bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐profile high‐gain slot antenna with Fabry‐Pérot cavity and mushroom‐like electromagnetic band gap structures
Authors: Liu Ying , Hao Yuwen , Gong Shuxi
Published: February 2015

A novel low‐profile high‐gain slot antenna based on a modified Fabry‐Pérot cavity (FPC) and a mushroom‐like electromagnetic band gap (EBG) structure is proposed and discussed. The low‐profile FPC composed of a planar artificial magnetic conductor and frequency selective surfaces is utilised to enhance gain. Moreover, the mushroom‐like EBG structure rather than a traditional reflector is used to reduce the profile and to increase gain. Eventually, an antenna prototype operating at the WLAN system coverage IEEE 802.11a (5.15–5.35 GHz) is fabricated and exemplified to validate high radiation performance. The measured results show that the proposed antenna achieves a high gain of up to 10.6 dBi at 5.25 GHz and an −10 dB impendence bandwidth for S11 ranging from 5.08 to 5.51 GHz.
Electrical predictive model of Zener diode under pulsed EOS
Authors: Zhu F. , Ravelo B. , Fouquet F. , Kadi M.
Published: February 2015

Electrical overstress (EOS) is assumed as one of the most misinterpreted electrical phenomena that can affect drastically the reliability of electronic components. To predict the behaviour of a circuit under EOS, a relevant predictive circuit model is required. An investigation of circuit degradation caused by the pulsed EOS is addressed. More precisely, the electrical response of the Zener diode BZX84B6V8 under square wave EOS is modelled. The proposed model is originally extracted from the diode electro‐thermal behaviour caused by the self‐heating induced by excessive EOS on the reverse voltage. The diode EOS model was emulated and implemented in VHDL‐AMS language. It has been found experimentally, with a 17 V amplitude and 8 ms period square wave EOS, that the diode transient electrical parameters enable experimental response prediction. The suggested model can be used for reliability analyses of electronic devices.
Numerical and experimental study of the effects of load and distance variation on wireless power transfer systems using magnetically coupled resonators
Authors: Rotaru Mihai Dragos , Tanzania Robin , Ayoob Raed , Kheng Tan Yen , Sykulski Jan K.
Published: February 2015

This work investigates a series resonant circuit designed to wirelessly transfer power to charge an electrical vehicle battery. A typical approach assumes the load connected to the power transfer system to be constant and then the wireless link efficiency is studied. In practical engineering applications, however, the load and the distance between coils will vary and the efficiency may strongly depend on these variations. The efficiency will also be affected by the presence of massive conducting or shielding structures in the proximity of the wireless system. Here, the authors study these effects with the help of an equivalent circuit extracted from a full wave simulation and correlated with measured results. The authors demonstrate that by changing the load resistance the efficiency of the system can be improved, even for a large separation between the two magnetically coupled resonators; however, the maximum efficiency point may not correspond to the maximum power that can be handled by the system. They then analyse the primary and secondary voltages and currents in support of the above findings.
Compact U‐shape radiating patch with rectangular ground planar monopole antenna
Authors: Sambhe Vijay Kisanrao , Awale Rahul Narayanrao , Wagh Abhay
Published: February 2015

A compact U‐shape radiating patch with rectangular ground planar monopole antenna is proposed. Antenna is fabricated on FR4 substrate with permittivity 4.4 and loss tangent 0.02 with dimension 75(LR) × 48(WR) × 1.6(h) mm3. Measured return loss is ≤ −10 dB for the entire impedance bandwidth (800–3500 MHz). In addition, different key parameters which affect the impedance bandwidth are analysed and results discussed. Moreover, antennas have acceptable gain flatness with good omnidirectional radiation patterns. Its ease of fabrication, compatibility with other electronic devices, and radiation pattern make it a competent candidate for global system of mobile (890–960 MHz), digital communication system (1700–1900 MHz) and Bluetooth (2.45 GHz) cellular communication applications.
A Protocol to Reduce Interobserver Variability in the Computed Tomography Measurement of Orbital Floor Fractures
Authors: Ang ChuanHan , Low JinRong , Shen JiaYi , Cai Elijah Zheng Yang , Hing Eileen Chor Hoong , Chan YiongHuak , Sundar Gangadhara , Lim ThiamChye
Published: February 2015

Orbital fracture detection and size determination from computed tomography (CT) scans affect the decision to operate, the type of surgical implant used, and postoperative outcomes. However, the lack of standardization of radiological signs often leads to the false-positive detection of orbital fractures, while nonstandardized landmarks lead to inaccurate defect measurements. We aim to design a novel protocol for CT measurement of orbital floor fractures and evaluate the interobserver variability on CT scan images. Qualitative aspects of this protocol include identifying direct and indirect signs of orbital fractures on CT scan images. Quantitative aspects of this protocol include measuring the surface area of pure orbital floor fractures using computer software. In this study, 15 independent observers without clinical experience in orbital fracture detection and measurement measured the orbital floor fractures of three randomly selected patients following the protocol. The time required for each measurement was recorded. The intraclass correlation coefficient of the surface area measurements is 0.999 (0.997–1.000) with p-value < 0.001. This suggests that any observer measuring the surface area will obtain a similar estimation of the fractured surface area. The maximum error limit was 0.901 cm2 which is less than the margin of error of 1 cm2 in mesh trimming for orbital reconstruction. The average duration required for each measurement was 3 minutes 19 seconds (ranging from 1 minute 35 seconds to 5 minutes). Measurements performed with our novel protocol resulted in minimal interobserver variability. This protocol is effective and generated reproducible results, is easy to teach and utilize, and its findings can be interpreted easily.
When is it Safe to Return to Driving after Spinal Surgery?
Authors: Scott Trevor P. , Pannel William , Savin David , Ngo Stephanie S. , Ellerman Jessica , Toy Kristin , Daubs Michael D. , Lu Daniel , Wang Jeffrey C.
Published: February 2015

Study Design

Prospective study.

Objective

Surgeons’ recommendations for a safe return to driving following cervical and lumbar surgery vary and are based on empirical data. Driver reaction time (DRT) is an objective measure of the ability to drive safely. There are limited data about the effect of cervical and lumbar surgery on DRT. The purpose of our study was to use the DRT to determine when the patients undergoing a spinal surgery may safely return to driving.

Methods

We tested 37 patients’ DRT using computer software. Twenty-three patients (mean 50.5 ± 17.7 years) received lumbar surgery, and 14 patients had cervical surgery (mean 56.7 ± 10.9 years). Patients were compared with 14 healthy male controls (mean 32 ± 5.19 years). The patients having cervical surgery were subdivided into the anterior versus posterior approach and myelopathic versus nonmyelopathic groups. Patients having lumbar spinal surgery were subdivided by decompression versus fusion with or without decompression and single-level versus multilevel surgery. The patients were tested preoperatively and at 2 to 3, 6, and 12 weeks following the surgery. The use of opioids was noted.

Results

Overall, the patients having cervical and lumbar surgery showed no significant differences between pre- and postoperative DRT (cervical p = 0.49, lumbar p = 0.196). Only the patients having single-level procedures had a significant improvement from a preoperative DRT of 0.951 seconds (standard deviation 0.255) to 0.794 seconds (standard deviation 0.152) at 2 to 3 weeks ( p = 0.012). None of the other subgroups had a difference in the DRT.

Conclusions

Based on these findings, it may be acceptable to allow patients having a single-level lumbar fusion who are not taking opioids to return to driving as early as 2 weeks following the spinal surgery.
Orbit-averaged quantities, the classical Hellmann-Feynman theorem, and the magnetic flux enclosed by gyro-motion
Authors: Perkins R. J. , Bellan P. M.
Published: February 2015

Action integrals are often used to average a system over fast oscillations and obtain reduced dynamics. It is not surprising, then, that action integrals play a central role in the Hellmann-Feynman theorem of classical mechanics, which furnishes the values of certain quantities averaged over one period of rapid oscillation. This paper revisits the classical Hellmann-Feynman theorem, rederiving it in connection to an analogous theorem involving the time-averaged evolution of canonical coordinates. We then apply a modified version of the Hellmann-Feynman theorem to obtain a new result: the magnetic flux enclosed by one period of gyro-motion of a charged particle in a non-uniform magnetic field. These results further demonstrate the utility of the action integral in regards to obtaining orbit-averaged quantities and the usefulness of this formalism in characterizing charged particle motion.
Peroxyacetyl radical: Electronic excitation energies, fundamental vibrational frequencies, and symmetry breaking in the first excited state
Authors: Copan Andreas V. , Wiens Avery E. , Nowara Ewa M. , Schaefer Henry F. , Agarwal Jay
Published: February 2015

Peroxyacetyl radical [CH3C(O)O2] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X̃) and first (Ã) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals.
Magnetic tunnel junctions using Co/Ni multilayer electrodes with perpendicular magnetic anisotropy
Authors: Lytvynenko Ia. , Deranlot C. , Andrieu S. , Hauet T.
Published: February 2015

Magnetic and magneto-transport properties of amorphous Al2O3-based magnetic tunnel junctions (MTJ) having two Co/Ni multilayer electrodes exhibiting perpendicular magnetic anisotropy (PMA) are presented. An additional Co/Pt multilayer is required to maintain PMA in the top Co/Ni electrode. Slight stacking variations lead to dramatic magnetic changes due to dipolar interactions between the top and bottom electrodes. Tunnel magneto-resistance (TMR) of up to 8% at 300 K is measured for the MTJ with two PMA electrodes. The TMR value increases when the top PMA electrode is replaced by an in-plane magnetized Co layer. These observations can be attributed to significant intermixing in the top Co/Ni electrode.
Complete photonic band gaps and tunable self-collimation in the two-dimensional plasma photonic crystals with a new structure
Authors: Zhang Hai-Feng , Ding Guo-Wen , Li Hai-Ming , Liu Shao-Bin
Published: February 2015

In this paper, the properties of complete photonic band gaps (CPBGs) and tunable self-collimation in two-dimensional plasma photonic crystals (2D PPCs) with a new structure in square lattices, whose dielectric fillers (GaAs) are inserted into homogeneous and nomagnetized plasma background are theoretically investigated by a modified plane wave expansion (PWE) method with a novel technique. The novel PWE method can be utilized to compute the dispersion curves of 2D PPCs with arbitrary-shaped cross section in any lattices. As a comparison, CPBGs of PPCs for four different configurations are numerically calculated. The computed results show that the proposed design has the advantages of achieving the larger CPBGs compared to the other three configurations. The influences of geometric parameters of filled unit cell and plasma frequency on the properties of CPBGs are studied in detail. The calculated results demonstrate that CPBGs of the proposed 2D PPCs can be easily engineered by changing those parameters, and the larger CPBGs also can be obtained by optimization. The self-collimation in such 2D PPCs also is discussed in theory under TM wave. The theoretical simulations reveal that the self-collimation phenomena can be found in the TM bands, and both the frequency range of self-collimation and the equifrequency surface contours can be tuned by the parameters as mentioned above. It means that the frequency range and direction of electromagnetic wave can be manipulated by designing, as it propagates in the proposed PPCs without diffraction. Those results can hold promise for designing the tunable applications based on the proposed PPCs.
(Quasi)-exact-solvability on the sphere Sn
Authors: Miller Willard , Turbiner Alexander V.
Published: February 2015

An Exactly Solvable (ES) potential on the sphere Sn is reviewed and a related Quasi-Exactly Solvable (QES) potential is found and studied. After mapping the sphere to a simplex, it is found that the metric (of constant curvature) is in polynomial form, and both the ES and the QES potentials are rational functions. Their hidden algebra is gln, realized in a finite-dimensional representation by first order differential operators acting on RPn. It is shown that variables in the Schrödinger eigenvalue equation can be separated in polyspherical coordinates and there is always complete integrability. The QES system is completely integrable for n = 2 and non-maximally superintegrable for n ≥ 3. There is no separable coordinate system in which it is exactly solvable. We point out that by taking contractions of superintegrable systems, such as induced by Inönü-Wigner Lie algebra contractions, we can find other QES superintegrable systems, and we illustrate this by contracting our Sn system to a QES non-maximal superintegrable system on Euclidean space En, an extension of the Smorodinsky-Winternitz potential.
Multi-speed solitary wave solutions for a coherently coupled nonlinear Schrödinger system
Authors: Wang Zhong , Cui Shangbin
Published: February 2015

Existence of multi-speed solitary wave solutions for a coherently coupled system of nonlinear Schrödinger equations is proved. Such solutions behave at large time as a couple of scalar solitary waves traveling at different speeds. Compared to incoherently coupled nonlinear Schrödinger systems which have enjoyed a lot of research during the past several decades, coherently coupled nonlinear Schrödinger systems have a significant different feature that their component masses are not conserved but only the total mass is conserved. Some restriction upon the phases and velocities of the two component solitary waves is therefore imposed to fit this situation.
Anomalous softening of yield strength in tantalum at high pressures
Authors: Jing Qiumin , Wu Qiang , Xu Ji-an , Bi Yan , Liu Lei , Liu Shenggang , Zhang Yi , Geng Huayun
Published: February 2015

The pressure dependence of the yield strength of tantalum was investigated experimentally up to 101 GPa at room temperature using a diamond anvil cell. A yield strength softening is observed between 52 and 84 GPa, whereas a normal trend is observed below 52 GPa and above 84 GPa. The onset pressure of the softening is in agreement with previous results obtained by the pressure gradient method and shock wave experiments. This unusual strength softening in tantalum is not related with structural transformation, preferred orientation, or material damage. Our measurements indicate that microscopic deviatoric strain is the major reason for the observed strength softening in tantalum.
Liquid methanol under a static electric field
Authors: Cassone Giuseppe , Giaquinta Paolo V. , Saija Franz , Saitta A. Marco
Published: February 2015

We report on an ab initio molecular dynamics study of liquid methanol under the effect of a static electric field. We found that the hydrogen-bond structure of methanol is more robust and persistent for field intensities below the molecular dissociation threshold whose value (≈0.31 V/Å) turns out to be moderately larger than the corresponding estimate obtained for liquid water. A sustained ionic current, with ohmic current-voltage behavior, flows in this material for field intensities above 0.36 V/Å, as is also the case of water, but the resulting ionic conductivity (≈0.40 S cm−1) is at least one order of magnitude lower than that of water, a circumstance that evidences a lower efficiency of proton transfer processes. We surmise that this study may be relevant for the understanding of the properties and functioning of technological materials which exploit ionic conduction, such as direct-methanol fuel cells and Nafion membranes.
Vortical disturbances in a linearly stratified linear shear flow. I. Linear theory
Authors: Shukhman Ilia G. , Tewner Shoshana Weiss , Cohen Jacob
Published: February 2015

The purpose of this theoretical study is to explore the combined effect of shear and stratification on the evolution of a three-dimensional localized vortical disturbance induced by an initial temperature perturbation embedded in linearly (stable) stratified linear shear flow. The base flow velocity includes only the horizontal component which together with the temperature field varies in the vertical direction. The geometrically small confinement of the disturbance relative to the characteristic scales of variation of the base flow velocity and temperature fields justifies the assumption that the vertical gradients of base flow velocity and temperature are uniform. Assuming a sufficiently weak disturbance, linear theory is applied for calculating the disturbed vorticity and temperature fields. The solution is carried out by first transforming the set of equations to Fourier space and a subsequent transition into Lagrangian variables. It is shown that the growth of the strength of the vortex (measured by its integrated volumetric enstrophy and its circulation) is caused by both shear and stratification while the characteristic curve of amplification (monotonic or oscillatory) depends on which one of the two factors dominates (shear or stratification). In the non-dissipative case, the enstrophy growth continues indefinitely (within the framework of linear theory); however, dissipative effects (viscosity and thermal diffusion) modify this growth to become transient. The disturbance is stretched in the streamwise direction by the shear. As long as the initial temperature disturbance is spherically localized and sufficiently weak, the centers of the induced vortical and temperature disturbances remain in their original position where the streamwise base flow velocity is zero. The rise of the disturbance and its consequence streamwise movement as a whole does not occur as it is a nonlinear effect. This and other nonlinear effects are considered in our complementary paper [Weiss Tewner et al., “Vortical disturbances in a linearly stratified linear shear flow. II. Nonlinear evolution,” Phys. Fluids 27, 024104 (2015)].
Vortical disturbances in a linearly stratified linear shear flow. II. Nonlinear evolution
Authors: Weiss Tewner Shoshana , Cohen Jacob , Shukhman Ilia G.
Published: February 2015

In this work, we concentrate on the evolution of a (relatively strong) localized three-dimensional temperature disturbance embedded in quiescent fluid or steady pure shear with uniform or linearly stratified temperature. The base flow velocity includes only the streamwise component which together with the temperature field vary along the vertical direction opposite to the gravitational acceleration. For solving the problem, we have extended an analytical-based numerical method derived for a localized vortical disturbance embedded in shear flow, to include the energy equation and the temperature term in the vorticity equation. The method has been verified by comparing the results to those obtained using commercial direct numerical simulation software. The spatio-temporal development of a buoyant disturbance is explored through several governing parameters. The evolution of an initially spherical disturbance is found to differ negligibly from that of an initially cubical one. The effect of the ratio between shear and buoyancy time scales is investigated. Stratification of a stationary base flow results in oscillation of the circulation, the frequency of which agrees with the Brunt-Väisälä frequency. The effect of added shear to a stratified ambient is characterized by the Richardson number (Ri). We observe that above Ri = 0.5 the disturbance enstrophy grows transiently and eventually decays, however for Ri < 0.5, it continues to grow for relatively long times and therefore may trigger nonlinear mechanisms before its eventual decay due to viscous effects.
Atomistic simulation of damage accumulation and amorphization in Ge
Authors: Gomez-Selles Jose L. , Claverie Alain , Sklenard Benoit , Benistant Francis , Martin-Bragado Ignacio
Published: February 2015

Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 1022 cm−3 which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions. We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.

At the request of the authors, this article is being retracted effective 24 January 2017.
Materials with constant anisotropic conductivity as a thermal cloak or concentrator
Authors: Chen Tungyang , Weng Chung-Ning , Tsai Yu-Lin
Published: February 2015

An invisibility cloak based on transformation optics often requires material with inhomogeneous, anisotropic, and possibly extreme material parameters. In the present study, on the basis of the concept of neutral inclusion, we find that a spherical cloak can be achieved using a layer with finite constant anisotropic conductivity. We show that thermal localization can be tuned and controlled by anisotropy of the coating layer. A suitable balance of the degree of anisotropy of the cloaking layer and the layer thickness provides a cloaking effect. Additionally, by reversing the conductivities in two different directions, we find that a thermal concentrating effect can be simulated. This finding is of particular value in practical implementation as a material with constant material parameters is more feasible to fabricate. In addition to the theoretical analysis, we also demonstrate our solutions in numerical simulations based on finite element calculations to validate our results.
The superspin glass transition in zinc ferrite nanoparticles
Authors: Kaman O. , Kořínková T. , Jirák Z. , Maryško M. , Veverka M.
Published: February 2015

Nanoparticles of the ZnxFe3−xO4 (x = 0.3–0.4) spinel phase having 5 and 15 nm size were synthesized by thermal decomposition of the respective acetylacetonates in a high boiling-point solvent employing surfactants. The collective behaviour of the nanoparticles was probed by dc and ac magnetic measurements of tightly compressed pellets of the particles and silica coated products which were prepared by reverse microemulsion technique. The assembly of bare 5 nm particles remains in the superparamagnetic state with Curie-Weiss characteristics down to 35 K when a rather sharp freezing of superspins is detected. The larger particles show a similar but more diffusive transition at 250 K. The cores encapsulated into the diamagnetic silica do not exhibit glassy freezing.
Improvement of force factor of magnetostrictive vibration power generator for high efficiency
Authors: Kita Shota , Ueno Toshiyuki , Yamada Sotoshi
Published: February 2015

We develop high power magnetostrictive vibration power generator for battery-free wireless electronics. The generator is based on a cantilever of parallel beam structure consisting of coil-wound Galfenol and stainless plates with permanent magnet for bias. Oscillating force exerted on the tip bends the cantilever in vibration yields stress variation of Galfenol plate, which causes flux variation and generates voltage on coil due to the law of induction. This generator has advantages over conventional, such as piezoelectric or moving magnet types, in the point of high efficiency, highly robust, and low electrical impedance. Our concern is the improvement of energy conversion efficiency dependent on the dimension. Especially, force factor, the conversion ratio of the electromotive force (voltage) on the tip velocity in vibration, has an important role in energy conversion process. First, the theoretical value of the force factor is formulated and then the validity was verified by experiments, where we compare four types of prototype with parameters of the dimension using 7.0 × 1.5 × 50 mm beams of Galfenol with 1606-turn wound coil. In addition, the energy conversion efficiency of the prototypes depending on load resistance was measured. The most efficient prototype exhibits the maximum instantaneous power of 0.73 W and energy of 4.7 mJ at a free vibration of frequency of 202 Hz in the case of applied force is 25 N. Further, it was found that energy conversion efficiency depends not only on the force factor but also on the damping (mechanical loss) of the vibration.
Numerical simulation to study the transient self focusing of laser beam in plasma
Authors: Sharma R. P. , Hussain Saba , Gaur Nidhi
Published: February 2015

In this paper, we present the numerical simulation for the coupled system of equations governing the dynamics of laser and Ion Acoustic Wave (IAW) in a collisionless plasma, when the coupling between the waves is through ponderomotive non-linearity. The nonlinear evolution of the laser beam is studied when the pump laser is perturbed by a periodic perturbation. By changing the perturbation wave number, we have studied its effect on the nonlinear evolution pattern of laser beam. In order to have a physical insight into the nonlinear dynamics of laser beam evolution in time and space, we have studied the laser and IAW spectra containing spatial harmonics. The magnitude of these harmonics changes with time and leads to time dependent localization of laser beam in spatial domain. The nonlinear dynamics of this localization is investigated in detail by using simulation and a semi-analytical model.
High compositional homogeneity of CdTexSe1−x crystals grown by the Bridgman method
Authors: Roy U. N. , Bolotnikov A. E. , Camarda G. S. , Cui Y. , Hossain A. , Lee K. , Lee W. , Tappero R. , Yang G. , Gul R. , James R. B.
Published: February 2015

We obtained high-quality CdTexSe1−x (CdTeSe) crystals from ingots grown by the vertical Bridgman technique. The compositional uniformity of the ingots was evaluated by X-ray fluorescence at BNL’s National Synchrotron Light Source X27A beam line. The compositional homogeneity was highly uniform throughout the ingot, and the effective segregation coefficient of Se was ∼1.0. This high uniformity offers potential opportunity to enhance the yield of the materials for both infrared substrate and radiation-detector applications, so greatly lowering the cost of production and also offering us the prospect to grow large-diameter ingots for use as large-area substrates and for producing higher efficiency gamma-ray detectors. The concentration of secondary phases was found to be much lower, by eight- to ten fold compared to that of conventional CdxZn1−xTe (CdZnTe or CZT).
Electronic structure, stability, and oxidation of boron-magnesium clusters and cluster solids
Authors: Reber Arthur C. , Khanna Shiv N.
Published: February 2015

Electronic structure studies on MgmBn− (1 ≤ n ≤ 15, 0 ≤ m ≤ 3) clusters have been performed to identify the nature of bonding and the origin of stability in the mixed clusters. Boron clusters are found to have planar structures marked by tangential, radial, and π aromaticity. The maximum stability is achieved for when all three types of aromaticity are quenched. The ring like Bn− clusters are shown to be electron deficient for n = 6-8, and the addition of Mg atoms is found to enhance the stability of the boron cluster through ionic bonding that quenches the aromaticity and produces umbrella-like structures. Several species including MgB6−, MgB8−, Mg2B−, and Mg3B7− are found to have the largest Mg binding energies due to this mechanism. The transfer of a single electron from the Mg atom to the boron cluster results in a Mg atom with a half-filled 3s orbital that may serve as an ignition center for combustion. Studies on the MgB7 and MgB4 cluster solids indicate that they are constructed from icosahedral and umbrella-like motifs and are semiconductors with band gap energies of 1.46 eV and 0.41 eV, respectively.
Resistance and internal electric field in cloud-to-ground lightning channel
Authors: Cen Jianyong , Yuan Ping , Xue Simin , Wang Xuejuan
Published: February 2015

Cloud-to-ground lightning with six return strokes has been recorded by slitless spectrograph and the system of fast antenna and slow antenna. The physical parameters of the discharge channel have been obtained based on the combination of spectra and synchronous radiated electric field. The resistance and internal electric field of the channel are studied as the focus in this paper. The results show that the resistances per unit length of the lightning channel are in the order of 10−2–10−1 Ω/m and the internal electric field strengths are in the order of 103 V/m.
Micromagnetic model analysis of integrated single-pole-type head with tilted spin-torque oscillator for high-frequency microwave-assisted magnetic recording
Authors: Katayama Takuto , Kanai Yasushi , Yoshida Kazuetsu , Greaves Simon , Muraoka Hiroaki
Published: February 2015

The spin-torque oscillator (STO) is the most important component in microwave-assisted magnetic recording. Some requirements for the STO are: large amplitude and stable oscillation, small injected current, and oscillation at a frequency that excites resonance in a recording medium. It is also necessary for the STO oscillation to closely follow the head coil current. In this paper, STOs were integrated into write heads and micromagnetic analyses carried out to obtain a write head structure with stable STO oscillation that could follow a high-frequency head coil current.
Capillary plasma jet: A low volume plasma source for life science applications
Authors: Topala I. , Nagatsu M.
Published: February 2015

In this letter, we present results from multispectroscopic analysis of protein films, after exposure to a peculiar plasma source, i.e., the capillary plasma jet. This plasma source is able to generate very small pulsed plasma volumes, in kilohertz range, with characteristic dimensions smaller than 1 mm. This leads to specific microscale generation and transport of all plasma species. Plasma diagnosis was realized using general electrical and optical methods. Depending on power level and exposure duration, this miniature plasma jet can induce controllable modifications to soft matter targets. Detailed discussions on protein film oxidation and chemical etching are supported by results from absorption, X-ray photoelectron spectroscopy, and microscopy techniques. Further exploitation of principles presented here may consolidate research interests involving plasmas in biotechnologies and plasma medicine, especially in patterning technologies, modified biomolecule arrays, and local chemical functionalization.
On the difference between breakdown and quench voltages of argon plasma and its relation to 4p–4s atomic state transitions
Authors: Forati Ebrahim , Piltan Shiva , Sievenpiper Dan
Published: February 2015

Using a relaxation oscillator circuit, breakdown (VBD) and quench (VQ) voltages of a DC discharge microplasma between two needle probes are measured. High resolution modified Paschen curves are obtained for argon microplasmas including a quench voltage curve representing the voltage at which the plasma turns off. It is shown that for a point to point microgap (e.g., the microgap between two needle probes) which describes many realistic microdevices, neither Paschen's law applies nor field emission is noticeable. Although normally VBD > VQ, it is observed that depending on environmental parameters of argon, such as pressure and the driving circuitry, plasma can exist in a different state with equal VBD and VQ. Using emission line spectroscopy, it is shown that VBD and VQ are equal if the atomic excitation by the electric field dipole moment dominantly leads to one of the argon's metastable states (4P5 in our study).
Polarized fluorescent emission from aligned electrospun nanofiber sheets containing semiconductor nanorods
Authors: Hasegawa Masaki , Hirayama Yuki , Dertinger Stephan
Published: February 2015

We fabricated sheets consisting of aligned electrospun polymer nanofibers embedded with semiconductor nanorods (NRs) and confirmed the production of polarized fluorescence emission. Electrospun nanofibers with embedded semiconductor NRs were rolled around a drum to form a sheet in which each nanofiber was aligned parallel to the rotation direction. The thickness and polarization ratio of the sheet were 1.5 μm and 0.6, respectively. We also examined how electrospinning parameters affected the polarization ratio of the sheet.
Electrostatic capacitance and Faraday cage behavior of carbon nanotube forests
Authors: Ya'akobovitz A. , Bedewy M. , Hart A. J.
Published: February 2015

Understanding of the electrostatic properties of carbon nanotube (CNT) forests is essential to enable their integration in microelectronic and micromechanical devices. In this study, we sought to understand how the hierarchical geometry and morphology of CNT forests determines their capacitance. First, we find that at small gaps, solid micropillars have greater capacitance, yet at larger gaps the capacitance of the CNT forests is greater. The surface area of the CNT forest accessible to the electrostatic field was extracted by analysis of the measured capacitance, and, by relating the capacitance to the average density of CNTs in the forest, we find that the penetration depth of the electrostatic field is on the order of several microns. Therefore, CNT forests can behave as a miniature Faraday cage. The unique electrostatic properties of CNT forests could therefore enable their use as long-range proximity sensors and as shielding elements for miniature electronic devices.
Formation of 300 nm period pore arrays by laser interference lithography and electrochemical etching
Authors: Liu J. , Kleimann P. , Laffite G. , Jamois C. , Orobtchouk R.
Published: February 2015

This paper highlights that combining laser interference lithography and electrochemical etching is a cost-effective, efficient method to realize periodic nanopore arrays in silicon with lattice pitch as small as 300 nm on centimeter-scale substrates. The fabrication of wide-area and high aspect ratio 2D pore arrays with 250 nm diameter and 5 μm depth is demonstrated. All the steps of the process have been optimized to achieve vertical sidewalls with 50 nm thickness, providing pore arrays with aspect ratio of 100 on n-type silicon substrates over an area of 2 × 2 cm2. These results constitute a technological advance in the realization of ordered pore arrays in silicon with very small lattice parameters, with impact in biotechnology, energy harvesting, or sensors.
Field noise in tunneling magnetoresistance sensors with variable sensitivity
Authors: Wisniowski P. , Dabek M. , Wrona J.
Published: February 2015

We demonstrate CoFeB/MgO/CoFeB sensors with field noise level below magnetic noise-sensitivity scaling limit and significant reduction of 1/f noise corner frequency. The sensors show more than three orders of magnitude reduction of voltage noise and drop of the corner frequency from 100 kHz to 1 kHz. We achieved this by changing the sensors field sensitivity from 127 (V/T) to 2.7 (V/T) via perpendicular anisotropy-induced field sensitivity modulation. The reduction of the field noise beyond the scaling limit presents sensors for specific field sensitivity. The field sensitivity modulation in our sensors enables magnetic noise reduction that improves field noise (detectivity) and shifts magnetic 1/f corner to lower frequency. The shift of 1/f corner frequency together with the magnetic noise reduction indicates importance of anisotropy-induced sensitivity modulation in reduction of low frequency magnetization fluctuations in CoFeB/MgO/CoFeB sensors.
Femtosecond laser ablation of polymethylmethacrylate via dual-color synthesized waveform
Authors: Yang Chan-Shan , Lin Chih-Hsuan , Zaytsev Alexey , Teng Kuei-Chung , Her Tsing-Hua , Pan Ci-Ling
Published: February 2015

We have demonstrated the laser ablation of PMMA using dual-color waveform synthesis of the fundamental (ω) and its second-harmonic (2ω) of a femtosecond Ti:Sapphire laser. A modest and yet clear modulation (∼22%) in ablated area versus relative phase between the 2ω and ω beams with a power-ratio of 15% (28/183 mW) is revealed. This is explained qualitatively by the dependence of ablation on multiphoton ionization of which the rate is related to the relative phase of the synthesized waveform. At higher peak power ratios, the modulation decreases rapidly, as the two-photon-ionization rate of the 2ω dominates over that of the three- to four- photon ionization of the ω beam. This technique demonstrates the feasibility of phase-controlled laser processing of materials.
Runaway of energetic test ions in a toroidal plasma
Authors: Eilerman S. , Anderson J. K. , Sarff J. S. , Forest C. B. , Reusch J. A. , Nornberg M. D. , Kim J.
Published: February 2015

Ion runaway in the presence of a large-scale, reconnection-driven electric field has been conclusively measured in the Madison Symmetric Torus reversed-field pinch (RFP). Measurements of the acceleration of a beam of fast ions agree well with test particle and Fokker-Planck modeling of the runaway process. However, the runaway mechanism does not explain all measured ion heating in the RFP, particularly previous measurements of strong perpendicular heating. It is likely that multiple energization mechanisms occur simultaneously and with differing significance for magnetically coupled thermal ions and magnetically decoupled tail and beam ions.
Characteristics of 2D magnetic field sensor based on magnetic sensitivity diodes
Authors: Zhao Xiaofeng , Yang Xianghong , Yu Yang , Wu Tong , Wen Dianzhong
Published: February 2015

A two-dimensional (2D) magnetic field sensor is proposed in this paper. It contains two Wheatstone bridges composed of four magnetic sensitivity diodes(MSDs)with similar characteristics and four loading resistances. In order to realize the axial symmetric distribution of four MSDs, two MSDs with opposite magnetic sensitive directions were located along the x and −x axes, and two with opposite magnetic sensitive directions were located along the y and −y axes. The experimental results indicate that when VDD = 5.0 V, the magnetic sensitivities of the 2D magnetic sensor can reach SxB  =  544 mV/T and SyB  =  498 mV/T in the x and y directions, respectively. Consequently, it is possible to measure the two-dimensional magnetic field.
Investigation of a metallic photonic crystal high power microwave mode converter
Authors: Wang Dong , Qin Fen , Xu Sha , Yu Aimin , Wu Yong
Published: February 2015

It is demonstrated that an L band metallic photonic crystal TEM-TE11 mode converter is suitable for narrow band high power microwave application. The proposed mode converter is realized by partially filling metallic photonic crystals along azimuthal direction in a coaxial transmission line for phase-shifting. A three rows structure is designed and simulated by commercial software CST Microwave Studio. Simulation results show that its conversion efficiency is 99% at the center frequency 1.58 GHz. Over the frequency range of 1.56-1.625 GHz, the conversion efficiency exceeds 90 %, with a corresponding bandwidth of 4.1 %. This mode converter has a gigawatt level power handling capability which is suitable for narrow band high power microwave application. Using magnetically insulated transmission line oscillator(MILO) as a high power microwave source, particle-in-cell simulation is carried out to test the performance of the mode converter. The expected TE11 mode microwave output is obtained and the MILO works well. Mode conversion performance of the converter is tested by far-field measurement method. And the experimental result confirms the validity of our design. Then, high power microwave experiment is carried out on a Marx-driven Blumlein water line pulsed power accelerator. Microwave frequency, radiated pattern and power are measured in the far-field region and the results agree well with simulation results. The experiment also reveals that no microwave breakdown or pulse shortening took place in the experimental setup.
Fire emission uncertainties and their effect on smoke dispersion predictions: a case study at Eglin Air Force Base, Florida, USA
Authors: Davis Aika Y. , Ottmar Roger , Liu Yongqiang , Goodrick Scott , Achtemeier Gary , Gullett Brian , Aurell Johanna , Stevens William , Greenwald Roby , Hu Yongtao , Russell Armistead , Hiers J. Kevin , Odman M. Talat
Published: February 2015

Prescribed burning is practiced to benefit ecosystems but the resulting emissions can adversely affect air quality. A better understanding of the uncertainties in emission estimates and how these uncertainties affect smoke predictions is critical for model-based decision making. This study examined uncertainties associated with estimating fire emissions and how they affected smoke concentrations downwind from a prescribed burn that was conducted at Eglin Air Force Base in Florida, US. Estimated variables used in the modelled emission calculation were compared with field measurements. Fuel loadings, fuel consumption and emission factors were simulated using Photo Series, Consume, and previously published values. A plume dispersion model was used to study the effect of uncertainty in emissions on ground concentration prediction. The fire emission models predicted fuel loading, fuel consumption and emission factor within 15% of measurements. Approximately 18% uncertainty in field measurements of PM2.5 emissions and 36% uncertainty attributed to variability in emission estimating models resulted respectively in 20% and 42% ground level PM2.5 concentration uncertainties in dispersion modelling using Daysmoke. Uncertainty in input emissions influences the concentrations predicted by the smoke dispersion model to the same degree as does the model’s inherent uncertainty due to turbulence.
Understanding social impact from wildfires: advancing means for assessment
Authors: Paveglio Travis B. , Brenkert-Smith Hannah , Hall Troy , Smith Alistair M. S.
Published: February 2015

There is no uniform means for assessing social impact from wildland fires beyond statistics such as home loss, suppression costs and the number of residents evacuated. In this paper we argue for and provide a more comprehensive set of considerations for gauging social impact following wildfires. These expanded considerations can advance methods for determining how social impacts from wildfire are changing over time and among diverse communities affected by fire. Our preliminary considerations for social impact from wildfire are drawn from the synthesis of the literature on wildfire and other hazards. We explain how our considerations cover existing research insights and advance them by accounting for wildfire-specific impacts. Considerations are presented as a series of questions that could be answered by an assemblage of outside professionals and local key informants in an affected area for comparison and policy purposes. Those considerations could also be used to advance research questions related to wildfire exposure and impact. We discuss multiple methodological strategies for collecting and analysing data that would be needed to answer considerations presented as part of this synthesis. This includes potential methods for using those considerations to assess social impact across communities.
Cold dark matter: Controversies on small scales
Authors: Weinberg David H. , Bullock James S. , Governato Fabio , Kuzio de Naray Rachel , Peter Annika H. G.
Published: February 2015

The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way’s dwarf galaxy satellites. We review the current observational and theoretical status of these “small-scale controversies.” Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years.
Rescue of homeostatic regulation of striatal excitability and locomotor activity in a mouse model of Huntington’s disease
Authors: Cao Yumei , Bartolomé-Martín David , Rotem Naama , Rozas Carlos , Dellal Shlomo S. , Chacon Marcelo A. , Kadriu Bashkim , Gulinello Maria , Khodakhah Kamran , Faber Donald S.
Published: February 2015

Significance

Neurons typically regulate their intrinsic excitability to prevent excessive excitation and to gate information transfer. This paper describes an activity-dependent decrease in intrinsic excitability following brief bursts of nerve impulses. This homeostatic mechanism, due to the recruitment, or sensitization, of voltage-gated potassium channels, the KCNQ2/3 channels, is reduced in striatal neurons of two transgenic mouse models of Huntington’s disease at an age when these neurons are hyperactive and motor symptoms begin to appear. Pharmacological activation of these channels restores homeostasis in transgenic neurons, in vitro, and reduces motor impairment in behaving mice, consistent with the hypothesis that hyperactivity enables establishment of dysfunctional neural circuits and that KCNQ channels could serve as therapeutic targets for the treatment of HD.