Effect of stimulus level and place of stimulation on temporal pitch perception by cochlear implant users

Three experiments studied the effect of pulse rate on temporal pitch perception by cochlear implant users. Experiment 1 measured rate discrimination for pulse trains presented in bipolar mode to either an apical, middle, or basal electrode and for standard rates of 100 and 200 pps. In each block of trials the signals could have a level of -0.35, 0, or +0.35 dB re the standard, and performance for each signal level was recorded separately. Signal level affected performance for just over half of the combinations of subject, electrode, and standard rate studied. Performance was usually, but not always, better at the higher signal level. Experiment 2 showed that, for a given subject and condition, the direction of the effect was similar in monopolar and bipolar mode. Experiment 3 employed a pitch comparison procedure without feedback, and showed that the signal levels in experiment 1 that produced the best performance for a given subject and condition also led to the signal having a higher pitch. It is concluded that small level differences can have a robust and substantial effect on pitch judgments and argue that these effects are not entirely due to response biases or to co-variation of place-of-excitation with level.     

Growth and analysis of octadecylsiloxane monolayers on Al2O3 (0001)

On solvent-cleaned and piranha-etched single-crystal Al2O3(0001) surfaces, uniform, robust, self-assembled monolayers of octadecylsiloxane (ODS) are formed by 48 h exposure to a solution containing octadecyltrichlorosilane (OTS) in an anhydrous atmosphere. X-ray photoelectron spectroscopy, atomic force microscopy, ellipsometry, and water contact angle measurements confirm the presence of a uniform, complete monolayer. Reducing the exposure time or omitting the piranha-etch leads to much less uniform coverage. The ODS monolayers are stable when stored in ambient atmospheres for month-long periods. Thermal desorption in a vacuum environment (10(-9) Torr) shows the ODS monolayer is thermally stable up to at least 420 K. When heated in 200 mTorr of flowing forming gas (N2-10% H2) for 1 h at 520 K, slow loss of ODS was indicated. A schematic model is proposed which involves island nucleation by covalent bonding of OTS to surface hydroxyl groups followed by growth through the addition of mobile ODS species.     

The electronic states of carbon monofluoride: Rydberg states

Hartree-Fock and multiconfiguration Hartree-Fock calculations are reported on some low-lying Rydberg states of CF and the ground state of CF⁺. For the CF⁺ ground state, ¹Σ⁺, the calculations give a bond length of 1.55 Å, a fundamental frequency of 1821 cm^?1, and a dissociation energy of 6.9 eV. Many interactions between the valence and Rydberg state manifolds are revealed. Also a strong mixing of the 3dσ and 4sσ components due to an accidental degeneracy is described.     

Polarized pp physics with internal jet targets at RHIC

The physics scope of RHIC could be extended to include fixed target experiments by the addition of a gas jet target. Two applications stand out among many possibilities. RHIC is the first accelerator to provide polarized proton beams with energy above 30 GeV. Extensive studies of pp colliding beams are planned for RHIC, but these will not cover the energy range covered with a fixed target, where the scattering of polarized protons from protons has not been adequately studied. Another important application is the possible use of a hydrocarbon jet to obtain a rapid and precise measurement of the polarization of the RHIC proton beams. A gas jet target with associated recoil detectors, electronics, and vacuum pumps is available and can be installed with low incremental costs on a short time scale.     

Reduced magnetic disorder at low temperature in Ca3Co2O6 via zinc substitution

ABSTRACT

The compound Ca₃Co₂O₆ undergoes a transition into a spin-density wave (SDW) state near 24?K. Below ～10?K, this unstable SDW state coexists with a nearly- degenerate commensurate antiferromagnetic state as well as short-range magnetic order. Clear signatures of this strong magnetic disorder have been observed in the response of entropy to changing magnetic field and temperature. We performed a calorimetry study of Ca₃Co₂O₆ and Ca₃Co_1.9Zn_0.1O₆ in order to compare their entropic responses at low temperature. Our results for Ca₃Co₂O₆ reveal that ΔS(T, H)?≡?S(T, H)?S(T, H?=?0) increases as either temperature or magnetic field increase. In contrast, ΔS data for Ca₃Co_1.9Zn_0.1O₆ were relatively unresponsive to changes in temperature or field, suggesting that Zn substitution may reduce the low-temperature magnetic disorder observed in Ca₃Co₂O₆. These results are discussed within the context of two cases (Ca₃Co₂O₆ under applied pressure and Ca_2.75R_0.25Co₂O₆ (R?=?Dy, Lu)) in which a single magnetic ground state is stabilised.     

Heat transfer during the melting of ice around a horizontal,isothermal cylinder

An experimental investigation of the melting of ice around a horizontal, isothermal cylinder is performed. Emphasis is placed on interpreting the heat transfer mechanisms which control solid-liquid interface position. Flow visualization and interferometric techniques are employed to study the transient flow patterns and corresponding temperature distributions in the melted region. It has been determined that density inversion plays an important role in the melting of water. The location of the maximum density surface in the liquid has a significant effect on natural convection, and hence on the shape and size of the melted region. Local Nusselt numbers at the surface of the cylinder and at the solid-liquid interface are determined and found to be complicated functions of time and imposed thermal conditions. Average Nusselt numbers at the solid-liquid interface and at the surface of the cylinder decrease with time and quasi-steady conditions are not reached.     

Rheological characterization of a solder paste for surface mount applications

Solder pastes used in surface mount soldering techniques (SMT) are very complex suspensions containing high volumes of metallic powder in a carrier fluid. The rheological complexity results largely from the carrier fluid itself, which is a suspension of colloidal particles. In this work, we have characterized the rheological properties of a typical carrier fluid and its solder paste containing 64 vol.% metallic powder. A six-blade vane geometry was used to avoid wall slip and sample fracture. All measurements were carried out following pre-shearing and rest time in order to obtain reproducible results. Steady shear experiments showed that the solder paste was highly shear-thinning and thixotropic. In oscillatory shear, the linear viscoelastic domain was found to be very narrow for both the suspending fluid and the paste. Frequency sweep tests in the linear domain revealed a gel-like structure with a nearly constant G′ for the suspending fluid and a slightly increasing G′ for the solder paste. From creep experiments, a yield stress of about 40 Pa was determined for the suspending fluid at temperatures between 25 and 40°C, and of 100 Pa at 4°C. A much larger yield stress, 480 Pa, was determined for the solder paste at 25°C.