Pitch ranking ability of cochlear implant recipients: a comparison of sound-processing strategies

Pitch ranking of sung vowel stimuli, separated in fundamental frequency (F0) by half an octave, was measured with a group of eleven Nucleus 24 cochlear implant recipients using different sound coding strategies. In three consecutive studies, either two or three different sound coding strategies were compared to the Advanced Combinational Encoder (ACE) strategy. These strategies included Continuous Interleaved Sampling (CIS), Peak Derived Timing (PDT), Modulation Depth Enhancement (MDE), F0 Synchronized ACE (FOSync), and Multi-channel Envelope Modulation (MEM), the last four being experimental strategies. While pitch ranking results on average were poor compared to those expected for most normal hearing listeners, significantly higher scores were obtained using the MEM, MDE, and FOSync strategies compared to ACE. These strategies enhanced coding of temporal F0 cues by providing deeper modulation cues to F0 coincidentally in time across all activated electrodes. In the final study, speech recognition tests were also conducted using ACE, CIS, MDE, and MEM. Similar results among all strategies were obtained for word tests in quiet and between ACE and MEM for sentence tests in noise. These findings demonstrate that strategies such as MEM may aid perception of pitch and still adequately code segmental speech features as per existing coding strategies.     

Intrinsic toroidal rotation, density peaking, and turbulence regimes in the core of tokamak plasmas

Observations in the ASDEX Upgrade tokamak show a correlation between the gradient of the intrinsic toroidal rotation profile and the logarithmic gradient of the electron density profile. The intrinsic toroidal rotation in the center of the plasma reverses from co- to countercurrent when the logarithmic density gradients are large, and the turbulence is either dominated by trapped electron modes or is at the transition between ion temperature gradient and trapped electron modes. A study based on local gyrokinetic calculations suggests that the dominant trend in the observations can be explained by the combination of residual stresses produced by E × B and profile shearing mechanisms.     

Stability of a 95-GHz slotted third-harmonic gyro-TWT amplifier

A low-magnetic-field moderate-voltage gyrotron amplifier has been designed for stable high-performance operation at 95 GHz. A slotted interaction circuit is utilized to achieve strong amplification near the third cyclotron harmonic frequency. The start-oscillation conditions were determined by an analytical theory and confirmed by a multimode particle-in cell simulation code. The dominant threat to the amplifier's stability is from a third-harmonic peniotron backward-wave interaction. A slow-timescale particle-tracing simulation code predicts the three-section slotted third-harmonic gyro-TWT, which utilizes an 11.6-kG magnet and a 50-kV 3-A υ_⊥/υ_z=1.4 axis-encircling electron beam with an axial velocity spread of 6% will yield an output power of 30 kW with an efficiency of 20%, a saturated gain of 40 dB, and a constant-drive bandwidth of 2%     

High-p jets in diffractive electroproduction

The diffractive production of high-p jets in deep-inelastic scattering is studied in the semiclassical approach. The p-spectra of and diffractive final states are found to be qualitatively different. For fina states, which are produced by ‘hard’ colour-singlet exchange, the p-spectrum is much softer than for final states, where the colour neutralization is ‘soft’. Furthermore, the two different final states can be clearly distinguished by their diffractive mass distributions.     

35-GHz 25-kW CW low-voltage third-harmonic gyrotron

A 50-kV third-harmonic gyrotron is shown to be capable of high efficiency. Operation at the third harmonic allows the required magnetic field for 35 GHz generation to be supplied by a 4.5-kG permanent magnet. Two gyrotrons employing sliced circuits for mode control have been evaluated with a large-signal nonself-consistent particle-tracing simulation code and found to be capable of producing 25 kW continuously. The preliminary design of a third-harmonic TE₄₁ gyrotron utilizing a magnetron injection electron gun is predicted to yield a device efficiency of 17%, which can potentially be increased to 46% with an ideal single-stage depressed collector, while an axis-encircling electron beam from a Cusp electron gun is predicted to drive a third-harmonic TE₃₁ gyrotron with a device efficiency of 23%, which can theoretically be increased to 45% through the use of an ideal depressed collector     

Silicone polycarbonates from new aryl-terminated siloxane precursors

Several synthetic routes to silicon polycarbonate copolymers utilizing aryl-terminated siloxanes have been examined. Anhydride capped siloxanes with varying polydimethylsiloxane units were prepared by the acid equilibration of 1,3-bis(4,4′-phthalicanhydride)tetramethyldisiloxane. These siloxanes were then imidized with aminophenol to the corresponding phenol capped siloxane. Reaction of these materials with 4,4′-isopropylidenediphenol (BPA) and phosgene (interfacially and non-interfacially) produced silicone polycarbonate copolymers. Similar copolymers were obtained by reaction with bis-chloroformate derivatives of 4,4′-isopropylidenediphenol (monomer and oligomers). The different synthetic routes significantly affect the thermal and mechanical properties as well as the composition of the new polymers. Materials synthesized by the bis-chloroformate route exhibit good hydrolytic and melt stabilities. Those made interfacially underwent phase separation in the melt.     

Dielectric-loaded wideband gyro-TWT

The bandwidth of a gyro-TWT (traveling-wave tube) can be widened by employing a dielectric-loaded waveguide to reduce the circuit's dispersion. Fast wave interaction allows the requirements on the beam's quality to be relaxed compared with slow wave interaction. A low-α (≡ν_⊥/ν_z) electron beam is chosen to avoid the absolute instability and minimize the possibility of dielectric charging. This device is investigated using a self-consistent single-mode, large-signal simulation based on a slow time scale formulation. Simulation results show that a constant drive bandwidth of 20% can be achieved for a 100 kV, 5 A electron beam with a velocity ratio of α=0.59 and an axial velocity spread of 2.0%. The growth rate is relatively low because of the low α of the electron beam. The design of a proof-of-principle experiment is described. The tube is expected to deliver a power of 80 kW from 9 to 11 GHz with 15% efficiency and a saturated gain of 30 dB. The performance of a single-anode magnetron injection gun designed to produce the required high-quality electron beam has been studied through simulation