bluuebunny/crossref_metadata_2025_split huggingface dataset:
Full band Monte Carlo study of ballistic effects in nanometer‐scaled strained P channel Double Gate MOSFETs
Authors: Huet K. , Chassat C. , Nguyen D.‐P. , Galdin‐Retailleau S. , Bournel A. , Dollfus P. 
Published: November 2007

AbstractBallistic transport in a 20 nm long P type Double Gate (DG) MOSFET structure is studied using a Monte Carlo (MC) technique. Hole transport being dominated by the strong anisotropy of the valence dispersion relation, the full bandstructure obtained by a 30 band k ·p calculation is used. The valence bandstructure is shown to be highly anisotropic. The deformation induced by strain is different whether biaxial tensile or compressive strain is applied. This will have an influence on the final density of states (DOS) and scattering rates, closely related to carrier mobility. In the on‐state of the transistor, we demonstrate the out‐of‐equilibrium nature of carrier transport in the entire channel. Microscopic quantities analysis with strain shows the influence of scattering, bandstructure change and ballistic effects on hole transport. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonequilibrium transport properties for a three‐site quantum wire model
Authors: Zheng Yangdong , Mizuta Hiroshi , Oda Shunri 
Published: November 2007

AbstractWe derive nonequilibrium electronic transport properties for a three‐site quantum wire model within Hartree‐Fock approximation making use of Keldysh formalism. Some rigorous formulas are provided for direct calculations when Coulomb repulsion is present. According to numerical calculations using these formulas, we investigate the conductance, transport current, and on site electronic charges of the wire in some special occasions. In noninteracting case, when site‐site couplings in the wire are tougher than wire‐electrode couplings, the resonant tunneling transport takes place and the phenomenon of conductance quantization can be easily observed. The transport properties of up‐spin are identical with those of down‐spin. When the Coulomb interaction is present, the line shapes of transport characteristics are changed because of electron‐electron repulsions. With the increase of U, the Coulomb blockade and metal‐insulator transition (Mott transition) phenomena are obvious if the self‐energies Γ have small values compared with U. The transport properties of the up‐spin also become quite different from those of the down‐spin indicating that the spin polarization takes place in the wire. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Resonant tunneling through a dilute nitride quantum well
Authors: Mori N. , Allison G. , Patanè A. , Eaves L. 
Published: November 2007

AbstractWe have developed a theory for resonant tunneling through a dilute nitride quantum well in the presence of a tilted magnetic field. We show that magneto‐tunneling spectroscopy provides a novel means of probing the scattering potential due to randomly distributed nitrogen impurities. This technique can be extended to probe other types and sources of disordered potential. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐field characteristics of ZnO and ZnO/ZnMgO heterostructures
Authors: Sasa S. , Hayafuji T. , Kawasaki M. , Nakashima A. , Koike K. , Yano M. , Inoue M. 
Published: November 2007

AbstractHigh‐field transport properties of ZnO and ZnO/ZnMgO heterostructures were investigated. Three types of structures, a 500‐nm‐thick ZnO and ZnO/ZnMgO single‐hetero‐ (SH) and single‐quantum‐well (SQW) structures containing a thin (10‐20 nm) ZnO channel layer, were grown on a‐plane sapphire substrates by plasma‐assisted molecular beam epitaxy. The dc and pulsed I ‐V characteristics were measured at room temperature by using two‐terminal devices with the source‐to‐drain spacing of 2‐8 μm. By using the pulsed I ‐V measurements, the velocity‐field (v ‐E) characteristics were observed for electric field up to about 100 kV/cm. The v‐E characteris‐ tics revealed that no velocity saturation was observed until the velocity reached at a value of 7.6 × 106 cm/s for the thick ZnO structure while a rapid reduction of the mobility thus a saturation of the velocity at a relatively low electric field was observed for the SH structure. The reduction of the mobility was even pronounced for SQW structure. The velocity saturation might be due to the interplay between the inhomogeneities and polarization in the heterostructures. To our knowledge, this is the first experimental report on the high‐field characteristics in ZnO and ZnO/ZnMgO heterostructures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation of highly circularly polarized light from uniform InAs/GaAs quantum dots
Authors: Kusunoki K. , Tsukiji N. , Umi T. , Tackeuchi A. , Yamaguchi K. 
Published: November 2007

AbstractHighly circularly polarized light is generated from highly uniform InAs/GaAs quantum dots. These quantum dots allowed us to observe the spin dynamics at each energy state selectively without disturbing the inhomogeneous broadening. Time‐resolved spin‐dependent photoluminescence measurements show that the spin polarization at the second excited state reaches a maximum of 45% at 10 K, and that the spin polarization is greater at higher‐energy states. This large spin polarization is explained by the spin Pauli blocking effect. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum theory of transport and optical gain in quantum cascade lasers
Authors: Kubis T. , Yeh C. , Vogl P. 
Published: November 2007

AbstractWe have developed a self‐consistent non‐equilibrium Green's function theory for charge transport and optical gain in quantum cascade lasers (QCL). Acoustic, polar‐optical phonon scattering, impurity, Hartree electron‐electron and interface roughness scattering within the self‐consistent Born approximation are taken into account. The incorporation of the full momentum and energy dependence of the scattering mechanisms turns out to be vital for the QCL device characteristics. The optical gain is calculated in linear optical response, taking into account the non‐equilibrium state occupations. For low‐doping THz GaAs/AlGaAs QCLs, we find the carrier transport at low bias to be dominated by multi‐barrier tunneling rather than by sequential tunneling. Importantly, interface roughness is shown to increase the current density drastically and up to a factor of 1.5 but suppress the gain by a factor of 10 for a realistic interface roughness. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum optics in semiconductor microcavities
Authors: Savasta Salvatore , Di Stefano Omar , Portolan Stefano 
Published: November 2007

AbstractPolaritons in semiconductor microcavities are hybrid quasiparticles consisting of a superposition of cavity photons and two‐dimensional excitons in embedded quantum wells (QWs). Owing to their exciton content, they have a strong mutual interaction which can be exploited for producing spontaneous parametric scattering of pump polaritons into signal‐idler polariton pairs. This process is able to produce polariton states exhibiting quantum correlations, and can thus be exploited for potential applications as well as to study quantum optical processes within a complex many‐body system. Here we present an overview of polariton parametric processes within a full quantum description based on the dynamics controlled truncation scheme. We also describe the results of an experiment that proves the existence of polariton pair correlations. This interpretation is confirmed by a microscopic theoretical analysis of the measured interference visibility. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microscopic theory of spin‐filtering in non‐magnetic semiconductor nanostructures
Authors: Kubis T. , Vogl P. 
Published: November 2007

AbstractIn this paper, we investigate the intrinsic spin‐Hall effect in mesoscopic systems, i.e. spin‐orbit induced spin‐polarizations with and without external magnetic fields in confined two‐dimensional systems at low temperatures. We employ a non‐equilibrium Green's function approach that takes into account the coupling of non‐equilibrium spin occupancies and spin‐resolved electronic scattering states in open nanometer quantum systems. Importantly, our calculations go beyond the widely used continuum approximation of the spin‐orbit interaction in the envelope function approximation and are based on a microscopic relativistic tight‐binding approach that ensures the spin‐orbit effects to be properly taken into account for any degree of charge confinement and localization and to all orders in the electron wave vector. We show that the qualitative trends and results in spin polarizations, their dependency on charge density, spin‐orbit interaction strength, and confinement, as obtained within the envelope function approximation, agree with the results of atomistic calculations. The quantitative results, on the other hand, can differ significantly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of hot electron effects on intersubband Raman laser in modulation‐doped GaAs/AlGaAs coupled double quantum wells
Authors: Miura M. , Katayama S. 
Published: November 2007

AbstractWe present a simulation of hot electron effects on inter‐subband Raman laser (IRL) consisting of modulation‐doped n‐type GaAs/AlGaAs coupled double quantum wells (CDQWs) with high 2D electron density. A time evolution for occupation number and electron temperature in each subband as well as the number of lasing Stokes photons are calculated self‐consistently for the modelled IRL. It is shown that Raman gain exhibits a characteristic reduction synchronizing an increase of Stokes photon density as time is evolved in sub‐nanosecond range. Then a saturation feature of output power is expected. The energy relaxation due to the confined LO phonons and the interface modes gives rise to interesting change of electron temperature in subband 1 and subband 2 during the Raman lasing. The threshold optical pumping intensity is estimated to be 50 kW/cm2. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cascade optical excitation of an artificial exciton molecule in a coupled quantum dot
Authors: Goshima Keishiro , Komori Kazuhiro , Sugaya Takeyoshi , Takagahara Toshihide 
Published: November 2007

AbstractWe investigated the formation dynamics of the artificial exciton molecule state, which consists of two different excitons confined in each quantum dot of a pair of quantum dots, namely a coupled quantum dot (CQD). By the selective optical excitation of the inherent energy states of two different excitons using two color continuous wave (CW) and pulsed lasers, we successively created Xb excitons and an artificial exciton molecule state, and monitored the photoluminescence, namely the population, of the artificial exciton molecule states. By employing the power dependence of the two colors and the excitation energy dependence, we succeeded in controlling the cascade optical excitation of an artificial exciton molecule. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A CFL‐like constraint for the fast marching method in inhomogeneous chemical kinetics
Authors: Escobedo Ramón 
Published: November 2007

AbstractLevel sets and fast marching methods are a widely used technique for problems with moving interfaces. Chemical kinetics has been recently added to this family, for the description of reaction paths and chemical waves in homogeneous media, in which the velocity of the interface is described by a given field. A more general framework must consider variable velocities due to inhomogeneities induced by chemical changes. In this case, a constraint must be satisfied for the correct use of fast marching method. We deduce an analytical expression of this constraint when the Godunov scheme is used to solve the Eikonal equation, and we present numerical simulations of a case which must be enforced to obey the constraint. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Solvent effect of aqueous media on properties of glycine: Significance of specific and bulk solvent effects, and geometry optimization in aqueous media
Authors: Tiwari Saumya , Mishra P. C. , Suhai S. 
Published: November 2007

AbstractGeometries of the normal (N) and zwitterionic (Z) forms of glycine (gly) and their complexes gly.(H2O)n, n = 0–2, were fully optimized in gas phase and aqueous media, and transition states located between the corresponding N and Z forms. The geometry was also optimized and vibrational spectra calculated for the gly.(H2O)3 complex of Z glycine. Density functional theory at the B3LYP/AUG‐cc‐pVDZ level was employed for the geometry optimization calculations in gas phase and aqueous media while single point energy calculations were performed at the MP2/AUG‐cc‐pVDZ level in each case. Solvation in bulk water was treated using the polarizable continuum model (PCM). Zero‐point energy correction to total energy and thermal energy correction to enthalpy were obtained at the B3LYP/AUG‐cc‐pVDZ level of theory in both gas phase and bulk aqueous media and these corrections were also considered to be valid for the corresponding single point energy calculations performed at the MP2/AUG‐cc‐pVDZ level of theory. When geometries of the complexes of glycine with water molecules are optimized in aqueous media, the calculated properties are found to be appreciably modified with respect to those obtained by gas phase geometry optimization followed by solvation in aqueous media. For several vibrational frequencies, the agreement between the calculated and experimentally observed results is improved appreciably when both the specific and bulk solvent effects are considered in combination with full geometry optimization in aqueous media. For certain vibrational frequencies, mode assignments have also been modified. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Maximum eigenvalues of the reciprocal distance matrix and the reverse Wiener matrix
Authors: Zhou Bo , Trinajstić Nenad 
Published: November 2007

AbstractWe report some properties of the maximum eigenvalues of the reciprocal distance matrix and the reverse Wiener matrix of a connected graph, in particular, various lower and upper bounds, and the Nordhaus–Gaddum‐type results for them. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Internal‐rotation and inversion potential energy surfaces for methylamine and methylphosphine
Authors: Kim Hae‐Won , Zeroka Daniel 
Published: November 2007

AbstractUsing the HF, MP2, and DFT methods with a 6‐311G** basis set, we examine the internal‐rotation and inversion of the amino and phosphino groups in methylamine and methylphosphine. The resulting energy surfaces are reported as a function of rotation and inversion descriptors. Both surfaces are characterized by several special points: three minimum energy states, three first‐order internal‐rotation transition states, six first‐order inversion transition states, and six second‐order inversion transition states. The MP2 method gave better agreement with experiment. For methylamine, the MP2 energy barrier for internal‐rotation is 8.73 kJ/mol; for first‐order inversion it is 22.80 kJ/mol and for second‐order inversion it is 22.41 kJ/mol. For methylphosphine, the MP2 energy barriers are 7.53, 149.88, and 149.65 kJ/mol, respectively. The energy barriers include ZPE correction contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Characterization ofin vitrometabolites of deoxypodophyllotoxin in human and rat liver microsomes using liquid chromatography/tandem mass spectrometry
Authors: Lee Sang Kyu , Jun In Hye , Yoo Hye Hyun , Kim Ju Hyun , Seo Young Min , Kang Mi Jeong , Lee Seung Ho , Jeong Tae Cheon , Kim Dong Hyun 
Published: November 2007

AbstractThein vitrometabolism of deoxypodophyllotoxin (DPT), a medicinal herbal product isolated fromAnthriscus sylvestris(Apiaceae), was investigated in rats and human microsomes and human recombinant cDNA‐expressed CYPs. The incubation of DPT with pooled human microsomes in the presence of NADPH generated five metabolites while its incubation with dexamethasone (Dex)‐induced rat liver resulted in seven metabolites (M1–M7) with major metabolic reactions including mono‐hydroxylation,O‐demethylation and demethylenation. Reasonable structures of the seven metabolites of DPT could be proposed, based on the electrospray tandem mass spectra. Chemical inhibition by ketoconazole and metabolism studies with human recombinant cDNA‐expressed CYPs indicated that CYP 3A4 and 2C19 are the major CYP isozymes in the metabolism of DPT in human liver microsomes. Copyright © 2007 John Wiley & Sons, Ltd.
Study on the formation of an amoxicillin adduct with methanol using electrospray ion trap tandem mass spectrometry
Authors: Grujic Svetlana , Vasiljevic Tatjana , Lausevic Mila , Ast Teodor 
Published: November 2007

AbstractThe possibility of using the protonated methanol‐adduct of antimicrobial amoxicillin for its identification and quantification at residue levels has been investigated, since it is impossible to completely suppress the formation of these adducts when methanol is present in the solvent system. This process has been monitored over time and as a function of concentration. It was determined that adducts were instantly formed and that the abundance of the protonated methanol‐adduct at m/z 398 increased at the expense of the protonated molecule m/z 366 with storage time. The effect of several common solvents and mobile‐phase additives on the ionization efficiency of amoxicillin and the formation of the methanol adduct has also been investigated. It was shown that the mass spectra of amoxicillin were strongly influenced by the solvent in which the analyte is dissolved and by the analyte concentration, as well as by the composition of mobile phase. Methanol was determined to be the best spray solvent, as it provided spectra with the lowest abundance of dimer ions. It was also determined that acetic acid as the mobile‐phase additive provided the highest signal intensities, while ammonium acetate should not be used as an additive for the determination of amoxicillin at residue levels. Using high‐performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI‐MS/MS), fragmentation of the protonated molecules and the protonated methanol‐adduct ions, in both positive and negative ion mode, has been performed. The fragmentation was stable and strong product ion spectra were obtained. The linearity of the MS detector response, and that of the chromatographic method, was tested. Due to the linear behaviour it was concluded that the protonated methanol‐adduct ion can be used for analytical purposes, i.e. for identification and quantification of amoxicillin at trace levels. Copyright © 2007 John Wiley & Sons, Ltd.
Neurostatistics: Applications, challenges and expectations
Authors: Georgopoulos Apostolos P. , Karageorgiou Elissaios 
Published: November 2007

AbstractBrain function and its relations to cognition and behavior can be elucidated only by the use of various complementary methods. Over the past 20 years, we have been studying the brain mechanisms underlying spatial processes using different methods, including the recording of single cell activity in behaving monkeys, functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) in human subjects, all performing the same tasks. These methods provide partially overlapping perspectives, resulting in a gain in knowledge beyond the province of the individual method. A common aspect in this endeavor is the statistical analysis of the data acquired by different methods, especially regarding the encoding of information in unitary elements (single cell activity in neurophysiology, blood oxygenation level‐dependent (BOLD) activation of voxels in fMRI, magnetic field strength in MEG) and the decoding of information from ensembles. In this paper we illustrate the various approaches, their data analysis and possible applications to medicine in the context of operations in space. Published in 2007 by John Wiley & Sons, Ltd.
Cyclotrimerization reactions of arynes and strained cycloalkynes
Authors: Peña Diego , Pérez Dolores , Guitián Enrique 
Published: November 2007

AbstractThe use of arynes and related species as substrates in metal‐catalyzed cycloaddition reactions leads to structurally interesting products. Palladium‐catalyzed cyclotrimerization of arynes provides a new method for the synthesis of polycyclic aromatic hydrocarbons. For instance, the chemoselective formal [2 + 2 + 2] cocycloaddition of 2,3‐triphenylynes with alkynes affords extended triphenylenes, which are good candidates to behave as liquid crystals. Cotrimerization of benzyne and electron‐deficient alkenes selectively affords dihydrophenanthrenes or ortho‐olefinated biaryls depending on the catalytic system employed. The use of 2,2′‐bis(diphenylphosphino)‐1,1′‐binophythyl (BINAP)‐based palladium(0) catalysts in the cocyclotrimerization of 7‐methoxynaphthalyne and dimethyl acetylenedicarboxylate affords an enantiomerically enriched tetrasubstituted pentahelicene, the first example of a metal‐catalyzed enantioselective reaction involving arynes. Strained cyclic alkynes can also participate in the palladium‐catalyzed cyclotrimerization reactions, which again lead to structurally interesting products. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 326–333; 2007: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20132
Early manifestations and spectrum of recipient twin cardiomyopathy in twin–twin transfusion syndrome: relation to Quintero stage
Authors: Michelfelder E. , Gottliebson W. , Border W. , Kinsel M. , Polzin W. , Livingston J. , Khoury P. , Crombleholme T. 
Published: November 2007

AbstractObjectivesTo examine cardiac structural and functional changes in twin–twin transfusion syndrome (TTTS), relative to Quintero stage, as a means of evaluating the spectrum of cardiomyopathy in TTTS.MethodsThis was a cross‐sectional, retrospective study of 42 consecutive cases of TTTS referred to a single fetal therapy center. Quintero stages were assigned by standard criteria. Presence of ventricular hypertrophy, cardiomegaly, atrioventricular valve regurgitation (AVVR), ventricular systolic dysfunction and right ventricular outflow tract obstruction on fetal echocardiography were noted. The Doppler myocardial performance index (MPI), an index of global ventricular function, was calculated for both ventricles in subjects with adequate Doppler data. We compared cardiac changes across Quintero stages.ResultsThere was no cardiomyopathy observed in donor twins. The majority of subjects presented at Quintero Stage I (n = 14), II (n = 14) or III (n = 11), with fewer at Stages IV (n = 2) or V (n = 1). As early as Quintero Stages I and II, a significant proportion of recipient twins had ventricular hypertrophy (17/28, 61%), AVVR (6/28, 21%) or quantitative abnormalities in either right (12/24, 50%) or left (14/24, 58%) ventricular function. Increasing prevalence of biventricular systolic dysfunction and cardiomegaly accompanied advancing Quintero stage.ConclusionsChanges in cardiac structure and function not reflected in Quintero staging occur in recipient twins early in the evolution of TTTS. Incorporation of cardiac findings into assessment of TTTS severity may prove useful in stratification of risk and treatment selection. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.