Ion acceleration by collisionless shocks in high-intensity-laser-underdense-plasma interaction

Ion acceleration by the interaction of an ultraintense short-pulse laser with an underdense-plasma has been studied at intensities up to 3 x 10(20) W/cm(2). Helium ions having a maximum energy of 13.2+/-1.0 MeV were measured at an angle of 100 degrees from the laser propagation direction. The maximum ion energy scaled with plasma density as n(0.70+/-0.05)(e). Two-dimensional particle-in-cell simulations suggest that multiple collisionless shocks are formed at high density. The interaction of shocks is responsible for the observed plateau structure in the ion spectrum and leads to an enhanced ion acceleration beyond that possible by the ponderomotive potential of the laser alone.     

Ultrafast all-optical demultiplexer based on monolithic Mach–Zehnder interferometer with integrated semiconductor optical amplifiers

A monolithically integrated and fully packaged Mach–Zehnder interferometer with semiconductor optical amplifiers (MZI-SOA) is demonstrated as polarisation-independent high-speed demultiplexer for up to 160 Gbit/s optical time division multiplexed (OTDM) data streams.     

Effect of chemical functionalization on the mechanical properties of polypropylene hollow fiber membranes

Chemical treatment of polymeric hollow fiber membranes (HFMs) is used to prepare their exterior surfaces for coatings. Typical treatments can cleave both C? C and C? H bonds of polypropylene, leading to lower mechanical strength of the fibers. This study evaluated the yield strength, maximum strain, ultimate tensile strength, and burst strength of HFMs treated with each of three common oxidizing reagents: ozone as a gas phase system, aqueous solutions of potassium persulfate, and ammonium persulfate for liquid phase systems. The yield strength and ultimate tensile strength of HFMs decreased continuously with increasing ozonation time. Batch treatments with aqueous oxidizing systems showed limiting values of the yield and ultimate tensile strengths with time. Swelling the hollow fibers with methanol prior to oxidation caused less reduction of the mechanical properties after persulfate treatment. Fibers pretreated with methanol showed lower losses of mechanical properties strength with aqueous oxidation systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1366–1373     

Calibration of otoacoustic emission probe microphones

Recently, investigators of otoacoustic emissions (OAEs) have shown interest in measuring OAEs to frequencies higher than 10 kHz. Most commercial instruments used to measure OAEs do not specify the microphone frequency response at higher frequencies, nor does their typically integrated design make it convenient to measure it. OAE probes manufactured by Etymotic Research have reasonably constant microphone sensitivity up to about 10 kHz and allow direct access to both the sound sources and microphone preamplifier output. A detailed procedure for calibrating the Etymotic Research OAE probe microphone to extend its usable frequency range to frequencies up to 20 kHz is described.     

Distortion-product otoacoustic emission suppression tuning curves in humans

Distortion-product otoacoustic emission (DPOAE) suppression data as a function of suppressor level (L(3)) for f(2) frequencies from 0.5 to 8 kHz and L(2) levels from 10 to 60 dB sensation level were used to construct suppression tuning curves (STCs). DPOAE levels in the presence of suppressors were converted into decrement versus L(3) functions, and the L(3) levels resulting in 3 dB decrements were derived by transformed linear regression. These L(3) levels were plotted as a function of f(3) to construct STCs. When f(3) is represented on an octave scale, STCs were similar in shape across f(2) frequency. These STCs were analyzed to provide estimates of gain (tip-to-tail difference) and tuning (Q(ERB)). Both gain and tuning decreased as L(2) increased, regardless of f(2), but the trend with f(2) was not monotonic. A roughly linear relation was observed between gain and tuning at each frequency, such that gain increased by 4-16 dB (mean ≈ 5 dB) for every unit increase in Q(ERB), although the pattern varied with frequency. These findings suggest consistent nonlinear processing across a wide frequency range in humans, although the nonlinear operation range is frequency dependent.     

Tone-burst-evoked otoacoustic emissions from normal-hearing subjects

Tone-burst-evoked otoacoustic emissions were measured as a function of tone-burst sound pressure level and frequency in normally hearing ears. Although the spectral and temporal properties varied across individual ears, there was a close correspondence between stimulus and response spectra. Both the spectral and latency characteristics of tone-burst-evoked emissions are consistent with the hypothesis that they are generated at sites along the cochlear partition corresponding to their frequency.     

A theoretical study of the 21Ag ← 11Ag two-photon transition and its vibronic band in trans-stilbene

The two-photon spectrum of the 2¹A_g ← 1¹A_g transition in trans-stilbene has been calculated at the complete active space self-consistent field (CASSCF) level of theory. Energies were obtained at the complete active space second-order perturbation (CASPT2) level of theory, while the geometries of both the initial and final states were optimized at the CASSCF level. The energy and the geometry optimizations were performed using an active space of 14 electrons in 14 active π orbitals. The vibrational frequencies of both states and the two-photon transition (TPT) cross-section were calculated with a smaller active space where the two lowest π orbitals were kept inactive. A newly implemented algorithm, in the quantum chemical package Molcas was used to determine the two-photon transition intensity. This method requires only the linear response of the CASSCF wavefunction. Furthermore, the vibronic structure of this TPT was studied. The Franck-Condon factors were obtained by calculating the overlap between the vibrational states involved, which were determined from the force fields of both the initial and final states, at the CASSCF level of theory. The results are in agreement with experiment.     

The ammonia dimer equilibrium dissociation energy: convergence to the basis set limit at the correlated level

The low-energy region of the intermolecular potential energy hypersurface (PES) of the ammonia dimer was studied at the level of second-order Moller-Plesset perturbation theory (MP2) using a very large basis set. Individual minima were located on the PES employing the counterpoise (CP) correction to account for the basis set superposition error (BSSE). Apart from these canonical MP2 calculations local MP2 (LMP2) calculations were performed. For the latter the BSSE at the correlated level is inherently absent by virtue of the local truncation of the virtual space. Results from canonical and local MP2 calculations are compared and the reliability of the LMP2 method for intermolecular complexes and clusters is discussed. The canonical MP2 calculations predicted five minimum structures, the four most stable ones lying energetically very close. For these four structures single point MP2 energy calculations with a further extended basis set (1024 functions for the ammonia dimer) were performed. The equilibrium dissociation energies so obtained are close to the one-particle basis set limit, as illustrated by a remaining BSSE of less than 0.2 kJ mol^?1. The geometry optimizations at the LMP2 level, using the three most stable canonical MP2 structures as initial geometries, all collapsed to a single minimum corresponding to an asymmetric structural arrangement. A canonical MP2 single point calculation, at that geometry, revealed that the LMP2 minimum structure is virtually as stable as the lowest minima on the canonical MP2 PES. Based on these calculations the global minimum of the ammonia dimer was assigned to a part of the PES represented by an asymmetric structure with an equilibrium dissociation energy of 13.5±0.3 kJ mol^?1     

Monte Carlo method for neutron spectrum recovery - a new approach based on the accelerated ions distribution

New method of neutron spectrum recovery described in the paper involves accelerated deuterons (that produce neutrons in DD reaction) and allows getting neutron spectrum in any direction from computed time-velocity characteristics of deuterons. Time of flight signals registered in various distances and directions are used, that makes information involved in the recovery process (Monte-Carlo simulation) more complete than in a one-directional case, although additional assumption about axial symmetry of deuterons motion, is required. In the paper recent results of two standard tests of the proposed method are presented demonstrating its capability to recover neutron spectrum from time-of-flight signals.     

Low-frequency and high-frequency distortion product otoacoustic emission suppression in humans

Distortion product otoacoustic emission suppression (quantified as decrements) was measured for f(2)=500 and 4000 Hz, for a range of primary levels (L(2)), suppressor frequencies (f(3)), and suppressor levels (L(3)) in 19 normal-hearing subjects. Slopes of decrement-versus-L(3) functions were similar at both f(2) frequencies, and decreased as f(3) increased. Suppression tuning curves, constructed from decrement functions, were used to estimate (1) suppression for on- and low-frequency suppressors, (2) tip-to-tail differences, (3) Q(ERB), and (4) best frequency. Compression, estimated from the slope of functions relating suppression "threshold" to L(2) for off-frequency suppressors, was similar for 500 and 4000 Hz. Tip-to-tail differences, Q(ERB), and best frequency decreased as L(2) increased for both frequencies. However, tip-to-tail difference (an estimate of cochlear-amplifier gain) was 20 dB greater at 4000 Hz, compared to 500 Hz. Q(ERB) decreased to a greater extent with L(2) when f(2)=4000 Hz, but, on an octave scale, best frequency shifted more with level when f(2)=500 Hz. These data indicate that, at both frequencies, cochlear processing is nonlinear. Response growth and compression are similar at the two frequencies, but gain is greater at 4000 Hz and spread of excitation is greater at 500 Hz.