-run species . . . will be
challenged in the next century," he contended.
Carlisle, a wetlands specialist at the Office of Coastal Zone
Management, said he expects the push to develop the northern
coastline and adjacent wetlands to continue but believes people will
make a greater effort "to preserve and protect those ecosystems that
make their areas unique."
"The buzz words are `smart growth' and `sustainable development,'
" he said. "I don't care what you call it as long as people work to
protect, preserve and in some cases, restore those ecosystems unique
to their communities."
His office, he said, is working with other state and federal
agencies and local groups such as The Trustees of Reservations and
Salem Sound 2000 to help educate citizens on the environment and to
empower them to protect it.
A series of pilot projects from Ipswich to Danvers started last
year have enabled local volunteers to monitor water quality in
estuaries on the North Shore, he said.
"We can see patterns of degradation of salt marshes over the last
century," he said, "from building roads, bridges, and other things
that change or restrict the flow of tidal waters."
"Generally," Carlisle said, "we're getting better at doing the
things we ought to do. We're now protecting salt marsh resources by
engaging in better stormwater management, by looking at buffered
development distance, and by making sure septic systems are up to
"There are many steps along the way. I feel pretty positive about
where we are right now," Carlile added.
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U.S. Water News Archives page
Return to the U.S. Water
Use a comma to separate e-mail addresses:
Hi, I thought you might like to read this article. | <urn:uuid:38f5afc7-27f6-4cc4-bd06-7c2d22e750fb> | 2.90625 | 936 | Truncated | Science & Tech. | 42.756336 |
Note: The following is a guest post by a regular reader and commenter, JohnD. You can find more of his work on his own blog, Factismals. He also performed a highly regarded review of the city’s record August, 2011 temperatures. Below, to see larger versions of the images, just click on them.
As we’ve done before, let’s spend a moment reviewing the basics before we investigate the main question: Was 2012 unusually hot?
The use of the average (a.k.a., the arithmetic mean) is fairly well-known, as is the idea of the mode and the median. And most of you know by now that a Gaussian normal curve (or bell curve, for the shape it makes) is the standard workhorse in statistics as it allows scientists to quickly estimate the odds of something happening by chance. You also know that when the skewness (distortion toward one side or the other) gets above about +/-0.5, then a Gaussian curve is no longer a good approximation. Similarly, the distribution may be flat (“have a negative kurtosis”) or very sharp (“have a positive kurtosis”); if the normalized kurtosis is above +/-1.5, then a Gaussian curve is no longer a good approximation. As always, I mention these rules of thumb so that you can decide for yourself if the data is good.
I’ve extracted the temperature data from two places. The Annual Mean Temperatures for the contiguous United States were taken from the NOAA web page. And the Monthly Mean Temperatures for Houston and Galveston were downloaded from the National Climactic Data server; the Galveston records were supplemented by Charles Roeseler of the Houston/Galveston office of the National Weather Service. Annual Mean Temperatures were calculated using the arithmetic average of the previous twelve months of Monthly Mean Temperatures.
Please allow me to digress briefly before we get into the analysis proper. One common concern about temperatures in general and those for Houston in specific is that the location where the temperature was taken has moved several times over the past 117 years. A related concern is that some of the locations are closer to the center of the city and so may by biased by the Urban Heat Island effect. In order to explore these questions, I plotted the Monthly Mean Temperatures for several locations around Houston over the past 93 years. As the plot shows, none of the areas is suspiciously anomalous; all of the values are very close together. This implies that the Urban Heat Island effect is not affecting the Houston records and that the changes of location have had minimal effect.
So what happens when we look at the Annual Mean Temperature for Houston, Galveston, and the Contiguous United States? Was last year truly anomalous (statistically speaking) or was it just hot? We’ll start by looking at the time series.
Looking at the plot of Annual Mean Temperatures for each of the regions, the difference between local weather and broad-scale climate becomes obvious. Houston suffered an exceptionally cool spell during the late 70s to early 80s, but Texas as a whole did not. In addition, the southern location of Houston and Galveston makes them nearly five degrees warmer on average than Texas as a whole, and more than 18 degrees warmer than the contiguous United States.
This becomes even more obvious if we look at the five-year means (i.e., the average of the previous five years’ worth of data). The spikes caused by short-term events are smoothed out by this technique and the overall long-term signal becomes even clearer. When temperatures in the contiguous United States trend upward, those in Houston and Galveston have larger swings and no clear pattern emerges. So local conditions clearly play a strong role in transforming climate into weather and make it harder to see long-term climactic shifts; put simply, if you want to see climate, you need to look over a large area and for a long time. Single-year records in single locations are not a reliable gauge of climate change.
So, with that caveat in mind, how unusual was last year? As always, we start by looking at the mean, standard deviation, skewness, and kurtosis for the data. The low skewness and kurtosis indicate that a Gaussian curve is a good approximation to the data. And that is what we see in the bar charts as well; in general, the data (blue bars) is fairly close to what would be expected for a Gaussian curve (red bars).
And that is what we see in the bar charts as well; in general, the data (blue bars) is fairly close to what would be expected for a Gaussian curve (red bars).
But what is truly interesting is how last year plots on the charts. For Houston, last year was the warmest but it is just barely outside of the 2-sigma limit; it was hardly worth noticing. The same is true for Texas as a whole; last year was exceptionally hot but not as mind-boggling as August of 2011 was. However, for both Galveston and the contiguous United States as a whole, 2012 was freakishly hot. We would expect to see a year that warm for the contiguous United States or Galveston about three times in ten thousand years. But we’d see one that warm every seventy years for Houston and every 130 years for Texas as a whole.
So, what can we conclude from all of this?
- Local one-year records say very little about long-term, broad-scale climate
- Houston’s strongly variable weather makes it very hard to see any climate signal
- Last year was absurdly hot in some locations (e.g., Galveston) and for the contiguous US as a whole, but hardly worth noticing here in Houston. | <urn:uuid:e073c59c-e949-4004-9ca8-16c786d61900> | 2.71875 | 1,222 | Personal Blog | Science & Tech. | 51.848369 |
GOLDEN GATE CETACEAN RESEARCH
Field Studies of Porpoises, Dolphins & Whales
in San Francisco Bay and on the Coast of Northern California
Goals and Methods: Using techniques developed with minke whales in the San Juan Islands and Monterey Bay, our project will collect the following data to use as values for parameters in the Mass-Balance Model --
Population Size: Photographic identification techniques are used to estimate minimum population size.
Individual Residency Patterns: We look for patterns that suggest whether individuals seasonally migrate or are year round residents.
Feeding Rates: The number of feeding events per hour is calculated to gauge individual foraging success rates. This can be used to compare over time and between areas. Changes in feeding rates within an area may indicate an environmental shift. Feeding represents a transfer of energy and material from one trophic level to another, “higher” one.
Foraging Behavior: We have identified two distinct feeding strategies employed by minke whales. Each strategy has its own costs and benefits (Hoelzel et al. 1989). What strategy do Bay Area minke whales use? Check back here, when we figure that out, you’ll be the first to know!! And we are also interested in search behavior.
Top-Down Effects: The impacts of top level predators on lower trophic levels. We are using computer models to estimate energy flow rates between trophic “compartments” in the the local marine ecosystem. Parameter values will be derived from the results of our field work.
This research is authorized by a Letter of Confirmation issued by the National Marine Fisheries Service. | <urn:uuid:7f3dd61b-16f7-4652-ae15-3ef4ee96afe9> | 3.203125 | 343 | Academic Writing | Science & Tech. | 33.37972 |
Eastern Pacific sea surface temperature since 1600 A.D.: The δ18O record of climate variability in Galápagos Corals
Article first published online: 4 MAY 2010
Copyright 1994 by the American Geophysical Union.
Volume 9, Issue 2, pages 291–315, April 1994
How to Cite
1994), Eastern Pacific sea surface temperature since 1600 A.D.: The δ18O record of climate variability in Galápagos Corals, Paleoceanography, 9(2), 291–315, doi:10.1029/93PA03501., , , and (
- Issue published online: 4 MAY 2010
- Article first published online: 4 MAY 2010
- Manuscript Accepted: 13 DEC 1993
- Manuscript Received: 11 AUG 1993
We measured stable oxygen isotope ratios and skeletal growth rates in the massive corals Pavona clavus and P. gigantea from the west coast of Isabela Island, Galápagos, to assess interannual to decadal climate variability in the eastern Pacific. Comparisons of instrumental data sets show that sea surface temperatures (SST) in the Galápagos region are representative of a broad portion of the eastern equatorial Pacific. The site is especially well-suited for long-term studies of the El Niño/Southern Oscillation (ENSO) phenomenon, as it lies within the eastern Pacific “center of action” for thermal anomalies associated with ENSO. The P. gigantea isotope record is nearly monthly in resolution, spans the period 1961–1982, and shows strong correlation with a Galápagos instrumental SST record (r = −0.90 for annual averages). Cross-spectral analysis shows that SST can explain greater than 80% of the variance in δ18O at both the annual cycle and within the high-frequency portion of the ENSO band (3-5 years). The P. clavus record is annual in resolution, extends from 1587 to 1953 A.D., and was obtained from a 10-m diameter colony preserved within the Urvina Bay uplift. Because seawater δ18O variations in the region are very small, we interpret the Urvina Bay coral δ18O record in terms of annual average SST. The isotopic record appears to be a very good, but not perfect, indicator of ENSO events and shows good correspondence with the historical ENSO reconstruction of Quinn et al. (1987). A number of low δ18O excursions that we observe during the 17th and 18th centuries very likely represent ENSO events that are missing from the historical tabulations. Most interannual δ18O variations between 1607 and 1953 A.D. represent annual average temperature excursions of 1° to 2.5°C. During the Little Ice Age, the annual δ18O series correlates well with many North American tree ring records and shows low temperatures during the early 1600s and early 1800s, and relatively warmer conditions during the 1700s. Unlike most northern hemisphere tree ring and instrumental records, we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling (<1°C). Oscillatory modes within the ENSO frequency band dominate the 347-year δ18O time series, accounting for >28% of the total variance. The main ENSO mode is centered at 4.6 years and accounts for 12% of the total variance. Additional significant oscillations occur at periods of 3.3, 6, 8, 11, 17, 22, and 34 years. Both annual growth rate and δ18O show variance at periods equivalent to the solar and solar magnetic periods (e.g., 11 and 22 years, respectively). In addition, the amplitude of the 11-year δ18O cycle generally varies with the amplitude of the solar cycle, supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics. The dominant oscillatory modes, both within the ENSO and interdecadal frequency bands, shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s. This may reflect major reorganizations within the tropical ocean-atmosphere system and suggests that tropical Pacific climate variability is linked across timescales ranging from years to decades. | <urn:uuid:df7dfeb0-1888-4772-8967-f73070157ec8> | 2.734375 | 905 | Academic Writing | Science & Tech. | 47.365372 |
In mathematics, the number four is an even number and the smallest composite number. Four is also the second square number after one. A small minority of people have four fingers and four toes, on each hand and foot, respectively. This proves difficult to count on your fingers. Four squared is 16, and four doubled is 8. | <urn:uuid:c139036b-f13a-43aa-af1a-2ba0f19c7f57> | 2.921875 | 66 | Knowledge Article | Science & Tech. | 64.653474 |
WatchList Species Account for Florida Scrub-Jay |
Qualifies for the list as a Red List Species
Photo: Daniel J. Lebbin
Federally listed as threatened, the Florida Scrub-Jay, Florida’s only endemic bird, is found in the north and central peninsular part of the state; key sites for it include Ocala National Forest, Canaveral Seashore, Avon Park Airforce Base, and Archbold Biological Station. This species has declined from about 10,000 breeding pairs in 1993 to only about 4,000 breeding pairs today. Today’s numbers are probably no more than 10% the population of presettlement times.
This jay's habitat is dry shrub and scrubby areas with several species of evergreen oaks which rarely exceed 6-7 feet in height, with a ground cover dominated by saw palmetto. Prime habitat may also include up to 15% cover of slash pines and sand pines. This rare xeric community occurs only on porous sandy soils, and contains 18 federally-listed plants. Optimal habitat develops 5-15 years after a fire.
Florida Scrub-Jays rarely wander far from where they were fledged. Their breeding system has been the subject of much study; in it, a pair of birds establishes a permanent territory, with offspring from previous years operating as nest helpers.
Threats to this species include habitat destruction and fragmentation from urban development and agriculture. Fire suppression creates late successional habitat which causes the birds to abandon areas as well. Off-road vehicles may cause disturbance to the species in Ocala National Forest.
To survive, the Florida Scrub-Jay needs large areas of diverse oak-scrub habitat, away from human settlement, that is burned regularly during the growing season before acorn caching is complete, and before hawk migration begins. Ideal areas would be 700 acres or more to support the 40 or so territories to create a long-term self-sustaining population. Existing habitat "islands" should be connected to each other by not more than 2-3 miles of scrub habitat.
Translocations of nest helpers to new areas of habitat will likely be required to establish new breeding populations, due to the sedentary nature of this species. | <urn:uuid:2c6c3888-0313-437c-ba4e-be135d249737> | 3.109375 | 468 | Knowledge Article | Science & Tech. | 40.747017 |
Lorrey, A., Williams, P., Salinger, J., Martin, T., Palmer, J., Fowler, A., Zhao, J.-X. and Neil, H. 2008. Speleothem stable isotope records interpreted within a multi-proxy framework and implications for New Zealand palaeoclimate reconstruction. Quaternary International 187: 52-75.
A master speleothem δ18O record (which is a proxy for temperature) was developed for New Zealand's eastern North Island for the period 2000 BC to about AD 1660 from data acquired from three speleothems of Disbelief and Te Reinga caves. This record revealed that the warmest time interval of the nearly 4000 years occurred between about AD 900 and 1100. Because the record did not extend beyond AD 1660, however, we cannot compare peak MWP warmth with peak CWP warmth. | <urn:uuid:70ca7a70-7077-4fcd-a0a9-b5890d169eda> | 2.734375 | 183 | Academic Writing | Science & Tech. | 68.212454 |
Introduction to VxWorks Programming
Some of the rudiments of VxWorks programming are presented here.
These do not appear in the same order presented in Ref
1, which should be read by any serious VxWorks programmer.
Rather they reenforce some of the material that can be found there,
but appear in a top-down order, with basic concepts described first,
followed by details.
In VxWorks, the unit of execution is the task, corresponding
to a Unix/Linux process. Tasks may be spawned (i.e.,
created), deleted, resumed, suspended, and preempted (i.e., interrupted)
by other tasks, or may be delayed by the task itself. A task
has its own set of context registers including stack. The term
thread, while not unknown in VxWorks jargon, does not exist
in a formal sense as in other operating systems. A thread, when
the term is used, may be thought of as a sub-sequence of connected
program steps inside a task, such as the steps the VxWorks kernel
performs in spawning a task, or the sequence of instructions in an
else-clause following an if-statement. Tasks can communicate
with each other in a manner similar to Interprocess Communications
in Unix and Linux.
Tasks are in one of four states, diagrammed in Figure 1-1, adapted
from Ref. 1.
Figure 1-1 Task State Diagram
A newly spawned task enters the state diagram through the suspended
Tasks may be scheduled for execution by assigning them priorities,
ranging from 0 (higest priority) to 255. Once started, that
is, having entered the ready state in Figure 1, a task may
execute to completion, or it may be assigned a fixed time slice in
round-robin scheduling. A task blocks (enters the pended
state) while another task takes control. A task may be prempted
because it has consumed its time slice, or because another task with
higher priority exists. Task priorities may be changed during execution.
A task may avoid being preempted by locking the scheduler while it
has control. (This does not prevent interrupts from occurring.)
A task may also enter the delayed state, for example while
waiting a fixed time between reading samples within a task before
processing them as a group, during which time another task may take
control. The delay is controlled by an external timer which
runs independently of processing (combined with a tick counter maintained
by the kernel) that awakens the delayed task and avoids having the
task tie up resources with an index counter which would prevent another
task from executing.
The suspended state is used to halt a task for debugging without
loss of its context registers.
Several system tasks exist concurrently with user defined tasks.
These are the root task, named tUsrRoot; the logging task tLogTask;
exception task tExcTask; and the network task tNetTask.
Intertask communication (corresponding to Unix/Linux Interprocess
Communication) can occur through semaphores that provide interlocking
and synchronization of tasks, and messaging that allow tasks to communicate
events or data with each other. Although semaphores and messaging
are implemented with different kernel mechanisms, it is customary
to treat them together.
Semphores can be categorized as ordinary binary semaphores
and a special class of binary semaphores called mutual exclusion
semaphores. Binary semaphores are used for task synchronization.
As implemented in VxWorks, a binary semaphore has two values: full
and empty. When full, it is available for a task. When
empty, it is unavailable. A pending task proceeds by taking
an available semaphore, which makes the semaphore empty or unavailable..
When the semaphore is no longer needed (because the task is about
to return to the pending state), it gives the semaphore which
makes it full or available for another task. A mutual
exclusion semaphore (also called a mutex) allow one task to
have exclusive use of a resource while it is needed.
The difference between an ordinary binary semaphore and a mutex semaphore
is in the way the semaphore is initialized. For an ordinary
binary semaphore, a task attempting to synchronize to an external
event creates an empty semaphore. When it reaches the point
to be synchronized, it attempts to take a semaphore. If unavailable,
it waits at this point. A second task which controls the synchronization
event gives the semaphore when it is no longer needed. The first
task receives notification that the semaphore is available and proceeds.
For a mutex semaphore, a task wishing to block other tasks from a
resouce first creates a full semaphore, and then takes the semaphore,
making it unavailable to other tasks. When it is no longer needed,
it the task gives the semaphore, making the resource available.
A mutual exclusion semaphore must have matching "takes"
These ideas can be illustrated with the following code segments.
Example of synchronization through binary semaphore
#define T_PRIORITY 50
SEM_ID syncExampleSem; // named
void initialize (void)
// set up FIFO queue with emtpy
syncSem = semBCreate (SEM_Q_FIFO, SEM_EMPTY);
// create task1
taskSpawn ("task1", T_PRIORITY, 0, 10000,
task1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
// create task2
taskSpawn ("task2", T_PRIORITY, 0, 10000,
task2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
void task1 (void)
// stay here until semaphore becomes available
semTake (syncExampleSem, WAIT_FOREVER);
// do something
void task2 (void)
// do something
// now let task1 execute
Example of resource
lockout through mutual exclusion semaphore
#define T_HI_PRIORITY 20
#define T_LO_PRIORITY 200
SEM_ID semMutex; // named semaphore
char alphabet; // memory resource to have
void initialize (void)
//create binary semaphore
which is initially full
semMutex = semBCreate (SEM_Q_PRIORITY,
// spawn high priority task
taskSpawn ("hi_priority_task", T_HI_PRIORITY, 10000, tHiPriorityTask,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
// spawn low priority task
taskSpawn ("lo_priority_task", T_LO_PRIORITY, 10000, tLoPriorityTask,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
// enter critical region - any other tasks wanting access to alphabet
// wait for available semaphore
semTake (semMutex, WAIT_FOREVER);
// write alphabet to global array
for (i= 0; i < 26; i++)
alphabet[i] = 'A' + i;
alphabet[i] = '\0';
// leave critical region
// enter critical region
semTake (semMutex, WAIT_FOREVER);
// array members guaranteed stable while being read by this task
printf ("alphabet= %s ", alphabet);
// leave critical region
problem can occur in the second example. Suppose a third task
with medium priority, say 50, between the high and low priority tasks
is also spawned, but doesn't require access to the mutually excluded
region. Assume that the high priority task is called repetitively
from somewhere else, requiring it to enter and leave the critical
region each time it's executed. This medium priority task will
preempt the low priority task, because of the difference in priorities.
If the third task is overly long, then the low priority task, which
reads the alphabet sequence is delayed in releasing its access to
the critical area, holding up execution of the high priority task,
as illustrated schematically in Figure 1-2. The medium priority
task has effectively assumed higher priority than the high priority
task. This is an example of priority inversion.
Figure 1-2 Priority Inversion
The solution is to promote
the low priority task temporarily to the same priority as the highest
priority task which prevents the low priority task from being preempted
by the medium priority task. The low priority task creates a
"inversion-safe" mutex semaphore which permits it to assume
the temporarily higher priority. Once it reaches this priority,
it remains here until all mutex semaphores owned by the task have
POSIX semaphores, not discussed here, may also be
used in VxWorks programs.
Closely related to the idea of semaphores is
the concept of the message which passes data between tasks.
Messaging could be used to accomplish task interlocking as well, but setting
up a message consumes more time than initializing a semaphore. Messaging
is useful for passing variables between asynchronous tasks. VxWorks
supplies seven functions for messaging: msgQCreate ( ), msgQDelete ( ),
msgQSend ( ), msgQReceive ( ), msgQNumMsgs ( ), msgQShow ( ), msgQInfoGet
( ). A message may be placed ahead of previous
messages by sending it with the attribute MSG_PRI_URGENT. As for
semaphores, POSIX messages may also be used in VxWorks programs, and in
fact, offer some capabilities that VxWorks messages don't possess.
The following fragment illustrates a common use for a message.
We will illustrate using VxWorks messges. The procedure is similar
for POSIX messages. Task 1 has written data to a file whose name
is not known to other tasks, and wishes to inform Task 2 that the data
is available in the specified file.
#define MAX_MSGS 10
#define MAX_MSG_LEN 50
strcpy (strFileName, "./filename1");
// write to file with name strFileName
and fd (file descriptor) handle file1
// create message
if ( (exampleMsgId = msgQCreate (MAX_MSGS,
MAX_MSG_LEN, MSQ_PRI_NORMAL) ) == NULL)
if (msgQSend (exampleMsgId, strFileName,
sizeof (strFileName) + 1, WAIT_FOREVER) == ERROR)
char msgBuf [MAX_MSG_LEN];
// fetch message from queue
if (msqQReceive (exampleMsgId, msgBuf, MAX_MSG_LEN,
WAIT_FOREVER) == ERROR)
// open file for reading
There are two things to note. The second
task may query the message exampleMsgId before it has been initialized.
But since the object is known to exist (it is a global variable),
this does not cause an error. Also note that the sender has closed
the file before informing the receiver of its name. This approach
requires sending the file's fully qualified path name as a possibly long
string, which consumes time at the sending and receiving ends. The
programmer could send the file's handle as message data, but this
would require that the writing task keep the file open for reading by
another task and leads to a new set of interlock problems which are best
In VxWorks, an input/output data stream in treated
as a file regardless of the I/O device. File I/O can be organized
by block or by character. Character devices include display terminals
and external hardware devices such as A/D converters or real-time clocks.
Block devices include local or network disk drives. File I/O can
be real, as in the previous examples, or virtual as in the case of pipes
and network sockets. Pipes enable tasks to communicate with each
other. The pipe driver is called pipeDrv. If the device
stream extends across a netowork, it becomes a socket. The stream
socket is similar in concept to the Unix or Windows TCP/IP socket.
(For TCP/IP, VxWorks uses Berkeley Software Distribution version. 4.x
Unix socket functions.)
A file is handled by its file descriptor fd
corresonding to a FILE structure in POSIX. For each kind of file,
there is a different kind of driver which permits the following I/O operations,
summarized in the following.
1.3.1 Basic I/O Operations
|creat (const char *name, int flag
||Create a file.
|open (const char *name, int
flags, int mode)
||Open (and possibly create) a file.
|close ( int fd)
||Close a file.
|remove ( const char *name)
||Remove a file.
|read ( int fd, char *buffer, size_t maxbytes)
||Read an existing file.
|write (int fd, char *buffer, size_t nbytes )
||Write to an existing file.
|ioctl (int fd, int function, int
||Perform control operations on a file.
BASIC I/O OPERATIONS
Note: mode specifies the file's permissions.
The string name denotes what kind of device the file is.
When a file is created or opened, the I/O system searches through a list
of device names, and physical file directories for at least a partial
beginning match of the names and a file descriptor is returned if a match
is established. If no match is found, a default device can be specified,
or if no default is specified (the more common case), then the I/O system
reports an error. Thereafter, the basic I/O operations specified
previously are mapped to the specific file's I/O routines. For instance,
read ( ) and write ( ) result in low-level calls to xxread( ) and
xxwrite ( ), which are defined in the device's driver in the case
of physical devices or in the local file system routines in the case of
1.3.2 Devices and Files
Two kinds of databases are maintained for I/O operations:
the Driver Table and the File Descriptor (FD) Table. The Driver
Table has entries for character devices, and the FD Table has entries
for block devices.
Each record in the Driver Table corresponds to a device
descriptor. A device descriptor describes a specific device,
for example a particular Ethernet port. The Driver Table is built
at boot by adding the device descriptors, which form a linked list.
The information in a device descriptor contains (a) the device name string,
e.g., "/tyE2/0"; (b) the corresponding record number in the Driver Table,
an integer assigned at the time the device is added (see below); (c) the
names of device-specific routines which implement the seven basic I/O
operations above. These will have the same names as the operation
prefixed by the device name, for example, ether3creat ( ) and ether3write
( ). These low level functions are implented in a device driver
file for the particular device. It is important to note that a different
driver exists for each physical device, which may use similar functions
for another driver (of an identical device). If Ether 1 and Ether
2 are the names of two devices, then after installation, there will be
an implentation of ether1creat ( ), and so forth, and ether2creat ( ),
The installation of a character device at boot is a
two-step process. A driver for the device is installed with iosDrvInstall
( ) which returns a record number
in the Driver Table where the driver was installed. The device is
added to the linked list of device descriptors (which contain the information
specific Driver Table record) with a call to iosDevAdd ( ). Both
operations must be completed before the device is installed.
The following table summarizes the type of I/O
device (or file) and the library where its driver(s) is(are) defined.
If the type of device is present, then the device's library should be
included in the VxWorks build.
|Local File Systems
| MSDOS (16-bit FAT), dosFs
| MSDOS (32-bit FAT), dosFs32
| Raw File System, rawFs
| Tape File System, tapeFs
| CD-ROM, cdromFs
| memory I/O (non-file)
| RAM files
|Network File System (NFS)
| Terminal driver
| Pseudo-terminal driver | <urn:uuid:0831318c-4095-44b2-91a6-72df3964f557> | 2.984375 | 3,677 | Tutorial | Software Dev. | 40.764038 |
On the other hand there are numerous positive feedbacks. Particularly that higher temperatures increase the amount of water vapour in the air (7% per 1 deg C) which is again a stronger GHG than CO2. Loss of ice cover over the sea changes the surface from reflecting 90% of the radiation to absorbing in excess of 80%.
Higher temperatures of themselves also increase the amount of carbon based GHGs in the atmosphere EG forest fires, increased methane emission's from tundra and peat areas
None of these positive feedbacks have actually been proven or observed, actually. If the net atmospheric feedbacks are negative, then the positive snow-albedo feedback would not be quite as great. With sea ice declines over the Arctic, you get more cloud cover, resulting in a negative feedback over the Arctic.
It has been observed that the climate system emits more OLR at a rate that is greater than a black body and is greater than the climate models, suggesting negative cloud feedback and neutral water vapor feedback.
The models had the greatest warming at 200-300 hPa, which is associated with a negative lapse rate feedback, as the upper troposphere in the models is warming faster than the surface.Once again, according to observations, we can see that there is a serious discrepency between the models and the observations at various locations in the upper troposphere.
If you think that Climate4you.com is cherry picking by selecting the HatAT dataset, look at Douglass et. al 2007, which has 3 MORE datasets that show that there is a serious discrepency between modeled and observational temperatures in the Tropical Troposphere.
The figure, from Douglass et. al 2007 (Source: http://scienceandpublicpolicy.org/image ... _wrong.pdf
) shows that the models were predicting a negative lapse rate feedback, which is seen with the higher temperature trend in the middle to upper troposphere than at the surface. Observations do not show any of this. They show that the lapse rate is positive, and that the surface is warming faster than the upper troposphere, consistent with a positive lapse rate feedback. The strongest negative lapse rate feedbacks in the IPCC GCMs were constantly associated with a the strongest positive water vapor feedbacks. The relationship between the two appears to be robust, so the lack of a negative lapse rate indicates that the water vapor feedback might not be positive, and even negative.
Or the fact that humidity levels are remaining constant as temperatures increase, as seen with Wang et. al 2008
And Sun et. al 2008 which finds that the negative cloud albedo feedback during ENSO events has been underestimated in climate models, and that the positive water vapor feedback in models ha been overestiamted. http://journals.ametsoc.org/doi/abs/10. ... HistoryKey | <urn:uuid:dddf4679-f92e-4661-98d0-c67470ef2e0c> | 3.453125 | 577 | Comment Section | Science & Tech. | 44.66732 |
Water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston to force the air through an opening connected to a turbine.
An oscillating water column device harnesses the motion of ocean waves as they pressurize a pocket of trapped air. This device is a partially submerged chamber with air trapped above the water surface. As waves enter and exit the chamber, the water surface moves up and down and acts like a piston. This generates electricity. The air trapped above the water level is compressed and decompressed by this movement to generate an alternating stream of high-velocity air through an exit blow hole. This air is channeled through a turbine-generator to produce electricity. These devices may be fixed to the ocean floor, hang from a floating or shoreline structure, or built into harbor jetties.
The Oscillating Water column is one of the most investigated and frequently installed technologies to date.
Illustration: As waves enter and exit the chamber, the water surface moves up and down and acts like a piston. This generates electricity.
Examples of the oscillating water column are Oceanlinx and Wavegen.
Read the latest issue here | <urn:uuid:5df7abbc-56aa-4ed1-b212-890a10c680c9> | 3.9375 | 255 | Knowledge Article | Science & Tech. | 33.727418 |
This is the VOA Special English ENVIRONMENT REPORT.
Doppler radar is an increasingly important tool to study weather. It is named after a physical effect first reported by an Austrian scientist, Christian Doppler. In eighteen-forty-two, he described how movement seems to influence the rate at which energy waves are produced.
Doppler found that the number of sound waves from a moving object would increase as the object came closer to an observer. The frequency would decrease as the object moved away. This became known as the Doppler effect.
You may have experienced it, for example, as a train goes by. As the train moves closer, the sound -- or pitch -- seems higher. As the train moves away, the pitch seems lower.
The number of sound waves that reach your ear in a given amount of time influences what you hear. In this case, the train moves a lot slower than the sound waves it produces. The waves that move out in the direction of travel get pushed together. So, to the observer, the frequency increases.
Behind the train, sound waves become spread out, so the frequency decreases. In reality, the sound of the train stayed the same. This effect happens with light and radio waves, too.
The ideas described by Christian Doppler are important to modern science. For example, they help scientists estimate the age of stars and the distance from Earth.
Doppler radar can tell more about storm systems than older radars could. Scientists hope to continue to improve the technology to warn people about severe storms. These can form suddenly -- like the tornadoes that tear across parts of the United States.
Weather scientists use radar systems to send out radio waves at moving objects, such as snowfall or raindrops in a storm. The radio waves hit the objects and return to the receiver. The period of time in between helps to show the storm's position and strength. But Doppler radar also measures changes in the frequency of the radio waves. This shows the direction and speed of winds. A computer combines all the measurements with a map, so scientists can follow the storm.
In recent years, information from Doppler radar has come into widespread use in the United States. Scientists say this has helped to improve the reporting of severe weather.
This Special English ENVIRONMENT REPORT was written by George Grow. | <urn:uuid:bf4b2af0-358a-4486-83ad-d76dc538155a> | 4.25 | 488 | Truncated | Science & Tech. | 57.899404 |
Hurricanes are violent storms that can form over the warm waters of the oceans. The warm water heats the air above it. Warm air rises, like steam from a teakettle. The rising warm air creates an area of low pressure. Other air rushes toward the low pressure area from all directions, creating strong winds if the low pressure is low enough. The strong winds form the hurricane.
This photograph from a weather satellite shows hurricane Erika. Hurricane Erika formed over the Atlantic Ocean in September, 1997. Hurricane Erika was a big storm. This photo, taken on September 11, 1997, shows that Erika was about 400 miles across, covering an area the size of Virginia and West Virginia combined! The storm path shows how the storm travelled north across the Atlantic Ocean. In just four days, Erika travelled almost 1400 miles across the ocean.
The eye of a hurricane is a small area of calm air at the very center of the storm. Although the eye is calm, winds of up to 200 miles per hour rage in the storm all around the eye.
These storms are called hurricanes in the Atlantic Ocean, and are called typhoons in the Pacific Ocean. Forecasting these storms and predicting their storm paths is important work. For information on hurricanes and forecasts, you can visit the U.S. National Oceanographic and Atmospheric Administration's National Hurricane Center web page at http://www.nhc.noaa.gov/products.html.
Meteorology (say "MEET-ee-or-ALL-oh-gee") is the science that studies storms like hurricanes. Visit the ReefNews Links to Other Pages about the Oceans for links to other web pages about meteorology, hurricanes, and photographs from weather satellites. | <urn:uuid:4c2402a3-0b66-4a71-865a-db87ef9f3114> | 3.90625 | 354 | Knowledge Article | Science & Tech. | 57.0858 |