bluuebunny/crossref_metadata_2025 huggingface dataset:
On the electron-electron counterbalance hole
Authors: Koga Toshikatsu , Sekiya Masahiro
Published: February 2008

When a many-electron system has spatial inversion symmetry, the electron-electron counterbalance hole implies that two electrons with parallel spins cannot be at opposite positions with respect to the inversion center, and its presence was pointed out in the literature [T. Koga, J. Chem. Phys. 108, 2515 (1998)] for any pairs of Hartree-Fock orbitals with the same inversion parity. We report here a generalized result that in all two-electron systems with spatial inversion symmetry, the electron-electron counterbalance hole always exists for any approximate and exact wave functions with even inversion parity. The same is also true in momentum space. An extension of the hole to systems with three or more electrons is discussed.
First-principles local density approximation+U and generalized gradient approximation+U study of plutonium oxides
Authors: Sun Bo , Zhang Ping , Zhao Xian-Geng
Published: February 2008

The electronic structure and properties of PuO2 and Pu2O3 have been studied from first principles by the all-electron projector-augmented-wave method. The local density approximation+U and the generalized gradient approximation+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by the choice of U as well as the choice of exchange-correlation potential. Also, oxidation reaction of Pu2O3, leading to formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U, it is promising to correctly and consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modeling of redox process involving Pu-based materials possible.
Quasielastic neutron scattering study of pyridinium cation reorientation in thiourea pyridinium nitrate inclusion compound
Authors: Pajzderska A. , Gonzalez M. A. , Wąsicki J.
Published: February 2008

The dynamics of the pyridinium cation in thiourea pyridinium nitrate inclusion compound has been studied using quasielastic neutron scattering in a wide temperature range (10–350K). The elastic incoherent structure factor was determined from neutron backscattering and time-of-flight measurements and its analysis allows to describe in detail the geometry of the motions of the pyridinium cation. Our study reveals two types of motion having two different correlation times. The pyridinium cation reorients about the axis perpendicular to its molecular plane over inequivalent threefold potential energy barriers and also executes a faster out-of-plane motion about the axis passing through two opposite atoms of the ring.
Generalized approximation to the reaction path: The formic acid dimer case
Authors: Matanović Ivana , Došlić Nadja , Johnson Bruce R.
Published: February 2008

A set of mass-weighted internal coordinates was derived and applied to the double proton transfer reaction in the formic acid dimer (FAD). The coordinate set was obtained starting from the Hirschfelder “mobile” by an optimization procedure consisting of a sequence of kinematic rotations. In FAD, the optimization procedure leads to three coordinates that do change significantly along the reaction path. These coordinates span the reaction space, whereas the remaining modes are treated in a harmonic approximation. The effect that the dimer dissociative motion has on the ground and excited vibrational states dynamics was explored. In the frequency region corresponding to the symmetric OH-stretch vibration four doublets have been identified with splittings of 2.76, 0.07, 0.60, and 4.03cm−1.
Reaction of molecular and atomic deuterium with methanol on Pd(111)
Authors: Demirci E. , Winkler A.
Published: February 2008

Multiplexed thermal desorption spectroscopy was used to study the influence of preadsorbed and postadsorbed deuterium on a methanol monolayer on Pd(111). In particular, the effect of atomic deuterium exposure on the reaction products was examined in detail. Preadsorbed deuterium hinders the formation of chemisorbed methanol and favors physisorption of methanol. This leads to a strong reduction of methanol dehydrogenation during sample heating. Postadsorption of molecular deuterium also changes partially chemisorbed to physisorbed methanol. No deuteration of methanol is found under these conditions. With atomic deuterium exposure, however, significant amounts of deuterated methanol, from methanol-D1 through methanol-D4, can be produced. In addition, D exposure also causes an increased dehydrogenation probability during sample heating. The probabilities for methanol deuteration, for methanol dehydrogenation, and for D-atom bulk absorption have been determined quantitatively.
Systematic optimization of long-range corrected hybrid density functionals
Authors: Chai Jeng-Da , Head-Gordon Martin
Published: February 2008

A general scheme for systematically modeling long-range corrected (LC) hybrid density functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochemistry, kinetics, and noncovalent interactions, when compared with common hybrid density functionals. The qualitative failures of the commonly used hybrid density functionals in some “difficult problems,” such as dissociation of symmetric radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid density functionals.
Enhanced microwave ferromagnetic resonance absorption and bandwidth using a microstrip meander line with step-impedance low-pass filter in a yttrium iron garnet–gallium arsenide layer structure
Authors: Qiu Gang , Tsai Chen S. , Kobayashi Masatoshi M. , Wang Bert S. T.
Published: February 2008

Simulations of the step-impedance low-pass filter (LPF) in gallium arsenide (GaAs) substrate show that, in contrast to a 50Ω microstrip, the magnetic fields of the propagating microwaves are heavily concentrated in its inductive elements. The concentrated local magnetic fields facilitate enhanced coupling into an yttrium iron garnet/gadolinium gallium garnet layer over the GaAs substrate and, thus, significantly increase the microwave power absorptions at the ferromagnetic resonance (FMR) frequencies. The large tunable range of FMR frequency and the corresponding S21 and S11 parameters measured have verified the simulation results. Simultaneous enhancement of FMR absorption level and widening of absorption bandwidth has been accomplished in a band-stop filter that utilizes a microstrip meander line with four identical step-impedance LPFs, each of 5.70mm long, inserted in a nonuniform bias magnetic field. A tunable FMR absorption frequency range of 5–21GHz, an absorption level of −35.5dB, and a corresponding 3dB absorption bandwidth as large as 1.70GHz, centered at 20.3GHz, have been demonstrated.
Three dimensional simulations of spin Hall effect in magnetic nanostructures
Authors: Sugano R. , Ichimura M. , Takahashi S. , Maekawa S.
Published: February 2008

We investigate the spatial distribution of spin/charge current in a nonlocal geometry of a magnetic nanostructure with Py∕I∕Cu and Cu∕Pt contacts and analyze the spin Hall effects by applying finite element method in three dimensions. We find that the inhomogeneous current distribution appears in the Cu∕Pt connection area, suggesting the possibility of the spin-signal enhancement by controlling the contact shape and the width of the electrodes. The calculated spin Hall voltage is consistent with the experimentally observed Hall resistance.
Construction of a standard test assembly for controlled laser studies in tissues: Preliminary study on human bone material
Authors: Beer Franziska , Passow Harald
Published: February 2008

The aim of the study is the construction of a test assembly, which facilitates objective, comparative studies on the cutting performance of lasers in hard tissue. To ensure the applicability of our own construction for the reproducible performance of laser incisions in hard tissue, eleven freshly extracted blocks (2×1.5cm2) of human bone were prepared with a Er,Cr:YSGG laser by using a handheld handpiece, respectively, using the constructed device for a standardized cutting. A total of 44 cuts were executed. The specimen were then histologically evaluated. The standard test assembly met the requirements concerning the provision of objective results. The findings of the histological evaluation prove the reproducibility of the results. The standard test assembly presented in this paper facilitates comparative studies of different laser systems by reducing subjective influence on the preparation to a minimum. The results of this preliminary study show that the precision of the guiding instrument for laser cutting reduces the error of cut width by 50-fold, from 50to1μm.
Ion-acoustic waves in a plasma consisting of adiabatic warm ions, nonisothermal electrons, and a weakly relativistic electron beam: Linear and higher-order nonlinear effects
Authors: Esfandyari-Kalejahi A. , Kourakis I. , Shukla P. K.
Published: February 2008

The nonlinear propagation of finite amplitude ion acoustic solitary waves in a plasma consisting of adiabatic warm ions, nonisothermal electrons, and a weakly relativistic electron beam is studied via a two-fluid model. A multiple scales technique is employed to investigate the nonlinear regime. The existence of the electron beam gives rise to four linear ion acoustic modes, which propagate at different phase speeds. The numerical analysis shows that the propagation speed of two of these modes may become complex-valued (i.e., waves cannot occur) under conditions which depend on values of the beam-to-background-electron density ratio α, the ion-to-free-electron temperature ratio σ, and the electron beam velocity v0; the remaining two modes remain real in all cases. The basic set of fluid equations are reduced to a Schamel-type equation and a linear inhomogeneous equation for the first and second-order potential perturbations, respectively. Stationary solutions of the coupled equations are derived using a renormalization method. Higher-order nonlinearity is thus shown to modify the solitary wave amplitude and may also deform its shape, even possibly transforming a simple pulse into a W-type curve for one of the modes. The dependence of the excitation amplitude and of the higher-order nonlinearity potential correction on the parameters α, σ, and v0 is numerically investigated.
Stability of polycrystalline and wurtzite Si nanowires via symmetry-adapted tight-binding objective molecular dynamics
Authors: Zhang D.-B. , Hua M. , Dumitrică T.
Published: February 2008

The stability of the most promising ground state candidate Si nanowires with less than 10nm in diameter is comparatively studied with objective molecular dynamics coupled with nonorthogonal tight-binding and classical potential models. The computationally expensive tight-binding treatment becomes tractable due to the substantial simplifications introduced by the presented symmetry-adapted scheme. It indicates that the achiral polycrystalline of fivefold symmetry and the wurtzite wires of threefold symmetry are the most favorable quasi-one-dimensional Si arrangements. Quantitative differences with the classical model description are noted over the whole diameter range. Using a Wulff energy decomposition approach it is revealed that these differences are caused by the inability of the classical potential to accurately describe the interaction of Si atoms on surfaces and strained morphologies.
Suppression of stray field between adjacent rings in one-dimensional ferromagnetic ring arrays
Authors: Kohda M. , Toyoda K. , Miyawaki T. , Fujita A. , Nitta J.
Published: February 2008

We have investigated the stray field effect among the adjacent rings with different inner diameters in the submicron-sized ferromagnetic ring array. The magnetization reversal process is measured with changing the edge-to-edge distance of the ring array by the magneto-optical Kerr effect. The stray field retains longer distance as the inner diameter decreases. This is due to the reduction of the circumferential shape anisotropy with the smaller inner diameter, where the magnetic moments favor to align along the direction of the one-dimensional array. For the high density storage using ring-shaped magnetic-random access memory, the ring array with the large inner diameter is preferable.
Toggle switching of weakly coupled synthetic antiferromagnet for high-density magnetoresistive random access memory
Authors: Fukuma Y. , Fujiwara H. , Visscher P. B.
Published: February 2008

The toggle-switching behavior for circular and elliptic cylinder shaped memory cells of weakly coupled synthetic antiferromagnet with a diameter and thickness (ferromagnetic layer) ranging from 200 to 400 and from 2.5to5.0nm, respectively, has been studied by micromagnetic simulation. The critical fields for a circular cylinder are much larger than those predicted by a single domain model. This is due to the formation of edge domains resulting in a so-called S state. The elliptic cylinder with an aspect ratio of >1.2 is found to be necessary to prevent the increase of the start field by the edge domains.
Improvements of sensing performance by specially designed magnetic shield layer in an in vitro tunneling magnetoresistance biosensor using immobilized ferrimagnetic nanoparticle agents
Authors: Kim Sunwook , Bae Seongtae , Lim Jang Kwon
Published: February 2008

The dependence of magnetic shield layer thickness, permeability of the shield materials, and shielding gap width on the sensing performance of an in vitro exchange biased tunneling magnetoresistance (TMR) spin-valve biosensor with immobilized ferrimagnetic sensor agents has been numerically analyzed by using a finite element method. It was numerically demonstrated that the specially designed magnetic shield layer on the surface of the TMR biosensors is considerably effective to improve the switching field uniformity and to eliminate an undesirable undershoot magnetic field formed on the sensor surface.
Spin accumulation and magnetotransport in NiFe∕Al∕NiFe single-electron transistors
Authors: Shyu J. H. , Tang T. F. , Yao Y. D. , Wu J. K. , Chen J. W.
Published: February 2008

Spin accumulation effect and anomalous magnetoresistance resulting in spin dependent transport in NiFe∕Al∕NiFe single-electron transistors have been studied. The magnetic tunneling process is strongly influenced by the charging energy and a superconducting gap. The magnetoresistance is enhanced with decreasing bias voltage. In addition, a suppressed superconducting gap caused by spin accumulation was experimentally demonstrated. For higher bias voltage, the spin accumulation induced by the spin-valve effect is seen as periodic oscillation in a Coulomb blockade region. Below the critical voltage, which is the sum of the superconducting gap and charging energy, spin accumulation can suppress the superconductivity and induce anomalous magnetoresistance.
Development of a high efficiency proton source for the Frankfurter-Neutronen-Quelle am Stern-Gerlach-Zentrum
Authors: Nörenberg R. , Ratzinger U. , Sun J. , Volk K.
Published: February 2008

A new version of high efficiency proton source is being developed for Frankfurter-Neutronen-Quelle am Stern-Gerlach-Zentrum, a worldwide unique pulsed neutron source. The injector will provide dc proton beam currents of 200mA at 120keV with a beam divergence angle of less than 50mrad. The new design consists of a plasma generator with a multiple filament arrangement and a compact pentode extraction system. The beam will be extracted from a seven hole outlet electrode. Great efforts are made to achieve an adequate operation time (∼3days) of the source as well as to obtain high reliability during that operation period with less than 1V breakdowns per hour. The following article will present the current status of the proton source development including beam formation simulations with IGUN.
Temperature and bias-voltage dependences of tunneling magnetoresistance in (Ga,Mn)As-based double-barrier magnetic tunnel junctions
Authors: Okabayashi J. , Watanabe M. , Yamaguchi T. , Yoshino J.
Published: February 2008

We have investigated the temperature and bias-voltage dependences in the tunneling magnetoresistance (TMR) curves for (Ga,Mn)As-based double-barrier magnetic tunnel junctions (DB MTJs). The coercive fields in each magnetic (Ga,Mn)As layer drastically decrease depending on the variations in the temperature. TMR ratios decrease monotonically with increasing temperature. Furthermore, we have demonstrated that DB-MTJs not only enhance the TMR ratio effectively but also improve the strong bias-voltage characteristics.
Single-particle, particle-pair, and multiparticle dispersion of fluid particles in forced stably stratified turbulence
Authors: van Aartrijk M. , Clercx H. J. H. , Winters K. B.
Published: February 2008

The dispersion of fluid particles in statistically stationary stably stratified turbulence is studied by means of direct numerical simulations. Due to anisotropy of the flow, horizontal and vertical dispersion show different behavior. Single-particle dispersion in horizontal direction is similar to that in isotropic turbulence for short times, but shows a long-time growth rate proportional to t2.1±0.1, larger than the classical linear diffusion limit. In vertical direction, three successive regimes can be identified: a classical t2-regime, a plateau that scales as N−2, and a diffusion limit where dispersion is proportional to t. By forcing the flow and performing long-time simulations, we are able to observe this last regime, which was predicted but not observed before in stratified turbulence. This diffusive regime is caused by molecular diffusion of the active scalar (density). The mean squared separation of particle pairs (relative dispersion) in vertical direction shows two plateaus that are not present in isotropic turbulence. They can be associated with the characteristic layered structure of the flow. In the long-time limit again a linear regime is found as for single-particle dispersion. Pair dispersion in horizontal direction behaves similar to that in isotropic turbulence except for long times. Finally, the study of multiparticle statistics in stably stratified turbulent flows is reported. The evolution of tetrads gives an impression of the shape of particle clouds. It is found that with increasing stratification, the volume of the tetrads decreases, and they become flatter and more elongated.
Magnetic property and charge ordering effect in polycrystalline LuFe2O4
Authors: Bang Bong Kyu , Kouh Taejoon , Kim Chul Sung
Published: February 2008

The charge ordering effect in LuFe2O4 powder is investigated with the vibrating sample magnetometer and Mössbauer spectroscopy. The crystal structure of LuFe2O4 shows the two-dimensional layered type rhombohedral(R3¯m) structure. The lattice constants are found to be a0=3.439Å and c0=25.258Å by the Rietveld refinement. The Néel temperature (TN) is determined to be 250K. The Mössbauer spectra consist of four sextets indicating the magnetic ordering below TN, where three sets are assumed to be Fe3+ phases and the other is Fe2+ at 4.2K, and two doublets splitting in a paramagnetic region. At room temperature, the electric quadrupole splittings (ΔEQ) of two doublets are 0.22±0.01 and 0.67±0.01mm∕s, respectively. The isomer shift value of a doublet with smaller ΔEQ is 0.18±0.01mm∕s relative to the Fe metal, which is consistent with the Fe3+ valence state, while the value of a doublet with larger ΔEQ is 0.83±0.01mm∕s indicating Fe2+ state. The Mössbauer spectra suggest that the observed asymmetry below 370K is due to the charge ordering effect between Fe2+ and Fe3.
From clusters to fibers: Parameters for discontinuous para-hexaphenylene thin film growth
Authors: Kankate Laxman , Balzer Frank , Niehus Horst , Rubahn Horst-Günter
Published: February 2008

All relevant steps of discontinuous thin film growth of para-hexaphenylene on muscovite mica (0 0 1) from wetting layer over small and large clusters to nanofibers are observed and investigated in detail by a combined polarized fluorescence and atomic force microscopy study. From a variation of film thickness and surface temperature, we determine effective activation energies for cluster growth of 0.17eV, for nanofiber length growth of 0.46eV, for width growth of 0.19eV, and for height growth of 0.07eV. The corresponding exponential prefactors for the nanofiber growth are 1×109, 6×104, and 3×102nm. Polarized fluorescence studies reveal that nanofibers grow along the grooves of the mica surface and that they do not change direction if they cross an even number of mica surface steps, while they change direction by 120° for an odd number of steps. These results are taken as an input for a model of the unidirectional growth process on mica. Absolute parameters allowing one to grow nanofibers of predetermined morphology via organic molecular beam epitaxy are also given.
Structural transition of nematic liquid crystal in cylindrical capillary as a result of the annihilation of two point defects
Authors: Svetec Milan , Slavinec Mitja
Published: February 2008

We study the annihilation of hedgehog-antihedgehog defects in confined nematic liquid crystals using Brownian molecular dynamics simulations. After the collision, merging of defects, and building a loop disclination structure, system can experience a structural transition into another nematic structure, triggered by a nucleation of loop disclination structure. In our rough theoretical approach we calculate the size of the emerged loop structure as the function of the typical size of the confining cavity. Attention is paid also to the dynamics of the loop structure after collision.
Infrared photocurrent response of charge-transfer exciton in polymer bulk heterojunction
Authors: Yang Chia-Ming , Tsai Pei-Yu , Horng Sheng-Fu , Lee Kuan-Chen , Tzeng Shin-Rong , Meng Hsin-Fei , Shy Jow-Tsong , Shu Ching-Fong
Published: February 2008

We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C61-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950nm. For films with micrometer thickness, the photon-to-electron conversion efficiency is about 60% at 750nm wavelength under reverse voltage bias and the photocurrent to dark current ratio is about 8.6 at 900nm and remains 3.6 even at 1000nm. Photodetector with high sensitivity covering exclusively the 650–1000nm near infrared region can therefore be made without a low bandgap material. The charge-transfer exciton absorption coefficient and photocurrent sensitivity depend on the annealing condition which controls the donor-acceptor morphology.
Kelvin waves with helical Beltrami flow structure
Authors: González Rafael , Sarasua Gustavo , Costa Andrea
Published: February 2008

In this work we show that when an inviscid axisymmetric Rankine flow experiences a soft expansion, rotating Kelvin waves can be excited. Downstream of the region where the expansion occurs (the transition region) the resulting flow can be expressed as the addition of a Rankine and a Beltrami flow. The Beltrami constant is determined from the Rankine upstream flow, and the helix pitch of the n=1 mode results from the boundary conditions downstream. Finally, a discussion of the process leading to oscillatory flow and a conjecture about the topological background that sustains the Beltrami flow structure are offered.
Dust acoustic shock wave in electronegative dusty plasma: Roles of weak magnetic field
Authors: Ghosh Samiran , Ehsan Z. , Murtaza G.
Published: February 2008

The effects of nonsteady dust charge variations and weak magnetic field on small but finite amplitude nonlinear dust acoustic wave in electronegative dusty plasma are investigated. The dynamics of the nonlinear wave are governed by a Korteweg–de Vries Burger equation that possesses dispersive shock wave. The weak magnetic field is responsible for the dispersive term, whereas nonsteady dust charge variation is responsible for dissipative term, i.e., the Burger term. The coefficient of dissipative term depends only on the obliqueness of the magnetic field. It is found that for parallel propagation the dynamics of the nonlinear wave are governed by the Burger equation that possesses monotonic shock wave. The relevances of the findings to cometary dusty plasma, e.g., Comet Halley are briefly discussed.
Forced dissociation of a biomolecular complex under periodic and correlated random forcing
Authors: Lin Han-Jou , Sheng Yu-Jane , Chen Hsuan-Yi , Tsao Heng-Kwong
Published: February 2008

The dissociation of a biomolecular complex under the action of periodic and correlated random forcing is studied theoretically. The former is characterized by the period τp and the latter by the correlation time τr. The rupture rates are calculated by overdamped Langevin dynamics and three distinct regimes are identified for both cases by comparison to local relaxation time τR and bond lifetime ⟨T⟩. For periodic forcing, the adiabatic approximation cannot be applied in the regime τp⪡τR and the bond lifetime is determined by the average pulling. As τR⪡τp⪡⟨T⟩, the rupture rate is enhanced by periodic forcing but is τp independent. Analytical expressions are obtained for small and large force amplitudes. As ⟨T⟩⪡τp, the rupture rate depends on the phase lag and the process behaves like it is under constant force or loading rate. The result of correlated random forcing is similar to that of periodic forcing. Since the fluctuating forces greater than the average force ⟨F⟩ contribute more than the fluctuating forces less than ⟨F⟩, the force fluctuations enhance the rupture rate. As ⟨T⟩<τr, the pulling felt by the bond before rupture cannot follow the random forcing protocol and, thus, force fluctuations decline with increasing τr.
Observations of the frequency tuning effect in the 14GHz CAPRICE ion source
Authors: Celona L. , Ciavola G. , Consoli F. , Gammino S. , Maimone F. , Mascali D. , Spädtke P. , Tinschert K. , Lang R. , Mäder J. , Roßbach J. , Barbarino S. , Catalano R. S.
Published: February 2008

A set of measurements with the CAPRICE ion source at the GSI test bench has been carried out to investigate its behavior in terms of intensity and shape of the extracted beam when the microwaves generating the plasma sweep in a narrow range of frequency (±40MHz) around the klystron center frequency (14.5GHz). Remarkable variations have been observed depending on the source and the beamline operating parameters, confirming that a frequency dependent electromagnetic distribution is preserved even in the presence of plasma inside the source. Moreover, these observations confirm that the frequency tuning is a powerful method to optimize the electron cyclotron resonance ion source performances. A description of the experimental setup and of the obtained results is given in the following.
Depth profiling of chemical states and charge density in HfSiON by photoemission spectroscopy using synchrotron radiation
Authors: Tanimura T. , Toyoda S. , Kumigashira H. , Oshima M. , Ikeda K. , Liu G. L. , Liu Z.
Published: February 2008

We have investigated chemical states and charge density in HfSiON films as a function of depth using x-ray irradiation time-dependent photoemission spectroscopy. N 1s core-level photoemission spectra deconvoluted into three components depend on HfSiON thickness, indicating the component, which is attributed to the N atoms bonded to Hf atoms, has peak near the surface. On the other hand, charge density estimated from band bending in Si from Si 2p photoemission spectra is also distributed mainly near the surface. These results indicate that the origin of the negative charge trapping can be directly related to the presence of Hf–N bonds.
Ion-temperature-gradient driven modes in very dense magnetoplasmas
Authors: Mirza Arshad M. , Shukla P. K.
Published: February 2008

By employing the quantum magnetohydrodynamic-Poisson model, a general dispersion relation for low-frequency electrostatic ion-temperature-gradient (ITG) modes in a very dense Fermi plasma is derived. The growth rate is found to be higher in the presence of ion-temperature gradients and electron corrections due to quantum fluctuations. Two new ITG driven modes in the Fermi plasma are found. These ITG modes are associated with an electron density response that differs from the Boltzmann law. It is expected that newly found ITG modes can play an important role in anomalous cross-field ion energy transport in the next-generation laser-solid density plasma experiments as well as in dense astrophysical bodies (e.g., neutron stars and the interior of white dwarfs).
Saturation of surface roughening instabilities by plastic deformation
Authors: Andersen Michael , Ghoniem Nasr , Takahashi Akiyuki
Published: February 2008

Surface roughening instabilities driven by a competition between elastic and surface energy contributions are shown to be saturated by plastic energy dissipation. It is shown that these morphological instabilities do not experience unbounded growth as predicted by consideration of elastic energy alone and that their growth is limited by dislocation emission from higher curvature grooves.
Magnetic force microscopy imaging of in-plane magnetic field gradient using transient oscillation
Authors: Saito H. , Egawa G. , Ishio S. , Li Guoqing
Published: February 2008

A new imaging method of the in-plane magnetic field gradient using the transient oscillation of a magnetic force microscopy (MFM) tip was demonstrated by detecting the frequency shift of a MFM tip which was driven at a constant frequency. The gradient of the in-plane magnetic field along the in-plane scanning direction was measured by using a MFM tip which was magnetized in the direction normal to the sample plane. The image contrast of the in-plane magnetic field gradients reversed by scanning the same line in opposite direction. Two-dimensional vector imaging was possible by using this method together with the conventional phase detection method which detects the perpendicular magnetic field gradients. From theoretical analysis, the signal of the present method was thought to correspond to the in-plane magnetic field gradient and the present method was expected to have a higher spatial resolution because the higher-order field gradient was detected by the presented method compared to the conventional phase detection method.
Radio frequency functional capacitors made of all-organic composites of thiourea in field-responsive polymers
Authors: Bayer I. S. , Biswas A. , Szczech J. B. , Suhir E. , Norton M. G.
Published: February 2008

By incorporating an organic high dielectric constant (κ) ferroelectric crystal, thiourea, in field-responsive polymers, we fabricated radio frequency functional all-organic and solution-processable dielectric composites. Two field-responsive polymer matrices with polyvinylidene fluoride (PVDF) and π-conjugated tris(8-hydroxyquinoline)aluminum(III) inclusions were used to fabricate six model high-κ capacitor devices. Promising frequency-independent capacitance density of about 12nF∕cm2 up to 100MHz with an estimated κ=54 was obtained from the model systems except when thin interpenetrating PVDF crystals formed within the amorphous matrix. These structures displayed significantly lower capacitance density (∼0.7nF∕cm2). High-κ composites with low loss tangent (∼0.03) could be implemented in flexible electronics.
The N-vortex problem on a symmetric ellipsoid: A perturbation approach
Authors: Castilho César , Machado Hélio
Published: February 2008

We consider the N-vortex problem on an ellipsoid of revolution. Applying standard techniques of classical perturbation theory, we construct a sequence of conformal transformations from the ellipsoid into the complex plane. Using these transformations, the equations of motion for the N-vortex problem on the ellipsoid are written as a formal series on the eccentricity of the ellipsoid’s generating ellipse. First order equations are obtained explicitly. We show numerically that the truncated first order system for the three vortex system on the symmetric ellipsoid is nonintegrable.
Exploration of dielectric constant dependence on evolution of microstructure in nanotube/ferroelectric polymer nanocomposites
Authors: Yao Sheng-Hong , Dang Zhi-Min , Xu Hai-Ping , Jiang Mei-Juan , Bai Jinbo
Published: February 2008

Multiwall carbon nanotube (MWNT) with high aspect ratio (AR=125–750) was dispersed into polyvinylidene fluoride (PVDF) to fabricate the MWNT/PVDF nanocomposites. Change of dielectric constant with increasing the length of tensile strain (LTS) was observed in the MWNT/PVDF composites with different mass concentration of MWNT (mMWNT=1.0% and mMWNT=2.0%). The results showed that an abrupt increase in dielectric constant appeared when the LTS was 4 and 2mm in the composites with mMWNT=1.0% and mMWNT=2.0%, respectively. By employing the evolutions of conductive pathway and microcapacitance structure during the tensile strain process, the increased dielectric constant could be explained well.
Magnetic properties of carbon nanotube terminally connecting metal molecular complexes
Authors: Si M. S. , Xue D. S.
Published: February 2008

Carbon nanotubes are good candidates to promote communication between paramagnetic centers at large distances through a highly delocalized π system. Our research uses ab initio methods to predict the equilibrium configuration and magnetic properties of dinuclear iron metal molecular complexes connected by carbon nanotubes. The results show that the presence of surprisingly strong exchange coupling at very large distances for this kind of system and the coupling is ferromagnetic.
Picosecond gain switching of an organic semiconductor optical amplifier
Authors: Amarasinghe D. , Ruseckas A. , Vasdekis A. E. , Turnbull G. A. , Samuel I. D. W.
Published: February 2008

All-optical switching of an individual pulse within a sequence of amplified pulses is demonstrated in a conjugated polymer optical amplifier. The switching was achieved using a control pulse resonant with the excited state absorption. An extinction ratio of ∼5.5dB was observed, while the intensities of the remaining pulses in the sequence, spaced at 50ps intervals, were unaffected. A pump-probe study was performed and showed full gain recovery within 2ps.
Raman gain from waveguides inscribed in KGd(WO4)2 by high repetition rate femtosecond laser
Authors: Eaton S. M. , Merchant C. A. , Iyer R. , Zilkie A. J. , Helmy A. S. , Aitchison J. S. , Herman P. R. , Kraemer D. , Miller R. J. D. , Hnatovsky C. , Taylor R. S.
Published: February 2008

We report the formation of waveguides in Raman-active KGd(WO4)2 with a focused, high repetition rate femtosecond laser. Parallel guiding regions, formed to either side of the laser-induced damage track, supported TE and TM modes that coupled efficiently to optical fiber at telecom wavelengths. Micro-Raman spectroscopy of the guiding regions revealed the preservation of the characteristic 768 and 901cm−1 Raman mode intensities. Raman gain with 6% efficiency was demonstrated for the 768cm−1 Raman line by pumping the waveguide with an infrared 80ps source, the first time Raman gain has been reported in laser formed waveguides.
Investigation of Pr3+ as a sensitizer in quantum-cutting fluoride phosphors
Authors: Lee Te-Ju , Luo Li-Yang , Cheng Bing-Ming , Diau Wei-Guang , Chen Teng-Ming
Published: February 2008

A quantum-cutting (QC) phosphor K2GdF5:Eu3+ shows poor optical absorption and a theoretical quantum efficiency (QE) of 107% in the ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectral ranges. Pr3+ was codoped as a sensitizer in K2GdF5:Eu3+, thus increasing the absorption in the UV and VUV spectral regions; the theoretical QE of K2GdF5:Eu3+,Pr3+ was increased to 138%. The spectra indicate that the possible mechanisms of QC and energy transfer differ from those of phosphors containing the Gd3+–Eu3+ couple. Temporally resolved measurements of fluorescence decay confirm the proposed QC mechanism for the phosphor containing the Gd3+–Eu3+,Pr3+ system.
Signal and charge transfer efficiency of few electrons clocked on microscopic superfluid helium channels
Authors: Sabouret G. , Bradbury F. R. , Shankar S. , Bert J. A. , Lyon S. A.
Published: February 2008

Electrons floating on the surface of liquid helium are possible spin qubits for quantum information processing. Varying electric potentials are not expected to modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This approach depends upon efficient intergate transfer of individual electrons. Measurements are presented here of the charge transfer efficiency of few electrons clocked back and forth above a short microscopic CCD-like structure. A charge transfer efficiency of 0.999 999 92 is obtained for a clocking frequency of 800kHz.
Nonlinear relaxation of zero-dimension-trapped microcavity polaritons
Authors: El Daif Ounsi , Nardin Gaël , Paraïso Taofiq K. , Baas Augustin , Richard Maxime , Brantut J.-P. , Guillet Thierry , Morier-Genoud Francois , Deveaud-Plédran Benoit
Published: February 2008

We study the emission properties of confined polariton states in shallow zero-dimensional traps under nonresonant excitation. We evidence several relaxation regimes. For slightly negative photon-exciton detuning, we observe a nonlinear increase of the emission intensity, characteristic of carrier-carrier scattering assisted relaxation under strong-coupling regime. This demonstrates the efficient relaxation toward a confined state of the system. For slightly positive detuning, we observe the transition from strong to weak coupling regime and then to single-mode lasing.
Nanograin nucleation initiated by intergrain sliding and/or lattice slip in nanomaterials
Authors: Bobylev S. V. , Ovid’ko I. A.
Published: February 2008

Stress-induced nucleation of nanoscale grains (nanograins) in deformed nanocrystalline metals and ceramics is theoretically described as a process initiated by intergrain sliding and/or lattice slip. The nanograin nucleation occurs through splitting and migration of grain boundaries containing disclination dipoles produced by intergrain sliding and/or lattice slip. It is shown that the nanograin nucleation is energetically favorable in mechanically loaded nanocrystalline Al and α-Al2O3 in certain ranges of their parameters and the external stress level.
Phosphorescence characteristics of ruthenium complex as an optical transducer for biosensors
Authors: Pieper Sean B. , Mestas Santano P. , Lear Kevin L. , Zhong Zhong , Reardon Kenneth F.
Published: February 2008

The saturation intensity, photobleaching, and decay lifetime of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) chloride [Ru(dpp)3] are investigated. The saturation point was estimated to be 11.8W∕cm2 and subsequently measured to be 11.5W∕cm2. Photobleaching of this dye at a peak absorbance equivalence of 6.6W∕cm2 is observed over 2days resulting in a 14% decrease in intensity within 20min and 47% decrease over two days yielding an unacceptably short operational lifetime under saturated conditions. Lower optical excitation levels in the application of oxygen sensitive fluorescence type fiber optic enzymatic biosensor systems are required and yield acceptable photobleaching rates.
Nonequilibrium atmospheric pressure plasma with ultrahigh electron density and high performance for glass surface cleaning
Authors: Iwasaki Masahiro , Inui Hirotoshi , Matsudaira Yuto , Kano Hiroyuki , Yoshida Naofumi , Ito Masafumi , Hori Masaru
Published: February 2008

We produced a nonequilibrium atmospheric pressure plasma by applying an alternative current between two electrodes. The gas temperature and electron density were evaluated using optical emission spectroscopy. It was found that the plasma had gas temperatures from 1800to2150K and ultrahigh electron densities in the order of 1016cm−3. A remarkably high oxygen radical concentration of 1.6×1015cm−3 was obtained at a 1% O2∕Ar gas flow rate of 15slm (standard liters per minute). Contact angles below 10° were obtained in the process of glass cleaning with a plasma exposure time of 23ms.
The measurement of the Stokes parameters: A generalized methodology using a dual photoelastic modulator system
Authors: Guan Wei , Jones Grenville A. , Liu Yanwei , Shen Tiehan H.
Published: February 2008

We derive a generalized theory of a dual photoelastic modulator system designed for the measurement of the Stokes parameters of an arbitrary light beam. Based on the theory, a critique of various potential configurations that could be used to effect such measurements is presented. A calibration procedure for the entire optical system is introduced which, among other things, renders a knowledge of the frequency response of the detector system unnecessary. An analysis of the errors due to incorrect setting of optical components is presented for some of the more practical cases. This allows an assessment of the relative merit of different experimental configurations.
Systematic investigation of structural and magnetic properties in molecular beam epitaxial growth of metastable zinc-blende CrTe toward half-metallicity
Authors: Sreenivasan M. G. , Bi J. F. , Teo K. L. , Liew T.
Published: February 2008

We report a systematic investigation on the structural and magnetic properties of molecular-beam epitaxial growth of CrTe thin films with different layer thicknesses and Cr∕Te flux ratios. A phase diagram of the growth parameters is established based on the detailed analyses of the reflection high-energy electron diffraction patterns, atomic force microscopy, and magnetization. Our high-resolution transmission electron microscopy results show that under appropriate growth conditions, a metastable zinc-blende (ZB) phase of CrTe film can be achieved with a nominal thickness of 5nm. The magnetic properties of ZB CrTe exhibit a strong in-plane anisotropy with an easy axis along the [001] direction and hard axes along the [011] and [01¯1] directions. Correspondingly, the uniaxial (KU) and cubic (KC) anisotropy constants are obtained through the fitting of the [011] hard-axis direction. The temperature dependence of the remanent magnetization indicates the TC∼100K of ZB CrTe is attained.
Enhanced light absorption in GaN∕AlGaN midinfrared detectors and application for pixel-less upconversion imaging
Authors: Wu L. K. , Hao H. L. , Shen W. Z.
Published: February 2008

Based on the experimental responsivity of single-period GaN∕AlGaN midinfrared (MIR) heterojunction interfacial work-function internal photoemission (HEIWIP) detectors, we have optimized in detail the single- and multiperiod GaN∕AlGaN MIR HEIWIPs to enhance the light absorption in the detectors. The yielded parameters of emitter, intrinsic, and bottom contact layers could achieve large improvement of the MIR peak absorption efficiency in the multiperiod GaN∕AlGaN MIR HEIWIPs. Employing the concept of photon frequency upconversion, we have further investigated the realization of MIR pixel-less upconversion imaging through the integration of GaN∕AlGaN MIR HEIWIP with a GaN∕AlGaN violet light-emitting diode (LED). Under the optimized device structures, good imaging characteristics and high upconversion efficiency could be expected in the GaN∕AlGaN HEIWIP-LED MIR upconverter.
Improvement of photovoltaic response based on enhancement of spin-orbital coupling and triplet states in organic solar cells
Authors: Xu Zhihua , Hu Bin , Howe Jane
Published: February 2008

This article reports an improvement of photovoltaic response by dispersing phosphorescent Ir(ppy)3 molecules in an organic solar cell of poly[2-methoxy-5-(2′-ethylhexyloxy)-1 4-phenylenevinylene] (MEH-PPV) blended with surface-functionalized fullerene 1-(3-methyloxycarbonyl)propy(1-phenyl [6,6]) C61 (PCBM). The magnetic field–dependent photocurrent indicates that the dispersed Ir(ppy)3 molecules increase the spin-orbital coupling strength with the consequence of changing the singlet and triplet ratios through intersystem crossing due to the penetration of the delocalized π electrons of MEH-PPV into the large orbital magnetic field of Ir(ppy)3 dopants. The tuning of singlet and triplet exciton ratios can lead to an enhancement of photovoltaic response due to their different contributions to the two different photocurrent generation channels: exciton dissociation and exciton-charge reaction in organic materials. In addition, the photoluminescence temperature dependence reveals that the dispersed Ir(ppy)3 reduces the recombination of dissociated charge carriers in the PCBM doped MEH-PPV. As a result, adjusting singlet and triplet ratios by introducing heavy-metal complex Ir(ppy)3 provides a mechanism to improve the photovoltaic response through controlling exciton dissociation, exciton-charge reaction, and recombination of dissociated charge carriers in organic bulk-heterojunction solar cells.
Surface photovoltage spectroscopy analyses of Cd1−xZnxTe
Authors: Cavalcoli D. , Fraboni B. , Cavallini A.
Published: February 2008

Cd 1 − x Zn x Te alloys have been studied by surface photovoltage spectroscopy (SPS) and energy dispersive spectroscopy (EDS). The analyses of surface photovoltage spectra have been perfomed at near and above band gap energies. Surface recombination effects on the surface photovoltage have been investigated. SPS analyses of Cd1−xZnxTe alloys with different surface conditions have shown that the surface recombination velocity significantly affects the SPS determination of the material band gap. Accounting for this and preparing the surfaces accordingly, SPS spectra of Cd1−xZnxTe samples have allowed an accurate determination of the optical band gap as a function of the Zn concentration, determined via EDS analyses. The local increases in the density of states associated with band structure features in Cd1−xZnxTe alloys have been investigated by SPS spectra in the above band gap energy range.
Dynamic modulation transfer function measurement of image intensifiers using a narrow slit
Authors: Zhu Hong-quan , Wang Kui-lu , Xiang Shi-ming , Song Gu-zhou
Published: February 2008

Modulation transfer function (MTF) is an important figure of image resolution of microchannel plate image intensifiers (MCPIIs). Dynamic MTFs of two Gen-II MCPIIs were measured under pulsed voltage operation (gated mode) using a narrow slit. The resolution determined by the MTF was calculated under various bias voltages and gate widths. Our numerical results show that with the increase of the reverse bias of MCPIIs, the resolution is improved rapidly below 40V and then gradually decreased. With the MCP bias increased, both MCPIIs start to suffer rapid reductions in resolution at 800 and 750V, respectively. The change of phosphor voltage has little influence on the resolution. The resolution declines rapidly with the decrease of the gate width below 20ns but goes steady above 30ns. We explored causes of these variations.
Compact metal insulator semiconductor delay lines
Authors: Khajooeizadeh Arash , Abhari Ramesh
Published: February 2008

Compact low-loss delay lines using a low-resistivity silicon substrate are designed and investigated in this paper. The studied lines have metal-insulator-semiconductor (MIS) substrate profiles. Substrate parameters such as layer thickness and resistivity are chosen in a way to allow for low-loss signal propagation in the slow-wave region. Subsequently, meander MIS microstrip lines are designed and their layout parameters are optimized to maximize the delay while maintaining the component area small.