text stringlengths 174 655k | id stringlengths 47 47 | score float64 2.52 5.25 | tokens int64 39 148k | format stringclasses 24 values | topic stringclasses 2 values | fr_ease float64 -483.68 157 | __index__ int64 0 1.48M |
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Option B is Correct. The
start() method causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.
Option A is wrong. There is no
init() method in the Thread class.
Option C is wrong. The
run() method of a thread is like the main() method to an application. Starting the thread causes the object's run method to be called in that separately executing thread.
Option D is wrong. The resume() method is deprecated. It resumes a suspended thread. | <urn:uuid:b174e7e0-cbef-48f3-97f2-b161589d4359> | 2.578125 | 108 | Q&A Forum | Software Dev. | 71.206 | 95,518,892 |
There are various approaches to the theory of Hamiltonian systems. They are described in [12, 74, 224, 233]. In this chapter we recall the definition of the basic concepts of Hamiltonian mechanics, and also present several examples of Hamiltonian systems which will be used in the sequel.
KeywordsRigid Body Hamiltonian System Invariant Measure Poisson Bracket Symplectic Structure
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Using Quantum Computers for Quantum Simulation
AbstractNumerical simulation of quantum systems is crucial to further our understanding of natural phenomena. Many systems of key interest and importance, in areas such as superconducting materials and quantum chemistry, are thought to be described by models which we cannot solve with sufficient accuracy, neither analytically nor numerically with classical computers. Using a quantum computer to simulate such quantum systems has been viewed as a key application of quantum computation from the very beginning of the field in the 1980s. Moreover, useful results beyond the reach of classical computation are expected to be accessible with fewer than a hundred qubits, making quantum simulation potentially one of the earliest practical applications of quantum computers. In this paper we survey the theoretical and experimental development of quantum simulation using quantum computers, from the first ideas to the intense research efforts currently underway. View Full-Text
Share & Cite This Article
Brown, K.L.; Munro, W.J.; Kendon, V.M. Using Quantum Computers for Quantum Simulation. Entropy 2010, 12, 2268-2307.
Brown KL, Munro WJ, Kendon VM. Using Quantum Computers for Quantum Simulation. Entropy. 2010; 12(11):2268-2307.Chicago/Turabian Style
Brown, Katherine L.; Munro, William J.; Kendon, Vivien M. 2010. "Using Quantum Computers for Quantum Simulation." Entropy 12, no. 11: 2268-2307. | <urn:uuid:422e6b74-2ea4-4493-b158-c0490bd7c180> | 2.828125 | 307 | Academic Writing | Science & Tech. | 42.991667 | 95,518,907 |
As NASAs Cassini spacecraft approached Saturn last July, it found evidence that lightning on Saturn is roughly one million times stronger than lightning on Earth.
Thats just one of several Cassini findings that University of Iowa Space Physicist Don Gurnett will present in a paper to be published Thursday, Dec. 16 in Science Express, an online version of the journal Science, and in a talk to be delivered Friday, Dec. 17 at a meeting of the American Geophysical Union in San Francisco.
Other findings include:
The comparison between Saturns enormously strong lightning and Earths lightning began several years ago as the Cassini spacecraft prepared for its journey to Saturn by swinging past the Earth to receive a gravitational boost. At that time, Cassini started detecting radio signals from Earths lightning as far out as 89,200 kilometers from the Earths surface. In contrast, as Cassini approached Saturn, it started detecting radio signals from lightning about 161 million kilometers from the planet. "This means that radio signals from Saturns lightning are on the order of one million times stronger than Earths lightning. Thats just astonishing to me!" says Gurnett, who notes that some radio signals have been linked to storm systems observed by the Cassini imaging instrument.
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
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Math Encounters: "From Simplicity to Complexity: What Happens Next?" with Roger Antonsen (7:00 pm)
Simple assumptions often give rise to surprising and delightful consequences. Think about games and puzzles like chess and Rubik's cube, where enormous complexity arises from simple rules. The same is true of cellular automata, juggling, fractals, and more! Discover how creative computer programming can be used to explore mathematical structures as Roger Antonsen, computer scientist and award-winning math communicator, presents a visual and playful talk on the connections between simple assumptions and their complex consequences.
Special introduction by mathematician and artist, Bob Bosch.
This page is for the 7:00 pm session. Click here to register for the 4:00 pm session instead.
Light refreshments will be served after the 4:00 pm session and at 6:30 in advance of second session.
Math Encounters is a public presentation series celebrating the spectacular world of mathematics, presented by the Simons Foundation and the National Museum of Mathematics.
Bring a new friend to Math Encounters and you’ll be on your way to winning a free t-shirt! friendme.momath.org
For further information, call the National Museum of Mathematics at (212) 542-0566 or e-mail firstname.lastname@example.org.
Please note, this presentation is designed to be accessible and engaging to a general audience. As a rule of thumb, it would be best enjoyed by participants ages 12 and up.
Please check our online shop for books by Math Encounters presenters.
11 E 26th St.
New York, NY 10010 | <urn:uuid:82756464-6677-4f62-aea9-5c20b5f02a2d> | 2.5625 | 346 | News (Org.) | Science & Tech. | 53.560343 | 95,518,922 |
Type Function Library json.* Return value Table Revision 2018.3333 Keywords json See also json.decode()
Decodes the contents of a file that is expected to contain
nil, the position of the next character that doesn't belong to the object, and an error message. Errors can either relate to issues opening the file or to JSON syntax issues.
filename parameter should usually be obtained from
system.pathForFile() so it can be correctly located in the application's sandbox. See the Example below.
json.decodeFile( filename [, position [, nullval]] )
String. String containing the name of a file containing JSON data.
Number. Index within file to start decoding (default is
1 if omitted).
Value to be returned for items with a value of
nil don't normally exist).
local json = require( "json" ) local filename = system.pathForFile( "datafile.json", system.ResourceDirectory ) local decoded, pos, msg = json.decodeFile( filename ) if not decoded then print( "Decode failed at "..tostring(pos)..": "..tostring(msg) ) else print( "File successfully decoded!" ) end | <urn:uuid:75558e9c-5f72-453c-8be6-1c86af30626e> | 2.578125 | 258 | Documentation | Software Dev. | 45.549715 | 95,518,935 |
I have the following task, and I need some help getting started: Write a response about: the importance of wind as an agent of erosion, and explain why statements that credit wind as having sculpted the landscape are probably inaccurate. Also comment on how climate influences mass wasting, and why might arid climates experience a great deal of mass wasting even though there is less annual rainfall?© BrainMass Inc. brainmass.com July 23, 2018, 9:59 am ad1c9bdddf
It is true that the earth's surface is constantly moving. This is true as a result of two processes: weathering and erosion. Both processes include wind, but wind is not the only process involved. When rocks are exposed to wind, water, cold and heat, they break down into smaller pieces by the process of weathering. This material is moved by gravity wind and water, a process called erosion.
There are two types of weathering, mechanical and chemical. Mechanical weathering is a gradual physical process from rock to clay, caused by hot and cold weather expanding and shrinking rocks to cause cracks. When water enter the cracks and freeze it can split the rock. Flowing water can turn the rock into sand, as can sand caught up in wind blowing across the rock. Even a glacier can rub debris against the rock to ...
A review of variations of erosion compared to weathering processes; comparing mass wasting in different climates. | <urn:uuid:722d8c0e-6e3b-4051-a74c-d4fdcc47c774> | 3.53125 | 290 | Q&A Forum | Science & Tech. | 57.396098 | 95,518,959 |
On the motion of a small particle in the atmosphere
- 78 Downloads
Equations of motion, valid for a water droplet or a dust particle less than about 50Μm in radius moving through the air, are derived. Thus, the behaviour of a particle in some simple nonuniform fluid flows is discussed. In particular, it is found that a particle may follow an approximately closed trajectory in an axisymmetric flow about a horizontal axis. Thus, it is argued that turbulence should cause particles to fall at a much slower rate than their terminal velocity, even in the absence of a mean updraft.
KeywordsAtmosphere Dust Fluid Flow Small Particle Horizontal Axis
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- Basset, A. B.: 1888,Hydrodynamics, Vol. II, Deighton, Bell and Co.Google Scholar
- Basset, A. B.: 1910, ‘On the Descent of a Sphere in a Viscous Liquid’,Quart. J. Pure Appl. Math. 41, 369–381.Google Scholar
- Batchelor, G. K.: 1967,Fuid Dynamics, Cambridge University Press.Google Scholar
- Corrsin, S. and Lumley, J.: 1956, ‘On the Equation of Motion for a Particle in Turbulent Fluid’,Appl. Sci. Res. 6A, 114–116.Google Scholar
- Hinze, J. O.: 1959,Turbulence, McGraw-Hill.Google Scholar
- Kreyszig, E.: 1962,Advanced Engineering Mathematics, Wiley and Sons.Google Scholar
- Rubinow, S. I. and Keller, J. B.: 1961, ‘The Transverse Force on a Spinning Sphere Moving in a Viscous Fluid’,J. Fluid Mech. 11, 447–459.Google Scholar
- Saffman, P. G.: 1965, ‘The Lift on a Small Sphere in a Slow Shear Flow’,J. Fluid Mech. 22, 385–440.Google Scholar
- Tchen, C. M.: 1947, ‘Mean Value and Correlation Problems Connected with the Motion of Small Particles Suspended in a Turbulent Fluid’, Ph. D. Thesis, Delft.Google Scholar
- Warner, J.: 1969, ‘The Microstructure of Cumulus Cloud. Part II: The Effect On Droplet Size Distribution of Cloud Nucleus Spectrum and Updraft Velocity’,J. Atmos. Sci. 26, 1272–1282.Google Scholar
- Warner, J.: 1970, ‘The Microstructure of Cumulus Cloud. Part III: The Nature of the Updraft’,J. Atmos. Sci. 27, 682–688.Google Scholar | <urn:uuid:0b22f224-bbf7-4770-814a-4c2202616a06> | 2.546875 | 601 | Academic Writing | Science & Tech. | 76.173922 | 95,518,995 |
Buckling of Cylindrical Shells
In this chapter, we derive the equations for buckling of cylindrical shells (Fig. 11-1) subjected to compressive forces. Two approaches for developing the buckling equations will be discussed. The first is that of Sturm (Sturm 1941) which is well suited for designing cylindrical shells at various temperatures using actual stress-strain curves as discussed in Section 11-5. This approach is used in many pressure vessel codes for the design of cylindrical shells.
KeywordsCylindrical Shell Lateral Pressure Outer Cylinder Design Equation Allowable Stress
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Charge Density in the Gallium Arsenide Crystal
Approximating the charge density in crystalline gallium arsenide by a spatial superposition of self-consistent charge densities of gallium and arsenic atoms, we have calculated several contours of constant charge density and examined the three-dimensional character of these contours. A novel feature of the present work is that computer graphics techniques have been used to present the results in the form of three short color movies.
KeywordsCharge Density Computer Graphic Gallium Arsenide Data Plane Electronic Band Structure
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- Schreiber, D. E. (1968) “A Generalized Equipotential Plotting Routine for Calculating a Scalar Function of Two Variables” IBM Research Report RJ-499.Google Scholar | <urn:uuid:812de121-cd13-40ad-bfd5-6b097f7c25c4> | 2.578125 | 171 | Academic Writing | Science & Tech. | 21.54431 | 95,518,997 |
domingo, 4 de diciembre de 2011
Astronomy [Image] Abell 39 --The Ghost Nebula --One of the Largest Spheres of the Milky Way
Abell 39, about 7000 light years away, is a ghostly remnant of a Sun-like star and one of the largest existing spheres in the Milky Way. Six light-years across, it was once a sun-like star's outer atmosphere expelled thousands of years ago. The nearly perfect spherical nature of Abell 39 allows astronomers to accurately estimate how much relative material is actually absorbing and emitting light.
Observations indicate that Abell 39 contains only about half of the oxygen found in the Sun, an intriguing but not surprising confirmation of the chemical differences between stars. The reason why the central star is slightly off center by 0.1 light-years is currently unknown. Several galaxies millions of light years away can be seen through and around the spectral nebula.
Image credit: NASA/ESO
Source: The Daily Galaxy
Publicado por Karla Segura Chavarría en 15:29 | <urn:uuid:80fab487-ebb8-4d70-8644-856b9490e063> | 3.6875 | 224 | Personal Blog | Science & Tech. | 40.161953 | 95,519,010 |
"It is surprising to have large, potentially complex fossils that far back," said Christopher H. House, professor of geosciences, Penn State, and lead author.
These are spindle-like microstructures from the Farrel Quartzite, Western Australia.
Credit: Christopher House, Penn State
However, the researchers not only showed that these inclusions in the rocks were biological in origin, but also that they were likely planktonic autotrophs -- free-floating, tiny ocean organisms that produce energy from their environment.
The researchers looked at marine sediment rocks from the Farrel Quartzite in Western Australia. Isotopic analysis using secondary ion mass spectrometry was carried out at UCLA. "Ken (Kenichiro Sugitani, professor, Graduate School of Environmental Studies, Nagoya University, Japan, and a co-author) discovered these unusually shaped microfossils embedded in really old rock," said House.
To determine if these inclusions were actually biological in origin, the researchers looked at 15 different samples of Farrel Quartzite and determined their stable carbon isotope ratios. The percentage of carbon 13 in the microfossils was indicative of material produced by biological processes. They found that the carbon 13 percentage in the background organic matter in the surrounding rock was different from that of the microstructures.
"When considered along with published morphological and chemical studies, these results indicate that the Farrel Quartzite microstructures are bona fide microfossils, and support the interpretation that the spindles were planktonic," the researchers report in the current issue of Geology. The morphological and chemical studies were done by Sugitani and Dorothy Oehler, who is also a co-author and research scientist, Astromaterials Research and Exploration Science Directorate, NASA -- Johnson Space Center.
The spindle-shaped microfossils are from 20 to 60 microns in length, about the size of fine sand and within the size range of today's microplankton.
Stable carbon isotope analysis can determine the biological origin of these microfossils because they used carbon dioxide to create energy and incorporated the carbon into themselves. During this process, the organisms selectively incorporate more carbon 12 than carbon 13 from the available carbon, producing a signature of biological origin.
Oehler notes that the spindles appear to be the same as those found in rocks from the Strelly Pool Formation in Western Australia and the Onverwacht Group in South Africa and Swaziland that are both 3.4 billion years old.
"The existence of these microfossils in diverse locations as far back as 3.4 billion years ago suggests that the oceans probably had life in them for a very extended period of time," said Oehler. "Moreover, this has implications beyond what we have done here, suggesting the evolution of diverse life proceeded quickly."
Also working on this project was Koichi Mimura, Graduate School of Environmental Studies, Nagoya University, Japan.
The NASA Astrobiology Institute, the Astromaterials Research and Exploration Science Directorate, Johnson Space Center and the Japan Society for the Promotion of Science supported this research.
A'ndrea Elyse Messer | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
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19.07.2018 | Earth Sciences
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Butterfly: Wingspan: 1 1/2 to to 2 3/8 inches (4.1-6 cm). Both sexes have bright yellow wings with black borders the upper surface. The yellow is often golden and may include orange. This can be seen in flight. Males have a solid black border; females have a wider border that is peppered with a row of yellow spots. There is a black spot on the upper center of the forewing of both sexes. The hindwing’s underside is yellow or greenish yellow with a double, red-rimmed silver spot in the center. Some females are white (alba) instead of yellow. In the field, these are virtually impossible to distinguish from female Clouded Sulphurs. Spring individuals are usually smaller, and orange is often restricted to wing bases.
ID Tip: Displays at least some gold/orange on forewing. Lacks a diagonal brown marking below.
Egg: Spindle-shaped. White when laid; turns orange/red.
Caterpillar: Caterpillars are grass green with a multicolored stripe along the lower edges of the body. The upper stripe is white followed by red/pink, white, and finally black. Clouded Sulphur caterpillars are so similar that they cannot be reliably separated in the field.
Chrysalis: The chrysalis is green with yellow and black dashes. The overwintering stage.
Once called the Alfalfa Butterfly, Orange Sulfur's primary populations were based in the western U.S. where their host plant of choice was (predictably) alfalfa. As eastern forests were cleared and converted to farmland, the alfalfa butterfly followed alfalfa’s eastward march, reaching Alabama in the 1930’s. By the 1950’s, the state’s alfalfa crops were declining due to boll weevil infestations, but Orange Sulphurs were here to stay, having discovered a treasure trove of other acceptable legumes. Today, clovers and vetches satisfy larval nutritional needs and probably serve as primary host plants.
Orange Sulphurs are remarkably similar to Clouded Sulphurs, and field ID's are often extremely difficult, if not impossible. However, female sulphurs are able to choose appropriate mates because they are able to detect ultraviolet patterns that differ in the two species. Orange Sulphur upper wing surfaces reflect UV light, while Clouded Sulphur wings absorb it. Even so, hybrids reportedly occur.
A dot on the county map indicates that there is at least one documented record of the species within that county. In some cases, a species may be common throughout the county, in others it may be found in only a specific habitat.
The sightings bar graphs depict the timing of flight(s) within each of three geographic regions. Place your cursor on a bar within the graph to see the number of individuals recorded during that period.
The abundance calendar displays the total number of individuals recorded within each week of the month. Both the graphs and the calendar are on based data collection that began in 2000.
The records analyzed here are only a beginning. As more data is collected, these maps and graphs will paint a more accurate picture of distribution and abundance in Alabama. Submit your sightings to email@example.com.
Sightings in the following counties: Baldwin, Barbour, Bibb, Blount, Calhoun, Chambers, Chilton, Clay, Cleburne, Colbert, Dallas, DeKalb, Fayette, Franklin, Hale, Jackson, Jefferson, Lawrence, Lee, Limestone, Madison, Madison , Marshall, Morgan, Perry, Pickens, Shelby, Sumter, Tuscaloosa
View county names by moving the mouse over a county or view a map with county names
Cultivated fields, roadsides, pastures and other sunny areas. Nearly any open, weedy site.
Members of the Pea family (Fabaceae), especially clovers (Melilotus and Trifolium spp.) and vetches (Vicia spp.), are reported.
Crimson Clover (Trifolium incarnatum) has been documented in Alabama.
For more information about the documented host plants and/or nectar plants, please visit the Alabama Plant Atlas using the following links:
Including a variety of flowers such as daisy fleabanes (Erigeron spp.), Black Eyed Susans (Rudbeckia spp.), Butterfly Milkweed (Asclepias tuberosa), asters (Symphyotrichum spp.), goldenrods (Solidago spp.), ironweeds (Vernonia spp.), Purple Coneflower (Echinacea purpurea), and Mistflower/Wild Ageratum (Conoclinium coelestinum) in your landscape will provide nectar for butterflies like Orange Sulphurs throughout the growing season. | <urn:uuid:bcc32215-4321-4195-afe1-e6d46acf29db> | 3.4375 | 1,033 | Knowledge Article | Science & Tech. | 41.610245 | 95,519,025 |
The telltale paw prints with huge 10 centimetre-long nails spoke volumes. But now definitive corroborating DNA evidence seals the case of the most northerly sighting of a grizzly bear. The discovery fuels mounting evidence that Canada’s High Arctic is no longer the sole preserve of the polar bear – Nanuk is having to make room for its southern cousin.
The evidence of the barren ground grizzly bear (Ursus arctos) was discovered on Melville Island, an uninhabited part of the western Arctic archipelago 1,500 kilometres due north of Yellowknife, and 1,000 kilometres north of the Arctic Circle. "We know grizzlies go out on the sea ice to hunt seals, but no one has ever seen one that far north," says Dr. John England a geology professor and the NSERC Northern Chair at the University of Alberta.
Dr. England got his first glimpse of the surprising Melville Island grizzly bear from the air during a helicopter ride to a geology research site in 2003. He photographed mid-distance shots of the large bear with characteristic grizzly features including a prominent shoulder hump, dark brown hair on and around the rear legs, and faded (grizzled) hair on the rest of the body.
Dr. Jonathan Doupé | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
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High School Earth Science/Absolute Ages of Rocks. from tree rings to the amounts of radioactive materials in a rock. In the process of radiometric dating,.
The Dating Game - Scientific American
Science 8: The Deep Time Diaries Name Date Per Radiometric Dating LabLet's Model Radioactive Decay to Show How Carbon Dating Works. Sign In. Subscribe. Radioactive material gets a bad rap,. science Do You Weigh More at.
Radiometric dating: In 1905, shortly after the discovery of radioactivity, the American chemist Bertram Boltwood suggested that lead is one of the disintegration.Geologic Time, Fossils, Radioactive Dating. Earth science. The data table shows the radioactive decay of carbon-14 and the age of fossil remains, in years (y).Radioactive Dating Copy and complete the numbered items. 25% if you just complete. 50% if you just copy. 100 if copied and completed with the correct answers.More radioactive dating - higher tier only Carbon dating. The amount of carbon-14 in the atmosphere has not changed in thousands of years. Even though it decays into.Quizlet provides radioactive dating science activities, flashcards and games. Start learning today for free!.
Radioactive Dating - Encyclopedia.com
Complex and microscopic structures and systems can be visualized, modeled, and used to describe phenomena. Plan your 60 minutes lesson in Science or radioactive.
radioactive dating..? | Yahoo AnswersRadioactive isotopes are commonly portrayed as. Fluctuations Show Radioisotope Decay Is Unreliable. But science clearly shows that radioisotope decay.
Radioactive Dating Explained - Part 2 - Science Against Evolution
Refuting "Radiometric Dating Methods Makes Untenable AssumptionsRadioactive ‘dating’ failure. More on radioactive dating problems “God Science” and the Age of the Earth; Related Media. Radioisotope dating—An.This is "Science Talk with Dr. Jay L. Wile, Episode 06 | Radioactive Dating" by Oikos on Vimeo, the home for high quality videos and the people who love them.
Radioactive or Absolute Dating Activity - Science with Mrs. BartonPrinciples of Radiometric Dating Radioactive decay is described in terms of the probability that a constituent particle of the.Earth Science: Fossils,. Absolute Dating. Uses the idea that Radioactive isotopes decay at a steady rate that allow scientists to calculate the age of rocks and.
Radioactive dating for wine: Science meets fine foods.Tips for Using PhET. Browse Activities. Accessibility. Donate. Browse Activities. Radioactive Dating Game. Radioactive Dating Game.docx - 23 kB;. science.
Let us critically examine each of these claims and see if they hold up against the science. different radiometric dating techniques. through radioactive dating.Get this from a library! Radioactive Geochronometry: a derivative of the Treatise on Geochemistry. [Heinrich D Holland; Karl K Turekian; Ebooks Corporation.] -- The.Radioactive dating is very interesting because often this is where history and science mingle. One example of radioactive dating is carbon-14 dating. Carbon-14 dating.Dating the science 70. Christians, take the age. Geology. Carbon dating service. Gotra system is between the abundance ratio of planet properties will determine the.Radiometric dating using the naturally-occurring radioactive elements is simple in concept even though technically complex. If we know the number of radioactive.
Quick Answer. Radioactive dating uses the decay rates of radioactive substances to measure absolute ages of rocks, minerals and carbon-based substances, according to How Stuff Works. Scientists know how quickly radioactive isotopes decay into other elements over thousands, millions and even billions of years.
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Radiometric dating (often called radioactive dating) is a way to find out how old something is. The method compares the amount of a naturally occurring radioactive.
Earth Science | Category | Radiometric Dating | Page 2What is Radioactive Dating?. Radioactive Dating and the Use of Isotopes. What is Radioactive Dating? - Definition & Facts Related Study Materials.Radioactive Decay and Half-Life. Science Enhanced Scope and Sequence. o How can radioactive dating be useful when the temperatures and pressures to which.Radiometric dating of rocks and minerals using naturally occurring, long-lived radioactive isotopes is troublesome for young. Earth and Planetary Science.
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Mr Schmitt - Science 10. Home Grades Ecosystems Chemistry Earth Science Motion Final Exam. rate of decay inquiry activity, radioactive dating game.The isotope 14 C, a radioactive form of carbon, is produced in the upper atmosphere by neutrons striking 14 N nuclei. The neutron is captured by the 14 N nucleus and knocks out a proton. Thus, we have a different element, 14 C. The isotope, 14C, is transported as 14 CO2, absorbed by plants, and eaten by animals.Science Fair Project: Making. How Old Is the Earth: Radioisotope Dating;. An important property of radioactive isotopes is the half-life — the time it takes.
Radioactive Dating and Low-Level Counting. Science 11 Aug 1967: Vol. 157, Issue 3789, pp. 726-727 DOI: 10.1126/science.157.3789.726 Article; Info.Define radiometric dating. radiometric. radioactive dating. radiometric dating and trace element analysis in pure and applied science in an.Plan your 60 minutes lesson in Science or radioactive dating with helpful tips from Mariana. To introduce the idea of radioactive decay and carbon dating,.Name Date Block Absolute Dating Radioactive Dating Resource Site: http://phet.colorado.edu/en/simulation/radioactive-dating-game. | <urn:uuid:ff7cdcd8-b021-49a4-b425-c8a8c2359fe1> | 3.515625 | 1,255 | Content Listing | Science & Tech. | 38.334916 | 95,519,047 |
This article needs to be updated.(November 2014)
|Developer(s)||University Of California, Berkeley|
|Initial release||May 17, 1999|
April 23, 2015
|Project goal(s)||Discovery of radio evidence of extraterrestrial life|
|Funding||Public funding and private donations|
Microsoft Windows, Linux, Android, macOS, Solaris,|
IBM AIX, FreeBSD, DragonflyBSD, OpenBSD, NetBSD, HP-UX, IRIX, Tru64 Unix, OS/2 Warp, eComStation
|Active users||103,480 (January 2018)|
|Total users||1,716,012 (January 2018)|
SETI@home ("SETI at home") is an Internet-based public volunteer computing project employing the BOINC software platform created by the Berkeley SETI Research Center and is hosted by the Space Sciences Laboratory, at the University of California, Berkeley. Its purpose is to analyze radio signals, searching for signs of extraterrestrial intelligence, and as such is one of many activities undertaken as part of the worldwide SETI effort.
SETI@home was released to the public on May 17, 1999, making it the third large-scale use of distributed computing over the Internet for research purposes, after Great Internet Mersenne Prime Search (GIMPS) was launched in 1996 and distributed.net in 1997. Along with MilkyWay@home and Einstein@home, it is the third major computing project of this type that has the investigation of phenomena in interstellar space as its primary purpose.
- 1 Scientific research
- 2 Procedure details
- 3 Results
- 4 Technology
- 5 Statistics
- 6 Project future
- 7 Competitive aspect
- 8 Challenges to the project
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
The two original goals of SETI@home were:
- to do useful scientific work by supporting an observational analysis to detect intelligent life outside Earth
- to prove the viability and practicality of the "volunteer computing" concept
The second of these goals is considered to have succeeded completely. The current BOINC environment, a development of the original SETI@home, is providing support for many computationally intensive projects in a wide range of disciplines.
The first of these goals has to date yielded no conclusive results: no evidence for ETI signals has been shown via SETI@home. However, the ongoing continuation is predicated on the assumption that the observational analysis is not an "ill-posed" one. The remainder of this article deals specifically with the original SETI@home observations/analysis. The vast majority of the sky (over 98%) has yet to be surveyed, and each point in the sky must be surveyed many times to exclude even a subset of possibilities.
SETI@home searches for possible evidence of radio transmissions from extraterrestrial intelligence using observational data from the Arecibo radio telescope and the Green Bank Telescope. The data are taken "piggyback" or "passively" while the telescope is used for other scientific programs. The data is digitized, stored, and sent to the SETI@home facility. The data are then parsed into small chunks in frequency and time, and analyzed, using software, to search for any signals—that is, variations which cannot be ascribed to noise, and hence contain information. Using distributed computing, SETI@home sends the millions of chunks of data to be analyzed off-site by home computers, and then have those computers report the results. Thus what appears a difficult problem in data analysis is reduced to a reasonable one by aid from a large, Internet-based community of borrowed computer resources.
- Spikes in power spectra
- Gaussian rises and falls in transmission power, possibly representing the telescope beam's main lobe passing over a radio source
- Triplets — three power spikes in a row
- Pulsing signals that possibly represent a narrowband digital-style transmission
- Autocorrelation detects signal waveforms.
There are many variations on how an ETI signal may be affected by the interstellar medium, and by the relative motion of its origin compared to Earth. The potential "signal" is thus processed in many ways (although not testing all detection methods nor scenarios) to ensure the highest likelihood of distinguishing it from the scintillating noise already present in all directions of outer space. For instance, another planet is very likely to be moving at a speed and acceleration with respect to Earth, and that will shift the frequency, over time, of the potential "signal." Checking for this through processing is done, to an extent, in the SETI@home software.
The process is somewhat like tuning a radio to various channels, and looking at the signal strength meter. If the strength of the signal goes up, that gets attention. More technically, it involves a lot of digital signal processing, mostly discrete Fourier transforms at various chirp rates and durations.
To date, the project has not confirmed the detection of any ETI signals. However, it has identified several candidate targets (sky positions), where the spike in intensity is not easily explained as noisespots, for further analysis. The most significant candidate signal to date was announced on September 1, 2004, named Radio source SHGb02+14a.
While the project has not reached the stated primary goal of finding extraterrestrial intelligence, it has proved to the scientific community that distributed computing projects using Internet-connected computers can succeed as a viable analysis tool, and even beat the largest supercomputers. However, it has not been demonstrated that the order of magnitude excess in computers used, many outside the home (the original intent was to use 50,000-100,000 "home" computers), has benefited the project scientifically. (For more on this, see § Challenges to the project below.)
Astronomer Seth Shostak stated in 2004 that he expects to get a conclusive signal and proof of alien contact between 2020 and 2025, based on the Drake equation. This implies that a prolonged effort may benefit SETI@home, despite its (present) eighteen-year run without success in ETI detection.
Anybody with an at least intermittently Internet-connected computer can participate in SETI@home by running a free program that downloads and analyzes radio telescope data.
Observational data are recorded on 2-terabyte SATA hard disk drives at the Arecibo Observatory in Puerto Rico, each holding about 2.5 days of observations, which are then sent to Berkeley. Arecibo does not have a broadband Internet connection, so data must go by postal mail to Berkeley. Once there, it is divided in both time and frequency domains work units of 107 seconds of data, or approximately 0.35 megabytes (350 kilobytes or 350,000 bytes), which overlap in time but not in frequency. These work units are then sent from the SETI@home server over the Internet to personal computers around the world to analyze.
The analysis software can search for signals with about one-tenth the strength of those sought in previous surveys, because it makes use of a computationally-intensive algorithm called coherent integration that no one else has had the computing power to implement.
The initial software platform, now referred to as "SETI@home Classic," ran from May 17, 1999, to December 15, 2005. This program was only capable of running SETI@home; it was replaced by Berkeley Open Infrastructure for Network Computing (BOINC), which also allows users to contribute to other distributed computing projects at the same time as running SETI@home. The BOINC platform will also allow testing for more types of signals.
On May 3, 2006, new work units for a new version of SETI@home called "SETI@home Enhanced" started distribution. Since computers now have the power for more computationally intensive work than when the project began, this new version is more sensitive by a factor of two concerning Gaussian signals and to some kinds of pulsed signals than the original SETI@home (BOINC) software. This new application has been optimized to the point where it will run faster on some work units than earlier versions. However, some work units (the best work units, scientifically speaking) will take significantly longer.
In addition, some distributions of the SETI@home applications have been optimized for a particular type of CPU. They are referred to as "optimized executables" and have been found to run faster on systems specific for that CPU. As of 2007[update], most of these applications are optimized for Intel processors and their corresponding instruction sets.
The results of the data processing are normally automatically transmitted when the computer is next connected to the Internet; it can also be instructed to connect to the Internet as needed.
With over 5.2 million participants worldwide, the project is the distributed computing project with the most participants to date[when?]. The original intent of SETI@home was to utilize 50,000-100,000 home computers. Since its launch on May 17, 1999, the project has logged over two million years of aggregate computing time.[when?] On September 26, 2001, SETI@home had performed a total of 1021 floating point operations. It was acknowledged by the 2008 edition of the Guinness World Records as the largest computation in history. With over 145,000 active computers in the system (1.4 million total) in 233 countries, as of 23 June 2013[update], SETI@home had the ability to compute over 668 teraFLOPS. For comparison, the Tianhe-2 computer, which as of 23 June 2013[update] was the world's fastest supercomputer, was able to compute 33.86 petaFLOPS (approximately 50 times greater).
There were plans to get data from the Parkes Observatory in Australia to analyze the southern hemisphere. However, as of 3 June 2018[update], these plans were not mentioned in the project's website. Other plans include a Multi-Beam Data Recorder, a Near Time Persistency Checker and Astropulse (an application that uses coherent dedispersion to search for pulsed signals). Astropulse will team with the original SETI@home to detect other sources, such as rapidly rotating pulsars, exploding primordial black holes, or as-yet unknown astrophysical phenomena. Beta testing of the final public release version of Astropulse was completed in July 2008, and the distribution of work units to higher spec machines capable of processing the more CPU intensive work units started in mid-July 2008.
SETI@home users quickly started to compete with one another to process the maximum number of work units. Teams were formed to combine the efforts of individual users. The competition continued and grew larger with the introduction of BOINC.
As with any competition, attempts have been made to "cheat" the system and claim credit for work that has not been performed. To combat cheats, the SETI@home system sends every work unit to multiple computers, a value known as "initial replication" (currently 2). Credit is only granted for each returned work unit once a minimum number of results have been returned and the results agree, a value known as "minimum quorum" (currently 2). If, due to computation errors or cheating by submitting false data, not enough results agree, more identical work units are sent out until the minimum quorum can be reached. The final credit granted to all machines which returned the correct result is the same and is the lowest of the values claimed by each machine. The claimed credit by each machine for an identical work unit often varies due to minor differences in floating point arithmetic on different processors.
Some users have installed and run SETI@home on computers at their workplaces — an act known as "Borging", after the assimilation-driven Borg of Star Trek. In some cases, SETI@home users have misused company resources to gain work-unit results — with at least two individuals getting fired for running SETI@home on an enterprise production system. There is a thread in the newsgroup alt.sci.seti which bears the title "Anyone fired for SETI screensaver" and ran starting as early as September 14, 1999.
Other users collect large quantities of equipment together at home to create "SETI farms", which typically consist of a number of computers consisting of only a motherboard, CPU, RAM and power supply that are arranged on shelves as diskless workstations running either Linux or old versions of Microsoft Windows "headless" (without a monitor).
Challenges to the project
There are other challenges to the project's future viability.
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Like any project of prolonged duration, there are factors that may result in its termination. Some of these are detailed below:
Potential closure of Arecibo Observatory
The decreasing operating budget for the observatory has created a shortfall of funds which has not been made up from other sources such as private donors, NASA, other foreign research institutions, nor private non-profit organizations such as SETI@home.
However, in the overall longterm views held by many involved with the SETI project, any usable radio telescope could take over from Arecibo, as all the SETI systems are portable and relocatable.
Alternative distributed computing projects
More restrictive computer use policies in businesses
In one documented case, an individual was fired for explicitly importing and using the SETI@home software on computers used for the U.S. state of Ohio. In another incident a school IT director resigned after his installation allegedly cost his school district $1 million in removal costs; however, other reasons for this firing included lack of communication with his superiors, not installing firewall software and alleged theft of computer equipment, leading a ZDNet editor to comment that "the distributed computing nonsense was simply the best and most obvious excuse the district had to terminate his contract with cause".
As of 16 October 2005[update], approximately one-third of the processing for the non-BOINC version of the software was performed on work or school based machines. As many of these computers will give reduced privileges to ordinary users, it is possible that much of this has been done by network administrators.
To some extent, this may be offset by better connectivity to home machines and increasing performance of home computers, especially those with GPUs, which have also benefited other distributed computing projects such as Folding@Home. The spread of mobile computing devices provides another large resource for distributed computing. For example, in 2012, Piotr Luszczek (a former doctoral student of Jack Dongarra), presented results showing that an iPad 2 matched the historical performance of a Cray-2 (the fastest computer in the world in 1985) on an embedded LINPACK benchmark.
There is currently no government funding for SETI research, and private funding is always limited. Berkeley Space Science Lab has found ways of working with small budgets, and the project has received donations allowing it to go well beyond its original planned duration, but it still has to compete for limited funds with other SETI projects and other space sciences projects.
In a December 16, 2007 plea for donations, SETI@home stated its present modest state and urged donations of $476,000 needed for continuation into 2008.
A number of individuals and companies made unofficial changes to the distributed part of the software to try to produce faster results, but this compromised the integrity of all the results. As a result, the software had to be updated to make it easier to detect such changes, and discover unreliable clients. BOINC will run on unofficial clients; however, clients that return different and therefore incorrect data are not allowed, so corrupting the result database is avoided. BOINC relies on cross-checking to validate data but unreliable clients need to be identified, to avoid situations when two of these report the same invalid data and therefore corrupt the database. A very popular unofficial client (lunatic) allows users to take advantage of the special features provided by their processor(s) such as SSE, SSE2, SSE3, SSSE3, SSE4.1, and AVX to allow for faster processing. The only downside to this is that if the user selects features that their processor(s) do not support, the chances of bad results and crashes rise significantly. Tools (such as CPU-Z) are freely available to tell users what features are supported by their processor(s).
Hardware and database failures
Currently,[when?] SETI@home is a test bed for further development not only of BOINC but of other hardware and software (database) technology. Under SETI@home processing loads these experimental technologies can be more challenging than expected, as SETI databases do not have typical accounting and business data or relational structures. The non-traditional database uses often do incur greater processing overheads and risk of database corruption and outright database failure. Hardware, software and database failures can (and do) cause dips in project participation.
The project has had to shut down several times to change over to new databases capable of handling more massive datasets. Hardware failure has proven to be a substantial source of project shutdowns—as hardware failure is often coupled with database corruption.
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- "DownloadOther – BOINC".
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- Nemiroff, R.; Bonnell, J., eds. (May 17, 1999). "How to Search for Aliens". Astronomy Picture of the Day. NASA. Retrieved 2006-10-06.
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Ernest Rutherford, 1871 - 1937, was a New Zealand chemist and physicist, who worked in Canada and England. His work pioneered our understanding of the atom.
Atomic structure, Radioactivity
Nobel (Chemistry) 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances"
Rutherford atom model. Concept of radioactive half-life and transmutation of elements through nuclear decay. Named alpha and beta radiation, and with Thomas Royds proved that apha radiation is the helium nucleus. First splitting of an atom (1917), in reaction between nitrogen and alpha particles, leading to the discovery of the proton. Rutherford predicted the existence of the neutron (1917).
Gold Foil (Geiger-Marsden alpha particle deflection experiment), which led to the discovery of the nucleus. Identification of alpha particle as helium nucleus. Discovery of proton. Transmutation of elements through decay.
With two students, Hans Geiger and Ernest Marsden, Ernest Rutherford ran a series of experiments between 1908 - 1913, known as the Gold Foil Experiment (or Geiger-Marsden Experiment). This experiment revealed that the nucleus of an atom was compact and small, and the remainder of the atom was empty space with electrons 'in orbit' around the positive nucleus.
This became the Rutherford Atom Model, which was superceded almost immediately by the Bohr Model of the Atom, which replaced the orbiting electrons by quantised electron energy states.
Rutherford received the Nobel Prize for Chemistry for this work in 1911. He went on to discovery the proton experimentally in 1917, and to successfully predict the existence of the neutron, which was proven correct by James Chadwick (one of his doctorate students) in 1932.
Rutherford is buried near Isaac Newton's tomb in Westminster Abbey. Element 104 (discovered in 1997) is named after him (rutherfordium).
(Biographies of famous scientists no. 12)
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Environmental Science is the most important of all sciences. As the world enters a phase of climate change, unprecedented biodiversity loss, pollution and human population growth, the management of our environment is vital for our futures. Learn about Environmental Science on ScienceLibrary.info.
1905 - 1973
Gerard Kuiper, 1905 - 1973, was a Dutch (American from 1937) astronomer who pioneered airborne infrared observations, and was a pioneer in planetary science.
Development promotes getting rich, but for the majority it only signifies the modernisation of their poverty.
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The command line does suck and is really boring but I can tell once I start becoming familiar with it everyday it will be second nature. Typing is static, but weakly enforced: all data has a type, but implicit conversions may be performed. Automatic memory allocation: temporary objects can be stored on the stack, and this space is automatically freed and reusable after the block in which they are declared is exited. But, you will get the big picture of programming concepts in the book which you may not find elsewhere.
Remember, you need to include stdio.h file in your program for this to work. I feel as though I put my best foot forward, and my inner software engineer has gotten back its spark. This is just one example. References ^ a b c d e Kernighan, Brian W.; Ritchie, Dennis M. (February 1978). https://en.wikipedia.org/wiki/C_(programming_language)
It was insufferable. I remember at the university, we would have to reach large and dense chapters on programming concepts before writing a line of code. This statement isn’t mandatory. To make this procedure even easier, follow this step by step guide.
Most of them (with Python being the most dramatic exception) are also very syntactically similar to C in general, and they tend to combine the recognizable expression and statement syntax of Comments may appear either between the delimiters /* and */, or (since C99) following // until the end of the line. Strings are not a separate data type, but are conventionally implemented as null-terminated arrays of characters. The C Programming Language (2nd Edition) This book provides the complete guide to ANSI standard C language.
Declarations either define new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, usually by writing the type followed by I'm following all of the instructions and everything makes sense, so I don't actually need help. Several C or near-C interpreters exist, including Ch and CINT, which can also be used for scripting. To run C programming in Ideone.com, select C language at the bottom of the editor, write C code and click Run.
Many of these had already been implemented as extensions in several C compilers. http://www.tutorialspoint.com/cprogramming/c_overview.htm? More than one assignment may be performed in a single statement. While C does not include some features found in some other languages, such as object orientation or garbage collection, such features can be implemented or emulated in C, often by way When download is completed, open Xcode and follow the wizard to install it.
Johnson made further changes to the language for several years to make it portable in Unix Operating system. Writing the simple database with dynamically allocated fields was more empowering than almost anything I've done as a programmer so far. ISBN7 302 02412 X. ^ "10 Common Programming Mistakes in C++". development tools and libraries.
Some examples of the use of C might be − Operating Systems Language Compilers Assemblers Text Editors Print Spoolers Network Drivers Modern Programs Databases Language Interpreters Utilities C Programs A C As mentioned, it’s a good language to start learning programming. The second edition of the book covers the later ANSI C standard, described below. However, many data structures can change in size at runtime, and since static allocations (and automatic allocations before C99) must have a fixed size at compile-time, there are many situations in
fedoraproject.org. C was originally first implemented on the DEC PDP-11 computer in 1972. Kevin I'm reading your book, Learn Python the Hard Way, and really enjoying it.
Libraries are often written in C because C compilers generate efficient object code; programmers then create interfaces to the library so that the routines can be used from higher-level languages like
Unlike many other intermediate languages, its representation is plain ASCII text, not bytecode or another binary format. For example, the operator == binds more tightly than (is executed prior to) the operators & (bitwise AND) and | (bitwise OR) in expressions such as x & 1 == 0, However, it’s considered good programming practice to use it. You can use comments in C programming by using //.
GCC, Solaris Studio, and other C compilers now support many or all of the new features of C99. The ISO C standard (section 18.104.22.168.1) requires both forms of main to be supported, which is special treatment not afforded to any other function. By design, C provides constructs that map efficiently to typical machine instructions, and therefore it has found lasting use in applications that had formerly been coded in assembly language, including operating C and the 8051 (3rd ed.).
This book is clear and comprehensive. If you don’t know C, you don’t know what you are doing as a programmer. The program prints "hello, world" to the standard output, which is usually a terminal or screen display. | <urn:uuid:36f90e7a-cd5a-4cb3-9ddf-a4f668a86608> | 2.953125 | 1,071 | Personal Blog | Software Dev. | 48.684744 | 95,519,101 |
We put the statuette on the force meter. The force meter showed a value 25 N. Then we placed the statuette on the force meter completely immersed in the water. The force meter showed a value 17 N. What is the volume of the statuette?
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Surface of the sphere is 2820 cm2, weight is 71 kg. What is its density?
- Air mass
What is the weight of the air in a classroom with dimensions 10 m × 0 m × 2.5 m ? The air density is 1.293 kg/m3.
How many 55% alcohol we need to pour into 14 liters 75% alcohol to get p3% of the alcohol? How many 65% alcohol we get?
Brick has volume 2.2 dm3. How many bricks can drive truck with capacity 23 ton? The density of brick is 1.6 g/cm3.
- Hollow sphere
Calculate the weight of a hollow tungsten sphere (density 19.3 g/cm3), if the inner diameter is 14 cm and wall thickness is 3 mm.
The cube weighs 24 kg. How weight is cube of the same material, if its dimensions are 2-times smaller?
- Lead cube
Calculate the edge of the cube made from lead, which weighs 19 kg. The density of lead is 11341 kg/m3. | <urn:uuid:f2ff5528-e9bb-44a8-aa4c-116986b078fd> | 2.921875 | 746 | Tutorial | Science & Tech. | 94.019373 | 95,519,109 |
The functional development of hair cells in the inner ear that mediate hearing and balance takes place over a period of just one day in mouse embryos, according to a study by a research team at the University of Virginia Health System.
The U.Va. scientists found that three essential elements for development in the mouse inner ear appear between day 16 and day 17 of gestation, roughly equivalent to the late second trimester or early third trimester in the human fetus. The finding is important for ongoing research on regeneration of sensory hair cells in the human inner ear, say researchers, writing in the October edition of Nature Neuroscience, found online at www.nature.com/neuro.
"We were surprised that development of hair cells in the inner ear takes place so rapidly," said researcher Jeffrey R. Holt, an assistant professor of neuroscience and otolaryngology at U.Va. "Suddenly, the hair cells began working. To eventually discover how to regenerate hair cells in the human ear, we have to know when and how the original hair cells develop. Thats why this research is so central to our knowledge."
Bob Beard | EurekAlert!
Colorectal cancer risk factors decrypted
13.07.2018 | Max-Planck-Institut für Stoffwechselforschung
Algae Have Land Genes
13.07.2018 | Julius-Maximilians-Universität Würzburg
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
13.07.2018 | Event News
13.07.2018 | Materials Sciences
13.07.2018 | Life Sciences | <urn:uuid:de4a4346-794e-4177-8355-deb556d9c915> | 3.8125 | 873 | Content Listing | Science & Tech. | 43.036445 | 95,519,110 |
In 1963, on the shore of Makah Bay, Washington, a tall, thirty-year-old biologist named Bob Paine started prising ochre starfish off the rocks with a crowbar, and hurling them into the sea. In doing so, he remade the beach. The animals that the starfish would have eaten bloomed in number and overran the shoreline—barnacles first, and then mussels. Limpets and algae were crowded out. Within a year, the number of species on the beach had halved.
By denuding the shore of starfish, Paine realised that some creatures are disproportionately influential. Entire communities of animals and plants depend on their presence, and can topple in their absence. He called them keystone species after the central stone that keeps an arch from crumbling. It’s an idea that has itself taken a central place in ecology.
But in analyzing the outcomes of his starfish experiment, Paine missed something obvious and important: his own part in them. Yes, the starfish were influential, but so was he. He, a single human, had reshaped a tiny corner of world. And yet, Paine left himself and his 7.4 billion peers out of the very framework that he had created. At a conference last October, Boris Worm, an ecologist who had known Paine for a few decades, asked him if he thought humans also counted as keystone species.
“Oh, we’re above that,” Paine replied. “We’re hyperkeystones.”
We are the influencer of influencers, the keystone species that disproportionately affects other keystone species, the ur-stone that dictates the fate of every arch.
Paine coined the term as a play on ‘hyperparasites’—organisms that parasitize other parasites. There are body-snatching wasps, for example, that lay eggs in the bodies of other insects, and other wasps that lay eggs in the eggs of those first ones—the latter are hyperparasites. So if hyperkeystone sounds grandiose, it’s not meant to; it’s almost the opposite.
The concept is clearest in the Pacific Northwest, the area where Paine and a large number of his students did most of their work. There, in the tidal zone, starfish control the numbers of mussels and barnacles. Sea otters keep kelp forests healthy by eating sea urchins that would graze the fronds down, and orcas hunt the otters. By migrating upstream, salmon carry nutrients from the sea into rivers; when they are killed by bears and wolves, their carcasses are dragged into the forests, where they fertilize the trees.
Bears, wolves, salmon, starfish, orcas, and sea otters: we influence the lot. Whether directly through hunting and fishing, or indirectly through light and noise pollution, climate change, or deforestation, we change the levels of keystone species everywhere.
“People now strongly influence all natural ecosystems,” says Julia Baum from the University of Victoria. “We do so to such an extent that as scientists we cannot even begin to understand how the ecosystems work if we do not first account for the ways in which people are changing them.”
Wait, aren’t we doing that? Isn’t that what ecology is all about?
Sort of, says Worm. He says that he and his peers have been increasingly obsessed with finding big patterns—how fish stocks rise and fall with time, or how communities of species change as temperatures rise. And in doing so, ecology had become a largely descriptive science. But in the meantime, it moved away from what Paine called “kick-it-and-see ecology”—experimental work that, like his starfish study, would reveal not only what is changing, but why and how.
“Bob felt that we had lost the way a little bit,” says Worm. “In the media, you read that we’re losing species, and birds are affected by plastic pollution, and tigers are dwindling, and that’s bad. That’s often the extent of it. But there’s a deeper and more profound side to this. Those losses set off these cascading interactions that we only know about in a few settings, largely because of people who are now in their seventies and eighties, like Bob.”
A few more recent examples hint at what we’re missing. In the northwest Atlantic, we overfished big sharks, releasing smaller sharks and rays from predatory control; they devoured shellfish and caused a century-old scallop fishery to collapse. In Ghana, we killed off lions and leopards in Ghana, allowing baboons to flourish; they then ate other primates, small antelopes, birds, and even crops, forcing local villagers to enlist school-age children as crop guards. In both cases, the direct consequences of our actions were clear, but it took a lot of work to understand everything that happened afterwards.
In the last few months, Worm and Paine wrote about the hyperkeystone concept in a new paper that’s meant to both galvanize and challenge their peers. Can they work out how exactly we are changing the world in our role as a hyperkeystone? We know about the Pacific Northwest, but what about the eastern seaboard, or East Africa, or Antarctica? And can we identify other hyperkeystones? Orcas might fit the bill: they, like us, are also far-ranging generalist predators. “Changes in such species are expected to have disproportionately large ecological impacts,” says Fiorenza Micheli from Stanford University. “Bob, as always throughout his career, has left us with a powerful concept.”
The hyperkeystone idea is a way of marrying the local domino effects that Paine observed with the global reach of our species. If fish stocks are falling, how does that affect the numbers of plankton or nutrients in the ocean, and how does ripple across ecosystems? To take just one example, when fish stocks fall in Ghanaian seas, hunting of bushmeat goes up and 41 land-based species go into decline. As hyperkeystones, we unite the entire world in a chain of falling dominoes. The question is how?
“We’re doing experiments all the time, by removing species in a replicated fashion,” says Worm. For example, he has shown that as fisheries throughout the Atlantic remove cod, shrimp and herring rise. “It was astonishing how predictable it was.” Other scientists are running large experiments, where they deliberately exclude or add animals to small patches of habitat to see what happens—a global version of Paine’s antics on Makah Bay.
Paine died of cancer last Tuesday, aged 83. By coincidence, the hyperkeystone paper was published on the same day. “It’s deeply moving to me,” says Worm.
“Bob was one of the most respected and admired marine scientists alive,” he adds. “But his original work ignored us and, of course, we cannot do ecology now by ignoring humans. Bob was part of that generation that treated humans as an externality. Very few of his papers had a human in the picture. We were the missing keystone. By adding us back, we make his insights relevant to the 21st century.”
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The integration of Planck's two instruments marks a major milestone for the mission. "We have been working on the design of these instruments for 14 years. For most of that time we have been living in a paper world; to finally have them as pieces of hardware feels great," says Jan Tauber, the Planck Project Scientist.
Combined focal plane of Planck's two instruments
The instruments are the key to the mission. Working in tandem, they will significantly advance our knowledge of the Big Bang. During the Big Bang, all of space was a tremendously hot furnace, filled with particles and radiation. In the approximately 13 thousand million years since then, the Universe has expanded and the radiation has cooled to become microwaves.
The Planck spacecraft will use a 1.5 metre mirror to systematically collect the cosmic microwave background radiation from the whole sky, and feed it to the two instruments.
The two instruments detect the collected radiation in different ways. The Low Frequency Instrument (or LFI) will convert the lower energy microwaves into electrical voltages, rather like a transistor radio.
The High Frequency Instrument (or HFI) works by converting the higher energy microwaves to heat, which is then measured by a tiny electrical thermometer.
These signals will be analysed for tiny differences in strength. Such variations indicate differences in the density of matter in the early Universe. Slightly denser regions became the galaxies we see today, whereas the less dense areas became the great voids that fill parts of space. This pattern is influenced by the amount of normal matter, dark matter and dark energy that fills the Universe. So using Planck's maps, astronomers will be able to place the most stringent limits yet on the quantities of these three universal components.
There is even a possibility that Planck will detect a slight distortion of the microwave background caused by a suspected period in cosmic history, known as the inflationary epoch. Inflationary theory postulates that the entire Universe underwent a period of enormously accelerated expansion just after the Big Bang. If so, it would cause the whole of space to ripple in a highly specific way. This slight ripple might show up in the Planck data. "Of all the exciting science that we will do, this is the most exciting possible measurement of all," says Tauber.
Between now and Planck's launch in mid-2008, there remain a number of important, additional milestones. For example, the entire spacecraft must be tested at a special cryogenic facility built at the Centre Spatial de Liège, Université de Liège, Belgium. "This will be a big test for us and the satellite," says Tauber.
"The test is necessary because the instruments must be operated at extremely cold temperatures," says Thomas Passvogel, ESA Project Manager for Herschel and Planck. "In the case of HFI, the operating temperature is just one tenth of a degree above absolute zero."
On launch day itself, Planck will be lofted into space by an Ariane 5 rocket from Europe's spaceport in Kourou, French Guiana. Inside the nose cone, Planck will be keeping company with ESA's Herschel infrared space telescope. With a 3.5 metre mirror, Herschel will be the orbiting telescope with the largest mirror ever deployed in space. Together Planck and Herschel will survey the cold Universe. Instead of looking for the formation of the Universe, however, Herschel's primary mission will be to see the formation of stars and galaxies.
Thomas Passvogel | alfa
First evidence on the source of extragalactic particles
13.07.2018 | Technische Universität München
Simpler interferometer can fine tune even the quickest pulses of light
12.07.2018 | University of Rochester
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
13.07.2018 | Event News
13.07.2018 | Materials Sciences
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By Richard Pashley, Marilyn Karaman
Utilized Colloid and floor Chemistry is a huge creation to this interdisciplinary box. Taking a surely utilized process, with functions drawn from a variety of industries, this e-book will meet the calls for of the coed at the moment operating within the field.The textual content comprises keynote sections written via practising commercial learn scientists, bringing to the reader a wealth of actual commercial examples. those examples diversity from water remedy via to soil administration in addition to examples taken from the coatings and photographic industries. to help accessibility, a number of the extra not easy mathematical derivations are separated from the most textual content, allowing them to be refrained from as required.With rigorously established chapters, beginning with studying goals, and containing educational questions with solutions and explanatory notes, this article is important for undergraduates taking a primary direction on colloid and floor chemistry. This publication can also be appropriate to postgraduates and pros, who desire an up to date account of the topic.
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Additional resources for Applied Colloid and Surface Chemistry
It is this open structure that gives photographic-quality inkjet paper its ‘apparently dry’ quality as it comes off the printer. Both the pore structure and pore wettability control the liquid invasion of the coated layer and therefore the final destination of dyes. Dispersion and stability of the colloidal system may require dispersant chemistries specific to the particle and solution composition. In many colloidal systems particle–particle interactions lead to flocculation which in turn leads to an increase in viscosity of the system.
Derivation of the Gibbs adsorption isotherm Let us consider the interface between two phases, say between a liquid and a vapour, where a solute (i) is dissolved in the liquid phase. 1. g. a surfactant) there must be a surface excess of solute nis, compared with the bulk value continued right up to the interface. 1 Diagram of the variation in solute concentration at an interface between two phases. e. g) as add component ‘i’ Note that the total free energy of the system always increases on addition of component ‘i’ and when its surface area is increased.
E. with concentration). 12) The change in mi is caused by the change in bulk solute concentration. This is the Gibbs surface tension equation. e. g). This, of course, is the principal action of surfactants, which will be discussed in more detail in a later section. 14) 2 Thus, in principle, we could determine the adsorption excess of one of the components from surface tension measurements, if we could vary m1 independently of m2. But the latter appears not to be possible, because the chemical potentials are dependent on the concentration of each component. | <urn:uuid:980dacbe-3d6f-4025-9ec2-bfb384b1af0f> | 2.59375 | 980 | Product Page | Science & Tech. | 24.385167 | 95,519,137 |
Cell polarization underlies many cellular and organismal functions. The GTPase Cdc42 orchestrates polarization in many contexts. In budding yeast, polarization is associated with a focus of Cdc42•GTP which is thought to self sustain by recruiting a complex containing Cla4, a Cdc42-binding effector, Bem1, a scaffold, and Cdc24, a Cdc42 GEF. Using optogenetics, we probe yeast polarization and find that local recruitment of Cdc24 or Bem1 is sufficient to induce polarization by triggering self-sustaining Cdc42 activity. However, the response to these perturbations depends on the recruited molecule, the cell cycle stage, and existing polarization sites. Before cell cycle entry, recruitment of Cdc24, but not Bem1, induces a metastable pool of Cdc42 that is sustained by positive feedback. Upon Cdk1 activation, recruitment of either Cdc24 or Bem1 creates a stable site of polarization that induces budding and inhibits formation of competing sites. Local perturbations have therefore revealed unexpected features of polarity establishment.https://doi.org/10.7554/eLife.26722.001
Living cells are not always symmetrical. Instead they are often polarized, with a distinct front and back or top and bottom. Cell polarization influences many processes, including how a cell moves and grows, and where it will divide. Breaking symmetry – in other words, making one part of a cell different from the rest – regularly involves a small protein called Cdc42, which can switch between an active and inactive form. This protein is found in a range of organisms from fungi to animals.
Budding yeast is a valuable model to study cell polarization. This single-celled fungus polarizes in order to produce a daughter cell or ‘bud’ that emerges out of one end of the mother cell. To become polarized, the mother cell accumulates active Cdc42 in a small area of the cell membrane. This region then becomes the front of the cell, from where the future bud will emerge. However, it is not fully understood how active Cdc42 accumulates at only one place. One model proposed that some molecules of active Cdc42 that are already present on the membrane, recruit polarity proteins that in turn activate other, inactive Cdc42 molecules. This self-amplifying loop could eventually build up a local pool of active Cdc42. However, it has proved challenging to directly test this model.
Optogenetics is a technique in which a beam of light is used to manipulate proteins inside cells in a precise manner. The method was first developed in the field of neuroscience over a decade ago, and has more recently been applied to cell biology. Now, Witte et al. have used optogenetics to move polarity proteins to defined places on the membrane of yeast cells and analyse how this change affected the pattern of Cdc42 activation. The experiments showed that polarity proteins not only activate Cdc42 but they also recruit more polarity proteins to the same place. The resulting positive feedback loop leads to active Cdc42 accumulating at one site on the membrane. Further work showed that this mechanism only operates in this manner just before the mother cell replicates its DNA, which is when a yeast cell will normally polarize.
These results provide a new perspective on how cells can make one part of the cell different from the rest. Beyond yeast, cell polarization plays a major role when animals, including humans, are developing as embryos or healing wounds. These processes are often controlled by a protein that is equivalent to Cdc42 or by other highly related switch-like proteins. This means that yeast will continue to provide a useful model to study these processes in the laboratory. Lastly, the optogenetics approach developed Witte et al. will be useful to dissect other processes that involve molecules being located at specific place in a cell at specific time.https://doi.org/10.7554/eLife.26722.002
Cell polarization occurs in all kingdoms of life. In metazoa, it is critical for many cellular events including cell migration, embryogenesis, and cytokinesis. Polarization is dynamic, enabling cells to reorient to changing spatial and temporal cues. The central, conserved regulator of cell polarity in eukaryotes is the small Rho-family GTPase, Cdc42 (Johnson and Pringle, 1990; Etienne-Manneville, 2004; Macara, 2004). Establishment of an axis of polarity frequently involves the accumulation of active Cdc42 at a unique position on the cell cortex. An initial cue induces Cdc42-GTP accumulation at a unique site, where it then concentrates via an amplification system. This amplification system maintains the polarity site (Thompson, 2013). While this general scheme of polarity establishment is fairly well established, the dynamic molecular interactions required for establishing, maintaining, and enforcing a single axis of polarity are not well understood.
One of the best studied cell polarization systems is bud site selection in Saccharomyces cerevisiae. Wild type yeast cells use landmark-directed cues to define the polarization axis (Figure 1A). However, cells lacking these spatial cues or the GTPase that transduces these cues, Rsr1, efficiently establish polarity in a process known as symmetry breaking. The current model of symmetry breaking suggests that stochastic accumulation of Cdc42-GTP induces a positive feedback loop mediated by a polarity complex containing the Cdc42 GEF, Cdc24, the scaffold protein, Bem1, and Cla4, which binds directly to activated Cdc42 (Howell et al., 2012) (Figure 1B). This tripartite complex is required for polarity establishment and its molecular features provide the requisite domains to result in positive feedback (Chenevert et al., 1992; Holly and Blumer, 1999; Bose et al., 2001; Butty et al., 2002). Computational models and in vivo analyses of symmetry breaking have uncovered behaviors consistent with positive feedback, including traveling waves and oscillatory accumulation of polarity proteins (Goryachev and Pokhilko, 2008; Ozbudak et al., 2005; Howell et al., 2012). However, important assumptions of the models have not been directly tested. For instance, whenever Cdc42 is active it should induce accumulation of the polarity complex; however, the validity of this critical assumption has yet to be established. Similarly, although polarity establishment has been dissected in considerable detail, the events preceding these have attracted relatively little attention. For example, in symmetry breaking polarization, do events in early G1 influence the site of symmetry breaking? To what extent are the functions of the polarity proteins influenced by the state of the cell cycle? These omissions are largely due to the absence of tools that permit controlled perturbation of Cdc42 activation.
In recent years, a number of genetically-encoded tools have been developed that allow control of diverse proteins using light (Tischer and Weiner, 2014). We have developed a set of small, highly engineered optogenetic protein tags, called TULIPs, that permit light-mediated control of protein-protein interactions (Strickland et al., 2012). In this system, the optically-responsive protein (LOVpep) is tethered to the plasma membrane whereas its cognate binding partner (ePDZ) freely diffuses in the cytoplasm. Illumination induces a conformational change in LOVpep that allows it to bind ePDZ, causing the rapid (<10 s) relocation of ePDZ to the membrane. LOVpep spontaneously relaxes to the dark state with a half-time of 80 s (Strickland et al., 2012). By fusing a protein of interest to ePDZ, we can potently and dynamically control its spatiotemporal localization using light. In previous proof of principle experiments, we demonstrated that local recruitment of Cdc24 directs formation of a mating projection in α-factor treated cells (Strickland et al., 2012).
Using optogenetic tools, we have probed the mechanism for yeast cell polarization. Our results provide direct evidence that positive feedback contributes to polarity establishment once Cdk1 is activated at START. However, while the current model predicts that the polarity components invariably function together in a potent positive feedback loop, we find that they do not do so prior to Cdk1 activation and that Cdc42 activation does not invariably induce the canonical positive feedback loop. Rather, we demonstrate the existence of a second positive feedback loop involving Cdc24 that precedes the canonical loop and appears to function independently of Bem1. Finally, we show that multiple nascent sites of polarization compete, and that this competition is particularly potent upon activation of the Bem1-dependent positive feedback loop. We conclude that two alternative modes of positive feedback function in concert to promote polarity initiation and establishment, with their respective behaviors under strict cell cycle control.
In order to probe the mechanism of cell polarization, we developed optogenetic tools to recruit yeast polarity proteins to defined sites on the cell cortex. Specifically, we co-expressed a membrane-tethered variant of LOVpep (Mid2-GFP-LOVpep) with either Bem1-ePDZ or Cdc24-ePDZ in diploid rsr1∆ cells. In all conditions, the TULIPs-tagged proteins were expressed under the control of a β-estradiol inducible promoter (Louvion et al., 1993), and the ePDZ-tagged polarity component was expressed in addition to its endogenous counterpart. We perturbed cells by illuminating at a single site with a diffraction-limited laser. The response to this perturbation was examined by following the recruitment of a Cdc42 biosensor derived from the Cdc42 effector protein Gic2 (Tong et al., 2007) and phase optics to observe bud emergence.
We first examined the ability of Cdc24 and Bem1 to bias the site of polarization in unpolarized cells as a function of illumination frequency. We measured the angle, θ, between the site of illumination and the position of the nascent bud. These values were linearly scaled such that budding at the center of the laser target was assigned a score of 1 and budding opposite the target was assigned a score of −1; these scores were averaged for a population of cells (Polarization Efficiency = average(1-2θ/π)) (Figure 1D). Recruitment of Cdc24 or Bem1 recruitment was able to bias the bud site at very low light doses; Bem1 was slightly more efficient than Cdc24 (Figure 1D). Additionally, recruitment of either component induced robust accumulation of active Cdc42 at the site of illumination, without altering the timing of polarization (~95 min between bud emergence events, regardless of photo-activation state or molecule recruited; data not shown). As the frequency of light increased, the ability of Cdc24 to bias the bud site remained roughly constant until the highest light dose, while the polarization efficiency of Bem1 dropped by ~50% once illumination increased to greater than 3 pulses per minute (Figure 1F, Figure 1—figure supplement 1). The reason for this drop is unclear though a similar drop is observed with ePDZ-mCherry (Figure 1—figure supplement 2); this may result from light-induced rupture of the LOV2-flavin mononucleotide adduct (Kennis et al., 2004). While symmetry breaking is predicted to be random relative to the previous bud site, the position of the new bud was not completely random. Additionally, targets were not randomly positioned, as the area around the previous bud site was underrepresented. These biases would cause a slight underestimation of polarization efficiency (Figure 1—figure supplement 3). Optogenetically recruited Cdc24 and Bem1 were also able to induce polarization of heterozygous RSR1/rsr1Δ diploids (Figure 1—figure supplement 4).
We next assessed how the response varied as a function of both cell cycle position and the frequency with which cells were illuminated. At all doses of light, cells that were at the start of the cell cycle (~10 min before bud emergence) activated Cdc42 in response to both Cdc24 and Bem1 recruitment. Some non-illuminated cells also exhibited Cdc42 activation at the target site, as the bud site occasionally coincided with the target position (Figure 1D,F). To determine whether cells were constitutively responsive to optogenetic recruitment of Cdc24 or Bem1, we illuminated polarized cells with small to medium-sized buds. At infrequent light pulses, polarized cells did not activate Cdc42 in response to Cdc24 or Bem1 recruitment (1–3 pulses, Figure 1E,F, Figure 1—figure supplement 5). When cells were illuminated at a greater frequency (>2 x per minute), those that expressed Cdc24-ePDZ activated detectable Cdc42 at all stages of the cell cycle. Conversely, Bem1 recruitment did not result in Cdc42 activation in polarized cells, even at higher illumination frequencies (Figure 1E,F, Figure 1—figure supplement 5). In summary, Cdc42 activation in unpolarized cells is readily induced in response to either Cdc24 or Bem1 recruitment; however, only high levels of Cdc24 recruitment can generate Cdc42-GTP in polarized cells, indicating that limitations to Cdc42 activation exist in polarized cells.
From these data, we conclude that local recruitment of either Cdc24 or Bem1 is able to efficiently bias the bud site. Because our primary interests lie in the endogenous regulation of Cdc42 activation, we chose to dissect polarity establishment using a light dose (3 pulses per minute) that efficiently biases the bud site, rather than the higher doses that might overcome the mechanisms that limit Cdc42 activation to one site in the cell.
To understand the role of Bem1 in regulating polarization, we induced Bem1 recruitment in cells expressing either the Cdc42 biosensor, Cdc24-tdTomato expressed on a low-copy plasmid from its endogenous promoter, or cells in which one copy of Bem1 was tagged with tdTomato. Optogenetic recruitment of Bem1 was sufficient to promote activation of Cdc42, accumulation of Cdc24 (Figure 2A,B), and was able to efficiently position the bud site (Figure 2D). Critically, we found that recruitment of Bem1 was able to induce the accumulation of endogenous Bem1 at the prescribed site, directly showing that polarization in yeast proceeds via positive feedback (Figure 2A,B). These results raise the possibility that the observed activation of Cdc42 represents a combination of the direct activation of Cdc42 by the Cdc24 directly interacting with optogenetically-recruited Bem1 and amplification by endogenous mechanisms. Although Bem1 recruitment efficiently induced cell polarization, it did not induce precocious Cdc42 activation, or precocious accumulation of Cdc24 or Bem1 as compared to control cells (Figure 2B, Figure 2—figure supplement 1). Thus, the activity of the Cdc24-Bem1-Cla4 feedback loop appears sensitive to cell cycle regulation.
If polarization induction by Bem1 proceeds via a positive feedback loop, Bem1 likely functions by directly interacting with the GEF Cdc24 (Kozubowski et al., 2008). To test this prediction, we introduced a mutation in the Bem1 PB1 domain that has previously been shown to abolish the Bem1-Cdc24 interaction (K482A) (Figure 2C) (Ito et al., 2001) and tested its ability to induce cell polarization. Mutational inactivation of the Bem1 PB1 domain ablated its polarization efficiency (Figure 2D) and its ability to induce recruit endogenous Bem1 (Figure 2—figure supplement 2). These results suggest that polarity induction by Bem1 requires direct interaction with Cdc24. In addition to its Cdc24-interacting domain, Bem1 contains a PxxP motif and SH3 domain that interact, as well as a region demonstrated to interact with phosphoinositides (PI) (Figure 2C). We introduced mutations known to abolish these activities (Irazoqui et al., 2003) and assayed each for their ability to bias the bud site. Both mutants exhibited partial activity (Figure 2D). Although the PI-binding region is required for Bem1 function (Irazoqui et al., 2003), light-mediated recruitment or indirect recruitment of endogenous Bem1 might compensate for this defect in this assay. We conclude that yeast polarization involves a positive feedback loop mediated by the Bem1-GEF complex. Furthermore, these data indicate that bud site selection requires activation of Cdc42.
To gain a mechanistic understanding of light-induced polarity establishment in response to recruitment of Cdc24 GEF, we determined which molecular features are required for induction of cell polarization (Figure 3A,B). In addition to GEF activity, Cdc24 also contains a PB1 domain that enables it to bind to a corresponding PB1 domain on Bem1 (Butty et al., 2002). Recently, it has been suggested that localization of Cdc24 is required for polarization via its ability to activate Cdc42 (Woods et al., 2015). As expected, we find that mutation of conserved surface residues in the GEF-GTPase interface (Rossman et al., 2002) rendered Cdc24 inactive for polarization activity (Figure 3A,B) and Cdc42 activation (data not shown). Deletion of the Bem1-binding domain of Cdc24 marginally reduced the polarization efficiency of the GEF (Figure 3A,B). These results indicate that local recruitment of Cdc24 polarizes yeast cell growth through its ability to activate Cdc42, and that the interaction of the recruited Cdc24 with other cellular proteins - including endogenous wild-type Cdc24 - is not sufficient to induce polarization.
To observe the dynamics of Cdc42 activation in response to optogenetic Cdc24 recruitment, we used the biosensor of active Cdc42 to visualize GTPase activation (Figure 3C, Video 1). In control cells, 50% of cells displayed Cdc42 activation 12 min prior to bud emergence (Figure 3D, Figure 3—figure supplement 1). In experiments in which Cdc24 was continuously recruited, we observed precocious Cdc42 activation; 50% of cells exhibited polarized accumulation of active Cdc42 27 min prior to bud emergence (Figure 3C,D). Precocious Cdc42 activation was less robust than that observed in the ~12 min prior to bud emergence. Thus, Cdc24 recruitment can induce Cdc42 activation at an earlier stage in the cell cycle than Bem1.
We next asked whether endogenous Bem1 precociously accumulated in a similar manner as activated Cdc42. Strikingly, Bem1 did not accumulate until ~13 min prior to bud emergence (Figure 3C,D). Indeed, despite accumulation of active Cdc42 as a consequence of Cdc24 recruitment, Bem1 accumulates at the same time relative to bud emergence in illuminated and mock-illuminated cells (−13 min and −12 min, respectively) (Figure 3D, Figure 3—figure supplement 1). Notably, the initial accumulation of Bem1 coincides with the time in which more robust Cdc42 activation is observed. These results suggest that, unlike previous models for the activity of the polarity proteins, Cdc42 activation does not invariably lead to recruitment of the intact polarity complex.
The differential accumulation of Bem1 and Cdc42 in response to optogenetic recruitment of Cdc24 indicates that Cdc24 has the potential to activate Cdc42 independently of Bem1, and that activated Cdc42 does not inevitably induce recruitment of the polarity complex. If this is the case, then Cdc24, Bem1, and Cdc42-GTP may not constitutively colocalize in non-perturbed cells. To test this hypothesis, we performed a detailed colocalization analysis of the three pairwise combinations of active Cdc42, Bem1, and Cdc24. In all strains expressing fluorescent Bem1, one copy of endogenous Bem1 was tagged. The Cdc42 biosensor was used to assess the pool of active Cdc42. To visualize Cdc24, we transformed cells with a low-copy plasmid encoding an extra copy of Cdc24-GFP under its own promoter. Though it localizes to the expected sites and it can be readily detected, Cdc24-GFP was dimmer than Bem1-tdTomato, Bem1-GFP, and the Cdc42 biosensor.
Using imaging conditions optimized for detection of faint signals (see Materials and methods), we acquired maximum intensity Z-projections of asynchronous cells. Using bud size and polarization as a guide, we sub-divided the cells into unbudded G1 cells, small-budded cells, and large-budded cells and characterized the localization pattern of each pair of probes in each cell cycle state. Unbudded cells were subdivided into two groups: early and late. Early cells were characterized by small distinct puncta of all three probes. Late cells featured a wide, cortically associated band in which all three probes localized. The categorization of these patterns as early and late is substantiated by previous studies (Ozbudak et al., 2005) and time-lapse imaging (see below, Figure 4C).
As expected, all three probes colocalize at the tips of small and nascent buds. However, at other stages of the cell cycle Bem1, Cdc24, and active Cdc42 do not completely colocalize (Figure 4A). In large-budded cells, activated Cdc42 and Bem1 localize throughout the growing bud, while the GEF is limited to the growing bud tip. Additionally, puncta of the Cdc42 biosensor are detected in the mother cell. In early G1 cells, Bem1 and Cdc24 each localize in cortically associated puncta, but surprisingly, these puncta do not fully overlap. Furthermore, both Bem1 puncta and Cdc24 puncta displayed limited overlap with the Cdc42 biosensor, with only 35% and ~50% of puncta colocalizing, respectively (Figure 4B, Figure 4—figure supplement 1). Single plane image sequences confirm significant differences between two probes and limited differences between sequential images of a single probe. Further control experiments with co-expression of individual polarity proteins separately tagged with two fluorophores reveals extensive overlap (Figure 4—figure supplement 2). Notably, the localization pattern shifted in late G1 cells as all three components localize to the wide band, and the amount of reciprocal overlap between Bem1-Cdc24 and Bem1-Cdc42 biosensor increased to greater than 70% (Figure 4B, Figure 4—figure supplement 1). This more extensive overlap amongst Cdc24, the Cd42 biosensor, and Bem1 in late G1 cells suggest that prior to the onset of polarization, Cdc24 has the potential to function independently of Bem1. Of note, the punctate patterns of Bem1, Cdc24, and Cdc42 seen in early G1 cells are below the limit of detection in the assays involving optogenetic recruitment. Exposure times in those experiments were far lower in order to limit photobleaching during long-term (>90 min) imaging.
To better understand the variation in protein localization at different cell cycle stages, we complemented the static imaging with time-lapse imaging. As proteins tagged with GFP tended to be dimmer than those tagged with tdTomato, we imaged cells expressing the tdTomato-tagged variants of the Cdc42 biosensor, Bem1, or Cdc24. Asynchronous populations of cells were imaged for a total of 10 min; images were acquired more frequently during the central four minutes. Each component was highly dynamic in the minutes leading up to the formation of a prominent wide band of accumulation, confirming that the punctate stage precedes polarization. While some puncta existed in the same spot for up to 3 min, appearance and disappearance of puncta were common (Figure 4C).
These results indicate that many Cdc24 and Bem1 molecules are not in a constitutive complex during early G1, which is consistent with the finding that recruitment of Cdc24, but not Bem1, induces Cdc42 activation at this stage of the cell cycle. Cell cycle regulated assembly of the polarity complex could readily explain both results.
To gain insight into cell cycle regulation of the polarity complex, we performed Cdc24 recruitment studies in strains co-expressing a marker of cell cycle entry, Whi5-tdTomato, and either the Cdc42 biosensor or Bem1-tdTomato. Nuclear import of Whi5 is a marker of Cdk1 inactivation. Whi5 is concentrated in the nucleus during the interval between mitotic exit until Cdk1 activation at Start (Costanzo et al., 2004; Skotheim et al., 2008) (~25 min prior to bud emergence, Figure 5—figure supplement 1). Mother cells that have not imported Whi5 into the nucleus are unresponsive to Cdc24 recruitment. Conversely, Cdc24 recruitment can induce Cdc42 activation in unbudded cells with nuclear Whi5 or unbudded cells in which Whi5 nuclear export has occurred (Figure 5A,B), suggesting that mitotic exit is required for the activity of optogenetically recruited Cdc24. In contrast, cortical recruitment of Bem1-tdTomato in response to Cdc24 recruitment did not occur until ~12 min after Whi5 nuclear export, corresponding to ~13 min prior to budding (Figure 5A,B, Figure 5—figure supplement 2). These results are consistent with a model in which Cdk1 activation promotes assembly of the Bem1-GEF complex to engage active Cdc42.
To directly test whether Cdk1 activation is required for Bem1 recruitment in response to active Cdc42, we utilized an allele of Cdk1, cdk1-as1, that can be inhibited by an ATP-analog, 1NM-PP1 (Bishop et al., 2000; McCusker et al., 2007). Asynchronous cells were pre-treated with 1NM-PP1 for 20 min and we subsequently monitored for the ability of recruited Cdc24 to induce Cdc42 activation or Bem1 accumulation. We limited our analysis to mother cells with large-budded daughter cells, indicative of mother cells in early G1. Consistent with previous reports (McCusker et al., 2007), cells lacking Cdk1 activity could not undergo bud emergence nor could buds grow significantly (Figure 5C,D). Nevertheless, Cdc24 recruitment induced accumulation of Cdc42 in 67% of Cdk1-inhibited cells (data not shown). Indeed, Cdc42 was activated with the same kinetics irrespective of the presence or absence of the inhibitor (Figure 5D). Strikingly, when Cdk1 activity was suppressed, Bem1 failed to accumulate within the time frame of the experiment (greater than 1.5 hr after addition of 1NM-PP1) (Figure 5C,D, Figure 5—figure supplement 3). Furthermore, when Bem1 was recruited, cells were unable to activate Cdc42 within the time frame of the experiment (data not shown). Cells expressing wild-type cdk1 were unaffected by the addition of 1NM-PP1 (Figure 5—figure supplement 4). These results demonstrate that Cdk1 activation promotes both Bem1 accumulation and bud emergence even in cells with locally activated Cdc42.
A prominent model for positive feedback posits that the Bem1-GEF complex is constitutive (Bose et al., 2001). However, our data indicates that, prior to Cdk1 activation, optogenetically-recruited Cdc24 and Bem1 function differently. The ability of Cdc24 to activate Cdc42 in the apparent absence of Bem1 lacks precedent; therefore we studied the characteristics of these optogenetically-initiated sites. Specifically, we sought to determine the stability of these sites and whether these nascent sites of polarization interact. To answer these questions, we exploited the ability of the optogenetic system to dynamically reposition the site of protein recruitment.
During the time window between the transition from isotropic growth and the time at which Cdc24 recruitment triggers Bem1 accumulation (i.e. ~13 min prior to bud emergence), Cdc24 recruitment can induce Cdc42 activation. To test whether these sites are self sustaining, the targets were removed after Cdc42 activation was detected in early G1. Optogenetic recruitment of ePDZ-tagged proteins is largely reversed within 3 min after discontinuing illumination (Strickland et al., 2012), ensuring that any remaining signal is not due to Cdc24-ePDZ remaining at the target site due to the optogenetic tag. Frequently, the region retained a faint but consistent signal of active Cdc42 for up to 30 min and ultimately resulted in budding from the specified site (Figure 6A,B). Conversely, Bem1 recruitment was only sufficient to bias the bud site if it was recruited within 15 min of bud emergence (Figure 6A,B). This observation shows that Cdc42 activity can be maintained at a unique site in the apparent absence of Bem1-mediated positive feedback. Thus optogenetic recruitment of Cdc24 can induce a self-sustaining pool of Cdc42 activation.
To determine how optogenetically-induced Cdc42 activation could be maintained in the absence of the optogenetic cue, we tested whether recruited Cdc24 induces a change in the localization of cytosolic Cdc24. To that end, we recruited Cdc24 and visualized Cdc24-tdTomato. Indeed, in 50% of cells in which Cdc24-ePDZ was recruited, Cdc24-tdTomato appeared on the cortex ~25 min before bud emergence, whereas in mock-illuminated cells, Cdc24-tdTomato appeared on the cortex ~15 min before bud emergence (Figure 6C–D, Figure 6—figure supplement 1). The kinetics of accumulation for Cdc24-tdTomato parallels that of activated Cdc42 in response to Cdc24 recruitment (Figure 3). Furthermore, catalytically inactive Cdc24-ePDZ was unable to induce Cdc24-tdTomato recruitment (Figure 6—figure supplement 2). From these data we conclude that recruitment of Cdc24 can induce both Cdc42 activation and Cdc24 recruitment prior to Cdk1 activation, both of which appear to occur independently of Bem1. Collectively, these results reveal the existence of a second pathway for positive feedback. The observed activation of Cdc42 likely represents a combination of direct Cdc42 activation by optogenetically recruited Cdc24 and its amplification by endogenous mechanisms.
Given that Cdc24-tdTomato accumulates at nascent sites, we hypothesized that it would remain at sites after the optogenetic cue was halted by removal of the target. Intriguingly, we observed Cdc24 was maintained at the site for ~6 min following cessation of optogenetic perturbation (Figure 6E). After this 6 min time window, the Cdc24 signal became more punctate and these puncta dynamically associated with the previously targeted region. Greater than 55% of cells budded from the targeted region when target removal occurred ~30 min prior to bud emergence (Figure 6F). These data indicate that optogenetically-initiated sites of Cdc42 activation are stable and are maintained, at least in part, by the accumulation of Cdc24, without accumulation of detectable Bem1.
To examine whether two sites of active Cdc42 in early G1 cells compete with one another, the target was repositioned within the same cell. Repositioning of the target caused Cdc42 accumulation at a new site and concomitant dissipation from the old site, with Cdc42 activity simultaneously detected at both sites for ~5 min (Figure 7A, Video 2). However, the site of Cdc42 accumulation could not be continuously repositioned. A qualitative change in behavior occurs prior to bud emergence. When targets are repositioned within ~13 min of bud emergence, accumulation of Cdc42 at the initial site remains and Cdc42 accumulates weakly at the new site. The cell eventually buds from the site where Cdc42 was active at the ~13 min transition point and Cdc42 signal from the alternate site dissipates upon bud emergence (Figure 7B). Our previous results demonstrate that Bem1 begins to accumulate at the targeted site ~13 min before bud emergence. To confirm that the basis for the qualitative switch relied on the ability of Cdc24 recruitment to induce Bem1 accumulation, we performed the same experiment in cells expressing Bem1-tdTomato. As previously shown, Bem1 only detectably accumulated at the target position defined at the ~13 min transition point and it did not accumulate at new sites if the target was repositioned prior to bud emergence (Figure 7C,D). These results indicate that activation of the Bem1-dependent positive-feedback loop stabilizes sites of Cdc42 activation. Furthermore, these data suggest that prior to Cdk1 activation, nascent sites of polarization influence Cdc42 activation at other sites.
Given that Bem1 accumulation at Cdc24-prescribed sites requires Cdk1 activation, we hypothesized that the dynamic properties of Cdc24-generated sites would persist in the absence of Cdk1 activation. To test this prediction, we repeated the experiment in cells expressing cdk1-as treated with 1NM-PP1 (Figure 7E). Again, limiting our analysis to mother cells with large-budded daughter cells, we found that Cdc42 activation could be dynamically repositioned for >70 min and that Bem1 was not detectably recruited within this time (Figure 7E,F). These results confirm that Cdk1 activation is required for Bem1-mediated positive feedback activity, which functions to establish the axis of polarity.
Combined, these results support three conclusions: (i) the ability of Cdc24 to induce Bem1 accumulation is cell cycle regulated, (ii) once active, the canonical positive feedback loop is highly stable and limits Cdc42 activation at competing sites, and (iii) maintenance of active Cdc42 and cytosolic Cdc24 before cell cycle entry appears independent of Bem1; therefore, the GTPase and the GEF participate in a positive feedback mechanism that functions earlier than the canonical Bem1-dependent positive feedback loop. This alternative positive feedback mechanism can be readily competed by a new site of Cdc24 recruitment. However, this activity may play a physiological role in establishing Cdc42 activity before Start in diploid cells.
As F-actin has been proposed to play a role in polarity establishment (Wedlich-Soldner et al., 2003; Freisinger et al., 2013; Jose et al., 2013), we examined whether actin depolymerization affects the response induced by local recruitment of Cdc24. Cells expressing light-recruitable Cdc24, Whi5-tdTomato and either the Cdc42 biosensor or Bem1-tdTomato were partially synchronized in G1 using a nocodazole block and release protocol and treated with Latrunculin A (LatA) to depolymerize F-actin. As previously shown, actin depolymerization partially inhibited cell polarization (Jose et al., 2013). While 88% of cells polarize Cdc42-GTP in the presence of f-actin, only 32% of cells polarize when actin is depolymerized (Figure 8). Actin depolymerization has a similar effect on the efficiency of Bem1-tdTomato polarization. Drug treatment also slows cell cycle entry as judged by the efficiency of Whi5 exit from the nucleus (Figure 8—figure supplement 1), indicating that actin depolymerization affects several cellular processes.
Filamentous actin has been suggested to facilitate delivery of Cdc42 to the cortex where it could be activated by Cdc24 (Wedlich-Soldner et al., 2003). If true, Cdc24 recruitment would not be predicted to correct the polarization defect. However, light-directed recruitment of Cdc24 dramatically increased the fraction of cells that locally accumulate Cdc42-GTP in the absence of actin. Similarly, Bem1 polarization was rescued by Cdc24 recruitment in cells treated with LatA (Figure 8). These results suggest that actin depolymerization does not appear to affect the availability of Cdc42, but rather it impacts the localization of the Bem1-Cdc24 complex, perhaps non-specifically.
In the previous experiments, only one Cdc24-targeted site was active at the moment when Cdk1 was activated resulting in activation of Bem1-mediated positive feedback loop. Cdc24 recruitment to multiple sites at this critical time might result in recruitment of Bem1 at multiple sites, leading to the formation of multiple buds. Alternatively, sites may compete with each other as they form resulting in only one site becoming fully established. Therefore, to investigate whether nascent sites interact, we recruited Cdc24 to two sites simultaneously in unpolarized cells. Both sites generated activated Cdc42 (Figure 9A, Video 3) and retained active Cdc42 until ~11 min before bud emergence. Subsequently, Cdc42 activity was limited to only one site (Figure 9B) and bud emergence occurred at that site. In a parallel experiment with recruited Cdc24, we monitored accumulation of Bem1 and observed that it accumulates at only one of the two sites, which invariably predicted the site of bud emergence (Figure 9A,B, Video 4). Furthermore, despite recruitment of Bem1-ePDZ to two sites simultaneously, in the overwhelming majority of cases (31/33 cells), Cdc42 activation and Bem1 accumulation occurred at one site, which ultimately defined the nascent bud (data not shown). These results indicate that multiple sites cannot coexist after activation of the Bem1-mediated positive feedback loop even under conditions in which they are simultaneously specified.
In this work, we have studied the mechanism for Cdc42 activation throughout G1. Traditional genetic and cell biological analyses have identified the key components and revealed many behaviors associated with cell polarization, which have led to a set of models that invoke positive feedback (Wedlich-Soldner et al., 2003; Irazoqui et al., 2003; Goryachev and Pokhilko, 2008; Howell et al., 2012; Howell and Lew, 2012). However, the field has lacked the tools that can directly interrogate the spatio-temporal dynamics of signaling molecules and critically test the models. Here, we used optogenetics to probe the endogenous regulatory mechanisms that control Cdc42 activity. We used low light doses to recruit limited amounts of Cdc24 to reproducibly induce cell polarization; these conditions only resulted in Cdc42 activation at specific cell cycle stages. Rather than examining the direct consequences of experimentally induced GTPase activation (Wagner and Glotzer, 2016), we sought to generate small perturbations and define the conditions in which those perturbations were amplified by the endogenous pathways. Using this approach, we have demonstrated the existence of a previously postulated positive feedback loop which promotes bud emergence. In addition, we have demonstrated that potent mechanisms ensure that only a single site can undergo positive feedback at a given time. We have also found that the activity of this pathway is temporally confined by cell cycle regulation. Finally, we have demonstrated the existence of a second, previously uncharacterized, positive feedback mechanism that can maintain a focus of Cdc42 activity prior to Cdk1 activation and which may play a role in symmetry breaking polarization.
The current model of symmetry breaking polarization posits that a stochastic accumulation of Cdc42-GTP activates a positive feedback loop mediated by the Cla4-Bem1-Cdc24 polarity complex, thereby generating a local focus of activated Cdc42 (Howell and Lew, 2012). A prediction of that model is that a seed of Cdc42-GTP would be sufficient to define the nascent bud site. We find that local, light-induced recruitment of either the GEF Cdc24 or the scaffold Bem1 is sufficient to bias the presumptive bud site (Figure 1). Furthermore, the ability of these proteins to induce polarization requires the molecular features necessary to generate active Cdc42; specifically, GEF activity for Cdc24 and Cdc24-binding ability for Bem1 (Figure 3 and Figure 2, respectively). These findings are consistent with the existing model for symmetry breaking, in which a positive feedback loop modulated by the polarity complex reinforces local activation of Cdc42 to promote bud emergence. We present direct evidence for positive feedback by optogenetically recruiting Bem1 and showing that endogenous Bem1 accumulates in response to that perturbation. Likewise, Cdc24 recruitment generates positive feedback by recruiting additional molecules of Cdc24 (Figure 6). In both cases, the ePDZ-tagged proteins must be capable of promoting Cdc42 activation to induce accumulation of their untagged counterparts. Unexpectedly, we find that the GEF Cdc24 functions in two distinct positive feedback pathways; the Bem1-dependent loop that is active upon Cdk1 activation, and an earlier, positive feedback mechanism that appears to be Bem1 independent. The molecular mechanism of positive feedback during early G1 remains to be characterized.
Other models for symmetry breaking polarization invoke actin-dependent delivery of Cdc42 to the cortex (Wedlich-Soldner et al., 2003; Freisinger et al., 2013; Jose et al., 2013). While depolymerization of actin does induce a polarity defect, that defect can be readily suppressed by light-mediated recruitment of Cdc24 to the plasma membrane (Figure 8). This result indicates that in the absence of polymerized actin, Cdc42 still associates with the plasma membrane. Thus, actin filaments are more likely to promote, either directly or indirectly, the localization of the Cla4-Bem1-Cdc24 complex in a subset of cells.
Although recruitment of either Bem1 or Cdc24 efficiently biases the site of polarization, at certain stages of the cell cycle the molecular consequences of their recruitment are quite distinct. In late G1, following commitment to the cell cycle, light-induced recruitment of either Bem1 or Cdc24 promotes accumulation of active Cdc42, endogenous Bem1, and cytosolic Cdc24 (Figure 2 and Figures 3 and 6, respectively). These results confirm prior models for polarization during the interval between Start and bud emergence. However, Bem1 recruitment does not induce precocious Cdc42 activation, Cdc24 accumulation, or endogenous Bem1 accumulation. In contrast, optogenetic recruitment of the GEF Cdc24 induces precocious activation of Cdc42 and accumulation of cytosolic Cdc24, though neither are sufficient to induce accumulation of endogenous Bem1 prior to Cdk1 activation (Figures 3 and 5, respectively). Synthetic lethality precluded generation of a conditional Bem1 allele compatible with our experimental approach which would be necessary to directly test the Bem1 independence of Cdc24-mediated activation of Cdc42 during early G1. Collectively, these results indicate that Cdk1 regulates the Bem1-Cdc24 complex; and, as a consequence of this regulation, previous models do not apply to the period prior to Start. Rather, a second mode of positive feedback operates in this interval.
Consistent with that interpretation, we find that Cdc24, Bem1, and Cdc42-GTP do not invariably colocalize, with the lowest level of colocalization occurring prior to Cdk1 activation (Figure 4). We detect Bem1 and Cdc24 in small, mobile clusters that partially overlap in G1 cells. The nature of these clusters requires further analysis; though, oligomerization may contribute to their formation as the Cdc24 DH domain is capable of oligomerization (Mionnet et al., 2008) and Bem1 contains a PxxP motif and a SH3 domain which interact (Irazoqui et al., 2003; Endo et al., 2003) and could mediate intermolecular association. The delay in Bem1-dependent positive feedback relative to Whi5 nuclear exit (Figure 5) suggests that the polarity complex is regulated by Cln1/2 (Skotheim et al., 2008). We propose that Cdk1 activity promotes assembly of the Bem1-Cdc24 complex, this interpretation is consistent with the accumulation of Bem1 at the bud neck in early G1 without accompanying Cdc42 activation (Atkins et al., 2013) (Figure 4), as well as a Cln2-dependent increase in exchange activity towards Cdc42 (Howell et al., 2009).
Cdk1 activity may regulate the association of both Cdc24 with Bem1 and Bem1 with Cla4. If the former were constitutive, then Bem1 recruitment during early G1 should also result in Cdc24 recruitment which would induce Cdc42 activation (Figure 10). However, Bem1 recruitment in early G1 had no detectable effect on Cdc42 activation. Likewise, if the latter was constitutive, Cdc42 activation during G1 should induce Cla4 recruitment which would be predicted to induce Bem1 recruitment. However, Cdc24 recruitment in early G1 results in Cdc42 activation but does not result in detectable Bem1 recruitment. These results suggest that the canonical polarity complex is not assembled prior to Start. G1 CDK activity is implicated in directly down regulating Rga2, a GTPase activating protein that plays a role in Cdc42 regulation (Sopko et al., 2007; Knaus et al., 2007). CDK activation at start may therefore promote Cdc42 activation by at least two parallel pathways.
There also appears to be regulation of the positive feedback pathway after bud emergence. In polarized cells, Cdc24 recruitment at high light doses - but not Bem1 recruitment - activates Cdc42, raising the possibility that the well studied Cdc24-Bem1-Cla4 complex functions as a unit for a limited fraction of the cell cycle surrounding polarization.
What could be the function of the secondary positive feedback resulting in Cdc42 activity before Start? Current models suggest that Cdc42 activation initiates upon Cdk1 activation (Howell and Lew, 2012). According to this model, stochastic activation of Cdc42 recruits the Cla4-Bem1-Cdc24 complex which amplifies this local inhomogeneity through positive feedback. Alternatively, polarization may be initiated by local association of Cla4-Bem1-Cdc24 via any of its myriad membrane association motifs. Indeed, our results show that local recruitment of members of this complex is indeed sufficient to induce symmetry breaking polarization and override the endogenous landmark-directed pathway. However, because Cdc24 can activate Cdc42 prior to Start, and because active Cdc42 is detected prior to Start (Figure 4), the site of polarization may not be dictated strictly by molecular noise or stochastic encounters of the Bem1-Cla4-Cdc24 complex with the membrane. Rather, a distinct mechanism(s) may exist that seeds the cortex with activated pools of Cdc42 during early G1 which pattern the ‘random’ choice of bud site upon passage through Start (Figure 10). Indeed, Bud3, which is a validated Cdc42 GEF, induces an early wave of Cdc42 activation (Kang et al., 2014). Though it is expressed in both haploid and diploid cells, Bud3 only impacts bud site selection in haploid cells (Chant et al., 1995). The linking of two mechanisms for Cdc42 activation could allow for more rapid axis specification than could be achieved by a reaction-diffusion based mechanism alone (Goryachev and Pokhilko, 2008; Kang et al., 2014). Indeed, such linked systems have been observed and modeled in a manner that can account for the speed of polarization events such as cell migration and the fixation of a single axis following an exploratory phase capable of reorientation (Goryachev and Leda, 2017; Brandman et al., 2005; Xiong et al., 2010).
Wild-type yeast cells rarely form multiple buds in a single cell cycle, suggesting the existence of mechanisms by which nascent bud sites compete in a winner take all competition. Recent work has shown that prior to bud emergence, cells are capable of forming multiple nascent foci. Yet, by employing mechanism(s) that appear to involve negative feedback, only one focus matures into the site of polarization (Howell et al., 2012), indicating competition between the nascent foci.
Cells have been genetically manipulated to generate multiple buds. For example, expression of activated alleles of Cdc42 can induce the formation of multiple buds (Caviston et al., 2002). Similarly, multiple buds result from membrane-tethering either Bem1 or a Cdc24 mutant that is resistant to negative feedback, while also hindering the membrane-cytoplasm exchange of Cdc42 by deleting the facilitating chaperone, Rdi1. (Wu et al., 2015). However, despite the fact that transient optogenetic membrane recruitment of Bem1 or Cdc24 can induce efficient polarization, neither proved robust enough to generate two buds, indicating that the competition mechanism(s) are sufficiently strong to extinguish multiple nascent sites so that only a single axis emerges the winner. Two sites containing active Cdc42 could be generated, but we did not detect Bem1 at two sites simultaneously, consistent with models in which the intact Cla4-Bem1-Cdc24 complex is tightly limited (Wu et al., 2015).
Nascent sites also compete during early G1, prior to Start. Whereas a pool of Cdc42 can be induced in early G1 and maintained, if Cdc24 is recruited to a new site within the cell, the pool of active Cdc42 at the original site dissipates within a few minutes in response to the new site (Figure 7). As these sites appear to be Bem1 deficient, this suggests that a distinct mechanism of competition is active during this time. Indeed, whereas optogenetic recruitment of Cdc24 can induce two sites of Cdc42 activation during G1 that can co-exist, once Cdk1 is activated, the competition is more stringent and Bem1 only accumulates to detectable levels at one of the two sites.
In this study we show the utility of optogenetics in dissecting cellular processes. The ability to control the spatiotemporal dynamics of signaling molecules allows novel perturbations of cells that can lead to new insights. By exogenously localizing a GEF, we find that yeast cells are capable of activating Cdc42 just after mitotic exit. We also uncovered a cell cycle regulated step in polarity establishment: activation of the canonical positive feedback loop by Cdk1 (Figure 5 and Figure 6). Furthermore, we discovered a second positive feedback loop that functions independently of the canonical positive feedback mechanism and is active prior to Cdk1 activation (Figure 6). Finally, because optogenetics allows proteins to be dynamically repositioned in one or more spots we found that yeast cells are remarkably resistant to formation of multiple sites of polarization.
DNA manipulations were simulated with SnapGene (GSL Biotech). Plasmids were generated using a combination of conventional ligation, homologous recombination (SLICE) in bacteria (Zhang et al., 2012), and Gibson Assembly (Gibson et al., 2009). All plasmids were verified by DNA sequencing.
All strains (Supplementary file 1A) were constructed in the W303 background (leu2-3 112 ura3-52 can1-100 ade2-1 his3-11 trp1-1). Haploid a and α cells were mated by incubating overnight in 500 µL YPD and then plating on selective media. All integrating plasmids were of the YIplac series. All low copy plasmids were of the pRS series (Supplementary file 1B). Gene deletions were generated by one-step gene disruptions using standard procedure. Yeast were transformed using lithium acetate, single-stranded carrier DNA and polyethylene glycol. All strains were verified by colony PCR. Endogenous genes were epitope tagged by one-step PCR (Longtine et al., 1998). PCR products for C-terminal td-Tomato fusions were amplified from a plasmid containing a tdTomato::HIS3MX cassette (DLB3299, a generous gift from Danny Lew). Cdc24 and Bem1 point mutants were assumed to accumulate at levels comparable to the wild-type proteins; most mutants were previously characterized (Ito et al., 2001; Irazoqui et al., 2003; Butty et al., 2002), the Dbs:Cdc42 co-crystal structure (Rossman et al., 2002) was used to identify point mutations to inactivate Cdc24 GEF activity. The endogenous Cdc24 promoter sequence consisted of 600 bp upstream of the cdc24 locus that was amplified from genomic DNA and inserted by Gibson Assembly into Cen plasmids that encoded for either Cdc24-GFP or Cdc24-tdTomato.
The cdc28-as1 allele was inserted by linearizing a hygromycin-resistant plasmid containing the cdc28-as1 coding sequence with an AflII restriction enzyme site adjacent to the F88G point mutation (pKW50); the plasmid encoding the cdc28-as1 allele was generously provided by Eric Weiss (pELW886).
Cells were grown in the dark at room temperature overnight in SC -His-Leu-Ura-Trp+Ade and diluted to OD600 = 0.1–0.2. For optogenetic experiments, cells were treated with 50 nM of ß-estradiol after 2 hr of growth to induce expression of the optogenetic components. After 2 hr of induction, cells were concentrated 10-fold to 20-fold in fresh media + ß-estradiol and prepped for imaging. Cells co-expressing Cdc24-tdTomato and Cdc24-ePDZ, were induced for 90 min to limit deleterious overexpression of the GEF. For experiments less than 2 hr, cells were imaged on a 2.5% agar pad soaked in minimal media + ß-estradiol + drug (where applicable) for >20 min. For experiments longer than 2 hr, cells were imaged in a CellASIC Onix microfluidic perfusion chamber (EMD Millipore Corporation) to provide continuous nutrients. For non-optogenetic experiments, cells were concentrated 10-fold to 20-fold after 2 hr of growth and imaged on 2.5% agar pad soaked in minimal media.
After 1.5 hr of induction with 50 nM ß-estradiol, cdk1-as cells were treated with 75 µM 1NM-PP1 or solvent (1% DMSO) at room temperature, in the dark, and without shaking for 20 min. Subsequently, cells were imaged for >90 min, for a total time in 1NM-PP1 of approximately 2 hr.
To synchronize diploid cells in early G1, exponentially growing cells were treated with 15 µg/ml nocodazole for 2 hr. Cells were induced with 50 nM ß-estradiol and treated with a second dose of nocodazole at 7.5 µg/ml. After 1 hr, cells were washed three times with fresh media and released into minimal media + 50 nM ß-estradiol for 30 min. Cells were treated with 100 µM Latrunculin A (Molecular Probes) or solvent (1% ethanol) for 20 min and then imaged for 90 min.
Cells were imaged on an Axiovert 200M microscope (Zeiss) equipped with a spinning disk confocal (CSU10, Yokogawa), a 20 mW, 561 nm laser (Cobolt), and an electron-multiplying charge-coupled device (EMCCD) camera (Cascade 512B, Photometrics) using a 63×, 1.4 numerical aperture objective (Zeiss). The microscope was controlled using MetaMorph (Molecular Devices). A 550 nm long-pass filter (Edmund Optics) was placed in the transmitted light path to avoid photoexciting the LOV domain when using phase optics. A galvanometer-steerable 440 nm dye laser (Micropoint, Photonics Instruments) for local photo excitation of Mid2-localized LOVpep. Illumination intensity was controlled by using an adjustable internal attenuator plate and an additional absorptive neutral density filter OD = 1 (ThorLabs) in the beam path.
For polarization experiments, cells were photo-excited using the Micropoint laser. The coordinates of targeted sites (x, y, t) were recorded with each photo-excitation. Following illumination, a confocal tdTomato image and phase contrast image were acquired. For control (dark state) experiments, the experiment was performed identically except that the Micropoint laser was off. Exposure times were 500 msec for tdTomato and 100 msec for phase contrast.
For non-optogenetic experiments, cells were imaged with a Zeiss Axioimager M1 equipped with a Yokogawa CSU-X1 spinning disk unit (Solamere) and illuminated with 50 mW, 488 nm and 50 mW, 561 nm lasers (Coherent). Images were captured on a Cascade 1K electron microscope (EM) CCD camera controlled by MetaMorph (Molecular Devices).
For maximum intensity Z-projection snapshots, cells were imaged through the center 3 µm at 0.25 µm slices. The GFP and tdTomato images were acquired sequentially, followed by a phase contrast image. Maximum intensity projections were generated using Metamorph. Single plane snapshots were acquired at the mid-plane of the cell, with GFP and tdTomato images acquired sequentially. Exposure times were 900 msec for tdTomato, 900 msec for GFP, and 66 msec for phase contrast.
Single plane snapshots of a confocal tdTomato image and phase contrast image were acquired at the mid-plane of the cell. Cells were imaged at a rate of once per minute for 3 min, followed by a rate of once per 30 s for 4 min, and finally imaged at a rate of once per minute for 3 min. Exposure times were 700 msec for tdTomato and 66 msec for phase contrast.
All images were analyzed in ImageJ (Schneider et al., 2012), with custom-written macros. To determine the angle between the laser position and the nascent bud site, we generated kymographs displaying the laser position, the site of bud emergence, and the intensity of the probe. To generate the kymographs, the cell outline was tracked using the plugin JFilament (Smith et al., 2010), which created a series of XY-coordinates that was converted into an ROI for each image in the stack. The ROI was then overlaid on its cognate image, linearized, and normalized to 100 pixels in length by six pixels in width. This was repeated iteratively through each slice of the stack to build kymographs. The kymographs were annotated with the center coordinate of each target in each frame of the time-lapse, the time and position of bud emergence, and the position of the previous bud site.
Polarization Efficiency was defined as (1-2θ/π)) where θ is the angle between the site of illumination and the position of the nascent bud. A population measure of polarization efficiency was found by taking the average of the polarization efficiency value for all cells.
To quantify the appearance time of a polarity component, the time of bud emergence, and the polarization efficiency, we analyzed time-lapse images as follows: cells were only scored if they underwent both polarization and bud emergence within the time-course of the movie. The analysis was limited to mother cells; cells that budded within the first 20 min were excluded. Whi5 nuclear exit was defined as when nuclear Whi5 signal equaled that of the cytoplasm. To quantify the appearance of weak fluorescent signals, accumulation was scored by blinding the fluorescent image and scoring probe accumulation manually, by eye.
To analyze colocalization, cells were separated into cell cycle stages depending on both the bud size and the distribution of the probes. Data were blinded and cells were pulled at random from each cell cycle subset. Puncta with colocalization (GFP with tdTomato and tdTomato with GP) were manually counted.
For cdk1-as cells, we limited our analysis to large-budded mother cells that accumulated Bem1 or the Cdc42 biosensor to the bud neck, indicative of early G1 cells. A ‘large-bud’ was considered to have an area more than 4.5 µm2. As cdk1-as cells treated with 1NM-PP1 do not undergo bud emergence, to be scored as polarized, they needed to maintain polarization for >15 min.
To quantify competition in dynamic reorientation experiments, a targeting event was scored as ‘Outcompeted’ if the Cdc42 biosensor signal disappeared from the initial position and accumulated at the new position within the time that the target was maintained at the new position. The event was deemed ‘Not Outcompeted’ if the Cdc42 biosensor neither disappeared from the initial position nor accumulated at the new position.
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Sheila McCormickReviewing Editor; University of California-Berkeley, United States
In the interests of transparency, eLife includes the editorial decision letter and accompanying author responses. A lightly edited version of the letter sent to the authors after peer review is shown, indicating the most substantive concerns; minor comments are not usually included.
[Editors’ note: a previous version of this study was rejected after peer review, but the authors submitted for reconsideration. The first decision letter after peer review is shown below.]
Thank you for choosing to send your work entitled "Cell cycle entry triggers a switch between two modes of Cdc42 activation during yeast polarization" for consideration at eLife. Your full submission has been evaluated by Vivek Malhotra (Senior Editor) and three peer reviewers, one of whom, Sheila McCormick, is a member of our Board of Reviewing Editors, and the decision was reached after discussions amongst the reviewers. Based on the discussions and the individual reviews below, we regret to inform you that your work will not be considered further for publication in eLife. We made this decision because, in our view, it would take you more than 2-3 months to carry out the additional experiments mentioned by the reviewers. However, we strongly encourage you to re-submit, provided, you can address the reviewer comments, as all reviewers think the work is interesting.
I think the topic is of interest and that they use interesting tools to address the question of how a single point of polarity is established. I have to admit that the paper was tough for me to follow, as I think it was not pitched to (or at least did not consider) readers that don't work on yeast – e.g., me – I work on a polar cell (pollen tubes) and have worked on GTPases and GEFs, but struggled. For example, it was difficult to follow the logic in the subsection “The structural requirements for Cdc24-mediated polarization” – they state that deleting the BEM1-binding site makes bud site more efficient but then their conclusion was something about recruitment. A little more "Therefore we think that this means[…]" and more links between an experimental result and their interpretation would have helped.
I liked the experiment in the last paragraph of the subsection “How do cells maintain a single axis of polarity?” (Figure 7) in which they put cdc24 at 2 sites on unpolarized cells.
Introduction, second paragraph – I wondered if the word should be absence and not presence, because as written it didn't make sense to me.
In this manuscript, the authors use an optogenetic system to probe the mechanism of symmetry breaking in the budding yeast S. cerevisiae. Building on their previously described TULIP light-induced interaction modules, they design experiments to locally recruit the Cdc42 GEF, Cdc24, or the scaffold Bem1 at the plasma membrane. Their data indicate that there is a strong cell cycle dependence on the efficacy of Cdc42-GTP polarization, with the scaffold Bem1 not being recruited during early G1 when Cdk1 activity is low. They interpret their data as a cell cycle-dependent regulation of the well-described positive feedback, which relies on Bem1 associating both with Cdc42 effectors (which bind Cdc42-GTP) and the GEF Cdc24 (which activates Cdc42).
The topic is very interesting and the approach used is highly original and promising. Unfortunately, the paper disappoints, as it falls very short of supporting the conclusions it claims to make. I have four main points, detailed below.
General set-up of the system:
The properties of the light-inducible dimerization system are not well described in this manuscript. How efficiently and how rapidly Cdc24-ePDZ is locally recruited is not shown. The timing between laser light and Cdc42-GTP localization is not shown. The off-rates are not probed nor discussed (see below).
The kymographs are also very difficult to interpret. It is not always clear why the laser site is being moved. Also, in most of the kymographs shown, there is another signal that is repetitively seen earlier than the signal at the laser site. What is this? Is that the division site? Clarification here would greatly help the reader. As it stands, it can be interpreted as polarization at a distinct cortical site at earlier timepoint, which is highly confusing regarding the timing issues that the authors are discussing.
Timing of Bem1 recruitment:
The data shown in figures do not always support the reported timings. For instance, in Figure 2A, the timings of Cdc42-GTP and Bem1 recruitments to the laser-induced sites relative to this other cytokinesis (?) signal seem very similar. This suggests that initiation of a new site may possibly be impeded by sequestration of proteins at the division site, which then only become released at cytokinesis. If this time was taken as a reference point, rather than budding, would Cdc42-GTP and Bem1 behave differently from each other?
Regarding the timing of Bem1 recruitment, in Figure 3A there seems to be some Bem1 signal recruited to the laser site at the cortex from the second image of the timelapse, before Whi5 nuclear exit, at least 35 min before bud emergence. In fact, if you compare to Figure 1E where the arrow denotes CRIB localization, the localization of Bem1 in Figure 3A second panel looks even stronger. I am thus not convinced by these images, which do not seem to correspond to the quantification shown in Figure 3B.
Similarly, in Video 4, Bem1 appears as a very dynamic signal, which certainly overlaps with all of the marked sites of laser light. It is not clear to me in what way this is different from Video 3, where active Cdc42 is also quite transiently present at all the laser sites. Thus, I do not feel that the statement that Bem1 "accumulates at only one of the two sites, which invariably predicted the site of bud emergence" is an accurate description of the situation. In addition, Bem1 has been previously used as a marker of the polarity patch and shown to display transient multi-site accumulation and oscillatory behavior. This is a bit disconcerting that the authors here describe that they only see it at a single site.
Finally, timings indicated in the text do not correspond to those shown on the graphs. For instance, in Figure 2B, 50% of Cdc42-GTP and Bem1 seem to happen at 12-13min, and about 28min, respectively, not 17 or 31 as indicated in the text.
The finding that the efficiency of symmetry breaking is regulated by Cdk1 activity is interesting. However, for the Cdk1 inhibition, the fact that asynchronous cells are used makes interpretation of results more difficult. Any cdc28-as cell treated with 1NM-PP1 to inhibit Cdk1 will be blocked in pre-metaphase if 1NM-PP1 was added when the cell was in this cell cycle stage. By focusing on large-budded mother cells, without monitoring mitosis, it is thus not clear that cells are G1.
Also, I do not understand the Bem1 signal on the kymograph of the treated cells in Figure 3D. There should not be any cell division without CDK1 (unless Cdk1 inhibition happened after anaphase). And the authors claim there is no polarization. What is the signal seen?
The conclusion that Bem1 is unable to recruit Cdc24 (or be recruited by Cdc24) in early G1 due to low Cdk1 activity would be made much stronger if the authors repeat the Bem1-ePDZ recruitment experiment in cdc28-as cells treated with 1NM-PP1. If Cdk1 controls Bem1, the prediction is that Bem1 would be completely unable to activate Cdc42.
Feedback and dynamics:
At the beginning of the Discussion, the authors state that they "have been able to directly test the positive feedback model for symmetry breaking in Saccharomyces cerevisiae". The paper does not test any feedback: it tests the effect of Cdc42 GEF Cdc24 local recruitment, which leads to local Cdc42 activation (as would be expected) and local Bem1 recruitment (as would also be expected from the known direct binding between Cdc24 and Bem1). In neither of these recruitments is there a need to invoke a feedback control. In fact, they even show in Figure 1F that deletion of the Bem1-interaction motif on Cdc24 leads to better polarization, so clearly, this does not require feedback signaling. Similarly, and contrary to their first conclusion statement in the fourth paragraph of the subsection “Cdc42 exhibits weak positive feedback in G1 and strong positive feedback after Cdk1 activation”, the authors do not show that it is active Cdc42 that induces Bem1 accumulation. The data shown is that Cdc24 local recruitment by photo-activation leads to Bem1 recruitment. To show feedback, they would for instance need to locally recruit an active PAK kinase and show that this leads to local Cdc42 activation. Alternatively, with their current setup, they could probe whether endogenous Cdc24 is recruited to the site of Cdc24-ePDZ recruitment. If this is the case, it would suggest positive feedback regulation.
They also suggest that "activation of the Bem1-dependent positive-feedback loop stabilizes sites of Cdc42 activation". A prediction from this statement is that the Cdc24∆PB1-ePDZ construct, which does not interact with Bem1, would fail to stabilize the polarization site and that the site could be dynamically re-positioned beyond the 13-min timepoint that they indicate in the arrival of Bem1. The fact that this mutant displays more robust polarization than wildtype Cdc24 is not very encouraging of this possible outcome, but it should be tested. On a more semantic level, the word "stabilization" may induce some confusion. In the wildtype situation, Cdc42 activation and Cdc24 and Bem1 recruitment are all concomitant. This is only because here Cdc24 is artificially activating Cdc42 early that such a distinction can be made.
Regarding the proposed Bem1-independent feedback in early G1: I do not see evidence for this. When "the targets were removed" (which I take to mean that the laser light was switched off?), it is not clear at all how long Cdc24-ePDZ perdures at the recruitment site. What is the off-rate of the ePDZ-LovPep interaction in the dark? These experiments do not per se indicate absence of feedback, they can simply denote slow off-rate of the optogenetic system. The general parameters of the system need to be much better defined to be able to make any conclusion regarding site stability or competition.
In this manuscript, Witte et al. use optogenetic tools to probe the regulation of Cdc42 activation in budding yeast. The authors employ a clever combination of techniques to address fundamental questions in the yeast polarity field with a focus on cell cycle inputs to Cdc42 positive feedback and the role of this circuit in competition between Cdc42-GTP foci. If the authors can perform the following experiments to bolster their key conclusions, this work definitely merits publication in eLife.
1) Role of Cdk1 in Cdc42 activation. One of the key conclusions of the paper is that Cdk1 regulates the timing of the Bem1 positive feedback loop, based on the observation that Cdk1 inhibition blocks the recruitment of Bem1 and impairs competition between Cdc42-GTP foci. However, a trivial explanation would be if Cdk1 activity is required to release their Cdc24-ePDZ construct from the nucleus, so a lack of Cdk1 could impair their optogenetic input instead of modulating Bem-1-based positive feedback. To address this possibility, the authors need to quantitate their optogenetic input (levels of Cdc24-ePDZ recruitment, not just timing) in the absence and presence of Cdk1 inhibition. Furthermore, I'd like to see a quantitation of the levels, not just timing, of Cdc42 generation by optogenetically recruited Cdc24 with and without Cdk1 inhibition, as there appears to be a significant inhibition of Cdc42 activation by their optogenetic input at times significantly before bud emergence, which would either indicate that Bem1 feedback is occurring at times significantly prior to bud emergence, that Cdk1 modulates Cdc24 activation directly (rather than via Bem1 positive feedback), or that Cdk1 operates through inhibiting the GAPping of Cdc42-GTP, as has previous been observed (PMID: 17853895-this reference should be cited and discussed in the revised manuscript).
2) On a related note to point 1, it is also important to quantitate Bem1-ePDZ recruitment (in Figure 4A) to ensure the lack of precocious Cdc42 activation by this input isn't due to a lack of optogenetically-induced Bem1-ePDZ recruitment. This would also help clarify whether the lack of Cdc24 recruitment at earlier timepoints of optogenetic recruitment of Bem1-ePDZ could stem from Cdk1 modulation of Bem1/Cdc24 interaction.
3) Role of Bem1 in positive feedback and competition. Throughout the paper Bem1 recruitment is used as a proxy for Bem1 positive feedback. The effect of perturbations such as Cdk1 inhibition is made in this light. Because Bem1 recruitment is not observed more than 15 minutes prior to bud emergence, the authors suggest that Bem1 positive feedback is absent at earlier stages. To test whether Bem1 has a functional role versus simply correlates with feedback, the authors need to test their optogenetic system in bem1Δ cells. I understand that these are synthetic lethal with rsr1 Δ and cannot be performed in their existing background, but there are other genetic means of destroying the landmark that are compatible with bem1 Δ (PMID: 24062340), and for some experiments (competition, role of Cdk1 in Cdc42 activation), it may not be necessary to destroy the landmarks. This is absolutely essential for clarifying which of their findings (Cdk1 regulation of Cdc42, precocious optogenetic Cdc42 activation by Cdc24, competition between Cdc42 foci only near bud emergence, etc.) are indeed dependent on Bem1 positive feedback.
4) Mechanism of competition. The authors make the striking observation that roughly equivalent optogenetically-generated Cdc42 foci can compete at the level of Bem1 recruitment. This is very surprising, as a simple Bem1 limiting component model would predict equal partitioning to both optogenetically induced Cdc24 foci. To determine whether these sites might also compete for the Cdc24-ePDZ optogenetic input (which would lead to a very different interpretation for the mechanism of competition), the authors need to quantitate the recruited Cdc24-ePDZ during the competition experiments.
5) The paper lacks any statistical tests. P values should be given for all experimental conditions that are being compared. This is important, because a number of statements are made (for example, Bem1P335A mutant is more detrimental than R369A, Figure 4D) that don't appear to be statistically significant.
[Editors’ note: what now follows is the decision letter after the authors submitted for further consideration.]
Thank you for resubmitting your work entitled "Cell cycle entry triggers a switch between two modes of Cdc42 activation during yeast polarization" for further consideration at eLife. Your article has been favorably evaluated by Vivek Malhotra (Senior Editor) and three reviewers, one of whom is a member of our Board of Reviewing Editors and one of whom is a new reviewer.
In this paper, the authors use an original optogenetic strategy to dissect the molecular mechanisms of Cdc42 polarization in budding yeast. They show that light-induced recruitment of the GEF Cdc24 or the scaffold protein Bem1 to specific cortical sites promotes local Cdc42 activation and biases the site of subsequent bud formation. This response depends on the cell cycle stage and the protein recruited. The authors conclude from their experiments that (i) they have significantly strengthened the case for a previous model of positive feedback mediated by Bem1-Cdc24 and Bem1-effector-Cdc42 interactions; (ii) they have uncovered a novel Bem1-independent positive feedback mechanism that acts earlier in the cell cycle; (iii) CDK1 activity regulates the association of Bem1 with its binding partners, so that Bem1-mediated positive feedback is gated by the cell cycle.
The optogenetic method is well-suited to the questions addressed, and the authors are to be commended for overcoming some major technical challenges. The manuscript is significantly improved, and the major conclusions may well be correct. However, there are several issues that remain unconvincing, and some aspects that were unclear and/or confusing, as detailed below. These should be relatively straightforward to fix, and if fixed this would be a valuable contribution to the field.
1) Is there really positive feedback pre-start?
This conclusion relies on two findings. First, optogenetic recruitment of Cdc24-ePDZ results in weak recruitment of Cdc24-tdTomato to the illuminated site (Figure 6E). However, this signal could be due to Cdc24 oligomerization instead of positive feedback. If Cdc24-tdTomato recruitment were shown to be dependent on the catalytic activity of Cdc24-ePDZ (as was done in the biasing of the bud site experiment), that would greatly strengthen the case. Second, the signal persists after cessation of illumination. This seemed clear for Cdc42-GTP (Figure 6A) but not obvious for Cdc24-tdTomato (Figure 6E and especially Figure 6—figure supplement 2). Without a convincing example of Cdc24 "maintained" after illumination ceases, it was not clear what the authors were quantifying with this label in Figure 6F. In aggregate, these problems made the case for pre-start positive feedback unconvincing.
2) Is the Bem1-Cdc24 interaction really regulated by CDK1?
This conclusion also relies on two findings. First, optogenetic recruitment of Bem1-ePDZ in "polarized" cells did not lead to local GTP-Cdc42 accumulation, unlike optogenetic recruitment of Cdc24-ePDZ. This could indeed be due to a lack of interaction between Bem1 and Cdc24 at that time of the cell cycle. But it seems equally plausible that some level of interaction is constitutive, but not every Bem1 comes with an associated Cdc24. In that case, recruitment of Bem1 would lead to significantly less recruitment of Cdc24 than direct recruitment of Cdc24-ePDZ, leading to less Cdc42 activation. This should be considered as a potential explanation in the text. Second, Figure 4 shows that small puncta containing Bem1 or Cdc24 often fail to co-localize in doubly marked strains. However, there are technical concerns with this experiment, in part because the nature of the puncta is not clear: why and how would such aggregates form? Do they reflect what is happening with the uniformly distributed pools of the proteins? Might small protein numbers in the puncta lead to stochastically varying ratios of the proteins that are then interpreted as lack of co-localization? Might dynamic disassembly/movement of puncta cause an apparent lack of co-localization (e.g. if a spot moves between acquisition of the different color images)? One way to ameliorate this concern would be to image puncta in cells with two colors of the same probe (e.g. green Bem1 and red Bem1). Would these always co-localize?
3) Confusing quantification:
The statistical analysis provided in Figure 1—figure supplement 4A and B shows no significant difference between Cdc42 activation in non-illuminated cells and any of the illumination strategies for either Cdc24- or Bem1-ePDZ in "non-polarized" cells. On the face of it, this would appear to invalidate the authors' conclusions! Similarly, in Figure 1F "non-polarized" the unilluminated cells show a Cdc42 signal as high as in many of the treated cells. At what location is the signal being measured? The relevant negative control site would be a mock-illuminated site, but given the high Cdc42 signal, one suspects that the authors have quantified Cdc42 at the pre-bud site instead. The location of this measurement should be stated explicitly, and we recommend that the statistics be re-done with the unilluminated control quantified at a mock-illuminated site.
4) Untested assumptions:
The narrative makes assumptions that are not directly tested. Articulating and justifying each assumption (with citations or references to salient experiments, or with some appropriate rationale) would be very helpful:
(i) It is assumed that more frequent light pulses result in greater recruitment of ePDZ fusions.
(ii) It is assumed that mutant ePDZ fusions are expressed at similar levels to WT fusions.
(iii) It is assumed that illumination has no effect except to recruit ePDZ fusions.
5) Description of feedbacks:
The text should also be more precise in the description of feedbacks. The authors show data that is consistent with positive feedback, but do not directly demonstrate positive feedback: recruitment of Bem1 by Bem1 is consistent with feedback, but equally consistent with oligomerization, and as highlighted above, Cdc24 recruitment by Cdc24 could also be due to oligomerization. The text should be clear on these alternative possibilities. Similarly, regarding the proposed pre-start feedback, there is no direct data showing Bem1 independence. While optogenetic recruitment of Cdc24-ePDZ does not lead to detectable recruitment of endogenous Bem1, absence of evidence is not evidence of absence. Without testing that Bem1 is indeed not required, the wording of the text should be changed to make this clear.https://doi.org/10.7554/eLife.26722.048
- Michael Glotzer
- Devin Strickland
- Kristen Witte
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
This work was supported by NIH R01GM85087. KW was funded (in part) by NIH T32 GM007183, and D.S. was supported by an American Cancer Society Postdoctoral Fellowship (119248-PF-10-134-01-CCG). We thank Eric Weiss and Danny Lew for generous gifts of reagents and Ed Munro, Mike Rust, Dave Kovar, Danny Lew, and members of the Glotzer lab for helpful discussions and support.
- Sheila McCormick, Reviewing Editor, University of California-Berkeley, United States
© 2017, Witte et al.
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Electron-Electron Interaction by Exchange of Virtual Phonons: Superconductivity
Figure 4.1 contains the graph of an interaction which we have not so far taken a close look at: an electron emits a virtual phonon, and this phonon is absorbed by another electron. This results in an effective, additional electron-electron interaction. The physical background is simple: the emission of virtual phonons by electrons means a deformation (polarization) of the lattice in the vicinity of the electron. If a second electron is near this polarization cloud, it experiences a force of attraction or repulsion which has nothing to do with the Coulomb interaction between the two electrons. It is with this interaction that we now want to concern ourselves.
KeywordsCooper Pair Persistent Current Critical Magnetic Field Fermi Sphere Particle Number Operator
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These conclusions are drawn in a new study in the early online edition of the Proceedings of the National Academy of Sciences,* October 22-26. The report states that “together, these effects characterize a carbon cycle that is generating stronger-than-expected climate forcing sooner than expected.”
Between 2000 to 2006, human activities such as burning fossil fuels, manufacturing cement, and tropical deforestation contributed an average of 4.1 billion metric tons of carbon to the atmosphere each year, yielding an annual growth rate for atmospheric carbon dioxide of 1.93 parts per million (ppm). “This is the highest since the beginning of continuous monitoring in 1959,” states the report. The growth rate of atmospheric carbon dioxide is significantly larger than those for the 1980s and 1990s, which were 1.58 and 1.49 ppm per year, respectively. The present atmospheric concentration of carbon dioxide is 381 ppm, the largest concentration in the last 650,000 years, and probably in the last 20 million years.
While the worldwide acceleration in carbon dioxide emissions had been previously noted, the current analysis provides insights into its causes. “The new twist here is the demonstration that weakening land and ocean sinks are contributing to the accelerating growth of atmospheric CO2,” says co-author Chris Field, director of the Carnegie Institution’s Department of Global Ecology.
Changes in wind patterns over the Southern Ocean resulting from human-induced global warming have brought carbon-rich water toward the surface, reducing the ocean’s ability to absorb excess carbon dioxide from the atmosphere. On land, where plant growth is the major mechanism for drawing carbon dioxide out of the atmosphere, large droughts have reduced the uptake of carbon.
Emissions from the burning of fossil fuels constituted the largest source of anthropogenic carbon, releasing an average of 7.6 billion metric tons each year between 2000 and 2006, a significant jump from 6.5 billion tons in the 1990s. Emissions generated by land-use changes such as deforestation have remained constant, but shifted in geographic focus.
The study also shows that the carbon intensity of the global economy (kilograms of carbon per dollar of economic activity) has increased since 2000 at about 0.3% per year, reversing a 30-year decline of about 1.3% per year. Because practically all proposed scenarios for managing future emissions postulate improvements in carbon intensity in the global economy, this deterioration of carbon intensity presents a serious challenge in stabilizing atmospheric carbon dioxide and mitigating climate change.
Chris Field | EurekAlert!
Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel
Oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”
05.07.2018 | European Geosciences Union
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To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
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Welcome! It is 7:12:27 PM on Sunday, July 15, 2018. This page has served 401994 lunatics and was last updated on Wednesday, May 7, 2014.
The Earth-Moon system was recorded by NASA's NearEarth Asteroid Rendezvous (NEAR) spacecraft on1/29/98. From Astronomy Picture of the Day
Portions of this work are from the article: Cummins, R.H., Ritger, S.D., and C.A. Myers. 1992. Using the moon as a tool for discovery-oriented learning. Journal of Geological Education. 40(2):142-146.
To excite students about the scientific approach to viewing the natural world, we use laboratory exercises that rely on personal observation, data collection, interpretation, and model development. In this laboratory exercise, which is suitable for introductory earth science courses, students are asked to (1) test the hypothesis that the moon revolves east to west around the earth, (2) determine, by lunar observation, approximately how many degrees the moon revolves per night, and (3) develop a scale model of the earth-sun-moon system with which students demonstrate the phases of the moon. Although this exercise can be frustrating for students at first, we have found that, given time, carefully managed discussion, and the opportunity to interact with others in the laboratory group, most students develop a good understanding of the earth-sun-moon system and, more importantly, benefit by arriving at the knowledge through self-directed and group-assisted observation and reasoning. We believe self-discovery is the most important component of this process. Advantages to using the moon include its familiarity (which makes it easier to generate student interest), its accessibility (assuming cooperative weather), and the relative ease with which required astronomical measurements can be made.
Picture taken by Nancy Teague and Jodi Forester, Junior Seminar, Interdisciplinary Studies
The Moon lab is used in Geol 499/599: Tropical Marine Ecology of San Salvador, Bahamas & Florida Keys and WCP 121: From the Universe to the Duck Pond: Exploring Patterns & Processes in Natural Systems to illustrate the importance of careful observation, the use of models to understand the natural world & the testing of a variety of hypotheses.
A Common Experience
Several years ago, I (Cummins) taught introductory geology to a class of about 50 students in a traditional geology department. Most were fulfilling a science requirement. As in many introductory science courses, I lectured three times each week and taught a two-hour laboratory. I did not go out of my way, other than an occasional query to the class, to raise questions in students' minds because I was intent on covering the material, which seemed indisputable anyway.
As in most introductory physical geology courses, we spent class time discussing origins of the universe and our solar system. Besides discussing the Big Bang theory, we covered the geologic characteristics of the inner and outer planets as well as earth-moon geometry as it relates to the phases of the moon. I used an illuminated orbiter planetarium (sun, earth, and moon) to demonstrate the phases of the moon, the proper earth- moon alignment for lunar and solar eclipses, and changes in seasons over the course of a year. Without doubt, many students easily followed my explanations while watching the demonstration. I was satisfied with this effort at first. However, I later regretted missing a golden opportunity to have had the students become active participants in the scientific method rather than passive listeners and observers of my demonstration.
Although I lectured with care and received good evaluations, my students were treated as if they were "empty vessels" waiting to be filled with the knowledge of a resident expert. Uncertainty and skepticism were not part of much of the course because it was "top-heavy" with facts. I covered necessary information. I wonder, though, what value those students place on this earth science course three years after they took it. Because I was so content-driven, students did not learn much about the scientific process. I know my experience is not atypical; is it so amazing that many students are bored and uninterested in science?
From these initial experiences, three of us teaching in the School of Interdisciplinary Studies at Miami University developed a lab exercise that (1) directly involves students in better understanding the phases of the moon--a phenomenon that many people assume they understand, and more importantly, (2) emphasizes the importance of active participation and the use of careful observation in the scientific method, so that students can practice science rather than just hear about it.
A fantastic GOES 10 satellite loop (animated gif) of the Feb. 26, 1998 Solar Eclipse! (From GOES Hot Stuff.)
The Moon Discovery Laboratory
The moon is an excellent object of study for a process-oriented, earth science lab (Johnston, 1967; Dexter, 1968). It is a celestial object with which we are all familiar. Countless legends are associated with its phases, including, but not restricted to, werewolves, romance, and (if you stretch it) bizarre behavior such as adolescent "mooning" activities. Calendars in many cultures are based upon its cycles. The ancient Babylonians based their calendar on the cycles of the moon. The Jewish and Moslem religions currently use a lunar calendar to measure the passage of months and years. Each lunar month begins with the appearance of a new moon. Ever wonder why the date of the Christian Easter holiday varies from year to year? Interestingly, the Easter holiday is always the first Sunday after the full moon which happens upon or after March 21.
Most people have heard the terms harvest moon, new moon, and blue moon, yet few have an understanding of what these terms mean. The movie A Private Universe, [Schneps, M. H. and P. M. Sadler (1987) Harvard-Smithsonian Center for Astrophysics, Science Education Department, Science Media Group, A Private Universe. Video. Washington, DC: Annenberg/CPB] which we often show in conjunction with this lab, shows recent Ivy League graduates unable to explain the basis of seasons or why there are phases of the moon.
The moon is of great scientific importance. Oceanographers model earth- moon-sun gravitational interactions to predict tides. Jastrow (1990) referred to the moon as a "Roseta Stone" because the moon provides us a glimpse of the history of our solar system. It is instructive to contrast the geology of our dynamic, rapidly weathering, plate tectonic driven earth with that of our comparatively static, unweathered, solid to the core companion. The moon has also often been cited as an example of the importance of extraterrestrial impact in our solar system's history (Marvin, 1986). Craters over 100 km in diameter on the moon attest to the numerous catastrophic collisions in the past. These can be compared with the hypothesized extraterrestrial impact on earth that may have caused the end Cretaceous mass extinction.
Because the moon is so familiar to us, it can be extremely useful in emphasizing the importance of careful observation--even the most familiar phenomena may require investigation to yield better understanding. Its use as a teaching tool in the earth sciences is very effective, in part, because the lessons learned by students (hypothesis testing or the power of observation, for example) are much more powerful when familiar objects are examined with new attention.
The Lab Project
To begin, we engage the class in a discussion of important lunar terms and concepts. These include synodic month, sidereal period, conjunction, opposition, earth-moon system, common center of mass, perigee, apogee, lunar and solar eclipses, orbital plane, occulation, declination, maria, highlands, and lunar phases (new moon, first quarter, full moon, and third quarter).
From Prof. Arnold V. Lesikar, Physics Dept., St. Cloud State University. This is an AMAZING Astronomy website!
Some Important Lunar Terms
Sidereal Month-The time it takes for the moon to complete one full orbit of the earth, measured with respect to the stars. This interval is the moon's true orbital period, ~ 27.3 days.
Synodic Month-The time it takes for the moon to complete one cycle of phases, i.e. new moon to new moon, or full moon to full moon ~ 29.5 days.
Why is the synodic month about 2 days longer than the sidereal month?
-As the moon is revolving around the earth, the earth is also revolving around the sun. The earth has completed about 1/12 of it's orbit around the sun in one lunar month.Therefore, the moon must travel slightly further than 360 degrees to get from one full moon to the next.
Opposition- That time during the moon's orbit when the earth is located between the moon on one side and the sun's rays on the other.
Conjunction- That time during the moon's orbit when the moon is located between the earth and sun. Sun-Moon-Earth line up.
Quadratures- That time during the moon's orbit when the sun, earth, and moon are positioned such that the moon, earth, and sun form a 90angle with one another.
Apogee- The moon's orbit around the earth is an ellipse. During apogee,
the moon is at it's greatest distance (about 405,800 km) from
Perigee- During perigee, the moon is at it's closest distance to the earth (about 375,200 km). Check out this amazing comparison of apparent size differences of the moon at perigee and apogee. The full moon on Dec. 22, 1999 , was "a full-perigee-solstice moon, reaching its full phase and perigee (the closest point in its orbit) on the solstice, the first day of northern hemisphere winter." From Astronomy Picture of the Day
Spring Tide- A tide which results in the greatest range between high and low tide. How frequently do spring tides occur each month?During which phase(s) does/do spring tides occur? Why?
Neap Tide- A tide which results in the least tidal range between high and low tide. How frequently do neap tides occur each month? During which phase (s) does/do neap tides occur? Why?
Gibbous- Designating the moon when it is in a phase between half moon
and full moon and the curves forming its outline are convex.
"Also known as the Moon's "ashen glow" or "the old Moon in the new Moon's arms", Earthshine is Earthlight reflected from the Moon's night side. A description of Earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci." Photo By Laurent Laveder. From Astronomy Picture of the Day
The lab should be scheduled to coincide with phases of the moon convenient for viewing; first quarter thru full moon works well. To whet appetites, we have a night of telescopic observation of the moon. Even small aperture telescopes do a wonderful job of interesting students in lunar features. We usually scan the lunar highlands and search out prominent craters such as Copernicus and Kepler. We discuss lunar geology and examine impact features in detail. Students work in groups of four.
Hypothesis Test-Exercise 1
In the first experiment, which requires a protractor, straw, and tape (to make an astrolabe), students test a hypothesis by observing the earth-sun-moon system and collecting the appropriate data.
We ask the following question: Given that the earth-moon system orbits a common center of mass resulting in a new moon, first quarter, full moon, and third quarter in the course of one lunar month, test the following hypothesis: "As viewed from a pre-defined location of your choice, the moon, during the course of your observations, revolves east to west around the earth." You are asked to observe the moon on consecutive nights and (a) derive a test for the hypothesis of lunar motion and (b) derive a method of determining the number of degrees the moon revolves around the earth in one day. Hint: This is not as simple as it may seem!
Earth-Sun-Moon Model-Exercise 2
The earth-sun-moon model. A map & a flag are used as frames of reference on a rotating earth. The student-generated vision of the world has Oxford, Ohio as its center.
The second exercise requires a flashlight, a pumpkin (or equivalent), and a squash (or approximate equivalents), which students use to develop a model that demonstrates the phases of the moon. Models are used to better understand the world around us. Models of atoms, our solar system, and chemical compounds, for instance, help us to see and imagine possibilities that would otherwise be inacessible. To gain a more profound impact using this earth-sun-moon model, it is important to generate a model to scale, at least at first. If your model were to scale, would you be able to continue with your understanding of the earth-moon system? Or, might you have to make some compromises to continue?
Some beginning questions: In your Earth-Sun-Moon system(using your model earth as your beginning frame of reference), if it were true to scale, what would be (1) the model flashlight diameter of the sun; (2) the diameter of the model moon? (3) What would be the distance between the model earth and sun? The model earth and moon? Ask students to make predictions before doing their calculations.
Actual diameter of the earth~12,756 km
Actual diameter of the moon: ~3476 km
Actual diameter of the sun~ 1,390,000 km
Average distance between the earth & moon~384,000 km
Average distance between the earth/sun~150,000,000 km
Go HERE: To pinpoint the exact time of: MOONRISE/MOONSET/PHASE for your location!
Phases of the Moon
A Waxing Moon! 1/9/98
When attempting to understand why there are phases of the moon, always think in terms of the angular relationships between the arrangement of the earth, moon, and sun in space. As these angular relationships change, so do the phases.
The flag marks the observer's location on earth. As the earth rotates, the field of view of an observer changes. During first-quarter, moonrise on the ?????? horizon takes place at about ??????? and moonset occurs on the ?????? horizon at ???????.
Several Hours Later on 1/9/98
Another Waxing Moon at Sunset, 2/8/98
Use your earth-sun-moon model to address these remaining questions:
Remember, a frame of reference on your "earth" model is very important!
Use the earth-sun-moon model to determine the direction that the earth rotates on its axis, approximate local times (sunrise, noon, sunset, and midnight) of moonrise, high moon, moonset, and times of visibility of the moon.
|Phase||Moonrise||High Moon||Moonset||Times of Visibility|
Now, using your model to guide you, can you explain why there are phases of the moon? If it all is just too much, visit the Astronomy Site of the Day for a wonderful diversion. The Phases of the Moon Site provides dates and phases of the moon for any month or year!
Ever think about what a Full Moon Looks like from Beyond Planet Earth? Check out this satellite perspective of a full moon over N America and Asia! (From GOES Hot Stuff.)
A brand new "new" moon, one day old, March 9, 1997. Cleveland National Forest, southern California. Photo by Emily Harrison and her buddy Sarah Bernhardt.
Many stargazers in the U. S. were able to watch a lovely lunar occultation early last Thursday morning (9/24/97) as a bright Moon passed in front of Saturn. Using a 1.2 meter reflector, astronomer Kris Stanek had an excellent view of this dream-like event from the Whipple Observatory atop Arizona's Mount Hopkins.This animated gif image was constructed by Wes Colley from 4 frames taken by Stanek at 35 second intervals as the ringed planet emerged from behind the Moon's dark limb. From Astronomy Site of the Day. Go here for more info on Ocullation Events.
Some Wonderful Moon Links
As viewed from your location on earth, are the shadows moving in the right direction as the moon changes phase?
Some Additional Questions:
1-Using your model, explain why LUNAR ECLIPSES occur only during full moon. If a full moon occurs every month, why don't we see lunar eclipses every month?
Bonus:I thought you might like to see a quicktime slideshow of the spectacular Lunar Eclipse on Saturday, Nov 8, 2003 as seen in Oxford, Ohio. It was very cold--temperatures were below freezing by 8:00pm! Totality was reached at 8:06 pm EST. The colors of the moon were fantastic, an impossible palette much too difficult to duplicate. The photos do not come close to reflecting reality! It was the most fantastic lunar eclipse of my life!
The Anatomy of a Lunar Eclipse, from the BBC's Skywatchers await lunar eclipse.
2- Using your model, explain why SOLAR ECLIPSES occur only during new moon. If a new moon occurs every month, why don't we see solar eclipses every month?
3- How would the relationships between the period of rotation
and revolution of the moon affect whether or not we see the "far
side" from the earth's surface? Since we don't see the other side,
what is your explanation? Use your model to generate an explanation.
4- What tests would you use to determine whether the moon formed
from the same dust cloud as the earth, was fragmented from the
proto-earth at some later date, was formed from a collision with
an extraterrestrail object, or was an alien body captured by the
earth as the satellite moved within the grasp of the earth's gravitational
field? Can you find the most recent literature references on this
5- A laser beam fired to the moon from the earth's surface strikes a mirror (left by the Apollo astronauts for the purpose of studying changes in distance between the earth and moon) and is reflected back to the earth. Travel time is 2.562 seconds. How many kilometers away is the moon from the earth?
Tides & Other Moon Links
And of course, there is the major discussion on Ocean Tides (This really cool site will present tidal predictions and graphs for many coastal locations in the US.) Go HERE for a question-answer WWW page on tides. I plan on adding more info about the tides on this web page, but that is for another day!
US Naval Observatory- Astronomical Applications computes, from fundamental astronomical reference data, the position, brightness, and other observable characteristics of celestial bodies, as well as the circumstances of astronomical phenomena.
For the latest NASA News on the moon, visit The Lunar Prospector site.
|Weather Home Base
A Complete Listing of "all things weather." Pretty Large Site. Can be slow to load.
|Radar Overview & Severe Weather
See Where the Action is!
A Quick Look!
A complete listing of satellite images and movies. Text based for fast downloads.
|Hurricanes & Tropical Weather
The Atlantic season is will be here before you know it!
|Satellite Downloads and Other Maps
Real-time satellite movies automatically downloaded. Graphics Intensive!
|Just the Maps & Views!
While far from complete, these downloaded views provide for a satisfying overview of North American Weather.
A complete weather listing, non-graphics based. Not as interesting, but download time is much quicker!
The "Taxonomy of Nuts and Bolts"
WEATHER & EARTH SCIENCE RESOURCES
OTHER ACADEMIC COURSES, STUDENT RESEARCH, OTHER STUFF
TEACHING TOOLS & OTHER STUFF
Any mail, comments or suggestions? You can Add to my Guestbook ,View the Guestbook or e-mail me privately at HaysC@miamioh.edu.
Thanks for stopping by!
Copyright © 1996-Infinity R. Hays Cummins; All rights | <urn:uuid:3a734dae-e9c2-48c0-a46f-8077c85e3c4b> | 3.5625 | 4,297 | About (Org.) | Science & Tech. | 52.585427 | 95,519,213 |
Working with an enzyme that degrades anti-cancer drugs in humans, University of North Carolina at Chapel Hill biochemists and colleagues have made a discovery that they believe eventually could help improve such drugs’ design and effectiveness.
The scientists have shown that the enzyme protein can be made to "fly through the vapor phase" -- from which solvent water is totally absent -- without changing its structure.
When a solution containing the enzyme was introduced as a fine spray into a vacuum created in a mass spectrometer in the laboratory, normal solvent molecules were completely evaporated, leaving bare, charged molecules known as ions, the researchers said. The protein ions were trapped in the extremely high vacuum for seconds, but in the new experiments, a single water molecule remained undisturbed, which was a surprise since no one ever saw that before. "This suggests how we might change an inhibitor molecule to make it fit the enzyme more perfectly and hence be more effective in blocking that enzyme’s action in destroying anticancer drugs," said Dr. Richard V. Wolfenden, Alumni Distinguished professor of biochemistry and biophysics at the UNC School of Medicine.
David Williamson | EurekAlert!
Colorectal cancer risk factors decrypted
13.07.2018 | Max-Planck-Institut für Stoffwechselforschung
Algae Have Land Genes
13.07.2018 | Julius-Maximilians-Universität Würzburg
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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To understand how this deep-water fish finds a shallow-feeding bird in offshore waters, researchers looked at when, where, and how these animals were most likely to be in the same place at the same time.
A dovekie, also known as little auk, is the smallest in the puffin species. Photo credit: Chris Melrose, NEFSC/NOAA
A goosefish or monkfish (Lophius americanus) is measured at sea. Photo credit: NOAA
Remains of fourteen dovekie were recovered from the stomachs of 14 goosefish caught during the winters between 2007 and 2010. The goosefish were captured in gillnets deployed at depths between 275 and 495 feet in waters 65 to 95 miles south of Chatham, Mass. The Cape Cod Commercial Hook Fishermen’s Association collected the specimens and provided them for the research study.
Researchers from NOAA’s Northeast Fisheries Science Center (NEFSC) in Woods Hole, Mass. and the USGS Patuxent Wildlife Research Center in Laurel, Md., wanted to know how the birds could be captured so far from shore by a fish that lives on the ocean bottom in deep water. Their findings, recently published online in the Northeastern Naturalist, suggest that it is all a matter of timing.
Goosefish (Lophius americanus) are highly opportunistic predators. Distributed from the Gulf of Maine to Cape Hatteras, N.C., the fish are typically partially buried on soft bottom habitats and attract a variety of prey by using a modified dorsal fin ray that resembles a fishing pole and lure.
Dovekies, a small black and white puffin species, breed along the Arctic coast and head south in the winter, typically as far as New England. The dovekie (Alle alle), also known as little auk, is the smallest of the auks. It lives in the open ocean and can dive to depths of more than 100 feet to prey on small fish, crustaceans, and zooplankton.
Study co-author Anne Richards of the NEFSC says tagging studies that she and colleagues have conducted reveal that goosefish swim considerable vertical distances from the bottom to near the surface, especially during their spring and fall migrations onshore and offshore in response to water temperatures and related factors.
Goosefish leave the bottom to use the currents during migration periods or to spawn at the surface. If prey items are encountered during their vertical movements, the goosefish take advantage. Hence, timing may be the key factor in bringing dovekies and goosefish together in the same place.
“Given the common name ‘goosefish’, it is not surprising to find birds in goosefish stomachs, but it is surprising to find that this predation occurs over deep water, “Richards said. “Goosefish do not actively seek out the dovekies, but when such tasty morsels are available in the water column, the fish are going to consume them.”
Another source of data used in the study is the NOAA NEFSC food-habits database, which contains decades of predation information collected from the stomachs of fish that are caught during regular research vessel surveys. While not a particularly good measure of how often or how many birds are eaten by fish, these data confirm that not only goosefish, but also spiny dogfish, Atlantic herring, pollock, Atlantic cod, red hake, and fourspot flounder will eat birds.
Lead author Matthew Perry, a research wildlife biologist at the USGS Patuxtent Wildlife Research Center, says he became interested in goosefish predation when he learned from a sea scalloper on Nantucket that Chatham gillnetters were finding birds inside goosefish stomachs.
“I was studying long-tailed ducks and thought, to avoid being eaten, these birds fly 30 to 50 miles to Nantucket Sound each night and return to the ocean in the morning,” said Perry, who studies several species of seaducks. “People ask why don't dovekies fly to Nantucket Sound at night like the long-tailed ducks to avoid goosefish? My explanation is that dovekies have small wings and can’t make the routine flight.”
“One thing we know is that dovekies cannot dive to the bottom in 300 to 400 feet of water,” Perry said. “Goosefish probably come up from the ocean bottom to within 10 to 20 feet of the water surface at night. As dovekies dive for amphipods, small crustaceans, in the morning at first light, goosefish seize the opportunity and might use their 'fishing lure' to simulate one of these prey species by attracting the dovekies with their typical ‘sit and wait’ behavior.”
The magnitude of fish predation on seabirds is poorly understood. Perry says most food habit studies for goosefish have been conducted during summer when the dovekies have migrated north to their Arctic breeding areas; thus, they seldom have been recorded as prey. Perry hopes more telemetry tracking of goosefish will be done in winter when birds are in the area and are potential prey.
As for what’s ahead, Richards says ongoing use of electronic tags on goosefish will provide more information on their vertical movements.
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Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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By: M Winston
224 pages, 75 line illus, 7 tabs
&i;`A wonderful reference and entree to the literature on anything you ever wanted to know about honey-bees ... encyclopedic in scope, timely and up to date. There is no other reference book that compares to it.'&o; Bernd Heinrich
Masterly...Without hesitation I recommend this book to a wide range of potential readers. -- John B. Free Science Mark Winston offers a comprehensive account, covering aspects of anatomy and physiology as well as systematics, ecology and behavior...A useful overview of the biology of an insect that holds considerable interest for both economic and academic reasons. Rich in descriptive detail and well referenced, it will also serve as a basis for more detailed exploration of particular aspects of honey bee biology. -- Sarah Corbet Times Higher Education Supplement This very readable book brings together the wealth of scattered information on the complex honey bee in a way that will serve as a standard for many years. -- Roger G. Bland Science Books & Films Winston's writing is brisk and enthusiastic and the book's illustrations clear and informative. This is a delightful study of an odd, yet oddly familiar, creature. -- John R. Alden Wall Street Journal
1. Introduction 2. The Origins and Evolutionary History of Bees 3. Form and Function: Honey Bee Anatomy 4. Development and Nutrition 5. Nest Architecture 6. The Age-Related Activities of Worker Bees 7. Other Worker Activities 8. The Chemical World of Honey Bees 9. Communication and Orientation 10. The Collection of Food 11. Reproduction: Swarming and Supersedure 12. Drones, Queens, and Mating 13. The Biology of Temperate and Tropical Honey Bees Reference Author Index Subject Index
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Mark L. Winston is a Fellow in the Morris J. Wosk Centre for Dialogue at Simon Fraser University.
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Gloeobacter(Redirected from Gloeobacteria)
Gloeobacter is a genus of cyanobacteria. It is the sister group to all other cyanobacteria. Gloeobacter is unique among cyanobacteria in not having thylakoids, which are characteristic for all other cyanobacteria and chloroplasts. Instead, the light-harvesting complexes (also called phycobilisomes), that consist of different proteins, sit on the inside of the plasma membrane among the (cytoplasm). Subsequently, the proton gradient in Gloeobacter is created over the plasma membrane, where it forms over the thylakoid membrane in cyanobacteria and chloroplasts.
Rippka, Waterbury, & Cohen-Bazire, 1974
The whole genome of G. violaceus (strain PCC 7421) and of G. kilaueensis have been sequenced. Many genes for photosystem I and II were found missing, likely related to the fact that photosynthesis in these bacteria does not take place in the thylakoid membrane as in other cyanobacteria, but in the plasma membrane.
G. violaceus produces several pigments, including chlorophyll a, β-carotene, oscillol diglycoside, and echinenone. The purple coloration is due to the relatively low chlorophyll content. G. kilaueensis grows with a few other bacteria as a purple-colored biofilm around 0.5 mm thick. Cultivated colonies are dark purple, smooth, shiny, and raised. G. kilaueensis is mostly unicellular, capsule-shaped, about 3.5×1.5 µm, and imbedded in mucus. They divide over the width of the cell. Cells color gramnegative, and lack vancomycin resistance. They are not motile and do not glide. Growth ceases in complete darkness, so Gloeobacter is very likely obligatory photoautotrophic.
Species and distributionEdit
G. violaceus was found on a limestone rock in the Swiss canton Obwalden. G. kilaueensis occurred within a lava cave at the Kilauea-caldera on Hawaii. It grew there at a temperature around 30 °C at very high humidity, with moisture condensing and dripping of the biofilm.
- Komárek J, Kaštovský J, Mareš J, Johansen JR (2014). "Taxonomic classification of cyanoprokaryotes (cyanobacterial genera) 2014, using a polyphasic approach" (PDF). Preslia. 86: 295–335.
- Enrique Flores AH (2008). The Cyanobacteria: Molecular Biology, Genomics and Evolution. Horizon. p. 3. ISBN 1-904455-15-8.
- Nakamura Y, Kaneko T, Sato S, et al. (2003). "Complete genome structure of Gloeobacter violaceus PCC 7421, a cyanobacterium that lacks thylakoids". DNA Res. 10 (4): 137–45. doi:10.1093/dnares/10.4.137. PMID 14621292.
- Saw JH, Schatz M, Brown MV, Kunkel DD, Foster JS, Shick H, et al. (2013). "Cultivation and Complete Genome Sequencing of Gloeobacter kilaueensis sp. nov., from a Lava Cave in Kīlauea Caldera, Hawai'i". PLoS ONE. 8 (10): e76376. doi:10.1371/journal.pone.0076376.
- B.E. Schirrmeister; M. Gugger; P.C.J. Donoghue (2015). "Cyanobacteria and the Great Oxidation Event: evidence from genes and fossils". Palaeontology: 1–17. doi:10.1111/pala.12178. PMC . | <urn:uuid:09bd1bf6-9eef-45f6-a9d4-b4cdd5c06cf3> | 3.078125 | 859 | Knowledge Article | Science & Tech. | 55.120696 | 95,519,260 |
|Science & Environmental Health Network|
Science, Ethics and Action in the Public Interest
The climate cost calculator
Economics whiz kid Peter Larsen is predicting big costs for adapting to a warming climate.|
By Erika Englehaupt, Environmental Science & Technology
Policy News – August 8, 2007
In the dark of Alaska's winter of 2006, resource economist Peter Larsen spent a little time cross-country skiing through the dimly lit snow. But most of the time he was in his office calling transportation officials to ask whether climate change had torn up any roads lately.
Thirty-one-year-old Larsen tallied the cost of wear and tear from climate change on every bridge and road in damage-prone Alaska.
"On more than one occasion, I got people who would laugh at me," Larsen says. Not one to be deterred, he kept calling. He called every Alaska agency he could find, looking for roads and bridges that were slumping as permafrost thawed beneath them and for facilities threatened by flooding and coastal erosion. Then, Larsen and his team mapped every scrap of public infrastructure in Alaska and estimated the cost that a changing climate will add to maintaining it all.
His estimated price tag: as much as $6.1 billion dollars between now and 2030 to repair or replace structures and up to $7.6 billion between now and 2080. That's on top of billions Alaska already spends keeping up with $40 billion worth of infrastructure in a harsh frozen environment, and it amounts to an extra 10–20% in those costs projected to 2030, according to a report Larsen and colleagues published through his institution, the University of Alaska's Institute of Social and Economic Research (ISER).
It's a small part of the toll that climate change will exact on Alaska, Larsen says. The nation's fastest-warming state is already grappling with big changes, and the rest of the world had better take notice, he adds.
Waking up to change
But few have. Larsen's work heralds a new approach to studying climate change: tallying the dollars and cents of adapting to a warmer world, one with a confusing array of droughts, floods, wildfires, and disappearing shorelines—in short, a city planner's nightmare. Until now, "most work has focused on predicting who will lose out in climate change and what adaptations they may need," says Joel Smith, who is the vice president of Stratus Consulting and is a consultant on the Alaska report. Now, he says, it's time for engineers and economists to get down to the business of planning and paying.
Even longtime climate skeptic Sen. Ted Stevens (R-AK) seems resigned to dealing with the problem. "Regardless of whether these changes are caused solely by human activity, we must take steps to protect people in the Arctic," Stevens said upon introducing climate-change legislation in July.
But there's a reason few have tackled this kind of project. First, Larsen's team had to track down all 16,000 pieces of infrastructure in Alaska. "A single piece of infrastructure could be a road that's 20 feet long, or an entire airport," Larsen says. Harbors, schools, the power grid, and sewer systems—19 classes of infrastructure in all—were counted, too. Next, they put dollar signs on climate wear and tear by combining engineering estimates of how fast climate impacts might shorten the useful life of infrastructure in vulnerable locations with the latest climate projections assembled by the National Center for Atmospheric Research from research institutes all over the world.
Even before the report came out in June, both it and its lead author were attracting attention. Larsen has been traveling the state presenting his findings to policy makers, and the report made its way into the hands of Sen. Lisa Murkowski (R-AK). She has recently changed her formerly conservative stance on climate change. After reading this and other reports about risks to Alaska, Murkowski helped introduce a bill to the U.S. Congress in July that would set mandatory carbon limits, called the Low Carbon Economy Act of 2007.
The new kid
Larsen has been blazing toward a position of influence since the beginning of his young career. In 2000, not long out of college, he landed a job at the prestigious environmental firm Stratus Consulting, where he dove into the economics of electricity market deregulation during the tumultuous days of the Enron energy scandal. "During the whole Enron crisis, I was the guy who flew to the East Coast and helped the New England power pool to program all their market surveillance software," Larsen says. When power plants placed bids to sell electricity, it was Larsen's statistical programs that tested the market for anticompetitive behavior. After California's market went haywire, he met with the state's central dispatcher to demonstrate his software and ended up offering some of it "to help those guys out because they were in a bad situation," he says.
Feeling pressure after a few years to return to school, Larsen entered a master's program at Cornell University, only to be recruited out of the program a year later as a key component in a new climate-change program at ISER. He finished writing his master's thesis, the first assessment of the entire U.S. economy's vulnerability to weather, as he started his new job.
Fran Ulmer recruited Larsen to Alaska. Ulmer is the university's chancellor and a 20-year veteran of the Alaska legislature, where she also served a stint as lieutenant governor. She took Larsen under her wing when she was director of ISER and says Larsen was the "perfect fit for what ISER needed to contribute to the public-policy conversation taking place right now." As she watched the fledgling economist step into the media spotlight with the recent report, she advised him not to oversell his results and to watch out for those who might try to use his age and short experience to discredit his work.
And with all that hard work, there's still one thing Larsen hasn't found the time for: finishing a Ph.D. He says he'll likely go back for one sooner or later (his colleagues say they hope it's not too soon), but for now he looks to role models like former Federal Reserve Chair Alan Greenspan, who received an honorary doctorate from New York University years after opting out of the academic route.
Larsen's credentials are "not an issue," says report coauthor Oliver Scott Goldsmith, ISER's current director. What's more important is that "he really gets inside questions and digs around," Goldsmith says, noting that when Larsen had questions about methods for modeling climate variability, he called renowned mathematician Benoit Mandelbrot for a chat. "He's not afraid to call up Mandelbrot," Goldsmith says. "He can see clearly where he wants to go."
Better sooner than later
"There's probably more economic value in a few square blocks of Manhattan than in all of Alaska; however, there's an enormous amount of cultural value that we can't, as ethical economists, put a value on," he says.
He points to the tiny coastal village of Shishmaref, which has been occupied by the Inupiaq people for more than 4000 years. Permafrost below the town is thawing, and the shore-fast ice that had always provided protection from storm surge is melting away. The cost to move the village: about $180 million. But beyond that price, "We're talking about cultures fundamentally changing here, and we can't put a dollar value on that," Larsen says. "And I won't."
One surprise in Larsen's models: over the long haul, the total cost of adapting infrastructure to climate change could be smaller the faster things heat up. "When I saw it, I thought there was a bug in the model," he says. But no, the model just revealed a fundamental aspect of human nature: procrastination. Larsen had programmed the model to trigger an adaptation, such as rebuilding or replacing a bridge, at the point when that item has lost 20% of its original value—about what engineers and planners tend to do. In the warmest of the three climate scenarios he studied, that threshold is crossed quickly, and people are forced to act to fix the infrastructure sooner, while it still has a lot of useful life remaining. "It saves people money down the line," Larsen says.
The type of estimate that Larsen is attempting is "becoming more important as people realize what's coming," Smith says. Ultimately, he says, society has to weigh the costs and benefits of investing in climate-change adaptations like new bridges or seawalls. "You don't have to make an investment," Smith says, "but you should at least consider it. To not consider it is derelict." —ERIKA ENGELHAUPT
Copyright © 2007 American Chemical Society
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From the warmest December on record to the "Blizzard of 2016" and snow in April, the winter of 2015-2016 will go down in the record books across the northeastern United States.
The transition to a strong El Niño brought a very different weather pattern to the region compared to the winter of 2014-2015 which featured copious amounts of snow.
The AccuWeather winter forecast for the Northeast and Great Lakes highlighted a mild start to the winter season as El Niño strengthened in the equatorial Pacific. The milder pattern would also lead to a weak lake-effect snow season across the Great Lakes.
“We were certain that the winter cold would be less persistent and less frequent compared to last year,” AccuWeather Long Range Meteorologist Paul Pastelok said.
The mild start to the season failed to produce significant bands of lake-effect snow.
“The mild pattern during November and December took over across the eastern United States and allowed very few lake-effect events to occur at the beginning of the season,” Pastelok said.
December became the warmest month on record across the Northeast, shattering the previous record.
Temperatures from Boston to New York City, Washington, D.C. and places in-between averaged more than 10 degrees Fahrenheit above normal for the month. Some locations broke their previous December average temperature by 3 to 5 degrees.
"The highlight of December was the warmth on Christmas Eve," AccuWeather Meteorologist Brett Rossio said.
The mild start to the beginning of the weather season helped to break a 117-year-old record for the latest measurable snowfall in Buffalo, New York. The new record is Dec. 18.
The record for the latest date for an inch of snow fell just shy of the record set on Jan. 4, 1937 when Buffalo received 1.9 inches of snow on New Year’s Day.
As the calendar shifted into 2016, enough cold air arrived for several lake-effect events to unfold. However, not enough snow fell to help erase the deficit from November and December.
“While the cold hit during January and February, there were a few big lake-effect events but most locations still received less than half of the normal snow typically received from lake-effect storms,” Pastelok said.
Cleveland, Ohio, for example, received only 33 inches of snow this season, exactly half of the normal snowfall of 66 inches. Buffalo, New York, received around 52 inches of snow, more than 40 inches below the normal of 93 inches.
With much of the interior Northeast relying on lake-effect snow as their main snowpack for each season, the winter season ended with below-normal snowfall. The same was not the case along the Interstate-95 corridor as a single storm produced more snow than some locations receive for an entire season.
The most memorable snowstorm of the winter season occurred during Jan. 22 and Jan. 23 across the mid-Atlantic states and became known as the Blizzard of 2016.
This powerful storm led to widespread snow totals of 1 to 3 feet, strong wind gusts between 30 and 50 mph and shut down major cities for days.
The major cities of Washington, D.C., Baltimore, New York City and Philadelphia shattered daily records for the most snow on Jan. 23.
This storm produced a typical entire season's worth of snowfall in a span of one and a half days across many locations along the Interstate-95 corridor.
“The big snowstorm from Jan. 22-23 across the mid-Atlantic led to portions of the mid-Atlantic toward New York City receiving above-normal snowfall for the season,” Pastelok said.
Philadelphia, received 22.4 inches of snow from the Blizzard of 2016 alone. Normal seasonal snowfall is around 22 inches for the city.
"New York City to Philadelphia and Washington, D.C. only received about 5 inches of snow outside of the Blizzard of 2016," AccuWeather Meteorologist Eric Leister said.
'Cold blob' to be a wild card in the 2016 Atlantic hurricane season
When will it warm up in the midwestern, northeastern US?
April cold threatens 'significant losses' of fruit crop in northeastern US
As many were looking forward to an early spring, cold and snow returned to the Northeast during the first two weeks of April.
As the polar vortex shifted south toward the Hudson Bay, shots of colder air plunged across the Northeastern states and opened the door for a few snowstorms to sweep from the Great Lakes to the mid-Atlantic coast.
The cold air and fresh snowpack caused some locations to set new record lows during early April. For others, enough snow fell to prevent this season from being the least snowiest on record.
Williamsport received enough snow on April 9 to fall short of the record for least amount of snow in a winter year. Williamsport has accumulated 7.7 inches this winter, slightly more than the current record of 7.0 inches set in the winter of 1988-1989.
Albany, New York, will mark this winter as the least snowiest on record at 16.9 inches. The previous record was 19.0 inches set in the winter of 1988-1989.
The chance for any additional snowstorms across the Northeast is unlikely until fall as milder air will return and stay for the remainder of April starting this week.
Comments that don't add to the conversation may be automatically or manually removed by Facebook or AccuWeather. Profanity, personal attacks, and spam will not be tolerated.
Severe thunderstorms tracked across Iowa on Thursday afternoon with several tornadoes touching down across the state.
Se estima que la región puede ser de 2 a 3 veces más propensa que el resto de la nación
An uptick in monsoon rainfall is expected to heighten the flood threat across eastern and northern India this weekend and early next week.
After several dry days, the weather will take a downhill turn as NASCAR drivers gear up for the Foxwoods Resort Casino 301 in Loudon, New Hampshire, on Sunday.
A change in the weather pattern will favor periodic bouts of wet and stormy conditions as well as unusually cool air at times for the Midwest for the duration of July.
While it has long been known that volcanic eruptions can alter global climate patterns, less has been documented on the impacts of localized weather patterns following an increase in nearby activity.
An 11-million-ton iceberg hovers over the town of Innaarsuit in Greenland. The massive iceberg floats dangerously close to shore, threatening the small town.
Two people suffered shark bites while swimming in the water off Fire Island in Suffolk County, New York, according to NBC New York. | <urn:uuid:1da1c0ec-01d2-4dde-abf7-41c4de3eca54> | 2.890625 | 1,402 | News Article | Science & Tech. | 58.457884 | 95,519,273 |
A microbial partnership thriving in an acidic hot spring in Yellowstone National Park has surrendered some of its lifestyle secrets to researchers at the Department of Energy’s Oak Ridge National Laboratory.
Mircea Podar of ORNL’s Biosciences Division led a team that isolated the archaeon Nanopusillus acidilobi, cultured these tiny microbes—just 100 to 300 billionths of a meter in size—and can now study how they interact with their host, another archaeon (Acidilobus). The relationships between these two organisms, detailed in a paper published in Nature Communications, can serve as a valuable model to study the evolution and mechanisms of more complex systems.
“This work demonstrates how organisms find ways to adapt and interact with specific organisms in a symbiotic or parasitic way to survive in hostile environments,” Podar said. “By integrating knowledge from genomics, proteomics and classical microbiology, we can culture wild organisms and sometimes manipulate them for practical applications that range from energy production to medicine.”
The Archaea domain consists of single-cell microorganisms that, like bacteria, have no cell nucleus or membrane-bound organelles, a sub-unit within a cell. These microbes have maintained an open environment-exposed cellular membrane, and Nanopusillus has developed a mechanism to acquire primary biosynthetic molecules from the host cell through cell-to-cell contact.
With habitats like hot pools in Yellowstone, the Nanopusillus acidilobi microbe has been particularly elusive, so this accomplishment is likely to create a stir.
Photo courtesy of Oak Ridge National Laboratory
One of the journal’s reviewers noted that the discovery and paper provide “new exciting insights into the microbial diversity with important phylogenetic implications and thus represents a very important contribution in the archaeal/microbial diversity field.”
Researchers also noted similarities between this microbe and its distant relative, the marine Nanoarchaeumm, which was cultured more than a decade ago. Through observations like this and by making comparisons over the years, scientists have been able to gain insight into structural and molecular properties of a host of novel groups of microbes.
This most recent accomplishment is especially satisfying, said Podar, who noted that it was a combination of diligence and chance and took several years.
“We discovered and cultured a novel organism from a group of organisms that people have been trying to get for over a decade, and in part that was due to prior genomic data we acquired from those organisms in Yellowstone,” Podar said, adding that the microbial system “abounds in unique, remarkable physiological and genomic features.”
Co-authors of the paper, titled “Genomics-informed isolation and characterization of a symbiotic Nanoarchaeota system from a terrestrial geothermal environment,” are ORNL’s Louie Wurch, Richard Giannone, Bernard Belisle, Cynthia Swift, Sagar Utturkar, Bob Hettich, and Anna-Louise Reysenbach of Portland State University.
DOE’s Office of Science and the National Science Foundation provided funding for this work, a collaboration with the University of Tennessee and Portland State University. Also, the Yellowstone National Park Service granted a permit to study the microbes.
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Date Block - Long Day Format.When the object is serialized out as xml, its qualified name is w:dayLong.
Assembly: DocumentFormat.OpenXml (in DocumentFormat.OpenXml.dll)
'Declaration Public Class DayLong _ Inherits EmptyType 'Usage Dim instance As DayLong
public class DayLong : EmptyType
[ISO/IEC 29500-1 1st Edition]
126.96.36.199 dayLong (Date Block - Long Day Format)
This element specifies the presence of a date block at the current location in the run content. A date block is a non-editable region of text which shall display the current date filtered through the specified date picture (see following paragraphs) . [Note: The date block is a legacy construct used for compatibility with older word processors, and should not be produced unless it was consumed while reading a document – it is recommended that the DATE field is used in its place. end note]
A date block shall be displayed using the primary editing language of the host application, regardless of the languages specified in the parent run’s lang property (§188.8.131.52).
The long day format date block shall use a date picture of DDDD, retrieving the long day format for the primary editing language.
[Example: Consider a WordprocessingML run with the following run content:
<w:r> <w:t xml:space="preserve">This is a long date: </w:t> <w:dayLong /> </w:r>
This run specifies that a long day format date block must be placed after the text string literal This is a long date: in the document. Assuming that the host application’s primary editing language is French (Canada) and today’s date is 2006-04-12, this run would be displayed as follows:
This is a long date: mercredi
r (§184.108.40.206); r (§220.127.116.11)
[Note: The W3C XML Schema definition of this element’s content model (CT_Empty) is located in §A.1. end note]
© ISO/IEC29500: 2008.
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. | <urn:uuid:65bb657d-2c10-4702-bb56-0c3e8858639a> | 2.9375 | 504 | Documentation | Software Dev. | 66.365882 | 95,519,295 |
Various Methods of Averaging
The design of engineering systems and the ability to predict their performance depend on the availability of experimental data and conceptual models that can be used to describe a physical process with a required degree of accuracy. From both a scientific and a practical point of view, it is essential that the various characteristics and properties of such conceptual models and processes are clearly formulated on rational bases and supported by experimental data. For this purpose, specially designed experiments are required which must be conducted in conjunction with and in support of analytical investigations. It is well established in continuum mechanics that the conceptual models for single-phase flow of a gas or of a liquid are formulated in terms of field equations describing the conservation laws of mass, momentum, energy, charge, etc. These field equations are then complemented by appropriate constitutive equations such as the constitutive equations of state, stress, chemical reactions, etc., which specify the thermodynamic, transport and chemical properties of a given constituent material, namely, of a specified solid, liquid or gas.
KeywordsConstitutive Equation Field Equation Boltzmann Transport Equation Disperse Flow Thermomechanical Theory
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Different combinations of genetic mutations may give rise to diverse human traits, including complex diseases such as schizophrenia, say scientists at the University of Toronto and McGill University in Montreal.
Drs. Brenda Andrews and Charles Boone of U of T and Howard Bussey of McGill used simple yeast cells to demonstrate that there are many different combinations of genetic mutations that can lead to cell death or reduced cell fitness. The research team will now focus on mapping gene interactions for those yeast genes that are similar to human genes. Their study appears in the Feb. 6 issue of the journal Science.
The researchers crossed a yeast strain carrying a mutation in a particular gene of interest with a collection or "array" of other yeast strains to determine which gene pairs were lethal. The team studied more than 4,000 of these interactions involving gene pairs and was able to provide a large scale "genetic interaction network" that provokes new ideas about how genes interact to produce different traits.
Elaine Smith | University of Toronto
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences | <urn:uuid:edba03aa-5428-46a5-905d-d72a7220e19a> | 3 | 778 | Content Listing | Science & Tech. | 37.895865 | 95,519,300 |
The creation of a polariton Bose-Einstein condensate in the solid state provides scientists with a unique opportunity to better understand and possibly exploit the quantum effects that occur in these very special conditions.
Images of the energy distribution of polaritons as a function of the excitation density. From left to right, below threshold for condensation, at threshold and above threshold. Front row, speed distributions, the speed increases from the center to the edges. Rear row, dispersion of polaritons, with their distribution.
Researchers at EPFL (Ecole Polytechnique Federale de Lausanne), collaborating with colleagues at University of Grenoble, Cambridge, Oxford and MIT, have reported the observation of polaritons displaying the defining features of Bose Einstein condensation --a macroscopically ordered state, long-range spatial coherence and polarization – for the first time in solid state. Their results appear in an article in the September 28 issue of the journal Nature.
Bose-Einstein condensates are sometimes referred to as a “fifth state of matter”, a special phase in which all the particles share the same quantum state. This phase was predicted by Satyendranath Bose and Albert Einstein in 1924. Getting atoms cold enough to provide experimental proof of its existence took seventy more years, and the first successful experiments using Rubidium atoms won Eric Cornell, Wolfgang Ketterle and Carl Wieman the 2001 Nobel prize in physics. Cooled to within a hair of absolute zero, the atoms in dilute clouds of bosonic gases stop moving and condense, not into a liquid, but into a new phase called a condensate, in which the atoms all share the same quantum state. Like photons in a laser, the particles are coherent, behaving en masse like a “super-particle.”
The possibility of a phase change into a Bose-Einstein-like condensate theoretically applies for all bosonic particles, including electron-hole pairs called excitons and half exciton, half photon quasi-particles called polaritons. Exploring Bose-Einstein condensation and its intriguing quantum effects using these quasi-particles is particularly interesting because their light mass makes things much easier. A polariton is a billion times lighter than a Rubidium atom, and 10,000 times lighter than an electron. This means that polaritons can transform into a Bose-Einstein condensate at a much higher temperature than alkali gases. Some of the possibilities that have been suggested for applications of the quantum effects of the Bose-Einstein phase -- quantum computing, quantum clocks or atomic or lasers that use matter instead of light – are only realistically conceivable if these condensates can be achieved at room temperature, or at least temperatures that can be reached using standard cryogenic techniques.
Signatures of exciton and polariton coherence have been previously observed in semiconductor microcavities, but conclusive proof, such as evidence of polarization and long range particle coherence, has remained elusive because the particles only live a trillionth of a second.
The experiments of the EPFL-led team provide the first convincing evidence of a Bose-Einstein like condensate in the solid state. The researchers confined photons in a semiconductor microcavity containing a large number of quantum wells, and then used a laser to excite the semiconductor, generating polaritons. At a critical density, at the easily attainable temperature of 19 degrees Kelvin (about -254 Celsius), the polaritons showed evidence of spontaneous coalescence into a single coherent ground state. The classic phase transition characteristics -- macroscopic polarization and spatial coherence across the entire condensate -- are clearly seen here, and for the first time in solid state.
According to Professor Benoit Deveaud, leader of the research team, condensates at even higher temperatures could perhaps be achieved using other semiconductor materials.
“The magical properties of superfluidity, where matter flows with zero friction, and superconductivity, where a current flows with zero resistance, are quantum effects, and in the Bose-Einstein condensate they are directly brought to our perception,” notes Deveaud. “It is exciting to envision exploring this magic without having to use an incredibly complex machine to get to temperatures just above absolute zero.”
What practical applications will this lead to? “We are still exploring the basic physics of this phenomenon,” says Deveaud. “But just achieving this phase in the solid state is exciting. In the mid 1900s, transistors replaced vacuum lamps, and now most useful devices are made in the solid state,” he explains. “Polaritons, although made with a photon, are really quasi-particles in the solid. It is likely that they can be manipulated much as electrons are – an advance that has led to incredible new technologies such as the CCD chips in digital cameras.”
Mary Parlange | alfa
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences | <urn:uuid:5ef290bf-bdd4-498e-bb1d-fea10231f848> | 3.84375 | 1,613 | Content Listing | Science & Tech. | 26.692141 | 95,519,301 |
- Views 1777
Dear Ruben Carlo Asuncion and Minsoo Lee,
Your excellent January 2017 Asian Development Bank Economics Working Paper Series No.507, Impacts of Sea Level Rise on Economic Growth in Developing Asia, in concluding that shore protection could use up 10% of the GDP of Developing Asian countries, makes the point that shore protection against global sea level rise may be the largest, and the most ignored, cost of runaway climate change.
I have argued this very point in vain for nearly 30 years, but yours is the first systematic discussion I have ever seen of the crippling economic costs of shore protection against global sea level rise!
More than 25 years ago I met with UNDP, GEF, and other international agencies to find out who was helping countries with shore protection against rising sea level, and discovered that NO agency took any programmatic responsibility for the problem, but all were incorrectly sure somebody else must be……..
As a result there is essentially no proactive planning, only disaster responses, asking for immediate aid after existing seawalls fall down and roads, trees, beaches, houses, hospitals, and airports fall into the sea, in order to throw more concrete and rocks into the water, which only postpones the repetition until the next extreme storm event.
When I searched on “shore protection” to find out what the world spends to keep the waves from washing their beaches away, every single hit I got was for “offshore asset protection”: I learned nothing about shore protection, but found long lists of all the money-laundering banks in the world.
Your seawall cost estimate of $6 million per meter height protected per kilometer is close to typical figures of $10-15 million dollars per kilometer for typical sea walls that are 2-3 meters high.
In my view, your long term cost estimates are too low, because they assume sea level will rise at the present rate, when in fact dramatic increases are inevitable if we don’t reverse CO2 increase soon, which can be done at low cost and with great benefits:
The problem with sea walls is 1) they don’t work, and 2) they cost many times more than alternatives that do!
Every single seawall built in an atoll country has collapsed, or soon will, many fell down before they finished building them.
All coastal engineers know that sea walls are inevitably doomed to collapse and repeated rebuilding, because they concentrate erosive forces that wash away all sand in front of them, and then under them, until they fall down, but they think they have no other option. Our methods work like coral reefs do, dissipating wave energy that passes through them without being reflected.
I have worked with local teams on coral reef, sea grass, mangrove, and beach restoration projects in Indonesia, Philippines, Thailand, Malaysia, Viet Nam, and many Pacific Small Island Developing States, including the Marshall Islands, Palau, Vanuatu, Samoa, and Fiji.
Restoring these habitats works far better to protect shores at much lower cost than sea walls do, while providing vast additional economic benefits in ecosystem services like fisheries habitat and ecotourism.
In 2016 in Indonesia we had almost no coral mortality on our properly maintained projects while more than 95% of the corals in nearby reefs died from heat stroke, we grew back a severely eroded beach naturally in just a few months, and socioeconomic studies showed that these projects had turned the poorest villages on their islands into some of the most prosperous because of the huge number of people coming from all over the world to swim in beautiful corals and fishes.
Our methods work rapidly where all other restoration methods fail because only our method causes much higher settlement, growth, survival, and resistance to environmental stress of all forms of life. These results are because only our method directly enhances their natural biochemical energy generating mechanisms.
Adapting to sea level rise need not be as costly as your study indicates when the new state-of-the-art ecosystem restoration measures are considered as an alternative to hard shoreline protection.
The sooner that they are, the sooner we can move forward to much more effective solutions with lower costs and higher benefits.
Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.
Coordinator, Soil Carbon Alliance
Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies
37 Pleasant Street, Cambridge, MA 02139
Tel: (1) 617-864-4226 | <urn:uuid:6a5fc84b-3f1a-495c-a459-28b0203bdd0e> | 2.53125 | 940 | News (Org.) | Science & Tech. | 25.931127 | 95,519,310 |
A recently discovered asteroid plays leapfrog with Earth as they both orbit around the Sun.
Our fair planet has a tiny companion, an asteroid that shares our annual journey around the Sun in a complex dance.
Astronomers recently announced the discovery of 2016 HO3, an asteroid between 40 and 100 meters in size that behaves as Earth's quasi-satellite. Discovered as a faint blip on April 27, 2016, by the Pan-STARRS 1 survey based on Haleakala, Hawai'i, 2016 HO3 occupies an orbit very much like Earth's. Calculations suggest that, though it evaded detection until this year, 2016 HO3 has hung out in Earth's vicinity for a century or so, and will continue to play orbital leapfrog with our world for centuries to come.
2016 HO3's Weird Orbit
“Since 2016 HO3 loops around our planet, but never ventures very far away as we go around the Sun, we refer to it as a quasi-satellite of Earth,” says Paul Chodas (NASA Jet Propulsion Laboratory). “In effect, this small asteroid is caught in a little dance with Earth.”
2016 HO3's orbit takes it alternately sunward and ahead of Earth for six months at a time, then it's slightly farther from the Sun and falls behind us. Its orbit is slightly tilted relative to the ecliptic plane, resulting in a corkscrew twist in the orbit over several decades. Too distant to be considered a true second moon, 2016 HO3's journey takes it as close as 38 times the Earth-Moon distance (9.1 million miles or 0.1 astronomical unit) from our planet, and as far as 100 times the Earth-Moon distance (24 million miles or 0.25 astronomical unit).
Chodas explains that this body doesn't qualify as a "minimoon" of Earth because our planet's gravity is simply too weak to truly capture it. "One easy way to distinguish a captured object from a quasi-satellite is the period of the loop about our planet," he explains. "Captured objects are true satellites of Earth and will loop around with periods as large as a few months, much less than 1 year. Quasi-satellites loop around Earth with periods of almost exactly 1 year."
As an Apollo asteroid, 2016 HO3 joins the small but growing list of objects tracked in a solar orbit near Earth. Asteroid 2003 YN107 was discovered by the LINEAR sky survey about a decade ago, when it followed a similar track, but the rock has since departed our neighborhood. Asteroid 2006 RH120 — the only true minimoon yet discovered — made several distant looping passes of Earth from April 2006 to September 2007 before ejection. It turns out that our Moon does a pretty good job at celestial goaltending, assuring such secondary hopefuls never hang around for long.
Simulations carried out by Mikael Granvik (University of Helsinki, Finland) in 2012 suggest that most "Temporarily Captured Objects" (TCOs) only complete three orbits of the Earth-Moon system before ejection, and only 1% ever impact Earth. (Read Sky & Telescope's September 2015 issue for more info.)
Claims for a tiny, second moon around Earth, dubbed "Lilith," go all the way back to alleged sightings in the 19th century. "Petit's Moon" created a temporary sensation in 1846, until it too proved to be spurious. In modern times, spent boosters from the China's Chang'e 2 and NASA's Apollo 12 lunar missions were temporarily identified as "asteroids" 2010 QW1 and J002E3, respectively. Other objects, such as 3753 Cruithne occupy strange horseshoe-shaped orbits around Earth. Venus also has its own quasi-satellite, designated 2002 VE68.
Hunting Temporary Minimoons
A new generation of all sky surveys could swell the ranks of known TCOs. The enormously successful PanSTARRS project, which currently operates with just one of four proposed telescopes, might one day get its full complement for such a dedicated search. A 2014 study suggests that the Subaru telescope could stand a 90% chance of nabbing a potential TCO after only 5 nights of dedicated scanning of the sky. Then there's the Large Synoptic Sky Survey, (LSST) set to see first light in 2022 — they're working on the primary mirrors now (watch the video below).
The discovery of 2016 HO3 spawns far more questions than it answers: Where did it come from? Did the rock spall off the Moon during an impact, or is it merely an asteroid that wandered too close to Earth? Could 2016 HO3 make the candidate list of possible targets for a future crewed mission to an asteroid? Future discoveries will help put 2016 HO3 into context and help reveal its origin. | <urn:uuid:bf6c5044-e03b-4969-b06b-77e0ad48e900> | 3.453125 | 1,008 | Knowledge Article | Science & Tech. | 53.990757 | 95,519,315 |
Effect of an Exit-Wedge Angle on Pinch-off and Mass Entrainment of Vortex Rings in Air
- 82 Downloads
The effects of exit-wedge angle on evolution, formation, pinch-off, propagation and diffusive mass entrainment of vortex rings in air were studied using digital particle image velocimetry. Vortex rings were generated by passing a solenoid-valve-controlled air jet through a cylindrical nozzle. Experiments were performed over a wide range of exit-wedge angles (10° ≤ α ≤ 90°) of the cylindrical nozzle, initial Reynolds numbers (450 ≤ Re ≤ 4,580) and length-to-diameter ratios (0.9 ≤ L/D ≤ 11) of the air jet. For sharp edges (α ≤ 10°), a secondary ring may emerge at high Reynolds numbers, which tended to distort the vortex ring if ingested into it. For blunt edges (α ≥ 45°), by contrast, stable vortex rings were produced. The formation phase of a vortex ring was found to be closely related to its evolution pattern. An exit-wedge angle of 45° was found to be optimal for rapid pinch-off and faster propagation and better stability of a vortex ring. Diffusive mass entrainment was found to be between 35% and 40% in the early stages of a vortex ring propagation and it gradually increased throughout the course of vortex ring propagation. Entrainment fraction was found to be sensitive to the L/D ratio of the initial jet and decreases when the L/D ratio is increased.
KeywordsVortex ring Evolution Pinch-off Mass entrainment
- 2.Lim, T.T., Nickels, T.B.: Vortex Rings. Fluid Vortices. Kluwer Academic, Norwell, pp. 95–153 (1995)Google Scholar
- 12.Muller, E.A., Didden, N.: Zur erzeugung der zirkulation bei der bildung eines ringwirbels an einer dusenmundung. Stroj. Casop. 31, 363–372 (1980)Google Scholar
- 20.Dziedic, M., Leutheusser, H.J.: An experimental study of viscous vortex rings. Exp. Fluids 21, 315–324 (1996)Google Scholar | <urn:uuid:41d5365d-fd07-4316-9cfa-19bea6087a41> | 2.515625 | 490 | Academic Writing | Science & Tech. | 67.440039 | 95,519,355 |
Synchronization of Sunspot Numbers and Sunspot Areas
- 101 Downloads
Sunspot activity is usually described by either sunspot numbers or sunspot areas. The smoothed monthly mean sunspot numbers (SNs) and the smoothed monthly mean areas (SAs) in the time interval from November 1874 to September 2007 are used to analyze their phase synchronization. Both the linear method (fast Fourier transform) and some nonlinear approaches (continuous wavelet transform, cross-wavelet transform, wavelet coherence, cross-recurrence plot, and line of synchronization) are utilized to show the phase relation between the two series. There is a high level of phase synchronization between SNs and SAs, but the phase synchronization is detected only in their low-frequency components, corresponding to time scales of about 7 to 12 years. Their high-frequency components show a noisy behavior with strong phase mixing. Coherent phase variables should exist only for a frequency band with periodicities around the dominating 11-year cycle for SNs and SAs. There are some small phase differences between them. SNs lag SAs during most of the considered time interval, and they are in general more asynchronous around the minimum and maximum times of a cycle than at the ascending and descending phases.
KeywordsSunspots, statistics Solar cycle, observations
Unable to display preview. Download preview PDF.
- Liu, H.L.: 1996, Statistics Course, Shanghai University of Finance and Economics Press, Shanghai, 202. Google Scholar
- Ponyavin, D.I., Zolotova, N.V.: 2004, In: Stepanov, A.V., Benevolenskaya, E.E., Kosovichev, A.G. (eds.) Multi-wavelength Investigations of Solar Activity, IAU Symp. 223, 141. Google Scholar | <urn:uuid:f0cd67e4-a184-45e7-8556-d0f0fb16adeb> | 2.84375 | 379 | Truncated | Science & Tech. | 43.732076 | 95,519,395 |
Many forms of sulfur are found on Kīlauea Volcano
Edge of the Kīlauea vog plume near Waikoloa Village on the west side of Hawai‘i Island as it is blown by trade winds across the island and toward the Pacific Ocean. For more information on sulfur dioxide emissions and vog, see https://vog.ivhhn.org/. USGS photo by A. Lerner, June 23, 2018.
For many Hawaii residents, interactions with Kīlauea Volcano's eruptions is through vog—a hazy mixture of sulfur dioxide gas and sulfate particles. However, sulfur on Kīlauea is not limited to vog components.
Sulfur is an exceptional element in that its atoms have a range of electron configurations (commonly referred to as oxidation states). This results in spectacularly diverse forms of sulfur, many of which are found on Kīlauea, some of which are described below.
Sulfur dioxide (SO2) and vog: Vog (volcanic air pollution) has impacted the Hawaiian Islands ever since island landmasses rose above the ocean's surface, which allowed volcanic gases to be released directly into the atmosphere.
rises toward the surface, decreasing pressure on the molten rock causes dissolved sulfur and other volatile elements to form various gases. When magma reaches shallow depths, dissolved sulfur primarily forms SO2 gas. Once emitted into the air, SO2 reacts with oxygen, atmospheric moisture, sunlight, and other gases and particles to create a visible haze (vog) that is blown downwind. The levels of vog experienced across the islands is controlled by the amount of SO2 gas released and changing winds.
With Kīlauea's ongoing lower East Rift Zone (LERZ) eruption and continued summit subsidence, SO2 emissions from the volcano have increased substantially—levels are now three to seven times higher than before the current activity began. Most of the SO2 released on the LERZ occurs as lava
is erupted from the active vents
), although some SO2 is also emitted from the lava flows and ocean entry.
High gas emissions from the LERZ, primarily fissure
8, have resulted in increased vog and poor air quality downwind of the active vents. During typical trade winds, vog is carried south and west across the Puna District, then on toward Ka‘ū and along the Kona coast, before being blown farther offshore. During certain wind conditions, vog has reached the summit of Mauna Kea and stretched across the Pacific as far away as Guam, about 6,440 km (4,000 mi) from Kīlauea!
Hydrogen sulfide: When SO2 gas from shallow magma interacts with groundwater, the SO2 dissolves and can be re-emitted as hydrogen sulfide gas (H2
S). This process produces the rotten egg scent noted at hydrothermal features on Kīlauea, such as Sulphur Banks in Hawai‘i Volcanoes National Park, and at steam vents along the volcano's lower East Rift Zone, many of which predate the current LERZ eruption.
Human noses are highly sensitive to H2
S, and most people can detect its rotten egg smell at a level of around one part per billion (ppb). This concentration is about ten thousand times lower than levels considered to be hazardous to health. In fact, our noses are more sensitive than any instruments we use to quantitatively measure H2
Native Sulfur: Sulfur is also stable in its elemental form, known as "native sulfur." This form of sulfur is a yellow crystalline solid that has historically been referred to as "brimstone." At Kīlauea, native sulfur is found at volcanic fumaroles
, such as Sulphur Banks, where both SO2 and H2
S gases are emitted.
Native sulfur, formed from a chemical reaction (SO2 + 2H2
S = 3S + 2H2
O), is stable in solid form only at relatively low volcanic temperatures of less than 115 degrees Celsius (about 240 degrees Fahrenheit). Above this temperature, sulfur melts, forming a vivid orange liquid. At hotter temperatures (near 200 degrees C, or about 390 degrees F), molten sulfur turns dramatic shades of red. If temperatures approach 450 degrees C (840 degrees F) and atmospheric oxygen is present, native sulfur burns, forming sulfur dioxide (S + O2 = SO2).
Continued degassing from fumaroles at fissures on Kīlauea Volcano's lower East Rift Zone produce native sulfur crystals when sulfur dioxide and hydrogen sulfide gases react and cool upon reaching the surface. The delicate sulfur crystals are 5–15 mm (0.2–0.6 in) long. USGS photos by A. Lerner, 2018.
Sulfur dioxide (along with sulfate particles in vog), hydrogen sulfide, and native sulfur all form at both Kīlauea Volcano's lower East Rift Zone and summit depending on vent
temperatures and how much the gases interact with groundwater. Additionally, sulfur binds with many other elements to form organic and inorganic gases and minerals, which are beyond the scope of today's Volcano Watch.
So, while vog and SO2 gas emissions have been on our minds for many years, and especially since May 3, 2018, it's worth noting that they are just some of the many forms of sulfur at Kīlauea.
Volcano Activity Update
On Kīlauea Volcano's lower East Rift Zone, lava
continues to erupt primarily from fissure
8. As of July 13, the channelized lava flow
west of Kapoho Crater was the main ocean entry at the southern edge of the flow, and despite no visible surface connection to the fissure 8 channel, lava was oozing out at several points on the 6 km (3.7 mi) wide flow front into the ocean. Sulfur dioxide emissions from the active fissure remains high. Residents in the lower Puna District of Hawai‘i Island should stay informed and heed Hawai‘i County Civil Defense closures, warnings, and messages (http://www.hawaiicounty.gov/active-alerts).
At Kīlauea's summit, collapse explosions occurred during the past week, producing ash
-poor steam plumes less than a few hundred meters (1,000 ft) above the ground. The energy released by these events were equivalent to earthquakes
of magnitudes 5.1 to 5.4. Inward slumping of the rim and walls of Halema‘uma‘u continues in response to ongoing subsidence at the summit, resulting in frequent felt earthquakes.
At Mauna Loa, HVO seismic and deformation
monitoring networks have recorded near background levels of seismicity
and ground motion for at least the last six months. These observations indicate that the volcano is no longer at an elevated level of activity. Accordingly, HVO dropped the Mauna Loa alert level to NORMAL and the aviation color code to GREEN on June 21, 2018. HVO continues to monitor the volcano closely and will report any significant changes. | <urn:uuid:8ec48e8e-9e10-4f5d-a613-a1740ec40a08> | 4.09375 | 1,501 | Knowledge Article | Science & Tech. | 45.956176 | 95,519,441 |
Learn to program with the world's leading programming language
Ultra–versatile C# is the most popular programming language in the world, and this book is your ultimate beginner's guide to programming using C# 7 and Visual Studio 2017. Even if you have never written a line of code, these expert Wrox authors will walk you through everything you need to know. You'll learn about variables, flow control, and object–oriented programming, then move into web and Windows programming as well as databases and XML. Exclusive "Try It Out" sections in the introductory chapters offer step–by–step instruction, enabling you to write your own usable code and build smarter, faster apps.
Beginning C# 7 Programming with Visual Studio 2017:
Wrox Beginning guides are crafted to make learning programming languages and technologies easier than you think, providing a structured, tutorial format that will guide you through all the techniques involved.
INTRODUCTION xxi I: THE C# LANGUAGE
CHAPTER 1: INTRODUCING C# 3
CHAPTER 2: WRITING A C# PROGRAM 15
CHAPTER 3: VARIABLES AND EXPRESSIONS 33
CHAPTER 4: FLOW CONTROL 59
CHAPTER 5: MORE ABOUT VARIABLES 83
CHAPTER 6: FUNCTIONS 117
CHAPTER 7: DEBUGGING AND ERROR HANDLING 149
CHAPTER 8: INTRODUCTION TO OBJECT–ORIENTED PROGRAMMING 179
CHAPTER 9: DEFINING CLASSES 203
CHAPTER 10: DEFINING CLASS MEMBERS 233
CHAPTER 11: COLLECTIONS, COMPARISONS, AND CONVERSIONS 269
CHAPTER 12: GENERICS 319
CHAPTER 13: ADDITIONAL C# TECHNIQUES 359PROGRAMMING
CHAPTER 14: BASIC DESKTOP PROGRAMMING 425
CHAPTER 15: ADVANCED DESKTOP PROGRAMMING 479PROGRAMMING
CHAPTER 16: BASIC CLOUD PROGRAMMING 533
CHAPTER 17: ADVANCED CLOUD PROGRAMMING AND DEPLOYMENT 559
CHAPTER 18: .NET STANDARD AND .NET CORE 579
CHAPTER 19: ASP.NET AND ASP.NET CORE 609
CHAPTER 20: FILES 641
CHAPTER 21: XML AND JSON 673
CHAPTER 22: LINQ 697
CHAPTER 23: DATABASES 731PART V: ADDITIONAL TECHNIQUES
CHAPTER 24: WINDOWS COMMUNICATION FOUNDATION 761
CHAPTER 25: UNIVERSAL APPS 793
APPENDIX: EXERCISE SOLUTIONS 821
About the authors
Benjamin Perkins is a Sr. Escalation Engineer at Microsoft. His experience includes designing, developing, deploying, administering, and managing enterprise–level IT solutions.
Jacob Vibe Hammer helps develop solutions for the health care industry as a Senior Software Engineer at Systematic in Denmark. He has co–authored a number of .NET books and works with numerous Microsoft technologies.
Jon D. Reid is a Product Solution Manager in Research and Development at IFS AB, specializing in Field Service Management using C# and .NET.
Visit us at wrox.com for free code samples.
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Overview of Fishes and Fish Assemblages
The mass of women and men who study ecology of fishes do indeed “lead lives of quiet desperation”—but not the world-weary despair of Thoreau. Most, like Reighard, exist in a state of chronic tension between deep satisfaction with their work and frustration from the fact that fishes are so complex that no individual can understand all that could be known about their ecology, even if there were no “university (or agency or museum) duties.” There are so many kinds of fishes, occupying such diverse habitats, evolving in such complex ways, and with such complicated ecological traits, that a total synthesis of “understanding fishes” will always elude ichthyologists and ecologists. This book is an attempt to synthesize what is known about ecology of freshwater fishes, to make sense of their distribution and abundance across the Earth, their membership in local assemblages, and the ways they, in turn, influence the ecosystems where they live. These are some of the “patterns in freshwater fish ecology” addressed in this book.
KeywordsFish Species Fish Assemblage Stream Fish East African Rift Vertebrate Group
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posted by tatiana
How would you make a serial dilution if you have 100mM of X
These are the values of X that she gave.
These are the values of X in the serial dilution. If you could help me out by start me off because I am kind of confused with the question. Help is appreciated.
I am confused by the table and what you want. Parhaps another tutor will be able to help unless you wish to clarify the question. | <urn:uuid:42ccb715-c6fd-4eab-8be0-040ed88506f1> | 2.53125 | 99 | Q&A Forum | Science & Tech. | 73.285285 | 95,519,459 |
In Chapter 7 we had solved the Schrödinger equation for the linear harmonic oscillator problem. In this chapter we will use Dirac’s bra and ket algebra to solve the same problem. Although the final results are the same, the analysis using bra and ket algebra is extremely elegant; it allows us to determine the various expectation values and also explicit expressions for the wave functions with considerable ease. The time evolution of the coherent state can also be studied in a very straightforward manner. For all this, we feel that the use of the operator algebra in solving the harmonic oscillator problem should be understood right in the beginning of the quantum mechanics course.
This is a preview of subscription content, log in to check access. | <urn:uuid:8966e0a2-ce78-4241-920d-8a00195c14d0> | 3.296875 | 146 | Truncated | Science & Tech. | 38.13351 | 95,519,466 |
It has studied the stratosphere of the Arctic and the Antarctic, it rose into the stratosphere over South America, Australia and soared over the Indian Ocean. As a result, the scientists, who are staff at the Central Upper-Air Observatory, have obtained a unique mass of data on the composition of the atmosphere at different altitudes. Analyzing these data, it is possible in the end to significantly raise the reliability of model calculations of both the current and future climates of Earth. The scientists are helped in their work by the International Science and Technology Centre.
Devices operating in automatic mode on board the aircraft enable data to be obtained on the composition of the stratosphere in different regions of the globe. Among them there are two devices, designed and built at the Central Upper-Air Observatory. One of them helps to determine the concentration of water vapours, even at a temperature of minus 90 degrees, when its content in the air is determined in millionths of shares of mass. The other helps to capture incredibly small concentrations of ozone, using a special, high-sensitive chemical reaction.
Project Manager Vladimir Yushkov, a Candidate of Physics and Mathematics agreed to explain why this information is necessary. “Global climate is that very instance where, without the present we can learn nothing at all about the future. And what is the “present” from the point of view of climate science? It is primarily precise knowledge of the condition of the environment. The more precise and voluminous the information on the condition of the atmosphere and the ocean, on the mechanisms of the formation of their temperature and dynamic regime and on solar activity, the more reliable the model calculations will be of future climatic changes”.
Unfortunately, it is rather difficult to capture climate change in accordance with data from observations conducted on the Earth’s surface. However, there are altitudes in the Earth’s atmosphere where even slight changes in the temperature of the Earth’s surface can bring about considerable temperature responses that can be measured to a fair degree of reliability. These are the stratospheric altitudes. But it is not enough to just know the temperatures of different layers of the stratosphere. One also has to know the composition of the stratospheric gases that influence the temperature regime. Primarily these are natural greenhouse gases, ozone and water vapour, the content of which is subjected to natural and anthropogenic changes. It is their concentration that was measured by the devices on board the high-altitude aircraft M-55 “Geophysica”.
However, it is not enough to have simply obtained these data. You also have to analyze them as it represents considerable interest for the study of exchange processes between the troposphere and the stratosphere, for identifying the mechanism of the chemical transfer of chemically active pollution to the ozone layer that reacts sensitively to them. The project of the Central Upper-Air Observatory, “The study of stratosphere-troposphere exchange” is devoted namely to this problem.
This problem really is interesting as, put very simply, in the troposphere, that is at altitudes of up to about 12km above the surface of the Earth, the temperature falls with a rise in altitude; the higher you go, the colder it becomes. And further still from the Earth, in the Stratosphere, everything is the reverse: the temperature rises the higher you go. The responsible party for this is the so-called ozone layer, the thickness of which depends on many things, including anthropogenic factors, of which one of the most important are chlorine- and bromide-containing compounds, the particularly woeful, well-known freons and certain other coolants. But how do they enter the altitude of the stratosphere from the surface, if we know that the troposphere and the stratosphere barely mix and exchange of chemical compounds between them is difficult?
The survey work of the Central Upper-Air Observatory will help to find an answer to this question. On the basis of data on the concentration of water vapours and ozone at different altitudes of the stratosphere over different sectors of the globe (in the Tropics and the polar latitudes), the researchers are developing models with which it will be possible, figuratively speaking, to “find the flow”. In other words, receiving new data on the mechanism of the distribution of greenhouse gases, their vertical and horizontal transfer. The scientists are confident that this research will significantly improve the model of the Earth’s climate and will produce predictions on its change that are more reliable.
Andrew Vakhliaev | alfa
New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz
Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
17.07.2018 | Power and Electrical Engineering | <urn:uuid:ae203a0b-5830-4120-b0b4-897e1b3af82d> | 3.71875 | 1,564 | Content Listing | Science & Tech. | 32.630372 | 95,519,473 |
Sptd.84, image statistics is no longer collected.Bugs fixed: bsod in DT adapter with Verifier; Minor fixes.Daemon Tools Lite.40.1 (2011).Daemon Tools Lite.40.1 (2011).Daemon Tools Lite 6 (2015) PC RePack by KpoJIuK.Daemon Tools Lite.torrent.Daemon Tools Lite 7 / Windows.#25 I'm gonna.#22 YouRead more
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23 Molecular evidence strongly suggest that at least two species of the o2micro smart card bus reader stick insect genus Timema have used only asexual (parthenogenetic) reproduction for one million years, the longest period known for any insect.
The solidworks 64 bit crack bacterial spores are also called endospores.Fragmentation is seen in many organisms, such as animals (some annelid worms and starfish fungi, and plants.5 Spore formation Main article: Sporogenesis Many multicellular organisms form spores during their biological life cycle in a process called sporogenesis.Fragmentation, fragmentation is another mode of asexual reproduction.However, mitotic sporogenesis is an exception and most spores, such as those of plants, most Basidiomycota, and many algae, are produced by meiosis.
Spore formation also occurs in bacteria such as Clostridium and Bacillus.
Capensis can reproduce asexually through a process called thelytoky.
8 In both cases, the sharks had reached sexual maturity in captivity in the absence of males, and in both cases the offspring were shown to be genetically identical to the mothers.
CBC News - Technology Science.
Another constraint on switching from sexual to asexual reproduction would be the concomitant loss of meiosis and the protective recombinational repair of DNA damage afforded as one function of meiosis.
Budding, back to Top, it is seen in certain fungi and multicellular animals.
Constraints on the evolution of asexual reproduction.This is called budding.Parthenogenesis Edit Main article: Parthenogenesis Parthenogenesis is a form of agamogenesis in which an unfertilized egg develops into a new individual.However, both events (spore formation and fertilization) are necessary to complete sexual reproduction in the plant life cycle.There are many types of asexual reproduction, all producing individuals that are genetically identical to the parent.Male apomixis can occur in rare cases, such as the Saharan cypress where the genetic material of the embryo are derived entirely from pollen.There is evidence to suggest that asexual reproduction has allowed the animals to evolve new proteins through the Meselson effect that have allowed them to survive better in periods of dehydration.Organisms which belong to the fungi group produce fulton harris representation theory pdf spores within a sac-like structure called sporangium. | <urn:uuid:9ac4de1c-8751-4937-8096-616b1732de23> | 2.5625 | 644 | Spam / Ads | Science & Tech. | 32.231749 | 95,519,480 |
Dr. Alan Rabinowitz, director of Science and Exploration Programs at the Wildlife Conservation Society, said that genetic corridors, where tigers can travel with less risk of inbreeding, are crucial for their long-term survival in Asia. The proposed corridor includes extensive areas of Bhutan, northeast India, Myanmar, Thailand and Malaysia, along with potential connectivity to Laos, Cambodia and Vietnam. It has already been endorsed by the new King of Bhutan, his Majesty Jigme Khesar Namgyel Wangchuck, who requested other heads of state to support similar efforts.
Rabinowitz, the co-director of Tigers Forever – a WCS/Panthera Foundation collaboration – made a clear request at the recent UN meeting that he and other tiger conservationists would be seeking additional approval and assistance from other heads of state.
“While Asia’s economic tigers are on the rise, wild tigers in Asia are in decline,” Rabinowitz said. “Much like the call-out for global agreements on banning tiger parts in trade, a similar cross-border initiative for genetic corridors is key to the survival of the tiger. Tiger range states need to work together, as tigers do not observe political borders nor do they require a visa or passport to travel where habitat and prey remain.”
Rabinowitz said corridors did not have to be pristine parkland but could in fact include agricultural areas, ranches, and other multi-use landscapes – just as long as tigers could use them to travel between wilderness areas.
“We’re not asking countries to set aside new parks to make this corridor a success,” Rabinowitz said. “This is more about changing regional zoning in tiger range states to allow tigers to move more freely between areas of good habitat.”
Twelve of 13 tiger range states were represented by ambassadors and delegates at the UN meeting. Other organizations working to save the tiger came out in force, including representatives from the National Fish and Wildlife Foundation’s Save the Tiger Fund, Conservation International, Rare Conservation, and the U.S. Fish and Wildlife Service. Actress Glenn Close was in attendance and spoke at the event.
Tigers Forever was launched in 2006 as a bold plan to grow tiger numbers by 50 percent at key sites over a ten year period. This increase is being achieved through collecting baseline data and long-term scientific monitoring of tigers, their prey, and their threats, to ensure that the goals can be met. Key threats are the direct killing of tigers, poaching of tiger prey, and habitat loss – all of which are being targeted and mitigated.
The meeting, hosted by UN Under-Secretary General Ambassador Joseph Verner Reed, was opened with a welcoming statement by Secretary-General Ban Ki-moon and marked the first time government, business, and conservationists have come together at the United Nations for the sake of conserving a single iconic species.
The Wildlife Conservation Society saves wildlife and wild places worldwide. We do so through science, global conservation, education and the management of the world's largest system of urban wildlife parks, led by the flagship Bronx Zoo. Together these activities change attitudes towards nature and help people imagine wildlife and humans living in harmony. WCS is committed to this mission because it is essential to the integrity of life on Earth. www.wcs.org
Panthera saves in situ populations of the world’s 36 species of wild cats and the landscapes they inhabit in all regions of the world. We achieve this by collaborating with, supporting and fostering the world’s leading wild felid conservationists in conducting rigorous scientific research, planning and implementing conservation actions, and working with local, national and international stakeholders to advance wild cat conservation. Panthera believes that large, contiguous populations of wild cats are important indicators of intact functioning ecosystems, and that the focused protection of wild cats furthers the conservation of a large number of other species present in those ecosystems.
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
18.07.2018 | Materials Sciences
18.07.2018 | Life Sciences
18.07.2018 | Health and Medicine | <urn:uuid:0def78ae-1dc0-4760-a8ae-a817f32aa8dc> | 3.15625 | 1,460 | Content Listing | Science & Tech. | 37.143478 | 95,519,489 |
Mars may have liquid water close to its surface, according to new data from NASA’s Curiosity rover which raises the chance of finding life on the red planet. Researchers have long known that there was water in the form of ice on Mars. Now, new research on data from Curiosity shows that it is possible that there is liquid water close to the surface of Mars.
— Curiosity Rover (@MarsCuriosity) April 13, 2015
The explanation is that the substance perchlorate has been found in the soil, which lowers the freezing point so the water does not freeze into ice, but is liquid and present in very salty salt water – a brine. “We have discovered the substance calcium perchlorate in the soil and, under the right conditions, it absorbs water vapour from the atmosphere,” said Morten Bo Madsen, associate professor and head of the Mars Group at the Niels Bohr Institute at the University of Copenhagen.
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“Our measurements from the Curiosity rover’s weather monitoring station show that these conditions exist at night and just after sunrise in the winter. Based on measurements of humidity and the temperature at a height of 1.6 meters and at the surface of the planet, we can estimate the amount of water that is absorbed,” said Madsen.
Madsen said when night falls, some of the water vapour in the atmosphere condenses on the planet surface as frost, but calcium perchlorate is very absorbent and it forms a brine with the water, so the freezing point is lowered and the frost can turn into a liquid.
“The soil is porous, so what we are seeing is that the water seeps down through the soil. Over time, other salts may also dissolve in the soil and now that they are liquid, they can move and precipitate elsewhere under the surface,” said Madsen. Observations by the Mars probe’s stereo camera have previously shown areas characteristic of old riverbed that clearly show that a long time ago there was flowing, running water with a depth of up to one meter.
Now the new close-up images taken by the rover all the way en route to Mount Sharp show that there are expanses of sedimentary deposits, lying as ‘plates’ one above the other and leaning a bit toward Mount Sharp. “These kind of deposits are formed when large amounts of water flow down the slopes of the crater and these streams of
water meet the stagnant water in the form of a lake. When the stream meets the surface, the solid material carried by the stream falls down and is deposited in the lake just at the lakeshore.
Gradually, a slightly inclined slope is built up just below the surface of the water and traces of such slanting deposits were found during the entire trip to Mount Sharp. Very fine-grained sediments, which slowly fell down through the water, were deposited right at the very bottom of the crater lake. “The sediment plates on the bottom are level, so
everything indicates that the entire Gale Crater may have been a large lake,” Madsen added.
The research was published in the scientific journal Nature. | <urn:uuid:44c526c8-5476-47d7-8d52-83fee1834682> | 3.9375 | 732 | News Article | Science & Tech. | 38.66607 | 95,519,500 |
It’s like Florida’s version of The Blob. Slow moving glops of toxic algae in the northeast Gulf of Mexico are killing sea turtles, sharks and fish, and threatening the waters and beaches that fuel the region’s economy.
Known as “red tide,” this particular strain called Karenia brevis is present nearly every year off Florida, but large blooms can be particularly devastating. Right now, the algae is collecting in an area about 60 miles wide and 100 miles long, about 5 to 15 miles off St. Petersburg in the south and stretching north to Florida’s Big Bend, where the peninsula ends and the Panhandle begins.
Fishermen who make a living off the state’s northwest coast are reporting fish kills and reddish water.
“It boils up in the propeller wash like boiled red Georgia clay. It’s spooky,” said Clearwater fisherman Brad Gorst as he steered the charter fishing boat Gulfstream 2 in waters near Honeymoon Island, where dead fish recently washed ashore.
Red tide kills fish, manatees and other marine life by releasing a toxin that paralyzes their central nervous system. The algae also foul beaches and can be harmful to people who inhale the algae’s toxins when winds blow onshore or by crashing waves, particularly those with asthma and other respiratory ailments.
In 2005, a strong red tide killed reefs, made beaches stinky and caused millions in economic damage. A weaker red tide in 2013 killed 276 manatees, state records show, after infecting the grasses eaten by the endangered creatures.
“This red tide … will likely cause considerable damage to our local fisheries and our tourist economy over the next few months,” said Heyward Mathews, an emeritus professor of oceanography at St. Petersburg College who has studied the issue for decades.
Despite years of study, there is nothing anyone has been able to do about it. In the 1950s, wildlife officials tried killing the red tide algae by dumping copper sulfate on it, which made the problem worse in some ways. But some researchers are working to change that.
Predicting when red tides are going to be especially bad can help fishermen and beach businesses prepare.
Right now, much of the information comes from satellite images, which are often obscured by clouds.
“In this particular red tide, we got a good image on July 23 – then we went weeks without another image,” said University of South Florida ocean scientist Robert Weisberg.
Weisberg is one among a team of researchers developing a prediction model based on ocean currents data, rather than satellite images.
The prediction model tracks the currents that bring natural nutrients like phytoplankton the red tide needs to gain a foothold. Unlike other red tide species, Karenia brevis is not believed to be caused by man-made pollution such as agricultural runoff, and historical accounts of what is believed to be the same red tide date back to the 1700s.
Using his method, Weisberg in March predicted the current late summer bloom that is now causing so much worry. It allowed state officials to issue a warning July 25.
While the project recently received “rapid response” money from the National Oceanic and Atmospheric Administration to send a data-collecting robotic glider into the bloom, future funding for this work is in doubt.
Weisberg said the team is still trying to develop a model that can look further into the future.
But the tides often start far offshore, where gathering data and images can be a time-consuming, expensive undertaking. The Florida Fish and Wildlife Commission has tried to stem this data gap by giving fishermen sampling jars to take out to sea with them.
While a good stopgap, Republican U.S. Rep. David Jolly, who represents St. Petersburg, has called for more NOAA funding to help prepare for future events.
“Using fishermen to collect samples clearly shows we have a research gap,” Jolly said. “The more we learn about it, the more we can prevent a spread and protect our shoreline.”
NOAA spokesman Ben Sherman said the president’s 2015 budget does ask for a $6 million increase for research related to red tide forecasting, including the Gulf of Mexico, but Congress still has to approve it.
Fishermen say a better warning system could help save time and money.
“If we had more of a head’s up we could plan out where we would go fish,” said Mike Colby, captain of the Double Hook fishing vessel in Clearwater. | <urn:uuid:54f3799a-53fd-4b69-a748-e45433b64cfc> | 3.1875 | 961 | News Article | Science & Tech. | 47.657173 | 95,519,503 |
Plasma antennas are the subject of intense theoretical and experimental studies. One of the types of plasma antennas is the so-called loop antenna, which is a curved gas discharge tube filled with cold plasma. An angle and curvature radius of the tube significantly affects radiation pattern and intensity of this antenna. In this paper, we theoretically study the model of the plasma loop antenna, which is a flat layer of plasma on a metal substrate with a small bending angle. Radiation patterns and energy transformation coefficients of the surface wave have been calculated for various parameters of the problem. It has been shown that up to 10 % of the surface wave energy is converted into radiation at a bending angle of 0.3 rad. Radiation patterns have one petal with a maximum at acute angles.
loop antennas, cold plasma, beam pattern
"Osoblyvosti vykorystannia plaskoho sharu plazmy z malym vyhynom v antennykh systemakh" [Features of using the flat plasma layer with small bending angle in antenna systems],
Scientific Works of Kharkiv National Air Force University, | <urn:uuid:6c64b8cd-5075-4f60-b627-91256c4c4194> | 2.859375 | 228 | Knowledge Article | Science & Tech. | 29.451304 | 95,519,535 |
Mary divides a circle into sectors. The central angles of these sectors, measured in degrees, are all integers and they form an arithmetic sequence. What is the degree measure of the smallest possible sector angle?
This problem is copyrighted by the American Mathematics Competitions.
Instructions for entering answers:
For questions or comments, please email firstname.lastname@example.org. | <urn:uuid:5cd2b49f-0423-421f-9d43-d7d15ff5814e> | 2.78125 | 77 | Customer Support | Science & Tech. | 30.683621 | 95,519,565 |
The CARMENES instrument is a pair of high-resolution (R⪆80,000) spectrographs covering the wavelength range from 0.52 to 1.71 μm, optimized for precise radial velocity measurements. It was installed and commissioned at the 3.5m telescope of the Calar Alto observatory in Southern Spain in 2015. The first large science program of CARMENES is a survey of ~ 300 M dwarfs, which started on Jan 1, 2016. We present an overview of all subsystems of CARMENES (front end, fiber system, visible-light spectrograph, near-infrared spectrograph, calibration units, etalons, facility control, interlock system, instrument control system, data reduction pipeline, data flow, and archive), and give an overview of the assembly, integration, verification, and commissioning phases of the project. We show initial results and discuss further plans for the scientific use of CARMENES.
The main goal of the CARMENES instrument is to perform high-accuracy measurements of stellar radial velocities (1 m/s) with long-term stability. CARMENES is installed at the 3.5 m telescope in the Calar Alto Observatory (Spain) and it is equipped with two spectrographs covering from the visible to the near-infrared. We present the software packages that are included in the instrument control layer. The coordination and management of CARMENES is handled by the Instrument Control System (ICS), which is responsible for carrying out the operations of the different subsystems providing a tool to operate the instrument in an integrated manner from low to high user interaction level. The ICS interacts with the following subsystems: the near-infrared (NIR) and visible channels, composed by the detectors and exposure meters; the calibration units; the environment sensors; the front-end electronics; the acquisition and guiding module; the interfaces with telescope and dome; and, finally, the software subsystems for operational scheduling of tasks, data processing, and data archiving. The software control framework and all the software modules and layers for the different subsystems contribute to maximize the scientific return of the instrument. The CARMENES workflow covers from the translation of the survey strategy into a detailed schedule to the data processing routines that extract radial velocity data from the observed targets. The control suite is integrated in the instrument since the end of 2015.
Astronomical observatories are complex systems requiring the integration of numerous devices into a common platform. We are presenting here the firsts steps to integrate the popular Robotic Operating System (ROS) into the control of a fully autonomous observatory. The observatory is also equipped with a decision-making procedure that can automatically react to a changing environment (like weather events). The results obtained so far have shown that the automation of a small observatory can be greatly simplified when using ROS, as well as robust, with the implementation of our decision-making algorithms.
CARMENES, the new Calar Alto spectrograph especially built for radial-velocity surveys of exoearths around M dwarfs, is a very complicated system. For reaching the goal of 1 m/s radial-velocity accuracy, it is appropriate not only to monitor stars with the best observing procedure, but to monitor also the parameters of the CARMENES subsystems and safely store all the engineer and science data. Here we describe the CARMENES data flow from the different subsystems, through the instrument control system and pipeline, to the virtual-observatory data server and astronomers.
The Exoplanet Characterisation Observatory (EChO) was an ESA mission candidate competing for a launch opportunity within the M3 call. Its main aim was to carry out research on the physics and chemistry of atmospheres of transiting planets. This requires the observation of two types of events: primary and secondary eclipses. The events of each exoplanet have to be observed several times in order to obtain measurements with adequate Signal-to-Noise Ratio. Furthermore, several criteria must be considered to perform an observation, among which we can highlight the exoplanet visibility, its event duration, and the avoidance of overlapping with other tasks. It is important to emphasize that, since the communications for transferring data from ground stations to the spacecraft are restricted, it is necessary to compute a long-term plan of observations in order to provide autonomy to the observatory. Thus, a suitable mission plan will increase the efficiency of telescope operation, and this will result in a raise of the scientific return and a reduction of operational costs. Obtaining a long-term mission plan becomes unaffordable for human planners due to the complexity of computing the large amount of possible combinations for finding a near-optimal solution. In this contribution we present a long-term mission planning tool based on Genetic Algorithms, which are focused on solving optimization problems such as the planning of several tasks. Specifically, the proposed tool finds a solution that highly optimizes the objectives defined, which are based on the maximization of the time spent on scientific observations and the scientific return (e.g., the coverage of the mission survey). The results obtained on the large experimental set up support that the proposed scheduler technology is robust and can function in a variety of scenarios, offering a competitive performance which does not depend on the collection of objects to be observed. Finally, it is noteworthy that the conducted experiments allow us to size some aspects of the mission with the aim of guaranteeing its feasibility.
The Cherenkov Telescope Array (CTA) project will be the next generation ground-based very high energy gamma-ray instrument. The success of the precursor projects (i.e., HESS, MAGIC, VERITAS) motivated the construction of this large infrastructure that is included in the roadmap of the ESFRI projects since 2008. CTA is planned to start the construction phase in 2015 and will consist of two arrays of Cherenkov telescopes operated as a proposal-driven open observatory. Two sites are foreseen at the southern and northern hemispheres. The CTA observatory will handle several observation modes and will have to operate tens of telescopes with a highly efficient and reliable control. Thus, the CTA planning tool is a key element in the control layer for the optimization of the observatory time. The main purpose of the scheduler for CTA is the allocation of multiple tasks to one single array or to multiple sub-arrays of telescopes, while maximizing the scientific return of the facility and minimizing the operational costs. The scheduler considers long- and short-term varying conditions to optimize the prioritization of tasks. A short-term scheduler provides the system with the capability to adapt, in almost real-time, the selected task to the varying execution constraints (i.e., Targets of Opportunity, health or status of the system components, environment conditions). The scheduling procedure ensures that long-term planning decisions are correctly transferred to the short-term prioritization process for a suitable selection of the next task to execute on the array. In this contribution we present the constraints to CTA task scheduling that helped classifying it as a Flexible Job-Shop Problem case and finding its optimal solution based on Artificial Intelligence techniques. We describe the scheduler prototype that uses a Guarded Discrete Stochastic Neural Network (GDSN), for an easy representation of the possible long- and short-term planning solutions, and Constraint Propagation techniques. A simulation platform, an analysis tool and different test case scenarios for CTA were developed to test the performance of the scheduler and are also described.
The main goal of the CARMENES instrument is to perform high-accuracy measurements of stellar radial velocities (1m/s) with long-term stability. CARMENES will be installed in 2015 at the 3.5 m telescope in the Calar Alto Observatory (Spain) and it will be equipped with two spectrographs covering from the visible to the near-infrared. It will make use of its near-IR capabilities to observe late-type stars, whose peak of the spectral energy distribution falls in the relevant wavelength interval. The technology needed to develop this instrument represents a challenge at all levels. We present two software packages that play a key role in the control layer for an efficient operation of the instrument: the Instrument Control System
(ICS) and the Operational Scheduler. The coordination and management of CARMENES is handled by the ICS, which is responsible for carrying out the operations of the different subsystems providing a tool to operate the instrument in an integrated manner from low to high user interaction level. The ICS interacts with the following subsystems: the near-IR and visible channels, composed by the detectors and exposure meters; the calibration units; the environment sensors; the front-end electronics; the acquisition and guiding module; the interfaces with telescope and dome; and, finally, the software subsystems for operational scheduling of tasks, data processing, and data archiving. We describe the ICS software design, which implements the CARMENES operational design and is planned to be integrated in the instrument by the end of 2014. The CARMENES operational scheduler is the second key element in the control layer described in this contribution. It is the main actor in the translation of the survey strategy into a detailed schedule for the achievement of the optimization goals. The scheduler is based on Artificial Intelligence techniques and computes the survey planning by combining the static constraints that are known a priori (i.e., target visibility, sky background, required time sampling coverage) and the dynamic change of the system conditions (i.e., weather, system conditions). Off-line and on-line strategies are integrated into a single tool for a suitable transfer of the target prioritization made by the science team to the real-time schedule that will be used by the instrument operators. A suitable solution will be expected to increase the efficiency of telescope operations, which will represent an important benefit in terms of scientific return and operational costs. We present the operational scheduling tool designed for CARMENES, which is based on two algorithms combining a global and a local search: Genetic Algorithms and Hill Climbing astronomy-based heuristics, respectively. The algorithm explores a large amount of potential solutions from the vast search space and is able to identify the most efficient ones. A planning solution is considered efficient when it optimizes the objectives defined, which, in our case, are related to the reduction of the time that the telescope is not in use and the maximization of the scientific return, measured in terms of the time coverage of each target in the survey. We present the results obtained using different test cases.
This paper gives an overview of the CARMENES instrument and of the survey that will be carried out with it
during the first years of operation. CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths
with Near-infrared and optical Echelle Spectrographs) is a next-generation radial-velocity instrument
under construction for the 3.5m telescope at the Calar Alto Observatory by a consortium of eleven Spanish
and German institutions. The scientific goal of the project is conducting a 600-night exoplanet survey targeting
~ 300 M dwarfs with the completed instrument.
The CARMENES instrument consists of two separate echelle spectrographs covering the wavelength range
from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by fibers from the Cassegrain focus of the telescope.
The spectrographs are housed in vacuum tanks providing the temperature-stabilized environments necessary to
enable a 1 m/s radial velocity precision employing a simultaneous calibration with an emission-line lamp or with
a Fabry-Perot etalon. For mid-M to late-M spectral types, the wavelength range around 1.0 μm (Y band) is the
most important wavelength region for radial velocity work. Therefore, the efficiency of CARMENES has been
optimized in this range.
The CARMENES instrument consists of two spectrographs, one equipped with a 4k x 4k pixel CCD for
the range 0.55 - 1.05 μm, and one with two 2k x 2k pixel HgCdTe detectors for the range from 0.95 - 1.7μm.
Each spectrograph will be coupled to the 3.5m telescope with two optical fibers, one for the target, and one
for calibration light. The front end contains a dichroic beam splitter and an atmospheric dispersion corrector,
to feed the light into the fibers leading to the spectrographs. Guiding is performed with a separate camera;
on-axis as well as off-axis guiding modes are implemented. Fibers with octagonal cross-section are employed to
ensure good stability of the output in the presence of residual guiding errors. The fibers are continually actuated
to reduce modal noise. The spectrographs are mounted on benches inside vacuum tanks located in the coud´e
laboratory of the 3.5m dome. Each vacuum tank is equipped with a temperature stabilization system capable
of keeping the temperature constant to within ±0.01°C over 24 hours. The visible-light spectrograph will be
operated near room temperature, while the near-IR spectrograph will be cooled to ~ 140 K.
The CARMENES instrument passed its final design review in February 2013. The MAIV phase is currently
ongoing. First tests at the telescope are scheduled for early 2015. Completion of the full instrument is planned
for the fall of 2015. At least 600 useable nights have been allocated at the Calar Alto 3.5m Telescope for the
CARMENES survey in the time frame until 2018.
A data base of M stars (dubbed CARMENCITA) has been compiled from which the CARMENES sample can
be selected. CARMENCITA contains information on all relevant properties of the potential targets. Dedicated imaging, photometric, and spectroscopic observations are underway to provide crucial data on these stars that
are not available in the literature. | <urn:uuid:2ee7ee94-ad06-49d0-b0ee-2da3f15b5bd8> | 2.515625 | 2,929 | Content Listing | Science & Tech. | 30.43677 | 95,519,576 |
Bildtext får vara max två rader text. Hela texten ska högerjusteras om den bara ska innehålla fotobyline! Photo: B. Christensen/Azote
System collapse and resilience
In October 2017 many were alarmed when researchers reported an apparent collapse in insect populations in Germany. The researchers found that the biomass of flying insects in protected areas had fallen a remarkable 77% over the past nearly three decades. They warned of an ‘ecological Armageddon’. “If we lose the insects then everything is going to collapse,” they said.
‘Collapse’ is an evocative word. It conjures dark images failure, disorder, and loss, and it implies that something has fallen into disorder. The word collapse is frequently used in discussions about sustainability, usually in terms of risks of collapse and the need to avoid collapse. However, developing an understanding of factors that actually cause or predict collapse has been limited by inconsistent and unclear definitions of collapse.
A review of social-ecological collapses by Graeme Cumming from Australia’s James Cook University and centre researcher Garry Peterson uses ideas from resilience theory to clarify thinking about collapse. Published in Trends in Ecology & Evolution, their paper reviews the study of collapse across economics, archeology, and ecology and then suggests a new framework for studying collapse in social-ecological systems.
Understanding collapse requires the comparing different cases of collapse, however when collapse is defined inconsistently and unclearly, such comparisons are impossible, and block the development and testing of different theories of collapse.
Collapse is the shadow of resilience, consequently studying collapse is indirectly the study of what makes a system resilient
Garry Peterson, co-author
In their proposed definition of ‘collapse’, Cumming and Peterson argue it is necessary to explicitly define what is collapsing. "Not doing this basic thing leads to confused conflicts about collapse among researchers who are focusing on different aspects of a place or system," Cumming explains.
Defining collapse, requires specifying the identity of the system being studied, as this can be used determine its elements, characteristics and thresholds of change. Once the system has been identified, the authors argue that its collapse can be determined using four criteria:
The first criterion is that the identity of the system must be lost. This can occur if important components of the system disappear.
The second criterion is that this loss should happen fast. The term ‘fast’ is relative to the system being considered, so it depends on the intrinsic rates of the system’s identifying components and varies accordingly. A gradual ‘degrading’ of the system would not qualify as system collapse under the second criterion.
The third criterion is that the collapse involves substantial loss of social-ecological capital. The key word here is ‘substantial’, which will vary between systems. Using case studies, Cumming and Peterson have found that quantitative thresholds are useful for focussing attention on the trends in the system. For example, a 99% decline in the Newfoundland Cod spawner biomass represented a substantial loss of social-ecological capital and was a solid indicator of the system’s collapse.
The fourth criterion is that the consequence of the collapse must be lasting. This criterion implies that short-term perturbations in system dynamics, while interesting, do not represent system collapse. Cumming and Peterson argue that if all four criteria for collapse are met, the system will undergo dramatic change in structure, function or both. Using a systematic approach to defining system collapse is the first step in developing our understanding of it.
So how does the study of collapse help us? An agreed framework for comparing collapse allows us to develop and test general theories about mechanisms of collapse. In their paper, Cumming and Peterson propose a framework that links the systematic definition of system identity and collapse with an understanding of system structure and dynamics to allow us to develop and test theories relating to the mechanisms of collapse.
In their review of system collapse case studies, the authors identified 14 potential mechanisms that may cause collapse in social-ecological systems. They were also able to link specific collapse mechanisms with different types of system structure. While there are disagreements about the exact causes of collapse in some of the case studies, the review does demonstrate the value of combining system identity with a clear definition of collapse in future work.
As Peterson explains, “Collapse is the shadow of resilience, consequently studying collapse is indirectly the study of what makes a system resilient.”
Trade-offs between the resilience of one part of a system and the fragility of another may be unavoidable, but knowing how and where a system is fragile gives people advanced warning as well as the capacity to work to reduce the risk of failure in that part of the system. As the world changes and new disruptions of current social-ecological systems occur, a science of collapse is needed to create a resilient and sustainable future.
Cumming and Peterson use a review of 17 case studies of social-ecological system collapse to propose a systematic approach to defining system collapse. Further to this, the authors propose a framework for collapse research that allows for comparison between case studies and the development of a general theory of collapse and its mechanisms in social-ecological systems. Drawing on previous work regarding system structure by the first author, the framework is shown to be able to link specific collapse mechanisms with the pre-collapse structure of the system. The authors proceed to discuss the benefits of a systematic approach to collapse research to the theory and practice of system management.
Garry Peterson is professor in environmental sciences with emphasis on resilience and social-ecological systems at the Stockholm Resilience Centre. His research combines three themes: abrupt systemic change, how ecological changes impacts people, and using futures thinking to improve navigating surprising social-ecological change. He is head of subject for the centre’s Sustainability Science PhD programme.
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New book chapter looks into the economic, cultural and ecological reasons why some people leave the fisheries and aquaculture sector, and what could be done to reverse the trend | <urn:uuid:1db4dedb-0dc1-4980-bf17-452d4f628810> | 3.25 | 1,444 | News (Org.) | Science & Tech. | 23.089856 | 95,519,581 |
Most of us have seen cute and charming penguins. Today's penguins create an image of little pleasant flightless birds but things were very different 57 million years ago. Researchers in New Zealand found the remnants of an ancient penguin encased in rock on a beach that stood as tall as a human.
The long-beaked penguin stood 5 feet 7 inches tall and weighed about nearly 100kg. Emperor penguins, the tallest penguin species alive today, reach only 1.2 metres when fully grown.
Penguins evolved from flying birds tens of millions of years ago, but lost the ability to get airborne and became accomplished swimmers instead. Once grounded, some penguin species became much larger, growing from about 80cm tall to twice the size.
More about it:
- According to The Guardian's report, the pieces of the latest skeleton, including wing, spine, breast and leg bones, were first discovered more than a decade ago, but the rock holding the fossilised bones was so hard that it has taken until now for researchers to prepare and study the remains
- Rather than the usual black-and-white colouring, the ancient penguin was probably brownish and had a longer beak than its modern-day cousins
- Researchers named the new species Kumimanu biceae, after the Maori words "kumi", meaning a large mythological monster, and "manu" for bird
- The second part of the name honours Beatrice Tennyson, known as "Bice", the mother of Alan Tennyson, a senior researcher on the team
- Another species of giant penguin, discovered in Antarctica in 2014, may have been even taller than Kumimanu biceae
- Bones from the 37million-year-old "colossus penguin", or Palaeeudyptes klekowskii, suggest the animal stretched two metres from beak to foot and weighed 115kg
- The latest specimen, reported in Nature Communications, suggests that some penguins became giants soon after penguins first evolved and switched from flight to diving
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Until recently, denitrification was thought to be the only significant pathway for N(2) formation and, in turn, the removal of nitrogen in aquatic sediments. The discovery of anaerobic ammonium oxidation in the laboratory suggested that alternative metabolisms might be present in the environment. By using a combination of (15)N-labeled NH(4)(+), NO(3)(-), and NO(2)(-) (and (14)N analogues), production of (29)N(2) and (30)N(2) was measured in anaerobic sediment slurries from six sites along the Thames estuary. The production of (29)N(2) in the presence of (15)NH(4)(+) and either (14)NO(3)(-) or (14)NO(2)(-) confirmed the presence of anaerobic ammonium oxidation, with the stoichiometry of the reaction indicating that the oxidation was coupled to the reduction of NO(2)(-). Anaerobic ammonium oxidation proceeded at equal rates via either the direct reduction of NO(2)(-) or indirect reduction, following the initial reduction of NO(3)(-). Whether NO(2)(-) was directly present at 800 micro M or it accumulated at 3 to 20 micro M (from the reduction of NO(3)(-)), the rate of (29)N(2) formation was not affected, which suggested that anaerobic ammonium oxidation was saturated at low concentrations of NO(2)(-). We observed a shift in the significance of anaerobic ammonium oxidation to N(2) formation relative to denitrification, from 8% near the head of the estuary to less than 1% at the coast. The relative importance of anaerobic ammonium oxidation was positively correlated (P < 0.05) with sediment organic content. This report of anaerobic ammonium oxidation in organically enriched estuarine sediments, though in contrast to a recent report on continental shelf sediments, confirms the presence of this novel metabolism in another aquatic sediment system.
Mendeley saves you time finding and organizing research
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It's Not A Bug, It's....
It's Not A Bug, It's....
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How many legs does a lamb have if I say the tail is a leg? The answer is 4, just because I say the tail is a leg does not make it a leg!
Bugs should be obvious, but we say It's not a bug, it's a feature because often it isn't obvious. Watson Humphrey felt that we should use the term defect and not bug because most people don't take bugs seriously, so let's use the term defect instead.
So when does a defect become a defect?
- When quality assurance tells you that you have a defect?
- When product management says that it is a defect?
- When the customer says that it is a defect?
Surprisingly, the answer is: none of the above. Now it might turn out that there is a problem and that code needs to change, but a defect only exists if code behaves differently than the requirements specification
This is important because most systems are under specified (if they are specified at all :-) ). Code can only be considered a defect if it differs from the specification. We call defects undocumented features because the problem is that the requirements were never written. Bugs depend on departures from the requirements, not subjective beliefs.
Incomplete and Inconsistent Requirements
Many organizations do not create sufficiently complete requirements before starting development, either because they don't know how to capture requirements properly or because they don't have resources capable of capturing complete requirements.
Incomplete (and inconsistent) requirements and unrealistic deadlines often force developers into making decisions about how to implement features. The end result is that developers are regularly told that they have defects in their code.
While this process is common, it is destructive. When requirements are under specified and inconsistent developers end up needing to perform serious rework. The rework will can require dramatic changes that will impact the architecture of the code.
The time required to find a work around (if it is possible) is rarely included in the project plan. Complicating matters is that the organizations that are reluctant to spend time creating requirements also tend to underestimate their projects. This puts tremendous pressure on the engineering department to deliver; this promotes the 5 worst practices in software development (see Stop it!, No... really stop it)
When poorly or undocumented systems require changes that are not specified we should call them change requests rather than defects.
Only 54% of Issues are Resolved by Engineers
The attitude that all defects must be resolved by the engineering department is severely misguided. Analysis by Capers Jones of over 18,000+ projects shows that only about 54% of all defects can be resolved by the engineers! (only the 3 highlighted rows below)
|Defect Role Category||Frequency||Role|
|Requirements defect||9.58%||BA/Product Management|
|Architecture or design defect||14.58%||Architect|
|Testing defect||15.42%||Quality Assurance|
|Documentation defect||6.25%||Technical Writer|
|Database defect||22.92%||Data base administrator|
This means that precious time will be wasted assigning issues to developers that they can not resolve. The time necessary to redirect the issue to the correct person is a major contributing factor to fire-fighting
Getting Control of the Defect Process
For most organizations fixing the defect process involves understanding and categorizing defects correctly. Organizations that are not tracking the different sources of defects probably have a bug tracker that has gone to hell. Here is how you can fix that problem, see Bug Tracker Hell and How to Get Out
At a minimum you need to implement the requirements defect, once you identify issues that are caused by poor requirements it will shine the white hot light of shame onto the resources that are capturing your requirements.
Once you realize how many requirements defects exist in your system you can begin to inform senior management about the requirements problem.
The best way to reduce fire fighting is to start writing better requirements (or writing requirements :-) ). To do so you need to figure out which of the following are broken:
- Not enough time is allocated to the requirements phase
- Unskilled people are capturing your requirements
In all likelihood both of these issues need to be fixed in your organization. When requirements are incomplete and inconsistent you will have endless fire-fighting meetings involving everyone (see Root cause of 'Fire-Fighting' in Software Projects)
Published at DZone with permission of Dalip Mahal , DZone MVB. See the original article here.
Opinions expressed by DZone contributors are their own. | <urn:uuid:6b6aacef-5754-4e88-a792-63fd67bbc719> | 2.71875 | 981 | Truncated | Software Dev. | 42.296061 | 95,519,603 |
Record in the Rock. What Processes Shape our Earth?. Earth Science- the study of earth and space Importance of Earth Science: Contributes to our knowledge of the world Understanding forces that shape our earth can better forecast potential disasters Provides valuable resources
What Processes Shape our Earth?
Importance of Earth Science:
Asthenosphere: part of mantle; less rigid than the lithosphere; convection currents flow here
Radioactive Decay: when elements break down
Radiometric Dating: rate at which radioactive decay takes place
Based on half-life (time to take ½ of element to decay)
Radioactive decay rates don’t change!
Nonliving: 3.9 billion year old rock of Uranium 238 Lead 206
Living: Carbon 14 Carbon 12Radiometric Dating
1/2 of the 1/2 = 1/4 the original sample.
You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.
are left after two
Law of Superposition- the bottom layer of an undisturbed section is older than the topTypes of Relative Dating
1. lived in a certain time span in many places
2. lived in great numbers
3. distinct features to identify
-Correlation- matching rocks by Index Fossil in different places
Seafloor & trench
A relatively recent theory that the Earth's crust is composed of rigid plates that move relative to one another.
Plate movements are on the order of a few centimeters/year - about the same rate as your fingernails grow!
There are 3 types of plate boundaries:
1. Eurasian 4. North American
2. Pacific 5. South American
3. African 6. Antarctic
2. Transform- plates move past one another in opposite directions or in the same direction at different speeds
Example- San Andreas fault
3. Convergent- two plates collide
-There are 3 types of plate boundaries
b. Oceanic and continental plates collide- the denser oceanic plate descends into the athenosphere.
- may form chain of volcanic mountains
- Earthquakes are common
c. Two continental plates collide- the continental rocks buckle and rise.
- mountain chains form
- earthquakes are common
- very little volcanic activity
occurs (1-5 cm per year) | <urn:uuid:824abeb0-4a5a-4844-b213-9fd26fb5e891> | 3.625 | 486 | Knowledge Article | Science & Tech. | 50.23957 | 95,519,628 |
I think I'm going to have a series of posts on the basics of thermodynamics and its application to chemistry because, well, it's so darn interesting.
In the previous post I outlined some basic concepts of chemical equilibrium. But the case that I gave was very specific and would only apply to a system that operates in a similar manner -- namely, that one molecule of X would combine with one molecule of Y to form one molecule of XY. This is not always the case. But before going into specific chemical equilibrium, I think it better to look at where the model for equilibrium comes from.
A model for physical systems can be constructed from the concept of a system and surroundings. Both are selected by the modeler, usually specifically selected for convenience of calculation, and in that sense are arbitrary. The system is simply what you are interested in. The surroundings includes everything else, but usually only the immediate surroundings are all that are taken into account -- a chemical example would be what is in a beaker for a system, and the lab that the beaker is in for the surroundings.
In designating a system/surroundings, you have some quantities that can describe both: Energy, Pressure, Temperature, Volume, and moles of gas. Any of these quantities can be exchanged between the system and the surroundings, and which quantities can be exchanged often describe the type of system that you are looking at.
A common example from physics is the mechanical equilibrium of a spring represented by the following force diagram.
(Do forgive my Paint abilities). According to Newton's Second Law
ΣF = Fs + Fg
Fs = -kx
Fg = mg
And, because this system is in equilibrium ΣF = 0
Therefore, Fs + Fg = 0, and Fs = -Fg, which means by substitution kx = mg
Which happens to usually be a highly convenient situation. In particular, note that the previous solution had no reference to time. This is something unique to equilibrium solutions: There is no reference to time, only to what each respective variable is at when no variable of interest is changing.
However, when dealing with the system/surroundings model, usually forces aren't the variables of interest. A close analogue. A common example of pressure equilibrium would be a balloon which has been tied off. The gas within the balloon would have a higher pressure than the exterior pressure, but pressure would not be exchanged between the system (the gas in the balloon) and the surroundings (the room the balloon is in).
This situation can occur between any variables of interest -- Pressure, Volume, Temperature, Energy, and chemical concentration. The final one is the one that chemists are first introduced to. This is, ultimately, just the application of thermodynamics/statistical mechanics to chemical systems. Ergo, the study of the model of equilibrium is actually the study of thermodynamics, which is one of the main branches of chemistry. The above explication of equilibrium should also clarify why it is that kinetics, despite being related to energy just as thermodynamics is related to energy, is a separate case of study: The concept of equilibrium requires things to not change with time, and the concept of equilibrium is the model within thermodynamics most often used to model chemical systems as, regardless of the time it takes, the system will tend towards concentrations which satisfy the equilibrium constant.
I think this is done mostly to simplify predictions: thermodynamics, I must admit, is still a bit of an impenetrable thick fog as it is. Not having to worry about time-dependence makes things a little easier.
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Software prototyping, refers to the activity of creating "disposable", threw-away version of software applications to test the key ideas of the architecture .
A prototype typically simulates only a key aspects of the system, avoiding bells and whistles and as such can use different, higher level implementation language then the final product. It also can be a virtual machine, not a software implementation in traditional sense (see below).
As Wikipedia article states
Prototyping has several benefits: The software designer and implementer can get valuable feedback from the users early in the project. The client and the contractor can compare if the software made matches the software specification, according to which the software program is built. It also allows the software engineer some insight into the accuracy of initial project estimates and whether the deadlines and milestones proposed can be successfully met. The degree of completeness and the techniques used in the prototyping have been in development and debate since its proposal in the early 1970s.
The monolithic "waterfall" approach to software development has been dubbed the "Slaying the (software) Dragon" technique, since it assumes that the software designer and developer is a single hero who has to slay the entire dragon alone. Prototyping can help in avoiding the great expense and difficulty of changing an almost finished software product due to changes in specification or understanding of the problem (and understanding of the problem often comes too late in the "prototype-less" development of software).
The process of prototyping involves the following steps
Approaches to prototyping
There are several appaches to prototyping. Among them there are two more or less realistic:
Also called close-ended prototyping. Throwaway or Rapid Prototyping refers to the creation of a model that will eventually be discarded rather than becoming part of the final delivered software. After preliminary requirements gathering is accomplished, a simple working model of the system is constructed to visually show the users what their requirements may look like when they are implemented into a finished system.
- Rapid Prototyping involved creating a working model of various parts of the system at a very early stage, after a relatively short investigation. The method used in building it is usually quite informal, the most important factor being the speed with which the model is provided. The model then becomes the starting point from which users can re-examine their expectations and clarify their requirements. When this has been achieved, the prototype model is 'thrown away', and the system is formally developed based on the identified requirements.
The most obvious reason for using Throwaway Prototyping is that it can be done quickly. If the users can get quick feedback on their requirements, they may be able to refine them early in the development of the software. Making changes early in the development lifecycle is extremely cost effective since there is nothing at that point to redo. If a project is changed after a considerable work has been done then small changes could require large efforts to implement since software systems have many dependencies. Speed is crucial in implementing a throwaway prototype, since with a limited budget of time and money little can be expended on a prototype that will be discarded.
Another strength of Throwaway Prototyping is its ability to construct interfaces that the users can test. The user interface is what the user sees as the system, and by seeing it in front of them, it is much easier to grasp how the system will work.
- …it is asserted that revolutionary rapid prototyping is a more effective manner in which to deal with user requirements-related issues, and therefore a greater enhancement to software productivity overall. Requirements can be identified, simulated, and tested far more quickly and cheaply when issues of evolvability, maintainability, and software structure are ignored. This, in turn, leads to the accurate specification of requirements, and the subsequent construction of a valid and usable system from the user's perspective via conventional software development models.
Prototypes can be classified according to the fidelity with which they resemble the actual product in terms of appearance, interaction and timing. One method of creating a low fidelity Throwaway Prototype is Paper Prototyping. The prototype is implemented using paper and pencil, and thus mimics the function of the actual product, but does not look at all like it. Another method to easily build high fidelity Throwaway Prototypes is to use a GUI Builder and create a click dummy, a prototype that looks like the goal system, but does not provide any functionality.
Not exactly the same as Throwaway Prototyping, but certainly in the same family, is the usage of storyboards, animatics or drawings. These are non-functional implementations but show how the system will look.
SUMMARY:-In this approach the prototype is constructed with the idea that it will be discarded and the final system will be built from scratch. The steps in this approach are:
- Write preliminary requirements
- Design the prototype
- User experiences/uses the prototype, specifies new requirements
- Repeat if necessary
- Write the final requirements
- Develop the real products
The main goal when using Evolutionary Prototyping is to build a very robust prototype in a structured manner and constantly refine it. "The reason for this is that the Evolutionary prototype, when built, forms the heart of the new system, and the improvements and further requirements will be built.
When developing a system using Evolutionary Prototyping, the system is continually refined and rebuilt.
- "…evolutionary prototyping acknowledges that we do not understand all the requirements and builds only those that are well understood."
This technique allows the development team to add features, or make changes that couldn't be conceived during the requirements and design phase.
- For a system to be useful, it must evolve through use in its intended operational environment. A product is never "done;" it is always maturing as the usage environment changes…we often try to define a system using our most familiar frame of reference---where we are now. We make assumptions about the way business will be conducted and the technology base on which the business will be implemented. A plan is enacted to develop the capability, and, sooner or later, something resembling the envisioned system is delivered.
Evolutionary Prototypes have an advantage over Throwaway Prototypes in that they are functional systems. Although they may not have all the features the users have planned, they may be used on an interim basis until the final system is delivered.
- "It is not unusual within a prototyping environment for the user to put an initial prototype to practical use while waiting for a more developed version…The user may decide that a 'flawed' system is better than no system at all."
In Evolutionary Prototyping, developers can focus themselves to develop parts of the system that they understand instead of working on developing a whole system.
- To minimize risk, the developer does not implement poorly understood features. The partial system is sent to customer sites. As users work with the system, they detect opportunities for new features and give requests for these features to developers. Developers then take these enhancement requests along with their own and use sound configuration-management practices to change the software-requirements specification, update the design, recode and retest.
Scripting language are ideal for software prototyping. Included among these benefits is the ability to address rapidly changing software requirements. In addition, the efficiency gained from user-centered design, which consists of constant user feedback impacting the software design, has received significant attention recently [Landauer95]. Fast compile-debug-test cycles, and high programming flexibility make dynamically typed languages such as Perl, Python, PHP and Tcl ideal for the rapid creation of prototypes both on compoment and system levels
Ousterhout was the first to argue that a two language approach is both feasible and practical for software development [Ousterhout97] and created the scripting language (TCL) that has a transparent interface with C and can be extended using C modules. Python also provide consistent interface to C to allow developers to move performance critical methods and procedures into C without modification of the calling code.
Supporting prototyping requires a language which can support transformation of components previously written in cscritping langue into low level statically typed compiled language (C or C++) and vise versa. Currently, few scripting languages allow for this type of flexibility.
If developers choose to use a statically typed language (for example Java) they often encounter problems in the early prototyping and development phases.
These limitations often make it difficult to use statically typed languages for rapid prototyping of all or part of an application.
On the other hand, if developers choose to use a single dynamically typed language they often encounter problems in the latter phases of development when performance, scalability, and maintainability become critical issues. They often encounter performance problems when writing computationally intensive code and tend to spend an unordinary amount of time optimizing code. They may also suffer scalability problems related to CPU and memory usage typical for scripting languages. The detection of all coding errors is delayed until the actual line of code containing the error is executed meaning that complex tests must be written in order to check the validity of code. Despite the benefits of a scripting languages, these limitations increase the cost of maintaining a large codebase.
Modern software development demands the use of Rapid Application Prototyping. Professor Luqi at the Naval Postgraduate School coined the term "Computer Aided Prototyping" to describe this work. Her leadership showed its effectiveness in gaining understanding of the requirements, reducing the complexity of the problem and providing an early validation of the system design. For every dollar invested in prototyping, one can expect a $1.40 return within the life cycle of the system development.
Dr. Barry Boehm's experiments showed that prototyping reduces program size and programmer effort by 40%. It is the technology that is the foundation for his Spiral development method. Prototyping is being used successfully to gain an early understanding of system requirements, to simplify software designs, to evaluate user interfaces and to test complex algorithms. It is a best-in-class software approach.
Fully 30 to 40% of system requirements will change without prototyping. Rapid Application Prototyping provides a look at the dynamic states of the system before we build it, whereas most other software engineering focuses on the source code. The special problems of reliability, throughput and response time as well as system features are addressed in the best prototypes. A new field of study, Software Dynamics, will emerge once Rapid Application Prototyping is widely practiced. It will focus on quantitative analysis of how software performs under various loads and include a set of design constraints that will make it possible for us to build components that can be hooked together without exhaustive coverage testing.
Software is hard because it has a weak theoretical foundation. Most of the theory that does exist focuses on the static behavior of the software, analysis of the source listing. There is little theory on its dynamic behavior, how it performs under load. To avoid serious network problems software systems are over-engineered with plenty of bandwidth for two or three times the expected load. Without analysis of the dynamic behavior, application designers have no idea of the resources they will need once their software is operational. Software has the awful propensity to fail with no warning. Even after we find and fix a bug, how do we restore the software to a known state, one where we have tested its operation? For most systems, this is impossible except with lots of custom design that is itself error-prone. Software prototyping has proven its mettle in helping designers avoid these problems in their production systems.
Much has been written about the best way to develop software applications. But there is no "best way." Both prototyping and requirements are necessary. The tried and true process of synthesis and analysis is used to solve Software Engineering problems. Bottom-up is synthesis. Top-down is analysis. Bottom-up is prototyping. Top-down is developing requirements. Prototyping is the best way to encourage synthesis. Prototyping also eases communication with the customer and with the designer. Formal written requirements are needed to establish a clear definition of the job, to control changes and to communicate the system capabilities between the customer and the developer.
So where does this leave us?
Start with an English language written statement of a problem and broadly outline its solution. Now build a prototype for the elements where you need insight. Analyze the prototype using computer aided prototyping technology and synthesize a new solution either by refining the prototype or building a new one. Once you and the customer agree on the workings of the prototype, write requirements that include features, performance goals, product costs, product quality, development costs and schedule estimates.
What do I mean by prototype?
Prototyping is the use of approximately 30% of the ultimate staff to build one or two working versions of various aspects of a system. It is not production code but it may eventually become pre-production code or it may be completely discarded. In the prototyping effort, we are not concerned with the maintainability of the code nor are we concerned with formally documenting it. Code resulting from prototyping is often used to train the programmers. Only after we have written specifications resulting from the experience with the prototype should we start the formal development process. If we are fortunate enough that some of the code that was developed for the prototypes can be carried forward, that's great, if not, there is no loss.
A prototype produces "running" software and the production development produces "working" software.
Recent project experience has led to the widespread acceptance of the concept that early prototyping is fundamental to the success of operations supporting software products.The reasons why prototyping is fundamental include:
- The prototype provides a vehicle for systems engineers to better understand the environment and the requirements problem being addressed.
- A prototype is a demonstration of what's actually feasible with existing technology, and where the technical weak spots still exist.
- A prototype is an efficient mechanism for the transfer of design intent from system engineer to the developer.
- A prototype lets the developer meet earlier schedules for the production version.
- A prototype allows for early customer interaction.
- A prototype demonstrates to the customers what is functionally feasible and stretches their imagination, leading to more creative inputs and a more forward-looking system.
- The prototype provides an analysis test bed and a vehicle to validate and evolve system requirements.
About the Author
Mr. Bernstein is president of the Center of National Software Studies and is a recognized expert in Software Technology. He provides consulting through his firm Have Laptop - Will Travel and is the Executive Technologist with Network Programs, Inc. building software systems for managing telephone services.
Mr. Bernstein was an Executive Director of AT&T Bell Laboratories where he worked for 35 years.
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THE LASER: A NEW OPTICAL RESEARCH TOOL by Philip E. Barnhart The principle of the operation of lasers has been known and understood for many years. It is perhaps one of the paradoxes of modern physics that man had only recently put the knowledge to use in view of the basic simplicity of operation and extremely wide application that results from laser action. A laser (an acronym tor Light Amplification by Stimulated Emission of Radiation) is a device based upon the processes of interaction between radiation, such as light or radio waves, and atoms or molecules. The product of a laser is coherent light, a commodity available in only limited quantities until now. Mass production of coherent light opens the door to the solutions of many problems of physical science. The laser is not a “death ray� as described in some popular publications. If handled in a careless way a laser beam can do bodily harm just as the light from the sun, if not treated with proper respect, can damage the human organism. | <urn:uuid:07c03298-be4a-4782-bdfa-b48ab29c567d> | 3.1875 | 209 | Truncated | Science & Tech. | 41.10346 | 95,519,700 |
In a cover story in Small, Baoshan Xing of UMass Amherst and colleagues report on toxicity for layered BP in three cell lines. They found disruption of cell membrane integrity related to particle size, concentration- and cell-type-dependent cytotoxicity
When environmental and soil chemist Baoshan Xing at the University of Massachusetts Amherst began reading in 2014 that a new, two-dimensional material known as layered black phosphorous (BP) was gaining the attention of biomedical researchers for use in drug delivery systems and tumor photothermal therapy, he was both intrigued and concerned.
A schematic diagram illustrating mechanisms of BP toxicity, which include disruption of cell membrane integrity related to layered BP particle size and generation of reactive oxygen species. Baoshan Xing at UMass Amherst, with colleagues in China, report the findings in a cover story in Small.
Credit: UMass Amherst/Baoshan Xing
"I am not only a soil chemist, but an environmental chemist," he notes. "As agricultural scientists, we are very familiar with phosphorous but I had never heard of two-dimensional black phosphorous. So we read all the nice papers about black phosphorous, and then, as environmental chemists, we started asking about nanoparticle toxicity. You have to be careful where you put such materials in the human body."
In a recent cover story of the journal, Small, his former postdoctoral fellow, Qing Zhao, currently a professor at the Institute of Applied Ecology at the Chinese Academy of Sciences, and Xing report toxicity test results for different thicknesses of layered BP in three cell lines. Briefly, they found disruption of cell membrane integrity related to layered BP particle size, plus concentration- and cell-type-dependent cytotoxicity.
Xing says, "We are among the first ones to work with this material, particularly in regard to its environmental implications." He and colleagues urge that "an in-depth understanding of BP's cytotoxicity is of utmost importance" to provide useful data for risk evaluation and safe biomedical applications.
The researchers acknowledge that the new material, which is collected as thin samples from phosphorous crystals by a technique known as exfoliating, that is, shaving off layers of different thicknesses, does have "unique optical and electrical properties," which might make it "a promising candidate for an efficient drug delivery vehicle and photothermal/photodynamic therapy in treating a variety of cancers."
Xing says, "I remember when single-layer graphene generated great excitement in the research community a decade ago, and I think people are getting excited now about a single layer of black phosphorous, that it might have many exciting applications." But the two materials differ a great deal in their single-layer structure, he adds, where single-layer graphene is perfectly flat, exfoliated BP has a zig-zagged structure.
Zhao, Xing and their colleagues point out that studies of layered BP toxicity conducted to date have used viability reagents, which can interfere with cytotoxicity results. By contrast, they have used a label-free, real-time cell analysis (RTCA) technique that does not need any fluorescent or colorimetric viability reagents.
Assaying layered BP toxicity in three cell types, mouse fibroblast cells (NIH 3T3), human colonic epithelial cells (HCoEpiC) and human embryonic kidney cells (293T), the UMass Amherst and Chinese research team found that layered BP's cytotoxicity is based on the fact that it generates reactive oxygen species (ROS). ROS are among the most potent cell-damaging agents known. Layered BP also disrupts cell membrane integrity in a particle-size-dependent manner. "The larger the BP is, less membrane integrity will be retained," they note.
Further, they say the IC50 values of layered BP can differ by dozens of times depending on particle size and cell type. IC50 values refer to a measure of how effective a material is in inhibiting a specific biological function. Xing and colleagues urge that "special attention should be paid to the size of layered BP and the types of target cell lines for its application in biomedical field."
They add, "Further study is undoubtedly necessary to explore the cytotoxicity mechanisms in depth," and that "given the results from our present study, the mechanisms of BP's cytotoxicity are strikingly complicated and have significant implications for the risk evaluation and safe biomedical applications of BP."
They plan to follow up with further experiments to test their hypothesis that layered BP, with its unusual electrical properties, might prove useful in removing both positively and negatively charged chemicals and organic contaminants from water.
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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16.07.2018 | Agricultural and Forestry Science | <urn:uuid:58f6449b-559b-487c-adcb-291e4a74e5ca> | 2.546875 | 1,617 | Content Listing | Science & Tech. | 33.0757 | 95,519,702 |
Detection and mapping crack patterns are key issues for structural assessment of concrete structures. The use of image processing for identification of pathologies has undergone major developments, since it is a noninvasive technique providing the precision and reliability required for the task. The authors have developed a method, named SurfCrete, to materials and damages classification on concrete structures, including mapping cracks. This is based on analysis of multi-spectral images, including visible and near infra-red (NIR) regions of the electromagnetic spectrum. Latest improvements include the use of hyperspectral image analysis for crack detection, based on image clustering. The drawbacks of the developed methods are the difficulties usually shown when dealing with surfaces presenting several damages and materials besides cracks, namely due to the presence of biological colonization, repairing mortars, delamination and efflorescence, among other anomalies commonly found on concrete structures. Furthermore, when surfaces are subjected to different light conditions, this also influences the accurate classification of cracks. In this paper, an evolution of the method previously developed, herein named SurfCrete-HSV, is presented. The new method is completely focused on classifying biological colonization based on the classification of HSV false colour images, being therefore more robust and reliable. These HSV images are built from hyperspectral images (wavelengths from 450 nm to 950 nm and 25 nm of bandwidth) by selecting three channels, one from NIR region and two from the visible region of electromagnetic spectrum. The HSV space allows isolating the colour in a single data dimension to enable a brightness free clustering. An image of a concrete specimen with simulation of biological colonization over a smooth surface is used from a database of hyperspectral images, to evaluate SurfCrete-HSV method. Results show that the SurfCrete-HSV method is reliable for detection of biological colonization on concrete surfaces. The best set of channels to use results from combining one from Near Infra-Red with Red and Blue regions of the electromagnetic spectrum, which reveals high accuracy values with acceptable recall.
Bruno O. Santos, Jónatas Valença, and Eduardo Júlio, "Classification of cracks of biological colonization on concrete surface using false colour HSV images, including near-infrared information," Proc. SPIE 10680, Optical Sensing and Detection V, 1068003 (Presented at SPIE Photonics Europe: April 23, 2018; Published: 9 May 2018); https://doi.org/10.1117/12.2307728.
Conference Presentations are recordings of oral presentations given at SPIE conferences and published as part of the conference proceedings. They include the speaker's narration along with a video recording of the presentation slides and animations. Many conference presentations also include full-text papers. Search and browse our growing collection of more than 12,000 conference presentations, including many plenary and keynote presentations. | <urn:uuid:89e56210-002a-4526-bb22-68834f2e2f97> | 2.609375 | 592 | Academic Writing | Science & Tech. | 17.932976 | 95,519,707 |
This makes our job harder, besides the unstable weather conditions, mainly the atmospheric pressure, funnel clouds
, and heavy showers.
Videos and pictures captured the freak phenomenon, known by weather experts as funnel clouds
, in Guisborough and Middlesbrough respectively.
The funnel clouds
can pack extremely damaging winds as well as water droplets, dust and debris; they're considered the most violent of atmospheric storms.
were spotted as far north as Illinois and Indiana, but no fatalities were reported.
typically occur in the Willamette Valley in the late afternoon, usually in the spring or fall, after a front of rain passes through and is followed by showers, Neuman said.
As they develop, we often see funnel-shaped clouds extending from the base of the cloud and it is only when these funnel clouds
touch the ground that we get a tornado.
I wouldn't be surprised if there are reports of funnel clouds
and a possible tornado as the storms move northwards.
He added: "We do get funnel clouds
at times in the UK, but they are normally small and relatively weak compared to the giant destructive forces we see in areas of America.
Paul said dust devils and even mini tornadoes - funnel clouds
that "touch down" on the ground - might be a more common sight in and around Huddersfield given the heatwave forecast for the next few days.
Additional tornadoes or funnel clouds
were detected in central Nebraska, behind the first wave of storms that appeared to dissipate as it moved eastward, weather officials said.
- tornadoes that do not touch the ground - had already swept across Scotland's Isle of Lewis and Co Londonderry in Northern Ireland.
If funnel clouds
packing winds upward of 100 mph and carrying the occasional flying cow don't scare Reed Timmer, why would the prospect of striking out on his own in the spirit of entrepreneurship? | <urn:uuid:3b397955-707a-421a-bcd6-710520193ee8> | 3.09375 | 392 | Personal Blog | Science & Tech. | 43.156593 | 95,519,715 |
A massive 23.8 m (78 feet) high wave has been measured near Campbell Island, New Zealand on May 9, 2018, making it the largest wave ever recorded in the southern hemisphere.
A new ocean buoy, installed March 2, 2018 and located about 640 km (400 miles) south of New Zealand’s South Island, measured a maximum wave height of 23.8 m (78 feet). The previous record for the southern hemisphere was a 22.03 m (72 feet) high wave registered off the Australian state of Tasmania in 2012.
“This is a very exciting event and to our knowledge, it is the largest wave ever recorded in the southern hemisphere,” Dr. Tom Durrant, a senior oceanographer at the MetOcean, part of New Zealand’s Met Service, said.
“Our own previous record was one year ago when we measured a 19.4 m (63.6 feet) wave, and before that in 2012 an Australian buoy recorded a maximum individual wave (Hmax) of 22.03 m. So, this is a very important storm to capture, and it will add greatly to our understanding of the wave physics under extreme conditions in the Southern Ocean.”
“The Southern Ocean is definitely the most under-observed ocean in the world. The region accounts for about 22% of the planet’s oceans, and it’s the most energetic part of the world’s oceans in terms of waves,” he said.
This solar-powered buoy samples the waves for just 20 minutes every three hours to conserve its solar-powered battery and then sends the data via a satellite link. During that 20 minute recording period, the height, period and direction of every wave is measured and statistics are calculated.
“It’s very probable that larger waves occurred while the buoy was not recording. They may have actually reached more than 25 m (82 feet) if the forecasts were correct,” Durrant said.
While this wave was large, it’s not a world record.
Furthermore, the World Meteorological Organization doesn’t measure maximum wave height, or, the largest individual wave.
It measures significant wave height, which is meant to represent general ocean conditions and measures the average of the waves. The WMO certified a world record for significant wave height in the North Atlantic in 2013 at 19 m (62 feet).
Significant wave height for May 9 in the Southern Ocean where the abovementioned buoy is located was 14.9 m (48.9 feet), which is also southern hemisphere’s record.
Featured image credit: MetOcean | <urn:uuid:ce69cc21-eb63-43f7-b741-fba9f94a8030> | 3.171875 | 545 | News Article | Science & Tech. | 62.200177 | 95,519,759 |
By Lynn Yarris, [email protected]
Researchers in LBL's Structural Biology Division (SBD), led by chemist Heinz Frei, have developed a technique in which red light is used to convert abundant hydrocarbons into valuable chemical compounds at no cost to the environment.
A central theme of current catalysis research is the redesigning of the industrial processes used to manufacture plastics and other synthetic materials.
Frei explains, "Many current synthesizing processes in industry create problems for the environment. They also waste energy. Industry needs new processes that are product specific, environmentally benign, and energy efficient."
Most synthetic materials are made through the oxidation of small hydrocarbons, one of Nature's most plentiful raw materials. For the past several years, Frei has been exploring the use of red and near-infrared radiation to initiate hydrocarbon oxidation in a tightly controlled fashion. Because red and near-infrared photons are the least expensive to artificially produce, this photochemical technique is economically competitive with other catalytic methods.
In earlier work, Frei and coworkers achieved oxidation reactions in a "cryogenic matrix environment," where potentially reactive molecules were immobilized in a frozen gas and irradiated with red and near-infrared photons. These photons are substantially lower in energy than the blue or ultraviolet light most often used in photochemistry.
"The use of low energy photons gave us access to low energy reaction pathways," Frei says. "This gave us product specificity because we were below the dissociation energies of the reaction partners. Excitation above dissociation energies often leads to unwanted byproducts."
Now, working with Fritz Blatter and Hai Sun, Frei has developed a new technique for selective hydrocarbon oxidation that not only permits the use of red and near-infrared photons, but also enables photochemical reactions to take place at room temperature. What makes this possible is the immobilization of reactants not in a cryogenic matrix, but in molecular-sized cages of inert solid materials called zeolites.
Zeolites are alumino silicates used widely in the petrochemical industry as catalysts. They feature unique pore structures inside which smaller molecules can be imprisoned. Using a synthetic version of a natural zeolite called faujasite, Frei and his colleagues successfully held and photo-oxidized small alkene molecules into industrially important chemical building blocks and intermediaries such as hydroperoxides, carbonyls, and epoxides. This was accomplished without the customary release of carbon dioxide, the chief contributor to global warming and the greenhouse effect.
To photo-oxidize their alkene molecules, Frei and Blatter loaded them as a gas into zeolite pellets and added oxygen. Reactant molecules paired with one another and were held together by the zeolite cages in close contact so that irradiation with red light triggered oxidation.
Says Frei, "Zeolites offer an ideal environment for the formation of new complexes at high concentrations. Excitation of these complexes with light allows us to access reaction surfaces and, in some cases, products that are not attainable through conventional thermal activation."
Another advantage in using zeolties, Frei points out, is that their inherently large electrostatic fields act to stabilize the excited charge-transfer energy states of hydrocarbon-oxygen complexes. This allows zeolite photochemistry to be performed with light from a conventional tungsten lamp rather than a laser.
Since practically all of the polymers from which come today's synthetic materials are manufactured from chemical building blocks that are themselves produced by oxidation of hydrocarbons, Frei's red-light photochemistry research has far-reaching industrial potential. He and his colleagues are now studying the application of their technique to organic compounds derived from hydrocarbons. | <urn:uuid:8e604109-d4da-45e6-8361-93763a4cb767> | 3.578125 | 775 | News (Org.) | Science & Tech. | 11.676836 | 95,519,773 |
3D model (JSmol)
|Molar mass||316.755 g/mol|
|Appearance||White monoclinic powder|
|Density||3.71 g/cm3, solid|
|Melting point||165 °C (329 °F; 438 K) (decomposes)|
|0.069 g/100 mL|
|Solubility||Soluble in dilute hydrochloric acid, KCN, ammonia |
slightly soluble in alcohol, ether
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|46 mg/kg (rat, oral)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Mercury(II) thiocyanate (Hg(SCN)2) is an inorganic chemical compound, the coordination complex of Hg2+ and the thiocyanate anion. It is a white powder. It will produce a large, winding “snake” when ignited, an effect known as the Pharaoh's serpent.
Synthesis and structure
The first synthesis of mercury thiocyanate was probably completed in 1821 by Jöns Jacob Berzelius:
- HgO + 2 HSCN → Hg(SCN)2 + H2O
Evidence for the first pure sample was presented in 1866 prepared by a chemist named Otto Hermes. It is prepared by treating solutions containing mercury(II) and thiocyanate ions. The low solubility product of mercury thiocyanate causes it to precipitate from solution. Most syntheses are achieved by precipitation:
- Hg(NO3)2 + 2 KSCN → Hg(SCN)2 + 2KNO3
The compound adopts a polymeric structure with Hg2+ centers linearly coordinated to two S atoms with a distance of 2.381 Å. Four weak Hg2+--N interactions are indicated with distances of 2.81 Å.
Mercury thiocyanate was formerly used in pyrotechnics causing an effect known as the Pharaoh's serpent or Pharaoh's snake. When the compound is in the presence of a strong enough heat source, a rapid exothermic reaction is started which produces a large mass of coiling serpent-like solid. An inconspicuous flame which is often blue but can also be yellow/orange accompanies the combustion. The resulting solid can range from dark graphite grey to light tan in color with the inside generally much darker than the outside.
The reaction has several stages as follows:
Igniting mercury thiocyanate causes it to form an insoluble brown mass that is primarily carbon nitride, C3N4. Mercury sulphide and carbon disulphide are also produced.
2Hg(SCN)2 → 2HgS + CS2 + C3N4
Carbon disulphide combusts to carbon dioxide and sulphur dioxide:
CS2 + 3O2 → CO2 + 2SO2
The heated C3N4 partially breaks down to form nitrogen gas and cyanogen:
2C3N4 → 3(CN)2 + N2
Mercury sulphide reacts with oxygen to form mercury vapour and sulphur dioxide. If the reaction is performed inside a container, a grey film of mercury coating on its inner surface can be observed.
HgS + O2 → Hg + SO2
This reaction was discovered by Wöhler in 1821, soon after the first synthesis of mercury thiocyanate: "winding out from itself at the same time worm-like processes, to many times its former bulk, a very light material the color of graphite...". For some time, a firework product called "Pharaoschlangen" was available to the public in Germany, but was eventually banned when the toxic properties of the product were discovered through the death of several children mistakenly eating the resulting solid.
A similar, although less extreme, effect to the Pharaoh's serpent can be achieved using a firework known as a black snake. These are generally benign products, usually consisting of sodium bicarbonate or a mixture of linseed oil and naphthalenes.
Mercury thiocyanate has a few uses in chemical synthesis. It is the precursor to potassium tris(thiocyanato)mercurate(II) (K[Hg(SCN)3]) and caesium tris(thiocyanato)mercurate(II) (Cs[Hg(SCN)3]). The Hg(SCN)3− ion can also exist independently and is easily generated from the compounds above, amongst others.
Its reactions with organic halides yield two products, one with the sulfur bound to the organic compound and one with the nitrogen bound to the organic compound.
Use in chloride analysis
It was discovered that mercury thiocyanate can improve detection limits in the determination of chloride ions in water by UV-visible spectroscopy. This technique was first suggested in 1952 and has been a common method for determination of chloride ions in laboratories worldwide ever since. An automated system was invented in 1964 and then a commercial chloroanalyzer was made available in 1974 by Technicon (Tarrytown, NY, USA). The basic mechanism involves the addition of mercury thiocyanate to a solution with unknown concentration of chloride ions and iron as a reagent. The chloride ions cause the mercury thiocyanate salt to dissociate and the thiocyanate ion to bind Fe(III), which absorbs intensely at 450 nm. This absorption allows for the measurement of concentration of the iron complex. This value allows one to calculate the concentration of chloride.
It can be used for determining the concentration of chloride ions in aqueous solution. Mercury thiocyanate without iron (III) is added to a solution with an unknown concentration of chloride ions, forming a complex of the mercury thiocyanate and chloride ion that absorbs light at a 254 nm, allowing more accurate measurements of concentration than the aforementioned technique using iron.
- Davis, T. L. (1940). "Pyrotechnic Snakes". Journal of Chemical Education. 17 (6): 268–270. doi:10.1021/ed017p268.
- Sekine, T.; Ishii, T. (1970). "Studies of the Liquid-Liquid Partition systems. VIII. The Solvent Extraction of Mercury (II) Chloride, Bromide, Iodide and Thiocyanate with Some Organic Solvents" (pdf). Bulletin of the Chemical Society of Japan. 43 (8): 2422–2429. doi:10.1246/bcsj.43.2422.[permanent dead link]
- Beauchamp, A.L.; Goutier, D. "Structure cristalline et moleculaire du thiocyanate mercurique" Canadian Journal of Chemistry 1972, volume 50, p977-p981. doi:10.1139/v72-153
- "Make a Pharaoh's Snake Firework". About.com Education. Retrieved 2016-02-08.
- Bowmaker, G. A.; Churakov, A. V.; Harris, R. K.; Howard, J. A. K.; Apperley, D. C. (1998). "Solid-State 199Hg MAS NMR Studies of Mercury(II) Thiocyanate Complexes and Related Compounds. Crystal Structure of Hg(SeCN)2". Inorganic Chemistry. 37 (8): 1734–1743. doi:10.1021/ic9700112.
- Kitamura, T.; Kobayashi, S.; Taniguchi, H. (1990). "Photolysis of Vinyl Halides. Reaction of Photogenerated Vinyl Cations with Cyanate and Thiocyanate Ions". Journal of Organic Chemistry. 55 (6): 1801–1805. doi:10.1021/jo00293a025.
- Cirello-Egamino, J.; Brindle, I. D. (1995). "Determination of chloride ions by reaction with mercury thiocyanate in the absence of iron(III) using a UV-photometric, flow injection method". Analyst. 120 (1): 183–186. doi:10.1039/AN9952000183.
- "Pharaoh's snake". YouTube. September 2, 2008.
- "How to make the Pharaoh's Serpent (Mercury (II) Thiocyanate)". YouTube. March 24, 2014 | <urn:uuid:774ffd4b-dd2d-4147-92fe-e88008c32401> | 2.796875 | 1,860 | Knowledge Article | Science & Tech. | 58.408261 | 95,519,775 |
New robot technology leads Antarctic exploration into a new epoch. It is now possible to study the underside of sea ice across large distances and explore a world previously restricted to specially trained divers only.
Splash. A Weddell seal weighing almost 500 kg lands inside the tent and blocks the hole laboriously sawn out by researchers in the two-metre-thick ice to launch drones under the sea ice. The tent is lovely and warm. Small petroleum ovens provide heat to keep the hole free from ice. Outside the Antarctic sea ice stretches for miles around and the thermometer shows -15 degrees. The seal finally glides back into the water foraging for more fish and the researchers have access to the open water. The advanced technology drone is carefully lowered into the icy cold sea.
Working here (right next to the old hut used by polar explorer Robert Falcon Scott in the Antarctic winter) are researchers Lars Chresten Lund Hansen, Brian Sorrell and PhD student Bibi Ziersen, Aarhus University, along with their colleagues from Australia and New Zealand. They are developing and testing a new method to map the distribution of ice algae on the underside of the sea ice in Antarctica.
The tent covers a hole in the ice measuring 3m x 1m, and the researchers send their torpedo-shaped underwater drone down through the hole to map the underside of the sea ice. Making the hole takes most of a day and requires a major equipment package with an oil burner and steam drill.
"The drone was actually designed to study the sea bed and map factors such as sediment types, but our Australian colleagues modified the drone so that it now looks up towards the bottom of the sea ice and measures the light coming through the ice with a radiometer," says Associate Professor Lars Chresten Lund Hansen, Aarhus University.
Ice algae on the underside of the ice absorb light at certain wavelengths, and the radiometer measures how much or how little light is absorbed at these wavelengths. Based on the light measurements, the researchers can calculate the amount of algal biomass under the ice, and thereby get an idea of where the ice algae are located and how many there are. The drone follows a pre-programmed course and it maps the distribution of ice algae over very large areas where studies have not previously been possible.
An important part of the project is controlling the drone's measurements by conventional methods where ice cores are drilled out. The algae are scraped off the underside of the cores and a chlorophyll measurement reveals the number of algae. The chlorophyll figures are subsequently compared with the drone's radiometer measurements.
The aim of these investigations is to understand which factors regulate the distribution of the algae. There are some indications that the rough texture on the underside of the ice plays an important role in the algal colonisation of the sea ice. On the underside of some areas of the ice, there are thin plate-like ice crystals protruding 5 to 10 centimetres out of the bottom. The crystals are wedged between each other, forming a large surface that provides a good habitat for the diatoms that make up the bulk of the ice algae community.
Ice algae are the Antarctic's harbingers of spring
The Antarctic is completely white above the ice, but there is an abundance of colour below the ice. The small greenish-brown unicellular diatoms can grow into large colonies that form entire mats on the underside of the ice.
Ice algae are an important component of the Antarctic ecosystem. They begin to grow under the ice as soon as the Sun emerges in early spring, and survive on the small amount of sunshine that penetrates the compact layers of ice. They are also the year's first producers of food for krill and other zooplankton in the food chain. They get life going so to speak under the ice, where small creatures can frolic in the hanging garden and feast on the algae and bacteria associated with algal life.
"The ice algae account for 15-20% of the primary production in the Antarctic sea ice area. They're particularly important because they utilise the weak light in spring, when there are no other primary producers to provide food and energy for the rest of the food chain," explains Associate Professor Brian Sorrell, Aarhus University.
There are promising signs from the initial data provided by the underwater drone, and the plan is to extend the project to Arctic locations in the coming field season - either at Station North in Greenland or north of Svalbard on the research vessel R/V Lance.
Lars Chresten Lund Hansen and his colleagues used a GoPro camera to record the launching of the underwater drone and the seal's visit. See the video on Youtube: http://youtu.
Lars Chresten Lund Hansen | EurekAlert!
Abrupt cloud clearing events over southeast Atlantic Ocean are new piece in climate puzzle
23.07.2018 | University of Kansas
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
23.07.2018 | Science Education
23.07.2018 | Health and Medicine
23.07.2018 | Life Sciences | <urn:uuid:a5e76bfb-7b0b-41ef-ab1a-a398b98536f4> | 3.8125 | 1,553 | Content Listing | Science & Tech. | 42.526804 | 95,519,790 |
|MLA Citation:||Bloomfield, Louis A. "Question 850"|
How Everything Works 16 Jul 2018. 16 Jul 2018 <http://howeverythingworks.org/print1.php?QNum=850>.
Like any electromagnetic wave, a microwave has a wavelength (the spatial distance between adjacent wave crests) and a period (the temporal spacing between adjacent wave crests). The electric current that a microwave propels through a metal travels about one microwave wavelength during one microwave period. Therefore, the current can work its way around a hole in the metal only if the hole is significantly smaller than the microwave wavelength. The amplitude of the microwave doesn't matter—increasing the amplitude of the microwave just makes more current flow. | <urn:uuid:6a364821-45f0-4766-981f-74d014c15526> | 3.796875 | 149 | Knowledge Article | Science & Tech. | 42.373905 | 95,519,795 |
The concentration of contaminants usually decreases with increasing distance from a point-source disturbance, so sampling to detect ecological impacts is usually done at 1 spatial scale, often at regular intervals from the point of discharge. There is, however, concern that the choice of an inappropriate scale will cause failure to detect impacts or failure to identify and estimate the size of impacts. In this study, the putative impact of a shoreline sewage outfall on the abundance of green ephemeral algae and gastropods was sampled at 2 spatial scales (tens of metres and several kilo- metres from the point of discharge) in order to determine whether the ecological impact of effluent was comparable across these, as would be expected if the abundance of species follows the gradient of contaminants. Such sampling also enabled the putative impact of this outfall on the spatial vari- ability of taxa to be examined at 3 spatial scales: (1) among quadrats in the site with the outfall com- pared to variance among quadrats in other sites on the shore with the outfall; (2) among quadrats in non-outfall sites on the shore with the outfall compared with variance among quadrats in sites on con- trol shores; (3) between non-outfall sites on the shore with the outfall in comparison to among sites on the control shores. A greater abundance of Enteromorpha spp. was found close to the outfall than fur- ther away at both spatial scales. Patterns in the abundance of many other taxa differed between the 2 spatial scales of sampling. The density of the limpet Patelloida latistrigata was much greater close to than far from the outfall, when considered on a large spatial scale. At the smaller scale among sites on a single shore, the impact was completely reversed—densities were much smaller close to than away from the outfall. Variances, like abundances, did not always follow the gradient of contami- nants and different patterns were often seen at different spatial scales. Thus, putative impacts should be sampled on multiple spatial scales using nested sampling designs. Where this is not possible, the spatial scale at which an impact might be detected or interpreted needs to be clearly stated because the generalisation that a disturbance has a similar impact at all spatial scales relevant to the popula- tion being studied cannot be made without explicit tests.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below | <urn:uuid:e5e7ecf4-5216-4268-9a2d-f533b54a00eb> | 2.640625 | 508 | Academic Writing | Science & Tech. | 21.579412 | 95,519,877 |
BrainPort - See With Your Tongue By Year's End
The Wicab BrainPort is a device that takes information gathered by the sensors in a pair of glasses and sends them to a "lollipop" electrode array that sits on your tongue.
(BrainPort Light-gathering glasses and 'lollipop')
About two million optic nerves are required to transmit visual signals from the retina—the portion of the eye where light information is decoded or translated into nerve pulses—to the brain's primary visual cortex. With BrainPort, the device being developed by neuroscientists at Middleton, Wisc.–based Wicab, Inc., visual data are collected through a small digital video camera about 1.5 centimeters in diameter that sits in the center of a pair of sunglasses worn by the user.
Bypassing the eyes, the data are transmitted to a handheld base unit, which is a little larger than a cell phone. This unit houses such features as zoom control, light settings and shock intensity levels as well as a central processing unit (CPU), which converts the digital signal into electrical pulses—replacing the function of the retina.
SciFi movie fans find this technology truly tasty, ever since something like it was demonstrated by Doctor Emilio Lizardo (aka Lord Whorfin, aka John Lithgow) in the 1984 cult classic The Adventures of Buckaroo Bonzai Across the 8th Dimension.
(Dr. Lizardo prepares to see into the past)
The BrainPort device seems to work well in practice: patients quickly learn how to find doorways and elevator buttons and even read letters and numbers. At table, users can easily pick out cups and forks; I suppose you'd take it out to eat.
The BrainPort should be approved for market by the end of 2009; it will cost about $10,000 per machine.
Via Scientific American; learn how the
BrainPort can be used by Navy Seals. Thanks to Meditating Bear for suggesting this story.
Scroll down for more stories in the same category. (Story submitted 8/16/2009)
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(PhysOrg.com) -- In the quest to slow down and ultimately understand chemistry at the level of atoms and electrons, University of Colorado at Boulder and Canadian scientists have found a new way to peer into a molecule that allows them to see how its electrons rearrange as the molecule changes shape.
Understanding how electrons rearrange during chemical reactions could lead to breakthroughs in materials research and in fields like catalysis and alternative energy, according to CU-Boulder physics professors and JILA fellows Margaret Murnane and Henry Kapteyn, who led the research efforts with scientist Albert Stolow of the Canadian National Research Council's Steacie Institute for Molecular Sciences.
"The Holy Grail in molecular sciences would be to be able to look at all aspects of a chemical reaction and to see how atoms are moving and how electrons are rearranging themselves as this happens," Murnane said. "We're not there yet, but this is a big step toward that goal."
To be able to chart a chemical reaction, scientists need to be able to see how bonds are formed or broken between atoms in a molecule during chemical reactions. But only extremely limited tools are available to view the rapidly changing electron cloud that surrounds a molecule as the atoms move around, Murnane said. Changes in the electron cloud can happen on timescales of less than a femtosecond, or one quadrillionth of a second, representing some of the fastest processes in the natural world.
In a paper to appear in the Oct. 30 issue of Science Express, the online version of the journal Science, the CU team describes how they shot a molecule of dinitrogen tetraoxide, or N2O4, with a short burst of laser light to induce very large oscillations within the molecule. They then used a second laser to produce an X-ray, which was used to map the electron energy levels of the molecule, and most importantly, to understand how these electron energy levels rearrange as the molecule changes its shape, according to Kapteyn.
"This is a fundamentally new way of looking at molecules," Kapteyn said. "This process allowed us to freeze the motion of electrons in a system, and to capture their dizzying dance."
The researchers describe their process of stretching the N2O4 molecule as being similar to pulling on a Slinky toy and then letting it go and watching it vibrate. They used the N2O4 molecule because it vibrates more slowly compared to other molecules, allowing them to observe the physical processes under way.
In many ways, molecules are like tiny masses connected by tiny springs of differing strengths, Murnane said. These springs are the chemical bonds, made up of shared electrons, which hold all matter together. In this experiment they used ultrafast laser pulses to "twang" these springs, making the nanoscale molecular Slinkies vibrate. However, unlike real springs, when researchers vibrate the molecules their properties can change, she said.
Being able to watch and understand why the electrons did what they did is very useful in fields like alternative energy, according to the researchers.
"If we understand the nature of these processes, in the future we can then translate that knowledge into better technology, such as creating more efficient light-harvesting molecules or catalysis or perhaps even solar cells," Stolow said.
Provided by University of Colorado at Boulder
Explore further: The future of electronics is chemical | <urn:uuid:da2affda-ce1f-4474-8e81-7599ea1c0686> | 3.5625 | 709 | News Article | Science & Tech. | 27.711444 | 95,519,903 |
In computer science, the term automatic programming identifies a type of computer programming in which some mechanism generates a computer program to allow human programmers to write the code at a higher abstraction level.
There has been little agreement on the precise definition of automatic programming, mostly because its meaning has changed over time. David Parnas, tracing the history of "automatic programming" in published research, noted that in the 1940s it described automation of the manual process of punching paper tape. Later it referred to translation of high-level programming languages like Fortran and ALGOL. In fact, one of the earliest programs identifiable as a compiler was called Autocode. Parnas concluded that "automatic programming has always been a euphemism for programming in a higher-level language than was then available to the programmer."
Program synthesis is one type of automatic programming where a procedure is created from scratch, based on mathematical requirements.
Mildred Koss, an early UNIVAC programmer, explains: "Writing machine code involved several tedious steps--breaking down a process into discrete instructions, assigning specific memory locations to all the commands, and managing the I/O buffers. After following these steps to implement mathematical routines, a sub-routine library, and sorting programs, our task was to look at the larger programming process. We needed to understand how we might reuse tested code and have the machine help in programming. As we programmed, we examined the process and tried to think of ways to abstract these steps to incorporate them into higher-level language. This led to the development of interpreters, assemblers, compilers, and generators--programs designed to operate on or produce other programs, that is, automatic programming."
Generative programming is a style of computer programming that uses automated source code creation through generic frames, classes, prototypes, templates, aspects, and code generators to improve programmer productivity.[not in citation given] It is often related to code-reuse topics such as component-based software engineering and product family engineering.
Source code generation is the process of generating source code based on an ontological model such as a template and is accomplished with a programming tool such as a template processor or an integrated development environment (IDE). These tools allow the generation of source code through any of various means. A macro processor, such as the C preprocessor, which replaces patterns in source code according to relatively simple rules, is a simple form of source code generator.Source-to-source code generation tools also exist.
Over the past decade,[better source needed] a new class of automatic programming has emerged targeting sophisticated end users and IT departments looking for rapid development. These tools allow development of applications in very short periods of time (weeks rather than months). In many cases, the applications are pre-developed but customizable. Products are sometimes targeted at end users, dissatisfied with turnaround times or with IT departments looking for major productivity enhancements. These tools typically operate at a higher level of representation than code generation tools for programming languages.
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Some IDEs for Java and other languages have more advanced forms of source code generation, with which the programmer can interactively select and customize "snippets" of source code. Program "wizards", which allow the programmer to design graphical user interfaces interactively while the compiler invisibly generates the corresponding source code, are another common form of source code generation. This may be contrasted with, for example, user interface markup languages, which define user interfaces declaratively.
Besides the generation of code from a wizard or template, IDEs can generate and manipulate code to automate code refactorings that would require multiple (error prone) manual steps, thereby improving developer productivity. Examples of such features in IDEs are the refactoring class browsers for Smalltalk and those found in Java IDEs like Eclipse.
A specialized alternative involves the generation of optimized code for quantities defined mathematically within a Computer algebra system (CAS). Compiler optimization consisting of finding common intermediates of a vector of size requires a complexity of or operations whereas the very design of a computer algebra system requires only operations. These facilities can be used as pre-optimizer before processing by the compiler. This option has been used for handling mathematically large expressions in e.g. computational (quantum) chemistry.
Jenifer is a full-scale code generator that provides a pattern called template, from which the code is generated. After definig screens, menus and reports, Genifer creates the data files, index files and programs.
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(hì'drəjən) [Gr.,=water forming], gaseous chemical element; symbol H; at. no. 1; interval in which at. wt. ranges 1.00784–1.00811; m.p. -259.14 degrees Celsius; b.p. -252.87 degrees Celsius; density 0.08988 grams per liter at STP; valence usually +1.
Atmospheric hydrogen is a mixture of three isotopes. The most common is called protium (mass no. 1, atomic mass 1.007822); the protium nucleus (protium ion) is a proton. A second isotope of hydrogen is deuterium (mass no. 2, atomic mass 2.0140), the so-called heavy hydrogen, often represented in chemical formulas by the symbol D. The deuterium nucleus, or ion, is called the deuteron; it consists of a proton plus a neutron. The two isotopes are found in atmospheric hydrogen in the proportion of about 1 atom of deuterium to every 6,700 atoms of protium. Protium and deuterium differ slightly in their chemical and physical properties; for example, the boiling point of deuterium is about 3 degrees Celsius lower than protium. The properties of compounds they form differ depending on the ratio of the two isotopes present.
Deuterium oxide (D2O), the so-called heavy water, is present in ordinary water; the concentration of deuterium oxide is increased by electrolysis of the water. The melting point (3.79 degrees Celsius), boiling point (101.4 degrees Celsius), and specific gravity (1.107 at 25 degrees Celsius) of deuterium oxide are higher than those of ordinary water. Deuterium oxide is used as a moderator in nuclear reactors. Deuterium is also of importance because of the wide use it has found in scientific research; for example, chemical reaction mechanisms have been studied by the use of deuterium atoms as tracers (i.e., deuterium is substituted for atoms of ordinary hydrogen in compounds), making it possible to follow the course of individual molecules in a reaction.
Tritium (mass no. 3, atomic mass 3.016), a third hydrogen isotope, is a radioactive gas with a half-life of about 121/4 years; it is often represented in chemical formulas by the symbol T. It is produced in nuclear reactors and occurs to a very limited extent in atmospheric hydrogen. It is used in the hydrogen bomb, in luminous paints, and as a tracer. The tritium nucleus, or ion, is called the triton; it consists of a proton plus two neutrons. Tritium oxide (T2O) has a melting point (4.49 degrees Celsius) higher than that of deuterium oxide.
Besides being a mixture of three isotopes, hydrogen is a mixture of two forms, an ortho form and a para form, which differ in their electronic and nuclear spins. At room temperature atmospheric hydrogen is about 3/4ortho-hydrogen and 1/4para-hydrogen. The two forms differ slightly in their physical properties.
Under ordinary conditions hydrogen is a colorless, odorless, tasteless gas that is only slightly soluble in water; it is the least dense gas known. It is the first element in Group 1 of the periodic table. Ordinary hydrogen gas is made up of diatomic molecules (H2) that react with oxygen to form water (H2O) and hydrogen peroxide (H2O2), usually as a result of combustion. A jet of hydrogen burns in air with a very hot blue flame. The flame produced by a mixture of oxygen and hydrogen gases (as in the oxyhydrogen blowpipe) is extremely hot and is used in welding and to melt quartz and certain glasses. Hydrogen gas must be used with caution because it is highly flammable; it forms easily ignited explosive mixtures with oxygen or with air (because of the oxygen in the air). At high temperatures hydrogen is a chemically active mixture of monohydrogen (atomic hydrogen) and the normal diatomic hydrogen (see allotropy).
Hydrogen has a great affinity for oxygen and is a powerful reducing agent (see oxidation and reduction). It reacts with nitrogen to form ammonia. With the halogens it forms compounds (hydrogen halides) that are strongly acidic in water solution. With sulfur it forms hydrogen sulfide (H2S), a colorless gas with an odor like rotten eggs; with sulfur and oxygen it forms sulfuric acid. It combines with several metals to form metal hydrides such as calcium hydride. Combined with carbon (and usually other elements) it is a constituent of a great many organic compounds, such as hydrocarbons, carbohydrates, fats, oils, proteins, and organic acids and bases.
It is theoretically possible for hydrogen to exhibit the properties of a metal, such as electrical conductivity. Although researchers have been able to squeeze hydrogen into liquid and crystalline solid states through applications of intense heat, cold, and pressure, the metallic form eluded them until 1996. By compressing liquid hydrogen to nearly 2 million atmospheres pressure and a temperature of 4,400 degrees Kelvin, a team at the Lawrence Livermore National Laboratory created metallic hydrogen for a millionth of a second. While there is no practical application for the accomplishment, proof of the existence of a metallic form of hydrogen may have implications for theories of how Jupiter's magnetic field is produced.
While hydrogen is only about one part per million in the atmosphere, it is the most abundant element in the universe. It is believed that hydrogen makes up about three quarters of the mass of the universe, or over 90% of the molecules. It is found in the sun and in other stars, where it is the major fuel in the fusion reactions (see nucleosynthesis) from which stars derive their energy.
Hydrogen is prepared commercially by catalytic reaction of steam with hydrocarbons, by the reaction of steam with hot coke (carbon), by the electrolysis of water, and by the reaction of mineral acids on metals. Millions of cubic feet of hydrogen gas are produced daily in the United States alone.
Hydrogen was formerly used for filling balloons, airships, and other lighter-than-air craft, a dangerous practice because of hydrogen's explosive flammability; there were disastrous fires, e.g., the immolation of the German airship Hindenburg at its mooring at Lakehurst, N.J., in 1937. Helium is preferable for use in lighter-than-air craft since it is not flammable. Hydrogen is used in the Haber process for the fixation of atmospheric nitrogen, in the production of methanol, and in hydrogenation of fats and oils. It is also important in low-temperature research. It can be liquefied under pressure and cooled; when the pressure is released, rapid evaporation takes place and some of the hydrogen solidifies.
Although hydrogen was prepared many years earlier, it was first recognized as a substance distinct from other flammable gases in 1766 by Henry Cavendish, who is credited with its discovery; it was named by A. L. Lavoisier in 1783. Deuterium was discovered by H. C. Urey, F. G. Brickwedde, and G. M. Murphy in 1932, although its existence had been suspected for some years. Deuterium oxide was also discovered by Urey and was first obtained in nearly pure form by G. N. Lewis. Tritium was synthesized by Ernest Rutherford, L. E. Oliphant, and Paul Harteck in 1935.
Hydrogen fuel cell vehicles like this prototype have the potential to function with greater efficiency than gasoline-powered vehicles...
The lightest chemical element ( atomic number = 1; relative atomic mass = 1.00794; melting point = 259.14°C; boiling point =...
The lightest of all gases, recognized as an element by Cavendish in 1766 and named by Lavoisier after water (Greek hudro , water). Hydrogen... | <urn:uuid:ca87052e-88dc-4c85-b6bd-413b1b2cc3a2> | 3.765625 | 1,696 | Knowledge Article | Science & Tech. | 49.553751 | 95,519,930 |
This website aims to tell you nearly everything you need (and may ever want) to know about convergent evolution. It allows you to explore the way that similar adaptive solutions have repeatedly evolved from unrelated starting points on the tree of life, as though following a metaphorical ‘map’.
We have identified hundreds of examples of convergence, so if you want to learn about convergence in sex (e.g. love-darts), eyes (e.g. camera-eyes in jellyfish), agriculture (e.g. in ants) or gliding (e.g. in lizards and mammals) then this is your best port of call.
A note to all book-lovers out there: many of the examples of convergence mentioned in the Map of Life can be found in Simon Conway Morris’s latest book, The Runes of Evolution.
Any of the information presented in the Map of Life may be freely reproduced, as long as it is acknowledged fully. Citation details can be found at the bottom of each Topic page.
Showcase Topic: Autumn leaf colouration
Autumn colours are likely to be adaptive, as the 'default' is simply to remain green up to leaf fall, and both red and yellow leaf colouration have evolved independently on many occasions in gymnosperms and woody angiosperms.
Spotlight on Research:
“Hear, hear: the convergent evolution of echolocation in bats?”
E.C. Teeling 2009, Trends in Ecology and Evolution, volume 24, pages 351-354
There is still controversy surrounding the evolutionary origins of laryngeal echolocation in bats, which revolves around how one chooses to interpret bat systematics. This review discusses recent findings from genetic studies with respect to the question how many times this astonishing sensory capacity evolved in bats.
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London: Scientists say a previously little known form of sulphur, may be the predominant form of the element in Earth`s lower crust and upper mantle.
Known as the trisulphur ion, or S3-, it is quite different from the better-known sulphate (SO42-) and sulphide, S2- sulphur ions.
Study`s first author Gleb Pokrovski, an experimental geochemist at Géosciences Environnement Toulouse in France, and colleagues did not sample this deep sulphur directly, reports Nature.
It is found too far down in Earth`s crust to be reached by drilling - not to mention that it would change chemically when drawn to the surface.
Instead, the team used a device known as a diamond anvil cell to heat sulphur-rich fluids to temperatures and pressures comparable to those 10-100 kilometres below the surface, using infrared Raman spectroscopy to monitor the types of chemical produced.
They found that the trisulphur ion is the most stable form of the element under such conditions. Diamond anvil cells are common in geochemical research, but using them to study fluids is tricky.
Although the finding sounds esoteric, it could be important in understanding the development of early Earth.
Conventional theory holds that Earth`s atmosphere was extremely low in oxygen before photosynthesis got going, about 2 billion-2.4 billion years ago.
This theory is based in part on ratios of the four stable isotopes of sulphur - 32S, 33S, 34S and 36S - found in mineral deposits from that era. These ratios, geochemists have found, can be affected by the amount of oxygen in the atmosphere, so they are useful proxies for oxygen levels. But studies of the ratios did not take into account how they might have been affected by S3-, says Pokrovski.
"Sulphur isotope geochemistry has been based on a fundamental assumption that sulphate (or sulphur dioxide) and hydrogen sulphide are the two principal sulphur-bearing aqueous species at high temperatures," says Hiroshi Ohmoto, a geochemist at Pennsylvania State University, University Park, Pennsylvania.
"This study showed that it was a too simplistic assumption, and suggests the importance of studying the kinetics of sulphur isotopic reactions among H2S, trisulphur ion, sulphate, and SO2 in order to correctly interpret sulphur isotope data on ore deposits and igneous rocks."
Ariel Anbar, a biogeochemist at Arizona State University in Tempe, agrees. "Sulphur-isotope variations have become a critical tool in assessing the evolution of oxygen in Earth`s ancient atmosphere," he says.
"The discovery that S3- can be an important form of sulphur in subduction-zone settings will probably lead to new ideas about the causes of some sulphur-isotope variations, particularly in sulphur derived from volcanic sources."
Craig Manning, a geochemist at the University of California, Los Angeles, adds that the finding could also be useful to those studying the formation of precious ores.
The study has been published today in Science1. | <urn:uuid:50366284-8927-4447-8dff-91633aa67c87> | 3.9375 | 672 | News Article | Science & Tech. | 33.03393 | 95,519,942 |
Isotopic values of Antarctic Krill in relation to foraging habitat of penguins
Cited 5 time in
- Isotopic values of Antarctic Krill in relation to foraging habitat of penguins
- Kokubun, Nobuo
- GPS tracking; Off-shelf; On-shelf; Phytoplankton; Stomach flushing
- Issue Date
- Kokubun, Nobuo, et al. 2014. "Isotopic values of Antarctic Krill in relation to foraging habitat of penguins". Ornithol. Sci., 14: 13-20.
- Antarctic Krill Euphausia superba is a key component of the Antarctic
coastal marine ecosystem. Investigations into stable isotopic values of krill in predation
hotspots are important in facilitating our understanding of the feeding environments
of krill in a local coastal ecosystem. In this study we investigated stable
isotopic values and maturity and size composition of krill at a small spatial scale,
by logging GPS tracks of five Chinstrap Pygoscelis antarcticus and seven Gentoo P.
papua penguins, and analyzing their stomach contents. The study was conducted at a
penguin colony on Barton Peninsula, King George Island, Antarctica. The main food
item of both species was Antarctic Krill (>98% wet mass). One Chinstrap and four
Gentoo penguin foraging trips were classified as “on-shelf” trips, and four Chinstrap
and three Gentoo Penguin foraging trips were classified as “off-shelf” trips. Krill
collected from off-shelf trips had higher δ15N (4.22±0.28‰) values than those from
on-shelf trips (3.78±0.29‰). The δ13C of the krill samples did not differ between
the two penguin species or between trip types. The proportion of juvenile krill taken
was higher for Chinstrap (13.04±4.97%) than Gentoo penguins (3.33±2.43%). Our
results suggest that the main food source of the krill in our sample originated as non
benthic planktonic/suspended organic matter, and that krill in off-shelf habitat may
occasionally consume higher trophic level prey compared to those in on-shelf habitats.
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Osaka - In the same way a glove will only fit one hand, molecules have the symmetry that controls their behavior and interactions. In drug design, this means reversing the symmetry of a molecule can mean the difference between an effective treatment or a compound that has serious negative effects. As a further complication, making chemicals as a single pure mirror image, or separating mixtures of the two types, is very difficult.
Now a team of chemists of Osaka and Iwate Medical University has now developed a highly efficient way to make a unique screw-like chemical that could offer new routes to pure mirror images of other molecules. They reported their findings in Organic Letters.
"The twisted shape of helicenes makes them ideal for use in asymmetric catalysis" lead author Tetsuya Tsujihara says. "We previously developed a simple synthesis and resolution for this class of molecule and now, for the first time, we have added a thiophene group."
Helicene is a molecule with six hexagonal benzene molecules fused together so the rings twist back over themselves out of the plane of the molecule. The direction of the twist is locked, meaning two possible helices are possible, each a mirror image of the other. Think of the way a screw might turn clockwise or anticlockwise depending on the direction of the thread.
The researchers built upon their earlier studies, making and separating the two mirror images of helicene molecules. This time they changed their structure to include a new sulfur-containing group. This change could allow the screw-shaped molecules to be used as asymmetric catalysts for controlling interactions of other chemicals in reactions to directly produce molecules of a single mirror image.
"Adding the thiophene group is new development of the helicene skeleton, which should change the physical properties of the molecule and make these much more interesting to materials scientists," coauthor Tomikazu Kawano says. "We are also continuing to explore the promising asymmetric reactivity of these twisted catalysts."
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A View from Emerging Technology from the arXiv
Black Holes Break Up During Star Collapse, Say Astrophysicists
The latest simulations show that black holes can fragment into several pieces during a supernova, say astrophysicists
But how exactly does such a collapse occur? The conventional view is that the collapse occurs symmetrically, like a shrinking balloon. But that’s really only because this is the simplest situation to explore mathematically. Include any small perturbations in the calculations that change the symmetry and the mathematics of general relativity immediately becomes unmanageable.
Unless you have a supercomputer to help. Fortunately, this kind of computing power is becoming more common and Burkhard Zink at Max Planck Institute for Astrophysics in Garching and a few buddies have put it to good use.
They’ve simulated what happens to a collapsing, rotating star which is radially oscillating like a bell. That’s a reasonable enough scenario for a collapsing star in the real universe.
Astrophysicists have long known that such a star immediately becomes unstable but exactly what happens to it has eluded them.
With the help of some useful astrophysical computing code called Cactus, Zink and pals have found out. They say the star breaks into two or more self-gravitating parts that each develop their own event horizons. In other words, the star fragments into several black holes as it collapses.
What’s interesting about this is that the black hole fragments begin to spiral in towards each other and this ought to generate a unique gravitational wave signature that the next generation of detectors may well be able to pick up.
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1. Generalist arthropod predators act as natural enemies of insect pests in agro-ecosystems. Crop management activities may cause a reduction in arthropod densities, either directly through mortality and emigration, or indirectly through habitat disruption. Our aim was to quantify direct mortality caused by mechanical crop treatments. For some treatments, we also quantified emigration and other indirect effects, such as population declines caused by the impact of habitat deterioration on reproduction and survival. 2. Direct mortality was determined by measuring predator densities simultaneously in control and treatment plots using closed emergence traps immediately following a mechanical treatment. Treatments consisted of the following crop management activities: ploughing, non-inversion tillage, superficial soil loosening, mechanical weed control and grass cutting. Predator densities were measured a second time 5-26 days after treatment to quantify emigration and indirect effects. 3. All treatments had a negative influence on one or more arthropod taxa. Direct mortality caused a 25-60% reduction in arthropod densities. Overall, spiders were more vulnerable to mechanical crop treatment than carabid and staphylinid beetles. Intensive soil cultivation, such as ploughing and soil loosening, did not kill more arthropods than weed harrowing and grass cutting. 4. We estimated the cumulative effects of mortality, emigration and indirect effects 3 weeks following treatment. The cumulative effect was greater than direct arthropod mortality, suggesting delayed effects of habitat disruption. 5. Grass cutting caused spiders and staphylinid beetles to move out of the crop, except in one case when the grass was left to dry, suggesting an important role of organic material or structural elements for arthropod persistence. Our results also suggest that arthropod predators aggregate in undisturbed or less disrupted habitats. 6. Synthesis and applications. Mechanical operations in arable crops and grass cutting cause mortality and emigration of generalist arthropod predators, especially spiders. Effects can be species-specific and are likely to be affected by the timing of management. In grassland, cutting and removal have greater adverse impacts than leaving cuttings that contribute to habitat structure. Adjacent, less-disturbed refuge areas are colonized by predators following husbandry events, demonstrating significant spatial dynamics among farmland arthropods. The negative effects of crop husbandry operations might be mitigated by the provision of refuge areas within and adjacent to fields and by maintaining crop and landscape diversity.
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On August 21, almost entire United States witnessed its first total solar eclipse in 99 years. During the eclipse, the moon completely blocked the light of the sun and plunged many places into the darkness in the midday.
However, the August solar eclipse did more than just give viewers a cosmic show on the ground. It not only casted a shadow on our planet but also generated bow waves in the Earth’s upper atmosphere.
Bow waves are mysterious ripples. They are similar to the waves created by the bow of a ship when it moves through the water. The waves are attributed to sudden change in temperature during solar eclipse. As the moon travels between the sun and Earth, its shadow blocks the sun's energy and rapidly cools the area beneath it.
The hypothesis that a solar eclipse would produce bow waves in the upper atmosphere emerged in 1970 but it never adequately measured or demonstrated until now.
When Moon's cool shadow swept across the United States in August’s solar eclipse, it moved with supersonic speed through the Earth's atmosphere. The movement was so quick it created waves in the Earth’s atmosphere.
“We were looking at some phenomena that were expected but never had the chance to be observed. That was the surprise we found... we had a large coverage and our system is sensitive enough to be able to see these smaller variations. That was really very interesting to us.” Study author Shun-Rong Zhang from the MIT Haystack Observatory told Gizmodo.
To investigate, MIT researchers used a large network of about 2,000 satellites placed across North America. The data collected from the satellites provided the evidence of tiny bow waves in Earth’s ionosphere, which is located about 37 miles above the surface. The bow waves moved mostly at the speed of 670 mph and lasted for about 1 hour. But they were not intense enough to have any negative effects on systems.
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Redox conditions are an important regulator of aqueous biogeochemistry and knowledge about them is crucial for an understanding of the fate and occurrence of nitrates, emerging substances, and organic compounds in shallow groundwater. The aim of this paper is to determine redox categories, along with prevailing redox processes, and the differences in groundwater quality between shallow alluvial aquifers of Serbia's major rivers. The research was conducted on public water-supply wells in the alluvial plain of the Velika Morava River, the Danube River, the Tisa River and the alluvial aquifer of the Sava River. The study period is 2010–2014 and the number of collected and analysed samples 243. The redox categories and processes are characterised by concentrations of aqueous redox species (dissolved oxygen, nitrate, dissolved iron, manganese, and sulphate and sulphide concentrations). Parameters such as Eh, total organic carbon, HCO3−, pH, total iron concentrations, temperature and specific conductivity were also analysed. Different geological and hydrogeological settings, groundwater abstraction, distances between the wells and the river, well depths, and anthropogenic impacts result in diverse redox conditions. Groundwater in selected alluvial aquifers is mostly defined as anoxic, with one predominant process, or mixed anoxic, with various redox processes occurring simultaneously.
Redox conditions and groundwater quality issues of selected alluvial aquifers in Serbia
B. Majkić-Dursun, J. Tončić, A. Petković, J. Čolić; Redox conditions and groundwater quality issues of selected alluvial aquifers in Serbia. Water Science and Technology: Water Supply 1 August 2016; 16 (4): 1086–1093. doi: https://doi.org/10.2166/ws.2016.027
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Thermodynamic origin and graphical methods of phase theory
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Thermodynamics is often considered difficult to understand due to extensive use of mathematics. In the present paper, a graphical approach will be used to explain the origin of phase diagrams starting from the fundamental equation of thermodynamics dU = Tds − Pdv defined by J.W. Gibbs. The characteristic variables of this equation are the specific entropy s and the specific volume v, which lead in a straightforward way to s-v phase diagrams. It will be demonstrated through monotonicity of the internal energy curves of the different phases of the system and graphical Legendre transformations how pressure-entropy (P-s) and temperature-volume (T-v) phase diagrams are linked to s-v phase diagrams and how the latter two phase diagrams are related to pressure-temperature (P-T) phase diagrams.
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Based on the future movement of Typhoon Jelawat and Tropical Storm Ewinar, cold air may plunge into part of the northern U.S. days later.
You could call it the typhoon teleconnection, or the Tokyo, Chicago-New York connection, or something of that sort.
AccuWeather.com meteorologists have observed for years that whether tropical cyclones in the Western Pacific curve away from Asia or plow inland over China determines whether or not cold air aims for portions of the Midwest and Northeast approximately 10 to 14 days later.
According to Expert Senior Meteorologist Bob Smerbeck, "When a typhoon or strong tropical storm curves to the northeast along the coast of Asia, the way the jet stream gets jumbled up in the process usually allows a batch of chilly air to plunge southward from Canada to the swath from the northern Rockies to the northeastern U.S."
The jet stream is a zone of high speed winds at high levels of the atmosphere that often marks the path weather systems will take. The jet stream typically marks the boundary between cool air to its north and warm air to its south.
In short, the way a tropical cyclone curves northeast of Japan amplifies the jet stream over the Pacific Ocean and North America.
Exactly how strongly the tropical system curves will determine the wavelength and position of jet stream ridges and troughs over the Pacific Ocean and North America. (A ridge is a northward bulge of warm in the jet stream; a trough is a southward dip of chilly air.)
"In the case of Typhoon Sanba, which curved away from southeastern China around Sept. 14, 2012, but slammed Korea before heading north of Japan around Sept. 16, we had big ridge set up in the western and eastern Pacific with a trough in the middle of the Pacific and a trough over the Upper Midwest and Northeast U.S. during the latter part of September," Smerbeck said.
The situation in the Western Pacific now is a bit more complex in that we have two tropical cyclones, so we may not have a textbook case of how the push of cold air behaves a couple of weeks later.
We do believe that as Jelawat curves northeastward across Japan and Ewinar curves east of Japan this weekend, a push of cold air will begin to drive southward next week over western Canada," Smerbeck said, "From there, the cold push may get hung up over the North Central states or could drive more into the Great Lakes and Northeast next weekend into week two of October."
When tropical cyclones plow northwestward into mainland China and diminish, there is no direct connection in the weather a couple of weeks later for the northern U.S. Neither Jelawat nor Ewinar are forecast to reach westward into mainland China.
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Twelve people were injured when a flying lava bomb punctured the roof of a lava tour boat, causing a large hole in the vessel.
While Trump and Putin met for a summit in Helsinki, Finland, on Monday morning, a message about climate change was hung from a church by an environmental activist group.
En promedio, 37 niños mueren anualmente al ser olvidados dentro de un auto.
The tournament is being held in eastern Scotland, a region which has a history of extreme weather that can create chaos for golfers and spectators.
Following a push of dry air during the middle part of this week, a humid and rather wet weather pattern is forecast to evolve over the eastern third of the nation during the latter part of July.
The ongoing Kilauea volcano eruptions in Hawaii have led to the formation of a tiny, new piece of land made of lava, which was initially considered to be an island.
An organizing tropical threat will heighten the risk for flooding from the Philippines to Vietnam and Laos into midweek.
A grueling heat wave caused at least eight deaths across Japan since Saturday, and the dangerous conditions are not forecast to subside through the duration of the week. | <urn:uuid:ff351fd9-a9ea-4491-8580-46e0fb221246> | 2.890625 | 871 | News Article | Science & Tech. | 50.231968 | 95,520,038 |
ScienceDaily (May 17, 2011) — Climbing is possibly one of the riskiest things an adult tarantula can do. Weighing in at anything up to 50g, the dry attachment systems that keep daintier spiders firmly anchored are on the verge of failure in these colossal arachnids.
"The animals are very delicate. They wouldn't survive a fall from any height," explains Claire Rind from the University of Newcastle, UK.
In 2006, Stanislav Gorb and his colleagues published a paper in Nature suggesting that tarantulas may save themselves from falling by releasing silk threads from their feet. However, this was quickly refuted by another group that could find no evidence of the silk. Fascinated by spiders and intrigued by the scientific controversy, Rind decided this was too good a challenge to pass up and discovered that tarantulas shoot silk from their feet when they lose their footing. She publishes her results in The Journal of Experimental Biology.
Teaming up with undergraduate Luke Birkett, Rind tested how well three ground-dwelling Chilean rose tarantulas kept their footing on a vertical surface. Gently placing one of the animals in a very clean aquarium with microscope slides on the floor, the duo cautiously upended the aquarium to see if the tarantula could hang on. "Given that people said tarantulas couldn't stay on a vertical surface, we didn't want to find that they were right," remembers Rind. But the spider didn't fall, so the duo gave the aquarium a gentle shake. The tarantula slipped slightly, but soon regained its footing. So the spider had held on against the odds, but would Rind find silk on the microscope slides?
Looking at the glass by eye, Rind couldn't see anything, but when she and Birkett looked closely under a microscope, they found minute threads of silk attached to the microscope slide where the spider had stood before slipping.
Next, Rind had to prove that the silk had come from the spiders' feet and not their web-spinning spinnerets. Filming the Chilean rose tarantulas as they were rotated vertically, Rind, Benjamin-James Duncan and Alexander Ranken disregarded any tests where other parts of the spiders' bodies contacted the glass and confirmed that the feet were the source of the silk. Also, the arachnids only produced their safety threads when they slipped.
But where on the spiders' feet was the silk coming from? Having collected all of the moulted exoskeletons from her Mexican flame knee tarantula, Fluffy, when she was young, Rind looked at them with a microscope and could see minute threads of silk protruding from microscopic hairs on Fluffy's feet. Next, the team took a closer look at moults from Fluffy, the Chilean rose tarantulas and Indian ornamental tarantulas with scanning electron microscopy and saw minute reinforced silk-producing spigots, which extended beyond the microscopic attachment hairs on the spiders' feet, widely distributed across the foot's surface. Rind also looked at the tarantula family tree, and found that all three species were only distantly related, so probably all tarantula feet produce the life-saving silk threads.
Finally, having noticed the distribution of the spigots, Rind realised that tarantulas could be the missing link between the first silk-producing spiders and modern web spinners. She explains that the spread of spigots on the tarantula's foot resembled the distribution of the silk spigots on the abdomen of the first silk spinner, the extinct Attercopus spider from 386 million years ago. The modern tarantula's spigots also looked more similar to mechanosensory hairs that are distributed over the spider's entire body, possibly making them an evolutionary intermediate in the development of silk spinning. So, not only has Fluffy settled a heated scientific debate but she also may be a link to the silk spinners of the past. | <urn:uuid:ca31d707-43f2-4835-8bf4-a584a27d3e37> | 3.3125 | 828 | Personal Blog | Science & Tech. | 39.92081 | 95,520,046 |
Polyphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic ring structures. In biology, the polyphosphate esters ADP and ATP are involved in energy storage. A variety of polyphosphates find application in mineral sequestration in municipal waters, generally being present at 1 to 5 ppm. GTP, CTP, and UTP are also nucleotides important in the protein synthesis, lipid synthesis, and carbohydrate metabolism, respectively.
The structure of tripolyphosphoric acid illustrates the principles which define the structures of polyphosphates. It consists of three tetrahedral PO4 units linked together by sharing oxygen centres. For the linear chains, the end phosphorus groups share one oxide and the others phosphorus centres share two oxide centres. The corresponding phosphates are related to the acids by loss of the acidic protons. In the case of the cyclic trimer each tetrahedron shares two vertices with adjacent tetrahedra.
Sharing of three corners is possible. This motif represents crosslinking of the linear polymer. Crosslinked polyphosphates adopt the sheet-structure Phyllosilicates, but such structures occur only under extreme conditions.
Formation and synthesis
Polyphosphates arise by polymerization of phosphoric acid derivatives. The process begins with two phosphate units coming together in a condensation reaction.
- 2 HPO42− ⇌ P2O74− + H2O
The condensation is shown as an equilibrium because the reverse reaction, hydrolysis, is also possible. The process may continue in steps; at each step another PO3 unit is added to the chain, as indicated by the part in brackets in the illustration of polyphosphoric acid. P4O10 can be seen as the end product of condensation reactions, where each tetrahedron shares three corners with the others. Conversely, a complex mix of polymers is produced when a small amount of water is added to phosphorus pentoxide.
Acid-base and complexation properties
Polyphosphates are weak bases. A lone pair of electrons on an oxygen atom can be donated to a hydrogen ion (proton) or a metal ion in a typical Lewis acid-Lewis base interaction. This has profound significance in biology. For instance, adenosine triphosphate is about 25% protonated in aqueous solution at pH 7.
- ATP4− + H+ ⇌ ATPH3−, pKa 6.6
Further protonation occurs at lower pH values.
The "high energy" phosphate bond
- ATP4− + Mg2+ ⇌ MgATP2−, log β 4
is particularly large. The formation of the magnesium complex is a critical element in the process of ATP hydrolysis, as it weakens the link between the terminal phosphate group and the rest of the molecule.
The energy released in ATP hydrolysis,
- ATP4− + H2O → ADP3− + Pi−
at ΔG -36.8 kJ mol−1 is large by biological standards. Pi stands for inorganic phosphate, which is protonated at biological pH. However, it is not large by inorganic standards. The term "high energy" refers to the fact that it is high relative to the amount of energy released in the organic chemical reactions that can occur in living systems.
High-polymeric inorganic polyphosphates
High molecular weight polyphosphates are well known. One derivative is the glassy (i.e., amorphous) Graham’s salt. Crystalline high molecular weight polyphosphates include Kurrol’s salt and Maddrell’s salt. These species have the formula [NaPO3]n[NaPO3(OH)]2 where n can be as great as 2000. In terms of their structures, these polymers consist of PO3− "monomers", with the chains are terminated by protonated phosphates.
High-polymeric inorganic polyphosphates were found in living organisms by L. Liberman in 1890. These compounds are linear polymers containing a few to several hundred residues of orthophosphate linked by energy-rich phosphoanhydride bonds.
Previously, it was considered either as “molecular fossil” or as only a phosphorus and energy source providing the survival of microorganisms under extreme conditions. These compounds are now known to also have regulatory roles, and to occur in representatives of all kingdoms of living organisms, participating in metabolic correction and control on both genetic and enzymatic levels. Polyphosphate is directly involved in the switching-over of the genetic program characteristic of the exponential growth stage of bacteria to the program of cell survival under stationary conditions, “a life in the slow line”. They participate in many regulatory mechanisms occurring in bacteria:
- They participate in the induction of rpoS, an RNA-polymerase subunit which is responsible for the expression of a large group of genes involved in adjustments to the stationary growth phase and many stressful agents.
- They are important for cell motility, biofilms formation and virulence.[clarification needed]
- Polyphosphates and exopolyphosphatases participate in the regulation of the levels of the stringent response factor, guanosine 5'-diphosphate 3'-diphosphate (ppGpp), a second messenger in bacterial cells.
- Polyphosphates participate in the formation of channels across the living cell membranes. The above channels formed by polyphosphate and poly-b-hydroxybutyrate with Ca2+ are involved in the transport processes in a variety of organisms.
- An important function of polyphosphate in microorganisms—prokaryotes and the lower eukaryotes—is to handle changing environmental conditions by providing phosphate and energy reserves. Polyphosphates are present in animal cells, and there are many data on its participation in the regulatory processes during development and cellular proliferation and differentiation—especially in bone tissues and brain.
In humans polyphosphates are shown to play a key role in blood coagulation. Produced and released by platelets they activate Factor XII which is essential for blood clot formation. Furthermore, platelets-derived polyphosphates activate blood coagulation factor XII (Hageman factor) that initiates fibrin formation and the generation of a proinflammatory mediator, bradykinin that contributes to leakage from the blood vessels and thrombosis. Inorganic polyphosphates play a crucial role in tolerance of yeast cells to toxic heavy metal cations.
- "Archived copy" (PDF). Archived from the original (PDF) on 2011-04-19. Retrieved 2011-04-20.
- Storer A, Cornish-Bowden A (1976). "Concentration of MgATP2- and other ions in solution. Calculation of the true concentrations of species present in mixtures of associating ions". Biochem J. 159 (1): 1–5. doi:10.1042/bj1590001. PMC . PMID 11772.
- Wilson J, Chin A (1991). "Chelation of divalent cations by ATP, studied by titration calorimetry". Anal Biochem. 193 (1): 16–9. doi:10.1016/0003-2697(91)90036-S. PMID 1645933.
- Garfinkel L, Altschuld R, Garfinkel D (1986). "Magnesium in cardiac energy metabolism". J Mol Cell Cardiol. 18 (10): 1003–13. doi:10.1016/S0022-2828(86)80289-9. PMID 3537318.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
- Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in Ullmann’s Encyclopedia of Industrial Chemistry 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_465.pub3
- Ruiz FA, Lea CR, Oldfield E, Docampo R (Oct 2004). "Human platelet dense granules contain polyphosphate and are similar to acidocalcisomes of bacteria and unicellular eukaryotes". J Biol Chem. 279 (43): 44250–7. doi:10.1074/jbc.M406261200. PMID 15308650.
- Müller F, Mutch NJ, Schenk WA, Smith SA, Esterl L, Spronk HM, Schmidbauer S, Gahl WA, Morrissey JH, Renné T (Dec 2009). "Platelet polyphosphates are proinflammatory and procoagulant mediators in vivo". Cell. 139 (6): 1143–56. doi:10.1016/j.cell.2009.11.001. PMC . PMID 20005807.
- "Newly discovered mechanism by which blood clots form". physorg.com. December 10, 2009. Retrieved 13 December 2009.
- Andreeva N, Ryazanova L, Dmitriev V, Kulakovskaya T, Kulaev I (Aug 2013). "Adaptation of Saccharomyces cerevisiae to toxic manganese concentration triggers changes in inorganic polyphosphates". FEMS Yeast Res. 13 (5): 463–470. doi:10.1111/1567-1364.12049. PMID 23663411.
- Pavlov E, Grimbly C, Diao CT, French RJ (September 2005). "A high-conductance mode of a poly-3-hydroxybutyrate/calcium/polyphosphate channel isolated from competent Escherichia coli cells". FEBS Lett. 579 (23): 5187–92. doi:10.1016/j.febslet.2005.08.032. PMID 16150446.
- Kulaev I, Vagabov V, Kulakovskaya T (1999). "New aspects of inorganic polyphosphate metabolism and function". J. Biosci. Bioeng. 88 (2): 111–29. doi:10.1016/S1389-1723(99)80189-3. PMID 16232585.
- Kulaev I, Kulakovskaya T (2000). "Polyphosphate and phosphate pump". Annu. Rev. Microbiol. 54: 709–34. doi:10.1146/annurev.micro.54.1.709. PMID 11018142. | <urn:uuid:cae114a3-af0b-4b11-a3c6-ce106935cfb2> | 3.6875 | 2,341 | Knowledge Article | Science & Tech. | 49.288007 | 95,520,066 |
With NASA’s Juno mission to Jupiter arriving next week, researchers look to our local, ancient behemoth to figure out how planets form – including our own – as Stephen Ornes reports
For the last five years, NASA’s Juno spacecraft has been barrelling towards its final destination: Jupiter, king of the planets. On 4 July this year (or 4 July in the US, at least, actually early morning on 5 July in Europe) the four-tonne, spinning craft – which looks like an oversized propeller that has abandoned its plane – will fire its thrusters and slow down enough to be captured by the gas giant’s gravity. The burn should only last about 40 minutes, but they’ll be a tense 40 minutes: during that time, as Juno shifts from orbiting the Sun to orbiting Jupiter, the rest of its devices will go quiet. (As will the physicists at NASA’s Jet Propulsion Laboratory in Pasadena, California, tracking the mission from the ground and, one imagines, with fingers crossed.) Then the instruments should flicker back on, and over the course of more than 35 long, loping polar orbits throughout the following year, Juno will execute an intimate and unprecedented observation of our local colossus, beaming data back to Earth.
Scott Bolton, Juno’s principal investigator, says the effort to study Jupiter is no less than a desire to understand the origin story of the solar system. Bolton is a space physicist at the Southwest Research Institute in San Antonio, Texas, and has led the $1.1bn mission from idea to execution. “When you want to understand where we all came from and how the planets were made, you have to start with Jupiter,” he says. Jupiter’s composition seems more star than planet, as it is dominated by hydrogen, followed by helium. At the same time, its atmosphere is drizzled with the heavier elements – including carbon, nitrogen and oxygen – that make life on Earth possible. “Jupiter is enriched with the same stuff we’re made of,” says Bolton. “We’re trying to understand our own history.”
Bolton’s words echo a growing wisdom among astronomers: if you want to know details about how the solar system formed, or how giant, gassy worlds coalesce around far-flung stars, you have to ask Jupiter. It likely formed early and fast, sweeping up most material left behind after the Sun formed. Jupiter is more than twice as massive as all the other planets, moons, asteroids, comets and Kuiper-belt objects in our system combined. Because of its age and heft, the gas giant probably played a critical role in arranging the solar system, helping to jockey planets into their current positions. (With 67 known moons, it effectively hosts its own planetary system too.) Astronomers even credit Jupiter’s gravitational oomph for diverting comets and asteroids that might otherwise have plummeted into Earth and brought a quick end to life as we know it.
Ancient civilizations watched the planet with awe and interest, and astronomers have been probing its mysteries since Galileo Galilei first studied it and its moons through a telescope more than 400 years ago – observations that showed that not everything in the heavens orbits Earth. The more scientists learn about Jupiter, the more unknowns they find. Even after centuries of inquiry, Jupiter is shrouded in mystery.
Scientists don’t know the structure of its thick, hot atmosphere, or how much water that atmosphere contains. Even more mysterious is the structure of its centre, hidden far below. Brilliant light shows, called auroras, encircle the opposite poles like twin crowns – and even exist deeper in the atmosphere – though researchers disagree on how they form (see “Extraterrestrial light shows”, July 2016, pp37–39 in print). Ground-based observations of Jupiter and its moons offer tantalizing hints at answers to these mysteries, but the best way to ask how the king of planets ticks is to go there and see for ourselves.
Juno’s goals are simple. How did the planet form and evolve? What hides beneath Jupiter’s clouds? The answers to those puzzles may help answer even bigger questions about why planets form at all. “We’re after the recipe for the solar system,” Bolton says.
The story so far
In Roman mythology, Juno was the wife (and sister) of Jupiter, king of the gods, and she didn’t take kindly to his extramarital interests. To conceal an affair with a mortal priestess named Io, Jupiter concealed himself with a dense cloud cover. Not to be fooled, Juno handily swept the clouds aside – an action that resonates with the modern Juno mission.
The planet Jupiter, long a source of fascination for stargazers, appears in one of the first bona fide science-fiction stories. In 1752 French philosopher Voltaire published Micromégas, a story that reads a bit like Gulliver’s Travels, but in space. The tale follows the adventures of a 37 km-tall alien and his 2 km-tall friend as they compare experiences and explore the solar system. Their trajectory takes them to the moons of Jupiter and briefly to the planet itself: “They stopped at Jupiter and stayed for a week, during which time they learned some very wonderful secrets,” which are not, unfortunately, revealed in the story. (The duo later visits Earth, but as its inhabitants are too small to be seen, they dismiss the possibility of finding intelligent life there.)
The Juno mission represents the ninth Jovian visit by a human-built ship. The most recent was New Horizons, en route to Pluto, in 2007. The first arrived in 1972, when the Pioneer 10 spacecraft snapped 300 images and took measurements as it zoomed by at 132,000 km/h, about 130,000 km above the tops of the clouds. Data from that mission helped scientists to make early hypotheses about the fluid-filled interior and to analyse plasma in the planet’s giant magnetosphere – the region in which charged particles are affected by Jupiter’s magnetic field. The mission wasn’t entirely smooth sailing: some of the onboard instruments malfunctioned due to the intensity of the radiation surrounding Jupiter, but those problems helped guide the design of better protection for future missions. The next year, on its way to Saturn, Pioneer 11 flew by Jupiter, even lower and faster than its predecessor. The Voyager 1 and 2 missions followed in the late 1970s, sending back more data – and unanswered questions.
“The Voyager missions opened up a bunch of unknowns,” says physicist Theodor Kostiuk of NASA’s Goddard Space Flight Center in Maryland, who uses ground-based telescopes to study Jupiter’s atmosphere. Voyager, for example, identified active volcanoes on Io, a large inner moon, that affect the entire planetary system. (Prior to Voyager, astronomers didn’t know that volcanic activity existed anywhere else in the universe.)
The Ulysses spacecraft measured Jupiter’s magnetosphere during flybys in 1992 and 2000, when it used gravitational assists from the planet to slingshot itself towards the Sun, its primary research target. The Cassini–Huygens spacecraft, while en route to Saturn, took tens of thousands of pictures of Jupiter and made detailed measurements of its atmosphere during a six-month period in 2000 and 2001. The first orbiter to reach Jupiter was Galileo, which spent eight years circling the planet’s equator and studying the Jovian moons, but it ran into problems and did not ultimately fulfil all of its scientific goals.
Planetary space physicist Fran Bagenal, of the University of Colorado at Boulder, worked on Galileo’s science team and now leads the plasma research teams for both Juno and New Horizons, the mission that reached Pluto last year (see “Our new view of Pluto”, July 2016, pp40–43 in print). “Galileo’s observations told us a lot about the moons, but it had this problem,” she says. In 1991 Galileo’s 4.8 m high-gain antenna, which was shaped like an umbrella and designed to radio data back to Earth, only partially opened. Scientists tried for five years to fix the problem from Earth, but to no avail. “It meant we couldn’t do a lot at the planet itself,” Bagenal recalls. The mission couldn’t send back as much data as scientists had anticipated, and the spacecraft disintegrated during its intentional, final plunge into Jupiter’s turbulent atmosphere.
Juno is the scientific heir to Galileo, but it differs in important ways. Galileo’s price tag was about $1.4bn, whereas Juno’s estimated cost is about $1.1bn. Where Galileo circumnavigated the equator, Juno will orbit the poles. Galileo, like most spacecraft, used nuclear fuel to travel through space. Juno relies on solar power. Its three radial arms are 9 m arrays that hold 19,000 solar cells, and in January of this year Juno set a record for the farthest distance travelled using solar power. (The record was previously held by the European Space Agency’s Rosetta spacecraft, which travelled to the asteroid belt between Mars and Jupiter.)
In Earth’s neighbourhood, Juno’s solar cells receive enough sunlight to generate 14 kW – which could power 10 microwave ovens at once. Near Jupiter, where sunlight is weaker, the cells collect only enough light for about 400 W. That’s not enough to power a hair dryer, but it’s sufficient for Juno’s suite of scientific instruments. “It demonstrates that solar power works in a new environment that we hadn’t thought possible,” says Bolton. The radiation belts around Jupiter, he says, are “one of the harshest regions in the solar system”.
Preparing for the storm
Jupiter is notoriously inhospitable. Winds blow at 650 km/h or more. Lightning strikes with 100 times the intensity of lightning on Earth. The Great Red Spot – the solar system’s biggest storm, which has been raging for more than three centuries – is so big it could swallow Venus.
The planet’s biggest threat to space travel, though, is radiation. Jupiter’s magnetic field is 10 times stronger than Earth’s. Indeed, its magnetosphere is the largest known structure in the entire solar system. If it glowed visibly, the magnetosphere would appear to observers on Earth more than twice as big as the full Moon. Such a sprawling magnetosphere traps a lot of high-energy particles, creating radiation belts that circle Jupiter, forming what must be the most hazardous doughnut in space. (The belts are similar in shape and structure to Earth’s Van Allen belts.)
“You’ve got this stream of electrons and protons circling the planet, and they’re lethal to spacecraft,” says astronomer and Juno team member Tobias Owen of the University of Hawaii, whose goal is to measure oxygen in Jupiter’s atmosphere. “Until now, spacecraft have been farther out. We’re going to be inside it.”
Instruments onboard Juno include a particle detector, magnetometer, ultraviolet and infrared spectrometers, and radio instruments for measuring fluctuations in the gravitational field. (The payload also includes three LEGO figurines, representing Juno, Jupiter and Galileo.) The electronic devices would ordinarily be crippled by the intense radiation, which is why they are safely housed in a protective vault with centimetre-thick titanium walls. Juno’s flight plan, which takes it over the poles, will also reduce exposure to the powerful radiation.
The same magnetic field that makes the mission so treacherous embodies one of the planet’s most pressing mysteries. Io’s active volcanoes, as Voyager observed, spew sulphur-dioxide particles that become ionized and fill the magnetosphere, says Bagenal. As they accelerate to high energies, many of the particles end up bombarding the atmosphere of Jupiter – a process that’s believed to contribute to the auroral light shows at the poles.
However, “we’ve never flown over the poles of Jupiter before, and we don’t know what it’s like up there” says Bagenal, whose research focuses on plasma in planetary magnetospheres. “We don’t know what processes accelerate those particles into the atmosphere.” Juno, she says, will be able to measure the magnetic field, charged particles and plasma waves as it looks down on the auroral emissions in the atmosphere. “We’re trying to put together the bigger picture of what causes the auroras, and how they work.”
Beneath the clouds
It’s tempting to assume that Jupiter’s auroras form like those on Earth, which arise after charged particles from the solar wind are accelerated along magnetic field lines into the upper atmosphere, where they collide with other particles and emit light. But such an explanation might be too simplistic for Jupiter. Ultraviolet images taken by the Hubble Space Telescope 20 years ago show that the auroras form round, oval-shaped structures near the poles. Though small-scale changes occasionally occur within and to each oval, “it really doesn’t vary a whole lot” says Bagenal.
That might be in part because Jupiter’s powerful magnetosphere protects its atmosphere from the solar wind. In that case, the auroras might be generated internally, from “an atmospheric region deep in the atmosphere” says Kostiuk. Using infrared imaging, Voyager identified a thermal aurora deeper in the atmosphere in the north hemisphere, which researchers have studied for three decades with ground-based measurements and, in 2001, data from the Cassini flyby. Kostiuk points out that recent ground-based measurements of the aurora in the infrared do show some variation with the solar cycle – suggesting a contribution from the solar wind.
From within or without? “That’s the big debate,” says Bagenal. She suspects the auroral emissions arise from how the plasma in the magnetosphere moves with respect to the planet, which completes a rotation in just under 10 hours. “At some point, the clutch begins to slip,” she says. “We think electric currents associated with that process are partly driving the auroras.” But scientists won’t know for certain until Juno takes a look.
Another of Juno’s scientific goals is to better understand the colourful, swirling bands of clouds. To date, it’s been difficult for scientists to probe the depths because it’s too hot, and the pressure is too great. Juno’s multi-frequency microwave radiometer will receive thermal radiation from the depths of Jupiter’s cloud cover, up to pressures about 1000 times Earth’s normal atmospheric pressure at sea level. That penetration will help researchers better understand the rotation of the atmosphere relative to the core – if it exists – and what elements exist there.
“The thing that’s most exciting to me is the determination of water deep in the atmosphere,” says Owen. “By measuring the water we’ll get an idea of the way that Jupiter came together.” Many astronomers have proposed models to explain Jupiter’s formation, but different models predict different levels of water. Measuring that abundance, says Owen, will help models get closer to approximating the origins of the planet. “Water abundance is key if you’re trying to understand how planets are formed in our solar system,” says Bolton.
Juno will also be studying what lies beneath the clouds. The planet likely contains a vast and bizarre ocean unlike anything found on Earth – and unlike anything that can even be simulated on Earth. It’s made of hydrogen under so much pressure that electrons separate from protons, and the fluid conducts electricity like a metal. As this strange sea rotates with the planet, it generates Jupiter’s powerful magnetic field. “We think that’s where the dynamo is produced,” says Bagenal.
But scientists don’t know how deep the liquid metallic hydrogen extends, or what’s underneath it. They hypothesize that Jupiter’s core is rocky and made of heavier elements. Since no device could reach the hydrogen sea – much less any core that lies beneath – Juno will map the interior structure by tracking changes in the planet’s gravitational field as it orbits.
The end of Juno
Juno will spend a full year measuring and sending data to astrophysicists on Earth, but Bolton warns that definite answers about Jupiter won’t show up immediately. “We’re limited on how we can interpret Juno’s data,” he says. Using gravity measurements to map the distribution of mass will be fairly straightforward. But to connect data on variables like temperature and pressure and forge one big, coherent picture will require physicists to agree on an equation of state to describe the conditions on Jupiter. That’s a challenge in and of itself: no-one has any idea how metallic hydrogen is supposed to behave. They also suspect, but can’t prove, that heavier elements likely dissolve in that strange soup.
Bagenal says the equation of state is a crucial and missing piece of the puzzle. “Every time we have a meeting of the interior working group of the Juno mission, these guys come up with a new equation of state,” she says. “They’re always improving, and always changing their minds. Since we launched, they’ve changed their minds a few times.”
At the same time, Juno’s data will immediately be put to use by theorists who come up with models of how Jupiter formed. “All theories on how Jupiter forms will have to be consistent with what Juno sees,” says Bolton. “By making these measurements, we will constrain the models.” Those limitations will, in turn, lead to more refined models that more accurately represent the reality of Jupiter.
Once Juno’s year-long data-gathering feast is over, it will change direction one last time. The spacecraft won’t be allowed to orbit indefinitely because of the unlikely chance it might collide with and contaminate Europa, a Jovian moon with a subsurface ocean where, one day, scientists would like to look for life. So instead of drifting off, Juno will end, like Galileo before it, by disintegrating during a final plunge into the heart of its host.
- Enjoy the rest of the July 2016 issue of Physics World from 1 July in our digital magazine or via the Physics World app for any iOS or Android smartphone or tablet. Membership of the Institute of Physics required | <urn:uuid:37e69d73-313e-4117-b3d5-787a25934cb8> | 3.65625 | 3,958 | Truncated | Science & Tech. | 45.316726 | 95,520,067 |
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The two most species-rich radiations of gall-inducing eriococcids are parasites of Eucalyptus: (1) the genus Apiomorpha R#bsaamen (ca 40 described species and many undescribed cryptic species), and (2) a monophyletic group composed of species currently placed in the genera Lachnodius Maskell, Opisthoscelis Schrader, Sphaerococcopsis Cockerell, Fragorbis Hardy and Gullan and Floracoccus Beardsley (ca 30 described species). We revise the genus Opisthoscelis Schrader, and erect the genus Tanyscelis gen. n. with Opisthoscelis pisiformis Froggatt as its type species. As a result of our taxonomic revision, Opisthoscelis has six species and Tanyscelis has 12 species. We describe the adult female and female gall of each species and galls of males for 10 species of Opisthoscelis and Tanyscelis, and provide photographs of the galls for most species. A key to the adult females of the species of both genera is included.
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Josephson current | Article about Josephson current by The Free Dictionary
Josephson current[′jō·səf·sən ‚kə·rənt]
The current across a Josephson junction in the absence of voltage across the junction, resulting from the Josephson effect.
References in periodicals archive
My first objective is to study the competition/cooperation between the magnetic and the superconducting correlations induced in the electrons of the nanoscopic metallic island by measuring the amplitude and phase of the superconducting Josephson current
At each of the peak voltages, the frequency of the AC Josephson current
resonates with the vibrational frequency of the nanstructure in the junction.
Shapiro, Josephson currents
in superconducting tunneling: the effects of microwaves and other observations, Phys. | <urn:uuid:91ed37de-04af-4708-8774-2e4bb1cd839b> | 2.71875 | 179 | Structured Data | Science & Tech. | -1.677105 | 95,520,076 |
Several commands are built-in in Eshell. In order to call the
external variant of a built-in command
foo, you could call
*foo. Usually, this should not be necessary. You can check
what will be applied by the
~ $ which ls eshell/ls is a compiled Lisp function in `em-ls.el' ~ $ which *ls /bin/ls
If you want to discard a given built-in command, you could declare an alias, Aliases. Example:
~ $ which sudo eshell/sudo is a compiled Lisp function in `em-tramp.el'. ~ $ alias sudo '*sudo $*' ~ $ which sudo sudo is an alias, defined as "*sudo $*"
If you would prefer to use the built-in commands instead of the external
Some of the built-in commands have different behavior from their
external counterparts, and some have no external counterpart. Most of
these will print a usage message when given the
diff(not to be confused with
ediff). See Comparing Files.
list. Allows you to create a list using Eshell syntax, rather than Elisp syntax. For example, ‘listify foo bar’ and
("foo" "bar")both evaluate to
locatefunction, which simply runs the external locate command and parses the results. See Dired and Find.
compile. See Compilation.
occur. See Other Repeating Search.
When it receives no argument at all, it changes to the home directory.
Giving the command ‘cd -’ changes back to the previous working directory (this is the same as ‘cd $-’).
The command ‘cd =’ shows the directory stack. Each line is numbered.
With ‘cd =foo’, Eshell searches the directory stack for a directory matching the regular expression ‘foo’ and changes to that directory.
With ‘cd -42’, you can access the directory stack by number.
Eshell knows a few built-in variables:
Aliases for the built-in variables ‘$*’, ‘$1’, ‘$2’, ..., in alias definitions. | <urn:uuid:52da327e-5af2-4688-b2ef-b47dbfc73e5e> | 2.90625 | 476 | Documentation | Software Dev. | 64.714384 | 95,520,080 |
Discussion of all aspects of cellular structure, physiology and communication.
5 posts • Page 1 of 1
Hi. We have a tendency to give DNA polymerase a special status because it is the enzyme replicating DNA. It was also the first enzyme of replication, discovered by Arthur Kornberg. However like major functions in the cells replication is assumed by nanomachines composed of many proteins working together (replisomes?). Initiation is performed by primases which are specialized for this. One could also ask also why primers are RNA and not DNA ? Is it because the initial biological world was RNA working both as an enzyme and information storage ? Then DNA appeared as a special tool to store information ?
DNA polymerase (DNAP) is a type of enzyme that is responsible for forming new copies of DNA, in the form of nucleic acid molecules. Nucleic acids are polymers, which are large molecules made up of smaller, repeating units that are chemically connected to one another. DNA is composed of repeating units called nucleotides or nucleotide bases. DNA polymerase is responsible for the process of DNA replication, during which a double-stranded DNA molecule is copied into two identical DNA molecules.
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"For the first time, we have evidence to support the hypothesis that human cells have the widespread ability to copy RNA as well as DNA," said co-author Bino John, Ph.D., assistant professor, Department of Computational and Systems Biology, Pitt School of Medicine. "These findings emphasize the complexity of human RNA populations and suggest the important role for single-molecule sequencing for accurate and comprehensive genetic profiling."
Scientists had thought that all RNA in human cells was copied from the DNA template, Dr. John explained. The presence of mechanisms that copy RNA into RNA, typically associated with an enzyme called RNA-dependent RNA polymerase, has only been documented in plants and simple organisms, such as yeast, and implicated in regulation of crucial cellular processes. Since thousands of such RNAs have been detected in human cells and because these RNAs have never before been studied, further research could open up new fronts in therapeutics, particularly diagnostics, Dr. John said.
In the study, the researchers profiled small RNAs from human cells and tissues, uncovering several new classes of RNAs, including antisense termini-associated short RNAs, which are likely derived from messenger RNAs of protein-coding genes by yet uncharacterized, pervasive RNA-copying mechanisms in human cancer cell lines.
"This class of non-coding RNA molecules has been historically overlooked because available sequencing platforms often are unable to provide accurate detection and quantification," said Patrice Milos, Ph.D., chief scientific officer at Helicos Biosciences. "Our technology provides the platform capability to identify and quantify these RNAs and reinforces the potential clinical advantages of our single molecule-sequencing platform."
Co-authors include A. Paula Monaghan, Ph.D., and Sang Woo Kim, Ph.D., University of Pittsburgh School of Medicine; Sylvain Foissac, Ph.D., Integromics Inc.; Stylianos Antonarakis, M.D., Ph.D., and Christelle Borel, Ph.D., University of Geneva Medical School; and Philipp Kapranov, Ph.D., and others from Helicos BioSciences.
The research was funded by the American Cancer Society, the National Institutes of Health, the Swiss National Science Foundation, Integromics Inc., and Helicos BioSciences Corporation.
Anita Srikameswaran | EurekAlert!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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Using x-ray crystallography, researchers have produced the first images of a large molecular complex that helps shape and load the small, bubble-like vesicles that transport newly formed proteins in the cell. Understanding vesicle "budding" is one of the prerequisites for learning how proteins and other molecules are routed to their correct destinations in the cell.
In an article published in the September 19, 2002, issue of the journal Nature, Howard Hughes Medical Institute (HHMI) investigator Jonathan Goldberg, Xiping Bi and Richard Corpina at Memorial Sloan-Kettering Cancer Center unveil the intricate architecture of the "pre-budding complex," which is a set of proteins that participates in the formation of vesicles on the cells endoplasmic reticulum (ER). The pre-budding complex is the triggering component of a protein coat called COPII that grabs a section of the ER membrane, pinches it off to form the vesicle and packages the protein cargo to be transported.
"The structure developed by Bi, Corpina and Goldberg makes an important contribution to the understanding of vesicle formation -- a process central to the transport of newly formed proteins," said HHMI investigator Randy Schekman, a pioneer in vesicle studies at the University of California, Berkeley. "It illuminates in detail the mechanism by which the core complex of the COPII protein coat assembles on the ER membrane to initiate the process of membrane cargo capture and vesicle budding." Schekman and James Rothman of Memorial Sloan-Kettering Cancer Center, working independently, have identified many of the fundamental details of protein transport and secretion.
Jim Keeley | EurekAlert!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
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What future holds for Java?
The future is always uncertain, but still from the few present and past factors we can assume some fragments of future through them. In the history, few invention got a tremendous success, more than ever anyone expected and JAVA is one of these inventions. The Java was developed as a general purpose computer programming language. But the high tech features of the Java makes it the first preference of the web developers. The ” Write once, run anywhere ” feature of the Java suits very well and with minimum work Java can run on any leading platform.
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Java is everywhere, the Java can be found on the every leading platform at any corner of the world. The easily adapting to any other platform makes the future of the Java bright. The Java is mainly used in developing smart card applications, mobile applications, or server-side enterprise applications. The Java has the best qualities of the programming language with great compressive sets of APIs. The Java is derived from the C and C++ languages, which makes it more compact.
Future of the Java is very bright and prosperous, as all the leading Android software’s and applications are Java based. The Java was the first choice of the leading smartphone company BlackBerry for the writing applications in it. The Java is a holy language of the today’s web developers and the features of Java are so dynamic, that this language is going nowhere in the long run. The Java is here to stay, so for the bright future get acquaintance with it.
The auspicious future of the Java developers:
We have already established that Java is a great programming language, but what makes it greater is the developer who runs this powerful language. The success of Java depends on the success of the Java developer and trust me on that the future as a Java developer is very illuminating. The Java developers have bright future in the following streams:
– the mobile application market is also always in search of the competent Java developers to construct dynamic applicants for the smartphone. As we have already discussed that Android applications are thoroughly Java based.
– the Java has very wide range, the middleware (Hadoop) also falls under the wide range of the Java. So, Java is like salt which can be found anywhere and can function on any platform.
– for the freelance web developers, Java is very helpful as plenty of freelance work is available for the Java developers.
To summarize the whole context, I can proudly say that the future of the Java & Java developers is very shining. A Java is going to be here for more few decades unless something as powerful as Java is developed, which is not an easy task and that’s why Java developers have their head deep stuck in the workload and money. So, adopt Java and utilize the benefits of this charming language.
Hello, I am Arpit. I am a content writer who usually loves to write technical stuff. I always try to write something very related to latest technologies and trend. I hope you like my blogs and have a good time reading them. | <urn:uuid:fe4ae45b-cb3c-4680-904c-e3e77092840b> | 2.515625 | 643 | Personal Blog | Software Dev. | 42.93522 | 95,520,103 |
In General > s.a. gas; fluids; states in statistical mechanics; thermodynamical
systems [including geometry of state space].
* Idea: A large collection of particles with no internal structure, non-interacting except for collisions (small hard spheres).
* Equation of state: The ideal gas law, obtained combining Boyle's volume-pressure law, Gay-Lussac's pressure-temperature law and Charles' law,
pV = nRT = NkBT ,
where R is the molar gas constant, and kB the
Boltzmann constant (> see constants); First
stated in 1834 by Émile Clapeyron; It does not hold at very low temperatures
or high densities, when quantum effects have to be taken into account.
* Remark: Most gases at room T and p behave like ideal gases, but as T → 0 they can't because of quantum effects.
* Internal energy: If s is the number of degrees of freedom (s = 3 for a monatomic gas),
U = (s/2) NkBT .
* Entropy: An explicit expression in terms of basic constants for a monatomic gas is given by the Sackur-Tetrode equation; The general form is given by
S = CV ln(T/T0) + NkB ln(V/V0) .
* Consequences: Aerosol cans get cold when used.
* In a gravitational field: The equilibrium pressure of a perfect gas in a constant gravitational field decreases exponentially with height (barometric formula).
Second-Order Quantities > see Compressibility; specific heat.
@ General: Creaco & Kalogeropoulos MPLB(09)-a0811 [thermodynamic limit, phase space measure]; Arnaud et al Ent(13)-a1105 [assumptions behind the ideal gas law].
@ Quantum: Meyer IJMPC(97)qp [quantum lattice gas]; Bloch pw(04)apr [in optical lattices]; Nattermann AJP(05)apr [scaling approach]; Velenich et al JPA(08) [Brownian gas, Poissonian ground state]; Dodonov & Vieira Lopes PLA(08) [temperature increase from sudden expansion]; Pérez & Sauer AHES(10)-a1004 [Einstein's work]; Nakamura et al PRE(11)-a1105 [in an expanding cavity]; Quevedo & Zaldivar a1512 [geometrothermodynamic approach]; > s.a. gas [fermion gas, boson gas]; Susceptibility.
@ Relativistic: Becattini & Piccinini AP(08), Becattini & Tinti AP(10)-a0911 [rotating]; Chakrabarti et al PhyA(10) [non-extensive statistics]; Basu & Mondal a1103 [4-velocity distribution]; Cannoni PRD(14)-a1311 [probability distribution for the relative velocity of colliding particles]; Montakhab et al PhyA(14)-a1406 [morphological phase transition]; > s.a. deformed special relativity; quantum-gravity phenomenology; statistical-mechanical systems.
@ Modified: Das et al PRD(09)-a0908 [DSR, equation of state]; Chandra & Chatterjee PRD(12)-a1108 [DSR, thermodynamics]; > s.a. phenomenology of modified uncertainty relations; thermodynamic systems [non-commutative, etc].
@ Entropy: Kolekar & Padmanabhan PRD(11)-a1012 [in a strong gravitational field]; Oikonomou & Bagci SHPMP(13) [monatomic gas, Clausius versus Sackur-Tetrode entropies]; > s.a. Gibbs Theorem.
@ From particles to fluid: Park JPCS(14)-a1310 [phase transition at finite particle number for ideal Bose gas].
@ Related topics: Landsberg et al AJP(94)aug, Pantellini AJP(00)jan [in a constant g field]; Boozer AJP(10)jan [1D, details]; Kothawala PLB(13)-a1108 [in free fall in curved spacetime]; > s.a. Boltzmann Equation; Maxwell-Boltzmann Distribution.
> Online resources: see Wikipedia page.
– journals – comments
– other sites – acknowledgements
send feedback and suggestions to bombelli at olemiss.edu – modified 31 may 2018 | <urn:uuid:0ec7b2c0-bd0b-4fa2-8dee-6eb954785c1f> | 2.6875 | 998 | Academic Writing | Science & Tech. | 42.507536 | 95,520,111 |
Description: Asteroids have the potential to cause catastrophic loss of life on our planet upon impact. In 2013 the Chelyabinsk meteor injured 1500 people when it exploded over Russia. If researchers could identify potential asteroids early enough they could change their orbit to eliminate the threat to Earth. This phenomenon could be used to explore the motion of orbiting objects in the solar system or to gain a better understanding of gravitational forces and fields.
Web Resource: Asteroid Impact Avoidance - Wikipedia | <urn:uuid:886a1e6c-9004-4afb-a7bf-b6d13c75abed> | 3.703125 | 95 | Knowledge Article | Science & Tech. | 26.48125 | 95,520,116 |
Researchers of the GFZ German Research Centre for Geosciences estimate that it will happen in the East of the metropole
The city of Istanbul is focus of great concern for earthquake researchers. This 15-million metropole is situated very close to the so-called North Anatolian Fault Zone which runs just outside of the city gates below the Marmara Sea. Here in the underground there is a constant build-up of energy which results from an interlocking of the tectonic plates causing plate movement to come to a halt until a great tremor releases this energy. Scientists, therefore, reckon with an earthquake with a magnitude of 7 or greater in this region in the coming years.
Marmara Sea region in northwestern Turkey with the North Anatolian Fault Zone (NAFZ) separating Eurasia from Anatolian. The offshore Marmara fault where a major earthquake is overdue is indicated by the red line. The black lines to either side are the two last major ruptures of the region, the 1912 Ganos and the 1999 Izmit earthquakes. The Marmara section has not produced a large earthquake since 1766 but is know to rupture every ~250 years based on historical records. The yellow stars mark the repeating earthquakes found in the now published study indicating fault creep (green rectangle) while the fault portion offshore of Istanbul (blue rectangle) is locked.
Credit: Christopher Wollin/GFZ
The extent of such seismic threat to this Turkish city of Istanbul actually depends on how strongly the plates are entangled and on the exact nucleation point of the earthquake. A team led by Marco Bohnhoff from the GFZ German Research Centre for Geoscience now presents a study indicating that the next major earthquake is more likely to originate in Istanbul's eastern Marmara Sea. "This is both good news and bad news for the city with over 15 million inhabitants. The good news: "The rupture propagation will then run eastwards i.e. away from the city", explains the researcher. "The bad news is that there will only be a very short early warning phase of a few seconds." Early warning times are extremely important in order to switch traffic lights to red, to block tunnels and bridges or to shut down critical infrastructure. The research results are now published in the scientific journal "Geophysical Journal International".
The estimations presented by Marco Bohnhoff and his team are based on the analysis of numerous small quakes along the Marmara fault. Results have shown that the degree of locking in the western part of the fracture zone is lower and that the two tectonic plates are creeping past one another at a very slow rate. During this process small tremors of the same signature, so-called "repeaters", occur at distinct recurrence times. Further east, close to Istanbul, however, repeaters have not been observed and the tectonic plates appear to be completely locked here. This leads to a build-up of tectonic energy and increases the probability of a large earthquake there.
Such observations were possible due to a new high-precision seismicity catalog for the region. For this purpose, the researchers have thoroughly evaluated the earthquake activity by combining the two major Turkish Earthquake Measurement Networks with measurement data from the GFZ Plate Boarder Observatory within the framework of a German-Turkish cooperation project. "In this way we have found recurring earthquakes below the western Marmara Sea" says Bohnhoff. "From this we deduce that below the western Marmara Sea the two tectonic plates (for the most part -- 25-75%) are moving slowly past each other thus accumulating less energy than if they were completely locked."
And what will happen if it actually comes to the feared strong earthquake below the western Marmara Sea? "In such a case there would likewise be good news and bad news," says Bohnhoff. Good would be a somewhat longer early warning period, bad would be the fact that the rupture propagation would then take place in the direction of Istanbul resulting in more severe ground shaking than if the origin was further east. However, the current data obtained suggests the opposite: an earthquake with an epicenter at the gates of the city, which would allow the people only very little time to find protection, but which would trigger less powerful ground movements.
Josef Zens | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
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"This summer has seen the highest global mean sea surface temperatures ever recorded since their systematic measuring started. Temperatures even exceed those of the record-breaking 1998 El Niño year," says Axel Timmermann, climate scientist and professor, studying variability of the global climate system at the International Pacific Research Center, University of Hawaii at Manoa.
From 2000-2013 the global ocean surface temperature rise paused, in spite of increasing greenhouse gas concentrations. This period, referred to as the Global Warming Hiatus, raised a lot of public and scientific interest.
Figure 1: a) NOAA Sea Surface Temperature anomaly (with respect to period 1854-2013) averaged over global oceans (red) and over North Pacific (0-60oN, 110oE-100oW) (cyan). September 2014 temperatures broke the record for both global and North Pacific Sea Surface Temperatures. b) Sea Surface Temperature anomaly of September 2014 from NOAA's ERSST dataset.
Credit: Axel Timmermann
However, as of April 2014 ocean warming has picked up speed again, according to Timmermann's analysis of ocean temperature datasets.
"The 2014 global ocean warming is mostly due to the North Pacific, which has warmed far beyond any recorded value (Figure 1a) and has shifted hurricane tracks, weakened trade winds, and produced coral bleaching in the Hawaiian Islands," explains Timmermann.
He describes the events leading up to this upswing as follows: Sea-surface temperatures started to rise unusually quickly in the extratropical North Pacific already in January 2014.
A few months later, in April and May, westerly winds pushed a huge amount of very warm water usually stored in the western Pacific along the equator to the eastern Pacific.
This warm water has spread along the North American Pacific coast, releasing into the atmosphere enormous amounts of heat--heat that had been locked up in the Western tropical Pacific for nearly a decade.
"Record-breaking greenhouse gas concentrations and anomalously weak North Pacific summer trade winds, which usually cool the ocean surface, have contributed further to the rise in sea surface temperatures.
The warm temperatures now extend in a wide swath from just north of Papua New Guinea to the Gulf of Alaska (Figure 1b)," says Timmermann.
The current record-breaking temperatures indicate that the 14-year-long pause in ocean warming has come to an end.
Gisela Speidel | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
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