bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrathin lightweight plate-type acoustic metamaterials with positive lumped coupling resonant
Authors: Ma Fuyin , Huang Meng , Wu Jiu Hui
Published: January 2017

The experimental realization and theoretical understanding of a two-dimensional multiple cells lumped ultrathin lightweight plate-type acoustic metamaterials structures have been presented, wherein broadband excellent sound attenuation ability at low frequencies is realized by employing a lumped element coupling resonant effect. The basic unit cell of the metamaterials consists of an ultrathin stiff nylon plate clamped by two elastic ethylene-vinyl acetate copolymer or acrylonitrile butadiene styrene frames. The strong sound attenuation (up to nearly 99%) at low frequencies is experimentally revealed by the precisely designed metamaterials, for which the physical mechanism of the sound attenuation could be explicitly understood using the finite element simulations. As to the designed samples, the lumped effect from the frame compliance leads to a coupling flexural resonance at designable low frequencies. As a result, the whole composite structure become strongly anti-resonant with the incident sound waves, followed by a higher sound attenuation, i.e., the lumped resonant effect has been effectively reversed to be positive from negative for sound attenuation, and the acoustic metamaterial design could be extended to the lumped element containing multiple cells, rather than confined to a single cell.
Kinetic modeling of Langmuir probe characteristics in a laboratory plasma near a conducting body
Authors: Rehman Saeed ur , Fisher Lisa E. , Lynch Kristina A. , Marchand Richard
Published: January 2017

Results are presented from kinetic modeling of Langmuir probe characteristics measured in the vicinity of a conducting sphere, in a well controlled laboratory plasma. In the experiment, the interaction of a drifting argon plasma with a conducting spherical sphere is studied using two cylindrical Langmuir probes located upstream and downstream of the sphere. Plasma parameters upstream of the sphere are determined by fitting an experimentally measured characteristic with the one obtained from simulations. Using the same upstream plasma parameters as input in simulations, the characteristic computed in the wake of the sphere is compared with the measured one. In addition to validating our simulation model for this type of experiment, the comparison serves to illustrate the importance of effects often neglected in the interpretation of Langmuir probe measurements, such as plasma with gradients and Earth magnetic field.
Effect of electric field on carrier escape mechanisms in quantum dot intermediate band solar cells
Authors: Dai Yushuai , Polly Stephen J. , Hellstroem Staffan , Slocum Michael A. , Bittner Zachary S. , Forbes David V. , Roland Paul J. , Ellingson Randy J. , Hubbard Seth M.
Published: January 2017

Carrier escape and recombination from quantum dot (QD) states reduce the probability of two-step photon absorption (TSPA) by decreasing the available carrier population in the intermediate band (IB). In order to optimize the second photon absorption for future designs of quantum dot embedded intermediate band solar cells, the presented study combined the results of simulations and experiments to quantify the effect of electric field on the barrier height and the carrier escape from the QDs in InAs/GaAs quantum dot solar cells with five-layer QD superlattices. The electric field dependent effective barrier heights for ground state electrons were calculated using eight band k·p theory at short circuit conditions. With an increase in electric field surrounding the QDs from 5 kV/cm to 50 kV/cm, the effective barrier height of the ground state electrons was reduced from 147 meV to 136 meV, respectively. Thus, the increasing electric field not only exponentially enhances the ground state electron tunneling rate (effectively zero at 5 kV/cm and 7.9 × 106 s−1 at 50 kV/cm) but also doubles the thermal escape rate (2.2 × 1011 s−1 at 5 kV/cm and 4.1 × 1011 s−1 at 50 kV/cm). Temperature-dependent external quantum efficiency measurements were performed to verify that the increasing electric field decreases the effective barrier height. Additionally, the electric field dependent radiative lifetimes of the ground state were characterized with time-resolved photoluminescence experiments. This study showed that the increasing electric field extended the radiative recombination lifetime in the ground state of the QDs as a consequence of the reduced wave-function overlap between the electrons and holes. The balance of carrier escape and recombination determines the probability of TSPA.
Theoretical analysis of modulation doping effects on intersubband transition properties of semipolar AlGaN/GaN quantum well
Authors: Fu Houqiang , Chen Hong , Huang Xuanqi , Lu Zhijian , Zhao Yuji
Published: January 2017

The effects of modulation doping on the intersubband transition (ISBT) properties of semipolar AlGaN/GaN quantum well (QW) are investigated theoretically using QW doping, barrier doping, and barrier δ-doping schemes at 150 K. Important ISBT parameters such as intersubband transition energies, dipole matrix elements, and absorption spectra are calculated for QW structures on both semipolar (202¯1) (i.e., with weak polarization) and (101¯3) (i.e., with strong polarization) planes. For (202¯1) QW with weak polarization, it is found that high doping concentrations can cause a significant band bowing to the QW structures, which reduce the absorption coefficients and wavelengths. This band bowing effect will become stronger when doping layers are closer to the QW. For (101¯3) QW with a strong polarization, however, a weak band bowing effect is observed due to the large polarization and large band tilting of (101¯3) QW. The study shows that modulation doping is a promising method to modify the ISBT properties of semipolar AlGaN/GaN QW to achieve an improved performance such as longer ISBT wavelength (e.g., >20 μm).
Normal-relaxor ferroelectric modulation of a-site complex perovskite ferroelectric (K1/2Bi1/2)TiO3 by post-annealing
Authors: Guo Jinjian , Zhu Mankang , Li Ling , Qing Tianhe , Wang Cong , Liu Liying , Zheng Mupeng , Hou Yudong
Published: January 2017

In this work, the A-site complex perovskite K1/2Bi1/2TiO3 (KBT) was first found to demonstrate a normal-relaxor ferroelectric modulation by the annealing temperature. KBT ceramics were synthesized by the solid-state reaction method and subjected to a post-annealing at 800 °C or 1000 °C, respectively. It is found that the post-annealing at 800 °C switches KBT to a relaxor ferroelectric while the post-annealing at 1000 °C makes KBT develop into a normal ferroelectric. Besides, the sample annealed at 800 °C presented an inflection at 155 °C to decrease the Pr due to the enhanced relaxor behavior. Moreover, annealing at 1000 °C could promote the growth of the domains and the local ordering of A-site cations. It is believed that the modulation of KBT between the normal ferroelectric and relaxor was attributed to the domain size and the local ordering of A-site cations.
Ultrasound directed self-assembly of three-dimensional user-specified patterns of particles in a fluid medium
Authors: Prisbrey M. , Greenhall J. , Guevara Vasquez F. , Raeymaekers B.
Published: January 2017

We use ultrasound directed self-assembly to organize particles dispersed in a fluid medium into a three-dimensional (3D) user-specified pattern. The technique employs ultrasound transducers that line the boundary of a fluid reservoir to create a standing ultrasound wave field. The acoustic radiation force associated with the wave field drives particles dispersed in the fluid medium into organized patterns, assuming that the particles are much smaller than the wavelength and do not interact with each other. We have theoretically derived a direct solution method to calculate the ultrasound transducer operating parameters that are required to assemble a user-specified 3D pattern of particles in a fluid reservoir of arbitrary geometry. We formulate the direct solution method as a constrained optimization problem that reduces to eigendecomposition. We experimentally validate the solution method by assembling 3D patterns of carbon nanoparticles in a water reservoir and observe good quantitative agreement between theory and experiment. Additionally, we demonstrate the versatility of the solution method by simulating ultrasound directed self-assembly of complex 3D patterns of particles. The method works for any 3D simple, closed fluid reservoir geometry in combination with any arrangement of ultrasound transducers and enables employing ultrasound directed self-assembly in a myriad of engineering applications, including biomedical and materials fabrication processes.
Theoretical modeling of electrical resistivity and Seebeck coefficient of bismuth nanowires by considering carrier mean free path limitation
Authors: Murata Masayuki , Yamamoto Atsushi , Hasegawa Yasuhiro , Komine Takashi , Endo Akira
Published: January 2017

In this study, the electrical resistivity and Seebeck coefficient of bismuth nanowires, several hundred nanometers in diameter, are calculated using the Boltzmann equation in the relaxation time approximation. The three-dimensional density of states and properties of single-crystalline bulk bismuth, such as carrier density, effective mass, and mobility, are used in the calculation without considering the quantum size effect. The relaxation times of the electrons and holes are calculated using Matthiessen's rule considering the carrier collisions at the wire boundary. The temperature, crystal orientation, and diameter dependence of the electrical resistivity and Seebeck coefficient are investigated. The calculation demonstrates that the electrical resistivity increases gradually with decreasing wire diameter, and the temperature coefficient of the electrical resistivity varies from positive to negative at low temperatures for thin wires with diameters less than approximately 500 nm. The diameter dependence of the electrical resistivity varies with the crystal orientation; the increase along the bisectrix axis is larger than that along the binary and trigonal axes. The temperature dependence of the Seebeck coefficient also strongly depends on the crystal orientation. The absolute value of the negative Seebeck coefficient along the bisectrix axis rapidly decreases with decreasing diameter and even changes sign from negative to positive at low temperatures despite the charge neutrality condition, while the Seebeck coefficients along the binary and trigonal axes do not differ significantly from those of single-crystalline bulk bismuth. We conclude that the thermoelectric properties of bismuth nanowires strongly depend not only on the wire diameter but also on the crystal orientation.
On the generality of Michaelian kinetics
Authors: Barel Itay , Brown Frank L. H.
Published: January 2017

The reversible Michaelis-Menten equation is shown to follow from a very broad class of steady-state kinetic models involving enzymes that adopt a unique free (i.e., not complexed to substrate/product) state in solution. In the case of enzymes with multiple free states/conformations (e.g., fluctuating, hysteretic, or co-operative monomeric enzymes), Michaelian behavior is still assured if the relative steady-state populations of free enzyme states are independent of substrate and product concentration. Prior models for Michaelian behavior in multiple conformer enzymes are shown to be special cases of this single condition.
A model of anomalous absorption of laser light on ion acoustic turbulence
Authors: Bychenkov V. Yu. , Rozmus W.
Published: January 2017

Instability of ion acoustic waves due to the return current driven by an electron heat flux is identified as a source of the ion-acoustic turbulence (IAT) in hot, inertial confinement fusion plasmas. Two mechanisms of anomalous absorption are studied, first due to enhanced electron collisionality on ion-acoustic fluctuations and second due to electromagnetic wave conversion into Langmuir waves at the critical density, which is enabled by IAT. An effective absorption coefficient is derived combining the two mechanisms with a stationary IAT spectrum derived from the theory of weak plasma turbulence. Estimates of the return current instability threshold and anomalous absorption are presented for hohlraum plasma in indirect drive fusion experiments. Anomalous absorption is anisotropic due to the angular anisotropy of the IAT spectrum and, according to our theory, can be remarkably effective near the critical density in high Z plasmas. Possible experiments which could identify IAT, and anomalous absorption mechanisms are discussed.
Patterns of synchrony for feed-forward and auto-regulation feed-forward neural networks
Authors: Aguiar Manuela A. D. , Dias Ana Paula S. , Ferreira Flora
Published: January 2017

We consider feed-forward and auto-regulation feed-forward neural (weighted) coupled cell networks. In feed-forward neural networks, cells are arranged in layers such that the cells of the first layer have empty input set and cells of each other layer receive only inputs from cells of the previous layer. An auto-regulation feed-forward neural coupled cell network is a feed-forward neural network where additionally some cells of the first layer have auto-regulation, that is, they have a self-loop. Given a network structure, a robust pattern of synchrony is a space defined in terms of equalities of cell coordinates that is flow-invariant for any coupled cell system (with additive input structure) associated with the network. In this paper, we describe the robust patterns of synchrony for feed-forward and auto-regulation feed-forward neural networks. Regarding feed-forward neural networks, we show that only cells in the same layer can synchronize. On the other hand, in the presence of auto-regulation, we prove that cells in different layers can synchronize in a robust way and we give a characterization of the possible patterns of synchrony that can occur for auto-regulation feed-forward neural networks.
A multi-technique study of CO2 adsorption on Fe3O4 magnetite
Authors: Pavelec Jiri , Hulva Jan , Halwidl Daniel , Bliem Roland , Gamba Oscar , Jakub Zdenek , Brunbauer Florian , Schmid Michael , Diebold Ulrike , Parkinson Gareth S.
Published: January 2017

The adsorption of CO2 on the Fe3O4(001)-(2 × 2)R45° surface was studied experimentally using temperature programmed desorption (TPD), photoelectron spectroscopies (UPS and XPS), and scanning tunneling microscopy. CO2 binds most strongly at defects related to Fe2+, including antiphase domain boundaries in the surface reconstruction and above incorporated Fe interstitials. At higher coverages,CO2 adsorbs at fivefold-coordinated Fe3+ sites with a binding energy of 0.4 eV. Above a coverage of 4 molecules per (2 × 2)R45° unit cell, further adsorption results in a compression of the first monolayer up to a density approaching that of a CO2 ice layer. Surprisingly, desorption of the second monolayer occurs at a lower temperature (≈84 K) than CO2 multilayers (≈88 K), suggestive of a metastable phase or diffusion-limited island growth. The paper also discusses design considerations for a vacuum system optimized to study the surface chemistry of metal oxide single crystals, including the calibration and characterisation of a molecular beam source for quantitative TPD measurements.
Phononic dissipation during “hot” adatom motion: A QM/Me study of O2 dissociation at Pd surfaces
Authors: Bukas Vanessa J. , Reuter Karsten
Published: January 2017

We augment ab initio molecular dynamics simulations with a quantitative account of phononic dissipation to study the non-equilibrium aftermath of the exothermic oxygen dissociation at low-index (111), (100), and (110) Pd surfaces. Comparing the hyperthermal diffusion arising from a non-instantaneous dissipation of the released chemical energy, we find a striking difference in the resulting “hot” adatom lifetime that is not overall reflected in experimentally recorded product end distances. We rationalize this finding through a detailed mode-specific phonon analysis and identify the dominant dissipation channels as qualitatively different groups of localized surface modes that ultimately lead to intrinsically different rates of dissipation to the Pd bulk. The thus obtained first-principles perspective on non-equilibrium adsorbate-phonon dynamics thereby underscores the sensitive dependence on details of the phononic fine structure, while questioning prevalent assumptions about energy sinks made in commonly used model bath Hamiltonians.
First-principles study of tantalum-arsenic binary compounds
Authors: Sun Jifeng , Singh David J.
Published: January 2017

The electronic properties and phase stability of binary tantalum arsenides are investigated using first-principles calculations. We find strong covalent bonding between Ta and As in TaAs2. In the lower As content compounds, the Ta is less covalent and donates charge to the As backbone. The covalency of other compounds becomes smaller with the increase of Ta composition. Compounds on the convex hull are TaAs2, TaAs, Ta5As4, and Ta3As, while Ta2As is slightly above the hull. Trends in the electronic and other properties are discussed. We identify the space group of TaAs2 to be centrosymmetric C2/m and find semimetallic behavior in TaAs and TaAs2. The other binary compounds are metallic systems with finite density of states at the Fermi level. The plasma energies show moderate conductivity anisotropy in Ta5As4 and Ta2As, which are also the most conductive compounds among the binary phases.
Accelerated onset of cellular breakdown at increased solidification speed after laser melting of indium in silicon
Authors: Warrender Jeffrey M. , Hudspeth Quentin , Chow Philippe K.
Published: January 2017

We report on the incidence of cellular breakdown in silicon wafers implanted with indium and pulsed laser melted at varying laser fluence. We predict from heat flow calculations that as laser fluence is decreased, (a) the melt depth decreases, (b) the solidification velocity increases, and (c) the solidification front should be more stable with respect to cellular breakdown (based on the binary alloy solidification theory), which should result in observed incidence of cellular breakdown at a relatively shallower depth below the surface. However, secondary ion mass spectrometry (SIMS) data show that cellular breakdown at lower fluence is observed deeper, indicating that the interface became unstable earlier in its solidification. The SIMS data show significant In evaporation, with greater evaporation occurring as fluence increases. Calculations show that surface evaporation can reduce the bulk liquid concentration during solidification, reducing the degree of instability. The longer melt durations after irradiation at higher fluence give more time for evaporation, which may result in a relatively larger delay in the onset of breakdown compared to lower fluence by suppressing the bulk liquid concentration and suppressing the growth of unstable perturbation. Under certain conditions, this effect could dominate over the role of reducing the interface speed, which would tend to accelerate amplification of a perturbation, which leads to breakdown. Calculations qualitatively support this interpretation.
Electronic properties of ionic surfaces: A systematic theoretical investigation of alkali halides
Authors: Wu Feng , Wang Huihui , Shen Yu-Chen , Jiang Hong
Published: January 2017

Bulk and surface electronic band structure properties of alkali halides are investigated by using density-functional theory (DFT) in generalized gradient approximation, the GW many-body quasi-particle theory and a quantitative ionic model that combines the atomic ionization potentials and electron affinities with all other parameters determined from first-principles DFT calculations. It is confirmed that the GW approach can predict the band gaps of all alkali halides in good agreement with the experiment with a mean absolute error of about 0.3 eV compared to the available experimental data. The ionic model can well reproduce the trends in the experimental band gaps and ionization potentials, and in some cases can even lead to a quantitative agreement with experiment, but it has severe limitations for the systems containing small ions like Li+ for which a reliable estimation of the polarization contribution is difficult to attain. The latter finding can provide clues for the development of new theoretical approaches to ionic systems by combining the ionic model with more sophisticated consideration of the ionic polarization.
Influence of Dy3+ and Tb3+ doping on 13C dynamic nuclear polarization
Authors: Niedbalski Peter , Parish Christopher , Kiswandhi Andhika , Fidelino Leila , Khemtong Chalermchai , Hayati Zahra , Song Likai , Martins André , Sherry A. Dean , Lumata Lloyd
Published: January 2017

Dynamic nuclear polarization (DNP) is a technique that uses a microwave-driven transfer of high spin alignment from electrons to nuclear spins. This is most effective at low temperature and high magnetic field, and with the invention of the dissolution method, the amplified nuclear magnetic resonance (NMR) signals in the frozen state in DNP can be harnessed in the liquid-state at physiologically acceptable temperature for in vitro and in vivo metabolic studies. A current optimization practice in dissolution DNP is to dope the sample with trace amounts of lanthanides such as Gd3+ or Ho3+, which further improves the polarization. While Gd3+ and Ho3+ have been optimized for use in dissolution DNP, other lanthanides have not been exhaustively studied for use in C13 DNP applications. In this work, two additional lanthanides with relatively high magnetic moments, Dy3+ and Tb3+, were extensively optimized and tested as doping additives for C13 DNP at 3.35 T and 1.2 K. We have found that both of these lanthanides are also beneficial additives, to a varying degree, for C13 DNP. The optimal concentrations of Dy3+ (1.5 mM) and Tb3+ (0.25 mM) for C13 DNP were found to be less than that of Gd3+ (2 mM). W-band electron paramagnetic resonance shows that these enhancements due to Dy3+ and Tb3+ doping are accompanied by shortening of electron T1 of trityl OX063 free radical. Furthermore, when dissolution was employed, Tb3+-doped samples were found to have similar liquid-state C13 NMR signal enhancements compared to samples doped with Gd3+, and both Tb3+ and Dy3+ had a negligible liquid-state nuclear T1 shortening effect which contrasts with the significant reduction in T1 when using Gd3+. Our results show that Dy3+ doping and Tb3+ doping have a beneficial impact on C13 DNP both in the solid and liquid states, and that Tb3+ in particular could be used as a potential alternative to Gd3+ in C13 dissolution DNP experiments.
Temperature dependent tunneling conductance of single molecule junctions
Authors: Kamenetska M. , Widawsky J. R. , Dell’Angela M. , Frei M. , Venkataraman Latha
Published: January 2017

We perform temperature dependent conductance measurements on sub-nanometer sized single molecules bound to gold electrodes using a scanning tunneling microscope-based break junction technique in Ultra-High Vacuum (UHV). We find a threefold increase in the conductance of amine-terminated conjugated molecules when the temperature increases from 4 K to 300 K in UHV. Furthermore, the conductance measured at 300 K in UHV is consistent with solution-based measurements under ambient conditions where the transport mechanism corresponds to off-resonant electron tunneling across the molecule. Our measurements indicate that at 300 K, conductance is largely independent of pressure or solvent around the junction. In addition, our data unambiguously show that temperature can affect the tunneling conductance of single molecule-metal junctions. We show that the structure of the metal electrodes that form in these junctions varies systematically with temperature, and hypothesize that this changing structure of the interface alters electron tunneling probability and propose a mechanism to explain our findings.
Scattering cross sections of the particles in the partially ionized dense nonideal plasmas
Authors: Shalenov E. O. , Dzhumagulova K. N. , Ramazanov T. S.
Published: January 2017

The electron-atom interaction taking account of dynamic screening is considered in the dense partially ionized plasmas. The phase-function method is used. It is shown that the phase shifts and differential cross sections of the electron scattering on the helium and argon atoms, calculated taking account of dynamic screening, are bigger than those obtained on the basis of the static interaction potential. This can have an influence on macroscopic properties such as transport coefficients.
Terahertz radiation generation by propagation of circularly polarized laser pulses in axially magnetized plasma
Authors: Sharma Pooja , Wadhwani Navina , Jha Pallavi
Published: January 2017

An analytical study is developed for the generation of terahertz radiation by propagation of a circularly polarized laser pulse in axially magnetized plasma, in the mildly relativistic regime. A perturbative technique is used to obtain the electric and magnetic wakefields within and behind the laser pulse. The emission of terahertz radiation via generated transverse wakefields is analyzed by determining mutually perpendicular electric and magnetic wakefields oscillating at the plasma frequency and having the same amplitude. It is shown that the generated transverse electric and magnetic wakefields constitute two off-axis, linearly polarized terahertz electromagnetic fields propagating along the laser pulse direction.
Secondary fast reconnecting instability in the sawtooth crash
Authors: Del Sarto D. , Ottaviani M.
Published: January 2017

In this work, we consider magnetic reconnection in thin current sheets with both resistive and electron inertia effects. When the current sheet is produced by a primary instability of the internal kink type, the analysis of secondary instabilities indicates that reconnection proceeds on a time scale much shorter than the primary instability characteristic time. In the case of a sawtooth crash, non-collisional physics becomes important above a value of the Lundquist number, which scales like S∼(R/de)12/5, in terms of the tokamak major radius R and of the electron skin depth de. This value is commonly achieved in present day devices. As collisionality is further reduced, the characteristic rate increases, approaching Alfvénic values when the primary instability approaches the collisionless regime.
Accelerating gradient improvement from hole-boring to light-sail stage using shape-tailored laser front
Authors: Wang W. P. , Shen B. F. , Xu Z. Z.
Published: January 2017

The accelerating gradient of a proton beam is a crucial factor for the stable radiation pressure acceleration, because quickly accelerating protons into the relativistic region may reduce the multidimensional instability grow to a certain extent. In this letter, a shape-tailored laser is designed to accelerate the protons in a controllable high accelerating gradient in theory. Finally, a proton beam in the gigaelectronvolt range with an energy spread of ∼2.4% is obtained in one-dimensional particle-in-cell simulations. With the future development of the high-intense laser, the ability to accelerate a high energy proton beam using a shape-tailored laser will be important for realistic proton applications, such as fast ignition for inertial confinement fusion, medical therapy, and proton imaging.
First principles calculation of the elasticity of ice VIII and X
Authors: Tsuchiya Jun , Tsuchiya Taku
Published: January 2017

The elastic constants of ice VIII and ice X phases under pressure have been determined at static 0 K conditions using first principles calculation. A step-like increase of the elastic constants of ice VIII phase occurred at 100-110 GPa due to hydrogen bond symmetrization. The elastic constants, and the pressure dependencies of these constants, of ice X and VIII are completely distinct. Due to these differences, these two phases can be distinguished on the basis of the elastic behavior. Conversely, the experimental elastic constant of C11 of ice VII gradually changes from an ice VIII like asymmetric hydrogen bond to a symmetric bond character within a wide pressure range. This finding suggests that the transition from ice VII to ice X starts around 30 GPa and completes at 110 GPa.
An analysis of beamed wireless power transfer in the Fresnel zone using a dynamic, metasurface aperture
Authors: Smith David R. , Gowda Vinay R. , Yurduseven Okan , Larouche Stéphane , Lipworth Guy , Urzhumov Yaroslav , Reynolds Matthew S.
Published: January 2017

Wireless power transfer (WPT) has been an active topic of research, with a number of WPT schemes implemented in the near-field (coupling) and far-field (radiation) regimes. Here, we consider a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel region. In this context, the dynamic aperture resembles a reconfigurable lens capable of focusing power to a well-defined spot, whose dimension can be related to a point spread function. The necessary amplitude and phase distribution of the field imposed over the aperture can be determined in a holographic sense, by interfering a hypothetical point source located at the receiver location with a plane wave at the aperture location. While conventional technologies, such as phased arrays, can achieve the required control over phase and amplitude, they typically do so at a high cost; alternatively, metasurface apertures can achieve dynamic focusing with potentially lower cost. We present an initial tradeoff analysis of the Fresnel region WPT concept assuming a metasurface aperture, relating the key parameters such as spot size, aperture size, wavelength, and focal distance, as well as reviewing system considerations such as the availability of sources and power transfer efficiency. We find that approximate design formulas derived from the Gaussian optics approximation provide useful estimates of system performance, including transfer efficiency and coverage volume. The accuracy of these formulas is confirmed through numerical studies.
Resist-free fabricated carbon nanotube field-effect transistors with high-quality atomic-layer-deposited platinum contacts
Authors: Mackus Adriaan J. M. , Thissen Nick F. W. , Mulders Johannes J. L. , Trompenaars Petrus H. F. , Chen Zhihong , Kessels Wilhelmus M. M. , Bol Ageeth A.
Published: January 2017

Carbon nanotubes are considered as alternative channel material for future transistors, but several challenges exist for reliable fabrication of these devices. In this work, carbon nanotube field-effect transistors (CNTFETs) were fabricated by patterning of Pt contacts using a combination of electron beam induced deposition and area-selective atomic layer deposition (ALD). This bottom-up technique eliminates compatibility issues caused by the use of resist films and lift-off steps. Electrical characterization of a set of 33 CNTFETs reveals that using this direct-write ALD process for Pt patterning yields improved contacts as compared to evaporated Pt, most likely due to improved wettability of the contacts on the carbon nanotube. Moreover, these CNTFETs can be characterized as unipolar p-type transistors with a very low off-state current.
Impact of N-plasma and Ga-irradiation on MoS2 layer in molecular beam epitaxy
Authors: Mishra Pawan , Tangi Malleswararao , Ng Tien Khee , Hedhili Mohamed Nejib , Anjum Dalaver H. , Alias Mohd Sharizal , Tseng Chien-Chih , Li Lain-Jong , Ooi Boon S.
Published: January 2017

Recent interest in two-dimensional materials has resulted in ultra-thin devices based on the transfer of transition metal dichalcogenides (TMDs) onto other TMDs or III-nitride materials. In this investigation, we realized p-type monolayer (ML) MoS2, and intrinsic GaN/p-type MoS2 heterojunction by the GaN overgrowth on ML-MoS2/c-sapphire using the plasma-assisted molecular beam epitaxy. A systematic nitrogen plasma (N2*) and gallium (Ga) irradiation studies are employed to understand the individual effect on the doping levels of ML-MoS2, which is evaluated by micro-Raman and high-resolution X-Ray photoelectron spectroscopy (HRXPS) measurements. With both methods, p-type doping was attained and was verified by softening and strengthening of characteristics phonon modes E2g1 and A1g from Raman spectroscopy. With adequate N2*-irradiation (3 min), respective shift of 1.79 cm−1 for A1g and 1.11 cm−1 for E2g1 are obtained while short term Ga-irradiated (30 s) exhibits the shift of 1.51 cm−1 for A1g and 0.93 cm−1 for E2g1. Moreover, in HRXPS valence band spectra analysis, the position of valence band maximum measured with respect to the Fermi level is determined to evaluate the type of doping levels in ML-MoS2. The observed values of valance band maximum are reduced to 0.5, and 0.2 eV from the intrinsic value of ≈1.0 eV for N2*- and Ga-irradiated MoS2 layers, which confirms the p-type doping of ML-MoS2. Further p-type doping is verified by Hall effect measurements. Thus, by GaN overgrowth, we attained the building block of intrinsic GaN/p-type MoS2 heterojunction. Through this work, we have provided the platform for the realization of dissimilar heterostructure via monolithic approach.
Communication: On the first ionization threshold of the C2H radical
Authors: Gans B. , Garcia G. A. , Holzmeier F. , Krüger J. , Röder A. , Lopes A. , Fittschen C. , Loison J.-C. , Alcaraz C.
Published: January 2017

The slow photoelectron spectrum of the ethynyl radical has been recorded for the first time by using the DESIRS beamline of the SOLEIL synchrotron facility. Ethynyl was generated using a microwave discharge flow tube. The observation of the X+Π3←XΣ+2 transition allowed the first direct measurement of the adiabatic ionization threshold of this radical (EI = 11.641(5) eV). The experimental results are supported by ab initio calculations. Our preliminary investigation of the cationic ground state potential energy surfaces predicts a non-negligible Renner-Teller effect which has not been discussed previously.
Spin-orbit coupling mediated tunable electron heat capacity of quantum wells
Authors: Sengupta Parijat , Bellotti Enrico
Published: January 2017

The heat capacity of conduction electrons obtained from the Sommerfeld expansion is shown to be tunable via the Rashba and Dresselhaus spin-orbit coupling parameters. Using AlInSb/InSb/AlInSb as a representative heterostructure with alterable well and asymmetric barrier regions, the heat capacity is higher for the spin-down electrons and suffers a reduction for wider wells. A further lowering is obtained through the application of a uniaxial strain. Finally, we suggest a method to determine the spin lifetimes for spin relaxing via the D'yakonov-Perel' mechanism from experimental estimates of thermodynamic potentials such as the Helmholtz free energy and the heat capacity.
Exceptional solutions to the Painlevé VI equation
Authors: Eremenko Alexandre , Gabrielov Andrei , Hinkkanen Aimo
Published: January 2017

We find all solutions of the Painlevé VI equations with the property that they have no zeros, no poles, no 1-points, and no fixed points.
Dynamic equivalent modeling of wind farm considering the uncertainty of wind power prediction and a case study
Authors: Li Longyuan , Teng Yufei , Wang Xiaoru
Published: January 2017

Currently, the clustering of dynamic multi-machine equivalent modeling of wind farm (WF) is based on the deterministic data. To serve the early warning calculation of power system dispatch better, a dynamic multi-machine equivalent modeling method of WF considering the uncertainty of wind power prediction is first proposed in this paper. First, the probability density functions of wind speed and wind power prediction errors are described and the multi-scenario sampling method is adopted to reflect the uncertainty. Second, the probabilistic clustering method is used to obtain the probability of each wind turbine generator (WTG) belonging to each cluster. The cluster with the biggest probability is selected as the clustering result of the WTGs in the spirit of the Bayesian classification. Third, the WTGs and collector system are simplified into a single-machine equivalent model in each cluster. Finally, the WF output response curve is compared among the detailed WF models, the conventional and the proposed equivalent models in the accurate and inaccurate scenarios of wind power prediction, respectively. The results show that the proposed equivalent method considers the uncertainty in reality and has a better accuracy in the inaccurate scenario of wind power prediction.
Magnetic tunnel junctions using perpendicularly magnetized synthetic antiferromagnetic reference layer for wide-dynamic-range magnetic sensors
Authors: Nakano T. , Oogane M. , Furuichi T. , Ando Y.
Published: January 2017

We developed CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with a perpendicularly magnetized synthetic antiferromagnetic (p-SAF) reference layer for magnetic sensor applications. The MTJs exhibited linear tunnel magnetoresistance curves to out-of-plane applied magnetic fields with dynamic ranges more than ±2.5 kOe, which are wider than those in CoFeB/MgO/CoFeB-MTJs reported to date. The performance metrics of MTJ sensors, i.e., sensitivity and nonlinearity, depend significantly on the anisotropy field of the free layer. We explained the dependences by a simple model based on the Stoner-Wohlfarth and Slonczewski models, which gives us a guideline to design the sensor performance metrics. These findings demonstrated that MTJs with a p-SAF reference layer are promising candidates for wide-dynamic-range magnetic sensors.
Laser ablation impulse generated by irradiating aluminum target with nanosecond laser pulses at normal and oblique incidence
Authors: Wang Bin
Published: January 2017

Impulse generation by irradiating aluminum targets with repetitive laser pulses at normal and oblique incidence was investigated using impulse measurements with a torsion pendulum at various incidence angles under different laser beam fluence conditions. The fluence varied from 5.8–20.0 J/cm2 for normal incidence. For oblique incidence, momentum coupling is sensitive to the incident angle at fluences of 6.3 J/cm2 and 9.2 J/cm2 because of target surface reflectivity changes and plume shielding effects. At fluence of 19.3 J/cm2, the fluence on the target surface becomes dominant for impulse generation compared with the angle of incidence effect in a large angular range. Beam fluence optimization for momentum coupling at oblique incidence is discussed based on the impulse characteristics obtained.
Energy harvesting via wrinkling instabilities
Authors: Haji Hosseinloo Ashkan , Turitsyn Konstantin
Published: January 2017

Conventional vibratory energy harvesters, working based on linear resonance, suffer from narrow bandwidth and are very inefficient at small scale for low frequency harvesting. Here, to improve the harvesting effectiveness, we propose to exploit surface instability or in general instability in layered composites where intriguing morphological patterns with large strain are formed under compressive loads. The induced large strains, which are independent of the excitation frequency, could be exploited to give rise to large strains in an attached piezoelectric layer to generate charge and, hence, energy. In this study, we particularly focus on wrinkling of a stiff interfacial layer embedded within a soft matrix. We derive the governing dynamical equation of thin piezoelectric patches attached at the peaks and troughs of the wrinkles. Results show that wrinkling could help to increase the harvested power by more than an order of magnitude.
Study of the effects of the perpendicular velocity gradient on a Doppler backscattering system using a 2D full wave code
Authors: Wang M. Y. , Zhou C. , Liu A. D. , Zhang X. H. , Hu J. Q. , Li H. , Lan T. , Xie J. L. , Ding W. X. , Liu W. D. , Yu C. X.
Published: January 2017

Doppler backscattering is a powerful diagnostic technique that is used to perform turbulence measurements in magnetic confinement devices. The effects of the perpendicular velocity distribution on a Doppler backscattering system are studied using a 2D full wave code, in which the finite-difference time-domain method is used to solve Maxwell's equations. A constant velocity and several different velocity gradients are considered, along with a wide range of density fluctuation levels. The numerical results show that the Doppler backscattering mainly occurs around the cut-off layer, and that it has a linear response to turbulence when the fluctuation level is low. However, at higher density fluctuation levels, nonlinear effects become important, and the influence of the area outside the cut-off layer becomes significant. The velocity gradient causes the backscattering spectrum to become non-Gaussian and asymmetrical; this effect has also been noticed in experiments in the Experimental Advanced Superconducting Tokamak.
Plasmonic absorbers with optical cavity for the enhancement of photothermal/opto-calorimetric infrared spectroscopy
Authors: Lee Dongkyu , Chae Inseok , Kwon Ohwon , Lee Kang-Ho , Kim Changwon , Kim Seonghwan , Thundat Thomas
Published: January 2017

Plasmonic absorbers with optical cavity are fabricated using deposition of thin gold films on both sides of nanoporous anodic aluminum oxide (AAO) microcantilevers. Photothermal/opto-calorimetric responses of the microcantilevers are investigated with respect to various pore sizes and gold coating thicknesses. Photothermal/opto-calorimetric response of the AAO cantilever is significantly amplified when the thickness of the gold layer is at 40 nm due to scattering and trapping of infrared (IR) radiation in the gold nanomesh/AAO nanochannels/gold layer structure. Unlike previous photothermal IR spectroscopy of adsorbed molecules with a bimetallic AAO cantilever, the reversed IR spectra are obtained due to significantly amplified baseline photothermal signal and IR absorption of free molecules. Molecular detection sensitivity is enhanced by an order of magnitude compared with the previous photothermal IR spectroscopy of adsorbed molecules on a bimetallic AAO cantilever. The acetone vapor molecules are selectively recognized using the reversed IR spectra.
Evaluation of parameter sensitivities for flux-switching permanent magnet machines based on simplified equivalent magnetic circuit
Authors: Zhang Gan , Hua Wei , Cheng Ming
Published: January 2017

Most of the published papers regarding the design of flux-switching permanent magnet machines are focused on the analysis and optimization of electromagnetic or mechanical behaviors, however, the evaluate of the parameter sensitivities have not been covered, which contrarily, is the main contribution of this paper. Based on the finite element analysis (FEA) and simplified equivalent magnetic circuit, the method proposed in this paper enables the influences of parameters on the electromagnetic performances, i.e. the parameter sensitivities, to be given by equations. The FEA results are also validated by experimental measurements.
Research on adiabatic shear failure character of pure copper and aluminum bronze based on empirical electron theory
Authors: Li Jin-quan , Xu Bi-cong , Zhang Yan-hui , Huang Shu-tao , Zhao Xia-
Published: January 2017

The valence electron structure (VES) parameters affecting adiabatic shearing failure under high speed impact load using split Hopkinson pressure bar (SHPB) were studied by empirical electron theory (EET) of solids and molecules. There is a problem of multiple solutions about VES parameters in EET. The statistics values of VES parameters related to adiabatic shearing sensitivity were calculated to substitute for the most probable value among the multiple solutions according to the view that the microstate statistics values can reflect the macro physical quantity. The research shows that the adiabatic shearing sensitivity is growing with the rise of the statistics value of bond energy of the strongest covalent bond, and is decreasing with the rise of the statistics value of the lattice electron number. The statistics value of bond energy of the strongest covalent bond in aluminum bronze (QAl9-4) is larger than that in pure copper, and the statistics value of the lattice electron number in QAl9-4 is smaller than that in pure copper. Therefore, QAl9-4 is prone to adiabatic shearing failure, and the grains were only elongated due to the large deformation for pure copper without any adiabatic shear band (ASB). It is of great significance for the selection and design of material with different adiabatic shearing sensitivity to research the effect of alloy elements on adiabatic shearing sensitivity from the electronic structure perspective.
Mortality, Dispersal, and Habitat Use of Stocked Juvenile Muskellunge in Two Western North Carolina Rivers
Authors: Owensby Dylan P. , Rice James A. , Aday D. Derek
Published: January 2017

The Muskellunge Esox masquinongy is a highly sought-after sport fish that is native to the Tennessee River drainage of western North Carolina. After the extirpation of Muskellunge from North Carolina in the 1950s, the North Carolina Wildlife Resources Commission began a stocking program to re-establish the species and produce viable Muskellunge fisheries in North Carolina. Although stocking efforts have created a Muskellunge fishery in, for example, the French Broad River (where the species was native), there is little evidence of success in North Carolina sections of the New River (where the species was not native). Possible mechanisms inhibiting stocking success are unclear because there is relatively little information available on the juvenile life stage of the Muskellunge, especially in the southern portion of its distribution. We addressed the perceived differences in recruitment between the two fisheries by using telemetry to investigate dispersal, mortality, and habitat use by stocked juvenile Muskellunge. Fifty hatchery-reared, age-0 Muskellunge (282–307 mm TL) were tagged prior to stocking in the New River (fall 2013) and French Broad River (fall 2014). Three months after stocking, known survival of tagged fish was 4% in the New River and 29% in the French Broad River; the survival probability after 3 months was estimated at 9% (range = 4–17%) in the New River and 37% (range = 25–56%) in the French Broad River. Extended survival in the French Broad River was 14% at 252 d poststocking. High dispersal was observed, with maximum individual dispersal of 67.4 km in the New River and 55.5 km in the French Broad River. Habitat suitability analyses indicated that juvenile Muskellunge in the FBR selected shallow nearshore areas with low water velocity, fine substrate, and substantial cover in the form of woody debris and overhanging vegetation. Information on the survival and behavior of stocked Muskellunge can facilitate efforts to successfully manage these fisheries.

Received December 4, 2015; accepted October 3, 2016Published online January 3, 2017