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Science subject and location tags
Articles, documents and multimedia from ABC Science
Friday, 14 January 2011
The fossil of a never-before seen species of dinosaur that could have been among the first to roam the planet 230 million years ago has been unearthed in Argentina.
Tuesday, 11 January 2011
Dying young was not the most likely reason Neanderthals went extinct, according to a study that suggests early modern humans had about the same life expectancy as their ancient cousins.
Friday, 3 December 2010
A dramatic climate change event which devastated Earth's rainforests just under 300 million years ago also opened the way for the rise of the reptiles, a new study shows.
Tuesday, 23 November 2010 21
Evolution If birds descended from dinosaurs, by what means did they become warm-blooded, assuming the dinosaurs were reptilian and cold-blooded?
Wednesday, 17 November 2010
One of Australia's biotechnology pioneers, whose work has been instrumental in cloning insulin and growth hormone, has taken out this year's Prime Minister's Prize for Science.
Thursday, 28 October 2010
Ancient fossilised teeth of small anthropoid monkeys discovered in Libya suggest our earliest ancestors may have migrated from Asia to Africa, according to newly published research.
Friday, 1 October 2010
Dinosaurs were much taller than previously thought, according to a new study that found cartilage extended the limbs of these animals by up to a third of a metre in length.
Thursday, 23 September 2010
Two enormous heads arrayed with horns are the first striking images of a pair of newly discovered dinosaur species announced today.
Thursday, 16 September 2010
Researchers have found the remains of what they believe was an enormous bony-toothed bird with the largest wingspan ever recorded.
Thursday, 9 September 2010
A large new carnivorous dinosaur unearthed in Spain sported a very unusual pointed hump-like structure on its back, muscular legs and evidence for some of the world's first feathers.
Wednesday, 8 September 2010
The evolution of oxygen-producing organisms has been pushed back another 270 million years through the discovery of new evidence in Western Australia's Pilbara region.
Wednesday, 18 August 2010
Animals have been on Earth for at least 650 million years, suggest recently found primitive sponge fossils from South Australia.
Thursday, 12 August 2010
Evidence from ancient bones found in Ethiopia suggest human ancestors were using stone tools to carve meat a million years earlier than previously thought.
Wednesday, 28 July 2010
A new study that suggests all living marsupials originated in South America and share a common ancestor has been disputed by an Australian palaeontologist as "simplistic".
Monday, 26 July 2010
Fossilised mammal burrows that appear to have been clawed out by a predator suggests dinosaurs dug into mammal dens to get furry morsels. | <urn:uuid:d2feda84-68d5-4a7f-be13-f00452420e50> | 3.234375 | 578 | Content Listing | Science & Tech. | 32.982655 |
The scientific apparatus was developed by the Ioffe Physics-Technical Institute (FTI), Saint Petersburg. It undertook fundamental astrophysics research in cosmic gamma rays. The mission was conducted in collaboration with NASA. The Konus-A was equipped with a gamma ray detector that allowed localization of astronomical gamma ray sources. The spacecraft carried 130 kg of scientific instruments, had a two year design life, and was placed in a 400 km altitude orbit. The US Wind spacecraft, deployed at the earths' L1 Lagrangian Point, synchronized its observations with Konus-A. The 1.5 million km separation between the two spacecraft allowed improved localization of gamma ray sources. The mission was completed in December 1995.
Gross mass: 3,500 kg (7,700 lb). | <urn:uuid:c5c388ba-fcec-4599-91c8-49de85871932> | 3.140625 | 157 | Knowledge Article | Science & Tech. | 49.125401 |
Return to my Mathematics pages
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Note: If your WWW browser cannot display special symbols, like ² or 2 or ±, then click here for the alternative Pythagorean Theorem page.
© Copyright 1997, Jim Loy
The Pythagorean Theorem states:
In a right triangle, with sides (legs) a and b, and hypotenuse c, then c²=a²+b².
A right triangle is a triangle with one right angle (an angle of 90°). Its hypotenuse is the side opposite the right angle.
Proof #1: The simplest proof is an algebraic proof using similar triangles ABC, CBX, and ACX (in the diagram):
Since corresponding parts of similar triangles are proportional, a/x=c/a or a²=cx. And b/(c-x)=c/b or b²=c²-cx or c²=cx+b². Substituting a² for cx, we get c²=a²+b². Which is what we were trying to prove.
This proof is by Legendre, and was probably originally devised by an ancient Hindu mathematician. Euclid's proof is quite a bit more complicated than that. It is actually surprising that he did not come up with a proof similar to the above. But, his proof is clever, as well.
Proof #2: Here is another nice proof:
We start with a right triangle (in gold, in the diagram) with sides a, b, and c. We then build a big square, out of four copies of our triangle, as shown at the left. We end up with a square, in the middle, with sides c (we can easily show that this is a square).
We now construct a second big square, with identical triangles which are arranged as in the lower part of the diagram. This square has the same area as the square above it.
We now sum up the parts of the two big squares:
Area=2ab + c²
Area=2ab + a² + b²
These two areas are equal:
2ab + c²=2ab + a² + b²
c²=a² + b²
Proof #3: This diagram might look familiar. I've just drawn the squares on the sides of our right triangle. And, I've drawn a line from the right angle of the triangle, perpendicular to the hypotenuse, through the square which is on the hypotenuse. The idea is to prove that the little square (in blue) has the same area as the little rectangle (also in blue). I've named the width of this rectangle, x.
Using similar triangles, within our right triangle:
The area of the blue rectangle is xc. So we just plug in a²/c for x:
So, the area of the blue rectangle is equal to the area of the blue square. Similarly, the area of the other rectangle (to the left of the blue one) is equal in area of the other square (b²).
So, the total area of the big square is:
c²=a² + b²
That was actually fairly easy. I made that proof up, as I studied Euclid's proof, below.
Proof #4: We now look at Euclid's proof. Although he proved many of the theorems of algebra in his books, he did not have the methods of algebra (the manipulation of symbols) available to him. So, we must add a few more lines. We label a few points (see the diagram), and draw lines BI and CE.
Triangle ACE is congruent to triangle AIB, by the side-angle-side theorem (it's a postulate, nowadays), because AC=AI, AE=AB and angle CAE=angle IAB (both angles are congruent to angle CAB + a right angle). [Note: I am using the=sign for congruence. And I am labelling a line segment as AC, because I lack more appropriate symbols].
But, the area of triangle AIB is equal to half the area of square ACHI (They have the same base AI and height IH), and the area of triangle ACE is equal to half the area of the rectangle AGFE. So, the square ACHI is equal, in area, to the rectangle AGFE. Likewise, we show that the area of the smaller square is equal to the area of the smaller rectangle.
So, the area of the large square is equal to the sums of the areas of the two smaller squares. So, we've proved the Pythagorean theorem, again.
Here is a square with two diagonals. The area of the four triangles is 2a². The area of the square is c². Obviously a²+a²=c², a special case of the Pythagorean Theorem. If a is 1, then c is sqrt(2) [the square root of 2]. Or if c is 1, then a is sqrt(2)/2. This diagram does not seem to help in proving the Pythagorean Theorem.
Mathematics historians are fairly certain that the Pythagorean Theorem was known before Pythagoras. Various cultures seem to have known the length of the diagonal of a square (sqrt(2)) fairly accurately, more accurately than they could measure with a ruler. See The 3-4-5 Right Triangle In Ancient Egypt, where I express the opinion that knowledge of a 3-4-5 right triangle does not imply knowledge of the Pythagorean Theorem.
The book The Pythagorean Proposition, By Elisha Scott Loomis, is a fairly amazing book. It contains 256 proofs of the Pythagorean Theorem. It shows that you can devise an infinite number of algebraic proofs, like the first proof above. It shows that you can devise an infinite number of geometric proofs, like Euclid's proof. And it shows that there can be no proof using trigonometry, analytic geometry, or calculus. The book is out of print, by the way.
The Pythagorean Theorem depends on the parallel postulate. So, it does not hold for the non-Euclidean geometries. In relation to the above proofs
We also have the problem that there are no squares in the non-Euclidean geometries.
Note: Congruence applies to geometric figures, including line segments and angles. Equality applies to numbers, such as areas, lengths of line segments, and the measures of angles. A square and a rectangle are not equal, their areas are equal.
See Rik Littlefield's proof, which is interesting. Also, see The 3-4-5 Right Triangle In Ancient Egypt. The Pythagorean Theorem is also mentioned in Isosceles Triangles.
Proof #5: This proof is attributed to President Garfield. Given the right triangle at the bottom of this diagram, duplicate it as shown, and complete the trapezoid as shown. The larger triangle (with two sides c) is a right triangle (fairly easy to show). The areas of the three triangles are ab/2, ab/2 and c²/2. The sum of these is ab+c²/2. The area of a trapezoid is 1/2 the sum of the parallel sides times the height. Here that is (a+b)(a+b)/2 or (a²+2ab+b²)/2. These two expressions (for the three triangles and the trapezoid) represent the same area:
2ab+c²=a²+2ab+b² [double both sides]
This proof has a great deal in common with our second proof, above.
Proof #6: This proof is attributed to Bhaskara, a Hindu mathematician of the 12th century. We are given the bottom right triangle. We construct a square by making three copies of the triangle, as shown. We assume that a is the smallest side, less than or equal to b. The area of the large square is c². The side of the small square is b-a, and its area is (b-a)² or b²-2ab+a². The area of our triangle is ab/2. The area of all four triangles is 2ab. Then the area of all four triangles, plus the area of the small square is b²+a². So c²=a²+b².
This proof also has a great deal in common with our second proof, above.
Pythagorean triples: Pythagorean triples are sets of three integers (a, b, and c) which satisfy the equation c²=a²+b². In other words, they can be the sides of a right triangle. The smallest non-trivial triple is 3, 4, 5. Another is 5, 12, 13. Triples can be multiplied by any integer to produce another triple. For example, 3, 4, 5 can be doubled to produce 6, 8, 10, which is a Pythagorean triple (and a triangle that is similar to the 3-4-5 right triangle). It is possible to devise a formula for producing Pythagorean triples. [Note: Trivial triples are like 0, 0, 0 or 0, 1, 1.] See Pythagorean Triples.
The study of Pythagorean triples leads to Fermat's Last Theorem, that cx=ax+bxhas no non-trivial solutions with integers for x>2.
In trigonometry ("trig" for short), which I will eventually write about at greater length, deals with angles and certain lengths and their ratios. In the right triangle at the left, the sine of angle A (abbreviated "sin a") is defined as a/c. All right triangles with the same angle A are similar (as shown by Euclid), so this ratio (a/c) is the same regardless of the size of the triangle. Similarly, the cosine of angle A is b/c. One fact (as well as a few other facts) of trig follows directly from the Pythagorean Theorem: for any angle x, sin² x + cos² x=1. To prove it, just plug in a/c for sin x and b/c for cos x, and the sum comes out to 1.
In a general triangle, not necessarily a right triangle, there is an equation similar to the Pythagorean Theorem: c²=a² + b² - 2ab cos C. This is called the Law of Cosines. Similarly, a²=b² + c² - 2bc cos A and b²=a² + c² - 2ac cos B. These can be proved in more than one way, using the Pythagorean theorem.
See My Three Triangle Puzzle.
Here are a few simple problems which use the Pythagorean Theorem:
Here are some answers and comments:
Proof #7:Here is another proof, similar to proof #2, and some of the others. The area of the figure on the left is a² + b² (it is made up of two squares). By rearranging the three pieces, we get the square on the right, with area c². This also shows us how to dissect two squares of any size and put the pieces back together to form one square (or vice versa).
The drawing on the right is similar to one found in the amazing book, 1000 PlayThinks by Ivan Moscovich. The book uses it as a dissection problem (using pieces of the smaller squares to make up the largest square). Then it says, "If you can do [this], what have you done?" The answer in the back of the book says, "Congratulations, you have demonstrated the truth behind the Pythagorean theorem." I have two problems with that. One is that (in mathematics) "demonstrate" means "prove," which we have not done. And second, the triangle in the diagram is not a right triangle (look closely at the "right angle," which is about 92 degrees here). If anything, it demonstrates the falsity of the Pythagorean theorem. Of course, it does neither, as the diagram was drawn sloppily. I intentionally drew mine sloppily. So be careful about "proving" things by drawing them.
Return to my Mathematics pages
Go to my home page | <urn:uuid:a21aeaac-db00-44ec-8a97-0de9d812bf2b> | 4.28125 | 2,639 | Personal Blog | Science & Tech. | 71.309367 |
In addition to the symmetries described above, nuclear scientists use a number of other approximate symmetries to describe and predict the behavior of nuclei. Examples of these are charge independence, the expectation that, at the nuclear level, neutron-proton systems should behave the same as proton-proton or neutron-neutron systems; and charge symmetry, the expectation that the interactions between two neutrons should be the same as that between two protons. Charge symmetry can be demonstrated by comparing "mirror nuclei," two low-mass nuclei that have their neutron and proton numbers interchanged and which have very similar nuclear structure, for example 13C (Z=6, N=7) and 13N (Z=7, N=6).
A related symmetry is isospin symmetry, which is related to interchanging the roles of neutrons and protons in certain nuclei. These three symmetries are destroyed when the Coulomb force becomes sufficiently strong, but nevertheless they have proved to be useful approximations in many areas of nuclear science. | <urn:uuid:68814f56-ecfa-4484-80e0-5da274075a30> | 3.921875 | 219 | Knowledge Article | Science & Tech. | 22.916491 |
What Is a Carbon Footprint?
By Susan Kathleen Moran
"I think it's time to move on. Turns out, true love comes in a size 7 1/2 with a four-inch heel."Shoes, $840, Sergio Rossi.
Photo Credit: Karin Catt
What the term means
Its a measure of the total amount of harmful greenhouse-gas emissions that people produce, either directly or indirectly. These gases warm the atmosphere by absorbing heat thats radiated by the earth, then releasing only a portion of that heat into space. The most dangerous, long-lasting greenhouse gases produced by humans are carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons (aerosols containing this were banned in the U.S. nearly 30 years ago). Carbon dioxide, or CO2, is the most pervasive of the evil gases (a molecule stays airborne for more than a century), and since its tough to separate and quantify each distinct greenhouse gas, scientists commonly use CO2 to measure the global-warming problem.
Why is it called a carbon footprint and not carbon-dioxide footprint?
All of the greenhouse gases we just mentioned have carbon in common. Analysts often convert these gases to carbon equivalents so they can compare apples to apples in terms of emissions.
Is carbon all bad?
Actually, its not. Diamonds are pure carbon, and whats not to like about them? Our bodies are mostly made of carbon, as is just about everything we touch and see, from tree stumps to trash bags. But carbon is also oil, natural gas, and coal hence, its polluting connotation. Match the carbon in the atmosphere with pairs of oxygen molecules that are created through the combustion of trees, dung, and fossil fuels, and it becomes CO2. The current global atmospheric concentration of carbon dioxide is as much as a whopping 40 percent higher than levels in the air before the industrial revolution.
MORE CARBON FOOTPRINT ARTICLES
The Top 3 Carbon Evils
Whose Carbon Footprint Is the Smallest? | <urn:uuid:63c8cb8c-d9b2-4f3f-a0ed-34593cadfd8c> | 2.75 | 426 | Personal Blog | Science & Tech. | 51.341436 |
Selective extraction of gold(III) in the presence of Pd(II) and Pt(IV) by salting-out of the mixture of 2-propanol and water.
- PubMed: 18968825
The mixture of 2-propanol with water has been employed to extract Au(III) along with other precious metals such as Pd(II) and Pt(IV) by using NaCl in the concentration range of 2.5-4.0 mol dm(-3). Upon the addition of NaCl within this concentration range (2.5-4.0 mol dm(-3)) phase separation was attained. Gold(III) in aqueous phase was quantitatively extracted into the 2-propanol phase at 2.5-4.0 mol dm(-3) of NaCl. The extraction of the other metals such as Pd(II) and Pt(IV) was much lower than for that of Au(III). Thus a maximal selective separation of Au(III) from these metals could be attained using the mixture of 2-propanol with water. A reaction mechanism involving the ion-pair of Na(+) and AuCl(4)(-) has been proposed to explain this extraction. | <urn:uuid:5b9b1ccb-3bbd-48e9-bb06-7bd3c953c579> | 2.703125 | 257 | Academic Writing | Science & Tech. | 79.477202 |
Tsunami: DART II Buoy
This giant Deep Ocean Assessment and Reporting of Tsunamis (DART) buoy was part of a tsunami warning system that consists of almost 40 buoys located in oceans around the world. Pressure sensors located thousands of feet below the buoy on the bottom of the ocean detect the tsunami as it passes by. The sensors relay data about the tsunami up to the buoy, which then passes the data on to a satellite and finally on to Tsunami Warning Centers.
On November 15, 2006, this buoy recorded a tsunami resulting from an 8.3-magnitude earthquake in Russia's Kuril Islands. During a storm in May of 2008, it broke free from its mooring and was deemed “Lost at Sea” by the National Oceanic and Atmospheric Administration (NOAA). It was found almost a year later washed up on a beach on Kodiak Island, Alaska, over 400 miles from its original location.
The DART buoy is just the beginning of the tsunami-related activities in Science Storms. | <urn:uuid:588cb1cc-2a9b-43a8-8c09-354a1dd87b64> | 4.03125 | 217 | Knowledge Article | Science & Tech. | 52.73632 |
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
Maps similar to those in Figure 3 of BN09 will result from each shift in mean temperature, except they will correspond to different atmospheric concentrations of CO2 (and their implied expected global average warming) rather than to different future periods. The main difference in our approach compared to the analysis in BN09 is the choice of shifting the distribution uniformly to the right rather than trying to build a new distribution of average temperature anomalies on the basis of model output. This is a choice dictated by the use of pattern scaling, which lacks the availability of an ensemble of fully coupled model runs for each CO2 target.
It could be argued that our analysis represents a conservative estimate of the expected changes in extreme seasonal temperatures, because we are assuming no change in the climatological distributions of temperatures besides a shift of their central locations. In particular, no change in the variability of seasonal average temperature is taken into consideration. Some studies (see for example Scherrer et al., 2005; Fischer and Schar, 2009 for the European region; Giorgi and Bi, 2005; Kitoh and Mukano, 2009 for global patterns) have shown that future variability of summer temperature is projected to increase, in association with drying.
In Figures 4.8 and 4.9 we show the resulting likelihoods of exceeding the 95th percentile, or the warmest anomaly of current average JJA and DJF temperatures (1971-2000 of 20C3M simulations) for the three levels of global warming. The patterns become redder (higher likelihood) as we look down each column (larger global average warming implies greater chances of exceeding the thresholds) and bluer (smaller likelihood) as we look across rows (higher thresholds make exceedances rarer).
4.6 PRECIPITATION EXTREMES
A general increase in atmospheric water vapor is predicted by essentially all climate models as temperatures increase, and an upward trend in column integrated water vapor has been observed in many regions (Trenberth et al., 2005). The consequences of this increase for the distribution of mean precipitation has been discussed in Section 4.2. As outlined below, models and simple theories also suggest that this increase in water vapor will increase the intensity of heavy rainfall events. Increasing trends in extreme precipitation have been documented in many regions, including much of North America (USCCSP, 2008c), but evidence for associated increases in floods is not compelling to date (Lins and Slack, 1999, 2005; WWAP, 2008).
As articulated by Trenberth (1999) and many others, precipitation in storms is related mostly to atmospheric moisture convergence rather than | <urn:uuid:bdbbefe9-1be2-4328-bccf-bc3916b7e2f8> | 3.015625 | 592 | Academic Writing | Science & Tech. | 25.010195 |
In your article on fingerprints, Stephen Meagher is quoted as saying: "individual fingerprints are effectively unique" (17 September, p 6). Can this be true? Wouldn't identical twins also have identical fingerprints?
The editor writes:
• Although identical twins share the same genes they do not have identical fingerprints. That's because the shape of the whorls and arches on our fingers are determined both by genes and the local environment around the dividing skin cells. So a twin's individual position in the womb will cause slight differences.
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:6a0b8b9e-8a0a-4860-9c3f-6e2d9d00dad9> | 3.265625 | 135 | Truncated | Science & Tech. | 43.515833 |
Hello, I would like to do an activity with the cub scouts.
I would like to have them build a telescope. I read up on the
Internet and it appears to be a simple thing, but so far my
telescope is not working. The telescope focuses, but objects in the
distance are not magnified and appear upside down. I am using a
telescoping mailing tube, 3 inches in diameter and up to 40 inches
in length. The objective lens is a double convex 50 mm diameter, 500
mm focal length lens. The eyepiece lens is double convex, 50 mm
diameter and 50 mm focal length. I attached the lenses to the tube
as described in the NASA web site, where they describe a way to
build a telescope. I am told that I should use a concave lens to
make the image right side up, but how do I fix the magnification?
That is the essence of the telescope. Can you give me some advice on
how to make this work?
The big objective lens in the front end must remain convex.
Replacing the small eyepiece lens in the rear end with a concave lens
would make the image right-side up.
You could look in Edmund Optics for a concave lens
of, say, 10mm diameter and -50mm focal length.
That is a negative number for concave lenses,
which cannot really bring a light beam to a focal point.
Comment: having an eyepiece so big (50mm) probably will not help
or even work easily.
A 50mm lens with 50mm focal length is so fat it does not really focus well.
It probably looks like a glass toadstool, i.e., at least 1 inch thick.
They are only used for herding lamp-light into one general direction,
so they are called "condenser lenses".
And they can be a little expensive because they are so fat.
Eyepiece lens 10mm diameter and +50mm focus (convex) would be nice.
Even 5mm diameter and +50mm focus would probably do.
Either could be concave, i.e, -50mm focal length.
You will need to make an end-cap with a hole in it to help mount
these lenses because they are smaller than the big tube.
If instead you use a cone or step down to a narrower cylinder,
that is good too but a little fancier to construct.
Convex or concave, the magnification will be that ratio of focal lengths.
For 500mm objective and 50mm eyepiece, that is 10x.
The scope is in focus when parallel rays entering the objective
taper down to a focal point in the tube
at same point the (convex) eyepiece lens focuses on.
So for clear-focus, the distance between the lenses is given by
the sum of their focal lengths.
For convex, 500mm + (+50mm) = 550mm.
I hope your telescoping tube-sets go down to 22 inches!
When you get it that short,
you should see some degree of focused image with your present lenses,
and it should have definite large magnification.
Let's hope that condenser lens does not shmoosh the image completely.
You may want to cut the tubes to 30-36 inches total maximum extension,
so they are only about 1/2 overlapped when set to 22 inches long.
For concave, 500mm + (-50mm) = 450mm.
Hmm, 4 inches shorter (18 inches), more tube-cutting....
Another tip- if your convex lenses are single-convex (flat on one side),
or one side is less curved than the other, (maybe your condenser lens?)
put the more curved surface outside where the light rays are parallel
and the flatter surface inside where the light rays are angled to converge.
That way tends to make better focus than the other way around,
for a given lens.
good luck, I think you are almost there-
If you truly have a 500 mm focal length lens as the objective and a 50 mm
focal length lens as the eyepiece you should have a factor of 10 magnification.
Please verify that you don't have magnification by comparing what you see when
looking through your telescope with what you see when looking through a tube
of the same length and diameter but without lenses. With a factor of ten
magnification on the telescope you should see much less through the telescope
than through empty tube.
You can verify the focal lengths of the lenses by focusing a distant light
source (more than 20 feet -- a street light at night would be good) and
measuring the distance from the lens to the focused image of the light.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:cf73cfe2-dc28-4801-89b7-124577a6bb69> | 2.921875 | 1,033 | Q&A Forum | Science & Tech. | 66.512013 |
NOAA / Space Weather Prediction Center
The top graph plots the annual average lead time of K6 Short-Term Warnings. Lead time is defined as the time between the warning being issued and when a K6 is measured at the Boulder magnetometer. A missed warning, where a K6 is observed but no warning was issued, is counted as a lead time of 0 minutes. The middle plot shows the annual average of the Heidke skill score. This score ranges from -1 to +1, where all correct warnings give a score of +1, no correct warnings give a score of -1, and no K6 observed or no warnings issued give a score of 0. The bottom histogram plots the annual frequency of K6 observed, warning hits, warning misses, and warning false alarms (Boulder, Colorado data). The K6 warning began in 1999 following the availability of continuous real-time solar wind data from the NASA ACE spacecraft.
Visually impaired users may contact SWPC for assistance.
Space Weather Topics:
Alerts / Warnings, Space Weather Now, Today's Space Wx, Data and Products, About Us ,
Email Products, Space Wx Workshop , Education/Outreach, Disclaimer, Customer Services, Contact Us | <urn:uuid:92bdae56-e830-4cc1-a427-544314fed52b> | 2.875 | 255 | Knowledge Article | Science & Tech. | 46.62177 |
|Pomarine Jaeger by Patrick Coin|
After the Superstorm Sandy, pomarine jaegers were found in many places as unlikely as Pennsylvania. Rescued pelicans in Rhode Island were flown back to a place more like their natural home, Florida.
Birds of all stripes follow the wind during their yearly migrations. Sometimes the process is interrupted by violent events like Sandy, and they may end up far from their preferred habitats. There were many such sightings after that massive northeastern hybrid storm: a Ross gull from the arctic turned up in Upstate New York, for instance, and in New Jersey a red-billed tropicbird was spotted.
Sandy is an example of how life itself is guided by the ubiquitous winds that move and shape clouds and weather. Sometimes the effects are gentle as well as beneficial. Throughout the world, the winds bring essential rain far inland, to places that lack their own source of moisture. The breezes of the earth disperse seeds so many species of plants need to propagate.
|See the relationship of wind and current in this NASA Scatterometer Image.|
The wind... although we can’t see it, we can feel it as an ever-present force. Like with Sandy, it reminds us that in life everything changes. The nature of the wind is written into our very thoughts and words. If change is near we say there something in the wind. Unpredictable people are said to be as fickle as the wind.
And on this earth the winds of change forever blow, reminding us nothing is permanent, not even the mountains that over geologic spans of time are beaten down by the wind and rain, and like great swells ultimately return to the waters of the ocean. | <urn:uuid:db63c277-35ba-41dc-bc7e-0543cb922332> | 3 | 359 | Personal Blog | Science & Tech. | 54.728245 |
Python os.fchown() Method
The method fchown() changes the owner and group id of the file given by fd to the numeric uid and gid. To leave one of the ids unchanged, set it to -1.
Note:This method is available Python 2.6 onwards.
Following is the syntax for fchown() method
os.fchown(fd, uid, gid);
fd -- This is the file descriptor for which owner id and group id need to be setup.
uid -- This is Owner ID to be set for the file.
gid -- This is Group ID to be set for the file.
This method does not return any value.
The following example shows the usage of fchown() method.
#!/usr/bin/python import os, sys, stat # Now open a file "/tmp/foo.txt" fd = os.open( "/tmp", os.O_RDONLY ) # Set the user Id to 100 for this file. os.fchown( fd, 100, -1) # Set the group Id to 50 for this file. os.fchown( fd, -1, 50) print "Changed ownership successfully!!" # Close opened file. os.close( fd )
Let us compile and run the above program, this will produce the following result:
Changed ownership successfully!! | <urn:uuid:6a8949ae-4a99-41ca-bd10-6d60da27166b> | 2.828125 | 297 | Documentation | Software Dev. | 87.046009 |
One of the things that I want to see before I die is the Aurora Borealis (or its Antarctic equivalent, the Aurora Australis). But if the folks at NASA and the New Scientist are correct, seeing them may be the last thing I do, at least before my and everyone else's world falls apart.
Here's the scenario:
It is midnight on 22 September 2012 and the skies above Manhattan are
filled with a flickering curtain of colourful light. Few New Yorkers
have seen the aurora this far south but their fascination is
short-lived. Within a few seconds, electric bulbs dim and flicker, then
become unusually bright for a fleeting moment. Then all the lights in
the state go out. Within 90 seconds, the entire eastern half of the US
is without power.
year later and millions of Americans are dead and the nation's
infrastructure lies in tatters. The World Bank declares America a
developing nation. Europe, Scandinavia, China and Japan are also
struggling to recover from the same fateful event - a violent storm,
150 million kilometres away on the surface of the sun.
To understand how and why millions of us are going to die, first a primer: however peaceful and happy the Sun looks from 93 miles away, it is, as your science teachers told you, a giant ball of burning gas that ejects billions of tons of electrically charged particles every few hours, a.k.a. the solar wind.
The best-case scenario: every day about 1000 tons of these particles reach Earth, where most of them are deflected by our blessed magnetic field (magnetosphere) and "dragged through the atmosphere towards the
poles." There, the particles collide with oxygen and nitrogen to produce the green and red lights of the aurora.
(Note, I said "most," not all. Some of the particles do get through. There's no end of speculation about their effects: everything from dropped cell phone calls to cancer to the genetic mutations that drive evolution has been linked by someone to these particles.) | <urn:uuid:bff7909a-5efa-402d-961d-fd5a19ff9c01> | 3.046875 | 428 | Personal Blog | Science & Tech. | 53.996579 |
Background page states:
The United States Historical Climatology Network (USHCN) is a high-quality data set of daily and monthly records of basic meteorological variables from 1218 observing stations across the 48 contiguous United States. Daily data include observations of maximum and minimum temperature, precipitation amount, snowfall amount, and snow depth; monthly data consist of monthly-averaged maximum, minimum, and mean temperature and total monthly precipitation. Most of these stations are U.S. Cooperative Observing Network stations located generally in rural locations, while some are National Weather Service First-Order stations that are often located in more urbanized environments. The USHCN has been developed over the years at the National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Center (NCDC) to assist in the detection of regional climate change. Furthermore, it has been widely used in analyzing U.S. climte. The period of record varies for each station. USHCN stations were chosen using a number of criteria including length of record, percent of missing data, number of station moves and other station changes that may affect data homogeneity, and resulting network spatial coverage.
Assumed open as from US government, but Disclaimer page states:
Documents provided from the web server were sponsored by a contractor of the U.S. Government under contract DE-AC05-00OR22725. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce these documents, or to allow others to do so, for U.S. Government purposes. These documents may be freely distributed and used for non-commercial, scientific and educational purposes.
Not clear whether this applies just to documents - or also to data.
|Skapare||Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory|
United States Historical Climatology Network (USHCN). Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory.
Retrieved 14:18, May 22, 2013 (UTC).
the Data Hub | <urn:uuid:3c6223e0-7116-4b77-86d1-d104727f0a57> | 2.859375 | 418 | Knowledge Article | Science & Tech. | 24.970221 |
Crystal structure of lonsdaleite
|Crystal symmetry||Hexagonal dihexagonal dipyramidal
H-M symbol: (6/m 2/m 2/m)
Space group: P 63/mmc
|Unit cell||a = 2.51 Å, c = 4.12 Å; Z=4|
Gray in crystals, pale yellowish to brown inbroken fragments
|Crystal habit||Cubes in fine-grained aggregates|
|Mohs scale hardness||7-8|
|Optical properties||Uniaxial (+/-)|
|Refractive index||n = 2.404|
Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice. In nature, it forms when meteorites containing graphite strike the Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with diamond.
Hexagonal diamond has also been synthesized in the laboratory (1966 or earlier; published in 1967) by compressing and heating graphite either in a static press or using explosives. It has also been produced by chemical vapor deposition, and also by the thermal decomposition of a polymer, poly(hydridocarbyne), at atmospheric pressure, under argon atmosphere, at temperature 110 °C (230 °F).
It is translucent, brownish-yellow in color, and has an index of refraction of 2.40 to 2.41, a specific gravity of 3.2 to 3.3, and a Mohs hardness of 7–8. The Mohs hardness of diamond is 10, and the lower hardness of lonsdaleite is chiefly attributed to impurities and imperfections in the naturally occurring material. A simulated pure sample has been found to be 58% harder than diamond.
Lonsdaleite has a hexagonal unit cell, related to the diamond unit cell in the same way that the hexagonal and cubic close packed crystal systems are related. The diamond structure can be considered to be made up of interlocking rings of six carbon atoms, in the chair conformation. In lonsdaleite, some of the rings are in the boat conformation instead. In diamond, all the carbon-to-carbon bonds, both within a layer of rings and between them, are in the staggered conformation, thus causing all four cubic-diagonal directions to be equivalent; while in lonsdaleite the bonds between layers are in the eclipsed conformation, which defines the axis of hexagonal symmetry.
Lonsdaleite is simulated to be 58% harder than diamond on the <100> face and to resist indentation pressures of 152 GPa, whereas diamond would break at 97 GPa. This is still below IIa diamond's <111> tip hardness of 162 GPa.
Lonsdaleite occurs as microscopic crystals associated with diamond in several meteorites: Canyon Diablo, Kenna, and Allan Hills 77283. It is also naturally occurring in non-bolide diamond placer deposits in the Sakha Republic. It has also been found in sediments dated to 12,900 years ago, at Lake Cutizeo, in the state of Guanajuato, Mexico, supportive of the controversial Younger Dryas impact hypothesis.
See also
- Lonsdaleite on Mindat.org
- Handbook of Mineralogy
- Lonsdaleite data from Webmineral
- Frondel, C.; U.B. Marvin (1967). "Lonsdaleite, a new hexagonal polymorph of diamond". Nature 214 (5088): 587–589. Bibcode:1967Natur.214..587F. doi:10.1038/214587a0.
- Frondel, C.; U.B. Marvin (1967). "Lonsdaleite, a hexagonal polymorph of diamond". Am.Min. 52.
- Bundy, F. P. (1967). "Hexagonal Diamond—A New Form of Carbon". Journal of Chemical Physics 46 (9): 3437. Bibcode:1967JChPh..46.3437B. doi:10.1063/1.1841236.
- He, Hongliang; Sekine, T.; Kobayashi, T. (2002). "Direct transformation of cubic diamond to hexagonal diamond". Applied Physics Letters 81 (4): 610. Bibcode:2002ApPhL..81..610H. doi:10.1063/1.1495078.
- Bhargava, Sanjay; Bist, H. D.; Sahli, S.; Aslam, M.; Tripathi, H. B. (1995). "Diamond polytypes in the chemical vapor deposited diamond films". Applied Physics Letters 67 (12): 1706. Bibcode:1995ApPhL..67.1706B. doi:10.1063/1.115023.
- Nishitani-Gamo, Mikka; Sakaguchi, Isao; Loh, Kian Ping; Kanda, Hisao; Ando, Toshihiro (1998). "Confocal Raman spectroscopic observation of hexagonal diamond formation from dissolved carbon in nickel under chemical vapor deposition conditions". Applied Physics Letters 73 (6): 765. Bibcode:1998ApPhL..73..765N. doi:10.1063/1.121994.
- Misra, Abha; Tyagi, Pawan K.; Yadav, Brajesh S.; Rai, P.; Misra, D. S.; Pancholi, Vivek; Samajdar, I. D. (2006). "Hexagonal diamond synthesis on h-GaN strained films". Applied Physics Letters 89 (7): 071911. Bibcode:2006ApPhL..89g1911M. doi:10.1063/1.2218043.
- Nur, Yusuf; Pitcher, Michael; Seyyidoğlu, Semih; Toppare, Levent (2008). "Facile Synthesis of Poly(hydridocarbyne): A Precursor to Diamond and Diamond-like Ceramics". Journal of Macromolecular Science Part A 45 (5): 358. doi:10.1080/10601320801946108.
- Nur, Yusuf; Cengiz, Halime M.; Pitcher, Michael W.; Toppare, Levent K. (2009). "Electrochemical polymerizatıon of hexachloroethane to form poly(hydridocarbyne): a pre-ceramic polymer for diamond production". Journal of Materials Science 44 (11): 2774. Bibcode:2009JMatS..44.2774N. doi:10.1007/s10853-009-3364-4.
- Pan, Zicheng; Sun, Hong; Zhang, Yi; and Chen, Changfeng (2009). "Harder than Diamond: Superior Indentation Strength of Wurtzite BN and Lonsdaleite". Physical Review Letters 102 (5): 055503. Bibcode:2009PhRvL.102e5503P. doi:10.1103/PhysRevLett.102.055503. PMID 19257519. Lay summary – Physorg.com (12-02-2009).
- Kaminskii, F.V., G.K. Blinova, E.M. Galimov, G.A. Gurkina, Y.A. Klyuev, L.A. Kodina, V.I. Koptil, V.F. Krivonos, L.N. Frolova, and A.Y. Khrenov (1985). "Polycrystalline aggregates of diamond with lonsdaleite from Yakutian [Sakhan] placers". Mineral. Zhurnal 7: 27–36.
- Israde-Alcantara, I.; Bischoff, J. L.; Dominguez-Vazquez, G.; Li, H.-C.; Decarli, P. S.; Bunch, T. E.; Wittke, J. H.; Weaver, J. C. et al. (2012). "Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis". Proceedings of the National Academy of Sciences 109 (13): E738. Bibcode:2012PNAS..109E.738I. doi:10.1073/pnas.1110614109. PMID 22392980.
Further reading
- Anthony, J. W. (1995). Mineralogy of Arizona (3rd ed.). Tucson: University of Arizona Press. ISBN 0-8165-1579-4..
- Mindat.org accessed 13 March 2005.
- Webmineral accessed 13 March 2005.
- Materials Science and Technology Division, Naval Research Laboratory website accessed 14 May 2006.
- Diamond no longer nature's hardest material
- lonsdaleite 3D animation | <urn:uuid:bd800d85-a5f3-4875-89b6-5132268265a9> | 3.578125 | 1,944 | Knowledge Article | Science & Tech. | 68.65209 |
Posted by Steve on October 31, 2002 at 22:54:03:
1. State the amplitude (A) the period (T) and the frequency (f) for the periodic function 120sin(100 "pi symbol" t)V
2. Through how many degrees does a wheel rotate in 10ms if its angular velocity is 8 rad/s
3. Sketch one cycle of the given function showing the values of each variable where the curve crosses the axis.
V = 50sin(4.2x10^2t)
I am really sorry for this, but please believe me that I am in desperate trouble if I don't hand these in...
Post a Followup | <urn:uuid:513f3805-a920-4b0e-a452-4dcd130cb888> | 3.15625 | 142 | Q&A Forum | Science & Tech. | 86.990176 |
Britain, as you may have noticed if you’re reading from there, has experienced some extreme weather in recent weeks. Floods have followed drought, with new records for rainfall in May and June. We’re not the only place facing bizarre weather. The US is halfway through another summer of extremes, with over 3,000 new record temperatures for June and 2,000 for July so far.
It’s natural to ask if the extremes that we’re experiencing are just freak incidents or part of climate change. Until recently, the answer would have been ‘it’s impossible to say’. We know that, in theory, warmer climates would see more precipitation and more extremes. In reality, it’s very hard to attribute specific weather events to climate change when there are so many other factors.
That’s beginning to change. As the body of science around climate change grows, scientists have been able to identify key areas that aren’t well understood and focus on them. The interplay of weather patterns and longer climate trends has been one such area of focus, bringing together meteorology and climate science to work across disciplines. That research is now paying off, and we’re beginning to see new studies with a much more sophisticated understanding of weather and climate.
As an example, a briefing from NOAA (pdf) this week looks at six extreme weather events in 2011 and assesses whether climate change was a factor or not. The floods in Thailand, it concludes, were not driven by climate change. Neither was Britain’s cold winter in 2010/11 – that was simply “a rare weather event”. On the other hand, the failed rains and resulting famine in East Africa was consistent with warming trends and climate change was probably a cause.
Some events aren’t so easy to call, such as the drought in Texas. “While we can provide evidence that the risk of hot and dry conditions has increased,” say the authors, “we cannot say that the 2011 Texas drought and heat wave was “extremely unlikely” to have occurred before this recent warming.”
This sort of language is important – ‘likely’ or ‘probable’ is still all we can say, because this is a matter of probabilities. As the climate warms, the odds of warm or cold temperatures shorten or lengthen accordingly. The Met Office describes the difference between two months in Britain’s winter conditions: “The extreme warm average temperature in November 2011 is 60 times more likely to have occurred than in the 1960s. The change in odds of the extremely cold December was considerably less, however, being only about half as likely. Even without climate change, unusual circulation patterns can still bring very cold winter months.”
Climate change isn’t progressing in a linear fashion, but in a complex dance of trends and patterns that sometimes reinforce and sometimes compete with the gradual warming of the earth. We’re understanding that better all the time. | <urn:uuid:af0f03ec-62f4-481c-88cb-3467a3952697> | 3.515625 | 624 | Knowledge Article | Science & Tech. | 47.478024 |
Starting with the number 180, take away 9 again and again, joining up the dots as you go. Watch out - don't join all the dots!
Mr McGregor has a magic potting shed. Overnight, the number of
plants in it doubles. He'd like to put the same number of plants in
each of three gardens, planting one garden each day. Can he do it?
If you have only four weights, where could you place them in order
to balance this equaliser?
This problem is based on a code using two different prime numbers
less than 10. You'll need to multiply them together and shift the
alphabet forwards by the result. Can you decipher the code?
Place the numbers 1 to 10 in the circles so that each number is the
difference between the two numbers just below it.
How have the numbers been placed in this Carroll diagram? Which
labels would you put on each row and column?
Can you see why 2 by 2 could be 5? Can you predict what 2 by 10
Start by putting one million (1 000 000) into the display of your
calculator. Can you reduce this to 7 using just the 7 key and add,
subtract, multiply, divide and equals as many times as you like?
Here is a chance to play a version of the classic Countdown Game.
Place the numbers from 1 to 9 in the squares below so that the difference between joined squares is odd. How many different ways can you do this?
Choose a symbol to put into the number sentence.
Can you put the numbers 1 to 8 into the circles so that the four
calculations are correct?
Can you make a cycle of pairs that add to make a square number
using all the numbers in the box below, once and once only?
Hover your mouse over the counters to see which ones will be
removed. Click to remover them. The winner is the last one to
remove a counter. How you can make sure you win?
Arrange the four number cards on the grid, according to the rules,
to make a diagonal, vertical or horizontal line.
Imagine a wheel with different markings painted on it at regular
intervals. Can you predict the colour of the 18th mark? The 100th
Investigate the smallest number of moves it takes to turn these
mats upside-down if you can only turn exactly three at a time.
Can you put the 25 coloured tiles into the 5 x 5 square so that no
column, no row and no diagonal line have tiles of the same colour
Can you make the green spot travel through the tube by moving the
yellow spot? Could you draw a tube that both spots would follow?
Can you complete this jigsaw of the multiplication square?
A game for 2 people that everybody knows. You can play with a
friend or online. If you play correctly you never lose!
An environment which simulates working with Cuisenaire rods.
This article gives you a few ideas for understanding the Got It! game and how you might find a winning strategy.
Try to stop your opponent from being able to split the piles of counters into unequal numbers. Can you find a strategy?
Have a go at this well-known challenge. Can you swap the frogs and toads in as few slides and jumps as possible?
What do the numbers shaded in blue on this hundred square have in common? What do you notice about the pink numbers? How about the shaded numbers in the other squares?
A game to be played against the computer, or in groups. Pick a 7-digit number. A random digit is generated. What must you subract to remove the digit from your number? the first to zero wins.
The idea of this game is to add or subtract the two numbers on the
dice and cover the result on the grid, trying to get a line of
three. Are there some numbers that are good to aim for?
An interactive activity for one to experiment with a tricky tessellation
Use the Cuisenaire rods environment to investigate ratio. Can you
find pairs of rods in the ratio 3:2? How about 9:6?
Find out how we can describe the "symmetries" of this triangle and
investigate some combinations of rotating and flipping it.
Use the interactivity to find all the different right-angled
triangles you can make by just moving one corner of the starting
How can the same pieces of the tangram make this bowl before and after it was chipped? Use the interactivity to try and work out what is going on!
A card pairing game involving knowledge of simple ratio.
Can you find all the different triangles on these peg boards, and
find their angles?
An interactive game for 1 person. You are given a rectangle with 50 squares on it. Roll the dice to get a percentage between 2 and 100. How many squares is this? Keep going until you get 100. . . .
You have 4 red and 5 blue counters. How many ways can they be
placed on a 3 by 3 grid so that all the rows columns and diagonals
have an even number of red counters?
There are nine teddies in Teddy Town - three red, three blue and three yellow. There are also nine houses, three of each colour. Can you put them on the map of Teddy Town according to the rules?
Choose the size of your pegboard and the shapes you can make. Can
you work out the strategies needed to block your opponent?
What are the coordinates of the coloured dots that mark out the
tangram? Try changing the position of the origin. What happens to
the coordinates now?
What shaped overlaps can you make with two circles which are the
same size? What shapes are 'left over'? What shapes can you make
when the circles are different sizes?
Use the sightings of the lion to guess the location of its lair.
A train building game for 2 players.
Find out what a "fault-free" rectangle is and try to make some of
Can you find all the different ways of lining up these Cuisenaire
Our 2008 Advent Calendar has a 'Making Maths' activity for every
day in the run-up to Christmas.
This 100 square jigsaw is written in code. It starts with 1 and
ends with 100. Can you build it up?
Using angular.js to bind inputs to outputs
Choose 13 spots on the grid. Can you work out the scoring system? What is the maximum possible score?
Try out the lottery that is played in a far-away land. What is the
chance of winning? | <urn:uuid:d8ee2a17-d5e3-4b8c-84c6-4a8e3d003958> | 4.0625 | 1,401 | Content Listing | Science & Tech. | 73.358256 |
Major Section: BOOKS
Example: ACL2 !>:cbd "/usr/home/smith/"The connected book directory is a nonempty string that specifies a directory as an absolute pathname. (See pathname for a discussion of file naming conventions.) When
include-bookis given a relative book name it elaborates it into a full book name, essentially by appending the connected book directory string to the left and
".lisp"to the right. (For details, see book-name and also see full-book-name.) Furthermore,
include-booktemporarily sets the connected book directory to the directory string of the resulting full book name so that references to inferior books in the same directory may omit the directory. See set-cbd for how to set the connected book directory string.
General Form: (cbd)This is a macro that expands into a term involving the single free variable
state. It returns the connected book directory string.
The connected book directory (henceforth called the ``
include-book to elaborate the supplied book name into a
full book name (see full-book-name). For example, if the
"/usr/home/smith/" then the elaboration of the book-name
"project/task-1/arith" (to the
".lisp" extension) is
full-book-name is what include-book opens to read the
source text for the book.
cbd may be changed using
set-cbd (see set-cbd).
Furthermore, during the processing of the events in a book,
include-book sets the
cbd to be the directory string of the
full-book-name of the book. Thus, if the
"/usr/home/smith/" then during the processing of events by
cbdwill be set to
"/usr/home/smith/project/task-1/". Note that if
"arith"recursively includes a subbook, say
"naturals", that resides on the same directory, the
include-bookevent for it may omit the specification of that directory. For example,
"arith"might contain the event
(include-book "naturals").In general, suppose we have a superior book and several inferior books which are included by events in the superior book. Any inferior book residing on the same directory as the superior book may be referenced in the superior without specification of the directory.
We call this a ``relative'' as opposed to ``absolute'' naming. The use of relative naming is preferred because it permits books (and their accompanying inferiors) to be moved between directories while maintaining their certificates and utility. Certified books that reference inferiors by absolute file names are unusable (and rendered uncertified) if the inferiors are moved to new directories.
Technical Note and a Challenge to Users:
After elaborating the book name to a full book name,
opens a channel to the file to process the events in it. In some
host Common Lisps, the actual file opened depends upon a notion of
``connected directory'' similar to our connected book directory.
Our intention in always elaborating book names into absolute
filename strings (see pathname for terminology) is to
circumvent the sensitivity to the connected directory. But we may
have insufficient control over this since the ultimate file naming
conventions are determined by the host operating system rather than
Common Lisp (though, we do check that the operating system
``appears'' to be one that we ``know'' about). Here is a question,
which we'll pose assuming that we have an operating system that
calls itself ``Unix.'' Suppose we have a file name, filename, that
begins with a slash, e.g.,
"/usr/home/smith/...". Consider two
successive invocations of CLTL's
(open filename :direction :input)separated only by a change to the operating system's notion of connected directory. Must these two invocations produce streams to the same file? A candidate string might be something like
"/usr/home/smith/*/usr/local/src/foo.lisp"which includes some operating system-specific special character to mean ``here insert the connected directory'' or, more generally, ``here make the name dependent on some non-ACL2 aspect of the host's state.'' If such ``tricky'' name strings beginning with a slash exist, then we have failed to isolate ACL2 adequately from the operating system's file naming conventions. Once upon a time, ACL2 did not insist that the
cbdbegin with a slash and that allowed the string
"foo.lisp"to be tricky because if one were connected to
"/usr/home/smith/"then with the empty
"foo.lisp"is a full book name that names the same file as
"/usr/home/smith/foo.lisp". If the actual file one reads is determined by the operating system's state then it is possible for ACL2 to have two distinct ``full book names'' for the same file, the ``real'' name and the ``tricky'' name. This can cause ACL2 to include the same book twice, not recognizing the second one as redundant. | <urn:uuid:e9024ecd-3878-495c-89dc-1ca1668d2abb> | 2.734375 | 1,109 | Documentation | Software Dev. | 42.116934 |
Ternary Search Tries
June 5, 2009
Several of our exercises (Mark V. Shaney, Word Frequencies, Dodgson’s Doublets, Anagrams) have used hash tables based on string keys. When the keys are strings, a useful alternative to hash tables is a data structure called a ternary search trie, which can be faster than a hash table because it takes advantage of the fact that keys are strings, and also provides in-order access to the keys. Ternary search tries were introduced by Jon Bentley and Robert Sedgewick at the 1997 SODA conference.
As the name implies, ternary search tries are a cross between binary search trees and radix tries. Ternary search tries consist of recursive nodes and leaves, just like binary search trees and radix tries. As the name implies, a node of a ternary search trie has three children, one for lesser children, one for greater children, and a third for equal children. Searches proceed character-by-character, as with a trie. At each level of the trie, the search compares the current character of the search string with the character stored in the node. If the search character is less, the search continues at the less-than child, and if the search character is greater, the search continues at the greater-than child. However, when the two characters are equal, the search continues recursively at the equal-to child, proceeding to the next character in the search string.
The picture below, taken from the Bentley/Sedgewick SODA paper, shows a ternary search trie containing twelve two-character words:
Your task is to implement the lookup, insert, update, delete and enlist operations on ternary search tries. When you are finished, you are welcome to read or run a suggested solution, or post your solution or discuss the exercise in the comments below.
Pages: 1 2 | <urn:uuid:409b6da4-39f2-477d-9ddf-6d1369b343b2> | 3.78125 | 409 | Tutorial | Software Dev. | 48.216293 |
By Dr. Scott Noakes The University of Georgia Center for Applied Isotope Studies
Ocean acidification, a decrease in seawater pH (acidity scale) caused by the increase of anthropogenic (human-induced) carbon dioxide (CO2) into the atmosphere, has received considerable attention in recent years. As scientists gain an understanding of the adverse affects of increased CO2 and decreased pH, a major concern of ocean acidification is the impact to organisms which use calcium to build their bones, skeletons or other structural components. Recent research has indicated that the oceans act as a net repository or "sink" for atmospheric CO2, but that this sink is not uniform worldwide. Many coastal regions oscillate between being a CO2 sink and source depending on the time of year. The effects of ocean acidification have yet to be fully understood in coastal regions were biogeochemical processes are often vastly different from regions dominated by upwelling.
Greg McFall finishes installing the new microcat (salinity and temperature probes) on the buoy bridle. (Photo: Sarah Fangman)
The coastal areas surrounding our continent (continental margins) are known to play a considerable role in determining global carbon cycling; however, little has been done to determine input from the coastal margins towards the total carbon "budget." Insufficient data exists to adequately determine the natural fluctuation ("flux") of air-sea CO2 with any level of confidence. The ability to explain the control mechanisms driving the variability of coastal partial pressure of CO2 (pCO2 or the concentration of CO2 in seawater) and pH is limited. Understanding these control mechanisms and how they affect pCO2 and pH is essential to predicting future changes in CO2 flux, pH and carbonate saturation in our oceans. The primary reason that scientists are not able to determine the control mechanisms for coastal ocean regions is the absence of long-term high-resolution data. The highly dynamic coastal margin, with its combined terrestrial and oceanic input makes understanding this region a necessity for determining what mechanisms control the fluctuation of carbon dioxide.
Gray's Reef National Marine Sanctuary (GRNMS), located in the South Atlantic Bight (SAB) along the southeastern United States is situated in a very unique and dynamic region. It sits along the divide between the inner and middle shelf with water depths in the 20 m range. The water at the sanctuary is primarily controlled by the middle shelf oceanic dynamics, but during heavy rain events, it can be affected by freshwater plumes coming from the numerous rivers along the Georgia and South Carolina coast. Temperature also plays a major role in the SAB pCO2 variability with seasonal changes being apparent. Recent research along the mid-outer shelf has suggested that the SAB is a CO2 net sink and the inner shelf acts as a net source releasing CO2 to the atmosphere. However, many factors such as ocean mixing, freshwater input, and Gulf Stream intrusions offer considerable input to the water chemistry at GRNMS.
Dr. Scott Noakes replacing pCO2 sensor system on the Grays Reef buoy. (Photo: Sarah Fangman)
The NOAA Pacific Marine Environmental Lab (PMEL) and The University of Georgia (UGA) have been involved in monitoring pCO2 offshore Georgia for many years. PMEL established a monitoring station at GRNMS and has successfully collected high-resolution data since 2006. The PMEL station currently collects pCO2 at the air-sea interface and in the atmosphere; surface seawater temperature; and salinity. Surface water samples have also been collected at the site and analyzed for dissolved inorganic carbon (DIC), total alkalinity, (TA), dissolved oxygen (DO), pH and salinity to gain a concept for the TA-salinity relationship. As a result of these research efforts, it has been noticed that there is a distinct relationship between the pCO2 concentrations and water temperature. As the seawater temperature increases, so does the pCO2 (Figure 1). This phenomenon has been replicated every year since data collection began in 2006. The average air pCO2 as measured at GRNMS is approximately 400 micro-atmospheres (µatm). The level is typically exceeded in the water column during the warm summer months forcing CO2 out of the water into the atmosphere. This data demonstrates the cyclical nature of the middle SAB cycling from serving as a place where CO2 is stored to becoming a provider of CO2 to the atmosphere.
Air-sea interface pCO2 data at GRNMS.
Conventional wisdom has always considered the coastal margin water column to be well mixed and that measurements collected at the surface should reflect conditions at the seafloor. However, preliminary data has shown that this is not the case at GRNMS (Figure 2). UGA has experimented with deployment of a high-resolution pCO2 sensor on the seafloor and has documented several events where the pCO2 on the surface and seafloor have not been in agreement. As much as 200 µatm increases in pCO2 have been detected on the seafloor as compared to the surface pCO2. Both instruments were in relatively good agreement before and after these events and were checked by calibration with gas standards. It was previously discussed that temperature played a definite role in the pCO2 concentrations in the SAB. However, it was noted that when the seafloor pCO2 concentrations increased dramatically, the temperature did not change. This is a major discovery indicating that the relationship between pCO2 and temperature did not play a role in generating these spikes and that other physical or chemical processes were the driving force.
Air-sea interface pCO2 (pink) and seafloor pCO2 (blue, left) and temperature (right). Click here for a larger image.
Several questions have come to light as a result of this research. Are the pCO2 spikes a real phenomenon and if so, are there distinctive changes in water chemistry that define the increase in pCO2? How do the benthic (bottom dwelling) organisms react to such rapid changes in pCO2? What physical or chemical process caused these swings in pCO2? It is anticipated that continued CO2 research at Grays Reef will explain how the benthic community will adapt and hopefully thrive as the Atlantic Ocean changes due to anthropogenic pressures. | <urn:uuid:73108229-6018-496f-8e41-108c9903a733> | 3.5 | 1,299 | Academic Writing | Science & Tech. | 29.953617 |
Jeffrey Marlow, a graduate student at the California Institute of Technology, writes from a workstation off the coast of Oregon, where he is studying life around deep-ocean vents.
Monday, Sept. 5
As the crew of the Atlantis swings the sample-laden gear elevator onto the starboard deck, crystal drops of seawater drip from its spindly steel legs. Wearing purple latex gloves, the science party grips buckets of chilled water, ready to transfer the cargo to the walk-in refrigerator, where the microbes, worms, snails and other creatures of the deep will be much more comfortable.
Ultimately, the carbonate rock samples make their way to a small room near the back of the boat, where several of us break them apart with hammers and chisels to set up experiments. It’s a messy business, and mud splatters across the walls like something out of a geological horror movie.
One of my partners in crime is Ben Grupe, a graduate student in Lisa Levin’s lab who is interested in the ecology of methane seeps, which he sees as a vastly understudied regime. Previous expeditions to Hydrate Ridge have picked up and characterized a species here and there, particularly in the softer sediment around the huge rock mounds, but the bigger picture of how everything interacts is still very fuzzy. “People have studied methane seeps for about 25 years,” Ben says as worm fragments fly across the room, “but we really have no idea who’s involved and what they’re doing in the carbonate rock system; it really hasn’t been described adequately.”
Ben is comparing Hydrate Ridge with another methane seep system off the coast of Costa Rica. It seems that despite more nutrients at Hydrate Ridge, the macrofauanal diversity is actually lower, confirming a well-accepted if slightly counterintuitive ecological principle. One often sees less diversity with higher nutrient availability because successful adaptations are accentuated: organisms that have found a better way of doing things can quickly outcompete their rivals. (The higher oxygen content of the water at Hydrate Ridge may also play a role, as it can be toxic to deep ocean critters.)
Jason, our remotely operated vehicle (ROV), has spent part of this expedition picking up Ben’s experiments — pieces of wood, whale bones, and carbonate rocks that have been on the seafloor for the last 13 months — that should help determine how deep ocean sites are colonized. Ben and the rest of the Levin lab have been plucking organisms off these materials with surgical precision; back at Scripps, they’ll classify and count the catch to see if certain species prefer a particular substrate.
We’re plenty busy processing samples today, but much of yesterday afternoon was occupied by a transit to Hydrate Ridge South, the sister site of the carbonate mounds we examined for the first few days of the cruise. Atlantis shifted into reverse (to minimize turbulence), and towed Jason and Medea to the southern complex of methane vents. One of the consequences of our joy ride through the North Pacific is a place in the record books for the longest Jason dive. We just passed the previous record of 104 hours, and if everything goes as planned, Jason will have spent 144 consecutive hours in the water by the time he and his pilots get a well-earned rest on Sept. 7.
Now that we’re in full shift-work mode, the most common greeting mumbled groggily in the narrow hallways is “Good morning and/or good night,” as one person’s dawn has become another’s dusk. Leaving an empty coffee pot is tantamount to treason. Of course, mild sleep deprivation is a good problem to have, as it’s symptomatic of abundant samples and an efficient expedition.
Meanwhile, cultural life is thriving in its own special way: pajama couture is the fashion of the moment on Atlantis’s aft deck runways (mud-splattered is also very much in); daily contests urge entrants to predict when the next sample elevator will arrive (winner gets a Frappuccino!); and an art show featuring disused lab equipment is in the works. Walking from lab to lab can be a survey of musical diversity, as Mendelssohn, Springsteen, Feist and Brad Paisley waft through the air.
The next sample elevator (#10b, for those of you keeping score at home) is due on deck shortly, meaning it’s time to sharpen the chisel and rinse off the gloves: more samples await. | <urn:uuid:020d47fa-dc71-4ded-a1f6-ec176b98fb5b> | 2.9375 | 963 | Personal Blog | Science & Tech. | 39.230627 |
Scientific proof: climate change is happening now
As global warming tightens its grip, the effects are being felt from the highest mountain peaks to the depths of the oceans. In just the last few years there are numerous examples of how this is affecting people and nature all over the world.
- Global warming is melting glaciers in every region of the world, putting millions of people at risk from floods, droughts and lack of drinking water.
- Arctic sea ice reached its second lowest recorded level during the melt season of 2008. The lowest level, since satellites measurements began in 1979, was 2007.
- 2003, Scotland's hottest year on record, saw hundreds of adult salmon die in Scotland’s famous fisheries, as rivers became too warm for salmon to be able to extract enough oxygen from the water.
- Coral reefs around the world have been severely damaged by unusually warm ocean temperatures. The Caribbean saw its warmest ever ocean temperatures in 2005, combined with the worst coral bleaching ever. At the current rate of degradation, the entire Great Barrier Reef could be dead within a human lifetime.
- Cities like Athens, Chicago, Milan, New Delhi and Paris have sweltered under heatwaves. The 2003 summer heatwave in Europe killed 14,800 people in France alone, according to official figures released in September 2003. The French National Institute for Health and Medical Research said that the death rate was on average 60% higher than usual.
- Summer temperatures in European capitals have increased by up to 2°C over the last 30 years, a WWF report showed.
- Rising sea levels threaten entire nations on low-lying islands in the Pacific and Indian Oceans. Read Climate Witness stories about the impact of rising sea levels in the South Pacific and India.
- A report released by WWF and leading meteorologists shows that human-induced global warming was a key factor in the severity of the 2002 drought in Australia, generally regarded as the worst ever.
Reference for first paragraph:
The world is the warmest it has been in the last 12,000 years as a result of rapid warming over the past 30 years.
Article: James Hansen, Makiko Sato, Reto Ruedy, Ken Lo, David W. Lea, and Martin Medina-Elizade. Global temperature change.PNAS 2006 103: 14288-14293. http://www.pnas.org/cgi/content/abstract/103/39/14288 | <urn:uuid:2e2cfd72-fd99-4a30-9509-bd5b5bff5988> | 3.59375 | 503 | Knowledge Article | Science & Tech. | 54.133453 |
carbon group elementArticle Free Pass
Except for germanium and the artificially produced flerovium, all of these elements are familiar in daily life either as the pure element or in the form of compounds, although, except for silicon, none is particularly plentiful in the Earth’s crust. Carbon forms an almost infinite variety of compounds, in both the plant and animal kingdoms. Silicon and silicate minerals are fundamental components of the Earth’s crust; silica (silicon dioxide) is sand. Tin and lead, with abundances in the crust lower than those of some so-called rare elements, are nevertheless common in everyday life. They occur in highly concentrated mineral deposits, can be obtained easily in the metallic state from those minerals, and are useful as metals and as alloys in many applications. Germanium, on the other hand, forms few characteristic minerals and is most commonly found only in small concentrations in association with the mineral zinc blende and in coals. Although germanium is indeed one of the rarer elements, it assumed importance upon recognition of its properties as a semiconductor (i.e., limited ability to conduct electricity).
In the periodic table, the elements with eight electrons outermost form the group known as the noble gases (Group 18 ), the least reactive of the elements. The carbon group elements (Group 14), with four electrons, occupy a middle position. Elements to the left of Group 14 have fewer than four electrons in the valence shell and tend to lose them (with their negative charges) to become positively charged ions, represented by the symbol for the element with a superscript indicating the number and sign of the charges; such elements are called metals. The nonmetals (except boron) are in the groups to the right of Group 14; each has more than four electrons in its outermost shell and tends to acquire electrons to complete its octet, forming negatively charged ions.
Chemical reactions result from the exchange of electrons among atoms. In general, if a metal loses its few valence electrons to a nonmetal, the resulting oppositely charged ions are attracted to one another and form a bond, classified as ionic or electrovalent. Two nonmetals, neither of which can actually lose its valence electrons in chemical reaction, may nevertheless share them in pairs in such a way that what is called a covalent bond results. Metal atoms will bond to one another in a third type of bond, which releases their valence electrons in a way that allows them to conduct electricity.
All the carbon group atoms, having four valence electrons, form covalent bonds with nonmetal atoms; carbon and silicon cannot lose or gain electrons to form free ions, whereas germanium, tin, and lead do form metallic ions but only with two positive charges. Even lead, the most metallic of the carbon group atoms, cannot actually lose all four of its valence electrons, because, as each one is removed, the remainder are held more strongly by the increased positive charge. Because the distinction between covalent and ionic (electrovalent) bonds is often a matter of convenience for the chemist, and because the actual bond structure within a molecule may be quite complicated, it is often useful instead simply to count the total number of electrons an element gains or loses in bonding without regard to the nature of the bonds. This number is called the oxidation number, or oxidation state, of the element; many elements have more than one oxidation state possible, each oxidation state being found in different compounds. The oxidation state of an element is conventionally written as a Roman numeral following the name of the element in a compound—for example, lead(II) means lead in the +2 oxidation state. An alternative system of representation uses an Arabic number after the element name; thus, lead in the +2 state is written lead(+2). With the chemical symbol of the element, the oxidation state may be written as a superscript, as in Pb2+. When the compounds are ionic, the oxidation state is also the actual ionic charge. Covalent bonds generally are considered to be formed by interaction of the orbitals (in most cases, only the s, p, and d orbitals) in specific and varied ways. The most common are called sigma and pi bonds, written σ and π, respectively. The sigma bonds are symmetrical with respect to the axis of the bond, whereas the pi bonds are not. Examples of sigma and pi bonding as well as of ionic bonding can be found among the compounds of the elements of the carbon group.
General properties of the group
The properties of the carbon group elements and those of their compounds are intermediate between properties associated with the elements of the adjacent boron and nitrogen groups. In all groups the metallic properties, resulting from the tendency to hold valence electrons more loosely, increase with atomic number. Within the carbon group, more than in any other, the change from nonmetallic to metallic character with increasing atomic number is particularly apparent. Carbon is a true nonmetal in every sense. Lead is a true metal. Silicon is almost completely nonmetallic; tin is almost completely metallic. Germanium is metallic in appearance and in a number of its other physical properties (see Table), but the properties of many of its compounds are those of derivatives of nonmetals. These changes are consequences of increase in atomic size with substantial screening of the larger nuclear charge by intervening electronic shells, as evidenced by decrease in ionization energy (energy required to remove an electron) and electronegativity power to attract electrons with increasing atomic number.
|colour of element||colourless (diamond), black (graphite)||gray|
|melting point (°C)||3,700||1,414|
|boiling point (°C)||4,027||3,265|
|density (grams per cubic centimetre)||1.9–2.3 (graphite), 3.15–3.53 (diamond)||2.33 (25 °C)|
|oxidation states||−4, (+2), +4||−4, (+2), +4|
|mass number of most common isotopes (terrestrial abundance, percent)||12 (98.89), 13 (1.11)||28 (92.23), 29 (4.68), 30 (3.09)|
|radioactive isotopes (mass numbers)||8–11, 14–22||22–27, 31–44|
|heat of fusion (calories per mole/kilojoules per mole)||25,100 (105)||12,000 (50.2)|
|heat of vaporization (kilojoules per mole)||715||359|
|heat of sublimation (kilocalories per gram atom)||170||85|
|heat capacity (joules per gram Kelvin)||0.709||0.712|
|critical temperature (°C)||—||about 4,920|
|critical pressure (atmospheres)||—||1,450|
|electrical resistivity (microhm-centimetres)||1,375||10|
|hardness (Mohs’ scale)||0.5||6.5|
|crystal structure||cubic (diamond), hexagonal (graphite)||cubic|
|ionization energy (kilojoules per mole)|
|colour of element||white metallic||white metallic (beta), gray (alpha)||bluish white metallic|
|melting point (°C)||938.25||231.93||327.5|
|boiling point (°C)||2,833||2,602||1,749|
|density (grams per cubic centimetre)||5.32 (25 °C)||5.75 (alpha), 7.31 (beta)||11.35|
|oxidation states||−4, +2, +4||(−4), +2, +4||(−4), +2, +4|
|mass number of most common isotopes (terrestrial abundance, percent)||70 (20.84), 72 (27.54), 73 (7.73), 74 (36.28), 76 (7.61)||112 (0.97), 114 (0.66), 115 (0.34), 116 (14.54), 117 (7.68), 118 (24.22), 119 (8.59), 120 (32.58), 122 (4.63), 124 (5.79)||204 (1.4), 206 (24.1), 207 (22.1), 208 (52.4)|
|radioactive isotopes (mass numbers)||60–69, 71, 75–89||100–111, 113, 121, 123, 125–137||181–205, 209–215|
|heat of fusion (calories per mole/kilojoules per mole)||7,600 (31.8)||1,700 (7)||1,140 (4.77)|
|heat of vaporization (kilojoules per mole)||334||290||178|
|heat of sublimation (kilocalories per gram atom)||—||78||47.5|
|heat capacity (joules per gram Kelvin)||0.32||0.227||0.13|
|electrical resistivity (microhm-centimetres)||4.6 x 107||11||20.648|
|hardness (Mohs’ scale)||6||1.5||1.5|
|crystal structure||cubic||cubic, tetragonal||close-packed, metallic|
|ionization energy (kilojoules per mole)|
What made you want to look up "carbon group element"? Please share what surprised you most... | <urn:uuid:bf0e5f91-9f97-4d59-9070-235b438cb436> | 4 | 2,093 | Knowledge Article | Science & Tech. | 58.724042 |
Simplify and write the trigonometric expression in terms of sine and cosine: sin x +(cot x)(cos x) = 1/f(x) f(x)= ?
If tan^2(t) - sin^2(t) = sin^a(t)\cos^b(t), then the positive power a = the positive power b =
If You do 100 j of work to elevate a bucket of water,what is its gravitational potential energy relative to its starting position?
A survey team is trying to estimate the height of a mountain above a level plain. From one point on the plain, they observe that the angle of elevation to the top of the mountain is 25 degrees. From a point 1225 feet closer to the mountain along the plain, they find that the a...
The radian measure of an angle of 182 degrees is ?
The radian measure of an angle of 182 degrees is
Pre calulus only 15 min left HELP!
((ln(x))^1/2)/(ln(x^1/2))=6 solve for x
500 calories of heat is added to 2.0 g of water at 80 degrees Celsius. How much steam is produced?
write the metric unit of length that is reasonable. a door is about 1 blank wide
For Further Reading | <urn:uuid:8706b98c-5bcd-4409-9014-bfc1fa9c3de4> | 2.890625 | 276 | Content Listing | Science & Tech. | 84.714449 |
Meteoroids are small particles from comets or asteroids, orbiting the sun.
Meteors are meteoroids that enter the Earth's atmosphere and vaporize, also known as shooting stars.
Meteorites are meteoroids that actually land on the Earth's surface. The pieces of the meteor that exploded in Russia are meteorites.
Generally meteorites are smaller than grains of sand and vaporize on passage through the atmosphere. But there are also larger meteorites.
Comets and asteroids are left over from when the solar system formed. There used to be more of them, but over time they've collided to form major planets, or they've got booted from the inner solar system to the Oort cloud or have been ejected from the solar system entirely.
3. Why didn't we see the Russian meteor coming?
Only one space rock that impacted the planet has ever been observed before it hit the Earth, Campbell-Brown said.
That's because objects that do hit the Earth tend to be smaller, and it's too hard to see them. The one sighting before impact happened in 2008, a day before a meteor exploded over Sudan.
Current estimates suggest that the Russian meteor was about 15 meters (49 feet) across, which is too small for telescopic surveys.
"Unfortunately the objects of this size have to be very close to Earth for us to be able to see them at all," Campbell-Brown said. | <urn:uuid:9211e4c4-8c52-4902-88d8-860de1f59b7a> | 3.96875 | 292 | Listicle | Science & Tech. | 54.645328 |
Activity 1: Southern Hemisphere, late summer or early fall
In this activity, students will be introduced to the factors that influence light pollution by observing the constellation Sagittarius.
Several websites have star maps that you can download. They include:
- Stellar magnitude
- Review the procedures for a nighttime field trip and pass out permission slips. Make copies of star charts and recording forms 1-4 for all of your students.
- Arrange for several parents to take calls in case of bad weather.
- Begin at least one hour after sun set. Once you gather the students at your observation place wait at least 15 minutes to allow your eyes and theirs time to adjust. While you are waiting, discuss any sources of light pollution and have your students write them in their journals.
- Instruct students to locate Sagittarius (using their star charts). Starting with recording form one, have the students circle every star on the chart that they can see in Sagittarius.
- If they see more stars than those on Recording form one, have them go on to recording form 2. Have them circle every star they can see on recording form two. Continue through the charts in this manner. Only locations with very little light pollution will be able to see stars on recording form four.
- Have the students staple their recording forms into their journals.
Students should bring their recording forms to class the day following your observation and discuss their answers.
Students should use their collective data to draw a conclusion regarding light pollution at your location.
Appendix: How to prepare for nighttime observation
Observe at least one hour after sunset to eliminate the effects of sunlight
Wait 10–15 minutes before observing to allow their eyes time to adjust to the dark. While the students are waiting they can look for artificial sources of light pollution such as street lights, or security lights.
Prepare your flashlight for nighttime use. The human eye needs to adjust to the dark before it can observe properly. Using a normal flashlight to help one record what they see in the sky would ruin any adjusting that the eye has done. Hence, a flashlight has to be specially prepared before it can be used while observing. To do this, place several layers of red cellophane or two coats of red fingernail polish over the flashlight. The color red does not disturb night vision as much as normal (white) light does.
National Science Teachers Association
1840 Wilson Boulevard
Arlington, Virginia 22201-3000
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|Jun1-10, 06:43 AM||#1|
What does the electric field inside of a circuit look like? How do the field lines go within and outside of the wires? I heard that the electric field is tangential to the wire at every point but I don't see how or why this should be.
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Narrator: This is Science Today. A robotic telescope system called ROTSE, which was the first to capture a gamma ray burst in action, is surprisingly inexpensive compared to the standards of modern science. James Wren of the Los Alamos National Laboratory says everything on this system was pulled together with off the shelf products.
Wren: The ROTSE system itself consists of four Cannon telephoto lenses, two hundred millimeter - just normal things you can put on your very own camera and attached to those are CCD cameras which are electronic cameras and they work just like a normal camera. All the computers we use are normal, store-bought desktop PCs.
Narrator: With such humble components, ROTSE has proved to be a valuable tool for astronomers. It has a wider field of vision than large telescopes and can take about a thousand images a night of different locations.
Wren: And this data is very useful to astronomers who are looking for objects that can change on time scales that are short, as opposed to large observatories which only look at a single region of sky sometimes once every few weeks.
Narrator: For Science Today, I'm Larissa Branin. | <urn:uuid:39592542-bf06-4191-a865-2374efaab61d> | 3.671875 | 243 | Audio Transcript | Science & Tech. | 37.112188 |
|Picture 1: Himalayan Balsam - beauty or danger (Photo: M. Wolfangel)?|
|Picture 2: Raccoon - threat or enrichment (Photo: R. Groß)?|
Foreign animals and plants brought to Germany are often described as "intruders" by the media in these days. In Germany, 1322 "new" animal species have been detected so far, 262 of which are already completely established in our ecosystems.
The most discussed species are those which are particularly striking or detrimental, for example in agricultural terms. The great importance of the forest on the one hand, and of the species brought to or introduced in it on the other hand, is too much neglected in most studies.
From our point of view, many domains of forest and forestry are concerned in the issue of introduced species. Forestry itself contributed to this topic as well, for example by introducing exotic tree species for silvicultural reasons, like douglas fir, northern white pine, red oak, black locust and black cherry.
thematic field touched by neozoics and neophytes is the forest protection. The
Dutch elm disease and the white pine blister rust (Cronartium ribicola) are
examples for fungus diseases which did not occur in our nature until they were
accidentally introduced, and have caused serious damages since then. The new
alder disease which seems to be the result of a hybridisation of two
Phytopthora species, is a new phenomenon for Middle Europe.
Traditionally, the domains of hunting and wildlife ecology are also concerned in the topic "new species"/ "Neobiota", as several of our game species are part of the class of neozoics, like fallow deer and mouflons, pheasant and rabbit, raccoon, raccoon dog and American mink.
At the moment, people interested in nature protection as well as the public in general pay a lot of attention to biological invasions. The agreement on the biodiversity (CBD) as a concrete result of the summit conference about the development of nature in Rio de Janeiro (June 1992) has assigned the invasive exotic species to those processes which endanger the biodiversity. Article 8 (h) expresses the obligation "to impede – as far as possible and if reasonable – the introduction and integration of alien species which endanger ecosystems, habitats and other species, and to control or remove these species." However, the decisive aspect of this issue is the question if the ecosystems, habitats and species are really endangered.
Many examples from all over the world illustrate the negative influence which newly introduced plant and animal species exert on the existing flora and fauna. In most cases, however, these examples concern islands or other biotopes which are isolated in some way (for example Lake Victoria/Nile perch). On the Galapagos Islands, a project exists to free the unique flora and fauna from the introduced dogs, cats, rats and goats. On Hawaii, 23 of the 67 indigenous bird species have already died since the discovery of the island – also in assistance of introduced species which turned out to be better competitors. On the Pacific island Guam, 21 endemic animal species have been exterminated so far by the Brown tree snake introduced form Australia during World War II.
In Middle Europe, however, the ecological risk has to be judged differently. There has never been the comparable situation that an indigenous plant or animal species was exterminated by an introduced one. But it is also not right to exclude that this has already occurred or will happen in future. The successful integration of new species requires the interaction of a large number of different factors.
The actual problem of many exotic plant and animal species is the fact that they are often discussed in an ideological, and not in an objective and professional manner. But we also have to keep in mind that our ecosystems are never static, but always dynamic with constant changes.
This is the term for all organisms in general which were brought on purpose or by chance in territories naturally inaccessible for them since 1492 (discovery of America) and which (still) succeed in reproduction and spreading.
According to the definition, neozoics are animal species which came to a certain territory with direct or indirect human assistance and which live there in wildness since 1492 (about 1.300 neozoics species exist in Germany).
This term is used to describe introduced or integrated plant species since the discovery of America. Besides particularly striking species like the American Waterweed (Elodea canadensis) or the Himalayan Balsam (Impatiens glandulifera), tree species which are relevant for forestry are also part of the neophytes, like red oak, northern white pine and douglas fir.
Fungi which have been introduced since 1492. At least 41 not indigenous large fungi have already been found in Germany.
To impede the dispersal of foreign noxious organisms, different laws and legal regulations do exist at the moment. The legal basis for quarantine measures is given by the Council’s guideline 2000/29/EG. In Germany, the plant protection services of the federal states are responsible for the carrying out of plant supervisions and the organisation of the corresponding measures. This is, for example, the Institute for Agriculture (Landesanstalt für Landwirtschaft, LfL) in Bavaria.
These strict quarantine regulations allowed for example to prevent successfully the protraction of the dangerous American oak disease (caused by Ceratocystis fagacearum) in Middle Europe. The Asian long-horned beetle (Anoplophora glabripennis), the pine wood nematode (Bursaphelencus xylophilus) and Phytophthora ramorum also belong to the class of new quarantine imposing vermin. The introduction of plant and animal species with damage potential particularly for indigenous tree species requires an attentive observation of existing stands by foresters and forest owners. The warning examples of the Dutch elm disease and the white pine blister rust should be taken seriously. Not panicmongering should be the aim, but the objective information about the damaging potential of such pathogenes. It is therefore also necessary to inform sufficiently forest personnel about damage potential and the symptomatic of the diseases and to engage further education in order to be able to implement competent controls on the spot.
Archaeophytes and archaeozoics are animals and plants which were already integrated in a certain territory since the prehistoric or the earliest historic age. The majority was brought in or naturalised during the beginning of farming and the development of the bigger settlements of the Late Stone Age, the neolithicum. Many cultivated plants belong to this class, like wheat or wine as well as the most field weeds (cornflower, f. ex.). But also tree species like European chestnut (Castanea sativa) and walnut (Juglans regia) were already cultivated in climatic favourable regions in Germany by the Romans and are hardly considered as "strangers" nowadays.
The movements of goods all over the world as a consequence of the increasing globalisation contributes involuntary to the process by which detrimental organisms cross borders and invade an increasing number of countries. For forest and forestry, imported wood package plays a particularly decisive role. One example: The Asian long-horned beetle was brought in to Austria in packaging wood and couldn’t be exterminated so far.
70 % of all container cargoes contain packaging wood or stow wood in some way. A detailed control by plant protection services is often hardly possible. According to a risk analysis of the USA, 97 % of all tree vermin are associated to packaging wood (Schröder 2004). It is important to recognise and determine new damages or noxious organisms as fast as possible. For ensuring this, attention on the spot as well as specialists, for example in forest entomology and mycology, are necessary to observe the phytosanitary standards (Schorn/Unger 2003).
Invasive species are those which – once brought in – spread rapidly and which give cause for concern: for ecological, economic or health related reasons.Not every alien species is "invasive". Many species are brought in, but disappear soon after they have occurred, or they adapt to the existing ecosystem. Others, however, endanger the indigenous nature by changing the environment, suppressing native species or by hybridisation and inbreeding of new genetic material. For foreign (allochthone) species which invade, disturb or even destroy indigenous (autochthone) plant associations, the term "invasive species" has established during the last years.As an example of invasive species, the Giant Hogweed (Heracleum mantegazzianum) or the bullfrog (Rana catesbaiana) can be mentioned.
The simple the question seems to be, the difficult it is to answer. A majority of the introduced alien plant and animal species will adapt without greater difficulties to our ecosystems, as long as free ecological niches do exist, and keep existing there in a more or less unobtrusive way. A small part, however, has to be observed with more attention considering their risk potential. Nevertheless, controlling measures will only be implemented after a cost-benefit-analysis in isolated cases. If measures for controlling neophytes in forests are planned, it first has to be considered critically if this species in fact threatens or suppresses indigenous living spaces or species, or impedes the regeneration of stands suited to site.
All in all, we should take care not to make a hasty judgement on newly introduced plant and animal species. Under no circumstance, we should let us overwhelm by hysteria and "eco-fascism". At the same time, however, we should not belittle these species in particular. We have to observe them attentively and, if a damage risk is known, impede the introduction to Middle Europe by a consequent carrying out of plant controls. To ensure this, detailed observations and contactable experts on the spot are indispensable.
Geiter, O.; Homma, S.; Kinzelbach, R. (2002): Bestandsaufnahme und Bewertung von Neozoen in Deutschland, Umweltbundesamt Texte 25/02, 174 S.
Reichholf, J. (1995): Die Natur wieder zulassen, in: Einwanderer - neue Tierarten erobern Österreich, Stapfia 37 ISBN 3-900746-78-8, 275 S.
Reichholf, J.; Deigele, C. (2001): Gebietsfremde Arten, die Ökologie und der Naturschutz, Bay. Akademie der Wissenschaften Bd. 22, Dr. Friedrich Pfeil Verlag, ISBN 3-931516-92-X.
Schorn, K.; Unger, J.-G. (2003): Schutz vor invasiven gebietsfremden Arten, AFZ/Der Wald 21/2003, S. 1100-1101.
T. (2004): Eingeschleppte Schadorganismen an Bäumen. Jahrbuch der Baumpflege
2004, S. 30-40. | <urn:uuid:fff48682-3271-49af-ae78-41bf7188bfcb> | 2.703125 | 2,338 | Knowledge Article | Science & Tech. | 32.500122 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2000 June 3
Explanation: Nine years ago the massive Compton Gamma Ray Observatory, the second of NASA's space-based great observatories, was deployed in low earth orbit. Lofted above the protective atmosphere, Compton's instruments could explore the extreme high-energy Universe in gamma rays -- photons with 100,000 times or more the energy of visible light. The premier gamma-ray observatory far exceeded expectations for a two- to five-year mission, but a recent gyroscope failure has prompted NASA to decide to steer the satellite safely back into the atmosphere. Illustrated above, the controlled re-entry will occur early tomorrow, June 4th, in a remote area of the Pacific Ocean, approximately 2,500 miles southeast of Hawaii. The re-entry location, the largest area (about 10 million square miles) devoid of any populated land available for the observatory's re-entry, was selected to virtually eliminate the risk of human casualty. Compton's lasting legacy of discovery will include the detection of more than 400 celestial gamma-ray sources, 10 times more than were previously known; and more than 2,500 gamma-ray bursts.
Authors & editors:
Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/GSFC
& Michigan Tech. U. | <urn:uuid:56669f9f-360b-4226-b709-e39a2343dce3> | 3.625 | 307 | Knowledge Article | Science & Tech. | 32.966923 |
Natural ecosystems, made up of abiotic factors (air, water, rocks, energy) and biotic factors (plants, animals, and microorganisms). The Earths biosphere, including the atmosphere (air), hydrosphere (water), and litosphere (land), constitutes a feedback of cybernatic system that reflects what Rene Dubos referred to as "a co-evolutionary process" between living things and their physical and chemical environments. Ecosystem is made up of many smaller ecosystems interlocked through cycles of energy and chemical elements. The flow of energy and matter through ecosystems, therefore, is regulated by the complex interactions of the energy, water, carbon, oxygen, nitrogen, phosphorus, sulfur, and other cycles that are essential to the functioning of the biosphere. (Eblen and Eblen, 1994, p. 185)
Rudolf Husar email@example.com Last updated 10/26/94. | <urn:uuid:3724b7f1-4842-4aa9-a3f7-beed36c15e29> | 3.234375 | 201 | Knowledge Article | Science & Tech. | 23.5708 |
The scheme/sandbox module provides utilities for creating “sandboxed” evaluators, which are configured in a particular way and can have restricted resources (memory and time), filesystem access, and network access.
input-program : any/c
The make-evaluator function creates an evaluator with a language and requires specification, and starts evaluating the given input-programs. The make-module-evaluator function creates an evaluator that works in the context of a given module. The result in either case is a function for further evaluation.
The returned evaluator operates in an isolated and limited environment. In particular, filesystem access is restricted. The allow argument extends the set of files that are readable by the evaluator to include the specified modules and their imports (transitively). When language is a module path and when requires is provided, the indicated modules are implicitly included in the allow list.
Each input-program or module-decl argument provides a program in one of the following forms:
an input port used to read the program;
a string or a byte string holding the complete input;
a path that names a file holding the input; or
In the first three cases above, the program is read using sandbox-reader, with line-counting enabled for sensible error messages, and with 'program as the source (used for testing coverage). In the last case, the input is expected to be the complete program, and is converted to a syntax object (using 'program as the source), unless it already is a syntax object.
The returned evaluator function accepts additional expressions (each time it is called) in essentially the same form: a string or byte string holding a sequence of expressions, a path for a file holding expressions, an S-expression, or a syntax object. If the evaluator receives an eof value, it is terminated and raises errors thereafter. See also kill-evaluator, which terminates the evaluator without raising an exception.
For make-evaluator, multiple input-programs are effectively concatenated to form a single program. The way that the input-programs are evaluated depends on the language argument:
The language argument can be a module path (i.e., a datum that matches the grammar for module-path of require).
In this case, the input-programs are automatically wrapped in a module, and the resulting evaluator works within the resulting module’s namespace.
The language argument can be a list starting with 'special, which indicates a built-in language with special input configuration. The possible values are '(special r5rs) or a value indicating a teaching language: '(special beginner), '(special beginner-abbr), '(special intermediate), '(special intermediate-lambda), or '(special advanced).
In this case, the input-programs are automatically wrapped in a module, and the resulting evaluator works within the resulting module’s namespace. In addition, certain parameters (such as such as read-accept-infix-dot) are set to customize reading programs from strings and ports.
This option is provided mainly for older test systems. Using make-module-evaluator with input starting with #lang is generally better.
Finally, language can be a list whose first element is 'begin.
In the new namespace, language is evaluated as an expression to further initialize the namespace.
The requires list adds additional imports to the module or namespace for the input-programs, even in the case that require is not made available through the language.
The following examples illustrate the difference between an evaluator that puts the program in a module and one that merely initializes a top-level namespace:
program:1:0: compile: unbound variable in module in: later
> (base-module-eval '(f))
> (base-top-eval '(+ 1 2))
> (base-top-eval '(define later 5))
> (base-top-eval '(f))
; equivalent to base-module-eval:
(make-module-evaluator '(module m scheme/base
(define (f) later)
(define later 5))))
In all cases, the evaluator operates in an isolated and limited environment:
It uses a new custodian and namespace. When gui? is true, it is also runs in its own eventspace.
The evaluator works under the sandbox-security-guard, which restricts file system and network access.
Evaluation can also be instrumented to track coverage information when sandbox-coverage-enabled is set. Exceptions (both syntax and run-time) are propagated as usual to the caller of the evaluation function (i.e., catch it with with-handlers). However, note that a sandboxed evaluator is convenient for testing, since all exceptions happen in the same way, so you don’t need special code to catch syntax errors.
Finally, the fact that a sandboxed evaluator accept syntax objects makes it usable as the value for "current-eval", which means that you can easily start a sandboxed read-eval-print-loop. For example, here is a quick implementation of a networked REPL:
(make-module-evaluator '(module m scheme/base)))
(fprintf o "\nBye...\n")
The evaluators that make-evaluator creates can be customized via several parameters. These parameters affect newly created evaluators; changing them has no effect on already-running evaluators.
A parameter that determines a thunk to be called for initializing a new evaluator. The hook is called just before the program is evaluated in a newly-created evaluator context. It can be used to setup environment parameters related to reading, writing, evaluation, and so on. Certain languages ('(special r5rs) and the teaching languages) have initializations specific to the language; the hook is used after that initialization, so it can override settings.
A parameter that determines a function to reads all expressions from (current-input-port). The function is used to read program source for an evaluator when a string. byte string, or port is supplies. The reader function receives a value to be used as input source (i.e., the first argument to read-syntax), and it should return a list of syntax objects. The default reader calls read-syntax, accumulating results in a list until it receives eof.
A parameter that determines the initial current-input-port setting for a newly created evaluator. It defaults to #f, which creates an empty port. The following other values are allowed:
an input port;
the symbol 'pipe, which triggers the creation of a pipe, where put-input can return the output end of the pipe or write directly to it;
a thunk, which is called to obtain a port (e.g., using current-input-port means that the evaluator input is the same as the calling context’s input).
A parameter that determines the initial current-output-port setting for a newly created evaluator. It defaults to #f, which creates a port that discrds all data. The following other values are allowed:
an output port, which is used as-is;
the symbol 'bytes, which causes get-output to return the complete output as a byte string;
the symbol 'string, which is similar to 'bytes, but makes get-output produce a string;
the symbol 'pipe, which triggers the creation of a pipe, where get-output returns the input end of the pipe;
a thunk, which is called to obtain a port (e.g., using current-output-port means that the evaluator output is not diverted).
Like sandbox-output, but for the initial current-error-port value. An evaluator’s error output is set after its output, so using current-output-port (the parameter itself, not its value) for this parameter value means that the error port is the same as the evaluator’s initial output port.
enabled? : any/c
A parameter that controls whether syntactic coverage information is collected by sandbox evaluators. Use get-uncovered-expressions to retrieve coverage information.
propagate? : any/c
When this boolean parameter is true, breaking while an evaluator is running evaluator propagates the break signal to the sandboxed context. This makes the sandboxed evaluator break, typically, but beware that sandboxed evaluation can capture and avoid the breaks (so if safe execution of code is your goal, make sure you use it with a time limit). The default is #t.
A parameter that holds a list of values that specify how to create a namespace for evaluation in make-evaluator or make-module-evaluator. The first item in the list is a thunk that creates the namespace, and the rest are module paths for modules that to be attached to the created namespace using namespace-attach-module.
The module paths are needed for sharing module instantiations between the sandbox and the caller. For example, sandbox code that returns posn values (from the lang/posn module) will not be recognized as such by your own code by default, since the sandbox will have its own instance of lang/posn and thus its own struct type for posns. To be able to use such values, include 'lang/posn in the list of module paths.
When testing code that uses a teaching language, the following piece of code can be helpful:
A parameter that determines a list of collection directories to prefix current-library-collection-paths in an evaluator. This parameter is useful for cases when you want to test code using an alternate, test-friendly version of a collection, for example, testing code that uses a GUI (like the htdp/world teachpack) can be done using a fake library that provides the same interface but no actual interaction. The default is null.
guard : security-guard?
A parameter that determines the initial (current-security-guard) for sandboxed evaluations. The default forbids all filesystem I/O except for things in sandbox-path-permissions, and it uses sandbox-network-guard for network connections.
A parameter that configures the behavior of the default sandbox security guard by listing paths and access modes that are allowed for them. The contents of this parameter is a list of specifications, each is an access mode and a byte-regexp for paths that are granted this access.
The access mode symbol is one of: 'execute, 'write, 'delete, 'read, or 'exists. These symbols are in decreasing order: each implies access for the following modes too (e.g., 'read allows reading or checking for existence).
The path regexp is used to identify paths that are granted access. It can also be given as a path (or a string or a byte string), which is (made into a complete path, cleansed, simplified, and then) converted to a regexp that allows the path and sub-directories; e.g., "/foo/bar" applies to "/foo/bar/baz".
The default value is null, but when an evaluator is created, it is augmented by 'read permissions that make it possible to use collection libraries (including sandbox-override-collection-paths). See make-evalautor for more information.
A parameter that specifieds a procedure to be used (as is) by the default sandbox-security-guard. The default forbids all network connection.
A parameter that determines the default limits on each use of a make-evaluator function, including the initial evaluation of the input program. Its value should be a list of two numbers, the first is a timeout value in seconds, and the second is a memory limit in megabytes. Either one can be #f for disabling the corresponding limit; alternately, the parameter can be set to #f to disable all limits (in case more are available in future versions). The default is (list 30 20).
When limits are set, call-with-limits (see below) is wrapped around each use of the evaluator, so consuming too much time or memory results in an exception. Change the limits of a running evaluator using set-eval-limits.
A parameter that determines the procedure used to create the inspector for sandboxed evaluation. The procedure is called when initializing an evaluator, and the default parameter value is make-inspector.
A parameter that determines the procedure used to create the logger for sandboxed evaluation. The procedure is called when initializing an evaluator, and the default parameter value is current-logger.
The following functions are used to interact with a sandboxed evaluator in addition to using it to evaluate code.
Releases the resources that are held by evaluator by shutting down the evaluator’s custodian. Attempting to use an evaluator after killing raises an exception, and attempts to kill a dead evaluator are ignored.
Sends a break to the running evaluator. The effect of this is as if Ctrl-C was typed when the evaluator is currently executing, which propagates the break to the evaluator’s context.
Changes the per-expression limits that evaluator uses to sec seconds and mb megabytes (either one can be #f, indicating no limit).
If (sandbox-input) is 'pipe when an evaluator is created, then this procedure can be used to retrieve the output port end of the pipe (when used with no arguments), or to add a string or a byte string into the pipe. It can also be used with eof, which closes the pipe.
if it was 'pipe, then get-output returns the input port end of the created pipe;
if it was 'bytes or 'string, then the result is the accumulated output, and the output is directed to a new output string or byte string (so each call returns a different piece of the evaluator’s output);
otherwise, it returns #f.
prog? : any/c = #t
src : any/c = 'program
Retrieves uncovered expression from an evaluator, as longs as the sandbox-coverage-enabled parameter had a true value when the evaluator was created. Otherwise, and exception is raised to indicate that no coverage information is available.
The prog? argument specifies whether to obtain expressions that were uncovered after only the original input program was evaluated (#t) or after all later uses of the evaluator (#f). Using #t retrieves a list that is saved after the input program is evaluated, and before the evaluator is used, so the result is always the same.
A #t value of prog? is useful for testing student programs to find out whether a submission has sufficient test coverage built in. A #f value is useful for writing test suites for a program to ensure that your tests cover the whole code.
The second optional argument, src, specifies that the result should be filtered to hold only syntax objects whose source matches src. The default, 'program, is the source associated with the input program by the default sandbox-reader – which provides only syntax objects from the input program (and not from required modules or expressions that were passed to the evaluator). A #f avoids filtering.
The resulting list of syntax objects has at most one expression for each position and span. Thus, the contents may be unreliable, but the position information is reliable (i.e., it always indicates source code that would be painted red in DrScheme when coverage information is used).
Note that if the input program is a sequence of syntax values, either make sure that they have 'program as the source field, or use the src argument. Using a sequence of S-expressions (not syntax objects) for an input program leads to unreliable coverage results, since each expression may be assigned a single source location.
Various aspects of the scheme/sandbox library change when the GUI library is available, such as using a new eventspace for each evaluator.
Executes the given thunk with memory and time restrictions: if execution consumes more than mb megabytes or more than sec seconds, then the computation is aborted and the exn:fail:resource exception is raised. Otherwise the result of the thunk is returned as usual (a value, multiple values, or an exception). Each of the two limits can be #f to indicate the absence of a limit. See also custodian-limit-memory for information on memory limits.
Sandboxed evaluators use call-with-limits, according to the sandbox-eval-limits setting and uses of set-eval-limits: each expression evaluation is protected from timeouts and memory problems. Use call-with-limits directly only to limit a whole testing session, instead of each expression.
(with-limits mb-expr body-expr body )
A macro version of call-with-limits.
v : any/c
exn : exn:fail:resource?
A predicate and accessor for exceptions that are raised by call-with-limits. The resource field holds a symbol, either 'time or 'memory. | <urn:uuid:0f0065c2-26ae-44d6-b7e4-aab5d79da63b> | 2.765625 | 3,658 | Documentation | Software Dev. | 38.325347 |
Casting out nines
Casting out nines is a sanity check to ensure that hand computations of sums, differences, products, and quotients of integers are correct. By looking at the digital roots of the inputs and outputs, the casting-out-nines method can help one check arithmetic calculations. The method is so simple that most schoolchildren can apply it without understanding its mathematical underpinnings.
The method involves converting each number into its "casting-out-nines" equivalent, and then redoing the arithmetic. The casting-out-nines answer should equal the casting-out-nines version of the original answer. Below are examples for using casting out nines to check addition, subtraction, multiplication, and division.
In each addend, cross out all 9s and pairs of digits that total 9, then add together what remains. These new values are called excesses. Add up leftover digits for each addend until one digit is reached. Now process the sum and also the excesses to get a final excess.
|2 and 4 add up to 6|
|8+1=9 and 4+5=9; there are no digits left|
|2, 4, and 6 make 12; 1 and 2 make 3.|
|2 and 0 are 2.|
|7, 3, and 1 make 11; 1 and 1 add up to 2.|
|The excess from the sum should equal the final excess from the addends.|
|First, cross out all 9s and digits that total 9 in both minuend and subtrahend (italicized).|
|Add up leftover digits for each value until one digit is reached!|
|Now follow the same procedure with the difference, coming to a single digit.|
|Because subtracting 2 from zero gives a negative number, borrow a 9 from the minuend.|
|The difference between the minuend and the subtrahend excesses should equal the difference excess.|
|First, cross out all 9s and digits that total 9 in each factor (italicized).|
|Add up leftover digits for each multiplicand until one digit is reached.|
|Multiply the two excesses, and then add until one digit is reached.|
|Do the same with the product, crossing out 9s and getting one digit.|
|*||The excess from the product should equal the final excess from the factors.|
*8 times 8 is 64; 6 and 4 are 10; 1 and 0 are 1
|Cross out all 9s and digits that total 9 in the divisor, quotient, and remainder.|
|Add up all uncrossed digits from each value to a single digits.|
|The dividend excess should equal the final excess from the other values.
In other words, you are performing the same procedure as in a multiplication, only backwards. 8x4=32 which is 5, 5+3 = 8. And 8=8.
How it works
The method works because the original numbers are 'decimal' (base 10), the modulus is chosen to differ by 1, and casting out is equivalent to taking a digit sum. In general any two 'large' integers, x and y, expressed in any smaller modulus as x' and y' (for example, modulo 7) will always have the same sum, difference or product as their originals. But this property is also preserved for the 'digit sum' where the 'base' and the 'modulus' differ by 1.
To see this take an example: Both 900 and 630 are exactly divisible by 9 and have the same digit sum - '63' changes into '90' by repeated addition of '09' and the change in the second digit always offsets the change in the first ('63' to '72' to '81' to '90'). For two 'decimal' numbers not generally congruent modulo 9 (like '914' and '673') the picture remains the same; we can consider their congruences pairwise ('900' with '630') plus ('09' with '36') plus ('5' with '7'). Thus the digit sum of any number and its congruence modulo 9 are always fixed in base 10.
If a calculation was correct before casting out, casting out on both sides will preserve correctness. However, it is possible that two previously unequal integers will be identical modulo 9 (on average, a ninth of the time).
One should note that the operation does not work on fractions, since a given fractional number does not have a unique representation.
A variation on the explanation
A nice trick for very young children to learn to add nine is to add ten to the digit and to count back one. Since we are adding 1 to the ten's digit and subtracting one from the unit's digit, the sum of the digits should remain the same. For example 9+2=11 with 1+1=2. When adding 9 to itself, we would thus expect the sum of the digits to be 9 as follows: 9+9=18 (1+8=9) and 9+9+9=27 (2+7=9). Let us look at a simple multiplication: 5×7=35 (3+5=8). Now consider (7+9)×5=16×5=80 (8+0=8) or 7×(9+5)=7×14=98 (9+8=17 1+7=8).
Any positive integer can be written as 9 × n + a where 'a' is a single digit 0 to 8 and 'n' is any positive integer. Thus, using the distributive rule (9 × n + a)×(9 × m + b)= 9 × 9 × n × m + 9 ×(am+bn) +ab. Since the first two factors are multiplied by 9, their sums will end up being 9 or 0, leaving us with 'ab'. In our example, 'a' was 7 and 'b' was 5. We would expect in any base system the number before that base would behave just like the nine.
Limitations to Casting out nines
While extremely useful, casting out nines does not "catch" all errors made while doing calculations. For example, 5x7=8. By the casting out nines method, it would appear that this multiplication is correct, which it is not. This would also happen with the result of 17, 26, et at. In other words there will be an "uncaught" mistake every nine numbers, this would yield a 90% effectiveness to the method.
Abjectio novenaria (Latin for "casting out nines") was known to the Roman bishop Hippolytos as early as the third century. Ibn Sina (Avicenna) (908–946) was a Persian physician, astronomer, physicist and mathematician who contributed to the development of this mathematical technique. It was employed by twelfth-century Hindu mathematicians. In the 17th century, Gottfried Wilhelm Leibniz not only used the method extensively, but presented it frequently as a model for rationality: "By means of this, once a reasoning in morality, physics, medicine or metaphysics is reduced to these terms or characters, one will be able to apply to it at any moment a numerical test, so that it will be impossible to be mistaken if one does not so desire...".
In Synergetics, R. Buckminster Fuller claims to have used casting out nines "before World War I." Fuller explains how to cast out nines and makes other claims about the resulting 'indigs,' but he fails to note that casting out nines can result in false positives.
The method bears striking resemblance to standard signal processing and computational error detection and error correction methods, typically using similar modular arithmetic in checksums and simpler check digits.
See also
- Cajori, Florian (1991), A History of Mathematics (AMS Chelsea Publishing) (5th ed.), New York, NY: AMS, ISBN 0-8218-2102-4
- Dub Trio (2004-09-14), Casting Out The Nines (MP3 Music ), ROIR, ASIN B000UO68AM
- Fuller, R. Buckminster (April 1982), Synergetics: Explorations in the Geometry of Thinking (New ed.), New York, NY: Macmillan Publishing Company, ISBN 0-02-065320-4
- Leibniz, Gottfried Wilhelm (2008-01-24), in Dascal, Marcelo, Gottfried Wilhelm Leibniz: The Art of Controversies, The New Synthese Historical Library (Paperback ed.), New York, NY: Springer, ISBN 978-1-4020-8190-3
- Masood, Ehsan (2006-01-15), Science and Islam: A History, Duxford, United Kingdom: Icon Books Ltd., ISBN 1-84831-081-1 | <urn:uuid:5a4feab6-82d2-47cc-b695-71b39fab9ae7> | 4 | 1,911 | Knowledge Article | Science & Tech. | 64.96383 |
"Broadens Understanding of Science"
From Optonics and Photonics Focus, February 18 2010:
Is Light slowing Down?
The speed of light is a universal constant — or is it? Some evidence seems to suggest it might actually be slowing down. Will we soon have to revise our cosmological beliefs?
If light were slowing down, we would have to revise many of our astronomical beliefs: from the age of the Universe to the distances between galaxies, from the dark matter to the definition of many physical constants. What a tremendous set of implications! Some evidence that this might indeed be the case starts piling up, as recently reported by Yves-Henri Sanejouand from the University of Nantes in France.
From Vertical News:
Research from Y.H. Sanejouand et al broadens understanding of science
2010 JAN 26 - (VerticalNews.com) -- According to a study from France, "Possible empirical evidences in favor of the hypothesis that the speed of light decreases by a few centimeters per second each year are examined. Lunar laser ranging data are found to be consistent with this hypothesis, which also provides a straightforward explanation for the so-called Pioneer anomaly, that is, a time-dependent blue-shift observed when analyzing radio tracking data from distant spacecrafts, as well as an alternative explanation for both the apparent time-dilation of remote events and the apparent acceleration of the Universe."
"The main argument against this hypothesis, namely, the constancy of fine-structure and Rydberg constants, is discussed. Both of them being combinations of several physical constants, their constancy implies that, if the speed of light is indeed time-dependent, then at least two other ''fundamental constants'' have to vary as well," wrote Y.H. Sanejouand and colleagues.
The researchers concluded: "This puts severe constraints on the development of any future varying-speed-of-light theory."
Sanejouand and colleagues published the results of their research in Epl (About some possible empirical evidences in favor of a cosmological time variation of the speed of light. Epl, 2009;88(5):59002). | <urn:uuid:a04c1ee8-fa68-4d73-8d87-b3980cbd72b9> | 2.84375 | 456 | Personal Blog | Science & Tech. | 38.174171 |
In the figure above, a circle with center O is inscribed in the square WXYZ. The segment XZ has a length of 3√2. What is the radius of the circle?
(B) Triangle XYZ is an isosceles right triangle. The length of each leg is 3. Since the diameter of the circle is equal to the height of the square, the diameter is equal to 3. So the radius is equal to 1.5 inches.Alternatively
, since the sides XY and ZY are equal, set them equal to x
. Then 2x
² = (3√2)² by the Pythagorean Theorem. Solving for x
² = 9 and so x
= 3. Since x
represents the side of the square or the diameter of the circle, we divide by 2 to get the radius. So, the radius must be 1.5. The correct answer is (B).
----------I am confused how right away in the answer we get the sides of the square to be three. | <urn:uuid:ade97d6c-59bb-4e62-8b70-9288077902c0> | 3.953125 | 218 | Q&A Forum | Science & Tech. | 91.002929 |
Common Lisp the Language, 2nd Edition
A name can be given to a function in one of two ways. A global name can be given to a function by using the defun construct. A local name can be given to a function by using the flet or labels special form. When a function is named, a lambda-expression is effectively associated with that name along with information about the entities that are lexically apparent at that point. If a symbol appears as the first element of a function-call form, then it refers to the definition established by the innermost flet or labels construct that textually contains the reference, or to the global definition (if any) if there is no such containing construct. | <urn:uuid:e5147dc5-3d3b-4037-b576-27aaebaa726d> | 3.671875 | 144 | Knowledge Article | Software Dev. | 42.929415 |
Flux footprint (also known as atmospheric flux footprint) is an upwind zone where the atmospheric flux measured by a scientific instrument is generated. Specifically, the term flux footprint describes an upwind zone observed by the instruments measuring vertical turbulent fluxes, such that heat, water, gas and momentum transport generated in this area is registered by the instruments. Another frequently used term, fetch, typically refers to the distance of the instrumentation from the tower when describing the footprint.
Visualization of the concept
As a practical example, consider an instrument measuring a flux of water (evapotranspiration) few meters above the surface in the situation with no wind. In such a case, the instrument would measure evapotranspiration generated immediately beneath the instrument location and brought upwards by mostly non-turbulent exchange. Now lets consider situation with a strong wind: it would blow air located under the instrument away, would bring in air generated somewhere upwind and brought upwards to a considerable degree due to turbulent exchange. So, the water flux footprint was just under the instrument in the first case, and was somewhere upwind in the second case.
In Figure 1, the general concept of the flux footprint is visualized: the darker the red color – the greater the contribution that is coming from the surface area a certain distance away for the instrument. So, the majority of the contribution usually derives, not from underneath the instrument or from kilometers away, but rather from a locus in between. Size and shape of the footprint are also dynamic variables that change over time.
Atmospheric transport can be viewed as a Lagrangian transport model. In such a case, the footprint is the zone of cumulative contribution to flux measurement computed from analytical solutions of the diffusion equation. For example, for near-neutral conditions, following Schuepp et al (1990) and Gash (1986), the mathematical representation of footprint would be that seen in Figure 2.
Main factors affecting flux footprint
Three main factors affecting the size and shape of flux footprint are: (1) measurement height, (2) surface roughness, and (3) atmospheric thermal stability.
Increase in measurement height, decrease in surface roughness, and change in atmospheric stability from unstable to stable would lead to an increase in size of the footprint and move peak contribution away from the instrument. The opposite is also true. Decrease in measurement height, increase in surface roughness, and change in atmospheric stability from stable to unstable would lead to a decrease in size of the footprint and move peak contribution closer to the instrument.
Examples of real-field flux footprint distribution
Degree to which flux footprint is affected by these factors is illustrated for the all three respective cases below on the example of actual evapotranspiration flux (ET) measured over prairie in summer time (Figures 3 through 5).
Relative contribution of the land surface area to the flux for two different measurement heights at near-neutral stability is shown in Figure 3. Please note that not only distance to the peak contributing was affected by a measurement height, but magnitude of the peak and overall distribution of the footprint was affected significantly as well.
Below is an example of relative contribution of the land surface area to the flux for two different surface roughnesses at near-neutral stability (Figure 4). Area under the curves on the plot above and on the two plots below sums up to nearly one hundred percent of the flux contribution. The remaining few percent of flux are coming from an area beyond 500 metres.
Example of the relative contribution of the land surface area to the flux for two different cases of thermal stability is shown below (Figure 5). This example is adopted from Leclerc, M.Y., and G.W. Thurtell (1990).
- Burba, G.G. 2001. Illustration of Flux Footprint Estimates Affected by Measurement Height, Surface Roughness and Thermal Stability. In K.G. Hubbard and M.V.K. Sivakumar (Eds.) Automated Weather Stations for Applications in Agriculture and Water Resources Management: Current Use and Future Perspectives. World Meteorological Organization publication No.1074.HPCS Lincoln, Nebraska – WMO Geneva, Switzerland, 77-87.
- Finn, D., Lamb, B., Leclerc, M.Y., and T.W. Horst: 1996, Experimental evaluation of analytical and Lagrangian surface layer flux footprint models, Boundary-Layer Meteorology 80: 283-308.Gash, J.H.C.: 1986, A note on estimating the effect of limited fetch on micrometeorological evaporation measurements, Boundary-Layer Meteorology 35: 409-413
- Horst, T.W.: 1979, Lagrangian similarity modeling of vertical diffusion from a ground level source, Journal of Applied Meteorology 18: 733-740.
- Leclerc, M.Y., and G.W. Thurtell: 1990, Footprint prediction of scalar fluxes using a Markovian analysis, Boundary-Layer Meteorology 52: 247-258. | <urn:uuid:ffcb8d4c-94b3-4919-b001-26b3fc7d8fca> | 3.53125 | 1,045 | Knowledge Article | Science & Tech. | 41.288869 |
In celebration of NOVA’s new episode, Hunting the Elements, we thought putting together a list of elemental resources would be appropriate. Here you will find interactives, video shorts, quizzes, and a full list of science programs that deal with the elements, their properties, and a host of fascinating characteristics they share. NOVA’s new program asks the question: Where do nature’s building blocks come from? Host David Pogue takes students through the world of weird, extreme chemistry: the strongest acids, the deadliest poisons, the universe’s most abundant elements, and the rarest of the rare--substances cooked up in atom smashers that flicker into existence for only fractions of a second. Check out this clip:
The Elements iPad App The free app, available now on the App Store, takes the periodic table off the wall and puts it into users' hands, bringing life to the world's elements in colorful and dynamic ways. NOVA Elements, featuring tech guru David Pogue, allows users to explore an interactive periodic table, build elements from their particles, construct 3D rotating molecules, and watch the two-hour NOVA program.
Graphing the Periodic Table Whether created by nature or in the lab, chemical substances are all made of some combination of just 118 pure elements. These elements come together to produce an amazing diversity of materials. In this interactive, explore patterns in the periodic table. See how the electron configurations and properties of the elements vary according to their place in the table. Investigate the patterns by plotting and comparing the elements by molar mass, atomic radius, ionic radius, melting point, boiling point, electronegativity, and ionization energies.
Metal Fundamentals Despite its ubiquity in our lives, most of us know little about metal. Why does it bend when other hard materials like ceramic or stone do not? What is the difference—a crucial one, it turns out—between hardness and toughness in metal? Why does it get stronger the more defects it has? In this interview with Dr. Rick Vinci, a Stanford-trained materials scientist and engineer at Lehigh University, find answers to these and other basic questions about metals, including how it all relates to that wonder of steel technology, the samurai sword.
An Elemental Quiz How well do you know your way around the periodic table? Can you tell a noble gas from neptunium? In this quiz, test your knowledge of some chemistry basics, history, and trivia, including the quest to create new, super heavy elements on the periodic table.
Light My Fire The ability of the elements to change phase—to transform from a solid to a liquid to a gas—is a perfect set-up for romantic comedy. Watch the story of an unlikely laboratory love affair, and learn about one of the basic properties of matter in the process.
Name that Element Do you know your helium from your hafnium? Can you even pronounce praseodymium and ytterbium? In this quiz, we challenge you to identify the names of 30 "mystery elements" as quickly as you can. For each element, you'll receive a series of clues over 30 seconds and you can share your score with friends on Facebook.
Island of Stability
In this video clip, a nuclear chemist aims to create entirely new elements to add to the periodic table.
Strange World of the Electron In this activity, students learn what an element is and discover that all elements on Earth were formed in stars. They examine the structure of atoms and discover that scientists' understanding of this structure has changed over time -- and will likely be refined even further. Lastly, they begin to explore the sometimes-strange arrangement and behavior of electrons and to connect these characteristics to the chemical properties of elements.
Subjects: Science & Technology | <urn:uuid:27232348-18b2-47bb-9973-6e4e90882446> | 3.21875 | 788 | Content Listing | Science & Tech. | 38.615374 |
Deprecated since version The: mutex module has been removed in Python 3.0.
The mutex module defines a class that allows mutual-exclusion via acquiring and releasing locks. It does not require (or imply) threading or multi-tasking, though it could be useful for those purposes.
The mutex module defines the following class:
class class mutex.mutex
Create a new (unlocked) mutex.
A mutex has two pieces of state — a “locked” bit and a queue. When the mutex is not locked, the queue is empty. Otherwise, the queue contains zero or more (function, argument) pairs representing functions (or methods) waiting to acquire the lock. When the mutex is unlocked while the queue is not empty, the first queue entry is removed and its function(argument) pair called, implying it now has the lock.
Of course, no multi-threading is implied – hence the funny interface for lock(), where a function is called once the lock is acquired.
mutex objects have following methods:
Check whether the mutex is locked.
“Atomic” test-and-set, grab the lock if it is not set, and return True, otherwise, return False.
Execute function(argument), unless the mutex is locked. In the case it is locked, place the function and argument on the queue. See unlock() for explanation of when function(argument) is executed in that case.
Unlock the mutex if queue is empty, otherwise execute the first element in the queue. | <urn:uuid:81efcc49-e0c9-4ac7-9c02-136109457c70> | 3.09375 | 332 | Documentation | Software Dev. | 53.484118 |
Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °
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So the angle netween a sloping side and the base is
I was trying to calculate the angle between two sloping sides.
My formula is
It took a page of algebra to get to this.
I'll post it if you ask nicely.
My expression is much more complicated.
Using your formula and with a = 4 and h = 3.265986 (which will make a regular pyramid = tetrahedron ) I got cos AGC = -5.9375 which is not possible!
I used my formulas and got angle = 70.528779 which is the Wiki value.
How did you get your expression?
I'll check your working.
Can you prove me right or wrong when i say: cosAGC 1-6h^2-2a^2)dvide by (a^2)
Hi bob? I did follow your work. The last part is like ok, but how u came to get GC, i didn't get it.
(iii) Find point G on VB so that CGV = 90
Second diagram shows true shape of VBC
(iv) The required angle is AGC
AG = GC
AC = a
I need a simplified formular for this. If not so explain how i can do it.
What is the angle between two adjacent plans of a equilateral triangular pyramid of length 'a' and the perpendicular height of the pyramid is 'h'? | <urn:uuid:e00e3e94-7ec7-4d01-af6e-35a6bf2d47ce> | 3.15625 | 377 | Comment Section | Science & Tech. | 87.010099 |
Photo courtesy of Jim Denny
Publish by: Anne Wiley - May 24, 2013
Most people have never heard of the Hawaiian petrel, an endangered, crow-sized seabird that spends the majority of its life searching for food over the North Pacific Ocean. Nevertheless, this bird is no stranger to human influence, and it has a stern lesson to teach us about the history of the open ocean. When it comes to what marine predators can find to eat, humans are changing things, and fast. My colleagues and I have spent a number of years studying the history of this amazing seafarer. We’ve come to view it as a sort of indicator of food web history in the oceanic zone of the North...
Tags: Food web
Bruce Duncan, USEPA
Publish by: Sean Sheldrake - May 8, 2013
As a research diver for the US Environmental Protection Agency (EPA), one of my jobs is to make sure that people and companies working in the fish industry don’t dump too much waste in the ocean. On my first dive at an underwater waste site, my old salt of a dive partner hinted, “you might see a shark… or three” with a wink. “Okay,” I thought, “I can deal with a couple of sharks.” Descending to the dump site, I soon saw circling dogfish and salmon sharks extending all the way from 80 feet to the surface—maybe 50 sharks, perhaps more. All those dogfish were drawn to a pile of Alaskan salmon...
Publish by: Daniel Botkin - May 2, 2013
Editor's note: This is an excerpt from Daniel Botkin's new book The Moon in the Nautilus Shell: Discordant Harmonies Reconsidered . He will be in Washington, D.C. on Wednesday, May 8th for a lecture and book signing through the Smithsonian Associates. The Nautilus and the Moon: (From Chapter 14) My mind meandered from thoughts of the shallow European sea to those of the far-off Pacific Ocean and one of its humblest and most obscure creatures, the chambered nautilus (Nautilus pompilius Linnaeus), which lives far from Venice in the southwestern Pacific. Although the shell of the chambered...
Wikimedia User "Mtpaley"
Publish by: Emily Frost - Apr 23, 2013
Even if you aren't a hardcore birder, chances are you have some hidden love for penguins. These flightless birds have captured our hearts through countless movies, beautiful images and their adorable fluffy young. Panoramic scenes of their large breeding colonies make penguin populations seem limitless, but the IUCN Red List of Threatened Species lists 11 of the 18 species as Vulnerable or Endangered. Penguins have certain characteristics that make them especially vulnerable to large-scale changes to our oceans and climate: their reproductive lifestyle of laying only one or two eggs,...
NOAA/NASA GOES Project
Publish by: Hannah Waters - Apr 22, 2013
Sometimes I think that our planet Earth, named for the Old English word for “dry land” (eorthe), should get a new name. Despite our knowledge that more than 70% of the planet’s surface is ocean—definitely not “dry land”—we still refer to our home by an 8th century description. The same goes for Earth Day. Since 1970, people around the world have set aside April 22nd of each year to think about protecting the environment. This includes the ocean, as it’s a huge part of Earth’s environment. But the sea often seems to play a background role compared to more terrestrial causes. What many people...
Publish by: Caine Delacy - Apr 17, 2013
We began this journey three months ago, a team of scientists and filmmakers traveling the East African coastline by boat to document and research the status of coral reefs from South Africa to Kenya. We have observed a lot of changes in the coral reef communities as we travel north. Some of these changes are natural shifts in biodiversity, species composition and structure of the reef communities. There are also those changes that are caused by humans . Where Have All the Big Fish (and Sharks) Gone? Immediately obvious when we dive a new location are the effects of fishing, fishing practices...
Publish by: Hannah Waters - Apr 11, 2013
April is National Poetry Month here in the United States. We'd like you to help us celebrate by penning a poem in the comment field below or on our Facebook page . The ocean has served as an inspiration for as long as poets have been writing poems. Some people are inspired by the ocean’s powerful, crashing waves, like when Homer wrote about the “wine dark sea” in the Odyssey . Its fascinating animals sparked Walt Whitman , while its depth and mystery drew in former US poet laureate Billy Collins. Even play on the beach can be a source of inspiration: it compelled E. E. Cummings to pen the...
Tags: Ocean art
Brian Henderson, Flickr user stinkenroboter
Publish by: Katrina Lohan - Mar 27, 2013
Hopefully you've never bitten into a delicious hunk of snow crab meat and instantly spit it out because instead of crab you tasted... aspirin?! If you have, it might have been crab meat infected with a species of Hematodinium , a parasitic dinoflagellate that is the cause of Bitter Crab Disease in cold-water crab species. This parasite lowers the “tasty factor” of commercially important cold-water crabs around the world. At present, there are reports of 39 species of crab and shrimp from 12 countries being infected. Recent victims include the snow crab ( Chionoecetes opilio ), the Norway...
Publish by: Amber Stubler - Mar 20, 2013
Boring sponges get a bad rap. Their own name betrays them, announcing to the world that they are unexciting, ordinary and quite frankly, boring. However, if ever a misnomer existed, this is it. More flatteringly referred to as excavating or bioeroding sponges, these animals play the important yet thankless role of breaking down and recycling calcium carbonate (the main component of eggshells, corals and shelled marine organisms). Using a combination of chemical and mechanical erosion, these sponges dissolve and slowly chip away at dead, diseased, and occasionally healthy corals. In doing so,...
Eduardo Zattara, Smithsonian Institution
Publish by: Catherine - Mar 12, 2013
With 1,400 named species of ribbon worms inhabiting every ecosystem on earth, seeking one out should be an easy proposition. But I quickly learned that it can be quite daunting when you’re looking for certain teeny-tiny mud-loving worms. I recently accompanied Dr. Jon Norenburg and postdoctoral fellow Dr. Eduardo Zattara, Smithsonian National Museum of Natural History research scientists in the Department of Invertebrate Zoology , on a research trip to Fort Pierce, Florida. The goal? Find ribbon worms (phylum Nemertea ) belonging to the genus Carinoma or to the family Hubrechtidae . Members... | <urn:uuid:0283ce2f-1d5a-4b1c-acf7-30c764522486> | 2.953125 | 1,513 | Content Listing | Science & Tech. | 55.190737 |
A standard candle
is an astronomical object that has a known luminosity
Standard candles are the basis for several important methods of deriving distances in extragalactic astronomy
in the cosmic distance ladder
Comparing its known luminosity (or its derived logarithmic quantity, the absolute magnitude
) and its observed brightness (apparent magnitude
) the distance to the object can be calculated as:
where D is the distance, kpc is kiloparsec (103 parsec),
m the apparent magnitude and M the absolute magnitude (both in the same band at rest). (Note that this is closely related to the distance modulus of an object.)
Standard candles include:
- RR Lyrae variables — red giants typically used for measuring distances within the galaxy and in nearby globular clusters.
- Eclipsing binaries — In the last decade, measurement of eclipsing binaries' fundamental parameters has become possible with 8 meter class telescopes. This makes it feasible to use them as indicators of distance. Recently, they have been used to give direct distance estimates to the LMC, SMC, Andromeda Galaxy and Triangulum Galaxy. Eclipsing binaries offer a direct method to gauge the distance to galaxies to a new improved 5% level of accuracy which is feasible with current technology up to a distance of around 3 Mpc.
- Cepheid variables — the preferred choice in extragalactic astronomy, out to the range of a few tens of Mpc.
- Type Ia Supernovae — that have a very well-determined maximum absolute magnitude as a function of the shape of their light curve and are useful in determining extragalactic distances up to a few hundred Mpc. A notable exception is SN 2003fg, the "Champagne Supernova," a type Ia supernova of unusual nature.
The following four indicators all use stars in the old stellar populations (Population II):
In galactic astronomy, X-ray bursts
(thermonuclear flashes on the surface of a neutron star
) are used as standard candles.
Observations of X-ray burst sometimes show X-ray spectra indicating radius expansion.
Therefore, the X-ray flux at the peak of the burst should correspond to Eddington luminosity
, which can be calculated once the mass of the neutron star is known (1.5 solar masses is a commonly used assumption).
This method allows distance determination of some low-mass X-ray binaries
Low-mass X-ray binaries are very faint in the optical, making measuring their distances extremely difficult.
Problems with standard candles
The primary issue with standard candles is the recurring question of how standard they are. For example, all observations seem to indicate that type Ia supernovae that are of known distance have the same brightness (corrected by the shape of the light curve). However, it is not known why they should have the same brightness, and the possibility that the distant type Ia supernovae have different properties than nearby type Ia supernovae exists.
That this is not merely a philosophical issue can be seen from the history of distance measurements using Cepheid variables. In the 1950s, Walter Baade discovered that the nearby Cepheid variables used to calibrate the standard candle were of a different type than the ones used to measure distances to nearby galaxies. The nearby cepheid variables were population I stars with much higher metal content than the distant population II stars. As a result, the population II stars were actually much brighter than believed, and this had the effect of doubling the distances to the globular clusters, the nearby galaxies, and the diameter of the Milky Way. | <urn:uuid:b3f475f9-7901-446b-8744-6eb9cc31f205> | 3.875 | 752 | Knowledge Article | Science & Tech. | 25.140431 |
In This Tutorial we want to describe you a code that helps you in understanding Get Last Line of File in Java . For this we have a class name "Get Last Line of File". Inside the main method we create an instance of file class by using a new operator and passing a text .txt as a argument.
1)Input Stream Reader - This is used to read the byte and decode it into character stream from the text.txt present in a file.
2)Buffered Reader- This is used to read the character stream from the text.txt present in stream reader.
We declare a String object name line using new string operator.
3)file.getname( )-This method return you the name of the file printed by System.out.println.
While loop evaluate the condition weather the stream is ready to read
4)br.readline( )-This method is used to read the whole line of the Text.txt and store in line object of string class, that is further printed by System.out.println.
Finally the last line of file is printed by the System.out.println.GetLastLineOfFile.java
If you are facing any programming issue, such as compilation errors or not able to find the code you are looking for.
Ask your questions, our development team will try to give answers to your questions. | <urn:uuid:063d0bb6-e824-4c73-8816-feb2f283456a> | 4.125 | 281 | Tutorial | Software Dev. | 71.359375 |
Observations and results
What is happening when you squeeze the Oobleck? What is happening when you release the pressure? Does the Oobleck remind you of anything else?
The Oobleck mixture isn't your typical liquid—or solid. The cornstarch-and-water mixture creates a fluid that acts more like quicksand than water: applying force (squeezing or tapping it) causes it to become thicker. If you were trapped in a tub of Oobleck, what would be the best way to escape?
Share your Oobleck observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.
Wash hands with water. Add plenty of extra water to the mixture before pouring it down the drain. Wipe up any dried cornstarch with a dry cloth before cleaning up any remaining residue with a damp sponge.
More to explore
"What is Jell-O?" from Scientific American
"Ask the Experts: What Is Quicksand?" from Scientific American
"States of Matter" overview from Idaho Public Television's Dialogue for Kids
Slime and Goo activities from the American Chemical Society's Science for Kids
Oobleck, Slime & Dancing Spaghetti: Twenty terrific at-home science experiments inspired by favorite children's books by Jennifer Williams, ages 4–8
The Everything Kids' Easy Science Experiments Book: Explore the world of science through quick and easy experiments! By J. Elizabeth Mills, ages 9–12
The Magic of Gravity
What you'll need
• Bottle, jar or canister with a small top opening (larger—but not too much bigger—than the coin)
• 3- by-5-inch note card or other sturdy piece of paper
• Pen or pencil
• Water (optional) | <urn:uuid:acd71f08-7ab2-42e2-a133-b1e45802a27b> | 3.609375 | 373 | Tutorial | Science & Tech. | 49.08849 |
During the week of May 13th, the CO2 level at the Mauna Loa Observatory in Hawaii topped 400 ppm repeatedly. Daily levels of CO2 can vary due to weather, and there are seasonal trends as well. The level of atmospheric greenhouse gases continues to increase, now over 120 ppm since the Industrial Revolution began. For more on the Keeling Curve, see http://keelingcurve.ucsd.edu/. Find out more about greenhouse gases and warming.
The week of May 19 brings dozens of tornadoes to Tornado Alley in the states of Oklahoma, Kansas, Iowa, Illinois and Missouri. On May 20th, a massive tornado struck Moore, Oklahoma, devastating communities - destroying over 100 homes and hitting two elementary schools and a hospital - with many casualties and deaths. Our thoughts are with our friends and colleagues suffering from these storms. For more on the May 20th storms, see the NOAA Storm Prediction Center Storm Report.
Did you know that, according to ancient Chinese myth, humans were generated from the fleas which lived on the body of the giant Pan-Ku?
Earth and Space Science Concept of the Day
Do you know what this word or phrase means?
xSeiche : A standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, and seas. The key requirement for formation of a seiche is that the body of water
Glaciovolcanoes, they're called, these rumbling mountains where the orange-red fire of magma meets the frozen blue of glaciers. Iceland's Eyjafjallajökull volcano, which erupted recently, is but one of...Read more | <urn:uuid:1b7e0828-4327-4d43-94a0-cc7d50d7c538> | 3.109375 | 355 | Content Listing | Science & Tech. | 53.306964 |
Q&A: Supernova Remnants and Neutron Stars
I saw the photo of the remnants of Cassiopeia A which exploded some 300 years ago (from our frame of reference). How can the gases still be at 50 million degrees? Wouldn't the density of the gas have decreased to a point that the temperature dropped significantly?
It's the low density of the gas in supernova remnants that results in its slow
cooling. Cooling processes like collisions act faster with high density
gas, and slower with low density gas. | <urn:uuid:ffe03f5a-a832-4658-9649-43d41709efab> | 3.015625 | 111 | Q&A Forum | Science & Tech. | 57.264182 |
common name: tortoise beetle
scientific name: Chelymorpha cribraria (Fabricius) (Insecta: Coleoptera: Chrysomelidae)
Introduction - Distribution - Identification - Biology - Hosts - Acknowledgments - Selected References
In September of 1993, a single specimen of an exotic tortoise beetle was collected on a species of Ipomoea (Convolvulaceae) in a weedy lot in Davie, Broward County. Further collecting turned up additional specimens at the original site and at other localities in Broward County. The beetle was identified as Chelymorpha cribraria (Fabricius), a widely distributed Neotropical species known to feed on sweet potato (Ipomoea batatas (L.) Lam.) and other morning glories. Subsequent surveys and collecting have revealed populations of Chelymorpha cribraria at other localities in Dade and Monroe counties.
Figure 1. Adult of the tortoise beetle, Chelymorpha cribraria (Fabricius), with antennae and legs extended. Photograph by Jeffrey Lotz, Division of Plant Industry.
This species is distributed throughout South America and the Antilles. Buzzi (1988) recorded Chelymorpha cribraria from Brazil, Cayenne, Colombia, Guadeloupe, and Paraguay. There are specimens in the Florida State Collection of Arthropods from Antigua, Argentina, Dominican Republic, and Panama. In Florida, it has been collected in the following localities: Broward County - Davie, Hallandale; Dade County - Camp Mahachee, Cape Florida State Park, Matheson Hammock, Virginia Key; Monroe County - Key Largo State Botanical Site.
The genus Chelymorpha Boheman contains more than 100 species, which are mostly Neotropical in distribution. Two species have been recorded (Blatchley 1924) previously from Florida: Chelymorpha cassidea (Fabricius) and Chelymorpha geniculata Boheman. The endemic Florida Chelymorpha geniculata has had a checkered taxonomic history. It is often considered either a synonym or subspecies of Chelymorpha cassidea (Balbaugh and Hays 1972). Both are uniformly tan to red-brown in color with 12 to 14 black spots on the elytra and four to six on the pronotum. Chelymorpha cribraria is extremely polymorphic in color (Vasconcellos-Neto 1988), and most of the color forms have been described as separate species. Only two color forms have been found in Florida so far. The most common color form in Florida is bicolored, with pronotum black and elytra brick-red or tan. Much less common is the color form having a tan ground color with metallic reflections, numerous black speckles, and longitudinal red stripes on the elytra.
Figure 2. Adult of the tortoise beetle, Chelymorpha cribraria (Fabricius), with antennae and legs drawn in. Photograph by James Castner, University of Florida.
Vasconcellos-Neto (1988) presented a model consisting of six tightly-linked genes responsible for color in Chelymorpha cribraria. He found eight color forms produced from 21 genotypes, and hypothesized that the stable polymorphism in Chelymorpha cribraria is maintained "... by selection through visually oriented predators." Adult Chelymorpha cribraria are unpalatable to some predators. In Brazil, Chelymorpha cribraria appears to belong to at least six different mimicry groups with two to four beetle species in each group.
Buzzi (1988) reviewed the biology of Neotropical cassidines and gave the following composite account of several species of Brazilian Chelymorpha, including Chelymorpha cribraria: Eggs are glued to leaves of the host plant in clusters; they hatch in six to eight days. There are five larval instars and time spent in the larval stage ranges from 13 to 18 days. Larvae possess a fecal fork and carry their feces over their body. This camouflage is thought to provide protection from predators and parasitoids. Pupation, which takes place on the host plant and under the fecal shield, lasts eight to 10 days. Females live an average of six months and lay about 1,500 eggs.
Chelymorpha cribraria has been recorded in the Neotropics from several species of Ipomoea, such as Ipomoea cairica (L.) Sweet. Per., Ipomoea cardiophylla Gray, and Ipomoea batatas (sweet potato). In Florida, it has been collected on various morning glories, but the only two that have been identified to species are Ipomoea indica (Burm. f.) Merr. and I. pes-capre (L.) R. Br., railroad vine. The two morning glories on Florida's list of endangered plants, Ipomoea microdactyla Griseb. and Ipomoea tensuissima Choisy (Coile 1994), occur in the areas where Chelymorpha cribraria is established.
I thank E.G. Riley, Texas A&M University, for his help in identifying Chelymorpha cribraria; Deborah L. Matthews and John Watts, University of Florida, for bringing the first specimen to my attention; Bonnie Coy, FDACS, for additional surveys; Roy Morris, Lakeland, for the specimen from Key Largo; and Jim Duquesnel, Florida Department of Environmental Protection, for finding the population of Chelymorpha cribraria at Cape Florida.
- Balsbaugh Jr. EU, Hays KL. 1972. The leaf beetles of Alabama (Coleoptera: Chrysomelidae). Auburn University, Agricultural Experiment Station Bulletin 441. 223 p.
- Blatchley WS. 1924. The Chrysomelidae of Florida. The Florida Entomologist 7: 33-39; 7: 49-57; 8: 1-7; 8: 17-23; 8: 39-46.
- Buzzi ZJ. 1988. Biology of Neotropical Cassidinae. pp. 559-580. In Jolivet P, Petipierre E, Hsiao TH (eds.). Biology of Chrysomelidae. Kluwer Academic Publishers, Dordrecht.
- Coile NC. 1994. Florida's endangered and threatened plants. Florida Department of Agriculture and Consumer Services, Bureau of Entomology, Nematology and Plant Pathology - Botany Contribution No. 29. 56 unnumbered p.
- Vasconcellos-Neto J. 1988. Genetics of Chelymorpha cribraria, Cassidinae: colour patterns and their ecological meanings. pp. 217-232. In P. Jolivet, E. Petitpierre, and T.H. Hsiao (eds.). Biology of Chrysomelidae. Kluwer Academic Publishers,Dordrecht. | <urn:uuid:3928619d-2d74-44b4-8045-0936fb019a1e> | 2.984375 | 1,499 | Knowledge Article | Science & Tech. | 36.194692 |
I've just started a C++ programming class and I need to write a program to total up one day's worth of bank activity with a small percentage, but I don't know where to even start. Here's the problem summary:
The Silly Savings and Loan Company just opened up with a cash balance of $1000, and a plan to get rich. Their plan to make money is simple. They will charge no fee for checks, and a 3% fee for all deposits. You will write a program for them. They will run your program and enter deposits as positive numbers, and checks as negative numbers. All transactions will be recorded in the order they happen. When they run out of things to enter at the end of the day, they will enter a value of 0 to stop the program.
The program needs to add up both sets of numbers (deposits and checks) and figure out the amount of cash they should have at the end of the day. For every deposit, the 3% fee will be removed from the amount actually deposited, that amount will be added in to the profit they expect to make.
Once the data entry has been completed, the program will print out the total amount of checks written (as a positive number), the total amount of deposits received, the amount of cash they should have on hand, and the total profit earned that day.
Here are the transactions for their first day of operation:
I started some code with the help of a friend, but I don't think it is correct. Can someone help me?
Here is was I had written before, thought I don't really understand what I have done.
What let you doubt "it is correct"? Have you got wrong result using this code?
Yes it gave me an error message. I realize now that I misspelled some words but the code still isn't quite working.
I'm trying to use the starting balance, add deposits, and subtract checks in order, take 3% of all the deposits and add it to the daily profit, then finally total up how much money the bank has at the end of the day.
When I solved the problem on paper, the end total came out to around $65. | <urn:uuid:60a005df-003b-497c-ad59-5ad8ce2d198e> | 2.984375 | 453 | Comment Section | Software Dev. | 69.001219 |
Dormice have been lost from at least 8 counties in the past 50 years but PTES is leading the fight back for this secretive but charming animal.
The lead Partners on the UK Biodiversity Action Plan for dormice are the Wildlife Trusts and Natural England.
Dormice have an unusual biology that affects their lifestyle. Information on dormice ecology can be found here
Hazel dormice have only really been studied by scientists over the past 30 years. Some of the scientific papers written on them are available
Are you involved with dormouse recording? Some copies of the Dormouse monitor are now online in case you have lost your copy.
We are trying to obtain and maintain an accurate and up-to-date record of dormouse distribution in the UK. In addition to your local records centre, or your local Wildlife Trust, please send a copy of your records to PTES to improve knowledge of their distribution in Britain.
Are you a woodland, or land manager, with a specific interest in dormouse conservation? We may have a leaflet or letter you can use. If you can’t find what you want please let us anything you may use so that we can make it available for others.
Dormice are very photogenic but there are very few good photographs of them because they are small, fast, and nocturnal. Follow these links to some nice images of dormice:
This page has the following sub pages. | <urn:uuid:c9de2912-4af4-4187-a9c0-93957c23be25> | 2.984375 | 299 | Knowledge Article | Science & Tech. | 45.4973 |
To prove this claim, let a, b, and c be the lengths of HG, EG and EH, respectively.
Given triangle GEH is a right triangle, then by using the pythagorian theorem gives us or It can be noted that length FG = BG = HG = a since all are radii of the circle as shown above.Therefore length EF = FG - EG = a - b and length BE = BG + GE = a + b. It follows that
area of rectangle BCDE = (base)*(height).
area of rectangle BCDE = (BE)*(ED)
area of rectangle BCDE = (BE)*(EF) given length EF = ED
area of rectange BCDE = (a + b)(a - b) as noted above
area of rectange BCDE =
area of rectangle BCDE == area of square HEKL as shown above.
Back to quadrature of rectange page | <urn:uuid:3e57f6da-54b2-4da3-9d7c-31d60b2bb8a9> | 3.0625 | 197 | Tutorial | Science & Tech. | 65.7272 |
[Tutor] requests/responses from urllib2
alan.gauld at btinternet.com
Mon Aug 11 10:49:28 CEST 2008
"Eric Abrahamsen" <eric at ericabrahamsen.net> wrote
> that traffic go in and out of my server machine? The python docs say
> that urllib2 requires the socket library to work, so I assume it's a
> socket of some sort, but I don't really understand how that socket
> is addressed, from the point of view of the third-party server that
> is receiving my urllib2 request, and returning the response.
Virtually all network comms is over sockets. Your web browser
uses sockets every time it connects to a web server. Your web
server is using sockets to receive those requests.
The urllib implementation has to use the Python socket
module so there is a dependency but thats just what you'd expect.
It has to talk to a socket somehow and if it didn't use the socket
library directly it would either use a higher level library that in
turn used socket, or else it would have to implement sockets
itself at the C level.
> it appear to be coming from? If my web server (lighttpd in this
> case) is set to listen on a particular port, is there any way that
> it can 'see' that traffic and interact with it, or is it purely
> between the python library and the outside world?
Your web server likely listens on port 80.
The urllib will send to port 80 by default.
Author of the Learn to Program web site
More information about the Tutor | <urn:uuid:a3528df9-2aa7-47d2-845a-fac9045d105c> | 2.8125 | 362 | Comment Section | Software Dev. | 60.294198 |
Experiments in physics designed to determine parameters in the functional relationship between quantities x and y involve a series of measurements of x and the corresponding y. In many cases not only are there measurement errors yi for each yj, but also measurement errors xj for each xj. Most physicists treat the problem as if all the xj = 0 using the standard least squares method. Such a procedure loses accuracy in the determination of the unknown parameters contained in the function y = f (x) and it gives estimates of errors which are smaller than the true errors.
The standard least squares method of Section 15 should be used only when all the xj << yi. Otherwise one must replace the weighting factors 1 / i2 in Eq. (24) with (j)-2 where
Eq. (24) then becomes
A proof is given in Ref. 7.
We see that the standard least squares computer programs may still be used. In the case where y = 1 + 2x one may use what are called linear regression programs, and where y is a polynomial in x one may use multiple polynomial regression programs. The usual procedure is to guess starting values for ðf / ð x and then solve for the parameters j* using Eq. (30) with j replaced by j. Then new [ðf / ð x]j can be evaluated and the procedure repeated. Usually only two iterations are necessary. The effective variance method is exact in the limit that ðf / ð x is constant over the region xj. This means it is always exact for linear regressions. | <urn:uuid:c6e3da1a-a4ba-4968-99a4-6d4340924285> | 3.703125 | 332 | Academic Writing | Science & Tech. | 62.02137 |
Counting Human Genes
Name: Robert W.
Date: April 2004
Counting the number of protein-encoding genes in the
human genome is a difficult process, as the "start" and "stop" boundaries
of transcribed genes are only imperfectly understood. Some researches
have taken a different approach, capturing mRNAs from the cytoplasm and
matching them with the human genome DNA sequence. They report finding
upward of 65,000 discrete mRNA-transcribing sequences in the genome. does
this mean that there are actually 65,000 human genes, rather than the
30,000 originally reported?
It IS very complicated. I was in a genetics seminar a few years ago and we spent an hour
and a half trying to come up with a new definition for a gene. Recall that transcripts
are edited before they leave the nucleus and that introns are removed and exons are
spliced together. One way of making the most of the genome is to splice different
exons together from within the same "gene". By capturing different mRNA's from the
cytoplasm researchers can see how many of these transcripts are active in different
kinds of cells. So I wouldn't say there are actually twice as many "genes", but
more ways to make the most of the "genes" we have.
Click here to return to the Molecular Biology Archives
Update: June 2012 | <urn:uuid:1199e667-42ef-4ec8-94d3-7487a6e2687f> | 3.1875 | 301 | Knowledge Article | Science & Tech. | 46.112617 |
Frogs and Summer Hibernation
Some of my 4th grade students want to know if frogs ever
hibernate in the summer? I suspect the students have observed frogs
burying themselves in summer in order to cool-off or keep moist.
Frog activity is based upon the temperature of their surroundings. Frogs
are heterothermic; this means their body is the temperature of the
environment for which they live. If the temperature is warm as it is in
the summer, frogs will not hybernate, but may bury themselves for
protection or to rest. They can breathe threw their skin, so periods of
time in the mud is not an issue.
During the fall when a certain low temperature is reached, this triggers
the behavior for the frog to bury itself and begin hibernation. The
warming of the mud in the spring activates the ending of hibernation.
Click here to return to the Zoology Archives
Update: June 2012 | <urn:uuid:37d0e32e-a6c2-4882-ba98-485fb85d6392> | 3.140625 | 201 | Personal Blog | Science & Tech. | 50.507938 |
In one of the few lucky breaks of sun that we have experienced lately, I made my way up to Mount Adams for a survey of oregon spotted frog egg clusters. Spotted frogs have declined in recent years due to a variety of reasons – some obvious (non-native frogs like bull frogs, wetland development) and some mysterious. They are not that easy to spot, but they are usually just under the surface so polarized sunglasses can help a lot.
Below, biologist Howard Browers from the U.S. Fish and Wildlife Service looks for egg masses
I had a chance to use my home-made underwater robot camera to grab a shot of the eggs just below the surface.
The the embryos develop faster in warm temperatures and on a sunny day the eggs nearest the top will grow faster than those at the bottom.
A gelatinous sticky mass holds the eggs together, and the embryos within the egg appear black.
Occasionally you will even see an actual frog such as the juvenile being held by research scientist Mark Hayes.
The population of oregon spotted frogs in this lake refuge has declined precipitously in the last few years for reasons that are still unclear. | <urn:uuid:8f2fcdb5-70e2-41da-b698-810fa32cd9ba> | 2.796875 | 238 | Personal Blog | Science & Tech. | 51.203899 |
Climate Update Pacific Issue 02, January, 2013
In this Climate Update, highlights include:
· Between 9 and 11 named Tropical Cyclones were forecast for the 2012 / 2013 South Pacific tropical cyclone season. 3 named Tropical Cyclones have occurred in the South Pacific so far.
· 11 Tropical Depressions have formed in the South Pacific since the beginning of the Tropical Cyclone Season.
· In the South Pacific, one Tropical Depression increased in intensity to Category 3 (Tropical Cyclone Garry) and two to Category 4 (Tropical Cyclone Evan and Freda).
· The North Pacific has experienced one Category 5 (Tropical Cyclone Bopha) which passed over southern Palau.
· In late February and early March more disturbed weather is expected when the Madden Julian Oscillation wave passes through the South Pacific.
· El Niño-Southern Oscillation (ENSO) is expected to remain in neutral range.
To learn more about OCHA's activities, please visit http://unocha.org/. | <urn:uuid:ad6f571c-8ba7-4cc8-8759-ede275985f08> | 3.03125 | 214 | Knowledge Article | Science & Tech. | 30.089835 |
Aperture photometry is the measurement of light which falls inside a particular aperture; usually, we mean a circular aperture of some fixed size. The XVista tv command allows you to perform simple aperture photometry by pointing the cursor to a star and pressing the "a" key.
The first thing you need to do is to gather a set of images to measure. I've chosen some images of the variable star IY UMa, taken on UT Apr 12, 2006, at the RIT Observatory. There are 100 cleaned images available, but you don't need them all. Please select a range of ten numbers between 1 and 100 -- say, 20 to 29. Then execute commands like the following to make copies of your ten images on the local machine.
curl -O http://spiff.rit.edu/classes/phys445/work/apr11_2006/iyuma-020.fit curl -O http://spiff.rit.edu/classes/phys445/work/apr11_2006/iyuma-021.fit ... curl -O http://spiff.rit.edu/classes/phys445/work/apr11_2006/iyuma-029.fit
You should end up with ten cleaned images in your current directory, with names like iyuma-020.fit, etc. Try displaying one right now, just to make sure that nothing has gone wrong.
When you have all your images, look around at the students sitting near you. Help anyone who is having problems. We'll move on when everyone is ready.
Before you can start measuring magnitudes, you need to pick a good size for the aperture. If you pick an aperture which is too big, you'll include light from neighboring stars:
The apertures below don't include light from neighboring stars ... but they are still large enough that MOST of the area included around a faint star is clearly background sky. The light from the star itself is concentrated at the very center.
The goal is to pick an aperture which will include
A good compromise is an aperture which is a little bigger than the visible extent of faint stars:
In practice, a good choice for the radius of an aperture is about 1.5 or 2.0 times the FWHM. You can quickly measure the FWHM by moving the cursor to an unsaturated star and pressing the "r" key. A little window showing the radial profile of the object should pop up, like this:
- measure the FWHM of your images, in pixels
- each pixel of these images is really a 3x3 binned "superpixel". The plate scale for these binned images is 1.85 arcseconds per pixel. What is the FWHM of your images in arcseconds?
- calculate a good aperture size, in pixels
- compare your aperture size to that of students using other sets of images. Are they all the same, or are there variations in the FWHM from set to set?
First, you need to set the size of the aperture. It is stored in the XVista symbol table, a little ASCII text file in the home directory of the CCD user. You can show the contents of the table by typing the XVista command xlet:
The aperture radius is controlled by the aperture_radius symbol; set it to the desired aperture radius in pixels:
You also need to set the radii of the annulus used to measure local background sky values for each star.
Reasonable values for the sky annuli are around 4-5 times the aperture radius for inner boundary, and around 6-7 times the aperture radius for outer boundary. It's okay if the annulus contains one or two stars, as long as the great majority of its pixels are purely background sky.
If you want to see just how big a radius of 10 pixels looks compared to the stars, you can define a circle at the position of a star (let's pretend it is at row 234, col 173) and then display it on all current images like so:
circle 1 cr=234 cc=173 rad=10 circle 1 show
Let's say you decide that the sky annulus should have radii 10 and 20 pixels.
xlet aperture_innersky=10 xlet aperture_outersky=20
Now, once you've set the apertures, you are ready to measure instrumental magnitudes. Display a clean image with the tv command, move the cursor to a star of interest (sometimes it helps to use the "z" key to zoom in for a closeup), and press the "a" key.
The computer will print a line of values every time you press the "a" key.
The instrumental magnitude is NOT the same as the "standard magnitude" of the star that you would find in a catalog; instead, it is simply the total (counts - sky) value inside your aperture, converted into a logarithmic form like so:
instrumental_mag = 25.0 - 2.5*log10(counts - sky)
If you find that star A has an instrumental magnitude which is about 1.2 brighter than star B, then it is probably true that the catalog magnitude of A will be around 1.2 brighter than the catalog magnitude of star B. But the zeropoint of your instrumental magnitudes is arbitrary.
It sometimes helps to plot a radial profile with the "r" key. The graph will give you some idea for the signal-to-noise ratio (S/N) of the measurement.
The height of the peak of this radial profile is a measure of the (sky-subtracted) signal from the star. The scatter of the pixel values far from the center is a measure of the noise in the sky background. The ratio of the two is one way to estimate the S/N of the stellar measurement.
It's a pretty bad way to make an estimate, since it presumes that all the light from the star falls into a single pixel; but scientists often use this "peak-to-scatter" method for very faint signals, which may appear to have signal only in a central pixel or two.The percentage of uncertainty in a magnitude measurement can be very roughly estimated by
1 percent uncertainty = 100 * ( ------ ) S/N
- What is the S/N ratio, based on the radial profile above?
- Estimate the precision of a single magnitude measurement of the star whose radial profile is shown above.
Please measure by hand the instrumental magnitudes of the variable star IY UMa and two comparison stars in each of your images. Use the stars marked "A" and "B" in this chart:
You should make a table which looks like this:
# image IY A B 1 13.079 12.592 13.670 2 13.091 12.612 13.642and so forth. The first column should be image index number, which we will use as a stand-in for time. You could look in the FITS header and convert the UT value to Julian Date if you wanted to put your results into a more official form.
After making your table, create a light curve -- a graph showing magnitude on the vertical axis (with bright at top, so smaller numbers at the top!) and time on the horizontal axis. Walk to the computer on which your instructor has created a simple spreadsheet. Type your numbers into the spreadsheet, making sure that your values go into the proper columns. After everyone has typed in his data, we will plot all the measurements.
- Why didn't I ask you to use the brightest star in the field (marked "Q" in the chart) as a comparison?
- Do you see any patterns in your light curve?
All the stars seem to grow brighter and fainter simultaneously.
- What could cause these common features?
The cure for this symptom is to pick one star as a reference, and calculate the difference between this star and every other star in the field. For example, if you were to pick star "A" as a reference, you would calculate
(IY - A) (A - A) (B - A)for each image. Then, instead of plotting the raw magnitude versus image index number (or time) to make a raw light curve, plot the differential magnitude versus image index (or time). All the common patterns should disappear -- as long as you picked a good reference star -- leaving only the instrinsic changes of each star.
Copyright © Michael Richmond. This work is licensed under a Creative Commons License. | <urn:uuid:294871bc-2fb0-41d5-ab62-245e44278ef7> | 3.484375 | 1,786 | Tutorial | Science & Tech. | 64.515412 |
The lovely, symmetric planetary nebula
cataloged as MWP1 lies some
4,500 light-years away in the northern constellation
Cygnus the Swan.
One of the largest
known, it spans about 15
Based on its expansion rate
the nebula has an age of 150 thousand years,
a cosmic blink of an eye
in the 10 billion year life of a sun-like star.
But planetary nebulae represent a very brief final phase in
evolution, as the nebula's central star shrugs off
its outer layers to become a hot white dwarf.
In fact, planetary nebulae ordinarily only last
for 10 to 20 thousand years.
As a result, truly
offers a beautiful
challenge to astronomers studying the evolution of its central star.
Credit & Copyright: | <urn:uuid:d85eec5c-88d1-4d5d-8a45-a043cd746f03> | 3.265625 | 174 | Knowledge Article | Science & Tech. | 46.154246 |
A mass, m1 = 3.00 kg, resting on a frictionless horizontal table is connected to a cable that passes over a pulley and then is fastened to a hanging mass, m2 = 12.0 kg, as in Figure P4.25. Find the acceleration of each mass and the tension in the cable.
Find the change in volume (in cubic cm) of an aluminum sphere with an initial radius of 11 cm when the sphere is heated from 0.0 C to 140 C. The linear expansion coefficient of aluminum is 23 x 10-6 /C .
A skier leaves the ramp of a ski jump with a velocity of v = 18.0 m/s, = 21.0 above the horizontal, as in the figure. The slope is inclined at 50.0 , and air resistance is negligible. (Assume up and right are positive, and down and left are negative.)Find the distance from the ramp to...
A golf ball is struck with a five iron on level ground. It lands 80.0 m away 4.60 s later. What was the magnitude and direction of the initial velocity? (Neglect air resistance.) 1 m/s 2 above the horizontal
A rocket is fired at a speed of 75.0 m/s from ground level, at an angle of 61.4 above the horizontal. The rocket is fired toward an 11.0 m high wall, which is located 21.5 m away. The rocket attains its launch speed in a negligibly short period of time, after which its engines shut down and the...
On a spacecraft two engines fire for a time of 565 s. One gives the craft an acceleration in the x direction of ax = 5.10 m/s2, while the other produces an acceleration in the y direction of ay = 7.30 m/s2. At the end of the firing period, the craft has velocity components of vx = 3610 m/s and vy...
A football is kicked at ground level with a speed of 15.0 m/s at an angle of 33.0 to the horizontal. How much later does it hit the ground?
The French train in a sample problem is traveling 301 km/h. When it is 360m from a road crossing, the engineer blows the whistle. If the speed of sound is 330 m/s, how many seconds after the whistle is heard at the crossing will the train cross there?
Romeo is chucking pebbles gently up to Juliet's window, and he wants the pebbles to hit the window with only a horizontal component of velocity. He is standing at the edge of a rose garden h = 4.5 m below her window and d = 5.0 m from the base of the wall. How fast are the pebbles going when...
On a spacecraft two engines fire for a time of 555 s. One gives the craft an acceleration in the x direction of ax = 5.10 m/s2, while the other produces an acceleration in the y direction of ay = 7.30 m/s2. At the end of the firing period, the craft has velocity components of vx = 3785 m/s and vy...
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1. Can you show me step by step how to solve this problem?:
- The Earth’s rate of rotation is constantly decreasing, causing the day to increase in duration. In the year 2000 the Earth takes about 0.548 s longer to complete 365 revolutions than it did in the year 1900.
- (a) What is the average angular acceleration of the Earth?
- (b) If this average acceleration remains constant, in what year will the Earths rotation come to rest?
2. I do not understand this Ideal Gas Law and Kinetic Theory question. Can you help me set it up?
- A spherical balloon is made from a material whose mass is 3.00-kg. The thickness of the material is negligible compared to the 1.5-m radius of the balloon. The balloon is filled with helium (He) at a temperature of 305-degrees K and just floats in the air, neither rising nor falling. The density of the surrounding air is 1.19-kg/m^3. Find the absolute pressure of the helium gas | <urn:uuid:3c589ccc-e79b-405b-8041-6c5dc94cb69c> | 3.6875 | 962 | Q&A Forum | Science & Tech. | 83.969604 |
|Index to this page|
Recombinant DNA is DNA that has been created artificially. DNA from two or more sources is incorporated into a single recombinant molecule.
5' GGATCC 3'
3' CCTAGG 5'
To be useful, the recombinant molecule must be replicated many times to provide material for analysis, sequencing, etc. Producing many identical copies of the same recombinant molecule is called cloning. Cloning can be done in vitro, by a process called the polymerase chain reaction (PCR). Here, however, we shall examine how cloning is done in vivo.Cloning in vivo can be done in
In every case, the recombinant DNA must be taken up by the cell in a form in which it can be replicated and expressed. This is achieved by incorporating the DNA in a vector. A number of viruses (both bacterial and of mammalian cells) can serve as vectors. But here let us examine an example of cloning using E. coli as the host and a plasmid as the vector.
|Electron micrograph showing plasmids (21K)|
Plasmids are replicated by the same machinery that replicates the bacterial chromosome. Some plasmids are copied at about the same rate as the chromosome, so a single cell is apt to have only a single copy of the plasmid. Other plasmids are copied at a high rate and a single cell may have 50 or more of them.
Genes on plasmids with high numbers of copies are usually expressed at high levels. In nature, these genes often encode proteins (e.g., enzymes) that protect the bacterium from one or more antibiotics.
Plasmids enter the bacterial cell with relative ease. This occurs in nature and may account for the rapid spread of antibiotic resistance in hospitals and elsewhere. Plasmids can be deliberately introduced into bacteria in the laboratory transforming the cell with the incoming genes.
5' GGATCC 3'that, as we saw above, is cut by the restriction enzyme BamHI
3' CCTAGG 5'
5' AAGCTT 3'that is cut by the restriction enzyme HindIII
3' TTCGAA 5'
If you remove the two restriction enzymes and provide the conditions for DNA ligase to do its work, the pieces of these plasmids can rejoin (thanks to the complementarity of their sticky ends).
Mixing the pKAN and pAMP fragments provides several (at least 10) possibilities of rejoined molecules. Some of these will not produce functional plasmids (molecules with two or with no replication origin cannot function).
One interesting possibility is the joining of
Sealed with DNA ligase, these molecules are functioning plasmids that are capable of conferring resistance to both ampicillin and kanamycin. They are molecules of recombinant DNA.
Because the replication origin, which enables the molecule to function as a plasmid, was contributed by pAMP, pAMP is called the vector.
However, E. coli can be simultaneously transformed by more than one plasmid, so we must demonstrate that the transformed cells have acquired the recombinant plasmid.
Electrophoresis of the DNA from doubly-resistant colonies (clones) tells the story.
5' GAATTC 3'This is cut by the restriction enzyme EcoRI, producing sticky ends.
3' CTTAAG 5'
If we treat any other sample of DNA, e.g., from human cells, with EcoRI, fragments with the same sticky ends will be formed. Mixed with EcoRI-treated plasmid and DNA ligase, a small number of the human molecules will become incorporated into the plasmid which can then be used to transform E. coli.
But how to detect those clones of E. coli that have been transformed by a plasmid carrying a piece of human DNA?
The key is that the EcoRI site is within the kanr gene, so when a piece of human DNA is inserted there, the gene's function is destroyed.
All E. coli cells transformed by the vector, whether it carries human DNA or not, can grow in the presence of ampicillin. But E. coli cells transformed by a plasmid carrying human DNA will be unable to grow in the presence of kanamycin.So,
All those clones that continue to grow on ampicillin but fail to grow on kanamycin (here, clones 2, 5, and 8) have been transformed with a piece of human DNA.
Using procedures like this, many human genes have been cloned in E. coli or in yeast. This has made it possible - for the first time - to produce unlimited amounts of human proteins in vitro. Cultured cells (E. coli, yeast, mammalian cells) transformed with the human gene are being used to manufacture: | <urn:uuid:3c1a2844-0811-4c7b-97b9-b9aeaae959eb> | 3.9375 | 1,010 | Knowledge Article | Science & Tech. | 46.392262 |
It contrasts with the dot product which produces a scalar result. In many engineering and physics problems, it is handy to be able to construct a perpendicular vector from two existing vectors, and the cross product provides a means for doing so. The cross product is also useful as a measure of perpendicularnessthe magnitude of the cross product of two vectors is equal to the product of their magnitudes if they are perpendicular and scales down to zero when they are parallel. The cross product is also known as the vector product. In mathematics, the cross product is a binary operation on two vectors in a three-dimensional Euclidean space that results in another vector which is perpendicular to the plane containing the two input vectors. The algebra defined by the cross product is neither commutative nor associative. The cross product is only defined in three or seven dimensions. Like the dot product, it depends on the metric of Euclidean space. Unlike the dot product, it also depends on the choice of orientation or handedness. Certain features of the cross product can be generalized to other situations.
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture. | <urn:uuid:7745336e-f436-4885-9ca0-47383ffb5ffc> | 4.65625 | 259 | Truncated | Science & Tech. | 38.673716 |
Environment Australia, 1999
ISBN 0 642 2546 363
Taxon summary: Golden-tipped Bat
Scientific name: Kerivoula papuensis Dobson, 1878
Common name: Golden-tipped Bat
Conservation status: Lower Risk (near threatened)
Past range and abundance
Not known. There are few records of the species before the 1980’s (Hall and Richards 1979). First recorded from Coomooboolaroo Station, south of Duaringa in central Queensland in 1884, although the exact locality is doubted (Schulz 1995a). This species was not recorded from 1897 until 1981, when it was ‘re-discovered’, with the capture of a single individual at Crystal Cascades on the hinterland of Cairns (Churchill 1998); for historical review see Schulz 1995a). Extralimitally, this species is found in Papua New Guinea and the type locality is Port Moresby (Flannery 1995, Bonaccorso 1999).
Present range and abundance
Not well known. Since the 1980’s this species has been captured with increasing regularity in regional fauna surveys with the refinement of trapping techniques and improvement of sonar detection systems (Walton et al. 1992, Clague et al. 1995, Schulz and Wainer 1997). The species has been recorded from sea level to over 1200m altitude in scattered localities ranging from Mumbulla State Forest, east of Bega in southern New South Wales north to Cape York Peninsula (Lunney and Barker 1986, Parnaby and Mills 1994, Clague et al. 1995, Schulz 1995a). It appears to have localised distributions and/or sparsely distributed within its range. The species is reasonably common in the north Queensland wet tropics region (Clague et al. 1995, Clague et al. 1995, Schulz 1995a). The majority of records have been collected in the north-east New South Wales and south-east Queensland biogeographical regions (New South Wales National Parks and Wildlife Service 1994, Schulz and Wainer 1997). The western limit of this species is poorly understood (Walton et al. 1992). While it is known from semi-evergreen vine thickets in the Tarong-Yarraman area of inland south-east Queensland, it has not been located in dry vine forests west of the Atherton Tablelands.
This species has been recorded predominantly from a variety of rainforest types, ranging from tropical mesophyll vine forest to semi-evergreen vine thickets, and rainforest ecotone areas, where it feeds on a range of both gleaned and aerially acquired dietary items (Clague et al. 1995, Schulz 1995a, Schulz and Wainer 1997). There are a small number of records from dry and wet sclerophyll forests lacking a rainforest subcanopy, riparian Casuarina cunninghamiana dominated forest, coastal Melaleuca forests, and several individuals have been recorded inside houses on the edge of residential areas (Schulz 1995a). However the majority of such records are situated within 1 km of rainforest patches.
Roosts have predominantly been recorded from the disused suspended nests of the Yellow-throated Scrubwren Sericornis citreogularis and the Brown Gerygone Gerygone mouki (Schulz 1995b, 1998). Individuals have also been recorded roosting in tree hollows and on the side of branches, and in suspended dead foliage of treeferns (Schulz 1995b). Outside Australia, this species has been recorded roosting in caves and in buildings (Flannery 1995).
Threats to this species are not well understood. However, clearing of drier rainforest types and lowland rainforest areas for agricultural and pastoral purposes, particularly in the western and coastal parts of its range, are likely to have caused decline of the species. Current potential threats include: continued clearing and fragmentation of forest, forest harvesting operations; the effect of prescribed fire regimes and ad hoc fires from leaseholders in production forests on foraging habitat; and predation by domestic and feral cats (known species roosts are within 5m of the ground). As the majority of roosts located so far, have been in the nests of the Yellow-throated Scrubwren and Brown Gerygone, it may be important to identify current threats facing these two rainforest bird species.
- Conduct surveys to clarify distribution (western range limits in Queensland, drier sections of coastal and sub-coastal Queensland e.g. between Rockhampton and Mackay).
- Conduct DNA analysis of collected material to identify whether the species is isolated in sections of its range.
- Continue ecological research to determine:
- habitat requirements;
- roost and maternity site selection, particularly where the Yellow-throated Scrubwren and Brown Gerygone are uncommon or absent;
- population dynamics; and
- threatening processes, particularly the impact of forestry practices in New South Wales and Queensland.
- Ensure protection of representative populations across the distributional range.
Bonaccorso F. 1999. Bats of Papua New Guinea. Conservation International, Washington.
Churchill S. 1998. Australian Bats. Reed New Holland, Sydney, NSW.
Clague C., Coles R.B., Spencer H.J. and Whybird O.J. 1995. Observations on the ecology and distribution of Murina florium and Kerivoula papuensis in the wet tropics region of Australia. (Abstract). Proceedings of the 1995 Scientific Meeting of the Australian Mammal Society. Australian Mammal Society, Townsville.
Flannery T.F. 1995. Mammals of New Guinea. Reed Books, Chatswood, NSW.
Hall L.S. and Richards G.C. 1979. Bats of Eastern Australia. Queensland Museum Booklet No. 12. Queensland Museum, Brisbane.
Lunney D. and Barker J. 1986. The occurrence of Phoniscus papuensis (Dobson) (Chiroptera: Vespertilionidae) on the south coast of New South Wales. Australian Mammalogy 9, 57–58.
NSW National Parks and Wildlife Service. 1994. Fauna of north-east NSW forests. North east Forests Biodiversity Study Report No.3. NSW National Parks and Wildlife Service, Sydney.
Parnaby H. and Mills D. 1994. A record of the Golden-tipped Bat from the escarpment forests of southern New South Wales. Australian Zoologist 29, 245–249.
Rhodes M. P. 1995. Wing morphology and flight behaviour of the golden-tipped Bat, Phoniscus papuensis (Dobson) (Chiroptera : Vespertilionidae). Australian Journal of Zoology 43, 657–663.
Schulz M. 1995a. A preliminary investigation of the Golden-tipped Bat Kerivoula papuensis in the Wet Tropics, north-eastern Queensland. Report to the Wet Tropics Management Authority, Cairns (unpublished).
Schulz M. 1995b. Utilisation of suspended bird nests by the Golden-tipped Bat (Kerivoula papuensis) in Australia. Mammalia 59, 280–283.
Schulz M. 1998. Bats in bird nests in Australia: a review. Mammal Review 28, 69–76.
Schulz M. and de Oliveira M.C. 1995. Microchiropteran fauna of Kroombit Tops, central Queensland, including a discussion on survey techniques. Australian Zoologist 30, 71–77.
Schulz M. and Wainer J. 1997. Diet of the golden-tipped bat Kerivoula papuensis (Microchiroptera) from north-eastern New South Wales, Australia. Journal of Zoology, London 243, 653–658
Walton D.W., Busby J.R. and Woodside D.P. 1992. Recorded and predicted distribution of the Golden-tipped Bat Phoniscus papuensis (Dobson, 1878) in Australia. Australian Zoologist 28, 52–54.
Woodside D.P. 1995. Golden-tipped Bat Kerivoula papuensis. pp. 490–491 in R. Strahan (Ed.) The Mammals of Australia. Reed Books, Chatswood, NSW.
Authors for the species | <urn:uuid:8cb72e82-9854-4658-b820-7478f5339746> | 3.484375 | 1,783 | Knowledge Article | Science & Tech. | 54.216552 |
IF there is a kind of music of the spheres, as Kepler suggested centuries ago, it could be thought of as the accompaniment to the solar system's stately cotillion of planets gliding around the Sun, spinning and sometimes nodding, most with partners, each responding in subtle ways to all the others.
Orderly and predictably harmonic this may seem, and in the short term it is, but scientists analyzing the motions of planets with powerful computers are realizing that there is a certain cacophony, as it were, to the music of the spheres. In the new scientific lexicon, the solar system is chaotic.
This means that over great spans of time an accumulation of small gravitational disturbances from neighboring planets, combined with their own slightly wobbly rotations, can cause significant fluctuations in the orbits and orientations of the planets. The changes are exponential, and this compounding effect leads to striking consequences over time scales of four million years. Scientists conclude that such behavior is essentially unpredictable.
It also means that the orientations of the spin axes of the inner planets, including Earth, have changed chaotically at some time in their history. Mars is still undergoing wild variations, which could explain its apparent history of extreme climate swings. Earth may be spared a similar fate because of the stabilizing influence of the Moon, the only large satellite in the inner solar system.
These implications of chaos in the solar system were described by a team of French scientists led by Dr. Jacques Laskar of the Bureau des Longitudes in Paris, reporting research results two weeks ago in the journal Nature, and by Dr. Jack Wisdom, an astronomer at the Massachusetts Institute of Technology, writing in the current issue of the journal Science.
The relatively new science of chaos explores the connections between different kinds of irregularities. Motions in nature, like flowing water, jagged lightning strokes and cloud formations, may appear random and disorderly, but on closer examination, can be seen to be quite deterministic, since their motions are fully determined by preceding events in accordance with physical laws. Only recently have high-speed computers enabled scientists to conduct the lengthy, complex calculations that revealed the chaotic motions of planets.
"Ten years ago, no one in planetary science knew about chaos," Dr. Wisdom said in an interview. "Everyone thought of the solar system as evolving very regularly."
Dr. Stanton J. Peale, an astrophysicist at the University of California at Santa Barbara, credited Dr. Wisdom's research in the early 1980's with "opening the door to our understanding of the chaotic nature of planetary motions."
Of all the inner planets, Mars is experiencing the most volatile effects. Because of its place and the timing of its orbit, complex gravitational perturbations combined with the mechanics of the planet's own wobbling rotation produce a phenomenon called resonance. Dr. Wisdom likened this to someone on a swing pumping his legs back and forth. If done at certain frequencies, the pumping will change the swinger's trajectory. In the case of Mars, the gravitational tug of other planets, coupled with its own speed of rotation, set up resonances which, over time, change the shape of the planet's orbit and the tilt of its spin axis.
The computer simulations by Dr. Wisdom and his graduate student, Jihad Touma, show that under the influence of perturbations over the last 100 million years the tilt of the Martian spin axis has probably fluctuated from 10 degrees to 50 degrees away from a line perpendicular to the plane of the planet's orbit. | <urn:uuid:842fa28b-b623-4e7b-afa9-a384ca915924> | 3.40625 | 716 | Truncated | Science & Tech. | 38.831898 |
I recently attended a small technical conference on stray light in Toulouse, France. It was sponsored by CNES (the French space agency) and by several European aerospace companies. It was basically an optical engineering conference on a very specialized area of optics called “stray light.” As you can imagine, this means light that you don’t want showing up on the detectors of your optical system. A familiar example is a “ghost image” that you might see on a photo that you shoot towards the sun. You might see rings or hexagonal shapes or patches in your picture, obscuring part of the actual picture. These are internal reflections from the lenses or apertures that normally would be too faint to see unless the source is very bright (like when the sun is partly or fully in the frame).
In spacecraft optical systems (telescopes or imaging systems for Earth or other planets), this is a big problem. The sensors for these systems are very sensitive, and there are many ways for photons you don’t want to bounce around and find their way to your sensors, even if you are careful and don’t point directly at the sun, moon, or Earth (the brightest sources for most spacecraft). Preventing or reducing stray light is an important part of design and fabrication of such optical systems and can even determine the success or failure of a mission.
A case in point from a paper presented by Mr. Thierry Viard of Thales Alenia Space in sunny Cannes, France. The COROT spacecraft was launched in December 2006 to search for exoplanets with short orbital periods, especially large terrestrial (Earth-like) planets. COROT is a relatively small and low-cost spacecraft, so launching it to a dark, distant Lagrange point (e.g., L2) was not possible. An 800 km polar orbit would have to do, which meant that the very bright Earth would always be nearby (in addition to the sun and moon, though the sun would always be kept “behind” the spacecraft by pointing to a different area of the sky depending on the season).
The “transit” method of detecting exoplanets depends on recording very slight changes in the brightness of rather dim stars as a small planet passes in front of the star as viewed from our direction. The telescope had to be designed with a form that would minimize the chances of light from “off-axis” objects (those outside of the desired pointing area) getting to the detectors. Several optical criteria used in the chosen design form helped with this, in addition to extensive “baffles” (black metal rings that only allow light from certain directions to get in).
But this was not enough for COROT to succeed. The engineers also determined that cleanliness would make or break this mission. The slightest dust in the spacecraft could also scatter light to the detector, and such scattering had to kept to about 10 photons per pixel per second from the nearby Earth (which is putting out about 10^20 photons per second per pixel, a huge, huge number). This required keeping particle contamination (dust) to something under 200 parts/million, which is very clean even for a clean room used to building delicate spacecraft. And there was no way to even test this without risking even more contamination, so it had to be based entirely on simulations. Pretty scary!
But guess what? The COROT optics team succeeded. When they first imaged the starry sky, it was pitch black except for the bright, distinct stars. Just as designed. They detected their first exoplanet in May 2007, and the first Earth-like exoplanet , COROT-7b (1.7 times Earth’s radius) in 2009.
Of course there is much more to this or to any spacecraft than the optical systems. This is just an example of the clever engineering, hard work, extreme attention to detail, and ultra-high quality needed for any successful space mission. Space is not easy.
Photos courtesy of CNES. | <urn:uuid:8ec91e1e-d4f8-48f6-ad31-c23ee83ffffa> | 3.390625 | 833 | Personal Blog | Science & Tech. | 53.662905 |
A projectile is any object that has been thrown, shot, or launched, and ballistics is the study of projectile motion. Examples of projectiles range from a golf ball in flight, to a curve ball thrown by a baseball pitcher to a rocket fired into space. The flight paths of all projectiles are affected by two factors: gravity and, on Earth at least, air resistance.
The effects of air resistance on the behavior of projectiles can be quite complex. Because effects due to gravity are much simpler and easier to analyze, and since gravity applies in more situations, we will discuss its role in projectile motion first. In most instances on Earth, of course, a projectile will be subject to both forces, but there may be specific cases in which an artificial vacuum has been created, which means it will only be subjected to the force of gravity. Furthermore, in outer space, gravity—whether from Earth or another body—is likely to be a factor, whereas air resistance (unless or until astronomers find another planet with air) will not be.
The acceleration due to gravity is 32 ft (9.8 m)/sec 2 , usually expressed as "per second squared." This means that as every second passes, the speed of a falling object is increasing by 32 ft/sec (9.8 m). Where there is no air resistance, a ball will drop at a velocity of 32 feet per second after one second, 64 ft (19.5 m) per second after two seconds, 96 ft (29.4 m) per second after three seconds, and so on. When an object experiences the ordinary acceleration due to gravity, this figure is rendered in shorthand as g. Actually, the figure of 32 ft (9.8 m) per second squared applies at sea level, but since the value of g changes little with altitude—it only decreases by 5% at a height of 10 mi (16 km)—it is safe to use this number.
When a plane goes into a high-speed turn, it experiences much higher apparent g. This can be as high as 9 g, which is almost more than the human body can endure. Incidentally, people call these " g -forces," but in fact g is not a measure of force but of a single component, acceleration. On the other hand, since force is the product of mass multiplied by acceleration, and since an aircraft subject to a high g factor clearly experiences a heavy increase in net force, in that sense, the expression " g -force" is not altogether inaccurate.
In a vacuum, where air resistance plays no part, the effects of g are clearly demonstrated. Hence a cannonball and a feather, dropped into a vacuum at the same moment, would fall at exactly the same rate and hit bottom at the same time. | <urn:uuid:ab35a6a6-9808-4501-b374-b22055335c26> | 4.1875 | 563 | Knowledge Article | Science & Tech. | 56.493696 |
After last week’s NASA public relations fizzle, when their lunar probe didn’t appear to produce any visible signs of a much touted plume rising into space, it seems they have been partially vindicated.
According to the agency’s news announcement on Friday, the trailing LCROSS probe did in fact snap photos of the resulting impact explosion by its booster rocket when it hit the moon.
The crash created a crater about one-fifth the size of a football field inside the shadowy bottom of a 98 km wide crater near the south pole last week. Mission scientists are not yet ready to say what the plume was made of but space buffs are hoping that it was filled with water.
Read more on the incoming results on LCROSS mission’s website.
Editor’s note: Take a peek at my latest Weather Network – Night Sky show video on the left-side bar or on the Videos page. Also check out the new scrolling Sky Calendar on the left-sidebar that gives a brief heads-up on the major astronomical events for the coming weeks. With plenty of notice, never miss another big sky event again!
Tags: impact, LCROSS
Posted in Solar System, Space Exploration, The Moon | 39 Comments »
Amateur and professional stargazers are anxiously awaiting this Friday morning’s kamikaze dive of two NASA rockets, part of the LCROSS mission, on the surface of the Moon. The hope is that the resulting impact in a 98 km wide crater near the south pole will create a visible water-rich debris cloud that will rise more than 10 km into space. The thinking by scientists is that there may be a large reservoir of water-ice sitting at the bottom of a deep, internally shadowed, crater called Cabeus. By punching a hole into that crater floor, it would kick up a bunch of that ice out into space for lunar orbiters to analyze. About 10 hours before the lunar smash up the LCROSS probe will separate from its 12 meter long Centaur booster rocket. This 2200 kg booster will be the first to impact and may throw up over 300 tonnes of lunar dust. The 700 kg probe will be right behind the rocket so it will be getting an up close and personal view of the impact- sending back, sure to be, amazing snapshots, before it too smashes into the moon 4 minutes later at 7:34 am EDT.
The hope also is that the impact and plume might be visible with telescopes here on Earth and in orbit. A fleet of professional observatories will be trained on the impact site on Friday morning at 4:30 am Pacific time/ 7:30 am Eastern Time for the first impact, but so will backyard astronomers with their telescopes. There is a real chance that stargazers with medium sized scopes, about 10 to 12 inches, may be able to witness first hand the explosion on the Moon, and the resulting expanding, ring-like plume that will rise up. Best chances to see this event will be for observers located west of Manitoba and west of the Mississippi River and the Pacific Ocean region. Unfortunately folks on the eastern side of the continent will have daybreak blinding them. If you are lucky enough to have the right instruments and are in the right location then you can be part of the mission and help scientists analyze this event by contributing your valuable observations.
Here is a great viewer’s guide called ‘Citizen Science – a Public Observing Campaign’ prepared by NASA on how you can contribute to the science behind this unique and exciting event. Also check out a detailed information guide (PDF file) to the timing and location of the impact.
But don’t fret if you are not able to watch the impact through a telescope yourself, because there will be LIVE broadcast of the event put on by NASA and observatories showing the latest video and photos beamed back from telescopes on the ground and in space. There will even be cameras aboard lunar orbiters only a few hundred km above the Moon that should have ring-side seats to the show. Stay tuned to my blog for the LIVE broadcast video. So mark down Friday 7:30 am EDT/4:30 am PDT on your calendars and stay tuned…
Tags: impact, LCROSS
Posted in Solar System, Space Exploration, The Moon | 17 Comments »
Reports are coming in this morning that Australia’s Anglo-Australian Observatory with its 3.9 meter telescope successfully detected a brief flash in the shadowy area of the Moon yesterday exactly when and where the Japanese probe, Kayuga was supposed to impact at 6 000 km per hour. From the photos it looks like that the impact flash was quite weak and probably too faint for amateurs to see it- but folks are waiting to hear if any reports do come in – so stay tuned. The question being asked in the blogosphere this week however, has been why did the Japanese decide to terminate the mission yesterday on a part of the moon that is so awkward for observers to find and when the moon was near full phase which makes its glare so blinding that it would be hard for anyone to see the show? You kind of wonder if the space agency really consider the true scientific and PR value properly when making their decisions. Hopefully NASA’s efforts in October with their LCROSS mission will be better planned. Anyway, check out the preliminary photo series of Kayuga impact from the giant observatory below- it’s pretty cool. That little dot in the dark area on the second frame is the explosion of the spacecraft on the lunar surface.
Tags: Kayuga, LCROSS
Posted in Satellites, Solar System, Space Exploration, The Moon | 5 Comments »
The web is abuzz with anticipation of the impending doom of the Japanese lunar probe, Kaguya. After a 2 years of conducting science in orbit, it is expected to take a suicide plunge into the lunar surface tomorrow, Wednesday around midday for us in North America. While skywatchers on this continent will be out of luck to see any potential flash and spray of lunar dust, folks in Asia will we well placed. The impact is supposed to happen on the lower right limb of the disk of the moon. For more info check out the mission website and a Lunar Impact alert page.
Later this year there will be an even better opportunity for North Americans to see a potential after effect from an satellite impact when NASA’s own lunar mission LCROSS probe (launching next week) will send impactors into a polar crater sometime in October. Sky and Telescope reports that this event may be within the reach of backyard telescopes 10 inches and bigger.
Posted in Solar System, Space Exploration, The Moon | 85 Comments » | <urn:uuid:c3e0f0e3-e02e-484a-a8a1-2ad48dc56acc> | 3.0625 | 1,385 | Personal Blog | Science & Tech. | 47.365048 |
Amietia wittei (Angel, 1924)
- kingdom Animalia
- phylum Chordata
- class Amphibia
- order Anura
- family Pyxicephalidae Bonaparte, 1850
- Sub-Family Cacosterninae Noble, 1931
- genus Amietia Dubois, 1987
Original Published Description:
Amietia wittei is found chiefly in the Kenyan central highlands along the Mau Escarpment, in the Aberdare Mountains, on Mount Kenya and within the Charangani Hills. The anuran has also been observed on Mount Meru in northern Tanzania. The Molo Frog is found only in the Kenyan central highlands and northern Tanzania in the East African montane moorlands ecoregion, and slightly lower in elevation in the East African montane forests ecoregion (Hogan, 2013).
Habitat and Ecology
A. wittei is found in montane moorlands and grasslands in the lower elevations of the East African montane moorlands ecoregion and in the upper elevations of the East African montane forests ecoregion (Hogan, 2013). The species habitat is in a climate of extreme temperature and solar insolation variations, with nightly freezes occurring in the moorlands, and extreme heat and sunlight intensity occurring almost every day in this equatorial high altitiude zone (Hogan, 2013). Soils in the moorland portion of the species range are of pronounced acidic characteristic (Hogan, 2013). This terrestrial anuran is associated with freshwater cold streams in montane moorland (Hogan, 2013), grassland (Lötters et al. 2004) and perhaps also forest, Moreover, it has also been found in one town (Lötters et al. 2004). Elevations of occurrence are bracketed between 2080 and 3100 metres (Lötters et al. 2004).
A. wittei is recorded only in the East African montane moorlands and the East African montane forests ecoregion. The following text will review not only true associate anurans to A wittei, but also endemics to the restricted geographic ecoregion of the East African montane moorlands. The Kenya River frog (Phrynobatrachus keniensis) is endemic to the Kenyan portion of the ecoregion, and is an associate within the same range. The Kinangop River Frog (Phrynobatrachus kinangopensis) is also endemic to the Kenyan portion of the ecoregion and thus also is not a true associate; in particular it is found only in the Mount Kenya and Aberdare National Parks at elevations around 3000 metres. The Marsabit Clawed Frog (Xenopus borealis) is a near endemic anuran associate, which is also found in the upper elevations of the East African montane forests ecoregion. The Tigoni Reed Frog (Hyperolius cystocandicans) is a Vulnerable near endemic associate, found only in Kenya in this ecoregion and the adjacent East African montane forests. Other associate amphibians present in the East African montane moorlands ecoregion include the Subharan Toad (Amietophrynus xeros), Cape River Frog (Amietia fuscigula), Senegal Running Frog (Kassina senegalensis), Common Reed Frog (Hyperolius viridiflavus), and Keith's Toad (Amietophrynus kerinyagae) (Hogan, 2013).
A. wittei breeds in cold streams and lentic pools at the high altitudes of the East African montane moorlands. Tadpoles generally are found among submerged plants by day, or sometimes basking upon mud or sand substrates in shallow water (Wasonga and Channing, 2007).
As with all tadpoles of the Amietia genus, tadpoles of A. wittei exhibit long low tails and multiple labial tooth rows (Wasonga & Channing, 2007). A single tadpole individual, at Gosner stage 39, was measured at 70.9 millimetres, with the head presenting as bluntly rounded. The large eyes are positioned dorsolaterally. The oral disc manifests a double row of rounded marginal papillae, with the rostral gap in the papillae spanning practically the entire labium. Labial teeth present as compound, with tips rounded. Both the lower and upper jaw sheaths exhibit pigmentation over half of their height, and each jaw sheath is finely serrated (Wasonga and Channing, 2007).
As of 2004 the IUCN noted no known threats to this species (Lötters et al. 2004); however, it is more likely that this anuran is under pressure from increased conversion of habitat to smallholder agricultural uses, livestock grazing pressures and deforestation, which activities have been documented in the ecoregions of species occurrence (Hogan, 2013).
Conservation Actions and Management
A. wittei occurs in Aberdare National Park and Mount Kenya National Park in Kenya, as well as in Arusha National Park in Tanzania (Lötters et al. 2004). More recently, A. wittei tadpoles have been recorded in Mount Elgon National Park in Kenya at 2209 metres in elevation within the East African montane forests ecoregion (Wasonga and Channing; Hogan, 2013).
- Phrynobatrachus Wittei Angel, 1924 (synonym)
- Rana aberdariensis Angel, 1925 (synonym)
- Rana (Rana) aberdariensis — De Witte, 1930 (synonym)
- Rana (Rana) wittei — Guibé, 1950 "1948" (synonym)
- Rana (Afrana) wittei — Dubois, 1992 (synonym)
- Afrana wittei — Visser and Channing, 1997 (synonym)
- Amietia wittei — Frost, Grant, Faivovich, Bain, Haas, Haddad, de Sá, Channing, Wilkinson, Donnellan, Raxworthy, Campbell, Blotto, Moler, Drewes, Nussbaum, Lynch, Green, and Wheeler, 2006 (synonym)
Molo Frog (English) | <urn:uuid:bd27b34f-61ec-4a2c-98a7-99bb667005ef> | 2.890625 | 1,344 | Knowledge Article | Science & Tech. | 27.470375 |
"Dwarf elliptical galaxies, such as NGC 185, pose a complex and little understood problem that might even be said to have a 'social' guise among astrophysicists," explains Aparicio, who heads the IAC's Stellar Populations group, which has carried out the study. This is because these galaxies were directly involved in the construction of one of the key paradigms of the astrophysics of this century: the concept of stellar populations, introduced by Walter Baade (1893-1960), an astronomer at the Carnegie Institute in Pasadena (California, USA). In the 1940s, Baade carried out a major synthesis of that imposed order on the chaos of apparently unconnected data in circulation among astronomers at the time concerning the properties of various types of stars in the Milky Way and other galaxies. As a result of this work, he introduced the concepts of Populations I and II. The latter essentially included the oldest stars, which were characterized by being very red. "One interesting aspect, which seemed at the time to be perfectly clear," says Aparicio, "was that there appeared to be objects that were composed exclusively of Population II stars, and that among these objects were the dwarf elliptical galaxies."
In 1944, Baade himself had realized that there were some blue (young) "stars" in the nuclei of some dwarf elliptical galaxies, and specifically in that of NGC 185. According to Aparicio, this presence was seen to be at odds with a Population II object and was a "disagreeable" exception to the ordered scheme of populations. Baade explained it away as an "impurity" and left it at that. Even stranger, the astronomers who succeeded him in the study of these galaxies continued in the same manner without paying much attention to this "impurity".
Researchers at the IAC began to study NGC 185 in 1996, using the Jakobus Kapteyn Telescope (JKT) and Nordic Optical Telescope (NOT) at the Roque de los Muchachos Observatory. "We identified Baade's supposed blue 'stars'," explains Martínez Delgado, "but there was a problem. If these objects were really stars, they had to be very luminous, very massive and therefore very young (less than 10 million years old). That implied two associated phenomena: first there had to be a great quantity of gas, which, however, was not the case, and second these massive stars had to be accompanied by a great number of intermediate-mass stars, which were nowhere to be seen. These two puzzles remained unsolved and resulted in the problem being temporarily shelved.
What has become clear from the new study is that the blue "stars" in NGC 185 are in fact star clusters, which, given their distance from us, appear practically point-like. According to the IAC team, this confused Baade, in whose photographic plates, the clusters were indistinguishable from stars. "And so we have solved the problem," says Aparicio. "The clusters are made up of thousands of stars, which no longer need be so luminous or therefore so massive or young: their combined luminosity is now sufficient to account for the total luminosity of the clusters, which is what we observe. Each star can be thousands of times less luminous than Baade supposed. Consequently, their ages turn out to be some hundreds of millions of years and their masses moderate. Neither is the presence of large quantities of gas necessary, since this would have been expelled long ago.
On the one hand, this result confirms the suspicion that dwarf elliptical galaxies do not merely comprise very old stars, and that star formation has therefore recently taken place. On the other hand, adds Aparicio, "the stellar clusters we have found are a trace of the last star formation episode that occurred in NGC 185, hundreds of millions of years ago (in comparison, the age of the galaxy and its oldest stars is some 10 000 to 15 000 million years). They are a reliable indication that star formation in these galaxies has continued into recent epochs and therefore that the Populations I and II scheme is over simplified."
Formation in the galaxy NGC 185
The observation of recent star formation in the galaxy NGC 187 contradicts the scheme established in the 1940s by the distinguished astronomer Walter Baade according to which dwarf elliptical galaxies are populated only by old stars. | <urn:uuid:234d6875-ea33-4278-93db-b6cf6737c72c> | 3.265625 | 899 | Knowledge Article | Science & Tech. | 33.79511 |
Comet C/1999 S4: A comet discovered in September 1999 by the Lincoln Near Earth Asteroid Research (LINEAR) project.
Caption: On July 14, 2000 Chandra observed the comet LINEAR for a total of 2½ hours. The X-ray emission proved to be due to collisions of electrically neutral elements in the atmosphere of the comet with nitrogen and oxygen ions in the solar wind. Observed variations in the amount of X-rays produced by the comet were probably due to an increase in the intensity of the solar wind from recent solar flares. The colors represent the intensity of the X-rays with white being the most intense, then yellow, orange, and red.
Scale: Image is 10 x 10 arcmin on a side.
Chandra X-ray Observatory ACIS Image | <urn:uuid:ca198f11-b33d-4103-8d4a-2fc4893f0378> | 3.15625 | 164 | Truncated | Science & Tech. | 52.538081 |
While engaging with this module, you will...
In the lesson about function overloading, you learned how you may create multiple functions with the same name that have (presumably related but) different functionality. Now you will learn how to create a function that will work for different types of parameters but have exactly the same functionality. You will create a function template from which template functions are created.
A function template is just exactly that: a template from which the compiler will build different instances of the same function, but they are built to service different parameter types. Thus, the functionality is not changing for the different types.
Function template code cannot be compiled since the types of the variables are not specified. So, this code must be placed
Also note that template functions are NOT prototyped.
Let’s take a look at an example and then discuss it in a little more detail.
template <typename T>
void swap ( T & t1, T & t2)
T temp = t1;
t1 = t2;
t2 = temp;
There are two new reserved words in this sample of the syntax, “template” and “typename”. The line that begins with “template” tells the compiler that the code to follow is indeed a function template. <typename T> tells the compiler that the identifier T will be used in place of the typename in this code. The use of ‘T’ as the typename parameter is just a convention; use upper case letters near the end of the alphabet. Any identifier will work, but you will quite often see T or U or S or …. I’ll use different identifiers in examples below just to demonstrate. The remainder of the code is the same as before except that the types of variables have been replaced with T. If we had wanted to use two different types in this template, then we would have employed a comma delimited list, e.g. template <typename T, typename U>. But in this example, we only need one type parameter.
How does this work? Every time we call this function with a previously unused type of parameter, the compiler will copy this code replacing T with that type, then compile the code. To continue the example, suppose we have this main function
int a = 8, b = 3;
float c = 4.3, d = 98.5;
char c1 ='y', c2 = '@';
swap ( a, b );
swap ( c1, c2 );
swap ( c, d );
During compiling, when the first swap call is encountered, the compiler notes that both arguments sent are ints. The compiler recognizes that there are no swap functions in its function table that take two ints. It then turns to the template seeing that this swap has two parameters of the same type name. It will then copy the template code replacing all instances of T, the template parameter, with int. Then it will compile the function. When the compiler reaches the second call to swap, it repeats the whole process again. And again, it will repeat with the third call. Thus you see that you will end up with multiple copies of the very same function. (This is sometimes referred to as “code bloat”.) All of this is to save you the time to reproduce this function for all the different types.
There is one thing that you must be very careful of when creating function templates. You must document the function adequately. Why is this so important for templates? This will become much more transparent later in the lessons when you learn how to create your own types. To make it clear now, I will have to use an example you may not fully understand.
template <typename U>
void print (const U u)
This is a very simple template: it outputs to the screen what I send to the function. However, if I send this function an array (I know, you don’t know what that is), it will fail! The << operator (called the “insertion operator”) is not defined for arrays.
So what is the lesson to be learned here? You MUST document function templates to alert the user of any operations forbidden for certain types. For the above function, I would have the following:
// Pre: The type to fill the template parameter must have the insertion operator
// defined for it.
This function will work fine for all the primitive, built-in types in C++ that you know, but it won’t work for arrays.
// Pre: The type of the template parameter must have the < operator defined.
template <typename T_type>
T_type min_value (const T_type t1, const T_type t2)
return (t1 < t2 ? t1 : t2);
// Pre: Both template types must have insertion operator defined.
template <typename T, typename U>
void repeater (const int num_times, const T t1, const U u1)
for (short i = num_times; i > 0; i--)
A typical call:
char some_character = ‘$’;
float a_float_value = 2.2;
repeater(4, some_character, a_float_value);
produces this output:
Once again, the use of the operators in these functions would disallow the instantiation of the template parameters with arrays and any other user-defined types (covered later in this course) which don’t have the required operators defined. | <urn:uuid:0b712bf6-a748-437f-9081-754e2d277413> | 4 | 1,188 | Tutorial | Software Dev. | 55.654294 |
Arctic ice-melt is not just a local issue, it affects climate, weather globally
Melting sea ice may appear to be or local at worst regional problem, but NOAA says that changes in the Arctic ice cover also influence weather in the mid-latitudes, where the majority of humans live.
Satellite images show a clear acceleration in the Arctic ice loss for the past 30 years. For additional information visit Will the Arctic be free of summer ice in 30 years?
Just about every model available for the Arctic ice cover in the future predict a continuation of the present pattern, an acceleration in the ice melt.
What happens when the open arctic waters absorb the additional heat?
The additional heat impacts the Arctic winds and therefore the Arctic atmosphere, increasing the variability and unpredictability of global wind patterns. For additional information visit How the loss of sea ice leads to a warmer Arctic
Cold arctic winds move to mid-altitude regions of the globe, spawning violent winter storm in the U.S. and Eurasia.
Teleconnections impact mid-latitudes
Warmer temperatures that result from huge losses in the sea ice cover give rise to higher pressure surfaces above the North Pole which in turn impact large scale wind patterns over the Northern Hemisphere. “Climate models show these connections with cold air moving south, producing low pressure areas and unusually cold winters in the eastern U.S. and eastern Asia, and cooler than usual weather in late winter from Europe to the Far East.” For additional information visit How changes in the Arctic impact weather and climate in Europe, Asia and the US.
How much warmer is the Arctic?
In the figures below, red, yellow and green colors indicate areas over the Arctic region where autumn near-surface air temperatures were from 2 to 6°C warmer than the normal values observed prior to 2002.
Anomalies for autumn in 2002-2005 represent deviations from the normal near surface air temperature values which were observed from 1968-1996. Figure from Overland and Wang via NOAA
Anomalies for autumn 2007-2008 represent deviations from the normal near surface air temperature values which were observed from 1968-1996. Figure from Overland and Wang via NOAA
Anomalies (above) represent deviations from normal pressure surface elevations over the Arctic. Figure from Overland and Wang via NOAA
The elevated pressure surfaces above the North Pole persist into early winter and impact large scale wind patterns over the Northern Hemisphere, allowing cold are to move southward.
Figure (below) shows the changes in the Northern Hemisphere wind fields that are associated with late autumn surface air temperature and earlier sea loss. Blue and purple colors indicate areas with wind deviations below normal. Note the much reduced winds north of Alaska and western Canada.2
The reduction in winds opposes the usual atmospheric circulation patterns, allowing outbreaks of cold Arctic air to move southward.
It must be noted that there is considerable year-to-year variability in pressure fields, and that modifications of mid-latitude weather by wind patterns associated with sea ice reduction can be complex (involving storm track and longwave interactions).
However a consequence of the changes in Arctic atmospheric temperature and pressure, following loss of sea ice, is increased likelihood of cold air moving southward via teleconnections to impact weather at mid-latitudes.
As summer Arctic open water area increases over the next decades, we anticipate an increasing influence of loss of summer sea ice on the atmospheric northern hemisphere general circulation in following seasons with resultant impacts on northern hemisphere weather. For more information visit source: Loss of summer Arctic sea ice … and Arctic Future Web site
Anomalies (above) represent deviations from normal east-west winds over the Arctic. Figure from Overland and Wang via NOAA | <urn:uuid:aa367095-7fd6-4a63-8d9f-9662be58d267> | 3.828125 | 761 | Content Listing | Science & Tech. | 29.568929 |
Spent Rockets and Redundant Satellites in Space
These are links to the four main sections in the article:
When rockets and shuttles are launched into space they are accompanied by various rocket stages, fuel tanks and engines. These are needed to get out of the earth's atmosphere and to counter gravity.
The problem is that these parts are too heavy to carry around in orbit, so these appendages are left behind.
These objects are left in orbit, and are supposed to re-enter the earths atmosphere, burn up and render themselves harmless.
The problem is that these chunks of metal orbit at enormous speeds, up to 20 000 mph or 5 miles a second. This, as you can imagine is an unbelievably dangerous situation to encounter even though the shuttle can achieve these speeds as well. Of course an old fuel tank could crack 22 000 mph and wipe out a rocket and its crew.
At the moment there are thought to be at least 10 000 fuel tanks, rocket boosters and engines orbiting earth and it is only going to be a matter of time until the first major collision between, for example a shuttle and a piece of space trash, as it is affectionately known.
It is thought that every 9 years, the amount of space debris doubles. Complementing that hideous fact is the increase of celestial travel, which is expected to decrease that timespan significantly very soon.
Due to the great expanse that space covers, the heavenly bodies are spread out
over millions of light-years and are therefore not a worry at the
The most damaging consequences that the space trash will cause will probably
involve us on earth. In typical human fashion we seem to have shot
ourselves in the foot once again.
Yet another mistake has surfaced recently, and incredible as it may sound reports have been made that there have even been rubbish capsules sent into space containg volatile chemicals. Not only this but there are thought to be Russian spycraft, leaking radioactive material into space.
In our view the space trash problem is a significant mistake
that we have made in the space age. It is one that needs to be taken
incredibly seriously and some serious money has to be put towards the cure.
If they can find one.
Clearly the only way to prevent the rocket stages and satellites from roaming around space is to get them back to earth. This poses a 'catch 22' situation, because to get something into space at the moment you have to drop a rocket booster stage in space. So what clearly needs to be done is to find a solution to the rocket booster stage problem.
Possibly the rockets could rendevous with the rocket stage on entering the earth's atmosphere again, however to pull that off is almost impossible because of the incredible speeds that the rockets travel at.
Personally I think that an alternative method of launching should be investigated. Surely there is another way of getting the shuttles out into orbit. If it is not an available option at the moment, possibly there should be a reduction of launches. If it is absolutely neccessary to launch, a detailed check should be made to ensure that the debris is kept to a minimum. Maybe the stages could be equipped with their own engine to get them back into the atmosphere where they will burn up.
At the moment there seems to be no way of getting the stages and satellites back to earth or to destroy them without making more smaller debris. It is a great challenge and is still going to be a while until we figure out a solution, but if everyone keeps it on their minds and thinks about it for a while, we are sure to come up with an answer. | <urn:uuid:81409bff-834d-455a-997f-b1e4b5e9dcdd> | 3.03125 | 746 | Nonfiction Writing | Science & Tech. | 48.749564 |
Physics is the science of inanimate matter. Cosmology is that part of this science that deals with the universe as a whole. It is the oldest and the youngest branch of physics. It is the oldest because the heavens were studied in the ancient times, in Greece and in Asia. It is the youngest because it has been re-invigorated in recent times due to observations with new, high resolution astronomical instrumentation (such as the Hubble telescope) and theoretical analyses in the context of current thinking in particle physics and relativistic dynamics. Voluminous works have been written on the order of the night sky. (The Greek word, ‘Cosmology’, means ‘order’ (logos) of the cosmos.) Astronomical laboratories have been constructed since the ancient times to study this order. Examples are the Stonehenge monument, built by the ancient Britons thousands of years ago, and similar ancient astronomical viewing sites in India, China, Australia, Peru, Mexico, and from other cultures in the different corners of the world, designed by the ancient and aboriginal peoples to see the star formations and their locations, the locations of the sun and the moon, at the different times of the year. In these ancient viewings, there was no magnification.
Archive for the ‘Articles’ Category
Do we see any major paradigm changes coming in the 21st century in physics – changes of fundamental ideas that underlie the material world? My answer is: Yes. It is because the leading ideas of contemporary physics are in conflict. The fundamental bases of the two revolutions of 20th century physics – the quantum theory and the theory of relativity – are both mathematically and conceptually incompatible!1 The main paradigm that has dominated 20th century physics has been that of the quantum theory. Yet the theory of relativity has given many correct predictions since its inception at the beginning of the 20th century. It must then be incorporated into all of the laws that underlie physics.
The subject, “unified field theory”, has been frequently referred to in the scientific literature over the past centuries. Yet it is not generally understood what this means and why it is significant for science. My purpose in this essay is to explain what a unified field theory refers to, for the lay readers of science as well as the professional physicists.
The human race has understandably been fascinated over the ages with the universe. From the periods of ancient Greece and Asia, a primary pursuit has been the observations of the stars and planets of the night sky – the subject of astronomy – and the speculations to understand them.
Whenever a new theoretical approach, that is foundational in physics, is proposed to explain some natural phenomenon, in any subject from elementary particle physics to cosmology, it is usually rejected by the establishment with this argument: This idea cannot be true because it violates a particular principle. But what is this principle other than a dogmatic, absolute assertion about the underlying truths of physics.
Some of these principles are a true accounting and some are dogmatic assumptions that imply that there will be no change henceforth in physics. It is this attitude that stifles real progress in science. I will now list some of these principles and comment on them individually.
Over the past century and to the present time, science fiction writers have often used the theme of time travel in their stories – H. G. Wells’ The Time Machine, the recent film, Back to the Future, the TV series, Star Trek, etc. – to name a few.
This is all right so long as it is emphasized that these stories are purely science fiction, written for the purpose of entertainment. They are not works that pursue scientific truth!
A unique occurrence in the History of Physics was the confluence of two simultaneous scientific revolutions in the 20th century – the theory of relativity and the quantum theory. Based on these developments, it is interesting for the future of physics that when examined in terms of their conceptual and mathematical bases, these theories are incompatible. On the other hand, each of these theories requires an incorporation of the other to proceed toward its completion. This is the dilemma we face in these early decades of the 21st century: Which of the two theories should be abandoned and which should be maintained?
Erwin Schrödinger wrote an interesting essay entitled:”What is Life?”1 He calls for a different type of physical force to explain the maintenance of a living organism in terms of ’negative entropy’.
There has been voluminous writing on the subject of time, since the earliest ancient periods. One interesting dispute between the scientists and philosophers, on the one hand, and the theologians on the other has been this: Is there a beginning of time? It is the question that is the focus of this essay.
What will be the most significant paradigm change in 21st Century Physics? In my opinion it is the holistic model of matter, in its replacing the atomistic model. | <urn:uuid:687c79e8-64aa-4a8c-bfb8-b01010791d65> | 2.921875 | 1,016 | Content Listing | Science & Tech. | 38.677128 |
This animation illustrates a sample chemical reaction using the Quantum Trajectory Method introduced by Bohm. The scene depicts an activated complex of a model reaction. The reactant coordinate axis is oriented from left to right, and the product axis extends out towards the viewer. The vertical cylinders represent the probability of the state, and this vertical scale is exaggerated. A grid in the original video has been removed from this web version to economize the storage requirement of the animation file.
As the animation proceeds, the reactant complex moves to the right, turning the transition state corner toward the viewer as product is formed. Near the end of the animation, reactants can be seen to start retreating back toward the left, away from the transition complex.
Quantum Trajectory Method
(3.1 Mb) QuickTime
The computations were performed by Robert E. Wyatt. This animation was produced by J. David Adcock, a graduate student in Prof. Wyatt's research group. The graphics were rendered using the POV Ray Version 3.0.1 program. For more information, send e-mail to firstname.lastname@example.org.
Last modified: October 1, 1999 | <urn:uuid:41894124-8071-4550-8841-bafa8eb6c4aa> | 2.953125 | 243 | Truncated | Science & Tech. | 48.908365 |
Sunday 19 May
Belgrandiella (Belgrandiella hessei)
Belgrandiella fact file
- Find out more
- Print factsheet
Belgrandiella hessei is a tiny, poorly-known freshwater snail found only in a single underground stream in Bulgaria (1). Snails within the Hydrobiidae family rarely have any colouration in the shell, which is ordinarily white (3). Belgrandiella hessei is likely to be most easily distinguished from related species by features of its reproductive system (1).Top
Belgrandiella hessei is a troglobite, meaning it is not able to survive outside its underground cave habitat (1). Little is known about the biology of Belgrandiella hessei; however, members of the Hydrobiidae family generally feed on organic debris and algal films on the surface of aquatic vegetation and rocks (4) (5).Top
Belgrandiella hessei is classified as Vulnerable (VU) on the IUCN Red List (1).Top
Belgrandiella hessei is not known to be facing any major threats at present. However, in the foreseeable future visitors to the Temnata Dupka cave may potentially cause pollution, resulting in habitat destruction. As Belgrandiella hessei is restricted to a single stream, it is particularly vulnerable to any changes in the amount or quality of the water in the cave, which could quickly lead to this species becoming Critically Endangered (CR).Top
There are currently no specific conservation measures known to be in place for Belgrandiella hessei. Habitat monitoring should be implemented in order to prevent the future degradation of its habitat (1).Top
Find out more
Discover more about invertebrate conservation:
Find out more about the habitat of this species:
ARKive - Mediterranean Basin:
Conservation International - Mediterranean Basin:
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
- Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- A species or taxonomic group that is only found in one particular country or geographic area.
- Karst formation
- An area of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns.
IUCN Red List (November, 2011)
- Georgiev, D.G. (2011) New species of Belgrandiella (Wagner 1927) (Mollusca: Gastropoda) from caves in northern Bulgaria. Acta Zoologica Bulgarica, 63: 7-10.
- Hershler, R. and Ponder, W.F. (1998) A Review of Morphological Characters of Hyrobioid Snails. Smithsonian Institute, Washington.
- Clark, S. (2004) Hydrobiidae. In: Perez, K.E., Claark, S.A. and Lydeard, C. (Eds.) Showing Your Shells: A Primer to Freshwater Gastropod Identification. Freshwater Mollusk Conservation Society, Tuscloosa, Alabama.
- Barker, G.M. (2001) The Biology of Terrestrial Molluscs. CABI Publishing, Oxford, UK.
More »Related species
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rosy apple aphid
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The rosy apple aphid (Dysaphis plantaginea) deforms fruit, producing “aphis apples.” Its feeding activity causes leaves to curl about it, providing some protection from insecticide sprays. The life cycle involves plantain plants as alternate hosts from which the aphid returns to the apple tree to deposit eggs in the fall. It also attacks pear, hawthorn, and mountain ash. It...
What made you want to look up "rosy apple aphid"? Please share what surprised you most... | <urn:uuid:754383d7-f76a-4820-a92a-f0a2635e5874> | 2.859375 | 153 | Knowledge Article | Science & Tech. | 52.409019 |
3x-1/x^2-10x+26 Find all (real) zeros of the function Find all (real) poles of the function The function has... A horizontal asymptote at 0? A non-zero horizontal asymptote? A slant asymptote? None of the above
mass is 64.0 and volume is 16.0 what is the density?
What type of sentence pattern is "Traditional gas-powered cars are harmful to the environment." ?
describe a triangle with sides of 9in., 4in. and 6in.
I guess I just don't know what value to use for A in the Arrhenius equation.
At room temperature (about 20C) milk turns sour in about 64 hours. In a refrigerator at 3C, milk can be stored for about three times as long before turning sour. (i) Determine the approximate activation energy for the reaction that causes milk to sour, and (ii) estimate how lo...
Nitrogen monoxide reacts with hydrogen gas to form nitrogen gas and water (vapor). Write a balanced equation for this reaction. the reaction is experimentally found to be (approximately) first-order in H2 and second-order in NO. Write down the form of the experimentally-determ...
If your solving for Y your answer is y=x/2 +1 If your solving for X your answer is x=2y-2
what variable are you solving for?
I agree with that..
For Further Reading | <urn:uuid:635f27fa-d2ed-43ca-91ae-14ec16cdb0a3> | 3.25 | 320 | Comment Section | Science & Tech. | 72.248 |
A LUNG-inspired hydrogen fuel cell can cut the amount of expensive catalyst needed and increase efficiency, its designers claim.
Despite decades of research, hydrogen fuel cells have failed to replace combustion engines in cars, thanks in large part to the cost of their platinum catalysts, says Signe Kjelstrup at the Norwegian Academy of Science and Letters in Oslo.
So Kjelstrup's team designed a cell that uses less platinum. It uses channels modelled on the bronchial structure of the lungs to supply hydrogen and oxygen gas to their respective electrodes. This helps to spread the gases more uniformly across the catalyst than current channel designs and provides a greater surface area so less platinum is needed, Kjelstrup claims (Energy & Fuels, DOI: 10.1021/ef100610w).
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:efa744a6-5708-47d4-b2d6-8f0e2c49e462> | 3.859375 | 195 | Truncated | Science & Tech. | 40.825711 |
Even though the risk of an accident is low, most of us aren’t prepared to drive our cars without insurance. The consequences of an uninsured fender bender are too great. So we prudently spend a small amount of money to hedge our bets against an unlikely but real risk.
Former Apollo astronaut Russell L Schweickart, chairman of the B612 Foundation, makes a compelling case that we should apply the same logic to the small but real and potentially catastrophic risk of an asteroid collision with the Earth.
The prospect of just such a natural disaster from space was highlighted in December 2004, with the re-discovery of the Near-Earth Asteroid (NEA) 99942 Apophis. For a few days, while predictions of its path were still being refined, estimates of the risk that the 51 million ton space rock would strike the Earth reached 1 in 37. Further observations ruled out an impact, but on Friday, April 13th, 2029, the asteroid will pass within 20,000 miles of the Earth’s surface. That’s a very close shave in cosmic terms – roughly the height at which communications satellites orbit.
A small chance remains, about 1 in 5500, of an impact during a later encounter in 2036 – but there’s actually a higher probability of some as yet uncataloged object hitting us first. The vast majority of NEAs remain undiscovered. There is a survey currently under way to find all the Earth-crossing NEAs over a kilometer in size – this will give a good understanding of the baseline threat from the estimated 1100 or so ‘planet killer’ asteroids. The Spaceguard survey is currently on target to have cataloged 90% of the NEAs of that size by 2008.
But that’s only a part of the risk. There are also an estimated 200,000 to 300,000 NEAs out there between 100 and 1000 meters in size. Any one of those might conceivably have our name on it. Indeed, such a rock is thought to hit the Earth once every two to four thousand years, with a destructive force on the order of a 80 megaton nuclear bomb.
But there is currently no official program or funding for a search to catalog the asteroids in this class. And if one were to be discovered next week, don’t take any comfort from the scenes of steely-eyed NASA missile men saving the day in movies such as Deep Impact and Armageddon: NASA currently has no program or mandate to develop an asteroid deflection capability.
So what, if anything, should we do? To come back to the automobile analogy, the time has come to invest in a little insurance. For the first time in the history of our planet, the technical capability exists to detect and deflect an incoming impactor, thereby averting a natural disaster of colossal proportions. The prudent course of action is to spend a modest amount of money now, to be better prepared for this eventuality in the future.
That’s where the B612 Foundation comes in. The B612 Foundation is a non-profit organisation comprised of scientists and astronauts concerned about the current lack of action to even lay the engineering groundwork to protect the Earth from impacting near Earth asteroids. Their goal is to get a demonstration mission flown by 2015 that will measurably alter the orbital parameters of a target asteroid in a controlled manner. For roughly the cost of a NASA Discovery-class mission, a prototype of their gravity tractor concept could prove out the capability to protect our planet long-term from the shooting gallery that is the inner solar system.
The gravity tractor in operation (Dan Durda/B612 Foundation)
I spoke to Rusty Schweickart about B612 and their efforts to promote the purchase of a little prudent ‘collision insurance’:
OotC: Asteroid impacts on the surface of the Earth are a form of natural disaster distinct from others, in that we now have the technology (if not yet a demonstrated capability) to detect and prevent collisions before they occur. Why isn’t more being done to take advantage of that?
Schweickart: First, the general public isn’t yet aware enough of the threat itself to have any sense that prevention is of importance. Consequently the pressure on Congress to take action on this issue is low to non-existent.
B612 Foundation is continually wrestling with the question, given its extremely limited resources, of where to apply its efforts, lobbying Congress for action, educating the general public, or focusing on our primary goal of getting a demonstration of deflection capability off the ground.
OotC: The B612 Foundation grew out of a one day workshop studying asteroid deflection techniques in 2001. What led you to that workshop, and subsequent involvement with B612?
Schweickart: At the Association of Space Explorer’s (ASE, www.space-explorers.org) annual Congress in Madrid in 2000, astronaut Franklin Chang-Diaz gave an update on the development of his VASIMR (plasma rocket) prototype. In passing Franklin mentioned that it could, among many other things, be used for asteroid deflection. Ed Lu and I spoke briefly afterward with Franklin about our shared interest in that application.
Subsequently Ed gave a lecture at Princeton where he and Piet Hut (Institute for Advanced Study) found common interest in the subject and agreed to call a meeting of other interested parties to discuss it. Ed called the meeting at NASA/JSC in October, 2001, invited me to attend and out of that we formed the B612 Foundation.
OotC: The B612 Foundation’s stated goal is to significantly alter the orbit of an asteroid in a controlled manner by 2015. How do you envision achieving that?
Schweickart: In any way possible, but with recognition that timing is important. Clearly the gravity tractor concept, with no new technology needed and no detailed knowledge needed re asteroid characteristics, can be accomplished in relatively short order, provided the money and motivation (or authorization, in the case of NASA) is available.
OotC: What level of financial resource will that require? What funding sources or strategies are you pursuing?
Schweickart: The specific answer to this will require some detailed preliminary mission analysis. This mission, however, is far simpler than most Discovery class missions since it need carry virtually no scientific payloads, and Discovery missions fall in the $300M realm.
At the moment we’re looking at what options for getting this mission underway make most sense.
OotC: While reading your website, I found these two simulations of what would happen if asteroid 2004MN4 (Apophis) were to strike in 2036 off the coast of California, or in the Gulf of Mexico. The risk of this actually happening is currently quantified as less than 1 in 5500, nonetheless these video simulations make sobering viewing. What sort of responses do you get when you talk to people about the risks from asteroids, and the B612 Foundation’s goals?
Schweickart: They are astounded by the power of asteroid impacts and incredulous that nothing is being done. AND… very few of the general public have been exposed to the issues so graphically illustrated in Steve Ward’s simulations. As you know everyone has a difficult time in dealing with very low probability events which have extremely high consequences. According to the economic loss model developed by Drs. Steve Ward and Steve Chesley the cost of the Pacific Ocean impact you refer to (modelled on an Apophis impact) is about $400 billion for infrastructure losses alone (i.e. destruction of “stuffâ€). I have no idea of what the total cost might be were one to count the loss of life and the general impact on the global economy.
One way for the ordinary person to grasp the situation is to think about car insurance as an analog. According to government statistics the probability of the average American driver having a reportable accident on any given day is about 1 in 10,000. If you assume that the average car costs $30,000 then multiplying the two together gives the amount one would rationally spend to insure against that loss, i.e., about $3/day.
In the case of Apophis the cost (infrastructure loss) is $400B and the current probability of impact (occurrence) is 1 in 5500 yielding a rational insurance expenditure of $7.3 M to mitigate against that potential loss. In fact we’re spending essentially $0.00.
An interesting additional note is that in the case of auto insurance that expenditure does nothing whatever to prevent an accident from occurring.. it just makes the replacement car (or repair) easier to take. In the asteroid case the expenditure can actually prevent the occurrence of the event itself. (for the mathematicians out there, the probability of occurrence would need to get up to perhaps 1 in 50 before expenditure on an actual deflection were taken on.)
OotC: B612 has had a dialog with NASA regarding a mission to place a transponder on Apophis (2004MN4) to more precisely determine its orbit. Also, in a recent speech to the American Geophysical Union, NASA administrator Michael Griffin mentioned the Foundation, saying “And I’m also very intrigued by Ed Lu and Rusty Schweickart’s ideas about nudging large near-Earth asteroids before they can pose a threat to humanity. We will most certainly continue our work to discover large asteroids close to the Earth.†It sounds like the Foundation’s plans are well received at NASA: Can you describe your relationship with them, and any possibilities for working together?
Schweickart: Our relationship with NASA is just fine. The problem is not our relationship but rather the fact that NASA has no assigned responsibility or budget for protection of the Earth from asteroid impacts. Nor does anyone else in government, US or elsewhere in the world. NASA’s circumstance is currently one where any money they do spend on this (even without authorization) would have to come out of something else (exploration or science) that they are doing. A zero-sum game, in other words. NASA’s role would have to be expanded to include a small, but real public safety component.
OotC: Do you see any synergies between B612’s goals and NASA’s plans to return to the Moon?
Schweickart: Not much. On the other hand going on to Mars might well incorporate an intermediate step of going on to certain near-Earth asteroids, for resource exploitation purposes, and others. (see Tom Jones’ Stepping stones to mars: The asteroid option, Aerospace America, June 2005)
OotC: Where are you at in terms of mission planning? Is the gravity tractor now your preferred mission approach?
Schweickart: Yes, the gravity tractor can be built and tested now, and by coincidence should we actually need an Apophis deflection (unlikely but possible) the gravity tractor is capable of doing the deflection job.
OotC: Has the data returned by previous asteroid missions such as NEAR, Deep Impact and even Hayabusa been a factor in the design changes from the original direct-contact plasma rocket concept?
Schweickart: Any information from or about asteroids is of use in designing any kind of deflection capability. Our earlier “asteroid tugboat†concept needs both new technology and more data than is currently available about the nature of asteroid surfaces. Near and Hayabusa data can definitely contribute to design, but so far the data needed to design a method to attach to an asteroid after docking is not available.
OotC: How closely is the B612 Foundation associated with the groups searching for NEAs – and is there currently an organised program to catalog the approximately 200,000 NEAs ranging in size between 50 and 1000 meters?
Schweickart: We’re in regular contact with both the JPL (Sentry) people and the University of Pisa (NEODyS) people… it’s a relatively small community. There have been many recommendations made (but none heeded) to modify the goal of the Spaceguard Survey down to 100-140 meter diameter asteroids. Congressman Dana Rohrabacher (R-CA) has sponsored legislation to allocate $20M for the next several years to improve the discovery capability, but no revision of the Spaceguard goal has yet been proposed or passed into law.
OotC: The risk of an asteroid collision is statistically low on any given day, but quite real over time – and the consequences if one were to occur are extreme. Given that, I would imagine people will want to see the goals of the B612 Foundation advanced with prudent speed. What can interested members of the public do to help?
Schweickart: The most important thing is to learn about the environmental (cosmic) circumstance in which the Earth is embedded. There’s lots of information on the web, most especially on JPL’s site at http://neo.jpl.nasa.gov. Beyond that the only option is to contribute… most easily in terms of letters to Congresspersons. There are also, of course, financial contributions to B612 Foundation to support our efforts. We’ve got Paypal and credit card buttons on the Contact Us page of our website, and we welcome whatever folks can contribute. | <urn:uuid:3706d7fa-3a2e-4329-b3e5-f22811d00e59> | 2.875 | 2,853 | Audio Transcript | Science & Tech. | 44.9063 |
HTML forms -- what would the web be without them? After you complete and submit a form, the input is usually sent to some script that processes it. The script may send the input via e-mail or insert it into a database.
Creating this type of functionality is usually a snap. First, you create an HTML form with whatever fields you want the user to fill out. Then you create a script that does something with the user input it receives from the form. The final step is to make the form's ACTION attribute point to the script, like this:
That's it. User input is collected via the form and processed by the script. Piece of cake, right?
But what if the user has to complete more than one form?
The tricky part is transferring the user's input from one form to the next until it reaches the script.
We must somehow store the user's input from previous forms as fields in the current form the user is on. That way all the answers will be carried over when the user submits the form.
To help accomplish this task, we'll use hidden input fields. If you've played around with forms before you're probably already familiar with them. They look like this:
All we're doing here is getting the name and value of an element and using them to construct a hidden input field. This segment of code serves as a template for generating the hidden input fields.
To sum it up, the script will loop through each element stored in $HTTP_POST_VARS and generate a hidden input field for it.
Just make sure you do the following:
1. Copy and paste the script somewhere between the
tags in whatever form(s) you want.
2. Use POST in the form's METHOD attribute. If you don't specify anything, it will use GET and the script won't work.
The following is the uncut version of the script, with comments and all. Feel free to modify the script to suit your needs.
$name; // Represents the name of the elements in $HTTP_POST_VARS
$value; // Represents the value of the elements in $HTTP_POST_VARS
// Do while there is an element in $HTTP_POST_VARS...
while (list($name, $value) = each($HTTP_POST_VARS))
/* ...get the name and value of the element and use it to construct a hidden input field.
Then go back to the beginning of the loop and do the same thing with the next element. */
echo "<input type=\"hidden\" value=\"$value\" name=\"$name\">\n"; | <urn:uuid:9ba887bb-b408-44b3-b4c8-c6125346aad8> | 3.3125 | 550 | Tutorial | Software Dev. | 73.278694 |
|Jun26-10, 06:39 PM||#1|
resistor power rating
i have a question about resistors. i thought they were described by their resistance - 20 ohm, 40 ohm, 2 Megaohm, etc.
how come I see "power" values on resistors? for example my lightbulb says 40 watts. but i thought the power is simply P = V^2/R and that would depend the voltage of my power outlet whatever that happens to be. The power would only be partially determined by the lightbulb. so what does it mean to see a power value on a resistor?
|Jun26-10, 06:52 PM||#2|
Q, If you put too much current through your resistor it will get too hot. There are different resistor types intended for different degrees of power they need to dissipate. Maybe P=I^2 * R, so it's a current limiting rating.
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The problems with decoherence and the many-worlds idea have led a sizable minority to support a view called GRW theory, according to Leggett. The concept was put forward in 1986 by GianCarlo Ghirardi and Tullio Weber of the University of Trieste and Alberto Rimini of the University of Pavia.
In the GRW scheme, the wave function of a particle spreads out over time. But there is a small probability that the spreading wave “hits” a mysterious “something” in the background. The wave function suddenly becomes localized. Individual particles have only a small chance of a hit, about once every 100 million years. But for a macroscopic cat, the chance that at least one of its roughly 1027 particles makes a hit is high, at least once every 100 picoseconds. The cat never really has a chance to enter any kind of superposition. Hence, there is no need for decoherence: the macroscopic state of the cat results from spontaneous microscopic collapses.
A few problems plague this model. One is that the timing factor that triggers the hit is entirely arbitrary; proponents simply choose one that produces reasonable results. More important, though, is the source of the trigger. “Basically, [there is] a sort of universal background noise that cannot itself be described by quantum mechanics,” Leggett explains. The noise is not simply random processes in the environment; it has a distinct mathematical flavor. Roger Penrose of the University of Oxford argues in his book Shadows of the Mind that the trigger may be gravity, which would neatly sidestep certain technical objections.
Other, more radical proposals abound. The most well known was put forth by the late David Bohm, who postulated that “hidden variables” underpin quantum mechanics. These variables—describing properties that in a way render wave functions as real forces—would eliminate the notion of superpositions and restore a deterministic reality. Like the many-worlds idea, Bohm’s theory cannot be verified: the hidden variables by definition remain, well, hidden.
Given such choices, many working physicists are subscribing to decoherence, which makes the fewest leaps of faith even if it arguably fails to resolve the measurement problem fully. “Decoherence does answer the physical aspects of the questions,” Zurek says, but does not get to the metaphysical ones, such as how a conscious mind perceives an outcome. “It’s not clear if you have the right to expect the answer to all questions, at least until we develop a better understanding of how brain and mind are related,” he muses.
Bigger superpositions may enable researchers to start ruling out some theories— GRW and decoherence predict them on different scales, for instance. “What we would like to do is to go to more complex systems and entangle more and more particles” than just the mere 10 trapped before, Haroche of the ENS says. Future NIST experiments are particularly suited to serve as “decoherence monitors,” Monroe contends. “We can simulate noise to deliberately cause the superposition to decay.” Leggett has proposed using sensors made from superconducting rings (called SQUIDs): it should be possible to set up large currents flowing in opposite directions around the ring simultaneously.
Still, there’s a long way to go. “Even in the most spectacular experiments, at most you’ve shown a superposition for maybe 5,000 particles. That’s a long way from the 1023 characteristic of the macroscopic world,” says Leggett, who nonetheless remains supportive. “My own attitude is that one should just try to do experiments to see if quantum mechanics is still working.”
Shrinking transistors, now with features less than a micron in size, may also lead to insights about the quantum-classical changeover. In a few years they may reach dimensions of tens of nanometers, a realm sometimes called the mesoscopic scale. Da Hsuan Feng of Drexel University speculates that quantum mechanics perhaps really doesn’t lead to classical mechanics; rather both descriptions spring from still undiscovered concepts in the physical realm between them. | <urn:uuid:be93bb8f-fe5e-4b3e-938e-6f240ae1f6e8> | 2.953125 | 893 | Knowledge Article | Science & Tech. | 37.218361 |
Most Polychaeta have pairs of parapodia, paddle-like appendages, running down the sides of their worm-like bodies. The parapodia are unjointed fleshy appendages, with upper and lower lobes terminating in a set of stiff bristles. These bristles may be used for walking, swimming or digging, depending on the lifestyle of the polychaete in question. A few polychaetes, known as fire-worms, have bristles which come equipped with a stinging poison.
The prostomium, the front portion of the head which extends out above the mouth, bears four eyes, palps and tentacles, an impressive array of sensory organs. The eyes of some polychaetes are quite complex, and a single individual may have eyes using two different mechanisms for vision. The polychaete Fabricia has eyes at both ends of its body, a useful thing to have, since it usually swims backwards.
In contrast to free-swimming species, sessile polychaetes will often lack complicated sense organs on their heads. Rather, they may come equipped with large spirals of feather-like tentacles, often brilliantly colored and quite beautiful. With these, the worm fans the water for food particles and small critters.
The earliest polychaetes had no jaws, but some later polychaetes developed hard jaws, which are sometimes mineralized with iron oxide. Such polychaete jaws are fairly common in the fossil record, and are known as scolecodonts. These are borne on a muscular proboscis which allows the jaws to be either retracted or extended. Some polychaete jaws are rather complex, having as many as nine individual parts. | <urn:uuid:808f0439-e92f-4a29-be24-1098c4707333> | 3.625 | 352 | Knowledge Article | Science & Tech. | 35.815 |
Artist's concept of a rocky planet in orbit around a distant star.
Click on image for full size
NASA, ESA and G. Bacon (STScI)
Planets around other Stars
Did you know that about 200 planets have been found around distant stars? The first planet around a star like our Sun was found in 1995. Since then, a new planet has been found almost every month!
The star and its planet move around each other. The planet moves in a wide orbit. The star just wobbles slightly. This causes a Doppler shift of the light. Most of the distant planets were discovered this way.
Some of the planets pass in front of their star. This blocks out some of the light. It makes the star look dimmer. It's like a solar eclipse. The planet only covers a small part of the star. Only a few of the planets pass in front of their stars.
All of the new planets are too far away to see directly. We can only see their effect on the star that they orbit.
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Satellites in the 1960's looked for a type of light called Gamma Rays. They found bursts of Gamma Rays coming from outer space! They can't hurt you. They are stopped by the Earth's atmosphere. We have...more | <urn:uuid:5a17391f-d649-4117-9c10-897a3df321a1> | 3.734375 | 597 | Content Listing | Science & Tech. | 73.438082 |
The folding of the Pacific plates that accompany the sinking of Indonesia during the 7 of 10 scenarios involves, as we have explained, the Mariana and Philippine plates tilting and flattening westward. This is nothing more than an existing trend, so is just a matter of the plates moving along faster in the direction they are already going. The Mariana Trench is a zone where the Pacific Plate is subducting under the Mariana Plate. The Pacific Plate curves down at this point, plunging under the Mariana Islands which ride on the Mariana Plate. The trench will be suddenly closed, so that rather than a trench there will be the Pacific Plate scraping along the Mariana Plate, and giving the Mariana Islands a temporary boost up as the plate tilts during this process. The Mariana Plate, thus tilted, will slide its western edge down along the Philippine Plate, as the Mariana Plate subducts under the Philippine Plate and this process will now be accelerating. The Philippine Plate likewise tilts its eastern side up, dropping its western side down. The exaggerated tilt accelerates the subduction of the Mariana Plate, and also accelerates the subduction of the Philippine Plate under the tongue holding Indonesia. The tilting of the Philippine Plate give the Philippine Islands a temporary boost up also, as these islands ride on the eastern edge of the tongue holding Indonesia. Meanwhile, the tongue holding Indonesia has been plunged down, ultimately pulling both the Mariana and Philippine plates down as they fold so the Mariana Islands do not have a permanent boost in elevation. Nancy has explained this as a deck of cards, scattered on a table top, being pulled together into a deck. The plates are folded against one another.
If the pressure on the point where the Pacific Plate noses into Japan was immense enough to cause the recent 9.1 quake there, what do you suppose the pressure is
on the edge of the Philippine Plate, and the vulnerable Mariana Trench? This is why in our 7 of 10 scenarios we predicted that these plates would fold. The
Mariana Trench collapses, tilting the Mariana Plate and pushing it under the Mariana Islands, and the Philippine Plate tilts and pushes under the Philippine Islands.
This process has started, but hardly completed as yet. Then look at the point where the Pacific Plate noses into the plate tongue holding Indonesia. This again is a
pressure point, and the fracture of small platelets there shows how much pressure has been applied in the past.
The reason the Japan quake happened at this time is because the points south have been compressing, making the Japan point the point of greatest pressure. The Indo-Australian Plate had been tilting in mid-2010, sinking the Indus River valley on the Pakistan/India border by 10 feet. This plate is also rising at the New Zealand end, as the recent quakes in Christchurch show. Indonesia has been folding like an accordion and sinking since December, 2010. And on occasion the buoys show that the Mariana and Philippine Plates have folded, somewhat. What now? Since subduction under Japan has eased the pressure, the pressure will return to points south again. This will prove to be iterative to some degree, until the 7 of 10 scenarios in Asia have completed.
Plate tectonics involves various dramas on the plate borders - clash or subduction bounaries, slip-slide boundaries, and stretch zones boundaries. Where plate
borders clash, one plate pushing against another, this most often has one of the plates either riding over or pushing under the other. Such border clashes are
invariably accompanied by massive quakes in the range of magnitude 8-10. Japan, the Andes, the West Coast of the N American continent, and the Himalayas are
examples of such border clashes. During such clashes there will be a point where the pressure is greatest, and that will be the spot where a quake will occur.
The Pacific is currently compressing, in step with a widening Atlantic, all caused by the jerking around that planet Earth is enduring during the daily Earth wobble caused by the magnetic push/pull from Planet X. The position of the Moon and its resultant gravity pull has scant influence on the matter. The parts of the Pacific Plate are themselves folding, down along the island chain that forms the Hawaiian Islands and on down to the Society Islands. These adjustments are primarily silent, for man, who does not have seismographs located on the deep ocean floor, but can be detected on occasion by the ocean buoys which show heaping water from one end of the Pacific to the other.
The Philippine Plate is tilting, plunging under the Philippine Islands and lifting slightly on the other end near the Mariana Islands. The Mariana Plate is also tilting and plunging under the Mariana Islands. Thus, pressure from the central Pacific is being relieved by this movement, where pressure on the north Pacific requires adjustments at Japan. A glance at a plate tectonic map shows that the recent quake in Japan happened at precisely the point where the pressure from the compressing Pacific would be the greatest. Now that an adjustment has been made at this point, further folding of the Philippine and Mariana Plates can occur. This may be iterative, returning to the Japanese coast on occasion, or to New Zealand, which is lifting. The pressure point will move, and result in a quake.
ZetaTalk March 19, 2011
We have predicted that the South Islands of Japan will be greatly affected as the 7 of 10 folding of the Mariana Trench and tilting and folding of the Mariana and
Philippine plates finalizes. Tsunami as high as 135 feet will occur as the plates tilt during the folding, acting like a giant platter under the sea to lift the water and force
it west. The Philippine Islands and the coast of China are likewise vulnerable to this tsunami. The size and force of this tsunami depends upon how rapidly the
Mariana and Philippine plates tilt, and to date this has been a slow process. Where it appears that Taiwan and the island of Luzon in the Philippines might disappear
when the Philippine Plate tips and folds, dropping its western parts, there is confusion about the exact plate boundary and these land masses are more firmly affixed
to parts west than to the Philippine Plate.
Nevertheless, the jolting that occurs when one plate slides under another, even though the slide is ameliorated by the underlying plate dropping at a radical angle, is a shock. We have predicted jolts as strong as a magnitude 8, though called magnitude 7 by the USGS, for Japan. Japan attempts to prepare for tsunami and quakes as much as any country in the world, and will likely survive the 7 of 10 plate folding going on nearby without undue disasters. It will be the next round of quakes that will cause devastation to Japan, when the Northern Hemisphere adjusts leading into the New Madrid and European tsunami. Japan's March 11, 2011 quake was deemed a 9 by the USGS though in truth it was a greater magnitude and created much devastation. This is an example of what to expect during the big quakes to afflict Japan preceding the New Madrid adjustment and of course during the hour of the pole shift itself. Yes, infrastructure will be shattered and ships capsized at that time.
ZetaTalk August 13, 2011
Note 7 of 10 Plate Movement commentary. | <urn:uuid:dcff1aa4-1bd6-4fd7-b1a8-0571e4645d22> | 3.6875 | 1,517 | Personal Blog | Science & Tech. | 43.281917 |
Turing machines are theoretical computers used to solve problems in mathematics, formal logic, and computer science. They form the basis of the modern concept of a computer, one with rewritable memory and programs. And as you’ll see below, they can be made from many things, especially very small things.
This is a Turing machine constructed using something nerds lovingly refer to as an “elementary cellular automaton,” meaning that it is a discrete model of interacting cells with “on” and “off” states.
The model shown above, known as Rule 110, is said to be “Turing complete,” it is capable—in theory—of modeling the behavior of a Turing machine and running any calculation or computer program.
Is it amazing that these little blocks can run any calculation or computer program? Is it elegant that we can do so much with so little? Does the similarity between simple computers and simple organisms point to something larger? How can you tell?
If you ever run out of storage space in the cloud, remember: there’s always rule 110. | <urn:uuid:84dd7823-bd03-4609-bd96-c1ec5b9c1895> | 3.921875 | 230 | Personal Blog | Science & Tech. | 44.285773 |
Hot answers tagged safety
A neutralization reaction occurs between Brönsted acids and bases to form a salt. In this case, you have to add a Brönsted base to neutralize your acid. If the final pH is important, you should work out the exact quantity of base to add. Otherwise, just use litmus paper to check the pH of your solution, and add base until it's neutral. EDIT In view of the ...
Only top voted, non community-wiki answers of a minimum length are eligible | <urn:uuid:69b9dce3-24e9-4b2c-a52e-10770f9c2b94> | 3.140625 | 105 | Q&A Forum | Science & Tech. | 61.140588 |
If you wanted to turn a rat into a fearless critter, unfazed by cats or bigger rats, the best way would be to neutralise a small pair of tiny structures in its brain called the dorsal premammillary nuclei, orPMD. According to new research by Simone Motta at the University of Sao Paolo, these small regions, nestled within a rat’s hypothalamus, control its defensive instincts to both predators and other rats.
But not all neurons in the PMD are equal. It turns out that the structures are partitioned so that different bits respond to different threats. The front and side parts (the ventrolateral area) are concerned with threats from dominant and aggressive members of the same species. On the other hand, the rear and middle parts (the dorsomedial area) process the threats of cats and other predators. And both areas are distinct from other networks that deal with the fear of painful experiences, such as electric shocks.
This complexity is surprising. Until now, scientists have mostly studied the brain’s fear system by focusing on an area called the amydgala, which plays a role in processing memories of emotional reactions. And they have generally assumed that fearful responses are driven by the same networks of neurons, regardless of the threat’s nature.
There’s good reason to think that. Hesitating in the face of danger is a sure-fire way to lose one’s life, so animals respond in a limited number of instinctive ways when danger threatens. They freeze to avoid detection, flee to outrun the threat, or fight to confront it. These automatic “freeze, fight or flight” responses are used regardless of the nature of the threat. Rats, for example, behave in much the same way when they are menaced by cats or electrified floors alike, and actually find it very difficult to do anything else.
This limited repertoire of action convinced scientists that animals process different fears in the same way, relying on the same network of neurons to save their hides from any and all threats. Motta’s research shows that this idea is wrong, certainly for rats and probably for other mammals too. The brain’s fear system isn’t a one-size-fits-all toolkit; it has different compartments that respond specifically to different classes of threats.
The wiping of unwanted memories is a common staple of science-fiction and if you believe this weekend’s headlines, you might think that the prospect has just become a reality. The Press Association said that a “drug helps erase fearful memories“, while the ever-hyperbolic Daily Mail talked about a “pill to erase bad memories“. The comparisons to The Eternal Sunshine of the Spotless Mind were inevitable, but the actual study, while fascinating and important, isn’t quite the mind-wiper these headlines might have you believe.
The drug in question is propranolol, commonly used to treat high blood pressure and prevent migraines in children. But Merel Kindt and colleagues from the University of Amsterdam have found that it can do much more. By giving it to people before they recalled a scary memory about a spider, they could erase the fearful response it triggered.
The critical thing about the study is that the entire memory hadn’t been erased in a typical sci-fi way. Kindt had trained the volunteers to be fearful of spidery images by pairing them with electric shocks. Even after they’d been given propranolol, they still expected to receive a shock when they saw a picture of a spider – they just weren’t afraid of the prospect. The drug hadn’t so much erased their memories, as dulled their emotional sting. It’s more like removing all the formatting from a Word document than deleting the entire file. Congatulations to Forbes and Science News who actually got it right.
Kindt’s work hinges on the fact that memories of past fears aren’t as fixed as previously thought. When they are brought back to mind, proteins at the synapses – the junctions between two nerve cells – are broken down and have to be created from scratch. This process is called “reconsolidation” and scientists believe that it helps to incorporate new information into existing memories. The upshot is that when we recall old memories, they have to be rebuilt on some level, which creates an opportunity for changing them.
A few years ago, two American scientists managed to use propranolol to banish fearful responses in rats. They injected the animals in their amygdalae, a part of their brains involved in processing emotional memories. The drug didn’t stop a fearful memory from forming in the first place, but it did impair the memory when the rats tried to retrieve it. Now, Kindt has shown that the chemical has the same effect in humans. | <urn:uuid:9feb00f2-d616-4adb-9dc5-63de24152de2> | 3.4375 | 1,017 | Personal Blog | Science & Tech. | 46.657846 |
Readers have inquired recently about how tropical speleothems are calibrated to temperature. Judd Partin, Kim Cobb (both of Georgia Tech) and associates wrote an excellent article last year (Cobb et al, EPSL 2007) on detailed O18 observations near a Borneo speleothem about which they had published. They introduced the article with the following observation that will resonate with most CA readers:
Detailed on-site analyses of the relationship between large-scale climate and local rainfall d18O are critical to accurate climatic interpretations of many terrestrial paleoclimate reconstructions based on ice core, tree ring, or stalagmite d18O, but few such studies exist.
They report a pronounced variation in northern Borneo dO18 values as follows (see graphic below):
Rainfall d18O values range from −11.5‰ to −2.5‰, with a mean of − 6.7 ± 2.8‰. A ~ 6‰ seasonal cycle is visible, with lighter values (− 10‰) occurring from August to October and heavier values (− 4‰) occurring from December to March.
Fig. 4. Interannual variability of northern Borneo precipitation (gridpoint centered at 3.75°N, 113.75°E,CMAPdata) (Xie and Arkin, 1997) plotted with the Southern Oscillation Index (http://www.cpc.noaa.gov/data/indices/). Both timeseries have been filtered with a 2–7 yr bandpass filter
They observe that these substantial variations cannot be explained by local temperature variations since:
Temperatures lie between 26 and 27°C year-round, as recorded by on-site temperature loggers.
Indeed, they note that this viewpoint is also held by other students of tropical speleothems:
In the tropics, stalagmite d18O records are largely interpreted as rainfall d18O reconstructions, with a minor role for relatively small temperature changes that occur in the tropics.
However, this seemingly plausible explanation cannot be transposed directly to northern Borneo as precipitation amount is not nearly as variable as the dO18 fluctuations. Cobb et al:
The ~ 6‰ seasonal cycle in rainfall d18O cannot be ascribed to seasonality of precipitation amount, which has a weak semi-annual nature, with relative rainfall maxima occurring in late boreal spring and from September to December (Fig. 2). In fact, a low correlation between Mulu rainfall d18O and Mulu precipitation (R = 0.05) suggests a limited role for a local “amount effect” stemming from fractionation in a local convective event. Likewise, the observed seasonal variability cannot be explained by variations in source water d18O, which are less than 1‰ across the Warm Pool (Brown et al., 2006).
An interesting conundrum. Strong annual variations in dO18, but not explainable either by temperature or precipitation amount.
The authors conclude that the strong variations are caused by changes in seasonal wind direction, with low dO18 coming when the wind direction leads to a water source further from northern Borneo and thus greater rainout.
Rather, we hypothesize that the observed rainfall d18O seasonality is caused by the increased rainout, and hence greater isotopic fractionation, that occurs during late boreal summer, and vice versa during late boreal winter. In late boreal summer, the ITCZ has reached its northernmost position, and mean southeasterly winds carry moisture from the Java Sea to Gunung Mulu, leading to significant rainout as moisture is carried long distances over the mountainous interior (Fig. 3). The remaining water vapor would be significantly depleted in d18O via both the “degree of rainout” and orographic fractionation mechanisms. Conversely, during late boreal winter, when the ITCZ lies south of Borneo, northeasterly winds carry moisture from the Sulu and South China Seas to Gunung Mulu (Fig. 3). The heavier rainfall d18O values measured during late boreal winter are consistent with the relatively short moisture pathway during this time of year.
All of which is fairly sensible.
People who like Hubert Lamb (of Little Ice Age and Medieval Warm Period fame) can hardly cavil at someone using wind direction as a proxy. So readers should not immediately start piling on to the obvious point that these dO18 records merely indicate wind direction, as Hubert Lamb placed great importance on prevailing wind directions as indicator of centennial climate fluctuations.
Equally, however, climate scientists who want to use such information in Mannomatics and the like need to remind themselves that the best information that they are getting from such records is information on wind direction. If you had detailed measurements of wind direction in northern Borneo (or south China or Yemen), how helpful would that be in determining global temperature?
Cobb, K. M., J. F. Adkins, J. W. Partin, and B. Clark. 2007. Regional-scale climate influences on temporal variations of rainwater and cave dripwater oxygen isotopes in northern Borneo. Earth and Planetary Science Letters 263, no. 3-4: 207-220. http://shadow.eas.gatech.edu/~kcobb/cobb07.pdf | <urn:uuid:77014b4d-3abe-41f6-91ea-3cc7875e35c9> | 2.984375 | 1,122 | Academic Writing | Science & Tech. | 42.980275 |
Leonardo of Pisa or Leonardo Pisano (Pisa, c. 1170 - Pisa, 1250), also known as Fibonacci, was an Italian mathematician. He is best known for the discovery of the Fibonacci numbers, and for his role in the introduction to Europe of the modern Arabic positional decimal system for writing and manipulating numbers (algorithm).
It is believed that his nickname came from the latin "filius bonacci" which means "son of Bonacci". Fibonacci wrote the book "Liber Abaci" (Book of Abacus). He is also known for a major contribution called the Fibonacci series. Fibonacci series starts by 1,1,2,3,5... The numbers in the series follow this pattern: each one is the result of the sum of it's previous two numbers. The numbers in this series have the quality that if you divide each of them by the one before them, the result is an approximation to the golden ratio. The larger the two consecutive Fibonacci numbers are, the closer their ratio is to the irrational golden ratio.
It is believe that Fibonacci series explains in some way nature's growth path, taking into account the plenty of times the golden ratio is rediscovered in nature.
Bibliography: Hakim, J. "The story of science, Aristotle leads the way" Smithsonian Books, 2004, US | <urn:uuid:82e2c506-b6cb-47a5-b1b4-01f2425e09c3> | 3.265625 | 287 | Knowledge Article | Science & Tech. | 47.998164 |
William Caire, R. Mark Hardisty, and Kenneth E. Lacy
Biology Department, Central State University, Edmond, OK 73060
The capture heights and times of 251 red bats mist netted in southeastern Oklahoma were examined. Average capture heights varied from 3.4 m in May to 2.2 m in August. Most red bats were captured within the first four hours after sunset. Reproductively active male bats were most active from 2 to 4 h after sunset which increased their chances of finding a mate. Southeastern Oklahoma may be a nursery region with males migrating into the area in late summer.
The red bat, Lasiurus borealis, is a solitary, nomadic, migratory, tree dweller (1), which makes it difficult to study. Since the literature reveals that much of what is known about this bat is anecdotal (2), any contribution to our knowledge of its ecology will be of great value. The purpose of this research was to examine the capture heights and times of red bats in southeastern Oklahoma.
The study was conducted in Choctaw, LeFlore, McCurtain, and Pushmataha counties of southeastern Oklahoma from May through August of 1985. There were 35 different collecting sites (see Caire (3) for habitat descriptions). Mist nests were set across tree-lined streams. A combination of standard-size mist nests (3.8-cm mesh, 9.121.3 m long by 2.1 m high) and "high" mist nests (three, 9.1-m by 2.1-m nets hoisted one above another to a height of 6.4 m) were used at each site. The bottom of the nets were within 15 cm of the substrate and no bats were observed flying under the net. During the study, 121 standard and 53 high mist nets were tended from sunset until dawn (usually 10 h). A total of 251 red bats were captured. A cage containing bats was occasionally placed near the nets so that the bat sounds would attract other bats. These captures were not included in capture heights and times analyses, but were included in the total number taken each month.
The following data were recorded for each bat: capture time; height above ground; sex; reproductive state (i.e.pregnant, lactating, postlactating, epididymides descended, or nonreproductive); and age (i.e., juvenile, subadult, or adult). Bats with no external signs of breeding activity were considered nonreproductive. Age was based on degree of phalangeal ossification, overall body size, appearance of pelage, relative wear on the canines, and reproductive state. Capture times were recorded to the nearest minute, then tallied into 2-h intervals, beginning at sunset. The time of sunset was adjusted for daily shifts using information furnished by the Oklahoma Climatological Survey in Norman, Oklahoma.
The numbers of bats netted each month (Table 1) were significantly different (X2 = 191.7, P < 0.05). Fewer numbers were taken in May and June. A similar scarcity of red bats in midsummer has been reported for other states (46, 8). The increase in bats in August was in part due to reproductive accruement. However, the large increase in adult males may reflect sexual differences in seasonal movements (6, 8). Southeastern Oklahoma may be a nursery region similar to that of eastern Kansas (9). The regional separation of the sexes in early summer would reduce intraspecific competition for similar food resources. If male and female red bat
diets were similar (7, 10), the seasonal geographic separation would allow females to forage more efficiently during the nursery period. A pronounced increase occurred in the number of adult males caught in August, soon after the young were flying (Table 1). A timely migration of males into southeastern Oklahoma near the end of the summer would facilitate mating in late summer and early fall (1).
Another explanation for the paucity of adult males in early summer was that mist nets were not set in microhabitats frequented. A seasonal shift in habitat use might account for the late summer increase in males. However, 35 different sites were sampled, most on several occasions, and, seemingly, some of the early summer habitats used by males would have been sampled. Adult females were also uncommon in late spring and early summer. Females were perhaps restricting their activities to parturition sites. Layne (5) noted that female red bats were uncommon in Illinois in mid-May. He suggested that during late pregnancy and nursing, female red bats curtail their activity, and are difficult to capture.
Capture heights over time were significantly different (Kruskal-Wallis test, H = 11.5, P < 0.05). Heights averaged 3.4 m in May (n = 15, SD = 2.0), 2.6 m in June (n = 8, SD = 1.5), 3.0 m in July (n = 56, SD = 1.8), and 2.2 m in August (n = 74, SD = 1.6). The small May and June samples consisted of adult bats except for one juvenile captured in June, while in the other months, especially July and August, samples were larger, but contained subadult as well as adult bats. A comparison of capture heights of adult male and female bats among months revealed no significant differences (Kruskal-Wallis test, H = 7.0, P > 0.05). Capture heights among male or female bats in differing reproductive states were not significantly different (Mann-Whitney test, P > 0.05). Why the differences exist in some of the capture heights is not readily apparent. There was no indication of the behavior of the bats prior to capture; e.g., prey pursuit, cruising from one area to another, predator avoidance, and competitor interactions. These different behaviors could have influenced the heights at which the bats flew and were subsequently captured. Prey items might also have occurred at varying heights during the summer.
In Arkansas, Texas, and elsewhere (1,11, 12), red bats were most active soon after sunset. A similar pattern was noted for southeastern Oklahoma red bats (Table 2). The number of bats captured per each 2-h post-sunset interval was significantly different (X2 = 90.6, P < 0.05). Within 4 h after sunset, 75% of all bats was captured. Eighty-one percent of all males and 71% of all females were captured within 4 h of sunset. A large percentage of each age class was also
captured within 4 h after sunset. The percentage of males and females for each age class was: adults, 75% and 75%, subadults, 92% and 75%, and juveniles 75% and 60%.
In the same time span, 80% of the pregnant and lactating females were captured as well as 69% of all other females. Of the potential breeding (postlactating and showing no signs of reproductive activity) females, 78% captured in August were netted within 4 h after sunset.
Ninety-one percent of the potentially reproductively active males and 80% of the nonreproductive males (from all months combined) were netted within 4 h after sunset. However, the percent captured in each of the 2-h intervals differed. During the study, 56% of the nonreproductive males captured was netted within the first 2 h after sunset while 65% of the reproductively active males was captured between 2 and 4 h after sunset. Perhaps this behavior minimized energy expenditure and enhanced reproductive success. Copulation, which may be initiated while the bats are in flight (13), is energy demanding and requires optimal use of flight time. During the first 6 h after sunset, 85% of all potentially breeding females was active (Table 2). By intensifying flight activity in the 2- to 4-h post-sunset interval, reproductively active males improved their chances of finding a mate by being available for early- and late-flying females.
We thank officials of the Oklahoma Department of Wildlife Conservation, the Ouachita National Forest, and the Weyerhaeuser Company for their assistance. We thank M. Thies, R. Jones, D. Hartman, S. Caire, J. Caire and W. Caire for field assistance. Jack Tyler reviewed an early draft of the manuscript. This research was supported by grants from the Oklahoma Nongame Wildlife Program and Central State University.
1. R. W. Barbour and W. H. Davis, Bats of America, University of Kentucky Press, Lexington, 1969, 286 pp.
2. K. A. Shump, Jr. and A. U. Shump, Mamm. Species 188:1-6 (1982).
3. W. Caire, Summer Ecology of the Bats in Southeastern Oklahoma. Final report, Nongame Wildlife Research Grant, Oklahoma Dept. Wildlife Conservation, Oklahoma City, 1985, 19 pp.
4. J. O. Whitaker, Jr. and R. E. Mumford, Proc. Indiana Acad. Sci. 81: 376-383 (1972).
5. J. N. Layne, Am. Midl. Nat. 60: 219-254 (1958).
6. R. K. Laval and M. L. Laval, J. Mammal. 60: 209-212 (1979).
7. T. H. Kunz, J. Mammal. 54:14-32 (1973).
8. T. H. Kunz, Am. Midl. Nat. 86: 477-486 (1971).
9. J. K. Jones, Jr., E. D. Fleharty, and P. B. Dunnigan, Misc. Publ. Mus. Nat. Hist., Univ. Kansas 46: 1-33 (1967).
10. A. Ross, Proc. Western Found. Vertebr. Zool. 1: 204-263 (1967).
11. J. A. Sealander, A Guide to Arkansas Mammals, River Road Press, Conway, AR, 1979,313 pp.
12. D. J. Schmidly, Texas Mammals East of the Balcones Fault Zone, Texas A & M Univ. Press, College Station, TX, 1983, 400 pp.
13. B. P. Glass, Proc. Okla. Acad. Sci. 46: 40-41(1966). | <urn:uuid:1a0a2f9a-d415-42bd-aa49-9d3b05334294> | 2.84375 | 2,177 | Academic Writing | Science & Tech. | 67.057078 |
Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||432||Public Records:||207|
|Specimens with Sequences:||454||Public Species:||15|
|Specimens with Barcodes:||312||Public BINs:||11|
|Species With Barcodes:||16|
The crocodile icefish or white-blooded fish (Channichthyidae) are a family of perciform fish found in the cold waters around Antarctica and southern South America. Water temperature can drop to -1.9 °C (the freezing point of seawater) in the Antarctic sea but stays rather constant. There are about 25 currently recognized species of crocodile icefish. They feed on krill, copepods, and other fish.
Icefish reach total length of 25-75 cm.
Respiratory and circulatory system
Their blood is yellow because it contains no hemoglobin. Red blood cells are usually absent and if present are rare and defunct. Oxygen is dissolved in the plasma and transported throughout the body without the hemoglobin protein. The fish can live without hemoglobin because of their low metabolic rates and the high solubility of oxygen in water at the low temperatures of their environment. However, the oxygen carrying capacity of their blood is less than 10% that of their relatives with hemoglobin.
To compensate for the loss of hemoglobin, they have larger blood vessels (including capillaries), greater blood volumes (four times that of other fish), bigger hearts and greater cardiac outputs (fivefold greater) compared to other fish. Their hearts lack coronary arteries and the ventricle muscles are very spongy, enabling them to absorb oxygen directly from the blood they pump. Their hearts, large blood vessels and low viscosity (RBC free) blood are specialized to carry out very high flow rates at low pressures. This helps to reduce the problems caused by the loss of hemoglobin. In the past, it has been widely supposed that their scaleless skin helps absorb oxygen. However, current analysis has shown that the amount of oxygen absorbed by the skin is much less than that absorbed through the gills. The little extra oxygen absorbed by the skin may play a part in supplementing the oxygen supply to the heart which receives venous blood from the skin and body before pumping it to the gills.
Channichthyidae are the only known vertebrates without hemoglobin, an oxygen transport protein in the blood. Although they do not manufacture hemoglobin, remnants of hemoglobin genes can be found in their genome. The hemoglobin protein is made of two subunits (alpha and beta). Almost all of the alpha and beta subunit genes have been lost from the genomes of 15 of the 16 icefish species. In only one of the icefish species, Neopagetopsis ionah, there is a more complete, but still nonfunctional hemoglobin gene.
Myoglobin is an oxygen transport protein used in muscles, but is also absent from all icefish skeletal muscles. In ten species, myoglobin is found in the heart muscle, specifically ventricles. Myoglobin has been lost[clarification needed] in icefish heart ventricles at least four separate times and by four different mechanisms.
The loss of hemoglobin was initially supposed to be an adaptation to the extreme cold; the higher solubility of O2 reduces the demand on hemoglobin and the lack of RBCs decreases the blood viscosity. However, current analysis has shown that the lack of hemoglobin—though not lethal—is still maladaptive. The fish have evolved fairly drastic changes to their physiology to compensate. These compensations include spending twice as much energy pumping blood compared to other fish.
These fish have descended from a sluggish demersal ancestor. The cold, well mixed, oxygen rich waters of the Antarctic ocean provided an environment where a fish with a low metabolic rate could survive even without hemoglobin—albeit less efficiently. During the mid-Tertiary period a species crash in the southern ocean opened up wide range of empty niches to colonize. Despite the hemoglobin-less mutants being less fit, the lack of competition allowed even the mutants to leave descendants that colonized empty habitats and evolved compensations for their mutations. Later the periodic openings of fjords created habitats that were colonized by a few individuals. This gave the opportunity for four lines of fish to even lose their myoglobin genes by a similar process.
- Froese, Rainer, and Daniel Pauly, eds. (2013). "Channichthyidae" in FishBase. February 2013 version.
- Sidell, Bruce D; Kristin M O'Brien (2006-05-15). "When Bad Things Happen to Good Fish: The Loss of Hemoglobin and Myoglobin Expression in Antarctic Icefishes". Journal of Experimental Biology 209 (10): 1791–1802. doi:10.1242/jeb.02091. ISSN 1477-9145 0022-0949, 1477-9145. PMID 16651546. Retrieved 2012-04-07.
- Ruud, Johan T. (1954-05-08). "Vertebrates without Erythrocytes and Blood Pigment". Nature 173 (4410): 848–850. doi:10.1038/173848a0. PMID 13165664. Retrieved 2012-04-07.
- Barber, D. L; J. E Mills Westermann, M. G White (1981-07-01). "The blood cells of the Antarctic icefish Chaenocephalus aceratus Lönnberg: light and electron microscopic observations". Journal of Fish Biology 19 (1): 11–28. doi:10.1111/j.1095-8649.1981.tb05807.x. ISSN 1095-8649. Retrieved 2012-04-07.
- Rankin, J.C; H Tuurala (1998-01). "Gills of Antarctic Fish". Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology 119 (1): 149–163. doi:10.1016/S1095-6433(97)00396-6. ISSN 1095-6433. Retrieved 2012-04-09.
- Tota, Bruno; Raffaele Acierno, Claudio Agnisola, Bruno Tota, Raffaele Acierno, Claudio Agnisola (1991-06-29). "Mechanical Performance of the Isolated and Perfused Heart of the Haemoglobinless Antarctic Icefish Chionodraco Hamatus (Lonnberg): Effects of Loading Conditions and Temperature". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 332 (1264): 191–198. doi:10.1098/rstb.1991.0049. ISSN 1471-2970 0962-8436, 1471-2970. Retrieved 2012-05-18.
- Zhao, Y. Q.; Ratnayake-Lecamwasam, M.; Parker, S. K.; Cocca, E.; Camardella, L.; Detrich, H. W. (1998). "The major adult alpha-globin gene of antarctic teleosts and its remnants in the hemoglobinless icefishes-calibration of the mutational clock for nuclear genes". Journal of Biological Chemistry 273: 14745–14752.
- Di Prisco, G.; Cocca, E.; Parker, S. K.; Detrich, H. W. (2002). "Tracking the evolutionary loss of hemoglobin expression by the white-blooded antarctic icefishes". Gene 295: 185–191.
- Di Prisco, G.; Eastman, J. T.; Giordano, D.; Parisi, E.; Verde, C. (2007). "Biogeography and adaptation of notothenioid fish: hemoglobin function and globin-gene evolution". Gene 398: 143–155.
- Near, T. J.; Parker, S. K.; Detrich, H. W. (2006). "A genomic fossil reveals key steps in hemoglobin loss by the antarctic icefishes". Molecular Biology and Evolution 23: 2008–2016.
- Sidell, B. D.; Vayda, M. E.; Small, D. J.; Moylan, T. J.; Londraville, R. L.; Yuan, M. L.; Rodnick, K. J.; Eppley, Z. A. et al. (1997). "Variable expression of myoglobin among the hemoglobinless antarctic icefishes". Proceedings of the National Academy of Sciences of the United States of America 94: 3420–3424.
To request an improvement, please leave a comment on the page. Thank you! | <urn:uuid:b858be7a-6f73-40c3-8035-940ac4c4943c> | 3.765625 | 1,874 | Knowledge Article | Science & Tech. | 60.987314 |
Sometimes lava touches the water. It can turn the water into acid.
When lava touches houses it can start a fire outside of the houses.
A volcano can make mud flows. Mud flows are thick sticky mud made by snow and ice melting.
When done erupting the weather can change, heavy rains, strong winds and mud flows occur.
Clouds blow down volcanic ash into the air and it makes it hFarder to breath.
Volcanoes may produce choking clouds of steam and poisonous gases.
Lava streams or lava steam can burn, bury or flatten anything and anyone in their path.
Volcanoes sometimes can make earthquakes.
When a volcano erupts it can cover a whole town in ash.
When a volcano erupts it can cause red sunsets, and block the sun's rays.
Sometimes tidal waves from a volcano can kill people.
Acid rain is made of ash that can burn people.
Heat from inside the earth seeps out slowly through cracks in the surface and you can use the heat for power. This is called geothermal power.
When volcanoes erupt in the water they make land. When thousands of eruptions underwater built up they emerged as the Hawaiian Islands.
Some farmers grow crops near volcanoes because the soil is good there. Ash from the volcano makes the dirt richer. Special plants can grow on a volcano. Did you know that sedge and other grasses and products can grow through the crust of ash?
Some small animals survive under the ash and snow packs. Scientists also found many tiny living things. | <urn:uuid:7af84aba-4cc0-417b-8553-bce69c60bc2f> | 3.578125 | 324 | Knowledge Article | Science & Tech. | 67.184933 |
Dec 03, Biology/Plants & Animals
"Pygmy mole crickets have solved the most difficult task of jumping from the surface of water," says Malcolm Burrows of the University of Cambridge. "For small insects, water can be a deadly, sticky trap: water grabs and holds an insect, offering it as an appetizing snack for an alert fish. Pygmy mole crickets turn the stickiness of water to their advantage and use this property to enable jumping."
Burrows came across this unique cricket behavior one day while sitting by the side of a pond in South Africa eating his lunch. He heard some odd noises coming from the direction of the pond and, after getting a closer look, discovered some insects jumping from the water toward the bank. He did what any good scientist would do: he caught a few and took them back to the lab, where he and colleague Gregory Sutton could catch their talents on high-speed film.
[video is available in the full version of this article (see link below)]
That's when he discovered the insect's oar-like paddles on its legs, which are spring loaded with a protein called resilin that Burrows says is "the perfect elastic." As those oars penetrate the water, they fan out. The crickets then "grab" a ball of water, sending it downward as their bodies soar in the opposite direction and to safety.
This curious bug strategy might even have some practical use.
"If we want to make small robotic vehicles that move under water, this is how we would have to design propellers or oars," Burrows says. "We would also have to use a material as good as resilin to impart elasticity, restore shape, and reduce drag."
In the meantime, the discovery is yet another example of amazing animal feats.
"This is an animal that has to do many things with its legs: dig burrows in the ground, jump rapidly to escape predators on land, and get itself out of water before it is eaten or drowns. It has solved a hugely difficult problem with a multifunctional mechanism that can propel jumps on land and water."
More information: Burrows et al.: "Pygmy mole crickets jump from water." Current Biology, DOI: 10.1016/j.cub.2012.10.045
Provided by Cell Press
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Search Loci: Convergence:
A human being is a part of the whole, called by us "Universe," a part limited in time and space. He experiences himself, his thoughts and feelings as something separated from the rest, a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest to us. Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty. Nobody is able to achieve this completely, but the striving for such achievement is in itself a part of the liberation and a foundation for inner security.
In H. Eves, Mathematical Circles Adieu, Boston: Prindle, Weber and Schmidt, 1977.
Leonardo da Vinci's Geometric Sketches
The Franciscan friar, Luca Pacioli (ca 1445-1509) is best known for his compendium of fifteenth century mathematics, Summa de arithmetica, geometrica, proportioni et proportionalita (1494). This book was intended to be a summary of the known mathematics of the time and included a special feature discussing double-entry bookkeeping. But Pacioli compiled and wrote other texts. In De divina proportione of 1509, he discusses the “golden proportion” and the properties of various polyhedra. Pacioli was fascinated by polyhedra, studied their properties and constructed wooden models for many of the solids. The friar also befriended many of the artists of the time, including Leonardo Da Vinci. Da Vinci briefly studied geometry with Pacioli but focused on considerations of shape, size and perspective, descriptive features of objects rather than their theoretical foundations. Da Vinci illustrated Divina proportione, supplying sixty plates for the work.
Below are facsimiles of several of these plates; specifically those illustrating the sphere, cone, cylinder, pyramid and the five Platonic solids. For the Platonic solids, Da Vinci supplied two views: a plane view and a “vacua” or empty view where he removes the sides to better reveal the compete structure of the polyhedron. These later “nets” of vertices and edges illustrate the artist’s graphic genius.
Table Of Contents | <urn:uuid:857d860d-841b-4f8b-a6cc-98379ee08275> | 3.140625 | 493 | Knowledge Article | Science & Tech. | 32.729266 |
Giant Toxic Coal Ash Spill Threatens Animals
Kelly Hearn in Kingston, Tennessee
for National Geographic News
|January 23, 2009|
It's been called the Exxon Valdez of coal ash—a wakeup call for a fossil fuel industry.
But the recent toxic ash spill in Tennessee is greater in scope than the 1989 oil spill, and despite what some conservationists are calling very real threats, the ash disaster has so far inspired apparently little concern for local wildlife.
On December 22 a billion gallons of poisonous sludge—largely coal ash, a byproduct of coal burning—broke through an earthen dike at the Kingston Fossil Plant. The torrent half-buried area homes and elevated long-running health concerns over heavy metals in the ash.
Those worries, experts say, are not limited to human health. In addition to the animals killed by the initial spill, wildlife may be threatened for years by the trace amounts of arsenic, cadmium, mercury, thallium, and other toxins in the coal ash.
(Related: "Heavy Metal-Eating 'Superworms' Unearthed in U.K." [October 7, 2008].)
"We're concerned about tremendous human health threats but also serious biological threats to animal species," said Stephen Smith, veterinarian and director of the Southern Alliance for Clean Energy.
"Already mussels, snails, and aquatic species are in grave danger, but no one seems to be talking about it."
Other local animals that could be affected include river otters, mink, muskrat, ospreys, and black-crowned night herons, according to the Tennessee Wildlife Resources Agency. No endangered species are believed to inhabit the spill region.
Toxins Accumulating in Animals?
Of the dead animals retrieved from the spill site so far, none had died of poisoning, according to Dave McKinney, chief of the Environmental Service Division of the Tennessee government's Wildlife Resources Agency.
"They were either buried in mud or stranded when a water surge pushed them into fields and forests and then receded," McKinney said.
Even so, he said, "there is certainly the potential that toxins will bioaccumulate"—build up in animals' bodies. "But we're talking months to years, not days to weeks."
State wildlife officials said they have collected live fish and will collect more in the coming months to monitor the situation.
The Tennessee Wildlife Resources Agency says it will work over the next three to five years with the U.S. Fish and Wildlife Service to assess the long-term impact of contaminants from the Kingston spill on animals.
Eventually any toxic effects in animals could work their way up the food chain to humans, officials say.
The Tennessee Department of Environment and Conservation has issued an advisory against eating striped bass caught in rivers around the spill zone as well as a precautionary advisory for catfish and sauger. A precautionary advisory means that children, pregnant women, and nursing mothers shouldn't eat those species, and everyone else should limit consumption to one meal a month.
Conservationists are particularly concerned over the fate of one ecologically important species, freshwater mussels, which live on river bottoms, where sediment and pollution accumulate.
Losing mussels could result in greater pollution levels in area rivers, because a single mussel can filter several gallons of water a day, "improving quality for human use," according to the U.S. Fish and Wildlife Service.
Mussels are also a major food source for ducks, birds, and fish, which could in turn suffer if the mussels are tainted by the ash spill. (Related: "Hatcheries Strengthen Mussel Species on Appalachian River" [December 6, 2005].)
Coal ash, or fly ash, is a residue left over from burning coal for power. It is collected in ponds like the one at Kingston in 32 U.S. states, according to the Associated Press. Massive amounts of ash are sold for use in concrete, mulch, construction fill, and other purposes.
The U.S. government considers the ash a health and environmental risk, but the residue remains unregulated, and debate burns over just how toxic coal ash is.
A 1998 study by the Electric Power Research Institute, a nonprofit association allied with the power industry, found that "health risks from coal ash are minimal, whether it is in the form of a waste coal combustion by-product or a material used in construction products."
The study pointed out that heavy metals make up a small proportion of coal ash—and that these same substances occur naturally in rocks and sand.
But other experts point to evidence that the toxins in coal ash—also called coal combustion residues (CCR)—build up in bodies over time, sometimes with lethal effects.
"Whether accidentally discharged into natural aquatic systems or present in impoundments that attract wildlife, CCR appears to present significant risks to aquatic and semiaquatic organisms," Michael McKinney, the chair of the University of Tennessee's environmental-studies program, said in an email.
Specifically, coal-ash spills have caused behavioral and physical problems in some vertebrates and invertebrates, McKinney said. For example, exposure to ash toxins has been found to lead to severe deformations of tadpoles and fish.
Coal-ash exposure has also led to "fish kills and extirpation [local extinction] of some fish species," McKinney added.
Biologist Robert Jenkins of Roanoke College in Virginia witnessed just such an event about 40 years ago on the Clinch River in Tennessee, which was partially filled with sludge from the December 22 spill.
"I saw hundreds of thousands of dead fish at that spill" in 1967, Jenkins said, noting that water alkalinity, or pH levels, shot to 12.0 to 12.7—slightly less alkaline than household bleach—from a normal range of 7.8 to 8.5. "That was a huge chemical shock," he said.
Tests to determine the post-spill alkalinity of the Clinch are pending.
Should Coal Ash Be Regulated?
The U.S. Environmental Protection Agency (EPA) has long held that coal ash poses no substantial risks to the environment.
Currently, the EPA has produced no coal-ash regulations and strongly supports the substance's use in commercial products such as paints, kitchen countertops, concrete, and agricultural products such as mulch.
Jim Roewer, executive director of the industry-funded Utility Solid Waste Activities Group, said that while the EPA may not have broad-ranging regulations governing the ash, individual states do.
Critics, however, see a void and want coal ash declared a toxic substance.
Kert Davies, research director for the environmental group Greenpeace, says hundreds of coal ash dumps across the country lack meaningful oversight.
Green groups are now pointing to the Tennessee spill as evidence of regulatory need, and they're pressing the new U.S. President to act.
A group of six Tennessee environmental groups recently sent a letter to President Obama, requesting that he move to declare coal ash a hazardous waste.
The Southern Alliance for Clean Energy has even filed a lawsuit seeking to force the Tennessee Valley Authority (TVA)—the federally owned utility that produced and stored the ash—to restore ecological health to the spill zone.
Dave Goss, executive director of the industry-affiliated American Coal Ash Association, said, "It doesn't surprise us that people are calling for a re-review of federal regulations.
"We are going to let the science speak for itself. It is dangerous to mix science, policy, and passion."
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Leonids Rain in Spain
Space Science News home
Leonids Rain in Spain
November 18, 1999: According to preliminary data reported
by the International Meteor Organization
and the Leonids Environment Operations
Center, there was an intense outburst of Leonid meteors over
Europe and the Middle East on Thursday morning, November 18.
Maximum activity was recorded around 0200 UT as the Earth passed
through the debris stream of comet Tempel-Tuttle.
An outburst of over 1500 Leonid meteors per hour
dazzled observers in Europe and the Middle East.
"We observed many, many, many Leonids falling from the sky," said Casper ter Kuile of the Dutch Meteor Society, who was working with a team of observers located between Valencia and Alicante in Spain. "Our experienced visual observers counted about 30 Leonids per minute!"
Above: Scores of meteors near the bowl of the Little Dipper, in a 10 to 12 minute exposure by A. Scott Murrell during the 1966 Leonid storm. He used a 50-mm f/1.9lens and Tri-X film in a camera tracking the stars at New Mexico State University Observatory. [credits]
The high rate noted by observers in Spain, over 1800 meteors per hour, was substantially greater than the 500 to 1000 per hour that most experts had predicted. The storm was even more intense over parts of the Middle East, where members of the Israeli Astronomical Association recorded 70 meteors per minute for just over a half an hour. Like other global observers, the Israeli team was struck by the abundance of faint meteors and the relative absence of bright fireballs. Preliminary reports by meteor watchers in the Canary Islands and near the Gorges du Verdon in France confirm this general picture of the outburst.
The meteor storm was not seen west of the Atlantic. In North America sky watchers saw relatively few Leonids -- at most 40 to 50 per hour. The majority of these were fast-moving and dim.
Radio measurements from Japan and the Czech Republic confirm the results of visual observers indicating a peak between 2:00 and 2:10 UT. This time coincides with the maximum at 2:08 UT predicted by Asher and McNaught. In their model of the Leonid meteoroid stream, the 1999 storm was caused by a dust trail created when the Leonids parent comet, Tempel-Tuttle, passed by the Sun about 100 years ago. The Asher-McNaught model predicts even bigger Leonid storms in 2001 and 2002.
Above: A global team of observers coordinated by the US Air Force and the University of Western Ontario are continuing to monitor Leonid activity for satellite operators and others. Preliminary data from their observing campaign show a sharp peak in meteor activity just after 200 UT on November 18. [more] Web Links
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Leonids Live! -site of the live webcast of the 1999 Leonids
North American Meteor Network - home page
Leonids on the Moon -- Nov 3, 1999. Leonid meteorite impacts on the Moon might be visible from Earth and provide a means for long-distance lunar prospecting.
NASA Meteor Balloon Rises Again -- Nov 1, 1999. NASA scientists are planning to launch a weather balloon into the stratosphere on November 18 to capture a recording of the Leonids meteor shower from 100,000 ft.
Leonids in the Crystal Ball -- Oct 27, 1999. Is 1999 the year for a Leonids meteor storm? Experts make their predictions.
Pop! Ping! Perseids! -- Aug 13, 1999. The Science@NASA meteor balloon popped before reaching the stratosphere but many meteor enthusiasts still saw and heard the Perseid shower.
Live! Balloon Flight Planned
-- Aug 6, 1999. A NASA weather balloon will ascend to the stratosphere
for a live webcast of the 1999 Perseids.
The Leonid Meteor Outburst of 1997 -- July 16, 1999.Newly released video shows a flurry of Leonids in 1997 that briefly rivaled the great meteor storm of 1966.
Tuning in to April meteor showers -- Apr. 27, 1999. Amateur astronomers capture radio echoes from fiery meteors in April 99.
April's Lyrid meteor shower -- Apr. 21, 1999. The oldest known meteor shower peaks this year on April 22.
A Wild Ride to the Stratosphere in Search of Meteors -- Apr. 14, 1999. The payload from the NASA Meteor Balloon has been recovered.
Meteor Balloon set for Launch -- Apr. 9, 1999. NASA scientists prepare to launch a weather balloon designed to capture micrometeoroids in the stratosphere.
Leonid Sample Return Update -- Apr. 1, 1999. Scientists will describe initial results from a program to catch meteoroids in flight at the NASA/Ames Leonids Workshop April 12-15, 1999.
The Ghost of Fireballs Past -- Dec. 22, 1998. RADAR echoes from Leonid and Geminid meteors.
Bunches & Bunches of Geminids -- Dec. 15, 1998. The Geminids continued to intensify in 1998
The 1998 Leonids: A bust or a blast? -- Nov. 27, 1998. New images of Leonid fireballs and their smoky remnants.
Leonids Sample Return payload recovered! -- Nov. 23, 1998. Scientists are scanning the "comet catcher" for signs of Leonid meteoroids.
Early birds catch the Leonids -- Nov. 19, 1998. The peak of the Leonid meteor shower happened more than 14 hours earlier than experts had predicted.
A high-altitude look at the Leonids -- Nov. 18, 1998. NASA science balloon catches video of 8 fireballs.
The Leonid Sample Return Mission -- Nov. 16, 1998. NASA scientists hope to capture a Leonid meteoroid and return it to Earth.
Great Expectations: the 1998 Leonid meteor shower -- Nov. 10, 1998. The basics of what the Leonids are and what might happen on November 17.
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The Nameless Hurricane
On March 28th, a surprising hurricane crashed into the coast of Brazil.
April 2, 2004: Hurricanes are terrifying. They rip trees right out of the ground, hurl cars into the air, and flatten houses. Their winds can blow faster than 100 mph. Some hurricanes have been known to pull a wall of water from the ocean 20 feet high … then fling it inland, inundating miles of coast. No other storms on Earth are so destructive.
Right: A hotel in Gulfport, Mississippi, flattened by Hurricane Camille in 1969. [More]
Or so memorable. The most powerful hurricanes are talked about for decades, long after the floods subside and trees grow back. What child in Mississippi today hasn't heard of Hurricane Camille, the monster storm that traumatized their parents in 1969? Hurricanes are the only storms we actually name, like people, to help us remember.
That is, until last week, on March 28th, when a nameless hurricane crashed into Brazil. The storm made landfall near Torres, a small town in the state of Santa Catarina about 500 miles south of Rio de Janeiro.
"This really caught everybody off guard," says NASA hurricane researcher Robbie Hood. "Hurricanes aren't supposed to be in that part of the world."
Weather satellites have been circling Earth for more than 40 years. During that time they've spotted hurricanes (also called "typhoons" or "cyclones") in the northern Atlantic Ocean, and on both sides of the equator in the Pacific and Indian Oceans, but never before in the south Atlantic.
Left: Hurricanes occur most often in the black-circled areas, and rarely outside. [More]
"Vertical wind shears in the south Atlantic are too strong for hurricanes," Hood explains. Winds in the upper troposphere (about 10 km high) are 20+ mph faster than winds at the ocean surface. This difference, or shear, rips storms apart before they intensify too much.
A typical hurricane starts out as a cluster of ordinary thunderstorms. Powered by heat from warm tropical waters and guided by Coriolis forces, the storms swirl together, joining forces to create a tropical depression … then a tropical storm … and finally a full-fledged hurricane. Wind shears in the south Atlantic usually stop this process at the stage of tropical depression.
There are exceptions. In 1991, for instance, the US National Hurricane Center documented a tropical storm off the coast of Congo. It lasted about five days as it drifted toward the central south Atlantic, but it never reached hurricane strength. (The minimum threshold for a hurricane is 74 mph winds.)
What was different about the March 2004 storm? Why did it become a hurricane? No one knows.
When the storm crashed into Brazil, local observers weren't even sure it was a hurricane. Brazil has no ground-based network of weather stations to measure wind and rain from tropical storms. "There are no 'Hurricane Hunters' in Brazil," adds Hood. "The storms are so rare."
Space satellites, however, gathered a great deal of data. "NOAA polar orbiting satellites measured the temperature of the storm's eye," says climate scientist Roy Spencer of the University of Alabama, Huntsville. "That told us how fast the winds were moving." It was a category 1 hurricane, he says, an estimate confirmed by NASA's wind-measuring QuikScat satellite. In addition, NOAA's GOES satellites and NASA's Terra and Aqua satellites took pictures of the storm at microwave, infrared, and visible wavelengths, allowing scientists to monitor the motions of moisture and heat energy through the storm--valuable data, indeed.
The TRMM spacecraft, a joint mission of NASA and the Japanese space agency, flew over the storm several times in the days before landfall, and it gathered perhaps the most revealing data of all. TRMM, short for Tropical Rainfall Measuring Mission, carries a precipitation radar, the only one in space. Beaming down through the clouds, the radar illuminated spiraling bands of rainfall; false color images of the storm resemble a pinwheel galaxy! Combining data from the radar and the spacecraft's microwave imager, researchers can estimate rain rates throughout the hurricane--from top to bottom, from eye to edge.
Right: A TRMM precipitation radar map of the March 28th south Atlantic hurricane. [More]
"This whole episode highlights the advantages of satellites for hurricane studies, especially where there are no aircraft standing by to fly through the storms," says Hood. "Satellites can monitor storms in all parts of the world."
But a problem remains: what to call them? The World Meteorological Organization maintains a list of hurricane names for every part of the world … except the south Atlantic. Sadly, the March 28th storm did damage to remember: 500 homes ruined, fishing boats sunk, at least two people dead and 1500 more homeless. Brazilians are going to be talking about the storm for a long time, and wondering about hurricanes to come.
South Atlantic hurricanes need names. Somebody somewhere, probably, is making a list.
Editor's note (April 7, 2003): This hurricane was too important to remain anonymous for long. The people of Brazil themselves have named it, unofficially, Hurricane Catarina, after the southern Brazilian state of Santa Catarina where the storm made landfall. | <urn:uuid:6b07edbc-31b4-4737-b700-02ce8400eacb> | 3.609375 | 1,105 | Knowledge Article | Science & Tech. | 46.997901 |