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The namespace contains channels that use the TCP protocol to transport messages and objects to and from remote locations. By default, the TCP channels encode objects and method calls in binary format for transmission, but other encoding and decoding formatter sinks can be specified in the configuration properties of a channel. One of the most important classes of the namespace is the TcpChannel class.
|TcpChannel||Provides a channel implementation that uses the TCP protocol to transmit messages.|
|TcpClientChannel||For remote calls, implements a client channel that uses the TCP protocol to transmit messages.|
|TcpServerChannel||Implements a server channel for remote calls that uses the TCP protocol to transmit messages.| | <urn:uuid:724c0ca8-2e85-407d-ae58-0cd9a0e3e28f> | 2.90625 | 144 | Documentation | Software Dev. | 35.494916 |
Have you got the Mach knack? Discover the mathematics behind
exceeding the sound barrier.
This article explores ths history of theories about the shape of our planet. It is the first in a series of articles looking at the significance of geometric shapes in the history of astronomy.
How efficiently can various flat shapes be fitted together?
Explain why, when moving heavy objects on rollers, the object moves
twice as fast as the rollers. Try a similar experiment yourself.
What 3D shapes occur in nature. How efficiently can you pack these shapes together?
An introduction to bond angle geometry.
The second in a series of articles on visualising and modelling shapes in the history of astronomy.
Mike and Monisha meet at the race track, which is 400m round. Just to make a point, Mike runs anticlockwise whilst Monisha runs clockwise. Where will they meet on their way around and will they ever. . . .
How efficiently can you pack together disks?
The net of a cube is to be cut from a sheet of card 100 cm square.
What is the maximum volume cube that can be made from a single
piece of card?
Problem solving is at the heart of the NRICH site. All the problems
give learners opportunities to learn, develop or use mathematical
concepts and skills. Read here for more information.
Can you visualise whether these nets fold up into 3D shapes? Watch the videos each time to see if you were correct.
If all the faces of a tetrahedron have the same perimeter then show that they are all congruent.
Find the point whose sum of distances from the vertices (corners)
of a given triangle is a minimum.
A cube is made from smaller cubes, 5 by 5 by 5, then some of those
cubes are removed. Can you make the specified shapes, and what is
the most and least number of cubes required ?
A cheap and simple toy with lots of mathematics. Can you interpret
the images that are produced? Can you predict the pattern that will
be produced using different wheels?
A circular plate rolls in contact with the sides of a rectangular
tray. How much of its circumference comes into contact with the
sides of the tray when it rolls around one circuit?
Some students have been working out the number of strands needed for different sizes of cable. Can you make sense of their solutions?
A circular plate rolls inside a rectangular tray making five
circuits and rotating about its centre seven times. Find the
dimensions of the tray.
On the 3D grid a strange (and deadly) animal is lurking. Using the tracking system can you locate this creature as quickly as possible?
A square of area 3 square units cannot be drawn on a 2D grid so that each of its vertices have integer coordinates, but can it be drawn on a 3D grid? Investigate squares that can be drawn.
Can you find a rule which connects consecutive triangular numbers?
Can you describe this route to infinity? Where will the arrows take you next?
This is an interactive net of a Rubik's cube. Twists of the 3D cube become mixes of the squares on the 2D net. Have a play and see how many scrambles you can undo!
Can you make sense of the charts and diagrams that are created and used by sports competitors, trainers and statisticians?
A box of size a cm by b cm by c cm is to be wrapped with a square piece of wrapping paper. Without cutting the paper what is the smallest square this can be?
The aim of the game is to slide the green square from the top right
hand corner to the bottom left hand corner in the least number of
There are 27 small cubes in a 3 x 3 x 3 cube, 54 faces being
visible at any one time. Is it possible to reorganise these cubes
so that by dipping the large cube into a pot of paint three times
you. . . .
This is a simple version of an ancient game played all over the world. It is also called Mancala. What tactics will increase your chances of winning?
A game for 2 players
An irregular tetrahedron has two opposite sides the same length a
and the line joining their midpoints is perpendicular to these two
edges and is of length b. What is the volume of the tetrahedron?
Place a red counter in the top left corner of a 4x4 array, which is
covered by 14 other smaller counters, leaving a gap in the bottom
right hand corner (HOME). What is the smallest number of moves. . . .
Can you find a rule which relates triangular numbers to square numbers?
Watch these videos to see how Phoebe, Alice and Luke chose to draw 7 squares. How would they draw 100?
Simple additions can lead to intriguing results...
Players take it in turns to choose a dot on the grid. The winner is the first to have four dots that can be joined to form a square.
Build gnomons that are related to the Fibonacci sequence and try to
explain why this is possible.
Jo made a cube from some smaller cubes, painted some of the faces
of the large cube, and then took it apart again. 45 small cubes had
no paint on them at all. How many small cubes did Jo use?
This task depends on groups working collaboratively, discussing and
reasoning to agree a final product.
We're excited about this new program for drawing beautiful mathematical designs. Can you work out how we made our first few pictures and, even better, share your most elegant solutions with us?
Two boats travel up and down a lake. Can you picture where they
will cross if you know how fast each boat is travelling?
What can you see? What do you notice? What questions can you ask?
Use the diagram to investigate the classical Pythagorean means.
Small circles nestle under touching parent circles when they sit on
the axis at neighbouring points in a Farey sequence.
I found these clocks in the Arts Centre at the University of
Warwick intriguing - do they really need four clocks and what times
would be ambiguous with only two or three of them?
A ribbon runs around a box so that it makes a complete loop with two parallel pieces of ribbon on the top. How long will the ribbon be?
A game for 2 people. Take turns joining two dots, until your opponent is unable to move.
Discover a way to sum square numbers by building cuboids from small
cubes. Can you picture how the sequence will grow?
Use a single sheet of A4 paper and make a cylinder having the greatest possible volume. The cylinder must be closed off by a circle at each end.
Can you recreate these designs? What are the basic units? What
movement is required between each unit? Some elegant use of
procedures will help - variables not essential. | <urn:uuid:2794dfdc-b71d-4527-8b81-df9833041d1d> | 3.84375 | 1,454 | Content Listing | Science & Tech. | 65.935541 |
I have been racking my brains over the differences between laser spectral width and something called the linewidth. The linewidth was written about in detail by Henry in 1982. The spectral width is the width at -20dB down from peak of the wavelength spectrum of the laser. I am looking at some laser data right now that is saying that laser x has 10 kHz linewidth and 60 pm spectral width. You can convert spectral width from frequency to wavelength as in this article and I have done that calculation. By that calculation, a laser with a linewidth of 10kHz should have a wavelength width of about 1x10^-6 nm, not 0.06 nm. Linewidth is often measured with self-heterodyne technique, not a spectrum analyzer. What am I missing?
I assume you are looking at a diode laser (LD) data sheet. In practical terms, spectral width is a measure of tunability of the LD as you vary injection current and temperature. This is quite useful in experiments (say atomic physics with alkali atoms).
The linewidth is related to the phase noise of laser. It is very complicated to derive the linewidth from first principles. Agarwal is a standard reference if you wish to know more.
A practical semi-conductor LD has a typical free running linewidth of 40Mhz. This means, the uncertainty in the frequency is 40MHz. However, this entire frequency band can shift with changes in temperature and fluctuations in injection current.
This rather broad linewidth can be narrowed by optical feedback to obtain the so called external/extended cavity diode laser (ECDL). Check out this seminal paper by Weimann and Hollberg (pdf) for more information. I have built many ECDL systems from the ground up with sub-MHz linewidths. It can be quite a tricky endeavor.
Measuring the linewidth can be quite tricky. The usual direct technique is to beat the unknown laser with a known standard reference and study the beat signal. The equipment necessary is very expensive. However, you can make rough estimates from say a simple saturation spectroscopy based frequency locking setup by studying the amplitude fluctuations of the "error signal". Granted that it is crude and limited to the natural linewidth of your atomic system, but it does not need super expensive equipment or complicated electronics. There are other ways to use atomic physics (EIT, CPT resonances etc) to make reasonable estimates of laser linewidth and it all depends on what your goal is. | <urn:uuid:836229a4-cd08-4483-917f-574b48f12b5f> | 2.90625 | 527 | Q&A Forum | Science & Tech. | 50.93625 |
Science on a sphere
By Margaret Harris in Washington, DC
No trip to the AAAS meeting would be complete without a tour of the exhibit hall, which for the past two days has been buzzing with visitors to “Family Science Days”, a public outreach-oriented event running in parallel with the more technical seminars.
One of the most eye-catching exhibits was the National Oceanic and Atmospheric Administration’s Science on a Sphere, which pretty much does what it says on the tin. The Sphere is the brainchild of Alexander McDonald, director of NOAA’s Earth Systems Research Laboratory, and there are now over 250 datasets that can be displayed on it. In this photo, it’s illustrating the shock waves that spread around the globe after the Boxing Day tsunami of 2004, but I also saw depictions of ocean currents, aeroplane flight paths, global temperatures and the past week’s weather. According to exhibitor Jana Goldman, there’s even one in a science fiction museum in Seattle, Washington that displays the (hypothetical) features of a (fictional) alien planet – so it’s definitely a versatile beast!
Another exhibit that got a lot of traffic was the US Department of Energy’s set of bicycle-powered light bulbs, which is designed to teach kids (and maybe some adults) about the differences between voltage and current, and to demonstrate in a very physical way how much power it takes to light up an incandescent 50 W bulb compared with fluorescent and LED bulbs. The young gentleman in this photo, for example, was having real trouble getting the incandescent bulb to give off any light, but despite being a little too short for the pedals, he managed the LED bulb just fine.
Bicycle-powered light bulbs
For the bigger kids, exhibitor Steve Eckstrand keeps a 12 V, 300 W hairdryer on hand. “They can usually get the 50 W bulb working just fine, and one girl did manage to pedal hard enough to get a faint glow out of the 100 W bulb,” he says. “But nobody can do more than get the hairdryer sort of gently warm.” | <urn:uuid:7745d617-d554-4f4f-ad17-b2f2a6c360ac> | 2.8125 | 454 | Personal Blog | Science & Tech. | 39.732077 |
By Brianne, Coastal Studies for Girls
Last Friday, Dr. David Fields, Senior Scientist at Bigelow Laboratory for Ocean Science, gave the students of Coastal Studies for Girls a tour around the buildings. One of the highlights of the trip was their vast algal collection. All seventeen of us piled into the little refrigerated room that held extra marine phytoplankton cultures that are stored as “back ups” in case the something devastating happens to the cultures in the main building.
The National Center for Culture of Marine Phytoplankton (CCMP) functions much like a library. Each species of alga is cataloged with its own code so that it can be easily identified. Scientists are able to order these samples online by looking up the desired species in the catalog and then submitting an electronic form. When an order comes in for a certain alga, a single cell of that alga is taken from the library, grown to the requested amount, and sent off.
CCMP was derived from the private culture collections of Dr. Luigi Provasoli at Yale University and Dr. Robert R. L. Guillard at Woods Hole Oceanographic Institution. This collection was originally small due to inadequate resources for maintaining a large collection. But in March of 1980, the Biological Oceanography Program of the National Science Foundation held a workshop on the culturing of marine phytoplankton and it was there suggested that Dr. Guillard would run a single, national collection of marine phytoplankton. The collection was initially maintained at the Woods Hole Oceanographic Institution in Woods Hole, MA, but in the fall of 1981, it was moved to Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor, Maine.
Currently the CCMP stores cultures at five different temperatures:(- 2°C, 4°C, 14°C, 20°C and 25°C); there are two culture chambers for each temperature. There are three sets of cultures of each strain, and a fourth located in a separate building and maintained as a back up for the three.
All the information about how to order and culture your own marine phytoplankton is on their Web site. Not only does the CCMP maintain over 2500 strains of phytoplankton from around the world, but they also have some freshwater and heterotrophic organisms. Currently they are also undergoing major construction to move the collection to East Boothbay in November.
I know that I thoroughly enjoyed this experience; it was absolutely amazing! I believe that all of my fellow students were awed as well. The vastness of the collection is incredible! So much work goes into maintaining these little test tubes full of phytoplankton. They have to be fed every day and kept under special lamps. I was especially amazed when I saw that it was exactly like a library except it had test tube cultures instead of books. As a young, aspiring scientist, it was so exciting for me to see the power of science. We can now collect and maintain strains of phytoplankton from all over the world for many, many years. The technology that scientists use is so advanced and I just cannot wait to get my hands on it when I am older. We are the next generation of scientists, and I hope this experience inspired the other students as much as it inspired me.
Coastal Studies for Girls is the country’s only residential science and leadership semester school for 10th grade girls. CSG is dedicated to girls who have a love for learning and discovery, an adventurous spirit, and a desire to challenge themselves. | <urn:uuid:79006fc9-6f80-400d-90f7-f3166963dd10> | 2.734375 | 743 | Personal Blog | Science & Tech. | 47.849838 |
public interface KeyHolder
Implementations of this interface can hold any number of keys. In the general case, the keys are returned as a List containing one Map for each row of keys.
Most applications only use on key per row and process only one row at a
time in an insert statement. In these cases, just call
to retrieve the key. The returned value is a Number here, which is the
usual type for auto-generated keys.
|Modifier and Type||Method and Description|
Retrieve the first item from the first map, assuming that there is just one item and just one map, and that the item is a number.
Return a reference to the List that contains the keys.
Retrieve the first map of keys.
Number getKey() throws InvalidDataAccessApiUsageException
Keys are held in a List of Maps, where each item in the list represents the keys for each row. If there are multiple columns, then the Map will have multiple entries as well. If this method encounters multiple entries in either the map or the list meaning that multiple keys were returned, then an InvalidDataAccessApiUsageException is thrown.
InvalidDataAccessApiUsageException- if multiple keys are encountered.
Map<String,Object> getKeys() throws InvalidDataAccessApiUsageException
InvalidDataAccessApiUsageException- if keys for multiple rows are encountered | <urn:uuid:af54ca2d-0b1e-4cf4-94a4-d0e9dbbf45c1> | 2.75 | 291 | Documentation | Software Dev. | 34.021902 |
Physics Tip Sheet #55 - October 12, 2005
Contact: James Riordon
American Physical Society
Highlights in this issue: the first ever molecules of light, virtual learning trumps reality in lab class, and focusing ocean waves for fun and power.
Molecules of light
M. Stratmann, T. Pagel, and F. Mitschke
Physical Review Letters
Researchers at the University of Rostock in Germany have made the world's first molecules of light, which might allow a significant increase in the data transfer rate of fiber optical systems. The molecules are built of solitons, pulses of light that do not dissipate or easily lose their shape like most other types of pulses. Solitons are useful for transmitting information because the signals can travel over long distances without degrading.
Solitons are waves that can have characteristics similar to material particles, like electrons and billiard balls. The researchers claim that this is the first time anyone has made solitons stick together to form structures analogous to molecules.
Fiber optical systems transmit information by sending light signals through a fiber as a combination of zeros (dark) and ones (light). The data transfer rate for binary coding is fast approaching its fundamental limits, but it may be possible to bypass the limit by transmitting information as zeros, ones, and twos with soliton molecules representing the number two.
The Rostock scientists propose that using soliton molecules as the “two” in information coding could take telecommunications technology to the next level without expensive infrastructure upgrades. They also believe that it may eventually be possible to represent higher numbers with molecules comprised of more complex groups of solitons.
Virtual lab class is better than the real thing
N. D. Finkelstein et al.
Physical Review Special Topics – Physics Education Research
Students master concepts and skills more effectively when they work with computer simulations than when they handle real world components and experiments, according to a study of physics lab students. Researchers at the University of Colorado and the Kavli Operating Institute in Santa Barbara reached the conclusion after comparing students studying elementary electrical circuits. One group of students assembled circuits with wires, batteries, resistors and light bulbs, another assembled the same circuits in a graphical computer simulation. Those who performed experiments with computers significantly outperformed students using real world components on tests of their conceptual grasp of physics principles.
Surprisingly, the students interacting with computers also outperformed their peers in a follow up test requiring them to assemble a circuit with real components. The researchers propose that the real world components can add complications and distractions in lab class that slow learning. Computer simulations, on the other hand, are neater, simpler, and provide constraints that prevent distraction. Computer simulations also helped instructors to make more efficient use of their time with students because they were able to focus on concepts rather than the minutia of mechanically assembling circuitry.
Focusing ocean waves for power and mongo surf
Xinhua Hu and C. T. Chan
Physical Review Letters 95, 154501 (2005)
A new water lens may allow engineers to focus ocean waves. Focusing water waves could potentially enhance the output of wave-powered energy generation schemes, protect ocean front real estate from wave damage, and even amplify waves for surfing and other seaside recreation activities.
Researchers from the Hong Kong University of Science and Technology showed that it would be possible to make a lens from an array of vertical cylinders secured below the water, which focus small ocean waves into larger ones.
The researchers reached their conclusions by simulating the propagation of water waves through an array of ocean bottom-mounted cylinders. By varying the size and spacing of the cylinders, they showed that they could control the reflection, transmission and direction of the water waves through the array, in much the same way that mirrors and glass lenses control light.
Kendra Rand, James Riordon, and Ernie Tretkoff contributed to these tips.
Journal articles are available to journalists on request.
For media assistance with these or other physics stories, contact:
Head of Media Relations
American Physical Society
Ph: +1 301 209 3238
Fax: +1 301 209 3264 | <urn:uuid:9ae5cf67-4ff4-4302-bda4-44b951d5daa6> | 3.5625 | 852 | Content Listing | Science & Tech. | 28.690885 |
The Atlantic Meridional Overturning Circulation or AMOC is a current that carries warm water north, where it cools, falls to the bottom and returns south. As you can see here, it is part of a larger worldwide current system, often called the thermohaline circulation:
A failure of the AMOC is believed to have caused the Younger Dryas episode. The possibility of another shut-down, caused by global warming, has been widely studied. See for example:
Details of the ‘standard model’ of the AMOC have been questioned here:
Abstract: To understand how our global climate will change in response to natural and anthropogenic forcing, it is essential to determine how quickly and by what pathways climate change signals are transported throughout the global ocean, a vast reservoir for heat and carbon dioxide. Labrador Sea Water (LSW), formed by open ocean convection in the subpolar North Atlantic, is a particularly sensitive indicator of climate change on interannual to decadal timescales. Hydrographic observations made anywhere along the western boundary of the North Atlantic reveal a core of LSW at intermediate depths advected southward within the Deep Western Boundary Current (DWBC). These observations have led to the widely held view that the DWBC is the dominant pathway for the export of LSW from its formation site in the northern North Atlantic towards the Equator. Here we show that most of the recently ventilated LSW entering the subtropics follows interior, not DWBC, pathways. The interior pathways are revealed by trajectories of subsurface RAFOS floats released during the period 2003–2005 that recorded once-daily temperature, pressure and acoustically determined position for two years, and by model-simulated ‘e-floats’ released in the subpolar DWBC. The evidence points to a few specific locations around the Grand Banks where LSW is most often injected into the interior. These results have implications for deep ocean ventilation and suggest that the interior subtropical gyre should not be ignored when considering the Atlantic meridional overturning circulation.
A shutdown of the AMOC will affect different parts of Europe in different ways. There are multiple equilibria in the AMOC model (“on” and “off” states). For a description of how they arise in a simple case, and for maps of the regional temperature anomaly simulated by some climate models, see: | <urn:uuid:ff95fdb1-43bb-4f0b-b4c2-a3350519e9d5> | 3.703125 | 498 | Knowledge Article | Science & Tech. | 20.317772 |
Simply begin typing or use the editing tools above to add to this article.
Once you are finished and click submit, your modifications will be sent to our editors for review.
...strains, the daughter buds have a flagellum and are motile, whereas the mother cells lack flagella but have long pili and holdfast appendages at the end opposite the bud. The related Planctomyces, found in plankton, have long fibrillar stalks at the end opposite the bud. In Hyphomicrobium a hyphal filament (prostheca) grows out of one end of the cell, and the bud grows...
What made you want to look up "Planctomyces"? Please share what surprised you most... | <urn:uuid:d829a882-ab4f-40b4-a24d-4e1467a585ec> | 2.796875 | 158 | Knowledge Article | Science & Tech. | 58.005 |
U.S. Physicists Crack Mystery of "Mini-LHC" With a Little Help From Einstein
March 23, 2011 9:30 AM
comment(s) - last by
Electrons "ride the wave" of BELLA's laser pulse (white point), accelerating (blue) to near the speed of light (orange/red is pocket of deceleration.
(Source: Lawrence Berkeley National Laboratory)
In a normal time-frame 3D simulations of the laser in action (seen here) are impossible to simulate at sufficient time scales with current technology.
(Source: Lawrence Berkeley National Laboratory)
By switching your perspective to that of the wavefront, with help from Einstein's theory of relativity, the picture becomes much clearer. Here we see the laser ploughing ahead (blue/red) and the plasma accelerating in its wake (silver ball).
(Source: Lawrence Berkeley National Laboratory)
Accelerator's laser burrows through plasma, relativistically
SLAC National Accelerator Laboratory
, measures in at 2 miles in length and can propel and electron beam with up to 50 billion electron volts (GeV). But many feel that a respectively tiny tabletop accelerator designed at California's
Lawrence Berkeley Laboratory
is an even more impressive achievement.
The BErkeley Lab Laser Accelerator (BELLA) uses a laser-plasma wakefield acceleration to achieve 10 GeV of beam power on a compact designs that fits on the table. You can think of this as the mini-cousin of CERN's famous
Large Hadron Collider
(LHC), an accelerator which is roughly 700 times as powerful,
operating at up to 7 trillion electron volts
(TeV)(athough it's worth noting that BELLA's capabilities are significantly different from the LHC's).
Like the SLAC and the LHC, the goal of BELLA is to produce highly energetic collisions,
spawning exotic particles
and unlocking mysteries of the physics world. But to properly support and understand your experimental evidence, you have to be able to properly "view" the system in simulated operation, navigating it in three dimensional computer images, in order to understand fully how the device works.
Such 3D views eluded even powerful supercomputers due to the physics driving BELLA. So a team led by Jean-Luc Vay at Berkeley Lab's Accelerator and Fusion Research Division (AFRD) tapped ideas of late great physicist Albert Einstein to try to solve the puzzle.
I. Mission Impossible: Riding the Laser Wave
BELLA is a fickle tool that operates in a wildly different length scales. The high-energy laser pulse navigates through a thin plasma tunnel measuring mere centimeters. The pulse creates a wake of plasma behind it, much like a speedboat. Electrons are excited by the laser jump on and hitch a ride on the waves, accelerating up to their top collision energy.
The wildly varying scales pose a huge headache for the physicists who tried to simulate it. Describes [
] Professor Vay, "Most researchers assumed that since the laws of physics are invariable, the huge complexity of these systems must also be invariable. But what are the appropriate units of complexity? It turns out to depend on how you make the measurements."
Simulations typically use grids, representing the electromagnetic fields inside the device. The narrow width and large length pose a major challenge, according to the AFRD's Cameron Geddes, who worked on the project.
Describes Geddes,"The most common way to model a laser-plasma wakefield accelerator in a computer is by representing the electromagnetic fields as values on a grid, and the plasma as particles that interact with the fields. Since you have to resolve the finest structures -- the laser wavelength, the electron bunch -- over the relatively enormous length of the plasma, you need a grid with hundreds of millions of cells."
To make matters worse, simulators also needed to simulate those hundreds of millions of cells through millions of timesteps, simulating the trajectory of the laser beam. In full 3D the task appeared impossible, even
for a supercomputer
. In grossly simplified 1D (linear) simulations, it still took 5,000 hours of supercomputer processor time at Berkeley Lab's National Energy Research Scientific Computing Center (NERSC) to run a single simulation.
Yet without that simulation the researchers wouldn't be able to fully perfect the device's operation or support/understand their results.
II. Cracking Space-Time
To solve the challenge the team implement an idea that Professor Vay proposed in 2007.
The laser beam travels at near the speed of light as it zooms through its little plasma tunnel. To the human perspective it creates wildly varying electromagnetic pulse fields, which are
hard to simulate (require fine time scales and lots of time steps).
But Albert Einstein suggested in the early twentieth century that while outside observers may perceive
light speed travelers
as moving in outlandish and hard to assess fashion, that the traveler themselves will perceive their actions as moving at a normal speed. In order to switch from the viewer to the traveler's perspective, you need a math trick called a Lorentz transformation.
Using the Special Theory of Relativity, the researchers were able to crack the puzzle.
From the laser's perspective, time slows, the plasma wave oscillation frequency decreases, and space contracts -- making the plasma shorter.
But despite that insight, the mystery wasn't yet fully solved. Shifting to the laser's viewpoint caused numerical instabilities, compromising the simulation's results. If they couldn't solve this problem, the method would be worthless.
So Professor Vay's team attempted to switch from the laser's perspective to the perspective of the electron wavefront, which accelerates along with the laser. The switch did the trick, eliminating the instabilities.
Thus the trick was not only to shift to a frame of reference closer to light speed, but to shift to the
By shifting from the stationary frame to the correct "boosted" laser frame with the help of Lorentz transformations, the physicists were able to accomplish the seemingly impossible -- create 3D views of BELLA's insides in action.
Describes Professor Vay, "We produced the first full multidimensional simulation of the 10 billion-electron-volt design for BELLA. We even ran simulations all the way up to a trillion electron volts, which establishes our ability to model the behavior of laser-plasma wakefield accelerator stages at varying energies. With this calculation we achieved the theoretical maximum speedup of the boosted-frame method for such systems -- a million times faster than similar calculations in the laboratory frame."
III. The Future is Laser-Bright
The team looks forward to new challenges, now that they've cracked BELLA's most critical mystery. Namely, for materials science and biology applications, the simulations will grow more complex and the technique may need to be tweaked slightly in order to properly predict what will happen.
These predictions will be critical as, along with the experimental evidence they will provide a semi-conclusive picture of how the device works.
In the meantime, Professor Vay and his team can enjoy the prestige generated by their new paper [
] in the peer-reviewed journal
Physics of Plasmas
. Along with the team leader, the paper's other coauthors were Cameron Geddes, Estelle Cormier-Michel of the Tech-X Corporation in Denver, and David Grote of Lawrence Livermore National Laboratory.
The team was supported by the U.S. Department of Energy's Office of Science.
This article is over a month old, voting and posting comments is disabled
3/24/2011 10:30:30 AM
How DARE you use deductive logic on a message board. Oh the insanity of using logic in this day and age. You sir, should be ashamed of yourself. /sarcasm
3/25/2011 3:59:18 AM
All I want to know is.. what type of new inventions could be made from their discoveries that would benefit life we have today...
"I'm an Internet expert too. It's all right to wire the industrial zone only, but there are many problems if other regions of the North are wired." -- North Korean Supreme Commander Kim Jong-il
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Thionin - The Two - Faced Reaction
Concept: Photochemical reaction, Oxidation/reduction, and Reversable chemical reaction
Preparation: Prepare 0.001 M thionin solution by adding 100 mL distilled water to 0.023g of thionin. Stir to dissolve. The thionin has a poor shelf life; use within one week.
Introduction: So far we have been making chemical reactions by mixing varous chemicals with each other. In this demo, no new chemicals are being added. What will be added though is a light source. Let's see what happens to this purple solution when light is added.
Next I will place the solution on the overhead with half of the solution exposed to the light and half covered up. What do you think will happen?
The result is what we like to call the two faced reaction. One half stays purple, the other half has turned colorless.
Explanation: Thionin is an organic compound that can exist in an oxidized form (purple) and a reduced form (colorless).
In this experiment, light induces the reduction of thionin by iron (II) ions.
2 Fe2+ + thionin (purple) 2 H+ + light ---> 2 Fe3+ + reduced thionin-H2+ (colorless)
In the presnece of light, the iron ions give 2 electrons to the thionin and it also picks up 2 hydrogen ions to convert to the reduced form of thionin. This is an example of light energy being converted into chemical energy.
When the solution is taken away from the light, the purple color of the oxidized form of thionin rapidly returns and demonstrates an equilibrium reaction. If part of the solution is shaded, the boundry between the colorless and purple form is very sharp.
Safety: Sulfuric acid is severely corrosive to eyes and skin and is toxic. Use extreme caution when handling. Ferrous sulfate is slightly toxic by ingestion. Wear goggles and chemical resistant gloves.
Waste Disposal: The two-faced solution can be rinsed down the drain with excess water.
Resource: Philip S. Chen, Entertaining and Educational Chemical Demonstrations, Chemical Elements Publishing Co., 1974, p. 57-58.
Flinn Scientific, Chem Fax, Thionin - the Two Faced Solution, Pub. No. 0815.00. | <urn:uuid:7ef99278-4413-4631-a50c-5ebabb7f3bd2> | 3.5 | 512 | Tutorial | Science & Tech. | 58.562864 |
contact action noun acceleration of a chemical reaction induced the presence of material that is chemically unchanged at the end of the reaction; `of the top 50 commodity chemicals, 30 are created ...
Found op http://wordnetweb.princeton.edu/perl/webwn?s=catalysis
(kә-tal´ә-sis) increase in the velocity of a chemical reaction or process produced by the presence of a substance that is not consumed in the net chemical reaction or process; negative catalysis denotes the slowing down or inhibition of a reaction or process by the presence of such a su...
Found op http://www.encyclo.co.uk/local/21001
• (n.) Dissolution; degeneration; decay. • (n.) A process by which reaction occurs in the presence of certain agents which were formerly believed to exert an influence by mere contact. It is now believed that such reactions are attended with the formation of an intermediate compound or com...
Found op http://thinkexist.com/dictionary/meaning/catalysis/
in chemistry, the modification of the rate of a chemical reaction, usually an acceleration, by addition of a substance not consumed during the ... [10 related articles]
Found op http://www.britannica.com/eb/a-z/c/36
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Cata...
Found op http://en.wikipedia.org/wiki/Catalysis
is a phenomena in which a relatively small amount of material augments the rate of reaction without itself being consumed.
Found op http://www.amgas.com/gloss.htm
The changing of a rate of a chemical reaction by the addition of a small amount of a substance which is unchanged at the end of the reaction. Such a substance is called a catalyst, though this term is usually reserved for substances which speed up reactions; additives which slow down reactions are c...
Found op http://www.daviddarling.info/encyclopedia/C/catalysis.html
Type: Term Pronunciation: kă-tal′i-sis Definitions: 1. The effect that a catalyst exerts on a chemical reaction.
Found op http://www.medilexicon.com/medicaldictionary.php?t=14935
1) Chemical action 2) Chemical change 3) Chemical process 4) Contact action
Found op http://www.mijnwoordenboek.nl/EN/crossword-dictionary/catalysis/1
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As of today, the Wikipedia entry for the hummingbird explains that the bird's flight generates in its wake a single trail of vortices that helps the bird hover.
But after conducting experiments with hummingbirds in the lab, researchers at the University of California, Riverside propose that the hovering hummingbird instead produces two trails of vortices — one under each wing per stroke — that help generate the aerodynamic forces required for the bird to power and control its flight.
The results of the study could find wide application in aerospace technology and the development of unmanned vehicles for medical surveillance after natural disasters.
The researchers used high-speed image sequences — 500 frames per second — of hummingbirds hover-feeding within a white plume (emitted by the heating of dry ice) to study the vortex wake from multiple perspectives. They also used particle image velocimetry (PIV), a flow-measuring method used in fluid mechanics, to quantitatively analyze the flow around the hummingbirds. PIV allowed the researchers to record the particles surrounding the birds and extract velocity fields.
The films and velocity fields showed two distinct jets of downwards airflow — one under each wing of the hummingbird. They also revealed that vortex loops around each jet are shed during each upstroke and downstroke.
The researchers therefore propose in their paper published online last month in the journal Experiments in Fluids that the hummingbird's two wings form bilateral vortex loops during each wing stroke, which is advantageous for maneuverability.
"Previous studies have indicated that slow-flying bats and faster flying birds produced different structures in their wakes," said Douglas Altshuler, formerly an assistant professor of biology at UC Riverside, whose lab led the research. "We have been investigating the wake structure of hovering hummingbirds because this allows us to decouple the effects of different types of wings — bat versus bird — from different forward flight speeds.
Hummingbirds each weigh 2-20 grams. Because they can hover with high precision, they are able to drink nectar from flowers without any jiggling movement to their bodies. Besides using upstrokes and downstrokes, hummingbirds can rotate their wings. They can even flap their wings from front to back with a 180-degree amplitude.
"We began this study to investigate how the hummingbird used its tail while hovering," said Marko Princevac, an associate professor of mechanical engineering and a coauthor of the research paper. "After all, many insects also hover, but they have no tail. Instead, however, our research showed something interesting about the hummingbird's wings: the bilateral vortex structure. Hummingbirds hovering should cost a lot of energy but these birds are able to hover for long periods of time. Ideally, unmanned vehicles need to be operated with a very limited energy supply, which is why understanding how the hummingbird maximizes its use of energy is tremendously beneficial."
Sam Pournazeri, a former Ph.D. graduate student in Princevac's lab and a co-author on the paper, explained that in a downstroke, the air pressure difference developed as a result of wing movement creates flow from the bottom to the top of the wing. The result is a circular movement or vortex.
"Based on theories in fluid mechanics, this vortex should close either on the wing/body or create a loop around it," he said. "It's these loops that provide circulation around the wings and cause the hummingbird to overcome its weight. Hovering requires the bird to create a lift that cancels its body weight. Although the two-vortex structure we observed increases the hummingbird's energy consumption, it provides the bird a big advantage: a lot more maneuverability."
Next, the research team plans to study the hummingbird in a wind tunnel to closely observe how the bird transitions from hovering to forward motion, and vice versa.
"Current technology is not successfully mimicking how living things fly," Princevac said. "Drones don't hover, and must rely on forward motion. Research done using hummingbirds, like ours, can inform the development of the next generation of drones."
The research was funded by a grant from the National Science Foundation to Altshuler, now a faculty member at the University of British Columbia, Canada.
Paolo S. Segre, a former UCR graduate student working with Altshuler at the University of British Columbia, also participated in the study. Pournazeri and Segre contributed equally to the research.
The University of California, Riverside is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus will open a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion. A broadcast studio with fiber cable to the AT&T Hollywood hub is available for live or taped interviews. UCR also has ISDN for radio interviews. To learn more, call (951) UCR-NEWS.
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|Kinesin dimer / David S. Goodsell, Scripps Research Institute|
One way to transport objects inside a cell is by the use of Kinesin motor proteins. Three things are required: a motor to move the cargo, a track along which to move it, and the cargo itself that needs to be delivered.
Proteins are essential components of cells that are involved in a number of processes. They are formed by linking amino acid molecules together in chains. The sequences of amino acids needed to build proteins are specified by genes as part of the genetic code.
Motor proteins are a special form of protein that do physical work. Remarkably, these proteins have the ability to move along surfaces, transport cargo that is attached to them, or produce force. They use the chemical Adenosine Triphosphate (ATP) as an energy source to power their movement. The motor protein myosin, for example, is involved in the contraction of muscle fibers in animals. Dynein is a motor protein that is found in flagella, the long tail-like structure that projects from certain types of cells like sperm to help the cell move.
Microtubules are one of the components of the cytoskeleton, the infrastructure that supports the cell. They are made by linking repeating units of the tubulin protein together. The resulting chain is then curled into a hollow cylindrical shape. They can grow or shrink to produce force, and also serve as conduits along which other cellular components can be transported.
Kinesin Cargo Transportation
Small molecules in the cell can move to where they are needed by the process of diffusion. However, larger molecules that are synthesized in the cell body are transported by motor proteins to their destinations. Kinesins are a type of motor protein that use microtubule tracks to walk along.
Two intertwined chains with globular heads on one end form a Kinesin dimer. To move, the heads repeatedly attach and detach to the tubulin units of the microtubule track, moving everything forward in a hand-over-hand fashion. The opposite ends of the dimer drag the cargo along that they are attached to.
Thanks to Nested Universe reader Faris Naji for inspiring this topic, and discovering the attached video which shows the Kinesin protein in action.
by Chris K. Haley, NestedUniverse.net
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Read more: "Special report: After Japan's megaquake"
Six days after the earthquake that rocked Japan and left thousands dead, the nation is now struggling to avert disaster at its Fukushima Daiichi nuclear power plant. Events have moved fast and risks are hard to assess.
The worst nuclear accident in history was the Chernobyl explosion of 1986 in what is now Ukraine. Nuclear experts have repeatedly stated that the Japanese situation cannot get as bad as Chernobyl. New Scientist explains why.
What has happened so far in Japan?
Following Friday's magnitude-9 earthquake off the coast of Japan, the nuclear reactors at Fukushima Daiichi automatically shut down – as they were meant to. However the cooling systems have repeatedly failed, leading the cores of some of the reactors to overheat.
This has led indirectly to explosions damaging both the outer buildings and parts of the containment systems intended to prevent radioactive material from escaping. Because of these breaches, some of that material has got into the atmosphere.
Additionally, ponds containing used fuel rods have been overheating, and could potentially lead to more contamination.
What happened at Chernobyl?
Staff at the plant were running tests to find out how well they could cope with a temporary shutdown of the reactor's cooling system. The test went wrong and there was a power surge. The staff tried to shut the reactor down, but instead the nuclear reaction accelerated rapidly.
"For a few seconds it was generating thousands of times the normal power output," says Michael Bluck of Imperial College London. The extreme heat from the nuclear reaction triggered an explosion, which blew the roof off both the reactor vessel and the building containing it – exposing the reactor core to the outside world – and sending radioactive material hurtling into the atmosphere.
Fires then started. Most were put out within hours, but the one in the damaged reactor burned for many days, spreading radioactive material still further.
How bad was Chernobyl?
Chernobyl is the only event ever to be given the maximum rating of 7 on the International Nuclear and Radiological Event Scale, which measures the severity of nuclear accidents. This means it released a major amount of radioactive material that covered a wide area.
It's too early to say how the Fukushima Daiichi incident will compare. The Japanese authorities provisionally put the event at level 4, a "local accident". Earlier this week, however, the French nuclear agency rated the disaster as at least a level 5 or 6.
What is different about the Fukushima Daiichi accident?
The Chernobyl reactor was actually running – albeit at low power – at the time of the accident there. By contrast the Fukushima Daiichi reactors automatically shut down as soon as they felt the earthquake, by inserting control rods so the nuclear reactions in their cores began slowing within seconds. This means that, from the outset, the amount of heat being produced was much smaller than at Chernobyl.
So why couldn't a runaway reaction happen at Fukushima Daiichi?
The Chernobyl reactor had a fundamentally different design to those at Fukushima Daiichi. Chernobyl ran on unenriched uranium, which is a fairly weak nuclear fuel. In order to use it, the reactor was designed in a way that made it easier for the nuclear reaction to accelerate. This allowed it to generate useful amounts of power, but it also left it vulnerable to running out of control.
Fukushima Daiichi runs on more powerful fuels than Chernobyl did, mostly enriched uranium. In contrast to the Ukrainian reactor, its design minimises the nuclear reaction unless its human operators boost it. "You have to actually try to make it go," Bluck says.
Ordinarily the reactor cores are surrounded by water. Heat from the nuclear reaction boils the water, creating steam that drives turbines which generate electricity. In doing so, the water also helps to cool the reactor.
But crucially, the water is also a "moderator": it helps keep the uranium fission reaction going by slowing down neutrons produced by the reaction as they hurtle out of the fuel rods. Slow neutrons sustain the reaction, by liberating still more neutrons and heat from uranium atoms in the rods; fast-moving neutrons just pass straight through the other fuel rods without colliding with other uranium atoms. If the water heats up too much, however, bubbles form within it and these allow the neutrons to escape, slowing down the nuclear reaction.
Effectively, if the coolant overheats, it starts shutting down the reaction without any human intervention. "It's a brilliant solution," Bluck says.
Nuclear engineers call this a "negative void coefficient", because having voids – bubbles – in the coolant slows down the reaction. By contrast Chernobyl had a positive void coefficient, so the reaction was more likely to accelerate.
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
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Thu Mar 17 18:59:45 GMT 2011 by Tom
Is it possible to get an update on Bluck's views?
It seems the worse case is that the cooling water drains, that the sea water added causes corrosion leading to leaks/cracks due to the effects of salt in the water, and that people aren't able to access the site to help the situation due to a potential rise in radiation above a certain level. Then the site is left to it's own devices.
There seems to be some circular reasoning as to worse/best case scenarios, assuming that the addition of water/coolant will be possible, for the length of the time that the site needs cooling.
So that'd be the follow up question - how long do the reactors, spent fuel in the pools need cooling? What would happen if no further cooling could be taken? Would there be the possibility that fires/explosions could bring radioactive material into the air that would travel further than initially expected?
"spent" Fuel Ponds
Fri Mar 18 14:38:17 GMT 2011 by Eve
"Spent" fuel ponds is a misnoma since a full core offload for reactor 4 occurred in November 2010 to allow inspections. The "Spent" fuel ponds therefore contain utlizable fuel. How much fuel, what configuration it is stored in and what efficiency these fuel rods were utilized at needs to be documented.
Sat Mar 19 02:09:18 GMT 2011 by etudiant
A seriously radioactive site which is cluttered with the debris of four exploding reactor buildings isolated in a lunar post tsunami landscape is tough enough.
Add 7 spent fuel pools, loaded with decades worth of spent fuel, at least one of which has been damaged enough for the fuel to be exposed and start reacting with the water setting off fires and explosions, plus radioactive plumes.
It seems very early to confidently state that this won't be another Chernobyl. The US, which recommends maintaining at least a 50 mile radius from the plant, seems less certain.
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Watch the video to find out what lichens can tell you about pollution levels in your local environment.
You can find out a lot about air quality in your area by studying lichens on local trees, as different lichens thrive in different conditions.
The golden shield lichen, Xanthoria parietina, for example, can live in areas with high levels of nitrogen, especially ammonia, and so it can be used to monitor nitrogen levels in the atmosphere. It is common on trees and buildings near farmland and on sea cliffs where seabirds provide nitrogen.
The golden shield lichen is made up of a fungus, which forms the body of the lichen, and a green alga. The alga provides nutrients for the fungus through photosynthesis while the fungus provides protection for the alga from drought and UV light.
This is an example of a symbiotic relationship, where 2 organisms live together and both benefit.
The Open Air Laboratories network is running an air survey to find out about pollution levels in the air all over the UK. Anyone can take part.Join the OPAL air survey | <urn:uuid:f68f33f5-890f-48db-8ce4-0570e2cf7a34> | 3.6875 | 224 | Knowledge Article | Science & Tech. | 47.508142 |
Reducing a Map Path Using Douglas-Peucker Algorithm
The Douglas-Peucker Algorithm
The Douglas-Peucker algorithm is used to reduce the number of points in a line. It does so by discarding points that do not deviate significantly between its surrounding points.
The amount a point may deviate before it is excluded is an input to the algorithm, and naturally will impact the number of points that are excluded.
The algorithm works as follows:
- Begin with the first and last points in the path (let's call them
Brespectively). These are always kept.
- Find the point between the first and last that is furthest away from the line joining the first and last line (the orthogonal distance).
- If this point is greater than the allowed tolerance, this point is kept (let's called it
- Repeat this algorithm twice: once using
Aas the first point and
Xas the last point, the other time using
Xas the first point and
Bas the last point.
This algorithm is recursive, and continues until all points have been checked.
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Among the many studies that have investigated the effects of urbanization on wildlife, few, if any, have focused on a species primarily valued as an economic commodity. This knowledge gap was recently addressed by researchers from the University of Illinois who studied the effects of anthropogenic landscape alterations on muskrats (Ondatra zibethicus). These animals, native to North America and invasive in Europe, Asia, and South America, are a valuable source of fur (at one recent auction, their pelts sold for approximately $6 apiece); in some areas, they are even eaten. Muskrats are particularly interesting in an anthropogenic disturbance context because, as semiaquatic animals, they are exposed to human habitat modifications while both on land and in the water.
(A muskrat, Ondatra zibethicus)
The muskrat study was designed to measure the animals' tolerance of 2 major anthropogenic habitat changes: introduction of an invasive species (reed canary grass, Phalaris arundinacea) and degradation of territory suitability via modification or removal of preferred habitat. The reed canary grass is thought to have lower nutritional value than native vegetation, and its introduction has led to dramatic reconfigurations of local ecosystems. Thus, the researchers anticipated that they would find fewer muskrats in areas with high levels of this invasive species. However, the broader landscape-level characteristics of anthropogenic disturbance--such as the presence of urban habitat and associated increases in stream flow--were predicted to have a positive impact on muskrats by, among other things, releasing them from the risks of predation and trapping.
The research was carried out in the Grand Prairie Region of central Illinois, an area containing 5 watersheds with a variety of streams ranging from small headwaters to large rivers. The study sites were selected such that 50% were near incorporated towns, and the other 50% were in more rural (i.e., agricultural) areas; thus, the researchers were able to survey muskrat habitat along an anthropogenic disturbance gradient. Over a 2-year study period, 518 surveys were conducted along 200-m stretches of stream at 90 sites.
(Reed canary grass, Phalaris arundinacea. Native to temperate Europe, Asia, and North America, this invasive species was introduced in the 1880's to provide forage for animals and help reduce erosion. According to a recent report by the Eastern Forest Environmental Threat Assessment Center, the species is now found in 43 of 50 U.S. states.)
The first goal during each survey was to locate evidence of muskrat occupancy--scat, tracks, signs of feeding, the presence of burrows, or, of course, muskrats themselves. The second goal was to record local and landscape-level habitat characteristics that might be associated with muskrat occupancy. These included variables associated with the stream and its banks--width and depth of the channel, percent sand in the soil, width of the wooded habitat on either side of the stream, and various aspects of the bank morphology--as well as type, amount, and dominant vegetation in the land cover within a 500-m buffer around each site. The scientists then constructed "occupancy models," which pinpoint the habitat characteristics most closely associated with the presence of muskrats.
During both years of the study, muskrats were detected in over half the sites surveyed. The probability of occupancy could be predicted by 4 major habitat characteristics: size of the stream, height of the stream bank, percentage of sand in the soil, and amount of urban land cover. Specifically, muskrats were more likely to be found in territories with larger streams that had higher banks (in which the muskrats dig their burrows), more clay-ey soil (which is easier to shape a burrow from), and higher levels of impervious surface cover and human structures. Surprisingly, and despite the fact that reed canary grass was the dominant species at approximately half of the sampling stations at each site, the presence of this nonnative plant did not seem to have an impact on muskrat occupancy. In fact, muskrats were frequently observed carrying reed canary grass clippings, suggesting that they were eating it, using it to build nests, or both.
The ability of muskrats to happily inhabit human-modified areas suggests that these animals are urban adaptors. This is not entirely surprising given their small body size and behavioral plasticity--two traits common in species that are tolerant of anthropogenic disturbances. Overall, anthropogenic habitats like the ones studied here provide many potential benefits for muskrats. Streams in and near urban areas are often deep and quick-running as a result of high levels of runoff from impervious surfaces. This means that they probably provide good cover from potential muskrat predators, such as American mink (Neovison vison), coyotes (Canis latrans), and red foxes (Vulpes vulpes). Human environments are characterized by the presence of culverts, the use of which helps muskrats avoid potential collisions with cars. Additionally, anthropogenic areas typically contain many small bodies of water (such as decorative ponds) that can act as "stepping stones" for dispersing individuals.
It is possible that muskrats in other locations at the extreme ends of the "disturbance spectrum"--such as those in more built-up cities or even "wilder" rural areas--might show different responses to the human disturbance factors measured here. It is also not clear whether the animals suffer nutritional deficits from the potential inclusion of reed canary grass in their diets. Finally, there is little information on the longer-term dynamics of territory selection and abandonment. Thus, additional data need to be collected before any definitive conclusions can be drawn about the health of muskrat populations in disturbed areas.
Cotner, L.A., Schooley, R.L. 2011. Habitat occupancy by riparian muskrats reveals tolerance to urbanization and invasive vegetation. Journal of Wildlife Management 75(7):1637-1645.
Thanks to the following websites for providing the images used in this post: | <urn:uuid:1bf979d1-cba4-42eb-8a6c-9898e97bee4d> | 3.703125 | 1,267 | Knowledge Article | Science & Tech. | 26.678466 |
The unusually high mortality reported among endangered sea turtles in the wake of the oil spill in the Gulf of Mexico raises legitimate fears for the future of these ocean-dependent creatures. An initial survey carried out 10 days after the Deepwater Horizon well blowout found 156 dead turtles, most of them Kemp's Ridleys. The case of this species, now in its nesting season, is particularly poignant. It has been saved from critical decline after an oil spill in the Gulf in 1979 from the Ixtoc 1 rig caused severe degradation of its nesting area. Miraculously, its numbers bounced back, from a few hundreds to several thousands, thanks to good conservation. The plumes of oil in the ocean now threaten that outcome. Decades of painstaking work by scientists, wildlife officials, and lay turtle lovers could now be undone. In a morbid twist, one website started accepting serious bets on the possible extinction of the Kemp's Ridley due to oil pollution. Such an end for these long-surviving creatures would be a shocking price to pay for the failure of the oil industry and governments to adhere to environmental safety norms. Surely, the time has come to end laissez faire regulatory policies that have allowed the oil industry to throw environmental safety to the winds.
The danger to the Kemp's Ridley from BP's Deepwater Horizon has turned the attention of conservation groups to the need for massive community mobilisation for rescue and rehabilitation in the near future. Here, the initiative of the Caribbean Conservation Corporation, a science-based non-profit organisation, to get rescuers trained in handling oil-affected turtles is laudable. The CCC initiative to celebrate Sea Turtle Day on June 16, and encourage citizens to have high-profile sea turtle ‘parties' in their neighbourhoods, is promising. Such events provide much-needed information on the long evolutionary heritage of these animals and fast-emerging threats. Such awareness is vital to impress upon legislators that permission for offshore drilling activity, which often translates into near-shore well sites, could prove devastating to the nesting beaches of turtles. There is also a strong case to inspect anew the drilling rigs in operation, to ascertain the safety mechanisms available to prevent environmental damage in an accident. Marine conservation groups have been particularly worried about the ability of a bigger BP-owned oil well in the Gulf of Mexico, the Atlantis, to handle a similar accident. It should be evident from the harm done recently that a green future for turtles and all other life lies in an energy paradigm that diverges from oil. | <urn:uuid:94da94f0-510d-4633-861b-16981769a4e2> | 3.375 | 506 | Nonfiction Writing | Science & Tech. | 31.095863 |
The 2010 hurricane forecast calls for an above average year for hurricanes and tropical storms. El Nino has weakened which means less wind shear in the tropics. Also, ocean temperatures are running 4 degrees warmer than average. Warm water is critical for storm development.
The oil spill in the gulf is small compared to a hurricane. Some hurricanes have been almost as large as the entire Gulf of Mexico itself. The turbulence caused by a cyclone would most likely disperse the oil but depending on landfall, the oil could get washed ashore, or get pulled out farther into the Gulf.
In other words, the oil spill itself will have virtually no impact on a hurricane, but the hurricane will have both a good and bad impact with the oil it interacts with.
Ed Buckner explains more and notes some more memorable hurricanes to affect Arkansas in this edition of Weather 101.
To learn more about the Gulf of Mexico oil spill, visit our special section on todaysthv.com for the latest tweets, photos and information. | <urn:uuid:884260cd-fbf5-44aa-9313-0daad5404896> | 2.703125 | 204 | Truncated | Science & Tech. | 49.042701 |
The staurolite structure consists of oxygen atoms in an approximately cubic close packing. However, the cation arrangement does do not have cubic symmetry. The structure consists of dioctahedral sheets joined by isolated octahedra. Silica tetrahedra fill the gaps between octahedra. A polyhedral model is below.
Below is a ball model of staurolite. Blue atoms are oxygen, yellow and orange are iron or magnesium, and green are silicon.
Created 18 September 1998, Last Update 22 September 1999
Not an official UW Green Bay site | <urn:uuid:aa815830-e3db-40ea-b845-4ce8d13324f7> | 2.734375 | 119 | Knowledge Article | Science & Tech. | 29.677108 |
During the last 5 years, a set of methodologies have become popular, called agile methodologies . An agile methodology is, in general, one that emphasizes incremental development and small design steps guided by frequent interactions with customers. The customer and developers get together and agree on the next set of features and capabilities for the software. Ideally, the work should take at most a few weeks. The developers then make the additions and the software is released to the customers, who react to it, perhaps making corrective suggestions.
Agile methodologies and open source would seem, at first glance, to be radically different: Agile methodologies are thought of as being about small, collocated teams and open source as being about large, distributed ones. A company might expect that the benefits of one are pretty different from the benefits of the other. Agile methodologies arose, largely, from the ranks of paid consultants, whereas open source seems like a hippie phenomenon. A company might, therefore, believe there is a sharp choice to be made between them, but the choice has more to do with the conversations, the diversity of participants, and the transparency of the process to the outside world than it does with the philosophy of design and development: The two approaches share many principles and values.
Some agile methodologies have special practices that set them apart from others--for example, extreme programming uses pair programming and test-driven development. Pair programming is the practice of two people sitting at the same computer screen with one person typing and the other observing and commenting. Instead of one person sitting alone with his or her thoughts, pair programmers engage in a conversation while working, which serves as a real-time continuous design and code review. Test-driven development is the practice of defining and implementing testing code before the actual product code is implemented. The following are the agile development principles taken from the Agile Manifesto website1 --most of these principles also apply to open source, except as noted.
In short, both the agile and open-source methodologies embrace a number of principles and values, which share the ideas of trying to build software suited especially to a class of users, interacting with those users during the design and implementation phases, blending design and implementation, working in groups, respecting technical excellence, doing the job with motivated people, and generally engaging in continuous (re)design.
A good example of a company-related open-source project that embraces both open-source and agile values is the Visualization ToolKit (VTK), which is partly sponsored by GE. VTK is a software system for 3D computer graphics, image processing, and visualization, and portions of it are subject to patents held by GE and a smaller company called Kitware. As its website states:
VTK supports a wide variety of visualization algorithms including scalar, vector, tensor, texture, and volumetric methods; and advanced modeling techniques such as implicit modelling, polygon reduction, mesh smoothing, cutting, contouring, and Delaunay triangulation. In addition, dozens of imaging algorithms have been directly integrated to allow the user to mix 2D imaging/3D graphics algorithms and data. The design and implementation of the library has been strongly influenced by object oriented principles. VTK has been installed and tested on nearly every Unix-based platform, PCs (Windows 98/ME/NT/2000/XP), and Mac OS X Jaguar or later.2
The kit is substantial, encompassing over 600 C++ classes and around half a million lines of code. There are over 2000 people on the VTK mailing list. GE's stance regarding VTK as a commercial advantage is summed up in the following statement: "We don't sell VTK, we sell what we do with VTK."3 GE has a number of internal and external customers of the toolkit--it is used in a variety of projects GE is involved with. Kitware provides professional services associated with VTK.
As an open-source project, VTK is a bit unusual, and this is the result of some of its principals being involved with GE, which is the prime supporter of a design and implementation methodology called six sigma . Six sigma refers to a statistic that states that a manufactured artifact is 99.99966% defect-free, and it also refers to a process in which factors important to the customers' perception of quality are identified and systematically addressed during a design and implementation cycle whose steps are Define, Measure, Analyze, Improve, Control (DMAIC). Open source involves the possibility of diverse innovations and also provides opportunities for interacting with customers in a direct way, which is appealing to an organization focused on customers, but there is also the possibility of erratic results when there is not a strong, explicit emphasis on quality that can be enforced. Therefore, open source went only part of the way to satisfying GE's goals for quality.
Moreover, the original VTK implementation team was small and dispersed within GE, and its members were admittedly not software engineers. The open-source component added to this the need to find a way to handle quality. The solution was to adopt some of the practices of Extreme Programming, which is one of the agile methodologies. Extreme Programming (or XP) emphasizes testing and advocates a practice called test-driven design in which tests are written at the same time as, or before, the code is designed and written.4 Writing tests first has the effect of providing a sort of formal specification--the test code--as well as a set of tests to be used for regression and integration testing. XP calls for frequent (tested) releases, and VTK combines this with the open-source practice of "release early, release often" to do nightly, fully tested builds.
The VTK developers implemented a regimen in which submitted code is tested overnight using a large corpus of regression tests, image regression tests (comparing program output to a gold standard), statistical performance comparisons, style checks, compilation, error log analyses, and memory leak and bounds-check analyses; the software's documentation is automatically produced; and the result is a quality dashboard that is displayed every day on the website. The dashboard is similar to those produced by the Mozilla project,5 but considerably more detailed. The tests are run on around 50 different builds on a variety of platforms across the Internet, and distributions are made for all the platforms.
This is not all. The VTK website provides excellent documentation and a coding style guide with examples. Most of the details of the mechanics of the code are spelled out in detail. Moreover, there are several textbooks available on VTK.
In short, the VTK open-source project has integrated open-source and extreme-programming practices to satisfy GE's need to express to customers its commitment to quality, even in projects only partially controlled by GE. Furthermore, GE has tapped into a larger development community to assist its own small team, so that its customers get the benefits of a high-functionality, high-quality system infused with GE values.
The primary source of similarities between open-source and the agile methodologies is their shared emphasis on continuous (re)design. Continuous design is the idea that design and building are intertwined and that changes to a design should be made as more is learned about the true requirements for the software. This is why both camps agree with the mantra, "release early, release often."
Continuous design is an approach that is predicated on recognizing that it is rarely possible to design perfectly upfront. The realization is that design is often the result of slowly dawning insights rather than of knowing everything at the start of the project and that, like most projects, the activities are progressive and uncertain. Specifications of software function, usability, and structure, for example, cannot be fully known before software is designed and implemented. In continuous design, software source code, bug databases, and archived online discussions capture and track the preferences and realities of co-emerging software systems and their user/developer communities in a continuous cycle of innovation, change, and design. Explicit and formal specifications and formal design processes rarely exist: The code itself along with the archived discussions are the specification.
Some open-source projects, especially hybrid company/volunteer projects, use more formal processes and produce more formal artifacts such as specifications, but even these projects accept the idea that the design should change as the requirements are better understood. In fact, we could argue that even software produced using the current principles of software design, software engineering, and software evolution are often discretized versions of continuous design--imposing the idea of formal design and specifications done largely upfront, but (unconsciously) allowing the effect of continuous design over a series of infrequent major releases rather than through small, essentially daily ones.
4. There is considerably more to Extreme Programming. Kent Beck's book, Extreme Programming Explained: Embrace Change is a good place to learn about it, as is the website http://www.extremeprogramming.org. | <urn:uuid:7cb2f8cd-ff8e-42c9-833b-26a695d561de> | 2.9375 | 1,830 | Knowledge Article | Software Dev. | 24.801984 |
Trigonometry/Circles and Triangles/Philo's Line
From Wikibooks, open books for an open world
Suppose any angle POQ and a point X between the lines OP and OQ. Philo's line is the shortest line AB through X such that A is on OP (or OP produced) and B is on OQ (or OQ produced).
If Y is the foot of the perpendicular from O to AB, then AY = BX. | <urn:uuid:03f50e77-e985-4d2a-bd79-55fdb565d7f5> | 3.40625 | 101 | Knowledge Article | Science & Tech. | 69.61615 |
How can you cut a doughnut into 8 equal pieces with only three cuts
of a knife?
The large rectangle is divided into a series of smaller
quadrilaterals and triangles. Can you untangle what fractional part
is represented by each of the ten numbered shapes?
Annie cut this numbered cake into 3 pieces with 3 cuts so that the
numbers on each piece added to the same total. Where were the cuts
and what fraction of the whole cake was each piece?
We had several good solutions to this
problem. They came from Cong who goes to St Peter's RC Primary,
Aberdeen; Terence from Brumby Engineering College and Ben at
Cong coloured the first image:
Cong then sent in a new version of the large
He goes on to say: | <urn:uuid:19e5abf6-8c77-4308-9250-513847b33bf0> | 3.046875 | 167 | Q&A Forum | Science & Tech. | 58.097067 |
The volume of the leftover material is equal to the volume of a 6" sphere.
First, let's look at the 2 dimensional equivalent of this problem. Two concentric circles where the chord of the outer circle that is tangent to the inner circle has length D. What is the annular area between the circles?
big circle radius is R little circle radius is r
area of donut = pi * R - pi * r
Start with a sphere of radius R (where R > 6"), drill out the 6" high hole. We will now place this large "ring" on a plane. Next to it place a 6" high sphere. By Archimedes' theorem, it suffices to show that for any plane parallel to the base plane, the cross- sectional area of these two solids is the same.
Take a general plane at height h above (or below) the center of the solids. The radius of the circle of intersection on the sphere is
so the area is
For the ring, once again we are looking at the area between two concentric circles. The outer circle has radius sqrt(R^2 - h^2), The area of the outer circle is therefore
The inner circle has radius sqrt(R^2 - 3^2). So the area of the inner circle is
the area of the doughnut is therefore
= pi (R^2 - h^2 - R^2 + 3^2)
Therefore the areas are the same for every plane intersecting the solids. Therefore their volumes are the same. QED | <urn:uuid:acda2335-66ef-4136-b45a-f9499ea9e242> | 3.59375 | 329 | Tutorial | Science & Tech. | 69.497461 |
Like a digital video puppet, the facial expressions of one person can be cloned in real time and mapped onto the digital face of another person. Barry-John Theobald, computer scientist at the University of East Anglia, explains the technique and Steven Boker, of the University of Virginia, explains what facial cloning can reveal about human nature. En Español
Video courtesy of Barry-John Theobald, Iain Matthews/Disney Research, Steven Boker. Music courtesy of Prelinger Archives. Produced by Flora Lichtman. | <urn:uuid:4b78a9c3-9dc8-4a3c-afce-0f8873cc69be> | 2.71875 | 113 | Truncated | Science & Tech. | 29.855 |
Pfitzer 1871 Category: Symmetrical biraphid
TYPE SPECIES: Plagiotropis baltica Pfitzer
The valve margins of Plagiotropis are lanceolate with narrow poles. The valve face is folded, with folds appearing as lines on either side of the raphe. The raphe itself is raised above the valve face and positioned within a keel. The axial area is narrow and the central area is variable in shape. Striae are parallel and composed of loculate areolae. In girdle view, cells appear constricted in the center.
Plagiotropis is an epipelic genus of brackish waters.
Cite This Page:
Spaulding, S., and Edlund, M. (2009). Plagiotropis. In Diatoms of the United States. Retrieved May 23, 2013, from http://westerndiatoms.colorado.edu/taxa/genus/Plagiotropis
Reviewer: Sam Rushforth | <urn:uuid:959d3856-fc7b-4642-a833-f168e9859652> | 3.03125 | 216 | Structured Data | Science & Tech. | 41.804139 |
It was the Russian scientist Konstantin Tsiolkovsky who first proposed the idea of a space elevator — an incredibly strong cable stretching from the surface of the Earth to a point 100,000 kilometers in space. Along this track elevator cars would move, powered by electricity and whisking people and cargo into space at a tiny fraction of the cost of today’s chemical rockets. Tsiolkovsky was always ahead of his time, but the key drawback to the plan was that there was no cable material strong enough to support such loads.
Enter Sumio Iijima, who discovered carbon nanotubes in 1991. Long, cylindrical molecules whose walls are made of carbon atoms, nanotubes may turn out to be 100 times as strong as steel at one sixth the density. Carbon-nanotube composite fibers have been produced at kilometer lengths, but they’re not yet strong enough to provide space elevator capabilities. Nonetheless, ongoing work at places like Carbon Designs Inc. in Dallas may produce workable answers within the next few years.
When Bradley Carl Edwards (who is founder and president of Carbon Designs) started plugging numbers into the space elevator concept, he came up with a $10 billion price tag for a single elevator, with a second (using the now proven technologies of the first, and leveraging its capabilities) running perhaps $3 billion. In terms of getting into space, subsequent costs are dirt-cheap. Here’s Edwards, writing in IEEE Spectrum Online: “The estimated operational cost for the first elevator is several hundred dollars per kilogram to any Earth orbit, the moon, or Mars, a drop of two orders of magnitude over the cost of current launch technologies. With the completion of subsequent elevators, the cost would drop even further, to a few dollars per kilogram.”
Image: A European Space Agency view of a space elevator anchored to an offshore sea platform in the Pacific. Credit: Erkki Halkka/ESA.
These numbers seem exaggerated to me, but read the entire Edwards article here; it’s laden with details. The overall plan is this: the elevator cable would rise from its anchor on the equator, passing through the geostationary orbit at 36,000 kilometers and continuing for another 64,000 kilometers until reaching a 600 ton counterweight. With its center of gravity at the geostationary orbit mark, the entire structure would move with Earth’s rotation. 20 ton cars would move up and down its cable. They would contain passenger quarters like a cruise ship, with windows opening to extraordinary views as the cars ascended, reaching geostationary orbit in about eight days.
Centauri Dreams’ take: dropping the cost of reaching space opens up everything from asteroid mining to solar power collectors in orbit. The contrast to today’s half-billion dollar a launch Shuttle situation is obvious. Other ideas for cheap space access are out there, including Leik Myrabo’s marvelous lightcraft concept. What is clear is that the old model of enormous chemical rockets lifting ever larger payloads will no longer suffice. As we set about building a space-based infrastructure in the inner Solar System, we will be putting the technologies into place that will one day produce robotic missions to nearby stars. The space elevator concept may get us going; it is robust enough to deserve intense and continuing scrutiny.
For more, see Marc Boucher’s The Space Elevator Reference, a weblog devoted to the concept. Be aware, too, of Edwards’ book The Space Elevator: A Revolutionary Earth-to-Space Transportation System (2003). Arthur C. Clarke’s The Fountains of Paradise remains the outstanding fictional treatment. | <urn:uuid:3cbec590-6cc0-47a5-97b0-cb7769b6cdd9> | 3.375 | 765 | Personal Blog | Science & Tech. | 39.701765 |
Looking for Cramster? Cramster is now Chegg Homework Help. Learn More
The electrons in the beam of a television tube have a kineticenergy
of 2.80 10-15 J. Initially, the electrons
movehorizontally from west to east. The vertical component of
theearth's magnetic field points down, toward the surface of
theearth, and has a magnitude of 2.0010-5 T.
(a) In what direction are the
electronsdeflected by this field component?
(b) What is the magnitude of the acceleration of an electron inpart
Anonymous answered10 minutes later
You need a Homework Help subscription to view this answer! | <urn:uuid:04c70f58-b163-4786-8f9b-6a77acd41899> | 3.109375 | 144 | Q&A Forum | Science & Tech. | 56.797063 |
Poplar wood rays are involved in seasonal remodeling of tree physiology
Understanding seasonality and longevity is a major challenge in tree biology. In woody species growth phases and dormancy follow one another consecutively. In the oldest living creatures the annual cycle may run for more than a thousand years. So far, however, not much is known about the processes triggering reactivation from dormancy. In this study we focused on wood rays, which are known to play an important role in tree development. The transition phase from dormancy to flowering in early spring was compared with the phase of active growth in summer. Rays from wood samples of poplar (Populus x canescens) were enriched by laser microdissection and transcripts were monitored by poplar whole genome microarrays. The resulting seasonally varying complex expression and metabolite patterns were subjected to pathway analyses. In February, the metabolic pathways related to flower induction were high, indicating that reactivation from dormancy was already taking place at this time of the year. In July, the pathways related to active growth like lignin biosynthesis, nitrogen assimilation and defense were enriched. Based on ‘marker’ genes identified in our pathway analyses we were able to validate periodical changes in wood samples by qPCR. These studies, and the resulting ray database, provide new insights into the steps underlying the seasonality of poplar trees. | <urn:uuid:8c496d82-9d2f-48d5-9080-ea4cd7ad0f26> | 2.8125 | 282 | Academic Writing | Science & Tech. | 21.906149 |
Atomic Weight and Number
The atomic number of an atom is simply the number of protons in its nucleus. The atomic weight of an atom is given in most cases by the mass number of the atom, equal to the total number of protons and neutrons combined. An atom may be conveniently symbolized by its chemical symbol with the atomic number and mass number written as subscript and superscript, respectively. For example, the symbol for uranium is U (atomic number 92); the isotopes of uranium with atomic weights 235 and 238 are indicated by
Sections in this article:
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
More on atom Atomic Weight and Number from Infoplease:
See more Encyclopedia articles on: Physics | <urn:uuid:b6a3a5d7-12c3-4409-86b4-fbc325bee90b> | 4.09375 | 161 | Knowledge Article | Science & Tech. | 34.802802 |
With the UK’s current drought expected to last until Christmas, we look at one possible way to bring the rain.
Suppliers are introducing hosepipe bans and urging customers to use less water.
But instead of using less, is there a way of producing more?
Experiments in cloud seeding suggest that it may be possible to artificially create rainfall.
Rainfall occurs when supercooled droplets of water – those that are still liquid but are at a temperature below the usual freezing point of zero centigrade – form ice crystals. Now too heavy to remain suspend in the air, these then fall, often melting on their way down to form rain.
Even in dry areas the air usually contains some water. This can be made to come together and form ice crystals by seeding the atmosphere with chemicals such as silver iodide or dry ice.
They work to promote rainfall by inducing nucleation – what little water is in the air condenses around the newly introduced particles and crystallises to form ice.
The ‘seeds’ can be delivered by plane or simply by spraying from the ground.
But does it work?
It’s hard to tell for sure. As is often the case with weather and climate, it’s impossible to carry out a controlled experiment – so, in areas of increased precipitation, we can’t know whether it would still have rained even if the clouds hadn’t been seeded.
Success has been claimed for trials in Australia, France, Spain and the US. In the United Arab Emirates, the technique is credited with the creation of 52 storms in the Abu Dhabi desert, while China boasts of having used the technology in reverse to keep the Beijing Olympic Games of 2008 dry.
Recent research, however, suggests that it’s not as effective as was previously believed.
So, until the rain naturally returns to its normal levels, the car might have to stay dirty – and the lawn a bit brown. | <urn:uuid:330befc3-7bfc-4dc8-a783-735cabca00db> | 3.703125 | 407 | Knowledge Article | Science & Tech. | 52.756961 |
Meitnerium is an artificially produced radioactive element. None of meitnerium's chemistry has been researched, but it should resemble other elements of group 9, like iridium.
Meitnerium does not have any known application and little is known about it.
Meitnerium in the environment
Meitnerium is not found free in the environment, since it is a synthetic element.
As it is so unstable, any amount formed would decompose to other elements so quickly that there’s no reason to study its effects on human health.
Due to its extremely short half-life (about 3.8 milliseconds), there’s no reason for considering the effects of meitnerium in the environment.
Back to chart periodic elements. | <urn:uuid:35034fd2-523a-4220-a51e-adf42de5175a> | 3.484375 | 158 | Knowledge Article | Science & Tech. | 43.512284 |
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Spintronics goes organic...
[Only registered users see links. ]
Spintronics goes organic
25 February 2004
Physicists have moved a step closer to creating a new generation of
"spintronic" devices that exploit the spin of electrons as well as their
charge. Jing Shi and colleagues at the University of Utah in the US have
made the first organic "spin valve" - a device that changes resistance
depending on the applied magnetic field. Previous spin valves were made from
metals or insulators (Z Xiong et al. 2004 Nature 427 821).
A spin valve consists of a thin layer of metal or insulator sandwiched
between two ferromagnetic electrodes. The spin of the electrons passing
through the device can be flipped by an external magnetic field, which
changes the resistance of the two ferromagnetic layers. This effect, known
as magnetoresistance, has already been used to make highly sensitive
magnetic-recording devices and memory chips.
Extending these spin-dependent effects to semiconductor materials has,
however, proved difficult. Shi and co-workers have now built a spin valve
with a 100 nanometre thick organic semiconductor made from aluminium and
hydroxyquinoline. The semiconductor was sandwiched between a layer of cobalt
and an alloy of lanthanum, strontium and magnesium (see figure).
To test their device, the Utah team first calculated the current that flowed
through the semiconductor when the two electrodes were magnetized in the
same direction - or parallel - and then in opposite directions - or
anti-parallel. Shi and colleagues found that that the current increased by
as much as 40% when the magnetization of the electrodes was switched from
anti-parallel to parallel. This constitutes giant magnetoresistance.
At present, the device only works at low temperatures - between about -260°C
to about -40°C - but Shi's team says that the experiment is "a proof of
concept that sets the stage for more practical applications". The long-term
aim is to make the device work at room temperature. The group believes that
organic semiconductors have many advantages over conventional
semiconductors, such as those made from silicon. They are simpler to make,
are flexible and their resistance can be tuned by doping.
Belle Dumé is Science Writer at PhysicsWeb
Bubba Do Wah Ditty
"Rarely is the question asked: Is our children learning?"
- Bushisms, 2000
|organic , spintronics|
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|'Spintronics' Could Enable A New Generation Of Electronic Devices, Physicists Say||Do Wah Ditty||Physics Forum||0||08-11-2003 12:34 PM| | <urn:uuid:b905c3d5-4239-4ca5-b063-1193f5f2d3e6> | 2.6875 | 772 | Comment Section | Science & Tech. | 44.637039 |
On some winter days, large swarms of water striders emerge from wherever they hide on cold days and go racing across the surface of Geronimo Creek.
The ones in the nearby photo were waltzing across the water when its temperature was 55.8 degrees. The air was 65.3 degrees.
While they are most commonly known as water striders, these fast-moving creatures spend much more time rapidly racing, skimming and scooting across the water than merely striding or promenading. That's why they are also known as pond skaters, water skimmers and similar names.
Water striders can be detected from a distance by the waves they create when they race across the water. Many such waves are formed when dozens or hundreds of them congregate together in an area of turbulent water smaller than a kitchen table.
Water striders do not float on water in the conventional meaning of the term. Instead, they rely on the surface tension of water to stand on its surface. Their feet and legs do not become wet.
It was once thought that a waxy coating on the legs of water striders assisted them in standing on water. But in 2004 Xuefeng Gao and Lei Jiang published an article in the journal Nature that revealed the real secret behind the water strider's ability to walk on water. The legs of the insect are covered with tiny hairs lined with exceedingly thin grooves. Air trapped within the grooves and hairs enhances the insect's ability to walk on water.
When the angle of the sun is right, the dimples in the surface of the water on which a strider's legs rest reflect bright specks of sunshine. This provides an eye-catching display of brilliant, flickering lights across a sheet of water, as it did on several recent days along Geronimo Creek.
Water striders are expert rowers. They can move so rapidly they are difficult to photograph. One report I found clocked striders racing along as fast as 4 or 5 feet in a second. The ones I've observed sweep their long middle legs back to rapidly propel themselves forward. They then slow to a stop before the next burst.
I've been trying to use a video camera to measure the speed of water striders zipping across Geronimo Creek. I will let you know if this experiment is successful.
Water striders are predators, and I once photographed a large one feeding on a smaller cousin. An excellent place to observe and photograph them is along the edge of the Guadalupe River fishing area below the dam at the Canyon reservoir in Comal County.
Forrest Mims III lives on Geronimo Creek near Seguin. His science is featured online at www.forrestmims.org and www.sunandsky.org. Follow him at twitter.com/fmims. E-mail him at firstname.lastname@example.org. | <urn:uuid:21aa8e3f-4118-4498-b308-ea0421a7feb8> | 3.359375 | 596 | Nonfiction Writing | Science & Tech. | 60.543136 |
Four years ago, Romanian explorer Stefan Milota made an amazing discovery in previously unknown caves deep within his country's Carpathian mountains: a jawbone that turned out to be the oldest modern human fossil found in Europe. More surprisingly, this mandible showed features that suggested early modern humans might have interbred with Neanderthals. With his climbing buddies at the explorers' club Pro Acva Grup, Milota helped scientists make the subterranean trek to Pestera cu Oase (Cave with Bones) for three seasons of dark, 10-hour days, much of them spent climbing, swimming or diving through tight passages. Fredric Heeren followed the cavers to ask Milota how he found the 35,000-year-old human remains and why he is drawn to the dark world underground.
When did you first start cave diving?
In 1996 I was involved in an ecological project to clean a lake in Romania that was littered with bottles and junk. It ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:6b1bc5fb-8e74-40aa-9c32-78c56bdcfac1> | 3.328125 | 225 | Truncated | Science & Tech. | 51.943273 |
0.13 °C. The amount the atmosphere is warming each decade
1.3 times as much CO2 is entering the atmosphere compared with just 20 years ago
3 kilometres. The depth to which the oceans have warmed
3.1 centimetres. The rise in sea level each decade
90 per cent certainty that we are to blame
The word they were most pleased with was "unequivocal". Three hundred government-appointed delegates from 113 countries were last week unanimous in agreeing what most climate scientists have believed for years: that the world is warming fast and that humans are almost certainly to blame.
Some 600 scientists wrote the summary of the fourth assessment by the Intergovernmental Panel on Climate Change, published this week. Virtually everything they wanted to say in it survived the politicians, but the IPCC's review process was so rigorous that research deemed controversial, not fully quantified or not yet incorporated into climate models ...
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OUR addiction to fossil fuels shows no sign of waning. An International Energy Agency report predicts that global coal use will continue to grow over the next five years.
Demand for coal will increase everywhere except the US, where cheap gas extracted by hydraulic fracturing or fracking will exceed it. By 2017, coal use will equal that of oil, currently our biggest energy source.
This is terrible news for the climate. Coal produces more greenhouse gas per unit of energy than any other fossil fuel. Yet even developed countries like Germany, scaling back on nuclear power after the accident at Fukushima Daiichi, Japan, in 2011, are building more coal-fired power stations. "This is going backwards," says Stuart Haszeldine at the University of Edinburgh, UK.
If more coal is to be used, then the only chance we have to limit warming to 2 °C is to capture the greenhouse gases it emits when burned. Carbon capture and storage (CCS) technology is available, but the political will to implement it has so far been lacking, says Haszeldine.
The European Union has set aside €275 million for CCS, but said in December that no projects had been awarded any money, mostly because their host countries had failed to stump up their required contribution.
Ultimately, CCS will have to be rolled out far beyond the EU. "Solving carbon emissions from coal means solving them in India and China, who will be burning two-thirds of global coal by 2017," Haszeldine says.
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Ccs Is 'difficult'
Sun Jan 06 05:15:45 GMT 2013 by Randall
Short term 'thinking' and a strong habit of taking easy options makes us look unlikely to capture and store carbon dioxide. Strict rules and taxes seem necessary, but our democracies make these impossible to implement. Extinction looms. It's a worry if one is logical.
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support. | <urn:uuid:aa212f9e-b2ca-4a85-b71a-15200b93788a> | 3.546875 | 522 | Truncated | Science & Tech. | 50.087934 |
Name: Omar G.
Why do the electrons in a charged body (take the metal for example)
that has an edged (I mean a special shape like ...
|____/ or similar to this |___> )
goes around (mostly) the edge of that shape (which is in the left side of
the figure drawn).
Electrons in a negatively charged body go near the edges because they push
away from each other. The electrons "try to get" as far from other
electrons as is possible. Consider a cube. By grouping together at the
eight corners of a cube, electrons can be near one-eighth of the other
electrons but far away from seven-eighths of them. It works out as better
than being evenly spaced.
Dr. Ken Mellendorf
Illinois Central College
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:5c103da4-1eb4-45f9-95aa-71c4cd2eda69> | 4.4375 | 189 | Q&A Forum | Science & Tech. | 64.514804 |
Name: Duncan B. Smith
Why do planets closer to the Sun travel faster than the outer planets?
The speed with which planets move around the Sun is proportional to the
force of Sun at the planet's position. The force falls off with distance as
inverse square so the planets closer to the Sun experience a larger force
and hence move faster. This is a rough description. A more rigorous
approach will involve mathematical constructs like the gravitational | <urn:uuid:30aefb8b-96d3-47cd-b500-2633c54d8b95> | 3.234375 | 92 | Q&A Forum | Science & Tech. | 52.170231 |
Mechanics: Newton's Laws of Motion
Newton's Laws of Motion: Audio Guided Solution
Dexter Eius is running through the cafeteria when he slips on some mashed potatoes and falls to the floor. (Let that be a lesson for Dexter.) Dexter lands in a puddle of milk and skids to a stop with an acceleration of -4.8 m/s/s. Dexter weighs 780 Newtons. Determine the coefficient of friction between Dexter and the milky floor.
Audio Guided Solution
Habits of an Effective Problem Solver
- Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
- Identify the known and unknown quantities in an organized manner. Equate given values to the symbols used to represent the corresponding quantity - e.g., vo = 0 m/s; a = 4.2 m/s/s; vf = 22.9 m/s; d = ???.
- Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
- Identify the appropriate formula(s) to use.
- Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.
Read About It!
Get more information on the topic of Newton's Laws of Motion at The Physics Classroom Tutorial.
Return to Problem Set
Return to Overview | <urn:uuid:fecc76f1-ead8-4a8a-b95f-e60c66398d61> | 3.640625 | 298 | Tutorial | Science & Tech. | 62.919545 |
Mammals in Ireland
By biologist Terry Flanagan, B.Sc., M.I.Biol.I., H.Dip. Ed.
Here is the table of contents, you can click on the links below to take you directly to read about the particular mammals or just read on...
Introduction to the Mammals in Ireland
Mammals of the air
What are mammals?
Mammals are the most highly evolved group of animals on Earth. They are characterised by the following features;
- They are warm blooded.
- They have hair.
- The young are fed with milk, (mammary glands).
- They have external ears called pinnae.
- They have a more highly developed brain than any other animals.
Where did mammals originate from?
It is believed that the mammals evolved about 200 million years ago from small shrew-like animals. By studying fossils, it is possible to say that these mammals evolved from early reptiles. At this early stage, the mammals were inconspicuous animals, dominated by the reptiles and in particular, the dinosaurs. From these early shrew-like mammals, have descended all mammals.
Exceptions to the Rule!
Almost every rule in Science has an exception:
And in the case of the mammals, not all mammals are viviparous. The Platypus and Spiny Anteater are egg layers. Why are they classed as mammals then? Because, taking all other features into account, they fit better into the Mammalia than any other group.
- All plants are green. Not true. Mushrooms are non-green plants.
- All animals can move. Not true. Barnacles on a rocky seashore can't move.
How many mammal species are there?
It is believed that there are between 4,000 - 5,000 species of mammals alive today worldwide. Although this may seem large, in comparison to other groups it is not so. (About 10,000 species of birds, 20,000 species of fishes and over 1 million species of insects!).
How successful are the mammals?
The struggle for survival affects all animals, including mammals. From the moment of its birth, the young mammal is dependent on it's mother. Unlike the reptiles, there is a high degree of parental care shown to the offspring over a long period of time. During this time, they are taught the skills necessary for later life, skills like hunting and survival.
The mammals, like all the other groups of plants and animals have become specialised to allow them take advantage of different conditions on Earth. The three basic requirements for all animals in life are:
Mammals are considered to be more highly evolved than all other groups of animals for three main reasons:
- The search for food.
- The need to reproduce.
- The ability to escape from enemies.
- A fourth requirement, curiosity, has also been accepted by scientists, and in the case of the mammals, this is especially important.
- A more complex brain.
- The ability to communicate with one another.
- In the case of the Primates, the opposable thumb.
Mammals around the world.
The number and variety of mammals on Earth is quite impressive. From the Polar Bear of the Arctic to the kangaroos of Australia. From the tiny Pygmy Shrew to the massive Blue Whale. From the Flying foxes that inhabit the skies of Australia to the seals that live in our oceans, mammals all found throughout the planet.
Adaptations of some of our mammals.
All plants and animals must be able to adapt in some way or other to their environment, otherwise they will, and some have, become extinct.
Bats use echo-location. This is a method whereby a bat emits a high-frequency sound and waits for the echo to return. In doing so, bats can determine objects in their path, including prey items, like moths. While at rest, bats emit pulses of about 10 per second. When flying, this increases to about 30 per second and up to 200 per second when it is approaching an insect. The ear of the bat is large to enable it pick up these sounds.
Hedgehogs have spines for protection. A hedgehog can have anything up to 7,000 spines covering its body. If danger presents itself, the hedgehog curls into a ball erecting its spines. Whereas, this is an effective defence against most animal predators, unfortunately, this is not the case along motorways and country roads. There is a school of thought at present, that hedgehogs are learning to stay on the inside of the markings along motorways and thereby staying safe!
Hedgehogs and bats also hibernate for the winter. This allows them to survive long periods of cold weather. Mammals living in very warms parts of the world undergo aestivation to allow them avoid very hot conditions.
Seals are capable of reducing their heartbeats to as little as 4 to 5 beats per minute when they are diving. This process, known as bradycardia, along with the ability to shut off blood flow to areas of the body where it is not needed, allows seals to dive deeper and stay under water without suffering from the bends.
Mammals in Ireland:
Although there are only about 60 species of mammals living inland or around our coasts, they play an important part in our lives. Ireland has long been separated from mainland Europe, thereby, preventing movement over land. There are a greater number of mammal species in Britain than here. It must not be forgotten that over 50% of the mammal species in Ireland have been introduced by man!
Our mammals can be divided up into
(1) Mammals of the air
(2) Land mammals
(3) Sea mammals | <urn:uuid:8a41f123-9fdc-44f2-92d5-190bec108d15> | 3.5625 | 1,204 | Knowledge Article | Science & Tech. | 58.242777 |
Web edition: December 31, 2009
Print edition: January 16, 2010; Vol.177 #2 (p. 31)
The fascinating article “Aping the Stone Age” (SN: 11/21/09, p. 24) led me to wonder whether researchers who work with chimps or other higher apes have ever introduced them to the modern tools used by humans, such as saws, axes, hammers or pliers. If so, it would be interesting to know whether the apes could grasp the tools’ purposes, employ them productively and/or demonstrate their utility to ape kin.
Jack J. Friedman, Fort Lauderdale, Fla.
Andrew Whiten of the University of St. Andrews in Scotland replies: An interesting question. Some studies have involved giving apes humanlike tools, as when Sue Savage-Rumbaugh and colleagues tested whether one chimpanzee could request the correct tool from another chimpanzee to open one of several boxes and share the food contents (as Savage-Rumbaugh describes in her book Ape Language, Columbia, 1986). However, these were specially designed tools, not regular human tools. Anecdotally, I know of chimpanzees who see a lot of human behavior, who on managing to purloin something like a screwdriver will attempt to undo the screws holding their cage together — which may partly explain the limits on this kind of inquiry! This implies that apes will appreciate the utility of certain tools from watching humans, consistent with what we have shown of apes’ ability to learn particular forms of tool use from others. See, for example, A. Whiten et al., “Transmission of multiple traditions within and between chimpanzee groups,”Current Biology, 2007.
I enjoyed Laura Beil’s piece “Breaking the Speed Limit” (SN: 12/5/09, p. 26) and learned some fascinating things. But as a bicyclist since the 1950s, I would like to point out a shortcoming in her comparison of [Oscar] Pistorius’ running with a cyclist: When the cyclist gears down, he pedals faster with less force without losing speed. Pistorius steps faster with less force than other runners to maintain the same speed, like a cyclist gearing down. Saying that switching to a lower gear permits a rider to pedal less without losing speed is simply wrong.
Conrad F. Nuthmann, Deland, Fla.
As an old relay anchor, I’d expect Usain Bolt’s top speed to be even faster on the home stretch of a 200-meter race or the back stretch of the 400. Top running speed depends more on length of stride and coordination than on “pounding the pavement,” and you can’t “hit your stride” in a race as short as 100 meters.Karl Staubach, Benicia, Calif. | <urn:uuid:024ba599-7e63-4f0f-8741-e17e415c702e> | 2.984375 | 595 | Comment Section | Science & Tech. | 59.213578 |
In 1999, a bold plan was laid out to establish a broad collaboration among biologists, oceanographers, engineers and computer scientists in the emerging field of “biologging” science. At a workshop held at Stanford University’s Hopkins Marine Station in Pacific Grove, California, more than 50 people gathered and developed a program using electronic tags to simultaneously follow the migrations and behaviors of 23 different species of marine animals – including whales, seals, fishes, sharks, seabirds, turtles and even squid. The scientsts’ vision was that, by following such a dive
The white shark research team has published two papers in the past few days, documenting the ability to recognize individual sharks year after year by the distinctive shapes and markings on their dorsal fins; and then using this information to estimate the total size of the white shark population in this region. The first study, which was published March 1 in the journal Marine Biology (Anderson et.
Back in the early days of TOPP, one of our goals was to see if it might be possible to one day use the data we get from tagged animals to help us understand the ocean itself. This concept, which we dubbed "Animals as Ocean Sensors," came a giant step closer to reality last week, with the birth of a new partnership between GTOPP and the national Integrated Ocean Observing System (IOOS).
Daniel Costa, Jennifer Burns, Mary Zavanelli, Michelle Shero and Luis Huckstadt, from McMurdo Station, Antarctica -
Field team January 2011 with the last tagged Weddell seal . First row (left to right): Dr. Dan Costa, Dr. Mary Zavanelli. Standing (left to right): Luis Huckstadt, Dr. Jennifer Burns, Michelle Shero . Photo by Dan Costa.
TOPP Researchers Describe Habitat Preferences of Leatherback Sea Turtles: A Key First Step in Open Ocean ConservationPosted February 8th, 2011 by RandyKochevar
Luis Huckstadt, Patrick Robinson, Kim Goetz, Jen Maresh in McMurdo Station, Antarctica-
If you want to study top predators, you have to follow them. That's it, no way around it (or at least we like to see it that way). So, as the enthusiastic biologists that we are, we were somehow happy about the new challenge in sight: Go to the white continent to study Weddell seals (Part II) right when the "spring season" would be hitting the continent, and the weather was changing from horrible to bad.
The 2010 TOPP white shark tagging expedition to the Farallon Islands was lead by Dr. Salvador Jorgensen and began on October 7 aboard the S.R.V. Derek M. Bayliss.
I had an incredible day out on Monterey Bay where I saw my dissertation come to life! I recently finished my thesis at UCSC with Dan Costa and my work focused on top predator hotspots for conservation along the West Coast.
On October 4 the international Census of Marine Life unveiled the discoveries made during the ten years since it was launched. The global press conference, held in London, has generated hundreds of articles around the globe. In the two days that followed, representatives from each of the Census field projects and National and Regional Implementation Committees (NRICs) presented summaries of their findings. The three days were capped off with an incredible celebration at the Museum of Natural History, which was decked out just for the special event. | <urn:uuid:4132ef88-f979-47c0-80d9-b357b6754d01> | 3.40625 | 709 | Content Listing | Science & Tech. | 46.573343 |
When known to the interpreter, the script name and additional arguments thereafter are passed to the script in the variable sys.argv, which is a list of strings. Its length is at least one; when no script and no arguments are given, sys.argv is an empty string. When the script name is given as '-' (meaning standard input), sys.argv is set to '-'. When -c command is used, sys.argv is set to '-c'. Options found after -c command are not consumed by the Python interpreter's option processing but left in sys.argv for the command to handle. | <urn:uuid:8b3c0d29-a341-452f-964b-a8ec034b9102> | 2.90625 | 129 | Documentation | Software Dev. | 78.859227 |
Show: Delphi C++
Generating a New Event Handler
From RAD Studio XE2
You can generate skeleton event handlers for forms and other components.
To create an event handler
- Select a component.
- Click the Events tab in the Object Inspector. The Events page of the Object Inspector displays all events defined for the component.
- Select the event you want, and then either double-click the Value column or press
Ctrl+Enter. The Code Editor opens with the cursor inside the skeleton event handler.
- At the cursor, type the code that you want to execute when the event occurs. | <urn:uuid:5ce5043e-c7c9-4da2-933e-d263978ded7f> | 2.96875 | 127 | Tutorial | Software Dev. | 54.095773 |
Regular singular point
In mathematics, in the theory of ordinary differential equations in the complex plane , the points of are classified into ordinary points, at which the equation's coefficients are analytic functions, and singular points, at which some coefficient has a singularity. Then amongst singular points, an important distinction is made between a regular singular point, where the growth of solutions is bounded (in any small sector) by an algebraic function, and an irregular singular point, where the full solution set requires functions with higher growth rates. This distinction occurs, for example, between the hypergeometric equation, with three regular singular points, and the Bessel equation which is in a sense a limiting case, but where the analytic properties are substantially different.
Formal definitions
More precisely, consider an ordinary linear differential equation of n-th order
with pi (z) meromorphic functions. One can assume that
If this is not the case the equation above has to be divided by pn(x). This may introduce singular points to consider.
The equation should be studied on the Riemann sphere to include the point at infinity as a possible singular point. A Möbius transformation may be applied to move ∞ into the finite part of the complex plane if required, see example on Bessel differential equation below.
Then the Frobenius method based on the indicial equation may be applied to find possible solutions that are power series times complex powers (z − a)r near any given a in the complex plane where r need not be an integer; this function may exist, therefore, only thanks to a branch cut extending out from a, or on a Riemann surface of some punctured disc around a. This presents no difficulty for a an ordinary point (Lazarus Fuchs 1866). When a is a regular singular point, which by definition means that
has a pole of order at most i at a, the Frobenius method also can be made to work and provide n independent solutions near a.
Otherwise the point a is an irregular singularity. In that case the monodromy group relating solutions by analytic continuation has less to say in general, and the solutions are harder to study, except in terms of their asymptotic expansions.
The regularity condition is a kind of Newton polygon condition, in the sense that the allowed poles are in a region, when plotted against i, bounded by a line at 45° to the axes.
An ordinary differential equation whose only singular points, including the point at infinity, are regular singular points is called a Fuchsian ordinary differential equation.
Examples for second order differential equations
In this case the equation above is reduced to:
One distinguishes the following cases:
- Point a is an ordinary point when functions p1(x) and p0(x) are analytic at x = a.
- Point a is a regular singular point if p1(x) has a pole up to order 1 at x = a and p0 has a pole of order up to 2 at x = a.
- Otherwise point a is an irregular singular point.
Listed below are several examples from ordinary differential equations from mathematical physics that have singular points and known solutions.
Bessel differential equation
Dividing this equation by x2 gives:
In this case p1(x) = 1/x has a pole of first order at x = 0. When α ≠ 0 p0(x) = (1 − α2/x2) has a pole of second order at x = 0. Thus this equation has a regular singularity at 0.
To see what happens when x → ∞ one has to use a Möbius transformation, for example x = 1 / (w - b). After performing the algebra:
- p1(w) = 1/(w − b)
has a pole of first order at w = b. And p0(w) has a pole of fourth order at w = b. Thus this equation has an irregular singularity w = b corresponding to x at ∞. There is a basis for solutions of this differential equation that are Bessel functions.
Legendre differential equation
Opening the square bracket gives:
And dividing by (1 - x2):
This differential equation has regular singular points at -1, +1, and ∞.
Hermite differential equation
One encounters this ordinary second order differential equation in solving the one dimensional time independent Schrödinger equation
for a harmonic oscillator. In this case the potential energy V(x) is:
This leads to the following ordinary second order differential equation:
This differential equation has an irregular singularity at ∞. Its solutions are Hermite polynomials.
Hypergeometric equation
The equation may be defined as
Dividing both sides by z (1 - z) gives:
This differential equation has regular singular points at 0, 1 and ∞. A solution is the hypergeometric function.
- Coddington, Earl A.; Levinson, Norman (1955). Theory of Ordinary Differential Equations. New York: McGraw-Hill.
- E. T. Copson, An Introduction to the Theory of Functions of a Complex Variable (1935)
- Fedoryuk, M.V. (2001), "Fuchsian equation", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1-55608-010-4
- A. R. Forsyth Theory of Differential Equations Vol. IV: Ordinary Linear Equations (Cambridge University Press, 1906)
- E. Goursat A Course in Mathematical Analysis, Volume II, Part II: Differential Equations p. 128-ff. (Ginn & co., Boston, 1917)
- Il'yashenko, Yu.S. (2001), "r/r080870", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1-55608-010-4
- E. L. Ince, Ordinary Differential Equations, Dover Publications (1944)
- T. M. MacRobert Functions of a Complex Variable p. 243 (MacMillan, London, 1917)
- Teschl, Gerald (2012). Ordinary Differential Equations and Dynamical Systems. Providence: American Mathematical Society. ISBN 978-0-8218-8328-0.
- E. T. Whittaker and G. N. Watson A course of modern analysis p. 188-ff. (Cambridge University Press, 1915) | <urn:uuid:e64b30df-296f-4dc9-89c3-0a300f837a51> | 2.9375 | 1,379 | Knowledge Article | Science & Tech. | 48.58366 |
Tuesday, August 31, 2010
It's quite sobering to be reminded that our picture of how all this crusty stuff operates, how the great plates of rock shift and slide around, is still very, very new. Fifty years ago and the idea of plate tectonics was only just taking proper shape. Fast forward and we now talk about the inevitability of plate tectonics on super-Earth's - rocky planets several times the mass of ours. We care about this because it seems that active plate tectonics and volcanism play a critical role in the long-term regulation of the Earth's climate - forcing surface temperatures into the regime where liquid water can exist.
It's intriguing therefore to see that our understanding of the physics behind plate tectonics is still a matter of intense debate and study. A couple of new results bubbled up during the summer. One is the claim of a new understanding of how the Earth's crust shifts and wiggles - based on essentially the same physics that explains how objects move through viscous fluids. In this picture then the way the planetary crust moves is very much a function of that crust itself, a bit like how your bobsled run is determined to a great extent by the mass and slipperiness of your ride, not just by the ice underneath. This runs against many previous models, where deep interior processes in the liquid part of the planet effectively determine what you see up top. Another work, employing state-of-the-art computer simulation has made recent claims to tie the deep ebb and flow of the Earth's interior to the frosty bump and drift of the outer plates. Rather nicely, this grand simulacrum also suggests that precisely how all the surface cracks and gaps, the faults and fault zones, fit together plays a critical role in determining how the overall plate tectonics of the planet operate.
Just like a fiendish jigsaw, you can't see the big picture until you know how all the small pieces go together. Perhaps not surprisingly, our crusty surface is a hugely non-linear system, hard to predict ab initio. This should raise some concerns for making claims about the nature of plate tectonics on distant exoplanets, but it also indicates a possible opportunity. It may well be that there are distinct types of crustal activity that can occur on rocky planets, from the kind of plate motions that we see on the modern Earth to more fractured styles, or more global styles. At some level these will all link into climate, history, and chemistry. Detecting the presence of atmospheric gases associated with geochemical processes - such as sulfur dioxide - could actually help tell us about the arrangement of continents (or not) on these distant worlds. | <urn:uuid:2b951261-354d-42da-bf53-0c4463d0a967> | 3.453125 | 554 | Personal Blog | Science & Tech. | 39.527249 |
Python Fundamentals Tutorial : Regular Expressions
At the simplest level, there are module-level functions in
re that can be used to search for regular expresssions. In many cases, calling the
search() function and checking for the presence of a return value is enough.
None if the pattern was not found.
It is customary in Python regular expressions to pass the patterns as raw strings (
>>> text = 'All your base are belong to us.' >>> re.search(r'o\s?u', text) <_sre.SRE_Match object at 0x10041f718>
Take note of the
match() function, which specifically only matches the beginning of the text being matched and does not search throughout for the pattern.
>>> re.match(r'o\s?u', text) >>> re.match('All', text) <_sre.SRE_Match object at 0x10041f718>
Regular expressions can also be used to split strings in more advanced ways than the
>>> re.split(r'o\s?u', text) ['All y', 'r base are belong t', 's.']
finditer() methods, it is possible to process all the matching groups.
findall() returns a list while
finditer() returns an iterator.
>>> re.findall(r'o\s?u', text) ['ou', 'o u'] >>> re.finditer(r'o\s?u', text) <callable-iterator object at 0x100516610>
If you need to use the same pattern multiple times, you can improve performance by compiling the regex and then using the methods of the regex object, rather than the module-level functions.
If groups are defined in the pattern, they can be accessed using the
group() method of the returned Match object. Note that they are 1-indexed to conform to most other regex utilities.
>>> text = 'All your base are belong to us.' >>> pattern = re.compile(r'you[r]?\s*(\S*)\s*are belong to us') >>> match = pattern.search(text) >>> match.group(1) 'base'
- Rename complexity-1-fileutil.py to fileutil.py
- Implement fileutil.py to pass the doctests
- Create a second file grep.py that accepts command line arguments and calls the function in grep.py
Accept the following command-line args:
- -v, --invert-match select non-matching lines
- -E, --extended-regexp PATTERN is an extended regular expression
- And a list of files | <urn:uuid:7204502b-25c2-4f2c-9ea5-84f0e7d27bbb> | 3.8125 | 577 | Tutorial | Software Dev. | 69.907447 |
This problem is about investigating whether it is possible to start at one vertex of a platonic solid and visit every other vertex once only returning to the vertex you started at.
You have 27 small cubes, 3 each of nine colours. Use the small
cubes to make a 3 by 3 by 3 cube so that each face of the bigger
cube contains one of every colour.
A and B are two interlocking cogwheels having p teeth and q teeth respectively. One tooth on B is painted red. Find the values of p and q for which the red tooth on B contacts every gap on the. . . .
A tilted square is a square with no horizontal sides. Can you
devise a general instruction for the construction of a square when
you are given just one of its sides?
Semi-regular tessellations combine two or more different regular polygons to fill the plane. Can you find all the semi-regular tessellations?
Use the interactivity to play two of the bells in a pattern. How do
you know when it is your turn to ring, and how do you know which
bell to ring?
A game for 2 players. Can be played online. One player has 1 red
counter, the other has 4 blue. The red counter needs to reach the
other side, and the blue needs to trap the red.
Slide the pieces to move Khun Phaen past all the guards into the position on the right from which he can escape to freedom.
Triangle numbers can be represented by a triangular array of
squares. What do you notice about the sum of identical triangle
Euler discussed whether or not it was possible to stroll around Koenigsberg crossing each of its seven bridges exactly once. Experiment with different numbers of islands and bridges.
A circle rolls around the outside edge of a square so that its circumference always touches the edge of the square. Can you describe the locus of the centre of the circle?
Here is a solitaire type environment for you to experiment with. Which targets can you reach?
You can move the 4 pieces of the jigsaw and fit them into both
outlines. Explain what has happened to the missing one unit of
Use the interactivity to listen to the bells ringing a pattern. Now
it's your turn! Play one of the bells yourself. How do you know
when it is your turn to ring?
How many different triangles can you make which consist of the
centre point and two of the points on the edge? Can you work out
each of their angles?
These formulae are often quoted, but rarely proved. In this article, we derive the formulae for the volumes of a square-based pyramid and a cone, using relatively simple mathematical concepts.
This rectangle is cut into five pieces which fit exactly into a triangular outline and also into a square outline where the triangle, the rectangle and the square have equal areas.
There are 27 small cubes in a 3 x 3 x 3 cube, 54 faces being
visible at any one time. Is it possible to reorganise these cubes
so that by dipping the large cube into a pot of paint three times
you. . . .
Six balls of various colours are randomly shaken into a trianglular
arrangement. What is the probability of having at least one red in
Start with any number of counters in any number of piles. 2 players
take it in turns to remove any number of counters from a single
pile. The winner is the player to take the last counter.
A game for two people, or play online. Given a target number, say 23, and a range of numbers to choose from, say 1-4, players take it in turns to add to the running total to hit their target.
Do you know how to find the area of a triangle? You can count the
squares. What happens if we turn the triangle on end? Press the
button and see. Try counting the number of units in the triangle
now. . . .
What is the relationship between the angle at the centre and the
angles at the circumference, for angles which stand on the same
arc? Can you prove it?
Can you locate the lost giraffe? Input coordinates to help you
search and find the giraffe in the fewest guesses.
Can you find a reliable strategy for choosing coordinates that will locate the robber in the minimum number of guesses?
Experiment with the interactivity of "rolling" regular polygons, and explore how the different positions of the red dot affects the distance it travels at each stage.
Practise your diamond mining skills and your x,y coordination in this homage to Pacman.
Mo has left, but Meg is still experimenting. Use the interactivity
to help you find out how she can alter her pouch of marbles and
still keep the two pouches balanced.
Learn how to use the Shuffles interactivity by running through these tutorial demonstrations.
Draw some isosceles triangles with an area of $9$cm$^2$ and a vertex at (20,20). If all the vertices must have whole number coordinates, how many is it possible to draw?
A game for 2 players that can be played online. Players take it in
turns to select a word from the 9 words given. The aim is to select
all the occurrences of the same letter.
To avoid losing think of another very well known game where the
patterns of play are similar.
Can you find a relationship between the number of dots on the
circle and the number of steps that will ensure that all points are
Can you find all the 4-ball shuffles?
Two engines, at opposite ends of a single track railway line, set
off towards one another just as a fly, sitting on the front of one
of the engines, sets off flying along the railway line...
Can you set the logic gates so that the number of bulbs which are
on is the same as the number of switches which are on?
Meg and Mo need to hang their marbles so that they balance. Use the
interactivity to experiment and find out what they need to do.
Work out how to light up the single light. What's the rule?
Here is a chance to play a version of the classic Countdown Game.
Try entering different sets of numbers in the number pyramids. How does the total at the top change?
What are the areas of these triangles? What do you notice? Can you generalise to other "families" of triangles?
The aim of the game is to slide the green square from the top right
hand corner to the bottom left hand corner in the least number of
A red square and a blue square overlap so that the corner of the red square rests on the centre of the blue square. Show that, whatever the orientation of the red square, it covers a quarter of the. . . .
Experiment with the interactivity of "rolling" regular polygons,
and explore how the different positions of the red dot affects its
speed at each stage.
Show how this pentagonal tile can be used to tile the plane and
describe the transformations which map this pentagon to its images
in the tiling.
Two circles of equal radius touch at P. One circle is fixed whilst the other moves, rolling without slipping, all the way round. How many times does the moving coin revolve before returning to P?
It's easy to work out the areas of most squares that we meet, but
what if they were tilted?
We can show that (x + 1)² = x² + 2x + 1 by considering
the area of an (x + 1) by (x + 1) square. Show in a similar way
that (x + 2)² = x² + 4x + 4
Can you spot the similarities between this game and other games you
know? The aim is to choose 3 numbers that total 15.
The opposite vertices of a square have coordinates (a,b) and (c,d). What are the coordinates of the other vertices? | <urn:uuid:84053f2c-64b4-435b-a4a4-1cd60e8aa994> | 3.265625 | 1,703 | Content Listing | Science & Tech. | 68.236869 |
Which of these is the current (also, what about voltage?) induced by an EMP pulse within a circuit most dependent on?
- The area of the region enclosed by the circuit
- The orientation of that area with respect to the originating direction of the pulse
- The total length of the circuit (e.g. a wire with two conductors potentially connected together at the ends has lots of length but not much area enclosed within the loop)
Suppose I were hypothetically trying to shield my computer and an iPhone connected to a USB cable to that computer from a high-altitude nuclear event. Does the thinness of the USB cord allow me to extend the cord outside the computer's Faraday cage and still have it be relatively safe? The phone would need to be in its own Faraday cage in this case, of course. What I'm wondering is if the exposed cable would have voltages induced in it. | <urn:uuid:a4478418-38fd-4a9b-a6a2-78cae5e19f67> | 2.703125 | 187 | Q&A Forum | Science & Tech. | 50.250775 |
Matt Strassler [December 13, 2012]
Every atom is a representative of one of about 100 chemical elements, and every chemical element is labelled by a name and an atomic number Z. (To review the basics about atoms, click here.) The atomic number tells you how many protons are in that atom’s nucleus, and also, if the atom is electrically neutral, how many electrons it has. But what about the number of neutrons? Let’s call the number of neutrons N. There’s a lot to be said about what values of N we find in nature, and much of it will be said in a future article about atomic nuclei. But there are a few simple things that are worth saying now.
Most elements come in a small number of varieties, or “isotopes”, which differ only in the number of neutrons that make up the nucleus; in other words, different isotopes of the same element have the same Z but different N. Since chemistry is mostly determined by the number of electrons, i.e., by the atomic number, and not by the properties of the nucleus, atoms from different isotopes of the same element have almost identical chemistry.
Almost identical, because there are small differences in the chemistry stemming from the fact that different isotopes of the same element have different masses. Most of an atom’s mass is in its nucleus, and since protons and neutrons have nearly the same mass (0.938 and 0.940 GeV/c²; this near-identity will be explained later), the mass of an atom is roughly equal to Z + N times the mass of a proton.
But most chemistry is determined by the properties of the outermost (“valence”) electrons, which are not impacted by N at all. So to a large extent, if molecules are like words, and atoms are like the letters that make up those words, then different isotopes of the same element are like the same letter written in a different font. Just as different isotopes of an element have identical function inside of molecules, any letter, such as “t”, always serves the same funcTion inside any particular word, no matter what font is used to wriTe it down. | <urn:uuid:e7ae3e46-d76c-4073-ab12-de943a7c2068> | 4.3125 | 475 | Personal Blog | Science & Tech. | 47.867327 |
Every browser that supports XHTML (Firefox, Opera, Safari, IE9) supports self-closing syntax on every element.
<br></br> all should work just fine. If they don't, then you have HTML with inappropriately added XHTML DOCTYPE.
DOCTYPE does not change how document is interpreted. Only MIME type does.
W3C decision about ignoring DOCTYPE:
The HTML WG has discussed this issue: the intention was to allow old
(HTML-only) browsers to accept XHTML 1.0 documents by following the
guidelines, and serving them as text/html. Therefore, documents served as
text/html should be treated as HTML and not as XHTML.
It's a very common pitfall, because W3C Validator largely ignores that rule, but browsers follow it religiously. Read
Understanding HTML, XML and XHTML from WebKit blog:
In fact, the vast majority of supposedly XHTML documents on the internet are served as
text/html. Which means they are not XHTML at all, but actually invalid HTML that’s getting by on the error handling of HTML parsers. All those “Valid XHTML 1.0!” links on the web are really saying “Invalid HTML 4.01!”.
To test whether you have real XHTML or invalid HTML with XHTML's DOCTYPE, put this in your document:
<span style="color:green"><span style="color:red"/>
If it's red, it's HTML. Green is XHTML.
It validates, and in real XHTML it works perfectly (see: 1 vs 2). If you can't believe your eyes (or don't know how to set MIME types), open your page via XHTML proxy.
Another way to check is view source in Firefox. It will highlight slashes in red when they're invalid.
In HTML5/XHTML5 this hasn't changed, and the distinction is even clearer, because you don't even have additional
Content-Type is the king. | <urn:uuid:187a2bf7-16f6-4dab-a504-53731a7331cd> | 2.984375 | 441 | Q&A Forum | Software Dev. | 77.41187 |
The world's first coral
reefs occurred about 500 million years ago, and the first close
relatives of modern corals developed in southern Europe about 230
million years ago. By comparison, the Great Barrier Reef is relatively
young at just 500,000 years old. The current reef's structure is much
younger at less than around 8,000 years old.
Most modern reefs have formed on hard surfaces in the ocean, such as a
base of an old reef that died during a period when sea level was lower,
or the edge of a rocky island. Depending on how they start out, several
types of reefs can form. Some coral reefs form in the deep ocean and are
called atolls. The theories on how coral reefs form were first put
forward by Charles Darwin (of The Origin of Species fame) who proposed
that atolls form around the edges of high volcanic islands that
gradually submerge beneath the sea with changes in sea level or
subsidence of the land. Thus an atoll starts life as a fringing reef,
then becomes more of a ring growing on the shrinking land-mass, until
the land disappears and just the coral circle remains. In some cases,
the coral growth is unable to keep pace with the sinking island, and
sunken dead reefs have been found.
Class: Anthozoa [includes corals, anemones and sea pens]
Habitat: Coral reefs are found in shallow water, ranging to
depths of 60 m. Some species prefer either cooler temperate water while
others are found along tropical reefs, such as the Great Barrier Reef,
with waters ranging in temperatures from 18 - 33 °C.
Living in colonies: They generally occur in large numbers as colonies of
individual polyps linked by tissue. Resources, such as food, are then
shared amongst the individuals in the colony.
Coral Size: Individual polyps range from 3 - 56 mm in diameter or
height; while colony size varies from 75 mm -1500 mm (1.5 m) in width,
height or length.
Some corals have a
mutualistic relationship with algae called zooxanthellae. A mutualistic
relationship is one where both parties benefit from their partnership.
The algae use sunlight and the polyp’s waste products to make oxygen and
food. These substances leak into the surrounding tissues of the polyp
and can provide up to 98% of the polyp’s dietary requirements. These
corals are found in shallow water, as they require sunlight to survive.
They are generally fawn, brown or green in colour, due to the
yellow-brown colour of the zooxanthellae.
Stinging cells: All Cnidarians have characteristic stinging cells called
nematocysts in the tentacles and body wall. Each nematocyst cell
contains a coiled thread under pressure, which is ejected from the cell
when triggered by touch. These stinging cells are used for catching prey
and for defense, some having barbed ends connected to poison sacs, while
others are sticky.
Coral polyps: Coral reefs consist of hundreds and thousands of
soft-bodied, invertebrate animals, having no backbone. These animals are
called coral polyps. The individual polyp is radially symmetrical and
has a tubular body with tentacles surrounding the mouth at the upper
end. Each polyp’s body wall consists of two layers of cells, an outer
layer called the ectoderm and an inner endoderm layer. A
gelatinous material called mesogloea is found in between these two
Hard corals: Hard corals build reefs by growing atop the stony
skeletons of previous coral colonies. They consist of limestone cases
made by coral polyps extracting calcium from seawater. These limestone
cases form a ‘house’ for the coral polyp, consisting of a floor, outer
walls and a number of internal partitions. Inside corals’ clear outer
tissues live microscopic algae, which transform sunlight into sugars
through Photosynthesis The hosts help themselves to some of the sugars
and gain some colour through the process.
Reproduction: Corals reproduce in two ways: asexually and
Some corals divide to form new individuals. This is known as asexual
reproduction. Sexual reproduction takes place as mass spawning, where
polyps release millions of eggs and sperm. Polyps are either male or
female or both male and female. After the eggs and sperm are released,
they float to the surface. The fertilised eggs that escape predation by
other animals hatch into larvae and drift with the plankton. The tiny
percent that survive and settle on the reef then begin new coral
Major Natural Predator:
The Crown-of-Thorns Seastar was once an animal of great controversy
causing terrible damage to the coral reefs of the Great Barrier Reef.
Many believed that this seastar was a pest species invading the coral
reef habitat predating on and killing corals in great numbers. Research
has indicated that the Crown-of-Thorns Seastar is only found in
and a native species to Australian waters. The role that the sea star
plays by eating coral polyps forms a population control, making more
room for new coral reefs to form. Plague proportions are thought to
coincide with rainfall and increases in nutrients from rivers during
floods, and often occur cyclically every 17 years. Further scientific
studies are still in progress to determine whether these plaques can be
Scuba diving & snorkeling
From Cairns and Port Douglas are the most sought after outing onto the reef. With so
much to see like ship wrecks, coral gardens, the thousands of species of
marine animals and under water canyons. Cairns Great Barrier Reef has many qualified scuba
diving courses available and are amongst the safest in the world, with
strict guidelines that trainers must follow. You can easily become a
certified scuba diver and enjoy all the underwater attractions that the
reef has to offer.
Australian Marine Life, by G.J.Edgar
Steve Parish: Amazing Facts about Australian Marine Life Encyclopedia
Britannica and http://www.reef.crc.org.au/sitemap.html | <urn:uuid:74da18eb-5207-4c13-ae95-88e300ac7e8b> | 4.21875 | 1,348 | Knowledge Article | Science & Tech. | 48.718078 |
h and Chi Persei
Simply begin typing or use the editing tools above to add to this article.
Once you are finished and click submit, your modifications will be sent to our editors for review.
...clusters and can be accounted for in detail by calculations of the rate of evolution of stars of different absolute magnitudes and mass. For example, the luminosity function for the young clusters h and χ Persei, when compared with the van Rhijn function, clearly shows a large overabundance of bright stars due to the extremely young age of the cluster, which is on the order of...
...clusters—for example, the double cluster h and χ Persei, the Pleiades, Praesepe, and M67—with the main feature distinguishing the clusters being their ages. The young cluster h and χ Persei, which is a few million years old, contains stars ranging widely in luminosity. Some stars have already evolved into the supergiant stage (in such a diagram the top of the...
What made you want to look up "h and Chi Persei"? Please share what surprised you most... | <urn:uuid:1fdff147-cde4-4a53-8bf4-2b26d80caf60> | 3.203125 | 235 | Truncated | Science & Tech. | 65.595 |
||Because of the important role radiation plays in the climate system, the Baseline Surface Radiation Network (BSRN) was established to provide a worldwide network to continuously measure radiative fluxes at the Earth's surface. Over 30 stations located throughtout the world are planned for BSRN. Many of these stations began operation in 1992 and each year more are added to the network. These stations provide data for the calibration of the Surface Radiation Budget (SRB) Project and other satellite-based measurements of radiative fluxes. BSRN data are also used to validate radiative flux models. The data are archived at the World Radiation Monitoring Center (WRMC) in Zurich, Switzerland. BSRN data is also available from the Langley DAAC.
Colorado State University
NASA Langley Research Center | <urn:uuid:a9e6d2be-6f25-4135-b3ee-d21beffa93d4> | 4 | 163 | Knowledge Article | Science & Tech. | 26.477581 |
Wednesday Science Night takes a look at different species of deadly animals such as the venomous Black Mamba, and crop crippling rats that are found in various geographic locations around the world today.
Nature Black Mamba 7 pm
The black mamba is one of Africa’s most dangerous and feared snakes, known for being very aggressive when disturbed. Rearing up with its head four feet above the ground, it strikes with deadly precision, delivering venom that is packed with three different kinds of toxins and is ten times more deadly than needed to kill an adult human. Without treatment the mortality rate is 100%, the highest among all venomous snakes in the world. Until now, little has been known about the black mamba’s natural behavior in the wild because in Africa most people kill a black mamba on sight and feel lucky to have done so. But in the tiny country of Swaziland in southern Africa, a team of herpetologists has an entirely different “take” on these creatures and hopes their six-week study will change public perception of what they feel is the world’s most misunderstood snake.
NOVA Rat Attack 8 pm
Every 48 years, the inhabitants of the remote Indian state of Mizoram suffer a horrendous ordeal known locally as mautam. An indigenous species of bamboo, blanketing 30 percent of Mizoram’s 8,100 square miles, blooms once every half-century, spurring an explosion in the rat population which feeds off the bamboo’s fruit. The rats run amok, destroying crops and precipitating a crippling famine throughout Mizoram. NOVA follows this gripping tale of nature’s capacity to engender human suffering, and investigates the botanical mystery that happens with clockwork precision every half century.
Killer Stress: A National Geographic Special 9 pm
Stress. It’s always been there to save our lives. It’s what made us run from predators and enabled us to take down prey. But today, humans are turning on that same stress response to deal with 30-year mortgages, difficult bosses, teenagers and traffic jams. Some of us are wallowing in corrosive hormones; for the first time, scientists can reveal just how measurable and dangerous that exposure can be. MacArthur “Genius Grant” recipient and Stanford University neurobiologist Robert Sapolsky and National Geographic search for answers to why stress seems to be killing us. | <urn:uuid:a8c9de98-fb5f-4910-8152-f6653cf5b1df> | 3.484375 | 499 | Content Listing | Science & Tech. | 41.391551 |
View your list of saved words. (You can log in using Facebook.)
In mathematics, the useful concept of a process with no end. As represented by the symbol , it is often mistakenly thought to be the largest number or a place on the real number line. Instead, it is the idea of a limit, as in the expression x , which suggests that the variable x increases without bound. For example, the function f(x) = 1/x, or the reciprocal of x, tends toward 0 as x approaches infinity as a limit. This process of approaching is crucial to the definition of the derivative and the integral in calculus, as well as to many other concepts of mathematical analysis.
This entry comes from Encyclopædia Britannica Concise. For the full entry on infinity, visit Britannica.com. | <urn:uuid:67fe80d4-a286-47cf-8306-50d675b8cb19> | 3.421875 | 168 | Knowledge Article | Science & Tech. | 56.863851 |
ONCE a century, a burst of super-energetic cosmic rays will strike the Earth within a kilometre of where you are standing. And, if that's not worrying enough, astrophysicists have no idea where these rays come from.
Last week, at a meeting in Chicago, physicists from 22 countries announced plans to build an array of cosmic ray detectors over an area twice the size of Oxfordshire. The detectors would be able to pinpoint the source of hugely high-energy cosmic rays. The project will cost around $80 million.
Each array would have 3000 solar-powered detector stations, each the size of a garage, arranged in a hexagonal pattern over 5000 square kilometres somewhere in the northern hemisphere - possibly the southwestern US, Spain or Kazakhstan. A similar array would be set up on the opposite side of the Earth, in the southern hemisphere.
High-energy cosmic rays - those above a billion gigaelectronvolts - ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:83a47dad-9dd4-4cd7-8559-7692378265ac> | 3.859375 | 220 | Truncated | Science & Tech. | 45.220388 |
Imagine floating 35,000 miles above the sunny side of Earth. Our home planet gleams below, a majestic whorl of colour and texture. All seems calm around you. With no satellites or space debris to dodge, you can just relax and enjoy the black emptiness of space.
But looks can be deceiving.
In reality, you've unknowingly jumped into an invisible mosh pit of electromagnetic mayhem - the place in space where a supersonic 'wind' of charged particles from the Sun crashes head-on into the protective magnetic bubble that surrounds our planet. Travelling at a million miles per hour, the solar wind's protons and electrons sense Earth's magnetosphere too late to flow smoothly around it. Instead, they're shocked, heated, and slowed almost to a stop as they pile up along its outer boundary, the magnetopause, before getting diverted sideways.
Space physicists have had a general sense of these dynamic goings-on for decades. But it wasn't until the advent of the Interstellar Boundary Explorer or IBEX, a NASA spacecraft launched in October 2008, that they've been able to see what the human eye cannot: the first-ever images of this electromagnetic crash scene. They can now witness how some of the solar wind's charged particles are being neutralised by gas escaping from Earth's atmosphere.
IBEX wasn't designed to keep tabs on Earth's magnetosphere. Instead, its job is to map interactions occurring far beyond the planets, 8 to 10 billion miles away, where the Sun's own magnetic bubble, the heliosphere, meets interstellar space.
Only two spacecraft, Voyagers 1 and 2, have ventured far enough to probe this region directly. IBEX, which travels in a looping, 8-day-long orbit around Earth, stays much closer to home, but it carries a pair of detectors that can observe the interaction region from afar.
Here's how: When fast-moving protons in the solar wind reach the edge of the heliosphere, they sometimes grab electrons from the slower-moving interstellar atoms around them, like batons getting passed between relay runners. This charge exchange creates electrically neutral hydrogen atoms that are no longer controlled by magnetic fields. Suddenly, they're free to go wherever they want - and because they're still moving fast, they quickly zip away from the interstellar boundary in all directions.
Some of these 'energetic neutral atoms,' or ENAs, zip past Earth, where they're recorded by IBEX. Its two detectors don't take pictures with conventional optics. Instead, they record the number and energy of atoms arriving from small spots of sky about 7 degrees across (the apparent size of a tennis ball held at arm's length). Because its spin axis always points at the Sun, the spacecraft slowly turns throughout Earth's orbit and its detectors scan overlapping strips that create a complete 360 degrees map every six months.
Because IBEX is orbiting Earth, it also has a front-row seat for observing the chaotic pileup of solar-wind particles occurring along the 'nose' of Earth's magnetopause, about 35,000 miles out. ENAs are created there too, as solar-wind protons wrest electrons from hydrogen atoms in the outermost vestiges of our atmosphere, the exosphere.
Other spacecraft have attempted to measure the density of the dayside exosphere, without much success. NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft probably detected ENAs from this region a decade ago, but its detectors didn't have the sensitivity to pinpoint or measure the source.
Now, thanks to IBEX, we know just how tenuous the outer exosphere really is. 'Where the interaction is strongest, there are only about eight hydrogen atoms per cubic centimetre,' explains Stephen A. Fuselier, the Lockheed Martin Space Systems researcher who led the mapping effort. His team's results appear in the July 8 issue of Geophysical Research Letters.
The key observations were made in March and April 2009, when IBEX was located far from Earth - about halfway to the Moon's orbit - and its detectors could scan the region directly in front of the magnetopause. During some of the March observations, the European Space Agency's Cluster 3 spacecraft was positioned just in front of the magnetopause, where it measured the number of deflected solar-wind protons directly. 'Cluster played a very important role in this study,' Fuselier explains. 'It was in the right place at the right time.'
The new IBEX maps show that the ENAs thin out at locations away from the point of peak intensity. This falloff makes sense, Fuselier says, because Earth's magnetopause isn't spherical. Instead, it has a teardrop shape that's closest to Earth at its nose but farther away everywhere else. So at locations well away from the magnetopause's centreline, even fewer of the exosphere's hydrogen atoms are hanging around to interact with the solar wind. 'No exosphere, no ENAs,' he explains.
Since its launch, IBEX has also scanned another nearby world, with surprising results. The moon has no atmosphere or magnetosphere, so the solar wind slams unimpeded into its desolate surface. Most of those particles get absorbed by lunar dust. In fact, space visionaries wonder if the moon's rubbly surface has captured enough helium-3, an isotope present in tiny amounts in the Sun's outflow, to serve as a fuel for future explorers.
Yet cosmic chemists have long thought that some solar-wind protons must be bouncing off the lunar surface, becoming ENAs through charge exchange as they do. So does the moon glow in IBEX's scans? Indeed it does, says David J. McComas of Southwest Research Institute in San Antonio, Texas, who serves as the mission's Principal Investigator.
In a report published last year in Geophysical Research Letters, McComas and other researchers conclude that about 10 percent of the solar-wind particles striking the Moon escape to space as ENAs detectable by IBEX. That amounts to roughly 150 tons of recycled hydrogen atoms per year.
Meanwhile, the squat, eight-sided spacecraft continues its primary task of mapping the interactions between the outermost heliosphere and the interstellar medium that lies beyond. McComas and his team are especially eager to learn more about the mysterious and unexpected 'ribbon' of ENAs that turned up in the spacecraft's initial all-sky map.
At NASA's Goddard Space Flight Centre in Greenbelt, Md., IBEX Mission Scientist Robert MacDowall says the spacecraft should be able to continue its observations through at least 2012. 'We weren't sure those heliospheric interactions would vary with time, but they do,' he explains, 'and it's great that IBEX will be able to record them for years to come.' | <urn:uuid:a6aa38aa-c075-421b-adcd-03016d47f3f6> | 3.578125 | 1,412 | Knowledge Article | Science & Tech. | 44.154614 |
This curled-up critter is one of seven new species of limbless amphibians found recently in the soil of northeastern India. It took researchers more than 1,000 hours of digging to discover all seven in 58 locations throughout the region.
This is not the first species this team has discovered. Sathyabhama Das Biju of the University of Delhi and his group have described 48 species. Biju worries, however, that many of his new species are in danger from the constant spread of development in northern India.
This article was originally published with the title What Is It?. | <urn:uuid:207baf79-c511-4ac0-abf8-8826236806a6> | 3.015625 | 122 | Knowledge Article | Science & Tech. | 56.229082 |
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A distant super-Earth named "55 Cancri e" is wetter and weirder than astronomers thought possible. The discovery has researchers re-thinking the nature of alien worlds.
FULL STORY at http://science.nasa.gov/science-news/science-at-nasa/2012/13jan_rethink/
A video version of this story is available at http://www.youtube.com/watch?v=H_CZCmJ2om0
[Site Home] [JPL News] [Cassini] [Science Toys] [JPL Home] [NASA KSC] [NTSB] [Telescopes] [Deep Creek Hot Springs] [Hot Spring Photos] [Yosemite Discussion] [Airline List] [NSF] [Saturn] [Mars] [JPL and the American Space Program] | <urn:uuid:245f7c3f-3daf-45d9-8b73-d927fb40f383> | 2.75 | 205 | Comment Section | Science & Tech. | 63.486176 |
But, my description was merely a proof of concept, not how to make use of the idea. That could happen at a much higher level than the Planck size world. This theory actually plays into another theory I have about mitigating apparent mass using magnetic fields. The problem is generating a magnetic field big enough without needing a generator the size of an aircraft carrier. If you can borrow energy from the universe then you need a much smaller power source. Remember that gravity only works on you because it see's you. And it only see's you because of your apparent mass, relative to other masses (like the earth). If you decrease your apparent mass then gravity will see less of you.
Superstring theory gives us a framework of ideas that could lead to our understanding of how mass couples you to the Higgs field (which creates what we call gravity). Remove that coupling, remove the gravitational force. Its so cool. If you've seen the science shows on tv where they show the fabric of space and how gravity distorts it. They always make the mistake of looking at it in too few dimensions which makes it look like a cone. That is incorrect. It is not a cone. Its a shape which we don't have a name for yet. To try and visualize it: think of a hot pot belly stove in the middle of your summer camp bunkhouse. The closer you get, the hotter you get. The further away, the cooler you get. Replace temperature with the density of space (the Higgs field).
Close to a mass the Higgs field is dense. Far away and the density is lower. Your mass is nothing but the coupling of the strings in the sub-atomic particles of your body to the Higgs field. And this coupling is what distorts the fabric of space. The Higgs field itself may be made of strings which vibrate at certain frequencies. The strings in your body vibrate at a complementary frequency (actually its more than just frequency - phase shift, amplitude, dimension, all play into it).
When we learn how to manipulate the strings we can play any tune we want. For example, we can travel without using time. We can travel faster than light without violating relativity. | <urn:uuid:a932a275-2b49-456f-8aed-266ec1a3f16a> | 2.859375 | 448 | Comment Section | Science & Tech. | 63.001628 |
As in principal components analysis, the results of correspondence analysis
are presented on graphs that represent the configurations of points in
projection planes, formed by the first principal axes taken two at a time. It
is customary to summarize the row and column coordinates in a single plot.
However, it is important to remember that in such plots, one can only interpret
the distances between row points, and the distances between column points, but
not the distances between row points and column points. However, it is
legitimate to interpret the relative positions of one point of one set with
respect to all the points of the other set
The joint display of row and column points shows the relation between a
point from one set and all points of another set, not between individual points
between each set. Except in special cases, it is extremely dangerous to
interpret the proximity of two points corresponding to different sets of
Some keys for interpreting the factorial maps are:
- Points near the origin have undifferentiated profile
distribution as a consequence of the origin being placed at the center of
gravity of both clouds N ( I ) and N ( J ).
- The points, which do not contribute essentially to the inertia
of each axis, are virtually identical to the average profile.
- Points of a cloud (or set) situated away from the origin, but
close to each other have similar profiles
- Geometrically, a particular row profile would be attracted to a
position in its subspace, that corresponds to
column variable categories prominent in that row profile.
- When correspondence analysis has more than two dimensions.
Proximity with one pair of axes may disappear when other axes are (added)
- It is customary to summarize the row and column coordinates in a
single plot. However, it is important to remember that in such plots, one
can only interpret the distances between row points, and the distances
between column points, but not the distances between row points and column
points. cannot be interpreted. The joint display
of coordinates shows the relation between a point from one set and all
points of the other set and not between individual points between each
- A point makes a high contribution to the inertia of a principal
axis in two ways –when it has a large distance from the barycenter,
even if it has a small mass, or when it has a large mass, but a small
distance. Considering all these points, it is necessary that the numerical
results of correspondence analysis, viz. mass. Absolute
contribution (CTR) and relative contribution COS2 j are
all taken into account for interpreting the results of correspondence | <urn:uuid:d0e01a44-ad73-4e45-a733-e20554abb978> | 2.984375 | 550 | Academic Writing | Science & Tech. | 27.126575 |
Note: GFF parsing is not yet integrated into Biopython. This documentation is work towards making it ready for inclusion. You can retrieve the current version of the GFF parser from: http://github.com/chapmanb/bcbb/tree/master/gff. Comments are very welcome.
Generic Feature Format (GFF) is a biological sequence file format for representing features and annotations on sequences. It is a tab delimited format, making it accessible to biologists and editable in text editors and spreadsheet programs. It is also well defined and can be parsed via automated programs. GFF files are available from many of the large sequencing and annotation centers. The specification provides full details on the format and its uses.
Biopython provides a full featured GFF parser which will handle several versions of GFF: GFF3, GFF2, and GTF. It supports writing GFF3, the latest version.
GFF parsing differs from parsing other file formats like GenBank or PDB in that it is not record oriented. In a GenBank file, sequences are broken into discrete parts which can be parsed as a whole. In contrast, GFF is a line oriented format with support for nesting features. GFF is also commonly used to store only biological features, and not the primary sequence.
These differences have some consequences in how you will deal with GFF:
- Files are first examined to determine available annotations and define items of interest.
- Sequences will often be parsed separately, from an associated FASTA file.
- Parsing needs to consider available memory, which can be quickly used up on files with many annotations. This problem can be solved via two methods:
- Limiting parsing to features of interest.
- Iterating over portions of the file.
The documentation below provides a practical guide to examining, parsing and writing GFF files in Python.
Examining your GFF file
Basic GFF parsing
Providing initial sequence records
Limiting parsed lines
Iterating over portions of a file | <urn:uuid:7afa985d-6829-4631-a869-994fc1021b01> | 3.03125 | 422 | Documentation | Software Dev. | 39.780839 |
Make Your Own Chemicals
How To Purify Alcohol Using Distillation
Denatured alcohol is toxic. If you need pure ethanol, you can purify denatured, contaminated or impure alcohol using distillation. Here's how to do it.
How to Prepare Gases
Here are simple instructions for preparing common gases from ordinary chemicals. The gases include carbon dioxide, oxygen, nitrogen, methane, nitrous oxide, chlorine, and several others.
Ammonia - How to Prepare Ammonia Gas
These are instructions for preparing ammonia gas from ammonium chloride and calcium hydroxide in water.
Carbon Dioxide - How to Prepare Carbon Dioxide Gas
These are instructions for preparing carbon dioxide gas from calcium carbonate and hydrochloric acid.
Chlorine Gas - How to Prepare Chlorine Gas
These are instructions for preparing chlorine gas from potassium permanganate and hydrochloric acid.
Copper Sulfate Preparation
Make copper sulfate or copper sulphate yourself from copper and sulfuric acid.
Hot Ice Video Tutorial
Hot ice is a non-toxic chemical you can make in the kitchen from baking soda and vinegar. You can cause the saturated solution of hot ice to crystallize in 'ice' that gives of heat or you can build crystalline towers as you pour the hot ice onto a container. Here a step-by-step video that shows you what to do.
How to Make Hydrogen Gas
It's easy to generate hydrogen gas using common household materials. Here's how to make hydrogen safely.
Potassium Chlorate from Bleach and Salt Substitute
Potassium chlorate is an important potassium compound that can be used as an oxidizer, disinfectant, source of oxygen, and component in pyrotechnics and chemistry demonstrations. You can make potassium chlorate from common household bleach and salt substitute.
How to Make Nitrous Oxide or Laughing Gas
Nitrous oxide or laughing gas is one of the easiest gases to prepare in the chem lab or home lab. Here are instructions for synthesizing and collection nitrous oxide or laughing gas.
Learn how to prepare nitrogen triiodide, an unstable compound that can be used to perform a stunning chemistry demonstration.
Potassium Nitrate Recipe
Make potassium nitrate (saltpeter) from common household ingredients. Potassium chloride from lite salt and ammonium nitrate from a cold pack are reacted to yield potassium nitrate and ammonium chloride. This is an easy way to make your own potassium chloride if you can't find it in a store or just want to try a fun chemistry experiment.
Silica or Pure Sand
Sand that you find on a beach consists of several minerals and organic matter. If you could separate out the impurities, you would have pure sand, which is silica or silicon dioxide. Here is how to prepare pure sand yourself in the lab.
Sodium Carbonate from Baking Soda
These are easy instructions for making sodium carbonate, also known as washing soda or soda ash, from baking soda or sodium bicarbonate.
Sulfuric Acid at Home
Sulfuric acid is a useful acid to have on hand for home chemistry projects. However, it is not easy to obtain. Fortunately, you can make it yourself.
How To Make Graphene
The discovery of graphene, a honeycomb sheet of carbon, was so important it earned a Nobel Prize, yet graphene isn't an exotic material. You can make it yourself! | <urn:uuid:ac1891e4-f8b1-4793-b785-3f2fb0b9b39e> | 3.5 | 721 | Tutorial | Science & Tech. | 31.135518 |
Brief SummaryRead full entry
BiologyBoth adults and larvae of this beetle are voracious predators, taking a wide range of prey including fish. They actively search for prey, and periodically swim to the surface in order to take in air (3). Adults often fly at night, and may land on glass surfaces or roads, mistaking them for water (2). When threatened, they exude a foul-smelling fluid from the anus that deters potential predators from eating them (5). Females lay their eggs in cavities, which they cut in the stems of water plants that protrude from the water. The eggs hatch after a number of weeks (5). | <urn:uuid:c00d76c8-ba1d-41e5-a1d2-b01d934317b3> | 2.984375 | 136 | Knowledge Article | Science & Tech. | 59.608994 |
(Phys.org) -- A team of American, Canadian and Chilean astronomers have stumbled onto a remarkably faint cluster of stars orbiting the Milky Way that puts out as much light as only 120 modest Sun-like stars. The tiny cluster, called Muñoz 1, was discovered near a dwarf galaxy in a survey of satellites around the Milky Way using the Canada-France-Hawaii Telescope (CFHT) and confirmed using the Keck II telescope, both of which are on Mauna Kea, Hawaii.
- VISTA finds 96 star clusters hidden behind dustWed, 3 Aug 2011, 10:34:40 EDT
- Stellar family in crowded, violent neighborhood proves to be surprisingly normalThu, 4 Jun 2009, 9:50:33 EDT
- First of missing primitive stars discoveredWed, 3 Mar 2010, 14:00:54 EST
- A swarm of ancient starsWed, 8 Dec 2010, 7:02:10 EST
- Old star is 'missing link' in galactic evolutionWed, 3 Mar 2010, 14:01:07 EST | <urn:uuid:231533fd-4357-4727-b395-151de437bb76> | 3.296875 | 214 | Content Listing | Science & Tech. | 37.413596 |
16th April 2004 - 09:04 PM
Research groups in the US and Austria say that they have found the best
evidence to date for superfluidity - the flow of a fluid without
resistance - in a Fermi gas made of ultracold lithium-6 atoms. The
results could help physicists understand more about other exotic systems
in nature, such as high-temperature superconductors, neutron stars and
the quark-gluon plasma.
27th August 2004 - 02:52 AM
Extract from the above post publication
"The Duke team says its experiment provides the most direct ever evidence for superfluidity. Earlier this year, a group at Boulder in the US created a Bose-Einstein condensate from a strongly interacting Fermi gas and studied the pairs of fermions that formed. “That was a good experiment, but it doesn’t establish superfluidity,” said Thomas in a press release. “To have superfluidity you’ve got to observe something like hydrodynamics, like we observed.”
Thomas admits that the work could be criticised because it does not demonstrate a well-defined transition at the point where the gas becomes a superfluid. In contrast, the experiment performed by Rudolf Grimm and colleagues at the University of Innsbruck shows an abrupt change - in the collective excitation frequency - at this crossover point (M Bartenstein et al. 2004 arXiv.org/abs/cond-mat/0403716). The transition is also accompanied by oscillations that last a long time."
The super fluidity problem here is that the particles are bunching together and being held in a psuedo bosonic state from which they can not flow. Even assuming they can get through the matrix now that youve doubled their size. This is not the case for bosonic particles which have greater freedom because they are naturally in this state and free to move
Your experiment is holding them in a psuedo bosonic state you have to let them go.
4th October 2008 - 01:50 PM | <urn:uuid:9fb60c2d-4085-4d51-9d38-7816f9efafd3> | 2.96875 | 434 | Comment Section | Science & Tech. | 45.683214 |
Most of the time I see matrix multiplication presented and defined, as a seemingly arbitrary sequence of operations. For example, the textbook I'm currently reading for a linear algebra course defines the product $AB$ as the $(i, j)$ entry in the $1 \times 1$ matrix that is the product of the ith row of $A$ and the jth column of $B$. Properties of matrix multiplication are subsequently proven based upon this definition. The definition is clear, but why the matrix product is useful is not clear to me as a student. A different textbook I'm referencing defines the product $AB$ in terms of linear combinations.
The problem I have is doing matrix multiplication quickly by hand, particularly when the $A$ is $p \times 1$ and $B$ is $1 \times q$. I would like to know of how to look at or define matrix multiplication, in a manner which makes it easy (for the average student) to compute by hand, while being intuitive and consistent for use for later proofs.
wikipedia has a great article. | <urn:uuid:19fdb2e7-8027-4639-8cdc-903553e0c27b> | 3.046875 | 219 | Q&A Forum | Science & Tech. | 47.991364 |
What was your best experience in the field covering this story?
Among the great pleasures of writing about an organism is gaining a window on the world of scientists obsessed by it. John Matthews, a young ecologist studying the migration of green darners, was among the dozens of wonderful and fanatical odonatologists I met the summer of 2005.
To understand the journeys of these big beautiful dragonflies, Matthews took a marathon journey of his own. He went from Canada to Florida, crisscrossing the United States from the East Coast as far west as Texas, collecting adult dragonflies and larvae at dozens of places along the way. We spent one fascinating day together at Cape May, New Jersey, watching thousands of green darners pass through, thick as mosquitoes and thrumming the warm air in the lee of the cape's dunes. After 7,450 miles (11,989 kilometers), two flat tires, 120 cans of Diet Coke, and hundreds of mosquito bites, Matthews amassed more than 700 samples and is now analyzing them to determine where these creatures begin their journeys and where they end up.
What was your worst experience in the field covering this story?
In July 2005, I attended a gathering of the Worldwide Dragonfly Association in Pontevedra, Spain, where there was much discussion of threats to dragonflies. While few kinds of dragonflies are facing extinction, some 350 species are considered threatened, in large part because the forests and freshwater ecosystems on which they depend are under siege. Freshwater ecosystems cover only 0.8 percent of Earth's surface, but they are the habitat for virtually 100 percent of the world's dragonflies. The degradation or loss of wetlands and fresh waters may imperil something like 20 percent of dragonfly species.
So, too, may the loss of forests, which provide essential and irreplaceable habitat for odonates. Only 6 percent or less of the original area of the world's tropical rainforests remains, and even this is disappearing at an alarming rate. If the destruction continues, many dragonfly species will vanish. It's simple, says Dennis Paulson of the University of Puget Sound in Tacoma, Washington: "Dragonflies are forest animals; if you take away the forests, you take away the dragonflies."
What was your quirkiest experience in the field covering this story?
Get a group of dragonfly biologists together and send them into a field or onto the banks of a pond, and out come the nets and specimen bottles. They're out to capture individual dragonflies to help capture the subtle distinctions among species.
I spent some time in the field with Mike May, an odonatologist at Rutgers University with an interest in taxonomy. When Mike didn't have a specimen bottle with him, he would pull a dollar bill from his pocket, fold it neatly into one of those origami paper cups, and tuck his specimen in. When he had more than one dragonfly to handle at a time, he would pop the extra insect between his lips while he readied another specimen envelope. A third hand? I once asked him. "Yes," he said, "but it could also be interpreted as a sign of affection." | <urn:uuid:ac6f7ccd-fb3c-40a9-856c-c47077ff35d7> | 2.96875 | 652 | Audio Transcript | Science & Tech. | 46.760023 |
This package contains a collection of problems from the NRICH
website that could be suitable for students who have a good
understanding of Factors and Multiples and who feel ready to take
on some. . . .
A student in a maths class was trying to get some information from
her teacher. She was given some clues and then the teacher ended by
saying, "Well, how old are they?"
Can you order the digits from 1-6 to make a number which is
divisible by 6 so when the last digit is removed it becomes a
5-figure number divisible by 5, and so on?
Find the smallest whole number which, when mutiplied by 7, gives a
product consisting entirely of ones.
These eleven shapes each stand for a different number. Can you use
the multiplication sums to work out what they are?
The planet of Vuvv has seven moons. Can you work out how long it is
between each super-eclipse?
Can you replace the letters with numbers? Is there only one
solution in each case?
Can you work out the arrangement of the digits in the square so
that the given products are correct? The numbers 1 - 9 may be used
once and once only.
Can you fill in this table square? The numbers 2 -12 were used to
generate it with just one number used twice.
How many different shaped boxes can you design for 36 sweets in one
layer? Can you arrange the sweets so that no sweets of the same
colour are next to each other in any direction?
Given the products of adjacent cells, can you complete this Sudoku?
Follow the clues to find the mystery number.
Suppose we allow ourselves to use three numbers less than 10 and
multiply them together. How many different products can you find?
How do you know you've got them all?
There is a clock-face where the numbers have become all mixed up. Can you find out where all the numbers have got to from these ten statements?
Can you find which shapes you need to put into the grid to make the
totals at the end of each row and the bottom of each column?
There are seven pots of plants in a greenhouse. They have lost
their labels. Perhaps you can help re-label them.
In a square in which the houses are evenly spaced, numbers 3 and 10
are opposite each other. What is the smallest and what is the
largest possible number of houses in the square?
If you take a three by three square on a 1-10 addition square and
multiply the diagonally opposite numbers together, what is the
difference between these products. Why?
A package contains a set of resources designed to develop
students’ mathematical thinking. This package places a
particular emphasis on “being systematic” and is
designed to meet. . . .
In the planet system of Octa the planets are arranged in the shape
of an octahedron. How many different routes could be taken to get
from Planet A to Planet Zargon?
On a digital clock showing 24 hour time, over a whole day, how many
times does a 5 appear? Is it the same number for a 12 hour clock
over a whole day?
Place eight queens on an chessboard (an 8 by 8 grid) so that none
can capture any of the others.
Tim had nine cards each with a different number from 1 to 9 on it.
How could he have put them into three piles so that the total in
each pile was 15?
There are 4 jugs which hold 9 litres, 7 litres, 4 litres and 2
litres. Find a way to pour 9 litres of drink from one jug to
another until you are left with exactly 3 litres in three of the
A few extra challenges set by some young NRICH members.
This challenge is to design different step arrangements, which must
go along a distance of 6 on the steps and must end up at 6 high.
This problem is based on the story of the Pied Piper of Hamelin. Investigate the different numbers of people and rats there could have been if you know how many legs there are altogether!
Add the sum of the squares of four numbers between 10 and 20 to the
sum of the squares of three numbers less than 6 to make the square
of another, larger, number.
Can you rearrange the biscuits on the plates so that the three
biscuits on each plate are all different and there is no plate with
two biscuits the same as two biscuits on another plate?
Katie had a pack of 20 cards numbered from 1 to 20. She arranged
the cards into 6 unequal piles where each pile added to the same
total. What was the total and how could this be done?
Find the product of the numbers on the routes from A to B. Which
route has the smallest product? Which the largest?
There are 78 prisoners in a square cell block of twelve cells. The
clever prison warder arranged them so there were 25 along each wall
of the prison block. How did he do it?
In a bowl there are 4 Chocolates, 3 Jellies and 5 Mints. Find a way
to share the sweets between the three children so they each get the
kind they like. Is there more than one way to do it?
When intergalactic Wag Worms are born they look just like a cube.
Each year they grow another cube in any direction. Find all the
shapes that five-year-old Wag Worms can be.
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?
An extra constraint means this Sudoku requires you to think in
diagonals as well as horizontal and vertical lines and boxes of
You have two egg timers. One takes 4 minutes exactly to empty and
the other takes 7 minutes. What times in whole minutes can you
measure and how?
There is a long tradition of creating mazes throughout history and across the world. This article gives details of mazes you can visit and those that you can tackle on paper.
Ten cards are put into five envelopes so that there are two cards in each envelope. The sum of the numbers inside it is written on each envelope. What numbers could be inside the envelopes?
Place the numbers 1 to 8 in the circles so that no consecutive
numbers are joined by a line.
There were chews for 2p, mini eggs for 3p, Chocko bars for 5p and
lollypops for 7p in the sweet shop. What could each of the children
buy with their money?
A mathematician goes into a supermarket and buys four items. Using
a calculator she multiplies the cost instead of adding them. How
can her answer be the same as the total at the till?
How many shapes can you build from three red and two green cubes? Can you use what you've found out to predict the number for four red and two green?
Find a cuboid (with edges of integer values) that has a surface
area of exactly 100 square units. Is there more than one? Can you
find them all?
Nina must cook some pasta for 15 minutes but she only has a 7-minute sand-timer and an 11-minute sand-timer. How can she use these timers to measure exactly 15 minutes?
Rather than using the numbers 1-9, this sudoku uses the nine
different letters used to make the words "Advent Calendar".
There are 44 people coming to a dinner party. There are 15 square
tables that seat 4 people. Find a way to seat the 44 people using
all 15 tables, with no empty places.
Make a pair of cubes that can be moved to show all the days of the
month from the 1st to the 31st.
Investigate the smallest number of moves it takes to turn these
mats upside-down if you can only turn exactly three at a time.
Use the clues to find out who's who in the family, to fill in the family tree and to find out which of the family members are mathematicians and which are not. | <urn:uuid:309bc584-6139-43d2-bb92-bea4a69ad4de> | 4.03125 | 1,765 | Content Listing | Science & Tech. | 71.012712 |
When you try to put democracy into action you quickly run into tricky maths problems. This is what happened to Andrew Duff, rapporteur for the European Constitutional Affairs Committee, who was charged with finding a fair way of allocating seats of the European Parliament to Member States. Wisely, he went to ask the experts: last year he approached mathematicians at the University of Cambridge to help come up with a solution. A committee of mathematicians from all over Europe was promptly formed and today it has published its recommendation.
In the 1930s the logician Kurt Gödel showed that if you set out proper rules for mathematics, you lose the ability to decide whether certain statements are true or false. This is rather shocking and you may wonder why Gödel's result hasn't wiped out mathematics once and for all. The answer is that, initially at least, the unprovable statements logicians came up with were quite contrived. But are they about to enter mainstream mathematics?
It requires only a little processing power, but it's a giant leap for robotkind: engineers at the University of Southampton have developed a way of equipping spacecraft and satellites with human-like reasoning capabilities, which will enable them to make important decisions for themselves.
It's been nearly 18 months since the Large
Hadron Collider at CERN started up and scientists are eagerly awaiting their first glimpse into the
cosmic mysteries it was designed to explore. But when can we realistically
expect the first ground-breaking discoveries to come through? Last week, John Ellis,
outgoing leader of the theory division at CERN, addressed an audience
of physicists at the University of Cambridge to update them on the
current state of play. Plus went along and also managed to
catch Ellis for a quick interview.
Many people like mathematics because it gives definite answers. Things are either true or false, and true things seem true in a very fundamental way. But it's not quite like that. You can actually build different versions of maths in which statements are true or false depending on your preference. So is maths just a game in which we choose the rules to suit our purpose? Or is there a "correct" set of rules to use? We find out with the mathematician Hugh Woodin.
This book is a mixture between an encyclopedia and a collection of intriguing ideas. In some sense, it's a plain English encyclopedia of maths, embellished with some examples for entertainment. So whether you're trying to get at the "true" meaning of something textbooks only define using passionless symbols, or are looking for a little diversion before going to sleep, this book can give you both.
This book tells the fascinating story of strange geometric objects that have achieved some fame outside of maths and even inspired a Woody Allen joke: they're called Calabi-Yau manifolds. When Plus recently interviewed one of its authors he was adamant that maths should be brought to the masses without dumbing down or glossing over the tricky parts. And this is just what this books sets out to achieve.
That geometry should be relevant to physics is no surprise — after all, space is the arena in which physics happens. What is surprising, though, is the extent to which the geometry of space actually determines physics and just how exotic the geometric structure of our Universe appears to be. Plus met up with mathematician Shing-Tung Yau to find out more.
Plus bumped into an old friend at the International Congress of Mathematicians this year: Keith Mansfield is the author of the Johnny Mackintosh series and commissioning editor for mathematics at Oxford University Press at the same time. In this interview he tells us how his he's built a career around his two talents, writing and maths.
Statistics are emotive — to some they are just lies, to others perplexing, some fear their power to reduce us all to a single number, while yet others (politicians and journalists especially) like to endow them with qualities like "damning" or "deathly". So what are (or should it be "is"?) statistics all about? And what do we need to be wary of? This little comic-style book (from the Introducing series) provides some friendly answers in 176 pages and a handy A6 format. | <urn:uuid:081bce36-04d2-4b20-8683-fc25ae8841e9> | 2.9375 | 867 | Content Listing | Science & Tech. | 44.345924 |
errno - error return value
The lvalue errno is used by many functions to return error values.
Many functions provide an error number in errno, which has type int and is defined in <errno.h>. The value of errno shall be defined only after a call to a function for which it is explicitly stated to be set and until it is changed by the next function call or if the application assigns it a value. The value of errno should only be examined when it is indicated to be valid by a function's return value. Applications shall obtain the definition of errno by the inclusion of <errno.h>. No function in this volume of IEEE Std 1003.1-2001 shall set errno to 0. The setting of errno after a successful call to a function is unspecified unless the description of that function specifies that errno shall not be modified.
It is unspecified whether errno is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual object, or a program defines an identifier with the name errno, the behavior is undefined.
The symbolic values stored in errno are documented in the ERRORS sections on all relevant pages.
Previously both POSIX and X/Open documents were more restrictive than the ISO C standard in that they required errno to be defined as an external variable, whereas the ISO C standard required only that errno be defined as a modifiable lvalue with type int.
An application that needs to examine the value of errno to determine the error should set it to 0 before a function call, then inspect it before a subsequent function call.
Error Numbers, the Base Definitions volume of IEEE Std 1003.1-2001, <errno.h>
First released in Issue 1. Derived from Issue 1 of the SVID.
The following sentence is deleted from the DESCRIPTION: "The value of errno is 0 at program start-up, but is never set to 0 by any XSI function". The DESCRIPTION also no longer states that conforming implementations may support the declaration:extern int errno;
Obsolescent text regarding defining errno as:extern int errno
Text regarding no function setting errno to zero to indicate an error is changed to no function shall set errno to zero. This is for alignment with the ISO/IEC 9899:1999 standard.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/23 is applied, adding text to the DESCRIPTION stating that the setting of errno after a successful call to a function is unspecified unless the description of the function requires that it will not be modified. | <urn:uuid:b550c442-971d-4053-9f07-dfafca7edfde> | 3.546875 | 565 | Documentation | Software Dev. | 53.795882 |
In Astrophysics, images, Interesting and funny, videos on March 28, 2013 at 06:47
An Image resembling an Angel has been captured by NASA’s Rover.
As is normal, this is being disputed.
Andel Like Form in Mars?
Now this is a mind blowing photo from the Opportunity Rover. It shows a human-like figure that seemingly has wings. Also it’s easy to make out its legs, a toga like robe and two antenna like objects coming from the top of its head. On its left side, its wing seems to have been in motion, because there is a slight blur there from being to fast for the camera to focus. This sits well with my theory that angels on Earth were actuallyancient aliens that have evolved into light beings. If you have doubts about this NASA photo, please click on the link above and see with your own eyes. SCW.
The Truth on UFO and Aliens remains reminding me of Leibnitz ‘I Know Not What”
Alien Like Creature Swims past The ISS[/caption]
In Astrophysics, videos on December 6, 2012 at 12:55
Rover is reported to have found Rat/Rat hole and NASA seems to be keeping quiet as it would of UFOs.
The following image is from NASA. Rat Hole in Mars?
There is speculation that this could be Mouse and that NASA is keeping mum.
This microscopic imager mosaic taken by NASA’s Mars Exploration Rover Opportunity shows the rock dubbed “Diamond Jenness.” It was taken on sol 177 (July 23, 2004) after the rover first ground into the rock with its rock abrasion tool, or “Rat.” The rover later ground into the rock a second time. A sliced spherule, or “blueberry,” is visible in the upper left corner of the hole. Opportunity has bored nearly a dozen holes into the inner walls of “Endurance Crater.” On sols 177 and 178 (July 23 and July 24, 2004), the rover worked double-duty on Diamond Jenness. Surface debris and the bumpy shape of the rock resulted in a shallow and irregular hole, only about 2 millimeters (0.08 inch) deep. The final depth was not enough to remove all the bumps and leave a neat hole with a smooth floor. This extremely shallow depression was then examined by the rover’s alpha particle X-ray spectrometer.
Rat Hole in Mars?
“A friend emailed this in to me today and its really amazing and strange. I guess thats why I love this one so much. Its a cute rodent on Mars. Note it’s lighter color upper and lower eyelids, it’s nose and cheek areas, its ear, its front leg and stomach. Looks similar to a squirrel camouflaged in the stones and sand by its colors. Hey, who doesn’t love squirrels right? That doesn’t look like a squirrel you say? Then have a look at the photo below of similar squirrel in the same position on Earth. This might have been the big historical announcement that NASA was suppose to make, however they decided life on Mars was a secret worth keeping since they don’t want China or Russia to beat America to Mars. So they shut up about it and can take their time to Mars this way. The scientist jumped the gun and told the public about a major historical discovery on Mars…this must be what he was talking about. SCW’
In Astrophysics, videos on September 15, 2012 at 11:00
NASA“s Curiosity Rover had found Spheres in Mars, which are baffling in Geological Terms.
Those in which the outer layer has been eroded contain concentric internal structure.
Small spherical objects fill the field in this mosaic combining four images from the Microscopic Imager on NASA’s Mars Exploration Rover Opportunity. The view covers an area about 2.4 inches (6 centimeters) across, at an outcrop called “Kirkwood” in the Cape York segment of the western rim of Endeavour Crater. The individual spherules are up to about one-eighth inch (3 millimeters) in diameter.
The Microscopic Imager took the component images during the 3,064th Martian day, or sol, of Opportunity’s work on Mars (Sept. 6, 2012). For a color view of the Kirkwood outcrop as Opportunity was approaching it two weeks earlier, see PIA16128 .
Opportunity discovered spherules at its landing site more than eight-and-a-half years earlier. Those spherules were nicknamed “blueberries.” They provided important evidence about long-ago wet environmental conditions on Mars because researchers using Opportunity’s science instruments identified them as concretions rich in the mineral hematite deposited by water saturating the bedrock. A picture of the “blueberries” from the same Microscopic Imager is PIA05564 .
The spherules at Kirkwood do not have the iron-rich composition of the blueberries. They also differ in concentration, distribution and structure. Some of the spherules in this image have been partially eroded away, revealing concentric internal structure. Opportunity’s science team plans to use the rover for further investigation of these spherules to determine what evidence they can provide about ancient Martian environmental conditions.
Image credit: NASA/JPL-Caltech/Cornell Univ./ USGS/Modesto Junior College. NASA write up. | <urn:uuid:223aa86c-19b0-4656-be13-cf747088f03d> | 2.796875 | 1,164 | Content Listing | Science & Tech. | 56.067166 |
Black holes have been the stuff of science fiction since their discovery in the late sixties. But now a new, nimble NASA telescope is using its powerful x-ray vision to hunt for these abundant yet invisible, massive space oddities.
As bizarre as black holes have been depicted in science fiction, the reality of black holes as described by science is far stranger.
The Endeavour flyover will make for a striking sight: Piggybacked to a 747, the shuttle will be flying at a low altitude of 1500 feet in some parts of the Bay Area.
Astrophotographer Rogelio Bernal Andreo's colorful wide field images of deep sky objects like galaxies, nebulae, star clusters has garnered him dozens of photography awards including the Royal Observatory of Greenwich's 2010 Best Astrophotographer of the Year.
Space exploration has caught up with science fiction (again): we have deployed laser-armed nuclear-powered robot on Mars, and nearly two weeks after landing, NASA's Mars Science Laboratory, the rover Curiosity, has fired that weapon on a Martian rock.
Scientists are looking for elements and molecules that signify life as we know it. But even if they don’t find those molecules, minerals contain important information about the Martian environment. That could help scientists determine if life could have survived on the planet.
Last Sunday, NASA scored a long-distance touchdown…on Mars! The Mars Science Laboratory, nicknamed "Curiosity" is the largest, most complex spacecraft ever to have set down on the Red Planet.
While nearly all eyes are focused on Mars, two astophysicists at NASA's Goddard Space Flight Center have been quietly staring at the sun instead.
Thirty-five years after beginning a remarkable journey that started with encounters of Jupiter and Saturn, Voyager 1 may once again be making a historic scientific encounter: the boundary between our Solar System and interstellar space!
SOFIA is more than a telescope tucked into a re-purposed commercial airliner. It's a complete flying astronomical observation platform which carries a dozen or more astronomers, observers and crew far above the clouds to observe objects and phenomena too cold to be seen in visible light.
Citizen scientist Marc Labriet and students from Valley Christian High School in Dublin, CA collaborated on a special balloon project to retrieve images from near space as well as test theories on gamma rays and radiation repercussion yields.
Don't miss the chance to experience history! Tuesday, June 5, 3:04 PM to 9:46 PM PDT, the Transit of Venus. Rare event. Historical scientific significance. Last chance to see it!
Turns out there are as many as ways to photograph as eclipse as there are to watch it. With a bit of preparation and the generosity of strangers, I got to experience five of them during Sunday's annular eclipse. | <urn:uuid:a9c813f5-47ea-41e2-84c0-23f2f9387a86> | 3.421875 | 575 | Content Listing | Science & Tech. | 40.568103 |
Olympus Mons, lopsided giant 11 February 2009Posted by admin in current research, geoscience, Mars, solar system, volcanology.
Tags: Mars, Olympus Mons, solar system volcanism
Olympus Mons, the largest mountain and the largest volcano we know of in the Solar System, is a huge shield volcano on Mars. It rises 23km above the Martian plain, is approximately 600km in diameter, and is lopsided, like a vast unsuccessful cake. The gently-sloping north-west flank of the volcano extends much further from the central caldera complex than does the steeply-sloping south-eastern flank; these flanks are also upwardly concave, showing an overall increase in the steepness of slope towards the centre, and are divided from the surrounding terrain by steep scarps, features not found in other sectors. A new paper on Olympus Mons in the February 2009 issue of Geology looks at the possible reasons for what it calls these ‘substantial asymmetries in its structure’. From the abstract:
The NW-SE asymmetries are aligned with the regional slope from the Tharsis rise, but an understanding of the underlying causes has remained elusive. We use particle dynamics models of growing, spreading volcanoes to demonstrate that these flank structures could reflect the properties of the basement materials underlying Olympus Mons. We find that basal slopes alone are insufficient to produce the observed concave-upward slopes and asymmetries in flank extent and deformation style that are observed at Olympus Mons; instead, lateral variations in basal friction are required. These variations are most likely related to the presence of sediments, transported and preferentially accumulated downslope from the Tharsis rise. Such sediments likely correspond to ancient phyllosilicates (clays) recently discovered by the Mars Express mission.
Thus the north-west flank of the edifice spreads more easily across the thickened sediments downhill from the Tharsis rise, while the south-east flank encounters the high-friction zone of the elevated pre-sediment basement which inhibits its spread. Result: a lopsided volcano. The sediments beneath forming the low-friction basal zone beneath Olympus Mons would need to be good at retaining water, making clays the obvious candidates, and the authors note that the spectral signatures of clay materials have been detected by the Mars Express OMEGA imaging spectrometer.
In the last, four-sentence, paragraph of the paper the authors suggest that ‘[these] results have implications for extant life on Mars’. The erupted lavas of Olympus Mons could have trapped a water reservoir in the sediments beneath: ‘This deep reservoir, warmed by geothermal gradients and magmatic heat and protected from adverse surface conditions, would be a favored environment for the development and maintenance of thermophilic organisms’. Hence the headline at Australia’s ABC Science today: ‘Martian volcano could shelter life’.
- Patrick K. McGovern & Julia K. Morgan, ‘Volcanic spreading and lateral variations in the structure of Olympus Mons, Mars’, Geology, vol. 37, no. 2 (February 2009), pp. 139-142. [Link to abstract only]
Image: mosaic of Olympus Mons created with the medium-resolution black and white MDIM combined with a low resolution color image mosaic acquired on the 735 orbit of Viking 1 on 22 June 1978. Image Processing by Jody Swann/Tammy Becker/Alfred McEwen, using the PICS (Planetary Image Cartography System) image processing system developed at the U.S. Geological Survey in Flagstaff, Arizona (NASA/NSSDC image).
Volcanic spreading and lateral variations in structure of Olympus Mons, Mars – ScienceDaily, 3 February 2009
Martian volcano could shelter life – ABC Science, 11 February 2009
ESA – Mars Express – home page for the ESA Mars Express mission
Unravelling part of Olympus Mons’ geologic history – HiRISE High Resolution Imaging Science Experiment (University of Arizona)
Volcanic Geology of Mars – from Albert T. Hsui, University of Illinois (Urbana-Champaign)
Highest and lowest points on Mars – Geology.com (on Olympus Mons and the Hellas Impact Crater)
Olympus Mons – Mike Dunford at The Questionable Authority shows just how big Olympus Mons is | <urn:uuid:167e2af2-19db-4e32-bb28-ef375227337d> | 3.59375 | 921 | Personal Blog | Science & Tech. | 27.952112 |
Educational - Cloud formation
Back to: Weather Q & A
Clouds form when air is cooled below its condensation temperature (dew point). The water vapor in the air condenses around tiny dust or salt particles suspended in the air, forming liquid water droplets, or if the temperature is cold enough, ice crystals (Dunlop and Wilson, 1982, p30). The key to forming clouds is to get air moving upwards. When air moves upwards, it expands and cools, and if the air is lifted high enough, it will cool to its dew point and form clouds. Clouds can be formed through three major mechanisms:
- Mechanical lifting by an object such as a mountain. When air moving horizontally hits a mountain, the air is forced upwards. The resulting cooling of the air creates clouds around the mountains.
- Radiant heating of the ground by the sun. On clear days, the sun heats the surface of the Earth, which warms the air near the surface. This warm air is less dense than the surrounding air, and rises. As the warm air rises, it expands and cools, forming puffy cumulus clouds (or cumulonimbus thunderstorm clouds) when the moisture in the air condenses.
- Moving air masses. When two masses of air of different temperatures and densities meet, the warmer, less dense air is forced upwards, resulting in cooling of the air and cloud formation. The boundary between these two air masses is called a front.
Appearance of clouds
Clouds appear white because water droplets in the clouds scatter all colors of light equally. Thick clouds can appear dark because not much light can penetrate through them. The color of a cloud depends on the position of the observer in relationship to the sun and cloud. If the observer and sun are on the same side of the cloud, it appears white. When the observer and sun are on opposite sides of a cloud, it appears dark (underneath a large storm cloud). Thin clouds appear bright from below because they are too thin to reflect much light.
Water can exist in the air in vapor, liquid, and gas forms. Humidity is a measure of the amount of water vapor in the air. This amount of water vapor the air can hold is related to its temperature. The higher the temperature, the more water vapor can be stored in the air. Relative humidity is measured as a ratio of the amount of water vapor actually present in the air to the maximum amount it can hold at that temperature.
Clouds are constantly changing. Water molecules constantly enter and leave a cloud. The molecules enter as vapor, condense into droplets, then evaporate. A good example is the cloud of steam coming out of a tea kettle. The cloud appears in the same place, but the individual water molecules in the cloud are continuously changing.
Above Ground Level
Clouds (Above Ground Level) means that the cloud elevations are above the ground. For example, Broken at 2500 ft means that there are partly cloudy conditions at 2500 ft above the ground. | <urn:uuid:ae8be51c-9ad3-4ee2-9cc0-b52d3e80b27f> | 4.625 | 622 | Knowledge Article | Science & Tech. | 58.263653 |
A recursive program calls itself as a subroutine. Recursion allows one to write programs that are powerful, yet simple and elegant. Often, a large problem can be handled by a small program which:
(defun factorial (n) (if (<= n 0) 1 (* n (factorial (- n 1))) ) )
Rule: Make sure that each recursive call involves an argument that is strictly smaller than the original; otherwise, the program can get into an infinite loop.
A good method is to use a counter or data whose size decreases with each call, and to stop at 0; this is an example of a well-founded ordering.
Contents Page-10 Prev Next Page+10 Index | <urn:uuid:69f3ce74-c21a-4fc1-a31d-da5f712f63ed> | 3.859375 | 151 | Academic Writing | Software Dev. | 47.83 |
Hydrogen sulfide gas is a naturally occuring chemical (chemical formula H2S).
The gas has a characteristic rotten egg odor at low concentrations. About half of the population can smell it at concentrations as low as 8 parts per billion (ppb) in air, and more than 90% can smell it at levels of 50 ppb. At higher concentrations, hydrogen sulfide rapidly deadens the sense of smell. For most people, this occurs at approximately 150 ppm.
Hydrogen sulfide is heavier than air, and it often settles in low-lying areas where it can accumulate in concentrations that can injure or kill livestock, wildlife, and human beings. Additionally, hydrogen sulfide has been found to migrate into surface soils and groundwater.
Sources of H2S
Hydrogen sulfide occurs naturally in the environment (e.g., in volcanic gases, marshes, swamps, sulfur springs, decaying organic matter). It is produced by living organisms, including human beings, through the digestion and metabolism of sulfur-containing materials. Hydrogen sulfide is also a byproduct of many industrial processes, such as paper manufacturing, sewage treatment, landfills, or concentrated animal feed operations (CAFOs).
Hydrogen sulfide gas also is found in petroleum and natural gas. Oil or natural gas is considered sour if it has a high percentage of hydrogen sulfide. Natural gas can contain up to 28 percent hydrogen sulfide gas, consequently, it may be an air pollutant near petroleum refineries and in oil and gas extraction areas. The principal source of anthropogenic hydrogen sulfide is as a by-product in the purification of natural gas and refinement of crude oil. Atmospheric releases of hydrogen sulfide represent the most significant public health concern for the geothermal energy industry. | <urn:uuid:e1a6c9c4-4d3c-4ab2-a33e-1f6e027188bb> | 4 | 361 | Knowledge Article | Science & Tech. | 33.521337 |
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Oceanography in 2025: Proceedings of a Workshop Ocean Measurements from Space in 2025 A. Freeman* OVERVIEW Ocean measurements from space have advanced significantly since the first sensors were flown on NASA satellites such as Seasat in the 1970s. New technologies have opened the door to new, unforeseen scientific questions and practical applications, which, in turn, have guided the next generation of technology development—a fruitful, mutual coupling between science and technology. Recent advances in modeling of ocean circulation and biochemistry are now also linked to improved measurement capabilities. Since the ocean is largely opaque over much of the usable electromagnetic spectrum, ocean measurements from space are largely confined to surface properties such as SSH, SST, surface wind vectors, sea surface salinity (SSS), ocean color, and surface currents. In some cases properties of the ocean beneath the surface can be inferred from such measurements, the most striking example being the determination of bathymetry from sea surface height measurements made by altimeters. Measurements of variations in the Earth’s gravity fields (e.g., by NASA’s Gravity Recovery and Climate Experiment [GRACE]) mission are somewhat a special case, and have been used to infer ocean bottom pressure, for example. With the release of the 2007 decadal survey for Earth Science and * California Institute of Technology
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Oceanography in 2025: Proceedings of a Workshop Applications from Space (NRC 2007), we are poised on the brink of a series of improvements in ocean measurements from space that will revolutionize oceanography from space in the next decade—as big an advance or bigger than the advent of ocean altimetry with TOPEX/Poseidon. This white paper looks forward to that timeframe and beyond, towards the type of measurements we should expect in 2025, and the science questions that we should be able to ask. OVERARCHING SCIENCE QUESTIONS The scientific and practical questions that are likely to drive developments in the 2025 timeframe are: Oceans as part of the coupled ocean-atmosphere-ice-land-biogeochemical system Most current ocean models that assimilate data are presently run in ‘forced’ mode; they do not affect the atmosphere. Most atmospheric models that assimilate data use an overly simplified representation of the oceans (a mixed layer) or worse, only sea surface temperature. These are due to computational expense, a barrier that is fast receding. CO2 uptake, hurricanes, ENSO, ice shelf disintegration and ice sheet advance are all examples where the coupling between the ocean and in these cases either the atmosphere or the cryosphere are critical. Description and prediction of the global water cycle in the context of global climate change can only be fully realized when the marine branch of the hydrological cycle is considered. Increased spatial and temporal resolution in ocean observations, ocean models, and climate models. Spin up / spin down time scales in the oceans depend on eddy (~ 100 km or less) parameterization. These time scales are essential for climate forecasts. Thus climate models need to resolve or parameterize properly ocean eddies for realistic climate simulations (Marshall, personal communication, 2008). In ocean models, dissipation of momentum is achieved through enhanced vertical viscosities and drag laws with little physical validation. Turbulent transport of tracers like heat, salt, carbon and nutrients is represented with unphysical constant eddy diffusivities in numerical ocean models. Ocean models running at sufficient resolutions to address submesoscale (1-100 km) dynamics have just begun to emerge (Capet et al. 2008).
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Oceanography in 2025: Proceedings of a Workshop Global observations at these scales are needed to constrain the models. For coastal work, forecasting for navigation, inundation, and marine resources critically depends on short length scales, controlled by the shallow ocean depth. Need to forecast with increasing accuracy and shorter time delays both short time scales (navigation, harmful algal blooms) and long ones (climate) for societal benefit. To address these questions, we believe a progressive improvement in measurement capability is necessary, across a broad range of parameters, as outlined in Table 1 and the discussion below. TECHNOLOGICAL ADVANCES The kind of technology advances that will enable the improvements in ocean measurements from space described above include: Miniaturized, more efficient radar components to reduce mass/power needs of radar electronics Efficient, high-power transmitters at shorter wavelengths (especially Ku- and Ka-Band) Increased onboard processing and/or downlink capability, allowing data acquisition at higher spatial and temporal resolution. Larger deployable antennas in the 6-12 m range, particularly employed in a conical scan mode, enabling higher resolution radiometry and scatterometry. A scanning interferometer pair of antennas, rotating through an azimuth scan of 360 degrees to provide along-track interferometry measurements of surface currents at high resolution. Precision formation flying, to enable bistatic wide-swath sea surface height measurements from two platforms flying in formation, and gravity measurements from multiple platforms. Laser interferometry to improve the accuracy of gravity measurements from future GRACE-like missions. Wide field of view imaging spectrometers with improved stability and signal to noise (SNR) and atmospheric correction capabilities, enabling global ocean biosphere measurements at moderate resolution (~1 km) on a daily basis and on fine resolution (60 m) on synoptic basis. Deployment of ocean color imagers on geostationary platforms to sample the highly dynamic processes of coastal ecosystems. The spaceborne implementation of active remote sensing of bio-
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Oceanography in 2025: Proceedings of a Workshop TABLE 1. State of Ocean Measurements from Space in 2009, in 2017, and in 2025 Measurement from Space 2009 2017a 2025 Sea Surface Height (SSH) 100 km spatial scales; 10 day revisit (TOPEX/Jason series) 10 km spatial scales; 10 day revisit (SWOT) 10 km spatial scales; 1 day revisit (Multiple SWOT satellites) Ocean Vector Winds (OVW) 25 km spatial scales; 1-2 day revisit (Quikscat/ASCAT) 3-25 km spatial scales; 6 hour revisit (XOVWM/ASCAT/Oceans II) 3-6 km spatial scales; 6 hour revisit (XOVWM and follow-ons) Sea Surface Salinity (SSS) 0.2 psu; 150-200 km spatial scales; 30 day time scale (SMOS 2009; Aquarius in 2010) 0.2 psu; 40 km spatial scales; 10-30 day time scale (SMAP) 0.1 psu; 20 km spatial scales; 7 day time scale (Aquarius follow-ons) Surface Currents Geostrophic only—100 km spatial scales; 10 day revisit (Topex/Jason series) No ageostrophic. Geostrophic cf. SSH Ageostrophic in coastal zones—< 1 km (DLR Tandem-X) Geostrophic cf. SSH Ageostrophic globally—< 1 km; 1-2 day revisit (Scanning ATI) Gravity 400 km spatial scales; monthly updates (GRACE) Improved precision; 400 km spatial scales; monthly updates (GRACE II + GOCE) Improved precision; <400 km spatial scales; weekly updates (GRACE follow-ons) CO2 Flux at the Surface 1000 km spatial scales; 0.4 gCm−2yr−1 flux; monthly updates (AIRS/OCO) 100 km spatial scales; 0.4 gCm−2yr−1 flux; weekly updates; day/night (ASCENDS) 10 km spatial scales; 0.1 gCm−2yr−1 flux; daily updates (ASCENDS follow-ons)
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Oceanography in 2025: Proceedings of a Workshop Measurement from Space 2009 2017a 2025 Sea Surface Temperature (SST) 1-2 km spatial scales; 1-day revisit; no visibility thru’ cloud (MODIS) 40 km spatial scales; 1-day revisit; all-weather (AMSR-E); DT = 0.3 – 0.7 K 1-2 km spatial scales; <1-day revisit; no visibility thru’ cloud (VIIRS on NPOESS) 40 km spatial scales; 1-day revisit; all-weather (AMSR-E); DT < 0.3 K 1-2 km spatial scales; <1-day revisit; no visibility thru’ cloud (VIIRS on NPOESS) 1-2 km spatial scales; 1-day revisit; all-weather (Next-gen Microwave radiometers); DT < 0.1 K Ocean Color/Biogeochem < 1 km spatial scales; 1 day revisit (CZCS/Seawifs/MODIS/MERIS) < 1km spatial; <1 day revisit (VIIRS on NPOESS) 50 m spatial; 17-day revisit (HyspIRI) .25 km spatial; 15 min revisit (GEOCAPE) 1 km spatial; 1 day revisit (ACE) .1–1 km spatial scales; 15 min revisit globally (GEO network) Sea Ice Area and Type 3 day revisit (Radarsat/Envisat) 1 day revisit (DESDynI) 1 day revisit (DESDynI follow-ons) Sea Ice Thickness Freeboard @ < 1 km scales (Icesat II + Radarsat/Envisat) Snow accumulation (Cryosat) Freeboard @ < 1 km scales (Icesat II + DESDynI) Snow Accumulation (TBD) Ice thickness @ < 1 km scales (TBD) aThe projections for 2017 assume that the relevant missions in the National Research Council’s decadal survey for Earth Science and Applications from Space (NRC 2007) are implemented on schedule.
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Oceanography in 2025: Proceedings of a Workshop chemical constituents of the ocean, including fluorescence spectroscopy instruments (UV/visible) and lasers at the blue end of the visible spectrum to measure mixed layer depth, as input to biochemical models. Increased computational power will allow more complex coupled models to be run at higher resolutions, and data assimilative models to assimilate data. ACKNOWLEDGEMENTS The work described in this paper was, in part, carried out by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Special thanks to V. Zlotnicki, T. Liu, L-L. Fu, B. Holt, R. Kwok, S. Yueh, I. Fukumori, J. Vazquez, D. Siegel, and G. Lagerloef for contributing to this white paper. REFERENCES NRC. 2007. Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. National Academies Press, Washington, D.C. Capet, X., J.C. McWilliams, M.J. Molemaker, and A.F. Shchepetkin. 2008. Mesoscale to Submesoscale Transition in the California Current System. Part II: Frontal Processes. Journal of Physical Oceanography. 38: 44-64. | <urn:uuid:38625743-ada9-45c5-be36-2990a243a06f> | 3 | 2,451 | Content Listing | Science & Tech. | 38.316353 |
Fires in Australia's Northern Territory
On October 13, 2012, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image of fires burning in northern Australia. Smoke from the fires streams to the northwest due to trade winds blowing from the southeast. Red outlines indicate hot spots where MODIS detected unusually warm surface temperatures associated with fires.
Large fires in the tropical savannas of northern Australia are common in the spring. On average, about one-third of the land surface in these fire-prone ecosystems burn every year. Northwest of the fires, large amounts of sediment carried by the Victoria River flow into the Timor Sea. The water is likely turquoise near the continent’s coasts because of tides stirring up river sediment on the seabed and circulating it throughout shallow ocean waters.
North Australia Fire Information. North Australian Fire Information. Accessed October 18, 2012.
NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC. Caption by Adam Voiland.
Instrument: Aqua - MODIS | <urn:uuid:badbb6ed-90e4-4faf-9e41-76beb4cac20e> | 3.984375 | 228 | Knowledge Article | Science & Tech. | 31.581776 |
There's more to rain and snow than just water falling from the sky.
Hailstones are the result of an ice pellet or graupel being caught in a thunderstorm updraft and cycled through the cloud for several minutes, accreting multiple layers of ice in the process.
These are the conditions most likely to lead to measurable snowfall. Like liquid droplets, crystals can collide, resulting in multiplication as the crystals shatter (normally in cold air) or growth as they combine (common in warmer air).
Very large snowflakes occur in this manner. They have generally fallen through a region of above freezing air. Frequently, a snowflake will fall through a region occupied by freezing rain. In these situations, the liquid may accrete, or rime, onto the crystal-freezing on contact, producing what is commonly known as graupel.
However, if the crystal falls through a deep enough superfreezing layer in the lower atmosphere, it will melt partially or entirely-and, depending on the temperature in the layer beneath that, may refreeze partially or entirely before reaching the surface.
If the crystal melts entirely, it will likely reach the surface as either rain or freezing rain. If it partially melts and then refreezes, ice pellets or sleet are normally the result. Often, snow grains or snow pellets fall from the sky.
These are forms of graupel and are generated in the same manner. Snow grains tend to fall from low stratus clouds as small ice crystals develop some rime accretion. The lack of sufficient vertical air currents permits them to fall at such small sizes.
Snow pellets, on the other hand, tend to be larger in size (up to about 5 mm diameter), and require thicker, moisture-laden cumulus clouds to form. The minor convection beneath these clouds allows the snow pellets to become larger than snow grains, but not quite as large as graupel before they precipitate.
A final type of frozen precipitation of which pilots should be aware is hail. This is normally the product of ice pellets or graupel that have been caught in the updraft of a cumulonimbus cloud. As the embryo travels upward through thousands of feet of supercooled rain droplets, it develops a mixed rime/glaze coat.
Subsequent cycling through warm and cold regions of the cloud deposits additional glaze coats, enlarging the stone. Eventually the stone becomes heavy enough to counter the updrafts, or more commonly, is ejected from the storm by either the updraft or a downdraft.
While pilots are aware of many of the generalizations about precipitation types and formation, it always helps to understand some of the details behind why we get the type of weather we must fly through.
It is that extra level of information that gives us a better insight into the atmosphere-insight that may allow us to make better decisions about the weather we face.
Karsten Shein is a climatologist with the National Climatic Data Center in Asheville NC. He formerly served as an assistant professor at Shippensburg University and was a scientist with NASA's Global Change Master Directory. Shein holds a commercial license with instrument rating. | <urn:uuid:1036b8c7-d6aa-4d41-b5b9-f684c5347efb> | 3.90625 | 662 | Nonfiction Writing | Science & Tech. | 43.879358 |
In this tutorial we are going to give you over view of JSP.
What is JSP ?
JSP is java based technology by using that you can develop web content that
holds both static and dynamic components.
It is developed by Sun Microsystems for server side development. It provides all the dynamic capabilities of Java Servlet technology but also provide better approach for creating static content.
Why use JSP ?
Process of JSP -
To process the JSP pages, web server requires a JSP engine. The JSP container is responsible for providing the runtime environment and other services which is required by JSP.
Here we are giving you steps of JSP processing -
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:57793264-e219-433c-af77-07f4796a0e96> | 3.21875 | 184 | Tutorial | Software Dev. | 53.25681 |
Yes, we’re excited.
Yes, we’re excited.
From hairy-chested yeti crabs to the deepest known fields, hydrothermal vents have been enjoying a bit of science celebrity in the last few weeks. Beneath the headlines, there has been an eruption of vent-related research published in the scientific literature and some exciting new expeditions just left port.
The exhaustive author list on this paper reads like a who’s who in hydrothermal vent biogeography. This is the paper that introduced “the Hoff” crab to the world, but the findings are far more significant. Hydrothermal vent systems are sorted into biogeographic provinces, with different regions supporting different communities. The iconic giant tube worms dominate the eastern Pacific, while the western Pacific (prominently featured in Deep Fried Sea) plays host to fist sized snails, and the Atlantic features shrimp as its dominant species. There are several missing gaps in our understanding of how these qualitatively different communities are connected – the Southern Ocean, the south Atlantic, the Indian Ocean, and the Cayman Trough, among others. Filling in these gaps in our knowledge can help us understand the history and evolution of hydrothermal vent ecosystems.
In Jules Verne’s 20,000 Leagues Under the Sea*, the iconic Captain Nemo announced that “in the depths of the ocean, there are mines of zinc, iron, silver and gold that would be quite easy to exploit” while predicting that the abundance of marine resources could satisfy human need. If the pace of development for deep-sea mining projects and the estimated value of deep-sea ores is any indicator, it seems as though our misanthropic mariner was wrong on both counts.
In The abundance of seafloor massive sulfide deposits, an international team of geologists attempts to quantify the total available copper and zinc contained in deep-sea massive sulfide mounds. Seafloor massive sulfide mounds are a byproduct of the processes that create deep-sea hydrothermal vents. As super-heated sea water emerges from the vent, it deposits heavy metals and other elements and minerals along the walls of the vent. Over thousands of years, an active vent field can build up a huge mound of metal and mineral rich ore – a massive sulfide mound. In addition to copper and zinc, these mounds can contain gold and silver. Generally, the ore is of much higher quality than its terrestrial counterpart. Over the last few decades, many exploration companies were eyeing these deposits, but it’s only recently that technological developments and economic incentives have aligned to permit potentially profitable deep-sea mining.
Slimehead is not a word you would expect to find on the menu of a fancy restaurant. Like dolphin*, toothfish*, goosefish*, mudbug*, hog*, and gizzard fish*, slimeheads have undergone a bit re-branding over the last few decades to make their name as palatable as their fillets. Enter the Orange Roughy, a dull, uninspired name that captures nothing of the grandeur of Hoplostethus atlanticus and ignores the defining characteristic of these deep-sea fishes.
What does Orange Roughy mean to you? Well, it’s probably orange, and I guess roughy means it might be rough, or something. The name is pretty uninformative. But slimehead! Slimehead tells you quite a bit about this creature, and leads to some interesting ecological questions. Why is it’s head covered in slime? What does the slime do? How is the slime contained in its head?
The Okeanos Explorer is diving on the Cayman Rise – the location of the deepest known hydrothermal vent field, and they are broadcasting the ROV feed live, right now. You can be experiencing this:
The deep benthos is simultaneously the largest and least explored ecosystem on the planet. Covering nearly 60% of the Earth’s surface, it supports an almost unimaginable reservoir of biodiversity, rivaling all terrestrial habitats combined. Its microbial and metabolic diversity have revolutionized our view of how life is sustained, not once, but twice (first with the discovery of chemoautotrophic organisms at hydrothermal vents, and again with the discovery of cognate communities at methane cold-seeps). In spite of these major discoveries, the deep benthos is essentially invisible. Only a select few will ever witness it first hand, while for the rest, it will remain a dark and unfathomable abyss.
This places the deep benthos in a precarious position. Human activities that influence the deep sea go unnoticed. Without a thorough understanding of its ecology, it is impossible to assess the damage caused by anthropogenic impacts. Although recent and ongoing studies have shed light on many species and communities, the deep benthos remains largely unexplored. Two studies, both released this week, reveal simultaneously how little we know about the deep benthos and how human impacts, even unintentional ones, could shape this ecosystem.
Megumi Shimizu is a second year PhD student at the Duke University Marine Lab. Since the news has so far only been reported in Japanese, we asked her to provide a short write-up of the discovery.
The first scaly-foot gastropod, Crysomallon squamiferum, was found in the Indian Ocean ten years ago (Van Dover et al 2001), and continues to attract deep-sea fan with its black appearance and iron-fortified shell and operculum. Last December a team from JAMSTEC (Japan Agency for Marine-Earth Science and Technology) reported the discovery of a white scaly-foot gastropod in the Indian Ocean. The exciting news was announced in Japan soon after the conclusion of the research cruise.
Except for its color, the shape and characteristics are the same as the black scaly-foot gastropod. Unlike the mysterious black one, the white one gives me different impression: pretty and innocent looking.
They found white scaly-foot gastropod during an investigation of habitats at newly found hydrothermal vents in November 2010. Several aggregations of white scaly-foot gastropods were found at the sites. Although scaly-foot gastropods are usually covered by iron sulfide shell and scales, the white scaly-foot gastropod does not assimilate iron sulfide.
The physiological details have not yet been revealed.
Many questions come to mind from this discovery: Are they same species? How did they evolved? Why do black scaly-foots need iron scales?
I am definitely looking forward to reading the final publication.
There are currently more than 7,500 offshore oil platforms actively probing the earth’s crust for black gold. Their relatively minimal appearance at the surface belies the shear magnitude of human construction beneath the waves. Oil platforms are among the world’s tallest man-made structures. Compliant tower platforms reach up to 900 meters in depth (in contrast, the tallest building is 828 meters). these rigs are not permanent structures. As the wells run dry and sea water corrodes steel jackets, the wells are capped and rigs decommissioned. At least 6500 offshore platforms are slated for decommission by 2025, which begs the question, what do we do with inactive oil platforms?
Now that Ocean of Pseudoscience Week has come to a close, we thought it would be a good time to talk about our favorite real sea monsters – amazing marine creatures that capture the imagination. For mine, we naturally have to take a trip to the deep sea to find Bathynomous, the giant deep-sea isopod.
Giant isopods are the monster cousins of the terrestrial isopod commonly know as the rolly-polly or pill bug. First discovered in 1879, these deep-sea scavengers can reach over a foot in length, dwarfing the much more minuscule common isopods, found on beaches and docks around the world.
Dr. M from Deep Sea News has done quite a bit of research on why these isopods get so big. Isopocalypse 2010 is a good place to start. IN short, giganticism is not uncommon in the deep sea, and may be a response to a food-limited environment. But you’ll have to check out the Deep Sea News post for more details.
The majestic Deep-sea Isopod
~Southern Fried Scientist | <urn:uuid:79a72a02-2cc1-4e3a-b7d8-3db568bf121d> | 3.25 | 1,749 | Personal Blog | Science & Tech. | 40.661926 |
Andy Reisinger and Dan Zwartz discuss the interplay between climate change observations and models, looking in particular at the issue of sea-level rise.
They present some of the field science that tells us how and why sea level has changed in the past, and how it is changing now. They also discuss how much uncertainty there is in projections of future sea-level rise and what this means for coastal planning in New Zealand.
Listen to the talk
Download a recording of this talk (MP3, 10.8MB)
Dan made his first trip to Antarctica more than 20 years ago, while studying geology at Victoria University's Antarctic Research Centre. He has spent years investigating how the Antarctic ice sheets affect global sea level, and has joined or led a number of expeditions to many locations in East Antarctica with the Australian, Dutch, and Japanese national research programmes.
In February 2012, Dan participated in Gareth Morgan's Our Far South voyage to raise New Zealanders' awareness of issues in the Southern Ocean and Antarctica.
Dr Andy Reisinger is Deputy Director (International) of the New Zealand Agricultural Greenhouse Gas Research Centre. His research interests include climate change impacts and adaptation with a focus on local government, exploring uncertainty and its implications for decision-making, and the role of agricultural greenhouse gas emissions in climate change policy.
Science Express @ Te Papa | <urn:uuid:2036d5e5-f5eb-438f-8292-bb33684a477d> | 3.078125 | 277 | Audio Transcript | Science & Tech. | 32.127666 |
Pi is an extremely interesting number, and the day to celebrate it is 3/14. The continuing pop culture references to Pi are evidence of the love people have for Math, and Math’s most widely known constant. Author of the Life of Pi, Yann Martel, said this of his choice of the name “Pi” for the novel’s protagonist: “I chose the name Pi because it’s an irrational number… Yet scientists use this irrational number to come to a ‘rational’ understanding of the universe. To me, religion is a bit like that, ‘irrational’ yet with it we come together, we come to a sound understanding of the universe.”
For those looking to celebrate the Pi Day with some fun math activities, we hope you enjoy this downloadable Notebook file. The video below describes how each page may be used.
Happy Pi Day! | <urn:uuid:00ff0ea8-505c-4a20-985f-bc784e1ac08a> | 2.828125 | 190 | Personal Blog | Science & Tech. | 46.13 |
Zircon (ZrSiO4) is the principal repository for zirconium. It has a fairly simple structure. It has a tetragonal unit cell with a = 6.6 Angstrom units and c = 6. Zircon is perhaps the most important tetragonal mineral. Zirconium atoms are at the corners of the unit cell, the center, and at altitudes of 1/4c and 3/4 c along the midlines of each vertical face. Silica tetrahedra are centered at top and bottom center, the midpoints of each edge parallel to c, and at 3/4c and 1/4 c along the midlines of each vertical face.
|The zircon structure seen from the top, looking along the c axis. Silica tetrahedra are in blue, zirconium atoms in orange, with darker hues for increasing distance. The coordination polyhedron for the central zirconium atom is shown in purple.|
|The zircon structure seen from the side, looking
perpendicular to the c axis. Silica tetrahedra are in blue, zirconium
atoms in orange, with darker hues for increasing distance. The silica
tetrahedra are slightly skewed for perspective, but are really symmetrical
about the faces. Silicon atoms are in green
.The coordination polyhedron for the central zirconium atom is shown in purple. The central zirconium atom, which is inside the purple polyhedron, is outlined in gray.
The one somewhat odd feature of this structure is the coordination polyhedron of the zirconium atoms. The zirconium atoms are surrounded by eight oxygens, two sets of four at slightly different distances, but is not a slightly distorted cube. It is very nearly a shape called a snub disphenoid or Siamese dodecahedron. The ideal shape has 12 equilateral triangle faces and tetragonal disphenoid symmetry. One way to picture it as a very flat disphenoid cut into two pairs of faces and pulled apart along the symmetry axis, with a zigzag band of 8 triangles added in between. Another way is to imagine gluing two pentagonal pyramids together base to base along three of the five edges, then squeezing from the side and adding two more triangles to fill the opening.
Created 26 February, 2001, Last Update 14 December 2009
Not an official UW Green Bay site | <urn:uuid:91b2e89d-0ebe-4656-aaf4-fd2d2e2f982b> | 3.265625 | 523 | Knowledge Article | Science & Tech. | 44.861797 |
Beginner’s Guide to Carbon Offsets
This offshore wind farm in Denmark includes 72 turbines and generates enough clean energy to power 110,000 homes.
Sometimes a person, family, company, city, or nation can not reduce the amount of carbon dioxide they release into the atmosphere from burning fossil fuels as much as they wish they could. They may desire to be “carbon neutral” and not add more carbon dioxide to the atmosphere, so they pay someone else to take as much carbon dioxide out of the atmosphere as they put in. For example, a town whose energy comes from a coal burning power plant, a power plant that puts carbon into the atmosphere, may decide to pay an organization thousands of miles away to plant trees in the tropics, trees that take carbon out of the atmosphere. This is called a carbon offset or a carbon credit. Several different types are described below.
Carbon Offsets Used to Plant Trees
Some people offset their carbon emissions by planting trees. There are several different ways that trees are used as carbon offsets. Trees may be planted in an area where trees had not grown before (a process called aforestation) or where trees used to grow but were cut down some time ago (a process called reforestation). Sometimes carbon credits are sold for not cutting existing trees down. For example, some carbon offsets fund programs that get people in developing nations to use more fuel efficient stoves that burn 30-50% less wood. This saves trees, trees that would have been cut down for use in the lower efficiency stoves.
Does planting trees really reduce carbon in the atmosphere? Trees take carbon out of the atmosphere by the process of photosynthesis. Planting trees, lots of trees, has the potential to take 100 Gigatonnes of carbon out of the atmosphere by 2050 according to the 2001 report by the Intergovernmental Panel on Climate Change. That’s a lot of carbon. However, it is only 10-20% of the carbon that is projected to be released into the atmosphere through burning of fossil fuels over the same timeframe.
While all plants do photosynthesis and thus take carbon from the atmosphere, trees are particularly efficient at this, taking up more carbon than grasses, flowers, cacti, and other types of plants. By doing this, trees decrease the amount of greenhouse gases in the atmosphere, and so more trees can have a cooling effect on global climate. However, this carbon-uptake is not the only way that trees affect climate. Forests can also warm the Earth by adding water vapor, another greenhouse gas, to the atmosphere. Plus, forests are dark in color, thus have a low albedo, and absorb solar energy. In high latitudes, forests can cover snow, preventing the snow from reflecting solar energy back out to space. All these complicating factors mean that not all trees are created equal when it comes to their effect on Earth’s climate. Thankfully, scientists have been researching how all these factors work together. They have found that the location of tree planting efforts has an effect on the climate. Tree planting in the humid tropics has a cooling effect on global climate because trees grow faster in the topics and remove, on average, 50 pounds (22 kg) of carbon dioxide from the atmosphere each year. Plus, there is little change to the amount of solar energy absorbed. At mid-latitudes, tree planting has little effect on global climate. At high latitudes, tree planting has been shown to warm climate due to the change in the amount of solar energy absorbed in areas where snow cover used to reflect the energy out to space.
One additional thing to think about: for a carbon offset used to plant trees to remove carbon long term, the tree (or its offspring) must live forever. Carbon sequestered by a tree will be released as carbon dioxide if the tree dies and decays (or is burned).
Carbon Offsets Used for Renewable Energy
Carbon emissions are also offset by building more renewable energy capacity that decreases the need for fossil fuels. Renewable energy sources include all types of energy that do not run out. Some types of renewable energy, including wind energy and solar energy, emit no greenhouse gases to the atmosphere. However, because the Sun is not always shining and the wind is not always blowing, there are limits to the amount of energy that we can "harvest" from solar panels and wind turbines so all of our energy needs can not be met with these types of energy. Other types of renewable energy, such as biofuels, do release greenhouse gases to the atmosphere. Renewable biofuels include ethanol, wood, and biodiesel. They are significantly less carbon neutral that other types of renewable energy because fossil fuels are used to produce them and because burning biofuels does release carbon dioxide and other greenhouse gases. However, if the plant material used to make biofuels is regrown then it will take the same amount of carbon dioxide out of the atmosphere as was put into the atmosphere through the fuel use. Biofuels still cause air pollution, including smog. Biodiesel has a particularly high nitrogen oxide output in some types of diesel engines.
As demand for biofuels increases, there can be unexpected consequences. For example, in 2006 the growing demand for corn-based ethanol, which is used as a biofuel and as an additive for fossil fuels, drove the cost of corn up more than 80%. This may be great if you are a corn farmer. However, if you are one of the millions of people who survive on a diet composed predominantly of corn, you might see a downside. The demand for ethanol has made corn too expensive for tortillas, a staple of the Mexican diet. In early 2007, tens of thousands of people protested the rising cost of tortillas in the streets of Mexico City. Their protest, known as the tortilla riots, prompted President Felipe Calderón to organize price fixes with corn suppliers. It is interesting to note, however, that more corn is used to feed farm animals than is used for ethonol or consumed by people.
The above, written by Lisa Gardiner, was designed for Earth System Science, a Climate Change Perspective, an online course for educators. Please visit NCAR Online Education for more information about this and other courses. | <urn:uuid:07b666de-122b-4e2b-8bb7-435147e0f053> | 3.734375 | 1,282 | Knowledge Article | Science & Tech. | 41.790118 |
5. Sensitivity of faint counts to the star formation history
Our simple SAM is not able to compute either the merging history of halos, or of the galaxies they host. However, we know that locally there is a tight correlation between major mergers on one side, LIRGs and ULIRGs on the other: at least 95 % of them are currently undergoing major mergers (see for instance Sanders & Mirabel 1996). It also seems fairly safe to assume that ISOPHOT and SCUBA sources are the high-redshift counterparts of such mergers. As a matter of fact, one could sum up the qualitative information from currently available datasets as follows. First, the objects seen by SCUBA have to be either very massive, or very efficient to extract energy from the gas, simply because their bolometric luminosity is larger than . Second, they have to be highly extinguished because most of this luminosity is emitted in the IR/submm. Third, for such numerous bright sources not to have been detected in the IRAS NEPR redshift survey at 60 µm, they have to be located in majority at redshifts greater than about , which seems to be the case for some of the SCUBA sources (Barger et al. 1999b).
In light of these observational facts, and as in GBHM, we define an ad-hoc "starburst" model, simply by pushing the limits of our quiescent models (SCDM, OCDM, or CDM), still powering the sources with star formation according to a Salpeter IMF. This consists merely in transforming a fraction of high-redshift quiescent objects into ULIRGs, while keeping all the parameters of the model fixed. The obvious interest of such an exercise is to assess whether one is able to reproduce the SCUBA source counts, along with preserving the quality of the fits of the optical counts used to calibrate the quiescent model, in the various cosmologies. We hereafter focus on the SCDM cosmology, for which the "quiescent" mode of star formation is unable to reproduce the submm counts.
In order to build such an ad-hoc model, we use the reasonable recipe that follows:
As a result of this phenomenological recipe, a typical halo of mass , with reduced spin parameter , that collapses at redshift , hosts by redshift (180 Myr after the starburst was triggered) a ULIRG of size 1 kpc that has consumed 98 % of its of cold gas initially present. The star formation rate averaged over this period is yr-1. The starburst galaxy has a typical column density of about , and a metallicity of 0.03, yielding a face-on optical depth in the B band of 128. Its absolute B magnitude and bolometric IR luminosity (between 3 and 1000 µm) reach and respectively.
Of course, such a model is quite drastic, but once again, it should be considered as the necessary extension of the quiescent models to produce the correct amount of FIR/submm luminosity. The interesting result is that such a SCDM model in which all massive objects that form at redshifts higher than 1.5 are ULIRGs produces almost enough IR/submm luminosity to match the ISOPHOT and SCUBA counts, as can be seen in Fig. 4. This is also the typical luminosity one can extract from star formation with a Salpeter IMF without ruining the UV/IR calibration of the counts. For instance, decreasing the mass above which the ULIRG phenomenon occurs by an order of magnitude strongly decreases the optical counts.
We also have to examine the possibility that a more efficient mechanism powers these sources, for instance a top-heavy IMF, with all the energy available through stellar nucleosynthesis being reprocessed in the IR/submm. The main features of such a model have been discussed in GHBM who take this solution to accommodate submm counts easily in an SCDM cosmology. We refer the reader to that paper for details. To test this possibility, we simply take our burst model and multiply the luminosity output of each ULIRG in the infrared per unit mass, , by a factor 2, while lowering the number of ULIRGs in the model by 2. This is to say, we trade the number of sources for more luminosity per source. Fig. 4 and Fig. 5 show that the influence of such a redistribution on the counts is weak. Of course, any combination of luminosity and number density of ULIRGs is possible.
In light of the previous work, and bearing in mind that we want to describe multi-wavelength galaxy counts, we can define a "best guess" model within a given cosmological model. We hereafter retain the CDM model as a typical example, since the optical and submm counts with the CDM model and the quiescent mode of star formation only are intermediate between the SCDM and OCDM. We take , , , , and . In terms of our astrophysical parameters, we keep the standard value , and we take , for the quiescent galaxies, and , for the starbursts. One ULIRG dwells in each halo that is more massive than and collapses before redshift 1.5. This ULIRG population evolves as the density squared at lower z, so that at redshift 0, its number density is about Mpc-3, corresponding to only one ULIRG for 2500 halos . The predictions for the faint counts are given in Fig. 6 and Fig. 7. The model provides a good fit of the faint counts at optical wavelengths (though the bright counts are slightly overestimated). The quality of the fit nicely compares with other faint counts obtained from SAMs (e.g Kauffmann et al. 1994). The ISOCAM 15 µm data and IRAS 60 µm data are also fairly reproduced, though the observed slope of the 15 µm counts seem to be slightly steeper than the model. The fit of the submm counts is also very satisfactory.
The redshift distributions are given in Fig. 8. The CFRS predictions now peak almost at the correct redshift. The NEPR predictions still exhibit a high-redshift tail as in GHBM, in contrast with the data, but the level is much lower than in GHBM. We recall that the NEPR sample is polluted by a supercluster in the first redshift bin. Moreover, a recent follow-up of this sample with ISOCAM at 15 µm seems to show that some of the sources are multiple and that the optical identifications might be ambiguous in these cases (Aussel et al. 2000). The relative levels of the two peaks in the redshift distribution at 175 µm are sensitive to the flux cut-off. Most of the sources in the redshift distribution for the SCUBA deep surveys at 850 µm are predicted to be at , but the comparison with data is still difficult because of identification uncertainties (see e.g. Barger et al. 1999b corrected after Smail et al. 1999).
Finally, Fig. 9 shows the Cosmic Background obtained by integrating the faint counts, and compare the predictions with current data in the optical, IR and submm. Whereas introducing ULIRGs in an ad-hoc way into our simple models suffices to reproduce the Cosmic IR Background and the submm counts at 850 µm, it falls marginally short of getting the required diffuse background flux at 140 and 240 µm, though it reproduces the ISOPHOT counts brighter than 100 mJy at 175 µm. These galaxies contribute only 10 % of the background. So this discrepancy may be due only to the fact that the 175 µm counts below 100 mJy are much steeper than our predictions. The model is too low by a factor of 2 with respect to the points corrected for warm galactic dust by Lagache et al. (1999), which are themselves a factor of 1.5 below the points without such a correction by Hauser et al. (1998). The difficulty to fit the points might indicate that this correction is still underestimated. Finally, one should also be aware that a contribution of intergalactic dust (with a grey extinction curve) to the background light is also possible (Aguirre & Haiman 2000). Adding these extra components might help reconcile models and observations.
We conclude from these figures that this fiducial model gives a satisfactory estimate of the luminosity budget of galaxies, and allows us to interpolate or extrapolate the observed faint counts to other wavelengths and fainter flux levels.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000 | <urn:uuid:b7f463d7-a16c-4745-9984-3346f61af6cb> | 2.71875 | 1,800 | Academic Writing | Science & Tech. | 52.284934 |
With scientists wanting to see stuff in ever-finer detail and computer geeks wanting more and more transistors on their silicon, it is becoming increasingly important to be able to efficiently generate extreme ultraviolet radiation (1-75nm). The problem is that, once you get above a certain photon energy (in other words, a short enough wavelength), it becomes much more difficult to efficiently generate light. The lamps used to generate extreme ultraviolet light tend to be huge affairs that involve plasmas, high voltages, and kilowatts of total output power. Unfortunately, only a tiny amount of that light is goes in the right direction and has the right wavelength, meaning that the lamp is really inefficient. The latest research out of South Korea may point researchers in a new direction, allowing them to construct extreme ultraviolet light sources that aren't quite so problematic.
The development of higher efficiency extreme ultraviolet light sources has taken a turn for the better with the development of high harmonic generation (HHG). In this work, a gas of atoms is illuminated by a very intense laser pulse—typically these lasers emit pulses that can be focused to intensities of more than 1013W/cm-2. This grabs a few of the electrons from the atom and causes them execute an extremely tight and fast elliptical loop before they crash back into the atom. As they do this, they absorb many photons from the illuminating laser, but emit a single photon at much higher energy. These experiments start with a laser emitting light at 800nm, which is too red to see under normal conditions, and end up with the gas emitting light with a wavelength of just a few nanometers (for reference, blue is 400nm).
This process is not very efficient, but it has advantages, in that the light is coherent and focusable, meaning that devices can make much more efficient use of the light. Alas, the draw back is the laser. These are not small lasers. In fact, there are usually at least three lasers involved. You need one laser to drive the laser that emits the 800nm light. Unfortunately, the second laser doesn't emit enough light, so you need an amplifier stage, which is nearly as complicated as any of the lasers. Then, just when you have filled up the first optical table, you need to use a laser to drive the amplifier. If you really want power then you can count on filling another optical table with amplifiers and drive lasers.
What we really needed was a way to get rid of the amplification stages. This is where plasmon interactions come into play. The researchers took a normal pulsed laser, which is too weak by a factor of 100 to generate high harmonics, and used it to illuminate a set of gold bow-tie shapes (two triangles separated by a tiny gap) on a sapphire plate. The electrons in the gold responded to the laser by oscillating coherently, which is called a plasmon. The plasmons generated a huge electric field across the gap. Critically, this field oscillates in sympathy with the illuminating laser, so the field from the laser and the field from the plasmons act together on whatever they encounter.
This is enough to drive the intensity up high enough to begin generating high harmonics. They demonstrated that, by spraying argon into the gap, they could generate harmonics with wavelengths as short as 47nm. I should note that this is a fantastic achievement. If they replace the argon atoms with ions, then they should be able to achieve even shorter wavelengths, which puts them squarely in the range of ultrahigh resolution microscopy. I don't know that they will ever generate enough power for this to be used in chip fabrication but it would certainly make the perfect seed—a seed is low intensity light that can be used to initiate HHG—to make classical HHG sources more efficient.
The key point is that they have turned something that takes a large room of equipment into something that could be attached to commercially available lasers. Unfortunately, they haven't rested there. Instead they go on to claim that this opens up the possibility of laptop sized extreme ultraviolet light sources, a claim that is simply not accurate.
The plate of sapphire with the gold bow-ties on it will certainly fit in a laptop enclosure. The optics that guide the light into and out of the box that contains the plate would fit into the same laptop enclosure. Unfortunately, the vacuum pumps that keep everything working won't. The laser that drives the HHG process currently won't, and that is unlikely to change (laser diodes do not generate short enough pulses and fiber lasers do not fit in a laptop box). The driving electronics and the cooling to the laser don't fit in the box very well, either.
I would love to be proven wrong about this. But science is often accused of over-selling itself, and I fear that this is what these researchers have done.
Nature, 2008, DOI: 10.1038/nature07012 | <urn:uuid:21378cda-93c6-440f-b86c-0c7334894217> | 3.84375 | 1,016 | Comment Section | Science & Tech. | 45.942294 |
Athens, Ga. Fish play a far more important role as contributors of nutrients to marine ecosystems than previously thought, according to researchers at the University of Georgia and Florida International University. In a pair of papers in the journal Ecology, they show that fish contribute more nutrients to their local ecosystems than any other sourceenough to cause changes in the growth rates of the organisms at the base of the food web.
Jacob Allgeier, a doctoral student in the UGA Odum School of Ecology, and Craig Layman, associate professor at Florida International University, led the study, which took place in the waters of a large bay on Abaco Island, Bahamas.
Most tropical coastal ecosystems are nutrient limited, meaning that the system's primary food sources such as algae and seagrass need to have enough nitrogen and phosphorusin the right proportionsto grow and thrive.
"We've been thinking about the role of fish and the nutrients they're excreting in these ecosystems for a while now," Allgeier said. In marine food webs, fish are usually thought of as predators, he explained, consuming microorganisms, plants and smaller animals. But fish have another important, although often overlooked, role in the system. Through excretion, they recycle the nutrients they take in, providing the fertilizer sea grass and algae need to grow.
To determine the impact of nutrients from fish, the team needed to compare sites with fish populations of different sizes. Knowing that fish tend to congregate around reefsthe larger the reef, the more fish it attractsthey built a series of artificial reefs of two sizes, large and small, and selected a number of control sites with no reefs at all.
Over the course of two years they surveyed each site periodically to record the number, size and species of fish present. Allgeier created models to estimate the supply of nutrients from all species of fish at the various sites.
|Contact: Jacob Allgeier|
University of Georgia | <urn:uuid:a1155a32-4b73-4eef-9631-14aaa4f63961> | 3.375 | 399 | Truncated | Science & Tech. | 33.512864 |
In today’s Programming Praxis exercise, our task is to print a list of all Oban numbers (numbers that don’t have an o if you write them in words). Let’s get started, shall we?
Since any number higher than 999 will have either the word “thousand” or one of the -illions in it, we only have to implement spelling numbers less than a thousand. Spelling the numbers is a simple recursive algorithm. After spelling, we just take the ones that don’t have an o.
obans :: [Int] obans = filter (notElem 'o' . spell) [1..999] where spell n | n < 20 = ones !! n | n < 100 = tens !! div n 10 ++ spell (mod n 10) | True = spell (div n 100) ++ "hundred" ++ spell (mod n 100) ones = "" : words "one two three four five six seven eight \ \nine ten eleven twelve thirteen fourteen \ \fifteen sixteen seventeen eighteen nineteen" tens = "" : "" : words "twenty thirty forty fifty sixty \ \seventy eighty ninety"
Printing the numbers is trivial.
main :: IO () main = mapM_ print obans
If we instead say print $ length obans we see that there are indeed 454 Oban numbers, as there should be. | <urn:uuid:93159c5d-bc27-48c0-be68-e45904b45cdd> | 3.984375 | 293 | Documentation | Software Dev. | 78.183581 |
It just started raining outside. The water that falls from the sky is assumed to be pure, resulting from the condensation of evaporated moisture generated from lakes, oceans and other physical water surfaces. A chemical analysis of Mt. Shasta snowfall water demonstrates excessive amounts of barium, strontium and aluminum. These elements do not naturally occur in air or water - how did they get there? Is it the geo-engineers spraying particulate to lower albedo or factories in China with very high smokestacks? This is not good water.
Water is a compound - it is not good or bad. It is the universal solvent (just as we are universal sovereigns). The formula is H2O. This represents one atom of oxygen and two atoms of hydrogen, which come together to form a complex that in bulk has a bond angle of 109.4 degrees and a bent shape. Water is polar, which means there are both a positive and negative side. If you look at a water molecule, you can see different orientations based on a C2v symmetry, which allows different bonding approaches.
Water is the key to life on earth - the mechanism for water to attach to other water molecules is called hydrogen bonding. In biologic systems, all the proteins, enzymes, carbohydrates and lipids, carry extra water around in a form called the hydration sphere. The depth of this hydration sphere seems to carry information to cells, organs and organisms that are key to metabolic processes. It seems to me as a scientist that water speaks the universal language and it the seat of real intellegiance.
My thinking cap is on and i am moving into novel territory. My thught is that the water atom can control the bond angle of the HOH bond by holding or dispersing energy. Individual atoms align in a regular array that allows energy to be held as currency between individual atoms in a lattice. This process is done in quantum increments and can be stored in the form of structure realignment. If the water atom has memory, it can reconfigure into shapes that it has once been exposed to - passing information by mimicing the resonances of the adjacent water molecules.
In science they tell us not to animate molecules, but in poetry we are taught onomonopoea - that images are created by the strings of words. Why not strings of water molecules in three dimensions that vibrate with resonant frequencies which emit information. It makes sense that life exists on other size scales. We understand micro-biology exists and are fascinated by other life forms three to six orders of magnitude smaller than ourselves. What would be micro-biology to that level is still many orders of magnitide larger than the scale of a single water molecule. The depth of intelligent life covers a much larger range than anyone currently concieve - this should be where SETI is focused.
We are part of a much larger entity, where our sun is to our galaxy as a nucleus is to a cell with the entire concievable solar system being clustes of water molecules bound together on different scales exuding intelligence in different forms. The ORMUS gold has the ability to adjust the temperence of water molecules - it signifies the beginning of a much larger conception. We have always broken things down to smaller and smaller. At each level of this break, we lose sight of emergent properties that come out based on actions of a whole. What i mean is that we think, but our brain detached from our body and isolated without the support system would be inanimate, just a lump of tissue.
But the water knows if the substance is alive or dead. How? The mechanisms used to explain how things work have broken down - things are not what they seem. We need to understand water a whole lot better, real quick to get a handle on the changes coming to what we call life. Iff* you are ready to delve into water deeper with me, let me know and i will enable an on-line course through ONRRI and NWETI.
* iff - if and only if | <urn:uuid:a61e6403-0774-447c-a16b-186bd8861dee> | 3.15625 | 831 | Personal Blog | Science & Tech. | 46.348036 |
The 2011 Nobel Prize in Physics, the most prestigious award given in the physics field, was announced on October 4. The winners are astronomers and astrophysicists who produced the first clear evidence of an accelerating universe. Not only is our universe as a whole expanding rapidly, it is in fact speeding up! It is not often that astronomers win the Nobel Prize since there is not a separate award for their discipline. The discovery of the acceleration in the universe’s expansion was made more or less simultaneously by two competing teams of astronomers at the end of the 20th century, in 1998, so the leaders of both teams share this Nobel Prize.
The new Nobel laureates, Drs. Saul Perlmutter, Adam Riess, and Brian Schmidt, were the leaders of the two teams studying distant supernovae, in remote galaxies, as cosmological indicators. Cosmology is the study of the properties of the universe on the largest scales of space and time. Supernovae are exploding stars at the ends of their lives. They only occur about once each fifty to one hundred years or so in a given galaxy, thus one must study a very large number of galaxies in an automated fashion to find a sufficient number to be useful. The two teams introduced new automated search techniques to find enough supernovae and achieve their results.
During a supernova explosion, driven by rapid nuclear fusion of heavy elements, the supernova can temporarily become as bright as the entire galaxy in which it resides. The astrophysicists studied a particular type of supernova known as Type Ia. These are due to white dwarf stellar remnants exceeding a critical mass. Typically these white dwarfs would be found in binary stellar systems with another, more normal, star as a companion. If a white dwarf grabs enough material from the companion via gravitational tidal effects, that matter can “push it over the edge” and cause it to go supernova. Since all occurrences of this type of supernova event have the same mass for the exploding star (about 1.4 times the Sun’s mass), the resultant supernova has a consistent brightness or luminosity from one event to the next.
This makes them very useful as so-called standard candles. We know the absolute brightness, which we can calibrate for this class of supernova, and thus we can calculate the distance (called the luminosity distance) by comparing the observed brightness to the absolute. An alternative measure of the distance can be obtained by measuring the redshift of the companion galaxy. The redshift is due to the overall expansion of the universe, and thus the light from galaxies when it reaches us is stretched out to longer, or “redder” wavelengths. The amount of the shift provides what we call the redshift distance.
Comparing these two different distance techniques provides a cosmological test of the overall properties of the universe: the expansion rate, the shape or topology, and whether the expansion is slowing down, as was expected, or not. The big surprise is that the expansion from the original Big Bang has stopped slowing down due to gravity and has instead been accelerating in recent years! The Nobel winners did not expect such a result, thought they had made errors in their analyses and checked and rechecked. The acceleration did not go away. And when they compared the results between the two teams, they realized they had confirmed each others’ profound discovery of the reality of a dark energy driven acceleration.
The acceleration result is now well founded since it can be seen in the high spatial resolution measurements of the cosmic microwave background radiation as well. This is the radiation left over from the Big Bang event associated with the origin of our universe.
The acceleration is now increasingly important, dominating during the past 5 billion years of the 14 billion year history of the universe. Coincidentally, this is about how long our Earth and Sun have been in existence. The acceleration has to overcome the self-gravitational attraction of all the matter of the universe upon itself, and is believed to be due to a nonzero energy field known as dark energy that pervades all of space. As the universe expands to create more volume, more dark energy is also created! Empty space is not empty, due to the underlying quantum physics realities. The details, and why dark energy has the observed strength, are not yet understood.
Amazingly, Einstein had added a cosmological constant term, which acts as a dark energy, to his equations of General Relativity even before the Big Bang itself was discovered. But he later dropped the term and called it his worst blunder, after the expansion of the universe was first demonstrated by Edwin Hubble over 80 years ago. It turns out Einstein was in fact right; his simple term explains the observed data and the Perlmutter, Riess, and Schmidt measurements indicate that ¾ of the mass-energy content of the universe is found in dark energy, with only ¼ in matter.
Our universe is slated to expand in an exponential fashion for trillions of years and more, unless some other physics that we don’t yet understand kicks in. This is rather like the ever-increasing pace of modern technology and modern life and the continuing inflation of prices.
We honor the achievements of Drs. Perlmutter, Riess, and Schmidt and of their research teams in increasing our understanding of our universe and its underlying physics. Interestingly, only a few weeks ago, a very important supernova in the nearby M101 galaxy was discovered, and it is also a Type 1a. Because it is so close, only 25 million light years away, it is yielding a lot of high quality data. Perhaps this celestial fireworks display was a harbinger of their Nobel Prize?
http://www.nobelprize.org/mediaplayer/index.php?id=1633 (Telephone interview with Adam Reiss)
http://supernova.lbl.gov/ (Supernova Cosmology Project) | <urn:uuid:c9103246-9d50-43e7-abd0-3cf290dd8386> | 3.78125 | 1,216 | Personal Blog | Science & Tech. | 40.314505 |
In a web application, you should verify that the following items are safe for operation in a multi-threaded environment:
- servlet classes
- servlet filter classes
- items placed in application scope
- items placed in session scope
Many applications use a framework. Frameworks usually define the servlet class, and the thread-safety of those servlets will be explicitly stated by a well-documented framework. Many frameworks require the application developer to define actions for implementing features. In this case, the framework owns the servlet, and the servlet in turn uses your action objects. A well-designed framework will create your action objects on the fly, on the single thread assigned to handle a single request. This in turn means that your actions will be confined to a single thread; thus, in this case, your action classes will have no need for thread-safety.
The most glaring example of a framework which violates this rule is Struts 1. In Struts 1, your actions must be designed for operation in a multi-threaded environment. This is a poor design for a framework, since ensuring a class is thread-safe is both non-trivial to implement and easy to forget. This is an onerous and unnecessary burden for an application developer.
In the case of servlet filters, a framework is not usually used when defining them. In this case, you have to be careful that your servlet filter class is indeed safe for operation in a multi-threaded environment.
For objects placed in either application scope or session scope, the simplest design is to ensure that the object is immutable, such that external synchronization is never necessary.
It's clear to most people that objects placed in application scope will be accessed by more than one thread. However, even objects placed in session scope can also be used by more than one thread. From the Servlet Specification:
"Multiple servlets executing request threads may have active access to a single session object at the same time. The Developer has the responsibility for synchronizing access to session resources as appropriate."
Here are some ways in which multiple threads might access the same session:
- web apps containing multiple servlets can share access to the same session
- Ajax requests from a single client
- multiple browser windows on a single client
- repeated clicks on a submit button
- using HTML frames to request multiple pages at the same time | <urn:uuid:4d71a859-09cd-4b33-94cd-6bde4fc1edaa> | 2.6875 | 490 | Tutorial | Software Dev. | 34.490652 |
Activity of the Month
Back to Table of Contents
Each month the Math Forum sponsors a student activity that can be done locally and shared globally. There are:
What is a magic square?In a magic square, the rows, columns, and diagonals all add up to the same number.
Let's begin with the first three numbers:
Can you fill in the empty cells?
Definition:Some mathematicians define a magic square formally as an arrangement of the numbers from 1 to n^2 (n-squared) in an nxn matrix, with each number occurring exactly once, and such that the sum of the entries of any row, any column, or any main diagonal is the same.
What is the sum of each row, column, diagonal of the magic square? Can a square be made that results in a different sum? [Advanced question: Why or why not?] How did you figure out what numbers to use and where to put them in the square? What number did you place in the middle? Is this the only number that can go in the middle? [Advanced question: Why or why not?] If we start with a puzzle like the one above, is there only one solution? [Advanced question: Why or why not?] [Advanced question: Can you show that the sum of the entries of any row, any column, or any main diagonal must be n(n^2+1)/2?]
Interactive exploration: a Magic Square Java Applet
A lesson plan for the classroom, by Suzanne Alejandre.
Home || The Math Library || Quick Reference || Search || Help | <urn:uuid:7fca1847-efa3-448f-b184-7f0caabea65e> | 3.375 | 332 | Content Listing | Science & Tech. | 63.668008 |
2.1. Supernova Types
Morphologically, Supernovae are distinguished into two main classes, Type I and Type II according to the main criterion of whether their spectra (thus, their ejecta) contain Hydrogen (Type II) or no Hydrogen (Type I).
Type II SNe are produced by the core collapse of massive stars, say, more massive than 8 M and at least as massive as 20 M (SN 1987A) or even 30 or more M (SN 1986J). Thus, the lifetime of a SNII progenitor is shorter than about 100 million years (and can be as short as a FEW million years). Therefore, SNII can be found only in galaxies that are either just formed or that have efficient, ongoing star formation, such as spiral and irregular galaxies.
|Optical||Metal lines||Metal lines||P Cyg lines|
|Spectrum||deep 6150 Å||no 6150 Å||Balmer series|
|Absolute||~ 4 × 109 L||~ 109 L||~ 109 L|
|Luminosity||small dispersion||small disp.?||large disp.|
|at max light||standard candles|
|UV spectrum||very weak||weak||strong|
|Emission||fast decay||slow decay|
|Location||all galaxies||spirals||spirals &|
|Progenitors||white dwarfs||moderately||massive stars|
|in binary systems||massive stars|
The class of Type I supernovae has been recognized (e.g., Panagia 1985) to consist of two subclasses, Type Ia and Type Ib/c that, although sharing the common absence of Hydrogen, are widely apart in other properties and, especially, in their origins. The spectroscopic criterion to discern the two subclasses from each other is the presence (Ia) or absence (Ib/c) (c) of a strong Si+ 6150Å absorption feature which is prominent in their early epoch spectra. The astrophysical difference between Type Ia and Ib/c SNe is that the former are found in all type of galaxies, from ellipticals through spirals to irregulars, whereas the latter are found exclusively in spiral galaxies, mostly associated with spiral arms and frequently in the vicinities of large ionized nebulae (giant HII regions). These characteristics indicate that SNIb/c are the end result of a relatively young population of stars (ages less than 100 million years) while SNIa progenitors must be stellar systems that have considerably longer lifetimes, of the order of 109 years or more.
The progenitors of SNIa are believed to be stars that would not produce a SN explosion if they were single stars but that end up exploding because, after reaching the white dwarf stage, they accrete enough mass from a binary companion to exceed the Chandrasekhar mass, and ignite explosive nucleosynthesis in their cores. This process of "nuclear bomb" is expected to disrupt the entire star while synthetizing about 0.6 M (Ia) of radioactive 56Ni, which will power the SN optical light curves. SNIa are very luminous objects and form a quite homogeneous class of SNe, both in their maximum brightness and their time evolution. Thus, SNIa constitute ideal "standard candles" for distance determinations on cosmological scales (see Sect. 2.4).
Type Ib/c, on the other hand, must be significantly more massive because they are only found in spiral galaxies, and often associated with their spiral arms: this suggests progenitor masses in excess of 5M. Therefore, either they represent the upper end of the SNIa class or they are a subclass of core collapse supernovae, possibly massive stars that occur in binary systems and are able to shed most of their outer H-rich layers before undergoing the explosion.
2.2. Radio Properties
A series of papers published over the past 18 years on radio supernovae (RSNe) has established the radio detection and/or radio evolution for 25 objects: 2 Type Ib supernovae, 5 Type Ic supernovae, and 18 Type II supernovae. A much larger list of almost 80 more SNe have low radio upper limits (e.g., Weiler et al. 1986, 1998). A summary of the radio information can be found at: http://rsd-www.nrl.navy.mil/7214/weiler/sne-home.html.
All known RSNe appear to share common properties of: 1) non-thermal synchrotron emission with high brightness temperature; 2) a decrease in absorption with time, resulting in a smooth, rapid turn-on first at shorter wavelengths and later at longer wavelengths; 3) a power-law decline of the flux density with time at each wavelength after maximum flux density (optical depth 1) is reached at that wavelength; and 4) a final, asymptotic approach of spectral index to an optically thin, non-thermal, constant negative value.
The current model for radio supernovae includes acceleration of relativistic electrons and compression of the magnetic field, necessary for synchrotron emission. These processes occur at the SN shock interface with a relatively high-density circumstellar medium (CSM) which has been ionized and heated by the initial UV/X-ray flash Chevalier (1982a, b). This CSM, which is also the source of the initial absorption, is presumed to have been established by a constant mass-loss () rate, constant velocity (w) wind (i.e., r-2) from a red supergiant (RSG) progenitor or a binary companion.
In our extensive study of the radio emission from SNe, several effects have been noted: 1) Type Ia are not radio emitters to the detection limit of the VLA (d) 2) Type Ib/c are radio luminous with steeper spectral indices and a fast turn-on/turn-off, usually peaking at 6 cm near or before optical maximum; and 3) Type II show a range of radio luminosities with flatter spectral indices and a relatively slow turn-on/turn-off. These results lead to the conclusion that most SNII progenitors were RSGs, SNIb/c result from the explosion of more compact stars, members of relatively massive binary systems, and SNIa progenitors had little or no appreciable mass loss before exploding, excluding scenarios that involve binary systems with red giant companions. In some individual cases, it has also been possible to detect thermal hydrogen along the line of sight (Montes, Weiler & Panagia 1997, Chu et al. 1999), to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material (e.g., Weiler, Sramek & Panagia 1990). More speculatively, it may be possible to provide distance estimates to radio supernovae (Weiler et al. 1998).
As an illustration we show that case of SN 1979C that exploded in April 1979 in the spiral galaxy NGC 4321 = M100. This supernova was first detected in the radio in early 1980 (Weiler et al. 1991) and is still bright enough to be accurately measured at different frequencies, thus offering a unique opportunity to do a very thorough study of its radio properties, the nature of the radio emission mechanisms and the late evolution of the SN progenitor. Figure 1 displays the time evolution of SN 1979C radio flux at two frequencies (1.47 and 4.88 GHz). One can recognize the "canonical" properties (non-thermal spectral index, flux peaking at later times for lower frequencies, asymptotic power law decline) that allows one to estimate the circumstellar material distribution, corresponding to a constant velocity pre-SN wind with a mass loss rate of ~ 2 × 10-4 M / year and a probable 20M progenitor. In addition, the almost sinosoidal modulation of the light curves reveals the presence of a 5M binary companion in a slightly elliptical orbit (Weiler et al. 1992). And the marked jump up of the flux about ten years after the explosion (Montes et al.2000) suggests that the progenitor had a rather sudden change in its mass loss rate about 10,000 years before exploding, possibly due to pulsational instability (Bono & Panagia 1999, in preparation).
Figure 1. The 1.47 and 4.88 GHz radio emission of SN 1979C as a function of time.
2.3. Supernova Rates
Determining the rates of SN explosions in galaxies requires knowing how many SNe have exploded in a large number of galaxies over the period of time during which they were monitored. Although it sounds easy, this process is rather tricky because data collected from literature usually do not report the control times over which the searches were conducted. On the other hand, more systematic searches that record all needed information have been started rather recently and the number of events thus recorded is rather limited, so that the statistics is still rather uncertain. In a recent study, Cappellaro et al. (1999) have thoroughly discussed this problem and, from the analysis of all combined data set available, have derived the most reliable SN rates for different types of galaxies. We have taken their rates and, for each galaxy class, we have renormalized them to the appropriate H-band (~ 1.65µm) luminosity rather than the B-band (~ 0.45µm) luminosity as done by Cappellaro et al. (1999). These new rates, displayed in Table 2, are essentially rates per unit galaxy mass because the H-band luminosity of a galaxy is roughly proportional to its mass. We see that SN rates closely reflect the star formation activity of the various classes, not only for type II and Ib/c SNe but also for SNIa. In particular, the rates for SNII-Ib/c are 3-4 times higher in late type spirals (Sbc-d) and irregulars than they are in early type spirals (S0-Sb): this is clear evidence that star formation is considerably more active in the former than it is in the latter group. Also, we notice that late type galaxies (i.e. the ones with most active star formation, Sbc through Irr) have SNIa rates which are 4-10 times higher that the earliest type galaxies (i.e. E-S0). This is a new result (Panagia 1999, in preparation) and implies that SNIa progenitors are intermediate mass stars (say, 8 > M / M > 3) and that early type galaxies are likely to capture and accrete star forming galaxies on a time scale of one to few billion years to replenish their reservoir of SNIa progenitors.
Recent estimates of the global history of star formation in the Universe were used by Madau, Della Valle & Panagia (1998) to compute the theoretical Type Ia and Type II SN rates as a function of cosmic time from the present epoch to high redshifts. They show that accurate measurements of the frequency of SN events already in the range 0 < z < 1, and even more so at higher redshifts, will be valuable probes of the nature of Type Ia progenitors and the evolution of the stellar birthrate in the Universe.
|Galaxy Type||SNIa||SNIb/c||SNII||All SNe|
|E-S0||0.05 ± 0.02||< 0.01||< 0.02||0.05 ± 0.02|
|S0a-Sb||0.10 ± 0.04||0.06 ± 0.03||0.24 ± 0.111||0.40 ± 0.12|
|Sbc-Sd||0.21 ± 0.08||0.14 ± 0.07||0.86 ± 0.35||1.21 ± 0.37|
|Sm, Irr||0.59 ± 0.24||0.33 ± 0.24||0.97 ± 0.60||1.87 ± 0.67|
2.4. Cosmological Applications
As mentioned before, SNIa are virtually ideal standard candles (e.g., Hamuy et al. 1996) to measure distances of truly distant galaxies, currently up to redshift around 1 and, considerably more in the foreseeable future (for a review, see Macchetto and Panagia 1999). In particular, Hubble Space Telescope observations of Cepheids in parent galaxies of SNe Ia (an international project lead by Allan Sandage) have lead to very accurate determinations of their distances and the absolute magnitudes of SNIa at maximum light, i.e. MB = - 19.50 ± 0.06 and MV = - 19.49 ± 0.06 (e.g., Sandage et al. 1996, Saha et al. 1999). Using these calibrations it is possible to determine the distances of much more distant SNe Ia. A direct comparison with the Hubble diagram (i.e. a plot of the observed magnitudes of SNIa versus their cosmological velocities) of distant SNe Ia (30, 000 km s-1 > v > 3, 000 km s-1) gives a Hubble constant (i.e. the expansion rate of the local Universe) of H0 = 60 ± 6 km s-1 Mpc-1 (Saha et al. 1999). Studying more distant SNIa (i.e. z > 0.1) it has benn possible to extend our knowledge to other cosmological parameters. The preliminary results of two competing teams (Riess et al. 1998, Perlmutter et al. 1999) agree in indicating a non-empty inflationary Universe with parameters lying along the line 0.8 - 0.6 = - 0.2 ± 0.1. Correspondingly, the age of the Universe can be bracketed within the interval 12.3-15.3 Gyrs to a 99.7% confidence level (Perlmutter et al. 1999).
c They are classified Ib if strong He lines are present in their spectra, and Ic otherwise. Back.
d The VLA is operated by the NRAO of the AUI under a cooperative agreement with the NSF. Back. | <urn:uuid:4d04ac3e-b10d-4156-9d59-73dabb331f5d> | 3.734375 | 3,050 | Academic Writing | Science & Tech. | 60.114205 |
Researchers find the source of an epidemic using relatively little information. Their technique could also help authorities track down contamination in water systems or locate problems in electrical grids.
Phys. Rev. Focus26, 20 (2010) – Published November 12, 2010
Foraging animals or other randomly moving entities can more easily avoid each other by taking more long-distance jumps, according to theoretical results, which may also apply to epidemics and database searches.
Phys. Rev. Focus20, 5 (2007) – Published July 31, 2007
A new technique can detect when electromagnetic waves moving through dense materials exhibit extreme changes in their behavior. It could help with surveying of geological structures or possibly scanning human bodies. | <urn:uuid:751faffc-450a-4673-bc51-c68cab215d24> | 3.28125 | 141 | Content Listing | Science & Tech. | 33.689444 |
It looks like the scientists who have predicted unending global warming caused by CO2 emissions may be in serious error.
No one knows exactly how much Earth's climate will warm due to carbon emissions, but a new study this week suggests scientists' best predictions about global warming might be incorrect. The study, which appears in Nature Geoscience, found that climate models explain only about half of the heating that occurred during a well-documented period of rapid global warming in Earth's ancient past. The study, which was published online today, contains an analysis of published records from a period of rapid climatic warming about 55 million years ago known as the Palaeocene-Eocene thermal maximum, or PETM.If this study holds up we are going to be wasting vast sums of money (robbed is a better term) if Waxman-Malarkey passes the Senate.
"In a nutshell, theoretical models cannot explain what we observe in the geological record," said oceanographer Gerald Dickens, a co-author of the study and professor of Earth science at Rice University. "There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models."
This is nothing new for regular readers of this blog. I have thought for a long time that the models were not well connected to reality. What is new is that the nails are getting more frequently pounded into the AGW coffin. People are starting to lose faith - especially considering the cold summer we have been having in much of the USA.
Consider a couple of books that have come out in the last year:
Air Con: The Seriously Inconvenient Truth About Global Warming
Heaven and Earth: Global Warming, the Missing Science
It seems that the faith is starting to lose adherents. It seems that the science is not so settled.
Even the guys at Real Climate are starting to hedge their bets.
Nature (with hopefully some constructive input from humans) will decide the global warming question based upon climate sensitivity, net radiative forcing, and oceanic storage of heat, not on the type of multi-decadal time scale variability we are discussing here. However, this apparent impulsive behavior explicitly highlights the fact that humanity is poking a complex, nonlinear system with GHG forcing – and that there are no guarantees to how the climate may respond.Say, weren't they very big promoters of "the science is settled" meme. Yes they were. I guess that now a days the science is not so settled. Some one call Al Gore. Stat.
H/T VG at Watts Up With That
Cross Posted at Classical Values | <urn:uuid:31a21f4c-c34c-494f-bbd9-9a062b4cfab6> | 2.796875 | 531 | Personal Blog | Science & Tech. | 44.584272 |