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- Infowars - http://www.infowars.com -
Sun’s protective ‘bubble’ is shrinking
October 20, 2008
New data has revealed that the heliosphere, the protective shield of energy that surrounds our solar system, has weakened by 25 per cent over the past decade and is now at it lowest level since the space race began 50 years ago.
Scientists are baffled at what could be causing the barrier to shrink in this way and are to launch mission to study the heliosphere.
The Interstellar Boundary Explorer, or IBEX, will be launched from an aircraft on Sunday on a Pegasus rocket into an orbit 150,000 miles above the Earth where it will “listen” for the shock wave that forms as our solar system meets the interstellar radiation.
Dr Nathan Schwadron, co-investigator on the IBEX mission at Boston University, said: “The interstellar medium, which is part of the galaxy as a whole, is actually quite a harsh environment. There is a very high energy galactic radiation that is dangerous to living things.
“Around 90 per cent of the galactic cosmic radiation is deflected by our heliosphere, so the boundary protects us from this harsh galactic environment.”
Article printed from Infowars: http://www.infowars.com
URL to article: http://www.infowars.com/suns-protective-bubble-is-shrinking/
Copyright © 2013 Infowars. All rights reserved. | <urn:uuid:588f57de-67d0-4ec6-a4c1-a1c319529393> | 2.96875 | 319 | Truncated | Science & Tech. | 52.833182 |
Asymmetric Rhythms and Tiling Canons
Rachel W. Hall and Paul Klingsberg
Anyone who listens to rock music is familiar with the repeated drum beat—one, two, three, four—based on a 4/4 measure. Fifteen minutes listening to a Top 40 radio station offers evidence enough that most rock music has this basic beat. But if we tune the radio to different frequencies, we may hear popular music (jazz, Latin, African) with different characteristic rhythms. Although much of this music is also based on the 4/4 measure, some instruments play repeated patterns that are not synchronized with the 4/4 beat, creating syncopation—an exciting tension between different components of the rhythm. This article is concerned with classifying and counting rhythms that are maximally syncopated in the sense that, even when shifted, they cannot be synchronized with the division of a measure into two parts. In addition, we discuss rhythms that cannot be aligned with other even divisions of the measure. Our results have a surprising application to rhythmic canons. Audio recordings of all examples discussed are available at http://www.sju.edu/~rhall/Rhythms.
Some Generalizations of the Notion of Bounded Variation
Pamela B. Pierce and Daniel J. Velleman
When Jordan introduced the notion of bounded variation in 1881, he was seeking a sufficient condition for a function f to have a Fourier series that sums to f. With this same motivation, Wiener, Young, and Waterman have extended the notion of bounded variation in several directions. We introduce these broader classes of functions, and ask how these spaces are related to one another. For certain spaces, we prove theorems that give a complete description of how the spaces are interleaved.
A Study of Core-Plus Students Attending Michigan State University
Richard O. Hill and Thomas H. Parker
One important measure of the effectiveness of a high school mathematics program is the success students have in subsequent university mathematics courses. Yet this measure is seldom considered in studies of high school curricula. This article describes a study that we undertook to quantify this measure for one particular curriculum. The study examined the university records of students arriving at Michigan State University from four high schools which began using the Core-Plus Mathematics program. The data show that these students placed into, and enrolled in, increasingly lower level mathematics courses as the implementation progressed. This downward trend is statistically robust (p < .0005). The grades these students earned in their first college mathematics courses are also below average (p < .01). ACT scores suggest the existence but not the severity of these trends. This article also includes suggestions for constructing similar large-scale studies of students' transitions from high school to college mathematics.
Sliding along a Chord through a Rotating Earth
Andrew J. Simoson
Dynamical Systems Method and a Homeomorphism Theorem
A. G. Ramm
A Simple Way of Proving the Jordan-Hölder-Schreier Theorem
Complex Numbers and the Ham Sandwich Theorem
A New Proof of Euclid’s Theorem
Problems and Solutions
Saunders Mac Lane: A Mathematical Autobiography.
By Saunders Mac Lane
Reviewed by Della D. Fenster
Ants, Bikes, and Clocks: Problem Solving for Undergraduates.
By William Briggs
Reviewed by Steven Galovich | <urn:uuid:21e6fa1b-95b7-44bd-a565-6904107d7062> | 2.796875 | 710 | Content Listing | Science & Tech. | 39.832048 |
By Dr. Norm Catto
How much of ongoing climate change is due
to people? How do we know that we contribute at all?
Current discussion about climate change is based on differences
of scientific opinion concerning both the significance and
magnitude of the changes recorded in temperature and precipitation
statistics, as well as on the “global” nature
of the change, and the appropriateness of applying records
from one region to another. One must always remember that
the discussion of climate deals with long-term averages, over
several decades. The weather for each individual day, month,
season, and year will continue to vary within that overall
In the scientific community, the discussion centres around
whether human activity is responsible for all of the climate
change in the past 150 years, or only for part of it, or if
it is dominantly natural in origin. Scientists agree that
climate change is happening, as it has since the origin of
Earth 4.6 billion years ago, but we’re not all in agreement
as to exactly how much blame should be put on our species,
and how much of the change is natural.
The suggestion that humans are responsible for at least a
significant component of climate change comes from several
lines of evidence. Theoretical considerations suggest that
discharging carbon dioxide and methane into the atmosphere
will cause atmospheric warming, as can be directly observed
above all cities in the developed world where energy use involves
burning fossil fuels. Measurements of carbon dioxide and methane
preserved in ice cores from Antarctica and Kallaallit Nunaat
indicate that the concentrations have been relatively stable
over the past 10,000 years. However, since 1800, the concentration
of carbon dioxide in the ice and the atmosphere has increased
by about 30 per cent, and the concentration of methane has
Increases in temperature have also been
recorded in most areas of North America since 1845. In the
Rocky Mountains, glacial recession and tree ring records (dendrochronology)
indicate that glaciers today occupy less area than they did
9,000 years ago. Most of these glaciers have retreated more
within the past 150 years than they had advanced in the previous
9,000 years. This indicates that climate warming and drying
have occurred in this region, and at an accelerated rate since
1845. Similar conclusions have been drawn from studying lakes
in the Canadian Prairies. In Canada as a whole, Environment
Canada statistics indicate that six of the eight warmest years
on record (i.e. since Fahrenheit invented the thermometer,
around 1800) have occurred since 1992.
We’re not all in agreement as to exactly how much blame
should be put on our species, and how much of the
change is natural.
Unfortunately, these statistics are limited in their usefulness
by the relatively short time that they represent. The longest
accurate temperature records, from Europe and New England,
span the period since Fahrenheit’s thermometer was considered
to be sufficiently reliable – less than 200 years. In
most areas of western North America, accurate temperature
records encompass 150 years at most; in arctic Canada, reliable
observations date from the Second World War. Climate, by definition,
involves long term averages. If climate change is to be recognized,
it is necessary to look beyond the numerical records.
Climate changes in the historic past are assessed by studying
human records based on climate-dependent human activities.
Among those studied are the dates of annual grape harvests
from European Monasteries; the timing of cherry blossoms at
Shinto temples in Japan; the success or failure of wheat cultivation
in the North Atlantic regions; iceberg numbers and time of
ships’ encounters off Iceland’s coast; and trapping
data from the Hudson’s Bay Company. All of these human
activities can be used as analogies to calculate the climate
at those times.
For earlier periods, or in areas where there are no written
records available, proxy data from natural systems are used.
Proxy data are those that can be used to infer climate. Among
the styles of proxy data used to assess past climates from
4.6 billion years ago to 1800 AD are ice core records from
continental and mountain glaciers; pollen analysis from lake
sediments; other microfauna and flora, including diatoms,
insect remains, and marine plankton; dendrochronology; glacial
advances and retreats; changes in ranges of animal and plant
species; changes in soil development and type; and changes
in the types of sediments or landforms, such as glacial features
and sand dunes.
In the countries surrounding the North Atlantic Ocean, abundant
proxy data exists for the last 1,000 years. This recorded
data, along with the impressions of contemporary writers,
allows reconstruction of the climate patterns. The results
show that much regional variability existed, even over very
short distances: adjacent mountain valleys record different
responses to the same weather and climate events. This should
not be surprising, as modern weather events produce equally
diverse responses and effects. When results are compared across
the expense of western Europe and mid-latitude North America,
however, a pattern of consistent climate change emerges.
In general, the period from about 700 to 1300 A.D. was marked
by relatively warm conditions (generally, slightly less warm
than those at the end of the 20th century). This interval
is referred to as the Little Climatic Optimum or the Mediaeval
Warming. Following this, temperatures cooled, resulting in
glacial advances in alpine areas. This event, referred to
as the Neoglacial or Little Ice Age, persisted until the mid-19th
century. The Neoglacial was followed by a cycle of climate
warming, which is currently in progress.
Proxy data, historical records, and numerical temperature
and precipitation observations allow comparison between what
has happened under the purely natural circumstances that undoubtedly
existed prior to 1800 AD, and what has happened since then.
The most striking difference is not in the type of climate
changes, or the areas of occurrence, or the consequences to
organisms: it is the speed at which the changes are occurring.
Changes that required hundreds, thousands, or tens of thousands
of years in the natural and geological records are now seen
within the span of decades. The rates of climate change are
increasing, along with increased human production of carbon
dioxide and methane. The acceleration of the rate of change
began in the early 1800s, just as human consumption of fossil
fuels increased. Ongoing climate changes directly above cities
are proportionate to the amount of energy consumed by each,
with differences evident due to city size, lifestyle, and
economic wealth. Taken all together, the acceleration of climate
change cannot be explained solely by natural causes: human
activity is the only factor that has changed substantially
in Earth’s climate system since 1800.
So, we are not responsible for all climate change: natural
factors continue to operate, as they have for 4.6 billion
years. However, the accelerated rate indicates that humans
have made a contribution in the past 200 years.
Regardless of the cause, however, impacts of climate change
are happening today, and we will all have to adapt. Considering
our resilience in the face of the province’s traditional
weather, we should be able to cope with that in the future.
Dr. Norm Catto has been with Memorial's Department of
Geography since 1989. His research and teaching interests
include the impacts of climate change, and the necessary adaptations,
in Newfoundland and Labrador, throughout Canada, and in Russia. | <urn:uuid:0c7179f7-c91d-4243-be98-cb9f77b0a637> | 3.8125 | 1,639 | Nonfiction Writing | Science & Tech. | 30.940215 |
Freshwater and Nutrient Inputs to a Mississippi River Deltaic Estuary with River Re-Introduction
In this study, I quantified freshwater and nutrient inputs in the Breton Sound estuary which is receiving freshwater reintroduction in an effort to restore deteriorating wetlands. Almost all wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. This has altered water and nutrient budgets and is a primary cause of the massive wetland loss in the delta. Maintenance of the delta depends on a healthy, functioning ecosystem which includes riverine input. The Breton Sound estuary is located southeast of New Orleans and until recently was hydrologically isolated from direct riverine input. In 1992, a freshwater diversion became operational at Caernarvon, LA that re-introduces freshwater, nutrients, and sediments from the Mississippi River into the estuary. Several inputs and losses were calculated for three annual (2000, 2001, and 2002) water budgets including precipitation (PPN), potential evapotranspiration (PET), the diversion, stormwater pumps, and groundwater. The inputs of ammonium (NH4-N), nitrate (NO3-N), total nitrogen (TN) and total phosphorus (TP) were determined for each of the water sources. There was a different precipitation pattern for each of the years for which water and nutrient budgets were calculated. Precipitation contributed 48-57% of freshwater input while the diversion structure accounted for 33-48%. The net input of fresh groundwater was 3 to 4 orders of magnitude less than diversion input and precipitation. Atmospheric deposition was the largest contributor of NH4-N accounting for 62-72% of the total NH4 input followed by the diversion (total annual NH4-N input was 1.39x105 to 1.96x105 kg). NO3-N input to the estuary was an order of magnitude greater than NH4-N input. The diversion was the greatest source of nitrate to the study area (7.78x105 to 1.64x106 kg) contributing 77-88% of total nitrate input. The diversion contributed 1.26x106 to 2.10x106 kg of TN, representing 77-79% of TN input. The diversion contributed 81-98% of TP input and was an order of magnitude greater than precipitation and stormwater pumps combined. Annual loading rates of NH4-N and NO3-N were 0.16-0.22 and 1.6-2.2 gNm-2y-1, respectively. TN ranged from 1.9-3.2 gNm-2y-1 and TP ranged from 0.17-0.29 gPm-2y-1.
Advisor:Dubravko Justic; John W. Day, Jr.; Enrique Reyes; Robert Gambrell
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Keywords:oceanography coastal sciences
Date of Publication:11/02/2004 | <urn:uuid:66463c98-5f83-494d-a667-43ef044ec775> | 2.953125 | 631 | Academic Writing | Science & Tech. | 56.532056 |
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Will the universe go on expanding forever and what is the shape of the universe? Read how we are trying to find the answers to these questions.
An animation of the movement of galaxies as the universe expands.
A long lisit of cosmology questions, dealing with subjects such as the Big Bang, dark matter, black holes, the expanding universe.
Alexander Friedmann of Russia is credited with developing a dynamic equation for the expanding universe in the 1910s.
Einstein proposed a modification of the Friedmann equation which models the expanding universe. He added a term which he called the cosmological constant.
Every lightcone contains infinitely many nearly complete, mutually exclusive, lightcones. This page looks at the maths of this, and its use as a cosmological model.
This fantastic site deals with cosmology : the study of the structure, history, and fate of the Universe. It's the place to go whether you want to know more about dark matter, how our universe formed ...
Find out how a fridge works by compressing and expanding a coolant in this interactive.
Stephen Hawking's Universe: explains some of the most important ideas and developments in human understanding of the universe. The Web pages include original essays in cosmology, original ...
A simple article from NASA which tries to show how big the Universe is and how long it would take to travel between stars!
Showing 1 - 10 of 81 | <urn:uuid:095d7119-ebec-4ed5-82ff-e4f144d5c9e7> | 2.890625 | 387 | Content Listing | Science & Tech. | 50.85037 |
Santa Barbara Field Guides - Butterflies|
Wingspread 1-1.5 in. |
Recognition: Male a shimmering light blue above, with black wing edges and a white fringe; females very pale blue to pale gray above; undersides of both sexes white with varied black markings.
Flight period: Adults active in early to midsummer.
Hostplants: Larvae feed only on buckwheats (Eriogonum - Polygonaceae).
Habitat: Found primarily in arid scrublands.
Distribution: The Blue Copper occurs throughout the Great Basin region, extending west into the mountains of southern California. It has not been definitely recorded from Santa Barbara County, but is known from neighboring Ventura County, and may be found at higher elevations in the Santa Barbara backcountry.
Other: Presence in Santa Barbara County requires confirmation. | <urn:uuid:df2685db-2b5c-46be-a0c9-d55b3116d877> | 2.703125 | 179 | Knowledge Article | Science & Tech. | 33.456461 |
Mar. 26, 2009 Insects such as honeybees and bumble bees are predictable in the way they move among flowers, typically moving directly from one flower to an adjacent cluster of flowers in the same row of plants. The bees' flight paths have a direct affect on their ability to hunt for pollen and generate "gene flow", fertilization and seed production that results when pollen moves from one plant to another.
The study of gene flow has experienced more attention in part due to the recent introduction of genetically modified organisms (GMOs) into the environment.
Scientists, plant breeders, and growers seek to understand flight patterns of honeybees, bumble bees, and other insect "pollinators" as a way to increase production and healthy produce. Although several studies have focused on pollen movement among cucurbits, the plant family that includes cucumbers, gourds, melons, or pumpkins, little research has looked at pollinator flight patterns and, until recently, none has determined pollen flow in watermelon plantings.
New research published in the February 2009 issue of HortScience by research scientists S. Alan Walters of Southern Illinois University and Jonathan R. Schultheis of North Carolina State University studied pollinator movements down and across rows in watermelon [Citrullus lanatus (Thunb.)] by tracking pollen flow. The direction of honeybees was tracked under field conditions during 2001 and 2002 at the Southern Illinois University Horticultural Research Center in Carbondale.
According to Walters, the study indicated that the evaluation of pollen flow showed a definite pattern of bee movement and gene migration in watermelon. "Although we detected pollinator movement that was strongly directional in both directions (east and west) down the row from the central block of donor plants, results also indicate that significant movement also occurred across rows in both directions (north and south) from the donor plot", he remarked.
Because watermelon vines grow in multiple directions, including across rows, bees can easily move across rows if the next closest flower is in that direction instead of down the row. Most pollen is deposited on the nearest neighboring flower from where pollen was collected.
Walters summarized the study stating, "Although significant amounts of linear pollinator movements occur down rows of watermelon plants, pollinator movements (in watermelon) are not as simple as just maintaining a linear direction straight down the row, but are related to the short flight distances that most likely occur to the closest neighboring flower from the one that was previously visited."
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- Walters, S. Alan, Schultheis, Jonathan R. Directionality of Pollinator Movements in Watermelon Plantings. HortScience, 2009 44: 49-52 [link]
Note: If no author is given, the source is cited instead. | <urn:uuid:1ea0aec9-125c-4f06-ba8d-9df8c538559f> | 4.21875 | 598 | Knowledge Article | Science & Tech. | 30.064467 |
Dead leaves? Grass clippings? Fruit and vegetable peels? Sure, you could compost them, or you could turn them into robot fuel or solar cells. Plus, a gadget for harvesting the power you generate while walking, and an app for showing off your gas and carbon savings from driving a plug-in vehicle.
Next week, the new series Quirky debuts on the Sundance Channel. We’ve featured lots of quirky ideas in the weekly green tech finds posts over the past two years, so in anticipation of the show I thought I’d go back to some of our most innovative (or, at least, most unusual) finds. And if you’ve just got to have the latest, we’ve got a few new ones, too.
Article: Green tech finds (12/9/10)
Fuel cells, iPhone apps, and chicken coops… this week’s green tech finds.
The fuel cell that does… everything: Think fuel cells are just for energy? Think again… researchers at the University of Colorado, Denver, are working on a microbial fuel cell that desalinates and cleans wastewater… in addition to producing electricity. (via Cleantechnica)
Border checkpoint to feature Living Machine: The US General Services Administration has approved a Living Machine wastewater treatment system for the border crossing point at Otay Mesa, California. That’s an artist’s rendering above… (via Water and Waste Water)
Article: Green tech finds (11/4/10)
Lots of electric vehicle news this week, plus mushroom plastics and watching watersheds with your iPhone… this week’s green tech finds.
- Sun-powered transportation… in the Sunshine State: Sarasota-area beachside community Pelican Bay will be using solar-powered trams to move people around the development. (via Cleantechnica)
- GE making massive EV purchase: General Electric will not only make components for electric vehicles, but plans to become the largest single purchaser of them.
Article: Green tech finds
Is the iPhone 4 green? That, and other questions answered, in this week’s green tech finds. Prize-winning biomimicry: Technology Academy Finland has awarded its biannual Millennium Technology Prize to Swiss scientist Michael Grätzel for his development of the dye sensitized solar cell, a cheaper alternative to photovoltaics that mimics photosynthesis. See the video above for details. (via…
Article: Green tech finds (2/4/10)
Hummer horse carts, cheap(er) wind power, and make-you-own toilet paper machines… this week’s green tech finds.
President Barack Obama today announced the award of $2.3 billion in Recovery Act Advanced Energy Manufacturing Tax Credits for 183 clean energy manufacturing projects across the United States.
Article: Green tech finds (12/10/09)
Another week, another group of green tech finds. First, a few more from Finland:
Jen Boynton at TriplePundit discusses four game-changing technologies you’ve never heard of…
Ian Thomson at Cleantechies gives his opinion of Tekes, Finland’s government agency for funding R&D and start-ups… I had a different take on this organization at sustainablog.
Article: Green tech finds (7/23/09)
Beer and gas? Sound like a National Lampoon movie… but it’s your green tech finds for the week.
Fart-powered fuel cells? Sort of… Danbury, Connecticut-based FuelCell Energy recently installed two fuel cell power plants at food processor Gills Onions that “…create electricity using old onions and a process that mimics how the human body expels gas”
Solar-powered parking: Austin, Texas is replacing traditional parking meters with “pay stations [that] are solar-powered, take credit cards, debit cards and coins, and will replace the 3,800 outdated single-space parking meters around the city.” | <urn:uuid:d5bfb5a3-ff57-41d8-8185-7173f299c2b9> | 2.71875 | 843 | Content Listing | Science & Tech. | 46.438864 |
LAKE EFFECT SNOW
Snow showers that are created when cold dry air passes over a large warmer lake, such as one of the Great Lakes, and picks up moisture and heat.
A diurnal coastal breeze that blows offshore, from the land to the sea. It is caused by the temperature difference when the sea surface is warmer than the adjacent land. Predominate during the night, it reaches its maximum about dawn. It blows in the opposite direction of a sea breeze.
The point at which a tropical cyclone's eye first crosses a land mass.
A small, weak tornado, which is not formed by a storm-scale rotation. It is generally weaker than a supercell tornado and is not associated with a wall cloud or mesocyclone. It may be observed beneath cumulonimbus or towering cumulus clouds and is the land equivalent of a waterspout.
LAPSE RATEabsolute instability »
The change of an atmospheric variable, usually temperature, with height. A steep lapse rate implies a rapid decrease in temperature with height and is a sign of instability.
LATENT HEATcondensation » and sublimation »
The energy released or absorbed during a change of state.
The location north or south in reference to the equator, which is designated at zero (0) degrees. Parallel lines that circle the globe both north and south of the equator. The poles are at 90° North and South latitude.
The side of an object or obstacle, such as a ship's sail, a mountain, or a hill, furthest away from the wind, and therefore, protected from the direct force of the wind. The opposite of windward.
LENTICULAR CLOUDDave's Dictionary »
A cloud species which has elements resembling smooth lenses or almonds and more or less isolated. These clouds are caused by a wave wind pattern created by the mountains. They are also indicative of down-stream turbulence on the leeward side of a barrier.
LEVEL OF FREE CONVECTION (LFC)
The level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely. This occurs most readily in a conditionally unstable atmosphere.
LIFTED INDEX (LI)
A measure of atmospheric instability that is obtained by computing the temperature that the air near the ground would have if it were lifted to a higher level and comparing it to the actual temperature at that altitude. Positive values indicate more stable air and negative values indicate instability.
LIFTING CONDENSATION LEVEL (LCL)
The height at which a parcel of moist air becomes saturated when it is lifted dry adiabatically.
LIGHTNINGball lightning » and heat lightning »
A sudden and visible discharge of electricity produced in response to the build up of electrical potential between cloud and ground, between clouds, within a single cloud, or between a cloud and surrounding air.
LIGHT WAVESvisible light »
That part of the electromagnetic spectrum that contains visible light. The colors, from longest wave length to shortest, are red, orange, yellow, green, blue, indigo, and violet (ROY G. BIV).
LINE ECHO WAVE PATTERN (LEWP)
A wave-shaped bulge in a line of thunderstorms. It may often be seen as a "S"-shaped radar echo signature and is often associated with severe weather.
Atmospheric phenomena which affect the state of the atmosphere. They constitute dry particles that hang suspended in the atmosphere, such as dust, smoke, sand, and haze.
The solid, outer portion of the earth's crust coupled to the rigid upper mantle. Part of the geosphere.
LONGITUDEGreenwich Mean Time »
The location east or west in reference to the Prime Meridian, which is designated as zero (0) degrees longitude. The distance between lines of longitude are greater at the equator and smaller at the higher latitudes, intersecting at the earth's North and South Poles. Time zones are correlated to longitude.
LONG WAVE TROUGH
A wave in the prevailing westerly flow aloft which is characterized by a large length and amplitude. A long wave moves slowly and is persistent. Its position and intensity govern weather patterns over a period of days or weeks.
A term used to signify clouds with bases below 6,000 feet and are of a stratiform or a cumuliform variety. Stratiform clouds include stratus and stratocumulus. Cumuliform clouds include cumulus and cumulonimbus. This altitude applies to the temperate zone. In the polar regions, these clouds may be found at lower altitudes. In the tropics, the defining altitudes for cloud types are generally higher.
The latitude belt between 30 and 0 degrees North and South of the equator. Also referred to as the tropical or torrid region.
LOW LEVEL JET (LLJ)jet stream »
Strong winds that are concentrated in relatively narrow bands in the lower part of the atmosphere. It is often amplified at night. The southerly wind over the US Plains states during spring and summer is a notable example.
LOW PRESSURE SYSTEMclosed low », cold low », and cut-off low »
An area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone.
An eclipse of the moon occurs when the earth is in a direct line between the sun and the moon. The moon does not have any light of its own, instead, it reflects the sun's light. During a lunar eclipse, the moon is in the earth's shadow. It will often look dim and sometimes copper or orange in color. | <urn:uuid:c8d01307-38cf-41a1-91bf-42b38e63dc62> | 3.375 | 1,223 | Structured Data | Science & Tech. | 45.483627 |
The estimated super high-pressure release of oil from under the earth's crust is between 80,000 to 100,000 barrels per day... that is equal to about an average of 6.3 Olympic sized swimming pools per DAY of crude oil geysering into the world's oceans.
The flow of oil and toxic gases is bringing up with it gas, and rocks, and sand which causes the flow to create a sandblasting effect on the remaining well head device currently in place to somewhat restrict the flow, as well as the drilled hole itself.
As this wellhead becomes worn down it enlarges the passageway allowing an ever-increasing flow of oil to geyser out.
Even if some device could be placed onto the existing wellhead, it would not be able to shut off the flow, because what remains of the existing wellhead would not be able to contain the pressure.
The wellhead piping is originally about 2 inches thick. It is now likely to be less than 1- inch thick, and thinning by each passing moment.
The oil has now reached the Gulf Stream and is entering the Oceanic current that is at least four times stronger than the current in the Gulf, which will carry deadly oil throughout the world within 18 months. Keep in mind that it takes the consumption of just one drop of oil to kill a fish.
But you have to be living to eat the oil. The oil, along with the gasses, including benzene and many other toxins, is deleting the oxygen in the water. This is killing all life in the ocean, creating massive dead zones.
Along with the oil along the shores, there are already many dead fish, etc. that will have to be gathered and disposed of. Even without the oil toxins, landbased pollution has been doing a fine job of it already, as this chart shows:
What you can expect ahead.
At some point the drilled hole in the earth will enlarge itself beneath the wellhead to weaken the area the wellhead rests upon. The intense pressure will then push the wellhead off the hole allowing a direct unrestricted flow of oil out, and the geyser will behave more like a volcano.
The hole will continue to increase in size allowing more and more oil to rise into the Gulf. After several BILLION barrels of oil have been released, the pressure within the massive cavity five miles beneath the ocean floor will begin to normalize.
This will allow the water, under the intense pressure at 1 mile deep, to be forced into the hole and the cavity where the oil was. The temperature at that depth beneath the earth and sea is near 400 degrees, possibly more.
The water will be vaporized and turned into steam, creating an enormous amount of force, lifting the Gulf floor. It is difficult to know how much water will go down to the core and therefore, its not possible to fully calculate the rise of the floor.
The tsunami wave this will create will be anywhere from 20 to 80 feet high, possibly more. Then the floor will fall into the now vacant chamber. This is how nature will seal the hole.
Depending on the height of the tsunami, the ocean debris, oil, and existing structures that will be washed away on shore and inland, will leave the area from 50 to 200 miles inland devoid of life.
Even if the debris is cleaned up, the contaminants that will be in the ground and water supply will prohibit re-population of these areas for an unknown number of years. Your grandchildren's grandchildren will be paying the price for this foolish accident, the height of human hubris and arrogance in regards to the environment.
And what can we do about it? Absolutely nothing. Why do I think that? Because humanity WILL NOT change to the reality that is destroying our planet. | <urn:uuid:bc2b2505-f063-456e-86c4-49cbd17a1935> | 3.3125 | 774 | Personal Blog | Science & Tech. | 59.878533 |
|We tend to view DC circuits in terms of their steady state values, but induced EMF can be important when the current is changing even in a mundane looking circuit. When the switch in a circuit is closed and current begins to flow, the current produces a magnetic flux through the loop. This magnetic flux changes with time, increasing and inducing an EMF in the circuit that opposes the change in magnetic flux. The opposing EMF, the back EMF, results in the current increasing gradually.|
Watch the phrasing in the passage and question. If the MCAT were going to be tricky about back EMF in a standard DC circuit, there would certainly be mention in the passage of induction. | <urn:uuid:8984325f-5fe1-4451-a365-db1dcd05146b> | 3.6875 | 141 | Knowledge Article | Science & Tech. | 58.73778 |
The analysis of astronomical data is commonly referred to as "data reduction". Data is analyzed (or "reduced") using software on a desktop computer. The most commonly used software package for optical and infrared data is the Image Reduction and Analysis Facility (IRAF). Learning the basics of IRAF is important if you expect to work with optical or infrared data. The IRAF homepage provides a tutorial, and many others are available on the web. IRAF can be downloaded and installed for free. Another commonly used set of software is IDL, for which a license must be purchased (usually a department-wide license is available).
During day-to-day research, you will frequently need to manipulate data from text files and perform various mathematical tasks. Learning some kind of programming or scripting language is necessary to do this. For computationally intensive tasks, fortran or C are options, but otherwise I use perl whenever possible, which is much more user friendly and versatile. Like Unix and IRAF, perl (or some equivalent scripting language) is very important to learn.
If you are responsible for installing the software on your computer, then this task is much easier with Fink.
Detailed advice specific to an astronomer using a Mac is available here.
Here is a list of the primary professional astronomy journals. ApJ is the most prestigious of these journals and its articles generally have the highest quality and impact. A scientist from any country can publish an article in any of these journals, but the papers in a journal tend to be authored predominantly by scientists from the country in which the journal resides, such as the US for ApJ and AJ, UK for MNRAS, and Europe for A&A.
Using the NASA Astrophysics Data System (ADS), you can search the astronomical literature for articles according to various criteria, including author name, title, subject, year, and refereed/non-refereed. For instance, if you want to see a list of the papers written by an astronmer, enter "Smith, J." in the author field. When the list of papers appears, you can then download the papers. For newer articles, your computer will need a license for the journal in question, which is usually available transparently if using a computer at an astronomy department. Older papers usually don't require a license and are free.
Finally, an important resource for publications is the archive of astronomy preprints, known as astro-ph. The time between when a paper is accepted for publication by a journal and when it appears in a printed issue of the journal is usually several months. To more quickly communicate their results to other scientists, most astronomers post a copy of their paper on astro-ph as soon as it is accepted for publication by the journal. (Some astronomers post the submitted versions of their papers before they have been accepted for publication, but I don't recommend this.) A new list of posted papers appears at astro-ph every weekday morning. It's good to develop a habit of checking astro-ph on a regular basis to keep up to date on the most recent work in your field.
NED is similar to Simbad, except specialized for extragalactic sources.
The Digitized Sky Survey (DSS) contains electronic scans of photographic plates of the entire sky that were taken decades ago. The image quality isn't good by the standards of modern telescopes, but it does cover the whole sky and is often useful for planning observations (e.g., making finding charts) and for the measuring proper motions or variability relative to newer images.
The Sloan Digitized Sky Survey (SDSS) is an optical imaging survey of 1/4 of the sky (modern version of DSS).
In 2010, the Wide-field Infrared Survey Explorer (WISE) obtained images of the entire sky at four mid-infrared bands (3.4, 4.6, 12, 22 um).
The Deep Near Infrared Survey of the Southern Sky (DENIS). Similar to 2MASS, except in the I, J, and H bands instead of J, H, and K and only for the southern hemisphere.
Most space observatories (Hubble, Spitzer, and Chandra) and newer and larger ground-based observatories (ESO/VLT, others) that are supported by public funding maintain archives of their data, or have plans to do so. The scientist for whom the data were obtained usually has a proprietary period of 1-2 years; after that, anyone can download and use the data.
The Infrared Science Archive (IRSA) provides an interface for accessing archives for many infrared and submillimeter missions, such as IRAS, ISO, 2MASS, SWAS, SDSS, MSX, and Spitzer.
The AAS hosts 2 conferences each year, which are usually the largest astronomy meetings in the country. A comprehensive list of all meetings in astronomy that are planned in the next few years is found here. It's good to check this once in a while to see if there are meetings planned for the next year that you would like to attend.
Mauna Kea on the big island of Hawaii hosts the greatest collection of telescopes in the world. The atmosphere above Mauna Kea typically is very stable and allows for sharp images, or excellent "seeing". Water in the atmosphere absorbs light at many wavelength ranges of the electromagnetic spectrum (e.g., mid-IR, or 10um), normally preventing observations of stars at those wavelengths. However, those observations are often possible from Mauna Kea because the atmosphere above it is very dry and thus suffers from less water absorption. These telescopes are operated by various consortia of governments and institutions. As part of the agreement with the state of Hawaii for allowing construction of these telescopes, the University of Hawaii is given a share of the time on all of them. Chile has a similar arrangement for all telescopes built within its borders.
3.0m NASA Infrared Telescope Facility (IRTF) is available for use by any professional astronomer. Half of the time is allotted for solar system research and the other half for the rest of astronomy. This telescope has a wonderful near-IR spectrometer (0.8-5um) called SpeX and offers remote observing from your home institution.
3.6m Canada-France-Hawaii Telescope (CFHT)
3.8m United Kingdom Infrared Telescope (UKIRT)
8m Gemini North (National Optical Astronomy Observatory (NOAO), United Kingdom, Canada, Chile, Australia, Argentina, Brazil, University of Hawaii) Most of its observations are performed by observatory staff (queue observing) rather than the astronomers themselves (classical observing).
8.2m Subaru Telescope (Japan)
2x10m Keck Observatory (Caltech, the University of California, NASA)
15m James Clerk Maxwell Telescope (JCMT) (UK, Canada, and Netherlands)
8x6m Submillimeter Array (SMA) (Smithsonian Astrophysical Observatory and Taiwan)
Major observatories are located on several mountains in Chile.
4m Blanco Telescope was one of the premiere telescopes in the world at one time but now is somewhat old with image quality that is lower than newer, state-of-the-art telescopes.
4.1m SOAR Telescope (on nearby Cerro Pachon) (NOAO, Brazil, the University of North Carolina, Michigan State University) SOAR was recently constructed and offers excellent image quality.
several smaller telescopes run by SMARTS consortium
8m Gemini South is on Cerro Pachon next to SOAR.
Las Campanas Observatory (LCO) is operated by the Observatories of the Carnegie Institution of Washington (OCIW). Because the altitude of Las Campanas is not particularly high, the site isn't as good as Hawaii or Paranal for mid-IR observations.
2x6.5m Magellan Telescopes (Carnegie, Harvard, Michigan Arizona, MIT) No ground-based telescope outside of Antarctica has better seeing than Magellan.
2.5m DuPont Telescope
1m Swope Telescope
3.5m New Technology Telescope (NTT)
several smaller telescopes
3.5m Wisconsin-Indiana-Yale-NOAO Telescope (WIYN)
2.3m Bok Telescope (University of Arizona).
several other 1-2m telescopes
6.5m MMT (SAO and Arizona)
1-2m telescopes, an optical/IR interferometer, and gamma ray telescope
other smaller telescopes
other smaller telescopes
Texas and New Mexico
2.7m Harlan Smith Telescope
other 1-2m telescopes
2.5m Sloan Digital Sky Survey Telescope
other smaller telescopes
3.9 m Anglo-Australian Telescope (AAT)
1.2 UK Schmidt
4.2m William Herschel (UK, Netherlands, Spain)
2.5m Isaac Newton (UK, Netherlands, Spain)
1.2, 2.2, 3.5m Calar Alto Observatory (MPIA, Spain) | <urn:uuid:d50702b9-95b3-42ee-b040-2a36e8763303> | 2.734375 | 1,885 | Knowledge Article | Science & Tech. | 41.360112 |
See more from this Session: Microbe, Plant , and Soil Interactions (Includes Graduate Student Poster Competition)
Monday, October 17, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
Methane (CH4) is a potent greenhouse gas and management strategies have been proposed to limit CH4 emissionsfrom freshwater wetlands. The methanotrophic bacteria can intercept much of the CH4 produced by methanogenicarchaea and thus management protocols for wetlands could conceivably include manipulations not only to limit theproduction of CH4 by methanogens, but also to enhance the consumption of CH4 by benthic or planktonicmethanotrophs. The hydrological characteristic of a wetland is a major determinant of the CH4 emission rates. Amajor consideration for CH4 production is whether a wetland is static or flowing (wetlands connected to rivers andstreams). Very little is known about the effects of hydrologic pulsing on wetland carbon dynamics and especially CH4 oxidation. Furthermore, although it has been established that methanotrophs are very active at the oxic sedimentwaterinterface of wetlands, little is known about the ecology of methanotrophs in the “pulsing fringe”. Stable Isotope Probing (SIP) of biomarker Phospholipid Fatty Acids provide a means to connect CH4 oxidation to specificmethanotrophs and track the shifts in community structure. Three landscape treatments were: 1) upland aerobic soil,2) the intermediately flooded zone, and 3) the permanently flooded site with two landscape level replicates in afreshwater pulsing experimental wetlands at the Olentangy River Wetland (ORW) Research Park, The Ohio StateUniversity, Columbus.Two soil depths (organic horizon, 0-8 cm that includes the oxidized layer in flooded sites and8-16 cm depth of surface mineral layer) were sampled at each site four times/year over a two-year period (earlyspring, mid summer, early fall and mid winter). Immediately after sampling the samples are stored at -20° C andtransported under dry ice to the Soil Microbial Ecology Lab, SENR, the Ohio State University, Columbus foranalysis. Samples were taken back to the lab to determine potential CH4 oxidation and 13C-PLFA analyses afterextraction and analysis on GC-C-IRMS.The PF sites had significantly higher (p<0.05) Potential Methane Oxidation(PMO) than the IF sites. PMO rates at 0-8 cm depth of soil were significantly higher than those at depth of 8-16 cm(p<0.05). PMO in Winter was also significantly higher than in Summer (p< 0.01). PLFA profiling of methanotrophsshowed that the Type type II methanotrophs and I methanotrophs were more pronounced in winter that was highlycorrelated by the seasonal dynamics of PMO. Concentrations of the Type II methanotroph PLFA biomarker (18:ω8c,18:ω9c and 18:ω7c) were significantly higher (p<0.05) than the Type I PLFA biomarkers (16:ω5c).The highest potential to oxidize the substrate-available methane in the Permanently Flooded site is entirely attributed to themethanotrophic population (as reflected by the relative abundance of the signature PLFAs). Even if with very low 13C incorporation, the PLFA profile in the Intermittently Flooded site is dominated by the Type II methanotrophs. | <urn:uuid:a58a529e-7260-42b0-be8d-9a39bbe163ec> | 2.84375 | 759 | Academic Writing | Science & Tech. | 26.526241 |
When you specify the thread stack size, you must account for the allocations needed by the invoked function and by each subsequent function called. The accounting should include calling sequence needs, local variables, and information structures.
Occasionally, you want a stack that differs a bit from the default stack. An obvious situation is when the thread needs more than the default stack size. A less obvious situation is when the default stack is too large. You might be creating thousands of threads with insufficient virtual memory to handle the gigabytes of stack space required by thousands of default stacks.
The limits on the maximum size of a stack are often obvious, but what about the limits on its minimum size? Sufficient stack space must exist to handle all stack frames that are pushed onto the stack, along with their local variables, and so on.
To get the absolute minimum limit on stack size, call the macro PTHREAD_STACK_MIN. The PTHREAD_STACK_MIN macro returns the amount of required stack space for a thread that executes a NULL procedure. Useful threads need more than the minimum stack size, so be very careful when reducing the stack size. | <urn:uuid:503fa767-1624-4aed-8bb9-76eb4213d518> | 2.9375 | 233 | Documentation | Software Dev. | 49.633618 |
This data set reports on dissolved nutrient concentrations, as well as dissolved oxygen, alkalinity, conductivity, turbidity, and pH measured in water samples collected from nine streams located in the state of Brasilia, Brazil, between September, 2004 and December, 2006. Streams were located in different land cover types including natural (forest), rural (agricultural), and developed landscapes. ... In addition, water samples from wells, lysimeters, surface runoff, and precipitation were collected from four sites, 2 natural and 2 rural, and analyzed for nutrient concentrations. Streams were sampled every 2-4 weeks; rain water was collected approximately monthly during the wet season and once during a dry season; wells and lysimeters were sampled monthly; and surface runoff collections were event based. There are three comma-delimited data files with this data set. | <urn:uuid:e73fa974-7a59-4731-9e1e-d3b0dab8162e> | 2.875 | 173 | Academic Writing | Science & Tech. | 23.377813 |
Using Table Aliases
The readability of a SELECT statement can be improved by giving a table an alias, also known as a correlation name or range variable. A table alias can be assigned either with or without the AS keyword:
table_name AS table alias
In the following example, the alias c is assigned to Customer and the alias s is assigned to Store.
USE AdventureWorks2008R2; GO SELECT c.CustomerID, s.Name FROM Sales.Customer AS c JOIN Sales.Store AS s ON c.CustomerID = s.BusinessEntityID ;
If an alias is assigned to a table, all explicit references to the table in the Transact-SQL statement must use the alias, not the table name. For example, the following SELECT generates a syntax error because it uses the name of the table when an alias has been assigned:
SELECT Sales.Customer.CustomerID, /* Illegal reference to Sales.Customer. */ s.Name FROM Sales.Customer AS c JOIN Sales.Store AS s ON c.CustomerID = s.BusinessEntityID ; | <urn:uuid:c622fe50-ec5d-4ea4-855b-305f541add49> | 3.28125 | 222 | Documentation | Software Dev. | 49.388889 |
What is the true color of the sun? why is it that
color and how did it become that color?
My science teacher says its white but my dad challenges that
statement by saying its yellow-orange.
Your teacher and father are coming at it from different view points.
Because the Sun is at a temperature of approximately 5500K
(essentially "white hot"), it is white in color. Another way to look
at this is to say that if the light from the Sun were to be passed
through a prism, it would be split into a rainbow of colors which
then suggests that it is white since all the colors are present.
However, when the Sun's rays pass through our atmosphere, the Sun's
rays are scattered by the particles in the air and gives it a yellow
color. In this sense, your dad is correct in that stars are
classified depending on their age and the color that they give when
their light passes through our atmosphere. Our Sun being a main
sequence star (which gives off heat through the fusion of hydrogen
and is neither contracting nor expanding) is classified as yellow.
About 100million stars are classified as such. The others are Red
Dwarves and Blue Giants.
Greg (Roberto Gregorius)
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:cdf74405-d1fc-4ed3-9f1c-e11103a28cff> | 3.765625 | 278 | Q&A Forum | Science & Tech. | 60.021266 |
Saving What Remains
Carbon Offset Programs
Plants take carbon dioxide out of the air during the process of photosynthesis and use it to makes sugars for growth and metabolism. Carbon is stored in wood and other tissues until the death of the plant when the stored carbon is released to the atmosphere via burning or decomposition or recycled in the forest ecosystem.
Given this process, industry can "offset" same of their carbon dioxide emissions by sponsoring the establishment of reserves or by funding improvements in degraded forest that sequesters an amount of carbon equivalent to their emissions. The US power-generating industry has been the most active to date in such off-set programs positioning themselves now to be able to take advantage of carbon trading when it is established.
One entire branch of carbon trading is based on the fact that as trees grow they absorb carbon dioxide. Growing forests and plantations absorb carbon, while old growth forests are in a state of equilibrium and no longer take up carbon. There is new concern that forests will make poor carbon sinks if temperatures rise. When plants are not photosynthesizing, they are respiring - taking in oxygen and releasing carbon dioxide. Whereas the uptake of carbon through photosynthesis is an instantaneous process, respiration increases with temperature which - in the case of global warming - has about a 50 year log time due to the thermal inertia of oceans. So as temperature increases catch up with the rise of carbon dioxide levels, respiration rates of soils and plants will also increase (initially at an exponential rate), releasing more carbon into the atmosphere. Even though atmospheric carbon dioxide levels will be increasing, extra carbon dioxide has a diminishing effect on plant growth so the net result will be to balance out what initially looked like carbon sinks in planting forests.
The Kyoto Protocol only recognizes credits generated through anthropogenic activities since 1990. Nonetheless, the carbon trade in North America and Europe could be worth $30-100 billion once it is fully operational.
|Sustainable Dev - Agriculture
Foods & Genetic Diversity
Medicinal Drugs & Pesticides
Types of Reserves
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Copyright Rhett Butler 1994-2005 | <urn:uuid:b7c03463-f1e8-4064-b1ed-d2806320daa7> | 4 | 454 | Knowledge Article | Science & Tech. | 22.696171 |
Free Search (10891 images)
Molecular clouds in the Taurus region
Rating: 0.00/5 (0 votes cast)
- Title Molecular clouds in the Taurus region
- Released 09/02/2012 3:14 pm
- Copyright ESA/Planck Collaboration; T. Dame et al., 2001
This image shows the Taurus molecular cloud complex as seen through the glow of carbon monoxide (CO) with Planck (blue). The same region is shown as imaged by previous CO surveys (Dame et al., 2001) for comparison (red).
Molecular clouds, the dense and compact regions throughout the Milky Way where gas and dust clump together, represent one of the sources of foreground emission seen by Planck. The vast majority of gas in these clouds consists of molecular hydrogen (H2), and it is in these cold regions that stars are born. Since cold H2 does not easily radiate, astronomers trace these cosmic cribs across the sky by targeting other molecules, which are present there in very low abundance but radiate quite efficiently. The most important of these tracers is carbon monoxide (CO), which emits a number of rotational emission lines in the frequency range probed by Planck's High Frequency Instrument (HFI).
Emission lines affect a very limited range of frequencies compared to the broad range to which each of Planck’s detectors is sensitive, and are usually observed using spectrometers. But some CO lines are so bright that they actually dominate the total amount of light collected by certain detectors on Planck when they are pointed towards a molecular cloud like the Taurus complex.
The all-sky CO map compiled with Planck data shows concentrations of molecular gas in portions of the sky that had never before been surveyed. Planck's high sensitivity to CO also means that even very low-density clouds can be detected, and new details can be revealed in clouds that were already known. This can be seen by comparing the two images of the Taurus cloud: the Planck image allows astronomers to study the cloud structure in greater detail.
Follow-up observations and further studies of this and other stellar nurseries will allow a detailed investigation of the physical and chemical conditions that lead to the formation of molecular clouds, shedding new light on the very early phases of star formation. | <urn:uuid:76ca21c4-90c8-42fe-a4ac-d07685806e6d> | 3.125 | 479 | Truncated | Science & Tech. | 43.0325 |
|In this tutorial, we will begin to explore the many ways to use ActionScript in your FlashR project. I'm not talking about the many things that you can make happen with ActionScript. I'm talking about how you can add ActionScript code to your Flash movie. |
In the beginning there was Flash. When you created a Flash project, you created an fla file. Then, when you were ready to publish your Flash to the web, you compiled your fla file into an swf file. However, after a few years people began to use ActionScript to enhance their Flash movies. At this point, the question was where to put the ActionScript. At first, programmers added their code inside the fla file. Now that Flash and ActionScript have grown up a little, most programmers find that it is more efficient to keep the ActionScript separate from, but part of, the Flash movie.
Add Code to the Timeline
The most basic method, and the method used most often in the past, was to combine ActionScript as an internal part of the Flash fla file. When writing ActionScript within the Flash movie, you can place the ActionScript on any frame of the timeline. Although there is no established rule about which frame to use, most programmers find it helpful to place their ActionScript code in the first frame on the timeline. To make things even easier, programmers usually create a special layer for their ActionScript, sometimes called the "Actions" layer.
This is the method that I use for most of my beginner's tutorials because it is less complicated than the other methods. For example, in a previous tutorial, we learned how to write ActionScript code that would draw a circle onto the stage.
Let's add this code to a new Flash movie. Start a new Flash project and name it RedCircle.fla.
Using an Include Statement
This second method of associating ActionScript with your Flash project is not much different from the method that we just discussed. Basically, we will move the ActionScript from the fla file to a separate file and add an include statement to our Flash movie which will tell Flash to read the ActionScript from that external file. | <urn:uuid:34813c42-555b-419b-82b8-8c4d522b211a> | 2.90625 | 450 | Truncated | Software Dev. | 57.32867 |
The chloroplast is the organelle in which photosynthesis takes place. Inside the chloroplast there are disk like structures called thylakoids arranged in stacks called granum. The light dependent reaction takes place across the membranes of the thylakoids while the Calvin Cycle takes place in the stroma, which is the semi liquid substance inside the chloroplast.
One of the key differences between plant and animal cells is that plant cells as you see here, have a specialized organelle inside of them called a chloroplast that name means itâs a [IB] which is a category of cell organelle that is green and that green color is key because it is what allows it to do photosynthesis, so the chloroplast is the organelle, and sometimes called of photosynthesis.
We zoom in closer on a chloroplast youâll see some basic structures that youâll find in every chloroplast and the first of which is its outer membrane. It actually has two membranes it has this outer membrane and then a nearly underneath it another membrane. This is evidence in part of how the chloroplast is developed through something called endosymbiosis probably about 500 million years ago give or take a few 100 million it used to be an independent organism but then it got eaten by a larger cell.
Once weâre through with that outer envelope, itâs sometimes called because it sounds cooler, youâre inside the chloroplast and youâll see a bunch of structures floating around in a watery liquid. That watery liquid is called the stroma. Thatâs very similar to the cytoplasm or cytosol of the larger outer cell that surround chloroplast.
Within the stroma youâll see these stacks of membrane discs. One individual stack is called a granum, collectively these stacks of discs are called grana. Now one disk within this granum is called a thylakoid, so the grana are made up of stacks of thylakoid membranes. The thylakoid membrane is the surface that has all the special molecules called chlorophyll and photosystems that allow for the absorption of light so that the plant organelle here, the chloroplast, can absorb that energy and then transfer it to enzymes that are floating around in the stroma those enzymes floating around the stroma then build glucose.
That process of absorbing light energy and then storing that energy in to glucose molecules is called photosynthesis thus the chloroplast is the organelle of photosynthesis. | <urn:uuid:b2f39c02-3a8d-4776-b423-48c30204fa2c> | 4.34375 | 522 | Knowledge Article | Science & Tech. | 31.441862 |
A Cube has 6 faces, all being squares of the same size.
It has 8 vertices (corners) and 12 edges.
It has 4 'space diagonals', all the same length.
A 'space diagonal' is a straight line joining two opposite vertices which do not belong to the same face. (If they do belong to the same face, it is a 'face diagonal'.)
With this shape it is only necessary to know one of its dimensions, and all the others can be derived from that.
Where (for brevity) it says 'edge', 'space diagonal' and so on, it should, more correctly, be something like 'size of edge' or 'edge-length' etc. | <urn:uuid:b224e844-9ceb-4b02-9a3e-8d0df9401729> | 3.578125 | 152 | Knowledge Article | Science & Tech. | 63.491667 |
What will happen after sun vaporizes Earth? Scorched planets hold clues.
Scientists say they've found two planets that survived being swallowed by a red-giant star. Earth won't be so fortunate when our sun becomes a red giant in 5 billion years, but the find shows what can happen to solar systems after such dramatic events.
Forget this season's final episode of "Survivor." The ultimate survivors appear to be two small planet-candidates engulfed for a billion years inside the searing envelope of a red-giant star. And they emerged to tell the tale.Skip to next paragraph
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The planets are a glimpse at what can happen to a solar system when a star begins its death throes, becoming bloated and red as it consumes the last of the hydrogen fuel in its core. The same fate awaits our sun in about 5 billion years.
The two planet-candidates announced Wednesday are among the tiniest yet revealed by data from NASA's planet-hunting Kepler spacecraft. And they hold the potential to shed light not only on how planets could survive such a torching, but also how they might affect the evolution of red-giant stars themselves.
"On many levels, it's very cool," says Elizabeth Green, a researcher with the University of Arizona's Steward Observatory and a member of the team reporting its observations in the Dec. 22 issue of the journal Nature.
A red giant originates as a star roughly like our sun – between 0.5 and 8 times the sun’s mass. As the star exhausts its hydrogen fuel, its core collapses. The heat of that event causes remaining hydrogen in the outer shell to begin fusion, and the star’s outer layer, or photosphere, expands.
By the time the red-giant phase of our sun ends, the Earth, Venus, and Mercury are likely to be vaporized. But scientists have examples of other objects – planets and brown-dwarf stars – that survived being enveloped by red-giant stars they orbited.
None of them, however, is like the ones reported Tuesday. All the previous examples were bigger objects that orbited farther from their parent stars to begin with. For that reason, they didn't spiral as deeply into their stars’ photospheres. When these stars’ red-giant phase ended – and the stars shrank back to become helium-burning so-called subdwarf B stars – the planets survived.
By contrast, the objects reported Tuesday appear to have traveled far deeper into the red-giant's photosphere and survived only as tiny remnants.
Indeed, the planet-candidates orbit so close to their subdwarf B star, named KIC 05807616, that their years are 5.8 hours and 8.2 hours long, respectively. With one side constantly facing the star, the planets’ sun-side faces would roast at between 14,000 and 16,000 degrees Fahrenheit.
So how did the planet-candidates survive such a blistering? The team suggests that the objects may represent the rocky cores of stripped-down gas-giant planets that once orbited farther away. | <urn:uuid:fcc053ca-c4b3-4eac-900d-342ef83749be> | 3.46875 | 662 | Truncated | Science & Tech. | 58.977177 |
M-theory, the theory formerly known as Strings
The Standard Model
In the standard model of particle physics, particles are considered to be points moving through space, tracing out a line called the World Line. To take into account the different interactions observed in Nature one has to provide particles with more degrees of freedom than only their position and velocity, such as mass, electric charge, color (which is the "charge" associated with the strong interaction) or spin.
The standard model was designed within a framework known as Quantum Field Theory (QFT), which gives us the tools to build theories consistent both with quantum mechanics and the special theory of relativity. With these tools, theories were built which describe with great success three of the four known interactions in Nature: Electromagnetism, and the Strong and Weak nuclear forces. Furthermore, a very successful unification between Electromagnetism and the Weak force was achieved (Electroweak Theory), and promising ideas put forward to try to include the Strong force. But unfortunately the fourth interaction, gravity, beautifully described by Einstein's General Relativity (GR), does not seem to fit into this scheme. Whenever one tries to apply the rules of QFT to GR one gets results which make no sense. For instance, the force between two gravitons (the particles that mediate gravitational interactions), becomes infinite and we do not know how to get rid of these infinities to get physically sensible results.
In String Theory, the myriad of particle types is replaced by a single fundamental building block, a `string'. These strings can be closed, like loops, or open, like a hair. As the string moves through time it traces out a tube or a sheet, according to whether it is closed or open. Furthermore, the string is free to vibrate, and different vibrational modes of the string represent the different particle types, since different modes are seen as different masses or spins.
One mode of vibration, or `note', makes the string appear as an
electron, another as a photon. There is even a mode describing the
graviton, the particle carrying the force of gravity, which is an
important reason why String Theory has received so much attention. The
point is that we can make sense of the interaction of two gravitons in
String theory in a way we could not in QFT. There are no infinities!
And gravity is not something we put in by hand. It has to be
there in a theory of strings. So, the first great achievement of
String Theory was to give a consistent theory of quantum gravity,
which resembles GR at macroscopic distances. Moreover String Theory
also possesses the necessary degrees of freedom to describe the other
interactions! At this point a great hope was created that String
Theory would be able to unify all the known forces and particles
together into a single `Theory of Everything'.
From Strings to Superstrings The particles known in
nature are classified according to their spin into bosons (integer
spin) or fermions (odd half integer spin). The former are the ones
that carry forces, for example, the photon, which carries
electromagnetic force, the gluon, which carries the strong nuclear
force, and the graviton, which carries gravitational force. The latter
make up the matter we are made of, like the electron or the quark.
The original String Theory only described particles that were bosons,
hence Bosonic String Theory. It did not describe Fermions. So quarks
and electrons, for instance, were not included in Bosonic String
By introducing Supersymmetry to Bosonic String Theory,
we can obtain a new theory that describes both the forces and the
matter which make up the Universe. This is the theory of
superstrings. There are three different superstring theories
which make sense, i.e. display no mathematical inconsistencies. In two
of them the fundamental object is a closed string, while in the third,
open strings are the building blocks. Furthermore, mixing the best
features of the bosonic string and the superstring, we can create two
other consistent theories of strings, Heterotic String Theories.
However, this abundance of theories of strings was a puzzle: If we are searching for the theory of everything, to have five of them is an embarrassment of riches! Fortunately, M-theory came to save us.
One of the most remarkable predictions of String Theory is that
space-time has ten dimensions! At first sight, this may be seen as a
reason to dismiss the theory altogether, as we obviously have only
three dimensions of space and one of time. However, if we assume that
six of these dimensions are curled up very tightly, then we may never
be aware of their existence. Furthermore, having these so-called
compact dimensions is very beneficial if String Theory is to describe
a Theory of Everything. The idea is that degrees of freedom like the
electric charge of an electron will then arise simply as motion in the
extra compact directions! The principle that compact dimensions may
lead to unifying theories is not new, but dates from the 1920's, since
the theory of Kaluza and Klein. In a sense, String Theory is the
ultimate Kaluza-Klein theory.
For simplicity, it is usually assumed that the extra dimensions are
wrapped up on six circles. For realistic results they are treated as
being wrapped up on mathematical elaborations known as Calabi-Yau
Manifolds and Orbifolds.
Apart from the fact that instead of one there are five different, healthy theories of strings (three superstrings and two heterotic strings) there was another difficulty in studying these theories: we did not have tools to explore the theory over all possible values of the parameters in the theory. Each theory was like a large planet of which we only knew a small island somewhere on the planet. But over the last four years, techniques were developed to explore the theories more thoroughly, in other words, to travel around the seas in each of those planets and find new islands. And only then it was realized that those five string theories are actually islands on the same planet, not different ones! Thus there is an underlying theory of which all string theories are only different aspects. This was called M-theory. The M might stand for Mother of all theories or Mystery, because the planet we call M-theory is still largely unexplored.
There is still a third possibility for the M in M-theory. One of the
islands that was found on the M-theory planet corresponds to a theory
that lives not in 10 but in 11 dimensions. This seems to be telling us
that M-theory should be viewed as an 11 dimensional theory that looks
10 dimensional at some points in its space of parameters. Such a
theory could have as a fundamental object a Membrane, as opposed to a
string. Like a drinking straw seen at a distance, the membranes would
look like strings when we curl the 11th dimension into a small circle.
Black Holes in M-theory
Black Holes have been studied for many years as configurations of
spacetime in General Relativity, corresponding to very strong
gravitational fields. But since we cannot build a consistent quantum
theory from GR, several puzzles were raised concerning the microscopic
physics of black holes. One of the most intriguing was related to
the entropy of Black Holes. In thermodynamics, entropy is the quantity
that measures the number of states of a system that look the same. A
very untidy room has a large entropy, since one can move something on
the floor from one side of the room to the other and no one will
notice because of the mess - they are equivalent states. In a very tidy
room, if you change anything it will be noticeable, since everything
has its own place. So we associate entropy to disorder. Black Holes
have a huge disorder. However, no one knew what the states associated
to the entropy of the black hole were. The last four years brought
great excitement in this area. Similar techniques to the ones used to
find the islands of M-theory, allowed us to explain exactly what
states correspond to the disorder of some black holes, and to explain
using fundamental theory the thermodynamic properties that had been
deduced previously using less direct arguments.
Many other problems are still open, but the application of string
theory to the study of Black Holes promises to be one of the most
interesting topics for the next few years.
[Back][Cosmology][Black holes][Cosmic strings][Inflation][Quantum Gravity][Home][Next] | <urn:uuid:994304b0-e95d-4056-af72-a9c2dbf05587> | 3.515625 | 1,823 | Knowledge Article | Science & Tech. | 42.268739 |
By PATRICK ROWAN
Asteroids and meteors and comets - oh my!
Recent stories almost make it seem like they're ganging up on us. Of course they are not, but a curious confluence of events makes it impossible to ignore these wild space beasts.
Soon after asteroid 2012 DA14 was discovered a year ago, it became apparent that it would make an unusually close approach to our world this February. And so it did on the 15th. At about 100 feet wide, it was not a huge asteroid … just big enough to destroy any city on Earth. We knew it would safely pass our planet, but close enough to make astronomers and others sit up and take notice.
Last year also brought the prospect that not one, but two bright comets might adorn our skies this year. Some - perhaps prematurely - began calling 2013 "the year of the comets." We have nothing to fear from these; just some great sky watching. Neither has any chance of colliding with Earth.
As if all this weren't enough, nature may have a real doozy in store for us - or more specifically for Mars. It now appears there is an outside chance that Comet Siding Spring (C/2013 A1) - discovered on Jan. 3 - could actually hit Mars late next year.
These stories alone made the start of this year noteworthy, but it was the Great Russian Meteor of 2013 that really caught the attention of the world.
About 16 hours before asteroid 2012 DA14's closest approach to Earth, a previously undetected, and totally unrelated asteroid sliced into Earth's atmosphere and lit up the dawn skies above Chelyabinsk and surrounding regions of Russia.
With roughly half the diameter of 2012 DA14, this 10,000-ton rock became the biggest space object to enter Earth's atmosphere since the half-million ton beast that came in over the Tunguska River valley in 1908.
The Tunguska airburst happened about 5 miles up and flattened 800 square miles of Siberian forest. This year's meteor (which is what the asteroid became on entering our atmosphere) exploded about 9 to 20 miles up. It delivered only around 5 percent the force of the Tunguska blast, but the resulting shock waves (which reached ground several minutes after the air explosion) damaged structures, broke countless windows, and injured about 1500 people.
Nuclear weapons monitoring stations as far away as Antarctica detected low-frequency sound waves from the blast.
Numerous automobile dashboard cameras captured the fireball as it grew in apparent size and brightness. For a moment, it outshone the sun. Some of these surreal videos were quickly uploaded to YouTube, and became an overnight sensation.
The sun had just come up here in the Pioneer Valley as I played a few of the videos for my wife Clara. Their impact was immediate, although, paradoxically, they also took a short while to really "sink in." With each look, the scenes became more compelling. "This is going to be big news" I said.
The first view was out of a car windshield as it headed east on some unnamed highway in a faraway place that I would not likely otherwise ever see. Literally out of the blue, a brilliant fireball splits the frosty dawn sky, and the driver says something that sounds like "weird" against the background of some Russian radio station.
I was struck by the object's apparent speed, which quickly convinced me that this was not a re-entering satellite or other man-made debris. Its actual speed was close to 40,000 miles per hour, more than twice a satellite's orbital velocity.
In another video we see the aftermath, the massive double-barreled smoke train nearly overhead left in the meteor's wake. The cameraman pans back and forth across the bizarre cloud, also seen through a window, but this time from an apparent residence several stories up among a cluster of similar-looking buildings.
The perplexed utterings of the cameraman are interrupted by an ear-splitting "bang" followed by the sound of shattering glass and triggered alarms. Birds scatter. Other excited voices join in as several more loud "booms" echo through the housing complex.
Yet another video captures the chaos in a school yard, flashing past the panicked faces of screaming students as it swings wildly skyward to the smoke train, and back down again.
Shots in other videos of people scattering beneath shattering windows made it seem likely there would be injuries.
We were seeing these videos as the sun rose for us here, just nine hours after the event itself had taken place, at about the time of their local sunrise. We knew it was still daylight there and the population was still grappling with the circumstances, giving us an intimate, candid look into this foreign culture.
In some videos, there appeared to be a curious lack of response to the event. Traffic continued flowing without interruption, and pedestrians seemed not to break stride as the sky lit up.
Almost as captivating as the meteor itself were the shadows shifting across the ground as the fireball (usually out of frame) flared and then dimmed.
These videos and more can be found at: http://say26.com/meteorite-in-russia-all-videos-in-one-place. Also check: http://www.youtube.com/user/TvoyaUlubka/videos?annotation_id=annotation_751404&feature=iv&src_vid=25znynpQz9E
The numerous videos and a hole in the ice on Lake Chebarkul allowed scientists to accurately trace the meteor's trajectory. Divers have not found a meteorite under that holel, but fragments have been recovered around it and beneath the meteor's track.
The meteor came in at a shallow angle - around 20 degrees. A steeper dive could have left far more than broken glass.
The Chelyabinsk meteor is now a part of history.
Comet PanSTARRS (C/2011 L4) was discovered in June 2011 with the Pan-STARRS telescope in Hawaii (whose primary mission is to hunt for potentially hazardous asteroids, by the way). While still a dim and distant telescopic object, the comet brightened at a rate indicating it could become easily visible to the naked eye this month.
That brightening has slowed however, and Comet PanSTARRS now looks destined to be a more difficult sight than hoped for. Still, you might try to catch it low in the west next to the crescent moon around dusk on the evening of March 12. After that, the waxing moon will climb higher and brighten, complicating viewing efforts, but the comet will remain there for the next few weeks. Try looking about 30 minutes after sunset. Clear skies and an unobstructed view to the horizon are crucial, and binoculars may be necessary.
Much more promising is C/2012 S1, better known as Comet Ison, discovered in September. NASA says it could "blossom into a striking naked eye object visible even in broad daylight" this coming November, but difficult to observe near the sun.
The better view might come in December after it rounds the sun's far side. It could display a long tail, or break into pieces, giving us a spectacular string of fragments with tails, reminiscent of the famous Comet Shoemaker-Levy 9 that hit Jupiter in 1994. It's simply too early to know for sure.
Perhaps more exciting is the outside chance that Comet Siding Spring (C/2013 A1) could actually hit Mars late next year. That would be a monumental event. The odds of a direct strike are low, although the possibility has yet to be ruled out.
Billionaire Dennis Tito may have to put his recently announced plans to fly a married couple past the red planet in 2018 on hold. Our Curiosity and Opportunity rovers, and the three satellites currently in Mars orbit, probably would not fare so well. A direct hit to Mars could yield an explosion equivalent to millions of the largest nuclear weapons ever exploded on Earth.
If the comet misses Mars - as it likely will - it may still come almost as close to Mars as Asteroid 2012 DA14 came to Earth last month. An asteroid is a big rock, so a miss is as good as a mile. A comet, however, has debris scattered all around it, so a near-miss might actually amount to a partial hit.
As with the previously mentioned comets, this one presents absolutely no danger to Earth.
Coincidentally, it was 20 years ago this month (March 1993) that Carol and Eugene Shoemaker, and David Levy - while searching for Near-Earth asteroids - found an unusual comet in a photograph taken at the Palomar Observatory in California.
Comet Shoemaker–Levy 9 was already broken into fragments by the strong pull of Jupiter's gravity, and for six days in July, one after another they pummeled that world. Backyard astronomers with modest telescopes, including this observer, had little difficulty seeing the black marks left on Jupiter's cloud tops.
Follow ever-changing celestial highlights in the Skywatch section of the Weather Almanac in the Daily Republican and Sunday Republican.
Patrick Rowan has written Skywatch for The Republican since 1987 and has been a Weather Almanac contributor since the mid 1990s. A native of Long Island, Rowan graduated from Northampton High School, studied astronomy at the University of Massachusetts-Amherst in the '70s and was a research assistant for the Five College Radio Astronomy Observatory. From 1981 to 1994, Rowan worked at the Springfield Science Museum's Seymour Planetarium, most of that time as planetarium manager. Rowan lives in the Florence section of Northampton with his wife, Clara, and cat, Luna. | <urn:uuid:c10beb6d-a62b-4776-bdc3-64afeead0847> | 3.3125 | 2,021 | Nonfiction Writing | Science & Tech. | 51.479699 |
Summary: Tomaso Aste and Tiziana Di Matteo
In the year 2000, exactly one hundred years after David Hilbert posed
his now famous list of 23 open problems, The Clay Mathematics Insti-
tute (CMI) announced its seven Millennium Problems. (http://www.
claymath.org/millennium). The Gazette has asked leading Australian
mathematicians to put forth their own favourite `Millennium Problem'.
Due to the Gazette's limited budget, we are unfortunately not in a posi-
tion to back these up with seven-figure prize monies, and have decided on
the more modest 10 Australian dollars instead.
In this final instalment, Tomaso Aste and Tiziana Di Matteo will explain
their favourite open problem that should have made it to the list.
In this note we describe our favourite problem in discrete geometry: how many equal spheres
can be packed inside a larger sphere?
This problem is related with the long standing `greengrocers dilemma': which is the most
space-efficient way of placing vegetables in a market stand? Such a dilemma might have
intrigued a few greengrocers (Fig. 1) but it has certainly attracted several mathematicians
becoming one of the best-known problems in discrete geometry. This problem is often
referred as the Kepler conjecture and it was included at the 18th place in the Hilbert's list.
Figure 1. The greengrocers dilemma: which is the most space-efficient way of
placing vegetables on a market stand? | <urn:uuid:6744ad8e-e490-4850-8ac2-136b72689cd4> | 2.734375 | 327 | Knowledge Article | Science & Tech. | 43.788276 |
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Visit this interactive site to explore the orbits of planets and their moons in our solar system and also in a wide selection of extrasolar planetary systems.
Planetary exploration vessels like Voyager I and Voyager II made use of propulsion maneuvers which gained energy from the planets and moons they passed.
A really interesting data visualisation of all the planets Kepler has found, complete with information about their size, temperature, and distance and period of orbit.
Shows cannonball projected off mountain. Different speeds produce different results. I particularly liked the "touch" when the ball completed an orbit and returned to where it left the mountain!
A relatively basic animation that allows you to view the entire Solar system, or just the inner planets (through the orbit of Mars).
Description of calculation to find an escape velocity such as for an object launched from earth to avoid orbit.
What shape is the Earth's orbit? How doe seasons work? Test your knowledge in this quiz aimed at revealing common misconceptions.
Pierre-Simon Laplace (1749 - 1817) was a French mathematician, astronomer, and physicist who is best known for his investigations into the solar system in particular the orbits of planets.
Doppler studies of this blue supergiant in Cygnus indicate a period of 5.6 days in orbit around an unseen companion. The mass of the companion is calculated to be 8-10 solar masses, much too large to ...
Use this site to find the velocity for a body to escape orbit.
Showing 21 - 30 of 38 | <urn:uuid:82540d37-5465-4dbf-a4ee-68ade3a0e802> | 3.109375 | 407 | Content Listing | Science & Tech. | 52.17323 |
Why do stars twinkle?
If you've ever watched the stars at night they twinkle.
The famous nursey rhyme, "Twinkle, twinkle little star" is based upon this very observation.
If however, you travel to the moon and observe the stars from there they would not twinkle.
Why do stars twinkle on Earth, but not on the moon? Any guesses?
Stars twinkle on Earth because the atmosphere consists of moving pockets of warm and cold air.
These pockets of air have different densities which bend the light in various directions. This creates a twinkle.
On the moon to here is no atmosphere or air to distort the light. Stars seen from the moon therefore, should not twinkle.
Did you know that?
- Stars change colour on twinkling. eg. from blue, red and yellow. This happens because the light from stars is composed of different colours which are bent in various directions by the atmosphere. See image above. This is why stars change colour on twinkling.
- Stars twinkle more near the horizon because there is a lot more air or atmosphere in this direction then directly above us.
- Planets do not twinkle. The light from stars comes to us as a single point source. The reflected light from a planet comes from numerous points in the sky due to the planets close distance. Any bending caused by atmospheric disturbances are averaged out. This produces a relatively clear image.
- The Hubble telescope has taken some very clear pictures of stars because there is no atmopshere in outer space to distort the image.
- The scientific term used to explain why stars twinkle is called "stellar scintillation"
Twinkle, Twinkle Little Star, played by Robot
Kindergarden - Junior school | <urn:uuid:a1625210-bf3d-4d12-b30a-55fca9eb2ae6> | 3.359375 | 370 | Knowledge Article | Science & Tech. | 58.741702 |
Summary: The Law of Demeter is discussed using Java source code examples.
Whenever you talk to a good, experienced programmer, they will tell you that "loosely coupled" classes are very important to good software design.
The Law of Demeter for functions (or methods, in Java) attempts to minimize coupling between classes in any program. In short, the intent of this "law" is to prevent you from reaching into an object to gain access to a third object's methods. The Law of Demeter is often described this way: | <urn:uuid:6a18e320-5c01-4954-99d4-aa8690e4dd1d> | 2.875 | 111 | Knowledge Article | Software Dev. | 46.068636 |
Ingersoll, Andrew P. and Summers, Michael E. and Schlipf, Steve G. (1985) Supersonic Meteorology of Io: Sublimation-Driven Flow of SO_2. Icarus, 64 (3). pp. 375-390. ISSN 0019-1035 http://resolver.caltech.edu/CaltechAUTHORS:20121205-141815339
Full text not available from this repository.
Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20121205-141815339
The horizontal flow of SO_2 gas from day side to night side of Io is calculated. The surface is assumed to be covered by a frost whose vapor pressure at the subsolar point is orders of magnitude larger than that on the night side. Temperature of the frost is controlled by radiation. The flow is hydrostatic and turbulent, with velocity and entropy per particle independent of height. The vertically integrated conservation equations for mass, momentum, and energy are solved for atmospheric pressure, temperature, and horizontal velocity as functions of solar zenith angle. Formulas from boundary layer theory govern the interaction between atmosphere and surface. The flow becomes supersonic as it expands away from the subsolar point, as in the theory of rocket nozzles and the solar wind. Within 35° of the subsolar point atmospheric pressure is less than the frost vapor pressure, and the frost sublimes. Elsewhere, atmospheric pressure is greater than the frost vapor pressure, and the frost condenses. The two pressures seldom differ by more than a factor of 2. The sublimation rate at the subsolar point is proportional to the frost vapor pressure, which is a sensitive function of temperature. For a subsolar temperature of 130°K, the sublimation rate is 10^(15) molecules/cm^2/sec. Diurnally averaged sublimation rates at the equator are comparable to the 0.1 cm/year resurfacing rate required for burial of impact craters. At the poles where both the vapor pressures and atmospheric pressures are low, the condensation rates are 100 times smaller. Surface pressures near the terminator are generally too low to account for the ionosphere discovered by Pioneer 10. The possibility of a noncondensable gas in addition to SO_2 must be seriously considered.
|Additional Information:||© 1985 Academic Press, Inc. Received August 19, 1985; revised November 4, 1985. This research was supported by the Planetary Atmospheres Program and the Planetary Astronomy Program of NASA.|
|Official Citation:||Andrew P. Ingersoll, Michael E. Summers, Steve G. Schlipf, Supersonic meteorology of Io: Sublimation-driven flow of SO2, Icarus, Volume 64, Issue 3, December 1985, Pages 375-390, ISSN 0019-1035, 10.1016/0019-1035(85)90062-4. (http://www.sciencedirect.com/science/article/pii/0019103585900624)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||05 Dec 2012 22:36|
|Last Modified:||05 Dec 2012 22:36|
Repository Staff Only: item control page | <urn:uuid:4c54ef7d-2c3b-4f60-bfb1-4c2e5ac4befd> | 2.734375 | 725 | Academic Writing | Science & Tech. | 47.519542 |
Surprisingly, you may find some wasps at your porch light after dark. Among the more common nocturnal hymenopterans are ichneumon wasps in the subfamily Ophioninae. They are large, gangly wasps, usually uniformly orange in color with long antennae and large ocelli (“simple eyes” arranged in a triangle at the crown of the head, between the compound eyes). The ovipositor is very short, if it is even evident at all.
If you see a slightly smaller orange ichneumon with a longer ovipositor, it is likely to be a wasp in the genus Netelia, in the subfamily Tryphoninae. There are currently 73 species in six subgenera in North America north of Mexico (Carlson, 2009).
Unlike many ichneumon wasps, the females of Netelia can sting painfully if handled carelessly. The sting is mostly used to temporarily paralyze the large caterpillar hosts of these parasites. The female then lays an egg on the stunned victim, puncturing the body wall of the caterpillar in doing so. The egg is stalked, and in newly deposited eggs the coil of the stalk is elastic. It later becomes rigid. The egg holds firmly to the flexible exoskeleton of the host larva by means of a plug or anchor.
The larval wasp that hatches from the egg remains attached to it via specialized bristles on its posterior end. The wasp larva feeds on the caterpillar as an external parasite. Parasites that do not arrest the development of their host, but allow it to grow normally instead, are called “koinobionts.” Netelia ichneumons are placed in this category. | <urn:uuid:5990866f-6fea-4e70-b02f-8d5dec187b68> | 3.421875 | 369 | Personal Blog | Science & Tech. | 42.399267 |
Q: What is trigonometry?
A: Trigonometry is the study of how the sides and angles of a triangle are related to each other.
Q: WHAT? That’s all?
A: Yes, that’s all. It’s all about triangles, and you can’t get much simpler than that.
Q: You mean trigonometry isn’t some big, ugly monster that
makes students turn green, scream, and die?
A: No. It’s just triangles.
Q: Oh. But isn’t that boring?
A: We’ll try to make it a little more fun by letting you play around with the triangles interactively.
Let’s start. Click on a topic to go to that page. If this is your first visit to these pages, we recommend that you start with the first item in the list.
This material assumes that you know:
If you aren’t familiar with these concepts, you’ll have to ask your math teacher to assist you with them.
Download the .ZIPped source files. | <urn:uuid:9ff41880-5bb1-4f01-807d-cb8ee846313a> | 3.1875 | 240 | Truncated | Science & Tech. | 87.092691 |
Today I want to write about some design patterns. There are really many out there and I want to summarize them a bit for you.
I will not write about design patterns of a specific language but for general. Many of them are really usefull!
Don’t you have sometimes the problem that you don’t know how to begin when you are programming a class or so?
You are thinking and thinking of how you could design the class or class hierachy (Polymorphism) that it is easy to understand, lightweight, not so much time consuming to implement it and so on…
Then after hours of thinking you have a solution but you are never sure if it’s really okay like that. You just implement the class and if something does not fit you have to change it.
But now think of it, is that really reasonable? You put so much time into designing a class or class hierachy but for what? That you can change everything in let’s say 200 files where you used that class? That shouldn’t be!
As an example we take a communication with a database. The standard in PHP is to use MySQL, that’s okay but what happens if you want to use PostgresSQL now? You maybe will have to change every query statement because it can be case that in this dialect something is written different than in the other. So it’s hard for use to change the database system just by replacing the connect call to a new one. We not only have the problem with the SQL statements, but you have to change the calls of the SQL statements too.
Here you can see a PHP example to know what I mean by that.
// Using PostgresSQL $conString= "host=localhost port=5432 ". "dbname=DATABASE ". "user=USERNAME ". "password=PASSWORD"; $connection = pg_connect($conString); $sql = "SELECT field FROM table WHERE field = '$something' "; $result = pg_query($connection, $sql); $fetch = pg_fetch_row($result); pg_close($connection); // ------------------- // Using MySQL $connection = mysql_connect("localhost", "USERNAME", "PASSWORD"); mysql_select_db ("DATABASE", $connection); $sql = "SELECT field FROM table WHERE field = '$something' "; $result = mysql_query($sql, $connection); $fetch = mysql_fetch_row($result); mysql_close($connection);
Here we don’t have a problem with the SQL statement, but what happens if you use the function mysql_query for about 500 times in 200 different files? Try to change that! Somebody will probably say now that there are tools which you can use to make such mass operations, but that’s not the point! What do you want to do now if we have a SQL statement that is not compatible to other SQL systems? You have to change nearly everything in your application to correct that. It’s really time consuming, so we should try to get to find a solution.
First of all think about something like a DAO class. DAO (Data Access Object) is really nice and saves you a lot of time. In a DAO class you make methods which give you back objects as result. Let’s say you have something like showing news on a website. Then make a method getNews() and just use that method everywhere you need the news. You can define parameters for that method and so on but you always get let’s say an array of news objects from that method. That’s really nice because you don’t have to think about what the name of the column was and so on, your IDE will suggest the methods and variables. This kind of system is very simmilar in some points to an ORM (Object Relation Mapping) system which don’t has any foreign keys but the objects which is related to the foreign keys. Of course you still have to implement data classes for each table but this will help you a lot.
So now we have a DAO object which handles the connection to the database and provides methods which give us arrays of objects but we still have the compability problem to other systems, for this I suggest to use PDO (PHP Data Object) in PHP. In Java we have JDBC, in .NET Linq and so on. With PDO you have only one class which uses drivers to communicate with the database systems, you only have methods like query() and fetch() so we don’t have to rename the calls any more.
// Using PDO $connectionString = "mysql:host=localhost;dbname=DATABASE"; $user = "USERNAME"; $pass = "PASSWORD"; $pdo = new PDO($connectionString, $user, $pass); $sql = "SELECT field FROM table WHERE field = '$something' "; $stmt= $pdo->query($sql); $fetch = $stmt->fetch(PDO::FETCH_NUM); $stmt->closeCursor();
As you can see, it’s easy and the best is, if you change the database system, you just have to change the connection string!
I hope you enjoyed this article and you will go on reading my texts about design patterns! | <urn:uuid:e1b71f12-9345-42bd-a0e9-0bd064ef4db3> | 3.03125 | 1,142 | Personal Blog | Software Dev. | 60.031098 |
The Earth is a spinning globe where a point at the equator is travelling at around 1100 km/hour, but a point at the poles is not moved by the rotation. This fact means that projectiles moving across the Earth's surface are subject to Coriolis forces that cause apparent deflection of the motion.
|The Coriolis force deflects to the right in the Northern hemisphere and to the left in the Southern hemisphere when viewed along the line of motion.|
If solar heating were the only thing influencing the weather, we would then expect the prevailing winds along the Earth's surface to either be from the North or the South, depending on the latitude. However, the Coriolis force deflects these wind flows to the right in the Northern hemisphere and to the left in the Southern hemisphere. This produces the prevailing surface winds illustrated in the adjacent figure.
example, between 30 degrees and 60 degrees North latitude the solar convection
pattern would produce a prevailing surface wind from the South. However, the
Coriolis force deflects this flow to the right and the prevailing winds at
these latitudes are more from the West and Southwest. They are called the
Realistic Weather Patterns
The adjacent animation shows
GOES-8 weather satellite
images over a 72-hour period from Dec. 29, 1996, through Jan. 1, 1997. This is
a geosynchrous satellite, which means that it orbits the Earth with the same
period as the Earth's rotation and therefore appears to be essentially
motionless over a fixed position on the Earth's surface. For GOES-8 this fixed
position looks down on North and South America.
In these composite images red indicates visible light (reflected sunlight), green indicates the 11 micron IR channel (thermal emission), and blue indicates the 3.9 micron channel (thermal + sunlight). At night the images are blue and green. The three periods of daylight in this 72 hour sequence are clearly visible as red-orange regions moving from East to West (right to left). In the IR channels, the natural intensity pattern has been inverted: warmer is darker, so that cool cloudtops stand out brightly.
One can see clearly the pronounced cloud flows associated with the strong westerlies at mid-latitudes in each hemisphere. (This is taken in Northern hemisphere Winter, so the heavier cloud cover in that hemisphere is not surprising.) Less obvious are the easterly trade winds and the polar easterlies, though one can see vestiges of each if one looks carefully. Also apparent are the swirling motions associated with frontal systems. These are particularly pronounced at the boundaries between the mid-latitude westerly and polar wind flows in each hemisphere.
Here is a similar weather animation (1.49 MB animated GIF) using GOES-8/9 IR images for North America over a 2 day period from December 31, 1996 through January 1, 1997. The large weather systems that move ashore from the Pacific in this animation produced catastrophic flooding in California, Oregon, and Washington in early January, 1997.
|Low pressure systems (left) and high pressure systems (right) in the Northern hemisphere|
Here is a pronounced example of a cyclone: a movie of Hurricane Andrew (653 kB). This animation is a loop of infrared satellite images showing the path of Hurricane Andrew across Florida and into Louisiana from Sunday, August 23 through Thursday, August 27, 1992 (Credit: Nathan Gasser). | <urn:uuid:4711a00d-7e69-4b25-a604-10e019bab67e> | 4.21875 | 709 | Knowledge Article | Science & Tech. | 46.077405 |
In engineering mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element.
The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically 1/10 or less, of the other two. When the length is considerably longer than the width and the thickness, the element is called a beam. For example, a closet rod sagging under the weight of clothes on clothes hangers is an example of a beam experiencing bending. On the other hand, a shell is a structure of any geometric form where the length and the width are of the same order of magnitude but the thickness of the structure (known as the 'wall') is considerably smaller. A large diameter, but thin-walled, short tube supported at its ends and loaded laterally is an example of a shell experiencing bending.
In the absence of a qualifier, the term bending is ambiguous because bending can occur locally in all objects. To make the usage of the term more precise, engineers refer to the bending of rods, the bending of beams, the bending of plates, the bending of shells and so on.
Quasistatic bending of beams
A beam deforms and stresses develop inside it when a transverse load is applied on it. In the quasistatic case, the amount of bending deflection and the stresses that develop are assumed not to change over time. In a horizontal beam supported at the ends and loaded downwards in the middle, the material at the over-side of the beam is compressed while the material at the underside is stretched. There are two forms of internal stresses caused by lateral loads:
- Shear stress parallel to the lateral loading plus complementary shear stress on planes perpendicular to the load direction;
- Direct compressive stress in the upper region of the beam, and direct tensile stress in the lower region of the beam.
These last two forces form a couple or moment as they are equal in magnitude and opposite in direction. This bending moment resists the sagging deformation characteristic of a beam experiencing bending. The stress distribution in a beam can be predicted quite accurately even when some simplifying assumptions are used.
Euler-Bernoulli bending theory
In the Euler-Bernoulli theory of slender beams, a major assumption is that 'plane sections remain plane'. In other words, any deformation due to shear across the section is not accounted for (no shear deformation). Also, this linear distribution is only applicable if the maximum stress is less than the yield stress of the material. For stresses that exceed yield, refer to article plastic bending. At yield, the maximum stress experienced in the section (at the furthest points from the neutral axis of the beam) is defined as the flexural strength.
The Euler-Bernoulli equation for the quasistatic bending of slender, isotropic, homogeneous beams of constant cross-section under an applied transverse load is
After a solution for the displacement of the beam has been obtained, the bending moment () and shear force () in the beam can be calculated using the relations
Simple beam bending is often analyzed with the Euler-Bernoulli beam equation. The conditions for using simple bending theory are:
- The beam is subject to pure bending. This means that the shear force is zero, and that no torsional or axial loads are present.
- The material is isotropic and homogeneous.
- The material obeys Hooke's law (it is linearly elastic and will not deform plastically).
- The beam is initially straight with a cross section that is constant throughout the beam length.
- The beam has an axis of symmetry in the plane of bending.
- The proportions of the beam are such that it would fail by bending rather than by crushing, wrinkling or sideways buckling.
- Cross-sections of the beam remain plane during bending.
Compressive and tensile forces develop in the direction of the beam axis under bending loads. These forces induce stresses on the beam. The maximum compressive stress is found at the uppermost edge of the beam while the maximum tensile stress is located at the lower edge of the beam. Since the stresses between these two opposing maxima vary linearly, there therefore exists a point on the linear path between them where there is no bending stress. The locus of these points is the neutral axis. Because of this area with no stress and the adjacent areas with low stress, using uniform cross section beams in bending is not a particularly efficient means of supporting a load as it does not use the full capacity of the beam until it is on the brink of collapse. Wide-flange beams (I-beams) and truss girders effectively address this inefficiency as they minimize the amount of material in this under-stressed region.
The classic formula for determining the bending stress in a beam under simple bending is:
- is the bending stress
- M - the moment about the neutral axis
- y - the perpendicular distance to the neutral axis
- Ix - the second moment of area about the neutral axis x.
Extensions of Euler-Bernoulli beam bending theory
Plastic bending
The equation is valid only when the stress at the extreme fiber (i.e., the portion of the beam farthest from the neutral axis) is below the yield stress of the material from which it is constructed. At higher loadings the stress distribution becomes non-linear, and ductile materials will eventually enter a plastic hinge state where the magnitude of the stress is equal to the yield stress everywhere in the beam, with a discontinuity at the neutral axis where the stress changes from tensile to compressive. This plastic hinge state is typically used as a limit state in the design of steel structures.
Complex or asymmetrical bending
The equation above is only valid if the cross-section is symmetrical. For homogeneous beams with asymmetrical sections, the axial stress in the beam is given by
where are the coordinates of a point on the cross section at which the stress is to be determined as shown to the right, and are the bending moments about the y and z centroid axes, and are the second moments of area (distinct from moments of inertia) about the y and z axes, and is the product of moments of area. Using this equation it is possible to calculate the bending stress at any point on the beam cross section regardless of moment orientation or cross-sectional shape. Note that do not change from one point to another on the cross section.
Large bending deformation
For large deformations of the body, the stress in the cross-section is calculated using an extended version of this formula. First the following assumptions must be made:
- Assumption of flat sections - before and after deformation the considered section of body remains flat (i.e., is not swirled).
- Shear and normal stresses in this section that are perpendicular to the normal vector of cross section have no influence on normal stresses that are parallel to this section.
Large bending considerations should be implemented when the bending radius is smaller than ten section heights h:
With those assumptions the stress in large bending is calculated as:
- is the normal force
- is the section area
- is the bending moment
- is the local bending radius (the radius of bending at the current section)
- is the area moment of inertia along the x-axis, at the place (see Steiner's theorem)
- is the position along y-axis on the section area in which the stress is calculated.
When bending radius approaches infinity and , the original formula is back:
Timoshenko bending theory
In 1921, Timoshenko improved upon the Euler-Bernoulli theory of beams by adding the effect of shear into the beam equation. The kinematic assumptions of the Timoshenko theory are:
- normals to the axis of the beam remain straight after deformation
- there is no change in beam thickness after deformation
However, normals to the axis are not required to remain perpendicular to the axis after deformation.
The equation for the quasistatic bending of a linear elastic, isotropic, homogeneous beam of constant cross-section beam under these assumptions is
where is the area moment of inertia of the cross-section, is the cross-sectional area, is the shear modulus, and is a shear correction factor. For materials with Poisson's ratios () close to 0.3, the shear correction factor for a rectangular cross-section is approximately
The rotation () of the normal is described by the equation
The bending moment () and the shear force () are given by
Dynamic bending of beams
The dynamic bending of beams, also known as flexural vibrations of beams, was first investigated by Daniel Bernoulli in the late 18th century. Bernoulli's equation of motion of a vibrating beam tended to overestimate the natural frequencies of beams and was improved marginally by Rayleigh in 1877 by the addition of a mid-plane rotation. In 1921 Stephen Timoshenko improved the theory further by incorporating the effect of shear on the dynamic response of bending beams. This allowed the theory to be used for problems involving high frequencies of vibration where the dynamic Euler-Bernoulli theory is inadequate. The Euler-Bernoulli and Timoshenko theories for the dynamic bending of beams continue to be used widely by engineers.
Euler-Bernoulli theory
The Euler-Bernoulli equation for the dynamic bending of slender, isotropic, homogeneous beams of constant cross-section under an applied transverse load is
where is the Young's modulus, is the area moment of inertia of the cross-section, is the deflection of the neutral axis of the beam, and is mass per unit length of the beam.
Free vibrations
For the situation where there is no transverse load on the beam, the bending equation takes the form
Free, harmonic vibrations of the beam can then be expressed as
and the bending equation can be written as
The general solution of the above equation is
where are constants and
|The mode shapes of a cantilevered I-beam|
Timoshenko-Rayleigh theory
In 1877, Rayleigh proposed an improvement to the dynamic Euler-Bernoulli beam theory by including the effect of rotational inertia of the cross-section of the beam. Timoshenko improved upon that theory in 1922 by adding the effect of shear into the beam equation. Shear deformations of the normal to the mid-surface of the beam are allowed in the Timoshenko-Rayleigh theory.
where is the polar moment of inertia of the cross-section, is the mass per unit length of the beam, is the density of the beam, is the cross-sectional area, is the shear modulus, and is a shear correction factor. For materials with Poisson's ratios () close to 0.3, the shear correction factor are approximately
Free vibrations
For free, harmonic vibrations the Timoshenko-Rayleigh equations take the form
This equation can be solved by noting that all the derivatives of must have the same form to cancel out and hence as solution of the form may be expected. This observation leads to the characteristic equation
The solutions of this quartic equation are
The general solution of the Timoshenko-Rayleigh beam equation for free vibrations can then be written as
Quasistatic bending of plates
The defining feature of beams is that one of the dimensions is much larger than the other two. A structure is called a plate when it is flat and one of its dimensions is much smaller than the other two. There are several theories that attempt to describe the deformation and stress in a plate under applied loads two of which have been used widely. These are
- the Kirchhoff-Love theory of plates (also called classical plate theory)
- the Mindlin-Reissner plate theory (also called the first-order shear theory of plates)
Kirchhoff-Love theory of plates
The assumptions of Kirchhoff-Love theory are
- straight lines normal to the mid-surface remain straight after deformation
- straight lines normal to the mid-surface remain normal to the mid-surface after deformation
- the thickness of the plate does not change during a deformation.
These assumptions imply that
where is the displacement of a point in the plate and is the displacement of the mid-surface.
The strain-displacement relations are
The equilibrium equations are
where is an applied load normal to the surface of the plate.
In terms of displacements, the equilibrium equations for an isotropic, linear elastic plate in the absence of external load can be written as
In direct tensor notation,
Mindlin-Reissner theory of plates
The special assumption of this theory is that normals to the mid-surface remain straight and inextensible but not necessarily normal to the mid-surface after deformation. The displacements of the plate are given by
where are the rotations of the normal.
The strain-displacement relations that result from these assumptions are
where is a shear correction factor.
The equilibrium equations are
Dynamic bending of plates
Dynamics of thin Kirchhoff plates
The dynamic theory of plates determines the propagation of waves in the plates, and the study of standing waves and vibration modes. The equations that govern the dynamic bending of Kirchhoff plates are
where, for a plate with density ,
The figures below show some vibrational modes of a circular plate.
See also
- Bending Machine (flat metal bending)
- Brake (sheet metal bending)
- Bending of plates
- Bending (metalworking)
- Flexure bearing
- List of area moments of inertia
- Shear strength
- Sandwich theory
- Vibration of plates
- Brazier effect
- Boresi, A. P. and Schmidt, R. J. and Sidebottom, O. M., 1993, Advanced mechanics of materials, John Wiley and Sons, New York.
- Libai, A. and Simmonds, J. G., 1998, The nonlinear theory of elastic shells, Cambridge University Press.
- Timoshenko, S. and Woinowsky-Krieger, S., 1959, Theory of plates and shells, McGraw-Hill.
- Shigley J, "Mechanical Engineering Design", p44, International Edition, pub McGraw Hill, 1986, ISBN 0-07-100292-8
- Gere, J. M. and Timoshenko, S.P., 1997, Mechanics of Materials, PWS Publishing Company.
- Cook and Young, 1995, Advanced Mechanics of Materials, Macmillan Publishing Company: New York
- Thomson, W. T., 1981, Theory of Vibration with Applications
- Han, S. M, Benaroya, H. and Wei, T., 1999, "Dynamics of transversely vibrating beams using four engineering theories," Journal of Sound and Vibration, vol. 226, no. 5, pp. 935-988.
- Rosinger, H. E. and Ritchie, I. G., 1977, On Timoshenko's correction for shear in vibrating isotropic beams, J. Phys. D: Appl. Phys., vol. 10, pp. 1461-1466. | <urn:uuid:9c31101f-45c1-4865-98f7-4264b2498322> | 3.890625 | 3,232 | Knowledge Article | Science & Tech. | 43.84032 |
Humans have had more of an impact on climate change over the last 40 years than they have had over the last 150 years. This is primarily due to the sharp increase in Greenhouse Gas concentrations over the last 40 or so years. This means that not all
of the warming over the last 40 years can be ascribed to natural causes.
With this in mind, we can start with Borie and Thoyaib 2006.
The abstract reads:Data for geomagnetic activity index aa and solar sunspot number Rz for 1868-2004 were subjected to
correlation analysis with the global surface temperature (GST). The annual-means GT show that it had
two warming phases and one cooling period. Observations of the Earth's near-surface temperature
showed a global-mean temperature increase of approximately 1.1° C since 1877, occurred from 1887 to
1940 and from 1970 to the 1998. The temperature change over the past 35 years (1970-2004) is unlikely
to be entirely due to internal climate variability. Attribution of the warming early in the century has
proved more elusive. The correlation analysis between the variation of global temperature and both aa
geomagnetics and solar activity are +0.5 ± 0.05, for any lag or lead, indicating a significant role in such
variation. All graphs have illustrated strong correlations between the solar activity and geomagnetics
and surface global temperature. Our results do not, by any means, rule out the existence of important
links between solar activity and terrestrial climate. Our results displayed that the present changes in aa
geomagnetics may reflect partially some future changes in the global surface temperatures.
From the conclusions:The excess of aa geomagnetics led to excess
solar energy which stored and accumulated for few future
years in the near-Earth system, leading to the global
temperature variability. The running coefficients for the
late years (1873-1930) displayed only negative
remarkable role of solar activity or/and aa geomagnetic in
global temperature change (Figure 5b). On contrast, the
aa index and the sunspot number played, direct or
indirect, a great role in global cooling temperature
throughout four decades from 1931 to 1970. During the
period 1971-1998, the correlation between Rz and
temperature persisted positively. So, the sensitivity of
global temperature to aa geomagnetics is significant and
may be real.Mufti and Shah 2011
The abstract and key points read:A long uninterrupted homogeneous data set on the annual mean Sea Surface Temperature (SST) anomaly records as a representative of the Earth's climatic parameter has been analyzed in conjunction with 158 year long time series on the annual sunspot indices, Rz and geomagnetic activity indices, aa for the period 1850–2007. The 11-year and 23-year overlapping means of global (δtg) as well as northern (δtn) and southern (δts) hemispheric SST anomalies reveal significant positive correlation with both Rz and aa indices. Rz, aa and δtg depict a similar trend in their long-term variation and both seem to be on increase after attaining a minimum in the early 20th century (∼1905). Whereas the results on the power spectrum analysis by the Multi-Taper Method (MTM) on δtg, Rz and aa reveal periodicities of ∼79–80 years (Gleissberg's cycle) and ∼9–11 years (Schwabe solar cycle) consistent with earlier findings, MTM spectrum analysis also reveals fast cycles of 3–5 years. A period of ∼4.2 years in aa at 99% confidence level appears recorded in δtg at ∼4.3 years at 90% confidence level. A period of ∼3.6–3.7 years at 99% confidence level found in δtg is correlating with a similar periodic variation in sector structure of Interplanetary Magnetic Field (IMF). This fast cycle parallelism is new and is supportive of a possible link between the solar-modulated geomagnetic activity and Earth's climatic parameter i.e. SST.
► Instrumental records of temperature anomalies analyzed in conjunction with sunspot, Rz and geomagnetic, aa indices. ► Significant positive correlation exists between Rz and aa when they are referred to long-term trends. ► Besides the 79 year and 11 year cycle the present investigation has also revealed fast cycle periods of 3–5 years in SST and aa. ► Geomagnetic activity could be a possible link through which solar activity may influence the Earth's climate. ► The Sun has a significant role to play in the long-term and short-term climate change.Raspopov et. al 2007
Found that long term trends in solar activity can create SIGNIFICANT temperature changes. A substantial lag can also occur with the sun and the temperature on the Earth, which would refute your earlier logic that just because the sun's irradiance according to PMOD has flatlined, does not bmean that it has not contributed to the recent warming. They also find that recent warming from 1945-2003 matches with expected predictions from a long term increase in solar activity.
From the abstract:The influence of ∼200-year solar activity variations (de Vries cyclicity) on climatic parameters has been analyzed. Analysis of palaeoclimatic data from different regions of the Earth for the last millennium has shown that ∼200-year variations in solar activity give rise to a pronounced climatic response. Owing to a nonlinear character of the processes in the atmosphere–ocean system and the inertia of this system, the climatic response to the global influence of solar activity variations has been found to have a regional character. The regions where the climatic response to long-term solar activity variations is stable and the regions where the climatic response is unstable, both in time and space, have been revealed. It has also been found that a considerable lag of the climatic response and reversal of its sign with respect to the solar signal can occur. Comparison of the obtained results with the simulation predictions of the atmosphere–ocean system response to long-term solar irradiance variations (T > 40 years) has shown that there is a good agreement between experimental and simulation results.Fig. 2. (a) Results of simulation of the spatial distribution of surface temperatures when the atmosphere–ocean system is affected by long-term solar irradiance variations (T > 40 years) (Waple et al., 2002). The asterisk (the North Atlantic region) and crosses show the sites the climatic data for which were used in our paper; (b) variations in annual average temperatures in the Northern Hemisphere for 1954–2003.
The sun's activity began to rise in 1900, according to this paper also by OM Raspopov et. al
Which Raspopov and Dergachev found was a 'controlling factor' in 20th Century warming.Yu 2002
found that great uncertainties still remain with GCRs and climate, and more research needs to be done to quantify these uncertainties.Kilcik 2005It is a clear fact that the Earth's climate has been changing since the pre-industrial era, especially during the last three decades. This change is generally attributed to three main factors: greenhouse gases (GHGs), aerosols, and solar activity changes. However, these factors are not all-independent. Furthermore, contributions of the above-mentioned factors are still disputed.We sought whether a parallelism between the solar activity variations and the changes in the Earth's climate can be established. For this, we compared the solar irradiance model data reconstructed by J. Lean to surface air temperature variations of two countries: USA and Japan. Comparison was carried out in two categories: correlations and periodicities. We utilized data from a total of 60 stations, 18 in USA and 42 in Japan. USA data range from 1900 to 1995, while Japan data range from 1900 to 1990.
Our analyses yielded a 42 per cent correlation for USA and a 79 per cent for Japan between the temperature and solar irradiance. Moreover, both data sets showed similar periodicities. Hence, our results indicate marked influence of solar activity variations on the Earth's climate.Kilcik et. al 2010By applying multitaper methods and Pearson test on the surface air temperature and flare index used as a proxy data for possible solar sources of climate-forcing, we investigated the signature of these variables on middle and high latitudes of the Atlantic–Eurasian region (Turkey, Finland, Romania, Ukraine, Cyprus, Israel, Lithuania, and European part of Russia). We considered the temperature and flare index data for the period ranging from January 1975 to the end of December 2005, which covers almost three solar cycles, 21st, 22nd, and 23rd.
We found significant correlations between solar activity and surface air temperature over the 50–60° and 60–70° zones for cycle 22, and for cycle 23, over the 30–40°, 40–50°, and 50–60° zones.
The most pronounced power peaks for surface air temperature found by multitaper method are around 1.2, 1.7, and 2.5 years which were reported earlier for some solar activity indicators. These results support the suggestion that there is signature of solar activity effect on surface air temperature of mid-latitudes.Fig. 1. Eleven year running mean sunspot numbers and departures of sea surface temperatures from the long term mean (units hundredths of a degree Celsius). The coherency between the solar activity and climate records can be seen in this figure comparing polynomial fits to the sunspot record and the global mean sea-surface temperature SST (Reid, 1999).
In Figure 4 of Dorman 2012
, it can be seen that GCRs can explain pretty much all temperature variability from 1937-1994.Carslaw et. al 2002
This paper shows that there is a long term decrease in GCRs over the 20th Century, which would correspond to a more active sun, as this would mean that there would be more solar wind to prevent GCRs from reaching Earth. It is also shown that in 1992, a record low in GCRs was recorded, indicating record high amounts of solar activity occured during the late-20th Century.Soon et. al 2011
(From the abstract:)The 20th century surface air temperature (SAT) records of China from various sources are analyzed using data which include the recently released Twentieth Century Reanalysis Project dataset. Two key features of the Chinese records are confirmed: (1) significant 1920s and 1940s warming in the temperature records, and (2) evidence for a persistent multidecadal modulation of the Chinese surface temperature records in co-variations with both incoming solar radiation at the top of the atmosphere as well as the modulated solar radiation reaching ground surface. New evidence is presented for this Sun–climate link for the instrumental record from 1880 to 2002. Additionally, two non-local physical aspects of solar radiation-induced modulation of the Chinese SAT record are documented and discussed.
Teleconnections that provide a persistent and systematic modulation of the temperature response of the Tibetan Plateau and/or the tropospheric air column above the Eurasian continent (e.g., 30°N–70°N; 0°–120°E) are described. These teleconnections may originate from the solar irradiance-Arctic–North Atlantic overturning circulation mechanism proposed by Soon (2009). Also considered is the modulation of large-scale land–sea thermal contrasts both in terms of meridional and zonal gradients between the subtropical western Pacific and mid-latitude North Pacific and the continental landmass of China. The Circum-global teleconnection (CGT) pattern of summer circulation of Ding and Wang (2005) provides a physical framework for study of the Sun–climate connection over East Asia. Our results highlight the importance of solar radiation reaching the ground and the concomitant importance of changes in atmospheric transparency or cloudiness or both in motivating a true physical explanation of any Sun–climate connection. We conclude that ground surface solar radiation is an important modulating factor for Chinese SAT changes on multidecadal to centennial timescales. Therefore, a comprehensive view of local and remote factors of climate change in China must take account of this as well as other natural and anthropogenic forcings.Tinsley et. al 2009
find that the CRF (Cosmic Ray Forcing) is a likely climate driver, and find that it needs to be represented in the models, since it has a very important role in climate change. Belov et. al 2005A method of prediction of expected part of global climate change caused by cosmic ray (CR) by forecasting of galactic cosmic ray intensity time variation in near future based on solar activity data prediction and determined parameters of convection-diffusion and drift mechanisms is presented. This gave possibility to make prediction of expected part of global climate change, caused by long-term cosmic ray intensity variation. In this paper, we use the model of cosmic ray modulation in the Heliosphere, which considers a relation between long-term cosmic ray variations with parameters of the solar magnetic field. The later now can be predicted with good accuracy. By using this prediction, the expected cosmic ray variations in the near Earth space also can be estimated with a good accuracy. It is shown that there are two possibilities: (1) to predict cosmic ray intensity for 1–6 months by using a delay of long-term cosmic ray variations relatively to effects of the solar activity and (2) to predict cosmic ray intensity for the next solar cycle. For the second case, the prediction of the global solar magnetic field characteristics is crucial. For both cases, reliable long-term cosmic ray and solar activity data as well as solar magnetic field are necessary. For solar magnetic field, we used results of two magnetographs (from Stanford and Kitt Peak Observatories). The obtained forecasting of long-term cosmic ray intensity variation we use for estimation of the part of global climate change caused by cosmic ray intensity changing (influenced on global cloudiness covering).
Climate Change can be forecasted based off of the predictions for the GCR Flux. Given how closely the model represents reality as shown in Figure 3, it is hard to discount their predictions of cooling in the near future due to an increasing GCR Flux.
In my next post I will have a compliation of peer reviewed papers that predict a cooling in the next couple to few decades. | <urn:uuid:72a64a1a-5e74-452e-98cc-8986f05ea172> | 3.4375 | 3,033 | Comment Section | Science & Tech. | 39.987154 |
Did you see the footage that so many people captured when a meteor streaked across the Russian sky on February 15th? If not, here's a slideshow and compilation video. The meteor originated in the asteroid belt, was visible in the sky for about 30 seconds, let loose several sonic booms as it entered the atmosphere, and disintegrated over Chelyabinsk, Siberia. Here are a few statistics about it:
- It was originally 55' (17m) long and had an estimated mass of 10,000 tons.
- It entered the atmosphere at about 40,000 mph (18km per second).
- It released nearly 500 kilotons of energy (about 30 times the power of the Hiroshima atomic bomb).
- it exploded at an altitude of 12 to 15 miles above the surface.
- Fragments left a 20' wide (6m wide) hole in the ice.
The cosmic event was the largest to have happened within the last century, and the only time a crashing meteor is known to have injured a large number of people, by shattering glass as they went to the windows to see what was happening. "[It] turns out to be the most widely witnessed asteroid strike in modern history." | <urn:uuid:4b20443e-f2d0-40b7-93cc-10ef1f1daa8b> | 3.734375 | 248 | Personal Blog | Science & Tech. | 52.830598 |
|Transmission of DENV - the principle mode is direct mosquito to human|
The group set out to understand the interactions between both DENV encoded proteins and those of its hosts – humans and Aedes mosquitos. Using previously determined structural information for human and fly (relatively closely related insect to Aedes) and how these proteins interact with each other, they were able to map these back on to host infection. They searched databases for structural similarities between dengue proteins and those from its host (human or fly) – these ‘dengue similar host proteins’ were used to search for host-host protein interactions as a surrogate for host-dengue interactions.
“The computational methodology employed to generate this map assumes that proteins with comparable structures will share interaction partners. Therefore, we predict that DENV2 proteins may merge into the host protein interactome at the points normally occupied by structurally similar host proteins, creating an interface for the manipulation of downstream host processes.”
Using this approach, they built up a network of possible host/pathogen interactions, assuming that DENV proteins can participate in the same interactions as host proteins. Of course, this method over estimates interactions so to counter this, they prioritised particular interactions for further study based on previously published, validated in vivo work and those interactions still left hopefully were functionally accurate and important. This approach had previously been used to study human-HIV-1 protein interactions.
|DENV capsid structure|
Following significantly limiting their map down to those that had been previously validated the biological functions of host target proteins and dengue-similar proteins were analysed to determine whether the predicted functions matched those that would be important for viral infection in both humans and mosquitoes. As shown above, DENV-like proteins participate in interactions involved in diverse processes – importantly including cell death, signalling cascades, immune response and metabolism. They focus the investigation into DENV manipulation of host apoptosis and innate immune signalling and also those proteins which are shared between both insect and human hosts.
They suggest that due to the disparity in the known molecular biology of dengue/host interactions this computational methodology has its limitations in this system yet these data should be used as a springboard for future investigations and hypotheses. This study highlights the importance of global computational analysis in determining basic host/pathogen biology especially in a system which has been poorly studied like DENV.
Doolittle, J., & Gomez, S. (2011). Mapping Protein Interactions between Dengue Virus and Its Human and Insect Hosts PLoS Neglected Tropical Diseases, 5 (2) DOI: 10.1371/journal.pntd.0000954
Dyer MD, Murali TM, & Sobral BW (2007). Computational prediction of host-pathogen protein-protein interactions. Bioinformatics (Oxford, England), 23 (13) PMID: 17646292 | <urn:uuid:d4b7c972-8042-4270-afb0-76ffa566337d> | 2.765625 | 595 | Academic Writing | Science & Tech. | 20.761544 |
Some cliff faces on Mars feature dark streaks that appear during the warm months, then disappear when weather turns colder. Writing in the journal Science, some researchers say that the streaks could be signs of briny water on the Martian surface. Planetary scientist Alfred McEwen discusses the findings, and what they might mean for future studies of the red planet.
Below: Time-lapse video over several seasons taken by the HIRISE imaging system on the Mars Reconnaissance Orbiter. NASA video.
Produced by Charles Bergquist, Director and Contributing Producer | <urn:uuid:bed272b7-90b9-47ba-9d38-eb0187bb4c97> | 3.3125 | 112 | Truncated | Science & Tech. | 39.959636 |
Maxwell’s demon is an interesting thought experiment on the 2nd law of thermodynamics. I have thought about this experiment for some time, and I think I have found a rebuttal.
In simple terms, this thought experiment suggests a way (using a tiny trapdoor between the A side and the B side of a gas container) to separate hot and cold gases without doing any work. The idea is that Maxwell’s demon opens the trapdoor when a fast moving molecule from A side approaches the trapdoor, thus allowing it to “leak” to B’s side, and similarly allowing for slow moving molecules from B side to leak to A side. If this way was theoretically possible, then we would be able to create more order, thus, in principle violating 2nd law of thermodynamics. Various criticisms have been given in an attempt to uphold our believe that 2nd law of thermodynamics is true (so, it is in fact a law).
Firstly, I must say that I do not agree with the rebuttals by Szilard, Brillouin and Charles Bennett, because their criticism is mostly on the energy that would be required to measure the speed of molecules and to operate the trapdoor. However, this is an assumption, not a fact. This assumption can be considered a fact, if we do choose to believe in many existing laws of physics, of which, second law of thermodynamis is one. Thus, this entire logic is circular.
My logic is different, and does not depend upon the assumption that energy is required to measure the speed of molecules. We consider two cases.
Case I: Trapdoor has a certain mass. If the trapdoor has mass, then to open or close it, we must expend some energy. thus the entire setup is not isolated. In that case, second law of thermodynamics is not violated at all.
Case II: Trapdoor is massless. If the trapdoor is massless, then we are not spending any energy in opening or closing it. However, if it is massless, then when a fast moving molecule hits it from the B side, some energy must be expended to keep the trapdoor from opening to A side. So, in this case second law of TD is not violated.
So, in all cases, we can see that Maxwell’s demon can be theoretically refuted. | <urn:uuid:df6fadd2-0222-48f4-bb29-79e8b5f57d44> | 2.734375 | 489 | Personal Blog | Science & Tech. | 54.204347 |
Into the Woods
If a tree once felled other trees in the woods, but was no longer
around to be studied, would it make for good research?
The American chestnut was once the most common canopy tree in the
deciduous forests of the eastern United States. It shaded areas from
New England to Georgia until the fungus Cryphonectria
parasitica wiped out the species in the infamous blight of the
early 20th century. The fungus continues to kill chestnuts before
they can mature.
The void left by the chestnut's demise is now filled with competing
species. Considerable research has gone into understanding what
happened to the American chestnut. But some scientists remain
interested in getting to the root not of its demise, but rather of
the centuries of dominance enjoyed by the massive, fragrant and
economically important tree. David B. Vandermast, a biology graduate
student at the University of North Carolina at Chapel Hill, and his
colleagues recently posited that Castanea dentata may have
been engaged in the chemically charged competition known as allelopathy.
An allelopathic plant releases potentially toxic substances into the
environment through its roots, its leaves or processes such as
evaporation. Black walnut, sycamore and sassafras trees are just a
few known allelopaths that limit the germination of competitors.
It's likely that the list will soon branch out to include the chestnut.
Vandermast's study, described in the July 15 issue of Forest
Ecology and Management, found that extracts from the
American chestnut leaf significantly limited the germination of
lettuce, eastern hemlock and unstratified rhododendron seeds. The
tree's rapid growth, dense foliage and slowly decaying leaf litter
may have allowed regular rainfalls to douse competitors with
leachate that defended against encroachment. The blight not only
ended the chestnut's dominance but also, as Vandermast notes,
contributed to changes in vegetative composition—and may have
even put chestnuts on the allelopathic receiving end.
Chestnut sprouts can reach five inches in diameter before the fungus
cuts them down, according to Vandermast. The sprouts are still
prolific, but anecdotal evidence suggests that something is limiting
"It's possible to find sprouts and dead trees in Southern
Appalachia," Vandermast says. "In areas where there are
dense rhododendron, there are old chestnut stumps, but no
sprouts." The same holds true in areas where hemlock grows
around chestnut stumps. "The hemlock didn't grow alongside the
chestnut [in its pre-blight days], even though it's
shade-tolerant," he says. But now, where there's hemlock,
there's a noticeable absence of chestnut sprouts.
The publication of the allelopathy study hints at the chemical
warfare waged throughout the forests. Coincidentally, it also
commemorates the 25th anniversary of David E. Flora's 1977 master's
thesis, "The American chestnut as an allelopath,"
completed at the University of Tennessee, Knoxville. Flora, under
the supervision of Frank W. Woods (two men whose names suggest they
were destined for careers in forestry), showed that the American
chestnut hindered the germination of radish seeds.
Flora also demonstrated in his discussion section how long it can
take for ideas to germinate into completed research when he noted:
"Tests of germination of native seeds ... might reveal whether
toxins are released from decaying leaves."
Vandermast says he learned of Flora's work after submitting his own
manuscript for publication. After reviewing it, he was relieved to
find that he hadn't duplicated someone else's work. "I was glad
to see that his results compared favorably with mine, and it is nice
that he suggested that someone should do what I | <urn:uuid:60e4c785-f67b-41ff-bb03-3ae1d38b0625> | 3.625 | 863 | Truncated | Science & Tech. | 36.720676 |
Quantifying leakage from CO<sub>2</sub> reservoirs
Jerome Neufeld, Dominic Vella, Herpert Huppert, and John Lister
ITG, DAMTP, University of Cambridge, England
Lay-language version of "Localized leakage from porous and viscous gravity currents"
Concern for the long-term fate of the Earth’s climate has increased in recent years, with many studies linking the increased atmospheric concentrations of carbon dioxide (CO2) with the rise in global mean annual temperature. One route to significant reductions in the CO2 emissions from stationary sources, such as power plants, is the capture and storage of large volumes of CO2 in the subsurface: so-called geological carbon sequestration. If geological carbon sequestration is to be implemented on a large scale, one key question is will it leak back to the surface and, if so, how quickly?
In several current implementations of carbon capture and storage (CCS), carbon dioxide emitted from stationary sources is collected and compressed before being injected into porous rock at depths of 1 km or more beneath the Earth’s surface. There the CO2, which is less dense than the salty water or brine it displaces, rises until it is stopped by a relatively impermeable cap rock such as a mudstone or clay. Its rise impeded, the injected CO2 then spreads laterally driven by its own buoyancy, much as honey spreads when poured onto toast.
As it spreads laterally, the CO2 current will come into contact with a large area of the overlying cap rock; any flaws in the cap rock are thus likely to be discovered by the current and could lead to leakage. These flaws may be natural, such as faults or fractures in the cap rock, or man-made, such as abandoned drilling wells. The magnitude and speed of leakage depend both on the geometry of the fault and on the characteristics of the reservoir.
Our work aims to study leakage in different scenarios (e.g., from a well-bore, or fault) by using analogue laboratory experiments combined with theoretical models to describe the flow of the CO2 current. A useful measure of the long term effectiveness of a geological storage site is the efficiency of storage, which we define as the ratio of permanently stored to injected CO2. If fluid never leaks from the reservoir the efficiency of storage is 100%. However, if fluid leaks from the reservoir the efficiency of storage decreases with time. Our models determine the dependence of the efficiency of storage on the geometry of a single leak and also on the time since the spreading CO2 current ‘discovered’ the leakage site. In each of the scenarios we have considered to date, we find that the efficiency of storage decreases indefinitely: ultimately a state is reached in which CO2 leaks at exactly the same rate as it is pumped in! Though this may sound like bad news for CCS, the crucial factor is the time taken for the efficiency of storage to decay to, say, 50%. Our study also predicts this time scale for several different scenarios.
What then are the implications for CO2 sequestration? The time scales involved in leakage are large – large enough that a further series of processes by which the CO2 may be permanently stored may have time to become significant. For example, as the CO2 current spreads a portion of the CO2 is trapped within the small pores of the rock, much as water is retained within a sponge. In addition, as the CO2 current spreads it dissolves into the brine already within the rock forming a mixture that is more dense than either the CO2 or the brine. This mixture therefore sinks to the base of the reservoir where it is stably sequestered. On even longer time scales CO2 may react with the host rock, forming mineral deposits, immobilising the CO2 permanently. In conclusion, while leakage may occur, the rates involved may be slow enough that the majority of injected CO2 will stay securely trapped beneath the surface. | <urn:uuid:2b220b8f-b501-4162-8673-d530b215c03b> | 2.6875 | 818 | Academic Writing | Science & Tech. | 35.050149 |
Over the last 20 years we have observed coral reefs declining at an alarming rate. What is causing this catastrophe and what can be done to prevent further damage?
This study room examines the causes of coral reef decline, including increasing ocean temperatures, overfishing, and runoff from coastal areas. The room describes research on coral disease and how coral organisms resist disease. The research is being conducted by graduate students, undergraduate students, and researchers, who describe their work in their own words.
This video is part 2 of 10 in the Coral Reef Sustainability series. | <urn:uuid:6601d5b2-4fda-4641-8d40-acce2ced8c95> | 3.25 | 113 | Truncated | Science & Tech. | 40.265219 |
Java is a popular language for beginning programmers, and earlier editions of this fun and friendly guide have helped thousands get started. Now fully revised to cover recent updates for Java 7.0, Beginning Programming with Java For Dummies, 3rd Edition is certain to put more first-time programmers and Java beginners on the road to Java mastery. ... Read More
The Struts framework is based on a classic Model-View-Controller (MVC) design paradigm that combines Java servlets, Java Server Pages ... Read More
The newest release of Java has more robust functionality to help web and mobile developers get the most ouf of this platform-independent programming language. Like its bestselling previous editions, Java All-in-One For Dummies, 3rd Editionhas what you need to get up and running quickly with the new version. Covering the enhanced mobile development and syntax features as ... Read More
Two complete e-books covering Java and Android application development for one low price!
This unique value-priced e-book set brings together two bestselling For Dummies books in a single e-book file. Including a comprehensive table of contents and the full text of each book, complete with cover, this e-book set gives you in-depth information on using the Java language to create powerful Android applications for mobile devices. Best of all, you'll ... Read More
As a platform-independent, object-oriented programming language, Java helps developers write once and run anywhere. With this dynamic combination of a full-color printed book and a Dummies interactive eLearning course on CD, you'll find a wealth of information on the latest release of Java. Featuring both written and animated step-by-step how-tos, practice labs, helpful videos, numerous examples, and ... Read More
Java is the platform-independent, object-oriented programming language used for developing web and mobile applications. The revised version offers new functionality and features that have programmers excited, and this popular guide covers them all. This book helps programmers create basic Java objects and learn when they can reuse existing code. It's just what inexperienced Java developers ... Read More
The demand for Android programming and web apps continues to grow at an unprecedented pace and Java is the preferred language for both. Java For Dummies Quick Reference keeps you moving through your coding while you solve a problem, look up a command or syntax, or search for a programming tip. Whether you're a Java newbie or a seasoned user, this fast reference offers you quick ... Read More | <urn:uuid:14ad9976-7aca-41f3-b4df-868335a51941> | 2.71875 | 507 | Content Listing | Software Dev. | 46.012459 |
Although native North American parasitoids do attack the birch leafminer, they haven't had much impact on this introduced sawfly's populations. In the 1970's European ichneumonid wasps were introduced in New Jersey, Delaware, Maryland, Pennsylvania, Massachusetts and Quebec. Lathrolestes nigricollis was one of two species that became established in several places and is now widespread throughout southern New England.
The effect of this parasitoid on the density of the birch leafminer in Massachusetts was evaluated over a 15 year period (1979-1995). At the original release site there was a decline in leaves mined by the first generation of the pest from 50-54% to under 3%.
By 1992, L. nigricollis had spread from a release site in western Massachusetts to the eastern side of the state, Rhode Island, Connecticut, eastern New York, and southern Vermont. Although birch leafminer densities are now acceptably low at sites close to the original release site, this is not true in all locations. The farther from the original release sites, the lower the parasitism and the higher the damage. Some sites, particularly roadside trees, still have high levels of mined leaves despite the presence of the parasitoid in the general area. This suggests that either it takes a while for this parasitoid to exert its full effect, or additional natural enemies may be needed.
This parasitoid might eventually spread naturally to the Midwest, or could be released here.
Van Driesche, R. G., R. Childs, R. A. Casagrande, and L. Tewksbury. 1997. Establishment, distribution, and impact in southern New England of Lathrolestes nigricollis (Thompson), an introduced parasitoid of the birch leafminer Fenusa pusilla (Lepeletier). Can. Entomol. 129: 601-611.
Return to Commodity Menu Vol. V No. 11
Return to Contents Menu Vol. V No. 11
Go To Index | <urn:uuid:ded46856-1bf0-4f92-8ae0-e94e71a34c9b> | 2.765625 | 429 | Academic Writing | Science & Tech. | 47.302606 |
Welcome to PhysLink.com - Your physics and astronomy online portal. Stay a while! Check out our extensive library of educational and reference materials. Also, check out our fun section!
How was the mass of a proton determined?
Asked by: David Slochower
The mass of the proton was determined in a similar way to how the mass of atoms are measured. The particle, whose mass is being determined, is accelerated through an electric field, the particle then passes through a perpendicular magnetic field which deflects the particle (particle must be charged, a proton or an ion for example, for it to deflect). The angle by which it deflects is dependent on the mass of the particle. The mass of the particle can be determined by using the following formula:
Centripetal Force = Force due to magnetic field(B)
(mv2)/r = Bqv
(where m = mass of particle, v = velocity of particle, r= radius of deflected path, B = magnetic field strength, q = charge of particle)
Answered by: Simon Hooks, Physics A-Level Student, Gosport, UK
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Blue Fiber Optic Light | <urn:uuid:e4a7d71b-df07-4b31-82f1-8767c6a5391f> | 3.640625 | 363 | Q&A Forum | Science & Tech. | 49.719512 |
Because Raptor is a staged combustion engine — like the main engines of NASA's now-retired space shuttle fleet — it is expected to be far more efficient than the open-cycle Merlin engines used by the Falcon 9.
While the Falcon 9’s engines use liquid oxygen (LOX) and kerosene, Raptor will use LOX and methane. Musk explained that "the energy cost of methane is the lowest, and it has a slight ISP [specific impulse] advantage over kerosene and doesn’t have any of the bad aspects of hydrogen." (Hydrogen is difficult to store at cryogenic temperatures, makes metal brittle and is very flammable.)
- The Boldest Mars Missions in History
- SpaceX's Quest For Rocketry's Holy Grail - SPACE.com Exclusive Video
- Special Report: The Private Space Taxi Race
Copyright 2012 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. | <urn:uuid:c1ecc8d2-8c4d-41c9-b326-0ebf0cac933f> | 3.3125 | 205 | Truncated | Science & Tech. | 39.000239 |
Meteorites Found from Asteroid 2008 TC3
This week I'm in Houston for the 40th annual Lunar & Planetary Science Conference, where 1,500 researchers have gathered to talk shop about the solar system. And indeed the big space news this week involves high-stakes interplanetary events — but the story should be datelined "Almahata Sitta, Sudan" instead of "Houston, Texas."
Our saga begins a few months ago, when Planet Earth got an unprecedented visit from a small asteroid designated 2008 TC3. A telescopic observer atop Mount Lemmon, Arizona, discovered this incoming chunk of rock on October 6th, and it slammed into the atmosphere over northern Sudan just 19 hours later. Since the 1970s astronomers have tracked down thousands of asteroids that might someday strike Earth — this is the first discovery that actually did.
"We thought that was the end of the story," recalls Steve Chesley, the orbital specialist at NASA's Jet Propulsion Laboratory who pinpointed where and when 2008 TC3 would end its 4½-billion-year existence.
But a couple of weeks later Chesley got a call from Peter Jenniskens, who wanted details about the final flight path. A meteor specialist at NASA's SETI Institute in Mountain View, California, Jenniskens had recently returned from a highly successful effort to study the atmospheric reentry of a European spacecraft, and the blazing piecemeal breakup he'd witnessed gave him hope that pieces of the shattered asteroid might have survived and fallen from the sky as meteorites. All too aware of the stones' scientific potential, Jenniskens was determined to look for them — though he admits, "It was a long shot."
Six weeks later Jenniskens found himself standing in the Nubian Desert of northern Sudan with Mauwia Shaddad and a busload of 45 students and staff from the University of Khartoum, where Shaddad teaches physics. All the available information about the asteroid's track — gleaned from civilian and military satellite photos, detection networks on the ground, and eyewitness accounts — suggested that any meteorites from 2008 TC3 should lie along a roughly east-west track about 20 miles southwest of a remote Sudanese railway station called Station 6.
A Scientific Coup
Jenniskens's long shot had paid off. Now he had everything he needed to piece together the entire story of 2008 TC3. Chesley had computed the space rock's exact orbit before it collided with Earth, and an observing team had managed to record a spectrum of the asteroid just 2 hours before its demise using the 4.2-meter William Herschel Telescope in the Canary Islands. And, remarkably, pieces of that same asteroid were in hand.
That in itself was unprecedented. Geologists have spent decades trying to match the spectra of various meteorite types with their most likely asteroidal sources, but the match is never exact and so the associations remain unproven. "We have more than 40,000 samples of asteroids as meteorites," explains Michael Zolensky of NASA's Johnson Space Center, "but we don't know where a single one of them came from."
Once back in the U.S., Jenniskens rushed samples of the newly recovered meteorite — now officially named Almahata Sitta, the Arabic phrase for "Station 6" — to labs around the country. Those analyses revealed that the fallen stones belong to a rare meteorite class known as ureilites, dark carbon-enriched rocks that were once at least partly molten.
But even as ureilites go, the Sudanese stones are unique. Scattered here and there are blotches of carbon that have undergone extreme heating. "Of all the meteorites we've ever studied," comments analyst Andrew Steele (Carnegie Institution of Washington), "the carbon in this one has been cooked to the greatest extent." Moreover, the stones' interiors are full of holes (technically, vugs) lined with coating crystals of the magnesium-rich silicates olivine and pyroxene. Their overall porosity ranges from 10% to 25%, and they crumble easily — making it all the more remarkable that any survived.
Meanwhile, the flat, featureless spectrum of the meteorites is a dead ringer for that of the asteroid itself. As it turns out, 2008 TC3 was also a rare and little-understood asteroidal breed known as an F type. At some point it was chipped off a larger object; conceivably that's the unnamed F asteroid designated 1998 KU2 and numbered 152679, an Earth-crosser estimated to be about 1.6 miles (2.6 km) across. Its rapid spin assures that the surface lacks a dusty coating, which means the observed spectrum reflects its true surface character.
A careful researcher, Jenniskens has kept all this very hush-hush for the past few months. But he and his extensive team of collaborators have now published their findings in today's issue of Nature (it's the cover story).
You can learn more about the flurry of activity surrounding the impact of 2008 TC3 and the recovery effort by checking out press releases issued by the SETI Institute, Carnegie Institution, and the UK's Science and Technology Facilities Council. NASA has posted many illustrations about these remarkable events here. | <urn:uuid:69d2c700-4adb-464e-b11b-f46c0efb7338> | 2.90625 | 1,085 | Personal Blog | Science & Tech. | 40.981015 |
Two Suns Raise Family of Planetary Bodies
This artist's animation depicts a faraway solar system like our own -- except for one big difference. Planets and asteroids circle around not one, but two suns. NASA's Spitzer Space Telescope found evidence that such solar systems might be common in the universe.
The movie begins by showing two snug, sun-like stars. It then pans out to show an Earth-like planet and a surrounding disk of asteroids and comets.
Spitzer did not see any planets directly, but it detected dust that is kicked up from disks like this one. The disks were spotted circling all the way around several double, or binary, stars, some of which were closer together than Earth is to our sun. In fact, Spitzer found more disks in orbit around close-knit binary stars than single stars. This could mean that planets prefer two parent stars to one, but more research is needed to figure out exactly what's going on.
Browse Videos in Science Animations
This artist's animation illustrates how silicate crystals like those found in comets can be created by an outburst fr... | <urn:uuid:c6ef561a-d8d2-4035-9f6a-f15548f08d94> | 3.46875 | 229 | Truncated | Science & Tech. | 55.404167 |
Atomic mass unit
|Unit system:||Physical constant
(Accepted for use with the SI)
|Symbol:||u or Da|
|Named after:||John Dalton|
|1 u or Da in...||is equal to...|
The unified atomic mass unit (symbol: u) or dalton (symbol: Da) is the standard unit that is used for indicating mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit is approximately the mass of a nucleon and is equivalent to 1 g/mol. It is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of 1.660538921(73)×10−27 kg. The CIPM has categorised it as a non-SI unit accepted for use with the SI, and whose value in SI units must be obtained experimentally.
The amu without the "unified" prefix is technically an obsolete unit based on oxygen, which was replaced in 1961. However, some sources still use the amu but now define it in the same way as u (based on carbon-12). In this sense, most uses of atomic mass units or amu today actually refer to unified atomic mass units or u.
Atomic mass unit does not stand for the unit of mass in the atomic units system, which is rather me.
The relative atomic mass (atomic weight) scale has traditionally been a relative scale, that is without an explicit unit, with the first relative atomic mass basis suggested by John Dalton in 1803 as 1H. Despite the initial mass of 1H being used as the natural unit for relative atomic mass, it was suggested by Wilhelm Ostwald that relative atomic mass would be best expressed in terms in units of 1/16 mass of oxygen. This evaluation was made prior to the discovery of the existence of elemental isotopes, which occurred in 1912.
The discovery of isotopic oxygen in 1929 led to a divergence in relative atomic mass representation, with isotopically weighted oxygen (i.e., naturally occurring oxygen relative atomic mass) given a value of exactly 16 atomic mass units (amu) in chemistry, while pure 16O (oxygen-16) was given the mass value of exactly 16 amu in physics.
The divergence of these values could result in errors in computations, and was unwieldy. The chemistry amu, based on the relative atomic mass of natural oxygen (including the heavy naturally-occurring isotopes 17O and 18O), was about 1.000282 more massive than the physics amu, based on pure isotopic 16O.
For these and other reasons, the reference standard for both physics and chemistry was changed to carbon-12 in 1961. The choice of carbon-12 was made to minimise further divergence with prior literature. The new and current unit was referred to as the "unified atomic mass unit" u. and given a new symbol "u," which replaced the now deprecated "amu" that had been connected to the old oxygen-based system.
However, modern sources often still use "amu" in place of "u" (as a synonym) and define "amu" in terms of carbon-12. In general, "amu" probably does not refer to the old oxygen standard amu, unless the material is older than the 1960s.
The "unified atomic mass unit" u was defined as:
The unified atomic mass unit and the dalton are different names for the same unit of measure. As with other unit names such as watt and newton, "dalton" is not properly capitalized in English, but its symbol Da is capitalized. With the introduction of the name "dalton", there has been a gradual change towards using that name in preference to the name "unified atomic mass unit":
- In 1993, the International Union of Pure and Applied Chemistry approved the use of the dalton with the qualification that the GCPM had not given its approval.
- In 2003 the Consultative Committee for Units, part of the CIPM, recommended a preference for the usage of the "dalton" over the "unified atomic mass unit" as it "is shorter and works better with prefixes".
- In 2005, the International Union of Pure and Applied Physics endorsed the use of the dalton as an alternative to the unified atomic mass unit.
- In 2006, in the 8th edition of the formal definition of SI, the CIPM cataloged the dalton alongside the unified atomic mass unit as a "Non-SI units whose values in SI units must be obtained experimentally: Units accepted for use with the SI". The definition also noted that "The dalton is often combined with SI prefixes ..."
- In 2009, when the International Organization for Standardization published updated versions of ISO 80000, it gave mixed messages as to whether or not the unified atomic mass unit had been deprecated: ISO ISO 80000-1:2009 (General), identified the dalton as having "earlier [been] called the unified atomic mass unit u", but ISO 80000-10:2009 (atomic and nuclear physics) catalogued both as being alternatives for each other.
- The 2010 version of the Oxford University Press style guide for authors in life sciences gave the following guidance "Use the Système international d'unités (SI) wherever possible ... The dalton (Da) or more conveniently the kDa is a permitted non-SI unit for molecular mass or mass of a particular band in a separating gel." At the same time, the author guidelines for the journal "Rapid Communications in Mass Spectrometry" stated "The dalton (Da) is a unit of mass normally used for the molecular weight ... use of the Da in place of the u has become commonplace in the mass spectrometry literature ... The "atomic mass unit", abbreviated "amu", is an archaic unit".
- In 2012, in response to the proposed redefinition of the kilogram, it was proposed that the dalton be redefined as being 0.001/NA kg, thereby breaking the link with C12. This would result in the dalton and the atomic mass unit having different definitions and differing from each other by a factor of the order of 10-9.
Relationship to SI
- The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12; its symbol is "mol".
- When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
The definition of the mole also determines the value of the universal constant that relates the number of entities to amount of substance for any sample. This constant is called the Avogadro constant, symbol NA or L, and is equal to 6.02214129(27)×1023 entities per mole.
Given that the unified atomic mass unit is one twelfth the mass of one atom of carbon-12, meaning the mass of such an atom is 12 u, it follows that there are NA atoms of carbon-12 in 0.012 kg of carbon-12. This can be expressed mathematically as
- NA (12 u) = 0.012 kg/mol, or
- NA u = 0.001 kg/mol
Masses of proteins are often expressed in daltons. For example, a protein with a molecular weight of 64000 g mol−1 has a mass of 64000 daltons or 64 kDa in short.
- A hydrogen-1 atom has a mass of 1.007 825 0 u (1.007 825 0 Da).
- By definition, a carbon-12 atom has a mass of 12 u (12 Da).
- A molecule of acetylsalicylic acid (Aspirin) has a mass of 180.16 u (180.16 Da).
- A molecule of small peptide hormone insulin has a mass of 5 808 u (5.808 kDa).
- A molecule of protein actin has a mass of about 42 000 u (42 kDa).
See also
- Stryer, Jeremy M. Berg; John L. Tymoczko; Lubert (2007). "2". Biochemistry (6. ed., 3. print. ed.). New York: Freeman. p. 35. ISBN 978-0-7167-8724-2.
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), p. 126, ISBN 92-822-2213-6
- Fundamental Physical Constants from NIST
- Petley, B. W., "The atomic mass unit", IEEE Trans. Instrum. Meas. 38 (2): 175–79, doi:10.1109/19.192268
- Holden, Norman E. (2004), "Atomic Weights and the International Committee—A Historical Review", Chem. Int. 26 (1): 4–7
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "unified atomic mass unit".
- Mills, Ian; Cvitaš, Tomislav; Homann, Klaus; Kallay, Nikola; Kuchitsu, Kozo (1993n). Quantities, Units and Symbols in Physical Chemistry International Union of Pure and Applied Chemistry; Physical Chemistry Division (2nd ed.). International Union of Pure and Applied Chemistry and published for them by Blackwell Science Ltd. ISBN 0-632-03583-8.
- "Consultative Committee for Units (CCU); Report of the 15th meeting (17 –18 April 2003) to the International Committee for Weights and Measures". Retrieved 14th Aug 2010.
- "IU14. IUPAC Interdivisional Committee on Nomenclature and Symbols (ICTNS)". Retrieved 2010-08-14.
- International Standard ISO 80000-1:2009 – Quantities and Units – Part 1: General, International Organization for Standardization, 2009
- International Standard ISO 80000-10:2009 – Quantities and units – Part 10: Atomic and nuclear physics, International Organization for Standardization, 2009
- "Instructions to Authors". AoB Plants. Oxford journals; Oxford University Press. Retrieved 2010-08-22.
- "Author guidelines". Rapid Communications in Mass Spectrometry (Wiley-Blackwell). 2010. Retrieved 2011-05-08.
- Leonard, B P (2012). "Why the dalton should be redefined exactly in terms of the kilogram". Metrologia (49): 487. doi:10.1088/0026-1394/49/4/487.
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), pp. 114,115, ISBN 92-822-2213-6
- atomic mass unit at sizes.com | <urn:uuid:71a2e5bb-84ac-4cdd-8f91-735c43ee061b> | 3.796875 | 2,345 | Knowledge Article | Science & Tech. | 58.977079 |
David Hebert: Hello and welcome to this USGS podcast, I'm David Hebert. On Wednesday of January 20th, a magnitude 5.9 aftershock struck Haiti which was alarming and notable considering the magnitude seven earthquake that devastated that country last week. So I'm here with Mike Blanpied, USGS Associate Earthquake Hazards Program Coordinator and he's going to fill us in on sort of the earthquake picture in the near future for Haiti and for the Caribbean at large.
Mike, I know you're very busy, thank you for joining us once again.
Mike Blanpied: I'm very happy to be here.
David Hebert: Let's start with the aftershocks. Again there was a significant aftershock yesterday. There had been other notable aftershocks since the main earthquake last week. Can you just talk a little bit about the aftershock picture, you know, what sort of probabilities are we looking at, how big, that kind of thing?
Mike Blanpied: Yes. Aftershocks have continued since immediately after the main magnitude seven earthquake.
As is always the case for large earthquakes, there are a number of aftershocks. It turns out that this sequence turns out to be particularly vigorous. We're seeing more aftershocks and we would expect on average say in California. There have been at least 15 aftershocks of magnitude five or larger over the nine days since the main shock.
Looking forward for the next few days and weeks, we expect that the aftershock sequence will continue. Of course we can't say exactly where or when any particular aftershock will occur. However, we can look at the sequence and using simple established models for the rate and statistics of aftershocks, we can make a projection of how likely aftershocks are at various sizes over the coming weeks.
For example, if we just look for the month ahead, we give in a probability that there will be more aftershocks that magnitude five level or above. That's about 90%.
In other words, it's almost assured that we'll see more aftershocks of that size and we may see even two or three of those. At a higher level of magnitude, magnitude six, we've not seen one of those in this sequence. We've seen five nine but not quite up to the six level and there's probably a one in four chance that we will see a magnitude six earthquake sometime in the next month.
And of course, the trouble there is that an earthquake of that magnitude can cause considerable damage especially to the weakened structures already existing in the region due to the previous earthquake.
David Hebert: OK, now with that in mind, what kinds of precaution should people in Haiti be taking right now?
Mike Blanpied: Right now people need to be extremely cautious when working around structures that are still standing or those that have been damaged in the main shock. If you're on the ground in Haiti, you must maintain some awareness of the situation with regard to your personal safety. You need to be aware that the ground could shake at any time so if you're working in or around structures, be ready to take quick action to take your self to safety if the ground begins to shake.
People should be aware that really it takes an authoritative engineer who's qualified in structural design to determine if a damaged building is safe to re-occupy. In some cases, they maybe but if you're not sure, the best guess is the structure that appears to be damaged is probably unsafe.
David Hebert: So what are some of the short-term concerns for Haiti as far as seismic activity goes?
Mike Blanpied: Right now scientists from USGS and elsewhere are working very hard to gain a better understanding of exactly how the earth behaved in the earthquake of nine days ago. The earthquake occurred on a very long fault; the Enriquillo fault zone that stretches through Dominican Republic, Haiti and then out to sea toward Jamaica, only a portion of that fault ruptured in the earthquake of magnitude seven.
This means that other sections of the fault which have not slipped recently remained hazardous and we're looking at a variety of types of evidence from a space photography, LiDAR and other types of investigations in order to determine what that fault looks like, how long ago it was that it slipped, how hazardous it is, so we can make an improved assessment of how likely it is that earthquakes will occur in the future.
David Hebert: Most transition were long-term picture both in terms of the infrastructure there in Haiti in trying to rebuild and geologic hazards on that fault system that you mentioned, what are some of the long-term concerns?
Mike Blanpied: Well, looking at the seismic situation in Haiti, it is part of the seismic zone that cuts through the Caribbean and Haiti itself has two major plate boundary fault zones; this one and one farther to the north.
And over the past centuries, three to four centuries, there had been several earthquakes of the size of the one last Tuesday that if they occurred today would cause considerable damage. And it's really been a century or in some cases, two or three centuries since portions of these faults have ruptured, meaning that they remain highly stressed today and pose a hazard.
As Haiti works hard to recover from this earthquake and begin the process of rebuilding, it's very important that there be an improved understanding of the seismic hazard that exists due to these large faults and there needs to be a sufficient understanding about the likely shaking in the urban area and elsewhere in Haiti so that building codes can be developed that will safeguard these buildings such that they don't fall down when the earth shakes some time in the future.
In the coming years and coming decades there will certainly be other earthquakes in the area. We can't say when, we can't say where but it is very likely that during the lifetime of buildings that are built now and the recovery from this earthquake, they will be shaking. And we need to make sure that those buildings don't fall down and hurt people when that shaking occurs.
David Hebert: So let's expand the picture a little bit here and look at the Caribbean as a whole. What sort of hazards are presented in the Caribbean as region?
Mike Blanpied: Well, looking at the Caribbean as a region, as you know it's an arch of violence, the Lesser Antilles and the Greater Antilles and what those islands represent is a boundary between two large tectonic plates; those of the Caribbean and North America. So this entire region is seismic reactive because these two plates are sheering past each other.
We talk frequently about a ring of fire around the Pacific due to the plate boundaries there, well, this is a little ring of fire located just to the southeast of the United States.
So every one of these countries has a certain degree of seismic hazard and looking forward now that this earthquake has highlighted so dramatically for us that there are these large risks. It's really incumbent upon everyone to make sure that earthquake safety policy is founded on a really a good understanding that there is a seismic hazard and a good assessment about what that hazard is and that goes both for the hazard of shaking and also that for tsunamis which can also occur.
David Hebert: Well, thank you again for your time, Mike. Is there anything else that you like to add or mention that you haven't had a chance to yet?
Mike Blanpied: Oh, I just like to conclude by saying that we in the United States are working hard to understand this earthquake and help in the recovery process. Our hearts go out to those who are living in the affected area.
David Hebert: Absolutely. Thank you very much for your time, Mike. Thank you to all of you out there for listening. If you'd like more information on USGS earthquake research and the earthquakes that are happening around the world, go to our earthquake.usgs.gov. If you like this podcast or any other USGS podcast, go to usgs.gov/socialmedia.
This podcast is a product of the U.S. Geological Survey, Department of the Interior. Thank you for listening.
The aftershock sequence of the magnitude 7 earthquake that struck Haiti on Jan. 12, 2010, will continue for months, if not years. The frequency of events will diminish with time, but damaging earthquakes will remain a threat.
Michael Blanpied, USGS Associate Earthquakes Hazards Program coordinator, discusses concerns and precautions for the future in Haiti and the Caribbean region as a whole.
Date Recorded: 1/21/2010
Audio Producer: David Hebert
, U.S. Geological Survey
Usage: This audio file is public domain/of free use unless otherwise stated. Please refer to the USGS Copyright section for how to credit this audio. | <urn:uuid:33fe5508-7574-4483-9282-48559ddbb625> | 3.1875 | 1,822 | Audio Transcript | Science & Tech. | 49.34821 |
The most important signal to be recorded at the Superconducting Gravimeter Observatory is gravity. For most Global Geodynamics Project (GGP) purposes the atmospheric correction to gravity is required ... and so the local measurement of pressure is also necessary. At most sites the effect of groundwater, often associated with rainfall, is an important contributor to gravity variations over periods of days to years. Superconducting Gravimeter groups are therefore urged to record rainfall and groundwater level at their sites as auxiliary data. Finally each station is asked to supply a log file of important events that might affect the data for each month. | <urn:uuid:486406d3-d714-4f48-b84d-fc5c1b3d890d> | 3.265625 | 119 | Knowledge Article | Science & Tech. | 29.008744 |
Copyright Peter Raedschelders
In mathematics, the best known solids are the 5 Platonic solids: tetrahedron,octahedron, cube, isocahedron and dodecahedron. These are regular solids constructed with only one sort of polygons. So is the cube constructed with 6 squares (4), the dodecahedron with 12 pentagons (5) .
Another sort of solids are the 13 Archimedean solids with names as cuboctahedron and isosidodecahedron. These are solids constructed with more the one sort of regular polygons. The best known is a football which is constructed with regular pentagons (5) surrounded with regular hexagons (6).
Is it known that a solids with pentagons (7) together with other regular polygons is impossible, but nevertheless we tried to construct one. The results is a solid with a regular pentagon (7), surrounded with pentagons (5) and "squares". However if we look closely, one can see that the pentagons (5) are not regular (since the angles are not always the same neither are the lengths of the sides). The same is true for the squares, they only look like squares. Only the pentagons (7) are regular.
A snake moves around through the solid and passes through every polygon.
Go to next print
Back to: Index | <urn:uuid:664489a6-0984-4365-bf8e-0a305c20b76b> | 3.03125 | 296 | Knowledge Article | Science & Tech. | 42.014723 |
I am given a base function of f=x2
and given a transformed equation of y = 7f((-1/6)(x-1))+1
I am being asked to describe the transformations that must be applied to the graph of the base function f(x) to obtain the transformed function, which I understand, and then I am ask to write the transformed equation in simplified form. This is where I'm hung up.
I guess the next line would be
y=7((-1/6)(x-1)2+1This is where I get stuck. How do I multiply -1/6 by x-1? What do I do with the square? Also, I don't know how to write fractions on the site yet, so -1/6 is negative one sixt to clear up any confusion. I've placed it in parenthesis to try to indicate that. | <urn:uuid:944a8ed6-9240-41be-ade5-66e98340e495> | 3.21875 | 187 | Q&A Forum | Science & Tech. | 83.751748 |
Manipulating Magnetic Field Shape
Is it possible to manipulate the magnetic lines of flux in such
a way as the lines extend into an oval, with the magnet towards one end of
the oval? If possible, please tell me how it might be done, or refer me to
some where with the information.
First, I want to clarify if you mean field lines or flux lines.
Typically flux lines represent a magnetic field perpendicular to a
surface, represented as vectors on a surface -- since a vector is just
a magnitude and a direction, it cannot be an oval. The ovals you
commonly see around a magnet are field lines, not flux lines.
Are you saying you want the field lines to go around the object, but
not into it? Then, no it is not possible -- field lines emanate from an
object with a magnetic field. If you are just saying you want to design
an arbitrary field shape (in this case, an oval) around your magnet,
then it becomes an engineering problem of orienting and controlling
the magnetic moment of the various ferromagnetic domains in your
magnet. You just need a more highly magnetized area on one side than
the other. I am assuming you mean a ferromagnet -- although the answer
is largely similar if you mean other kinds of magnets, but the way you
magnetize it is different.
As for practically how you should do that, there are custom magnets
you can buy on the Internet, which might be the easiest way -- but if
you want to do it yourself, you will have a challenging task of
sintering magnetic powder then applying various levels of different
magnetic fields in order to 'magnetize' according to the field shape
Hope this helps,
Well, Michael, sounds like it might not be possible.
In empty space, magnetic field lines (and electric)
tend to arrange themselves into minimum-energy positions
which tend to have a roughly spherical intensity distribution.
Energy-density of either field goes as square of field strength in Tesla (or v/m)
Number of field lines are fixed by the ampere-turns or the trapped static electric charges
which caused the field to exist in the first place.
The equations which govern the preferred distribution derive from those two things.
To modify the preferred distribution requires something to modify the permeability
(or permitivity) of the space. Only matter does that; energy does not.
so making a magnetic field reach out farther in one direction than another
would require some magnetic matter on one side to help propagation
(like transformer iron or mu-metal)
or on the other side to hinder propagation (like superconductor).
Air-core copper-wire solenoid coils shape it too,
but only by adding "new" magnetic flux of their own.
The key thing is that matter is needed for any of that.
As an example you can imagine a bar magnet being gradually bent into a horseshoe magnet.
The strength distribution of a field around a bar magnet is pretty symmetric,
either spherical or ellipsoidal up to 2:1. I forget which.
Look up equations for a "magnetic dipole" field.
When it is bent, say, tips toward the right,
perhaps the field reaches out to the right a little more than to the left, but not by much.
Mostly it is like a dipole stretching across the empty space between the two right-pointing tips.
The permanent-magnet material has helped the flux-lines transit from tip1 to tip2
travelling a U-shaped path inside the magnet metal,
and matter can do that kind of thing.
No "remote influence on empty space" can do that,
with the possible exception of gross general-relativistic gravitational spatial distortions,
(such as proximity to black holes, or science-fiction warp-drives)
which are not really available for practical use in this century.
I suppose a dipole field around an object travelling near light speed would be compressed in the direction of travel,
by special relativity. Not too complicated.
But it would still be symmetric. Reach in opposite directions would be equal.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:fb8a014a-133a-494c-94f8-4cb3e3a542c9> | 2.9375 | 905 | Q&A Forum | Science & Tech. | 43.807882 |
publications > paper > mangroves, hurricanes, and lightning strikes
Mangroves, Hurricanes, and Lightning Strikes
Assessment of Hurricane Andrew suggests an interaction across two differing scales of disturbance
Thomas J. Smith, III, Michael B. Robblee, Harold R. Wanless, and Thomas W. Doyle
|Posted with permission from BioScience. Thomas J. Smith, III, Michael B. Robblee, Harold R. Wanless, and Thomas W. Doyle, Mangroves, Hurricanes, and Lightning Strikes, BioScience Vol. 44 No. 4, April 1994. Copyright, American Institute of Biological Sciences.
The track of Hurricane Andrew carried it across one of the most extensive mangrove forests in the New World. Although it is well known that hurricanes affect mangrove forests, surprisingly little quantitative information exists concerning hurricane impact on forest structure, succession, species composition, and dynamics of mangrove-dependent fauna or on rates of ecosystem recovery (see Craighead and Gilbert 1962, Roth 1992, Smith 1992, Smith and Duke 1987, Stoddart 1969).
After Hurricane Andrew's passage across south Florida, we assessed the environmental damage to
the natural resources of the Everglades and Biscayne National Parks. Quantitative data collected during subsequent field trips (October 1992 to July 1993) are also provided. We present measurements of initial tree mortality by species and size class, estimates of delayed (or continuing) tree mortality, and observations of geomorphological changes along the coast and in the forests that could influence the course of forest' recovery. We discuss a potential interaction across two differing scales of disturbance within mangrove forest systems: hurricanes and lightning strikes.
|The recovery of Florida's mangrove forests is by no means assured
Mangrove Landscapes >
Thomas J. Smith III is the research coordinator at the Rookery Bay National Estuarine Research Reserve, Florida Department of Environmental Protection, Naples, FL 33962. Michael B. Robblee is a research ecologist at the South Florida Research Center, Everglades National Park, Homestead, FL 33030. Harold Wanless is a professor in the Department of Geological Sciences, University of Miami, Coral Gables, FL 33124. Thomas W. Doyle is a wetlands ecologist in the US National Biological Survey, National Wetlands Research Center, Lafayette, LA 70506.
Please note: At the time of publication, Thomas J. Smith III was the research coordinator at the Rookery Bay National Estuarine Research Reserve. He is currently at the United States Geological Survey, 600 Fourth Street South, St. Petersburg, FL 33701. | <urn:uuid:80d131a1-6980-41ed-a087-2248cd5bd2e8> | 3.0625 | 544 | Academic Writing | Science & Tech. | 33.574571 |
(To complete all classifications ETI has added the Kingdom and the Phyla of all the different taxa treated on this DVD-ROM without higher classification descriptions. Texts from Lynn Margulis and Karlene V. Schwartz, Five Kingdoms. CD-ROM. © 2002 ETI / Freeman & Co Publishers).
[Editor's note: in the book South Atlantic Zooplankton the Forminifera were classified within the "old" Phylum Sarcomastigophora instead of the Granuloreticulosa].
Granuloreticulosans are easily defined: these organisms bear reticulopods, cells that fuse to form networks in which bidirectional (two-way) streaming can be seen. Two classes make up this phylum: Reticulomyxida and Foraminifera (from the Latin foramen, little hole, perforation, and ferre, to bear). By far the better-known class, Foraminifera — affectionately known as forams — have pore-studded shells, or tests. In contrast, reticulomyxids are “snot shaped” slimy nets of messy, bactivorous soft masses that lack shells. Very few have been studied. These “naked forams,” reticulomyxids, are the presumed ancestral group; therefore, with their discovery, the former Phylum Foraminifera was renamed.
Forams are exclusively marine organisms. The smallest are some 10 mm in diameter, and the largest ones, visible to the naked eye, grow to several centimeters in diameter. The majority are tiny and live in sand or mud or attached to rocks, algae, or other organisms. Two families of free-swimming modern planktonic forams (Globigerinidae and Globorotalidae) are very important in the economy of the sea as food for many marine animals.
The pore-studded tests of forams are composed of organic materials, often reinforced with minerals. Some are made of sand grains; most are neatly cemented granules of calcium carbonate deposited from sea water. Some forams, by mechanisms that are still unknown, choose echinoderm plates (Subphylum Urochordata) or sponge spicules (Phylum Porifera) to construct their tests. The test and the organism itself may be brilliantly colored—salmon, red, or yellow brown. Whereas the simplest forams have single-chambered tests, most are multichambered. A typical test looks like a clump of blobs of partial spheres. Pores in the test permit thin cytoplasmic projections, the microtubule-reinforced filopodia, to emerge. Anastomosing (linked-up) filopodia form nets called reticulopodia. The filopodia are used for feeding, swimming, and gathering materials for tests. Forams are omnivorous: they eat algae, ciliates (Phylum Ciliophora), actinopods (Phylum Actinopoda), and even nematodes and crustacean larvae. Many forams, probably most that live in shallow water, harbor photosynthetic symbionts—dinomastigotes (Phylum Dinomatigota), chrysomonads (Phylum Chrysomonada, planktonic), and diatoms (Phylum Diatoms or Bacillariophyta).
Although some foram genera (for example, Textularia) have been seen reproducing only by asexual budding into multiple offspring, others that have been well studied—some dozen species—show a remarkably complex life cycle. The known cycles are variations on the theme of Rotaliella. Meiosis takes place in the agamont, a fully adult diploid organism that produces and releases smaller haploid forms called agametes. These agametes disperse and grow by mitotic cell divisions into a second kind of adult, called gamonts. The gamonts reproduce sexually, by fusion of haploid nuclei, to produce diploid offspring, which are agamonts.
The alternation of the diploid agamont and haploid gamont generations is obligatory in the forams that have been studied, just as alternation of generations is obligatory in plants, such as mosses (Phylum Bryophyta) and ferns (Phylum Filicinophyta). In fact, forams are the only heterotrophic protoctists that alternate morphologically distinct free-living adult generations. What complicates matters is that, unlike other organisms except ciliates (Phylum Ciliophora), forams show a striking nuclear dimorphism. The agamonts of Rotaliella roscoffensis, for example, contain four diploid nuclei. Three of these nuclei, the generative nuclei, reside in a chamber separate from that in which the larger somatic nucleus remains. The somatic nucleus never undergoes meiosis; it eventually becomes pycnotic (it stains heavily) and disintegrates. The three generative nuclei give rise to 12 haploid products by meiosis. These products become the nuclei of the small haploid agametes. Later, in the gamonts, pairs of haploid nuclei, apparently of opposite sex, fuse to form diploid zygotes. In effect, these organisms show programmed cell death (selective “death” of the somatic nucleus), and each gamont fertilizes itself, although neither egg nor sperm is formed.
Foram tests have contributed greatly to the sediment on the bottom of marine basins, especially since the Triassic period. There are fossil giant forams of great fame. Some, such as Lepidocyclina elephantina, had tests as thick as 1.5 cm. Camerina laevigata (also known as Nummulites, the “coin stone”) was a large (10 cm wide) foram that lived in warm shallow waters during the Cenozoic era from the Eocene to the Miocene epoch (some 38 million to 7 million years ago). Rocks bearing Miocene forams, many of them easily visible to the naked eye, abound on the shores of the Mediterranean. It is from such “nummulitic” limestone that the pyramids of Egypt were constructed.
The abundance of foram tests and their detailed architecture (the earliest ones appeared in the Cambrian) make them excellent stratigraphic markers. Geologists use the 40,000 or so fossil species to identify geographically separate sediment layers of the same age. Because the tests are often found in strata that cover oil deposits, recognition of foram morphology and knowledge of their distribution is helpful in petroleum exploration. | <urn:uuid:8341263f-4171-4086-84fb-a938864eb9ac> | 3.59375 | 1,428 | Knowledge Article | Science & Tech. | 21.903633 |
Instances of a structured type hold more than one value. Structured types include arrays and records.. A type can have unlimited levels of structuring.
An array represents an indexed collection of elements of the same type (called the base type). Because each element has a unique index, arrays, unlike sets, can meaningfully contain the same value more than once. Arrays can be allocated statically or dynamically.
Static arrays have a fixed size or length:
array[indexType1..indexType2] of baseType;
...where each indexType is an ordinal type whose range does not exceed 2GB. Since the indexTypes index the array, the number of elements an array can hold is limited by the product of the sizes of the indexTypes. indexTypes are Integers.
In the simplest case of a one-dimensional array, there is only a single indexType. For example:
var MyArray: array [1..100] of Char;
declares a variable called MyArray that holds an array of 100 character values. Given this declaration, MyArray denotes the third character in MyArray. If you create a static array but don't assign values to all its elements, the unused elements are still allocated and contain random data; they are like uninitialized variables.
A multidimensional array is an array of arrays. For example:
type TMatrix = array[1..10] of array[1..50] of Single;
TMatrix represents an array of 500 real (in this case, Single) values. A variable MyMatrix of type TMatrix can be indexed like this: MyMatrix.
The standard functions Low and High operate on array type identifiers and variables. They return the low and high bounds of the array's first index type. The standard function Length returns the number of elements in the array's first dimension.
Dynamic arrays do not have a fixed size or length. Instead, memory for a dynamic array is reallocated when you assign a value to the array or pass it to the SetLength or SetArrayLength procedure. For example:
var MyFlexibleArray: array of Single;
...declares a one-dimensional dynamic array of singles. The declaration does not allocate memory for MyFlexibleArray. To create the array in memory, call SetLength. For example, given the previous declaration:
...allocates an array of 20 reals, indexed 0 to 19. Dynamic arrays are always integer-indexed, always starting from 0.
If X and Y are variables of the same dynamic-array type, X := Y points X to the same array as Y (There is no need to allocate memory for X before performing this operation). For example, after this code executes:
the value of A is 2 (If A and B were static arrays, A would still be 1).
A, B: array of Integer;
A := 1;
B := A;
B := 2;
Assigning to a dynamic-array index (for example, MyFlexibleArray := 7) does not reallocate the array. Out-of-range indexes are not reported at compile time.
When dynamic-array variables are compared, their references are compared, not their array values. Thus, after execution of the code:
A = B returns False but A = B returns True.
A, B: array of Integer;
A := 2;
B := 2;
Once a dynamic array has been allocated, you can pass it to the standard functions Length, High, and Low. Length returns the number of elements in the array, High returns the array's highest index (that is, Length - 1), and Low returns 0. In the case of a zero-length array, High returns -1 (with the anomalous consequence that High < Low).
Note: In some function and procedure declarations, array parameters are represented as array of baseType, without any index types specified. For example, function CheckStrings(A: array of String): Boolean;
This indicates that the function operates on all arrays of the specified base type, regardless of their size, how they are indexed, or whether they are allocated statically or dynamically.
Multidimensional Dynamic Arrays:
To declare multidimensional dynamic arrays, use iterated array of ... constructions. For example:
type TMessageGrid = array of array of string;
var Msgs: TMessageGrid;
...declares a two-dimensional array of strings.
You can create multidimensional dynamic arrays that are not rectangular. The first step is to call SetLength, passing it parameters for the first n dimensions of the array. For example:
var Ints: array of array of Integer;
allocates ten rows for Ints but no columns. Later, you can allocate the columns one at a time (giving them different lengths); For example:
makes the third column of Ints five integers long. At this point (even if the other columns haven't been allocated) you can assign values to the third column - for example, Ints := 6.
A record represents a heterogeneous set of elements. Each element is called a field; the declaration of a record type specifies a name and type for each field. The syntax of a record type declaration is:
where recordTypeName is a valid identifier, each type denotes a type, and each fieldList is a valid identifier or a comma-delimited list of identifiers. The final semicolon is optional.
recordTypeName = record
For example, the following declaration creates a record type called TDateRec:
TDateRec = record
Month: (Jan, Feb, Mar, Apr, May, Jun,
Jul, Aug, Sep, Oct, Nov, Dec);
Each TDateRec contains three fields: an integer value called Year, a value of an enumerated type called Month, and another integer between 1 and 31 called Day. The identifiers Year, Month, and Day are the field designators for TDateRec, and they behave like variables. The TDateRec type declaration, however, does not allocate any memory for the Year, Month, and Day fields; memory is allocated when you instantiate the record, like this:
var Record1, Record2: TDateRec;
This variable declaration creates two instances of TDateRec, called Record1 and Record2.
You can access the fields of a record by qualifying the field designators with the record's name:
Or use a with statement:
Record1.Year := 1904;
Record1.Month := Jun;
Record1.Day := 16;
with Record1 do
Year := 1904;
Month := Jun;
Day := 16;
You can now copy the values of Record1's fields to Record2:
Record2 := Record1;
Instead of defining record types, you can use the record construction directly in variable declarations:
var S: record
However, a declaration like this largely defeats the purpose of records, which is to avoid repetitive coding of similar groups of variables. Moreover, separately declared records of this kind will not be assignment-compatible, even if their structures are identical. | <urn:uuid:d216ccec-662a-4979-a805-a1cb560f0bfd> | 3.484375 | 1,488 | Comment Section | Software Dev. | 45.294354 |
Peridotites from the boundary between the Atlantic Ocean crust and the West Iberia continental margin (west of Portugal) were drilled during Leg 149 in Holes 897C, 897D, and 899B. These peridotites have been serpentinized intensively with more than 90% of the primary phases being essentially lizardite. No talc or antigorite were detected.
During an early episode of hydrothermal interaction (500° to 350°C), rare tremolites and chlorites formed after pyroxenes and spinel. Amphiboles are undeformed except in narrow shear zones. Serpentinization cannot be linked with this high-temperature hydrous event.
Like the serpentines drilled 100 km to the north at Hole 637A, Leg 103, the great majority of serpentines from the Leg 149 peridotites have 18O values around 10‰ and have large 18Oserpentine–magnetite (12‰), which confirms that the serpentinization event occurred at low temperature (<200°C) as a consequence of the introduction of a large amount of seawater.
Calcite, which fills veins and cracks in the peridotites, precipitated from seawater at very low temperatures (19° to 13°C).
We think the lack of deep-seated serpentinization mineralogical records (antigorite and talc) that would have formed a deep low-velocity zone (shown by seismic studies at the roof of the mantle peridotites at 5 to 7 km below the top of the sediment-free basement) may be explained by retrogression of antigorite and talc to low-temperature lizardite. Another explanation is the possibility that Leg 149 peridotites do not record a high-temperature serpentinization episode because serpentinization in this deep zone was not possible. However, the complete absence of antigorite and talc in the Hole 899B peridotites (in which the low-temperature serpentines overprinted the peridotites much less intensively) and 18O/16O ratios of the lizardites do not support the first possibility unless a complete dissolution-precipitation process affected all the antigorite and the talc. The second possibility suggests that the deep low-velocity zone would not be made of serpentines.
of how to reference the whole or part of this volume can be found under "Citations"
in the preliminary pages of the volume.
2Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe, 2 place Jussieu, F-75251 Paris cedex 05, France. email@example.com
3Laboratoire de Pétrologie, Département des Sciences de la Terre, Université de Nantes, 2 rue de la Houssiniére, F-44072 Nantes cedex 03, France.
4Laboratoire de Géodynamique Sous-Marine, CNRS Université Pierre et Marie Curie, BP 48, F-06230 Villefranche sur Mer, France.
Date of initial receipt: 17 January 1995
Date of acceptance: 3 November 1995
Reproduced online: 21 May 2004 | <urn:uuid:fe773796-fb29-4a2e-8269-f4e465eb6c96> | 2.75 | 699 | Academic Writing | Science & Tech. | 21.650658 |
I just began but been noticing that most sites say you end with ; but looking more some other codes use " or > to end. I was wondering what is the difference?
all statements in c++ ends with ;
and when u see " or > at the end, it means its not the end of the statement
it continues on the next line until it hits ';'
Is there any examples for compound statements?
Thanks in advance. | <urn:uuid:3661ec97-4ec4-493e-b9a6-29c47478ff8b> | 2.9375 | 92 | Comment Section | Software Dev. | 67.54 |
Carolina Environmental Diversity Explorations
Hurricanes on sandy shorelines · By Dirk Frankenberg
Living in dunefields
Figure 18 shows three choices for construction on nearshore dunes. Most of the house on the left is built in front of the dune, the middle house is built on top of it, and the one on the right is built behind it. The risk of damage from storm surge and overwash decreases with distance from, and height above, the open beach. The dunefield here is relatively high, so the houses in the middle and on the left are theoretically better protected than the one on the left, but all three appear to have survived Floyd and Dennis without much damage. | <urn:uuid:22dc66f0-9d40-4686-8f45-c9c144de0b7b> | 2.6875 | 144 | Knowledge Article | Science & Tech. | 37.144185 |
Seaweed is a term applied to multicellular, marine algae which are large enough to be seen by the eye unaided. Some can grow to up to 60 metres in length. Seaweeds include members of the red, brown and green algae. They are members of the kingdom Protista meaning they are not Plants. They do not have the vascular system (internal transport system) of plants and do not have roots, stems, leaves and flowers or cones. Like plants they use the pigment chlorophyll for photosynthesis but also contain other pigments which may be coloured red, blue, brown or gold.
Blue-green algae are not marine algae. They are in a group called cyanobacteria and are more closely related to bacteria. Some cyanobacteria form brown, green, red or purple tufts on coral reefs.
To survive seaweeds need salty or brackish water, sunlight and a surface to attach themselves to. Because of these factors they are generally found in the littoral zone (this includes the intertidal zone but generally extends out much further). They are usually found on rocky rather than on sand or shingle shores.
Seaweeds are a food source for marine animals such as sea urchins and fishes, and are the base of some marine food webs. They also provide shelter and a home for numerous fishes, invertebrates, birds and mammals.
The kelps form dense forests which support entire underwater communities providing both food and shelter. Intertidal seaweeds can be exposed to many environmental stresses including drying out when not under water, temperature and salinity changes and wave action.
Kelp (a brown alga) forest
Structure of seaweeds
Thallus: the entire body of a seaweed. Lamina: a flattened structure that is resembles a leaf. Sorus: a cluster of spores spore. Air bladders: a hollow, gas-filled structure organ which helps the seaweed float, found on the blade). Other seaweeds (e.g. kelp) have floats which are located between the lamina and stipe. Stipe: a stem-like structure, not all seaweeds have these. Holdfast: a specialized structure on the base of a seaweed which acts as an “anchor” allowing it to attach to a surface (e.g. a rock). Haptera: finger-like extensions of holdfast anchoring to benthic substrate.
Seaweeds play a very important roles in many marine communities. They are a food source for many marine animals such as sea urchins and fishes, and form the base of some food webs. They also provide shelter and a home for numerous fishes, invertebrates, birds, and mammals.
Structure of marine algae
Seaweed life and reproductive cycles can be quite complicated. Some seaweeds are perennial, living for many years, while are annuals. Annual seaweeds generally begin to grow in the spring, and continue throughout the summer. Some red seaweeds have a life span of 6 to 10 years.
Seaweeds can reproduce sexually, by the joining of specialized male and female reproductive cells, called gametes. After they are released from the sporophyte, the spores settle and grow into male and female plants called gametophytes. The gametophytes produce gametes (sperm or eggs). The sperm and eggs are either retained within the gametophyte plant body, or released into the water. Eggs are fertilized when the sperm and egg fuse together, and a zygote is formed. Zygotes develop and grow into sporophytes, and the life cycle continues.
Seaweeds display a variety of different reproductive and life cycles and the description above is only a general example of one type, called alternation of generations. In a few species there is an alternating sexual and asexual reproductive process with every generation.
Seaweeds can also reproduce asexually through fragmentation or division. This occurs when parts of a plant break off and develop directly into new individuals. All offspring resulting from asexual reproduction are clones; they are genetically identical to each other and the parent seaweed.
Reproduction of algae
Uses of Seaweed
Seaweeds area food source for humans especially in East Asia, it is most commonly associated with Japanese food. Seaweeds also are used to make a number of food additives such as alginates and carrageenan which is used in cooking and baking as a vegetarian alternative to gelatine.
Many seaweeds are used as medicine. Alginates are used in wound dressings and in the production of dental moulds and agar is used very widely in Microbiology to help grow bacterial cultures.
Seaweeds are ingredients in toothpaste, cosmetics and paints and are used in industrial products such as paper coatings, adhesives, dyes, gels, explosives and many more.
Much of the oil and natural gas we use today formed from seaweeds which partially decomposed on the sea floor many millions of years ago.
Japanese food uses seaweeds extensively - Kombu a brown alga and Kim nori a red alga
Algae: The World's Most Important Plants
Believe it or not, your life depends on algae! Join Scripps' Institution's Russell Chapman
as he discusses the important roles algae have played in the development of life as we know it.
Series: "Perspectives on Ocean Science" [12/2006] [Science] [Show ID: 11931]
I would sincerely like to thank the many members of the Flickr community who have given me permission to use their wonderful images for this unit. Their contributions really make this unit come alive! | <urn:uuid:66eda191-ae7f-4066-9ba2-a98695f6f615> | 4.34375 | 1,185 | Knowledge Article | Science & Tech. | 39.446279 |
How Does Glue Work?
How can glue stick things together?
There are many variants of glue and there are some slight differences in the
details of how they work, so I will just talk about how glues work in general.
The first requirement is that glues must be able to creep or flow into the
crevices of the two objects that are being attached together. At the microscopic
level, even surfaces that appear smooth will, in general, be very rough - full of
mountains and valleys and crevices. The glue has to be able to seep into these
crevices. The second requirement is that the glue must be able to change its
molecular structure so that it changes from a fluid to a solid - it must harden.
There are many ways this can be achieved. Reaction with atmospheric oxygen,
addition of a cross-linker, thermosetting (hardening due to an application of
heat), etc. All of these processes have the result of making the glue harden or
So, what we can imagine then, is that the glue, as a fluid will seep into the
microscopic cracks and crevices of the two objects that are being attached
together. Then, through some predetermined mechanism, the glue hardens or cures.
The result is that the parts of the glue that have seeped into the objects at the
microscopic level are like anchors and hold onto the objects. The hardening
prevents those anchors from getting dislodged and also makes the glue a hard
object to break.
Greg (Roberto Gregorius)
Click here to return to the Material Science Archives
Update: June 2012 | <urn:uuid:d31b8d1f-851c-4608-92e0-edc4a3eb3d23> | 4.15625 | 355 | Knowledge Article | Science & Tech. | 52.380842 |
Reflectivity: White vs Silver
Name: Elizabeth H.
Date: Sunday, September 15, 2002
Which reflects more light,a white polished surface or a
silver mirrored surface?
In most cases, they would reflect very similar amounts. The biggest
difference is where they reflect it. A shiny mirror reflects almost all of
the light in the same direction. This makes a clear image in the mirror. A
white polished surface reflects the light in all directions. This why walls
in reading rooms are often painted white. The light from a few bulbs
I do not know that there is a definite rule. It would depend on the material
and possibly on the color light used. A good test is sunlight. Take two
shiny white plates. Cover the top of one with aluminum foil, shiny side
out. Be sure the foil is very smooth and there is not any air between the
plate and the foil. Put a paper grocery bag or large piece of cardboard on
the ground in the sunlight on a hot day when the sun is very bright. Place
both plates on the bag. After fifteen minutes, take the foil off. See
which plate is hottest. The hottest plate absorbed the most light. The
coolest plate reflected the most light.
Dr. Ken Mellendorf
Illinois Central College
This is not as straight forward as it sounds on first reading. When light
(or other electromagnetic radiation) strikes a FLAT surface it can do one or
more of several things:
1. It can be REFLECTED at angle equal to the angle
of incidence (usually measured as the angle from the perpendicular of the
2. In can be TRANSMITTED through the surface. In this case the
path of the light will be changed depending upon the index of refraction of
the substance, (the quantitative amount is determined by a relation called
3. ALL of the light can be ABSORBED by the substance, in which
case the surface will appear BLACK.
4. SOME of the wavelengths of the light
can be ABSORBED by the substance. If the incident light is WHITE, that is
composed equally of all wavelengths of visible light, the REFLECTED light
will appear colored. The color will be the COMPLEMENT of the absorbed
wavelengths. That is, WHITE light MINUS the absorbed wavelengths. So if blue
light is absorbed, the REFLECTED light will appear yellow; if red light is
absorbed, the REFLECTED light will appear green.
5. The light can be REFLECTED and SCATTERED. That is the angle of reflection
in different than the angle of incidence. If the surface is rough and
randomly irregular, the REFLECTED light will appear white.
6. If the surface
is irregular, but irregular in a regular way, such as a series or closely
spaced scratch marks, the light will be DIFFRACTED, and the surface is
called a GRATING. Then the reflected light will be the color of the rainbow.
And incident white light will be decomposed into its various contributing
All of these six things are going on at the same time to a
greater or lesser extent, so it is difficult to say with confidence whether
a surface that is white and polished, or is a mirror, whether the amount of
total energy reflected is greater or less for one or the other.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:d1ea263f-979a-4a8d-a157-2a0d2c365248> | 3.640625 | 735 | Q&A Forum | Science & Tech. | 59.601743 |
12.307 Weather and Climate Laboratory (MIT)
Course 12.307 is an undergraduate course intended to illustrate, by means of 'hands on' projects, the basic dynamical and physical principles that govern the general circulation of the atmosphere and ocean and the day to day sequence of weather events. The course parallels the content of the new undergraduate textbook Atmosphere, Ocean and Climate Dynamics by John Marshall and R. Alan Plumb.
Interdisciplinary Science Near Space Student Document
Near Space is an introduction to some of the scientific concepts of the global climate system, and to the concept of anthropogenic climate change. In this module we will look at physical, chemical and biological influences on the climate.
Interdisciplinary Science Earth Through Time Student Document
The Earth Through Time module examines our planet in terms of its major systems; the atmosphere, hydrosphere, cryosphere, geosphere and the biosphere, all of which are constantly interacting. The module explores the topic of climate change throughout Earth’s history; climate change is not just a contemporary phenomenon, it has happened in the geological past at times abruptly and catastrophically.
Second Life Guides
These Second Life training guides have been split into three parts. Part 1 takes you through your first steps in achieving a Second Life by setting up your account and creating your avatar (your virtual persona in Second Life). Part 2 reminds you of the basic skills you require to operate in Second Life and enjoy the experience. Part 3 is about taking part in or directing groups for learning in Second Life.
This module challenges you to come up with ways to think more about climate change and the action your organisation can take to reduce its carbon footprint, whilst improving healthcare. Online interactive learning resource from HealthKnowledge website, for Public Health practitioners, healthcare workers and all those wishing to increase their public health skills.
Oceans research: News from the "Big Blue"
This Oxford at Said seminar was dedicated to the subject of oceans. Three researchers from the University of Oxford cover the topics oceans and the impact of climate change, understanding ocean ecology and how to generate energy from the tides. All life comes out of the ocean and is connected with the ocean. Over 70 per cent of the Earth's surface is covered by oceans earning planet earth the nick name the blue planet. Life within the sea evolved 3 billion years prior to life on land, yet much o
Utilities management (Energy and water) Session Outline
Part Five of Greening Business: Organizations can make many improvements to their management of energy and water, from energy conservation measures through individual behaviour, smart energy systems and building improvements, to maximising their energy supply from renewable sources and energy generation on site. Water conservation measures can be implemented including low flush toilets and low flow taps, through to investigating water efficiency in industrial processes and water harvesting sche
Doing the right thing : corporate social responsibility in a global marketplace
Globalisation, mass consumer awareness and public accountability are all factors in persuading companies to adopt ethical policies. As companies become more accountable not only for their own actions but for those within their supply chain, they have to adapt to ensure success within the context of the global society they operate in. Professor Jeremy Moon (Professor of Corporate Social Responsibility at the University of Nottingham Business School and Director of the International Centre for Cor | <urn:uuid:432b0184-b83f-416c-a1a7-3dcc31df2663> | 2.6875 | 668 | Content Listing | Science & Tech. | 20.921609 |
On Science Podcast
Learning juicy details about someone can change the way you see them — literally, according to a new study.
Learning negative information about people can change the way you see them — literally, according to a new study. It's an unconscious response orchestrated by your brain's visual processing system, and it may have helped early humans exploit gossip to get ahead.
May 19, 2011 The red-crested tree rat hadn't been seen by scientists for more than a century — until this May. The guinea pig-sized creature, with a fiery-red patch of fur on its head and a long black and white tail, was spotted by two conservationist volunteers working in Columbia.
May 16, 2011 Astronomers at the SETI Institute say California's budget crisis has forced the shutdown of the Allen Telescope Array, a powerful tool in the search for extraterrestrial intelligence. | <urn:uuid:01560f76-b620-4471-9ed4-757c28bd1812> | 3.046875 | 179 | Content Listing | Science & Tech. | 44.609144 |
|Jan1-07, 05:03 PM||#1|
What is a reflection
1. The problem statement, all variables and given/known data
The point Q is the reflection of P(-1,3,4), in the plane with equation 2x-y+z=1.
Determine the coordinates of Q
2. Relevant equations
3. The attempt at a solution
Well im not really looking for a solution. I just want to know what I am trying to find. What is a reflection in three space. Where is point Q
|Jan1-07, 09:43 PM||#2|
Q is on the opposite side of the plane, at the same distance from the plane as P.
There's only one straight line from P to the plane that is perpendicular to the plane. Follow the continuation of that line (through the plane) until you are as far away from the plane as P. That point is Q.
|Jan2-07, 06:34 AM||#3|
What Fredrik said. And it is called a reflection because that is how your reflection in a mirror appears: your reflection appears to be on the other side of the mirror in such a way that the mirror is a perpendicular bisector of any straight line from a point on your body to the reflection of that point.
Find the parametric equations of the line through P perpendicular to the plane (that's the easy part and it is very easy to choose the parameter so that P corresponds to parameter equal to 0. Find the parameter where the line intersects the plane (solve a single linear equation). If P corresponds to parameter 0, then Q will have parameter equal to twice that of the point of intersection.
|Jan2-07, 10:03 AM||#4|
What is a reflection
Thanks for the help so far
This is what I have done so far
I know that the plane is 2x-y+z=11
Therefore all line perpindicular to that plane have a direction of (2,-1,1)
The parametric equation of the line which passes through point P and hits the plane are
I substituted those values into the equation of the plane (2x-y+z=11)
and got t=2
I plugged t=2 back into the parametric equations and got the intersection point between between the line and the plane to be (3,1,6)
Now I am a little confused on what to do from here.
What i guessed to do is subtract the point (-1,3,4) from (3,1,6), and got (4,-2,2,) and i added that to (3,1,6) to get (7,-1,8)
if this is right why, and if it is wrong, how do i approach this..thanks
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Graphing Sunspot Cycles
An activity adapted from Rice University-Houston Museum of Natural Sciences, Summer Solar Institute, Being a Solar Astronomer
Type of Lesson: Investigation with evaluation worksheet
Time Needed: 90 minutes (or 2 class periods)
MEGOSE ES5 Describe and explain common observations of the day and night skies.
MEGOSE ES7 Compare our sun to other stars and star systems.
MEGOSE ES8 Explain common observations of the day and night sky.
Quick Summary of Lesson
The student will be able to determine existing patterns in sunspot numbers.
The student will be able to plot sunspot numbers to determine these relationships.
The student will be able to use these relationships to determine the approximate number of sunspots for a year in the near future.
sunspot numbers (available on Student Activity Sheet down below)
1. Have students complete the sunspot plot for the table of sunspot numbers given on the student worksheet.
2. Students should then complete the questions on the student worksheet. It might be helpful to lead a discussion concerning the questions.
Student Activity Sheet
Please click here for student activity sheets. All activities on the Windows to the Universe site may be printed and reproduced if being used for educational purposes.
Notes to the Teacher
If students are graphing all of the given sunspot numbers, it will likely take them more than an hour to graph. They can get a good feel for the solar cycle and answer the questions on the student worksheet by just graphing a subset of the given sunspots. If you want to take less time to do this activity, have students graph from 1850 to present.
An example of the sunspot plot your students should come up with appears here. You'll see the labelling of the maximums with "M" and minimums with "m". There is of course a regular pattern of sunspot numbers. Scientists say the sunspot cycle is 11 years long. The average your students should get from the years represented in this table is ~10.8. The year 2000 was a solar maximum. The year 2011 should also be close to a solar maximum, making 2017 close to a minimum.
Sunspots have been known and recorded for hundreds of years. The reporting techniques have not always been consistent. Currently we can determine the average number of sunspots appearing each day. The yearly number is the annual average daily sunspot number. It is highly instructive to determine the nature of the cyclic characteristics of sunspot numbers. A large number of natural phenomena have been related to sunspots (or the periods of great numbers or few, etc.). A new area of scientific research called spaceweather has been formed to try and explain these Sun-Earth connections.
Need More Information? Try Using Windows to the Universe
Please use these links for further ideas or more information:
The Difference Between the Sun and Other Stars
Plotting Sunspots another classroom activity
The Solar Cycle
Tracking an Active Region another classroom activity
Last modified January 19, 2009 by Jennifer Bergman.
The source of this material is Windows to the Universe, at http://windows2universe.org/ from the National Earth Science Teachers Association (NESTA). The Website was developed in part with the support of UCAR and NCAR, where it resided from 2000 - 2010. © 2010 National Earth Science Teachers Association. Windows to the Universe® is a registered trademark of NESTA. All Rights Reserved. Site policies and disclaimer. | <urn:uuid:fe9a187f-69dc-418f-9ca8-0e8a1ccf2a88> | 3.765625 | 728 | Tutorial | Science & Tech. | 48.366547 |
Functions for number conversion and formatted string output.
Output not more than size bytes to str according to the format string format and the extra arguments. See the Unix man page snprintf(2).
Output not more than size bytes to str according to the format string format and the variable argument list va. Unix man page vsnprintf(2).
PyOS_snprintf() and PyOS_vsnprintf() wrap the Standard C library functions snprintf() and vsnprintf(). Their purpose is to guarantee consistent behavior in corner cases, which the Standard C functions do not.
The wrappers ensure that str*[*size-1] is always '\0' upon return. They never write more than size bytes (including the trailing '\0') into str. Both functions require that str != NULL, size > 0 and format != NULL.
If the platform doesn’t have vsnprintf() and the buffer size needed to avoid truncation exceeds size by more than 512 bytes, Python aborts with a Py_FatalError.
The return value (rv) for these functions should be interpreted as follows:
The following functions provide locale-independent string to number conversions.
Convert a string s to a double, raising a Python exception on failure. The set of accepted strings corresponds to the set of strings accepted by Python’s float() constructor, except that s must not have leading or trailing whitespace. The conversion is independent of the current locale.
If endptr is NULL, convert the whole string. Raise ValueError and return -1.0 if the string is not a valid representation of a floating-point number.
If endptr is not NULL, convert as much of the string as possible and set *endptr to point to the first unconverted character. If no initial segment of the string is the valid representation of a floating-point number, set *endptr to point to the beginning of the string, raise ValueError, and return -1.0.
If s represents a value that is too large to store in a float (for example, "1e500" is such a string on many platforms) then if overflow_exception is NULL return Py_HUGE_VAL (with an appropriate sign) and don’t set any exception. Otherwise, overflow_exception must point to a Python exception object; raise that exception and return -1.0. In both cases, set *endptr to point to the first character after the converted value.
If any other error occurs during the conversion (for example an out-of-memory error), set the appropriate Python exception and return -1.0.
New in version 3.1.
Convert a double val to a string using supplied format_code, precision, and flags.
format_code must be one of 'e', 'E', 'f', 'F', 'g', 'G' or 'r'. For 'r', the supplied precision must be 0 and is ignored. The 'r' format code specifies the standard repr() format.
flags can be zero or more of the values Py_DTSF_SIGN, Py_DTSF_ADD_DOT_0, or Py_DTSF_ALT, or-ed together:
If ptype is non-NULL, then the value it points to will be set to one of Py_DTST_FINITE, Py_DTST_INFINITE, or Py_DTST_NAN, signifying that val is a finite number, an infinite number, or not a number, respectively.
The return value is a pointer to buffer with the converted string or NULL if the conversion failed. The caller is responsible for freeing the returned string by calling PyMem_Free().
New in version 3.1.
Case insensitive comparison of strings. The function works almost identically to strcmp() except that it ignores the case.
Case insensitive comparison of strings. The function works almost identically to strncmp() except that it ignores the case. | <urn:uuid:a7c7795a-94a2-4cf3-86fb-bf1f63a32c4e> | 3.359375 | 841 | Documentation | Software Dev. | 62.007133 |
This page describes the International Standard that defines the C programming language as a guide to those who are new to either. It's based on what a newcomer to comp.lang.c would find useful to know about the Standard without getting specific about the contents and scope of the Standard. See also questions 11.1, 11.2 and 11.2b of the FAQ.
Versions of the C Standard
There are currently two main versions of the Standard: ISO/IEC 9899:1990 (commonly referred to as C89 or C90) and ISO/IEC 9899:1999 (commonly referred to as C99). As the naming indicates, C99 was ratified in 1999 and supersedes C89/C90, which was ratified in 1990. C99 has not been widely implemented in full so relying on its features for portability is not yet wise, although most C compilers fully implement C89/C90. Many compilers implement a subset of C99's features - sometimes as extensions.
C89/C90 and C99 are ISO standards, however C89/C90 was originally ratified by ANSI as X3.159-1989. The ANSI and ISO C89/C90 Standards are technically equivalent, but the section numbering of the Standard differs in its ANSI and ISO forms.
Prior to ANSI and ISO standardisation, C was unofficially standardised around "The C Programming Language", by Brian Kernighan and Dennis Ritchie (Prentice Hall, 1978). This unofficial C Standard is commonly referred to as K&R, although whether it can be considered to be purely based on the specification within this book (Appendix A of Edition 1) is not clear: actual implementations did not accurately follow the specifications of Appendix A - there were several generally accepted changes and some considered the AT&T reference manual to be more authoritative - hence the need for an official standard (the previous sentence is based on a comp.std.c post, 2 Nov 2005, by Douglas Gwyn).
The Committee (WG14)
The ISO Working Group that currently manages the Standard is known as WG14. Much documentation is available through their website.
Drafts of the Standard are circulated for comment prior to ratification and publication. There are freely available drafts of both versions of the Standard, although an accessible C89/C90 draft with ISO section numbering is not known to exist. The drafts, whilst useful, are not definitive: the official versions of the Standard do differ from the draft versions although not dramatically. A commonly referenced draft is N869 (a draft of C99), although many people think that post-C99 drafts are better because there were changes between N869 and the final standard.
The next version of the Standard (not currently being actively worked on) is commonly referred to as C0X. The starting point for this version is the N1124 draft, which incorporates the first two technical corrigenda on top of the C99 Standard and N1256 which contains the first three.
Each version of the Standard has a freely available rationale describing the intent of its authors and other helpful background.
Corrections and updates
Each version of the Standard has corrections and updates in the form of amendments and technical corrigenda, detailed on the WG14 homepage.
The terms C89/C90 generally refer to the Standard as corrected by Technical Corrigendum 1 (ISO/IEC 9899 TCOR1), 1994, and Technical Corrigendum 2 (ISO/IEC 9899 TCOR2), 1996.
The term C94 (or C95) is sometimes used to refer to C89/C90 plus Normative Addendum (aka Amendment) 1, whose primary addition was support for international character sets. This amendment was integrated into the later C99 version of the Standard, so it is necessary as a separate document only for C89/C90.
There is a process for proposing amendments or requesting clarification on the Standard. These proposals/requests are known as Defect Reports (DRs).
Obtaining the Standard
Neither the Standard nor its amendments are available free of charge, although its drafts, rationales, technical corrigenda (TCs) and defect report responses are.
The Standard can be purchased in hardcopy and/or downloadable digital format from national affiliates as described on the WG14 website. Two such national bodies are ANSI - through its eStandards Store - and SAI Global (originally Standards Australia) which sells all of the ISO C Standard publications. One international source is Techstreet.
Listed below are direct links to pages for purchase or free download of the Standard, its TCs, amendments, drafts, rationales and defect report responses for each version of the Standard. The set of documents is comprehensive whereas the list of sources obviously is not.
When comparing prices, a tool such as XE.com's currency converter can be useful.
- Purchase the Standard
- as an ISO publication from SAI Global (hardcopy only)
- as the Australian-ratified standard AS 3955-1991 from ANSI or from SAI Global.
- as the UK-ratified standard EN 29899:1993 from ANSI
- as part of Herbert Schildt's book The Annotated ANSI C Standard. Mr. Schildt's book, however, is well known in the community for being one of the worst books ever written on C and the C standard. It has been widely and deeply discredited.
- Purchase Amendment 1 (upgrades the Standard to C94 aka C95)
- View Technical Corrigendum 1 (1994) on the WG14 site (html)
- View Technical Corrigendum 2 (1996) on the WG14 site (html)
- Download a Draft, ANSI-based from Flash Gordon's site (plain-text; ANSI section numbering) which was previously hosted by Dan Pop at http://danpop.home.cern.ch/danpop/ansi.c
- View the Rationale on Lysator's C site
- Download the Defect Reports and Responses from the WG14 site (gzip-compressed tar archive of plain-text files)
- Purchase the Standard
- Purchase the Standard as an ISO publication from ANSI or from SAI Global or from the ISO store
- Purchase The C Standard - includes the C Rationale - Incorporating Technical Corrigendum No.1 John Wiley & Sons ISBN 978-0-470-84573-8
- Download Technical Corrigendum 1 (2001) from the WG14 site (pdf) or from the ISO/IEC ITTF site (pdf) or from ANSI (pdf)
- Download Technical Corrigendum 2 (2004) from the WG14 site or from ANSI (pdf) or from ISO's store (registration required) or from SAI Global (registration required)
- Download Technical Corrigendum 3 (2007) from Open Standards (pdf)
- Download a Draft, N869 from the WG14 site (poorly formatted, gzip-compressed plain-text) or from Charles B. Falconer's site (reformatted, bzip2-compressed plain-text)
- Download the Rationale from the WG14 site (pdf)
- View the Defect Reports and Responses on the WG14 site
Commentary, differences and incompatibilities
These links document some of the differences between versions of the Standard, as well as with the C++ Standard.
- The New C Standard (version b; 10.1 Mb pdf) (Derek M Jones)
- C0x Annotated Changes (companion site to the above book; with search facility)
- Differences Between C90 and C99 (Thomas Wolf)
- Are you Ready For C99? (Kuro5hin article)
- Incompatibilities Between ISO C and ISO C++ (David Tribble)
- Commentary on Normative Addendum (Amendment) 1 (Clive D.W. Feather; courtesy Lysator's C Site; was applied to C89/C90 and upgrades it to "C94" aka "C95")
Standards-compliance in compilers
Most C compilers do not yet fully support the C99 standard although C89/C90 support is widespread. See the C Compilers page for a list of compilers that support C89/C90 - C99 support is listed there where known.
There are several commercial validation suites; the owner of one of them, Perennial, maintains a page where it lists compilers and libraries that it has certified to C99.
The vendor of a compiler that claims C99 conformance (though not listed on Perennial's certification page) - Comeau C/C++ - provides the Online Comeau C/C++ Compiler which can be used without charge to syntax-check C89/C90 and C99 code using a web interface.
The vendor of a commercial library listed on Perennial's certification page - Dinkumware - have run tests that purport to show that none of the popular compiler's libraries fully implement C99; the results of these tests are disputed - see this post and its follow-ups in the GNU libc mailing list archives. | <urn:uuid:7b02b2bd-d1f2-47cd-97d8-c8ec7befd3bd> | 3.09375 | 1,944 | Documentation | Software Dev. | 51.994532 |
“Red and dead” is the unflattering label astronomers attach to giant elliptical galaxies full of aged stars. But funeral plans may be premature. With the help of the Hubble Space Telescope’s recently enhanced vision, researchers have uncovered flickers of star formation in these quiescent galaxies.
Nobody had ever observed star birth in red-and-dead galaxies (old stars glow red, while younger stars are bluer), but University of Michigan astronomer Joel Bregman had a hunch that some of them still harbor enough pristine gas to sustain a stellar nursery. He decided to point Hubble’s Wide Field Camera 3, an addition made to the scope in 2009, at four nearby aging galaxies to hunt for the telltale ultraviolet glow of young stars. Bregman considered three of them promising candidates. The fourth, named Messier 105, was the ultimate test: It was the reddest and deadest galaxy he could find. “We looked at probably the universe’s most boring galaxy,” he says. “We thought nothing would be going on there.”
As Bregman hoped, dozens of young stars turned up in each of the three promising galaxies—and as an added surprise, they even appeared in Messier 105. The rate of star formation is a small fraction of what goes on in a younger galaxy like the Milky Way, but even these low levels of activity will force theorists to revise their models of how galaxies evolve. | <urn:uuid:f800f23c-f2ba-484e-9984-4eb98c71b2af> | 3.046875 | 300 | Truncated | Science & Tech. | 46.190909 |
The data format used by pickle is Python-specific. This has the advantage that there are no restrictions imposed by external standards such as XDR (which can't represent pointer sharing); however it means that non-Python programs may not be able to reconstruct pickled Python objects.
By default, the pickle data format uses a printable ASCII representation. This is slightly more voluminous than a binary representation. The big advantage of using printable ASCII (and of some other characteristics of pickle's representation) is that for debugging or recovery purposes it is possible for a human to read the pickled file with a standard text editor.
There are currently 3 different protocols which can be used for pickling.
Refer to PEP 307 for more information.
If a protocol is not specified, protocol 0 is used. If protocol is specified as a negative value or HIGHEST_PROTOCOL, the highest protocol version available will be used.
Changed in version 2.3: The bin parameter is deprecated and only provided for backwards compatibility. You should use the protocol parameter instead.
A binary format, which is slightly more efficient, can be chosen by specifying a true value for the bin argument to the Pickler constructor or the dump() and dumps() functions. A protocol version >= 1 implies use of a binary format.
See About this document... for information on suggesting changes. | <urn:uuid:6dade427-d05a-41ab-8be5-c671c0303214> | 3.4375 | 282 | Documentation | Software Dev. | 41.8675 |
See also:mathematics, a
See also:curve having ordinates which are a measure of the
See also:area (or quadrature) of another curve . The two most famous curvesof this class are those of Dinostratus and E . W . Tschirnhausen, which are both related to the circle . The quadratrix of Dinostratus was well known to the
See also:ancient Greek geometers, and is mentioned by
See also:Proclus, who ascribes the invention of the curve to a contemporary of
See also:Socrates, probably Hippias of Elis . Dinostratus, a Greek geometer and
See also:disciple of
See also:Plato, discussed the curve, and showed how it effected a
See also:mechanical solution of squaring the circle . Pappus, in his Collections, treats of its
See also:history, and gives two methods by which it can be generated . (I) Let a
See also:line be
See also:drawn on a right circular cylinder; a
See also:surface is then obtained by
See also:drawing lines from every point of this spiral perpendicular to its
See also:axis . The orthogonal
See also:projection of a section of this surface by a
See also:plane containing one of the perpendiculars and inclined to the axis is the quadratrix . (2) A right cylinder having for its
See also:base an Archimedean spiral is intersected by a right circular
See also:cone which has the generating line of the cylinder passing through the initial point of the spiral for its axis . From every point of the curve of intersection, perpendiculars are drawn to the axis . Any plane section of the screw (plectoidal of Pappus) surface so obtained is the quadratrix .
Another construction is shown in fig . 1 .
See also:ABC is a quadrant in which the line AB and the arc AC are divided into the same number of equal parts. c Radii are drawn from the centre of the quadrant to the points of division of the arc, and these radii are intersected by the lines drawn parallel to BC and through the corresponding points on the
See also:radius AB . The locus of these intersections is the quadratrix . A mechanical construction is as follows: Let AMP be a semicircle with centre 0 (fig . 2) . Let PQ be the
See also:ordinate of the point P on the circle, and let M be another point on the circle so related to P that the ordinate PQ moves from A to 0 in the same
See also:time as the vector OM describes a quadrant . Then the locus of the intersection of PQ and OM is the quadratrix of Dinostratus . The cartesian equation to the curve is y = x cot 2a, which shows that the curve is symmetrical about the axis of y, and that it consists of a central portion flanked by infinite branches (fig . 2) . The asym- ptotes are x= 2na, n being an integer . The intercept on the axis of y is 2a/a; therefore, if it were possible to accurately construct the curve, the quadrature of the circle would be effected .
The curve also permits the solution of the problems of duplicating a
See also:cube (q.v.) and trisecting an
See also:angle . The quadratrix of Tschirnhausen is constructed by dividing the arc and radius of a quadrant in the same number of equal parts as before . The mutual intersections of the lines drawn from the points of division of the arc parallel to AB, and the lines drawn parallel to BC through the points of division of AB, are points on the quadratrix (fig . 3) . The cartesian equation is y = a cos ,rx/2a . The curve is periodic, and cuts the axis of x at the points x= = (2n–1)a, n being an integer; the maximum values of y are =a . Its properties are similar to those of the quadratrix of Dinostratus .
QUADRATURE (from Lat. quadratura, a making square)
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Links to articles and home page are encouraged. | <urn:uuid:df66e11d-6cdc-4f5f-946e-45ee2588a232> | 3.578125 | 949 | Knowledge Article | Science & Tech. | 54.260556 |
Aquatic environments in Antarctica have changes over time with a changing climate. Small aquatic zones on the surface of glaciers ablation zones are comparatively constant and represent perhaps the largest volume of freshwater in many catchments. Recent research suggests that they harbour a variety of organisms, and may act as refugia for much of the Antarctic freshwater biota during adverse ... climatic excursions.
The aim of this study was to determine the role of ice-based habitats in conferring resilience. To this end we set out to compare the structure and function of ecosystems in ice-based, periglacial and nearby rock-based aquatic ecosystems to explore the hypothesis that they are linked through time and space and each provides a refuge and source of propagules for the other.
pH, major ions, nutrients, suspended particluates and benthic microbial mats were sampled for at a variety of locations over several seasons.
Samples were collected from three types of aquatic habitats in several sub-regions of the wider McMurdo Sound area of the Ross Sea region. The three types of habitat were supraglacial (cryoconite holes), perigalcial (proglacial ponds) and terrestrial ponds. One location was at ~400 m elevation on the Diamond Glacier (80 S) and two were on the Koettlitz Glacier (78 S), one close to sea level and one at 400 m elevation. The other locations were close to sea level on the McMurdo Ice Shelf at Bratina Island, the mouth of the Miers Valley, Upper and Lower Wright Valley, Hut Point Peninsula, Cape Evans, Cape Royds, and lakes Joyce, Vanda and Hoare. At each site we collected a suite of measurements of water chemistry, biological identity and genomic samples for bacteria and cyanobacteria. The data will be analysed to address our hypotheses regarding diversity and connectivity between aquatic habitats across a range of geographic scales. | <urn:uuid:ee05d0f9-06d1-4b4e-b177-123ddcd642f6> | 2.84375 | 392 | Academic Writing | Science & Tech. | 30.53398 |
Main difference between URL-rewriting and URL-encoding is that URL-rewriting is a technique to maintain user session if cookies are not enabled on client browser or browser doesn't support cookie while URL-encoding is a way to pass string to server containing special characters by converting special characters like space into some other characters like + . people often confuse between URL encoding and URL rewriting because of there names which sounds quite similar for new guys but functionality wise they are totally different to each other, Also servlet encodeURL() method adds more confusion because its sounds like its used for URL Encoding but indeed used for URL Rewriting. This is also a very popular servlet and JSP interview questions , I have also shared some more questions on my posts 10 Servlet Interview questions answers and 10 JSP interview questions and answers for Java programmer.
Difference between URL Rewriting and URL Encoding in JSP Servlet
You often need to encode URL before sending it to server and need to rewrite URL with session id in order to maintain session where cookie is not present. here are some more differences between URL-rewriting and URL encoding in Servlet JSP
1) java.servlet.http.HttpServletResponse methods encodeURL(String url) and encodeRedirectURL(String URL) is used to encode SesssionID on URL to support URL-rewriting. don't confuse with name encodeURL() because it doesn't do URL encoding instead itembeds sessionID in url if necessary. logic to include sessionID is in method itself and it doesn't embed sessionID if browser supports cookies or session maintenance is not required. In order to implement a robust session tracking all URL from Servlet and JSP should have session id embedded on it.
In order to implement URL-rewriting in JSP you can use use JSTL core tag all URL passed to it will automatically be URL-rewriting if browser doesn't support cookies.
While java.net.URLEncoder.encode() and java.net.URLDecoder.decode()is used to perform URL Encoding and decoding which replace special character from String to another character. This method uses default encoding of system and also deprecated instead ofthis you can use java.net.URLEncoder.encode(String URL, String encoding) which allows you to specify encoding. as per W3C UTF-8 encoding should be used to encode URL in web application.
2) In URL rewriting session id is appended to URL and in case of URL-encoding special character replaced by another character.
That's all on difference between URL-rewriting and URL-encoding, let me know if you come across some more differences between these URL Encoding vs URL-rewriting in Servlet and JSP. | <urn:uuid:4fa2b2bf-92bd-4193-ab02-e2834cdce5f5> | 2.984375 | 586 | Personal Blog | Software Dev. | 43.547869 |
Identifying acid-base species
Being able to readily identify a species with regards to its acid/base behavior is a very useful skill. This page provides basic drill and practice in this area. Though most of the species should be easily recognized, feel free to use whatever reference materials you wish. Ultimately the goal is to be able to run through the drills without the need of such aids.
- When you press "New Species", a formula will appear to the right of the table.
- Click on the appropriate bubble.
- Since the goal of this page is accuracy, you only get one attempt per compound. If you misidentify the species, the answer will appear and you will no longer be able to submit an answer to that question. | <urn:uuid:d00e73dd-703e-4552-bd9b-21182f0336a2> | 2.75 | 152 | Tutorial | Science & Tech. | 54.16282 |
Astronomers have discovered an exoplanet that experiences temperature swings of as much as 700 degrees within a matter of hours -- and are working to model the weather patterns there. Writing in the journal Nature, a team of astronomers describe the unusual behavior of planet HD80606b. The planet has an extremely irregular orbit. Most of the time, its distance from its sun is comparable to the distance of Earth and Venus from our own sun. Every 111 days, however, it makes a very close encounter with its sun, passing just a few million miles away. During that flyby, the radiation hitting the atmosphere of the gas giant increases by over 800fold. That rapid burst of heat results in massive storms, wind gusts measured in the thousands of miles per hour, and skies glowing red. We'll find out more.
Produced by Charles Bergquist, Director and Contributing Producer | <urn:uuid:f0e5764d-ea63-4b9c-8a89-45b451cf904f> | 3.671875 | 178 | Truncated | Science & Tech. | 46.924949 |
OpenLaszlo for HTML developers
HTML uses the <html> and <body> tags. Text can be wrapped in <p>, <div>, <span>, or left naked.
LZX uses the <canvas> tag. Text must be inside a <text> tag, or another tag that contains text (such as <inputtext> or <button>).
LZX is XML. Tags in LZX are case-sensitive, and require close tags. This makes LZX more like XHTML than like HTML 4.0.
Tags in LZX are case-sensitive.
<button>one</button> <BUTTON>two</BUTTON> <Button>three</buTToN>
LZX (and HTML):
LZX tags require close tags, either like this: <view></view>, or this: <view />.
LZX (and HTML):
HTML uses the <img> tag. In LZX, images are an attribute (source), not a tag; any LZX view can contain an image.
<img src="image.jpg" />
<view source="image.jpg" /> <image src="image.jpg" /> // OpenLaszlo 3.1+ only
HTML lays inline elements out horizontally, and block elements vertically (by default).
<p>one line</p> <p>another</p>
LZX only lays elements out if they're inside a view that contains a layout. These lines will display on top of each other:
<text>one line</text> <text>another</text>
But these won't, because they're inside a view that contains a layout:
<view> <simplelayout /> <text>one line</text> <text>another</text> </view>
and this means the same thing:
<view layout="axis: y"> <text>one line</text> <text>another</text> </view>
In HTML, elements resize to fit their contents.
In LZX, this is true of view elements, but not text. Text elements stay the size that they're created at, by default, even if the text changes later. To create a resizing text element, set the resize attribute to true.
<div>Content that will change</div>
<text resize="true">Content that will change</text>
TBD: list vs. combobox.
LZX also has some elements that aren't present in HTML, such as grid, tree, tabbed view, datepicker, and slider.
Getting Elements by ID
In LZX, the id attribute automatically creates a global variable with that name.
var myElement = document.getElementById('id')
var myElement = id;
// each of these calls myFunc() when element receives a click event element.addEventListener("click", myFunc, captureFlag); // W3C DOM element.attachEvent("onclick", myFunc); // IE5+ element.onclick = myFunc; // IE4+ NN3+
var delegate = new LzDelegate(object, "myFunc"); delegate.register(element, "onclick"); // This calls object.myFunc(arg) when element receives a click event.
<button onclick="myFunc()" />
In general, the presentation elements in an LZX program (view, text, and other subclasses of LzNode) don't support the W3 DOM commands. The reference documentation lists the APIs that apply to LZX source and presentation elements.
"You can write FORTRAN in any language." You can write HTML in any language too. The sections above explain how to translate some HTML concepts and idioms to LZX, but if you write LZX as though it were HTML, you'll just be frustrated by how unlike HTML LZX is.
LZX has some very powerful features that don't have analogues in HTML. To get the most out of LZX, you will want to learn about data binding, constraints, datasets, states, user defined classes, and animation. Some avenues to do this are to read the reference, the guide (including the tutorials), and to look at the sample programs and demos, to see how they do what they do. | <urn:uuid:64da4a3e-abd4-42fc-a9ae-deb3f1d83b33> | 2.8125 | 910 | Documentation | Software Dev. | 65.809852 |
The microbial carbon pump in the ocean
The biological pump is a process whereby CO2 in the upper ocean is fixed by primary producers and transported to the deep ocean as sinking biogenic particles or as dissolved organic matter. The fate of most of this exported material is remineralization to CO2, which accumulates in deep waters until it is eventually ventilated again at the sea surface. However, a proportion of the fixed carbon is not mineralized but is instead stored for millennia as recalcitrant dissolved organic matter. The processes and mechanisms involved in the generation of this large carbon reservoir are poorly understood. Here, we propose the microbial carbon pump as a conceptual framework to address this important, multifaceted biogeochemical problem.
N Jiao, G.J. Herndl, D. Hansell, R. Benner, G. Kattner, Steven Wilhelm, D.L. Kirchman, M.G. Weinbauer, T. Luo, F. Chen, and F. Azam. "The microbial carbon pump in the ocean" Nature Reviews Microbiology 8 (2010): 593-599. | <urn:uuid:75459225-3ee8-4c8d-ae9d-0fe565306509> | 3.03125 | 230 | Academic Writing | Science & Tech. | 51.103776 |
Science subject and location tags
Articles, documents and multimedia from ABC Science
Thursday, 12 April 2012
A new study of ancient stars known as red giants has provided fresh insights into how newly created atoms and dust grains are spread out into space.
Wednesday, 11 April 2012
StarStuff Podcast No decision yet about over who will host the world's largest radio telescope as a new working group examines the bids. Plus; supernova remnant Cassiopeia-A has turned itself inside out, and did the Moon sink the Titanic?
Wednesday, 4 April 2012
StarStuff Podcast Scientists say it's time to abandon existing theories that Earth is composed of the same material as chondritic meteoroids. Plus, pinpointing when dark energy became the dominate force in the universe, and North Korea prepares controversial missile launch.
Wednesday, 28 March 2012
StarStuff Podcast Chemical samples that show the Earth and the lunar surface are virtually identical challenge theories about how the Moon was born. Plus Mercury's unusual internal dynamics raise fresh questions, and an Australian submarine reaches lowest point on Earth.
Wednesday, 21 March 2012
StarStuff Podcast Ancient rocks indicate early Earth regularly flipped between an oxygen-rich atmosphere and a thick hydrocarbon haze like Saturn's moon Titan. Plus CERN confirms neutrinos don't travel faster than the speed of light; and a new theory about why the 'Man in the Moon' faces Earth.
Tuesday, 20 March 2012 16
Great Moments in Science Why daytime is bright and night-time dark is not as simple as black and white. Dr Karl explains why the vast canopy of stars we see can't light up the night sky.
Wednesday, 14 March 2012
StarStuff Podcast More powerful solar storms hit Earth as the Sun moves towards solar max. Plus astronomers discover oldest galaxy cluster ever detected; and physicists trap antihydrogen.
Thursday, 8 March 2012
Scientists have discovered the oldest galaxy cluster ever detected.
Wednesday, 7 March 2012
StarStuff Podcast Astronomers debate how to deflect potentially destructive asteroids. Plus atmosphere detected on Saturn moon; and light from the Moon used to find life on Earth.
Tuesday, 6 March 2012 4
Great Moments in Science The more reliant we become on electronic gadgetry, the more vulnerable we are to a solar superstorm. Dr Karl tries to look on the sunny side.
Thursday, 1 March 2012
Scientists have developed a new method to study reflected light from the Earth, that can correctly measure the amount of cloud cover, ocean and vegetation our planet has.
Thursday, 23 February 2012
Astronomers discover some of the fastest winds ever detected coming from a black hole near the centre of our galaxy.
Tuesday, 14 February 2012 13
Ask an Expert Why do we need such a big telescope? What will it look like? How will it be built? How will it handle the data?
Tuesday, 14 February 2012 12
Opinion Lisa Harvey-Smith explains what the Square Kilometre Array telescope can offer science - and why Australia should host it.
Wednesday, 8 February 2012
StarStuff Podcast NASA announces its most complete observation of what lies beyond the solar system. Plus: astronomers discover 'potentially habitable' planet; and Iran launches new spy satellite. | <urn:uuid:3079b3e3-a7b3-439c-8e29-f1e19fb10034> | 3 | 664 | Content Listing | Science & Tech. | 49.573471 |
October 5, 2010
There may be a shortage of blog posts over the next two weeks because I am busy compiling the all new 2011 abc27 Weather Almanac. I know many folks who rely on this each year for weather data, interesting weather stories, and lots of other fun facts. It also makes a great stocking stuffer and will once again be out just before Christmas this year. I am very excited about this year's edition, but it is requiring a lot of my time that I will have to steal from here in the coming days. Therefore, I wanted to post a story today that will appear in the Almanac this year and give you a little taste of what's inside.
This story deals with the issue of urban heat islands and why big cities are often warmer than rural areas nearby. I hope you enjoy the read and I hope you pick up your copy of the 2011 abc27 Weather Almanac in a couple months when it's released. Enjoy!
Urban Heat Islands
Changes often occur in the landscape around urban areas as they develop. Infrastructures such as buildings, roads, and traffic lights replace open land and vegetation. Permeable and moist surfaces become impermeable and dry. These changes cause urban regions to become warmer than their rural surroundings, forming an "island" of higher temperatures within the landscape.
On a hot and sunny summer day, the sun can heat dry, exposed urban surfaces, such as roofs and pavement, to temperatures 50-90 degrees Fahrenheit hotter than the air. Shaded or moist surfaces, often in more rural locations, remain close to air temperatures. Urban heat islands at the surface are usually present both day and night, but tend to be strongest during the day when the sun is shining.
Heat islands not only occur at the surface, but can also form within the atmosphere. However, in contrast with their surface counterparts, atmospheric heat islands are often weak during the late morning and throughout the day and become more pronounced after sunset due to the slow release of heat from urban infrastructure. The annual mean air temperature of a city with 1 million people or more can be 1.8-5.4 degrees Fahrenheit warmer than its surroundings. On a clear, calm night, however, the temperatures difference can be as much as 22 degrees Fahrenheit.
The graph below shows how urban temperatures are typically lower at the urban-rural border than in dense downtown areas. It also shows how parks, open land, and bodies of water can create cooler areas within a city or town. | <urn:uuid:6085dd8c-05eb-4f1d-ad64-a57fdae24a14> | 3.265625 | 512 | Personal Blog | Science & Tech. | 53.320736 |
this is a simple selection sort C program ok(sorry for letting me put up a C progam in a C++ forum, I hope its just the syntax change and this is a very basic program so you wont mind)
printf("size of the array:");
printf("enter the terms:");
temp = a[i];
printf("\n\t The ascending order list os ..:\n");
Can some one explain the program properly?
1) Does the program doesnt have the value or N right? as in the no. of terms.?
2) first for loop, i=1, that 1 is the address of the set of numbers or it is the no it self?
3) If it is the numbers that are to be ordered in ascending order, then say N=5, it will be 1 2 3 4 5 right? So the first forloop i=1, the 1 is the address right?
4) The second for loop, N-1? Can you please explain how for loops exactly works
5) The main problem is that i am not able to get a proper perspective of coding to a computer. Step by step. please explain the program properly and also the for loops.
I understood the swapping part. But I dont understand where the comparing part is done . | <urn:uuid:fe7ab750-174b-4a2e-81bd-f826ce85d00d> | 3.421875 | 271 | Q&A Forum | Software Dev. | 91.207981 |
It’s upsetting to think about the canaries in the mines singing to their heart’s content only to topple over and die when toxic gases make their presence felt during the mining process. The alternative, of course, is to sacrifice miners. Thankfully, choosing the lesser of two evils will no longer be necessary (actually, I don’t they’ve used canaries in quite a while) as scientists work on sensors that can detect any number of things not just toxic gases in the mines. The University of Massachusetts at Lowell is the latest to announce work on sensors (from the Nov. 15, 2012 news item on Nanowerk),
To detect the toxicity of engineered nanomaterials, such as carbon nanotubes, on living cells, electrical engineering Assoc. Prof. Joel Therrien — along with biology Prof. Susan Braunhut, chemistry Prof. Kenneth Marx and work environment Asst. Prof. Dhimiter Bello — has developed a “nanocanary,” the modern-day, high-tech equivalent of the canary in a coal mine that warned miners of dangerous buildups of toxic gases in the mine shaft.
The nanocanary is an ultrasensitive biosensor designed to continuously monitor tiny physiological changes in the live cells contained within it.
The Nov. 14, 2012 news release by Edwin L. Aguirre, which originated the news item, mentions a recent podcast by one of the researchers (Joel Therrien),
In a recent podcast produced by the Museum of Science in Boston, Therrien talked about the importance of studying how nano-sized particles affect human health and the environment as well as in the safe development of commercial nano products.
“Our biosensor has a wide range of applications, from testing for toxicity in nanomanufacturing to drug development and customized cancer therapeutics,” notes Therrien.
“In testing the toxicity of carbon nanotubes, for example, since the sensor can directly detect adverse effects on living cells, we are able to identify the threshold concentration at which carbon nanotubes lead to the cells’ death,” he explains. “The sensor can also be used to test the response of normal and cancerous cells to drug therapies. In the future, this technology may help guide oncologists in selecting the most appropriate drug for a cancer patient. We also see the potential for this to partially replace animals in testing drugs and other products.”
Therrien’s 16 min. podcast can be heard here. | <urn:uuid:4c17df28-b1ce-4a3b-91ae-cd2f24f91dbe> | 3 | 522 | Personal Blog | Science & Tech. | 39.551752 |
The usual way to reference a variable is to write the symbol which names it. See Symbol Forms.
Occasionally, you may want to reference a variable which is only
determined at run time. In that case, you cannot specify the variable
name in the text of the program. You can use the
function to extract the value.
This function returns the value stored in symbol's value cell. This is where the variable's current (dynamic) value is stored. If the variable has no local binding, this is simply its global value. If the variable is void, a
void-variableerror is signaled.
If the variable is lexically bound, the value reported by
symbol-valueis not necessarily the same as the variable's lexical value, which is determined by the lexical environment rather than the symbol's value cell. See Variable Scoping.(setq abracadabra 5) ⇒ 5 (setq foo 9) ⇒ 9 ;; Here the symbol
abracadabra;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value 'abracadabra)) ⇒ foo ;; Here, the value of
abracadabra, ;; which is
foo, ;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value abracadabra)) ⇒ 9 (symbol-value 'abracadabra) ⇒ 5 | <urn:uuid:5160860c-7aa6-4205-866b-82e445d2842f> | 3.640625 | 314 | Documentation | Software Dev. | 44.921594 |
A time object has type, seconds and nanoseconds fields representing a point in time starting from some epoch. This is an arbitrary point in time, not just a time of day. Although times are represented in nanoseconds, the actual resolution may be lower.
The following variables hold the possible time types. For instance
(current-time time-process) would give the current CPU process
Universal Coordinated Time (UTC).
International Atomic Time (TAI).
Monotonic time, meaning a monotonically increasing time starting from an unspecified epoch.
Note that in the current implementation
time-monotonic is the
time-tai, and unfortunately is therefore affected by
adjustments to the system clock. Perhaps this will change in the
A duration, meaning simply a difference between two times.
CPU time spent in the current process, starting from when the process began.
CPU time spent in the current thread. Not currently implemented.
#t if obj is a time object, or
#f if not.
Create a time object with the given type, seconds and nanoseconds.
Get or set the type, seconds or nanoseconds fields of a time object.
set-time-type! merely changes the field, it doesn’t convert the
time value. For conversions, see SRFI-19 Time/Date conversions.
Return a new time object, which is a copy of the given time.
Return the current time of the given type. The default
Note that the name
current-time conflicts with the Guile core
current-time function (see Time) as well as the SRFI-18
current-time function (see SRFI-18 Time). Applications
wanting to use more than one of these functions will need to refer to
them by different names.
Return the resolution, in nanoseconds, of the given time type.
The default type is
#f according to the respective relation
between time objects t1 and t2. t1 and t2
must be the same time type.
Return a time object of type
time-duration representing the
period between t1 and t2. t1 and t2 must be
the same time type.
time-difference returns a new time object,
time-difference! may modify t1 to form its return.
Return a time object which is time with the given duration
added or subtracted. duration must be a time object of type
subtract-duration return a new time
subtract-duration! may modify
the given time to form their return. | <urn:uuid:9a5347a0-da34-4a20-a8ab-bb78a735a27a> | 3.171875 | 552 | Documentation | Software Dev. | 51.253739 |
Fishers near marine protected areas end up traveling farther to catch fish but maintain their social and economic well-being, according to a study by fisheries scientists at Washington State University and in Hawaii.
The study, reported in the journal Biological Conservation, is one of the first to look closely at how protected areas in small nearshore fisheries can affect where fishers operate on the ocean and, as a consequence, their livelihood.
"Where MPAs are located in relation to how fishers operate on the seascape is critical to understand for fisheries management and this is an important lesson to draw from this study," said Todd Stevenson, the paper's lead author, who did the research as part of his WSU doctorate.
Marine protected areas have become a cornerstone of ocean conservation, setting aside specific waters to preserve and manage vulnerable resources like declining fish stocks. In theory, the MPAs will provide a refuge in which fish can breed and help replenish nearby, open areas with their offspring. Nearly 6,000 MPAs have been set up around the world, according to a 2010 report by the International Union for Conservation of Nature and Natural Resources.
Stevenson focused on a network of MPAs on the west coast of the island of Hawaii, home to an aquarium fish trade and one of the state's most lucrative nearshore fisheries. While the fishery is relatively small, with only about 40 active fishers, small-scale fisheries actually employ more people than large-scale operations and catch fish more efficiently. Their small size also makes fishers more vulnerable to changes, as a poorly placed MPA can have a large effect on their options.
Starting in 1999, the west Hawaii MPAs closed more than one-third of the coast to aquarium fishing. Many areas were closed to avoid conflicts with dive charters and the tourism industry, particularly in the more populated central part of the west coast. This is where most ports and launches are, too. As a result, fishers had to go farther in search of fish.
Analyzing social surveys and state catch reports, Stevenson and his colleagues found just that.
"Fishing cost and distances traveled were perceived to have significantly worsened," he and his colleagues wrote, "while economic status was perceived to have significantly improved."
"It's not uncommon to establish MPAs in areas where fishers operate, as these are usually biologically and economically productive spots that receive heavy fishing pressure and thus need the most protection," said Stevenson. "When MPAs are placed in these locations, they displace fishers into new, slightly less optimal fishing spots.
"This happened in Hawaii," he said, "and it appears to have had little impact on the socioeconomic well-being of fishers who remained involved in the fishery since before the MPAs were in place, which is somewhat counterintuitive and makes our study interesting."
Without a separate economic analysis, said Stevenson, it's hard to say how the changing fish stocks might have affected fishing incomes. He and his co-authors—WSU Professor Brian Tissot and Bill Walsh of Hawaii's Division of Aquatic Resources—conjecture the fishers had higher yields, in part because they were steered toward underexploited or more biologically productive areas.
Fishers also benefited from rising prices for yellow tang, the most abundant and popular fish in Hawaii's aquarium trade, and price wars among island buyers working to satisfy the growing demand from coral aquarium tank owners.
Eric Sorensen | Source: EurekAlert!
Further information: www.wsu.edu
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This morning at 05:45 CEST, the earth trembled beneath the Okhotsk Sea in the Pacific Northwest. The quake, with a magnitude of 8.2, took place at an exceptional depth of 605 kilometers.
Because of the great depth of the earthquake a tsunami is not expected and there should also be no major damage due to shaking.
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A fried breakfast food popular in Spain provided the inspiration for the development of doughnut-shaped droplets that may provide scientists with a new approach for studying fundamental issues in physics, mathematics and materials.
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Droplets in this toroidal shape made ...
Frauhofer FEP will present a novel roll-to-roll manufacturing process for high-barriers and functional films for flexible displays at the SID DisplayWeek 2013 in Vancouver – the International showcase for the Display Industry.
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08.05.2013 | Event News | <urn:uuid:706cdd65-862c-4e42-a788-f63a6ccaa80b> | 3.328125 | 1,372 | Content Listing | Science & Tech. | 42.682089 |
Step 3: The beginning of a website
Open your editor and make sure you are on a page you can code (might be the source or code tab on GUI editors)
Make sure it is blank before starting. Some GUI editors add information to the code.
The beginning of every HTML page must start with the command <html>. This can be written as <HTML> <hTMl> <Html>. It doesn't matter. Capitals are exactly the same as lower case in html.
The ending of every page will end with </html>. The forward slash signifies the end of any command.
So far your page should look like this
*-*-*-* - Signifies code. Ignore the starts and dashes
View this as a webpage
Nothing to see so far, but technically this is a webpage. | <urn:uuid:b2e558c2-7365-4883-8d13-9f29aebd921c> | 2.765625 | 171 | Tutorial | Software Dev. | 69.792663 |
|Aug7-12, 09:31 AM||#1|
Muon and Scintillator
I am trying to set up a lab experiment on muon detection and determination of its decay time.
I know that when a muon first reaches the scintillator it slows down because of ionization and atomic excitation of solvent molecules. The deposited energy is transferred to the fluor molecules (of the scintillator matter) whose electrons are promoted to excited states. The electrons then start emitting light. This is the first event of scintillation.
After that muon decays into an electron, a neutrino and an anti-neutrino. This electron then produces scintillator light again. The question is by what means, how does it make the scintillator to emit light? Is that because the electrons move at high speed and lose its kinetic energy in the same way as muon did?
|Aug7-12, 10:09 AM||#2|
Welcome to PF;
Imagine you could "inject" a slow electron into the crystal somehow ... what do you think it would do?
You can check your idea BTW: how much energy is released in the beta decay of a stationary muon?
|decay, electron, muon, scintillator|
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Last week we presented a general outline of how trees lift water. Donald J. Merhaut of Monrovia Nursery Company, headquartered in Azusa, Calif., has provided a more detailed reply:
"Water is often the most limiting factor to plant growth. Therefore, plants have developed an effective system to absorb, translocate, store and utilize water. To understand water transport in plants, one first needs to understand the plants' plumbing. Plants contain a vast network of conduits, which consists of xylem and phloem tissues. This pathway of water and nutrient transport can be compared with the vascular system that transports blood throughout the human body. Like the vascular system in people, the xylem and phloem tissues extend throughout the plant. These conducting tissues start in the roots and transect up through the trunks of trees, branching off into the branches and then branching even further into every leaf.
"The phloem tissue is made of living elongated cells that are connected to one another. Phloem tissue is responsible for translocating nutrients and sugars (carbohydrates), which are produced by the leaves, to areas of the plant that are metabolically active (requiring sugars for energy and growth). The xylem is also composed of elongated cells. Once the cells are formed, they die. But the cell walls still remain intact, and serve as an excellent pipeline to transport water from the roots to the leaves. A single tree will have many xylem tissues, or elements, extending up through the tree. Each typical xylem vessel may only be several microns in diameter.
"The physiology of water uptake and transport is not so complex either. The main driving force of water uptake and transport into a plant is transpiration of water from leaves. Transpiration is the process of water evaporation through specialized openings in the leaves, called stomates. The evaporation creates a negative water vapor pressure develops in the surrounding cells of the leaf. Once this happens, water is pulled into the leaf from the vascular tissue, the xylem, to replace the water that has transpired from the leaf. This pulling of water, or tension, that occurs in the xylem of the leaf, will extend all the way down through the rest of the xylem column of the tree and into the xylem of the roots due to the cohesive forces holding together the water molecules along the sides of the xylem tubing. (Remember, the xylem is a continuous water column that extends from the leaf to the roots.) Finally, the negative water pressure that occurs in the roots will result in an increase of water uptake from the soil.
"Now if transpiration from the leaf decreases, as usually occurs at night or during cloudy weather, the drop in water pressure in the leaf will not be as great, and so there will be a lower demand for water (less tension) placed on the xylem. The loss of water from a leaf (negative water pressure, or a vacuum) is comparable to placing suction to the end of a straw. If the vacuum or suction thus created is great enough, water will rise up through the straw. If you had a very large diameter straw, you would need more suction to lift the water. Likewise, if you had a very narrow straw, less suction would be required. This correlation occurs as a result of the cohesive nature of water along the sides of the straw (the sides of the xylem). Because of the narrow diameter of the xylem tubing, the degree of water tension, (vacuum) required to drive water up through the xylem can be easily attained through normal transpiration rates that often occur in leaves."
Alan Dickman is curriculum director in the biology department at the University of Oregon in Eugene. He offers the following answer to this oft-asked question:
"Once inside the cells of the root, water enters into a system of interconnected cells that make up the wood of the tree and extend from the roots through the stem and branches and into the leaves. The scientific name for wood tissue is xylem; it consists of a few different kinds of cells. The cells that conduct water (along with dissolved mineral nutrients) are long and narrow and are no longer alive when they function in water transport. Some of them have open holes at their tops and bottoms and are stacked more or less like concrete sewer pipes. Other cells taper at their ends and have no complete holes. All have pits in their cell walls, however, through which water can pass. Water moves from one cell to the next when there is a pressure difference between the two. | <urn:uuid:aabc730d-93bd-48a5-9000-24b705db911f> | 4.09375 | 957 | Knowledge Article | Science & Tech. | 48.11715 |
Narrator: This is Science Today. The health of coral reefs has been known to be at risk due to direct stressors such as water pollution, climate change and over-fishing, all of which can cause an overgrowth of algae that smothers the corals. Now, a team of scientists has discovered for the first time, an indirect microbial process in which bacteria and algae are combining to kill corals. Marine ecologist, Stuart Sandin of the University of California, San Diego 's Scripps Institution of Oceanography, was part of the study.
Sandin: So, this study was an effort to try to look at some of these indirect effects between the some of the relationships between algae and corals. In regions where there was more sugar in the water, the coral dies more.
Narrator: The researchers discovered that the sugars that algae release, feed bacterial communities living on the coral, causing them to flourish and kill the corals by cutting off their oxygen supply. This frees up more space for algae and the decline continues.
Sandin: We know that in many regions, we're increasing the growth rates of algae on coral reefs. If we want to keep it around, we've got to start doing something for it.
Narrator: For Science Today, I'm Larissa Branin. | <urn:uuid:0d0f1638-e0f8-4455-8614-5780377dc92e> | 3.765625 | 272 | Audio Transcript | Science & Tech. | 50.305459 |
Magnetic field lines from a computer simulation of the solar corona show some of the complexity of the Sun's magnetic field. Colors on the Sun's surface show the strength of the magnetic field (yellow is largest).
Click on image for full size
Helmet Streamers and the Magnetic Structure of the Corona
The gas in the solar corona is at very
high temperatures (typically 1-2 million
in most regions) so it is almost completely in a plasma
state (made up of charged particles, mostly protons and electrons).
Strong magnetic fields thread through the corona. Where these magnetic lines
of force are closed, the magnetic field is strong enough to trap
the solar plasma and keep it from escaping. Plasma accumulates
in these regions and forms the beautiful structures call helmet
streamers seen during solar eclipses.
Prominences are often situated beneath helmet streamers, and active
regions occur beneath streamers near the equator (sometimes called
active regions streamers). In some regions, the coronal magnetic
field cannot confine the plasma, and the plasma expands outward,
reaching supersonic velocities. Regions on the Sun with these
open magnetic field lines (which stretch far out into the solar system)
correspond to coronal holes and are the source of the solar wind, which
accelerates outward from the Sun and fills interplanetary space.
The electrons in the coronal hole plasma are typically cooler and
less dense than streamers,
and so they show up as dark regions in both X-rays and white light.
Shop Windows to the Universe Science Store!Cool It!
is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store
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Plasma is known as the fourth state of matter. The other three states are solid, liquid and gas.Almost everything is made up of atoms (your dog, your science book, this computer...). The atom has a nucleus...more
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Most of the energy we receive from the Sun is the visible (white) light emitted from the photosphere. The photosphere is one of the coolest regions of the Sun (6000 K), so only a small fraction (0.1%)...more
The gas in the solar corona is at very high temperatures (typically 1-2 million kelvins in most regions) so it is almost completely in a plasma state (made up of charged particles, mostly protons and electrons)....more | <urn:uuid:949ae3f2-42fc-4fab-a710-271c3f4c7e70> | 3.296875 | 730 | Content Listing | Science & Tech. | 56.126921 |
The Impact of Federal Policies on Aquatic Environments and
Teacher Note: Depending on the length of class time available, this lesson may take 2-3 sessions to complete.
Students will describe factors that affect productivity and species distribution in aquatic environments.
Steps to the Lesson
- Discuss key vocabulary.
- Watch a video on how human activity and government policy has impacted a river system in British Columbia.
- Complete a Graphic Organizer while viewing the video.
- Conduct an investigation on how to save endangered rivers in British Columbia.
- Reflect on the process.
- Students will analyze how federal policies and human activity have affected aquatic systems in British Columbia.
- Students will identify and analyze alternatives to issues affecting endangered rivers in British Columbia.
Students will conduct an investigation on endangered rivers in British Columbia and write proposals for alternative solutions on how to save the respective rivers.
Activate Prior Knowledge:
Students complete a mind map activity entitled 'The Many Ways People Use Water' found in the McGraw-Hill Ryerson textbook BC Science 8 (page 359). While completing the activity, students should focus specifically on what human activities impact river and lake systems.
Predict and Question:
In Canada, there is a plentiful supply of water and we rarely pay attention to how much water we use in our daily lives or how our actions impact local aquatic areas like rivers and lakes.
What are the students wondering about how human activity has impacted their local rivers, lakes and oceans?
Before viewing the video, students need to understand the meaning of the following terms.
Key vocabulary to discuss: anadromous, confluence, extinction, fathom, mitigate, resident (Definitions)
Students watch the following video and track their thinking using the Graphic Organizer. Students should try to identify some key effects and implications of federal policy on the Sinixt Nation.
Reminder: It is important to stop throughout the story and give students (A/B partners) opportunity to talk or respond to the story.
Click above to view video in Mac OSX (Quicktime)
Video Length (4 mins)
Click above to view video in Windows (Media Player)
Video Length (4 mins)
Having viewed the video above, students need to share their ideas from the video Graphic Organizer (A/B partner recommended). Teachers ask student pairs to share their main ideas and generate a list of ideas and evidence on the board or overhead. Teachers lead class discussion on the significance of the ideas generated (and those not generated) and how federal policies have impacted the environment and Aboriginal people on the Columbia River system.
Now that students have learned how federal policies and human activity have impacted a regional river system (Columbia River), students will now conduct an investigation on how to save other endangered rivers in British Columbia. Working in A-B partners or groups of four, students conduct an investigation activity found in the McGraw-Hill Ryerson textbook BC Science 8 (pages 444-445). Using the chart provided on page 445 in the textbook, students will choose a local river (or river of their choice) to research and write a proposal to save an endangered river. Student groups report out their proposals to the class in the form of an oral presentation, using either poster boards, written reports, or Powerpoint presentations.
Upon completion of the investigation activity, students complete a Reflection Sheet to reflect on what they liked/disliked about the investigation process and how their thinking towards how Canadian Federal Government policy impacts the environment and Aboriginal people has changed.
Extend learning or next lesson
One of the key ideas from the video is the impact that Canadian federal government policies have had on an Aboriginal population in British Columbia (Sinixt nation). There are many other examples of how government policies have affected the environment and populations in Canada. Some of these include:
- Governments adopting (or not adopting) Kyoto Protocol emission targets.
- The Canadian federal government imposing a moratorium on seabed oil and gas exploration off the coast of British Columbia.
- The Canadian federal government policies regarding pollution standards in the Alberta northern Oil Tar Sands.
- The Kashechewan Reserve water crisis in Northern Ontario.
Students can complete a research report on these and other issues affecting the environment and Aboriginal populations in Canada. | <urn:uuid:d7ad182e-38d0-4083-bf62-8ef8b07de5dc> | 3.734375 | 877 | Tutorial | Science & Tech. | 24.273428 |
Some new classes were introduced in Foundation.framework as part of Mac OS X 10.8 (Mountain Lion) to help ease the pain associated with performing IPC (inter-process communication) in Mac OS applications. Among them were NSXPCConnection, NSXPCListener, NSXPCListenerDelegate and NSXPCInterface. You can find the documentation inside the development portal or as part of the Xcode bundle but this post is meant to show you how easy it truly is to package up messages and send them off to other processes.
But first, a bit of background. What is IPC? Courtesy of WikiPedia, “IPC is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared memory, and remote procedure calls (RPC). The method of IPC used may vary based on the bandwidth and latency of communication between the threads, and the type of data being communicated.”
Originally, you could have done IPC in OS X using mach messages, which is how drivers traditionally communicated.
While information sharing and modularity are definitely some of the benefits of IPC, one of the biggest wins in my mind is the fact that we can perform privilege separation with IPC. Consider the following: you have wrote some code that will take some user input and crunch on it and then return a result. Note that this doesn’t have to be intensive computation, it could be as easy as interpolating an NSString. User input is a taint source, meaning that the input data is untrusted and could potentially (and perhaps unintentionally) be malicious. If your program were running in a privileged mode or had some increased set of ACLs, then if the input were able to exploit a vulnerability, then it would be able to inherit the same privilege level as the application.
Another benefit of this separation is that suppose the input causes the program to crash. If the processing were done in the main application, it would crash the entire application. If the processing is done in the daemon, then the daemon can crash and the application would still be alive and well.
I have attached a project that demonstrates NSURLConnection’s ability to say “Hello.” hello.tar.gz | <urn:uuid:51fd84c6-9fc5-4ac5-971e-1cc5b9a0d293> | 2.78125 | 494 | Personal Blog | Software Dev. | 42.216333 |
Animal Species:Braconid wasps
Braconid wasps are a large family of wasps with over 800 Australian species. They are closely related to the ichneumonid wasps and parasitise the larvae of many insect groups in a similar way.
Braconid wasps are found throughout Australia.
Braconid wasps live in urban areas, forests and woodlands, wetlands.
Feeding and Diet
Braconid wasps can be seen around Sydney woodlands searching for beetle larvae in logs and the trunks of fallen trees.
Braconid wasps use the egg and adult stages of other insects as hosts for their young. On finding a suitable host, eggs are laid on or in the victim, providing the wasp larvae with a meal when they hatch.
Some braconid wasps play an important role in controlling pest species of insects such as aphids. | <urn:uuid:361ad431-b789-4085-bddb-2ac6d881b608> | 3.703125 | 186 | Knowledge Article | Science & Tech. | 53.304451 |
The Three R's
About Our Site
Water is the major constitutent of living matter. From 50 to 90 percent of the weight of living organisms is water. Protoplasm, the basic material of living cells, consists of a solution in water of fats, carbohydrates, proteins, salts, and similar chemicals. Water acts as a solvent, transporting, combining, and chemically breaking down these substances. Blood in animals and sap in plants consist largely of water and serve to transport food and remove waste material. Water also plays a key role in the metabolic breakdown of such essential molecules as proteins and carbohydrates. This process, called hydrolysis, goes on continually in living cells.|
Water is useful to us and nature in many ways. They provide a home for creatures such as the whale, otter, etc. These sea-creatures depend on the water to live. The whale can't be out of the water for long before it dies. The sea-otter live on the shell-fish and fish that live in the water. Ducks eat the sea-weed that live in the water and some also eat fish. Lots of what these animals eat also live in the water. As you know, water has three states, liquid, gas, and solid. The solid state of water is ice. Ice is also a habibtat. Penguins, seals, and other types of animals live on huge pieces of ice. Many penguin species live on Antarctica and the North Pole. Seals also live on these pieces of ice. Not all of the are permanent homes. A seal might just want to stop by at a glacier and rest. | <urn:uuid:70b10cdb-5214-4caa-b896-0e0e6130d659> | 3.390625 | 335 | Knowledge Article | Science & Tech. | 60.898182 |
See also the
Dr. Math FAQ:
Browse High School Polyhedra
Stars indicate particularly interesting answers or
good places to begin browsing.
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I am trying to discover the lengths of the edges of a cuboid when only
the diagonal, area, and volume are known.
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Can you give me information on the math behind geodesics?
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I'm looking for ideas for a geometry and soccer bulletin board.
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Can you give us a hint for a formula that will tell you the number of
hidden faces in an arrangement of a cubes if you know the number of
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If a pyramid is 2 feet tall, and crumbles into sand, how many 2-inch
pyramids can be created from the sand used to create the original
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Is there any standard way of finding out how many different possible
rectangular solids can fit into an 3^3 cube?
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Why is surface area so important? What kinds of things depend on surface
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I would appreciate it if you would tell me a bit about KaleidoTile.
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What is the length of a line segment in three dimensions with endpoints
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I have a piece of glass that is 14" by 72". What dimensions would I need
to make a glass cage with maximum volume?
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Why are cereal boxes the size they are? Is it just to maximize volume?
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calculate the maximum amount of square footage that I can enclose in
a rectangle using the fence?
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of a prism whose ends are equilateral triangles and whose other faces
are rectangles. What is the maximum surface area of this prism?
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I am weatherproofing my home, and have to mitre boards in a pyramid
with a rectangular - not square - base, and an apex that is directly
over the centre of one edge of the base.
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What do monogon and digon polygons look like? How can you have a
polygon with fewer than three sides?
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Choose dimensions (length, width, and height) and find the surface area
and volume of a box; then draw a flat pattern of the box.
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What is the "net" of a shape?
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How many ways are there to make dice out of the Platonic solids (i.e. 4,
6, 8, 12, and 20 sides)? How many of those ways have opposite face sums
equal? What would the opposing face sums be for each type?
- Open Box Problem [06/22/2003]
Find the formula for the greatest volume box you can make from a sheet
of cardboard with different-sized corners cut out of it.
- Orbit and Stabilizer in Rotational Symmetry [11/11/2004]
Calculate the orders of the following groups of rotations: of a
regular tetrahedron, a regular octahedron, a regular dodecahedron, and
a regular icosahedron. I'm having trouble figuring out the
stabilizers. I know that the order of the group of rotations is equal
to the order of the orbit times the order of the stabilizer.
- Orthocentric Tetrahedron [11/30/2002]
Recall that the opposite edges of an orthocentric tetrahedron are
perpendicular. Let ABCD be an orthocentric tetrahedron. Show that AB^
2 + CD^2 = AD^2 + BC^2.
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Is there such a thing as a regular 7-hedron?
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Can a pole 6.5m long fit into a truck with dimensions of 3m, 3.5m, and
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I would like to know how polyhedrons are classified, which figures can be
used for the faces, and the theorem relating the faces, edges, and
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of diameter 2.9 m?
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How many faces share each edge?
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I'd like to do a project involving tetrahedra. What would you suggest?
- Polyhedron Vertices [02/25/2003]
What is the least number of vertices that a polyhedron may have?
- Pyramids and Triangular Prisms [05/09/2000]
What's the difference between a pyramid and a triangular prism?
- Pythagorean Theorem and Cubes [02/14/1998]
In a cube if a diagonal is drawn from the front top corner to the back
bottom corner, how long must each side be using the Pythagorean Theorem?
- Pythagorean Theorem in Three Dimensions [05/18/2001]
Given a tetrahedron with a trirectangular vertex S. Let A, B, and C be
the areas of the three faces that meet at S, and D be the area of the
face opposite S. Prove that D^2 = A^2 + B^2 + C^2.
- Rectangular Solids from Blocks [09/25/1998]
How many rectangular solids can be made from "n" cube-shaped blocks?
- Rhombicuboctahedron [05/14/1999]
How can you make a soccer ball out of a particular shape - for example
- Snub Cube [08/08/1998]
What is a snub cube?
- The Spider and the Fly [12/23/1999]
A spider and a fly are on opposite walls of a rectangular room... Does
the spider get the fly?
- Spiral Inside a Hexagonal Room [09/03/2003]
Two walls meet at 120 degrees, and you have a piece of cardboard with
an angle of 137.5 degrees that you want to tilt until its sides are
snug against the wall. How do you find the angle of tilt?
- Stella Octangula [6/17/1996]
What is the name of the polyhedron that looks like the union of two
tetrahedrons joined at their bases?
- Stellated Dodecahedron [12/3/1995]
A student asks for help finding information on stellated dodecahedrons. | <urn:uuid:5b6357ce-a148-4559-bd4a-9c2dde1475f1> | 3.15625 | 1,820 | Q&A Forum | Science & Tech. | 67.100775 |
Have a look at this video. (N.B. it is played back at normal speed)
After the numbers 1 through 9 make a split-second appearance on a computer screen, the chimp, Ayumu, gets to work. His index finger moves quickly across the screen, tapping white squares where the numbers had appeared, in order. Ayumu’s talent caused a quite a stir when researchers first reported it (Matsuzawa, 2009).
In an upcoming Trends in Cognitive Sciences essay, Nicholas Humphrey floats a different explanation for Ayumu’s superlative performance: Ayumu might have a curious brain condition that allows him to see numbers in colors. A simple experiment could reveal whether Ayumu is synesthetic: Changing the white square to colored squares would throw him off if he was relying on colors to order the numbers. According to ScienceNews Matsuzawa, who declined to comment directly on Humphrey’s theory, has no plans to test this.
Nicholas Humphrey (2012). ‘This chimp will kick your ass at memory games – but how the hell does he do it?’ Trends in Cognitive Science DOI: 10.1016/j.tics.2012.05.002
Tetsuro Matsuzawa (2009). Symbolic representation of number in chimpanzees Current Opinion in Neurobiology, 19 (1), 92-98 DOI: 10.1016/j.conb.2009.04.007 | <urn:uuid:fba866db-8527-4d7b-9f26-cf95ed76eaaf> | 2.875 | 303 | Personal Blog | Science & Tech. | 69.280538 |
Depending on who is talking, Poincaré’s conjecture can sound either daunting or deceptively simple. It asserts that if any loop in a certain kind of three-dimensional space can be shrunk to a point without ripping or tearing either the loop or the space, the space is equivalent to a sphere.
The conjecture is fundamental to topology, the branch of math that deals with shapes, sometimes described as geometry without the details. To a topologist, a sphere, a cigar and a rabbit’s head are all the same because they can be deformed into one another. Likewise, a coffee mug and a doughnut are also the same because each has one hole, but they are not equivalent to a sphere.
From this NYTimes story about a century-old conjecture, and about Grigory Perelman, the Russian mathematician who made the key breaktrhough needed for proving it. Just how hard has it been to prove this conjecture?
Poincaré’s conjecture was subsequently generalized to any number of dimensions, but in fact the three-dimensional version has turned out to be the most difficult of all cases to prove. In 1960 Stephen Smale, now at the Toyota Technological Institute at Chicago, proved that it is true in five or more dimensions and was awarded a Fields Medal. In 1983, Michael Freedman, now at Microsoft, proved that it is true in four dimensions and also won a Fields.
“You get a Fields Medal for just getting close to this conjecture,” Dr. Morgan said. | <urn:uuid:1fc1fa45-7ec4-4663-be89-861c4b4a6ecb> | 2.921875 | 319 | Personal Blog | Science & Tech. | 45.929967 |
Sep 10, 2012, 4:53 AM
Post #2 of 3
If the special variable $_ matches:
start of string, followed by one or more non white space characters folowed by one or more white space characters followed by one or more digits followed by one or more digits followed by anything...
In addition, the parentheses lead to the following captures:
- the first series of non white characters is captured in variable $1
- the series of digits is captured into variable $2
The i option makes the match case insensitive, which is quite useless here since there is no upper or lower case letter. | <urn:uuid:e76621ce-d1c1-4dbd-a0a0-5b4a2491fb41> | 2.9375 | 126 | Comment Section | Software Dev. | 41.889041 |
To add a slightly more detailed answer than yesterdays kids's answer:
X-rays are electromagnetic waves, like light. They're different from visible light because they have a higher frequency, and therefore a higher energy per photon. That also means they have a lower wavelength (since f*λ=c)
Metals are solid materials in which some electrons are not strongly bound to a single nucleus, but instead form a electron cloud dispersed throughout the whole object. These electrons can therefore move easily, which is why metals conduct electricity.
An x-ray photon that hits a metal object may have enough energy to shoot straight through. If not, it will hit an electron and kick it away at high speed. The energy and momentum is taken from the x-ray photon, which means it's scattered in another direction at lower energy (and could then be absorbed outright).
So, it's the metals electron (band) structure that causes the interference with x-rays. | <urn:uuid:723ec999-c383-4e05-a48d-0a76080b6446> | 3.78125 | 197 | Q&A Forum | Science & Tech. | 48.614498 |