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  • American Institute of Physics (AIP)  (241,953)
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  • 1
    Publication Date: 2017-01-07
    Description: This paper investigates hydrothermal fluid circulation in pre- and syn-tectonic sediments associated with detachments faults. The study area, located in the Err Nappe (SE-Switzerland), preserves a portion of the Adriatic distal margin. Two sites were studied in combining fieldwork, petrography, geochemistry and fluid inclusion analysis: the Piz Val Lunga and Fuorcla Cotschna areas. Both preserve relationships between a spectacularly exposed rift-related extensional detachment fault and its footwall and hangingwall that consist of extensional allochthons and syn- to post-tectonic sediments. These areas register a complex fluid flow history characterized by dolomitization, de-dolomitization, calcite cementation, dolomite and quartz veining and diffuse silicification. Meso- and micro-scale observations allow defining two steps in fluid evolution, which are related to Jurassic rift activity. A first carbonate-rich event occurred before the exhumation of the granitic basement, and this was followed by a second event marked by a change in the fluid towards a silica-dominated chemistry. Homogenization temperatures of fluid inclusions (average Th = 120−130 °C), negative δ18O values and a radiogenic 87Sr/86Sr signatures of carbonate minerals support the hypothesis that both the pre-tectonic rocks constituting the allochthons and the syn-tectonic sediments overlying the detachment fault were crossed by a flux of over-pressured hydrothermal fluids originating from seawater that penetrated into the basement through fault and fracture systems. Field relationships show that this fluid circulation started latest in middle Early Jurassic time, when fault activity migrated from the proximal to the future distal margin. We propose that it evolved chemically as a result of the involvement of the granitic basement forming the footwall of the extensional detachment system. Hydrothermal activity continued until the Middle/Late Jurassic, when tectonic activity shifted outwards leading to the exhumation of mantle rocks. This paper provides an original contribution to better understand the complex evolution of hyperextended continental rift domains and to constrain their thermal regimes. ©2017 Swiss Geological Society
    Print ISSN: 1661-8726
    Electronic ISSN: 1661-8734
    Topics: Geosciences
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  • 2
    Publication Date: 2017-01-10
    Description: The structure of Alpine-type orogenic belts is widely assumed to have been strongly influenced by the inherited structure of the rifted continental margins from which they were formed. The challenge lies in deciphering these influences when orogenic contraction is strong. Contractional deformation in the Kamchia basin (SW Black Sea), caught between the Balkan orogenic belt and the stable Moesian block, has been arrested, preserving the early development of an Alpine-type orogen. We use 3D seismic and well-data to examine the tectonic and stratigraphic structure of this basin. Significant deformation has occurred underwater, through inversion tectonics within the basin itself. However, the basin margin structures have not reactivated. This margin is marked by a low-angle unconformity across which sediment was routed from the platform into the fledgling syn-orogenic basins. Such pathways may explain non-orogen-derived sediment within parts of the ancestral Apennine foredeep, for example. The role of platform margins to focus contractional deformation may have been over-emphasised elsewhere in the Alpine system. Further, the more strongly subsided portions of rifted margins may have accommodated significant contractional deformation through reactivation of basin faults. In the western Alps the complexity of structural juxapositions across thrust sheets in the Brianconnais may reflect these early-orogenic deformations rather than be the product of deformation that happened after tectonic burial. These early deformations are likely to be recorded in early syn-tectonic depositional sequences. ©2017 Swiss Geological Society〈br /〉〈br /〉〈a href="http://doi.org/10.1007/s00015-016-0238-z" target="_blank"〉〈img src="http://bib.telegrafenberg.de/typo3temp/pics/f2f773b55e.png" border="0"〉〈/a〉
    Print ISSN: 1661-8726
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    Topics: Geosciences
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  • 3
    Publication Date: 2016-11-24
    Description: A novel, simple, and readily usable method is proposed for measuring the electrical conductivity and temperature of a plasma. The method is based on the interaction of the test plasma with a pulsed magnetic field. The electric signals induced by the magnetic field in the circuits of two probes (miniature solenoids), one immersed in the test plasma and the other placed outside the plasma, provide data for estimating the plasma parameters. The method was verified experimentally by determining the parameters of the plasma flows generated in the cathode spots high-current pulsed vacuum arcs that were used to form cylindrical shells of bismuth Z-pinch plasma.
    Print ISSN: 1070-664X
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  • 4
    Publication Date: 2016-11-24
    Description: This paper carries out the spatial confinement effect on laser-induced Cu breakdown spectroscopy in a cylindrical cavity via a nanosecond pulsed Q-switch Nd:YAG laser operating at a wavelength of 1064 nm. The temporal evolution of the laser-induced plasma spectroscopy is used to investigate the characteristics of spectral persistence. The atomic spectral persistence in plasma generated from Cu with spatial confinement is experimentally demonstrated, where the results indicate that the diameter of the confinement cavity plays a very important role in the persistence of an excited neutral Cu emission line, while the depth of the confinement cavity is almost independent of Cu (I) line persistence. As the diameter of the confinement cavity increases, the persistence of the Cu (I) line in the plasma grows longer under a certain limit. The likely reason for this phenomenon is that under spatial confinement, the reflected shockwave compresses the plasma and leads to an increase in the plasma temperature and density at a certain delay time, which causes further excitation of atomic population to higher excited levels. Finally, the collision rate between particles in the plasma plume is increased.
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  • 5
    Publication Date: 2016-11-24
    Description: In recent years, lifetime measurements by means of the Time Correlated Single Photon Counting (TCSPC) technique have led to a significant breakthrough in medical and biological fields. Unfortunately, the many advantages of TCSPC-based approaches come along with the major drawback of a relatively long acquisition time. The exploitation of multiple channels in parallel could in principle mitigate this issue, and at the same time it opens the way to a multi-parameter analysis of the optical signals, e.g., as a function of wavelength or spatial coordinates. The TCSPC multichannel solutions proposed so far, though, suffer from a tradeoff between number of channels and performance, and the overall measurement speed has not been increased according to the number of channels, thus reducing the advantages of having a multichannel system. In this paper, we present a novel readout architecture for bi-dimensional, high-density Single Photon Avalanche Diode (SPAD) arrays, specifically designed to maximize the throughput of the whole system and able to guarantee an efficient use of resources. The core of the system is a routing logic that can provide a dynamic connection between a large number of SPAD detectors and a much lower number of high-performance acquisition channels. A key feature of our smart router is its ability to guarantee high efficiency under any operating condition.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 6
    Publication Date: 2016-11-15
    Description: Photoluminescence and optically detected magnetic resonance (ODMR) spectroscopies are used to investigate the formation and role of defects in GaAs/GaN x As 1-x core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates. Gallium vacancies, which act as non-radiative recombination (NRR) centers, are identified by ODMR. It is shown that the defects are formed in bulk regions, i.e., not on the surface, of the GaNAs shell and that their concentration increases with increasing nitrogen content. Temperature dependent photoluminescence experiments reveal, on the other hand, suppressed thermal quenching of the near-band-edge emission with increasing [N]. This leads to the conclusion that the dominant NRR processes in the studied NWs are governed by surface defects, whereas the role of gallium vacancies in the observed thermally activated NRR is minor.
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  • 7
    Publication Date: 2016-11-15
    Description: Metal oxide devices that exhibit resistive switching are leading candidates for non-volatile memory applications due to their potential for fast switching, low-power operation, and high device density. It is widely accepted in many systems that two-state resistive behavior arises from the formation and rupture of conductive filaments spanning the oxide layer. However, means for controlling the filament geometry, which critically influences conduction, have largely been unexamined. Here, we explore the connection between filament geometry and conductance in a model resistive switching system based on the junction of two nickel/nickel oxide core/shell nanowires. Variable temperature current-voltage measurements indicate that either wide metallic filaments or narrow semiconducting filaments can be preferentially formed by varying the current compliance during electroformation. Metallic filaments behave as a conventional metallic resistance in series with a small barrier, while semiconducting filaments behave as quantum point contacts. The ability to tune filament geometry and behavior through the electroforming process may open avenues for enhanced functionality in nanoscale memristive systems.
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  • 8
    Publication Date: 2016-11-15
    Description: We report that epitaxial Sr 2 IrO 4 thin-films can be selectively grown using pulsed laser deposition (PLD). Due to the competition between the Ruddlesden-Popper phases of strontium iridates (Sr n+1 Ir n O 3n+1 ), conventional PLD methods often result in mixed phases of Sr 2 IrO 4 (n = 1), Sr 3 Ir 2 O 7 (n = 2), and SrIrO 3 (n = ∞). We have discovered that reduced PLD plume dimensions and slow deposition rates are the key for stabilizing pure Sr 2 IrO 4 phase thin-films, identified by real-time in-situ monitoring of their optical spectra. The slow film deposition results in a thermodynamically stable TiO 2 \\SrO\IrO 2 \SrO\SrO configuration at an interface rather than TiO 2 \\SrO\SrO\IrO 2 \SrO between a TiO 2 -terminated SrTiO 3 substrate and a Sr 2 IrO 4 thin film, which is consistent with other layered oxides grown by molecular beam epitaxy. Our approach provides an effective method for using PLD to achieve pure phase thin-films of layered materials that are susceptible to several energetically competing phases.
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  • 9
    Publication Date: 2016-11-15
    Description: We report a significant off-state current reduction by an order of magnitude in the NbO 2 -based selector devices by inserting an ultrathin TiO 2 (∼2 nm) tunneling barrier. Moreover, the ultrathin TiO 2 layer improves the reliability and uniformity of voltage-induced insulator-to-metal transition (IMT) in the NbO 2 selector devices by thermodynamically suppressing the formation of a surface Nb 2 O 5 layer. Our study suggests that the suitable combination of tunneling barrier and IMT materials can minimize the “off” current of IMT selector devices and improve their applicability in high-density three dimensional cross point array memory devices.
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  • 10
    Publication Date: 2016-11-15
    Description: Contemporary research into diagonal active region terahertz quantum cascade lasers for high temperature operation has yielded little success. We present evidence that the failure of high diagonality alone as a design strategy is due to a fundamental trade-off between large optical oscillator strength and long upper-level lifetime. We hypothesize that diagonality needs to be paired with increased doping in order to succeed, and present evidence that highly diagonal designs can benefit from much higher doping than normally found in terahertz quantum cascade lasers. In assuming the benefits of high diagonality paired with high doping, we also highlight important challenges that need to be overcome, specifically the increased importance of carrier induced band-bending and impurity scattering.
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  • 11
    Publication Date: 2016-11-15
    Description: Material architectures that balance optical transparency and electrical conductivity are highly sought after for thin-film device applications. However, these are competing properties, since the electronic structure that gives rise to conductivity typically also leads to optical opacity. Nanostructured metal films that exhibit extraordinary optical transmission, while at the same time being electrically continuous, offer considerable flexibility in the design of their transparency and resistivity. Here, we present design guidelines for metal films perforated with arrays of nanometer-scale holes, discussing the consequences of the choice of nanostructure dimensions, of the type of metal, and of the underlying substrate on their electrical, optical, and interfacial properties. We experimentally demonstrate that such films can be designed to have broad-band optical transparency while being an order of magnitude more conductive than indium tin oxide. Prototypical photovoltaic devices constructed with perforated metal contacts convert ∼18% of the incident photons, compared to
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  • 12
    Publication Date: 2016-11-15
    Description: Vapor-deposited, porous, amorphous, water-ice films, also called amorphous solid water (ASW), crack spontaneously during growth when the film thickness exceeds a critical value ( L c ). We measured the L c during growth of ASW films as a function of growth temperature ( T g  = 10 K, 30 K, and 50 K) and deposition angle ( θ  = 0°, 45°, and 55°) using a quartz crystal microbalance, an optical interferometer, and an infrared spectrometer. The critical thickness, 1–5  μ m under our experimental conditions, increases with T g and θ , an indication of film porosity. We suggest that ASW films undergo tensile stress due to the mismatch between substrate adhesion and contracting forces derived from the incompletely coordinated molecules on the surfaces of the pores. We provide a model to explain the observed dependences of L c on the T g and θ in the context of Griffith theory and estimate the tensile strength of low-temperature ASW to be ∼25–40 MPa. Our model can be applied more generally to describe fracture of other solids with microporous structures, such as metallic or ceramic materials with voids.
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  • 13
    Publication Date: 2016-11-15
    Description: Submonolayer quantum dots promise to combine the beneficial features of zero- and two-dimensional carrier confinement. To explore their potential with respect to all-optical signal processing, we investigate the amplitude-phase coupling ( α -parameter) in semiconductor optical amplifiers based on InAs/GaAs submonolayer quantum dots in ultrafast pump-probe experiments. Lateral coupling provides an efficient carrier reservoir and gives rise to a large α -parameter. Combined with a high modal gain and an ultrafast gain recovery, this makes the submonolayer quantum dots an attractive gain medium for nonlinear optical signal processing.
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  • 14
    Publication Date: 2016-11-15
    Description: Light transport in curved quasi two-dimensional waveguides is considered theoretically. Within transformation optics and tensor theory, a concise description of curvature effects on transverse electric and magnetic waves is derived. We show that the curvature can induce light focusing and photonic crystal properties, which are confirmed by finite element simulations. Our results indicate that the curvature is an effective parameter for designing quasi two-dimensional optical devices in the fields of micro and nano photonics.
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  • 15
    Publication Date: 2016-11-15
    Description: We introduce a double metal terahertz quantum cascade laser meant for astrophysical heterodyne measurements. The laser ridge is embedded in benzocyclobutene, and the device exhibits single mode, continuous wave operation around 4.745 THz with a peak power of almost 1.8 mW at 10 K and a power consumption of ≈1.6 W. Moreover, thanks to the integration of a top metal contact with a patch array antenna for light out-coupling the beam of the emitted light has a low-divergence single-lobe profile and an FWHM of ≈30°.
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  • 16
    Publication Date: 2016-11-15
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  • 17
    Publication Date: 2016-11-29
    Description: Unintentionally doped (UID) AlGaN epilayers graded over Al compositions of 80%–90% and 80%–100% were grown by metal organic vapor phase epitaxy and were electrically characterized using contactless sheet resistance ( R sh ) and capacitance-voltage ( C–V ) measurements. Strong electrical conductivity in the UID graded AlGaN epilayers resulted from polarization-induced doping and was verified by the low resistivity of 0.04 Ω cm for the AlGaN epilayer graded over 80%–100% Al mole fraction. A free electron concentration ( n ) of 4.8 × 10 17  cm −3 was measured by C–V for Al compositions of 80%–100%. Average electron mobility ( μ ¯ ) was calculated from R sh and n data for three ranges of Al composition grading, and it was found that UID AlGaN graded from 88%–96% had μ ¯  = 509 cm 2 /V s. The combination of very large band gap energy, high μ ¯ , and high n for UID graded AlGaN epilayers make them attractive as a building block for high voltage power electronic devices such as Schottky diodes and field effect transistors.
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  • 18
    Publication Date: 2016-11-29
    Description: This article describes the generation of elastic shear waves in a soft medium using a laser beam. Our experiments show two different regimes depending on laser energy. Physical modeling of the underlying phenomena reveals a thermoelastic regime caused by a local dilatation resulting from temperature increase and an ablative regime caused by a partial vaporization of the medium by the laser. The computed theoretical displacements are close to the experimental measurements. A numerical study based on the physical modeling gives propagation patterns comparable to those generated experimentally. These results provide a physical basis for the feasibility of a shear wave elastography technique (a technique that measures a soft solid stiffness from shear wave propagation) by using a laser beam.
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  • 19
    Publication Date: 2016-11-29
    Description: This paper is concerned with the asymptotical stabilization for a class of unstable delay differential equations. Continuous-time delayed feedback controller (C-TDFC) and discrete-time delayed feedback controller (D-TDFC) are presented and studied, respectively. To our best knowledge, applying Hopf bifurcation theory to delay differential equations with D-TDFC is original and meaningful. The difficulty brought by the introduction of sampling period has been overcome. An effective control range which ensures the asymptotical stability of equilibrium for the system with C-TDFC is obtained. Sequently, another effective control range for the system with D-TDFC is gotten, which approximates the one of C-TDFCS provided that the sampling period is sufficiently small. Meanwhile, efforts are paid to estimate a bound on sampling period. Finally, the theoretical results are applied to a physiological system to illustrate the effectiveness of the two control ranges.
    Print ISSN: 1054-1500
    Electronic ISSN: 1089-7682
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  • 20
    Publication Date: 2016-11-29
    Description: We have investigated the temperature-dependent oxygen behavior in the lithium battery cathode Li x Ni 0.5 Mn 1.5 O 4 (LNMO) materials in the temperature range 30-1000 °C. As the temperature increases, oxygen release occurs and the change of crystal structures from the face centered cubic spinel at 30 °C to other phases follows. The amount of released oxygen and the changed crystalline phases are dependent on Li content and temperature. These phenomena are reversible against temperature in air, but not in vacuum and argon gas environments. This study illustrates the important role of temperature and atmospheric environments in synthesizing the LNMO battery materials.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 21
    Publication Date: 2016-11-29
    Description: We devised a single-step mechanochemical synthesis/densification procedure for Cu 2 X (X = S, Se) thermoelectric materials via applying a pressure of 3 GPa to a stoichiometric admixture of elemental Cu and X for 3 min at room temperature. The obtained bulk materials were single-phase, nearly stoichiometric structures with a relative packing density of 97% or higher. The structures contained high concentration of atomic scale defects and pores of 20-200 nm diameter. The above attributes gave rise to a high thermoelectric performance: at 873 K, the ZT value of Cu 2 S reached 1.07, about 2.1 times the value typical of samples grown from the melt. The ZT value of Cu 2 Se samples reached in excess of 1.2, close to the state-of-the-art value.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 22
    Publication Date: 2016-11-29
    Description: Two-dimensional MoS 2 attracts much attention because of its potential application in electronic and optoelectronic devices at present. However, the preparation of large and uniform single crystal MoS 2 nanosheets is still a challenge, which restricts its further application. Herein, monolayer single crystal MoS 2 nanosheets with large and uniform grain size have been synthesized by chemical vapor deposition using a double-tube system. Within the main growth area, the grain size reaches 146  μ m on the substrate of SiO 2 /Si, and the portion of MoS 2 nanosheets with grain size between 50  μ m and 100  μ m is up to 78%. Meanwhile, the grain size keeps constant in the direction perpendicular to the tubes and changes slightly in the parallel direction. This is attributed to the concentration distribution of intermediate product MoO 3−x in the one-side sealed inner tube set in a quartz tube, i.e., the double-tube system, which provides a way to the controllable and uniform synthesis of large monolayer single crystal MoS 2 nanosheets.
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  • 23
    Publication Date: 2016-11-29
    Description: We report the fabrication of a set of new rare-earth-free magnetic compounds, which form the Fe 3 Co 3 Ti 2 -type hexagonal structure with P -6 m 2 symmetry. Neutron powder diffraction shows a significant Fe/Co anti-site mixing in the Fe 3 Co 3 Ti 2 structure, which has a strong effect on the magnetocrystalline anisotropy as revealed by first-principle calculations. Increasing substitution of Fe atoms for Co in the Fe 3 Co 3 Ti 2 lattice leads to the formation of Fe 4 Co 2 Ti 2 , Fe 5 CoTi, and Fe 6 Ti 2 with significantly improved permanent-magnet properties. A high magnetic anisotropy (13.0 Mergs/cm 3 ) and saturation magnetic polarization (11.4 kG) are achieved at 10 K by altering the atomic arrangements and decreasing Fe/Co occupancy disorder.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 24
    Publication Date: 2016-11-29
    Description: The linewidth enhancement (α factor) due to fluctuations in the refractive index induced by carrier fluctuations of intersubband lasers was initially expected to be zero. However, values ranging from −0.5 to 3 have been found experimentally. This paper resolves this controversy showing that counter rotating terms, usually ignored in simulations, are the actual fundamental origin of nonzero α at peak gain even without the inclusion of nonparabolicity and manybody effects, which are however needed to explain negative values. For laser without inversion conditions, significant as a potential out of the box solution for the elusive room temperature operation of terahertz lasers, α is found to be larger, but still at the same order of magnitude of conventional inverted medium lasers, thus ensuring their applicability to a huge number of spectroscopic applications that require sharp laser linewidths.
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  • 25
    Publication Date: 2016-11-29
    Description: As important members of nonclassical states of light, squeezed states and entangled states are basic resources for realizing quantum measurements and constructing quantum information networks. We experimentally demonstrate that the two types of nonclassical optical states can be generated from an optical parametric oscillator (OPO) involving a periodically poled KTiOPO 4 crystal with a domain-inversion period of 51.7  μ m, by changing the polarization of the pump laser. When a vertically polarized 671 nm laser is used to pump the OPO, the intra-cavity frequency-down-conversion with type-0 quasi-phase matching is realized and the output optical beam is a quadrature amplitude squeezed state of light at the wavelength of 1342 nm with the fluctuation of quadrature component of 3.17 dB below the quantum noise limit (QNL). If the pump laser is horizontally polarized, the condition of the type-II quasi-phase matching is satisfied and the output optical beam becomes Einstein-Podolsky-Rosen entangled state of light with correlation variances of both quadrature amplitude-sum and quadrature phase-difference of 2.2 dB below the corresponding QNL.
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  • 26
    Publication Date: 2016-11-29
    Description: We report a simple and efficient electrical sensing scheme that can be used to overcome the “diffusion limit” of affinity-based biosensors by incorporating the structural advantage of a concentric electrode biosensor platform and the microstirring effect of AC electrothermal flow (ACEF). To prove the effect of ACEF on the biosensor performance, we performed both simulations and experiments for the detection of cardiac troponin-I, which is a biomarker for acute myocardial infarction. The finite element simulation results indicate that AC bias to the electrode (which has a concentric structure in our device) can induce fast convection flow, which facilitates the transport of the target molecules to the binding region located between the two electrodes. In our device, the channel region made of a carbon nanotube network decorated with gold nanoparticles, which act as the attaching sites of the probe molecules, is used as a highly sensitive electrical channel. We find that the electrical sensing method exhibited extremely fast sensing speeds compared with those under no bias (diffusion-limited) conditions.
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  • 27
    Publication Date: 2016-11-29
    Description: Experiments in the T-10 tokamak [Alikaev et al. , Plasma Phys. Controlled Fusion 30 , 381 (1988)] have demonstrated the possibility of control of the plasma current and prevention of formation of the non-thermal (E γ  〉 150 keV) electron beams after an energy quench at the density limit disruption using electron cyclotron heating (ECRH) and controlled operation of the Ohmic power supply system. Quasi-stable plasma operation with repetitive sawtooth oscillations can be restored after an energy quench using high auxiliary power P ec  〉 2–5 P oh . Optimal conditions of the plasma discharge recovery after an energy quench using auxiliary heating are identified. At high auxiliary power, restoration of the plasma discharge can be provided with the location of the EC resonance zone within the whole plasma cross section. The auxiliary power required for discharge restoration is minimal when the power is deposited around the m = 2, n = 1 magnetic island (here m and n poloidal and toroidal wave numbers). The threshold ECRH power increases linearly with plasma current. Prevention of the non-thermal electron beams during density limit disruption is associated with stabilization of bursts of the magnetohydrodynamic modes, creation of the saturated magnetic islands, and heating of the background plasma using ECRH. Plasma discharge recovery after an energy quench in a tokamak reactor using auxiliary heating and controllable reduction of the plasma current is discussed.
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  • 28
    Publication Date: 2016-11-29
    Description: The main objective of this research is to investigate the degree to which variations in mechanical properties of constitutive composite materials can influence the aeroelastic behavior of a wind turbine blade. First, structural behavior of a full-scale wind turbine blade is evaluated from different aspects of bending, torsional and axial rigidities. For this purpose, simplified model of the blade is constructed and it is validated with experimental data of the full-scale blade. Then, a parametric study is performed to determine the most dominant mechanical properties which have a severe impact on the structural behavior of the blade. Identified dominant properties are varied randomly and independently. Thus, stochastic analysis is performed to investigate the variations in natural frequencies of the blade as the governing parameter in defining aeroelastic behavior. Finally, susceptibility of the blade to dynamics instability is also examined. Aeroelastic effects are found to have a stronger effect on the blade with lower material properties that lead to more power reduction.
    Electronic ISSN: 1941-7012
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 29
    Publication Date: 2016-11-30
    Description: Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO 3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO 3 , this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d 33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.
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  • 30
    Publication Date: 2016-11-30
    Description: The metastable nature of metallic glasses (MGs) limits their applications. We report the formation of a stable Pd 40.16 Ni 9.64 Cu 30.12 P 20.08 MG with bulk size under high pressure at room temperature. The stable MG shows remarkably enhanced thermal and kinetic stability with substantially increased glass transition temperature T g , crystallization temperature T x , density and mechanical properties. The unique stability can be further reinforced by higher pressure and maintained even above T g . This result can advance the glass design and the understanding of the fundamental issues in MGs.
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  • 31
    Publication Date: 2016-11-30
    Description: We present physical and electrical characterization of niobium-doped zinc oxide (NbZnO) for thin film transistor (TFT) applications. The NbZnO films were deposited using atomic layer deposition. X-ray diffraction measurements indicate that the crystallinity of the NbZnO films reduces with an increase in the Nb content and lower deposition temperature. It was confirmed using X-ray photoelectron spectroscopy that Nb 5+ is present within the NbZnO matrix. Furthermore, photoluminescence indicates that the band gap of the ZnO increases with a higher Nb content, which is explained by the Burstein-Moss effect. For TFT applications, a growth temperature of 175 °C for 3.8% NbZnO provided the best TFT characteristics with a saturation mobility of 7.9 cm 2 /Vs, the current On/Off ratio of 1 × 10 8 , and the subthreshold swing of 0.34 V/decade. The transport is seen to follow a multiple-trap and release mechanism at lower gate voltages and percolation thereafter.
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  • 32
    Publication Date: 2016-11-30
    Description: The enhancement in electrical conductivity and optical transparency induced by a phase transition from amorphous to polycrystalline in lightly silicon-doped indium oxide (InSiO) thin films is studied. The phase transition caused by simple thermal annealing transforms the InSiO thin films from semiconductors to conductors. Silicon atoms form SiO 4 tetrahedra in InSiO, which enhances the overlap of In 5 s orbitals as a result of the distortion of InO 6 octahedral networks. Desorption of weakly bonded oxygen releases electrons from deep subgap states and enhances the electrical conductivity and optical transparency of the films. Optical absorption and X-ray photoelectron spectroscopy measurements reveal that the phase transition causes a Fermi energy shift of ∼0.2 eV.
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  • 33
    Publication Date: 2016-11-30
    Description: Quantum communications have garnered an increasing amount of interest over the last several years. One of the key components, a deterministic single photon source, requires both high quantum efficiency and suitable emission wavelengths, particularly for ubiquitous fiber-based systems. Solid state single photon sources, comprised of a crystal with isolated, optically active defects, are particularly advantageous in terms of their potential for fine control, reproducibility, ease of operation, and scalability. However, random orientation of single defects presents challenges in terms of scalable manufacturing of such sources. In this paper, we numerically demonstrate Mie resonant core–shell structures that are to a large degree insensitive to random impurity dipole orientations and at the same time decouple spurious decay channels by enhancing both absorption and emission rates. Applying the simple core-shell design to Xenon-related color centers in diamond nanocrystals enhances emission rates into the main zero phonon line by a factor of 23 relative to the bulk diamond. Addition of a Bragg-mirror shell to the Mie core-shell permits a great deal of further increase in the enhancement factor: e.g., a factor of 1273 for a two-bilayer Bragg mirror. A great deal of insensitivity to both the emitting dipole orientation and positioning within the nanocrystal was demonstrated.
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  • 34
    Publication Date: 2016-11-30
    Description: Quasiperiodic chaos (QC), which is a combination of quasiperiodic sets and a chaotic set, is uncovered in the six dimensional Poincaré map of a symmetric three-degree of freedom vibro-impact system. Accompanied by symmetry restoring bifurcation, this QC is the consequence of a novel intermittency that occurs between two conjugate quasiperiodic sets and a chaotic set. The six dimensional Poincaré map P is the 2-fold composition of another virtual implicit map Q , yielding the symmetry of the system. Map Q can capture two conjugate attractors, which is at the core of the dynamics of the vibro-impact system. Three types of symmetry restoring bifurcations are analyzed in detail. First, if two conjugate chaotic attractors join together, the chaos-chaos intermittency induced by attractor-merging crisis takes place. Second, if two conjugate quasiperiodic sets are suddenly embedded in a chaotic one, QC is induced by a new intermittency between the three attractors. Third, if two conjugate quasiperiodic attractors connect with each other directly, they merge to form a single symmetric quasiperiodic one. For the second case, the new intermittency is caused by the collision of two conjugate quasiperiodic attractors with an unstable symmetric limit set. As the iteration number is increased, the largest finite-time Lyapunov exponent of the QC does not converge to a constant, but fluctuates in the positive region.
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  • 35
    Publication Date: 2016-11-30
    Description: Dynamics of many multi-agent systems is influenced by communication/activation delays τ . In the presence of delays, there exists a certain margin called the delay margin τ * , less than which system stability holds. This margin depends strongly on agents' dynamics and the agent network. In this article, three key elements, namely, the delay margin, network graph, and a distance threshold conditioning two agents' connectivity are considered in a multi-agent consensus dynamics under delay τ . We report that when the dynamics is unstable under this delay, its states can be naturally bounded, even for arbitrarily large threshold values, preventing agents to disperse indefinitely. This mechanism can also make the system recover stability in a self-regulating manner, mainly induced by network separation and enhanced delay margin. Under certain conditions, unstable consensus dynamics can keep separating into smaller stable subnetwork dynamics until all agents stabilize in their respective subnetworks. Results are then demonstrated on a previously validated robot coordination model, where specifically robustness of τ * is studied against the delay τ inh inherently present in the orientation measurements of the robots. To this end, a mathematical framework to compute τ * with respect to τ inh in quasi-state is developed, demonstrating that τ * can be sensitive to τ inh , yet robot regrouping and stabilization of subnetworks is still possible.
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  • 36
    Publication Date: 2016-11-30
    Description: Individuals in a group may obtain information from other group members about the environment, including the location of a food source or the presence of a predator. Here, we model how information spreads in a group using a susceptible-infected-removed epidemic model. We apply this model to a simulated shoal of fish using the motion dynamics of a coupled oscillator model, in order to test the biological hypothesis that polarized or aligned shoaling leads to faster and more accurate escape responses. The contributions of this study are the (i) application of a probabilistic model of epidemics to the study of collective animal behavior; (ii) testing the biological hypothesis that group cohesion improves predator escape; (iii) quantification of the effect of social cues on startle propagation; and (iv) investigation of the variation in response based on network connectivity. We find that when perfectly aligned individuals in a group are startled, there is a rapid escape by individuals that directly detect the threat, as well as by individuals responding to their neighbors. However, individuals that are not startled do not head away from the threat. In startled groups that are randomly oriented, there is a rapid, accurate response by individuals that directly detect the threat, followed by less accurate responses by individuals responding to neighbor cues. Over the simulation duration, however, even unstartled individuals head away from the threat. This study illustrates a potential speed-accuracy trade-off in the startle response of animal groups, in agreement with several previous experimental studies. Additionally, the model can be applied to a variety of group decision-making processes, including those involving higher-dimensional motion.
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  • 37
    Publication Date: 2016-11-30
    Description: Damage detection of mechanical structures such as bridges is an important research problem in civil engineering. Using spatially distributed sensor time series data collected from a recent experiment on a local bridge in Upper State New York, we study noninvasive damage detection using information-theoretical methods. Several findings are in order. First, the time series data, which represent accelerations measured at the sensors, more closely follow Laplace distribution than normal distribution, allowing us to develop parameter estimators for various information-theoretic measures such as entropy and mutual information. Second, as damage is introduced by the removal of bolts of the first diaphragm connection, the interaction between spatially nearby sensors as measured by mutual information becomes weaker, suggesting that the bridge is “loosened.” Finally, using a proposed optimal mutual information interaction procedure to prune away indirect interactions, we found that the primary direction of interaction or influence aligns with the traffic direction on the bridge even after damaging the bridge.
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  • 38
    Publication Date: 2016-12-01
    Description: The effect of coupling between the extensional bulk mode and the flexural mode of a cantilever beam resonator has been experimentally studied by exciting the two modes simultaneously. The modal frequency shift of linear extensional bulk mode shows a quadratic relationship with the square of flexural mode's amplitude displacement, and a frequency shift up to 1492 Hz is observed when the flexural mode is driven by a AC signal V ac of 3 V and a DC bias of 30 V. The flexural mode shows a Duffing-like behavior with a softening nonlinearity and its frequency shift is influenced not only by its own nonlinear amplitude-frequency effect but also the extensional mode's amplitude as predicted. The nonlinear coupling coefficient is found to be about two orders of magnitude larger than the softening nonlinearity.
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  • 39
    Publication Date: 2016-12-01
    Description: Metal-oxide-semiconductor (MOS) devices with graphene as the metal gate electrode, silicon dioxide with thicknesses ranging from 5 to 20 nm as the dielectric, and p -type silicon as the semiconductor are fabricated and characterized. It is found that Fowler-Nordheim (F-N) tunneling dominates the gate tunneling current in these devices for oxide thicknesses of 10 nm and larger, whereas for devices with 5 nm oxide, direct tunneling starts to play a role in determining the total gate current. Furthermore, the temperature dependences of the F-N tunneling current for the 10 nm devices are characterized in the temperature range 77–300 K. The F-N coefficients and the effective tunneling barrier height are extracted as a function of temperature. It is found that the effective barrier height decreases with increasing temperature, which is in agreement with the results previously reported for conventional MOS devices with polysilicon or metal gate electrodes. In addition, high frequency capacitance-voltage measurements of these MOS devices are performed, which depict a local capacitance minimum under accumulation for thin oxides. By analyzing the data using numerical calculations based on the modified density of states of graphene in the presence of charged impurities, it is shown that this local minimum is due to the contribution of the quantum capacitance of graphene. Finally, the workfunction of the graphene gate electrode is extracted by determining the flat-band voltage as a function of oxide thickness. These results show that graphene is a promising candidate as the gate electrode in metal-oxide-semiconductor devices.
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  • 40
    Publication Date: 2016-12-01
    Description: Nanoscale metal oxide memristors have potential in the development of brain-inspired computing systems that are scalable and efficient. In such systems, memristors represent the native electronic analogues of the biological synapses. In this work, we show cerium oxide based bilayer memristors that are forming-free, low-voltage (∼|0.8 V|), energy-efficient (full on/off switching at ∼8 pJ with 20 ns pulses, intermediate states switching at ∼fJ), and reliable. Furthermore, pulse measurements reveal the analog nature of the memristive device; that is, it can directly be programmed to intermediate resistance states. Leveraging this finding, we demonstrate spike-timing-dependent plasticity, a spike-based Hebbian learning rule. In those experiments, the memristor exhibits a marked change in the normalized synaptic strength (〉30 times), when the pre- and post-synaptic neural spikes overlap. This demonstration is an important step towards the physical construction of high density and high connectivity neural networks.
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  • 41
    Publication Date: 2016-12-01
    Description: We report on a comparative study of high performance isotropic cobalt ferrite (CoFe 2 O 4 ) powder processed by dry and surfactant assisted (wet) ball milling. Milling times as short as 1.5 min (dry) and 6 min (wet) have resulted in a 4-fold increase in coercivity, with a maximum achieved value above 318 kA/m (4 kOe). The use of surfactant is shown to be advantageous in the formation of a more homogeneous structure constituted by non-agglomerated and strained nanoparticles. A record ( BH )   max value of 18.6 kJ m   − 3 (2.34 MGOe) has been obtained for isotropic powder after post-processing annealing. This magnetic performance combined with the required short processing times and the unnecessary requirement of oxygen avoidance in the milling process, makes this CoFe 2 O 4 powder a good candidate for permanent magnet applications.
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  • 42
    Publication Date: 2016-12-01
    Description: We propose a detection scheme for charged molecules or particles based on optically excited semiconductor nanopores. By means of numerical simulations, we show that the band gap of the semiconductor nanopore can be tuned allowing actuation by light. Molecules translocating through the semiconductor nanopore modulate the fluorescence from the nanopore enabling molecule detection. Our approach will enable us to perform a parallel readout of a translocating molecule without the need of chemical modification of the translocating molecules.
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  • 43
    Publication Date: 2016-12-01
    Description: In this paper, we demonstrated a floating-gate organic thin film transistor based nonvolatile memory, in which the core architecture was processed by a sequential three-step solution spin-coating method. The molecular semiconductor 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pen) distributing in the matrix of polymer poly(styrene) (PS), acting as the floating-gate and tunneling layer, respectively, was processed by one-step spin-coating from their blending solution. The effect of the proportion of TIPS-Pen in the matrix of PS on the memory performances of devices was researched. As a result, a good nonvolatile memory was achieved, with a memory window larger than 25 V, stable memory endurance property over 500 cycles and retention time longer than 5000 s with a high memory ratio larger than 10 2 , at an optimal proportion of TIPS-Pen in the matrix of PS.
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  • 44
    Publication Date: 2016-12-01
    Description: We report on the fabrication of nano-contact spin-torque oscillators based on single layers of the epitaxially grown half-metal NiMnSb with ultralow spin wave damping. We demonstrate magnetization auto-oscillations at microwave frequencies in the 1–3 GHz range in out-of-plane magnetic fields. Threshold current densities as low as 3 × 10 11 A m −2 are observed as well as minimum oscillation linewidths of 200 kHz, both of which are much lower than the values achieved in conventional metallic spin-valve-based devices of comparable dimensions. These results enable the fabrication of spin transfer torque driven magnonic devices with low current density requirements, improved signal linewidths, and in a simplified single-layer geometry.
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  • 45
    Publication Date: 2016-12-01
    Description: By means of angle- and spin-resolved photoemission, we demonstrate a possibility of the out-of-plane spin polarization of topological surface states and corresponding lifting of the Kramers degeneracy at the Dirac point induced in magnetically-doped topological insulator Bi 1.37 V 0.03 Sb 0.6 Te 2 Se by circularly polarized synchrotron radiation (SR) at room temperature. It has been shown that the induced out-of-plane polarization is created due to an “optically”-generated uncompensated spin accumulation with transferring the induced torque to the diluted V 3 d ions. We have found theoretically a relation between the imbalance in depopulation of the Dirac cone states under photoexcitation, the generation of steady-state uncompensated spin accumulation and the induced magnetization that can be managed by the polarization of SR.
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  • 46
    Publication Date: 2016-11-30
    Description: A new experiment is described to detect a permanent electric dipole moment of the proton with a sensitivity of 10 −29 e ⋅ cm by using polarized “magic” momentum 0.7 GeV/c protons in an all-electric storage ring. Systematic errors relevant to the experiment are discussed and techniques to address them are presented. The measurement is sensitive to new physics beyond the standard model at the scale of 3000 TeV.
    Print ISSN: 0034-6748
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  • 47
    Publication Date: 2016-11-30
    Description: We have designed and installed a new Langmuir-probe (LP) array diagnostic to determine basic three-dimensional (3D) features of plasmas in TORPEX. The diagnostic consists of two identical LP arrays, placed on opposite sides of the apparatus, which provide comprehensive coverage of the poloidal cross section at the two different toroidal locations. Cross correlation studies of signals from the arrays provide a basic way to extract 3D information from the plasmas, as experiments show. Moreover, the remarkable signal-to-noise performance of the front-end electronics allows us to follow a different approach in which we combine information from all probes in both arrays to reconstruct elementary 3D plasma structures at each acquisition time step. Then, through data analysis, we track the structures as they evolve in time. The LP arrays include a linear-motion mechanism that can displace radially the probes located on the low field side for experiments that require fine-tuning of the probe locations, and for operational compatibility with the recently installed in-vessel toroidal conductor.
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  • 48
    Publication Date: 2016-11-30
    Description: We have developed a new instrument combining a scanning probe microscope (SPM) and an X-ray scattering platform for ambient-pressure catalysis studies. The two instruments are integrated with a flow reactor and an ultra-high vacuum system that can be mounted easily on the diffractometer at a synchrotron end station. This makes it possible to perform SPM and X-ray scattering experiments in the same instrument under identical conditions that are relevant for catalysis.
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  • 49
    Publication Date: 2016-11-30
    Description: An instrument used for measuring multiple scintillators’ light output and energy resolution was developed. The instrument consisted of a light sensor array which was composed of 64 discrete SiPMs (Silicon Photomultipliers), a corresponding individual channel readout electronics system, and a data processing algorithm. A Teflon grid and a large interval between adjacent SiPMs were employed to eliminate the optical cross talk among scintillators. The scintillators’ light output was obtained by comparing with a reference sample with known light output. Given the SiPM temperature dependency and the difference among each SiPM, a temperature offset correction algorithm and a non-uniformity correction algorithm were added to the instrument. A positioning algorithm, based on nine points, was designed to evaluate the performance of a scintillator array. Tests were performed to evaluate the instrument’s performance. The uniformity of 64 channels for light output measurement was better than 98%, the stability was better than 98% when temperature varied from 15 °C to 40 °C, and the nonlinearity under 511 keV was better than 2%. This instrument was capable of selecting scintillators and evaluating the packaging technology of scintillator arrays with high efficiency and accuracy.
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  • 50
    Publication Date: 2016-12-01
    Description: A systematic study of pressure ionization is carried out in the chemical picture by the example of fluid helium. By comparing the variants of the chemical model, it is demonstrated that the behavior of pressure ionization depends on the construction of the free energy function. In the chemical model with the Coulomb free energy described by the Padé interpolation formula, thermodynamical instability induced by pressure ionization is found to be manifested by a discontinuous drop or a continuous fall and rise along the pressure-density curve as well as the pressure-temperature curve, which is very much like the first order liquid-liquid phase transition of fluid hydrogen from the first principles simulations. In contrast, in the variant chemical model with the Coulomb free energy term empirically weakened, no thermodynamical instability is induced when pressure ionization occurs, and the resulting equation of state achieves a good agreement with the first principles simulations of fluid helium.
    Print ISSN: 1070-664X
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  • 51
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    Unknown
    American Institute of Physics (AIP)
    Publication Date: 2016-12-01
    Description: One-dimensional and quasi-one-dimensional strongly coupled dusty plasma rings have been created experimentally. Longitudinal (acoustic) and transverse (optical) dispersion relations for the one-ring are measured and found to be in excellent agreement with the theory for an unbounded straight chain of particles interacting through a Yukawa (i.e., screened Coulomb or Debye-Hückel) potential. These rings provide a new experimental system to directly study one-dimensional and quasi-one-dimensional linear and nonlinear phenomena.
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  • 52
    Publication Date: 2016-12-01
    Description: Numerical study of electromagnetic (EM) wave transmission through the magnetized plasma layer is presented in this paper. The plasma parameters are derived from computational fluid dynamics simulation of the flow field around a blunt body flying at supersonic speed and serve as the background plasma condition in the numerical modeling for EM wave transmission. The EM wave is generated by our newly designed coaxial feed GPS patch antenna. The external magnetic field is applied and assumed to vary linearly as a function of wall distance. The effects of the external applied magnetic field and the plasma parameters on wave transmission are studied, and the results show that EM wave propagation in the non-uniformly magnetized plasma is a matter of impedance matching, and the EM wave transmission can be adjusted only when the proper strength of the magnetic field is applied.
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  • 53
    Publication Date: 2016-12-02
    Description: A method is proposed that enables the imaging of the photocurrent collected by a solar cell under arbitrary operating conditions. The method uses a series of luminescence images under varying illumination to derive the total photocurrent collection efficiency at a given voltage bias. The resulting total photocurrent collection image directly relates to the difference between the dark and illuminated current-voltage characteristics of the cell. A crystalline silicon solar cell is used to test the method, and the images of the total photocurrent collection efficiency are used to quantify the influence of a crack on the total collected photocurrent of the solar cell.
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  • 54
    Publication Date: 2016-12-02
    Description: Magnetic resonant wireless power transfer system based on dielectric disk resonators made of colossal permittivity ( ε  = 1000) and low loss (tan  δ  = 2.5 × 10 –4 ) microwave ceramic is experimentally investigated. The system operates at the magnetic dipole mode excited in the resonators providing maximal power transfer efficiency of 90% at the frequency 232 MHz. By applying an impedance matching technique, the efficiency of 50% is achieved within the separation between the resonators d  = 16 cm (3.8 radii of the resonator). The separation, misalignment and rotation dependencies of wireless power transfer efficiency are experimentally studied.
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  • 55
    Publication Date: 2016-12-02
    Description: A selective electrothermal magnetic annealing technique is introduced that provides programming capabilities for mechanical micro-resonators. In the proposed approach, the magnetic properties of resonators can be locally tuned in a post-fabrication batch-compatible process step. A prototype is implemented in a standard microfabrication process, where resonating ferromagnetic elements are suspended on top of a polysilicon resistive heater. The ferromagnetic elements consist of electroplated Nickel (Ni) with minor Iron (Fe) impurities. The electro-thermo-mechanical heating phenomenon is simulated for design purposes. The magnetization of micro-resonators with and without magnetic annealing is measured. The resulting magnetic property enhancement is illustrated by hysteresis (M-H) loop variations.
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  • 56
    Publication Date: 2016-12-02
    Description: Microcrystals of LiNbO 3 (size ∼200 nm) can be selectively precipitated in a glass matrix which can assist in the photocatalytic activity through ferroelectricity. Glass with the composition 30SiO 2 -35Li 2 CO 3 -35Nb 2 O 5 was utilized for the process. A remarkably high Estriol (E3) degradation rate of 232.54 min −1  m −2 was obtained. The degradation was monitored using fluorescence spectroscopy with a detection limit in nanomolar (nM) range. From the fitting of fluorescence intensity versus time, it was observed that degradation of estriol follows a pseudo first-order reaction kinetics. The results indicate that LiNbO 3 based glass-ceramics have a great potential to be employed as a well embedded photocatalyst.
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  • 57
    Publication Date: 2016-12-02
    Description: Floating gate memory operations are demonstrated in a single-electron transistor (SET) fabricated by a chemical assembly using the Au nanogap electrodes and the chemisorbed Au nanoparticles. By applying pulse voltages to the control gate, phase shifts were clearly and stably observed both in the Coulomb oscillations and in the Coulomb diamonds. Writing and erasing operations on the floating gate memory were reproducibly observed, and the charges on the floating gate electrodes were maintained for at least 12 h. By considering the capacitance of the floating gate electrode, the number of electrons in the floating gate electrode was estimated as 260. Owing to the stability of the fabricated SET, these writing and erasing operations on the floating gate memory can be applied to reconfigurable SET circuits fabricated by a chemically assembled technique.
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  • 58
    Publication Date: 2016-12-02
    Description: Ferroelectrets are non-polar polymer foams or polymer systems with internally charged cavities. They are charged through a series of dielectric barrier discharges (DBDs) that are caused by the electrical breakdown of the gas inside the cavities. Thus, the breakdown strength of the gas strongly influences the charging process of ferroelectrets. A gas with a lower breakdown strength has a lower threshold voltage, thus decreasing the onset voltage for DBD charging. However, a lower threshold voltage also leads to a lower value for the remanent polarization, as back discharges that are caused by the electric field of the internally deposited charges can take place already at lower charge levels. On this basis, a charging strategy is proposed where the DBDs start in a gas with a lower breakdown strength (in the present example, helium) and are completed at a higher breakdown strength (e.g., nitrogen or atmospheric air). Thus, the exchange of the gas in the cavities during charging can significantly enhance the charging efficiency, i.e., yield much higher piezoelectric coefficients in ferroelectrets at significantly lower charging voltages.
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  • 59
    Publication Date: 2016-12-02
    Description: The obscure nature of glass physics has led to develop various correlations between different parameters and properties of metallic glasses. Despite these correlations, the clear picture of plastic deformation is still lacking. We have measured elastic recovery in metallic glasses by indentation, and found the elastic recovery correlate with different properties and parameters of metallic glasses. All these observations can be quite well explained with flow unit model which could provide clearer picture on the plastic deformations and nature of the metallic glasses.
    Print ISSN: 0021-8979
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  • 60
    Publication Date: 2016-12-02
    Description: Classical molecular dynamics (MD) simulations were performed to study non-adhesive contact at the atomic scale. Starting from the case of Hertzian contact, it was found that the reduced Young's modulus E * for shallow indentations scales as a function of, both, the indentation depth and the contact radius. Furthermore, the contact of two representative rough surfaces was investigated: one multi-asperity, Greenwood-Williamson-type (GW-type) rough surface — where asperities were approximated as spherical caps — and a comparable randomly rough one. The results of the MD simulations were in agreement for both representations and showed that the relative projected contact areas A r p c were linear functions of nominal applied pressures, even after the initiation of plastic deformation. When comparing the MD simulation results with the corresponding continuum GW and Persson models, both continuum models were found to overestimate the values of A r p c relative to the MD simulation results.
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  • 61
    Publication Date: 2016-12-02
    Description: A new concept, Phase Segregation Annealing (PSA), was investigated for implementing simultaneous ohmic contacts (SOCs) to p - and n -type 4H-SiC. Test structures with selected ratio compositions of co-sputtered Pt:Ti contacts were fabricated in p -type 4H-SiC epitaxial layers having aluminum acceptor concentrations, N a  = 2 × 10 19 , 7 × 10 19 , and 2.5 × 10 20  cm −3 , and a nitrogen doped n -type epitaxial layer having donor concentration, N d  = 7 × 10 18  cm −3 . The ratios of the co-sputtered Pt-Ti metallization were 80:20, 50:50, and 30:70 at. %. After rapid thermal annealing (RTA) ranging between 800 and 1200 °C in vacuum and confirming SOCs by linear current-voltage (I-V) measurement, the specific contact resistance ( ρ c ) values were extracted using the Transfer Length Measurement method. SOCs were realized with the Pt80:Ti20 composition starting from 1000 °C, and the Pt30:Ti70 composition from 1100 °C, with both exhibiting eutectic and segregated phases. The Pt50:Ti50 composition produced no SOC and eutectic and segregated phases were absent. The Pt80:Ti20 composition had the lowest pair of average ρ c values of 7 × 10 −5 Ω cm 2 and 7.3 × 10 −4 Ω cm 2 on the highest doped p -type and the n -type samples after RTA at 1000 °C, respectively. Auger electron spectroscopy and focused ion beam field emission scanning electron microscopy with energy dispersive x-ray spectroscopy indicated distinct phase segregation via the eutectic-liquidus-eutectic transitions, the coalescence of likely Pt 3 Si and Pt 2 Si binary phases, and solid phases of Ti 3 Si, Ti 5 Si 3 , and TiC, with all the active phases maintaining intimate contact to both the p - and n -type 4H-SiC surfaces. The SOC formation was attributed to the disparate work functions of these phases, which was in good agreement with the proposed PSA model.
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  • 62
    Publication Date: 2016-12-02
    Description: In this paper, the electrical properties of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/silicon nanowire hybrid solar cell have been analyzed and an optimized structure is proposed. In addition, the planar PEDOT:PSS/c-Si hybrid solar cell is also modeled for comparison. We first developed a simulation software which is capable of modeling organic/inorganic hybrid solar cells by including Gaussian shape density of states into Poisson and drift-diffusion solver to present the tail states and trap states in the organic material. Therefore, the model can handle carrier transport, generation, and recombination in both organic and inorganic materials. Our results show that at the applied voltage near open-circuit voltage (V oc ), the recombination rate becomes much higher at the PEDOT:PSS/Si interface region, which limits the fill factor and V oc . Hence, a modified structure with a p-type amorphous silicon (a-Si) layer attached on the interface of Si layer and an n + -type Si layer inserted near the bottom contact are proposed. The highest conversion efficiency of 16.10% can be achieved if both structures are applied.
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  • 63
    Publication Date: 2016-12-02
    Description: Found in our recent dielectric study of a planar and rigid glass-former, 1-methylindole (1MID), is an unusual secondary relaxation unrelated in its dynamic properties to the structural α-relaxation. We speculated that it originates from the in-plane motion of the molecules, and the supposedly universal Johari-Goldstein (JG) β-relaxation with strong connection to the structural α-relaxation in rigid glass-formers is not resolved [X. Q. Li et al. J. Chem. Phys. 143 , 104505 (2015)]. In this work, dielectric measurements are performed in binary mixtures of 1MID with two aromatics of weak polarity, ethylbenzene (EB) and triphenylethylene (TPE), in the highly viscous regimes near glass transition. EB and TPE have smaller and larger molecular sizes and glass transition temperatures T g than 1MID, respectively. Strikingly, the results show that the resolved secondary relaxations of 1MID in the two mixtures share the same relaxation time and their temperature dependence as pure 1MID, independent of the mode and degree of dilution. The results indicate that the unusual secondary relaxation is not directly coupled with the α-relaxation, and support the in-plane-rotation interpretation of its origin. On the other hand, the supposedly universal and intermolecular JG β-relaxation coming from the out-of-plane motion of the planar molecule has weaker dielectric strength, and it cannot be resolved from the more intense in-plane-rotation secondary relaxation because the dipole moment of 1MID lies on the plane.
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  • 64
    Publication Date: 2016-12-02
    Print ISSN: 0021-9606
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    Topics: Chemistry and Pharmacology , Physics
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  • 65
    Publication Date: 2016-12-02
    Description: The initial stages of cobalt metal growth by atomic layer deposition are described using the precursors bis(1,4-di- tert -butyl-1,3-diazadienyl)cobalt and formic acid. Ruthenium, platinum, copper, Si(100), Si–H, SiO 2 , and carbon-doped oxide substrates were used with a growth temperature of 180 °C. On platinum and copper, plots of thickness versus number of growth cycles were linear between 25 and 250 cycles, with growth rates of 0.98 Å/cycle. By contrast, growth on ruthenium showed a delay of up to 250 cycles before a normal growth rate was obtained. No films were observed after 25 and 50 cycles. Between 100 and 150 cycles, a rapid growth rate of ∼1.6 Å/cycle was observed, which suggests that a chemical vapor deposition-like growth occurs until the ruthenium surface is covered with ∼10 nm of cobalt metal. Atomic force microscopy showed smooth, continuous cobalt metal films on platinum after 150 cycles, with an rms surface roughness of 0.6 nm. Films grown on copper gave rms surface roughnesses of 1.1–2.4 nm after 150 cycles. Films grown on ruthenium, platinum, and copper showed resistivities of
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  • 66
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-02
    Description: The present study focuses on the Be 2 + , Be 2 , Be 2 − , and Be 3 species with the aim to unveil their bonding pattern. The ground states of the above molecules are examined mainly through multi reference configuration interaction methods using an aug-cc-pVQZ basis set. Previous work is scrutinized with an eye to the instability problems inherent in various Hartree-Fock schemes. Under this point of view, we rationalize previous findings and put them in a unified context of what and why should be done in similar hard to crack cases. In all the above species, the covalently bound ground states are formed just because the Be atom is found in its first excited 3 P(2 s 1 2 p 1 ) state.
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  • 67
    Publication Date: 2016-12-02
    Description: A systematical method is formulated for extracting skin-friction fields from Temperature Sensitive Paint (TSP) images in the sense of time-averaging and phase-averaging. The method is applied to an underwater cylinder in crossflow at two subcritical regimes ( Re = 72 000 and 144 000). TSP maps are decomposed in a time-averaged, a phase-averaged, and a random component. The asymptotic form of the energy equation at the wall provides an Euler-Lagrange equation set that is solved numerically to gain the relative skin friction time- and phase-averaged fields from the TSP surface temperature maps. The comparison of the time averaged relative skin-friction profiles with the literature data shows an excellent agreement on the whole laminar boundary layer up to the laminar separation line. Downstream of separation, time averaged results identify the secondary reattachment/separation events, which are lost in the available literature data. The periodic behavior of the skin-friction is taken, describing how the laminar separation bubble evolves by providing the time history of the laminar separation line and of the secondary reattachment/separation over the entire vortex shedding period. Instantaneous skin friction maps reveal the existence of coherent structures by capturing their footprint on the cylinder’s surface. An array of Π -shaped traces marks the existence of counter-rotating, streamwise-oriented vortices just before the laminar separation line. Their interaction with the laminar boundary layer and with the separation line is briefly described. An example of the intermittent excerpt of their influence through the laminar separation line is reported.
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  • 68
    Publication Date: 2016-12-02
    Description: Distribution of electrostatic potential in direct current reflex discharge plasma has been studied experimentally. Measurements have been conducted by the single floating probe method. The influence of 0–0.2 T magnetic field, 1–200 mTorr pressure, 0–2 kV discharge voltage, and electrodes geometry on plasma column electrostatic potential was investigated. The possibility for the formation of a preset potential profile required for the realization of plasma separation of spent nuclear fuel was demonstrated.
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  • 69
    Publication Date: 2016-12-02
    Description: Asymmetric mode competitions are observed in the design of an X-band triaxial klystron amplifier with an asymmetric input cavity, and the generation mechanism of the asymmetric mode competition is analyzed in the paper. The results indicate that the asymmetric modes are excited in the buncher cavity. The asymmetric mode (coaxial TM 612 mode) in the buncher cavity with the highest shunt impedance can start up first among the asymmetric modes with negative beam loading conductance. The coupling of the corresponding coaxial TE mode between the buncher and input cavity exacerbates the start oscillation of the asymmetric mode competition. The rationality of the analysis is demonstrated by cutting off the propagation of the corresponding coaxial TE modes between the buncher cavity and the input cavity, and the asymmetric mode competitions are thoroughly suppressed by specially designed reflectors and lossy material. In simulation, a microwave with a power of 1.28 GW and a frequency of 9.375 GHz is generated, and the extraction efficiency and the gain are 34.5% and 41.5 dB, respectively.
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  • 70
    Publication Date: 2016-12-02
    Description: The focused high-intensity pulsed ion beam (HIPIB) of 100 ns order pulse is generated with respect to its spatial stability in two types of magnetically insulated ion diodes (MIDs) with geometrical focusing configuration using the passive anode, i.e., insulation of electrons with an external magnetic-field and a self-magnetic field, respectively. Anode plasma formation for the ion beam generation is based on different processes in the two types of MIDs, as the surface breakdown on the polymer-coated anode operated in the unipolar pulse mode for the external-magnetic field MID and the explosive electron emission on the graphite anode in the bipolar-pulse mode for the self-magnetic field MID. Typical energy density per pulse is in the range of 3–6 J/cm 2 , at an accelerating voltage of 200–300 kV with a pulse duration of 120–150 ns. The spatial deviations of the HIPIB is evaluated by measuring the energy density distribution by using an infrared diagnostic method considering neutralizing during the ion beam propagation to the focal plane with a spatial resolution of 1 mm. The ion beam deviation is about ±1.5 mm for the external-magnetic field MID and ±2.5 mm for the self-magnetic field MID, leading to a fluctuation in the energy density of 1%–12%, and 9%–27% within a 10 mm range at the focal point, respectively. It is revealed that the displacement of different parts of a beam spot occurs nonsynchronously, mainly attributable to the intrinsic diode processes of plasma generation and expansion, and ion beam extraction from the anode–cathode gap, while the influence of magnetic field in the transportation region is negligible. The ion beam spatial deviation has a major influence on the shot-to-shot stability of ion beam, and it is suggested that the stability can be enhanced via diode process improvement.
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  • 71
    Publication Date: 2016-12-02
    Description: Wave breaking is a ubiquitous nonlinear phenomenon in plasma that is followed by sudden drop of wave amplitude after a wave steepening. We perform fluid simulation of the ion acoustic solitary waves (IASWs) to investigate the start time of the wave steepening and breaking process. This simulation demonstrates that a long wavelength perturbation in the electron and ion equilibrium densities evolves into two long wavelength IASWs. These IASWs steepens and breaks into short wavelength solitary structures, which become stable ion acoustic solitons at later time. From the detailed analysis of simulation output, we accomplish the criteria for steepening and breaking of the IASWs based on the (a) acceleration of IASWs (b) balance between maximum potential energy and the maximum electron kinetic energy. Furthermore, we examined the ponderomotive potential and the ponderomotive frequency of the electrons and ions during the process of the generation, steepening and breaking of these IASWs. It is observed that the maximum ponderomotive potential of both electrons and ions enhances during the steepening and attains the maximum close to the breaking of the IASWs. The simulation shows that the electron (ion) average ponderomotive frequency is considerably higher than the electron plasma frequency in the initial phase of generation of IASWs, which rapidly oscillates and approaches to frequencies much smaller than electron (ion) plasma frequency. These ponderomotive frequencies remain unchanged until the start of steepening of the IASWs; however, both frequencies are found to increase during the steepening and breaking of these IASWs. Based on this information, we propose that the ponderomotive potential and ponderomotive frequencies of electrons and ions can be used as proxies to determine the steepening and breaking time of the IASWs. We find that the onset time of the wave breaking varies inversely with the thermal velocity of the electrons and the amplitude of the initial density perturbation (IDP), while it is directly proportional to the width of the IDP. It is also noted that the number of solitons formed in the system and their characteristics depends on the electron temperature, width, and amplitude of the IDP.
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  • 72
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
    Print ISSN: 0031-9228
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  • 73
    Publication Date: 2016-12-03
    Description: In the present paper, a scheme for generation of terahertz (THz) radiation in electron-neutral collisional plasma based on beating of two Gaussian laser array beams has been proposed. It is shown that the efficiency of THz radiation based on the Gaussian laser array beams can be enhanced drastically in comparison with the efficiency of THz radiation based on the Gaussian one. Furthermore, the producing THz radiation by the Gaussian laser array beams, which has an exclusive field profile, is affected by some array structure parameters. It can also be used to overcome the negative consequences of electron neutral collisions in plasma, which may be occurring in the THz radiation generation process. Optimizing the collisional plasma, laser beams and array structure parameters, THz radiation efficiency up to 0.07% can be obtained in our scheme which is about three times greater than the maximum efficiency obtained for standard (single) Gaussian laser beam. Also, considering the electrostatic energy channel in solving the THz wave equation, and reduction of THz radiation efficiency to 0.054%, in this assumption, the ratio between the efficiency of Gaussian laser array beams and standard Gaussian laser beam remained unchanged.
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  • 74
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
    Description: The cellular nature of space reveals itself in the angular distribution of μ and μ‾ produced at the accelerator.
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  • 75
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
    Description: SAMI 9000, one of the world’s most sophisticated artificial intelligences, has allowed human colleagues to probe his brain as he drifts in and out of consciousness.
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  • 76
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
    Description: The spirals may be long-sought evidence of a gravitational instability predicted by hydrodynamic theory.
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  • 77
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
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  • 78
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
    Description: The state’s new law mandating neural-network-based screenings has driven workers statewide to vent their anger.
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  • 79
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
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  • 80
    Publication Date: 2016-12-03
    Description: In order to maximize the O concentration generated by the atmospheric pressure plasma jets (APPJs), several different methods of adding O 2 additive to working gas have been proposed. However, it is not clear, which method is capable of generating the highest concentration of O atom. In this paper, the concentration of O atoms in an APPJs by adding O 2 to (1) the working gas, to (2) the downstream inside the tube, and (3) to the shielding gas is investigated by two-photon absorption laser-induced fluorescence spectrometry. The results clearly demonstrate that the highest O density is achieved when 1.5% of O 2 is added to the working gas rather than the other two methods. In other words, the most effective way to generate O atoms is by premixing O 2 with the working gas. Further investigation suggests that O atoms are mainly generated around the electrode region, where the electric field is highest. In addition, when O 2 is added to the working gas, if in the meantime extra O 2 is added to the downstream inside the tube, a significant decrease of O density is observed.
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  • 81
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
    Description: But his space policy underwhelmed, and the combination of a GOP-led Congress and fiscal constraints limited his science budgets.
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  • 82
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-03
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