bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolation and manipulation of living adherent cells by micromolded magnetic rafts
Authors: Gach Philip C. , Wang Yuli , Phillips Colleen , Sims Christopher E. , Allbritton Nancy L.
Published: September 2011

A new strategy for magnetically manipulating and isolating adherent cells with extremely high post-collection purity and viability is reported. Micromolded magnetic elements (termed microrafts) were fabricated in an array format and used as culture surfaces and carriers for living, adherent cells. A poly(styrene-co-acrylic acid) polymer containing well dispersed magnetic nanoparticles was developed for creating the microstructures by molding. Nanoparticles of γFe2O3 at concentrations up to 1% wt./wt. could be used to fabricate microrafts that were optically transparent, highly magnetic, biocompatible, and minimally fluorescent. To prevent cellular uptake of nanoparticles from the magnetic polymer, a poly(styrene-co-acrylic acid) layer lacking γFe2O3 nanoparticles was placed over the initial magnetic microraft layer to prevent cellular uptake of the γFe2O3 during culture. The microraft surface geometry and physical properties were altered by varying the polymer concentration or layering different polymers during fabrication. Cells plated on the magnetic microrafts were visualized using standard imaging techniques including brightfield, epifluorescence, and confocal microscopy. Magnetic microrafts possessing cells of interest were dislodged from the array and efficiently collected with an external magnet. To demonstrate the feasibility of cell isolation using the magnetic microrafts, a mixed population of wild-type cells and cells stably transfected with a fluorescent protein was plated onto an array. Microrafts possessing single, fluorescent cells were released from the array and magnetically collected. A post-sorting single-cell cloning rate of 92% and a purity of 100% were attained.
Dielectrophoretic microfluidic device for the continuous sorting of Escherichia coli from blood cells
Authors: Kuczenski Robert Steven , Chang Hsueh-Chia , Revzin Alexander
Published: September 2011

Microfluidic diagnostic devices promise faster disease identification by purifying and concentrating low-abundance analytes from a flowing sample. The diagnosis of sepsis, a whole body inflammatory response often caused by microbial infections of the blood, is a model system for pursuing the advantages of microfluidic devices over traditional diagnostic protocols. Traditional sepsis diagnoses require large blood samples and several days to culture and identify the low concentration microbial agent. During these long delays while culturing, the physician has little or no actionable information to treat this acute illness. We designed a microfluidic chip using dielectrophoresis to sort and concentrate the target microbe from a flowing blood sample. This design was optimized using the applicable electrokinetic and hydrodynamic theories. We quantify the sorting efficiency of this device using growth-based assays which show 30% of injected microbes are recovered viable, consistent with the electroporation of target cells by the dielectrophoretic cell sorters. Finally, the results illustrate the device is capable of a five-fold larger microbe concentration in the target analyte stream compared to the waste stream at a continuous sample flow rate of 35 μl/h.
Compositional instability in strained InGaN epitaxial layers induced by kinetic effects
Authors: Huang Yong , Melton Andrew , Jampana Balakrishnam , Jamil Muhammad , Ryou Jae-Hyun , Dupuis Russell D. , Ferguson Ian T.
Published: September 2011

In this article several kinetic effects are proposed that induce compositional instabilities in thick InGaN heteroepitaxial layers on GaN templates grown by metalorganic chemical vapor deposition. It was found that by reducing the growth temperature, or increasing the growth rate, or introducing Mg doping, the epitaxial layer changes from a pseudomorphic InGaN with a low indium mole fraction to a relaxed InGaN with a high indium mole fraction. In certain circumstances, both phases can be present in a single layer. The composition and strain inhomogeneity was correlated to the surface morphology and crystalline quality, governed by the growth conditions. It is believed that the compositional instability in InGaN originates from the coupled effects of compressive strain and surface morphology. A smooth surface allows for the growth of pseudomorphic low-indium InGaN, whereas a rough surface promotes the formation of a relaxed high-indium InGaN layer.
Vibrations of H+(D+) in stoichiometric LiNbO3 single crystal
Authors: Szalay Viktor , Lengyel Krisztián , Kovács László , Timón Vicente , Hernández-Laguna Alfonso
Published: September 2011

A first principles quantum mechanical calculation of the vibrational energy levels and transition frequencies associated with protons in stoichiometric LiNbO3 single crystal has been carried out. The hydrogen contaminated crystal has been approximated by a model one obtains by translating a supercell, i.e., a cluster of LiNbO3 unit cells containing a single H+ and a Li+ vacancy. Based on the supercell model an approximate Hamiltonian operator describing vibrations of the proton sublattice embedded in the host crystal has been derived. It is further simplified to a sum of uncoupled Hamiltonian operators corresponding to different wave vectors (\documentclass[12pt]{minimal}\begin{document}$\bm {k}$\end{document}ks) and each describing vibrations of a quasi-particle (quasi-proton). The three dimensional (3D) Hamiltonian operator of \documentclass[12pt]{minimal}\begin{document}$\bm {k}=\bm {0}$\end{document}k=0 has been employed to calculate vibrational levels and transition frequencies. The potential energy surface (PES) entering this Hamiltonian operator has been calculated point wise on a large set of grid points by using density functional theory, and an analytical approximation to the PES has been constructed by non-parametric approximation. Then, the nuclear motion Schrödinger equation has been solved by employing the method of discrete variable representation. It has been found that the (quasi-)H+ vibrates in a strongly anharmonic PES. Its vibrations can be described approximately as a stretching, and two orthogonal bending vibrations. The theoretically calculated transition frequencies agree within 1% with those experimentally determined, and they have allowed the assignment of one of the hitherto unassigned bands as a combination of the stretching and the bending of lower fundamental frequency.
Multiphysics simulation of high-frequency carrier dynamics in conductive materials
Authors: Willis K. J. , Hagness S. C. , Knezevic I.
Published: September 2011

We present a multiphysics numerical technique for the characterization of high-frequency carrier dynamics in high-conductivity materials. The technique combines the ensemble Monte Carlo (EMC) simulation of carrier transport with the finite-difference time-domain (FDTD) solver of Maxwell’s curl equations and the molecular dynamics (MD) technique for short-range Coulomb interactions (electron-electron and electron-ion) as well as the exchange interaction among indistinguishable electrons. We describe the combined solver and highlight three key issues for a successful integration of the constituent techniques: (1) satisfying Gauss’s law in FDTD through proper field initialization and enforcement of the continuity equation, (2) avoiding double-counting of Coulomb fields in FDTD and MD, and (3) attributing finite radii to electrons and ions in MD for accurate calculation of the short-range Coulomb forces. We demonstrate the strength of the EMC/FDTD/MD technique by comparing the calculated terahertz conductivity of doped silicon with available experimental data for two doping densities and showing their excellent agreement.
Design, construction, and testing of a large-cavity, 1-10 GHz Flygare-Balle spectrometer
Authors: Kukolich Stephen G. , Sarkozy Laszlo C.
Published: September 2011

A large pulsed-beam, Fourier transform microwave spectrometer employing 48 in. diameter mirrors and 35″ (NHS-35) diffusion pump has been constructed at the University of Arizona. The Fabry-Perot-type cavity, using the large mirrors provides Q-values in the 15 000 to 40 000 range. Test spectra were obtained using transverse and coaxial injection of the pulsed-nozzle molecular beams. The measured molecular resonance linewidths were 8 kHz for the transverse injection and 2 kHz for coaxial molecular beam injection. Good signal to noise ratios were obtained for the test signals. Strong lines for butadiene iron tricarbonyl were seen with a single beam pulse (S/N = 5/1). Transitions were measured as low as 900 MHz and some previously unresolved hyperfine structure is now resolved for the butadiene iron tricarbonyl spectra. The spectrometer is operated using a personal computer with LABVIEW programs, with provisions for automatic frequency scanning. The extended, low-frequency range of this spectrometer should make it very useful for making measurements on significantly larger molecules and complexes than have been previously studied. The improved resolution, in the coaxial beam mode, will allow better resolution of hyperfine structure. The large diffusion pump allows a higher beam pulse frequency to compensate for the generally lower sensitivity at lower frequencies.
On the effect of particle porosity and roughness in magnetorheology
Authors: Vereda Fernando , de Vicente Juan , Segovia-Gutiérrez Juan P. , Hidalgo-Alvarez Roque
Published: September 2011

We report a study on the mechanical properties of magnetorheological (MR) fluids prepared with porous iron particles with rough surfaces. These particles were obtained by reducing a magnetite precursor in a H2 atmosphere at 400 °C. Small-amplitude dynamic oscillatory and steady shear flow measurements were carried out in the presence of external magnetic fields. Results were compared with those obtained for MR fluids prepared with conventional solid carbonyl iron particles of comparable size. We found significant differences between the rheology of both types of suspensions, and, more importantly, we found that simple available models can predict quantitatively those differences as long as the average density of the particles is known and is used to calculate their effective volume magnetization and the real volume fraction of the MR fluids prepared with them. By doing so, we obtained for both the porous iron suspensions and the solid iron suspensions a single master curve of the dimensionless storage modulus at saturation [G'sat/(μoMs2)] as a function of volume fraction (φ), and a good collapse of the viscosity versus Mason number curves as well as of the yield stress versus applied field curves. Particle porosity is thus an important factor in MR fluids and should be considered in their design and modeling. Finally, the porous iron suspensions also exhibited an atypical thickening behavior that was not observed in the solid iron analogues and that we tentatively ascribe to the rougher surface of the porous particles.
Note: An underwater multi-channel plasma array for water sterilization
Authors: Yang Y. , Kim H. , Starikovskiy A. , Cho Y. I. , Fridman A.
Published: September 2011

A simple yet effective method to generate multi-channel plasma array in water is presented in this paper. Thin circular metal disks sandwiched between dielectric layers were used, allowing the production of large-volume underwater plasma array with higher stability. The system can be further scaled up by stacking multiple metal disks, making it suitable for large-scale industrial water treatment. Generation of UV and reactive species was identified by optical emission spectroscopy. Sterilization experiments were performed. Results show that the device was effective in deactivating E. coli in water over a wide range of initial concentrations ranging from 104 to 108 CFU/ml.
Optics clustered to output unique solutions: A multi-laser facility for combined single molecule and ensemble microscopy
Authors: Clarke David T. , Botchway Stanley W. , Coles Benjamin C. , Needham Sarah R. , Roberts Selene K. , Rolfe Daniel J. , Tynan Christopher J. , Ward Andrew D. , Webb Stephen E. D. , Yadav Rahul , Zanetti-Domingues Laura , Martin-Fernandez Marisa L.
Published: September 2011

Optics clustered to output unique solutions (OCTOPUS) is a microscopy platform that combines single molecule and ensemble imaging methodologies. A novel aspect of OCTOPUS is its laser excitation system, which consists of a central core of interlocked continuous wave and pulsed laser sources, launched into optical fibres and linked via laser combiners. Fibres are plugged into wall-mounted patch panels that reach microscopy end-stations in adjacent rooms. This allows multiple tailor-made combinations of laser colours and time characteristics to be shared by different end-stations minimising the need for laser duplications. This setup brings significant benefits in terms of cost effectiveness, ease of operation, and user safety. The modular nature of OCTOPUS also facilitates the addition of new techniques as required, allowing the use of existing lasers in new microscopes while retaining the ability to run the established parts of the facility. To date, techniques interlinked are multi-photon/multicolour confocal fluorescence lifetime imaging for several modalities of fluorescence resonance energy transfer (FRET) and time-resolved anisotropy, total internal reflection fluorescence, single molecule imaging of single pair FRET, single molecule fluorescence polarisation, particle tracking, and optical tweezers. Here, we use a well-studied system, the epidermal growth factor receptor network, to illustrate how OCTOPUS can aid in the investigation of complex biological phenomena.
Comparing ab initio density-functional and wave function theories: The impact of correlation on the electronic density and the role of the correlation potential
Authors: Grabowski Ireneusz , Teale Andrew M. , Śmiga Szymon , Bartlett Rodney J.
Published: September 2011

The framework of ab initio density-functional theory (DFT) has been introduced as a way to provide a seamless connection between the Kohn–Sham (KS) formulation of DFT and wave-function based ab initio approaches [R. J. Bartlett, I. Grabowski, S. Hirata, and S. Ivanov, J. Chem. Phys. 122, 034104 (2005)10.1063/1.1809605]. Recently, an analysis of the impact of dynamical correlation effects on the density of the neon atom was presented [K. Jankowski, K. Nowakowski, I. Grabowski, and J. Wasilewski, J. Chem. Phys. 130, 164102 (2009)10.1063/1.3116157], contrasting the behaviour for a variety of standard density functionals with that of ab initio approaches based on second-order Møller-Plesset (MP2) and coupled cluster theories at the singles-doubles (CCSD) and singles-doubles perturbative triples [CCSD(T)] levels. In the present work, we consider ab initio density functionals based on second-order many-body perturbation theory and coupled cluster perturbation theory in a similar manner, for a range of small atomic and molecular systems. For comparison, we also consider results obtained from MP2, CCSD, and CCSD(T) calculations. In addition to this density based analysis, we determine the KS correlation potentials corresponding to these densities and compare them with those obtained for a range of ab initio density functionals via the optimized effective potential method. The correlation energies, densities, and potentials calculated using ab initio DFT display a similar systematic behaviour to those derived from electronic densities calculated using ab initio wave function theories. In contrast, typical explicit density functionals for the correlation energy, such as VWN5 and LYP, do not show behaviour consistent with this picture of dynamical correlation, although they may provide some degree of correction for already erroneous explicitly density-dependent exchange-only functionals. The results presented here using orbital dependent ab initio density functionals show that they provide a treatment of exchange and correlation contributions within the KS framework that is more consistent with traditional ab initio wave function based methods.
Impedance spectroscopy of bilayered bismuth ferrite thin films
Authors: Wu Jiagang , Wang John , Xiao Dingquan , Zhu Jianguo
Published: September 2011

Bi0.90La0.10Fe0.85Zn0.15O3/Bi0.90La0.10Fe0.95Zn0.05O3 bilayers with different thickness ratios were deposited on Pt-coated silicon substrates by radio frequency sputtering. A polycrystalline structure with a random grain orientation is induced for all bilayers, owing to the introduction of the bottom Bi0.90La0.10Fe0.95Zn0.05O3 layer with a random orientation. Impedance spectroscopy shows that oxygen vacancies dominate the dielectric relaxation and electrical conduction of these bilayers, and their dielectric relaxation process gradually endures a transition from a long-range relaxation, the coexistence of long-range and localized relaxation, to a localized relaxation with increasing thickness ratios of Bi0.90La0.10Fe0.85Zn0.15O3. Scaling behavior indicates that their dielectric relaxation and conduction mechanisms are independent of the measurement temperature. Different electrical conduction behavior in impedance determines the electrical properties of these bilayers. The bilayer with a higher thickness ratio of Bi0.90La0.10Fe0.95Zn0.05O3 exhibits a higher remanent polarization owing to the involvement of a low defect concentration, as confirmed by the impedance spectroscopy and the dielectric behavior.
Mott insulators: An early selection criterion for materials for photoelectrochemical H2 production
Authors: Huda Muhammad N. , Al-Jassim Mowafak M. , Turner John A.
Published: September 2011

For the last four decades, materials based on oxides have been the primary focus for studies of photo-catalysts for hydrogen production. So far, under visible-light illumination, this approach has not been much successful; only under ultraviolet radiation have oxides shown some limited success. Therefore, it is important to understand the fundamental problem of the photo-conduction properties in oxides at an electronic level. It can be shown that due to their highly localized electronic features, oxides that are Mott insulators are not suitable for photoelectrochemical (PEC) hydrogen production. Even with considerable doping/alloying, improving photo-current in these materials is unlikely. This represents a criterion by which future metal oxide candidates should be screened. Among metal oxides, the 3d elements have greater abundance and are receiving increased attention for application of solar conversion (photovoltaic and PEC), however the issues discussed here would appear to limit their usefulness for this purpose.
Formation of nanoscale gold chain on a Si(110) surface: A density functional investigation
Authors: AlZahrani A. Z. , Srivastava G. P.
Published: September 2011

The adsorption of gold (Au) atoms on a Si(110) surface is theoretically investigated by employing the first-principles plane wave pseudopotential method and the density functional scheme. We have examined the atomic geometries of stable atomic Au wire formation, leading to (1 × 2) and (2 × 5) reconstructions of the Si(110) surface, corresponding to the Au coverages of 0.25 monolayer and 0.4 monolayer, respectively. Both reconstructions are found to have metallic nature, with at least two dispersive bands crossing the Fermi level. The effective mass values of the near-Fermi bands are estimated and compared with the available experimental findings.
Universality for eigenvalue correlations from the unitary ensemble associated with a family of singular weights
Authors: Xu Shuai-Xia , Zhao Yu-Qiu , Zhou Jian-Rong
Published: September 2011

We study the asymptotic behavior of the eigenvalue correlations for the unitary ensemble associated with a family of singular weights w(x; μ) = exp { − (1 − x2)−μ}, x ∈ ( − 1, 1) for μ > 0. When μ ∈ (0, 1/2) these are Szegö class weights, and are non-Szegö when μ ⩾ 1/2. It is proved that the behavior in the bulk of the spectrum is described in terms of the sine kernel, which persists the so-called universality results. While the local behavior at the edge of the spectrum is described in terms of the Airy kernel. A specific scaling of the limit reflects the singular behavior of orthogonal polynomials on [ − 1, 1], with respect to the weight w(x; μ).
Influence of the surface structure and vibration mode on the resistivity of Cu films
Authors: Zhao Ya-Ni , Qu Shi-Xian , Xia Ke
Published: September 2011

The influence of the surface structure and vibration mode on the resistivity of Cu films and the corresponding size effect are investigated. The temperature dependent conductivities of the films with different surface morphologies are calculated by the algorithm based upon the tight-binding linear muffin-tin orbital method and the Green’s function technique. The thermal effect is introduced by setting the atomic displacements according to the Gaussian distribution with the mean-square amplitude estimated by the Debye model. The result shows that the surface atomic vibration contributes significantly to the resistivity of the system. Comparing the conductivities for three different vibration modes, we suggest that freezing the surface vibration is necessary for practical applications to reduce the resistivity induced by the surface electron-phonon scattering.
Diagnostics of laser plasma plume dynamics within an electrically biased confining cavity
Authors: Yeates P. , Kennedy E. T.
Published: September 2011

The dynamics of laser generated plasma plumes expanding within confining surfaces display a two-phase nature. Early phase enhancement due to hydrodynamic containment results in higher temperatures, densities, and average charges states in comparison to freely expanding plasma plumes. Later phase dynamics result in rapid decay of the plasma plume due to lossy plasma—surface interactions. This paper examines laser plasma generation and expansion within rectangular aluminium cavities biased to high voltages (Vbias = ±9 kV). “Hydro-electro-dynamic” confinement of the laser plasma plumes and the expansion dynamics were studied via space and time resolved visible emission spectroscopy. The charged confining cavities displayed enhanced emission, higher electron densities (Ne) and longer emission durations compared to those of an unbiased cavity. This behavior is attributed to the influence of the electric fields in the cavity on the charged particle dynamics within the cavity volume. The degree of enhancement depended strongly on the applied polarity.
Bonded hydrogen in nanocrystalline silicon photovoltaic materials: Impact on structure and defect density
Authors: Xu L. , Li Z. P. , Wen C. , Shen W. Z.
Published: September 2011

We have performed a detailed structural and optical investigation of hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared by plasma-enhanced chemical vapor deposition. The microstructural properties of these thin films are characterized and interpreted physically based on the growth mechanism. Infrared spectroscopy reveals that the bonded hydrogen in a platelet-like configuration, which is believed to be located at grain boundaries, greatly affects oxygen incursions into nc-Si:H thin films, whereas electron spin resonance observations link these incursions to the introduction of dangling bond defects. Consequently, we propose that in nc-Si:H thin films, high bonded-hydrogen content in grain boundaries is of great importance in forming hydrogen-dense amorphous tissues around the small crystalline grains, i.e., compact grain boundary structures with good passivation. Such structures effectively prevent post-deposition oxidation of grain boundary surfaces, which might lead to the formation of dangling bond defects.
Hole effective mass in silicon inversion layers with different substrate orientations and channel directions
Authors: Donetti L. , Gámiz F. , Thomas S. , Whall T. E. , Leadley D. R. , Hellström P.-E. , Malm G. , Östling M.
Published: September 2011

We explore the possibility to define an effective mass parameter to describe hole transport in inversion layers in bulk MOSFETs and silicon-on-insulator devices. To do so, we employ an accurate and computationally efficient self-consistent simulator based on the six-band k·p model. The valence band structure is computed for different substrate orientations and silicon layer thicknesses and is then characterized through the calculation of different effective masses taking account of the channel direction. The effective masses for quantization and density of states are extracted from the computed energy levels and subband populations, respectively. For the transport mass, a weighted averaging procedure is introduced and justified by comparing the results with hole mobility from experiments and simulations.
Mn-activated Na2SiF6 red and yellowish-green phosphors: A comparative study
Authors: Arai Takahiro , Adachi Sadao
Published: September 2011

Mn4+- and Mn2+-activated red and yellowish-green phosphors have been synthesized by the wet chemical etching of Si wafers in aqueous HF/NaMnO4 · H2O and HF/Na2Cr2O7 · 2H2O/Mn solutions, respectively. X-ray diffraction patterns suggest that the synthesized powders are Na2SiF6:Mn4+ and Na2SiF6:Mn2+ with a trigonal structure (space group = D32-P321). Photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and diffuse reflectance measurements were carried out to investigate the optical properties of the phosphors. Franck-Condon analyses of the PL and PLE spectra were performed to determine the zero-phonon energies of the Mn4+- and Mn2+-related transitions in Na2SiF6. Temperature-dependent PL and luminescence decay time measurements were performed from 20 to 300 K, and the obtained results are explained on the basis of the energy level diagram of the 3d3 (Mn4+) and 3d5(Mn2+) electrons in Na2SiF6, taking into account the thermal quenching effect. Electron spin resonance measurements were also performed. This is the first reported synthesis of a yellowish-green phosphor using Na2XF6 (X = a tetravalent metallic ion) as the host crystal.
Local structure and paramagnetic properties of Zn1-xMnxO
Authors: Phan The-Long , Zhang P. , Yang D. S. , Nghia N. X. , Yu S. C.
Published: September 2011

Having based on x-ray absorption spectroscopy, we point out structural phase separation in polycrystalline Zn1-xMnxO ceramics prepared by solid-state reaction. The samples are single phase in the wurtzite structure as x < 0.04. A Mn-concentration increase with x ≥ 0.04 results in the formation of a secondary phase of tetragonal ZnMn2O4 spinel. The feature of x-ray absorption spectra for the Mn K edge reveals an existence of Mn2+ and Mn3+ ions in Zn1-xMnxO, which are responsible for room-temperature paramagnetism. Particularly, when Mn content is increased, there is a chemical shift of the absorption edge toward higher energies, indicating an increase in concentration of Mn3+ ions. Fourier analyses for the spectra of extended x-ray absorption fine structure (EXAFS) shows up the substitution of Mn for Zn sites in the ZnO host lattice. The parameters related to the local structure have been determined and discussed in detail.
Large piezoelectric effect in Pb-free Ba(Ti,Sn)O3-x(Ba,Ca)TiO3 ceramics
Authors: Xue Dezhen , Zhou Yumei , Bao Huixin , Gao Jinghui , Zhou Chao , Ren Xiaobing
Published: September 2011

We designed a Pb-free pseudo-binary system, Ba(Sn0.12Ti0.88)O3-x(Ba0.7Ca0.3)O3 (BTS-xBCT), characterized by a phase boundary starting from a tricritical triple point of a paraelectric cubic phase, ferroelectric rhombohedral, and tetragonal phases. The optimal composition BTS-30BCT exhibits a high piezoelectric coefficient d33 ∼ 530 pC/N at room temperature. In view of the recent report of high piezoelectricity in another Pb-free system BZT-BCT (Liu and Ren, Phys. Rev. Lett. 103, 257602 (2009)), which possesses a similar tricritical triple point in the phase diagram, it seems that forming a suitable phase boundary starting from a tricritical triple point could be an effective way to develop high-performance Pb-free piezoelectrics.
High-precision frequency measurements in the THz spectral region using an unstabilized femtosecond laser
Authors: Füser Heiko , Judaschke Rolf , Bieler Mark
Published: September 2011

We perform high-precision frequency measurements in the THz frequency range using an unstabilized femtosecond laser. A simple and flexible algorithm is used to correct the beating signal resulting from the THz source and one comb line of the rectified optical comb for fluctuations of the laser repetition rate. Using this technique, we demonstrate an accuracy of our measurement device as high as (9 ± 3) · 10−14 for the measurement of a 100 GHz source. This is two orders of magnitude better than previous precision measurements in this frequency range employing femtosecond lasers.
Note: Femtosecond laser micromachining of straight and linearly tapered capillary discharge waveguides
Authors: Wiggins S. M. , Reijnders M. P. , Abuazoum S. , Hart K. , Welsh G. H. , Issac R. C. , Jones D. R. , Jaroszynski D. A.
Published: September 2011

Gas-filled capillary discharge waveguides are important structures in laser-plasma interaction applications, such as the laser wakefield accelerator. We present the methodology for applying femtosecond laser micromachining in the production of capillary channels (typically 200–300 μm in diameter and 30–40 mm in length), including the formalism for capillaries with a linearly tapered diameter. The latter is demonstrated to possess a smooth variation in diameter along the length of the capillary (tunable with the micromachining trajectories). This would lead to a longitudinal plasma density gradient in the waveguide that may dramatically improve the laser-plasma interaction efficiency in applications.
Ab initio potential energy surface and bound states for the Kr–OCS complex
Authors: Feng Eryin , Sun Chunyan , Yu Chunhua , Shao Xi , Huang Wuying
Published: September 2011

The first ab initio potential energy surface of the Kr–OCS complex is developed using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)]. The mixed basis sets, aug-cc-pVTZ for the O, C, and S atom, and aug-cc-pVQZ-PP for the Kr atom, with an additional (3s3p2d1f) set of midbond functions are used. A potential model is represented by an analytical function whose parameters are fitted numerically to the single point energies computed at 228 configurations. The potential has a T-shaped global minimum and a local linear minimum. The global minimum occurs at R = 7.146 a0, θ = 105.0° with energy of −270.73 cm−1. Bound state energies up to J = 9 are calculated for three isotopomers 82Kr–OCS, 84Kr–OCS, and 86Kr–OCS. Analysis of the vibrational wavefunctions and energies suggests the complex can exist in two isomeric forms: T-shaped and quasi-linear. The calculated transition frequencies and spectroscopic constants of the three isotopomers are in good agreement with the experimental values.
Geometrical structure and spin order of Gd13 cluster
Authors: Yuan H. K. , Chen H. , Kuang A. L. , Wu B.
Published: September 2011

The spin-polarized generalized gradient approximation to the density-functional theory has been used to determine the lowest energy structure, electronic structure, and magnetic property of Gd13 cluster. Our results show that the ionic bonding is combined with the covalent characteristics in stabilizing the Gd cluster. The ferrimagnetic icosahedron is found to be the lowest energy configuration, in which the centered Gd atom couples antiferromagnetically with the rest Gd atoms surrounding it. No spin non-collinear evidence has been detected in our calculations. It is identified that the local magnetic moments of Gd atom are about 8 μB regardless of geometrical structure. Finally, the comprehensive electronic structure analyses show that the indirect long-range magnetic coupling between the polarized 4f is mediated by the polarization of 5d, 6s, and 6p conduction electrons, which is the typical Ruderman-Kittel-Kasuya-Yosida interactions.
Cut-off frequencies of Lamb waves in various functionally graded thin films
Authors: Cao Xiaoshan , Shi Junping , Jin Feng
Published: September 2011

An analytical study is carried out on the cut-off frequencies of Lamb waves in freestanding thin films made of various functionally graded elastic, piezoelectric, or piezoelectric–piezomagnetic materials. Results show that the set of cut-off frequencies is a union of two series of approximate arithmetic progression, in which the differences are inversely proportional to the definite integral of a function of the material parameters along thickness. Given the simple and universal relationship between cut-off frequencies and material parameters, this study provides theoretical guidance not only for nondestructive evaluation in engineering applications but for designing high-performance sensors based on Lamb waves.
Whittaker modules over Virasoro-like algebra
Authors: Guo Xiangqian , Liu Xuewen
Published: September 2011

In this paper, we study Whittaker modules over Virasoro-like algebra relative to some total order. We determine all Whittaker vectors and the irreducibilities of the universal Whittaker modules. For the reducible ones, we determine their unique maximal submodules, and the corresponding irreducible quotient modules are just those modules constructed by Batra et al. [J. Algebra 322(12), 4163–4180 (2009)]. Using their results we can deduce more properties on the maximal submodules and irreducible modules.
Effective-mass Klein-Gordon-Yukawa problem for bound and scattering states
Authors: Arda Altuğ , Sever Ramazan
Published: September 2011

Bound and scattering state solutions of the effective-mass Klein-Gordon equation are obtained for the Yukawa potential with any angular momentum ℓ. Energy eigenvalues, normalized wave functions, and scattering phase shifts are calculated as well as for the constant mass case. Bound state solutions of the Coulomb potential are also studied as a limiting case. Analytical and numerical results are compared with the ones obtained before.
Intrinsic point defect incorporation in silicon single crystals grown from a melt, revisited
Authors: Vanhellemont Jan
Published: September 2011

The so-called Voronkov criterion states that the dominant intrinsic point defect in a silicon single crystal grown from a melt is determined by the ratio of pulling speed over temperature gradient near the melt/solid interface. Above a critical value of this ratio, the crystal is vacancy-rich, while for a ratio below this value, the crystal is interstitial-rich. Applying the Voronkov criterion implies, however, intrinsic point defect diffusivities and/or thermal equilibrium concentrations that can differ strongly from those experimentally determined using self- and metal-diffusion experiments. Furthermore, for a given hot zone, crystal diameter, and length, the thermal gradient itself at the melt/solid interface is a function of the pulling speed, so that the criterion in principle can be replaced by one for the thermal gradient only. There is also experimental evidence, based on crystal detaching experiments, that the growing crystal is always vacancy-rich at the solid/melt interface. In the present paper, the validity of the Voronkov criterion is critically reviewed and the impact of stress, in particular on intrinsic point defect thermal equilibrium concentrations, is taken into account and discussed. It is shown that the temperature and stress gradient near the melt-solid interface have an important impact on the intrinsic point defect incorporation and on the formation of grown-in defects that can be observed in the as-grown and thermally treated crystal. It is also likely that both types of intrinsic point defects can be present in supersaturation in different temperature windows during crystal pulling, leading to the observed coexistence of vacancy and self-interstitial clusters in the as-grown crystal. It is shown that, when taking into account stress effects, there is no need to assume intrinsic point defect diffusivities and thermal equilibrium concentrations that are different from those determined, e.g., from self- and metal-diffusion experiments and from ab initio calculations.
On the use of the term “ambipolar”
Authors: Champlain James G.
Published: September 2011

The term ambipolar has been used extensively in association with carbon nanotube and graphene-based field effect transistors, often in a varied manner, leading to a confused understanding of the term. Through the use of established scientific definitions and theoretical work on device operation, this paper attempts to clarify the understanding of the term and present a discussion of its appropriate use.
Nb3Sn nucleation and growth in multifilament superconducting strands monitored by high resolution synchrotron diffraction during in situ reaction
Authors: Thilly L. , Di Michiel M. , Scheuerlein C. , Bordini B.
Published: September 2011

The Nb3Sn volume, crystallite size, and Sn content evolution during the reaction of a recent high critical current density Nb3Sn/Cu composite wire has been monitored by high energy, high resolution synchrotron x-ray diffraction. Thanks to the high flux of high energy x-rays at the ID15A beamline of the European Synchrotron Radiation Facility. It was possible to monitor the Nb3Sn crystallite growth in situ from the early stages of Nb3Sn nucleation at 540 °C up to nearly complete transformation of the Nb precursor into Nb3Sn. Simultaneously, the uptake of Sn in the A15 phase could be monitored by Nb3Sn lattice parameter measurements.
Highly doped p-type nanocrystalline silicon thin films fabricated by low-frequency inductively coupled plasma without H2 dilution
Authors: Yan W. S. , Wei D. Y. , Xu S. , Zhou H. P.
Published: September 2011

p-type nanocrystalline silicon thin films with a series of thicknesses were deposited on both glass and n-type (100) silicon wafer substrates through a low-frequency inductively coupled plasma. No H2 dilution was employed in the growth process. The structural and electric properties of nanocrystalline silicon films were investigated by XRD, Raman spectra, and a Hall effect measurement system. The XRD patterns show an obvious enhancement of the peak intensity with increasing thickness. The crystalline volume fraction of the films ranges from 83% to 87%, depending on the film thickness. The carrier concentration of the films is in the range of 8.1×1019/cm3 – 8.6×1019/cm3. The realization of high doping concentration of p-type nanocrystalline silicon films is related with high electron density (the order of 1011cm-3–1012cm-3) in the chamber. On the basis of these studies, simple structured solar cells, consisting of ZnO: Al thin film (80 nm)/highly doped p-type nanocrystalline silicon films with a series of thickness/n-type (100) silicon wafer substrates, were fabricated and used to assess the performance of p-type nanocrystalline silicon films. The conversion efficiency increases with decreasing the film thickness of p-type nanocrystalline silicon thin films and achieves the largest value of 8.2% when the thin film thickness is near 90 nm.
Enhanced magnetization in erbium doped GaN thin films due to strain induced electric fields
Authors: Woodward N. T. , Nepal N. , Mitchell B. , Feng I. W. , Li J. , Jiang H. X. , Lin J. Y. , Zavada J. M. , Dierolf V.
Published: September 2011

The ferromagnetic properties of erbium-doped GaN (GaN:Er) epilayers grown by metal-organic chemical vapor deposition were studied. It is found that the different tensile strains produced by the respective lattice mismatch for different substrates used (GaN/Al2O3, AlN/Al2O3, GaN/Si (111), and c-GaN bulk) correlate well with the observed room-temperature saturation magnetization. Under application of a magnetic field, the photoluminescence of the erbium dopant, which causes the ferromagnetism, indicates that the magnetic states of the ions are coupled to the electronic states of the host. These results hold promise for the use of strain to control the magnetic properties of GaN:Er films for spintronic applications.
Evidence that the upper critical field of Nb3Sn is independent of whether it is cubic or tetragonal
Authors: Zhou Jian , Jo Younjung , Hawn Sung Zu , Zhou Haidong , Lee Peter J. , Larbalestier David C.
Published: September 2011

Although 2011 marks the 50th anniversary of Nb3Sn as the first high field superconductor, real understanding of its upper critical field behavior Hc2 is incomplete. Here, we show surprising Hc2 data on highly homogeneous bulk samples that exhibit identical upper critical field Hc2(0.3 K) ∼ 29 ± 0.2 T with or without undergoing the cubic-to-tetragonal transition, a result in strong contrast to widely used multiple-source data compilations that show a strong depression of Hc2(0 K) from 29 T to 21.4 T in the tetragonal state.
Measurements of the near-wall hindered diffusion of colloidal particles in the presence of an electric field
Authors: Kazoe Yutaka , Yoda Minami
Published: September 2011

Understanding near-wall diffusion of small particles and biomolecules is important in colloid science and many microfluidic devices. Our experimental measurements of the diffusion of 110–460 nm radii suspended particles in the presence of electric fields up to 3.1 kV/m using particle tracking are in agreement with theoretical predictions for diffusion hindered by the presence of a solid surface. The results suggest that the external electric field has little, if any, effect upon the hindered diffusion of colloidal particles, even when the electrophoretic force exceeds the Stokes drag.
Dark current filtering in unipolar barrier infrared detectors
Authors: Savich G. R. , Pedrazzani J. R. , Sidor D. E. , Maimon S. , Wicks G. W.
Published: September 2011

Control of dark current mechanisms is essential to improving the performance of infrared photodetectors and many other electronic devices. Unipolar barriers can readily be applied to practically and efficiently filter out multiple dark current components exhibited by infrared photodetectors. Via careful placement of unipolar barriers in a standard photodetector architecture, effective suppression of dark currents due to surface leakage, direct band-to-band tunneling, trap-assisted tunneling, and Shockley-Read-Hall generation is demonstrated. We present unipolar barrier photodiodes exhibiting six orders of magnitude improvement in RoA and near Auger-limited device performance.
Modelling Laboratory Data of Bidirectional Reflectance of a Regolith Surface Containing Alumina
Authors: Bhattacharjee C. , Deb D. , Das H. S. , Sen A. K. , Gupta R.
Published: September 2011

Bidirectional reflectance of a surface is defined as the ratio of the scattered radiation at the detector to the incident irradiance as a function of geometry. Accurate knowledge of the bidirectional reflection function for layers composed of discrete, randomly positioned scattering particles is essential for many remote sensing, engineering, and biophysical applications, as well as for different areas of astrophysics. Computations of bidirectional reflection functions for plane parallel particulate layers are usually reduced to solving the radiative transfer equation by the existing techniques. In this work we present our laboratory data on bidirectional reflectance versus phase angle for two sample sizes of alumina, 0.3 and 1 μm, for the He–Ne laser at wavelengths of 632.8 nm (red) and 543.5 nm (green). The nature of the phase curves of the asteroids depends on the parameters like particle size, composition, porosity, roughness, etc. In the present study we analyze data which are being generated using a single scattering phase function, that is, Mie theory of treating particles as a compact sphere. The well-known Hapke formula, along with different particle phase functions such as Mie and Henyey–Greenstein, will be used to model the laboratory data obtained at the asteroid laboratory of Assam University.
The Parkes Observatory Pulsar Data Archive
Authors: Hobbs G. , Miller D. , Manchester R. N. , Dempsey J. , Chapman J. M. , Khoo J. , Applegate J. , Bailes M. , Bhat N. D. R. , Bridle R. , Borg A. , Brown A. , Burnett C. , Camilo F. , Cattalini C. , Chaudhary A. , Chen R. , D'Amico N. , Kedziora-Chudczer L. , Cornwell T. , George R. , Hampson G. , Hepburn M. , Jameson A. , Keith M. , Kelly T. , Kosmynin A. , Lenc E. , Lorimer D. , Love C. , Lyne A. , McIntyre V. , Morrissey J. , Pienaar M. , Reynolds J. , Ryder G. , Sarkissian J. , Stevenson A. , Treloar A. , van Straten W. , Whiting M. , Wilson G.
Published: September 2011

The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 105 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70 cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.
State Response to Informal Groups
Authors: Butterfield Jim
Published: September 2011

I am not entirely satisfied with the term “informal groups.” The terminology is borrowed from the Soviets; it is the term they use most frequently. Many of these informal groups are in fact very formal, they are very sophisticated with committees and subcommittees, agendas, charters, mechanisms for leadership turnover, for membership selection, and in a few cases, some of them are even registered with the State as officially registered unofficial informal groups. I tend to use the terms “social groups” or “social action groups.” Perhaps “unofficial groups” would be a better term.
Pamyat: A Force for Change?
Authors: Krasnov Vladislav
Published: September 2011

Since May 1987 when the Russian nationalist group Pamyat sponsored a number of demonstrations in Moscow, it has been roundly condemned in both the Soviet and Western media for its self-declared anti-Zionism and alleged antisemitism. This rare unanimity of usually opposite views should warrant a pause for sound skepticism and thoughtful analysis. Strangely enough, while Western reaction to Pamyat has been long on condemnation, it remains short on analysis and on understanding of both Pamyat and its condemnation in the Soviet press.
Pamyat's Political Platform: Myth and Reality
Authors: Midford Paul
Published: September 2011

The Patriotic Front Pamyat has received a name recognition and notoriety in the Soviet and western academic literature and press which is unrivaled to this day by any other Russian nationalist organization. The vast majority of observers view Pamyat as a neo-fascist or neo-Stalinist movement. This view of Pamyat is often reenforced by drawing links between the Front and conservatives in the Party and bureaucracy. Thus, many see Pamyat either as a vehicle for conservative reaction from “above” or as a manifestation from “below” of a significant segment of the Russian population opposed to the decentralizing, liberalizing, and westernizing tendencies of perestroika. More often than not, Pamyat is viewed as both.
Pamyat and the Jewish Menace: Remembrance of Things Past
Authors: Klier John D.
Published: September 2011

For veterans of the Russian winter, the term “thaw” will ever remain an appropriate metaphor for the waning of periods of control and repression. Unfortunately, many Soviet political thaws have given way quickly to resurgent winters. Perhaps most significant in the current Soviet thaw, the policies of glasnost and perestroika associated with Mikhail Gorbachev, has been the extent to which Soviet society has been invited to participate in it. Society, in its turn, has responded with the creation of numerous grassroots, unofficial social-action groups (samodeiatelnye obshchestvennye organizatsii).