Detection and discrimination of spectral peaks and notches at 1 and 8 kHz

The ability of subjects to detect and discriminate spectral peaks and notches in noise stimuli was determined for center frequencies fc of 1 and 8 kHz. The signals were delivered using an insert earphone designed to produce a flat frequency response at the eardrum for frequencies up to 14 kHz. In experiment I, subjects were required to distinguish a broadband reference noise with a flat spectrum from a noise with either a peak or a notch at fc. The threshold peak height or notch depth was determined as a function of bandwidth of the peak or notch (0.125, 0.25, or 0.5 times fc). Thresholds increased with decreasing bandwidth, particularly for the notches. In experiment II, subjects were required to detect an increase in the height of a spectral peak or a decrease in the depth of a notch as a function of bandwidth. Performance was worse for notches than for peaks, particularly at narrow bandwidths. For both experiments I and II, randomizing (roving) the overall level of the stimuli had little effect at 1 kHz, but tended to impair performance at 8 kHz, particularly for notches. Experiments III-VI measured thresholds for detecting changes in center frequency of sinusoids, bands of noise, and spectral peaks or notches in a broadband background. Thresholds were lowest for the sinusoids and highest for the peaks and notches. The width of the bands, peaks, or notches had only a small effect on thresholds. For the notches at 8 kHz, thresholds for detecting glides in center frequency were lower than thresholds for detecting a difference in center frequency between two steady sounds. Randomizing the overall level of the stimuli made frequency discrimination of the sinusoids worse, but had little or no effect for the noise stimuli. In all six experiments, performance was generally worse at 8 kHz than at 1 kHz. The results are discussed in terms of their implications for the detectability of spectral cues introduced by the pinnae.     

Adsorption and solution of H2 and N2 by Ta and Nb

The condensation and desorption kinetics of H₂ and N₂ on polycrystalline wires of Ta and Nb are examined for solute concentrations between 0.1 and 100 monolayers. Accurate comparisons of adsorbate densities and sticking coefficients on Ta, Nb, Mo and W are obtained by making simultaneous measurements on all four substrates in the same vacuum system. Desorption exhibits second order kinetics for all substrates at all coverages. Desorption activation energies are higher on Ta and Nb than on W and Mo for both gases. Diffusion limited desorption is observed for H₂ at high heating rates. Solution of H₂ occurs at measurable rates (s ? 0.01) in Ta and Nb even at 78 °K while for N₂ no solution is observed for T < 600 °K.     

Temporal and spectral masking release in low- and mid-frequency regions for normal-hearing and hearing-impaired listeners

"Masking release" (MR), the improvement of speech intelligibility in modulated compared with unmodulated maskers, is typically smaller than normal for hearing-impaired listeners. The extent to which this is due to reduced audibility or to suprathreshold processing deficits is unclear. Here, the effects of audibility were controlled by using stimuli restricted to the low- (≤1.5 kHz) or mid-frequency (1-3 kHz) region for normal-hearing listeners and hearing-impaired listeners with near-normal hearing in the tested region. Previous work suggests that the latter may have suprathreshold deficits. Both spectral and temporal MR were measured. Consonant identification was measured in quiet and in the presence of unmodulated, amplitude-modulated, and spectrally modulated noise at three signal-to-noise ratios (the same ratios for the two groups). For both frequency regions, consonant identification was poorer for the hearing-impaired than for the normal-hearing listeners in all conditions. The results suggest the presence of suprathreshold deficits for the hearing-impaired listeners, despite near-normal audiometric thresholds over the tested frequency regions. However, spectral MR and temporal MR were similar for the two groups. Thus, the suprathreshold deficits for the hearing-impaired group did not lead to reduced MR.     

Pitch discrimination and phase sensitivity in young and elderly subjects and its relationship to frequency selectivity.

Frequency difference limens for pure tones (DLFs) and for complex tones (DLCs) were measured for four groups of subjects: young normal hearing, young hearing impaired, elderly with near-normal hearing, and elderly hearing impaired. The auditory filters of the subjects had been measured in earlier experiments using the notched-noise method, for center frequencies (fc) of 100, 200, 400, and 800 Hz. The DLFs for both impaired groups were higher than for the young normal group at all fc's (50-4000 Hz). The DLFs at a given fc were generally only weakly correlated with the sharpness of the auditory filter at that fc, and some subjects with broad filters had near-normal DLFs at low frequencies. Some subjects in the elderly normal group had very large DLFs at low frequencies in spite of near-normal auditory filters. These results suggest a partial dissociation of frequency selectivity and frequency discrimination of pure tones. The DLCs for the two impaired groups were higher than those for the young normal group at all fundamental frequencies (fo) tested (50, 100, 200, and 400 Hz); the DLCs for the elderly normal group were intermediate. At fo = 50 Hz, DLCs for a complex tone containing only low harmonics (1-5) were markedly higher than for complex tones containing higher harmonics, for all subject groups, suggesting that pitch was conveyed largely by the higher, unresolved harmonics. For the elderly impaired group, and some subjects in the elderly normal group, DLCs were larger for a complex tone with lower harmonics (1-12) than for tones without lower harmonics (4-12 and 6-12) for fo's up to 200 Hz. Some elderly normal subjects had markedly larger-than-normal DLCs in spite of near-normal auditory filters. The DLCs tended to be larger for complexes with components added in alternating sine/cosine phase than for complexes with components added in cosine phase. Phase effects were significant for all groups, but were small for the young normal group. The results are not consistent with place-based models of the pitch perception of complex tones; rather, they suggest that pitch is at least partly determined by temporal mechanisms.     

Gain and bandwidth of the gyro-TWT and CARM amplifiers

Issues concerning the interpretation of gain and bandwidth from the dispersion relation are examined for the gyrotron traveling wave tube (gyro-TWT) and the cyclotron auto-resonance maser (CARM) amplifiers. A general method for the determination of the critical current for oscillation is illustrated. Despite the broad bandwidth predicted for the CARM amplifier by the commonly employed dispersion relation, it is seen in particle simulation that single-particle interaction. Rather than collective amplification, prevails over much of the band. Reasons for the discrepancy are analyzed     

Experimental and computational investigation of extinction and autoignition of propane and n-heptane in nonpremixed flows

An experimental and computational investigation is carried out to characterize the influence of reactants on critical conditions for extinction and for autoignition of propane and n-heptane in nonpremixed counterflow configurations. Propane or vaporized n-heptane mixed with nitrogen is transported in one stream while the other stream is made up of air mixed with nitrogen. Measurements of the oxidizer stream temperature needed for autoignition are made at fixed values of the strain rate, either with the fuel mass fraction varied at a fixed oxygen mass fraction or with the oxygen mass fraction varied at a fixed fuel mass fraction. Extinction strain rates for propane are measured as a function of the oxygen mass fraction with room-temperature feed streams and the fuel mass fraction fixed and for n-heptane as a function of the fuel mass fraction with the oxygen mass fraction and feed-stream temperatures fixed. Predictions of critical conditions for extinction and autoignition are made employing detailed kinetic mechanisms. Predictions of critical conditions for extinction are in reasonable agreement with measurements, but there are significant discrepancies for autoignition. Measurements show that increasing the mass fraction of either fuel or oxygen increases the overall reactivity thereby reducing the autoignition temperature. The kinetic models predict the increase in reactivity of the mixing layer with increasing mass fraction of fuel but predict very little change in reactivity of the mixing layer with increasing mass fraction of oxygen, thus failing to predict the influence of oxygen on autoignition. It is concluded that there may exist kinetic pathways responsible for this disagreement that are yet to be discovered, and paths that fail to explain the results are identified.     

Divergence- and Curl-Preserving Prolongation and Restriction Formulas

We present new second-order prolongation and restriction formulas which preserve the divergence and, in some cases, the curl of a discretized vector field. The formulas are suitable for adaptive and hierarchical mesh algorithms with a factor-of-2 linear resolution change. We examine both staggered and collocated discretizations for the vector field on two- and three-dimensional Cartesian grids. The new formulas can be used in combination with numerical schemes that require a divergence-free solution in some discrete sense, such as the constrained transport schemes of computational magnetohydrodynamics. We also obtain divergence-preserving interpolation functions which may be used for streamline or field line tracing.     

XeI and XeII radiative lifetimes and transition probabilities

The lifetimes of ten levels of the xenon atom and two levels of the ion were measured. The probabilities for several transitions are calculated. The effective decay cross section is calculated for collisions for the 2p₈ level of the xenon atom.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp.24–29, March, 1971.The authors thank V. S. Mel'chenko for assistance in this study.     

激光功率和能量计量技术的现状与展望

功率和能量是激光器的两个基本参数,激光功率和能量测量一直是激光参数计量中最基础的测量工作.总结了美国标准技术研究院(NIST)、英国国家物理实验室(NPL)以及中国国家计量院(NIM)在激光功率能量计量方面的技术现状,重点介绍了国防科工委光学计量一级站激光功率能量计量方面已具备的条件,详细说明了所采用的测量原理以及所达到的测量范围和测量不确定度等技术指标.提出了激光功率和能量计量的发展趋势和发展方向.     

Frequency and intensity discrimination in humans and monkeys

Frequency and intensity DLs were compared in humans and monkeys using a repeating standard "yes-no" procedure in which subjects reported frequency increments, frequency decrements, intensity increments, or intensity decrements in an ongoing train of 1.0-kHz tone bursts. There was only one experimental condition (intensity increments) in which monkey DLs (1.5-2.0 dB) overlapped those of humans (1.0-1.8 dB). For discrimination of both increments and decrements in frequency, monkey DLs (16-33 Hz) were approximately seven times larger than those of humans (2.4-4.8 Hz), and for discrimination of intensity decrements, monkey DLs (4.4-7.0 dB) were very unstable and larger than those of humans (1.0-1.8 dB). For intensity increment discrimination, humans and monkeys also exhibited similar DLs as SL was varied. However, for frequency increment discrimination, best DLs for humans occurred at a high (50 dB) SL, whereas best DLs for monkeys occurred at a moderate (30 dB) SL. Results are discussed in terms of various neural mechanisms that might be differentially engaged by humans and monkeys in performing these tasks; for example, different amounts of temporal versus rate coding in frequency discrimination, and different mechanisms for monitoring rate decreases in intensity discrimination. The implications of these data for using monkeys as models of human speech sound discrimination are also discussed.     

Structure and magnetism of neutral and anionic palladium clusters

The properties of neutral and anionic Pd(N) clusters were investigated with spin-density-functional calculations. The ground-state structures are three dimensional for N>3 and they are magnetic with a spin triplet for 2 < or = N < or = 7 and a spin nonet for N = 13 neutral clusters. Structural and spin isomers were determined and an anomalous increase of the magnetic moment with temperature is predicted for a Pd7 ensemble. Vertical electron detachment and ionization energies were calculated and the former agrees well with measured values for Pd(-)(N).     

Theorems connecting surface energies and electrostatic potentials of finite and semi-infinite jellia and cavities

A Pauli-Hellmann-Feynman theorem for finite neutral jellia derived in an earlier paper by the authors and connecting energy and electrostatic potential with each other is generalized to the case of non-neutral systems and is shown to split into two theorems. For an arbitrary cavity in an otherwise homogeneous jellium a general theorem is derived. Theorems for cavities with special symmetry (void, tube, slit) are compared with each other and with theorems for corresponding jellia (sphere, wire, slab).     

Generalized Brillouin theorem and generalized forces in SCF and MC SCF theories and their Hartree-Fock limits

A formula for the change of energy is derived, valid for any infinitesimal change of the hamiltonian and the wave function in CI, SCF and MC SCF theories. A general form of MC Hartree-Fock equations is derived in a somewhat new form. A closed MC theory is defined and a condition of self-consistency is derived for this theory. The role of deorthogonalization of spin orbitals is discussed. The Hellmann-Feynman theorem and the generalized Brillouin theorem are rederived in a unique and simple way. It is shown that in the case of the closed MC SCF theory the Brillouin theorem derived by Levy and Berthier can be strengthened.

Formulae for generalized forces are derived, valid for closed-shell, openshell and multiconfigurational SCF theories also far from the Hartree-Fock limit.     

黑克、布劳、及伯曼-温采尔代数的诱导及分导系数和量子经典李代数的耦合与重新耦合系数

本文总结了计算黑克、布劳、及伯曼 温采尔代数在各种工数链下诱导及分导系数的线性方程方法(LEM)。特别强调了关于A,B,C,D型李代数及其量子情形与其中心代数之间的舒尔 魏尔 布劳双关性关系。这一关系使我们能够利用相应中心代数的诱导及分导系数计算出经典李代数及其量子情形的耦合与重新耦合系数。讨论了从该方法得到B,C,D型李代数不可约表示克罗内克积分解的应用。基于LEM还得到了处理对应于置换群CG系列问题的黑克代数张量积的方法。     

Consistent and covariant anomalies in gauge and gravitational theories

The gauge structure of anomalies and the related currents is analyzed in detail. We construct the covariant forms for both the currents and the anomalies for general gauge theories in even-dimensional space-time. The results are then extended to determine the structure of gravitational anomalies. These can always be interpreted as anomalies for local Lorentz transformations.     

Single and double ionization of neon 2s- and 2p-subshells by proton and electron impact

Absolute single and double ionization cross sections of neon 2s- and 2p-subshells for proton (40–900 keV) and electron impact (0.2–10 keV) have been measured using photon spectroscopy in the spectral range of the vacuum ultraviolet. Cross sections for double ionization decrease more rapidly with increasing impact energy than cross sections for single ionization. No definite asymptotic energy dependence of a Bethe-Fano-plot could be found for double ionization in contrast to single ionization. The experimental results are compared with theoretical predictions of the shake-off model and Gryzinski's classical binary encounter theory. Better agreement is found with the latter, indicating that successive binary collisions have to be considered as a strong mechanism for double ionization by protons or electrons of the investigated energy range. Comparison is made with other experimental results for double ionization by photon impact or capture ionization by proton impact.     

Conductance and Statistical Properties of Chaotic and Integrable Electron Waveguides

We show that the S-matrix for electrons propagating in a waveguide has different statistical properties depending on whether the waveguide cavity shape gives rise to chaotic or integrable behavior classically. We obtain distributions of energy level spacings for integrable and chaotic billiards shaped like the waveguide cavity. We also obtain distributions for Wigner delay times and resonance widths for the waveguide, for integrable and chaotic cavity geometries. Our results, obtained by direct numerical calculation of the electron wave function, are consistent with the predictions of random matrix theory.     

Description and application of an intense and short diagnostic source between 1000 and 1600 nm

We describe a possibility to obtain by a mode-locked YAG neodynium laser and a simple Raman conversion into O₂ and NO gas, a very fast and intense source for diagnosis centered on convenient wavelength (1060-1300-1600 nm) which allows to characterize devices used for optical fiber systems or for iodine laser.     

Polarization and spin effects in neutralino production and decay

We study the production of neutralinos with polarized beams and the subsequent decays and , including the complete spin correlations between production and decay. We present analytical formulae for the differential cross section of the combined process of production and decay of neutralinos. We also allow for complex couplings. The spin correlations have a strong influence on the decay angular distributions and the corresponding forward–backward asymmetries. They are very sensitive to the SUSY parameters and depend strongly on the beam polarizations. We present numerical results for the cross section and the electron forward–backward asymmetry for , . We study the dependence on the parameter for various mass splittings between and and different beam polarizations. Received: 28 March 1999 / Published online: 28 May 1999     

Modeling coevolution and sympatric speciation of flowers and pollinators

A model based on quantitative genetics for the coevolution of plants and their pollinators is proposed. The model is characterized by competition for resources and by a two-fold coupling between the two types of species: pollinators depend on plants for resources and plants on pollinators for pollination. Starting with unimodal trait distributions, we study the dynamics of the model using computer simulations with discrete generations and alternating reproduction and selection. Under a variety of conditions we observe an evolution towards bimodal distributions, with two subpopulations that are reproductively isolated to a large extent. We also find sympatric speciation in situations where two pollinators pollinate the same plant, and where one pollinator pollinates two plants.