text stringlengths 174 655k | id stringlengths 47 47 | score float64 2.52 5.25 | tokens int64 39 148k | format stringclasses 24 values | topic stringclasses 2 values | fr_ease float64 -483.68 157 | __index__ int64 0 1.48M |
|---|---|---|---|---|---|---|---|
Sequencing the DNA in a scoop of dirt can tell scientists what creatures are living nearby, a new study using soil from safari parks shows, and the amount of DNA present can even tell how many individuals of each species there are, which could allow field biologists to get preliminary surveys of species. But though the team managed to identify nearly all the species they had expected in the parks, from wildebeest to elephants, they are still addressing how to take samples that accurately represent the area’s biodiversity—one would have to avoid elephant latrines or wildebeest sleeping areas, for instance—and there is the additional problem that rare or small creatures, like insects, might easily be missed. That said, it’s still an unusual and interesting way to take a look at an area’s inhabitants without actually tracking them down.
Read more at Scientific American.
Image courtesy of malcyzk / flickr
RNAs from rice can survive digestion and make their way into mammalian tissues, where they change the expression of genes.
What’s the News: It’s no secret that having lunch messes with your biochemistry. Once that sandwich hits your stomach, genes related to digestion have been activated and are causing the production of the many molecules that help break food down. But a new study suggests that the connection between your food’s biochemistry and your own may be more intimate than we thought. Tiny RNAs usually found in plants have been discovered circulating in blood, and animal studies indicate that they are directly manipulating the expression of genes.
Children of older mothers, scientists have long known, are at higher risk for certain genetic disorders such as Down syndrome. But the father’s age is matters, too. As a father’s age increases, research shows, so does his child’s risk of mental illness, schizophrenia and autism in particular. In Scientific American, Nicole Grey explores the link between a father’s age and his child’s health, as well as the tricky questions about what mechanisms are behind the that link: genes, epigenetic changes, environment, or some combination of the three.
What’s the News: Whether genes can be property is an ongoing controversy in the world of biotechnology, and last week saw the latest court battle in that war: Upon appeal, a suit brought by the ACLU charging that genes aren’t products of human ingenuity and thus cannot be patented was settled largely in favor of Myriad Genetics, the biotech company that has patents on two BRCA genes. The genes are linked to hereditary breast and ovarian cancer, and plaintiffs charged that Myriad’s exclusive test for the genes kept patients from getting second opinions.
A detailed description of the court’s reasoning can be found over at Ars Technica. But for those of you who are thinking, what? someone else can own my genes?, chew on this: About 20% of human genes are patented or have patents associated with them, according to a comprehensive analysis. Here’s why.
What’s the News: What if the egg is fine and the sperm is dandy, but you still can’t seem to have a baby? Couples who are having trouble conceiving can testify to the frustration of learning that there’s no clear reason for their infertility. Now, however, scientists have found a genetic mutation that makes outwardly normal sperm much less fertile, potentially explaining many such cases and suggesting new routes to conception.
What’s the News: By knocking out a single gene, scientists at the University of Pennsylvania have significantly increased the physical endurance of lab mice, as explained in their recent paper in the Journal of Clinical Investigation. The researchers also found that certain variants of the same gene may be linked to greater endurance in humans.
What’s the News: Scientists have been rooting around in the rice genome for years, and the same goes for wheat. But now the long-recalcitrant potato genome has finally been sequenced. Time for a celebration? Perhaps, but biologists can’t rest for long: in addition to the just-published genome, there are still three more to sequence in each commercial potato.
What’s the News: When personal genotyping service 23andMe was founded in 2006, most people were understandably focused on the benefits and the dangers of knowing your chances of getting an incurable disease. But a major part of the company’s business plan was eventually leveraging their users’ information to explore the genetic basis of disease.
With more than 100,000 people now in their database, 23andMe has been turning that into a reality. They’ve just published their first paper focusing on the origins of disease, pinpointing two new areas of the genome involved in Parkinson’s.
What’s the News: While you may be able to hide your age with makeup and plastic surgery, don’t think that your deception is foolproof. Researchers have now developed a technique to ascertain your age to within five years using only your saliva. The new method, published in the journal PLoS One, could someday be used by forensic experts to pinpoint the age of crime suspects. | <urn:uuid:046c4c60-e012-45e8-8c8d-b75aba3d33a3> | 3.046875 | 1,074 | Content Listing | Science & Tech. | 41.204243 | 1,800 |
Date of this Version
Published in Chem. Eng. Technol. (2011) 34:12, 1989–1996. DOI: 10.1002/ceat.201100353
Sugarcane bagasse was partially acetylated to enhance its oil-wicking ability in saturated environments while holding moisture for hydrocarbon biodegradation. The water sorption capacity of raw bagasse was reduced fourfold after treatment, which indicated considerably increased hydrophobicity but not a limited capability to hold moisture for hydrocarbon biodegradation. Characterization results by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and surface area analyzer suggested that treated bagasse exhibited enhanced hydrophobicity and surface area. Oil wicking test results indicate that treated bagasse is more effective in wicking oil from highly saturated environments than raw bagasse and suggest that application of this material in remediation of oil spills in highly saturated wetlands is promising. | <urn:uuid:c424336a-d59f-47a6-a7f0-dd5aafde6626> | 2.609375 | 205 | Truncated | Science & Tech. | 15.744235 | 1,801 |
Download Full Text (938 KB)
To understand the climate variability and weather prediction in the Earth’s atmosphere, measurements of winds, temperature and wave activities are very crucial. The Earth’s atmosphere is believed to act as a source and sink for the waves of a broader spectrum with periods from few seconds to years. Generally, the Earth’s atmosphere is stably stratified except the planetary boundary layer and thus makes a reasonable assumption for the presence of atmospheric waves. A barotropic atmosphere in a resting basic state is able to support these spectra of waves. These waves move diagonally upward or downward and horizontally. The mean zonal circulation is mainly driven by these atmospheric waves, which are believed to be generated in the troposphere and propagates horizontally and vertically in to the middle and upper atmosphere. These waves transport energy and momentum from one region to another without the transport of material medium thereby impinging the signature of the source region on to the sink region. The waves propagating in Earth's atmosphere are expected to be both anisotropic and dispersive. The anisotropic characteristics of these waves mean that the properties of the waves are not uniform in all the directions. The propagating waves can be characterized by the amplitude and phase, which depends on time and space. When the wave frequency depends on the wavelength (2/K) then the wave is dispersive. For such waves the group velocity is different from the phase velocity. A better understanding of the vertical coupling by these wave activities will provide a deeper insight into the processes that control the dynamics and energetics of the whole atmosphere.
Modern Climatology, whole system, historical statistics, variability, atmosphere, prediction
Climate | Earth Sciences | <urn:uuid:18244538-150f-4cef-8e9c-2fbf3d6ef73e> | 3.71875 | 348 | Knowledge Article | Science & Tech. | 20.532846 | 1,802 |
The following methods can be defined to emulate numeric objects. Methods corresponding to operations that are not supported by the particular kind of number implemented (e.g., bitwise operations for non-integral numbers) should be left undefined.
%, divmod() pow()
|). For instance, to evaluate the expression x
+y, where x is an instance of a class that has an __add__() method,
x.__add__(y)is called. The __divmod__() method should be the equivalent to using __floordiv__() and __mod__(); it should not be related to __truediv__() (described below). Note that __pow__() should be defined to accept an optional third argument if the ternary version of the built-in pow() function is to be supported.
/) is implemented by these methods. The __truediv__() method is used when
__future__.divisionis in effect, otherwise __div__() is used. If only one of these two methods is defined, the object will not support division in the alternate context; TypeError will be raised instead.
%, divmod() pow()
|) with reflected (swapped) operands. These functions are only called if the left operand does not support the corresponding operation. For instance, to evaluate the expression x
-y, where y is an instance of a class that has an __rsub__() method,
y.__rsub__(x)is called. Note that ternary pow() will not try calling __rpow__() (the coercion rules would become too complicated).
|=). These methods should attempt to do the operation in-place (modifying self) and return the result (which could be, but does not have to be, self). If a specific method is not defined, the augmented operation falls back to the normal methods. For instance, to evaluate the expression x
+=y, where x is an instance of a class that has an __iadd__() method,
x.__iadd__(y)is called. If x is an instance of a class that does not define a __iadd() method,
y.__radd__(x)are considered, as with the evaluation of x
+, abs() and
Noneif conversion is impossible. When the common type would be the type of
other, it is sufficient to return
None, since the interpreter will also ask the other object to attempt a coercion (but sometimes, if the implementation of the other type cannot be changed, it is useful to do the conversion to the other type here).
Coercion rules: to evaluate x op y, the
following steps are taken (where __op__() and
__rop__() are the method names corresponding to
op, e.g., if op is `
+', __add__() and
__radd__() are used). If an exception occurs at any point,
the evaluation is abandoned and exception handling takes over.
x.__coerce__(y); skip to step 2 if the coercion returns
x.__op__(y); otherwise, restore x and y to their value before step 1a.
y.__coerce__(x); skip to step 3 if the coercion returns
y.__rop__(x); otherwise, restore x and y to their value before step 2a.
+' and x is a sequence, sequence concatenation is invoked.
*' and one operand is a sequence and the other an integer, sequence repetition is invoked. | <urn:uuid:6d180ad6-d124-4b8e-a711-061c7906bcd6> | 3.421875 | 757 | Documentation | Software Dev. | 56.978462 | 1,803 |
A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and carbon dioxide (helium can also be used) as coolant. Although there are many other types of reactor cooled by gas, the terms GCR and to a lesser extent gas cooled reactor are particularly used to refer to this type of reactor.
The GCR was able to use natural uranium as fuel, enabling the countries that developed them to fabricate their own fuel without relying on other countries for supplies of enriched uranium, which was at the time of their development only available from the United States or Soviet Union.
There were two main types of generation I GCR:
The main difference between these two types is in the fuel cladding material. Both types were mainly constructed in their countries of origin, with a few export sales: Magnox plants to Italy and Japan, and a UNGG to Spain. Both types used fuel cladding materials that were unsuitable for medium term storage under water, making reprocessing an essential part of the nuclear fuel cycle.
Both types were, in their countries of origin, also designed and used to produce weapons-grade plutonium, but at the cost of major interruption to their use for power generation despite the provision of online refuelling.
In the UK, the Magnox was replaced by the advanced gas-cooled reactor (AGR), an improved Generation II gas cooled reactors. In France, the UNGG was replaced by the pressurized water reactor (PWR). More recently, GCRs based on the declassified drawings of the early Magnox reactors have been constructed by North Korea at the Yongbyon Nuclear Scientific Research Center.
Gas-cooled reactor types include:
- Heavy Water Gas Cooled Reactor (HWGCR)
- Gas-cooled reactor (graphite moderated)
- Advanced gas-cooled reactor
- Gas-cooled fast reactor
- Gas turbine modular helium reactor, General Atomics design : He-cooled, Graphite moderated
- High temperature gas cooled reactor
- Pebble bed reactor
- Very high temperature reactor
See also
|This article about nuclear power and nuclear reactors for power generation is a stub. You can help Wikipedia by expanding it.| | <urn:uuid:1f7422aa-c3b6-4027-b8c1-aba8f41a1d79> | 3.71875 | 466 | Knowledge Article | Science & Tech. | 28.071141 | 1,804 |
Having tests that verify only one thing makes troubleshooting easier. It's not to say you shouldn't also have tests that do test multiple things, or multiple tests that share the same setup/teardown.
Here should be an illustrative example. Let's say that you have a stack class with queries:
and methods to mutate the stack
Now, consider the following test case for it (I'm using Python like pseudo-code for this example.)
self.stack = new Stack()
assert stack.top() == 1, "top() isn't showing correct object"
assert stack.getSize() == 1, "getSize() call failed"
From this test case, you can determine if something is wrong, but not whether it is isolated to the
pop() implementations, or the queries that return values:
If we add individual test cases for each method and its behavior, things become much easier to diagnose. Also, by doing fresh setup for each test case, we can guarantee that the problem is completely within the methods that the failing test method called.
assert stack.getSize() == 0
assert stack.top() == 1, "top returns wrong object after push"
assert stack.getSize() == 1, "getSize wrong after push"
assert stack.getSize() == 0, "getSize wrong after push"
As far as test-driven development is concerned. I personally write larger "functional tests" that end up testing multiple methods at first, and then create unit tests as I start to implement individual pieces.
Another way to look at it is unit tests verify the contract of each individual method, while larger tests verify the contract that the objects and the system as a whole must follow.
I'm still using three method calls in
test_push, however both
getSize() are queries that are tested by separate test methods.
You could get similar functionality by adding more asserts to the single test, but then later assertion failures would be hidden. | <urn:uuid:87ea5e88-3fc7-484a-b434-6c7e5f78723e> | 2.5625 | 412 | Q&A Forum | Software Dev. | 55.596575 | 1,805 |
clipped from www.theglobeandmail.com
Lab-made genome gives new life to ethics debate
If you thought that designing life was the sole domain of nature or a divine power – think again.
A team of U.S. scientists is reporting that it has constructed the genome of a living organism for the first time. Assembling bits of lab-made DNA, researchers at the J. Craig Venter Institute in Maryland say they have built the genetic structure of a bacterium from scratch in the lab.
The feat marks an historic, and controversial, milestone in the fledgling field known as synthetic biology. It uses chunks of synthetic DNA like Lego blocks, with an aim to creating life forms that can be genetically programmed to perform useful tasks.
Its proponents envision making micro-organisms that gobble up pollution, produce hard-to-make drugs, pump out clean energy, or, at the whimsical end, flowers designed to bloom on your birthday. | <urn:uuid:a2a53f83-f0e4-4b4b-ad5e-27f5fbf6ef46> | 2.796875 | 198 | News Article | Science & Tech. | 53.609685 | 1,806 |
Advanced Camera for Surveys
One of the Hubble Space Telescope's advanced instruments is referred to as the ACS.
Hubble's newest science instrument-the Advanced Camera for Surveys - brought the telescope into the 21st century. With its wider field of view, sharper image quality, and enhanced sensitivity, the new camera doubles Hubble's field of view and expands its capabilities significantly. Upgrading the telescope with ACS's cutting-edge technology made it ten times more effective and prolonged its useful life.
ACS is actually a team of three different cameras: the wide field camera, the high-resolution camera, and the solar blind camera. It outperforms all previous instruments flown aboard the Hubble Space Telescope, primarily because of its expanded wavelength range. Designed to study some of the earliest activity in the universe, ACS sees in wavelengths ranging from far ultraviolet to infrared.
ACS maps the distribution of dark matter, detects the most distant objects in the universe, searches for massive planets, and studies the evolution of clusters of galaxies. To accommodate these science goals, each of ACS's three cameras was designed to perform a specific function.
With a field of view twice that of WFPC2, ACS's wide field camera conducts broad surveys of the universe. Astronomers use it to study the nature and distribution of galaxies, which reveal clues about how our universe evolved.
The high-resolution camera takes extremely detailed pictures of the inner regions of galaxies. It searches neighboring stars for planets and planets-to be, and takes close-up images of the planets in our own solar system.
The solar blind camera, which blocks visible light to enhance ultraviolet sensitivity, focuses on hot stars radiating in ultraviolet wavelengths.
ACS was installed during Servicing Mission 3B in March 2002. The new instrument was built between 1996 and 1999 by scientists and engineers at The Johns Hopkins University, Ball Aerospace, the Space Telescope Science Institute, and NASA's Goddard Space Flight Center. (Text adapted from NASA description.) | <urn:uuid:7b9f7faf-9823-4b57-9216-9451009c13ca> | 3.59375 | 400 | Knowledge Article | Science & Tech. | 32.185344 | 1,807 |
See also the
Dr. Math FAQ:
probability in the
Browse High School Probability
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Odds vs. probability.
- Coin Flipping [01/26/1998]
How can I figure out the chances of flipping a coin five times with the
- Coin Landing on Edge [11/20/2001]
Is there a way to calculate the odds of a coin dropped from a known
height landing on its edge rather than heads or tails?
- Coin Landing on Edge [11/29/2001]
What are the chances of a coin landing on edge? A Canadian copper penny,
- Coin Tosses, Dealing Cards... [12/08/1998]
Several questions on discrete math - probability and combination;
deducing recurrence relations.
- Coin-Tossing Game [05/09/2001]
Three men toss a coin in succession for a prize to be given to the person
who first obtains a head. What is each man's chance of winning the prize?
- Collecting a Complete Set [03/15/2000]
I have a very large box filled with 8 different frying pan handles in
equal proportions. What is the probability that I will have to remove 32
handles before I get a complete set?
- Collecting a Set of Coupons [02/03/2000]
Given N different types of coupons, what is the expected number of
different types of coupons that are contained in a set of (n) coupons?
What is the variance and the expected number of coupons one one needs to
collect before obtaining a complete set?
- Colored and Numbered Discs [05/25/2001]
Drawing colored and numbered discs from boxes; rolling colored and
- Combinations of Married Couples [11/08/1996]
What is the probability that 12 people can be grouped into 6 pairs where
each pair is a married couple?
- Combinatorial Probability Tournament [01/23/2002]
A tennis tournament for 2^n players is organised as a knock-out
tournament with n rounds, the last round being the final. Two players are
chosen at random. Calculate the probabilities they meet a) in the first
round; b) in the final; c) in any round.
- Complex Ratio Problem [07/31/1997]
If you randomly throw 3 points on a plane, you get a triangle... What is
the probability that the triangle will become obtuse...?
- Conditional Probability [05/25/2000]
Suppose used car salesmen tell the truth 2/5 of the time, and 1/3 of the
trees in a forest are oak...
- Conditional Probability [12/31/1997]
I tutor probability and statistics and people seem to be confused by the
use of the multiplication rule in conditional probability...
- Consecutive Failures in Bernoulli Trials [07/07/1999]
What is the probability that out of n experiments there will be a string
of at least k experiments in a row that fail?
- Contest Probabilities [10/14/1998]
Players of equal skill meet in an elimination contest. With n players,
what is the probability that a player will compete in i rounds?
- Craps [5/24/1996]
Can you give me information on the probability and outcome of the game
- Creating a Mathematical Model of a Complicated Situation [10/09/2005]
I am riding a bike and have several possible routes, each of which
contains various traffic lights, amounts of traffic, the possibility
of being stopped by a policeman for running a light, and other factors
which influence the time it will take to ride each route. How can I
model the routes to predict which will be the best choice?
- Cupcakes and Boxes: Conditional Probability [01/03/2002]
Given 3 boxes, each with 2 cupcakes (1 box has two vanilla, 1 has 2
chocolate, and 1 has one of each). A box is selected randomly and a
cupcake is selected that turns out to be chocolate. What's the
probability that the other cupcake in that box will be chocolate?
- Darts and Wilensky's Paradox [03/17/1999]
What is the probability of scoring 25 points with 2 darts if the
dartboard is made up of 4 concentric circles?
- Defining Independent Events [07/14/2009]
My book says two events E and F are independent if P(E|F) = P(E). Do
we also have to have P(F|E) = P(F) or does this automatically follow?
Could there be a situation where P(E|F) = P(E) but P(F|E) =/= P(F)?
- Defining Probability [4/30/1996]
Is a probability number equal to a percent or a decimal?
- Definite Integral of e^(-x^2) and e^((-x^2)/2)) [08/18/1999]
How can I find the integrals of e^(-x^2) or e^((-x^2)/2)) from x = 0 to
- Deriving the Normal From the Binomial [07/11/1998]
How is the normal distribution derived from the binomial distribution?
Does the normal approximate the binomial?
- Dice: Full House [6/28/1996]
What is the probability of rolling a full house with 5 six-sided dice?
- Dice Game and Expected Value [04/18/2005]
You pay $6 to play a game where you roll a die with a payoff as
follows: $8 for a 6, $7 for a 5, and $4 for any other result. What are
your expected winnings? Is the game fair?
- Die Roll Probabilities in Gaming [01/06/2001]
Players fight battles by rolling two dice and adding modifiers according
to each player's advantages. Generate a chart giving the odds of victory
based on modifiers.
- Distribution of Cards in Bridge [05/03/2001]
In bridge, it often happens that you and your partner have 9 cards of a
suit between you. In all the bridge books that I have read, it is stated
that the probability of the remaining 4 cards splitting 2-2 is 40.7%. Can
this be proven?
- Do Prior Outcomes Affect Probabilities of Future Ones? [05/26/2008]
I know that the probability of flipping a coin and getting a head is
1/2. But if I've gotten ten straight tails, isn't it more likely that
the next one will be a head?
- Drawing Aces [06/12/1997]
What is the probability that you will pick two aces in a row out of a 52-
- Drawing Marbles [05/05/1998]
A jar contains 19 different marbles. I draw 13 marbles, one at a time,
but replace the marble back before taking the next....
- Drawing Prizes [07/06/2003]
If there are many cheap prizes, does the probability of getting a good
prize go up as more prizes are drawn?
- Drunk Drivers and Traffic Deaths [05/14/1997]
Knowing the total traffic fatalities and the number involving alcohol,
what is the probability that a traffic death may be attributed to
- Empirical and Mathematical Probabilities [12/04/1998]
What is the difference between empirical probability and mathematical
- Empirical Probability [01/15/1999]
If I flipped a coin 10 times and got heads each time, would the
probability of a head on the next flip be 1/2 or almost 1?
- English Exam Probability [12/17/2001]
Given a list of 25 potential exam questions, with 10 of them on the
actual exam and of which students write essays on 2, how many questions
should be prepared to be 95% confident you won't write on a question you
- Even Number of Heads [02/12/2002]
What is the probability of getting an even number of heads when tossing a
- Executive Committee Vote [01/21/1997]
124 delegates must elect a 13-member executive committee from a list of
26 candidates. If each delegate votes for 10 candidates, what is the
least number of votes a candidate can get and be elected?
- Expected Tosses for Consecutive Heads with a Fair Coin [06/29/2004]
What is the expected number of times a person must toss a fair coin to
get 2 consecutive heads?
- Expected Value [12/09/1997]
What is expected value?
- Expected Value [11/07/2001]
I am playing a game where I toss a fair coin. I get a bead if I flip a
head and I lose a bead if I flip a tail... to get a total of 5 beads,
what is the expected number of coin tosses I must make? | <urn:uuid:08a02f21-1199-444a-994a-864f66d8b530> | 2.765625 | 1,977 | Q&A Forum | Science & Tech. | 69.063443 | 1,808 |
Tides of Change
Library Home || Full Table of Contents || Suggest a Link || Library Help
|Mark Schneider; SCORE Mathematics|
|This lessons deals with collecting data, charting data, and interpreting data, based on the changing ocean tide. Aligned to the California State Standards. From the Schools of California Online Resources for Educators SCORE Mathematics Lessons.|
|Levels:||High School (9-12)|
|Resource Types:||Lesson Plans and Activities|
|Math Topics:||Data Analysis, Statistics, Geology|
© 1994-2013 Drexel University. All rights reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education. | <urn:uuid:f4cb62dd-863e-4105-980c-8756226d113d> | 2.953125 | 149 | Content Listing | Science & Tech. | 26.450887 | 1,809 |
Assembly: PresentationFramework (in PresentationFramework.dll)
This method pauses the storyboard, but has no discernible effect if it is not active or currently paused. As a side effect, all associated children are also paused.
A controllable storyboard can pause, resume, seek, stop, and be removed. To make a storyboard controllable in code, you must use the appropriate overload of the storyboard's Begin method and specify true to make it controllable. For an example, see How to: Control a Storyboard After It Starts.
Beginning a Paused Storyboard
When you Begin a storyboard that was paused, it appears to resume and restart. However, that is not what actually happens. The Begin method actually replaces the paused Storyboard with a new unpaused version. Each time the Begin method is called, clock objects are created for the storyboard. These clocks are distributed to the properties they animate. So, when the Begin method is called again, it does not restart its clocks; it replaces them with new clocks.
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements. | <urn:uuid:f1b02587-fdff-4c3d-a1b7-659220598ed2> | 2.765625 | 298 | Documentation | Software Dev. | 45.761366 | 1,810 |
CORVALLIS, Ore. – A new study has found that each step of the marine food chain is clearly controlled by the trophic level below it – and the driving factor influencing that relationship is not the abundance of prey, but how that prey is distributed.
The importance of the spatial pattern of resources – sometimes called “patchiness” – is gaining new appreciation from ecologists, who are finding the overall abundance of food less important than its density and ease of access to it.
Results of the study are being published this week in the Royal Society journal Biology Letters.
Kelly Benoit-Bird, an Oregon State University oceanographer and lead author on the study, said patchiness is not a new concept, but one that has gained acceptance as sophisticated technologies have evolved to track relationships among marine species.
“The spatial patterns of the resource ultimately determine how the ecosystem functions,” said Benoit-Bird, who received a prestigious MacArthur Fellowship in 2010. “In the past, ecologists primarily used biomass as the determining factor for understanding the food chain, and the story was always rather muddled. We used to think that the size and abundance of prey was what mattered most.
“But patchiness is not only ubiquitous in marine systems, it ultimately dictates the behavior of many animals and their relationships to the environment,” she added.
Benoit-Bird specializes in the relationship of different species in marine ecosystems. In one study in the Bering Sea, she and her colleagues were estimating the abundance of krill, an important food resource for many species. Closer examination through the use of acoustics, however, found that the distribution of krill was not at all uniform – which the researchers say explained why two colonies of fur seals and seabirds were faring poorly, but a third was healthy.
“The amount of food near the third colony was not abundant,” she said, “but what was there was sufficiently dense – and at the right depth – that made it more accessible for predation than the krill near the other two colonies.”
The ability to use acoustics to track animal behavior underwater is opening new avenues to researchers. During their study in the Bering Sea, Benoit-Bird and her colleagues discovered that they could also use sonar to plot the dives of thick-billed murres, which would plunge up to 200 meters below the surface in search of the krill.
Although the krill were spread throughout the water column, the murres ended up focusing on areas where the patches of krill were the densest.
“The murres are amazingly good at diving right down to the best patches,” Benoit-Bird pointed out. “We don’t know just how they are able to identify them, but 10 years ago, we wouldn’t have known that they had that ability. Now we can use high-frequency sound waves to look at krill, different frequencies to look at murres, and still others to look at squid, dolphins and other animals.
“And everywhere we’ve looked the same pattern occurs,” she added. “It is the distribution of food, not the biomass, which is important.”
An associate professor in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University, Benoit-Bird has received young investigator or early career awards from the Office of Naval Research, the White House and the American Geophysical Union. She also has received honors from the Acoustical Society of America, which has used her as a model scientist in publications aimed at middle school students.
Her work has taken her around the world, including Hawaii where she has used acoustics to study the sophisticated feeding behavior of spinner dolphins. Those studies, she says, helped lead to new revelations about the importance of patchiness.
Ocean physics in the region results in long, thin layers of phytoplankton that may stretch for miles, but are only a few inches thick and a few meters below the surface. Benoit-Bird and her colleagues discovered a layer of zooplankton – tiny animals that feed on the plankton – treading water a meter below to be near the food source. Next up in the food chain were micronekton, larger pelagic fish and crustaceans that would spend the day 600 to 1,000 meters beneath the surface, then come up to the continental shelf at night to target the zooplankton. And the spinner dolphins would emerge at night, where they could reach the depth of the micronekton.
“The phytoplankton were responding to ocean physics,” Benoit-Bird said, “but all of the others in the food chain were targeting their prey by focusing on the densest patches. We got to the point where we could predict with 70 percent accuracy where the dolphins would show up based just on the phytoplankton density – without even considering the zooplankton and micronekton distribution.”
Ocean “patchiness” is not a new concept, Benoit-Bird reiterated, but may have been under-appreciated in importance.
“If you’re a murre that is diving a hundred meters below the surface to find food, you want to maximize the payoff for all of the energy you’re expending,” Benoit-Bird said. “Now we need more research to determine how different species are able to determine where the best patches are.” | <urn:uuid:7928be75-496b-4509-8c71-acd60c67189f> | 3.796875 | 1,157 | News (Org.) | Science & Tech. | 37.496225 | 1,811 |
Ask the user what's her name
When prompting the user with a question it is probably the best to use the prompt function. Similarly to say it prints to the screen, but without the newline at the end. Then it waits for the user to type in something.
It reads up to the ENTER the user presses, but passes over only the the part before the newline. (Perl 5 users could think about it as having autochomp)examples/scalars/read_stdin.p6
#!/usr/bin/env perl6 use v6; my $name = prompt("Please type in yourname: "); say "Hello $name"; | <urn:uuid:df63d47e-82b0-4502-86dd-dc9c8a4569c3> | 2.921875 | 141 | Documentation | Software Dev. | 69.399524 | 1,812 |
(PhysOrg.com) -- On Earth, helium is a gas used to float balloons, as in the movie "Up." In the interior of Jupiter, however, conditions are so strange that, according to predictions by University of California, Berkeley, scientists, helium condenses into droplets and falls like rain.
Helium rain was earlier proposed to explain the excessive brightness of Saturn, a gas giant like Jupiter, but one-third the mass.
On Jupiter, however, UC Berkeley scientists claim that helium rain is the best way to explain the scarcity of neon in the outer layers of the planet, the solar system's largest. Neon dissolves in the helium raindrops and falls towards the deeper interior where it re-dissolves, depleting the upper layers of both elements, consistent with observations.
"Helium condenses initially as a mist in the upper layer, like a cloud, and as the droplets get larger, they fall toward the deeper interior," said UC Berkeley post-doctoral fellow Hugh Wilson, co-author of a report appearing this week in the journal Physical Review Letters. "Neon dissolves in the helium and falls with it. So our study links the observed missing neon in the atmosphere to another proposed process, helium rain."
Wilson's co-author, Burkhard Militzer, UC Berkeley assistant professor of earth and planetary science and of astronomy, noted that "rain" - the water droplets that fall on Earth - is an imperfect analogy to what happens in Jupiter's atmosphere. The helium droplets form about 10,000 to 13,000 kilometers (6,000-8,000 miles) below the tops of Jupiter's hydrogen clouds, under pressures and temperatures so high that "you can't tell if hydrogen and helium are a gas or a liquid," he said. They're all fluids, so the rain is really droplets of fluid helium mixed with neon falling through a fluid of metallic hydrogen.
The researchers' prediction will help refine models of Jupiter's interior and the interiors of other planets, according to Wilson. Modeling planetary interiors has become a hot research area since the discovery of hundreds of extrasolar planets living in extreme environments around other stars. The study will also be relevant for NASA’s Juno mission to Jupiter, which is scheduled to be launched next year.
Militzer and Wilson are among the modelers, using "density functional theory" to predict the properties of Jupiter's interior, specifically what happens to the dominant constituents - hydrogen and helium - as temperatures and pressures increase toward the center of the planet. These conditions are yet too extreme to be reproduced in the laboratory. Even experiments in diamond-anvil cells can only produce pressures at the Earth's core. In 2008, Militzer's computer simulations led to the conclusion that Jupiter's rocky core is surrounded by a thick layer of methane, water and ammonia ices that make it twice as large as earlier predictions.
The two modelers embarked on their current research because of a discovery by the Galileo probe that descended through Jupiter's atmosphere in 1995 and sent back measurements of temperature, pressure and elemental abundances until it was crushed under the weight of the atmosphere. All elements seemed to be as slightly enriched compared to the abundance on the sun - which is assumed to be similar to the elemental abundances 4.56 billion years ago when the solar system formed - except for helium and neon. Neon stood out because it was one-tenth as abundant as it is in the sun.
Their simulations showed that the only way neon could be removed from the upper atmosphere is to have it fall out with helium, since neon and helium mix easily, like alcohol and water. Militzer and Wilson's calculations suggest that at about 10,000 to 13,000 kilometers into the planet, where the temperature about 5,000 degrees Celsius and the pressure is 1 to 2 million times the atmospheric pressure on Earth, hydrogen turns into a conductive metal. Helium, not yet a metal, does not mix with metallic hydrogen, so it forms drops, like drops of oil in water.
This provided an explanation for the removal of neon from the upper atmosphere.
"As the helium and neon fall deeper into the planet, the remaining hydrogen-rich envelope is slowly depleted of both neon and helium," Militzer said. "The measured concentrations of both elements agree quantitatively with our calculations."
Saturn's helium rain was predicted because of a different observation: Saturn is warmer than it should be, based on its age and predicted rate of cooling. The falling rain releases heat that accounts for the difference.
Jupiter's temperature is in accord with models of its cooling rate and its age, and needed no hypothesis of helium rain until the discovery of neon depletion in the atmosphere. Interestingly, theoretician David Stevenson of the California Institute of Technology (Caltech) predicted neon depletion on Jupiter prior to the Galileo probe's measurements, but never published a reason for his guess.
Explore further: EUROnu project recommends building Neutrino Factory
More information: Sequestration of Noble Gases in Giant Planet Interiors, Hugh F. Wilson and Burkhard Militzer, Phys. Rev. Lett. 104, 121101 (2010) - Published March 22, 2010, Download PDF (free) | <urn:uuid:df77d959-fc88-4965-82bc-eb38d1be1de9> | 3.609375 | 1,069 | News Article | Science & Tech. | 38.636131 | 1,813 |
DocumentFragment is a "lightweight" or "minimal" Document object. It is very common to want to be able to extract a portion of a document's tree or to create a new fragment of a document. Imagine implementing a user command like cut or rearranging a document by moving fragments around. It is desirable to have an object which can hold such fragments and it is quite natural to use a Node for this purpose. While it is true that a Document object could fulfill this role, a Document object can potentially be a heavyweight object, depending on the underlying implementation. What is really needed for this is a very lightweight object. DocumentFragment is such an object.
Furthermore, various operations — such as inserting nodes as children of another Node — may take DocumentFragment objects as arguments; this results in all the child nodes of the DocumentFragment being moved to the child list of this node.
The children of a DocumentFragment node are zero or more nodes representing the tops of any sub-trees defining the structure of the document. DocumentFragment nodes do not need to be well-formed XML documents (although they do need to follow the rules imposed upon well-formed XML parsed entities, which can have multiple top nodes). For example, a DocumentFragment might have only one child and that child node could be a Text node. Such a structure model represents neither an HTML document nor a well-formed XML document.
When a DocumentFragment is inserted into a Document (or indeed any other Node that may take children) the children of the DocumentFragment and not the DocumentFragment itself are inserted into the Node. This makes the DocumentFragment very useful when the user wishes to create nodes that are siblings; the DocumentFragment acts as the parent of these nodes so that the user can use the standard methods from the Node interface, such as insertBefore and appendChild.
Direct Base Classes: AbstractContainerNode
Inherited Functions: addEventListener, appendChild, attributes, autoRelease, bubbleEvent, captureEvent, childNodes, cloneNode, copyNode, dispatchAttrModified, dispatchCharacterDataModified, dispatchEvent, dispatchNodeInserted, dispatchNodeInsertedIntoDocument, dispatchNodeRemoved, dispatchNodeRemovedFromDocument, dispatchSubtreeModified, duplicate, events, eventsSuspended, findAttribute, findElement, findNode, firstChild, getNodeByPath, getNodeByPathNS, getNodeValue, hasAttributeValue, hasAttributes, hasChildNodes, innerText, insertBefore, isSupported, lastChild, localName, namesAreEqual, namespaceURI, nextSibling, nodeName, nodeType, nodeValue, normalize, ownerDocument, parentNode, prefix, previousSibling, release, removeChild, removeEventListener, replaceChild, setNodeValue, setOwnerDocument
const XMLString & nodeName() const;
See also: Poco::XML::AbstractNode::nodeName()
unsigned short nodeType() const;
See also: Poco::XML::Node::nodeType()
See also: Poco::XML::AbstractNode::copyNode() | <urn:uuid:fd7e1aff-a6bf-42bb-abb2-bf9a10b89f0d> | 2.734375 | 654 | Documentation | Software Dev. | -5.994607 | 1,814 |
publications > information sheet > summary of geer workshop: hydrologic modeling and processes
Summary of Greater Everglades Ecosystem Restoration Workshop:
2. Hydrologic Modeling and Processes, May 7-8, 2002
During April and May 2002, the United States Geological Survey (USGS) Greater Everglades Place Based Studies (PBS) held five information workshops in south Florida to discuss status of greater Everglades ecosystem research, and to solicit suggestions for additional studies from Everglades restoration partners. The Hydrologic Modeling and Related Processes Workshop was held at NOVA Southeastern University in Fort Lauderdale, May 7-8, 2002.
The greater Everglades restoration program is prescribing ecosystem-wide changes to some of the physical, hydrological, and chemical attributes of the Everglades ecosystem. The ability to accurately understand the complex interactions between contaminants, nutrients, hydrology, and other processes and their effects on the landscape and habitat within the greater Everglades ecosystem, during the present, recent past, and prior to significant human alteration, is crucial for the success of greater Everglades ecosystem restoration and successful implementation of the Comprehensive Everglades Restoration Plan (CERP). Knowledge of these processes and their interactions produces better informed planning, project implementation, and land management decisions. Getting the water quantity, quality, distribution and timing right, as required by CERP, requires a complementary program of hydrologic research, monitoring, and modeling.
|Measuring flow velocity in Taylor Slough wetlands to develop a simulation model. [larger version]
Many organizations and programs are dependent on scientific knowledge and more accurate hydrologic and ecologic models for restoring the greater Everglades ecosystem. These include federal, state, and local agencies, Native American tribal governments, as well as private organizations.
Research needs, including those directly related to hydrologic modeling and processes, and those relevant to other research topics, were compiled during the workshop based on discussions among the represented organizations and individuals having interests and roles within greater Everglades restoration. For the purposes of this summary, these needs have been divided into 1) hydrological modeling and related research needs and 2) other needs discussed that are relevant to one of the other four workshop topics.
Hydrologic Modeling Needs
- Enhance connectivity between SFWMM (South Florida Water Management Model) and Southern Inland and Coastal System (SICS) and Tides and Inflows in Mangroves of the Everglades (TIME) models.
- Develop internet-accessible SICS and TIME model real-time animations.
- Collect TIME equivalent data from outside of TIME model domain.
- Develop additional salinity simulation capability to support Across Trophic Level System Simulation (ATLSS) program for developing estuarine species models.
- Expand boundaries of SICS and TIME models to the entire CERP project area including areas east of US 1.
- Incorporate solute-transport and simple settling algorithms in regional models to assist in setting CERP water quality performance measures.
- Model CERP implementation impacts on transport of nutrients within the Everglades.
- Incorporate seepage effects associated with the eastern boundary of the Everglades within all applicable models.
- Complete additional work to couple water quality and hydrologic monitoring data with SICS and TIME models.
- Increase spatial resolution of surface water and groundwater elevation and salinity monitoring.
- Improve discharge and recharge estimates associated with stormwater treatment areas.
- Increase spatial extent of monitoring of flow structure in wetlands to assess flow impacts on landscapes and habitat, including tree islands.
- Conduct additional studies on the hydraulic properties of the surficial aquifer system including the overlying peat and marl unit.
- Collect additional information on Floridian Aquifer hydrogeology.
- Develop additional models and model inputs for the southwest coast of Florida.
- Develop stochastic methods for generating rainfall input data needed for applicable models.
- Improve understanding of groundwater solute transport and upwelling (such as sulfates), and subsequent surface water mixing in central Everglades, particularly WCA-3A south of Alligator Alley.
- Create probabilistic/stochastic approaches to better define trends and certainties within models.
- Incorporate climate-change variables into model simulations.
Research Needs Relevant to Other Workshops Topics
- Complete USGS Aerial Height Finder (AHF) topographic survey in Everglades National Park, Loxahatchee, Big Cypress and Water Conservation Areas.
- Map and delineate unique landscape features such as tree islands and
hammocks using AHF system.
- Establish NAVD88 control along the southwest Gulf coast in Everglades National Park.
- Conduct bathymetric surveys of tidal rivers and creeks along the southwest coast of Florida.
- Create a centralized ecosystem data repository system.
- Gather reliable farm elevation/ topographic information at appropriate resolution.
- Use multi-agency collaboration to address data quality issues.
Participation by greater Everglades restoration partners during the 85-person Hydrologic Modeling Workshop (excluding USGS participants. [larger version]
For Further Information
For further information on these projects, please visit:
U.S. Department of the Interior
Greater Everglades Science Program
U.S. Geological Survey
July 2002 PBS Information Sheet IS 02-02 | <urn:uuid:cce80bfa-94be-4ab7-bfbd-c2ca717405e2> | 2.8125 | 1,129 | Academic Writing | Science & Tech. | 3.861177 | 1,815 |
According to the USGS, the total energy from an earthquake includes energy required to create new cracks in rock, energy dissipated as heat through friction, and energy elastically radiated through the earth. Of these, the only quantity that can be measured is that which is radiated through the earth. It is the radiated energy that shakes buildings and is recorded by seismographs on the Richter scale.
Even though it usually destroys homes and other structures that are built to stand on solid ground, the sheer amount of kinetic energy produced by an earthquake makes scientists very excited.
Published by WellHome | <urn:uuid:d8a12e13-5e3f-45af-9e05-cbfbeaf883f1> | 3.625 | 120 | Knowledge Article | Science & Tech. | 32.564 | 1,816 |
Story submitted by Jens Raunsø Jensen
The IPCC dismisses in its AR4 report of 2007 natural climate variability as a major reason for the global temperature increase in the second half of the 20th century. The basic arguments are “greenhouse physics”, increasing and accelerating temperatures in the second half of the 20th century, and the inability of climate models to reproduce the temperature changes if only natural processes are considered.
However, many local, regional and global temperature curves for 1960-2010 may be summarised as consisting of step changes, coinciding with one or more major ENSO-related events (El Niño) and separated by periods of near constant temperature. Thus, the temperature increase (proxy for global warming) in the second half of the 20th century could have taken place in steps driven by major ENSO events. This challenges IPCC’s notion of increasing and accelerating temperatures and IPCC’s modelling argument for accepting the anthropogenic global warming (AGW) hypothesis as the major explanation for the observed temperature changes.
Temperature curves have been analysed with many different tools to establish a perceived underlying pattern for statistical and/or for attribution purposes: smoothing, linear regression, waves and periodicities, break points, shifts etc. They all have their merits and limitations, and there is no general agreement on the pattern except as consisting of a relatively cold period from the mid 1940s to mid 1970s, followed by a warmer period during the 1980s and 1990s.
This post analyses temperature data using a tool for identifying step changes in the mean temperature, focusing on the period 1960-2010. This analysis complements many other similar analyses in the peer reviewed literature and on this and other blogs (see eg. Bob Tisdale here
). The focus is on the land-based temperature record, the use of data up to 2010, and the application of a statistical tool that does not require a priori assumptions of the time or number of step changes. It is noted, that 1960 was selected as the start year for the analysis in order to cover the main period of interest from a global warming perspective. The step changes presented below remain the same when the entire historical observational records are analysed.
The tool, I have relied upon, is available from NOAA’s homepage and has been documented in the peer-reviewed literature (www.beringclimate.noaa.gov/). Trial runs on different annual temperature datasets suggest, that a robust solution (maximum correlation and low sensitivity to parameter setting) is obtained when using the following settings: a cut-off length parameter in the interval of 8 to 14 years (12 selected), a correction for autocorrelation by the IPN4 method, and an outlier definition of 3 s deviation in order to effectively give equal weight to all observations.
The Fig.1 below shows the result for two of the many cases I have looked at: global (crutem3gl;
) and Denmark, DK (t_dk_k, from Danish Meteorological Institute DMI;
The T-anomaly is with reference to 1961-1990 (note: the DK curve has been shifted upwards by 2 oC to avoid overlap). At the bottom in the figure, the warm (red) and cold (blue) state of the pacific decadal oscillation (PDO) is shown together with major volcanoes (squares) and El Niños (triangles). Vertical lines show the PDO shift in 1976 and the start of El Niños in 1986 and 1997.
Notwithstanding the confounding influence of anthropogenic forcings, it is hard not to see this figure as suggesting, that natural processes have had a major influence on the course of the global warming in the second half of the 20th century, contrary to the assessment of the IPCC.
The identified steps are statistically highly significant, and 85% of the variation in the global land temperature during 1960-2010 may be explained by 3 upward steps, separated by periods of near constant temperature and with a lack of warming (insignificant trend) during the most recent 13 years. The step curve for Denmark explains 40% of the variance (as compared to 30% by the Gauss-filtered smoothing model of DMI), with a lack of warming during the most recent 23 years.
The three steps in the global curve occur at 1977, 1987 and 1998. This could be a statistical coincidence as eg. any curve with a true linear trend may be summarised as a step curve. However, the three years have a documented physical significance: 1977, the great pacific shift, with the PDO turning to the warm mode, and 1987 and 1998 being years of major ENSO activity. Thus, in terms of the accumulated nino3.4 anomaly, the El Niños of 1997/98 and 1986/88 were the most extreme on record (NOAA data, 3-month average nino3.4-anomaly). Furthermore, the linear trends of the four periods separating the change points are all non-significantly different from zero, but the power of this test is of course reduced in the periods of shorter length. (It is noted that the hadcrut3 and the GISS land-ocean datasets give essentially the same result, with steps at 1977/1990/1997 and 1977/1987/1997, respectively).
Local and regional temperatures are generally known to be differently affected by ENSO events. Accordingly, many local temperature curves across the globe can similarly be summarised by the step model, with one or more steps at or close to one or more of the steps identified above in the global record. For example, the Denmark curve in Fig. 1 displays one step in 1988; Alaska curves display only one but very significant step in 1977 (GHCN data, 4 stations analysed, not shown); USA have steps in 1986 and 1998 (GISS, contiguous 48 states, not shown); and Australia have steps in 1979 and 2002 (BOM data, not shown).
Finally, sidestepping a bit with some food for thoughts: inspired by the current discussion on the role of natural causes for the changes in the atmospheric CO2 concentration, it may be mentioned, that the annual change in ppmv CO2 at Mauna Loa displays significant upward shifts in 1977 and in 1998, on average increasing the annual concentration increment by 58% and a further 33%, respectively. It seems that there could be a strong influence of ENSO also on the annual increment on the CO2 curve during 1960-2010.
It is demonstrated above that the temperature increase in the second half of the 20th century could have taken place in steps driven by major ENSO events. The significance of the finding does not mainly rest on the statistical significance of the model fit, but on the physical support of the ENSO observations for the step changes, identified without making a priori assumptions on the timing or number of steps.
If this was indeed the case – and it could be, unless proven otherwise – then the following implications arise:
1. Natural processes in the ocean-atmosphere system may have had a major influence on the global temperature change in the second half of the 20th century. If so, then something must be wrong with IPCC’s climate models, as the models according to the AR4 can not at all reproduce the observed temperature curve by considering natural causes only. This could question the climate sensitivity of the models and the models ability to adequately describe the natural processes in oceans and atmosphere (eg. ENSO phenomena). While it is generally accepted, that ENSO events can produce abrupt changes in global temperatures, the IPCC considers such effects to be short lived (albeit based on a poor ability to model ENSO processes), whereas the observational data when summarised as step changes imply a longer term effect on both local and higher-level average temperature curves.
2. The linearity assumption underlying the use of linear regressions for trend analysis of the temperature records is in principle violated by the presence of steps. Thus, the global temperature should not be considered as simply uniformly increasing or accelerating, and claims of average temperature increases and accelerations may be erroneous and misleading. The use of linear regression for analysing temperature (and other climate-related) curves should be reconsidered.
3. Regional and global temperature anomaly curves are “apples and oranges”, as they average over locations differently influenced by natural processes and in different states of the climate system. There is a need to emphasise more on the analysis of local temperature curves.
4. It was recently suggested, that the lack of warming during 1998-2008 was driven largely by natural factors (Kauffmann et al., 2011). Referring to Fig. 1, then what is the explanation for the apparent lack of increase in global temperature during 1977-1986 and 1987-1997? And what is then the conclusion for the overall cause of global warming during 1960-2010?
Finally, I want to make it clear, that I do agree with the presence of an anthropogenic greenhouse effect. But I find reasons in the observational data to doubt, that the IPCC, in its current analysis (AR4, including only data up to 2005), has assessed the relative importance of natural and anthropogenic causes for the temperature changes correctly. The role of natural processes could have been significantly underestimated. | <urn:uuid:b96d07e9-d969-4e2f-a6ed-067d810b744b> | 3.3125 | 1,917 | Nonfiction Writing | Science & Tech. | 35.852959 | 1,817 |
Click on the image to see an enhanced diagram.
Heat is energy in transit from warmer systems to colder systems.
Heat is associated with the internal potential and kinetic energy (an apparently disorganized molecular motion) of a system.
If heat is a form of energy associated to the particles’ rotational, translational and vibratory movements, how does the heat move through the space between the Sun and the Earth, which density is extremely low? The answer is: heat could be transferred from warmed systems by radiation. The thermal radiation is electromagnetic radiation that consists of particles and waves, i.e. photons and waves, the same as visible light. Thus, the radiative heat transfer can take place through vacuum.
The energy always moves from a warmer system to a colder system. The energy which is moving from one system to another is known as heat. The transfer or dispersion of heat can occur by means of three main mechanisms, conduction, convection and radiation:
CONDUCTION: It is the flow of heat through solids and liquids by vibration and collision of molecules and free electrons. The molecules of a given point of a system which are at higher temperature vibrate faster than the molecules of other points of the same system -or of other systems- which are at lower temperature. The molecules with a higher movement collide with the less energized molecules and transfer part of their energy to the less energized molecules of the colder regions of the structure. For example, the heat transfer by conduction through the bodywork of a car.
Metals are the best thermal conductors; while non-metals are poor thermal conductors. For comparison, the thermal conductivity (k) of the copper is 401 W/m*K, while the thermal conductivity (k) of the air is 0.0263 W/m*K. The thermal conductivity of the carbon dioxide (CO2) is 0.01672 W/m*K, almost the thermal conductivity of an isolator.
Formula to calculate the conductivity gradient for a given system:
q = - kA (Δ T/Δ n)
Where Δ T/Δ n is the temperature gradient in the direction of area A, and k is the thermal conductivity constant obtained by experimentation in W/m.K.
CONVECTION: Flow of heat through currents within a fluid (liquid or gas). Convection is the displacement of volumes of a substance in a liquid or gaseous phase. When a mass of a fluid is heated up, for example when it is in contact with a warmer surface, its molecules are carried away and scattered causing that the mass of that fluid becomes less dense. For this reason, the warmed mass will be displaced vertically and/or horizontally, while the colder and denser mass of fluid goes down (the low-kinetic-energy molecules displace the molecules in high-kinetic-energy states). Through this process, the molecules of the hot fluid transfer heat continuously toward the volumes of the colder fluid.
For example, when heating up water on a stove, the volume of water at the bottom of the pot will be warmed up by conduction from the metallic bottom of the pot and its density decreases. Given that it gets lesser dense, it shifts upwards up to the surface of the volume of water and displaces the upper -colder and denser- mass of water downwards, to the bottom of the pot.
Formula of Convection:
q = hA (Ts - T ∞)
Where h is for convective heat transfer coefficient, A is the area implied in the heat transfer process, Ts is for the temperature of the system and T ∞ is a reference temperature.
RADIATION: It is heat transfer by electromagnetic waves or photons. It does not need a propagating medium. The energy transferred by radiation moves at the speed of light. The heat radiated by the Sun can be exchanged between the solar surface and the Earth's surface without heating the transitional space.
For example, if I place an object (such as a coin, a car, or myself) under the direct sunbeams, I will note in a little while that the object will be heated. The exchange of heat between the Sun and the object occurs by radiation.
The formula to know the amount of heat transferred by radiation is:
q = e σ A [(ΔT)^4]
Where q is the heat transferred by radiation, E is the emissivity of the system, σ is the constant of Stephan-Boltzmann (5.6697 x 10^-8 W/m^2.K^4), A is the area involved in the heat transfer by radiation, and (ΔT)^4 is the difference of temperature between two systems to the fourth or higher power.
A Heat Sink is a system capable of absorbing heat from an object with which it is in thermal contact without a phase change or a significant variation in temperature.
At Earth's location, the outer space, the gravity field (Guth. 1999. Pp. 29-31) and the false void are heat sinks.
Water has a specific Heat of 4.190 kJ/Kg.K, while air has a specific heat of 1.0057 kJ/Kg.K, and soil have a Specific Heat of 0.725 kJ/Kg.K.
Water has a Specific Heat higher than soil and air; then, the Thermal Capacity of water is higher than the Thermal Capacity of the air and the soil. To a greater Thermal Capacity, a slower rate of dissipation of heat.
The atmosphere and the soil don't maintain a load of heat for longer periods than water because they have a specific heat capacity lower than water, so water absorbs more heat for inreasing its temperature for a determined interval. For equal volumes (1Kg, for example), water absorbs more heat than air or soil. The absorbed heat will be transformed into kinetic and potential energy. A body with a high energy density will lose its inner energy slower than a body with a lower energy density. For example, if you have ten dollars and your friend has five dollars, and each one is obliged to spend one dollar per day, you will delay ten days to spend your money, while your friend will delay only five days to consume his money.
In general, the soil and the air have independently 1/4 of the specific heat of water. For example, the Specific Heat of Carbon Dioxide is 850 J/Kg °C; to be precise, 4.92 times less than the Specific Heat of water; then, its Thermal Capacity will be less than the Thermal Capacity of water. For equal masses of the evaluated substances, at controlled temperatures and pressure, the Carbon Dioxide will release its internal heat five times faster than the water. If one Kilogram of water at 30 °C is cooled by 10 °C in 10 minutes, one Kilogram of Carbon Dioxide at 30 °C would be cooled by 10 °C in two minutes. The rule is: If you get it fast, you will lose it fast. As an interesting datum, the Hydrogen has a Specific Heat of 14200 J/Kg -°C; while Methane, another of the famous "Greenhouse" gases, has 2200 J/Kg °C. Steam water has a Specific Heat of 2100 J/Kg-°C (Data on Specific Heat of the substances obtained from MONACHOS ENGINEERING and from Wittemann).
Water absorbs the incoming solar Infrared Radiation because the frequency of the internal vibration of the water molecules is the same frequency of the waves of the solar Infrared Radiation. This form of Radiative Heat transfer is known as Resonance Absorption.
We humans feel the heat radiated by the Sun and other systems with a higher temperature because our bodies contain 55-75% of water. The radiative energy inciding on our skin is absorbed by the molecules of water in our bodies by Resonance Absorption. Just then, the Infrared Radiation absorbed by our bodies leads to a more intense internal vibration of the water molecules in our bodies and our bodies get warmer. However, in general, living beings possess thermoregulatory systems that permit us to eliminate the excess of heat from our bodies, maintaining a quasi-stable internal temperature (it is one of the homeostatic processes of biosystems).
If the Earth did not have water, nights would be extremely cold.
For example, if the atmospheres of Mars and Earth had the same density, Mars would have an atmospheric CO2 concentration of 11998.5 ppmv. However, due to the lower density of Mars' atmosphere, the concentration of CO2 in that planet's atmosphere is equivalent to 0.95% on Earth; nevertheless, Mars is a frozen planet because Mars has only vestiges of water (0.03%) and it has not ponds, lakes and oceans, as Earth has.
Have you read that “the main explanation of the blazing Venus surface and the frosty Martian surface has been quite clear and straightforward: the "greenhouse effect”? This assertion is ambiguous because the real cause is the distance of Venus (nearly) and Mars (distant) from the Sun, and because Mars and Venus do not have water as Earth has. If the greenhouse effect was the responsible, then Mars, a planet with 95% of Carbon Dioxide in its atmosphere, would not be an iced, but a tepid planet. Besides, Mars only receives 589.2 W/m+e2 of solar irradiance, while Earth receives 1367.6 W/m+e2 of solar irradiance (2.32 times higher than Mars). Mars’ core has a temperature of 1727 °C (Fei and Bertka, Science; 2005), while the temperature of the Earth's core is 7,200 °C, ¡This is a core temperature four times higher than Mars' core temperature! Despite the low density of the Martian atmosphere, it has a concentration of carbon dioxide (CO2) of 0.95%, which is 29.5 times higher than the concentration of CO2 in Earth’s atmosphere. If the global temperature was determined by CO2, Mars would be comfortably warm. On the other hand, NASA has reported a Climate Change on Mars -i.e. a Martian Global Warming due to the "shrunk" of frozen deposits of CO2 on Mars means that its atmosphere's temperature has increased far from normal. The report on the Martian Global Warming from NASA says, “New impact craters formed since the 1970s suggest changes to age-estimating models. And for three Mars summers in a row, deposits of frozen carbon dioxide near Mars' South Pole have shrunk from the previous year's size, suggesting a climate change in progress.” (cursives are mine). Scientists have also observed that Venus, Jupiter, Saturn and its satellite Titan are experiencing Climate Changes, which indicates that the Climate Change and the Global Warming are phenomena which are taking place in the whole Solar System, which denotes a cosmic origin.
Many authors say that “Greenhouse” gases act as a “blanket” which reflects the heat back to Earth -i.e. “Some re-radiated heat reflected back to Earth” (Ultimate Visual Dictionary – The Atmosphere. DK publishing, Inc. p. 301. 1998) and “The reason is that the atmosphere functions like the crystals of a glasshouse. This is, the properties of absorption and conduction of glass are similar to those of the atmospheric greenhouse gases …” (Wilson, Jerry D. College Physics-2nd Edition; p. 382. Prentice Hall Inc. 1994).
There are other authors who discuss thermal events similarly as the writers I have quoted in the previous paragraph; I have found the same mistakes written on reports from NASA, NOA, EPA, etc. Those unintentional faults have been inflated by some pseudo-environmentalists and politicians that enforce the erroneous concept of "Greenhouse Gases", “Anthropogenic Global Warming” and “Manmade Climate Change”, closing their eyes to the Laws of Thermodynamics, Heat Transfer, Thermal Expansion, Physics Laws, etc.
The atmosphere is not a “glass”, nor acts like a glass. It either is a blanket that “reradiates” heat to the surface, or that obstructs convection. Far from impeding convective heat transfer, gases allow convection. CO2 is able to absorb the energy emitted by the ground and the oceans and transforms it into kinetic and potential energy. By these transformations from one class of energy into another, the CO2 emits radiant energy (energy in transit or heat), which is transferred by convection to the upper atmosphere layers. After it has been transferred to the upper layers of the atmosphere, the heat is released to the outer space (Heat Sink). However, we have understood that the current concentration of Carbon Dioxide cannot be a source of “Global Warming”. We would need about 560 ppmv for increasing the Earth’s surface temperature up to 0.7 °C.
The terrestrial atmosphere is a stratum composed by a mixture of gases (air) that wraps the Earth and is retained by Earth’s gravity.
The atmosphere stratifies according to differences of density and temperature. Nitrogen and Oxygen are the predominant constituents in all layers, but each layer is less dense than the previous layer, starting up from the troposphere which is the denser layer (density = magnitude of mass per unit of volume; for example, the density of liquid water is 1 Kg per liter).
The quantity of mass of air per unit of volume decreases as height increases. At sea level and 288.2 K (15.2 °C or 59.36 °F), the density of air is 1.225 Kg/m+e3 and its thermal conductivity is 0.02596 W/m K.
However, like all materials, when gases warm up their density decreases because their molecules vibrate faster and are scattered (expansion). Thus, the volume of air is enlarged to a maximum value, but its density decreases because its molecules distribute in a greater volume. If the gas expansion were not feasible, then the pressure exerted by the gas would increase; for example, inside a closed container or into the cylinders of a modern engine.
At my childhood, I performed a very dangerous experiment with an empty glass container (a flask of instantaneous coffee) that I placed into an empty wood box (after all, I took a few precautions). I placed the box on a firewood stove and kept waiting. I do not remember how long it delayed, but the flask was cracked out and, after few minutes, it exploded (DO NOT TRY IT AT HOME!). The expansion of the glass cracked the flask, and the expansion of the air trapped inside the flask blew it up. Obviously, thermal energy was the driver.
Vertical convection does not occur in the stratosphere because in this layer of the atmosphere the gases move only horizontally; consequently, the main modes of heat transfer in the stratosphere are radiation and conduction; however there is horizontal convection in the stratosphere known like advection, which is a horizontal heat transfer due to the horizontal displacement of air masses. The advection in the stratosphere is chaotic (cat’s eyes).
QUESTION FROM A STUDENT: If air has a density of 1.29 Kg/cubic meter and the water's density is 1.00 Kg/cubic meter, why the air does not submerge into liquid water?
ANSWER: First of all, you forgot to write "x 10+e3" after the density of liquid water. You should have written: "If air has a density of 1.29 Kg/cubic m and the water's density is 1.00 X 10+e3 Kg/cubic m..." If we express the quantities without the notations based on 10, we will read the phrase as follows: "If air has a density of 1.29 Kg/cubic m and the water's density is 1000 Kg/cubic m...", which clearly denotes that the air is less dense than the water. Regarding your question, if placed in denser mediums, the less dense materials would tend to float. As the air is less dense than water, it will move to the surface of water.
When we deal with ice (water in solid phase), given that the ice has a density of 920 Kg/cubic m, which is less dense than the water in liquid phase (1000 Kg/cubic m), the ice will tend to float in the mass of liquid water; however, only a portion will remain totally submerged in the water because the relation between the densities of ice and liquid water is 92%; this means that only the 8% of the ice will float above the surface of the water in the liquid phase. For an iceberg, we would only see an 11% of the complete block of ice above the level of water because seawater has a density of 1030 Kg/cubic m (920 ÷ 1030 = 0.89; 0.89 is equal to 89%).
ALGORITHM AND EXAMPLE FROM REAL LIFE
If soil absorbs heat and its temperature in 31 March 2007 at 13:15 hrs is 348.15 K (75 °C) and the temperature of air is 300.15 K (27 °C), what would be the tropospheric ΔT if we consider the absorptivity-emissivity of CO2?
To know the answer, we have to know first the heat transfer from the soil to the mixed air. Primary, we have to obtain the Grashof Number and the Convective Heat Transfer Coefficient for those particular conditions:
Gr L = g β (Ts – T ∞) D^3 / v^2
g is the gravitational constant (9.8 m/s)
β is the volumetric expansion coefficient
T1-T2 is the difference of temperature between two adjacent systems expressed in Kelvin
D is the distance between the two systems
v is the velocity of heat transfer between two systems.
Gr L = (9.8 m/s^2) (2.857 x 10^-3 K^-1) (48 K) (1 m)^3 / (2.076 X 10^-3)^2 m^4 /s^2 = 0.699965 m^4/s^2 / (2.076 X 10^-3)^2 m^4 /s^2 = 3.12 x 10^5
Convective Heat Transfer Coefficient:
Ћ = ------- (C) [(Gr) (Pr)]^1/4
k is the thermal conductivity
D is the distance between the two systems
C is a correction factor for heterogeneous systems
Gr is the Grashof Number
Pr is the Prandtl Number
a is the constant of proportionality for natural laminar systems.
Ћ = ------------------------------ (0.60) [(3.12 x 10^5) (0.697)]^1/4 = 0.389 W/m^2*K
The heat transfer from soil to mixed air is:
q = Ћ A (Ts – T ∞) = 0.389 W/m^2*K (1 m)^2 (48 K) = 18.7 W
18.7 W = 4.47 cal/s
If m of mixed air = 1.18 Kg/m and the Cp of mixed air at 300.15 K = 1005.7 J/kg*K (240.37 cal), then:
Δ T = q / m (Cp) = 4.47 cal/s / (1.18 Kg/m^3 ) (240.37 cal) = 4.47 cal / 283.64 = = 0.016 °C/s
If 0.016 °C is the ΔT caused by the thermal transfer by conduction-convection from the ground to the total mixture of air each second, then we must first warm up the soil and the oceans for the next reason:
The energy absorbed by dry air from incoming Solar radiation is 697.04 W/m^2 X 0.14 (absorptivity of dry air at T = 300.15 K, and P = 1 atm) = 18.7 W/m^2 = 4.47 |cal/s| / m^2.
Considering the same conditions but including water vapor (relative humidity of 50%), the temperature caused by the heat absorbed by water vapor and carbon dioxide, taken independently, is:
Heat absorbed by water vapor: 278 W = 278 J/s (absorptivity = 0.75)
Heat absorbed by carbon dioxide: 0.4 W = 0.4 J/s (absorptivity = 0.001 at its current partial pressure)
Change of temperature by the load of heat absorbed by water vapor:
ΔT = 278 J / 0.013 Kg (1864 J/Kg °C) = 11.5 °C
Change of temperature by the load of heat absorbed by carbon dioxide:
ΔT = 0.4 J / 0.00067 Kg (871 J/Kg °C) = 0.7 °C
Applying the algorithm to know the load of heat absorbed by CO2:
q Stored = m (Cp) (ΔT) / Δt
Mass of atmospheric CO2 = 0.00067 kg
Cp CO2 = 871 J/kg K
ΔT = 48 K (348.15 K - 300.15 K)
Δt = 60 s
q Stored = 0.00067 Kg (871 J/kg K) (48 K / 60 s) = 0.47 J/s
Δ T = q / m (Cp) = (0.47 J/s)/ |0.00067 kg (871 J/Kg*°C)| = 0.8 °C
Therefore, water vapor is the main driver of the warming effect of the atmosphere. On this case, water vapor absorbed the infrared radiation, emitted by the surface, 14 times more efficiently than CO2. (Martin Chaplin. 2009)
The following diagrams illustrate the mechanisms of heat transfer between the surface and the atmosphere in Earth, as well as how clouds and rain and hail are produced, and the effect of induced emission upon spontaneous emission. | <urn:uuid:e75d3108-a88b-48fc-9d90-3b168a47faff> | 4.15625 | 4,758 | Knowledge Article | Science & Tech. | 68.071847 | 1,818 |
Ron Coleman is a Canadian currently an Assistant Professor at California State University, Sacramento. He is interested in cichlids both as a scientist and as a hobbyist. As a scientist, he tries to understand how and why parent fish take care of their kids. This has led him to a great interest in egg size and he is founder of the Cichlid Egg Project. He works both in the lab and in Costa Rica and writes for the scientific literature as well as various hobbyist publications, including Cichlid News. His favorite fish is Tomocichla tuba.
Ron also maintains the Great Cichlid Research home page.
Ron puts his interest in cichlids as follows;
I am interested in cichlids from two angles, both as a scientist and as a hobbyist. On the hobbyist side, it is hard to beat cichlids as entertaining an just plain interesting animals to have around. They are intelligent and curious creatures that come in so many shapes, sizes and colors that I find it hard to believe that anyone could not be fascinated by them.
Many of these same qualities of cichlids make them fascinating to me as a scientist. The sheer diversity of the family offers countless opportunities to evolutionary biologists like myself.
The goal of my research is to understand the key processes that shape the characteristics of organisms. Those characteristics might be solid physical things, like the size of the body, or more intangible things like behavior.
The approach I use is called life history theory which in a nutshell argues that most every aspect of an organism is the product of tradeoffs. This means that there are costs and benefits to every aspect of organismal design. For example, why is the giraffe's neck so long? The giraffe gains many benefits from its long neck: the ability to forage on vegetation far above the ground, the ability to see potential predators at great distances, etc. But, balanced against these benefits are an equal number of costs: giraffes have great difficulty drinking, they aren't very well balanced, can't jump hardly at all, and are pretty easy to spot at great distances as well.
As I see it, the goal of modern biology is to understand the costs and benefits of the characteristics of organisms we see around us. In this way, we can hope to understand what is "driving" nature and this will allow us to make intelligent choices on this ever-more-crowded planet.
Cichlids, are nature's gift to the evolutionary biologist. So many questions of evolutionary biology are stiffled because of the lack of diversity in many groups of organisms. For example, the North American sunfish are a fabulously interesting group of fishes and few things can match a male bluegill sunfish protecting his nest and babies. And yet, we can never answer the question of why it is the male bluegill that guards his nest rather than the female by studying sunfish. Why? Because it is the same for all sunfish. All species in the family exhibit male care so we have nothing to compare them with. This is not the case in cichlids. There are so many cichlids, doing so many different things, that we can look into this vast treasure chest of diversity and seek out comparisons to help illuminate the biology we see. In vertebrates, cichlids are unmatched for this breadth of opportunity. | <urn:uuid:a50d5274-e0de-499f-8179-913eb8e6fd6e> | 2.71875 | 701 | About (Pers.) | Science & Tech. | 45.549552 | 1,819 |
The meteor that slammed into Russia in February injured about 1,000 people and freaked out many more. Recent months have highlighted the danger of larger space objects that could bring doomsday if they collide with our planet.
Aside from death and taxes, there's another thing certain in life: meteors. To get a historical perspective on just how many dazzling space rocks have fallen through our skies in recent times, peep at Carlo Zapponi's visual graph called Bolides, which puts meteor strikes in a chronological view.
Inspired by the Greek word bolis (missile), Bolides features data from a range of historical meteor records, ranging from MetBase to London's Natural History Museum catalog of meteorites, and displays the data in a way that makes you want to click around and explore. … Read more
Shortly after a large meteor hit Russia in February, injuring about 1,000 people, President Obama's administration announced that the U.S. would work on asteroid tracking technology to avoid potentially more severe Earth collisions. On Monday, top NASA administrator Charles Bolden reiterated this pledge.
Bolden spoke at the Human to Mars Summit in Washington, D.C. on Monday and said that a robotic spacecraft mission currently being planned will "prepare efforts to prevent an asteroid from colliding with devastating force into our planet,"according to U.S. News & World Report.
The government's plan is … Read more
The meteor shower created by the debris trail of Halley's Comet will peak Sunday evening, and NASA is providing a live view of the celestial fireworks show.
Prime viewing of the annual Eta Aquarid meteor shower should be around 9 p.m. ET, providing stargazers with 30 to 40 meteors an hour, according to NASA. A camera at NASA's Marshall Space Flight Center in Hunstsville, Ala., will provide live video of the event from 8 p.m. ET to 3 a.m. ET Monday (see below).
The Lyrid meteor shower is peaking right now, and NASA wants to make sure you don't miss this once-a-year space fireworks show.
Mindful that some stargazers may not have optimum viewing conditions because of local weather conditions or the moon's glow, NASA has set up a camera at the Marshall Space Flight Center in Huntsville, Ala., to broadcast live images of the meteor shower.
"If you'd like to catch a last look at 2013 Lyrid meteror shower, this is your chance!" NASA said in a statement. "Although a bright moon may interfere with viewing, … Read more
Apparently the bright object that people reported seeing shooting over the East Coast of the United States last night -- and that left a glittery trail across Twitter -- may well have been a meteor.
Bill Cooke of NASA's Meteoroid Environmental Office told the Associated Press that, "going on visual reports," the flash was "a single meteor event."
"The thing is probably a yard across. We basically have (had) a boulder enter the atmosphere over the northeast," he added.
The object lit up Twitter last night at about 8 p.m. East Coast … Read more
At a House Committee hearing today, NASA administrator Charles Bolden Jr. was asked what America would do if a meteor similar to the one that hit in Russia on February 15 was found to be on a path toward New York, with impact three weeks away. His response? "Pray."
At the moment, we might be lucky to get even three weeks' warning. The United States and the rest of the world simply do not have the ability to detect many "small" meteors like the one that exploded over Russia, which has been estimated at roughly 55 … Read more
Capitalism is certainly alive and well in today's Russia, as demonstrated by the growing number of attempts to cash in on the recent and much-recorded (thanks to the help of ubiquitous Russian dashboard cams) meteor strike in Siberia.
The meteor that broke up over the city of Chelyabinsk while also producing a window-shattering sonic boom and momentarily outshining the sun has become a cash cow for many opportunistic folks now offering up purported fragments of the space stone on eBay and elsewhere online.… Read more
Subscribe to Crave:
This week on Crave, William Shatner has some choice words for J.J. Abrams, and we toss one back in the greatest drinking game ever invented. Cheers! Plus, we dodge a bullet the size of a football field as an asteroid nearly collides with Earth. Phew. … Read more
Leaked from today's 404 episode:
- Fiery meteor explodes over Russia's Ural Mountains; 1,100 injured as shock wave breaks windows.
- Watch asteroid 2012 DA14 fade out via streaming video.
- Iceland wants to ban Internet porn.
- Chubby Checker in a twist over an old app.
- One Direction's new toothbrush streams sound vibrations through your teeth.… Read more | <urn:uuid:83832394-1775-42ae-9db8-8eac0782a93f> | 3.515625 | 1,033 | Content Listing | Science & Tech. | 56.716944 | 1,820 |
Lecture 9: Understanding Run-time Environment Representation and Control
In Algol-like languages like Pascal, Algol W, and C/C++, all of the environments that exist at any point during a computation can be collectively represented using a stack. This representation for environments is particularly advantageous because the environment stack can be implemented as an elaboration of the control stack included in the architecture of a modern computer to support procedure calls.
Algol-like languages are almost always compiled to machine code instead of interpreted like LC and Jam. Nevertheless, during program execution, the compiled machine code must perform all of the same operations on program data structures as interpreted code. The major difference between the two approaches is that a compiler typically has the opportunity to perform far more program analysis enabling it to precompute quantities that are computed by an interpreter during program execution.
Almost all modern machines provide a control stack to store the return addresses of procedure calls. In addition, other context information (such as the contents of registers that must be restored by the called procedure) is typically saved with the return address in a frame on the control stack. To return, the called procedure pops the current ("top") frame off the stack, restores the saved context information (typically the contents of registers that by convention must be preserved across procedure calls) and jumps to the specified return address. The popping of the "top" stack frame off the stack restores the stack to the form it had before the call (although some of the bindings for local variables stored in the stack may have changed).
Some machines also pass argument values to procedures in the stack. The argument values are pushed on the stack along with the return address and the saved context information. Another common convention is to pass arguments (assuming the number is small) in registers. The result returned by a procedure is typically returned in a register because the stack frame associated with the call is deallocated on return. (Another possible convention is to store the return value in a designated location in the calling stack frame.)
Now let us relate the stack representation of environments to our understanding of the evaluation of programming languages with lexical scoping, i.e., the (recursive) let and lambda constructs. We have discussed lexical scope in the context of mostly functional languages based on the lambda-calculus, but exactly the same lexical constructs are present in Algol-like languages. In Algol-like language, a rec-let is called a block and a lambda (which must occur as a rhs of a definition introduced in a block [rec-let definition]) is called a procedure declaration.
In a stack-based implementation of a lexically-scoped language, a new environment is constructed (the extend-env process in our LC interpreter) to evaluate the body of a let or a lambda application by allocating a new frame called an activation record on the control stack. The activation record contains:
In this representation, an environment consists of a linked list of activation records; the link field connecting this list static link in each record. The first record in the sequence gives the local bindings (static distance 0), the second record gives the bindings at static distance 1, and so forth. The length of this list is simply the lexical nesting level of the body of the let form or lambda application being evaluated.
For let invocations (regardless of whether let is recursive)
(let ([x1 e1] ... [xn en]) E)
and raw lambda applications
((lambda (x1 ... xn) E) e1 ... en),
the static link and dynamic link in the new activation record both point to the same place, namely the preceding activation record on the stack (the activation record for the enclosing let form or lambda application.
For a function application
(f e1 ... en)
the static link in the new activation points to the activation record in the static chain corresponding the static distance between the application site and the definition of f. For a simple recursive function call (e.g., the recursive call in the usual definition of factorial), this static link is identical to the static link in the calling activation record (the preceding activation record on the stack).
In Algol-like languages, the only closures are functions that are passed as arguments to other functions. These closures are represented by a pair of pointers. One pointer points to a representation of the the function consisting of a record with the code for the function (or a pointer it) and a template describing the format of its activation record. The other pointer is the static link to be stored in the activation record for the closure when it is invoked (the saved environment for the closure).
In Algol-like languages, closures can only be passed as function arguments. As a result, the activation record identified by the static link stored in the closure is always available on the stack when the closure in invoked. When that activation is finally freed, the corresponding closure is guaranteed to be inaccessible. (Since C/C++ has no nested blocks or procedure definitions, closures degenerate to function pointers.)
The stack representation of environments breaks if a closure can be invoked after the activation record to which it points (through its static link) is deallocated ("popped"). The activation record no longer exists and the storage it occupied may have been reused. If the closure code tries to refer to a variable in the deallocated record, it retrieves corrupt data. Algol-like languages restrict the usage of closures to prevent this problem from occurring. (In C/C++ the same problem can arise if a data structure points to an object on the stack. Unfortunately, C/C++ does nothing to prevent the catastrophe that occurs if the activation record containing the object is deallocated while the reference still exists.)
In the absence of tail-call optimization which converts procedure calls to jumps, every procedure call allocates a new stack frame. Hence, a recursive procedure may allocate a large number of stack frames. The standard definition of the factorial function, for example, allocates 1001 frames to evaluate 1000! In this case, all of the activation records for invocations of factorial have the same static link.
Programs written in "advanced" languages like Scheme, ML, Jam, and LC can obviously be restricted to accommodate the stack representation of environments by prohibiting closures from being returned as values or stored in data structures. But this restriction reduces these advanced language to Algol with a garbage-collected heap. To accommodate general closures, two implementation strategies are widely used.
The first strategy is to abandon the stack discipline for managing activation records by allocating activation records in the heap and relying on garbage collection to reclaim the storage occupied by activation records. This approach does not use the control stack mechanism provided by the underlying computer architecture.
The second strategy uses a hybrid representation scheme for environments that supplements the stack representation with information stored in the heap. The critical flaw in the stack implementation is that it destroys variables when the evaluation of the corresponding lambda returns. If such variables are stored in the heap and the closure knows how to find them, then the static link stored in the closure representation is unnecessary: all lookups that would have followed the static chain simply access the appropriate variables in the heap. Such an implementation must identify the set of variables that occur free in each lambda-expression and force them to be allocated on the heap (adding a level of indirection to the access protocol). The activation records that would have contained these variables now contain pointers to them (located in the heap) instead. Fortunately, the "closure analysis" required to determine which variables must be heap allocated is easy for a compiler to do.
In the hybrid strategy for supporting closures, the activation record template used to represent a closure must include a pointer field for each free variable in the closure. When a lambda-expression is evaluated, an activation record template is allocated and the values of the pointers to free variables are copied from the relevant activation records on stack.
It is possible to build a good language implementation using either strategy. The hybrid scheme adds a level of indirection to some variable accesses (ordinary lookups of heap allocated variables) but reduces it in others (free variable lookups from within closure bodies). Overall, the hybrid scheme has a modest advantage because it manages memory allocation for activation records more efficiently (through memory reuse and less fragmentation). In addition, the hybrid scheme tends to recover more free memory during garbage collection because it only retains the variable bindings that actually appear in closure bodies, while the brute force heap allocation scheme retains all bindings in the activation records accessible to closures.
In the course of an computation, an exceptional condition may be encountered that requires abandoning a subcomputation. If that subcomputation has a large number of associated stack frames, the "bubbling" action require to pass a special value back up the call chain is time-consuming and awkward to program. What we want is a construct that lets us label a selected stack frame as a recovery point and return a value directly to that frame (just as if the next stack frame had returned normally). The "direct return" operation deallocates all of the stack frames from the current frame back to the recovery frame; this can be done simply by changing the contents of the register serving as the stack pointer. In addition, it places the return value in the standard place (usually a register) in determined by the procedure calling conventions.
In the simple stack representation of environments described above, the only two control operations are function invocation/block entry and function return/block exit. What if want to return a value directly to an activation record many layers above the activation record identified by the dynamic link? In a vanilla Algol-like language, we cannot do this. We must ``bubble'' the value up through intervening stack frames (via return operations in each context) until we get to the target context.
We need a more general control construct than function return to jump back through multiple stack frames as a single operation. An exception facility like catch/throw in Java is such a construct. Throwing an exception unwinds the stack (following the dynamic chain) until a matching catch operation is found. The matching catch can then extract a value embedded in the exception object. A naive implementation of the throw operation literally follows the dynamic chain and performs the requisite tests. A more sophisticated implemented includes a catch link in each frame pointing the nearest frame on the dynamic chain with an attached catch handler. Then only catch links need to be followed. An even more sophisticated implementation (which works for a simple exception system) maintains a global table of the matching activation record address for each possible exception. (In Java, the appropriate design for this table is an interesting problem because exception matching is hierarchical, catch construction may include finally clauses that must be executed regardless of whether any of the catch clauses match, and programs can be dynamically extended during execution!)
Standard Scheme does not include an exception facility because it includes
a significantly more powerful control operator called letcc. (R4RS
Scheme uses a syntactic variant of letcc called call/cc.)
Here are some examples of the behavior of
(letcc Xit (+ (Xit 15) 5)) = 15
(letcc Xit (lambda (x) (+ (Xit (lambda (x) 5)) x)))cannot be evaluated any further;
(lambda ...)is a value, and
Xitoccurs free in it
((letcc Xit (lambda (x) (+ (Xit (lambda (x) 5)) x))) 25)
= (letcc Xit2 ([lambda (x) (+ ((lambda (v) (Xit2 [v 25])) (lambda (x) 5)) x)] 25))
= (letcc Xit2 (+ ((lambda (v) (Xit2 [v 25])) (lambda (x) 5)) 25)
= (letcc Xit2 (+ (Xit2 [(lambda (x) 5) 25]) 25)
= (letcc Xit2 (+ (Xit2 5) 25)
In general, when a
letcc expression is evaluated, it turns its current
context (as in, ``complete textual context'') into a procedural object. This procedural
object is also known as a continuation object. When a continuation object
is applied, it forces the evaluator to remove the current evaluation context and
to re-create the context of the original
letcc expression, filled
with the value of its argument. Like procedures, continuation objects are first-class
values, which means they can be stored in data structures or tested by predicates.
In essence, letcc takes the current activation record and program counter at the point of invoking letcc and encapsulates them as a procedure waiting for a value to be returned. The body of the letcc is evaluated in the current environment extended by the binding of the letcc continuation name to the encapsulated procedure -- just as the body of a conventional let would be evaluated in an environment extending by the bindings specified in the definitions at the head of the let.
Now we understand the semantics of
letcc, but how do we use it
to write programs? We need to also understand its pragmatics. For instance,
letcc can be used for exception handling.
Let us write a procedure,
lod ::= null | (cons [0-9] lod)
Our procedure might look like this:
(define PiHelp (lambda (l) (cond ((null? l) 1) (else (* (car l) (PiHelp (cdr l)))))))
However, suppose it is possible that we can get an invalid digit (in the range
((bad? (car l)) (Xit #f))
We use the following recipe for constructing such programs:
If we pass this new procedure exceptional data, we get
(Pi '(1 2 b)) ==> (letcc Abort (PiHelp '(1 2 b) XXX)) ==> (letcc Abort (* 1 (*2 (PiHelp #f)))) ==> #f
There are numerous control constructs that we can add to LC. Some of these are:
(raise M)stops computation and returns the value of
(raise M)corresponds to an exceptional datum condition for the meta-evaluator. Hence, it can be added to the evaluator by following the steps above.
raiseby delimiting the extent to which it can escape. Such a construct is called an abort delimiter, and is sometimes written as
(lambda (f G) (open-file f) (G f) (close-file f))
raisestatement, then the file will never be closed. This might be undesirable. To prevent this, we can instead write
(lambda (f G) (open-file f) (# (G f)) (close-file f))
#can be added to the evaluator with the following code:
((#? M) (letcc NewXit (MEval (#-body M) env NewXit)))
(# M H)where
His invoked only if
Maborts. (The code in
Hmight typically be used to perform some clean-up action.) Additional extensions are possible: we could have labeled exceptions, and we could also have restartable exceptions (where
raisereturns a value and the continuation active at the time it was invoked).
Here is the core of an interpreter that implements
This version of
# takes a body and a handler, as outlined above.
The handler takes one argument, which is the value ``thrown'' by
(define MEval/ec (lambda (M env Exit) (cond ... ((raise? M) (Exit (MEval/ec (raise-expr M) env Exit))) ((#? M) ((letcc new-Exit (lambda () (MEval/ec (#-body M) env (lambda (raised-value) (new-Exit (lambda () (MApply/ec (MEval/ec (#-handler M) env Exit) raised-value Exit))))))))))))
(Note that all calls to the former
MEval will now have to call
instead, passing on the
Exit handler unchanged; only
installs new handlers.
MApply/ec is similarly modified.)
At this point, we will conclude our study of meta-interpreters. We have thus far covered the following:
It would be worthwhile to note in passing some of the topics that we did not cover but which could be studied with the same methodology: | <urn:uuid:300e8cb1-2f85-4e7a-9f72-9628af51c9f1> | 3.640625 | 3,448 | Academic Writing | Software Dev. | 37.32947 | 1,821 |
Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Accelerated erosion and loss of surface soil (continued)
Grazing animal density in the Extensive Land-use Zone [L Indicators 1.2A and 1.2B]
The arid and semi-arid regions that make up what is often described as the Extensive Land-use Zone (ELZ) (Graetz et al. 1996) occupy nearly 6 million km2, of which nearly two-thirds carries domestic stock for commercial grazing. Animal densities are very low throughout, but range from extremely low (0.5 cattle units/km2) in the less fertile western half of the continent, to low (1-2 cattle units/km2) in the more fertile eastern rangelands.
Domestic grazing animal numbers in this vast region account for less than 13% of total sheep and 25% of total cattle numbers in Australia (Figure 10). These differences in density are associated with broad differences in productive capacity. In the western spinifex sandplains and chenopod shrublands of the west and south it takes 10-20 hectares to support one sheep (1 cattle unit or 8-10 DSE per km2), compared with the savanna woodlands and Mitchell grass plains of the north-east where the safe stocking rate is 4-6 cattle unit per km2. As a general rule, sheep predominate in the southern parts of the rangelands and cattle in the north. However, there are significant areas of overlap in the Channel Country, and in the mulga lands of north-western New South Wales and south-western Queensland.
Figure 10: Domestic stock densities in 1997.
Source: NLWRA 2001
In the period 1990-1998 the total number of sheep declined steadily from 173 million to 121 million, whereas the number of cattle fluctuated only 1-2 million around the average of 23 million. The steady decline in sheep numbers during this period can be safely attributed to the continuing low wool prices and unprofitability of sheep-based enterprises over much of the decade (Ha and Chapman 2000). Live cattle exports to South East Asia and fattening enterprises directing stock into high-value markets in Japan and north America have influenced the higher numbers of cattle in the tropical, northern parts of the rangelands (ABARE 1999).
There is considerable evidence that the worst pressure on much of the pastoral rangelands in recent decades occurred in the 1970s, when stock numbers were about twice the numbers in the 1990s, and before the Landcare movement was established in 1989. In many areas these pressures and earlier periods of overgrazing led to massive vegetation loss and accelerated erosion that have left landscapes permanently degraded.
There has also been more intensive action to control feral cattle through the brucellosis and tuberculosis eradication programs in northern Australia. Feral pigs, goats, donkeys, horses, and buffalo have all been subjected to control programs coordinated through national strategies, and the rabbit calicivirus disease (RCD) has had its greatest effect in reducing rabbit populations in the more arid regions. All told it is estimated that these may have reduced grazing pressure to between 10 and 90% of the levels experienced in the 1980s.
The National Land and Water Resources Audit (NLWRA) rangelands theme recently estimated the long-term changes in stocking numbers (and other vertebrate herbivore numbers) in the Extensive Land-use Zone (ELZ). The project will later relate these to modelled biomass production based on climate statistics and the 'Aussie-grass' pasture growth model (McKeon et al. 1990). Figure 11 shows the changes in stocking density for two selected years: 1996 and 1999. Some regions have experienced very large changes over the period.
Figure 11: Reductions and increases in stocking densities (DSE/km2) in the Extensive Land-use Zone, 1996 and 1999.
Sources: Hall et al. (2001), NLWRA.
In 1993 a very thorough review was undertaken to assess the economic viability and ecological sustainability of the rangelands (Wilcox and Cunningham 1994), following a comprehensive survey of the record the condition, productivity and sustainability of pasture lands of northern Australia by Tothill and Gillies (1992). Both reports identified widespread vegetational degradation and other ecological changes, such as extensive weed invasion, rill and gully features, soil salinisation, and bare scald extension linked to overgrazing.
Part of the degradation in the Northern Territory and Western Australia, such as that in Victoria River district and Ord River catchments, is largely the result of earlier periods of mismanagement. Eradication campaigns against bovine brucellosis and tuberculosis in the 1980s and 1990s have controlled animal numbers, and reduced feral animal populations. Unfortunately, recent surveys (e.g. ABARE 1999) suggest that the higher-productivity regions of the central and eastern rangelands are still being used unsustainably, with consequent continuation of vegetation and land degradation. This is occurring particularly where the more productive regions are fragmented topographically within larger areas of low productivity.
Before the National Land and Water Resources Audit, the principal aim of land condition surveys was to assess rangelands from the perspective of grazing industry utilisation, rather than ecosystem integrity. Nevertheless these surveys show clearly that land, where there are the signature indicators of severe soil erosion, such as gullying, bare salt scalds, complete loss of topsoil ('Class 3' land) and large tracts of land where there is often massive weed invasion largely through overgrazing of more palatable herb and grasses ('Class 2' land) cannot support continuing 'business-as-usual' pastoralism, from an economic as well as ecological perspective (Tothill and Gillies, 1992, Johnston et al. 1996, Water and Rivers Commission 1997).
Table 5 compares some of the features from the combined Tothill and Gillies (1992) and Wilcox and Cunningham (1994) studies with those undertaken for the National Land and Water Resources Audit and other recent studies.
|Region||Major vegetation types||1993 A estimated area of land degraded||1993 B stock animal numbers||Change in stock animal numbers 1996-1999 C||1997-1999 estimated area of land degraded|
|KimberleyPilbara||Eucalypt woodland, various grasslands, Sorghum australiense, spinifex with bare ground||1 6% severe gully/sheet erosion, 20% degraded vegetation||643,000 cattle, some sheep in central-south, (WA Bushlands)||Cattle densities unchanged between 0.4-5.4 /100 ha. Sheep few, densities have declined to 0.5/100 ha||20-25% overgrazed in Timor Sea drainage division: 50% overgrazed in Indian Ocean division D|
|Darwin-Gulf||Kangaroo-grass, perennial sorghum grass, spinifex, some Mitchell grass patches||< 1% soil or vegetation degraded, but poor productivity||232,000 cattle||Cattle no change (0.4-3/100 ha). Sheep declined from 5-0.5 /100 ha||No more recent information available|
|Victoria River and Barkly Tableland||Mitchell grass and bluebush, soft spinifex||2.5-5% severely affected. Lack of data elsewhere||384 000 cattle (Victoria River)457 000 cattle (Barkly Tableland)||Cattle increase from about 5-10 /100 ha.Sheep down to <1/100 ha||Death of some Mitchell grass due to drought in NW F|
|Alice Springs||Spinifex predominates; some mulga with annual grasses||Severe bare areas in Todd River plains; Eragrostis degraded||297 000 cattle||No change in cattle densities (0.4-1.5 /100 ha). Sheep static or less||No more recent information available|
|Cape and Gulf||Low eucalypt woodland with various grass types||Declining grassland condition, cover and type||586 000 cattle||Cattle no change (average 3/100 ha). Sheep decreased from 5-0.5/100 ha||No more recent information available|
|North East Uplands, Queensland||Eucalypt woodland, brigalow, bluegrass treeless plains. Black speargrass, Aristida spp. , some Mitchell and soft spinifex||8 out of 10 grass types more degraded over 1980-1990s||1.2 million cattle and 2.2 million sheep||Cattle some increase (6-10/100 ha) big range in sheep but increasing, from 6-34, to 10-50/100 ha||Aristida sp. communities declined 1992-1997; prickly acacia (A. nilotica) now covers 28% of Mitchell grass shires F|
|Western Plains Queensland||Extensive grasslands, mulga, gidgee, other Acacia woodlands, spinifex||18 pasture types, with 6 degraded, 5-50% degraded by erosion, parthenium and prickly Acacia weeds||
2 million cattle and
8 million sheep
|Cattle no change (1.5-3), sheep decreasing, from 2-10/100 ha to 0.5-6/100 ha||No more recent information available|
|Western Division NSW (Far Western Plains)||Mulga woodland, box and cypress pine, mallee woodlands, floodplain grasses, saltbush and bluebush||11 systems, all showing soil erosion, weed invasion, rabbit warrens and vegetation depletion D||
137 000 cattle and
5 million sheep
|Cattle have doubled in number, sheep down by 25% E||
Kangaroos more than monitored. G50 000 ha woody weed cleared
(20 000 per year) I , 202 000 ha cleared of warrens. ELess than 5% vegetation types in reserves I
|WA Bushlands (south and east of Pilbara to Nullarbor)||NW-SE tussock grasses and acacias, mulga, mallee eucalypts, chenopod shrubs||<1% severe erosion, 30% degraded vegetation, 33% fair condition, rest not grazed||
2.5 million sheep,
|Low densities and few cattle, sheep no change (0.5-3.5/100 ha)||<10-15% of Western Plateau division in poor-fair vegetation condition. 70% not grazed and undisturbedD|
|Northern South Australia||Low shrublands and mulga to north, saltbush, bluebush, grasses and acacias to south||Up to 30% of historically degraded vegetation, but most regions better in 1990 than in 1970 from controls||137 000 cattle north of dog fence, 1.3 million sheep south of dog fence||Cattle increase (0.4- 1.4/100 ha), sheep increase, from 0.5-2.1 to 2.1-4/100 ha||20-30% still degraded from past effects. Only slow recovery despite destocking because poor seasons H|
A Wilcox and Cunningham (1994).
B Tothill and Gillies (1992).
C Hall et al. (2001), NLWRA rangeland grazing pressures project (unpublished).
D Waters and Rivers Commission (1997).
E Kerin and Hyder Consulting (2000).
F State of Queensland (1999).
G Pople and Grigg (1999).
H SA Department of Environment, Heritage and Aboriginal Affairs (1998).
I EPA NSW (2001).
Cattle and sheep densities show the general trend of increased cattle densities in the northern, more fertile regions, but decreasing sheep densities in most areas. Low-productivity regions such as the Western Australian Bushlands and northern South Australia have maintained low or declining densities. More recent information on the condition of rangelands in the north and eastern parts of the rangelands will be welcome when the NLWRA rangeland project on historical trends in grazing density and pressure is completed, as little additional information has been forthcoming from State of the Environment reports for Queensland (State of Queensland 1999) or New South Wales (EPA NSW 2001).
The effect of RCD has been very great in the southern half of the rangelands where rabbits have been reduced to less than 10% of their former numbers. The challenge now is to sustain this improvement and to extend the effect into the higher rainfall regions.
The issue of how vegetation type affects the susceptibility to degradation and erosion pressure has been the focus of concern in the animal grazing industries and among conservation ecologists, particularly in north-eastern Australia, where woody weeds are a serious concern to pastoralists (see Introduction of novel biota into native habitats and communities). Many grazing properties in this area have experienced a large increase in woody weeds over the past two to three decades; 50% of cattle properties in Queensland have an average of 2000 hectares of woody regrowth (ABARE 1999). On these properties more than 90% of the land grazed is woodland of some type or other and is described either as forest or woodland by the National Forest Inventory (see Agricultural best practice).
Pastoralists consider it essential to clear some timbered land to maintain grazing productivity, and 63% considered their productivity has declined as a result of woody regrowth in ABARE's (1999) survey. Nevertheless, woody regrowth in many cases takes place as the result of current or past grazing practices, and occurs predominantly in native woodlands that are grazed. Whether such regrowth is regarded in a negative or positive light is a matter of value judgement, reflecting the diversity of opinion that exists on this matter.
Regeneration of trees is restricted where animals graze in woodlands, as seedlings are grazed out. A reduction in grazing pressure has been associated with rapid regrowth of shrubs and trees when sheep have been removed (Cooney 1995). The Regional Forest Agreement process is redefining grazing lease areas in some areas as old growth forests in NSW and Queensland, leading to strong adverse reaction from graziers (The Land 2000). This provides a telling example of the tensions that arise from different views about how these forests and woodlands should be used.
Vegetation and land cover increase when total grazing pressure is reduced by a combination of low commodity prices, vertebrate pest control and good seasons. The increase in cropping area during the 1990s was less than many believe, and there has been some substitution of cattle for sheep in some regions. On the whole, adjustments have affected the degree to which more marginal land within each SLA or farm is used or not, rather than reducing grazing pressure equally everywhere.
One of the main reasons that we cannot assess the impact of grazing animals adequately is the uncertainty of ABS statistical data on pastures.
Grazing management represents the single biggest, and least costly method of managing vegetation cover. It is probably the most important management tool in combating most land degradation problems. Well-controlled grazing greatly assists in increasing tree and shrub regeneration, maintaining a balanced assemblage of grasses and herbs in the understorey, and controlling weeds. Unfortunately, the level of animal control needed (particularly through fencing off remnant vegetation, watercourses and overgrazed areas) is frequently not available.
The current debate about grazing and land management hinges on whether total grazing pressure is a useful management tool when compared to concepts of safe thresholds for specific ecosystems (McLeod 1997).
In rangeland ecology around the world, the concept of carrying capacity is often disputed, because it leads to a more static management approach than is required in regions of highly erratic rainfall and patchiness of vegetation. The 'state-transition' see-saw is regarded as a more representative analogy of the way in which rangelands operate. This concept has led to the development of an 'adaptive management' approach of action-learning and partnership between pastoralists and scientists that is proving very successful. Nevertheless, in recent government inquiries into rangeland condition, both pastoralists and scientists have continued to use 'safe carrying capacity' to evaluate whether stocking densities are leading to land degradation or loss of productive capacity (Johnston et al. 1996).
In more reliable rainfall regions, pasture management includes inputs such as fertiliser, herbicide control of weeds, sowing of exotic species of high palatability and nutritional value, and use of animal grazing to control pasture composition. In the mixed farming regions, pastures are rotated with crops to maintain soil fertility and break cycles of disease. In high rainfall districts, pastures are permanent and inputs vary according to the roughness of terrain, value of land and animals, and proportion of off-farm income. In all these environments, the stocking rate is highly dependent on the level of inputs and sophistication of the grazing management (Sustainable Grazing Systems 1998).
Queensland and Northern Territory specialist cattle properties have performed more profitably than other specialist cattle producers in mixed farming or high rainfall regions in recent years (ABARE 1999). This has occurred because of their geographical advantage in the live cattle export trade to Indonesia and Singapore, which survived the vicissitudes of the Asian economic crisis. However, apart from the large corporate farms, average farm business profits have been negative in all areas through much of the decade (ABARE 1999). In the most difficult cases, where pastoralists have been unprofitable for over a decade, structural adjustments have been proposed in which leaseholders would become environmental stewards, with a shift in emphasis to enterprises such as ecotourism and conservation. Consultations with pastoralists have demonstrated their interest in these proposals, but land title acts are often restrictive and new legislation may be required to alter the primary activities on many rangeland leases.
Large amounts of money and volunteer effort have gone into land restoration using labour-intensive tree and shrub planting schemes, contouring, and weed control. But until recently very little has been done to destock, fence out and encourage vegetation regeneration through reduction in grazing pressure. Some Catchment Management Authorities in Victoria are now discussing the possibility using a variety of market-based mechanisms to encourage landholders to manage land for environmental outcomes, such as trading salinity credits for destocking (DNRE Victoria, pers comm.). As yet there are few other regions where this option is being taken seriously.
Nationally, the impact of grazing pressure continues unabated except on lands that have been converted either to conservation reserves, or to more intensive uses not involving stock, such as viticulture and horticulture. While there have been some recent proposals to destock vast tracks of the rangelands (Archer et al. 1997), the feasibility of this is questioned.
In Western Australia the Department of Conservation and Land Management has fenced off the Peron Peninsula across its 3 km width and systematically cleared it of nearly all foxes and most cats with a four-year control program. Now the reintroduction of native fauna is possible. Similar exercises have been undertaken over small areas in South Australia, New South Wales and Queensland. However, the cost of such an exercise makes it prohibitive for large areas.
It is widely accepted in all pest, weed and disease management strategies that total eradication is an almost impossible and highly expensive operation that cannot be undertaken other than in the most threatening situations. What we must consider is where the most damage is occurring, both from a land degradation point of view and a biodiversity point of view. This issue is discussed in more detail in the Biodiversity Theme Report. | <urn:uuid:d396675b-218c-4b58-b83e-ae630b5bb24d> | 3.21875 | 4,123 | Academic Writing | Science & Tech. | 36.060725 | 1,822 |
All > Science > Climate Change
- The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted. See radiation.
EPA - Cite This Source - This Definition
- Heat balance of the Earth-atmosphere system, insolation, Mount Pinatubo, Photovoltaic and solar thermal energy, radiation, Solar energy, Solar Radiation, solar variability, ultraviolet radiation, Ultraviolet Radiation (UV) | <urn:uuid:075ccc65-864c-446b-a011-fa0fc4406e3c> | 2.703125 | 97 | Structured Data | Science & Tech. | 3.33435 | 1,823 |
Effect of Hypersonic Speeds
Recently, intense research has gone into the development of planes that can fly at hypersonic speeds, approximately five times or more than the speed of sound. At these speeds the properties of air change radically; there is a rapid increase in temperature associated with the air flowing at such speeds along a plane's surface. The U.S. Air Force is working to develop an aircraft that could travel at 13,000 mph (21,000 kph), a speed that would generate temperatures greater than 3,500°F (2,000°C).
Sections in this article:
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved. | <urn:uuid:2bce410d-bbcd-4d4b-9a28-a446f5d0b13f> | 3.765625 | 148 | Knowledge Article | Science & Tech. | 55.905357 | 1,824 |
configure is designed so that it appears to do everything itself, but there is actually a hidden slave: config.status. configure is in charge of examining your system, but it is config.status that actually takes the proper actions based on the results of configure. The most typical task of config.status is to instantiate files.
This section describes the common behavior of the four standard
AC_CONFIG_LINKS. They all
have this prototype:
AC_CONFIG_ITEMS(tag..., [commands], [init-cmds])
where the arguments are:
You are encouraged to use literals as tags. In particular, you should avoid
... && my_foos="$my_foos fooo" ... && my_foos="$my_foos foooo" AC_CONFIG_ITEMS([$my_foos])
and use this instead:
... && AC_CONFIG_ITEMS([fooo]) ... && AC_CONFIG_ITEMS([foooo])
special tag values: they may have the form ‘output’ or
‘output:inputs’. The file output is instantiated
from its templates, inputs (defaulting to ‘output.in’).
‘AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk])’, for example, asks for the creation of the file Makefile that contains the expansion of the output variables in the concatenation of boiler/top.mk and boiler/bot.mk.
The special value ‘-’ might be used to denote the standard output when used in output, or the standard input when used in the inputs. You most probably don't need to use this in configure.ac, but it is convenient when using the command line interface of ./config.status, see config.status Invocation, for more details.
The inputs may be absolute or relative file names. In the latter
case they are first looked for in the build tree, and then in the source
tree. Input files should be text files, and a line length below 2000
bytes should be safe.
The variables set during the execution of configure are not available here: you first need to set them via the init-cmds. Nonetheless the following variables are precomputed:
The current directory refers to the directory (or pseudo-directory) containing the input part of tags. For instance, running
AC_CONFIG_COMMANDS([deep/dir/out:in/in.in], [...], [...])
with --srcdir=../package produces the following values:
# Argument of --srcdir srcdir='../package' # Reversing deep/dir ac_top_build_prefix='../../' # Concatenation of $ac_top_build_prefix and srcdir ac_top_srcdir='../../../package' # Concatenation of $ac_top_srcdir and deep/dir ac_srcdir='../../../package/deep/dir'
independently of ‘in/in.in’.
var. init-cmds is typically used by configure to give config.status some variables it needs to run the commands.
You should be extremely cautious in your variable names: all the init-cmds share the same name space and may overwrite each other in unpredictable ways. Sorry...
All these macros can be called multiple times, with different tag values, of course! | <urn:uuid:1c39b6e3-b7ea-4c82-b264-eeab08d8dadc> | 2.5625 | 748 | Documentation | Software Dev. | 51.682322 | 1,825 |
The following procedures raise, handle and wait for signals.
Scheme code signal handlers are run via a system async (see System asyncs), so they’re called in the handler’s thread at the next safe opportunity. Generally this is after any currently executing primitive procedure finishes (which could be a long time for primitives that wait for an external event).
Sends a signal to the specified process or group of processes.
pid specifies the processes to which the signal is sent:
The process whose identifier is pid.
All processes in the current process group.
The process group whose identifier is -pid
If the process is privileged, all processes except for some special system processes. Otherwise, all processes with the current effective user ID.
sig should be specified using a variable corresponding to the Unix symbolic name, e.g.,
A full list of signals on the GNU system may be found in Standard Signals in The GNU C Library Reference Manual.
Sends a specified signal sig to the current process, where
sig is as described for the
Install or report the signal handler for a specified signal.
signum is the signal number, which can be specified using the value
of variables such as
If handler is omitted,
sigaction returns a pair: the
CAR is the current signal hander, which will be either an
integer with the value
SIG_DFL (default action) or
SIG_IGN (ignore), or the Scheme procedure which handles the
#f if a non-Scheme procedure handles the signal.
The CDR contains the current
sigaction flags for the
If handler is provided, it is installed as the new handler for
signum. handler can be a Scheme procedure taking one
argument, or the value of
SIG_DFL (default action) or
SIG_IGN (ignore), or
#f to restore whatever signal handler
was installed before
sigaction was first used. When a scheme
procedure has been specified, that procedure will run in the given
thread. When no thread has been given, the thread that made this
sigaction is used.
flags is a
logior (see Bitwise Operations) of the
following (where provided by the system), or
0 for none.
SIGCHLD is signalled when a child process stops
SIGSTOP), and when a child process terminates.
SIGCHLD is only signalled
for termination, not stopping.
SA_NOCLDSTOP has no effect on signals other than
If a signal occurs while in a system call, deliver the signal then
restart the system call (as opposed to returning an
from that call).
The return value is a pair with information about the old handler as described above.
This interface does not provide access to the “signal blocking” facility. Maybe this is not needed, since the thread support may provide solutions to the problem of consistent access to data structures.
Return all signal handlers to the values they had before any call to
sigaction was made. The return value is unspecified.
Set a timer to raise a
SIGALRM signal after the specified
number of seconds (an integer). It’s advisable to install a signal
SIGALRM beforehand, since the default action is to terminate
The return value indicates the time remaining for the previous alarm, if any. The new value replaces the previous alarm. If there was no previous alarm, the return value is zero.
Pause the current process (thread?) until a signal arrives whose action is to either terminate the current process or invoke a handler procedure. The return value is unspecified.
Wait the given period secs seconds or usecs microseconds (both integers). If a signal arrives the wait stops and the return value is the time remaining, in seconds or microseconds respectively. If the period elapses with no signal the return is zero.
On most systems the process scheduler is not microsecond accurate and
the actual period slept by
usleep might be rounded to a system
clock tick boundary, which might be 10 milliseconds for instance.
scm_std_usleep for equivalents at
the C level (see Blocking).
Get or set the periods programmed in certain system timers. These timers have a current interval value which counts down and on reaching zero raises a signal. An optional periodic value can be set to restart from there each time, for periodic operation. which_timer is one of the following values
A real-time timer, counting down elapsed real time. At zero it raises
SIGALRM. This is like
alarm above, but with a higher
A virtual-time timer, counting down while the current process is
actually using CPU. At zero it raises
A profiling timer, counting down while the process is running (like
ITIMER_VIRTUAL) and also while system calls are running on the
process’s behalf. At zero it raises a
This timer is intended for profiling where a program is spending its time (by looking where it is when the timer goes off).
getitimer returns the current timer value and its programmed
restart value, as a list containing two pairs. Each pair is a time in
seconds and microseconds:
. interval_usecs) (periodic_secs
setitimer sets the timer values similarly, in seconds and
microseconds (which must be integers). The periodic value can be zero
to have the timer run down just once. The return value is the timer’s
previous setting, in the same form as
(setitimer ITIMER_REAL 5 500000 ;; first SIGALRM in 5.5 seconds time 2 0) ;; then repeat every 2 seconds
Although the timers are programmed in microseconds, the actual accuracy might not be that high. | <urn:uuid:d7170610-df81-4a15-a7a0-8613d9334e2e> | 2.96875 | 1,236 | Documentation | Software Dev. | 47.244207 | 1,826 |
Improving the Performance of Platinum Electrocatalysts in Fuel Cells
12 January 2007
The journal Science and its online companion Science Express this week provide two reports from different research teams on efforts to improve the stability and performance of platinum electrocatalysts in PEM fuel cells.
Scientists at the US Department of Energy’s (DOE) Brookhaven National Laboratory have discovered that the addition of gold clusters to platinum electrocatalysts stabilizes them for use in fuel cells.
A PEM fuel cell converts hydrogen and oxygen into water and, as part of the process, produces electricity. Hydrogen is oxidized when electrons are released and hydrogen ions are formed; the released electrons supply current for an electric motor. Oxygen is reduced by gaining electrons, and in reaction with hydrogen ions, water, the only byproduct of a fuel cell reaction, is produced. Platinum electrocatalysts speed up these oxidation and reduction reactions (ORR).
In reactions during the stop-and-go driving of an electric car, however, the platinum dissolves, which reduces its efficiency as a catalyst—a major impediment for vehicle-application of fuel cells.
Under lab conditions that imitate the environment of a fuel cell, the Brookhaven researchers added gold clusters to the platinum electrocatalyst, which kept it intact during an accelerated stability test. This test is conducted under conditions similar to those encountered in stop-and-go driving in an electric car. The research is reported in the 12 January 2007 edition of the journal Science.
Fuel cells are expected to become a major source of clean energy, with particularly important applications in transportation. Despite many advances, however, existing fuel-cell technology still has drawbacks, including loss of platinum cathode electrocatalysts, which can be as much as 45 percent over five days, as shown in our accelerated stability test under potential cycling conditions. Using a new technique that we developed to deposit gold atoms on platinum, our team was able to show promise in helping to resolve this problem. The next step is to duplicate results in real fuel cells.—Radoslav Adzic, co-author
In the unique method developed at Brookhaven, the researchers displaced a single layer of copper with gold on carbon-supported platinum nanoparticles. After being subjected to several sweeps of 1.2 volts, the gold monolayer transformed into three-dimensional clusters. Using x-rays as probes at Brookhaven’s National Synchrotron Light Source, a scanning transmission microscope at Brookhaven’s Center for Functional Nanomaterials, and electrochemical techniques in the laboratory, the scientists were able to verify the reduced oxidation of platinum and to determine the structure of the resulting platinum electrocatalyst with gold clusters, which helped them to gain an understanding of the effects of the gold clusters.
In the Brookhaven experiment, the platinum electrocatalyst remained stable with potential cycling between 0.6 and 1.1 volts in more than 30,000 oxidation-reduction cycles, imitating the conditions of stop-and-go driving.
The gold clusters protected the platinum from being oxidized. Our team’s research raises promising possibilities for synthesizing improved platinum-based catalysts and for stabilizing platinum and platinum-group metals under cycling oxidation/reduction conditions.—Radoslav Adzic
This research is funded through the US Department of Energy’s Hydrogen Program.
In a separate study published online in Science Express, researchers enhanced the performance of platinum electrocatalysts in fuel cells. The slow rate of the oxygen reduction reaction (ORR) in PEM fuel cell is a major limiter for automotive applications.
The team from Argonne National laboratory, the University of Liverpool, Lawrence Berkeley National Laboratory and the University of South Carolina developed a Pt3Ni(111) catalyst that is 10-fold more active for the oxygen reduction reaction than the corresponding Pt(111) surface, and 90-fold more active than current state-of-the-art Pt/C catalysts.
The Pt3Ni(111) surface has an unusual electronic structure (d-band center position) and arrangement of surface atoms in the near-surface region. Under operating conditions relevant to fuel cells, its near-surface layer exhibits a highly structured compositional oscillation in the outermost and third layers are Pt rich and the second atomic layer is Ni rich. The weak interaction between the Pt surface atoms and non-reactive oxygenated species increases the number of active sites for O2 adsorption.
“Stabilization of Platinum Oxygen-Reduction Electrocatalysts Using Gold Clusters”; J. Zhang, K. Sasaki, E. Sutter, R. R. Adzic; Science 12 January 2007: Vol. 315. no. 5809, pp. 220 - 222 DOI: 10.1126/science.1134569
“Improved Oxygen Reduction Activity on Pt3Ni(111) via Increased Surface Site Availability”; Vojislav R. Stamenkovic, Ben Fowler, Bongjin Simon Mun, Guofeng Wang, Philip N. Ross, Christopher A. Lucas, Nenad M. Markovic; Science Express DOI: 10.1126/science.1135941
TrackBack URL for this entry:
Listed below are links to weblogs that reference Improving the Performance of Platinum Electrocatalysts in Fuel Cells: | <urn:uuid:10eb12ab-073b-481f-a025-a15ecd75f5d4> | 2.96875 | 1,108 | News (Org.) | Science & Tech. | 30.616154 | 1,827 |
Tue May 15, 2012
Aletta Becomes Western Hemisphere's First Tropical Storm Of 2012
Aletta — a modest tropical storm spinning of the western coast of Mexico with 40 mph winds — is already special because of two reasons: It the first tropical storm in the Western Hemisphere and it has now broken a 41-day streak in which Earth did not see a cyclone.
Jeff Masters at Weather Underground provides a little more detail:
-- Second: "The formation of Aletta ends a 41-day streak without a tropical storm anywhere in the world. According to the UK Met Office, the 41-day period storm-less period is the longest span Earth has gone without a tropical storm in at least 70 years."
Aletta, by the way, is not expected to bother anyone. That's why The Washington Post jumps ahead and asks: Does this early storm — the Atlantic Hurricane season doesn't start until June 1 — mean we're in for an early start?
"The birth of Aletta in the eastern Pacific signals activity is picking up in tropical regions around the world," the Capital Weather Gang reports. "The agitated appearance of the cloud field in the eastern Pacific suggests there may be more development there in during the next few days."
Back in April, William Gray, the legendary meteorologist, released his forecast (pdf) for the hurricane season. He said he expected a season with "reduced activity."
"We anticipate a below-average probability for major hurricanes making landfall along the United States coastline and in the Caribbean," Gray wrote. | <urn:uuid:81fb2b76-f043-447b-afb3-6a95560d40a7> | 2.875 | 317 | News Article | Science & Tech. | 44.138605 | 1,828 |
The Trojan asteroids lie in Jupiter's orbit equidistant from Jupiter and the sun. They are an example of what is known as the restricted three-body problem: the motion of a small body, an asteroid, under the influence of two massive bodies whose motion is not affected by the presence of the asteroid. The gravitational forces exerted by the sun and Jupiter combine to give the asteroid a stable orbit with Jupiter's period of rotation. (Some trigonometry is needed to show that the Trojan site forms an equilateral triangle with the sun and Jupiter). In the applet, the massive bodies executing circular orbits about their common centre of mass can have mass ratios ranging from 9 up to the value for sun-earth system. It is convenient to view the motion of the asteroid in a frame rotating with the massive bodies. This is a non-inertial frame, and both centrifugal ( - m w x (w x r) ) and Coriolis ( - 2 m w x v ) forces appear in Newton's Law. Viewed in the rotating frame, the asteroid in a stable orbit remains at rest at the point where the net gravitational attraction balances the repulsive centrifugal force. Points with this property show up clearly on a color plot of the effective potential in the rotating frame. This potential is the sum of three negative terms: a centrifugal potential that varies as the square of the distance from the centre of mass (much like an "upside down" harmonic potential), and two gravitational wells centered on the massive bodies. Points where the effective potential falls within a specified range share a common color, and the scale factor is adjusted to place the Trojan site near a color boundary. Such plots usually use linear or logarithmic scales, but here an inverse scale is used to give suitable numbers and widths of the color bands (this produces color bands of constant width near a massive body). The plot is centred on the centre of mass of the system, with the more massive body (M) on the left and the less massive body (m) a distance d to its right. Choose a mass ratio, and press either "Tro" for an orbit starting near a Trojan site or "Sad" for an orbit starting near a saddle point (a point of equilibrium on the centreline).
The most prominent features of the potential plots are the red regions surrounding the Trojan sites. As the red regions are the crests of hills, it is not obvious that a Trojan orbit can be stable. As the mass ratio changes, the shape of a crest changes, but it remains a crest. It can be shown analytically that orbits for M/m greater than 25 are stable, but the calculation requires more than the trigonometry needed to find the equilateral triangle. The numerical study of stability, on the other hand, requires only the Feynman algorithm for velocity-dependent forces (such as the Coriolis force). Each plot shows the path taken by the asteroid when it is released from rest (in the rotating frame) with a y-displacement of d/400 (about 1/3 of a pixel) from the equilibrium site. For a Trojan site, the displacement puts the asteroid on the far side of the hill from the centre of mass, and initially it moves outward as we would expect. As soon as it acquires a significant velocity, the Coriolis force deflects it to the right (in a frame rotating counterclockwise). What happens then depends on the mass ratio. For low mass ratios it spirals outward. For intermediate mass ratios it traces out loops close to the Trojan site. At higher mass ratios the potential crest becomes an elongated ridge, and the orbit bumps its way around it.
On 9 Nov 02 my car radio informed me that an asteroid the size of a football field had recently been found to share the earth's orbit. In a frame rotating with the earth, it was said to have a horseshoe-shaped orbit. As I drove along, I visualized the crest I had already plotted for Jupiter turning into a ridge that circles the sun, and the asteroid bouncing along the crest in a horseshoe orbit until it turns at a low point near the earth. That evening I extended the Trojan applet to include the sun/earth mass ratio, and found the horseshoe orbit plotted here. It has a period of 160 years.
If you select the "Sad" option, the program finds the three equilibrium points that lie on the M/m axis, one outside each mass, and one between them. They are all saddle points: the region they are in is bounded by different colors in the x and y directions. The axis and the force are shown in white on the plot, and a bisection algorithm is used to locate the equilibrium points. If a Trojan hill can produce a stable orbit there is no reason to assume that a saddle point cannot. The program tests stability using the same y-displacement used at a Trojan site. The saddle points on either side of m are unstable for all mass ratios, but the one to the left of M generates a horseshoe orbit for the sun/Jupiter and sun/earth systems. (Note that the other two saddle points are not plotted for these systems, and that the PostScript program does not deal with any of the saddle points).
The Trojan and horseshoe orbits are closely-related examples of stable orbits: closed curves that rotate about the centre of mass in sync with m. Horseshoe orbits can be generated for both the sun/Jupiter and sun/earth systems with a d/400 y-displacement from the left saddle point. A Trojan orbit can be generated for the sun/earth system with a d/1600 y-displacement from the Trojan site. A horseshoe orbit can be generated for the sun/Jupiter system with a d/70 (2 pixel) y-displacement from the Trojan site. (The size of the displacement needed can be seen on the horseshoe orbit generated from the saddle point). | <urn:uuid:6f3ce9dc-a162-41b8-a378-42a369a5def2> | 3.796875 | 1,236 | Tutorial | Science & Tech. | 50.43042 | 1,829 |
In general, the TOC is determined by oxidizing a water sample. The produced CO2 is detected and defined quantitatively. However, not all methods succeed in the complete oxidation of a sample. Often enough this may result only in SOC (Some Organic Carbon) instead of the TOC.
With this oxidation method the sample will be combusted in a reactor. Usually, a maximum temperature of about 1000°C will be reached, which however does not allow the complete oxidation of all carbon compounds. Therefore, a catalyst, such as copper oxide or platinum, must be used at this temperatures. Normally, the catalytic combustion method can handle a TOC concentration of up to 4,000 mg/l. To reach higher ranges the sample usually needs to be diluted with demin water.
LAR AG offers a unique and patented high temperature (HT) method at 1200°C. This temperature enables the complete oxidation of all carbon compounds without any catalysts. It measures TOC concentrations up to 50,000 mg/l without dilution. In a special heat resistant ceramic reactor the water sample is evaporated and all carbons are completely oxidized to CO2 gas. Afterwards, the CO2 concentration will be analysed with a Non-Dispersive Infrared (NDIR) detector. Thus, the TC, TOC and TIC can be determined within only 3 minutes.
This HT method is used for both, the most challenging and highly contaminated waters ( QuickTOCultra, QuickTOCairport) and waters relativily free of solid maters ( QuickTOCeffluent). LAR uses the batch injection method with the advantage that the analysers can easily handle sticky, oily and hard to oxidise dissolved and suspended organics resulting in a fast, reliable and accurate analysis. Even with rapidly fluctuating TOC levels the correct TOC concentration will be measured, whereby peaks throughout the course of the day are determined without any memory or adsorption effects.
For applications with purified water, this LAR method allows the patented* simplified, ready-at-any-time calibration and validation method ( QuickTOCcondensate, QuickTOCpurity, QuickTOCpharma).
Photochemical Oxidation (UV-Persulphate Method)
Here the TOC is oxidized by means of UV light and a digesting reagent, sodium persulphate, and the produced CO2 is measured with a NDIR detector. This method suits the determination of TOC in clean water (drinking water, condensate, boiler feed water), since particles are hard to oxidize completely.
The QuickTOCuv combines this technique with the direct TOC method or Non-Purgable Organic Carbon (NPOC) method, whereby the continuously provided water samples will be treated in a multi stage process.
Wet Chemical Oxidation
With this method the water sample is oxidized by means of strong chemicals as oxidants such as ozone, which are slightly dangerous to health and environment. The ozone oxidation acids and bases are used to adjust the pH value of the sample along the pH scale.
However, the oxidation potential of such methods is relative, since particles and more complex carbon compounds can only be partially digested or not at all. With regards to the latest standards of occupational safety and environmental protection these methods are not recommended.
*pat. 10/583,932; 2347221; 04803562.0-2204; 200480038582.7 | <urn:uuid:02ba6c77-3758-4f96-a3c5-57e73541cecc> | 2.71875 | 715 | Documentation | Science & Tech. | 32.119411 | 1,830 |
In part two of this book excerpt series on the .NET Framework Class Library from O'Reilly's VB.NET Core Classes in a Nutshell, get an introduction to the .NET Framework Class Library (FCL).
The .NET Framework includes the .NET Framework Class Library (FCL), a vast collection of thousands of types (that is, of classes, interfaces, structures, delegates, and enumerations) that aim at encapsulating the functionality of core system and application services in order to make application programming easier and faster. There are classes that you can use to manipulate the file system, access databases, serialize objects, and launch and synchronize multiple threads of execution, to name just a few.
To make working with these classes easy, classes with similar functionality are grouped together in namespaces. Therefore, there is a namespace containing types for drawing, a number of namespaces for .NET remoting, etc. In fact, the "intrinsic" functions of the Visual Basic language (such as InStr, Len, and UBound) are implemented as class methods in the Microsoft.VisualBasic namespace. In total, the .NET FCL places more than 80 namespaces at your disposal.
The .NET FCL includes classes with the following functionality:
Some members of the System namespace, such as the Object, String, Int32, and Single classes, form the data types used by Visual Basic .NET (as well as by other .NET languages that rely on the .NET Common Type System).
When an exception is generated, the CLR provides exception information to the Exception class (in the System namespace) or to one of the derived classes found throughout the .NET FCL.
The signature of event handlers is represented by the EventHandler delegate (in the System namespace) or one of its derived delegates. The event information passed to an event handler is represented by the EventArgs class (in the System namespace) or one of its derived classes.
Attributes allow custom items of information about a program element to be stored with an assembly's metadata. Since this information becomes a permanent part of the program element's description, it is always available and can be used to modify the design time, compile time, or runtime behavior of a program element. Attributes are classes derived from the Attribute class (in the System namespace) or one of its derived classes found throughout the .NET FCL.
The .NET FCL features a number of general-purpose and more specialized collection classes. The general-purpose classes include the Array class (in the System namespace) and the ArrayList and CollectionBase classes (in the System.Collection namespace). Specialized classes include the Stack class, a last-in, first-out structure, the Queue class, a first-in, first-out structure, in the System.Collection namespace, and the ListDictionary class, a linked list dictionary class, in the System.Collection.Specialized namespace.
The .NET FCL provides full support for custom Windows and web controls that integrate with design-time environments like Visual Studio through a number of classes, including the Container class in the System.ComponentModel namespace or the CollectionEditor class in the System.ComponentModel.Design namespace.
Using the .NET FCL, you have easy access to application configuration information from configuration files using classes such as AppSettingsReader and DictionarySectionHandler in the System.Configuration namespace. You can also access registry data using the Registry, RegistryHive, and RegistryKey classes in the Microsoft.Win32 namespace. Finally, you can access ActiveDirectory information using the members of the System.DirectoryServices namespace.
The .NET FCL makes a large number of debugging, diagnostic, and informational classes available that can help in locating and fixing bugs, as well as in improving overall performance. These include the Debug, Debugger, EventLog, and PerformanceCounter classes in the System.Diagnostics namespace.
The FCL provides a full set of graphics objects, such as the Color structure, the Brush class, the Font class, and the Graphics class in the System.Drawing namespace.
The FCL allows you to read the standard input, standard output, and standard error streams, as well as to access the file system, through classes like File, FileInfo, StreamReader, and StreamWriter in the System.IO namespace.
Through the Type class in the System namespace and classes like Assembly, Module, EventInfo, MethodInfo, and ParameterInfo in the System.Reflection namespace, the .NET FCL provides support for reading metadata (the data that describes particular program elements) at any time.
Through classes such as ObjRef, RemotingConfiguration, and RemotingServices in the System.Runtime.Remoting namespace, the .NET FCL adds support for remoting (calls that cross process or machine boundaries).
Interestingly, in the .NET Framework, strings are immutable. This means that simple operations such as string concatenation involve an enormous performance penalty. The StringBuilder class in the System.Text namespace makes it possible to perform string concatenation efficiently. The RegEx and Match classes in System.Text.RegularExpressions make it possible to perform regular expression searches on strings.
In previous versions of Visual Basic, threading was a factor that enormously impacted VB applications but over which the VB developer had no control. With classes like Thread, Mutex, and Monitor in the System.Threading namespace, the .NET FCL for the first time places threading under the direct control of the VB.NET developer.
In This Series
An Introduction to the .NET FCL, Part 1
The .NET FCL features a brand new data access technology, ADO.NET. It is represented by classes like the DataSet class in the System.Data namespace, the OleDbConnection, OleDbCommand, and OleDbDataReader classes in the System.Data.OleDb namespace, and the SqlConnection, SqlCommand, and SqlDataReader classes in the System.Data.SqlClient namespace.
The forms and controls that made Visual Basic the premier Rapid Application Development package for Windows have their equivalent in the .NET FCL. These classes, such as the Form class, the Button class, and the TextBox class, are found in the System.Windows.Forms namespace.
In addition to Windows controls, the .NET FCL features two sets of controls for web application development. HTML server controls execute on the server but otherwise correspond more or less directly to standard client-side HTML controls. They are found in the System.Web.UI.HTMLControls namespace. Web controls (also known as ASP controls) are server controls that abstract the functionality of controls in a web application. They are found in the System.Web.UI.WebControls namespace.
A web service is simply a function call over the Internet. The .NET FCL supports the development of web services through the types in the System.Web.Services namespace.
As you can see, the functionality offered by the .NET FCL is extensive--and in this overview of the .NET FCL, we've only emphasized the highlights.
In the next installment, learn to work with the .NET FCL.
Copyright © 2009 O'Reilly Media, Inc. | <urn:uuid:b6d127ed-c522-4560-8aad-70771c371362> | 2.859375 | 1,503 | Truncated | Software Dev. | 41.284533 | 1,831 |
Space Ring Could Shade Earth and Stop Global Warming
A wild idea to combat global warming suggests creating an artificial ring of small particles or spacecrafts around Earth to shade the tropics and moderate climate extremes.
There would be side effects, proponents admit. An effective sunlight-scattering particle ring would illuminate our night sky as much as the full Moon, for example.
And the price tag would knock the socks off even a big-budget agency like NASA: $6 trillion to $200 trillion for the particle approach. Deploying tiny spacecraft would come at a relative bargain: a mere $500 billion tops.
But the idea, detailed today in the online version of the journal Acta Astronautica, illustrates that climate change can be battled with new technologies, according to one scientist not involved in the new work.
Mimic a volcano
All scientists agree that Earth gets warmer and colder across the eons. A delicate and ever-changing balance between solar radiation, cloud cover, and heat-trapping greenhouse gases controls long-term swings from ice ages to warmer conditions like today.
Those who are often called experts admit to glaring gaps in their knowledge of how all this works. A study last month revealed that scientists can't pin down one of the most critical keys: how much sunlight our planet absorbs versus how much is reflected back into space.
Nonetheless, most scientists think our climate has warmed significantly over the past century and will grow warmer over the next hundred years. Various studies claim the planet is destined to warm by anywhere from 1 to 20 degrees Fahrenheit over the next few centuries. Seas will rise dramatically, the scenario goes, inundating coastal cities. But another group of scientists argue that the temperature data supporting a warming planet is not firm and that projections, based on computer modeling, might be wildly off the mark.
Either way, perhaps our fate is more in our hands than we might have imagined.
"Reducing solar insolation by 1.6 percent should overcome a 1.75 K [3 degrees Fahrenheit] temperature rise," contends a group led by Jerome Pearson, president of Star Technology and Research, Inc. "This might be accomplished by a variety of terrestrial or space systems."
The power of scattering sunlight has been illustrated naturally, the scientists note. Volcanic eruptions, such as that of Mt. Pinatubo in 1991, pumped aerosols into the atmosphere and cooled the global climate by about a degree. Other researchers have suggested such schemes as adding metallic dust to smoke stacks, to flood the atmosphere and reflect more sunlight back into space.
In the newly outlined approach, reflective particles might come from the mining of Earth, the Moon or asteroids. They'd be put into orbit around the equator. Alternately, tiny micro-spacecraft could be deployed with reflective umbrellas.
A ring created by a batch of either "shades the tropics primarily, providing maximum effectiveness in cooling the warmest parts of our planet," the scientists write. An early version of their idea was presented but not widely noticed in 2002.
Eccentric but reassuring
Those researchers who don't buy the argument that global warming is occurring at any significant rate nor that humans are largely to blame may warm up quickly to the new idea.
Benny Peiser, a social anthropologist at Liverpool John Moores University in the UK, tracks climate research and the resulting media coverage. He's among the small but vocal group that goes against mainstream thought on the topic of global warming.
"I don't think that the modest warming trend we are currently experiencing poses any significant or long-term threat," Peiser told LiveScience. "Nevertheless, what the paper does show quite impressively is that our hyper-complex civilization is theoretically and technologically capable of dealing with any significant climate change we may potentially face in the future."
Peiser also notes that the Kyoto Protocol, a global agreement to reduce greenhouse gas emissions, is estimated to cost the world economy some $150 billion a year. He also sees a broader rationale for supporting the seemingly bizarre manner of managing Earth's temperature budget.
"I believe that this mindset, despite its apparent eccentricity, is actually rather reassuring," Peiser said. "It provides concerned people with ample evidence of the extraordinary human ingenuity that, as so often in the past, has helped to overcome many predicaments that were regarded as impenetrable in previous times."
He also sees an ultimate big-picture reasoning to look favorably on the notion of controlling Earth's climate.
"Whatever the cost and regardless of whether there is any major risk due to global warming," Peiser said, "it would appear to me that such a space-based infrastructure will evolve sooner or later, thus forming additional stepping stones of our emerging migration towards outer space."
MORE FROM LiveScience.com | <urn:uuid:43d496e6-d8e0-4d17-8c9a-8bfc2f973e84> | 3.828125 | 977 | News Article | Science & Tech. | 36.89875 | 1,832 |
Carbonaceous chondrite meteorites contain vital clues to the evolution of carbon compounds in our solar system preceding the origin of life.
Adapted from an Arizona State University press release
Scientists have conducted an organic analysis of the Tagish Lake meteorite, a rare, carbon-rich meteorite classified as a carbonaceous chondrite. The meteorite fell on a frozen Canadian lake in January 2000, and is the most pristine carbonaceous chondrite specimen ever studied.
The analysis suggests there can be a different outcome for the evolution of organic chemicals in space than from what has been observed in other carbonaceous meteorites. This difference could be due to the possibility that the Tagish Lake meteorite contains carbon molecules that may have accumulated during the formation and development of the solar system.
Carbonaceous chondrite meteorites contain vital clues to the evolution of carbon compounds in our solar system. For example, the Murchison meteorite, a carbonaceous chondrite found in Australia in 1969, contains numerous amino acids and a variety of other organic compounds that are the building blocks for life. Many scientists now believe that such meteorites could have seeded the Earth with the ingredients necessary for life to arise.
A team headed by chemist Sandra Pizzarello, a research scientist at Arizona State University, conducted the organic analysis of the Tagish Lake meteorite. 4.5 grams were taken from the sealed interior of the meteorite, and while the organic compounds found in the meteorite have some similarities to other known carbonaceous chondrites, there are also clear differences - most notably the near-absence of amino acids.
"The chemistry here is different from that we have seen in any other meteorite," says Pizzarello. "It's simple when compared with Murchison, and probably represents a separate line of chemical evolution. However, it still includes compounds that are identical to biomolecules."
In an article published in the August 24 issue of the online journal Science Express, the team notes that the chemistry of the Tagish Lake meteorite appears to have preserved organics that accumulated or developed in the early history of the Solar System. This includes molecular bubbles of carbon (fullerenes or "buckyballs") containing the noble gases helium and argon in a ratio similar to the gas and dust cloud that formed the planets. Thus, the meteorite perhaps reflects an early stage of evolution of complex carbon compounds in space.
The Science paper notes that many of the organic compounds found in the Tagish Lake sample have also been found in other meteorites, but that the distribution of compounds is different, particularly for the amino acids and carboxylic acids.
"We found some compounds identical to some in Murchison that show the same - interstellar connection - in their abundance of deuterium (heavy hydrogen), while some others differ from Murchison in amounts and variety," says Pizzarello, meaning that for some groups of organic molecules, only the simplest species were found in Tagish Lake, as opposed to a broader distribution of species found in Murchison. "Overall, Tagish Lake represents a simpler, more unaltered stage than we have seen before."
Other members of the research team include Yongsong Huang from the Department of Geological Sciences at Brown University; Luann Becker from the Institute for Crustal Studies at the University of California Santa Barbara; Robert J. Poreda from the Department of Earth and Environmental Sciences, University of Rochester; George Cooper from the NASA Ames Research Center; and Ronald A. Nieman and Michael Williams, both also from ASU.
"Some people have been disappointed that we found virtually no amino acids, but scientifically this is very exciting," Pizzarello said. "This meteorite shows the complexity of the history of organic compounds in space - it seems to have had a distinct evolution."
Pizzarello notes that while the meteorites like Tagish Lake may lack amino acids, they still could have contributed the molecular precursors of biomolecules that are necessary for the origin of life.
Louis Allamandola, astrochemist with the NASA Ames Research Center and NAI member, says the absence of amino acids and other simple organic molecules could mean the meteorite was exposed to high heat or energy levels during its travels through space.
"The main signature of the meteorite is that of sooty, cross polymerized aromatic material -- probably much like the black soot from a diesel engine or sooty candle flame," says Allamandola. "From an organic chemical point of view, this is the kind of material you get when you heat any organic material above about 400 degrees Celsius (752 degrees Fahrenheit). So, all this means is that this particular rock had a different history from that of the Murchison meteorite. It had a rougher go on its transit from deep space to Earth."
Carbonaceous chondrite meteorites generally show little evidence of being shaped by high temperatures. Even entry into our atmosphere does not heat their interiors to any great degree, as their porous texture tends to bleed away heat. But Allamandola says it wouldn't come as a surprise if the meteorite had been heated or energetically processed before entering the Earth's atmosphere - the vast reaches of space contain many different levels of radiation, temperatures, densities, and environments.
"There are at least two ways to look at it," says Allamandola. "Either carbon goes through some sort of process to form amino acids, and this meteorite therefore represents an early window on the evolution of carbonaceous chondrites before the amino acids develop. Or, the rock might have been so energetically processed that the amino acids were destroyed."
"Basically," Allamandola says, "this draws attention to the fact that only very few meteorites have been studied in any detail, and that we really don't know what most of them contain. It's a tough game." | <urn:uuid:799b4de9-78b6-443d-93be-2921035b705e> | 3.9375 | 1,226 | News Article | Science & Tech. | 21.008388 | 1,833 |
ECOSYSTEM PROPERTIES FOR WHICH SATELLITE DATA ARE REQUIRED
measurement of canopy height with lidar. Others are derived from the statistics of direct measurements, such as estimates of landscape heterogeneity used in conservation biology and ecosystem management and the inference of surface sources and sinks of CO2 from space-based measurements of column-integrated atmospheric CO2. A third category includes quantities that result from using direct observations as inputs in physical, biological, or statistical models; an example is the estimation of carbon uptake and release through photosynthesis and respiration in marine or terrestrial systems, which are inferred from space-based estimates of photosynthetic light absorption. A final category includes quantities estimated from time series of measurements, which by their rate of change define some other process (for example, the integral of photosynthesis over time can define biological productivity).
The currently available long-term record of ecosystem dynamics from a variety of sensors is critical for understanding and managing ecosystems in the coming decades. The panel places high priority on maintaining and enhancing this record. The role of multiyear time series in understanding ecological dynamics has long been recognized. From classic examples like the scientific exploitation of the Canadian Lynx-Hare data set through the establishment of the Long Term Ecological Research (LTER) network and newer classic papers that used decadal eddy covariance record, long time series have shaped the field. Understanding of global-scale processes has been substantially advanced through long time series, including the ice-core records, the Keeling record of atmospheric CO2, the CZCS-SeaWiFS-MODIS records of ocean color, and the AVHRR and Landsat records of photosynthesis and land-cover change. Long-term records of photosynthetic activity have enabled forecasts of impending food shortages, pest outbreaks, and other key ecological linkages with human health. To meet the challenges for understanding and managing ecosystems in the coming decade, the maintenance and extension of long-term ecosystem records are paramount. Here, the panel briefly reviews critical applications, problems, requirements, and opportunities.
There are three fundamental long-term satellite records of ecosystem dynamics, and each addresses a separate issue. First is ocean color, which began with the Coastal Zone Color Scanner and continues with | <urn:uuid:ebb8e64b-d7ac-4099-ae55-1611e8a18564> | 3.203125 | 462 | Academic Writing | Science & Tech. | 2.767457 | 1,834 |
The integrating power of the eye has been tested for short flashes of light, ranging in duration from 10-2 to 8 × 10-9 sec. The shorter flashes were produced by passing the image of the straight filament of an electric lamp across a narrow slit, the light having been reflected from a mirror mounted on an air-driven turbine. The longer flashes were produced by means of a sectored disk. In all cases the number of flashes received by the eye was great enought to avoid flicker and the intensity was well above that required to produce the sensation of vision. It was concluded that the response of the eye depends only upon the total amount of light in the beam and is independent of the length of the light flash. The limit of error was 1.5 percent.
THOMAS E. GILMER, "The Integrating Power of the Eye for Short Flashes of Light," J. Opt. Soc. Am. 27, 386-386 (1937) | <urn:uuid:8b63c035-96b4-4881-8a5a-f7c76b74fc8a> | 3.171875 | 198 | Academic Writing | Science & Tech. | 73.021389 | 1,835 |
Harrisburg, PA—Ten months after Tropical Storm Lee led to record flooding that devastated the Susquehanna Valley, a new PennEnvironment Research & Policy Center report confirms that extreme rainstorms and snowstorms are happening 52 percent more frequently in Pennsylvania since 1948.
“As the old saying goes, when it rains, it pours—especially in recent years as bigger storms have hit Pennsylvania more often,” said Adam Garber, Field Director for PennEnvironment Research & Policy Center. “We need to heed scientists’ warnings that this dangerous trend is linked to global warming, and do everything we can to cut carbon pollution today.”
Based on an analysis of state data from the National Climatic Data Center, the new report found that heavy downpours or snowstorms that used to happen once every 12 months on average in the state now happen every 7.9 months on average. Moreover, the biggest storms are getting bigger. The largest annual storms in Pennsylvania now produce 23 percent more precipitation, on average, than they did 65 years ago.
Scientists have concluded that the rise in the frequency and severity of heavy rainstorms and snowstorms is linked to global warming. Warming increases evaporation and enables the atmosphere to hold more water, providing more fuel for extreme rainstorms and heavy snowstorms.
Garber pointed to the rainstorm that hit the Susquehanna Valley in September of 2011 as an illustration of what more extreme rainstorms and snowstorms could mean for the state. That rainstorm, which led to over 10,000 residents being evacuated, resulted in record-breaking crests of the Susquehanna River. It even required the Governor’s Mansion in Harrisburg to empty out due to flooding.
Other recent extreme precipitation events in Pennsylvania include:
- In August of 2011 Hurricane Irene dumped 4.55 inches of rain in only a few hours, led to 400,000 power outages, 400 downed trees, and 7 collapsed buildings in Philadelphia alone.
- The snowstorm that hit Pittsburgh in February of, which dumped 21 inches on the area as the fourth largest snowstorm in Pittsburgh, led to suspended public transportation, closed schools and slippery conditions for commuters.
The new PennEnvironment Research & Policy Center report, When It Rains, It Pours: Global Warming and the Increase in Extreme Precipitation from 1948 to 2011, examines trends in the frequency and the total amount of precipitation of extreme rain and snow storms across the contiguous United States from 1948 to 2011. Using data from 3,700 weather stations and a methodology originally developed by scientists at the National Climatic Data Center and the Illinois State Water Survey, the report identifies storms with the greatest 24-hour precipitation totals at each weather station, and analyzes when those storms occurred. The report also examines trends in the amount of precipitation produced by the largest annual storm at each weather station.
Nationally, the report found that storms with extreme precipitation increased in frequency by 30 percent across the contiguous United States from 1948 to 2011. Moreover, the largest annual storms produced 10 percent more precipitation, on average. At the state level, 43 states show a significant trend toward more frequent storms with extreme precipitation, while only one state (Oregon) shows a significant decline.
“The data is clear,” remarked Irina Marinov from the Department of Earth and Environmental Science at the University of Pennsylvania. “Emissions of CO2 and other greenhouse gases are changing the climate and damaging our environment. More extreme weather, to be expected in our warming climate, should be of high concern, not just to specialists in my field, but to every Pennsylvania citizen.”
Key findings for Pennsylvania and the Mid-Atlantic include:
- Extreme rainstorms and snowstorms are becoming more frequent. Pennsylvania experienced a 52% percent increase in the frequency of extreme rainstorms and snowstorms from 1948 to 2011. In other words, heavy downpours or snowstorms that happened once every 12 months on average in 1948 now happen every 7.9 months, on average.
- Storms with extreme precipitation increased in frequency by 55 percent in the Mid-Atlantic during the period studied. The Mid-Atlantic region ranks 2nd nationwide for the largest increase in the frequency of storms with heavy precipitation.
- The biggest rainstorms and snowstorms are getting bigger. The amount of precipitation released by the largest annual storms in Pennsylvania increased by 23 percent from 1948 to 2011.
Raymond Najjar, a climate scientist in Penn State’s Department of Meteorology, joined PennEnvironment in releasing today’s report.
“Decades of climate research have led us to the inescapable conclusion that fossil-fuel emissions make the atmosphere warmer, moister, and more prone to producing intense precipitations,” added Dr. Najjar. “The good news is that we can minimize the most harmful impacts through emissions reductions, better land-use planning, and improved infrastructure.”
Garber was careful to note that an increase in the frequency and severity of extreme rainstorms does not mean more water will be available for human use. Higher temperatures fuel extreme rainstorms by increasing rates of evaporation. At the same time, however, that evaporation dries soils. Moreover, scientists expect that, as global warming intensifies, longer periods with relatively little precipitation will tend to mark the periods between heavy rainstorms. As a result, droughts are likely to become more frequent and severe in some regions of the United States. Currently, more than half of the lower United States is suffering through prolonged drought, aggravated by the fact that the last six months have been the hottest January-June period on record.
According to the most recent science, the United States must reduce its total global warming emissions by at least 35 percent below 2005 levels by 2020 and by at least 85 percent by 2050 in order to prevent the most devastating consequences of global warming. PennEnvironment Research & Policy Center highlighted two proposals from the Obama administration—carbon pollution and fuel efficiency standards for cars and light trucks through model year 2025, and the first ever carbon pollution standards for new power plants—as critical steps toward meeting these pollution reduction targets.
“How serious this problem gets is largely within our control –but only if we act boldly to reduce the pollution that fuels global warming,” said Garber. “We applaud the Obama administration for their proposals to cut carbon pollution from vehicles and new power plants, and urge them to move forward with finalizing these critical initiatives this year.” | <urn:uuid:61481f35-17d6-4bc3-8560-463cded91086> | 3.171875 | 1,331 | News (Org.) | Science & Tech. | 32.677334 | 1,836 |
Scientists meet to chart roadmap to fusion
Posted October 12, 2012; 01:30 p.m.
The crucial next steps on the roadmap to developing fusion energy will be the focus of more than 70 top fusion scientists and engineers from around the world who will gather at the University of California-Los Angeles (UCLA) this month. The Oct. 15-18 session will kick off a series of annual workshops under the auspices of the International Atomic Energy Agency (IAEA) that will address key scientific and technological challenges facing countries developing fusion as a source of clean and abundant energy for producing electricity.
"There's nothing like face-to-face talk and presentations to help people resolve common challenges," said Hutch Neilson, who directs advanced projects at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) and will chair the workshop at UCLA.
PPPL hosted a worldwide gathering of fusion scientists at Princeton University last year that led to planning for the workshops. "We felt there was a compelling need for international discussions to look at a wide range of options in an unbiased way," said Stewart Prager, director of PPPL. "There's proven to be a lot of interest in the international community."
The workshops aim to help participants chart pathways to the demonstration fusion power plants that the major world programs envision. Such "DEMO" plants would mark the final step before the construction of commercial fusion power stations that could operate by mid-century.
Fusion powers the sun and stars. The process takes place when the atomic nuclei — or ions — in electrically charged gas called plasma fuse under extreme heat and pressure and release a burst of energy. Fusion programs seek to recreate this process on Earth under laboratory conditions.
The IAEA gathering comes against the backdrop of the construction of ITER, a huge experimental facility that the European Union, the United States and five other countries are building in the south of France to showcase fusion as a practical source of energy. Plans call for ITER to produce 500 million watts of fusion power for up to 500 seconds by the late 2020s.
Individual countries are exploring their own next steps toward fusion with different degrees of urgency, based on their perceived need for such energy. The steps themselves remain tentative and subject to government confirmation. "What's needed at present is for the planners to come together and discuss their different roadmaps," said nuclear engineering professor Mohamed Abdou, who will host the workshop as director of the Fusion Science and Technology Center at UCLA. "This will help us understand the goals and assumptions behind the plans of the major fusion programs."
The chief candidate for development as a fusion power plant is the tokamak, the most widely used experimental fusion device today. Tokamaks heat plasma to tens of millions of degrees Celsius and confine it inside a magnetic field that is shaped like a donut or a cored apple, depending on the machine. ITER will be the largest and most powerful tokamak to date. An alternate candidate for a DEMO is the stellarator, a potentially promising but currently less-studied device. Stellarators heat and confine plasma inside a magnetic field that is shaped like a cruller — a spiral wrapped around a circle.
A look at the possible roadmaps that countries are considering:
China—The world's most populous nation seeks to reduce its dependence on coal, which produces 70 percent of its electric power. China is currently pushing ahead with plans for a device called China's Fusion Engineering Test Reactor (CFETR) that would develop the technology for a demonstration fusion power plant. Construction of the CFETR could start around 2020 and be followed by operation of a DEMO in the 2030s.
Europe and Japan—These programs are jointly building a powerful tokamak called JT-60SA in Naka, Japan, as a complement to ITER. Plans call for construction to be completed in 2019. The Japanese and Europeans will then pursue similar but independent timelines. Both programs contemplate starting engineering design work on a DEMO around 2030, following the achievement of ITER milestones, and placing the DEMO in operation in the 2030s.
India—The country could begin building a device called SST-2 to develop components for a DEMO around 2027. India could then start construction of a DEMO in 2037.
Korea—The program plans to build a machine that it calls K-DEMO — a tokamak that would develop components in its first phase, called K-DEMO-1, and then utilize the components in the second phase, or K-DEMO-2. Construction could commence in the mid-to-late 2020s, with operations starting in the mid 2030s.
Russia—Plans call for the development of a fusion neutron source (FNS), a next-step facility that would produce neutrons, the chief form of energy created by fusion reactions, in preparation for a DEMO. The FNS project is part of a Russian commercial development strategy that runs to 2050.
United States—A next-step Fusion Nuclear Science Facility (FNSF) is under consideration. It would be used to investigate materials properties under fusion conditions, and develop components for a DEMO. Construction of the device could start in the 2020s.
Heading the agenda for the first IAEA workshop will be issues ranging from options for materials for fusion facilities to the mission for next-step machines. "These workshops will help us understand the risks of different paths and the costs and benefits," Prager said. "And that really is important for determining the best roadmap." | <urn:uuid:7bfc3b1f-75b4-4333-b9f7-568f9501d6b0> | 2.765625 | 1,148 | News (Org.) | Science & Tech. | 43.61557 | 1,837 |
Posted 14 September 2010 - 02:49 PM
We know that a six base pair sequence AGAATA occurs 1 time in 4096 nucleotides [ (1/4)^6 = 4096 ] correct?
Let's say we have a DNA library that is 50,000 base pairs in total (small library of 50 clones to keep numbers small) it should occur roughly ~12 times [ 50000/4096 = 12.2 ] with 100% probability?
1. What is the probability that it would occur twice? How about 5 times?
2. What is the probability it would occur once in a single clone from this library if the clone is 500 bp long? What about twice?
3. And finally, let's say AGAATA occurs 3 times in one 500 bp clone. Is this significant? What is the equation? I wanted to know basically, "This six base pair sequence has an X-percent probability of occurring within the clone, and an x-percent probability of occurring in the whole library. Thanks.
Posted 14 September 2010 - 06:49 PM
Posted 14 September 2010 - 07:41 PM
Let's assume it's 25% each. And I can replace this sequence with any sequence. I'm just looking on how to do the math. | <urn:uuid:23e83e71-27ba-4d90-a99e-54022cb39fc7> | 2.8125 | 262 | Q&A Forum | Science & Tech. | 85.931199 | 1,838 |
News Releases 2003
NOAA Home Page
NOAA Public Affairs
Above-average precipitation throughout much of the United States during the past three months led to improving drought conditions in many areas, according to scientists at the National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center (NCDC) in Asheville, N.C. NOAA is part of the Commerce Department.
Twenty-four percent of the contiguous United States was in moderate-to-extreme drought in April, down from 37 percent in January and 50 percent during the summer of 2002, based on a widely used measure of drought severity, the Palmer Drought Index.
NCDC researchers said precipitation averaged across the contiguous United States was 0.5 inch (12.7 mm) above the 1895-2003 long-term mean for the February through April three-month period, based on preliminary data. Twenty seven states were significantly wetter than average and 11 states were significantly drier than average. Wetter-than-average conditions were prevalent in the Mid-Atlantic, Southeast and in most states of the western United States. Near-average to drier-than-average conditions stretched from Maine to the Upper Midwest and southwest to Texas.
The precipitation helped alleviate extremely dry conditions in many areas, but the rain and snowfall were not sufficient to end the drought in many parts of the West, where severe drought has occurred for much of the past three to five years. In Colorado, which had its driest year on record in 2002, a single snow storm in March brought a near-record snowfall of 32 inches to Denver Stapleton Airport and totals exceeding 80 inches in higher-elevation locations to the west.
Snow pack, an important source of water for western states, was near or above average at the end of April in much of the front range of the Rocky Mountains from Montana to Colorado and the Sierra Mountains, but snow pack remained below average in large parts of the West. Reservoir storage was also below average in every western state except Washington at the end of April, and river flows remained below average in a large part of the western two-thirds of the nation.
In Montana, where conditions in parts of the state during the summer of 2002 were similar to those experienced during the Dust Bowl years of the 1930's, above average precipitation during the past several months led to a marked improvement in drought conditions. However, according to the U.S. Drought Monitor, severe drought continued to affect a large part of the state at the end of April.
Based on the Palmer Drought Index, the percent of the West in moderate to extreme drought decreased from 81 percent in November 2002 to 44 percent in April. The most widespread drought in the instrumental record occurred in July of 1934, when 97 percent of the West and 80 percent of the contiguous United States were in moderate to extreme drought. The percent of the contiguous United States in moderate to extreme drought fell to 24 percent in April.
Temperatures during the February-April 2003 period were near average to slightly warmer than average across most of the country. The Northeast was the only region with significantly cooler-than-average temperatures. For the contiguous United States as a whole the February-April temperature was 43.3 F (6.3 C), slightly warmer than the 1895-2003 mean. In Alaska the three-month period was 6.0 F (3.3 C) warmer than the 1971-2000 average. During the past 25 years, temperatures in Alaska have averaged 3.2 F (1.8 C) warmer than during the preceding 50 years.
The moderate El Niño episode that began in 2002 weakened during the February-April period, while the average global temperature for combined land and ocean surfaces (based on preliminary data) during April was 0.9 F (0.5 C) above the 1880-2002 long-term mean. This was the fourth warmest April but 0.4 F (0.2 C) cooler than the record warm April which occurred near the end of the 1997-98 El Niño episode. The land-surface temperature average was the seventh warmest on record for April (1.4 F above average), and the global ocean-surface temperature was 0.7 F above average, approximately 0.2 F cooler than April 1998. The year-to-date global average for combined land and ocean surfaces was the third warmest on record.
NOAA Environmental Satellites, Data and Information Service is the nation’s primary source of space-based meteorological and climate data. It operates the nation's environmental satellites, which are used for weather forecasting, climate monitoring and other environmental applications such as fire detection, ozone monitoring and sea surface temperature measurements.
NOAA Environmental Satellites, Data and Information Service also operates three data centers, which house global data bases in climatology, oceanography, solid earth geophysics, marine geology and geophysics, solar-terrestrial physics, and paleoclimatology.
NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources.
On the Web:
NOAA Environmental Satellites, Data and Information Service: http://www.nesdis.noaa.gov
and Global Data: http://www.ncdc.noaa.gov/oa/climate/research/2003/apr/apr03.html | <urn:uuid:284a09fa-3bba-431d-93ed-2895204e7c2c> | 2.84375 | 1,123 | News (Org.) | Science & Tech. | 45.854515 | 1,839 |
Dec. 8, 2009 Nanoscale machines expected to have wide application in industry, energy, medicine and other fields may someday operate far more efficiently thanks to important theoretical discoveries concerning the manipulation of famous Casimir forces that took place at the U.S. Department of Energy's Ames Laboratory.
The groundbreaking research, conducted through mathematical simulations, revealed the possibility of a new class of materials able to exert a repulsive force when they are placed in extremely close proximity to each other. The repulsive force, which harnesses a quantum phenomenon known as the Casimir effect, may someday allow nanoscale machines to overcome mechanical friction.
Though the frictional forces in nanoscale environments are small, they significantly inhibit the function of the tiny devices designed to operate in that realm, explained Costas Soukoulis, a senior physicist at the Ames Lab and Distinguished Professor of physics at Iowa State University, who led the research effort.
Soukoulis and his teammates, including Ames Laboratory assistant scientist Thomas Koschny, were the first to study the use of exotic materials known as chiral metamaterials as a way to harness the Casimir effect. Their efforts have demonstrated that it is indeed possible to manipulate the Casimir force. The findings were published in the Sept. 4, 2009 issue of Physical Review Letters.
Understanding the importance of their discovery requires a basic understanding of both the Casimir effect and the unique nature of chiral metamaterials.
The Casimir effect was named after Dutch physicist Hendrik Casimir, who postulated its existence in 1948. Using quantum theory, Casimir predicted that energy should exist even in a vacuum, which can give rise to forces acting on the bodies brought into close proximity of each other. For the simple case of two parallel plates, he postulated that the energy density inside the gap should decrease as the size of the gap decreases, also meaning work must be done to pull the plates apart. Alternatively, an attractive force that pushes the plates closer together can be said to exist.
Casimir forces observed experimentally in nature have almost always been attractive and have rendered nanoscale and microscale machines inoperable by causing their moving parts to permanently stick together. This has been a long-standing problem that scientists working on such devices have struggled to overcome.
Remarkably, this new discovery demonstrates that a repulsive Casimir effect is possible using chiral metamaterials. Chiral materials share an interesting characteristic: their molecular structure prevents them from being superimposed over a reverse copy of themselves, in the same way a human hand cannot fit perfectly atop a reverse image of itself. Chiral materials are fairly common in nature. The sugar molecule (sucrose) is one example. However, natural chiral materials are incapable of producing a repulsive Casimir effect that is strong enough to be of practical use.
For that reason, the group turned its attention to chiral metamaterials, so named because they do not exist in nature and must instead be made in the lab. The fact that they are artificial gives them a unique advantage, commented Koschny. "With natural materials you have to take what nature gives you; with metamaterials, you can create a material to exactly meet your requirements," he said.
The chiral metamaterials the researchers focused on have a unique geometric structure that enabled them to change the nature of energy waves, such as those located in the gap between the two closely positioned plates, causing those waves to exert a repulsive Casimir force.
The present study was carried out using mathematical simulations because of the difficulties involved in fabricating these materials with semiconductor lithographic techniques. While more work needs to be done to determine if chiral materials can induce a repulsive Casimir force strong enough to overcome friction in nanoscale devices, practical applications of the Casimir effect are already under close study at other DOE facilities, including Los Alamos and Sandia national laboratories. Both have expressed considerable interest in using the chiral metamaterials designed at Ames Laboratory to fabricate new structures and reduce the attractive Casimir force, and possibly to obtain a repulsive Casimir force.
Funding for this research was provided by the DOE Office of Science.
Other social bookmarking and sharing tools:
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
- Zhao et al. Repulsive Casimir Force in Chiral Metamaterials. Physical Review Letters, 2009; 103 (10): 103602 DOI: 10.1103/PhysRevLett.103.103602
Note: If no author is given, the source is cited instead. | <urn:uuid:8dd4d113-9bac-4b8e-bad4-be3b9931562e> | 3.71875 | 960 | News Article | Science & Tech. | 18.044504 | 1,840 |
by Staff Writers
Durham NC (SPX) Nov 23, 2011
If you're a snack-sized squid or octopus living in the ocean zone where the last bit of daylight gives way, having some control over your reflection could be a matter of life and death.
Most predators cruising 600 to 1,000 meters below the surface spot the silhouette of their prey against the light background above them. But others use searchlights mounted on their heads.
Being transparent and a little bit reflective is a good defense against the silhouette-spotters, but it would be deadly against the "headlight fish," says Duke postdoctoral researcher Sarah Zylinski.
Transparency is the default state of both Japetella heathi, a bulbous, short-armed, 3-inch octopus, and Onychoteuthis banksii, a 5-inch squid found at these depths. Viewed from below against the light background, these animals are as invisible as they can be. Their eyes and guts, which are impossible to make clear, are instead reflective.
But when hit with a flash of bluish light like that produced by headlight fish, they turn on skin pigments, called chromatophores, to become red in the blink of an eye.
During ship-board experiments over the Peru-Chile trench in 2010, Zylinski shined blue-filtered LED light on specimens of both creatures to watch them rapidly go from clear to opaque.
When the light was removed, they immediately reverted to transparent. On a second research cruise in 2011 in the Sea of Cortez, Zylinski measured the reflectivity of the octopuses and found they reflected twice as much light in their transparent state as in the opaque state.
Zylinski experimented with 15 to 20 different species of cephalopod pulled up from the deep by the research ships, but only these two responded to the blue light.
"I went through several things I thought would stimulate behaviors," she says. Shallow-water cephalopods (squid, ocotopi and cuttlefish) will change their body patterns for a shadow or shape passing overhead, but these deeper water animals don't, Zylinski says.
The animals could be seen tracking the movements of probes around them, but it was only the light that made them switch on the their pigments.
Zylinski next would like to investigate the link between transparency and habitat depth for the Japetella octopus.
"Smaller young animals are found higher in the water column and have fewer chromatophores, so they are more reliant on transparency, which makes sense because there won't be predators using searchlights there," Zylinski says.
But the mature adults have a higher density of chromatophores making them potentially more opaque and they can be found in deeper waters (below 800 meters) where bioluminescence becomes the dominant light source.
"Mesopelagic Cephalopods Switch Between Transparency and Pigmentation to Optimize Camouflage in the Deep," Sarah Zylinski and Sonke Johnsen. Current Biology 21, Nov. 22, 2011. DOI: 10.1016/j.cub.2011.10.014
Water News - Science, Technology and Politics
Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.
Tuna fishing countries vow to protect shark
Istanbul (AFP) Nov 19, 2011
Countries involved in bluefin tuna fishing have decided to do more to protect a species of shark against collateral killing, environmental groups said Saturday. Elizabeth Griffin Wilson of the Oceana group said the 48-state International Commission for the Conservation of Atlantic Tunas (ICCAT) had ruled that tuna fishermen who find a silky shark in their nets must put it back in the sea. ... read more
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2011 - Space Media Network. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement| | <urn:uuid:b3341e2f-d121-453d-99d3-f68a7c16e1e3> | 3.40625 | 910 | Truncated | Science & Tech. | 44.679049 | 1,841 |
BERLIN (AP) -- A meteor exploded in the sky above Russia on Friday, causing a shockwave that blew out windows injuring hundreds of people and sending fragments falling to the ground in the Ural Mountains. Here's a look at those objects in the sky:
What's the difference between a meteor and a meteorite?
Meteors are pieces of space rock, usually from larger comets or asteroids, which enter the Earth's atmosphere. Many are burned up by the heat of the atmosphere, but those that survive and strike the Earth are called meteorites. They often hit the ground at tremendous speed -- up to 30,000 kilometers an hour (18,642 mph) according to the European Space Agency. That releases a huge amount of force.
How common are meteorite strikes?
Experts say smaller strikes happen five to 10 times a year. Large impacts such as the one Friday in Russia are rarer but still occur about every five years, according to Addi Bischoff, a mineralogist at the University of Muenster in Germany. Most of these strikes happen in uninhabited areas where they don't cause injuries to humans.
What caused the damage in Russia?
Alan Harris, a senior scientist at the German Aerospace Center in Berlin, said most of the damage would have been caused by the explosion of the meteor as it broke up in the atmosphere. The explosion caused a shockwave that sent windows and loose objects flying through the air in a radius of several kilometers. By the time the remaining fragments hit the ground they would have been too small to cause significant damage far from the site of impact, he said.
Is there any link to the asteroid fly-by taking place later Friday?
No, it's just cosmic coincidence, according to European Space Agency spokesman Bernhard von Weyhe, who says Asteroid 2012DA14 is unrelated to the meteorite strike in Russia.
When was the last comparable meteorite strike?
In 2008, astronomers spotted a meteor heading toward Earth about 20 hours before it entered the atmosphere. It exploded over the vast African nation of Sudan, causing no known injuries. The largest known meteorite strike in recent times was the "Tunguska event" that hit Russia in 1908. Even that strike, which was far bigger than the one that happened over Russia on Friday, didn't injure anyone. Scientists believe that an even larger meteorite strike may have been responsible for the extinction of the dinosaurs about 66 million years ago. According to that theory, the impact would have thrown up vast amounts of dust that blanketed the sky for decades and altered the climate on Earth.
What can scientists learn from Friday's strike?
Bischoff says scientists and treasure hunters are probably already racing to find pieces of the meteorite. Some meteorites can be very valuable, selling for up to €500 ($670) per gram depending on their exact composition. Because meteors have remained largely unchanged for billions of years -- unlike rocks on Earth that have been affected by erosion and volcanic outbreaks -- scientists will study the fragments to learn more about the origins of matter. Harris, of the German Aerospace Center, says some meteorites are also believed to carry organic material and may have influenced the development of life on Earth.
What would happen if a meteorite hit a major city?
Scientists hope never to find out, but they're still trying to prepare for such an event. Von Weyhe, the European Space Agency spokesman, says experts from Europe, the United States and Russia are already discussing how to spot potential threats sooner and avert them. But don't expect a Hollywood style mission to fly a nuclear bomb into space and blow up the asteroid.
"It's a global challenge and we need to find a solution together," he said. "But one thing's for sure, the Bruce Willis "Armageddon" method won't work." | <urn:uuid:6a6d3e99-a2c5-4fc6-88c0-fdbf51275145> | 3.484375 | 787 | News Article | Science & Tech. | 46.563733 | 1,842 |
These pictures were taken 13 November 2005 at about 1:15 PM from the bay shore on the UW-Green Bay. Water levels in Green Bay dropped more than 3 feet from strong southwest to northeast winds.
Point Sable is shown at the horizon.
Bay Beach and the power plant near the mouth of the Fox River in Green Bay, WI.
( source: NOAA Great Lakes Water Level Data http://tidesandcurrents.noaa.gov; choose Products, Great Lakes Water Levels, Active Stations from the pull-down menu; and then choose Lake Michigan and Green Bay)
Water levels changed by more than 5 feet in a two day period. Winds from about 200 to 240 degrees SW drive water out of the lower bay. This was the case on November 13, 2005 when water levels dropped below 574 feet. Winds peaked at 56 mph from a direction of 220 degrees on November 13th. Winds from the NE (30 to 60 degrees) funnel water into the lower bay as was the case on November 15th when water levels peaked at 579.5 feet.
|NWS Daily Wind data for November 2005, Green Bay, WI|
|Day||Daily avg||Peak 2min||Peak Wind|
(above created March 21, 2005 KJF)
Wind Event of 11 May 2006.
Greater than 2 feet of INCREASE. Strong NE winds were from a low pressure system that was over southern L. Michigan. Area also received about 3 inches of rain on Thursday 11 May 2006.
updated 18 May 2006 | <urn:uuid:0fcc547e-d988-422d-a639-cfcebeeb5bfb> | 2.9375 | 320 | Knowledge Article | Science & Tech. | 84.161987 | 1,843 |
8. Predicates and Utilities
Now that we know how to create classes, access slots, and define
methods, it might be useful to verify that everything is doing ok. To
help with this a plethora of predicates have been created.
- Function: class-v class
- Return a vector with all the class's important parts in it. This vector
is not a copy. Changing this vector changes the class. The CLOS method
find-class will have the same effect.
- Function: find-class symbol &optional errorp
- CLOS function. In EIEIO it returns the vector definition of the class.
If there is no class,
nil is returned if errorp is
- Function: class-p class
- Return non-
nil if class is a class type.
- Function: object-p obj
- Return non-
nil if obj is an object.
- Function: slot-exists-p obj-or-class slot
- Return Non-
nil if obj-or-class contains slot in its class.
- Function: slot-boundp object slot
nil if OBJECT's SLOT is bound.
Setting a slot's value makes it bound. Calling slot-makeunbound will
make a slot unbound.
OBJECT can be an instance or a class.
- Function: class-name class
- Return a string of the form #<class myclassname> which should look
similar to other lisp objects like buffers and processes. Printing a
class results only in a symbol.
- Function: class-option class option
- Return the value in CLASS of a given OPTION.
(class-option eieio-default-superclass :documentation)
Will fetch the documentation string for
- Function: class-constructor class
- Return a symbol used as a constructor for class. This way you can
make an object of a passed in class without knowing what it is. This is
not a part of CLOS.
- Function: object-name obj
- Return a string of the form #<object-class myobjname> for obj.
This should look like lisp symbols from other parts of emacs such as
buffers and processes, and is shorter and cleaner than printing the
object's vector. It is more useful to use
object-print to get
and object's print form, as this allows the object to add extra display
information into the symbol.
- Function: object-class obj
- Returns the class symbol from obj.
- Function: class-of obj
- CLOS symbol which does the same thing as
- Function: object-class-fast obj
- Same as
object-class except this is a macro, and no
type-checking is performed.
- Function: object-class-name obj
- Returns the symbol of obj's class.
- Function: class-parents class
- Returns the direct parents class of class. Returns
it is a superclass.
- Function: class-parents-fast class
- Just like
class-parent except it is a macro and no type checking
- Function: class-parent class
- Deprecated function which returns the first parent of class.
- Function: class-children class
- Return the list of classes inheriting from class.
- Function: class-children-fast class
- Just like
class-children, but with no checks.
- Function: same-class-p obj class
t if obj's class is the same as class.
- Function: same-class-fast-p obj class
- Same as
same-class-p except this is a macro and no type checking
- Function: object-of-class-p obj class
t if obj inherits anything from class. This
is different from
same-class-p because it checks for inheritance.
- Function: child-of-class-p child class
t if child is a subclass of class.
- Function: generic-p method-symbol
method-symbol is a generic function, as
opposed to a regular emacs list function.
It is also important to note, that for every created class, a two
predicates are created for it. Thus in our example, the function
data-object-p is created, and return
t if passed an object
of the appropriate type. Also, the function
is created which returns
t if the object passed to it is of a
type which inherits from
This document was generated
by XEmacs Webmaster on October, 2 2007 | <urn:uuid:682e5e0f-50d3-4857-b1c8-1f2831d215f0> | 2.671875 | 979 | Documentation | Software Dev. | 68.943805 | 1,844 |
Scientists have apparently broken the universe’s speed limit.
For generations, physicists believed there is nothing faster than light moving through a vacuum — a speed of 186,000 miles per second.
But in an experiment in Princeton, N.J., physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering.
The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum.
Researchers say it is the most convincing demonstration yet that the speed of light — supposedly an ironclad rule of nature — can be pushed beyond known boundaries, at least under certain laboratory circumstances.
“This effect cannot be used to send information back in time,” said Lijun Wang, a researcher with the private NEC Institute. “However, our experiment does show that the generally held misconception that ‘nothing can travel faster than the speed of light’ is wrong.”
The results were published in Thursday’s issue of the journal Nature.
The achievement has no practical application right now, but experiments like this have generated considerable excitement in the small international community of theoretical and optical physicists.
Previously Thought Impossible “This is a breakthrough in the sense that people have thought that was impossible,” said Raymond Chiao, a physicist at the University of California at Berkeley who was not involved in the work. Chiao has performed similar experiments using electric fields.
In the latest experiment, researchers at NEC developed a device that fired a laser pulse into a glass chamber filled with a vapor of cesium atoms. The researchers say the device is sort of a light amplifier that can push the pulse ahead.
Previously, experiments have been done in which light also appeared to achieve such so-called superluminal speeds, but the light was distorted, raising doubts as to whether scientists had really accomplished such a feat.
The laser pulse in the NEC experiment exits the chamber with almost exactly the same shape, but with less intensity, Wang said.
The pulse may look like a straight beam but actually behaves like waves of light particles. The light can leave the chamber before it has finished entering because the cesium atoms trade energy with the leading edge of the waves as they pass through.
This produces an almost identical light pulse that exits the chamber and travels about 60 feet before the main part of the laser pulse finishes entering the chamber, Wang said.
Wang said the effect is possible only because light has no mass; the same thing cannot be done with physical objects.
The Princeton experiment and others like it test the limits of the theory of relativity that Albert Einstein developed nearly a century ago.
According to the special theory of relativity, the speed of particles of light in a vacuum, such as outer space, is the only absolute measurement in the universe. The speed of everything else — rockets or inchworms — is relative to the observer, Einstein and others explained.
Only in the Lab In everyday circumstances, an object cannot travel faster than light.
The Princeton experiment and others change these circumstances by using devices such as the cesium chamber rather than a vacuum.
Ultimately, the work may contribute to the development of faster computers that carry information in light particles.
Not everyone is convinced the NEC scientists did what they claim.
Aephraim Steinberg, a physicist at the University of Toronto, said the light particles coming out of the cesium chamber may not have been the same ones that entered, so he questions whether the speed of light was broken.
Still, the work is important, he said: “The interesting thing is how did they manage to produce light that looks exactly like something that didn’t get there yet?” | <urn:uuid:407aeee2-2230-4a8f-8647-4aed4b649a2d> | 3.578125 | 766 | News Article | Science & Tech. | 38.07652 | 1,845 |
Size Adult females may attain a body length of 56 mm and males 47 mm.
Description The adult frog has a somewhat flattened body; an eye with a dark, horizontal band running through it and a vertically elliptical pupil; and long limbs with large, spatulate adhesive pads at the tips of the fingers and toes. While the fingers lack webbing, the toes are extensively webbed up to the last segment of the fifth toe (and this sometimes extends to the tip). No thumb-like metacarpal tubercle is present. A glandular fold is present behind the eye (above the tympanum). The upper body surface is generally green to brown and covered with well-defined reddish brown spots and patches of variable size. There are distinct transverse bands present on the limbs of most specimens. The underside colour is mainly whitish except for the limbs which are fleshy-orange, while the skin is densely granular except on the throat. The advertisement call is a clear high-pitched ringing note produced at a rate of about one per second.
Biology This species is endemic to certain mountain ranges in the winter rainfall region of the Western Cape . It only occurs in undisturbed habitat within the Mountain Fynbos or Afromontane Forest vegetation types and is dependent on clear, fast flowing, perennial mountain streams for breeding. When they are not breeding, ghost frogs utilize damp terrestrial habitat surrounding the streams and have even been found sheltering under rocks several hundred metres away from the nearest watercourse. They are well adapted for climbing in steep, rocky terrain and enter rock crevices and caves. By means of the adhesive pads on their fingers and toes they are able to climb virtually any wet or damp surface, including smooth, vertical rock faces.
Breeding takes place from early to mid-summer (about October to January) when stream flow has reduced following the rainy season. The males can be heard calling both during the day and after dark. They call from positions adjacent to waterfalls, cascades and small rapids such as from rock cracks or from rocks either on the banks of streams or protruding from the water. Ghost frogs have a complex courtship display but actual egg-laying has not been observed. The eggs, which are laid singly, have been found scattered in exposed positions in small quiet, shady pools connected to the main stream. They are large and yellow with each one contained in a stiff jelly capsule. Clutch sizes have been found to vary from 50 to 208 eggs. The eggs hatch after four or five days. Initially the young tadpoles live off a large reserve of yolk, where after they feed by grazing over algae-covered rocks, and these “feeding trails” can be seen on rocks in quieter pools. The distinctive tadpoles attain a length of about 60 mm and are well-adapted for a life in fast flowing streams. In particular, they have large sucker-like mouths for clinging to rocks in fast flowing water and even use their mouths to climb slippery rock faces such as waterfalls. During the day, the tadpoles are usually found attached to the underside of submerged rocks. They are slow developers, taking over twelve months to develop into frogs, and are generally ready to leave the water during the period from March to May.
Distribution This species is endemic to certain Cape Fold Mountains in the western part of the Western Cape Province.
Distribution in GCBC This extends from the higher mountains of the Cederberg southwards into the Groot Winterhoek Mountains.
Conservation status Not threatened.
Threats No serious threats.
Current studies This species was assessed in the Southern African Frog Atlas Project (published in 2004). A project to investigate the genetic diversity in the Cape Fold Mountain ghost frogs is currently underway. | <urn:uuid:79ca8b7a-838d-4030-9fff-d37b3895249e> | 3 | 775 | Knowledge Article | Science & Tech. | 48.637492 | 1,846 |
Science Wednesday: Ready for Takeoff
Each week we write about the science behind environmental protection. Previous Science Wednesdays.
While I’ve come to expect extra scrutiny when flying, I was momentarily flustered when the pilot needed to know my weight so he could compute his preflight plans. (155 pounds.)
This morning I joined Eric Vance, EPA’s chief photographer, EPA scientist Steve Klein, and U.S. Fish and Wildlife Service pilot V. Ray Bentley aboard a four-seat, single-engine plane for a flight over the Willamette River Valley in western Oregon.
The landscape we flew over is the subject of the Willamette Ecosystem Services Project (WESP), an ambitious, large-scale, integrated, and multi-disciplinary research effort to quantify the benefits people derive from the environment. The study also focuses on exploring how human activities stress those benefits. The overall goal is to provide decision makers, stakeholders, and others across the Willamette River Valley with rigorous scientific information they can use to assess current conditions and plan for the future of their community.
All told, the Willamette River Valley Ecosystem includes some 7.5 million acres. To get a better picture of what’s happening across such a large area, it helps to get a bird’s eye view.
Time to fly.
Our flight took us over the Willamette River as it winds from Corvallis to the suburbs of Eugene, a diverse and productive landscape. Over the drone of the engine and intermittent blasts of cool air that roared into cockpit when Eric opened his window to take pictures, Steve explained what he was seeing from a scientist’s perspective: how the flow and course of the river has been shaped by human forces, the patterns and types of forest and other natural habitats, what types of crops where growing in the large agricultural fields below, and the shifting boundaries between agriculture, forest, and what he referred to as “the built environment” (homes, roads, and industry, including the massive paper mill we could not only see, but smell—a thick, burnt-syrup kind of aroma).
My flight was just one of the many excellent experiences I’ve had this week visiting with scientists in EPA’s Western Ecology Division. I’ve learned about research projects as diverse as the 7.5-million-acre WESP, to plans to investigate the potential environmental impacts of things as tiny as those used in nanotechnology.
It’s been a great week and I’ll have lots to think about on the flight back to Washington. I won’t even flinch if the pilot asks me how much I weigh.
About the Author: Aaron Ferster is the chief science writer in EPA’s Office of Research and Development. He is the Science Wednesday editor, and a regular contributor.
Editor's Note: The opinions expressed in Greenversations are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog. | <urn:uuid:ce3fb446-5624-42bb-b177-69478ceb1f84> | 2.671875 | 642 | News (Org.) | Science & Tech. | 44.003369 | 1,847 |
Oddities of Physics (Oct, 1937)
Oddities of Physics
Science is much closer to our daily lives than many of us believe. Some of the simplest phenomena and everyday occurrences which do not strike one as of any particular interest, abound with scientific explanations.
WHO would imagine, when watching soldiers marching across a bridge, that they do so under orders to “break step.” If this were not done there would be a rhythmic motion set up in the bridge structure—a steady tramp-tramp—which would likely disrupt any small bridge and perhaps even a very large one (Fig. 1).
Can a submarine remain stationary at any desired level?
The answer is that it cannot, unless a slight headway is maintained or water is admitted to and discharged from the trimming tanks. A submarine cannot find a state of hydrostatic equilibrium or a point at which all pressures are equal.
Is it possible for a ship like the Titanic to sink in deep water, and eventually reach a point where the water pressure is great enough to prevent the ship from settling to the bed of the sea?
Although this question has been argued pro and con many times in the columns of scientific journals, the fact remains that no such effect will be found; the wrecked ship will descend until it rests on the ocean bed.
How fast would an airplane have to fly to leave the influence of this earth forever?
Scientists have computed, that any space flyer would have to be hurled from the earth at an initial velocity in excess of 7 miles per second. Such a ma- chine would reach the moon in less than 10 hours. (However, gradual acceleration could effect a departure, without such a high starting speed.) Could one man hold a Zeppelin?
The answer is yes, if the ship is carefully trimmed and balanced, as is the case when she is just brought out from the hangar preparatory to a flight.
Does putting oil on the water help to quiet angry waves?
Yes, this is a regular recognized practice at sea when the waves are running high and a ship is in distress. The oil helps to prevent white caps, but it does not stop the general swell of the waves.
Does the rotation of the earth cause wear on certain banks of a river?
Yes, theoretically, at least. There doesn’t seem to be any measurable proof. In rivers running north and south, in the Northern Hemisphere, there is a tendency to wear away right-hand banks, as shown in the diagram in Fig. 7, due to the rotation of the earth. In the Southern Hemisphere it is the left-hand banks that receive the most wear.
How does science help in releasing a tight pulley.’ A usual method of removing a pulley is to apply heat from a blow-torch to the pulley and ice bags to the steel shaft. The resulting contraction and expansion often permit the removal of the pulley when it otherwise refuses to yield.
Fig. 9 shows one way to stop a “flue” fire, simply by placing a cap or pan over the top of the chimney and thus checking draft of air through the chimney. Another trick is to put salt in the fire in a stove con- nected with the burning flue; the gases gen-crated help to snuff out the flames in the chimney.
Fig. 10 shows how violins and other high-pitched instruments are placed near the “mike” in broadcasting, while the bass violins, etc., are placed further back. The low notes, emitted by bass instruments, have more energy in them, or are stronger than the high-pitched notes coming from the flute, violin, etc., hence, in broadcasting studios, the majority of wind instruments are usually placed further away from the “mike,” as are drums, etc.
An interesting and everyday occurrence in homes and offices is the vibration of a metal picture frame, or other similar object, when a certain note is sounded on the piano, or radio (Fig. 11). This is due to the fact that the frame has a natural frequency corresponding to the note struck, hence it vibrates sympathetically.
It is not generally known that if a high voltage direct current is passed through a wire grid in a chimney, smoke from the boilers can be eliminated. The high voltage electrical charges cause the carbon particles, comprising the smoke, to become charged and they are precipitated to the bottom of the stack.
Fig. 13 shows an interesting problem which public address engineers have to conjure with at times. A person sitting a certain distance from the speaker’s platform may experience the unusual sensation of hearing the speaker’s voice coming out of the loudspeaker before he hears the natural voice coming from the stage. This is due to the fact that sound travels only at about 1100 feet per second in air, while the electrical current, carrying the voice from the “mike” to the loud speaker, travels at 186,000 miles per second. Consequently, good judgment has to be used by the engineers in planning P. A. systems.
If a tank full of water has 3 openings, as shown in Fig. 14, the middle jet will produce the longest stream.
Does smoke blowing downward from a chimney indicate rain?
No. This is an old theory, but it has little to recommend it. Smoke rises because of its higher temperature. If the outside air is as warm as the smoke, or if the smoke is “chilled,” as on a moist, humid day, the smoke will fall.
In a double-track railroad running north and south there is a greater wear on the outer rails. This is due to the earth’s rotation. Any train, in the northern hemisphere, running north has a greater eastward motion at the point of its location a moment before than at the moment the analysis is made. Hence, in case 1, the track presses harder against the train, causing greater wear on the outer rail, while in case 2, the train presses more strongly against the outer rail, causing extra wear there.
Why is air pumped down to divers under the water?
Air is pumped through a hose constantly to submerged divers partly to counter-balance the pressure of the water. The greater the depth the higher the air pressure pumped to him.
A problem in weighing: If a druggist found that someone had taken some of the weights for the scale and only left a 2-oz. and a 5-oz. weight, how could the druggist weigh 1 oz. of powder?
He puts the 5-oz. weight in one pan, in the other pan he puts the 2-oz. weight and enough powder to balance the scales. He now has 3 oz. of powder in the pan. Then he puts the 2-oz. weight in one pan and the powder in the other, removing sufficient powder to balance the scale. The 1 oz. of powder removed to effect a balance will be the quantity desired.
The principle of inertia is well shown in the simple trick of striking the end of an axe handle with a hammer in order to drive the axe more firmly on to the handle, as shown in Fig. 19. When the end of the handle is struck as at “H” the steel axe, due to its inertia, tends to preserve its position and thus the wooden handle is driven more firmly into the axe.
From what depth can an ordinary pump lift water?
About 26 feet is the maximum lift for an ordinary pump. If a force-pump is employed, then a check valve is placed well down in the pipe so as to be fairly close (18 to 24 feet) to the water, this valve being operated by a rod inside the pipe. Theoretically, the pressure of the atmosphere will raise water about 32 feet when a vacuum is established inside the pump lift pipe, but due to losses in the valves, etc., about 26 feet is a good working limit.
An interesting every-day problem concerns cars fitted with a vacuum-tank system for “sucking” gas from the tank at the rear. These sometimes get out of order, or leak, or they may have been drained while making repairs on the car. A trick worth remembering is that gas may be forced up into the vacuum tank by exerting air pressure on the pipe where the tank is ordinarily filled, as shown in Fig. 21. With a piece of rubber hose or inner tube, air may be blown into the tank from the mouth or from a tire pump. | <urn:uuid:df45235b-2e7c-425e-a092-456287ff6504> | 3.09375 | 1,774 | Personal Blog | Science & Tech. | 64.020219 | 1,848 |
U.S.: Hurrican Sandy - The New "Normal"
Some called it Frankenstorm Sandy, some Superstorm Sandy, needless to say Hurricane Sandy was the worst storm the New York Metro area and New Jersy has seen in decades, if not ever. Earlier in October many islands in the Carribean were devastated by the storm. As it made it's way north up the Atlantic coast of the U.S. it became apparent that Hurricane Sandy would turn to the west and slam directly into the densly populated Metro Area. Photos of the aftermath [here, here and here] give a sense of the destruction, but it's the stories [here, and here] on the ground that describe the impact on people, the environment and other species.
While some referred to Hurricane sandy as a 100-year, or even a 500-hundred year storm, many climate watchers pointed out the obvious: a warmer climate facilitates stronger storms. And none other than respected climate scientists like James Hansen have the data. The devastation of Sandy on the New York Metro area now has even moderate politicians finally speaking up about climate change. That in the wake of three U.S. presidential debates where the word "climate" never even came up. Most people picking up what's left of their homes and lives on the east coast of the United States and in the Carribean probably think it's time to end climate silence now . | <urn:uuid:912e7e36-ed94-4f5c-9119-7c651b0b1543> | 2.5625 | 289 | News Article | Science & Tech. | 52.258483 | 1,849 |
||The Curve of
The key to energy production in stars lies in what nuclear physicists call the
curve of binding energy, which is illustrated in the following figure.
Curve of binding energy.
This plot shows the amount of binding energy per nucleon (A nucleon is either a
neutron or a proton. The nucleon number is the sum of the number of
protons in a nucleus; thus, it is equal to the atomic mass number)
as a function of the atomic mass number A. The energy units
are MeV, which stands for "million electron-volts", a standard unit of energy in
This curve indicates how stable atomic nuclei are; the higher the curve the more
stable the nucleus. Notice the characteristic shape, with a peak near A=60. These
nuclei (which are near iron in the periodic table and are called
the iron peak nuclei) are the most stable in the
Universe. The shape of this curve suggests two possibilites for converting
significant amounts of mass into energy.
From the curve of binding energy, the heaviest nuclei are less stable than the
nuclei near A=60. This suggests that energy can be released if heavy nuclei split
apart into smaller nuclei having masses nearer A=60. This process is called
fission. It is the process that powers atomic bombs and nuclear power
The curve of binding energy suggests a second way in which energy could be released
in nuclear reactions. The lightest elements (like hydrogen and helium) have nuclei
that are less stable than heavier elements up to A~60. Thus, sticking two light
nuclei together to form a heavier nucleus can release energy. This process is
called fusion, and is the process that powers hydrogen (thermonuclear)
bombs and (perhaps eventually)
fusion energy reactors.
In both fission and fusion reactions the total masses after the reaction are
less than those before. The
"missing mass" appears as energy, with the amount
given by the famous Einstein equation.
Stellar Energy Production
Both fission and fusion reactions have the potential to convert a small amount of
mass into a large amount of energy and could conceivably account for the energy
sources of stars. However, stars are made from light elements (mostly hydrogen and
helium). Thus, fission cannot be initiated in stars as a source of energy, but
fusion is quite possible if the right conditions prevail. As we shall see, these
conditions can be found in the cores of stars, and thermonuclear fusion is the
primary source of stellar energy. | <urn:uuid:08974a84-13f5-438a-a98a-8f4dc8b77b64> | 4 | 556 | Academic Writing | Science & Tech. | 45.999487 | 1,850 |
An accessor method is an instance method that gets or sets the value of a property of an object. In Cocoa’s terminology, a method that retrieves the value of an object’s property is referred to as a getter method, or “getter;” a method that changes the value of an object’s property is referred to as a setter method, or “setter.” These methods are often found in pairs, providing API for getting and setting the property values of an object.
You should use accessor methods rather than directly accessing state data because they provide an abstraction layer. Here are just two of the benefits that accessor methods provide:
You don’t need to rewrite your code if the manner in which a property is represented or stored changes.
Accessor methods often implement important behavior that occurs whenever a value is retrieved or set. For example, setter methods frequently implement memory management code and notify other objects when a value is changed.
Because of the importance of this pattern, Cocoa defines some conventions for naming accessor methods. Given a property of type
type and called
name, you should typically implement accessor methods with the following form:
The one exception is a property that is a Boolean value. Here the getter method name may be
isName. For example:
This naming convention is important because much other functionality in Cocoa relies upon it, in particular key-value coding. Cocoa does not use
getName because methods that start with “get” in Cocoa indicate that the method will return values by reference. | <urn:uuid:fa5c2fa1-af36-4ff5-8788-a254b8275e51> | 4.3125 | 334 | Documentation | Software Dev. | 33.366527 | 1,851 |
In addition to using data manipulation statements directly, as just described, it is also possible to manipulate table data by calling a procedure. Procedures perform the specific data manipulations laid out in the procedure definition.
Any SQL statement in the grouping procedural-sql-statement, see the Mimer SQL Reference Manual, Chapter 12, Procedural SQL Statements, can be used in a procedure, and this includes all the data manipulation statements.
The use of procedures allows data manipulation within the database to be controlled both in terms of strictly defining which data manipulation operations are performed and also in terms of regulating which database objects can be affected.
A procedure is invoked by using the CALL statement. In the case of a result set procedure, used in an ESQL context, the CALL statement is not used directly but is specified in a cursor declaration. An ident requires EXECUTE privilege on a procedure in order to call it.
In the CALL statement, the value-expressions or assignment targets specified for each of the procedure parameters must be of a data type that is assignment-compatible, see the Mimer SQL Reference Manual, Chapter 6, Assignments, with the parameter data type.
See the Mimer SQL Reference Manual, Chapter 12, CALL, for full details of the CALL statement and the Mimer SQL Programmer's Manual, chapter 12, Mimer SQL Stored Procedures, for a general discussion of the stored procedure functionality supported in Mimer SQL.
Examples of Calling Procedures
Invoke the procedure called SEARCH in the MIMER_STORE_MUSIC schema:CALL mimer_store_music.search(:title, :artist, 0);
Declare a cursor that will be used when result-set data is fetched from the result set procedure called BARCODE:DECLARE c_2 CURSOR FOR CALL mimer_store.barcode(itm.ean_code);
Upright Database Technology AB
Voice: +46 18 780 92 00
Fax: +46 18 780 92 40 | <urn:uuid:8183da38-272d-4f14-8018-c0e29c672f1b> | 2.71875 | 418 | Documentation | Software Dev. | 24.696794 | 1,852 |
File:Recent Sea Level Rise.png
From Global Warming Art
This figure shows the change in annually averaged sea level at 23 geologically stable tide gauge sites with long-term records as selected by Douglas (1997). The thick dark line is a three-year moving average of the instrumental records. This data indicates a sea level rise of ~18.5 cm from 1900-2000. Because of the limited geographic coverage of these records, it is not obvious whether the apparent decadal fluctuations represent true variations in global sea level or merely variations across regions that are not resolved.
For comparison, the recent annually averaged satellite altimetry data from TOPEX/Poseidon are shown in red. These data indicate a somewhat higher rate of increase than tide gauge data, however the source of this discrepancy is not obvious. It may represent systematic error in the satellite record and/or incomplete geographic sampling in the tide gauge record. The month to month scatter on the satellite measurements is roughly the thickness of the plotted red curve.
Much of recent sea level rise has been attributed to global warming.
Original data for this figure is from the Permanent Service for Mean Sea Level (PSMSL). Douglas (1997), defined the following criteria for selecting records from the PSMSL which were long, reliable, and avoided large vertical geologic changes:
- Each record should be at least 60 years in length
- Not be located at collisional plate boundaries
- At least 80% complete
- Show reasonable agreement at low frequencies with nearby gauges sampling the same water mass
- Not be located in regions subject to large post-glacial rebound
He subsequently identified 24 PSMSL records meeting all five of these criteria:
- Auckland, New Zealand, 1903-2000
- Balboa, Panama, 1908-1996
- Brest, France, 1807-2000
- Buenos Aires, Argentina, 1905-1987
- Cascais, Portugal, 1882-1993
- Cristobal, Panama, 1909-1980
- Dunedin, New Zealand, 1900-1998
- Fernandina, Florida, 1897-2003
- Genova, Italy, 1884-1997
- Honolulu, Hawaii, 1905-2003
- Key West, Florida, 1913-2003
- Lagos, Portugal, 1908-1999
- La Jolla, California, 1924-2003
- Lyttelton, New Zealand, 1924-2000
- Marseille, France, 1885-2000
- Newlyn, Cornwall, England, 1915-2003
- Pensacola, Florida, 1923-2003
- Quequen, Argentina, 1918-1982
- San Diego, California, 1906-2003
- San Francisco, California, 1854-2003
- Santa Cruz de Tenerife, Canary Islands, 1927-1990
- Santa Monica, California, 1933-2003
- Trieste, Italy, 1905-2001
- Wellington, New Zealand, 1901-1988
After slight corrections following Douglas (1997) for any remaining post-glacial rebound at these sites (typically ~3 cm/century), the tide gauge data from these sites were plotted in no particular order as the thin lines in the above figure. One site, Wellington, was omitted because the author of this figure was unable to locate the corresponding record from the PSMSL.
This figure was prepared from publicly available data by Robert A. Rohde.
- [abstract] [ Bruce C. Douglas (1997). "Global Sea Rise: A Redetermination". Surveys in Geophysics 18: 279-292.
GWArt images and pages linking to this file
Wikipedia pages and images linking to this file
Click on a date/time to view the file as it appeared at that time.
|current||18:38, 3 February 2007||800×561 (80 KB)||Robert A. Rohde|
|00:06, 18 November 2005||537×373 (47 KB)||Robert A. Rohde| | <urn:uuid:f043ae14-22cc-4ca6-b2ac-331ed18bcea0> | 3.484375 | 821 | Knowledge Article | Science & Tech. | 45.548251 | 1,853 |
Thousands of inventors, engineers and entrepreneurs gathered in a suburban Washington convention center on Monday for the annual three-day meeting of Arpa-E, the Advanced Research Projects Agency – Energy. It wasn’t quite the Oscars. At the registration desk, attendees received a goody bag that included a report on clean energy from the Pew Charitable Trusts and a refrigerator magnet that showed the periodic table of the elements.
But the breakout sessions held true to Arpa-E’s tradition: there were lots of swing-for-the-fence ideas. These included finding a high-efficiency, low-cost way to turn surplus natural gas into liquid fuel for cars and trucks, and identifying something to burn other than hydrocarbons so that carbon dioxide is not one of the byproducts.
One researcher proposed burning aluminum instead. One challenge is that the ashes, or oxidized metal, would be hard to recycle back into aluminum without big releases of carbon dioxide.
Arpa-E is the Energy Department’s effort to imitate the better-known Pentagon arm known as the Defense Research Projects Agency, or Darpa. Darpa laid the groundwork for the Internet and still finances high-potential ideas in their early speculative stages in the expectation that a few will be major breakthroughs; Arpa-E tries to do the same in energy.
So far the agency has invested $770 million in 285 projects, “and we’re proud of every single one of them,’’ said Cheryl Martin, the agency’s deputy director, in opening remarks to several thousand attendees. Although most will never be commercialized, the strikeouts are not as important as the home runs.
One particularly ambitious idea presented on Monday was to re-engineer plants so that their leaves reflect rather than absorb more light. In an age of global climate change, with shifting rainfall patterns, changing reflectivity holds appeal. The technology would save water, which means saving energy because the water that the plants need often must be pumped. It could prove a way to help crops grow with less rainfall.
Some of those crops can be used to produce energy as well. And increasing the amount of light that bounces back into space would help to limit global warming.
The notion is that crops will absorb light in the visible spectrum yet reflect some of the infrared and ultraviolet light, which heats the leaves. “Plants have a maximum efficiency of about 6 percent,’’ said Robert Conrado, an agency scientist. And plants regulate their temperature much the way people do, by giving off water, which cools as it evaporates. “All energy that is not able to be captured is dissipated as heat,’’ he said. “And that’s a lot of water.’’
In a hot climate, a cornfield can give off the equivalent of eight inches of rainfall in a month, he said, and agricultural irrigation accounts for 81 percent of water use in this country. The proportion is even higher in poorer places, which have fewer dishwashers and washing machines.
And some of that energy would radiate back into space, reducing global warming, Dr. Conrado said.Whether butterfly wings or fruits, he said, “nature has already evolved mechanisms for tailored light reflection.” | <urn:uuid:9c7ff38d-f59d-4c6a-9f4c-55a526aa301b> | 3.0625 | 687 | News Article | Science & Tech. | 43.410171 | 1,854 |
The Physics Factbook™
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
topic index | author index | special index
The purpose of this analysis is to determine the evolution of gravity in the Mario video game series as video game hardware increases.
Gravity is force which is responsible for keeping us on the ground. It is also the force that prohibits us from jumping 50 feet in the air. However, in Mario's world, gravity does not quite work that way. Mario is able to jump 5 times his height and fall with accelerations that would be deadly to humans.
We will find Mario's acceleration due to gravity by using the formula
s = s0 + v0t + ½ at2
where s is the distance he falls, s0 is his initial distance, which is 0, v0 is his initial vertical velocity, which is also 0, a is his acceleration due to gravity, and t is the time it takes for him to fall. When we solve this formula for a, we get
a = 2s / t2
First, you must find the time it took Mario to fall from the edge of the ledge to the ground in each game. To do this, we opened each clip in Quicktime movie player, and using the frame by frame option, found the total number of frames it took Mario to fall. We then used the formula:
Time = (Number of Frames) / (Frame Rate)
To find the time of each of Mario's falls. Once we knew the time, we needed to figure out the distance Mario fell in each game. We used a screen shot of Mario next to the ledge he fell from in each game, and found the height of Mario and the ledge in pixels. According to Wikipedia, Mario is "a little over five feet tall.", so we used 5 feet, or 1.524 meters, as Mario's height. We used the formula:
HeightMario[m] / HeightMario[pixels] = Distance[m] / Distance[pixels]
Distance = (HeightMario[m] / HeightMario[pixels]) x Distance[pixels]
Once we had the distance Mario fell in each instance, we were able to use the formula
s = s0 + v0t + ½ at2
to find Mario's acceleration in each game. Mario was in free fall in each case, so this acceleration was equal to gravity. His initial velocity was 0, as was his initial position. Our results in m/s2 as well as in multiples of g are outlined in the table below.
|Height of Mario
|Distance of Fall
|Distance of Fall
|Super Mario Bros.||15||0.5||39||292||11.4||91.28||9.31|
|Super Mario Bros. 2||12||0.4||45||255||8.6||107.95||11|
|Super Mario Bros. 3||15||0.5||35||265||11.5||92.31||9.42|
|Super Mario World||15||0.5||38||193||7.7||61.92||6.32|
|Super Mario 64||10||0.33||86||217||3.8||69.22||7.06|
|Super Mario Sunshine||23||0.77||119||988||12.7||43.05||4.4|
|Super Paper Mario||12||0.4||288||748||4||49.47||5.05|
Finally, we graphed the acceleration due to gravity in each game as the bit rate of the graphics processor increased. Since Super Mario Bros. 1, 2, and 3 were from the same console, we took an average of the three values. Also, the Nintendo Wii never clearly defined its bit rate, but sources say that it is 96 Bits, which is actually less than that of the Nintendo GameCube. As for the other systems, the NES is an 8 Bit system, the SNES is 16 bit, the N64 is 64 Bit, and the GCN is 128 Bit. We set a power fit to this graph, and the result is shown below.
We determined that, generally speaking, the gravity in each Mario game, as game hardware has increased, is getting closer to the true value of gravity on earth of 9.8 m/s2. However, gravity, even on the newest consoles, is still extreme. According to Wikipedia, a typical person can withstand 5 g before losing consciousness, and all but the very latest of Mario games have gravity greater than this. Also, with gravity that great, it is a wonder Mario can perform such feats as leaping almost 5 times his own body height!
The primary source of error in this experiment would be the assumption that Mario is 5 feet tall, and that his height stays constant in each game. In most Mario games, he can become bigger by consuming mushrooms or other powerup objects, and the 5 foot height may be referring to this state. Also, in the 3D Mario games, the camera angle was always angled down, so when measuring the height of Mario and the ledge, this angle caused the measured distance to be different than the actual distance.
Adam Lefky, Artem Gindin -- 2007
External links to this page:
Physics on Film pages in The Physics Factbook™ for 2007
|Another quality webpage by
|home | contact
bent | chaos | eworld | facts | physics | <urn:uuid:01cf0aab-1e40-4f28-ac0c-7c3ac31aa266> | 3.65625 | 1,154 | Knowledge Article | Science & Tech. | 78.163547 | 1,855 |
The 2008 Solar Eclipse Expedition
Why and how a handful of IfA astronomers travelled to the Gobi desert in China in search of iron in the solar corona.
This year we celebrate the 400th anniversary of Galileo's use of the telescope for astronomy. Was he that important?
The Magnificent Sky
Why it must be protected from light polution.
The Floodgates Open
The start of science from the Pan-STARRS Sky Surveys.
The Story of O
How studying the spectra of galaxies in the distant Universe has revealed the origin of the oxygen atoms we breathe every day.
Videos produced by Mitch Kahle and Holly Huber | <urn:uuid:dd5b9c8a-2f86-4878-b2e0-7fdeda9bd05d> | 2.625 | 136 | Content Listing | Science & Tech. | 46.839182 | 1,856 |
Your municipality withdraws 10,000 gallons per day from an aquifer that originally held 1,000,000 gallons. The recharge rate to the aquifer is 2,000 gallons per day. How long will it take before the aquifer is depleted?
You have to make an equation that relates the amount of water (w) in the aquafier to time (t).
Start with the original amount:
Now, we know that every day ten thousand gallons are taken out so we have:
And we also know that every day two thousand gallons are added so we have:
To find when the water runs out, set the equation equal to 0 and solve for t:
So, the water will run out after 125 days. | <urn:uuid:84be61a4-9360-49ee-9102-e14d330dd196> | 3.09375 | 151 | Tutorial | Science & Tech. | 61.215 | 1,857 |
Executes the specified script in the provided language.
Syntaxvar retval = window.execScript(code, language);
- code [in]
String that specifies the code to be executed.
- language [in]
String that specifies the language in which the code is executed. The language defaults to JScript.
Type: Variant of type null
This method always returns null.
There are no standards that apply here.
Script executed through the execScript method can access all global variables available to the calling script. This can be useful when you want the functionality of another scripting language that would not otherwise be available in JScript, such as the Microsoft Visual Basic Scripting Edition (VBScript) MsgBox function.
Build date: 11/27/2012 | <urn:uuid:a1df673b-9f9e-4df3-a9f1-e7f43c998939> | 2.59375 | 160 | Documentation | Software Dev. | 44.643175 | 1,858 |
Introduction to Visual C++ for UNIX Users
This topic provides information for UNIX users who are new to Visual C++ and want to become productive with Visual C++.
You can use Visual C++ from the command line in a similar way that you would use a UNIX command-line environment. You compile from the command prompt with the command-line C and C++ compiler (CL.EXE) and tools, including NMAKE.EXE, the Microsoft version of the UNIX make utility.
In UNIX, commands are installed in a common folder, such as /usr/bin. In Visual C++, the command-line tools are installed in your installation directory at VC\bin (on a typical installation at Program Files\Microsoft Visual Studio 8\VC\bin). To use the command-line tools, run vsvars32.bat, which is located in your installation directory at Common7\Tools. This adds your bin directory to your path and sets up other paths that are necessary to compile Visual C++ programs from the command line.
If you open a command prompt with the Visual Studio Command Line Prompt from the Start menu, then vsvars32.bat is run for you.
To take advantage of more powerful features, such as the debugger, statement completion, and so on, you need to use the development environment. For more information, see Building on the Command Line and Walkthrough: Compiling a Native C++ Program on the Command Line (C++).
If you use the command line and run your applications on your development workstation, you will see that a dialog box to run the Visual Studio debugger is displayed when your code encounters a memory access violation, unhandled exception, or other unrecoverable errors. If you click OK, then the Visual Studio development environment is started, and the debugger will open to the point of failure. It is possible to debug your applications this way, and, in this case, your source code would only be available if you compiled with the /Z7, /Zi, /ZI (Debug Information Format) switch. For more information, see Debugging Native Code and Using the Visual Studio IDE for C++ Development.
It is easier to use the development environment to edit and build your source code in a project. A project is a collection of source and related files that will be compiled into a single unit, such as a library or executable. A project also contains information on how the files are to be built. Information about projects is stored in a project file with the extension .prj.
An application that consists of multiple libraries and executables, each potentially built with a different set of compiler options or even in a different language, are stored in multiple projects that are part of a single solution. A solution is an abstraction for a container to group multiple projects together. Information about solutions is stored in a solution file with the extension .sln. For more information, see Managing Solutions, Projects, and Files and Using the Visual Studio IDE for C++ Development.
You can use Visual C++ to use existing code that is set up to compile with or without a makefile and put it into a Visual Studio project. For more information, see the Create Project From Existing Code Files Wizard. For more information, see How to: Create a C++ Project from Existing Code.
You can create new projects in the development environment. Visual C++ provides numerous templates that provide standard code for various common projects. You can use application wizards to generate projects with code outlines for various application types.
You can start with an empty project by using the Console Application (Win32) Wizard. Select the Empty Project check box. You can then add new and existing files to the project later.
When you create a project, you must name the project. By default, the project name equals the name of the dynamic-link library (DLL) or executable that is build from the project. For more information, see Creating Solutions and Projects.
Visual C++ contains several extensions to the standard C++ programming language. These extensions are used to specify storage class attributes, function calling conventions, and based addressing, among other things. For a complete list of all Visual C++ extensions, see Microsoft-Specific Modifiers.
You can disable all Microsoft-specific extensions to C++ by using the /Za compiler option. This option is recommended if you want to write code to run on multiple platforms. For more information on the /Za compiler option, see /Za, /Ze (Disable Language Extensions). For more information on Visual C++ conformance, see Compatibility and Compliance Issues in Visual C++.
The Microsoft C and C++ compilers provide options for precompiling any C or C++ code, including inline code. Using this performance feature, you can compile a stable body of code, store the compiled state of the code in a file, and, during subsequent compilations, combine the precompiled code with code that is still under development. Each subsequent compilation is faster because the stable code does not need to be recompiled.
By default, all precompiled code is specified in the files stdafx.h and stdafx.cpp. The New Project wizard will automatically create these files for you unless you deselect the Precompiled header option. For more information on precompiled headers, see Creating Precompiled Header Files. | <urn:uuid:3867767e-9ad3-43a2-b6ea-2474563aae72> | 3.25 | 1,108 | Documentation | Software Dev. | 43.66282 | 1,859 |
High-resolution radar as well as hyperspectral optical imagery was acquired during flights across two test areas in southern Tunisia. Meanwhile ground teams precisely documented ground vegetation and terrain at sampling sites within these test areas, with samples taken to local laboratories for detailed analysis. And ESA's Envisat, ERS-2 and Proba satellites acquired images of these sites around the same time. The aim was to scale up the findings from the ground, and at the same time to use this 'ground truth' to calibrate satellite imagery with reality on the sandy arid ground as well as seeing what can be learnt about the water beneath it.
The Sahara has altered through the ages: during the last Ice Age, 10 000 years ago, there was savannah here with rivers, lakes and plentiful rains. That landscape has vanished now, but the rains from that period progressively percolated beneath the ground to be collected in layers of water-bearing rock known as aquifers.
This 'fossil water' is today used in North African nations for irrigating agriculture and to support population growth. It is a valuable resource but also a non-renewable one - distributed across national boundaries - which requires careful management to be employed in a sustainable way. Over-exploitation risks exhaustion of groundwater, plus loss of artesian pressure to put remaining supplies out of reach or induce contamination from nearby saline water deposits.
Working with partners including African water agencies, ESA has commenced a project called Aquifer to develop satellite-derived products and services to suppo
Contact: Mariangela D'Acunto
European Space Agency | <urn:uuid:f86c47d0-e6c1-45f7-9846-e83cc1e11e19> | 3.75 | 327 | News Article | Science & Tech. | 19.065848 | 1,860 |
This image shows water quality changes in the Gulf of Mexico. Reds and oranges represent high concentrations of algae and river sediment. Under certain conditions excessive algal growth can result in a "dead zone" of low oxygen.
Credit (via NASA/Goddard Conceptual Image Lab)
An illustration of the flow of water from tributaries in the middle of the United States, down the Mississippi River, and into the Gulf of Mexico. Pollutants impacting the health of the River and Gulf can originate far inland. | <urn:uuid:10f4c9b4-0718-4564-b799-a790e9ed9d70> | 3.140625 | 105 | Knowledge Article | Science & Tech. | 38.113711 | 1,861 |
Identifying time lags in the restoration of grassland butterfly communities: a multi-site assessment
Woodcock, B.A.; Bullock, J.M.; Mortimer, S.R.; Brereton, T.; Redhead, J.W.; Thomas, J.A.; Pywell, R.F.. 2012 Identifying time lags in the restoration of grassland butterfly communities: a multi-site assessment. Biological Conservation, 155. 50-58. 10.1016/j.biocon.2012.05.013Full text not available from this repository.
Although grasslands are crucial habitats for European butterflies, large-scale declines in quality and area have devastated many species. Grasslandrestoration can contribute to the recovery of butterfly populations, although there is a paucity of information on the long-term effects of management. Using eight UK data sets (9–21 years), we investigate changes in restoration success for (1) arable reversion sites, were grassland was established on bare ground using seed mixtures, and (2) grassland enhancement sites, where degraded grasslands are restored by scrub removal followed by the re-instigation of cutting/grazing. We also assessed the importance of individual butterfly traits and ecological characteristics in determining colonisation times. Consistent increases in restoration success over time were seen for arable reversion sites, with the most rapid rates of increase in restoration success seen over the first 10 years. For grasslands enhancement there were no consistent increases in restoration success over time. Butterfly colonisation times were fastest for species with widespread host plants or where host plants established well during restoration. Low mobility butterfly species took longer to colonise. We show that arable reversion is an effective tool for the management of butterflycommunities. We suggest that as restoration takes time to achieve, its use as a mitigation tool against future environmental change (i.e. by decreasing isolation in fragmented landscapes) needs to take into account such time lags.
|Programmes:||CEH Topics & Objectives 2009 onwards > Biodiversity|
|CEH Sections:||CEH fellows
|Additional Keywords:||arable reversion, calcareous, grassland enhancement, mesotrophic, functional traits, recreation|
|NORA Subject Terms:||Ecology and Environment|
|Date made live:||12 Sep 2012 15:38|
Actions (login required) | <urn:uuid:4cc9b21b-9ac9-4733-b1e7-35a758cedd90> | 2.84375 | 497 | Academic Writing | Science & Tech. | 31.319651 | 1,862 |
A November 2, 1979 article by John Yemma in the Christian Science Monitor outlined Jesco Von Puttkamer's vision of America's future in space. Von Puttkamer was a planner for NASA and even consulted on the first Star Trek movie.
By the late '80s or early '90s, a huge solar power satellite may be constructed to beam microwave energy to Earth. And after that, a natural step as Mr. Von Puttkamer sees it, will be space colonies built with nonterrestial material and using solar energy.
Space Colonies by Don Davis
Sport in Space Colonies (1977)
Solar Energy for Tomorrow's World (1980) | <urn:uuid:540d8913-8456-469f-96ff-0b4740cd2aa5> | 3.125 | 138 | Personal Blog | Science & Tech. | 49.580369 | 1,863 |
If you take a bunch of random particles and put them together, why should a pole form on each side of this collection?
Some particles already have a magnetic field. Many particles are polar, such that they will orient themselves in a magnetic field. If you jumble them all together, they will self align, and eventually one strong field will be externally detectable even though their individual fields were small and unorganized at the start.
Perform this experiment: Drop a bunch of magnetic powder and dirt into a bag. Shake vigorously. What is the resulting clump's magnetic signature?
Is it in practice possible to create a device capable of canceling the earth's magnetic field in a region the size of the north sea?
No. What you want is a Helmholtz coil, adjusted electronically to react to the earth's changing field.
However, the area of the field required, even though it would be relatively low magnetic force, would require entirely too much energy to be practical. Further, an ideal Helmholtz coil, where the field is uniformly 0 everywhere inside the coils, requires essentially a cubic structure. The North Sea is 970 KM long, and thus the coils would need to be 970KM in diameter, vertically oriented, buried a significant portion of that depth into the ground on either side of the north sea.
Further, it would really mess up the compasses of people traveling anywhere near the coils, not to mention other animals that appear to depend on magnetic fields, such as some migrating birds. | <urn:uuid:56a7c8f9-ece0-406d-acf3-3311fe68c27b> | 3.5625 | 307 | Q&A Forum | Science & Tech. | 48.958142 | 1,864 |
Table-top test targets quantum foam
Nov 29, 2012 15 comments
One of the biggest challenges in physics – finding evidence for quantum gravity – could be tackled using a simple table-top experiment, according to Jacob Bekenstein from the Hebrew University of Jerusalem. Bekenstein, who is best known for studying the thermal properties of black holes, has come up with an interesting new proposal for using single photons to probe what is known as "quantum foam". The foam, which was introduced in 1955 by the US physicist John Wheeler, is believed to exist on length scales so small that quantum fluctuations affect space–time.
Bekenstein's proposal is the latest effort in the quest to understand how quantum mechanics can be unified with Einstein's general theory of relativity – a problem that has eluded physicists since they first began to understand the quantum and relativistic worlds in the early 20th century. One of the main reasons why physicists have struggled with developing a theory of quantum gravity is a complete lack of experimental evidence. The problem is that the effects of quantum gravity are only expected to be measurable over extremely small distances.
Some theories of quantum gravity suggest that experiments must probe distances smaller than the Planck length, which is 1.61 × 10–35 m. Probing this scale using an accelerator would involve colliding particles at enormous energies of more than 1016 TeV. This would be well beyond the capabilities of the Large Hadron Collider, which has a maximum collision energy of 14 TeV, or indeed of any conceivable future collider. Bekenstein's proposal, in contrast, is much more modest; he says it could be done in a small physics lab mostly using existing equipment.
Photons at the ready
The experiment would involve firing single photons at a piece of glass or crystal, suspended by a tiny thread. When the photon moves from the vacuum into the material, it loses speed because the material has a higher refractive index than that of the vacuum. The result is that a tiny amount of momentum is transferred to the material, causing it to move an extremely small distance. In the case of a blue photon with a wavelength of 445 nm, Bekenstein says it would cause a 150 mg piece of high-lead glass to deflect by about 2 × 10–35 m, which is on a par with the Planck length.
The bottom line is that if a photon is detected on the other side of the material, it means the mass was deflected by a distance greater than the Planck length. But if the energy of the photon is reduced (or alternatively the mass of the glass increased) until the deflection becomes equal to or smaller than the Planck length, then quantum gravity will affect how the glass responds to each photon.
In particular, Bekenstein believes that the presence of the foam would prevent the glass from recoiling in exactly the same way when struck by a succession of identical photons. Just as electromagnetic fluctuations can have measurable effects on much larger objects – an example being the Casimir force – space–time fluctuations should also affect how an object moves extremely small distances. In the case of Bekeinstein's proposed experiment, photons would not be able to travel through the glass, which would be observed as a drop in the number of photons detected on the other side.
The experiment is challenging but not beyond what experimental physicists can do today
Jacob Bekenstein, Hebrew University of Jerusalem
Bekenstein admits that the experiment is "challenging", but claims it "is not beyond what experimental physicists can do today". Indeed, creating and detecting single photons is a routine part of quantum-optics experiments that are done in many labs around the world. Minimizing the effects of thermal noise will also be a challenge, with Bekenstein calculating that the apparatus must be cooled to about 1 K and operated in an ultrahigh vacuum of about 10–10 Pa – both of which are achievable using existing technology.
Other table-top schemes
Bekenstein is not the only physicist to have proposed a table-top probe of quantum gravity. Earlier this year, for example, Igor Pikovski and colleagues at the University of Vienna and Imperial College London described a way of making optical measurements on a mechanical oscillator with a mass close to the Planck mass (about 22 μm). Indeed, Pikovski told physicsworld.com that Bekenstein's plan seems feasible. "A big advantage is that physicists can control single photons very well and detect them extremely efficiently," he says.
Pikovski also points out that the technique could prove very useful even if experimental issues prevent it from probing distances down to 10–35 m. This is because some theories of quantum gravity predict that quantum foam or some other effect of quantum gravity could emerge at length scales as great as 10–25 m.
While it is still not clear whether the table-top experiments proposed by Bekenstein, Pikovski or others will succeed, Pikovski believes that laboratory measurements will provide important information about quantum gravity within a decade or so.
About the author
Hamish Johnston is editor of physicsworld.com | <urn:uuid:c43d7f3a-b1d6-4607-8053-534f6b355ede> | 3.625 | 1,043 | News Article | Science & Tech. | 36.06871 | 1,865 |
Photons lost in a maze
Enhancing the interaction between light and matter is the essence of many research disciplines, including quantum information science, energy harvesting and optical biosensing. The traditional method has been to strongly confine light in, for example, a highly ordered nanocavity. Surprisingly, an alternative approach to confinement of waves exists, originally proposed by Philip Anderson, and for which he was awarded the Nobel Prize in physics. Using this approach, disordered materials are employed, giving rise to random and multiple scattering of the propagating light waves. For a certain amount of randomness of the structures, so-called Anderson localized modes form spontaneously: light is trapped in a maze. A challenge in this research field has been to determine how well light can be confined based on random disorder. In a recent paper in New Journal of Physics researchers from The Quantum Photonics Group at DTU Fotonik have developed an efficient method for exciting Anderson-localized modes by embedding nanoscopic light sources (so-called quantum dots) inside the disordered material. By analyzing the statistics of the emitted light, the quality and extent of light confinement can be extracted. Surprisingly, the subtle interplay between the amount of disorder and the underlying periodic structure of the system studied can be exploited to confine light very efficiently, proving the potential of employing disorder for enchancement of light–matter interaction. | <urn:uuid:b3dc7260-f3ee-4673-852d-cdf094ddaa69> | 3.3125 | 279 | Academic Writing | Science & Tech. | 15.015942 | 1,866 |
…is a smaller species of oceanic sunfish found in tropical and temperate seas worldwide. Like its more well known relative M. mola the slender sunfish is pelagic and roams the vast oceans feeding on jellyfish. Also like most molids the slender sunfish will recruit other animals like cleaner fish and seabirds to pick parasites off of them. Molids will usually go to the surface and lay on their sides to signify they want to be cleaned, which makes it look like they are sunbathing, hence the name.
One of the ocean’s oddest looking fish, the Mola Mola possesses a truly bizarre body shape, likened to a gigantic ‘swimming head.’ Female sunfish are known to produce up to 300 million eggs at one time, the largest number of eggs ever recorded in a vertebrate.
Where and when the sunfish spawns is not well known, although five possible areas have been identified in the North and South Atlantic, the North and South Pacific, and in the Indian Ocean, where there are central rotating oceanic currents, called gyres. The newly hatched sunfish measure just 0.25 centimetres in length, and will increase in mass by over 60 million times in order to reach the size of a 3 metre adult.
(via: MIssion Blue - Sylvia Earle Alliance) (Photo: (c) Sailroe)
National Geographic explorer Tierney Thys divides her time between research on the giant ocean sunfish (Mola mola) and making science education films. In our latest podcast (recorded at this month’s SciCafe), Ms. Thys discusses how science and art can be used to raise awareness for ocean conservation.
The Mola mola is the largest bony fish living today, and only the three largest sharks (the blue shark, basking shark, and great white shark) regularly outweigh this behemoth of the open ocean.
Like many of the giants of the animal kingdom, the sunfish has a diet that’s almost paradoxically nutrient-poor. All of the calories taken in by adult sunfish are provided by jellyfish and small fry and eggs of other fish, so they spend a large amount of their time eating. Their presence in an area can indicate nutrient-rich waters where endangered species can often be found.
The status of sunfish in the wild is not currently known, though they’re caught often enough that they’re assumed to not be threatened at this point. A multi-year survey of the worldwide sunfish populations is currently underway.
Image: Giant ocean sunfish caught by W.N. McMillan of E. Africa, at Santa Catalina Isl., Cal. April 1st, 1910. Its weight was estimated at 3,500 pounds.
Two years later, alien-like sea creature gains Internet stardom
by Pete Thomas, GrindTV.com
Among the more bizarre-looking visitors to California waters this summer are Mola molas, or ocean sunfish, which are being seen in unusually high numbers. But it’s a stunning photograph of one of these gentle giants that appears to be getting the most attention. The image, captured off San Diego by Daniel Botelho, became an instant hit after being posted last week on his Facebook page…
The oceanic sunfish is known to bask flat on the ocean surface. It has theorized that this behavior may be a method to ‘thermally recharge’ itself before diving to deeper depths. Seabirds have also been observed to land on the sunfish and pick parasites off its body whilst in this position.
In the course of its evolution, the caudal fin (tail) of the sunfish disappeared, to be replaced by a lumpy pseudo-tail, the clavus. This structure is formed by the convergence of the dorsal and anal fins.Without a true tail to provide thrust for forward motion and equipped with only small pectoral fins, Mola mola relies on its long, thin dorsal and anal fins for propulsion, driving itself forward by moving these fins from side to side. | <urn:uuid:c5361d60-74f0-4148-9149-036087fb5d09> | 3.75 | 853 | Personal Blog | Science & Tech. | 51.327209 | 1,867 |
This programming language may be used to instruct a computer to perform a task.
If you know UNIX Shell, please write code for some of the tasks not implemented in UNIX Shell.
There are many UNIX Shells and most of them can be categorized into two families. For purposes of the Rosetta Code, all examples are in Bourne-compatible syntax. The other family of shells, with a markedly different syntax, are csh (C Shell) and it's tcsh (Tenex C Shell) "clone." Common Bourne compatible shells include the original Bourne Shell (/bin/sh on most versions of UNIX), the GNU Bourne Again SHell (bash --- which is linked to /bin/sh on many distributions of Linux, making it their default shell), the Korn Shell (ksh), the Public Domain Korn SHell (pdksh), the Almquist SHell (ash) and the Debian Almquist SHell (dash) and the Z SHell (zsh).
Main article: UNIX Shell Implementations
While UNIX Shells vary in the programming languages they support, such languages carry a minimum set of features. Each language allows the programmer to execute system commands as though he were typing the commands himself, and each language allows for a header line which specifies which shell implementation is used to interpret the script.
This one tells the operating system to use the Bourne Shell:
This line tells the operating system to use the Bourne Again SHell:
And this one tells the operating system to use the Korn Shell:
Each header line consists of a hash, a bang, and the path to the interpreter binary.
This category has the following 5 subcategories, out of 5 total.
Pages in category "UNIX Shell"
The following 200 pages are in this category, out of 200 total. | <urn:uuid:375553c1-7e10-4938-ac0a-29e9b60c9e20> | 3.546875 | 380 | Knowledge Article | Software Dev. | 45.89991 | 1,868 |
Populations of the American eel have massively declined in recent years.
By Douglas Main
Nobody knows exactly how American eels make it to the Sargasso Sea, a mysterious expanse of flotsam-ridden waters in the middle of the Atlantic Ocean where the animals breed.
But a recent study to chart the migration of these enigmatic eels only deepened the mystery, when six of the eight eels tracked with satellite tags were eaten by sharks.
Soon after the eels were tagged in Gulf of St. Lawrence, all eight devices were found floating on the surface of the water suggesting the animals had met an untimely end. The tags, which record depth and temperature, revealed that before surfacing the devices had suddenly entered an environment much warmer than the gulf's frigid waters.
Further analysis found that these conditions could be encountered only one way: inside the body of a porbeagle shark, according to a release from Dalhousie University in Halifax, Nova Scotia, Canada, where some of the study authors work.
The study, detailed in the online journal PLOS ONE, suggests that efforts to conserve eels, whose populations have massively declined in recent decades, could be confounded by predation by porbeagle sharks. These sharks were one of the species that were themselves voted to be protected under the Convention on International Trade in Endangered Species (CITES) earlier this week.
"Both species are in trouble, and measures to conserve one may well be at odds with efforts to protect the other," said Julian Dodson, a researcher a Laval University in Quebec City and study author, in the statement. "What we really need now are studies to quantify just how important eels are in the diets of sharks and just what impact shark predation has on eel abundance."
Eels breed in the Sargasso Sea but return to freshwater streams as adults, making them vulnerable to pollution, urban development and the construction of dams.
"We could hope that there will be increased pressure to protect eels in fresh water, particularly during downstream migration through power dams," said study author Mélanie Beguer-Pon, also a Laval researcher, in the statement. "We can't do anything about shark predation, but we can limit mortality in turbines."
An additional 113 adult eelswere fitted with simpler acoustic tags, which can be detected by receivers moored in the ocean. The study found that only four of these eels made it out of the Gulf of St. Lawrence into the Atlantic Ocean, according to the release. Many of these eels were also likely eaten by porbeagle sharks, the statement said.
- Quest for Survival: Incredible Animal Migrations
- In Images: 100 Most Threatened Species
- On the Brink: A Gallery of Wild Sharks
Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. | <urn:uuid:b1888591-8b2a-44ed-ae65-0f0d3ed1a996> | 3.234375 | 608 | News Article | Science & Tech. | 34.538077 | 1,869 |
Sci. STKE, 29 February 2000
Differentiation Defining the Boundary
The Drosophila wing precursor is divided into two non-intermingling groups of cells, the Anterior (A) compartment and the Posterior (P) compartment. Dahmann and Basler addressed the issue of how the boundary between the A and P compartment is established. The P cells express Hedgehog (Hh) and Engrailed (En); the A cells express the Hh receptor, Smo, which, upon Hh stimulation, converts the transcription factor Cubitus interruptus (Ci) from the repressor to the activator form. Transgenic cells, in which the Hh signaling pathway or the En pathway was altered, were introduced into fly larvae, and the wing precursors from such flies were analyzed to identify the positions (A or P) of the mutant cells and the amount of intermingling with the neighboring cells. Segregation into the A or P compartments was dependent on the balance between the activator form of Ci and the repressor form. Without Ci, the cells segregated away from both the A and P cells and assumed a position that straddled the A/P boundary. The authors also propose that the boundary may be defined by the abundance of the adhesion molecule DE-cadherin because cells engineered to overexpress DE-cadherin segregated away from neighboring cells in both the A and P compartments.
Dahmann, C. and Basler, K. (2000) Opposing transcriptional outputs of Hedghog signaling and Engrailed control compartmental cell sorting at the Drosophila A/P boundary. Cell 100: 411-422. [Online Journal]
Citation: Defining the Boundary. Sci. STKE 2000, tw2 (2000).
The editors suggest the following Related Resources on Science sites:
In Science Signaling
Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882 | <urn:uuid:bb6e5019-511c-4e42-a62a-8729cd1fe659> | 2.59375 | 431 | Academic Writing | Science & Tech. | 51.409288 | 1,870 |
Sorry for the delay; it’s getting crowded around here again.
Anyway, an irreducible module for a Lie algebra is a pretty straightforward concept: it’s a module such that its only submodules are and . As usual, Schur’s lemma tells us that any morphism between two irreducible modules is either or an isomorphism. And, as we’ve seen in other examples involving linear transformations, all automorphisms of an irreducible module are scalars times the identity transformation. This, of course, doesn’t depend on any choice of basis.
A one-dimensional module will always be irreducible, if it exists. And a unique — up to isomorphism, of course — one-dimensional module will always exist for simple Lie algebras. Indeed, if is simple then we know that . Any one-dimensional representation must have its image in . But the only traceless matrix is the zero matrix. Setting for all does indeed give a valid representation of . | <urn:uuid:6f079210-a79b-44cf-96f8-e099ba38271d> | 2.703125 | 220 | Personal Blog | Science & Tech. | 37.340802 | 1,871 |
|Diamondoid Monolayers as Monochromatic Electron Source|
Diamondoids are nanometer-sized molecules that feature diamond-crystal cage structures. Adamantane, the smallest member in the family, consists of one cage structure, diamantane two, triamantane three, tetramantane four, and so on. On all of these, the dangling bonds on the outer surfaces are terminated by hydrogen atoms. Because of their potential to possess novel properties of both diamond and nanomaterial, intensive efforts have been made to synthesize the larger diamondoid molecules, but to no avail. This situation was finally changed in 2003 when significant quantities of higher diamondoids were found in petroleum by researchers in MolecularDiamond Technologies. Now, scientists from Berkeley Lab, Stanford University, Lawrence Livermore National Laboratory, and Germany have used photoelectron spectroscopy at the ALS to reveal an intriguing feature: monochromatized electron emission from a self-assembled monolayer of diamondoids. This discovery has immediately attracted the attention of people who are searching for materials for next-generation electron emitters.
Materials for electron emitters have long been sought because electrons emitted into vacuum can be precisely controlled and easily integrated into elaborate devices. They lie at the heart of a number of modern technologies, such as field-emission flat-screen displays, electron microscopes, electron lithography, and next-generation free-electron lasers. For electron emitters, one of the biggest challenges is to develop large, uniform surfaces that emit electrons with a sharp energy distribution.
In the late 1970s, scientists found that hydrogen-terminated diamond surfaces are characterized by negative electron affinity (NEA), meaning for electrons, the energy level of the vacuum is lower than that of the diamond conduction bands. At surfaces with NEA, electrons excited into the conduction band will spontaneously fall out into vacuum even at low temperature. Thus, NEA-based electron emitters have several advantages over conventional emitters. They exhibit electron emission at extremely low bias voltage (zero in the ideal case), and the energy distribution of the emitted electron is extremely narrow. However, two critical issues prevented NEA semiconductors from being used in commercialized products. One is the nonuniform emission normally observed on diamond surfaces. The other is the difficulty of supplying electrons to the emission surface, because diamond and other NEA semiconductors are wide-gap materials with low electron conductivity.
Diamondoids, being diamond-like nanoclusters, provide us with the opportunity to sustain the NEA feature of diamond while avoiding the conventional problems of bulk NEA materials. Toward this end, the collaborators replaced one of the hydrogen atoms on the surface of tetramantane (four-cage diamondoids) with a thiol group (hydrogen + sulfur). This substitution chemically "functionalizes" the tetramantane, i.e., it promotes bonding with other molecules, enabling it to form more complex structures, like nanosized tinker toys. The researchers found that these diamondoid–thiol complexes would then self-assemble into a uniform monolayer on metal surfaces such as silver or gold.
Photoelectron spectroscopy was then performed on the tetramantane–thiol monolayers at Beamline 10.0.1, where a strong, sharp peak was detected. The outstanding peak observed in the spectra is a strong indication of NEA. Furthermore, up to 68% of all the emitted electrons were within this single energy peak, with a width of less than 0.5 eV. This is several times as strong as the same measurement for bulk diamond. Technologically, this means most electrons are emitted from the diamondoid monolayer at the same energy, i.e., speed.
The result directly shows that diamondoid monolayers can be superior to conventional materials as electron emitters. The molecules can be purified and functionalized under precise control. They can be inexpensively self-assembled into large-area, uniform monolayers. More importantly, they perform better than previous materials in terms of the energy distribution of the emitted electrons. Further investigations are under way to fully understand this striking phenomenon, as well as to make real devices based on diamondoids.
Research conducted by W.L. Yang, N. Mannella, K. Tanaka, and X.J. Zhou (Stanford University and ALS); J.D. Fabbri, W. Meevasana, M.A. Kelly, N.A. Melosh, and Z.-X. Shen (Stanford University); T.M. Willey, J.R.I. Lee, and T. van Buuren (Lawrence Livermore National Laboratory); J.E. Dahl and R.M.K. Carlson (MolecularDiamond Technologies, Chevron Technology Ventures); P.R. Schreiner, B.A. Tkachenko, and N.A. Fokina (Justus-Liebig University, Germany); A.A. Fokin (Justus-Liebig University, Germany, and Kiev Polytechnic Institute, Ukraine); and Z. Hussain (ALS).
Research funding: U.S. Department of Energy, Office of Basic Energy Sciences (BES). Operation of the ALS is supported by BES.
Publication about this research: W.L. Yang, J.D. Fabbri, T.M. Willey, J.R.I. Lee, J.E. Dahl, R.M.K. Carlson, P.R. Schreiner, A.A. Fokin, B.A. Tkachenko, N.A. Fokina, W. Meevasana, N. Mannella, K. Tanaka, X.J. Zhou, T. van Buuren, M.A. Kelly, Z. Hussain, N.A. Melosh, and Z.-X. Shen, "Monochromatic electron photoemission from diamondoid monolayers," Science 316, 1460 (2007). | <urn:uuid:93b4ecea-e98a-462c-a6b9-fe9279c80cd0> | 3.40625 | 1,249 | Knowledge Article | Science & Tech. | 38.446973 | 1,872 |
The perils of polonium
News Analysis Polonium-210, the highly toxic radioactive isotope found in the body of poisoned former Russian spy Alexander Litvinenko is a very rare, exotic material that is difficult to obtain, scientists say.
The UK's Health Protection Agency says Litvinenko, who died last week in a London hospital, had a significant amount of the radioactive isotope in his body.
But how it got there and where it came from is a mystery.
Radiation and chemistry experts say large-scale equipment, such as a nuclear reactor, would be needed to produce sufficient amounts to kill.
"It is not as simple as the idea that somebody might have broken into a radioactivity cabinet at some local hospital and walked off with some polonium," says Dr Andrea Sella, a lecturer in chemistry at University College London.
Although scientists would not speculate on the source of the polonium, Sella says Litvinenko's death is not a random killing.
"This is not a tool chosen by a group of amateurs. These people had some serious resources behind them," he says.
Polonium is a by-product of uranium that was discovered by Polish chemist Marie Curie in the late 19th century.
It's a rare but naturally occurring metalloid found in the soil and atmosphere, and even in the human body.
But at high doses it is highly toxic if ingested or inhaled; it emits alpha particles that can damage the body's tissues and organs.
"[Alpha particles] are unable to penetrate a sheet of paper and so it is not a hazard unless ingested," says Professor William Gelletly of the University of Surrey.
Long-term exposure to radiation can cause mutations and cancer. But exposure to a short, intense burst of radiation causes major damage to key control centres in cells.
"An alpha particle strikes a strand of DNA. It snips it in two, which is bad news, or glues two strands together. Either way normal cell repair mechanisms may be unable to sort that out," says Sella.
"The result is that essentially the cellular command and control network [in the body] falls apart. That is what radiation sickness is all about."
Professor David Ray, of the University of Nottingham, says even if a high dose of radiation could not be detected externally after Litvinenko was admitted to hospital a fatal dose could have concentrated in deep tissues such as bone marrow.
"The limited information that has been released about Mr Litvinenko's condition and the timing of his death is consistent with either radiation poisoning or chemicals that stop cell division," he says.
Polonium-210 also has a very short half-life of 138 days, at which point it loses half of its radioactivity.
"That is long enough so you can handle it and deliver it to your target and it will pack a punch," Sella says.
Polonium-210 is used in research and medicine, as well as a heating source for space components.
But in those forms it is not conducive to easy poisoning, scientists say. | <urn:uuid:7e7c4e71-d668-4c02-a8f9-64a6e5aaf1ac> | 3.09375 | 639 | News Article | Science & Tech. | 44.488546 | 1,873 |
No coal fired power stations. No SUV’s.
And they are warning the planet's atmosphere could have similar levels of the greenhouse gas within hundreds of years.
An international team led by German scientists and involving University of Queensland Environmental Geologist Dr Kevin Welsh has found tropical palms grew on the coast of Antarctica 52 million years ago.
At that warm period in the earth's history, there was twice as much CO2 in the atmosphere as there is now and winter temperatures of 10C meant Antarctica's 4km thick ice sheet didn't exist.
Fancy that, no ice in Antarctica 52 million years ago.
Below is what I wrote on the same subject for Menzies House on 24th July 2011:
Global warming. Rising sea levels. Massive volcanic activity around the world. Widespread climate change.
It’s not a scene from the Hollywood disaster film, The Day After Tomorrow, but the Earth as it appeared during the mid-to late-Cretaceous geological period, 145 million to 65 million years ago, when the largest dinosaurs such as Tyrannosaurus Rex ruled the planet.
Our planet during the late Cretaceous period was very different than it is today. Not only were dinosaurs like T-Rex present, but the climate was extremely warm and global sea levels were significantly higher than they are today. This was a time when there were no glaciers in either the Arctic or Antarctic.
Late Cretaceous atmospheric carbon dioxide levels were two to four times higher than today, which resulted in a greenhouse climate with tropical sea-surface temperatures rising to more than 34 degrees Celsius, 3 to 7 degrees Celsius warmer than today.
Calderia and Rampino concluded in their 1991 paper - The mid-Cretaceous super plume, carbon dioxide, and global warming - that carbon dioxide emissions resulting from super‐plume tectonics could have produced atmospheric carbon dioxide levels from 3.7 to 14.7 times the modern pre‐industrial value of 285 ppm. Carbon dioxide levels today are around 390 ppm. According to Calderia and Rampino, temperature sensitivity to carbon dioxide increases used in the weathering‐rate formulations, would have caused global warming of from 2.8 to 7.7°C over today's global mean temperature.
Further supporting Calderia and Rampino’s 1991 paper is John Tarduno and his collaborators 1998 paper - Evidence for Extreme Climatic Warmth from Late Cretaceous Arctic Vertebrates.
In 1996, Tarduno’s expedition team literally stumbled across a unique fossil find: vertebrate remains from fish, turtles and Champsosaurs.
The fossils indicate that at least once in Earth's history, high amounts of the greenhouse gas warmed Earth to much higher temperatures than usual.
The highlight of the expedition find are bones that belonged to an eight-foot Champsosaur, a now-extinct crocodile-like beast with a long snout and razor-sharp teeth.
The reptiles, which were tied to their freshwater environment on Axel Heiberg Island, needed an extended warm period each summer to survive and reproduce. Based on the numbers and sizes of the animals found, the Tarduno’s team estimated that the annual mean temperature in the Arctic during the late Cretaceous period, from about 92 million to 86 million years ago, was about 14 degrees Celsius. That means it was rarely if ever freezing during the winter, and summer temperatures consistently reached between 27 and 32°C.
The Arctic today is defined as being the area where the average temperature for the warmest month (July) is minus 10°C.
The fossils of the Champsosaur are a record of what was happening in the Arctic just as extreme volcanism on Earth was winding down.
Most of the volcanic activity didn't resemble spectacular eruptions like Mt. Pinatubo. Instead, the eruptions were "basaltic" – billions of tons of lava oozed out, and carbon dioxide floated skyward. Besides huge amounts of lava in the Arctic, where hardened lava rock today measures more than a kilometre thick in some places, magma oozed from volcanoes in the Caribbean, in the Pacific Ocean northeast of Australia, in the Indian Ocean, off the coasts of Madagascar and Brazil, in South Africa and in the Southwestern United States.
Understanding how our past atmosphere, land and ocean system interacted while in this global greenhouse mode is very relevant if we want to understand the fate of our future climate.
It also further illustrates that we live on a dynamic planet who's climate is always changing over the millennia.
Whilst no one denies that the world’s industrialisation has increased considerably the output of greenhouse gases, to ascribe the current phase of our ever changing climate to one single variable (carbon dioxide) or, more specifically, to a very small proportion of one variable (i.e. human produced carbon dioxide) is not science, for it requires us to abandon all we know about our planet Earth, the Sun, our Galaxy and the Cosmos.
And believing that putting a price on Carbon Dioxide will make any difference to the Earth’s climate is madness. The only sensible action to tackle climate change is by adaption, as trying to prevent it is a fool’s game. | <urn:uuid:30bc0048-2d31-4c07-afe0-15786ed57ea5> | 3.765625 | 1,080 | Personal Blog | Science & Tech. | 41.273169 | 1,874 |
Posted: September 08, 2008
On Wednesday, the world’s largest particle accelerator – the Large Hadron Collider (LHC) – will be powered up to receive an injection of particle beams for the very first time as it begins the heroic quest to solve some of the biggest mysteries of our Universe. Astronomy Now will be attending this momentous scientific milestone via a live link-up from Westminster to the ceremony at CERN (the European Organisation for Nuclear Research) and we’ll have a full report later in the week.
The LHC has a circumference of 27 kilometres, stretching from Geneva airport in the lower left, to the open French countryside in the upper right. Image: CERN.
Buried one hundred metres below the French/Swiss border and boasting a circumference of 27 kilometres, the LHC is the largest and most ambitious physics experiment in history. By accelerating particles to speeds of 99.9999991 percent that of light, and watching what happens when they collide, it will probe questions surrounding the nature and existence of dark matter and antimatter, the weakness of gravity and even if extra dimensions exist.
The dual beams of the LHC consist of bunches of particles a few tens of centimetres in length containing 100 billion protons. There will be 3000 going around the collider in each direction at any one time, with each beam containing the energy equivalent to the Eurostar travelling at over 90 miles per hour. Sub-atomic smash-ups will occur between the beams 600 million times a second, and detectors situated along the accelerator’s circumference will be on the look-out for the resulting debris of subatomic particles.
On the LHC’s shopping list is the elusive higgs boson particle, which is widely believed to be the origin of the well-known property mass. The Standard Model of particle physics predicts two types of particles: mass-less particles like photons, and those with mass, like quarks (protons and neutrons that make up atomic nuclei) and electrons. The Standard Model also predicts the existence of the higgs boson and states that particles that possess mass do so because they interact with the resulting higgs field, as if they were travelling through treacle. This is important from a cosmological viewpoint, because the presence of dark matter can only be inferred from its gravitational effect, and this gravitational effect results from dark matter possessing mass. In essence, understanding the higgs boson could help scientists finally understand the ins and outs of dark matter, which itself is thought to comprise around 23 percent of the Universe’s energy density while ‘normal’ baryonic matter comprises four percent, and dark energy, which is thought to play a dominant role in the expansion of the Universe, makes up 73 percent. The LHC, therefore, has the potential to open up a treasure trove of information about the nature of the Universe.
But the LHC can’t directly detect a higgs boson; instead its presence can be detected by looking at what it decays into. However, what it decays into is determined by its mass, which is an unknown quantity. There are certain probabilities, however, and by comparing the signatures of what is detected by the LHC compared with what is expected from other processes, any significant statistical ‘anomaly’ could point towards the higgs boson.
Another mystery that the LHC will help solve is why gravity is so weak compared to the other forces of nature such as electromagnetic and nuclear forces. Gravity is well-known to play a dominant role in the Universe but it has no apparent influence at the particle level. Indeed, the 'graviton' particle hasn't actually been discovered. Suggestions as to why gravity appears so weak have resulted in the consideration of more dimensions than the three – width, depth and height – that we currently know about. Could gravity be leaking into our three dimensional Universe from another dimension? The LHC might just be capable of probing these dimensions, which could be curled up smaller than sub-atomic particles.
Another aim of the LHC is to try and find the missing link between two of the most successful theories of physics – General Relativity and quantum theory, in which one cannot currently be explained with the other, thus presenting a major hurdle to finding the holy grail ‘theory of everything’ that has been the goal of scientists for decades. The LHC could find out what the bridge between the theories is, and confirm or refute the idea that string theory is part of the equation. String theory states that all different particles are different vibrations in higher-dimensional string structures. One of the things that string theory predicts is the existence of micro black holes, something that could be identified in the LHC in terms of the particles that they decay into. Such a result would provide the first real validation for string theory. But despite scare mongering by the popular media that the Earth will ultimately be consumed in one of these ‘man-made’ black holes, such an event is impossible since they would decay almost immediately, lacking the energy to grow, let alone be sustained.
Moreover, the sub-atomic collisions that the LHC will bare witness to are just a patch on what happens naturally in nature. In its 4.6 billion year existence, the Earth has been subject to a phenomenal number of cosmic ray collisions of far higher energies than could ever be achieved in the LHC, with no ill effects. The only real danger from the LHC is that the machine could damage itself should the magnets that keep the beams inside the collider fail. The result would be that the particle beams would destroy the magnets. To gradually test the full capabilities of the LHC, therefore, the beams won’t be switched on with full intensity at first, but will gradually be powered up over several months before getting down to serious business.
Astronomy Now will be attending the LHC powering up ceremony via a live link-up to CERN. We’ll have a full report later in the week. In the meantime, you can read more about the LHC in the July issue of Astronomy Now magazine.
This special publication features the photography of British astro-imager Nik Szymanek and covers a range of photographic methods from basic to advanced. Beautiful pictures of the night sky can be obtained with a simple camera and tripod before tackling more difficult projects, such as guided astrophotography through the telescope and CCD imaging.
U.S. & WORLDWIDE STORE
Mars rover poster
This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
U.S. & WORLDWIDE STORE
HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORES | SPACEFLIGHT NOW
© 2010 Pole Star Publications Ltd. | <urn:uuid:c17254c3-ce43-4dd0-9bb0-5a503afb60df> | 3.640625 | 1,418 | News (Org.) | Science & Tech. | 40.811181 | 1,875 |
About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.
Viruses are tiny geometric structures that can only reproduce inside a living cell. They range in size from 20 to 250 nanometers (one nanometer is one billionth of a meter). Outside of a living cell, a virus is dormant, but once inside, it takes over the resources of the host cell and begins the production of more virus particles. Viruses are more similar to mechanized bits of information, or robots, than to animal life.
Bacteria are one-celled living organisms. The average bacterium is 1,000 nanometers long. (If a bacterium were my size, a typical virus particle would look like a tiny mouse-robot. If an average virus were my size, a bacterium would be the size of a dinosaur over ten stories tall. Bacteria and viruses are not peers!) All bacteria are surrounded by a cell wall. They can reproduce independently, and inhabit virtually every environment on earth, including soil, water, hot springs, ice packs, and the bodies of plants and animals.
Most bacteria are harmless to humans. In fact, many are quite beneficial. The bacteria in the environment are essential for the breakdown of organic waste and the recycling of elements in the biosphere. Bacteria that normally live in humans can prevent infections and produce substances we need, such as vitamin K. Bacteria in the stomachs of cows and sheep are what enable them to digest grass. Bacteria are also essential to the production of yogurt, cheese, and pickles. Some bacteria cause infections in humans. In fact, they are a devastating cause of human disease.
I Hope that help you out my friend , much success to you and your future goals
Peace out Brother
Viruses are too small to be seen by the naked eye. They can't multiply on their own, so they have to invade a 'host' cell and take over its machinery in order to be able to make more virus particles.
Viruses consist of genetic materials (DNA or RNA) surrounded by a protective coat of protein. They are capable of latching onto cells and getting inside them.
Bacteria are organisms made up of just one cell. They are capable of multiplying by themselves, as they have the power to divide. Their shapes vary, and doctors use these characteristics to separate them into groups.
Bacteria exist everywhere, inside and on our bodies. Most of them are completely harmless and some of them are very useful. But some bacteria can cause diseases, either because they end up in the wrong place in the body, or simply because they are 'designed' to invade us.
Last edited by canalon on Fri Jul 24, 2009 9:21 pm, edited 1 time in total.
Reason: Spamming in sig
Both are microscopic,
Bacteria can double its population in 20 minutes.
Viruses cannot multiply on their own and have to take over other cells to multiply.
Bacterial infections are easy to cure with the use of anti-biotics, where-as viruses can be insufferably hard to cure or vaccinate against. For example: We still don't have a cure for the common cold.
Sources: Biology teachers, Nelson Biology VCE Units 1&2
viruses - bacteria
1) they are showing both the - they are exclusively living forms.
characteristics of living
as well as non living.
2) they are crystallizable. - noncrystallizable.
3) are only parasitic in nature,
depend on host for all its - independent or may be saprophytic, parasitic, in nature.
4) uses host machinery for its - have ther own genetic material for replication.
this is Viruses，and that is a Bacteria as follow：
A Strong Man Can Save Himself A Great Man Can Save Another.
It seems a waste of time answering these questions when the asker can easily google them up or look it up in ANY biology or microbiology book. Especially, that the asker have not the decency to put neither a thank you nor a comment. Seems the effort of the experts here have gone to waste.
I agree to the 2nd post (by mith) that the poster should look harder. True, we all know the answer but if we spoonfeed all the answers to such obviously simple question makes us accomplices in making the poster lazy. Whereas, if we point him/her to the right direction, or give 'em a nudge...then we are teaching them to THINK.
We are not here as sages on the stage, but guides by the side.
Who is online
Users browsing this forum: No registered users and 0 guests | <urn:uuid:0e946847-cec2-4c13-a019-a5979cb5faf9> | 3.890625 | 999 | Comment Section | Science & Tech. | 47.932544 | 1,876 |
As we look at the numerous graben and valleys that wind through the Martian highlands, it is not always clear which geological processes created them. Some valleys have very similar characteristics to those on Earth carved out by the flow of surface water; others possess a morphology where this is not so obvious. These images, acquired by the High Resolution Stereo Camera (HRSC) operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) on board ESA’s Mars Express spacecraft, show the upper reaches of the Reull Vallis region, a valley that was, at times, shaped by the flow of glacial ice.
Reull Vallis is an outflow channel stretching over 1500 kilometres across the massifs of Promethei Terra, in the highlands of Mars' southern hemisphere, towards Hellas Planitia, an impact basin that, with a diameter of almost 2300 kilometres, is the largest impact structure on our planetary neighbour. The High Resolution Stereo Camera (HRSC) on Mars Express has been used numerous times to acquire images of Reull Vallis and the surrounding mountains (see images published on 8 December 2004). The images of the upper reaches of Reull Vallis shown here were acquired on 14 May 2012, during orbit 10,657, from an altitude of around 320 kilometres. They show details down to a size of 16 metres. The centre of the image is at 41 degrees south and 107 degrees east. The region shown here is around 15,000 square kilometres in size, and covers an area of 180 by 80 kilometres.
Using stereoscopic HRSC image data, from which digital terrain models can be derived, the topography of the surroundings of Reull Vallis and the profile of the graben-shaped valley can be deduced. Over one 80-kilometre stretch, the valley has a continuous width of around seven kilometres and is bound by steep, sharply contoured walls around 300 metres high. The box-shaped profile of Reull Vallis is conspicuous, very different from the familiar V- or U-shaped valleys here on Earth.
Material from the surroundings transported into the valley by ice
The bottom of Reull Vallis is covered with deposits, on the surface of which is an eye-catching pattern indicating the flow of the material and mostly running parallel to the edges of the valley, although in some places structures intertwined like braided hair are visible. This pattern was probably created by the flow of ice – a glacier on the surface of which a large volume of rubble and boulders has been transported down into the valley. On Earth, we see comparable phenomena known as rock glaciers in the Alpine and Polar regions. In these, the glacial ice is completely covered by boulders that have slid onto the ice from the valley walls.
Similar structures to those in the Reull valley are also found in the material filling nearby impact craters. This can be seen particularly well in two small craters northwest of the valley (upper right in the vertical overhead views and in one of the perspective views). The rocks certainly prevented the underlying ice from melting and – in the chilly temperatures prevalent on Mars – from sublimating (transitioning directly from a solid to a gaseous state) for much longer. However, at these 'temperate' Martian latitudes, there is a strong possibility that there is no longer any ice left under the sediments deposited by the glacier.
Terraces indicate an earlier water level in the sediments
Coming in from the north (right in the overhead view), a tributary valley flows into the main channel of Reull Vallis. Looking at the local environment in the topographical map, it can be seen that a side arm branches off further up the valley. Here, about 100 kilometres further southeast, it rejoins the main valley. To the north of Reull Vallis (in the right half of the overhead views), several of Promethei Terra's two to three thousand metre high massifs can be seen as well. Their somewhat smooth morphology indicates that erosion processes have been at work here for some time. Contours of extensive layers with tongue-shaped edges and occasionally smooth surfaces can be seen between the mountains; in some places they also have a pattern that follows the topography of their surroundings, as in the craters. These might also be sediments left behind by glacial ice. However, the smooth-surfaced layers could also be volcanic deposits.
Fairly evidently, a large volume of material have been carried away from the flanks of the mountains and transported into lower-lying regions, where it has tended to accumulate in impact craters. Also, the streaked pattern of the deposits in this crater that follows the circular crater rim is highly reminiscent of structures formed by glaciers on Earth. Stepped terraces on the inner walls of the craters could indicate the presence of a higher level of glacial ice covered by rubble and boulders, and that only when the ice and melt water disappeared did the sedimentary layer sink to where it is today.
Image processing and the HRSC experiment on Mars Express
The colour plan view (3/6) was acquired using the nadir channel, which is directed vertically down onto the surface of Mars, and the colour channels of the HRSC; the perspective oblique views (1/6 and 2/6) were computed from data acquired by the HRSC stereo channels. The anaglyph image (5/6), which creates a three-dimensional impression of the landscape when viewed with red/blue or red/green glasses, was derived from the nadir channel and one stereo channel. The colour-coded view (6/6) is based on a digital terrain model of the region, from which the topography of the landscape can be derived.
The HRSC camera experiment on board the European Space Agency's Mars Express mission is headed by Principal Investigator (PI) Professor Gerhard Neukum (Freie Universität Berlin), who was also responsible for the technical design of the camera. The science team consists of 45 co-investigators from 32 institutions in 10 nations. The camera was developed at DLR under the leadership of the PI and it was built in cooperation with industrial partners EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH. The instrument is operated by the DLR Institute of Planetary Research in Berlin-Adlershof. The systematic processing of the HRSC image data is carried out at DLR. The images shown here were created by the Institute of Geological Sciences at Freie Universität Berlin in cooperation with the DLR Institute of Planetary Research, Berlin. | <urn:uuid:448d7b44-6eab-4cb1-b5d5-0a8e3f5b8419> | 4.03125 | 1,378 | Knowledge Article | Science & Tech. | 38.119526 | 1,877 |
The camera that can capture 1 trillion frames a second - fast enough for slow-motion video of light particles
Scientists from the Massachusetts Institute of Technology (MIT) needed some very specialised equipment to pull off the feat, as light travels around a million times faster than a bullet.
The team used a camera that collected the light beams at a rate of roughly one trillion frames per second - that's fast enough to produce a slow-motion video of a burst of light traveling the length of a one-litre bottle, bouncing off the cap and reflecting back to the bottle’s bottom.
‘We have built a virtual slow motion camera where were can see photons, or light particles, moving through space,’ explained Ramesh Raskar, Associate Professor of the MIT Media Lab.
http://www.dailymail.co.uk/sciencetech/ ... z23RLACR9t | <urn:uuid:4bf5e9ca-4dfe-4264-bb06-da13bdb39d85> | 3.046875 | 188 | News Article | Science & Tech. | 56.042342 | 1,878 |
The sun is a natural nuclear fusion reactor, fusing hydrogen to helium. Our current understanding of physics is quite clear about what happens, four hydrogen nuclei (protons), with and without the help of catalysts are transformed into helium, neutrinos and energy. The energy is released as gamma rays and as kinetic energy of the particles, including the neutrinos.
Neutrinos were originally theorized to make up the energy and angular momentum difference when a neutron decays into a proton and an electron. Neutrinos were later demonstrated to exist, but accomplishing this was difficult because they have negligible mass, travel very close to the speed of light, and have no electric charge nor magnetic moment (thus don't interact electromagnetically). They also don't interact through the strong nuclear force. Neutrinos do interact with other matter through the weak nuclear force (that is how they are produced). Large heavy water (water that has deuterium instead of hydrogen) tanks with arrays of photocells are usually used to detect neutrinos.
The detectors used to capture solar neutrinos are huge, usually deep underground to avoid noise from cosmic rays. As the technology progressed, and bigger detectors were built, it became clearer that we just weren't getting as many neutrinos from the sun as our models of solar combustion predicted. In various experiments, the number of detected neutrinos was between 1/3 and 1/2 of the predicted number. Therefore either our models of the sun were wrong or our models of neutrino behavior were wrong. This is known as the Solar neutrino problem.
The solutions based on the models of the sun being wrong were based on the premise that the temperature and pressure in the interior of the sun was not what we thought it was. For example, since neutrinos measure the amount of current nuclear fusion, it was suggested that the nuclear processes in the core of the sun might have temporarily shut down, and since it takes thousands of years for heat energy to move from the core to the surface of the sun, this would not immediately be apparent.
Solutions based on incorrect understanding of solar physics were rendered untenable by helioseismology which observes how waves propagate through the sun. Based on these observations it became possible to measure the interior temperatures of the sun and these agreed with the standard solar models.
Currently, the solar neutrino problem is believed to result from an inadequate understanding of the properties of neutrinos. According to the Standard Model of particle physics (prior to 1999), there are three different kinds of neutrinos:
The first evidence for neutrino oscillation came in 1998 from the Super-Kamiokande collaboration in Japan. It produced observations consistent with muon-neutrinos (produced in the upper atmosphere by cosmic rays) changing into tau-neutrinos. More direct evidence came in 2002 from the Sudbury Neutrino Observatory (SNO) in Canada. It detected all types of neutrinos coming from the sun, and was able to distinguish between electron-neutrinos and the other two flavors. After extensive statistical analysis, it was found that about 35% of the arriving solar neutrinos are electron-neutrinos, with the others being muon- or tau-neutrinos. The total number of detected neutrinos agrees quite well with the earlier predictions from nuclear physics based on the fusion reactions inside the sun. | <urn:uuid:d1f9168b-eab1-4e45-b2ab-fb002ef59652> | 4 | 713 | Knowledge Article | Science & Tech. | 29.686194 | 1,879 |
Heat escape routes
Take a look at this diagram showing heat loss from a house.
Heat energy is transferred from homes through the
Examples of convective losses: cold air can enter the house through gaps in doors and windows, and convection currents can transfer heat energy in the loft to the roof tiles.
Heat energy also leaves the house by radiation through the walls, roof and windows.
Red shows where most heat is lost - through the windows and roof
Ways to reduce heat loss
There are some simple ways to reduce heat loss, including fitting carpets, curtains and draught excluders.
Heat loss through windows can be reduced using double glazing. There may be air or a vacuum between the two panes of glass. Air is a poor conductor of heat, while a vacuum can only transfer heat energy by radiation.
Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall, which reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.
Heat loss through the roof can be reduced by laying loft insulation. This works in a similar way to cavity wall insulation.
If some heat escapes from the house, it costs money and wastes resources. In deciding how cost-effective an energy-saving measure is, we need to know what its pay-back time is. In other words, taking the example of double-glazing: how long will it take before the cost of having the double-glazing installed will be recovered by what we save in fuel bills? The calculation is:
pay-back time in years = cost of energy-saving measure ÷ money saved each year
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science | <urn:uuid:183e5efc-3b83-47f6-867c-8661256d209c> | 4 | 385 | Tutorial | Science & Tech. | 54.938824 | 1,880 |
The Unicode Standard, Version 2.0 (TUS2.0) provides different ways to encode accented characters, either decomposed (a combining character sequence [CCS]) or composed (as a single precomposed character). For example, the following are equivalent:
|Ã||A + ~|
The TUS2.0 specifies an algorithm for determining whether any two sequences of Unicode characters are canonical equivalent (see TUS2.0, pages 3-9 through 3-10). This algorithm basically decomposes any precomposed characters, then sorts them according to special rules, based on each character's combining class. This produces a normalized form.
Two common functions on Unicode text are to fully decompose the text (as far as possible), and to fully compose the text (as far as possible). In both cases, the correct result can only be achieved if the text is first converted to a normalized form.
The following describes mechanisms for composing and decomposing Unicode text that do not require fully normalizing the text, and yet produce the correct results. By avoiding the normalization phase, they represent significant performance advantages.
|Note:||In the following discussion, we will abbreviate the Unicode names for brevity. Thus LATIN CAPITAL LETTER G WITH BREVE will be represented as G-breve. A plus sign will be used to indicate a sequence of characters.|
The following discussion requires that the reader have first read Chapter 3 of TUS2.0.
The simple method for producing a normalized decomposed form is to replace each character by its decomposition, then normalize the entire string. However, this does more work than is necessary, especially in the common cases. The optimized method works as follows:
This method avoids bubble-sorting all of the combining marks in a string, and optimizes for the common cases:
Since you are guaranteed that the decomposition is already in normalized order, as each successive combining character is appended, it is bubble-sorted up in the decomposition. Since the sequence starts in normalized order, and after each successive character the result is in normalized order, then the final result is in normalized order.
|Ã`||A + ~||A + ~ + `|
|Ã.||A + ~||A + . + ~|
The simple method for producing a normalized composed form is to match each possible CCS against a database to see what matches, then replace the CCS with the result. However, this does more work than is necessary, especially in the common cases. The optimized method works as follows:
The following algorithm depends on the fact that except for one anomolous case, every CCS of length greater than two (which is canonical equivalent to a precomposed character) is also equivalent to a CCS of length exactly two. For example, C + cedilla + acute is equivalent to C-cedilla + acute, and C + acute + cedilla is equivalent to C-acute + cedilla.
Since all combinations of characters that could combine are in the mapping table, in every order that they could occur in, all the precomposed forms will be generated. Since we scan for illegal reversals, we eliminate non-canonical equivalents. At each point in this process, the result string contains a valid composition of the initial portion of the source string.
|Notes:||If we didn't scan the intervening combining characters, then we could end up with a non-canonical equivalent sequence. For example, consider the following sequence: G + acute + breve. If we didn't scan, then this would produce G-breve + acute, since G-breve is a precomposed Unicode character, but G-acute is not. When decomposed, this represents G + brev + acute, which is not a cononical equivalent to the orginal string, since breve and acute have the same canonical class.|
|The one anomolous precomposed character does require a special case in this algorithm--for simplicity of presentation, this complication is omitted.| | <urn:uuid:9f958add-2fd0-4d46-8105-6110fc8ebcca> | 3 | 850 | Documentation | Software Dev. | 34.731385 | 1,881 |
silicon carbide, chemical compound, SiC, that forms extremely hard, dark, iridescent crystals that are insoluble in water and other common solvents. Widely used as an abrasive, it is marketed under such familiar trade names as Carborundum and Crystolon. It is heat resistant, decomposing when heated to about 2,700°C; it is used in refractory materials, e.g., rods, tubes, firebrick, and in special parts for nuclear reactors. Very pure silicon carbide is white or colorless; crystals of it are used in semiconductors for high-temperature applications. Silicon carbide fibers, added as reinforcement to plastics or light metals, impart increased strength and stiffness. Silicon carbide is prepared commercially by fusing sand and coke in an electric furnace at temperatures above 2,200°C; a flux, e.g., sodium chloride, may be added to eliminate impurities. Silicon carbide was discovered (1891) by E. G. Acheson; early studies of it were made by Henri Moissan.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
More on silicon carbide from Infoplease:
See more Encyclopedia articles on: Compounds and Elements | <urn:uuid:81fb236c-32ae-4f71-9e06-73de5298b345> | 4.09375 | 271 | Knowledge Article | Science & Tech. | 31.761652 | 1,882 |
Weaver Ants, Oecophylla spp.
This Order of insects include sawflies, horntails, wood wasps, ensign wasps, Ichneumonids, fairyflies, fig wasps, chalcids, gall wasps, cuckoo wasps, yellow-faced bees, sweat bees, leafcutter bees, carpenter bees, honey bees, bumble bees, orchid bees, velvet ants, spider wasps, paper wasps, yellow jackets, hornets, mud-dauber wasps and ants.
This image illustrates how important it is to have the right chemical scent. Members of an individual colony possess the same “nest odor.” Even members of the same species found stumbling into a neighboring colony will not possess the correct genetic and environmentally determined odor and will generally be attacked as an intruder. These Weaver Ants exhibit refined societal coordination and create advanced camouflaged structure. They build nests by pulling together leaves and gluing them together with silk excreted from accommodating larval ants. | <urn:uuid:2e1a4015-06d3-4507-a13d-66ca4ca5855a> | 3.84375 | 216 | Knowledge Article | Science & Tech. | 31.600294 | 1,883 |
UAVSAR: An Airborne Window on Earth Surface Deformation
Jan. 20 & 21
The Earth's surface is constantly undergoing surface deformation at the millimeter to meter scale both from natural forces such as earthquakes, volcanoes, and glacier motion and from anthropogenic causes such as oil and ground water pumping.
From Crust to Core, GRAIL Reveals the Lunar Interior
Feb. 17 & 18
The Moon is the most accessible and best studied rocky, or "terrestrial", body beyond Earth.
WISE: The Infrared Full Sky Survey
Mar. 17 & 18
In early January, 2010, the Wide-field Infrared Survey Explorer (WISE) began imaging the entire sky with sensitivities in the mid-Infrared hundreds of times greater than previous surveys.
A Unique Opportunity: Scientific Research and Human Space Flight in the Shuttle Era
April 14 & 15
For an entire generation around the world, thirty years of access to low-Earth orbit using the Space Shuttle orbiter and solid rocket boosters has created the almost iconic image of the winged ascending spacecraft lighting up the Florida sky.
John F. Kennedy and Project Apollo
May 25 of this year will mark the fiftieth anniversary of the 1961 speech to a joint session of Congress in which President John F. Kennedy, just four months in office, proposed sending Americans to the Moon "before this decade is out."
Climate Change Impact on Civilizations: Lessons from Space Data and Archaeology
June 9 & 10
Recently, NASA and other remote sensing data have enabled significant progress in archaeological research.
Hot Water: The Oceans and Global Warming
July 21 & 22
Water covers nearly 70 percent of its surface, so it's no wonder that the world's oceans play such an important role in global climate changes.
NASA's Deep Space Network: Our Link to Spacecraft around the Solar System
Aug. 18 & 19
NASA's Deep Space Network is the largest and most sensitive scientific communications system in the world. A linchpin of spacecraft communication, DSN is our connection to worlds beyond and an essential piece of JPL's exploration of space.
From A to Z: Getting Curiosity to the Launch Pad
Sept. 15 & 16
The Mars Science Laboratory, "Curiosity", is the latest project in NASA's Mars Exploration Program, a long-term program of robotic exploration of the Red Planet.
A Self-Powered Underwater Robot for Ocean Exploration and Beyond
Oct. 13 & 14
The Sounding Oceanographic Lagrangrian Observer Thermal RECharging (SOLO-TREC) autonomous underwater vehicle is the first unmanned underwater vehicle (UUV) that is completely powered by renewable energy.
The American Rocketeer
NASA’s Jet Propulsion Laboratory invites the public to attend a special screening of The American Rocketeer at Caltech’s Beckman Auditorium. The first episode, part of a three-part miniseries entitled JPL and the Beginnings of the Space Age, tells the little- known and controversial story of Frank Malina. Viewers will follow Malina’s life from his early days at Caltech and rocket engine tests in Pasadena’s Arroyo Seco that set in motion the founding of the Jet Propulsion Laboratory.
Bringing the High Energy Universe Into Focus
Nov. 10 & 11
The Nuclear Spectroscopic Telescope Array (NuSTAR) will carry into orbit the first astronomical telescope capable of focusing high energy X-rays. | <urn:uuid:0e941192-95b9-447e-ba95-2c4b1910758d> | 3.515625 | 722 | Content Listing | Science & Tech. | 38.439142 | 1,884 |
Incredible Batch of Rare and New Species Discovered
A chameleon (Chamaeleo gracilis) found during a 2006 expedition to Ghana's Atewa Range Forest Reserve led by Conservation International's Rapid Assessment Program.
CREDIT: Piotr Naskrecki, Conservation International
Two species of primates that are of global conservation concern, eight new species of katydids, a critically endangered frog species, 17 rare butterfly species and wild birds such as the brown-cheeked hornbill are among the finds of an expedition to a forest reserve in Ghana.
Scientists exploring one of the largest remaining blocks of tropical forest in Western Africa discovered these animals as part of significant populations of new, rare and threatened species, underscoring the area’s high biological diversity and value.
The findings came from a 2006 expedition to Ghana’s Atewa Range Forest Reserve (Atewa) led by Conservation International’s Rapid Assessment Program and were presented in a report made public Thursday.
The discoveries include:
--A critically endangered frog species (Conraua derooi) whose presence in Atewa may represent the last viable population in the world.
--An unusually high 22 species of large mammals and six species of primates including two species that are of global conservation concern: Geoffroy’s pied colobus (Colobus vellerosus) and the olive colobus (Procolobus verus).
--17 rare butterfly species, including the magnificent Papilio antimachus, whose wingspan is the widest in the world. Another, called Mylothris atewa, is found nowhere else in the world and has been proposed as globally critically endangered. The new report contains the first photo of this species in the wild;
--The highest diversity of katydids (a grasshopper relative) in all of Africa, including eight species new to science, making 13 percent of all species of katydids in Atewa new to science.
--An unusually high 155 bird species. Six species of global conservation concern including the brown-cheeked hornbill and the Nimba flycatcher (first time recorded in Ghana).
--19 fish species of significant potential value in the aquarium trade. These species indicate that the streams run through high quality, intact forest, which is becoming exceedingly rare in West Africa.
--The only tree fern species (Cyathea manniana) found in Ghana. Other places where similar species are found include forests in Brazil and Madagascar.
--A strange new species of spider tick, with a lineage dating back to the Age of the Dinosaurs, looks like a cross between a spider and a crab, and males have their reproductive organs on their legs. They are considered quite rare, with only 57 other species known from this group throughout the world.
“While this forest has long been known to harbor a high number of species and to serve as an essential source of water for local villages and for Accra, it is only recently that the global importance of this reserve has been confirmed,” said Okyeame Ampadu-Agyei, an expedition member in Ghana associated with Conservation International, which led the expedition. “We must quickly take action to protect the incredible diversity of Atewa for future generations and to prevent the extinction of the 36 globally threatened species that we know to live in Atewa.”
The reserve's animals and habitats are under pressure from illegal timber harvesting and bushmeat hunting, the researchers said.
From June 6 to June 24, 2006, a team of 22 scientists, post-graduate students and assistants from Ghana and abroad surveyed the 58,472 acre Atewa tract in south-eastern Ghana. The scientists found an intact forest ecosystem, which is unusual and significant for West Africa, where most forests are highly fragmented and disturbed.
Established as a national forest reserve in 1926, and since designated as one of Ghana’s Globally Significant Biodiversity Areas, Atewa’s importance has long been recognized because it contains the headwaters of three river systems, essential sources of domestic, agricultural and industrial water for local communities and many of Ghana’s major population centers, including Accra.
In their final report, scientists called for the government to upgrade the area’s protection status such as to a National Park, create of a buffer zone around the park and develop a management plan that includes conversation measures and economic development strategies compatible with conservation goals.
The report points to eco-tourism as an optimal industry to develop because of Atewa’s beauty, richness in species and close proximity to the capital city.
- Dinosaur Quiz: Test Your Smarts
- 10 Amazing Things You Didn't Know About Animals
- Colorful Butterflies
MORE FROM LiveScience.com | <urn:uuid:8793f85a-f93a-4853-bb66-68484db758ed> | 3.5 | 1,005 | News Article | Science & Tech. | 22.293735 | 1,885 |
A novel chip-scale instrument made from carbon nanotubes may simplify absolute measurements of laser power. Developers of the unit at the National Institute of Standards and Technology (NIST) say it may prove especially useful for measuring light signals transmitted by optical fibers in telecom networks.
After the 2010 Nobel Prize in Physics was awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene," even more research and development efforts have been focused on two-dimensional nanostructures. Illustrating the importance of this area in future applications, Two-Dimensional Nanostructures covers the fabrication methods and properties of these materials.
While the interdisciplinary field of materials science and engineering is relatively new, remarkable developments in materials have emerged for biological and medical applications, from biocompatible polymers in medical devices to the use of carbon nanotubes as drug delivery vehicles. Exploring these materials and applications, Materials in Biology and Medicine presents the background and real-world examples of advanced materials in biomedical engineering, biology, and medicine. | <urn:uuid:a940782c-b67e-41df-8f22-0005aea153e0> | 2.71875 | 216 | Knowledge Article | Science & Tech. | -11.478427 | 1,886 |
The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia
4.9 OCEAN ACIDIFICATION
The oceanic uptake of excess atmospheric carbon dioxide alters the chemistry of seawater, which may impact a wide range of marine organisms from plankton to coral reefs (Doney et al., 2009a,b; NRC, 2010) (see also Section 6.3). Ocean acidification is in fact a series of interlinked and wellknown changes in acid-base chemistry and carbonate chemistry due to the net flux of CO2 into surface waters (Figure 4.26). The chemical shifts include increases in the partial pressure of carbon dioxide (pCO2), the concentration of aqueous CO2, and the hydrogen ion (H+) concentration and decreases in pH (pH = –log10[H+]). The increase in hydrogen ion concentration acts to lower the concentration of carbonate ions (CO32–) through the reaction H+ + CO32– => HCO3–, even though the total amount of dissolved inorganic carbon (DIC) goes up (DIC = [CO2] + [HCO3–] + [CO32–]). Declining CO32– in turn lowers calcium carbonate (CaCO3) mineral saturation state, Ω = [Ca2+][CO32–]/Ksp, where Ksp is the thermodynamic solubility product that varies with temperature, pressure, and mineral form. Ocean surface waters
FIGURE 4.26 Schematic indicating the effects on seawater carbonate chemistry due to the uptake of excess carbon dioxide (CO2) from the atmosphere. Ocean acidification causes increases in some chemical species (red) and decreases in other species (blue). Ocean acidification also causes a reduction in pH (pH = –log10[H+]) and the saturation states, Ω, of calcium carbonate minerals in shells and skeletons of planktonic and benthic organisms and in carbonate sediments. On millennial and longer time scales, ocean pH perturbations are buffered by external inputs of alkalinity, denoted by calcium ions (Ca2+) and changes in the net burial rate of carbonate sediments. | <urn:uuid:3e031665-0ef1-403c-997c-5c389ce54d7b> | 3.15625 | 503 | Knowledge Article | Science & Tech. | 29.897243 | 1,887 |
NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, is now perched atop its Pegasus XL rocket, strapped to the plane that will carry the mission to an airborne launch. Launch is scheduled for June 13, no earlier than 8:30 a.m. PDT (11:30 a.m. EDT).
The plane -- the L-1011 "Stargazer" aircraft -- is now at Vandenberg Air Force Base in central California. It is scheduled to fly to Kwajalein Atoll in the central Pacific Ocean from June 5 to 6. About an hour before launch, the plane will lift off from the island, and drop NuSTAR and its rocket over the ocean. The rocket will then ignite, carrying NuSTAR to its final orbit around Earth's equator.
NuSTAR will be the first space telescope to create sharp images of X-rays with high energies, similar to those used by doctors and dentists. It will conduct a census for black holes, map radioactive material in young supernovae remnants, and study the origins of cosmic rays and extreme physics around collapsed stars.
NuSTAR is a Small Explorer mission led by the California Institute of Technology in Pasadena and managed by NASA's Jet Propulsion Laboratory, also in Pasadena, for NASA's Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Va. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley; Columbia University, New York; NASA's Goddard Space Flight Center, Greenbelt, Md.; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, Calif.; and ATK Aerospace Systems, Goleta, Calif. NuSTAR will be operated by UC Berkeley, with the Italian Space Agency providing its equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Rohnert Park, Calif. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.
Launch management and government oversight for the mission is the responsibility of NASA's Launch Services Program at the Kennedy Space Center in Florida. | <urn:uuid:e67573b7-17f7-4c58-9a17-769c5b83d4eb> | 3 | 441 | News (Org.) | Science & Tech. | 43.283182 | 1,888 |
THE Japanese government is planning to build two deep holes vertically into the ground. The largest, 720 metres deep, will be in a disused coal mine in the northern island of Hokkaido and, from summer next year, you will be able to drop up to 1 tonne down the shaft for only 800 000 yen (about Pounds sterling 3000).
The aim of this project is for researchers to be able to carry out experiments that experience about 10 seconds of micro gravity. The usual way to carry out such an experiment is to blast it into orbit. It is much cheaper to drop it into a hole in the ground, but it is far from certain that Japan's scientists will fall for the scheme.
The Ministry of International Trade and Industry, which is running the project, says the Japan Microgravity Centre will offer the world's largest 'drop tower'. Capsules containing ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:c6706d13-2453-4037-9d48-2f89ff17cf77> | 3.5 | 204 | Truncated | Science & Tech. | 63.08037 | 1,889 |
|25 May 2010|
Take a walk along the coast and help us monitor the effects of climate change and invasive species on the UK's seaweeds.
Seaweeds are easy to find and occur all around the UK coastline. There are a staggering 650 seaweed species in the UK, around 7% of the world's species, and they play a vital role in the functioning of the marine environment.
Scientists think that the effects of climate change and the spread of invasive species are starting to have an effect on where they are found but they need more information to be sure.
This is where you can help. Identify the seaweeds you spot on the UK's coast and tell us what you find. This will help researchers from the British Phycological Society and Natural History Museum to find out what is happening to our seaweeds.
The aim of the Big Seaweed Search is to map the distribution of 12 key kinds of seaweed that can be found around the UK coast. We hope to track how these distributions are changing through time.
You don't need to be an expert as our easy-to-use identification guide should allow everyone, from children to scientists, to take part.
When you get home from carrying out your survey, tell us about the seaweeds you find using our online system, or by posting completed forms to the Museum.
There is no deadline - you can send in records at any time of the year and take part as many times as you like.
Your data will be added to our online interactive map. As we analyse the data, we will post updates on what your records show and how they are being used. | <urn:uuid:fe71d926-98d8-4e90-b1fc-3b27f154d4fa> | 3.484375 | 339 | News (Org.) | Science & Tech. | 60.299801 | 1,890 |
Use of RNA:DNA ratios for assessing secondary production of planktonic food webs effects of temperature, salinity, food and heavy metals /
Abstract (Summary)Acartia tonsa is a dominant copepod in coastal waters and is an important link in the food web between microplankton and higher trophic levels. RNA:DNA ratios have been used to describe growth and nutritional condition of field collected copepods and to show strong correlation between group egg production and RNA:DNA ratios. A method was developed using a sensitive, nucleic acid fluorescent dye and automated microplate fluorometer to measure RNA, DNA and RNA:DNA ratio of individual A. tonsa. RNA, DNA, RNA:DNA ratios and egg production were all significantly higher in copepods fed Thalassiosira spp. compared to starved copepods. There was a general trend toward an increase in RNA:DNA ratios with increase in egg production, but due to the high degree of variation in both RNA:DNA ratios and egg production of individual copepods no significant correlation between RNA:DNA ratios and egg production was found. Significant differences in the RNA:DNA ratios between fed (7.2) and starved (3.4) copepods were found after 2 days. In the future this assay may be applied to other species of copepods sampled directly from the field, to provide an index of the health of planktonic food webs in nature.
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:copepoda rna dna marine plankton
Date of Publication: | <urn:uuid:75ddf350-00f0-4913-95b0-2da1f15a3b0b> | 3.390625 | 330 | Academic Writing | Science & Tech. | 34.88186 | 1,891 |
Our pick of the latest physics stories from around the world wide web.
The winner of Robo Mara Full event in Osaka is expected to set a world record of around four days.
At least three powerful solar flares on the sun have hurled billions of tonnes of material towards the Earth, which could light up the night sky in a spectacular aurora borealis.
A machine originally designed to check the quality of wine could soon lift the current restrictions on taking liquids aboard airplanes.
wo US spacecraft have moved either side of the Sun to establish observing positions that should return remarkable new information about our star.
Astronomers have identified some 54 new planets where conditions may be suitable for life.
Bees navigate by the sun – so how do they manage when it's cloudy? It turns out that they read clues to the hidden sun's position in polarised light.
There is now even more evidence that life on Earth may have been seeded by material from asteroids or comets.
Scientists look at alternatives to the mass of platinum used as international standard measure, which has lost 50 micrograms.
The climate secrets of the deepest part of the ocean, the Marianas Trench in the western Pacific Ocean, have been probed by scientists.
With more than a trillion pixels, this is the most detailed digital picture of the universe ever produced. | <urn:uuid:e4f37120-9f5e-4f29-84d0-da9bf36bf5c5> | 2.578125 | 272 | Content Listing | Science & Tech. | 46.090115 | 1,892 |
Describing Motion with Words
Visit The Physics Classroom's Flickr Galleries and take a visual overview of 1D Kinematics.
Distance and Displacement
Distance and displacement are two quantities that may seem to mean the same thing yet have distinctly different definitions and meanings.
- Distance is a scalar quantity that refers to "how much ground an object has covered" during its motion.
- Displacement is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position.
To test your understanding of this distinction, consider the motion depicted in the diagram below. A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North.
Even though the physics teacher has walked a total distance of 12 meters, her displacement is 0 meters. During the course of her motion, she has "covered 12 meters of ground" (distance = 12 m). Yet when she is finished walking, she is not "out of place" - i.e., there is no displacement for her motion (displacement = 0 m). Displacement, being a vector quantity, must give attention to direction. The 4 meters east cancels the 4 meters west; and the 2 meters south cancels the 2 meters north. Vector quantities such as displacement are direction aware. Scalar quantities such as distance are ignorant of direction. In determining the overall distance traveled by the physics teachers, the various directions of motion can be ignored.
Now consider another example. The diagram below shows the position of a cross-country skier at various times. At each of the indicated times, the skier turns around and reverses the direction of travel. In other words, the skier moves from A to B to C to D.
Use the diagram to determine the resulting displacement and the distance traveled by the skier during these three minutes. Then click the button to see the answer.
As a final example, consider a football coach pacing back and forth along the sidelines. The diagram below shows several of coach's positions at various times. At each marked position, the coach makes a "U-turn" and moves in the opposite direction. In other words, the coach moves from position A to B to C to D.
What is the coach's resulting displacement and distance of travel? Click the button to see the answer.
To understand the distinction between distance and displacement, you must know the definitions. You must also know that a vector quantity such as displacement is direction-aware and a scalar quantity such as distance is ignorant of direction. When an object changes its direction of motion, displacement takes this direction change into account; heading the opposite direction effectively begins to cancel whatever displacement there once was.
Check Your Understanding
1. What is the displacement of the cross-country team if they begin at the school, run 10 miles and finish back at the school?
2. What is the distance and the displacement of the race car drivers in the Indy 500? | <urn:uuid:499e5940-0bb4-41c6-875d-f331ac36f52c> | 3.625 | 618 | Tutorial | Science & Tech. | 55.004262 | 1,893 |
Conception/Leipzig. Even the snow on Aconcagua Mountain in the Andes is polluted with PCBs. An international team of researchers detected low concentrations of these toxic, carcinogenic chlorine compounds in samples taken from America's highest mountain. The snow samples taken at an altitude of 6200 metres are among the highest traces found anywhere in the world of these substances, which have been banned since 2001. In particular, the samples contained more persistent compounds like hexachlorobiphenyl (PCB 138) and heptachlorobiphenyl (PCB 180). Mountain ranges could be a natural trap for persistent organic pollutants that are transported by the atmosphere all over the world, say the scientists from IIQAB in Barcelona (Now IDAEA), the UFZ in Leipzig and the University of Concepcion in Chile, writing in the journal Environmental Chemistry Letters. According to the researchers, these findings highlight the need to investigate further the role of mountains in the spread of these pollutants and the associated risks. Just a few weeks ago, Swiss researchers found similar persistent environmental pollutants in glacial lakes in the Alps and pointed to potential risks to drinking water supplies.
Polychlorinated biphenyls (PCBs) are among the 'dirty dozen' persistent organic pollutants banned worldwide under the Stockholm Convention. Until the 1980s, PCBs were used primarily in transformers and capacitors and as hydraulic fluids and diluents. As well as causing chronic effects like acne, hair loss and liver damage, PCBs are also a suspected cause of male infertility. The toxin also represents a danger to a large number of animals because it accumulates in fatty tissue and is passed on via the food chain.
The study of environmental pollution in remote mountain regions is difficult because they are not easily accessible. "This is compounded by the fact that the concentrations are often so small that researchers have to bring back large quantities of snow just to reach the detection limit. While conventional extraction methods need at least a litre of snow, the solvent-free method we used works with 40 ml," explains Peter Popp of the Helmholtz Centre for Environmental Research (UFZ), who analysed the samples in the laboratory in Leipzig. Roberto Quiroz of IIQAB, the Spanish research institute for environmental chemistry (now researcher at the EULA Chile Environmental Sciences Centre), adds, "On expeditions to high mountain peaks, every gram counts. We would never have been able to carry 40 litres of snow per sample. So we were very pleased that only 40 ml per sample were required for analysis in Leipzig." Aconcagua is in the southern Andes, close to the Chile-Argentina border, and has five large glaciers. It was a holy mountain of the Incas. As one of the Seven Summits (the highest mountains of each of the seven continents) Aconcagua is now a popular destination for mountaineers. The first to reach the summit was Swiss mountaineer Matthias Zurbriggen in 1897.
During the 2003 expedition, the Chilean researchers took samples at altitudes of 3500, 4300, 5000, 5800 and 6200 metres. The concentrations measured do not represent any immediate danger to mountaineers, who melt small quantities of snow to obtain water. The PCB concentration on Aconcagua was less than half a nanogram per litre. Compared with the values measured in other mountain and polar regions, the concentrations on the mountain peak in the Andes were relatively low. Concentrations four times higher have been measured in the Italian Alps, for instance – an indication that pollution in the southern hemisphere is less severe than in the northern hemisphere.
The PCB concentrations measured around the peak of Mount Aconcagua were approximately one-tenth of those found in earlier samples taken from Sierra Velluda, a mountain just 3500 metres high on the west side of the Andes in Chile. "This could be because of the way in which these pollutants accumulate in the snow. But it could also have something to do with the three hydroelectric power stations on the lower slopes of Sierra Velluda. Their transformers are potential sources of PCBs," suggests Ricardo Barra of the EULA-Chile Centre for Environmental Research at Concepcion University. "However, detecting PCBs in the snow on top of Aconcagua clearly shows that these compounds are transported to the Andes by the atmosphere and accumulate there."
The research findings are also relevant in relation to climate change: "The shrinking of the glaciers could lead to the pollutants stored in the glacier snow being carried down with the melt water," fears Roberto Quiroz. South America is not the only part of the world in which water from melting glaciers plays an important role in irrigation for farming and as a source of drinking water. | <urn:uuid:c3e80b2d-2be0-4118-b330-c15d3c60178f> | 2.9375 | 990 | News Article | Science & Tech. | 35.03297 | 1,894 |
Mar. 22, 2009 The territory where the Higgs boson may be found continues to shrink. The latest analysis of data from the CDF and DZero collider experiments at the U.S. Department of Energy's Fermilab now excludes a significant fraction of the allowed Higgs mass range established by earlier measurements. Those experiments predict that the Higgs particle should have a mass between 114 and 185 GeV/c2. Now the CDF and DZero results carve out a section in the middle of this range and establish that it cannot have a mass in between 160 and 170 GeV/c2.
“ The outstanding performance of the Tevatron and CDF and DZero together have produced this important result,” said Dennis Kovar, Associate Director of the Office of Science for High Energy Physics at the U.S. Department of Energy. “We're looking forward to further Tevatron constraints on the Higgs mass."
The Higgs particle is a keystone in the theoretical framework known as the Standard Model of particles and their interactions. According to the Standard Model, the Higgs boson explains why some elementary particles have mass and others do not.
So far, the Higgs particle has eluded direct detection. Searches at the Large Electron Positron collider at the European laboratory CERN established that the Higgs boson must weigh more than 114 GeV/c2. Calculations of quantum effects involving the Higgs boson require its mass to be less than 185 GeV/c2.
"A cornerstone of NSF's support of particle physics is the search for the origin of mass, and this result takes us one step closer," said Physics Division Director Joe Dehmer, of the National Science Foundation.
The observation of the Higgs particle is also one of the goals of the Large Hadron Collider experiments at CERN, which plans to record its first collision data before the end of this year.
The success of probing the Higgs territory at the Tevatron has been possible thanks to the excellent performance of the accelerator and the continuing improvements that the experimenters incorporate into the analysis of the collider data.
“Fermilab’s Tevatron collider typically produces about ten million collisions per second,” said DZero co-spokesperson Darien Wood, of Northeastern University. “The Standard Model predicts how many times a year we should expect to see the Higgs boson in our detector, and how often we should see particle signals that can mimic a Higgs. By refining our analysis techniques and by collecting more and more data, the true Higgs signal, if it exists, will sooner or later emerge.”
To increase their chances of finding the Higgs boson, the CDF and DZero scientists combine the results from their separate analyses, effectively doubling the data available.
“A particle collision at the Tevatron collider can produce a Higgs boson in many different ways, and the Higgs particle can then decay into various particles,” said CDF co-spokesperson Rob Roser, of Fermilab. “Each experiment examines more and more possibilities. Combining all of them, we hope to see a first hint of the Higgs particle.”
So far, CDF and DZero each have analyzed about three inverse femtobarns of collision data---the scientific unit that scientists use to count the number of collisions. Each experiment expects to receive a total of about 10 inverse femtobarns by the end of 2010, thanks to the superb performance of the Tevatron. The collider continues to set numerous performance records, increasing the number of proton-antiproton collisions it produces.
The Higgs search result is among approximately 70 results that the CDF and DZero collaborations presented at the annual conference on Electroweak Physics and Unified Theories known as the Rencontres de Moriond, held March 7-14. In the past year, the two experiments have produced nearly 100 publications and about 50 Ph.D.s that have advanced particle physics at the energy frontier.
Other social bookmarking and sharing tools:
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Note: If no author is given, the source is cited instead. | <urn:uuid:bbdf5547-de56-4b9a-abca-f4b5f6a5e6e8> | 2.75 | 903 | News (Org.) | Science & Tech. | 43.17614 | 1,895 |
June 3, 2009 Florida Institute of Technology researchers are trying to solve one of the great mysteries in nature: how thunderstorms make lightning. Because, in principle, lightning is a big spark it should behave like other sparks—like the ones created when we touch a door knob on a dry day. Scientists have accumulated evidence, however, that lightning sometimes behaves in very un-spark-like ways.
Lightning can start in regions of thunderstorms that have relatively low electric fields and, so, should create no sparks. Because lightning obviously is made by thunderstorms, scientists are left wondering what they are missing.
Three such scientists, Joseph Dwyer and Hamid Rassoul from Florida Tech and Martin Uman from the University of Florida developed a new technique to remotely measure thunderstorm electric fields on the ground.
By measuring small radio pulses made by cosmic-rays passing through these storms, they calculate that they can reconstruct the electric fields along the high-energy particle's paths. This could allow them to measure any lightning initiation pockets that might exist.
One idea is that thunderstorms generate big electric fields capable of making sparks, but those strong fields are localized in very small pockets—too small to be easily detected by the balloons and aircraft sent into thunderclouds to measure the fields. Although this seems reasonable, the problem has been how to test it. Indeed, for decades scientists have struggled in vain to find such pockets where lightning might be initiated.
"Cosmic-rays are high-energy particles from outer space that constantly rain down on our planet. They form a natural probe for measuring thunderstorms," explained Dwyer, professor of physics and space sciences, who is leading the research effort. "Thunderstorms are big, violent, and dangerous places. Cosmic-ray air showers allow us to study them from a relatively safe location on the ground."
"It's a daunting task to find these high field regions," explained Rassoul, professor of physics and space sciences. "Thunderstorms are large and the chance that a balloon would find its way into exactly the right place at the right time to catch lightning initiation is small."
This summer at the UF/Florida Tech International Center for Lightning Research and Testing at Camp Blanding, Fla., scientists are conducting experiments to search for these lightning initiation pockets. If successful, researchers will be closer to understanding lightning, a phenomenon that has mystified people for thousands of years.
Other social bookmarking and sharing tools:
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
- Remote measurement of thunderstorm electrostatic fields. Journal of Geophysical Research, (in press)
Note: If no author is given, the source is cited instead. | <urn:uuid:97cbbbd9-0745-4915-a8dd-3eccbd1e50ea> | 4.03125 | 558 | News (Org.) | Science & Tech. | 39.838333 | 1,896 |
On the island of Flores in Indonesia, villagers have long told tales of a diminutive, upright-walking creature with a lopsided gait, a voracious appetite, and soft, murmuring speech.
They call it ebu gogo, "the grandmother who eats anything." Scientists¿ best guess was that macaque monkeys inspired the ebu gogo lore. But last October, an alluring alternative came to light. A team of Australian and Indonesian researchers excavating a cave on Flores unveiled the remains of a lilliputian human--one that stood barely a meter tall--whose kind lived as recently as 13,000 years ago.
This article was originally published with the title The Littlest Human. | <urn:uuid:35a7b569-d11d-4701-adb3-669a7ca0927e> | 2.640625 | 149 | Truncated | Science & Tech. | 35.347251 | 1,897 |
More 60-Second Earth
In 1959 physicist Gilbert Plass warned in Scientific American that increasing concentrations of carbon dioxide in the atmosphere was causing climate change. In 1965 President Lyndon Johnson warned Congress of the risk. In 1979 the U.S. National Academy of Sciences warned against a wait-and-see attitude (pdf).
But we have waited. And now most of us see. Increasing concentrations of greenhouse gases are changing the climate. And a new report from the U.S. National Research Council argues—again—that we urgently need a national approach to reducing that pollution since its impacts will be with us for hundreds or even thousands of years.
One possibility is to make polluters pay for the cost of greenhouse gas emissions. For example, a tax on fossil fuel burned would spur investment in cleaner energy technologies, such as renewables or nuclear power.
Other nations will also have to reduce such pollution. But this latest report suggests that if the U.S. reduces its emissions, we're in a better position to influence others, such as China, to do the same. One thing remains clear—the time for waiting is over.
[The above text is an exact transcript of this podcast.] | <urn:uuid:06e096fe-b0bd-4793-9f3f-1becd617fcfd> | 2.734375 | 242 | Truncated | Science & Tech. | 56.379689 | 1,898 |
Flying Out to GJ 436 and its Planets
Astronomers using NASA's Spitzer Space Telescope have detected what they believe is an alien world just two-thirds the size of Earth - one of the smallest on record. The exoplanet candidate, known as UCF-1.01, orbits a star called GJ 436, which is located a mere 33 light-years away. UCF-1.01 might be the nearest world to our solar system that is smaller than our home planet.
This artist's animation depicts a Star Trek-like voyage out to GJ 436, finished with a flyby of UCF-1.01.
Starting from Earth, we quickly zoom out of the solar system into our sun's local neighborhood, populated by the closest stars that lie within a few light-years of Earth. Swinging around, we shift our attention to the dwarf star GJ 436, which is so faint that it is invisible to us until we get close enough to see its dim glow.
Because of GJ 436's proximity to our solar system, the star field around it shares many of our culture's famous cosmic landmarks. As we circle around the faint star, the constellation of Orion moves into view on the right, though in a distorted shape compared to our vantage point on Earth.
From here we move into the GJ 436 system, at first seeing the candidate planet UCF-1.01 as it transits its star. Although probably rocky in composition like Earth, UCF-1.01 would be a terrible place for life. The world orbits scorchingly close to its star, so in all likelihood this planet lacks an atmosphere and might even have a molten surface, as shown in this animation.
Near the end of the movie, a Neptune-sized exoplanet already known to exist around GJ 436, designated GJ 436b, appears in the background. Evidence for UCF-1.01 turned up when astronomers were studying this previously known world.
Browse Videos in Science Animations | <urn:uuid:79134cf7-4a38-4caa-864a-c3482606b729> | 3.3125 | 416 | Truncated | Science & Tech. | 68.45878 | 1,899 |