bluuebunny/crossref_metadata_2025 huggingface dataset:
Proliferation and multi-differentiation potentials of human mesenchymal stem cells on thermoresponsive PDMS surfaces grafted with PNIPAAm
Authors: Shi Dongyan , Ma Dan , Dong Feiqing , Zong Chen , Liu Liyue , Shen Dan , Yuan Wenji , Tong Xiangmin , Chen Hengwu , Wang Jinfu
Published: May 2009

The thermo-responsivity of PNIPAAm [poly(N-isopropylcarylamide)]-grafted PDMS [poly(dimethylsiloxane)] surface is a property that could be feasibly used for detaching cells adhered on the surface. We used benzophenone-initiated photopolymerization to graft PNIPAAm on PDMS substrates to construct the PNIPAAm-grafted PDMS surface and this PDMS surface was highly thermo-responsive. hMSCs (human mesenchymal stem cells) were used to analyse the proliferation and multi-differentiation of stem cells on the PNIPAAm-grafted PDMS surface. The results showed that hMSCs could adhere on the PNIPAAm-grafted PDMS surface at 37°C and form cell colonies, and then become fibroblastic. The proliferation potential of hMSCs on the PNIPAAm-grafted PDMS surface was not significantly different from that on a plate surface coated with gelatin. However, as it proved easier to detach cells from the surface, by changing temperature, a higher viability of detached cells could be obtained with the PNIPAAm-grafted PDMS surface, using a temperature shift, compared with a gelatin-coated surface, where cells are detached by treatment with trypsin. hMSCs on the PNIPAAm-grafted PDMS surface were induced into osteoblasts, adipocytes and neurocytes under osteogenic medium, adipogenic medium and neurogenic medium respectively. The PNIPAAm-grafted PDMS surface was favourable for osteogenesis of hMSCs, although the potentials of adipogenesis and neurogenesis of hMSCs on the PNIPAAm-grafted PDMS surface were similar to those on the plate surface coated with gelatin. The above results demonstrate that the PNIPAAm-grafted PDMS surface not only kept the potentials of proliferation and multi-differentiation of hMSCs, but also increased the viability of hMSCs.
Primary edge localized mode filament structure in the National Spherical Torus Experiment
Authors: Maqueda R. J. , Maingi R. ,   NSTX team
Published: May 2009

Edge localized modes (ELMs) are routinely seen in the National Spherical Torus Experiment (NSTX) [M. Ono, Nucl. Fusion 40, 557 (2000)]. These unstable modes give rise to plasma filaments that burst radially outward during the nonlinear phase of the instability, moving across flux surfaces into the scrape-off layer. Fast-frame visible imaging is used in NSTX to study the evolution and characteristics of the post-ELM filaments. These edge filaments, which are well aligned with the local magnetic field, are seen to evolve from a perturbation of the edge that within 40–50 μs develops into the relatively high density/temperature primary filaments. The distribution of primary filaments in toroidal angle is seen to agree with a random model with moderate average toroidal mode numbers. At the same time, gas puff imaging shows that the perturbation of the edge leading to the burst of the ELM into the scrape-off layer is characterized by a broadband increase in fluctuations at much smaller poloidal wavelengths (λpol∼2–12 cm). These two measurements suggest that early development of turbulence may play a role in the development of primary ELM filamentation.
Quantum mechanics of Proca fields
Authors: Zamani Farhad , Mostafazadeh Ali
Published: May 2009

We construct the most general physically admissible positive-definite inner product on the space of Proca fields. Up to a trivial scaling this defines a five-parameter family of Lorentz invariant inner products that we use to construct a genuine Hilbert space for the quantum mechanics of Proca fields. If we identify the generator of time translations with the Hamiltonian, we obtain a unitary quantum system that describes first-quantized Proca fields and does not involve the conventional restriction to the positive-frequency fields. We provide a rather comprehensive analysis of this system. In particular, we examine the conserved current density responsible for the conservation of the probabilities, explore the global gauge symmetry underlying the conservation of the probabilities, obtain a probability current density, construct position, momentum, helicity, spin, and angular momentum operators, and determine the localized Proca fields. We also compute the generalized parity (P), generalized time-reversal (T), and generalized charge or chirality (C) operators for this system and offer a physical interpretation for its PT-, C-, and CPT-symmetries.
Spherical nanoindentation and Vickers microhardness study of the deformation of poled BaTiO3 single crystals
Authors: Buchs R. , Basu S. , Elshrief O. A. , Coward R. , Barsoum M. W.
Published: May 2009

In this work, Vickers microhardness and spherical nanoindentation (NI) experiments—with hemispherical radii, R, of 13.5, 5, and 1.4μm—were used to explore the room temperature deformation behavior of poled barium titanate (BaTiO3) single crystals with two orientations: (001) and (110). At 209±11 and 193±11GPa, Young’s moduli of the (001) and (110) surfaces, respectively, were comparable. The (001) surface deforms elastically, before a pop-in event, followed by a strain-hardening regime. The pop-in stresses are stochastic in nature and can be described by Weibull statistics. The (110) surface deforms elastically, then plastically at lower stresses, before cracks are initiated, beyond which the strain-hardening regime is almost identical to that of the (001) surface. This three-regime behavior of the (110) surface was confirmed by postindentation scanning electron microscope micrographs. This work confirms that the room temperature deformation of single crystal BaTiO3 occurs by glide on the {110} slip planes that are also the cleavage planes. Furthermore fully reversible reproducible stress/strain loops were observed and attributed to the formation and annihilation of fully reversible dislocation loops, whose threshold stresses were a function of the domain size that forms under the various indenters. The domain sizes appear to scale with R and are believed to be responsible for the NI size effect observed.
Dipole induced anomalous S-shape I-V curves in polymer solar cells
Authors: Kumar Ankit , Sista Srinivas , Yang Yang
Published: May 2009

A kink is sometimes seen in the I-V curves for organic solar cells. In literature charge blocking has been speculated to be responsible for such kind of anomalous features. In this manuscript, we use poly(3-hexylthiophene):[6, 6]-phenyl-C61-butyric acid methyl ester as our model polymer system and investigate different device structures using ultraviolet photoelectron spectroscopy as our primary tool to investigate the reason for this S-shaped kink. We attribute this anomalous feature to the presence of strong interface dipoles. We further propose a model based on the standard set of Poisson equation, continuity equation, and current density equations including both drift and diffusion components.
Strategy and enhanced temperature determination in a laser heated diamond anvil cell
Authors: Deemyad Shanti , Papathanassiou Anthony N. , Silvera Isaac F.
Published: May 2009

We show that a strategy for increased accuracy in temperature determination by optical pyrometry when the wavelength dependence of the emissivity is unknown is to measure the spectral irradiance at short wavelengths. We then introduce an improved method of determining the temperature in laser heated diamond anvil cells. In general a blackbody source is used to determine the optical transfer function required for determining the blackbody curve. By using the thermal radiation of a heated absorber at ambient pressure and known temperature, uncertainties in the temperature determination caused by the wavelength dependence of the emissivity of the heated absorber can be eliminated. Temperature determination reduces to a one-parameter fit to the blackbody curve rather than the usual two parameters (emissivity and temperature), leading to increased precision and accuracy.
A partial equilibrium theory for liquids bonded to immobile solids
Authors: Searcy Alan W. , Beruto Dario T. , Barberis Fabrizio
Published: May 2009

In order to obtain consistency with the force balance theory of Young and Laplace, which quantitatively predicts the height of capillary rise from the contact angles of drops on solid surfaces, Gibbs made chemical potentials in interface functions of the integral interface free energies. We cite evidence that equilibrium chemical potentials in one-component systems are identical at interfaces to equilibrium chemical potentials in bulk phases. We evaluate two postulates. (1) Partial free energies of liquids at an interface with a solid are functions of the strength and range of attractive fields outside solid phase boundaries. (2) At equilibrium, the chemical potentials in all interfaces of a one-component liquid equal the chemical potential in its interior when the liquid is bonded to one or more immiscible solids. These postulates yield equations for partial equilibrium (PE) states of drops, films, and liquids. The PE equations yield the same prediction of the height of a meniscus from the contact angle of drops as does Young–Laplace theory and also the same dependence of the volume of capillary condensate on vapor pressure as does the Kelvin equation. But our measurements of the contact angles of water on glass and Teflon and between their close-spaced surfaces contradict the YL supposition that meniscus angles are the same as angles of drops on glass and Teflon surfaces and support the PE postulate that attraction by the external fields of solids, not meniscus curvature, is responsible for capillary rise. We use published data to illustrate the validity of the PE conclusion that divergence or convergence at the saturation pressure of a parent liquid depends on whether or not the attractive field of a solid surface imparts to the liquid more than twice the energy required to create two liquid-vapor interfaces. For divergent water films on quartz, the PE equation provides a quantitative fit to experimental data for films of any thickness greater than 1.5 nm. No previous theory has accomplished that. In an appendix, we illustrate applications of PE theory to evaluating the complex interactions between inherently reversible chemical diffusion and inherently irreversible forces introduced by strains.
Numerical errors in the computation of subfilter scalar variance in large eddy simulations
Authors: Kaul C. M. , Raman V. , Balarac G. , Pitsch H.
Published: May 2009

Subfilter scalar variance is a key quantity for scalar mixing at the small scales of a turbulent flow and thus plays a crucial role in large eddy simulation of combustion. While prior studies have mainly focused on the physical aspects of modeling subfilter variance, the current work discusses variance models in conjunction with the numerical errors due to their implementation using finite-difference methods. A priori tests on data from direct numerical simulation of homogeneous turbulence are performed to evaluate the numerical implications of specific model forms. Like other subfilter quantities, such as kinetic energy, subfilter variance can be modeled according to one of two general methodologies. In the first of these, an algebraic equation relating the variance to gradients of the filtered scalar field is coupled with a dynamic procedure for coefficient estimation. Although finite-difference methods substantially underpredict the gradient of the filtered scalar field, the dynamic method is shown to mitigate this error through overestimation of the model coefficient. The second group of models utilizes a transport equation for the subfilter variance itself or for the second moment of the scalar. Here, it is shown that the model formulation based on the variance transport equation is consistently biased toward underprediction of the subfilter variance. The numerical issues in the variance transport equation stem from discrete approximations to chain-rule manipulations used to derive convection, diffusion, and production terms associated with the square of the filtered scalar. These approximations can be avoided by solving the equation for the second moment of the scalar, suggesting that model’s numerical superiority.
Electronic paramagnetic resonance power saturation of wooden samples
Authors: Brai Maria , Longo Anna , Maccotta Antonella , Marrale Maurizio
Published: May 2009

The deterioration of wood used for artifacts of artistic interest involves the production of different free radicals from the macromolecules of the wooden matrix (cellulose, lignin, and hemicellulose). Among the techniques able to provide information about these free radicals, the contribution of electronic paramagnetic resonance (EPR) can be very valuable. In this paper, the study of EPR signals (with g≈2) of both modern and ancient wooden taxa was undertaken in order to analyze some features of the free radicals in natural wood. In particular, we have studied the microwave power saturation behaviors of seasoned wooden samples from ten species, and we have found remarkable differences between softwoods and hardwoods. These differences can be correlated to dissimilarities in the relaxation times T1 and T2 attributable to the different microscopic structures of the two trees’ categories. The method has been also applied to ancient woods belonging to works of art in order to assess the conservation state of these artifacts. The analysis of the saturation curves has been found to be sensitive to the wood decay state. Indeed the deterioration process of the wooden matrix involves a variation of the relaxation times; this could be ascribed to both possible structure modifications and to concentration increments of the free radicals inside ancient woods due to decay induced by natural (biological, chemical, and physical) agents. This analysis method seems to be promising for the characterization of the wooden decay state and, therefore, it could provide valuable diagnostic indications which are necessary for the restoration and conservation of many artifact of historical-artistic-archaeological interest.
Direct measurement of interfilament resistance in Nb3Sn strands
Authors: Corato V. , Muzzi L. , Vetrella U. Besi , della Corte A.
Published: May 2009

In modeling the properties of superconducting multifilamentary strands, transverse resistivity plays a crucial role in the definition of the coupling losses in ac regime, as well as of the current transfer length, that affects the transport properties of Nb3Sn wires subject to bending strain. We present the first direct measurement of the interfilament transverse resistance in superconducting strands from room temperature to 4.2 K. Results have been compared to the transverse resistance of a sample on which the outer copper stabilization layer has been removed by chemical etching, obtaining interesting indication on the preferential current paths within the wire cross section. An excellent agreement between experimental data and theoretical models has been found in describing the whole strand, while improvements are required in modeling the filamentary region alone.
Theoretical quest for photoconversion molecules having opposite directions of the electric dipole moment in S and S1 states
Authors: Mori Hirotoshi , Takeshita Kouichi , Miyoshi Eisaku , Ohta Nobuhiro
Published: May 2009

Ab initio calculations at the level of CASPT2 with Dunning’s correlation consistent cc-pVXZ (X=D, T, Q) basis sets have been carried out for pyrimidine, quinoxaline, phthalazine, and their substituted compounds to find candidates that show a change in the direction of the electric dipole moment for the S0→S1 transition. The present calculations reveal that 6,7-difluorophthalazine and 6,7-dichlorophthalazine are strong candidates having a large and clear change in the direction of the electric dipole moment on the S0→S1 transition.
A low-temperature high resolution scanning tunneling microscope with a three-dimensional magnetic vector field operating in ultrahigh vacuum
Authors: Mashoff T. , Pratzer M. , Morgenstern M.
Published: May 2009

We present a low-temperature ultrahigh vacuum (UHV) scanning tunneling microscope setup with a combination of a superconducting solenoid coil and two split-pair magnets, providing a rotatable magnetic field up to 500 mT applicable in all spatial directions. An absolute field maximum of B=7 T(3 T) can be applied perpendicular (parallel) to the sample surface. The instrument is operated at a temperature of 4.8 K. Topographic and spectroscopic measurements on tungsten carbide and indium antimonide revealed a z-noise of 300 fmpp, which barely changes in magnetic field. The microscope is equipped with a tip exchange mechanism and a lateral sample positioning stage, which allows exact positioning of the tip with an accuracy of 5 μm prior to the measurement. Additional contacts to the sample holder allow, e.g., the application of an additional gate voltage. The UHV part of the system contains versatile possibilities of in situ sample and tip preparation as well as low-energy electron diffraction and Auger analysis.
An optimized optical system for backlit imaging
Authors: Ghandhi J. B. , Heim D. M.
Published: May 2009

An optimized optical system for back-illuminated imaging was developed and was applied to automotive-type fuel injectors; the system provides significantly higher light collection efficiency than standard flood illumination. An engineered diffuser is used to distribute an extended light source through a controlled range of angles, and a field lens is used to redirect the light to the camera. A ray tracing analysis provides the required source size and diffuser angle to ensure that the necessary range of ray angles is included to allow fully diffuse imaging. Direct comparison with a flood illumination system showed that the collection efficiency increased by more than two orders of magnitude without any degradation of image quality.
Influence of octahedral tilting on the microwave dielectric properties of A3LaNb3O12 hexagonal perovskites (A=Ba, Sr)
Authors: Rawal Ritesh , McQueen Andrew J. , Gillie Lisa J. , Hyatt Neil C. , McCabe Emma E. , Samara Kumaravinothan , Alford Neil McN. , Feteira Antonio , Reaney Ian M. , Sinclair Derek C.
Published: May 2009

Rietveld refinement of room temperature (RT) neutron diffraction (ND) data reveals 12R-type hexagonal perovskites Ba3LaNb3O12 (BLN) and Sr3LaNb3O12 (SLN) to adopt space group R3¯ with tilted NbO6 octahedra. The presence of an octahedral tilt transition (Ttilt) at 465 K in BLN from R3¯ to R3¯m is proposed from a combination of high temperature ND data and fixed frequency permittivity measurements. Ttilt is estimated to be much higher at ∼720 K for SLN. The large difference in the RT temperature coefficient of the resonant frequency (τf), −100 ppm/K for BLN compared to −5 ppm/K for SLN, is attributed to the closer proximity of Ttilt to RT for BLN. τf in these 12R-type hexagonal perovskites can therefore be tuned by controlling the tolerance factor and therefore Ttilt in a manner similar to that used for many Ba- and Sr-based 3C-type ABO3 perovskites.
Revisiting the finite temperature string method for the calculation of reaction tubes and free energies
Authors: Vanden-Eijnden Eric , Venturoli Maddalena
Published: May 2009

An improved and simplified version of the finite temperature string (FTS) method [W. E, W. Ren, and E. Vanden-Eijnden, J. Phys. Chem. B 109, 6688 (2005)] is proposed. Like the original approach, the new method is a scheme to calculate the principal curves associated with the Boltzmann–Gibbs probability distribution of the system, i.e., the curves which are such that their intersection with the hyperplanes perpendicular to themselves coincides with the expected position of the system in these planes (where perpendicular is understood with respect to the appropriate metric). Unlike more standard paths such as the minimum energy path or the minimum free energy path, the location of the principal curve depends on global features of the energy or the free energy landscapes and thereby may remain appropriate in situations where the landscape is rough on the thermal energy scale and/or entropic effects related to the width of the reaction channels matter. Instead of using constrained sampling in hyperplanes as in the original FTS, the new method calculates the principal curve via sampling in the Voronoi tessellation whose generating points are the discretization points along this curve. As shown here, this modification results in greater algorithmic simplicity. As a by-product, it also gives the free energy associated with the Voronoi tessellation. The new method can be applied both in the original Cartesian space of the system or in a set of collective variables. We illustrate FTS on test-case examples and apply it to the study of conformational transitions of the nitrogen regulatory protein C receiver domain using an elastic network model and to the isomerization of solvated alanine dipeptide.
From nanoglasses to bulk massive glasses
Authors: Şopu D. , Albe K. , Ritter Y. , Gleiter H.
Published: May 2009

Molecular dynamics simulations are presented that provide evidence for the existence of diluted interfaces in nanoglasses, which is a class of material that can be synthesized by consolidating glassy nanoparticles. By comparing simulations of a covalently bonded Ge nanoglass and a metallic CuZr nanoglass, we show that the delocalization of the excess free volume initially located within the interfaces depends on the flow strain of the material. Our results suggest that the density distribution within a nanoglass can be controlled by the initial particle size and the annealing conditions. Therefore, nanoglasses represent an alternative route for controlling the properties of glassy materials.
A mechanical approach to mean field spin models
Authors: Genovese Giuseppe , Barra Adriano
Published: May 2009

Inspired by the bridge pioneered by Guerra among statistical mechanics on lattice and analytical mechanics on 1+1 continuous Euclidean space time, we built a self-consistent method to solve for the thermodynamics of mean field models defined on lattice, whose order parameters self-average. We show the whole procedure by analyzing in full detail the simplest test case, namely, the Curie–Weiss model. Further, we report some applications also to models whose order parameters do not self-average by using the Sherrington–Kirkpatrick spin glass as a guide.
Detection of template binding to molecularly imprinted polymers by Raman microspectroscopy
Authors: Kantarovich Keren , Belmont Anne-Sophie , Haupt Karsten , Bar Ilana , Gheber Levi A.
Published: May 2009

We report on sensitive and specific detection and quantification of a template in a molecularly imprinted polymer (MIP) using Raman microspectroscopy. The β-blocking drug S-propranolol and its enantiomer, R-propranolol, were used as target molecules since the selectivity of this MIP is well established and serves as an appropriate validation standard. Specific peaks originating in the template were identified in the Raman spectrum, allowing quantification of bound target molecule. We demonstrate that label-free monitoring can be achieved from volumes as small as 1 μm3 of MIP, based on a single identifying peak.
The hydrogen abstraction reaction H+CH4. I. New analytical potential energy surface based on fitting to ab initio calculations
Authors: Corchado Jose C. , Bravo Jose L. , Espinosa-Garcia Joaquin
Published: May 2009

A new analytical potential energy surface is presented for the reaction of hydrogen abstraction from methane by a hydrogen atom. It is based on an analytical expression proposed by Jordan and Gilbert [J. Chem. Phys. 102, 5669 (1995)], and its fittable parameters were obtained by a multibeginning optimization procedure to reproduce high-level ab initio electronic structure calculations obtained at the CCSD(T)/cc-pVTZ level. The ab initio information employed in the fit includes properties (equilibrium geometries, relative energies, and vibrational frequencies) of the reactants, products, saddle point, points on the reaction path, and points on the reaction swath. No experimental information is used. By comparison with the reference results we show that the resulting surface reproduces well not only the ab initio data used in the fitting but also other thermochemical and kinetic results computed at the same ab initio level, such as equilibrium constants, rate constants, and kinetic isotope effects, which were not used in the fit. In this way we show that the new potential energy surface is correctly fitted and almost as accurate as the CCSD(T)/cc-pVTZ method in describing the kinetics of the reaction. We analyze the limitations of the functional form and the fitting method employed, and suggest some solutions to their drawbacks. In a forthcoming communication, we test the quality of the new surface by comparing its results with experimental values.
Probability distribution function for self-organization of shear flows
Authors: Kim Eun-jin , Liu Han-Li , Anderson Johan
Published: May 2009

The first prediction of the probability distribution function (PDF) of self-organized shear flows is presented in a nonlinear diffusion model where shear flows are generated by a stochastic forcing while diffused by a nonlinear eddy diffusivity. A novel nonperturbative method based on a coherent structure is utilized for the prediction of the strongly intermittent exponential PDF tails of the gradient of shear flows. Numerical simulations using Gaussian forcing not only confirm these predictions but also reveal the significant contribution from the PDF tails with a large population of supercritical gradients. The validity of the nonlinear diffusion model is then examined using a threshold model where eddy diffusivity is given by discontinuous values, elucidating an important role of relative time scales of relaxation and disturbance in the determination of the PDFs.
Confinement effects on diffusiophoretic self-propellers
Authors: Popescu M. N. , Dietrich S. , Oshanin G.
Published: May 2009

We study theoretically the effects of spatial confinement on the phoretic motion of a dissolved particle driven by composition gradients generated by chemical reactions of their solvent, which are active only on certain parts of the particle surface. We show that the presence of confining walls increases in a similar way both the composition gradients and the viscous friction, and the overall result of these competing effects is an increase in the phoretic velocity of the particle. For the case of steric repulsion only between the particle and the product molecules of the chemical reactions, the absolute value of the velocity remains nonetheless rather small.
Auger recombination rates in nitrides from first principles
Authors: Delaney Kris T. , Rinke Patrick , Van de Walle Chris G.
Published: May 2009

We report Auger recombination rates for wurtzite InGaN calculated from first-principles density-functional and many-body-perturbation theory. Two different mechanisms are examined—inter- and intra-band recombination—that affect different parts of the emission spectrum. In the blue to green spectral region and at room temperature the Auger coefficient can be as large as 2×10−30 cm6 s−1; in the infrared it is even larger. Since Auger recombination scales with the cubic power of the free-carrier concentration it becomes an important nonradiative loss mechanism at high current densities. Our results indicate that Auger recombination may be responsible for the loss of quantum efficiency that affects InGaN-based light emitters.
Solution-processed flexible organic transistors showing very-low subthreshold slope with a bilayer polymeric dielectric on plastic
Authors: Liu Zihong , Oh Joon Hak , Roberts Mark E. , Wei Peng , Paul Bipul C. , Okajima Masaki , Nishi Yoshio , Bao Zhenan
Published: May 2009

We demonstrate low-voltage, solution-processed organic transistors on rough plastic substrates with a carrier mobility over 0.2 cm2/V s, a turn-on voltage of near 0 V, and a record low subthreshold slope of ∼80 mV/decade in ambient conditions. These exceptional characteristics are attributed to (1) a device stacking architecture with a conducting polymeric gate and a double layered dielectric composed of low-temperature cross-linked poly(4-vinylphenol), (2) a low interface trap density achieved by modifying the dielectric surface with a phenyl-terminated self-assembled monolayer from 4-phenylbutyltrichlorosilane, and (3) controlled crystallization of a small-molecule organic semiconductor film with favorable charge transport microstructure and a low bulk trap density as deposited by an optimized solution-shearing process. The device performance under different operating voltages was also examined and discussed.
Electroelastic optical fiber positioning with submicrometer accuracy: Model and experiment
Authors: Kofod Guggi , Mc Carthy Denis N. , Krissler Jan , Lang Günter , Jordan Grace
Published: May 2009

We present accurate electromechanical measurements on a balanced push-pull dielectric elastomer actuator, demonstrating submicrometer accurate position control. An analytical model based on a simplified pure-shear dielectric elastomer film with prestretch is found to capture the voltage-displacement behavior, with reduced output due to the boundary conditions. Two complementary experiments show that actuation coefficients of 0.5–1 nm/V2 are obtainable with the demonstrated device, enabling motion control with submicrometer accuracy in a voltage range below 200 V.
Generation of coherent terahertz radiation in ultrafast laser-gas interactions
Authors: Kim Ki-Yong
Published: May 2009

The generation of intense terahertz radiation in ultrafast laser-gas interactions is studied on a basis of transient electron current model. When an ultrashort pulse laser’s fundamental and its second harmonic fields are mixed to ionize a gas, a nonvanishing, directional photoelectron current can be produced, which simultaneously emits terahertz radiation in the far field. Here, the generation mechanism is examined with an analytic derivation and numerical simulations, in which tunneling ionization and subsequent electron motion in the combined laser field play a key role. In the simulations, three types of laser-gas interactions are considered: (i) mixing the fundamental and its second harmonic fields, (ii) mixing nonharmonic, two-color fields, and (iii) focusing single-color, few-cycle pulses. In these interactions, terahertz generation and other nonlinear effects driven by the transient current are investigated. In particular, anticorrelation between terahertz and second (or third) harmonic generation is observed and analyzed.
Simulation of the enhanced Curie temperature in Mn5Ge3Cx compounds
Authors: Slipukhina I. , Arras E. , Mavropoulos Ph. , Pochet P.
Published: May 2009

Mn 5 Ge 3 C x films with x≥0.5 were experimentally shown to exhibit a strongly enhanced Curie temperature TC compared to Mn5Ge3. In this letter we present the results of our first principles calculations within Green’s function approach, focusing on the effect of carbon doping on the electronic and magnetic properties of the Mn5Ge3. The calculated exchange coupling constants revealed an enhancement of the ferromagnetic Mn–Mn interactions mediated by carbon. The essentially increased TC in Mn5Ge3C is well reproduced in our Monte Carlo simulations and together with the decrease of the total magnetization is found to be predominantly of an electronic nature.
Crystal structure and electronic and thermal properties of TbFeAsO0.85
Authors: Kaurav N. , Chung Y. T. , Kuo Y. K. , Liu R. S. , Chan T. S. , Chen J. M. , Lee J.-F. , Sheu H.-S. , Wang X. L. , Dou S. X. , Lee S. I. , Shi Y. G. , Belik A. A. , Yamaura K. , Takayama-Muromachi E.
Published: May 2009

The crystal structure and the electronic and thermal properties of a high-quality polycrystalline TbFeAsO0.85 sample made by a high-pressure technique are investigated. The crystal structure, as determined by synchrotron X-ray powder diffraction, possesses a tetragonal unit cell (space group: P4/nmm) with lattice parameters of a=b=3.8851 Å and c=8.3630 Å. In order to elucidate the electronic structure and oxidation states of corresponding elements, X-ray absorption near-edge structure (XANES) spectra are presented. The XANES spectra confirm that the oxidation states of Fe, As, and Tb in the TbFeAsO0.85 sample are ∼Fe2+, ∼As3−, and ∼Tb3+, respectively, which are consistent with the previously reported band structure calculations. The n-type character of the charge carriers as revealed from XANES spectra is corroborated by the negative sign of the Seebeck coefficient (S) in the present study. The heat capacity (CP) measurement shows an anomaly in the vicinity of the superconducting transition temperature (Tc=42.5 K), which confirms the bulk nature of the superconductivity in this material.
Enhanced efficiency and reduced roll-off in blue and white phosphorescent organic light-emitting diodes with a mixed host structure
Authors: Lee Jonghee , Lee Jeong-Ik , Lee Jun Yeob , Chu Hye Yong
Published: May 2009

We report a significant enhancement and a reduced efficiency roll-off in blue and white phosphorescent organic light-emitting diodes (PHOLEDs) based on a mixed host structure. The combination of a hole-transport-type host and an electron-transport-type host as a mixed host emissive layer resulted in an effective charge carrier injection and distribution of the recombination zone, and therefore highly efficient blue PHOLEDs with peak external quantum and power efficiencies of 21.6% and 44.9 lm/W were achieved. Moreover, white PHOLEDs with a mixed host structure showed a power efficiency of 37 lm/W, which is over four times higher than 8.7 lm/W in a single host structure device at a luminance of 1000 cd/m2.
Transformation of silver nanospheres embedded in glass to nanodisks using circularly polarized femtosecond pulses
Authors: Stalmashonak A. , Graener H. , Seifert G.
Published: May 2009

We prove by help of optical microspectroscopy that spherical Ag nanoparticles embedded in glass can be transformed to oblate (disklike) shapes by irradiation with circularly polarized femtosecond laser pulses. The symmetry axis (short axis) of the oblate spheroids produced by this method is oriented along the laser propagation direction. This observation also confirms the assumption that the mechanism of shape transformation starts with directed photoionization of nanoparticles induced by laser irradiation in combination with the electric field enhancement at the particle-glass interface.
Optical properties of switchable mirrors based on magnesium-calcium alloy thin films
Authors: Yamada Y. , Bao S. , Tajima K. , Okada M. , Yoshimura K.
Published: May 2009

Switchable mirrors based on magnesium-calcium alloy thin films were prepared using a direct-current magnetron sputtering method and their gasochromic properties have been investigated. Pd-capped Mg1−zCaz (0.04<z<0.20) films showed excellent switchable mirror properties. The visible transmittance in the transparent state increased with Ca composition, z, and after reaching a maximum of ∼46% at z∼0.06, the transmittance decreased gradually with increasing Ca composition. In the transparent state with z<0.08, the optical transmittance spectra of these switchable mirrors were fairly flat in the visible range and their color looked completely neutral. The achromatic properties with high visible transmittance may be because the hydrogenated switchable mirrors are composed of MgH2 and MgCaH3.72 with grayish neutral color appearance.
Tip-enhanced two-photon excited fluorescence microscopy with a silicon tip
Authors: Hayazawa Norihiko , Furusawa Kentaro , Taguchi Atsushi , Kawata Satoshi , Abe Hiroshi
Published: May 2009

The use of silicon tips and nonlinear response of materials can be used in overcoming the two major drawbacks of the near-field fluorescence detection which are quenching and background signals. Silicon tips allow for quenching free detection while the two-photon excitation scheme selectively enhances the scattering rate near the tip apex, so that the fluorescence signal from this tiny volume outweighs the one from diffraction limited focused spot. We demonstrate tip-enhanced two-photon excited fluorescence microscopy using a commercially available silicon cantilever tip, and show that individual quantum dots can be clearly resolved with spatial separation of 70 nm.
Modeling and fabrication of electrically tunable quantum dot intersubband devices
Authors: Wu Wei , Dey Dibyendu , Memis Omer G. , Mohseni Hooman
Published: May 2009

We propose an idea of forming quantum dot intersubband transition devices based on lateral electrical confinement on quantum wells. Numerical simulations show that the energy level separation in the structure can be as large as about 50 meV, and with different electric field, the energy levels can be tuned. We also demonstrate the fabrication of a large number of field-induced quantum dots by our super lens lithography technique. We achieved uniform arrays of contacts that are about 200 nm using a conventional UV source of λ∼400 nm.
Effect of Ka-band microwave on the spin dynamics of electrons in a GaAs/Al0.35Ga0.65As heterostructure
Authors: Luo Haihui , Qian Xuan , Gu Xiaofang , Ji Yang , Umansky Vladimir
Published: May 2009

We report experimental results of the effect of Ka-band microwave on the spin dynamics of electrons in a two-dimensional electron system (2DES) in a GaAs/Al0.35Ga0.65As heterostructure via time-resolved Kerr rotation measurements. While the microwave reduces the transverse spin lifetime of electrons in the bulk GaAs, it significantly increases that in the 2DES, from 745 to 1213 ps, when its frequency is close to the Zeeman splitting of the electrons in the magnetic field. Such a microwave-enhanced spin lifetime is ascribed to the microwave-induced electron scattering which leads to a “motional narrowing” of spins via D’yakonov–Perel’ mechanism.
Electrochemical fabrication and magnetization properties of CoCrPt nanowires and nanotubes
Authors: Shamaila S. , Liu D. P. , Sharif R. , Chen J. Y. , Liu H. R. , Han X. F.
Published: May 2009

Magnetization properties of CoCrPt alloy nanocylinders (nanowires and nanotubes) fabricated by low cost electrodeposition method have been investigated. Angular dependence of coercivity depicts curling mode of magnetization reversal process for CoCrPt nanowires (NWs) while for nanotubes (NTs) there is a transition from curling to coherent mode as a function of field angle. The effective anisotropy during reversal process is determined from a competition between the magnetostatic interactions, surface effects, and shape anisotropy in NTs while in NWs shape anisotropy is the dominant anisotropy. Furthermore, magnetization and remanence curves describe that the surface effects and dipolar coupling are increased in NTs as compared to the NWs due to their geometry. These results depict that the magnetization properties are influenced by the geometry of nanocylinders, which can become good candidate for ultrahigh density magnetic recording media.
Centred Egocentric, Decentred Egocentric, and Allocentric Spatial Representations in the Peripersonal Space of Congenital Total Blindness
Authors: Coluccia Emanuele , Mammarella Irene C , Cornoldi Cesare
Published: May 2009

The distinction between different spatial representations in the peripersonal space was examined in two experiments by requiring sighted blindfolded and blind participants to remember the locations of objects haptically explored. In experiment 1, object relocation took place from either the same position as learning—with the same (centred egocentric condition) or 90°-rotated (rotated egocentric condition) object array—or from a position different from the learning position (allocentric condition). Results revealed that, in both sighted and blind people, distance errors were higher in the allocentric and rotated conditions than in the centred egocentric condition, and that blind participants made more distance errors than sighted subjects only in the allocentric condition. Experiment 2 repeated rotated egocentric and allocentric conditions, while the centred egocentric condition was replaced by a decentred egocentric condition in which object relocation took place from the same position as learning (egocentric) but started from a decentred point. The decentred egocentric condition was found to remain significantly different from the rotated condition, but not from the allocentric condition. Moreover, blind participants performed less well in the allocentric condition, but were specifically impaired. Overall, our results confirm that different types of spatial constraints and representations, including the decentred egocentric one, can be distinguished in the peripersonal space and that blind people are as efficient as sighted in the egocentric and rotated conditions, but they encounter difficulties in recalling locations also in the peripersonal space, especially when an allocentric condition is required.
Philosophy, Perception, and Neuroscience
Authors: Smythies John
Published: May 2009

This paper presents the results of some recent experiments in neuroscience and perceptual science that reveal the role of virtual reality in normal visual perception, and the use of television technology by the visual brain. This involves particularly the cholinergic system in the forebrain. This research throws new light on the nature of perception and the relation of phenomenal consciousness and its brain. It is directly relevant to criticisms by certain analytical philosophers of aspects of neuroscience relating to these matters. Particular attention is paid to their support for Naive Realism.
The Effect of Visuo-Spatial Organisation in Recognition-Memory Tasks
Authors: Petrini Laura , Hennings Kristian , Arendt-Nielsen Lars
Published: May 2009

We investigated whether recognition memory benefits when stimuli are organised in a visuo-spatial array. Three different memory tasks were compared: (a) verbal task (what); (b) spatial task (where); (c) combination task, where both verbal and spatial informations were combined together (what/where). We hypothesised that when visual stimuli are organised in a spatial array the recognition is better. Recognition memory was assessed by quantifying the speed of correct responses and the total number of correct responses in a group of male volunteers ( N = 20). Subjects' task was to recognise a stimulus probe from sequences (one versus three) of stimuli. All stimuli appeared randomly in one of nine locations on a 3 × 3 grid. The results show that subjects were faster and more accurate when they had to recognise only spatial information (where) than when they had to recognise verbal information (what) or the combination of both verbal and spatial information (what/where). Additionally, when the stimuli were presented in a spatial array there were benefits for the spatial task, whilst verbal and combination tasks were unaffected. Additionally, asymmetry between left and right hemifields has been found. These findings are discussed with regard to different memory processes that operate independently.
Cultural scripts for multiple and concurrent partnerships in southern Africa: why HIV prevention needs anthropology
Authors: Leclerc-Madlala Suzanne
Published: May 2009

Background: Multiple and concurrent sexual partnerships have been identified as southern Africa’s key behavioural driver of HIV, resulting in calls to make partner reduction programming central to an intensified HIV prevention focus. Various efforts are currently being made in the region in response to this call. Such efforts will likely have as limited success as past prevention efforts if the cultural milieu in which sexual partnering practices are located and reproduced remains poorly understood, unaccounted for, and unaddressed in prevention programming. Methods: Focussed ethnographic discussions were held between October 2007 and November 2008 with 228 members of southern African non-government organisations representing seven countries. Discussions formed part of follow-up activities to a high level regional meeting and were aimed at exploring contextual factors in HIV transmission, most especially the role of culture in relation to multiple and concurrent partnerships. Results: Common patterns in cultural scripts for the performance of sexuality were discernable. Several predominant scripts that tend to affirm and lend cultural legitimacy to multiple and concurrent partnering were identified, discussed and analysed. Conclusion: Effectuating change at the level of cultural scripting to discourage multiple and concurrent partnerships is required for sustainable long-term protection of people and communities against HIV. The success of partner reduction programs will be largely determined by the extent to which they are informed by anthropological knowledge and work with cultural logics to allow people to envision how they can transform obstacles into support for risk reduction.
The impact of immigration on the burden of HIV infection in Victoria, Australia
Authors: Horyniak Danielle , Stoové Mark , Yohannes Keflemariam , Breschkin Alan , Carter Tom , Hatch Beth , Tomnay Jane , Hellard Margaret , Guy Rebecca
Published: May 2009

Background: Accurate estimates of the number of people diagnosed and living with HIV infection within a health jurisdiction provide the basis for planning of clinical service provision. Case reporting of new diagnoses does not account for inwards and outwards migration of people with HIV infection, thereby providing an inaccurate basis for planning. Methods: The Victorian passive surveillance system records all cases of HIV diagnosed in Victoria and distinguishes between new Victorian diagnoses (cases whose first ever HIV diagnosis was in Victoria) and cases previously diagnosed interstate and overseas. In order to gain an understanding of the impact of population movement on the burden of HIV infection in Victoria, we compared the characteristics of people first diagnosed in Victoria with those previously diagnosed elsewhere. Results: Between 1994 and 2007 there were 3111 HIV notifications in Victoria, including 212 (7%) ‘interstate diagnoses’ and 124 (4%) ‘overseas diagnoses’. The proportion of cases diagnosed outside Victoria increased from 6.4% between 1994 and 2000 to 13.8% between 2001 and 2007. Compared with ‘new diagnoses’, a larger proportion of ‘interstate diagnoses’ reported male-to-male sex as their HIV exposure, were Australian-born and diagnosed in Victoria at a general practice specialising in gay men’s health. Compared with ‘new diagnoses’, a larger proportion of ‘overseas diagnoses’ were female, reported heterosexual contact as their HIV exposure, and were diagnosed in Victoria at a sexual health clinic. Conclusions: Between 1994 and 2007 more than 10% of Victorian HIV diagnoses were among people previously diagnosed elsewhere. Characteristics of both interstate and overseas diagnoses differed from new diagnoses. Service planning needs to be responsive to the characteristics of people moving to Victoria with previously diagnosed HIV infection.
Arteriovenous malformation as a consequence of a scar pregnancy
Authors: RYGH ASTRID B. , GREVE OLE J. , FJETLAND LARS , BERLAND JANNICKE M. , EGGEBØ TORBJØRN M.
Published: May 2009

A scar pregnancy is an ectopic pregnancy implanted in a previous lower segment cesarean scar, and the incidence of this complication may be expected to rise along with increasing cesarean section rates. Arteriovenous malformation of the uterus may be congenital, associated with early pregnancy loss, trophoblastic disease, or surgical procedures. We describe a case of uterine arteriovenous malformation as a consequence of a scar pregnancy, complicated by recurrent, serious bleeding. The condition was diagnosed using three‐dimensional ultrasound with color Doppler and magnetic resonance imaging and appears not to have been described before. Selective embolization was performed, but eventually surgical intervention with resection of the affected uterine segment was necessary, and the patient recovered. The diagnosis was confirmed by pathologic‐anatomical diagnosis showing trophoblastic cells in the resected area. Because of collateral formation, non‐surgical options may be limited and not successful.