bluuebunny/crossref_metadata_2025 huggingface dataset:
Hafnium, neodymium, and strontium isotope and parent‐daughter element systematics in basalts from the plume‐ridge interaction system of the Salas y Gomez Seamount Chain and Easter Microplate
Authors: Kingsley Richard H. , Blichert‐Toft Janne , Fontignie Denis , Schilling Jean‐Guy
Published: April 2007

We present a comprehensive data set with Hf, Nd, and Sr isotope ratios and parent‐daughter trace element concentrations in 111 basalts and glasses from seamounts of the western Easter–Salas y Gomez Seamount Chain (ESC), the Easter Microplate (EMP) spreading centers, and the East Pacific Rise (EPR). Sr and Pb radiogenic isotope ratios and related ratios of highly incompatible parent to lesser incompatible daughter elements grade from high values near the Salas y Gomez (SyG) hot spot location to low values 1000 km west. Here the west rift of the EMP is dominated by typical depleted mid‐ocean ridge basalt (MORB). Hf and Nd radiogenic isotope ratios show the opposite gradients, which also reflect the long‐term enriched nature of the hot spot source and mixing of the hot spot with the depleted upper mantle. Gradients of these parameters occur north and south along the EMP boundaries. These observations confirm the plume‐ridge interaction model proposed for this region by Schilling et al. and further characterize the SyG hot spot. The binary mixing relationship evident in the isotope variations of the basalts is somewhat compromised when the trace elements are considered. This complexity can be explained by modification of trace element abundances during the process of partial melting of the two end‐member components (enriched hot spot and depleted upper mantle). In addition, the melting variability is evident in the basalt bulk compositions, which range from tholeiitic (EMP to 108°W) to alkali basalts (108°W to SyG). A single highly correlated data array in Pb‐isotope space and a linear Pb‐Sr isotope relation indicate that the SyG hot spot is homogeneous. The similarity of the Pb isotope ratios of the SyG hot spot to other long‐term high‐U/Pb mantle domains suggests an origin in subduction‐modified altered oceanic crust. The SyG end‐member isotope composition appears to be pervasive in the south central Pacific mantle, evoking a widespread mantle contamination event by the SyG hot spot in the past.
Satellite evidence of ecosystem changes in the White Sea: A semi‐enclosed arctic marginal shelf sea
Authors: Pozdnyakov Dmitry V. , Johannessen Ola M. , Korosov Anton A. , Pettersson Lasse H. , Grassl Hartmut , Miles Martin W.
Published: April 2007

Recent observations suggest an arctic climate system in broad transformation, yet the regional marine‐ecosystem response is poorly known. Here, we develop and analyze a comprehensive biogeophysical dataset of key water constituents – chlorophyll (chl), suspended sediments (sm) and dissolved organic matter (doc) – using satellite ocean‐color data from the White Sea in the Russian Arctic, for the period 1998–2004. The revealed changes in chl, sm and doc are more pronounced in the bays (e.g., the southeastern bay trends are −20%, +18% and +11%, respectively) than in the central basin (−5%, +5% and +3%, respectively). The chlorophyll decreases reflect the impact of enhanced runoff on sm and doc, which make the water more turbid and less favourable for phytoplankton growth, in contrast to other arctic seas where increased phytoplankton is expected. This case study supports our hypothesis that the marine ecosystems of semi‐enclosed arctic shelf seas respond rapidly to climate change and are thus particularly vulnerable to future global warming.
Evidence of Jovian active longitude: 2. A parametric study
Authors: Galopeau Patrick H. M. , Boudjada Mohammed Y. , Rucker Helmut O.
Published: April 2007

In a previous work, we developed a model allowing a theoretical location of the Io‐controlled decameter radio sources (Io‐A, Io‐B, Io‐C, and Io‐D) in the central meridian longitude‐Io phase diagram. This model considers the cyclotron maser instability to be at the origin of most auroral planetary radio emissions. We derive the efficiency of this theoretical mechanism at the footprint of the Io flux tube during a complete revolution of the satellite around Jupiter, and we show that some longitudes in the northern and southern hemispheres favor the radio decameter emission and lead to a probability of higher occurrence. In order to make the calculation easier, we suppose that electrons are accelerated in the neighborhood of Io and follow an adiabatic motion along magnetic field lines carried by the satellite. We also assume that the source of free energy needed by the cyclotron maser instability to amplify the waves derives from a loss cone distribution function built up by electrons which have disappeared in Jupiter's ionosphere. We study the effect of several parameters on the theoretical location of the sources in the central meridian longitude‐Io phase diagram, in particular the Jovicentric declination of the Earth and the frequency of emission.
Upper mantle structure of South America from joint inversion of waveforms and fundamental mode group velocities of Rayleigh waves
Authors: Feng Mei , van der Lee Suzan , Assumpção Marcelo
Published: April 2007

A new tomographic S wave velocity model for the upper mantle beneath South America is presented. We developed and applied a new method of simultaneously inverting regional S and Rayleigh waveforms and fundamental mode Rayleigh wave group velocities, to better constrain upper mantle S velocity structure and Moho depth. We used ∼5700 Rayleigh wave group velocity dispersion curves and 1537 regional wave trains with paths principally passing through the South American continent. The joint inversion of this data set provided a new three‐dimensional (3‐D) upper mantle S velocity model and a Moho depth model for South America, which fits both the group velocity and regional waveform data sets well. New features of the final three‐dimensional (3‐D) S velocity and Moho depth model correlate well with known geotectonic units on a regional scale. The Moho depth ranges from 30 km in the central Chaco basin to 42 km beneath the Amazonian craton and 45–70 km beneath the orogenic Andean belt. The imaged S velocity indicates an average lithosphere thickness of around 160 km for the Amazonian craton. High velocities are imaged beneath the Amazon and part of the Paraná and Parnaíba basins down to about 150 km. Low to very low velocities are imaged beneath the central Andes and the Chaco, Pantanal, and northwestern Paraná basins.
Late Cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the Tian Shan Mountains
Authors: Sun Jimin , Xu Qinghai , Huang Baochun
Published: April 2007

The folded Neogene deposits in the northern foreland basin of the Tian Shan Mountains provide important information about tectonic history and environmental changes of northwestern China. On the basis of lithostratigraphic and magnetostratigraphic evidence, we develop a new chronology for the previous studied Kuitun He section. Our palynological study on the late Miocene–Pliocene sediment of the Dushanzi section yields new information about vegetation and climate change during the period of 8.7–2.58 Ma. The results indicate that steppe taxa (Artemisia and Chenopodiaceae) were generally dominant in the studied areas between 8.7 and 2.58 Ma, implying that a dry climate has occurred in the inland basins of northwestern China at least since 8.7 Ma ago. Although the general climate pattern indicated by our palynological results displays to some extent of drought, a warm and humid phase occurred at 5.8–3.9 Ma ago. This climatic optimum is comparable with the other records from the Chinese Loess Plateau, central Japan, the Sub‐Himalayan Zone, and the marine eustatic sea level rise, implying this seems to be, at least, a regional climatic optimum.
Thermal conductivity of landfast Antarctic and Arctic sea ice
Authors: Pringle D. J. , Eicken H. , Trodahl H. J. , Backstrom L. G. E.
Published: April 2007

We present final results from a program to measure the thermal conductivity of sea ice with in situ thermistor arrays using an amended analysis of new and previously reported ice temperatures. Results from landfast first‐year (FY) ice near Barrow, Alaska, and McMurdo Sound, Antarctica, are consistent with predictions from effective‐medium models but 10–15% higher than values from the parameterization currently used in most sea ice models. We observe no previously reported anomalous near‐surface reduction, which is now understood to have been an artifact, nor a convective enhancement to the heat flow, although our analysis is limited to temperatures below −5°C at which brine percolation is restricted. Results for landfast multiyear (MY) ice in McMurdo Sound are also consistent with effective‐medium predictions, and emphasize the density dependence. We compare these and historical measurements with effective‐medium predictions and the representation commonly used in sea ice models, developed originally for MY Arctic ice. We propose an alternative expression derived from effective‐medium models, appropriate for both MY and FY ice that is consistent with experimental results, k = (ρ/ρi)(2.11 − 0.011 θ + 0.09 (S/θ) − (ρ − ρi)/1000), where ρi and ρ are the density of pure ice and sea ice (kg m−3), and θ (°C) and S (ppt) are sea ice temperature and salinity. For the winter and spring conditions studied here, thermal signatures of internal brine motion were observed rarely (22 times in 1957 days), and their maximum contribution to the total heat flow is estimated to be of the order of a few percent.
Development of a possibilistic method for the evaluation of predictive uncertainty in rainfall‐runoff modeling
Authors: Jacquin Alexandra P. , Shamseldin Asaad Y.
Published: April 2007

Using a possibilistic approach, this study develops a methodology for the evaluation of predictive uncertainty in rainfall‐runoff modeling. The methodology proposed herein can be regarded as a further extension of the well‐known generalized likelihood uncertainty estimation (GLUE) methodology. Both methods are based on the equifinality paradigm, under which it is accepted that there may be many model structures and parameter sets (within a given model structure) that are compatible with the knowledge available about the real system. In both methodologies, uncertainty bounds of the model predictions are obtained using Monte Carlo simulations. The essential difference between them is that while in the GLUE methodology the likelihood weights of behavioral simulations are used to obtain prediction quantiles, in the possibilistic methodology the possibility distributions of the model outputs are used to derive the prediction uncertainty bounds. The methodology presented in this study is applied to a conceptual type rainfall‐runoff model.
A constitutive model for layer development in shear zones near the brittle‐ductile transition
Authors: Montési Laurent G. J.
Published: April 2007

The microstructure of ductile shear zones differs from that of surrounding wall rocks. In particular, compositional layering is a hallmark of shear zones. As layered rocks are weaker than their isotropic protolith when loaded in simple shear, layering may hold the key to explain localization of ductile deformation onto ductile shear zones. I propose here a constitutive model for layer development. A two‐level mixing theory allows the strength of the aggregate to be estimated at intermediate degrees of layering. A probabilistic failure model is introduced to control how layers develop in a deforming aggregate. This model captures one of the initial mechanism of phase interconnection identified experimentally by Holyoke and Tullis (2006a, 2006b), fracturing of load bearing grains. This model reproduces the strength evolution of these experiments and can now be applied to tectonic modeling.
Boundary layer effects above a Himalayan valley near Mount Everest
Authors: Sun Fanglin , Ma Yaoming , Li Maoshan , Ma Weiqiang , Tian Hui , Metzger Stefan
Published: April 2007

Periodical Wind Profiler and Radio Acoustic Sounding System observations have been commenced at the Himalayas' northern slope nearby Mount Everest in September 2005. Primarily data sets obtained 25 km remote from the glacier edge are utilized for a preliminary discussion of planetary boundary layer circulation resembling high alpine mountainous regions. Substantial findings include the detection of two wind shears and the phenomenon of glacier wind at a distance of 25 km from the glaciers. The latter lead to a reversed compensatory flow in a vertical scale of up to 2000 m above ground level, pointing at supra regional impact.
Cannabinoids as therapeutic agents in cardiovascular disease: a tale of passions and illusions
Authors: Mendizábal V E , Adler‐Graschinsky E
Published: April 2007

In addition to their classical known effects, such as analgesia, impairment of cognition and learning and appetite enhancement, cannabinoids have also been related to the regulation of cardiovascular responses and implicated in cardiovascular pathology. Elevated levels of endocannabinoids have been related to the extreme hypotension associated with various forms of shock as well as to the cardiovascular abnormalities that accompany cirrhosis. In contrast, cannabinoids have also been associated with beneficial effects on the cardiovascular system, such as a protective role in atherosclerosis progression and in cerebral and myocardial ischaemia. In addition, it has also been suggested that the pharmacological manipulation of the endocannabinoid system may offer a novel approach to antihypertensive therapy. During the last decades, the tremendous increase in the understanding of the molecular basis of cannabinoid activity has encouraged many pharmaceutical companies to develop more potent synthetic cannabinoid analogues and antagonists, leading to an explosion of basic research and clinical trials. Consequently. not only the synthetic THC dronabinol (Marinol) and the synthetic THC analogue nabilone (Cesamet) have been approved in the United States, but also the standardized cannabis extract (Sativex) in Canada. At least three strategies can be foreseen in the future clinical use of cannabinoid‐based drugs: (a) the use of CB1receptor antagonists, such as the recently approved rimonabant (b) the use of CB2‐selective agonists, and (c) the use of inhibitors of endocannabinoid degradation. In this context, the present review examines the effects of cannabinoids and of the pharmacological manipulation of the endocannabinoid system, in cardiovascular pathophysiology.

British Journal of Pharmacology(2007)151, 427–440; doi:10.1038/sj.bjp.0707261
Magnetic Rayleigh-Taylor instability mitigation and efficient radiation production in gas puff Z-pinch implosions
Authors: Sze H. , Levine J. S. , Banister J. , Failor B. H. , Qi N. , Steen P. , Velikovich A. L. , Davis J. , Wilson A.
Published: April 2007

Large radius Z-pinches are inherently susceptible to the magnetic Rayleigh-Taylor (RT) instability because of their relatively long acceleration path. This has been reflected in a significant reduction of the argon K-shell yield as was observed when the diameter of the load was increased from 2.5to>4cm. Recently, an approach was demonstrated to overcome the challenge with a structured gas puff load that mitigates the RT instability, enhances the energy coupling, and leads to a high compression, high yield Z-pinch. The novel load consists of a “pusher,” outer region plasma that carries the current and couples energy from the driver, a “stabilizer,” inner region plasma that mitigates the RT growth, and a “radiator,” high-density center jet plasma that is heated and compressed to radiate. In 3.5-MA, 200-ns, 12-cm initial diameter implosions, the Ar K-shell yield has increased by a factor of 2, to 21kJ, matching the yields obtained on the same accelerator with 100-ns, 2.5-cm-diam implosions. Further tests of such structured Ar gas load on ∼6MA, 200-ns accelerators have achieved >80kJ. From laser diagnostics and measurements of the K-shell and extreme ultraviolet emission, initial gas distribution and implosion trajectories were obtained, illustrating the RT suppression and stabilization of the imploding plasma, and identifying the radiation source region in a structured gas puff load. Magnetohydrodynamic simulations, started from actual initial density profiles, reproduce many features of the measurements both qualitatively and quantitatively.
Phase-locked spin torque oscillators: Impact of device variability and time delay
Authors: Persson J. , Zhou Yan , Akerman Johan
Published: April 2007

We have carried out detailed Landau–Lifshitz-Gilbert simulations of pairs of serially connected spin torque oscillators (STOs) in parallel with a resistive load. To study the impact of realistic process variations on STO synchronization we let the two STOs have different in-plane anisotropy fields (Hk). The simulation also provides for a time delay (τ). We construct a phase diagram of the STO synchronization as a function of Hk and direct current (Idc) at different τ. The phase diagram turns out to be quite rich with different types of synchronized precession modes. While the synchronized state is originally very sensitive to STO process variations and can only sustain up to 4% Hk variation, the addition of a small time delay dramatically improves its robustness and allows as much as 145% Hk variation in the entire out-of-plane precession regime.
Cryogenic DT and D2 targets for inertial confinement fusion
Authors: Sangster T. C. , Betti R. , Craxton R. S. , Delettrez J. A. , Edgell D. H. , Elasky L. M. , Glebov V. Yu. , Goncharov V. N. , Harding D. R. , Jacobs-Perkins D. , Janezic R. , Keck R. L. , Knauer J. P. , Loucks S. J. , Lund L. D. , Marshall F. J. , McCrory R. L. , McKenty P. W. , Meyerhofer D. D. , Radha P. B. , Regan S. P. , Seka W. , Shmayda W. T. , Skupsky S. , Smalyuk V. A. , Soures J. M. , Stoeckl C. , Yaakobi B. , Frenje J. A. , Li C. K. , Petrasso R. D. , Séguin F. H. , Moody J. D. , Atherton J. A. , MacGowan B. D. , Kilkenny J. D. , Bernat T. P. , Montgomery D. S.
Published: April 2007

Ignition target designs for inertial confinement fusion on the National Ignition Facility (NIF) [W. J. Hogan , Nucl. Fusion41, 567 (2001)] are based on a spherical ablator containing a solid, cryogenic-fuel layer of deuterium and tritium. The need for solid-fuel layers was recognized more than 30 years ago and considerable effort has resulted in the production of cryogenic targets that meet most of the critical fabrication tolerances for ignition on the NIF. At the University of Rochester’s Laboratory for Laser Energetics (LLE), the inner-ice surface of cryogenic DT capsules formed using β-layering meets the surface-smoothness requirement for ignition (<1-μm rms in all modes). Prototype x-ray-drive cryogenic targets being produced at the Lawrence Livermore National Laboratory are nearing the tolerances required for ignition on the NIF. At LLE, these cryogenic DT (and D2) capsules are being imploded on the direct-drive 60-beam, 30-kJ UV OMEGA laser [T. R. Boehly , Opt. Commun.133, 495 (1997)]. The designs of these cryogenic targets for OMEGA are energy scaled from the baseline direct-drive-ignition design for the NIF. Significant progress with the formation and characterization of cryogenic targets for both direct and x-ray drive will be described. Results from recent cryogenic implosions will also be presented.
Magnetothermopower in Nd1−xEuxNiO3 compounds
Authors: Barbeta V. B. , Jardim R. F. , Escote M. T. , Dilley N. R.
Published: April 2007

We have measured magnetization M(T,H), thermal conductivity κ(T,H), and thermopower S(T,H) of polycrystalline samples of Nd1−xEuxNiO3, 0⩽x⩽0.35, as a function of temperature and external magnetic field. The data indicate a metal-insulator (MI) transition in a wide range of temperature (200<TMI<325K). The magnetic susceptibility χ(T) data, after the subtraction of the rare-earth contribution, exhibit a Curie-Weiss-like behavior at temperatures above TMI. Although a clear antiferromagnetic AF transition of the Ni sublattice is observed at TN⩽TMI, χ(T) still increases down to 5K, suggesting a heterogeneous ground state. The thermal conductivity of the NdNiO3 compound is not affected by an external magnetic field of 90kOe in a wide range of temperature, and its temperature dependence below 15K is approximately quadratic, strongly suggesting the presence of disorder. S(T) is negative above TMI and varies linearly with temperature. Below TMI, there is a minimum close to 120K, and S(T) changes its sign at T∼30K, indicating a competition between two types of charge carriers. A pronounced peak in S(T) at TS∼20K is observed and the peak remains unaltered under magnetic fields up to 90kOe. However, its magnitude is enhanced by ∼25% with applied magnetic field, exhibiting a clear magnetothermopower effect. The combined results indicate a coexistence of ordered and disordered phases below TN and that an applied magnetic field is suitable for enhancing the thermoelectric properties close to TS.
Linear stability of thermocapillary flow in partially confined half-zones
Authors: Shiratori Suguru , Kuhlmann Hendrik C. , Hibiya Taketoshi
Published: April 2007

The thermocapillary flow in cylindrical half-zones is investigated numerically for low-Prandtl-number fluids. We consider a configuration in which part of the cylindrical surface is covered by a very thin rigid film and another part is uncovered, supporting thermocapillary stresses. The steady axisymmetric flow is calculated by finite differences. Besides the aspect ratio, the structure of the toroidal vortex flow depends strongly on the location and relative size of the cylindrical free-surface strip. The stability with respect to arbitrary three-dimensional perturbations of the steady two-dimensional flow is investigated by a linear stability analysis. The critical Reynolds numbers and the physical mechanisms are analyzed depending on the aspect ratio of the liquid bridge, the axial position of the uncovered part of the surface, and the free-surface fraction ξ, i.e., the ratio of the height of the free surface to the full height of the liquid zone. When only a small area of the liquid zone is covered by the solid film, i.e., ξ≈1, the well-known stationary instability for the conventional unconfined half-zone is recovered, which is driven by a combination of the elliptic and the centrifugal mechanism. Decreasing ξ, new instabilities can appear. It is found that all critical modes are likewise driven by the elliptic mechanism, the centrifugal mechanism, or a combination of both. When the unconfined free surface is located adjacent to the hot wall, the linear stability boundary shows an intricate behavior. Four qualitatively different instability modes can arise depending on the free-surface fraction ξ and the aspect ratio. One of the time-dependent modes that is strongly driven by the elliptic mechanism resembles an oscillatory Kelvin mode on a strained vortex. The other oscillatory modes show a different behavior as they are mainly driven by centrifugal mechanisms. Quite generally, the importance of the elliptic mechanism diminishes as ξ is further decreased until, for a very small free-surface fraction ξ, an instability appears that is purely centrifugal and stationary. When the free surface is located next to the cold wall, the types of instabilities are the same as for the unconfined half-zone, and the azimuthal wave numbers increase with decreasing ξ.
Planar radiative shock experiments and their comparison to simulations
Authors: Reighard A. B. , Drake R. P. , Mucino J. E. , Knauer J. P. , Busquet M.
Published: April 2007

Recent experiments have obtained radiographic data from shock waves driven at >100km∕s in xenon gas, and Thomson scattering data from similar experiments using argon gas. Presented here is a review of these experiments, followed by an outline of the discrepancies between the data and the results of one-dimensional simulations. Simulations using procedures that work well for similar but nonradiative experiments show inconsistencies between the measured position of the interface of the beryllium and xenon and the calculated position for these experiments. Sources of the discrepancy are explored.
Experiment on the mass-stripping of an interstellar cloud in a high Mach number post-shock flow
Authors: Hansen J. F. , Robey H. F. , Klein R. I. , Miles A. R.
Published: April 2007

The high Mach number flow that follows an astrophysical shock can strip mass from interstellar clouds located in the flow. Eventually, the mass-stripping may fully strip the cloud, dispersing the entire cloud mass into the flow, and incidentally ending the cloud’s star formation. Experiments have been carried out at the Omega laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)], attempting to simulate and quantify the mass-stripping as it occurs when a shock passes through interstellar clouds. Ten laser beams with 5kJ of energy drive a strong shock into a cylinder filled with low-density foam with an embedded 120μm Al sphere simulating an interstellar cloud. The density ratio between Al and foam is ∼9. Time-resolved x-ray radiographs show the cloud getting compressed by the shock (t≈5ns), undergoing a classical Kelvin-Helmholtz roll-up (12ns) followed by a Widnall instability (30ns), an inherently 3D effect that breaks the 2D symmetry of the experiment. Material is continuously being stripped from the cloud at a rate that is shown to be inconsistent with laminar models for mass-stripping (the cloud is fully stripped by 80−100ns, ten times faster than the laminar model). A new model for turbulent mass-stripping is presented that agrees with the observed rate. The model should scale to astrophysical conditions and may also be used as a benchmark for hydrodynamic computer codes.
H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod
Authors: Hubbard A. E. , Hughes J. W. , Bespamyatnov I. O. , Biewer T. , Cziegler I. , LaBombard B. , Lin Y. , McDermott R. , Rice J. E. , Rowan W. L. , Snipes J. A. , Terry J. L. , Wolfe S. M. , Wukitch S. ,   The Alcator C-Mod Group
Published: April 2007

This paper reports on studies of the edge transport barrier and transition threshold of the high confinement (H) mode of operation on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)], over a wide range of toroidal field (2.6–7.86T) and plasma current (0.4–1.7MA). The H-mode power threshold and edge temperature at the transition increase with field. Barrier widths, pressure limits, and confinement are nearly independent of field at constant current, but the operational space at high B shifts toward higher temperature and lower density and collisionality. Experiments with reversed field and current show that scrape-off-layer flows in the high-field side depend primarily on configuration. In configurations with the B×∇B drift away from the active X-point, these flows lead to more countercurrent core rotation, which apparently contributes to higher H-mode thresholds. In the unfavorable case, edge temperature thresholds are higher, and slow evolution of profiles indicates a reduction in thermal transport prior to the transition in particle confinement. Pedestal temperatures in this case are also higher than in the favorable configuration. Both high-field and reversed-field results suggest that parameters at the L-H transition are influencing the evolution and parameters of the H-mode pedestal.
New coherent state representation for the imaginary time propagator with applications to forward-backward semiclassical initial value representations of correlation functions
Authors: Pollak Eli , Martin-Fierro Eva
Published: April 2007

There have been quite a few attempts in recent years to provide an initial value coherent state representation for the imaginary time propagator exp(−βH). The most notable is the recent time evolving Gaussian approximation of Frantsuzov and Mandelshtam [J. Chem. Phys. 121, 9247 (2004)] which may be considered as an expansion of the imaginary time propagator in terms of coherent states whose momentum is zero. In this paper, a similar but different expression is developed in which exp(−βH) is represented in a series whose terms are weighted phase space averages of coherent states. Such a representation allows for the formulation of a new and simplified forward-backward semiclassical initial value representation expression for thermal correlation functions.
Negative dynamic conductivity of graphene with optical pumping
Authors: Ryzhii V. , Ryzhii M. , Otsuji T.
Published: April 2007

We study the dynamic ac conductivity of a nonequilibrium two-dimensional electron-hole system in optically pumped graphene. Considering the contribution of both interband and intraband transitions, we demonstrate that at sufficiently strong pumping the population inversion in graphene can lead to the negative net ac conductivity in the terahertz range of frequencies. This effect might be used in graphene-based coherent sources of terahertz radiation.
New criterion of glass forming ability for bulk metallic glasses
Authors: Du X. H. , Huang J. C. , Liu C. T. , Lu Z. P.
Published: April 2007

It has been confirmed that glass-forming ability (GFA) is related to not only liquid phase stability but also the crystallization resistance. In this study, it was found the liquidus temperature Tl and supercooled liquid region Tx−Tg could reflect the stability of glass-forming liquids at the equilibrium and undercooled state, respectively, while the onset crystallization temperature Tx could indicate the crystallization resistance during glass formation. Thus, a modified γ parameter, defined as γm=(2Tx-Tg)∕Tl, has been established. This parameter shows an excellent correlation with the GFA of bulk metallic glasses, with the statistical correlation factor of R2=0.931.
Observation of geometrical resonance in optical throughput of very small aperture lasers associated with surface plasmons
Authors: Ohno T. , Bain J. A. , Schlesinger T. E.
Published: April 2007

Very small aperture lasers utilizing single rectangular apertures with geometrically resonant surface plasmons are experimentally characterized. Bimetal layers of tungsten and silver were employed to realize narrow apertures in a focused ion beam etching process. The tungsten overlayer acts as a mask suppressing aperture opening induced by the tail of a gallium ion beam. We observed strong enhancements in the optical output of narrow apertures (<45 nm) fabricated by single-pass mode, which we attribute to the geometrical resonance of surface plasmons within the apertures. Wider apertures (160 nm) fabricated in raster mode did not exhibit this enhancement, consistent with the explanation of geometrical resonance.
Ferroelectric fatigue endurance of Bi4−xLaxTi3O12 thin films explained in terms of x-ray photoelectron spectroscopy
Authors: Simões A. Z. , Riccardi C. S. , Cavalcante L. S. , Longo E. , Varela J. A. , Mizaikoff B. , Hess D. W.
Published: April 2007

The nature of defects in polycrystalline Bi4−xLaxTi3O12 (BLT) thin films with x=0.00, 0.25, 0.50, and 0.75 was evaluated by x-ray photoemission spectroscopy measurements. The influence of oxygen vacancies and substitution of Bi for La atoms were discussed. In the BLT thin films, it was found that the oxygen ions at the metal-oxygen octahedral were much more stable than those at the [Bi2O2] layers. On the other hand, for Bi4Ti3O12 (BIT) thin film, oxygen vacancies could be induced both at the titanium-oxygen octahedral and at the [Bi2O2] layers. The oxygen-vacancy defect pairs determined in BIT and Bi3.75La0.25Ti3O12 (BLT025) can pin the polarization of surrounding lattices leading to fatigue of capacitors. Meanwhile, the concentration of similar defect pairs is relatively low in heavily doped BIT films and then good fatigue resistance is observed.
Second harmonic generation in the near field and far field: A sensitive tool to probe crystalline homogeneity
Authors: Mahieu-Williame Laurent , Grésillon Samuel , Cuniot-Ponsard Mireille , Boccara Claude
Published: April 2007

In order to probe crystalline orientation of SrxBa1−xNb2O6 (SBN:x) thin film, we have developed a detection scheme based on a scanning near-field optical microscope (SNOM). It is used to image simultaneously the fundamental and the second harmonic generation (SHG) of light by the sample under pulsed laser illumination. We demonstrate on SBN thin films that an apertureless SNOM can dramatically improve the resolution and the sensitivity of SNOM-SHG. Tip direction and focalization are the two crucial parameters in the SNOM-SHG experiments. Moreover, we show the ability of our setup to separate near field from far field contribution to the SHG. This is indeed very helpful in order to measure surface-SHG coefficients.
Study of the structural phase transitions in RbCuCl3 and CsCuCl3 single crystals with the electric-magnetic-type interactions using a R87b and C133s nuclear magnetic resonance spectrometer
Authors: Lim Ae Ran , Kim Sun Ha
Published: April 2007

RbCuCl 3 and CsCuCl3 single crystals were grown by the slow evaporation method, and the spin-lattice relaxation times and the resonance lines of the R87b and C133s nuclei in the resulting crystals were investigated using Fourier transform nuclear magnetic resonance (FT NMR) spectrometry. The temperature dependence of the relaxation time of the R87b nucleus in the RbCuCl3 crystals exhibited a discontinuity near TC2(=260 K), which was attributed to a structural phase transition. Although the R87b relaxation data showed no change indicative of a phase transition at TC1(=340 K), the splitting of the R87b resonance lines did change abruptly at TC1, indicating that the R87b nuclei depends on the local environments surrounding these nuclei. For the CsCuCl3 crystals, the relaxation time of the C133s nucleus underwent large, abrupt changes at TN (=10.5 K) and near TC (=423 K), which coincide with a magnetic and a structural phase transition, respectively. The RbCuCl3 and CsCuCl3 results are compared with those obtained previously for other ABCl3 (A=Rb, Cs, B=Cd, Mn) perovskite crystals.
Laser prepulse dependency of proton-energy distributions in ultraintense laser-foil interactions with an online time-of-flight technique
Authors: Yogo Akifumi , Daido Hiroyuki , Fukumi Atsushi , Li Zhong , Ogura Koichi , Sagisaka Akito , Pirozhkov Alexander S. , Nakamura Shu , Iwashita Yoshihisa , Shirai Toshiyuki , Noda Akira , Oishi Yuji , Nayuki Takuya , Fujii Takashi , Nemoto Koshichi , Woo Choi Il , Hee Sung Jae , Ko Do-Kyeong , Lee Jongmin , Kaneda Minoru , Itoh Akio
Published: April 2007

Fast protons are observed by a newly developed online time-of-flight spectrometer, which provides shot-to-shot proton-energy distributions immediately after the irradiation of a laser pulse having an intensity of ∼1018W∕cm2 onto a 5-μm-thick copper foil. The maximum proton energy is found to increase when the intensity of a fs prepulse arriving 9ns before the main pulse increases from 1014 to 1015W∕cm2. Interferometric measurement indicates that the preformed-plasma expansion at the front surface is smaller than 15μm, which corresponds to the spatial resolution of the diagnostics. This sharp gradient of the plasma has the beneficial effect of increasing the absorption efficiency of the main-pulse energy, resulting in the increase in the proton energy. This is supported by the result that the x-ray intensity from the laser plasma clearly increases with the prepulse intensity.
The role of ammonia in atomic layer deposition of tungsten nitride
Authors: Mukhopadhyay Atashi B. , Musgrave Charles B.
Published: April 2007

The authors use density functional theory to investigate the atomic layer deposition of WN using bis-(tert-butylimido)-bis(dimethylamido)tungsten and ammonia. They find that ligand exchange involving two proton transfers from ammonia to the imido nitrogen eliminating tert-butylamine is the lowest barrier pathway. Elimination of isobutene by β-hydrogen transfer from the tert-butyl group involves high barriers. NH3 catalytically lowers the β-hydrogen transfer barrier; however, the catalyzed barrier is still substantially above the barrier for the ligand exchange reaction. Thus, incorporation of nitrogen from ammonia is favored over mechanisms that incorporate nitrogen from the precursor, and ammonia acts as a reactant in this system rather than a catalyst.
Scattering rule in soliton cellular automaton associated with crystal base of Uq(D4(3))
Authors: Yamada Daisuke
Published: April 2007

In terms of the crystal base of a quantum affine algebra Uq(g), we study a soliton cellular automaton (SCA) associated with the exceptional affine Lie algebra g=D4(3). The solitons therein are labeled by the crystals of quantum affine algebra Uq(A1(1)). The scatteing rule is identified with the combinatorial R matrix for Uq(A1(1)) crystals. Remarkably, the phase shifts in our SCA are given by three times of those in the well-known box-ball system.
Nitrous oxide dimer: Observation of a new polar isomer
Authors: Dehghani M. , Afshari Mahin , Abusara Z. , Moazzen-Ahmadi N. , McKellar A. R. W.
Published: April 2007

Spectra of the nitrous oxide dimer (N2O)2 are studied in the region of the N2O ν1 fundamental band around 2230cm−1 using a rapid-scan tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. The previously known band of the centrosymmetric nonpolar dimer is analyzed in improved detail, and a new band is observed and assigned to a polar isomer of (N2O)2. This polar form of the dimer has a slipped parallel structure, rather similar to the slipped antiparallel structure of the nonpolar form but with a slightly larger intermolecular distance. The accurate rotational parameters determined here should enable a microwave observation of the polar N2O dimer. The need for a modern ab initio investigation of the N2O–N2O intermolecular potential energy surface is emphasized.
Nonlinear mode mixing in dual-wavelength semiconductor lasers with tunnel junctions
Authors: Nekorkin S. M. , Biryukov A. A. , Demina P. B. , Semenov N. N. , Zvonkov B. N. , Aleshkin V. Ya. , Dubinov A. A. , Gavrilenko V. I. , Maremyanin K. V. , Morozov S. V. , Belyanin A. A. , Kocharovsky V. V. , Kocharovsky Vl. V.
Published: April 2007

The authors demonstrate and study two- and three-wavelength generations in the semiconductor diode laser with a tunnel junction separating two different quantum-well active regions integrated within a single waveguide. To avoid resonant cross absorption of the modes at different frequencies and achieve phase matching, the laser waveguide is designed to generate the first-order transverse mode at a longer wavelength and the third-order mode at a shorter wavelength. Excellent agreement with the designed and measured device parameters is observed. Intracavity nonlinear mixing leading to sum-frequency and second-harmonic generation is demonstrated.
Precise frequency estimation in a microelectromechanical parametric resonator
Authors: Requa Michael V. , Turner Kimberly L.
Published: April 2007

The authors report here on precise resonant frequency estimation using the nonlinear spectral features of parametric resonance. Demonstration of 100 parts per 109 frequency resolution at room temperature is accompanied by a technique to observe the phase trajectories of escape in bistable parametrically resonant systems. The system offers an expanded dynamic range over similar linear resonators. Precise frequency estimation has implications in resonant mass sensing.
Back side thermal imaging of integrated circuits at high spatial resolution
Authors: Tessier G. , Bardoux M. , Boué C. , Filloy C. , Fournier D.
Published: April 2007

In integrated circuits, most of the heating is produced in the active layers below the surface, making thermal measurements extremely difficult. The authors demonstrate that near infrared thermoreflectance can provide thermal imaging inside the circuit, through its silicon substrate. The use of an InGaAs camera with a noncoherent illumination in the 1.1–1.7μm band allows fast thermal imaging with a diffraction-limited resolution of 1.7μm. A silicon solid immersion lens was then used to further improve the resolution to 440nm, corresponding to an effective numerical aperture of 2.36.
Submicron mapping of strained silicon-on-insulator features induced
Authors: Murray Conal E. , Sankarapandian M. , Polvino S. M. , Noyan I. C. , Lai B. , Cai Z.
Published: April 2007

Real-space maps of strain within silicon-on-insulator (SOI) features induced by adjacent, embedded shallow-trench-isolation (STI) SiO2 regions were obtained using x-ray microbeam diffraction. The quantitative strain mapping indicated that the SOI strain was largest at the SOI/STI interface and decreased as a function of distance from this interface. An out-of-plane residual strain of approximately −31με was observed in the blanket regions of the SOI. A comparison of the depth-averaged strain distributions to the strain profiles calculated from an Eshelby inclusion model indicated an equivalent eigenstrain of −0.55% in the STI regions acting on the SOI features.
Scanning probe microscopy study of microcells from the organ surface Bonghan corpuscle
Authors: Kwon Joonhyung , Baik Ku Youn , Lee Byung-Cheon , Soh Kwang-Sup , Lee Nam Joo , Kang Chi Jung
Published: April 2007

Microcells from organ surface Bonghan corpuscles [B. H. Kim, J. Acad. Med. Sci. DPR Kor. 90, 1 (1963)] of mammals have been studied by using optical microscopy, transmission electron microscopy and immunohistochemistry. In order to further investigate their physical and electrical properties at better resolution, many different modes of scanning probe microscopy were used in this research. Their surface morphology was studied by topography imaging and error-signal imaging of atomic force microscopy and their mechanical properties were investigated by force modulation microscopy. Electrostatic force microscopy was also used for their electrical characterization.
Continuum percolation of nanocomposites with fillers of arbitrary shapes
Authors: Li Chunyu , Chou Tsu-Wei
Published: April 2007

A versatile simulation method for modeling percolation in nanocomposites containing multiple fillers of arbitrary shapes is proposed. The regular or irregular filler shape is approximated by a polygon. The contact status between two fillers is identified by a sequential side-by-side procedure. An effective fitting approach for obtaining the relationship between percolation probability and filler volume fraction has also been developed. The results indicate that wavy nanotubes with a larger curl ratio have a higher percolation threshold, but the effect of curl ratio tends to decrease with the increase of nanotube aspect ratio.
Gradual degradation of red-emitting high-power diode laser bars
Authors: Ziegler Mathias , Tien Tran Quoc , Schwirzke-Schaaf Sandy , Tomm Jens W. , Sumpf Bernd , Erbert Götz , Oudart Myriam , Nagle Julien
Published: April 2007

The authors analyze early stages of gradual degradation in highly reliable 650nm emitting high-power diode laser arrays with continuous wave emission powers of 2.5W (facet load of 4mW∕μm). In all cases the edges of the metallized emitter stripes are identified as the starting points of gradual degradation. The magnitude of the observed degradation signatures, however, is highly correlated with the bar-specific packaging-induced strain at each emitter. We find a bar-specific effect, namely, the presence of packaging-induced strain, to be the driving force of gradual degradation. Our findings point to the significance of proper strain management in advanced device structures.
Enhanced L1 chemical ordering and FePt∕Fe3O4 core/shell structure formation in Zn-doped FePt nanoparticles
Authors: Kim Ki-Eun , Lee Myung-Ki , Sung Yun-Mo , Kim Tae Geun
Published: April 2007

FePt nanoparticles doped with ∼12at.% Zn were successfully synthesized using the polyol and thermolysis methods. Their chemical ordering to the face-centered tetragonal (L10) phase was found to occur at a remarkably reduced temperature of ∼324°C. The nanoparticles annealed at 400°C for 60min were identified to be in a highly crystalline L10 phase, showing formation of the distinct FePt∕Fe3O4 core/shell structure. Also, they demonstrated strong ferromagnetic characteristics due to the high crystallinity with the L10 phase and the exchange coupling between the FePt core and the Fe3O4 shell.
Effect of spin-polarized electric current on spin-wave radiation by spin-valve nanocontacts
Authors: Demidov Vladislav E. , Demokritov Sergej O. , Reiss Günter , Rott Karsten
Published: April 2007

Using a spatially resolved microfocus Brillouin light scattering technique with spatial resolution of 250nm, the authors have studied radiation of spin waves by a spin-valve nanocontact into a continuous underlying magnetic film. They have found that a spin-polarized electric current flowing through the contact affects the intensity of radiated spin waves. They show that for one of the directions of the current, the spin-wave intensity is noticeably increased, whereas for the other direction, spin waves are suppressed. They associate the findings with an amplification of spin waves due to spin-torque-transfer phenomena.
Room temperature gas sensing of p-type TeO2 nanowires
Authors: Liu Zhifu , Yamazaki Toshinai , Shen Yanbai , Kikuta Toshio , Nakatani Noriyuki , Kawabata Tokimasa
Published: April 2007

Tellurium dioxide (TeO2) nanowires with a tetragonal structure have been grown by thermally evaporating tellurium metal at 400°C in air. The nanowires produced have diameters ranging from 30to200nm and have lengths of several tens of micrometers. Gas sensors were fabricated using the obtained TeO2 nanowires. The sensing behavior to NO2, NH3, and H2S gases at room temperature showed typical characteristics of a p-type semiconductor. The results demonstrate the potential to develop TeO2 nanowire based gas sensors with low power consumption.
Low voltage complementary thin-film transistor inverters with pentacene-ZnO hybrid channels on AlOx dielectric
Authors: Oh Min Suk , Hwang D. K. , Lee Kimoon , Im Seongil , Yi S.
Published: April 2007

The authors report on the fabrication of complementary thin-film transistor (CTFT) inverters with pentacene (p type) and ZnO (n type) hybrid channels on rf-deposited AlOx dielectrics. All deposition processes were carried out on glass substrates at low temperatures (<100°C). Since our p-channel TFT showed somewhat equivalent field mobility of 0.11cm2∕Vs compared to that of the n-channel device (0.75cm2∕Vs), the hybrid CTFT inverters were designed with identical dimensions for both channels. The CTFT device demonstrated an excellent voltage gain of ∼21 with a low static power dissipation of ∼1.5nW at a low supply voltage of 7V.
Detection of foreign body using fast thermoacoustic tomography with a multielement linear transducer array
Authors: Nie Liming , Xing Da , Yang Diwu , Zeng Lvming , Zhou Quan
Published: April 2007

Current imaging modalities face challenges in clinical applications due to limitations in resolution or contrast. Microwave-induced thermoacoustic imaging may provide a complementary modality for medical imaging, particularly for detecting foreign objects due to their different absorption of electromagnetic radiation at specific frequencies. A thermoacoustic tomography system with a multielement linear transducer array was developed and used to detect foreign objects in tissue. Radiography and thermoacoustic images of objects with different electromagnetic properties, including glass, sand, and iron, were compared. The authors’ results demonstrate that thermoacoustic imaging has the potential to become a fast method for surgical localization of occult foreign objects.