bluuebunny/crossref_metadata_2025 huggingface dataset:
The Reinvention of Feminism in Pakistan
Authors: Zia Afiya Shehrbano
Published: March 2009

This article argues that there has been a significant turn in the discourse of feminist politics in the Islamic Republic of Pakistan. The author suggests that the rise of a new feminism – rooted in Islamic discourse, non-confrontational, privatized and personalized, whose objective is to ‘empower’ women within Islam – is not a post-9/11 development but rather a result of unresolved debates on the issue of religion within the progressive women's movement. It has been due to the accommodation of religion-based feminist arguments by the stronger secular feminist movement of the 1980s that paved the way for its own marginalization by giving feminist legitimacy to such voices. The author argues that the second wave of feminism may have become diluted in its effectiveness and support due to discriminatory religious laws, dictatorship, NGO-ization, fragmentation, co-option by the state and political parties in the same way as the global women's movement has. Yet it has been the internal inconsistency of the political strategies as well as the personal, Muslim identities of secular feminists that have allowed Islamic feminists to redefine the feminist agenda in Pakistan. This article voices the larger concern over the rise of a new generation of Islamic revivalist feminists who seek to rationalize all women's rights within the religious framework and render secular feminism irrelevant while framing the debate on women's rights exclusively around Islamic history, culture and tradition. The danger is that a debate such as this will be premised on a polarized ‘good’ vs ‘bad’ Muslim woman, such that women who abide by the liberal interpretation of theology will be pitted against those who follow a strict and literal interpretist mode and associate themselves with male religio-political discourse. This is only likely to produce a new, radicalized, religio-political feminism dominating Pakistan's political future.
Field and bias dependence of high-frequency magnetic noise in MgO-based magnetic tunnel junctions
Authors: Guan Y. , Abraham D. W. , Gaidis M. C. , Hu G. , O’Sullivan E. J. , Nowak J. J. , Trouilloud P. L. , Worledge D. C. , Sun J. Z.
Published: March 2009

We present room-temperature measurements of high-frequency magnetization fluctuation (mag noise) in MgO-based nanopillar magnetic tunnel junctions (MTJs) biased with a direct current (dc). In the frequency range of 1–13 GHz, double mag-noise peaks are observed for some MTJs while others only show a single mag-noise peak. The in-plane field dependence of the mag-noise peak frequency is consistent with the Kittel formula. For all MTJs measured, the bias-dependent shift in the mag-noise peak frequency has a pronounced asymmetry. In addition, we find nonmonotonic variations in peak linewidth as a function of the external in-plane magnetic field and of the dc bias current. These suggest the possible involvement of nonmacrospin modes in spin-torque-dependent thermal mag-noise generation.
Adjusting the magnetic properties of semiconductor epilayers by the crystallographic orientation of embedded highly anisotropic magnetic nanoclusters
Authors: Lacroix Christian , Lambert-Milot Samuel , Desjardins Patrick , Masut Remo A. , Ménard David
Published: March 2009

GaP:MnP samples, which consist of GaP(001) epilayers with embedded MnP nanoclusters occupying approximately 7% of the epilayer volume, were grown at three different substrate temperatures (600, 650, and 700 °C) using metal-organic vapor phase epitaxy. Angle dependent ferromagnetic resonance (FMR) spectroscopy indicates that, in all samples, MnP clusters are crystallographically oriented along specific GaP directions and possess high magnetic anisotropy fields. FMR results also suggest that the growth temperature significantly modifies the distribution of clusters among the possible orientations. This is verified from the measured angular dependence of the remanent magnetization, which shows a different crystallographic orientation of the GaP:MnP effective magnetic easy axis for each growth temperature. Modeling of the remanent magnetization allowed the determination of the relative volume fraction of clusters corresponding to each MnP c-axis orientation at a given growth temperature. These results support our assumption that the clusters are monodomains and suggest that the growth temperature could eventually be used to adjust the magnetic properties of these GaP:MnP structures.
Quantum boundary effect on the work output of a micro-/nanoscaled Carnot cycle
Authors: Nie Wenjie , He Jizhou
Published: March 2009

In this paper, the work output (W) and efficiency (η) of a Carnot cycle in micro-/nanoscale are calculated, in which the quantum boundary effect of gas particles as a working substance of cycle is considered. It is found that under the quantum boundary effect conditions, the work output of cycle depends sensitively on the surface area of the system (boundary of cycle) and cannot be predicted by the classical approximate result (WC), while the efficiency of cycle is independent of the surface area of the system and equals the Carnot efficiency (ηC). Further, the difference of work output of the micro-/nanoscaled Carnot cycle to that of the classical one, ΔW=W−WC, is introduced and can be expressed as the function of the temperature ratio τ=TL/TH of the two heat reservoirs, the volume ratio rV=V3/V1, and the surface area ratio rA=A3/A1 of the two isochoric processes. Variations of difference of work output, ΔW, with the temperature ratio τ and volume ratio rV for the different surface ratio rA are examined, which reveals the quantum boundary effect of gas particles on the work output of a micro-/nanoscaled Carnot cycle. The results obtained in here may provide some guidance for designing a micro-/nanoscaled Carnot cycle device and conduce to confirming experimentally the quantum boundary effect on the micro-/nanoscaled devices.
Effect of bombardment with different ions (H, He, Ar) on ordering transformation of Fe48Pt52 films
Authors: Sun A. C. , Yuan F. T. , Hsu Jen-Hwa , Liao W. M. , Lee H. Y.
Published: March 2009

Fe 48 Pt 52 thin films with a thickness of 50 nm were deposited at room temperature before undergoing glow-discharge-induced ion bombardment at 300 °C for 1 h. The energy of the incident ions was adjusted by applying a radio-frequency bias (Vb) from 200 to 600 V. H2, He, and Ar were used as the working gases. Significant ordering enhancement was only found in the H-ion bombarded films. The coercivity of such films is greatly increased from 0.5 kOe, for the sample without any bias, to around 8 kOe at Vb=200–600 V, which result is similar to that for a film annealed at 400 °C in a vacuum. This result suggests that H-ion bombardment has the effect of a 100 °C increase in annealing temperature. Microstructural studies reveal that the average grain size of the H-ion bombarded films is about 30 nm, which is much smaller than that of 400 °C-annealed films. The film thickness of He-ion bombarded samples decreases linearly as Vb increases because of the intensive sputtering effect. Under Ar-ion bombardment, most of the film is removed even at Vb=200 V.
Cluster spin-glass state and Kondo behavior in Sm-based bulk metallic glasses
Authors: Lu C. L. , Dong S. , Wang K. F. , Liu J.-M. , Wang Q. , Dong C.
Published: March 2009

We investigate the magnetization and electrical transport properties of Sm-based ternary magnetic bulk metallic glasses at low temperatures. A cluster spin-glass phase is evidenced below Tf∼25 K, which is probably ascribed to competition among the multifold magnetic interactions and intrinsic structural inhomogeneity, and further demonstrated by the magnetic hysteresis under field-cooling conditions. It is shown that the short-range magnetic clusters play as scattering centers for conductive electrons and result in a Kondo-like transport behavior in highly spin disordered Sm50Al25Co25 at low temperature.
Self-organization of a neural network with heterogeneous neurons enhances coherence and stochastic resonance
Authors: Li Xiumin , Zhang Jie , Small Michael
Published: March 2009

Most network models for neural behavior assume a predefined network topology and consist of almost identical elements exhibiting little heterogeneity. In this paper, we propose a self-organized network consisting of heterogeneous neurons with different behaviors or degrees of excitability. The synaptic connections evolve according to the spike-timing dependent plasticity mechanism and finally a sparse and active-neuron-dominant structure is observed. That is, strong connections are mainly distributed to the synapses from active neurons to inactive ones. We argue that this self-emergent topology essentially reflects the competition of different neurons and encodes the heterogeneity. This structure is shown to significantly enhance the coherence resonance and stochastic resonance of the entire network, indicating its high efficiency in information processing.
Dynamical mechanism of intrinsic localized modes in microelectromechanical oscillator arrays
Authors: Chen Qingfei , Huang Liang , Lai Ying-Cheng , Dietz David
Published: March 2009

Experimental evidence of intrinsic localized modes (ILMs) in microelectromechanical oscillator arrays has been reported recently. In this paper, we carry out a detailed analysis of a new mechanism for ILMs in typical experimental settings; that is, spatiotemporal chaos is ubiquitous and it provides a natural platform for actual realization of various ILMs through frequency control. We find that unstable periodic orbits associated with ILMs are pivotal for spatiotemporal chaos to arise and these orbits are the keys to stabilizing ILMs by frequency modulation.
Al doped ZnO nanoplate arrays and microbox structures grown by thermal deposition
Authors: Ortega Y. , Fernández P. , Piqueras J.
Published: March 2009

Al doped ZnO arrays of nanoplates and of ordered nanoneedles have been grown by a thermal evaporation-deposition method. The nanoplates, which have mainly triangular shape. Interpenetrating triangles and crossing of the triangles with other planar arrangements form a structure consisting of arrays of microboxes. The influence of Al on the luminescence of the nanostructures has been studied by cathodoluminescence (CL) in the scanning electron microscope. Intense CL emission from the internal faces of the microboxes is related to the presence of deep level defects.
Influence of Ga coverage and As pressure on local droplet etching of nanoholes and quantum rings
Authors: Heyn Ch. , Stemmann A. , Eiselt R. , Hansen W.
Published: March 2009

We study the formation of nanoholes and quantum rings in GaAs and AlGaAs surfaces by local droplet etching (LDE) with Ga and In. The quantum rings are formed by the droplet etching process and surround the nanohole openings. Our data show that a low As pressure is essential for LDE and that process conditions with high Ga coverage yield formation of additional hillocks or large hills. With atomic force microscopy we establish that the amount of material removed from the nanoholes is equal to the amount of material stored in the quantum rings. Basing on the experimental observations, we propose a model of nanohole and quantum ring formation.
Ultrafast nonlinear optical properties of alkyl-phthalocyanine nanoparticles investigated using Z-scan technique
Authors: Rao S. Venugopal , Venkatram N. , Giribabu L. , Rao D. Narayana
Published: March 2009

We report our results on the femtosecond nonlinear optical studies of alkyl-phthalocyanine nanoparticles dispersed in water and dissolved in chloroform. Nonlinear refractive and absorptive properties were investigated using the closed and open aperture Z-scan techniques. The nonlinear optical coefficients obtained for nanoparticles suspended in water are compared with those dissolved in chloroform, which resulted in simple phthalocyanine solutions. Our studies clearly demonstrate the nonlinear refractive index of nanoparticles to be positive, while that of the nanoparticles in chloroform was negative. Our results and analysis point out a high nonlinearity in the ultrafast domain for both the nanoparticles and solutions indicating their potential in optical signal processing and limiting applications.
Reduced conductivity in poly(3,4-ethylenedioxythiophen)-poly(styrene sulfonate) and indium tin oxide nanocomposite for low indium tin oxide content
Authors: Mechau Norman , Groeger Roland , Prodi-Schwab Anna , Schmechel Roland
Published: March 2009

We studied the electrical conductivity of nanocomposite layers of p-type conductive polymer poly(3,4-ethylenedioxythiophen)-poly(styrene sulfonate) (PEDT/PSS) and the n-type conductive indium tin oxide (ITO) nanoparticles. A decrease in electrical conductivity of PEDT with increasing ITO content up to a volume fraction of about 16 vol % is observed. Above the volume fraction of 16 vol % the conductivity increases very steeply, most probably due to percolation between the ITO-nanoparticles. The analysis of characteristic PEDT infrared absorption bands yields a decrease in the bipolaron absorption and an increase in polaron absorption with increasing ITO content. The shift from bipolaron to polaron absorption is interpreted as “undoping” of PEDT due to a charge transfer between the p-type PEDT/PSS and the n-type conductive ITO nanoparticles. However, an estimation of the depletion length leads to the conclusion that depleted charge carriers only cannot explain the decrease in conductivity. Morphological changes of the system PEDT/PSS by incorporating of the ITO nanoparticles are considered as additional origin for the decrease in conductivity.
Alignment of multiwalled carbon nanotubes in bulk epoxy composites via electric field
Authors: Zhu Yue-Feng , Ma Chen , Zhang Wei , Zhang Ren-Ping , Koratkar Nikhil , Liang Ji
Published: March 2009

We demonstrate the alignment of multiwalled carbon nanotubes in bulk epoxy matrices by application of external electric field. The composites were prepared by a macro-layer-by-layer method; UV light was used to rapidly polymerize the epoxy and preserve the aligned nanotube network. The nanotube alignment generated strong anisotropy in the composite’s properties. The composite’s storage modulus was increased by ∼50%, and the electrical conductivity was improved by four orders of magnitude in the direction of nanotube alignment. Compared to pristine nanotubes, amine functionalized nanotubes showed enhanced storage modulus but reduced electrical conductivty. The enhanced modulus for amine functionalized nanotubes is an artifact of their enhanced compatibility with the epoxy, while their reduced conductivity may result from the shortening of the nanotube length during functionalization. In addition to the rapid alignment of nanotubes parallel to the field direction, we also report a tendency for lateral agglomeration (perpendicular to the field) of the aligned nanotubes over time. Such a coarsening effect can be mitigated by minimizing the polymerization (or cure) time of the epoxy.
Toward the parametrization of the Hubbard model for salts of bis(ethylenedithio)tetrathiafulvalene: A density functional study of isolated molecules
Authors: Scriven Edan , Powell B. J.
Published: March 2009

We calculate the effective Coulomb repulsion between electrons/holes Um(v) and site energy for an isolated bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecule in vacuo. Um(v)=4.2±0.1 eV for 44 experimental geometries taken from a broad range of conformations, polymorphs, anions, temperatures, and pressures (the quoted “error” is one standard deviation). Hence we conclude that Um(v) is essentially the same for all of the compounds studied. This shows that the strong (hydrostatic and chemical) pressure dependence observed in the phase diagrams of the BEDT-TTF salts is not due to Um(v). Therefore, if the Hubbard model is sufficient to describe the phase diagram of the BEDT-TTF salts, there must be significant pressure dependence on the intramolecular terms in the Hamiltonian and/or the reduction in the Hubbard U due to the interaction of the molecule with the polarizable crystal environment. The renormalized value of Um(v) is significantly smaller than the bare value of the Coulomb integral, F0=5.2±0.1 eV, across the same set of geometries, emphasizing the importance of using the renormalized value of Um(v). The site energy (for holes), ξm=5.0±0.2 eV, varies only a little more than Um(v) across the same set of geometries. However, we argue that this variation in the site energy plays a key role in understanding the role of disorder in bis(ethylenedithio)tetrathiafulvalene salts. We explain the differences between the βL and βH phases of (BEDT-TTF)2I3 on the basis of calculations of the effects of disorder.
Role of geometry and fluid properties in droplet and thread formation processes in planar flow focusing
Authors: Lee Wingki , Walker Lynn M. , Anna Shelley L.
Published: March 2009

Droplet formation processes in microfluidic flow focusing devices have been examined previously and some of the key physical mechanisms for droplet formation revealed. However, the underlying physical behavior is still too poorly understood to utilize it for generating droplets of precise size. In this work, we formulate scaling arguments to define dimensionless variables which capture all the parameters that control the droplet breakup process, including the flow rates and the viscosities of the two immiscible fluids, the interfacial tension between the fluids and the numerous dimensions in the flow focusing device. To test these arguments, we perform flow focusing experiments and systematically vary the dimensional parameters. Through these experiments, we confirm the validity of the scaling arguments and find a power law relationship between the normalized droplet size and the capillary number. We demonstrate that droplet formation can be separated into an upstream process for primary droplet formation and a downstream process for thread formation. These results are key to the ability to tune the flow focusing process for specific applications that require monodisperse micron and submicron droplets and particles.
Simulation of a hot coaxial jet: Direct noise prediction and flow-acoustics correlations
Authors: Bogey Christophe , Barré Sébastien , Juvé Daniel , Bailly Christophe
Published: March 2009

A coaxial jet originating from parallel coplanar pipe nozzles is computed by a compressible large eddy simulation (LES) using low-dissipation and low-dispersion schemes in order to determine its acoustic field and to study noise generation mechanisms. The jet streams are at high velocities, the primary stream is heated, and the Reynolds number based on the primary velocity and the secondary diameter is around 106. High levels of turbulence intensity are also specified at the nozzle exit. The jet aerodynamic field and the near-pressure field are both obtained directly from the LES. The far-field noise is calculated by solving the linear acoustic equations, from the unsteady LES data on a cylindrical surface surrounding the jet. A good agreement is observed in terms of directivity, levels, and narrow-band spectra with noise measurements carried out during the EU project CoJeN for a coaxial jet displaying same stream velocities and temperatures, coplanar nozzle outlets with identical area ratio, and a high Reynolds number. However, certainly due to differences in the properties of the nozzle-exit boundary layers with respect to the experiment, some unexpected peaks are noticed in the simulation spectra. They are attributed to the development of a Von Kármán street in the inner mixing layer and to vortex pairings in the outer shear layer. High correlation levels are also calculated between the pressure waves radiated in the downstream direction and flow quantities such as axial velocity, vorticity norm, density, and temperature, taken around the end of the primary and secondary potential cores. Noise generation in the coaxial jet therefore appears significant around the end of the two potential cores. These flow regions are characterized by intermittency, a dominant Strouhal number, and variations in the convection velocity as similarly found in single jets. The use of density or temperature to compute flow-noise correlations finally seems appropriate for a heated jet flow, but might lead to correlations with acoustic disturbances in the potential core.
Characterizing trapped charge dynamics in imprinted poly(vinylidene fluoride-trifluoroethylene) ferroelectric thin films using the fast ramp thermally stimulated current technique
Authors: Lew Connie , Thompson Michael O.
Published: March 2009

Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric thin films are promising materials for sensors, nonvolatile memory applications, and energy harvesting. Imprint, the time-dependent resistance to polarization reversal, is a key material property that limits electronic applications and is poorly understood. In this work, we investigated the link between imprint and charge trap states within the film. A fast ramp rate thermally stimulated current (FR-TSC) measurement was developed to quantify and characterize trapped charge dynamics in imprinted P(VDF-TrFE) thin films in an appropriate time frame. Thin films of P(VDF-TrFE) on oxidized Si substrates were characterized following controlled initialization, polarization, and imprint. Trap states were thermally filled/emptied by temperature cycling between 20 °C and 100 °C using heating and cooling rates of 1 K/s. Dynamics of this fast-ramp TSC indicate the presence of not only trap states but also reversible and irreversible charge accumulation. Results also show an asymmetry with respect to poling orientation, indicating that traps are influenced by processing conditions and contact materials. The development of this FR-TSC technique provides understanding of polarization dynamics and material interactions affecting ferroelectric properties of P(VDF-TrFE).
Electron-stimulated reactions and O2 production in methanol-covered amorphous solid water films
Authors: Akin Minta C. , Petrik Nikolay G. , Kimmel Greg A.
Published: March 2009

The low-energy, electron-stimulated desorption (ESD) of molecular products from amorphous solid water (ASW) films capped with methanol is investigated versus methanol coverage (0–4×1015 cm−2) at 50 K using 100 eV incident electrons. The major ESD products from a monolayer (ML) of methanol on ASW are quite similar to the ESD products from bulk methanol film: H2, CH4, H2O, C2H6, CO, CH2O, and CH3OH. For 40 ML ASW films, the molecular oxygen, hydrogen, and water ESD yields from the ASW are suppressed with increasing methanol coverage, while the CH3OH ESD yield increases proportionally to the methanol coverage. The suppression of the water ESD products by methanol is consistent with the nonthermal reactions occurring preferentially at or near the ASW/vacuum interface and not in the interior of the film. The water and molecular hydrogen ESD yields from the water layer decrease exponentially with the methanol cap coverage with 1/e constants of ∼6×1014 and 1.6×1015 cm−2, respectively. In contrast, the O2 ESD from the water layer is very efficiently quenched by small amounts of methanol (1/e∼6.5×1013 cm−2). The rapid suppression of O2 production by small amounts of methanol is due to reactions between CH3OH and the precursors for the O2—mainly OH radicals. A kinetic model for the O2 ESD, which semiquantitatively accounts for the observations, is presented.
Instabilities of rare rotating cold molecular clouds
Authors: Nekrasov A. K.
Published: March 2009

New electromagnetic streaming instabilities of rare rotating molecular clouds induced by the relative drift of ions, electrons, and dust grains in the equilibrium state are studied. The cases of a weak and strong collisional coupling of neutrals and ions in the perturbed state are involved. The dust grains are considered as unmagnetized having weak collisional coupling with neutrals in perturbations. The compressibility is taken into account. Axisymmetric perturbations with growth rates much larger than the rotation frequency are found.
Experimental study of Rayleigh–Taylor instability with a complex initial perturbation
Authors: Olson D. H. , Jacobs J. W.
Published: March 2009

Experiments have been performed investigating the Rayleigh–Taylor instability initialized with a complex initial perturbation. The experiments utilize a miscible fluid combination with Atwood number A≈0.2. The initially stably stratified fluids are contained within a Plexiglas tank mounted to a linear rail system. The tank was then oscillated vertically to impose nearly sinusoidal three-dimensional internal waves of varying wavelength and complexity at the fluid interface. After imposing this perturbation, the tank is accelerated down the rails at a rate greater than Earth’s gravity (g0) resulting in a body force of approximately 0.8g0. The flow is visualized with either backlit photography or planar laser induced fluorescence. Image sequences from the experiments show bubble and spike merging, leading to a growth of length scale with time. Averaged vertical concentration distributions show self-similarity after ∼233 ms with a total experiment time of ∼300 ms. In addition, after this time, the square root of the mixing zone width appears to grow linearly with (Ag)1/2t. Values for the self-similar growth parameter, α, obtained by curve fitting to the linear portion of these curves yield values that are lower than those obtained in other experiments but are in good agreement with values found in computational studies initiated with perturbations similar to those used here. The measured α values do not show a dependence on the initial perturbation amplitude. The method for the determination of α using the expression α=ḣ2/4Agh proposed by Cabot and Cook [Nat. Phys. 2, 562 (2006)] yields a value in agreement with that measured by curve fitting the h1/2 versus Agt curves, and which is also in better agreement with computational studies.
Exchange bias, training effect, hysteretic behavior of angular dependence, and rotational hysteresis loss in NiFe/FeMn bilayer: Effect of antiferromagnet layer thickness
Authors: Gao T. R. , Shi Z. , Zhou S. M. , Chantrell R. , Asselin P. , Bai X. J. , Du J. , Zhang Z. Z.
Published: March 2009

For NiFe/FeMn bilayers, the correlation among the exchange field, the coercivity, the training effect, the hysteretic effect of the angular dependence of the exchange bias, and the rotational hysteresis loss has been studied as a function of the antiferromagnet layer thickness tAFM. With increasing tAFM, all these quantities undergo nonmonotonic variations, except for the monotonic change in the exchange field. The maximal values of the coercivity, its relative change, and the rotational hysteresis loss are almost located at the same tAFM of 3.8 nm. The maximal values of the relative change in the exchange field and of the hysteretic effect of the angular dependence are located at 2.5 and 3.0 nm, respectively. The rotational hysteresis loss and the hysteretic behavior of the angular dependence of the exchange bias have different characteristics. The variations of all physical quantities with tAFM can be ascribed to the irreversible reversal of the antiferromagnet spins, which are governed by the Arrhenius–Néel law, except for that of the rotational hysteresis loss.
The development of generalized synchronization on complex networks
Authors: Guan Shuguang , Wang Xingang , Gong Xiaofeng , Li Kun , Lai C.-H.
Published: March 2009

In this paper, we numerically investigate the development of generalized synchronization (GS) on typical complex networks, such as scale-free networks, small-world networks, random networks, and modular networks. By adopting the auxiliary-system approach to networks, we observe that GS generally takes place in oscillator networks with both heterogeneous and homogeneous degree distributions, regardless of whether the coupled chaotic oscillators are identical or nonidentical. We show that several factors, such as the network topology, the local dynamics, and the specific coupling strategies, can affect the development of GS on complex networks.
Ion acoustic waves in pair-ion plasma: Linear and nonlinear analyses
Authors: Saeed R. , Mushtaq A.
Published: March 2009

Linear and nonlinear properties of low frequency ion acoustic wave (IAW) in pair-ion plasma in the presence of electrons are investigated. The dispersion relation and Kadomtsev–Petviashvili equation for linear/nonlinear IAW are derived from sets of hydrodynamic equations where the ion pairs are inertial while electrons are Boltzmannian. The dispersion curves for various concentrations of electrons are discussed and compared with experimental results. The predicted linear IAW propagates at the same frequencies as those of the experimentally observed IAW if ne0∼104 cm−3. It is found that nonlinear profile of the ion acoustic solitary waves is significantly affected by the percentage ratio of electron number density and temperature. It is also determined that rarefactive solitary waves can propagate in this system. It is hoped that the results presented in this study would be helpful in understanding the salient features of the finite amplitude localized ion acoustic solitary pulses in a laboratory fullerene plasma.
Phase-contrast and holographic computed laminography
Authors: Helfen L. , Baumbach T. , Cloetens P. , Baruchel J.
Published: March 2009

In-line phase contrast is combined with laminography to image in three dimensions regions of interest in laterally extended flat specimens of weak absorption contrast. The principle of the method and a theoretical description of the imaging process are outlined. The present instrumental implementation enables reconstructing nondestructively the internal structure at different lateral specimen positions with micron resolution. The feasibility and application potential are demonstrated for both phase-contrast and holographic (i.e., using phase retrieval) laminography by the three-dimensional imaging of fuel-cell diffusion layers.
Mode coupling and flow energy harvesting by a flapping foil
Authors: Zhu Qiang , Peng Zhangli
Published: March 2009

As demonstrated in recent studies, the bioinspired flapping foils are capable of harvesting kinetic energy from incoming wind or current. A practical measure to achieve this is via the coupling between different modes in a system with multiple degrees of freedom. A typical scenario includes external activation of one motion mode and extracting the mechanical energy from other modes that follow. In this study we create a numerical model based upon the Navier–Stokes equations to investigate the performance of such a system in low Reynolds numbers. The effects of both the mechanical design and the operational parameters are examined. Specifically, we concentrate on the vorticity control mechanisms involved in the process, and demonstrate that through vortex-body interactions energy of the leading-edge vortices can be partially recovered to enhance the energy harvesting capacity.
Single-turn extraction from a K110 AVF cyclotron by flat-top acceleration
Authors: Kurashima Satoshi , Miyawaki Nobumasa , Okumura Susumu , Ishibori Ikuo , Nara Takayuki , Agematsu Takashi , Yoshida Ken-ichi , Yokota Watalu , Nakamura Yoshiteru , Arakawa Kazuo , Fukuda Mitsuhiro
Published: March 2009

Single-turn extraction from the Japan Atomic Energy Agency AVF cyclotron with a K number of 110 using a flat-top (FT) acceleration system has been achieved to reduce the energy spread of an ion beam for microbeam formation with energy up to hundreds of MeV and to increase extraction efficiency from the cyclotron. In order to generate a FT waveform voltage using the fifth-harmonic frequency on a dee electrode, a FT resonator was designed using MAFIA code to achieve downsizing and low power consumption. The FT resonator, coupled to the main resonator through a coupling capacitor, covered the full range of the fifth harmonic frequency from 55 to 110 MHz. Various ion beams, accelerated using different acceleration harmonic modes of h=1 and 2, such as 220 MeV C125+ (h=2), 260 MeV N20e7+ (h=2), and 45 MeV H+ (h=1), were developed by FT acceleration. A clear turn separation of the beam bunches was successfully observed at the extraction region of the large-scale AVF cyclotron with number of revolutions greater than 200. As a result, high extraction efficiency (over 95%) from the cyclotron was achieved. Single-turn extraction was confirmed by counting the number of beam bunches out of the cyclotron for an injected beam pulsed by a beam chopping system in the injection line. The energy spread of the 260 MeV N20e7+ beam was measured using an analyzing magnet, and we verified a reduction in the energy spread from ΔE/E=0.1% to 0.05% by single-turn extraction after FT acceleration.
First-principles investigation on bonding formation and electronic structure of metal-graphene contacts
Authors: Ran Qiushi , Gao Mingzhi , Guan Ximeng , Wang Yan , Yu Zhiping
Published: March 2009

Metal-graphene contacts play a critical role in graphene-based electronics. It is found through first-principles calculation of contacts between graphene and 12 different metals that there exist two types of contacts depending on the strength of interaction between d-orbitals in metals and pz-orbitals in graphene. Fermi level shift in the contacted graphene from the freestanding one is investigated, and the electronic structure and electrostatic potential are calculated. The carrier transport through these contacts is calculated using the extended Hückel theory-based non-equilibrium Green’s function formalism, and one type of contact is shown to have less contact resistance than the other.
The magnetoelectric effects in multiferroic composite nanofibers
Authors: Zhang C. L. , Chen W. Q. , Xie S. H. , Yang J. S. , Li J. Y.
Published: March 2009

In this letter, we analyze the quasistatic and dynamic magnetoelectric responses of multiferroic composite nanofibers consisting of both ferroelectric and ferromagnetic phases and demonstrate that the nanofibers exhibit magnetoelectric responses orders of magnitude higher than multiferroic composite thin films of similar compositions. The analysis suggests that the multiferroic nanofibers are promising for magnetoelectric applications.
Co-doped TiO2 films grown on glass: Room-temperature ferromagnetism accompanied with anomalous Hall effect and magneto-optical effect
Authors: Yamasaki T. , Fukumura T. , Yamada Y. , Nakano M. , Ueno K. , Makino T. , Kawasaki M.
Published: March 2009

Room-temperature ferromagnetic oxide semiconductor Co-doped TiO2 films are grown on glass substrates by sputtering method. Conducting films are ferromagnetic at room temperature that is consistent with the carrier-mediated nature of the ferromagnetism. Nearly full-polarized magnetization, large magneto-optical effect, and anomalous Hall effect are observed at room temperature. The magneto-optical effect shows nearly fourfold enhancement in a one-dimensional magnetophotonic crystal structure with a standard dielectric multilayer (SiO2/TiO2).
Novel technique to control oxygen fugacity during high-pressure measurements of grain boundary conductivities of rocks
Authors: Dai Lidong , Li Heping , Hu Haiying , Shan Shuangming
Published: March 2009

This paper describes the development and application of a novel method for the measurement of grain boundary electrical conductivity of rock at high temperature and pressure. In this method, the metal electrodes, the corresponding metal shielding case, and the sleeves are altered in order to appropriately adjust and monitor the oxygen fugacity in a sample cavity in a high-pressure apparatus. As an example, a series of oxygen buffers including Fe3O4+Fe2O3, Ni+NiO, Fe+Fe3O4, Fe+FeO, and Mo+MoO2 was selected and tested, and the oxygen fugacity was confirmed as adjusted during the process of electrical conductivity measurements. Application of this method provides a powerful means of restricting specific thermodynamic conditions at high temperature and pressure.
Multiphoton induced cubic-to-quartic intensity dependent transition of anti-Stokes Raman signal
Authors: Mondal Partha Pratim , Gilbert Richard J. , So Peter T. C.
Published: March 2009

We show an interesting cubic-to-quartic pump intensity dependent crossover of anti-Stokes Raman signal. This is achieved by multiphoton induced excitation of higher vibronic states. The steady state solution of the population dynamics displays a fourth power dependence for anti-Stokes Raman signal in the pump dominated regime, while Stokes Raman signal continues to show cubic power dependence. Proposed nonlinear intensity dependence has the potential for realizing strong enhancement in anti-Stokes Raman signal and an efficient rejection of background noise.
Polarization reversal behavior of spray deposited sodium nitrite:poly(vinyl alcohol) composite films
Authors: Sekhar K. C. , Nath R.
Published: March 2009

The time dependence of polarization reversal current of spray deposited sodium nitrite:poly(vinyl alcohol) composite films has been investigated. The switching current transients have been analyzed by considering domain growth limited process with the Lorentzian distribution function of characteristic domain growth times based on nucleation limited switching model. This model gives excellent agreement with the experimental polarization reversal transients throughout the whole time range. The switching parameters were determined in the composite films deposited at different substrate temperatures (Ts). The minimum value of the activation field at Ts=200 °C makes the polarization reversal more probable. The peak value of polarization current exhibits exponential dependence on the external applied field.
Low temperature Schottky anomalies in the specific heat of LaCoO3: Defect-stabilized finite spin states
Authors: He C. , Zheng H. , Mitchell J. F. , Foo M. L. , Cava R. J. , Leighton C.
Published: March 2009

Measurement of the low temperature specific heat of LaCoO3 single crystals reveals a previously unobserved Schottky anomaly with an energy level splitting, 0.5 meV, that is associated with the first excited spin state of the Co3+ ion. These states persist well below 2 K and have a g-factor around 3.5, consistent with the high-spin spin-orbit triplet, implying the existence of a low density (approximately 0.1% of the sites) of finite-spin Co ions even in the T=0 limit. We propose that these states are trapped at defects and are consistent with the magnetic excitons observed in earlier work.
Photosensitivity of solution-based indium gallium zinc oxide single-walled carbon nanotubes blend thin film transistors
Authors: Lee Keun Woo , Heo Kon Yi , Kim Hyun Jae
Published: March 2009

We studied the optical and electrical properties of solution-based indium gallium zinc oxide single-walled carbon nanotubes blend thin film transistors (SB-IGZO/SWNTs blend TFTs). When the SB-IGZO/SWNTs blend TFTs were illuminated at a wavelength of 660 nm, the off-state drain current slightly increased, while below 550 nm, it increased significantly. The SB-IGZO/SWNTs blend TFTs were incredibly sensitive, with deep-level defects at approximately 2.25 eV, near the midgap. We also presented the photosensitivity (signal-to-noise ratio) of these TFTs. Our results demonstrate that the SB-IGZO/SWNTs blend could be a good candidate for an ultraviolet photodetector.
Continuum modeling of van der Waals interactions between carbon nanotube walls
Authors: Lu W. B. , Liu B. , Wu J. , Xiao J. , Hwang K. C. , Fu S. Y. , Huang Y.
Published: March 2009

Prior continuum models of van der Waals force between carbon nanotube walls assume that the pressures be either the same on the walls or inversely proportional to wall radius. A new continuum model is obtained analytically from the Lennard-Jones potential for van der Waals force, without the above assumptions. Buckling of a double-wall carbon nanotube under external pressure is studied, and the critical buckling pressure is much smaller than those models involving the above assumptions.
The polarization mechanism in CdTe Schottky detectors
Authors: Cola Adriano , Farella Isabella
Published: March 2009

Schottky CdTe nuclear detectors are affected by bias-induced polarization phenomena when operating at room temperature. A space charge buildup occurs at the blocking contact causing the degradation in detection performance. By means of Pockels effect, we study the electric field distribution inside the detector and its variation with time and temperature. The analysis of the space charge has allowed us to point out the role of the Schottky contact and of carrier detrapping from deep levels in the polarization mechanism. Moreover, measured current transients have been quantitatively accounted for by the increase in the electric field at the blocking junction.
Si
/
Si
0.2
Ge
0.8
/
Si
quantum well Schottky barrier diodes
Authors: Kuo P.-S. , Peng C.-Y. , Lee C.-H. , Shen Y.-Y. , Chang H.-C. , Liu C. W.
Published: March 2009

The hole confinement due to the valence band offset of the Si/SiGe/Si quantum well causes the shrinkage of depletion region for the n-type Si/Si0.2Ge0.8/Si Schottky barrier diodes with Pt gates. The capacitance of Si/Si0.2Ge0.8/Si Schottky diodes has approximately two times the capacitance of the control Si device. Moreover, the high electrical field leads to a high thermionic-field emission current and a large image-force lowering at both reverse and forward biases. The conventional capacitor-voltage method cannot be used to accurately measure the barrier height of Si/SiGe/Si quantum well Schottky diodes due to the shrinkage of depletion region.
Multilayer friction and attachment effects on energy dissipation in graphene nanoresonators
Authors: Kim Sung Youb , Park Harold S.
Published: March 2009

We utilize classical molecular dynamics to study the effects of intrinsic, interlayer friction between graphene monolayers, as well as extrinsic attachment or clamping strength between graphene and a model silicon substrate on the energy dissipation (Q-factors) of oscillating graphene nanoresonators. Both interlayer friction and attachment effects are found to significantly degrade the graphene Q-factors, with an increase in energy dissipation with increasing temperature, while both effects are found to be strongly dependent on the strength of the van der Waals interactions, either between adjacent layers of graphene or between graphene and the underlying substrate.
A quantum ring terahertz detector with resonant tunnel barriers
Authors: Huang G. , Guo W. , Bhattacharya P. , Ariyawansa G. , Perera A. G. U.
Published: March 2009

The electronic properties of InAs/GaAs quantum rings and the characteristics of resonant tunnel intersubband terahertz detectors with quantum ring active regions have been studied. The electronic states of the quantum rings have been calculated and measured by the capacitance-voltage technique. The detectors exhibit extremely low dark current density values ∼5×10−5, 4.7×10−2, and 3.5×10−1 A/cm2 under a −1 V bias at 4.2, 80, and 300 K, respectively. Three prominent response peaks are observed at ∼6.5, 10, and 12.5 THz up to T=120 K. At 80 K, the responsivity of the peaks varies from 0.07 to 0.02 A/W.
A new model for studying tissue-specific
mdr
1a gene expression in vivo by live imaging
Authors: Gu Long , Tsark Walter M. , Brown Donna A. , Blanchard Suzette , Synold Timothy W. , Kane Susan E.
Published: March 2009

Multidrug resistance continues to be a major impediment to successful chemotherapy in cancer patients. One cause of multidrug resistance is enhanced expression of the
mdr
1 gene, but the precise factors and physiological conditions controlling
mdr
1 expression are not entirely known. To gain a better understanding of
mdr
1 transcriptional regulation, we created a unique mouse model that allows noninvasive bioimaging of
mdr
1 gene expression in vivo and in real time. The model uses a firefly luciferase (
fLUC
) gene inserted by homologous recombination into the murine
mdr
1a genetic locus. The inserted
fLUC
gene is preceded by a
neo
expression cassette flanked by
lox
P sites, so that Cre-mediated recombination is required to configure the
fLUC
gene directly under the control of the endogenous
mdr
1a promoter. We now demonstrate that the
mdr
1a.
fLUC
knock-in is a faithful reporter for
mdr
1a expression in naive animals, in which
fLUC
mRNA levels and luminescence intensities accurately parallel endogenous
mdr
1a mRNA expression. We also demonstrate xenobiotic-inducible regulation of
mdr
1a.
fLUC
expression in real time, in parallel with endogenous
mdr
1a expression, resulting in a more detailed understanding of the kinetics of
mdr
1a gene induction. This mouse model demonstrates the feasibility of using bioimaging coupled with Cre/
lox
P conditional knock-in to monitor regulated gene expression in vivo. It represents a unique tool with which to study the magnitude and kinetics of
mdr
1a induction under a variety of physiologic, pharmacologic, genetic, and environmental conditions.
Discrete stack of an odd number of polarized aromatic compounds revealing the importance of net vs. local dipoles
Authors: Yamauchi Yoshihiro , Yoshizawa Michito , Akita Munetaka , Fujita Makoto
Published: March 2009

Three polarized aromatic guest molecules (pyrene-4,5-dione, 1) form a triple-layered stack in the box-shaped cavity of an organic pillared coordination cage in water. The cavity size strictly limits the number of stacked planar guests but does not restrict guest orientation, and thus enables the study of discrete stacks of polarized guests and their preferred conformations. Crystallographic study shows that the guest molecules in the cavity are rotated 120° with respect to each other, canceling the net dipole moment rather than the local dipole moment. The unique conformation of a discrete, triple stack of 1 sharply contrasts to the standard head-to-tail conformation in infinite stacks of 1.
Fe65 is required for Tip60-directed histone H4 acetylation at DNA strand breaks
Authors: Stante Maria , Minopoli Giuseppina , Passaro Fabiana , Raia Maddalena , Vecchio Luigi Del , Russo Tommaso
Published: March 2009

Fe65 is a binding partner of the Alzheimer's β-amyloid precursor protein APP. The possible involvement of this protein in the cellular response to DNA damage was suggested by the observation that Fe65 null mice are more sensitive to genotoxic stress than WT counterpart. Fe65 associated with chromatin under basal conditions and its involvement in DNA damage repair requires this association. A known partner of Fe65 is the histone acetyltransferase Tip60. Considering the crucial role of Tip60 in DNA repair, we explored the hypothesis that the phenotype of Fe65 null cells depended on its interaction with Tip60. We demonstrated that Fe65 knockdown impaired recruitment of Tip60-TRRAP complex to DNA double strand breaks and decreased histone H4 acetylation. Accordingly, the efficiency of DNA repair was decreased upon Fe65 suppression. To explore whether APP has a role in this mechanism, we analyzed a Fe65 mutant unable to bind to APP. This mutant failed to rescue the phenotypes of Fe65 null cells; furthermore, APP/APLP2 suppression results in the impairment of recruitment of Tip60-TRRAP complex to DNA double strand breaks, decreased histone H4 acetylation and repair efficiency. On these bases, we propose that Fe65 and its interaction with APP play an important role in the response to DNA damage by assisting the recruitment of Tip60-TRRAP to DNA damage sites.