bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of regional cloud climate simulations over Scandinavia using a 10‐year NOAA Advanced Very High Resolution Radiometer cloud climatology
Authors: Karlsson Karl‐Göran , Willén Ulrika , Jones Colin , Wyser Klaus
Published: January 2008

A satellite‐derived (NOAA Advanced Very High Resolution Radiometer) cloud climatology over the Scandinavian region covering the period 1991–2001 has been used to evaluate the performance of cloud simulations of the Swedish Meteorological and Hydrological Institute Rossby Centre regional climate model (RCA3). Several methods of adapting the satellite and model data sets to allow a meaningful comparison were applied. RCA3‐simulated total cloud cover was shown to agree within a few percent of the satellite‐retrieved cloud amounts on seasonal and annual timescales. However, a substantial imbalance between the respective RCA3 contributions from low‐, medium‐ and high‐level clouds was seen. The differences from satellite‐derived contributions were +2.4% for high‐level clouds, −5.2% for medium‐level clouds and +4.0% for low‐level clouds. In addition, an overrepresentation of cloud categories with high optical thicknesses was seen for all vertical cloud groups, particularly during the summer season. Some specific features of the geographical distribution of cloudiness were also noticed. Most pronounced were the excess of cloud amounts over the Scandinavian mountain range and a deficit leeward of the mountains. The overall results imply problems with the RCA3‐modeled surface radiation budget components by causing reduced incoming solar radiation and increased downwelling longwave radiation.
A comparison of ground and satellite observations of F region vertical velocity near the dip equator
Authors: Oyekola O. S. , Ojo Akin , Akinrimisi J.
Published: January 2008

Nighttime F region vertical electrodynamic drifts were made at the magnetic equatorial stations in Africa, Ibadan (7.4°N, 3.9°E; 6°S dip), and Ouagadougou (12°N, 1.5°W; 5.9°N dip) using ionosondes hmF2 data during 1957/1958 International Geophysical Year (IGY) and 1990 periods, respectively; for high solar flux and geomagnetic quiet time conditions. We compare the seasonal averages of vertical drifts with observations made by Incoherent Scatter Radar (ISR) at Jicamarca (11.95°S, 76.87°W; 2°N dip) and Atmospheric Explorer E (AE‐E) satellite for equatorial F layer vertical drifts reported by Fejer et al. (1995). The results indicate good accord between the three techniques at periods when convection dominates other factors (e.g., around prereversal enhancement) except for June solstice drifts. However, when the drifts are completely downward (negative) between 2000 and 0500 LT sector, the mean discrepancies between ionosondes and ISR drifts are of 8–11 m/s (December solstice), 14–17 m/s (equinoxes) but comparable during June solstice with a value of about 14 m/s. Conversely, the typical values of the differences among ionosondes and AE‐E downward velocities are 7–10 m/s (December solstice), 9–12 m/s (equinoxes), yet again similar in winter with a significantly smaller value of about 3 m/s. The evening reversal times are in excellent agreement, apart from June solstice drifts, which exhibits large fluctuations. The morning reversal times show small variations. Equinoctial prereversal enhancement velocities have amplitudes of approximately 17–35 m/s between the methods. Our data are useful for global ionospheric modeling and for the predictions of development of nighttime equatorial F region irregularities at the African region where there is paucity of data.
Study of effects of changes of earthing resistances on geomagnetically induced currents in an electric power transmission system
Authors: Pirjola Risto
Published: January 2008

“Geomagnetically induced currents” (GIC) are a potential source of problems in ground‐based technological conductor systems. Power grids, which are discretely‐earthed networks, constitute an example. When calculating GIC in a system the low frequencies involved enable a dc treatment. In principle, the computation of GIC can be carried out exactly based on geoelectric data if the configuration and resistances of the network are known. In practice, however, the parameters often involve uncertainties. This especially concerns earthing resistance data, partly because they are usually only known at ac frequencies and partly because lower‐voltage networks that are neglected when considering a high‐voltage system may affect them. To investigate the influence of changes of earthing resistances on GIC, we present results from several computations. Although the calculations refer to the Finnish 400 kV power grid the observations also have more general relevance. It is seen that the impact of possible small uncertainties in the earthing resistances is not large regarding practical applications, in which knowledge of the level of GIC, rather than of precise values, is needed. It is also shown that additional resistances in the earthings provide a possible means to decrease GIC risks. In addition, the results indicate that interactions between different stations, i.e., the effects of off‐diagonal elements in the earthing impedance matrix, are minor.
Updated verification of the Space Weather Prediction Center's solar energetic particle prediction model
Authors: Balch Christopher C.
Published: January 2008

This paper evaluates the performance of an operational proton prediction model currently being used at NOAA's Space Weather Prediction Center. The evaluation is based on proton events that occurred between 1986 and 2004. Parameters for the associated solar events determine a set of necessary conditions, which are used to construct a set of control events. Model output is calculated for these events and performance of the model is evaluated using standard verification measures. For probability forecasts we evaluate the accuracy, reliability, and resolution and display these results using a standard attributes diagram. We identify conditions for which the model is systematically inaccurate. The probability forecasts are also evaluated for categorical forecast performance measures. We find an optimal probability and we calculate the false alarm rate and probability of detection at this probability. We also show results for peak flux and rise time predictions. These findings provide an objective basis for measuring future improvements.
Water balance versus land surface model in the simulation of Rhine river discharges
Authors: Hurkmans R. T. W. L. , de Moel H. , Aerts J. C. J. H. , Troch P. A.
Published: January 2008

Accurate streamflow simulations in large river basins are crucial to predict timing and magnitude of floods and droughts and to assess the hydrological impacts of climate change. Water balance models have been used frequently for these purposes. Compared to water balance models, however, land surface models carry the potential to more accurately estimate hydrological partitioning and thus streamflow, because they solve the coupled water and energy balance and are able to exploit a larger part of the information provided by regional climate model output than water balance models. Owing to increased model complexity, however, they are also more difficult to parameterize. The purpose of this study is to investigate and compare the accuracy of streamflow simulations of a water balance approach (Spatial Tools for River basins and Environment and Analysis of Management (STREAM)) and a land surface model (Variable Infiltration Capacity (VIC)) approach. Both models are applied to the Rhine river basin using regional climate model output as atmospheric forcing, and are evaluated using observed streamflow and lysimeter data. We find that VIC is more robust and less dependent on model calibration. Although STREAM performs better during the calibration period (Nash‐Sutcliffe efficiency (E) of 0.47 versus E = 0.29 for VIC), VIC more accurately simulates discharge during the validation period, including peak flows (E = 0.31 versus E = 0.21 for STREAM). This is the case for most locations throughout the basin, except for the Alpine part where both models have difficulties due to the complex terrain and surface reservoirs. In addition, the annual evaporation cycle at the lysimeters is more realistically simulated by VIC.
Neher and Sakmann Win Physiology Nobel for Cell Membrane Studies
Authors: Zeman Ellen J.
Published: January 2008

Many biological functions—such as nerve impulses, muscle contraction, vision and even conception—have their basis in a sudden change in cell membrane permeability. Specific membrane proteins act as gates or agents of active transport, regulating the flow of molecules and ions between the cell and its environment. Members of one class of membrane proteins, the ion channels, open in response to electrical, chemical or mechanical stimuli to allow the spontaneous flow of ions down a concentration or potential gradient across the cell membrane. In 1976 Erwin Neher and Bert Sakmann reported using a tiny yet simple electrode, called a patch clamp electrode, pressed up against a frog muscle cell to record for the first time the opening and closing of a single ion channel1 in a biological membrane. For their invention, refinement and application of the patch clamp and of the electronics for recording the minute currents it samples, Neher and Sakmann, now at the Max Planck Institutes in Göttingen and Heidelberg, respectively, have been awarded the 1991 Nobel Prize in Physiology or Medicine. In honoring the two, the Nobel Assembly at the Karolinska Institute cited “their discoveries concerning the function of single ion channels in cells.”
Making Stars to See Stars: DOD Adaptive Optics Work is Declassified
Authors: Collins Graham P.
Published: January 2008

Since the 1970s, researchers working first for the Defense Advanced Research Projects Agency and later under the aegis of the Strategic Defense Initiative have been developing and testing adaptive optics systems—systems for nullifying the effects of atmospheric turbulence on light that passes through it. In May 1991, to the delight of the astronomical community, much of the work became declassified. Adaptive optics works by measuring the distorting effects of the atmosphere on the light from a guide star and adjusting a deformable mirror to conjugate these effects. In particular, the declassified research involves the use of laser beams to create one or more artificial beaconsin the sky to act as guide stars.
Hanford Seeks Short- and Long-Term Solutions to its Legacy of Waste
Authors: Levi Barbara Goss
Published: January 2008

The 560 square miles of desert occupied by the Hanford Site in southeastern Washington are strewn with the silent hulks of reactors and processing plants that once produced plutonium for nuclear weapons. Lurking beneath the surface is the legacy of those plants—nearly 50 years' accumulation of chemical and nuclear waste, including over 60% by volume of the nation's high-level radioactive waste from weapons production. Some of the wastes will remain sequestered from the general public long enough to allow research on the best longrange solution to the problem of their disposal. But others require immediate action. Among the most urgent are the 177 million-gallon storage tanks for high-level wastes, some of which contain potentially explosive mixtures of chemicals.
Experiments Remove Resistance to the Notion of Persistent Currents
Authors: Levi Barbara Goss
Published: January 2008

Superconductors are not the only materials in which current can flow virtually without attenuation. Theories have predicted, and recent experiments have now indicated, that isolated rings of normal metals threaded by a magnetic flux can support persistent equilibrium currents. But this surprising phenomenon can occur only when the wavefunctions of the electrons remain in phase around the circumference and the electrons do not become localized in part of the ring. This condition requires the phase coherence length to exceed the ring's circumference and restricts experiments to micronsized rings even for the cleanest of metals. Even then the signal—a magnetic response induced by the current—is expected to be remarkably faint, less than 10−7 times the superconducting flux quantum φs which is 2.07×10−7 gauss-cm2.
Some Benefits of Quantum Interference Become Transparent
Authors: Levi Barbara Goss
Published: January 2008

Some atoms fail to absorb radiation even when the energy of the photons corresponds to the difference between two atomic levels. This phenomenon was discovered in 1961 by Ugo Fano of the University of Chicago, who explained it in terms of destructive interference: In the atoms that show this effect, there are two pathways leading to the same excited state, and their sum determines the probability for light to be absorbed. When these amplitudes interfere destructively, no photons are absorbed. One example is the transition from the ground state of helium to the 2s2p state, which lies in the continuum. The atom may be photoionized directly, or it may pass to the continuum via the discrete, autoionizing 2s2p state. As a result there is a window in the absorption spectrum for helium.
Experiments Map the Magnetic Phases of High-Tc Superconductors
Authors: Levi Barbara Goss
Published: January 2008

One of the early promises of high-Tc superconductors was their potential to superconduct at relatively high magnetic fields. As type II-superconductors, they allow the magnetic field to penetrate in quantized flux lines while still remaining superconducting except in the cores of the flux lines. In fact, the oxide materials should have vanishing resistivity at magnetic fields much higher than those that destroy superconductivity in conventional superconductors—if you ignore thermal fluctuations. But thermal fluctuations do play a large role in the oxide materials, and experimenters soon discovered that in magnetic fields, the resistance of the new materials remains quite high down to temperatures that are a fraction of the zero-field superconducting transition temperature Tc. At 5 tesla, for example, Bi2Sr2CaCu2O8, with a Tc of 90 K, doesn't beat out copper until the thermometer drops below about 30 K.
Quantum Cryptography Defies Eavesdropping
Authors: Collins Graham P.
Published: January 2008

Students of physics can be Students of physics can be excused for finding their quantum mechanics courses a little cryptic from time to time. Now researchers are using the properties of quantum mechanics to encrypt information for secure transmission.
Earthquake Jostles the New Stanford Linear Collider
Authors: Schwarzschild Bertram
Published: January 2008

On 12 October the Stanford Linear Accelerator Center announced its finding that Nature has only three families of elementary particles.’ (See PHYSICS TODAY, October, page 17) Five days later, as if in anger at having its secret revealed, Nature shook the offending instrument—the recently completed Stanford Linear Collider—by the throat. All things considered, the SLC has suffered relatively little damage from the historic earthquake that struck the San Francisco Bay area at 5:04 pm on 17 October. Still, the small misalignments caused by the quake have interrupted the physics schedule of the collider for more than a month. As of this writing, the fond expectation at SLAC is for “a few more Z°'s by Christmas.”
COBE Satellite Finds No Hint of Excess in The Cosmic Microwave Spectrum
Authors: Schwarzschild Bertram
Published: January 2008

For several years cosmologists have been kept busy puzzling over reports of a large excess in the cosmic microwave background spectrum at wavelengths shorter than 1 mm. Now they've been given a brief respite. At the January meeting of the American Astronomical Society in Washington, DC, John Mather of NASA's Goddard Space Flight Center presented the first spectral results from COBE—the Cosmic Background Explorer—which had been launched into Earth orbit just eight weeks earlier. The moment Mather placed the COBE spectrum (reproduced on this page) on the overhead projector, the packed lecture hall burst into sustained applause. The contrast with all the earlier, fragmentary data was astonishing. The spectral measurements, from 1 cm down to 0.5 mm, fit perfectly to a Planck blackbody radiation curve for a temperature of 2.735±0.06 K. At the 1% level one could see no deviation from an ideal blackbody spectrum. And it's not just a question of fitting a shape. With only one free parameter—temperature—the normalization also has to come out right. For a given temperature the absolute brightness of a blackbody spectrum is specified.
Gigantic Structures Challenge Standard View of Cosmic Evolution
Authors: Schwarzschild Bertram
Published: January 2008

These are exciting times for cosmologists. The “standard cosmological model” that purports to describe the evolution of the universe is being tested at both ends by spectacular astronomical observations. On the one hand are the recently discovered “Great Wall” and “Great Attractor,” enormous agglomerations of galaxies that attest to coherent structures stretching over half a billion light years in the present epoch. On the other hand are the new measurements of the uniformity of the cosmic microwave background, which tell us that the universe was amazingly smooth when it first became transparent—some 300 000 years after the Big Bang. The question at issue is: How did the cosmos evolve from these almost wrinkle-free beginnings to a present-day structure of such manifest inhomogeneity?
Hubble's Primary Mirror has the Wrong Shape
Authors: Schwarzschild Bertram
Published: January 2008

When the two principal mirrors of the Hubble Space Telescope were being ground, polished and coated a decade ago, great pains were taken to ensure that their surfaces not deviate from the desired hyperboloids of revolution by more than 100 angstroms. (See the article by C. R. O'Dell in PHYSICS TODAY, April, page 32.) In a sense, these exacting requirements have been met. The star images sent back by the orbiting observatory appear to confirm that the HST's 2.4-meter concave primary mirror and the 30-cm convex secondary are as close to being perfect, axially symmetric hyperboloids as one could wish.
Physicists Puzzle Over Gel Electrophoresis of DNA
Authors: Khurana Anil
Published: January 2008

The human genome project aims to determine the sequence in which the four bases of DNA occur in each of the 24 different chromosomes in the nucleus of a human cell. Chemical staining techniques indicate that the human chromosomes are all discernibly different in size, and contain between 50 million and 250 million base pairs. But present-day techniques cannot give more definitive numbers for the sizes of the human chromosomes, in part because they are the largest well-defined molecules modern science has encountered and weight standards and analytical techniques for handling such large molecules are not very well developed.
Special Issue: Andrei Sakharov
Authors: Lubkin Gloria B.
Published: January 2008

Until Andrei Sakharov published his essay “Reflections on Progress, Peaceful Coexistence and Intellectual Freedom,” most physicists had never heard of him. That year, 1968, I was attending an international conference on plasma physics and controlled fusion in Novosibirsk. A highlight of that meeting was the Soviet announcement of new experimental results on the tokamak that demonstrated its outstanding confinement properties. The Soviet results led to a major reorientation of magnetic fusion research. But one of the inventors of the tokamak, Sakharov, was absent. When one of us Americans asked after him, our host, Andrei Budker, replied, “Don't ask about him or you may be visited by the KGB.”
Highest Tc Continues to Increase Among Organic Superconductors
Authors: Khurana Anil
Published: January 2008

The first organic superconductor was discovered in 1980. Its critical temperature was less than 1 K. The highest critical temperature for superconductivity in an organic material crossed the 10-kelvin mark in 1988. That temperature has increased again: Researchers at Argonne National Laboratory now report synthesis of two new organic superconductors. The critical temperature for one is 11.6 K at ambient pressure; the second material becomes superconducting at 12.8 K under a pressure of 0.3 kbar. (See the figure on page 18.)
Uranium-Thorium Dating Sets the Clock Back on Carbon-14 Ages
Authors: Levi Barbara Goss
Published: January 2008

It's long been known that ages based on radiocarbon dating tend to be too young. The radiocarbon dates can be calibrated against tree-ring ages for the time period over which tree-ring samples are available—that is, over the last 8000–9000 years—but the corrections needed for earlier times have been unknown. Now a new chronometer is available that may permit some calibration back tens of thousands of years before the present era. The new benchmark is based on measurements of the decay of uranium into thorium. Researchers have dated materials using the uraniumthorium decay for many years, but the method they used was not very precise. Nor was there any set of samples systematic enough to use for C14 calibration. Two developments in the past few years have changed that: A Caltech team in 1987 adapted a mass spectrometry technique to obtain high-precision uranium-thorium results with small samples and established the validity of the uraniumthorium ages. This year a group from Columbia University's Lamont-Doherty Geological Observatory applied the new technique to samples of submerged corals collected off Barbados and was able to calibrate the C14 dates back at least 40 000 years.
Are Fractures Fractal or Quakes Chaotic?
Authors: Levi Barbara Goss
Published: January 2008

Just over one year ago, as San Franciscans were settling down to an evening of home runs and strikeouts, they got instead a few moments of shock and terror. The earthquake that struck them was not totally unexpected for that general area, but it certainly had not been pinpointed to the exact day and location. Earthquakes still defy accurate prediction, despite intensive efforts to understand their complex underlying dynamics.
Construction Proposals Take Aim at Top and Bottom Quarks
Authors: Schwarzschild Bertram
Published: January 2008

Cornell and Stanford are competing to build a B-meson “factory,” and Fermilab wants to build a new injector ring for its Tevatron Collider. These are the two principal new construction initiatives proposed by the US highenergy-physics community for completion by the middle of this decade. They are intended to address the two remaining “dangling participles” of the spectacularly successful standard model of the elementary particles: Understanding the violation of CP symmetry would seem to require a new source of B mesons much more profuse than the existing electronpositron rings; and determining the properties of the (still missing) top quark in adequate detail appears to necessitate an order of magnitude increase in the luminosity of the Tevatron proton-antiproton collider.
Study of the dissociation of nitrous oxide following resonant excitation of the nitrogen and oxygen K-shells
Authors: Céolin D. , Travnikova O. , Bao Z. , Piancastelli M. N. , Tanaka T. , Hoshino M. , Kato H. , Tanaka H. , Harries J. R. , Tamenori Y. , Prümper C. , Lischke T. , Liu X.-J. , Ueda K.
Published: January 2008

A photochemistry study on nitrous oxide making use of site-selective excitation of terminal nitrogen, central nitrogen, and oxygen 1s→3π excitations is presented. The resonant Auger decay which takes place following excitation can lead to dissociation of the N2O+ ion. To elucidate the nuclear dynamics, energy-resolved Auger electrons were detected in coincidence with the ionic dissociation products, and a strong dependence of the fragmentation pathways on the core-hole site was observed in the binding energy region of the first satellite states. A description based on the molecular orbitals as well as the correlation between the thermodynamical thresholds of ion formation and the first electronic states of N2O+ has been used to qualitatively explain the observed fragmentation patterns.
Shear-induced crystallization in phase-separated blend of isotactic polypropylene and poly (ethylene-co-octene)
Authors: Meng Kun , Dong Xia , Hong Song , Wang Xin , Cheng He , Han Charles C.
Published: January 2008

Isothermal crystallization after shear in a blend of isotactic polypropylene (iPP) and poly (ethylene-co-octene) (PEOc) was investigated by in situ optical microscopy and shear hot stage under various thermal and shear histories. Crystalline cylindrites during growth were observed in phase-separated iPP∕PEOc blends for the first time. According to our results, the very long cylindrites are formed which are much longer than the dimensions of the liquid-liquid phase-separated domains under shear, and the cylindrites appear to grow through noncrystallizable domains, as well as through crystallizable ones. Obviously, the nuclei (“shish”) come from the oriented and entangled network strands instead of pulled-out long chains. The number of cylindrites and the distortion and breakup of the cylindrites are related to the shear rate and shear time. On the other hand, the number of spherulites increases not only with shear rate but also with liquid-liquid phase separation time. Spherulites always form with longer induction time than cylindrites due to the different nucleation mechanism. The shish is nucleated through the shear-induced mechanism, and most of the spherulites are nucleated through liquid-liquid spinodal decomposition and crossover after the cessation of shear. During the process of experiments, we also found three kinds of shish-kebab structures, which provide further physical insights into the mechanism of the shish formation in polymer blend after liquid-liquid phase separation under shear.
Structure and electronic properties of PbnM (M=C, Al, In, Mg, Sr, Ba, and Pb; n=8, 10, 12, and 14) clusters: Theoretical investigations based on first principles calculations
Authors: Rajesh Chinagandham , Majumder Chiranjib
Published: January 2008

A systematic theoretical study of the PbnM (M=C, Al, In, Mg, Sr, Ba, and Pb; n=8, 10, 12, and 14) clusters have been investigated to explore the effect of impurity atoms on the structure and electronic properties of lead clusters. The calculations were carried out using the density functional theory with generalized gradient approximation for exchange-correlation potential. Extensive search based on large numbers of initial configurations has been carried out to locate the stable isomers of PbnM clusters. The results revealed that the location of the impurity atom depends on the nature of interaction between the impurity atom and the host cluster and the size of the impurity atom. Whereas, the impurity atoms smaller than Pb favor to occupy the endohedral position, the larger atoms form exohedral capping of the host cluster. The stability of these clusters has been analyzed based on the average binding energy, interaction energy of the impurity atoms, and the energy gap between the highest occupied and lowest unoccupied energy levels (HLG). Based on the energetics, it is found that p-p interaction dominates over the s-p interaction and smaller size atoms interact more strongly. The stability analysis of these clusters suggests that, while the substitution of Pb by C or Al enhances the stability of the Pbn clusters, Mg lowers the stability. Further investigations of the stability of PbnM clusters reveal that the interplay between the atomic and electronic structure is crucial to understand the stability of these clusters. The energy gap analysis reveals that, while the substitution of Mg atom widens the HLG, all other elements reduce the gap of the PbnM clusters.
Prediction of the adsorption behavior of elements 112 and 114 on inert surfaces from ab initio Dirac-Coulomb atomic calculations
Authors: Pershina V. , Borschevsky A. , Eliav E. , Kaldor U.
Published: January 2008

The interaction of elements 112 and 114 with inert surfaces has been studied on the basis of fully relativistic ab initio Dirac-Coulomb CCSD(T) calculations of their atomic properties. The calculated polarizabilities of elements 112 and 114 are significantly lower than corresponding Hg and Pb values due to the relativistic contraction of the valence ns and np1∕2 orbitals, respectively, in the heavier elements. Due to the same reason, the estimated van der Waals radius of element 114 is smaller than that of Pb. The enthalpies of adsorption of Hg, Pb, and elements 112 and 114 on inert surfaces such as quartz, ice, and Teflon were predicted on the basis of these atomic calculations using a physisorption model. At the present level of accuracy, −ΔHads of element 112 on these surfaces is slightly (about 2kJ∕mol) larger than −ΔHads(Hg). The calculated −ΔHads of element 114 on quartz is about 7kJ∕mol and on Teflon is about 3kJ∕mol smaller than the respective values of −ΔHads(Pb). The trend of increasing −ΔHads in group 14 from C to Sn is thus reversed, giving decreasing values from Sn to Pb to element 114 due to the relativistic stabilization and contraction of the np1∕2 atomic orbitals. This is similar to trends shown by other atomic properties of these elements. The small difference in ΔHads of Pb and element 114 on inert surfaces obtained within a picture of physisorption contrasts with the large difference (more than 100kJ∕mol) in the chemical reactivity between these elements.
Physics News in 1986
Authors: Schewe Phillip F.
Published: January 2008

The American Institute of Physics is a not-for-profit membership corporation chartered in New York State in 1931 for the purpose of promoting the advancement and diffusion of the knowledge of physics and its application to human welfare. Leading societies in the field of physics and astronomy are its members. AIP's activities include providing services to its Member Societies in the publishing, fiscal, and educational areas, as well as other services which can best be performed by one operating agency rather than dispersed among the constituent societies.
Effect of excluded volume interactions on the interfacial properties of colloid-polymer mixtures
Authors: Fortini Andrea , Bolhuis Peter G. , Dijkstra Marjolein
Published: January 2008

We report a numerical study of equilibrium phase diagrams and interfacial properties of bulk and confined colloid-polymer mixtures using grand canonical Monte Carlo simulations. Colloidal particles are treated as hard spheres, while the polymer chains are described as soft repulsive spheres. The polymer-polymer, colloid-polymer, and wall-polymer interactions are described by density-dependent potentials derived by Bolhuis and Louis [Macromolecules 35, 1860 (2002)]. We compared our results with those of the Asakura-Oosawa-Vrij model [J. Chem. Phys. 22, 1255 (1954); J. Polym Sci 33, 183 (1958); Pure Appl. Chem. 48, 471 (1976)] that treats the polymers as ideal particles. We find that the number of polymers needed to drive the demixing transition is larger for the interacting polymers, and that the gas-liquid interfacial tension is smaller. When the system is confined between two parallel hard plates, we find capillary condensation. Compared with the Asakura-Oosawa-Vrij model, we find that the excluded volume interactions between the polymers suppress the capillary condensation. In order to induce capillary condensation, smaller undersaturations and smaller plate separations are needed in comparison with ideal polymers.
Do Asteroid Impacts Trigger Geomagnetic Reversals?
Authors: Schwarzschild Bertram
Published: January 2008

It's been about 700 000 years since the last time the Earth's magnetic field reversed its polarity. Considering that the average over the last 30 million years has been about four geomagnetic reversals per million years, we're a bit overdue. But if Berkeley physicists Richard Muller and Donald Morris are right, the onset of the next reversal will be more than just an inconvenience to navigators. In the November issue of Geophysical Research Letters, they make an intriguing, if rather speculative, case for the thesis that many, perhaps all, polarity reversals of the dynamo churning in our planet's liquid-iron outer core are caused by the impact of large extraterrestrial objects falling to Earth.
Herschbach, Lee and Polanyi Receive 1986 Chemistry Nobel
Authors: Andersen Per H.
Published: January 2008

For “contributions concerning the dynamics of chemical elementary processes” the Royal Swedish Academy of Sciences has awarded the 1986 Nobel Prize in Chemistry to Dudley R. Herschbach (Harvard), Yuan T. Lee (Berkeley) and John C. Polanyi (University of Toronto). Their research in chemical physics—specifically reaction dynamics—is basic to a detailed understanding of chemical reactions. The award honors the development of two important techniques for probing what happens when molecules collide and atoms rearrange themselves to form new molecules. These techniques, crossed molecular beams and infrared chemiluminescence, provide a basis for the determination of the potential energy surfaces of specific reactions.
Superconductivity Seen Above the Boiling Point of Nitrogen
Authors: Khurana Anil
Published: January 2008

Since the observation by Karl Alex Müller and Johannes Georg Bednorz (IBM Zurich) in January 1986 that an oxide of barium, lanthanum and copper might be superconducting at temperatures up to 35 K, several groups around the world have reported seeing superconductivity above 90 K in a number of ternary oxides containing rare earth elements. Many laboratories are already exploring applications for these materials. Why they are superconducting at such high temperatures is one of many questions that theorists are trying to answer.
High Tc May Not Need Phonons; Supercurrents Increase
Authors: Khurana Anil
Published: January 2008

Were any surprising and unexpected new results presented at the special panel discussion on new high-temperature superconductors, a reporter asked at the first of the two press conferences AIP organized on the morning after the historic, all-night panel discussion on 18 March at the APS meeting in New York. Among interesting new results, physicists at the press conference concurred, were evidence for a transition to an antiferromagnetic state in lanthanum-copper oxide, anomalies at 120 K in the resistivity of some oxides similar to those that become superconducting between 90 K and 95 K, suggesting that it might be possible to achieve superconductivity at even higher temperatures, and fabrication of wires containing the recently discovered superconducting material lanthanum-strontium-copper oxide, with a better current-carrying capacity in the superconducting state. The first of these results, they hoped, could provide the key to understanding why these oxides remain superconducting at temperatures up to 90 K; the last could open the door to useful applications of these materials. (See PHYSICS TODAY, April, page 17.)
Neutral B Mesons Show Surprisingly Large Flavor Mixing
Authors: Schwarzschild Bertram
Published: January 2008

In its heyday in the 1950s and 60s, the K meson was a spectacular source of profound surprises. Its “strange” longevity gave us the first hint of flavor conservation in the strong interactions, and eventually the concept of quarks as the carriers of these hadronic flavors. Its decay into states of opposite parity freed us from rigid adherence to mirror symmetry Then the neutral kaon was seen to oscillate wondrously between states of opposite strangeness, and finally, in 1964, one of its decay modes yielded up the last great surprise. It provided us the only example we have to this day of CP violation. We had known since 1957 that P (parity inversion) was not an inviolate symmetry of nature. Now the last hope for mirror symmetry—invariance under the combined operation of P and C (charge conjugation)—was also dashed.
Ripples in the Universal Hubble Flow
Authors: Andersen Per H.
Published: January 2008

Large streaming velocities indicate bulk motions on scales as large as superclusters—clusters of clusters of galaxies—in addition to a smooth cosmological Hubble expansion. The existence of such motion has long been controversial. “None of the standard models can easily explain streaming,” says Jeremiah Ostriker (Princeton). “One might say that the velocities are not just Doppler shifts, but that would be iconoclastic.”
Special Issue: Physics in Japan
Authors: Lubkin Gloria B.
Published: January 2008

Because of Japan's recent remarkable achievements in science and industry, we offer you this special issue on physics in Japan. The articles all deal with topics where Japanese physicists are working at the frontiers of knowledge.
On the performance of two-component energy-consistent pseudopotentials in atomic Fock-space coupled cluster calculations
Authors: Figgen Detlev , Wedig Anja , Stoll Hermann , Dolg Michael , Eliav Ephraim , Kaldor Uzi
Published: January 2008

The four-component atomic intermediate-Hamiltonian Fock-space coupled cluster (IHFSCC) code of Landau et al. [J. Chem. Phys. 115, 6862 (2001)] has been adapted to two-component calculations with relativistic pseudopotentials of the energy-consistent variety. Recently adjusted energy-consistent pseudopotentials for group 11 and 12 transition elements as well as group 13 and 14 post-d main group elements, which were fitted to atomic valence spectra from four-component multiconfiguration Dirac-Hartree-Fock calculations, are tested in IHFSCC calculations for ionization potentials, electron affinities, and excitation energies of a variety of atoms and ions. Where comparison is possible, the deviations from experimental data are in good agreement with those found in previously published IHFSCC all-electron calculations: experimental data are usually reproduced within a few hundred wavenumbers.
Phase-locked laser system for use in atomic coherence experiments
Authors: Marino Alberto M. , Stroud C. R.
Published: January 2008

We describe a phase-coherent laser system designed for use in experiments involving coherently prepared atomic media. We implement a simple technique based on a sample-and-hold circuit together with a reset of the integrating electronics that makes it possible to scan continuously the relative frequency between the lasers of over tens of gigahertz while keeping them phase locked. The system consists of three external-cavity diode lasers operating around 795nm. A low-power laser serves as a frequency reference for two high-power lasers which are phased locked with an optical phase-locked loop. We measured the residual phase noise of the system to be less than 0.04rad2. In order to show the application of the system towards atomic coherence experiments, we used it to implement electromagnetically induced transparency in a rubidium vapor cell and obtained a reduction in the absorption coefficient of 92%.
Internal loss, modal characteristics, and bend loss of asymmetric cladding ridge waveguide lasers at 850 nm
Authors: Price R. K. , Verma V. B. , Elarde V. C. , Coleman J. J.
Published: January 2008

The upper cladding and residual guide thickness have been varied to develop an optimal asymmetric cladding ridge waveguide geometry for use in photonic integrated circuits (PICs). Measured values of the intrinsic loss, threshold current, and lateral modal characteristics allowed the determination of the geometry that simultaneously achieved good active device performance and a strong lateral index step. The bend loss was found by fabricating curved-waveguide y-branch lasers. These characteristics are important for fabricating low-loss routing structures in PICS. This experimental work analyzed an asymmetric cladding ridge waveguide for use with photonic integrated circuits; however, the method presented here generally can be used for the experimental optimization of ridge waveguide lasers.
Restricted primitive model for electrolyte solutions in contact with solid surface modified by grafted chains: A density functional approach
Authors: Smagala T. G. , Patrykiejew A. , Sokołowski S. , Pizio O. , Fawcett W. R.
Published: January 2008

We have studied the microscopic structure and the thermodynamic and electric properties of the restricted primitive model for electrolyte solutions in contact with a chemically modified uncharged and charged solid surface. The modification of the surface is performed by the tethering of chain particles via a specific single segment at the stage preceeding the adsorption of the restricted primitive model. Some fraction of segments belonging to a chain particle can be charged such that the system models adsorption on an electrode covered by an electrolyte brush. We apply the density functional method which combines previously developed approach for inhomogeneous chain fluids, and the weighted density mean spherical approximation energy route for the description of inhomogeneous ionic fluids. The theory is formulated in the semigrand canonical ensemble. Our principal findings are concerned with the density profiles of the species, the adsorption isotherms of ions in the presence of grafted chain particles, the charge density profile and the potential of zero charge (all as the functions of the grafted density), and other parameters related to the solid surface and its modification.
Dust ion-acoustic waves in magnetized quantum dusty plasmas with polarity effect
Authors: Khan S. A. , Mushtaq A. , Masood W.
Published: January 2008

The obliquely propagating two-dimensional quantum dust ion-acoustic solitary waves in a magnetized quantum dusty plasma are studied by using the quantum hydrodynamic model. A linear dispersion relation is obtained using the Fourier analysis, and a nonlinear quantum Zakharov-Kuznetsov equation is derived for small-amplitude perturbations. A stationary solution of this equation is obtained to investigate the effects of quantum corrections, concentration of dust particles, and the angle of propagation on the amplitude, width, and energy of the soliton. The relevance of the present investigation to the astrophysical dusty plasmas is discussed.
Epitaxial growth and properties of (001)-oriented TbBaCo2O6−δ films
Authors: Kasper N. V. , Wochner P. , Vigliante A. , Dosch H. , Jakob G. , Carstanjen H. D. , Kremer R. K.
Published: January 2008

Thin epitaxial films of TbBaCo2O6−δ cobaltites have been synthesized using pulsed laser deposition. It was found that the film properties are extremely sensitive to the oxygen pressure during deposition, temperature of the substrate, and the cooling rate. Growth parameters were optimized for δ≈0.5 films with ordered Tb and Ba ions, as well as oxygen vacancies. The properties of these c-axis oriented films are similar to bulk TbBaCo2O5.5: they show a metal-insulator phase transition at TMI≈350 K, ferromagnetic order below TC=285 K, and antiferromagnetism at T<Ti≈230 K.
Effect of aspect ratio on the magnetic properties of nickel nanowires
Authors: Das B. , Mandal K. , Sen Pintu , Bandopadhyay S. K.
Published: January 2008

Nickel nanowires with a diameter of ∼200 nm were prepared using the electrodeposition technique. The length of the nanowires was varied from 0.7 to 5.6 μm, which corresponds to the change in the aspect ratio from 3.5 to 28. Field emission scanning electron microscopy and x-ray diffraction spectra confirm the formation of nickel nanowires. In-plane and out-of-plane coercivity and remanence of the samples determined from direct current magnetic hysteresis loops suggest the magnetic easy axis of the nanowires along their transverse direction. As a result, magnetic hardness along the axis of the nanowires is higher than that perpendicular to it. The temperature dependence (80 K≤T≤350 K) of coercivity and squareness ratio of the samples has also been studied in detail. The vortex configuration of magnetization in the individual nanowires along with magnetostatic interaction among them has been suggested as the possible explanation for the observed magnetic properties of these nanowires in the present study.
Copper ion drift in integrated circuits: Effect of boundary conditions on reliability and breakdown of low-k dielectrics
Authors: Achanta Ravi S. , Gill William N. , Plawsky Joel L.
Published: January 2008

Copper drift in current interconnect structures is a reliability issue leading to premature low-k dielectric breakdown. Copper ions drift through insulating low-k dielectrics leading to an increase in the local electric field that, if high enough, could lead to device failure. We have solved the coupled continuity and Poisson’s equation using the boundary condition that the flux of copper ions equals zero [J(t,L)=0] at the cathode or dielectric-semiconductor interface. This condition closely mirrors the actual physics in interconnects and leads to a buildup or accumulation of copper ions at the dielectric-semiconductor interface. Significant differences are observed in the copper concentration and local electric field behavior near the interface when the condition of a blocking electrode [J(t,L)=0] compared to the concentration equals zero [C(t,L)=0] with implications for the reliability of the low-k dielectric and time to failure for the interconnect structure. The time to failure (TTF) is shown to depend on the boundary condition at the cathode Ce, the copper ion solubility in the dielectric, as well as the drift of copper ions through the dielectric. When intrinsic thermal effects are included in addition to the mass transport, a close fit is achieved with experimental TTF results of Hwang et al. [J. Appl. Phys. 101, 074501 (2007)] The inclusion of mass transport simulates the nonlinearity in TTF at low fields, a characteristic that has been observed experimentally.
Magnetic, magnetothermal, and magnetotransport properties in SmMn2Si2−xGex compounds
Authors: Kumar Pramod , Suresh K. G. , Nigam A. K. , Malik S. K.
Published: January 2008

The effect of Ge substitution for Si in SmMn2Si2−xGex compounds has been studied. The Sm ordering temperature is found to be much larger in the compound with x=2, as compared to the compounds with x=0 and 1. The increase in the intralayer Mn–Mn distance is attributed to this variation. Among these three compounds, SmMn2Ge2 is found to show reentrant ferromagnetism at low temperatures. The magnetic contribution to the heat capacity has been calculated in all the three compounds. The splitting of the ground state multiplet has been estimated by fitting the magnetic part of the heat capacity data, using the Schottky formula. The isothermal magnetic entropy change is found to remain the same for x=0 and 1 but decreases in the compound with x=2, though the nature of magnetic transition changes from second order to first order, as x is increased from 0 to 2. The electrical resistivity increases with Ge concentration. The excess resistivity in the antiferromagnetic region has been calculated.
Chirality dependence of the adsorption of H2 on 4Å carbon nanotubes
Authors: Miao L. , Liu H. J. , Wen Y. W. , Zhou X. , Hu C. Z.
Published: January 2008

Density functional calculations and the nudged elastic band technique are used to study the adsorption of H2 on 4Å single-wall carbon nanotubes. It is found that both the chemical and physical adsorptions of H2 are possible and the calculated adsorption barriers are considerably lower than those of larger diameter nanotubes. There is a strong chirality dependence of the energy barriers, and the (5,0) tube seems to be the best choice for the hydrogen storage among three kinds of 4Å nanotubes.