bluuebunny/crossref_metadata_2025 huggingface dataset:
Producing an intense collimated beam of sound via a nonlinear ultrasonic array
Authors: Gibson Daniel , Smith Martin , Scales John , Zadler Brian
Published: June 2012

We have designed and built an ultrasonic parametric array with an emphasis on creating an intense, collimated beam of low frequency sound. With this device, we can insonify a small area of ground or a small target at range and induce vibrations. These vibrations can be synchronously detected with any stand-off device such as a laser-Doppler vibrometer or the millimeter wave vibrometer we describe in Smith et al. [J. Appl. Physics 108, 024902 (2010)]. Despite nonlinear conversion losses, the array produces sound pressure levels in excess of 90 dB at 1 kHz, 1.5 m in front of the array using 25 low-cost 40 KHz transducers.
Development of a force field for zeolitic imidazolate framework-8 with structural flexibility
Authors: Hu Zhongqiao , Zhang Liling , Jiang Jianwen
Published: June 2012

A force field is developed for zeolitic imidazolate framework-8 (ZIF-8) with structural flexibility by combining quantum chemical calculations and classical Amber force field. The predicted crystalline properties of ZIF-8 (lattice constants, bond lengths, angles, dihedrals, and x-ray diffraction patterns) agree well with experimental results. A structural transition from crystalline to amorphous as found in experiment is observed. The mechanical properties of ZIF-8 are also described fairly well by the force field, particularly the Young's modulus predicted matches perfectly with measured value. Furthermore, the heat capacity of ZIF-8 as a typical thermophysical property is predicted and close to experimental data available for other metal-organic frameworks. It is revealed the structural flexibility of ZIF-8 exerts a significant effect on gas diffusion. In rigid ZIF-8, no diffusive behavior is observed for CH4 within the simulation time scale of current study. With the structural flexibility, however, the predicted diffusivities of CH4 and CO2 are close to reported data in the literature. The density distributions and free energy profiles of CH4 and CO2 in the pore of ZIF-8 are estimated to analyze the mechanism of gas diffusion.
Optically gated tunable terahertz filters
Authors: Busch Stefan F. , Schumann Steffen , Jansen Christian , Scheller Maik , Koch Martin , Fischer Bernd M.
Published: June 2012

We present a fast and flexible terahertz filter based on diffractive gratings combined with an optically gated modulator. The terahertz radiation is diffracted by blazed gratings, and the individual frequency components are focused onto an optically excited semiconductor. Different light patterns are used to create free carriers in the bulk semiconductor material, leading to a spatial modulation of its transmission. This approach enables us to damp arbitrary frequencies and allows us to design and implement filters with almost any frequency response. By using the digital light processing technique, the switching time between different filter settings is as short as 16 ms.
Mechanical characterization of an electrostrictive polymer for actuation and energy harvesting
Authors: Eddiai A. , Meddad M. , Touhtouh S. , Hajjaji A. , Boughaleb Y. , Guyomar D. , Belkhiat S. , Sahraoui B.
Published: June 2012

Electroactive polymers have been widely used as smart material for actuators in recent years. Electromechanical applications are currently focused on energy harvesting and actuation, including the development of wireless portable electronic equipment autonomous and specific actuators such as artificial muscles. The problem to be solved is to make its devices the most efficient, as possible in terms of harvested energy and action. These two criteria are controlled by the permittivity of the electrostrictive polymer used, the Young’s modulus, and their dependence on frequency and level of stress. In the present paper, we presented a model describing the mechanical behaviour of electrostrictive polymers with taking into account the mechanical losses. Young’s modulus follows a linear function of strain and stress. However, when the elongation becomes higher, the data obtained from this strain linear trend and significant hysteresis loops appear the reflections on the existence of mechanical losses. In this work, to provide the analysis of the experimental observations, we utilized a theoretical model in order to define a constitutive law implying a representative relationship between stress and strain. After detailing this theoretical model, the simulation results are compared with experimental ones. The results show that hysteresis loss increases with the increase of frequency and strain amplitude. The model used here is in good agreement with the experimental results.
The dispersion interaction between quantum mechanics and effective fragment potential molecules
Authors: Smith Quentin A. , Ruedenberg Klaus , Gordon Mark S. , Slipchenko Lyudmila V.
Published: June 2012

A method for calculating the dispersion energy between molecules modeled with the general effective fragment potential (EFP2) method and those modeled using a full quantum mechanics (QM) method, e.g., Hartree-Fock (HF) or second-order perturbation theory, is presented. C6 dispersion coefficients are calculated for pairs of orbitals using dynamic polarizabilities from the EFP2 portion, and dipole integrals and orbital energies from the QM portion of the system. Dividing by the sixth power of the distance between localized molecular orbital centroids yields the first term in the commonly employed London series expansion. A C8 term is estimated from the C6 term to achieve closer agreement with symmetry adapted perturbation theory values. Two damping functions for the dispersion energy are evaluated. By using terms that are already computed during an ordinary HF or EFP2 calculation, the new method enables accurate and extremely rapid evaluation of the dispersion interaction between EFP2 and QM molecules.
Burgers’ equation and the sticky particles model
Authors: Moutsinga Octave
Published: June 2012

Under general assumptions on the initial data, we show that the entropy solution (x, t) ↦ u(x, t) of the one-dimensional inviscid Burgers’ equation is the velocity function of a sticky particles model whose initial mass distribution is Lebesgue measure. Precisely, the particles trajectories (x, t) ↦ X0, t(x) are given by a forward flow: \documentclass[12pt]{minimal}\begin{document}$\forall \,(x,s,t)\in \mathbb {R}\times \mathbb {R}_+\times \mathbb {R}_+, X_{0,s+t}(x)=X_{s,t}\big (X_{0,s}(x)\big )\;\mbox{ and}\; \frac{\partial }{\partial t} X_{s,t}\break=u(X_{s,t},s+t)=\mathrm{E}[u(\cdot ,s)|X_{s,t}];\,\, u(x,t)=\mathrm{E}[u(\cdot ,0)|X_{0,t}=x].$\end{document}∀(x,s,t)∈R×R+×R+,X0,s+t(x)=Xs,tX0,s(x)and∂∂tXs,t=u(Xs,t,s+t)=E[u(·,s)|Xs,t];u(x,t)=E[u(·,0)|X0,t=x].
Numerical estimates for the bulk viscosity of ideal gases
Authors: Cramer M. S.
Published: June 2012

We estimate the bulk viscosity of a selection of well known ideal gases. A relatively simple formula is combined with published values of rotational and vibrational relaxation times. It is shown that the bulk viscosity can take on a wide variety of numerical values and variations with temperature. Several fluids, including common diatomic gases, are seen to have bulk viscosities which are hundreds or thousands of times larger than their shear viscosities. We have also provided new estimates for the bulk viscosity of water vapor in the range 380–1000 K. We conjecture that the variation of bulk viscosity with temperature will have a local maximum for most fluids. The Lambert-Salter correlation is used to argue that the vibrational contribution to the bulk viscosities of a sequence of fluids having a similar number of hydrogen atoms at a fixed temperature will increase with the characteristic temperature of the lowest vibrational mode.
A subgrid-scale model for large-eddy simulation based on the physics of interscale energy transfer in turbulence
Authors: Anderson Brian W. , Domaradzki J. Andrzej
Published: June 2012

The scale-similarity model in large-eddy simulation (LES) leads to an attractive, functionally simple expression for the subgrid-scale (SGS) stress tensor. It is well known, however, that the similarity model fails to accurately predict some of the most fundamental quantities in turbulent flows, perhaps the most important being the global energy transfer and the associated subgrid-scale dissipation. To address this, additional dissipative terms are usually added to the similarity model to improve its performance. In the present paper, considerations of interscale energy transfer have been used to identify sources of the observed deficiencies of the similarity model, specifically its inadequate balancing of terms contributing energy to the smallest scales and its duplication of terms producing effects in the largest scales. These considerations provide guidance in the development of a new model, which shows more favorable characteristics of energy transfer while preserving the functional simplicity of the scale-similarity model. Partial nonlinear terms are used to decompose the nonlinear transfer present in LES and to formulate a model expression capable of balancing small-scale production terms depositing energy near the LES cutoff. The proposed model is formulated in the same vein as the scale-similarity model, consisting of test filtered velocities and their products, but offers clear improvements in predictions of mean flow quantities and the global energy flux from the resolved to subgrid scales without the need for additional terms to augment subgrid-scale energy dissipation. The application of the new interscale transfer model in LES of wall-bounded flows leads to predictions of mean and RMS flow quantities comparable to those obtained for other, established SGS models.
Optical emission of a molecular nanoantenna pair
Authors: Rice E. M. , Andrews D. L.
Published: June 2012

The optical emission from a pair of nanoantennas is investigated within the theoretical framework of quantum electrodynamics. The analysis of fluorescent emission from a pair of molecular antenna species in close proximity is prompted by experimental work on oriented semiconductor polymer nanostructures. Each physically different possibility for separation-dependent features in photon emission by any such pair is explored in detail, leading to the identification of three distinct mechanisms: emission from a pair-delocalized exciton state, emission that engages electrodynamic coupling through quantum interference, and correlated photon emission from the two components of the pair. Although each mechanism produces a damped oscillatory dependence on the pair separation, each of the corresponding results exhibits an analytically different form. Significant differences in the associated spatial frequencies enable an apparent ambiguity in the interpretation of experiments to be resolved. Other major differences are found in the requisite conditions, the associated selection rules, and the variation with angular disposition of the emitters, together offering grounds for experimental discrimination between the coupling mechanisms. The analysis paves the way for investigations of pair-wise coupling effects in the emission from nanoantenna arrays.
Local relativistic exact decoupling
Authors: Peng Daoling , Reiher Markus
Published: June 2012

We present a systematic hierarchy of approximations for local exact decoupling of four-component quantum chemical Hamiltonians based on the Dirac equation. Our ansatz reaches beyond the trivial local approximation that is based on a unitary transformation of only the atomic block-diagonal part of the Hamiltonian. Systematically, off-diagonal Hamiltonian matrix blocks can be subjected to a unitary transformation to yield relativistically corrected matrix elements. The full hierarchy is investigated with respect to the accuracy reached for the electronic energy and for selected molecular properties on a balanced test molecule set that comprises molecules with heavy elements in different bonding situations. Our atomic (local) assembly of the unitary exact-decoupling transformation—called local approximation to the unitary decoupling transformation (DLU)—provides an excellent local approximation for any relativistic exact-decoupling approach. Its order-N2 scaling can be further reduced to linear scaling by employing a neighboring-atomic-blocks approximation. Therefore, DLU is an efficient relativistic method well suited for relativistic calculations on large molecules. If a large molecule contains many light atoms (typically hydrogen atoms), the computational costs can be further reduced by employing a well-defined nonrelativistic approximation for these light atoms without significant loss of accuracy. We also demonstrate that the standard and straightforward transformation of only the atomic block-diagonal entries in the Hamiltonian—denoted diagonal local approximation to the Hamiltonian (DLH) in this paper—introduces an error that is on the order of the error of second-order Douglas–Kroll–Hess (i.e., DKH2) when compared with exact-decoupling results. Hence, the local DLH approximation would be pointless in an exact-decoupling framework, but can be efficiently employed in combination with the fast to evaluate DKH2 Hamiltonian in order to speed up calculations for which ultimate accuracy is not the major concern.
Theoretical model for geometry-dependent magnetoelectric effect in magnetostrictive/piezoelectric composites
Authors: Wang Yaojin , Hasanyan Davresh , Li Menghui , Gao Junqi , Li Jiefang , Viehland D. , Luo Haosu
Published: June 2012

A quasistatic theoretical model including geometry effect is presented for predicting the magnetoelectric (ME) coefficients in a ME multilayer composite consisting of magnetostrictive and piezoelectric layers. The model is developed based on average-field method considering the geometry effect. The model characterizes the ME coefficient in terms of not only the parameters of two composite components and the thickness fraction but also the length and width fractions for the piezoelectric or magnetostrictive components. Analytical predictions indicate that the width and length fractions strongly influence the maximum ME coefficient and the corresponding thickness fraction also. Clearly, geometry effects cannot be ignored in predicting ME coefficient. Theoretical ME coefficients are also compared to experimental test data, demonstrating excellent agreement.
The I2 dissociation mechanisms in the chemical oxygen-iodine laser revisited
Authors: Waichman K. , Barmashenko B. D. , Rosenwaks S.
Published: June 2012

The recently suggested mechanism of I2 dissociation in the chemical oxygen-iodine laser (COIL) [K. Waichman, B. D. Barmashenko, and S. Rosenwaks, J. Appl. Phys. 106, 063108 (2009)10.1063/1.3213380; K. Waichman, B. D. Barmashenko, and S. Rosenwaks, J. Chem. Phys. 133, 084301 (2010)]10.1063/1.3480397 was largely based on the suggestion of V. N. Azyazov, S. Yu. Pichugin, and M. C. Heaven [J. Chem. Phys. 130, 104306 (2009)]10.1063/1.3081454 that the vibrational population of O2(a) produced in the chemical generator is high enough to play an essential role in the dissociation. The results of model calculations based on this mechanism agreed very well with measurements of the small signal gain g, I2 dissociation fraction F, and temperature T in the COIL. This mechanism is here revisited, following the recent experiments of M. V. Zagidullin [Quantum Electron. 40, 794 (2010)]10.1070/QE2010v040n09ABEH014357 where the observed low population of O2(b, v = 1) led to the conclusion that the vibrational population of O2(a) at the outlet of the generator is close to thermal equilibrium value. This value corresponds to a very small probability, ∼0.05, of O2(a) energy pooling to the states O2(X,a,b, v > 0). We show that the dissociation mechanism can reproduce the experimentally observed values of g, F, and T in the COIL only if most of the energy released in the processes of O2(a) energy pooling and O2(b) quenching by H2O ends up as vibrational energy of the products, O2(X,a,b), where the vibrational states v = 2 and 3 are significantly populated. We discuss possible reasons for the differences in the suggested vibrational population and explain how these differences can be reconciled.
Dielectric spectroscopy study on ionic liquid microemulsion composed of water, TX-100, and BmimPF6
Authors: Chen Zhen , Nozaki Ryusuke
Published: June 2012

We report here a broadband dielectric spectroscopy study on an ionic liquid microemulsion (ILM) composed of water, Triton X-100 (TX-100), and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). It is found that the phase behavior of this ILM can be easily identified by its dielectric response. The dielectric behavior of the ILM in the GHz range is consistent with that of TX-100/water mixtures with comparable water-to-TX-100 weight ratio. It consists of the relaxations due to ethylene oxide (EO) unit relaxation, hydration water dynamics, and/or free water dynamics. The water content dependence of the EO unit relaxation suggests that this relaxation involves dynamics of hydration water molecules. In the IL-in-water microemulsion phase, it is found that bmimPF6 molecules are preferentially dissolved in water when their concentration in water is lower than the solubility. An additional dielectric relaxation that is absent in the TX-100/water mixtures is observed in the frequency range of 107–108 Hz for this ILM. This low-frequency relaxation is found closely related to the bmimPF6 molecule and could be attributed to the hopping of its cations/anions between the anionic/cationic sites.
A theoretical rationalization of a total inelastic electron tunneling spectrum: The comparative cases of formate and benzoate on Cu(111)
Authors: Burema S. R. , Lorente N. , Bocquet M.-L.
Published: June 2012

Inelastic electron tunneling spectroscopy (IETS) performed with the scanning tunneling microscope (STM) has been deemed as the ultimate tool for identifying chemicals at the atomic scale. However, direct IETS-based chemical analysis remains difficult due to the selection rules that await a definite understanding. We present IETS simulations of single formate and benzoate species adsorbed in the same upright bridge geometry on a (111)-cleaved Cu surface. In agreement with measurements on a related substrate, the simulated IET-spectra of formate/Cu(111) clearly resolve one intense C–H stretching mode whatever the tip position in the vicinity of the molecular fragment. At variance, benzoate/Cu(111) has no detectable IET signal. The dissimilar IETS responses of chemically related molecules–formate and benzoate adsorbates–permit us to unveil another factor that complements the selection rules, namely the degree of the vacuum extension of the tunneling active states perturbed by the vibrations. As a consequence, the lack of a topmost dangling bond orbital is entirely detrimental for STM-based inelastic spectroscopy but not for STM elastic imaging.
Superferromagnetism and coercivity in Co-Al2O3 granular films with perpendicular anisotropy
Authors: Timopheev A. A. , Bdikin I. , Lozenko A. F. , Stognei O. V. , Sitnikov A. V. , Los A. V. , Sobolev N. A.
Published: June 2012

Magnetic properties of nano-granular Co0.55–(Al2O3)0.45 films have been studied by vibrating sample magnetometry, ferromagnetic resonance, and magnetic force microscopy (MFM). The films possess a growth-induced perpendicular anisotropy related to the shape anisotropy of the granules. Being unpercolated physically, the films demonstrated a clear magnetic percolation behavior in the temperature dependence of the coercivity and MFM scans. The temperature dependence of the coercivity measured along the easy magnetization axis of the granules indicates the presence of a collective long-range magnetic state sustained by a ferromagnetic interparticle interaction. This interaction is supposed to form a homogeneously magnetized superferromagnetic state, however, the perpendicular anisotropy and the competition between the dipole-dipole and ferromagnetic interactions lead to the emergence of an inhomogeneous labyrinth-like magnetic stripe-domain structure with the averaged domain width being about two orders of magnitude larger than the averaged granule size. The temperature evolution of the spontaneous magnetization inside the stripe domains has been measured by the MFM up to the temperature of superferromagnetic ordering (420 K). The formerly developed mean-field-based model of the coercivity of an interacted ensemble has been tested and found to yield adequate quantitative predictions.
Franz-Keldysh electro-absorption modulation in germanium-tin alloys
Authors: Soref R. A. , Sun G. , Cheng H. H.
Published: June 2012

The direct-bandgap Franz-Keldysh theory has been applied to relaxed crystalline Ge1-xSnx alloys for 0 ≤ x ≤ 0.1 taking into account the light- and heavy-hole contributions. For electro-absorption modulation, the change-in-absorption spectrum Δα(ω, ɛ) was calculated for an applied electric field ɛ of 33 to 100 kV/cm using a B parameter determined by curve-fitting the zero-field absorption spectrum α(ω, ɛ) for each alloy. At a photon energy ∼10 meV below the gap, it was found that the figure of merit Δα(ω, ɛ)/α(ω, 0) ranged from 0.4 to 1.0 for 2% Sn, 0.5 to 1.2 for 5% Sn, 0.6 to 1.4 for 7.5% Sn, and 0.7 to 1.6 for 10% Sn. For a figure of merit ∼1, the waveguided resonant low-Q GeSn microdisk-and-bus modulator is expected to give a higher on/off contrast ratio than the non-resonant GeSn channel waveguide modulator.
Low resistance Ti Ohmic contacts to 4H-SiC by reducing barrier heights without high temperature annealing
Authors: Huang Lingqin , Liu Bingbing , Zhu Qiaozhi , Chen Suhua , Gao Mingchao , Qin Fuwen , Wang Dejun
Published: June 2012

Ti Ohmic contacts to relatively highly doped (1 × 1018 cm−3) n-type 4H-SiC have been produced, without high temperature annealing, by means of low temperature electronic cyclotron resonance microwave hydrogen plasma pre-treatment (HPT) of the SiC surface. The as-deposited Ti/4H-SiC contacts show Ohmic properties, and the specific contact resistance obtained is as low as 2.07 × 10−4 Ω·cm2 after annealing at low temperatures (400 °C). This is achieved by low barrier height at Ti/SiC interface, which could be attributed to decrease of surface states density by the HPT releasing Fermi level pinning, and to band-gap narrowing, image-force, and thermionic-field emission at high doping.
Morphotropic phase boundary and electric properties in (1−x)Bi0.5Na0.5TiO3-xBiCoO3 lead-free piezoelectric ceramics
Authors: Guo Fei-Fei , Yang Bin , Zhang Shan-Tao , Liu Xiao , Zheng Li-Mei , Wang Zhu , Wu Feng-Min , Wang Da-Li , Cao Wen-Wu
Published: June 2012

Lead-free (1−x)Bi0.5Na0.5TiO3-xBiCoO3 (x = 0, 0.015, 0.025, 0.03, 0.035, 0.04, and 0.06) piezoelectric ceramics have been synthesized and their structure and electric properties have been investigated systemically. The rhombohedral-tetragonal morphotropic phase boundary (MPB) locates near x = 0.025–0.035. For the ceramics with x = 0.025, the saturated polarization (Ps), remnant polarization (Pr), coercive field (Ec), strain(S), piezoelectric constant (d33), and thickness electromechanical coupling factor (kt) are 40.6 μC/cm2, 35.4 μC/cm2, 5.25 kV/mm, 0.11%, 107pC/N, and 0.45, respectively. The low temperature humps of relative dielectric constant, which is indicative of TR-T, are becoming inconspicuous gradually with the increasing x and almost disappear at x = 0.04. The depolarization temperature Td decreases first and then increases with the increasing x. Our results may be helpful for further work on Bi0.5Na0.5TiO3-based lead-free piezoelectric ceramics.
Effect of size-dependent grain structures on the dynamics of nanoparticle coalescence
Authors: Zhang Yiyang , Li Shuiqing , Yan Wen , Tse Stephen D.
Published: June 2012

The effect of grain structure on the coalescence dynamics of anatase TiO2 nanoparticles at different temperatures is investigated using classical molecular dynamics (MD) simulation. Examination of local-lattice-orientation distributions reveals that the grain morphology of particles is highly dependent on size. For a single anatase nanoparticle below the melting temperature, an amorphous-to-crystalline transition occurs for diameters ranging from 2 to 2.5 nm as temperature increases. Below the transition diameter (for a given temperature), the entire nanoparticle is amorphous. Above the transition diameter, the nanoparticle consists of a crystalline core and an amorphous shell (4–6 Å). Considering that such grain-structure characteristics may lead to different dynamic behaviors, the coalescence between pairs of 2 nm–2 nm, 3 nm–3 nm, and 2 nm–3 nm nanoparticles is investigated. For 2 nm–2 nm nanoparticle coalescence, the process is independent of initial temperature and is seemingly viscosity-controlled with a dynamic temperature rise due to energy transfer from surface to internal kinetic (thermal). For 3 nm–3 nm nanoparticle coalescence, the process is sensitive to initial temperature. Above the melting temperature, the dynamics are similar to the 2 nm–2 nm amorphous case. Just below the melting point, coalescence consists of melting of the crystalline cores with subsequent large increase in temperature due to recrystallization. For 2 nm–3 nm nanoparticle coalescence, recrystallization of the 2 nm particle significantly increases the total temperature compared to the 2 nm–2 nm case.
Effect of nanoparticles on charge transport in nanofluid-impregnated pressboard
Authors: Du Yuefan , Lv Yuzhen , Li Chengrong , Chen Mutian , Zhong Yuxiang , Zhang Shengnan , Zhou You
Published: June 2012

Transformer pressboard impregnated in mineral oil modified by nanoparticles (nanofluid) exhibits substantially higher AC and DC breakdown voltage than that of the pure oil-impregnated pressboard (OP). Charge transport and decay characteristics of both pressboards were measured by pulse electroacoustic technique. It reveals that nanofluid-impregnated pressboard (NP) has a more uniform internal electric field and a higher charge decay rate compared to OP, which is caused by an increase of shallow trap density in NP related to the difference of internal structures, based on the test results of thermally stimulated current and Fourier transformed infra-red spectroscopy.
Field orientation dependent decorrelation of magnetization reversal in uniaxial Co-films
Authors: Arregi J. A. , Idigoras O. , Vavassori P. , Berger A.
Published: June 2012

Magnetization reversal correlation is studied as a function of the applied field angle for thin Co-films showing in-plane uniaxial magnetocrystalline anisotropy. We find that the field orientation angle has a profound effect onto the magnetization reversal process leading to a suppression of long-range correlation at sufficiently large field angles in the presence of grain alignment disorder. Correspondingly, this behavior allows for a tuning and the local confinement of magnetization reversal even in strongly exchange-coupled films and therefore presents a most desirable scenario for ultrahigh density magnetic recording.
On the sensitivity of terahertz gyrotron based systems for remote detection of concealed radioactive materials
Authors: Nusinovich G. S. , Sprangle P. , Semenov V. E. , Dorozhkina D. S. , Glyavin M. Yu
Published: June 2012

This paper analyzes some features of systems intended to remotely detect concealed radioactive materials by using a focused THz radiation. This concept is based on possibility to focus high-power THz radiation in a small spot where the wave field exceeds the breakdown threshold. However, in the absence of any sources of ionization, the probability to have in this breakdown-prone volume any seed electrons is very low. Thus, high breakdown rate in a series of THz pulses will indicate the presence of concealed radioactive materials in the vicinity of a focused wave beam. The goal of the present paper is to determine by using the statistical theory THz pulse duration required for reliable initiation of the discharge. Then, the detectable mass of the radioactive material is determined as the function of distance and of the THz wave power and pulse duration. Lastly, possible benefits from using pulse compressors, which shorten the pulse duration but increase the wave power and, hence, the breakdown-prone volume, are analyzed. It is shown that the use of pulse compressors can significantly improve the sensitivity of THz gyrotron based systems for remote detection of concealed radioactive materials.
Effects of doping on the lattice parameter of SrTiO3
Authors: Janotti Anderson , Jalan Bharat , Stemmer Susanne , Van de Walle Chris G.
Published: June 2012

The effects on the lattice parameter due to incorporation of high concentrations of donor impurities in SrTiO3 are examined both experimentally and theoretically. Experimental lattice parameters were obtained from x-ray diffraction on La-doped films grown on bulk SrTiO3 substrates with carrier concentrations up to 2 × 1021 cm−3. The observed increase in lattice parameter is attributed to two causes: impurity-size and electronic effects. The latter can be attributed in part to the energy gain by lowering the conduction band upon volume expansion. These contributions are evaluated explicitly using hybrid functional calculations, with a net result in very good agreement with experiment.
First results of the SOL reflectometer on Alcator C-Mod
Authors: Lau C. , Hanson G. , Lin Y. , Wilgen J. , Wukitch S. , Labombard B. , Wallace G.
Published: June 2012

A swept-frequency X-mode reflectometer has been built on Alcator C-Mod to measure the scrape-off layer (SOL) density profiles adjacent to the lower hybrid launcher. The reflectometer system operates between 100 and 146 GHz at sweep rates from 10 μs to 1 ms and covers a density range of ∼1016–1020 m−3 at B0 = 5–5.4 T. This paper discusses the analysis of reflectometer density profiles and presents first experimental results of SOL density profile modifications due to the application of lower hybrid range-of-frequencies power to L-mode discharges. Comparison between density profiles measured by the X-mode reflectometer and scanning Langmuir probes is also shown.
Optimal control of coherent anti-Stokes Raman scattering image contrast
Authors: Bergner Gero , Schlücker Sebastian , Kampe Bernd , Dittrich Peter , Dietzek Benjamin , Popp Jürgen
Published: June 2012

Optimal control of coherent anti-Stokes Raman scattering (CARS) image contrast is reported. The setup combines an evolutionary strategy and a closed-loop feedback with a liquid-crystal spatial modulator to control the spectrum of the Stokes pulse within a CARS scheme to optimize the vibrational contrast of CARS images. The CARS excitation spectrum is optimized for image contrast at a pre-determined wavenumber position. The optimization feedback uses an image-contrast parameter generated from the image itself as the experimentally imposed fitness parameter. This strategy allows for enhancing the image contrast by a factor of up to 2.6.
On the evolution of nanocluster size distribution in a nanocluster aggregation source
Authors: Turkin A. A. , Dutka M. V. , Pei Y. T. , Vainshtein D. I. , De Hosson J. Th. M.
Published: June 2012

This paper presents a detailed model of cluster formation from a supersaturated atomic vapor in an inert buffer gas. The population balance equations for the cluster size distribution are based on the Smoluchowski coagulation equation and take into account (i) convective diffusion of clusters, (ii) cluster loss to walls of an aggregation chamber, and (iii) formation of fractal-like aggregates. The model predictions are confronted to experimental observations, and they agree with experimental data on Cu particle formation in NC200-UHV nanocluster source. The model can be used as an aid in tuning the experimental parameters for attaining a desired nanoparticle size distribution.
Surface plasmon enhanced photoluminescence from fullerene C60 film on Au nanoparticles array: Resonant dependence on excitation frequency
Authors: Yeshchenko O. A. , Kondratenko S. V. , Kozachenko V. V.
Published: June 2012

The photoluminescence from the fullerene C60 thin films on array of the gold nanoparticles was studied at various energies of exciting laser photons. An enhancement of the photoluminescence of C60 film on array of Au nanoparticles was observed. The observed enhancement is due to strong local field of surface plasmon excited in the gold nanoparticles. Tuning of the exciting photon energy allowed to control the quantum yield of C60 film photoluminescence. When the exciting photon energy is close to the surface plasmon resonance, the quantum yield reaches its maximum. This fact confirms the resonant character of the surface plasmon enhancement of the studied photoluminescence of C60 film.
Lag synchronization and scaling of chaotic attractor in coupled system
Authors: Bhowmick Sourav K. , Pal Pinaki , Roy Prodyot K. , Dana Syamal K.
Published: June 2012

We report a design of delay coupling for lag synchronization in two unidirectionally coupled chaotic oscillators. A delay term is introduced in the definition of the coupling to target any desired lag between the driver and the response. The stability of the lag synchronization is ensured by using the Hurwitz matrix stability. We are able to scale up or down the size of a driver attractor at a response system in presence of a lag. This allows compensating the attenuation of the amplitude of a signal during transmission through a delay line. The delay coupling is illustrated with numerical examples of 3D systems, the Hindmarsh-Rose neuron model, the Rössler system, a Sprott system, and a 4D system. We implemented the coupling in electronic circuit to realize any desired lag synchronization in chaotic oscillators and scaling of attractors.
Ambipolar inverters using SnO thin-film transistors with balanced electron and hole mobilities
Authors: Yan Liang Ling , Tao Cao Hong , Bo Chen Xiao , Min Liu Zhi , Zhuge Fei , Luo Hao , Li Jun , Cheng Lu Yi , Lu Wei
Published: June 2012

Ambipolar thin film transistors have attracted increasing research interests due to their promising applications in complementary logic circuits and the dissipative charge transporting devices. Here, we report the fabrication of an ambipolar transistor using tin mono-oxide (SnO) as a channel, which possesses balanced electron and hole field-effect mobilities. A complementary metal oxide semiconductor-like inverter using the SnO dual operation transistors is demonstrated with a maximum gain up to 30 and long-term air stability. Such logic device configuration would simplify the circuit design and fabrication process, offering more opportunities for designing and constructing oxide-based logic circuits.
Photon ratchet intermediate band solar cells
Authors: Yoshida M. , Ekins-Daukes N. J. , Farrell D. J. , Phillips C. C.
Published: June 2012

In this paper, we propose an innovative concept for solar power conversion—the “photon ratchet” intermediate band solar cell (IBSC)—which may increase the photovoltaic energy conversion efficiency of IBSCs by increasing the lifetime of charge carriers in the intermediate state. The limiting efficiency calculation for this concept shows that the efficiency can be increased by introducing a fast thermal transition of carriers into a non-emissive state. At 1 sun, the introduction of a “ratchet band” results in an increase of efficiency from 46.8% to 48.5%, due to suppression of entropy generation.
Study of envelope electron acoustic solitary waves under transverse perturbations having kappa distributed hot electrons
Authors: Bedi Chanchal , Gill T. S.
Published: June 2012

As is well known, the envelope electron acoustic (EA) nonlinear waves are expressed by nonlinear Schrödinger equation. In this paper, we find that under transverse perturbations, this kind of nonlinear waves can be described by Davey-Stewartson equation. In this work, modulational properties of EA wave and its stability regions in two-dimensional plasma have been studied.
Non-inductive current start-up assisted by energetic electrons in Q-shu University experiment with steady-state spherical tokamak
Authors: Ishiguro Masaki , Hanada Kazuaki , Liu Haiqing , Zushi Hideki , Nakamura Kazuo , Fujisawa Akihide , Idei Hiroshi , Nagashima Yoshihiko , Hasegawa Makoto , Tashima Saya , Takase Yuichi , Kishimoto Yasuaki , Mitarai Osamu , Kawasaki Shoji , Nakashima Hisatoshi , Higashijima Aki
Published: June 2012

After intensive discharge cleaning of the chamber wall, non-inductive current start-up experiments have been successfully performed in QUEST in moderate vertical fields of about 1.0–1.5 mT with positive n-index. Simultaneously, with increasing plasma current, an asymmetric toroidal flow of energetic electrons was observed and direct measurements of current driven by this asymmetric flow were taken with a newly developed Langmuir probe technique. A numerical study of the energetic electron orbits indicates that the total current is enough to play a dominant role in the formation of a closed flux surface in QUEST.
Mechanism of heating of pre-formed plasma electrons in relativistic laser-matter interaction
Authors: Paradkar B. S. , Krasheninnikov S. I. , Beg F. N.
Published: June 2012

The role of the longitudinal ambipolar electric field, present inside a pre-formed plasma, in electron heating and beam generation is investigated by analyzing single electron motion in the presence of one electromagnetic plane wave and “V” shaped potential well (constant electric field) in a one dimensional slab approximation. It is shown that for the electron confined in an infinite potential well, its motion becomes stochastic when the ratio of normalized laser electric field a0, to normalized longitudinal electric field Ez, exceeds unity, i.e., a0/Ez≳1. For a more realistic potential well of finite depth, present inside the pre-formed plasma, the condition for stochastic heating of electrons gets modified to 1≲a0/Ez≲L, where L is the normalized length of the potential well. The energy of electron beam leaving such a potential well and entering the solid scales ∼a02/Ez, which can exceed the laser ponderomotive energy (∼a0) in the stochastic regime.
High-stability oxygen sensor based on amorphous zinc tin oxide thin film transistor
Authors: Chen Yu-Chun , Chang Ting-Chang , Li Hung-Wei , Chung Wan-Fang , Wu Chang-Pei , Chen Shih-Ching , Lu Jin , Chen Yi-Hsien , Tai Ya-Hsiang
Published: June 2012

This research presents a sol-gel derived zinc tin oxide thin film transistor (TFT) as a high-stability oxygen sensor. Due to its high sensitivity, oxygen has been traditionally regarded as having a negative influence on the electrical characteristics of zinc-based TFTs; however, TFTs can also act as an oxygen sensor. After illumination with visible light in oxygen-rich ambient, a significant increase in drain current of nearly 104 times occurs with fixed gate and drain voltages. It is expected that an optimized method of illumination can help to reset the electrical characteristics or distinguish the on/off state of this reliable oxygen sensor.
Nanoparticle free polymer blends for light scattering films in liquid crystal displays
Authors: Takei Satoshi , Mochiduki Kazuhide , Kubo Naoya , Yokoyama Yoshiyuki
Published: June 2012

This paper reports an approach using nanoparticle free polymer blends for light scattering films in liquid crystal displays. The ability to create the regularly structured circle of approximately 200 nm diameter in the light scattering film by blending two specified polymers with carboxylic acid groups and epoxy groups was demonstrated. The developed light scattering film based on thermosetting system indicated regularly structured nanomorphology, high light scattering rates of more than 3.9% at 300–600 nm of wavelength, and fast thermal cross-linking reaction at 150 °C and 60 s in thermosetting conditions for high productivity.
On the optimum sizing of metal hydride tank filled AB2 type alloy
Authors: Hilali İsmail
Published: June 2012

When the metal hydride tanks that are used in hydrogen storage are thermally coupled to the fuel cell, thermal management of metal hydride tank is to get importance in the development of the fuel cell performance. Heat transfer has been shown to be the rate limiting process controlling hydrogen uptake or removal. Discharge capacity of the tank has a major impact on the fuel cell efficiency. In this paper, a thermoeconomic optimization analysis is presented yielding a simple algebraic formula for estimating optimum metal hydride tank surface area for heat transfer enhancement. A simple economic method is used in the study, together with thermal analysis. The optimum area of the metal hydride tank filled with commercially available AB2 type alloy (Ti0,98Zr0,02V0,43Fe0,09Cr0,05Mn1,5) is calculated by this method as 0.16 m2. The optimum net savings is about 902.7$ and the value of payback is determined as 1.3 years. Excessive area of the metal hydride tank will not be economical as the optimum tank area.
The War on Induction: Whewell Takes On Newton and Mill (Norton Takes On Everyone)
Authors: Achinstein Peter
Published: June 2012

I consider and reject William Whewell's attack on the inductivism of Isaac Newton and John Stuart Mill, as well as John Norton's attack on any universal system of inductive rules. I also explain how a system of inductive rules of the sort proposed by Newton and Mill should be understood.
Extrapolation, Analogy, and Comparative Process Tracing
Authors: Guala Francesco
Published: June 2012

Comparative process tracing is the best analysis of extrapolation inferences in the philosophical and scientific literature so far. In this essay I examine some similarities and differences between comparative process tracing and former attempts to capture the logic of extrapolation, such as the analogical approach. I show that these accounts are not different in spirit, although comparative process tracing supersedes previous proposals in terms of analytical detail. I also examine some qualms about the possibility of drawing extrapolation inferences in the social sciences and conclude by suggesting that there may be cases of extrapolation without process tracing.
The Resilience of Computationalism
Authors: Piccinini Gualtiero
Published: June 2012

Computationalism—the view that cognition is computation—has always been controversial. It faces two types of objection. According to insufficiency objections, computation is insufficient for some cognitive phenomenon X. According to objections from neural realization, cognitive processes are realized by neural processes, but neural processes have feature Y, and having Y is incompatible with being (or realizing) computations. In this article, I explain why computationalism has survived these objections. To adjudicate the dispute between computationalism and its foes, I will conclude that we need a better account of computation.
Homeostasis, Higher Taxa, and Monophyly
Authors: Boyd Richard
Published: June 2012

Several authors have argued that higher taxa are monophyletic homeostatic property cluster natural kinds. On the traditional definition of monophyly, this will not work: the emergence of taxon-defining homeostatic property clusters would not always correspond to unique speciation events. An alternative conception of monophyly is developed and advocated, which can accommodate the homeostatic property cluster proposal. Recent work in philosophy of science shows that it meets appropriate standards of objectivity and precision.
Quantification of Uncertainties of Future Climate Change: Challenges and Applications
Authors: Mearns Linda O.
Published: June 2012

Increasing societal concerns regarding the potential deleterious effects of future climate change have galvanized efforts to manage the problem both through reduction of greenhouse gases (mitigation) and through development of plans to reduce the impacts of climate change that cannot be avoided (adaptation). These critical activities require making decisions under conditions of considerable uncertainty regarding future conditions in physical and human systems. As the focus on providing information about future climate for taking actions to cope with climate change, the science of uncertainty of climate change will develop more and more with the needs of decision makers in mind.
A Role for Representation in Cognitive Neurobiology
Authors: Sullivan Jacqueline Anne
Published: June 2012

What role does the concept of representation play in the contexts of experimentation and explanation in cognitive neurobiology? In this article, a distinction is drawn between minimal and substantive roles for representation. It is argued by appeal to a case study that representation currently plays a role in cognitive neurobiology somewhere in between minimal and substantive and that this is problematic given the ultimate explanatory goals of cognitive neurobiological research. It is suggested that what is needed is for representation to instead play a substantive role.
Forces and Causes in Evolutionary Theory
Authors: Stephens Christopher
Published: June 2012

The traditional view of evolutionary theory asserts that we can usefully understand natural selection, drift, mutation, migration, and the system of mating as forces that cause evolutionary change. Recently, Denis Walsh and Robert Brandon have objected to this view. Walsh argues that the traditional view faces a fatal dilemma and that the force analogy must be rejected altogether. Brandon accepts the force analogy but argues that drift, rather than the Hardy-Weinberg law, is the best candidate for a zero-force law. Here I defend the traditional view against these objections.
Complex First? On the Evolutionary and Developmental Priority of Semantically Thick Words
Authors: Werning Markus
Published: June 2012

The Complex-First Paradox consists in a set of collectively incompatible but individually well-confirmed propositions that regard the evolution, development, and cortical realization of the meanings of concrete nouns. Although these meanings are acquired earlier than those of other word classes, they are semantically more complex and their cortical realizations more widely distributed. For a neurally implemented syntax-semantics interface, it should thus take more effort to establish a link between a concept and its lexical expression. However, in ontogeny and phylogeny, capabilities demanding more effort, ceteris paribus, develop and evolve later than those demanding less effort. The paradox points to an explanatory deficit in linguistic theory.
Mixed-Level Explanation
Authors: Wilson Mark
Published: June 2012

Explanations in physics commonly appeal to data drawn from different length or time scales, as when a “top-down” macroscopic constraint such as rigidity is used to evade the complexities one would confront in attempting to model the situation in a purely “bottom-up” fashion. Such techniques commonly embody rather complex shifts in explanatory strategy.
Thermodynamics and Chemistry: How Does a Theory Formulated without Reference to Matter Explain the Properties of Matter?
Authors: Vemulapalli G. K.
Published: June 2012

Varieties of chemical and phase equilibria are controlled by the minimum Gibbs energy principle, according to which the Gibbs energy for a system will have the minimum value at any given temperature and pressure. It is understood that the minimum is with respect to all nonequilibrium states at the same temperature and pressure. The abstract relation between Gibbs energy and the equilibrium constant is deduced from fundamental laws of thermodynamics. However, actual use of this relation calls for the Gibbs energy as a function of concentrations of the chemicals. Since thermodynamics is formulated without any reference to materials, how does one get that relation? This article provides the answer, and in the process shows that application of theory to experiments requires several intermediate layers where theory and experiment commingle.