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A herbivore is an animal that obtains its energy and nutrients by feeding on plants. Different types of herbivores eat different plant parts. For example, folivores feed on leaves, frugivores feed on fruits, granivores feed on seeds, pollinivores feed on pollen, and nectarivores feed on nectar. Herbivores can vary greatly in size, ranging from the largest terrestrial animals (elephants) and large marine mammals such as manatees and dugongs to small insects, nematodes and thrips. Herbivores are primary consumers (they receive their energy by consuming primary producers), so they play an important trophic role in ecological communities and food webs.
The Koala (Fascolarctos cinereus) is an Australian arboreal folivore. Photos by August, Hsueh-Cheng Ho. Australian Koala Foundation Because mature leaves are low in nutrients, and difficult to digest because of their high cellulose content, animals use many different strategies to eat leaves. Animals that feed on grass leaves are generally known as grazers. Grazers are typically not too choosy and eat all parts of leaves. Many grazers have mutualistic relationship with microbes that help them digest cellulose found in leaves. Buds and young leaves are often more nutritious and less-well defended, so browsers selectively choose to feed on high quality plant parts. Some insects actually feed inside of leaves (leaf mining). Many folivores spend most of their time feeding in trees (e.g., koalas, sloths, and folivorous monkeys).
Because leaves are low in nutrients, folivores must consume a significant biomass of leaves to meet their daily needs. Because of the heavy weight of leaves in their guts, there are very few flying herbivorous mammals or birds.
Mammals such as muskrats and moose are common folivores in North American marshes. Interstingly, the hippopotamus, the largest aquatic herbivorous mammal, obtains most of its food while foraging on land.
Large animals such as manatees, dugongs, and green turtles feed on vascular "sea grasses" that grow in shallow waters near the coast. Many invertebrates, such as sea urchins and abalone, reptiles such as the marine iquana, and many fishes feed on algae. Marine fishes us a variety of strategies to feed on algae (see Coral reef fish feeding behavior in the Caribbean). For example, parrotfishes, common tropical herbivorous fishes, scrape algae off of the rocks with their large beak-like teeth. Some damselfishes "farm" algae in small territories that they defend from other fishes,
Because eating a seed kills a potential plant, granivores are considered to be seed predators. Some granivores remove seeds directly from the plant whereas other granivores forage for seeds that lie dormant in the soil seed bank.
Some granivores play a role in seed dispersal, when they are unable to re-locate seeds that they have cached, and these seeds are thus able to germinate and grow.
The Ruby-throated hummingbird feeding on nectar. Photo by Ken Thomas. enature.com Many nectarivores form mutualistic relationships with plants because they carry pollen from flower to flower so that pollination can occur. Other nectarivores only feed on nectar without transfering pollen and are there fore known as nectar robbers. Coevolution between plant and pollinator often results in animals with phenotypic adaptations that allows them to effectively remove nectar from the flower and successfully carry pollen from one flower to another.
Pollinivores are animals that feed on pollen.There are pollinivorous invertebrates (e.g., mites, spiders, springtails, and insects) and vertebrates (e.g., marsupials, rodents, bats, and birds). Some pollinivores successfully transfer pollen from one flower to another so they act as pollinators whereas other pollinivores act only as "pollen predators". Most pollinivores remove pollen directly from the flower, but Neotropical canopy-dwelling ants in the genus Cephalotes forage for the pollen of wind-dispersed plants that has settled on leaves in the canopy.
Aphids feeding on ploem. Note the drop of honeydew secreted by the aphid. Photo from Cheadle Center of Biodiversity and Ecological Restoration. UCSB. Some bugs in the order Hemiptera feed on phloem by inserting their elongated mouthparts into the plant's vascular tissues. Because phloem is rich in sugar, but low in nutrients, some phloem-feeding insects have symbiotic micro-organisms that proved them with amino acids and others convert excess sugar into long-chain oligosaccharides that are extruded as "honeydew". Interestingly, some animals, e.g., some ants, indirectly feed on phloem by consuming honeydew. Some bird, such as sapsuckers, drill holes into the bark so that they can consume the phloem juices that are released.
Animals that feed on wood are known as xylovores. Such species act as herbivores while consuming wood from living plants, and as decomposers when feeding on dead wood. Some arthropods that feed on wood have symbiotic protists or bacteria living in their gut to aid in the digestion of cellulose whereas termites produce their own wood-digesting enzymes.
The cambium is the layer of actively dividing cells between the xylem and ploem tissues of plants and make up a small ring beneath the bark of woody plants. Becasue the living tissues of the cambium layer are more nutritious than the dead xylem tissues that make up wood, some animals feed selectively on the cambium. Some wood boring insects eat their way through the cambium.
Bark makes up the outer layer of the branches of woody plants. Some animals such as elephants, beavers, and squirrels strip the bark off of branches and eat them whereas insects such as bark beetles feed by burrowing through the bark tissue.
Some insects, both larvae and adults, nematodes, and mammals such as gophers feed on roots. Some animals will burrow into the ground to feed on tubers.
Herbivores in ecological communities
Herbivores are considered to be primary consumers because they feed on plants (primary producers). Thus, herbivores feeding on plants form the first link in almost all food chains. The abundance of herbivores can control the biomass of plants and and the abundance of secondary consumers that form the next higher trophic level.
The removal of the herbivore trophic level can allow plant growth to get out of control. For example the removal of herbaceous fishes by fishing and the loss of the herbaceus sea urchin, Diameda antillarum, has led to an increase in the standing crop of algae on many coral reefs in the Caribbean Sea. Similarly, the increase in the population size of herbivore, often caused by an decrease in the population size of their predators, can greatly reduce the biomass of plants. The invasion of introduced herbivores can have harmful effects on the native plant community.
Pollination by nectarivores and pollinivores and seed dispersal by frugivores and granivores have an important influence on the distribution and abundance of plants in ecological communities.
Plants that feed on other plants
Although some plants receive energy and nutrients by "feeding" on other plants, these plants are referred to as "parasitic plants" rather than herbivorous plants.
References and further reading
- Cautious climbing and folivory: a model of hominoid differentation E. E. Sarmiento in Human Evolution Volume 10, Number 4, August, 1995
- Frugivore Wikipedia
- Nectarivore Wikipedia
- Xylophagy Wikipedia
- Phloem-sap feeding by animals: problems and solutions. A.E. Douglas
- Insects: Bee San Diego Zoo
- Pollenivory in ants (Hymenoptera:Formicidae) seems to be much more common that it was thought. W. Czechowksi, B. Mark, K. Er?s, and E. Csata. | <urn:uuid:327aa761-d1f4-4278-82cf-07922d468ab7> | 3.796875 | 1,773 | Knowledge Article | Science & Tech. | 37.340206 |
Synchronous orbit: An orbit where the satellite has an orbital period equal to the average rotational period (earth's is: 23 hours, 56 minutes, 4,091 seconds) of the body being orbited and in the same direction of rotation as that body. To a ground observer such a satellite would trace an analemma (figure 8) in the sky.
Semi-synchronous orbit (SSO): An orbit with an altitude of approximately 20200 km (12544.2 miles) and an orbital period of approximately 12 hours
Geosynchronous orbit (GEO): Orbits with an altitude of approximately 35786 km (22240 miles). Such a satellite would trace an analemma (figure 8) in the sky.
Geostationary orbit (GSO): A geosynchronous orbit with an inclination of zero. To an observer on the ground this satellite would appear as a fixed point in the sky.
Clarke orbit: Another name for a geostationary orbit. Named after the writer Arthur C. Clarke.
Supersynchronous orbit: A disposal / storage orbit above GSO/GEO. Satellites will drift west. Also a synonym for Disposal orbit.
Subsynchronous orbit: A drift orbit close to but below GSO/GEO. Satellites will drift east.
Graveyard orbit: An orbit a few hundred kilometers above geosynchronous that satellites are moved into at the end of their operation.
Disposal orbit: A synonym for graveyard orbit.
Junk orbit: A synonym for graveyard orbit.
Areosynchronous orbit: A synchronous orbit around the planet Mars with an orbital period equal in length to Mars' sidereal day, 24,6229 hours.
Areostationary orbit (ASO): A circular areosynchronous orbit on the equatorial plane and about 17000 km(10557 miles) above the surface. To an observer on the ground this satellite would appear as a fixed point in the sky.
Heliosynchronous orbit: An heliocentric orbit about the Sun where the satellite's orbital period matches the Sun's period of rotation. These orbits occur at a radius of 24,360 Gm (0,1628 AU) around the Sun, a little less than half of the orbital radius of Mercury.
Special classifications
Sun-synchronous orbit: An orbit which combines altitude and inclination in such a way that the satellite passes over any given point of the planets's surface at the same local solar time. Such an orbit can place a satellite in constant sunlight and is useful for imaging, spy, and weather satellites.
Moon orbit: The orbital characteristics of earth's moon. Average altitude of 384403 kilometres (238857 mi), elliptical-inclined orbit.
Pseudo-orbit classifications
Horseshoe orbit: An orbit that appears to a ground observer to be orbiting a certain planet but is actually in co-orbit with the planet. See asteroids 3753 (Cruithne) and 2002 AA29.
Exo-orbit: A maneuver where a spacecraft approaches the height of orbit but lacks the velocity to sustain it.
Orbital spaceflight: A synonym for exo-orbit.
Lunar transfer orbit (LTO)
Prograde orbit: An orbit with an inclination of less than 90°. Or rather, an orbit that is in the same direction as the rotation of the primary.
Retrograde orbit: An orbit with an inclination of more than 90°. Or rather, an orbit counter to the direction of rotation of the planet. Apart from those in sun-synchronous orbit, few satellites are launched into retrograde orbit because the quantity of fuel required to launch them is much greater than for a prograde orbit. This is because when the rocket starts out on the ground, it already has an eastward component of velocity equal to the rotational velocity of the planet at its launch latitude.
Satellites can also orbit Lagrangian points. | <urn:uuid:de56bcb6-e057-4b7b-9d62-3554b6c7b328> | 3.953125 | 831 | Structured Data | Science & Tech. | 43.910368 |
Such a scenario could make floods fiercer, damage more crops, and worsen the spread of diseases such as malaria, scientists say.
Rainfall patterns are already shifting as Earth warms under a blanket of humanmade greenhouse gases, experts say.
Study co-author Richard P. Allan, an atmospheric scientist at the
University of Reading in Berkshire, United Kingdom, said previous
studies have shown that "wet regions are becoming wetter, and dry
The study team analyzed satellite images of rainfall over tropical oceans over nearly two decades, from 1988 to 2004.
The researchers found that during El Niño
years, which tend to be warmer, rain fell in heavier showers. An El
Niño is a climate event where the flow of abnormally warm surface
Pacific waters temporarily changes global weather patterns.
"This is something that climate models had predicted," Allan said. "But getting the data from observations is very important."
Many previous rainfall pattern studies have relied on
measurements from rain gauges. Such gauges are sparsely distributed
across land, Allan said, whereas satellites can see large areas as a
Global Warming Forecast
Although our planet is warming overall, Earth's climate still varies between warmer and wetter El Niño years and cooler and drier La Niña years.
Looking at these changes in rainfall can give scientists a good
estimate of what will happen with continued global warming, according
to Allan and his co-author, Brian Soder of the University of Florida.
With continued global warming, the changes in Earth's rainfall
patterns will be worse than previously forecast, Allan and Soder write.
For every 1.8 degree Fahrenheit (1 degree Celsius) rise in global
temperature, heavy rain showers became more common, with most intense
category jumping 60 percent, says the study, which will be published
tomorrow in the journal Science. | <urn:uuid:67ef92ef-593c-4617-ada1-2abd0abfe4d8> | 3.78125 | 391 | Truncated | Science & Tech. | 36.753378 |
Joined: 16 Mar 2004
|Posted: Tue Apr 03, 2007 11:23 am Post subject: Silica particle sparks life in protein
|Tiny formless particles in water solution take on a well-ordered and functional structure as soon as they come into contact with nanoparticles of silica. A unique breakthrough by researchers at Linkoping University in Sweden creates new potential in medicine and biochemistry and at the same time provides a new piece of the puzzle in theories about the origins of life.
Normally, inorganic materials like silica are unwelcome in biological systems, since they disrupt the form and function of proteins.
“We wanted to reverse the thinking and try to design proteins that take on their function only after encountering an inorganic surface,” says Bengt-Harald Jonsson, professor of molecular biotechnology.
He directs the research team that is now presenting its findings in Angewandte Chemie.
The team designed a peptide (a short protein) with a specific distribution of positive charges. The peptide was mixed into a solution of spherical silica particles, about 9 nanometers (billionths of a meter) across. When the peptide was free in the solution it had no structure whatsoever, but when it connected with the negatively charged silica ball it assumed the form of a helix. The result was a complex of a silica particle and a functional protein.
When the researchers added amino acids to their peptide, the complex took on the properties of a catalyst, a function similar to that of enzymes in living cells.
The method has several possible fields of application:
-- recognition of organic molecules
-- catalyzing of chemical reactions with precise control
-- target-seeking particles for medical uses
But the Linköping University scientists’ successful experiment may also shed light on the eternal question of the origin of life. Particles of clay containing silica in the ‘primeval soup’ may have attracted unstructured peptides with amino acids attached and given rise to the first functional proteins.
“We know that RNA (which plays a decisive role in the transfer of information in cells) can bind with clay particles whose surfaces have negative charges. The probability of peptides with amino acids having formed well-defined structures with the clay at an early stage of development is considerably greater, since they are more diversified than RNA is,” says Bengt-Harald Jonsson.
Source: Linköping University & PhysOrg.com
This story was first posted on 6th December 2006. | <urn:uuid:78b3301c-0dbd-437d-95bd-2fe3201894a0> | 3.015625 | 523 | Comment Section | Science & Tech. | 25.759205 |
A prize of $25 million for anyone who can come up with a system for removing greenhouse gases from the atmosphere was launched on Friday. It is the biggest prize in history, claims its sponsor, Richard Branson.
The head of Virgin Group said at the launch in London, UK, that the prize was not for removing emissions from power plants before they reach the atmosphere and storing them deep underground - an existing technology known as carbon capture and sequestration.
Instead, the brief is to devise a system to remove a "significant amount" of greenhouse gases - equivalent to 1 billion tonnes of carbon dioxide or more - every year from the atmosphere for at least a decade. It was inspired by the £20,000 prize for developing a way of measuring longitude won by 18th century clockmaker John Harrison, and recounted in the book Longitude. The $10 million X-Prize for private human spaceflight, won in 2004, was also an inspiration.
The initial closing date for Branson's Earth Challenge is 8 February 2010. If the judges deem that no design submitted by that stage is worthy of the prize, it will re-open for two more year-long phases.
Branson has received impressive backing for his new environmental initiative. His five co-judges are former US vice president Al Gore, Jim Hansen, director of the NASA Goddard Institute, James Lovelock, the father of the Gaia theory, Australian conservationist Tim Flannery, and Crispin Tickell, director of the Policy Foresight Programme at Oxford University, UK.
Steve Howard, chief executive of The Climate Group and an advisor to the judges, said: "For $25 million, people will do extraordinary things. It's to fire people up and say: 'let's do this.'"
Environmentalists have welcomed the initiative, but Friends of the Earth said it should not distract from the need to reduce carbon dioxide emissions at source, "including unsustainable air travel".
Celine Herweijer, climatologist at US-based Risk Management Solutions, says: "While we should welcome initiatives like this that aim to limit the amount of climate change in the future, we also need more creative solutions to the problems that climate change is already causing."
Conflict of interests?
Branson has been criticised for his conflicting activities: running a large airline company on the one hand, and engaging in a number of environmental initiatives, including pledging $3 billion of his companies' profits to research into biofuels.
There are also a few catches in the prize's fine print. The winner will initially only be give $5 million, with the remaining $20 million being paid "at the end of 10 years if the judges decide that the goals set out have been achieved". And the conditions include that the removal must have long term effects, "measured over, say, 1000 years", but gives no indication of how this will be assessed.
Furthermore, the researchers will have to find independent ways of financing the development of their design. When questioned about this by New Scientist, Branson said if an idea had promise but no funding, "we will help them find it".
But Stuart Haszeldine, a geologist at the University of Edinburgh, UK, says: "Richard Branson is ahead of the pack in getting to grips with CO2 in the atmosphere. I hope all other businesses, large and small, follow his lead. Yes, its true Branson's company may benefit eventually, but we will all benefit, by a cleaner greener planet."
Climate Change - Want to know more about global warming - the science, impacts and political debate? Visit our continually updated special report.
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Mon Jul 30 16:44:18 BST 2007 by MR. KENNETH SHORT.
WITH THE RECENT COTAMINATION OF POTABLE WATER IN THE WEST COUNTRY FROM SEWERAGE, WHY IS SEWERAGE NOT CONTAINED AND IT'S PERMENANT MOVEMENT USED TO GENERATE POWER. SEWERAGE IS ONE SOURCE OF ENERGY THAT RUNS CONTINUOSLY AND IS NOT USED EFFIENTLY IN THE PRODUCE OF ENERGY, SURELY THE FUNDS FROM IT'S ENERGY CREATION WOULD FUND IT TO BE CONTAINED.
virgins 25 million greenhouse prize
Sat Aug 04 23:21:26 BST 2007 by fred treutlein
simple and short. more trees and plants lesser people. plant 1 tree per person each month or so and global warming does not get worster and over time reduze population so everybody has an sustainable amount of land somehow. all of this as a wider program of individual freedom and corresponding responsibility. cost much lesser than it makes money. unbeatable so won the 25 million. thanks.
Virgins 25 Million Greenhouse Prize
Mon Oct 20 12:37:38 BST 2008 by Burton Nelson
The idea is simple, but it overlooks too may variables. How do you plan on convincing people to stop reproducing? Human nature isn't likely to take kindly to having governments dictate what happens in thir own homes. Ask the Chineese people about that.
As for planting all those trees, great idea, but you neglect to mention how to feed the remaining people. Planting trees and reducing population would reduce greenhouse gasses, but the cost in human advancement would be far to great an expense for humanity to allow.
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
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WHAT happened before our universe began? According to two theoretical physicists, if there was a universe before ours then it should have been remarkably similar to this one, with the same basic ingredients and properties. It may even be possible to see a faint picture of our parent universe imprinted on the sky.
Questions about a time before the big bang were once thought to be meaningless, because according to Einstein's general theory of relativity, the universe began at a singularity - a mathematical point with infinite density at which all calculations break down.
However, physicists now believe that the theory of relativity is limited and the effects of quantum mechanics would have blurred out the singularity just a little, so at a crucial moment the density of matter and radiation was not infinite. If this was the case, it becomes possible to try to work out what led up ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:aad56013-318d-41af-b21b-0b18aadfc772> | 3.484375 | 196 | Truncated | Science & Tech. | 35.309412 |
YES! Just what Reeko likes to see - a kid interested in learning! Check
back here every week to see what the new Science Word of the Day is. Just
think, after a year of this you'll be a genius!
We all know we must have water, or H2O, to survive. Since water makes up 66 percent of the human body, it’s pretty easy to understand that without water, we will not live long. Water lurks in the spaces between the cells and it constantly being excreted through sweat, urination, and when we exhale. You have to replace all that lost water but, you can indeed drink too much water.
In 2010, a 28-year-old California lady entered a radio contest. The contestants had to drink water and not go to the bathroom. Whoever drank the most water and held it the longest, was the winner. The lady won the contest but ended up throwing up and going home with an extreme headache. Later she died from what is called “water intoxication”.
In the human body, the kidneys control the amount of water that is allowed to leave the kidney and be distributed throughout the cells. If you drink too much water, the kidneys cannot keep up and the blood becomes waterlogged. The water leaves the blood and enters the cells which swell like balloons. Most cells have room to expand because they are surrounded by flexible tissue. But brain cells are packed tightly inside your skull and have no room to expand. Too much water can lead to brain swelling, or edema, which will almost always prove to be fatal. | <urn:uuid:68340330-c582-4122-9929-54bb36a79f26> | 2.921875 | 332 | Personal Blog | Science & Tech. | 68.604899 |
seen on the previous page
that the Julia Set has four independent
parameters (the real and imaginary components of the start-value of z,
and the real and imaginary components of c, the
added constant), so, technically the full Julia Set is a
it's traditional to use slices taken through the AB
can generate cross-sections through it at any angle we like
four dimensions, and with any offset.
The Mandelbrot Set is
a section of the 4D Julia Set
The Mandelbrot Set exists as a cross-section
through the 4D Julia Set, in
the plane CD, with A and B
to zero. Since it cuts through
the shape at right angles to our usualAB-plane Julia Set
images, the intersection isn't obvious when we compare the images.
a three-dimensional space, two angled planes are
guaranteed to intersect somewhere to form a line, but in
space they're only guaranteed to intersect at a point. So in order to
able to see the tell-tale signs of intersection, we need to start
assembling collections of AB
Julia Set images to be able to see the
larger pattern emerging.
our earlier table of Julia Set images, and calculate it again, to a
With just a couple of hundred Julia Set images,
shadow of the Mandelbrot Set is starting to emerge.
next image is built from a rectangular array of several
thousand tiny Julia images.
The pattern of Julia Sets that have a
dark centre builds up to form a
noticeable Mandelbrot Set outline. More precisely, the
exact centre point in a given Julia Set
selected using (0, 0) (C, D) will be identical to
correspondong point on the Mandelbrot Set (0,0), (x,y)
... so if we'd only plotted the single
of each Julia Set in our 2D array,
we'd actually be plotting the Mandelbrot Set. Since this map is a
of two-dimensional images, it's technically a four-dimensional
image (with very
thing that we notice from these images is that although the Mandelbrot
outline is visible, we can also see what appears to be
additional overlaid detail. The
interior of our shape isn't entirely black, because
we've been plotting
more than just the centre pixel of each Julia image. Pixels away from
the centre of the individual Julia tiles are also playing a part in
picture, and are showing us hints of further detail that exists
away from the
Mandelbrot plane. When we look at the overall image (above), we're not
seeing the shadow of the Mandelbrot Set, we're also seeing
glimmerings of additional
compacted into 2D.
Maps and Subsets
images above illustrate how the Mandelbrot Set can be used to as a map
of the usual Julia Set images. A "zoom in" on a particular point on
the Mandelbrot Set reveals characteristics reminiscent of the
character of the Julia Set image that would have been called
up by using those same two coordinates as "selection numbers"
regions of the Mandelbrot Set tend to correspond to "spiky" Julia set
images, "twisty" regions on the Mandelbrot tend to correspond to
"twisty" julia images, and so on. This
appears because the larger 4D Julia Set shows local
in four dimensions – local
themes that appear
in the CD
(Mandelbrot) plane also tend to "infect" small intersecting regions of
(standard Julia) plane, and vice versa.
the effect is very striking. If we zoom in on the Mandelbrot, we find
smaller shapes that are noticeably "Mandelbrot-like", and it's said
if we zoom in far enough, we can also find
points on the Mandelbrot Set that seem to correspond to full Julia Set
images. This might suggest to us that the Julia Sets are somehow contained
within the Mandelbrot set.
reality, it's the other way around.
get carried away and say that the Mandelbrot Set contains perfect
copies of itself, it doesn't.
The Mandelbrot Set has the
property (for a cross section of the full 4D shape) that all points on
boundary are connected within the plane. This means that if we placed
the point of an infinitely-sharp pencil onto one part of the Mandelbrot
boundary, and traced out an infinite length of line, we'd end up back
at our starting position having traced out the entire set. The shape
has no separated "islands" (unlike most of the standard Julia
So when we find a "mini-Mandelbrot" within
the larger Mandelbrot Set, by definition, it can't be a perfect copy,
condition of "connectedness" means that the smaller offspring must be
connected to the parent by threads and tendrils that the original
parent doesn't have. Similarly, although some people have claimed to
have found things that look like Julia Set
islands floating within the Mandelbrot Set, they must have
internal interconnections that don't necessarily exist in the
corresponding "standard" Julia Set image, and must have external
connections that definitely won't exist in the
although the Mandelbrot Set can be considered as a "map" of how certain
aspects of the full Julia Set change with location across two of its
four dimensions, technically, the Mandelbrot Set is a subset
of the Julia Set, rather than the other way around.
zoom in on the Mandelbrot and obtain a perfect standard
However, we can slice the
full 4D Julia Set and obtain a perfect Mandelbrot.
Into the Fourth Dimension
Given that the full Julia Set is
four-dimensional, how can we visualise it?
we want to slice the Julia Set to produce 2D images, we have six main
ways of doing it. We're familiar with the "Mandelbrot" slice (0,
y), and with the usual Julia Set image slices [(x,
n)], but we also have four other
planes that we can use for taking cross-sections through the solid's
Here they all are:
of these six planes can then be extended in one other
dimension to create
a three-dimensional solid. Stripping away the duplicates, we then end
with four different major solids: (ABC)
[(x, y), (z, 0)], ABD [(x,
y), (0, z)],
ACD [(z, 0), (x,
y), and BCD [(0, z), (x, y)].
Each of these incorporates three of the six primary
Solids (click images to enlarge)
free to slice the four-dimensional shape at any angle and
offset we like,
but these four
images show the four primary solids.
Solids # 1 &
The first two of
these solids have the central "circle" AB
someone familiar with the usual Julia Set images, these two are the
most easily visualisable – they can be assembled by
Set images from
our earlier arrays. The first solid represents a "stack" of
images taken along the central "spine" of the map, and shows a
"Mandelbrot-like evolution from the bottom of the diagram to the top,
starting with thin "spike-like" features, developing into a
bulb, which is then followed by a large void terminated in a
However, if we cut the ABC
solid in the hopes of finding a Mandelbrot, we fail. We can get a sort
of triangular wedge that looks a little like a
Mandelbrot, but the
"side detail" is all wrong. That detail is contained in parameter D,
which isn't used in this solid.
we now look at the ABD solid, we can produce
cross-sections that are
reminiscent of the Mandelbrot's side-bulbs, but the earlier "spine"
evolution is missing (because of the lack of parameter C).
we're trying to visualise the full four-dimensional shape, it's
probably easiest to think of ABC as the
mirror-symmetrical "core set"
of the full Julia Set, and to visualise D as a
parameter that makes the
shape break up and twist to the left or the right, depending
whether D is positive or negative.
# 3 & 4
combinations of three parameters, the contained Mandelbrot is more
explicit. In the second two images, we're using ACD
and BCD ,where C
and D describe the Mandelbrot plane. These two
images have been coloured
according to the magnitude of A or B,
and as a result they're showing
a central horizontal red band which, if we cut along it, would give the
set as a cross-section.
The first image
(left) shows the effect of varying A, the initial
"real" component of z.
The last image
shows the effect of varying B, the initial
"imaginary" component of z.
we now look back at our Julia Set mosaic image, with its hints of
additional four-dimensional detail, those details correspond to the
additional detail that
appears in these last two images.
With these two last shapes, we see something odd:
as well as the central Mandelbrot cross-section, there seem to be some
suspiciously similar-looking shapes intersecting these solids at 45
degrees. How come?
the Mandelbrot also "echoes" through the main Julia Set. If
Mandelbrot is given by 0,0, x,y, and the first two
parameters are the
values of z, and the second two (x
and y) are the constant offset, c,
that gets added at each stage,
then we can see that after one iteration,
squaring 0,0 again gives 0,0
(no change) and adding x,y
this gives us (x,y),
So, if we start
at (x,y), (x,y), we'd seem to be entering the same
with a "one iteration" head start. So as well as a Mandelbrot
cross-section cutting through the 4D Julia hypersolid in the CD
plane (0,0), (x,y), we might also expect a
Mandelbrot section at (x,y),
(x,y), and perhaps another at (-x,-y), (x,y).
So there ought to be some 45-degree Mandelbrot
resonances within the larger four-dimensional
Julia Set plot,
(A&B), C, D
(click to enlarge))
Working out an
for the number of perfect Mandelbrots that we can obtain from
the Julia Set, using various types of flat and curved cross-sections is
trickier problem, but perhaps mathematicians will have a crack
it one day.
Here are some animated renderings of parts of the
full four-dimensional Julia solid: | <urn:uuid:0ce5ee66-c70e-496f-a49b-5625a6dbe3a8> | 3.375 | 2,445 | Tutorial | Science & Tech. | 43.776415 |
|www . Science-Projects . com|
SURVIVAL CURVES and MINIMUM LETHAL HITS
| go to previous page on how to use semilog graph paper |
This collection of "dose plots" or "survival curves" starts with it origin at the red "1". From it arise three plots, a, b, and c. Plot "a" is of the most sensitive critter, while that of "c" is of the least sensitive critter.
Game theorists have proven that if you extend asymptotes from the straight portions of the curves back to the vertical axis, where that line crosses indicates the minimum number of lethal hits.
Let's discuss the meaning of that for a moment. It has been shown in battle scenarios that the average soldier is usually shot several times and still doesn't die - although it is plausible that one bullet in just the right place - brain, heart, can kill. Thus the minimum number of hits to be lethal for a soldier is one. On the other hand, if we talk not about bullets but gamma rays, then the minimum number of lethal hits in a human must be much larger for immediate death. Perhaps there are a critical 1,000 cells in the body such that if ALL of them are knocked out - each by a single gamma ray, then the minimum number of lethal hits is 1,000. Thus if you were to irradiate a large population of people with gamma rays and make your dose plot, you would find the extrapolated asymptote crossing the vertical axis at 1,000. (Again, remember that most people will be hit with millions of gamma rays - but most of them would be in inconsequential places.)
Thus when you look at this figure, you see that both "a" and "b" are critters for which the minimum number of lethal hits is one. But for "c" the line extrapolates to "2", and so that critter requires at least two hits to kill it.
Another consideration that you can derive from these plots is the LD50 ("lethal dose for 50%"; the dose that kills 50% of the critters). For "a" the LD50 is about 5. You find this by moving down the red line to where it crosses the horizontal 0.5 line and at that point look down at the bottom to see how many hits that indicates.
For "b" LD50 is about 10, but you run into a problem with "c" because its curve doesn't start declining immediately. So, for "c", you must go to a straight portion and then determine how many hits it takes to decrease the number to a half. So go down the blue line where it is straight to some convenient place and then measure off how many more hits it takes to drop in half. You should get something like 16 hits.
| Site's Table of Contents | Site's Index | | <urn:uuid:97e089d9-eea3-40ff-974a-f67dc74a7c41> | 3.546875 | 606 | Tutorial | Science & Tech. | 66.451112 |
Researchers report that they've found a strain of bacteria that can swap arsenic for the element phosphorus in its metabolism -- even incorporating arsenic into its DNA. Writing this week in the journal Science, the scientists describe the bacteria harvested from the highly saline, arsenic-containing waters of Moro Lake, California. In lab experiments the researchers were able to culture the bacteria in growth media, swapping phosphorus-containing salts for ones containing arsenic. Over time, the bacteria incorporated arsenic compounds into their cellular makeup, even in nucleic acids and proteins. We'll talk about the find, and what it might mean for the search for life elsewhere in the universe.
Produced by Charles Bergquist, Director and Contributing Producer | <urn:uuid:eadee963-4d0d-49b1-b863-140209ac74fb> | 3.015625 | 140 | Truncated | Science & Tech. | 23.718288 |
Related Information Links
NOTE: this application requires that you have a calculator capable of doing MATRICES. Most if not all graphical calculators have this capability. This reading uses the Texas Instrument TI-82 Graphical Calculator as an example.
Early on in your chemistry studies, you will have ample opportunity to balance equations! This is a fundamental skill in chemistry, as you might have noticed from the short reading in stoichiometry! Balancing equations means writing chemical equations such that the amount of stuff you start with in the reaction equals the amount of stuff you end up with as a product. In other words, if I start baking bread with 10 pounds of flour, I should end up with 10 pounds of bread, unless some is lost onto the floor or if some of it goes up in smoke!
A simple example goes a long way. We can form water by combing hydrogen gas (H2) and oxygen (O2) in the presence of electricity. The reaction looks like this:
If you do some of the gram molecular weight calculations you will find this:
They're not lost, we just haven't balanced the equation! You might have also noticed that there are two oxygens on the left and only one on the right! We need to get things in the correct proportions for this reaction to be balanced. The balanced reaction looks like this:
This says that we need two hydrogen molecules to combine with one oxygen molecule to form two new water molecules. If we do the math:
Balancing equations is an art, but if you have a calculator that can handle what is known as a "matrix", you have a foolproof way of balancing equations! A matrix is a group of numbers, arranged in rows and columns, like this:
This is called a "2 by 2" or "2 x 2" matrix, because it has two rows (going across) and two columns (going down). In this application, you will have to do three matrix operations:
Fortunately, graphing calculators make this particularly easy! To help you understand a little of what you are doing, let's explain finding the determinant. The determinant is a single number generated by cross-multiplying the terms in the matrix. You must have a square matrix (n X n) to be able to find the determinant. The equation for finding the determinant is:
The example below the equation shows a sample calculation for a 2 x 2 matrix. Notice that you are cross multiplying the opposite terms, then subtracting out the other set of opposite set of multiplied terms. Pretty easy.
Here is how this is done on the TI-82 Graphical Calculator. These instructions are SPECIFIC to the TI-82:
Now we are ready to talk about balancing equations. Let's choose a simple reaction:
We have two different elements, Cr and O, so we will need two different equations. We are trying to calculate the values of a, b, and c, the coefficients of the reaction. The two equations look like this:
Cr: 1a + 0b = 2c
The "1a" means that there is one Cr behind the "a" coefficient, zero Cr's behind the "b" coefficent, and 2 Cr's behind the c coefficient. We use the same technique for oxygen. We now have two matrices (called Matrix A and Matrix B):
To obtain the values of a, b, and c, do these steps:
Here is how to do the first step:
To do the second part, calculating c:
The balanced equation is now:
Try It Out
Copyright © 1996-2008 Shodor
Please direct questions and comments about this page to | <urn:uuid:d5e9851e-9d7e-4764-9af5-7eb30babbb5a> | 4.21875 | 760 | Tutorial | Science & Tech. | 56.499272 |
We mapped substantial migration of the river channel between the City of Winslow and the Navajo Nation community of Leupp; in a human lifetime the river has moved more than a mile across its valley floor.
Explains biological soil crusts, organism-produced soil formations commonly found in semiarid and arid environments, with special reference to their biological composition, physical characteristics, and ecological significance.
Fact sheet on the need to protect biological soil crusts in the desert. These crusts are most of the soil surface in deserts not covered by green plants and are inhabited by cyanobacterium (blue-green algae) and other organisms useful to the ecosystem.
GIS data set from the USGS National Landslides Hazards Program showing major landslide events in the United States and Puerto Rico with metadata. Map layer can be downloaded in shapefile format or SDTS format.
Detailed measurements of elevation help to understand the extent and severity of subsidence. Study asks if subsidence indicates the aquifer system is compacting temporarily or permanently, and are the changes human-induced or tectonic.
Modified version of paper by F.T. Manheim and A.G. McIntire, Civil Engineering Practice, Vol. 13, No. 1, pp. 35-48 (1998). A new shoreline file has been created for Boston Harbor by digitizing and combining the most recent charts.
The Eastern Earth Surface Processes Team provides geologic mapping regional geologic studies to determine stratigraphy and geologic structure, topical studies to understand geologic and surficial processes, and syntheses of earth science data. | <urn:uuid:126a1689-ba09-4185-b976-9ecf50226dbd> | 3.171875 | 329 | Content Listing | Science & Tech. | 31.927187 |
Life in the Deep Ocean
The deep ocean is very cold, under high pressure, and always dark because sunlight can not get down that far. Less life can survive in the deep ocean than in other parts of the ocean because of these conditions. For some animals, food comes from the bodies of dead fish, dead plankton, and even dead whales that rain down from the open ocean waters above.
But there are two extreme environments in the deep sea where life is more abundant. These are cold seeps and hydrothermal vents. In these environments, food chains do not begin with plants or algae that make food from sunlight.
Cold seeps are areas where methane and hydrogen sulfide are released into the ocean. Cold seeps are home to clams, mussels, shrimp, crabs, bacteria, and tubeworms. For food, these animals depend on certain types of single-cell Archaea and Eubacteria microbes that live off the methane and hydrogen sulfide from the seep. There are cold seeps in many different places in the world’s ocean. They are often at the edges of continents.
Hydrothermal vents are another type of extreme environment in the deep sea. While most of the water in the deep ocean is close to freezing, the water at hydrothermal vents is very hot. It is heated by volcanic activity at tectonic spreading ridges. The hot water spews from holes in the crust called vents, looking like dark smoke because of the dissolved chemicals it picked up underground. Certain types of Archaea and Eubacteria microbes are able to turn the chemicals from the hot water into the energy they need to survive. Many other types of living things including fish, shrimp, giant tubeworms, mussels, crabs, and clams thrive in this environment as well. They, too, are adapted to the hot water and high pressure. Some of them, like mussels, clams, and the giant, 2-meter (6-foot) tubeworms, get the nutrition they need from microbes living within their bodies. Others, like shrimp and barnacles, eat the Archaea and Eubacteria. | <urn:uuid:e9a2b82f-d368-4da9-a914-3a41d5e95f2e> | 4.03125 | 443 | Knowledge Article | Science & Tech. | 51.482941 |
Search results for 1 - 10 of 77
- Biography of Albert Einstein
- Albert Einstein was a German-born theoretical physicist. He is best known for his theory of relativity and specifically mass-energy equivalence, E = mc2. Einstein received the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the pho...
- Stephen Hawking
- A biography of one the world's best-known astrophysicists, Stephen Hawking. Bibliography: http://hawking.org.uk/index.php/about-stephen/briefhistoryhttp://hawking.org.uk/index.php/disability/thecomputerhttp://www.telegraph.co.uk/health/healthnews/5189411/Stephen-Hawkings-key-discoveries.htmlhttp://w...
- Planck vs Einstein
- This timeline shows the interaction between the academic and political paths of Max Planck and Albert Einstein and the controversy which surrounded them. Content by Nigel Kuan.
- Time line of Renaissance period scientists and important people. | <urn:uuid:88ea97ef-3e73-4e59-9b03-6dc9b6758f87> | 2.875 | 234 | Content Listing | Science & Tech. | 54.701836 |
Country of Origin: United States of America
3-D Test: 8.9 x 8.9 x 1.3cm (3 1/2 x 3 1/2 x 1/2 in.)
Contents Overall: Metal, plastic, rubber insulation
This bio-harness was flown aboard Apollo 11 in July 1969, but was not worn during the mission. It is not identified as to which astronaut it was assigned. The Apollo Bio-Harness Assembly was worn under either the intra-vehicular or extra-vehicular pressure suit.
The complete assembly consisted of a cotton duck belt fitted with snap fastners and teflon-coated beta cloth pockets, which attached the assembly to either the constant wear garment or the liquid cooling garment. The components consisted of an electrocardiograph signal conditioner, an impedance pneumograph signal conditioner, and a DC-DC converter. These instruments monitored the physiological functions of the astronaut.
Transferred by NASA to the National Air and Space Museum in 1970.
Transferred from NASA/JSC | <urn:uuid:983b5135-f579-4f16-9006-b6d82419c565> | 2.765625 | 214 | Knowledge Article | Science & Tech. | 57.859707 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2000 December 25
Explanation: If you look closely at the shadow of this tree, you will see something quite unusual: it is composed of hundreds of images of a partially eclipsed Sun. Early today, trees across North America will be casting similar shadows as a partial eclipse of the Sun takes place. In a partial eclipse, the Moon does not cover the entire Sun. The above effect is created by small spaces between leaves and branches acting as pinhole lenses. Looking at shadows involving eclipse light is relatively safe - looking directly at the Sun, even during an eclipse, is dangerous and proper precautions should be taken. The above picture was taken in 1994 on the campus of Northwestern University.
Authors & editors:
Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/GSFC
& Michigan Tech. U. | <urn:uuid:81376508-38f2-46af-a684-b570ceefd37b> | 3.375 | 214 | Knowledge Article | Science & Tech. | 42.143077 |
Even a small degree of global warming will have large effects on ecosystems, and ultimately on us. Take, for example, the rivers in upstate New York and New England, where reduced ice cover is changing the life along the river.
Lilliputian wildflowers will soon line the Hudson's banks. In what are known as riverside ice meadows, an ancient cycle of ice formation and melting gives rise to swamp candles, ladies'-tresses, wood lilies and other rare, diminutive flowers.
In New York's Adirondack Mountains, ice that forms on the river in winter is pushed onto its banks in spring; there it scours the sloping cobble shores, keeping them free of shrubs and small trees and leaving space for wildflowers to sprout in fragile, arctic-like ice meadows.
But the future for these floral pixies, which depend on late-melting river ice, is bleak. The number of days of ice on northeastern rivers has declined significantly in recent winters, said hydrologist Glenn Hodgkins of the U.S. Geological Survey (USGS) Maine Water Science Center in Augusta.
The trend could spell disaster for the ice meadows. It also signals trouble ahead for endangered Atlantic salmon and other fish, for wetlands plants and animals, and for Northern economies, all of which are sustained by winters with icy rivers.
If the pattern continues, say scientists, only in Currier and Ives prints will ice skaters twirl across frozen New England rivers.
"Northeastern rivers have 20 fewer days of ice cover each winter now than they did in 1936," said Hodgkins, who said the total now averages 92 days. "A lot of that decrease has occurred since the 1960s."
Like so many other environmental problems, changes due to global warming will have an impact on us.
If the salmon population dies off - along with reductions of other fish populations - there is going to be a lot less for people to eat.
"Lack of ice on rivers severely affects fish, especially anadromous fish like endangered Atlantic salmon," said Trial, a biologist at the Maine Atlantic Salmon Commission in Bangor. "Ice cover insulates rivers and streams, protecting young salmon from cold. Without that cover, the salmon are also more susceptible to predators." Bald eagles, for example, are able to snare their piscine prey only from open water.
Atlantic salmon are in peril for several reasons, but scientists Terry Prowse and Joseph Culp of the National Hydrology Research Center of Environment Canada in Saskatoon, say lack of river ice has the potential to kill large numbers of salmon eggs, as well as juvenile and adult fish.
The most difficult winter situation for salmon and other fish, biologists say, is on-again, off-again ice cover: rivers that freeze over one week and then are open the next.
Photo of Ladies Tresses Orchid by Gary M. Stolz / USFWS. | <urn:uuid:1cd01053-9f41-4caa-a34b-896cfee547d3> | 3.734375 | 617 | Personal Blog | Science & Tech. | 44.677394 |
Characteristics of tree hollows used by Australian arboreal and scansorial mammals
Goldingay, RL 2012, 'Characteristics of tree hollows used by Australian arboreal and scansorial mammals', Australian Journal of Zoology, vol. 59, no. 5, pp. 277-294.
Published version available from:
Many species of non-flying mammal depend on tree hollows (cavities or holes) for shelter and survival. I reviewed the published literature on tree hollow use by Australian non-flying arboreal and scansorial mammals to provide a synthesis of tree hollow requirements, to identify gaps in knowledge and to stimulate future research that may improve the management of these species. The use of hollows was described in some detail for 18 of 42 hollow-using species. Most information was for possums and gliding possums, whereas dasyurid marsupials and rodents were largely neglected. The paucity of data for many species must be addressed because it represents an impediment to their conservation. Hollow abundance appears to be the primary determinant of tree preferences. This accounts for the frequent use of standing dead trees by most species. Most hollow-bearing trees used as dens were at least 100 years of age. Further studies that describe the dynamic processes that govern the availability of tree hollows are needed. The few studies that document attrition of hollow-bearing trees suggest that land managers need to improve strategies for the effective retention and long-term replacement of these trees. | <urn:uuid:d3c86f0d-1f1a-405e-b84c-3752d91a73e6> | 3.578125 | 302 | Academic Writing | Science & Tech. | 36.718466 |
Why python and unicode leads to frustration
In python-2.x, there's two types that deal with text.
str is for strings of bytes. These are very similar in nature to how strings are handled in C.
unicode for strings of unicode codepoints.
In the python-2.x world, these are used pretty interchangably but there are several important APIs where only one or the other will do the right thing. When you give the wrong type of string to an API that wants the other one, you may end up with an exception being raised (
UnicodeEncodeError). However, these exceptions aren't always raised because python implicitly converts between types... sometimes.
Although doing the right thing when possible seems like the right thing to do, it's actually the first source of frustration. A programmer can test out their program with a string like:
"The quick brown fox jumped over the lazy dog" and not encounter any issues. But when they release their software into the wild, someone enters the string: <code>"I sat down for coffee at the café" and suddenly an exception is thrown. The reason? The mechanism that converts between the two types is only able to deal with ASCII characters. Once you throw non-ASCII characters into your strings, you have to start dealing with the conversion manually.
So, if I manually convert everything to either bytes or strings, will I be okay?
A few solutions
Use kitchen to convert at the border
In python-2.x I've started work on a library that can help with unicode issues. The part that's especially relevant is the converter functions. They allow you to transform your text from bytes to unicode and unicode to bytes pretty painlessly.
If you're writing APIs to deal with text, there's a few techniques to use. However, you must be wary in what you do as each method has some drawbacks. | <urn:uuid:d2f88d39-00f4-4312-9afe-f69b106ccc6f> | 2.734375 | 400 | Personal Blog | Software Dev. | 61.975689 |
Measurement of the downhole velocity of the CIROS-1 drillhole after the completion of drilling by lowering a hydrophone down the drillhole was unsuccessful due to equipment failure. Determination of the dip, faults and strong reflectors in the geologic structure in the immediate vicinity of the CIROS-1 drillhole was conducted using seismic reflection techniques. Testing of various seismic ... reflection techniques was also conducted for any future reflection projects on the sea-ice. It is important to link the geological structure determined by drilling with the horizons detected in other seismic surveys in the western Ross Sea, in order to date these horizons and their deformation. The reflection survey would also possible reveal some of the deformation history in the vicinity of the drillhole as well as the possible presence of reflecting strata at depths greater than reached by the drilling project. Two seismic lines were shot running at right angles from the CIROS-1 drillhole and records appear to have primary reflected energy down at least to 800m sub-seafloor. The aim was to determine the geological structure in the CIROS-1 immediate vicinity and to evaluate marine airgun sound sources as an alternative to explosive operation. | <urn:uuid:781f63dc-dac0-4c1a-9555-6b4329ad2704> | 2.828125 | 243 | Academic Writing | Science & Tech. | 27.792545 |
Calling Function Modules
This section describes calling function modules from the Function Builder.
Finding Function Modules
Before programming a new function or creating a new function module, you should look in the Function Builder to see whether there is an existing function module that already performs the same task.
For more information about this, refer toFinding Function Modules in the ABAP Workbench documentation. For example, you might look for function modules that process strings by entering *STRING* as a search criterion in the Repository Information System. This is an extract from the list of function modules found:
The title CSTR is the function group. There is a main program SAPLCSTR that contains these function modules. If you select a function module, you can display its attributes in the Function Builder.
The documentation describes the purpose of the function module, lists the parameters for passing data to and from the module, and the exceptions. It tells you how you can pass data to and from the function module, and which errors it handles.
This section provides further information about the interface parameters and exceptions, and how to use the function module. For further information, refer to
You can specify the types of the interface parameters, either by referring to ABAP Dictionary types or elementary ABAP types. When you call a function module, you must ensure that the actual parameter and the interface parameters are compatible.
Interface parameters are, by default, passed by value. However, they can also be passed by reference. Tables parameters can only be passed by reference. You can assign default values to optional importing and changing parameters. If an optional parameter is not passed in a function module call, it either has an initial value, or is set to the default value.
Exceptions are used to handle errors that occur in function modules. The calling program checks whether any errors have occurred and then takes action accordingly.
Testing Function Modules
Before you include a function module in a program, you can test it in the Function Builder.
For more information about this, refer toTesting Function Modules in the ABAP Workbench documentation.
Calling Function Modules in ABAP
To call a function module, use the CALL FUNCTION statement:
CALL FUNCTION <module>
[EXPORTING f1 = a 1.... f n = a n]
[IMPORTING f1 = a 1.... f n = a n]
[CHANGING f1 = a 1.... f n = a n]
[TABLES f1 = a 1.... f n = a n]
[EXCEPTIONS e1 = r 1.... e n = r n [ERROR_MESSAGE = r E]
[OTHERS = ro]].
You can specify the name of the function module <module> either as a literal or a variable. Each interface parameter <fi> is explicitly assigned to an actual parameter <a i>. You can assign a return value <r i> to each exception <e i>. The assignment always takes the form <interface parameter> = <actual parameter>. The equals sign is not an assignment operator in this context.
You can use the EXCEPTIONS option to handle the exceptions of the function module. If an exception <ei > is raised while the function module is running, the system terminates the function module and does not pass any values from the function module to the program, except those that were passed by reference. If <e i > is specified in the EXCEPTION option, the calling program handles the exception by assigning <r i > to SY-SUBRC. <r i > must be a numeric literal.
If you specify of ERROR_MESSAGE in the exception list you can influence the message handling of function modules. Normally, you should only call messages in function modules using the MESSAGE ... RAISING statement. With ERROR_MESSAGE you can force the system to treat messages that are called without the RAISING option in a function module as follows:
If you specify OTHERS after EXCEPTIONS, the system assigns a single return code to all other exceptions that you have not specified explicitly in the list.
You can use the same number <ri > for several exceptions.
The recommended and easiest way to call a function module is to use the Insert statement function in the ABAP Editor. If you select Call Function and specify the name of the function module (F4 help is available), the system inserts a CALL FUNCTION statements with all of the options of that function module in the source code.
Optional parts of the function call are inserted as comments. In the above example, STRING and POS are obligatory parameters. LANGU, on the other hand, is optional. It has the default value SY-LANGU (the system field for the logon language). Handling export parameters is optional. Handling exceptions is also theoretically optional. However, you should always do so. That is why the EXCEPTIONS lines are not commented out.
You can trigger exceptions in the function module using either the RAISE or the MESSAGE ... RAISING statement. If the calling program handles the exception, both statements return control to the program. The MESSAGE ..... RAISING statement does not display a message in this case. Instead, it sets the following system fields:
You can use the system fields to trigger the message from the calling program.
To ensure that you use the right data types for the actual parameters, you must refer to the function module interface. If you double-click the name of a function module in the source code of your program, the system navigates to its source code in the Function Builder. You can then display the interface by choosing Goto → Interface.
For example, in the above case
A complete call for the function module STRING_SPLIT_AT_POSITION might look like this:
DATA: TEXT(10) TYPE C VALUE '0123456789',
TEXT1(6) TYPE C,
TEXT2(6) TYPE C.
PARAMETERS POSITION TYPE I.
CALL FUNCTION 'STRING_SPLIT_AT_POSITION'
STRING = TEXT
POS = POSITION
STRING1 = TEXT1
STRING2 = TEXT2
STRING1_TOO_SMALL = 1
STRING2_TOO_SMALL = 2
POS_NOT_VALID = 3
OTHERS = 4.
WRITE: / TEXT, / TEXT1, / TEXT2.
WRITE 'Target field 1 too short!'.
WRITE 'Target field 2 too short!'.
WRITE 'Invalid split position!'.
WRITE 'Other errors!'.
The function module splits an input field at a particular position into two output fields. If the contents of POSITION are in the interval [4,6], the function module is executed without an exception being triggered. For the intervals [1,3] and [7,9], the system triggers the exceptions STRING2_TOO_SMALL and STRING2_TOO_SMALL respectively. For all other values of POSITION, the exception POS_NOT_VALID is triggered. | <urn:uuid:c0390c3a-f959-49eb-98b3-18729d047a5d> | 2.703125 | 1,504 | Documentation | Software Dev. | 51.322743 |
Motion makes the world go 'round. Motion makes the moon go 'round too. In fact, motion makes lots of things go. When we think of motion we often think of cars, bicycles, kids running, basketballs bouncing and airplanes flying. But motion is so much more. Motion is important to our lives and impacts so many things that we do. Motion is the changing of position or location. But motion requires a force to cause that change. Let's learn about force and motion and the effects of these physical laws in our world.
What is Force?
Force is just a fancy word for pushing or pulling. If I push on something or pull on it, then I am applying a force to it. Force makes things move or, more accurately, makes things change their motion. Two natural forces that we have experienced are the force of gravity and magnetic forces.
These two forces act at a distance and do not require direct contact between the objects to function. Gravity produces a force that pulls objects towards each other, like a person towards the ground. It is the force that keeps the Earth revolving around the sun and it's what pulls you toward the ground when you trip.
See D4K's site on Gravity.
Magnetism produces a force that can either pull opposite ends of two magnets together or push the matching ends apart. A magnet also attracts objects made of metal.
Types Of Contact Forces
There are 6 kinds of forces which act on objects when they come into contact with one another. Remember, a force is either a push or pull. The 6 are:
Let's investigate how these forces can be seen in our lives.
A book resting on a table has the force of gravity pulling it toward the Earth. But the book is not moving or accelerating, so there must be opposing forces acting on the book. This force is caused by the table and is known as the normal force. You can "see" the normal force in some situations. If you place a thin piece of wood or plastic (a ruler works) so that it is supported by both ends (by books perhaps) and place a small heavy object in the center, the piece of wood will bend. Of course it wants to straighten out so it exerts an upward force on the object. This upward force is the normal force. You can feel the force yourself if you push down in the center of the piece of wood. The harder you push, the more the wood bends and the harder it pushes back.
Applied force refers to a force that is applied to an object such as when a person moves a piece of furniture across the room or pushes a button on the remote control. A force is applied.
Frictional force is the force caused by two surfaces that come into contact with each other. Friction can be helpful as in the friction that allows a person to walk across the ground without sliding or it can be destructive such as the friction of moving parts in a motor that rub together over long periods of time.
Tension force is the force applied to a cable or wire that is anchored on opposite ends to opposing walls or other objects. This causes a force that pulls equally in both directions.
The spring force is the force created by a compressed or stretched spring. Depending upon how the spring is attached, it can pull or push in order to create a force.
Resisting forces like air resistance or friction change motion. Whether the forces actually stop or slow something depends upon your point of view. Air friction makes a leaf travel along in the wind. When you pick up a pencil, it's friction with your fingers that gets the pencil in motion. In each case, the friction makes the two things (like the air and the leaf) move together.
What is Inertia?
Inertia is actually not a force at all, but rather a property that all things have due to the fact that they have mass. The more mass something has the more inertia it has. You can think of inertia as a property that makes it hard to push something around.
What is Friction?
Friction is a force that happens when objects rub against one another. Say you were pushing a toy train across the floor. It doesn't take much effort or force, because the toy is light. Now say you try to push a real train. You probably can't do it because the force of friction between the train and the ground is more intense. The heavier the object, the stronger the force of friction.
Velocity is the speed of an object in one direction. If an object turns a corner, it changes its velocity because it is no longer moving in its original direction.
Newton's Laws of Motion
Some consider Sir Isaac Newton to be the greatest English mathematician of his time and perhaps one of the greatest scientists the world has known. According to a story, Newton saw an apple fall to the ground and he figured out that the same force which caused the apple to fall also governed the motion of the Moon and the planets. In 1687 Newton published his three laws of motion in the "Principia Mathematica Philosophiae Naturalis." His three laws explained how the concepts of force and motion work.
Newton's first law of motion states: A body in motion tends to remain in motion, a body at rest tend to remain at rest unless acted on by an outside force.
So, if an object is moving - its inertia (mass) will tend to keep it in motion, and if something is at rest, its inertia will tend to keep it at rest.
From the Goddard Space Center: learn more about Newton's First Law.
Newton's second law of motion states that a force, acting on an object, will change its velocity by changing either its speed or its direction or both.
If your basketball goes rolling into the street and is hit by a bike, either the ball will change direction or its speed or both. It will also be true of the bike.
From the Goddard Space Center: learn more about Newton's Second Law.
The third law is probably the best known of Newton's laws. It states that for every force and action, there is an equal and opposite reaction.
This is what causes a cannon to recoil when it fires. The 'kick' from the firing of the ammunition is what makes the cannon jump backwards.
From the Goddard Space Center: learn more about Newton's Third Law. | <urn:uuid:833860a3-ff52-489e-aac5-d8d6b77703db> | 3.921875 | 1,317 | Knowledge Article | Science & Tech. | 66.522594 |
Among the problems caused by climate change, we’ve been told, is its grave threat to polar bears. Earthjustice, for one, says the animals “are facing unprecedented threats” from global warming. Well, not exactly.
Eight years ago, Environment Canada estimated that by 2011, the polar bear population on the western shore of the Hudson Bay region would fall to about 610.
Last year, the World Wildlife Fund screamed in a headline in its climate blog: “Polar Bear Population In Canada’s Western Hudson Bay Unlikely To Survive Climate Disruption.”
And in the summer of 2010, the U.K. Independent reported on fear “that the bears could die out in 25 to 30 years, or perhaps in as few as 10.”
Really, the rumors of their extinction have been greatly exaggerated. A new survey by the Nunavut Territory government has found that the polar bear population along the western shore of the Hudson Bay is increasing. The study found 1,013 of them in the region, far more than the 610 the alarmists projected. | <urn:uuid:4448f7fa-836a-4b15-afa0-c834eb1d900b> | 3.359375 | 225 | Comment Section | Science & Tech. | 58.837136 |
Reply to comment
The Intergovernmental Panel on Climate Change (IPCC) predicted that between 20-30% of all species on Earth could become extinct by the end of the century because of climate change and habitat loss.
According to the IPCC, global warming is no longer a question. It is estimated that by 2050, between 20 an 30% of all species on Earth could be extinct -- roughly 1 million species. This would be a result of rising sea levels, melting ice caps, warming temperatures, and severe food, water, and habitat loss.
Click Here for more Live Earth India Tips & Solutions. | <urn:uuid:feddfcfc-dbf4-4626-8298-798ba0ca85d8> | 3.203125 | 123 | Comment Section | Science & Tech. | 53.428909 |
It seems that there is a lot of confusion as to what isotopes, radioisotopes, nuclides, and radionuclides are. First, we have to go back to chemistry class and remember the periodic table of elements, which lists all of the chemical elements in an organized fashion.
The periodic table reports each element with its average properties. Each chemical element on the periodic table has a distinct number of protons. The reason we say “average properties” here is because each element has a number of different isotopes. The word “isotope” indicates an equal number of protons, hence the prefix “iso” and the letter “p” in the name (note that isotones represent nuclides with the same number of neutrons). For example, hydrogen (1 proton) consists of 3 natural isotopes: hydrogen (0 neutrons), deuterium (1 neutron), and tritium (2 neutrons). The same is true of uranium, where U-235 is an isotope that can undergo fission. The number 235 represents the sum of neutrons and protons that make up the nucleus of the uranium atom (92 protons and 143 neutrons). The term “nuclide” is just a general name for any isotope of a chemical element.
The prefix “radio” in front of “isotope” and “nuclide” refers to radioactivity. This indicates the spontaneous transformation (decay) of unstable nuclides to more stable ones. In order to accomplish this, nuclides may emit a spectrum of particles including alpha particles, beta particles (electrons or positrons), neutrons, gamma rays (photons), or x-rays. In order to characterize the probability of a nuclide decaying, each radionuclide has a half-life. The half-life of a radionuclide is the expected time it takes for one half of the amount of one isotope to decay into another isotope. In terms of radiation safety, it is desirable for unstable nuclides to eventually decay to stable nuclides. The amount of radionuclide present, when there is no source producing it, undergoes an exponential rate of decay.
Activity is another term that is used when talking about radioisotopes. Activity, measured in the unit of Bequerel (Bq), is the number of decays occurring per unit time. It is not necessarily equal to the rate at which particles are emitted. For example, cobalt-60 emits both beta and gamma radiation each time it decays. The activity of an isotope also follows a similar exponential trend as shown above. It is also often expressed in units of Curie (Ci), where 1 Ci = 3.7 x 1010 Bq.
There is also a big difference between nuclear reactions and chemical reactions. Nuclear reactions are quite different for different isotopes of the same element, while chemical reactions are quite similar for different isotopes of the same element. All isotopes of the same element (I-127, I-131, and I-135 are all isotopes of iodine) have similar chemical interactions, but they could result in different health effects due to different levels of radioactivity. This is because chemical reactions involve changing electron configurations in the atom. Since all isotopes of a given chemical element have the same electron configuration, they will have similar chemical reactions. A good example is the use of iodine tablets. Different isotopes of iodine will have similar chemical interactions in the body. Therefore, if the body is already saturated with non-radioactive iodine, it is already full and radioactive iodine has a lower chance of being absorbed. For nuclear reactions, each isotope of an element will have different nuclear reaction characteristics. For example, slow neutrons have a much higher chance of causing fission in U-235 than in U-238. | <urn:uuid:45b4a729-c23e-48cb-8490-f0b05e647840> | 4.875 | 813 | Knowledge Article | Science & Tech. | 32.35329 |
Tracking Debris from the Tohoku Tsunami
by NASA Earth Observatory, creative commons/attribution, flickr.
The map above shows the output of the Surface Currents from Diagnostic (SCUD) model, an attempt to simulate where and how that debris would disperse. Orange and red shaded areas represent parcels of water with a high probably of containing floating debris. The deeper the red color, the higher the likely concentration. The debris field stretches roughly 5,000 kilometers by 2,000 kilometers across the North Pacific.
A 66-foot dock washes ashore in Oregon: | <urn:uuid:81cc62ec-d873-45a5-b4e6-f95b1ffd2959> | 2.90625 | 122 | Personal Blog | Science & Tech. | 40.045 |
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In 1959, physicist Richard Feynman presented an
amazing talk entitled There's Plenty of Room at the Bottom, in which he proposed making very small circuits out of molecules. More than forty years later, people are starting to realize his vision. Thanks to Scanning Tunneling Microscope (STM) probes and "self-assembly" fabrication techniques, it is now possible to connect electrodes to a molecule and measure its conductance. In 2004, Mark Hersam et al. reported the first experimental measurement of a molecular resonant tunneling device on silicon. This new field of Molecular
Electronics may someday provide the means to miniaturize circuits beyond the limits of silicon, keeping Moore's Law in force for many years to come.
Learn more about molecular electronics from the resources on this site, listed below. More information on Molecular electronics can be found here.
Scanning Probe Microscopes
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15 Mar 2005 | Animations | Contributor(s): EPICS LSPM Team
Laura explains how scanning probe microscopes can be used to create images of small devices, molecules, and even atoms! A large-scale version of the scanning probe microscope is built out of Legos …
Feasibility of Molecular Manufacturing
14 Mar 2005 | Animations | Contributor(s): EPICS LSPM Team
Martin and Laura have an interesting debate about the feasibility of Molecular Manufacturing. Can molecular assemblers be developed to create new materials, new devices, and even macroscopic …
nanoHUB.org, a resource for nanoscience and nanotechnology, is supported by the National Science Foundation and other funding agencies. | <urn:uuid:800a392e-872e-4086-ae87-8190cc3b2e30> | 3.609375 | 386 | Content Listing | Science & Tech. | 27.015974 |
The term "POJO" is widely used in the Java programming world, but is sometimes used to mean something more specific than what was originally intended.
Furthermore, such code (whether called POJO or not by its authors) is a style which I think would be useful to give a specific name to.
What's a POJO?
The original meaning of POJO was a plain old Java object - that is, an object that isn't tied to a framework (for example, having to implement specific interfaces). A concrete example of a non-POJO would be entity beans (from EJB).
NOJOs are (instances of) classes which define fields, setters and getters but no other methods. They are popular in enterprise Java code and I think deserve a specific term, to distinguish them from the rather general term POJO.
NOJO stands for "Non Object-oriented Java Object". Although it might sound "negative" it is merely intended to be accurate and have a catchy acronym.
What defines an object?
An "object" (in object-oriented programming) has identity, state and behaviour. A NOJO has identity and state. A function has behaviour but not state. An object has identity, state and behaviour.
Why do you need a term for NOJO?
In many programming languages, there is a language construct for NOJOs (or something very similar) - e.g. "struct" in C, or "record" in Pascal. In Java there isn't an equivalent language construct - so the term NOJO is intended to mean the use of a Java class to implement such a thing, to make it easier to talk about such code.
Are NOJOs a Good Thing?
Left as an exercise for the reader. | <urn:uuid:66f63b14-1b36-442e-bc8a-b267f44e6244> | 3.140625 | 366 | Personal Blog | Software Dev. | 52.495 |
Are Household Powders Acids or Bases?
Talk It Over
Many everyday substances are either acids or bases. Orange juice, vinegar, and cola drinks are acids. Many cleaners, such as household ammonia, are bases. Some substances, called indicators, are one color in an acid and another color in a base. You can use them to tell acids and bases apart.
- 1-cup measuring cup
- Rubbing alcohol
- Measuring spoon
- Ground turmeric (from the spice aisle Rolling pin at the supermarket)
- Coffee filter
- Small jam jar
- 1 gallon distilled water (available in the laundry products aisle at the supermarket)
- Ziptop plastic sandwich bags
- Rolling pin
- Powders to test such as baking soda,baking powder, washing soda, salt, sugar,cream of tartar, chalk, Epsom salts, dishwasher powder, powder laundry detergent, borax, laundry soap, or pills such as calcium, vitamin C, antacids, or aspirin
- First, make an indicator from turmeric, following these steps:
- Measure ¼ cup of rubbing alcohol into the measuring cup.
- Add ¼ teaspoon ground turmeric.
- Stir well with a spoon.
- Put the sieve on top of the jar.
- Put the coffee filter in the sieve.
- Pour the alcohol/turmeric mixture through.
- When all the liquid has run through the coffee filter, remove the sieve and put the filter in the trash.
- Add ½ cup of distilled water to the alcohol/turmeric mixture in the jar. Stir.
- This is your turmeric indicator. It will turn an acid bright yellow. It will turn a base bright red.
- To test a powder, use a clean, dry spoon to put a small amount of the powder on a plate. Using the dropper, add a few drops of your turmeric indicator and note the color change, if any. (If the indicator remains pale yellow, the powder is neither an acid nor a base.)
- To test a pill, place it in a ziptop bag and roll with a rolling pin to crush it into a powder. Then test as in step 2.
Rubbing alcohol is poisonous and can hurt your eyes. Do not use rubbing alcohol without an adult's help. Some cleaning powders can burn your skin. Never put any of the materials used in this experiment in your mouth or eyes. If you get some on your skin, wash with water immediately.
The "Go" procedure will work for you. Try testing three powders: dishwasher powder, salt, and baking soda.
Turmeric isn't the only useful indicator you can make at home. Boil some red cabbage in a small amount of water and use it to test powders. Relating it to your turmeric data, you should be able to infer what its color changes show. Purple grape juice and the packing juice from canned blueberries are worth a try also. Read more in the following project about the pH scale and how it is used to measure acids and bases. If time permits, order some pH paper from a scientific supply house or borrow some from your school. Use it to check the conclusions you drew from your indicator experiments. | <urn:uuid:e41f130e-6bc2-4654-988e-a5ccf5a48af8> | 3.21875 | 681 | Tutorial | Science & Tech. | 59.492948 |
February 23 2009 / by Garry Golden / In association with Future Blogger.net
Category: Technology Year: General Rating: 7 Hot
One of the most exciting areas of 'Nano-bio' research is the engineered integration of 'wet' and 'dry' nanoscale systems that might revolutionize research in genetics and proteomics (Study of Proteins). But how do you explain this breaking down the barriers of biological and human-made systems? Through 3D animation videos on YouTube, of course!
ScienceBlogs has featured a video of Oxford Nanopore Technologies's new label free DNA sequencing system that reads A-C-G-T segments as they pass through a nanopore. | <urn:uuid:bba784b6-5d27-4268-9163-961b8808ee40> | 2.71875 | 145 | Truncated | Science & Tech. | 39.724058 |
Knowledge Networks and Neural Networks
A knowledge network cheats - it uses different operators to do different things.
Neural networks are somehow considered "pure" because each node is precisely the same as every other node, the only thing that differs is the weighting in the connections. That would be of benefit in developing a theory of cognition if one could show similarity of nodes in a neural network to the neurons in a brain. As critics of neural networks have pointed out, neurons in a reasoning area of a brain are not all the same, and presumably do not have the same characteristics. We don't need to look inside people's heads to see the falsity of the argument.
People learn things, then use what they have learnt to learn more complex things. If a human has struggled as a child to learn the concept of plus, there is presumably no barrier to setting up some part of a more complex mental model as the plus they already know. On the contrary, neural networks start from scratch each time, and there is no obvious way they can be combined. Humans may take a week to learn their multiplication tables, then a week to learn Ohm's Law and a lifetime to understand
but the multiply operator did not require another week in each case - they already knew what it meant. What this says is that humans can copy structure - neuronal connection patterns - that have certain properties.
As a model of human cognition, artificial neural networks fail at the first hurdle, unable to learn by aggregation of existing structure.
Knowledge networks bundle up behaviour into operators - a PLUS operator knows how to add. The operator is copied into wherever it is relevant.
Some critics have said that the backpropagation in neural networks has no basis in human neuronal behaviour, because there is no obvious feedback path. Have they never watched a dog dreaming. It is obviously capable of providing input to its sensory system, and then responding to that input.
Knowledge networks go much further than "backprop", superseding the concept of diode - resistor structure of the neural network. Not only can errors flow back into the structure, but information can flow anywhere to anywhere, "back" having no meaning. It is no more startling than what happens when two people speak to each other - there are two centres of control, with information flowing to and fro. Information from one can alter the states and connections in the other, which can then alter the states and connections in the first one. Is this too difficult to imagine as a way in which networks of neurons may learn?
Artificial Neural networks or ANNs (to give them their full name) do not pass control to individual neurons - there isn't anything there to give control to. The popular notion of massive computational parallelism is entirely fallacious. The sum of incoming signals and their weightings for each node is calculated to produce an outgoing weighting - the control algorithm knows exactly what to do because all the neurons have a stereotypical output behaviour. There can be amusing variations on how the weights are calculated, but never is a neuron individually queried about what it would like to do in the circumstances. If human neurons were all the same, one might congratulate the designers of neural networks on their perspicacity. On the contrary, human neurons switch, transmit complex messages, have refractory periods, have feedback of their own states, on and on. The notion that this behaviour can be captured by a resistor-diode combination with a static value across it, being driven by a control program, and the weighting curve be differentiable to make it easy to model, seems ludicrous.
A knowledge network has no idea of what to do next except give control to an operator which has a changed input. The operator then decides to change an output (including possibly the connection on which the changed input appeared) or do nothing. The message transmitted is not limited to a single value, and while hardly comparable with a complex neuronal firing pattern, it does allow some complexity - ranges, lists, including lists of alternatives, and structures.
The act of ceding control means that the network is "micro-scheduling" its behaviour, based on activation patterns. An algorithm wasn't needed to work out what to do next, except to grab the next job off the activation queue. Usually the hardest part of algorithm design is to work out what to do next, and what the right level of granularity should be. The granularity in the knowledge network is atomic.
Neural networks avoid the problem of what to schedule when by having a simple control program that is incapable of responding to change while it is operating. In fact, neural networks avoid all the problems that must be faced by systems wishing to emulate the behaviour of humans, including whether two fully interacting systems can be emulated by one control program.
But isn't the knowledge network just another algorithm, just a little more complicated than the neural network control program.
The knowledge network can respond to change by changing its structure, which changes its notional algorithm.
But neural networks can change their weightings.
A change in connection is much more than changing a weighting. A new connection can change the topology, so the behaviour changes radically - rather as tying a snake's head to its tail changes its behaviour because its topology is different. Less dramatically, a new connection from output to input, while the system is in operation, can lead to large changes. The greater the range over which this connection can be made, the more drastic can the change in behaviour be - the snake again. The neural network has neatly separated the learning and running states, perhaps necessary for study of its behaviour in a laboratory, but rather useless for operational behaviour.
One can imagine a neural network with zero weighted connections to every other possible point, but one would also need some means of identification for which connection to change - identifiability which the neural network lacks. One could add named variables and... and finish up with a knowledge network or active structure.
We show an active structure reading complex legal text - inconceivable for an ANN, and also inconceivable for a network of real neurons, until we get sufficient layering that its base properties - particularly its directionality - disappear. | <urn:uuid:95a7cfd3-b9dd-4c7c-9652-2221f7346c4f> | 3.171875 | 1,262 | Knowledge Article | Science & Tech. | 38.911597 |
11 April 2011
Posted in Science Live!
DNA Day at the Orlando Science Center is just a month away, so in honor of this amazing molecule I thought it would be neat to look over some genetics news.
This article is from last year, but the research continues. Neanderthals, or cavemen, have long been thought to be dull, slow and stupid, (thus the whole Geico thing about being so easy a caveman could do it). Ever since the reconstruction of the remains at La Chapelle aux Saints in 1911 by Marcellin Boule, the general public has had the idea that Neanderthals stood hunched-over, with their arms drooping down and that they moved slowly. In fact, this is a mistake. The remains from La Chapelle Aux Saints turn out to be those of an old man who had severe arthritis. Of course he would have walked slowly and been hunched over, but Boule thought this idea applied to all Neanderthals.
Much work had been done since then, but analyzing bones can only get you so far. That’s where this study comes in; a group of researchers from the Max Planck Institute are looking into DNA preserved in different specimens. What can we tell from this? For one, we can see how different Neanderthals really were from modern humans and we can get ideas about why you don’t see more cavemen around today.
If you think this is cool, imagine what it would be like to ask one of these researchers questions about their findings. On May 7, DNA Day, you can have that chance; Dr. Emily Hodges from the research team will be available via Skype for questions!
For more information, click here to view the full article.
Stephanie is a Science Interpreter at the Science Center and often is found in DinoDigs or Careers for Life. Paleontology, Anthropology and Anatomy are her passion and jumps at every opportunity to talk about it. Stop in and say Hello! | <urn:uuid:4d1b508c-5a59-41ad-ace6-359e210b08cf> | 3.0625 | 414 | Personal Blog | Science & Tech. | 59.742416 |
In numerical analysis
, Aitken's delta-squared process
is a series acceleration
method, used for accelerating the rate of convergence
of a sequence. It is named after Alexander Aitken
, who introduced this method in 1926. It is most useful for accelerating the convergence of a sequence that is converging linearly.
Given a sequence
, one associates to this sequence the new sequence
which can also be written as
(To use this nice operator notation, one has to allow for the indices to start from n = 2 on, or apply a translation operator which first shifts the sequence indices by two, or to adopt the convention that xn = 0 for all n < 0.)
Obviously, Ax is ill-defined if Δ²x contains a zero element, or equivalently, if the sequence of first differences has a repeating term. From a theoretical point of view, assuming that this occurs only for a finite number of indices, one could easily agree to consider the sequence Ax restricted to indices n>n0 with a sufficiently large n0. From a practical point of view, one does in general rather consider only the first few terms of the sequence, which usually provide the needed precision. Moreover, when numerically computing the sequence, one has to take care to stop the computation when rounding errors become too important in the denominator, where the Δ² operation may cancel too many significant digits.
Aitken's delta-squared process is a method of acceleration of convergence
, and a particular case of a nonlinear sequence transformation
When converges linearly to , then
is not a linear operator, but a constant term drops out, viz: , if is a constant. This is clear from the expression of in terms of the finite difference operator .
Although the new process does not in general converge quadratically, it can be shown that for a fixed point process, that is, for an iterated function sequence for some function , converging to a fixed point, the convergence is quadratic. In this case, the technique is known as Steffensen's method.
Empirically, the A-operation eliminates the "most important error term". One can check this by considering a sequence of the form , where | <urn:uuid:9f5179b0-f67a-4f5c-aa9c-053a7e8cd162> | 3.09375 | 461 | Knowledge Article | Science & Tech. | 29.770054 |
Cuttlefish change the patterns on their body for courtship rituals, when they eat a snack, and most famously when they want to blend in. How they change their skin patterns may tell us something about how they see the world, says Duke biologist Sarah Zylinski. Her work suggests that when cuttlefish see incomplete shapes, they fill in the visual blanks -- much like humans do. Can't get enough saltwater camouflage? See: "Where's The Octopus."
photographs, footage: sarah zylinski, archival: archive.org, produced by flora lichtman | <urn:uuid:b8049373-685f-4431-9f7b-97e6a511c417> | 2.984375 | 122 | Truncated | Science & Tech. | 56.533178 |
Some forms of bacteria are known as Archaea
Click on image for full size
To date, the oldest known life forms are certain types of bacteria that have been found in
Australian rocks that date back 3.5 billion years ago. At this time, oxygen was not present
in the Earth's atmosphere, thus these bacteria must have been anaerobic.
These bacteria have been found within rock itself, miles underneath the surface.
Bacteria such as this give off ammonia as a waste product. Thus one way to detect increased activity by such creatures is to measure levels of nitrogen in the atmosphere.
This is page 5 of 20
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NASA studies long-term climate warming trendJanuary 19th, 2013 at 6:30 pm by Natalie Stoll under Weather
From NASA Science:
NASA Finds Long-Term Climate Warming Trend
Jan. 15, 2013: NASA scientists say 2012 was the ninth warmest of any year since 1880, continuing a long-term trend of rising global temperatures. With the exception of 1998, the nine warmest years in the 132-year record all have occurred since 2000, with 2010 and 2005 ranking as the hottest years on record.
NASA’s Goddard Institute for Space Studies (GISS) in New York, which monitors global surface temperatures on an ongoing basis, released an updated analysis Tuesday that compares temperatures around the globe in 2012 to the average global temperature from the mid-20th century. The comparison shows how Earth continues to experience warmer temperatures than several decades ago.
The average temperature in 2012 was about 58.3 degrees Fahrenheit (14.6 Celsius), which is 1.0 F (0.6 C) warmer than the mid-20th century baseline. The average global temperature has risen about 1.4 degrees F (0.8 C) since 1880, according to the new analysis.
Scientists emphasize that weather patterns always will cause fluctuations in average temperature from year to year, but the continued increase in greenhouse gas levels in Earth’s atmosphere assures a long-term rise in global temperatures. Each successive year will not necessarily be warmer than the year before, but on the current course of greenhouse gas increases, scientists expect each successive decade to be warmer than the previous decade.
“One more year of numbers isn’t in itself significant,” GISS climatologist Gavin Schmidt said. “What matters is this decade is warmer than the last decade, and that decade was warmer than the decade before. The planet is warming. The reason it’s warming is because we are pumping increasing amounts of carbon dioxide into the atmosphere.”
Read the rest of the article here. | <urn:uuid:cb991e72-1dcc-4e0b-a8d6-81dffee91108> | 3.296875 | 411 | Truncated | Science & Tech. | 51.101574 |
Reposted from ENERGY BULLETIN (http://www NULL.energybulletin NULL.net/stories/2012-08-23/building-resilience-changing-climate)
Climate shocks are on the way. We’ve already spewed so much carbon into the atmosphere that a cascade of worsening crop failures, droughts, floods, and freak storms is virtually guaranteed. You, your family, and your community will feel the effects.
Ironically, however, avoiding climate change also has its costs. It makes sense from a climate-protection standpoint to dramatically and rapidly reduce our use of fossil fuels, which drive global warming. But these fuels largely, well, fueled the spectacular economic growth of the past 200 years, and weaning ourselves from them quickly now—while most industrial economies are over-indebted and starved for growth—could risk financial upheaval.
Oil, the most economically pivotal of the fossil fuels, is getting more expensive anyway. Cheap, onshore, conventional crude is depleting; its replacements—deepwater oil, tar sands, and tight oil—cost more to produce, in both dollar and environmental terms. Though high oil prices discourage driving (good for the climate), they also precipitate recessions (bad for the economy). While renewable energy sources are our hope for the future and we should be doing everything we can to develop them, it will be decades before they can supply all our energy needs.
In the face of impending environmental and economic shocks, our best strategy is to build resilience throughout society. Resilience is the subject of decades of research by ecologists and social scientists (http://www NULL.resalliance NULL.org/index NULL.php/key_concepts) who define it as “the capacity of a system to tolerate disturbance without collapsing into a qualitatively different state that is controlled by a different set of processes.” In other words, resilience is the capacity to absorb shocks, reorganize, and continue functioning.
In many respects a resilient society defies the imperative of economic efficiency. Resilience needs dispersed inventories and redundancy, while economic efficiency—in its ruthless pursuit of competitive advantage—eliminates inventories and redundancies everywhere it can. Economic efficiency leads toward globalization, resilience toward localization. Economic efficiency pursues short-term profit as its highest objective, while resilience targets long-term sustainability. It would appear that industrial society circa 2012 has gone about as far in the direction of economic efficiency as it is possible to go, and that a correction is necessary and inevitable. Climate change simply underscores the need for that course correction.
Building resilience means helping society to work more like an ecosystem—and that has major implications for how we use energy. Ecosystems conserve energy by closing nutrient loops: plants capture and chemically store solar energy, which is then circulated as food throughout the food web. Nothing is wasted. We humans—having developed the ability to draw upon ancient, concentrated, cheap, and abundant (though ultimately finite) fossil fuels—have simultaneously adopted the habit of wasting energy on a colossal scale. Our food, transport, manufacturing, and dwelling systems burn through thirty billion barrels of oil and eight billion tons of coal per year; globally, humans use over four hundred quadrillion BTUs of energy in total. Even where energy is not technically going to waste, demand for it could be substantially reduced by redesigning our basic systems.
For example, we could reduce transport energy used in food systems by producing food more locally; at the same time, we could reduce other fossil fuel inputs to those systems (fertilizers, pesticides, herbicides, and packaging) by changing farming practices and consumer habits. We could retrofit our buildings so they require far less energy for heating and cooling. And we could reduce the need for motorized transportation by redesigning cities around mixed-use neighborhoods that are friendly to pedestrians and bicyclists.
By cutting our reliance on fossil fuels, by reducing energy requirements in general, and by eliminating our economic system’s need for perpetual growth (and hence for perpetually increasing energy consumption), we can make our way of life less vulnerable to energy shortages and price spikes while also reducing carbon emissions.
Ecosystems build resilience through biodiversity. Thus if the population of one organism that plays a crucial role in an ecosystem is greatly reduced, another organism that performs a similar function will be there to take its place. When we reduce diversity in human systems in the name of economic efficiency, we trade away resilience and increase vulnerability to systemic collapse. For example, industrial agriculture favors monocrops, which present a huge opportunity to any pest that manages to evolve immunity to the chemicals that farmers use to keep it at bay.
Communities can build economic diversity and resilience by encouraging and investing in small businesses and family farms, rather than offering incentives to giant retail or manufacturing companies to locate in town, only to see them move or outsource jobs a few years later.
Feedback loops (either balancing or self-reinforcing) control energy flows and populations in ecosystems, stabilizing or destabilizing the system. Climate change is itself subject to both kinds of feedbacks: forests and oceans absorb carbon and help keep the climate system in balance, while melting permafrost releases greenhouse-enhancing methane, thus reinforcing global warming. Part of the challenge of building community resilience is to identify reinforcing and balancing feedback loops, to learn how they affect human systems, and to make them work for us.
Once we start down the path of building resilience, the positive effects become synergetic. For example, by reprocessing recycled materials locally rather than sending them to far-off countries for reprocessing, and by composting local food waste and sewage, communities can conserve energy while creating jobs, building topsoil, and reducing dependence on increasingly unreliable distant sources of food and materials. Again: resilience helps us adapt to inevitable shocks and changes, while also aiding proactive efforts to reduce energy consumption and thus avert future global warming. Building resilience helps us address a range of problems with just a few basic strategies.
Resilience can’t remove all the challenges and hardships ahead. For example, people typically don’t adapt to intense, prolonged drought—they move elsewhere, as tens of thousands did during the Dust Bowl of the 1930s. No strategy will guarantee immunity to impacts from acidifying oceans, melting glaciers, and weird weather. But resilience buys us a better insurance plan. And in the bargain, it might also revive our communities, create economic opportunity, and make life more satisfying.
Content on this site is subject to our fair use notice (http://www NULL.energybulletin NULL.net/fair-use-notice).
Energy Bulletin is a program of Post Carbon Institute (http://postcarbon NULL.org), a nonprofit organization dedicated to helping the world transition away from fossil fuels and build sustainable, resilient communities. | <urn:uuid:6f502c80-76d1-4737-9e4a-c05ab1f0a19b> | 2.90625 | 1,411 | Nonfiction Writing | Science & Tech. | 21.914687 |
As history has proven, earthquakes are one of the most destructive natural disasters. Engineers and scientists study them to determine how, where and why they happen to reduce the damage they can cause.
More than 100 years ago on April 18, an earthquake struck California. It lasted almost 60 seconds long and is known as the Great 1906 San Francisco Earthquake. It spanned 296 miles from the city and ranks as the most significant of its time because experts were able to gather scientific knowledge that led to the study of earthquake cycles. An earthquake is movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move. (A fault is a break in a body of rock.)
When they happen on the ocean floor, they are called tsunamis, like the one that hit Japan in March 2011. The drop and rise of the ocean floor sets off the low waves that increase in height as they get close to shore causing massive flooding and destruction.
Remembering these two natural disasters makes us aware of the important job scientists have when it comes to predicting earthquakes and the amount of energy they release.
Source: usgs.gov; Earth Science by Holt, Rinehart and Winston. A Harcourt Education Company.
Content provided by Oakland University. | <urn:uuid:aec6ae1e-5590-48f9-8ecd-432c5486ae59> | 4.125 | 257 | Knowledge Article | Science & Tech. | 53.385351 |
#haskell asked whether you could recover a function's name from its value, i.e.
GHCi> name id "id" GHCi> name map "map"
This is easy in some languages. But Haskell is not designed to provide this kind of run-time information. We'll need some non-portable hacks. I tested this code with GHC 6.12.1 on
amd64 Linux; see below for portability notes.
How it works
Closures exist to store data. But the run-time system also needs operational information about each closure: how to garbage-collect it, how to force its evaluation, etc. This information is known at compile time and is shared between many closures. All algebraic values with the same constructor will share this information, as will all function values created from the same lambda in the program's source.
So each closure stores a pointer to an info table, holding this operational information. Info tables are generated at compile time, and stored as part of an executable's read-only data section. This means that they have statically-known addresses, with associated names in the executable's symbol table. We'll use these symbol names to name our functions.
We can dump an executable's symbol table with
$ nm -f posix foo ... ghczmprim_GHCziBool_Bool_closure_tbl D 0000000000749978 ghczmprim_GHCziBool_False_closure D 0000000000749970 ghczmprim_GHCziBool_False_static_info T 00000000004e4dd8 ghczmprim_GHCziBool_True_closure D 0000000000749990 ghczmprim_GHCziBool_True_static_info T 00000000004e4d80 ghczmprim_GHCziDebug_debugErrLn1_closure D 00000000007499a0 ghczmprim_GHCziDebug_debugErrLn1_info T 00000000004e4ec0 ...
Haskell identifiers can contain characters not allowed in symbol names. GHC uses a name-mangling scheme to build symbol names. For example, the first symbol above decodes to
Reading the symbols
We'll also use the GHC API to un-mangle symbol names. GHC is a 20-year effort that has evolved alongside the Haskell language. It follows some legacy conventions like a mostly-flat module hierarchy. So the module we need is named simply
import Control.Parallel ( pseq )
import qualified Data.Map as Map
import qualified System.Posix.Files as Posix
import qualified System.Process as Proc
import qualified Foreign.Ptr as Ptr
import qualified GHC.Vacuum as Vac
import qualified Encoding as GHC
nm as a subprocess and parse its output:
type Symbols = Map.Map Word String
getSymbols :: IO Symbols
getSymbols = do
exe <- Posix.readSymbolicLink "/proc/self/exe"
out <- Proc.readProcess "nm" ["-f", "posix", exe] ""
let offset = 0x10
let f (sym:_:addr:_) = Just (read ("0x"++addr) - offset, GHC.zDecodeString sym)
f _ = Nothing
return . Map.fromList . catMaybes . map (f . words) . lines $ out
We're using the Linux
proc filesystem to get a symbolic link to our application's executable.
The symbols in memory appear at an address
0x10 = 16 bytes or 2 machine words lower than in the executable's symbol table. I'm not sure why; perhaps it's because of GHC's "tables next to code" optimization.
Resolving a symbol
Once we have the symbol table, looking up a value is relatively easy:
name :: Symbols -> a -> String
name syms x = fromMaybe unk $ Map.lookup ptr syms where
ptr = x `pseq` (fromIntegral . Ptr.ptrToWordPtr . Vac.getInfoPtr $ x)
unk = printf "<unknown info table at 0x%016x>" ptr
We use vacuum to get the value's info table pointer, convert this to a
Word, then look it up in the symbol table.
We explicitly evaluate
pseq, to avoid seeing a thunk.
We'll test with
$ ghc --make name.hs -package ghc $ ./name
Each test below is commented with the expected output. First, let's try a few non-function values:
main :: IO ()
main = do
syms <- getSymbols
let test = putStrLn . name syms
test 3 -- integer-gmp_GHC.Integer.Type_S#_con_info
test (3 :: Int) -- ghc-prim_GHC.Types_I#_static_info
test "xyz" -- ghc-prim_GHC.Types_:_con_info
GHC defaults to
3 :: Integer, as
-Wall will tell you. As we see,
Int are both implemented as algebraic data:
= S# Int#
| J# Int# ByteArray#
data Int = I# Int#
"xyz" is a list built out of
Next let's try a few functions:
test map -- base_GHC.Base_map_info
test getChar -- base_System.IO_getChar_info
test (+) -- integer-gmp_GHC.Integer_plusInteger_info
(+) defaults to operating on
Integer, and GHC inlines the type class dictionary, giving us the underlying
Now let's see the limits of this technique:
test (\_ -> 'x') -- s1jD_info
test (const 'x') -- stg_PAP_info
test test -- stg_PAP_info
Our lambda expression gets a useless compiler-generated name. The application of
const is worse; it uses an info table common to all partial applications. However, we could use vacuum to follow the fields of the
PAP closure, which I'll leave as an exercise to the reader. ;)
test itself is also a partial application. It's defined by applying two arguments to the function
(.) defined as
(.) f g x = f (g x)
If we eta-expand
let test x = putStrLn $ name syms x
then we'll get another compiler-generated name like
This is a hack, and probably not suitable for any serious purpose. Shelling out to
nm to get a symbol table is particularly ugly. I tried to use bindings to BFD, but ran into some segfaults.
The above code will work only on 64-bit machines, but could be adapted for 32-bit. I bet the magic offset would change. It works on GHC 6.12.1, and should work on other recent versions, if you can get vacuum to build.
It definitely requires a Unix system, and specifically Linux or something emulating Linux's
proc filesystem. You'll need
nm from GNU Binutils, which is standard on a system configured for C development.
It won't work if you run
strip on your binaries... | <urn:uuid:10bd8a58-dc72-4bf1-a3a9-e82b99662c37> | 2.71875 | 1,568 | Documentation | Software Dev. | 62.963374 |
Two trains set off at the same time from each end of a single
straight railway line. A very fast bee starts off in front of the
first train and flies continuously back and forth between the. . . .
Have you ever wondered what it would be like to race against Usain Bolt?
Can you rank these sets of quantities in order, from smallest to largest? Can you provide convincing evidence for your rankings?
In which Olympic event does a human travel fastest? Decide which events to include in your Alternative Record Book.
These Olympic quantities have been jumbled up! Can you put them back together again?
Explore the relationship between resistance and temperature
Various solids are lowered into a beaker of water. How does the
water level rise in each case?
Can you draw the height-time chart as this complicated vessel fills
Use your skill and knowledge to place various scientific lengths in order of size. Can you judge the length of objects with sizes ranging from 1 Angstrom to 1 million km with no wrong attempts?
The triathlon is a physically gruelling challenge. Can you work out which athlete burnt the most calories?
Imagine different shaped vessels being filled. Can you work out
what the graphs of the water level should look like?
Can you work out which processes are represented by the graphs?
Andy wants to cycle from Land's End to John o'Groats. Will he be able to eat enough to keep him going?
Can you suggest a curve to fit some experimental data? Can you work out where the data might have come from?
To investigate the relationship between the distance the ruler drops and the time taken, we need to do some mathematical modelling...
In Fill Me Up we invited you to sketch graphs as vessels are filled with water. Can you work out the equations of the graphs?
Use trigonometry to determine whether solar eclipses on earth can be perfect.
Practice your skills of measurement and estimation using this interactive measurement tool based around fascinating images from biology.
What shape would fit your pens and pencils best? How can you make it?
Simple models which help us to investigate how epidemics grow and die out.
What shapes should Elly cut out to make a witch's hat? How can she make a taller hat?
How would you design the tiering of seats in a stadium so that all spectators have a good view?
Learn about the link between logical arguments and electronic circuits. Investigate the logical connectives by making and testing your own circuits and fill in the blanks in truth tables to record. . . .
If I don't have the size of cake tin specified in my recipe, will the size I do have be OK?
Analyse these beautiful biological images and attempt to rank them in size order.
Work with numbers big and small to estimate and calulate various quantities in biological contexts.
Water freezes at 0°Celsius (32°Fahrenheit) and boils at
100°C (212°Fahrenheit). Is there a temperature at which
Celsius and Fahrenheit readings are the same?
Formulate and investigate a simple mathematical model for the design of a table mat.
An observer is on top of a lighthouse. How far from the foot of the lighthouse is the horizon that the observer can see?
How do you write a computer program that creates the illusion of stretching elastic bands between pegs of a Geoboard? The answer contains some surprising mathematics.
Which dilutions can you make using only 10ml pipettes?
Can you visualise whether these nets fold up into 3D shapes? Watch the videos each time to see if you were correct.
Where should runners start the 200m race so that they have all run the same distance by the finish?
Can you work out which drink has the stronger flavour?
Work with numbers big and small to estimate and calculate various quantities in biological contexts.
Can Jo make a gym bag for her trainers from the piece of fabric she has?
When a habitat changes, what happens to the food chain?
Explore the properties of perspective drawing.
Can you work out what this procedure is doing?
Explore the properties of isometric drawings.
This problem explores the biology behind Rudolph's glowing red
Is it cheaper to cook a meal from scratch or to buy a ready meal? What difference does the number of people you're cooking for make?
Investigate circuits and record your findings in this simple introduction to truth tables and logic.
Get some practice using big and small numbers in chemistry.
Work out the numerical values for these physical quantities.
How much energy has gone into warming the planet?
Estimate these curious quantities sufficiently accurately that you can rank them in order of size
10 graphs of experimental data are given. Can you use a spreadsheet to find algebraic graphs which match them closely, and thus discover the formulae most likely to govern the underlying processes?
Is it really greener to go on the bus, or to buy local?
Work with numbers big and small to estimate and calculate various quantities in physical contexts. | <urn:uuid:9c1a6fbe-5ae5-4c3e-902e-8d8bcdf471a1> | 3.53125 | 1,047 | Content Listing | Science & Tech. | 59.042759 |
So you really just want to make a mess and blow something up, but if you learn scientific method along the way, we’ll call it a win-win!
First, check out the description of the reaction and photos from those that have tried it, here:
Mentos Diet Coke Geyser at Steve Spangler Science
Then, using what you have learned on this website, design a “real” experiment with it. Most judges have seen this demonstration, so the key will be in the details of designing your own experiment. I also recommend going beyond the one experiment and done approach. If you want to transform this demonstration into a winning project, you’ll need to have several linked experiments. Let’s start with some examples.
Examples of questions include:
Which soda produces the most explosive reaction?
Does diet soda react more or less explosively than regular soda?
How does the color of the soda affect the explosiveness of the reaction?
How does the temperature of the soda affect the explosiveness of the reaction?
Problems to overcome:
1. Defining and measuring “explosiveness of reaction” (the dependent variable) – HINT – think about what comes out of the bottle and how, but also consider what says in the bottle…
2. Proper Replication – i.e., getting the same number of candies into the bottle in a repeatable (i.e. consistent) way | <urn:uuid:f94f30d6-12c7-4715-891f-fb8e54833e3d> | 3.53125 | 303 | Tutorial | Science & Tech. | 54.945563 |
Science Fair Project Encyclopedia
The relationship between heat and energy is similar to that between work and energy. Heat flows between regions that are not in thermal equilibrium; in particular, it flows from areas of high temperature to areas of low temperature. All objects (matter) have a certain amount of internal energy that is related to the random motion of their atoms or molecules. This internal energy is directly proportional to the temperature of the object. When two bodies of different temperature come into thermal contact, they will exchange internal energy until the temperature is equalized. The amount of energy transferred is the amount of heat exchanged. It is a common misconception to confuse heat with internal energy, but there is a difference: heat is related to the change in internal energy and the work performed by the system. The term heat is used to describe the flow of energy; while the term internal energy is used to describe the energy itself. Understanding this difference is a necessary part of understanding the first law of thermodynamics.
When a body releases heat into its surroundings, Q<0. When a body absorbs heat from its surroundings, Q>0.
Total heat, heat transfer rate, and heat flux are all notated with different permutations of the letter Q. They are often confusingly switched in different contexts.
Total heat is notated as Q, and is measured in joules in SI units.
Heat transfer rate, or heat flow per unit time, is labeled
to indicate a change per unit time. In Unicode, this is Q̇, though it may not display correctly in all browsers. It is often shown as ˙Q, .Q, Q·, or as a Q with no dot, where it is not easy to produce a dotted Q. Some form of dotted Q, such as .Q, is preferable, since undotted Q is used for total heat. It is measured in watts.
Heat flux is defined as amount of heat per unit time per unit cross-sectional area, and is abbreviated q, and is measured in watts per meter squared. It is also sometimes notated as Q″ or q″ or
Changes of temperature
The amount of heat energy, ΔQ, required to change the temperature of a material from an initial temperature, T0, to a final temperature, Tf depends on the heat capacity of that material according to the relationship:
The heat capacity is dependent on both the amount of material that is exchanging heat and its properties. The heat capacity can be broken up in several different ways. First of all, it can be represented as a product of mass and specific heat capacity (more commonly called specific heat):
or the number of moles and the molar heat capacity:
Both the molar and specific heat capacities only depend upon the physical properties of the substance being heated, not on any specific properties of the sample. The above definitions of heat capacity only work approximately for solids and liquids, but for gases they don't work at all most of the time. The molar heat capacity can be "patched up" if the changes of temperature occur at either a constant volume or constant pressure. Otherwise, it's generally easiest to use the first law of thermodynamics in combination with an equation relating the internal energy of the gas to its temperature.
Changes of phase
A boiling pot of water, at sea level and normal atmospheric pressure, will always be at 100 °C no matter how much heat is added. The extra heat changes the phase of the water from liquid into water vapor. The heat added to change the phase of a substance in this way is said to be "hidden," and thus it is called latent heat (from a Latin word for hidden). Latent heat is heat per unit mass necessary to change the state of a given substance. Thus:
where Mo is the amount of mass initially in the new phase, and M is the amount of mass that ends up in the new phase.
L generally doesn't depend on the amount of mass that changes phase, so the equation can normally be written:
Sometimes L can be time-dependent if pressure and volume are time-varying, so that the integral can be handled:
someone check the above, please, to see if the latent heat really depends on where on the (P, V, T) curve the transition is taking place.
Heat transfer mechanisms
As mentioned previously, heat tends to move from a high temperature region to a low temperature region. This heat transfer may occur by the mechanisms conduction, and radiation. The term convection is used to describe the combined effects of conduction and fluid flow. In the past, this has been regarded as a third mechanism of heat transfer, but, logically, it is not a mechanism of its own.
Conduction is the most common means of heat transfer in a solid. On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms.
The "electron fluid" of a conductive metallic solid conducts nearly all of the heat current through the solid. (Phonon currents are still there, but carry less than 1% of the energy.) Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, usually also conducts heat well.
The Peltier-Seebeck effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid. Thermoelectricity is caused by the relationship between electrons, heat currents and electrical currents.
Convection is usually the dominant form of heat transfer in liquids and gases. This is a term used to characterize the combined effects of conduction and fluid flow. In convection, enthalpy transfer occurs by the movement of hot or cold portions of the fluid together with heat transfer by conduction. For example, when water is heated on a stove, hot water from the bottom of the pan rises, heating the water at the top of the pan. Two types of convection are commonly distinguished, free convection, in which gravity and buoyancy forces drive the fluid movement, and forced convection, where a fan, stirrer, or other means is used to move the fluid. Buoyant convection is due to the effects of gravity, and absent in microgravity environments.
Radiation is a means of heat transfer. Radiative heat transfer is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.
For room temperature objects (~300 K), the majority of photons emitted (and involved in radiative heat transfer) are in the infrared spectrum, but this is by no means the only frequency range involved in radiation. The frequencies emitted are partially related to black-body radiation. Hotter objects—a campfire is around 700 K, for instance—transfer heat in the visible spectrum or beyond. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF hair removal.
Heat transfer features
- Latent heat: Transfer of heat through a physical change in the medium such as water-to-ice or water-to-steam involves significant energy and is exploited in many ways: steam engine, refrigerator etc. (see latent heat of fusion)
- Heat pipe: Using latent heat and capilliary action to move heat, it can carry many times as much heat as a similar sized copper rod and is starting to have applications in laptop personal computers.
In cold climates, houses with their heating systems form dissipative systems. In spite of efforts to insulate such houses, to reduce heat losses to their exteriors, considerable heat is lost, or dissipated, from them which would make their interiors uncomfortably cool or cold. The house is an open system inasmuch as it is incapable of preventing heat from escaping. Furthermore, the interior of the house must be maintained out of thermal equilibrium with its exterior for the sake of its inhabitants.
In such a house, a thermostat is a device capable of starting the heating system when the house's interior falls to a set temperature, and of stopping that same system when another set temperature has been achieved. Thus the thermostat controls the flow of energy into the house, that energy eventually being dissipated to the exterior.
Preventing heat transfer
It is often desired to prevent heat transfer.
Weatherization slows convective heat flow in buildings. Insulation slows conductive heat flow. Reflective barriers or radiant barriers slow radiative heat flow, and often couple directly with insulation.
- Internal energy
- Heat pump
- Shock heating
- Heat death of the Universe
- Heat transfer coefficient
- Heat equation
- Definition of symbols used in conduction theory, including disambiguation of different Q notations
- Charge current versus heat current
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:f9b083b2-1638-47da-8a2f-0d362bbef0ea> | 4.0625 | 1,981 | Knowledge Article | Science & Tech. | 39.707563 |
Case Study: Friedrich Bessel and the Companion of Sirius
Important advances in astronomy often come from increased precision of observations. The work of the German astronomer and mathematician Friedrich Wilhelm Bessel (1784 –1846) provides a good illustration. Among his many other accomplishments, Bessel developed techniques to measure the positions of stars with far greater accuracy than previously possible. For example, he made the first precise measurements of refraction of light by the Earth’s atmosphere. Refraction is the bending of light rays as they pass at an angle through different substances, like glass, water, or air. When a star is near the horizon, its apparent position can differ from its true position by as much as the diameter of the Moon. This effect was poorly-quantified until Bessel studied it in 1811. His tables of refraction allowed observers to measure star positions to an unprecedented accuracy of less than a tenth of a second of arc (the size of a small coin as seen from a mile away).
This kind of precision in astrometry (the branch of astronomy that measures stellar positions) allowed Bessel in 1838 to find the first reliable distance to another star. He discovered the long-sought stellar parallax—the extremely tiny shift in the apparent position of a star when observed from opposite sides of the Earth’s orbit. Since the size of the Earth’s orbit was known, the observed parallax angle allowed Bessel to calculate the distance to the star 61 Cygni by triangulation. This discovery also provided the most convincing proof that the Earth really moves around the Sun.
Bessel went on to obtain precise positional measurements of Sirius, the brightest star in the sky. His observations revealed that Sirius was slowly changing its position as if it were being pulled around in orbit by the gravity of another star. In 1844, Bessel had a sufficient number of precise observations to announce that Sirius must have an unseen companion. The orbital period of the two stars around each other turned out to be about fifty years.
Astronomers searched for the companion star but couldn’t find it. Finally, in 1862, after Bessel died, the American telescope maker Alvan Clark, while testing a new telescope on the bright star Sirius, actually discovered the companion. It was indeed a star, but so very faint that it was almost lost in the glare of Sirius. Because the companion was about twice as far as Sirius from their common center of mass, it had to weigh about half as much (like a child twice as far from the center of a see-saw balancing an adult). Why then was the companion almost a thousand times fainter?
Around 1915, Walter Adams at Mt. Wilson Observatory obtained the spectrum of the companion and was astonished to find that the faint star was nearly three times hotter than Sirius. Using the laws of physics, astronomers can calculate the size of a star if they know its temperature and luminosity (light output). To be so hot and yet so faint, the companion of Sirius had to be as small as the Earth, but its mass, calculated from Bessel’s astrometry, equalled that of the Sun. Here was a star with the mass of the Sun packed into a volume no larger than the Earth. It had to be about three million times more dense than water. A thimbleful of this stuff would weigh about ten tons on Earth! The companion of Sirius was made of some strange new form of matter, far beyond anything in human experience. The nature of such dense objects, now called white dwarfs, remained a complete mystery until the development of quantum mechanics—the physics of atomic particles.
In 1930, a young Indian graduate student, Subrahmanyan Chandrasekhar, on a sea voyage to England to study astronomy at Cambridge, applied the new quantum ideas to the physics of stellar structure. He realized that when a star like the Sun exhausts its nuclear fuel, it will collapse due to its own gravity until a new form of pressure comes into play. This pressure is due to the so-called Pauli exclusion principle, which prevents the electrons in matter from getting too close to one another. The fact that the electrons cannot be compressed beyond a certain point determines the very high but stable density of a white dwarf. Chandrasekhar found that electron pressure can support a white dwarf only if the star has less than 1.4 times the mass of the Sun. More massive stars would continue to collapse to some then-unknown fate. This idea was the theoretical breakthrough that pointed the way to neutron stars and black holes, and would later earn Chandrasekhar the Nobel Prize for Physics.
Although difficult to observe due to their small size, white dwarfs actually turn out to be quite common in the Galaxy. In fact, we now know that all low mass stars like the Sun collapse into white dwarfs when they run out of nuclear fuel.
The story of the companion of Sirius has a peculiar sequel. In 1950 the French anthropologist Marcel Griaule published a study of the Dogon tribe of Mali in West Africa, in which he described an elaborate Dogon ceremony centered around the star Sirius. The Dogon informed Griaule that Sirius was accompanied by a very heavy, metallic companion star that was completely invisible. Excited by this information, UFO enthusiasts took it as proof that the Dogon had been visited long ago by aliens who taught them about the white dwarf companion of Sirius. How else could they possibly have known about it? But the astronomer Carl Sagan suggested a much simpler and more human explanation. He noted that the existence of the unseen, dense companion of Sirius was widely known in Europe long before Griaule recorded the Dogon mythology. The tribe had often been visited by missionaries and travelers. It is quite possible, even probable, that one of these visitors, perhaps during an exchange of sky lore with the Dogon, told them about the companion of Sirius, particularly since the Dogon used the appearance of Sirius to mark the changing seasons. The Dogon, recognizing a good story when they heard it, incorporated the invisible companion of Sirius into their own traditions, which were later recorded by Griaule.
This is an excerpt from COSMIC HORIZONS: ASTRONOMY AT THE CUTTING EDGE, edited by Steven Soter and Neil deGrasse Tyson, a publication of the New Press. © 2000 American Museum of Natural History.
More About This Resource...
This online article, from Cosmic Horizons: Astronomy at the Cutting Edge, takes a look at the first white dwarf to be discovered. It provides an overview of the following findings related to Sirius B:
- Friedrich Bessel's discovery of the long-sought stellar parallax and his discovery of Sirius' companion star.
- The first sighting of Sirius B, by telescope maker Alvan Clark.
- Walter Adams' discovery that the faint Sirius B was nearly three times hotter than the very bright Sirius.
- Subrahmanyan Chandrasekhar's use of the new quantum physics to explain how white dwarfs are created.
- The spread of all this knowledge to a tribe in West Africa, who incorporated it into their mythology.
Less than 1 period
Supplement a study of astronomy with an activity drawn from this essay about the discovery of Sirius B and white dwarfs.
- Ask students to describe how they think an astronomer in the 1800s could discover a white dwarf before the technology existed to see the star.
- Send students to this online article, or print copies of the essay for them to read.
- Have them write a one-page reaction to the article, focusing on what they learned about astrometry and the discoveries Bessel made by measuring stellar positions. | <urn:uuid:d5dd9191-42ef-41a7-9c45-0cd9b2b6b817> | 3.890625 | 1,583 | Knowledge Article | Science & Tech. | 45.242884 |
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In the eastern tropics, Nypa fruticans may form dense colonies on estuarine muds; these pure stands of nipa palm ( Nypa) extend for hundreds of hectares in eastern Sumatra and parts of Borneo. In other situations, dicotyledonous mangrove species occur with the nipa palm. The genus Manicaria (bussu palm) occupies similar habitats in some New World areas. Palms are dominant in...
...the surface of the soil and producing the crown at ground level, while others are high-climbing vines. Rare instances of regular branching (in Allagoptera, Chamaedorea, Hyphaene, Nannorrhops, Nypa, Vonitra) appear to involve equal or subequal division at the apex that results in a forking habit. The two newly formed branches may continue equally, or one may be overtopped by the other...
What made you want to look up "Nypa"? Please share what surprised you most... | <urn:uuid:0b1c8644-690d-4e12-b157-9040d37ed9a1> | 3.140625 | 256 | Knowledge Article | Science & Tech. | 45.877115 |
This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
Not sure, what made you to think it is sorted. In your code, the values are printed in the order of system.out.println(). You overwrote the value of key m1 and therefore the latest value of m1 is being printed.
Originally posted by Shiv Mohan (i) just meant,based on the keys (referencevariable m1,m2,m3) that order ,values are sorted.
1- You have not overridden equals() and hashCode() methods of the Obejct class in your class named MyClass. It is recommended that when you are using your own class as a key, you should give definition to both the methods to compare when two objects should be treated equals. What default implementation of the equals() says, two objects are equal if their reference variable are referring to the same object on the heap.
So far as your confusion of ordering is concerned: there is no magic with get() method: get method takes the object reference(key) and returns the value, you confusion is running around the same; you may be thinking that get is returning the objects in the same way you have stored. But it is nothing like that, you can try by changing the order:
There is nothing like order in the HashMap. And no order means no sorting of course. | <urn:uuid:7005681a-06a3-4458-9ad7-2be2cd400521> | 2.90625 | 318 | Comment Section | Software Dev. | 58.854429 |
class player: def sethp(self, hp): self.hp = hp def setmp(self, mp): self.mp = mp def setatt(self, att): self.att = att def setdef(self, arm): self.arm = arm def battle(hero, noob): print("hero hp"), hero.hp,("noob hp"), noob.hp battlechoice = input(int("what would u like to do")) if battlechoice==1: noob.hp-(hero.att-noob.arm) else: noob.hp-(hero.att-noob.arm) print("hero hp"), hero.hp,("noob hp"), noob.hp def noob: setmp(noob, 10) sethp(noob, 10) setatt(noob, 10) setdef(noob, 5) def hero: setmp(hero, 10) sethp(hero, 10) setatt(hero, 15) setdef(hero, 10) name = raw_input("enter heroes name") print "what would u like to do", name print "1. fight" choice = input() if choice==1: battle(hero, noob) else: print("boo")
I get a syntax error with the : after defining noob. I'm not sure why. Also i tried to put the class and and the noob and hero definitions in another file and import it but i got an error. I don't fully or much at all understand modules so i just put all the code in one file.
This isn't something that i intend to finish or be enjoyable i am just attempting to produce something with what little python i know to help to not forget it and get a better understanding.
thx for the help guys. I plan on buying the O'reily book on learning python. any good?
This post has been edited by jmanelson: 20 March 2009 - 05:48 PM | <urn:uuid:57a87d6c-a9c3-4f47-9d8c-313c4ede8632> | 2.796875 | 414 | Comment Section | Software Dev. | 92.186685 |
Emissions-free flight could be a possibility in the future, as Boeing is working to develop a light plane that is powered by fuel cells and an electric motor instead of fossil fuels in 12 month's time. The only emissions from such a plane would be water vapor.
At this point, the plane would be a small craft, and might have a top speed of only 70 miles per hour. It's not going to be a replacement for commercial passenger craft any time soon. But it's certainly another avenue for research and development toward what might some day be cleaner, greener air travel.
written by Luke, September 06, 2006
written by SparkySpider, November 04, 2006
written by fdsfsdf, February 12, 2007
written by Easyjet, February 12, 2007
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Are you getting ready for the holidays? You can still fit in some family math into your busy schedule. There's something here for all ages!
Holiday Calorie Count
Are you eating more than normal? I know I eat more chocolate over the holidays!
Try tracking what you eat and your activities for the day, charting the calories consumed and burned. This requires both measuring and arithmetic.
Demonstrate your results on a bar graph. This is a great time to also discuss nutrition and health. Do candy canes count as a red vegetable?
Take your favorite recipe, double it, convert it to metric and use only a teaspoon and ¼ cup to measure. Use an oven thermometer to compare the actual temperature to the stove setting. Convert this to Celsius. Or be extra crazy for math and change the ingredient amounts into math questions! By the way, how long does it take a turkey to cook in seconds?
Check out this great site with Gingerbread Man Math Activities!
Get everyone to prepare a shopping budget and stick to it! Teach the kids how to use a spreadsheet. Compare your actual expenditures with your budget at the end.
How many Christmas lights are on your house? How many extra watts of power are they using? How about your street, the neighborhood, your city, the world?
- How much energy and money can a community save by switching to LED lights?
- How Christmas Lights Work
Count down and chart the days, minutes and seconds till the big day. Make up your own advent calendar. Have older kids include minutes and seconds.
Have your tape measure handy to measure the dimensions of the package. How much wrapping paper will you need? Try estimating. Make your own wrapping paper using tessellations!
Christmas Trees and Snowflakes
Explore symmetry and fractals through snowflakes and Christmas trees. Create your own decorations. Don't forget to measure the height of your Christmas tree using trigonometry!
- Snowflake Photographs
- Snowflake Math Lesson
- Snowflake Creator
- Paper Snowflake Instructions
- Fractals in Snowflakes
- How Tall is That Tree?
Make up your own Christmas card puzzles in cryptarithm. Decorate the cover with a tangram candle, dove or other thematic creation.
- What is cryptarithm?
- Christmas Puzzle using cryptaritm
- Tangram Game to Practice
- Tangram Template to Print
- More Tangram Ideas
Ornaments and Decorations
Construct your own polyhedral paper ornaments for the tree. Create patterns as you string popcorn and cranberries to decorate the tree. Make a Christmas paper chain with a math fact on each loop!
This is a great exercise in geography, distance, speed and times zones.
Check out how far Santa has to travel. You may even need Pi!
Compare portion's of Santa's trip on your globe with a map using Mercator projection.
Where does Santa live?
- How far is it to the North Pole?
- Take a virtual expedition to the North Pole
- How cold is it at the North Pole?
What's the temperature at the North Pole?
Does Santa have any daylight?
Why can't we find Santa? Maybe he actually lives at the magnetic North Pole which changes every year!
- The Road to the Magnetic North Pole
- Expedition to the Magnetic North Pole
- How Does a Compass Work? How to Make Your Own Compass
What will Santa do if we live on another planet?
The Twelve Days of Christmas
Explore Pascal's Triangle and the 12 Days of Christmas. By the way, what would you prefer — the twelve gifts or $1 doubled for 12 days? What about 12! (that's twelve factorial).
- 2007 cost of gifts rises to $78,100!
- The Twelve Days of Christmas and Pascal's Triangle
- The Twelve Days of Christmas: Music Meets Math
- The Twelve Days of Christmas Pricing Activity
- Total of Gifts in the Twelve Days of Christmas
Keeping in Touch
Have you sent out any Christmas cards? How much were the stamps? How much more is an international letter? How much is a roll of 50 stamps? Calculate how much money you can save this year by calling all your relatives over the internet for free!
I just started using Skype to keep in touch with my parents. It was surprisingly easy to set up. We are saving at least $20 a month.
The Mathematics (and the Magic) of Christmas
New Year's Eve
Learn about time zones as different countries welcome in the New Year.
- Countdown to New Years Eve
- Time Square Earth Cam
- The World Clock: Time Zones
- Map of World Time Zones
Christmas Worksheets and Math Problems
- Christmas Factor Trees
- Addition: Santa's List
- Addition: Santa's List 2 digit
- Ordering 0-50: Christmas Tree Ornaments
- Ordering 1-100
- Ordering 1-1000
- Dot to Dot Christmas Tree (0-50)
- Maze: Fireplace
- Christmas Maze
- Christmas Math Word Problems
- Christmas Math Stories
- Logic Problem with Candy Canes and Ornaments
- Christmas Logic Patterns (Easy)
- Christmas Logic Patterns (Difficult)
- Christmas Sudoku Puzzles (Kids)
- More Christmas Worksheets: Various
- Merry Christmas Math Problems (and Solutions)
- Christmas Worksheets (probability, pie chart, surveys) from About.com
(Deb Russell the mathematics guide has a great newsletter you can sign up to receive!)
History and Culture
Don't forget to enjoy a bit of history and culture! (You can always find math in dates, distances and geography statistics).
More Christmas Fun
- Build a Snowman Online Game
- Make Your Own Snowflake
- Sleepy Santa Paper Craft
- Fold and Cut Gingerbread Man
- Apple Santa Craft
- Smack a Penguin!
Unwrapping Gifts (and Math)
Well, I doubt anyone will be in the mood, but here goes! Determine the probability that Dad gets a tie. Estimate and time how long it takes to unwrap all the presents. Compare and contrast this with how long it took to wrap them. Chart the number of gifts received versus given. Estimate and weigh the bags of recycled wrapping paper. Explore nets with the extra boxes and measure them using cubits. Sort your gifts into Venn diagrams and make a pie chart to illustrate your findings. Line up all the Christmas chocolates into arrays, sort, group and put into sets. Use the leftover ribbon to explore topology and create a gigantic mobius strip. Try to build a rhombicosidodecahedron out of the recycled wrapping paper or just take a break from math and have googols of fun! | <urn:uuid:94256fa0-7a68-455e-8ea8-6c042c7c9349> | 2.828125 | 1,429 | Content Listing | Science & Tech. | 60.476836 |
We live in a world that is defined by three spatial dimensions and one
time dimension. Objects move within this domain in two ways.
or changes location, from one
point to another.
And an object
or changes its attitude.
In general, the motion of any object
involves both translation and rotation.
The translations are in direct response to external
The rotations are in direct response to external
torques or moments (twisting forces).
of a rocket
is particularly complex because the rotations and translations
are coupled together; a rotation affects the magnitude
and direction of the forces which affect translations.
To understand and describe the motion of a rocket, we usually try
to break down the complex problem into a series of easier problems.
We can, for instance, assume that the rocket translates from one
point to another as if all the mass of the rocket were collected
into a single point called the
center of gravity.
We can describe the motion of the center of gravity by using
laws of motion. In general, there are four
forces acting on the rocket; the weight,
thrust, drag and lift.
Forces, Torques and Motion:
Beginner's Guide Home | <urn:uuid:7d12496b-d5f6-4b61-afeb-142a3f5d53ff> | 4.1875 | 254 | Tutorial | Science & Tech. | 43.937203 |
|Contents||Plain text (including entities)|
The TITLE element gives the document's title. Each document must have exactly one TITLE within the HEAD. TITLE contains plain text and entities; it may not contain other markup.
A good TITLE should be short and specific to the document's content so that it can be used as a title for a user's bookmark, a title for the display window, and a link from a search engine. A suggested limit for the number of characters in a TITLE is 60. | <urn:uuid:9177774a-5861-4164-a8dc-ed95ef765a2a> | 3.25 | 108 | Documentation | Software Dev. | 61.109636 |
Converting to String
String class provides us with the method String.valueOf(some stuff) that basically converts "some stuff" into a string..
But we can also concatenate "some stuff" with an empty String ("").
Both these methods result in a String representation of an object(or other data type) so my question is what is the difference between the two, advantages of one over the other, disadvantages of one over the other and which method do you guys usually use when forced to convert something to a String and why??
Re: Converting to String
Indirectly, both of these methods are calling the objects' toString() method.
I normally just call this method to get the object to a string, or alternatively you can directly "add" your object to a string, automatically calling the toString() method and concatenating the strings together. This makes the code easy to read and understand.
Technically, calling the toString() method is the most efficient and uses the least memory, but the performance of all the methods are virtually identical. Note that concatenating strings can become very slow for repeated concatenations of large strings because it does have to create a new character array and copy over both string's to get the new string.
If you have to build large strings, the recommended method would be to use the StringBuilder class. | <urn:uuid:ea249daa-902a-4e62-b6d5-87c0f47ac142> | 2.796875 | 283 | Comment Section | Software Dev. | 45.32897 |
A runaway star, plowing through the depths of space and piling up interstellar material before it, can be seen in this ultraviolet image from NASA’s Galaxy Evolution Explorer. The star, called CW Leo,...› View Image
This is the Helix nebula, as seen in ultraviolet light. It is a star like our sun but at the very end of its life. The star is a small dot in the center, surrounded by billowy layers of expelled mater...› View Image
Hot stars burn brightly in this new image from NASA's Galaxy Evolution Explorer, showing the ultraviolet side of a familiar face.
At approximately 2.5 million light-years away, the Androm...
This image of the Cartwheel galaxy shows a rainbow of multi-wavelength observations from NASA missions, including the Galaxy Evolution Explorer (blue), the Hubble Space Telescope (green), the Spitzer ...› View Image
A galaxy sprouts stars far from its central hub, as seen here where the blue dots line the red, spindly, spiral arms. Ultraviolet data from the Galaxy Evolution Explorer are color-coded blue and green...› View Image
Astronomers suspect that this pair of galaxies is locked in a gravitational dance. In this ultraviolet image, a spiral arm from the central galaxy appears to be wrapped around the smaller galaxy, loca...› View Image
By combining ultraviolet data from the Galaxy Evolution Explorer with infrared observations from NASA's Spitzer Space Telescope, astronomers get a clear picture of the various components of a galaxy. ...› View Image
These images show the galaxy nicknamed "Ghost of Mirach" in visible-light (left) and in ultraviolet (right) as seen by the Galaxy Evolution Explorer. A ring around the galaxy -- which is the white spo...› View Image
Observations from the Galaxy Evolution Explorer allowed astronomers to trace the development of galaxies, from their wild, youthful days to their more settled, older years.
› View Image
These images, taken with NASA's Galaxy Evolution Explorer and the Pan-STARRS1 telescope in Hawaii, show a brightening inside a galaxy caused by a flare from its nucleus. The arrow in each image points...› View Image
Astronomers believe they have caught the galaxy NGC 3810 at a critical point in its history, just as it is making the transition from a vigorous spiral galaxy to a quiescent elliptical galaxy whose st...› View Image
Time is running out for the galaxy NGC 3801, seen in this composite image combining light from across the spectrum, ranging from ultraviolet to radio. NASA's Galaxy Evolution Explorer and other instru...› View Image
Wispy tendrils of hot dust and gas glow brightly in this ultraviolet image of the Cygnus Loop nebula, taken by NASA’s Galaxy Evolution Explorer. The nebula lies about 1,500 light-years away, and is a ...› View Image
This diagram illustrates two ways to measure how fast the universe is expanding. In the past, distant supernovae, or exploded stars, have been used as "standard candles" to measure distances in the un...› View Image
Astronomers think that the expansion of the universe is regulated by both the force of gravity, which acts to slow it down, and a mysterious dark energy, which pushes matter and space apart. In fact, ...› View Image
NASA's Galaxy Evolution Explorer is helping to solve a mystery -- why do the littlest of galaxies produce the biggest of star explosions, or supernovae?
These postage-stamp images were ta...
This artist's concept illustrates a young, red dwarf star surrounded by three planets. Such stars are dimmer and smaller than yellow stars like our sun, which makes them ideal targets for astronomers ...› View Image
Astronomers have found unexpected rings and arcs of ultraviolet light around a selection of galaxies, four of which are shown here as viewed by NASA's and the European Space Agency's Hubble Space Tele...› View Image
NASA's Galaxy Evolution Explorer found a tail behind a galaxy called IC 3418. The star-studded tail can be seen on the left, as detected by the space telescope in ultraviolet light. The tail has escap...› View Image
This diagram illustrates the extent to which astronomers have been underestimating the proportion of small to big stars in certain galaxies. | <urn:uuid:574b5e7c-3928-4e5e-9644-bc1b0ddbc5c1> | 2.765625 | 906 | Content Listing | Science & Tech. | 49.782396 |
An assertion is a statement in the Java TM programming language that enables you to test your assumptions about your program. For example, if you write a method that calculates the speed of a particle, you might assert that the calculated speed is less than the speed of light. Each assertion contains a boolean expression that you believe will be true when the assertion executes. If it is not true, the system will throw an error. By verifying that the boolean expression is indeed true, the assertion confirms your assumptions about the behavior of your program, increasing your confidence that the program is free of errors. Experience has shown that writing assertions while programming is one of the quickest and most effective ways to detect and correct bugs.
This story is probably familiar: You're writing a test program and you need to pause for some amount of time, so you call Thread.sleep() . But then the compiler or IDE balks that you haven't dealt with the checked InterruptedException . What is InterruptedException , and why do you have to deal with it? The most common response to InterruptedException is to swallow it -- catch it and do nothing (or perhaps log it, which isn't any better) -- as we'll see later in Listing 4 .
Occasionally it is important for an application to know its PID, specially if this application cooperates with other non-java applications. Currently there is no direct support for retrieving an application's process id by using standard Java api (this might change in the future if RFEs like 4250622 , 4244896 or 4890847 are resolved). I found five ways how to get the PID from my Java code: Using the java management and monitoring API (java.lang.management): ManagementFactory.getRuntimeMXBean().getName(); returns something like: 28906@localhost where 28906 is the PID of JVM's process, which is in fact the PID of my app.
In an equaly distributed table, a single cell is an intersection of a single row and a single column. However, for design purposes, it is often convenient to use group table column headers (above a sequence of cells), and sometimes several vertical cells are containing the same data, so they can be merged into one single large cell. Word processing and spreadsheet software usually uses terms like “merged cells” for joined cells, and in HTML terminology, merged cells are often denoted by column-spanning and row-spanning. We will use HTML terminology here, since it is more precise and takes into account a difference betweek horizontal (column) and vertical (row) merging. Column spanning is a HTML cell property that defines how much “logical” columns a table cell contains.
Have you ever thought of how tools like "http://checkstyle.sourceforge.net/">Checkstyle or "http://findbugs.sourceforge.net/">FindBugs perform a static code analysis, or how Integrated Development Environments (IDEs) like NetBeans or "http://www.eclipse.org/">Eclipse execute quick code fixes or find the exact references of a field declared in your code? In many cases, IDEs have their own APIs to parse the source code and generate a standard tree structure, called an Abstract Syntax Tree (AST) or "parse tree," which can be used for deeper analysis of the source elements. The good news is that it is now possible to accomplish the said tasks plus a lot more with the help of three new APIs introduced in Java as part of the Java Standard Edition 6 release. The APIs that might be of interest to developers of Java applications that need to perform source code analysis are the "http://www.jcp.org/en/jsr/detail?id=199">Java Compiler API (JSR 199), the "http://www.jcp.org/en/jsr/detail?
Code by Any Other Name Reflecting generics by Ian Robertson June 23, 2007 Summary Type arguments to generic classes are not available for reflection at runtime - or are they? The type arguments for statically declared types can be discovered at runtime. A look at how to do this, and why you might want to. Probably the most common complaint about generics in Java is that they are not reified - there is not a way to know at runtime that a List<String> is any different from a List<Long> . I've gotten so used to this that I was quite surprised to run across Neil Gafter's work on Super Type Tokens .
All text and content found at URLs starting with http://www.AngelikaLanger.com/GenericsFAQ/ (collectively, "the Java Generics FAQ") are the sole property of Angelika Langer. Copyright @ 2004-2013 by Angelika Langer . All rights reserved. Except as specifically granted below, you may not modify, copy, publish, sell, display, transmit (in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise), adapt, distribute, store in a retrieval system, create derivative works, or in any other way use or exploit the contents of the Java Generics FAQ, without the prior consent of the author. All rights, titles and interest, including copyrights and other applicable intellectual property rights, in any of the material belongs to the provider of the material. You do not acquire proprietary interest in such materials by accessing them on my web site.
My earlier post covered in-built annotations supported by Java 5. Today we will look at developing custom java annotations on our own. Let’s begin by defining our own custom java annotation called Documentation. The definition of the annotation class is as below: The only difference between an interface definition and that of an annotation is the presence of @ before the interface keyword. Now the annotation can have its own members.
This year one of my goals is to try and become proficient in using ANTLR. I think that learning to translate text or build an external DSL is skill that, although not used everyday, will be very useful to know. For my first attempt I settled on something fairly easy, a SQL like grammar that could be used to search for files and the content within those files.
Design patterns form a cohesive language that can be used to describe classic solutions to common object oriented design problems. These patterns enable us to discuss systems of objects as quasi-encapsulated entities. By using design patterns to solve programming problems, the proper perspective on the design process can be maintained. These pattern discussions, except for the Null and Model-View-Controller patterns are adapted from the classic text, Design Patterns by Gamma, Helm, Johnson and Vlissides (Addison Wesley Longman, 1995.
Posted by alexfromsun on February 16, 2006 at 11:49 AM PST It's taken some time to study all possible ways of detecting Event Dispatch Thread rule violations, and now I feel I this topic is about to be closed. But let me tell from the beginning:
Awesome tip for debugging Swing by Sep 29
Oracle Oracle Technology Network > Java Article Why, Where, and How JavaFX Makes Sense CaptainCasa moved from Swing to JavaFX for front-end infrastructure, explaining that implementing an employee desktop front end with native technology is a valid approach and that JavaFX is a good fit.
Need a digest, summary, compressed form, precis of what's up with Java SE 6 'Mustang', currently in beta ? Here it is, the top 10 things you need to know. 1. Web Services All developers get first class support for writing XML web service client applications.
You are here: Home / Java 7 This page lists the proposed features in Java 7 and information about them. At this point, no Java 7 JSR has been created (although Danny Coward apparently is working on it). So, consider this a list of possible features and libraries, not the actual future contents of Java 7. I formerly published a weekly roundup of discussion on what’s been added to this page.
Javadoc Home Page This document describes the style guide, tag and image conventions we use in documentation comments for Java programs written at Java Software, Oracle. It does not rehash related material covered elsewhere: For reference material on Javadoc tags, see the Javadoc reference pages . For the required semantic content of documentation comments, see Requirements for Writing Java API Specifications . | <urn:uuid:608310d5-72ed-442e-b3bc-6f1833346bc1> | 3.40625 | 1,728 | Comment Section | Software Dev. | 46.336603 |
Vectors - Fundamentals and Operations
Explore nine lessons from a two-week unit on vectors by the Center for Innovation in Science and Engineering Education (CIESE).Curriculum Corner
Learning requires action. Give your students this sense-making activity from The Curriculum Corner.Treasures from TPF
Need ideas? Need help? Explore The Physics Front's treasure box of catalogued resources on vectors.Physics-Math Connection
This tutorial contrasting the typical math and physics approach to vectors can be an enlightening read.
Vectors and Direction
A study of motion will involve the introduction of a variety of quantities that are used to describe the physical world. Examples of such quantities include distance, displacement, speed, velocity, acceleration, force, mass, momentum, energy, work, power, etc. All these quantities can by divided into two categories - vectors and scalars. A vector quantity is a quantity that is fully described by both magnitude and direction. On the other hand, a scalar quantity is a quantity that is fully described by its magnitude. The emphasis of this unit is to understand some fundamentals about vectors and to apply the fundamentals in order to understand motion and forces that occur in two dimensions.
Examples of vector quantities that have been previously discussed include displacement, velocity, acceleration, and force. Each of these quantities are unique in that a full description of the quantity demands that both a magnitude and a direction are listed. For example, suppose your teacher tells you "A bag of gold is located outside the classroom. To find it, displace yourself 20 meters." This statement may provide yourself enough information to pique your interest; yet, there is not enough information included in the statement to find the bag of gold. The displacement required to find the bag of gold has not been fully described. On the other hand, suppose your teacher tells you "A bag of gold is located outside the classroom. To find it, displace yourself from the center of the classroom door 20 meters in a direction 30 degrees to the west of north." This statement now provides a complete description of the displacement vector - it lists both magnitude (20 meters) and direction (30 degrees to the west of north) relative to a reference or starting position (the center of the classroom door). Vector quantities are not fully described unless both magnitude and direction are listed.
Vector quantities are often represented by scaled vector diagrams. Vector diagrams depict a vector by use of an arrow drawn to scale in a specific direction. Vector diagrams were introduced and used in earlier units to depict the forces acting upon an object. Such diagrams are commonly called as free-body diagrams. An example of a scaled vector diagram is shown in the diagram at the right. The vector diagram depicts a displacement vector. Observe that there are several characteristics of this diagram that make it an appropriately drawn vector diagram.
- a scale is clearly listed
- a vector arrow (with arrowhead) is drawn in a specified direction. The vector arrow has a head and a tail.
- the magnitude and direction of the vector is clearly labeled. In this case, the diagram shows the magnitude is 20 m and the direction is (30 degrees West of North).
Vectors can be directed due East, due West, due South, and due North. But some vectors are directed northeast (at a 45 degree angle); and some vectors are even directed northeast, yet more north than east. Thus, there is a clear need for some form of a convention for identifying the direction of a vector that is not due East, due West, due South, or due North. There are a variety of conventions for describing the direction of any vector. The two conventions that will be discussed and used in this unit are described below:
- The direction of a vector is often expressed as an angle of rotation of the vector about its "tail" from east, west, north, or south. For example, a vector can be said to have a direction of 40 degrees North of West (meaning a vector pointing West has been rotated 40 degrees towards the northerly direction) of 65 degrees East of South (meaning a vector pointing South has been rotated 65 degrees towards the easterly direction).
- The direction of a vector is often expressed as a
counterclockwise angle of rotation of the vector about
its "tail" from due East. Using this
convention, a vector with a direction of 30 degrees is a
vector that has been rotated 30 degrees in a
counterclockwise direction relative to due east. A vector
with a direction of 160 degrees is a vector that has
been rotated 160 degrees in a counterclockwise direction
relative to due east. A vector with a direction of 270
degrees is a vector that has been rotated 270 degrees in
a counterclockwise direction relative to due east. This
is one of the most common conventions for the direction
of a vector and will be utilized throughout this
Observe in the first example that the
vector is said to have a direction of 40 degrees. You can
think of this direction as follows: suppose a vector
pointing East had its tail pinned down and
then the vector was rotated an angle of 40 degrees in the
counterclockwise direction. Observe in the second example that the
vector is said to have a direction of 240 degrees. This
means that the tail of the vector was pinned down and the
vector was rotated an angle of 240 degrees in the
counterclockwise direction beginning from due east. A
rotation of 240 degrees is equivalent to rotating the vector
through two quadrants (180 degrees) and then an additional
60 degrees into the third quadrant.
The magnitude of a vector in a scaled vector diagram is depicted by the length of the arrow. The arrow is drawn a precise length in accordance with a chosen scale. For example, the diagram at the right shows a vector with a magnitude of 20 miles. Since the scale used for constructing the diagram is 1 cm = 5 miles, the vector arrow is drawn with a length of 4 cm. That is, 4 cm x (5 miles/1 cm) = 20 miles.
Using the same scale (1 cm = 5 miles), a displacement vector that is 15 miles will be represented by a vector arrow that is 3 cm in length. Similarly, a 25-mile displacement vector is represented by a 5-cm long vector arrow. And finally, an 18-mile displacement vector is represented by a 3.6-cm long arrow. See the examples shown below.
In conclusion, vectors can be represented by use of a scaled vector diagram. On such a diagram, a vector arrow is drawn to represent the vector. The arrow has an obvious tail and arrowhead. The magnitude of a vector is represented by the length of the arrow. A scale is indicated (such as, 1 cm = 5 miles) and the arrow is drawn the proper length according to the chosen scale. The arrow points in the precise direction. Directions are described by the use of some convention. The most common convention is that the direction of a vector is the counterclockwise angle of rotation which that vector makes with respect to due East.
In the remainder of this lesson, in the entire unit, and in future units, scaled vector diagrams and the above convention for the direction of a vector will be frequently used to describe motion and solve problems concerning motion. For this reason, it is critical that you have a comfortable understanding of the means of representing and describing vector quantities. Some practice problems are available on-line at the following WWW page: | <urn:uuid:516dbb46-2058-4d08-bf82-4cf5e7861530> | 4.28125 | 1,547 | Truncated | Science & Tech. | 49.341327 |
View Full Version : Chemistry Problem
05-12-2008, 08:38 PM
Ok, so i have this lab on the molar mass of butane, except im totally having a brain fart, and cant remember how to do it, like i have the PV=nRT, but once i have the number from there im stuck, any ideas?
05-12-2008, 10:36 PM
Oooh this is right up my ally. I just finished college Chemistry.
n = moles
Molar Mass = Mass of gas/N
I'm fairly certain, anyway.
If you could give me the exact problem I'm pretty sure I could do it. My best unit in Chem was the gas laws.
Is this by chance Webassign?
05-13-2008, 02:43 AM
CH3CH2CH2CH3 is butane, I forget if that helps, it's been 3 years since I took chemistry. I was under the impression that you could find the atomic mass of each atom in the substance, add them up then multiply it by Avogadro's number, 6.02214×10^23, which is how many molecules per mol there are. I'm nearly certain now that's wrong or inaccurate to anything aside from 20* Celsius at 1atm pressure because you'll have to account for the mass gain due to excess energy.
I found this while googling: http://www.chem.uiuc.edu/chem103/molar_mass/introduction.htm | <urn:uuid:71d275c3-1d30-45e1-9465-1204b1923e2d> | 3 | 322 | Comment Section | Science & Tech. | 84.513433 |
Narrator: This is Science Today. Radioactive waste decays over time and this poses long-term storage problems because materials currently used to encase radioactive waste are ultimately damaged and are then susceptible to rupturing or leaching. Scientist Kurt Sickafus of the Los Alamos National Laboratory says one of the major limitations of long-term storage has been the absence of a material that is both chemically durable, as well as radiation-resistant.
Sickafus: They need to be tolerant of the damage that's introduced by the radioactive decay and this is something that is a very difficult problem to solve to have a material that's robust over very long periods of time.
Narrator: But researchers at the Los Alamos Lab have proposed materials - a set of crystalline-ceramic oxides - which appear to have a very high radiation tolerance.
Sickafus: They do appear very attractive. So you're essentially relying on the high stability of these rock-like oxides to hold your radioactive constituents and keep them out of any environmental situations where they would come back to interact with the living environment.
Narrator: For Science Today, I'm Larissa Branin. | <urn:uuid:b55bfdf1-b4ba-46f0-b4a5-7334fe8ef927> | 3.96875 | 241 | Audio Transcript | Science & Tech. | 23.146378 |
Predaceous diving beetles
Dytiscidae - Family of insects in the order Coleoptera. These species are mostly black, dark brown, or dark green, but some have golden and other highlights. They have sharp and short jaws for biting their prey. Most are about 25 mm long but some can grow up to 45 mm long. The larvae are commonly known as water tigers.
- Quick facts
- Status of knowledge
- Richness and diversity in Canada
- Species spotlight - Hydroporus carri
- Species spotlight - Dytiscus dauricus
- Species spotlight - Graphoderus manitobensis
- Species spotlight - Agabus immaturus
- Results of general status assessment
- Threats to Canadian predaceous diving beetles
- Further information
- Canada has at least 275 of the 500 species of predaceous diving beetles known from North America and roughly 4000 species known world-wide. Predaceous diving beetles are distributed over most of the world.
- When excluding species ranked as Extinct, Extirpated, Undetermined, Not Assessed, Exotic or Accidental, the great majority (98%) of predaceous diving beetles in Canada have Canada General Status Ranks (Canada ranks) of Secure, while 1% have Canada ranks of Sensitive and 1% have Canada ranks of May Be At Risk. However, it should be noted that many of the predaceous diving beetle species were ranked as Undetermined.
- The family name Dytiscidae (from the genus Dytiscus) is reportedly derived from the Greek word dytikos meaning “able to dive”.
- Eggs are laid inside aquatic plant tissue and hatch in about three weeks. Once the larvae grow, they move to the water’s edge, burrow into the soil and pupate.
- The larvae, commonly known as water tigers, are effective and active predators, but some adults may also scavenge dead prey, eat their own species, or even eat plants.
- Larvae are quite terrifying in appearance, with elongate bodies with a round flat head. They seize their prey with their strong jaws, inject it with powerful digestive enzymes and then suck in the liquefied internal parts.
- Water surface tension can be quite a barrier for diving beetles wanting to leave the water to fly to other locations. Ingested water expelled rapidly through the rectum can help smaller beetles push through this barrier and become air born.
Like all water beetles, predaceous diving beetles are air-breathing terrestrial insects that have evolved body features that allow them to live in the water. Larvae and adults are aquatic but they have to go to the surface to obtain air. Adults exchange and store fresh air under their wing coverts, or elytra, while larvae store air within their bodies. Diving beetles control or maintain their buoyancy in the water by controlling the size of the air pocket under their wings. This works well when they are eating well and have a full digestive system. When their stomach and abdomen is empty, they have to ingest water to prevent them from continuously floating to the surface. Adults swim by sculling or rowing with modified hind legs, but not all of these beetles are strong swimmers. Some less stream-lined types live in dense underwater vegetation, in gravel or under rocks. Like loons and other aquatic birds with legs modified for swimming, many predaceous diving beetles also walk awkwardly on land.
These beetles feed on a wide range of smaller invertebrates but some larger species can also eat amphibians, fish, and even reptiles. In turn, they can be abundant in some areas and serve an important food source for fish and aquatic and shore birds.
The larvae of some species are relatively dense-bodied and poor swimmers and live on the bottom, creeping over vegetation or burrowing in the mud. Others are buoyant and float or live on near the water surface when not actively swimming using all their legs. Larvae can flex their abdomens rapidly to move quickly over short distances to escape predators.
All but two Canadian species of diving beetles appear to be able to fly as adults. These beetles fly to populate new habitat, find suitable overwintering areas, or to avoid aquatic environments that are changing or drying up. Water beetles fly both during the day and at night, and are sometimes attracted to the shiny surfaces of cars, plastic or wet pavement which may look like water to them. For many Canadians, their first face to face encounter with a predacious diving beetle is in their backyard swimming or wading pool.
The life cycle of species in Canada are largely influenced by the freezing of aquatic habitats and spring snow melt, but season rain patterns do control how species behave in southern warm and arid ecosystems. Different kinds of predaceous diving beetles overwinter either as eggs, larvae, or adults.
Status of knowledge
All Canadian species of predaceous diving beetles are herein assessed for the first time in the Wild Species series. On a cautionary note, scientific diving beetle experts report that while most North American species are well described, some are difficult to identify and more research is needed before a stable and reliable classification system is obtained. Much remains to be learned about their basic life history or basic biology, offering Canadians from all walks of life an opportunity to make a significant contribution to our knowledge of these remarkable creatures.
Richness and diversity in Canada
In many groups of plants or animals there is an increase in species diversity in lower latitudes, but this does not seem to hold true for predacious diving beetles in Canada – our dytiscid fauna is about as diverse as other regions in the world based on the same area. One suggestion for this anomaly is that their ability to disperse by flight aided the relatively rapid recolonization of Canada’s diverse post-glacial aquatic habitats. One Alberta boreal pond was found to support up to 50 species!
Canada’s 275 species are classified into six subfamilies and 35 genera. The largest genera include Agabus (66 species), Hydroporus (41 species) and Hygrotus (29 species). Predacious diving beetles can be found in all provinces and territories in Canada.
Species spotlight - Hydroporus carri
This small (4 mm) uncommon Alberta species is found in springs. It is black to dark brown but sports a small reddish spot above each antenna. This species is found in small springs and seepages in foothill and subalpine areas in prime ranching country where its habitat is susceptible to damage from livestock. Considered at risk in much of its range (Alberta, Idaho, Utah and Oregon) it has been ranked by the General Status assessment process as May Be At Risk in Alberta and Canada. Conservation measures such as managing livestock access to water and its ability to colonize suitable habitat suggests that humans can create opportunities to conserve this species.
Species spotlight - Dytiscus dauricus
This large (up to 40 mm) black diving beetle has a greenish reflective upper surface and a reddish-yellow underside. Its antennae are yellow at the base and its legs are mainly yellow to reddish. It is widely distributed in Canada and across about one-half of the USA. It is also found in northern Eurasia. It is found in permanent ponds in forested areas from sea level in the north and at higher elevations in the south. In Arizona, it is known to feed on larval salamanders. The General Status rank of Secure was assigned to this species based on its readily available and abundant habitat and its wide distribution in Canada.
Species spotlight - Graphoderus manitobensis
This medium-sized (13-15 mm) diving beetle was first described by Wallis in 1933 from a specimen collected in Winnipeg, Manitoba (known as the “Type Locality”). It has elsewhere only been collected thus far in some localities in southern Wisconsin. It occurs in large sedge and cattail marshes and ponds in open areas. It was assessed with a general status rank of Undetermined because there is insufficient information about its range and relative abundance in Manitoba and Canada. It is distinguished from a similar species, Graphoderus fascicollis, by the unique shape of a front claw and by the male’s genitals. Additional search efforts should enable a better assessment of its general status in 2015.
Species spotlight - Agabus immaturus
This small (7.6 -7.9 mm) dark red headed and legged diving beetle is known only from one location in Canada; a sedge marsh in Tabusintac, New Brunswick. In the United States it is similarly limited in distribution to a few locations in Michigan and Wisconsin. The general status rank of Undetermined was assigned to this and many other diving beetles, highlighting the extent of our ignorance of the basic criteria or information needed to assign more definitive conservation status ranks.
Results of general status assessment
Most predaceous diving beetles have a Canada general status rank of Secure (75%). However, 23% of the species are not well known enough and are ranked as Undetermined. Finally, three species are considered Sensitive and two species are considered as May Be At Risk (figure 12 and table 17). Because of a general lack of information in many regions, the assessement of the predaceous diving beetles included in the Wild Species 2010 report is likely to change in the future reports of the series with a potential improved knowledge on these species.
|Canada rank||Number and percentage of species in each rank category|
|1||At Risk||0 (0%)|
|2||May Be At Risk||2 (1%)|
|6||Not Assessed||0 (0%)|
Threats to Canadian predaceous diving beetles
Predaceous diving beetles have not been commonly used as indicators of local environmental degradation in North America because of a lack of species-specific studies on the tolerance of each species along environmental gradients. Likewise, the concern about the conservation of water beetles and their habitats is not common or widespread. The drainage of wetlands is known to reduce their abundance and diversity, and chemical pollution and the use of insecticides negatively affects populations. But people also create habitat for these beetles by creating water bodies – many of them are adapted to unstable habitats and environments. Those species with a limited distribution and that are habitat specialists are at the greatest risk. For example, see the species spotlight for Hydroporus carri. It is these species that need sound habitat management or protected areas to ensure their continued survival from human activities that alter these habitats.
Most studies on predaceous diving beetles have been on documenting where they occur, and the time of year when adults are found. Some studies have described beetle community diversity and habitat associations. More research is needed on their population status and trends, basic natural history, environmental tolerances, and especially about their life as larvae.
- Canadian Biodiversity Information Facility. http://www.cbif.gc.ca/home_e.php (Accessed December 30, 2009).
- Larson, D. J., Alarie, Y. and Roughley, R. E. 2000. Predaceous diving beetles (Coleoptera: Dytiscidae) of the Nearctic Region, with emphasis on the fauna of Canada and Alaska. NRC Research Press, Ottawa: 982 pp. | <urn:uuid:92ca5902-a8b3-4d36-a458-b15b5496ce5c> | 3.390625 | 2,339 | Knowledge Article | Science & Tech. | 37.105507 |
URL translation into a Page Class
In Agile Toolkit, pages are objects created from classes. For each user request only one page object is initialized. The process where an API class determines the name of the page class to initilaize is called "routing".
Let me start with an example. The page you are reading right now was determined by Agile Toolkit as:
This page is determined from the URL above: /learn/understand/page/route. Please note that "/" and "_" are treated identically by Agile Toolkit.
In Agile Toolkit the API class determines how routing is done. You must already know that there is a selection of different API clasess in Agile Toolkit and their approach to page routing is different.
ApiFrontend — the application class you are most likely to use — diverts all web requests into a single file: index.php. This is achieved by either using the mod_rewrite rule (RewriteRule .* index.php) or by building the URLs with the argument "page". The default installation of Agile Toolkit uses URLs like this: "http://localhost/agiletoolkit/?page=dbtest".
Open the index.php with a text editor and notice that the job of the file is to initialize your Application class and pass execution to it.
ApiWeb — is a good application class if you can't use frontend controller or will need to use different routing. It is most useful when you need to integrate Agile Toolkit with a different framework.
This class assumes that you'll be executing it from the command-line and will not even try to determine the page.
The rest of this chapter will focus on ApiFrontend routing leaving other API implementations aside.
Building a URL from the page name
The logic used by ApiFrontend when determining a corresponding class to a page is simple:
|http://example.com/preferences.html||preferences||Agile Toolkit completely ignores the extension and uses remaining location to determine page name.|
|http://example.com/?page=user/add||user/add||Your default install of Agile Toolkit is not configured to use mod_rewrite. Therefore the URL in the browser will address index.php passing page=XX. GET['page'] will always override determined page-name.|
|http://example.com/profile/change-password.do||profile/changepassword||Dashes cannot be used in a function or class, they are eliminated from the page name automatically. Any extension can be used as long as .htaccess directs them to index.php|
|http://example.com/?abc=123||index||If URL does not contain page, then "index" page name is used.|
|http://example.com/admin/logout||logout||Agile Toolkit does not have to be in your web-root directory. If it's installed into subdirectory, Agile Toolkit will detect it and will eliminate the installation point (base_path) from the name of the page.|
PageManager is a controller used by ApiFrontend. It detects the URL of the browser and splits it into 3 components:
- base_url — http://example.com
- base_path — /atktest/
- page — user/settings
The page you are looking at right now is called "learn/understand/page/route".
The page object follows the standard pattern; And executes the init() method after it's initialized. A Page may have a custom template, but if it does not, the default page layout is used to display an empty page. | <urn:uuid:915cdd4d-25c1-4d12-9cc9-4e0d98ae62e2> | 2.6875 | 778 | Documentation | Software Dev. | 46.713116 |
The Pioneer Effect is a mysterious observation of a number of man-made probes that venture through and beyond the Solar System. Originally noticed in the slight drift of the Pioneer 10 and Pioneer 11 spacecraft (launched in 1972 and 1973) from their calculated trajectories, scientists have been at a loss to explain the tiny, yet constant, extra-sunward acceleration.
Some theories suggest that invisible clouds of dark matter are slowing these probes down, causing them to be influenced by the Sun’s gravity more than expected. Other suggestions include ideas that Einstein’s theory of General Relativity needs to be tweaked when considering interplanetary distances.
However, there are other, more mundane ideas. Perhaps there is a tiny fuel leak in the probes’ mechanics, or the distribution of heat through the spacecraft is causing a preferential release of infrared photons from one side, nudging them off course.
Finding an answer to the Pioneer effect probably won’t surface any time soon, but it is an enduring mystery that could have a comparatively simple explanation, within the realms of known science, but there’s also the possibility that we could also be looking at some entirely new physics.
In an attempt to single out whether the Pioneer anomaly is an artefact with the spaceships themselves, or unknown in the physics of the Universe, astronomers decided to analyse the orbits of the planets in the outer Solar System. The rationale being that if this is a large-scale influence, some observable periodic effects should be evident in the orbit of Pluto.
So far, no effect, periodic or otherwise, has been observed in the orbit of Pluto. If the effect isn’t big enough to influence Pluto, does this mean we can narrow the search down to spaceship-specific artefacts?
Not so fast.
Gary Page and John Wallin from George Mason University in Virginia and David Dixon from Jornada Observatory in New Mexico, have published a paper pointing out that the suggestion that the Pioneer effect doesn’t influence Pluto is flawed. Pluto’s orbit is far less understood than the orbits of the inner Solar System planets, as, let’s face it, Pluto is far away.
We simply don’t possess the data required to cancel out the Pioneer effect on planetary bodies in the outer-Solar System to reach the conclusion the anomaly doesn’t influence Pluto.
“Of course, this does not mean that the Pioneer effect exists. It does mean that we cannot deny the existence of the Pioneer effect on the basis of motions of the Pluto as currently known.” — Page et al., 2009
So, back to the drawing board. This is a fascinating study into a true Solar System mystery; bets are on as to the real reason why our interplanetary probes are being knocked off course…
Source: The Physics arXiv Blog | <urn:uuid:755b10ac-edea-4e7a-9b0f-8f56e812890b> | 3.828125 | 582 | Personal Blog | Science & Tech. | 39.085573 |
Missouri Frost Line
Commercial Agriculture/University of Missouri Extension
Many factors such as air temperature, snow cover, ground cover, soil type, soil moisture etc. will determine how deep the frost line penetrates but some long term soil temperature observations for the state can be utilized to get a general idea. There are only a handful of sites that have established official records of soil temperatures at multiple depths in Missouri. These sites include Spickard (Grundy county), Columbia (Boone), and Mount Vernon (Lawrence). Soil temperature observations at these University of Missouri Agricultural Experiment Stations began in 1967 and are collected at various depths including under a bare soil at a depth of 2 inches and under a sod at 4, 8, 20 and 40 inches.
Using the historical soil temperature records for the three aforementioned regions in Missouri, we can get a general idea of how deep the frost line has penetrated in the past 43 years. For northern Missouri, in Spickard, the coldest 8-inch soil temperature was 29° in 1977 and 1982 and the coldest 20-inch temperature was 35° in 1977, 1978 1994 and 1997. The coldest 40-inch temperature was 37° in 1986 and 1994. In mid-Missouri, the frost line at Columbia has also never reached the 20-inch depth. The coldest temperature at 20 inches was 35° in 1996, and the coldest 40-inch temperature was 42° in 1978. The coldest 8-inch temperature was 28° in 1982 and 1996. Soil temperature records in southern sections of the state indicate the frost line has never reached the 20-inch depth at Mount Vernon. The coldest temperature at the 8-inch depth was 28° in 1979 and the coldest 20-inch temperature was 36° in 1977 and 1979. The coldest 40-inch temperature was 40° in 1979.
Fortunately, during most bitterly cold outbreaks, Missouri will have a blanket of snow. Snow is an excellent insulator and will prevent freezing temperatures from penetrating too deep into the soil surface. There have been occasions, however, where minimal snow cover (less than 1-inch) was on the ground and an arctic outbreak ensued. In fact, the coldest outbreak on record for Missouri occurred between February 8-12, 1899 when the average statewide temperature was -6°F, or 40 degrees below normal! During this time, most of east central, south central, and southeastern Missouri had an insulating blanket of snow but northern and western sections reported bare ground. Actual soil temperature records were not taken at this time but a subjective report from an observer in Oregon, MO stated the ground was frozen 2-3 feet deep! | <urn:uuid:026ca88c-6d3d-442f-9e44-9811550268f9> | 3.375 | 545 | Knowledge Article | Science & Tech. | 48.948783 |
Content on this page was last updated in 2009. Some of the content may be out of date. For more information: http://coralreef.noaa.gov/
Coral reef ecosystems of the U.S. Virgin Islands
Coral reefs are a major and conspicuous component of the shelf regions of the U.S. Virgin Islands. Four other ecologically distinct marine habitats (seagrass beds, algal plains, mangrove forests and salt ponds) interact in various ways with the coral reefs and are considered to be part of the coral reef ecosystem. Other habitats such as octocoral hardbottom, sand communities, shallow mud, and fine sediment habitats also interact with the coral reefs.
Extensive coral reefs lie in deeper water along the shelf edge in depths from approximately 37 to 61 meters. These deeper reefs are dominated by plating forms of the Agaricia spp. and Montastraea spp. complexes, while corals in shallower water vary from columnar forms of Montastraea spp. to Acropora spp. to gorgonian dominated habitats. Maps of USVI benthic habitats (to 30 meters) show that 61 percent of the 485 km2 area is coral reefs and corals on hard bottom; 33 percent is predominantly seagrass beds, and 4 percent is sediment or rocky bottom.
Fringing and patch reefs, along with spur and groove formations, are typical of St. John and St. Thomas. St Croix, on the other hand, has several large barrier reefs, some of which are associated with well-developed lagoons. Several threatened and endangered species, in addition to elkhorn and staghorn corals, feed, reproduce, nest, rest, or calve in the waters of the USVI. Vertebrates, such as humpback whales, pilot whales, four species of dolphins, several sea birds, and marine turtles all use portions of these waters. The reefs of the USVI also provide habitats for many species of reef fishes, invertebrates, and plants.
A coral reef at St. Croix. The photograph features blue chromis, stoplight parrotfish, elkhorn coral, branching fire coral, sea plumes, sea rods, and sea whips. (Photo: NOAA CCMA Biogeography Team)
The highly productive seagrass beds provide food and shelter for a great variety of marine vertebrates and invertebrates. Seagrasses also act as sediment filters and consequently improve the water clarity over coral reefs. Four major sea grasses occur in the U. S. Virgin Islands: shoal grass, Halodule wrighti), turtle grass (Thalassia testudinum), manatee grass (Syringodium filiformis, and small turtle grass (Halophila baillonis). All four of these species have been recorded in St. Croix (probably because of well-protected lagoons). Shoal grass, turtle grass, and manatee grass are reported from St. John, while only turtle grass and manatee grass are known to occur in St. Thomas. In the U. S. Virgin Islands (as elsewhere) seagrass beds are typically limited to shallow, clear-water areas which have good water circulation.
A turtle grass meadow at St Croix (Photo: NOAA CCMA Biogeography Team)
Algal plains occur over coral rubble and coarse sand. They are best developed at depths of approximately 18 meters. Various species of green, brown, and red algae, and the spermatophyte Halophila baillonis (Florida Keys seagrass) are the dominant plants. Associated biota includes sponges, tunicates, bryozoans, mollusks, polychaete worms, and gorgonians. Fifty-two species of algae and 43 species of fishes have been recorded from a typical algal plain off St. Thomas.
Mangrove forests help stabilize shorelines and protect low-lying lands by buffering them against severe tropical storms, winds, and waves. Mangrove prop roots and leaf litter provide excellent habitat for a large number of invertebrate species as well as nursery areas for coral reef fishes (Boulon, 1992). They also provide nesting areas for birds. Mangrove root systems trap and cycle nutrients and organic materials. Mangrove forests are poorly developed in the U. S. Virgin Islands, accounting for only three percent of the total land area. Based on a survey undertaken by the U. S. Geological Survey (USGS, 1994) there were 960 acres of mangrove/salt pond habitat on St. Croix, 424 acres on St. John, and 320 acres on St. Thomas. Red mangrove (Rhizopora mangle), black mangrove (Avicennia germinans) and white mangrove (Laguncularia racemosa) are the dominant trees in the mangrove forests.
Salt ponds are tidal flats or basins which are at least partially separated from the sea by beach berms. They are a dominant feature of the wetlands of the U. S. Virgin Islands (more than eighty have been counted on the three main islands). Salinities vary from 10 to 100 parts per thousand (ppt). Salt ponds also trap sediments before the sediments reach the nearshore reefs.
Protected and managed areas
Both the federal government and USVI environmental agencies share responsibility for protecting the coral reef ecosysems in the U.S. Virgin Islands. These include the Virgin Islands National Park (St. John), The Buck Island National Monument (St. Croix), the Virgin Islands National Monument (St. John), Marine Conservation Districts, the East End Marine Park (St. Croix), and marine sanctuaries.
The monument south of St. John contains predominantly deep algal plains with communities of mostly red and calcareous algae. Scattered areas of raised hard bottom are colonized with hard corals, sponges, gorgonians, and other invertebrates. They provide shelter for spiny lobsters, sea basses, and snappers, as well as spawning sites for some reef fish species. These algal plains and raised hard bottom areas link the shallow water reef, sea grass, and mangrove communities with the deep water shelf and shelf edge communities of fishes and invertebrates. | <urn:uuid:dd71f2bb-b6a1-4b92-ab2b-dd370470e50d> | 3.78125 | 1,337 | Knowledge Article | Science & Tech. | 49.699754 |
print_stmt: "print" [ expression ("," expression)* [","] ]
print evaluates each expression in turn and writes the resulting object to standard output (see below). If an object is not a string, it is first converted to a string using the rules for string conversions. The (resulting or original) string is then written. A space is written before each object is (converted and) written, unless the output system believes it is positioned at the beginning of a line. This is the case (1) when no characters have yet been written to standard output, (2) when the last character written to standard output is "\n", or (3) when the last write operation on standard output was not a print statement. (In some cases it may be functional to write an empty string to standard output for this reason.)
A "\n" character is written at the end, unless the print statement ends with a comma. This is the only action if the statement contains just the keyword print.
Standard output is defined as the file object named
in the built-in module sys. If no such object exists, or if
it does not have a write() method, a RuntimeError
exception is raised.
print also has an extended form, defined as
print_stmt: "print" ">>" expression [ ("," expression)+ [","] ]
In this form, the first expression after the
evaluate to a ``file-like'' object, specifically an object that has a
write() method as described above. With this extended form,
the subsequent expressions are printed to this file object. If the
first expression evaluates to
used as the file for output.
See About this document... for information on suggesting changes. | <urn:uuid:8ad1bc23-0b1d-4422-befa-cbc25a4002c9> | 3.40625 | 363 | Documentation | Software Dev. | 55.147972 |
Problem: Derive the double angle identities
Solution: Recall from linear algebra how one rotates a point in the plane. The matrix of rotation (derived by seeing where and go under a rotation by , and writing those coordinates in the columns) is
Next, note that to rotate a point twice by , we simply multiply the point (as a vector) by twice. That is, multiply by :
Computing gives the following matrix:
But rotating twice by is the same as rotating once by , so we have the equality:
The matrices are equal, so they must be equal entrywise, giving the identities we desire.
Discussion: There are (painful, messy) ways to derive these identities by drawing triangles on the unit circle and cultishly chanting “soh-cah-toa.” The key idea in this proof that one might study geometric transformations, and it is a truly mature viewpoint of mathematics. Specifically, over the last two hundred years the field of mathematics has changed focus from the study of mathematical “things” to the study of transformations of mathematical things. This proof is an elementary example of the power such perspective can provide. If you want to be really high-brow, start asking about transformations of transformations of things, and transformations of those transformations, and recurse until you’re doing something original. | <urn:uuid:ffbf7406-0f0c-41ef-8377-fa34f7e72f54> | 3.75 | 277 | Personal Blog | Science & Tech. | 28.27347 |
The question asks me to solve
So I put it into the form :
Then I equate the coefficients:
of cos x:
of sinx:
Divide by to get:
Square and add and to get:
Except that last statement doesn't seem to be true, according to
the answers in my book and when I have a look at the two curves in a
graphing application. I tried in the graphing app and
that seems to be correct...
What have I done wrong? Why am I getting a positive value for
alpha when I should be getting the same number but negative?
The only way I can see to get -49.4 would be by introducing a minus
sign when dividing by . But I don't see how to justify that.
Have I made a simple error? I can't spot it ...
Any help would be much appreciated, thanks in advance. | <urn:uuid:d3dc873b-6497-48d8-ba96-15b52e9062ef> | 2.703125 | 196 | Q&A Forum | Science & Tech. | 82.475453 |
11.4.5. Model Fitting
a) HI Distribution and Rotation Curve
The technique of taking a model distribution for a source and smoothing it by the observing beam is well known. We can do rather better with line observations, as the distribution of HI in a particular velocity range is a function of both the density and velocity distribution of the gas. For a rotating galaxy with isovelocity contours, as in Figure 11.2, observations in the different velocity channels are essentially of the regions delimited by the isovelocity contours. The shape of these is determined by the rotation curve and other motions in the galaxy. Profiles of brightness temperature versus velocity may be generated from a model for the rotation curve and the neutral hydrogen distribution. The generation of model profiles is usually performed with a digital computer and many input models can be tried. The HI distribution and rotation curve, which give profiles that most resemble the observed profiles, are to be preferred. The chief drawback to this procedure is that there must always be two multi-parameter inputs: the rotation curve and the hydrogen distribution. These interact in the generation of the model profiles and it is usually possible to get a good fit to the observed profiles with more than one input model.
b) Minor Axis Profiles
The region radiating in a small velocity range about the systemic velocity of a rotating galaxy lies close to the minor axis (see Figure 11.2). In a direction orthogonal to the minor axis the region observed may be much narrower than the beamwidth. With limited resolution the shape of the hydrogen distribution in a small velocity range about the systemic velocity (viz., the minor axis profile) is often observed to be double-peaked or flat-topped. This observation has led to the suggestion (Roberts, 1967) that the distribution of hydrogen along the minor axis is also double-peaked and that a ring-shaped distribution of hydrogen, as in M31, is a common feature of the HI distribution in external galaxies. Consideration of Figure 11.2 shows that the shape of the minor axis profile is a function of both the distribution of HI along the minor axis and the shape of the isovelocity contours defining the minor axis region observed.
In M31 the neutral hydrogen distribution along the minor axis is double-peaked in the integrated neutral hydrogen distribution as well as in a small velocity range centered on the systemic velocity, and the description of the overall distribution of HI as a ring is a good one. M33 has a similar double-peaked minor axis profile in a small velocity range, but this is due to the shape of the isovelocity contours, and the HI distribution is really rather flat-topped. It remains to be seen from higher-resolution observations whether a ring is a good general description of the neutral hydrogen distribution in external galaxies (see Section 7.3).
c) Mass Derivations
In many cases the internal motion of an external galaxy is well approximated by a rotation law, v(r), and if we assume that the rotating galaxy is in dynamic equilibrium under self-gravitation, it is possible to derive a mass distribution from the rotation law. Several schemes have been used for calculating a mass distribution from the rotation curve. Most mass derivations based on optically measured rotation curves have used a mass model of the form of concentric spheroids developed by Burbidge, Burbidge, and Prendergast (1963). The mass is calculated by fitting a polynomial to the rotation curve, and substituting this into the equation for the equilibrium of the concentric spheroids to derive the density as a function of radius. Use of a polynomial with more than five or six terms produces unrealistic oscillations in the rotation curve, and the calculated mass distribution is not particularly sensitive to the number of terms in the polynomial used.
Many spiral galaxies are highly flattened and a variable density disk is a good model. Model rotation curves developed by Brandt and Belton (1962) have been much used in neutral hydrogen work, as they may be inverted to give a mass distribution directly. The necessary functions are well tabulated (Brandt and Scheer, 1965). The Brandt curves are characterized by a maximum rotation velocity Vmax at a radius Rmax, also called the turn-over radius. There is also a shape parameter n, which gives more sharply peaked rotation curves for larger values of n. The general equation is
The only physical feature of the Brandt curve is that, at large radii; the galaxy must appear as a point mass and the rotation velocity is then Keplerian. There is very little evidence from observations as to the nature of actual rotation curves beyond the turnover radius, but the Brandt curve is often a good fit up to this point, and the derived mass within this radius compares well with masses derived by fitting concentric spheroids. The total mass derived by extrapolating the observed rotation curve along the best-fitting Brandt curve is, however, much larger, and we have the rather unsatisfactory result that much of the mass of the galaxy lies beyond the observed region. Fitting a rotation curve model to a number of galaxies does offer a convenient and standard way of comparing the mass and derived quantities of these galaxies, but some care must be exercised in interpreting the results. The best procedure seems to be to quote a mass out to some standard radius such as the Holmberg (1958) radius. The angular momentum distribution may also be derived from the fitted density distribution, and this is of interest with respect to theories of galaxy formation from a condensing cloud of gas. The Brandt curve is characterized by only three parameters: Rmax, Vmax, and the shape parameter n. Since the angular momentum scales as Rmax2 Vmax3 and the mass as Rmax Vmax2, we must avoid comparing any two parameters such as mass and angular momentum derived by fitting the Brandt curve, as they will then be mathematically correlated, independent of any real physical correlation between mass and angular momentum. Indeed, in the absence of real correlation between mass and angular momentum a graph of Rmax2 Vmax3 versus Rmax Vmax2 has a slope determined by the relative dispersion in the distributions of Rmax and Vmax. Measurements of angular momentum are also rather unsatisfactory, as most of the angular momentum lies beyond the observed rotation curve.
For those 21-cm observations where there is insufficient angular resolution to measure the radius of maximum rotation velocity directly, a mass may still be obtained by estimating Vmax from the width of the profile and Rmax from the optical size of the galaxy. Figure 11.3(b) is a plot of Rmax / a [where a is the Holmberg (1958) diameter] for 21 galaxies for which the rotation curves have been determined optically from long-slit spectroscopy of HII regions. The ratio is not a function of the morphological type, and the histogram is quite sharply peaked with Rmax 0.1a. If Rmax cannot be measured, then we can estimate it as one-tenth a in order to obtain a mass estimate. For irregular galaxies a mass may be estimated from the virial theorem (e.g., Volders and Högbom, 1961); the mass will be
where a is the diameter of the galaxy, G is the gravitational constant, Vr.m.s. is estimated from the width of the velocity profile, and k is a constant of order unity which depends upon an assumed model for the density and velocity distribution.
Figure 11.3. Plot against morphological type of galaxy and a histogram for (a) turnover radius, /a, for galaxies observed by Rogstad, Rougoor, and Whiteoak (1967) (b) radius of maximum rotation velocity for optically derived rotation curves (c) radius of maximum HII region count, R(HII) / a, for galaxies observed by Paul Hodge. [M. C. H. Wright, Astrophys. J. (1971) 166:455.1
d) Noncircular Velocities
Noncircular velocities are apparent as departures of the isovelocity contours from symmetry about the major and minor axes. In particular we are interested in analyzing the isovelocity contours for expanding hydrogen and for streaming motions in the vicinity of spiral arms as predicted by the density wave theory (see Chapter 4 and also Lin, Yuan, and Shu, 1969). Analysis of these effects may be made by fitting the isovelocity contours with a model rotation curve, V = V(r), and a set of parameters such as the systemic velocity, inclination, position angle, and rotation center.
The fitting for V(r) can take place over the whole plane of the galaxy, with a higher weight given to points near the major axis. Having obtained the best-fit rotation curve, model isovelocity contours can then be subtracted from the observed isovelocity contours to give the residual velocity field. Examination of the residuals then shows, more clearly the systematic noncircular or "peculiar" velocities. It should be noted that the isovelocity contours and the residual velocity field are velocities weighted by the hydrogen distribution within the beam area, and particular care must be taken in interpreting the results. The effect of beam smoothing is to bias the measured velocity toward that of hydrogen concentrations within the beam. Two examples may be given
A galaxy which is a few beamwidths in diameter and which has a steep rotation curve toward the center has isovelocity contours drawn at intervals of the velocity resolution with a separation less than the observing beamwidth. Broad-frequency profiles will be observed, and the estimated rotation curve will have a smaller slope than the true curve.
Suppose that the hydrogen distribution has the form of spiral arms with separation rather less than the observing beamwidth. Observations between the spiral arms where there is not much HI will give a beam-smoothed profile with a velocity biased toward that of the nearest spiral arm. There is usually a gradient in the rotation velocity, and observations on the inner and outer edges of the spiral hydrogen concentration will yield velocities biased in opposite directions. We may be looking for just this sort of velocity, perturbation resulting from streaming motions near spiral arms! Clearly, caution must be exercised in drawing conclusions from observed peculiar velocities. | <urn:uuid:f37e6515-2cbe-47b6-8ca2-6e624404fdc6> | 2.765625 | 2,146 | Academic Writing | Science & Tech. | 34.120128 |
Since July 2011, heavy monsoon rains in southeast Asia have resulted in catastrophic flooding. In Thailand, about one third of all provinces are affected. On Oct. 23, 2011, when this image from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft was acquired, flood waters were approaching the capital city of Bangkok as the Ayutthaya River overflowed its banks. In this image, vegetation is displayed in red, and flooded areas are black and dark blue. Brighter blue shows sediment-laden water, and gray areas are houses, buildings and roads. The image covers an area of 35.2 by 66.3 miles (56.7 by 106.9 kilometers) and is located at 14.5 degrees north latitude, 100.5 degrees east longitude.
With its 14 spectral bands from the visible to the thermal infrared wavelength region and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet. ASTER is one of five Earth-observing instruments launched Dec. 18, 1999, on Terra. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and data products.
The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance.
The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate, Washington, D.C.
More information about ASTER is available at http://asterweb.jpl.nasa.gov/. | <urn:uuid:f78293af-4e17-4341-adfe-3599dbd5c36f> | 3.75 | 422 | Knowledge Article | Science & Tech. | 44.607755 |
Archives of Ask A Scientist!
About "Ask A Scientist!"
On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.
Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.
A few animals have infrared "vision", which works by detecting heat. Heat produces infrared radiation, which is invisible to the human eye. In some snakes (for example, rattle snakes, that hunt mainly at night), this infrared vision is well developed. This vision only works when there is a temperature difference between objects, say between a warm blooded rodent and the background.
Night vision goggles allow to us see the infrared radiation with reasonable clarity, if there is a temperature difference between objects, but the sharpness of the view is not as high as with our usual daylight vision.
Infrared radiation and visible light are all part of the electromagnetic spectrum. They are waves of different frequency. Radio waves, microwaves, infrared and visible radiation, ultraviolet rays (which give sun burns) and X-rays are all part of that spectrum - each at different frequencies. These waves interact with matter (including us) in different ways depending on their frequencies.
- Is a horse's leg bone bigger than a human leg bone? If so, when a horse's bone breaks why is it so much harder to heal?
- What is it about the human eye that limits the types of wavelengths in the electromagnetic spectrum that can be seen as visible light? Why are other animals capable of interpreting infrared waves as well?
- Does every one in the world have cancer cells in their body?
- Why are eyeballs wet?
- How do eye glasses improve a persons sight?
- Why don't you see two things if you have two eyes?
- Why do men grow hair on their face, while most women don't?
- Why do people get seasick or carsick?
- Why can't we hold our breath like the whales?
- Why are cats so flexible? | <urn:uuid:c73736ba-2290-4ef4-8129-d023c5c754d7> | 3.1875 | 568 | Q&A Forum | Science & Tech. | 57.442565 |
A thick spherical shell has an inner radius a and an
outerradius b. It is made of dielectric material with a
in which A is a constant and r is the distance from thecenter.
No free charge is present. Find D and E in thedielectric. | <urn:uuid:8742f993-1b64-4f29-b5b0-d743bc3a7bb0> | 3.0625 | 59 | Q&A Forum | Science & Tech. | 75.09625 |
Interviewee: Eric Lander.
Eric Lander talks about building on scientific discovery.
Each new fundamental discovery about life gives rise to a set of tools to use in the lab to make more discoveries. So understanding the structure of DNA suggests how it replicates, and then isolating the polymerases that copy DNA, well once you've got those polymerases in hand they're not just the fundamental understanding about how life copies DNA, they give you the ability to copy DNA. So you can do things for example like DNA sequencing. Once you understand how DNA is propagated in a bacterial cell with little vectors, you can use those vectors to do cloning. Once you understand how bacteria defend themselves against viruses by chopping things up with restriction enzymes, you can use those restriction enzymes. Once you understand how the body uses its immune system to make antibodies, you can make antibodies, monoclonal antibodies, to recognize proteins, etc., etc., etc.
David Baltimore, Howard Temin and Renato Dulbecco shared the 1975 Nobel Prize in Physiology or Medicine for the discoveries concerning the interaction between tumor viruses and the genetic material of the cell. | <urn:uuid:6db3d219-caa7-4490-bca3-bb33941a4f0b> | 3.09375 | 233 | Audio Transcript | Science & Tech. | 30.198344 |
When we enter the decline phase of conventional oil—likely before 2020—we will scramble to fill the gap with alternative liquid fuels. The Hirsch Report of 2005, commissioned by the U.S. Department of Energy, took a hard look at alternatives that could respond to the scale of the problem in time to have an impact. Not one of the approaches deemed to be currently viable in the report departs from fossil fuels. But what about biofuels? To what extent can they solve our problem? We’ll dip our toes into the math and see where a first-cut analysis leaves us.
If you add up all the photosynthetic activity on the planet—accounting for virtually all life except for oddball extremophiles—you get a number like 80 TW (80 trillion watts; I see credible estimates ranging from 40–140 TW). About half is from all the plankton in the ocean (and its derivative food chain), and the other half happens on land, capturing every microbe, plant, and dependents. Compare this to human power consumption around 13 TW, and to human metabolic activity of about 500 GW (7 billion people operating on a little less than 100 W, or 2000 kcal/day).
First, note that the human industrial power scale is comparable to the photosynthetic scale. If you react by saying that 13 does not look much like 80, fair enough. But I’m impressed by the similarity in the exponent: both are within a factor of three of 3×1013 W! Of all the places the comparison could have ended up, it’s about the same order-of-magnitude.
Next, observe that humans comprise about 0.6% of the total biological activity on the planet. I oscillate between thinking that this makes us a massively dominant species (of the millions of species, for any one to account for nearly 1% is impressive) to thinking that this is a small number compared to what I sense in my human-dominated daily life. But I don’t see the vast oceans or rain forests every day.
Finally, reflect on the fact that our industrial enterprise has amplified human power by a factor of 25 or more (13 TW compared to 0.5 TW). We carry a lot of muscle, thanks to fossil fuels. Let me see those biceps!
So our first stop along the way is to notice that converting our fossil fuel enterprises to biofuels would mean commandeering (enslaving?) a substantial fraction of the Earth’s bio-activity for our purposes. Factoring in the massive energy it would take to harvest the Earth’s bounty year after year, we would have to—for all intents and purposes—take over the Earth’s ecosphere to serve our ends.
Note that the dream of continuing growth to five times the current scale, as discussed in the post on what “sustainable” means is not possible via the bio-route alone.
On the global scale, we can say that 70% of the sunlight incident on the πR² projected face of the Earth is collected by the Earth (the rest is reflected by clouds, atmosphere and land), and 50% of the total is absorbed at ground level. At 1370 W/m² of incident power flux, this means that the Earth’s surface is absorbing about 100,000 TW of solar energy. Thus global photosynthetic efficiency is about 0.1%. Pretty weak.
Okay, in fairness to photosynthesis, the limitation on the scale of bio-activity tends to be availability of water and mineral nutrients—not incident sunlight. Plankton blooms are associated with discharges or upwellings of (often nitrogen-rich) nutrients. Our agricultural fields achieve “corn blooms” year after year thanks to the use of fossil-fuel-derived fertilizers to provide such nutrient services.
How does an individual plant fare, given adequate care and feeding? One way to estimate our way into an answer is to guess at the mass put on by a plant in its growing season or lifetime, assign a caloric value of 4 kcal/g for the carbohydrates (and cellulosic) material, and compare this to the solar flux presented to its leafy area in the same time period.
Let’s pick the carb-o-licious potato plant for an example of an energy storage machine. Let’s say that our plant produces a half-dozen half-pound potatoes (about 1.5 kg) in a growing season—plus an equivalent mass in leaves, stems, and roots for good measure. 3 kg at 4 kcal/g yields 12,000 kcal of energy storage, or about 50 MJ (see page on energy relations for conversions). Meanwhile, perhaps a 0.5 m² footprint at an average summer insolation of 350 W/m² delivers about 2 GJ of solar energy in four months (the insolation estimate factors in day, night, weather, and the fact that plants are not flat—so better at collecting light than a flat panel would be). The result is 2.5% efficiency.
This is not too far from reported photosynthetic efficiencies: many plants in the world realize 0.01–0.1% efficiency, while well-tended crop plants tend to be around 1–2% efficient, and algae can reach numbers like 4–6%. I have to say that I gain much more trust in such reported numbers when common-sense estimation puts me in the same ballpark. | <urn:uuid:577a2664-0c4a-47af-8b9a-ff566615e4e0> | 2.9375 | 1,137 | Personal Blog | Science & Tech. | 60.537143 |
This reference manual describes the Erlang programming language. The focus is on the language itself, not the implementation. The language constructs are described in text and with examples rather than formally specified, with the intention to make the manual more readable. The manual is not intended as a tutorial.
Information about this implementation of Erlang can be found, for example, in System Principles (starting and stopping, boot scripts, code loading, error logging, creating target systems), Efficiency Guide (memory consumption, system limits) and ERTS User's Guide (crash dumps, drivers).
It is assumed that the reader has done some programming and is familiar with concepts such as data types and programming language syntax.
In the document, the following terminology is used:
- A sequence is one or more items. For example, a clause body consists of a sequence of expressions. This means that there must be at least one expression.
- A list is any number of items. For example, an argument list can consist of zero, one or more arguments.
If a feature has been added recently, in Erlang 5.0/OTP R7 or later, this is mentioned in the text.
For a complete list of BIFs, their arguments and return values, refer to erlang(3).
The following are reserved words in Erlang:
after and andalso band begin bnot bor bsl bsr bxor case catch cond div end fun if let not of or orelse query receive rem try when xor
In Erlang 4.8/OTP R5A the syntax of Erlang tokens was extended to allow the use of the full ISO-8859-1 (Latin-1) character set. This is noticeable in the following ways:
All the Latin-1 printable characters can be used and are shown without the escape backslash convention.
Atoms and variables can use all Latin-1 letters.
|200 - 237||128 - 159||Control characters|
|240 - 277||160 - 191||- ¿||Punctuation characters|
|300 - 326||192 - 214||À - Ö||Uppercase letters|
|330 - 336||216 - 222||Ø - Þ||Uppercase letters|
|337 - 366||223 - 246||ß - ö||Lowercase letters|
|370 - 377||248 - 255||ø - ÿ||Lowercase letters| | <urn:uuid:4b264c26-acae-4bfc-b6a2-e11da6ad7f92> | 2.84375 | 509 | Documentation | Software Dev. | 57.757168 |
Physical Science: Session 1
A Closer Look: Is the Moon Matter?
How Do We Know the Moon is Made of Matter?
In the video we define matter as "having weight and taking up space." Certainly the Moon seems to take up space — it appears in the sky every night, sometimes blocking our view of the stars, other planets, and even the sun during an eclipse. But how do we know that it has weight?
In the video, we define weight as the measurement of the Earth’s pull on a particular piece of matter. To be more precise, in physics the measure of the amount of stuff in matter is called its mass, which is a quantity independent of whether the matter is on Earth or not. Anything that has mass exerts a pull, or the force we call “gravity,” on other things that have mass. On Earth, we call the measurement of this pull on a particular piece of matter weight.
Since the Moon clearly isn’t on Earth, the question becomes, How do we know if the Moon has mass?
Since antiquity people have observed the moon reliably in the sky, never seeming to fly out of its orbit. This fact provides a clue that there might be some pulling going on. Newton’s third law — for every action, there is an equal and opposite reaction — describes the relationship. If the Earth is pulling the Moon, the Moon is also pulling on the Earth with an equal force and in the opposite direction. So, if the Earth is pulling on the Moon, and the Moon is also pulling back on the Earth, then they both have mass and both take up space, and so by definition are made of matter.
Now that we know that the moon is made of matter and has mass, how could we actually determine how much mass?
You may remember that during the Apollo missions in the 1970s, the Command and Service Module, with one astronaut remaining on board, was in orbit around the Moon for a couple of Earth days. By carefully recording the motion of the CSM as it passed close to the Moon, it was possible to determine the strength of the Moon's pull on the CSM, which results from its mass. This is the closest we can come to actually weighing the Moon!
It turns out that the Moon contains about 1/80 of the mass of the Earth. If we scale the weight of the Earth to that of an elephant (11,000 pounds), the Moon would weigh as much as the average person (about 140 pounds). Interestingly, the Moon’s matter is almost all solid, with just a small amount of carbon and hydrogen gases, and no liquid.
|prev: session 1 intro| | <urn:uuid:42439eab-961c-4ec4-9a01-ec6488c8948b> | 3.9375 | 556 | Truncated | Science & Tech. | 66.241892 |
James Urquhart, contributor
What would it look like to follow a monster hurricane as it develops? A new visualisation created by Advanced Visualization Laboratory at the National Center for Supercomputing Applications at the University of Illinois shows the dramatic evolution of hurricane Katrina, the storm that wreaked havoc along the east coast of the US in August 2005. It's based on a complex numerical model developed by the National Center for Atmospheric Research in Boulder, Colorado.
The video is a 36-hour time-lapse that shows the hurricane unfold in unprecedented detail, as it gathers momentum over the Bahamas. In the beginning, warm water evaporates from the ocean and condenses in the atmosphere to form storm clouds and rain. This process releases latent heat from the water vapour and warms the surrounding air, effectively feeding energy to the system. This sustains an area of extremely low pressure accompanied by warm air in the central eye, which causes powerful winds to spiral inwards. In this video, warm rising air is represented in yellow while colder sinking air is shown in blue.
The animation is part of a full-length planetarium film called Dynamic Earth which explores the inner workings of the Earth's climate engine. It was screened at the Fulldome UK festival on 12-13 March.
If you enjoyed this video, you might also like to see a clip from Fractals! another film that was shown at the Fulldome UK event. | <urn:uuid:83c17eb9-59ac-4bd6-ae17-83ba1b3065e4> | 3.796875 | 291 | Personal Blog | Science & Tech. | 39.888974 |
Data reported by the weather station: 76530
Latitude: 43.33 | Longitude: 5.05 | Altitude: 27
|Main||Year 1988 climate||Select a month|
To calculate annual averages, we analyzed data of 363 days (99.18% of year).
If in the average or annual total of some data is missing information of 10 or more days, this is not displayed.
The total rainfall value 0 (zero) may indicate that there has been no such measurement and / or the weather station does not broadcast.
|Annual average temperature:||15.5°C||363|
|Annual average maximum temperature:||19.5°C||363|
|Annual average minimum temperature:||11.8°C||363|
|Annual average humidity:||76.8%||362|
|Annual total precipitation:||692.92 mm||363|
|Annual average visibility:||17.5 Km||363|
|Annual average wind speed:||22.6 km/h||363|
Number of days with extraordinary phenomena.
|Total days with rain:||77|
|Total days with snow:||0|
|Total days with thunderstorm:||5|
|Total days with fog:||9|
|Total days with tornado or funnel cloud:||0|
|Total days with hail:||0|
Days of extreme historical values in 1988
The highest temperature recorded was 36°C on August 9.
The lowest temperature recorded was -8.5°C on February 28.
The maximum wind speed recorded was 96.5 km/h on August 22. | <urn:uuid:8e19af43-7c8a-4ee0-adb4-37e12a7d64cd> | 2.6875 | 354 | Structured Data | Science & Tech. | 72.726738 |
Should we go to the Moon first?
The return to the Moon could be a useful steppingstone to Mars - or a costly and unnecessary delay.
June 22, 2009
|In January 2004, President George W. Bush announced the Vision for Space Exploration (VSE). It called for completing the International Space Station, building a new human launch system to replace the shuttle, returning to the Moon, and — eventually — sending astronauts to Mars.|
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You've probably heard of the "Pacific garbage patch," also called the "trash vortex." It's a region of the North Pacific ocean where the northern jet stream and the southern trade winds, moving opposite directions, create a vast, gently circling region of water called the North Pacific Gyre — and at its center, there are tons of plastic garbage. You may even have seen this picture of the garbage patch, above — right? Wrong.
That image, widely mislabeled as a shot of the Pacific garbage patch, is actually from Manila harbor. And it's just one of many misconceptions the public has about what's really happening to plastics in the ocean. We talked with Scripps Institution marine biologist Miriam Goldstein, who has just completed a study of how plastic is changing the ecosystem in the North Pacific Gyre, about myths and realities of the Pacific garbage patch.
"That picture of the guy in the canoe has been following me around my whole career!" Goldstein laughed when I brought it up. "I think it's an example of media telephone, where somebody wanted something dramatic to illustrate their story — and then through the magic of the internet, the picture got mislabeled." Goldstein has gone on several research trips to the garbage patch, 1,000 miles off the coast of California, and has even swum in it. "We have never seen anything like that picture," she asserted. "I've never seen it personally, and we've never seen it on satellite."
MYTH: There is a giant island of solid garbage floating in the Pacific.
FACT: There are millions of small and microscopic pieces of plastic, about .4 pieces per cubic meter, floating over a roughly 5000 square km area of the Pacific. This amount has increased significantly over the past 40 years.
In reality, Goldstein said, most pieces of garbage in the Pacific are "about the size of your pinkie fingernail." Though she and her team have found some larger pieces of plastic, like buoys and tires, most are microscopic. What's alarming about them isn't their size, but the sheer amount of plastic. To figure out how much there really is, she and her team have trawled the surface of the ocean in random locations over a 1700 square mile region in the gyre. Once a day, they drag a very fine, specialized net behind the boat. On one such sampling trip, she and her team found plastic pieces in 117 out of 119 random samples. On another, they found plastic in all 28 samples they took.
This is a video of Goldstein in 2010, talking about some of the group's earlier research trips to collect samples from the surface of the ocean in the North Pacific Gyre.
Since the 1970s, scientists have been using the same sampling methods — and the same kinds of trawling nets, invented by oceanographer Lanna Cheng — to measure the amount of plastic in the ocean. So Goldstein and her colleagues are able to make historical comparisons, and measure increases in plastic density. In a recent paper, they write, "Microplastic debris in the North Pacific increased by two orders of magnitude between 1972–1987 and 1999–2010 in both numerical and mass concentrations."
MYTH: All this plastic is killing animals.
FACT: Some animals are being harmed, but others are thriving. Here's why that could be a problem.
Nobody who studies ocean ecosystems would ever argue that this plastic isn't harmful. But many documentaries and articles about the garbage patch make it seem as if the main problem is that the garbage is killing animals. Birds and fish mistake the plastic for food, eat it, and then slowly starve to death. Goldstein points out that there is clear evidence that both birds and fish are eating the plastic, but it's very hard to draw conclusions about whether eating it is killing them. Generally, scientists are only able to examine the stomachs of animals who are already dead. "Some studies of albatrosses show plastic correlating with poor nutrition — and you do see a lot of dead chicks with their stomachs absolutely stuffed with plastic," Goldstein explained. The problem is that we don't know whether there are also birds who eat the plastic and survive. "We're not going to go around killing baby albatrosses to examine their stomach contents," she added.
This is an even more difficult issue when it comes to fish, since she and many other researchers have found living fish with plastic in their stomachs. It's not clear whether these fish are suffering malnutrition, or are unharmed by eating plastic because they can just pass it out in their excrement. Fish digestive systems are a lot different from those of birds, so it's possible that what's harmful to the albatrosses isn't affecting the fish as much.
And finally, there is a class of creatures who are actually thriving as a result of the plastic influx. These are water skater insects, small crabs, barnacles, and invertebrates called bryozoans, who live on hard surfaces in the water. Some of them, like the barnacles and bryozoans, can do a lot of damage to ship hulls and have caused harm in other ecosystems they've invaded. Usually, these creatures lead a hardscrabble life, barely making it in the deep ocean where hard surfaces are limited to, as Goldstein put it, "the odd floating tree trunk, rare shells, feathers, or pieces of pumice." But now, with all the plastic floating around, these once-rare creatures are enjoying a boom time.
In her recent paper, Goldstein and her colleagues offer persuasive evidence that water skaters are laying their eggs on pieces of plastic in much greater numbers than ever before. Does this mean a glut of water skaters? Not necessarily. Their eggs are large and yellow, which means they stand out in a world of clear blue water. Possibly what's happening is that all these eggs are easy prey for fish and crabs who eat them. No matter what's happening to these eggs, we're going to see an imbalance in this ecosystem, where suddenly a lot more water skaters or crabs are competing with the locals for more food.
MYTH: The plastisphere is killing the ocean.
FACT: The plastisphere is an ecosystem out of balance.
The "plastisphere" is a term coined by marine biologist Erik Zettler to describe the creatures — like water skaters — who thrive in an environment with hard surfaces in the water. They are similar to creatures who cling to piers or the hulls of ships. Before human-made hard surfaces were everywhere, they would have lived on rocks or flotsam. The problem with the plastisphere is that it's radically changing the balance of a sea ecosystem that was once mostly just open ocean creatures.
"One thing that people worry about is that hard surfaces can transport invasive species," Goldstein said. "Some animals are good at hitching a ride and they can be destructive. By adding big chunks of plastic these species can move around better, and could be introduced to places like the Northwest Pacific Islands, where there are some of the best coral reefs in the world." In other words, the plastisphere isn't destroying the ocean ecosystem — the creatures who ride on the plastic are. We're witnessing an ecosystem that is slowly falling off balance.
For now, the open ocean is still mostly inhabited by lantern fish. "There's one lantern fish for every cubic meter of ocean," Goldstein explained, noting that these fish are probably more common than the pieces of plastic her team has sampled. But if trends continue, we're going to see more plastic than fish. And with that plastic will come more invasive species, more water skaters, and more creatures to eat the water skaters' eggs. The danger is that this could alter the open ocean forever — and destroy all the native life there that has kept the oceans healthy for thousands of years.
Read Goldstein, et. al.'s paper about water skaters in Biology Letters. | <urn:uuid:c83a6104-7db0-4e89-81a3-ea4e50ea5b07> | 3.09375 | 1,645 | Truncated | Science & Tech. | 51.542236 |
In UNIX there is a specific error number which can be returned from system calls. This error, EAGAIN is used by the OS kernel whenever it has a complex state in which it is deemed too hard to resolve a proper answer to the userland application. The solution is almost a non-solution: you punt the context back to the user program and ask that it goes again and retries the operation. Then the kernel gets rid of the complex state and the next time the program enters the kernel, we can be in another state without the trouble.
Here is an interesting psychological point: we can use our code to condition another persons brain to cook up a specific program that serves our purpose. That is, we can design our protocols such that they force the user to adapt certain behaviour to his programs. One such trick is deliberate fault injection.
Say you are serving requests through a HTTP server. Usually, people would imagine that 200 OK is what should be returned always on succesful requests, but I beg to differ. Sometimes—say 1/1000 requests—we deliberately fail the request. We return a 503 Service Unavailable back to the user. This conditions the user to write error-handling code for this request early on. You can't use the service properly without handling this error, since it occurs too often. You can even add a "Retry-After" header and have him go immediately again.
This deliberate fault injection has many good uses.
- First, it enforces users of your service to adapt a more biological and fault tolerant approach to computing. Given enough of this kind of conditioning, programmers will automatically begin adding error-handling code to their requests, because otherwise it may not work.
- Second, it gives you options in case of accidents: say your system is suddenly hit by an emergency which elevates the error rate to 10%. This has no effect, since your users are already able to handle the situation.
- Third, you can break conflicts by rejecting one or both requests.
- Fourth, you can solve some distribution problems by failing the request and have the client retry.
- Fifth, simple round-robin load balancing is now useful. If you hit an overloaded server, you just return 503 and the client will retry another server.
I have a hunch that Amazons Web Services uses this trick. Against S3, I've seen an error rate suspiciously close to 1/500. It could be their own way of implementing a chaos monkey and then conditioning all their users to write code in a specific way with it.
The trick is also applicable in a lot of other contexts. Almost every protocol has some point where you can deliberately inject faults in order to make other clients behave correctly. It is very useful in testing as well. Use QuickCheck to randomly generate requests and let a certain amount be totally wrong. These wrong requests must then be rejected by the system. Otherwise something is wrong with it.
More generally, this is an example of computer programs being both formal and chaotic at the same time. One can definitely find interesting properties of biological processes to copy into computer systems. While it is nice to be able to prove that your program is correct, the real world is filled with bad code, faulty systems, breaking network switches and so on. Having a reaction to this by having your system be robust to smaller errors is definitely going to be needed. Especially in the longer run, where programs will become even more complex and communicate even more with other systems; other systems over which you have no direct control.
You can see fault-injection as a type of mutation. The programs coping with the mutation are the programs which should survive in the longer run.
Consider hacking the brain of your fellow programmers. And force them to write robust programs by conditioning their minds into doing so.
Thanks to DeadZen for proof-reading and comments. | <urn:uuid:982ccb69-2182-4d8b-a4d1-38d57e5afd15> | 2.796875 | 797 | Personal Blog | Software Dev. | 50.911695 |
for the electron in the Hydrogen atom, the orbital motion doesn't interact with the electron's spin, so "the wave function" pretty much means just a complex $\psi(x,y,z)$. You may choose the electron's spin to be up or down independently of that.
However, you must realize that a wave function of three quarks has many more components. First of all, there are three particles in relative motion rather than two. It means that even if you decouple the center-of-mass coordinates, the relative wave function is a function of six coordinates, $x_1,y_1,z_1,x_2,y_2,z_2$.
So you can't really visualize the full wave function in a simple way because it is a function of six variables rather than three and of course, it doesn't factorize into a product of functions of three variables (something that is strictly speaking true even for all atoms more complicated than the Hydrogen atom).
Moreover, you must understand that the quarks have many discrete degrees of freedom that are not decoupled from the orbital motion in this case. Each of the three quarks has 1 of 3 colors and 1 of 2 possible values of the spin. The combinations of the color really force you to consider 27 combinations of the quark colors - 27 different wave functions (only 6 of them are nonzero and equal to each other, up to a sign) - and 8 combinations of the three quarks' spin. The spins are correlated as well.
So the right wave function for 3 quarks is really a set of $27 \times 8$ complex functions of six variables. Of course, you may visualize various aspects of these functions by integrating it in space and so on.
It's important that the strong force between the non-relativistic quarks is spin-dependent. That's why the protons' spin is not arbitrary - it equals $1/2$ instead. So one of the quarks' spin differs from the remaining two.
Even if you managed to invent ways how to visualize the $27\times 8$ wave functions of 6 variables describing the relative positions of the three quarks, with the best correlations between the colors, spins, and motion, it would still be a hugely oversimplified model of the proton. In reality, it is not true that the proton only contains 3 quarks. Those 3 quarks we normally talk about are analogous to "valence electrons" in an atom but there is also a large see of equally real gluons and quark-antiquark pairs - additional partons whose total color vanishes.
To really describe the wave function of the proton, you need to talk about the right theory of the proton's structure - quantum chromodynamics (QCD) - which is an example of a quantum field theory - one discovered in the early 1970s. It has infinitely many degrees of freedom, like any field theory, so the right "wave function" is really a "wave functional" or a function of infinitely many variables.
You must realize that many approximations valid in atomic physics break down. For example, the speed of electrons in the atoms is very small - effectively controlled by the fine-structure constant $1/137$ that tells you the speed in the units of the speed of light. That allows you to use non-relativistic quantum mechanics. However, the proton's "strong" fine-structure constant relevant for the "three quarks only" is close to one, so the speed of quarks in the proton is always comparable to the speed of light. Consequently, the extra relativistic energy/mass is comparable to the rest mass as well as the interaction energy, and the proton always has enough energy to create quark-antiquark pairs and so on. It's a mess where relativity is needed much like particle creation and annihilation.
In some sense, it's true that "the 3 quarks", if you select them from the sea of the infinitely many partons, like to occupy three different regions in the ground state. But to be more accurate about what this statement actually means for the wave function(al) of the actual proton, you would have to go through a series of so many approximations and idealizations that it's not worth it. The goal of quantum field theory is not to visualize the structure of something; the goal is to calculate the results of the experiments and one can't really design good experiments that would probe the detailed shape of the wave function of the proton.
The parton distribution functions are the closest observables to this information. However, their very assumption is that the proton has infinitely many rather than 3 partons (quarks, antiquarks, or gluons). To summarize, don't expect anything that is as valid yet as useful as the pictures for the atomic physics. Proton's analogy to an atom has severe limitations. | <urn:uuid:914804b2-9b55-4451-bb36-75c4604d631d> | 3.234375 | 1,032 | Q&A Forum | Science & Tech. | 48.247094 |
The cloud-free pictures, taken with a high-resolution visible and infrared imager aboard a Nasa and National Oceanic and Atmospheric Administration satellite, capture the night lights of Earth in unprecedented detail.
The sensor can capture the equivalent of three lowlight images simultaneously, giving researchers the opportunity to study Earth's atmosphere, land and oceans at night.
Source: The Telegraph. Read full article. (link) | <urn:uuid:98d9965b-890a-4bea-91d2-1c422081fe8e> | 2.78125 | 82 | Truncated | Science & Tech. | 21.395 |
Humans have walked the Earth for 190,000 years, a mere blip in Earth's 4.5-billion-year history. Learn more about the planet's tumultuous past.
More About the Prehistoric World
Follow the blog from the Spitsbergen Expedition as they unearth "sea monsters″ from the Upper Jurassic Period 150 million years ago.
National Geographic's interactive time line takes you on a 4.5-billion-year-old trip through Earth's history⎯from its Precambrian birth to the birth of Homo sapiens some 190,000 years ago.
The largest animals that ever flew, pterosaurs ruled the Mesozoic skies for 150 million years, flapping and soaring long before the first bird ruffled a single feather.
In the international fossil trade, even priceless specimens have a price tag. Ancient bones can end up in a movie star's mansion as easily as in a museum.
Phenomena: A Science Salon
National Geographic Magazine
Our genes harbor many secrets to a long and healthy life. And now scientists are beginning to uncover them
All the elements found in nature—the different kinds of atoms—were found long ago. To bag a new one these days, and push the frontiers of matter, you have to create it first.
Burn natural gas and it warms your house. But let it leak, from fracked wells or the melting Arctic, and it warms the whole planet. | <urn:uuid:58248785-5781-4f58-8c3a-4aab7be7f11f> | 3.46875 | 301 | Content Listing | Science & Tech. | 61.42087 |
by: Bruce Stutz
Summary: Veronique Carola
Today we are shifting from the ideology of mitigating carbon dioxide emissions to mostly making adaptation to climate changes a main priority for affected communities. With the rate of continuing C0² emission around the world, expectations that we could keep atmospheric C0² levels below the acceptable rate of 450 parts per million and global warming rate below 2º Celsius, has deviated some-what. In realising such, adaptation to climatic changes seems the next best option.
Adaptation measures would mean countries have to be prepared to deal with issues such as water scarcity, rising sea-level, the spread of diseases and the complication of preserving biodiversity. It is expected that wet regions will become wetter and dry regions drier which carries grave implications for agricultural productivity. ‘The key to coping would be to make farming as resilient as possible’, it is said.
Low lying countries are already suffering with sea-level rise. Coastlines that have been greatly altered over the century through development and agriculture surely have a weakened resistance to flooding and erosion, a fact that will be most prominent during storm surges. Restoration of mangrove ecosystems is one alternative to curb impacts.
Water borne diseases will be a major problem with areas likely to experience wetter seasons, and so are the regions likely to experience more flooding and contamination of water supplies. Studies at understanding the changes expected are best to be taken seriously, especially since these help us understand the options and identify the vulnerabilities. | <urn:uuid:693aaf8b-0771-4dc9-9d85-e4a4b2c8cd46> | 3.625 | 306 | Personal Blog | Science & Tech. | 21.646522 |
Climate Change Information Sheet 3
Greenhouse gases and aerosols
- Greenhouse gases (GHGs) control energy flows in the atmosphere by absorbing infrared radiation. These trace gases comprise less than 1% of the atmosphere. Their levels are determined by a balance between "sources" and "sinks". Sources are processes that generate greenhouse gases; sinks are processes that destroy or remove them. Humans affect greenhouse gas levels by introducing new sources or by interfering with natural sinks.
- The largest contributor to the natural greenhouse effect is water vapour. Its presence in the atmosphere is not directly affected by human activity. Nevertheless, water vapour matters for climate change because of an important "positive feedback". Warmer air can hold more moisture, and models predict that a small global warming would lead to a rise in global water vapour levels, further adding to the enhanced greenhouse effect. On the other hand, it is possible that some regions may become drier. Because modelling climate processes involving clouds and rainfall is particularly difficult, the exact size of this crucial feedback remains unknown.
- Carbon dioxide is currently responsible for over 60% of the "enhanced" greenhouse effect, which is responsible for climate change. This gas occurs naturally in the atmosphere, but burning coal, oil, and natural gas is releasing the carbon stored in these "fossil fuels" at an unprecedented rate. Likewise, deforestation releases carbon stored in trees. Current annual emissions amount to over 7 billion tonnes of carbon, or almost 1% of the total mass of carbon dioxide in the atmosphere.
- Carbon dioxide produced by human activity enters the natural carbon cycle. Many billions of tonnes of carbon are exchanged naturally each year between the atmosphere, the oceans, and land vegetation. The exchanges in this massive and complex natural system are precisely balanced; carbon dioxide levels appear to have varied by less than 10% during the 10,000 years before industrialization. In the 200 years since 1800, however, levels have risen by almost 30%. Even with half of humanity's carbon dioxide emissions being absorbed by the oceans and land vegetation, atmospheric levels continue to rise by over 10% every 20 years.
- A second important human influence on climate is aerosols. These clouds of microscopic particles are not a greenhouse gas. In addition to various natural sources, they are produced from sulphur dioxide emitted mainly by power stations, and by the smoke from deforestation and the burning of crop wastes. Aerosols settle out of the air after only a few days, but they are emitted in such massive quantities that they have a substantial impact on climate.
- Aerosols cool the climate locally by scattering sunlight back into space. Aerosol particles block sunlight directly and also provide "seeds" for clouds to form, and often these clouds also have a cooling effect. Over heavily industrialized regions, aerosol cooling may counteract nearly all of the warming effect of greenhouse gas increases to date.
- Methane is a powerful greenhouse gas whose levels have already doubled. The main "new" sources of methane are agricultural, notably flooded rice paddies and expanding herds of cattle. Emissions from waste dumps and leaks from coal mining and natural gas production also contribute. The main sink for methane is chemical reactions in the atmosphere, which are very difficult to model and predict.
- Methane from past emissions currently contributes 1520% of the enhanced greenhouse effect. The rapid rise in methane started more recently than the rise in carbon dioxide, but methane's contribution has been catching up fast. However, methane has an effective atmospheric lifetime of only 12 years, whereas carbon dioxide survives much longer. This means that the relative importance of methane versus carbon dioxide emissions depends on the "time horizon". For example, methane emitted during the 1980s is expected to have about 80% of the impact of that decade's carbon dioxide emissions over the 20year period 19902010, but only 30% over the 100year period 19902090 (see figure).
- Nitrous oxide, chlorofluorocarbons (CFCs), and ozone contribute the remaining 20% of the enhanced greenhouse effect. Nitrous oxide levels have risen by 15%, mainly due to more intensive agriculture. CFCs increased rapidly until the early 1990s, but levels of key CFCs have since stabilised due to tough emission controls introduced under the Montreal Protocol to protect the stratospheric ozone layer. Ozone is another naturally-occurring greenhouse gas whose levels are rising in some regions in the lower atmosphere due to air pollution, even as they decline in the stratosphere.
- Humanity's greenhouse gas emissions have already disturbed the global energy budget by about 2.5 Watts per square metre. This equals about one percent of the net incoming solar energy that drives the climate system. One percent may not sound like much, but added up over the earth's entire surface, it amounts to the energy content of 1.8 million tonnes of oil every minute, or over 100 times the world's current rate of commercial energy consumption. Since greenhouse gases are only a by-product of energy consumption, it is ironic that the amount of energy humanity actually uses is tiny compared to the impact of greenhouse gases on natural energy flows in the climate system.
The Convention - Info for Participants - Info for Media - Official Documents
Daily Programme - Special Events - Exhibits - List of Participants - Special Features
Kyoto Information - COP3 Links - COP3 Home Page - UNFCCC Home Page - Feedback - Sitemap | <urn:uuid:f73a9af5-9bf7-4bec-8565-1c4e13e8c02b> | 4.125 | 1,103 | Knowledge Article | Science & Tech. | 28.936207 |
Further Quick Divisibility Tests
Test for multiples of 5
- If the last digit is either 5 or 0, then the whole number is a multiple of 5.
Here is an interactive panel for you to practice on:
Test for multiples of 10
- This is easy - if the last digit is 0, the whole number is a multiple of 10, otherwise it is not!
For example, 3295 ends in 5 so is not divisible by 10. But 3290 ends with 0 and so is a multiple of 10.
Combining Divisibility Tests
Now we know quick methods for divisibility by 2, 3, 4, 5, 8, 9, and 10. With these we can easily test for divisibility by any number that is a product of 2, 3, 4, 5, 8, 9 and 10!
So, for example, let's take 6, the smallest number missing from the list above.
Quick tests for Divisibility by 6
Since 6 = 2 times 3, numbers divisible by 6 must be divisible by both 2 AND by 3.
- This is a multiple of 2 because it ends in 2 which is even;
It is also a multiple of 3 since its digits sum to 4+3+2=9 which is a multiple of 3.
So 432 is a multiple of 6.
- This is a multiple of 2 because it ends with 4 which is even;
Its digit sum is 5+1+4=10 which is not a multiple of 3, so 514 is not a multiple of 3.
Since 514 has failed one of the tests for divisibility by 2 AND by 3, it is NOT a multiple of 6.
- This time, 513 has a digit sum of 5+1+3=9, and so 513 is exactly divisible by 3;
However, it ends with 3 which is not even, so 513 is not a multiple of 2.
Again, one of the two tests has been failed, so 513 is NOT a multiple of 6.
Quick test for Divisibility by 12
To be divisible by 12, a number must also be divisible by 2 and 3 and 4 and 6, that is, by all the factors of 12. So a multiple of 12 must pass all the divisibility test for 2, 3, 4 and 6. But we have just seen that, if it is divisible by both 2 and 3, it is automatically divisible by 6, so we do not need to test for 6 explicitly.
Similarly, if a number is divisible by 4 it must automatically be a multiple of 2 also. So testing for divisibility by 4 is enough and we can forget about testing for 2 as well.
So we need to test just for divisibility by 3 and by 4 only - that's sufficient!
- Divisible by 4? The last 2 digits are 32 and 32 is a multiple of 4, so, yes, 432 is divisible by 4.
Divisible by 3? The digit sum is 4+3+2=9 which is a multiple of 3, so, yes, 432 is divisible by 3.
Therefore 432 is also divisible by 12.
- Divisible by 4? Yes.
Divisible by 3? 4+2+8=14, not a multiple of 3, so No!
So 428 is not a multiple of 12.
- Divisible by 4? No because 35 is not a multiple of 4.
So even if it was divisible by 3 (which it is) it won't be a multiple of 12.
You can make up more divisibility tests of your own for 15, 18, 20, 24 and so on.Here is an interactive panel for you to practice on:
Primes, Factors and Divisibility | <urn:uuid:922b8480-66b0-4e08-827e-ba099cae42ec> | 3.546875 | 804 | Tutorial | Science & Tech. | 83.60087 |
In 1875, Tesla began studying electrical engineering at the Polytechnic Institute in Graz, Austria. Again, with obsessive effort that permitted only study, he excelled. In Graz, Tesla was able to observe the new Gramme machine which generated direct current electricity using electromagnets and could also be reversed to operate as an electricity-driven motor. The demonstration planted an intuitive seed in Tesla's brain. Why was it necessary to go to such lengths to convert the alternating (AC) current produced by the dynamo to direct (DC) current? Why not leave the current AC and run the motor that way?
The electrical standard at that time was DC, the same mode produced by a battery the mode that everyone was used to and accepted. To even imagine usable alternating current was visionary. Tesla's strong instincts told him this was possible but at that time, in spite of his visualization efforts and the mental gymnastics of picturing many operating dynamo models, he failed to find the solution to this nagging problem. | <urn:uuid:239de55b-35f2-4564-8d11-7812d0f209c5> | 3.296875 | 207 | Knowledge Article | Science & Tech. | 33.889837 |
Volcanoes erupt because the earth's movement causes openings or vents in the crust. Volcanoes can be mountains, vents or under sea rifts. Volcanism is an eruption of molten rock at the earth's surface. Sometimes there is explosive gases and rock fragments. Magma is soft rock in the earth's mantle. It usually flows into cracks by the earth's surface. When the magma hits the earth's surface, it is called lava. Lava cools, hardens, and forms rocks. This process is part of the rock cycle .
Volcanic eruptions can be similar, but each one is unique. Before each eruption there are several small earthquakes. The magma presses against the upper mantle and breaks through to the earth's surface. The earth moves and the magma pushes to the surface and forms a volcano. The combination of magma and water causes a violent eruption. There is often a big cloud of smoke that is vaporized water, cinders and ash. Most volcanoes are located in an area called the Pacific Ring of Fire .
- Parts of a Volcano in Spanish and English
- Free Volcano Mini Book
- Volcano Diagram
- Volcano Composite
- Label the Volcano Diagram
- Volcano Diagram Printout
- Erupting Volcano Card
- Exploding Volcano Card
- Lava Flow Card
- Planet Earth Bingo Cards Vocabulary
- Picture of 6 Types of Volcanoes
- Cross Section of the Earth
- Create Your Own Volcano
- Clay Volcano
- Science Daily Volcano News
posted at 1:22 a.m. on May 3, 2012
My ideal topics.
posted at 1:30 a.m. on April 16, 2013
Cool post! How much stuff did you have to look up in order to write this one? I can tell you put some work in.
names to send out newsletters on occasion.
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With the establishment of the human genome project, biology moved into the uncharted territory of 'big science'. Not only would funding require levels previously familiar only to physical science - upwards of $3 billion - but also novel ways of doing science would at some point in the venture become necessary. Behind the recent fuss over the possible loss to the US of Britain's biggest and most important DNA sequencing project is the signal that this point has been reached (see This Week, this issue).
The project, to map and sequence the genome of the nematode, a small worm, is a joint venture, shared between the Medical Research Council's Laboratory of Molecular Biology, Cambridge, and Washington University, St Louis. The success of its first phase may now undermine the international element of the project, because its continuation demands a new kind of science: large-scale sequencing.
Reading millions of DNA bases ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:3feeeae1-4cfe-4c25-b758-fa1b2d00350a> | 3.125 | 206 | Truncated | Science & Tech. | 41.057447 |
Totally Liquid Planet
Name: Josh A.
Is it possible to have a 100% liquid planet?
Yes it is possible in principle, but the details depend on both the material and on
the mass of the planet. If the liquid was iron or nickel and if it is hot enough
then it is possible for a planet to be completely liquid from the surface to the
core. However, the planet would loose heat into space and progressively solidify.
The heat inside the Earth is maintained by the decay of radioactive elements that
are spread throughout the interior. Therefore, the heating can be maintained for a
period that depends on the amount of radioactive material present. If the planet
is too massive, then the iron/nickel will be in a solid phase in the core because
of the high pressures there.
What about a "water" planet?
When far from its star, the liquid will freeze (as with comets) and when too close
it will boil off into space. In the narrow range of temperature where the liquid
phase could exist, the liquid would immediately boil because it is surrounded by
the vacuum of space (there is no liquid phase possible in a vacuum). The
atoms/molecules would then form a gaseous atmosphere provided
there was enough mass to keep the atmosphere from drifting off into space. But if
it formed an atmosphere it would no longer be a "liquid" planet.
Grant Christie (by way of Howard Barnes)
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:ff1a214f-0e49-4622-a900-ac28c30bfacd> | 3.046875 | 321 | Q&A Forum | Science & Tech. | 49.372308 |
Name: Briony C
I have heard that the Portuguese man-of-war is actually a
colony of individual polyps which perform different tasks (e.g.
digestion, reproduction) and are dependent on each other for survival.
What is it about the polyps that means they are classified as separate
creatures within a colony rather than just different parts of the same
Each could survive on its own, if it were separated from the others. The
complete interdependence that characterizes the cells of multicellular
organisms has not quite developed in the cells of these beautiful
Ellen S. Mayo
Click here to return to the Zoology Archives
Update: June 2012 | <urn:uuid:63063d3a-6393-4529-9246-636f5a5e37c7> | 2.6875 | 146 | Nonfiction Writing | Science & Tech. | 35.680355 |
The Big Sleep
By Sue Olcott
During this time of year we become more aware of the difficulties wild animals must overcome to survive in West Virginia. Trees are dropping their leaves. Days are quiet since most song birds have migrated south to find food and escape the coming cold. Deer are increasing the thickness and length of their coats as protection from the cold. Some animals have disappeared like the songbirds — but they haven't migrated. They are involved in an equally amazing process called hibernation.
Hibernation is an extreme form of inactivity or torpor — a profound lowering of an animal's body temperature and metabolism to save energy. It is similar to lowering the thermostat in your house to save on heating costs. Instead of fossil fuels or wood, though, stored fat is the energy source the animal is using and trying to conserve during torpor.
In this part of North America, an animal usually enters torpor because its regular food source has become scarce or because it cannot survive harsh weather conditions, or both. Places where animals hibernate, called hibernacula , range from caves and old mines, to burrows dug beneath the frost line, to basements and crawlspaces in buildings. Each species has a specific range of environmental conditions that need to be met within the hibernaculum . These factors typically include temperature, humidity, safety from predators and, for some, space to store food.
Many animals enter into a short-term or daily torpor as a matter of course. During cold winter nights, a chickadee typically allows its body temperature to fall 10 to 15 degrees. This lowering of the thermostat requires less energy to maintain and literally allows a chickadee to survive, for it cannot store enough fat to maintain its normal body temperature through a cold winter night. If it tried, it would starve. Chickadees are one of the earliest risers because they need to replenish their depleted fat stores. They relish black-hulled sunflower seeds, suet and peanut butter because these high-energy foods aid their precarious winter survival.
During long summer days, bats must fast up to 15 hours - and even longer further north. A lowered body temperature means less energy is being used to maintain important body functions like breathing, digestion, blood circulation and, for females with young, milk production. Bats often seek out roosts that provide them with a range of temperatures that they can move into depending on their needs. Male bats may use roosts that are cooler early in the day so they can lower their body temperature and conserve energy, and warmer late in the day to help them raise their body temperature in preparation for flight and feeding. Females with young may use roosts that remain very warm throughout the day to keep the body temperatures of their offspring high to help them grow more quickly.
Hibernators differ from animals that enter daily torpor because the decrease in body temperature and other functions is much greater. For example, a hibernating little brown bat's body temperature drops to near freezing, breathing decreases to less than one breath per minute, and the heart rate slows from 400 to 25 beats per minute. True hibernators also stay in this state longer at a stretch than animals that don't hibernate — in some ground squirrels 30 days and in bats up to 83 days.
Most of the energy a hibernating animal expends during the winter is used to periodically rouse the body to allow it to perform certain tasks such as urination, which is impossible at lower temperatures. A single waking period of a few hours in a bat can use as much stored fat as 67 days of hibernation. These waking periods also take a long time to achieve — up to 30 minutes for a bat and several days for a woodchuck. Hibernators walk a thin line between how often they wake up and the amount of fat they store. If they are disturbed or wake too many times, or if the winter is especially long, they will run out of fat reserves and starve. In most species that hibernate, a significant cause of mortality is death during hibernation. Those that succumb may have stored too little fat to sustain them through the hibernation period or have chosen a hibernaculum that was too cold or too dry. A hibernaculum that is too dry may cause the animal to lose too much water vapor during respiration, resulting in death.
The length of time that an animal remains in its hibernaculum depends in large part upon its elevation above sea level and its latitude. Marmots, western relatives of woodchucks, enter hibernation earlier and emerge later at higher, and therefore colder and harsher, elevations. Franklin's ground squirrel, a species common in the high prairies of the United States and Canada, has a hibernation period that ranges from seven to eight months depending upon its latitude. Additionally, in many species, adults enter hibernation first. The young, eating and growing as fast as they can, may enter hibernation months later because they can not store enough fat to survive hibernation until they have reached their adult size.
Some of our common hibernators are chipmunks, woodchucks, little brown and pipistrelle bats, snakes, frogs and toads, and many insects. In two orders of mammals, the rodents and the bats, development of hibernation enabled these groups to become highly successful — inhabiting almost all ecosystems on earth and collectively numbering over half of all mammalian species.
A common misconception is that bears hibernate. While it is true that bears are inactive for much of the winter, they are not true hibernators. Although they sleep for weeks at a time, their body temperature only drops 10 to 15 degrees, and they can wake up very quickly, as any researcher working with bears will tell you. They also bear their young during this time, an activity that requires them to produce milk — a process impossible in true hibernation. Other of our winter residents such as raccoons, fishers and deer mice sleep for varying periods of time through the worst weather when foraging for food is all but impossible.
In all of these animals, different degrees of torpor help to conserve their energy stores so they can survive until spring returns with its abundant food supply and milder weather conditions.
Sue Olcott is a DNR wildlife biologist stationed in Fairmont. | <urn:uuid:e9932359-bde5-445f-bea5-e794c3e7887d> | 4.15625 | 1,314 | Nonfiction Writing | Science & Tech. | 39.909896 |
A googolplex is the number 10googol, i.e. 1010100. In pure mathematics, the magnitude of a googolplex could be related to other forms of large-number notation such as tetration, Knuth's up-arrow notation, Steinhaus–Moser notation, or Conway chained arrow notation. The reciprocal of the googolplex is called googolminex.
In 1938, Edward Kasner's nine year old nephew, Milton Sirotta, coined the term googol which is 10100, then proposed the further term googolplex to be "one, followed by writing zeroes until you get tired". Kasner decided to adopt a more formal definition "because different people get tired at different times and it would never do to have Carnera be a better mathematician than Dr. Einstein, simply because he had more endurance and could write for longer". It thus became standardized to 1010100.
In the PBS science program Cosmos: A Personal Voyage, Episode 9: "The Lives of the Stars", astronomer and television personality Carl Sagan estimated that writing a googolplex in standard form (i.e., "10,000,000,000...") would be physically impossible, since doing so would require more space than the known universe provides.
An average book of 60 cubic inches can be printed with 5×105 zeroes (5 characters per word, 10 words per line, 25 lines per page, 400 pages), or 8.3×103 zeros per cubic inch. The observable (i.e. past light cone) universe contains 6×1083 cubic inches (4/3 × π × (14×109 light years in inches)3). This math implies that if the universe is stuffed with paper printed with 0s, it could contain only 5.3×1087 zeros—far short of a googol of zeros. In fact there are only about 2.5×1089 elementary particles in the observable universe, so even if one were to use an elementary particle to represent each digit, one would run out of particles well before reaching a googol digits.
Consider printing the digits of a googolplex in unreadable, one-point font (0.353 mm per digit). It would take about 3.5×1096 metres to write a googolplex in one-point font. The observable universe is estimated to be 8.80×1026 metres, or 93 billion light-years, in diameter, so the distance required to write the necessary zeroes is 4.0×1069 times as long as the estimated universe.
The time it would take to write such a number also renders the task implausible: if a person can write two digits per second, it would take around about 1.51×1092 years, which is about 1.1×1082 times the age of the universe, to write a googolplex.
A Planck space has a volume of a Planck length cubed, which is the smallest measurable volume, at approximately 4.222×10−105 m3 = 4.222×10−99 cm3. Thus 2.5 cm3 contain about a googol Planck spaces. There are only about 3×1080 cubic metres in the observable universe, giving about 7.1×10184 Planck spaces in the entire observable universe, so a googolplex is far larger than even the number of the smallest measurable spaces in the observable universe.
In pure mathematics
In pure mathematics, there are several notational methods for representing large numbers by which the magnitude of a googolplex could be represented, such as tetration, Knuth's up-arrow notation, Steinhaus-Moser notation, or Conway chained arrow notation.
In the physical universe
One Googol is presumed to be greater than the number of hydrogen atoms in the observable universe, which has been variously estimated to be between 1079 and 1081. A googol is also greater than the number of Planck times elapsed since the Big Bang, which is estimated at about 8×1060. Thus in the physical world it is difficult to give examples of numbers that compare to the vastly greater googolplex. In analyzing quantum states and black holes, physicist Don Page writes that "determining experimentally whether or not information is lost down black holes of solar mass ... would require more than 1076.96 measurements to give a rough determination of the final density matrix after a black hole evaporates". The end of the Universe via Big Freeze without proton decay is suspected to be around 101075 years into the future, which is still short of a googolplex.
If the entire volume of the observable universe (taken to be 3 × 1080 m3) were packed solid with fine dust particles about 1.5 micrometres in size, then the number of different ways of ordering these particles (that is, assigning the number 1 to one particle, then the number 2 to another particle, and so on until all particles are numbered) would be approximately one googolplex.
See also
- Edward Kasner & James R. Newman (1940) Mathematics and the Imagination, page 23, NY: Simon & Schuster
- Lineweaver, Charles; Tamara M. Davis (2005). "Misconceptions about the Big Bang". Scientific American. Retrieved 2008-11-06.
- Page, Don, "How to Get a Googolplex", 3 June 2001.
- Mass, Size, and Density of the Universe Article from National Solar Observatory, 21 May 2001.
- convert age of the universe to Planck times – Wolfram|Alpha, 8 August 2011
- Page, Don N., "Information Loss in Black Holes and/or Conscious Beings?", 25 Nov. 1994, for publication in Heat Kernel Techniques and Quantum Gravity, S. A. Fulling, ed. (Discourses in Mathematics and Its Applications, No. 4, Texas A&M University, Department of Mathematics, College Station, Texas, 1995)
- Weisstein, Eric W., "Googolplex", MathWorld.
- googolplex at PlanetMath
- Padilla, Tony; Symonds, Ria. "Googol and Googolplex". Numberphile. Brady Haran.
- Googolplex written out | <urn:uuid:b4e24f15-e275-4de9-a7a5-56acb2aa8069> | 3.359375 | 1,334 | Knowledge Article | Science & Tech. | 56.428269 |
Brief SummaryRead full entry
Species AbstractThe Black dolphin (scientific name: Cephalorhynchus eutropia), is more commonly known as the Chilean dolphin, is only found in freshwater estuaries, and coastal areas surrounding Chile. It is a marine mammal, a member of the family Delphinidae, part of the order of cetaceans. The species is so named for its black coloring on its fins, tail, and back. It is also known as the Chilean dolphin, Piebald dolphin, Southern dolphin, and White-bellied dolphin.
Because of their preference for shallow coastal waters, these dolphins are often threatened by local fisherman. This dolphin is frequently used in Chile as crab bait, as well as a food source for humans. The species population is decreasing because of this practice, and is now considered Near Threatened. Hunting restrictions have been established in Chile, however, the government has had difficulty enforcing this law in remote areas.
Resembling fellow Cephalorhynchus species, Chilean dolphins are generally described as small and chunky with lengths of about 1.65 meters for both males and females. These dolphins weigh approximately 57 kilograms, females may be slightly larger than males (slight sexual dimorphism). Chilean dolphins have a stout, torpedo-like shape and can have a girth of up to two-thirds of their length. The head is conical in shape and lacks a beak and melon. However, black dolphins have a large number of teeth: 24 to 31 on each side of each jaw. | <urn:uuid:befe6244-a08e-4237-a3f6-0e336c6ac9af> | 3.84375 | 325 | Knowledge Article | Science & Tech. | 44.731768 |
Accurate tectonic reconstructions provide an essential framework for evaluating and modelling long-term palaeoenvironmental data. Reconstructions of large parts of the Pacific Ocean for mid-Cenozoic and earlier times are particularly difficult to constrain because it is almost encircled by subduction zones. However, in the southernmost Pacific the conjugate passive margins offshore from New Zealand and Marie Byrd Land provide an opportunity to produce well-constrained reconstructions from the Late Cretaceous onwards (Larter et al., 2002). In addition to providing a framework for studying palaeoenvironmental evolution of the Southern Ocean, reconstructions of this region are also the key link in the global plate circuit tying plate motions in the Pacific Ocean basin to the rest of the world (Cande et al., 1995). Until recently, however, the scarcity of marine geophysical data from the remote area off Marie Byrd Land has placed a severe limitation on the reliability of such reconstructions.We present a new animated reconstruction showing South Pacific plate kinematics since 90 Ma (Eagles et al., 2004). In this reconstruction sections of the modern marine free-air gravity field are rotated with the tectonic plates. Reconstruction of gridded data limits the problem of subjective interpretation of features used in reconstructions to identification of plate boundaries. Animation of reconstructions is a useful way of illustrating kinematic evolution, and of exposing inconsistencies in tectonic scenarios depicted by static reconstructions. The combination of these two techniques provides a powerful new tool for considering the spatial and temporal context of palaeoenvironmental data. Future work will include integration of this reconstruction with reconstructions of the Tasman and Drake Passage gateways that flank the studied region, and production of gridded palaeobathymetric reconstructions for use in palaeoclimate modelling.ReferencesCande, S.C., Raymond, C.A., Stock, J. & Haxby, W.F., 1995. Geophysics of the Pitman Fracture Zone and Pacific-Antarctic plate motions during the Cenozoic. Science, 270, 947-953.Eagles, G., Gohl, K. & Larter, R.D., 2004. High-resolution animated tectonic reconstruction of the South Pacific and West Antarctic margin. Geochemistry, Geophysics, Geosystems, 5(7), Q07002, doi:10.1029/2003GC000657.Larter R.D., Cunningham, A.P, Barker, P.F., Gohl, K. & Nitsche, F.O., 2002. Tectonic evolution of the Pacific margin of Antarctica 1. Late Cretaceous tectonic reconstructions. J. Geophys. Res. 107(B12), 2345, doi:10.1029/2000JB000052.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > MAR2-Palaeo Climate Mechanisms and Variability | <urn:uuid:75c8016d-6541-4f8a-a962-4ba7d44e13f8> | 3.03125 | 620 | Academic Writing | Science & Tech. | 39.01171 |
Debugging the compiler
When compiling GHC:
- add -DDEBUG to your GhcStage1HcOpts and/or GhcStage2HcOpts in mk/build.mk. This enables assertions and extra debug code.
When compiling the program (see also the relevant User Manual section):
- Use -v3 or -v4 to get an idea about what GHC is doing when the problem occurs.
- Add -dcore-lint the GHC command line when compiling each Haskell module. This makes GHC type-check the intermediate program after every optimisation pass, which often nails a fault.
- Add -ddump-simpl to see the optimised Core output. There are a number of other -ddump-x flags; see the user manual.
- The flag -dppr-debug makes the -ddump-x flags print much more verbose output. Use this if you are getting desperate!
Adding debugging code to the compiler
- Outputable.pprTrace is a nice way to print trace messages from the compiler
- ASSERT(p), ASSERT2(p,msg), WARN(p,msg) are assertions and warning enabled only when the compiler is compiled with -DDEBUG. There are also variants of these that work better in a monad setting; see compiler/HsVersions.h. | <urn:uuid:dd3f68f2-920c-484b-845a-a6539111238b> | 2.6875 | 285 | Documentation | Software Dev. | 61.626813 |
This investigation explores using different shapes as the hands of
the clock. What things occur as the the hands move.
How many different shaped boxes can you design for 36 sweets in one
layer? Can you arrange the sweets so that no sweets of the same
colour are next to each other in any direction?
What happens if you join every second point on this circle? How
about every third point? Try with different steps and see if you
can predict what will happen.
Well, in this country, and perhaps in yours, lots of young folk
are wearing bracelets - both girls and boys. I was looking at some
that my students wear and found that some were magnetic!
Many seem to have beads that are spherical and they go around
the wrist quite comfortably. There are lots of different sizes and
some have large beads and some quite small beads.
I suppose that most wrists are kind of oval - squashed circles -
in shape and with the string or wire through the beads they fit
It was playing with the magnetic beads off the person's wrist
that gave me some ideas. There were $18$ beads altogether and they
were all the same colour but I've chosen to show them in a variety
I found I could put them into different shapes:-
mind you, you'd have to have a triangular wrist for them to stay
Now suppose we play around with this idea and make a rule that
there has to be some shaped hole in the middle for a wrist. But
we'll allow that to be all kinds of shapes :- vaguely triangular,
rectangular, hexagonal etc.
You could try this out with marbles, circular counters,
tiddly-winks, coins or with a drawing program on your computer.
I think we'll make a rule that the circles/spheres have to be
the same size and you don't have to imagine that they're
So here are some that I found with $18$ beads:-
I liked that one as it is the longest rectangle you could make -
remembering to keep a wrist-hole. I then went on to:-
and then, almost a square :-
I like the next one - although it was a little hard to do on the
Have a go at making these with your circles!
I then moved on to $24$ circles - it seemed to be a "good"
number to choose - I wonder why?
I managed to get this regular shape:-
But then I thought that since I had $24$, perhaps I could make
two that were exactly the same. So there's a new rule: You can make
more than one bracelet as long as they're both the same.
Have a go at using $24$ circles and make a large triangle and a
Well, now it's time to explore, to see what other bracelets you
can make. Remember that there's to be a "wrist-hole". The shapes
should be kind of "regular" but not strictly so, because then we
could not use rectangles.
Other things to investigate:-
So whatever shape you make, how many will you need to make the
next size up? How does each shape grow? Look at the first shape I
made using $24$:-
What will the next size up of this look like? | <urn:uuid:308515fd-1c0f-4242-afb1-861b54e95d53> | 3.15625 | 696 | Personal Blog | Science & Tech. | 65.943071 |
It is pretty clear that the hedgehogs of the world understand what the hyenas don't, that given enough measurements the imperfections in individual weather stations average out and you are left with reliable trends, at least if you understand what area averaging is and how to correct for things like the time of day that different folks measure at. John V (in the comments, and the graphs have disappeared in the reorganization of the site, here they are, thanks to Valtteri Maja and Zeke Hausfather) at Climate Audit and later at Hyena Watt's place figured that out early when he compared the trends in the best and the worst stations and found essentially no difference..
However, there are surprises. The bunnies bring words in several threads at Rabett Run that Matthew J. Menne, Claude N. Williams, Jr., and Michael A. Palecki from the NOAA/National Climatic Data CenterNational Climate Data Center have been looking at dirty pictures of weather stations in the US Historical Climatology Network (USHCN), and those in the carefully sited, but new US Climate Reference Network (USCRN) and come to the conclusion:
Recent photographic documentation of poor siting conditions at stations in the U.S. Historical Climatology Network (USHCN) has led to questions regarding the reliability of surface temperature trends over the conterminous U.S. (CONUS). To evaluate the potential impact of poor siting/instrument exposure on CONUS temperatures, trends derived from poor and well-sited USHCN stations were compared. Results indicate that there is a mean bias associated with poor exposure sites relative to good exposure sites; however, this bias is consistent with previously documented changes associated with the widespread conversion to electronic sensors in the USHCN during the last 25 years. Moreover, the sign of the bias is counterintuitive to photographic documentation of poor exposure because associated instrument changes have led to an artificial negative (“cool”) bias in maximum temperatures and only a slight positive (“warm”) bias in minimum temperatures. These results underscore the need to consider all changes in observation practice when determining the impacts of siting irregularities. Further, the influence of non-standard siting on temperature trends can only be quantified through an analysis of the data. Adjustments applied to USHCN Version 2 data largely account for the impact of instrument and siting changes, although a small overall residual negative (“cool”) bias appears to remain in the adjusted maximum temperature series. Nevertheless, the adjusted USHCN temperatures are extremely well aligned with recent measurements from instruments whose exposure characteristics meet the highest standards for climate monitoring. In summary, we find no evidence that the CONUS temperature trends are inflated due to poor station siting. | <urn:uuid:33817600-f95e-40db-9229-531a537da949> | 2.90625 | 569 | Personal Blog | Science & Tech. | 25.076192 |
Simply begin typing or use the editing tools above to add to this article.
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...while erosion stripped away the overlying rocks. The researchers used a new geochemical technique to analyze and date the mineral apatite that existed in trace amounts within the sediments. The helium-uranium-thorium dating procedure determined when the apatite crystal in the heated rock cooled to about 70 °C (160 °F). The crystal typically reached that temperature when the buried...
What made you want to look up "helium-uranium-thorium dating"? Please share what surprised you most... | <urn:uuid:d97fb117-3c07-40e0-b492-08841f4e142b> | 3.765625 | 143 | Truncated | Science & Tech. | 46.777 |
heart urchinArticle Free Pass
heart urchin, any echinoid marine invertebrate of the order Spatangoidea (phylum Echinodermata), in which the body is usually oval or heart-shaped. The test (internal skeleton) is rather fragile with four porous spaces, or petaloids. The body is covered with fine, usually short spines.
Heart urchins live in burrows lined with mucus. Long tentacles (modified tube feet) reach out over the sand to pick up small particles of food; other tube feet have respiratory and sensory (not locomotive) functions. Movement is carried out by means of the spines.
What made you want to look up "heart urchin"? Please share what surprised you most... | <urn:uuid:d79c6a23-d3ff-410d-a341-d2220c0b496f> | 3.34375 | 161 | Knowledge Article | Science & Tech. | 44.959547 |
Chemistry in History
Explore the story of chemistry across centuries.
Science is a human pursuit. Meet the people behind some of chemistry’s most important milestones.
Chemistry has made innumerable contributions to our understanding of the world. Explore some of the areas in which chemists work.
Engage your hands and mind! Bring chemistry and its history to life with these activities. | <urn:uuid:9c0a078c-7f96-44d0-84b8-3e1b887e3f02> | 2.84375 | 78 | Content Listing | Science & Tech. | 39.885082 |
A quantum dot is a semiconductor whose excitons are confined in all three spatial dimensions. As a result, they have properties that are between those of bulk semiconductors and those of discrete molecules. They were discovered by Louis E. Brus, who was then at Bell Labs. The term "Quantum Dot" was coined by Mark Reed.
Researchers have studied quantum dots in transistors, solar cells, LEDs, and diode lasers. They have also investigated quantum dots as agents for medical imaging and hope to use them as qubits.
In layman's terms, quantum dots are semiconductors whose conducting characteristics are closely related to the size and shape of the individual crystal. Generally, the smaller the size of the crystal, the larger the band gap, the greater the difference in energy between the highest valence band and the lowest conduction band becomes, therefore more energy is needed to excite the dot, and concurrently, more energy is released when the crystal returns to its resting state. For example, in fluorescent dye applications, this equates to higher frequencies of light emitted after excitation of the dot as the crystal size grows smaller, resulting in a color shift from red to blue in the light emitted. The main advantages in using quantum dots is that because of the high level of control possible over the size of the crystals produced, it is possible to have very precise control over the conductive properties of the material.
Read more at Wikipedia. | <urn:uuid:4eafc774-10ad-4d9e-ac82-609782c264e7> | 3.9375 | 294 | Knowledge Article | Science & Tech. | 35.533102 |
Science Main Index
Of the million or more animal species in the world, more than 98% are
invertebrates. Invertebrates don't have an internal skeleton made of bone.
Many invertebrates have a fluid-filled, hydrostatic skeleton, like the
jelly fish or worm. Others have a hard outer shell, like insects and crustaceans.
There are many types of invertebrates. The most common invertebrates include
the protozoa, annelids, echinoderms, mollusks and arthropods. Arthropods include insects, crustaceans and arachnids.
Click on the picture or name of the animals below for more information. | <urn:uuid:1ff2cbde-178e-4c95-9b19-6e5cf53eea3c> | 3.34375 | 149 | Knowledge Article | Science & Tech. | 28.244249 |