bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of two off‐line soil analysis schemes for assimilation of screen level observations
Authors: Mahfouf J.‐F. , Bergaoui K. , Draper C. , Bouyssel F. , Taillefer F. , Taseva L.
Published: April 2009

Two analysis schemes are developed within an off‐line version of the land surface scheme ISBA for the initialization of soil water content and temperature in numerical weather prediction models. The first soil analysis is based on optimal interpolation that is currently operational in a number of weather centers. The second soil analysis is an extended Kalman filter (EKF) which will allow the assimilation of satellite observations. First, it is shown, by comparing the Kalman gain of both analysis schemes, that it is possible to assimilate screen level temperature and relative humidity in an off‐line system. This is of great interest for future combined assimilations of conventional and satellite data. The reduced computing time in running the land surface scheme outside the atmospheric model makes Kalman filter approaches compatible with operational requirements. The methodology for coupling the land surface data assimilation with the atmospheric analysis system is explained in order to highlight the existing feedbacks between the two systems (in comparison to fully decoupled land data assimilation systems). The linearity of the observation operator Jacobians estimated by finite differences and the relevance of the soil prognostic variables to be initialized are assessed. Finally, the two systems are compared over western Europe for the month of July 2006 by assimilating screen level temperature and relative humidity every 6 h. The EKF has been simplified by keeping the covariance matrix of background errors constant. The two soil analysis schemes behave similarly in response to screen level atmospheric errors. The EKF is superior in identifying situations where the near‐surface atmosphere is sensitive to soil perturbations, which leads to better use of observations. Over France, the capability of both systems to moisten the soil when rain events are absent from the forcing is demonstrated.
An analysis of simulated wet deposition of mercury from the North American Mercury Model Intercomparison Study
Authors: Bullock O. Russell , Atkinson Dwight , Braverman Thomas , Civerolo Kevin , Dastoor Ashu , Davignon Didier , Ku Jia‐Yeong , Lohman Kristen , Myers Thomas C. , Park Rokjin J. , Seigneur Christian , Selin Noelle E. , Sistla Gopal , Vijayaraghavan Krish
Published: April 2009

A previous intercomparison of atmospheric mercury models in North America has been extended to compare simulated and observed wet deposition of mercury. Three regional‐scale atmospheric mercury models were tested: the Community Multiscale Air Quality (CMAQ) model, the Regional Modeling System for Aerosols and Deposition (REMSAD), and the Trace Element Analysis Model (TEAM). These models were each employed using three sets of lateral boundary conditions to test their sensitivity to intercontinental transport of mercury. The same meteorological and pollutant emission data were used in each simulation. Observations of wet deposition were obtained from the National Atmospheric Deposition Program's Mercury Deposition Network. The regional models can explain 50–70% of the site‐to‐site variance in annual mercury wet deposition. CMAQ was found to have slightly superior agreement with observations of annual mercury deposition flux in terms of the mean value for all monitoring sites, but REMSAD showed the best correlation when measured by the coefficient of determination (r2). With the exception of one CMAQ simulation, all of the models tended to simulate more wet deposition of mercury than was observed. TEAM exceeded the observed average annual wet deposition by 50% or more in all three of its simulations. CMAQ and REMSAD were better able to reproduce the observed seasonal distribution of mercury wet deposition than was TEAM, but TEAM showed the highest correlation for weekly wet deposition samples. An analysis of model accuracy at each observation site showed no obvious geographic patterns for correlation, bias, or error. Adjusting simulated mercury deposition on the basis of the difference between observed and simulated precipitation data improved the correlation and error scores for all of the models.
Reverse propagation of T waves from the Emperor seamount chain
Authors: Obara Kazushige , Maeda Takuto
Published: April 2009

Analysis of seismo‐acoustic T waves associated with an intermediate‐depth earthquake beneath northern Japan reveals that the detected T waves are secondary waves scattered by distant seamounts. The timing of T‐wave onset, 3000 s after occurrence of the earthquake, indicates that the detected T waves did not follow a direct path from the solid‐liquid conversion point near the Japan Trench to the observation stations in northeast Japan. It is hypothesized that the original T waves were reverse‐scattered back toward Japan by peaks of the Emperor seamount chain after propagation in the northern Pacific Ocean. The synthesized envelope patterns for acoustics scattered at the seamounts considering this multi‐path effect reproduce the travel time and amplitude pattern of the observed T waves well, with each seamount group producing a discrete amplitude peak of the scattered wave. These observations suggest that topographical obstructions act as a secondary source for T‐wave propagation in the ocean.
How rare are the 2006–2008 positive Indian Ocean Dipole events? An IPCC AR4 climate model perspective
Authors: Cai W. , Sullivan A. , Cowan T.
Published: April 2009

The occurrence of three consecutive positive Indian Ocean Dipole (pIOD) events through 2006–2008, along with the unusual pIOD‐La Niña combination in 2007, calls for a statistical assessment into the rarity of such events. To this end, we take 50 years from 19 climate models submitted for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (AR4) to provide a 950‐year realization. Only six models produce a total of nine pIOD‐La Niña pairs, with one occurrence of three consecutive pIOD events. The rarity is not due to an overly strong model El Niño‐pIOD coherence. Two models produce the 2006–2007 sequence of one pIOD with an El Niño followed by a pIOD in a La Niña year, however, no models simulate the observed mechanism. Although the triggering processes vary between models, a commonality is that the trigger resides in the ocean, highlighting the importance of subsurface ocean observations in predicting pIODs.
Microstructural investigation supporting an abrupt stress induced transformation in amorphous carbon films
Authors: Lau D. W. M. , Partridge J. G. , Taylor M. B. , McCulloch D. G. , Wasyluk J. , Perova T. S. , McKenzie D. R.
Published: April 2009

The intrinsic stress of carbon thin films deposited by filtered cathodic arc was investigated as a function of ion energy and Ar background gas pressure. The microstructure of the films was analyzed using transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy. The stress at given substrate bias was reduced by the presence of an Ar background gas and by the presence of a Cu underlayer deposited onto the substrate prior to deposition. Auger electron spectroscopy depth profiles showed no evidence of Ar incorporation into the films. A sharp transition from a sp2 to sp3 rich phase was found to occur at a stress of 6.5±1.5 GPa, independent of the deposition conditions. The structural transition at this value of stress is consistent with available data taken from the literature and also with the expected value of biaxial stress at the phase boundary between graphite and diamond at room temperature. The microstructure of films with stress in the transition region near 6.5 GPa was consistent with a mixture of sp2 and sp3 rich structures.
Experimentally identifying masked sources applying time reversal with the selective source reduction method
Authors: Anderson B. E. , Ulrich T. J. , Griffa M. , Le Bas P.-Y. , Scalerandi M. , Gliozzi A. S. , Johnson P. A.
Published: April 2009

This paper describes a time reversal (TR) method of spatially illuminating a source signal which has been masked by another source signal. This masking occurs as a result of inherent limitations in the traditional TR process. The selective source reduction (SSR) method employs a subtraction technique where one TR focus is selectively reduced to illuminate the masked focus. Experimental results and considerations are presented to demonstrate the SSR method for two elastic wave pulses emitted simultaneously from two spatially separated surficial sources and to examine the limitations of the method. A blind test was conducted to demonstrate that no a priori information about the source(s) is required. Spatial and/or temporal characteristics of multiple close-proximity sources can be resolved with the use of the illumination method. The measurements show that the SSR method’s limitations are chiefly due to imperfect temporal reconstruction of the source function in the time reversed focal signal, which consequently limits signal reduction.
Robust control of Josephson charge qubits
Authors: Wenin M. , Roloff R. , Pötz W.
Published: April 2009

Typical for qubit realizations are two performance-limiting shortcomings: the physical system is not a perfect two-level system and it couples to an environment. In this work we investigate the limits of performance of the Josephson charge qubit due to the interplay of leakage into unwanted states and dissipative effects due to environmental noise within optimal control theory. For the example of the Hadamard transformation, we show that external control field-gate bias and magnetic flux, which perform the operation for the ideal qubit perfectly, show different robustness regarding leakage into unwanted states and against dissipation. Proper selection of the temporal evolution of gate bias and magnetic flux leads to performance improvements of typically 20% regarding dissipative effects with a predicted optimal fidelity of typically 98%, presuming perfect initial-state preparation and switching times of the order of 500 ps.
Square microwave-assisted magnetic recording at lower frequencies
Authors: Goh Chi-Keong , Yuan Zhi-min , Liu Bo
Published: April 2009

Microwave-assisted magnetic recording uses the transverse oscillating field at the level of Larmor frequency to record at substantially reduced write fields. However the ferromagnetic resonance frequency is proportional to media anisotropy and there is a limitation to generate such high frequency sinusoidal microwave fields. On the other hand, square microwave fields facilitate further reduction in write fields at much lower frequencies. As compared to sinusoidal microwave fields, the operating frequency regime of square microwave fields is broader in the presence of anisotropy distribution and less susceptible to variations in media parameters. These characteristics allow for the development of practical high anisotropic magnetic recording systems.
Effect of temperature and elastic constant on the piezoresistivity of silicon nanobeams
Authors: Zhang Jia-Hong , Huang Qing-An , Yu Hong , Wang Jing , Lei Shuang-Ying
Published: April 2009

A strain k⋅p model is used to investigate lattice temperature dependence of the piezoresistivity of p-doped silicon nanobeams in the range of 100–600 K, based on the self-consistent solution to the coupled Schrödinger–Poisson equations. According to quasiharmonic approximation, an analytical semicontinuum atomistic lattice model is presented to describe the effect of size and temperature on elastic constants of the silicon nanobeam by using the anharmonic Keating model. The result presented here indicates the piezoresistive coefficient of the silicon nanobeam, which is dependent on quantum confinement effects, has a negative and nonlinear temperature coefficient. A quantitative comparison of the piezoresistive coefficients calculated with and without considering the elastic constant correction shows that it is crucial to incorporate the size-dependent elastic constant correction in order to quantify the piezoresistivity.
Dielectric function analysis of superstoichiometric samarium dihydride films
Authors: Sakai M. , Nanbo T. , Tanji Y. , Nakamura O. , Endo M. , Tajima H.
Published: April 2009

We have carried out an experimental study to reveal the dielectric function of SmHx(x=2.28,2.42,2.56,2.57) films based on room-temperature reflectivity for photon energies ranging from 0.05 to 6.5 eV. The derivation of the dielectric functions has been carried out using model dielectric functions as well as Kramers–Kronig analysis. It is inferred from our analysis that when the H/Sm value is increased from 2.28 to 2.57, (i) the interband transition band located in the ultraviolet region shows a redshift of about 1 eV, (ii) the relatively weak transition band located in the near-infrared region shows a reduction in intensity, and (iii) the unperturbed plasma frequency of free carriers decreases slightly. The behaviors (i), (ii), and (iii) caused by the H/Sm value change are thoroughly approximately the same as those observed for YHx, suggesting that these trends are characteristic of H–M systems showing a metal-insulator transition. It was also confirmed from our structural analysis that these changes in the dielectric function are achieved without a change in the lattice constant. The origin of this constancy in the lattice constant in our samples with different H/Sm values is discussed by assessing the T- and O-site hydrogen concentrations. The hydrogen incorporation effect is also observed in the magnitude of the unperturbed plasma frequency, about 1.7 eV, which is unexpectedly small compared to conventional metals. This characteristic can possibly be attributed to mass enhancement of mobile carriers; we obtained an effective mass of about 10m0 (where m0 is the free electron mass) when the carrier density estimated from the Hall coefficient value is used.
Upper bound to the thermal conductivity of carbon nanotube pellets
Authors: Chalopin Yann , Volz Sebastian , Mingo Natalio
Published: April 2009

Using atomistic Green’s function calculations, we find that the phonon thermal conductivity of pellets composed of ∼μm long carbon nanotubes has an upper bound of a few W/m K. This is in striking contrast with the extremely high thermal conductivity of individual nanotubes (∼3000 W/m K). We show that, at room temperature, this upper bound does not depend on the nanotube diameter. Conversely, for low temperatures, an inverse proportionality with nanotube diameter is predicted. We present concrete results as a function of nanotube length and chirality, pellet density, and temperature. These results imply that carbon nanotube pellets belong to the category of thermal insulators, contrasting with the good conducting properties of parallel nanotube arrays, or individual nanotubes.
Comparative study of the role of the nucleation stage on the final crystalline quality of (111) and (100) silicon carbide films deposited on silicon substrates.
Authors: Portail M. , Zielinski M. , Chassagne T. , Roy S. , Nemoz M.
Published: April 2009

We study the impact of the nucleation step on the final crystalline quality of 3C-SiC heteroepitaxial films grown on (111) and (100) oriented silicon substrates by low pressure chemical vapor deposition. The evolution of both the structural and morphological properties of 3C-SiC epilayers in dependence on the only nucleation parameters (propane flow rate and duration of the process) are investigated by means of x-ray diffraction, scanning electron, atomic force, and optical microscopies. At first, we show how the formation of interfacial voids is controlled by the experimental parameters, as previously reported, and we correlate the density of voids with the substrate sealing by using an analytical model developed by V. Cimalla et al. [Mater. Sci. Eng., B 46, 190 (1997)]. We show that the nucleation stage produces a more dense buffer layer in case of (111) substrates. Further, we investigate the impact of the nucleation parameters on the crystalline quality of 3C-SiC epilayers. Within our experimental setup, the crystalline quality of (100) oriented 3C-SiC films is more rapidly evolving than (111) films for low propane contents (0.025%–0.05% in hydrogen), whereas a common degradation of the crystalline quality is reported for both cases for the higher propane contents. In parallel, we investigate the morphological features of the epilayers. The (111) oriented epilayers are well coalesced irrespectively of the nucleation condition, contrarily to the (100) films. Finally, for both orientations we report on the dependence of the formation of double positioning domains (twins) on the nucleation conditions. Such defects can be suppressed within (111) films but not within (100) films. We highlight the role of the substrate sealing and discuss in what extent it can be responsible of the observations by reducing the contribution of the silicon outdiffusing and by allowing a more pronounced two-dimensional growth mode for (111) oriented 3C-SiC films.
Terrestrial gamma-ray flashes caused by neutron bursts above thunderclouds
Authors: Paiva G. S.
Published: April 2009

In this work, it is suggested that upward pulses of fast neutrons, which are produced by energetic intracloud lightning, will form terrestrial gamma-ray flashes (TGFs) through neutron inelastic scattering by atoms in the atmosphere. About 1015 fast neutrons produce gamma-ray photons that compose the TGF pulse in altitude of about 20 km, in good agreement with the altitude of TGF source estimated by Dwyer and Smith [Geophys. Res. Lett. 32, L22804 (2005)].
Onset of turbulence in a regular porous medium: An experimental study
Authors: Horton N. A. , Pokrajac D.
Published: April 2009

This paper presents the results from an experimental study on turbulent flows through a regular porous matrix of spheres packed in a cubic arrangement. The special pore geometry made it possible to measure the velocity within individual pores, using the ultrasonic velocity profiler (UVP). The UVP recorded the time series of the average cross-sectional velocity at a series of points along the pore. The measurements were performed for various hydraulic gradients resulting in a pore Reynolds number between 70 and 430. Three different regimes were detected: unsteady laminar, transition to turbulence, and turbulent. An additional measurement was performed using particle image velocimetry (PIV), which recorded two velocity components within a window which covered only the widest pore section. The PIV test had a Reynolds number of 370, which corresponds to transitional flow just before the onset of turbulence. The PIV result revealed the spatial distribution of mean velocities and turbulence intensities, as well as the shapes of coherent flow structures during significant turbulent events.
Optical and vibrational properties of 2H-, 4H-, and 6H-AlN: First-principle calculations
Authors: Cheng Y. C. , Chen H. T. , Li X. X. , Wu X. L. , Zhu J. , Li S. H. , Chu Paul K.
Published: April 2009

The optical and vibrational properties of 2H-, 4H-, and 6H-AlN are studied based on the ab initio pseudopotential density functional theory. Three polymorphs have similar electronic and optical properties implying that 4H- and 6H-AlN are also of importance to optoelectronics. Infrared spectra of the three polymorphs show two main modes at 660 and 690 cm−1 and an additional mode at 570 cm−1 can only be observed from 4H- and 6H-AlN. The Raman spectra of 4H- and 6H-AlN show more active modes than that of 2H-AlN. These infrared and Raman features can be used as the fingerprints to distinguish the three polymorphs.
A comparative study of the dendritic avalanche in MgB2 thin films synthesized by pulsed laser deposition and hybrid physical chemical vapor deposition methods
Authors: Lee Jae-Yeap , Lee Hu-Jong , Lee Sung-Ik , Zhuang C. G. , Wang Y. Z. , Feng Q. R. , Gan Z. Z. , Xi X. X. , Choi Eun-Mi , Cho Jae-Hun , Jo Young-Hun
Published: April 2009

It is known that MgB2 thin films synthesized by using hybrid physical chemical vapor deposition (HPCVD) do not show dendritic avalanche, which is in contrast to those prepared by using pulsed laser deposition (PLD). To find the cause that makes the difference between the two cases, we studied the microscopic film structure by the scanning electron microscopy and the magnetic hysteresis by using the superconducting quantum interference device magnetometry. The critical current density (Jc), estimated from the magnetic hysteresis based on the Bean’s critical-state model, shows a much higher Jc in the PLD film than in a HPCVD film. This indicates higher vortex pinning in the PLD film. We surmise that high local joule heating beyond the high Jc in the PLD film, as a vortex penetrates into the superconducting thin film, gives a path for the next vortex and induces a positive feedback effect that is absent in the HPCVD film.
Lie equations for asymptotic solutions of perturbation problems of ordinary differential equations
Authors: Chiba Hayato , Iwasa Masatomo
Published: April 2009

Lie theory is applied to perturbation problems of ordinary differential equations to construct approximate solutions and invariant manifolds according to the renormalization group approach of Iwasa and Nozaki [“A method to construct asymptotic solutions invariant under the renormalization group,” Prog. Theor. Phys. 116, 605 (2006)]. It is proved that asymptotic behavior of solutions is obtained from the Lie equations even if original equations have no symmetries. Normal forms of the Lie equations are introduced to investigate the existence of invariant manifolds.
Beneficial influence of Ru on the thermoelectric properties of Mo3Sb7
Authors: Candolfi Christophe , Lenoir Bertrand , Leszczynski Juliusz , Dauscher Anne , Guilmeau Emmanuel
Published: April 2009

Zintl phases have recently been identified as potential thermoelectric materials typified by the discovery of a high thermoelectric figure of merit in the Yb14MnSb11 compound above 1000 K. We report on the synthesis and the thermoelectric properties measurements over a wide temperature range (300–1000 K) of other Zintl phases exhibiting a complex crystalline structure, namely, Mo3Sb7 and its related compounds Mo3−xRuxSb7. While the binary compound displays low figure of merit values due to its metallic nature, we show that the partial substitution of Mo by Ru significantly improves its value to reach 0.45 at 1000 K in Mo2.2Ru0.8Sb7.
Low-voltage operation and excellent data retention characteristics of metal-ferroelectric-insulator-Si devices based on organic ferroelectric films
Authors: Lu Xubing , Yoon Joo-Won , Ishiwara Hiroshi
Published: April 2009

Metal-ferroelectric-insulator-Si (MFIS) diodes using poly(methyl methacrylate) (PMMA)-blended poly(vinylidene fluoride)-trifluoroethylene [P(VDF-TrFE)] as a gate ferroelectric film were fabricated and their electrical characteristics were investigated. A wide memory window of 1.2 V was observed in a Au/3 wt % PMMA-blended P(VDF-TrFE) (46 nm)/HfTaO(6 nm)/Si MFIS diode for the voltage sweep between −3 and +3 V. Excellent data retention characteristics were also observed in these MFIS diodes. After a small programing voltage of 3 V is applied, the high and low capacitances remained very stable for the retention period over 4 h.
The role of oxygen pressure and thickness on structure and pyroelectric properties of Ba(Ti0.85Sn0.15)O3 thin films grown by pulsed laser deposition
Authors: Wang S. J. , Lu L. , Lai M. O. , Fuh J. Y. H.
Published: April 2009

The roles of oxygen pressure and thickness on the microstructure, electrical, and pyroelectric properties of Ba(Ti0.85Sn0.15)O3 (BTS) thin films have been studied. The highly (h00)-oriented BTS thin films were deposited on the SiO2/Si substrates with a LaNiO3 layer as the bottom electrode by pulsed laser deposition. It was found that the texture and the microstructures of the as-deposited thin films are strongly dependent on the oxygen pressure, and that the BTS thin films deposited at higher oxygen pressures possess better electrical properties. The study on the thickness dependence of the dielectric and pyroelectric properties showed that the tensile stresses on the LNO and BTS thin films decreased as the thickness of the BTS film was increased. With the high textured thin film, a larger dielectric constant and pyroelectric coefficient were therefore achieved.
A comprehensive study of magnetoresistance mobility in short channel transistors: Application to strained and unstrained silicon-on-insulator field-effect transistors
Authors: Cassé M. , Rochette F. , Thevenod L. , Bhouri N. , Andrieu F. , Reimbold G. , Boulanger F. , Mouis M. , Ghibaudo G. , Maude D. K.
Published: April 2009

Magnetoresistance (MR) measurements is used to extract the electron mobility on strained and unstrained thin film fully depleted silicon-on-insulator metal-oxide-semiconductor field-effect transitors (MOSFETs) with channel length down to 40nm, and in a wide temperature range from 300 down to 20K. In particular the signature of Coulomb scattering (CS) on MR mobility is carefully studied and experimentally clarified. We demonstrate that MR mobility corrected for nonstationary effects can be extracted. The mobility data thus corrected for series resistance and ballistic effects show that an additional scattering really occurs in deep-100-nm scaled MOSFETs. This mobility degradation is effective for both strained and unstrained short channel devices, over the whole gate voltage range. The temperature and inversion carrier density dependences, as well as the analysis of the strain effect on mobility reveal a strong additional CS in short channel devices. Despite this dominant mechanism, a mobility gain as high as 50% at room temperature is still observable for strained deeply scaled MOSFETs.
An electron-preceding perspective on the deformation of materials
Authors: Ayers Paul W. , Jenkins Samantha
Published: April 2009

Elements of Bader’s theory of atoms in molecules are combined with density-functional theory to provide an electron-preceding perspective on the deformation of materials. From this perspective, a network of atoms is changed by moving the bonds that connect them; the nuclei then follow. The electronic stress tensor is the key to understanding this process. Eigenvectors of the electronic stress tensor at critical points of the electron density provide insight into the “normal electronic modes” that accompany structural dynamics and rearrangements. Eigenvectors of the second-derivative matrix of the electron density emerge as effective approximations to the eigenvectors of the stress tensor; this makes it possible to apply our results to experimentally and computationally determined electron densities. To demonstrate the usefulness of our analysis, we show that (a) the low-frequency modes of ice Ic can be predicted from the eigenvectors of the second-derivative matrix and (b) the eigenvectors of the second-derivative matrix are associated with the direction of structural change during the pressure-induced phase transition from ice XI to a ferroelectric ice VIII-like structure. We conclude that the eigenvectors of the second-derivative matrix of the electron density are the key ingredient for constructing a dynamical theory of atoms in molecules.
Laser ablation of metallic targets with high fluences: Self-consistent approach
Authors: Kundrapu Madhusudhan , Keidar Michael
Published: April 2009

Ablation of metallic target using Gaussian profile laser pulse with duration of 30 ns and fluence extending up to 100 J/cm2 is studied. A self-consistent model that involves numerical simulation to obtain the thickness of a hydrodynamic layer is proposed. The influence of the hydrodynamic layer thickness on Knudsen layer properties, and hence the rate of evaporation, is demonstrated. Self-consistent model is compared with model based on assumption about sonic speed at the Knudsen layer outer edge and validated with experimental results for Al alloy and Cu. Finally, sample calculations are performed using the proposed model to obtain depth of evaporation of Al alloy for single pulse duration.
The influence of intergranular interaction on the magnetization of the ensemble of oriented Stoner–Wohlfarth nanoparticles
Authors: Timopheev A. A. , Ryabchenko S. M. , Kalita V. M. , Lozenko A. F. , Trotsenko P. A. , Stephanovich V. A. , Grishin A. M. , Munakata M.
Published: April 2009

The influence of interparticle interaction on the processes of magnetization reversal is considered for an ensemble of oriented Stoner–Wohlfarth nanoparticles. This is done through a solution of a kinetic equation describing the relaxation of the total magnetization to its equilibrium value in an effective mean field which includes a term proportional to the instantaneous value of the magnetization. It is shown that the interparticle interaction influences the temperature dependence of a coercive field. Under certain conditions, the presence of the interparticle interaction can lead to the formation of the so-called superferromagnetic state with the correlated directions of the magnetic moments of the particles. If the system is unable to come to the equilibrium during the time interval necessary to perform measurements, some measured quantities become dependent on the measurement time. It is shown that the blocking temperature Tb and the temperature dependence of coercive field at TTb, however, the coercivity, if exists, does not depend on the measurement time. The data of magnetostatic measurements, carried out on the (CoFeB)x–(SiO2)1−x nanogranular films with the concentration of ferromagnetic particles slightly lower than a percolation threshold, are in compliance with the results of the calculations.
Tuning the magnetic entropy change of Ni50−xMn35+xIn15 alloys by varying the Mn content
Authors: Gao B. , Hu F. X. , Shen J. , Wang J. , Sun J. R. , Shen B. G.
Published: April 2009

Magnetocaloric effect associated with the first-order martensitic transition (TM) is investigated in polycrystalline Ni50−xMn35+xIn15 alloys with varying Mn content but fixing In content. It is found that when Mn content reaches x=3, a field-induced metamagnetic transition takes place. An external magnetic field can reduce TM to a lower temperature at a rate of 3.5 K/T, thereby yielding a large magnetic entropy change ΔS near room temperature. The ΔS magnitude attains to 33 J/kg K under a magnetic field of 5 T at 285 K for the sample with x=3, while the temperature span of the ΔS peak can reach 15 K because of the reduction in TM by the external magnetic field. The calculated refrigerant capacity reaches 279 J/kg for the sample with x=3. These values of the magnetocaloric parameters suggest that these alloys are suitable candidates for magnetic refrigerants.
How do magnetic microwires interact magnetostatically?
Authors: Pereira A. , Denardin J. C. , Escrig J.
Published: April 2009

The magnetostatic interaction between two ferromagnetic microwires is calculated as a function of their geometric parameters and compared with those measured through magnetic hysteresis loops of glass-coated amorphous Fe77.5Si7.5B15 microwires. The hysteresis loops are characterized by well-defined Barkhausen jumps corresponding each to the magnetization reversal of individual microwires, separated by horizontal plateaux. It is shown that the magnetostatic interaction between them is responsible for the appearance of these plateaux. Finally, using the expression for the magnetostatic interaction is trivial to obtain the interacting force between microwires. Our results are intended to provide guidelines for the use of these microwires with technological purpose such as the fabrication of magnetic sensors.
Gd
2
O
3
:
Eu
3
+
particles prepared by glycine-nitrate combustion: Phase, concentration, annealing, and luminescence studies
Authors: Ningthoujam R. S. , Shukla R. , Vatsa R. K. , Duppel V. , Kienle L. , Tyagi A. K.
Published: April 2009

Eu 3 + doped Gd2O3 particles have been prepared by glycine-nitrate combustion route. Eu–O charge transfer peak shifts to higher wavelength from 260 to 273 nm with increasing Eu3+ concentration, whereas the linewidth at half maximum intensity varies with Eu3+ concentrations and annealing temperatures as well. Lifetime for D50 level of Eu3+ increases with annealing temperature from 500 to 900 °C, and this is related to decreasing surface to volume atomic ratio of particles. Asymmetric ratio defined by the ratio of intensity of electrical dipole transition to that of magnetic dipole transition is found to be 10, which is more than the reported values (3–4) indicating enhancement in luminescence by this synthesis route.
Prevalence of approximate t relaxation for the dielectric α process in viscous organic liquids
Authors: Nielsen Albena I. , Christensen Tage , Jakobsen Bo , Niss Kristine , Olsen Niels Boye , Richert Ranko , Dyre Jeppe C.
Published: April 2009

This paper presents dielectric relaxation data for organic glass-forming liquids compiled from different groups and supplemented by new measurements. The main quantity of interest is the “minimum slope” of the α dielectric loss plotted as a function of frequency in a log-log plot, i.e., the numerically largest slope above the loss peak frequency. The data consisting of 347 spectra for 53 liquids show prevalence of minimum slopes close to −1/2, corresponding to approximate t dependence of the dielectric relaxation function at short times. The paper studies possible correlations between minimum slopes and (1) temperature (quantified via the loss peak frequency); (2) how well an inverse power-law fits data above the loss peak; (3) degree of time-temperature superposition; (4) loss peak half width; (5) deviation from non-Arrhenius behavior; (6) loss strength. For the first three points we find correlations that show a special status of liquids with minimum slopes close to −1/2. For the last three points only fairly insignificant correlations are found, with the exception of large-loss liquids that have minimum slopes that are numerically significantly larger than 1/2. We conclude that—excluding large-loss liquids—approximate t relaxation appears to be a generic property of the α relaxation of organic glass formers.
Dispersion of CdX(X=Se,Te) nanoparticles in P3HT conjugated polymer
Authors: Verma Deepak , Dutta V.
Published: April 2009

Hybrid absorber layers of P3HT having surfactant free CdTe and CdSe nanoparticles dispersed in it were deposited using spin coating technique. 1HNMR spectra confirmed the chemical interaction between the P3HT and the nanoparticles, which differs for the two nanoparticles. Optical absorbance extended from 350nm to near IR region for higher concentrations of the nanoparticles and the effect of charge transfer complex (CTC) were also seen. Photoluminence measurements on the hybrid films confirmed the photo-induced charge transfer between the polymer and nanoparticles. The difference in the properties of hybrid P3HT films shows the role of nanoparticles dispersion.
Orientational order of near D3h solutes in nematic liquid crystals
Authors: Danilović Zorana , Burnell E. Elliott
Published: April 2009

Solutes that are similar in size, have a shape that is close to D3h symmetry but contain dissimilar substituent groups (methyl versus chloro, contributing different electrostatic interactions to the anisotropic intermolecular potential), are used to delineate the short- and long-range anisotropic intermolecular interactions that lead to solute orientational order in nematic liquid crystals. The short-range interactions should be similar for all solutes and for D3h symmetry should yield a single independent order parameter, whereas the long-range interactions are expected to differ with solute. Short-range size and shape mechanisms account for solute orientational order measured in magic mixtures (e.g., 55 wt % ZLI-1132/N-p-ethoxybenzylidene-p′-n-butylaniline), whereas additional mechanisms are required in other nematic liquid-crystal solvents. The results obtained for long-range interactions cannot be rationalized in detail using simple mean-field models that incorporate solute dipoles, quadrupoles, or polarizabilities. The results suggest that details of the solute electrostatics may need to be incorporated into the description of the anisotropic intermolecular potential.
Orientational order of near D3h solutes in nematic liquid crystals. II. Description via Gay–Berne model with embedded quadrupoles
Authors: Sokolovskii R. O. , Burnell E. Elliott
Published: April 2009

We perform Monte Carlo simulations of a mixture of soft ellipsoids with embedded quadrupoles as a model of various chloro- and methyl-substituted benzenes dissolved in nematic liquid crystals. We find that oblate Gay–Berne ellipsoids with multiple embedded quadrupoles qualitatively reproduce the trend in the order parameter asymmetry experimentally observed in NMR spectra. The trend is opposite to what is expected on the basis of the interaction of the solute’s quadrupole with the solvent’s average electric field gradient “felt” by dissolved dihydrogen molecules. We identify the specific minimum of the solute-solvent interaction energy landscape that may produce the unexpected sign of the order parameter asymmetry that is seen in the experiment and the simulation.
Laser-triggered ion acceleration from a double-layer foil
Authors: Brantov A. V. , Tikhonchuk V. T. , Bychenkov V. Yu. , Bochkarev S. G.
Published: April 2009

A simple analytic model of light-ion acceleration in a double-layer foil target is proposed. It accounts for ion acceleration in the electrostatic sheath and Coulomb interaction between heavy and light ions. The model is used to study proton acceleration, and the conditions for a quasimonoenergetic proton beam formation are defined. Comparison with the hybrid and two-dimensional particle-in-cell kinetic simulations verifies the model results.
A first principles study on tunneling current through Si/SiO2/Si structures
Authors: Yamada Y. , Tsuchiya H. , Ogawa M.
Published: April 2009

In this paper, we study tunneling current properties through SiO2 gate oxides in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) by applying a first principles method based on the density-functional theory and nonequilibrium Green’s function approach. We employed three structural models of SiO2 layers, which are β-quartz, β-cristobalite, and β-tridymite. As a result, we found that the β-cristobalite and β-tridymite models indicate similar tunneling current properties, while the β-quartz model predicts a substantially lower tunneling current. Further, the largest tunneling current is obtained for the β-tridymite SiO2 model, which is consistent with bandstructure parameters estimated for bulk SiO2 crystals. Therefore, electronic properties of bulk SiO2 crystals can still be important for tunneling current analysis in the nanoscale range of oxide thickness.
The electronic structure and bonding of AlNAl
Authors: Kalemos Apostolos , Mavridis Aristides
Published: April 2009

We have studied 16 states, 7 doublets, and 9 quartets of the AlNAl isomer mainly through multireference methods and correlation consistent basis sets. We report equilibrium geometries, energetics, and dipole moments, whereas for a number of low lying states we have constructed dissociation AlN–Al potential energy profiles. For the same states we also analyze their bonding character using valence–bond–Lewis diagrams. Our results are consistent with the limited experimental data.
Modeling outer-sphere disorder in the symmetry breaking of PPV
Authors: Liu L. Angela , Yaron David J.
Published: April 2009

Disorder plays an important role in the photophysics of conjugated polymers such as poly(para-phenylene vinylene) (PPV). The dipole moments measured by electroabsorption spectroscopy for a centrosymmetric system such as PPV provide a direct quantitative measure of disorder-induced symmetry breaking. Although inner-sphere (structural) disorder is present, outer-sphere (environmental) disorder dominates the symmetry breaking in PPV. This paper develops and compares six models of outer-sphere disorder that differ in their representation of the electrostatic environment of PPV in glassy solvents. The most detailed model is an all-atom description of the solvent glass and this model forms the basis for comparison of the less detailed models. Four models are constructed in which multipoles are placed at points on a lattice. These lattice models differ in the degree to which they include correlation between the lattice spacings and the orientations of the multipoles. A simple model that assigns random Gaussian-distributed electrostatic potentials to each atom in the PPV molecule is also considered. Comparison of electronic structure calculations of PPV in these electrostatic environments using the all-atom model as a benchmark reveals that dipole and quadrupole lattices provide reasonable models of organic glassy solvents. Including orientational correlation among the solvent molecules decreases the effects of outer-sphere disorder, whereas including correlation in the lattice spacings increases the effects. Both the dipole and quadrupole moments of the solvent molecules can have significant effects on the symmetry breaking and these effects are additive. This additivity provides a convenient means for predicting the effects of various glassy solvents based on their multipole moments. The results presented here suggest that electrostatic disorder can account for the observed symmetry breaking in organic glasses. Furthermore, the lattice models are in general agreement with the dipole and quadrupole lattice models used to explain the Poole–Frenkel behavior in charge transport through disordered organic materials.
Evidence of elastic to plastic transition in the zona pellucida of oocytes using atomic force spectroscopy
Authors: Papi Massimiliano , Sylla Lakamy , Parasassi Tiziana , Brunelli Roberto , Monaci Maurizio , Maulucci Giuseppe , Missori Mauro , Arcovito Giuseppe , Ursini Fulvio , De Spirito Marco
Published: April 2009

We have investigated the mechanical properties of the zona pellucida (ZP), a multilayer glycoprotein coat that surrounds mammalian eggs, using atomic force spectroscopy. The response of the membrane to mechanical stress has been reconstructed using a modified Hertz model. The transition from elastic behavior, which occurs when low stress forces are applied (characterized by a Young’s modulus E=(22±5) kPa), toward plastic behavior is observed. The critical indentation necessary to induce plastic deformations occurs at δyield=(550±50) nm. This high critical value, corresponding to two ZP layers, well supports the noncovalent long lifetimes of interactions that take place between constituent glycoproteins.
Bilayered smectic phase polymorphism in the dipolar Gay–Berne liquid crystal model
Authors: Houssa Mohammed , Rull Luis F. , Romero-Enrique Jose M.
Published: April 2009

We present computer simulations of the Gay–Berne model with a strong terminal dipole. We report the existence of different stable antiferroelectric interdigitated bilayered phases in this model with diverse in-plane organization. The occurrence of these phases depends crucially on the value of the molecular elongation κ. For κ=3 we find an interdigitated bilayered smectic-A phase (absent when there is no dipole) and a bilayered smectic-T (or crystal) with positional in-plane tetragonal ordering, different from the hexatic observed in the absence of the molecular dipole. For κ=4, bilayered smectic-A and in-plane hexatic-ordered smectic-B (or crystal) phases are observed.
Measurements of electric charge and screening length of microparticles in a plasma sheath
Authors: Nakamura Y. , Ishihara O.
Published: April 2009

An experiment is described in which microparticles are levitated within a rf sheath above a conducting plate in argon plasma. The microparticles forming a two-dimensional crystal structure are considered to possess Debye screening Coulomb potential ϕ(r)=(Q/4πε0r)exp(−r/λ), where Q is the electric charge, r is distance, and λ is the screening length. When the crystal structure is slanted with an angle θ, a particle experiences a force Mg sin θ, where M is the mass of the particle and g is acceleration due to gravity, which must be equal to the Debye screened Coulomb force from other particles. By changing θ, relations for λ(Q) are measured. The screening length λ and Q are determined uniquely from the crossing points of several relations. The electric charge Q is also estimated from a floating potential measured with a probe. The measured λ is nearly equal to an ion Debye length.
Correlation of spectral, spatial, and angular characteristics of an ultrashort laser driven proton source
Authors: Ter-Avetisyan S. , Schnürer M. , Nickles P. V. , Sandner W. , Nakamura T. , Mima K.
Published: April 2009

The laser driven ion source is a highly organized dynamical system. It relies on a well defined interrelation between the spatial and momentum distributions of emitted ions. This correlation is found by a consecutive spectral characterization of distinct proton beamlets emitted from different spatial target positions and under different angles. In case of a flat target and a perfectly round laser focal spot, the proton source is circular symmetric and each source point behaves similarly: the higher the proton energy the smaller the source size and the larger the emission angle for a similar source extension. Only the symmetry axis is unique; here all protons are emitted at 0° to the target normal.
Thermocapillary migration of interfacial droplets
Authors: Greco Edwin F. , Grigoriev Roman O.
Published: April 2009

We study the thermocapillary driven motion of a droplet suspended at an interface of two fluid layers subjected to an imposed temperature gradient parallel to the interface. We compute the temperature and velocity fields inside and outside of the droplet using a boundary collocation numerical scheme in the limit of small capillary and thermal Péclet numbers and compare the results with the classical problem of thermocapillary migration of a droplet in the bulk. In particular, we find that, for typical values of parameters, interfacial droplets migrate in the direction opposite to the temperature gradient, while in the classical problem migration is always in the direction of the gradient. Furthermore, we find that a rich variety of flow structures can emerge inside interfacial droplets. We also confirm that for parameters matching a recent experimental study of mixing inside interfacial microdroplets [R. O. Grigoriev, V. Sharma, and M. F. Schatz, Lab Chip 6, 1369 (2006)] the interior flow can be approximated with reasonable accuracy by assuming the droplet to be completely submerged in the bottom layer.