bluuebunny/crossref_metadata_2025 huggingface dataset:
Microquasars: an observational review.
Authors: Corbel Stéphane
Published: February 2011

In the past decade, several considerable achievements have been reached in the field of Galactic microquasars, especially in light of the extreme variability of their relativistic jets. These jets are now known to exist in at least three different flavours: the self absorbed compact jets in the hard state, the transient and discrete ejection events associated with the state transitions, and the emission associated with the interaction of the jets on the interstellar medium. Although their phenomenology is now starting to be rather well established, their emission and contribution to the total energy budget of microquasars is still the subject of active debate. One way to probe the origin of their emission at various wavelengths is to use the broadband correlations that may exist between different energy domains. Initiated in the radio and X-ray ranges, these broadband flux correlations now include optical and infrared observations of black hole candidates and also neutron star systems. In this review, I also outline the current observational status of the emission of relativistic jets at high energy.
Jets from neutron star X-ray binaries: towards a unified scheme
Authors: Migliari Simone
Published: February 2011

Systematic multi-wavelength studies of neutron stars (NSs) have shown a jet and disk-jet coupling phenomenology which resembles, although with some important differences, that observed in black holes; ultra-relativistic transient ejection, steady compact jets, accretion-ejection cycles are indeed observed in NSs. I will review our observational knowledge of jet in NS X-ray binaries, focusing on the role of the parameters of the system which might be involved in the production of jets. First, I will discuss the role of the accretion rate, presenting aunified schemefor accretion-jet production throughout the different sub-classes of low-magnetic field NSs. Then, I will attempt to (make the first steps to) quantify the role of spin and magnetic field in powering the jet.
On the nature of the “radio quiet” black hole binaries
Authors: Soleri Paolo , Fender Rob
Published: February 2011

The accretion/ejection coupling in accreting black hole binaries has been described by empirical relations between the X-ray/radio and X-ray/optical-infrared luminosities. These correlations were initially supposed to be universal. However, recently many sources have been found to produce jets that, given certain accretion-powered luminosities, are fainter than expected from the correlations. This shows that black holes with similar accretion flows can produce a broad range of outflows in power Here we discuss whether typical parameters of the binary system, as well as the properties of the outburst, produce any effect on the energy output in the jet. We also define a jet-toy model in which the bulk Lorentz factor becomes larger than ~1 above ~0.1% of the Eddington luminosity. We finally compare the “radio quiet” black holes with the neutron stars.
The physics of disk winds, jets, and X-ray variability in GRS 1915+105
Authors: Neilsen Joseph , Lee Julia C. , Remillard Ron
Published: February 2011

We present new insights about accretion and ejection physics based on joint RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the first time, with fast phase-resolved spectroscopy of the ρ state, we are able to show that changes in the broadband X-ray spectrum (RXTE) on timescales of seconds are associated with measurable changes in absorption lines (Chandra HETGS) from the accretion disk wind. Additionally, we make a direct detection of material evaporating from the radiation-pressure-dominated inner disk. Our X-ray data thus reveal the black hole as it ejects a portion of the inner accretion flow and then drives a wind from the outer disk, all in a bizarre cycle that lasts fewer than 60 seconds but can repeat for weeks. We find that the accretion disk wind may be sufficiently massive to play an active role in GRS 1915+105, not only in quenching the jet on long timescales, but also in possibly producing or facilitating transitions between classes of X-ray variability.
GRS1915+105: a comparison of the plateau state to the canonical hard state
Authors: van Oers Pieter , Markoff Sera
Published: February 2011

GRS 1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however – referred to as the plateau state – may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. To investigate the relationship between the plateau and the hard state, we fit two multi-wavelength observations using a steady-state outflow-dominated model, developed for hard state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fit model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates.
Gamma-rays and neutrinos from accreating neutron stars
Authors: Bednarek Włodek
Published: February 2011

Dense wind of a massive star can be partially captured by a companion neutron star (NS) creating a very turbulent and magnetized transition region at some distance from the NS surface. We consider the consequences of electron and hadron acceleration at such a transition region. Electrons lose energy on the synchrotron process and the inverse Compton (IC) scattering of thermal radiation from the NS surface and/or the massive star. We calculate the synchrotron spectra (from X-rays to soft γ-rays) and IC spectra in the case of sources accreting the matter under the accretor and propeller scenarios. It is argued that a population of accreting massive binaries, recently discovered by the INTEGRAL observatory, can be detectable by the Fermi LAT telescope. On the other hand, TeV γ-ray emission from other class of massive binaries can be interpreted in terms of a magnetar accreting matter in the propeller scenario. We also calculate the expected neutrino event rates in a km2 detector produced by relativistic hadrons accelerated in such scenario.
Instabilities in the Gamma Ray Burst central engine. What makes the jet variable?
Authors: Janiuk Agnieszka , Yuan Ye-Fei , Perna Rosalba , Di Matteo Tiziana
Published: February 2011

Both types of long and short gamma ray bursts involve a stage of a hyper-Eddington accretion of hot and dense plasma torus onto a newly born black hole. The prompt gamma ray emission originates in jets at some distance from this ‘central engine’ and in most events is rapidly variable, having a form of sipkes and subpulses. This indicates at the variable nature of the engine itself, for which a plausible mechanism is an internal instability in the accreting flow. We solve numerically the structure and evolution of the neutrino-cooled torus. We take into account the detailed treatment of the microphysics in the nuclear equation of state that includes the neutrino trapping effect. The models are calculated for both Schwarzschild and Kerr black holes. We find that for sufficiently large accretion rates (>~10M⊙ s−1 for non-rotating black hole, and >~1M⊙ s−1 for rotating black hole, depending on its spin), the inner regions of the disk become opaque, while the helium nuclei are being photodissociated. The sudden change of pressure in this region leads to the development of a viscous and thermal instability, and the neutrino pressure acts similarly to the radiation pressure in sub-Eddington disks. In the case of rapidly rotating black holes, the instability is enhanced and appears for much lower accretion rates. We also find the important and possibly further destabilizing role of the energy transfer from the rotating black hole to the torus via the magnetic coupling.
Simulation of relativistic shocks and associated radiation from turbulent magnetic fields
Authors: Nishikawa K.-I. , Niemiec J. , Medvedev M. , Zhang B. , Hardee P. , Mizuno Y. , Nordlund A. , Frederiksen J. , Sol H. , Pohl M. , Hartmann D. H. , Fishman G. J.
Published: February 2011

Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has different properties from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We will present detailed spectra for conditions relevant to various astrophysical sites of collisionless shock formation. In particular we will discuss application to GRBs and SNRs.
Radio observations of jets from massive young stars
Authors: Rodríguez Luis F.
Published: February 2011

The formation of low mass stars takes place with the assistance of an accretion disk that transports gas and dust from the envelope of the system to the star, and a jet that removes angular momentum and allows accretion to proceed. In the radio, these ionized jets can be studied very close to the star via the thermal (free-free) emission they produce and at larger scales by the molecular outflows that result from their interaction with the surrounding medium. Is the same disk-jet process responsible for the formation of massive stars? I will review recent evidence for the presence of collimated jets and accretion disks in association with forming massive stars. The jets in massive protostars have large velocities that could produce a synchrotron component and I discuss the evidence for the presence of this non-thermal process in the jet associated with the HH 80-81 system.
A FORMALIZATION OF KANT’S TRANSCENDENTAL LOGIC
Authors: ACHOURIOTI T. , VAN LAMBALGEN M.
Published: February 2011

Although Kant (1998) envisaged a prominent role for logic in the argumentative structure of hisCritique of Pure Reason, logicians and philosophers have generally judged Kant’s logic negatively. What Kant called ‘general’ or ‘formal’ logic has been dismissed as a fairly arbitrary subsystem of first-order logic, and what he called ‘transcendental logic’ is considered to be not a logic at all: no syntax, no semantics, no definition of validity. Against this, we argue that Kant’s ‘transcendental logic’ is a logic in the strict formal sense, albeit with a semantics and a definition of validity that are vastly more complex than that of first-order logic. The main technical application of the formalism developed here is a formal proof that Kant’s Table of Judgements in Section 9 of theCritique of Pure Reason, is indeed, as Kant claimed, complete for the kind of semantics he had in mind. This result implies that Kant’s ‘general’ logic is after all a distinguished subsystem of first-order logic, namely what is known as geometric logic.
Multisite probabilistic forecasting of seasonal flows for streams with zero value occurrences
Authors: Wang Q. J. , Robertson D. E.
Published: February 2011

Skillful and reliable forecasts of seasonal streamflows are highly valuable to water management. In a previous study, we developed a Bayesian joint probability (BJP) modeling approach for seasonal forecasting of streamflows at multiple sites. The approach has been adopted by the Australian Bureau of Meteorology for seasonal streamflow forecasting in Australia. This study extends the applicability of the BJP modeling approach to streams with zero flow occurrences. The aim is to produce forecasts for these streams in the form of probabilities of zero seasonal flows and probability distributions of above zero seasonal flows. We turn a difficult mathematical problem of mixed discrete‐continuous multivariate probability distribution modeling into one of continuous multivariate probability distribution modeling by treating zero flow occurrences as censored data. This paper presents the mathematical formulation and implementation of the modeling approach, methods for forecast verification, and results of a test application to the Burdekin river catchment in northern Queensland, Australia.
Cotransport of Pseudomonas putida and kaolinite particles through water‐saturated columns packed with glass beads
Authors: Vasiliadou Ioanna A. , Chrysikopoulos Constantinos V.
Published: February 2011

This study is focused on Pseudomonas putida bacteria transport in porous media in the presence of suspended kaolinite clay particles. Experiments were performed with bacteria and kaolinite particles separately to determine their individual transport characteristics in water‐saturated columns packed with glass beads. The results indicated that the mass recovery of bacteria and clay particles decreased as the pore water velocity decreased. Batch experiments were carried out to investigate the attachment of Pseudomonas putida onto kaolinite particles. The attachment process was adequately described by a Langmuir isotherm. Finally, bacteria and kaolinite particles were injected simultaneously into a packed column in order to investigate their cotransport behavior. The experimental data suggested that the presence of clay particles significantly inhibited the transport of bacteria in water‐saturated porous media. The observed reduction of Pseudomonas putida recovery in the column outflow was attributed to bacteria attachment onto kaolinite particles, which were retained onto the solid matrix of the column. A mathematical model was developed to describe the transport of bacteria in the presence of suspended clay particles in one‐dimensional water‐saturated porous media. Model simulations were in good agreement with the experimental results.
Numerical evaluation of subsurface soil water evaporation derived from sensible heat balance
Authors: Sakai Masaru , Jones Scott B. , Tuller Markus
Published: February 2011

A recently introduced measurement approach allows in situ determination of subsurface soil water evaporation by means of heat‐pulse probes (HPP). The latent heat component of subsurface evaporation is estimated from the residual of the sensible heat balance. This heat balance method requires measurement of vertical soil temperature and estimates of thermal properties for soil water evaporation determination. Our objective was to employ numerically simulated thermal and hydraulic processes using constant or diurnally cycled surface boundary conditions to evaluate and understand this technique. Three observation grid spacings, namely, 6 mm (tri‐needle HPP), 3 mm (penta‐needle HPP) and 1 mm, along with three soil textures (sand, silt, and silty clay) were used to test the heat balance method. The comparison of heat balance–based evaporation rate estimates with an independent soil profile water balance revealed substantial errors when thermal conductivity was averaged spatially across the evaporation front. Since the conduction component of heat flux is the dominant process at the evaporation front, the estimation of evaporation rate was significantly improved using depth‐dependent instead of a space‐averaged . A near‐surface “undetectable zone” exists, where the heat balance calculation is irreconcilable, resulting in underestimation of total subsurface evaporation. The method performs better for medium‐ and coarse‐textured soils than for fine‐textured soils, where portions of the drying front may be maintained longer within the undetectable zone. Using smaller temperature sensor spacing near the soil surface minimized underestimation from the undetectable zone and improved accuracy of total subsurface evaporation rate estimates.
Complete-fosmid and fosmid-end sequences reveal frequent horizontal gene transfers in marine uncultured planktonic archaea
Authors: Brochier-Armanet Céline , Deschamps Philippe , López-García Purificación , Zivanovic Yvan , Rodríguez-Valera Francisco , Moreira David
Published: February 2011

The extent of horizontal gene transfer (HGT) among marine pelagic prokaryotes and the role that HGT may have played in their adaptation to this particular environment remain open questions. This is partly due to the paucity of cultured species and genomic information for many widespread groups of marine bacteria and archaea. Molecular studies have revealed a large diversity and relative abundance of marine planktonic archaea, in particular of Thaumarchaeota (also known as group I Crenarchaeota) and Euryarchaeota of groups II and III, but only one species (the thaumarchaeote Candidatus Nitrosopumilus maritimus) has been isolated in pure culture so far. Therefore, metagenomics remains the most powerful approach to study these environmental groups. To investigate the impact of HGT in marine archaea, we carried out detailed phylogenetic analyses of all open reading frames of 21 archaeal 16S rRNA gene-containing fosmids and, to extend our analysis to other genomic regions, also of fosmid-end sequences of 12 774 fosmids from three different deep-sea locations (South Atlantic and Adriatic Sea at 1000 m depth, and Ionian Sea at 3000 m depth). We found high HGT rates in both marine planktonic Thaumarchaeota and Euryarchaeota, with remarkable converging values estimated from complete-fosmid and fosmid-end sequence analysis (25 and 21% of the genes, respectively). Most HGTs came from bacterial donors (mainly from Proteobacteria, Firmicutes and Chloroflexi) but also from other archaea and eukaryotes. Phylogenetic analyses showed that in most cases HGTs are shared by several representatives of the studied groups, implying that they are ancient and have been conserved over relatively long evolutionary periods. This, together with the functions carried out by these acquired genes (mostly related to energy metabolism and transport of metabolites across membranes), suggests that HGT has played an important role in the adaptation of these archaea to the cold and nutrient-depleted deep marine environment.
Regulation of cellular iron metabolism
Authors: Wang Jian , Pantopoulos Kostas
Published: February 2011

Iron is an essential but potentially hazardous biometal. Mammalian cells require sufficient amounts of iron to satisfy metabolic needs or to accomplish specialized functions. Iron is delivered to tissues by circulating transferrin, a transporter that captures iron released into the plasma mainly from intestinal enterocytes or reticuloendothelial macrophages. The binding of iron-laden transferrin to the cell-surface transferrin receptor 1 results in endocytosis and uptake of the metal cargo. Internalized iron is transported to mitochondria for the synthesis of haem or iron–sulfur clusters, which are integral parts of several metalloproteins, and excess iron is stored and detoxified in cytosolic ferritin. Iron metabolism is controlled at different levels and by diverse mechanisms. The present review summarizes basic concepts of iron transport, use and storage and focuses on the IRE (iron-responsive element)/IRP (iron-regulatory protein) system, a well known post-transcriptional regulatory circuit that not only maintains iron homoeostasis in various cell types, but also contributes to systemic iron balance.
An accurate continuous calibration system for high voltage current transformer
Authors: Tong Yue , Li Bin Hong
Published: February 2011

A continuous calibration system for high voltage current transformers is presented in this paper. The sensor of this system is based on a kind of electronic instrument current transformer, which is a clamp-shape air core coil. This system uses an optical fiber transmission system for its signal transmission and power supply. Finally the digital integrator and fourth-order convolution window algorithm as error calculation methods are realized by the virtual instrument with a personal computer. It is found that this system can calibrate a high voltage current transformer while energized, which means avoiding a long calibrating period in the power system and the loss of power metering expense. At the same time, it has a wide dynamic range and frequency band, and it can achieve a high accuracy measurement in a complex electromagnetic field environment. The experimental results and the on-site operation results presented in the last part of the paper, prove that it can reach the 0.05 accuracy class and is easy to operate on site.
Relationships among coarse-grained field theories of fluctuations in polymer liquids
Authors: Morse David C. , Qin Jian
Published: February 2011

Two closely related field-theoretic approaches have been used in previous work to construct coarse-grained theories of corrections to the random phase approximation for correlations in block copolymer melts and miscible polymer blends. The “auxiliary field” (AF) approach is based on a rigorous expression for the partition function Z of a coarse-grained model as a functional integral of an auxiliary chemical potential field. The “effective Hamiltonian” (EH) approach is instead based on an expression for Z as a functional integral of an observable order parameter field. The exact effective Hamiltonian Heff in the EH approach is defined as the free energy of a system with a constrained order parameter field. In practice, however, Heff has often been approximated by a mean-field free energy functional, yielding what we call a mean-field effective Hamiltonian (MFEH) approximation. This approximation was the starting point of both the Fredrickson–Helfand analysis of fluctuation effects in diblock copolymers and earlier work on the Ginzburg criterion in polymer blends. A more rigorous EH approach by Holyst and Vilgis used an auxiliary field representation of the exact Heff and allowed for Gaussian fluctuations of this field. All applications of both AF and EH approaches have thus far relied upon some form of Gaussian, or “one-loop” approximation for fluctuations of a chemical potential and/or order parameter field about a mean-field saddle-point. The one-loop EH approximation of Holyst and Vilgis and the one-loop AF theory are equivalent to one another, but not to the one-loop MFEH theory. The one-loop AF and MFEH theories are shown to yield predictions for the inverse structure factor S−1(q) that (in the absence of further approximations to either theory) differ by a function that is independent of the Flory–Huggins interaction parameter χ. As a result, these theories yield predictions for the peak scattering intensity that exhibit a similar χ-dependence near a spinodal. The Fredrickson–Helfand theory for the structure factor in disordered diblock copolymer melts is an asymptotic approximation to the MFEH one-loop theory that captures the dominant asymptotic behavior of very long, symmetric copolymers very near the order–disorder transition.
Magnetoelectric coupling and phase transition in BiFeO3 and (BiFeO3)0.95(BaTiO3)0.05 ceramics
Authors: Wang T.-H. , Tu C.-S. , Chen H.-Y. , Ding Y. , Lin T. C. , Yao Y.-D. , Schmidt V. H. , Wu K.-T.
Published: February 2011

In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO–5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)–orthorhombic (O)–cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO–5%BT exhibits a R–C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO–5%BT remains less than 0.04 below 150 °C.
Direct measurement of versatile surface plasmon polaritons excited by split polarization
Authors: Lan Tzu-Hsiang , Ho Chen-Yeh , Tien Chung-Hao
Published: February 2011

We report on the concept, generation, and observation of versatile excited surface plasmon polariton (SPP) patterns via focused split polarization. Unlike the conventional subwavelength features such as holes array, grating, or other protrusion to satisfy the phase matching condition for SPP excitation, we utilized a structured focus to form either counterpropagating interference or a multiple casting plasmonic pattern by means of the arrangement of split polarization and corresponding focus position. The characteristics of the near-field SPP image are in close agreement with the finite-difference time-domain calculation and confirm its feasibility associated with SPP excitations in many areas.
Optimal streaks in a Falkner–Skan boundary layer
Authors: Sánchez-Álvarez José J. , Higuera María , Vega José M.
Published: February 2011

This paper deals with the optimal streaky perturbations (which maximize the perturbed energy growth) in a wedge flow boundary layer, which involves a favorable streamwise pressure gradient. These three-dimensional perturbations are governed by a system of linearized boundary layer equations around the Falkner–Skan base flow. Based on an asymptotic analysis of this system near the free-stream and the leading edge singularity, we show that for acute wedge semi-angle, all solutions converge after a streamwise transient to a single streamwise-growing solution of the linearized equations, whose initial condition near the leading edge is given by an eigenvalue problem first formulated in this context by Tumin [Phys. Fluids 13, 1521 (2001)]. Such a solution may be regarded as a streamwise evolving most unstable streaky mode, in analogy with the usual eigenmodes in strictly parallel flows, and shows an approximate self-similarity, which was partially known and is completed in this paper. An important consequence of this result is that the optimization procedure based on the adjoint equations heretofore used to define optimal streaks is not necessary. Instead, a simple low-dimensional optimization process is proposed and used to obtain optimal streaks. Comparison with previous results by Tumin and Ashpis [AIAA J. 41, 2297 (2003)] shows an excellent agreement. The unstable streaky mode exhibits transient growth if the wedge semi-angle is smaller than a critical value that is slightly larger than π/6, and decays otherwise. Thus, the cases of right and obtuse wedge semi-angles exhibit less practical interest, but they show a qualitatively different behavior, which is briefly described in the supplementary material.
Quantum Monte Carlo study of the first-row atoms and ions
Authors: Seth P. , Ríos P. López , Needs R. J.
Published: February 2011

Quantum Monte Carlo calculations of the first-row atoms Li–Ne and their singly positively charged ions are reported. Multideterminant-Jastrow-backflow trial wave functions are used which recover more than 98% of the correlation energy at the variational Monte Carlo level and more than 99% of the correlation energy at the diffusion Monte Carlo level for both the atoms and ions. We obtain the first ionization potentials to chemical accuracy. We also report scalar relativistic corrections to the energies, mass-polarization terms, and one- and two-electron expectation values.
A special asymptotic limit of a Kampé de Fériet hypergeometric function appearing in nonhomogeneous Coulomb problems
Authors: Ancarani L. U. , Gasaneo G.
Published: February 2011

In the investigation of two-body Coulomb Schrödinger equations with some types of nonhomogeneities, the particular solution can be expressed in terms of a two-variable Kampé de Fériet hypergeometric function. The asymptotic limit of the latter—for both variables being large but their ratio being a bound constant—is required in order to extract relevant physical information from the solutions. In this report the mathematical limit is provided. For that purpose, a particular series representation of the hypergeometric function—in terms of products of Kummer and Gauss functions—is first derived.
Structural and energetic origin of defects at the interface between germanium and a high-k dielectric from first principles
Authors: Elliott S. D. , Greer J. C.
Published: February 2011

Atomic-scale models of the abrupt high-k/Ge interface with a range of suboxide stoichiometries GeOx are presented and compared to their Si analogs. Molecular dynamics and geometry optimization were carried out at the density functional theory level to yield structures and energetics. Cohesion across the interface becomes stronger with increasing oxidation of the Ge suboxide. Three-coordinate Ge is identified as the main defect and is formed at low energetic cost, which accounts for the observed abundance of defects at oxide/Ge interfaces. The optimum low temperature interface is defect-free, predominantly Ge2+ with some Ge+.
Recombination in compensated crystalline silicon for solar cells
Authors: Macdonald Daniel , Cuevas Andrés
Published: February 2011

Deliberate compensation of crystalline silicon results in a decrease in the equilibrium carrier concentration, which leads to an increased carrier lifetime for the intrinsic recombination processes of Auger and radiative recombination. We present modeling which reveals that compensation also often leads to a significant increase in lifetime for recombination through defects via the Shockley–Read–Hall mechanism, a conclusion which is confirmed experimentally for the case of interstitial iron in p-type silicon. We show that the increased Shockley–Read–Hall lifetime can result from either an injection-level effect for deep levels, or from a Fermi-level effect for shallower levels. For cases where the defect exhibits no injection dependence of the carrier lifetime, compensation does not lead to an increased lifetime. Further modeling demonstrates that in certain cases, the lifetime increase can be expected to significantly outweigh the competing reductions in carrier mobilities and net doping, resulting in an improved short-circuit current, open-circuit voltage, and solar cell efficiency.
Defect states at III-V semiconductor oxide interfaces
Authors: Lin L. , Robertson J.
Published: February 2011

Models of insulating interfaces between (100)GaAs and HfO2, Gd2O3, and Al2O3 are constructed and used to host various interfacial defects to see which give rise to gap states. The antibonding state of As–As dimers is found to lie in the upper band gap and is identified as a possible major source of the interface gap states which cause Fermi level pinning in GaAs-oxide interfaces and field effect transistors.
Ab initio spectroscopic characterization of the HNNO and ONHN radicals
Authors: Peterson Kirk A. , Francisco Joseph S.
Published: February 2011

A composite coupled cluster methodology is used with systematic sequences of correlation consistent basis sets to accurately determine the structure, vibrational frequencies, and isotopic shifts for trans-HNNO (2A′), cis-HNNO (2A′), and ONHN (2A′). Anharmonic corrections to the vibrational frequencies and rotational constants are obtained using density functional theory. With basis sets larger than double-zeta, large differences between restricted open-shell Hartree–Fock (ROHF)-based and unrestricted Hartree–Fock (UHF)-based coupled cluster harmonic frequencies are calculated, with the UHF-based ones judged to be more reliable based on an analysis of the orbital hessian eigenvalues. The final calculated anharmonic vibrational band origins are generally in good agreement with the experimental values measured in rare gas matrices. The calculation of the vibrational band origins of the isovalent NO2 molecule at similar levels of theory exhibits an agreement with experiment to within a few wavenumbers. In the latter case, however, a ROHF treatment was required since the UHF approach failed to provide realistic frequencies for the antisymmetric stretching mode. The heat of formation at 0 K of trans-HNNO is calculated to be 50.5 ± 0.5 kcal/mol using a very similar composite coupled cluster methodology as in the structure and harmonic frequency determinations.
Porous medium acoustics of wave-induced vorticity diffusion
Authors: Müller T. M. , Sahay P. N.
Published: February 2011

A theory for attenuation and dispersion of elastic waves due to wave-induced generation of vorticity at pore-scale heterogeneities in a macroscopically homogeneous porous medium is developed. The diffusive part of the vorticity field associated with a viscous wave in the pore space—the so-called slow shear wave—is linked to the porous medium acoustics through incorporation of the fluid strain rate tensor of a Newtonian fluid in the poroelastic constitutive relations. The method of statistical smoothing is then used to derive dynamic-equivalent elastic wave velocities accounting for the conversion scattering process into the diffusive slow shear wave in the presence of randomly distributed pore-scale heterogeneities. The result is a simple model for wave attenuation and dispersion associated with the transition from viscosity- to inertia-dominated flow regime.
Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes
Authors: Endo Ayataka , Sato Keigo , Yoshimura Kazuaki , Kai Takahiro , Kawada Atsushi , Miyazaki Hiroshi , Adachi Chihaya
Published: February 2011

A material possessing a very small energy gap between its singlet and triplet excited states, ΔE1−3, which allows efficient up-conversion of triplet excitons into a singlet state and leads to efficient thermally activated delayed fluorescence (TADF), is reported. The compound, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)-1,3,5-triazine, breaks the restriction of a large energy gap, with a ΔE1−3 of just 0.11 eV, while maintaining a high fluorescent radiative decay rate (kr∼107). The intense TADF provides a pathway for highly efficient electroluminescence.
Atomic structure of tip apex for spin-polarized scanning tunneling microscopy
Authors: Rodary G. , Girard J.-C. , Largeau L. , David C. , Mauguin O. , Wang Z.-Z.
Published: February 2011

We present a high resolution transmission electron microscopy study of a Cr-coated W tip apex prepared for spin-polarized scanning tunneling microscopy (SP-STM). The characterization of the tip apex structure has been done with atomic resolution. We show that the Cr film is epitaxially grown on W and presents a monocrystalline phase. The surface analysis of the apex reveals roughness which gives rise to structures that can be considered as nanotips. In spite of the monocrystalline structure of these nanotips, we show that their spin arrangement and resulting magnetization direction cannot be controlled. SP-STM measurements on a Cr/MgO(001) sample confirm this conclusion.
Determination of the photoluminescence quantum efficiency of silicon nanocrystals by laser-induced deflection
Authors: Potrick K. , Schmidt T. , Bublitz S. , Mühlig Chr. , Paa W. , Huisken F.
Published: February 2011

The oxidation and passivation of freshly prepared silicon nanocrystals (Si NCs) have been studied by exciting them with a low-fluence violet laser at 406 nm and measuring both the heat generated by nonradiative transitions and the photoluminescence (PL) resulting from radiative charge carrier recombination over a period of 31 days. Laser-induced deflection was employed as a sensitive tool to determine the heat transferred to the phonon bath. The PL quantum efficiency of Si NCs passivated in air was found to develop with a time constant of 8 d from zero to a terminal saturation value of approximately 65%.
Electromagnetically induced Talbot effect
Authors: Wen Jianming , Du Shengwang , Chen Huanyang , Xiao Min
Published: February 2011

By modulating transmission function of a weak probe field via a strong control standing wave, an electromagnetically induced grating can be created in the probe channel. Such a nonmaterial grating may lead to self-imaging of ultracold atoms or molecules in the Fresnel near-field regime. This work may offer a nondestructive and lensless way to image ultracold atoms or molecules.
Thermally driven isotropic crystallinity breaking of nanocrystals: Insight into the assembly of EuS nanoclusters and nanorods with oleate ligands
Authors: He Weidong , Dickerson James H.
Published: February 2011

Clusters of EuS nanocrystals formed through the thermal assembly of 2.5 nm nanocrystal monomers by varying the annealing temperature from 300 to 340 °C. Below 310 °C, oleate ligands stabilized on the surface of the EuS nanocrystals, giving rise to their low solubility in triethanolamine while facilitating monomer–monomer oriented attachment into short-chain structures. Above 320 °C, the oleate ligands thermally detached from the surface and were replaced by oleyamine. This reaction mechanism was a multilevel oriented attachment, based on calculations of the nanocrystal growth kinetics, whose evolution gave rise to the formation of EuS nanorods at 340 °C.
Foveal Spatial Summation in Human Cone Mechanism
Authors: O'Donell Beatriz M , Colombo Elisa M
Published: February 2011

We measured at the fovea the chromatic contrast threshold for stimuli modulated along different chromatic directions in the isoluminant plane of MBDKL colour space, considering the two cardinal axes ( L/M) and S/( L + M) and other intermediate non-cardinal directions. This psychophysical determination was conducted as a function of stimulus size. The test stimulus was a foveal isoluminant Gaussian patch with a raised cosinusoidal temporal profile superimposed on a neutral background. The task was performed binocularly. The increment threshold was measured for three observers by a Bayesian adaptive psychometric method (QUEST). The Ricco area of complete spatial summation was estimated from the threshold-versus-area curves. The perceptive fields are smaller for the L/M-cone opponent direction than the S/( L + M)-cone opponent. The perceptive field sizes for the stimuli in non-cardinal chromatic directions and stimuli modulated at the ( L/ M)-cone opponent direction present similar values. Measurements were made at two luminance levels, 5 and 40 cd m−2 but the differences found were small. The perceptive field sizes found could be associated with LGN area.
Touching My Left Elbow: The Anatomical Structure of the Body Affects the Illusion of Self-Touch
Authors: White Rebekah C , Davies Anne M Aimola
Published: February 2011

A self-touch paradigm is used to create the illusion that one is touching one's own left elbow when one is actually touching the examiner's arm. Our new self-touch illusion is sensitive to the anatomical structure of the body: you can touch your left elbow with your right index finger but not with your left index finger. Illusion onset was faster and illusion ratings were higher when participants administered touch using the plausible right index finger compared with the implausible left index finger.
Perceiving Numbers Affects the Subjective Temporal Midpoint
Authors: Vicario Carmelo Mario
Published: February 2011

Temporal experience can be modulated by several environmental factors. There is increasing evidence that numerical quantity may also influence temporal processes. Here, it is shown that merely looking at numbers causes a bias in a time-bisection task that depends on its magnitude. In the first experiment, a group of healthy subjects was submitted to a time-bisection task in which numerical cues were blocked (blocked design). In the second experiment, a new group of participants performed a time-bisection task in which the previous numbers were all randomly arranged in the same block (intermingled design). Results show that temporal performance is biased when numbers of different magnitude are arranged in an intermingled design. These findings argue for a functional interaction between time and numbers, depending on the implicit extrapolation of the size difference between the displayed numbers rather than on the numerical size itself.
Implementation and outcomes of a zero tolerance of bullying and harassment program
Authors: Meloni Marion , Austin Michelle
Published: February 2011

This case study describes the implementation of a zero tolerance of bullying and harassment program and its outcomes in an ACT hospital. The significance of bullying and harassment within this hospital workplace and its impact became apparent in the 2005 employee satisfaction survey. The results showed low staff satisfaction, a relatively high occurrence of perceived bullying and harassment in the workplace, and a low level of trust by staff in the management of bullying and harassment issues in comparison to the health sector norms. A bullying and harassment program was therefore put in place led by the hospital’s Organisational Development Unit and a zero-tolerance approach towards bullying and harassment was adopted and embraced by the leadership group. After nearly 3 years the program has had a positive impact, including contributing to an overall increase in staff satisfaction and improvements in the bullying and harassment section of the latest employee satisfaction survey. Additional initiatives have been implemented and improved employee satisfaction results are expected in 2010–11.
Bottom-up approach for the fabrication of spin torque nano-oscillators
Authors: Darques M , Dussaux A , Khvalkovskiy A V , De la Torre Medina J , Abreu Araujo F , Guillemet R , Bouzehouane K , Fusil S , Grollier J , Avanesyan G G , Zvezdin K A , Cros V , Piraux L
Published: February 2011

We report on a bottom-up approach for the fabrication of spin-transfer nano-oscillators (STNOs). Porous alumina is used as a template for the growth by electrodeposition of metallic spin valves in series. Under specific magnetic field and injected current conditions, emission of microwave current is detected with frequency in the 1.5 GHz range and linewidth as low as 8 MHz. We find strong indications that the microwave emission is due to spin-transfer-driven vortex oscillations. This technique is promising for the fabrication of dense arrays of STNOs in view of device synchronization.
Quantitative optical extinction-based parametric method for sizing a single core–shell Ag–Ag2O nanoparticle
Authors: Santillán J M J , Scaffardi L B , Schinca D C
Published: February 2011

This paper develops a parametric method for determining the core radius and shell thickness in small silver–silver-oxide core–shell nanoparticles (Nps) based on single particle optical extinction spectroscopy.

The method is based on the study of the relationship between plasmon peak wavelength, full width at half maximum (FWHM) and contrast of the extinction spectra as a function of core radius and shell thickness. This study reveals that plasmon peak wavelength is strongly dependent on shell thickness, whereas FWHM and contrast depend on both variables. These characteristics may be used for establishing an easy and fast stepwise procedure to size core–shell NPs from single particle absorption spectrum. The importance of the method lies in the possibility of monitoring the growth of the silver-oxide layer around small spherical silver Nps in real time.

Using the electrostatic approximation of Mie theory, core–shell single particle extinction spectra were calculated for a silver particle's core size smaller than about 20 nm and different thicknesses of silver oxide around it. Analysis of the obtained curves shows a very particular characteristic of the plasmon peak of small silver–silver-oxide Nps, expressed in the fact that its position is strongly dependent on oxide thickness and weakly dependent on the core radius. Even a very thin oxide layer shifts the plasmon peak noticeably, enabling plasmon tuning with appropriate shell thickness.

This characteristic, together with the behaviour of FWHM and contrast of the extinction spectra can be combined into a parametric method for sizing both core and shell of single silver Nps in a medium using only optical information. In turn, shell thickness can be related to oxygen content in the Np's surrounding media.

The method proposed is applied to size silver Nps from single particle extinction spectrum. The results are compared with full optical spectrum fitting using the electrostatic approximation in Mie theory. The method may be the basis for developing a plasmonic sensor for O2 concentration based on Ag single NP spectroscopy.
Controllable synthesis and field emission enhancement of Al2O3 coated In2O3 core–shell nanostructures
Authors: Wang Yang , Li Yawei , Yu Ke , Zhu Ziqiang
Published: February 2011

Four types of indium oxide (In2O3) nanostructures were synthesized on Au-catalysed silicon substrate via a VLS method. A rod-like In2O3 nanostructure was chosen to fabricate In2O3–Al2O3 core–shell nanostructures with different shell thicknesses via a two-step method. Core–shell nanostructures with shell thickness of 30 nm are reprocessed by annealing and H2 plasma treating. Field emission (FE) properties of all the samples were measured and compared. It is found that Al2O3 coatings remarkably decrease the effective work function and improve the FE capabilities of In2O3 nanostructures (turn-on field decreases from 1.34 to 1.26 V µm−1, threshold field decreases from 3.60 to 2.64 V µm−1). Annealing and H2 plasma treating can promote the improvement even further (turn-on field 1.23 V µm−1, 1.21 V µm−1 and threshold field 2.50 V µm−1, 2.14 V µm−1, respectively). The FE enhancement is attributed to the electron accumulation in the insulating Al2O3 nanostructure and the electron redistribution at the heterojunction.
Experimental investigation of hydrodynamics of melt layer during laser cutting of steel
Authors: Hirano Koji , Fabbro Remy
Published: February 2011

In a laser cutting process, understanding of the hydrodynamics of melt layer is significant, because it is an important factor which controls the final quality. In this work, we observed the hydrodynamics of melt layer on a kerf front in the case of laser cutting of steel with an inert gas. The observation shows that the melt flow on the kerf front exhibits strong instability, depending on cutting velocity. In the intermediate range of velocities, the flow on the central part of the kerf front is continuous, whereas the flow along the sides is discontinuous. It is first confirmed that the instability in the side flow is the cause of striation initiation from the top part of the kerf. The origin of the instability is discussed in terms of instabilities in thermal dynamics and hydrodynamics. The proposed model shows reasonable agreement with experimental results.