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Wood borers are highly specialised animals which penetrate wooden structures such as boats, wharves, jetties, driftwood and even living mangrove trees. Many can digest the wood owing to cellulose-digesting bacteria or protozoa living in their guts. Only a few species can actually produce their own cellulose-digesting enzymes (cellulases).
These are actually bivalves, the body being worm-like and protected within a calcium-lined tunnel. At the posterior end, the siphons stick out of the wood at high tide and have two calcium plugs (pallets) to seal the entrance of the tunnel at low tide. At the front end, the original shell valves are used to grind away the wood. In the days when wooden ships were important, shipworms were major pests.
These bivalves drill holes into wood, usually at very high tidal levels. They can cause extensive damage to structures like floating fish farms. They drill through mechanical action, using the two shell valves as abrasive surfaces. (Length 1-2cm)
Wood-boring isopods drill holes by mechanically scraping their way in. It is not certain if they actually feed on the wood or are detrital/filter feeders. Many of the species also drill into soft rock. They often concentrate in great numbers, giving the wood a honeycombed appearance. (Length 0.5-1 cm).
From A Guide to Seashore Life by Dr Leo W H Tan and Peter K L Ng
Published by the Singapore Science Centre and sponsored by BP
@Raffles Museum of Biodiversity Research and Singapore Science Centre | <urn:uuid:0a179f92-79cb-4064-a794-8274c46fbcd0> | 3.828125 | 337 | Knowledge Article | Science & Tech. | 50.36159 |
Prove $0! = 1$ from first principles
Why does 0! = 1?
All I know of factorial is that x! is equal to the product of all the numbers that come before it. The product of 0 and anything is 0, and seems like it would be reasonable to assume that 0! = 0. I'm perplexed as to why I have to account for this condition in my factorial function (Trying to learn Haskell). Thanks. | <urn:uuid:45979943-783c-4eee-9b7d-5a054ea47384> | 3.109375 | 96 | Q&A Forum | Science & Tech. | 90.82414 |
Gravitational Lensing and Number of Images
Why does "Einstein's Cross" (found in the constellation
Pegasus) have four outer points? I understand the concept of
gravitational lensing but why 4 points? what not 3 or 5? Or is this
just a chance occurrence? Would it have anything to do with the
amount of arms the galaxy has that is doing the 'lensing'?
It is largely chance how they will appear to us. However, you are correct
that how matter in the lens is distributed will determine what we see. For
a purely symmetrical lens, then the image is a ring. As you add more matter
and more variation to the lens, then the ring becomes smeared arcs, and with
enough variation, individual spots as what you see in "Einstein's Cross."
Look for "Einstein Rings" on the Internet and you will see several examples.
Some even have 3 spots.
While the lensing that we see does depend upon variations within extremely
massive objects, the effect is probably coming from the core of the galaxy
and not due to the arms themselves. However, the fact that arms are present
in the galaxy could lead to some asymmetries in the distribution of extremely
massive stars at the core of the galaxy. However at this point we are well
beyond my area of expertise, so that is speculation.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:e699b180-30e0-46f0-aaab-f3e4c886c292> | 3.3125 | 305 | Q&A Forum | Science & Tech. | 56.372458 |
Twentieth-century science completely overturned our view of cosmology. We now know that our solar system is one of many in our galaxy, and our galaxy is one of many in the universe. These galaxies are spread throughout space in a nearly uniform distribution, and distant galaxies are mutually moving apart from each other as the universe expands. Over ten billion years ago the entire collection emerged from an incredibly hot and dense state: the Big Bang.
In the twenty-first century, new discoveries are offering new challenges to our understanding. Ordinary matter comprises only about four percent of the stuff in the universe; the rest is dark matter and dark energy. Structures in the universe grew from a very smooth primeval state; the tiny deviations from perfect smoothness may have been caused by a period of inflationary expansion in the very early universe. New experiments are being designed to extend our understanding further into the unknown.
This primer provides a brief introduction to these ideas, the basic picture of modern cosmology. The intended audience includes anyone with curiosity about science; no technical background is assumed.
A brief summary of the major features of our universe.
- The Expanding Universe
The basic picture of modern cosmology: a smooth, expanding spacetime.
- The Evolving Universe
A schematic timeline of major events, from the Big Bang to today.
- The Luminous Universe
What we see when we look into the sky, from galaxies to cosmic rays.
- The Dark Universe
Most of the stuff in the universe is unseen: dark matter and dark energy.
- The Early Universe
Remnants of the Big Bang: the microwave background and primordial nuclei.
- The Really Early Universe
Inflation, baryogenesis, and the beginning of time.
- The Measured Universe
The instruments and techniques we use to do observations and experiments.
Frequently Asked Questions about cosmology.
- Additional Resources
Links to resources elsewhere. | <urn:uuid:a2023bc3-851d-45c0-9e7d-9bf142aad133> | 3.96875 | 397 | Truncated | Science & Tech. | 28.321532 |
May 23, 2006 > TechKnow Talk
by Todd Griffin
Is glass a liquid or a solid? A very old window, like hundreds of years old, is thicker at the bottom than the top. This proves that glass is a liquid, right? It just flows very, very slowly.
When the TechKnow Guy was in high school (and dinosaur meat was on the cafeteria menu) he was taught that glass is a viscous fluid, specifically a supercooled liquid. However, most scientists now agree that glass is in fact an amorphous solid. Nonetheless, the myth of the liquid nature of glass has become so widespread that some science textbooks still include it as fact, and many people still believe it.
Let's start by addressing the question of fluidity or flow in glass. It is true that some glass windows in very old buildings, European churches for example, are thicker at the bottom than at the top. Some tour guides in these buildings have propagated the "flowing glass" theory to explain this phenomenon. After all, it does make a nice story. To understand the true cause, we will need a brief primer on medieval glass craftsmanship.
Most window glass manufactured prior to the 20th century, when the modern float glass process was commercialized, was produced using the crown glass process. Glass was blown, then rolled and worked in its molten state, flattened out, and finally spun into a disc shape. This yielded glass with a rippled, uneven surface. More importantly to this topic, it resulted in glass somewhat thinner and more uniform in thickness near the edge of the disc than in the center or crown, near the "umbilical" used to spin it.
The best quality windows were made of small, usually diamond-shaped sections cut from near the edge of the disc, and assembled into the desired window dimensions using a lead lattice. When larger, rectangular panes were cut, they were necessarily thicker at one end (typically the end nearer the center) than at the other. When such single panes were framed and mounted into a window enclosure, they were installed with the thicker end down, presumably to better bear the weight.
If you are not convinced, try thinking about it this way. If the glass had flowed over the centuries to such an extent as to noticeably thicken at the bottom, it would also have flowed over and around the frame at the bottom. Yet these aged windows, some nearly 1000 years old, show no signs of flowing onto their frames. If you want to make the tour guide uncomfortable, ask about that.
Scientists have also examined the oldest surviving examples of man-made glass, ancient Roman and Egyptian figurines dating back 2000 years. They exhibit no indications of flow. Yet another convincing argument involves very sophisticated optical instruments such as telescopes. The lens of a telescope or interferometer is ground and polished to an exceedingly fine tolerance. If glass flowed over time, even very slightly, large telescopes would soon go out of focus. But in fact, this does not happen.
So let's agree that glass does not flow like a liquid. That doesn't specifically address the question of its state of matter. Despite its lack of flow, glass is a sufficiently unique material to defy easy categorization as solid or liquid. Most solid materials are crystalline, meaning their atoms or molecules are arranged in a very orderly manner. Think of filling a can with marbles. The marbles position themselves in a structured pattern, touching each other in the same ways, and leaving spaces that are of the same size and shape.
But glass is quite different. Its atoms arrange themselves in a haphazard, random manner, with no repeatable, orderly structure. Think of filling a can with pennies. They pack themselves in a disorderly and irregular fashion, touching each other in different ways, and leaving spaces of varying size and shape. Thus the arrangement of atoms in glass resembles a very cold liquid more than a solid. Many plastics have similar molecular structures. This is known as an amorphous solid, opposed to a crystalline solid such as ice, metal, or stone.
Again, most scientists agree that, at least for practical purposes, we can categorize glass as an amorphous solid. However, some argue it is a highly viscous liquid (that does not flow!). This is known as a viscoelastic liquid. Others claim glass is sufficiently different from both solids and liquids to merit a category all its own, neither solid nor liquid. The bottom line is that glass behaves very much like a solid material. Dropping a wine glass on the kitchen floor is an easy way to confirm this.
People talk about giving something the "acid test," which means finding out if it will really work. Is there a real acid test, and if so what does it test?
The expression derives from the California gold rush of the mid-19th century, if not earlier. One dictionary defines it as "a crucial, final test of the value or quality of a thing or person." As you pointed out, it is used to refer to the ultimate or most telling measure of something, often its practical application, as opposed to the theoretical or conceptual stages. For example, a design for a new mousetrap may look great, but the acid test is whether it catches mice.
As implied above, the original acid test was to verify the authenticity of gold. In those days, a prospector or assayer may have used simple nitric acid, which will not harm gold but will strongly oxidize copper, present in nearly all minerals that appear similar to gold. Copper oxide is a distinctive blue color, and readily signals false gold. Today, jewelers and assayers use more sophisticated techniques. A modern acid test uses a combination of nitric and hydrochloric acid called aqua regia. The reaction of the material in question is sometimes compared to a known sample of gold to refine the test.
By the way, the widespread myth that gold is not affected by bleach, such as the common household product Clorox, is an unfortunate lie. Do not put your jewelry into bleach in an attempt to determine if it is solid gold; it can be seriously damaged. White gold is especially susceptible to attack by bleach. Even worse than harming your jewelry is getting an acid burn. Never try the acid test yourself. Take your jewelry to a reputable jeweler who is trained to evaluate it accurately, safely, and inexpensively. | <urn:uuid:f43e3cdd-5a0e-4605-859f-9f437f16cc2d> | 3.59375 | 1,318 | Comment Section | Science & Tech. | 49.579995 |
The Maldives have become a symbol of the dangers of global warming, amid fears the low-lying nation could disappear as a result of rising sea levels. But one team of scientists believes the truth is more complicated. The Maldives coral islands, they postulate, may be growing with the rising waters...More discussion and explanation at Der Spiegel.
The geomorphologists compared old aerial photographs taken in World War II with current satellite images. To their surprise, they found that most of the atolls they were studying had either grown or remained unchanged in the last few decades, even though the sea level has already risen by 12 centimeters (about 5 inches).
As soon as it was published, the study became ammunition in the political battle over global warming. Climate activists questioned its conclusions, which would normally be welcomed as good news. Skeptics of anthropogenic climate change, on the other hand, seized upon the study as evidence that all the excitement over global warming is completely unnecessary. | <urn:uuid:af441fa1-8413-41be-aa96-32105e36265c> | 2.984375 | 197 | Personal Blog | Science & Tech. | 39.645438 |
The pattern of seasonal temperature odds across Australia is due to higher
than average temperatures in both the Pacific and Indian Oceans, with the effect
from the Pacific being dominant.
Averaged over the coming three months, the chances are mainly between 60 and
80% for higher than normal maximum temperatures northeast of a line from Derby
in northwest WA to Sydney. Within this region, the chances peak above 80%
in eastern Arnhem Land and in an area of north Queensland surrounding the east
coast of the Gulf of Carpentaria (see map).
So in years with ocean patterns like the current, about six to eight February to
April periods out of every ten are expected to be hotter than average in these
parts of northern and eastern Australia, with about two to four out of ten being cooler.
Contrasting this, there are 60 to 65% chances (i.e. 35 to 40% chances of higher
than average) for a cooler than normal February to April period in a band stretching
from the interior of WA, across western and southern SA to central Victoria. A few
patches across Tasmania also have similar probabilities.
Outlook confidence is related to how consistently the Pacific and Indian
Oceans affect Australian temperatures. During the February to April period, history
shows this effect on maximum temperatures to be moderately consistent
over Queensland, the northern NT, central WA and patches in SA, Victoria, NSW and
Tasmania. In western WA and in a band from the southern NT to most of NSW, the
effect is only weak or very weak (see background information).
The chances of seasonal minimum temperatures being higher than the median are
between 60 and 80% over most of the northern tropics, indicating
a moderate to strong shift in the odds towards warmer than normal conditions.
In contrast, cooler than average nights (i.e. a 30 to 40% chance for warmer than normal)
are favoured in the southeast of the mainland.
History shows the oceans' effect on minimum temperatures during the February to April period
to be moderately consistent over large parts of the country. | <urn:uuid:6fbfb55a-d91d-443d-b835-580b73e29134> | 2.875 | 434 | Knowledge Article | Science & Tech. | 43.75875 |
The interior of the Earth is hot, mainly from energy released by decay of radioactive elements. In some places on the planet, the crust is either thin enough or fractured enough that some of that heat comes close to the surface. Geothermal electricity is created by using this heat to run turbines.
On paper, geothermal would seem to be an ideal non-carbon source of energy. The earth's heat is nearly inexhaustible from our perspective. Geothermal facilities require very little land compared to other renewable energy generating plants. Also unlike most renewable sources of energy, geothermal offers the possibility of base load power production: a geothermal plant could in theory run nearly non-stop.
That's not to say there are no environmental downsides to geothermal. For one thing, it's location dependent: in order to be economical, geothermal facilities must be sited where the earth's interior heat rises to within striking distance from the surface. For the moment that rules out places like Nebraska, where the crust is thick. Geothermal power plants are, at present, limited to volcanically and tectonically active parts of the planet. Iceland, which is thought to sit atop a volcanic plume or "hot spot," derives a third of its total energy consumption from geothermal.
There are, however, some experimental plants in parts of the US that aren't particularly geologically active, such as the lower Mississippi basin. Depending on the success of these experiments, we may someday be able to develop cost-effective geothermal power in states without earthquakes or volcanoes.
The United States has the largest geothermal infrastructure of any nation, though it contributes only a small amount of out total electrical consumption. Nevada and California lead the pack among the 15 states with geothermal installations, with installations totaling just under 4,000 megawatts and 2,000 megawatts, respectively. Northern California's cluster of geothermal plants at The Geysers is the largest in the world, at 725 megawatts of capacity.
There are three basic kinds of geothermal power plants:
- Dry steam, in which steam created naturally deep underground is harnessed to drive turbines. (The plants at The Geysers are of this type.)
- Flash steam, in which subterranean water that is still in liquid form due to high pressure is pumped into lower-pressure tanks, where it "flashes" into steam that then drives turbines. The geothermal plants in the Imperial Valley are of this type.
- Binary cycle plants, which take advantage of geothermal water that's not quite hot enough to drive turbines on its own. In these plants, the geothermal water is pumped out of the ground (rather than emerging due to its own pressure) into a heat exchanger, where it heats a secondary fluid with a lower boiling point than water. This secondary fluid, usually a light hydrocarbon like butane, then drives the turbines. There's one of these in Mammoth Lakes.
The environmental effects of geothermal generally stem from taking geothermal water out of the ground.
Most straightforward is the threat of altering the water table, drying up hot springs and possibly even causing land subsidence, as has happened at one geothermal field in New Zealand.
Geothermal water also carries with it a significant amount of dissolved material, and releasing that into the surface environment can cause problems. This material can include heavy metals and other toxic elements such as mercury, arsenic, and boron; dissolved gases like methane, hydrogen sulfide and carbon dioxide, and even radioactive elements. When flash steam plants in the Imperial Valley condense their used geothermal water back into "production brine," it may contain as much as 30% of its weight in these dissolved substances. Solids are separated out of production brine and the remaining liquid is reinjected into the geothermal field. The remaining solid waste -- called "filter cake" -- is sent to a hazardous waste facility. In the Imperial Valley's geothermal fields the total annual production of this hazardous solid waste runs between 40,000 and 60,000 tons.
One other technique often referred to as geothermal energy is the use of ground source heat pumps to heat and cool buildings. This is probably better referred to with some other terminology, as it doesn't generally involve taking advantage of the heat generated within the earth, but actually relies on subsoil and bedrock functioning as a thermal mass. A ground source heat pump moves air from a building through a series of pipes buried 20 feet or so beneath the surface. That deep, the earth tends to maintain a constant temperature somewhere between 50° and 60° F: a heat exchanger at that depth can provide room air that's moderately warm in winter, and comfortably cool in summer. A drawback of the technique is that electrical power is generally needed to operate the air pump, which can reduce the heat pump's carbon benefit if the power comes from conventional sources. | <urn:uuid:cc40b841-7991-4048-972f-fd1d2b6de33d> | 4.15625 | 998 | Knowledge Article | Science & Tech. | 37.041872 |
> Climate Change
> Climate Change 101
The ABCs of Climate Change
What is the greenhouse effect?
The “greenhouse effect” is a natural occurrence. Energy from the sun passes through the atmosphere and is absorbed by the Earth’s surface - some of that energy is then emitted back to the atmosphere as heat. A portion of the heat is absorbed by heat-trapping gases in the atmosphere (among them carbon dioxide (CO2) and methane (CH4)), which creates an insulating layer around the Earth. The trapped heat, which would otherwise be released into space, raises the temperature of the atmosphere and, subsequently, the Earth’s surface. Human activities that produce additional greenhouse gases increase the amount of heat trapped in the atmosphere, thus causing global warming and climate change.
What is global warming?
Global warming refers to the rise in the Earth’s temperature resulting from an increase in heat-trapping gases in the atmosphere.
What are the primary greenhouse gases (GHG)?
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Water vapor
- Other gases
What are some of the projected impacts of climate change?
Species in natural ecosystems will attempt to migrate with the changing climate, but will differ in their degree of success. Some ecosystems will either flourish or decline in health, at least over the short-term.
To learn more about Climate Change, check out these programs. | <urn:uuid:836428fa-4f20-4829-9aa0-cf6bc1a2f992> | 3.984375 | 310 | Knowledge Article | Science & Tech. | 40.203775 |
Computation is the fire in our modern-day caves. By 2056, the computational revolution will be recognised as a transformation as significant as the industrial revolution. The evolution and widespread diffusion of computation and its analytical fruits will have major impacts on socioeconomics, science and culture.
Within 50 years, lives will be significantly enhanced by automated reasoning systems that people will perceive as "intelligent". Although many of these systems will be deployed behind the scenes, others will be in the foreground, serving in an elegant, often collaborative manner to help people do their jobs, to learn and teach, to reflect and remember, to plan and decide, and to create. Translation and interpretation systems will catalyse unprecedented understanding and cooperation between people. At death, people will often leave behind rich computational artefacts that include memories, reflections and life histories, accessible for all time.
Robotic scientists will serve as companions in discovery by ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:513bf32c-5c35-4852-aff4-926b1d73cadb> | 3.203125 | 212 | Truncated | Science & Tech. | 25.644934 |
Motion Characteristics for Circular Motion
Improve your problem-solving skills with problems, answers and solutions from The Calculator Pad.Flickr Physics
Visit The Physics Classroom's Flickr Galleries and enjoy a visual overview of the topic of circular motion.
The Uniform Circular Motion activity from the Shockwave Studios is an excellent accompaniment for this reading.The Laboratory
Looking for a lab that coordinates with this page? Try the Making the Turn Lab from The Laboratory.Curriculum Corner
Learning requires action. Give your students this sense-making activity from The Curriculum Corner.
Speed and Velocity
Any moving object can be described using the kinematic concepts discussed in Unit 1 of The Physics Classroom. The motion of a moving object can be explained using either Newton's Laws (Unit 2 of The Physics Classroom) and vector principles (Unit 3 of The Physics Classroom) or by means of the Work-Energy Theorem (Unit 5 of The Physics Classroom). The same concepts and principles used to describe and explain the motion of an object can be used to describe and explain the parabolic motion of a projectile. In this unit, we will see that these same concepts and principles can also be used to describe and explain the motion of objects that either move in circles or can be approximated to be moving in circles. Kinematic concepts and motion principles will be applied to the motion of objects in circles and then extended to analyze the motion of such objects as roller coaster cars, a football player making a circular turn, and a planet orbiting the sun. We will see that the beauty and power of physics lies in the fact that a few simple concepts and principles can be used to explain the mechanics of the entire universe. Lesson 1 of this study will begin with the development of kinematic and dynamic ideas that can be used to describe and explain the motion of objects in circles.
Suppose that you were driving a car with the steering wheel turned in such a manner that your car followed the path of a perfect circle with a constant radius. And suppose that as you drove, your speedometer maintained a constant reading of 10 mi/hr. In such a situation as this, the motion of your car could be described as experiencing uniform circular motion. Uniform circular motion is the motion of an object in a circle with a constant or uniform speed.
Uniform circular motion - circular motion at a constant speed - is one of many forms of circular motion. An object moving in uniform circular motion would cover the same linear distance in each second of time. When moving in a circle, an object traverses a distance around the perimeter of the circle. So if your car were to move in a circle with a constant speed of 5 m/s, then the car would travel 5 meters along the perimeter of the circle in each second of time. The distance of one complete cycle around the perimeter of a circle is known as the circumference. With a uniform speed of 5 m/s, a car could make a complete cycle around a circle that had a circumference of 5 meters. At this uniform speed of 5 m/s, each cycle around the 5-m circumference circle would require 1 second. At 5 m/s, a circle with a circumference of 20 meters could be made in 4 seconds; and at this uniform speed, every cycle around the 20-m circumference of the circle would take the same time period of 4 seconds. This relationship between the circumference of a circle, the time to complete one cycle around the circle, and the speed of the object is merely an extension of the average speed equation stated in Unit 1 of The Physics Classroom.
The circumference of any circle can be computed using from the radius according to the equation
Combining these two equations above will lead to a new equation relating the speed of an object moving in uniform circular motion to the radius of the circle and the time to make one cycle around the circle (period).
where R represents the radius of the circle and T represents the period. This equation, like all equations, can be used as an algebraic recipe for problem solving. It also can be used to guide our thinking about the variables in the equation relate to each other. For instance, the equation suggests that for objects moving around circles of different radius in the same period, the object traversing the circle of larger radius must be traveling with the greatest speed. In fact, the average speed and the radius of the circle are directly proportional. A twofold increase in radius corresponds to a twofold increase in speed; a threefold increase in radius corresponds to a three--fold increase in speed; and so on. To illustrate, consider a strand of four LED lights positioned at various locations along the strand. The strand is held at one end and spun rapidly in a circle. Each LED light traverses a circle of different radius. Yet since they are connected to the same wire, their period of rotation is the same. Subsequently, the LEDs that are further from the center of the circle are traveling faster in order to sweep out the circumference of the larger circle in the same amount of time. If the room lights are turned off, the LEDs created an arc that could be perceived to be longer for those LEDs that were traveling faster - the LEDs with the greatest radius. This is illustrated in the diagram at the right.
Objects moving in uniform circular motion will have a constant speed. But does this mean that they will have a constant velocity? Recall from Unit 1 of The Physics Classroom that speed and velocity refer to two distinctly different quantities. Speed is a scalar quantity and velocity is a vector quantity. Velocity, being a vector, has both a magnitude and a direction. The magnitude of the velocity vector is the instantaneous speed of the object. The direction of the velocity vector is directed in the same direction that the object moves. Since an object is moving in a circle, its direction is continuously changing. At one moment, the object is moving northward such that the velocity vector is directed northward. One quarter of a cycle later, the object would be moving eastward such that the velocity vector is directed eastward. As the object rounds the circle, the direction of the velocity vector is different than it was the instant before. So while the magnitude of the velocity vector may be constant, the direction of the velocity vector is changing. The best word that can be used to describe the direction of the velocity vector is the word tangential. The direction of the velocity vector at any instant is in the direction of a tangent line drawn to the circle at the object's location. (A tangent line is a line that touches a circle at one point but does not intersect it.) The diagram at the right shows the direction of the velocity vector at four different points for an object moving in a clockwise direction around a circle. While the actual direction of the object (and thus, of the velocity vector) is changing, its direction is always tangent to the circle.
To summarize, an object moving in uniform circular motion is moving around the perimeter of the circle with a constant speed. While the speed of the object is constant, its velocity is changing. Velocity, being a vector, has a constant magnitude but a changing direction. The direction is always directed tangent to the circle and as the object turns the circle, the tangent line is always pointing in a new direction.
1. A tube is been placed upon the table and shaped into a three-quarters circle. A golf ball is pushed into the tube at one end at high speed. The ball rolls through the tube and exits at the opposite end. Describe the path of the golf ball as it exits the tube. | <urn:uuid:485f894f-62c2-4c89-aa51-39cd09429731> | 4.3125 | 1,559 | Tutorial | Science & Tech. | 48.48425 |
JTable Display Data From MySQL Database
This section will describe you the displaying of data of a database table into a JTable. Here you will read about how to create a table in Java swing, how can you add column header's name, how can you show data into the table..
clone method in Java
clone() method in Java is used to create and return copy of the object. Clone() method is used in class where Cloneable interface is implemented but throws a CloneNotSupportedException where a Cloneable interface is not implemented..
Java Queue example
Queue Interface is part of java.util package. Queue generally works on FIFO (First In First Out) in ordering elements. In FIFO, new element is added at the end while in other cases ordering properties has to be specified. Queues are bounded which means that number of elements are restricted in it..
BufferedReader in Java
BufferedReader in Java is used to to read characters, arrays, lines and File Line by line. It also reads text from a character-input stream. A programmer can change the buffer size or can use default size..
Logger in Java
In this section we will learn how to use the Logger in Java program. Logger in Java is part of java.util.logging are used to log the error and messages into the log file. The name of Logger are dot-separated and should be the package name or class name..
Applets in Java
Applet is a Java program embedded within HTML pages. Java applets is compatible with almost all the web browsers like Mozilla Firefox, Google Chrome, Internet explorer, Netscape navigator and others that are java enabled. Applets make a website more dynamic and are secure..
How to copy a file in java
In this section you will learn about how to copy a content of one file to another file. In java, File API will not provide any direct way to copy a file..
Why and how to use Integer.parseInt() in java
Integer.parseInt() method is used to convert an string value into integer. JVM reads each element as String and hence we have to convert an entered String value into respective data type.
What is HashSet in java
In following example we will discuss about HashSet in Java. The HashSet class implements the set interface. We have stored data of collection used for HashSet method.hashSet stored only object HashSet class in java.util package. The HashSet does not accept duplicate value..
Static variable in java
Static is a keyword in java used to create static methods, variable inside a class and static class.Static variable is also called class variable which belongs to class not to object.Static variable is declared inside a class but outside the method or Constructor..
Java final keyword
The final is a very important keyword in java, which is used to restrict user. A programmer must not declare a variable or class with the name "Final" in a Java program. We can have final methods, final classes, final data members, final local variables and final parameters. .
Arraylist in java
ArrayList is a class that extends AbstractList and implements List Interface. Standard java array are of fixed length, that mean we should know the size of array how many element it will hold, they cannot grow or shrink. but for indefinite number of elements.
A part of String is called substring. Substrings are also a String. Substring is used to create small strings. Sometimes a programmer needs only a part of String so, how they can find the substring..
What is Public static void main
In most of the Programming language, main function is the first function where program start execution. This is the first method from where Java Virtual Machine(JVM) start executing. Following are the variation of main method..
How to Read a File in Java
In this section we are going to know, How to read a file in Java. We have to follow three step to read a File. .
File Handling In Java
This section describes you about how to perform file handling in Java. In this section you will read what is file handling in Java, how to do file handling in Java, what is stream, file handling package, file handling classes and methods, java.io.File. .
In this section we will discuss about the interface in Java. .
Java Abstract Class Example
Abstract class in Java is a class which is created for abstracting the behaviour of classes from the outside environment. Abstract class can be created using 'abstract' keyword. An abstract class may contain abstract as well as non-abstract methods. .
Java Password Field
In this section we will discuss how to use password field in Java. .
JFrame Close On Button Click
This example explains you how a frame can be closed on an action event i.e. a frame should be close when clicked on the button on a frame. In this example we will use the dispose() method to close the frame..
Java Word Occurrence Example
This example explains you that how you can count the occurrences of each word in a file. In this example we will use the HashMap for putting and getting the values. This program takes the file name from command line which returns the number of occurrences of each word separated by a single white space. In this example I have used the java.io and java.util packages. .
Java Method Return Multiple Values
This example explains you how a multiple values can be return by a method. This example explains you all the steps required in to return multiple values in Java. In this example you will see how we can return multiple values using the return statement..
Java Find Next Date Example
This example explains you about how to display the next date of input date. This tutorial explains you all the steps involved in developing this application. To develop this application we will use the Eclipse IDE and JDK 1.6..
Java Swing Set And Get Values
In this tutorial we will learn about how to set and get values using setter and getter methods. This example explains you how to use setter and getter method in Java Swing..
Java Math.pow() Example
This example explains you about the pow() method in Java. This tutorial explains you about the Math.pow() method using a simple example. In this example you can see that how can we find the power of a number in Java. Power means the exponent of a number i.e. n^p (n raised to the power of p) for example if the expression has written like 2^3 then it should be calculated as 2*2*2..
Java Square Root And Cube Root Example
This example explains you about finding the square root and cube root of a number. This tutorial explains about all the steps of how to find the square root and cube root. In this example we will use JDK 1.6 and the Eclipse IDE for writing, compiling and executing the code. .
Java Program Floyd's Triangle
In this section you will read about how to write a Java program to print Floyd's triangle. .
How To Retrieve Image From From MySQL Using Java
In this section we will discuss about how to retrieve image from the MySQL using Java. .
How To Store Image Into MySQL Using Java
In this section we will discuss about how to store an image into the database using Java and MySQL. .
Java current date - How to get current date in Java
This article explains how to get the current date in Java. There are many ways you can get the current date in Java..
Core Java Hello World Example
This tutorial explains you how to create a simple core Java "Hello World" application. The Hello World application will print the text "Hello World" at the console. This example explains you about all the steps in creating Hello World application. .
Java JLayeredPane example
In this section we will discuss about how to overlap the JPanels. .
Java JButton Key Binding Example
In this section we will discuss about how to bind a specific key to the button. .
Java JTabbedPane Example
In this section we will discuss about how to add the Tab pane in JFrame. .
Java LinkedList Example
In this section we will discuss about the own implementation of Linked List in Java. .
In this section we will discuss about the javax.swing.JTextArea. .
How To Fetch Data From Database Into JTextArea
In this section we will read about how to get the data from database table into JTextArea. .
How To Remove Array Element In Java
In this section we will discuss about how to remove a given array element. .
Java array copy example
In this section we will discuss about the arrayCopy() in Java. .
First Java Program Example
In this section we will discuss about the first java program example. .
Java JComboBox Get Selected Item Value
In this section we will discuss about how to get the selected item value form JComboBox..
How To Read File In Java
In this section we will discuss about about how data of a file can be read in Java..
Java Construct File Path
In this section we will discuss about how to construct file path in Java. .
How To Create a New File
In this section we will discuss about how to create a new file in Java. .
Java IO File
In this section we will discuss about the File class in Java..
How To Read Integer From Command Line In Java
In this section we will discuss about how an integer can be read through the command line. .
How To Read String From Command Line In Java
In Java command line argument is entered when an application is invoking. This command line argument is entered after giving the name of the class. There is no limit of arguments giving from the command line.
Command Line Standard Error In Java
In this section we will discuss about the Command Line Java IO Standard Error. .
Command Line Standard Output In Java
In this section we will discuss about the Command Line Java IO Standard Output. .
Command Line Standard Input In Java
In this section we will discuss about the Java IO Standard Input through Command Line. . | <urn:uuid:9bf56eeb-f77d-44f5-86f8-0d1074df8c14> | 3.5625 | 2,124 | Content Listing | Software Dev. | 59.77635 |
There are different types of Numbers
in the number system. Perfect Numbers
are one of such types. The perfect number is a positive number whose factors when added give back the number as answer. The factors of the numbers are less than the number.
Some examples of perfect numbers are given below:
1. The factors of number 6 are 1, 2 and 3.
1 + 2+ 3 = 6
So, 6 is a perfect number.
2. The factors of 28 are 1, 2, 4, 7, and 14.
1 + 2 + 4 + 7 + 14 = 28
So, 28 is a perfect number.
There are others such as 496, 8128 and many higher numbers.
In a perfect number, the product of its even factor and prime factor gives the number itself. The perfect numbers are both even and odd. But there is a confusion that whether a odd perfect number really do exist. Mathematician found one but it gives an approximate answer.
The formula for finding even perfect number is given as,
Let us consider, p = 2 which is a prime number.
-1) = 7 which is also a prime number.
The perfect numbers were used in ancient cultures and religion of certain regions. The perfect number are also used in computer science or computer application as a coding problem and it finds ways in generating these numbers using computer coding in different computer languages. | <urn:uuid:c2fc4699-65c6-4853-8715-b1667acab1fc> | 3.515625 | 290 | Tutorial | Science & Tech. | 69.239211 |
Satellite images indicate the moisture in the atmosphere over a given location.
The moisture can indicate one of two things: clouds or fog.
There are different types of satellites.
The ones most frequently used in our weather center are visible satellites and infrared satellites.
Visible satellites are pictures from space (that can only be used during daylight hours).
Infrared measures temperatures from the clouds and can be used day or night (most frequently used). | <urn:uuid:c2219f60-4caa-4f8c-8dc2-16576cd170d8> | 3.265625 | 91 | Knowledge Article | Science & Tech. | 26.25991 |
XGetErrorText(display, code, buffer_return, length)
int (*handler)(Display *);
XGetErrorDatabaseText(display, name, message, default_string, buffer_return,
char *name, *message;
The XGetErrorText function copies a null-terminated string describing the specified error code into the specified buffer. The returned text is in the encoding of the current locale. It is recommended that you use this function to obtain an error description because extensions to Xlib may define their own error codes and error strings.
The XDisplayName function returns the name of the display that XOpenDisplay would attempt to use. If a NULL string is specified, XDisplayName looks in the environment for the display and returns the display name that XOpenDisplay would attempt to use. This makes it easier to report to the user precisely which display the program attempted to open when the initial connection attempt failed.
The XSetIOErrorHandler sets the fatal I/O error handler. Xlib calls the program's supplied error handler if any sort of system call error occurs (for example, the connection to the server was lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O error handler does return, the client process exits.
Note that the previous error handler is returned.
The XGetErrorDatabaseText function returns a null-terminated message (or the default message) from the error message database. Xlib uses this function internally to look up its error messages. The text in the default_string argument is assumed to be in the encoding of the current locale, and the text stored in the buffer_return argument is in the encoding of the current locale.
The name argument should generally be the name of your application. The message argument should indicate which type of error message you want. If the name and message are not in the Host Portable Character Encoding, the result is implementation-dependent. Xlib uses three predefined ``application names'' to report errors. In these names, uppercase and lowercase matter.
Table of Contents | <urn:uuid:41eda461-2b3b-4421-9350-89ccc48860be> | 2.78125 | 436 | Documentation | Software Dev. | 34.426579 |
Vulture Roosting Behaviors
By Phil Miller, Wildlife Biologist, Wildlife and Freshwater Fisheries Division
Vultures are some of the most common species of birds found in Alabama and throughout the southeast. Vultures commonly seen in the Southeast are classified as one of two species, the turkey vulture (Cathartes aura) or the black vulture (Coragyps atratus). The common name for these two species is derived from their appearance. The turkey vulture has a red, wrinkled head and a dark body that resembles a wild turkey from a distance. The black vulture, with its head and neck being a dark to light gray and furrowed with wrinkles, has a black appearance.
These two species of birds are commonly seen circling in the sky or standing along the roadside eating the carcass of dead animals. Known as “scavengers of the skies,” vultures were once hunted in large numbers because of the belief that they carry diseases. But over time, they have come to be seen as a beneficial asset by cleaning up the remains of dead animals. Today, most view the vulture as one of nature’s most efficient, natural recyclers.
At the end of a long day of feeding and searching for food, vultures begin to move back to their roosting sites. Both species form large communal roosts, with some containing over a thousand birds. Vultures will usually return to the same roost each night and generally roost on the same branch as previous nights. These roosts may or may not be made up of family members. Observations of vulture roosts showed both species will occupy the same roosts and use them year after year. Some of these roosts are believed to be over 100 years old and are shared by parents and grandparents.
Common roosting sites preferred by vultures are power lines, radio towers, tall trees, or old buildings. These roosts create a foul smell and may seem unsanitary to the human eye, but due to the unique digestive system of vultures any bacteria or disease they may ingest is killed. Their droppings and pellets (undigested bones and fur) are considered disease free.
During the early morning, vultures can be observed at their roosting site with their wings stretched outward. This wing stretch allows the birds to use the sun and early morning warmth to repair damaged feathers, raise body temperature and dry flight feathers after wet weather.
Once the morning temperature warms up and thermals begin to form, turkey vultures begin to leave their roost individually. Most black vultures wait about an hour longer than the turkey vulture before leaving their roost. The late departure of black vultures is due to having a heavier wing load and waiting for stronger thermals to stay aloft. When the thermals are right, black vultures begin to leave their roost in groups.
Vultures may seem unattractive or disgusting, but they play an important role in the animal world. Nature uses these birds to help clean up the environment of decaying animals. This clean-up crew provides a service that could prevent the spread of certain diseases. | <urn:uuid:780553ea-e67a-45c8-8ed5-c024f56ba080> | 3.875 | 668 | Knowledge Article | Science & Tech. | 47.397788 |
Study Will Explore How Solar Storms Affect Earth’s Atmosphere
UMass Lowell, 4th January 2013
We all rely on local weather forecasts to plan our travels and outdoor activities, or even to decide whether to water the lawn.
But researchers like Prof. Paul Song in the Department of Physics & Applied Physics are also interested in “space weather,” the constantly changing environmental conditions in interplanetary space, especially between the sun’s atmosphere and earth’s outer atmosphere. While meteorologists deal with clouds, air pressure, wind, precipitation and the jet stream, space-weather scientists concentrate on changes in the ambient plasma (ionized gas), solar wind, magnetic fields, radiation and other matter in space.
“Predicting space weather is the next frontier in weather forecasting,” says Song, who directs UMass Lowell’s Center for Atmospheric Research (CAR).
Comment: More news of space weather research but we are told clearly that space weather is affecting Earth’s atmosphere and weather… I believe there is enough information in the public domain to justify the belief that space weather is the true reason for the panic amongst scientists about extreme weather… Press releases from NASA and the European Space Agency amongst other scientific bodies and groups in recent years informs us clearly that Earth is rapidly losing its cosmic defenses. The scientific research carried out already, especially by NASA, informs us that there is a distribution of electric currents linking the magnetosphere with the ionosphere. The Honorary Chairman of the World Forum International Congress “GEOCATACLYSM-2011” states in his paper the following:
“An important role in climate change is attributed to global changes in the parameters of the geomagnetic field and magnetosphere; this refers in particular to the more than 500% increase in the North Magnetic Pole’s drift rate and reduction of the geomagnetic field intensity. Today, the impact of magnetospheric processes on Earth’s climate is considered a proven scientific fact.”
PROCEEDINGS: Natural Cataclysms and Global Problems of the Modern Civilization, WORLD FORUM – INTERNATIONAL CONGRESS September 19-21, 2011 – Istanbul, Turkey Source: (43.7 MB .pdf) Link.
A few Russian scientists took it upon themselves to warn the world many years ago. The Russian report titled, Planetophysical State of The Earth and Life (1997, 1998 in English) report also discusses climate change and simply states:
The temperature regime of any given phase of climatic reorganization is characterized by contrasts, and instabilities. The widely quoted, and believed, “Greenhouse Effect” scenario for total climatic changes is by far the weakest explanation, or link, in accounting for this reorganization.
There were reports of a global temperature maximum in 1994, and the almost uninterrupted existence of an “El-Nino” like hydrological effect. Satellite air surface layer temperature tracking [49,50] allowed the detection of a 0.22 degrees C global temperature variation (within a typical specific time period of about 30 days) that correlated with recorded middle frequency magnetic oscillations. The Earth’s temperature regime is becoming more, and more, dependent on external influences. [...]
There is a growing probability that we are moving into a rapid temperature instability period similar to the one that took place 10,000 years ago. This not so ancient major instability was revealed by the analysis of ice drilling core samples in Greenland . [...]
Such high-speed transformations of the global climatic mechanism parameters, and its effects on Earth’s physical and biospheric qualities has not yet been rigorously studied by the reigning scientific community. But, researchers are now insisting more, and more, that the Earth’s temperature increases are dependent upon, and directly linked to, space-terrestrial interactions [52,53]; be it Earth-Sun, Earth-Solar System, and/or Earth-Interstellar.
Source: Planetophysical State of The Earth and Life, By DR. ALEXEY N. DMITRIEV, Published in Russian, IICA Transactions, Volume 4, 1997, 1998 in English.
Giant leap: Kolkata to get its own space centre [INDIA]
Times of India, 7th January 2013
KOLKATA: The city is all set to score another scientific first in the middle of this year.
The central government is funding the Kolkata-based Indian Institute of Science, Education and Research (IISER) for setting up a Centre of Excellence in Space Sciences. IISER received a letter dated December 21, 2012, from the deputy secretary in the HRD ministry saying that it has been selected for the funding.
Speaking to TOI on Sunday, Dibyendu Nandi, who will be the coordinator of the space centre, said it will be first unit of its kind in West Bengal. “The cost of funding is about Rs 4 crore and is spread over a five-year period,” he said. The centre is expected to become opera-tional in the summer of 2013, he added. [...]
Nandi, who is involved with India’s maiden solar mission ‘Aditya’, said initially the centre will focus on space weather and supporting national astrophysics missions like ‘Aditya’ — provisionally slated for lift-off in 2016 — and the Laser Inter Ferro Metry Gravitational Observatory network in collaboration with a number of Indian scientific institutions and the US.
Explaining the importance of space weather, Nandi said it impacts our day-to-day lives like the operation of cellphones, GPS networks, electric grids and air traffic on polar routes. “It can also affect satellite operations and astronaut safety. Space weather will play an important role in our forthcoming mission to Mars to be lau-nched in October-November this year,” he said.
Comment: Another country setting up new space weather tracking facilities.
Oxford University Press Blog, 7th January 2013
We are all used to blaming things (rightly or wrongly) on the weather, but now it seems that this tendency has been extended to space weather. Space weather, for those who are uncertain, describes the effects that flares and other events on the Sun produce on Earth.
Consult many of the sites on the World Wide Web that are devoted to events on a particular day in history, and you will be told that on 16 August 1989, a geomagnetic storm caused the Toronto Stock Exchange to crash. The trouble is that this is an urban myth. The Toronto Stock Exchange did crash that day, but because of hardware and software failures, not because of a geomagnetic storm.
Comment: The Oxford University’s Storm Dunlop (what a name for meteorologist…) is a Fellow of both the Royal Astronomical Society and the Royal Meteorological Society, so we have someone with some pedigree providing a basic tutorial on space weather.
Al Gore’s Payday From Oil-Rich Qatar ‘Reeking With Irony’
Bloomberg News, 4th January 2013
Al Gore, who shared the 2007 Nobel Peace Prize for his fight against global warming, may gross about $70 million from the sale of his Current TV network to Al Jazeera, the cable channel funded in part by oil-rich Qatar.
Al Jazeera will pay about $500 million for Current TV, including the stake held by Gore, 64, according to two people with knowledge of the deal. The network is one of dozens of investments made by the former vice president since he lost the 2000 presidential race by a slim margin.
“It’s reeking with irony,” said Jeff Sonnenfeld, senior associate dean at the Yale School of Management, who studies corporate governance. “It seems to be at least a paradox in terms of his positions on sustainability and geopolitics.” [...]
“Many Americans are tired of borrowing huge amounts of money from China to buy huge amounts of oil from the Persian Gulf to make huge amounts of pollution that destroys the planet’s climate,” Gore said in September 2006 at the New York University School of Law. “Increasingly, Americans believe that we have to change every part of that pattern.”
Comment: Al Gore the zealous climate czar and hypocrite…. The Climate realists are laughing hysterically but I don’t have time to be amused…. See more headlines at Climate Depot . | <urn:uuid:250666d4-3d11-4c59-beb5-59d085d85a59> | 3.015625 | 1,757 | Content Listing | Science & Tech. | 38.294141 |
Glenn Chaple's observing basics: Blinded by the moonlight
December 2005: Bright moonlit skies hide fainter meteors, diminishing the visual impact of these cosmic fireworks.
December 1, 2005
|Would you attend a Fourth of July fireworks display if it were held at midday? Probably not. The midday Sun would all but obliterate the event. For a similar reason, skygazers tend to pass up meteor showers that occur around Full Moon. Bright moonlit skies hide fainter meteors, diminishing the visual impact of these cosmic fireworks. |
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Data Type Tips
The reserved words
smallint are a few names, taken from only two programming languages, that indicate a two-byte signed integer.
The names and storage mechanisms for various kinds of data have become as varied as the colors of leaves in New England in the fall. This really isn't so bad if you spend all your time programming in just one language. However, if you're like most developers, you are probably using a number of languages and technologies, which requires you to write code to convert data from one data type to another frequently.
Many developers for one reason or another resort to using variant data types, which can further complicate matters, require more CPU processing, and are usually abused. Variant data types definitely have their place but they are often abused. The fact is that a programmer should understand the strengths, weaknesses and implications of using any data type. One good example of where variants might be employed are functions specifically designed to accept and handle various types of data that might be passed into one or more variant parameters. One bad example of using variants would be to use them so frequently that language data type rules are effectively nullified.
You can ease data type complexity when writing conversions by using an apples to apples common reference point to describe data in much the same way that many countries with varied cultures and tongues have a common, standard language to speak. The benefit of designing your code around such an idea results in modular reusable code that makes sense and centralizes data conversion to one place.
The following data types are just commonplace subset of what is available and can store just about anything:
boolean true or false single-byte char unicode char unsigned integer 8 bit unsigned integer 16 bit unsigned integer 32 bit unsigned integer 64 bit signed integer 8 bit signed integer 16 bit signed integer 32 bit signed integer 64 bit float 32 bit double 64 bit string undetermined length string fixed length unicode string undetermined length unicode string fixed length unspecified binary object undetermined length
The trick is to write code to convert your various data types to your "common tongue" and alternately write code to convert them back. If you do this for the various systems in your organization, you will have a data-type conversion code base that can move data to and from every system you did this for. This will speed data conversion tremendously.
This same technique works for moving data to and from disparate database software, accounting SDK interfaces, CRM systems, and more.
Now, converting and moving complex data types such as record structures, linked lists, and database tables obviously complicates things. Nonetheless, the same principles apply. Whenever you create a staging area whose layout is well defined, like the data types listed above, and write code to move data into a structure from a given source as well as the mechanism to move it back, you create valuable programming opportunities.
To summarize, it's important to consider what each data type offers and their implications in the language they are used in. Additionally, when considering systems integrations where disparate technologies are in use, it is wise to know how data types map between the systems to prevent dataloss.
Most organizations are very aware of the fetters that vendor lock-in creates. By devising a common tongue for all your systems to speak in, you manufacture a powerful tool to loosen those bonds.
The details may be in the data, but the data is stored in your data types.
By Jason P Sage
This work is licensed under a Creative Commons Attribution 3
Back to 97 Things Every Programmer Should Know home page | <urn:uuid:6f06b2fd-2622-4760-8554-10b0aae16d0d> | 3.53125 | 721 | Knowledge Article | Software Dev. | 27.55854 |
Scientific Assessment of Ozone Depletion: 2002
The 2002 WMO/UNEP assessment, Scientific Assessment of Ozone Depletion: 2002, contains the most up-to-date understanding of ozone depletion at the time and reflects the thinking of 275 international scientific experts who contributed to its preparation and review. Co-chairs of the Assessment were Dr. Daniel L. Albritton of the NOAA Aeronomy Laboratory, Dr. Ayité-Lô Nohende Ajavon of the Université de Lomé, Dr. Gérard Mégie of the Centre National de la Recherche Scientifique, and Dr. Robert T. Watson of the World Bank. Other members of the Aeronomy Laboratory made substantial contributions to the report, serving as lead authors, co-authors, contributors, reviewers, coordinating editor, and editorial and computing support staff.
The Assessment consists of the Executive Summary, five detailed chapters and "Twenty Questions and Answers About the Ozone Layer", listed with the names of the Lead Authors:
Chapter 1. Controlled Substances and Other Source Gases Stephen A. Montzka and Paul J. Fraser
Chapter 2. Very Short-Lived Halogen and Sulfur Substances Malcolm K.W. Ko and Gilles Poulet
Chapter 3. Polar Stratospheric Ozone: Past and Future Paul A. Newman and John A. Pyle
Chapter 4. Global Ozone: Past and Future Martyn P. Chipperfield and William J. Randel
Chapter 5. Surface Ultraviolet Radiation: Past and Future James B. Kerr and Gunther Seckmeyer
Twenty Questions and Answers About the Ozone Layer David W. Fahey
Text of the Executive Summary
A full formatted copy of the Executive Summary
The Executive Summary gives a synopsis of major scientific findings of the five chapters of the full 2002 Assessment. This includes:
- Recent Major Findings and Current Scientific Understanding
- Additional Scientific Evidence and Related Information
- Implications for Policy Formulation
"Twenty Questions and Answers About the Ozone Layer"
In the 2002 Assessment, the international scientific community included this section to answer several of the general questions that are most frequently asked by students, the general public, and leaders in industry and government. A draft of this component of the 2002 Assessment was reviewed and discussed by the 74 scientists who attended the Panel Review Meeting for the 2002 report in June 2002. In addition, subsequent contributions, reviews, or comments were made by individuals listed on the publication's inside cover .
A full formatted copy of the "Twenty Questions and Answers About the Ozone Layer"
Individual components, including each question and associated figures:
- OZONE IN OUR ATMOSPHERE
- What is ozone and where is it in the atmosphere?
- How is ozone formed in the atmosphere?
- Why do we care about atmospheric ozone?
- Is total ozone uniform over the globe?
- How is ozone measured in the atmosphere?
- THE OZONE DEPLETION PROCESS
- What are the principal steps in stratospheric ozone depletion caused by human activities?
- What emissions from human activities lead to ozone depletion?
- What are the reactive halogen gases that destroy stratospheric ozone?
- What are the chlorine and bromine reactions that destroy stratospheric ozone?
- Why has an "ozone hole" appeared over Antarctica when ozone-depleting gases are present throughout the stratosphere?
- STRATOSPHERIC OZONE DEPLETION
- How severe is the depletion of the Antarctic ozone layer?
- Is there depletion of the Arctic ozone layer?
- How large is the depletion of the global ozone layer?
- Do changes in the Sun and volcanic eruptions affect the ozone layer?
- CONTROLLING OZONE-DEPLETING GASES
- Are there regulations on the production of ozone-depleting gases?
- Has the Montreal Protocol been successful in reducing ozone-depleting gases in the atmosphere?
- IMPLICATIONS OF OZONE DEPLETION
- Does depletion of the ozone layer increase ground-level ultraviolet radiation?
- Is depletion of the ozone layer the principal cause of climate change?
- STRATOSPHERIC OZONE IN THE FUTURE
- Understanding Stratospheric Ozone Depletion
- Heavier-Than-Air CFCs
- Global Ozone Dobson Network
- The Discovery of the Antarctic Ozone Hole
- Replacing the Loss of "Good" Ozone in the Stratosphere
List of International Authors, Contributors, and Reviewers of the 2002 Assessment
Hundreds of scientists from around the world write and review the periodic WMO/UNEP "state-of-the-science" assessments of ozone depletion; hundreds of additional scientists author the studies that are referenced within them. As a result, the WMO/UNEP assessments are truly "global" documents, reflecting the thinking of the international scientific community.
275 international scientists from the developed and developing world contributed to the preparation and review of the latest WMO/UNEP assessment, Scientific Assessment of Ozone Depletion: 2002. Listed are the names of those individuals and the supporting organizations and staff. | <urn:uuid:7daabc76-a2b6-4bbe-a045-09e441894f4c> | 2.734375 | 1,085 | Knowledge Article | Science & Tech. | 29.390418 |
Use this grid to shade the numbers in the way described. Which
numbers do you have left? Do you know what they are called?
Work out Tom's number from the answers he gives his friend. He will
only answer 'yes' or 'no'.
Use cubes to continue making the numbers from 7 to 20. Are they sticks, rectangles or squares?
Can you make square numbers by adding two prime numbers together?
Take the number 6 469 693 230 and divide it by the first ten prime
numbers and you'll find the most beautiful, most magic of all
numbers. What is it?
This problem is based on a code using two different prime numbers
less than 10. You'll need to multiply them together and shift the
alphabet forwards by the result. Can you decipher the code?
Using all ten cards from 0 to 9, rearrange them to make five prime
numbers. Can you find any other ways of doing it?
These two group activities use mathematical reasoning - one is
numerical, one geometric.
What happens if you join every second point on this circle? How
about every third point? Try with different steps and see if you
can predict what will happen.
Arrange the four number cards on the grid, according to the rules,
to make a diagonal, vertical or horizontal line.
A game in which players take it in turns to choose a number. Can you block your opponent?
Can you find just the right bubbles to hold your number?
Use the interactivities to complete these Venn diagrams. | <urn:uuid:bfeb29f8-d385-4f94-b4a7-c761f1483522> | 3.5 | 331 | Tutorial | Science & Tech. | 71.757906 |
This week’s visual illusion is related to Mach bands, and similar in some ways to the watercolor effect. It’s called the Craik-O’Brien-Cornsweet effect (or just the Cornsweet effect)1. This is the best example I’ve ever seen (from here):
What you should see is a dark square over a light square (almost white). Now take your finger and place it over the boundary between the two squares. What do you see? Two squares of the same color!
What’s going on here? Well, at the boundary between the two squares, the top one really is dark, and the bottom one really is white. The visual system seems to be taking the dark gray and white at the edges of the squares, and spreading it across them (sort of like the visual system spreads the boundary colors throughout the center of the watercolor effect figures), so that otherwise identical squares look very different. Here is a more traditional version2:
How this happens, exactly, is still a matter of contention, but most explanations do include our old friend the center-surround receptive field, working much as they do in perceiving Mach bands (see the post linked above). As with Mach bands, Dale Purves and his colleagues have argued that the Cornsweet effect is instead a result of the way our visual system is wired. Since the visual system is wired the way it is because of the normal properties of the visual environment it was built to interpret, it can be fooled when some properties of a stimulus mimic properties commonly found in the visual environment, while others don’t. If this explanation is true, then making Cornsweet effect stimuli look even more like ordinary visual scenes should enhance the Cornsweet effect, while making the stimuli look less like ordinary scenes should decrease the effect. Purves et al. (reference in footnote 2) tested this prediction in several ways, one of which was to change the orientation of the stimuli. I’ll let Purves et al. describe their reasoning to you:
Because humans evolved in an environment in which the primary source of illumination is usually from above (i.e., from the sun), the spatial arrangement of the same objects can look quite different when they are turned upside down. Thus, if the Cornsweet stimulus is rotated from its usual horizontal presentation such that the dark gradient is above and the light gradient below… the stimulus is more likely to have been generated by light from above (because the direction of the gradients is consistent with a doubly curved surface arranged in this way). If, on the other hand, the same stimulus is rotated 180°… this likelihood is diminished.
Accordingly, when the equiluminant territory adjoining the dark gradient is uppermost its surface is likely to be less reflective than that of the lower territory. The reason is that the possible sources of the stimulus include at some higher level of probability an object whose uppermost surface is better lit than the lower surface (as indicated in the cutaway view to the right of the stimulus). When two surfaces return the same amount of light to the eye and one is better lit than the other, the better lit surface will always have been the less reflective. Because the visual system, according to our theory, constructs percepts based on the relative probabilities of the possible sources of the stimulus, the statistical influence of this increased probability causes the uppermost of the two equiluminant adjoining surfaces to appear darker than the lower one. (p. 8547)
So, the Cornsweet effect should be much stronger when, at the boundary between the two squares, the dark color is on top and the lighter color on the bottom, than when the light color is on the top and the dark on the bottom. To see that this is the case, check out Purvis et al.’s stimuli:
Consistent with Purves et al.’s prediction, the effect should be stronger for the figure on the left than the one on the right. As with Mach bands then, it may turn out that our visual system is just perceiving these figures the way it is “designed” to, based on the statistical properties of its environment. Or, it could still turn out to be the case that the receptive fields on the retina and directly connected to those on the retina are being tricked by overlapping areas of differing brightness. Only further research will tell.
One thing is certain, though. No matter how many times we look at these figures knowing that they are the same color, some part of our visual system is going to be tricked, and we’re going to perceive one as being lighter than the other. When you think about it, that’s a little disturbing. No matter how much we know, we still can’t see the figures the way they actually are. Reality matters to the visual system only statistically.
1Cornsweet, T.N. (1970). Visual Perception. New York, NY: Academic Press.
2From Purves, D., Shimpi, A., Lotto, R.B. (1999). An empirical explanation of the Cornsweet effect. Journal of Neuroscience, 19, 8542-8551. | <urn:uuid:f6b375b4-e1a8-4798-9f68-627895cb6f82> | 3.71875 | 1,073 | Personal Blog | Science & Tech. | 53.387467 |
From Erlang Community
Matthias Lang, with important ideas from Brian Zhou
Why Cross Compile
Cross compiling means using one type of system to compile the Erlang runtime system for a different type of system. A typical example would be using an x86-based linux system to compile Erlang for an embedded MIPS CPU.
You usually cross compile when you want to run Erlang on a system which doesn't have its own development environment, i.e. no C compiler, libraries and make system.
In this howto, the term target means the system you want to run Erlang on when you're finished. The term build platform means the system you're using to compile the Erlang runtime system.
- A working C compiler and C libraries. Verify that it generates object files which run on the target, for instance by writing hello world. This howto assumes that your build platform is a unix or unix-like system.
- The autoconf tools.
- The Erlang/OTP source code, from erlang.org. The examples assume R10B-10.
- Some cross-compiling experience. If you've never cross-compiled before, it's probably worth starting with something a bit simpler than Erlang, just to get a feeling for how it's meant to work. One suggestion: busybox.
- Experience with native compiling Erlang. If you haven't built the Erlang runtime from source before, do that first, to get a feeling for how it's meant to work.
- A generous serving of gumption.
Unpack the source
Make a directory for the cross compiling work, say /usr/local/src/mips_erlang/ and untar the source distribution there.
Patch the configure script
A couple of small changes to the configure script supplied with the Erlang source makes cross compiling much easier. Take this patch:
--- configure.in.orig 2006-03-17 17:38:39.000000000 +0100 +++ configure.in 2006-03-17 17:29:23.000000000 +0100 @@ -1322,7 +1322,7 @@ exit(0); #endif } -], poll_works=true, poll_works=false, poll_works=false) +], poll_works=true, poll_works=false, poll_works=true) case $poll_works in true) AC_MSG_RESULT(ok) @@ -1365,7 +1365,12 @@ DED_CFLAGS="$DED_CFLAGS -fPIC" fi -DED_LD=ld +if test "x$LD" = x; then + DED_LD=ld +else + DED_LD=$LD +fi + DED_LD_FLAG_RUNTIME_LIBRARY_PATH="-R" STATIC_CFLAGS=""
and apply it in the erts/ directory in the source tree you just unpacked.
After applying the patch, you need to re-run autoconf to update the configure script:
cd erts autoconf configure.in > configure
Set environment variables for non-detectable features
In a native compile, the 'configure' script autodetects many settings by compiling and running small C programs. When cross compiling, this isn't possible, so you need to do some manual setup to override the autodetection:
export ac_cv_prog_javac_ver_1_2=no export ac_cv_c_bigendian=yes export ac_cv_func_setvbuf_reversed=no export ac_cv_func_mmap_fixed_mapped=yes export ac_cv_sizeof_long_long=8 export ac_cv_sizeof_off_t=8
The values of the variables above are correct for an AU1000 MIPS CPU running linux 2.4.x. They're probably not correct for your particular system. You need to manually figure out the right settings, i.e. is your system bigendian? How large is a long_long on your system? If you're not sure, write a short C program to find out, and run the C program on your target.
Set environment variables to set up the C compiler
Next, we need to set up the environment so that we use the right C compiler and related tools:
export PATH=$PATH:/usr/local/eldk31/usr/bin/ export CC=mips-linux-gcc export CXX=mips-linux-g++ export SHLIB_LD=mips-linux-gcc export LD=mips-linux-ld export AR=mips-linux-ar export RANLIB=mips-linux-ranlib export CROSS_COMPILE=mips_4KC- export CFLAGS=-Os
The above settings are correct for an Au1000 MIPS on linux target. Your settings are likely to be different.
Manually disable parts of HiPE
Some HiPE-related code attempts to run during the build process in spite of the --disable-hipe flag. The code fails because it expects the build host and target system to be the same.
A quick and dirty way to disable that is to manually edit erts/emulator/Makefile.in and kill HIPE_GENERATE. In addition, edit lib/Makefile and remove hipe from the OTHER_SUB_DIRECTORIES list.
Run the configure script
./configure --prefix=/tmp/cross_compiled --without-ssl --without-java --disable-hipe --host=mips-linux --build=i686-pc-linux-gnu
Assuming configure ran all the way through without failing, we're now ready to compile. At this point, it's worth spending five minutes manually browsing through 'config.h' and checking that everything looks reasonable. For instance, you can check that the endianness settings are correct for your system.
TARGET=mips-linux make noboot | cat > buildlog
The above will take a while. After it's done, you probably want to install the Erlang runtime somewhere. Become root, and then:
TARGET=mips-linux make install
There's one thing left to manually fix: the installed copy of the Erlang runtime will have some incorrect paths in it. Edit 'bin/erl' by hand to fix that.
The build system in Open Source Erlang includes some relatively unappetising support for cross compiling to a VxWorks target.
Matthias Lang realised that for "similar build and target systems", it was possible to run 'configure' natively on the build system, hack the resulting makefiles to take into account differences between the build and target and then compile using a cross compiler.
Brian Zhou then pointed out how to use manual overrides through environment variables to avoid much of the hacking.
The methods described in this article are used to cross-compile Erlang for Motorola MPC 860 PPC systems, Au1000 MIPS systems and NSLU2. | <urn:uuid:66ba41e8-733b-4bb6-be7a-2d366c8fe835> | 3.34375 | 1,520 | Tutorial | Software Dev. | 55.967516 |
The Medieval Warm Period in Greenland
Vinther, B.M., Jones, P.D., Briffa, K.R., Clausen, H.B., Andersen, K.K., Dahl-Jensen, D. and Johnsen, S.J. 2010. Climatic signals in multiple highly resolved stable isotope records from Greenland. Quaternary Science Reviews 29: 522-538.
Working with 20 ice core records from 14 different sites, all of which stretched at least 200 years back in time, as well as near-surface air temperature data from 13 locations along the southern and western coasts of Greenland that covered approximately the same time interval (1784-2005), plus a similar temperature data set from northwest Iceland (said by the authors to be employed "in order to have some data indicative of climate east of the Greenland ice sheet"), Vinther et al. proceeded to demonstrate that winter δ18O was "the best proxy for Greenland temperatures." Then, based on that determination and working with three longer ice core δ18O records (DYE-3, Crete and GRIP), they developed a temperature history that extended more than 1400 years back in time.
In examining the reconstructed temperature history, the seven scientists note that "temperatures during the warmest intervals of the Medieval Warm Period," which they defined as occurring "some 900 to 1300 years ago, "were as warm as or slightly warmer than present day Greenland temperatures [italics added]." As for what this finding implies, the researchers conditionally -- and rather amusingly -- state that further warming of present day Greenland climate "will result in temperature conditions that are warmer than anything seen in the past 1400 years." But, of course, their work more directly and unconditionally implies that late 20th-century and early 21st-century weather has not yet been warm enough to confer "unprecedented" status upon Greenland air temperatures. What is more, Vinther et al. readily admit that the independent "GRIP borehole temperature inversion suggests that central Greenland temperatures are still somewhat below the high temperatures that existed during the Medieval Warm Period." | <urn:uuid:f098cf46-1065-4445-b96e-78dd40a3b901> | 3.546875 | 434 | Academic Writing | Science & Tech. | 46.797285 |
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Comparatively Speaking: Arrow Symbols in Organic Chemistry*
By: Anthony J. O'Lenick Jr., Siltech LLC; and James Ashenhurst, PhD,
Posted: September 25, 2012
There are eight different types of arrows encountered in organic chemistry. Here is a little guide to them.
The Forward Arrow
This arrow, shown in Figure 1, is otherwise known as the “reaction arrow.” The purpose of this arrow is to show action. “BH3, then NaOH/H2O2″ might not seem like “action,” but alkene's double bond is being ripped asunder in order to form new bonds to boron and hydrogen. With the addition of H2O2, the bond to boron is replaced with one to oxygen. That is a eventful day in the life of an alkene. There isn’t any hard and fast rule about what is supposed to go above or below the arrow, although reagents tend to go above and solvents tend to go below. You’ll often see a sequence of reactions placed over the arrow and numbered “1) , 2), 3)," etc. These represent individual steps that could often be shown with individual arrows of their own, but they are placed in series here over the arrow to save space.
The Equilibrium Arrow
This arrow, shown in Figure 1, shows a reaction that is reversible, usually in the context where the reversibility is being highlighted (such as in a reaction mechanism). To further highlight the position of an equilibrium, occasionally one of the arrows is longer than the other, showing that the equilibrium favors the starting materials or products.
The Resonance arrow.
Not to be confused with the equilibrium arrow, this double-headed arrow (see Figure 2) shows two (or more) species that are resonance structures of each other. They differ in the arrangements of their electrons and nothing else. Although it’s a separate discussion, it’s important to note that the molecule *does not* shuffle back and forth between these forms, but instead the “true picture” of the molecule is a combination or hybrid of these structures.
The Dashed Arrow
This arrow, shown in Figure 2, is often used to show a speculative or theoretical transformation, where conditions might have yet to be discovered. Alternatively, in a test situation, it’s a way of visually depicting the question, “How would you do this?” | <urn:uuid:1c09fe32-a8f9-426a-bb2b-86c4fb511e90> | 3.765625 | 540 | Knowledge Article | Science & Tech. | 47.732002 |
Following up on earlier theoretical predictions, MIT researchers have now demonstrated experimentally the existence of a fundamentally new kind of magnetic behavior, adding to the two previously known states of magnetism.
Ferromagnetism — the simple magnetism of a bar magnet or compass needle — has been known for centuries. In a second type of magnetism, antiferromagnetism, the magnetic fields of the ions within a metal or alloy cancel each other out. In both cases, the materials become magnetic only when cooled below a certain critical temperature. The prediction and discovery of antiferromagnetism — the basis for the read heads in today’s computer hard disks — won Nobel Prizes in physics for Louis Neel in 1970 and for MIT professor emeritus Clifford Shull in 1994.
“We’re showing that there is a third fundamental state for magnetism,” says MIT professor of physics Young Lee. The experimental work showing the existence of this new state, called a quantum spin liquid (QSL), is reported in the journal Nature.
The QSL is a solid crystal, but its magnetic state is described as liquid: Unlike the other two kinds of magnetism, the magnetic orientations of the individual particles within it fluctuate constantly, resembling the constant motion of molecules within a true liquid.
There is no static order to the magnetic orientations, known as magnetic moments, within the material, Lee explains. “But there is a strong interaction between them, and due to quantum effects, they don’t lock in place,” he says.
Although it is extremely difficult to measure, or prove the existence, of this exotic state, Lee says, “this is one of the strongest experimental data sets out there that [does] this. What used to just be in theorists’ models is a real physical system."
Philip Anderson, a leading theorist, first proposed the concept in 1987, saying that this state could be relevant to high-temperature superconductors, Lee says. “Ever since then, physicists have wanted to make such a state,” he adds. “It’s only in the past few years that we’ve made progress.”
The material itself is a crystal of a mineral called herbertsmithite. Lee and his colleagues first succeeded in making a large, pure crystal of this material last year — a process that took 10 months — and have since been studying its properties in detail.
“This was a multidisciplinary collaboration, with physicists and chemists,” Lee explains. “You need both … to synthesize the material and study it with advanced physics techniques. Theorists were also crucial to this.”
Through its experiments, the team made a significant discovery, Lee says: They found a state with fractionalized excitations, which had been predicted by some theorists but was a highly controversial idea. While most matter has discrete quantum states whose changes are expressed as whole numbers, this QSL material exhibits fractional quantum states. In fact, the researchers found that these excited states, called spinons, form a continuum. This observation, they say in their Nature paper, is “a remarkable first.”
To measure this state, the team used a technique called neutron scattering, which is Lee’s specialty. To actually carry out the measurements, they used a neutron spectrometer at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md.
The results, Lee says, are “really strong evidence of this fractionalization” of the spin states. “That’s a fundamental theoretical prediction for spin liquids that we are seeing in a clear and detailed way for the first time.”
It may take a long time to translate this “very fundamental research” into practical applications, Lee says. The work could possibly lead to advances in data storage or communications, he says — perhaps using an exotic quantum phenomenon called long-range entanglement, in which two widely separated particles can instantaneously influence each other’s states. The findings could also bear on research into high-temperature superconductors, and could ultimately lead to new developments in that field, he says.
“We have to get a more comprehensive understanding of the big picture,” Lee says. “There is no theory that describes everything that we’re seeing.”
Subir Sachdev, a professor of physics at Harvard University who was not connected with this work, says that these findings, which have been anticipated for decades, “are very significant and open a new chapter in the study of quantum entanglement in many-body systems.” The detection of such states, he says, was an “exceptionally difficult task. Young Lee and his group brilliantly overcame these challenges in their beautiful experiment.”
This story is reprinted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source. | <urn:uuid:28215da7-450d-4f95-ad17-91a20212a66a> | 3.046875 | 1,048 | Truncated | Science & Tech. | 36.163308 |
Our "NanoTube" collection of informative and noteworthy videos
in the areas of nanosciences and nanotechnology
The world's smallest smiley
This atomic smiley is written on a Ag(111) surface by manipulating individual silver atoms extracted from the native surface with the STM-tip. It has a radius of 18 nm. It is probably the world smallest smiley. It is created for public outreach, especially for the kids to inspire nanoscience. The big smile of this smiley is generated by surface electron standing waves. Yes, at the nanoscale, the electron can behave not only as a particle but also as a wave, a famous phenomenon known as wave particle duality. That is why we can see the electrons as water waves here creating a big smile. | <urn:uuid:29e00745-3f99-4199-ac76-04902c07a02f> | 2.96875 | 161 | Truncated | Science & Tech. | 40.179286 |
South American Coati, Nasua nasua
The South American coati (Nasua nasua), also known as the ring-tailed coati, is native to South America. Its range is large and includes lowland tropical and subtropical habitats. The only South American country where this species does not occur is Chile. It can be found at elevations of up to 8,200 feet. This species is locally known as quati in the Portuguese language. It holds thirteen recognized subspecies.
The South American coati can reach an average body length between thirty-three and forty-four inches, with an average weight of up to sixteen pounds. Its tail is long, taking up nearly half of its body length. The coloring of this species can vary, and the rings found on the tail can be dark or light. Unlike its relative, the white-nosed coati, this species does not have a white nose.
The South American coati is active during the day, and can be found in trees or on the ground. Males are typically solitary, but females will gather groups known as bands, which consist of fifteen to thirty individuals. Because males differ in habit so much from females, they were once thought to be a separate species, and were given the name coatimundis. Neither males nor females hold a distinct territory. Females will communicate using soft whining vocalizations. When sounding an alarm, alerting other coatis to danger, a loud barking noise is emitted. After this call is made, the coatis will climb into the trees, dropping down soon after to scatter. Common predators of this species include jaguars, foxes, domesticated dogs, and jaguarundis, and they are also hunted by humans. The diet of this species consists mainly of fruit and invertebrates, but it will eat birds, eggs, and other small creatures.
The breeding season for the South American coati occurs when fruit is most abundant. Females will mate with many males, and after a pregnancy period of seventy-seven days, a litter between two and four young is born. Before giving birth, females will leave their group to raise their young, which can take up to six weeks. Once the young are weaned, they will return to the group with their mother. Females typically remain in their birth group, while males disperse at about three years of age. The average lifespan of this species is seven years in the wild and fourteen years in captivity. The South American coati appears on the IUCN Red List with a conservation status of “Least Concern.”
Image Caption: A young Ring Tailed Coati (Nasua nasua). Amiens Zoo. Credit: Vassil/Wikipedia | <urn:uuid:dab26050-2c9f-45c8-b3e5-2fecdfbf9525> | 3.765625 | 559 | Knowledge Article | Science & Tech. | 50.958333 |
May 6, 2002 Astronaut photography of the Earth from the International Space Station has achieved spatial resolutions of less than six meters, an analysis of more than 13,000 images has shown. This means scientists can use photographs taken from the space station to study changes that are occurring in very small features on the Earth's surface.
The results of this study are discussed in an article in the April 23 edition of the American Geophysical Union journal Eos Transactions.
"The sharpness of the photographs taken by the station astronauts surprised both them and the scientists on the ground," said Dr. Julie Robinson, lead author of the paper and a Lockheed Martin scientist in the Earth Sciences and Image Analysis Laboratory at NASA's Johnson Space Center in Houston. "It has really changed our view of how much detail humans can photograph from orbit."
The first three resident space station crews took 13,442 images of the Earth using digital still cameras, 35-mm cameras, 70-mm cameras and a variety of lenses. Crewmembers were able to produce higher-resolution photographs with the high-magnification lenses by learning to compensate for the relative motion of the Earth below while pointing cameras through a specially built window in the station's Destiny Laboratory.
"Astronauts now consciously track the ground when photographing the Earth," said Dr. Cynthia Evans, co-author of the paper and the manager of the Earth Sciences and Image Analysis Laboratory for Lockheed Martin Space Operations. "Their digital cameras provide instant feedback, allowing crewmembers to refine their tracking and focus techniques. Because each crew has demonstrated this capability, we can reliably plan for scientific studies that require more detailed imagery that might not otherwise be available to Earth Science researchers."
"Since the birth of the space program, astronaut photographs of the Earth have engaged the public," Robinson said. "Scientists also use these photographs as valuable records of the state of the Earth. With new digital technologies, and high-resolution capabilities, astronauts on the International Space Station continue to acquire Earth imagery that has scientific relevance."
A searchable database containing more than 30 years of astronaut photography is available on the Web at: http://eol.jsc.nasa.gov/sseop
Other social bookmarking and sharing tools:
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Note: If no author is given, the source is cited instead. | <urn:uuid:b3f3fa1d-5b7d-4923-bd98-c3bbb0241dc9> | 3.875 | 489 | Truncated | Science & Tech. | 36.442222 |
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The United States has been a space-faring nation for just over 50 years, ever since Alan Shepard's suborbital pop shot aboard Freedom 7 on May 5, 1961. In the following eight years, the US, and mankind, went from being earthbound to making the first lunar landing.
Projects Mercury, Gemini, and Apollo were followed by the longest lull in America's manned space program to date, but starting in 1981 with the maiden flight of Columbia, the space shuttle program became the stalwart backbone of America's manned space flight program. With the final planned shuttle mission only hours from its scheduled launch, we take a moment to look back at over 30 years of history, achievements, and tragic failures.
The Space Shuttle—solid rocket boosters, external tank, and orbiter stack—is one of (if not the most) complicated machine ever built. It is simply an engineering marvel, but the complexity comes at a cost. I recall hearing that the Saturn V moon rocket had over a million separate components; that meant even a 99.9 percent success rate for parts left over 1,000 parts to fail. The shuttle is far more complex than a conventional Saturn V; ponder the perfection needed to keep such a machine flying and spaceworthy.
Early estimates by managers at NASA put the risk of catastrophic failure during a mission at 1 in 100,000; engineers, on the other hand, put the estimate at 1 in 100. A study recently released using all the data available from 30 years of flights reveals that the danger was in fact much higher.
According to the report, the chances of catastrophic loss of craft and crew during the first nine flights was a pucker-inducing 1 in 9. Later flights and safety improvements decreased this risk to 1 in 90. Given these numbers, NASA statistically had a only a six percent chance of completing 25 flights without the loss of an astronaut crew!
Even given those dire odds, astronauts bravely took bold steps beyond the terrestrial confines in order to count themselves among the few in human history who have traveled to outer space. Many of them did so on the shuttle.
The Post-Apollo era
As Eugene Cernan stepped off the ground of the Taurus-Littrow valley and onto the ladder of the lunar module Challenger, he became the last man to step foot on another astronomical body. His mission, Apollo 17, took place in December 1972; 39 years later, we haven't left the confines of low Earth orbit again.
After the cancellation of Apollo, NASA used the leftover Saturn rockets to perform two classes of missions. First was the launch and manning of Skylab, America's first and only space station. Three manned missions were flown to Skylab in 1973 and 1974, allowing astronauts to live and work in the small space station for a total of 171 days. The last flight of Apollo was in July 1975, for the Apollo-Soyuz test project. While the Cold War simmered on earth, US astronauts and Russian cosmonauts met in orbit and shook hands above France.
But after the Apollo-Soyuz Test Project, NASA conducted no manned spaceflights until the first flight of the shuttle program six years later.
People started thinking about the craft that would become the Space Shuttle long before anyone set foot on the Moon. The idea of a spaceplane that would land horizontally has its foundations in the X-15 program of the 1950s, but serious discussion of a space shuttle began in 1969, when the National Aeronautics and Space Council met to discuss the direction of US manned spaceflight in a post-Apollo era. The council seriously considered four choices: a manned mission to Mars, further lunar missions and exploration, low earth orbit infrastructure (Earth-to-orbit shuttle and space station), and the disbanding of manned flight altogether.
The group decided on the construction of a low Earth orbit infrastructure. While this has brought numerous benefits, it has also trapped us in an awkward space-faring adolescence, with nowhere in particular to go. However, this decision left NASA with a number of goals and research avenues to pursue.
The first issue became what the primary focus should be: the construction of an orbital space station or the creation of a new launch platform? Even if the focus were to be a space station, questions remained about how to get the necessary parts to orbit.
One option was developing a new platform and building a space station over the course of many, many flights. An alternative was to continue building and using the existing Saturn V infrastructure—which could get the needed space station components to orbit in relatively few launches. In the end, the decision was made to go with a new, reusable launch platform. It was argued that, given enough launches, a reusable launch system would be the cheaper route.
Since the first days of Robert Goddard's liquid-fueled rockets, manned launch vehicles had followed a similar one-shot design. A powerful rocket, storing all its needed fuel to get to its destination—in one or multiple stages—would be discarded after its usefulness to the flight was over. Often, the only part to return to Earth in one piece was the crew module that kept the astronauts safe, and none of these were ever designed to be reused for spaceflight again. In the design of the space shuttle, the question became one of how reusable was it going to be?
In the end, the Shuttle design was a drastic departure from the multi-stage rockets of the prior NASA missions. The Space Shuttle is not a single vehicle; rather, it's what is referred to as the "stack": an external fuel tank (to keep the main craft's weight down and payload area up), a pair of reusable solid rocket boosters (chosen for their simpler design), and the orbital vehicle itself (a winged, lifting-body glider) powered by three liquid-fueled main engines. In this setup, both of the solid rocket boosters (SRBs) and the entire orbital vehicle were designed to be completely reusable.
In the 30+ years that the Shuttle program has been active, a total of five different spaceworthy orbiters—Columbia, Challenger, Discovery, Atlantis, and Endeavour—have been built and have flown over 130 missions. Those missions have included the construction of the International Space Station (ISS), which has fulfilled the second goal that the National Aeronautics and Space Council had chosen shortly after man first set foot on the Moon. | <urn:uuid:3cac1373-05f0-49db-a2f1-f003e8d4f9f0> | 3.59375 | 1,317 | Knowledge Article | Science & Tech. | 46.361382 |
Describe the phenomenon of natural radioactive decay
Describe alpha, beta and gamma radiation and their properties
In the same way that a rock at a top of hill is not stable and has “too much” potential energy and “wants” to get rid of it by rolling down the hill, the nucleus of an atom can become unstable, essentially this means that it has to much energy and wants to get rid of its energy. This can be due to the number of protons and neutrons in the nucleus. If there are too many protons (more than 83) then the atom is not stable no matter how many neutrons are added (there is some thought that huge stable atoms may be able to be created, but that’s another story). Neutrons hold the protons together, but neutrons themselves are not stable, an isolated neutron will decay in a short period of time, if the nucleus gets large and there is a larger number of neutrons then neutrons become more and more isolated from protons and thus can decay. If there are not enough neutrons then the protons will repel each other and result in an unstable nucleus. The nucleus can also be excited, much in the same way that electrons in orbit around the nucleus get excited.
When a nucleus is unstable it gets more stable or loses energy in many different ways. One of the ways is natural radioactivity decay, radioactive decay is a completely random process that is governed by the weak nuclear force. There are three main types of decay:
Alpha Decay – is the process in which the nucleus ejects an alpha particle which is a helium nucleus, 2 protons and 2 neutrons
Where a U-238 atom fissions into Th-234 and a Helium nucleus. Alpha particles with their typical kinetic energy of 5 MeV (that is ≈0.13% of their total energy, i.e. 110 TJ/kg), have a speed of 15,000 km/s. Alpha particles do not penetrate very far, they tend to lose their energy very quickly. This makes this not very dangerous to humans if the radioactive source is outside the body, the alpha particles will generally be stopped by the layer of dead skin. However if the source is inside the body, they become very dangerous. Radon gas is a common example of a dangerous alpha source. Alpha decay is governed by the strong nuclear force. Alpha particles have a large ionizing energy.
Beta Decay – There are two types of beta decay, positive and negative. Positive beta decay is the process by which a neutron decay into a proton and an electron. The neutron is made of three quarks, one up quark and two down quarks. One of the down quarks is converted to an up quark by the emission of a W boson… thus the quark changes flavor. Beta decay is governed by the weak nuclear force. The electron does not have enough energy to escape the pull of the positively charged nucleus (protons), so the electron must quantum mechanically tunnel out of the nucleus, that is it borrows energy to “jump” outside the nucleus then returns the energy and travels away from the nucleus with its initial energy. The emission of the electron is also accompanied by the emission of anti-electron-neutrino. Negative beta decay is given by the following equation:
Negative beta decay is the process by which a proton decays into a neutron and a positron and emits a electron neutrino. The mass of the neutron is greater than the mass of the proton. Therefore negative beta decay does not happen without an input of energy, the binding energy is lower in the original nucleus.
Beta particles are emitted at close to the speed of light and thus have a much great penetration ability and therefore more hazardous to humans, they have less ionizing energy than alpha particles.
Gamma Decay – Is the process by which an excited nucleus decays to a lower energy level, much in the same way that electrons can be excited and decay to lower orbitals and thus releasing energy in the form of light. In the case of the nucleus decaying to a lower energy level energy is still released in the form of an electromagnetic wave, but in this case which large amounts of energy, thus a gamma ray. Gamma rays are typically defined as photons with energy greater than 10 keV. Compare this to the maximum energy released by an electron transition in the hydrogen atom of 13.6 eV. Because of their high energy and no charge gamma rays can penetrate easily and can ionize, making them a significant danger to humans.
Describe the ionizing properties of radiation and its use in the detection of radiation
The Geiger-Muller tube and the ionization chamber are examples of such detection devices. Only a qualitative understanding of the operation of the devices is required.
A Geiger-Muller tube, the predecessor to the Geiger Counter. Is a tube filled with inert gas (helium, neon, etc…). Inside the tube is a cathode and an anode, that create a strong electric field in the tube. When the ionizing radiation enters the tube it has enough energy to strip electrons off the gas molecules (atoms) thus creating ions, the ions are accelerated by the electric field. As the ions are accelerated they gain enough energy to create more ions by collision, thus an avalanche of ions is created and a short pulse of current is generated. The current is detected and counted.
Explain why some nuclei are stable while others are unstable
Essentially there are either not enough neutrons to “glue” the protons together, thus the nucleus has an unstable balance of kinetic and potential energy, i.e. the protons are trying to get away from each other. There can be two many neutrons, so that neutrons are effectively isolated from protons. Neutrons are not stable by themselves, a free neutron, a neutron outside of a nucleus, has a half life of about 15 minutes. A third way that a nucleus can be unstable is if it simply has too much energy, its like the hyperactive kid in the back of the room…
Determine the atomic and mass numbers of the products of nuclear decay in a transformation or in a series of transformations.
Nuclear transformations or nuclear reactions are governed by three laws:
Conservation of charge – the total charge of a system can neither be increased nor decreased in a nuclear reaction.
Conservation of nucleons – the total number of nucleons in the interaction must remain unchanged.
Conservation of mass-energy – the total mass-energy of the system must remain unchanged in nuclear reaction.
State that radioactive decay is a random process and that the average rate of decay for a sample of radioactive isotope decreases exponentially with time.
Radioactive decay is a random process and that the average rate of decay for a sample of radioactive isotope decreases exponentially with time.
Hmm, that was hard.
Define the term half-life
Determine the half-life of a nuclide from a decay curve
Solve radioactive decay problems
The half life of a radioactive isotope is the length of time in which one-half of its unstable nuclei will decay.
So if you have one kilogram of a radioactive substance, after one half life you will have one-half kilogram of the substance and half a kilo of the decay products. After another half-life you will have one quarter of the original substance and three quarters of a kilo of the decay substances… as so on. This is weird it should bug you.
Its important to know and realize that radioactive decay is truly a random process and can only be described by the language of probability. After one half-life approximately half of the radioactive substance will decay it is very unlikely that it is exactly half. With large numbers this is not a problem, but if the sample was only 3 or 4 atoms then we would start to have problems predicting what will occur. The extreme would be a sample of 1 atom leading to some philosophical questions… See Schrödinger's cat.
One last term:
Activity – is the number of decays per second measured in Becquerel. More specifically 1 Bq = 1 nuclear decay per second (from comments below).
The half-life is the amount of time for half of the material to decay. Thus after one half-life there would be half as many decays occurring. So the amount of time that is required for the activity to drop in half is equal to the half life.
Looks like I somehow lost an example. Sorry. | <urn:uuid:4d4fd5ba-c69b-4a99-a27f-0653c92f07ef> | 4.125 | 1,776 | Content Listing | Science & Tech. | 44.553155 |
Rust, Steel, Heat, and Magnetism
We rusted some steel wool with bleach and vinegar as
catalyst. We removed the wool and drained the liquid through a coffee filter. We
tested the dried residue, which was no longer magnetic. We then heated it in a
spoon over a candle flame, which turned it black. It was magnetic
again. What was the process that "remagnetized" it?
Probably what you did is drive off some of the oxygen from the rust
(hematite or goethite) turning it into magnetite, which is black and
magnetic. The balanced chemical reaction starting with goethite would
12 FeO(OH) --> 4 Fe3O4 + 6 H2O + O2
That is the most realistic, since rust is generally hydrated. The
reaction is a little easier to balance from hematite:
6 Fe2O3 --> 4 Fe3O4 + O2
Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
Some oxides of iron are non-magnetic, others are magnetic.
Fe2O3 . nH2O (red rust) is definitely non-magnetic.
"Magnetite" mineral is an iron oxide about like hematite,
something like Fe2O3 . FeO. (aka Fe3O4)
FeO is blackish not red, and the mixes tend to be gray-black too.
Your residue lost all water and a little oxygen
and maybe also recrystallized while in the solid state,
to a form more appropriate to its new composition. .
Check out whether your estimated peak temperature, in degrees K,
was more than 1/3 to 1/2 of the melting point of Fe3O4, also in degK.
If so some recrystallization should be able to occur on the molecular
level, though perhaps not to crystals large enough to be visible.
It is possible the gasses in the candle flame helped chemically,
not just thermally, with some of the oxygen removal.
If the flame wrapped around the spoon on all sides,
it might create an oxygen-depleted or reducing atmosphere in the spoon.
Carbon monoxide, unburned wax fumes, and soot are all reducing agents
for the conversion of Fe2O3 to Fe3O4.
Click here to return to the Physics Archives
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Learn to Forecast
By Tiffany Means, About.com Guide
Weather maps are a visual way of communicating weather information at-a-glance. Knowing how to read them is an important forecasting skill.
- Weather Map Symbols
- Weather Fronts
- High Pressure Systems
- Low Pressure Systems
- Isobars - Lines of Constant Pressure
Before meteorologists issue a forecast, they must first get a general idea of what the atmosphere is doing. They do this by looking at and analyzing data from a variety of sources, like...
Build your personal forecast skills with these easy-to-remember techniques. | <urn:uuid:13aef15b-96bb-439d-b83e-fe0874e9af0c> | 3.375 | 127 | Tutorial | Science & Tech. | 43.434239 |
Where on Earth...? MISR Mystery Image Quiz #17
Here's another chance to play geographical detective! This natural-color image from the Multi-angle Imaging SpectroRadiometer (MISR) represents an area of about 372 kilometers x 425 kilometers, and was captured by the instrument's vertical-viewing (nadir) camera in December, 2000. Only some of the following 9 statements about the region shown are true.
This image highlights the Pampas of Argentina and spans more than 158,000 square kilometers over 3 Argentinean provinces - the southern parts of La Pampa and Buenos Aires and the northernmost part of Rio Negro. Answers to the 9 questions are below.
1. Of the two large smoke plumes rising from fires near image center, one is burning within 10 kilometers of a major gas pipeline.
False. The major gas pipeline (the Nueba II) connecting the gas field in Neuquen to the port city of Bahia Blanca runs almost parallel and quite close to the highway (apparent as a thin white line crossing the Rio Colorado from southwest to northeast) that connects the two cities. At its closest point, this pipeline is at least 50 kilometers away from either of the two smoke plumes.
2. The blue, green, and silver-colored lakes and lagoons, and the white salt-encrusted lakes and marshes that appear throughout the image area, are usually drier during winter and wetter in the summer.
Both True and False accepted. La Pampa and Buenos Aires provinces receive most rainfall during summer, when the long dry season is broken. However, some years are driest during the middle of summer. In the summer of 2000/2001, the rains were late and the region was dry until after mid-summer.
3. Agriculture in this region is devoted primarily to vegetable and fruit production.
False. The main agricultural products are livestock, forage and cereal crops, soybeans and oil seeds. Fruit and vegetable production does not predominate.
4. There are fewer trees and forests in the region today than there were 500 years ago.
False. The native grasslands of the Pampas are reknowned for the scarcity of trees. Although there has been forest loss in surrounding regions, and although much of the native vegetation of the Pampas has been replaced by modern agriculture and cattle ranching, there were no forests in the Pampas 500 years ago.
5. The fresh waters that feed the silver-colored lakes in the upper-right corner of the image are described as an aid to digestion in a 19th century novel by a French science fiction author.
True. The waters of a small brook that feeds this chain of lakes (the Rio Guamini) is praised in Jules Verne’s book "In Search of the Castaways."
6. The silver-colored area along the right-hand edge at image center is situated along the boundary of a city that was originally named for its white beaches.
True. The silver area corresponds with the outskirts of Bahia Blanca. The city was called “White Bay” because of its white, salt-encrusted shores that surround the bay. The bay and the city itself are not shown.
7. In the same year in which this image was acquired, a water contamination event occurred and residents of the aforementioned city were warned not to drink from the municipal water supply.
True. In April 2000 the city of Bahia Blanca warned its 420,000 residents to avoid using tap water because of the presence of toxic bacteria in the water at that time.
8. The dark blue lake apparent at left-hand edge of image center is named for its sweet waters and supports year-round commercial and sport fishing.
False. The dark blue lake, "La Dulce," is named for its fresh water, and there is sport and commercial fishing for "pejerrey," but there are long closed seasons, or "vedas," and commercial fishing is allowed only a few months of the year.
9. The waters of the river that ends in a large alluvial fan (situated near the right-hand edge below image center), are saltier than the waters of the river below it, which continues to flow beyond the right-hand image edge.
True. The river that ends in the large alluvial fan is the Rio Colorado, and the river below it is the Rio Negro. At times, the excessively salty waters of the Salado-Chadileuvu-Curaco river system contaminate the waters of the Rio Colorado.
87 people from all over the world sent in responses before the deadline. Although no one replied with correct answers to all 9 questions, individuals who gave correct answers to at least 7 questions are listed below. The prize winners are indicated by an asterisk.
Individuals who answered 8 questions correctly:
1. Monika Draga, Bad Kissingen, Germany
2. Yu Wei, Xiamen, China*
3. George Chaniot, Potter Valley, CA, USA*
4. Jim Armstrong, Potter Valley, CA, USA*
5. Doug Jackson, Arlington, VA, USA
6. Paul de Krock, Belgium
Individuals who answered 7 questions correctly:
1. Benjamin Steele, Oak Park, CA, USA
2. J.A, West Farmington, ME, USA
3. Kaz Hikida, Kamakura, Japan
4. Marion Florjancic, Crotone, Italy
5. Andrzej Szuksztul, Poland
MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.
Credit: Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
<< RETURN TO QUIZZES
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Rainbow-tinted slicks and globules of oil have been cropping up in the Gulf of Mexico during the past 10 days or so, and it’s not clear where it is all coming from. BP, whose Macondo well spewed 4.1 million barrels of oil into the Gulf last summer after the Deepwater Horizon disaster, has denied that the oil is coming from that well. But some scientists say it’s certainly possible.
A crack team of physicists, mining engineers and even a hydrogen bomb expert is the latest brain trust to tackle the Deepwater Horizon undersea oil disaster.
Energy Secretary Steven Chu hand-picked the five scientists, who each have experience in solving complex problems, to figure out how to stop the oil leak. He also wants them to come up with "plan B, C, D, E and F," Bloomberg reports.
Huge C-130 aircraft from the U.S. Air Force Reserve have joined the fight against the Deepwater Horizon oil slick, which now threatens to ravage the local ecosystems and fishing industry in the Gulf of Mexico.
The massive oil spill from a BP offshore drilling rig threatens marine ecosystems and fisheries as it makes its way to the shoreline. Here's how it looks from above.
The Macondo well is spilling 5,000 barrels of oil per day into the gulf, about five times more than well owner British Petroleum initially reported. Efforts to stem the leak using controlled burning and even undersea robots have been unsuccessful so far.
Sponge-like substance could help clean up oil spills
By Chris Sweeney
Posted 02.20.2009 at 12:54 pm 3 Comments
It’s no secret that cleaning up an oil spill is a difficult task. When most of us think of oil spills, we think of incidents like the Exxon Valdez accident, which released more than 10 million gallons of oil into the Prince William Sound in 1989. But what we don’t think about are the more than 200 million gallons of used oil that pollute U.S. wastewater every year after being dumped into sewers, streams and landfills.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more. | <urn:uuid:102d18d2-9e8e-4fa0-8eae-41022c4863d2> | 3.0625 | 491 | Content Listing | Science & Tech. | 64.382075 |
- Jul 10, 2008 Definition and other additional information on Peripatric speciation from Biology- Online.org dictionary.
- PERIPATRIC SPECIATION DRIVES DIVERSIFICATION AND
- PERIPATRIC SPECIATION IN REEF HERMITS. Jokiel and Martinelli 1992).
- Are there species – and why?
- SPECIATION / EVA KISDI / 2010 FALL / LECTURE 6. 1. Allopatric speciation in the lab.
- Phylogenetic comparative methods and the geography of speciation
- such as the suggestions that PERIPATRIC SPECIATION is relatively rare and that SYMPATRIC SPECIATION is surpris- ingly common [2,8,11,14,19].
- WHY ARE THERE SO MANY?
- Allopatric & Peripatric Speciation. Secondary contract: • behavioural adaptations that prevent them from mating.
- SYMPATRIC SPECIATION
- 17 Nov Lecture 35 - Species and Speciation. 19 Nov Lecture 36 - Species, allopatric speciation. 29 Nov Lecture 37 - Sympatric speciation.
- Peripatric speciation - Conservapedia
- Oct 24, 2008 Peripatric speciation is a version of the allopatric speciation mode and happens when one of the isolated populations has very few individuals.
Peripatric Speciation is described in multiple online sources, as addition to our editors' articles, see section below for printable documents, Peripatric Speciation books and related discussion.
Suggested Pdf Resources
Suggested News Resources
Suggested Web Resources
Great care has been taken to prepare the information on this page. Elements of the content come from factual and lexical knowledge databases, realmagick.com library and third-party sources. We appreciate your suggestions and comments on further improvements of the site.
Peripatric Speciation Topics
Related searchesyona kosashvili
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Ionizing radiation enters the detector chamber and ionizes the mixture of gas in it. The electrons drift towards the positive electrode and ions move towards the negative electrode. Thus, ampere meter detects a current.
The number of ion pairs is proportional to the number of ionizing particles entering the detector chamber. Thus, the current is proportional to the intensity of ionizing radiation.
The light electrons drift 100,000 times faster than the heavy ions. The motion of electrons is mostly responsible for the current.
Rutherford placed a thorium oxide (ThO2) sample directly in the detector chamber. He noticed that the radioactivity increased with time. After removing the sample carefully without changing the air in the chamber, he found the air remained radioactive. The radioactive air decayed with a specific half life. Other radioactive samples did not give the same observation. His experiment suggested the existence of a radioactive gaseous element. The experiment was later interpreted as due to the decay of Th ( , a) Ra ( , a) Rn. Several isotopes of thorium produce radon isotopes in their decays. Such a simple ionization chamber led to the discovery of a decay series.
. . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . .
At some hundreds volts, the improvement in sensitivity is more than collecting all the When voltages applied to electrodes of ionization chambers increase, the sensitivities increase. Electrons and ions on the electrode. The currents corresponding to multiples of ions and electrons produced by radioactivity. To distinct them from simple ionization chambers, these detectors are called proportional counters.
In proportional counters, the high voltage applied to the electrodes created a strong electric field, which accelerate electrons. The electrons, after having acquired the energy, ionize other molecules. Production of secondary ion pairs initiates an avalanche of ionization by every primary electron generated by radiation. Such a process is called gas multiplication.
The gas multiplication makes the detection much more sensitive. Yet, the current is still proportional to the number of primary ion pairs.
When voltages applied to proportional counters get still higher, sparks jump (arcs) between the two electrodes along the tracks of ionizing particles. These detectors are called spark chambers, which give internal amplification factors up to 1,000,000 times while still giving an initial signal proportional to the number of primary ion pairs.
The voltages depend on the mixture of gases in the detector chamber. At a high voltage, a single primary ion pair causes a spark to jump between the electrodes.
Every spark gives a pulse registered either accross the two electrodes of the chamber or accross the resister. Electronic means count the number of pulses. The counter can also be made to give an audible signal for each pulse.
The intensity of the pulse is related to the number of primary ion pairs, but we are often more interested in the number of ionizing particles entering the chamber.
Something about dead time has yet to be added.
If the source radiation is really strong, the Geiger counter may give a zero reading.
In a solid semiconductor, atoms are fixed in their locations. Electrons are tightly bound to atoms or chemical bonds.
At liquid nitrogen temperature, the number of carriers is dramatically reduced to almost zero. At low temperature, it is easier to distinguish signals due to electrons freed by radiation from those due to thermal carriers.
A P-N junction of semiconductors is placed under reverse bias, thus no current flows. Passage of ionizing radiation through the depleted region excites electrons into the conduction band, causing a temporary conduction which gives rise to a pulse corresponding to the number of excited electrons or energy entering the solid state.
The electronics used to analyze the pulses does more than counting. It separates the pulses into hundreds of groups called channels according to the pulse heights. Therefore, the equipment is often called multi-channel analyzer. When intensities of these channels are displayed according to their energies, the measurement gives a spectrum. A gamma-ray spectrum of 56Co measured using a solid state detector is shown here. The continuous background is due to Compton scattering. Single and double escape peaks (marked SEP and DEP) are also shown.
The output pulses from a scintillation counter are proportional to the energy of the radiation. Electronic devices have been built not only to detect the pulses, but also to measure the pulse heights. The measurements enable us to plot the intensity (number of pulses) versus energy (pulse height), yielding a spectrum of the source.
Photons striking a sodium iodide (NaI) crystal, which contains 0.5 mole percent of thallium iodide (TlI) as an activator, cause the emission of a short flash of light in the wavelength range of 3300-5000 A (in the ultraviolet region). The light flashes are detected by a photomultiply tube, which gives a pulse corresponding to the light intensity. These pulses are measured by a multi-channel counter.
J.J. Thomson used fluorescence screens to see electron tracks in cathode ray tubes. In 1895, R”ntgen saw the shadow of his skeleton on fluorescence screens. His screen was made of barium-platinocyanide. Rutherford observed alpha particle on scintillation material zinc sulfide, ZnS. Fluorescence screens are important detectors for ionizing radiation and high energy photons.
Fluorescence material absorbs invisible light and the energy excites the electron. De-exciting of these electrons results in the emission of visible light. By mixing different materials together, we have engineered many different fluorescence materials to emit lights of any desirable colors.
C.T.R. Wilson (1869-1959) perfected the cloud chamber, and the detector made the careers for many individuals. Rutherford once remarked that "the cloud chamber was the most original and wonderful instrument in scientific history."
Photographic films recorded the images of X-rays and radioactive decays leading to discoveries that changed the world of science and technology. | <urn:uuid:1eeda502-4a11-4b47-bcfa-98923b523a39> | 3.921875 | 1,258 | Knowledge Article | Science & Tech. | 39.7252 |
Science Fair Project Encyclopedia
Pheromone (honey bee)
Honey bee pheromones (Greek:“carrier of excitement”) are chemical substances released by individual bees into the hive or environment, which cause changes in the physiology and behaviour of other bees. Pheromones may be volatile or non-volatile. The pheromones are chemical messengers, secreted by a queen, drone or worker bee that elicits a response by another honey bee. The chemical messages are received by the bee's antenna and other body parts. Honey bee (Apis mellifera) pheromones can be grouped into pheromones with short term and long term effects.
1.1 Alarm pheromone
Short term effect pheromones
Short term effect pheromones are also called releaser pheromones. They trigger an almost immediate behavioral response from the receiving bee.
Released by the Koschevnikov gland, near the sting shaft, consisting of more than 40 chemical compounds including isopentyl acetate (IPA), butyl acetate, 1-hexanol], 1-butanol, 1-octanol , hexyl acetate, octyl acetate, n-pentyl acetate and 2-nonanol . The chemical compounds have low molecular weights, are highly volatile and appear to be the least specific of all pheromones. Alarm pheromone is released by worker bees to alert other bees of danger or when a bee stings another animal. This pheromone attracts other bees to the location and causes the other bees to behave defensively, i.e. sting or charge. Smoke can mask the bees alarm pheromone.
Brood recognition pheromone
One rarely finds evidence of a laying worker in a colony that still has live brood. Both larvae and pupae apparently emit Brood Recognition pheromone. In a colony it inhibits the ovarian development in worker bees. The brood recognition pheromone also helps nurse bees distinguish worker larvae, drone larvae and its pupae.
Drones produce a pheromone that attracts other flying drones to promote drone aggregations at sites suitable for mating with virgin queens.
Egg marking pheromone
Helps nurse bees distinguish between eggs layed by the queen bee and eggs layed by a laying worker.
These are left by bee feet when they walk and are useful in enhancing Nasonov pheromones in searching for nectar.
Oily secretion of the queen's tarsal glands that is deposited on the comb as the queen walks across them. Secretion diminishes as the queen ages, inhibits queen cell construction (thereby inhibiting swarming)
These are used for orientation and include different terpenoids including Geraniol, Nerolic acid , Citral and Geranic acid. Bees use these to find the entrance to their colony or hive, and they release them on flowers so other bees know which flowers have nectar. Synthetic Nasonov consisted of Citral and Geraniol in a 2:1 ratio.
Queen mandibular pheromone (QMP)
The QMP, emitted by the queen, is one of the most important pheromones in the bee hive. It effects social behavior, maintenance of the hive, swarming, mating behavior, and inhibition of ovary development in worker bees. The effects are short and long term. Some of the chemicals found in QMP are carboxylic acids and aromatic compounds.
- (E)-9-oxodec-2-enoic acid (9-ODA) - inhibits queen rearing as well as ovarian development in worker bees; strong sexual attractant for drones when on a nuptial flight; critical to worker recognition of the presence of a queen in the hive
- (R,E)-(-)-9-hydroxy-2-enoic acid (9-HDA) promotes stability of a swarm, or a "calming" influence
- Methyl-p-hydroxybenzoate (HOB)
- 4-hydroxy-3-methoxy phenylethanol (HVA)
- methyl (Z)-octadec-9-enoate (methyl oleate )
- (E)-3-(4-hydroxy-3-methoxyphenyl)-prop-2-en-1-ol (coniferyl alcohol )
- (Z9,Z12,Z15)-octadeca-9,12,15-trienoic acid (linolenic acid)
Synthetic queen mandibular pheromone (QMP) is a mixture of five components 9-ODA , (-) isomer (9-HDA), (+) isomer of (9-HDA), HOB and HVA in a ratio of 118:50:22:10:1.
Queen Retinue Pheromone (QRP)
Long term effect pheromones
These pheromones, which are also called primer pheromones exert relatively slow effects that fundamentally alter developmental, physiological, and neural systems.
Ethyl oleate is released by older forager bees to slow the maturing of nurse bees. This pheromone acts as a distributed regulator to keep the ratio of nurse bees to forager bees in the balance that is most beneficial to the hive. Primer pheromones are slow acting pheromones.
- Queen mandibular pheromone in apis mellifera accessed of the web Feb, 2005
- George Imrie's Pink Pages November 1999] accessed Feb. 2005
- Moritz, R.F.A. and H. Burgin. 1987. Group response to alarm pheromones in socialwasps and the honeybees. Ethology 76, 15-26
- Maschwitz, U. 1964. Alarm substances and alarm behavior in social Hymenoptera Nature 204, 324-327.
- Boch, R. and D.A. Shearer. 1971. Chemical releasers of alarm behaviour on the honey-bee, Apis mellifera. Journal of Insect Physiology 17, 2277-2285
- Butler, C. 1609. The Feminine Monarchie. On a Treatise Concerning Bees, and the Due Ordering of them. Joseph Barnes: Oxford.
- Vander Meer, R.K. et al. 1998. Pheromone Communication in Social Insects; Boulder: Westview Press
- Wager, B.R. and M.D. Breed. 2000. Does honeybee sting alarm pheromone give orientation information to defensive bees? Annals of the Entomological Society of America 93(6), 1329-1332
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:f7205931-4316-4837-b691-60a8ae4eddc9> | 3.765625 | 1,453 | Knowledge Article | Science & Tech. | 44.281991 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
February 11, 1997
Explanation: Astronaut Carl Walz waves at his colleagues from the aft end of the Space Shuttle Discovery's payload bay - during a 1993 spacewalk to evaluate tools, tethers, and a foot restraint slated for use in the first Hubble Space Telescope servicing mission. Today's successful launch of Discovery begins the second servicing mission to the Hubble. Discovery's crew will rendezvous with the orbiting telescope and capture it with the shuttle's manipulator arm. With Hubble in the payload bay the crew will conduct spacewalks to replace two existing instruments with new ones. To be installed are the Space Telescope Imaging Spectrograph and the Near Infrared Camera and Multi-Object Spectrometer. Other hardware will also be replaced and upgraded including the telescope's Fine Guidance Sensor. The improved instrumentation will extend the Hubble's ability to explore the distant Universe.
Authors & editors:
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U. | <urn:uuid:3b1be234-f565-43b6-a2dd-8d00a04f08fc> | 3.28125 | 245 | Knowledge Article | Science & Tech. | 36.327368 |
Cosmic timeline 08
Simulation of a super-symmetry event (showing leptons and missing transverse energy), with a Higgs particle decaying to two Z particles and to four muons in the full Compact Muon Solenoid detector. The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the proton-proton Large Hadron Collider (LHC) at CERN in Switzerland and France.
The Lepton Epoch
The lepton epoch is defined as the time between 1 second and 10 seconds after the Big Bang. The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons and anti-leptons dominating the mass of the universe.
What is a lepton?
Leptons are a family of elementary particles, alongside quarks and gauge bosons. The name lepton comes from the Greek λεπτός or leptos, meaning thin, and was first used by physicist Léon Rosenfeld in 1948. So the name implies that all the leptons are of small mass. The first lepton identified was the electron, discovered by J.J. Thomson and his team of British physicists in 1897. Then in 1930, Wolfgang Pauli postulated the electron neutrino. Before the muon was discovered by Carl D. Anderson in 1936, the electron neutrino was simply known as the neutrino, as it was not yet known that neutrinos came in different flavours (or different “generations”). Then the tauon was first detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl. Like quarks, leptons are fermions and are subject to the electromagnetic force, the gravitational force, and weak interaction, but unlike quarks, leptons do not participate in the strong interaction.
Approximately 10 seconds after the Big Bang the temperature of the universe falls to the point where new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons are eliminated in annihilation reactions, leaving a small residue of leptons.
So far our timeline pages have covered only the first 10 seconds of the Big Bang theory of the origins of our universe, but from this point the timeline of subsequent epochs begins to stretch for hundreds of thousands of years. | <urn:uuid:bac3810d-6d65-411b-b118-bdacd5667466> | 3.859375 | 506 | Knowledge Article | Science & Tech. | 43.760052 |
LocalTime = 41.5 - 2 * (SkyTime + Month)
Tillerman asked the question why is the constant 41.5?
Good question - but I'm not an astronomer, and haven't done these calculations before, but then that is what Wikipedia is for so here goes.
Firstly lets rearrange the equation so the constant which we'll call K (we maths types like short variables) is on one side:
K = LT + 2 * (ST + M)
We want is to derive are all the terms on the right and hence we can calculate K, but how?
So what do we know? Well lets start with the two stars Alpha Ursae Majoris and Beta Ursae Majoris, and Wikipedia gives their right ascension (RA) and declination. These are the astronomical equivalents of longitude and latitude respectively, and the RAs are very similar - which is what you'd expect for something that points at Polaris Its like two points with different latitude but the same longitude: you know that line is going to head up to the poles.
But how to match RA to longitude? Classically you'd use the equinox, when RA = long = 0 and the sun is due south from Greenwich, but that's no longer used as it doesn't include effects such as nutation, so now we need to consider J2000.
J2000 is the time reference used for most celestial mechanics applications and is referenced to 1st January 2000 at midday, 12:00 UT, or JD 2451545.0, and it is this frame that is used to define the RA of these two stars as around 11 hours.
To convert from RA to longitude we need the sidereal time equation:
GMST = 18.697 374 558 + 24.065 709 824 419 08 * D
Here D is Julian Date and everything is in hours, which is great, as that's the units that all the terms in the equation are in.
If we find a date at which the GMST is zero then the RA will be the same as the longitude and the constellations should look similar to the graphic above. I used the iPad app Red Shift with observer at London and time set so that theta should be zero, hence the two stars should be at longitude 11 hours, or in degrees 165E.
In the graphic above the up arrow goes over one's head (standing in London looking north) and then down the longitude = 0 line to the Antarctic. Meanwhile the down arrow is the other side of the Earth, going down the international date line.
The date and time that GMST is around zero around the spring equinox - to be more precise, using the equation above, around 36 seconds after noon on the 21st of March 2013. With our back to front clock the leading lights of the Plough are at a time of 11/2 + 6 = 11.5
The divide by 2 is because the sky clock goes round 12 sky hours to 24 on Earth and the + 6 because the zero line at the top is sky clock 6:
Hmm.... the projection here makes it look like those two stars don't line up with Polaris, but of course that's just an illusion.
So we know (rounding a bit):
ST = 11.5 hours
LT = 12 hours
But what is the month? Is it:
Month = 12 * Day / 365
That would be mathematically nice but not how non-maths types are likely to answer. If the month is March then the answer is 3, despite there being a 31 day range covered by a single integer.
To minimise error lets say that month = 3 is mid March, hence our reference date of 21st March is a little more than 3 - in fact Excel suggests 3.26 or so.
So we now know all three parameters and can plug them into our equation to work out the constant:
K = 41.58142726
That's reassuring close to the number we were looking for (or at least it is to me - I know there will be some that are hoping it would be either 42 or 43).
Does that sound plausible? | <urn:uuid:096e805d-b83a-48b2-89f1-03284c8685ec> | 2.921875 | 870 | Personal Blog | Science & Tech. | 74.235144 |
// C_ASSERT() can be used to perform many compile-time assertions: // type sizes, field offsets, etc. // An assertion failure results in error C2118: negative subscript. #define C_ASSERT(e) typedef char __C_ASSERT__[(e)?1:-1]
You might ask: How the hell does it work? Well, as the comments explain, it works by using a negative subscript (-1) in an array when the expressions to check for is false, which is of course invalid and will cause a compilation error, otherwise, if the expression is true, a positive subscript is used, which is alright. It does this by declaring (but not creating) an array with the size as the subscript.
Hope someone finds it useful. | <urn:uuid:e955acd0-6347-4d8e-85e9-d54e74c2582e> | 3.390625 | 163 | Comment Section | Software Dev. | 56.896786 |
||This article may require cleanup to meet Wikipedia's quality standards. The specific problem is: among other problems, it uses "we". (December 2007)|
||This article needs additional citations for verification. (July 2007)|
- This article is about artificial seismic sources. For natural seismic sources, see Earthquake, Volcano, and related articles.
A seismic source is a device that generates controlled seismic energy used to perform both reflection and refraction seismic surveys. A seismic source can be simple, such as dynamite, or it can use more sophisticated technology, such as a specialized air gun. Seismic sources can provide single pulses or continuous sweeps of energy. Both types of seismic sources generate seismic waves, which travel through a medium such as water or layers of rocks. Some of the waves then reflect and refract and is recorded by receivers, such as geophones or hydrophones.
Seismic sources may be used to investigate shallow subsoil structure, for engineering site characterisation, or to study deeper structures, usually in the search for petroleum or mineral deposits, or for scientific investigation. The returning signals from the sources are detected by seismic sensors (geophones or hydrophones), laid in known locations relative to the position of the source. The recorded signals are then subjected to specialist processing and interpretation to yield comprehensible data about the subsurface.
Source model
A seismic source signal has the following characteristics:
- generated as an impulsive source
- the generated waves are time-varying
The generalized equation that shows all above properties is:
where is the maximum frequency component of the generated waveform.
Types of sources
Explosives, such as dynamite, can be used as crude but effective sources of seismic energy. Generally the explosive charges are placed between 6 and 76 metres (20 and 250 ft) below ground. The charges are placed in a hole that is drilled with dedicated drilling equipment for this purpose. This type of seismic drilling is often referred to as "Shot Hole Drilling".
A common drill rig used for "Shot Hole Drilling" is the ARDCO C-1000 drill mounted on an ARDCO K 4X4 buggy. These drill rigs often use water or air in assisting the drilling.
Air gun
An air gun is used for marine reflection and refraction surveys. It consists of one or more pneumatic chambers that are pressurized with compressed air at pressures from 14 to 21 MPa (2,000 to 3,000 psi). The air gun array is submerged below the water surface, and is towed behind a ship. When the air gun is fired, a solenoid is triggered, which releases air into a fire chamber which in turn causes a piston to move, thereby allowing the air to escape the main chamber and to produce a pulse of acoustic energy. Air gun arrays are built up of up to 48 individual air guns with different size chambers, the aim being to create the optimum initial shock wave with minimum reverberation of the bubble after the first shot.
Gun arrays can be fired in flip-flop mode; typically this would be 48 guns per source, which would be selected and fired alternately. Large chambers (i.e., greater than 1.15 L or 70 cu in) tend to give low frequency signals, and the small chambers (less than 70 cubic inches) give higher frequency signals. The air gun is made from the highest grades of corrosion resistant stainless steel.
Plasma sound source
A plasma sound source (PSS), otherwise called a spark gap sound source, or simply a sparker, is a means of making very low frequency sonar pulse underwater.
For each firing, it stores electric charge in a large high-voltage bank of capacitors, and then releases all the stored energy in an arc across electrodes in the water. The underwater spark discharge produces a high-pressure plasma and vapor bubble, which expands and collapses, making a loud sound. Most of the sound produced is between 20 and 200 Hz.
Thumper truck
Dynamite was the only source used until 1953 when the weight dropping Thumper technique was introduced.
A thumper truck (or weight-drop) truck is a vehicle mounted ground impact which can be used to provide the seismic source. A heavy weight is raised by a hoist at the back of the truck and dropped, possibly about three metres, to impact (or "thump") the ground. To augment the signal, the weight may be dropped more than once at the same spot, the signal may also be increased by thumping at several nearby places in an array whose dimensions may be chosen to enhance the seismic signal by spatial filtering.
Thumping might be less damaging to the environment than firing explosives in shot-holes, though a heavily thumped seismic line with transverse ridges every few metres might create long-lasting disturbance of the soil. An advantage of the thumper (later shared with Vibroseis), especially in politically unstable areas, was that no explosives were required.
Thumper’s advanced technology what we call AWD "Accelerated Weight Drop" seismic energy source, where a high pressure gas (min 6.9 MPa (1,000 psi)) is used to accelerate a heavy weight Hammer (5,000 kg) to hit a base plate coupled from a distance of 2 to 3 m, which is coupled to the ground to generate an acoustic pulse. Several thumps were stacked to enhance signal to noise ratio.
The very basic assumption for choosing a seismic source are all satisfied by AWD as follows
1. Target Depth: Penetration of the required depth
2. Frequency Content of the seismic wavelet: Bandwidth for the required resolution
3. Strength: Signal to Noise ratio
4. Environment friendly
5. Economic:Availability and cost
It has been estimated that approximately 1% of the chemical energy of a small charge of dynamite is converted into useful P wave energy of the seismic signal. It is unknown how inefficient mechanical impulsive sources are in converting primary energy into useful seismic energy. To overcome these inefficiencies and obtain a higher amplitude of the seismic wavelet or increase the signal to noise ratio, it is usual to either
1) Increase the primary energy of the source (increase the dynamite from 1 to 10 kg, drop a weight from 2 meters instead of 1 meter), and/or
2) synchronize two or more sources to fire simultaneously, and/or
3) stack records sequentially
Each of these methods has trade-offs.
Electromagnetic Pulse Energy Source (Non-Explosive)
EMP sources based on the electrodynamic and electromagnetic principles.
Seismic vibrator
A Seismic vibrator propagates energy signals into the Earth over an extended period of time as opposed to the near instantaneous energy provided by impulsive sources. The data recorded in this way must be correlated to convert the extended source signal into an impulse. The source signal using this method was originally generated by a servo-controlled hydraulic vibrator or shaker unit mounted on a mobile base unit, but electro-mechanical versions have also been developed.
Boomer sources
Boomer sound sources are used for shallow water seismic surveys, mostly for engineering survey applications. Boomers are towed in a floating sled behind a survey vessel. Similarly to the plasma source, it stores energy in capacitors, but it discharges through a flat spiral coil instead of generating a spark. A copper plate adjacent to the coil flexes away from the coil as the capacitors are discharged. This flexing is transmitted into the water as the seismic pulse.
Originally the storage capacitors were placed in a steel container (the bang box) on the survey vessel. The high voltages used, typically 3,000 V, required heavy cables and strong safety containers. Recently, low voltage boomers have become available. These use capacitors on the towed sled, allowing efficient energy recovery, lower voltage power supplies and lighter cables. The low voltage systems are generally easier to deploy and have fewer safety concerns.
Noise sources
Correlation-based processing techniques also enable seismologists to image the interior of the Earth at multiple scales using natural (e.g., the oceanic microseism) or artificial (e.g., urban) background noise as a seismic source. For example, under ideal conditions of uniform seismic illumination, the correlation of the noise signals between two seismographs provides an estimate of the bidirectional seismic impulse response.
See also
- Crawford, J. M., Doty, W. E. N. and Lee, M. R., 1960, Continuous signal seismograph: Geophysics, Society of Exploration Geophysicists, 25, 95-105.
- Snieder, R., 2004, Extracting the Green's function from the correlation of coda waves: A derivation based on stationary phase, Phys. Rev. E., 69, 4, 046610.
- Seismic Wave Propagation Modeling and Inversion, Phil Bording
- Derivation of Seismic wave equation can be found here.
- Seismic Wave Propagation Modeling and Inversion, Phil Bording
- Sheriff R. E., 1991, Encyclopedic Dictionary of Exploration Geophysics, Society of Exploratino Geophysicists, Tulsa, 376p
- Jopling J. M., Forster P. D., Holland D. C. and Hale R. E., 2004, Low Voltage Seismic Sound Source, US Patent No 6771565
- Photos of Thumper trucks in action
- Arctic Refuge thumper trails
- Utah thumper trails
- Non-Lethal Swimmer Neutralization Study by The University of Texas, May 2002 page 42
- Vibroseis, Omnilaw International, a Texas Corporation | <urn:uuid:3bda26c8-826a-469e-bfa0-e9697d0a638c> | 3.4375 | 2,036 | Knowledge Article | Science & Tech. | 41.39122 |
The National Climatic Data Center released their monthly state of the climate for July. They note that “Higher-than-average temperatures engulfed much of the contiguous U.S. during July, with the largest temperature departures from the 20th century average occurring across most of the Plains, the Midwest, and along the Eastern Seaboard. Virginia had its warmest July on record, with a statewide temperature 4.0°F above average. In total, 32 states had July temperatures among its ten warmest, with seven states having their second warmest July on record.”
Of the 118 years on record, the warmth of this year is shown. Subtract the number shown on each state from 118 to find how many years had warmer July’s. Virginia’s 118 - 118 = none warmer; 2012 set the record. | <urn:uuid:813bb489-0b6a-47d6-91c7-105d70fe3a67> | 3.375 | 172 | Personal Blog | Science & Tech. | 57.274378 |
The device model/sysfs "class" subsystem is a mechanism which allows
different kernel subsystems to export device-independent interfaces to user
space. With a recent kernel, a number of interesting class hierarchies
can be found. For example, /sys/class/net
represents all of the
network interfaces in the system, /sys/class/sound
shows the audio
devices, and /sys/class/graphics
can be used to find frame
The class API has changed little since it was documented in this LWN driver porting article.
Kernel code registers a class structure to create a directory in
/sys/class, then populates it with class_device objects.
This API has worked for some time, but it has its limitations; it forces a
two-level class->device structure which is unable to represent all of
the relevant data structures in the kernel. For many class hierarchies,
such as the network device class tree shown in the diagram to the right,
two levels is sufficient. Other subsystems, however, have had trouble with
Consider, for example, the block subsystem, as represented by the
simplified diagram to the left. The block subsystem deals in block
devices, of course, and those are represented in the second layer of the
diagram. Each block device, however, can contain partitions, which are
(virtual) block devices in their own right. Putting all of those
partitions in the
top layer of the block class hierarchy would lose the relationship between
those partitions and the physical devices where they live; the deeper
hierarchy truly does make sense. There are also other
objects, such as the request queue, which need to be present in the class
tree. The fact that the class
subsystem cannot represent this structure is one of the reasons why the
block layer has its own sysfs subtree, under /sys/block, even
though it logically belongs under /sys/class.
This issue recently came to a head when Dmitry Torokhov reworked the input
subsystem to make use of sysfs. The input class tree also fails to
fit neatly into the class subsystem, though for slightly different
reasons. The input layer can export multiple interfaces to the same
device; a touch screen can show up as a serial device, as an event
generator, or as a mouse, for example. Even a straightforward mouse can
appear by itself, or as part of the multiplexed "mice" device.
As a way of representing the structure of the input subsystem, Dmitry
implemented a "subclass" mechanism. Various objections to the
implementation were raised, however, and Greg Kroah-Hartman went off to
design a solution he liked better. His patch has now been posted for
review; it is also part of the -mm tree.
Greg's solution does not involve subclasses at all; instead, the
class_device structure has acquired a new parent field.
The function which creates class_device structures has a new
struct class_device *class_device_create(struct class *cls,
struct class_device *parent,
struct device *device,
char *fmt, ...);
The parent argument is new. If it is non-NULL, the new
class_device will be placed under the parent class_device
in sysfs, rather than directly under the class itself. Needless to say,
this change breaks all users of the class subsystem; if it goes into the
mainline, all out-of-tree code using classes will have to be updated.
This interface should work reasonably well in the block case, where
partitions can truly be thought of as child devices. Dmitry is less pleased with it for the input subsystem,
however. He would like to be able to set up different hotplug handlers for
lower-level entries, but, since those handlers are set up at the class
level, an implementation without subclasses does not provide that
capability. There are other objections as well; the parent mechanism makes
it a little harder to set up the sort of hierarchy Dmitry would like to
create, for example.
As of this writing, there has been no further discussion of the interface.
There is a distinct chance that it could change before it makes its way
into the mainline. In one way or another, however, support for a deeper
/sys/class is likely to be merged.
to post comments) | <urn:uuid:58916509-2206-4d81-9cba-08bcbd37419c> | 2.71875 | 948 | Comment Section | Software Dev. | 45.812842 |
Dr. Paul Stanford departed from our recent lectures on applied mathematics and contest preparation to give our students a glimpse into the fascinating world of pure mathematics. Dr. Stanford is particularly skilled at teaching deep ideas without the need to resort to complex algebra, I’ll attempt in this recap to do his lecture a small bit of justice.
Dr. Stanford began with one of the simplest concepts, points on a plane and arrows connecting those points. Many of these arrows considered together and connecting a set of points yield all sorts of interesting directed graphs or “digraphs.“ This idea becomes more interesting when restrictions are imposed such as the rule that no two arrows can originate from the same point. When a sequence of arrows loop back upon themselves they form a shape like a “hairy circle” from the title of the lecture.
Dr. Stanford further restricted the cases with the following rules: no two arrows can connect to the same point and no symmetry is allowed. These restrictions yielded only four possibilities including those with only a single point connecting back on itself and the possibility of having no points or arrows at all.
Dr. Stanford then proceeded to show how basic arithmetic could be carried out in each of these four systems by shifting along the chains of arrows and by considering the very special case of the arrow that points back to its own origin.
In the second half of the lecture, Dr. Stanford built upon this foundation as he introduced the Collatz Problem:
Think of a number.
If it is even, divide by two.
Otherwise, triple it and add one.
Does this always reach one?
Dr. Stanford lead the students through multiple examples using positive integers, some of which filled both whiteboards but eventually came back to one. In fact Dr. Stanford told us that while this process always yields one for numbers from 1 to , nobody has proven that it is true of all positive integers! Dr. Stanford reminded the students that for mathematicians multiple examples are not “proof” and that numbers even as large as 23 thousand, trillion are not especially large to mathematicians.
However, when Dr. Stanford started the Collatz problem with negative integers, it was common that loops would appear. Drawn on the board, the chain of calculations was strangely similar to the hairy circles from the previous lecture. This lead to a discussion of how one could detect when loops appear in an algorithm. At this point the lecture began to bridge between pure mathematics and some real problems in computer science.
One method for detecting a loop would be to track and remember every point in the path but this would burden even the most powerful computer. A more clever method is the “tortoise and the hare” strategy. This involves sending two runners through the system, one moving twice as quickly as the other.
Dr. Stanford proved how this method would eventually prove the existence of a loop and how a second tortoise could confirm the exact point where the loop begins.
The two lectures formed an exciting and satisfying trip through the world of numbers. If I have misrepresented or ignored pertinent points from the lecture please feel free to mention them in the comments section below.
Read Full Post » | <urn:uuid:b5ef9212-5f78-47fc-84f0-bdc7a887257e> | 3.4375 | 649 | Personal Blog | Science & Tech. | 53.144471 |
Voyagers at the Termination Shock
Data from Voyager 1 and 2 was used to define our solar system's final frontier, a vast region at the edge of our solar system where the solar wind runs up against the thin gas between the stars.
Voyager 2 crossed the heliosheath boundary, called the solar wind termination shock, about 10 billion miles away from Voyager 1 and almost a billion miles closer to the sun. It confirmed that our solar system is "squashed" or "dented" -- that the bubble carved into interstellar space by the solar wind is not perfectly round.
Even though Voyager 2 is the second spacecraft to cross the shock, it is scientifically exciting for a couple of reasons. The Voyager 2 spacecraft has a working Plasma Science instrument that can directly measure the velocity, density and temperature of the solar wind. This instrument is no longer working on Voyager 1 and estimates of the solar wind speed had to be made indirectly. Secondly, Voyager 1 may have had only a single shock crossing and it happened during a data gap. But Voyager 2 had at least five shock crossings over a couple of days (the shock "sloshes" back and forth like surf on a beach, allowing multiple crossings) and three of them are clearly in the data. They show us an unusual shock.
In a normal shock wave, fast-moving material slows down and forms a denser, hotter region as it encounters an obstacle. However, Voyager 2 found a much lower temperature beyond the shock than was predicted. This probably indicates that the energy is being transferred to cosmic ray particles that were accelerated to high speeds at the shock.
Last Update: 27 Jun 2011 (AMB) | <urn:uuid:5d260d3c-786f-4d2b-abef-3e965ad59ceb> | 3.96875 | 341 | Knowledge Article | Science & Tech. | 50.79582 |
Science subject and location tags
Articles, documents and multimedia from ABC Science
Friday, 5 November 2010
A spacecraft has successfully conducted a close fly-by of the comet Hartley 2, providing the most extensive observations of a comet in history.
Thursday, 4 November 2010
StarStuff Podcast Discovery of a neutron star twice the size of our Sun causes a rethink by astronomers. Plus: lost generation of stars found in 'stellar jewel box'; and scientists trace our solar system's orbit through Milk Way.
Wednesday, 3 November 2010
Scientists may have a new tool to help them work out what sort of environment our solar system's been experiencing during its journey through our galaxy, the Milky Way.
Friday, 29 October 2010
Scientists have found a lost generation of stars in the galaxy's most densely populated stellar cities known as globular clusters.
Wednesday, 27 October 2010
StarStuff Podcast Astronomers detect over 13-billion-year-old galaxy. Plus: black hole formation theory goes bang; and more water than expected found on our Moon.
Friday, 22 October 2010
A head-on collision by a NASA spacecraft last year has confirmed the presence of confirmed significant quantities of water and frozen volatiles on the surface on the Moon, according to a series of new studies.
Thursday, 21 October 2010
StarStuff Podcast Asteroid passes 45,000 kilometres over Singapore. Plus: mysterious pulsar provides fresh clues about magnetic neutron stars; and galactic evolution revisited.
Friday, 15 October 2010
Astronomers may have to go back to the drawing board after the discovery of an unusual pulsar, which doesn't appear to be slowing down.
Wednesday, 13 October 2010
StarStuff Podcast Australian scientists discover galaxies from the distant past. Plus: Saturn's moon, Titan, holds ingredients of life; and NASA leads new mission to Mars.
Monday, 11 October 2010
The long lost lunar rover Lunokhod 1, has been rediscovered by astronomers using laser pulses, thirty-six years after it disappeared.
Wednesday, 6 October 2010
StarStuff Podcast StarStuff celebrates 500 episodes. Plus: first Earth-like planet discovered; mathematical theory predicts the end of the world; and China launches its second mission to the moon.
Wednesday, 29 September 2010
StarStuff Podcast New generation atomic clocks make Einstein's theory more relative. Plus: new phenomenon 'coreshine' discovered in star-forming nebula; and docking failure threatens cosmonauts.
Tuesday, 21 September 2010
StarStuff Podcast Moon's craters reveal its tortured past. Plus: Methane on Mars; and oldest-ever supermassive black holes detected.
Wednesday, 15 September 2010
StarStuff Podcast New telescope to study volcanoes on distant planets. Plus: evidence supports recent liquid water on Mars; and new clues about the origins of our solar system.
Friday, 10 September 2010
Scientists will soon be able to study volcanoes on worlds beyond our solar system, according to a new study. | <urn:uuid:1c5a5050-85fb-4ad7-8c3a-218477d3e23c> | 2.9375 | 616 | Content Listing | Science & Tech. | 42.585316 |
The 29 September 2009 Samoa Islands Tsunami: Simulations Based on the First Focal Mechanism Solutions and Implications on Tsunami Early Warning Strategies
The tsunamigenic earthquake (Mw = 8.1) that occurred on 29 September 2009 at 17:48 UTC offshore of the Samoa archipelago east of the Tonga trench represents an example of the so-called outer-rise earthquakes. The areas most affected were the south coasts of Western and American Samoa, where almost 200 people were killed and run-up heights were measured in excess of 5 m at several locations along the coast. Moreover, tide gauge records showed a maximum peak-to-peak height of about 3.5 m near Pago Pago (American Samoa) and of 1.5 m offshore of Apia (Western Samoa). In this work, different fault models based on the focal mechanism solutions proposed by Global CMT and by USGS immediately after the 2009 Samoan earthquake are tested by comparing the near-field recorded signals (three offshore DART buoys and two coastal tide gauges) and the synthetic signals provided by the numerical simulations. The analysis points out that there are lights and shadows, in the sense that none of the computed tsunamis agrees satisfactorily with all the considered signals, although some of them reproduce some of the records quite well. This partial agreement and partial disagreement are analysed in the perspective of tsunami forecast and of Tsunami Early Warning System strategy. | <urn:uuid:082494df-4059-4c4f-bc19-d9f2ae42f207> | 2.6875 | 296 | Academic Writing | Science & Tech. | 33.812222 |
This article shows how you can install Ruby on Rails (RoR) and integrate it in Apache2 on a Debian Etch system (including a short section at the end showing how to use RoR in a web site created with ISPConfig).
Read it at howtoforge
Ruby on Rails is a web application framework which is rapidly gaining popularity among web programmers. It aims to increase the speed and ease with which database-driven web sites can be created and offers skeleton code frameworks (scaffolding) from the outset. Applications using the RoR framework are developed using the Model-View-Controller design pattern. | <urn:uuid:c3486c26-e96a-483d-b573-d6b58cebad9d> | 2.921875 | 124 | Truncated | Software Dev. | 35.102 |
Found from Greenland to South America, the American eel is one of earthís most unique creatures, spending most of its life in freshwater, returning to the ocean to spawn, and undergoing amazing transformations in the process.
In the North Atlanticís Sargasso Sea, fertilized eggs float to the surface and hatch into small, transparent larvae. Over the next year, larval eel are transported and dispersed by the Gulf Stream along the East Coast. The transparent juveniles (glass eels) enter the Chesapeake from February to June, gradually becoming pigmented (elvers).
Moving into freshwater rivers and streams they become yellow eels and begin a 5- to 15-year growth phase. They swim and feed at night on insects, fish and other aquatic life. A slimy coat protects them from disease and their ability to absorb oxygen through their skin allows them to traverse barriers.
Each fall, sexually mature eels leave our Bay. Fat reserves fuel their long migration back to their birthplace, as they cease feeding. Mating occurs several thousand feet below the Sargassoís surface with females laying up to 10 million eggs. Although never witnessed, they are believed to die soon after their only spawn.
Illustration of American Eel (Anguilla rostrata)
For more information: | <urn:uuid:48ecd105-bd8a-4ed0-bd61-32d347d61b78> | 3.84375 | 263 | Knowledge Article | Science & Tech. | 44.124622 |
EarthNews Radio: Cultural Diversity
When we think of "biodiversity," we generally think about the varying plants and animals on the planet. However, there are different levels of biodiversity, including human cultural diversity.
Jerry Kay spoke to Dr. Healy Hamilton of the Center for Biodiversity Research and Information at the California Academy of Sciences.
Hamilton says that diversity includes the cultural diversity that is the history, language, and practices of a culture. Within the human species, our biodiversity includes written and oral traditions, and the different ways a culture might use plants and animals for medicine. We're losing this diversity, however.
This loss, happening at the rate of one culture per year, is tragic, says Hamilton. Biodiversity within the human species needs protection.
You can learn more about this and many other topics at the California Academy of Sciences website here: www.calacademy.org.
EarthNews Radio provides interesting information about science and the environment 90 seconds at a time. A number of Jerry Kay's interviews with scientists, environmentalists, and green-oriented businesspeople can be found here on ENN, on the homepage of EarthNews Radio. | <urn:uuid:bc38a639-8acc-43b2-8b7c-29be076d5be1> | 3.046875 | 238 | Truncated | Science & Tech. | 26.508986 |
Climate change hitting bird species, shows study
By Madeline Chambers
BONN, Germany (Reuters) - One in eight of the world's birds are at risk of extinction as climate change puts birds under great pressure, a leading conservation group warned on Monday.
The population of rare birds such as the Floreana mockingbird of the Galapagos Islands or the spoon-billed sandpiper, which breeds in northeastern Russia and winters in south Asia, has declined sharply and they could go extinct, the International Union for Conservation of Nature said in a report.
The 2008 "Red List for Birds" report, published on the first day of a May 19-30 U.N. conference about biodiversity in the German city of Bonn, said 1,226 species of bird were now threatened.
The annual report, closely watched among conservationists, added eight of the world's 10,000 bird species to the Critically Endangered category, the greatest level of threat.
"The latest update of the IUCN Red List shows that birds are under enormous pressure from climate change," said Jane Smart, head of the IUCN Species Programme. The IUCN groups governments, conservation groups and scientists.
Long-term drought and sudden extreme weather are putting additional stress on habitats that threatened species depend on, said the report, noting that extinction rates were rising on continents, rather than on islands where, historically, most extinctions have occurred.
Of the 26 species that moved category due to changes in their population size, rate of decline or range size, 24 were moved up to a higher level of threat.
They included the Eurasian curlew and Dartford warbler, which lives in Europe and north-west Africa. Both were previously in the "Least Threatened" category.
"We urge governments to take the information contained in (the report) seriously and do their level best to protect the world's birds," said Smart. The U.N. Climate Panel says that burning of fossil fuels is stoking global warming.
The report showed that Brazil and Indonesia had the highest number of threatened bird species with 141 and 133 respectively.
The group picked out several other species, including the Mallee emuwren in Australia which has suffered from years of drought and is seeing its population shrink sharply.
Its habitat has become so fragmented that a single bushfire could be catastrophic, said the report.
In the Galapagos Islands, the population of the Floreana mockingbird has fallen to fewer than 60 from an estimated 150 in 1996 and is now on the Critically Endangered list because the species is vulnerable to extreme weather.
The report also pointed to some species that had fared better as a result of conservation efforts, including the Marquesan Imperial-pigeon and the little spotted kiwi.
Around 4,000 delegates at the U.N. meeting of the Convention on Biodiversity will discuss ways to safeguard the range of species and try to slow the rate of extinctions among plants and animals.
(Editing by Ibon Villelabeitia) | <urn:uuid:9eb1d963-2813-4a6c-85f8-ce4abf7263ff> | 3.359375 | 632 | Truncated | Science & Tech. | 44.561011 |
m (+See also)
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Revision as of 05:58, 15 November 2011
Kinds classify types. Kinds are to types and type-constructors what types are to values.
Ordinary types have kind *. Type constructors have kind P -> Q, where P and Q are kinds. For instance:
Int :: * Maybe :: * -> * Maybe Bool :: * a -> a :: * :: * -> * (->) :: * -> * -> *
In Haskell 98, * is the only inhabited kind, that is, all values have types of kind *. GHC introduces another inhabited kind, #, for unboxed types. | <urn:uuid:f53bf120-c559-4132-bbe9-a811f4a17f3f> | 3.171875 | 144 | Documentation | Software Dev. | 66.74 |
This problem appeared in the Bafflers thread as exercise #2 and has some algebraic solutions.
A ship is sailing on a course from the origin. It follows the path y= 3.14 x. It has a speed of 1 / 3 units per second. A submarine is located at (5,0). The sub knows the ship is oblivious to its existence. The sub would like to torpedo the warship. Torpedoes travel at 1 / 2 units per second and travel in straight lines. The sub commander's hobby is mathematics. He fires and sinks the ship! What is the equation of the torpedoes flight?
One solution is to realize that what is required is triangle with one side being the line y = 3.14 x the base being the x axis from 0 to 5 and some line passing through (5,0) and intersecting y = 3.14 x. See fig 1. With the condition that the red line is 1.5 times longer than the other side of the triangle. Let's use Geogebra to solve the problem.
1)Draw the point (5,0) and call it Sub.
2)Enter in the input bar f(x) = 3.14 x
3)Place a slider on the drawing. Set it at Min=0 and Max = 10 with an increment of .1
It should be called a.
4)Enter (a,3.14*a) and call it Ship. Move the slider and you will see the point is constrained along y = 3.14 x.
5)Make a point at (0,0) and call it Start and hide it.
7) Set in options, rounding = 15 decimals, immediately you will see b = some value. That is the ratio of the torpedoes distance to the ships distance.
8)Move the slider using shift arrows until you get b = 1.497666014479171
9)Right click the top part of the slider to get the properties and set the increment to .01
Make sure you click the top part of the slider to select it after pressing close.
10)Press Shift left arrow until you get b = 1.499835795083569 and a = 1.038
11)Repeat 9 but set the increment to .001
12)Repeat the above loop always getting an answer as close to 1.5 as possible and slightly smaller.
I get b = 1.49999993088931 with an increment of 0.000001, how did you do?
13)Draw a line between Ship and Sub using the line tool and read off the equation of that line. I got
See the second drawing to check your work. | <urn:uuid:bcec40ed-45d8-437c-9dd9-a972e2ddfd28> | 3.453125 | 564 | Comment Section | Science & Tech. | 95.494185 |
Linear Pair Property,
Congruent Triangles (SAS,
The situation is represented in the diagram below:
|In this example, each of the roads leading up to the intersection is one block
long. We found earlier that the angles opposite each other in the intersection
have equal measure due to the Vertical Angle Theorem. Since the
sides have equal length and the included angles are the same, the two triangles
formed, Triangle ABC and Triangle EDC are congruent
by SAS. If you think about the Parallel Line Property,
congruency could also be proved by AAS and ASA...
Note that there is a footpath that extends from vertex C down
to segment DE (in the colored diagram). This footpath actually splits vertex C
into two equal angles. This would then be called an angle bisector.
We also note that in this case the footpath bisects segment DE
at a perpendicular angle. Consequently, the footpath could also be known as a
The Linear Pair Property (LPP) is shown above as well. The
LPP simply refers to a line that is intersected by another line and creates
two angles that add up to 180 degrees. For example, angles 6 and 7
form a linear pair. | <urn:uuid:59a118fe-ce53-43a5-b872-17957cbce57b> | 3.9375 | 265 | Academic Writing | Science & Tech. | 59.083622 |
The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Aftershocks are an extreme example of short-term earthquake clustering that appears to be quite distinct from the long-term regional clustering of large earthquakes discussed above. Aftershocks can temporarily increase the local seismicity rates to more than 10,000 times the pre-mainshock level. Although Coulomb stress interactions provide an explanation for many aftershock patterns, those models alone do not account for either the rates of seismicity that occur in response to the stress changes or the subsequent decay of rates inversely proportional to time, as expressed in Omori’s aftershock decay law (Equation 2.8). The most fully developed explanation for these and other properties of aftershocks is based on the rate- and state-dependent fault frictional properties observed in laboratory experiments (see Section 4.4). These frictional properties require that the initiation of earthquake slip (earthquake nucleation) be a delayed instability process in which the time of an earthquake is nonlinearly dependent on stress changes (35). This approach has resulted in a state-dependent model for earthquake rates that provides quantitative explanations for observed aftershock rates in response to a stress change, the Omori decay law, and various other features of aftershocks (Box 5.1).
Aftershocks can also be generated by dynamic stresses during the passage of seismic waves. At large epicentral distances, these transients are much greater than the static Coulomb stresses, although they act only over short intervals. Short-term dynamic loading was responsible for triggering seismicity across the western United States after the 1992 Landers, California earthquake (36). Immediately following the Landers earthquake, bursts of seismicity were observed at locations more than 1000 kilometers from the mainshock (Figure 5.2). The mechanisms for after-
BOX 5.1State-Dependent Seismicity
A physically based method for quantitative modeling of the relationships between stress changes and earthquake rates is provided by the rate- and state-dependent representation of fault friction. This approach treats seismicity as a sequence of earthquake nucleation events and specifically includes the time and stress dependence of the earthquake nucleation process as required by rate- and state-dependent friction. The result is a general state-dependent formulation for earthquake rates:1
where R is earthquake rate (in some magnitude interval), ? is a state variable, t is time, and S is Coulomb stress. The normalizing constant r is defined as the steady-state earthquake rate at the reference stressing rate . A is a dimensionless fault | <urn:uuid:f2a7187b-5734-47bd-88fb-6b8bee0ac469> | 3.25 | 558 | Academic Writing | Science & Tech. | 24.699701 |
05.07.13 - Join us on May 7 at 1 p.m. EDT for a video chat with Bill and Linda Hunt. They will answer student questions about NASA's Earth-observing satellites, which are used by scientists to study Earth's atmosphere.
05.05.13 - On the night of May 5, NASA meteor expert Bill Cooke answered your questions about the 2013 Eta Aquarid meteor shower.
04.04.13 - On April 4, 2013, Bonnie Buratti, Ph.D., principal investigator for several NASA projects, answered questions about the New Horizons mission, Pluto, and the Kuiper Belt.
03.14.13 - On March 14, 2013, Lou Mayo, a Planetary Scientist, answered student questions about the Sun-Earth connection and the effect of the projected increase in solar activity during the upcoming solar maximum.
02.22.13 - On Feb. 22, 2013, engineer Dave Pierce answered questions about engineering, engineering careers and the launching capabilities at Wallops Flight Facility.
02.05.13 - On Feb. 5, 2013, Dabney answered student questions about the Landsat launch and how it will affect what we know about Earth. He also described how his education has come in handy with his job.
01.24.13 - On Jan. 24 at 1 p.m. EST, students asked Dr. Mary Ann Meador questions about her discovery of aerogel and rod-coil block copolymers and about the uses for each.
The 2012 Geminid meteor shower is always a good show! On the night of Dec. 13-14, NASA astronomers answered your questions via live Web chat.
› Chat Transcript (PDF, 409 Kb)
12.07.12 - On Dec. 7,2012, Walter Bruce, a Senior Thermal Engineer at NASA of Langley Research Center, answered student questions about NASA's light-weight IRVE-3, an experiment of an inflatable thermal protection system for spacecraft.
12.05.12 - If you've ever wondered what it takes to test-fire a rocket engine, now is your chance. Make plans to join NASA experts on Dec. 5 for a Twitter chat.
Scientists believe meteorites may solve mysteries about our solar system. On Thursday, Nov. 8, NASA experts discussed why meteorites matter.
› Chat Transcript (PDF, 145 Kb)
11.29.12 - On Nov. 29, 2012, electro-optics engineer Julie Williams-Byrd addressed student questions about current and future technologies needed for human spaceflight exploration.
11.02.12 - Students tuned in on Nov. 2, 2012 for a special event with NASA's DLN and NES commemorating space shuttle Atlantis.
10.24.12 - On Oct. 24, 2012, Aerospace Engineer Nicole Smith answered student questions on Orion's Multi-Purpose Crew Vehicle, America's new spacecraft for human exploration.
The 2012 Orionid meteor shower peaked on the night of Oct. 20-21. NASA astronomers hosted an "Up All Night" Web chat.
› Chat Transcript (PDF, 212 Kb) | <urn:uuid:7379871b-4221-47af-ac3e-bffa1edf1cbc> | 2.75 | 649 | Content Listing | Science & Tech. | 77.921444 |
A version of this piece was originally commissioned by the Richard Dawkins Foundation for Science and Reason and also appears on their website RichardDawkins.net.
Read more: "LHC sees hint of lightweight Higgs boson"
As the world awaits news of the possible discovery of the Higgs boson, there remains a lot of confusion about what it is, why we have had to work hard to find it – and why we should care. Here's why.
First, the short answer:
If the Higgs is discovered, it will represent perhaps one of the greatest triumphs of the human intellect in recent memory, vindicating the construction of one of science's greatest theories and the most complicated machine ever built. That's the good news.
But if the Higgs is all that is found at the Large Hadron Collider (LHC), a huge amount will remain to be discovered. Crucial experimental guidance that physicists need to understand fundamental questions about our existence – from whether all four forces in nature are unified in some grand theory to determining what may have caused the big bang – will still be absent. Answering these questions may be beyond our technical and financial capabilities in this generation.
Now for the long answer:
If our ideas about the Higgs boson turn out to be correct, then everything we see is a kind of window dressing based on an underlying fabric of reality in which we shouldn't exist. The particles that make us up – which bind together to form protons, neutrons, nuclei and ultimately atoms – have mass. Without the Higgs, these particles would be massless, like photons.
We all know from our own experience that how heavy something feels depends on where it is located. For example, objects that are heavy on land appear lighter in water. Similarly, if you try to push a spoon through treacle it appears heavier than if you push it through air.
The standard model of particle physics implies that there is a "Higgs field" that permeates all space. This field interacts with particles, and does so with varying strengths. Particles that interact more strongly experience more resistance to their motion and appear heavier. Some particles, such as photons, do not interact with the field at all and remain massless.
In this way, the mass of everything is determined by the existence of the field, and mass is an accident of our circumstances because we exist in a universe in which such a background field happens to have arisen.
Playing subatomic catch
But why a Higgs particle? Relativity tells us that no signal can travel faster than light. Incorporating this into quantum mechanics tells us that forces which we think of as being due to fields are actually transmitted between objects by the exchange of particles. The way particles transmit forces is a bit like a game of catch: if I throw a ball and you catch it, I will be pushed backwards by the act of throwing and you will be pushed backwards by the act of catching. Thus we act as if we repel each other.
So if there is a Higgs field, it turns out that there has to be a particle associated with this field, and this is the Higgs particle.
This seems a fanciful framework, rather like imagining angels on the head of a pin. What would drive scientists to imagine such a scenario? One of the greatest successes of the past 50 years was the unification of two of the forces of nature: electromagnetism and the weak interaction. In this "electroweak" theory, electromagnetic forces arise by the long-range exchange of massless photons, and the short-range weak force is due to the exchange of massive particles called W and Z particles, predicted in the 1960s and discovered in the 1980s at CERN, the European particle physics laboratory near Geneva, Switzerland, which is now the home of the LHC.
In order for this theoretical unification to make mathematical sense, all three particles have to be massless in the underlying theory, and therefore the forces they mediate would be almost identical. Only if the W and Z particles obtain a mass by interacting with a background field – the Higgs field – will the underlying unified theory explain why the two forces appear different at the scales we measure them today, while remaining mathematically consistent.
Theory suggests that the mass of a Higgs particle should be about 100 times the mass of the proton; however, the exact mass is not predicted.
For over 25 years since the discovery of the W and Z particles, experimental physicists have been trying to build particle accelerators with the energy necessary to produce a Higgs particle, if it exists. The Tevatron accelerator at Fermilab in Batavia, Illinois, was able to reach up to about 120 times the mass of the proton (about 120 gigaelectronvolts) but did not find the Higgs.
The LHC was designed to probe for Higgs masses heavier than this. If the Higgs particle is announced with a mass of 125 GeV, as the rumours suggest, it will be the crown jewel of our theoretical understanding of the electroweak unified theory, our own origins and the origin of almost all mass we measure in the universe.
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Wed Dec 14 03:37:03 GMT 2011 by Torvince
One of the most interesting, well explained, yet concise, science article i've read in some time. Thanks.
Thu Jul 05 14:06:27 BST 2012 by adiousir
What is not explained is the correspondence between inertial mass - how hard something is to accelerate - and gravitational mass - how much a massive particle attracts another massive particle.
I would like to know if the Higgs field addresses this or, as it has so far been explained to my understanding, only addresses inertial mass.
I Am Far From Convinced That The Higgs Has Been Discovered
Sun Dec 25 22:21:32 GMT 2011 by Julian Mann
I agree with Lawrence that a Higgs discovery at 125 GeV would require a heavier partner perhaps the apparent discovery at 140 GeV. However it looks like this second Higgs has fallen away(despite the 3 Sigma tag) and that we are left with just the 125 GeV. Also it looks like it would not be correct to combine the results of Atlas and CMS(to give 3 Sigma) as both experiments used the same background shape parameterizations. Had the experimenters chosen different ones, I agree it would be more reasonable to combine both data sets and derive a higher Sigma. As it is, I believe that both results so far stand on their own, and their significance is greatly reduced as a result.
Even if there is confirmation of a particle during the coming year at 125 GeV, it could be something else(I have seen suggested elsewhere that it could be a quark) particularly if there is no evidence for a super-partner.
Fri Jul 06 23:48:39 BST 2012 by Eric Kvaalen
I can't make sense of this sentence: "Indeed, other arguments suggest that we need new physics to explain why quantum mechanical effects should not make this scale of masses is not much higher."
And then there's this: "...mass is an accident of our circumstances because we exist in a universe in which such a background field happens to have arisen."
Happens to have arisen? Isn't it a law of physics, if it exists?
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A lists of FAQs about quantum computing including information on quantum computers, entanglement and cryptography.
Popular physics author Brian Clegg explains the basics of quantum entanglement and its applications for quantum computers and teleportation.
A comprehensive guide to quantum entanglement and its implications for quantum computing, teleportation and cryptography.
Amazing demonstration of quantum levitation by Tel Aviv University's quantum levitation group.
Really useful guide to all aspects of quantum mechanics.
This is the introduction page to various sections on quantum topics.
Comprehensive site aimed at high school student learning about quantum phenomena. Excellent!!
News from New Scientist on the topic of quantum.
Good clear article from the National Geographic on quantum teleportation, including its use in cryptography.
A useful introduction to a range of modern quantum mechanics principles with many animations and examples of everyday situations.
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Updated at 9:22 pm on 3 August 2010
A census of marine life has found there could be tens of thousands of unidentified marine species in New Zealand's waters.
The census, conducted over a 10-year period, is the largest global research programme to be undertaken on marine biodiversity.
The lead author of the research, Mark Costello, says the National Institute of Water and Atmospheric Research has listed more than 12,000 species.
Dr Costello, an Associate Professor of Marine Ecology at Auckland University, says the census found there are about 4000 un-named species and a further 17,000 still to be discovered.
Scientists expect to eventually name the unknown species using imaging technology previously not available.
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Help on using online audio: formats, software, podcasts, downloading, and troubleshooting. | <urn:uuid:b5a6962f-ea19-4420-b2fa-9ca9ac026c35> | 2.78125 | 280 | Truncated | Science & Tech. | 43.953541 |
More In This Article
On the morning of January 7, 2010, a bright orange ship, squat and round-bellied, passed the northern tip of the Antarctic Peninsula. The Nathaniel B. Palmer, a 94-meter research icebreaker serving the U.S. National Science Foundation, had chugged southward for three days since leaving port in Punta Arenas, Chile, at the southern tip of South America. It had weathered a roller coaster of 8- to 12-meter sea swells, and winds over 100 kilometers per hour, as it crossed the Drake Passage between South America and Antarctica. The ship, with two dozen scientists on board, had come to investigate the effects of climate change on the thawing peninsula.
The Antarctic Peninsula has warmed by more than 2 degrees Celsius in recent decades—four times faster than other parts of the planet. This heating has triggered a dramatic series of glacial ice collapses: since 1980, over 5,000 square kilometers of floating glacial ice, 200 to 300 meters thick, has crumbled into the ocean. Those floating ice shelves had helped to stabilize glaciers behind them on land, slowing the glaciers’ flow into the sea. But with the ice shelves gone, the glaciers have accelerated into the ocean, speeding up by 2- to 9-fold.
The scientists on board the Palmer planned to investigate the mechanisms of those collapses. They also hoped to put the sudden, recent changes into a broader context, by reconstructing the history of ice shelves and glaciers in this part of Antarctica since the close of the last ice age, roughly 12,000 years ago.
As the Palmer sailed along the peninsula, multi-beam sonars on its underside fired chirps into the water—audible on every deck, in every cabin, every few seconds, day and night. Those pings painted a swath of orange-yellow-green across a computer monitor in a crowded laboratory on Deck 1—a topographic map of the ocean floor, with colors representing different depths. The swaths of color revealed undersea canyons that human eyes have never witnessed—deep grooves, 1,000 meters down, that glaciers had carved as they advanced outward from the Antarctic coast over the seafloor during the Ice Age.
Another set of sonars, operating at different frequencies that would penetrate the seafloor, returned images of the layers of sediment that have accumulated over the millennia in certain areas. Those layers held a record of glacial activity: coarse gravels deposited as a glacier 1,000 meters thick slithered over the ocean floor; finer muds laid down after the glacier retreated but the area was still shaded by a floating ice shelf 300 meters thick; and finally, layers of mud rich in ancient diatoms, microscopic organisms deposited after the ice shelf retreated and allowed sunlight to pierce cold, open water between the seasonal freezing of ice to about a meter thick.
In places where the sonar showed especially thick layers of sediment, the ship stopped. A crane swung over its rear deck, 1,000 meters of cable was spooled into the water and a core of that sediment was extracted from the ocean floor.
When a core was laid out on the laboratory on Deck 1, Eugene Domack, a marine geologist with Hamilton College, examined it, centimeter by centimeter with an eyepiece, to document its sequence of layers. Stefanie Brachfeld, a geologist from Montclair State University, analyzed the magnetic orientations of microscopic mineral grains in the sample. This sequence of changing orientations, which track movements in Earth's magnetic poles over thousands of years, would help to document the age of the sediment layers in places where organic carbon was too sparse to allow carbon 14 dating. A team of paleobiologists also sampled the microscopic shells of ancient organisms in the core for clues about the changing climate. | <urn:uuid:78bc5d9d-76f0-48a5-a826-c53362f9b198> | 3.875 | 787 | Truncated | Science & Tech. | 37.678819 |
Green Tree Python
Facts about this animal
This is an arboreal python, with a length of 1,5 - 1,8 m. It has a slender, laterally compressed body. Its head is diamond shaped and as in other pythons, the head scales are irregular, numerous and finely granular. The head also is much wider than and appears disproportional to the width of the body They have three thermosensory pits wirthin the upper and five to seven within the lower labials. These thermosensory (heat sensitive) pits help them notice changes in temperature, with which they are able to detect infra-red heat from warm-blooded prey. Their pupil is vertical. Adult green tree pythons have – irrespective of where they come from – different colours and patterns. There exist brilliant leaf-green specimens, but also individuals with yellow-green spots and even blue ones. Often, they are distinguished by a broken, vertebral stripe of white or yellow that runs down their back. Also, there may be flecks of blue, white, and yellow scattered over the body. This color pattern is a helpful tool in minimizing predation, as they tend to blend well with trees and bushes in which they rest. The underside is cream-white to yellow. Young animals are bright yellow or red, but also brick-red or brow-red with broken stripes and spots. They change colours at 6 to 12 months. Adults have a strong dentition with teeth up to 2 cm. That is the reason in addition to their particular position when resting in trees (see below) for the belief that birds – held fast with these long teeth - would be the main part of their prey. Indeed green tree pythons have a particular way of resting in the branches of trees: they loop a coil or two over the horizontal branches in a saddle position and place their head in the middle. And indeed C. viridis have a very interesting, confirmed method of luring their food to them: While lying very still on a branch they dangle their tail. When the prey, curious about the wiggling tail, gets close enough, they strike. Prey is captured by holding onto a branch using the prehensile tail and striking out from an s-shape position. But although they spend almost their entire life in the treetops, they are not exclusively tree-dwellers and can on rare occasions also be observed on the ground in particular at night. In fact evidence shows that they actively ground forage at night and sleep during the day. However they do not wander far. Like most snakes also the green tree python remains true to its site as long as there is enough food. Evidence has shown- contrary to belief – that they eat predominantly reptiles and small mammals (including such that live exclusively on ground). Despite many references in the literature, their diet, according to recent findings does not include birds. Though it has been reported to have taken place in all months of the year, the reproductive cycle occurs most frequently in the fall and winter months (September to October). After reaching sexual maturity (app. 2 years) they are looking for a sexual partner. If the female meets several males, several matings are possible with different partners. Copulation occurs when the pelvic spurs, which are found in both males and females, are used to anchor the male genital organs to the female cloaca. The male has two intromittant organs, called hemipenes but only one is engaged during mating. After successfully mating the females stop eating and are looking for a nesting site, predominantly hollows situated high in trees, but also other hidden sites that offer protection from enemies and enough humidity will be accepted. However in captivity, the female must have an elevated nesting box or the eggs will drop to the ground. The 5 – 35 eggs are deposited after 70 to 90 days (i.e. usually in February to March). The size of the clutch depends upon the size and age of the female. Like most python species also the green tree python protects and incubates its eggs. The female wraps her body around them and uses muscular shivers as a means of keeping or even increasing her body temperature, thus producing and keeping an incubation temperature of 29,5 o Celsius. If the temperature is too high she losens the body loops. On average, hatching occurs 45-65 days after the eggs are deposited. Since in principle matings, egg depositions and hatchings may happen any time of the year in this “non seasonal snake” this means that young can be seen any time of the year. They are about 30 cm long and have, as mentioned, very striking colours unlike from those of adults.
An extraordinary and most spectacular phenomenon in the animal kingdom is the change of colour in the young (“ontogenetic colour change”), as it is known also from some other snake species. When hatching, the colour of the young green tree pythons is a brilliant yellow, red or brown-red. Hatchlings from the same clutch may have different colours. At the age of six to twelve months their colour changes into the typical green. This colour change can be completed within a few days or a few weeks but can also last up to 2 or 3 years (in particular in specimens from Biak) and takes place completely independently from moulting. Green tree pythons from Biak change colour only to a certain extent. Adult specimens from this region often have still a significant portion of yellow colour, what makes them particularly attractive. The colour change seems also not to be influenced by the amount of food intake: Animals of the same clutch changed colours at the same time although some of them had eaten significantly less than others or even had to be force fed. Also other external stimuli do not seem to affect the colour change. The colour of the hatchlings gives no clue for the extent and intensity of the green colouration when adult. Indeed the mechanism for this colour change is not fully understood yet. Really remarkable is the fact that the young of the equally arboreal emerald tree boa (Corallus caninus) from Central and South America, which could, as adults, easily be mistaken for a green tree python (see below) also change their colour in their first year of life. Interestingly enough, also adult green tree pythons can still change colour: During ovulation females can become lighter coloured and during the gestation they can become slightly bluish. This bluish colour may persist after deposition of the eggs. Therefore “blue” adults are usually older females that have produce offspring several times and blue males can be found only very rarely.
The green tree python has a striking resemblance to the emerald tree boa (Corallus caninus) from South and Central America, with which it could be mixed up easily. Through adaptation to their very similar habitats and ways of life in different parts of the world these two Boidae species have become deceptively similar in their appearance. They therefore represent one of the most impressive examples of convergence in the world of snakes. “Convergence” or parallel evolution means a very similar design of the exterior through natural selection in not closely related species. Chondropython viridis is a representative of the Pythoninae, while Corallus caninus is a representative of the Boinae. However though the resemblance in appearance and behavior is strong, there are significant differences as well. At closer examination it can be seen that Chondropython viridis has very small granular scales on the top of its head, while the scales on top of the head of Corallus caninus are significantly bigger and have developed into shields. Also the labial pits are more distictive in Corallus caninus: 9 to 13 are between the scales of the upper lip (Supralabialia) and 11 to 16 between the scales of the lower lip (Infralabialia). While with Chondropython viridis fewer pits are within these scales not beween them. Corallus caninus grows to a larger size than Chondropython viridis. And last but not least Corallus caninus, like other boas bears live young, whereas like all other python species, C. viridis is oviparous.
Did you know?
The natives of Papua New Guinea call the green tree python „Jamumong“ and on the Indonesian part of the island some tribes call it „Ular hijau“. Both names, freely translated mean “green snake”. Its earlier denomination Chondropython viridis was derived from the greek words „kohndros“ meaning „with a rough surface“ and „puthon“, which means „snake-like dragon“ in the greek mythology. The species denomination „viridis“ means simply „green“.
|Name (Scientific)||Morelia viridis|
|Name (English)||Green Tree Python|
|Name (French)||Python arboricole vert australien|
|Name (German)||Grüner Baumpython|
|Name (Spanish)||Pitón arborícola verde|
|CITES Status||Appendix II|
|CMS Status||Not listed|
Photo Copyright by
Micha L. Rieser
|Range||Australia (Cape York), Indonesia (Misool, Salawati, Aru Islands, Schouten Islands , most of Western New Guinea) Papua New Guinea (including nearby islands)|
|Habitat||Morelia viridis inhabits tropical jungles, bamboo thickets, rain forests, and monsoon forests where vegetation is thick and the climate is very humid (80-95% humidity) and warm (28-35oC), from sea level up to 2000 m asl. It can be found however also at forest margins and in secondary growth, bushes and shrubs, occasionally even in gardens and hedges that surround buildings. As its name says, it is primarily an arboreal snake and can be found mostly in trees as high as 30 meters above ground, but occasionally also on ground.|
|Wild population||The largest threat to the species is habitat destruction, particularly in the Indonesian (western) part of New Guinea, which is being logged by the Indonesian government, but also hunting for food and for a limited skin trade.| | <urn:uuid:76095949-0845-4a6e-8af2-84a66a448899> | 3.9375 | 2,159 | Knowledge Article | Science & Tech. | 43.985994 |
Microformats give us the opportunity to add more machine-readable semantic value to HTML documents using structures with standardized class names.
So more precisely, what are microformats - Microformats? Microformats are a way of thinking about data, design principles for formats, highly correlated with semantic XHTML, a set of simple open data format standards that a diverse community of individuals and organizations are actively developing and implementing for more/better structured blogging and web microcontent publishing in general and much more. It is a way to write code and markup that a Bot should like and as such have the potential to improve your SE ranking.
2. An example: http://microformats.org/wiki/hcard
hCard is a simple, open, distributed format for representing people, companies, organizations, and places, using a 1:1 representation of vCard (RFC2426) properties and values in semantic HTML or XHTML. hCard is one of several open microformat standards suitable for embedding in HTML, XHTML, Atom, RSS, and arbitrary XML.
3. Microformats and SEO
How microformats affect search engine optimization ( SEO ) - USWeb Blog - Internet and Search Engine Marketing Blog
"So if you haven’t heard by now there is this new term called microformats spreading like crazy across the net. At first it can seem overly confusing but when digging into the heart of the matter the exact opposite is true. So what are microformats? Microformats are sets of simple data formats built for today’s technology (XHTML mostly) to solve simple problems. To speak in plain English a Microformat in most cases is a set of XHTML code embedded in web pages that provides a structured set of data that can be utilized for other means".
Googling for microformats - Joost de Valk's SEO Blog
"Imagine, you can type in a query like "joost de valk class:vcard" and Google comes up with my contact page, because that has a vcard class in it's markup, the main class of the hCard microformat. This was suggested today on the uf-discuss mailing list, a mailing list I've been lurking on for quite a while now, and it made me go "YES! That's what I want!"."
This is definitely a standard that has the potential to improve the SERP's.
4. SEO tools
SEO Goodies | Tag Cloud tool, SEO Keyword Discovery Tool, SEO Books
5. Dan Webb's Sumo Java Script parser.
Parsing microformats is difficult, but Dan Webb has written one parser:
For more information see: | <urn:uuid:8b620fad-68f1-4f6d-8224-e4295ed6b4d0> | 3.1875 | 559 | Comment Section | Software Dev. | 48.725509 |
Quantum mechanics is a realm of weirdness: electrons being linked to each other even though the vastness of the universe might separate them, things being in two places at once, and, of course, knowledge precluding knowledge. This last is the standard bearer of quantum oddity: measuring the momentum of an object precludes precise knowledge of where that object is. But I think I have found something that is stranger than them all.
Researchers have suggested that it might be possible to make measurements that trick a photon into thinking it is, in fact, a crowd of photons.
Let's imagine that we want to introduce a phase shift to one single photon through a control photon. A phase shift is basically a time delay. In traditional optics this delay is applied through high-intensity light beams: a high intensity pulse can modify the refractive index of the medium through which it propagates. Our signal photon traveling through that medium will see that different refractive index and either be delayed or sped up.
The problem is that we want to do this all with single photons, and just one photon does not fit the definition of high intensity.
It seems a bit hopeless, right? However, in quantum mechanics, things are not all that they seem. One type of measurement in particular—called a weak measurement—can give very strange results. For instance, if you measure the spin of an electron using a weak measurement, you can be reasonably certain that you haven't disturbed the spin state of the electron, but, you might get a strange value. Electrons only take on spin values of +1/2 or -1/2, but a weak measurement could return something like 100. So, under the right circumstances, that single electron can behave as if it had the spin effect of 200 electrons.
In our case, we're using two photons. A single control photon goes through a beam splitter where it gets the choice of going through the medium with a signal photon—the one we want to phase shift—or go through a separate channel. These paths are then recombined at another beam splitter, but this beam splitter isn't quite balanced. In a perfectly balanced splitter, the control photon will always exit the beam splitter in the same direction, called the bright port. In an unbalanced beam splitter, it's possible for a photon to sometimes head off in a different direction, called the dark port.
When you calculate the possible ways that a photon could hit a detector looking at the dark port, one of them is that there are simply more photons traveling through the medium with the signal photon than on the path outside the medium. Even better, the closer to balanced the detector is, the rarer the clicks on the detector for the dark port are. So, to get a click, you need a much larger number of photons in the medium with the signal photon. Even if you know you only send in one photon at a time.
In other words, we are measuring the number of photons, but getting an answer that is wrong by several orders of magnitude. The truly weird thing: nature believes us rather than reality.
If we make a weak measurement on the number of photons in the control photon beam, then a single photon is misreported as several hundred. And, if everything is set up correctly—which, in this case, means that we only look for phase shifts on the signal photon when the dark port detector clicks—that lone control photon will have a much larger effect on the refractive index of the medium. The end result is that the phase of the signal photon is shifted by lot more than would normally be expected.
The catch is that this is a work of theory. And the phase shifts, even with this amplification factor, may be really small. Even so, I can imagine that if you chose your medium correctly (say an alkali metal gas), and your wavelengths correctly (right on the edge of an absorption feature of the gas), then it might well be possible to observe the amplification of the phase shift.
Like the Bell inequalities and entanglement, we will have to wait before this can be tested. But, unlike some quantum phenomena, it won't be decades from theory to experiment.
Physical Review Letters, 2011, DOI: 10.1103/PhysRevLett.107.133603 | <urn:uuid:cdd5ae32-3034-4b6e-b134-0ce5f52b9869> | 3.09375 | 884 | Nonfiction Writing | Science & Tech. | 53.461047 |
Nital is a name and is a solution of alcohol and nitric acid commonly used for routine etching of metals. It is especially suitable for revealing the microstructure of carbon steels. The alcohol can be methanol, ethanol or methylated spirits.
Mixtures of ethanol and nitric acid are potentially explosive. This commonly occurs by gas evolution, although ethyl nitrate can also be formed. Methanol is not liable to explosion but it is toxic.
A solution of ethanol and nitric acid will become explosive if the concentration of nitric acid reaches over 10% (by weight). Solutions above 5% should not be stored in closed containers. Nitric acid will continue to act as an oxidant in dilute and cold conditions. | <urn:uuid:e57a32c2-246e-4e9c-8e96-6974d958df5b> | 2.828125 | 152 | Knowledge Article | Science & Tech. | 35.286154 |
PLANT SCIENCE: Enhanced: The Right Time and Place for Making Flowers -- Blázquez 309 (5737): 1024 -- Science:
Reproductive success in plants depends on the synchronization of flowering within a given species. Many plants have developed a highly complex signaling network that monitors environmental conditions, such as day length, temperature, or nutrient availability, and determines the appropriate timing for flowering (1, 2). This is the case for the model plant Arabidopsis thaliana and the pea that both flower in spring when day length and ambient temperature increase, or certain rice varieties and soybean that flower early in the fall when days get shorter. The initiation of flowering requires an additional developmental program to specify the floral identity of the new structures that continuously arise at the shoot apex (3). For instance, during the long vegetative phase in Arabidopsis, every primordium, the groups of cells poised to differentiate, forms a leaf. However, once the decision to flower has been made, all newly emerging primordia follow a developmental program that culminates in the formation of flowers rather than leaves. Thus, constructing a flower requires both temporal and spatial information that restricts the initiation of flowering to specific locations. But how this information is integrated has not been clear. Three studies now reveal the molecular mechanism by which this integration is achieved. In this issue, Abe et al. on page 1052 (4) and Wigge et al. on page 1056 (5) report that interaction between Flowering Locus T (FT), a protein encoded by a gene that is expressed in leaves, and FD, a bZIP transcription factor that is present only in the shoot apex, triggers the expression of floral identity genes in the new primordia. The third paper by Huang et al. in this week's Science Express (6) reports how the two factors meet--FT transcript travels from leaf to shoot via the plant vascular tissue.
Common descent reveals the way flowers form. | <urn:uuid:52f7cef3-5412-4f0e-ab4f-530cb730a7dd> | 3.21875 | 402 | Personal Blog | Science & Tech. | 38.730208 |
Chromatography is a technique used to isolate the various components of a mixture and this makes its application in analysis of biomolecules very important. It is used to separate and analyse the complex DNA sequences and other compounds, and also the concentration of the samples. There are many types of chromatography used in the study of biomolecules which range from DNA/RNA to recombinant proteins and antibodies. Here are some types of chromatography that you should know about.
High Performance Liquid Chromatography
Small particles and High pressure is required to carry out this type of liquid chromatography. HPLC has many forms and its application revolves around drug analysis and other forensic applications. There are forms of HPLC which specifically deal with enzymology and purification of other biomolecules.
The reversed phase chromatography has a larger application in industry. In this the stationary phase is non-polar, while the solvent or mobile phase used is polar which is opposite to normal chromatography where stationary phase is polar and the mobile phase is non-polar. The advantage of reverse phase liquid chromatography is that it allows the separation of a large variety of samples, with a wide range of molecular weights and polarities involved. It is easy to use and results are attained rapidly.
Fast Protein Liquid Chromatography
FPLC is also a form of liquid chromatography and it specializes in separating proteins from complexes, as the name suggests. FPLC is popularly used in enzymology, with a complete setup designed especially for separation of proteins and other biomolecules. Cross linked agarose beads are used.
Aqueous- Normal Phase Chromatography
This type of chromatography has a special feature, it has a mobile phase which is somewhere between polar and non-polar. The mobile phase is based on an organic solvent and a small amount of water which results in it being semi polar.
This type is again used in the purification of proteins which are bound to tags. The proteins being analysed are marked or labelled with compounds like antigens or biotins. To get pure proteins in the end, the labels are removed; the labels are just there to provide accurate separation of proteins. The mechanism uses a property of biomolecules i.e. affinity for metals, hence various metals are used in the chromatography columns. Immobilized Metal Affinity Chromatography is an advanced and much refined version of affinity chromatography used in identification of biomolecules these days. | <urn:uuid:31d668ab-2f30-47d3-8cbb-23a47519bf01> | 3.359375 | 500 | Listicle | Science & Tech. | 20.617326 |
I have a fondness for collecting brain lore–memes about the wonders of the human brain that race around the world for decades. The classic of brain lore is the “ten-percent myth.” As I wrote here, people often claim we only use ten percent of our brain, implying that we’d be supergeniuses if we could just switch on the rest. But that’s just based on a misinterpretation of some studies in the 1930s. Actually, the energy consumed by the cortex is only enough to power one percent of its neurons at any time.
According to Boahen, the brain is capable of performing 10 quadrillion (that’s 10 to the 16th) “calculations,” or synaptic events, per second using only 10 watts of power. At this rate, he says, a computer as powerful as the human brain would require 1 gigawatt of power.
The ultimate “computer,” our own brain, uses only ten watts of power — one-tenth the energy consumed by a hundred-watt bulb.
It’s a claim that falls in that gray zone, the intersection of cool and crazy. So to see if it was actually true, I asked Bill Leonard, an expert on the evolution of human brains at Northwestern University. He responded thusly:
This is really interesting. The 10 watt estimate looks pretty close to being correct — perhaps a bit on a the low side, but certainly in the ballpark.
In terms of calories, here is how the 10 watts translate:
10 watts = 10 joules/sec = 207 kcal/day for the brain
At 200-210 kcals, this is enough energy to support a brain of about 1000 grams, at the low end of the modern human range.
For an average size human brain — 1300 -1400 grams — the costs would be a bit higher — between 250-300 kcal/day. However, this would only up the “wattage” to about 15.
So there you go. One urban myth survives the cold scrutiny of reason! Pass it on in the full confidence that it’s true (not to mention amazing). | <urn:uuid:cdb49bb1-0060-4c43-a534-4c2950c87853> | 2.921875 | 459 | Personal Blog | Science & Tech. | 65.792313 |
projects > impacts of hydrological restoration on three estuarine communities of the southwest florida coast and on associated animal inhabitants
Impacts of Hydrological Restoration on Three Estuarine Communities of the Southwest Florida Coast and on Associated Animal Inhabitants
A primary goal of Everglades restoration is the recreation of water flows and water quality more closely approximating pre-drainage conditions in both freshwater and estuarine ecosystems within Everglades National Park. These estuarine systems include submerged aquatic vegetation, mangroves (tidal forests), and brackish marshes. Three primary groups of animals are closely associated with, and often dependent upon, one or more of these ecosystems: fish and decapod crustaceans (shrimp, crabs), manatees, and wading birds. This project will focus on fish and decapod crustaceans, and manatees. (Wading birds will be addressed in future efforts.) The present proposal addresses how hydrological changes upstream are likely to affect: (1) the distribution, abundance and composition of submerged aquatic vegetation and selected animal inhabitants; and (2) the distribution and abundance of selected biota associated with mangroves and brackish marshes.
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/projects/index.php?project_url=impacts_est
Comments and suggestions? Contact: Heather Henkel - Webmaster
Script last updated: 15 January 2013 @ 01:46 PM by BJM. Record creator: BJM. Record last updated by: BJM. | <urn:uuid:7592f4b0-aea2-41a3-88e0-bfa41e710b24> | 3.609375 | 341 | Knowledge Article | Science & Tech. | 23.013782 |
The many-eyed Earth watcher
Solve this crossword about Earth. You will know all the answers if you first read the story below about MISR, the multi-eyed Earth watcher and look at the 3-D pictures!
Put the mouse on a numbered square to see the clue. Click if you want to enter the word. For some squares, you may see both an Across Clue and a Down Clue. If you want to enter the word that goes across, hit the letter "a" first. If you want to enter the word that goes down, hit the letter "d" first. If you change your mind about entering a word, hit the ESCape key. You will earn points for every correct word. If you start a new puzzle before finishing the one you're working on, you will lose 40 points.
The Nine-eyed MISR
There are no easy answers up there in the sky! We need to learn a lot more in order to understand how our human activities may be causing unwanted changes on our home planet.
One of the instruments is the Multi-angle Imaging SpectroRadiometer, or MISR ("Miser") for short. MISR is nine cameras in one, each pointing in a different direction. As MISR passes over an area, each camera gets a shot from its own angle. Seeing the same piece of Earth's surface or atmosphere from nine different angles tells scientists a lot more than seeing it from just one angle.
Here are some examples. Click on the small pictures to see bigger ones and to find out what they are. Some are 3-D images that you can see if you have a pair of red/blue 3-D glasses.. | <urn:uuid:a96173d0-df2e-4d5f-8695-1343c9b9b340> | 3.203125 | 351 | Tutorial | Science & Tech. | 74.294626 |
JRapid applications use a relational database schema as the persistent storage layer. For every entity defined, a database table is created with columns modeling the properties of the entity. In some cases, more than one table is created to represent a special type of relationship with other entity or collection of primitive data types. In certain other cases, such as transient variables in the POJO or formulas, the variables exist in the java object but are not persisted to the database.
Auto-generated tables and columns
Creating an entity in the designer will create a database table. The title of the table will be the same as the entity although it will not be capitalized. The table will also have an auto-increment id field created to uniquely identify each instance in cases where the user has not defined a primary key. Java objects can easily be identified as persisted to the database or not by the presence of a valid id. Objects yet to be persisted will have an id of 0 and will return a new id on calls to store() which will persist the object.
Properties of the entity with a few exceptions will also create columns in the particular table. Transient properties by definition are not persisted. Also, formulas are generated values so they will not have columns. Additional properties will map to columns of the equivalent data type. String properties will map to varchar fields, text will map to text columns, dates will map to date columns, and booleans will be represented by bits. Unique columns will be unique at the database level in addition to including a "checkUniqueFor<Property>" in the entity's service class.
References between entities where one entity has a property that is a different entity will be reflected by the containing entity having a column in its table which holds the id of referenced entity. When an entity refers to one or more, or a collection of other entities, then JRapid will generate a table that holds the references of the original entity to as many of the child entity as necessary. The new table will be <ParentEntity>_<ChildPropertyName> with any uppercases becoming lowercase. The table will contain one field for the parent table name with the id value and a second field for the property name containing the id of the referenced table.
For built-in types like text, or doubles, creating a collection functions nearly identically. The table will be created as <ParentEntity>_<Property> with the second column being the actual value, for text varchar, for floating points a double.
Viewing the database
Every JRapid project stores the database connection information in the jrapid.properties file located in the /JavaSource folder. You may easily access this information through the Database link in the Project box at the top left of the JRapid Designer screen to gain access and view your generated database.
When you click the link the JRapid Designer switches to the Files view and opens the jrapid.properties file.
Using these credentials you may connect using any SQL client. The image below shows an example for the MySQL Query Browser.
Development Database Schema
Every JRapid project is created with an associated development database schema. This schema is hosted in the JRapid development servers in the JRapid Cloud. You may access the schema using any SQL client for debugging and fine tuning your application.
Hibernate Database Configuration
Hibernate is responsible for the connection to the database and the configuration parameters are passed through the hibernate.properties file located in the /JavaSource folder of the project. Hibernate is a widely used tool to create simple java objects from persisted data.
Change Database Engine
To change the database engine used by you application you must modify the following properties in the hibernate.properties file.
For example, if switching to Oracle, the new values should be as shown below.
If you are using MySQL 5.5 as your database engine, make sure you change your dialect like this.
If you need to specify a database schema for the connection, add the following property.
During the development process the business objects you define at first may need to be modified later. JRapid's code generation process and the separation of custom code into classes that are not overwritten make it very easy to introduce changes and iterate over and over in your development process.
However, there are some situations in which the application running in the development environment may get locked in a state from which it may not recover without some human assistance. The developer must manually alter the database in order to maintain it in concordance with the hibernate layer without the need of dropping the whole schema and loosing test data.
If you do not care about loosing all the test data in the database, you may choose to drop all the tables and have them created again. To do this, click on the Manage -> Restore Database menu option.
A confirmation dialog will be shown warning about the lose of all the information stored in the database tables. Click on Submit to confirm.
JRapid drops every existing database table and refreshes the application context, causing hibernate to create all the required tables according to the current mapping files.
For example, take the following definition.
<entity label="State" menu="Places" name="State" order="name"> <property display="primary" label="Name" name="name"/> <property display="secondary" entity="Country" label="Country" name="country" required="required"/> </entity> <entity label="Country" menu="Places" name="Country" order="name"> <property display="primary" label="Name" name="name"/> </entity>
This creates the following tables in the database.
Note the id columns present in each entity table. There are no id properties defined explicitly in the entities. These properties are automatically added by JRapid when no property is defined as a primary key.
Another example that shows an extra database table required to represent a many-to-many relationship.
<entity label="Company" menu="Companies" name="Company"> <property display="primary" label="Name" name="name" required="required"/> <property display="secondary" label="Active" name="active" type="boolean"/> <property display="secondary" entity="Country" label="Country" name="country"/> <property entity="State" label="State" name="state"/> <property label="Address" name="address" type="text"/> <property collection="set" entity="Industry" label="Industries” name="industries"/> </entity> <entity label="Industry" menu="Menu" name="Industry"> <property display="primary" label="Name" name="name"/> </entity>
This creates the following tables in the database.
Including a built-in type, phone number as a set for the company will create the following structure (VARCHAR(255) is the internal phone representation):
<entity label="Company" menu="menu" name="Company"> ... <property collection="set" label="Phone Numbers" name="phoneNumbers" type="phone"/> </entity> | <urn:uuid:d7c63a1f-6025-4966-b9a2-76df5097b355> | 2.984375 | 1,483 | Documentation | Software Dev. | 26.623114 |
MammalsMammals are a class of species that regulate their body temperature internally. Except for monotremes, the young are born live and suckle milk from the female. Most have some hair or fur on their body.
Mammal species profiles
Fish & MarineFish are any scaly vertebrate animal that lives in water. Unlike mammals and birds, the body temperature of most fish is regulated by the ambient temperature of their environment.
Fish species profiles
ReptilesReptiles are of the class Reptilia. They lay eggs and their skin is covered with scales. They are often referred to as "cold-blooded" because unlike "warm blooded" mammals they cannot regulate their own body temperature internally. Instead their body temperature is determined by the ambient temperature of their environment.
Reptile species profiles | <urn:uuid:88973515-5539-4e09-8ab9-b25f4d0aaa68> | 3.28125 | 169 | Knowledge Article | Science & Tech. | 24.332814 |
Ask a question about 'Sion's minimax theorem'
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Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
, and in particular game theory
Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...
, Sion's minimax theorem
is a generalization of John von Neumann
John von Neumann was a Hungarian-American mathematician and polymath who made major contributions to a vast number of fields, including set theory, functional analysis, quantum mechanics, ergodic theory, geometry, fluid dynamics, economics and game theory, computer science, numerical analysis,...
's minimax theorem.
be a compact
In mathematics, specifically general topology and metric topology, a compact space is an abstract mathematical space whose topology has the compactness property, which has many important implications not valid in general spaces...
In Euclidean space, an object is convex if for every pair of points within the object, every point on the straight line segment that joins them is also within the object...
subset of a linear topological space and
a convex subset of a linear topological space. If
is a real-valued function
In mathematics, a function associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output. A function assigns exactly one output to each input. The argument and the value may be real numbers, but they can...
- upper semicontinuous and quasiconcave
In mathematics, a quasiconvex function is a real-valued function defined on an interval or on a convex subset of a real vector space such that the inverse image of any set of the form is a convex set...
on , , and
- is lower semicontinuous and quasi-convex on , | <urn:uuid:ca4606f0-af91-46f9-b46e-54eb7019132d> | 3.484375 | 467 | Q&A Forum | Science & Tech. | 34.003685 |
In 1999, Leonids Meteor Shower came to an impressive crescendo.
Observers in Europe saw a
sharp peak in the number of
meteors visible around 0210
during the early morning hours of November 18.
Meteor counts then exceeded 1000 per hour - the minimum needed to define a
true meteor storm.
At other times and from other locations around the world, observers
respectable rates of between 30 and 100
meteors per hour.
This photograph is a 20-minute exposure ending just
before the main Leonids peak began.
Visible are at least five
streaking high above the Torre de la Guaita,
an observation tower used during the 12th century in
Over the next few nights, the
are expected to put on the best
meteor show of this year.
Juan Carlos Casado | <urn:uuid:8d9c2653-bd41-4161-9eba-2264c7262d8f> | 3.1875 | 182 | Truncated | Science & Tech. | 51.011354 |
“The diffraction barrier responsible for a finite focal spot size and limited resolution in far-field fluorescence microscopy has been fundamentally broken.” With that blunt assessment, published in the Proceedings of the National Academy of Science in 2000, Stefan Hell introduced the world to a “super-resolution” microscopy technique called stimulated emission depletion, or STED.
Or rather, he reintroduced the technique. Hell had first described STED—which cracks the diffraction limit that has for so long bounded optical microscopy—in a brief two-and-a-half page mathematical treatise six years earlier. “I had a very hard time to convince people it would work,” Hell recalls. The idea of a “diffraction barrier,” a physical constraint on light microscopy resolution, was simply too well ingrained.
Following his 2000 article, though, researchers started paying attention; the publication has racked up some 310 citations, according to the ISI Web of Knowledge. It also attracted the notice of microscopy manufacturer Leica Microsystems who licensed STED technology in 2001 and began converting it into a viable commercial system. It would take some five years. Along the way, Leica's engineers, physicists, and microscopists, aided by members of Hell's own lab, would have to rethink most of the original benchtop design.
The Seed of STED
In the late 1980s Hell was a physics graduate student at the University of Heidelberg using confocal microscopy to measure features on computer microchips. “The actual thesis subject … was so technical that I started to think about more fundamental things that one could do with this outdated field of physics,” he says, referring to optical microscopy. “I thought about breaking the diffraction barrier, which seemed to me a goal worthwhile to pursue scientifically.”
The diffraction barrier (also known as the Abbe limit) limits how closely together two objects in a cell can be and still be resolved using a light microscope. A function of the wavelength of light illuminating a sample and the physical properties of the optics used to visualize it, this barrier hovers around 200–250 nm, and it explains why microscopists cannot resolve macromolecular complexes such as densely packed microtubules into individual subunits via fluorescence light microscopy.
Hell, though, had a gut feeling the barrier was less solid than imagined. He suspected it might be possible to overcome it by manipulating the “light-driven state transitions” of fluorescent dyes: in other words tinkering with the process by which the dyes absorb and release energy. He pursued the idea in the early 1990s, first at the European Molecular Biology Laboratory and then at the University of Turku in Finland, where he had a senior postdoctoral fellowship. In 1993, he had a breakthrough. “I realized that one could do it by turning off a dye by stimulated emission.”
Hell's vision was to use two superimposed laser spots, an excitation beam and a beam for molecularde-excitation, and alternate their pulses so that some of the molecules in the excitation area are prevented from fluorescing – the foundation of STED. “STED introduces a mechanism by which we keep molecules dark even though they are illuminated with excitation light,” he says.
As in standard confocal microscopy, the excitation beam excites the fluorophores in a diffraction-limited region in the sample, rasterizing across the sample and collecting fluorescence intensity spot-by-spot. First, though, the STED beam—shaped like a doughnut with a hole in the center—deactivates the dyes at the periphery of that relatively large spot by forcing them back down to their ground state without fluorescing, acting like a light-based photomask. The net result is to shrink the effective excitation region below the diffraction limit.
“The purpose of that ring is to keep molecules fluorescent at the center of the doughnut while at the periphery, where the [STED laser] intensity is strong, the molecules are shut off,” Hell explains. “So the region in which molecules are allowed to emit is made smaller in the end, and so it's possible to see much finer detail.” | <urn:uuid:dc4ba108-382e-4fb8-b4ae-ddb3a7c8acc1> | 3.3125 | 890 | Knowledge Article | Science & Tech. | 30.698372 |
In most programming languages, procedures are strongly typed, and any call to the procedure must use the same types that are used in the definition of the procedure. Thus, to reuse someone else's procedure, you must understand the types they use and conform to those types.
With views, you only need to describe how your data correspond to the abstract data used in the generic procedures. User interfaces are provided that make the views for you, either automatically or based on a few simple choices that you specify. There are two systems for making views: one for data structure views, and one for mathematical views.
Before making views, you must define your data structure(s). Then click the Make a View command. The system will present menus and/or a graphical interface to allow you to specify the view.
linked-list. The data structure views that are available include:
In general, these data structures contain pointers to other data of the same type. If your data structure contains such pointers, the view will be made using those pointers. Otherwise, the system will define a "carrier record" that contains your data plus the necessary pointers.
If there is more than one choice for an item, the system will present
a menu to allow you to select the choice to be made. In some cases, the
system can make the view automatically. In other cases, it will ask
questions, such as what field to sort on and whether the sort should
An example data declaration for a
person data structure is:
(person (name string) (age integer) (salary real) (friend (^ person)))This data structure could be viewed as a
friendpointer as the link field. It could also be viewed as a
sorted-linked-listwith sorting on
vectorabstract type used by the generic procedures is an (x,y) vector, but your vector type might be a polar (r,theta) vector.
The mathematical views that are available include:
When you request a mathematical view, a graphical window is created that
gives a diagram of the mathematical object and a menu of the fields
available from your data. The diagram contains labeled "buttons" for
parameters of the mathematical object. To make a view, click the mouse on
a diagram button; then click the corresponding item in the menu of your
data. A line is drawn between the selected items to show the correspondence.
When a sufficient definition of the object has been specified,
As a simple example, suppose that the data type
has been defined:
(pizza (diameter real) (topping string))To view a
circle, click the mouse on the
dbutton of the
circlediagram, then click the
diameterin the menu of the
pizzadata type. Then click the
Donecommand. Then you can select Make Programs to make a program to calculate, say, the | <urn:uuid:11f2c458-088d-44ea-b8cd-d0e1a9d75960> | 3.34375 | 605 | Tutorial | Software Dev. | 41.370218 |
isoprene or 2-methyl-1,3-butadiene (Īˈsəprēn, byōˌtədĪˈēn) [key], colorless liquid organic compound. It is a hydrocarbon, and is insoluble in water but soluble in many organic solvents; it boils at 34°C. The isoprene molecule contains two double bonds. It is readily polymerized by the use of special catalysts; large numbers of isoprene molecules join together to form a single large, threadlike polyisoprene molecule. Isoprene polymers also occur naturally. The natural rubber caoutchouc is cis -1,4-polyisoprene, and trans -1,4-polyisoprene is present in the natural rubbers balata and gutta-percha. (The cis and trans polyisoprenes are structural isomers.)
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
More on isoprene from Fact Monster:
See more Encyclopedia articles on: Organic Chemistry | <urn:uuid:24948e2b-116a-419a-9bf1-43c43bdae29a> | 3.328125 | 235 | Knowledge Article | Science & Tech. | 26.392308 |
In a study funded by the National Science Foundation, Stephen Rothstein, professor of zoology, and Adrian O'Loghlen, a research scientist in the Department of Ecology, Evolution and Marine Biology, have documented how male brown-headed cowbirds use songs and physical displays to elicit responses from females. Their studies are the first to use video recordings of males to show that the visual components of singing behavior can influence the sexual responses of female songbirds.
"This is the kind of breakthrough that we've been trying to develop," O'Loghlen said. "We're able to communicate visual information to the female cowbirds. It's really good evidence that they're extracting visual information. There are so many questions we can ask in our studies using this technique. The potential for this research is mind-blowing."
There are thousands of researchers who study birds, according to the UCSB scientists. The study of birds remains one of the major areas of research in biology, due in part to the challenge of discovering how they learn their songs. "In humans," Rothstein said, "everyone knows that you can learn a new language much easier early in life. And with these songbirds, learning new songs is limited to an early period of life. It's either the first or second year."
"There are many parallels to language development in humans," O'Loghlen said. "The birds go through various stages that are very similar. Babies babble. Birds babble. Babies memorize a lot of sounds before they ever try to produce them. Birds do the same."
Many scientists believe that birdsong may be the best animal model for the study of cultural evolution that occurs in people. "It has a parallel with genetic evolution, where the structure within a species changes over time," Rothstein said. "Our lives are totally different than they were over a hundred years ago because of cultural changes, yet we have undergone little or no genetic evolution. The best example of cultural evolution within species in non-human animals is with these birds and their different song dialects. They clearly have evolved different cultures in different places."
For many years, a primary method used in studying how songbirds communicate was to use audio playback. A male cowbird would sing and the sounds were recorded and played back to the females or to other males to see how they would respond. Males sing to other males as a form of aggression, while males sing to females as part of the courting ritual.
"Until the work we've done recently, it looked like it was the same signal to the male and female," Rothstein said. "Just the receiver of the information knew it had different meanings. But what we found is that there is some difference in how the song is presented to a male by a male, and the way a male presents a song to a female."
When researchers previously attempted to use audiovisual recordings to observe the birds' behavior, the results were disappointing. The flickering of old cathode ray tube monitors was distracting to the birds. But when flat-screen, liquid crystal display (LCD) monitors came along, the possibility of adding video to birdsong experiments became a reality. The LCD monitors have a much faster refresh rate, which doesn't seem to bother the birds.
Rothstein and O'Loghlen built an audiovisual lab at the aviaries on the UCSB campus. By using two small cages placed side-by-side, with a webcam between the cages, the researchers were able to record males directing songs at females or other males. They then used an LCD monitor and laptop computers to present these video recordings to females, and to record the females' responses.
The video recordings documented the songs of the males (like most songbirds, only male cowbirds sing) and the physical displays of both males and females. The males would spread their wings and bow deeply in a show of aggression when singing to other males, while the displays that accompanied songs directed at females always involved less extreme motions. The female cowbirds would react to the video playback by freezing, almost becoming rigid, in what the researchers call a copulation solicitation display. "She's actually saying, ‘Whoa, that's really sexy, you can mate with me,' " O'Loghlen said.
"We realized that the intensity of male-directed and female-directed physical displays was very different," O'Loghlen said. "We quantified the differences in these two types of displays the first time anyone had done this."
The results of their research were published earlier this year in the journal Animal Behaviour, and additional findings appeared more recently in The Condor, an international journal that publishes original research reports pertaining to the biology of wild bird species.
Rothstein, who has devoted most of his 38 years as a professor at UCSB to the study of birds, believes videos are the key to unlocking even more secrets about cowbirds and other species.
"Birds are both visual and auditory creatures," Rothstein said. "That's the way they perceive the world and the way they communicate with each other. We and other researchers have looked at the audio component a lot. With this video, it's much more natural. It's one of the reasons bird-watching is so popular, because people and birds see the world in the same way through sight and sound."
†A still-frame from a video recording of a female brown-headed cowbird, left,doing a copulation solicitation display. Her head and bill are pointing up and her tail is also elevated. She has just finished viewing a recording of a male, seen on the monitor screen at right, singing a song and performing the bowing display that generally accompanies cowbird songs. | <urn:uuid:9800288d-d4b5-4c04-986e-9806bde1faf6> | 4.09375 | 1,180 | Knowledge Article | Science & Tech. | 45.862788 |
PLUTO's status as a planet is in danger. Astronomers have found a similar object more than half Pluto's diameter in the Kuiper Belt, a collection of primordial icy bodies beyond the orbit of Neptune. The object, dubbed "Quaoar", is the biggest thing found in the Solar System since the discovery of Pluto.
Many researchers feel that because Quaoar isn't counted as a planet - it's more like a big dirty snowball - then Pluto, which also orbits in the Kuiper Belt, shouldn't be called a planet either. "This helps to displace the opinion that Pluto is a planet," says Brian Marsden of the Harvard-Smithsonian Center for Astrophysics.
Astronomers have found several hundred Kuiper Belt objects besides Pluto since the first was discovered in 1992, but Quaoar is by far the largest. Mike Brown and Chad Trujillo of Caltech first spotted it in June this year, after months of surveying the ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:548b4592-d6de-49d7-92c3-f260d52c38cf> | 3.515625 | 230 | Truncated | Science & Tech. | 56.586442 |
Light-seeking algae might become the workhorses of the next generation of lab-on-a-chip devices, the Materials Research Society meeting in Boston heard last week. Labs-on-a-chip are used for medical and genetic analysis, and typically consist of arrays of microscopic wells containing chemicals that react with any biological cells that are added. Researchers are constantly on the lookout for better ways to get the cells to the right wells.
He coated 1-micrometre-wide polystyrene beads with peptides that the alga likes to bind to and placed them at one end of an 18-centimetre-long microchannel. When
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:0ee3f70e-e974-4b06-8e09-e7905df92040> | 2.984375 | 160 | Truncated | Science & Tech. | 41.588476 |
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The calculation of the maximum mass of 1.44 solar masses for a white dwarf was done by Subrahmanyan Chandrasekhar on a ship on the way from India to England to begin graduate study in physics at ...
Extensive overview of our solar system, covering history, mythology, and current scientific knowledge of planets, moons, asteroids in our solar system, with many links.
More than 15 hands-on science activities are provided in classroom-ready pages for both teachers and students for exploring Earth, the planets, geology, and space sciences.
Cool facts about our planet.
Diagram showing forces of attraction with planet alignment.
A blog post looking at how scientist adjust colours of scientific images.
Take a virtual tour of a martian base and discover the technology that might be used to set up camp on the red planet
Images and animations on how our planet's magnetic poles have flipped in the past, and how they may flip again.
A catalogue of satellite images of our home planet detailing everything from atmospheric data to city lights or natural disasters.
A site about exoplanets from hyperphysics.
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In the currency of the cosmos, stars come cheap. There are hundreds of billions of them in our galaxy alone. The true prizes, as astronomers have always known, are planets. It took earthly observers millennia to discover the ones circling our own little sun. Whether any existed around other stars remained a mystery until 1995, when the first so-called exoplanets were found.
The biggest question on people's minds when the discovery of the new worlds was announced was whether they could harbor life. The answer: not even close. They were too big, too close to their stars or both. In the decade and a half since, with nearly 500 exoplanets under their belts, astronomers still haven't found an Earth-size planet in a star's habitable zonealso known as the Goldilocks region, where things are not too hot, not too cold, but just right for life. It looked as though they'd finally done it a few weeks ago with the announcement of a planet called Gliese 581g identified by a team of American astronomers. But as other scientists have studied the data, they've raised serious questions about whether the planet exists at all.
Disappointing as that has been, errors are to be expected in the planet-hunting game simply because the work is so hard. At multiple-light-year distances, even the largest planets cannot be seen with telescopes. Instead, scientists must use the back-and-forth gravitational wobbles, or radial velocity, a planet imposes on its parent star to infer its existence. Measure that movement and you can determine the planet's mass. Another method, known as transiting, occurs when a planet passes in front of its star, blocking a tiny bit of the light the star emits. By measuring the dimming, astronomers can calculate how large the blocking object is. A final approach, gravitational microlensing, involves analyzing how light from one star is bent as it travels around a planet orbiting another star closer to Earth.
The Kepler space telescope, which has been orbiting the sun since 2009, uses transiting to hunt for exoplanets, keeping its sensors fixed on about 100,000 sunlike stars. If it detects dimming in one of them, and if that dimming happens about once every year, it means the planet has an orbit like Earth'sand we're smack in the middle of the habitable zone. The Kepler scientists will make their first major reveal in February, announcing the planets they've found so far. The sheer number of stars out there makes some Earth-like worlds all but inevitable. The search will then be on for any Earth-like life upon them. | <urn:uuid:b90abf81-b831-4c22-9f22-2294af6bb1ec> | 3.734375 | 537 | Truncated | Science & Tech. | 52.027069 |
Tuesday May 21, 2013
Last week researchers at Oregon Health and Science announced they had made human embryo clones using skin cells. The technique was similar to the one used to clone Dolly, the sheep, almost 20 years ago. Why has it taken so long to clone humans? Are we that different than sheep?
In fact, cloning resarch has a long history and there has been pretty continuous progress with mammalian cloning over the past 25 years. Mice, dogs, cats, and even camels have been cloned. The latest result in Oregon is only the most recent discovery in a field that has been gradually unraveling the processes of how a single cell can develop into complex organism for over 100 years starting with work on sea urchins.
Of course, this recent work by the lab in Oregon has received much more attention than most other cloning experiments because it involves humans. The experiment sparked immediate controversy as soon as it was published. However, as a recent USA Today article points out, a clone is basically an identical twin so there is nothing particularly strange about them.
Also, the Oregon group did not actually create a human clone, just a cloned embryo. While the work has brought us close to being able to fully clone a human being, this is not really the main purpose of the study. Based on the group's previous work with primates, the embryo would not likely even be able to develop into a human. We still do not known enough about development to successfully produce a cloned person.
This gap in our understanding, though, is sort of the point. Although only time will tell if this technique will ever find useful clinical applications, the embryos produced by this process will be very useful to generate embryonic stem cells for biomedical research. The technique provides an essential research tool to investigate the process of development and differentiation that enables one cell to produce a whole person. It provides a basis on which to build a more sophisticated understanding of this miraculous transformation. In the end, it is this deeper knowledge that will provide new and better medical treatments.
You can read more information on this cloning breakthrough and the history of cloning research in two recently posted articles:
Monday May 13, 2013
Back in February the Supreme Court heard arguments from farmer Vernon Bowman on why he didn't need to pay royalties to Monsanto for growing their patented GMO soybeans that have been genetically modified to be resistant to the pesticide in Round-Up. Today, Mr. Bowman lost his case when the Court unanimously ruled against him. He owes Monsanto $84,000 in royalties.
Bowman bought uncharacterized soybeans intended as animal feed from a local supplier. He admited that he thought most of the generic soybeans would probably be Round-Up ready GMO varieties even though they weren't labeled that way or sold as crop seeds. Since he didn't specifically buy Round-Up ready seeds, however, he argued that he didn't infringe on Monsanto's patent. In fact, he claimed it was the seeds themselves that replicated the patented invention.
All the Justices disagreed with Bowman. "But we think that blame-the-bean defense tough to credit." noted Justice Elena Kagen in delivering the Court's opinion. "Bowman was not a passive observer of his soybeans' multiplication; or put another way, the seeds he purchased...did not spontaneously create eight successive soybean crops....Bowman devised and executed a novel way to harvest crops from Roundup Ready seeds without paying the usual premium."
Justice Kagen points out that the Court's opinion is based understanding that, "Under the doctrine of patent exhaustion, the authorized sale of a patented article gives the purchaser, or any subsequent owner, a right to use or resell that article. Such a sale, however, does not allow the purchaser to make new copies of the patented invention."
For more on the ruling, see a summary on ScienceInsider.
Tuesday May 7, 2013
The lab of Rudolf Jaenisch, who developed the first transgenic mouse in 1974, has developed a new approach to genetically engineer mice in just weeks, rather than years which are currently needed. This new technique does not rely on engineering embryonic stem (ES) cells, but rather, directly introduces the genetic changes in developing mouse embryos. In addition to making production of transgenic mice and rats for laboratory research faster and easier, it should also work with other types of organisms whose embryonic cells are difficult to engineer and manipulate.
The new approach takes advantage of a unique response bacterial developed as a defense against invading viruses. Bacteria can target and cut the DNA of invading viruses. To do this, they use short sequences of DNA that match some part of the DNA of the invading virus. Many bacteria seem to have a "catalog" of short stretches of DNA that match parts of many different types of viruses. These regions of DNA were dubbed Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) when they were first discovered.
Researchers found that they could co-opt this bacterial defense system to target and inactivate specific genes in more advanced non-bacterial cells. To do this, they only needed to introduce the gene that cuts the targeted viral DNA in bacteria--the CRISPR-associated protease (Cas). Basically, it seems that almost any gene in most cells can be cut by introducing DNA that makes the Cas protein and a CRISPR construct with a short sequence that recognize some small part the gene. Even though a cell will fix a gene that has been cut, it does not get fixed correctly (because of the way Cas cuts it). Then, the gene will no longer work, so it has been "knocked out".
Inactivating or "knocking out" genes is a common approach researchers use to understand how particular genes function and also generate mice or rat strains that model various human diseases. One of the big difficulties of engineering animals with certain genes knocked out, though, is that almost all genes come in pairs--one from each parent. Both copies of a gene need to be inactivated to fully knockout a gene. Unless the knock out technique is very efficient, this is rare. However, the CRISPR approach seems to be exceptionally effective.
In a Cell publication this week, the researchers in Dr. Jaenisch's lab describe how they were able to simultaneously and specifically knock out two genes with a single injection of a mouse embryo. Further, they also used the technique to produce embryonic mouse stem cells with disruptions of 5 distinct genes simultaneously. Mice produced using these embryonic stem cells would then carry all 5 of these mutations.
For a more information, you can read the press release from the Whitehead Institute at MIT describing the paper.
Saturday May 4, 2013
Thirteen of the world's leading stem cell researchers just published a statement in the European Molecular Biology Organization (EMBO) Journal expressing alarm about initiatives to deregulate stem cell therapies. Recent actions by the Italian government allowing unapproved stem cell treatments precipitated the researchers' statement.
Last year, the Italian Medicines Agency or AIFA (equivalent to the FDA in the US), ordered a halt to unapproved stem cell treatment program being carried out at the Brescia Civilian Hospital on the basis that there was no scientific evidence for its effectiveness. The treatment was being done under the direction of the Stamina Foundation, founded by Davide Vannoni, a psychology professor at the University of Udine. According to an article in Nature, 32 terminally ill patients, mostly children, were being treated using the therapy. However, the treatment was never approved by AIFA.
Protests in response to the interruption of the treatment prompted Italy's Minister of Health, Renaldo Balduzzo to override the AIFA order in March. Despite the strong objections in an open letter to the Minister from thirteen Italian scientists researching stem cells, the Italian Parliament, in one of its last acts before new elections, issued a decree allowing the Stamina therapy to continue.
As a result, the authors of the EMBO article felt the need to emphasize the importance of "strident regulation" of medical applications of stem cells to ensure "the translation of science into effective therapies." They point to the current situation in Italy, as well as recent stem cell regulatory battles in the US and a case in Germany in which unregulated stem cell treatments resulted in death, as examples of how rules set out by regulatory bodies such as the FDA and EMA have so far been effective in protecting patients from serious risks associated the indiscriminate use of unproven therapies, and voice their concern that these rule seem to be changing for stem cell therapies.
In reference to the current case in Italy, the article notes that, "The treatment, offered by a private non-medical organization, may not be safe, lacks a rationale, and violates current national laws and European regulation." Also, the authors understand the augment for reinstating treatment in the Italian case was that "safety is not a concern in the face of severely ill children or adults, for whom there are no therapeutic alternatives." However, they emphasize that:
"Compassion only applies when one offers a safe and potentially effective remedy. That a remedy is effective must be supported by published clinical data. If such data are not available, there is no legitimate assumption of effectiveness in the individual patient, and therefore no 'compassion'."
You can read more about the article in the press release from EMBO. | <urn:uuid:181e13ad-778f-4d17-87f1-d25273213e19> | 3.640625 | 1,920 | Content Listing | Science & Tech. | 38.299282 |
We begin building a LabVIEW application by creating a blank virtual instrument (VI) using, for example, the Blank VI option on LabVIEW’s Getting Started splash screen. This brings up two windows: a front panel and a block diagram. The former contains the user interface of the VI which the user creates using controls and indicators, each of which is selected from a palette of options. Code to control the objects in the front panel is added by the user to the block diagram; this is a manifestation of LabVIEW’s visual programming paradigm, which sees an application as being made up of a collection of nodes that are connected together in a way which reflects the flow of data between them.
Our simple example application is built around the NAG method g01aa, which calculates the mean, standard deviation and various other statistical quantities from a set of ungrouped data (details about the documentation for the NAG Library for .NET is available here, while the documentation for the g01aa routine in the NAG Fortran library is here). To load the method, we first bring up the Functions Palette, using the option on the View menu on the block diagram window. Next, we open the Connectivity collection from the palette, and then the .NET item. This palette contains a variety of functions for creating .NET objects, setting properties or calling methods on those objects. We select the Invoke Node item – which invokes methods or performs actions on an object – and drag it onto the block diagram in order to initialize it.
To specify the class on which to execute the property, we right-click on the node and select Select Class >> .NET >> Browse.... This brings up the Select Object From Assembly dialog box. If the NAG Library is not listed in the Assembly component, then we find it (typically in a location like C:/Program Files/NAG/NAG Library for .NET/) using the Browse... component, choosing either NAGLibrary32.dll or NAGLibrary64.dll, depending on our machine architecture. Double-clicking on the NagLibrary item in the Objects component on the dialog box then shows the objects which are available in this assembly; in our example we select G01, followed by OK to load it into the Property Node. To select the desired method from within the G01 class, we right-click once again on the node and select Create >> Method for NAGLibrary.G01 class >> g01aa (note that the items on the method menu explicitly show the function argument list, including the .NET types; they’re also prefixed with [S] if they’re a static .NET method). This creates a node corresponding to a new instance of the g01aa method in the block diagram (see figure 1).
The next step in building our demo is to add LabVIEW controls and indicators to handle, respectively, the input and output of our application. These get placed on the front panel and corresponding objects appear on the block diagram, where they’re then connected to other objects to specify the flow of data and control through the program. In our application (see figure 2), we use a Numeric Indicator to display each output quantity from g01aa, and a Numeric Control within an Array shell control to allow the user to enter the data values for which the routine will calculate the statistics (see here for more information on creating and using array controls in LabVIEW).
Figure 2. Front panel of our demo application, with the (input) data array on the left, and the (output) statistics on the right
The block diagram of our application is shown in Figure 3. Along with the objects corresponding to the controls and indicators described above, we’ve also used the Array Size function to determine the number of elements in the Data values array. The output from this is used as input for g01aa's input parameter n (i.e., the length of the array x, which contains the data values), and also as the dimension size input parameter for the Initialize Array function. The other input parameter for this function is element, which specifies the value to which all elements of the array are to be set; we use a DBL Numeric Constant to set this to zero, and the resultant array is used as input for g01aa's input parameter wt, which is the array used to weight the data values in the in the calculation. In fact, in this example, all values are weighted equally; we specify this by using a Numeric Constant to set g01aa's input parameter iwt to zero (see the g01aa documentation for more details).
Figure 3. Block diagram for our demo application. Inputs to g01aa are on the left, and outputs on the right
Although simple in application, this example has hopefully given a flavour of the way in which the NAG library for .NET can be used within LabVIEW. Other methods which are offered by the library address the more complicated problems of local and global optimization of multivariate functions, pseudo and quasi random number generation, wavelet transforms, least-squares and eigenvalue determination, curve and surface fitting, summation of series and interpolation; more details about its functionality are available here.
If you have any questions about this work (or want to know more about using the NAG Fortran Library or the NAG C Library with LabVIEW), then please get in touch. I’d really love to hear from users (or prospective users) of NAG and/or LabVIEW, and want to build new examples that will be useful to researchers in this area.
Finally, I’m grateful to my colleague Jeremy Walton for his help in preparing this post, and his interest in this work. | <urn:uuid:cc189d1a-a646-4a93-aa5c-51c3d565de19> | 2.78125 | 1,186 | Documentation | Software Dev. | 48.649226 |
Madin, K.
"Turtle skulls prove to be shock-resistant
Oceanus, vol. 47, issue 2, Woods Hole, Massachusetts, Woods Hole Oceanographic Institution, pp. 36-37, 09/2009.
Scientists and engineers from Woods Hole Oceanographic Institution (WHOI) and the U.S. Navy have discovered that sea turtles’ skulls and shells not only protect them from predators but also from extraordinarily powerful underwater shockwaves. The research, originally intended to help the Navy avoid harming turtles, could also point the way to designing improved body armor and helmets for soldiers on land. | <urn:uuid:ba20c76e-be84-4481-8980-5acf5d274fed> | 2.703125 | 124 | Academic Writing | Science & Tech. | 48.581364 |
September 19, 2011
It is believed California is currently undergoing desertification. The long-term impacts and environmental costs associated with this process will take a devastating toll on the environmental future of the state. According to an article from Remote Sensing by Doris Lam, Tarmo Remmel and Taly Drezner, the present conditions of the majority of California’s lands are arid and semi-arid, which makes California highly susceptible to climate changes and anthropogenic impacts leading to desertification.
There are a combination of factors that when placed together can have the potential for disaster. During the 1930′s in Oklahoma, the combination of drought, arid climate, and land misuse led to the dust bowl resulting in depression, a mass exodus of people, poverty, hunger, high economic costs, loss of biodiversity, and unusable land for agriculture. Currently, because of California’s arid climate, land erosion and misuse, and rising global temperatures, the potential for disastrous environmental impacts is on a greater scale and drawing near.
U.S. Secretary of Energy, Steven Chu, projects the future of California’s agricultural lands to decline. According to the climate reports Chu has reviewed, global temperatures are only expected to reach staggering heights. Along with these increases in temperatures come major environmental impacts such as shortages in water supplies and loss of agricultural land. Without a secure water supply, agricultural processing and more importantly food production, could be in danger. In an article from Nature Geoscience, Diana Wall warns that the lack of water will cause great damage to the essential functions of healthy soil, which include providing proper environments for crop growth with various nutrients and other levels of biodiversity.
The rise in temperatures will also affect levels of precipitation and perhaps even cause valuable lands to lose their ability to sustain abundant crops for California’s growing population. A twenty-five percent drop in precipitation levels beginning in 2007 and lasting through 2009 is an example of this situation. The consequence of this occurrence was that the stream flows were forty percent below normal standards.
As a result, farmers pumped groundwater as a short-term answer to their water problems. However, in the long run, the groundwater resources were depleted greatly and a valuable resource was used unsustainably. A total reduction in groundwater during the drought proved to be 48 times worse than reductions in a comparable period earlier in the decade. A continuation of similar events in using water resources unsustainably will eventually force the water-deprived grounds of California to move quickly towards desertification.
The state of California’s economy relies heavily on its agriculture. A report from the 2010-2011 edition of the California Agricultural Resource Directory states that in 2009, California agricultural exports reached 12.4 billion, which was a 66 percent increase over a length of seven years. A sudden plummet to California’s agricultural productions due to the presence of desertification would result in not only a decrease in harvested crop acreage but also in jobs for Californian residents.
California’s success in farming over the years has earned the state the title of “the agricultural powerhouse of the United States.” The state’s economy is heavily dependent on the profits of their agricultural productions. The environmental impacts and costs of desertification in California will have a huge toll on millions of people. Not only will it do damage to the state’s economy but it will also cause a great increase in unemployment rates. Moreover, the total cost of attempts toward restoring the deteriorated agricultural lands will most likely continue to rise since the chances of restoring those lands to its native standards are close to impossible. The desertification of California agricultural lands will be detrimental to the entire population of the state.
About the authors: Ticia Lee and Wendy Whitcombe are working towards their bachelor’s degrees in Environmental Studies in the USC Dana and David Dornsife College of Letters, Arts and Sciences. | <urn:uuid:bcc660a7-f3a9-47f6-b17f-11ab104b432b> | 4.03125 | 793 | Academic Writing | Science & Tech. | 22.776521 |
The Global Positioning System has completely revolutionised how geologists study the deformation of the Earth. If you leave a GPS receiver in a fixed location for days, months and years, it is precise enough to measure motions on the mil...
The Global Positioning System has completely revolutionised how geologists study the deformation of the Earth. If you leave a GPS receiver in a fixed location for days, months and years, it is precise enough to measure motions on the millimetre scale, allowing us to track strain building up across active faults, and even the incremental drift of the tectonic plates themselves across the Earth’s surface. But on the 26th December 2004, stations across a sizeable slice of the Earth’s surface suddenly found themselves being jerked around a bit more rapidly. The plots below are from stations in southern India and northern Taiwan, respectively.
If you are thinking that date sounds a bit familiar, you’d be right: that jerk is the signal of the massive magnitude 9.3 earthquake that ruptured a 500 km length of the Sunda Trench off the coast of Indonesia on Boxing Day 2004, and unleashed a devastating tsunami.
What’s impressive is that we are seeing permanent deformation of the crust due to motion on a fault (what is known as coseismic deformation) an extremely long way away. As we can see on the map below, the Indian GPS station IISC is some 2,300 miles away, and the Taiwanese station TNML is 3,600 miles away, from the Sunda Trench. And yet, even at that distance, the Sumatra-Andaman earthquake shifted the land beneath these points about a centimetre – a little less for the Taiwan, a little more for India.
The figure above also compares the actual motion observed with GPS (black arrows) with predictions from a model of the Boxing Day rupture (grey arrows). What this figure doesn’t show is the predicted coseismic deformation at places not occupied by GPS stations. Fortunately, a paper just published in the Journal of Geophysical Sciences contains a much nicer visualisation of the output of a similar model. This model – rather mind-blowingly – indicates that the Sumatran-Andaman earthquake rupture directly deformed a sizeable fraction of the Earth’s surface, including Africa, Arabia, the eastern half of Asia, and most of the Americas.
Paul Tregoning and his co-authors have gone on to calculate the cumulative coseismic deformation resulting from all 15 magnitude 8 or greater earthquakes that have occurred since the turn of the millennium on the Earth’s surface. Unsurprisingly, the big three earthquakes in this period – the Sumatra-Andaman, the magnitude 9.1 Tohoku earthquake in March 2011, and the magnitude 8.8 Chilean earthquake in February 2010 – are the major contributors, but the smaller ones fill in some gaps in the southwest Pacific.
Modelled global coseismic deformation due to all M 8+ earthquakes since 2000, from Tregoning et al., 2013
Basically, outside of western Europe and the Arctic Circle, pretty much the entire surface of the planet has been shifted at least a millimetre or two by an earthquake since the turn of the millennium. And this has real world consequences. The interiors of the Earth’s tectonic plates are generally assumed to be rigid and undeforming, and are used as a fixed reference point for measuring deformation at the plate boundaries. The red arrows in the figure above show exactly how much you’d be wrong if you are assuming that for a given point on the Earth’s surface. Even when you’re a long way from a plate boundary, coseismic deformation from distant, large earthquakes is causing your ‘fixed’ reference point to be not so fixed. Spooky tectonic action at a distance, indeed.
Corné Kreemer, Geoffrey Blewitt, William C. Hammond, & Hans-Peter Plag (2006). Global deformation from the great 2004 Sumatra-Andaman Earthquake observed by GPS: Implications for rupture process and global reference fram Earth, Planets, Space, 58 (2), 141-148
Tregoning, P., Burgette, R., McClusky, S., Lejeune, S., Watson, C., & McQueen, H. (2013). A decade of horizontal deformation from great earthquakes J | <urn:uuid:5d29fdf9-a92a-45bf-a21e-2b5f2e3b05c1> | 3.703125 | 921 | Nonfiction Writing | Science & Tech. | 47.42743 |
When number pyramids have a sequence on the bottom layer, some interesting patterns emerge...
Imagine we have four bags containing numbers from a sequence. What numbers can we make now?
A little bit of algebra explains this 'magic'. Ask a friend to pick 3 consecutive numbers and to tell you a multiple of 3. Then ask them to add the four numbers and multiply by 67, and to tell you. . . .
A game for 2 players with similaritlies to NIM. Place one counter on each spot on the games board. Players take it is turns to remove 1 or 2 adjacent counters. The winner picks up the last counter.
An article for teachers and pupils that encourages you to look at the mathematical properties of similar games.
This article for teachers describes several games, found on the
site, all of which have a related structure that can be used to
develop the skills of strategic planning.
Pick a square within a multiplication square and add the numbers on
each diagonal. What do you notice?
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 collection of games on the NIM theme
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
Can you describe this route to infinity? Where will the arrows take you next?
Charlie and Lynne put a counter on 42. They wondered if they could
visit all the other numbers on their 1-100 board, moving the
counter using just these two operations: x2 and -5. What do you
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.
Spotting patterns can be an important first step - explaining why it is appropriate to generalise is the next step, and often the most interesting and important.
Jo has three numbers which she adds together in pairs. When she
does this she has three different totals: 11, 17 and 22 What are
the three numbers Jo had to start with?”
The sum of the numbers 4 and 1 [1/3] is the same as the product of 4 and 1 [1/3]; that is to say 4 + 1 [1/3] = 4 × 1 [1/3]. What other numbers have the sum equal to the product and can this be so for. . . .
Try entering different sets of numbers in the number pyramids. How does the total at the top change?
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.
Do you notice anything about the solutions when you add and/or
subtract consecutive negative numbers?
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
Take any whole number between 1 and 999, add the squares of the
digits to get a new number. Make some conjectures about what
happens in general.
Many numbers can be expressed as the sum of two or more consecutive integers. For example, 15=7+8 and 10=1+2+3+4. Can you say which numbers can be expressed in this way?
Can you find sets of sloping lines that enclose a square?
List any 3 numbers. It is always possible to find a subset of
adjacent numbers that add up to a multiple of 3. Can you explain
why and prove it?
Imagine starting with one yellow cube and covering it all over with
a single layer of red cubes, and then covering that cube with a
layer of blue cubes. How many red and blue cubes would you need?
In each of the pictures the invitation is for you to: Count what
you see. Identify how you think the pattern would continue.
Think of a number, add one, double it, take away 3, add the number
you first thought of, add 7, divide by 3 and take away the number
you first thought of. You should now be left with 2. How do I. . . .
How many moves does it take to swap over some red and blue frogs? Do you have a method?
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.
A country has decided to have just two different coins, 3z and 5z
coins. Which totals can be made? Is there a largest total that
cannot be made? How do you know?
Can you see how to build a harmonic triangle? Can you work out the
next two rows?
Can you find the values at the vertices when you know the values on
A package contains a set of resources designed to develop
pupils’ mathematical thinking. This package places a
particular emphasis on “generalising” and is designed
to meet the. . . .
Caroline and James pick sets of five numbers. Charlie chooses three of them that add together to make a multiple of three. Can they stop him?
If you can copy a network without lifting your pen off the paper and without drawing any line twice, then it is traversable.
Decide which of these diagrams are traversable.
How could Penny, Tom and Matthew work out how many chocolates there
are in different sized boxes?
What are the areas of these triangles? What do you notice? Can you generalise to other "families" of triangles?
Triangle numbers can be represented by a triangular array of
squares. What do you notice about the sum of identical triangle
Can you work out how to win this game of Nim? Does it matter if you
go first or second?
The number of plants in Mr McGregor's magic potting shed increases
overnight. He'd like to put the same number of plants in each of
his gardens, planting one garden each day. How can he do it?
The NRICH team are always looking for new ways to engage teachers
and pupils in problem solving. Here we explain the thinking behind
The diagram shows a 5 by 5 geoboard with 25 pins set out in a square array. Squares are made by stretching rubber bands round specific pins. What is the total number of squares that can be made on a. . . .
Take a look at the multiplication square. The first eleven triangle
numbers have been identified. Can you see a pattern? Does the
You can work out the number someone else is thinking of as follows. Ask a friend to think of any natural number less than 100. Then ask them to tell you the remainders when this number is divided by. . . .
Pick the number of times a week that you eat chocolate. This number must be more than one but less than ten.
Multiply this number by 2. Add 5 (for Sunday). Multiply by 50... Can you explain why it. . . .
What would be the smallest number of moves needed to move a Knight
from a chess set from one corner to the opposite corner of a 99 by
99 square board?
Use the interactivity to investigate what kinds of triangles can be
drawn on peg boards with different numbers of pegs.
Draw a square. A second square of the same size slides around the
first always maintaining contact and keeping the same orientation.
How far does the dot travel?
Take any two digit number, for example 58. What do you have to do to reverse the order of the digits? Can you find a rule for reversing the order of digits for any two digit number?
Start with two numbers. This is the start of a sequence. The next
number is the average of the last two numbers. Continue the
sequence. What will happen if you carry on for ever? | <urn:uuid:ac28a887-4a55-4dee-ae15-f49f67e45639> | 3.421875 | 1,744 | Content Listing | Science & Tech. | 74.996376 |
A proposal for obtaining optical resolution better than the classical limit by means of spatially entangled quantum states of light opens a new frontier in the fields of quantum optical imaging, metrology, and sensing.
The blurring effects of diffraction pose an obstacle to transmitting an image with all-optical technology. A method to reduce diffraction that takes advantage of the thermal motion of atoms could prove a way to keep images sharp.
Metamaterials can be designed to rotate light as it passes through them. If the effect is strong enough, it can lead to the material having a negative index of refraction and light bouncing around very differently than expected.
Preparing a harmonic oscillator in a state with a well-defined energy is a tricky business. With the new tools provided by cavity and circuit quantum electrodynamics it is now possible to make these pure quantum states and watch how they evolve in time.
Physics1, 20 (2008) – Published September 15, 2008
Thick layers of disordered materials, such as milk or snow, scatter light so that very little of it gets through. Theorists say that a properly designed combination of incident light waves would be almost completely transmitted and we now have experimental proof of this remarkable result. | <urn:uuid:b1fb6ccf-9325-4a97-96e5-15c1d6ade090> | 3.421875 | 254 | Content Listing | Science & Tech. | 33.498696 |
Major Section: BOOKS
A book, say
"arith", is said to have a ``certificate'' if there
is a file named
"arith.cert". Certificates are created by the
certify-book and inspected by
sums are used to help ensure that certificates are legitimate and
that the corresponding book has not been modified since
certification. But because the file system is insecure and check
sums are not perfect it is possible for the inclusion of a book to
cause inconsistency even though the book carries an impeccable
The certificate includes the version number of the certifying ACL2. A book is considered uncertified if it is included in an ACL2 with a different version number.
The presence of a ``valid'' certificate file for a book attests to
two things: all of the events of the book are admissible in a
certain extension of the initial ACL2 logic, and the non-
events of the book are independent of the
(see local-incompatibility). In addition, the certificate
contains the commands used to construct the world in which
certification occurred. Among those commands, of course, are the
defpkgs defining the packages used in the book. When a book is
included into a host world, that world is first extended
by the commands listed in the certificate for the book. Unless that
causes an error due to name conflicts, the extension ensures that
all the packages used by the book are identically defined in the
Because the host file system is insecure, there is no way ACL2 can guarantee that the contents of a book remain the same as when its certificate was written. That is, between the time a book is certified and the time it is used, it may be modified. Furthermore, certificates can be counterfeited. Check sums (see check-sum) are used to help detect such problems. But check sums provide imperfect security: two different files can have the same check sum.
Therefore, from the strictly logical point of view, one must consider even the inclusion of certified books as placing a burden on the user:
We say that a given execution of
The non-erroneous inclusion of a certified book is consistency preserving provided (a) the objects read by
include-bookfrom the certificate were the objects written there by a
certify-bookand (b) the forms read by
include-bookfrom the book itself are the forms read by the corresponding
include-bookis ``certified'' if a certificate file for the book is present and well-formed and the check sum information contained within it supports the conclusion that the events read by the
include-bookare the ones checked by
certify-book. When an uncertified
include-bookoccurs, warnings are printed or errors are caused. But even if no warning is printed, you must accept burdens (a) and (b) if you use books. These burdens are easier to live with if you protect your books so that other users cannot write to them, you abstain from running concurrent ACL2 jobs, and you abstain from counterfeiting certificates. But even on a single user uniprocessor, you can shoot yourself in the foot by using the ACL2 io primitives to fabricate an inconsistent book and the corresponding certificate.
Note that part (a) of the burden described above implies, in particular, that there are no guarantees when a certificate is copied. When books are renamed (as by copying them), it is recommended that their certificates be removed and the books be recertified. The expectation is that recertification will go through without a hitch if relative pathnames are used. See pathname, which is not on the guided tour.
Certificates essentially contain two parts, a portcullis and a
keep. There is a third part, an
expansion-alist, in order
to record expansions if
make-event has been used, but the user
need not be concerned with that level of detail.
See portcullis to continue the guided tour through books. | <urn:uuid:5f2a6bdc-8b03-491c-9ea5-9e8896e590ad> | 2.984375 | 851 | Documentation | Software Dev. | 35.933332 |
SQL Server Certificates and Asymmetric Keys
Public Key Cryptography (PKI) is a form of message secrecy in which a user creates a public key and a private key. The private key is kept secret, whereas the public key can be distributed to others. Although the keys are mathematically related, the private key cannot be easily derived by using the public key. The public key is used to encrypt data and the private key is used to decrypt data. A message that is encrypted by using the public key can only be decrypted by using the correct private key. Since there are two different keys, these keys are asymmetric.
Certificates and asymmetric keys are both ways to use asymmetric encryption. Certificates are often used as containers for asymmetric keys because they can contain more information such as expiry dates and issuers. There is no difference between the two mechanisms for the cryptographic algorithm, and no difference in strength given the same key length. Generally, you use a certificate to encrypt other types of encryption keys in a database, or to sign code modules.
Certificates and asymmetric keys can decrypt data that the other encrypts. Generally, you use asymmetric encryption to encrypt a symmetric key for storage in a database.
A public key does not have a particular format like a certificate would have, and you cannot export it to a file.
SQL Server contains features that enable you to create and manage certificates and keys for use with the server and database. SQL Server cannot be used to create and manage certificates and keys with other applications or in the operating system.
A certificate is a digitally signed security object that contains a public (and optionally a private) key for SQL Server. You can use externally generated certificates or SQL Server can generate certificates.
SQL Server certificates comply with the IETF X.509v3 certificate standard.
Certificates are useful because of the option of both exporting and importing keys to X.509 certificate files. The syntax for creating certificates allows for creation options for certificates such as an expiry date.
Using a Certificate in SQL Server
Certificates can be used to help secure connections, in database mirroring, to sign packages and other objects, or to encrypt data or connections. The following table lists additional resources for certificates in SQL Server.
Explains the command for creating certificates.
Displays information about how to use certificates with Service Broker
Shows information about how to use certificates to sign software packages.
Details how to use certificates with dialogs.
Covers information about how to use certificates with Database Mirroring.
Explains how to encrypt connections to SQL Server
Asymmetric keys are used for securing symmetric keys. They can also be used for limited data encryption and to digitally sign database objects. An asymmetric key consists of a private key and a corresponding public key. For more information about asymmetric keys, see CREATE ASYMMETRIC KEY (Transact-SQL).
Asymmetric keys can be imported from strong name key files, but they cannot be exported. They also do not have expiry options. Asymmetric keys cannot encrypt connections.
Using an Asymmetric Key in SQL Server
Asymmetric keys can be used to help secure data or sign plaintext. The following table lists additional resources for asymmetric keys in SQL Server.
Microsoft provides tools and utilities that will generate certificates and strong name key files. These tools offer a richer amount of flexibility in the key generation process than the SQL Server syntax. You can use these tools to create RSA keys with more complex key lengths and then import them into SQL Server. The following table explains shows where to find these tools. | <urn:uuid:fd7921bb-d21b-444d-b751-7e68c1a339ac> | 3.765625 | 753 | Documentation | Software Dev. | 32.560507 |
abstract class sys::Obj
Obj is the root class of all classes.
Return a negative integer, zero, or a positive integer if this object is less than, equal to, or greater than the specified object:
this < that => <0 this == that => 0 this > that => >0
3.compare(8) => -1 8.compare(3) => 1 8.compare(8) => 0 3 <=> 8 => -1 // shortcut for 3.compare(8)
x.toStrto standard output. If
xis null then print "null". If no argument is provided then print an empty line.
Compare this object to the specified for equality. This method may be accessed via the == and != shortcut operators. If not overridden the default implementation compares for reference equality using the === operator. If this method is overridden, then hash() must also be overridden such that any two objects which return true for equals() must return the same value for hash(). This method must accept
nulland return false.
virtual Int hash()
Return a unique hashcode for this object. If a class overrides hash() then it must ensure if equals() returns true for any two objects then they have same hash code.
Return if this Obj is immutable and safe to share between threads:
- an instance of a const class
- the result of
- a Func object may or may not be immutable - see
- other instances are assumed mutable and return false
Obj constructor for subclasses.
Get an immutable representation of this instance or throw NotImmutableErr if this object cannot be represented as an immutable:
- if type is const, return this
- if already an immutable List, Map, or Func return this
- if a List, then attempt to perform a deep clone by calling toImmutable on all items
- if a Map, then attempt to perform a deep clone by calling toImmutable on all values (keys are already immutable)
- some Funcs can be made immutable - see
- any other object throws NotImmutableErr
virtual Str toStr()
Return a string representation of this object.
Trap a dynamic call for handling. Dynamic calls are invoked with the -> shortcut operator:
a->x a.trap("x", null) a->x() a.trap("x", null) a->x = b a.trap("x", [b]) a->x(b) a.trap("x", [b]) a->x(b, c) a.trap("x", [b, c])
The default implementation provided by Obj attempts to use reflection. If name maps to a method, it is invoked with the specified arguments. If name maps to a field and args.size is zero, get the field. If name maps to a field and args.size is one, set the field and return args. Otherwise throw UnknownSlotErr.
Typeinstance which represents this object's class. Also see`Type.of` or
This method called whenever an it-block is applied to an object. The default implementation calls the function with
this, and then returns | <urn:uuid:92edab53-3576-4301-aef5-4b3b6d771897> | 3.703125 | 665 | Documentation | Software Dev. | 65.307609 |
Tomorrow is National DNA Day, in commemoration of the 1953 discovery of the molecule’s double helix structure and the 2003 completion of the Human Genome Project. But while the focus of the government-conceived holiday is on the DNA of one familiar species, homo sapiens, there are some other genomes worth considering on a day devoted to nucleic acid.
The Human Genome Project, as I learned researching for an interview on genetic testing with Nancy Spinner, began in 1990 and was originally planned to take 15 years. Advances in sequencing technology moved so quickly that the project finished two years early. In 2005, the NSF, USDA, and DOE funded a project at Washington University and Iowa State University to sequence the maize genome. The two institutions published a draft of the genome in February of this year.
News of the corn genetic sequencing arrived the same week the Svalbard Seed Vault opened in Norway—a coincidence I noted on Science Progress. Each project represents different but complementary approaches to plant genetic resources: the sequencing an understanding and control over biological materials, the seed bank a commitment to the preservation of biodiversity.
But in light of some of the most complicated global resource problems of late—soaring energy and food prices, and competition between crops grown for food, fuel, and feed—DNA day could be a moment to reflect on the sustainability of genetic resources beyond our own.
The Senate today passed the Genetic Information Non-discrimination Act, designed to protect patients from abuses of their genetic information by insurance companies or employers. Cutting people from insurance rolls is one possible scary use of genetic information that is getting easier to obtain. Another is the reckless creation of synthetic organisms (like nasty pathogens) from readily available cassettes of DNA—which enabled the construction of the first artificial bacteria genome at the Craig Venter Institute just a few months ago.
But what does Venter plan to do with those engineered microbes? Make biofuels.
The point being that understanding and celebrating achievements in genetics isn’t just going to make us healthier. Genetics already plays a significant role in determining what we eat—and that role will only increase—but DNA will also shape the fuel we use to move that food around. | <urn:uuid:6b24a47f-4894-4f4a-afb8-dbfe3131e227> | 3.34375 | 450 | Personal Blog | Science & Tech. | 28.786572 |
Pot beetle (Cryptocephalus primarius)
|Size||Female length: 6-8 mm|
Male length: 5-7 mm
Classified as Endangered in the UK.
This rather shiny beetle (one of the larger Cryptocephalus species) has orange wing-cases (elytra), each with five black spots. The head and thorax are shining black. Both sexes have black legs and antennae, which are relatively longer in males.
Although this beetle has been recorded from five sites as far apart as Perthshire and Dorset, its last known haunt was Rodborough Hill, near Dursley in west Gloucestershire. Outside of the British Isles, it is found in central and southern Europe.
The adult beetles are associated with common rock-rose (Helianthemum nummularium), growing on warm, calcareous hillsides. The preferred adult and larval host plant is probably rock-rose.
Very little is known about the life of these beetles. The adults are found between May and July. Larvae develop at the base of the host plant, probably feeding on leaf litter. There is no evidence to suggest a link with ants, which have been shown to pay no attention to Cryptocephalus eggs.
The chief threats to this species are the loss of the calcareous grassland habitat and inappropriate grazing regimes.
This species of leaf beetle is listed in the UK Biodiversity Action Plan (UK BAP) and included in English Nature's Species Recovery Programme. It is important that more information is gathered about this species' habitat requirements and its ecology, as well as the other members of the Cryptocephalus group of leaf beetles.
The rare UK members of the genus Cryptocephalus were subjects of a post-graduate study by Ross Piper of Leeds University.
Information supplied by English Nature.
- Antennae: one of a pair of sensory structures on the head of invertebrates.
- Calcareous: containing free calcium carbonate, chalky.
- Elytra: in beetles and earwigs, the hard fore wings. They are held aloft when the insect flies, and are often coloured or patterned.
- Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Thorax: part of the body located near the head in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs. | <urn:uuid:1f90ee36-1f1f-405e-9d10-1ada9ef93999> | 3.046875 | 535 | Knowledge Article | Science & Tech. | 45.532102 |
partitionArticle Free Pass
partition, in mathematics and logic, division of a set of objects into a family of subsets that are mutually exclusive and jointly exhaustive; that is, no element of the original set is present in more than one of the subsets, and all the subsets together contain all the members of the original set.
A related concept, central to the mathematical topics of combinatorics and number theory, is the partition of a positive integer—that is, the number of ways that an integer n can be expressed as the sum of k smaller integers. For example, the number of ways of representing the number 7 as the sum of 3 smaller whole numbers (n = 7, k = 3) is 4 (5 + 1 + 1, 4 + 2 + 1, 3 + 3 + 1, and 3 + 2 + 2).
What made you want to look up "partition"? Please share what surprised you most... | <urn:uuid:00a1868d-52f3-49a2-8519-a6e2e568089e> | 3.609375 | 193 | Knowledge Article | Science & Tech. | 60.189865 |
TED Talks series, FILMED JUL 2009 • POSTED SEP 2009 • TEDGlobal 2009
Photographer James Balog shares new image sequences from the Extreme Ice Survey, a network of time-lapse cameras recording glaciers receding at an alarming rate, some of the most vivid evidence yet of climate change.
To demonstrate how photography can be used as a tool to support evidence of climate change.
ACTIVITY DESCRIPTION AND TEACHING MATERIALS
Watch >> TED Talks: James Balog: Time-lapse proof of extreme ice loss
Listen or Download >> TED Talks: James Balog: Time-lapse proof of extreme ice loss
Assessment is at the discretion of the educator and how this video is applied.
REFERENCES AND RESOURCES
James Balog is an American photographer whose work revolves around the relationship between humans and nature. His latest work, the Extreme Ice Survey, captures the twisting, soaring forms of threatened wild ice. Full Bio » | <urn:uuid:97a8db1e-7a1a-4956-87f6-8d696a72b571> | 2.859375 | 203 | Truncated | Science & Tech. | 22.503 |
Loess is fine-grained material that has been transported and deposited by the wind. The sediments come from glacial outwash plains, where glaciers deposit fine particles of silt and clay, or from desert areas that have little vegetation to anchor small particles. Prevailing wind patterns blowing across these environments can produce thick deposits of loess downwind of the area. Examine the images to interpret how loess is formed.
! Click each image to see a larger view. | <urn:uuid:63df1a0c-2ee1-440f-a262-48dd445caf87> | 4.03125 | 97 | Truncated | Science & Tech. | 45.928333 |
My Saved Article
|Atomic Number:||36||Atomic Symbol:||Kr|
|Atomic Weight:||83.80||Electron Configuration:||2-8-18-8|
|Melting Point:||-157.2oC||Boiling Point:||-153.4oC|
History(Gr. kryptos, hidden) Discovered in 1898 by Sir William Ramsay
and M.W. Travers of Britain, in the residue left after liquid air had nearly
SourcesKrypton is present in the air to the extent of about 1 ppm. The
atmosphere of Mars has been found to contain 0.3 ppm of krypton.
- It is one of the "noble" gases.
- It is characterized by its brilliant green and orange spectral lines.
- Naturally occurring krypton contains six stable isotopes.
- Seventeen other unstable isotopes are now recognized.
- The spectral lines of krypton are easily produced and some are very sharp.
Solid krypton is a white crystalline substance with a face-centered cubic
structure which is common to all the "rare gases."
- In 1960 it was internationally agreed that the fundamental unit of length,
the meter, should be defined in terms of the orange-red spectral line of
- This replaced the standard meter of Paris, which was defined in terms of a
bar made of a platinum-iridium alloy.
- In October 1983 the meter, which originally was defined as being one ten
millionth of a quadrant of the earth's polar circumference, was again redefined
by the International Bureau of Weights and Measures as being the length of a
path traveled by light in a vacuum during a time interval of 1/299,792,458 of a
While krypton is generally thought of as a rare gas that normally does not
combine with other elements to form compounds, it now appears that the existence
of some krypton compounds is established.
Krypton difluoride has been prepared in gram quantities and can be made by
A higher fluoride of krypton and a salt of an oxyacid of krypton also have
Molecule-ions of ArKr+ and KrH+ have been identified and investigated, and
evidence is provided for the formation of KrXe or KrXe+.
Krypton clathrates have been prepared with hydroquinone and phenol.
85Kr has found recent application in chemical analysis.
By imbedding the isotope in various solids, kryptonates are formed.
The activity of these kryptonates is sensitive to chemical reactions at the
Estimates of the concentration of reactants are therefore made possible.
Krypton is used in certain photographic flash lamps for high-speed
Uses thus far have been limited because of its high cost.
CostKrypton gas presently costs about $30/l. | <urn:uuid:1e7bc841-cd36-47d0-9863-4e4212be5fff> | 3.53125 | 627 | Knowledge Article | Science & Tech. | 47.315688 |