bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-gating effects in carbon nanotube network based liquid gate field effect transistors
Authors: Kim Dong Wan , Choe Gyu Sik , Seo Sung Min , Cheon Jun Ho , Kim Hansuk , Ko Jung Woo , Chung In Young , Park Young June
Published: December 2008

We developed a field effect transistor which has two concentric electrodes as the source and drain with the carbon nanotube network as a semiconductor channel layer. When this device is placed in an aqueous solution for sensor applications, the electric potential of the liquid is stabilized to the electric potential of the enclosing electrode due to the larger electrical double layer capacitance between the liquid and the enclosing electrode, performing a gate reaction to the carbon nanotube network channel. This new phenomenon, hereafter called the self-gating effect, brings benefits to reliable operation of devices removing the need of an additional external reference electrode.
An example of mathematical authorship attribution
Authors: Basile Chiara , Benedetto Dario , Caglioti Emanuele , Esposti Mirko Degli
Published: December 2008

In this paper we discuss a novel mathematical approach to authorship attribution which we implemented recently to face a concrete problem of author recognition. The fundamental ideas for our methods came from statistical mechanics and information theory. We combine two approaches. Both of them use similarity measures between couples of texts as indicators of stylistic closeness: the first one is based on the comparison of frequencies of fixed length substrings (n-grams) throughout the texts; the second one relies on a suitable use of compression algorithms as relative entropy approximators, in the spirit of the so-called Ziv–Merhav theorem. The two methods were separately developed and then combined, together with a suitable and theoretically founded ranking analysis, to produce an original authorship attribution procedure that yielded very successful results on the specific problem to which it was applied. This ranking analysis could be of interest also in other application fields.
Numerical study of a linear accelerator using laser-generated proton beams as a source
Authors: Antici P. , Fazi M. , Lombardi A. , Migliorati M. , Palumbo L. , Audebert P. , Fuchs J.
Published: December 2008

The injection of laser-generated protons through conventional drift tube linear accelerators (linacs) has been studied numerically. For this, we used the parameters of the proton source produced by ultraintense lasers, i.e., with an intrinsic high beam quality. The numerical particle tracing code PARMELA [L. M. Young and J. H. Billen, LANL Report No. LA-UR-96-1835, 2004] is then used to inject experimentally measured laser-generated protons with energies of 7±0.1 MeV and rms un-normalized emittance of 0.180 mm mrad into one drift tube linac tank that accelerated them to more than 14 MeV. The simulations exhibit un-normalized emittance growths of 8 in x direction and 22.6 in y direction, with final emittances lower than those produced using conventional sources, allowing a potential luminosity gain for the final beam. However, the simulations also exhibit a limitation in the allowed injected proton charge as, over 0.112 mA, space charge effect worsens significantly the beam emittance.
Vibrational energy levels of CH5+
Authors: Wang Xiao-Gang , Carrington Tucker
Published: December 2008

We present a parallelized contracted basis-iterative method for calculating numerically exact vibrational energy levels of CH5+ (a 12-dimensional calculation). We use Radau polyspherical coordinates and basis functions that are products of eigenfunctions of bend and stretch Hamiltonians. The bend eigenfunctions are computed in a nondirect product basis with more than 200×106 functions and the stretch functions are computed in a product potential optimized discrete variable basis. The basis functions have amplitude in all of the 120 equivalent minima. Many low-lying levels are well converged. We find that the energy level pattern is determined in part by the curvature and width of the valley connecting the minima and in part by the slope of the walls of this valley but does not depend on the height or shape of the barriers separating the minima.
Comparative study of photoluminescences for Zn-polar and O-polar faces of single-crystalline ZnO bulks
Authors: Oh D. C. , Kato T. , Goto H. , Park S. H. , Hanada T. , Yao T. , Kim J. J.
Published: December 2008

The authors have an extensive study of photoluminescences for Zn-polar and O-polar faces of single-crystalline ZnO bulks. In the photoluminescence (PL) spectra at 10 K, Zn-polar and O-polar faces show a common emission feature: neutral donor-bound excitons and their longitudinal-optical (LO) phonon replicas are strong and free excitons are very weak. However, in the PL spectra at room temperature (RT), Zn-polar and O-polar faces show extremely different emission characteristics: the emission intensity of Zn-polar face is 30 times larger than that of O-polar face and the band edge of Zn-polar face is 33 meV redshifted from that of O-polar face. The temperature dependence of photoluminescence indicates that the PL spectra at RT are closely associated with free excitons and their phonon-assisted annihilation processes. As a result, it is found that the RT PL spectra of Zn-polar face are dominated by the first-order LO phonon replica of A free excitons, while that of O-polar face is determined by A free excitons. This is ascribed to the difference in exciton-phonon coupling strengths that Zn-polar phase has larger coupling strength than O-polar face.
Low-temperature field-effect and magnetotransport properties in a ZnO based heterostructure with atomic-layer-deposited gate dielectric
Authors: Tsukazaki A. , Ohtomo A. , Chiba D. , Ohno Y. , Ohno H. , Kawasaki M.
Published: December 2008

A top-gate field-effect device with atomic-layer-deposited Al2O3 dielectric was fabricated to investigate magnetotransport properties of two-dimensional electron gas (2DEG) at a semi-insulating ZnO–Mg0.12Zn0.88O double heterostructure grown by laser molecular-beam epitaxy. Hall mobility monotonically increased as the density of accumulated electrons increased. The highest mobility at 2K was recorded to be 5000cm2V−1s−1 at a 2DEG density of 1.2×1012cm−2, which is comparable to the previously reported value for a metallic ZnO∕Mg0.2Zn0.8O heterostructure. Insulator-to-metal transition was observed at a critical density of 6×1011cm−2. The metallic-state channel exhibited Shubnikov–de Haas oscillations, demonstrating an electric-field tunable quantum device based on transparent oxide semiconductor.
A two-dimensional model for enhanced adhesion of film-terminated fibrillar interfaces by crack trapping
Authors: Shen Lulin , Hui Chung-Yuen , Jagota Anand
Published: December 2008

Experiments on a recently developed bioinspired film-terminated fibrillar array show significantly enhanced adhesion compared to a flat unstructured control sample. Adhesion is enhanced because the interfacial crack is trapped close to fibril edges. Using a finite element method and approximate analysis, we study a two-dimensional version of the fibrillar structure to understand the behavior observed in experiments. Several experimental observations are explained by the model: (1) the work to separate a unit area of the interface (W+) is larger than the work of adhesion (Wad) of the flat control sample; (2) the work to heal a unit area of the interface (W−) is smaller than the work of adhesion of the flat control sample; (3) W+ increases with fibril spacing; (4) W+ decreases with film thickness; and (5) W+ decreases with fibril height.
Temporally and spatially resolved measurements of multi-megagauss magnetic fields in high intensity laser-produced plasmas
Authors: Gopal A. , Tatarakis M. , Beg F. N. , Clark E. L. , Dangor A. E. , Evans R. G. , Norreys P. A. , Wei M. S. , Zepf M. , Krushelnick K.
Published: December 2008

We report spatially and temporally resolved measurements of self-generated multi-megagauss magnetic fields produced during ultrahigh intensity laser plasma interactions. Spatially resolved measurements of the magnetic fields show an asymmetry in the distribution of field with respect to the angle of laser incidence. Temporally resolved measurements of the self-generated third harmonic suggest that the strength of the magnetic field is proportional to the square root of laser intensity (i.e., the laser B-field) during the rise of the laser pulse. The experimental results are compared with numerical simulations using a particle-in-cell code which also shows clear asymmetry of the field profile and similar magnetic field growth rates and scalings.
Dynamics of microscale shock/vortex interaction
Authors: Koffi Kossi , Andreopoulos Yiannis , Watkins Charles B.
Published: December 2008

Molecular simulations in a dilute monatomic gas were carried out to characterize the mutual interactions of impinging planar shocks of up to Mach 3 with transverse microvortices having core sizes comparable to the thickness of the shock. Time dependent simulations were performed using the direct simulation Monte Carlo method and then analyzed by applying transport theory to the sampled molecular results. Several flow cases were computed for initially stationary, composite vortices. The results reveal the generic features of the interaction, the effect of vortex size, and the effects of shock strength. In all cases, the applied straining compression in the shock was of the same order as the time scale of the vortex rotation. Most of the features found in shock interaction with a macroscale vortex of the same type were also found at microscale. These include acoustic wave formation, shock diffraction and refraction, vortex deformation and displacement, and dilatational vorticity generation greater than baroclinic vorticity generation. However, the major characteristic that dominated at microscale was the viscous attenuation of the vortex. In contrast to the net vorticity production due to interaction that has been demonstrated at macroscale, the attenuation overwhelmed the vorticity generation mechanisms at microscale, within the parameter ranges studied. The data allowed for the direct computation of the dissipation rate of kinetic energy, which was found to be high inside the shock wave throughout the interaction and significantly higher than a local thermodynamic equilibrium rate computed using the Newtonian continuum constitutive law with Stokes’ hypothesis. The differences between the two rates were substantial for a Mach 3 shock; but at Mach 2 they were close enough to decompose the continuum rate expression to infer the contributions of the various forms of dissipation to the actual rate.
Equilibrium sizes and formation energies of small and large Lennard-Jones clusters from molecular dynamics: A consistent comparison to Monte Carlo simulations and density functional theories
Authors: Julin Jan , Napari Ismo , Merikanto Joonas , Vehkamäki Hanna
Published: December 2008

We have performed molecular dynamics simulations of Lennard-Jones argon clusters in equilibrium with a surrounding vapor and combined them with simulations of nucleation events in supersaturated vapor to investigate the dependence of critical cluster size on the vapor density in the cluster size range of 20–300 atoms. The simulations are performed at reduced temperature T′=0.662, which with the parameter values of Lennard-Jones argon corresponds to 80 K. We obtain bulk equilibrium values by simulating a planar liquid-vapor interface. In the studied cluster size range, we find a linear relation between critical size ΔN∗ and Δμ−3, where Δμ is the chemical potential difference between supersaturated vapor and saturated vapor, but the slope of the line is not given by the Kelvin relation of classical nucleation theory. With this relation, along with the known formation energy of the small critical cluster of the nucleation simulations, we proceed to calculate the formation energies for larger critical sizes by integrating the nucleation theorem. We compare the molecular dynamics results to results from Monte Carlo simulations and both perturbative density functional theory and square gradient theory calculations. We find that the molecular dynamics results are in excellent agreement with the density functional and square gradient values. However, the Monte Carlo critical sizes and formation energies are somewhat lower than the molecular dynamics ones.
Fast vibrational calculation of anharmonic OH-stretch frequencies for two low-energy noradrenaline conformers
Authors: Benoit David M.
Published: December 2008

We introduce a new reduced-coupling technique to accelerate direct calculations of a selected number of vibrational frequencies in large molecular systems. Our method combines the advantages of the single-to-all correlation-corrected vibrational self-consistent field (STA-CC-VSCF) approach [D. M. Benoit, J. Chem. Phys. 125, 244110 (2006)] with those of the fast-CC-VSCF technique [D. M. Benoit, J. Chem. Phys. 120, 562 (2004)] and allows the ab initio calculation of only the relevant parts of the required potential energy surface (PES). We demonstrate, using a set of five aliphatic alcohol molecules, that the new fast-STA-CC-VSCF method is accurate and leads to very substantial time gains for the computations of the PES. We then use the fast-STA-CC-VSCF method to accelerate the computation of the OH-stretch and NH-stretch frequencies of the two lowest-energy conformers of noradrenaline, namely, AG1a and GG1a. Our new approach enables us to run the calculation 89 times faster than the standard CC-VSCF technique and makes it possible to use a high-level MP2/TZP description of the PES. We demonstrate that the influence of the strong mode-mode couplings is crucial for a realistic description of the particular OH-stretch vibrational signature of each conformer. Finally, of the two possible low-energy conformers, we identify AG1a as the one most likely to have been observed in the experiments of Snoek et al. [Mol. Phys. 101, 1239 (2003)].
Time-dependent charge distributions in polymer films under electron beam irradiation
Authors: Yasuda Masaaki , Kainuma Yasuaki , Kawata Hiroaki , Hirai Yoshihiko , Tanaka Yasuhiro , Watanabe Rikio , Kotera Masatoshi
Published: December 2008

The time-dependent charge distribution in polymer film under electron beam irradiation is studied by both experiment and numerical simulation. In the experiment, the distribution is measured with the piezoinduced pressure wave propagation method. In the simulation, the initial charge distribution is obtained by the Monte Carlo method of electron scattering, and the charge drift in the specimen is simulated by taking into account the Poisson equation, the charge continuity equation, Ohm’s law, and the radiation-induced conductivity. The results obtained show that the negative charge deposited in the polymer film, whose top and bottom surfaces are grounded, drifts toward both grounded electrodes and that twin peaks appear in the charge distribution. The radiation-induced conductivity plays an important role in determining the charge distribution in the polymer films under electron beam irradiation.
Ab initio study of substitutional impurity atoms in 4H-SiC
Authors: Miyata Masanori , Higashiguchi Yoshitsune , Hayafuji Yoshinori
Published: December 2008

We have investigated the formation energies, ionization energies, and chemical natures of substitutional group-II, III, V, and VI impurity atoms in 4H-SiC. It is shown that the impurity atoms have lower formation energies on a carbon site than on a silicon site for nitrogen, oxygen, and sulfur regardless of the crystal growth conditions, whereas the favorable sites for boron and selenium depend on the composition. With the exception of the above elements, impurity atoms always substitute on a silicon site. The cluster calculations suggest that antimony introduces a much shallower donor level than those of conventional n-type dopants such as nitrogen and phosphorus. However, its high energy of formation will make it difficult to dope SiC with a high impurity concentration. These results suggest that antimony is a good candidate for an extremely shallow n-type dopant.
Intense white photoluminescence emission of V-implanted zinc oxide thin films
Authors: Müller Sven , Lorenz Michael , Czekalla Christian , Benndorf Gabriele , Hochmuth Holger , Grundmann Marius , Schmidt Heidemarie , Ronning Carsten
Published: December 2008

Pulsed laser deposited ZnO films were implanted with vanadium ions using ion energies between 30 and 250 keV with different fluences yielding vanadium concentrations in the range between 0.8 and 5 at. %. After annealing under oxygen ambient at 800 °C, a broad luminescence band observed by photoluminescence covers nearly the total visible spectral region. This luminescence is a superposition of different bands triggered by the incorporated V and remaining implantation defects. The visual impression of the bright whitish emission of the implanted ZnO has been quantified using the color space map of the Commission internationale de l’Éclairage. Furthermore, the intensity of the white emission strongly increases with increasing V concentration, whereas Ar-implanted reference sample shows only weak white emission.
Spin-current rectification in an organic magnetic/nonmagnetic device
Authors: Hu Guichao , He Keliang , Xie Shijie , Saxena Avadh
Published: December 2008

We propose a spin diode based on an organic magnetic co-oligomer or a magnetic/nonmagnetic heterojunction structure. The current and its spin polarization in the device are calculated with the spin-dependent Landauer–Büttiker formula. It is found that, by reversing the applied bias, the charge current and the spin current (SC) may be rectified at the same time or separately. A normal charge-current rectification usually takes place if the spatial electric structure is asymmetric. While a spin-current rectification may appear in two forms or their combination: one is that the spin-polarized orientation keeps unchanged but the magnitude of the SC is asymmetric with the bias; another is that only the spin orientation of the SC flips when the bias is reversed. By designing a suitable organic spin device, either of the two kinds of spin-current rectifications is obtained in our calculations. Finally, the effects of the properties of the organic interlayer and the structural asymmetry on the rectification are discussed.
Tunable surface band gap in MgxZn1−xO thin films
Authors: Xue Mingshan , Guo Qinlin , Wu Kehui , Guo Jiandong
Published: December 2008

Mg x Zn 1 − x O thin films epitaxially grown on Mo(110) substrate under ultrahigh vacuum condition were studied in situ by various surface analysis techniques including x-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, and high resolution electron energy loss spectroscopy. The results indicate that as-grown MgxZn1−xO films are soluble phase, and a phase transition from wurtzite to cubic structure occurs in the region of x=0.55–0.67. The surface band gap can be tuned continuously with altering the content of Mg in MgxZn1−xO films, and its tunable window width is about 1.9 eV. Based on heterojunction and quantum well structure, this kind of materials can be applied in wide-band-gap semiconductor devices, such as short-wavelength light-emitting devices.
Ferroelastic domains in bilayered ferroelectric thin films
Authors: Mahjoub R. , Anbusathaiah V. , Alpay S. P. , Nagarajan V.
Published: December 2008

We investigate theoretically ferroelastic domain fractions in a heteroepitaxial bilayer consisting of (001) tetragonal PbZrxTi1−xO3 and (001) rhombohedral PbZr1−xTixO3 on a thick (001) passive substrate as a function of the lattice misfit strain between layers and the substrate. By considering the self-strain in each layer and the indirect elastic interaction between the layers, we provide a numerical analysis of the relative domain fractions in the tetragonal layer of a (001)PbZr0.2Ti0.8O3/(001)PbZr0.8Ti0.2O3 and (001)PbZr0.4Ti0.6O3/(001)PbZr0.6Ti0.4O3 bilayer structure as a function of the tetragonal layer thickness on (001)LaAlO3, (001)SrTiO3, and (001) MgO. It is found that the elastic coupling between the tetragonal and rhombohedral layers leads to an excess elastic energy in the tetragonal layer, resulting in a two to three times increase in the ferroelastic domain volume fraction of the tetragonal layer compared to single-layer films of similar thickness. These results show alternate ways of engineering ferroelastic domain structures in ferroelectric thin films.
Y
2
O
3
:
Bi
nanophosphor: Solution combustion synthesis, structure, and luminescence
Authors: Jacobsohn L. G. , Blair M. W. , Tornga S. C. , Brown L. O. , Bennett B. L. , Muenchausen R. E.
Published: December 2008

Photoluminescence (PL), radioluminescence (RL), and thermoluminescence (TL) investigation of Y2O3:Bi nanophosphors prepared by solution combustion synthesis using urea, glycine, and hexamethylenetetramine (HMT) as fuels was carried out. The as-prepared nanopowders have increasing crystallinity and average crystallite sizes for urea, glycine, and HMT, respectively. Luminescence is composed of two emission bands centered at 408 and 505 nm due to two nonequivalent Bi3+ sites with symmetry S6 and C2, respectively. The occupancy of these sites depends on the synthesis conditions, in agreement with theoretical predictions. Annealing at 1000 °C for 1 h improves PL and RL efficiency due to enhanced crystallinity of the nanopowders and activation of recombination centers (Bi3+ ions). No shift in the PL peak position was observed as a function of average crystallite size. The concentration quenching was experimentally determined to have a maximum emission of around 3 mol % of the dopant. TL spectra present several peaks between 50 and 300 °C, and the total TL signal is correlated with the heat of combustion of the fuel and thus crystallinity increases. Most likely, increases in RL and TL are also due to the increase in the concentration of recombination centers.
Changes in dielectric and ferroelectric properties of Fe3+/Nb5+ hybrid-doped barium titanate ceramics under compressive stress
Authors: Unruan M. , Sareein T. , Tangsritrakul J. , Prasertpalichatr S. , Ngamjarurojana A. , Ananta S. , Yimnirun R.
Published: December 2008

The influences of compressive stress on the dielectric and ferroelectric properties of Fe3+/Nb5+ hybrid-doped barium titanate (BaTiO3) ceramics were investigated. Superimposed compressive stress had a pronounced effect on the electrical properties of the ceramics. The response of low-field dielectric properties to stress changed from soft to hard piezoelectric behavior with increasing Nb5+ content. While ferroelectric properties decreased with stress, hardening behavior was observed with increasing Nb5+ content in hybrid-doped BaTiO3 ceramics. A mechanism based on induced change in the acceptor valence by the donor dopant in hybrid-doped BaTiO3 ceramics was proposed to explain the results obtained.
Comparative studies of magnetocaloric effect and magnetotransport behavior in GdRu2Si2 compound
Authors: Samanta Tapas , Das I. , Banerjee S.
Published: December 2008

Studies on magnetocaloric effect (change in magnetic entropy ΔS) and magnetotransport (difference in resistivity due to magnetic field Δρ) have been performed on polycrystalline GdRu2Si2. Due to the presence of several field-induced metamagnetic transitions and superzone energy gap effect below the antiferromagnetic transition temperature (∼45 K), the system exhibits complex magnetotransport behavior. Such a complicated magnetotransport behavior has been analyzed by the comparative studies on Δρ and ΔS. The anomalous regions of Δρ, where it is not dominated by the change in the orientation of magnetic moments, have been highlighted by showing the difference in the variation in ΔS and Δρ. The origin of similar and dissimilar behaviors of ΔS and Δρ at different regions of temperature and magnetic field has been discussed. The comparative study of ΔS and Δρ indicates that it is a powerful technique to understand the complex magnetotransport behavior of the magnetic materials. Interestingly, the intricate magnetic phase diagram of GdRu2Si2 generated by taking magnetization, magnetotransport, or magnetocaloric data appeared to be identical, indicating the usefulness of these physical quantities to generate magnetic phase diagram.
Sequential multiphoton strategy for semiconductor-based terahertz detectors
Authors: Castellano Fabrizio , Iotti Rita C. , Rossi Fausto
Published: December 2008

A semiconductor-based terahertz-detector strategy, exploiting a bound-to-bound-to-continuum architecture, is presented and investigated. In particular, a ladder of equidistant energy levels is employed, whose step is tuned to the desired detection frequency and allows for sequential multiphoton absorption. Our theoretical analysis demonstrates that the proposed multisubband scheme could represent a promising alternative to conventional quantum-well infrared photodetectors in the terahertz spectral region.
Phase transformation properties of finite size ferroelectric thin film with structural transition zones
Authors: Zhou Jing , Lü Tianquan , Cui Lian , Chen Hui , Cao Wenwu
Published: December 2008

By considering structural transition zones in the lateral and thickness directions of finite size ferroelectric thin film, phase transformation properties of the thin film are investigated based on a transverse Ising model. The influence of the lateral size of the thin film on the polarization and the Curie temperature has been quantified. Our results indicate that the lateral size of the film plays a crucial role in determining the phase transformation properties for a small size ferroelectric thin film.
Effect of La doping on the properties of Sr2−xLaxFeMoO6 double perovskite
Authors: Kahoul A. , Azizi A. , Colis S. , Stoeffler D. , Moubah R. , Schmerber G. , Leuvrey C. , Dinia A.
Published: December 2008

We report on the carrier doping effect (achieved through La doping) on the electronic structure, crystalline structure, grain morphology, and electric and magnetic properties of the ferromagnetic perovskite Sr2FeMoO6. X-ray diffraction on Sr2−xLaxFeMoO6 (x=0, 0.25, 0.5, and 1) ceramic powders shows that all compounds have the tetragonal crystal structure with I4∕mmm symmetry. The cell parameter a and the volume of the tetragonal structure increase with the La doping and the grain size is halved with respect to that of undoped Sr2FeMoO6. Mössbauer spectroscopy shows that the presence of La reduces the degree of ordering on the Fe and Mo sites which causes a reduction of the saturation magnetization MS. However, the addition of electrons in the system results in an increase of the Curie temperature of the Sr2FeMoO6. All these results are supported by ab initio calculations which indicate that the half-metallic character is preserved upon doping and that the magnetization decreases for perfect samples by 1μB∕La atom in a formula unit.
Architectural considerations of micro- and nanoresonators for mass detection in the presence of a fluid
Authors: Vignola Joseph F. , Judge John A.
Published: December 2008

The sensitivity of various microscale and nanoscale resonator platforms, for use as mass sensors for detection of chemical or biological agents in air or water, is examined in terms of architectural considerations, including shape, scale, vibration mode, and fluid environment. Simple models for estimating damping due to various sources are used to calculate Q for several resonator designs: cantilevers and doubly fixed beams in flexure and extensional bar and disk resonators. The scaling of various contributions to Q is discussed, and the effects of support loss and fluid loss are compared as a function of aspect ratio for beam resonators. The minimum detectable mass is estimated for each of the four resonator designs, both for the case in which additional mass adsorbs uniformly over the resonator surface and the case in which functionalization of the surface is limited in order to maximize sensitivity and minimize added dissipation. The mass sensitivity is best for resonators undergoing extensional motion and worst for flexural devices with high length-to-thickness ratio. The minimum detectable mass is shown to be proportional to scale to the power of 1.75 for microresonator scenarios in which resonator quality factor is limited by viscous damping and proportional to scale squared when the resonator is sufficiently small that continuum fluid models are inappropriate and quality factor is limited by dissipation via momentum transfer to individual fluid molecules.
Effect of wafer bow on electrostatic chucking and back side gas cooling
Authors: Goodman Daniel L.
Published: December 2008

Electrostatic chucks (ESCs) are used in the semiconductor industry to clamp wafers to a pedestal and combined with back side gas (BSG) cooling to control temperature during processing. The effect of wafer bow in an ESC/BSG system is studied theoretically and experimentally. An equilibrium model is developed that predicts the maximum allowed bow for initial chucking and the maximum BSG pressure once the wafer is chucked. Experimental chucking and BSG pressure data show the maximum initial bow that can be chucked agree with model predictions. Hysteresis in pressure versus flow data is also consistent with the model. The model does not predict some features of thin wafers with highly stressed films. However, deviations between the model and data in this nonlinear regime are expected. By combining the theory with the experimental data, a method to determine a safe BSG/ESC operating range is given.
Analytical solution to space charge limited currents with exponentially distributed traps
Authors: Chen Chao-Wei , Wu Chih-I
Published: December 2008

An analytic solution to space charge limited currents with exponentially distributed traps is developed. While early theoretical work predicts a power law relation between current and voltage, our analytic solution predicts a voltage dependent slope and much higher current magnitudes than the conventional solution because of the contribution of background carriers. Fitting the experimental data to the model suggests a much higher value for the parameter l=Tc/T=30, indicating a broad exponential trap distribution in tris(8-hydroxyquinoline)aluminum. Data fitting strategies and possible misleading fits are discussed.
Synthesis and compression of nanocrystalline silicon carbide
Authors: Zhu Hongyang , Ma Yanzhang , Yang Haibin , Selvi Emre , Hou Dongbin , Ji Cheng
Published: December 2008

Nanocrystalline silicon carbide (SiC) with a diameter of 7 nm was synthesized in a high voltage electrical explosion. It has a larger lattice parameter (0.1%) than its bulk material. Synchrotron x-ray diffraction measurements of nanocrystalline SiC were carried out to 15.8 GPa. The bulk modulus was determined to be K0T=201±10 GPa, which is substantially smaller than those of bulk material and nanocrystalline with large grain sizes. It is considered to be caused by the weaker atomic bonding strength and the imperfections of the nanocrystalline SiC.
Low frequency noise analysis on organic thin film transistors
Authors: Ke Lin , Dolmanan Surani Bin , Shen Lu , Vijila Chellappan , Chua Soo Jin , Png Rui-Qi , Chia Perq-Jon , Chua Lay-Lay , Ho Peter K.-H.
Published: December 2008

Bottom-contact organic field-effect transistors (OFETs) based on poly(3-hexylthiophene) with different channel lengths were fabricated under different substrate pretreatment process conditions. These OFET devices were characterized using low frequency noise (LFN) spectroscopy, and the device performance parameters were correlated with the level of LFN. It is observed that the devices with higher noise levels showed poorer device properties when compared with the devices operated at same Ids of the same channel length. It is also observed that the noise level increased with the increase in channel length for devices with the same pretreatment conditions, which is due to increased trapping and detrapping in the channel material interface domain. The OFET device operating around the threshold voltage Vth will have a 1/f noise slope that is flatter, having a gradient that is smaller in magnitude. The threshold voltage of a device can thus be observed to be at the gate voltage in which 1/f noise intensity is the highest at low frequencies.
Depth-resolved soft x-ray photoelectron emission microscopy in nanostructures via standing-wave excited photoemission
Authors: Kronast F. , Ovsyannikov R. , Kaiser A. , Wiemann C. , Yang S.-H. , Bürgler D. E. , Schreiber R. , Salmassi F. , Fischer P. , Dűrr H. A. , Schneider C. M. , Eberhardt W. , Fadley C. S.
Published: December 2008

We extend conventional laterally-resolved soft x-ray photoelectron emission microscopy to provide depth resolution along the surface normal down to a few angstroms. This is achieved by using standing-wave excitation. The sample is a Ag/Co/Au trilayer, grown on a Si/MoSi2 multilayer mirror, with the bottom Ag layer in a wedge profile. Tuning the incident x-ray to the mirror Bragg angle sets up a standing x-ray wave field in the multilayer and the trilayer wedge structure. We demonstrate the resulting depth resolution by imaging the standing-wave fields as they move through the trilayer wedge structure.
Self-controlled formation of microlenses by optical breakdown inside wide-band-gap materials
Authors: Grojo D. , Gertsvolf M. , Jean-Ruel H. , Lei S. , Ramunno L. , Rayner D. M. , Corkum P. B.
Published: December 2008

By repeatedly illuminating fused silica slabs with focused femtosecond pulses, we permanently decrease the local refractive index without increasing the linear absorption or scattering. This progressively forms a biconvex lens in the prefocal region. With linearly polarized light, the index change reaches several percent and is associated with the formation of an array of planar nanocracks. We analyze the polarization-dependent focusing power of the subwavelength periodic structure. While the detailed material modification changes, spontaneous defocusing lens formation is a common feature of every wide-band-gap transparent materials that we have studied (SiO2, BK7, LiF, sapphire, and mica).
Influence of the mean flow on zonal flow generation
Authors: Lashkin Volodymyr M.
Published: December 2008

Excitation of zonal flow by the modulational instability in the presence of mean shear flow is considered. The presence of the mean flow without large amplitude increases the modulational instability growth rate and favors zonal flow generation, whereas sufficiently strong mean shear significantly reduces the instability growth rate.
Multilayered optical data storage using a spatial soliton
Authors: Hisaka Masaki , Yoshida Kosuke
Published: December 2008

Multilayered optical data storage using a spatial soliton, which has the potential to increase the number of recording layers, is proposed and experimentally investigated. A Ti:sapphire pulsed laser focusing near the surface of a Ce-doped Sr0.75Ba0.25Nb2O6 crystal generated a second-harmonic (SH) beam associated with the self-focusing fundamental laser and induced SH collision responses to the counterpropagating laser pulses. Using threshold controls, single-bit data were recorded with a domain-reversal technique at the collision point, and its data were read out through a quasi-phase-matched SH generation process enhanced at the reversed domains. Multilayered recording and selective data rerecording were also demonstrated.
Tunable electric and magnetic properties of CoxZn1−xS nanowires
Authors: Lu Ming-Yen , Chen Lih-Juann , Mai Wenjie , Wang Zhong Lin
Published: December 2008

We report the growth of ZnS nanowires doped with cobalt using a one-step thermal evaporation method. The magnetism of the nanowires was maintained at room temperature, and the saturated magnetization increased with cobalt contents. Current-voltage measurements of a single nanowire showed not only a linear relationship, which implies Ohmic contacts of nanowire devices, but also tunable conductivities by doping concentration.
Demonstration of an ultraviolet 336 nm AlGaN multiple-quantum-well laser diode
Authors: Yoshida Harumasa , Yamashita Yoji , Kuwabara Masakazu , Kan Hirofumi
Published: December 2008

We have demonstrated laser operation of an AlGaN multiple-quantum-well (MQW) laser diode (LD) with a peak wavelength of 336.0 nm under pulsed current mode at room temperature. The LD was fabricated on a low-dislocation-density Al0.3Ga0.7N grown on a sapphire substrate using a hetero-facet-controlled epitaxial lateral overgrowth method. The laser emission is strongly transverse electric polarized with a peak output power of 3 mW and a differential external quantum efficiency of 1.1%. This demonstration of the LD lasing in ultraviolet-AII spectral band (320–340 nm) suggests that the AlGaN MQW LDs can be potent devices opening a path to deeper ultraviolet LDs.
Partitioning of polynuclear aromatic hydrocarbons into water from biodiesel fuel mixtures
Authors: Chen Colin S. , Lai Yun-Wei , Tien Chien-Jung
Published: December 2008

Environmental context. The dwindling fossil fuel sources have led to a major interest in expanding the use of bioenergy. While biodiesel is moving towards the mainstream as an alternative source of energy, a thorough understanding of the potential impact and risk posed by spills of biodiesel and biodiesel fuel mixtures should be obtained. We present new data here that will allow the prediction of biodiesel behaviour and the extent of contamination in soils and groundwater in the event of such a spill.
Abstract. Partition coefficients of polynuclear aromatic hydrocarbons (PAHs) between biodiesel fuel mixtures (i.e. B1, B5, and B20) and water were determined by the frequently applied estimation method of Raoult’s law. The experimental partition coefficients were compared with calculation by polyparameter linear free energy relationship (PP-LFER) approaches. Deviations from poor recovery of PAHs from the aqueous phase in partition experiments and parameters in the PP-LFER equation are discussed. The results suggest that the extent of deviation from ideal behaviour for biodiesel–water partitioning is relatively small (i.e. errors remain within a factor of two). The concentrations of PAHs in water in equilibrium with these biodiesel fuel mixtures, estimated from the model presented, may be considered as a reasonable approximation for most field-scale applications.
Determination of tag density required for digital transcriptome analysis: Application to an androgen-sensitive prostate cancer model
Authors: Li Hairi , Lovci Michael T. , Kwon Young-Soo , Rosenfeld Michael G. , Fu Xiang-Dong , Yeo Gene W.
Published: December 2008

High-throughput sequencing has rapidly gained popularity for transcriptome analysis in mammalian cells because of its ability to generate digital and quantitative information on annotated genes and to detect transcripts and mRNA isoforms. Here, we described a double-random priming method for deep sequencing to profile double poly(A)-selected RNA from LNCaP cells before and after androgen stimulation. From ≈20 million sequence tags, we uncovered 71% of annotated genes and identified hormone-regulated gene expression events that are highly correlated with quantitative real time PCR measurement. A fraction of the sequence tags were mapped to constitutive and alternative splicing events to detect known and new mRNA isoforms expressed in the cell. Finally, curve fitting was used to estimate the number of tags necessary to reach a “saturating” discovery rate among individual applications. This study provides a general guide for analysis of gene expression and alternative splicing by deep sequencing.
Regulation of lymphocyte progenitor survival by the proapoptotic activities of Bim and Bid
Authors: Mandal Malay , Crusio Kelly M. , Meng Fanyong , Liu Suqing , Kinsella Marcus , Clark Marcus R. , Takeuchi Osamu , Aifantis Iannis
Published: December 2008

On their entry into the thymus, developing lymphocyte progenitors depend on signaling from the pre-T cell receptor (pre-TCR), which orchestrates differentiation, cell proliferation, and survival. The exact mechanism of pre-TCR-mediated suppression of T cell death remains unclear and controversial. Here, we identify Bim and Bid, 2 members of the BH3-only group of the BCL2 family, as important regulators of pre-T cell death. Both factors are highly expressed in proapoptotic thymocytes and their expression is suppressed on signaling through the pre-TCR. Their expression is directly regulated by the transcription factors FoxO3a and p53. Bid expression and p53 activity are related to the ongoing rearrangement of the TCR loci and induced DNA damage responses. Bim expression and FoxO3a nuclear translocation are directly controlled by the pre-TCR by means of its downstream kinase Akt/PKB. Interestingly, deletion of either gene on a pre-TCR
−/−
background rescues survival, but fails to induce further progenitor differentiation uncoupling the 2 processes.
Maintenance of host variation in tolerance to pathogens and parasites
Authors: Best A. , White A. , Boots M.
Published: December 2008

Tolerance and resistance provide hosts with two distinct defense strategies against parasitism. In resistance the hosts “fight” the parasite directly, whereas in tolerance the hosts fight the disease by ameliorating the damage that infection causes. There is increasing recognition that the two mechanisms may exhibit very different evolutionary behaviors. Although empirical work has often noted considerable variance in tolerance within hosts, theory has predicted the fixation of tolerance due to positive frequency dependence through a feedback with disease prevalence. Here we reconcile these findings through a series of dynamic game theoretical models. We emphasize that there is a crucial distinction between tolerance to the effects of disease-induced mortality and tolerance to the effect of the disease-induced reductions in fecundity. Only mortality tolerance has a positive effect on parasite fitness, whereas sterility tolerance is neutral and may therefore result in polymorphisms. The nature of the costs to defense and their relationship to trade-offs between resistance and tolerance are crucial in determining the likelihood of variation, whereas the co-evolution of the parasite will not affect diversity. Our findings stress that it is important to measure the effects of different mechanisms on characteristics that affect the epidemiology of the parasite to completely understand the evolutionary dynamics of defense.
ATP hydrolysis is required for DEAD-box protein recycling but not for duplex unwinding
Authors: Liu Fei , Putnam Andrea , Jankowsky Eckhard
Published: December 2008

DEAD-box proteins, the largest helicase family, catalyze ATP-dependent remodeling of RNA–protein complexes and the unwinding of RNA duplexes. Because DEAD-box proteins hydrolyze ATP in an RNA-dependent fashion, the energy provided by ATP hydrolysis is commonly assumed to drive the energetically unfavorable duplex unwinding. Here, we show efficient unwinding of stable duplexes by several DEAD-box proteins in the presence of the nonhydrolyzable ATP analog ADP-beryllium fluoride. Another ATP analog, ADP-aluminum fluoride, does not promote unwinding. The findings show that the energy from ATP hydrolysis is dispensable for strand separation. ATP binding, however, appears necessary. ATP hydrolysis is found to be required for fast enzyme release from the RNA and multiple substrate turnovers and thus for enzyme recycling.
Pregnancy outcome after ovulation induction with aromatase inhibitors or clomiphene citrate in unexplained infertility
Authors: BADAWY AHMED , SHOKEIR TAREK , ALLAM ABDEL FATTAH , ABDELHADY HESHAM
Published: December 2008

Objective. To evaluate the pregnancy outcome after ovulation induction with aromatase inhibitors or clomiphene citrate (CC). Design. A prospective, randomized, controlled trial. Setting. A university hospital center and a private practice setting. Population. The study comprised a total of 796 infertile women (1,100 cycles) and 200 spontaneously pregnant women (298 cycles) as a control group. Methods. Patients were allocated treatment either with 100 mg of CC daily (420 patients, 634 cycles), 5 mg of letrozole daily (269 patients, 323 cycles) or 1 mg of anastrozole daily (107 patients, 143 cycles) for 5 days starting on day 3 of menses. Main outcome measures. The occurrence of pregnancy, miscarriage and neonatal condition. Results. Pregnancy occurred in 167/1,398 cycles (11.9%) in total without significant differences between groups. The total miscarriage rate was 16.1% (varied between 14.2% in CC group and 19.9% in anastrozole group) without difference between spontaneous and stimulated pregnancies. There were 129 deliveries in all groups. There were no significant differences between the stimulated and spontaneous pregnancies as regards mean gestational age, premature deliveries, birth weight, SGA<10th percentile or five minutes Apgar score. There was one case of complete cleft palate and one case of major congenital heart problem in the letrozole group. There were two cases of talipus equinovarus in the CC and spontaneous pregnancy group. Conclusion. Aromatase inhibitors and CC resulted in favorable pregnancy outcomes and average miscarriage rates. Safety of the drugs for both the mother and fetuses was documented.
Determination of the Efficacy of Sterile Barrier Systems Against Microbial Challenges During Transport and Storage
Authors: Dunkelberg Hartmut , Schmelz Ulrich
Published: December 2008

Objective.

The sterility assurance level of 10−6 is an established standard that defines the quality of sterile products. The aim of the present study was to develop a method that correlated the results from microbial-barrier testing of flexible sterile barrier systems with the estimated microbial challenge that the package encounters during storage and transport.

Methods.

The effectiveness of microbial-barrier packaging was determined by the use of an exposure chamber test with 20 periodic atmospheric pressure changes of 50 and 70 hPa. Flexible peel pouches were used as sterile barrier systems. The logarithmic reduction value of a sterile barrier system was calculated on the basis of the experimental results and compared with the logarithmic reduction value required for the microbial challenges to maintain sterility during transport and storage.

Results.

For pouches made of paper and plastic-film material, a logarithmic reduction value of 5.4 was obtained on the basis of 30 of 99 plates becoming nonsterile after being exposed to a 50 hPa difference in periodic atmospheric pressure changes. For pouches made of paper and plastic-film material, a logarithmic reduction value of 5.2 was obtained on the basis of 48 of 100 plates becoming nonsterile after being exposed to a 70 hPa difference in atmospheric pressure. For pouches made of nonwoven and plastic-film material, logarithmic reduction values of 6.38 (ie, 3 of 99 plates became nonsterile after being exposed to a 50 hPa pressure difference) and 6.07 (ie, 3 of the 99 plates became nonsterile after being exposed to a 70 hPa pressure difference) were obtained. Calculating an expected microbial challenge during transport and storage that requires barrier properties corresponding to a logarithmic reduction value of 5.83 and taking the sterility assurance level into account, we found that only the nonwoven pouches fulfilled the European standard EN 556-1.

Conclusions.

Using the data obtained in a microbial exposure test with a specified flow rate of a bacterial aerosol, we found that the effectiveness of the sterile barrier system against the actual microbial challenge can be examined and evaluated at the sterility assurance level of 10−6.