December 2nd, 2009 in Space & Earth / Space Exploration
This blink comparison aids evaluation of a drive by NASA's Mars Exploration Rover Spirit during the rover's 2,099th Martian day, or sol (Nov. 28, 2009). Image Credit: NASA/JPL-Caltech

(PhysOrg.com) -- Spirit's right-rear wheel stalled again on Sol 2099 (Nov. 28, 2009) during the first step of a two-step extrication maneuver.

This stall is different in some characteristics from the stall on Sol 2092 (Nov. 21). The Sol 2099 stall occurred more quickly and the inferred rotor resistance was elevated at the end of the stall. Investigation of past stall events along with these characteristics suggest that this stall might not be result of the terrain, but might be internal to the right-rear wheel actuator. Rover project engineers are developing a series of diagnostics to explore the actuator health and to isolate potential terrain interactions. These diagnostics are not likely to be ready before Wednesday.

Plans for future driving will depend on the results of the diagnostic tests.

Before the Sol 2099 drive ended, Spirit completed 1.4 meters of wheel spin and the rover's center moved 0.5 millimeters (0.02 inch) forward, 0.25 millimeters (0.01 inch) to the left and 0.5 millimeters (0.02 inch) downward. Since Spirit began extrication on Sol 2088, the rover has performed 9.5 meters (31 feet) of wheel spin and the rover's center, in total, has moved 16 millimeters (0.63 inch) forward, 10 millimeters (0.39 inch) to the left and 5 millimeters (0.20 inch) downward.

Provided by JPL/NASA (news : web)
http://www.physorg.com/news178990566.html

Comment:
So, who forgot to pack the snow chains???

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Robert Karl Stonjek

December 2nd, 2009 in Physics / Quantum Physics
A pair of laser beams (red arrows) impinges upon an ultracold gas cloud of rubidum atoms (green oval) to create synthetic magnetic fields (labeled Beff). (Inset) The beams, combined with an external magnetic field (not shown) cause the atoms to "feel" a rotational force; the swirling atoms create vortices in the gas. Credit: JQI

In a strange inversion, the laser-illuminated neutral atoms react to the varying magnetic field in a way that is mathematically equivalent to the way a charged particle responds to a uniform magnetic field. The neutral atoms experience a force in a direction perpendicular to both their direction of motion and the direction of the magnetic field gradient in the trap. By fooling the atoms in this fashion, the researchers created vortices in which the atoms swirl in whirlpool-like motions in the gas clouds. The vortices are the "smoking gun," Spielman says, for the presence of synthetic magnetic fields.

 

More information: Y.J. Lin, R.L. Compton, K. Jimenez-Garcia, J.V. Porto and I.B. Spielman. Synthetic magnetic fields for ultracold neutral atoms. Nature, Dec. 3, 2009.

December 2nd, 2009 in Space & Earth / Space Exploration
First light limb scan from the SSULI 002 instrument on DMSP F18. The x-axis represents wavelength, the y-axis is altitude and the color represents accumulated counts in 1 second. Source: Naval Research Laboratory

The Special Sensor Ultraviolet Limb Imager (SSULI) developed by NRL's Spacecraft Engineering Department and Space Science Division, launched October 18, 2009 on the U.S. Air Force Defense Meteorological Satellite Program (DMSP) F18 (flight 18) satellite, observed first light on December 1, 2009.

In a sample airglow profile (see figure above) the spectral emission features in the data are clean and show no anomalies.

"The SSULI team is very excited to continue with early orbit testing and begin the calibration and validation process with this instrument," said Andrew Nicholas, SSULI principal investigator, NRL Space Science Division.

Offering global observations, that yield near real-time altitude profiles of the ionosphere and neutral atmosphere, over an extended period of time, SSULI makes measurements from the extreme ultraviolet (EUV) to the far ultraviolet (FUV) over the wavelength range of 80 nanometers (nm) to 170 nm with 1.5 nm resolution.

SSULI data products, once calibrated and validated, will be used operationally at the Air Force Weather Agency (AFWA) as standalone operational data products and also as inputs into operational Space Weather models.

Provided by Naval Research Laboratory (news : web)
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November 30th, 2009 in Space & Earth / Astronomy
This artist's impression shows how jets from supermassive black holes could form galaxies, thereby explaining why the mass of black holes is larger in galaxies that contain more stars. Credit: ESO/L. Calçada

(PhysOrg.com) -- Which come first, the supermassive black holes that frantically devour matter or the enormous galaxies where they reside? A brand new scenario has emerged from a recent set of outstanding observations of a black hole without a home: black holes may be “building” their own host galaxy. This could be the long-sought missing link to understanding why the masses of black holes are larger in galaxies that contain more stars.

"The 'chicken and egg' question of whether a galaxy or its black hole comes first is one of the most debated subjects in astrophysics today," says lead author David Elbaz. "Our study suggests that supermassive black holes can trigger the formation of stars, thus 'building' their own host galaxies. This link could also explain why galaxies hosting larger black holes have more stars."

To reach such an extraordinary conclusion, the team of astronomers conducted extensive observations of a peculiar object, the nearby quasar HE0450-2958, which is the only one for which a host galaxy has not yet been detected. HE0450-2958 is located some 5 billion light-years away.

Until now, it was speculated that the quasar's host galaxy was hidden behind large amounts of dust, and so the astronomers used a mid-infrared instrument on ESO's Very Large Telescope for the observations. At such wavelengths, dust clouds shine very brightly, and are readily detected. "Observing at these wavelengths would allow us to trace dust that might hide the host galaxy," says Knud Jahnke, who led the observations performed at the VLT. "However, we did not find any. Instead we discovered that an apparently unrelated galaxy in the quasar's immediate neighbourhood is producing stars at a frantic rate."

These observations have provided a surprising new take on the system. While no trace of stars is revealed around the black hole, its companion galaxy is extremely rich in bright and very young stars. It is forming stars at a rate equivalent to about 350 Suns per year, one hundred times more than rates for typical galaxies in the local Universe.

Colour composite image of a peculiar object, the nearby quasar HE0450-2958, which is the only one for which no sign of a host galaxy has yet been detected. A team of astronomers has identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars. The mid-infrared part of this image was obtained with the VISIR instrument on ESO’s Very Large Telescope, while the visible image comes courtesy of the Hubble Space Telescope and the Advanced Camera for Surveys.

Earlier observations had shown that the companion galaxy is, in fact, under fire: the quasar is spewing a jet of highly energetic particles towards its companion, accompanied by a stream of fast-moving gas. The injection of matter and energy into the galaxy indicates that the quasar itself might be inducing the formation of stars and thereby creating its own host galaxy; in such a scenario, galaxies would have evolved from clouds of gas hit by the energetic jets emerging from quasars.

"The two objects are bound to merge in the future: the quasar is moving at a speed of only a few tens of thousands of km/h with respect to the companion galaxy and their separation is only about 22 000 light-years," says Elbaz. "Although the quasar is still 'naked', it will eventually be 'dressed' when it merges with its star-rich companion. It will then finally reside inside a host galaxy like all other quasars."

Hence, the team have identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars.

"A natural extension of our work is to search for similar objects in other systems," says Jahnke.

Future instruments, such as the Atacama Large Millimeter/submillimeter Array, the European Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope will be able to search for such objects at even larger distances from us, probing the connection between black holes and the formation of galaxies in the more distant Universe.

More information: This research was presented in papers published in the journal Astronomy & Astrophysics: "Quasar induced galaxy formation: a new paradigm?" by Elbaz et al., and in the Astrophysical Journal "The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG" by Jahnke et al. Research papers: http://www.aanda.org/10.1051/0004-6361/200912848/pdf and http://arxiv.org/abs/0906.0365

Source: ESO (news : web)
http://www.physorg.com/news178804126.html

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November 29th, 2009 in Physics / General Physics

The concept of confinement is one of the central ideas in modern physics. The most famous example is that of quarks which bind together to form protons and neutrons. Now Prof. Bella Lake from Helmholtz-Zentrum Berlin (Germany) together with an international team of scientists report for the first time an experimental realization and a proof of confinement phenomenon observed in a condensed matter system.

The concept of confinement states that in certain systems the constituent particles are bound together by an interaction whose strength increases with increasing particle separation. In the case of quarks they are held together by the so called strong force, a force that grows stronger with increasing distance. As a consequence individual particles like quarks don't exist in a free state and their properties can be observed only indirectly.

In the 1990s Prof Alexei Tsvelik from Brookhaven National Laboratory (USA) and co-workers predicted an analogous confinement process in systems known as spin-ladders found in condensed mat-ter physics. Experimental confirmation of this phenomenon has however only been achieved recently as described by Bella Lake et al in the current issue of the journal Nature Physics.

Spin-ladders consist of two chains of copper oxide chemically bonded together. This makes the electrons interact strongly with each other. A remarkable feature of a single chain is that the individual electrons, which behave as an elementary charge combined with magnetic spin, co-operate in concert to separate into independent spin and charge parts. According to Bella Lake "The spin parts, known as spinons, have different properties to those of the original electrons. In fact they are analogous to quarks, the building blocks of protons and neutrons." On coupling two chains together to form a spin ladder the spin parts are found to recombine, but in a new way. "We have found, that excitations of individual chains, so called spinons, are confined in a similar way to that in which elementary quarks are held together", Bella Lake said.

The team of scientists have found evidence for the confinement idea by neutron scattering experiments on magnetic crystals of calcium cuprate (a copper-oxide material synthesized at the Leibniz Institute for Solid State and materials research in Dresden). The neutron experiments were performed using the MAPS spectrometer at the ISIS pulsed neutron source at Rutherford Appleton Laboratory, UK. Further the crystal and magnetic structure were investigated from neutron data collected on the E5 instrument at the research reactor BER II in Berlin.

The neutron scattering data show that the electrons essentially first split into spins and charges on the chains, then the spinons pair up again due to ladder effects. Prof Alan Tennant, the head of "Institute Complex Magnetic Materials" at HZB, explained: "The geometry of the ladder in fact plays a special role: the spinons always appear in pairs and when they move apart, they force a reorganisation of the intervening electrons that costs energy. The energy cost grows with separation - like a rubber band." According to Bella Lake "This strong pairing up of two spinons is like quarks binding together to form subatomic particles like hadrons and mesons."

Prof Alexei Tsvelik who developed the theoretical description explained "The formation of hadrons is well established on a qualitative level, but its quantitative aspects remain unresolved. It is unknown how to relate the theoretical parameters to the observed hadron masses. This is one of the reasons why condensed matter analogues are interesting. They provide examples of confinement for which detailed descriptions have been achieved."

More information: Nature Physics, DOI: 10.1038/NPHYS1462

Source: Helmholtz Association of German Research Centres (news : web)
http://www.physorg.com/news178724926.html

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Robert Karl Stonjek

November 27th, 2009 in Physics / General Physics

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(PhysOrg.com) -- A group in The Netherlands has achieved a first: injection of spin-polarized electrons in silicon at room temperature. This has previously been observed only at extremely low temperatures, and the achievement brings spintronic devices using silicon as a semiconductor a step closer.

Spintronics, or spin electronics, is an emerging field of electronics that aims to be able to represent digital information by using the spin of electrons as well as their charge. When fully developed, spintronic devices could profoundly change data storage devices, computer architecture and so on, and they could reduce energy use to ultra-low levels.

Electrons are basically a two-state system with their spins either "up" or "down". For a spintronics device to work, it must have a system (the spin injector) that produces a spin-polarized electric current, which has more of its electrons in one spin state than the other. It also needs a spin detector that can detect whether the electrons are up or down.

In metallic systems spin polarization is generally achieved by passing an electric current through a ferromagnet. (It is magnetic because the electrons within it are polarized, and as they pass from the magnet to the metal they remain polarized for a short time.) Spin polarization has also been achieved at room temperature in ferromagnetic semiconductors such as manganese-doped gallium arsenide.

Until recently spin polarization in non-magnetic semiconductors like silicon has only been achieved at temperatures of 150 K, but new research has achieved spin polarization at ambient temperature. Scientists Saroj P. Dash and colleagues at the MESA Institute for Nanotechnology at the University of Twente in The Netherlands used a single nickel-iron electrode on top of silicon, with a layer of aluminum oxide between them. When they applied a current to the electrode they observed a "puddle" of electrons in the silicon, which could then be dissipated by applying a magnetic field. This caused an observable voltage drop across the contact.

As a control they inserted a layer of ytterbium between the electrode and the aluminum oxide, since ytterbium is known to destroy spin polarization. When the current and magnetic field were applied, no voltage drop was observed, which indicates that spin polarized electrons had caused the effect.

Spintronics could eventually lead to extremely low energy use devices, and perhaps ultimately to quantum computers. More research is needed to prove the spin-polarized currents really flow through the silicon, and it may still be several years before the promised ultra-low power devices are developed.

The research was published yesterday in the journal, Nature.

More information: Electrical creation of spin polarization in silicon at room temperature, Nature 462, 491-494 (26 November 2009), doi:10.1038/nature08570

© 2009 PhysOrg.com
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November 27th, 2009 in Space & Earth / Astronomy
Enlarge

Figure 1. Credit: ESA

(PhysOrg.com) -- The European Space Agency has today released spectacular new observations from the Herschel Space Observatory, including the UK-led SPIRE instrument. Spectrometers on board all three Hershel instruments have been used to analyse the light from objects inside our galaxy and from other galaxies, producing some of the best measurements yet of atoms and molecules involved in the birth and death of stars.

The SPIRE Fourier Transform Spectrometer (FTS), which covers the whole submillimetre wavelength range between 194 and 672 microns, will be invaluable to astronomers in determining the composition, temperature, density and mass of interstellar material in nearby galaxies and in star-forming clouds in our own galaxy.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), which provides the UK funding for Herschel, said “Herschel has once again returned some spectacular indications of what is to come. This wealth of new data exists because of the dedication and skill of the scientists working on this project and will vastly expand our knowledge of the life cycle of stars.”

Professor Matt Griffin of Cardiff University, who is the SPIRE Principal Investigator, said: “Some trial observations have been made during initial testing of the spectrometer, and it is clear that the data are of excellent quality, and even these initial results are very exciting scientifically, especially our ability to trace the presence of water throughout the Universe. The spectrometer was technically very challenging to build, and the whole team is delighted that it works so well.”

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Figure 2. Credit: ESA

Professor Glenn White, of the Open University and STFC’s Rutherford Appleton Laboratory, and an expert in the field of molecular astronomy for which the SPIRE spectrometer is designed, said: "The exquisite sensitivity and quality of these early data reveal spectacular spectroscopic signatures that show the diversity and complexity of the birth processes common to the formation of star and planets. Herschel is going to help us trace the evolution and life of stars, to map the chemistry in our galactic neighbourhood, and allow us to detect water and complex molecules in distant galaxies."

Professor Mike Barlow of University College London, who will use the SPIRE instrument to study the material ejected into space by stars near the end of their lives, said: “The unprecedented spectral range and the wealth of detail revealed by the SPIRE spectrometer, in a hitherto almost unexplored region of the spectrum, promises to revolutionise our understanding of the formation of molecules and dust particles during the final stages of the lives of stars. These dust particles go on to play a crucial role in the formation of new stars and provide the raw material for the planetesimals and planets that form around them."

Figure 1 shows part of the SPIRE spectrum of VY Canis Majoris (VY CMa), a giant star near the end of its life, which is ejecting huge amounts of gas and dust into interstellar space, including elements such as carbon, oxygen and nitrogen (which form the raw material for future planets, and eventually life). The inset is a SPIRE camera image of VY CMa, in which it appears as a bright point-source near the edge of a large extended cloud. The spectrum is amazingly rich, with prominent features from carbon monoxide (CO) and water (H₂O). More than 200 other spectral features have also been identified, many due to water, showing that the star is surrounded by large quantities of hot steam. Observations like these will help to establish a detailed picture of the mass loss from stars and the complex chemistry occurring in their extended envelopes.

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Figure 3. Credit: ESA

Figure 2 is a spectrum of one position on the Orion Bar, part of the Orion nebula in which the gas on the edge of the nebula is partly ionised by intense radiation from nearby hot young stars. The inset shows a near infrared picture from NASA’s Spitzer Space Telescope. The SPIRE spectrum has many features from CO, appearing as the dominating narrow lines, seen here for the first time together in a single spectrum. These mean that the entire spectrum is observed at the same time and calibrated together. The brightness of the spectral features will allow astronomers to estimate the temperature and density of interstellar gas. The spectrum also shows the first detection of an emission feature from the molecular ion methylidynium (CH⁺), a key building block for larger carbon-bearing molecules. This and similar regions are large, and the SPIRE spectrometer’s will be extremely powerful in characterising how the gas properties vary within such sources.

Figure 3 shows a SPIRE spectrum of Arp 220, a galaxy 250 million light years away from Earth with very active star formation triggered when two large spiral galaxies collided to produce the complex object we see today. Arp 220 is an important template for understanding even more distant galaxies and galaxy formation in the early universe. The spectrum shows many emission features of CO, and H₂O features are seen both in emission and absorption. The inset is an optical image of Arp 220 made with the Hubble Space Telescope.

Figure 4 shows the spectrum of Messier 82 (M82), a nearby galaxy (only 12 million light years away) with very active star formation. It is part of an interacting group of galaxies including the large spiral M81. The accompanying image (inset) is a spectacular three-colour composite picture of the two galaxies made with the SPIRE camera, showing material being stripped from M81 by the gravitational interaction with M82. The SPIRE spectrum of M82 shows strong emission lines from CO over the whole wavelength range, as well as emission lines from atomic carbon and ionized nitrogen.

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Figure 4. Credit: ESA

The SPIRE FTS observations were carried out as part of the performance verification of the observatory. The scientific rights of some of these observations are owned by Key Programme consortia: for Arp 220 and M82, the Nearby Galaxies consortium lead by C. Wilson; for VY CMa the MESS consortium led by M. Groenewegen; for the Orion Bar, the Evolution of Interstellar Dust consortium led by A. Abergel.

Provided by Science and Technology Facilities Council (news : web)
http://www.physorg.com/news178551842.html

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Robert Karl Stonjek

November 27th, 2009 in Physics / Condensed Matter
Image of the ferroelectric domains of the multiferroic compound BiFeO3. © A. Mougin, CNRS 2009

(PhysOrg.com) -- Is it possible to make even more compact digital memories for portable electronic devices and which consume even less energy? A team of French researchers has recently demonstrated that it is feasible, thanks to a new class of materials known as multiferroics, which combine unusual electric and magnetic properties.

At a microscopic scale, atoms and molecules produce electric and magnetic fields. At our own scale, in the majority of crystals, the electric and magnetic properties of the various atoms offset one another and cancel each other out. Sometimes, however, this is not the case and in certain compounds, known as ferromagnetics, magnetic properties subsist at a macroscopic scale and can therefore act as a magnet.

Less commonly, an electric order can exist at the macroscopic scale; such is the case with what are known as ferroelectric compounds. Even more rarely, electric and magnetic orders exist at one and the same time, as is the case with multiferroic materials. Moreover, in these materials, the electric and magnetic orders interact. Such interaction offers the opportunity of controlling the spins (the magnetic moments) of the atoms via an electric field, thus opening whole new perspectives particularly as regards information storage.

Researchers at the Laboratoire de Physique des Solides, the Institut Rayonnement-Matičre de Saclay and the Institut Néel first synthesized the multiferroic compound BiFeO₃ and then demonstrated the interaction between its electric and magnetic orders. They then produced a material formed of a layer of BiFeO₃ and a ferromagnetic film and showed that they were able to modify the preferential orientation of the magnetization of the ferromagnetic film by applying an electric field. These pioneering results validate the concept of storing and writing magnetic data using an electric field.

In today's hard discs, data - or bits - are written using a magnetic field that directs the magnetization, which imposes the bit value. There are two possible magnetization states and thus two possible bit values (designated 0 or 1). With a multiferroic material, each memory element could be placed in four distinct states instead of two (two electrical polarization states and two magnetization states). Magnetic memories with two states (like existing memories), but which can be modified through the application of an electric field, could also be envisaged.

This possibility of writing and erasing data using an electric field constitutes a decisive advantage in mobile electronic devices (mobile phones, laptop computers, GPS, etc.) from two points of view. Firstly, the application of an electric field requires less energy than the application of a magnetic field and therefore batteries would last longer. Secondly, the electric field would be more local, which would mean more memory elements could be packed onto a given surface and thus enable component miniaturization to be pushed even further.

More information: Electric field switching of the magnetic anisotropy of a ferromagnetic layer exchange coupled to the multiferroic compound BiFeO3. D. Lebeugle, A. Mougin, M. Viret, D. Colson, L. Ranno. Physical Review Letters, 18 November 2009.

Provided by CNRS
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November 26th, 2009 in Space & Earth / Space Exploration
This image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter shows a sample of the variety and complexity of processes that may occur on the walls of Martian craters, well after the impact crater formed. Image Credit: NASA/JPL-Caltech/University of Arizona

(PhysOrg.com) -- This image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter shows a sample of the variety and complexity of processes that may occur on the walls of Martian craters, well after the impact crater formed.

At the very top of the image is the high crater rim. At the bottom of the image is the crater's central peak, a dome of material rising above the surrounding crater floor. The central peak was uplifted during the impact event.

Reaching down the walls of the crater are winding and crooked troughs, or gullies. Some of these gullies may have formed with the help of liquid water, melted from ice or snowpack on the crater walls or from groundwater within the walls. Also notable is the long tongue-like lobe stretching down the middle of the image, with a darker, rounded snout and prominent parallel grooves on its surface. These characteristics, together with faint cracks on its surface, suggest that this lobe may have formed by movement of ice-rich material from up on the crater wall down to the crater floor.

Because surface features on this lobe and on most of the gullies do not appear sharp and pristine, and because wind-blown dunes have blown up on the front snout of the lobe, and because there are several small craters on the lobe's surface, the movements of ice-rich material and possibly water have probably not occurred very recently.

This image covers a swath of ground about 6 kilometers (4 miles) wide, centered at 32.4 degrees south latitude, 103.2 degrees east longitude. It is one product from HiRISE observation ESP_013726_1475, made on July 1, 2009. Other image products from this observation are available at http://hirise.lpl.arizona.edu/ESP_013726_1475 .

Provided by JPL/NASA (news : web)
http://www.physorg.com/news178453746.html

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November 24th, 2009 in Physics / General Physics

Researchers at the University of Minnesota have developed a unique new computer model called the Virtual StreamLab, designed to help restore real streams to a healthier state. The Virtual StreamLab, which demonstrates the physics of natural water flows at an unprecedented level of detail and realism, was unveiled for the first time this week at the 2009 American Physical Society Division of Fluid Dynamics meeting in Minneapolis, one of the largest conferences in fluid dynamics with more than 1,500 attendees from around the world.

The University of Minnesota team of researchers led by civil engineering professor Fotis Sotiropoulos, director of the University's St. Anthony Falls Laboratory (SAFL), developed the Virtual StreamLab to help improve stream restoration processes. They have completed their first simulation of SAFL's Outdoor StreamLab, a scaled natural stream along the Mississippi River. More than 90 million data points have been mapped into the team's computer model resulting in the most accurate model of a real stream to date. The Virtual StreamLab employs sophisticated numerical algorithms that can handle the arbitrarily complex geometry of natural waterways, features advanced turbulence models, and utilizes the latest advances in massively parallel supercomputers.

The ability to simulate water flow over topography with this degree of realism provides researchers with the insights necessary to improve sustainable stream restoration strategies, helping to optimize techniques to fight erosion, help prevent flooding and restore aquatic habitats in degraded waterways.

Recent national data shows that 44 percent of the nation's 3.5 million miles of rivers and streams have become degraded due to sedimentation and excess nutrients. This decline has led to impaired water quality over entire watersheds, rendering many streams unhealthy for recreation and public contact. The effects also have serious consequences for the health of aquatic life. Efforts to restore these bodies of water have resulted in an annual cost of more than $1 billion in the United States alone.

Historically, efforts have involved installing structures in the stream to change the direction and speed of the water, but with little ability to fine-tune a stream's reactions. Past computer models often oversimplify the stream systems and can't accurately simulate the beds, complicated bank shapes, turbulence, and natural or man-made structures within them.

"The practice of stream restoration has had a rocky rate of success as practitioners have struggled to alter a natural system with countless unknowns," Sotiropoulos said. "The need for more effective and reliable stream restoration strategies is clear, but the underlying physical processes which govern the behavior of a stream and its inhabitants are very complex. Our new Virtual StreamLab should provide researchers with a deeper understanding of those complexities."

Source: University of Minnesota (news : web)
http://www.physorg.com/news178315462.html

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Robert Karl Stonjek

November 25th, 2009 in Space & Earth / Astronomy
Peering through the thick dust clouds of our galaxy's central parts (the "bulge") with an amazing amount of detail, a team of astronomers has revealed an unusual mix of stars in the stellar grouping known as Terzan 5. Never observed anywhere in the bulge before, this peculiar cocktail of stars suggests that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of a dwarf galaxy that merged with the Milky Way during its very early days. This near-infrared image was obtained with the Multi-conjugate Adaptive Optics Demonstrator (MAD) instrument on ESO's Very Large Telescope. Observations in two bands (J and K) were combined. The field of view is 40 arcseconds across. Credit: ESO/F. Ferraro

(PhysOrg.com) -- Peering through the thick dust clouds of our galaxy's "bulge" (the myriads of stars surrounding its center), a team of astronomers has unveiled an unusual mix of stars in the stellar grouping known as Terzan 5. Never observed anywhere in the bulge before, this peculiar "cocktail" of stars suggests that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of a dwarf galaxy that merged with the Milky Way during its very early days.

"The history of the Milky Way is encoded in its oldest fragments, globular clusters and other systems of stars that have witnessed the entire evolution of our galaxy," says Francesco Ferraro, lead author of a paper appearing in this week's issue of the journal Nature. "Our new study opens a new window on yet another piece of our galactic past."

Like archaeologists, who dig through the dust piling up on top of the remains of past civilisations and unearth crucial pieces of the history of mankind, astronomers have been gazing through the thick layers of interstellar dust obscuring the bulge of the Milky Way and have unveiled an extraordinary cosmic relic.

The target of the study is the star cluster Terzan 5. The new observations show that this object, unlike all but a few exceptional globular clusters, does not harbour stars which are all born at the same time — what astronomers call a "single population" of stars. Instead, the multitude of glowing stars in Terzan 5 formed in at least two different epochs, the earliest probably some 12 billion years ago and then again 6 billion years ago.

"Only one globular cluster with such a complex history of star formation has been observed in the halo of the Milky Way: Omega Centauri," says team member Emanuele Dalessandro. "This is the first time we see this in the bulge."

The galactic bulge is the most inaccessible region of our galaxy for astronomical observations: only infrared light can penetrate the dust clouds and reveal its myriads of stars. "It is only thanks to the outstanding instruments mounted on ESO's Very Large Telescope," says co-author Barbara Lanzoni, "that we have finally been able to 'disperse the fog' and gain a new perspective on the origin of the galactic bulge itself."

This wide-field image, based on data from Digitized Sky Survey 2, shows the whole region around the stellar grouping Terzan 5.

A technical jewel lies behind the scenes of this discovery, namely the Multi-conjugate Adaptive Optics Demonstrator (MAD), a cutting-edge instrument that allows the VLT to achieve superbly detailed images in the infrared. Adaptive optics is a technique through which astronomers can overcome the blurring that the Earth's turbulent atmosphere inflicts on astronomical images obtained from ground-based telescopes; MAD is a prototype of even more powerful, next-generation adaptive optics instruments.

Through the sharp eye of the VLT, the astronomers also found that Terzan 5 is more massive than previously thought: along with the complex composition and troubled star formation history of the system, this suggests that it might be the surviving remnant of a disrupted dwarf galaxy, which merged with the Milky Way during its very early stages and thus contributed to form the galactic bulge.

"This could be the first of a series of further discoveries shedding light on the origin of bulges in galaxies, which is still hotly debated," concludes Ferraro. "Several similar systems could be hidden behind the bulge's dust: it is in these objects that the formation history of our Milky Way is written."

More information: This research was presented in a paper that appears in the 26 November 2009 issue of Nature , "The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge", by F. R. Ferraro et al.

Source: ESO (news : web)
http://www.physorg.com/news178377940.html

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Robert Karl Stonjek

November 25th, 2009 in Other Sciences / Mathematics
(PhysOrg.com) -- In 1811, Joseph Fourier, the 43-year-old prefect of the French district of Isčre, entered a competition in heat research sponsored by the French Academy of Sciences. The paper he submitted described a novel analytical technique that we today call the Fourier transform, and it won the competition; but the prize jury declined to publish it, criticizing the sloppiness of Fourier’s reasoning. According to Jean-Pierre Kahane, a French mathematician and current member of the academy, as late as the early 1970s, Fourier’s name still didn’t turn up in the major French encyclopedia the Encyclopædia Universalis.

Now, however, his name is everywhere. The Fourier transform is a way to decompose a signal into its constituent frequencies, and versions of it are used to generate and filter cell-phone and Wi-Fi transmissions, to compress audio, image, and video files so that they take up less bandwidth, and to solve differential equations, among other things. It’s so ubiquitous that “you don’t really study the Fourier transform for what it is,” says Laurent Demanet, an assistant professor of applied mathematics at MIT. “You take a class in signal processing, and there it is. You don’t have any choice.”

The Fourier transform comes in three varieties: the plain old Fourier transform, the Fourier series, and the discrete Fourier transform. But it’s the discrete Fourier transform, or DFT, that accounts for the Fourier revival. In 1965, the computer scientists James Cooley and John Tukey described an algorithm called the fast Fourier transform, which made it much easier to calculate DFTs on a computer. All of a sudden, the DFT became a practical way to process digital signals.

To get a sense of what the DFT does, consider an MP3 player plugged into a loudspeaker. The MP3 player sends the speaker audio information as fluctuations in the voltage of an electrical signal. Those fluctuations cause the speaker drum to vibrate, which in turn causes air particles to move, producing sound.

An audio signal’s fluctuations over time can be depicted as a graph: the x-axis is time, and the y-axis is the voltage of the electrical signal, or perhaps the movement of the speaker drum or air particles. Either way, the signal ends up looking like an erratic wavelike squiggle. But when you listen to the sound produced from that squiggle, you can clearly distinguish all the instruments in a symphony orchestra, playing discrete notes at the same time.

That’s because the erratic squiggle is, effectively, the sum of a number of much more regular squiggles, which represent different frequencies of sound. “Frequency” just means the rate at which air molecules go back and forth, or a voltage fluctuates, and it can be represented as the rate at which a regular squiggle goes up and down. When you add two frequencies together, the resulting squiggle goes up where both the component frequencies go up, goes down where they both go down, and does something in between where they’re going in different directions.

The DFT does mathematically what the human ear does physically: decompose a signal into its component frequencies. Unlike the analog signal from, say, a record player, the digital signal from an MP3 player is just a series of numbers, representing very short samples of a real-world sound: CD-quality digital audio recording, for instance, collects 44,100 samples a second. If you extract some number of consecutive values from a digital signal — 8, or 128, or 1,000 — the DFT represents them as the weighted sum of an equivalent number of frequencies. (“Weighted” just means that some of the frequencies count more than others toward the total.)

The application of the DFT to wireless technologies is fairly straightforward: the ability to break a signal into its constituent frequencies lets cell-phone towers, for instance, disentangle transmissions from different users, allowing more of them to share the air.

The application to data compression is less intuitive. But if you extract an eight-by-eight block of pixels from an image, each row or column is simply a sequence of eight numbers — like a digital signal with eight samples. The whole block can thus be represented as the weighted sum of 64 frequencies. If there’s little variation in color across the block, the weights of most of those frequencies will be zero or near zero. Throwing out the frequencies with low weights allows the block to be represented with fewer bits but little loss of fidelity.

Demanet points out that the DFT has plenty of other applications, in areas like spectroscopy, magnetic resonance imaging, and quantum computing. But ultimately, he says, “It’s hard to explain what sort of impact Fourier’s had,” because the Fourier transform is such a fundamental concept that by now, “it’s part of the language.”

Provided by Massachusetts Institute of Technology (news : web)
http://www.physorg.com/news178356724.html

Posted by
Robert Karl Stonjek