Dispersion of surface plasmons in dielectric-metal coatings on concave diffraction gratings

Anomalies in the intensity ofp-polarized light from concave diffraction gratings (Wood's anomalies) have been used to obtain surface plasmon dispersion curves for dielectric-metal layers on the grating surface. These include a 350 Å MgF₂ layer and Al₂O₃ layers varying from a few angstroms to over 800 Å on an Al substrate. The wavelength range of the incident and diffracted light is from the visible to the vacuum ultraviolet (7,500?500 Å). Anomalous polarization peaks for Al₂O₃ layers in the vacuum ultraviolet (at ～ 1,600 Å) are shown to shift significantly to longer wavelengths for only a few angstroms (up to 50 Å) of oxide thickness, while for thicknesses greater than ～ 50 Å any further shift is small. In the visible region (> 4,000 Å), on the other hand, the wavelength shifts are small for dielectric thicknesses up to ～ 50 Å, but are large for thicknesses of several hundred angstroms. These results are in substantial agreement with the theoretical dispersion curves for these cases. Also considered are some of the effects of diffusion pump oil.     

Perception of sentences, words, and speech features by profoundly hearing-impaired children using a multichannel electrotactile speech processor

Fourteen prelinguistically profoundly hearing-impaired children were fitted with the multichannel electrotactile speech processor (Tickle Talker) developed by Cochlear Pty. Ltd. and the University of Melbourne. Each child participated in an ongoing training and evaluation program, which included measures of speech perception and production. Results of speech perception testing demonstrate clear benefits for children fitted with the device. Thresholds for detection of pure tones were lower for the Tickle Talker than for hearing aids across the frequency range 250-4000 Hz, with the greatest tactual advantage in the high-frequency consonant range (above 2000 Hz). Individual and mean speech detection thresholds for the Ling 5-sound test confirmed that speech sounds were detected by the electrotactile device at levels consistent with normal conversational speech. Results for three speech feature tests showed significant improvement when the Tickle Talker was used in combination with hearing aids (TA) as compared with hearing aids along (A). Mean scores in the TA condition increased by 11% for vowel duration, 20% for vowel formant, and 25% for consonant manner as compared with hearing aids alone. Mean TA score on a closed-set word test (WIPI) was 48%, as compared with 32% for hearing aids alone. Similarly, mean WIPI score for the combination of Tickle Talker, lipreading, and hearing aids (TLA) increased by 6% as compared with combined lipreading and hearing aid (LA) scores. Mean scores on open-set sentences (BKB) showed a significant increase of 21% for the tactually aided condition (TLA) as compared with unaided (LA). These results indicate that, given sufficient training, children can utilize speech feature information provided through the Tickle Talker to improve discrimination of words and sentences. These results indicate that, given sufficient training, children can utilize speech feature information provided through the Tickle Talker to improve discrimination of words and sentences. These results are consistent with improvement in speech discrimination previously reported for normally hearing and hearing-impaired adults using the device. Anecdotal evidence also indicates some improvements in speech production for children fitted with the Tickle Talker.     

Spontaneous symmetry breaking in large scale nervous activity

A theory is outlined of the nature and origin of drug-induced visual hallucination patterns. It is shown that such patterns correspond to blobs or stripes of visual neo-cortical activity. A neuronal circuit is described that generates such patterns whenever its homogeneous resting state becomes unstable. Such a process is shown to be an example of spontaneous symmetry-breaking, similar to that occurring in electro-weak interactions, and in fluid convection. It is suggested that the neuronal instability is produced by the action of hallucinogens on monoamine secreting brain-stem neurons.     

Preliminary evaluation of a multichannel electrotactile speech processor

Speech discrimination testing, using both open- and closed-set materials, was carried out with four severely to profoundly hearing impaired adults and seven normally hearing subjects to assess performance of a wearable eight-channel electrotactile aid (Tickle Talker). Significant increases in speechtracking rates were noted for all subjects when using the electrotactile aid. After 70 h of training, mean tracking rate in the tactile plus lipreading condition was 55 words per minute (wpm), as compared with 36 wpm for lipreading alone, for the normally hearing group. For the hearing impaired group, the mean tracking rate in the aided condition was 37 wpm, as compared with 24 wpm for lipreading alone, following 35 h of training. Performance scores on Central Institute for the Deaf (CID) everyday sentences, Consonant Nucleus Consonant (CNC) words, and closed-set vowel and consonant identification were significantly improved when using the electrotactile aid. Performance scores, using the aid without lipreading, were well above chance on consonant and vowel identification and on elements of the Minimal Auditory Capabilities Battery. Two hearing impaired subjects have used the device satisfactorily in the home environment.     

Development of a pure cryogenic positron plasma using a LINAC positron source

The development of a high density cryogenic pure positron plasma trap at the LLNL positron beam facility opens new possibilities for antihydrogen research. We discuss a planned measurement of the three-body collisional recombination rate in magnetized plasmas, a possible antihydrogen atomic beam experiment, and other applications of pure positron plasmas.     

Far infrared photoconductivity of TTF-TCNQ

The spectral dependence of the far-infrared photoconductivity of TTF-TCNQ at low temperatures shows an interband transition with an edge at approximately 22 meV. We associate this gap with the d.c. conductivity maximum near 70 K, and suggest that at least two distinct mean-field transition temperatures are important for the observed electrical and magnetic properties of the material.     

Photonuclear fission from high energy electrons from ultraintense laser-solid interactions

A new regime of laser-matter interactions in which the quiver motion of plasma electrons is fully relativistic, with energies extending well above the threshold for nuclear processes, is studied using a petawatt laser system. In solid target experiments with focused intensities exceeding 10(20) W/cm(2), high energy electron generation, hard bremsstrahlung, and nuclear phenomena have been observed. We report here a quantitative comparison of the high energy electrons and the bremsstrahlung spectrum, as measured by photonuclear reaction yields, including the photoinduced fission of 238U.     

Overcoming Fundamental Limitations in Adsorbent Design: Alkene Adsorption by Non-porous Copper(I) Complexes

Purifying alkenes from alkanes requires cryogenic distillation. This consumes energy equivalent to countries of ca. 5 million people. Replacing distillation with adsorption processes would significantly increase energy efficiency. Trade-offs between kinetics, selectivity, capacity, and heat of adsorption have prevented production of an optimal adsorbent. We report adsorbents that overcome these trade-offs. [Cu-Br]₃ and [Cu-H]₃ are air-stable trinuclear complexes that undergo reversible solid-state inter-molecular rearrangements to produce dinuclear [Cu-Br⋅(alkene)]₂ and [Cu-H⋅(alkene)]₂ . The reversible solid-state rearrangement, confirmed in situ using powder X-ray diffraction, allows adsorbent design trade-offs to be overcome, coupling low heat of adsorption (−10 to −17 kJ mol⁻¹_alkene), high alkene:alkane selectivity (47; 29), and uptake capacity (>2.5 mol_alkene mol⁻¹_Cu3). Most remarkably, [Cu-H]₃ displays fast uptake and regenerates capacity within 10 minutes.     

Regularity of semi-stable solutions to fourth order nonlinear eigenvalue problems on general domains

We examine the fourth order problem $\Delta ^2 u = \lambda f(u) $ in $ \Omega $ with $ \Delta u = u =0 $ on $ {\partial \Omega }$ , where $ \lambda > 0$ is a parameter, $ \Omega $ is a bounded domain in $\mathbb{R }^N$ and where $f$ is one of the following nonlinearities: $ f(u)=e^u$ , $ f(u)=(1+u)^p $ or $ f(u)= \frac{1}{(1-u)^p}$ where $ p>1$ . We show the extremal solution is smooth, provided $$\begin{aligned} N < 2 + 4 \sqrt{2} + 4 \sqrt{ 2 - \sqrt{2}} \approx 10.718 \text{ when} f(u)=e^u, \end{aligned}$$ and $$\begin{aligned} N < \frac{4p}{p-1} + \frac{4(p+1)}{p-1} \left( \sqrt{ \frac{2p}{p+1}} + \sqrt{ \frac{2p}{p+1} - \sqrt{ \frac{2p}{p+1}}} - \frac{1}{2} \right) \end{aligned}$$ when $ f(u)=(u+1)^p$ . New results are also obtained in the case where $ f(u)=(1-u)^{-p}$ . These are substantial improvements to various results on critical dimensions obtained recently by various authors. To do that, we derive a new stability inequality satisfied by minimal solutions of the above equation, which is more amenable to estimates as it allows a method of proof reminiscent of the second order case.