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In 1905, Einstein published four revolutionary papers in the journal Annalen der Physik, including papers explaining the photoelectric effect and the fundamentals of his special theory of relativity. His work laid the foundation for the field of quantum physics, though he himself had some concerns about the conceptual implications of his own work.
Specifically, Einstein didn't like the fact that quantum physics allows (conceptually at the time, though it has since been demonstrated) that information about a system can be "communicated" instantaneously through quantum entanglement. This violates one of the principles of relativity, which is that no information can travel faster than the speed of light. Einstein's friendly, though heated, debate with colleague Niels Bohr on this issue went on for years, and provided key insights into the developing quantum theory.
In the later years of his life, Einstein focused his work on the attempt to derive a Unified Field Theory (more often called Grand Unified Theory, or GUT, at the time) which would unify the fundamental forces of physics into a single conceptual framework. This attempt was not successful, but it is still the holy grail of physics research, resulting in theories such as string theory, quantum gravity, and loop quantum gravity.
In addition to his work in physics, he also became a prominent figure in popular culture, obtaining a status akin to a modern day rock star. His distinctive appearance may have helped with this, and certainly has made him popular among cartoonists. He wrote a letter to President Franklin Delano Roosevelt in 1939, expressing concern that Germany might be using his own research to develop nuclear weapons. This letter motivated FDR to initiate the Manhattan Project to develop such a weapon for the Allies first.
Einstein later became a vocal supporter of the Zionist movement, although he also expressed concerns about the specifics of the decision to form Israel ... concerns which the continued violence in that region & border dispute shows to have been prescient. He was asked to be Israel's second president, but he chose to decline it.
More about Albert Einstein: | <urn:uuid:92074c1b-4aa3-4d58-b69b-9da90caee06b> | 3.640625 | 415 | Knowledge Article | Science & Tech. | 36.222543 |
Tom Wessels, MA
Department of Environmental Studies
Protecting biodiversity at a local level is integral to protecting global biodiversity. An inventory of plant communities for one town gives a representation of the spectrum of plant species which a region might support. This paper surveys the plant communities of Canterbury, New Hampshire, and documents the species present at nine wetland and ten upland sites, with management recommendations for some of the sites. The site descriptions are prefaced by a brief geological and land use history for the region. When possible, notes on land use history and succession are given at specific sites. | <urn:uuid:3efa55d4-1ae6-4b73-877f-00750823230b> | 2.6875 | 119 | Academic Writing | Science & Tech. | 22.995366 |
A variety of human activities pose serious threats to life in the Mojave Desert. Use of desert lands for livestock grazing can strip land of most of its vegetation. Farming and urbanization both result in increased use of groundwater that can leave desert plants and animals without the water they need to survive. The growing popularity of off-highway vehicles (OHVs) causes further damage to plants and fragile desert soils. When desert plants are damaged, the thin soil begins to erode, making the area unsuitable for living things. Once the damage is done, the process of recovery is extremely slow. There are many reasons for this, including temperature extremes, sunlight intensity, high winds, and lack of rainfall. Another factor is the sparse vegetation that is characteristic of the desert. Fewer plants mean less humus, which is formed from the decomposed remains of plants and animals. Humus provides many of the nutrients plants need to survive.
By examining the composition of soil and making soil mixtures of our own, we can begin to understand ways in which soil contributes to plant growth and the long process that is involved in its formation. We’ll also come to appreciate why it’s important to protect the thin, fragile layer of soil in the desert.
- natural soil samples, at least 0.25 L per student, collected from several outdoor locations (make sure you have permission to dig samples if you’re not digging on school property)
- an assortment of “ingredients” for students to make their own soil mixtures, such as leaves, small rocks, broken shells, sand, clay, grass clippings, small sticks, etc., (assemble enough so that each student will be able to make about 0.5 L of soil) water
- plastic trays, cardboard box tops, or sections of newspaper, at least 25 cm by 40 cm containers of varying sizes, such as large coffee cans and plastic cups or planting pots, with a capacity of at least 0.25 L
- hand lenses, spoons, toothpicks, and other “excavating” devices
- fast-germinating seeds, such as zucchini, beans, zinnia, and cosmos
Procedure and Questions
1. Students spread samples of the natural soil out on plastic trays and use hand lenses to examine them. Can they see pieces of rock or sand? Any living things? Encourage students to smell and feel their soil samples as well, and to describe their samples as precisely as possible.
2. Remind students that soil contains both organic and inorganic materials and that its formation involves a long, complex process.
3. Next, students develop their own “recipes” for soil mixtures that they think will be capable of supporting plant life. The goal should be to produce about 0.5 L of soil mix. One approach could be to divide the class in half, with one group of students attempting to replicate desert soil and the second group working on mixtures that are more likely to be found in a forest environment. Before they begin mixing their ingredients, students need to consider the following questions:
- How would the balance of ingredients differ between forest soils and desert soils? (Desert soils would contain more sand, while forest soils are likely to contain more organic matter and, depending on where they come from, possibly more clay.)
- What ingredients would provide organic matter to plants? (From the above list of materials, leaves, grass clippings, and sticks would provide organic matter.) What ingredients would provide minerals? (rocks and shells)
- What materials would improve drainage? (sand and other larger particles)
- What materials would help retain water? (clay and other smaller particles)
- What materials would help anchor plant roots? (clay)
Following a discussion of these questions, students adjust their recipes if they wish.
4. Students then combine their ingredients to make the soil, adding a few tablespoons of water to each mixture. Stir until the ingredients are thoroughly moistened.
5. Discuss with the class the ways in which their mixtures are similar to and differ from the natural soil samples they examined in Step 1. What might account for differences? (Answers will vary depending on where the natural samples came from and what ingredients were used in students’ recipes, but the major factor accounting for differences is time: The natural processes that create soil occur slowly.)
6. How do students think plants will grow in the soils they made? To test their ideas, have students put their soil mixtures into plastic pots and plant seeds in them. Seeds should also be planted in the natural soils for comparison. Place all the pots in a well-lighted area, and water every couple of days with equal amounts of water.
This activity aligns with the following National Science Education Standard: Content Standard C: Life Science – Diversity and Adaptations of Organisms
Desert animals have developed many ways to cope with the heat and sun. Many come out only at night or during the early morning and late evening. They spend their days in the shade or they burrow into the sand, where temperatures are cooler. Students can easily test the value of such strategies by measuring temperature differences in the schoolyard or in their own backyards.
- two indoor-outdoor or classroom thermometers, 15–20 cm long
- 5 kg of sand
- a deep box or small wastebasket, about 15 L in capacity
- plenty of sunshine
Procedure and Questions
1. Students place one thermometer out in the bright sun for at least an hour, and a second one in the shade of a tree or large boulder for the same length of time. (Make sure that this second thermometer stays in the shade for the entire testing period.) At the prescribed time, read the temperatures on the two thermometers. Students should discover that the temperature in the shady area is considerably lower than that in the sunny location.
2. Next, fill the box or small wastebasket with sand. The sand should be about 25–30 cm deep. Put the container in an area where the sun will shine on it all day. In the afternoon, push the end of one thermometer just slightly into the sand. After a minute or so, record the temperature. Place the second thermometer deep in the sand. Again, wait about a minute and record the temperature. How much lower is the temperature beneath the sand?
Assign each student or student group a specific desert animal to research and report on. Students should focus on ways in which their animal is adapted to its environment. Students should be encouraged to use the Internet as a resource in their research; some good websites to use as starting points are:
Mojave National Preserve–Desert Plants and Animals at http://www.nps.gov/moja/naturescience/index.htm
Desert USA-Desert Animals and Wildlife at http://www.desertusa.com/animal.html | <urn:uuid:0a733281-eb6c-4ff3-95cf-a78e9e84be53> | 4.03125 | 1,446 | Tutorial | Science & Tech. | 54.361283 |
Halupka, L., Dyrcz, A. and Borowiec, M. 2008. Climate change affects breeding of reed warblers Acrocephalus scirpaceus. Journal of Avian Biology 39: 95-100.
What was done
The authors documented various breeding parameters of reed warblers -- long-lived passerine birds that spend their winters in Africa but breed in reed beds of marshlands in the Palaearctic, with some of them nesting in fishponds of the Stawy Milickie Reserve in southwest Poland -- during twelve breeding seasons (1970-73, 1980-83, 1994, 2003 and 2005-06) that encompassed the period 1970-2006, after which they compared trends in what they measured with concomitant trends in mean monthly temperatures.
What was learned
Halupka et al. report that mean breeding season (April-August) temperatures increased significantly between 1970 and 2006, as did the mean temperatures of each individual month of the breeding season, with average temperatures for the May-July period rising by 2°C. In response to these changes, they found that in 2005 and 2006, egg-laying (measured by the first egg date of the earliest pair of breeding birds) started three weeks earlier than in 1970, and that the median first egg date shifted forward in time by eighteen days. The end of egg-laying, however, did not change significantly in either direction, so there was a corresponding increase in the total length of the egg-laying period.
With the longer laying period available to them, more birds were able to rear second broods. In the 1970s and 1980s, for example, the Polish researchers report that "only about 0-15% of individuals laid second clutches," but that "between 1994 and 2006 up to 35% of birds reared second broods." In addition, they report that "during seasons with warm springs, early nests were better protected by being hidden in newly emerged reeds," and that "as a result, these nests suffered fewer losses from predation."
What it means
As stated by the researchers in their concluding paragraph, "it would appear that the studied population of reed warblers benefits from climate warming," which is something we probably won't read about any time soon in the popular literature ... which is a matter of some significance in and of itself!!! | <urn:uuid:c1999679-be64-41bb-a620-b8f703e4ca5e> | 3.40625 | 492 | Knowledge Article | Science & Tech. | 57.586866 |
You may never be able to escape the effects of gravity (in its entirety), but you can reduce it, freeing yourself from the stress of lifting objects of greater density than yourself.
One of the best places to do this is by launching yourself beyond the sky in order to get a glimpse of the heavens above. But staying there for long periods could have harmful effects upon your health, hurting not only your heart, bones, and immune system, but also aiding the deadly bacteria trying to kill you.
Currently scientists are trying to find ways to combat this issue, using everything from drugs to brain surgery. Although these options may eventually liberate us from the side effects of microgravity, it may be “less messy” to find a technological solution (as it may have less side effects).
While futuristic technologies such as plasma rockets and space elevator stations may hold much promise for our young race (gravity wise), we may be better off constructing orbital space stations–with a Bigelow twist.
Having already successfully launched two inflatable space stations (with a third one planned for human habitation), Bigelow plans on launching these inflatable modules, and connecting them together to form a space station that may rival the ISS.
But what if Bigelow Aerospace could alter the design of their inflatable modules to make several of them connect in a circle? They could then slowly rotate the entire structure (note: which may be an engineer’s nightmare) in order to simulate artificial gravity via centrifugal force.
Bigelow’s modules on the other hand, may not only be cheaper to launch into space, but may be safer as well, as its thick outer skin may be able to take “a greater punch” than its metallic rivals.
These inflatable modules may also more expendable than their more rigid cousins, as it would be much easier to replace a module or two (like a Pontoon bridge), than an entire section of a more traditional space station.
Whether or not Bigelow eventually decides to move in this direction, only time will reveal. But if so, Bigelow could ultimately allow us to safely venture out into the blackness of space, without the fear of losing our health in the process.
Editors Note (3/31): Ken Talton of the Brickmuppet Blog points out that the engineering/math to rotate
Bigelow’s inflatable space stations in order to simulate gravity has already been figured out, and can be seen over here (pdf).
Update (3/31): The space stations are not exactly like Bigelow, but they do provide some “hard science” towards the idea. | <urn:uuid:d261cfdb-a4e9-422e-8b85-593af50964a2> | 3.109375 | 548 | Personal Blog | Science & Tech. | 33.677241 |
Meteor impact that gouged 30-mile crater on Mars reveals traces of ancient reservoir
- Crater reveals layers thought to have been carved by groundwater reservoir
- Lends weight to idea that Mars was once very different
- Mars has 'undergone radical climate change'
By Rob Waugh
Two side-by-side meteor craters on Mars have revealed that the Red Planet has undergone serious climate change in its history.
One crater in particular reveals dark traces of sediment thought to have been cemented together by water from an ancient groundwater reservoir, before being carved away by howling Martian wind.
The find, by the European Space Agency's Mars Express orbiter, has lent weight to the idea that Mars was once very different to the dead orb we see now.
One crater in particular reveals dark traces of sediment thought to have been cemented together by water from an ancient groundwater reservoir, before being carved away by howling Martian wind
The ancient 'climate change' that turned Mars from a wet planet - possibly capable of supporting life - to the dusty, wind-scoured orb that we see today was probably caused by changes in the axis of the planet's rotation.
Similar forces are thought to have an impact on the cycle of ice ages on Earth.
On 19 June 2011, Mars Express pointed its high-resolution stereo camera at the Arabia Terra region of Mars, imaging the Danielson and Kalocsa craters.
Danielson crater is named after the late George E. Danielson, who was instrumental in the development of many spacecraft cameras flown to Mars, and is 40 miles across.
Kalocsa crater lies in the center of the image and is smaller, about 20 miles in diameter.
Danielson crater, like many in the Arabia Terra region, is filled with layered sediments, which in this instance have been heavily eroded over time. Within the crater are peculiarly layered buttes, known as yardangs.
The find, by the European Space Agency's Mars Express orbiter, has lent weight to the idea that Mars was once very different to the dead orb we see now
Yardangs are streamlined hills carved from bedrock or any consolidated or semi-consolidated material by abrasive dust and sand particles carried in the wind.
They are seen on Earth in desert regions, with notable examples in North Africa, Central Asia and Arizona in the United States.
In the case of Danielson crater, it is believed that sediments were cemented by water, possibly from an ancient deep groundwater reservoir, before being eroded by the wind.
The orientation of the yardangs leads scientists to theorize that strong north-northeasterly winds (from the lower right in the image) both deposited the original sediments and then caused their erosion. | <urn:uuid:09f50e68-1c0e-48d0-945c-782b43818fce> | 3.09375 | 567 | Truncated | Science & Tech. | 31.061 |
A smooth, sleek reptile with scales and no legs. No, it’s not the Slytherin house’s mascot from Harry Potter – snake. It is a legless lizard! It is one of the 14 newly discovered species in central Brazil’s Cerrado, the sixth largest ecoregion in the world. More than half of its original area has been lost to agriculture, endangering thousands of species like this one, and some yet to be discovered. “We don’t know exactly what we’re losing,” laments Conservation International Biologist Cristiano Nogueira, team leader of the expedition.
The soil under your feet may have a solution to global warming. Researchers from Newcastle University, UK, are planning to design special soils, which will remove carbon from the atmosphere permanently. The basic principle is that plants absorb carbon dioxide during photosynthesis, and pump out the surplus carbon through their roots into the soil around them.
From here, this carbon escapes back to the atmosphere or enters groundwater. But these special soils will “lock” this carbon with the help of calcium. The calcium in the soils will react with the carbon and form a harmless stable compound – calcium carbonate. Thus, preventing the carbon from escaping back to the environment.
The clue to the next-generation computing lies in a bug – a beetle from Brazil. For a long time, researchers have been trying to build an ideal ‘photonic crystal’ to manipulate visible light and create ultra-fast optical computers. In other words, these superfast computers will run on light (photons), instead of electricity (electrons). Recently, chemists at the University of Utah, US, discovered that the structures already exist in the iridescent green scales of the beetle (Lamprocyphus augustus).
“It appears that a simple creature like a beetle provides us with one of the technologically most sought-after structures for the next generation of computing,” says study leader Michael Bartl, an assistant professor of chemistry and adjunct assistant professor of physics at the University. The researchers are now trying to design a synthetic version of the beetle’s photonic crystals. Great things come in small packages!
Scientists have recently made a black wet suit – for a penguin. Yes, you heard it right. This was done for Pierre, an African penguin (or Jackass Penguin) at the California Academy of Sciences, US. He is special because when most of these penguins only live to 20, he is the oldest at 25.
Pierre started balding or shedding his waterproof insulating feathers, and thus, was left cold and too embarrassed to be with his fellow penguins. So the scientists made him wear a wet suit. And it worked wonders, and he was back in action! Any comment?
Now shark tails will be used to collect oceanic energy. Not the real shark tails, but mechanical ones. Tim Finnigan, a professor of ocean engineering at the University of Sydney, Australia, has designed an ‘oceanic energy collector’ – a device that harnesses the power of the sea – mimicking the design of shark tails.
“I realised the systems that function the best are the ones that already exist there,” says Professor Finnigan. The fins are crescent-shaped and stiff and effectively generate a powerful and seamless thrust. Inspiration can come from anywhere…
Your computer might fuel your car in the next 10 years! Researchers in Romania and Turkey have developed a way to recycle printed circuit boards, which contain high levels of pollutants like heavy metals and flame-retardants. A combination of high temperatures, catalysts and chemical filtration removes the toxic substances.
And converts the waste into environmentfriendly raw materials! These materials can be used as feedstock and fuels, says researcher Cornelia Vasile and her colleagues. Another great idea for making wealth from waste! | <urn:uuid:ae7e6351-5de3-4ca5-8186-3d5a07ea4137> | 3.515625 | 812 | Content Listing | Science & Tech. | 44.401257 |
- Infowars - http://www.infowars.com -
‘Perfect’ Invisibility Cloak Uses Metamaterials To Bend Light
November 12, 2012
The days when invisibility cloaks were confined to the world of “Harry Potter” may soon be over. Physicists at Duke University announced Monday that they had successfully cloaked an object with “perfect” invisibility.
Attempts at creating an invisibility “cloak” began in 2006, when David Smith (also a co-author of the new study) and colleagues developed theory of “transformation optics,” BBC News reported. The theory centers on redirecting electromagnetic fields around an object, rendering it invisible, ScienceNOW reported.
No effort had achieved “perfect” invisibility until Dr. Smith and graduate student Nathan Landy modified earlier cloak models with composite structures known as metamaterials. These materials can be designed to bend light and other electromagnetic radiation around them.
Article printed from Infowars: http://www.infowars.com
URL to article: http://www.infowars.com/perfect-invisibility-cloak-uses-metamaterials-to-bend-light/
Copyright © 2013 Infowars. All rights reserved. | <urn:uuid:087143ec-8366-4e93-8bc1-dc94bdae37c1> | 2.78125 | 273 | Truncated | Science & Tech. | 31.469859 |
The Scripter’s Journey Series
3. Controlling the FlowTable of Contents
I. The Importance of Program Flow!
II. Conditional Operators!
III. Logical Operators!
IV. Relational Operators!
V. All about Looping!
VI. ConclusionThe Importance of Program Flow!
Program flow is essential. What is program flow you ask? Well, program flow is basically the order or the sequence in which lines or blocks of code are executed. Hence, the title “Controlling the flow” means in this lesson we’ll be learning how to control the sequence of our programs. This is important because being able to control this program flow allows us to adjust to different user inputs or anything in the program that allows for different “routes” (I’ll call these things “situations” and I’ll explain them more throughout the tutorial). For example if the user buys a Wooden Sword at the local equipment shop we want a specific block of code to run when they buy it (like the sound effect that plays and the additional stats). In order to run that specific block of code, we would need to “control the flow” of the program and change the sequence so that we run the specific block of code that we want. Programming languages always give a lot options at your disposal in order to control this program flow and we’ll be going through everything you’ll need to know to effectively direct your program. Conditional Operators!
So, the main idea of this tutorial is to be able to account for every possible “route” or situation so that you can direct your program in the right sequence or order to address this situation (Like the buying of the Wooden Sword example, this would be a “situation”). Situations can be thought of as Boolean Expressions. Remember last tutorial we talked about Booleans and how they can be equal to either true or false, Boolean Expressions are just the same except instead of just being a variable, it is an expression or “situation” that is evaluated to either true or false. (For example, 1 equals 1 is an expression that evaluates to true). Operators in general (at least the types of operators we’ll be discussing) allow us to “define” our situation (when I say situation I’m referring the Boolean Expression we just discussed). More specifically, Conditional Operators prefix this definition of the situation and establishes when the block or line of code will execute in relation to the situation. Here is a list of the conditional operators that you’ll be using frequently: “if”, “elsif”, “else”, “unless”, “while”, and “until”.
“If”, “elsif”, and “else” are all essentially the same idea. “If” is the mother of all conditional operators, it’s the conditional operator that is used undoubtedly used the most. Here is a basic example of the usage of “if” to help you understand it’s basic idea:
IF my dog runs down the street…(certain block of code will execute, in this case, you’ll run down the street like a lunatic to save your dog).
So as you can see, “if” basically says that the code will execute if the situation evaluates to “true”. Now “elsif” and “else” cannot exist by themselves, they need to be paired with “if”. So here is another basic example:
IF my dog runs down the street…I’ll run down the street like a lunatic to save my dog.
ELSIF (basically establishing another possible situation) my dog runs to my backyard…I’ll laugh and go use the bathroom.
ELSIF my dog watches television..I’ll watch television with him.
ELSE…I don’t care if he is doing anything else.
Through this example I hope you understand the jist of these guys, but let me further elaborate. Elsif is basically another “if” condition, it just needs to come after the original “if” condition to establish that you now after more “situations”. “Else” is basically the “if all else fails” condition and does not prefix a “situation”, else pretty much takes in every other infinitely possible situation and points it to one block of code or line of code. In the above example if the dog doesn’t do any of the possible situations, then you don’t care anymore. Now, time to give a more serious, but straightforward example to show how you would structure an actual if statement in your Script Editor (Also, don’t worry about the == sign, we’ll get to that later):
if 1 == 1
elsif 1 == 3
print “that makes no sense”
You must always end an if statement with an “end” keyword, even if there wasn’t any “elsif” or “else” tags, a simpler example for you to understand would be:
if 1 == 1
Now, let’s move on to the next Conditional Operator which will be “unless”. As I said before, Conditional Operators prefix the definition of the situation and establish when the block of code will execute in relation to the situation. In if statements (when I say “statements” that basically refers to the situation and the block or line of code that is associated with the Conditional Operator) the block of code occurs when the situation defined, evaluates to true. In unless statements, the line or block of code occurs if the situation evaluates to false.
UNLESS my dog runs down the street…(certain block of code will execute, in this case, I’ll be happy that he is safe in my house).
So if the dog doesn’t run down the street, the situation evaluates to “false” and the code can now execute. Here’s it in code form:
unless 1 == 1
print “Yea!” # Will never print this because 1 always equals 1 therefore it is not ‘false’
Next, we’ll discuss the “while” and “until” Conditional Operators. I won’t go too in depth about that them now because we’ll be discussing them more in “All about looping”. While is basically just like an if statement, if the situation evaluates to true, the block of code will execute. The key difference is that the code will continually execute, over and over again. Until is basically just like an unless statement, if the situation evaluates to false, the block of code will execute, except it will execute continually, over and over again. This is the basic premise of looping and like I said, we’ll go into that later.Logical Operators!
Like I said earlier, operators help us “define” our situation (a.k.a Boolean Expression). Logical Operators allow us to specifically modify the “truth” or “false” aspect of a Boolean Expression’s evaluation. The logical operators that are used in RGSSX are “and”, “or”, and “not”.
IF my dog AND my neighbor’s dog run down the street…blahblahblah
As you can see “and” basically tells us that more than one situation need to evaluate to true for the code to execute. So basically, two situations need to be true in order for the block of code to execute, not one, but two.
UNLESS my dog OR my neighbor’s dog runs down the street…blahblahblah
Each situation is divided by the “and” or “or” Logical Operators to produce and overall situation. As we know before from unless statements, the block of code executes if the situation evaluates to false. “Or” basically says though that only ONE of the situations need to be true or relevant for anything to happen. So if “my dog runs down the street” or “my neighbor’s dog runs down the street” evaluate to true then the code won’t execute. But if both of them evaluate to false, than the code will execute. Let’s use an if statement with “or” so you can better understand it:
IF my dog OR my neighbor’s dog runs down the street…blahblahblah
Again, when you see “or” or “and” that means you have a new situation. When you see “or”, each situation is completely independent, and “and” each situation is tied together and rely on each other. In if statements the situation needs to evaluate to true for the code to execute. Since we’re using “or” though, only one situation needs to be true for “if” to work. So if “my dog runs down the street” evaluates to true, then bingo, the code runs. Now let’s use some RGSSX examples:
if 1 == 1 and 2 == 2
if 1 == 1 or 2==3
print “Nice.” # Only one needs to be true, and since 1 equals 1, then we’re in business.
unless 1==1 and 2== 2
print “Nice.” # since the situation evaluates to true, this will never execute.
unless 1 == 1 or 2 == 3
print “Nice.” # Since only one of the situations need to be true, this code won’t execute.
Now, since we have “and” and “or” understand, let’s cover “not”. Not basically means “the opposite of” a Boolean Expression or situation.
IF NOT 1 equals 1…blahblahblah
Don’t look at the “not”, just look at the Conditional Operator at the beginning, and the situation. It reads “if one equals one”. That evaluates to true, one always equals one. So since we have “not” in front of that, that switches the value from true to false. Since if statements only run when the situation evaluates to true, this statement won’t run. So “not” is used to reverse the evaluation. Here is code example:
if not 1 == 2
print “yea” # 1 == 2 normally evaluates to false, but since we have “not” in font, it’s reversed
Now since you have a grasp on all three Logical Operators, there is one last little cool tip I’ll discuss to wrap up this section. There is a shorthand way to write down these operators. You can use && to represent “and”, || to represent “or”, and ! to represent “not”.
if 1 == 1 && 2 == 2Relational Operators
Relational Operators are the easiest type of Operators to grasp. Basically Relational Operators simply compare and contrast different elements in a situation, such as the == operator we’ve been using. The list of Relational Operators are as follows: >, >=, <, <=, !=, and ==
First let’s go over == which simply means “equals to”, do NOT confuse this with = which is the Assignment Operator and assigns a value to a variable. It’s easy understand, basically just use this if you’d like to determine if something is equal to something else.
donkey = 5
monkey = 4
if donkey == monkey
print “that’s weird”
Next, we have the != Operator which means “not equal to” or just the opposite as the last == Operator.
The > Operator means “greater than”, the < Operator means “less than”, the >= Operator means “greater than or equal to”, and the <= Operator means “less than or equal to”. You guys should already know this though from basic math courses. Here is a code example:
if (1 > 0 and 2 < 3 ) or (2 > 4)
Just a side note, the parenthesis allow us to group ideas together. So in this case the first parenthesis is all one idea while the second parenthesis is all one idea.All About Looping!
As opposed to previous examples in which if something evaluates to true or false, the code will execute once, looping means the code will continue to run over and over again as long as the Boolean Expression is evaluating to the correct value (whether it be true or false). There are several topics to cover under looping so let’s begin.
First of all, let’s get back into while and until. While is basically, like I said before, and if statement in “loop” form. So if the situation evaluates to true, the code will execute continually as long as the Boolean Expression keeps evaluating to true, if it fails to do so, it will break out of the loop.
while 1 == 1
print “this will print forever!”
Until is basically an unless statement in “loop” form. If the situation evaluates to false, the code will execute continually as long as the Boolean Expression keeps evaluating to false.
unless 1 == 2
print “this will print forever!”
Ok, now that you have a grasp of “while” and “until”, let’s move on. Now were going to discuss ranges and “for” loops. Loops don’t always need to run forever unless the Boolean Expression evaluates to the opposite value, sometimes, if you provide a “range” or values to loop through, the loop will end after going through each value in the range. A range can be defined using periods.
This range has five values, from ‘1’ to ‘5’.
This range has 4 values, from ‘1’ to ‘4’. When you use three dots, the last number is omitted from the range. The way I think about it is that if you add something (the extra dot) you have to lose something (the last number which is 5). So now let’s apply this knowledge on ranges to what we call “for” loops.
for i in 1..5
Results: 1, 2, 3, 4, 5
Let’s dissect this code. First of all “i” is a variable that is constructed within the for loop. You do not make this variable and put in the loop, you simply give it’s name after the “for” keyword and it is automatically made. I call this variable the “Range Variable”, because it is equal to each value in the range. The way this works is that we have our range (since we have two dots it extends from one to five), and the for loop goes through each number individually and assigns this value in the range to the Range Variable (which is i). We then print that variable (which is equal to one of the values in the range) each time the loop goes through until it finishes. Also as a sidenote, each time a loop “goes” through a value, that is called an “iteration”, this will be important when we discuss how to control our loops.
Next we’ll discuss the most basic loop, which is the “loop do” loop and is provided with no condition and runs forever unless broken out from within (while talk about this later when we discuss how to control our loops).
print “I’ll keep printing forever until this computer EXPLODES”
Now that we understand all the basic types of loops, let’s look to how to control our loops. Loops can be controlled through four key terms: “break”, “next”, “retry”, and “redo”.
Break applies to all loops. Basically, break is like an emergency escape pod, it allows you to exit a loop. For example let’s take our last “loop do” loop that runs forever, we don’t want that to happen, so we would apply a break.
one = 1
one += 1
print “I’ll keep printing forever! I think…”
if one == 6
First of all, the += sign is simply an Increment Sign that allows you to add on to a value. So in this case, after each iteration of the loop, the “one” variable increase by 1, and the loop will break out when one equals 6.
The next three keywords to discuss work best with “for” loops. Next allows us to skip the current iteration and go to the next iteration.
for i in 1..5
if i == 3
This code would skip 3 so therefore 3 would never be printed. Redo causes us to redo the iteration and “play” it over again.
for i in 1..5
if i == 3
What would happen here is that 3 would continually be printed over and over again. Finally we have retry which is just like redo except it goes through the WHOLE loop over again.
Finally, I have one last note to add to this tutorial before I conclude. You may have found it annoying to put the whole:
if i == 3
Since there is only one word or a couple words that come when the condition is met. So this can be solved through the use of Statement Modifiers:
retry if i == 3Conclusion
break if 1 == 1
next if i != 2
redo if i > 1
So from this tutorial you’ve learned that it is very important to direct the flow of your program based on different situations (Boolean Expressions) that arise during the course of your program. Three types of Operators helps us do so: Conditional, Logical, and Relational. Finally, looping also allows to direct program flow and stay in a certain block of code for a certain of time as a long as a condition is met or if the use of Loop Controllers (break, next, redo, and retry) are implemented.
The order of how these tutorials will progress: http://www.rpgrevolution.com/forums/index....showtopic=54953 | <urn:uuid:1a923f51-af52-4c6c-b82e-c0df9085e4f4> | 3.953125 | 4,035 | Comment Section | Software Dev. | 60.99064 |
The Latin prefix "infra" means "below" or "beneath." Thus "infrared" refers to the region beyond or beneath the red end of the visible color spectrum. The infrared region is located between the visible and microwave regions of the electromagnetic spectrum. Because heated objects radiate energy in the infrared, it is often referred to as the heat region of the spectrum. All objects radiate some energy in the infrared, even objects at room temperature and frozen objects such as ice.
The higher the temperature of an object, the higher the spectral radiant energy, or emittance, at all wavelengths and the shorter the predominant or peak wavelength of the emissions. Peak emissions from objects at room temperature occur at 10 µm. The sun has an equivalent temperature of 5900 K and a peak wavelength of 0.53 µm (green light). It emits copious amounts of energy from the ultraviolet to beyond the far IR region.
Much of the IR emission spectrum is unusable for detection systems because the radiation is absorbed by water or carbon dioxide in the atmosphere. There are several wavelength bands, however, with good transmission.The long wavelength IR (LWIR) band spans roughly 8-14 µm, with nearly 100% transmission on the 9-12 µm band. The LWIR band offers excellent visibility of most terrestrial objects. The medium wavelength IR (MWIR or MIR) band (3.3-5.0 µm) also offers nearly 100% transmission, with the added benefit of lower, ambient, background noise. Visible and short wavelength IR (SWIR or near IR, NIR) light (0.35-2.5 µm) corresponds to a band of high atmospheric transmission and peak solar illumination, yielding detectors with the best clarity and resolution of the three bands. Without moonlight or artificial illumination, however, SWIR imagers provide poor or no imagery of objects at 300K. | <urn:uuid:419a23ca-cd84-459f-9163-fced83b11afd> | 3.921875 | 391 | Knowledge Article | Science & Tech. | 53.160421 |
The countries affected by the 2004 Asian tsunami contain the most diverse and extensive coral reefs and mangroves of the Indian Ocean, and some of the richest in the world. Not only are these ecosystems among the most threatened in the world, they also provide numerous essential ecosystem services.
It is thus not surprising that reefs and mangroves received widespread attention after the tsunami, with three principal questions posed: Are the tsunami's impacts on reefs and mangroves a further threat to their future survival? Did reefs and mangroves play a role in shoreline protection and reduce structural damage and human mortality? How could reconstruction efforts include actions to maintain these ecosystems and reduce further threats to them?Resource Type: Journal Papers
Coral reefs are the most biologically diverse of shallow water marine ecosystems but are being degraded worldwide by human activities and climate warming. Analyses of the geographic ranges of 3235 species of reef fish, corals, snails, and lobsters revealed that between 7.2 and 53.6 of each taxon have highly restricted ranges, rendering them vulnerable to extinction. Restricted-range species are clustered into centers of endemism, like those described for terrestrial taxa. The 10 richest centers of endemism cover 15.8 of the world's coral reefs (0.012 of the oceans) but include between 44.8 and 54.2 of the restricted-range species. Many occur in regions where reefs are being severely affected by people, potentially leading to numerous extinctions. Threatened centers of endemism are major biodiversity hotspots, and conservation efforts targeted toward them could help avert the loss of tropical reef biodiversity.Resource Type: Journal Papers
We made a complete survey of all the extant populations in Djibouti and to collect samples for genetic analysis with a view conserving the palm for the future.
Our survey revealed that there were a total of 314 adults, 20 juveniles, 134 rosettes, 210 small rosettes (more than 6 leaves) and 465 seedlings (<3 leaves) living in the Bankouale area of Djibouti. These are distributed unequally amongst three valley systems. 65% of the adults, 85% of the juveniles, 75% of the rosettes, 76% of the small rosettes, and 93 % of the seedlings were found in the Bankouale valley.
The threat posed to coral reefs by biological invasion is unlikely to diminish and should therefore be considered in analyses of the effectiveness of Marine Protected Areas.Resource Type: Journal Papers
Small local hunting communities in Siberia are very distant from any governmental control. Hunted waterbird species, including globally and regionally threatened species, rely for their well-being on the self regulation of remote hunting communities. Interviewed hunters showed a profound knowledge of Baikal Teal, its population status, and the causes of their past decline. Whether the knowledge is shared by other communities in the region and beyond in Northern Siberia needs verification.
This study demonstrates the utility of carbon isotope discrimination in describing genetic adaptation to arid environments, although it is probably most useful in detecting differentiation when the strategy of the species under investigation is to increase water use efficiency, rather than drought-avoidance. The results suggest that populations on the eastern and western sides of the Andes should be treated as separate management units for the purposes of conserving the genetic resource of this species.Resource Type: Journal Papers
The importance of non-timber forest products (NTFPs) to rural income was examined in a highland community in the Sierra de Manantlán Biosphere Reserve, Jalisco-Colima, Mexico. Rapid Rural Appraisal (RRA) techniques were used to interview 70 of households in the community of El Terrero. Of the nine plant species identified as NTFP sources, the two principal species traded by the community were tila (derived from the flowers and fruits of the tree Ternstroemia lineata), and blackberry (Rubus spp.). Collecting and selling of NTFPs was almost exclusively undertaken by women, with 80 of respondents participating. NTFP sale ranked as the most important source of cash income for 30 of women interviewed, and either second- or third-most important for the remainder. The research examined harvesting impact on populations of T. lineata, an understory tree species characteristic of cloud forest, which this was assessed in the four most-frequented collecting sites. Our results suggested that current harvesting approaches appear to be sustainable, although 95 of the women interviewed reported a decline in resource availability within the last 15 years, apparently resulting from illegal cutting. Suggestions are made with respect to the sustainable development of NTFP resources to help alleviate poverty within the Reserve.Resource Type: Journal Papers
Global and regional coral reef area statistics are of considerable value in fields ranging from global environmental change to fisheries to conservation. Although widely quoted, Smith's 1978 figure of 600 000rkm2 is only an approximate calculation. The World Conservation Monitoring Centre has prepared a new estimate of reef coverage by mapping emergent reef crest and very shallow reef systems. These data were rasterised, using 1rkm grid squares, as a means of reducing errors arising from variation in scale. Global and regional reef coverages were calculated from the resultant grid. The total global area is estimated at 255 000rkm2, considerably lower than many previous estimates. Variation in reef area estimates is, in part, a function of variation in reef definition.Resource Type: Journal Papers
©2013 UNEP All rights reserved | <urn:uuid:a2f61387-7763-4a36-9dbd-12a83ad6e3e5> | 4 | 1,123 | Content Listing | Science & Tech. | 28.501277 |
We can also compile each C file separately using the cc -c option. This produces an object file with the same name, but ending in .o. After this, the object files are linked using the linker. This would require the four following commands for our current example.
cc -c prog.c cc -c func1.c cc -c func2.c ld prog.o func1.o func2.o -o progEach file is compiled before the object files are linked to give a runnable file.
The advantage of separate compilation is that only files which have been edited since the last compilation need to be re-compiled when re-building the program. For very large programs this can save a lot of time.
The make utility is designed to automate this re-building process. It checks the times of modification of files, and selectively re-compiles as required. It is an excellent tool for maintaining multi-file programs. Its use is recommended when building multi-file programs. | <urn:uuid:6755327b-07aa-4abc-9e6f-6ec915211efc> | 2.9375 | 210 | Tutorial | Software Dev. | 61.401856 |
Cells and Organelles
There are two main types or categories of cells: prokaryotic cells and eukaryotic cells. Both of these types of cells have several things in common. All cells are surrounded by a plasma membrane, which is made of a double layer (a bilayer) of phospholipids. Within this membrane, is the cytoplasm which is composed of the fluid and organelles of the cell.
Bacteria (Kingdom Monera) are prokaryotes. They do have
but it is not organized into a true nucleus with a nuclear
envelope around it. Also, they lack many other internal organelles such as mitochondria and chloroplasts.
Organisms in the other four kingdoms are eukaryotes. Their DNA is organized into a true nucleus surrounded by a nuclear envelope which consists of two bilayer membranes. The nucleus of eukaryotic cells contains the genetic material which chemically directs all of the cells activities. Usually this is in the form of long strands of chromatin made of DNA and affiliated proteins. When a cell is getting ready to divide, the chromatin coils and condenses into individual, distinguishable chromosomes. Because the nuclear envelope consists of two bilayer membranes, there is a space between these two membranes called a lumen.
Branching off from and continuous with the outer membrane of the nuclear envelope is a double walled space which zigzags through the cytoplasm. This is the endoplasmic reticulum (ER for short) and its central space or lumen is a continuation of the lumen between the membranes of the nuclear envelope. There are two kinds of ER: smooth ER and rough ER. Typically ER closer to the nucleus is rough and that farther away is smooth. Smooth ER is a transition area where chemicals like proteins the cell has manufactured are stored in the lumen for transportation elsewhere in the cell. Pieces of the smooth ER called vesicles pinch off from the smooth ER and travel other places in the cell to transfer their contents. Rough ER gets its name because it has other organelles called ribosomes attached, which give it a rough appearance when viewed by an electron microscope. Rough ER and its associated ribosomes are involved in protein synthesis, with the new polypeptide being threaded into the lumen of the ER as it is formed.
Ribosomes are special organelles that are directly involved in protein synthesis. They are made of RNA (ribonucleic acid) and protein and are manufactured in the nucleus (from a DNA template), then go out into the cytoplasm to function. Ribosomes of prokaryotes and eukaryotes are chemically different enough that some of our antibiotics such as tetracycline, streptomycin, and the new Zithromax® (azithromycin), can interfere with bacterial ribosomes ability to do protein synthesis without also interfering with our ribosomes.
Vacuoles and vesicles are similar in that both are storage organelles. Generally, vacuoles are larger than vesicles. Plant cells generally have one large central vacuole that takes up most of the space within the cell and is used for storage of all sorts of molecules. Paramecium have a special type called a contractile vacuole that serves to excrete water from the cell, sort of like our kidneys excrete water from our bodies. Vesicles are small enough and mobile enough that they are often used to move chemicals to other locations in the cell where they might be needed.
One of the places to which vesicles travel is the Golgi apparatus or Golgi bodies. These look like stacks of water-balloon-pancakes. They are sort of like the shipping and receiving department of the cell. Materials are received as
vesicles unite with the Golgi apparatus, and sent elsewhere as other vesicles pinch off. Materials are temporarily stored in the Golgi bodies, and some further chemical reactions do take place there.
Mitochondria are found in nearly all eukaryotic cells, usually several or many per cell. They burn sugar for fuel in the process of cellular respiration: theyre the engine of the cell. Mitochondria consist of a smooth outer membrane and a convoluted inner membrane separated by an intermembrane space. The convolutions of the inner membrane are called cristae and the space inside the inner membrane is the mitochondrial matrix. As sugar is burned for fuel, a mitochondrion shunts various chemicals back and forth across the inner membrane (matrix to/from intermembrane space).
Plant cells normally contain another type of organelle that is not found in animals: chloroplasts. Chloroplasts convert light energy (from the sun) to chemical energy via the process of photosynthesis. The main pigment (green color) located in chloroplasts and involved in photosynthesis is chlorophyll. Chloroplasts are surrounded by an outer membrane and inner membrane separated by an intermembrane space. The fluid within the center of the chloroplast is called stroma. Within this fluid is an interconnected system of stacks of disks, kind of like more water-balloon-pancakes. Each sack is called a thylakoid. and has chlorophyll and other useful pigments built into its membranes. A stack of thylakoids is called a granum.
It has been suggested that mitochondria and chloroplasts may have originally arisen from prokaryotic invaders. Evidence for this includes the fact that both of these organelles contain their own DNA (separate from that in the nucleus) and program some, but not all, of their own protein synthesis. They control their own replication within the cell, and often can move around within the cell and change shape. They are both surrounded by two bilayer membranes suggesting one membrane originated from the plasma membrane of the cell and one from the plasma membrane of the hypothetical invader. Interestingly, because of the way human eggs and sperm are formed and unite, while half of the DNA in the nucleus of the newly formed embryo comes from the mother and half comes from the father, since sperm do not pass any of their mitochondria to the offspring, the mitochondrial DNA comes only from the mother. This has enabled some rather interesting studies to be done tracing relationships among various ethnic groups of people around the world based on mitochondrial DNA.
The cytoskeleton is made of various types of special proteins.
are hollow tubes made of globular proteins. Most notably, they are found in
and centrioles. The arrangement of microtubules in cilia and flagella consists of nine doublets around the edge and two single microtubules in the center, all running the length of the structure. This
is referred to as the nine-plus-two formula.
In centrioles, microtubules are arranged in 9 sets of 3 each. Animal cells typically have a pair of centrioles located just outside the nucleus and oriented at right angles to each other. These function in cell division.
Microfilaments are also part of the cytoskeleton and are made of solid rods of globular proteins.
Copyright © 1996 by J. Stein Carter. All rights reserved.
This page has been accessed times since 15 Aug 2000. | <urn:uuid:91ca7c29-06da-42d4-ac66-42ef580fd200> | 4.375 | 1,518 | Knowledge Article | Science & Tech. | 36.764297 |
Take a virtual tour through 400,000 charted galaxies.
No, that isn’t a field of stars. It’s a field of galaxies containing trillions of stars.
The stargazers at the Harvard-Smithsonian Center for Astrophysics have released a huge three-dimensional map of outer space, a core part of its six-year survey of the skies. Encompassing four billion light-years cubed, the researchers hope to use the map to retrace the movements of the universe through the last six billion years.
Brought to you by federal grants for educational institutions and the Department of Energy Office of Science.
Update — I scheduled this post this afternoon before the news broke that Neil Armstrong, the first man on the moon, died at the age of 82. RIP | <urn:uuid:3c7f159c-be88-493b-8e03-ed0e371c8529> | 3.421875 | 165 | Personal Blog | Science & Tech. | 57.85622 |
file-position stream => position
file-position stream position-spec => success-p
Arguments and Values:
position-spec---a file position designator.
position---a file position or nil.
success-p---a generalized boolean.
Returns or changes the current position within a stream.
When position-spec is not supplied, file-position returns the current file position in the stream, or nil if this cannot be determined.
When position-spec is supplied, the file position in stream is set to that file position (if possible). file-position returns true if the repositioning is performed successfully, or false if it is not.
An integer returned by file-position of one argument should be acceptable as position-spec for use with the same file.
For a character file, performing a single read-char or write-char operation may cause the file position to be increased by more than 1 because of character-set translations (such as translating between the Common Lisp f#\Newline character and an external ASCII carriage-return/line-feed sequence) and other aspects of the implementation. For a binary file, every read-byte or write-byte operation increases the file position by 1.
(defun tester () (let ((noticed '()) file-written) (flet ((notice (x) (push x noticed) x)) (with-open-file (s "test.bin" :element-type '(unsigned-byte 8) :direction :output :if-exists :error) (notice (file-position s)) ;1 (write-byte 5 s) (write-byte 6 s) (let ((p (file-position s))) (notice p) ;2 (notice (when p (file-position s (1- p))))) ;3 (write-byte 7 s) (notice (file-position s)) ;4 (setq file-written (truename s))) (with-open-file (s file-written :element-type '(unsigned-byte 8) :direction :input) (notice (file-position s)) ;5 (let ((length (file-length s))) (notice length) ;6 (when length (dotimes (i length) (notice (read-byte s)))))) ;7,... (nreverse noticed)))) => tester (tester) => (0 2 T 2 0 2 5 7) OR=> (0 2 NIL 3 0 3 5 6 7) OR=> (NIL NIL NIL NIL NIL NIL)
When the position-spec argument is supplied, the file position in the stream might be moved.
The value returned by file-position increases monotonically as input or output operations are performed.
If position-spec is supplied, but is too large or otherwise inappropriate, an error is signaled.
file-length, file-string-length, open
Implementations that have character files represented as a sequence of records of bounded size might choose to encode the file position as, for example, <<record-number>>*<<max-record-size>>+<<character-within-record>>. This is a valid encoding because it increases monotonically as each character is read or written, though not necessarily by 1 at each step. An integer might then be considered ``inappropriate'' as position-spec to file-position if, when decoded into record number and character number, it turned out that the supplied record was too short for the specified character number. | <urn:uuid:70cbe893-a3e3-422b-853a-1c8c48573df5> | 2.859375 | 731 | Documentation | Software Dev. | 41.601019 |
Flow Boiling in a Micro-Channel Coated With Carbon Nanotubes
Date of this Version9-2009
This document has been peer-reviewed.
This study examines the heat transfer enhancement attributes of carbon nanotubes (CNTs) applied to the bottom wall of a shallow rectangular micro-channel. Using deionized water as working fluid, experiments were performed with both a bare copper bottom wall and a CNT-coated copper wall. Boiling curves were generated for both walls, aided by high-speed video analysis of interfacial features. CNT arrays promoted earlier, abundant and intense bubble nucleation at low mass velocities, consistent with findings from previous pool boiling studies. However, high mass velocities compromised or eliminated altogether any enhancement in the nucleate boiling region. The enhancement achieved at low mass velocities appears to be the result of deep, near-zero-angle cavities formed by the mesh of CNT arrays. On the other hand, high mass velocities tend to fold the CNTs upon the wall, greatly reducing the depth of the CNT-mesh-induced cavities, and compromising the effectiveness of CNTs at capturing embryos and sustaining the bubble nucleation process. CHF enhancement was also achieved mostly at low mass velocities. It is postulated CNT arrays enhance CHF by increasing the heat transfer area as well as by serving as very high conductivity fins that penetrate into the cooler, bulk liquid flow and take advantage of the liquid subcooling away from the wall. While these mechanisms are prevalent at low velocities, they are both weakened, especially the fin effect, at high mass velocities because of the folding of CNT arrays upon the wall.
Nanoscience and Nanotechnology | <urn:uuid:20efa600-af4d-4f98-ad8a-fe3bd76528c2> | 2.796875 | 361 | Academic Writing | Science & Tech. | 29.005163 |
The dictionary effectively defines four tables, the spaces, vendors,
attributes/fields and values tables.
Each table entry contains a number, a name, and a few variables that
define the entry's properties, except for those in the vendors and
values tables, which are simple name/number mappings, nothing more.
A space is something that enables the packet decoder (and encoder, but
decoding is easier to think about) to decode a block of data. In order
to do so, a space has the following properties:
atr_ofs and atr_size: define the place and size of an attribute nr.
field to be used for finding items to apply, if any;
vnd_ofs and vnd_size: idem for a vendor field.
If a space's atr_size is 0, then the space has no numbered attributes/
fields/dictionary items (all used interchangably in the dictionary and
its code) and provides no way to walk the block, other than to apply
each field defined in that space one after another.
Once the decoder finds a dictionary item (an attribute/field) to apply,
either by applying all defined in the space in sequence, or by looking
one up based on the vendor and attribute numbers obtained from the block
at the given places, it proceeds by decoding the block at the current
offset using the dictionary item found.
A dictionary item has the following properties to that end:
len_ofs, len_size and len_adj: define the place, size and adjustment
for a length field in the A/V pair or field, if any, relative to the
val_ofs, val_size and val_type: define the place, size and type of
the value of the attribute, relative to the enclosing block.
The relation between the size of the original data block, len_adj and
val_size is as follows.
Take the value of the length field, as given by len_ofs and len_size.
If there is no length field (len_size is 0), take the size of the
Calculate the 'skip length' for the attribute, that is, the offset of
the next attribute relative to the current one, using len_adj: if
len_adj is positive, then that's the skip length, disregarding step 1
(although if the skip length takes the decoder past the enclosing block,
you get a decode error); if len_adj is negative or zero, then subtract
len_adj from the length obtained in step 1 to get the skip length.
If val_size is positive, then that's the length of the value as it will
be in the decoded A/V pair list; if val_size is negative or zero, then
subtract val_size from skiplen (obtained in step 2) to get the value
If 'nodec' is not 0, then a new A/V pair is created on the request list.
If 'subspace' is defined, then the value is decoded by applying the
given space to the block given by the value.
Encoding goes the other way around, based on the same information. There
are some subtleties involving catch all attributes and some other
things, but if you grasp the above, you should be able to create working
dictionaries for anything that even remotely resembles RADIUS attributes
using the stuff that's already there. | <urn:uuid:19fc7d91-6567-43b0-ade5-b2b7ca645b55> | 2.96875 | 749 | Documentation | Software Dev. | 33.983392 |
To solve this problem...
Find the missing angle "?":
The angle measure of all the angles of a triangle add up to 180
. See the
angle rule notes
for an explanation of the sum of the angles of a triangle.
Enter your answer:
Your answer may be in any of the following forms:
Decimal (must be accurate to 4 places)
Fraction (e.g., '3/4')
Mixed number (e.g., '4 3/4')
Scientific notation (e.g., '1.2e-02')
Single words, correctly spelled (e.g.,'isosceles') | <urn:uuid:292bc98f-7f59-431f-8ed5-add9bd32db30> | 3.34375 | 140 | Tutorial | Science & Tech. | 86.62451 |
Archive for the ‘xhtml’ tag
Programmers are often required to write HTML code. Recently, on reviewing such code, I found some glaring mistakes. Based on this experience, I have assembled some points which programmers should note when developing HTML.
Version of HTML
Before writing HTML, decide upon version compliance. HTML 4.01 and XHTML 1.0 are popular choices.
Specify Version of HTML as DOCTYPE
For HTML 4.01 it is:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
For XHTML 1.0:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
For a detailed list, visit: http://webdesign.about.com/od/xhtml/a/aa011507.htm
Don’t use deprecated elements like <font>
<font> has been deprecated since version 4.01 of HTML.
Use CSS for styling
For styling purposes (specifying font, color, background-color, border, etc.) use only CSS. For example, for setting the background of a page, the earlier method is:
This is better written as:
<body style="background: blue;">
Please ensure you open and close the HTML elements in proper order. Always have the discipline of closing open elements.
HTML is also source code which is maintained by humans. Please respect yourself and the people who will be maintaining it later: write readable HTML with proper indentation.
Use a proper validation service before publishing your HTML. You may also use tools like xmllint also to validate your HTML.
Test in target browser
All our development systems are Linux. We developers test our HTMLs in Firefox. But our clients use IE. Situations like these demand additional testing effort in IE.
If HTML/XHTML provides some kind of script exclusion so that scripts placed inside a particular scope do not reveal their functions and variables globally across the page, it is going to be helpful. For example:
In the rare case when a script needs to access some variable defined in different package, it can use some namespace mechanism. Any ideas? | <urn:uuid:aa61c305-8279-4c34-b082-7b610f823e49> | 2.765625 | 522 | Personal Blog | Software Dev. | 70.391587 |
See also the
Dr. Math FAQ:
Browse High School Puzzles
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to frequently posed puzzles:
Getting across the river.
How many handshakes?
Last one at the table.
Monkeys dividing coconuts.
Squares in a checkerboard.
Weighing a counterfeit coin.
What color is my hat?
- Change for a Dollar [11/05/1999]
When changing a dollar bill, you can give 1 coin (1 silver dollar), 2
coins (2 half-dollars), 3 coins (2 quarters and 1 half-dollar), and so
on. What is the least positive number of coins that is impossible to give
as change for a dollar bill?
- Checkerboard Rectangles [03/24/2003]
A checkerboard has 8 horizontal boxes and 8 vertical boxes. How many
rectangles are possible inside that board?
- Choosing 3 of 6 Colors [03/03/2000]
Patrick has a box of crayons with red, blue, yellow, orange, green and
purple. How many different ways can Patrick select 3 colors?
- Circle Packing [01/22/2001]
If circles packed in a 100 by 100 square are repacked so that the centers
of any three tangent circles form an equilateral triangle, what is the
maximum number of additional circles that can be packed?
- A Circular Massacre [09/25/1998]
Ten thousand sailors are arranged in a circle; starting with the first
one, every other sailor is pushed overboard ....
- Claim the Last Flag [10/25/2002]
Two teams face 21 flags. Teams take turns choosing 1, 2, or 3 flags at
each turn. The team that can claim the last flag wins.
- Clock Hands and Hours Worked [01/29/2003]
A man arrives at work between 8:00 and 9:00 a.m. at exactly the
moment the minute hand and hour hand of the clock point in the same
direction.... How many hours did the man work?
- Clock Hands Diametrically Opposite [10/10/2001]
At what time between two and three o'clock are the hands of a clock
- Clock Hands Trisecting Face? [04/05/1999]
At what time (if any) do the three hands of a clock trisect its face?
- Closest Palindromic Dates [02/07/2000]
Using the abbrevation date.month.year, what are the two palindromic dates
closest together in the 1900s?
- Cockroach Traveling Along an Elastic Tightrope [05/15/1998]
Finding the harmonic series in a problem of related rates.
- Coconut and Monkey Puzzle [12/18/1997]
How many coconuts were in the original pile?
- Coconut Piles [10/12/1998]
What is the least number of coconuts they could have started with?
- Coconuts, Forwards and Backwards [02/02/2010]
Doctor Greenie answers a chestnut about repeated division and
remainders, first working the question forwards before using the
inverse of a function to solve the same problem backwards much more
- Coffee or Tea? [07/09/2001]
Is there more coffee in the tea, or more tea in the coffee, or are they
- Coin Patterns [08/26/2003]
Each of four rows of coins has exactly one penny, one nickel, one
dime, and one quarter. No row, either horizontal, vertical, or
diagonal, has more than one coin of each kind. How are the coins
- Coins in Change under $1 [03/13/2001]
Is there a formula or equation for determining the smallest number of
coins a person could receive when given change less than $1.00?
- Concept of Farmer Crossing a River [04/30/2002]
What concept does the farmer, fox, and chicken problem use, and how
does it relate to the sheriffs and outlaws problem, husband and wives
problem, and missionaries and cannibals problem?
- Connecting the Boxes [12/28/1998]
I have an arrangement of boxes and am trying to draw one continuous line
connecting them all. Can this be done?
- Constructing a Conditional Table [04/14/1998]
I have a table that is 5 columns wide and 7 rows high and contains either
a 0 or a 1 in each cell...
- Counterfeit Coin Challenge [05/12/2007]
In a set of 13 coins, either zero or two of them are counterfeit and
are lighter. You must identify the counterfeit coins, if any, after
four or fewer weighings on a balance scale.
- Counting Even Digits in Three-Digit Numbers [10/24/2004]
How many 3-digit numbers are there in which the number of even digits
- Counting Rectangles [05/23/2001]
How can I find the number of different rectangles in a square grid
containing "c" columns and "r" rows?
- Counting Rectangles Cut By a Diagonal [06/15/1999]
How can we find an equation for the number of unit squares that are cut
by a line going from corner to corner on a rectangle?
- Counting Triangles [05/27/1999]
In a large triangle with 36 small ones inside, how many triangles are
there in all?
- Covering a Checkerboard after Removing a Random Square [05/11/2008]
Use mathematical induction to prove that for any positive integer n,
if any one square is removed from a 2^n x 2^n checkerboard, then the
remaining squares can be completely (and exactly) covered with
L-shaped pieces composed of three squares.
- Criminal Logic Problem [02/19/2005]
A challenging logic problem involving five criminals charged with five
crimes. The names of the criminals are the same as the crimes, but no
criminal commited the crime of his name. Using several clues,
determine who committed murder.
- Crossing a Desert with 45 Watermelons [07/08/1998]
A boy carries 45 watermelons across a 15 mile desert, 15 at a time,
eating 1 per mile. What is the most he can carry to the other side?
- Crossing the Bridge [05/12/1997]
Four men want to cross a bridge but only two may cross at a time...
- Crossing the Desert [05/22/2001]
A truck gets one mile per gallon, and can hold 400 gallons at a time. How
much is the minimum amount to cross a 1000-mile desert?
- Cryptography without Numbers [12/07/2003]
You want to send a valuable object to a friend. You have a box and
several locks with keys. But your friend does not have the key to any
lock that you have, and any key you send might be copied. How can you
send to object safely?
- Crypto-Number Puzzle [01/21/1997]
A Pascal program to find numerical values for the letters in: ONE + TWO +
TWO + THREE + THREE = ELEVEN.
- Cutting a Cake into 8 Pieces with 3 Cuts [09/08/2002]
How do you cut a cake into 8 pieces making only 3 cuts? How do you cut
a doughnut into 12 pieces with only 3 cuts?
- Cutting a Cylinder out of a Sphere [02/25/1999]
What is the remaining volume after a cylinder of length 6" has been cut
through the centre of a sphere?
- Dartboard Scoring [03/01/1999]
Find the highest score you cannot get with the center worth 9 points and
the outer ring worth 4.
- Dates that Read the Same Backwards and Forwards [02/02/2010]
A student sees a palindrome in the date 01 02 2010, and wonders how to
generate all such palindromic dates. Building on another math doctor's
work with date arithmetic, Doctor Carter shares a program written in C,
then goes on to explain the purpose of each line of code.
- DEFABC = 6(ABCDEF) [12/10/2001]
Let abcdef be a 6-digit integer such that defabc is 6 times the value of
abcdef. Find the value of a + b + c + d + e + f.
- Difference of Two Cubes [05/24/2001]
The difference of two cubes is 56,765. What two positive integers satisfy
- Digital Clock Lights [06/29/1998]
If the only light source in a room is a digital alarm clock (red LEDs),
at what time is the room the darkest? Lightest?
- Digit Reversal Trick Explained [03/23/2001]
Take a 3-digit number and subtract its reverse. Then, take the result and
add its reverse. Why is the answer is always 1089, no matter what the
initial numbers were? | <urn:uuid:a0032252-c541-427c-8580-08d7fa55cb4a> | 2.90625 | 1,992 | Q&A Forum | Science & Tech. | 73.982928 |
Relativity and Density
Name: Richard S.
If relativity predicts mass increases with velocity and
length decreases in the direction of motion, if you moved an object to a
high enough velocity would its density reached a point at which it would
collapse upon itself and become a black hole?
A person observing it fly by might think so, unless he thought the
relative motion was due to his flying in the opposite direction. In
either case, a person moving at the same velocity as the mass would see it
at rest and could find no increase in density.
Relativity has many strange effects, but the effects of relative motion
can be among the most difficult to understand. Good luck!
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:92dbaedc-b06f-480f-997e-25afd0d1cbdb> | 3.375 | 159 | Knowledge Article | Science & Tech. | 43.62641 |
After launch from Kourou, SMART-1 was placed in its initial Earth orbit. This was followed by the commissioning of the spacecraft, including the ion engine. With the engine fully prepared for nominal operations, SMART-1's orbit was boosted by firings of the engine during the thrust arcs.
SMART-1 Earth Bound
Over the next 13 months, the ion engine's cumulative thrust resulted in an outward spiralling orbit, continuously raising the perigee and apogee altitude, bringing the spacecraft ever closer to the first Lagrange point of the Earth-Moon system. After crossing this point, SMART-1 left its Earth bound orbit and entered lunar orbit. This page lists the key events during the Earth bound orbit.
29 September 2003 - Early commissioning of spacecraft
Status report: No. 1 - Initial Spacecraft Operations
30 September 2003 - First firing of ion engine
6 October 2003 - Ion engine fully tuned
Status Report: No. 2 - Early Ion Drive Performance
6 January 2004 - Spiralling out of radiation belts
Status Report: No. 14 - SMART-1 Escapes the Radiation Belts
February 2004 - Instrument commissioning, first images
From 30 January to 24 February 2004 the ion engine was inactive for a period of just over three weeks. The resulting stable platform conditions allowed the commissioning of the scientific instruments.
Status Report: No. 17 - Ion Engine Switched Off, Commissioning Begins
April 2004 - Insights from ion engine operations
A lot is learned from SMART-1's ion engine operations and performance in the vacuum of space. The gathered information provides new insights that are of great importance for any future mission that will use an electric propulsion system.
Status Report: No. 21 - SMART-1 as a Bench Test for Electric Propulsion
August-November 2004 - Lunar Resonances
Over the period mid August to mid November, SMART-1's orbit was altered at regular intervals (27.4 days) by a lunar resonance which occurred while SMART-1 was at apogee. This was in addition to the orbit boosts induced by the ongoing firings of the ion engine.
11 November 2004 - Crossing the first Lagrange point of the Earth-Moon system
On 11 November 2004 at 10:30 UTC, close to the 331st Earth apogee, SMART-1 was at the first Lagrange point of the Earth-Moon system, where the orbit is neither Earth, nor Moon bound. SMART-1 then crossed over to the region where the Moon's gravitational pull on the spacecraft is stronger than that of the Earth and was on its way to lunar capture.
Status report: No. 31 - SMART-1 from Earth-bound to Moon-bound | <urn:uuid:6a67b4d5-db6e-45c8-960b-7332fcc817c9> | 3.125 | 566 | Knowledge Article | Science & Tech. | 54.899735 |
Infinite sets [change]
Cardinality is also used for determining the "size" of infinite sets. Although one might first think that all infinite sets are equally large, this is not always true. Infinite sets can be broken down into two types, countable and uncountable.
An infinite set is considered countable if they can be listed without missing any. Examples include the rational numbers, integers, and natural numbers. Such sets have a cardinality that we call (read as: aleph null, aleph naught or aleph zero). Sets such as the real numbers are not countable. If given any finite or infinite list of real numbers, you can create a number not on that list. The real numbers have a cardinality of c. | <urn:uuid:17745540-1a73-435a-b528-3faaa45de76b> | 3.65625 | 156 | Knowledge Article | Science & Tech. | 44.831251 |
|YPM ICH 8902|
And here is a photo of a bioluminescent midshipman fish specimen:
|Photo taken from this website|
|YPM ICH 8902|
|Image from NOAA|
Another hypothesis is that the photophores function in something known as "counterillumination." This is a form of bioluminescent defense against predators that is used in many types of organisms, including crustaceans and various fishes. Essentially what happens is that an organism using this "counterillumination" will use photophores on its underside to match any dim light coming from the surface of the water. In so doing, they can make a potential shadow disappear and thus camouflage themselves. This hypothesis has actually been tested and supported! It's been showed in laboratory experiments that midshipman fishes can match the intensity and color (among other things) of downwelling light (Harper and Case 1999). This hypothesis also makes intuitive sense because most of the photophores are concentrated on the bottom of the fishes-- where they would need to be for counterillumination.
One last hypothesis is that the glowing photophores function in courtship (Crane 1965). Various authors have expressed skepticism about this hypothesis, however, because there is a population of midshipman fish in Puget Sound, Washington, that has no luminescence capability, yet they still live and reproduce successfully. If the photophores were necessary for courtship, the Puget Sound population shouldn't exist (Warner and Case 1980).
How do midshipman fish get their ability to glow? By eating tiny bioluminescent crustaceans called ostracods. Without ostracods, the midshipman fishes' photophores are useless. This is where midshipman fishes get luciferin, which is a compound that bioluminescent organisms need to emit light. Many organisms produce luciferin on their own, but others, like the midshipman fishes, have to acquire it through their diet. It was actually the Puget Sound population of midshipman fishes that clued scientists in to the fact that midshipman fishes get their luciferin from ostracods. It turns out that the Puget Sound population has no luminescence capability because the there are no bioluminescent ostracods for them to eat there (Warner and Case 1980)! They can easily luminesce, however, if they are fed the proper ostracods.
And here's one last picture of one of our specimens, species Porichthys porosissimus, collected in the Gulf of Mexico off Galveston, Texas, in 1932 by the vessel Mabel Taylor.
|YPM ICH 8900|
*I should note that Jack is no longer a midshipman, although I think he was when that photo was taken. He graduated from the Naval Academy in 2008 and is now a fully commissioned Navy pilot serving in the Middle East.
Crane, J. M., 1965. Bioluminescent courtship display in the teleost Porichthys notatus. Copeia, 2 : 239-241.
Harper R.D., Case J.F. 1999. Disruptive counterillumination and its anti-predatory value in the plainfish midshipman Porichthys notatus. Mar. Biol. 134: 529–40.
Tsuji F.I., Haneda Y., Lynch III R.V., Sugiyama N. 1971. Luminescence cross-reactions of Porichthys luciferin and theories on the origin of luciferin in some shallow-water fishes. Comp Biochem Physiol 40A: 163-179.
Warner J.A., Case J.F. 1980. The zoogeography and dietary induction of bioluminescence in the midshipman fish, Porichthys notatus. Biol Bull mar biol Lab, Woods Hole 159: 231-246. | <urn:uuid:307e9239-92df-492b-939e-ee0ae708ca4d> | 3.4375 | 833 | Personal Blog | Science & Tech. | 46.335443 |
From issue 2671 of New Scientist magazine
27 August 2008, page 31-33
Find out what the LHC could discover
To get the particles traveling at such energies in a ring requires steering so precise that it can only be provided by intense magnetic fields created by superconducting magnets. These operate without loss of power when chilled below a critical temperature. The SSC had not pushed the technological boundaries, though, opting for superconducting magnets cooled by liquid helium to a relatively tepid 4.5 K, which were already being used in other accelerators. This proved to be its undoing.
For a given radius of tunnel, the more energetic the particles, the more powerful the magnets need to be. Since the SSC's magnets were not powerful enough, the tunnel had to be 87 kilometers round. The cost of building a machine this big doomed the SSC.
The RF cavities and the magnets had to be compact enough to fit into the small-bore tunnel, while carrying extremely high currents.
This means it has zero viscosity and can slip through microscopic cracks. So the thousands upon thousands of welds in the plumbing had to be,
By the late 1990s, the most pressing concern was the massive cavern needed to house ATLAS, the 7000-tonne detector that will track the particles that fly out from the collisions. Among the most important of these are muons, heavier versions of electrons, and the way to measure their momentum is to bend their paths in a magnetic field.
Because of the LHC's power, these muons will be more energetic and faster moving than anything seen in previous colliders, so the magnetic fields have to be very strong. The stronger the field, the more the particles bend, and the more precisely their properties can be measured.
It's so big that the cavern's hydrostatic pressure causes it to rise rather like a bubble in water, albeit extremely slowly.
To cross-check the findings from ATLAS, a second catch-all experiment called the Compact Muon Solenoid (CMS) will hunt for the same particles using different technology. It has thrown up its own share of challenges.
This spelled trouble.
First, the engineers had to dig two 60-metre-deep shafts, one for elevators and one to lower the detector.
When they got there, they found that the area consisted of loose, gravelly moraine that was permeated by two aquifers, so they borrowed a technique from the mining industry known as ground-freezing. Miners rarely have to contend with the fast-moving water found at the CMS site, though. The workers drilled holes along the periphery of the shafts into which they sank 60-metre pipes.
For six months, they circulated brine at -5 °C through them. Then, for a month, they filled the pipes with liquid nitrogen at -196 °C. This created a 3-metre-thick retaining wall of ice that kept the groundwater at bay, while the workers dug the dry earth within and constructed the shafts.
The CMS team decided to outdo ATLAS when it came to the strength of its magnetic field and built one twice as strong. Key to its 10,000-tonne magnet are superconducting coils designed to withstand an outward force of 60 atmospheres generated by the magnet's 4-tesla field - about 100,000 times stronger than Earth's magnetic field. However, the technology was so advanced and varied that no one company, or country, could do the job.
So the magnet's coils were shunted around Europe on a journey that started in Finland and took in Switzerland, France and Italy en route to CERN.
It is crucial that the entire LHC and its detectors work from the word go, as repairing them once the system is up and running will be far from trivial.
To repair the LHC, for instance, it would have to be allowed to warm back up to room temperature, which takes about five weeks.
Afterwards, its 40,000 tonnes of magnets would need to be cooled back to 1.9 K, a process that takes another five weeks and requires nearly 10,000 tonnes of liquid nitrogen and 130 tonnes of superfluid helium.
Still, the engineers have done their bit. Now it's the scientists' turn.
The Large Hadron Collider - find
out more about the world's biggest experiment in our cutting-edge | <urn:uuid:c7181306-0e16-4dee-a6b4-b8ebfbe71fb5> | 3.828125 | 916 | Truncated | Science & Tech. | 57.490205 |
Simply begin typing or use the editing tools above to add to this article.
Once you are finished and click submit, your modifications will be sent to our editors for review.
There are a few methods that employ foams to achieve separations. In these, the principle of separation is adsorption on gas bubbles or at the gas-liquid interface. Two of these methods are foam fractionation, for the separation of molecular species, and flotation, for the separation of particles. When dissolved in water, a soap or detergent forms a foam if gas is bubbled through the solution....
What made you want to look up "foam fractionation"? Please share what surprised you most... | <urn:uuid:ca953c10-6054-4cec-aa08-a3c23307a63c> | 3.921875 | 141 | Knowledge Article | Science & Tech. | 53.061813 |
The Wide-field Infrared Survey Explorer (WISE) is a NASA-funded Explorer mission that will provide a vast storehouse of knowledge about the solar system, the Milky Way, and the Universe. Among the objects WISE will study are asteroids, the coolest and dimmest stars, and the most luminous galaxies.
WISE is an unmanned satellite carrying an infrared-sensitive telescope that will image the entire sky. Since objects around room temperature emit infrared radiation, the WISE telescope and detectors are kept very cold (below -430° F /15 Kelvins, which is only 15° Centigrade above absolute zero) by a cryostat -- like an ice chest but filled with solid hydrogen instead of ice.
Solar panels provide WISE with the electricity it needs to operate, and always point toward the Sun. Orbiting several hundred miles above the dividing line between night and day on Earth, the telescope looks out at right angles to the Sun and always points away from Earth. As WISE orbits from the North Pole to the equator to the South Pole and then back up to the North Pole, the telescope sweeps out a circle in the sky. As the Earth moves around the Sun, this circle will move around the sky, and after six months WISE will have observed the whole sky.
As WISE sweeps along the circle a small mirror scans in the opposite direction, capturing an image of the sky onto an infrared sensitive digital camera which will take a picture every 11 seconds. Each picture covers an area of the sky 3 times larger than the full moon. After 6 months WISE will have taken nearly 1,500,000 pictures covering the entire sky. Each picture has one megapixel at each of four different wavelengths that range from 5 to 35 times longer than the longest waves the human eye can see. Data taken by WISE is downloaded by radio transmission 4 times per day to computers on the ground which combine the many images taken by WISE into an atlas covering the entire celestial sphere and a list of all the detected objects.
Total Ozone Mapping Spectrometer (TOMS)
Launched in 1996, the Total Ozone Mapping Spectrometer (TOMS) satellite was expected to map and understand the magnitude of polar ozone depletion for two years. More than ten years later, it was still in orbit and providing valuable scientific data. Its life was extended thanks to the collaboration with SOI, whose students became lead controllers of the NASA spacecraft in 2002, first from Goddard Space Flight Center and then from a control center on campus.
Using students for TOMS mission support reduced NASA’s operational cost from millions of dollars a year to a few hundred thousand dollars, making the extended mission operations possible. The partnership also gave the students an important hands-on learning experience. The Capitol College team demonstrated that a small contingent of engineering students could perform a number of complex technical tasks well with limited subject-matter expert supervision.
In December 2006, TOMS had a catastrophic failure of the transmitter in its second transponder, resulting in the total loss of all data downlink capability and the termination of the mission. TOMS delivered some of the most critical and influential environmental data ever recorded, documenting the long-term decline of global atmospheric ozone and the emergence and development of the Antarctic ozone hole. It allowed the world to view and understand the ozone in a new way, helping to shape international environmental perspectives and policy.
Today, the work done by the TOMS program has been taken over by the Ozone Monitoring Instrument (OMI) aboard the Aura satellite. The Space Operations Institute TOMS Operations Team was recognized as a recipient of the prestigious William T. Pecora Award for developing innovative techniques for providing mission support and science data capture.
ERBS and UARS
The SOI took over operations for the Earth Radiation Budget Satellite (ERBS) and the Upper Atmosphere Research Satellite (UARS) upon receiving the Basic Grant from NASA in 2002. Both satellite operations were decommissioned in 2006, the process for which was accomplished without incident.
ERBS was part of the NASA's three-satellite Earth Radiation Budget Experiment (ERBE), designed to investigate how energy from the sun is absorbed and re-emitted by the Earth. This process of absorption and re-radiation was one of the principal drivers of the Earth's weather patterns. Observations from ERBS were also used to determine the effects of human activities (such as burning fossil fuels) and natural occurrences (such as volcanic eruptions) on the Earth's radiation balance. The other instruments of the ERBE were flown on NOAA 9 and 10.
The UARS satellite was launched in 1991 by the Space Shuttle Discovery to measure ozone and chemical compounds found in the ozone layer which affect ozone chemistry and processes. UARS also measures winds and temperatures in the stratosphere as well as the energy input from the sun. Together, these help define the role of the upper atmosphere in climate and climate variability. The satellite is 35 feet long, 15 feet in diameter, weighs 13,000 pounds, and carries 10 instruments. UARS orbits at an altitude of 375 miles with an orbital inclination of 57 degrees. Designed to operate for three years, six of its ten instruments are still functioning. | <urn:uuid:71966554-ccf2-4b4c-83e8-11db1c8561ac> | 4.0625 | 1,071 | Knowledge Article | Science & Tech. | 33.774288 |
Static-cast TypecastStatic casts are only available in C++. Static casts can be used to convert one type into another, but should not be used for to cast away const-ness or to cast between non-pointer and pointer types. Static casts are prefered over C-style casts when they are available because they are both more restrictive (and hence safer) and more noticeable.
Static casts are expressed in terms of a template that takes as a template parameter the type to convert to.
static_cast<<type>>(<value>);This example casts an int to a double for the purpose of avoiding truncation due to integer division:
double result = static_cast<double>(4)/5; | <urn:uuid:9adb8181-6f81-467e-b216-998b544cde93> | 3.46875 | 146 | Documentation | Software Dev. | 33.857939 |
long duration balloon in flight
shortly after launch. Click to enlarge.
half of what you see.
by Paul Doherty
December 21, 2001 a long duration balloon was launched near
McMurdo station in Antarctica. A balloon launch is different
from a rocket launch. When the balloon is released it departs
in complete silence. After release, the balloon rises in slow
motion. Over four hours it rises to its final altitude of
120,000 feet or 24 miles (36 km) ascending an average of 500
feet per minute.( I have a hard time running uphill at 50
feet per minute.) Then it holds its altitude in the stratosphere
while winds blow it on a circular path around Antarctica.
view of a balloon fully inflated above 100,000 ft. Click
higher the balloon rises, the lower the air pressure at its
elevation. The helium inside the balloon expands in the lower
pressure environment. The helium bubble inside the balloon
initially has a diameter of 150 feet (45m), when the balloon
reaches cruising altitude it is a sphere 900 feet (270m) in
volume of the balloon doubles after it rises to 18,000 feet
(5500m) then doubles again by 35,000 feet(11,000m). Above
35,000 feet the volume doubles every 15,000 feet (4,500 m).
By the time the balloon reaches 120,000 feet it has doubled
its volume 8 times, so its volume is 2^8 or 256 times larger.
As the balloon rises through the lowest layer of the atmosphere,
the troposphere, the temperature decreases below -40 C. However,
when the balloon enters the stratosphere the temperature remains
the naked eye, the balloon at altitude looks slightly
smaller than the full moon. Click to enlarge.
I watched the balloon rise more and more slowly and then stop
rising. This was an illusion. The balloon was still rising,
and yet it appeared to stop. If the balloon were a constant
size object it would get smaller and smaller as it moved away
from me. However, the balloon was growing in diameter as it
rose. If I see an object growing in size and there are no
other clues to its distance, I assume it is moving toward
me. At one altitude near 75,000 feet (23,000 m)as the balloon
rises, it grows in volume at just the right rate to keep its
apparent size constant. Even though it is moving away from
me the balloon image stays the same size on my retina and
I "see" it standing still. As the balloon rises
at first it looks like it is getting smaller then above 75,000
feet it gets larger again.
120,000 feet the 900 foot diameter balloon has an angular
diameter of 0.4 degrees. Its diameter is 80% the size of the
sun or the full moon. Many pilots have seen these balloons
and reported that they needed to change their flight path
to avoid colliding with the balloon. Even though the balloon
was over 20 miles higher than they were. There were no clues
about the size of the balloon so they had no idea how far
away it was.
balloon is so far away that if you drive along the ground
it stays in the same position relative to you. (Note that
as you drive nearby trees rapidly move backwards, but distant
mountains seem to stay in the same place.) To many people
the balloon in the sky appears to follow them. When these
high altitude balloons are launched over populated areas many
UFO reports are made. | <urn:uuid:4ee10a5c-b305-4bd8-83ca-6449b422c94d> | 3.59375 | 758 | Nonfiction Writing | Science & Tech. | 66.632584 |
Thinking about Weight and Gravity
The pull of the Earth's gravity keeps us on the ground. The Earth is
massive, so the pull of its gravity is strong.
The Moon is much smaller than the Earth.
Show a friend: What would it be like to move around, if the Earth's gravity
were twice as strong?
The pull of the Earth's gravity makes you heavy - its force on you is called
Explain to a friend: What would it be like to walk on the Moon?
Use your imagination: What would it be like if the Earth had no gravity?
[ Flights of Inspiration | Your Own Flight | Forces of Flight | Weight ] | <urn:uuid:c8bb89f2-4ba4-4347-b73d-78ea91032eee> | 3.296875 | 141 | Tutorial | Science & Tech. | 76.781824 |
Rocky Mountain Research Station Home >
Science Program Areas
> Air, Water and Aquatics >
Stream Temperature Modeling and Monitoring > Spatial Statistical Stream Temperature Model
> Study Overview
Spatial Statistical Stream Temperature Model
Spatial Statistical Stream
Many natural resource agencies routinely collect digital stream
temperature data. However, a lack of coordinated sampling efforts typically
results in temperature observations within a stream network that are spatially
clustered, non-random, and autocorrelated. Recently, a
new class of spatial statistical models that account for network topology (i.e.,
flow direction and volume) has been developed to address these issues (Ver Hoef
et al. 2006).
the application of these models, we
assembled a large stream temperature database (n = 780 records) spanning a 14-year period from 1993 – 2006 for the 6,900 km2 Boise River basin in
central Idaho. Predictor variables that potentially affected stream temperature
were quantified using automated GIS routines to obtain measurements of
geomorphic features (e.g., elevation, channel slope, and valley confinement),
imagery to estimate solar radiation changes from wildfire, and climate stations
to provide information on stream flow and air temperatures. Spatial models with
four fixed-effect predictors and a mixed model spatial error structure accounted
for 93% and 86% of the variation in summer mean and maximum stream temperatures,
respectively, during the 14-year study period.
models yield more accurate parameter estimates than traditional,
non-spatial models and offer much improved predictive ability.
These models are
being used to map past and future thermal conditions and suitable habitat
distributions for native salmonid species in this basin, but could also be used
to better understand factors that affect stream temperature, determine
compliance with water quality standards, or optimize temperature sampling
designs. Preliminary results from this project have been presented at several
scientific meetings and a peer-reviewed manuscript has been drafted for
Ver Hoef, J.M., E. Peterson, and D. Theobald. 2006.
Spatial statistical models that use flow and stream distance. Environmental
and Ecological Statistics 13:449-464. | <urn:uuid:103f8afa-84be-409f-90af-15fe1f02215a> | 2.859375 | 458 | Knowledge Article | Science & Tech. | 20.885436 |
Algae (singular alga), a name derived from the Latin word for seaweed, are a large and diverse group of photosynthetic, eukaryotic, plant-like organisms that use chlorophyll in capturing light energy, but lack characteristic plant structures such as leaves, roots, flowers, vascular tissue, and seeds. Although they have historically been regarded as simple plants, they are generally classified in the kingdom Protista, rather than Plantae.
Although algae range from single-celled organisms to multicellular organisms, if they are both multicellular and marine, and are easily seen by the naked eye, they are generally called seaweeds. Single-celled or few-celled organisms are not usually called seaweeds. Seaweeds themselves have many forms, including those that appear as if they are terrestrial plants with leaves and stems, looking like moss, mushrooms, leaf lettuce, or even a palm tree. Some are quite large: the multicellular giant kelp reaches 60 meters in length.
Various seaweeds serve as a habitat and food for other sea creatures. For humans, seaweed also can be used as food and as fertilizer. Red algae are a source of agar, a gelatinous polysaccharide that is used as a culture medium for microbiological work, as well as vegetarian gelatin substitute, a thickener for soups, in jellies, ice cream, and so forth.
Rather than a specific taxa, seaweed can be one of several types of algae: brown algae, red algae, or green algae. Most of the seaweeds of the warm oceans are red algae. They absorb the deep penetrating blue light, allowing them to exist deeper than other algae. The brown algae include the major seaweeds found on the shores in the temperate zones and the large, offshore beds of kelps. There are few green algae that are seaweeds, but one is the sea lettuce.
Types of seaweed
Seaweeds are classified into brown algae (Phaeophyta), red algae (Rhodophyta), and green algae (Chlorophyta). Note that in reality the term algae is mainly used for convenience, rather than taxonomic purposes, as there appears little relationship between the various phyla.
Seaweeds are often confused with other photosynthetic organisms. Seaweeds are popularly described as plants, but biologists typically do not consider them true Plantae. They also should not be confused with seagrasses, which are vascular plants. In addition, a few species of cyanobacteria bear a resemblance to seaweed algae.
Some biologists prefer the term "marine macroalgae" over "seaweeds."
The Phaeophyta, or brown algae (Class Phaeophyceae, Division Heterokontophyta or Phaeophyta, Kingdom Protista or Plantae or Chromalveolata), are a large group of multicellular, mostly marine algae, and include many seaweeds of colder Northern Hemisphere waters.
One example of brown algae seaweed is Sargassum, which creates unique habitats in the tropical waters of the Sargasso Sea. This is one of the few areas where a large biomass of brown algae may be found in tropical waters.
Kelp are large seaweeds belonging to the brown algae and are classified in the order Laminariales. There are about 30 different genera. Kelp grows in underwater forests (kelp forests) in clear, shallow oceans. They require nutrient rich water below about 20 °C. Kelp is known for its high growth rate and is the largest seaweed. Macrocystis, a member of the Laminariales, may reach 60 meters in length and grows up to 30 centimeters per day.
The red algae (Phylum Rhodophyta, from Greek rhodon = rose + phyton = plant, thus red plant) are a large group of mostly multicellular, marine algae, including many notable seaweeds. Red algae are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans, and other food additives.
The Chlorophyta, or green algae (Division Chlorophyta), include about eight thousand species of mostly aquatic organisms. Like the land plants (Bryophyta and Tracheophyta), green algae contain chlorophylls a and b, and store food as starch in their plastids. They contain both unicellular and multicellular species. While most species live in freshwater habitats, and a large number in marine habitats, other species are adapted to a wide range of environments. Few are actually seaweeds, however, either because they are freshwater or microscopic. The sea lettuces (genus genus) are a notable exception.
Seaweeds' appearance often resembles non-arboreal, terrestrial plants. For example, they have root-like structures (holdfast) that anchor them to the substrate. However, in function they are unlike terrestrial plants, since they do not absorb nutrients, but solely serve to hold the seaweed in place. Examples of similar structures on the algal body (thallus) include:
- thallus: the algal body
- stipe: a stem-like structure (may be absent)
- holdfast: specialized basal structure providing attachment to a surface, often a rock or another alga.
- lamina: a flattened structure that is somewhat leaf-like
- sorus: spore cluster
- on Fucus, air bladders: float-assist organ (on blade)
- on kelp, floats: float-assist organ (between lamina and stipe)
The stipe and blade are collectively known as fronds. Some seaweeds have gas in the fronds that help them to be buoyant and float at or near the surface.
Seaweed serves a number of ecological, commercial, and medical uses. For example, seaweed offers protection to some sea creatures and food for others. Some seaweeds are used as fertilizer.
Through the nineteenth century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). Soda ash is used in the manufacture of glass, pulp and paper, detergents, and some chemicals. It is used as an alkaline agent in many chemical industries, and used as a water softener for laundry, among other uses. The seaweeds used in obtaining soda ash included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes (OED 1989).
Food and other commercial uses
Seaweeds are extensively used as food by coastal peoples, particularly in Japan and Korea, but also in China, Vietnam, Indonesia, Peru, Taiwan, the Canadian Maritimes, Scandinavia, Ireland, Wales, Philippines, and Scotland, among other places.
For example, Porphyra is a red alga used in Wales to make laverbread. In Japan, dried seaweed, formed into sheets called nori, is widely used in soups, and for wrapping sushi, boiled rice stuffed with bits of raw fish, sea urchin roe, or other ingredients. Chondrus crispus (commonly known as Irish moss or carrageen moss) is another red alga used in producing various food additives, along with Kappaphycus and various gigartinoid seaweeds.
Seaweeds are also harvested or cultivated for the extraction of alginate, agar, and carrageenan, gelatinous substances collectively known as hydrocolloids or phycocolloids. Hydrocolloids have attained commercial significance, especially in food production, with the food industry utilizing the gelling, water-retention, emulsifying, and other physical properties of these hydrocolloids.
Agar is used in foods such as confectionery, meat and poultry products, desserts and beverages, and molded foods. Carrageenan is used in preparation of salad dressings and sauces, dietetic foods, and as a preservative in meat and fish products, dairy items, and baked goods.
Alginates enjoy many of the same uses as carrageenan, but are also used in production of industrial products such as paper coatings, adhesives, dyes, gels, explosives, and in processes such as paper sizing, textile printing, hydro-mulching, and drilling.
Medicine and science
In the biomedicine and pharmaceutical industries, alginates are used in wound dressings and production of dental molds, and have a host of other applications. In microbiology research, agar is extensively used as culture medium for bacteria. Carrageenans, alginates, and agaroses (the latter are prepared from agar by purification), together with other lesser-known macroalgal polysaccharides, also have several biological activities or applications in biomedicine.
A number of research studies have been conducted to investigate claims of seaweed's effects on human health. It has been asserted that seaweeds may have curative properties for a number of aliments. However, Guiry (2006) notes that many of the reported medicinal effects have not been substantiated. He does recognize, however, that Corallina is being used in bone-replacement therapy, some kelps have polysaccharides that apparently correlate with reduction in the occurrence of breast cancer, and some seaweeds, such as Sargassum, are used in Chinese medicine, including for treatment of cancer.
- Guiry, M. 2006. Seaweed: Medicinal Uses. Retrieved August 27, 2007.
- Lewis, J. R. 1964. The Ecology of Rocky Shores. The English Universities Press Ltd.
- Oxford English Dictionary (OED). 2006. “Kelp,” In Oxford English Dictionary, 2nd online edition. Oxford University Press.
- Round F. E. 1962. The Biology of the Algae. Edward Arnold Ltd.
- Smith, G. M. 1944. Marine Algae of the Monterey Peninsula, California, 2nd edition. Stanford Univ.
All links retrieved August 27, 2007.
- The Seaweed Site by Michael Guiry
- AlgaeBase – Aearchable taxonomic, image, and utilization database of freshwater, marine and terrestrial algae, including seaweeds
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
- Seaweed (Dec 25, 2006) history
- Brown_algae (Dec 25, 2006) history
- Red_algae (Dec 25, 2006) history
- Chlorophyta (Dec 25, 2006) history
- Kelp (Dec 25, 2006) history
- Agar (Dec 25, 2006) history
- Sodium_carbonate (Dec 25, 2006) history
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<ref> tags exist, but no
<references/> tag was found | <urn:uuid:aee79017-ad04-4384-bfdf-0e5096b581e1> | 4.15625 | 2,412 | Knowledge Article | Science & Tech. | 31.884286 |
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Work, Energy and Power
When a force moves in the direction along which it acts, work is done.
Work is the process of converting energy.
Energy is the ability to do work.
To calculate the work done by a moving force:
the unit of work or energy is the Newton meter or Joule
If the direction of the displacement is not the same as the direction of the force, we use the component of the force which is parallel to the displacement. For example, when a body is caused to accelerate down an inclined plane by the force of gravity:
Therefore, the more general equation to calculate work done is
where is the angle between the force and the displacement.
Although force and displacement are both vectors, work (or energy) is a scalar quantity.
The Law of Conservation of Energy
Energy is never destroyed, it is just converted from one form to another.
Examples of Energy Conversions
Power is work done per second (or energy converted per second).
unit of power is the Joule per second, Js-1 | <urn:uuid:098baf24-c7fe-4167-830e-0e24407fe8ae> | 3.828125 | 227 | Tutorial | Science & Tech. | 40.767695 |
Courtesy alvherre at FlickrAcclaimed astrophysicist and author, Stephen Hawking, the former Lucasian Professor of Mathematics at the University of Cambridge - a position once held by Sir Isaac Newton - turns 70 years old today. Stricken with Amyotrophic lateral sclerosis (aka ALS or Lou Gehrig's disease), Hawking has defied doctors by living well-past their predicted "few years" when he was first diagnosed with the disease in 1963. A celebration in Britain took place today but Hawking was ill and couldn't attend the celebration. A recorded speech by Hawking was presented instead. Despite his debilitating disorder, Professor Hawking has managed to raise a family and through the use of computers to write several best-selling books, including A Brief History of Time. Here's an interview with Hawking's biographer, Kitty Ferguson. In Great Britain, ALS is known as motor neuron disease.
Courtesy NASAVoyager 1, an unmanned NASA space probe is nearing the outer edge of our solar system and will soon enter the vast, unknown region known as interstellar space. The crossover will remove the spacecraft from the influence of solar winds (from our Sun), into a relatively empty expanse of cold space influenced mostly by countering pressures created by supernovae, collapsed stars that died in immense catastrophic explosions. Voyager 1's primary mission, when it was launched 34 years ago on September 5, 1977, was to visit and photograph the giant gas planets in our solar system. It accomplished that goal and sent back spectacular images of the planets Jupiter, Saturn, Uranus, and Neptune. Right now Voyager 1 is about 11 billion miles from the sun, its cameras switched off, and poised for the next stage of its journey. The edge of the heliosphere is estimated to be somewhere between 10-14 billion miles from the Sun, so the probe could crossover anytime soon. NASA's Voyager program included two probes sent out with data gathering instruments and cultural souvenirs from the inhabitants of planet Earth, just in case they somehow got intercepted by some extraterrestrial lifeforms. Voyager 2, although launched two weeks before , trails some 2 billion miles behind Voyager 1, and will cross the boundary after its twin. You can read (and hear) more about it at the NPR website.
Courtesy NASA/ESA/Garth Illingworth (UCSC)/Rychard Bouwens (UCSC/Leiden University)/HUDF09 TeamThe Hubble Space Telescope has captured what astronomers are claiming is the oldest galaxy in the universe. Here's some of what NASA's Hubble website says about the discovery:
The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope. This is the deepest infrared image taken of the universe. Based on the object's color, astronomers believe it is 13.2 billion light-years away.
The dim object is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe's current age. It is tiny and considered a building block of today's giant galaxies. Over one hundred such mini-galaxies would be needed to make up our Milky Way galaxy.
Think of that - the light from this object we're seeing now took 13.2 billion years to reach our eyes. That's mind-boggling. We're actually looking back in time. Anyway, the study which appears in the journal Nature, was led by Rychard Bouwens at the Leiden Observatory in the Netherlands, and Garth Illingworth, of the University of California, Santa Cruz. The tiny smudge of light will be further studied and confirmed when the infrared-optimized James Webb Space Telescope is up and running in 2014.
By the way, the Hubble Space Telescope is featured in one of five films at this year's Omnifest playing now through February 17th here at the Science Museum of Minnesota. Take it from me, the images in the film are quite spectacular and worth seeing.
Images captured by the Hubble Space Telescope show what NASA scientists claim is the aftermath of a collision of two asteroids. US and European scientists involved in the study say the collision probably took place in early 2009, and that the debris trail stretches out for hundreds of thousands of kilometers behind a 360 foot-wide chunk of remaining rock.
Courtesy ESA HFI and LFI consortiaA new map created from data gathered by the Planck Space Telescope shows new aspects of our universe not before seen. The telescope’s sensors captured in long wavelengths of light invisible to the human eye that show gigantic plumes of dust and matter swirling above and below the plane of our Milky Way galaxy.
"What you see is the structure of our galaxy in gas and dust, which tells us an awful lot about what is going on in the neighborhood of the Sun; and it tells us a lot about the way galaxies form when we compare this to other galaxies."-- Professor Andrew Jaffe, Planck Space Telescope team member
The Planck research team hopes to answer several questions concerning the origins and structures of the universe. It will concentrate on the cosmic microwave background, the remnant radiation from the Big Bang that permeates the entire universe. It will also search out the secrets of other phenomenon such as gravitational waves, and dark energy and matter. A second version of the map is in the process of being created and there are plans for two additional ones.
In May of 2009, the European Space Agency (ESA) launched the Planck Space Telescope and the Herschel telescope together into space. Both telescopes function from an orbital position called the second Lagrange point located some one million miles away from the dark side of the Earth, and both in the infrared light range. Over the last six months the Planck telescope has been busy scanning and mapping the full sky searching out answers to how galaxy form and the very origins of the universe. The scope’s sensitive instruments were built to function in the extreme conditions of space, some at temperatures just 1/10th of a degree above absolute zero! Since the observatory is viewing the universe in long wavelengths of light it’s not really seeing stars themselves but rather the materials – dust and gas – from which stars are formed.
But if you’re like me, being restricted to a single wavelength just doesn’t do it, so for views of the universe in other wavelengths I suggest you visit Chromascope.net, a nifty website that allows you to view the universe in all sorts of wavelengths on the electromagnetic spectrum.
I don't know. Maybe.
Courtesy Public domain via WikimediaScientists at Princeton University and elsewhere spent the last couple years testing Albert Einstein's Theory of General Relativity and have come to the conclusion that the theory holds up just as well in the vast and distant regions of the universe as it does in our own solar system. First published in 1915, the landmark theory describes the very fabric of time and space, and gravity, and the way they interact with each other. It was further confirmed with experiments done during a total eclipse of the sun in 1919. The new research findings appear in the recent issue of Nature.
Princeton University story
Courtesy Public domainIf you’re like me, you’re fretting about what to buy your significant other this coming holiday season. Let it go. We have bigger problems. There’s a humongous star in the constellation Canis Major that’s in its final death throes and could go supernova at any time. VY Canis Majoris, as it is referenced, is the largest star known to science, and is so huge, if it were placed in the center of our Solar System, it would encompass all the space between our Sun and the orbit of the planet Saturn (see diagram). But don’t worry, the unstable red hypergiant is nearly 5000 light-years away, and is being monitored closely (in far-infrared and submillimeter portions of the light spectrum) by the European Space Agency's new space telescope Herschel. Read more here about what's actually going on.
NOVA - MUSICAL MINDS at 8PM ET/PT (please check local listings)
Can the power of music make the brain come alive? Throughout his career Dr. Oliver Sacks, neurologist and acclaimed author, whose book Awakenings was made into a Oscar-nominated feature film starring Robin Williams and Robert De Niro, has encountered myriad patients who are struggling to cope with debilitating medical conditions. While their ailments vary, many have one thing in common: an appreciation for the therapeutic effects of music. NOVA follows four individuals—two of whom are Sacks’s case studies—and even peers into Sacks’s own brain, to investigate music’s strange, surprising, and still unexplained power over the brain.
NOVA scienceNOW hosted by Neil deGrasse Tyson at 9PM ET/PT (please check local listings)
The fast-paced science magazine series NOVA scienceNOW returns on
June 30 on PBS with a new, 10-week season full of fresh new perspectives, fascinating
scientists, cutting-edge innovations, and provocative stories from the frontlines of science,
technology, and medicine. Hosted by renowned author and astrophysicist Neil deGrasse
Tyson, the series also introduces a brand-new correspondent this season, Ziya Tong (former
host and producer of Wired Science).
Courtesy NASA/JPL-CaltechScientists now have a better idea why stars can still form out of giant molecular clouds being ripped apart by the gravitational pull of a nearby massive black hole.
The observed existence of huge stars in eccentric orbits around the super-massive black hole believed to be located at the center of our Milky Way galaxy has puzzled scientists. How can stars form in such extreme environments? Gravitational forces would be tremendous near the black hole, tearing apart everything in the immediate region.
The computer simulations, done by researchers from St Andrews University in the UK, show how a molecular cloud – a normal stellar nursery – is torn apart by the black hole’s immense gravitation pull. Although the powerful gravity-well eats a huge portion of the gas cloud, the remaining gases are still able to accrete more material and coalesce into stars.
This is possible because as a molecular cloud enters the black hole’s gravitational field it begins to form into a spiraling elliptical disk. The disk’s matter nearest the black hole is sucked into the gravitational vortex, while energy is transferred to the remaining outer material. This transferred energy allows the remnants to retain the eccentric orbital path as they form into huge stars many times the mass of the Sun.
"These simulations show that young stars can form in the neighborhood of super-massive black holes as long as there is a reasonable supply of massive clouds of gas from further out in the galaxy," said co-author Ian Bonnell. The study’s results appear in the current issue of Science.
The stars live fairly short lives - perhaps only about 10 million years. But their existence could help explain some of the mysteries surrounding black holes in galaxies. | <urn:uuid:46263ed7-c862-4e2b-a567-42f5885412d0> | 2.796875 | 2,285 | Content Listing | Science & Tech. | 41.772343 |
All right. If you’ve understood all the previous Chapter 1 stuff, you are ready to dip your toe into the ocean of glory that is Calculus.
First, let’s go over what you’ve learned:
The essence of this chapter is that there are many types of functions with many different qualities. That’s a little vague, I know, but it’s important. If you’re trying to understand something in reality, whether it’s a math theorem or a physical phenomenon or a simulation you’re designing, you need to have this library of functions in your head. You need to know how a function behaves over time and how operations on it result in changes.
I will probably say this many times as we branch out into different areas, but it’s worth noting – you have GOT to work problems. If you don’t, you have no sense of what skill level you possess. You may very well understand a concept completely on the first read, but you can’t be sure till you try out a few problems. It is very often the case that you have some small gap in your understanding that will only be brought to light when you fail to answer some question correctly.
So, whenever you’re new at something, AT LEAST work the odd problems. If you’re still feeling fuzzy, work the evens. Remember, mathematics, more than any other field, is a tower of knowledge. If you have a shoddy layer anywhere, everything above it can fall apart.
That’s a cliche metaphor, but let me give you the less obvious aspect of it. If you build on a shitty foundation, the house might not fall over with the first or second or third story. But, eventually it will. How well you cement these basics will determine how high you can go later.
We’ve all heard the story of the awesome high school mathematician who gets knocked on her ass the moment she bumps into differential equations or linear algebra. It’s not because she’s stupid or because there’s a cap on her abilities – it’s because she didn’t understand the fundamentals. With a rough understanding, you really can coast through a lot of calculus without understanding what you’re doing or why it works. With enough rote learning, you can even solve tricky problems. But, if you don’t really know what you’re doing, sooner or later, you’re going to hit a wall.
Now then, onward to the good stuff. Before we go, I give you a quote from Winston Churchill, on his math studies as a young man:
Further dim chambers lighted by sullen, sulphurous fires were reputed to contain a dragon called the’Differential Calculus.’ But this monster was beyond the bounds appointed by the Civil Service Commissioners who regulated this stage of Pilgrim’s heavy journey. We turned aside…
Well, loyal readers, we will not be turning aside. We will meet the dragon, crush his will, and… make him solve equations for us. | <urn:uuid:ce284544-b920-449c-be4a-425f62015b86> | 2.890625 | 656 | Personal Blog | Science & Tech. | 63.113006 |
The following uses for uranium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).
Uranium gives interesting yellow and green colours and fluorescence effects when included to glass in conjunction with other additives. The image below is a Czech late 19th Century "Moser" Karlsbad vase showing a characteristic yellow-green colour. The image is reproduced with the permission of Ken Tomabechi at the Uranium Glass Gallery in Japan, where you can find further information about uranium glass. This type of glass is sometimes referred to as "vaseline glass" in the UK and USA and as "Annagelb" (yellow) or "Annagruen" (green) in Germany.
WebElements now has a WebElements shop at which you can buy periodic table posters, mugs, T-shirts, games, molecular models, and more. | <urn:uuid:e9997aca-a500-4c9a-a9b3-e4c26cf42ce4> | 2.734375 | 203 | Knowledge Article | Science & Tech. | 31.360201 |
This module defines one class called Popen:
|args, bufsize=0, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=False, shell=False, cwd=None, env=None, universal_newlines=False, startupinfo=None, creationflags=0)|
args should be a string, or a sequence of program arguments. The program to execute is normally the first item in the args sequence or string, but can be explicitly set by using the executable argument.
On Unix, with shell=False (default): In this case, the Popen class uses os.execvp() to execute the child program. args should normally be a sequence. A string will be treated as a sequence with the string as the only item (the program to execute).
On Unix, with shell=True: If args is a string, it specifies the command string to execute through the shell. If args is a sequence, the first item specifies the command string, and any additional items will be treated as additional shell arguments.
On Windows: the Popen class uses CreateProcess() to execute the child program, which operates on strings. If args is a sequence, it will be converted to a string using the list2cmdline method. Please note that not all MS Windows applications interpret the command line the same way: list2cmdline is designed for applications using the same rules as the MS C runtime.
bufsize, if given, has the same meaning as the corresponding argument to the built-in open() function: 0 means unbuffered, 1 means line buffered, any other positive value means use a buffer of (approximately) that size. A negative bufsize means to use the system default, which usually means fully buffered. The default value for bufsize is 0 (unbuffered).
The executable argument specifies the program to execute. It is
very seldom needed: Usually, the program to execute is defined by the
args argument. If
shell=True, the executable
argument specifies which shell to use. On Unix, the default shell
is /bin/sh. On Windows, the default shell is specified by the
COMSPEC environment variable.
stdin, stdout and stderr specify the executed
programs' standard input, standard output and standard error file
handles, respectively. Valid values are
PIPE, an existing file
descriptor (a positive integer), an existing file object, and
PIPE indicates that a new pipe to the child
should be created. With
None, no redirection will occur; the
child's file handles will be inherited from the parent. Additionally,
stderr can be
STDOUT, which indicates that the stderr
data from the applications should be captured into the same file
handle as for stdout.
If preexec_fn is set to a callable object, this object will be called in the child process just before the child is executed. (Unix only)
If close_fds is true, all file descriptors except 0, 1 and 2 will be closed before the child process is executed. (Unix only)
If shell is True, the specified command will be executed through the shell.
If cwd is not
None, the child's current directory will be
changed to cwd before it is executed. Note that this directory
is not considered when searching the executable, so you can't specify
the program's path relative to cwd.
If env is not
None, it defines the environment variables
for the new process.
If universal_newlines is True, the file objects stdout
and stderr are opened as text files, but lines may be terminated by
'\n', the Unix end-of-line convention,
the Macintosh convention or
'\r\n', the Windows convention.
All of these external representations are seen as
'\n' by the
Python program. Note:
This feature is only available if Python is built
with universal newline support (the default). Also, the newlines
attribute of the file objects stdout, stdin and
stderr are not updated by the communicate() method.
The startupinfo and creationflags, if given, will be passed to the underlying CreateProcess() function. They can specify things such as appearance of the main window and priority for the new process. (Windows only) | <urn:uuid:cce85cd7-4f7e-407d-8ce7-f6d5f90e31c2> | 3.421875 | 940 | Documentation | Software Dev. | 43.697099 |
Science Fair Project Encyclopedia
14 in two suborders, see text. The octopus is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs. The term may also refer to only those creatures in the genus Octopus . In the larger sense, there are 289 different octopus species, which is over one-third the total number of cephalopod species.
Octopuses are characterized by their eight arms, usually with sucker cups on them. Unlike most other cephalopods, octopuses have almost entirely soft bodies; they have neither a protective outer shell like the nautilus, nor any vestige of an internal shell or bones, like cuttlefish or squids. A beak, similar in shape to a parrot's beak, is their only hard part. This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from morays or other predating fish.
Three defensive mechanisms are typical of octopuses: ink sacs , camouflage, and autonomising limbs . Most octopuses can eject a thick blackish ink in a large cloud to aid in escaping from predators. They also have specialized skin cells both for color changing (chromatophores) and light reflection and refraction (iridophores and leucophores ). They use this ability to blend into the environment to hide, as communication with other octopuses, or as a warning: the very poisonous Blue-ringed Octopus becomes bright yellow with blue rings when it is provoked. When under attack, some octopuses can detach and autonomise their limbs, in a similar manner to skinks and other lizards. The crawling arm serves as a distraction to would-be predators; this ability is also used in mating. A few species have a fourth defense mechanism, in that they can combine their highly flexible bodies with their color changing ability to accurately mimic other, more dangerous animals such as lionfish and eels.
Octopuses have a relatively short life span, and some species live for as little as six months. Larger species, such as the North Pacific Giant Octopus , may live for up to five years if they do not reproduce. However, reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch, for they spend nearly all their time caring for their eggs, and do not eat during this period.
Octopus blood contains the copper-rich protein hemocyanin for transporting oxygen. Less efficient than the iron-rich hemoglobin of vertebrates, the hemocyanin is dissolved in the plasma instead of being bound in red blood cells and gives the blood a blue color.
Octopuses are highly intelligent, probably the most intelligent of the invertebrates. Maze and problem-solving experiments show that they have both short- and long-term memory, although their short lifespans limit the amount they can ultimately learn.
An octopus has a highly complex nervous system, only part of which is localized in its brain. Two-thirds of an octopus's neurons are found in the nerve cords of its arms, which have a remarkable amount of autonomy. Octopus arms show a wide variety of complex reflex actions arising on at least three different levels of the nervous system.
In laboratory experiments, octopuses can be readily trained to distinguish between different shapes and patterns. They are able to open jars after learning from observation . Octopuses have also been engaged in what may be described as play; repeatedly releasing bottles or toys into a circular current in their aquariums and then catching them. Octopuses often break out of their aquariums (and sometimes into others) in search of food. They have even boarded fishing ships and opened holds to eat crabs.
Octopuses have keen eyesight. Although their slit-shaped pupils might be expected to afflict them with astigmatism, it appears that this is not a problem in the light levels in which an octopus typically hunts. Surprisingly, they do not appear to have color vision, although they can distinguish the polarization of light. Attached to the brain are two special organs, called statocysts, that allow the octopus to sense the orientation of its body relative to horizontal. An autonomic response keeps the octopus's eyes oriented so that the pupil slit is always horizontal.
Octopuses also have an excellent sense of touch. The octopus's suckers are equipped with chemoreceptors so that the octopus can taste what it is touching. The arms contain tension sensors so that the octopus knows whether its arms are stretched out. Surprisingly, however, the octopus has a very poor proprioceptive sense. The tension receptors are not sufficient for the octopus brain to determine the position of the octopus's body or arms. (It is not clear that the octopus brain would be capable of processing the large amount of information that this would require; in vertebrates, the brain needs to process only the position of the joints; in contrast the position of an octopus's arms is much more variable.) As a result, the octopus does not seem to form a mental image of the overall shape of the object it is handling. It can detect local texture variations, but cannot integrate the information into a larger picture.
The neurological autonomy of the arms means that the octopus has great difficulty learning about the detailed effects of its motions. The brain may issue a high-level command to the arms, but the nerve cords in the arms execute the details. There is no neurological path for the brain to receive feedback about just how its command was executed by the arms; the only way it knows just what motions were made is by observing the arms visually. It is sometimes said that octopuses can "learn" to open jars, but this appears to be incorrect. The only thing that octopuses appear to be capable of learning about opening jars is to be persistent and vigorous.
In 2005 it was reported that some octopuses can walk on two arms on a solid surface, while at the same time imitating a coconut or a clump of seaweed (see 'Science', vol. 307, p. 1927, including short movies).
Though octopuses can be hard to keep in captivity, some people keep them as pets. Octopuses often escape, however, even from supposedly secure tanks, due to their intelligence and problem solving skills. The variation in size and life span among octopus species makes it difficult to know how long a new specimen can naturally be expected to live. That is, a small octopus may be just born or may be an adult, depending on the species. By selecting a well-known species, such as the California Two-spot Octopus, one can choose a small octopus (around the size of a tennis ball) and be confident that it is young with a full life ahead of it.
A common belief is that when stressed, an octopus may begin to eat itself. However, limited research conducted in this area has revealed that the cause of this abnormal behaviour may be due to a virus that attacks the octopus's nervous system, thus this behaviour is more correctly labeled as a mental disease.
A note on the plural form: Fowler's Modern English Usage states that "the only acceptable plural in English is octopuses", and that octopi is misconceived and octopodes pedantic. Octopi derives from the mistaken notion that octopus is Latin. It is not. It is (Latinized) Greek, from oktopous (ὀκτώπους), gender masculine, whose plural is oktopodes (ὀκτώποδες). If the word were Latin, it would be octopes ('eight-foot') and the plural octopedes, analogous to centipedes and millipedes, as the plural form of pes ('foot') is pedes. In modern, informal Greek, it is called khtapodi (χταπόδι), gender neuter, with plural form khtapodia (χταπόδια).
That said, Merriam-Webster and other dictionaries accept octopi as a plural form. The Oxford English Dictionary lists octopuses, octopi, and octopodes (the order reflecting decreasing frequency of use), stating that the last form is rare. The term octopod (either plural octopods and octopodes can be found) is taken from the taxonomic order octopoda but has no classical equivalent. The collective form octopus is usually reserved for animals consumed for food. Finally worth mentioning is Octopussy, a play on words which found its way back from the movie title to a term of endearment for the animals that have originally inspired it.
- CLASS CEPHALOPODA
- Subclass Nautiloidea: nautilus
- Subclass Coleoidea
- Superorder Decapodiformes: squid, cuttlefish
- Superorder Octopodiformes
- Order Vampyromorphida: Vampire Squid
- Order Octopoda
- Suborder Cirrina : finned deep-sea octopus
- Suborder Incirrina
- Family Alloposidae: Seven-arm Octopus
- Family Amphitretidae: telescope octopus
- Family Argonautidae: argonauts
- Family Bolitaenidae: gelatinous octopus
- Family Idioctopodidae
- Family Octopodidae: benthic octopus
- Family Ocythoidae: Tuberculate Pelagic Octopus
- Family Tremoctopodidae: blanket octopus
- Family Vitreledonellidae: Glass Octopus
- Octopussy, the thirteenth James Bond film
- Tentacool and Tentacruel, two octopus-like pokemon
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:0cbceaac-aa1b-492c-89db-a6615a553de2> | 4.21875 | 2,109 | Knowledge Article | Science & Tech. | 33.782776 |
Desolvation, in biochemistry, is the process where in an aqueous solution containing an enzyme and a substrate, water that is surrounding the substrate is replaced by the enzyme. In other words, water molecules that were once in between the substrate and the enzyme are displaced to allow the interaction of the substrate with the enzyme. The process also increases the entropy of the reaction, making the formation of the enzyme-substrate complex more thermodynamically favorable.
The method of desolvation involves drying a sample in a solution. An example of this involves electro-statically bound particles to dissociate by releasing water in an aqueous solution. This method is commonplace in atomic absorption spectroscopy, in which an atomic gas is created through a liquid sample. It can also be used in vaporization. | <urn:uuid:deb15a0e-e34e-46af-a708-38611b4d6ca9> | 3.671875 | 163 | Knowledge Article | Science & Tech. | 22.038846 |
In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this the volume of the immersed object can be deduced (the volume of the immersed object will be exactly equal to the volume of the displaced fluid).
An object that sinks displaces an amount of fluid equal to the object's volume. Thus buoyancy is expressed through Archimedes' principle, which states that the weight of the object is reduced by its volume multiplied by the density of the fluid. If the weight of the object is less than this displaced quantity, the object floats; if more, it sinks. The amount of fluid displaced is directly related (via Archimedes' Principle) to its weight.
In the case of an object that sinks (is totally submerged), the volume of the object is displaced. In the case of an object that floats, the amount of fluid displaced will be equal in weight to the displacing object.
Applications of displacement
This method can be used to measure the volume of a solid object, even if its form is not regular. Several methods of such measuring exist. In one case the increase of water level is registered as the object is immersed into the water. In the second case the object is immersed into a vessel full of water, causing it to overflow. Then the spilled water is collected and its volume measured. In the third case the object is suspended under the surface of the water and the increase of weight of the vessel is measured. It is equivalent to the weight of the amount of water that has the volume equal to the one of the suspended object.
The weight of an object or substance can be measured by floating a sufficiently buoyant receptacle in the cylinder and noting the water level. After placing the object or substance in the receptacle, the difference in weight of the water level volumes will equal the mass of the object.
See also
- Hughes, Stephen W. (2005). "Archimedes revisited: a faster, better, cheaper method of accurately measuring the volume of small objects". Physics Education 40 (5): 468–474. doi:10.1088/0031-9120/40/5/008. Unknown parameter | <urn:uuid:cb704912-c5cd-4470-893f-c3500d1df910> | 4.28125 | 469 | Knowledge Article | Science & Tech. | 54.045302 |
Stomolophus meleagris Agssiz, 1862
Dome-shaped bell can be up to 25 cm (10 inches) in diameter.
Ecology and Distribution
'Stomolophus is usually described as the most abundant scyphozoan in the Gulf, particularly in the late summer and fall when it 'swarms' around inlet passes.' (Rountree 1983)
'The scyphozoan Stomolophus meleagris , when disturbed (held in a container), discharges a sticky mucus. Toxins released into the mucus and water kill some fish and crustaceans and can immediately alter fish behavior, but did not affect a crab predator of S. meleagris . The mucus contains discharged and undischarged nematocysts. The toxins in the mucus are probably associated with these nematocysts.' (Oldendorf 1988)
'After swimming actively for 2-5 days, the ciliated planula larvae settled and scyphistoma morphogenesis occurred. Fully developed scyphistomae were cone-shaped and bore a whorl of about 16 tentacles around a dome- or knob-shaped proboscis. Podocyst formation was the only observed method of asexual reproduction in cultures of scyphistomae maintained for one month. Strobilation began as soon as nine days after scyphistoma morphogenesis and occurred in scyphistomae with as few as eight tentacles... Most strobilae produced two ephyrae each, although the number varied from one to three. Some scyphistomae began to strobilate a second time within a week after completion of an initial round of strobilation.' (Calder 1982)
Feed on zooplankton and red drum larvae.
'A pilot plant process was developed to produce salted dried jellyfish product from cannonball jellyfish (Stomolophus meleagris). Processed products containing an average of 68% moisture, 5.5% protein, 26% ash and 25% salt were obtained by brining with different mixtures of salt (7.5–25%) and alum (1–2.5%) over 1 wk. Mechanical drying was also tested by using a heat pump system dryer. Chemical and physical analyses and sensory properties of cannonball jellyfish products compared favorably with market products. Levels of calcium, magnesium and iron in the jellyfish were higher than those of zinc and copper.' (Huang 2006) | <urn:uuid:0a7dd8e5-8d8d-478e-bb96-27b4ce5692a9> | 3.25 | 528 | Knowledge Article | Science & Tech. | 38.89945 |
ADO Fundamentals, and the HelloData example in particular, introduced the four primary operations involved in creating an ADO application: getting data, examining data, editing data, and updating data. This section discusses getting data in more detail.
On a basic level, several ADO objects contribute to the operations of getting data. First you must connect to a data source using an ADO Connection object. Then you pass instructions to the data source using an ADO Command object. Finally, you most often receive data in an ADO Recordset object.
This section contains the following topics. | <urn:uuid:4872f26f-875a-4a80-be75-61abe324d39a> | 3.03125 | 120 | Documentation | Software Dev. | 25.969355 |
4.4. X-rays from AGN
One June 18, 1962, an Aerobee sounding rockets blasted skyward from White Sands proving ground in New Mexico. It carried a Geiger counter designed to detect astronomical sources of X-rays. The experiment, carried out by Giacconi et al. (1962), discovered an X-ray background and a "large peak" in a 10 degree error box near the Galactic center and the constellation Scorpius. A rocket experiment by Bowyer et al. (1964) also found an isotropic background, confirmed the Scorpius source, and detected X-rays from the Crab nebula. Friedman and Byram (1967) identified X-rays from the active galaxy M 87. A rocket carrying collimated proportional counters sensitive in the 1 to 10 keV energy range, found sources coincident with 3C 273, NGC 5128 (Cen A), and M 87 (Bowyer, Lampton, and Mack 1970). The positional error box for 3C 273 was small enough to give a probability of less that 10-3 of a chance coincidence. The X-ray luminosity, quoted as ~ 1046 erg s-1, was comparable with quasar's optical luminosity.
The first dedicated X-ray astronomy satellite, Uhuru, was launched in 1970. Operating until 1973, it made X-ray work a major branch of astronomy. X-rays were reported from the Seyfert galaxies NGC 1275 and NGC 4151 (Gursky et al. 1971). The spectrum of NGC 5128 was consistent with a power law of energy index = - 0.7, where L ; and there was low energy absorption corresponding to a column density of 9 × 1022 atoms cm-2, possibly caused by gas in the nucleus (Tucker et al. 1973). Early variability studies were hampered by the need to compare results from different experiments, but Winkler and White (1975) found a large change in the flux from Cen A in only 6 days from OSO-7 data. Using Ariel V observations of NGC 4151, Ives et al. (1976) found a significant increase in flux from earlier Uhuru measurements. Marshall et al. (1981), using Ariel V data on AGN gathered over a 5 year period, found that roughly half of the sources varied by up to a factor of 2 on times less than or equal to a year. A number of sources varied in times of 0.5 to 5 days. Marshall et al. articulated the importance of X-ray variability observations, which show that the X-rays "arise deep in the nucleus" and "relate therefore to the most fundamental aspect of active galaxies, the nature of the central `power house'."
Strong X-ray emission as a characteristic of Sy 1 galaxies was established by Martin Elvis and his coworkers from Ariel V data (Elvis et al. 1978). This work increased to 15 the number of known Seyfert X-ray sources, of which at least three were variable. Typical luminosities were ~ 1042.5 to 1044.5 erg s-1. The X-ray power correlated with the infrared and optical continuum and H line. Seyfert galaxies evidently made a significant contribution to the X-ray background, and limits could be set on the evolution of Seyfert galaxy number densities and X-ray luminosities in order that they not exceed the observed background. Elvis et al. considered thermal bremsstrahlung (107 K), synchrotron, and synchrotron self-Compton models of the X-ray emission.
HEAO-1, the first of the High Energy Astronomy Observatories, was an X-ray facility that operated from 1977 to 1979. It gathered data on a sufficient sample of objects to allow comparisons of different classes of AGN and to construct a log N-log S diagram and improved luminosity function. HEAO-1 provided broad-band X-ray spectral information for a substantial set of AGN, showing spectral indices - 0.7, with rather little scatter, and absorbing columns < 5 × 1022 cm-2 (Mushotzky et al. 1980).
The Einstein Observatory (HEAO-2) featured grazing incidence focusing optics allowing detection of sources as faint as ~ 10-7 the intensity of the Crab nebula. Tananbaum et al. (1979) used Einstein data to study QSOs as a class of X-ray emitters. Luminosities of 1043 to 1047 erg s-1 (0.5 to 4.5 keV) were found. OX169 varied substantially in under 10,000 s, indicating a small source size. This suggested a black hole mass not greater than 2 × 108 M, if the X-rays came from the inner portion of an accretion flow. By this time, strong X-ray emission was established as a characteristic of all types of AGN and a valuable diagnostic of their innermost workings. | <urn:uuid:c1f6423b-7a22-44a0-b5b0-3ae1f45258a5> | 3.5625 | 1,039 | Academic Writing | Science & Tech. | 66.374537 |
I always see pictures of the solar system where our sun is in the middle and the planets surround the sun. All these planets move on orbits on the same layer. Why?
We haven't ironed out all the details about how planets form, but they almost certainly form from a disk of material around a young star. Because the disk lies in a single plane, the planets are broadly in that plane too.
But I'm just deferring the question. Why should a disk form around a young star? While the star is forming, there's a lot of gas and dust falling onto it. This material has angular momentum, so it swirls around the central object (i.e. the star) and the flow collides with itself. The collisions cancel out the angular momentum in what becomes the vertical direction and smear the material out in the horizontal direction, leading to a disk. Eventually, this disk fragments and forms planets. Like I said, the details aren't well understood, but we're pretty sure about the disk part, and that's why the planets are co-planar. | <urn:uuid:a69ff38b-3300-4399-996b-f7995a04be43> | 3.5 | 221 | Q&A Forum | Science & Tech. | 69.455 |
It is well known that if you blow horizontally on a bottle top it creates a sound. Pouring water to the bottle changes the pitch. I have been doing experiments on the relation between the sound's ...
I play the flute as a hobby, and I've noticed that when playing middle D or E flat, one can interrupt the air column by releasing a certain key (which is near the middle of the air column), and yet ...
Why does the sound pitch increase on every consecutive tick at the bottom of a filled cup of coffee?
Since I don't know the proper physical terms for this, I describe it in everyday English. The following has kept me wondering for quite some time and so far I haven't found a reasonable explanation. ...
We know that from our experience when we tear up a piece of paper, we can hear a characteristic sound. What is the underlying mechanism behind it? What do the dominant frequencies (edit: I don't mean ... | <urn:uuid:d3e3e27b-19dc-46eb-9ffe-17d7ad8839df> | 3.3125 | 196 | Q&A Forum | Science & Tech. | 73.521053 |
Emperor Has No Clothes Pt. 2
Newport Beach at Sunset in 2007, the day someone argued to the National Research Council that "dark energy" would be very bad for science. Along with a changing speed of light, another prediction has come true.
The term "dark energy" has started to slowly fade. Yesterday August 13 a decadal survey on the future of astronomy was released by the US National Academy of Sciences. The report recommends a Wide Field Infrared Space Telescope (WFIRST) as a priority Space mission to be launched around 2020. WFIRST would be a 1.5 meter instrument remarkably similar to the Joint Dark Energy Mission (JDEM) studied for years by the US Department of Energy. The term "dark energy" is gone from the mission's name. WFIRST's mission will be to search for terrestrial planets around other solar systems, and look for "dark energy" on the way. This hedges everyone's bet when they admit that dark energy doesn't exist. Nature.com article.
At one time "dark energy" was the hottest ticket in science. An ambitious JDEM would launch around 2009 to find its equation of state. The hypothetical DE has not led to solution, but rather a divergence of speculative ideas. Even if the JDEM were launched, it would not return a single particle, just an "equation of state" which could easily be explained by a changing speed of light. First the DE researchers split into 3 competing camps, each with its own Principal Investigator (PI), each proposing a different mission. (Remember SNAP and DESTINY? Read The Dark Side from 2006!)
In September 2008 NASA and DOE tried to bring the 3 teams together for a combined proposal. The PI hopefuls were reduced to advisors in the new plan. The merged mission looked so expensive that NASA asked ESA to contribute. DOE, feeling jilted for the Europeans, dropped out and pursued their own experiment. When all this mate-swapping was finished, the alphabet soup agencies were back to three competing proposals.
Nature.com reported in 2009, Dark Energy Rips Cosmos and Agencies. DE was called by Nature.com a "fudge factor." As for JDEM, the article quoted, "This is an example of a satellite blowing up before it gets built." In addition to a divergence of speculative ideas, DE has led to splits in science. Cost of the proposed mission has risen from 600 million to at least 1.6 billion US.
As readers know, "dark energy" is not a repulsive force, but an effect created by a changing speed of light. It can be predicted by a simple algebraic equation, too simple for scientists to figure out. For the solution, check the Nature.com physics blogs. Just beneath FQXi is a little blog known by Nature as "GM=tc^3." It's not the same as a paper in Nature, but it is very popular blog! | <urn:uuid:09758bcf-0006-41d1-9f46-95eb1dda0f5f> | 2.6875 | 605 | Personal Blog | Science & Tech. | 61.423006 |
First Look at HadCRUT4
Posted on 18 April 2012 by dana1981
Morice et al. (2012) explains the changes in HadCRUT4, which incorporates land temperatures from CRUTEM4 (as described by Jones et al. 2012) and sea surface temperatures (SSTs) from HadSST3 (as described by Kennedy et al. 2011 Part 1 and Part 2).
CRUTEM4 has been updated to include more data:
"US station data have been replaced with the newly homogenized US Historical Climate Network (USHCN) records [Menne et al., 2009]. Many new data have been added from Russia and countries of the former USSR, greatly increasing the representation of that region in the database. Updated versions of the Canadian data described in [Vincent and Gullett, 1999, Vincent et al., 2002] have been included. Additional data from Greenland, the Faroes and Denmark have been added, obtained from the Danish Meterological Institute [Cappeln et al., 2010, 2011, Vinther et al., 2006]. An additional 107 stations have been included from a Greater Alpine Region (GAR) data set developed by the Austrian Meteorological Service [Auer et al., 2001], with bias adjustments accounting for thermometer exposure applied [Böhm et al., 2010]. In the Arctic, 125 new stations have been added from records described in Bekryaev et al. . These stations are mainly situated in Alaska, Canada and Russia. See Jones et al. for a comprehensive list of updates to included station records."
HadSST3 includes both an increased number of SST measurements, and new adjustments for recently-identified biases. Gavin Schmidt provides a good discussion of some of the issues with historical SST measurements at RealClimate.
Kevin C has produced a great animated GIF comparing the global coverages of HadCRUT3 and HadCRUT4, illustrating that the most notable difference is better coverage in HadCRUT4 (Figure 1).
Figure 1: global geographic coverages of HadCRUT3 and HadCRUT4. Colors represent mean(2006-2010) minus mean(1996-2000), from +2°C (red) to -2°C (blue).
Figure 2 compares HadCRUT4 to the previous version, HadCRUT3. Note that so far HadCRUT4 data are only available through 2010.
Figure 2: HadCRUT4 (blue) vs. HadCRUT3 (red) annual global surface temperatures
The largest change comes during the mid-20th Century, for example due to an adjustment to account for the sources of SST data switching during World War II from European fleets to almost exclusively US fleets (discussed by Schmidt at the link above). These adjustments, which somewhat dampen the mid-century cooling, are quite apparent in Figure 3, which takes the difference between HadCRUT4 and HadCRUT3.
Figure 3: HadCRUT4 minus HadCRUT3 annual global surface temperature data
In HadCRUT4, the hottest years on record are 2010 and 2005, with 1998 right behind in a statistical tie. This brings HadCRUT4 into better agreement with the surface temperature records from NCDC and GISS, which also have 2010 and 2005 as the hottest years on record, whereas HadCRUT3 had 1998 as the hottest.
This is something of a dark day for the many climate "skeptics" who in recent years have exclusively used HadCRUT3 to argue the myth that global warming has stopped, thanks to its cool bias. In fact, they were already attacking CRUTEM4 a month ago.
There is no longer any excuse for using HadCRUT3, and HadCRUT4 is in better agreement with the two other major surface temperature data sets. In fact, the HadCRUT4 linear trend in recent years now falls between the other two, a bit higher than NCDC but a bit lower than GISS. For example, the 15-year trends (1996 through 2010, which can be found with the SkS temperature trend calculator) are:
0.157 +/- 0.146°C/decade (GISS)
0.136 +/- 0.145°C/decade (HadCRUT4)
0.121 +/- 0.140°C/decade (NCDC)
0.098 +/- 0.156°C/decade (HadCRUT3)
So we can probably expect to see the 'skeptics' using NCDC surface temperature data from now on. | <urn:uuid:29040e95-4bf0-4162-8267-f88fcb87bc90> | 3.046875 | 942 | Personal Blog | Science & Tech. | 57.705201 |
open(), lseek() to the end of file, getting the size of file using tell(), and then allocating memory accordingly would work well as suggested above.
Unless there is specific reason to do it, fopen(), fseek(), ftell() is a better idea (portable staying within the C standard library).
This certainly assumes that the file you are opening is small. If you are working with large files, allocating memory for the whole of file may not be a good idea at all.
You may like to consider using memory mapped files for large files. POSIX systems provide mmap() and munmap() functions for mapping files or devices in memory. See mmap man page for more description. Memory mapped files work similar to C arrays though the responsibility of getting actual file data is left to the OS which fetches appropriate pages from disk as and when required while working on the file.
Memory mapped files approach has limitations if the file size is bigger than 32-bit address space. Then you can map only part of a file at a time (on 32-bit machines). | <urn:uuid:36ab3a53-9019-42fd-8803-3a5ca3d82fab> | 2.78125 | 223 | Q&A Forum | Software Dev. | 48.911451 |
Evolution in a nutshell
By AMY ADAMS
The HMS Beagle launched on its second survey expedition from England’s Devenport Harbor on Dec. 27, 1831, with a crew of 73. Charles Darwin, a 22-year-old gentleman with a penchant for collecting beetles, was aboard to serve as naturalist. Though the trip was planned to last two years, it spanned five; Darwin spent more than three of those years on land exploring parts of South America, the Galapagos Islands, Tahiti, Australia and New Zealand.
The great diversity of animals and plants — especially in the Galapagos — amazed him. When he reflected on what he’d seen during his travels, Darwin had a novel thought: Perhaps a species changes over time to adapt to its environment.
He saw signs of shifting species everywhere he looked, including the fossil record that contained seemingly ancestral forms of modern animals. The idea that populations weren’t immutable shocked people of his time and continues to raise consternation today.
Back in England, Darwin’s thoughts returned to the Galapagos, especially the finch populations, which were unique to each island. He theorized that a single ancestral population settled each island and then adapted to that island’s environment. Hundreds of thousands of years later the result was animal populations that natives could identify on sight as belonging to a specific island.
Darwin surmised that a process he called natural selection led to adaptations such as the ones he saw in the finch populations. According to his idea, animals with adaptive traits produce more offspring than other animals. If a bird with a particular beak shape could eat more seeds and was therefore healthier, that bird was also more likely to reproduce successfully and pass along its handy beak.
Darwin collected a great many specimens and recorded pages and pages of notes, but it wasn’t until 1859, 20 years after he first theorized about natural selection, that he would consolidate all of his observations in The Origin of Species.
Connecting Darwin’s dots
Darwin died in 1882, almost 100 years before molecular genetics research would reveal the how behind his ideas. A crucial element in the theory of evolution by natural selection is that animals can pass along their physical traits. It turns out that DNA is where the recipe for those physical traits resides.
Every population has somewhat varied individuals because the population contains many versions of each gene. For example, a finch with a particular version of a growth-promoting gene might grow ever so slightly larger than a finch with a different version of that gene. In a habitat that favors larger birds, the larger finches have more chicks, and as a result the growth-promoting version of the gene shows up in a greater proportion of the birds. Those larger offspring interbreed and over time the entire population becomes larger.
New traits can also pop up in a population. Each time a cell divides there’s a chance for a mutation to sneak in and get passed on to offspring. Sometimes those mutations make no difference whatsoever. Other mutations are deadly. Still other mutations might produce slight variations, like a growth-promoting gene that produces an even larger finch, or a growth gene that gets used during a different time in development, producing a normal-sized bird with particularly large wings.
In some environments that big-winged bird might fail completely, but on the right island that bird might become a reproductive ace, passing along that trait to future offspring, thereby altering the look of that population.
Natural selection reigns as evolution’s most celebrated force, but it’s not the only player. Any event that influences a population’s genetic diversity shapes the evolutionary trajectory. Some of the most important forces that drive evolutionary change or alter genetic diversity are:
Natural selection. Individuals that are more suited to an environment produce more offspring. Eventually, the trait that made those individuals so fruitful becomes common in the population.
Random mutation. Mutations happen at random throughout the genome. Some of these mutations help the organism flourish and produce more offspring to propagate that mutation. Other mutations are neutral, but persist in the population by chance. Either way, the mutation and its associated trait become common in that population.
Genetic drift. In some cases a trait might be neither helpful nor harmful, but for statistical reasons, more organisms with that feature reproduce and the trait ends up becoming common.
Bottleneck. A big storm or dramatic event can kill off a large portion of a population. The remaining individuals are left to rebuild the species. If those survivors include a few individuals that had unusual features, that feature will become common in the renewed population.
Founder effect. If a few individuals migrate together or are cut off from the main population they will go on to build a population of their own. That new population will reflect the genetics of the founders rather than the genetics of the original population.
Comments? Contact Stanford Medicine at | <urn:uuid:d92e6ba8-ef4f-4b11-a109-90f42daf9f36> | 3.984375 | 1,022 | Nonfiction Writing | Science & Tech. | 38.043825 |
When Louis de Broglie proposed in 1924 that the wave-particle duality applies not only to photons but also to electrons, he forged a metaphoric link that has had profound effects on the way we understand the physical world. De Broglie's insight, which suggested that electrons might be better understood if they were treated more like photons, made possible Schrödinger's wave equation, the basis of quantum mechanics. The beauty of metaphors, of course, is that they go both ways: we can reverse the direction of de Broglie's insight and try to develop our knowledge of photons by treating them as electrons. Recent work at the University of Würzburg in Germany continues the extension of de Broglie's rich scientific metaphor in just this way.
The research has its antecedents in structures known as electronic quantum dots, which were first fabricated in the 1980s. These tiny conducting islands, which can be as small as tens of nanometers across, are formed using a variety of techniques (see "Science Observer," July–August 1996). These structures can confine a specific number of electrons, much as individual atoms confine their electrons. As a consequence, quantum dots are also known as "artificial atoms."
Alfred Forchel and his colleagues at the University of Würzburg have been working with quantum dots that confine not electrons but photons. Their research group drew on calculations made by two American physicists, Thomas Reinecke of the Naval Research Laboratory in Washington D.C., and Peter Knipp, of Christopher Newport University in Virginia. The structures involved were first created in 1996 at Würzburg and at a laboratory operated by France Telecom. Forchel's group makes their "photonic atoms" by sandwiching a 7-nanometer-thick "active" layer of indium gallium arsenide (InGaAs) between two thicker layers of another semiconductor, gallium arsenide (GaAs). They sandwich this stack between thin, alternating layers of aluminum arsenide (AlAs) and GaAs. Finally, they etch the entire layered material to leave a box-like structure a few microns on each side with particular electromagnetic properties.
When stimulated with visible light, the active InGaAs layer emits infrared photons. These photons are kept in the dot horizontally because of the difference in refractive index between GaAs and the surrounding air. They are confined vertically by the alternating AlAs and GaAs layers, which form a structure known as a Bragg mirror. By manipulating the dot's size, the physicists are able to control the exact energy of the confined photons—just as the length of a taut string determines the frequency and wavelength of the sound it produces, the size of a photonic dot affects the same characteristics of the light it emits. Tuning the dot's size makes it favor certain photonic wave structures, or modes, over others.
The Würzburg group's real innovation was to extend the "artificial atom" metaphor still further. If they could make individual atoms that contained electrons or photons, why not construct "artificial molecules?" Artificial molecules built from electronic dots have been around in various forms since the early 1990s. Manfred Bayer, one of Forchel's colleagues, thought to try it with photonic dots. Bayer proposed a "photonic molecule" in which two photonic atoms would be connected by a narrow segment between them. The group etched these structures and then studied the results of varying the length of the connection.
Using spectroscopy, Bayer and colleague Thomas Gutbrod measured the energy of the photons emitted by the InGaAs layer (although most of the photons are confined to the molecule, some leak out and can be measured). Photons with particular energies correspond to specific peaks on the spectroscopic graph. When the photonic dots were far apart, the physicists found a spectroscopic emission peak around 891 nanometers (nearly the same wavelength the dots would emit if there were no connecting segment between them). As the dots were brought closer together, this single peak split into two—one indicating lower energy than the original and the other higher energy. The photonic modes of the two dots were apparently interacting, so that the initially equivalent modes were replaced by two unequal ones.
This is strikingly similar to what happens when real atoms approach each other and form a covalent bond. When atoms are far apart, their electrons occupy independent atomic orbitals and do not interact. As the atoms approach each other, this changes. The electron interaction "splits" the initially equivalent orbitals into two orbitals with different energies—one lower and one higher than the original orbital energy—just as the photonic modes are split in the photonic atom.
In real atomic interactions, when the phase of one atom's electron matches that of the other atom (phase is a property that indicates whether the electron's wave amplitude is positive or negative in a given region), the two electrons can be shared across both atoms, creating a molecular orbital with lower energy than the original. Because this orbital has a lower energy than the one created when the electrons are out of phase, the electrons "prefer" to occupy it. The lower energy orbital is a bonding molecular orbital, whereas the higher energy orbital is an antibonding one. To test further the analogy with their photonic molecule, Bayer and colleagues from the Russian Academy of Sciences measured the angular distribution of photons with particular energies to get a sense of the area they occupied within the photonic molecule. They found that photons of different wavelengths occupied areas remarkably similar to those occupied by electrons of different energies in diatomic molecules such as hydrogen (H2). The lowest-energy photons occupied an area analogous to a bonding molecular orbital, whereas photons with higher energies occupied antibonding regions, as well as other higher-energy orbitals (Figure 1).
Forchel hopes that, in addition to providing a nice illustration of the parallels between photons and electrons, the work will have some practical use. The group has been experimenting, for example, with larger photonic molecules (Figure 2), which might be used to make waveguides that steer certain wavelengths of light down particular paths—a function useful in optical telecommunications.
Whether photonic chemistry will ever match the productivity or richness of electronic chemistry remains to be seen. Since photonic atoms are less dynamic than real atoms—they are, after all, fixed to a semiconductor substrate—it isn't clear how one could produce real-time "reactions." But even if practical applications are elusive, the most lasting effect of the work may be that it provokes further creative extensions of a scientific metaphor with an illustrious past and a bright future.—Daniel B. Radov | <urn:uuid:c05eb18a-6eb0-498e-9a1f-88b6c349ebe6> | 3.625 | 1,367 | Knowledge Article | Science & Tech. | 28.893656 |
|Horseshoe Crab Home | Education Home | Fisheries Home | DNR Home|
SPECIES OF LIMULUS|
At one time, there were many species of horseshoe crabs, however, only four have survived. Three of these can be found along the shores of Southeast Asia and nearby islands. The fourth species, Limulus polyphemus, is found in the waters of the North American continent. They range intermittently from the Yucatan peninsula to northern Maine. Each major estuary along the coast is believed to have a discrete horseshoe crab population that can be distinguished by adult size, carapace color, and eye pigmentation. Check out a map of the world showing where all four species are located.
Along the Atlantic coast, horseshoe crabs are most abundant between Virginia and New Jersey with Delaware Bay at the epicenter of the species distribution.
Horseshoe crabs are bottom-dwelling organisms that belong to the largest group of all living animals, the phylum known as arthropods. The presence of chelicera (pincer-like appendages), 5 pairs of walking legs and book gills, and lack of jaws and antennae make horseshoe crabs more similar to spiders, ticks and scorpions than to "true" crabs. Within the diversity of arthropods, horseshoe crabs have their own class called “Merostomata”, meaning “legs attached to the mouth”.
Of the four species of horseshoe crabs that exist today, all have a similar ecology and morphology. Taxonomic Classification of the Horseshoe Crab (Limulus polyphemus)
Kingdom – Animalia | Phylum – Arthropoda | Subphylum – Chelicerata | Class – Merostomata
Subclass - Xiphosura | Order – Xiphosurida | Family – Limulidae
Genus - Limulus | Species – polyphemus
|Updated April 28, 2006| | <urn:uuid:11b62d2d-989b-4cb9-b5e6-fd49869bc221> | 3.71875 | 417 | Knowledge Article | Science & Tech. | 21.525286 |
toadstool: see mushroom.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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- Encyclopedia: Moneran and Protistan - Encyclopeadia articles concerning Moneran and Protistan. | <urn:uuid:38ecc236-19ed-4dff-b97d-f11a017d1f77> | 3.234375 | 206 | Knowledge Article | Science & Tech. | 39.851857 |
It’s like the northern lights – just 100 times more awesome…
Also called ‘zodiacal light’, what causes this glow that can light up the night sky?
Watch the first rocket-powered flight of Virgin Galactic’s SpaceShipTwo
Take a look at the spacecraft that carried the first person into space
The remnants of stars have cores of crystallised carbon, resulting in massive galactic gems
Most stars in the Milky Way are actually found in pairs or groups. Read on to find out more
Why is the gas giant Osiris dissolving into space?
Learn why the internal structure of this Jupiter moon might harbour life
Did the Andromeda galaxy form 1 million years ago? How about 1 billion? Find out the truth after the jump
What is this sprawling celestial feature and how was this stunning image captured?
Famous astrophysicist Carl Sagan explains the laws governing the movement of celestial bodies
Examine the major minerals and chemicals that make up your average comet
See a massive comet colliding into our Solar System’s star now
If you don’t know your quasars from your pulsars then this is the post for you. Read on and be enlightened
HIW examines the main sections of the work-in-progress Chinese space station
Why are there millions of rocks orbiting between Mars and Jupiter?
A look at some of the most incredible craters to be found in the Solar System
Is it one mile? Ten miles? 100 miles? Find out now…
How does this gas giant exert such a large influence on the Solar System?
The International Space Station was constructed by many nations over the course of a decade… | <urn:uuid:866226b4-1c1e-47d6-808c-b78e6136f598> | 3.28125 | 344 | Content Listing | Science & Tech. | 49.846522 |
Today Second Life took us all the way to London to learn about how the Sun affects the Earth. We talked to Dr. Joanna Haigh, a scientist who studies how changes in the sun may affect Earth’s climate. The Sun even appeared in the auditorium during the talk!
The Sun takes part in Dr. Joanna Haigh’s talk in Second Life
Not only did we learn about the Sun today, we found a way to view it safely through a telescope on the Museum’s rooftop Weintraub Observatory. We could clearly see sunspots on the surface – these are “cool” regions of the Sun because they’re “only” 3000°C. (I guess that’s cool compared to the surrounding 6000°C temperatures!) Solar flares, which occur around sunspots, are solar storms that can actually disrupt communications here on Earth. It’s incredible that something 93 million miles away affects us!
Rooftop solar observations
After using the telescopes, we made our own camera out of a potato chip can (and got to eat the chips too). We cut the can into two sections, and put it back together with the lid in between – this would be the screen for the camera. We poked a tiny hole in the bottom of the can, and when we looked through it, everything was upside down and backwards! Can you figure out why?
You always hear people say that we need to have our next generation be strong in science, technology, engineering, and math. We are the next generation, but it’s hard to know sometimes how we get there. What do you really do as a climatologist, an atmospheric scientist, or a meteorologist? And what should you study in school to get there? Today the Museum held a Climatology Career Day for students in the Museum’s Youth EXPO, Digital WAVE, and Upward Bound programs to answer these questions.
Dr. Clement makes a cloud in a jar
We’ve all learned about climate change, but now we get to hear more about how we can really be a part of it. We talked with a Robert Molleda, Warning Coordination Meteorologist from the National Weather Service; Maria Beotegui, Education Coordinator from Biscayne National Park; David Bernard, CBS4 Chief Meteorologist; Dr. Arturo Rodriguez, Professor of Chemistry and Meteorology from Miami Dade College; Erik Salna, Associate Director of the International Hurricane Research Center at Florida International University; Dr. Amy Clement, Professor of Meteorology and Oceanography from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science; and Dr. Kevin Helmle, Research Scientist from the National Oceanographic and Atmospheric Administration (NOAA). Not to mention Michael Garay, Senior Physics Engineer from NASA’s Jet Propulsion Laboratory, who was the keynote speaker for the event and spoke with us through Second Life.
Speakers L to R: David Bernard, Robert Molleda, Erik Salna, Dr. Arturo Rodriguez, Dr. Kevin Helmle, Maria Beotegui, Dr. Amy Clement
These people were all so different, but they all seemed to have something in common – when they were younger, some kind of spark inspired them to get into science, and they worked really hard to get where they wanted to go. All we need to do now is follow our own inspiration.
Who knew there was a missing link between soft drinks, forests, ocean acidity, wild fires, cement production, and volcanoes? Today Mike Gunson of NASA’s Jet Propulsion Laboratory talked to us via Second Life about this “carbon dioxide puzzle” and about how we know from data that humans are a piece of that puzzle.
So when we say that burning fossil fuels releases about 8.5 gigatons of carbon into the atmosphere per year, what does that mean? It’s hard to really understand a word like “gigaton” because it means 1 BILLION tons. To give you a comparison, if 1 Mazda Miata weighs about 1 ton, then you’d need 8.5 billion Miatas to make 8.5 billion tons. That’s enough Miatas to circle the Earth 850 times!
It just so happened that the Museum had a Great Energy Challenge event this day. So after we learned about how important it was to have cleaner and more efficient energy, we went through the Museum and made some clean energy ourselves!
Kennedy Space Center. This is the place where Space Shuttles and rockets are launched. The place where you can re-live the history of the US Space Program, walk under rockets that took men to the Moon, and even meet astronauts. We went for a day to Kennedy Space Center, and got to do all these things. Listening to Astronaut Tom Jones talk about the day he saw 16 sunsets and 16 sunrises from the International Space Station makes you realize how lucky astronauts are.
Outside in the Rocket Garden, we walked across a walkway, just like the one that astronauts walk across to enter the Space Shuttle. But we did it in slow motion, just like in the “hero shot” in movies when the astronauts are on their way to accomplish a dangerous, but vital, mission. Everyone has a little bit of astronaut explorer blood in them!
Visiting Space Shuttle replica at Kennedy Space Center
It was the greatest video game ever: there was a control pad, and a maneuverable object. Our control pad was a computer remotely hooked up to the Marine Resources Development Foundation in Key Largo. And our maneuverable object was a real, remotely operated vehicle (ROV) in waters off the Florida Keys! Working with a scientist sitting in a habitat almost 50 feet under the surface of Largo Sound, each of us took a turn maneuvering the ROV from our lab at the Museum.
ROVs can provide tons of climate information for us, by exploring where humans can’t – underwater caves, the frozen polar regions, oil rigs and shipwrecks. They can use claws to take samples, and probes to take temperature readings, and can observe habitats without disturbing the inhabitants very much. And we were able to operate one! It may be hard to tell from the picture, but it was like a real-life game. You can see our controls on the left, and the view from the ROV’s “eye” as it follows an underwater pipe. Some took to it more quickly than others – it definitely is a skill, and not as easy as it looks!
Navigating an underwater ROV from our lab in the Museum
The material is based upon work supported by NASA Competitive Program for Science Museums and Planetariums under award No. NNX09AL31G. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration. | <urn:uuid:f5c8cf83-3eba-48ae-bf01-0b1763b7bd1d> | 3.125 | 1,458 | Personal Blog | Science & Tech. | 51.514545 |
DEQ has identified stream temperature as one of the water quality standards that is not being met for streams in both eastern and western Oregon. Furthermore, the Oregon Plan identifies the need for action plans that will support recovery of water quality. This Best Management Practices (BMP) monitoring project supports both DEQ concerns and goals in the Oregon Plan by focusing on the relationship between riparian stand characteristics and shade because of its link with stream temperature.
This project was implemented in basins within the north coast and northeastern regions of Oregon. Data were collected, with the help of a fish-eye lens, on both harvested stream reaches and those with no recent history of harvest. One goal of this project was to determine the range of shade levels provided over streams under varying forest management scenarios. A second goal was to investigate possible links between site and stand characteristics and shade.
FPMP Technical Report #13 (pdf) - Shade Conditions Over Forested Streams in the Blue Mtn and Coast Range Georegions of Oregon, August 2001 | <urn:uuid:fc186f1a-0c5b-415f-8d70-8208e9c426b9> | 3.03125 | 206 | Knowledge Article | Science & Tech. | 34.28431 |
More Than Meets the Eye: Invisible propane gas flows, unlit, from a torch. On hitting the rhodium-studded ceramic honeycomb from a catalytic converter, it burns without flame, heating the ceramic red-hot. Mike Walker
To a chemist, burning means the rapid combination of a fuel with oxygen, called oxidation. You might say, for instance, “Oh, no, we didn’t have a fire at the nuclear power plant, we just had a ‘rapid oxidation event,’ ” a phrase that won officials at Three Mile Island the Doublespeak Award in 1979. | <urn:uuid:add16809-6008-4332-8450-8306196c934f> | 3.046875 | 131 | Content Listing | Science & Tech. | 47.370351 |
As milestones go, this could be seen as a small one. After all, China merely performed a feat that Americans achieved more than 45 years earlier (and its space station is about the size of the Salyut 1 Russia flew about 40 years ago). There was a key difference, though: While the first American docking was with a manned Gemini capsule and an unmanned Agena upper stage, the Chinese performed the entire operation with unmanned spacecrafta feat that the U.S. had never actually performed until recently, and a tribute to the intervening decades of technological development. The question now is: What does Chinas recent success say about its goals in space?
When NASA achieved its first orbital docking in 1966, it was a key demonstration needed to develop the confidence to later go to the moon. Thats because the Apollo mission required a similar rendezvous and docking in lunar orbit between the ascending lunar module and the orbiting command module in order to get the astronauts back home to earth.
Chinese leaders openly want to have a manned space station by the end of the decade, and this demonstration is crucial to that goal for two reasons. First, assembling a space station during multiple missions (as the U.S. and other nations did with the International Space Station) requires the capability to mate two pieces in orbit. And even if the station could be launched in a single piece (as Skylab was in the 1970s), every visit to a space station requires a rendezvous and docking. With this mission a success, expect manned flights on Shenzhou missions in the next couple years.
But how about beyond low Earth orbit (LEO)? Former NASA administrator Mike Griffin, who for years has warned that China could go to the moon before the U.S. could break out its holding pattern in LEO, testified before Congress on this subject just a few weeks ago. In this telling exchange, he outlines how Chinataking advantage of the docking sophistication it displayed this weekcould mount a mission to the moon without even building a heavy-lift rocket:
I know the Chinese Long March 5 rocket is in development. I wondered if you could compare that to anything we have in the American inventory. When its built will it really be larger than anything we have? And why do you think that the Chinese are building such a large rocket?
But its a very significant capability and in fact by launching and rendezvousing four of those in LEO it would be possible for the Chinese to construct a manned lunar mission with no more than that rocket and no more than Apollo technology. And I have in the past written up on how that mission would work from an engineering perspective. So with the Long March 5 the Chinese inherently possess the capability to return to the moon should they wish to do so.
And you are saying that we do not have anything comparable to that other than what had been talked about?
Actually, contrary to Griffins implication, the Delta IV Heavy has flown, so its more than "view graphs." And the Long March 5 isnt scheduled to fly until 2014. But even in that timeline, China could be thinking about a moon visit relatively soon. In the U.S., by comparison, the Space Launch System NASA is now mandated to build couldnt return Americans to the moon until at least the late 2020s (and would add tens of billions to the cost), according to a recently leaked NASA internal document.
China has yet to make any specific commitments to manned lunar missions, though the Change series of unmanned lander missions, which are planned to culminate in a sample return rocket in 2020, could be a precursor to such missions. The nations nonmilitary space program (though its somewhat hard to separate military from nonmilitary, as China doesnt have a civil space agency like NASA and its "taikonauts" are military personnel) seems aimed primarily at national prestige and cementing relations with the developing world through cooperative activities. Its not clear how a lunar program will fit into that.
However, some aerospace bigwigs see aggressive lunar goals in Chinas future. A couple weeks ago, at a space conference in Las Cruces, N.M., space real-estate developer and Bigelow aerospace founder Bob Bigelow made a second major speech in 2011, warning that, in his view, the Chinese plan not only to visit, but also to claim the moon, casting aside the 1967 Outer Space Treaty that forbids nations from claiming sovereignty of off-planet property. "China already has a grand national vision," he said then. "Their vision is that China wants to be indisputably No. 1 in the world, measured any way you want to measure."
And Washington certainly isnt doing anything to diminish the idea of a second space race based on national pride. The same day China achieved its space docking, Virginia Congressman Frank Wolfe, chairman of the appropriations committee for NASA, called a hearing to find out why administrator Charles Bolden and presidential science adviser John Holdren had been meeting with Chinese space officials, when the NASA budget expressly forbids any cooperation with China. (The dispute is over $3,500 spent to host the meeting, so this is simply a symbolic squabble.)
But Congress should perhaps be careful what they wish for in excluding China from cooperative space activities. In the 1970s, the French were upset by what they considered unreasonable demands for American control over the use of satellites that they were going to launch in the Space Shuttle, then in development. The result was the European Ariane rocket, which has taken a lot of launch business not just from the Shuttle, but also from American commercial launch providers over the past decades.
Besides, theres one other point to consider in how much of a threat the Chinese are. Chinas space industry has expressed concerns that it wont be able to compete with the SpaceX Falcon on cost, even with Chinese government subsidies. So as long as we dont regulate our own competitive private industry out of business, we may not need to be so restrictive. | <urn:uuid:b4c00285-56ff-4f5e-bdd0-59c3306cc29b> | 3.375 | 1,213 | Nonfiction Writing | Science & Tech. | 44.148502 |
By February 3, Orbiter had broken the flight duration record of 146 hours and 44 minutes set by Fossett during his first around-the world attempt from St. Louis in January 1997, which ended in Pakistan--although not his distance record of 10,360 miles. But the remainder of the flight was in question. China had refused to permit the balloon to fly over its territory so controllers had "parked" it in slow moving air over the Indus River. If China changes its mind, the balloon can rise directly into the jet stream. But if not, the team was considering whether to try to fly around China (a time--and fuel--consuming maneuver) or to come down in the area of Calcutta, India or in Bangladesh, thereby also establishing a new distance record.
Still waiting in the wings is a team headed by Virgin Group magnate Richard Branson. They experienced a setback on December 9 when the envelope of the Virgin Global Challenger broke loose from the gondola and flew off on its own from Marrakech, Morocco. A new envelope quickly constructed in England by Lindstrand Balloons is now beig tested in Morocco. Another group of hopefuls, crewing the Dymocks Flyer, plans to attempt the feat in the Southern Hemisphere, flying a balloon based on the designs of the National Aeronautics and Space Administration's unmanned high-altitude balloons. They await friendly winds in Alice Springs, Australia.
The history of balloon flight dates to 1783 when two French brothers, Joseph and Etienne Montgolfier discovered that filling a bag with hot air would cause it to rise. They demonstrated their principle at Annonay, France, on June 5, 1783 with an unmanned balloon made of linen and paper. Amazed villagers watched as it rose to an altitude nearing 6,000 feet and landed in a field about a mile away. Just months later, on November 21, Pilatre de Rozier and the Marquis d'Arlandes became the first humans to fly in a manmade craft when they ascended from the center of Paris in a Montgolfier balloon.
Early hot air balloons had to be fueled on the ground (or carry dangerous open fires aloft) and, rather inconveniently, they came back down when they cooled. So they were soon replaced by envelopes filled with buoyant gases, such as hydrogen and helium. These balloons continued to rack up records for long duration flights. Balloons were used by the military as observation posts (and a few fairly futile attempts to drop bombs) and have a rich history of carrying scientific payloads into the upper atmosphere. Indeed, the first astronauts were balloonists who ascended to the edge of the atmosphere in a 1950s program known as the Manhigh Project..
The National Aeronautics and Space Administration operates a Scientific Ballooning Program that has collected data about cosmic rays in the upper atmosphere. Fossett, the only balloonist in the current race with a scientific project, was testing an "aerobot" designed by NASA's Jet Propulsion Laboratory to probe the atmospheres of Mars and Venus.
But when it comes to long-distance flight, gas filled balloons are also limited. As the sun heats the gas in the envelope, the balloon rises uncontrollably and so gas has to be vented; when the gas cools, the balloon sinks and pilots must drop ballast to maintain altitude. Sooner or later, they run out of gas or ballast and the journey is over. The problem was solved in the 1960's when Edward Yost equipped a balloon with an onboard propane burner. This device allows pilots to control the balloon's buoyancy by changing the amount of heat injected into the envelope. His innovation created the present boom in sport ballooning and opened the prospect of an around-the-world flight. | <urn:uuid:5474e043-80ca-465f-8ef8-3fe9e206fe51> | 3.78125 | 782 | Knowledge Article | Science & Tech. | 47.398134 |
|Fracking can cause earthquakes, but oil and gas extraction may cause more||
Furthermore, the greatest risk of earthquakes due to fracking does not come from drilling into deep shale or cracking it with pressurized water and chemicals.
Rather, it comes from pumping the wastewater from those operations back down into deep sandstone or other formations for permanent disposal, instead of storing it in tanks or open ponds at the surface.
In January, wastewater injection was blamed for earthquakes that had just occurred in Youngstown, Ohio, on Christmas Eve and again on New Year's Eve, measuring 2.7 and 4.0 on the Richter scale, respectively. Wastewater injection is also commonly used during conventional oil and gas production.
The National Research Council report, “Induced Seismicity Potential in Energy Technologies,” was released today. It documents earthquakes associated with a full range of underground energy technologies, but doesn’t determine any kind of “rate” at which they might occur. It associates a number of earthquakes with conventional oil and gas wells, more so when those wells are somewhat drained and are injected with water or gas to force out the remaining, hard-to-get fuel. The report also links earthquakes to geothermal energy (tapping into hot underground reservoirs of steam or water) and so-called enhanced geothermal (forcing water into hot underground rock, to turn it to steam).
Two related technologies
Two related technologies were investigated as well: wastewater injection, as noted, and carbon sequestration and storage. Only one sequestration project exists worldwide thus far, so data for the technique are meager. The report includes a map showing the sites of induced quakes.
Overall, technologies that basically balance the amount of fluid removed or injected, such as conventional oil wells, induced fewer seismic events than those that involve net injection or extraction.
The “two techniques with the largest imbalance are carbon sequestration and wastewater injection,” said Murray Hitzman, professor of economic geology at the Colorado School of Mines and chairman of the committee that wrote the report, at a press briefing. The two techniques increase subsurface pressure across large areas, so there is a greater chance of running across a fault, which could lead to an earthquake, Hitzman said.
The report notes that enhanced geothermal might also create an imbalance. In recent years several worrisome earthquakes have been linked to geothermal operations, including a 3.4 magnitude temblor in Basel, Switzerland, and smaller quakes close to an operation known as The Geysers in Santa Rosa, Calif.
The committee work was motivated by federal and state agencies that regulate various aspects of underground injection work, which seem to have little standard data or analyses to draw from. Most troubling, the committee found, was that no set of industry “best practices” for minimizing the risk of earthquakes exists for any of the technologies, which in turn makes it difficult for regulators to establish sensible rules. The committee strongly recommends that energy companies work with the Department of Energy to establish such practices. It notes that best practices are important because all indications are that more and more underground extraction of energy will occur in the future.
(Source: Scientific American)
Subscribe to our RSS feed to stay in touch and receive all of TT updates right in your feed reader | <urn:uuid:dbdcf276-6563-4e0a-9177-2ebeac393cc7> | 3.375 | 676 | Truncated | Science & Tech. | 27.399326 |
Write comments between coding
It is very important comments writing in html coding to read and understand coding. because, if page need changes, It can help to edit coding next time.
Keep good coding structure
Write code with good structure as shown below, It can also understandable to read coding. if it does not appear in the coding, then code ready can be hard to read it.
Avoid colspans if It possible
too much colspans very headache to understand coding and change design with coding. use nested structure or use Divs.
Compress images as well as possible.
It is also very important thing to load web pages very fast. there are several formates to show images in web pages, chose best compressed formate and good quality display.
Code should be W3.org standards.
Code should be w3.org standards, Write meta tags and titles to web page according to page content, Images for alt tags. It can help to search optimization.
follow code standards to develop knowledge and to be best expert in coding. some times, some code writers uses tds instead of ul or ol like below example.
Improve css usage tips
It is also good technique to decrease page code. Few same CSS classes can be use to several pages and use several times. To know few css usage tips click here. | <urn:uuid:4ea330ba-7a0a-4e88-a025-cb1eef5fc424> | 3.3125 | 276 | Tutorial | Software Dev. | 57.393684 |
Al Gore says global warming is a planetary emergency. It is difficult to see how this can be so when record low temperatures are being set all over the world. In 2007, hundreds of people died, not from global warming, but from cold weather hazards.
Since the mid-19th century, the mean global temperature has increased by 0.7 degrees Celsius. This slight warming is not unusual, and lies well within the range of natural variation. Carbon dioxide continues to build in the atmosphere, but the mean planetary temperature hasn’t increased significantly for nearly nine years. Antarctica is getting colder. Neither the intensity nor the frequency of hurricanes has increased. The 2007 season was the third-quietest since 1966. In 2006 not a single hurricane made landfall in the U.S.
South America this year experienced one of its coldest winters in decades. In Buenos Aires, snow fell for the first time since the year 1918. Dozens of homeless people died from exposure. In Peru, 200 people died from the cold and thousands more became infected with respiratory diseases. Crops failed, livestock perished, and the Peruvian government declared a state of emergency.
Unexpected bitter cold swept the entire Southern Hemisphere in 2007. Johannesburg, South Africa, had the first significant snowfall in 26 years. Australia experienced the coldest June ever. In northeastern Australia, the city of Townsville underwent the longest period of continuously cold weather since 1941. In New Zealand, the weather turned so cold that vineyards were endangered.
Last January, $1.42 billion worth of California produce was lost to a devastating five-day freeze. Thousands of agricultural employees were thrown out of work. At the supermarket, citrus prices soared. In the wake of the freeze, California Gov. Arnold Schwarzenegger asked President Bush to issue a disaster declaration for affected counties. A few months earlier, Mr. Schwarzenegger had enthusiastically signed the California Global Warming Solutions Act of 2006, a law designed to cool the climate. California Sen. Barbara Boxer continues to push for similar legislation in the U.S. Senate.
In April, a killing freeze destroyed 95 percent of South Carolina’s peach crop, and 90 percent of North Carolina’s apple harvest. At Charlotte, N.C., a record low temperature of 21 degrees Fahrenheit on April 8 was the coldest ever recorded for April, breaking a record set in 1923. On June 8, Denver recorded a new low of 31 degrees Fahrenheit. Denver’s temperature records extend back to 1872.
Recent weeks have seen the return of unusually cold conditions to the Northern Hemisphere. On Dec. 7, St. Cloud, Minn., set a new record low of minus 15 degrees Fahrenheit. On the same date, record low temperatures were also recorded in Pennsylvania and Ohio.
Extreme cold weather is occurring worldwide. On Dec. 4, in Seoul, Korea, the temperature was a record minus 5 degrees Celsius. Nov. 24, in Meacham, Ore., the minimum temperature was 12 degrees Fahrenheit colder than the previous record low set in 1952. The Canadian government warns that this winter is likely to be the coldest in 15 years.
Oklahoma, Kansas and Missouri are just emerging from a destructive ice storm that left at least 36 people dead and a million without electric power. People worldwide are being reminded of what used to be common sense: Cold temperatures are inimical to human welfare and warm weather is beneficial. Left in the dark and cold, Oklahomans rushed out to buy electric generators powered by gasoline, not solar cells. No one seemed particularly concerned about the welfare of polar bears, penguins or walruses. Fossil fuels don’t seem so awful when you’re in the cold and dark.
If you think any of the preceding facts can falsify global warming, you’re hopelessly naive. Nothing creates cognitive dissonance in the mind of a true believer. In 2005, a Canadian Greenpeace representative explained global warming can mean colder, it can mean drier, it can mean wetter. In other words, all weather variations are evidence for global warming. I can’t make this stuff up.
Global warming has long since passed from scientific hypothesis to the realm of pseudo-scientific mumbo-jumbo.
David Deming is a geophysicist, an adjunct scholar with the National Center for Policy Analysis, and associate professor of Arts and Sciences at the University of Oklahoma.
'Your papers, please' must never be heard in America
Independent voices from the TWT Communities
Things to do, places to go, new spots to enjoy with friends and family from Norfolk to Washington, D.C., to Delaware and all points inbetween.
Wall Street news before (and occasionally after) the opening bell.
Life Happens and the Law either protects you or foils you. Here you will learn how to stay ahead of the game.
Benghazi: The anatomy of a scandal
Vietnam Memorial adds four names
Cinco de Mayo on the Mall | <urn:uuid:62b24326-c067-493b-8705-742bbaaf3ac9> | 3.375 | 1,023 | Nonfiction Writing | Science & Tech. | 51.957645 |
As you go higher in the mesosphere, the air gets colder.
Click on image for full size
Original artwork by Windows to the Universe staff (Randy Russell).
Temperature in the Mesosphere
The top of the mesosphere is the coldest part of the atmosphere. It can get down to -90° C (-130° F) there! As you go higher in the mesosphere, the air gets colder.
The air is much thinner (less dense) in the mesosphere than in the stratosphere below. There are fewer air molecules to absorb incoming electromagnetic radiation from the Sun. That includes molecules of ozone, which absorb ultraviolet radiation and heat the stratosphere. In the mesosphere, the thin air and small amounts of ozone keep the air from warming much.
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Text for this level has not been written yet. Please see the "Intermediate" text for this page if you want to learn about this topic. To get to the "Intermediate" text, click on the blue "Intermediate"...more
Ozone is a special kind of oxygen molecule. Normal oxygen molecules (O2), the kind we need to breathe, have two oxygen atoms. Ozone molecules (O3) have three oxygen atoms. Ozone forms when a photon of...more
Rainbows appear in the sky when there is bright sunlight and rain. Sunlight is known as visible or white light and is actually a mixture of colors. The sun's rays pass through millions of raindrops. A...more
It takes the Earth one year to travel around the sun one time. During this year, there are four seasons: summer, autumn, winter, and spring. Each season depends on the amount of sunlight reaching the...more
Scientists sometimes travel in airplanes that carry weather instruments in order to gather data about the atmosphere. These research aircraft bring air from the outside into the plane so scientists can...more
An anemometer is a weather instrument used to measure the wind (it can also be called a wind gauge). These instruments can be used in a backyard weather station or on a well-equipped scientific research...more
Thermometers measure temperature. "Thermo" means heat and "meter" means to measure. You can use a thermometer to measure the temperature of many things, including the temperature of...more | <urn:uuid:d2e5ca01-585c-49d4-a5ee-e87a266e3a56> | 3.96875 | 538 | Content Listing | Science & Tech. | 55.405959 |
How Sodium Polyacrylate Absorbs
Superabsorbent polymers are partially neutralized polyacrylate, with incomplete cross-linking between units. Only 50–70% of the COOH acid groups have been converted to their sodium salts. The final chemical has very long carbon chains bonded with sodium atoms in the center of the molecule. When sodium polyacrylate is exposed to water, the higher concentration of water outside the polymer than inside (lower sodium and polyacrylate solute concentration) draws the water into the center of the molecule via osmosis. Sodium polyacrylate will continue to absorb water until there is an equal concentration of water inside and outside the polymer.
Why Diapers Leak
To some extent, diapers leak because pressure on the beads can force water out of the polymer. Manufacturers counter this by increasing the cross-link density of the shell around the bead. The stronger shell allows the beads to retain water under pressure. However, leaks occur mainly because urine is not pure water. Think about this: you can pour a liter of water into a diaper with no spill, but the same diaper probably can't absorb a liter of urine. Urine contains salts. When a child uses the diaper, water is added, but also salts. There will be salts outside of the polyacrylate molecules as well as inside, so the sodium polyacrylate won't be able to absorb all the water before the sodium ion concentration is balanced. The more concentrated the urine, the more salt it contains, and the sooner the diaper will leak. | <urn:uuid:58af78fc-4ffc-45d2-87f7-014ee4cb5ddb> | 3.453125 | 324 | Knowledge Article | Science & Tech. | 36.822143 |
DistributionRead full entry
Range DescriptionThe Hog Deer historically occurred from Pakistan, throughout northern and northeastern India, including the Himalayan foothill zone, east across non-Sundaic Southeast Asia and, marginally, southern China (southern Yunnan province), but is now reduced to isolated populations within this range. It is almost extirpated from east of Myanmar. It is extinct in Thailand (where it has, however, been introduced) and almost certainly in Viet Nam and Lao PDR (Humphrey and Bain 1990; Duckworth et al. 1999; Tordoff et al. 2005; R.J. Timmins pers. comm. 2008). Very small numbers have been found recently in Bangladesh, in one small region of Cambodia (Khan 2004; Maxwell et al. 2007), and, reportedly, China (per B.P.L. Chan pers. comm. 2008); although details of the latter have not yet been traced, it is believed to involve a population of at most a few dozen, at one site. Hog Deer still probably occur in at least several areas of Myanmar (J.W. Duckworth in litt. 2008, from various sources), and localised populations survive in northern and northeastern India, Nepal, Bhutan (few recent data) and Pakistan (status uncertain) (Biswas and Mathur 2000; Biswas 2004). Hog Deer has been introduced into Sri Lanka, Australia (specifically the coastal regions of south and east Gippsland; Moore and Mayze 1990), and the United States (Texas, Florida, and Hawaii) (Grubb 2005) (but is not mapped in these last two). | <urn:uuid:4b820538-9467-43d9-bd0f-ca24c9fa9965> | 2.953125 | 337 | Knowledge Article | Science & Tech. | 59.777625 |
A centroid of a triangle is the point where the three medians of the triangle meet. A median of a triangle is a line segment from one vertex to the mid point on the opposite side of the triangle.
The centroid is also called the center of gravity of the triangle. If you have a triangle plate, try to balance the plate on your finger. Once you have found the point where it will balance, that is the centroid of that triangle.
The centroid of triangle ABC
Now, someone might raise the question of how do we know if the three medians actually meet at one point. That is a very good question and lets test a couple of different triangles to see if this is the case. Click HERE to open a GSP file and experiment yourself.
To test whether the three medians were concurrent, let us first construct the midpoints D, E, and F on each sides of the triangle. Then, let us connect the points B and E, and C and F and label the intersection point G.
Then, let us construct a ray from point A to point G, and test if this ray (orange colored) goes through the mid point D for different shape of triangles.
Testing of whether three medians intersect at one point
From these samples, it is clear that the ray AG arrows through the mid point D exactly, and the three medians indeed meet at one point. To prove the concurrency of the three medians, we will need to use the Ceva's theorem.
This theorem was proved by Giovanni Ceva (1648-1734). To get a full introduction to this theorem, CLICK HERE, and to see a proof of Ceva's theorem, CLICK HERE.
Theorem: In a triangle ABC, three lines AD, BE and CF intersect at a single point K if and only if
Now using Ceva's theorem, it will be straightforward to prove that the three medians intersect at one point. Since the medians divide each sides of the triangle in half, it follows that AF = FB = 1/2, BD = DC = 1/2, and CE = EA = 1/2. Hence, AF/FB = 1, BD/DC = 1, CE/EA = 1, and the product of the three ratios equal to 1.
There is another special characteristic of the centroid. Can you see any patterns from the diagrams below?
Do you see anything special about the Centroid?
The centroid divides each median in a special ratio 2:1. In the diagrams above, I inserted the mid points of AG, BG and CG, to make it easier to compare the lengths. Now let us prove that the centroid divides each median in the ratio 2:1.
The centroid divides each median in the ratio 2:1.
Let us connect the two midpoints E and F,
Then the triangles AEF and ACB are similar, because
It follows that because triangles AEF and ACB are similar, the lines EF and CB are parallel and CB = 2 * EF.
Now look at triangles EGF and BGC. Because the lines EF and CB are parallel,
Also, angle GDE equals angle GBC because they are opposite one another.
Thus, triangles EGF and BGC are similar. Furthermore, because CB = 2 * EF, this means that the length of the sides of the triangles BGC and EGF are in the ratio 2:1, and we have
Similary, by constructing a line from point D to F, and using the two similar triangles DFG and AGC, we can prove that
Return to David's Home | <urn:uuid:1b43acab-1594-4a83-a0de-fcf88d1a1c1e> | 4.125 | 756 | Academic Writing | Science & Tech. | 72.933919 |
Single neurons can detect sequences?
ScienceDaily tells us that
If this holds up, it might help explain how some people (not all, of course) have come back from serious brain injuries, even at an advanced age, when neuron production may be low.
Single Neurons Can Detect Sequences
ScienceDaily (Aug. 13, 2010) — Single neurons in the brain are surprisingly good at distinguishing different sequences of incoming information according to new research by UCL neuroscientists.
The study, published August 12 in Science and carried out by researchers based at the Wolfson Institute for Biomedical Research at UCL, shows that single neurons, and indeed even single dendrites, the tiny receiving elements of neurons, can very effectively distinguish between different temporal sequences of incoming information.
This challenges the widely held view that this kind of processing in the brain requires large numbers of neurons working together, as well as demonstrating how the basic components of the brain are exceptionally powerful computing devices in their own right. | <urn:uuid:17a4df07-4ced-4668-84af-178aea6dbbbd> | 2.953125 | 203 | Personal Blog | Science & Tech. | 25.374444 |
This Topic deals with the occurrence of marine invertebrates in Nova Scotia waters, The marine environment includes the diverse intertidal habitats (H2.1 - H2.5), the ocean bottom (H1.2) and water of the open sea (H1.1). Common species are included in the habitat descriptions.
The Canadian Atlantic marine fauna is generally well known, since it has been studied for more than a century. Significantly more effort has been expended on studies in intertidal and shallow nearshore habitats than in offshore areas. Marine research in Atlantic Canada has always had a strong relationship with fisheries, and to a great extent the study of invertebrates and marine plants for their own sake was neglected. In recent years, however, much new information has been obtained through the efforts of universities and government research agencies. This reflects the realization that all commercial species interact with other species to maintain balanced ecosystems.
A general review of the literature suggests there are approximatley 1600 species of marine invertebrates. At least 400 of them spend some stage of their life as plankton. These species numbers are conservative estimates.
This Document Includes:
Warm Temperate and Tropical Fauna
Download PDF File (246k, 7 pages, 8 figures, 1 table)
T4.3 Post-glacial Colonization by Animals
T6.2 Oceanic Environments
T6.3 Coastal Aquatic Environments
T11.14 Marine Fishes
Copyright © The Province of Nova Scotia, Canada | <urn:uuid:0fc50830-9ec1-4826-8ec2-50aef8dab870> | 3.203125 | 312 | Truncated | Science & Tech. | 38.136228 |
HTML Tag: Symbols used to define the structure and formatting of an HTML document. This includes the structure of the document with <head> and <body> tags, layout of the document with tags like <table> or <div> and formatting of text with tags like <b> for bold and <i> for italic. Tags have a starting form like <this> and an ending like </this> and can have a number of attributes like <tag attribute="value"> this.
Tags can be written by hand, generated by a formatting program or created by a WYSIWYG (what you see is what you get) editor such as Microsoft Frontpage. HTML tags are used in Ruby usually in conjunction with embedded Ruby or an HTML or XML builder interface. | <urn:uuid:0164e078-2d15-4ae7-82a2-23744e73f5c8> | 3.8125 | 159 | Knowledge Article | Software Dev. | 52.225719 |
Feb. 20, 2009
NASA's Fermi Gamma-ray Space Telescope has detected a record-setting gamma-ray burst with the greatest total energy and fastest motions ever seen.
Feb. 20, 2009
Are there other worlds like ours? Are we alone? NASA's Kepler spacecraft is about to begin an unprecedented journey that could answer these ancient questions.
Feb. 19, 2009
Something is about to happen on Saturn that is so pretty, even Hubble will pause to take a look. Backyard astronomers can see it, too. Four of Saturn's moons will transit Saturn and cast their shadows on the planet's cloudtops at the same time.
Feb. 10, 2009
NASA spacecraft are monitoring blasts of gamma-ray energy from a star 30,000 light years away. Some of the flares have packed more total energy than the sun puts out in 20 years.
Feb. 6, 2009
Even in space, someone has to clean the bathroom. ISS Astronautsare using a tricorder-like device to help them 'swab the decks.'
Feb. 4, 2009
Comet Lulin is approaching Earth for a 38-million-mile close encounter later this month. The green double-tailed comet is putting on a fine show for backyard telescopes and could soon become visible to the unaided eye.
Feb. 2, 2009
A private photographer has used NASA's Mars technology to create a 1,474 megapixel panoramic photo of President Obama's inauguration. The interactive mega-snapshot has become an international sensation, viewed by more than two million people in 186 countries.
Jan. 23, 2009
Today, NASA researchers announced an event that will transform our view of the Sun and super-charge the field of solar Physicsfor many years to come.
Jan. 21, 2009
A new NASA-funded study details what might happen to our modern, high-tech society in the event of a 'super solar flare' followed by an extreme geomagnetic storm. Some of the conclusions might surprise you.
Jan. 15, 2009
The last place you'd expect to find icicles is around the rim of a scalding hot and thundering rocket engine. Yet an engine being used by NASA to develop technologies for next-generation lunar landers has been caught producing icicles of unlikely beauty. | <urn:uuid:6d08dca5-2743-486b-b73f-e996155b74e2> | 2.921875 | 477 | Content Listing | Science & Tech. | 62.656616 |
by G Lyon
Name_______________________ Date___________ Per.______
This is a laboratory that simulates a population census technique commonly used by
wildlife biologists in the field. The first step is to trap a random sample of animals
of the desired species. These animals are then ear-tagged or marked in some other
manner and released. The next step is to trap once again. Some of the animals captured
may have been marked from the first sample. Using a simple ratio, the biologist
can come up with a quick population estimate.
____ = ____
M=Number of animals captured and marked in first sample
n=Number of animals captured in second sample
m=Number of "n" that were already marked
- Put 4-6 large handfulls of pinto beans into a shoe box. Do not count them. Then
make an estimate as to how many beans are in the box. Write your estimate here___________.
- Now we shall use the mark- recapture technique to get an estimate of the population.
- Pick out a handful of beans and count them. This is your first trapping sample,
- To mark these beans merely replace them with colored beans (white or red). These
marked individuals must be released back into the population (shoe box).
- Shake the box and, without looking, grab another handful of beans. This is your
second trapping sample, n. n=__________
- How many of the beans in your second trapping sample were already marked (colored
- Now use the equation above to calculate your population estimate, N. N=__________
- Count the actual number of beans in your box. Write the number here ___________.
- Was your estimate using the ratio closer than your initial guess?
- How could you increase the accuracy of your estimate?
- What species of animal would this technique work well for? What species of animal
would this technique not work for? Why?
- Can you think of a better way to estimate the number of beans in the box? | <urn:uuid:8dc5f43b-d6c4-45bf-abf2-0987221f9dde> | 3.609375 | 428 | Tutorial | Science & Tech. | 61.956227 |
Kempner has established the existence of a basis for residual polynomials in one variable with respect to a composite modulus. A residual polynomial modulo m is by definition a polynomial f(x) with integer coefficients which is divisible by m for every integral value of x, and a residual congruence is written f(x) = 0 (mod m). By a basis for a given modulus is meant a finite set of residual polynomials pi(x) which fulfills two requirements: (i) every residual polynomial modulo m is expressible as a sum of products of pi(x) b polynomials in x with integral coefficients; (ii) no member of the set pi(x) can be written identically equal to a sum of products of the remaining members of the set by polynomials in x with integral coefficients.
For this work, the following notation is used. The symbol μ(d) denotes the least positive integer for which d divides μ!. A special set of divisors of m is chosen: separate all divisors of m which exceed 1 into groups such that μ(d) has the same value for all the d's of a group but different values for the d's of different groups; select the largest d of each group and denote this set by d1,..., ds. Finally, Π(μ) = x(x–1)...(x–μ+1); when x is replaced by xj, the product will be denoted by Πj(μ); Π(1) is interpreted as 1. Employing this notation, Dickson gave a brief proof of the theorem due to Kempner:
Every residual polynomial f(x) modulo m is a sum of products of m and (m/di)Π(μ(di)) for i = 1, ..., s by polynomials in x with integral coefficients.
In a later paper, Kempner considered the problem for n variables. In attempting to apply Dickson's method to the proof of the existence of a basis for residual polynomials in more than one variable, I found that Kempner had omitted from the set pi(x1,...,xn) certain residual polynomials in several variables. This was brought to my attention by an example in two variables modulo 12. For this modulus, the d1, ..., ds are d1=12, d2=6, d3=2; the corresponding μ's are μ1=4, μ2=3, μ3=2. Write qi = m/di. The part of the basis containing one variable is composed of
(1) 12, qiΠ1(μi), qiΠ2(μi) (i = 1,2,3).
Kempner would include in the basis pi(x1, x2) modulo 12 only the seven terms (1). However, the residual polynomial,
must be added since, as is shown below, it is impossible to write the identity
where c, fi, gi are polynomials in x1, x2 with integral coefficients. By use of (x1, x2) = (0,0), (2,0), (0,2) we prove the constant terms of c, f3, g3 even. The pair (x1, x2) = (2,2) shows the right side of (2) divisible by 24 and the left side equal to 12. | <urn:uuid:e5760ebe-416c-4e68-b998-9017b42962fa> | 2.796875 | 750 | Academic Writing | Science & Tech. | 77.518011 |
Ground States Of A Collection Of N Point-Like Particles
Ground states of a collection of N point-like particles constrained to lie on the surface of a torus and interacting via a cubic potential. The lattices are labeled by (r,N), where r is the ratio between the largest and smallest radius of the torus. The figure shows prominent example of topological defects such as dislcinations (5-fold disclinations are marked in red and 7-fold disclinations in blue), dislocations and grain-boundaries. While in planar crystals these defects are energetically costly and don't appear in the ground state, on a surface of non-zero Gaussian curvature defects proliferate in order to balance the elastic strain introduced by the curvature of the underlying medium. L. Giomi and M. J. Bowick, Eur. Phys. J. E 27, 275 (2008) & M. Bowick and L. Giomi, Adv. Phys. 58, 449 (2009).
Image courtesy: Dr. L. Giomi, School of Engineering and Applied Science, Harvard University. | <urn:uuid:7cafbd7f-f4a1-4d64-9225-00680a1b9ced> | 2.875 | 230 | Knowledge Article | Science & Tech. | 61.4 |
What is it?
It was found at the bottom of the sea aboard an ancient Greek ship.
Its seeming complexity has prompted decades of study,
although some of its functions remained unknown.
X-ray images of the device have confirmed the nature of the
and discovered several surprising functions.
The Antikythera mechanism has been
discovered to be a
mechanical computer of an accuracy thought
in 80 BC, when the ship that carried it
Such sophisticated technology was not thought to be developed by humanity for another 1,000 years.
Its wheels and gears create a portable
orrery of the sky
that predicted star and planet locations as well as
shown above, is 33 centimeters high and therefore
similar in size to a large book.
Credit & License: Wikipedia | <urn:uuid:2fbd0c5e-8696-47ae-8258-86b101f5035a> | 3.90625 | 164 | Knowledge Article | Science & Tech. | 41.464219 |
|What happens when a star runs out of
For stars about the mass of our Sun, the center condenses into a
while the outer atmospheric layers are
expelled into space and appear as a
pictured above and designated
Shapley 1 after the famous astronomer
Harlow Shapley, has a very apparent annular ring like structure.
Although some of
appear like planets on the sky
(hence their name), they actually surround stars far outside
our Solar System. | <urn:uuid:121b62c6-de8a-4dc4-98c6-b32d49992ef1> | 3.4375 | 102 | Content Listing | Science & Tech. | 24.3885 |
Space Environment Center -- The official U.S. government bureau
for real-time monitoring of solar and geophysical events, research
in solar-terrestrial physics, and forecasting solar and geophysical
Optics -- the first place to look for information about sundogs,
pillars, rainbows and related phenomena. See also Snow
Solar and Heliospheric Observatory -- Realtime and archival images of the Sun from
SOHO. (European Mirror
Daily Sunspot Summaries -- from the NOAA Space Environment
Images --a gallery of up-to-date solar pictures from the
National Solar Data Analysis Center at the Goddard Space Flight
Center. See also the GOES-12 Solar X-ray
Recent Solar Events -- a nice summary of current solar conditions from
SOHO Farside Images of the Sun from SWAN
The Latest SOHO Coronagraph Images -- from the Naval Research Lab
The Sun from Earth -- daily images of our star from the Big Bear Solar
List of Potentially Hazardous
Asteroids -- from the Harvard
Minor Planet Center.
Observable Comets -- from the Harvard Minor Planet Center.
What is the Interplanetary Magnetic
Field? -- A lucid answer from
the University of Michigan. See also the Anatomy
of Earth's Magnetosphere.
Real-time Solar Wind Data -- from NASA's ACE spacecraft. How powerful are
solar wind gusts? Read this
story from Science@NASA.
Real-time Solar Wind Data --
from the Solar and Heliospheric Observatory Proton Monitor.
Aurora Forecast --from the University of Alaska's Geophysical Institute
Daily Solar Flare and Sunspot
Data -- from the NOAA Space
Lists of Coronal Mass Ejections -- from 1998 to 2001
What is an Iridium
flare? See also Photographing
Satellites by Brian Webb.
Vandenberg AFB missile launch
What is an Astronomical
Unit, or AU?
in Finland; An
Introduction to Mirages;
NOAA Solar Flare and Sunspot Data: 1999;
Space Audio Streams: (University of
Florida) 20 MHz radio emissions from Jupiter: #1, #2, #3, #4;
(NASA/Marshall) INSPIRE: #1;
(Stan Nelson of Roswell, New Mexico) meteor radar: #1,
Recent International Astronomical Union
GLOSSARY | SPACE WEATHER | <urn:uuid:1f3a42f6-57fc-4b0b-9559-6c58c2d4deb4> | 2.796875 | 516 | Content Listing | Science & Tech. | 32.644623 |
“Researchers at the Scripps Research Institute have made important steps toward understanding how life originated by shedding light on the ‘RNA World’ hypothesis. The ‘RNA World’ refers to the idea that life on Earth went through a stage where RNA was used to store information and act as a catalyst, much like DNA and proteins are used in organisms today. A critical component of this stage would be that RNA molecules would have to replicate themselves. The team at Scripps has now synthesized RNA enzymes that can replicate themselves without the help of additional molecules. These RNA-based, self-replicating systems could be a model for how life on Earth first began to operate.” — Quote from Nasa’s coverage page.
Read the entire article here: http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2999&mode=thread&order=0&thold=0
The implications of this research are staggering. Not only for the depth of the knowledge we’ll get, but for the application of the science in ways to benefit us all … it’s truly a wonderful thing! | <urn:uuid:8745cae7-72a0-402d-829c-62a0b1ad401f> | 3.375 | 250 | Personal Blog | Science & Tech. | 52.667725 |
Q&A: Dark Matter
Regarding the Dark Matter Mystery. Did the equation for the mass
of the galaxy include planetary zones for the stars? Just
looking at our own solar system, a large proportion of the mass
seems to be in the planetary zone and made up of elements with
much greater mass than just hydrogen. Also these planets and
debris fields probably wouldn't emit much in the way of radio
energy and if planets existed in sufficient numbers would
increase the mass of the galaxy by quite a lot.
The mass of all the planets in our solar system is about 0.1
percent of mass of the Sun, so if our solar system is typical,
the total mass of planets in the galaxy is small compared to
that of stars. | <urn:uuid:418efe5c-58b5-4c50-a75e-c9cd29fe2783> | 2.84375 | 159 | Q&A Forum | Science & Tech. | 59.026059 |
Actinopterygii (ray-finned fishes) > Perciformes
(Perch-likes) > Pomacentridae
(Damselfishes) > Pomacentrinae
Etymology: Pomacentrus: Greek, poma, -atos = cover, operculum + Greek, kentron = sting (Ref. 45335). More on author: Jordan, Seale.
Environment / Climate / Range
Marine; reef-associated; non-migratory; depth range 1 - 45 m (Ref. 7247). Tropical; 33°N - 23°S
Size / Weight / Age
Maturity: Lm ? range ? - ? cm
Max length : 10.0 cm FL male/unsexed; (Ref. 5525)
soft rays: 15 - 16. The background color of this species varies from light tan to deep blue or dark brownish purple. The juvenile is similar to that of P. bankanensis, but lacks a bluish stripe on the exact mid-dorsal line of the snout forehead.
Pacific Ocean: Moluccas to Samoa, north to the Izu Islands, south to Rowley Shoals in the eastern Indian Ocean and New Caledonia.
Comprises several color forms, or geographical variations (Ref. 48636). Adults are found in mixed coral and rubble areas of lagoon and seaward reefs from the lower surge zone to a depth of 40 m (Ref. 1602). Solitary (Ref. 37816). Feed on filamentous algae and small invertebrates (Ref. 1602). Oviparous, distinct pairing during breeding (Ref. 205). Eggs are demersal and adhere to the substrate (Ref. 205). Males guard and aerate the eggs (Ref. 205).
Allen, G.R., 1991. Damselfishes of the world. Mergus Publishers, Melle, Germany. 271 p.
IUCN Red List Status (Ref. 90363)
Threat to humans
ReferencesAquacultureAquaculture profileStrainsGeneticsAllele frequenciesHeritabilityDiseasesProcessingMass conversion
Estimates of some properties based on empirical models
Phylogenetic diversity index (Ref. 82805
= 0.5000 [Uniqueness, from 0.5 = low to 2.0 = high].
Bayesian length-weight: a=0.02580 (-0.07529 - 0.12689), b=2.91 (2.84 - 2.98), based on LWR estimates for species & genus-BS (Ref. 93245
Trophic Level (Ref. 69278
): 3.1 ±0.33 se; Based on food items.
Resilience (Ref. 69278
): High, minimum population doubling time less than 15 months (Preliminary K or Fecundity.).
Vulnerability (Ref. 59153
): Low vulnerability (23 of 100) . | <urn:uuid:303f7f5b-d7d0-4126-b917-b5e7bd19c4c0> | 2.734375 | 625 | Knowledge Article | Science & Tech. | 65.635439 |
Scientists at Harvard University have created a cyborg tissue consisting of lab-grown flesh embedded with nano-wires that has the same "sensing" properties as human skin. This is all going to end very poorly. Probably with an army of cyborgs that look human.
'Ultimately, this is about merging tissue with electronics in a way that it becomes difficult to determine where the tissue ends and the electronics begin.'
The [Harvard] Gazette notes that the researches initially worried about how the 'skin,' once implanted, would sense and react to chemical and electrical changes.
Normal human skin is capable of sensing oxygen, pH, and other elements in the air, and reacts to each one accordingly.
The challenge, then, was engineering skin that would do the same.
I'm sure there actually are some positive applications for this technology like aiding those who have lost limbs, but you know what? If I lose my arms I don't want cyborg ones. I want legs. Then I could finally run on all fours and start a new life with my animal friends in the forest.
Hit the jump for a microscopic view of the stuff.
Thanks to AJ, my pal SonicAlligator, Ryan, carvin and Shegs, who agree the only skin robots should have is the gross kind that forms on the top of pudding when you cook it. | <urn:uuid:a1e3ce23-2c2b-4505-ad1b-e3d817d906f9> | 2.890625 | 279 | Personal Blog | Science & Tech. | 55.411692 |
Video: Volcanic vents
At this depth, the spewing water is hot enough to melt lead, and the pressure it exerts means that every square centimetre has to withstand the weight of five hefty men.
"It was like wandering across the surface of another world," says Bramley Murton, a geologist at the National Oceanographic Centre (NOC) in Southampton, UK, who piloted the Hy-Bis underwater vehicle around these deep volcanic vents and filmed them for the first time.
"The rainbow hues of the mineral spires and the fluorescent blues of the microbial mats covering them were like nothing I had ever seen before," Murton says.
These are the first images to be beamed back from the depths of the Cayman trough, the world's deepest undersea volcanic rift, which runs across the floor of the Caribbean.
An international collaboration of researchers that goes by the name InterRidge is currently exploring the rift with submersible vehicles. They team will stay in the area until 21 April. A second expedition to the Cayman trough is planned for the near future.
The previous deepest known vent was 4200 metres down on the Mid-Atlantic ridge, but most deep-sea vents visited so far have been less than 3800 metres from the surface. The latest vents, with their slender spires made of copper and iron ores, are 5000 metres down. The InterRidge team may yet dive to 6000 metres.
"We are still studying these new vents," says Doug Connelly, also of the NOC. "We don't have a temperature measurement yet – it's not easy to take the temperature of a deep-sea vent. But because the temperature of vents depends on their depth to some degree, these could be very hot."
Whether they are hotter than the current record of 464 °C, found at two black smokers 3000 metres below the waves on the Mid-Atlantic ridge, we shall wait to see, Connelly says.
Deep-sea creatures have also been found at the new vents, but the team is not yet revealing any details. "We've seen deep-sea creatures down there, just as at shallower deep-sea vents," says Jon Copley, a marine biologist at the University of Southampton. "But our findings need to be checked by other scientists before we can talk about them."
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Follow The Expedition Online!
Mon Apr 12 01:16:51 BST 2010 by CA
The expedition team have a live website where you can follow their progress at http://www.thesearethevoyages.net
The Weight Of Five Hefty Men
Mon Apr 12 01:43:36 BST 2010 by katherine
so what's that in polar bears then? Or how about SI units? Not that we are scientists or anything...
The Weight Of Five Hefty Men
Tue Apr 13 12:07:13 BST 2010 by Steve
I'm not a mathematician or anything but I did do some sums so I can't tell you if my answer is right but I think it works out to about one average male polar bear/cm squared (see below).
The water pressure at 5000m depth should be 513kg/cm squared and the average (mean) weight of a male polar bear is 520kg. Given this information we can also deduce that a hefty man weighs between 102.6 - 104kg. :)
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support. | <urn:uuid:c38b2385-898a-4df4-ae23-67e20f78d28b> | 3.3125 | 838 | Truncated | Science & Tech. | 61.70007 |
Determining Distance to Object, Retina Image
Date: Fall 2011
What is the formula for determining the distance away an object is, given the apparent size versus the actual size? For example, an airplane flying overhead. I live near an airport and curiosity got me thinking about this. It might be one inch to my retina versus say, a thousand feet long actually. What is it's distance away?
You can first estimate the angular diameter of the object in your
view. That is the length or diameter of the object in terms of
angular units (e.g., degrees). For example, both the moon and the
sun are about 0.5 degrees in diameter from our vantage point on
Earth. The distance from horizon to horizon would be 180 degrees.
Estimating the angular diameter may not be very easy and can be
prone to error. Since the moon is very familiar, you can estimate
the object in terms of how many moons in length/diameter it is, then
convert to degrees.
Now if you know the actual length or diameter of the object you are
looking at, you can use simple trigonometry to figure out the
distance. The tangent of half the angular distance you estimated
above (let us call that "a") would be equal to half the actual
diameter or length (let us call that "d") divided by the actual
distance (let us call that "D").
So, if we draw out the triangles we can see that tan(a/2) = (d/2) / D
or, D = (d/2) / tan(a/2)
For example, we know the moon is about 3476 km. So then D = 1738 km
/ tan(0.25 deg) = 398,000 km. And that turns out pretty close to the
known average distance to the moon which is 384,000 km.
You can use this same procedure another way. Say you hold your left
arm straight out in front of you and stick out your index finger to
the right so you can see it clearly. You measure the distance from
your eye to your finger and it is 45 cm. You measure the thickness
of your finger and it is 1.5 cm. This means there is a factor of 30
when you use your finger as a measuring guide. So if you see an
airplane fly directly overhead, and you use your measuring finger to
see that your finger just barely covers the wing, and you know the
wing is 33 foot span, then you can quickly estimate that the
airplane is about 1000 feet overhead. If the plane is two fingers in
span, then its 500 feet above you. If half your finger is enough to
cover the plane, then its 2000 feet above you.
John C. Strong
It is a matter of the ratio of triangles where:
The ratio of the perceived dimensions = The ratio of the real dimensions.
First you calculate the perceived dimensions, and since you know one
"real" dimension ( the length of the plane), you can then solve for
the last dimension - the distance.
Plot on a sheet of paper the flight path of the plane overhead, and
note each time the plane travels its length as perceived by your
eye, until you record, say about 10 of them.
Then, draw a line from the point of origin, where the plane started
overhead, to this 10th point you plotted and label this line X.
Measure and record the length of X. If to your eye, the plane is 1"
long, then your line X should be approximately 12".
Then on that same sheet of paper, draw a vertical line from the
point where the plane started overhead, down to your home, and label
that distance Y.
Next draw a line from the 10th point the plane traveled to your home
and label that line H.
Now measure the angle between the vertical line Y and the line
H. You can call this angle Theta. The reason for plotting 10
points is to get a good angle measurement.,
Also from Trig, the Tangent of an Angle = distance opposite the
angle / distance adjacent to
the angle. The distance opposite the angle is the distance the
plane traveled, and the distance adjacent is the distance over your
head. So in your picture, tan(Theta) = X/Y.
If you perceived the plane length to be 1"' then the measured
distance traveled, X, on your paper, should be 12". From there,
then the distance overhead can be calculated by rearranging the
equation above to solve for Y:
Y = X / tan(Theta)
Now the matter of ratios; but before that, we have to divide X by
10. Remember we plotted 10 plane lengths to get a good measurement
of angle Theta.
Equate Z=X/10, in your case Z=1.2"
Now we have dimensions for two triangles. One the perceived
triangle and the other the "real" triangle.
The ratio of the perceived dimensions (Z/Y) is equivalent to the
ratio of the "real" dimensions (Plane's length / Distance overhead).
Rearranging, we get: Distance Overhead = Plane's Length / (Z/Y)
With that, we get Distance = 1000 feet / (1.2/20) is approximately
Sounds about right given the floor (minimum height) restriction for
a residental area is typically 10,000 to 15,000 feet. You can
confirm by asking any pilot or look at flight maps, or call the airport! =)
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:cef3216d-7950-4cad-a845-bc20bcf269ec> | 3.859375 | 1,205 | Knowledge Article | Science & Tech. | 70.00861 |
Freezing Water and Life
water is the only compound I know that expands while
freezing. Why is it essential that it does to guarantee our survival?
What are all the reasons why we would perish if this property was
absent of water?
ALL the reasons? You're not paying us enough.
ONE big reason is that if ice sank, the oceans would be mostly solid. Why?
sinking ice would fall to the bottom, never to be seen again. More ice
forming at the surface would sink and add the the ever-growing pile.
Eventually, most of the biosphere would be solid ice.
As it is, cold water sinks, but ice floats. When surface water cools, it
sinks and mixes with the water below it, providing oxygenation throughout.
Ice, however, doesn't accumulate on the bottom.
Pretty convenient, huh?
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
Click here to return to the Zoology Archives
Update: June 2012 | <urn:uuid:dc586c2a-eac7-4638-bae6-c7e1ad241cd3> | 2.90625 | 220 | Personal Blog | Science & Tech. | 67.211528 |
A new visual illusion is predicted from the assumption that the perceived distance along any path depends on the discriminability for position along the path. A disk is placed between two dots, so that the straight path between the dots is nearly tangent to the disk. It is predicted that, for the perceived straight path between the dots to be tangent to the disk, the disk must overlap the physically straight path between the dots by an amount proportional to its radius. Furthermore, certain patternings of the disk are predicted to reduce the amount of illusion. All predictions are confirmed in detail. The results are compared with those obtained in an experiment on the filled-space illusion.
MAURICE M. TAYLOR, "Geometry of a Visual Illusion," J. Opt. Soc. Am. 52, 565-568 (1962) | <urn:uuid:55e649a9-b6c6-461a-987f-fc9e2fd3d86f> | 2.890625 | 170 | Academic Writing | Science & Tech. | 58.439419 |
HTTP has a very thorough and well supported caching mechanism, but in this age of the dynamic Web page, it often goes unused when it is needed the most. So what do we, as Web programmers, need to do to make sure our pages are cached correctly? Let's have a look.
What is the point of caching? The idea is that on the Web, it is often better to have stale data than to wait for the network. Data only changes every so often and even if it has changed, it's not always important that the client has the latest data, so caching it either at the client, or at an intermediary, isn't a problem and should infact be a good idea. RFC2616 says:
Caching would be useless if it did not significantly improve performance. The goal of caching in HTTP/1.1 is to eliminate the need to send requests in many cases, and to eliminate the need to send full responses in many other cases. The former reduces the number of network round-trips required for many operations; we use an "expiration" mechanism for this purpose. The latter reduces network bandwidth requirements; we use a "validation" mechanism for this purpose.
Allowing clients and intermediaries to cache our pages will lighten the load on our servers and create a faster user experience. One of the problems with dynamic Web applications is that your Web server thinks it is sending new data every request and so can't set the correct caching headers, you need to do a little extra work yourself within your application to make sure caching is working for you.
There are two types of caching in HTTP, we'll look at both, how they work, how they work together, and how to make sure your Web application is taking advantage of them.
The expiration model is a way for the server to say how long a requested resource stays fresh for, user agents should cache the resource response and re-use it until its cache is no longer fresh.
Expiration is excellent for resources that change at known times or the change very rarely and whose staleness does not matter. For example, images and style sheets that are used across a site often do not change very often and so should be sent with a expiration date of at least 24 hours. The user agent will then only download them once, no matter how many pages of the site they visit.
If we are serving resources from a dynamic data source, for example say we have a graphic that portrays the current weather outside, if we know that the data only updates once an hour, we can set the expiration date to an hour so that clients only request it once per hour.
The simpliest way of doing this is with the HTTP Expires header, it just contains the date and time of when the resource will become stale:
The Expires header has a few problems like requiring the server and client to have clocks that are in sync. So HTTP 1.1 replaced it with the Cache-Control header that offers more flexibility:
The cache control header has a number of clauses that can be used to control the way the client caches the resource.
The validation model allows a client to ask the server whether a cached version of a resource is still fresh. If the client doesn't have a fresh cached version, the server will respond with a fresh version of the resource, while if it does, the server will say so and send nothing.
This is useful as it allows our server to tell a client it already has the freshest version and not do any processing. If the resource is dynamic, we can save our server from having to do all the work involved in producing the response since the client already has it in its cache.
Like the expiration model, there are two HTTP headers that control validation, the Last-Modified header is defined in HTTP 1.0 and sends the client the date/time when the resource was last modified:
When a client sends a "If-Modified-Since" request header, the date/time sent in that header can be compared with the resources last modified date/time, and if it matches, a 304 Not Modified HTTP response sent.
The Last-Modified header suffers the same problems as the Expires header, and thus was replaced in HTTP 1.1 with the Etag header. An Etag is a string that uniquely identifies a resource, they should be generated by the server in a way as to change whenever the resource does, a common Etag value is the MD5 hash of the resource or of the resources URL and its modified date/time stamp.
When a client sends a "If-None-Match" request header, the Etag value in that header should be compared to the resource and if it matches, a 304 Not Modified response sent.
So to make sure your dynamic resource behaves well when it comes to HTTP caching, you need to support validation and optionally send a expiration header from within your script.
Supporting validation in PHP this is pretty simple, sending the correct headers is just a case of:
And doing the actual validation just requires a function like:
If you want to tell clients when your resource expires, you need a function like:
As well as HTTP caching, your Web application may also want to use various application caching mechanisms. If you're hitting a database often you may want to place an object cache like Memcache in front of it so that often requested data can be cached in Web server memory rather than being re-requested from the database. If your dynamic app has lots of pages that don't update very often you may want to place a reverse proxy like Squid in front of it to save re-generation of all non-changed pages across users. The setting up and using of other caches are beyond the scope of this article, an intro to using Squid as a reverse proxy can be found here and the PHP memcached extensions documentation is here.
For more info on HTTP caching, check out section 10 of RFC2616 and for an easier read, have a look at Mark Nottingham's Caching Tutorial. | <urn:uuid:65bf77f5-d0e3-4b20-adf1-bcffb9e3e884> | 3.125 | 1,239 | Documentation | Software Dev. | 48.888557 |
Discrete Fourier seriesAssume we are given a periodic discrete-time signal x with period p. Just as with continuous-time signals, this signal can be described as a sum of sinusoids,
x(n) = A0 + ∑(k=1 to (p-1)/2) Ak cos (kω0n + φ k )
for p odd and
x(n) = A0 + ∑(k=1 to p/2) Ak cos (kω0n + φ k )
for p even, where ω0 = 2 π /p is the fundamental frequency.
Unlike the continuous-time case, the sum is finite. Intuitively, this is because sampled signals cannot represent frequencies above a certain value. We will examine this phenomenon in more detail later, but for now, it proves extremely convenient. Mathematically, the above relation is much simpler than the continuous-time Fourier series. All computations are finite. There are a finite number of samples in one period of the waveform. There are a finite number of terms in the Fourier series representation for each sample. Unlike the continuous-time case, it is easy for computers to manage this representation. Given a finite set of values, A0, …, Ap-1, a computer can calculate x(n). Moreover, the representation is exact for any periodic signal. No approximation is needed. In the continuous-time case, the Fourier series representation is accurate only for certain signals. For the discrete-time case, it is always accurate.
The discrete-time Fourier series (DFS), given above, can be calculated efficiently on a computer using an algorithm called the fast Fourier transform (FFT). All of the computer-generated Fourier series examples that you have seen use the FFT algorithm. | <urn:uuid:ac29348e-f774-4d4e-bd01-2d7182512e51> | 3.59375 | 382 | Academic Writing | Science & Tech. | 48.309539 |
what is the difference between enum and final class in java?
The java.lang.Enum is an abstract class, it is the common base class of all Java language enumeration types. The definition of Enum is:
public abstract class Enum> extends Object implements Comparable, Serializable
All enum types implicitly extend java.lang.Enum.
A final class cannot be extended. A final class implicitly has all the methods as final, but not necessarily the data members. | <urn:uuid:3ff163e3-320c-48be-9a3c-c4ec2baf0dec> | 3.3125 | 100 | Q&A Forum | Software Dev. | 43.840667 |
Redoubt Volcano erupted for 3 months in 2009, generating spectacular ash clouds and producing a large lava dome that remains in place today. Both this eruption and the last eruption in 1989 were preceded by bursts of earthquake activity -- known as earthquake swarms-- that provided scientists with early warning of the imminent eruption.
When more earthquake swarms occurred around the vent in the year after the eruption, the alert levels were raised in anticipation of eruptive activity.
No eruption occurred, however, so the earthquakes were dismissed as having occurred either within the cooling lava dome or in the summit glaciers rather than being generated by the volcano. Helena Buurman and colleagues show that deeper earthquakes identical to those recorded during the 2009 eruption were reactivated during these earthquake swarms.
Because these deeper earthquakes were recorded during eruptive activity, their presence after the eruption suggested that the magmatic system at Redoubt was still active.
An active gas vent on the lava dome also closed after the last of the earthquake swarms, providing further evidence that although the volcano had not been erupting, the system had remained open and active for nearly a year before finally closing -- much longer than previously thought.
Helena Buurman et al., Alaska Volcano Observatory, Geophysical Institute, University of Alaska Fairbanks, DOI:10.1130/G34089.1 | <urn:uuid:acb464c3-afa4-49ac-b9f7-0295409942cc> | 3.890625 | 269 | Knowledge Article | Science & Tech. | 23.657541 |
Galls are something you can be forgiven for overlooking, but they’re an important and surprisingly common feature of the natural world. In fact, gall expert Ron Russo has found as many as 30 species of galls on a single blue oak, and even casual observers may run across giant ones nicknamed “oak apples” that are formed by the California Gall Wasp (Andricus quercuscalifornicus).
But what are galls exactly? The short answer is that they are any kind of abnormal swelling of plant tissues caused by a wide variety of insects, bacteria, fungi, and mistletoes. Either accidentally through irritation, or intentionally through the release of chemicals, these invaders cause plant cells to proliferate or grow abnormally large, creating a tumor-like growth.
Galls typically arise when insects, such as cynipid wasps or tephritid fruit flies, insert their eggs into plant tissues, and the plant swells until it forms a protective growth around the developing larvae. It’s a case of insects co-opting plant defense systems for their own ends.
Galls come in an astonishing variety of shapes and sizes and can be found on nearly any type of plant. They may be as small as the period at the end of this sentence or as large as four feet across; they may be smooth, warty, spiny, or hairy; and they may be shaped like cups, saucers, donuts, sea urchins, or caterpillars.
Even more amazing is that out of the thousands of species of insects and other organisms that cause galls, each one creates its own distinctive and unique type of gall. This allows biologists called “cecidologists” to identify and study these galls with a high degree of specificity.
Spring is the best time to observe galls because insects prefer to lay their eggs in rapidly developing plant tissues like buds and shoots which are being supplied with enormous amounts of sugars and carbohydrates. The developing insect larvae then co-opt these nutrients for their own growth.
California has a particularly rich diversity of galls associated with its oak trees, so an oak grove is an excellent place for a spring walk in search of galls. Try finding some “oak apples” which start out smooth red or green before aging to dark brown, and look like out-of-place potatoes dangling among the oak branches. Examine a few leaves closely and you might discover the bubblegum-pink sea urchin-shaped galls of the crystalline tube gall wasp (Trichoteras tubifaciens). Or the measles-spotted ping pong balls of the speckled gall wasp (Besbicus mirabilis).
Not only are galls fascinating in their variety and ecology, but very little is known about the insects that cause them. Many species remain to be discovered and named, and virtually nothing is known about the identification and biology of even some of the commonly observed galls.
If you’ve ever wanted to try your hand at discovering new species, cecidology might be the field for you. If nothing else, the fact that so little is known about galls might add a little mystery to your next walk this spring, so keep your eyes open and see how many types you can find.
David Lukas, co-author of Sierra Nevada Natural History | <urn:uuid:7ee156b8-3d73-4f3f-9e91-32cb60a0b112> | 3.875 | 702 | Personal Blog | Science & Tech. | 41.663396 |
NGC 281 in 60 Seconds
Narrator (April Hobart, CXC): High-mass stars are important because they are responsible for much of the energy pumped into a galaxy over its lifetime. Unfortunately, these stars aren’t understood very well because they are usually found relatively far away in places where lots of gas and dust can impede out line of sight. The star cluster NGC 281 is an exception to this rule. It is located about 6,500 light years from Earth and almost 1,000 light years above the plane of the Galaxy. This means it’s away from much of stuff that blocks our view. Here we see NGC 281 in X-rays from Chandra and infrared data from Spitzer. The high-mass stars in NGC 281 have powerful winds flowing from their surfaces and intense radiation that heats surrounding gas, "boiling it away" into interstellar space. This process results in the formation of large columns of gas and dust, as seen on the left side of the image. These structures likely contain newly forming stars. The eventual deaths of massive stars as supernovas will also seed the galaxy with material and energy. | <urn:uuid:42882447-cdec-42bf-aa4a-d888696da747> | 3.84375 | 234 | Truncated | Science & Tech. | 58.063588 |
One very important design principle I came across years ago was something called MVC; Model View Controller. Essentially what that entails is instead of bunging all your PHP code (and MVC does not only refer to PHP, its a design concept used in lots of other languages) into one file to represent a page, like database connection, running a query on the database, formatting that data and manipulating it, followed by echo'ed HTML to display that data in tables or whatever format is desired, MVC seeks to seperate all the different parts of a web application to make managing them easier.
Model refers to the actual object classes that describe the database schema your data is stored in. Instead of writing your own SQL queries by hand and hard-coding things like database, table and column names, the model is the intermediary. The model is responsible for connecting to the database, generating a query based on parameters you have passed to it, manipulating that returned data and then sending the end result back to whatever called it ready for use.
View refers the actual presentation on screen that an end user would see. The view doesn't care what the database looks like or even if one exists at all as long as it has the data it needs to create the presentation it is supposed to. It will generate the HTML needed for that data the model extracted to be displayed in a way that makes sense to the user.
Controller is the intermediary. It will take the events generated from the View, such as mouse clicks, page loads, etc, analyse what the view has done, decide what the next step will be, such as load another view or ask the model to return more data and then send that data to another view, etc. The controller can be thought of as the glue that binds the model and views together.
Whew! Ok, enough of that lecture. There is one problem with this seemingly clever seperation of tasks. Coding an MVC framework can be a nightmarish task and the complexity of making an MVC alone work can be more effort than its worth. This is where symfony comes in. Symfony is an already pre-built MVC framework for PHP, and while setting up your own MVC structure would be laborious, symfony's is ready to go and using the framework as opposed to writing your own PHP code from scratch actually makes the job even faster than using no MVC at all.
So why is symfony so great? Well, feel free to try it yourself. Symfony's philosophy is convention over configuration which means that, instead of explictly defining the relationships between classes and database schema, for example, that there is an implied relationship. For example, if you had a table called "sales_history", the model class that deals with interacting with that table is called "SalesHistory". Its a convention, we agree to use it this way. It is only if you decide to not use this convention and name your class "SalesMade" that you need to worry about reconfiguring aspects of your code to do that.
Because of this convention scenario you can do the following steps, after having installed symfony, to have a fully working set of database-agnostic model classes ready to use in your application:
- Go to a terminal and enter:
/path/to/symfony generate:project project_name
- Then go to "/path/to/project_name/config/schema.yml" and define your database structure in the easy to use YAML syntax
- Go to terminal and enter "symfony propel:build-model;"
At Synaq, we have been using symfony for over a year now on a specific, large, and complex project and it has proved invaluable. There has been a lot of learning and experimentation involved in getting to know and use the framework to its best, but the experience has been well worth it seeing how quickly, even with the learning curve, we have been able to produce results.
There is far too much involved with symfony for me to be able to go into great detail here, and I will be giving more information in future on tricks and tips we have learnt while using it. Suffice it to say, if you want to simplify the way you develop large projects, feel free to go give symfony a look. | <urn:uuid:5a3e16e3-0f69-4013-81e1-ebc5d161e775> | 2.953125 | 900 | Personal Blog | Software Dev. | 43.193979 |
An estimation of the galaxy's span resulted in a conclusion of 150,000 light years, which is slightly larger than the Milky Way.
The Cartwheel galaxy shows non-thermal radio and optical spokes, but they are not the same spokes.
The galaxy was once a normal spiral galaxy like the Milky Way before it apparently underwent a head-on collision with a smaller companion approximately 200 million years ago (i.e., 200 million years prior to the image). When the nearby galaxy passed through the Cartwheel Galaxy, the force of the collision caused a powerful shock wave through the galaxy, like a rock being tossed into a sandbed. Moving at high speed, the shock wave swept up gas and dust, creating a starburst around the galaxy's center portion that were unscathed. This... Read More | <urn:uuid:d1b0d9bd-c9e6-4e70-b7f9-87f1f1e854c8> | 3.734375 | 162 | Truncated | Science & Tech. | 58.044235 |
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Here Are 20 Mathematicians Who Changed The World
Before scientists can develop medicines or engineers can advance technology, they throw numbers onto whiteboards using concepts laid out by mathematicians sometimes centuries earlier.
Generations of school children will disagree, but no other field of study has played a bigger role in changing the course of history as mathematics.
Unfortunately, mathematicians often get little recognition for their contributions to history.
We’re changing that right now.
We’ve identified the 20 mathematicians responsible for the modern world.
William Playfair, inventor of charts
William Playfair, a Scottish engineer, was the founder of graphical statistics. Besides that signature accomplishment, he was at various times in his life a banker, an accountant, a journalist, an economist, and one of the men to storm the Bastille.
It’s difficult to overstate his importance. He was the inventor of the line graph, bar chart, and the pie chart. He also pioneered the use of timelines. You’re probably familiar with his work.
James Maxwell, the first color photographer
Maxwell was a Scottish mathematician who formed the classical electromagnetic theory. This combined centuries of research in magnetism, electricity, and optics into a single theoretical framework. He was the first to demonstrate that electricity traveled through space at the speed of light.
How crucial was he? Einstein kept a framed photo of Maxwell on his desk beside pictures of Michael Faraday and Issac Newton. He was the first to develop a color photograph. Connecting light with electromagnetism is considered one of the greatest accomplishments of modern physics. He’s in many ways the founder of his field.
Alan Turing, World War II codebreaker
Alan Turing is a British mathematician who is hailed as the father of computer science. His work laid the groundwork for the PC you’re presumably reading this on.
Turing is especially unique on this list for his efforts during the Second World War. Working at the famous Bletchley Park, Turing is credited as one of most important people in devising the techniques for breaking the German Enigma cipher.
He developed the method by which the Bombe – a massive electromechanical machine built by the Allies – could crack the Enigma on an industrial scale, allowing them to read nearly all German communication. In that regard, he is one of the founders of modern cryptanalysis, and by all rights played one of the most crucial parts in winning the Battle of the Atlantic for the Allies. | <urn:uuid:170f5ab6-6dfe-4ded-b104-c5b8ef4da7bd> | 2.953125 | 750 | Listicle | Science & Tech. | 33.535543 |
Department of Physics and Astronomy
Points of Emphasis
The purpose of this lab is to introduce the students to a number of electric and magnetic phenomena which they will be studying in depth throughout the term. The standard version consists of six lab stations.
Station 1: Electrostatics
This section demonstrates a number of ways that static charges can be created and separated. Activities include: (1) rubbing a rubber rod with cat fur and dipping the rod into balsa chips, (2) rubbing a rubber rod with cat fur and observing what happens to the leaves of an electroscope when the charged rod is brought close and when it is allowed to touch the electroscope, (3) using an electrophorus to induce charges on the electroscope and on to large metal spheres and (4) placing a string wig onto a van de Graff generator and observing what happens when the generator is turned on.
Station 2: Magnetic Eddy Currents
This section demonstrates magnetic forces and the process of magnetic induction. Activities include: (1) running an "aluminum saw" between the poles of an electromagnet both with and without current in the electromagnet and observing the difference in effort needed to move the saw and (2) observing the difference in behavior between a solid and a slotted ring of aluminum when they are allowed to drop between the poles of the electromagnet (with current flowing in the electromagnet).
Station 3: The Oscilloscope
Part I. Students look at Lissajous figures formed by feeding sine waves from two function generators into the X and Y inputs of an oscilloscope. Students can vary the frequency and relative amplitudes of the sine waves to determine the effect on the Lissajous figures.
Part II. Students connect a microphone to an oscilloscope and look at the voltage patterns formed by singing into the microphone, striking a tuning fork, ringing a bell, etc.
Station 4: Standing Waves on a Wire
This section gives the student some direct experience with electric and magnetic acting together. An AC current is produced in a piano wire strung between two post. The wire runs between the poles of a horseshoe magnet (magnetic field perpendicular to the motion of the electron). The oscillating electrons feel a magnetic force perpendicular to both their motion and the magnetic field. This force drives the wire up and down. Students can observe the fundamental and the first five harmonics of the standing waves in the wire. They can also vary the tension in the wire to observe its effect on the fundamental frequency.
Station 5: Electric Currents Produce Magnetic Fields
Part I. Students place a light flexible wire between the poles of a horseshoe magnet and connect the wire to a car battery via a momentary switch. Students are asked to observe what happens to the wire when current from the battery flows through the wire when the momentary switch is depressed.
Part II. Students use a compass needle to examine the magnetic field around a wire in which a current is flowing.
Station 6: Electromagnetic Induction
Part I. Students move a bar magnet in and out of a coil of wire connected to a galvanometer. They are asked to observe how the direction and speed of the motion of the bar magnet effect the indications on the galvanometer.
Part II. Students turn the crank on a small generator and observe the difference in effort required between when the generator is connected to a light bulb and when the generator is disconnected from the light bulb.
Site contact: largent@Dartmouth.EDU | <urn:uuid:8d9ab527-370c-42ea-ad9c-3bbbae198bfa> | 3.8125 | 725 | Tutorial | Science & Tech. | 40.787712 |
Scarlet Kingsnakes (milk snakes) can thrive in a variety of habitats. They are usually found around coniferous or deciduous forest edges, but they can also be found in tropical hardwood forests, open woodland, dry or wet prairies, savannahs, rocky hillsides, small streams or marshes, and agricultural or urban areas. These snakes do not fear human proximity.
South Central Virginia southward to Key West, Florida and westward to the Mississippi River. The species is more abundant along the Coastal Plain but has been collected inland at altitudes of almost 2,000 feet.
Georgia Wildlife Web
Reptiles and Amphibians of Eastern/Central North America. A Peterson Field Guide. Roger Conant and Joseph Collins 3rd Edition. Houghton Mifflin, New York, NY. 1998. | <urn:uuid:8134ef70-1e4e-4adf-9607-b884732a83be> | 3.09375 | 173 | Knowledge Article | Science & Tech. | 46.884231 |
Introduction to Apache Ant
The Apache Ant package is a
Java-based build tool. In theory,
it is kind of like make, but without make's wrinkles. Ant is different. Instead of a model that is
extended with shell-based commands, Ant is extended using Java classes. Instead of writing shell
commands, the configuration files are XML-based, calling out a
target tree that executes various tasks. Each task is run by an
object that implements a particular task interface.
This package is known to build and work properly using an LFS-7.2
Apache Ant Dependencies
User Notes: http://wiki.linuxfromscratch.org/blfs/wiki/apache-ant
Installation of Apache Ant
If it is not possible to install the recommended JUnit package, install Apache Ant by removing the reference to the
test instructions (note that the tests will not be performed):
sed -i 's;jars,test-jar;jars;' build.xml
otherwise copy the junit jar file
to the local directory tree.
cp -v /usr/share/junit-4.10/junit-4.10.jar lib/optional/junit.jar
Install Apache Ant by running the
The unit regression tests are performed during the build step below
unless JUnit is not installed.
Now, as the
./build.sh -Ddist.dir=/opt/ant-1.8.4 dist &&
ln -v -sfn ant-1.8.4 /opt/ant
Make sure the JAVA_HOME environment variable is set for the
sed -i 's;jars...: If
the JUnit package is not
installed, the regression tests cannot be performed.
cp -v /usr/share/junit-4.10/4.10.jar
...: This command copies the JUnit jar file into
the directory where Apache Ant will look for it.
dist: This command does everything. It builds,
tests, then installs the package into
ln -v -sfn ant-1.8.4
/opt/ant: This command is optional, and creates a
Configuring Apache Ant
Some packages will require ant to be in the search path
$ANT_HOME environment variable
defined. Satisfy these requirements by adding the following lines
/etc/profile or to individual
ant, antRun, antRun.pl,
complete-ant-cmd.pl, runant.pl, and runant.py
is a Java based build
tool used by many packages instead of the conventional
is a support script used to start ant build scripts in a
is a Perl script that
provides similar functionality offered by the
is a Perl script that
allows Bash to complete
is a Perl wrapper script
used to invoke ant.
is a Python wrapper
script used to invoke ant.
files are the Apache Ant
Java class libraries.
Last updated on 2013-02-11 18:51:17 +0000 | <urn:uuid:3c0f2bf8-24ee-474c-a777-2272980cb93e> | 3.4375 | 647 | Documentation | Software Dev. | 70.751674 |
New research from a global group of scientists and engineers, including from the University of Southampton, supports the use of tidal power, which has the potential to provide more than 20 per cent of the UK's electricity demand.
NASA scientists say 2012 was the ninth warmest of any year since 1880, continuing a long-term trend of rising global temperatures. With the exception of 1998, the nine warmest years in the 132-year record all have occurred since 2000, with 2010 and 2005 ranking as the hottest years on record.
The 12.0% record cell on a standard size of 1.1 square cm combines two patented absorber materials, which convert light of different wavelengths. Using two different absorber materials creates a stronger absorption of photons and improves energetic utilization through a higher photovoltage.
A leading coastal scientist has warned that some of the world's best known beach resorts may not survive projected sea level rises and that problems caused by changing sea levels are compounded by a lack of political will and short-term coastal management initiatives.
A validated multi-physics numerical model that accounts for charge and species conservation, fluid flow, and electrochemical processes has been used to analyze the performance of solar-driven photoelectrochemical water-splitting systems. The modeling has provided an in-depth analysis of conceptual designs, proof-of-concepts, feasibility investigations, and quantification of performance.
To meet 21st-century food, water and energy challenges, the world needs more women and men with interdisciplinary training and access to world problems on the ground. As a result, Cornell and five other universities have partnered with The Nature Conservancy to establish the NatureNet Science Fellows Program, which is intended to help develop a new breed of interdisciplinary scientists with academic savvy, and skills and opportunity to solve real-world problems.
Black carbon is the second largest man-made contributor to global warming and its influence on climate has been greatly underestimated, according to the first quantitative and comprehensive analysis of this pollutant's climate impact..
In addition to causing smoggy skies and chronic coughs, soot - or black carbon - turns out to be the number two contributor to global warming. It's second only to carbon dioxide, according to a four-year assessment by an international panel. | <urn:uuid:824031f7-aefa-48f3-9fb3-9d6fe891be1c> | 2.921875 | 464 | Content Listing | Science & Tech. | 31.561908 |
How to Find Life: When starlight passes through a planet’s atmosphere, certain elements absorb specific wavelengths of light, and these show up as dips in the spectrum. McKibillo
If aliens are out there, the best shot at finding them—assuming they resemble the life-forms on Earth—is to look for planets like ours. E.T.’s home will probably require an atmosphere to have liquid water and keep out solar radiation, so astronomers search for perfectly sized and situated planets surrounded by blankets of life-supporting gases like oxygen and water vapor. Now they know how to recognize that ideal atmosphere. | <urn:uuid:aedd4ac7-1b2d-43bb-9dbd-b6af8e1ee233> | 3.171875 | 127 | Truncated | Science & Tech. | 48.137047 |
Richard F. Holman is a professor of physics at Carnegie Mellon University. He offers this response:
Wormholes are solutions to the Einstein field equations for gravity that act as "tunnels," connecting points in space-time in such a way that the trip between the points through the wormhole could take much less time than the trip through normal space.
The first wormhole-like solutions were found by studying the mathematical solution for black holes. There it was found that the solution lent itself to an extension whose geometric interpretation was that of two copies of the black hole geometry connected by a "throat" (known as an Einstein-Rosen bridge). The throat is a dynamical object attached to the two holes that pinches off extremely quickly into a narrow link between them.
Theorists have since found other wormhole solutions; these solutions connect various types of geometry on either mouth of the wormhole. One amazing aspect of wormholes is that because they can behave as "shortcuts" in space-time, they must allow for backwards time travel! This property goes back to the usual statement that if one could travel faster than light, that would imply that we could communicate with the past.
Needless to say, this possibility is a disturbing one; time travel would allow for a variety of paradoxical situations, such as going back into the past and killing your grandfather before your father was born (the grandfather paradox). The question now arises of whether it would be possible to actually construct a wormhole and move it around in such a way that it would become a usable time machine.
Wormhole geometries are inherently unstable. The only material that can be used to stabilize them against pinching off is material having negative energy density, at least in some reference frame. No classical matter can do this, but it is possible that quantum fluctuations in various fields might be able to.
Stephen Hawking conjectured that while wormholes might be created, they cannot be used for time travel; even with exotic matter stabilizing the wormhole against its own instabilities, he argued, inserting a particle into it will destabilize it quickly enough to prevent its use. This is known as the Chronology Protection Conjecture.
Wormholes are great theoretical fun, and are seemingly valid solutions of the Einstein equations. There is, however, no experimental evidence for them. This should not stop any budding science-fiction writers from using them as needed!
William A. Hiscock is a professor of physics at Montana State University, Bozeman, and is the director of the Montana Space Grant Consortium. He adds some details:
A wormhole is a tunnel-like connection through space-time, much like the real tunnels bored by worms in a (Newtonian) apple. At present, space-time wormholes are only theoretical constructs derived from general relativity; there is no experimental evidence for their existence. Nevertheless, theoretical physicists study the mathematical properties of space-times containing wormholes because of their unusual properties. Study of such strange geometries can help better distinguish the boundaries of behavior permitted in the theory of general relativity, and also possibly provide insights into effects related to quantum gravity.
A wormhole has two mouths connected by a "throat," and provides a path that a traveler could follow to a distant point. The path through the wormhole is topologically distinct from other routes one could follow to the same destination.
What is meant by topologically distinct? If an ant wished to crawl from one side of an apple to another, there are many possible paths on the surface connecting the starting point to the destination. These paths are not distinct topologically: a piece of elastic string fixed at the starting and ending points, and lying along one such path, could be slid and stretched over the surface to lie along any other such path. Now imagine that the ant instead crawls through a wormhole in the apple. A piece of string passing through the wormhole cannot be smoothly moved in such a way as to lie along one of the surface paths (or through another wormhole with the same end points but different route). | <urn:uuid:572c582e-ad57-482d-9ef6-e15877cc37a2> | 3.28125 | 837 | Comment Section | Science & Tech. | 34.257267 |
The Doppler effect (or Doppler shift), named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.
For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered.
Doppler first proposed the effect in 1842 in his treatise "Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels" (On the coloured light of the binary stars and some other stars of the heavens). The hypothesis was tested for sound waves by Buys Ballot in 1845. He confirmed that the sound's pitch was higher than the emitted frequency when the sound source approached him, and lower than the emitted frequency when the sound source receded from him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848 (in France, the effect is sometimes called "effet Doppler-Fizeau"). In Britain, John Scott Russell made an experimental study of the Doppler effect (1848).
An English translation of Doppler's 1842 treatise can be found in the book The Search for Christian Doppler by Alec Eden.
In classical physics (waves in a medium), where the source and the receiver velocities are not supersonic, the relationship between observed frequency f and emitted frequency f0 is given by:
The frequency is decreased if either is moving away from the other.
The above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle (but still with a constant velocity), the observed frequency that is first heard is higher than the object's emitted frequency. Thereafter, there is a monotonic decrease in the observed frequency as it gets closer to the observer, through equality when it is closest to the observer, and a continued monotonic decrease as it recedes from the observer. When the observer is very close to the path of the object, the transition from high to low frequency is very abrupt. When the observer is far from the path of the object, the transition from high to low frequency is gradual.
In the limit where the speed of the wave is much greater than the relative speed of the source and observer (this is often the case with electromagnetic waves, e.g. light), the relationship between observed frequency f and emitted frequency f0 is given by:
|Observed frequency||Change in frequency|
These two equations are only accurate to a first order approximation. However, they work reasonably well when the speed between the source and receiver is slow relative to the speed of the waves involved and the distance between the source and receiver is large relative to the wavelength of the waves. If either of these two approximations are violated, the formulae are no longer accurate.
The frequency of the sounds that the source emits does not actually change. To understand what happens, consider the following analogy. Someone throws one ball every second in a man's direction. Assume that balls travel with constant velocity. If the thrower is stationary, the man will receive one ball every second. However, if the thrower is moving towards the man, he will receive balls more frequently because the balls will be less spaced out. The inverse is true if the thrower is moving away from the man. So it is actually the wavelength which is affected; as a consequence, the received frequency is also affected. It may also be said that the velocity of the wave remains constant whereas wavelength changes; hence frequency also changes.
If the source moving away from the observer is emitting waves through a medium with an actual frequency f0, then an observer stationary relative to the medium detects waves with a frequency f given by
where vs is positive if the source is moving away from the observer, and negative if the source is moving towards the observer.
A similar analysis for a moving observer and a stationary source yields the observed frequency (the receiver's velocity being represented as vr):
where the similar convention applies: vr is positive if the observer is moving towards the source, and negative if the observer is moving away from the source.
These can be generalized into a single equation with both the source and receiver moving.
With a relatively slow moving source, vs,r is small in comparison to v and the equation approximates to
However the limitations mentioned above still apply. When the more complicated exact equation is derived without using any approximations (just assuming that source, receiver, and wave or signal are moving linearly relatively to each other) several interesting and perhaps surprising results are found. For example, as Lord Rayleigh noted in his classic book on sound, by properly moving it would be possible to hear a symphony being played backwards. This is the so-called "time reversal effect" of the Doppler effect. Other interesting conclusions are that the Doppler effect is time-dependent in general (thus we need to know not only the source and receivers' velocities, but also their positions at a given time), and in some circumstances it is possible to receive two signals or waves from a source, or no signal at all. In addition there are more possibilities than just the receiver approaching the signal and the receiver receding from the signal.
All these additional complications are derived for the classical, i.e., non-relativistic, Doppler effect, but hold for the relativistic Doppler effect as well.
Craig Bohren pointed out in 1991 that some physics textbooks erroneously state that the observed frequency increases as the object approaches an observer and then decreases only as the object passes the observer. This would be the case if the source travels directly to the observer (and through the observer). In other cases, the observed frequency of an approaching object declines monotonically from a value above the emitted frequency, through a value equal to the emitted frequency when the object is closest to the observer, and to values increasingly below the emitted frequency as the object recedes from the observer. Bohren proposed that this common misconception might occur because the intensity of the sound increases as an object approaches an observer and decreases once it passes and recedes from the observer and that this change in intensity is misperceived as a change in frequency.
The siren on a passing emergency vehicle will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer. Astronomer John Dobson explained the effect thus:
In other words, if the siren approached the observer directly, the pitch would remain constant (as vs, r is only the radial component) until the vehicle hit him, and then immediately jump to a new lower pitch. Because the vehicle passes by the observer, the radial velocity does not remain constant, but instead varies as a function of the angle between his line of sight and the siren's velocity:
where vs is the velocity of the object (source of waves) with respect to the medium, and θ is the angle between the object's forward velocity and the line of sight from the object to the observer.
The Doppler effect for electromagnetic waves such as light is of great use in astronomy and results in either a so-called redshift or blue shift. It has been used to measure the speed at which stars and galaxies are approaching or receding from us, that is, the radial velocity. This is used to detect if an apparently single star is, in reality, a close binary and even to measure the rotational speed of stars and galaxies.
The use of the Doppler effect for light in astronomy depends on our knowledge that the spectra of stars are not continuous. They exhibit absorption lines at well defined frequencies that are correlated with the energies required to excite electrons in various elements from one level to another. The Doppler effect is recognizable in the fact that the absorption lines are not always at the frequencies that are obtained from the spectrum of a stationary light source. Since blue light has a higher frequency than red light, the spectral lines of an approaching astronomical light source exhibit a blue shift and those of a receding astronomical light source exhibit a redshift.
Among the nearby stars, the largest radial velocities with respect to the Sun are +308 km/s (BD-15°4041, also known as LHS 52, 81.7 light-years away) and -260 km/s (Woolley 9722, also known as Wolf 1106 and LHS 64, 78.2 light-years away). Positive radial velocity means the star is receding from the Sun, negative that it is approaching.
Another use of the Doppler effect, which is found mostly in plasma physics and astronomy, is the estimation of the temperature of a gas (or ion temperature in a plasma) which is emitting a spectral line. Due to the thermal motion of the emitters, the light emitted by each particle can be slightly red- or blue-shifted, and the net effect is a broadening of the line. This line shape is called a Doppler profile and the width of the line is proportional to the square root of the temperature of the emitting species, allowing a spectral line (with the width dominated by the Doppler broadening) to be used to infer the temperature.
The Doppler effect is used in some types of radar, to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source. Each successive radar wave has to travel farther to reach the car, before being reflected and re-detected near the source. As each wave has to move farther, the gap between each wave increases, increasing the wavelength. In some situations, the radar beam is fired at the moving car as it approaches, in which case each successive wave travels a lesser distance, decreasing the wavelength. In either situation, calculations from the Doppler effect accurately determine the car's velocity. Moreover, the proximity fuze, developed during World War II, relies upon Doppler radar to explode at the correct time, height, distance, etc.
An echocardiogram can, within certain limits, produce accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any arbitrary point using the Doppler effect. One of the limitations is that the ultrasound beam should be as parallel to the blood flow as possible. Velocity measurements allow assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves (valvular regurgitation), and calculation of the cardiac output. Contrast-enhanced ultrasound using gas-filled microbubble contrast media can be used to improve velocity or other flow-related medical measurements.
Although "Doppler" has become synonymous with "velocity measurement" in medical imaging, in many cases it is not the frequency shift (Doppler shift) of the received signal that is measured, but the phase shift (when the received signal arrives).
Velocity measurements of blood flow are also used in other fields of medical ultrasonography, such as obstetric ultrasonography and neurology. Velocity measurement of blood flow in arteries and veins based on Doppler effect is an effective tool for diagnosis of vascular problems like stenosis.
Instruments such as the laser Doppler velocimeter (LDV), and acoustic Doppler velocimeter (ADV) have been developed to measure velocities in a fluid flow. The LDV emits a light beam and the ADV emits an ultrasonic acoustic burst, and measure the Doppler shift in wavelengths of reflections from particles moving with the flow. The actual flow is computed as a function of the water velocity and face. This technique allows non-intrusive flow measurements, at high precision and high frequency.
Developed originally for velocity measurements in medical applications (blood flows), Ultrasonic Doppler Velocimetry (UDV) can measure in real time complete velocity profile in almost any liquids containing particles in suspension such as dust, gas bubbles, emulsions. Flows can be pulsating, oscillating, laminar or turbulent, stationary or transient. This technique is fully non-invasive.
In military applications the Doppler shift of a target is used to ascertain the speed of a submarine using both passive and active sonar systems. As a submarine passes by a passive sonobuoy, the stable frequencies undergo a Doppler shift, and the speed and range from the sonobuoy can be calculated. If the sonar system is mounted on a moving ship or another submarine, then the relative velocity can be calculated.
The Leslie speaker, associated with and predominantly used with the Hammond B-3 organ, takes advantage of the Doppler Effect by using an electric motor to rotate an acoustic horn around a loudspeaker, sending its sound in a circle. This results at the listener's ear in rapidly fluctuating frequencies of a keyboard note.
A laser Doppler vibrometer (LDV) is a non-contact method for measuring vibration. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface. | <urn:uuid:1f8e58a0-f975-4fdd-883a-345895336f57> | 4.3125 | 2,923 | Knowledge Article | Science & Tech. | 33.474732 |
Increase In Fresh Water Flowing Into Arctic Ocean Could Threaten Gulf Stream
The effect of the Gulf Steam slowing or stopping on weather across Europe is a familiar theme in talking about the future impact of climate change--the climate there would become decidedly colder if that happened. And it seems that current levels of warming are creating, in the words of New Scientist, "a new and fast-growing pool of fresh water in the Arctic Ocean."
The water is mostly coming from melting permafrost and rising rainfall, which is increasing flows in Siberian rivers that drain into the Arctic, such as the Ob and Yenisei. More comes from melting sea ice, says Laura de Steur of the Royal Netherlands Institute of Sea Research in 't Horntje, who is tracking the build-up.This is important, so read the whole account: New Scientist
More on Global Climate Change
Only 10% of Permafrost Melting Could Tip Planet Towards Catastrophic Warming
No Day After Tomorrow Yet: Gulf Stream Doesn't Appear To Be Slowing Down | <urn:uuid:471b2579-d90f-4616-8cc1-366da8dd3fc0> | 3.265625 | 215 | Truncated | Science & Tech. | 29.923533 |