bluuebunny/crossref_metadata_2025 huggingface dataset:
Using coherent population trapping in test atoms for magnetic field measurements in toroidal plasmas
Authors: Akhmedzhanov R. A. , Gushchin L. A. , Zelensky I. V. , Litvak A. G. , Tokman M. D.
Published: September 2007

A way to measure the profile of the safety factor in toroidal controlled-fusion setups has been developed. The method is based on measuring the ratio of the poloidal magnetic field and the toroidal one locally, based on a modification of the optical resonance-fluorescence signal. The effect of partial suppression of resonance fluorescence is used, which depends on the orientation of the magnetic field relative to the laser beam, and takes place in case of coherent population trapping in test atoms with the Zeeman split-level structure, as affected by double-frequency laser radiation.
Wave transmission characteristics of a wave-cutoff probe in weakly ionized plasmas
Authors: Jun Hyun-Su , Na Byung-Keun , Chang Hong-Young , Kim Jung-Hyung
Published: September 2007

The physical properties of a wave transmission spectrum were analyzed using a wave-cutoff probe and a three-dimensional wave simulation in weakly ionized plasma. The experimental wave transmission was compared to the calculated wave transmission. The new path of wave transmission below the wave-cutoff frequency was found, and the wave transmission properties depending on the chamber geometry above the wave-cutoff frequency were also analyzed. Through these wave transmission results, the causes of an electromagnetic propagation phenomenon below the wave-cutoff frequency were examined. Moreover, the impacts of a cavity mode within the plasma chamber on the features of wave transmission were identified.
Existence and stability of alternative ion-acoustic solitary wave solution of the combined MKdV-KdV-ZK equation in a magnetized nonthermal plasma consisting of warm adiabatic ions
Authors: Das Jayasree , Bandyopadhyay Anup , Das K. P.
Published: September 2007

The purpose of this paper is to present the recent work of Das et al. [J. Plasma Phys. 72, 587 (2006)] on the existence and stability of the alternative solitary wave solution of fixed width of the combined MKdV-KdV-ZK (Modified Korteweg-de Vries-Korteweg-de Vries-Zakharov-Kuznetsov) equation for the ion-acoustic wave in a magnetized nonthermal plasma consisting of warm adiabatic ions in a more generalized form. Here we derive the alternative solitary wave solution of variable width instead of fixed width of the combined MKdV-KdV-ZK equation along with the condition for its existence and find that this solution assumes the sech profile of the MKdV-ZK (Modified Korteweg-de Vries-Zakharov-Kuznetsov) equation, when the coefficient of the nonlinear term of the KdV-ZK (Korteweg-de Vries-Zakharov-Kuznetsov) equation tends to zero. The three-dimensional stability analysis of the alternative solitary wave solution of variable width of the combined MKdV-KdV-ZK equation shows that the instability condition and the first order growth rate of instability are exactly the same as those of the solitary wave solution (the sech profile) of the MKdV-ZK equation, when the coefficient of the nonlinear term of the KdV-ZK equation tends to zero.
Dust in the magnetized sheath
Authors: Pandey B. P. , Samarian A. , Vladimirov S. V.
Published: September 2007

In the present work the structure of the magnetized sheath is investigated in the multifluid framework. The ambient magnetic field is assumed parallel to the wall and the effect of the plasma magnetization, plasma ionization, and plasma-neutral collisions on the sheath is examined. It is shown that the width of the non-neutral boundary layer is dependent on the collision frequencies as well as on the plasma magnetization. The size of the sheath layer can decrease with the increase in magnetic field. The increase in the ion-neutral collision can also adversely affect the sheath size. The equilibrium and levitation of the dust particles in a collisional magnetized sheath are shown to depend on the collision frequencies and on the magnetization. Further, the increase in the collision or magnetization invariably leads to the presence of the positively charged grains near the plasma wall suggesting that the grain levitation inside the charged layer is implicitly dependent on the plasma parameters in a nontrivial way.
Cryptand based solid-state electrolytes in polymer light-emitting devices
Authors: Mauthner Gernot , Scherf Ullrich , List Emil J. W.
Published: September 2007

In order to gain improved insight into the fundamental mode of operation of light-emitting electrochemical cells (LECs), LECs were prepared from a solid-state electrolyte, consisting of the cryptand (Kryptofix® 222, [2.2.2] cryptand) and lithium triflate, and a blue emitting low-Stokes-shift poly(para-phenylene). The devices reveal LEC-like characteristics, however, their evolution appear on a longer time scale, which is a consequence of reduced cation conductivity of the [2.2.2] cryptands compared to commonly used ion conductors and decelerated electrochemical n doping near the cathode. It is possible to study the location and direction of the emission zone shift during device operation.
Laser generated proton beam focusing and high temperature isochoric heating of solid matter
Authors: Snavely R. A. , Zhang B. , Akli K. , Chen Z. , Freeman R. R. , Gu P. , Hatchett S. P. , Hey D. , Hill J. , Key M. H. , Izawa Y. , King J. , Kitagawa Y. , Kodama R. , Langdon A. B. , Lasinski B. F. , Lei A. , MacKinnon A. J. , Patel P. , Stephens R. , Tampo M. , Tanaka K. A. , Town R. , Toyama Y. , Tsutsumi T. , Wilks S. C. , Yabuuchi T. , Zheng J.
Published: September 2007

The results of laser-driven proton beam focusing and heating with a high energy (170J) short pulse are reported. Thin hemispherical aluminum shells are illuminated with the Gekko petawatt laser using 1μm light at intensities of ∼3×1018W∕cm2 and measured heating of thin Al slabs. The heating pattern is inferred by imaging visible and extreme-ultraviolet light Planckian emission from the rear surface. When Al slabs 100μm thick were placed at distances spanning the proton focus beam waist, the highest temperatures were produced at 0.94× the hemisphere radius beyond the equatorial plane. Isochoric heating temperatures reached 81eV in 15μm thick foils. The heating with a three-dimensional Monte Carlo model of proton transport with self-consistent heating and proton stopping in hot plasma was modeled.
Gyrokinetic simulations of collisionless magnetic reconnection
Authors: Rogers B. N. , Kobayashi S. , Ricci P. , Dorland W. , Drake J. , Tatsuno T.
Published: September 2007

Linear and nonlinear gyrokinetic simulations of collisionless magnetic reconnection in the presence of a strong guide field are presented. A periodic slab system is considered with a sinusoidally varying reconnecting magnetic field component. The linear growth rates of the tearing mode in both the large and small Δ′ regimes are compared to kinetic and fluid theory calculations. In the nonlinear regime, focusing on the limit of large Δ′, the nonlinear reconnection rates in the gyrokinetic simulations are found to be comparable to those obtained from a two-fluid model. In contrast to the fluid system, however, for Ti⪢Te and very small initial perturbation amplitudes, the reconnection in the gyrokinetic system saturates in the early nonlinear phase. This saturation can be overcome if the simulation is seeded initially with sufficient random noise.
Design-atom approach for the quantum mechanical/molecular mechanical covalent boundary: A design-carbon atom with five valence electrons
Authors: Xiao Chuanyun , Zhang Yingkai
Published: September 2007

A critical issue underlying the accuracy and applicability of the combined quantum mechanical/molecular mechanical (QM/MM) methods is how to describe the QM/MM boundary across covalent bonds. Inspired by the ab initio pseudopotential theory, here we introduce a novel design atom approach for a more fundamental and transparent treatment of this QM/MM covalent boundary problem. The main idea is to replace the boundary atom of the active part with a design atom, which has a different number of valence electrons but very similar atomic properties. By modifying the Troullier-Martins scheme, which has been widely employed to construct norm-conserving pseudopotentials for density functional calculations, we have successfully developed a design-carbon atom with five valence electrons. Tests on a series of molecules yield very good structural and energetic results and indicate its transferability in describing a variety of chemical bonds, including double and triple bonds.
Preferred orientation relationship between Cu6Sn5 scallop-type grains and Cu substrate in reactions between molten Sn-based solders and Cu
Authors: Suh J. O. , Tu K. N. , Tamura N.
Published: September 2007

A strong crystallographic orientation relationship between the Cu6Sn5 scallop-type grains and their Cu substrate has been found by synchrotron micro-x-ray diffraction study. Even though the crystal structures of Cu6Sn5 (monoclinic) and Cu (face-centered-cubic) are very different, angular distributions of crystallographic directions between Cu6Sn5 and Cu revealed a strong orientation relationship. Both SnPb solder and pure Sn showed the same result, indicating that this is general behavior between Sn-based solders and Cu. The strong orientation relation suggests that Cu6Sn5 forms prior to Cu3Sn in the wetting reactions. A total of six different orientation relationships were found. In all the cases, the [1¯01] direction of Cu6Sn5 preferred to be parallel to the [110] direction of Cu with a misfit of 0.24%. Due to pseudohexagonal structure of the Cu6Sn5, the six relationships can be categorized into two groups. From the orientation distribution, one group was found to be less rigid then the other group.
Electromagnetic pulse reflection at self-generated plasma mirrors: Laser pulse shaping and high order harmonic generation
Authors: Bulanov S. S. , Macchi A. , Maksimchuk A. , Matsuoka T. , Nees J. , Pegoraro F.
Published: September 2007

A thin layer of overdense plasma is created when an electromagnetic pulse interacts with a rapidly ionizing thin foil. This layer will reflect the incoming pulse, forming a so-called plasma mirror. A simple realistic model based on paired kinetic and wave equations is used to analytically describe the process of mirror formation and the reflection and transmission of the incident pulse. The model incorporates the exact description of the ionization process in the foil and the polarization and conduction currents that follow. The analytical description of the reflected and transmitted pulses as well as their dependence on foil parameters, and initial pulse amplitude and form are presented. Possible application and effectiveness of this process to improve laser pulse contrast are discussed. In the case of the linearly polarized incident pulse, harmonic generation occurs, that is absent in the case of the circular polarization. The spectra of the reflected pulses for different initial forms and amplitudes are studied.
Mica sheets with embedded metal nanorods: Chemical imaging in a topographically smooth structure
Authors: Graca Malgorzata , Turner Jeff , Marshall Michael , Granick Steve
Published: September 2007

We demonstrate the concept to combine topographical smoothness and plasmonic properties to produce flat substrates with surface enhanced Raman spectroscopy activity—properties that may find use in nanotribology and other thin film applications. Preliminary findings to this end are described. A dual-beam focused ion beam (FIB) system is used to drill large arrays of small pores in single crystals of mica, 2–6μm thick, yielding controlled cross sections (squares, triangles, and circles), sizes (100nm to many microns), and arrangements (square, hexagonal, and random). When filled with metals, arrays result to embedded nanorods with their long axis oriented normal to the surface. As an extension of this method, arrays of nanorods standing perpendicular to a supporting surface can also be produced.
Brownian dynamics simulations of polyelectrolyte molecules traveling through an entropic trap array during electrophoresis
Authors: Lee Yong Min , Joo Yong Lak
Published: September 2007

Using Brownian dynamics simulations of wormlike chain bead-spring models, the dynamics of linear and star-branched polyelectrolyte molecules traveling through an array of entropic traps during electrophoresis have been investigated. First, the effectiveness of using coarse-grained bead-spring systems for linear molecules to model the electrophoretic process was demonstrated and compared to previous bead-rod (Kramers) chain simulations by Panwar and Kumar [Macromolecules 39, 1297 (2006)]. Second, the coarse-grained bead-spring model has been extended to investigate the effect of branching on the dynamics of molecules through the entropic trap array. Initial studies indicate the reduced mobility of star-branched molecules as compared to equivalent linear molecules. The radius of gyration of the polymer molecule appears to be the dominating factor governing the time scales encountered during traversal of the entropic trapping array.
The stability of plane Couette flow of a power-law fluid with viscous heating
Authors: Eldabe Nabil T. M. , El-Sabbagh M. F. , El-Sayed(Hajjaj) M. A.-S.
Published: September 2007

Linear stability analysis is carried out to examine the effect of shear thinning and shear thickening on the stability of plane Couette flow with viscous heating for a power-law fluid that obeys Arrhenius-type law. The relation between shear stress and shear rate is plotted, and the maximum shear stress that must be applied to the system is calculated for different values of the power-law index n. The results showed that the S-shaped curve characterizing the fluid flow that obeys Arrhenius-type law appears at smaller values of the activation energy parameter β, in contrast to the Newtonian case, as a result of shear thinning effect. The resulting eigenvalues are calculated using the Chebyshev collocation method with the QZ algorithm {QZ algorithm is used in solving the singular generalized eigenvalue problem [SIAM J. Numer. Anal. 10, 241 (1973)]}. It is found, for shear thinning/thickening fluid, that the instability occurs at lower/higher values of the Brinkman number Br than in the Newtonian case. Also, the results indicate, for both Newtonian and power-law fluids, that two modes of the instability occur: one termed an inviscid mode, and the second a coupled mode, not a viscous mode as conjectured in C. S. Yueh and C. I. Weng, “Linear stability analysis of plane Couette flow with viscous heating,” Phys. Fluids 8, 1802 (1996).
Matrix Green’s function analysis of multicomponent diffusion in multilayered assemblies
Authors: Kulkarni K. N. , Ram-Mohan L. R. , Dayananda M. A.
Published: September 2007

In order to describe interdiffusion in layered structures in multicomponent systems, matrix Green’s functions may be employed in seeking solutions to multicomponent diffusion equations. A transfer matrix method employing a matrix notation is utilized for this analysis. For single-phase multilayered assemblies set up with thin alloy layers of different compositions between thick terminal alloy disks, expressions for the temporal and spatial evolution of the concentration profiles are developed on the basis of a set of constant interdiffusion coefficients. The theory is developed in general for multilayered diffusion assemblies containing any number of finite layers. It is applied to an experimental ternary diffusion assembly containing one layer sandwiched between two thick terminal alloys in the Cu–Ni–Zn system. The Cu–Ni–Zn layered diffusion assembly was assembled with three α (fcc) Cu–Ni–Zn alloys of different compositions and annealed at 775 °C for 4 days. The agreement between the experimentally observed concentration profiles and the predicted concentration profiles is found to be quite satisfactory.
Depolarization mechanism under compressive stress in Pb(Mg1/3Nb2/3)1−xTixO3 system
Authors: Pruvost Sébastien , Sebald Gaël , Lebrun Laurent , Guyomar Daniel
Published: September 2007

In this article, depolarization mechanisms under compressive stress were reported in ferroelectric materials. For this purpose, measurements were carried out at different scale (microscopic and macroscopic). The percentage of switched domains was calculated from x-ray diffraction diagrams for ceramics with rhombohedral symmetry and the polarization was simulated from these data. It has been underlined that depolarization is mainly caused by domain switching (i.e., extrinsic contribution) for both tetragonal and rhombohedral structures. A discussion on long range dipole-dipole is presented based on the assumptions made for polarization simulation. The main thermodynamic driving force for domain switching is thus shown to be only mechanical under compressive stress. As a consequence, tetragonal material is harder than rhombohedral one due to a larger domain switching induced strain.
Analysis of photon recycling using metallic photonic crystal
Authors: Kim Yong-Sung , Lin Shawn-Yu , Chang Allan S. P. , Lee Jae-Hwang , Ho Kai-Ming
Published: September 2007

We investigate a photon recycling scheme using two-dimensional metallic photonic crystals made of silver to improve the energy efficiency of an incandescent light source. A theoretical framework is presented to analyze the resultant photon-recycled lighting system. Calculation results show that the system can reach a maximum luminous efficiency of 125 lm/W, which is 8 times higher than that of a bare blackbody radiation at 2800 K. The color temperature of the system is calculated to be around 3500 K or below, while the color rendering index is between 68 and 90. These results suggest that a photon-recycled incandescent light source using metallic photonic crystals can be a viable alternative future lighting solution.
Time dependence of CO2 laser pulses recorded in the mixed detector regime of the photon drag and Seebeck effects in n-doped GaAs
Authors: Kotov V. , Stiens J. , Shkerdin G. , Vandermeiren W. , Borghs G. , Vounckx R.
Published: September 2007

In this paper, we present experimental work on the temporal profiling of transversly excited atmosphere (TEA) CO2 laser pulses by using a particular kind of semiconductor photodetector. The detector exploits the combined effects of two fast sensing mechanisms, namely, the electron temperature related Seebeck and photon drag effects, and one slow mechanism, the phonon related Seebeck effect. The design of the photodetector is such that the typical emitted TEA CO2 laser pulses (100ns peak pulses in combination with a microsecond long tail) induce a transit response between the fast and the slow sensing mechanisms. In the fast regime, the output voltage is proportional to the temporal evolution of the pulse intensity. Starting from the falling edge of the pulses, this proportionality changes its characteristics gradually such that the output voltage becomes proportional to the time dependence of the laser pulse energy. All experimental results are backed by a theoretical model and numerical simulations.
Universal properties of highly frustrated quantum magnets in strong magnetic fields
Authors: Derzhko O. , Richter J. , Honecker A. , Schmidt H.-J.
Published: September 2007

The purpose of the present paper is twofold. On the one hand, we review some recent studies on the low-temperature strong-field thermodynamic properties of frustrated quantum spin antiferromagnets which admit the so-called localized-magnon eigenstates. On the other hand, we provide some complementary new results. We focus on the linear independence of the localized-magnon states, the estimation of their degeneracy with the help of auxiliary classical lattice-gas models, and the analysis of the contribution of these states to thermodynamics.
Impurity induced Dirac point smearing in graphene
Authors: Skrypnyk Y. V. , Loktev V. M.
Published: September 2007

It is shown that in a two-dimensional system with linear dispersion a resonance is present in the vicinity of the Dirac point, when the impurity perturbation magnitude exceeds the bandwidth. The corresponding spectrum rearrangement, which follows at a certain critical impurity concentration, results in a square-root dependence of the width of the concentration smearing region on the concentration. If the perturbation magnitude does not exceed the bandwidth, or the critical concentration is not reached, the width of the concentration smearing region remains exponentially small.
Polarization dependence of vibrational coupling signals in femtosecond stimulated Raman spectroscopy
Authors: Frontiera Renee R. , Mathies Richard A.
Published: September 2007

The polarization dependence of vibrational coupling signals seen in femtosecond stimulated Raman spectroscopy (FSRS) is investigated. Changing the polarization of a pulse used to impulsively excite coherent low frequency chlorine bending motion in CDCl3 has a dramatic effect on the line shape of vibrational sidebands which arise from the anharmonic coupling of the pumped modes at 262 and 365cm−1 with the higher frequency symmetric stretching mode at 652cm−1. The asymmetric bend sideband (652+262cm−1) changes sign and magnitude as the impulsive pulse polarization is rotated relative to the Raman pulses, while the symmetric bend sideband (652+365cm−1) is relatively polarization independent. These experiments demonstrate the ability of FSRS to obtain time-resolved information on not only the vibrational coupling strength but also the symmetry of anharmonically coupled modes.
Characteristic functions for uniformly twisted birefringent media
Authors: Valyukh Iryna , Valyukh Sergiy , Arwin Hans , Chigrinov Vladimir
Published: September 2007

We present two functions for characterization of birefringent media with application to twisted nematic liquid crystal (LC) cells in the field off state. The first function is for reflective LC cells and the second is for transmissive LC cells. Based on the Stockes formalism, it is shown that these functions describe the ability of a layer of the twisted birefringent medium to change polarization of the output light and are invariant to the layer orientation. The characteristic functions are found in simple procedures and can be used for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving optimization problems.
Magnetic and transport properties of nanocrystalline
Nd
0.5
Sr
0.5
MnO
3
Authors: Biswas Anis , Das I.
Published: September 2007

Nanocrystalline Nd0.5Sr0.5MnO3 of average particle size 30 and 55 nm are prepared by the sol-gel technique. Transport, magnetotransport, magnetization, specific heat, and current-voltage characteristics studies have been performed on the samples. Our experimental results indicate that the ferromagnetic transition temperatures of the nanocrystalline samples decrease in comparison with the bulk form of the sample. However, the ferromagnetic to charge ordered antiferromagnetic transition does not occur down to 2 K. The properties of the nanoparticles are discussed in detail which will provide a deeper insight into the physics of charge ordering and related phenomena in the rare-earth based manganites especially in their nanocrystalline form.
Multimillion-atom nanoindentation simulation of crystalline silicon carbide: Orientation dependence and anisotropic pileup
Authors: Chen Hsiu-Pin , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya , Szlufarska Izabela
Published: September 2007

We have performed multimillion-atom molecular dynamics simulations of nanoindentation on cubic silicon carbide (3C-SiC) surfaces corresponding to three different crystallographic directions, (110), (001), and (111), using pyramidal-shaped Vickers indenter with 90° edge angle. Load-displacement (P-h) curves show major and minor pop-in events during loading. Detailed analysis of the (110) indentation shows that the first minor discontinuity in the P-h curve is related to the nucleation of dislocations, whereas the subsequent major load drops are related to the dissipation of accumulated energy by expansion of dislocation loops and changes of slip planes. Motion of dislocation lines in the indented films involves a kink mechanism as well as mutually repelling glide-set Shockley partial dislocations with associated extension of stacking faults during the expansion of dislocation loops. Our simulations provide a quantitative insight into the stress distribution on slip planes and stress concentration at kinks and dislocation cores. The estimated Peierls stress is 7.5GPa≈3.9×10−2G, where G is the shear modulus. We find that similar deformation mechanisms operate during nanoindentation of the three surfaces but the calculated hardness values are different, the highest being 27.5GPa for the (111) plane. Anisotropic pileup patterns are observed after the indenter is unloaded and they all reside on (111) and (1¯1¯1) slip planes. These patterns are closely related to dislocation activities on the two slip planes. The anisotropy is a consequence of the asymmetry of the 3C-SiC crystal in which only (111) and (1¯1¯1) slip planes are active out of the {111} family.
Water soluble CdS nanoparticles with controllable size prepared via femtosecond laser ablation
Authors: Gong Weiwei , Zheng Zhuhong , Zheng Jinju , Hu Xuebing , Gao Wei
Published: September 2007

Small water soluble CdS nanocrystals (NCs) with excellent colloidal stability were prepared by femtosecond laser ablation of a bulk CdS target without using any surfactant. CdS NCs of different sizes ranging from 2.0 to 8.6 nm can be produced by simply adjusting the laser fluence at low values, which are just above the ablation threshold. The obtained CdS NCs show a relatively narrow size distribution, which gradually narrows as the laser fluence decreases, as can be seen in the transmission electronic microscopic images. UV-vis optical absorption, photoluminescence, and fluorescence lifetime were also used to characterize the NCs. These as-prepared small crystals show excellent water solubility and have good colloidal stability. Their size is easily controlled as well. Together, the above-mentioned properties make these NCs of interest for luminescence labeling and sensing applications.
Enhanced oxygen out-diffusion in silicon crystal doped with germanium
Authors: Chen Jiahe , Yang Deren , Ma Xiangyang , Fan Ruixin , Que Duanlin
Published: September 2007

Out-diffusion of oxygen during high temperature annealing has been investigated in Czochralski silicon with germanium doping through the spreading resistance profile and secondary ion mass spectrometry techniques. It has been suggested that oxygen out-diffusion in silicon could be enhanced by germanium doping when annealed at 1050 °C−1200 °C. Such enhancement effect increases with the annealing temperature applied to materials as well as increases with the germanium concentration introduced in silicon. It is proposed that the enhanced oxygen out-diffusion may be due to the fast diffusion channel for the interstitial oxygen atoms, which is induced by the substituted germanium atoms in silicon.
Use of DNA in the fabrication of solid state dye sensitized solar cells
Authors: Bandyopadhyay A. , Ray A. K. , Sharma A. K.
Published: September 2007

Double stranded calf-thymus deoxyribonucleic acid (DNA) and elementary adenine DNA base were employed as solid state electrolytes in a dye sensitized nanocrystalline titanium dioxide (TiO2) solar cell, where the sensitizing dye was Rose Bengal. Depending upon the type of the DNA used, the short circuit currents in the cells increases between 200% and 400%. The stability of adenine based devices was found to be higher than those made of calf-thymus DNAs. Thus self-refueling of solid-state dye-sensitized solar cells using DNA has been demonstrated.
Interlayer tunneling and the problem of superfluidity in bilayer quantum Hall systems
Authors: Fil D. V. , Shevchenko S. I.
Published: September 2007

A possibility of nondissipative transmission of electrical current from the source to the load using superfluid electron-hole pairs in bilayers is studied. The problem is considered with reference to quantum Hall bilayers with the total filling factor VT=1. At nonzero interlayer tunneling the current pattern looks as a sum of uniform planar counterflow currents and Josephson vortices. The difference of electrochemical potentials of the layers (that is required to support the current in the load circuit) causes the motion of the Josephson vortices. In such a situation the second superfluid viscosity comes into play and results in dissipation of energy. It is found that the loss power is proportional to the square of the matrix element of the interlayer tunneling and depends nonlinearly on the load resistance.
Spin modes in electron Fermi liquid of organic conductors
Authors: Peschansky V. G. , Stepanenko D. I.
Published: September 2007

The propagation of spin waves in Q2D layered conductors placed in a magnetic field is studied. It is shown, that at certain orientations of the magnetic field with respect to the layers the collisionless absorption is absent and weakly damping spin waves can propagate even under the strong spatial dispersion. We have analyzed the spectrum of spin modes at an arbitrary form of Landau-Silin correlation function.
A Monte Carlo study of the Falicov-Kimball model in the perturbative regime
Authors: Musiał G. , Dȩbski L. , Wojtkiewicz J.
Published: September 2007

Finite-temperature properties of the Falicov-Kimball model on the square lattice have been studied in the perturbative regime, i.e., for t/U⪡1, where t is the hopping constant and U denotes the Coulomb interaction strength. In our study, we have determined the phase diagram of the model in the second-order of the perturbation theory, where the antiferromagnetic Ising model in the magnetic field emerges. In the fourth-order, where our model constitutes the Ising model with more complicated frustrated antiferromagnetic interactions, the sketch of the phase diagram was established. The Monte Carlo method was employed and the behavior of Binder cumulants based on the order parameters was analyzed to determine the type of ordering and phase boundaries in the diagram.
Investigation of effective-medium approximation, alloy, average-composition, and graded-composition models for interface analysis by spectroscopic ellipsometry
Authors: Kim T. J. , Ghong T. H. , Kim Y. D. , Aspnes D. E. , Klein M. V. , Ko D-S. , Kim Y-W. , Elarde V. C. , Coleman J. J.
Published: September 2007

We critically test the capabilities of the effective-medium approximation (EMA) and alloy models to describe multilayer samples with gradual interfaces by analyzing spectroscopic ellipsometric (SE) data of two AlGaAs samples grown expressly for this purpose. The dielectric functions ε of the interfaces are calculated in the EMA and alloy models, and the interfaces themselves simulated either as a single layer of Al0.5Ga0.5As or a stack of layers of AlxGa1−xAs with x increasing or decreasing between 0.1 and 0.9 in increments of 0.1. The EMA essentially fails completely for either interface representation. For the alloy model the stepwise-graded representation is significantly better, not only simulating the data more accurately but also yielding thicknesses in essential agreement with those obtained by cross-sectional transmission electron microscopy. The results highlight the types of errors that are encountered with the different models, and show that the analysis of SE data can provide information about these interfaces.
Magnetic and magneto-optical properties of Nd3Ga5O12 in high magnetic fields
Authors: Wang Wei
Published: September 2007

In this article, we theoretically investigate the magnetic and magneto-optical properties of Nd3Ga5O12 in high magnetic fields (up to 35 T). Here, in view of the antiferromagnetism below the Néel temperature, a particular consideration of two magnetic sublattices A and B in Nd3Ga5O12 is presented. Taking account of the indirect exchange interaction, the complicated nonlinearity of magnetization (M) with the external magnetic field (He) is quantitatively described. In addition, we detailedly deduce the relation of Faraday rotation (θF) with the external magnetic fields. In our theoretical model, it is emphasized that θF strongly depends on the magnetization of the two different magnetic sublattices (MA and MB) and He. Referring to the values of MA and MB, the Faraday rotations are simulated at four different wavelengths in Nd3Ga5O12. Our theoretical results can excellently fit the experimental work by Guillot.
Strong enhancement of flux pinning in thick NdBa2Cu3O7-δ films grown on ion-beam assisted deposition-MgO templates via three-dimensional self-assembled stacks of BaZrO3 nanodots
Authors: Wee S. H. , Goyal A. , Li J. , Zuev Y. L. , Cook S.
Published: September 2007

Thick, epitaxial NdBa2Cu3O7-δ (NdBCO) films (up to 2.1 μm) with a high density of nanoscale columnar defects parallel to the c-axis of the film were deposited on ion-beam assisted deposition-MgO templates via pulsed laser deposition. The columnar defects were composed of self-assembled BaZrO3 (BZO) nanodots. A significant enhancement in Jc for H∥c is found for these films. In addition, an overall improvement in the in-field Jc at all field orientations is observed. Compared to pure NdBCO of similar thickness, the in-field Jc at H∥c for 0.7 μm thick NdBCO+BZO film is improved by a factor of 2–4 in the field range of 0.1–4 T and 10–20 at 7–8 T at 77 K. In addition, a smaller α∼0.17 is found in the field regime where Jc∼H−α. Also, a higher maximum pinning force, Fpmax∼14 GN∕m3, is found at 3 T and a larger Hirr over 8 T is found for the NdBCO films with columnar defects.
ac electroosmotic pumping induced by noncontact external electrodes
Authors: Wang Shau-Chun , Chen Hsiao-Ping , Chang Hsueh-Chia
Published: September 2007

Electroosmotic (EO) pumps based on dc electroosmosis is plagued by bubble generation and other electrochemical reactions at the electrodes at voltages beyond 1 V for electrolytes. These disadvantages limit their throughput and offset their portability advantage over mechanical syringe or pneumatic pumps. ac electroosmotic pumps at high frequency (>100 kHz) circumvent the bubble problem by inducing polarization and slip velocity on embedded electrodes,1 but they require complex electrode designs to produce a net flow. We report a new high-throughput ac EO pump design based on induced-polarization on the entire channel surface instead of just on the electrodes. Like dc EO pumps, our pump electrodes are outside of the load section and form a cm-long pump unit consisting of three circular reservoirs (3 mm in diameter) connected by a 1×1 mm channel. The field-induced polarization can produce an effective Zeta potential exceeding 1 V and an ac slip velocity estimated as 1 mm/sec or higher, both one order of magnitude higher than earlier dc and ac pumps, giving rise to a maximum throughput of 1 μl∕sec. Polarization over the entire channel surface, quadratic scaling with respect to the field and high voltage at high frequency without electrode bubble generation are the reasons why the current pump is superior to earlier dc and ac EO pumps.
Effective conformational search methods for biological macromolecules
Authors: Çelik T.
Published: September 2007

The configuration space of many complex physical systems presents a rough energy landscape consisting of tremendous number of local minima separated by high energy barriers. One way to overcome these barriers is to perform the simulation in a generalized ensemble where each state is weighted by a non-Boltzmann probability weight factor. The multicanonical ensemble approach (MUCA) overcomes this difficulty by performing a random walk in one-dimensional energy space. Our attempts to design hybrid generalized ensemble algorithms will be reported. The folding of a protein into its native structure involves one or more transitions between distinct phases. The representation of the energy landscape would be useful for the determination of the conformational transition temperatures. Such a study would lead to clear indications of the equilibrium conformations of proteins and provide a detailed picture of the folding pathway. The topographic structure of energy landscape of short peptides is presented.
An auto-incrementing nanosecond delay circuit
Authors: Jang H. U. , Blieck J. , Veshapidze G. , Trachy M. L. , DePaola B. D.
Published: September 2007

We describe a circuit that acts as an auto-incrementing delay. The circuit allows the user to adjust the total number of delays in a cycle, the incremental delay value, and the amount of time that is spent at each delay step. The circuit is stand-alone, yet is readily interfaced to data acquisition systems. Depending on the delay chip used and the number of steps required, the delay step can be as short as 250 ps or as long as 640 ns. The circuit has been used to control the temporal separation between pulses from independent lasers. This was instrumental in our measurement of population dynamics in an optically excited three-level ladder system.
Magnetostriction measuring device based on an optical fiber sensor with an annular photodiode
Authors: de Manuel V. , del Real R. P. , Alonso J. , Guerrero H.
Published: September 2007

A new simple and sensitive dilatometer to measure magnetostriction of ribbons has been developed, based on an optical fiber sensor using an annular photodiode. The optical fiber is used bidirectionally, both for emission and detection of light, simplifying the access to the ribbon under test. The working principle is based on the measurement by reflection of the longitudinal displacement of the ribbon end. For a Vitroperm® amorphous ribbon of 100 mm length, 21 μm thickness, and 8.3 mm width, a displacement of 2.571 μm with a maximum uncertainty of 8 nm has been obtained.
Spring constant calibration of atomic force microscopy cantilevers with a piezosensor transfer standard
Authors: Langlois E. D. , Shaw G. A. , Kramar J. A. , Pratt J. R. , Hurley D. C.
Published: September 2007

We describe a method to calibrate the spring constants of cantilevers for atomic force microscopy (AFM). The method makes use of a “piezosensor” composed of a piezoresistive cantilever and accompanying electronics. The piezosensor was calibrated before use with an absolute force standard, the NIST electrostatic force balance (EFB). In this way, the piezosensor acts as a force transfer standard traceable to the International System of Units. Seven single-crystal silicon cantilevers with rectangular geometries and nominal spring constants from 0.2 to 40 N∕m were measured with the piezosensor method. The values obtained for the spring constant were compared to measurements by four other techniques: the thermal noise method, the Sader method, force loading by a calibrated nanoindentation load cell, and direct calibration by force loading with the EFB. Results from different methods for the same cantilever were generally in agreement, but differed by up to 300% from nominal values. When used properly, the piezosensor approach provides spring-constant values that are accurate to ±10% or better. Methods such as this will improve the ability to extract quantitative information from AFM methods.
A flexible curvilinear electromagnetic filter for direct current cathodic arc source
Authors: Dai Hua , Shen Yao , Li Liuhe , Li Xiaoling , Cai Xun , Chu Paul K.
Published: September 2007

Widespread applications of direct current (dc) cathodic arc deposition are hampered by macroparticle (MP) contamination, although a cathodic arc offers many unique merits such as high ionization rate, high deposition rate, etc. In this work, a flexible curvilinear electromagnetic filter is described to eliminate MPs from a dc cathodic arc source. The filter which has a relatively large size with a minor radius of about 85mm is suitable for large cathodes. The filter is open and so the MPs do not rebound inside the filter. The flexible design allows the ions to be transported from the cathode to the sample surface optimally. Our measurements with a saturated ion current probe show that the efficiency of this flexible filter reaches about 2.0% (aluminum cathode) when the filter current is about 250A. The MP density measured from TiN films deposited using this filter is two to three orders of magnitude less than that from films deposited with a 90° duct magnetic filter and three to four orders of magnitude smaller than those deposited without a filter. Furthermore, our experiments reveal that the potential of the filter coil and the magnetic field on the surface of the cathode are two important factors affecting the efficacy of the filter. Different biasing potentials can enhance the efficiency to up to 12-fold, and a magnetic field at about 4.0mT can improve it by a factor of 2 compared to 5.4mT.
The breakdown of the fingerprinting of vortices by hysteresis loops in circular multilayer ring arrays
Authors: Rose V. , Cheng X. M. , Keavney D. J. , Freeland J. W. , Buchanan K. S. , Ilic B. , Metlushko V.
Published: September 2007

Microscale single-layer ferromagnetic rings typically exhibit a magnetic vortex state at remanence, characterized by a flux-closed magnetic state with zero stray fields. Magnetic reversal in such systems yields a vanishing remanent magnetization. In contrast, the authors show that in individual layers in thin rings, which alternate magnetic and nonmagnetic materials (NiFe∕Cu∕Co), layer-resolved hysteresis loops, measured using x-ray resonant magnetic scattering, exhibit the characteristics of a vortex formation, although photoelectron emission microscopy and micromagnetic simulations clearly prove that multidomain states are formed. This result is of considerable importance for the development of pseudo-spin-valve-type structures for applications.
A high-throughput thermoelectric power-factor screening tool for rapid construction of thermoelectric property diagrams
Authors: Otani M. , Lowhorn N. D. , Schenck P. K. , Wong-Ng W. , Green M. L. , Itaka K. , Koinuma H.
Published: September 2007

The authors have developed a high-throughput screening tool that maps out thermoelectric power factors of combinatorial composition-spread film libraries. The screening tool allows one to measure the electrical conductivity and Seebeck coefficient of over 1000 sample points within 6h. Seebeck coefficients of standard films measured with the screening tool are in good agreement with those measured by traditional thermoelectric measurement apparatus. The rapid construction of thermoelectric property diagrams is illustrated for two systems: (Zn, Al)–O binary composition-spread film on Al2O3 (0001) and (Ca,Sr,La)3Co4O9 ternary composition-spread film on Si (100).
Single molecule analysis of bacterial polymerase chain reaction products in submicrometer fluidic channels
Authors: Stavis Samuel M. , Corgié Stéphane C. , Cipriany Benjamin R. , Craighead Harold G. , Walker Larry P.
Published: September 2007

Laser induced fluorescence in submicrometer fluidic channels was used to characterize the synthesis of polymerase chain reaction (PCR) products from a model bacterial system in order to explore the advantages and limitations of on chip real time single molecule PCR analysis. Single oligonucleotide universal bacterial primers and PCR amplicons from the 16S rDNA of Thermobifida fusca (325 bp) were directly detected at all phases of the reaction with low sample consumption and without post-amplification purification or size screening. Primers were fluorescently labeled with single Alexa Fluor 488 or Alexa Fluor 594 fluorophores, resulting in double labeled, two color amplicons. PCR products were driven electrokinetically through a fused silica channel with a 250 nm by 500 nm rectangular cross section. Lasers with 488 nm and 568 nm wavelengths were focused and overlapped on the channel for fluorescence excitation. All molecules entering the channel were rapidly and uniformly analyzed. Photon burst analysis was used to detect and identify individual primers and amplicons, and fluorescence correlation and cross-correlation spectroscopy were used to account for analyte flow speed. Conventional gel and capillary electrophoresis were also used to characterize the PCR amplification, and the results of differences in detection sensitivity and analyte discrimination were examined. Limits were imposed by the purity and labeling efficiency of the PCR reagents, which must be improved in parallel with increases in detection sensitivity.
Measurement of dynamic full-field internal stresses through surface laser Doppler vibrometry
Authors: Holland Stephen D. , Renshaw Jeremy , Roberts Ron
Published: September 2007

We present a method for evaluating internal dynamic stresses in a solid vibrating body from measurements of surface motion. The method relies on the same mathematics as boundary element method: A boundary reciprocity integral represents interior motion as a surface integral of boundary motion times the Green’s function. The surface motions are measured with a laser vibrometer rather than simulated, giving a direct measurement of internal motions and internal dynamic stresses. Experimental results on a flexing beam demonstrate that stresses measured in this fashion match those calculated from elementary theory.
Resistive magnetodielectric property of polycrystalline γ-Fe2O3
Authors: Bonaedy T. , Koo Y. S. , Sung K. D. , Jung J. H.
Published: September 2007

We have systematically investigated the magnetodielectric property of polycrystalline γ-Fe2O3. The dielectric constants of γ-Fe2O3 seem to follow the Maxwell-Wagner model, i.e., their large enhancement and strong temperature and frequency dependences. Positive magnetodielectric property is observed with negative magnetoresistance, at least above 180K. The value of magnetodielectric effect is maximized at the specific frequency, which is inversely proportional to resistivity. Based on the Maxwell-Wagner model and the magnetoresistance, we can reproduce the magnetodielectric effect of γ-Fe2O3.
Critical radii of ferroelectric domains for different decay processes in LiNbO3 crystals
Authors: Kan Yi , Lu Xiaomei , Bo Huifeng , Huang Fengzhen , Wu Xiaobo , Zhu Jinsong
Published: September 2007

The LiNbO3 crystals were polarized at fixed points and characterized by means of scanning probe microscope. The growth evolution and the decay process of the fabricated domains were carefully studied. Two critical radii rC and Rc that determine a different decay behavior of domains were put forward, where rC is considered to correspond to the point when the domains just penetrate the crystal. Those domains with radius larger than rC could exist beyond 5days, those between rC and Rc experienced a distinct metastable state before completely disappearing, while those smaller than Rc were even invisible under piezoresponse force mode.
Use of insulin glargine during pregnancy
Authors: PÖYHÖNEN‐ALHO MARITTA , RÖNNEMAA TAPANI , SALTEVO JUHA , EKBLAD ULLA , KAAJA RISTO J.
Published: September 2007

Background. Good metabolic control maintained throughout pregnancy reduces maternal and fetal complications in diabetic women. The long‐acting insulin analogue glargine has 24‐h persistence and a peakless action profile, and could contribute to more stable daily plasma glucose levels and improved glycemic control. We evaluated the metabolic control associated with insulin glargine during pregnancy in comparison with conventional basal insulin therapy. Methods. Retrospective case‐control analysis of glycemic control and pregnancy complications in 100 type 1 diabetic pregnancies with intermediate‐acting NPH insulin or insulin glargine prior to conception and throughout pregnancy. Results. Overall, glycemic control was not different between the groups, though the decrease in HbA1c from the first to the third trimester was greater with insulin glargine (0.8 versus 0.3%, p = 0.04). The rate of hypoglycemia was comparable. Conclusions. Our findings suggest that, as regards metabolic control, insulin glargine in women with type 1 diabetes is comparable with NPH insulin as basal insulin therapy. No adverse effects were associated with glargine use at the time of conception and during pregnancy.