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Pub. date: 2008 | Online Pub. Date: April 25, 2008 | DOI: 10.4135/9781412963893 | Print ISBN: 9781412958783 | Online ISBN: 9781412963893| Publisher:SAGE Publications, Inc.About this encyclopedia
Impacts of Global Warming
IMPACTS FROM THE phenomenon known as global warming include environmental, social, and economic effects. Environmental impacts include sea-level rise, melting of the polar ice caps, and an average increase in temperature. These impacts are documented in the reports of the Intergovernmental Panel for Climate Change (IPCC), which commissions reports by scientists worldwide on the issue of climate change. The IPCC Report of 2007 is the first one that reflects scientific consensus that global warming is underway, and that it is primarily human induced. For example, human activities, such as fossil fuel burning, land-use changes, agricultural activity, and the production and use of halocarbons are among the factors causing climate change. The economic report by Nicholas Stern in 2007 highlights that climate change has potentially disastrous consequences for humanity. Perhaps best known, is that temperature variability, specifically temperature increase, will be one of the effects of climate change. While the range ... | <urn:uuid:e9b9663e-a503-4a1d-b284-16f1447bf5b3> | 3.9375 | 252 | Content Listing | Science & Tech. | 30.482857 |
ok but then il try say for x=1 and y=2
i find f(x+y) not equal to f(x)+f(y) which makes 10 not equal 14. so this is not linear also? can someone give me an example of a linear function that works.
......... wait so the these properties cannot be satisfied if there is a constant, but i thought a linear function could be plotted y=mx+b im confused
But Linear Algebra uses a more stringent definition for "linear transformation"- we must have f(x+ y)= f(x)+ f(y) and f(ax)= af(x). As I said above, the only "linear" functions in that sense, from R to R are of the form f(x)= ax for some number a. | <urn:uuid:54ca889c-bbbd-4038-93d3-5cd0cb2dc9f0> | 2.984375 | 167 | Q&A Forum | Science & Tech. | 96.373957 |
I am going through Effective Java and some of my things which I consider as standard are not suggested by the book, for instance creation of object, I was under the impression that constructors are the best way of doing it and books says we should make use of static factory methods, I am not able to few some advantages and so disadvantages and so am asking this question, here are the benefits of using it.
- One advantage of static factory methods is that, unlike constructors, they have names.
- A second advantage of static factory methods is that, unlike constructors, they are not required to create a new object each time they’re invoked.
- A third advantage of static factory methods is that, unlike constructors, they can return an object of any subtype of their return type.
- A fourth advantage of static factory methods is that they reduce the verbosity of creating parameterized type instances.
- The main disadvantage of providing only static factory methods is that classes without public or protected constructors cannot be subclassed.
- A second disadvantage of static factory methods is that they are not readily distinguishable from other static methods.
Reference: Effective Java, Joshua Bloch, Edition 2, pg: 5-10
I am not able to understand the fourth advantage and the second disadvantage and would appreciate if someone can explain those points. I would also like to understand how to decide to use whether to go for Constructor or Static Factory Method for Object Creation. | <urn:uuid:ec7eb7c4-ee94-46d6-b3a6-a8c0f1b8f37d> | 2.953125 | 301 | Q&A Forum | Software Dev. | 27.404821 |
A "domain specific language" is one in which a class of problems (or solutions to problems) can be expressed succinctly, usually because the vocabulary aligns with the that of the problem domain, and the notation is similar (where possible) to that used by experts that work in the domain.
What this really means is a grammar representing what you can say, and a set of semantics that defines what those said things mean. This makes DSLs just like other conventional programming langauges (e.g., Java) in terms of how they are implemented. And in fact, you can think of such conventional languages as being "DSL"s that are good at describing procedural solutions to problems (but not necessary good at describing them). The implications are that you need the same set of machinery to process DSLs as you do to process conventional languages, and that's essentially compiler machinery.
Groovy has some of this machinery (by design) which is why it can "support" DSLs.
See Domain Specific Languages for a discussion about DSLs in general, and a particular kind of metaprogramming machinery that is very helpful for implementing them. | <urn:uuid:2d9b3ae0-6feb-41db-8372-2afec1a10b90> | 2.796875 | 235 | Q&A Forum | Software Dev. | 44.52 |
Today, a global warming progress report. The University of Houston's College of Engineering
presents this series about the machines that make our civilization
run, and the people whose ingenuity created them.
When I face questions about global warming, it's
usually a struggle to point out that the problem must be kept in the scientific
domain and out of politics. Any of us can fall into the trap of naming whatever political
figure we like least, and taking the position opposite to his or hers.
With that in mind, let's look a a helpful summary article in this week's Science
magazine. It's by a group of climate experts from NASA, the Scripps Institute, and
institutes in Germany, Australia, and France.
What they've done is straightforward. First, they graph the increase of CO2
concentration, temperature, and sea level, since 1975. Each increases a bit more strongly than
a simple linear rise. Maybe they're rising exponentially, maybe not.
The changes might not seem extreme. In thirty years, CO2
concentrations are up fifteen percent, Earth's temperature has risen just under a degree
Fahrenheit, and sea level has risen three inches.
The authors also display the most important predictions made back in 1990. It turns out that
CO2 concentration has risen pretty much exactly
as it was predicted. Global temperature has risen in accordance with the worst case predictions.
And sea level is up 25 percent beyond the worst case predicted. While some other doomsday
predictions were far too high, the climate ones were not.
So climatologists in 1990 were not Chicken Little, telling us the sky was falling.
None of them overestimated what was happening. In fact, it'd be easy to look at this and
let ourselves become Chicken Little. One could curve-fit an exponential extrapolation to the
data. But extrapolation is no more trustworthy than blindly opposing the
We need good analytical predictions. They, in turn, must be built upon a thorough knowledge
of weather, chemistry, fluid mechanics, and global economics. The 1990 predictions were pretty
good, although somewhat conservative. Predictions are better now.
To gain just an inkling of the complexity, let's look again at rising sea levels. The overall
rise reflects the ice-cap melting that we're all seeing (although part of the rise comes from
thermal expansion of warming oceans). But that net value is an average of larger local sea level
variations. The tectonic plates, upon which we live, rise and fall relative to one another.
Since Louisiana and Texas are dropping, we see the sea level rising sharply. But Alaska is
rising, so Alaskans see their sea level dropping. New Orleans might go under while Anchorage
remains dry, or rising sea levels might catch up with tectonic subsidence and flood both.
In any case, we are faced with climate change and it's hard to doubt that we play a significant
role in that change. Nor can one reasonably doubt the importance of reducing consumption, waste,
and emissions, while we look for better information -- while we focus, not on the people we like
or dislike, but on the data.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
S. Rhamstorf, A. Cazenave, J. A. Church, J. E. Hansen, R. F. Keeling, D. E. Parker,
R. C. J. Somerville, Recent Climate Observations Compared to Projections. Science,
Vol. 316, 4 May, 2007, pg. 709. To see the data,
For more on sea level variation, see:
And I find this a useful statement from J. E. Hansen at NASA:
Is this relevant? Only hard data can tell us. (photo by JHL)
The Engines of Our Ingenuity is
Copyright © 1988-2006 by John H. | <urn:uuid:20e81113-3097-40a1-b921-c35da330d771> | 3.125 | 840 | Nonfiction Writing | Science & Tech. | 57.711664 |
In quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
, the particle in a box
model (also known as the infinite potential well
or the infinite square well
) describes a particle free to move in a small space surrounded by impenetrable barriers. The model is mainly used as a hypothetical example to illustrate the differences between classical
What "classical physics" refers to depends on the context. When discussing special relativity, it refers to the Newtonian physics which preceded relativity, i.e. the branches of physics based on principles developed before the rise of relativity and quantum mechanics...
and quantum systems. In classical systems, for example a ball trapped inside a heavy box, the particle can move at any speed within the box and it is no more likely to be found at one position than another. However, when the well becomes very narrow (on the scale of a few nanometers), quantum effects become important. The particle may only occupy certain positive energy levels. Likewise, it can never have zero energy, meaning that the particle can never "sit still". Additionally, it is more likely to be found at certain positions than at others, depending on its energy level. The particle may never be detected at certain positions, known as spatial nodes.
The particle in a box model provides one of the very few problems in quantum mechanics which can be solved analytically, without approximations. This means that the observable properties of the particle (such as its energy and position) are related to the mass of the particle and the width of the well by simple mathematical expressions. Due to its simplicity, the model allows insight into quantum effects without the need for complicated mathematics. It is one of the first quantum mechanics problems taught in undergraduate physics courses, and it is commonly used as an approximation for more complicated quantum systems. See also: the history of quantum mechanics
The history of quantum mechanics, as it interlaces with the history of quantum chemistry, began essentially with a number of different scientific discoveries: the 1838 discovery of cathode rays by Michael Faraday; the 1859-1860 winter statement of the black body radiation problem by Gustav...
The simplest form of the particle in a box model considers a one-dimensional system. Here, the particle may only move backwards and forwards along a straight line with impenetrable barriers at either end.
The walls of a one-dimensional box may be visualised as regions of space with an infinitely large potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
. Conversely, the interior of the box has a constant, zero potential energy. This means that no forces act upon the particle inside the box and it can move freely in that region. However, infinitely large force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
s repel the particle if it touches the walls of the box, preventing it from escaping. The potential energy in this model is given as
is the length of the box and
is the position of the particle within the box.
In quantum mechanics, the wavefunction
Not to be confused with the related concept of the Wave equationA wave function or wavefunction is a probability amplitude in quantum mechanics describing the quantum state of a particle and how it behaves. Typically, its values are complex numbers and, for a single particle, it is a function of...
gives the most fundamental description of the behavior of a particle; the measurable properties of the particle (such as its position, momentum and energy) may all be derived from the wavefunction.
can be found by solving the Schrödinger equation
The Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....
for the system
is the reduced Planck constant,
is the mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the particle,
is the imaginary unit
In mathematics, the imaginary unit allows the real number system ℝ to be extended to the complex number system ℂ, which in turn provides at least one root for every polynomial . The imaginary unit is denoted by , , or the Greek...
Inside the box, no forces act upon the particle, which means that the part of the wavefunction inside the box oscillates through space and time with the same form as a free particle
In physics, a free particle is a particle that, in some sense, is not bound. In classical physics, this means the particle is present in a "field-free" space.-Classical Free Particle:The classical free particle is characterized simply by a fixed velocity...
are arbitrary complex number
A complex number is a number consisting of a real part and an imaginary part. Complex numbers extend the idea of the one-dimensional number line to the two-dimensional complex plane by using the number line for the real part and adding a vertical axis to plot the imaginary part...
s. The frequency of the oscillations through space and time are given by the wavenumber
In the physical sciences, the wavenumber is a property of a wave, its spatial frequency, that is proportional to the reciprocal of the wavelength. It is also the magnitude of the wave vector...
and the angular frequency
In physics, angular frequency ω is a scalar measure of rotation rate. Angular frequency is the magnitude of the vector quantity angular velocity...
respectively. These are both related to the total energy of the particle by the expression
which is known as the dispersion relation
In physics and electrical engineering, dispersion most often refers to frequency-dependent effects in wave propagation. Note, however, that there are several other uses of the word "dispersion" in the physical sciences....
for a free particle.
The size (or amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
) of the wavefunction at a given position is related to the probability of finding a particle there by
. The wavefunction must therefore vanish everywhere beyond the edges of the box. Also, the amplitude of the wavefunction may not "jump" abruptly from one point to the next. These two conditions are only satisfied by wavefunctions with the form
is a positive, whole number. The wavenumber is restricted to certain, specific values given by
is the size of the box. Negative values of
are neglected, since they give wavefunctions identical to the positive
solutions except for a physically unimportant sign change.
Finally, the unknown constant
may be found by normalizing the wavefunction so that the total probability density of finding the particle in the system is 1. It follows that
may be any complex number with absolute value
In mathematics, the absolute value |a| of a real number a is the numerical value of a without regard to its sign. So, for example, the absolute value of 3 is 3, and the absolute value of -3 is also 3...
√(2/L); these different values of A
yield the same physical state, so A
= √(2/L) can be selected to simplify.
The energies which correspond with each of the permitted wavenumbers may be written as
The energy levels increase with
, meaning that high energy levels are separated from each other by a greater amount than low energy levels are. The lowest possible energy for the particle (its zero-point energy
Zero-point energy is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state. All quantum mechanical systems undergo fluctuations even in their ground state and have an associated zero-point energy, a consequence of their wave-like nature...
) is found in state 1, which is given by
The particle, therefore, always has a positive energy. This contrasts with classical systems, where the particle can have zero energy by resting motionless at the bottom of the box. This can be explained in terms of the uncertainty principle
In quantum mechanics, the Heisenberg uncertainty principle states a fundamental limit on the accuracy with which certain pairs of physical properties of a particle, such as position and momentum, can be simultaneously known...
, which states that the product of the uncertainties in the position and momentum of a particle is limited by
It can be shown that the uncertainty in the position of the particle is proportional to the width of the box. Thus, the uncertainty in momentum is roughly inversely proportional to the width of the box. The kinetic energy of a particle is given by
, and hence the minimum kinetic energy of the particle in a box is inversely proportional to the mass and the square of the well width, in qualitative agreement with the calculation above.
In classical physics, the particle can be detected anywhere in the box with equal probability. In quantum mechanics, however, the probability density for finding a particle at a given position is derived from the wavefunction as
For the particle in a box, the probability density for finding the particle at a given position depends upon its state, and is given by
Thus, for any value of n
greater than one, there are regions within the box for which
, indicating that spatial nodes
exist at which the particle cannot be found.
In quantum mechanics, the average, or expectation value of the position of a particle is given by
For the steady state particle in a box, it can be shown that the average position is always
, regardless of the state of the particle. For a superposition of states, the expectation value of the position will change based on the cross term which is proportional to
If a particle is trapped in a two-dimensional box, it may freely move in the
-directions, between barriers separated by lengths
respectively. Using a similar approach to that of the one-dimensional box, it can be shown that the wavefunctions and energies are given respectively by
where the two-dimensional wavevector is given by
For a three dimensional box, the solutions are
where the three-dimensional wavevector is given by
An interesting feature of the above solutions is that when two or more of the lengths are the same (e.g.
), there are multiple wavefunctions corresponding to the same total energy. For example the wavefunction with
has the same energy as the wavefunction with
. This situation is called degeneracy
In physics, two or more different quantum states are said to be degenerate if they are all at the same energy level. Statistically this means that they are all equally probable of being filled, and in Quantum Mechanics it is represented mathematically by the Hamiltonian for the system having more...
and for the case where exactly two degenerate wavefunctions have the same energy that energy level is said to be doubly degenerate
. Degeneracy results from symmetry in the system. For the above case two of the lengths are equal so the system is symmetric with respect to a 90° rotation.
Because of its mathematical simplicity, the particle in a box model is used to find approximate solutions for more complex physical systems in which a particle is trapped in a narrow region of low electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
between two high potential barriers. These quantum well
A quantum well is a potential well with only discrete energy values.One technology to create quantization is to confine particles, which were originally free to move in three dimensions, to two dimensions, forcing them to occupy a planar region...
systems are particularly important in optoelectronics
Optoelectronics is the study and application of electronic devices that source, detect and control light, usually considered a sub-field of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light...
, and are used in devices such as the quantum well laser
A quantum well laser is a laser diode in which the active region of the device is so narrow that quantum confinement occurs. The wavelength of the light emitted by a quantum well laser is determined by the width of the active region rather than just the bandgap of the material from which it is...
, the quantum well infrared photodetector
A quantum well infrared photodetector , is an infrared photodetector made from semiconductor materials which contain one or more quantum wells. These can be integrated together with electronics and optics to make infrared cameras for thermography. A very common well material is gallium arsenide,...
and the quantum-confined Stark effect
The quantum-confined Stark effect describes the effect of an external electric field upon the light absorption spectrum or emission spectrum of a quantum well . In the absence of an external electric field, electrons and holes within the quantum well may only occupy states within a discrete set...
The probability density does not go to zero at the nodes if relativistic effects are taken into account.
- Finite potential well
The finite potential well is a concept from quantum mechanics. It is an extension of the infinite potential well, in which a particle is confined to a box, but one which has finite potential walls. Unlike the infinite potential well, there is a probability associated with the particle being found...
- Delta function potential
- Gas in a box
In quantum mechanics, the results of the quantum particle in a box can be used to look at the equilibrium situation for a quantum ideal gas in a box which is a box containing a large number of molecules which do not interact with each other except for instantaneous thermalizing collisions...
- Particle in a ring
In quantum mechanics, the case of a particle in a one-dimensional ring is similar to the particle in a box. The Schrödinger equation for a free particle which is restricted to a ring is...
- Particle in a spherically symmetric potential
- Quantum harmonic oscillator
The quantum harmonic oscillator is the quantum-mechanical analog of the classical harmonic oscillator. Because an arbitrary potential can be approximated as a harmonic potential at the vicinity of a stable equilibrium point, it is one of the most important model systems in quantum mechanics...
- Delta potential well (QM)
The delta potential is a potential that gives rise to many interesting results in quantum mechanics. It consists of a time-independent Schrödinger equation for a particle in a potential well defined by a Dirac delta function in one dimension....
- Semicircle potential well
- Configuration integral (statistical mechanics) | <urn:uuid:516275b6-3f1a-40a3-a982-aa6176296f9e> | 3.390625 | 3,228 | Knowledge Article | Science & Tech. | 37.941987 |
ABOUT SNOWFLAKES: Snow is a form of precipitation. Rising warm air carries water vapor high into the sky, where it cools and condenses into water droplets. Some vapor freezes into tiny ice crystals, which can attract cooled water drops to form snowflakes. As snowflakes fall, they may meet warmer air and melt into raindrops, unless temperatures are below freezing close to the ground: then we get snow. A snow crystal is a single crystal of ice. It usually forms the shape of a hexagonal prism, but as the crystals grow, branches sprout from the corners, creating more complex shapes. Conditions such as temperature and humidity in the atmosphere can influence a snowflake's shape.
WHAT'S THE FORECAST: Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Humankind has attempted to predict the weather since ancient times. For millennia people have tried to forecast the weather. In 650 BC, the Babylonians predicted the weather from cloud patterns. In about 340 BC, Aristotle described weather patterns in Meteorologica. Chinese weather prediction lore extends at least as far back as 300 BC. Ancient weather forecasting methods usually relied observed patterns of events. For example, it might be observed that if the sunset was particularly red, the following day often brought fair weather. This experience accumulated over the generations to produce weather lore. Today, weather forecasts are made by collecting data about the current state of the atmosphere and using computer models of the atmospheric processes to project how the atmosphere will evolve.
The American Meteorological Society, the American Mathematical Society, the Mathematical Association of America, the American Statistical Association and the Society for Industrial and Applied Mathematics contributed to the information contained in the TV portion of this report. | <urn:uuid:a0e37488-f43a-4545-b743-364b9bb57970> | 3.890625 | 366 | Knowledge Article | Science & Tech. | 31.530721 |
Threats to Frogs
One of the most pressing threats to frogs today is the chytrid fungus, a deadly skin fungus that has moved across the globe causing amphibian declines in Australia, South America, North America, Central America, New Zealand, Europe, and Africa killing frogs by the millions. The chytrid fungus is responsible for over 100 frog and other amphibian species extinctions since the 1970’s. Chytrid fungus has been detected on at least 285 species of amphibians (including frogs) from 36 countries.
Climate change is also having an impact on frogs that live on mountain tops. They are being hit hard since they are dependant on moist leaf litter found in cloud forests as a suitable place to lay their eggs. As temperatures increase further up mountain sides, clouds are being pushed further away and leaves are drying out leaving less suitable habitat for frogs to lay their eggs. As frogs migrate further up the mountain they are faced with the inevitable problem that once they reach the top, unlike birds, they can go no further.
Frogs are also facing many threats from many different environmental factors: pollution, infectious diseases, habitat loss, invasive species, climate change, and over-harvesting for the pet and food trades are all contributing to the rapid rise of frog extinctions since 1980.
Reasons for Hope
Chytrid fungus has been recognized as one of the largest threats to amphibian populations around the world. In 2009 a group of organizations came together to respond to the crisis. Defenders of Wildlife (Washington DC), Africam Safari Park (Mexico), Cheyenne Mountain Zoo (Colorado), the Smithsonian National Zoological Park (Washington DC), the Smithsonian Tropical Research Institute (Panama), Zoo New England (Massachusetts) and Houston Zoo (Texas) have launched the Panama Amphibian Rescue and Conservation Project.
There are yet undiscovered species of frogs in the world. A new species of flying frog was discovered in the Himalayan Mountains in 2008. | <urn:uuid:41cc0e52-1089-47c4-b367-00aac24e3935> | 4 | 408 | Knowledge Article | Science & Tech. | 35.836035 |
Creature Spotlight of the Week- OrcaBY EARTHFIRST
The killer whale which is commonly referred to as the orca is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the freezing Arctic and Antarctic regions to tropical seas. Killer whales as a species have a diverse diet they feed on fish and also marine mammals such as sea lions, seals, walruses and even large whales.
Killer whales are highly social sea mammals that have powerful hunting skills, which enable them to kill sea creatures that are much larger than they are. This is partly where their name originated.
Many people believe that orcas should not be held in captivity. In aquariums, orcas tend to live for about 13 years, compared to those in the wild who live 40 to 60 years.
The IUCN has assessed the Orca's conservation status and they are not currently listed as a threatened species, however their numbers have declined over the years due to a variety of reasons including declining food stocks, habitat loss, pollution (by PCBs), capture for marine mammal parks, and conflicts with fisheries.
For more info visit the WWF | <urn:uuid:2c91a7e2-624f-4f8f-a586-14d6382e9f2f> | 3.546875 | 241 | Knowledge Article | Science & Tech. | 42.82976 |
C14 - The Double Cluster
Algol - Eclipsing Binary Star
Perseus lies along the plane of the Milky Way, but as we view it, we are looking away from the galactic centre, so that there are fewer clusters within its boundaries than when looking towards Sagattarius or Scorpius. However, the two clusters that form the Perseus Double Cluster provide one of the best binocular sights in the heavens and Perseus also harbours a very interesting star system, Algol. Whilst, for northern observers, Perseus comes high overhead in the latter months of the year, for southern observers it only just rises above the northern horizon so that, whilst they should be able to observe Algol, sadly, the Double Cluster will lie below their horizon.
C14 - Twin Open Clusters B M
Visible to the unaided eye as a hazy patch in the Milky Way, binoculars or a small telescope at low power can show both these two beautiful clusters in the same field of view. They are most easily found by sweeping with your eyes, binocular or finder scope to the east and a little south of Cassiopeia, following the line set by its bright stars Gamma and Delta. The bright cores of the two clusters are separated by just less than one Moon diameter, 25 arc minutes, and together they cover over a degree of sky. Given their separation and individual visual brightness of between 4th and 5th magnitude, one should be able to see them as separate entities. But this is not usually the case. Surprisingly perhaps, the best chance to do so is by observing them just as twilight ends; when they first appear to the eye but the background stars of the Milky Way are still invisible. (In a similar fashion, the brighter stars of constellation - those that form the patterns that we learn - show up far more clearly under twilight or light-polluted conditions than when seen in really dark conditions. This is why you are advised to learn the shapes and locations of the constellations when the sky conditions are not too good!) The two clusters, also known as h and Chi Persei, are a beautiful sight in 10x50 binoculars; each cluster having a bright centre and many individually resolved stars. With a low-power eyepiece both can be seen in the same field and then, moving up to medium power, each can be observed in detail. They lie in the Perseus spiral arm of the Milky Way some 7300 light years away, and were both formed about 3 million years ago.
Position: 2h 20.5m +57deg 08min
Algol - Eclipsing Binary Star E B
Algol is one of the most remarkable and most famous individual stars in the sky. Its Arabic name is Al Ghul, which means the 'demon' star (Ghul is related to 'ghoul', a ghost). Why a demon? Because it winks! Every 2.87 days its brightness quickly drops from magnitude 2.1 to 3.4 and then rises again to 2.1 over a period of 10 hours. John Goodricke of York was one of the first astronomers who discovered its regular brightness variations in 1782–3. Much later, in 1881, astronomers realised that the effect could be caused by a binary system in which the orbital plane of the two stars was almost in line with the Earth, so that every 2.87 days there is a partial eclipse! This is when the fainter star of the two comes in front of the brighter. In between each major drop in brightness, there is a much smaller drop as the brighter star comes in front of the fainter. The primary star is a blue B-type star with a surface temperature of 12,000K. The secondary is a much larger but dimmer K-type orange giant star. Interestingly, the two stars do not seem to be following the normal rules of stellar evolution. More massive stars evolve faster than less massive ones, so the orange giant - which has evolved away from the main sequence - should be more massive than the blue primary star. But it has less mass! It appears that material may be flowing from the giant star (so reducing its mass) onto the normal star whose mass is thus increasing.
Position: 3h 8.2m +40deg 57min | <urn:uuid:d4face32-c368-4fdf-a8be-4dc11dd9121c> | 3 | 890 | Knowledge Article | Science & Tech. | 60.366302 |
Lesser Long-nosed Bats:
Nectar-powered Bat Math!
Counting the Calories in Cactus
Contributed by Ginny Dalton, Bat Biologist
Merlin D. Tuttle,BCI
ever wonder: How much energy does it take to operate a bat? How many
flowers must a bat visit to stay alive?
Get ready to count the calories in a cactus flower! After reading this page,
you'll know everything necessary to answer these questions:
- How many
saguaro flowers does a bat have to visit to sustain it for one day?
- For how
many minutes does a bat have to forage to get the nectar it needs
- How many
saguaro plants do you think would be needed to feed a maternity colony
of 10,000 Leptos?
is the minimum number of hectares of land required to feed a bat
colony containing 10,000
Much Energy to Operate a Bat?
Let's look at how much energy is required by an adult Lepto. Here's an animal
with a big energy demand for its size! (Now, nobody has ever measured this
exactly for Leptos, but we can use information about other bats and extend
the results logically.) It takes roughly 20.2 kcal to maintain one of these
bats for a day. A Lepto uses about 100 times less energy in a day than a human
does, as you can see on the chart below. But it weighs 2,000 times less. Obviously
it takes more energy to operate an ounce of bat that an ounce of human! Why?
Well, for one thing, bats fly--and the energetic cost of flight is high.
*NOTE ABOUT CALORIES: There is confusion in the layman's literature
regarding calories. The calorie in everyday use is actually a kilocalorie (kcal,
also designated Calorie, with a capital "C"), 1000
times larger than a calorie with a lower case "c"). In
fact, the makers of labels on food boxes and cans in the grocery
store are careless in their representation of this energy unit. The
labels correctly use the upper case when stating total Calories of
the food within, but then many of them say "based on a 2,000
calorie diet." Note the lower case "c." If literally
interpreted, it is based on a 2 Cal (or kcal) diet, which doesn't
make any sense. You and I can't live on 2 Calories a day!! They actually
meant to write "Calorie;" instead they wrote "calorie."
Calories in Cactus Flowers
How much energy is available in the nectar of the flowers Leptos visit?
(Lepto is short for Leptonycteris curasoae, or lesser long-nosed bats.)
It has been calculated that the nectar in saguaro flowers is about 24% sugar.
This nectar if very sweet: For comparison, Classic Coke is 10% sugar! Each
flower holds about 1.0 ml (milliliter) nectar. A single bat only takes about
0.1 ml with each visit to a flower. A bat's stomach can hold about 4 ml of
fluid when full. Of those stomachs measured, 3 ml are sugar water and the remaining
1 ml was pollen.
There are about 4 calories (= 0.004 kcal) in a mg (milligram) of sugar. There
is 1.0 mg sugar in each microliter (.001 ml) of nectar. So how many calories
in 1.0 ml, the amount a flower holds? If a bat drains an entire flower, how
many visits would the bat have to make to the flower? And how many total calories
would it get from that single flower? (Don't forget to multiply your answer
in cal/ml by 0.24 since the nectar contains only 24% sugar.) I got 960 cal
(0.960 kcal) in a single flower that contains 1.0 ml nectar. So, since a bat
takes about 0.1 ml for each visit, a bat would have to visit about 10 flowers
to get those 960 cal.
Q. How many flowers total
does a bat have to visit to sustain it for one day (20,200 cal = 20.2
8 flowers per saguaro per night, how many saguaro plants would have
to be visited? _______
it takes about 30 seconds per visit to a flower (that includes transit
time to the flower) for one sip (0.1 ml) of nectar. That makes us wonder:
Q. For how
many minutes does a bat have to be flying to get the nectar
it needs each day (24 hours)? _____________
More Bat Math: Mama and Baby Bats
Each female gives birth to a single young each year.
Just think how much energy will be needed by the pregnant bats
after they give birth and start nursing! Not enough information
is available for calculating the exact requirements for pregnant
females, but a near-term fetus of a 22- gram female bat can weigh
as much as 8 grams. A pregnant bat carrying that heavy a load can
require about 40% more power for flight. Of all the calculations
conducted on females during the various reproductive stages, lactation
(when the young are nursing) is the most energetically demanding
on the female.
that, for the two months a female is pregnant, she requires an average
of 27 flowers per night, since pregnant females require more energy.
During pregnancy, how many flowers will one female require? ______
How many flowers will be required by 10,000 females? _______From studies
conducted around Tucson, Arizona, the average saguaro produces 295
flowers per plant per growing season. (A single plant blooms from 27
to 61 days and each plant can produce from 82 to 980 blossoms!)
Q. How many saguaro
plants do you think would be needed to feed a maternity colony
of 10,000 Leptos? _________
are 6 saguaro plants per hectare on average. Using the figure of 295
flowers per plant per nearly 2-month season, what is the minimum number
of hectares of land required to feed a bat colony containing 10,000
pregnant bats? _______________ | <urn:uuid:21b711b3-73d7-4ee0-8113-2f9006242494> | 3.109375 | 1,359 | Tutorial | Science & Tech. | 69.242251 |
For a transaction to take place between a client and a server, a conversation must be established. A conversation is established when a client makes a request by broadcasting a service name and topic name, and a server responds. Transactions can then take place across the conversation. When no more transactions are to be made, the conversation is terminated.
The following list identifies the elements involved with client/server activity:
A conversation is established when a server responds to a client.
A service name is a string broadcast by a client hoping to establish a conversation with a server that recognizes the service name. The service name is usually clearly related to the server application name.
The topic name identifies what the conversation between client and server is to be about. For example, it could be the name of a file that is open in the server application. Each topic is attached to one particular server. A server can have many topics.
The item usually identifies an element of the file identified by the topic which should be read (in the case of a request) or written to (in the case of a poke). For example, it might refer to a cell in a spreadsheet document.
LispWorks User Guide and Reference Manual - 21 Dec 2011 | <urn:uuid:ab27fc5f-2d86-45bb-8493-e416cd46d33e> | 3.46875 | 247 | Documentation | Software Dev. | 42.490322 |
Moon Crater Shapes
Date: 1999 - 2000
The craters on the moon are obviously round but
impacts with a grazing incidence should leave a V shaped crater. I would think that some percentage of the impacts would be at shallow angles of attack but this does not appear to be the case in photos.
Have they discovered such craters and if not why??
It doesn't work that way. A crater is like a frozen ripple, and
ripples are round. There is an asymmetric distribution of matter in
the ripple, and the blanket of stuff ejected from the surface, that do
record the angle of incidence. These are superimposed on the ripple,
but it's the ripple that is most noticeable because of its sharp
Actually, impacts at a grazing angle will also make a round hole. This was
a controversial point regarding Meteor Crater in Arizona, which was
basically the first site recognized on Earth as a meteor impact site. The
fact that no meteorite fragments were found in the earth below the center
of the crater was initially taken as evidence against the hypothesis that
the structure was an impact crater, but further research showed that if the
impact is very energetic, such as a rifle bullet fired into mud, the
resulting hole is round, even if the impact angle is quite flat.
Richard Barrans Jr., Ph.D.
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:b485f2c8-49c9-4268-91c3-d88b5c45c43b> | 4.15625 | 299 | Comment Section | Science & Tech. | 53.441538 |
The Law of Momentum Conservation
Improve your problem-solving skills with problems, answers and solutions from The Calculator Pad.Flickr Physics
Visit The Physics Classroom's Flickr Galleries and take a visual tour of the topic of momentum and collisions.
Enjoy a rich source of instructional, demonstration and lab ideas on the topic of momentum and impulse.The Laboratory
Looking for a lab that coordinates with this page? Try the Action-Reaction Lab from The Laboratory.The Laboratory
Looking for a lab that coordinates with this page? Try the What's Cooking Lab from The Laboratory.Treasures from TPF
Need ideas? Need help? Explore The Physics Front's treasure box of catalogued resources on momentum.
Momentum Conservation in Explosions
As discussed in a previous part of Lesson 2, total system momentum is conserved for collisions between objects in an isolated system. For collisions occurring in isolated systems, there are no exceptions to this law. This same principle of momentum conservation can be applied to explosions. In an explosion, an internal impulse acts in order to propel the parts of a system (often a single object) into a variety of directions. After the explosion, the individual parts of the system (that is often a collection of fragments from the original object) have momentum. If the vector sum of all individual parts of the system could be added together to determine the total momentum after the explosion, then it should be the same as the total momentum before the explosion. Just like in collisions, total system momentum is conserved.
Momentum conservation is often demonstrated in a Physics class with a homemade cannon demonstration. A homemade cannon is placed upon a cart and loaded with a tennis ball. The cannon is equipped with a reaction chamber into which a small amount of fuel is inserted. The fuel is ignited, setting off an explosion that propels the tennis ball through the muzzle of the cannon. The impulse of the explosion changes the momentum of the tennis ball as it exits the muzzle at high speed. The cannon experienced the same impulse, changing its momentum from zero to a final value as it recoils backwards. Due to the relatively larger mass of the cannon, its backwards recoil speed is considerably less than the forward speed of the tennis ball.
In the exploding cannon demonstration, total system momentum is conserved. The system consists of two objects - a cannon and a tennis ball. Before the explosion, the total momentum of the system is zero since the cannon and the tennis ball located inside of it are both at rest. After the explosion, the total momentum of the system must still be zero. If the ball acquires 50 units of forward momentum, then the cannon acquires 50 units of backwards momentum. The vector sum of the individual momenta of the two objects is 0. Total system momentum is conserved.
As another demonstration of momentum conservation, consider two low-friction carts at rest on a track. The system consists of the two individual carts initially at rest. The total momentum of the system is zero before the explosion. One of the carts is equipped with a spring-loaded plunger that can be released by tapping on a small pin. The spring is compressed and the carts are placed next to each other. The pin is tapped, the plunger is released, and an explosion-like impulse sets both carts in motion along the track in opposite directions. One cart acquires a rightward momentum while the other cart acquires a leftward momentum. If 20 units of forward momentum are acquired by the rightward-moving cart, then 20 units of backwards momentum is acquired by the leftward-moving cart. The vector sum of the momentum of the individual carts is 0 units. Total system momentum is conserved.
Just like in collisions, the two objects involved encounter the same force for the same amount of time directed in opposite directions. This results in impulses that are equal in magnitude and opposite in direction. And since an impulse causes and is equal to a change in momentum, both carts encounter momentum changes that are equal in magnitude and opposite in direction. If the exploding system includes two objects or two parts, this principle can be stated in the form of an equation as:
If the masses of the two objects are equal, then their post-explosion velocity will be equal in magnitude (assuming the system is initially at rest). If the masses of the two objects are unequal, then they will be set in motion by the explosion with different speeds. Yet even if the masses of the two objects are different, the momentum change of the two objects (mass velocity change) will be equal in magnitude.
The diagram below depicts a variety of situations involving explosion-like impulses acting between two carts on a low-friction track. The mass of the carts is different in each situation. In each situation, total system momentum is conserved as the momentum change of one cart is equal and opposite the momentum change of the other cart.
In each of the above situations, the impulse on the carts is the same - a value of 20 kgcm/s (or cNs). Since the same spring is used, the same impulse is delivered. Thus, each cart encounters the same momentum change in every situation - a value of 20 kgcm/s. For the same momentum change, an object with twice the mass will encounter one-half the velocity change. And an object with four times the mass will encounter one-fourth the velocity change.
Since total system momentum is conserved in an explosion occurring in an isolated system, momentum principles can be used to make predictions about the resulting velocity of an object. Problem solving for explosion situations is a common part of most high school physics experiences. Consider for instance the following problem:
A 56.2-gram tennis ball is loaded into a 1.27-kg homemade cannon. The cannon is at rest when it is ignited. Immediately after the impulse of the explosion, a photogate timer measures the cannon to recoil backwards a distance of 6.1 cm in 0.0218 seconds. Determine the post-explosion speed of the cannon and of the tennis ball.
Like any problem in physics, this one is best approached by listing the known information.
m = 1.27 kg
d = 6.1 cm
t = 0.0218 s
m = 56.2 g = 0.0562 kg
The strategy for solving for the speed of the cannon is to recognize that the cannon travels 6.1 cm at a constant speed in the 0.0218 seconds. The speed can be assumed constant since the problem states that it was measured after the impulse of the explosion when the acceleration had ceased. Since the cannon was moving at constant speed during this time, the distance/time ratio will provide a post-explosion speed value.
The strategy for solving for the post-explosion speed of the tennis ball involves using momentum conservation principles. If momentum is to be conserved, then the after-explosion momentum of the system must be zero (since the pre-explosion momentum was zero). For this to be true, then the post-explosion momentum of the tennis ball must be equal in magnitude (and opposite in direction) of that of the cannon. That is,
The negative sign in the above equation serves the purpose of making the momenta of the two objects opposite in direction. Now values of mass and velocity can be substituted into the above equation to determine the post-explosion velocity of the tennis ball. (Note that a negative velocity has been inserted for the cannon's velocity.)
vball = - (1.27 kg) (-280 cm/s) / (0.0562 kg)
vball = 6323.26 cm/s
vball = 63.2 m/s
Using momentum explosion, the ball is propelled forward with a speed of 63.2 m/s - that's 141 miles/hour!
It's worth noting that another method of solving for the ball's velocity would be to use a momentum table similar to the one used previously in Lesson 2 for collision problems. In the table, the pre- and post-explosion momentum of the cannon and the tennis ball. This is illustrated below.
= -355 kgcm/s
The variable v is used for the post-explosion velocity of the tennis ball. Using the table, one would state that the sum of the cannon and the tennis ball's momentum after the explosion must sum to the total system momentum of 0 as listed in the last row of the table. Thus,
Solving for v yields 6323 cm/s or 63.2 m/s - consistent with the previous solution method.
Using the table means that you can use the same problem solving strategy for both collisions and explosions. After all, it is the same momentum conservation principle that governs both situations. Whether it is a collision or an explosion, if it occurs in an isolated system, then each object involved encounters the same impulse to cause the same momentum change. The impulse and momentum change on each object are equal in magnitude and opposite in direction. Thus, the total system momentum is conserved.
1. Two pop cans are at rest on a stand. A firecracker is placed between the cans and lit. The firecracker explodes and exerts equal and opposite forces on the two cans. Assuming the system of two cans to be isolated, the post-explosion momentum of the system ____.
a. is dependent upon the mass and velocities of the two cans
b. is dependent upon the velocities of the two cans (but not their mass)
c. is typically a very large value
d. can be a positive, negative or zero value
e. is definitely zero
2. Students of varying mass are placed on large carts and deliver impulses to each other's carts, thus changing their momenta. In some cases, the carts are loaded with equal mass; in other cases they are unequal. In some cases, the students push off each other; in other cases, only one team does the pushing. For each situation, list the letter of the team that ends up with the greatest momentum. If they have the same momentum, then do not list a letter for that situation. Enter the four letters (or three or two or ...) in alphabetical order.
3. Two ice dancers are at rest on the ice, facing each other with their hands together. They push off on each other in order to set each other in motion. The subsequent momentum change (magnitude only) of the two skaters will be ____.
a. greatest for the skater who is pushed upon with the greatest force
b. greatest for the skater who pushes with the greatest force
c. the same for each skater
d. greatest for the skater with the most mass
e. greatest for the skater with the least mass
4. A 62.1-kg male ice skater is facing a 42.8-kg female ice skater. They are at rest on the ice. They push off each other and move in opposite directions. The female skater moves backwards with a speed of 3.11 m/s. Determine the post-impulse speed of the male skater.
5. A 1.5-kg cannon is mounted on top of a 2.0-kg cart and loaded with a 52.7-gram ball. The cannon, cart, and ball are moving forward with a speed of 1.27 m/s. The cannon is ignited and launches a 52.7-gram ball forward with a speed of 75 m/s. Determine the post-explosion velocity of the cannon and cart. | <urn:uuid:9b183fd2-00c9-493b-8c99-e1c8a1a5edc9> | 3.9375 | 2,390 | Tutorial | Science & Tech. | 60.538752 |
|Jul29-06, 08:44 AM||#1|
Question on light intensity at the focus of a lens.
From using a magnifying lens under the Sun, I gather it can focus all or most of the light impinging on its surface area to a small spot and that is how it is able to create a greater intensity light at its focus (disregarding absorption in the lens.) Correct? What portion of the total light falling on the lens would be delivered to the focal spot ignoring absorption?
This would be true no matter how far away the focal point. So the normal dimunition of intensity by the square of distance would not apply. So for example if you had a lens of focal distance 1 AU and put this lens right next to the Sun and directed the lens to shine toward the Earth, the full intensity of the Sun at its surface could be delivered to the Earth. True?
In a more realistic scenario if you put the lens some ten to hundreds of thousands of kilometers away from the Sun's surface so it could survive the heating then the intensity delivered to the Earth would still be many times the Sun's normal intensity at the Earth. So for example taking 1 AU as about 150,000,000 km, if we made the focus of the lens be 1 AU and put it 150,000 km from the Sun. Then the intensity of the light at the surface of the lens would be 1000^2 = 1,000,000 (one million) times greater than that normally at the Earth.
The lens would deliver all or a large portion of the light falling on it to the focal spot on the Earth. If the area of this spot was 1/1000th that of the area of the lens, then the intensity at the focal spot would then be 1,000,000,000 (one billion) times the intensity normally at the Earth.
The intensification of the light at the focus is familiar with a convergent lens, such as with a magnifying lens. But if you had a diverging lens so the focal spot was larger than the lens then the intensity would be less than at the surface of the lens. But the total amount of light delivered to the focal spot would still be all or a large portion of that falling on the surface of the lens. And this would still be true no matter how far is the focal length. Correct?
|Jul29-06, 10:21 AM||#2|
|Jul30-06, 07:44 PM||#3|
You can do a sort of sanity check type of experiment by testing this with an ordinary light bulb as a light source. There is no question that, by moving the lens closer to the source, you can capture more light, BUT you can't focus it as tightly with a longer focal length lens. These are the types of interplays you can test.
Finally I will remark that acheiving intesities 1 billion times greater than normal sunlight at the Earths surface is actually not that significant when you consider that high powered lasers can acheive peak intensities at and above this level.
Nonetheless an interesting thought experiment.
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Scientists study the illusive snow leopard in Northern Afghanistan (The New York Times)
- Snow leopards have the advantage of living in “one of the most remote and isolated mountain landscapes in the world,” away from the human threats other large cats face.
- Increasingly, snow leopards have been eating livestock, and these encounters with humans might threaten this already endangered species as tensions arise.
- Scientists estimate there are between 4,500 and 7,500 snow leopards in the wild, but Dr. Schaller said, “those figures are just wild guesses.”
Q&A with Will Potter about his new book: Green Is the New Red: An Insider’s Account of a Social Movement under Siege (Grist)
- Will Potter discusses how corporations and lobbyists are attacking the environmental movement with accusations of terrorism, much like red scare.
- “As the scale of the ecological crisis we are facing becomes more apparent, and as the backlash against social movements that are challenging our self-destructive culture intensifies, it is difficult to not feel dark, to feel helpless.”
Puma commits to eliminating all hazardous waste releases into Chinese waterways as part of Greenpeace’s detox challenge (Greenpeace)
- Puma, the third largest sportswear producer in the world, just committed to stop releasing toxic chemical in Chinese rivers by 2020, “beating” both Nike and Adidas in the detox challenge.
The National Petroleum Reserve, bustling with biodiversity of arctic life, is soon to be tapped (Yale Environment 360)
- “This wetland is home to the most spectacular gathering of migratory birds from all over the world, numbering in the millions.”
- The 23 million acre reserve will have is its fate decided in a year, and scientists are hurrying to study “special spots,” which the US will protect within the reserve.
And lastly a video to inspire, relish and even lament conservation efforts (TreeHugger)
If the above embedded video does not display, here to view it. | <urn:uuid:5db0eaf8-dc27-4e80-b8f1-1935edb19e7d> | 3.125 | 437 | Content Listing | Science & Tech. | 27.048713 |
Composition of Solutions
Problems and Solutions
Calculate the volume of a 0.753 M sodium hydroxide solution that is neutralized by the addition of 100 mL of a 1.203 M sulfuric acid solution.
If the volume of a 100 L solution of 1.1 moles of hydrogen in 6.0 moles argon is suddenly doubled, what happens to the mole fraction of hydrogen in that solution?
What is the concentration of HCl stock solution that can create 250 mL of a 1.0 M solution that is prepared by the dilution of 50 mL of the HCl stock solution? | <urn:uuid:8bcee731-1a98-4d6f-a6e6-b9a1474d0e87> | 2.703125 | 127 | Tutorial | Science & Tech. | 76.5535 |
Jeanna Bryner LiveScience Staff Writer LiveScience.comWed Mar 21, 4:30 PM ET
The fossil of an ancient amphibious reptile with a crocodile's body and a fish's tail has been unearthed in Oregon. Scientists believe the creature's remains were transported by geologic processes nearly 5,000 miles away from where it originally died more than 100 million years ago.
The new fossil is the oldest crocodilian ever unearthed in Oregon and one of the few to be unearthed on this side of the Pacific. The “hybrid” animal is thought to be a new species within the genus Thalattosuchia, a group of crocodilians living during the age of dinosaurs.
The reptile roamed a tropical environment in Asia about 142 to 208 million years ago. Called a Thalattosuchian, the amphibious creature [image] represents an early milestone in evolutionary history, marking a transition during which these reptiles moved from being semi-aquatic to wholly ocean species. | <urn:uuid:8ac6ce54-16e9-4a3b-a93c-d6805e297bb6> | 3.46875 | 206 | Comment Section | Science & Tech. | 34.538077 |
WebRef Update: Featured Article: X(ML) Marks the Spot
X(ML) Marks the Spot
Never before has an Internet development witnessed such rave reviews before thorough implementation and testing as the eXtensible Markup Language (XML). XML is definitely the latest buzzword in the developer community. However, you must crawl before you can walk. The idea of creating an XML based e-commerce solution is exciting, but what about a simple XML page which has standard Web media elements such as graphics or Flash files?
XML promises to give us intelligent document structures, object oriented document manipulations, synchronized media and a whole lot more. But what is XML exactly, and why has it created such a stir? This article is for those developers who are looking for a hands-on explanation of XML basics.
What is XML?
The eXtensible Markup Language and HTML are both subsets of Standard Generalized Markup Language (SGML). SGML is a very powerful technology that can be viewed as the parent of many markup languages, which include HTML and XML. With XML, it is possible to create new variations such as the Wireless Application Protocol Markup Language (WAPML or WML), which makes communicating and transactions between a mobile phone and a Web server possible.
Of all the aspects of XML, the following is probably the most important: XML only recently became an official W3C recommendation. This means that the consortium still hasn't made a decision about standard XML. Many XML elements used in Explorer 5.0 are based on the W3C draft and they will probably be included in the official XML specs. Netscape has probably made the wise decision to wait with releasing their XML compliant version 5 browser until the official specs have been determined.
Enough background information. Let's get into the real deal. The big difference between XML and HTML is the following: an HTML document has three different elements: The first element being the text (e.g. "Welcome to my homepage"). The second element is the document structure such as tables and linebreaks. The third element is the visual markup such as bold text, italic text, graphics and other visual elements.
An XML document, however, can actually consist of two or three different pages. Because seeing is believing, I've included a short example below.
1. The first page is the actual XML information you wish to display. In first generation XML sites, this information will probably be text contained in the page called "whatever.xml". This page doesn't have any structure such as a table or visual markup (bold, italic or color).
Whatever.xml looks like:<?XML version="1.0" ?> <?XML-stylesheet type="text/xsl" href="whatever.xsl"?> <people> <friend> <name>Lee</name> <address>25 Malvern street</address> <telephone>123 456 789</telephone> </friend> <friend> <name>Susanna</name> <address>11 Durban road</address> <telephone>987 654 231</telephone> </friend> </people>
2. The second page has the Extensible Stylesheet Language (whatever.xsl). This page has HTML and "tags" which takes the data out of whatever.xml and puts into "whatever.xsl". The xsl document has the mark-up such as <body>, <table> and <font>.
Whatever.xsl looks like:<?XML version="1.0"?> <xsl:stylesheet XMLns:xsl="http://www.w3.org/TR/WD-xsl"> <xsl:template match="/"> <HTML> <head><title>XML Developer</title></head> <body> <table border="1" cellpadding="3" cellspacing="3"> <xsl:for-each select="people/friend"> <tr> <td><b>Name:</b><br/></td> <td><xsl:value-of select="name"/></td> </tr> <tr> <td>Address:<br/></td> <td><i><xsl:value-of select="address"/></i></td> </tr> <tr> <td>Telephone:<br/></td> <td><i><xsl:value-of select="telephone"/></i><br/></td> </tr> </xsl:for-each> </table> </body> </HTML> </xsl:template> </xsl:stylesheet>
3. The third page is the Document Type Definition. The good news is that a DTD is not always necessary, especially in a simple XML document. The bad news is that a DTD is pretty darn difficult. It contains elements such as attributes and data types. For more information on DTDs, take a look at:
The XML version of linebreak is <br/> instead of the HTML <br>. Herein lies the secret in getting around the most common and frustrating markup language bugs [or features, depending on your point of view -eds.], which go by the name of validity or "well- formed code." In the good old Internet days, developers were very meticulous when it came to their coding. If you opened a <font> tag, you'd have to close it with </font>. When browsers got smarter, coders became lazier. As HTML evolved, people also decided that it wasn't necessary to include certain quotes in their code. So what was once <font color="white"> became <font color=white>. And then XML hit the scene.
Next: XML Needs Clean Code
Revised: May 16, 2000 | <urn:uuid:f2be1028-3e4e-4f08-8e06-dbf40b98a018> | 3.140625 | 1,209 | Truncated | Software Dev. | 67.677158 |
Forecast an El Nino or La Nina!
|You can see if an El Nino or a La Nina is coming!|
|Who hasn't heard of El Nino and la Nina? Almost no one! But who can tell if one of these events that change our weather and climate is coming. Scientists are working to forecast El Nino and La Nina events but as yet our best way to tell what is coming is to look at satellite ocean data and watch for these features as they travel across the ocean. And you can do that!|
First let's think about what an El Nino or La Nina is and how it affects
us. The simple explantion is that they are hot and cold ocean events
that start in the tropical Pacific Ocean. These 'hot and cold' events cover
large areas of the tropics, move from weat to east, and can spread north
and south along the coasts of the Pacific ocean. The events are so large
that they affect the local weather and change the jet stream which affects
global weather. For more information read further!
|Let's take a look at the ocean!!|
This picture was made from data taken from a satellite that measures the height of the ocean. By measuring the height of the ocean surface we can make a map that gives us information about the amount of heat in the ocean. The 'bottom line' is that hot water expands and is higher and cold water takes up less space so it is lower. Think about designing an experiment to prove this? (Hint!)
Check out this image taken from our TOPEX/Poseidon satellite
- Why are there stripes on this image? Hint!
- What color is shows a 'normal' sea surface height and temperature? Hint!
- Where in the ocean are the high areas indicating warm water?
- What areas of the world (countries) are near high (warm) or low (cool) water?
Now for another view .....
- Let's look at a recent image that uses 10 days of data which gives a more global coverage.(Why's that? Hint!) Check out where TOPEX/Poseidon is now!
- In this image green shows areas that are a normal height, blue and purple are lower (cooler) than average and yellow, red and white are areas that are higher (warmer) than average.
- How much is 14 cm?
- Where are the high areas indicating warm water?
- What areas of the world are near high (warm) or low (cool) water?
|Let's compare and forecast!|
||The image to the left is taken at the height of the '97-'98 El Nino. Note the area of higher and warmer than average water (white) in the east.||
||The image to the left is the '98-'99 La Nina. Note the area of lower and cooler water in the tropical Pacific, this later moved to the east|
|How does the ocean make a difference in the weather?|
The ocean affects the temperature and the amount of moisture in the
air. How could you do an experiment to test this? Hint!
With more moisture in the air, it is more likely to rain if the air is cooled. How could you do an experiment to test this? Hint!
With less moisture in the air, even as the air cools going over mountains there will be little rain.
Check out these graphics and write your own captions!
|So why do we need to know what's coming next?|
The El Nino and La Nina conditions are not necessarily bad, its just that we and the landscape adapt to average or 'normal' conditions, so when the weather is not normal, it often causes problems.
Map showing some of the impacts from the 1997-98 El Nino
Drought is when there is not enough rainfall to support activities that
usually occur on a piece of land. These activites include growth
of natural vegetation, use of the land for grazing or support of a city.
In the case of the latter, the affects of the drought can often be lessened,
but in natural areas the affects often result in dramatic natural population
-What is your average rainfall?
- What would happen to the area that you live in if you had half your annual rainfall?
- If you knew that you would be getting half the average rainfall what could people do so it would matter less?
-When are fires 'good' and when are they 'bad'
Satellite view of Hurricane Mitch
(Courtesy:Same old Someone Else)
|What would be affected in your life if you were without power for a
How would a farmer be affected?
How would a city be affected? | <urn:uuid:64c95389-69c4-4e78-a832-cba6209b2e46> | 3.734375 | 996 | Tutorial | Science & Tech. | 68.224935 |
Fixing Potholes with Non-Newtonian Fluid
potholes? Forget waiting around for 5 road workers to stand around and watch
while one guy fills the pothole with asphalt! Just grab a bit of non-Newtonian
fluid and, there – you fixed it:
The students, undergraduates at Case Western Reserve University
in Cleveland, devised the idea as part of an engineering contest sponsored
by the French materials company Saint-Gobain—and took first prize
last week. The objective was to use simple materials to create a novel
"So we were putzing around with different ideas and things
we wanted to work with—and we were like, what’s a common, everyday
problem all around the world that everybody hates?" explains 21-year-old
team member Curtis Obert. "And we landed on potholes." He
and four other students decided on a non-Newtonian fluid as a solution
because of its unusual physical properties. "When there’s no force
being applied to it, it flows like a liquid does and fills in the holes,"
says Obert, "but when it gets run over, it acts like a solid."
What? Don’t believe us? Check out this video clip of people
walking on water in a pool filled with non-Newtonian liquid. | <urn:uuid:5af6453b-641b-45b8-a8d0-06568ad68016> | 3.015625 | 289 | Truncated | Science & Tech. | 54.622506 |
Today’s the big day, when Asteroid 2005 YU55 will pass within about 200,000 miles (and come slightly closer to the moon tomorrow) of our fair planet.
This closeness of the approach can be seen in the short movie below (click it to activate).
The very dark asteroid is estimated to measure about 400 meters across. Here’s a photo of the rock as it sped through space in our direction yesterday. It’s a pretty good shot considering the rock was still more than 600,000 miles away at the time.
We’re all familiar with asteroids presenting end-of-the-world scenarios because of movies like Armageddon, in which a “Texas”-sized asteroid threatened Earth.
This, of course, is laughable because Texas is about 1,400 kilometers across and the largest known asteroid in the solar system, Ceres, measures just 900 km in diameter. For a deeper dissection of Armageddon’s scientific flaws, see here.
(Side note: The final scene of Armageddon offers an interesting take on the Russian approach to fixing mechanical problems with spaceflight equipment, especially in light of Sunday night’s launch of a Soyuz spacecraft. But I digress.)
Anyway, it wouldn’t take an asteroid the size of Texas to cause a global catastrophe. According to NASA an asteroid would need to have a diameter in excess of 2 km to pose planetary-wide environmental consequences.
And 2005 YU55 is much smaller than that. Which is not to say it would not have an impact.
So what would happen if YU55, traveling relative to Earth at a velocity of 30,000 mph, struck the planet? Bad things, but not catastrophic things unless you’re living underneath the impact.
Just for fun, let’s say it hit land about 100 miles west of Houston (it was nice knowing you, Schulenburg).
This particular asteroid would probably produce a crater about 4 miles across. If it hit 100 miles from Houston it would produce a wind moving through the city at about 35 mph, and make a noise something like very loud traffic. We would also experience seismic shaking equivalent to about a 6.8 magnitude earthquake. There would be some dust.
If you’re planning ahead, for those living in Katy, be sure to evacuate toward the east.
You can model your own asteroid impact effects at the delightful Impact: Earth! website. | <urn:uuid:b34240de-d4be-4df7-8f7e-a3dc08b94b51> | 3.4375 | 505 | Personal Blog | Science & Tech. | 58.808991 |
Sequencing the DNA in a scoop of dirt can tell scientists what creatures are living nearby, a new study using soil from safari parks shows, and the amount of DNA present can even tell how many individuals of each species there are, which could allow field biologists to get preliminary surveys of species. But though the team managed to identify nearly all the species they had expected in the parks, from wildebeest to elephants, they are still addressing how to take samples that accurately represent the area’s biodiversity—one would have to avoid elephant latrines or wildebeest sleeping areas, for instance—and there is the additional problem that rare or small creatures, like insects, might easily be missed. That said, it’s still an unusual and interesting way to take a look at an area’s inhabitants without actually tracking them down.
Read more at Scientific American.
Image courtesy of malcyzk / flickr
RNAs from rice can survive digestion and make their way into mammalian tissues, where they change the expression of genes.
What’s the News: It’s no secret that having lunch messes with your biochemistry. Once that sandwich hits your stomach, genes related to digestion have been activated and are causing the production of the many molecules that help break food down. But a new study suggests that the connection between your food’s biochemistry and your own may be more intimate than we thought. Tiny RNAs usually found in plants have been discovered circulating in blood, and animal studies indicate that they are directly manipulating the expression of genes.
Children of older mothers, scientists have long known, are at higher risk for certain genetic disorders such as Down syndrome. But the father’s age is matters, too. As a father’s age increases, research shows, so does his child’s risk of mental illness, schizophrenia and autism in particular. In Scientific American, Nicole Grey explores the link between a father’s age and his child’s health, as well as the tricky questions about what mechanisms are behind the that link: genes, epigenetic changes, environment, or some combination of the three.
What’s the News: Whether genes can be property is an ongoing controversy in the world of biotechnology, and last week saw the latest court battle in that war: Upon appeal, a suit brought by the ACLU charging that genes aren’t products of human ingenuity and thus cannot be patented was settled largely in favor of Myriad Genetics, the biotech company that has patents on two BRCA genes. The genes are linked to hereditary breast and ovarian cancer, and plaintiffs charged that Myriad’s exclusive test for the genes kept patients from getting second opinions.
A detailed description of the court’s reasoning can be found over at Ars Technica. But for those of you who are thinking, what? someone else can own my genes?, chew on this: About 20% of human genes are patented or have patents associated with them, according to a comprehensive analysis. Here’s why.
What’s the News: What if the egg is fine and the sperm is dandy, but you still can’t seem to have a baby? Couples who are having trouble conceiving can testify to the frustration of learning that there’s no clear reason for their infertility. Now, however, scientists have found a genetic mutation that makes outwardly normal sperm much less fertile, potentially explaining many such cases and suggesting new routes to conception.
What’s the News: By knocking out a single gene, scientists at the University of Pennsylvania have significantly increased the physical endurance of lab mice, as explained in their recent paper in the Journal of Clinical Investigation. The researchers also found that certain variants of the same gene may be linked to greater endurance in humans.
What’s the News: Scientists have been rooting around in the rice genome for years, and the same goes for wheat. But now the long-recalcitrant potato genome has finally been sequenced. Time for a celebration? Perhaps, but biologists can’t rest for long: in addition to the just-published genome, there are still three more to sequence in each commercial potato.
What’s the News: When personal genotyping service 23andMe was founded in 2006, most people were understandably focused on the benefits and the dangers of knowing your chances of getting an incurable disease. But a major part of the company’s business plan was eventually leveraging their users’ information to explore the genetic basis of disease.
With more than 100,000 people now in their database, 23andMe has been turning that into a reality. They’ve just published their first paper focusing on the origins of disease, pinpointing two new areas of the genome involved in Parkinson’s.
What’s the News: While you may be able to hide your age with makeup and plastic surgery, don’t think that your deception is foolproof. Researchers have now developed a technique to ascertain your age to within five years using only your saliva. The new method, published in the journal PLoS One, could someday be used by forensic experts to pinpoint the age of crime suspects. | <urn:uuid:046c4c60-e012-45e8-8c8d-b75aba3d33a3> | 3.046875 | 1,074 | Content Listing | Science & Tech. | 41.204243 |
The following methods can be defined to emulate numeric objects. Methods corresponding to operations that are not supported by the particular kind of number implemented (e.g., bitwise operations for non-integral numbers) should be left undefined.
%, divmod() pow()
|). For instance, to evaluate the expression x
+y, where x is an instance of a class that has an __add__() method,
x.__add__(y)is called. The __divmod__() method should be the equivalent to using __floordiv__() and __mod__(); it should not be related to __truediv__() (described below). Note that __pow__() should be defined to accept an optional third argument if the ternary version of the built-in pow() function is to be supported.
/) is implemented by these methods. The __truediv__() method is used when
__future__.divisionis in effect, otherwise __div__() is used. If only one of these two methods is defined, the object will not support division in the alternate context; TypeError will be raised instead.
%, divmod() pow()
|) with reflected (swapped) operands. These functions are only called if the left operand does not support the corresponding operation. For instance, to evaluate the expression x
-y, where y is an instance of a class that has an __rsub__() method,
y.__rsub__(x)is called. Note that ternary pow() will not try calling __rpow__() (the coercion rules would become too complicated).
|=). These methods should attempt to do the operation in-place (modifying self) and return the result (which could be, but does not have to be, self). If a specific method is not defined, the augmented operation falls back to the normal methods. For instance, to evaluate the expression x
+=y, where x is an instance of a class that has an __iadd__() method,
x.__iadd__(y)is called. If x is an instance of a class that does not define a __iadd() method,
y.__radd__(x)are considered, as with the evaluation of x
+, abs() and
Noneif conversion is impossible. When the common type would be the type of
other, it is sufficient to return
None, since the interpreter will also ask the other object to attempt a coercion (but sometimes, if the implementation of the other type cannot be changed, it is useful to do the conversion to the other type here).
Coercion rules: to evaluate x op y, the
following steps are taken (where __op__() and
__rop__() are the method names corresponding to
op, e.g., if op is `
+', __add__() and
__radd__() are used). If an exception occurs at any point,
the evaluation is abandoned and exception handling takes over.
x.__coerce__(y); skip to step 2 if the coercion returns
x.__op__(y); otherwise, restore x and y to their value before step 1a.
y.__coerce__(x); skip to step 3 if the coercion returns
y.__rop__(x); otherwise, restore x and y to their value before step 2a.
+' and x is a sequence, sequence concatenation is invoked.
*' and one operand is a sequence and the other an integer, sequence repetition is invoked. | <urn:uuid:6d180ad6-d124-4b8e-a711-061c7906bcd6> | 3.421875 | 757 | Documentation | Software Dev. | 56.978462 |
Advanced Camera for Surveys
One of the Hubble Space Telescope's advanced instruments is referred to as the ACS.
Hubble's newest science instrument-the Advanced Camera for Surveys - brought the telescope into the 21st century. With its wider field of view, sharper image quality, and enhanced sensitivity, the new camera doubles Hubble's field of view and expands its capabilities significantly. Upgrading the telescope with ACS's cutting-edge technology made it ten times more effective and prolonged its useful life.
ACS is actually a team of three different cameras: the wide field camera, the high-resolution camera, and the solar blind camera. It outperforms all previous instruments flown aboard the Hubble Space Telescope, primarily because of its expanded wavelength range. Designed to study some of the earliest activity in the universe, ACS sees in wavelengths ranging from far ultraviolet to infrared.
ACS maps the distribution of dark matter, detects the most distant objects in the universe, searches for massive planets, and studies the evolution of clusters of galaxies. To accommodate these science goals, each of ACS's three cameras was designed to perform a specific function.
With a field of view twice that of WFPC2, ACS's wide field camera conducts broad surveys of the universe. Astronomers use it to study the nature and distribution of galaxies, which reveal clues about how our universe evolved.
The high-resolution camera takes extremely detailed pictures of the inner regions of galaxies. It searches neighboring stars for planets and planets-to be, and takes close-up images of the planets in our own solar system.
The solar blind camera, which blocks visible light to enhance ultraviolet sensitivity, focuses on hot stars radiating in ultraviolet wavelengths.
ACS was installed during Servicing Mission 3B in March 2002. The new instrument was built between 1996 and 1999 by scientists and engineers at The Johns Hopkins University, Ball Aerospace, the Space Telescope Science Institute, and NASA's Goddard Space Flight Center. (Text adapted from NASA description.) | <urn:uuid:7b9f7faf-9823-4b57-9216-9451009c13ca> | 3.59375 | 400 | Knowledge Article | Science & Tech. | 32.185344 |
Tides of Change
Library Home || Full Table of Contents || Suggest a Link || Library Help
|Mark Schneider; SCORE Mathematics|
|This lessons deals with collecting data, charting data, and interpreting data, based on the changing ocean tide. Aligned to the California State Standards. From the Schools of California Online Resources for Educators SCORE Mathematics Lessons.|
|Levels:||High School (9-12)|
|Resource Types:||Lesson Plans and Activities|
|Math Topics:||Data Analysis, Statistics, Geology|
© 1994-2013 Drexel University. All rights reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education. | <urn:uuid:f4cb62dd-863e-4105-980c-8756226d113d> | 2.953125 | 149 | Content Listing | Science & Tech. | 26.450887 |
Ask the user what's her name
When prompting the user with a question it is probably the best to use the prompt function. Similarly to say it prints to the screen, but without the newline at the end. Then it waits for the user to type in something.
It reads up to the ENTER the user presses, but passes over only the the part before the newline. (Perl 5 users could think about it as having autochomp)examples/scalars/read_stdin.p6
#!/usr/bin/env perl6 use v6; my $name = prompt("Please type in yourname: "); say "Hello $name"; | <urn:uuid:df63d47e-82b0-4502-86dd-dc9c8a4569c3> | 2.921875 | 141 | Documentation | Software Dev. | 69.399524 |
According to the USGS, the total energy from an earthquake includes energy required to create new cracks in rock, energy dissipated as heat through friction, and energy elastically radiated through the earth. Of these, the only quantity that can be measured is that which is radiated through the earth. It is the radiated energy that shakes buildings and is recorded by seismographs on the Richter scale.
Even though it usually destroys homes and other structures that are built to stand on solid ground, the sheer amount of kinetic energy produced by an earthquake makes scientists very excited.
Published by WellHome | <urn:uuid:d8a12e13-5e3f-45af-9e05-cbfbeaf883f1> | 3.625 | 120 | Knowledge Article | Science & Tech. | 32.564 |
The meteor that slammed into Russia in February injured about 1,000 people and freaked out many more. Recent months have highlighted the danger of larger space objects that could bring doomsday if they collide with our planet.
Aside from death and taxes, there's another thing certain in life: meteors. To get a historical perspective on just how many dazzling space rocks have fallen through our skies in recent times, peep at Carlo Zapponi's visual graph called Bolides, which puts meteor strikes in a chronological view.
Inspired by the Greek word bolis (missile), Bolides features data from a range of historical meteor records, ranging from MetBase to London's Natural History Museum catalog of meteorites, and displays the data in a way that makes you want to click around and explore. … Read more
Shortly after a large meteor hit Russia in February, injuring about 1,000 people, President Obama's administration announced that the U.S. would work on asteroid tracking technology to avoid potentially more severe Earth collisions. On Monday, top NASA administrator Charles Bolden reiterated this pledge.
Bolden spoke at the Human to Mars Summit in Washington, D.C. on Monday and said that a robotic spacecraft mission currently being planned will "prepare efforts to prevent an asteroid from colliding with devastating force into our planet,"according to U.S. News & World Report.
The government's plan is … Read more
The meteor shower created by the debris trail of Halley's Comet will peak Sunday evening, and NASA is providing a live view of the celestial fireworks show.
Prime viewing of the annual Eta Aquarid meteor shower should be around 9 p.m. ET, providing stargazers with 30 to 40 meteors an hour, according to NASA. A camera at NASA's Marshall Space Flight Center in Hunstsville, Ala., will provide live video of the event from 8 p.m. ET to 3 a.m. ET Monday (see below).
The Lyrid meteor shower is peaking right now, and NASA wants to make sure you don't miss this once-a-year space fireworks show.
Mindful that some stargazers may not have optimum viewing conditions because of local weather conditions or the moon's glow, NASA has set up a camera at the Marshall Space Flight Center in Huntsville, Ala., to broadcast live images of the meteor shower.
"If you'd like to catch a last look at 2013 Lyrid meteror shower, this is your chance!" NASA said in a statement. "Although a bright moon may interfere with viewing, … Read more
Apparently the bright object that people reported seeing shooting over the East Coast of the United States last night -- and that left a glittery trail across Twitter -- may well have been a meteor.
Bill Cooke of NASA's Meteoroid Environmental Office told the Associated Press that, "going on visual reports," the flash was "a single meteor event."
"The thing is probably a yard across. We basically have (had) a boulder enter the atmosphere over the northeast," he added.
The object lit up Twitter last night at about 8 p.m. East Coast … Read more
At a House Committee hearing today, NASA administrator Charles Bolden Jr. was asked what America would do if a meteor similar to the one that hit in Russia on February 15 was found to be on a path toward New York, with impact three weeks away. His response? "Pray."
At the moment, we might be lucky to get even three weeks' warning. The United States and the rest of the world simply do not have the ability to detect many "small" meteors like the one that exploded over Russia, which has been estimated at roughly 55 … Read more
Capitalism is certainly alive and well in today's Russia, as demonstrated by the growing number of attempts to cash in on the recent and much-recorded (thanks to the help of ubiquitous Russian dashboard cams) meteor strike in Siberia.
The meteor that broke up over the city of Chelyabinsk while also producing a window-shattering sonic boom and momentarily outshining the sun has become a cash cow for many opportunistic folks now offering up purported fragments of the space stone on eBay and elsewhere online.… Read more
Subscribe to Crave:
This week on Crave, William Shatner has some choice words for J.J. Abrams, and we toss one back in the greatest drinking game ever invented. Cheers! Plus, we dodge a bullet the size of a football field as an asteroid nearly collides with Earth. Phew. … Read more
Leaked from today's 404 episode:
- Fiery meteor explodes over Russia's Ural Mountains; 1,100 injured as shock wave breaks windows.
- Watch asteroid 2012 DA14 fade out via streaming video.
- Iceland wants to ban Internet porn.
- Chubby Checker in a twist over an old app.
- One Direction's new toothbrush streams sound vibrations through your teeth.… Read more | <urn:uuid:83832394-1775-42ae-9db8-8eac0782a93f> | 3.515625 | 1,033 | Content Listing | Science & Tech. | 56.716944 |
Effect of Hypersonic Speeds
Recently, intense research has gone into the development of planes that can fly at hypersonic speeds, approximately five times or more than the speed of sound. At these speeds the properties of air change radically; there is a rapid increase in temperature associated with the air flowing at such speeds along a plane's surface. The U.S. Air Force is working to develop an aircraft that could travel at 13,000 mph (21,000 kph), a speed that would generate temperatures greater than 3,500°F (2,000°C).
Sections in this article:
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved. | <urn:uuid:2bce410d-bbcd-4d4b-9a28-a446f5d0b13f> | 3.765625 | 148 | Knowledge Article | Science & Tech. | 55.905357 |
The following procedures raise, handle and wait for signals.
Scheme code signal handlers are run via a system async (see System asyncs), so they’re called in the handler’s thread at the next safe opportunity. Generally this is after any currently executing primitive procedure finishes (which could be a long time for primitives that wait for an external event).
Sends a signal to the specified process or group of processes.
pid specifies the processes to which the signal is sent:
The process whose identifier is pid.
All processes in the current process group.
The process group whose identifier is -pid
If the process is privileged, all processes except for some special system processes. Otherwise, all processes with the current effective user ID.
sig should be specified using a variable corresponding to the Unix symbolic name, e.g.,
A full list of signals on the GNU system may be found in Standard Signals in The GNU C Library Reference Manual.
Sends a specified signal sig to the current process, where
sig is as described for the
Install or report the signal handler for a specified signal.
signum is the signal number, which can be specified using the value
of variables such as
If handler is omitted,
sigaction returns a pair: the
CAR is the current signal hander, which will be either an
integer with the value
SIG_DFL (default action) or
SIG_IGN (ignore), or the Scheme procedure which handles the
#f if a non-Scheme procedure handles the signal.
The CDR contains the current
sigaction flags for the
If handler is provided, it is installed as the new handler for
signum. handler can be a Scheme procedure taking one
argument, or the value of
SIG_DFL (default action) or
SIG_IGN (ignore), or
#f to restore whatever signal handler
was installed before
sigaction was first used. When a scheme
procedure has been specified, that procedure will run in the given
thread. When no thread has been given, the thread that made this
sigaction is used.
flags is a
logior (see Bitwise Operations) of the
following (where provided by the system), or
0 for none.
SIGCHLD is signalled when a child process stops
SIGSTOP), and when a child process terminates.
SIGCHLD is only signalled
for termination, not stopping.
SA_NOCLDSTOP has no effect on signals other than
If a signal occurs while in a system call, deliver the signal then
restart the system call (as opposed to returning an
from that call).
The return value is a pair with information about the old handler as described above.
This interface does not provide access to the “signal blocking” facility. Maybe this is not needed, since the thread support may provide solutions to the problem of consistent access to data structures.
Return all signal handlers to the values they had before any call to
sigaction was made. The return value is unspecified.
Set a timer to raise a
SIGALRM signal after the specified
number of seconds (an integer). It’s advisable to install a signal
SIGALRM beforehand, since the default action is to terminate
The return value indicates the time remaining for the previous alarm, if any. The new value replaces the previous alarm. If there was no previous alarm, the return value is zero.
Pause the current process (thread?) until a signal arrives whose action is to either terminate the current process or invoke a handler procedure. The return value is unspecified.
Wait the given period secs seconds or usecs microseconds (both integers). If a signal arrives the wait stops and the return value is the time remaining, in seconds or microseconds respectively. If the period elapses with no signal the return is zero.
On most systems the process scheduler is not microsecond accurate and
the actual period slept by
usleep might be rounded to a system
clock tick boundary, which might be 10 milliseconds for instance.
scm_std_usleep for equivalents at
the C level (see Blocking).
Get or set the periods programmed in certain system timers. These timers have a current interval value which counts down and on reaching zero raises a signal. An optional periodic value can be set to restart from there each time, for periodic operation. which_timer is one of the following values
A real-time timer, counting down elapsed real time. At zero it raises
SIGALRM. This is like
alarm above, but with a higher
A virtual-time timer, counting down while the current process is
actually using CPU. At zero it raises
A profiling timer, counting down while the process is running (like
ITIMER_VIRTUAL) and also while system calls are running on the
process’s behalf. At zero it raises a
This timer is intended for profiling where a program is spending its time (by looking where it is when the timer goes off).
getitimer returns the current timer value and its programmed
restart value, as a list containing two pairs. Each pair is a time in
seconds and microseconds:
. interval_usecs) (periodic_secs
setitimer sets the timer values similarly, in seconds and
microseconds (which must be integers). The periodic value can be zero
to have the timer run down just once. The return value is the timer’s
previous setting, in the same form as
(setitimer ITIMER_REAL 5 500000 ;; first SIGALRM in 5.5 seconds time 2 0) ;; then repeat every 2 seconds
Although the timers are programmed in microseconds, the actual accuracy might not be that high. | <urn:uuid:d7170610-df81-4a15-a7a0-8613d9334e2e> | 2.96875 | 1,236 | Documentation | Software Dev. | 47.244207 |
The Trojan asteroids lie in Jupiter's orbit equidistant from Jupiter and the sun. They are an example of what is known as the restricted three-body problem: the motion of a small body, an asteroid, under the influence of two massive bodies whose motion is not affected by the presence of the asteroid. The gravitational forces exerted by the sun and Jupiter combine to give the asteroid a stable orbit with Jupiter's period of rotation. (Some trigonometry is needed to show that the Trojan site forms an equilateral triangle with the sun and Jupiter). In the applet, the massive bodies executing circular orbits about their common centre of mass can have mass ratios ranging from 9 up to the value for sun-earth system. It is convenient to view the motion of the asteroid in a frame rotating with the massive bodies. This is a non-inertial frame, and both centrifugal ( - m w x (w x r) ) and Coriolis ( - 2 m w x v ) forces appear in Newton's Law. Viewed in the rotating frame, the asteroid in a stable orbit remains at rest at the point where the net gravitational attraction balances the repulsive centrifugal force. Points with this property show up clearly on a color plot of the effective potential in the rotating frame. This potential is the sum of three negative terms: a centrifugal potential that varies as the square of the distance from the centre of mass (much like an "upside down" harmonic potential), and two gravitational wells centered on the massive bodies. Points where the effective potential falls within a specified range share a common color, and the scale factor is adjusted to place the Trojan site near a color boundary. Such plots usually use linear or logarithmic scales, but here an inverse scale is used to give suitable numbers and widths of the color bands (this produces color bands of constant width near a massive body). The plot is centred on the centre of mass of the system, with the more massive body (M) on the left and the less massive body (m) a distance d to its right. Choose a mass ratio, and press either "Tro" for an orbit starting near a Trojan site or "Sad" for an orbit starting near a saddle point (a point of equilibrium on the centreline).
The most prominent features of the potential plots are the red regions surrounding the Trojan sites. As the red regions are the crests of hills, it is not obvious that a Trojan orbit can be stable. As the mass ratio changes, the shape of a crest changes, but it remains a crest. It can be shown analytically that orbits for M/m greater than 25 are stable, but the calculation requires more than the trigonometry needed to find the equilateral triangle. The numerical study of stability, on the other hand, requires only the Feynman algorithm for velocity-dependent forces (such as the Coriolis force). Each plot shows the path taken by the asteroid when it is released from rest (in the rotating frame) with a y-displacement of d/400 (about 1/3 of a pixel) from the equilibrium site. For a Trojan site, the displacement puts the asteroid on the far side of the hill from the centre of mass, and initially it moves outward as we would expect. As soon as it acquires a significant velocity, the Coriolis force deflects it to the right (in a frame rotating counterclockwise). What happens then depends on the mass ratio. For low mass ratios it spirals outward. For intermediate mass ratios it traces out loops close to the Trojan site. At higher mass ratios the potential crest becomes an elongated ridge, and the orbit bumps its way around it.
On 9 Nov 02 my car radio informed me that an asteroid the size of a football field had recently been found to share the earth's orbit. In a frame rotating with the earth, it was said to have a horseshoe-shaped orbit. As I drove along, I visualized the crest I had already plotted for Jupiter turning into a ridge that circles the sun, and the asteroid bouncing along the crest in a horseshoe orbit until it turns at a low point near the earth. That evening I extended the Trojan applet to include the sun/earth mass ratio, and found the horseshoe orbit plotted here. It has a period of 160 years.
If you select the "Sad" option, the program finds the three equilibrium points that lie on the M/m axis, one outside each mass, and one between them. They are all saddle points: the region they are in is bounded by different colors in the x and y directions. The axis and the force are shown in white on the plot, and a bisection algorithm is used to locate the equilibrium points. If a Trojan hill can produce a stable orbit there is no reason to assume that a saddle point cannot. The program tests stability using the same y-displacement used at a Trojan site. The saddle points on either side of m are unstable for all mass ratios, but the one to the left of M generates a horseshoe orbit for the sun/Jupiter and sun/earth systems. (Note that the other two saddle points are not plotted for these systems, and that the PostScript program does not deal with any of the saddle points).
The Trojan and horseshoe orbits are closely-related examples of stable orbits: closed curves that rotate about the centre of mass in sync with m. Horseshoe orbits can be generated for both the sun/Jupiter and sun/earth systems with a d/400 y-displacement from the left saddle point. A Trojan orbit can be generated for the sun/earth system with a d/1600 y-displacement from the Trojan site. A horseshoe orbit can be generated for the sun/Jupiter system with a d/70 (2 pixel) y-displacement from the Trojan site. (The size of the displacement needed can be seen on the horseshoe orbit generated from the saddle point). | <urn:uuid:6f3ce9dc-a162-41b8-a378-42a369a5def2> | 3.796875 | 1,236 | Tutorial | Science & Tech. | 50.43042 |
In general, the TOC is determined by oxidizing a water sample. The produced CO2 is detected and defined quantitatively. However, not all methods succeed in the complete oxidation of a sample. Often enough this may result only in SOC (Some Organic Carbon) instead of the TOC.
With this oxidation method the sample will be combusted in a reactor. Usually, a maximum temperature of about 1000°C will be reached, which however does not allow the complete oxidation of all carbon compounds. Therefore, a catalyst, such as copper oxide or platinum, must be used at this temperatures. Normally, the catalytic combustion method can handle a TOC concentration of up to 4,000 mg/l. To reach higher ranges the sample usually needs to be diluted with demin water.
LAR AG offers a unique and patented high temperature (HT) method at 1200°C. This temperature enables the complete oxidation of all carbon compounds without any catalysts. It measures TOC concentrations up to 50,000 mg/l without dilution. In a special heat resistant ceramic reactor the water sample is evaporated and all carbons are completely oxidized to CO2 gas. Afterwards, the CO2 concentration will be analysed with a Non-Dispersive Infrared (NDIR) detector. Thus, the TC, TOC and TIC can be determined within only 3 minutes.
This HT method is used for both, the most challenging and highly contaminated waters ( QuickTOCultra, QuickTOCairport) and waters relativily free of solid maters ( QuickTOCeffluent). LAR uses the batch injection method with the advantage that the analysers can easily handle sticky, oily and hard to oxidise dissolved and suspended organics resulting in a fast, reliable and accurate analysis. Even with rapidly fluctuating TOC levels the correct TOC concentration will be measured, whereby peaks throughout the course of the day are determined without any memory or adsorption effects.
For applications with purified water, this LAR method allows the patented* simplified, ready-at-any-time calibration and validation method ( QuickTOCcondensate, QuickTOCpurity, QuickTOCpharma).
Photochemical Oxidation (UV-Persulphate Method)
Here the TOC is oxidized by means of UV light and a digesting reagent, sodium persulphate, and the produced CO2 is measured with a NDIR detector. This method suits the determination of TOC in clean water (drinking water, condensate, boiler feed water), since particles are hard to oxidize completely.
The QuickTOCuv combines this technique with the direct TOC method or Non-Purgable Organic Carbon (NPOC) method, whereby the continuously provided water samples will be treated in a multi stage process.
Wet Chemical Oxidation
With this method the water sample is oxidized by means of strong chemicals as oxidants such as ozone, which are slightly dangerous to health and environment. The ozone oxidation acids and bases are used to adjust the pH value of the sample along the pH scale.
However, the oxidation potential of such methods is relative, since particles and more complex carbon compounds can only be partially digested or not at all. With regards to the latest standards of occupational safety and environmental protection these methods are not recommended.
*pat. 10/583,932; 2347221; 04803562.0-2204; 200480038582.7 | <urn:uuid:02ba6c77-3758-4f96-a3c5-57e73541cecc> | 2.71875 | 715 | Documentation | Science & Tech. | 32.119411 |
The integrating power of the eye has been tested for short flashes of light, ranging in duration from 10-2 to 8 × 10-9 sec. The shorter flashes were produced by passing the image of the straight filament of an electric lamp across a narrow slit, the light having been reflected from a mirror mounted on an air-driven turbine. The longer flashes were produced by means of a sectored disk. In all cases the number of flashes received by the eye was great enought to avoid flicker and the intensity was well above that required to produce the sensation of vision. It was concluded that the response of the eye depends only upon the total amount of light in the beam and is independent of the length of the light flash. The limit of error was 1.5 percent.
THOMAS E. GILMER, "The Integrating Power of the Eye for Short Flashes of Light," J. Opt. Soc. Am. 27, 386-386 (1937) | <urn:uuid:8b63c035-96b4-4881-8a5a-f7c76b74fc8a> | 3.171875 | 198 | Academic Writing | Science & Tech. | 73.021389 |
Posted 14 September 2010 - 02:49 PM
We know that a six base pair sequence AGAATA occurs 1 time in 4096 nucleotides [ (1/4)^6 = 4096 ] correct?
Let's say we have a DNA library that is 50,000 base pairs in total (small library of 50 clones to keep numbers small) it should occur roughly ~12 times [ 50000/4096 = 12.2 ] with 100% probability?
1. What is the probability that it would occur twice? How about 5 times?
2. What is the probability it would occur once in a single clone from this library if the clone is 500 bp long? What about twice?
3. And finally, let's say AGAATA occurs 3 times in one 500 bp clone. Is this significant? What is the equation? I wanted to know basically, "This six base pair sequence has an X-percent probability of occurring within the clone, and an x-percent probability of occurring in the whole library. Thanks.
Posted 14 September 2010 - 06:49 PM
Posted 14 September 2010 - 07:41 PM
Let's assume it's 25% each. And I can replace this sequence with any sequence. I'm just looking on how to do the math. | <urn:uuid:23e83e71-27ba-4d90-a99e-54022cb39fc7> | 2.8125 | 262 | Q&A Forum | Science & Tech. | 85.931199 |
by Staff Writers
Durham NC (SPX) Nov 23, 2011
If you're a snack-sized squid or octopus living in the ocean zone where the last bit of daylight gives way, having some control over your reflection could be a matter of life and death.
Most predators cruising 600 to 1,000 meters below the surface spot the silhouette of their prey against the light background above them. But others use searchlights mounted on their heads.
Being transparent and a little bit reflective is a good defense against the silhouette-spotters, but it would be deadly against the "headlight fish," says Duke postdoctoral researcher Sarah Zylinski.
Transparency is the default state of both Japetella heathi, a bulbous, short-armed, 3-inch octopus, and Onychoteuthis banksii, a 5-inch squid found at these depths. Viewed from below against the light background, these animals are as invisible as they can be. Their eyes and guts, which are impossible to make clear, are instead reflective.
But when hit with a flash of bluish light like that produced by headlight fish, they turn on skin pigments, called chromatophores, to become red in the blink of an eye.
During ship-board experiments over the Peru-Chile trench in 2010, Zylinski shined blue-filtered LED light on specimens of both creatures to watch them rapidly go from clear to opaque.
When the light was removed, they immediately reverted to transparent. On a second research cruise in 2011 in the Sea of Cortez, Zylinski measured the reflectivity of the octopuses and found they reflected twice as much light in their transparent state as in the opaque state.
Zylinski experimented with 15 to 20 different species of cephalopod pulled up from the deep by the research ships, but only these two responded to the blue light.
"I went through several things I thought would stimulate behaviors," she says. Shallow-water cephalopods (squid, ocotopi and cuttlefish) will change their body patterns for a shadow or shape passing overhead, but these deeper water animals don't, Zylinski says.
The animals could be seen tracking the movements of probes around them, but it was only the light that made them switch on the their pigments.
Zylinski next would like to investigate the link between transparency and habitat depth for the Japetella octopus.
"Smaller young animals are found higher in the water column and have fewer chromatophores, so they are more reliant on transparency, which makes sense because there won't be predators using searchlights there," Zylinski says.
But the mature adults have a higher density of chromatophores making them potentially more opaque and they can be found in deeper waters (below 800 meters) where bioluminescence becomes the dominant light source.
"Mesopelagic Cephalopods Switch Between Transparency and Pigmentation to Optimize Camouflage in the Deep," Sarah Zylinski and Sonke Johnsen. Current Biology 21, Nov. 22, 2011. DOI: 10.1016/j.cub.2011.10.014
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Tuna fishing countries vow to protect shark
Istanbul (AFP) Nov 19, 2011
Countries involved in bluefin tuna fishing have decided to do more to protect a species of shark against collateral killing, environmental groups said Saturday. Elizabeth Griffin Wilson of the Oceana group said the 48-state International Commission for the Conservation of Atlantic Tunas (ICCAT) had ruled that tuna fishermen who find a silky shark in their nets must put it back in the sea. ... read more
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2011 - Space Media Network. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement| | <urn:uuid:b3341e2f-d121-453d-99d3-f68a7c16e1e3> | 3.40625 | 910 | Truncated | Science & Tech. | 44.679049 |
These pictures were taken 13 November 2005 at about 1:15 PM from the bay shore on the UW-Green Bay. Water levels in Green Bay dropped more than 3 feet from strong southwest to northeast winds.
Point Sable is shown at the horizon.
Bay Beach and the power plant near the mouth of the Fox River in Green Bay, WI.
( source: NOAA Great Lakes Water Level Data http://tidesandcurrents.noaa.gov; choose Products, Great Lakes Water Levels, Active Stations from the pull-down menu; and then choose Lake Michigan and Green Bay)
Water levels changed by more than 5 feet in a two day period. Winds from about 200 to 240 degrees SW drive water out of the lower bay. This was the case on November 13, 2005 when water levels dropped below 574 feet. Winds peaked at 56 mph from a direction of 220 degrees on November 13th. Winds from the NE (30 to 60 degrees) funnel water into the lower bay as was the case on November 15th when water levels peaked at 579.5 feet.
|NWS Daily Wind data for November 2005, Green Bay, WI|
|Day||Daily avg||Peak 2min||Peak Wind|
(above created March 21, 2005 KJF)
Wind Event of 11 May 2006.
Greater than 2 feet of INCREASE. Strong NE winds were from a low pressure system that was over southern L. Michigan. Area also received about 3 inches of rain on Thursday 11 May 2006.
updated 18 May 2006 | <urn:uuid:0fcc547e-d988-422d-a639-cfcebeeb5bfb> | 2.9375 | 320 | Knowledge Article | Science & Tech. | 84.161987 |
Size Adult females may attain a body length of 56 mm and males 47 mm.
Description The adult frog has a somewhat flattened body; an eye with a dark, horizontal band running through it and a vertically elliptical pupil; and long limbs with large, spatulate adhesive pads at the tips of the fingers and toes. While the fingers lack webbing, the toes are extensively webbed up to the last segment of the fifth toe (and this sometimes extends to the tip). No thumb-like metacarpal tubercle is present. A glandular fold is present behind the eye (above the tympanum). The upper body surface is generally green to brown and covered with well-defined reddish brown spots and patches of variable size. There are distinct transverse bands present on the limbs of most specimens. The underside colour is mainly whitish except for the limbs which are fleshy-orange, while the skin is densely granular except on the throat. The advertisement call is a clear high-pitched ringing note produced at a rate of about one per second.
Biology This species is endemic to certain mountain ranges in the winter rainfall region of the Western Cape . It only occurs in undisturbed habitat within the Mountain Fynbos or Afromontane Forest vegetation types and is dependent on clear, fast flowing, perennial mountain streams for breeding. When they are not breeding, ghost frogs utilize damp terrestrial habitat surrounding the streams and have even been found sheltering under rocks several hundred metres away from the nearest watercourse. They are well adapted for climbing in steep, rocky terrain and enter rock crevices and caves. By means of the adhesive pads on their fingers and toes they are able to climb virtually any wet or damp surface, including smooth, vertical rock faces.
Breeding takes place from early to mid-summer (about October to January) when stream flow has reduced following the rainy season. The males can be heard calling both during the day and after dark. They call from positions adjacent to waterfalls, cascades and small rapids such as from rock cracks or from rocks either on the banks of streams or protruding from the water. Ghost frogs have a complex courtship display but actual egg-laying has not been observed. The eggs, which are laid singly, have been found scattered in exposed positions in small quiet, shady pools connected to the main stream. They are large and yellow with each one contained in a stiff jelly capsule. Clutch sizes have been found to vary from 50 to 208 eggs. The eggs hatch after four or five days. Initially the young tadpoles live off a large reserve of yolk, where after they feed by grazing over algae-covered rocks, and these “feeding trails” can be seen on rocks in quieter pools. The distinctive tadpoles attain a length of about 60 mm and are well-adapted for a life in fast flowing streams. In particular, they have large sucker-like mouths for clinging to rocks in fast flowing water and even use their mouths to climb slippery rock faces such as waterfalls. During the day, the tadpoles are usually found attached to the underside of submerged rocks. They are slow developers, taking over twelve months to develop into frogs, and are generally ready to leave the water during the period from March to May.
Distribution This species is endemic to certain Cape Fold Mountains in the western part of the Western Cape Province.
Distribution in GCBC This extends from the higher mountains of the Cederberg southwards into the Groot Winterhoek Mountains.
Conservation status Not threatened.
Threats No serious threats.
Current studies This species was assessed in the Southern African Frog Atlas Project (published in 2004). A project to investigate the genetic diversity in the Cape Fold Mountain ghost frogs is currently underway. | <urn:uuid:79ca8b7a-838d-4030-9fff-d37b3895249e> | 3 | 775 | Knowledge Article | Science & Tech. | 48.637492 |
Oddities of Physics (Oct, 1937)
Oddities of Physics
Science is much closer to our daily lives than many of us believe. Some of the simplest phenomena and everyday occurrences which do not strike one as of any particular interest, abound with scientific explanations.
WHO would imagine, when watching soldiers marching across a bridge, that they do so under orders to “break step.” If this were not done there would be a rhythmic motion set up in the bridge structure—a steady tramp-tramp—which would likely disrupt any small bridge and perhaps even a very large one (Fig. 1).
Can a submarine remain stationary at any desired level?
The answer is that it cannot, unless a slight headway is maintained or water is admitted to and discharged from the trimming tanks. A submarine cannot find a state of hydrostatic equilibrium or a point at which all pressures are equal.
Is it possible for a ship like the Titanic to sink in deep water, and eventually reach a point where the water pressure is great enough to prevent the ship from settling to the bed of the sea?
Although this question has been argued pro and con many times in the columns of scientific journals, the fact remains that no such effect will be found; the wrecked ship will descend until it rests on the ocean bed.
How fast would an airplane have to fly to leave the influence of this earth forever?
Scientists have computed, that any space flyer would have to be hurled from the earth at an initial velocity in excess of 7 miles per second. Such a ma- chine would reach the moon in less than 10 hours. (However, gradual acceleration could effect a departure, without such a high starting speed.) Could one man hold a Zeppelin?
The answer is yes, if the ship is carefully trimmed and balanced, as is the case when she is just brought out from the hangar preparatory to a flight.
Does putting oil on the water help to quiet angry waves?
Yes, this is a regular recognized practice at sea when the waves are running high and a ship is in distress. The oil helps to prevent white caps, but it does not stop the general swell of the waves.
Does the rotation of the earth cause wear on certain banks of a river?
Yes, theoretically, at least. There doesn’t seem to be any measurable proof. In rivers running north and south, in the Northern Hemisphere, there is a tendency to wear away right-hand banks, as shown in the diagram in Fig. 7, due to the rotation of the earth. In the Southern Hemisphere it is the left-hand banks that receive the most wear.
How does science help in releasing a tight pulley.’ A usual method of removing a pulley is to apply heat from a blow-torch to the pulley and ice bags to the steel shaft. The resulting contraction and expansion often permit the removal of the pulley when it otherwise refuses to yield.
Fig. 9 shows one way to stop a “flue” fire, simply by placing a cap or pan over the top of the chimney and thus checking draft of air through the chimney. Another trick is to put salt in the fire in a stove con- nected with the burning flue; the gases gen-crated help to snuff out the flames in the chimney.
Fig. 10 shows how violins and other high-pitched instruments are placed near the “mike” in broadcasting, while the bass violins, etc., are placed further back. The low notes, emitted by bass instruments, have more energy in them, or are stronger than the high-pitched notes coming from the flute, violin, etc., hence, in broadcasting studios, the majority of wind instruments are usually placed further away from the “mike,” as are drums, etc.
An interesting and everyday occurrence in homes and offices is the vibration of a metal picture frame, or other similar object, when a certain note is sounded on the piano, or radio (Fig. 11). This is due to the fact that the frame has a natural frequency corresponding to the note struck, hence it vibrates sympathetically.
It is not generally known that if a high voltage direct current is passed through a wire grid in a chimney, smoke from the boilers can be eliminated. The high voltage electrical charges cause the carbon particles, comprising the smoke, to become charged and they are precipitated to the bottom of the stack.
Fig. 13 shows an interesting problem which public address engineers have to conjure with at times. A person sitting a certain distance from the speaker’s platform may experience the unusual sensation of hearing the speaker’s voice coming out of the loudspeaker before he hears the natural voice coming from the stage. This is due to the fact that sound travels only at about 1100 feet per second in air, while the electrical current, carrying the voice from the “mike” to the loud speaker, travels at 186,000 miles per second. Consequently, good judgment has to be used by the engineers in planning P. A. systems.
If a tank full of water has 3 openings, as shown in Fig. 14, the middle jet will produce the longest stream.
Does smoke blowing downward from a chimney indicate rain?
No. This is an old theory, but it has little to recommend it. Smoke rises because of its higher temperature. If the outside air is as warm as the smoke, or if the smoke is “chilled,” as on a moist, humid day, the smoke will fall.
In a double-track railroad running north and south there is a greater wear on the outer rails. This is due to the earth’s rotation. Any train, in the northern hemisphere, running north has a greater eastward motion at the point of its location a moment before than at the moment the analysis is made. Hence, in case 1, the track presses harder against the train, causing greater wear on the outer rail, while in case 2, the train presses more strongly against the outer rail, causing extra wear there.
Why is air pumped down to divers under the water?
Air is pumped through a hose constantly to submerged divers partly to counter-balance the pressure of the water. The greater the depth the higher the air pressure pumped to him.
A problem in weighing: If a druggist found that someone had taken some of the weights for the scale and only left a 2-oz. and a 5-oz. weight, how could the druggist weigh 1 oz. of powder?
He puts the 5-oz. weight in one pan, in the other pan he puts the 2-oz. weight and enough powder to balance the scales. He now has 3 oz. of powder in the pan. Then he puts the 2-oz. weight in one pan and the powder in the other, removing sufficient powder to balance the scale. The 1 oz. of powder removed to effect a balance will be the quantity desired.
The principle of inertia is well shown in the simple trick of striking the end of an axe handle with a hammer in order to drive the axe more firmly on to the handle, as shown in Fig. 19. When the end of the handle is struck as at “H” the steel axe, due to its inertia, tends to preserve its position and thus the wooden handle is driven more firmly into the axe.
From what depth can an ordinary pump lift water?
About 26 feet is the maximum lift for an ordinary pump. If a force-pump is employed, then a check valve is placed well down in the pipe so as to be fairly close (18 to 24 feet) to the water, this valve being operated by a rod inside the pipe. Theoretically, the pressure of the atmosphere will raise water about 32 feet when a vacuum is established inside the pump lift pipe, but due to losses in the valves, etc., about 26 feet is a good working limit.
An interesting every-day problem concerns cars fitted with a vacuum-tank system for “sucking” gas from the tank at the rear. These sometimes get out of order, or leak, or they may have been drained while making repairs on the car. A trick worth remembering is that gas may be forced up into the vacuum tank by exerting air pressure on the pipe where the tank is ordinarily filled, as shown in Fig. 21. With a piece of rubber hose or inner tube, air may be blown into the tank from the mouth or from a tire pump. | <urn:uuid:df45235b-2e7c-425e-a092-456287ff6504> | 3.09375 | 1,774 | Personal Blog | Science & Tech. | 64.020219 |
An accessor method is an instance method that gets or sets the value of a property of an object. In Cocoa’s terminology, a method that retrieves the value of an object’s property is referred to as a getter method, or “getter;” a method that changes the value of an object’s property is referred to as a setter method, or “setter.” These methods are often found in pairs, providing API for getting and setting the property values of an object.
You should use accessor methods rather than directly accessing state data because they provide an abstraction layer. Here are just two of the benefits that accessor methods provide:
You don’t need to rewrite your code if the manner in which a property is represented or stored changes.
Accessor methods often implement important behavior that occurs whenever a value is retrieved or set. For example, setter methods frequently implement memory management code and notify other objects when a value is changed.
Because of the importance of this pattern, Cocoa defines some conventions for naming accessor methods. Given a property of type
type and called
name, you should typically implement accessor methods with the following form:
The one exception is a property that is a Boolean value. Here the getter method name may be
isName. For example:
This naming convention is important because much other functionality in Cocoa relies upon it, in particular key-value coding. Cocoa does not use
getName because methods that start with “get” in Cocoa indicate that the method will return values by reference. | <urn:uuid:fa5c2fa1-af36-4ff5-8788-a254b8275e51> | 4.3125 | 334 | Documentation | Software Dev. | 33.366527 |
In addition to using data manipulation statements directly, as just described, it is also possible to manipulate table data by calling a procedure. Procedures perform the specific data manipulations laid out in the procedure definition.
Any SQL statement in the grouping procedural-sql-statement, see the Mimer SQL Reference Manual, Chapter 12, Procedural SQL Statements, can be used in a procedure, and this includes all the data manipulation statements.
The use of procedures allows data manipulation within the database to be controlled both in terms of strictly defining which data manipulation operations are performed and also in terms of regulating which database objects can be affected.
A procedure is invoked by using the CALL statement. In the case of a result set procedure, used in an ESQL context, the CALL statement is not used directly but is specified in a cursor declaration. An ident requires EXECUTE privilege on a procedure in order to call it.
In the CALL statement, the value-expressions or assignment targets specified for each of the procedure parameters must be of a data type that is assignment-compatible, see the Mimer SQL Reference Manual, Chapter 6, Assignments, with the parameter data type.
See the Mimer SQL Reference Manual, Chapter 12, CALL, for full details of the CALL statement and the Mimer SQL Programmer's Manual, chapter 12, Mimer SQL Stored Procedures, for a general discussion of the stored procedure functionality supported in Mimer SQL.
Examples of Calling Procedures
Invoke the procedure called SEARCH in the MIMER_STORE_MUSIC schema:CALL mimer_store_music.search(:title, :artist, 0);
Declare a cursor that will be used when result-set data is fetched from the result set procedure called BARCODE:DECLARE c_2 CURSOR FOR CALL mimer_store.barcode(itm.ean_code);
Upright Database Technology AB
Voice: +46 18 780 92 00
Fax: +46 18 780 92 40 | <urn:uuid:8183da38-272d-4f14-8018-c0e29c672f1b> | 2.71875 | 418 | Documentation | Software Dev. | 24.696794 |
File:Recent Sea Level Rise.png
From Global Warming Art
This figure shows the change in annually averaged sea level at 23 geologically stable tide gauge sites with long-term records as selected by Douglas (1997). The thick dark line is a three-year moving average of the instrumental records. This data indicates a sea level rise of ~18.5 cm from 1900-2000. Because of the limited geographic coverage of these records, it is not obvious whether the apparent decadal fluctuations represent true variations in global sea level or merely variations across regions that are not resolved.
For comparison, the recent annually averaged satellite altimetry data from TOPEX/Poseidon are shown in red. These data indicate a somewhat higher rate of increase than tide gauge data, however the source of this discrepancy is not obvious. It may represent systematic error in the satellite record and/or incomplete geographic sampling in the tide gauge record. The month to month scatter on the satellite measurements is roughly the thickness of the plotted red curve.
Much of recent sea level rise has been attributed to global warming.
Original data for this figure is from the Permanent Service for Mean Sea Level (PSMSL). Douglas (1997), defined the following criteria for selecting records from the PSMSL which were long, reliable, and avoided large vertical geologic changes:
- Each record should be at least 60 years in length
- Not be located at collisional plate boundaries
- At least 80% complete
- Show reasonable agreement at low frequencies with nearby gauges sampling the same water mass
- Not be located in regions subject to large post-glacial rebound
He subsequently identified 24 PSMSL records meeting all five of these criteria:
- Auckland, New Zealand, 1903-2000
- Balboa, Panama, 1908-1996
- Brest, France, 1807-2000
- Buenos Aires, Argentina, 1905-1987
- Cascais, Portugal, 1882-1993
- Cristobal, Panama, 1909-1980
- Dunedin, New Zealand, 1900-1998
- Fernandina, Florida, 1897-2003
- Genova, Italy, 1884-1997
- Honolulu, Hawaii, 1905-2003
- Key West, Florida, 1913-2003
- Lagos, Portugal, 1908-1999
- La Jolla, California, 1924-2003
- Lyttelton, New Zealand, 1924-2000
- Marseille, France, 1885-2000
- Newlyn, Cornwall, England, 1915-2003
- Pensacola, Florida, 1923-2003
- Quequen, Argentina, 1918-1982
- San Diego, California, 1906-2003
- San Francisco, California, 1854-2003
- Santa Cruz de Tenerife, Canary Islands, 1927-1990
- Santa Monica, California, 1933-2003
- Trieste, Italy, 1905-2001
- Wellington, New Zealand, 1901-1988
After slight corrections following Douglas (1997) for any remaining post-glacial rebound at these sites (typically ~3 cm/century), the tide gauge data from these sites were plotted in no particular order as the thin lines in the above figure. One site, Wellington, was omitted because the author of this figure was unable to locate the corresponding record from the PSMSL.
This figure was prepared from publicly available data by Robert A. Rohde.
- [abstract] [ Bruce C. Douglas (1997). "Global Sea Rise: A Redetermination". Surveys in Geophysics 18: 279-292.
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|00:06, 18 November 2005||537×373 (47 KB)||Robert A. Rohde| | <urn:uuid:f043ae14-22cc-4ca6-b2ac-331ed18bcea0> | 3.484375 | 821 | Knowledge Article | Science & Tech. | 45.548251 |
Your municipality withdraws 10,000 gallons per day from an aquifer that originally held 1,000,000 gallons. The recharge rate to the aquifer is 2,000 gallons per day. How long will it take before the aquifer is depleted?
You have to make an equation that relates the amount of water (w) in the aquafier to time (t).
Start with the original amount:
Now, we know that every day ten thousand gallons are taken out so we have:
And we also know that every day two thousand gallons are added so we have:
To find when the water runs out, set the equation equal to 0 and solve for t:
So, the water will run out after 125 days. | <urn:uuid:84be61a4-9360-49ee-9102-e14d330dd196> | 3.09375 | 151 | Tutorial | Science & Tech. | 61.215 |
This image shows water quality changes in the Gulf of Mexico. Reds and oranges represent high concentrations of algae and river sediment. Under certain conditions excessive algal growth can result in a "dead zone" of low oxygen.
Credit (via NASA/Goddard Conceptual Image Lab)
An illustration of the flow of water from tributaries in the middle of the United States, down the Mississippi River, and into the Gulf of Mexico. Pollutants impacting the health of the River and Gulf can originate far inland. | <urn:uuid:10f4c9b4-0718-4564-b799-a790e9ed9d70> | 3.140625 | 105 | Knowledge Article | Science & Tech. | 38.113711 |
Identifying time lags in the restoration of grassland butterfly communities: a multi-site assessment
Woodcock, B.A.; Bullock, J.M.; Mortimer, S.R.; Brereton, T.; Redhead, J.W.; Thomas, J.A.; Pywell, R.F.. 2012 Identifying time lags in the restoration of grassland butterfly communities: a multi-site assessment. Biological Conservation, 155. 50-58. 10.1016/j.biocon.2012.05.013Full text not available from this repository.
Although grasslands are crucial habitats for European butterflies, large-scale declines in quality and area have devastated many species. Grasslandrestoration can contribute to the recovery of butterfly populations, although there is a paucity of information on the long-term effects of management. Using eight UK data sets (9–21 years), we investigate changes in restoration success for (1) arable reversion sites, were grassland was established on bare ground using seed mixtures, and (2) grassland enhancement sites, where degraded grasslands are restored by scrub removal followed by the re-instigation of cutting/grazing. We also assessed the importance of individual butterfly traits and ecological characteristics in determining colonisation times. Consistent increases in restoration success over time were seen for arable reversion sites, with the most rapid rates of increase in restoration success seen over the first 10 years. For grasslands enhancement there were no consistent increases in restoration success over time. Butterfly colonisation times were fastest for species with widespread host plants or where host plants established well during restoration. Low mobility butterfly species took longer to colonise. We show that arable reversion is an effective tool for the management of butterflycommunities. We suggest that as restoration takes time to achieve, its use as a mitigation tool against future environmental change (i.e. by decreasing isolation in fragmented landscapes) needs to take into account such time lags.
|Programmes:||CEH Topics & Objectives 2009 onwards > Biodiversity|
|CEH Sections:||CEH fellows
|Additional Keywords:||arable reversion, calcareous, grassland enhancement, mesotrophic, functional traits, recreation|
|NORA Subject Terms:||Ecology and Environment|
|Date made live:||12 Sep 2012 15:38|
Actions (login required) | <urn:uuid:4cc9b21b-9ac9-4733-b1e7-35a758cedd90> | 2.84375 | 497 | Academic Writing | Science & Tech. | 31.319651 |
A November 2, 1979 article by John Yemma in the Christian Science Monitor outlined Jesco Von Puttkamer's vision of America's future in space. Von Puttkamer was a planner for NASA and even consulted on the first Star Trek movie.
By the late '80s or early '90s, a huge solar power satellite may be constructed to beam microwave energy to Earth. And after that, a natural step as Mr. Von Puttkamer sees it, will be space colonies built with nonterrestial material and using solar energy.
Space Colonies by Don Davis
Sport in Space Colonies (1977)
Solar Energy for Tomorrow's World (1980) | <urn:uuid:540d8913-8456-469f-96ff-0b4740cd2aa5> | 3.125 | 138 | Personal Blog | Science & Tech. | 49.580369 |
If you take a bunch of random particles and put them together, why should a pole form on each side of this collection?
Some particles already have a magnetic field. Many particles are polar, such that they will orient themselves in a magnetic field. If you jumble them all together, they will self align, and eventually one strong field will be externally detectable even though their individual fields were small and unorganized at the start.
Perform this experiment: Drop a bunch of magnetic powder and dirt into a bag. Shake vigorously. What is the resulting clump's magnetic signature?
Is it in practice possible to create a device capable of canceling the earth's magnetic field in a region the size of the north sea?
No. What you want is a Helmholtz coil, adjusted electronically to react to the earth's changing field.
However, the area of the field required, even though it would be relatively low magnetic force, would require entirely too much energy to be practical. Further, an ideal Helmholtz coil, where the field is uniformly 0 everywhere inside the coils, requires essentially a cubic structure. The North Sea is 970 KM long, and thus the coils would need to be 970KM in diameter, vertically oriented, buried a significant portion of that depth into the ground on either side of the north sea.
Further, it would really mess up the compasses of people traveling anywhere near the coils, not to mention other animals that appear to depend on magnetic fields, such as some migrating birds. | <urn:uuid:56a7c8f9-ece0-406d-acf3-3311fe68c27b> | 3.5625 | 307 | Q&A Forum | Science & Tech. | 48.958142 |
…is a smaller species of oceanic sunfish found in tropical and temperate seas worldwide. Like its more well known relative M. mola the slender sunfish is pelagic and roams the vast oceans feeding on jellyfish. Also like most molids the slender sunfish will recruit other animals like cleaner fish and seabirds to pick parasites off of them. Molids will usually go to the surface and lay on their sides to signify they want to be cleaned, which makes it look like they are sunbathing, hence the name.
One of the ocean’s oddest looking fish, the Mola Mola possesses a truly bizarre body shape, likened to a gigantic ‘swimming head.’ Female sunfish are known to produce up to 300 million eggs at one time, the largest number of eggs ever recorded in a vertebrate.
Where and when the sunfish spawns is not well known, although five possible areas have been identified in the North and South Atlantic, the North and South Pacific, and in the Indian Ocean, where there are central rotating oceanic currents, called gyres. The newly hatched sunfish measure just 0.25 centimetres in length, and will increase in mass by over 60 million times in order to reach the size of a 3 metre adult.
(via: MIssion Blue - Sylvia Earle Alliance) (Photo: (c) Sailroe)
National Geographic explorer Tierney Thys divides her time between research on the giant ocean sunfish (Mola mola) and making science education films. In our latest podcast (recorded at this month’s SciCafe), Ms. Thys discusses how science and art can be used to raise awareness for ocean conservation.
The Mola mola is the largest bony fish living today, and only the three largest sharks (the blue shark, basking shark, and great white shark) regularly outweigh this behemoth of the open ocean.
Like many of the giants of the animal kingdom, the sunfish has a diet that’s almost paradoxically nutrient-poor. All of the calories taken in by adult sunfish are provided by jellyfish and small fry and eggs of other fish, so they spend a large amount of their time eating. Their presence in an area can indicate nutrient-rich waters where endangered species can often be found.
The status of sunfish in the wild is not currently known, though they’re caught often enough that they’re assumed to not be threatened at this point. A multi-year survey of the worldwide sunfish populations is currently underway.
Image: Giant ocean sunfish caught by W.N. McMillan of E. Africa, at Santa Catalina Isl., Cal. April 1st, 1910. Its weight was estimated at 3,500 pounds.
Two years later, alien-like sea creature gains Internet stardom
by Pete Thomas, GrindTV.com
Among the more bizarre-looking visitors to California waters this summer are Mola molas, or ocean sunfish, which are being seen in unusually high numbers. But it’s a stunning photograph of one of these gentle giants that appears to be getting the most attention. The image, captured off San Diego by Daniel Botelho, became an instant hit after being posted last week on his Facebook page…
The oceanic sunfish is known to bask flat on the ocean surface. It has theorized that this behavior may be a method to ‘thermally recharge’ itself before diving to deeper depths. Seabirds have also been observed to land on the sunfish and pick parasites off its body whilst in this position.
In the course of its evolution, the caudal fin (tail) of the sunfish disappeared, to be replaced by a lumpy pseudo-tail, the clavus. This structure is formed by the convergence of the dorsal and anal fins.Without a true tail to provide thrust for forward motion and equipped with only small pectoral fins, Mola mola relies on its long, thin dorsal and anal fins for propulsion, driving itself forward by moving these fins from side to side. | <urn:uuid:c5361d60-74f0-4148-9149-036087fb5d09> | 3.75 | 853 | Personal Blog | Science & Tech. | 51.327209 |
Sorry for the delay; it’s getting crowded around here again.
Anyway, an irreducible module for a Lie algebra is a pretty straightforward concept: it’s a module such that its only submodules are and . As usual, Schur’s lemma tells us that any morphism between two irreducible modules is either or an isomorphism. And, as we’ve seen in other examples involving linear transformations, all automorphisms of an irreducible module are scalars times the identity transformation. This, of course, doesn’t depend on any choice of basis.
A one-dimensional module will always be irreducible, if it exists. And a unique — up to isomorphism, of course — one-dimensional module will always exist for simple Lie algebras. Indeed, if is simple then we know that . Any one-dimensional representation must have its image in . But the only traceless matrix is the zero matrix. Setting for all does indeed give a valid representation of . | <urn:uuid:6f079210-a79b-44cf-96f8-e099ba38271d> | 2.703125 | 220 | Personal Blog | Science & Tech. | 37.340802 |
No coal fired power stations. No SUV’s.
And they are warning the planet's atmosphere could have similar levels of the greenhouse gas within hundreds of years.
An international team led by German scientists and involving University of Queensland Environmental Geologist Dr Kevin Welsh has found tropical palms grew on the coast of Antarctica 52 million years ago.
At that warm period in the earth's history, there was twice as much CO2 in the atmosphere as there is now and winter temperatures of 10C meant Antarctica's 4km thick ice sheet didn't exist.
Fancy that, no ice in Antarctica 52 million years ago.
Below is what I wrote on the same subject for Menzies House on 24th July 2011:
Global warming. Rising sea levels. Massive volcanic activity around the world. Widespread climate change.
It’s not a scene from the Hollywood disaster film, The Day After Tomorrow, but the Earth as it appeared during the mid-to late-Cretaceous geological period, 145 million to 65 million years ago, when the largest dinosaurs such as Tyrannosaurus Rex ruled the planet.
Our planet during the late Cretaceous period was very different than it is today. Not only were dinosaurs like T-Rex present, but the climate was extremely warm and global sea levels were significantly higher than they are today. This was a time when there were no glaciers in either the Arctic or Antarctic.
Late Cretaceous atmospheric carbon dioxide levels were two to four times higher than today, which resulted in a greenhouse climate with tropical sea-surface temperatures rising to more than 34 degrees Celsius, 3 to 7 degrees Celsius warmer than today.
Calderia and Rampino concluded in their 1991 paper - The mid-Cretaceous super plume, carbon dioxide, and global warming - that carbon dioxide emissions resulting from super‐plume tectonics could have produced atmospheric carbon dioxide levels from 3.7 to 14.7 times the modern pre‐industrial value of 285 ppm. Carbon dioxide levels today are around 390 ppm. According to Calderia and Rampino, temperature sensitivity to carbon dioxide increases used in the weathering‐rate formulations, would have caused global warming of from 2.8 to 7.7°C over today's global mean temperature.
Further supporting Calderia and Rampino’s 1991 paper is John Tarduno and his collaborators 1998 paper - Evidence for Extreme Climatic Warmth from Late Cretaceous Arctic Vertebrates.
In 1996, Tarduno’s expedition team literally stumbled across a unique fossil find: vertebrate remains from fish, turtles and Champsosaurs.
The fossils indicate that at least once in Earth's history, high amounts of the greenhouse gas warmed Earth to much higher temperatures than usual.
The highlight of the expedition find are bones that belonged to an eight-foot Champsosaur, a now-extinct crocodile-like beast with a long snout and razor-sharp teeth.
The reptiles, which were tied to their freshwater environment on Axel Heiberg Island, needed an extended warm period each summer to survive and reproduce. Based on the numbers and sizes of the animals found, the Tarduno’s team estimated that the annual mean temperature in the Arctic during the late Cretaceous period, from about 92 million to 86 million years ago, was about 14 degrees Celsius. That means it was rarely if ever freezing during the winter, and summer temperatures consistently reached between 27 and 32°C.
The Arctic today is defined as being the area where the average temperature for the warmest month (July) is minus 10°C.
The fossils of the Champsosaur are a record of what was happening in the Arctic just as extreme volcanism on Earth was winding down.
Most of the volcanic activity didn't resemble spectacular eruptions like Mt. Pinatubo. Instead, the eruptions were "basaltic" – billions of tons of lava oozed out, and carbon dioxide floated skyward. Besides huge amounts of lava in the Arctic, where hardened lava rock today measures more than a kilometre thick in some places, magma oozed from volcanoes in the Caribbean, in the Pacific Ocean northeast of Australia, in the Indian Ocean, off the coasts of Madagascar and Brazil, in South Africa and in the Southwestern United States.
Understanding how our past atmosphere, land and ocean system interacted while in this global greenhouse mode is very relevant if we want to understand the fate of our future climate.
It also further illustrates that we live on a dynamic planet who's climate is always changing over the millennia.
Whilst no one denies that the world’s industrialisation has increased considerably the output of greenhouse gases, to ascribe the current phase of our ever changing climate to one single variable (carbon dioxide) or, more specifically, to a very small proportion of one variable (i.e. human produced carbon dioxide) is not science, for it requires us to abandon all we know about our planet Earth, the Sun, our Galaxy and the Cosmos.
And believing that putting a price on Carbon Dioxide will make any difference to the Earth’s climate is madness. The only sensible action to tackle climate change is by adaption, as trying to prevent it is a fool’s game. | <urn:uuid:30bc0048-2d31-4c07-afe0-15786ed57ea5> | 3.765625 | 1,080 | Personal Blog | Science & Tech. | 41.273169 |
Heat escape routes
Take a look at this diagram showing heat loss from a house.
Heat energy is transferred from homes through the
Examples of convective losses: cold air can enter the house through gaps in doors and windows, and convection currents can transfer heat energy in the loft to the roof tiles.
Heat energy also leaves the house by radiation through the walls, roof and windows.
Red shows where most heat is lost - through the windows and roof
Ways to reduce heat loss
There are some simple ways to reduce heat loss, including fitting carpets, curtains and draught excluders.
Heat loss through windows can be reduced using double glazing. There may be air or a vacuum between the two panes of glass. Air is a poor conductor of heat, while a vacuum can only transfer heat energy by radiation.
Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall, which reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.
Heat loss through the roof can be reduced by laying loft insulation. This works in a similar way to cavity wall insulation.
If some heat escapes from the house, it costs money and wastes resources. In deciding how cost-effective an energy-saving measure is, we need to know what its pay-back time is. In other words, taking the example of double-glazing: how long will it take before the cost of having the double-glazing installed will be recovered by what we save in fuel bills? The calculation is:
pay-back time in years = cost of energy-saving measure ÷ money saved each year
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science | <urn:uuid:183e5efc-3b83-47f6-867c-8661256d209c> | 4 | 385 | Tutorial | Science & Tech. | 54.938824 |
The Unicode Standard, Version 2.0 (TUS2.0) provides different ways to encode accented characters, either decomposed (a combining character sequence [CCS]) or composed (as a single precomposed character). For example, the following are equivalent:
|Ã||A + ~|
The TUS2.0 specifies an algorithm for determining whether any two sequences of Unicode characters are canonical equivalent (see TUS2.0, pages 3-9 through 3-10). This algorithm basically decomposes any precomposed characters, then sorts them according to special rules, based on each character's combining class. This produces a normalized form.
Two common functions on Unicode text are to fully decompose the text (as far as possible), and to fully compose the text (as far as possible). In both cases, the correct result can only be achieved if the text is first converted to a normalized form.
The following describes mechanisms for composing and decomposing Unicode text that do not require fully normalizing the text, and yet produce the correct results. By avoiding the normalization phase, they represent significant performance advantages.
|Note:||In the following discussion, we will abbreviate the Unicode names for brevity. Thus LATIN CAPITAL LETTER G WITH BREVE will be represented as G-breve. A plus sign will be used to indicate a sequence of characters.|
The following discussion requires that the reader have first read Chapter 3 of TUS2.0.
The simple method for producing a normalized decomposed form is to replace each character by its decomposition, then normalize the entire string. However, this does more work than is necessary, especially in the common cases. The optimized method works as follows:
This method avoids bubble-sorting all of the combining marks in a string, and optimizes for the common cases:
Since you are guaranteed that the decomposition is already in normalized order, as each successive combining character is appended, it is bubble-sorted up in the decomposition. Since the sequence starts in normalized order, and after each successive character the result is in normalized order, then the final result is in normalized order.
|Ã`||A + ~||A + ~ + `|
|Ã.||A + ~||A + . + ~|
The simple method for producing a normalized composed form is to match each possible CCS against a database to see what matches, then replace the CCS with the result. However, this does more work than is necessary, especially in the common cases. The optimized method works as follows:
The following algorithm depends on the fact that except for one anomolous case, every CCS of length greater than two (which is canonical equivalent to a precomposed character) is also equivalent to a CCS of length exactly two. For example, C + cedilla + acute is equivalent to C-cedilla + acute, and C + acute + cedilla is equivalent to C-acute + cedilla.
Since all combinations of characters that could combine are in the mapping table, in every order that they could occur in, all the precomposed forms will be generated. Since we scan for illegal reversals, we eliminate non-canonical equivalents. At each point in this process, the result string contains a valid composition of the initial portion of the source string.
|Notes:||If we didn't scan the intervening combining characters, then we could end up with a non-canonical equivalent sequence. For example, consider the following sequence: G + acute + breve. If we didn't scan, then this would produce G-breve + acute, since G-breve is a precomposed Unicode character, but G-acute is not. When decomposed, this represents G + brev + acute, which is not a cononical equivalent to the orginal string, since breve and acute have the same canonical class.|
|The one anomolous precomposed character does require a special case in this algorithm--for simplicity of presentation, this complication is omitted.| | <urn:uuid:9f958add-2fd0-4d46-8105-6110fc8ebcca> | 3 | 850 | Documentation | Software Dev. | 34.731385 |
Weaver Ants, Oecophylla spp.
This Order of insects include sawflies, horntails, wood wasps, ensign wasps, Ichneumonids, fairyflies, fig wasps, chalcids, gall wasps, cuckoo wasps, yellow-faced bees, sweat bees, leafcutter bees, carpenter bees, honey bees, bumble bees, orchid bees, velvet ants, spider wasps, paper wasps, yellow jackets, hornets, mud-dauber wasps and ants.
This image illustrates how important it is to have the right chemical scent. Members of an individual colony possess the same “nest odor.” Even members of the same species found stumbling into a neighboring colony will not possess the correct genetic and environmentally determined odor and will generally be attacked as an intruder. These Weaver Ants exhibit refined societal coordination and create advanced camouflaged structure. They build nests by pulling together leaves and gluing them together with silk excreted from accommodating larval ants. | <urn:uuid:2e1a4015-06d3-4507-a13d-66ca4ca5855a> | 3.84375 | 216 | Knowledge Article | Science & Tech. | 31.600294 |
UAVSAR: An Airborne Window on Earth Surface Deformation
Jan. 20 & 21
The Earth's surface is constantly undergoing surface deformation at the millimeter to meter scale both from natural forces such as earthquakes, volcanoes, and glacier motion and from anthropogenic causes such as oil and ground water pumping.
From Crust to Core, GRAIL Reveals the Lunar Interior
Feb. 17 & 18
The Moon is the most accessible and best studied rocky, or "terrestrial", body beyond Earth.
WISE: The Infrared Full Sky Survey
Mar. 17 & 18
In early January, 2010, the Wide-field Infrared Survey Explorer (WISE) began imaging the entire sky with sensitivities in the mid-Infrared hundreds of times greater than previous surveys.
A Unique Opportunity: Scientific Research and Human Space Flight in the Shuttle Era
April 14 & 15
For an entire generation around the world, thirty years of access to low-Earth orbit using the Space Shuttle orbiter and solid rocket boosters has created the almost iconic image of the winged ascending spacecraft lighting up the Florida sky.
John F. Kennedy and Project Apollo
May 25 of this year will mark the fiftieth anniversary of the 1961 speech to a joint session of Congress in which President John F. Kennedy, just four months in office, proposed sending Americans to the Moon "before this decade is out."
Climate Change Impact on Civilizations: Lessons from Space Data and Archaeology
June 9 & 10
Recently, NASA and other remote sensing data have enabled significant progress in archaeological research.
Hot Water: The Oceans and Global Warming
July 21 & 22
Water covers nearly 70 percent of its surface, so it's no wonder that the world's oceans play such an important role in global climate changes.
NASA's Deep Space Network: Our Link to Spacecraft around the Solar System
Aug. 18 & 19
NASA's Deep Space Network is the largest and most sensitive scientific communications system in the world. A linchpin of spacecraft communication, DSN is our connection to worlds beyond and an essential piece of JPL's exploration of space.
From A to Z: Getting Curiosity to the Launch Pad
Sept. 15 & 16
The Mars Science Laboratory, "Curiosity", is the latest project in NASA's Mars Exploration Program, a long-term program of robotic exploration of the Red Planet.
A Self-Powered Underwater Robot for Ocean Exploration and Beyond
Oct. 13 & 14
The Sounding Oceanographic Lagrangrian Observer Thermal RECharging (SOLO-TREC) autonomous underwater vehicle is the first unmanned underwater vehicle (UUV) that is completely powered by renewable energy.
The American Rocketeer
NASA’s Jet Propulsion Laboratory invites the public to attend a special screening of The American Rocketeer at Caltech’s Beckman Auditorium. The first episode, part of a three-part miniseries entitled JPL and the Beginnings of the Space Age, tells the little- known and controversial story of Frank Malina. Viewers will follow Malina’s life from his early days at Caltech and rocket engine tests in Pasadena’s Arroyo Seco that set in motion the founding of the Jet Propulsion Laboratory.
Bringing the High Energy Universe Into Focus
Nov. 10 & 11
The Nuclear Spectroscopic Telescope Array (NuSTAR) will carry into orbit the first astronomical telescope capable of focusing high energy X-rays. | <urn:uuid:0e941192-95b9-447e-ba95-2c4b1910758d> | 3.515625 | 722 | Content Listing | Science & Tech. | 38.439142 |
The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia
4.9 OCEAN ACIDIFICATION
The oceanic uptake of excess atmospheric carbon dioxide alters the chemistry of seawater, which may impact a wide range of marine organisms from plankton to coral reefs (Doney et al., 2009a,b; NRC, 2010) (see also Section 6.3). Ocean acidification is in fact a series of interlinked and wellknown changes in acid-base chemistry and carbonate chemistry due to the net flux of CO2 into surface waters (Figure 4.26). The chemical shifts include increases in the partial pressure of carbon dioxide (pCO2), the concentration of aqueous CO2, and the hydrogen ion (H+) concentration and decreases in pH (pH = –log10[H+]). The increase in hydrogen ion concentration acts to lower the concentration of carbonate ions (CO32–) through the reaction H+ + CO32– => HCO3–, even though the total amount of dissolved inorganic carbon (DIC) goes up (DIC = [CO2] + [HCO3–] + [CO32–]). Declining CO32– in turn lowers calcium carbonate (CaCO3) mineral saturation state, Ω = [Ca2+][CO32–]/Ksp, where Ksp is the thermodynamic solubility product that varies with temperature, pressure, and mineral form. Ocean surface waters
FIGURE 4.26 Schematic indicating the effects on seawater carbonate chemistry due to the uptake of excess carbon dioxide (CO2) from the atmosphere. Ocean acidification causes increases in some chemical species (red) and decreases in other species (blue). Ocean acidification also causes a reduction in pH (pH = –log10[H+]) and the saturation states, Ω, of calcium carbonate minerals in shells and skeletons of planktonic and benthic organisms and in carbonate sediments. On millennial and longer time scales, ocean pH perturbations are buffered by external inputs of alkalinity, denoted by calcium ions (Ca2+) and changes in the net burial rate of carbonate sediments. | <urn:uuid:3e031665-0ef1-403c-997c-5c389ce54d7b> | 3.15625 | 503 | Knowledge Article | Science & Tech. | 29.897243 |
THE Japanese government is planning to build two deep holes vertically into the ground. The largest, 720 metres deep, will be in a disused coal mine in the northern island of Hokkaido and, from summer next year, you will be able to drop up to 1 tonne down the shaft for only 800 000 yen (about Pounds sterling 3000).
The aim of this project is for researchers to be able to carry out experiments that experience about 10 seconds of micro gravity. The usual way to carry out such an experiment is to blast it into orbit. It is much cheaper to drop it into a hole in the ground, but it is far from certain that Japan's scientists will fall for the scheme.
The Ministry of International Trade and Industry, which is running the project, says the Japan Microgravity Centre will offer the world's largest 'drop tower'. Capsules containing ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:c6706d13-2453-4037-9d48-2f89ff17cf77> | 3.5 | 204 | Truncated | Science & Tech. | 63.08037 |
Use of RNA:DNA ratios for assessing secondary production of planktonic food webs effects of temperature, salinity, food and heavy metals /
Abstract (Summary)Acartia tonsa is a dominant copepod in coastal waters and is an important link in the food web between microplankton and higher trophic levels. RNA:DNA ratios have been used to describe growth and nutritional condition of field collected copepods and to show strong correlation between group egg production and RNA:DNA ratios. A method was developed using a sensitive, nucleic acid fluorescent dye and automated microplate fluorometer to measure RNA, DNA and RNA:DNA ratio of individual A. tonsa. RNA, DNA, RNA:DNA ratios and egg production were all significantly higher in copepods fed Thalassiosira spp. compared to starved copepods. There was a general trend toward an increase in RNA:DNA ratios with increase in egg production, but due to the high degree of variation in both RNA:DNA ratios and egg production of individual copepods no significant correlation between RNA:DNA ratios and egg production was found. Significant differences in the RNA:DNA ratios between fed (7.2) and starved (3.4) copepods were found after 2 days. In the future this assay may be applied to other species of copepods sampled directly from the field, to provide an index of the health of planktonic food webs in nature.
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:copepoda rna dna marine plankton
Date of Publication: | <urn:uuid:75ddf350-00f0-4913-95b0-2da1f15a3b0b> | 3.390625 | 330 | Academic Writing | Science & Tech. | 34.88186 |
Constructing an octahedron and Kepler's conjecture To make an interesting skeletal model of an octahedron, start with 12 identical squares of paper or light card.
Net for the octahedron Downloaded from http: // mathworld. wolfram. com / pdf / Octahedron. pdf For more information, see the MathWorld entry http: // mathworld. wolfram. com / Octahedron. html
Modular Structures for Manned Space Exploration: The Truncated Octahedron asa Building Block O. L. deWeck, W. D. Nadir †, J. G. Wong ‡, G. Bounova § and T. M. Coee ¶ Massachusetts Institute of Technology, Cambridge, MA, 02139, USA Modular space exploration systems have been built in the ...
octahedron isometric colorless to pale yellows, browns and grays non metallic white Yes octahedron Yes conchoidal 3.5 Galena 2 cube, octahedron isometric
Platonic Solids 2 A regular tetrahedron and a regular octahedron are two of the five known Platonic Solids. These five “special” polyhedra look the same from any vertex, their faces are
One might suppose that these forms are also infinite, but in fact they are, as Lewis Carroll once expressed it, "provokingly few in number."There are only five regular convex solids: the regular tetrahedron, hexahedron (cube), octahedron, dodecahedron, and icosahedron (see Figure 1).
Octahedron? Dodecahedron? Icosahedron? What'sthesolidwhose vertices are the midpoints of the edges of the tetrahedron? Cube? Octahedron? Dodecahedron?
17 Octahedron And Cuboctahedron We mentioned earlier that octahedron and cuboctahedron can be defined as transformed icosahedra. You can also imagine the 6 square faces of the cuboctahedron as diagonal connections (1*sqrt2) of two rectangular triangles.
When the device is switched 'on', the interior is isolated from its surroundings by the superluminal rotating magnetic field and octahedron antenna. | <urn:uuid:4609f201-efc1-4e08-8c9f-87ebe3e2ea74> | 3.8125 | 497 | Content Listing | Science & Tech. | 31.837121 |
Treading Heavily on the Environment: China's Growing Eco-Footprint Highlighted in New Report
photo by Sheila via flickr
We've written about the concept of Eco-Footprint a number of times--what it is, how to calculate it, and how to reduce yours--and with the Olympics upon us it comes as no surprise that China's environmental footprint might come into the spotlight.
A new report by the Global Footprint Network, WWF, and the China Council for International Cooperation on Environment and Development does just that. While China is the obvious focus, really this report highlights how humanity as a whole is increasingly overshooting the biological capacity of the planet. It also includes recommended steps that China can take to address the issue of its increasingly heavy environmental impact.China Has Low Individual Footprint, But High National FootprintWhat the report finds is that, per capita, China ranks 69th in the world, with each person requiring 1.6 hectares of biocapacity to support them. This is lower than the global average of 2.2 hectares per person, and quite a bit lower than the United States' world-leading 10 hectares per person.
However, because of the of the overall size of the country, China ranks 3rd in total global eco-footprint, trailing the United States and the entire European Union.
Footprint Grows Along With GDPThe result is that currently China requires the equivalent of two times its biocapacity to support its current population and current level of economic activity. As China's GDP grows the amount of resources it requires only increase. Therefore, it has to effectively import biocapacity from elsewhere.
Export Manufacturing Responsible To enable this, approximately 75% of China's total biocapacity imports are consumed by this process. Only slightly more than 25% of these remain in the country for domestic consumption. We recently highlighted a report that shows that roughly a third of China's carbon emissions are directly tied to manufacturing of consumer goods for export.
As of 2003, the nearest year for which data is available, China consumed 15% of the total biocapacity of the planet. The report points out that if China were to follow the lead of the United States, in terms of levels of natural resource consumption, it alone would require the entire biological capacity of the planet. Obviously this would be an impossibility, so something needs to change, both in China and in the rest of the world.
Where To Go From Here?The report recommends five areas that need to be addressed. This is where all nations should pay attention. These areas are:
Population -- Slow and reverse population growth by offering better family planning opportunities, increasing education and economic opportunity for women. This is probably the most uncomfortable aspect of our environmental problems, but also one most in need of action.
Consumption -- Essentially, we need to increase consumption at the bottom end of the scale to lift people out of poverty, while reducing (radically, I'd say) consumption at the top end. The report points out that the average Italian uses half as many resources to have a standard of living equal if not better than in some ways than the average US citizen. It is possible to do more with less when it comes to consumption and we must do that, particularly in the United States.
photo by Ruth LozanoTechnology -- Not a technological quick fix, but improvements in energy efficiency both in manufacturing and in the home, waste reduction and recycling increase, reduction of the distance which goods travel between factory and marketplace.
Area -- Reclaim and rehabilitate lands suffering from environmental degradation to increase biological capacity.
Productivity -- Increase the useful production per hectare of land through better land management. The report points out that while intensive agriculture can increase crop yields, this comes at the expense of biodiversity loss and increased fertilizer and energy usage, both which ultimately increase ecological footprint. As a recent UN report essentially said, we need a revolution in farming that takes a more holistic, ecosystems approach to agriculture, rather than the continued industrial viewpoint.
What Can You Do?Some of these steps really require large-scale action, but that can be led to some degree at the individual level. A good first step, as we've said many times, is to assess your own ecological footprint. I'll plug The Footprint Networks' Personal Eco-Footprint calculator as the report I've been referencing comes from them, though there are plenty of other good calculators on the internet.
From there you can look at ways you can reduce your own eco-footprint, keeping in mind that there is a line below which you can't go simply because of the structure of the society in which you live. That's where the heavy lifting has to come in and structural changes have to be made.
There's more on this report, and more on eco-footprints in general at :: The Footprint Network.
All charts: The Footprint NetworkEcological FootprintBrazil and India Top Greendex; USA, Canada and France Finish LastYour Ecological Footprint: Defining, Calculating and Reducing Your Environmental FootprintAfricans' Modest Eco-Footprint Still Has Negative Impacts in Some CountriesChinaChina Gets Dubious Honor of World's #1 CO2 EmitterIt's Not You, It's Me: 33% of China's CO2 Emissions From Export Manufacturing | <urn:uuid:a71cbc30-cd29-430f-8b78-f08c2763a387> | 2.78125 | 1,097 | Personal Blog | Science & Tech. | 31.015367 |
Classical General Relativity in more than four spacetime dimensions has been the subject of increasing attention in recent years. Among the reasons why it should be interesting to study this extension of Einstein’s theory, and in particular its black hole solutions, we may mention that
- String theory contains gravity and requires more than four dimensions. In fact, the first successful statistical counting of black hole entropy in string theory was performed for a fivedimensional black hole. This example provides the best laboratory for the microscopic string theory of black holes.
- The AdS/CFT correspondence relates the properties of a d-dimensional black hole with those of a quantum field theory in d − 1 dimensions.
- The production of higher-dimensional black holes in future colliders becomes a conceivable possibility in scenarios involving large extra dimensions and TeV-scale gravity.
- As mathematical objects, black hole spacetimes are among the most important Lorentzian Ricci-flat manifolds in any dimension.
And the translation:
Traditional general of relativity in more than four masses of that the time of the space was the subject of the increase attention these the slipped years. To the relations of transformation, so that he had that to being interesting, to this extension of the theory of Einstein to study and in the detail of the relative solutions to perforate black color, that we can we mentioned this
- The theory of the series of the characters will count the force of the gravity and it more has the necessity of the one of mass four. They executed the first guessed right statistical client of the entropy of the black color that really perforates in the theory of the series of the characters the end to perforate the black color of the fivedimensional. This better example releases the laboratory available for the microscopic theory of the series of the characters of the black color of the perforations.
- The correspondence of AdS/CFT connects the characteristics of a D dimensional schwarzen that the sacadores with those with a theory of the zone of the section of the time in the D without mass 1.
- The production of the perforations that the high-dimensional-black color in her the future transforms of colliders inside the great possibilities imaginable ones into the writing of the suggestion adds of the film and in the fairs of TeV the force of the gravity.
- As matemati of the messages those we belong spacetimes of the black color that the sacadores to the tubes the greatest piece of the important Stocherkaehne I gave curly Lorentzian in each possible measurement.
I hope that clarifies everything.
Makes me wonder why there is no requirement these translation maps be invertible. | <urn:uuid:152ce7f1-8d02-4546-a969-0b59a15efdeb> | 2.765625 | 560 | Personal Blog | Science & Tech. | 27.993433 |
Panama’s San Lorenzo forest reserve is around the size of Manhattan. For two years, this small area was host to 102 scientists, working together to count everything that crept and crawled. They came from 17 countries, and converged upon a half-hectare of the forest, about the size of half a rugby pitch. They dug into the soil, and ascended into the 40-metre-tall treetops with ropes, balloons, and a giant crane. They unleashed fogs, set up sticky traps, and hacked into pieces of wood.
Together, they were part of the largest ever systematic attempt to answer a disarmingly simple question: in a patch of tropical rainforest, how many species of insects and other arthropods are there?
After collecting the critters in 2003 and 2004, and analysing the material for eight years, they got an answer: 6,144 species in that patch of forest. Using computer simulations to scale that up, they estimate that the entire 6,000-hectare Manhattan-sized forest is home to around 25,000 arthropod species.
When the fruit bat Pteropus allenorum was finally described by scientists, it was already extinct. One specimen of the bat was shot in Samoa in 1856, skinned, stored in alcohol, and shipped to the United States. It spent the next 153 years, inconspicuous and ignored, on a shelf in the Academy of Natural Sciences in Drexel University. When bat specialist Kristofer Helgen visited the museum, he immediately recognised that it was a new species. Sadly, it was too late. There are no fruit bats in Samoa nowadays, so the jar on the shelf represents our only encounter with this now-extinct animal.
The fruit bat’s story isn’t an original one. The beetle Meligethes salvan was collected from the Italian Alps in 1912 and sat in Frankfurt’s Senckenberg Museum until it was described in 2003. In the intervening time, the valley from which it came had been almost entirely destroyed in the process of building a hydroelectric power plant. Biologists searched in the nearby valleys but couldn’t find it. The beetle may be extinct.
These examples show that the shelves and drawers of the world’s museums are among the planet’s most diverse habitats—ecosystems brimming with different species, many of which have never been seen before.
People often think that discoveries are made when biologists see new species in the field, and immediately recognise them as such. That’s largely not true. Field biologists often collect their specimens en masse, taking them back to their respective institutions, and keeping them in storage until they get a chance to peer at them properly. This means that many of the planet’s new species are sitting pretty in jars and drawers, gathering dust while they wait to be formally described.
How long is this shelf life? For the bat, it was 153 years, and for the beetle, 92. On average, it’s around 21 years, according to a new study from Benoît Fontaine from the Natural History of Museum in Paris.
A.ervi attacks a pea aphid, by Alexander Wild
In a British lab, a wasp has become (locally) extinct. And then, another wasp follows it into oblivion. That’s odd because these two insects are not competitors. They don’t attack one another, and they don’t even eat the same food. They do, however, remind us that it’s very hard to predict how the decline of one species will affect those around it.
Some consequences are obvious. If an animal goes extinct, its loss will cascade up and down the food web, so that its predators will suffer but its prey will probably thrive. But food webs are webs for a reason, rather than a set of isolated linear “food chains”. Consequences can ripple across, as well as up and down.
If wasps didn’t exist, picnics would be a lot more fun. But the next time you find yourself trying to dodge a flying, jam-seeking harpoon, think about this: without wasps, many of your ingredients might not exist at all. Irene Stefanini and Leonardo Dapporto from the University of Florence have found that the guts of wasps provide a safe winter refuge for yeast – specifically Saccharomyces cerevisiae, the fungus we use to make wine, beer and bread. And without those, picnics would be a lot less fun.
S.cerevisiase has been our companion for at least 9,000 years, not just as a tool of baking and brewing, but as a doyen of modern genetics. It has helped us to make tremendous scientific progress and drink ourselves into stupors, possibly at the same time. But despite its significance, we know very little about where the yeast came from, or how it lives in the wild.
The wild strains do grow on grapes and berries, but only found on ripe fruits rather than pristine ones. And they’re usually only found in warm summery conditions. So, where do they go in the intervening months, and how do they move around? They certainly can’t go airborne, so something must be carrying them.
Stefanini and Dapporto thought that wasps were good candidates. They’re active through the summer, when they often eat grapes. Fertilised females hibernate through the winter and start fresh colonies in the spring, feeding their new larvae with regurgitated food. In the digestive tracts of wasps, yeasts could get a ride from grape to grape, from one wasp generation to the next, and from autumn to spring.
When Rachel Carson wrote her famous book Silent Spring, she envisioned a world in which chemical pollutants killed off wildlife, to the extent that singing birds could no longer be heard. Pesticides aside, we now know that humans have challenged birds with another type of pollution, which also threatens to silence their beautiful songs – noise.
A man-made world is a loud one. Between the din of cities and the commotion of traffic, we flood our surroundings with a chronic barrage of sound. This is bad news for songbirds. We know that human noise is a problem for them because some species go to great lengths to make themselves heard, from changing their pitch (great tits) to singing at odd hours (robins) to just belting their notes out (nightingales). We also know that some birds produce fewer chicks in areas affected by traffic noise.
Now, Julia Schroeder from the University of Sheffield has found one reason for this. She has shown that loud noises mask the communication between house sparrow mothers and their chicks, including the calls that the youngsters use to beg for food. Surrounded by sound, the chicks eat poorly. “City noise has the potential to turn sparrow females into bad mothers,” says Schroeder.
Even though most spiders are harmless to us, many people suffer from a crippling fear of them. Imagine then, what a grasshopper must feel. The threat of venomous fangs isn’t something that the insects can shrug off. It’s a perpetual danger that chemically alters their bodies, triggering changes that ripple through an entire ecosystem.
Now, Dror Hawlena from Yale University has found just how far-reaching these changes can be. In an elegant experiment, he showed that the fear instilled by spiders can extend into the very soil, affecting how quickly leaf litter decays.
Hawlena raised red-legged grasshoppers in outdoor enclosures, half a metre wide. Half the enclosures contained a single nursery-web spider, whose mouthparts had been glued shut, so they couldn’t actually kill any of the hoppers. Their presence, however, was felt.
Last September, I travelled to Peru to meet a fascinating scientist who is mapping the Amazon by plane. The piece was published in Wired UK earlier this year, and I’m reprinting it here now. This was one of the most enjoyably things I got to write last year. I hope you enjoy it too
A small, twin-propeller plane flies over the Amazon rainforest in eastern Peru. The scale of the vegetation is extraordinary. The tree canopy stretches as far as the eye can see — an endless array of broccoli florets bounded only by haze and horizon. Greg Asner, 43, has seen the rainforest from this vantage point many times before, but he still stares out of the window in rapt fascination.
This patch of forest in the Tambopata National Reserve is rich with life, even by the Amazon’s standards. A 50-hectare patch of forest — the size of as many rugby pitches — contains more plant species than the whole of North America. “We might as well be exploring Mars,” says Asner. “These are areas where no human has ever been. There’s no access.”
Access isn’t a problem for Asner. Behind him are three state-of-the-art sensors of his own devising which, as the plane flies along, take the forest’s measure. “We’re trying to do something really new,” He says. “This world is changing and it requires science that isn’t incremental.” Using the technology he’s developed, Asner is mapping the shape and size of the trees, down to individual branches, from two kilometres above. He can measure the carbon stored in trunks, leaves and soil. He can even identify individual plant species based on the chemicals they contain. With wings and lasers, Asner is conducting one of the most ambitious ecology studies ever staged. He accumulates more data in a single hour than most ecologists glean in a lifetime. With this data, he aims to influence governments, steer the course of climate-change treaties and save the forests over which he soars.
It turns out that if you unleash giant snakes into a place that didn’t previously have giant snakes, the other local animals don’t fare so well. That seems obvious, but you might be surprised at just how badly those other animals fare.
Since 2000, Burmese pythons have been staging an increasingly successful invasion of Florida. No one knows exactly how they got there. They normally live in south-east Asia and were probably carried over by exotic wildlife traders. Once in America, they could have escaped from pet stores or shipping warehouses. Alternatively, overambitious pet owners could have released when they got too large for comfort. Either way, they seem to be thriving.
With an average length of 12 feet (4 metres), the pythons are formidable predators. They suffocate their prey with powerful coils, and they target a wide variety of mammals and birds. The endangered Key Largo woodrat and wood stork are on their menu. So are American alligators (remember this oft-emailed photo?). Conservationists are trying to halt the spread of the giant snakes, out of concern that their booming numbers could spell trouble for local wildlife.
Michael Dorcas from Davidson College thinks they are right to be concerned. In the first systematic assessment of the pythons’ impact, Dorcas has found that many of Florida’s mammals have plummeted in numbers in places where the snakes now live.
A leaf falls from the rainforest canopy, but it never hits the ground. Instead, it becomes trapped by nets of sticky fungi. While other lost leaves litter the forest floor, this one has joined the jungle’s mezzanine level – a layer of litter suspended in mid-air and hanging by a thread.
The fungi belong to a single genus called Marasmius, which extend networks of root-like filaments through the air. They act like a web that catches falling matter from the branches above. They have gone unappreciated, but Jake Snaddon from the University of Oxford has found just how important they can be.
By snaring leaves, the fungi provide room and board to insects, spiders and other canopy creepy-crawlies that might otherwise be confined to the ground. When Snaddon removed the fungi, the numbers of these animals plummeted by 70 percent.
I’ve got a new piece in Nature about a newly discovered species of “yeti crab” that farms bacteria on its arms, then eats them. It lives in the deep ocean, near seeps that belch out methane. The bacteria living on its bristly arms (hence the name “yeti crab”) feed off the seeping gases, and the crab encourage the bacteria to grow by rhythmically waving their arms.
Go to Nature to read the full piece. Meanwhile, I loved this quote from lead author Andrew Thurber, which gets across how much there is left to discover about the oceans: “It was a big surprise. There’s a tonne of them, they’re not small, and they’re six hours off a major port in Costa Rica.”
(Photos by Andrew Thurber) | <urn:uuid:02aa08dd-851d-4e0d-b30a-d216d7782699> | 3.828125 | 2,756 | Personal Blog | Science & Tech. | 55.634264 |
Nonlinear Complex Resistivity
complex resistivity (NLCR) is a geophysical method of stimulating materials
with an electrical current sine wave of variable frequency and measuring
the voltage response. The ratio of the amplitudes of the voltage
to the current normalized by the geometry of the electrodes is the magnitude
of the resistivity. The shift in time between the stimulus current
and response voltage is a phase shift. Deconvolved response by stimulus
and summed root mean square harmonics are the total harmonic distortion.
Deviation of the real and imaginary parts of the complex resistivity transfer
function versus frequency from the Hilbert transform expectation are Hilbert
Distortions. Both distortions are measures of nonlinearity.
complex resistivity measurements as a function of frequency from 0.001
Hz to 1,000 Hz are useful in a variety of applications where remote measurements
of active chemical processes are important. As all chemical reactions
involve electron charge movement, NLCR can measure or observe nearly all
chemical processes (some are too fast or too slow). NLCR is used
in the laboratory, in boreholes, between boreholes or between holes and
the surface, from the surface and inside tunnels. It requires contact
with the ground to inject a current and has not been successfully employed
from airborne platforms. It has applications to the study of corroding
metals, ore exploration and delineation, clay-organic reactions for petroleum
exploration, environmental characterization and monitoring, ground water,
archaeology, and agriculture.
<more to come>
Copyright 1999 by Gary R. Olhoeft.
All Rights Reserved. | <urn:uuid:48c7089b-7243-45b2-9ab7-c054ed071daf> | 3.28125 | 339 | Knowledge Article | Science & Tech. | 20.921333 |
Search Journal of Online Mathematics and its Applications:
Journal of Online Mathematics and its Applications
Page 1 of 1
Dealing with Data: A 'Simple' Linear Fit
[Note: The activities in this module make reference to the computer algebra system (CAS) Maple. Any other CAS can be used instead (e.g., Mathematica, Mathcad, etc.) as long as the user is familiar with that CAS system. In other words, while preferred here, Maple is not required for the use of this module.]
The first true test of any scientific theory is whether or not people can use it to make accurate predictions. Calculus, being the study of quantities that change, provides the language and the mathematical tools to discuss and understand change in a precise, quantitative way. An important prerequisite to using calculus to analyze "real-world" situations is having a good understanding of the basic "elementary" functions: polynomials, logarithms, trigonometric functions, and all their compositions, inverses, etc.
With an understanding of the calculus of the basic functions, it is often possible to formulate a mathematical model of (an idealized version of) a phenomenon in one of two ways: First, enough might be understood about the phenomenon so that a mathematical formulation of it is directly attainable. For example, Newton's second law of motion -- force is the derivative of momentum, where momentum is the product of mass and velocity -- is such a model. At the other extreme are models which are derived purely empirically -- data are collected, and one searches for an appropriate formula to match the data with reasonable accuracy. Many economic models are derived in this manner.
More often, however, mathematical models are developed with a combination of the two approaches: one has some basic understanding of a phenomenon, enough to restrict the class of functions appropriate to model it. Very often, one knows enough so that the functions are determined except for a few parameters, such as the coefficients of a polynomial, or some other kind of multiplicative factor. Then, experimental data are used to determine the values of the missing parameters. Many of the "constants", "coefficients" and "numbers" one encounters in science (e.g., rate constants of chemical reactions, half-lives of radioactive elements, coefficients of thermal conductivity, the gravitational constant, etc.) started out as the last unknown parameters in a mathematical model, which had to be determined by collecting experimental data.
Linear fits: In many situations, researchers want to understand how some quantity will change when another quantity is varied. A simple example of this might be the following sports-physics experiment: A basketball is dropped from different heights, and the height of the first bounce is measured each time. What is the relationship between the height of the drop and the height of the bounce? We can try a simple mathematical experiment to look at the problem. Below is an interactive program that allows you to enter several data points (possibly non-physical) claiming to be data representing the starting height and subsequent bounce heights of a basketball. Enter the x,y values for any points you like, then use the mouse to click on any two positions inside the graph area. The program draws a line between the two points and indicates the endpoints and the midpoints with circles. By clicking near the center of any of the circles, you can drag the line around. As you do so, you will see a display of the distance between the closest approach of the line to each data point. You also see at the bottom a display of a number which characterizes how "badly" the line fits the points. The smaller the "badness" number, the better the line should appear to represent the points. Try it!
Dr. DeTurck collected the following data by dropping a basketball in his garage. After each drop, he measured the height of the first bounce:
To get ready for our subsequent analysis, we use Maple to make a list of the drop heights and the corresponding bounce heights:
#Make an ordered list of data points # drop:=[36,40,40,44,44,48,52,56,60]: bounce:=[25,29,28.5,31.5,32,35,38,42,46]:The square brackets indicate to Maple that the set of numbers is an ordered list. The two statements end with colons, rather than semicolons, so that there will be no output from them (because in this case, Maple would just parrot back the input).
It will be helpful to have Maple make what statisticians call a "scatter plot" of the data points. To plot points from a list, Maple expects an ordered list containing the x-coordinate of the first point followed by the y-coordinate of the first point, followed by the x-coordinate of the second point, etc. To transform our drop and bounce lists into ordered pairs, we enter the following command (this is pretty advanced Maple-speak, so don't worry if you wouldn't have thought of it):
This defines the variable points to be the list of points we want to plot. Be careful when you type this statement that you distinguish carefully between parentheses and square brackets.
The variable points has the drop height and the corresponding bounce height right next to each other, for use with plot. So try plotting the data ("style=POINT" and "symbol=cross" are to keep Maple from connecting the dots):
plot(points, style=POINT, symbol=cross);
The data look pretty linear, but how do we find the line that "best" describes it? There are several different definitions of "best" in use. We will be using the so-called "least-squares" fit. For our drop-bounce data, the least squares line is obtained as follows:
with(stats,fit); with(fit,leastsquare); leastsquare[[x,y],y=a*x+b]([drop,bounce]);
y = .8502604294 x - 5.567708941.
Now we can plot the data and the line to see how well Maple did with fitting the data. Since we want to combine two different kinds of plots, we will be using the display command.
First, let's assign a name to the equation Maple returned.
fitlin := .8502604294*x - 5.567708941;
Now we can plot both the line and data and store those plots as variables. The names stand for what Maple calls "plot structures", which are Maple's internal directions for making plots. It is very important to use colons at the end of statements that assign plots to names. You defnintely do not want to see the plot structures!
fitplot := plot(fitlin,x=35..60): pointplot := plot(points, style=POINT, symbol=cross):
We can display the plot commands we've saved. Before we do that, we have to have Maple load the display command.
Fit this data with a least-squares line. What interpretation do you give to the slope of your line? Using your linear model, predict the winning height in the 2000 Olympics... in the 2096 Olympics. According to your model, in what year will pole vaulters be able to "leap tall buildings in a single bound"? (The Empire State building is 1250 feet tall.)
Comment on the reasonableness of your model (including comments about the residuals).
Problem 2. In a physics experiment, students measure the period of a pendulum (i.e., the amount of time the pendulum takes to swing back and forth) as a function of its length. One group of students obtained the following data:
As you did in the first problem, find the least squares line that best fits this data. Compute and plot the residuals -- these are the differences between the measured values of the period and the value predicted by the least squares equation for each measurement. Explain why these indicate that a different model is needed.
Published July 2001
© 2001 by Larry Gladney and Dennis DeTurck | <urn:uuid:3afc882f-3743-40dc-b6ea-15777e6ec5c4> | 3.484375 | 1,704 | Documentation | Science & Tech. | 53.700603 |
Arcs, Cevians, Tangents
Theorem 4.5 The lines tangent to the circumcircle of a triangle at its vertices cut the opposite sides in three collinear points.
The proof in the text is as follows: Let the tangent to the circumcircle at A meet line BC at L. Then Angle BAL is congruent to angle C since each angle is measured by half of arc AB. *****That would be fine, but I don't know how they determine this... *****. Also we have that angle LAC = 180 - angle ABC, since these angles are measured by halves of the two opposite arcs AC. *****Again, I am lacking the theorem which is used to deduce this******.... the rest of the proof is trivial and I don't need help with it.
Can someone please give me the theorems they use for those parts of the proof.
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It's elementary theorem that angles on the circumference of the circle 'looking' at the same arc of that circle are themselves equal. (the proof is a bit long but if necessary I can try to write it, try this Circumferential Angle Is Half Corresponding Central Angle ; the theorem works for any circumferential angle.)
BAL is 'looking' at the arc AB but is degenerated.
When you know this you can find the second part easily just observing the angles ABC and the angle at A 'looking' at arc AC.
Sorry if my English was bad. | <urn:uuid:a48c710c-cee8-4d73-8702-0f1548da2c2b> | 3.375 | 318 | Q&A Forum | Science & Tech. | 71.270484 |
|El NiƱo-Southern Oscillation
The most common way of monitoring the El NiƱo-Southern Oscillation phase is by looking at sea surface temperatures in the equatorial Pacific Ocean. The animated map below shows sea surface temperature anomalies over the past three months. Warm/positive anomalies are associated with the El NiƱo phase, while cool/negative anomalies are associated with the La NiƱa phase.
Several climate models also provide ENSO forecasts, again based on sea surface temperatures over a specific region in the equatorial Pacific Ocean. The graph below shows the observed ENSO phase for the previous three-month period (as a red circle near the left side of the image), along with computer model forecasts for the next year-and-a-half. The light blue square represents the model consensus forecast.
In North Carolina, a warm/positive phase (El NiƱo) event is often associated with cooler, wetter conditions and an increased chance of winter weather. Likewise, a cool/negative phase (La NiƱa) event often brings North Carolina warmer and drier conditions. The impacts of ENSO on North Carolina are most prominent during the winter.
Because ENSO conditions are generally slow to change, with a frequency on the order of months to seasons, we have some skill at issuing forecasts on a seasonal and even annual basis.
For more information about ENSO, visit our information page or the Climate Prediction Center's page that includes past, current and forecast conditions. | <urn:uuid:5e01c03d-a1e5-4b30-abfe-34ab14544b5c> | 3.28125 | 323 | Knowledge Article | Science & Tech. | 27.113896 |
The manned research submersible Alvin.
September 8 - October 1, 2001
The Deep East Expedition completed its field season on October 1. Scientists explored three regions of the Atlantic Ocean, from Maine to Georgia, including the submarine canyons of Georges Bank and Bear Seamount off the New England coast; Hudson Submarine Canyon, an ancient extension of the Hudson River Valley that extends more than 400 nautical mi seaward from the New York-New Jersey Harbor; and Blake Ridge off the Georgia coast. Even though these areas are very close to home, until now, little was known about the living and nonliving resources there.
Using the manned submersible Alvin, scientists ventured to the bottom of the Atlantic, collected video footage, measured the biological, geological, and chemical features of these areas, and collected biological and geological samples for further analysis. During the expedition, scientists examined deep-water corals and methane hydrates, and discovered previously unknown deep-sea resources and processes.
Background information about the expedition are found on the left side of this page. Daily updates are included below. Detailed daily logs of the expedition's activities are found on the right.
Read a summary of some of the preliminary findings from this fascinating expedition. On Dec 12, NPR Marketplace ran a special feature on the Deep East expedition. You can listen to it here (click on RealAudio link, then advance to 22:05).
Updates & Logs
Leg 3 Blake Ridge
Click images or links below for detailed mission logs.
The Deep East Expedition spanned 1,000 mi, from Georges Bank to the Blake Ridge off the U.S. Eastern Seaboard. Of the planned 15 dives, 11 descended to depths reaching 3,000 meters -- more than a mile and a half below the ocean surface. The expedition's accomplishments included the collection of eggs and sperm packets from two deep-water species of anemone and coral. Analysis of these samples will provide the first picture of invertebrate reproduction in deep-sea habitats.
The preliminary results of geological studies showed an elevated methane signal throughout the Hudson Canyon region, indicating that active methane vents occur in the area. Pending further analysis of samples collected at Blake Ridge, scientists expect to find several new species of sea creatures, including shrimps, worms, and clams. Some of these organisms may harbor new symbiotic relationships that could change our fundamental understanding of the global web of life.
Winds are sustained at 37 kts with higher gusts
and the seas are mess8 feet and continuing to build. Weather
predictions take the winds to 50 kts, and the Captain says that the
seas will probably reach 20 feet. The final Alvin
dive of the Deep East Voyage of Discovery has been cancelled. The underwater transponders that have navigated Alvin
again and again to the site of our deep sea finds have been retrieved. Dr. Carolyn Ruppel continues to gather the multibeam points to further expand our knowledge of the bathymetry at Blake Ridge.
Samples are being packed up and the Atlantis
has begun the task of getting her ready for the tours that will be
part of NOAAs Ocean Exploration Day in Charleston.
makes Dive 3712 on Area E on the
Blake Ridge, the weather report reads "Developing gale, 33 N 70W moving NE 30 kts. Forecast area of N winds 25-35 kt, seas 10-18 ft. within area S of 34Nw of 75W associated with the gale center south of the area." Although
is approximately 60 nautical miles east-southeast the affected area, there
is already an air of anticipation about whether tomorrows dive
will be affected by seas
kicked up by the developing system. Students from around the country have been participating in the Deep East Web Forum over the past four days. This online conversation concluded today with a very successful audio Deep East Web Chat with students from as far away as Washington and as close as South Carolina posing questions live via a satellite phone to scientists on board the Atlantis
It is an overcast day and the seas are calm. As Alvin makes Dive 3,711
the Blake Ridge, Dr. Joan Bernhard and graduate student Katie Knick
are experiencing the deep sea in a way that few of us ever will. Dr.
Carolyn Ruppel continues her work using the multibeam system to "fill in" details
of Blake Ridge bathymetry with 120 measurements that are sent back
to the ship with each ping of the multibeam instrument. And Dr. Joan
Bernhard discovers yet another new find on the Blake Ridge.
is making its second dive on the Blake Ridge. Dr. Barun Sen Gupta and Dr. Paul Aharon are in the submersible with pilot Dudley Foster as they explore for evidence of gas hydrates
. Dr. Joan Bernhard reported during the morning science meeting that microscopic examinations of sediment cores late last night revealed that, in fact, bacterial mats of Beggiatoa
were collected yesterday, the first chemoautotrophic (feeding on methane) bacteria to be collected at this site. Alvin
returns to us after a full day of diving and delivers incredible video tapes of gas hydrates, mussels that are larger than the ones collected yesterday, and live clams--yet another historic day of exploration on the deep seafloor of the Blake Ridge.
made its first dive on the Blake Ridge to a depth of 2,155 meters, almost a mile and a half under the surface of the ocean. Today will be a memorable one in deep sea research
as it goes down in history as being the first day that live samples were brought up from the deep ocean floor at Blake Ridge using the Alvin
. "Amazing, just amazing," says
Dr. Cindy Van Dover. These are by far the biggest mussels I have ever
arrived at the first station at approximately 1230 today. Transponders were released to aid the Alvin
underwater navigation for tomorrows dive. An expendable bathythermograph
(XBT) was deployed to measure temperature of the water column with
depth. A multibeam survey is underway to create a plot of the bathymetry
of the area. Seas are calm and scientists and crew are busy preparing for the first dive on Blake Ridge
scheduled to take place at 0800 tomorrow.
The R/V Atlantis
continues on her way to the Blake Ridge. We are currently 47 miles due east of Cape Hatteras, North Carolina. We have slowed in speed due to the presence of the Gulf Stream, which we are now crossing
as it makes an eastward bend off the coast of North Carolina. At the present speed of 11.1 kts, our estimated time of arrival on station is 1200 (noon) tomorrow. The seas are calm, despite the fact that the tropical depression has now been upgraded to Tropical Storm Humberto. Predictions continue to take it from its current northern track to a more northeastern track over the next 12 hours.
Leg 2 � Hudson Canyon
We have packed up our gear and are ready for departure. Much planning and organization went into our coming together for this leg of the Deep East Expedition, so in one sense, the trip was a culmination of the dreams and efforts of many people. In another way, the data we have collected, ideas we have exchanged, things we have learned, and questions we have raised make this a new beginning. We will leave the research vessel (R/V) Atlantis with a tremendous sense of accomplishment,
as well as new reasons and increased motivation to further explore the deep ocean and the dynamic ecosystems that characterize the Hudson Canyon.
Everyone woke to the excitement of having two Alvin
dives today.The first dive would carry a teacher, and the second, a graduate student. As teacher Holly Donovan approached her dive time, she was very nervous, but anxious to see the wonders of the sea.
While waiting for the second dive, graduate student Grant Law sat in the computer lab playing the guitar. As both dives came aboard, anxious scientists gathered around to hear the stories, collect their samples, and reminisce about the past week.
September 19 Today, Alvin dove to the northern edge of the Hudson Canyon.
This region is located on the outer edge of the continental shelf, near the head of the canyon. During this dive, scientists Fred Grassle and Ken Able were able to identify 21 species of fish. One of the most striking sights was a variety of predators (squid, hake, and crab) feeding feverishly on thousands of lantern fish near the bottom of the canyon at a depth of about 200 m.
The day started at 2:30 am, when the first box core was lowered into the ocean
then departed at 8:30 on its way to the plume site. As Alvin
returned, a rumor spread that a large animal had been captured. As Alvin
into its "garage," many scientists and others gathered
around to see the sight -- a huge anemone. Then the box cores,
niskin bottles, and Alvin
push cores were all unloaded. The evening came to an end with three box cores over the side at 8:30 and 11 pm, and finally at 1:30 am on Sept. 19. Mud was flying everywhere.
After our early morning attempt to launch the CTD rosette, which had been postponed due to weather conditions, we continued watching the wind speed and the size of the swells to determine whether our scheduled first dive with Alvin
would indeed occur. The initial launch time of 8 am was postponed until 9:30, at which time the launch was successfully completed
descended to the 106-mi Dumpsite. Box cores, water samples, and core samples were taken to study the evolution of the ecology and geology of the site since the last sampling in 1996. After dinner, the CTD rosette was successfully launched and retrieved. Its water samples will be tested later for methane.
Excitement was in the air as moving day approached. Scientists scurried around moving on board, while crew members busily loaded and tied down all the equipment needed for the trip. As the R/V Atlantis
pulled away from the dock, most of the scientists' paused to take one last look at land before heading out to sea
. Now they were ready to get to work.
Leg 1 Georges Bank Canyons
September 15 The first Leg of Deep East came to a close today, as we returned to dock in Woods Hole
at 9:15 am. The weather is getting rougher, and all those aboard are relieved that Leg 2 of Deep East will disembark from Woods Hole instead of from Staten Island, NY, as planned. Originally, the scientists participating in Leg 2 were to board a transfer boat on Staten Island and come out to sea to meet the Atlantis
. When the two boats rendez-voused, Leg 1 scientists would board the Staten Island transfer boat. When it became clear that the port of New York would be closed, however, Woods Hole became the exchange point.
At long last, the wind and waves subsided enough to allow Alvin
to dive safely into Hydrographer Canyon. The benthic substrate of this canyon was considerably different from that of Oceanographer Canyon. Instead of a rocky substrate, this canyon was steep and muddy. No corals were found in Hydrographer Canyon, but a rich community of fish and invertebrates was observed.
The science team wrapped up this leg of Deep East with an Alvin
ritual -- sending decorated Styrofoam cups down on the submersible. The crushing hydrostatic pressure shrinks them into tiny miniatures.
After four days at sea and only one dive day, the crew and science party once again woke to rough seas and high winds.
Some members of the science party kept busy editing digital video footage and still photos, while others caught up on missed sleep.The R/V Atlantis'
SeaBeam multibeam sonar system was pressed into service to map the depths of Bear and Physalia Seamounts. The Atlantis
crew set a course for Hydrographer Canyon, with high hopes for low winds and calm seas for Friday's planned Alvin
Weather conditions at sea have forced the cancellation of the dive at Bear Seamount. The swells from Hurricane Erin, approximately 150 mi southeast of the R/V Atlantis,
can be felt aboard ship, and the captain has ordered all hands to remain inside
until further notice. Work continues aboard the ship, while the crew and science staff monitor news updates from the U.S. mainland.
The R/V Atlantis
left Woods Hole at 12 noon and headed to Oceanographer Canyon, the first dive site. Shortly after departure, we encountered the WHOI vessel R/V Oceanus
to port. Once south of the Nantucket Shoals, the crew and science
staff participated in safety demonstrations and received advice on "getting their sea legs." An evening meeting for the science staff will discuss the next days dive, and the status of Hurricane Erin.
We'll also get to see slides of deep-sea coral species, courtesy of Dr. Barbara Hecker.
Prior to the cruise, preparations for the Deep East Expedition took place on the dock at Woods Hole Oceanographic Institution (WHOI) in Woods Hole, MA. Science equipment, food, and other supplies lined the dock as the crew, scientists, educators, and WHOI staff made a final inspection of the vessel and completed last-minute tasks.
A Deep East Professional Development Institute was provided for educators on Cape Cod, which included a tour of the R/V Atlantis
. As the excitement and anticipation began to build, a new element was added to the mix -- Hurricane Erin, whose path will be closely monitored as departure time approaches.
Sign up for the Ocean Explorer E-mail Update List. | <urn:uuid:25d2e1c4-c7e1-4ead-a970-89b1a6a25b89> | 3.40625 | 2,884 | Knowledge Article | Science & Tech. | 51.487519 |
Ion strings make brilliant beams
Aug 15, 2001
Physicists have long struggled to combat heating in the ion beams used in high-energy experiments. Laser cooling can be used to reduce collisions between the ions, which create heat and reduce the energy of the beam. Now Ulrich Schramm and colleagues at the University of Münich have created the first 'crystalline' ion beam, which is virtually free from collisions. "The crystalline beam is the ultimate state for an ion beam in terms of brilliance and stability", Schramm told PhysicsWeb. "It represents a different phase and has its own properties" (T Schätz et al 2001 Nature 412 717).
Collisions in high-energy ion beams reduce the beam intensity and can be remedied by extra focusing devices or the use of low-density beams. However, physicists predicted 20 years ago that in a sufficiently cool beam, the ions would not collide because their Coulomb repulsion would outweigh their kinetic energy.
Such 'crystallization' has been achieved before in ion traps - in which the ions are stationary - but it is more difficult in a circulating beam because of the motion of the ions and interactions between the beam and the storage ring. These problems affect both large storage rings - such as the Relativistic Heavy Ion Collider at Brookhaven - and smaller ones.
Schramm and co-workers injected magnesium ions into their 0.36-metre circumference storage ring, PALLAS - the Paul laser cooling acceleration system. The beam was laser-cooled and its fluorescence monitored. The team found that, at a certain laser wavelength, the diameter of the beam fell and the fluorescence peaked sharply. This pinpoints the transition to the crystalline state, during which the range of ion velocities drops by 75%.
The fluorescence measurements showed that the ring contained around 18 000 ions, and the temperature of the beam fell from 30 to 0.4 kelvin as the crystalline state emerged. In this new phase, the ions reach a speed of 2800 metres per second - corresponding to a beam energy of 1 electron volt - and resemble a one-dimensional thread. The beam can perform over 3000 revolutions of their storage ring without further cooling
According to Schramm, the technique could be used for a wide range of experiments. "Crystalline ion beams could aid inertial confinement fusion - which mimics stellar nuclear reactions - while precise experiments with relativistic beams could test special relativity", he says.
About the author
Katie Pennicott is Editor of PhysicsWeb | <urn:uuid:bc6e3879-d2fd-478e-832b-124df80bfc06> | 3.59375 | 529 | Truncated | Science & Tech. | 42.617974 |
A range of designs have been proposed for space habitats. Some appear to be mostly artistic concepts, others are much more serious. They include:
(From Wikipedia http://en.wikipedia.org/wiki/Space_habitat)
- Bernal sphere - "Island One", a spherical habitat for about 20,000 people.
- Stanford torus - A larger alternative to "Island One."
- O'Neill cylinder - "Island Three", the largest design.
- Lewis One A cylinder of radius 250m with a non rotating radiation shielding. The shielding protects the micro-gravity industrial space, too. The rotating part is 450 long and has several inner cylinders. Some of them are used for agriculture.
- Kalpana One, revisedA short cylinder with 250 m radius and 325 m length. The radiation shielding is 10 t/m2 and rotates. It has several inner cylinders for agriculture and recreation.
There are other well-known structures from science fiction literature, including
- Rama (a 20x50km rotating cylinder) from Arthur C. Clarke’s novel, Rendezvous With Rama
- Space Station V (from the movie 2001: A Space Odyssey)
- Babylon 5
Of these, the most complete design is “Kalpana One, Revised,” which properly accounts for issues such as shielding and rotational stability. Most designs presume that it is best to provide windows to admit natural sunlight, but there are many reasons to prefer artificial light sources, primarily involving heat, but also the need for shielding. For adequate shielding from radiation and meteors, the outer walls of the habitat must mass about ten tons per square meter. While transparent quartz windows could be built of this thickness, most designs involving natural sunlight use mirrors to deflect sunlight around shields of stone. But the admitted heat is the real problem (discussed below).
In my previous posts, including Our First Colonies In Space, Life in an Asteroid, and Our Homes, the Comets, I assumed that we would tunnel into asteroids and comets, enclose and spin them for gravity if they were small enough, or build spinning structures inside them if they were too large.
But while writing a sequel to my short story Apophis 2029, I realized that the best choice was simply to build one or more space habitats from the raw materials of the asteroids and comets. I came to this conclusion because of considerations for effective use of space, the stresses of spinning large objects for gravity, and (most importantly) thermal dissipation.
People consume energy in their homes, workplaces, and travel. Much more important, food requires a large amount of energy in the form of light for growing crops. After extensive research on plant needs, high-intensity farming, and lighting technologies, I concluded that the minimum light levels needed requires 4 kilowatts of very-high-efficiency LED lights to grow the food for one person (assuming a primarily vegetarian diet – you need more to grow additional crops for livestock). Add to that the per-capita electric consumption in the U.S.A. of about 1.5 kilowatts, add a little more for contingencies, and I realized we need to plan on 6 kilowatts of energy consumption for every human aboard the habitat.
That’s not too bad, especially considering that readily available solar power can easily provide such levels and at a modest cost.
But energy consumption turns into heat, and heat must be radiated away. The bottom line is that we must allot 19 square meters per person of surface area assuming black body radiation at a temperature of 0 degrees C. It does not help to plant little radiators all over the surface, as they interfere with each other. All that matters is the apparent size of the habitat from a distance, and how closely it approaches the ideals of a black body radiator. Of course, we could use active cooling to heat radiators to much higher temperatures while cooling the interior, but I prefer passive techniques so that a failure of the cooling system doesn’t rapidly result in cooking the inhabitants.
There goes my idea that a million people could thrive in a cubic kilometer of comet. There is plenty of room, more than enough materials. Unfortunately, their waste heat would rapidly boil their home away.
Also, solar light has a large content of heat – and that excess, too, must be radiated away. Sunlight is not energy efficient for growing crops in a thermos bottle (which is what a habitat in space effectively is).
So, my revised plan calls for 20 square meters of surface per person. Also, to provide radiation and meteor shielding equivalent to the Earth’s surface requires 10 tons of shielding per square meter of surface – and thus 200 tons of shield mass per person (regolith is fine, slag works well and is dense, ice is best as long as it doesn’t boil away). But the needed surface area and shield mass per person are constants.
My earlier thoughts on structure did not consider rotational stability, and the folks that designed Kalpana One came up with some very strong arguments that a spinning cylinder is best, and that the width of the cylinder should be 1.3 times the radius. Thus, a cylinder of radius 100 meters (spinning at 3 rpm for 1 G gravity along the outer rim) should be 130 meters wide. That gives a 1-G living area of a little over 80,000 square meters, a total surface area of over 144,000 square meters, and thus a maximum population of 7,200. This structure provides 11.25 square meters (121 square feet) per person of 1-G living space. Is that enough?
It’s comparable to the space provided (per person) in many hotel rooms and cruise ships. But few couples want to live in a 242 square foot efficiency for long, although 28 sm (300 sf) studio apartments are common in many expensive cities.
There is no need to live only on the outer 1-G surface. Assuming 3-meter intervals, the next level up provides 97% of a G. Surely that is adequate. And now we have 22.5 square meters per person of available living space, equivalent to 450 square feet per couple – or 900 square feet for a family of 4. A third living level raises the per-person space to over 33 square meters – 675 sf per couple – 1350 sf for a family of four. Not spacious, but certainly comfortable.
Humans need space for living, working, and of course for growing food. We must allot some space for office space, work space, schools. A single level should suffice (11 square meters per person), partly because some people will work in the farms, or in their homes, or outside the habitat entirely (such as in the mines, the smelters, the steel mills, the solar power satellites, etc.).
Each person requires approximately 64 cubic meters for crops, but crops don’t require 3-meter ceilings. Allocating 2 levels for agriculture may be tight, but 3 levels is more than enough and provides some excess capacity for the production of meat, milk, and eggs.
We need a little more space for overhead: storage, aisles, conduits for air, water, sewage. So we add an 8th level for good measure. That still leaves an interior cylinder with a radius of 75 meters as a park or recreation area. It has 3/4ths of a G of gravity. The opposite side is more than 500 feet overhead – it will feel spacious enough, and 15+ acres of playgrounds, hiking paths, trees, and grass will provide a little bit of Earth in space.
But there’s no need to leave the end caps – the walls of our cylinder – as bare metal. We should build offices, low-gravity facilities (perhaps hospitals), hotels, etc. along those walls. Allocating 15 meters of depth along each end-cap for such purposes still leaves a hundred-meter-wide park, now with only 12 acres of usable space, 100 meters wide by 470 meters around. The lowest level of the end caps is a perfect place for shops and restaurants.
The above ramble describes the capacity of a 100-meter radius cylinder, spinning at 3 rpm to provide Earth-normal gravity. This spin rate is often considered the maximum for a rotating space habitat, as most people (but not all) can adjust to it. More people can adjust to 2 rpm, and essentially everyone has no problem with 1 rpm. So how much room do we get with these and larger structures? Can they be built?
This table shows the size, possible population, and mass (in kilotons or kT) of the external steel shell, the internal steel infrastructure, and the shield (total mass of steel shell plus rock). Note that once the steel shell reaches a mass of 10 tons per square meter, additional shielding is not needed. For a reference point, the total mass of steel in a modern aircraft carrier is about 60,000 tons, about 20% less than the smallest habitat. The dimensions given are of the habitable volume; the outer walls are assumed to be an extra 5 meters in thickness to provide the volume needed to contain the shield mass (but that extra external area raises the maximum population as well). The thickness of the outer steel shell is also given, in meters, and it ranges from 3cm (1.2 inches) in the 100 meter cylinder to 1.31 meters (4 feet) in the largest. The table also shows the percentage of the asteroid Apophis needed to build this structure, or alternatively the minimum size of a rocky asteroid large enough to build it. *Note that the largest structure would require a nickel-iron asteroid, as there is no rocky shield mass needed.
|Steel Shell (kT)||38||105||385||2,092||23,258||129,560||3,154,722|
|Steel Structure (kT)||36||71||168||519||2,584||8,117||68,166|
|Total Mass (kT)||1,653||3,273||7,769||24,018||119,664||376,078||3,222,888|
|% Apophis (27 mT)||6.12%||12.12%||28.78%||88.95%||443.20%||1392.88%||11936.62%|
It is clear that Apophis contains enough raw materials to build habitats supporting 125,000 colonists in up to 16 structures. It is interesting that a 1-kilometer nickel-iron asteroid (of which there are approximately 50,000 in the main belt) provides enough iron that (adding the resources of a small carbonaceous chondrite for carbon, oxygen, and water) a 9x6 kilometer cylinder could be built, supporting over 15 million people. Still larger structures may be constructed; steel has adequate tensile strength for structures large enough to support a billion people, but they become wildly inefficient, requiring nearly 10 times the steel per person.
I plan additional posts providing details on farming in space, on solar power satellites, and on the economics of life in space. It is clear that space habitats are feasible, and that commerce based upon tourism and the construction and maintenance of solar power satellites can pay for it. The obstacles are the difficulty of the bootstrap process:
- capturing an asteroid such as Apophis into Earth orbit
- Launching the tools to mine the riches of the asteroid, the tools to smelt its ores into steel and other valuable materials, the tools to shape that steel into the plates, beams, and girders needed to build things
- Launching the people to make it possible with enough consumables to get past the bootstrap.
- Designing and implementing closed-system recycling facilities capable of efficiently converting human wastes (and crop residues) into food, oxygen, and water.
Once enough infrastructure is in place, the colony should not need the addition of oxygen, water, food, or structural materials. High tech tools will be needed, including whatever is needed to construct solar cells, but the raw materials would already be in place. The Earth will export technology, tools, vitamins, pharmaceuticals, and people. In exchange, the Earth will receive bountiful energy from the Sun, with zero carbon footprint.
But that, too, will take time, energy, and especially people. In the long run, the demand for people in orbit is likely to exceed our capabilities of putting them there. And that, too, is the subject of a future post. | <urn:uuid:6a270838-120e-4dc2-bbe9-cf890b8f9054> | 3.375 | 2,625 | Personal Blog | Science & Tech. | 55.352559 |
Layzej writes "Two new papers indicate that we are likely already seeing some of the predicted impacts of global warming. The first used Monte Carlo simulations to analyze how many new record events you expect to see in a time series with a trend. They applied the technique to the unprecedented Russian heat wave of July 2010, which killed 700 people and contributed to soaring wheat prices. According to the analysis, there's an 80 percent chance that climate change was responsible. The authors have described their methods and how they improved on previous studies. The second group studied wintertime droughts in the Mediterranean region. They found that 'the magnitude and frequency of the drying that has occurred is too great to be explained by natural variability alone. This is not encouraging news for a region that already experiences water stress, because it implies natural variability alone is unlikely to return the region's climate to normal.'" | <urn:uuid:346d42c8-2bb5-4cf2-a2d3-bddeacb77888> | 2.9375 | 175 | Comment Section | Science & Tech. | 36.036644 |
SLOSH (Sea, Lake and Overland Surges from Hurricanes) is a computerized model run by the National Hurricane Center (NHC) to estimate storm surge heights and winds resulting from historical, hypothetical, or predicted hurricanes by taking into account pressure, size, forward speed, track and winds.
Graphical output (124kb or 348kb) from the model displays color coded storm surge heights for a particular area in feet above the model's reference level, the National Geodetic Vertical Datum (NGVD), which is the elevation reference for most maps.
The calculations are applied to a specific locale's shoreline, incorporating the unique bay and river configurations, water depths, bridges, roads and other physical features. If the model is being used to estimate storm surge from a predicted hurricane (as opposed to a hypothetical one), forecast data must be put in the model every 6 hours over a 72-hour period and updated as new forecasts become available.
The SLOSH model is generally accurate within plus or minus 20 percent. For example, if the model calculates a peak 10 foot storm surge for the event, you can expect the observed peak to range from 8 to 12 feet. The model accounts for astronomical tides (which can add significantly to the water height) by specifying an initial tide level, but does not include rainfall amounts, riverflow, or wind-driven waves. However, this information is combined with the model results in the final analysis of at-risk-areas.
The point of a hurricane's landfall is crucial to determining which areas will be inundated by the storm surge. Where the hurricane forecast track is inaccurate, SLOSH model results will be inaccurate. The SLOSH model, therefore, is best used for defining the potential maximum surge for a location.
For more information, visit NOAA Online.
St. Charles Parish SLOSH Models
(Click on each thumbnail to open a larger image in a new window. Please keep in mind the storm surge estimates do not take into account the elevation of particular areas. Storm surge predictions are made by taking this information into account.)
For more information, contact St. Charles Parish Public Information Officer Renee Allemand Simpson at (985) 783-5000 or firstname.lastname@example.org. | <urn:uuid:5e904fc9-0c1a-484f-87b9-b790d6416511> | 3.234375 | 462 | Knowledge Article | Science & Tech. | 35.896066 |
Sci. STKE, 12 September 2006
PLANT BIOLOGY Touché! Plants and Bacteria Battle at Leaf Pores
Plants have special openings on the surface of the leaf known as stomata, which allow gas exchange essential for respiration and osmotic balance. However, the stomata also provide a route by which infectious bacteria can gain access to internal tissues. The stomata are opened and closed in response to changes in exposure to light, humidity, and other stimuli, but new evidence shows that they can also be closed as part of the plants' immune defense against bacterial infection. Melotto et al. showed that Arabidopsis plants closed their stomata within 2 hours of exposure to the pathogenic bacterium P. syringae but then reopened them within a couple more hours. Microscopic observation of the bacteria showed that they were able to detect and migrate toward open stomata, perhaps sensing nutrients or other molecules released from the plant interior. The authors showed that flg22, a peptide derived from the bacterial flagellin protein, or lipopolysaccharide, a component of the bacterial outer cell wall, could also trigger stomatal closure. Plants are known to have immune receptors that recognize these molecules. The reopening of the stomata observed when leaves were exposed to whole bacteria led the authors to test whether the strain of P. syringae that they used produced a virulence factor to override the host plant's protective mechanism. Indeed, they found that the bacterially produced polyketide toxin coronatine was required to allow reopening of the stomata. The work reveals that plants have developed an innate immune mechanism to protect themselves from bacterial invasion and that, in response, some bacteria have developed a virulence factor that forces the pores open again to allow further infection.
M. Melotto, W. Underwood, J. Koczan, K. Nomura, S. Y. He, Plant stomata function in innate immunity against bacterial invasion. Cell 126, 969-980 (2006). [Online Journal]
Citation: Touché! Plants and Bacteria Battle at Leaf Pores. Sci. STKE 2006, tw315 (2006).
Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882 | <urn:uuid:5f6a3fc9-0fad-4906-89a7-fe02130381e2> | 3.515625 | 493 | Academic Writing | Science & Tech. | 43.048826 |
This, from the free daily UK paper called the Metro:
- "If you felt a bit soggy while walking through the snow this week, it's because your relatives were sponges. Well, your ancestors who lived 635 million years ago were.
Mankind is thought to have evolved from primitive sea sponges, according to a study of fossils found in rocks in Oman.
They are thought to date to the last ice age, according to the US research in Nature journal."
- Meet the ancestors: Earliest evidence of life suggests humans descended from sponges 635 million years ago
- "Now scientists say they have discovered the missing link in the chain of evolution. They have found evidence of the oldest animal life yet discovered on Earth – ancient sponges that lived 635 million years ago".
Anyone reading this on the 8.20 tube from Cockfosters would understand that the research is about discovering ancestors (i.e., missing links, a poriferan Adam & Eve). I had to see what Brocks & Butterfield (2009) wrote about 'ancestors':
- "So, what exactly were the organisms that produced these biomarkers? The most obvious answer, and the one that the authors plump for, is that demosponges had evolved and become ecologically prominent by at least the late Cryogenian. But this conclusion overlooks the evolutionary nature of biological taxa and the incremental assembly of defining characteristics along (now-extinct) 'stem lineages'. It is only with a full complement of such characteristics — in the last common ancestor of the extant 'crown group' — that modern taxonomic boundaries apply (...) Combined with new biomarker data and molecular phylo genomics, the identification of such signals promises to pinpoint the first appearance of our earliest animal ancestors." (Brocks and Butterfield, 2009: 673).
The Daily Mail Online however, do go on to publish a Reuters report by Michael Kahn that best summaries the research: "Chemical traces left in 635 million-year-old rocks in Oman provide the earliest evidence so far of animal life, researchers said Wednesday". Why the Mail didn't go with Reuter's original title Scientists find earliest evidence of animal life has more to do with sensationalism than with science journalism.
Jochen J. Brocks, Nicholas J. Butterfield (2009). Biogeochemistry: Early animals out in the cold Nature, 457 (7230), 672-673 DOI: 10.1038/457672a | <urn:uuid:6e02f333-c3d3-43c0-a9cc-020297cd2558> | 3.125 | 523 | Comment Section | Science & Tech. | 47.497408 |
WordCount Example in Python
The program reads text files and counts how often words occur. The input is text files and the output is text files, each line of which contains a word and the count of how often it occured, separated by a tab. To create some input, take your a directory of text files and put it into DFS.
bin/hadoop dfs -put my-dir in-dir
Each mapper takes a line as input and breaks it into words. It then emits a key/value pair of the word and 1. Each reducer sums the counts for each word and emits a single key/value with the word and sum.
As an optimization, the reducer is also used as a combiner on the map outputs. This reduces the amount of data sent across the network by combining each word into a single record.
To compile the example, build the Hadoop code and the python word count example:
ant cd src/examples/python ./compile cd ../../..
Note that you need to have jythonc and javac on your path for the compilation to work.
To run the example, the command syntax is:
bin/hadoop jar src/examples/python/wc.jar in-dir out-dir
The results of the word count will be in out-dir/part-*. | <urn:uuid:84d7d53e-7a88-4b17-817f-c836c9ec7b43> | 3.546875 | 288 | Documentation | Software Dev. | 76.271389 |
Fluid Thread Patterns
Thin threads of fluids show how conveyor belt speeds control fluid pattern behavior in both experiments and models. A thin thread of viscous fluid (translucent threads at left) is poured onto a moving belt, creating a dazzling array of intricate patterns. Simulations (gold threads at right) reproduce this rich and complex behavior, confirming the accuracy of a theoretical model developed to describe the phenomenon.
Reporters and Editors
Reporters may freely use this image. Credit format: Image courtesy of Columbia University (2011). | <urn:uuid:a6b79502-7ba7-46fb-a1c2-3dd995d5c3ea> | 3.421875 | 109 | Truncated | Science & Tech. | 34.683 |
In this blog i have explained OOPS Features of C# in brief to help new comer's to crack an interview,i have explained these feature in brief because of focsing on new comer's to give them a idea how to answer thes questions which are often asked in an interview .
programming in which data is logically represented in the form of a class and
physically represented in the form an object is called as object oriented
programming (OOP). OOP has the following important features.
In OOP languages it is must
to create a class for representing data. Class contains variables for storing data
and functions to specify various operations that can be performed on data. Class
will not occupy any memory space and hence it is only logical representation of
Within a class variables are
used for storing data and functions to specify various operations
that can be performed on data. This process of wrapping up of data and functions
that operate on data as a single unit is called as data
encapsulation. Within a class if a member is
that member can
not be accessed from out side the class. I.e. that member is
hidden from rest of the program. This process of hiding the details of a class
from rest of the program is called as data abstraction. Advantage of data
abstraction is security.
Class will not occupy any
memory space. Hence to work with the data represented by the
class you must create a variable for the class, which is called as an object.
When an object is created by using the keyword new, then memory
will be allocated for the class in heap memory area, which is called as an
instance and its starting address will be stored in the object in stack memory
When an object is created without
the keyword new, then memory will not be allocated in heap I.e. instance will
not be created and object in the stack contains the value null.
When an object contains null, then it is not possible to access the members of
the class using that object.
Creating a new class from an
existing class is called as inheritance. When a
new class requires same
members as an existing class, then instead of recreating those members the new
class can be created from existing class, which is called as inheritance.
Advantage of inheritance is reusability of the code. During inheritance, the
class that is inherited is called as base class and the class that does the
inheritance is called as derived class.
Polymorphism means having
more than one form. Polymorphism can be
achieved with the help of
overloading and overriding concepts. Polymorphism is classified into compile
time polymorphism and runtime polymorphism.
I hope this blog is useful for all readers,if you have any suggestion then contact me. | <urn:uuid:886541f2-eb3a-4752-b999-da437f733bce> | 3.359375 | 587 | Personal Blog | Software Dev. | 49.700203 |
Nematodes are nonsegmented roundworms that are abundant in freshwater lakes. Nematodes often comprise 15% of the total biomass on lake bottoms. This reflects the incredible abundance of these organisms, since most only grow to a maximum length of a centimeter.
Life stages of these species are often as complex as they are abundant. Some are free living their entire lives while others are only free living as adults or juveniles. At other stages some are parasitic on invertebrates, vertebrates, or even plants.
Most freshwater free-living nematodes are about 1 mm in length though parasitic forms are often even smaller. Their body wall is covered by a cuticle that is four layers thick. As the worm grows it moults, sloughing off the outer layer. At the same time another layer is created on the inside. The pseudocoel is small in the free-living forms but tends to be much larger in the parasitic forms. All freshwater nematodes bear a spinneret at the tip of their hind end that secretes a sticky mucous which anchors the worm in place whether it be a on rock or inside an intestine.
Non-parasitic roundworms are adapted to swimming along lake and stream bottoms. In fact "swimming" may not be an accurate word to describe their motion. Nematodes have only longitudinal muscles for movement, unlike segmented worms (like earthworms) that also have circular muscles to help with locomotion. Movement is therefore limited to a side-to-side flailing that pushes them forward.
Nematodes have a pair of amphids (one on each side of the body) which are structures at the anterior end of the worm that were once considered to aid in equilibrium. Now, they are seen as chemosensory structures, perhaps for the purpose of detecting food. Due to the wide variation their structure, amphids are also used to classify horsehair worms taxonomically. Some freshwater species have separate light sensors referred to as ocelli or pseudocelli. They are seen as pigmented spots also situated at the anterior end.
Most nematode species are aerobic, meaning that they need oxygen to survive. However, some species can survive short periods of anoxia, and a few can live without oxygen indefinitely. There are not any specialized systems for acquiring oxygen for any member of this phylum. Because they are small animals with a large surface area, they can exchange gases through the skin surface with enough efficiency to survive.
Nitrogenous waste is eliminated though the body wall in the form of ammonium ions. Osmoregulation, and excretion of other metabolites is controlled either by excretory gland cells, an excretory canal system, or a combination of both. These structures are unique to the nematodes.
Nematodes usually possess separate sexes and all fertilization is internal. In most freshwater species the males have spicules that enter the female's vagina where the sperm is released Other species specialize in "traumatic fertilization" in which the male simply punctures the cuticle of the female with his spicules and releases the sperm directly into her body cavity.
Feeding structures and strategies are determined by the lifestyle of the nematode. Species parasitic on plants have stylets within the stoma (mouth) that can be extended outward and into the plant tissues. These stylets are used like straws to suck out nutritious plant juices. Species parasitic on invertebrates have a slightly modified stylet of the same nature to pierce the cuticle of their prey, for the purpose of feeding on haemolymph. Nematodes that feed on microorganisms need only a small tubular stoma to engulf their prey. Finally, the predators have an enlarged stoma with either a spear-like structure or rows of pointed teeth.
Predaceous nematodes are often the worst enemies of other nematodes. This is understandable since both have roughly the same oxygen and pH requirements, so they therefore live in the same places on the lake bottom. Other predators include crayfish, turbellarians, and nemertean worms. Freshwater nematodes are often infected with protozoan diseases and microsporidia.
Freshwater nematodes survive in very diverse environments. Many species that exist in Canada are apparently found all over the world. Some species can survive in snow pools while others occur in hot springs. Aphelenchoides sp. can survive in a temperature of 61.3°C, the highest temperature tolerance by any multi-celled animal on the planet. Most nematodes have drought-resistant stages in which the roundworm becomes inactive. This attribute is most common in the juvenile stages as this is the most sensitive period for many freshwater species. A steady supply of food and oxygen are necessities for health and growth and when these become unavailable the quickest defense is to dry down until conditions improve. Some species have been known to survive in a dried state for up to 25 years before being reanimated in water. These dessication-resistant stages are the primarily means of dispersal. Flash floods or high winds can carry these nematodes to different areas. There is even the possibility of transport in mud that is attached to animals that frequent different water bodies for drinking or bathing.
Eutely is a phenomenon found in a few organisms, including nematodes, wherein each member of a species has exactly the same number of cells. For example, males of the species Caeonorhabditis elegans have exactly 1031 cells, while females have 959 cells, almost half of which are designated to the nervous system. | <urn:uuid:692fb250-5513-48d8-9012-6601c442388e> | 4.21875 | 1,162 | Knowledge Article | Science & Tech. | 32.649554 |
Predation Did Not Come from Evolution
by Daniel Criswell, Ph.D. *
Although the origin of predation is poorly understood, it is incorrect to attribute to young-earth creation the assertion that predatory animals quickly and recently evolved the physical features necessary for predation. It is a common fallacy that carnivores evolved from a change in form and function. No physical evolution was required to change herbivores to predators--it was merely a change in behavior.
The view that an alteration of genomes and phenotypes, such as sharp teeth and claws, would have been required to supply the physical features for predation from herbivorous features common in plant-eating animals is not correct. The shape of the teeth, the ability to run fast for short distances, and all the other physical attributes given to predators can be used for acquiring plant food sources as well. A few examples of mammal diets will verify this quite well.
Large, sharp teeth are not used solely for killing and ripping flesh from other animals. Fruit bats have sharp, pointed teeth, similar to those in cats, designed to quickly tear flesh from fruit. These teeth easily could remove flesh from an animal, but the fruit bat does not use them for this purpose. The same teeth in many kinds of predatory animals used to shred meat can also be used to shred plant material.
Large canine teeth are also used in communication. Many animals--including chimpanzees, dogs (wild and domestic), big cats, and other predators--expose their canines to communicate ownership of mates, animal groups, food resources, and territory. Teeth are vital to the success of animals, both for communication as well as for feeding.
Bears of the American northwest provide the best example in the wild of how behavior determines diet. Grizzly bears and black bears are well-equipped to destroy the life of other animals. But they also use their physical tools to eat fruits and vegetables. As a biologist, I have personally witnessed bears clean apples out of an apple tree, consume large quantities of clover, and strip all the berries from wild raspberry, huckleberry, and choke cherry plants. These activities are also well documented in the scientific literature. Although classified as carnivores, bears are actually opportunistic omnivores and are quite capable of living off a vegetarian diet if the food source is available. Many "meat-eating" animals fall into this category. This "predatory" animal, like others, will eat the most nutritious meals that are the most easily obtainable.
Domesticated animals also provide an excellent example of how the behavior of an animal can be altered to utilize a specific food source. Dogs and cats have the same tooth structure as wild wolves and lions, respectively, yet these animals are able to change their behavior and eat processed food (cereal) made mostly from corn meal, soybean meal, and rice.
The ability and desire to eat prepared cereal or "chow" emphasizes another misconception concerning social predators. Most people are under the impression that these animals are after the same meat that we would use for roasts and steaks. They aren't. The choice portions of a killed herbivore are the internal organs that are rich in vitamins and other nutrients acquired from a vegetarian diet. This is what social predators, like wolves and lions, are after. The lower ranking animals are left with the steaks, roasts, and bones, while the higher ranking animals enjoy the benefits of a more nutritious, "vegetarian" diet found in the gut. The need for predation by these animals clearly results from a change in behavior, not from a change in form and function. It is also interesting to note that, typically, predators have to learn to kill. Social predators are not born with the knowledge of how to hunt and kill. They must learn these skills from the other animals in their group.
A change in form and function implies evolution has occurred through new genetic information, while a change in behavior requires no new genetic information. The latter is what we clearly observe, and it is perfectly consistent with a literal rendering of Genesis 1:30: "And to every beast of the earth, and to every fowl of the air, and to every thing that creepeth upon the earth, wherein there is life, I have given every green herb for meat: and it was so."
* Dr. Daniel Criswell has a Ph.D. in Molecular Biology.
Cite this article: Criswell, D. 2009. Predation Did Not Come from Evolution. Acts & Facts. 38 (3): 9. | <urn:uuid:7c3ae2d6-280f-4242-becc-3823e717b85e> | 3.453125 | 931 | Truncated | Science & Tech. | 43.610463 |
SWADDLED in a cloud of dust and gas, a baby solar system 450 light years away offers one of the best peeks yet at what our sun may have looked like in its infancy. The star is surrounded by enough raw material to build at least seven Jupiter-sized planets.
But it was unclear from previous studies whether the disc of debris swirling around developing star L1527 IRS was moving in the necessary way to spawn planets.
John Tobin of the National Radio Astronomy Observatory in Charlottesville, Virginia, and colleagues found that the disc's motion mirrors the way planets orbit stars, hinting that it has all the right moves for planet formation (Nature, doi.org/jxm).
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Air Pressure and Resistance
Name: Loretta H.
Is there a relationship between air pressure and air
resistance? Recently, I had said that the air resistance acting on a
falling object is actually the air pressure that is acting on the object.
This did not sound right. Air pressure that is acting on an object is I
know a constant value per square area. However, what I was trying to say
was that since air resistance is actually a force that is acting on the
falling object and it is acting on every area of the object, and since we
know that Pressure = Force divided by Area, therefore, air resistance is
somehow related to the pressure of air acting on that object. Please do
enlighten me on this. Thanks.
Air resistance is due to the force exerted on the air by the falling
object to push the air aside to let the object proceed through the
air. By Newton's third law (for every force there is an equal and
opposite reaction) the air pushes on the object with an equal and
opposite force. The air comes together behind the object, of course,
but the resulting pressure there is less that the pressure in front of
the object. The difference in these pressures (times an area, as you
mention) is the cause of the air resistance.
Since, for a stationary object, the air pressure is equal on all sides
of the object, it exerts no net force on the object. If the air
pressure is increased, the net force on a stationary object is still
zero. The net force on a moving object will increase due to the fact
that the air is denser and the object has to push more air aside.
The detailed calculation of air resistance is complicated, but the
basic idea, as stated here, is simple.
Best, Dick Plano
Hi, Loretta !!!
I can only understand this problem by considering
that the bigger the pressure, the more resistance
there will be against the movement of a body.
And that because there will be more air to be
crossed. The behavior of the limit layer surely
will show us that at the front the pressure will
be greater than behind, where greater turbulence
should be expected. If there were no movement
the only force acting on the body is that due to
pressure differences, vertical, from the bottom to
the top. This force is independent from the value
of pressure. If the body moves across the air,
there will be a greater pressure ahead and vacuum
at the tail ( depending upon how big is the speed ).
If a body falls, the resistance will be increasingly
bigger, till it reaches a value where there will be no
more acceleration, or be, constant speed. On the
other extreme, without air, there always will be
acceleration, what means increasing velocity.
When comets reach the earth atmosphere - as
you know - the friction is so high that the tempe-
ture increases and oxygen starts a chemical
reaction and burns the comet. In a planet where
the gravity is bigger than at the earth, there will
be more gases present, and the friction will be
You are ok in this as long as you are careful about what you mean by air
pressure. The pressure that acts to oppose an object moving through
air is not the ambient air pressure. That pressure exerts the same
force on all sides of the object, so the net force from it is zero.
When an object moves through the air, its motion causes the air
pressure in front to increase while the pressure behind decreases, and
this pressure difference produces a net force on the object. If the
object suddenly stops moving, it will take a while for the higher
pressure air in front to leak around to the back, and while this is
happening, the object will still feel a net force from the pressure
difference. So it is the pressure that causes the force.
But drag is more complicated than this because there are other things
that happen as the object moves. The air and the object are heated,
there is turbulence, jets make a condensation trail, etc. All of these
things must be "paid for" out of the momentum (and energy) of the
moving object, and any time momentum changes, there is by definition a
force of some kind.
There is a relation between air pressure and air resistance, but air
resistance and air pressure are not the same thing. If air pressure were
zero, air resistance would also be zero. Still non-zero air pressure does
not mean any air resistance is being felt.
Air pressure is from all directions. Air pressure can be different on
different parts of an object, but in most cases it is quite large all
around. Air pressure is due to molecules crashing into the object from all
Air resistance is due to the motion of an object through the air. The
object pushes the air molecules out of the way. The molecules push back.
Because the air molecules in front get squeezed together more tightly,
pressure in front is greater. Air molecules in back get a little spread
out, so air pressure in back is less. The net effect is a force opposite
the direction of motion.
Just as important to air resistance is the shape of the moving object. A
narrow, pointed object pushes the molecules aside quite easily. A flat
front must push the molecules harder to get them to the side. It is like
hammering a sharp nail versus a dull peg into a piece of wood. For an
arrow, the air molecules in front do not get so tightly squeezed together as
for the dull peg.
Air pressure may be viewed as part of why air resistance exists, but it is
not air resistance itself.
Dr. Ken Mellendorf
Illinois Central College
Air pressure does act on all (exposed) surfaces of an object. The presence of
air pressure does not depend on the state of motion of an object, or even the
presence of an object. It is a property of the air alone.
Wind resistance can only be talked about in terms of the resistance to motion
of an object in the air. The presence of a body to be acted on and the motion
of the air around it creates an increase in the air pressure in front of the
object compared to the air pressure behind the object. This DIFFERENCE in air
pressure results in a new force resisting the motion of the object, which we
call wind resistance.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:06d4b085-8c24-4c00-8131-bf1405beaba3> | 3.40625 | 1,390 | Q&A Forum | Science & Tech. | 53.916471 |
Mathematica Notebook for This Page.
All trignometric functions sine, cosine, tangent, secant, cosecant, cotangent can all be simply defined in terms of a single function sine. Sine, as associated with trigonometry, began in early civilization as a very important measuring science. When the function concept and calculus and analytic geometry were introduced in about 1700, sine became a function and has little to do with triangles. The sine function appears unexpectedly throughout analysis, because in essence it captures the idea of a wave, a fundamental concept in physics.
From Robert Yates:
Trigonometry seems to have been developed, with certain traces of Indian influence, first by the Arabs about 800 as a aid to the solution of astronomical problems. From them the knowledge probably passed to the Greeks. Johann Müller (c.1464) wrote the first treatise: De triangulis omnimodis; this was followed closely by others.
See also: History of trigonometric functions.
Sine curve is the curve of the sine function. It is also known as sinusoid. Sine is sometimes called circular function because the essential feature of the sine function can be thought of as a point moving around a circle in constant speed, and the value of sine being the height of the point.
Step by step description:
In the formula y == a*Sin[x/p+s], a is the amplitude, p the period, and s the phase shift. sine_plot.gcf
All trig functions is defined in terms of sine.
If a right triangle is placed in a standard position (That is: in the Cartesian coordinate system such that it lies in the first quadrant, and the right angle vertex lies on the x-axes, and the hypotenuse touches the origin), and if r denote (the length of) the hypotenuse, x the bottom side, y the vertical side, θ the angle of x and r, then we have the following formulas:
|Sin[θ] == y/r|
|Cos[θ] == x/r|
|Tan[θ] == y/x|
See: List of trigonometric identities.
Sine curve is the development of a obliquely cut right circular cylinder. (the edge of the cylinder rolled out is a sinusoid). graphics code..
Tracing Sinusoid Sinusoid Fun Animation
Robert Yates: Curves and Their Properties.
Trigonometric functions.blog comments powered by Disqus | <urn:uuid:045fd621-b315-45a4-b532-be448460ba76> | 4.125 | 544 | Tutorial | Science & Tech. | 48.515928 |
Serving wine usually involves a rather elaborate ceremony in which the host tastes the wine before pouring it for the guests. One reason for this is the possibility that the wine may have been spoiled by exposure to air.
Certain bacterial enzymes are capable of converting ethanol to ethanoic acidIn Arrhenius theory, a substance that produces hydrogen ions (hydronium ions) in aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bond. (acetic acid) when oxygen is present:
The same reaction occurs when cider changes into vinegar, which contains 4 to 5 percent acetic acid. Acetic acid gives vinegar its sour taste and pungent odor and can do the same thing to wine.
Acetic acid, CH3COOH, is an example of the class of compounds called carboxylic acids, each of which contains one or more carboxylThe functional group consisting of a carbon atom bonded to a hydroxyl group and doubly bonded to an oxygen atom; found in carboxylic acids: -C(=O)OH. groups, COOH. The general formula of a carboxylic acid is RCOOH. Some other examples are
Formic acid (the name comes from Latin word formica meaning “ant“) is present in ants and bees and is responsible for the burning pain of their bites and stings. Butyric acid, a component of rancid butter and Limburger cheese, has a vile odor. Adipic acid is an example of a dicarboxylic acid—it has two functional groups—and is used to make nylon.
Since the carboxyl group contains a highly polarDescribes a molecule that has separated, equal positive and negative charges that consitute a positive and a negative pole; such a molecule tends to assume certain orientations more than others in an electric field. as well as an OH group, hydrogen bonding is extensive among molecules of the carboxylic acids. Pure acetic acid is called glacial acetic acid because its melting pointThe temperature at which a solid becomes a liquid. Also called freezing point. of 16.6°C is high enough that it can freeze in a cold laboratory. As you can see from the table below, acetic acid boils at a higher temperatureA physical property that indicates whether one object can transfer thermal energy to another object. than any other organic substance whose molecules are of comparable size and have but one functional group. It is also quite thick and syrupy because of extensive hydrogen bonding.
Boiling Points of Some Organic Compounds Whose Molecules Contain 32 or 34 Electrons.
Below is a Jmol model of acetic acid. In the general menu to the left, click on partial charges. Each atom in the molecule will be assigned a partial charge. It is clear that the oxygen atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. are sharing electrons unequally and causing other parts of the molecule to gain a partial positive charge in the carboxyl carbon and hydrogen. Further, this induces a partial negative charge on the methyl carbon, leading to positive charges on the methyl hydrogen atoms.
An even better way to view the electron distribution is with the Molecular Electrostatic Potential (MEP) Surface options. One can look at "MEP on isopotential surface", which show surfaces where electrostatic potential is the same, but the most informative option here is the "MEP on Van der Waals Surface" radio button. This shows the potential along the van der Waals surface of the molecule. The closer to red on the color spectrum, the more negative the potential at that surface is, the closer to blue, the more positive. One can see that both oxygen atoms are centers of partial negative charge, while the acidic hydrogen atom has a substantial partial positive charge, and the methyl group is also has a partial positive charge. One more way to look at the molecule, is to use the "MEP on a plane" button. Choose the XY plane, and then click "Set Plane Equation." This will show the electrostatic potential along the axis of symmetry for the molecule. While two hydrogen atoms on the methyl group are out of the plane, this view still allows one to see how partial charge is distributed along the backbone of the molecule in a way the van der Waals surface does not. From this modeling of the acetic acid molecule, hopefully it is becoming clear how the macroscopic properties we discussed arise.
Acetic acid is synthesized commercially according to the reaction shown above, but silver is used as a catalystA substance that increases the rate of a chemical reaction but that undergoes no net change during the reaction. instead of bacterial enzymes. It is also prepared by reading air with propane separated from natural gasA state of matter in which a substance occupies the full volume of its container and changes shape to match the shape of the container. In a gas the distance between particles is much greater than the diameters of the particles themselves; hence the distances between particles can change as necessary so that the matter uniformly occupies its container.. The liquidA state of matter in which the atomic-scale particles remain close together but are able to change their positions so that the matter takes the shape of its container acetaldehyde obtained in this reaction is then combined with oxygen in the presence of manganese(II) acetate to make acetic acid. About half the acetic acid produced in the United States goes into cellulose acetate from which acetate fibers are made. | <urn:uuid:e66e40a8-9165-40c0-9c90-f4295980351d> | 3.515625 | 1,194 | Knowledge Article | Science & Tech. | 32.01548 |
Just to clear up a common misconception, one that seems to be at the root of every newcomer's approach to coding for standards, you do not use divs instead of tables. That's important enough to repeat, "you do not use divs instead of tables".
What do you use? You use well structured, semantic and well formed html instead of table layouts. A non-trivial table layout cannot be well structured nor semantic, though it can contain well formed (valid) html.
The div element is a non-semantic structural container that lets you form groupings of other, semantic, elements. Notice, I said elements. A div should never contain bare nekkid content, only elements.
These groupings provide independent styling contexts. Think of the div as a drawer in a chest. You can arrange and re-arrange the socks, handkerchiefs and underwear in one drawer (div) without affecting the contents of other drawers. Further, you can arrange and re-arrange the positioning of the drawers in the chest without affecting the contents of the drawers.
Keep in mind that the div is semantically neutral. It says nothing about what its %flow element contents are. Use the div only for its proper structural purposes. Replacing tables is not it. | <urn:uuid:9d2852e2-12ae-406e-8b2b-a3c32618f5e4> | 2.765625 | 267 | Personal Blog | Software Dev. | 58.425177 |
|Back to . . .
Clerk Maxwell ( 1831-1879 )
14 India Street
epoch ended and another began with James Clerk Maxwell."
"The special theory
of relativity owes its origins to Maxwell's
equations of the electromagnetic field."
James Clerk Maxwell was one of the greatest scientists and
mathematicians of the 19th century. With talents rarely united
today, he made landmark
contributions to both theoretical and experimental science.
Maxwell published phenomenal work in two areas. First, building
upon the experimental data of Michael
Faraday, and applying highly sophisticated mathematical methods,
he predicted the existence of electromagnetic waves (1864).
Moreover, he calculated the waves would travel at the speed of
Later, Heinrich Hertz discovered these waves (1887) thereby
paving the way for radio, television, radar, and even the boom in
computer science. For Maxwell, the great mental
breakthrough came in thinking of electricity as an electromagnetic
not some sort of mechanical process.
"The true logic of
this world is in the calculus of probabilites."
James Clerk Maxwell
Maxwell's other spectacular contribution was in the dynamical theory of
gases. His first great paper in the field was published in
1859. Today this subject is part of thermodynamics.
Willard Gibbs, on the other side of the Atlantic at Yale University,
would join Maxwell in opening the door for exploration of the
physical and chemical properties of gases and other states of matter.
As is evident by his place of birth, Maxwell was the son of prosperous
parents. He was educated across town at the University of
Edinburgh, entering at the age of 16, and then Trinity College,
Cambridge. Eventually he became Cambridge University's first
teacher of experimental physics. He left retirement to serve as
the founding director of the Cavendish Laboratory of Cambridge
He is buried with his family in the church yard of
Parton Kirk, Galloway, Scotland.
| The house
where Maxwell was born is in a nice neighborhood near a park close to
the center of Edinburgh. The house now serves as a meeting place
for mathematicians and scientists and is home of the Foundation.
|Feynman on Maxwell's Contributions
the most dramatic moment in the development of physics during the 19th
century occurred to J. C. Maxwell one day in the 1860's, when he
combined the laws of electricity and magnetism with the laws of the
behavior of light. As a result, the properites of light were partly
unravelled -- that old and subtle stuff that is so important and
mysterious that it was felt necessary to arrange a special creation for
it when writing Genesis. Maxwell could say, when he was finished
his discovery, 'Let there be electricity and magnetism, and there
Feynman in The Feynman
Lectures on Physics, vol.
of the JCM Foundation at 14 India Street . . . .
"To promote, encourage, and advance the study of, research into, and
the dissemination of knowledge of and relating to physics, chemistry
and physical chemistry in all their aspects and in particular, but
without prejudice to the foregoing generality, colloids and interfaces."
Scotland has honored Maxwell
in a number of significant ways . . .
and at Yale
|Maxwell himself on how to visualize a
single center of electrified force . . . .
"I am anxious that these diagrams should
be studied as illustrations of the language of Faraday in speaking of
'lines of force,' the 'forces of an electrified body,' etc. . . .
Now the quantity of electricity in a body is measured, according to
Faraday's ideas, by the number
of lines of force, or rather of induction, which proceed from it.
These lines of force must all terminate somewhere, either on bodies in
the neighborhood, or on the walls and roof of the room, or on the
earth, or on the heavenly bodies, and wherever they terminate there is
a quantity of electricity exactly equal and opposite to that on the
part of the body from which they proceeded. By examining the
diagrams this will be seen to be the case.
These diagrams are constructed in the following
manner:- First, take the case of a single centre of
force, a small electrified body with a charge E. The potential at a
is V = (E/r); hence, if we make
r = (E/V), we shall find r, the radius of the sphere for
which the potential is V
If we now give to V the
values 1, 2, 3, etc., and draw the corresponding spheres, we shall
obtain a series of equipotential surfaces, the potentials corresponding
to which are measured by the natural numbers. The sections of
these spheres by a plane passing through their common centre will be
circles, which we may mark with the number denoting the potential of
each. These are indicated by the dotted circles on the right
James Clerk Maxwell, "An elementary treatise on electricity,"
of this material will join the National
Bank - A MATH Archive in thanking the Huntington Library, San
Marino, CA, for permitting us to enjoy Maxwell's explanation and
assuming there is no
or magnetic material (free space).
Note #4 is the same equation as
on the San Marino stamp.
Hertz on the left with Maxwell
on the right. | <urn:uuid:944e23b5-e2d2-48db-9603-b8e7fe4abc96> | 3.203125 | 1,160 | Knowledge Article | Science & Tech. | 47.083809 |
#include <stdlib.h>char *getpass(const char *prompt);
#include <unistd.h>char *getpass(const char *prompt);
The getpass() function opens the process's controlling terminal, writes to that device the null-terminated string prompt, disables echoing, reads a string of characters up to the next newline character or EOF, restores the terminal state and closes the terminal.
The getpassphrase() function is identical to getpass(), except that it reads and returns a string of up to 256 characters in length.
Upon successful completion, getpass() returns a pointer to a null-terminated string of at most PASS_MAX bytes that were read from the terminal device. If an error is encountered, the terminal state is restored and a null pointer is returned.
The getpass() and getpassphrase() functions may fail if:
The function was interrupted by a signal.
The process is a member of a background process attempting to read from its controlling terminal, the process is ignoring or blocking the
SIGTTIN signal or the process group is orphaned.
OPEN_MAX file descriptors are currently open in the calling process.
The maximum allowable number of files is currently open in the system.
The process does not have a controlling terminal.
The return value points to static data whose content may be overwritten by each call.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE| | <urn:uuid:1960dbfd-a7c7-471a-bfcb-14f2049c3a7a> | 3.015625 | 323 | Documentation | Software Dev. | 43.052737 |
The Application Programmer's Interface to Python gives C and C++ programmers access to the Python interpreter at a variety of levels. The API is equally usable from C++, but for brevity it is generally referred to as the Python/C API. There are two fundamentally different reasons for using the Python/C API. The first reason is to write extension modules for specific purposes; these are C modules that extend the Python interpreter. This is probably the most common use. The second reason is to use Python as a component in a larger application; this technique is generally referred to as embedding Python in an application.
Writing an extension module is a relatively well-understood process, where a ``cookbook'' approach works well. There are several tools that automate the process to some extent. While people have embedded Python in other applications since its early existence, the process of embedding Python is less straightforward than writing an extension.
Many API functions are useful independent of whether you're embedding or extending Python; moreover, most applications that embed Python will need to provide a custom extension as well, so it's probably a good idea to become familiar with writing an extension before attempting to embed Python in a real application. | <urn:uuid:da5fb3b0-48cd-4024-9047-45131b2274e3> | 2.96875 | 244 | Documentation | Software Dev. | 28.808571 |
Partition function (statistical mechanics)
In physics, a partition function describes the statistical properties of a system in thermodynamic equilibrium. They are functions of temperature and other parameters, such as the volume enclosing a gas. Most of the aggregate thermodynamic variables of the system, such as the total energy, free energy, entropy, and pressure, can be expressed in terms of the partition function or its derivatives.
There are actually several different types of partition functions, each corresponding to different types of statistical ensemble (or, equivalently, different types of free energy.) The canonical partition function applies to a canonical ensemble, in which the system is allowed to exchange heat with the environment at fixed temperature, volume, and number of particles. The grand canonical partition function applies to a grand canonical ensemble, in which the system can exchange both heat and particles with the environment, at fixed temperature, volume, and chemical potential. Other types of partition functions can be defined for different circumstances; see partition function (mathematics) for generalizations.
Canonical partition function
As a beginning assumption, assume that a thermodynamically large system is in constant thermal contact with the environment, with a temperature T, and both the volume of the system and the number of constituent particles fixed. This kind of system is called a canonical ensemble. Let us label with s = 1, 2, 3, ... the exact states (microstates) that the system can occupy, and denote the total energy of the system when it is in microstate s as Es. Generally, these microstates can be regarded as analogous to discrete quantum states of the system.
The canonical partition function is
where the "inverse temperature", β, is conventionally defined as
with kB denoting Boltzmann's constant. The exponential factor exp(−βEs) is known as the Boltzmann factor. (For a detailed derivation of this result, see canonical ensemble). In systems with multiple quantum states s sharing the same Es, it is said that the energy levels of the system are degenerate. In the case of degenerate energy levels, we can write the partition function in terms of the contribution from energy levels (indexed by j ) as follows:
where gj is the degeneracy factor, or number of quantum states s which have the same energy level defined by Ej = Es.
The above treatment applies to quantum statistical mechanics, where a physical system inside a finite-sized box will typically have a discrete set of energy eigenstates, which we can use as the states s above. In classical statistical mechanics, it is not really correct to express the partition function as a sum of discrete terms, as we have done. In classical mechanics, the position and momentum variables of a particle can vary continuously, so the set of microstates is actually uncountable. In this case we must describe the partition function using an integral rather than a sum. For instance, the partition function of a gas of N identical classical particles is
- pi indicate particle momenta
- xi indicate particle positions
- d3 is a shorthand notation serving as a reminder that the pi and xi are vectors in three dimensional space, and
- H is the classical Hamiltonian.
The reason for the factorial factor N! is discussed below. For simplicity, we will use the discrete form of the partition function in this article. Our results will apply equally well to the continuous form. The extra constant factor introduced in the denominator was introduced because, unlike the discrete form, the continuous form shown above is not dimensionless. To make it into a dimensionless quantity, we must divide it by h3N where h is some quantity with units of action (usually taken to be Planck's constant).
where Ĥ is the quantum Hamiltonian operator. The exponential of an operator can be defined using the exponential power series. The classical form of Z is recovered when the trace is expressed in terms of coherent states and when quantum-mechanical uncertainties in the position and momentum of a particle are regarded as negligible. Formally, one inserts under the trace for each degree of freedom the identity:
where |x, p⟩ is a normalised Gaussian wavepacket centered at position x and momentum p. Thus,
A coherent state is an approximate eigenstate of both operators and , hence also of the Hamiltonian Ĥ, with errors of the size of the uncertainties. If Δx and Δp can be regarded as zero, the action of Ĥ reduces to multiplication by the classical Hamiltonian, and Z reduces to the classical configuration integral.
Meaning and significance
It may not be obvious why the partition function, as we have defined it above, is an important quantity. First, let us consider what goes into it. The partition function is a function of the temperature T and the microstate energies E1, E2, E3, etc. The microstate energies are determined by other thermodynamic variables, such as the number of particles and the volume, as well as microscopic quantities like the mass of the constituent particles. This dependence on microscopic variables is the central point of statistical mechanics. With a model of the microscopic constituents of a system, one can calculate the microstate energies, and thus the partition function, which will then allow us to calculate all the other thermodynamic properties of the system.
The partition function can be related to thermodynamic properties because it has a very important statistical meaning. The probability Ps that the system occupies microstate s is
The partition function thus plays the role of a normalizing constant (note that it does not depend on s), ensuring that the probabilities sum up to one:
This is the reason for calling Z the "partition function": it encodes how the probabilities are partitioned among the different microstates, based on their individual energies. The letter Z stands for the German word Zustandssumme, "sum over states". This notation also implies another important meaning of the partition function of a system: it counts the (weighted) number of states a system can occupy. Hence if all states are equally probable (equal energies) the partition function is the total number of possible states. Often this is the practical importance of Z.
Calculating the thermodynamic total energy
In order to demonstrate the usefulness of the partition function, let us calculate the thermodynamic value of the total energy. This is simply the expected value, or ensemble average for the energy, which is the sum of the microstate energies weighted by their probabilities:
Incidentally, one should note that if the microstate energies depend on a parameter λ in the manner
then the expected value of A is
This provides us with a method for calculating the expected values of many microscopic quantities. We add the quantity artificially to the microstate energies (or, in the language of quantum mechanics, to the Hamiltonian), calculate the new partition function and expected value, and then set λ to zero in the final expression. This is analogous to the source field method used in the path integral formulation of quantum field theory.
Relation to thermodynamic variables
In this section, we will state the relationships between the partition function and the various thermodynamic parameters of the system. These results can be derived using the method of the previous section and the various thermodynamic relations.
As we have already seen, the thermodynamic energy is
The variance in the energy (or "energy fluctuation") is
The heat capacity is
The entropy is
Partition functions of subsystems
Suppose a system is subdivided into N sub-systems with negligible interaction energy, that is, we can assume the particles are essentially non-interacting. If the partition functions of the sub-systems are ζ1, ζ2, ..., ζN, then the partition function of the entire system is the product of the individual partition functions:
If the sub-systems have the same physical properties, then their partition functions are equal, ζ1 = ζ2 = ... = ζ, in which case
However, there is a well-known exception to this rule. If the sub-systems are actually identical particles, in the quantum mechanical sense that they are impossible to distinguish even in principle, the total partition function must be divided by a N! (N factorial):
This is to ensure that we do not "over-count" the number of microstates. While this may seem like a strange requirement, it is actually necessary to preserve the existence of a thermodynamic limit for such systems. This is known as the Gibbs paradox.
Grand canonical partition function
We can define a grand canonical partition function for a grand canonical ensemble, which describes the statistics of a constant-volume system that can exchange both heat and particles with a reservoir. The reservoir has a constant temperature T, and a chemical potential μ.
The grand canonical partition function, denoted by , is the following sum over microstates
Here, each microstate is labelled by , and has total particle number and total energy . This partition function is closely related to the Grand potential, , by the relation
This can be contrasted to the canonical partition function above, which is related instead to the Helmholtz free energy.
It is important to note that the number of microstates in the grand canonical ensemble may be much larger than in the canonical ensemble, since here we consider not only variations in energy but also in particle number. Again, the utility of the grand canonical partition function is that it is related to the probability that the system is in state :
An important application of the grand canonical ensemble is in deriving exactly the statistics of a non-interacting many-body quantum gas (Fermi-Dirac statistics for fermions, Bose-Einstein statistics for bosons), however it is much more generally applicable than that. The grand canonical ensemble may also be used to describe classical systems, or even interacting quantum gases.
See also
- J. R. Klauder, B.-S. Skagerstam, Coherent States --- Applications in Physics and Mathematical Physics, World Scientific, 1985, p. 71-73.
- Huang, Kerson, "Statistical Mechanics", John Wiley & Sons, New York, 1967.
- A. Isihara, "Statistical Physics", Academic Press, New York, 1971.
- Kelly, James J, (Lecture notes)
- L. D. Landau and E. M. Lifshitz, "Statistical Physics, 3rd Edition Part 1", Butterworth-Heinemann, Oxford, 1996.
- Vu-Quoc, L., Configuration integral, 2008 | <urn:uuid:2d23088a-355c-4d5a-89fb-97e7d23e4b29> | 3.453125 | 2,195 | Knowledge Article | Science & Tech. | 30.677008 |
sth is right. You can also use os.popen(), but where available (Python 2.4+) subprocess is generally preferable.
However, unlike some languages that encourage it, it's generally considered bad form to spawn a subprocess where you can do the same job inside the language. It's slower, less reliable and platform-dependent. Your example would be better off as:
baz is a directory and I'm trying to get the contents of all the files in that directory
? cat on a directory gets me an error.
If you want a list of files:
If you want the contents of all files in a directory, something like:
for leaf in os.listdir('/tmp/baz'):
path= os.path.join('/tmp/baz', leaf)
or, if you can be sure there are no directories in there, you could fit it in a one-liner:
foo= ''.join(open(os.path.join(path, child), 'rb').read() for child in os.listdir(path)) | <urn:uuid:ce066de4-b043-45a7-a206-5c651d394563> | 3.09375 | 228 | Q&A Forum | Software Dev. | 73.124533 |
Our Solar System: In Order From the Sun
7 of 10
The sixth planet from the Sun is the majestic Saturn. It takes 29 years for Saturn to make one trip around the Sun. Orbiting this giant, gas-filled planet are its famous rings. The rings are a collection of billions of boulder-sized chunks of ice. Saturn's intense gravitational field keeps its icy rings from clumping together.
Fun Fact: Saturn rotates rapidly, making each day only 10 hours long.
Photo source: NASA | <urn:uuid:b13dd7f6-d747-409d-9fd4-1edc25b78540> | 3.015625 | 104 | Listicle | Science & Tech. | 66.732143 |
A reentrant lock is one where a process can claim the lock multiple times without blocking on itself. It's useful in situations where it's not easy to keep track of whether you've already grabbed a lock. If a lock is non re-entrant you could grab the lock, then block when you go to grab it again, effectively deadlocking your own process.
Reentrancy in general is a property of code where it has no central mutable state that could be corrupted if the code was called while it is executing. Such a call could be made by another thread, or it could be made recursively by an execution path originating from within the the code itself.
If the code relies on shared state that could be updated in the middle of its execution it is not re-entrant, at least not if that update could break it.
A use case for re-entrant locking
A (somewhat generic and contrived) example of an application for a re-entrant lock might be:
You have some computation involving an algorithm that traverses a graph (perhaps with cycles in it). A traversal may visit the same node more than once due to the cycles or due to multiple paths to the same node.
The data structure is subject to concurrent access and could be updated for some reason, perhaps by another thread. You need to be able to lock individual nodes to deal with potential data corruption due to race conditions. For some reason (perhaps performance) you don't want to globally lock the whole data structure.
You computation can't retain complete information on what nodes you've visited, or you're using a data structure that doesn't allow 'have I been here before' questions to be answered quickly.
An example of this situation would be a simple implementation of Dijkstra's algorithm with a priority queue implemented as a binary heap or a breadth-first search using a simple linked list as a queue. In these cases, scanning the queue for existing insertions is O(N) and you may not want to do it on every iteration.
In this situation, keeping track of what locks you've already acquired is expensive. Assuming you want do the locking at the node level a re-entrant locking mechanism alleviates the need to tell whether you've visited a node before. You can just blindly lock the node, perhaps unlocking it after you pop it off the queue.
A simple mutex is not re-entrant as only one thread can be in the critical section at a given time. If you grab the mutex and then try to grab it again a simple mutex doesn't have enough information to tell who was holding it previously. To do this recursively you need a mechanism where each thread had a token so you could tell who had grabbed the mutex. This makes the mutex mechanism somewhat more expensive so you may not want to do it in all situations.
IIRC the POSIX threads API does offer the option of re-entrant and non re-entrant mutexes. | <urn:uuid:c78af1d7-ca10-4975-a938-d2dea12b4a6b> | 3.0625 | 622 | Q&A Forum | Software Dev. | 50.108782 |
Coastal & Marine Geology InfoBank
Our Mapping Systems
The USGS and Science Education
USGS Fact Sheets
ground penetrating radar
Comment: 11:53 - 13:06 (01:13)
Source: Annenberg/CPB Resources - Earth Revealed - 4. The Sea Floor
Keywords: subduction, "Grand Canyon", vessel, instrument, "camel-grab", "box corer", "James Sadd"
Our transcription: Subduction begins at enormous underwater trenches, some of them several times deeper than the Grand Canyon.
Because of the great depth, marine geologists have had to come up with a host of ingenious ways of exploring the deep sea floor.
The primary tool used by Earth scientists to study the ocean floor is a research vessel like this one, outfitted with a variety of oceanographic sampling instruments.
Mounted on the stern of the vessel, is this A-frame, which is a hydraulically movable rack used to lift and deploy the instruments.
The oceanographic sampling instruments are tethered to the vessel with this steel cable wound around a revolving drum.
Scientists can take a bite of sediment or rock from the ocean bottom using a sampling instrument like this "camel-grab".
It takes sediment samples very quickly but only of the upper few centimeters of ocean bottom.
Often times, an undisturbed sample of the deeper layers is required to examine variations in the accumulated sediment on the ocean bottom with time.
This "box corer" takes an entire column of sediment, which later can be split open and the individual layers analyzed like pages in a book.
Geology School Keywords | <urn:uuid:42b1e945-abcd-4ae4-9b84-8465df6d50b2> | 4.03125 | 343 | Knowledge Article | Science & Tech. | 37.567739 |
In the 1920s, examining photographic plates from the
Mt. Wilson Observatory's
100 inch telescope,
Edwin Hubble determined the distance to the
decisively demonstrating the existence of other galaxies far beyond
the Milky Way.
His notations are evident on the historic plate image
inset at the lower right, shown in context with ground based
and Hubble Space Telescope images of the region made
nearly 90 years later.
By intercomparing different plates, Hubble
searched for novae, stars which underwent a
sudden increase in brightness.
He found several on this plate and marked them with an "N".
Later, discovering that the one near the upper right corner (marked by
lines) was actually a type of
variable star known as
he crossed out the "N" and wrote "VAR!".
Thanks to the work of Harvard
astronomer Henrietta Leavitt, cepheids,
regularly varying pulsating stars, could be used as standard candle
Identifying such a star allowed Hubble to show
that Andromeda was not a small cluster of stars and gas within our own
galaxy, but a large galaxy in its own right at a substantial
distance from the Milky Way.
discovery is responsible for establishing our modern concept of a
Universe filled with galaxies.
R. Gendler, Z. Levay and the
Hubble Heritage Team | <urn:uuid:c4a12908-519a-4291-bce8-43604a6d0a46> | 3.984375 | 294 | Knowledge Article | Science & Tech. | 42.238893 |
Isentropic LiftLifting of air that is traveling along an upward-sloping isentropic surface.
Isentropic lift often is referred to erroneously as overrunning, but more accurately describes the physical process by which the lifting occurs. Situations involving isentropic lift often are characterized by widespread stratiform clouds and precipitation, but may include elevated convection in the form of embedded thunderstorms.
You can either type in the word you are looking for in the box below or browse by letter.
Browse by letter:# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | <urn:uuid:1fc62f10-767f-404c-a08f-e128aea15f12> | 2.71875 | 139 | Structured Data | Science & Tech. | 47.450708 |
Physics and Star WarsThe Interstellar triology, Star Wars, uses science and technology in their settings and storylines, though they were not considered "hard" science fiction. Star Wars concentrates mainly on the epic drama and not on the "technobabble". It has borrowed freely from the scientific world. The series has showcased many interesting technological concepts, both in the movies and in an extensive line of novelss and comics. These vivid imaginings, and the discussions they have started amongst fanss, have inspired many people to enter the world of science.
The Star Wars movies are a vehicle for entertainment and their primary aim is to deliver drama, not scientific knowledge. Many of the on-screen technologies created or borrowed for the Star Wars universe were used mainly as plot devices, and not as elements of the story in their own right.
The iconic status that Star Wars has gained in popular culture allows it to be used as an accessible introduction to real scientific concepts. Many of the technologies used in the Star Wars universe are impossible, according to current theory. However, the process of understanding why they are considered impossible can educate people while simultaneously entertaining them.
|Table of contents|
2 External links, resources, references
Compare with: Physics and Star Trek | <urn:uuid:fbff2c91-3597-4911-8675-20a68a31984e> | 2.9375 | 254 | Knowledge Article | Science & Tech. | 29.614286 |
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Rockies Research: Mountaintop lakes may be environmental sentinels
Stretched across the border between Wyoming and Montana lie the Beartooth Mountains, part of the central U.S. Rockies. Among these mountains are more than 3,000 lakes at elevations ranging from 5,000 feet to over 11,000 feet.
These lakes remain frozen for as many as 10 months of the year due to the extreme cold and deep snowpack that develops. Because of the severe climate, these lakes respond strongly to outside pressure.
They are sensitive indicators — sentinels — of both local and larger scale environmental changes. For example, while visitors to the region may remark about the pristine beauty of the lakes, research has demonstrated that nitrogen deposition from cities throughout the western U.S. has been falling on the mountains in snow and rain, slowly enriching the lakes with nitrogen.
This gradual nitrogen increase has stimulated greater algae growth and altered the underwater ecosystems in many ways. In nearby Red Lodge, Mont., records of snowfall date back many decades, highlighting dramatic changes the region has experienced. Since 1970, average annual snowfall has decreased from about 250 inches to about 100 inches per year. Such dramatic changes, common throughout the western U.S., affect everything from the prevalence of wildfires to the transparency of the lakes.
Scientists from Miami University of Ohio and the University of Maine are conducting research on a series of alpine and subalpine lakes throughout the Beartooth Mountains. Alpine lakes, lying above the tree line, are often cold and clear.
In order to understand these sensitive ecosystems better, researchers from Miami deployed a data buoy this summer in Heart Lake, a remote alpine lake with an elevation of 10,350 feet located just inside Montana. Heart Lake lies in a small granitic watershed; steep walls shelter water that is deeper than 100 feet.
Despite its beauty, Heart Lake is unusual by alpine lake standards. While most lakes in the region are low in both dissolved organic carbon (DOC) and chlorophyll (an indicator of algal biomass), Heart Lake has unusually high chlorophyll, often as high as 15-20 µg/L. In contrast, the average chlorophyll concentration of many lakes in the region is about 1.5 µg/L. The high concentration in Heart Lake is more commonly found in Midwest agricultural reservoirs than Montana cold mountain lakes.
Challenging terrain, lack of roads, and thin air meant researchers had to think creatively in order to study Heart Lake. The remoteness of the lake meant all equipment had to be carried in backpacks. Additionally, since the deployment was in a National Forest, the buoy needed to have a low profile.
Working with Fondriest Environmental, graduate students at Miami designed a mobile buoy that was modular and lightweight. For example, anchors were fashioned from sleeping bag stuff sacks filled with shoreline rocks, instead of the more traditional 70-pound pyramid weights. The final buoy weight was 35 pounds (not including sensors). When scientists first visited Heart Lake in early July, several inches of ice remained. Warm summer temperatures, however, quickly melted the ice, and the buoy was deployed. Scientists visited the lake weekly throughout the rest of the summer, collecting manual samples, changing data logger batteries, and calibrating sensors.
Connected to the buoy was a YSI sonde with temperature, conductivity, dissolved oxygen, chlorophyll, and turbidity probe units. Also suspended beneath the buoy was a Turner CDOM sensor (with Zebra-Tech wiper), a Biospherical radiometer sensors measuring transparency to both UV and PAR at two depths, and a temperature string to help understand the lake’s thermal structure. Finally, a topside-mounted Vaisala weather station measured air temperature, wind speed, wind direction, relative humidity, barometric pressure, and rainfall. Sensors were powered and run by a NexSens SDL500 submersible data logger.
The data show that Heart lake changes rapidly once the ice cover melts. For example, the chlorophyll concentration, as estimated from the YSI probe, climbed rapidly from less than 5 µg/L to more than 11 µg/L within a week. It then quickly settled back down to a long period of about 2 µg/L until the buoy was removed in late August.
This suggests that the high chlorophyll concentration may be stimulated by nutrients in the watershed that enter the lake during snowmelt. Other data analyses are still being conducted, but these initial results suggest that alpine lakes exhibit clear signals of broader landscape phenomenon. This sentinel quality makes alpine lakes an ideal (and beautiful) place to study environmental processes and changes.
— Kevin Rose is a PhD candidate in the Department of Zoology at Miami University working with Dr. Craig Williamson. Kevin’s research focuses on understanding optical indicators of allochthony and carbon cycling in aquatic ecosystems. | <urn:uuid:5d0ce22a-9aa6-4c66-adbf-27f73a5aaf44> | 3.09375 | 1,163 | Content Listing | Science & Tech. | 37.247121 |
The functions described in this section (
printf and related
functions) provide a convenient way to perform formatted output. You
printf with a format string or template string
that specifies how to format the values of the remaining arguments.
Unless your program is a filter that specifically performs line- or
character-oriented processing, using
printf or one of the other
related functions described in this section is usually the easiest and
most concise way to perform output. These functions are especially
useful for printing error messages, tables of data, and the like. | <urn:uuid:c91e3746-12cd-405b-bf1b-7be5876c989e> | 3.03125 | 114 | Documentation | Software Dev. | 32.207486 |
Doomsday and the Big Bang Experiment
It is expected that nuclear research known as CERN experiment will reveal how the universe was created. Everything depends on the success of the experiment. This is the world's largest experiment which may have positive or negative outcomes. This may cost lives of human beings or disclose the secrets of this universe.
But apart from the debate on the success of the experiment it is also important to consider that in this world, where millions of people live below poverty line, millions are dying due to natural calamity, there are increasing global warming issues and terrorism worldwide, was it correct to do this experiment. The amount of money invested on this experiment might have helped the universe in tackling other problems and their solutions.
There is another piece of CERN LHC News that says a group of people hacked it and leave it on the extreme point by just mentioning that there are loopholes in the security of the project. The Large Hydron Collider (LHC) experiment could be helpful for the entire universe or it may destroy the universe, or it could have some positive and negative impacts too. The entire thing will be disclosed by the final stage of the experiment.
So now when the experiment has already started and there is so much to look forward to, let's hope for the best. The final decision will be what is destined.
Tags: LHC CERN News , Large Hydron Collider Exp , LHC News , Doomsday , World Ending , Experiment
This work is licensed under a Creative Commons Attribution 3.0 License. | <urn:uuid:cdc80be4-639f-4d09-a1b1-90fe3885d28a> | 3.03125 | 310 | Truncated | Science & Tech. | 42.946238 |
ISAAC ASIMOV would probably have been horrified at the experiments under way in a robotics lab in Slovenia. There, a powerful robot has been hitting people over and over again in a bid to induce anything from mild to unbearable pain - in apparent defiance of the late sci-fi sage's famed first law of robotics, which states that "a robot may not injure a human being".
But the robo-battering is all in a good cause, insists Borut Povše, who has ethical approval for the work from the University of Ljubljana, where he conducted the research. He has persuaded six male colleagues to let a powerful industrial robot repeatedly strike them on the arm, to assess human-robot pain thresholds.
It's not because he thinks the first law of robotics is too constraining to be of any practical use, but rather to help future robots adhere to the rule. "Even robots designed to Asimov's laws can collide with people. We are trying to make sure that when they do, the collision is not too powerful," Povše says. "We are taking the first steps to defining the limits of the speed and acceleration of robots, and the ideal size and shape of the tools they use, so they can safely interact with humans."
Povše and his colleagues borrowed a small production-line robot made by Japanese technology firm Epson and normally used for assembling systems such as coffee vending machines. They programmed the robot arm to move towards a point in mid-air already occupied by a volunteer's outstretched forearm, so the robot would push the human out of the way. Each volunteer was struck 18 times at different impact energies, with the robot arm fitted with one of two tools - one blunt and round, and one sharper.
The volunteers were then asked to judge, for each tool type, whether the collision was painless, or engendered mild, moderate, horrible or unbearable pain. Povše, who tried the system before his volunteers, says most judged the pain was in the mild to moderate range.
The team will continue their tests using an artificial human arm to model the physical effects of far more severe collisions. Ultimately, the idea is to cap the speed a robot should move at when it senses a nearby human, to avoid hurting them. Povše presented his work at the IEEE's Systems, Man and Cybernetics conference in Istanbul, Turkey, this week.
"Determining the limits of pain during robot-human impacts this way will allow the design of robot motions that cannot exceed these limits," says Sami Haddadin of DLR, the German Aerospace Centre in Wessling, who also works on human-robot safety. Such work is crucial, he says, if robots are ever to work closely with people. Earlier this year, in a nerve-jangling demonstration, Haddadin put his own arm on the line to show how smart sensors could enable a knife-wielding kitchen robot to stop short of cutting him.
"It makes sense to study this. However, I would question using pain as an outcome measure," says Michael Liebschner, a biomechanics specialist at Baylor College of Medicine in Houston, Texas. "Pain is very subjective. Nobody cares if you have a stinging pain when a robot hits you - what you want to prevent is injury, because that's when litigation starts."
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A Very Complex Problem
Wed Oct 13 22:40:07 BST 2010 by Henry Harris
I'm not sure where this gets us since this is actually a very complex problem that has many dimensions. For example is the subject an adult or a child? Is the subject male or female? Is the subject a friend? Is the subject a boss? Is the subject a hostile carrying a weapon? Human robot interactions are a pandora's box of complications.
A Very Complex Problem
Thu Oct 14 10:07:17 BST 2010 by Freederick
Actually, they are trying to address a very specific situation: there is an industrial robot working on an assembly line. A human is detected entering the work area. How much should the robot slow down its movements? Too slow, and work stalls. Too fast, and you risk injury to the human.
This is a narrowly defined industrial safety problem, and such factors as weapon possession, age, or friendship are totally irrelevant here. We are not talking about adapting robots for social interaction in human society, at least not yet.
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Sun Feb 24 07:17:00 GMT 2013 by Liza
Eric, bacteria convert organic matter to CO2 *after* the organism has died. As long as the plants are alive and growing, they won't get the chance. So: arctic summer- air temperature's warm enough to have plants growing- bacteria don't touch live plants- plants die (partly) off during arctic winter- the dead parts fall under the live plants, or are the lowest, oldest plant parts anyway, so they're sandwiched between live plants and permafrost- the dead parts are shaded and don't thaw in summer- bacteria can't eat them because they're frozen- permafrost accumulates. There may be a small amount of dead material at the surface sufficiently explosed to thaw in summer to get decomposed, but the total balance will be towards accumulation of frozen organic matter. | <urn:uuid:7d11046d-dcbc-4263-b526-c0ebca3365d8> | 3.375 | 188 | Comment Section | Science & Tech. | 38.251884 |
In Java, thread scheduler can use the thread priorities in the form of integer value to each of its thread to determine the execution schedule of threads . Thread gets the ready-to-run state according to their priorities.
This page discusses - Synchronized Threads.
Multithreading in Java
This page discusses - Multithreading in Java.
This page discusses - Interthread Communication.
Creation of MultiThreads
Like creation of a single thread, You can also create more than one thread (multithreads) in a program using class Thread or implementing interface Runnable. | <urn:uuid:a1d3e8da-fdfc-4674-a483-50916bdd4005> | 3.5625 | 122 | Documentation | Software Dev. | 37.189951 |
by Elizabeth K. Gardner
West Lafayette IN (SPX) Dec 02, 2011
A drop in carbon dioxide appears to be the driving force that led to the Antarctic ice sheet's formation, according to a recent study led by scientists at Yale and Purdue universities of molecules from ancient algae found in deep-sea core samples.
The key role of the greenhouse gas in one of the biggest climate events in Earth's history supports carbon dioxide's importance in past climate change and implicates it as a significant force in present and future climate.
The team pinpointed a threshold for low levels of carbon dioxide below which an ice sheet forms in the South Pole, but how much the greenhouse gas must increase before the ice sheet melts - which is the relevant question for the future - remains a mystery.
Matthew Huber, a professor of earth and atmospheric sciences at Purdue, said roughly a 40 percent decrease in carbon dioxide occurred prior to and during the rapid formation of a mile-thick ice sheet over the Antarctic approximately 34 million years ago.
A paper detailing the results was published Thursday (Dec. 1) in the journal Science.
"The evidence falls in line with what we would expect if carbon dioxide is the main dial that governs global climate; if we crank it up or down there are dramatic changes," Huber said. "We went from a warm world without ice to a cooler world with an ice sheet overnight, in geologic terms, because of fluctuations in carbon dioxide levels."
For 100 million years prior to the cooling, which occurred at the end of the Eocene epoch, Earth was warm and wet. Mammals and even reptiles and amphibians inhabited the North and South poles, which then had subtropical climates.
Then, over a span of about 100,000 years, temperatures fell dramatically, many species of animals became extinct, ice covered Antarctica and sea levels fell as the Oligocene epoch began.
Mark Pagani, the Yale geochemist who led the study, said polar ice sheets and sea ice exert a strong control on modern climate, influencing the global circulation of warm and cold air masses, precipitation patterns and wind strengths, and regulating global and regional temperature variability.
"The onset of Antarctic ice is the mother of all climate 'tipping points,'" he said. "Recognizing the primary role carbon dioxide change played in altering global climate is a fundamentally important observation."
There has been much scientific discussion about this sudden cooling, but until now there has not been much evidence and solid data to tell what happened, Huber said.
The team found the tipping point in atmospheric carbon dioxide levels for cooling that initiates ice sheet formation is about 600 parts per million. Prior to the levels dropping this low, it was too warm for the ice sheet to form. At the Earth's current level of around 390 parts per million, the environment is such that an ice sheet remains, but carbon dioxide levels and temperatures are increasing.
The world will likely reach levels between 550 and 1,000 parts per million by 2100. Melting an ice sheet is a different process than its initiation, and it is not known what level would cause the ice sheet to melt away completely, Huber said.
"The system is not linear and there may be a different threshold for melting the ice sheet, but if we continue on our current path of warming we will eventually reach that tipping point," he said. "Of course after we cross that threshold it will still take many thousands of years to melt an ice sheet."
What drove the rise and fall in carbon dioxide levels during the Eocene and Oligocene is not known.
The team studied geochemical remnants of ancient algae from seabed cores collected by drilling in deep-ocean sediments and crusts as part of the National Science Foundation's Integrated Ocean Drilling program. The biochemical molecules present in algae vary depending on the temperature, nutrients and amount of dissolved carbon dioxide present in the ocean water.
These molecules are well preserved even after many millions of years and can be used to reconstruct the key environmental variables at the time, including carbon dioxide levels in the atmosphere, Pagani said.
Samples from two sites in the tropical Atlantic Ocean were the main focus of this study because this area was stable at that point in Earth's history and had little upwelling, which brings carbon dioxide from the ocean floor to the surface and could skew measurements of atmospheric carbon dioxide, Huber said.
In re-evaluating previous estimates of atmospheric carbon dioxide levels using deep-sea core samples, the team found that continuous data from a stable area of the ocean is necessary for accurate results.
Data generated from a mix of sites throughout the world's oceans caused inaccuracies due to variations in the nutrients present in different locations.
This explained conflicting results from earlier papers based on the deep-sea samples that suggested carbon dioxide increased during the formation of the ice sheet, he said.
Constraints on temperature and nutrient concentrations were achieved through modeling of past circulation, temperature and nutrient distributions performed by Huber and Willem Sijp at the University of New South Wales in Australia.
The collaboration built on Huber's previous work using the National Center for Atmospheric Research Community Climate System Model 3, one of the same models used to predict future climates, and used the UVic Earth System Climate Model developed at the University of Victoria, British Columbia.
"The models got it just about right and provided results that matched the information obtained from the core samples," he said.
"This was an important validation of the models. If they are able to produce results that match the past, then we can have more confidence in their ability to predict future scenarios."
In addition to Huber, Pagani and Sijp, paper co-authors include Zhonghui Liu of the University of Hong Kong, Steven Bohaty of the University of Southampton in England, Jorijntje Henderiks of Uppsala University in Sweden, Srinath Krishnan of Yale, and Robert DeConto of the University of Massachusetts-Amherst.
The National Science Foundation, Natural Environment Research Council, Royal Swedish Academy and Yale Department of Geology funded this work.
In 2004 the team used evidence from deep-sea core samples to challenge the longstanding theory that the ice sheet developed because of a shift from warm to cool ocean currents millions of years ago.
The team found that a cold current, not the warm one that had been theorized, was flowing past the Antarctic coast for millions of years before the ice sheet developed. Huber next plans to investigate the impact of an ice sheet on climate.
"It seems that the polar ice sheet shaped our modern climate, but we don't have much hard data on the specifics of how," he said. "It is important to know by how much it cools the planet and how much warmer the planet would get without an ice sheet."
Climate Dynamics Prediction Laboratory
Beyond the Ice Age
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Carbon cycling was much smaller during last ice age than in today's climate
Bristol UK (SPX) Nov 23, 2011
Atmospheric carbon dioxide (CO2) is one of the most important greenhouse gases and the increase of its abundance in the atmosphere by fossil fuel burning is the main cause of future global warming. In past times, during the transition between an ice age and a warm period, atmospheric CO2 concentrations changed by some 100 parts per million (ppm) - from an ice age value of 180 ppm to about ... read more
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