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The scaling of reaction yields in light ion fusion to low reaction energies is important for our understanding of stellar fuel chains and the development of future energy technologies. Experiments become progressively more challenging at lower reaction energies due to the exponential drop of fusion cross sections below the Coulomb barrier. We report on experiments where deuterium-deuterium (D-D) fusion reactions are studied in a pulsed plasma in the glow discharge regime using a benchtop apparatus. We model plasma conditions using particle-in-cell codes. Advantages of this approach are relatively high peak ion currents and current densities (0.1 to several A/cm2) that can be applied to metal wire cathodes for several days. We detect neutrons from D-D reactions with scintillator-based detectors. For palladium targets, we find neutron yields as a function of cathode voltage that are over 100 times higher than yields expected for bare nuclei fusion at ion energies below 2 keV (center of mass frame). A possible explanation is a correction to the ion energy due to an electron screening potential of 1000 ± 250 eV, which increases the probability for tunneling through the repulsive Coulomb barrier. Our compact, robust setup enables parametric studies of this effect at relatively low reaction energies. [ABSTRACT FROM AUTHOR]

We report a systematic study on the structural and electronic properties of Bi2Te3-xSex topological insulator alloy grown by molecular beam epitaxy(MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3-xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3-xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBEgrowth conditions, Bi2Te3-xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound. [ABSTRACT FROM AUTHOR]

The resonant-Auger - interatomic Coulombic decay (ICD) cascade was recently suggested as an efficient means of controlling the course of the ICD process. Recent theoretical and experimental works show that control over the energies of the emitted ICD electrons can be achieved either by varying the photon energy to produce different initial core excitations or by changing the neighboring species. This work presents a theoretical investigation on the role of the rare-gas neighbor and clarifies how the latter influences the ICD process. For this purpose, we compare fully ab initio computed ICD-electron and kinetic energy release spectra following the 2p3/2 → 4s, 2p 1/2 → 4s and 2p3/2 → 3d of Ar in ArKr and Ar2. We demonstrate that the presence of the chemically "softer" partner atom results in an increase in the energies of the emitted ICD electrons, and also in the appearance of additional ICD-active states. The latter leads to a threefold increase in the ICD yield for the case of the 2p3/2,1/2 → 4s parent core excitations. [ABSTRACT FROM AUTHOR]

A scheme utilizing excitation of core electrons followed by the resonant-Auger - interatomic Coulombic decay (RA-ICD) cascade was recently proposed as a means of controlling the generation site and energies of slow ICD electrons. This control mechanism was verified in a series of experiments in rare gas dimers. In this article, we present fully ab initio computed ICD electron and kinetic energy release spectra produced following 2p3/2 → 4s, 2p1/2 → 4s, and 2p3/2 → 3d core excitations of Ar in Ar2. We demonstrate that the manifold of ICD states populated in the resonant Auger process comprises two groups. One consists of lower energy ionization satellites characterized by fast interatomic decay, while the other consists of slow decaying higher energy ionization satellites. We show that accurate description of nuclear dynamics in the latter ICD states is crucial for obtaining theoretical electron and kinetic energy release spectra in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

Excitation of HeNe by synchrotron light just below the frequency of the 1s→3p transition of isolated He has been recently shown to be followed by resonant interatomic Coulombic decay (ICD). The vibrationally resolved widths of the ICD states were extracted with high precision from the photoion spectra. In this paper, we report the results of ab initio calculations of these widths. We show that interaction between electronic states at about the equilibrium distance of HeNe makes dark states of He accessible for the photoexcitation and subsequent electronic decay.Moreover, the values of the calculated widths are shown to be strongly sensitive to the presence of the non-adiabatic coupling between the electronic states participating in the decay. Therefore, only by considering the complete manifold of interacting decaying electronic states a good agreement between the measured and computed ICD widths can be achieved. [ABSTRACT FROM AUTHOR]

The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the coupling coefficient and, thus, broaden the bandwidth of SAW devices. For the Sezawa mode, it is illustrated that using a Ti layer with a layer thickness-to-wavelength ratio of 0.02 the maximum coupling coefficient is 2.546% and the associated SAW phase velocity is 10657 m/s at the AlN films’ thickness-to-wavelength ratio of 0.14. This coupling coefficient is 105% higher than that in the IDT/AlN/diamond structure. The research results can be applied to design SAW devices using diamond based structures in the super high frequency band. [ABSTRACT FROM AUTHOR]

We analyze in detail the accessible relaxation pathways via electron emission of the Ne2+Ar states populated via the K-LL Auger decay of Ne+(1s-1)Ar. In particular, we concentrate on the “direct” interatomic Coulombic decay (ICD) of the Ne2+(2s-12p-1)Ar weakly bound doubly ionized states into the manifold of the Ne2+(2p-2)–Ar+(3p-1) repulsive triply ionized ones. To carry out the present study the potential energy curves of the NeAr ground state, the core ionized state Ne+(1s-1)Ar, the relevant dicationic and tricationic states, and the corresponding ICD transition rates have been computed using accurate ab initio methods and basis sets. The total and partial ICD electron spectra are computed within the framework of the time-dependent theory of wave packet propagation. Thereby, the impact of nuclear dynamics accompanying the electronic decay on the computed ICD-electron spectra is investigated in detail. [ABSTRACT FROM AUTHOR]

HfO2/SiOx/Si layer structures have been fabricated using atomic layer deposition and subsequently annealed at partial oxygen pressures close to the equilibrium pressure of bulk SiO2. These ultralow oxygen partial pressures at around 10-40 atm have been achieved by a solid state buffer method. An interfacial SiOx layer with an approximate thickness of 1 nm is shown to be part of the equilibrium configuration of HfO2 on Si even at an oxygen activity eight orders of magnitude below the equilibrium pressure of bulk SiO2. Elimination of the silica-rich interfacial layer in any process permitting approach toward thermodynamic equilibrium seems highly improbable. By comparison with the case of pure SiOx on Si, it is shown that HfO2 acts as a “surfactant” to SiOx leading to a smooth film structure, while the pure SiOx on Si exhibits island formation under the same conditions. Furthermore, the oxidation state of Si in SiOx and the silicate composition at the HfO2/SiOx interface can be tailored by the partial oxygen pressure. [ABSTRACT FROM AUTHOR]

The van der Waals-London dispersion (vdW-Ld) spectra are calculated for the [9,3,m] metallic and [6,5,s] semiconducting single wall carbon nanotubes (SWCNTs), graphite, and graphene (a single carbon sheet of the graphite structure) using uniaxial optical properties determined from ab initio band structure calculations. The [9,3,m], exhibiting metallic optical properties in the axial direction versus semiconducting optical properties in the radial direction, highlights the strong anisotropic nature of metallic SWCNTs. Availability of both efficient ab initio local density band structure codes and sufficient computational power has allowed us to calculate the imaginary parts of the frequency dependent dielectric spectra, which are then easily converted to the required vdW-Ld spectra for Hamaker coefficient calculations. The resulting Hamaker coefficients, calculated from the Lifshitz quantum electrodynamic theory, show that neither graphite nor graphene are accurate model materials for estimating the Hamaker coefficients of SWCNTs. Additionally, Hamaker coefficients were calculated between pure radial-radial, radial-axial, and axial-axial components of both SWCNTs. Analysis of these coefficients reveals that the vdW-Ld interactions will depend on both chirality and the particular orientation between neighboring SWCNTs. The minimization of energy, with respect to orientation, predicts that vdW-Ld alignment forces will arise as a result of the anisotropic optical properties of SWCNTs. [ABSTRACT FROM AUTHOR]

Low-temperature (10 K) microcathodoluminescence spectroscopy with a scanning electron microscope has been used to probe shallow and deep levels within the grains of Bi[SUB2]O[SUB3]-doped ZnO powders prepared under different process conditions. These studies reveal strong electronic state variations between the bulk and boundaries of these submicron ZnO grains, including new emissions at ~3.329 eV at grain boundaries attributed to Bi phase segregation and/or the formation of new electrically active defects. The characteristic deep level defect emission at 2.4 eV due to nonstoichiometric point defects varies spatially, appearing much stronger in the grain bulk than at the boundaries. The 3.329 eV emissions become more pronounced with higher doping concentration and annealing temperature, indicating a strong dependence on processing. The strong temperature and composition dependence of these boundary-specific features are consistent with the known influence of process conditions on the varistor properties of ZnO powder. [ABSTRACT FROM AUTHOR]

Presents a study which examined the effects of processing thermal history on the formation and morphology of grain boundary phases and on the composition of BaPb[sub0.75]Bi[sub0.25]O[sub3] (BPB) superconductor. Characteristics of BPB superconductor; Overview of microstructural and microchemical studies on BPB; Implications of the results for cuprate superconductors.

Presents a study that examined the temperature and composition dependence of grain boundary segregation in lanthanum-strontium-copper-oxide polycrystalline superconducting materials. Methodology; Determination of the bulk and grain boundary concentrations of strontium; Correlation between the resistivity and the temperature characteristics of the superconducting samples.

The acoustic performance of a microperforated panel (MPP) absorber array in the nonlinear regime is investigated both numerically and experimentally. The MPP absorber array is constructed by three parallel-arranged MPP absorbers with different cavity depths. A finite element model is used to simulate the acoustic response of the MPP absorber array by adopting the nonlinear impedance model. The results show that the absorption of the MPP absorber array is affected by the incident sound pressure when it is beyond around 100 dB. With appropriate structural and perforation property of MPP, the MPP absorber array in non-linear regime outperforms that in linear regime due to the improvement of equivalent acoustic impedance matching with ambient air over wide frequency range. However, when the sound pressure excitation is too high, the local resonance effect of the resonating component MPP absorber is diminished and the sound absorption is decreased. With the carefully chosen properties of MPP, the performance degradation induced by panel vibration can be avoided. An optimal set of MPP properties to avoid the performance degradation induced by panel vibration is determined. The measured normal absorption coefficients of a prototype MPP absorber array compare well with the numerical prediction in both linear and nonlinear regimes. [ABSTRACT FROM AUTHOR]

The noise attenuation of fan-ducted noise at low blade-passage frequency remains a challenge. The present study investigates the noise reduction mechanism of a tensioned membrane housing device that directly controls the sound radiation from the doublet which is enclosed in an infinitely long duct with a point vortex. The time dependent sound radiation mechanism and the vibro-acoustics coupling mechanism of the systems are studied by adopting the potential theory and matched asymptotic expansion technique. The silencing performance of such a passive approach depends on the amplitude and phase of the sound field created by the doublet and the acoustic pressure induced by the membrane oscillation in order to achieve sound cancellation. Results show that the response of membrane vibration is strongly associated with the flow field induced by the grazing uniform flow and also the fluid loading generated by the inviscid vortex. The geometrical property of the cavity and the mechanical properties of the flexible membranes play important roles in controlling the performance of the proposed device. [ABSTRACT FROM AUTHOR]

It is for the first time that in three-dimensional granular cobaltites (La1-x Srx)1-yAgyCoO3 with a grain size of about 1 μm and replacement ratios x = 0.35 and y = 0, 0.05 a 'metal-nonmetal' conductivity transition was observed, presumably associated with the AFM ordering of granule moments. This transition manifests itself as a minimum in the temperature dependence of resistance of the samples. An explanation of the nature of the minimum is proposed, based on the intragranular mechanism of electron correlation on the basis of the Zener double-exchange and on the intergranular mechanism of spin-polarized electron tunneling between the nearest neighbors under the antiferromagnetic exchange interaction of granule moments. Numerical calculation of the system conductance is made via the model based on summation of intragranular phase conductivities of the electronic system and on the computation of the total impedance of the system as a sum of resistances of individual granules with a given resistive contribution of intergranular tunneling. It is found that the external magnetic field of up to 10 T does not affect the depth of the minimum and its position on the temperature scale, suggesting that the intergranular antiferromagnetic interaction is stable to external magnetic fields. [ABSTRACT FROM AUTHOR]

Single-phase PbPd0.81Co0.19O2 film with a body-centered orthorhombic structure was prepared using the sol-gel spin-coating technique and an oxidation treatment. Film resistivity has a power dependence on temperature. The insulator-metal transition temperature was 358 K, markedly higher than the reported values of similar material systems. Ferromagnetism and superparamagnetism coexisted in the film and the ferromagnetism persisted up to 380 K. As temperature increased, the notable increasing tendencies were found for the film's saturation magnetization and for the magnetic field where saturation magnetization decreases abruptly. The special spin gapless band structure and the film's nanograin microstructure are likely responsible for these interesting properties. [ABSTRACT FROM AUTHOR]

We propose to use magnetization-induced second harmonic generation (MSHG) technique to explore the magnetization reversal process of cobalt granular thin films. The three-dimensional magnetization reversal process can be visualized by analyzing the polarization dependent MSHG hysteresis curves. It is found that the magnetization reversal process involves not only the in-plane but also the out-plane magnetization rotation because of the uniaxial anisotropy of cobalt granular thin films. This study demonstrates that MSHG can be a versatile optical technique to investigate the magnetic property of not only ferromagnetic epitaxial thin films but also ferromagnetic granular thin films. [ABSTRACT FROM AUTHOR]

A single crystalline thin film of Ge on glass is fabricated using wafer bonding and smart cut. A simple metal-insulator-semiconductor detector is demonstrated for visible light and telecommunication wavelength. The implantation damage of separated Ge film bonded on glass is removed by chemical etching, and the surface roughness is reduced from 14 to 4 nm. The defect removal reduces the dark current by a factor of 30 and increases the responsivity by a factor of 1.85 at visible wavelength. The responsivity of 0.27 A/W at 1.3 μm wavelength for an unetched device does not increase after damage removal due to the decrease of the absorption layer thickness. [ABSTRACT FROM AUTHOR]

In this paper we study the impact of interatomic Coulombic decay (ICD) on molecular photodissociation. The investigation reveals the hitherto unrecognized ability of ICD to quench processes involving nuclear rearrangements. Numerical computations of the nuclear dynamics, initiated by photoexciting the B1Σ+ Rydberg state of CO in CO·Mg complexes, are carried out. The efficiencies of ICD and photoinduced predissociation are compared for the four lowest vibrational levels of the corresponding electronic state. We also show the impact of CO vibrations on the ICD electron spectrum. Finally, we discuss the growing efficiency of ICD to quench the dissociation as the number of neighboring Mg atoms is increased. [ABSTRACT FROM AUTHOR]

Thin films in the Bi-Sr-Ca-Cu-O system have been synthesized from homogeneous liquid citrate precursors by a spin-coating and pyrolysis method. Films prepared on SrTiO3 substrates of [100] orientation show strongly textured orientations with the c axis of the predominant Bi4 Sr3 Ca3 Cu4 O16+x phase normal to the film plane. In a single coating and firing, crack-free films of 0.2–0.5 μm thickness are obtained. For films fired to peak temperatures of 850–875 °C, linearly decreasing resistance with temperature is observed, with ρ (300 K)∼460 μΩ cm and ρ (300 K)/ρ (100 K)∼2.4. Clear onsets of superconductivity are observed at 90–100 K, with occasional films showing smaller resistant drops at 110–120 K. For all films, Tc (R=0) occurs in the range 70–75 K. High critical current densities at 4.2 K of 5–8×105 A/cm2 are measured by direct transport. [ABSTRACT FROM AUTHOR]

It is shown that unique defect thermodynamics and transport properties result for oxides of a few nanometers crystallite size. Fully-dense CeO2-x polycrystals of ∼10 nm grain size were synthesized, and their electrical properties compared with those of samples coarsened from the same material. The nanocrystals showed reduced grain boundary resistance, 104 higher electronic conductivity, and less than one-half the heat of reduction of its coarse-grained counterpart. These properties are attributed to a dominant role of interfacial defect formation. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A gait measurement system is a useful tool for rehabilitation applications. Such a system is used to conduct gait experiments in large workplaces such as laboratories where gait measurement equipment can be permanently installed. However, a gait measurement system should be portable if it is to be used in clinics or community centers for aged people. In a portable gait measurement system, the workspace is limited and landmarks on a subject may not be visible to the cameras during experiments. Thus, we propose a virtual-marker function to obtain positions of unseen landmarks for maintaining data consistency. This work develops a portable clinical gait measurement system consisting of lightweight motion capture devices, force plates, and a walkway assembled from plywood boards. We evaluated the portable clinic gait system with 11 normal subjects in three consecutive days in a limited experimental space. Results of gait analysis based on the verification of within-day and between-day coefficients of multiple correlations show that the proposed portable gait system is reliable. [ABSTRACT FROM AUTHOR]

This study examined the influence of background noise on the localization of lead-lag noise-burst pairs and on echo threshold for the same stimuli. Experiments were conducted in an anechoic chamber with a leading stimulus delivered from a loudspeaker at 45 degrees to the right of center and a lagging stimulus from 45 degrees left. Lead and lag stimuli were 4-ms bursts of Gaussian noise. In experiment 1, with lead and lag at equal levels and the lag delay fixed at 2 ms, the perceived location of the image produced by the lead-lag stimulus was estimated from subjects' left/right judgments relative to bursts from a "comparitor" loudspeaker whose position could be adjusted. In experiment 2, the dominance of the leading burst on perceived location was measured by determining the increase in level of the lagging burst necessary to produce an image estimated to be centered at 0 degree azimuth. Experiment 3 was concerned with echo threshold. Subjects reported whether or not they heard a sound in the vicinity of the lagging loudspeaker as the lag-burst delay was varied. In all three experiments, data were obtained for four to five stimulus levels in quiet and for three levels of background white noise from a loudspeaker at 180 degrees. The results revealed a substantial weakening effect of background noise on the precedence effect in experiments 2 and 3, and a nonsignificant effect in experiment 1.

Saberi and Perrott [Acustica 81, 272-275 (1995)] found that the in-head lateralization of a relatively long-duration pulse train could be controlled by the interaural delay of the single pulse pair that occurs at onset. The present study examined this further, using an acoustic pointer measure of lateralization, with stimulus manipulations designed to determine conditions under which lateralization was consistent with the interaural onset delay. The present stimuli were wideband pulse trains, noise-burst trains, and inharmonic complexes, 250 ms in duration, chosen for the ease with which interaural delays and correlations of select temporal segments of the stimulus could be manipulated. The stimulus factors studied were the periodicity of the ongoing part of the signal as well as the multiplicity and ambiguity of interaural delays. The results, in general, showed that the interaural onset delay controlled lateralization when the steady state binaural cues were relatively weak, either because the spectral components were only sparsely distributed across frequency or because the interaural time delays were ambiguous. Onset dominance can be disrupted by sudden stimulus changes within the train, and several examples of such changes are described. Individual subjects showed strong left-right asymmetries in onset effectiveness. The results have implications for understanding how onset and ongoing interaural delay cues contribute to the location estimates formed by the binaural auditory system.

Normal-hearing subjects' recognition of spectrally degraded speech was evaluated under conditions in which the consonant-vowel (C-V) intensity ratio was modified. Subjects identified 22 consonants presented in an /a-Consonant-a/ format at suprathreshold and near threshold conditions. Prior to C-V ratio modification, the stimuli were processed to limit spectral information. In the suprathreshold experiment, stimuli were presented at the natural C-V ratio and at six modified C-V ratios. C-V ratio manipulations had dramatic effects on recognition scores for some groups of consonants. Scores for glides and sibilant fricatives increased with increasing C-V ratio, while scores for nasals and weak fricatives were best at low C-V ratios. Recognition scores for the stops and affricates were generally independent of C-V ratio. For nearly all consonants, changes in recognition scores as a function of C-V ratio were associated with changes in a general response bias toward those sounds. Performance was poor when the spectrally smeared VCVs were presented at low SN ratios in a second experiment. The influence of C-V ratio on percent correct scores was generally similar to the suprathreshold results, but consonant audibility, which was not a factor in the suprathreshold experiment, appeared to alter the effect of C-V ratio modification for some consonants.