The role of spectral components of the head-related transfer functions in evaluation of the virtual sound source motion in the vertical plane

Perception of virtual sound sources moving in the range of elevation from −45° to 45° (at zero azimuth) was studied with participation of listeners aged 57–73. The virtual sound source trajectory was created using nonindividualized head-related transfer functions and artificially synthesized spectral components specific to these functions. The percentage of correct responses in determining the direction of virtual motion depended on the way of imitation by increasing from low to high for the following succession of imitation methods: (i) displacement of the spectral minimum of broadband noise pulses within a frequency band of 5–12 kHz (the minimum retained a constant width of 1 kHz), (ii) variation of the spectral minimum width of noise pulses within 6–12 kHz, (iii) variation of the spectral maximum width within 4–8 kHz, (iv) simultaneous variation of the spectral minimum and maximum widths, (v) displacement of the spectral minimum and simultaneous variation of the spectral maximum width, and (vi) displacement of the spectral minimum and simultaneous variation of the spectral maximum width and power. For the latter stimulus, the mean percentage of correct responses (90 ± 5)% did not differ from the corresponding percentage (94 ± 3)% observed for the stimulus that was synthesized on the basis of nonindividualized head-related transfer functions and used as reference in synthesizing the spectral components.     

Noise spectrum of the 140-GHz gyrotron designed for controlled thermonuclear fusion installations

A method for measurement of gyrotron amplitude noise using the Mach-Zehnder interferometer as a rejection filter, the measurement facility, and results of testing a 140-GHz industrial high-power gyrotron are discussed. The method improved the sensitivity by two orders of magnitude over that of the direct detection method. The experimental relative power spectral density in a frequency range of 50–250 MHz from the line center is 7 × 10⁻²⁰–5 × 10⁻¹⁹ 1/Hz.     

Low-Noise single-frequency He-Ne laser with stable output power at a wavelength of 1.52 µm

The results of investigation of the energy and spectral characteristics of a He-Ne laser (λ_rad=1.52 μm) with transverse microwave discharge are presented. A single-frequency generation mode at a pressure above 6.0 mm Hg was obtained with radiation power 7.0 mW and low level of amplitude noise (10⁻⁵ Hz^−1/2). Active stabilization of the laser power was carried out, which allows reduction in radiation intensity fluctuations from 1–5 to 0.1 %. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 127–128, January–February, 2000.     

Determination of reference values for optical characteristics in multiwavelength optical detection and ranging (lidar) measurements of atmospheric extinction coefficients

We have studied multiple regressions between the spectral aerosol extinction coefficient ε, backscatter indicatrix g_π, and light-scattering coefficients β_θ at angles of θ = 1–180°, which we used to select the optimal scattering angle for determining the extinction coefficient at the wavelengths 0.350, 0.532, and 1.060 μm. We have estimated the errors in determination of the values of ε and g_π at the given wavelengths for different atmospheric situations with different meteorological parameters. We have shown that it is possible to use the spectral β_θ values at a 33° angle to determine the reference values for ε(λ) and g_π(λ) at λ = 0.350, 0.532, and 1.060 μm in laser detection and ranging (lidar) measurements, and we give examples of recovering the vertical profiles of ε in a slightly turbid atmosphere from the results of simultaneous multiwavelength lidar and nephelometric measurements. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 767–772, November–December, 2007.     

Underwater sounds of the Pacific Ocean in the shelf zone of Shikotan Island

Results of underwater sounds measurement in the Shikotan’s shelf zone of the Pacific Ocean at the depth of 130 m in the range of frequencies 1.9–11000 Hz at the wind velocity from 0 to 40 m/s are presented. The statistic non-linear relation between the variations of the underwater sound levels and wind velocities has been revealed. Data on biological, seismic, as well as the sounds of rain and ice of this region are presented.     

Submicrometre particle size distribution from 0.1–0.45 μm in the urban plume of the city of Valladolid

Summary Particle size distribution in the urban plume of the city of Valladolid was measured with a laser spectrometer during a one-month sampling campaign carried out over the winter period. Experimental results of the number of particles covering the 0.10–0.12, 0.12–0.15, 0.15–0.20, 0.20–0.25, 0.25–0.35 and 0.35–0.45 μm ranges are presented. Using spectral analysis as a statistical technique, two 12 h and 24 h significant peaks are obtained for each size range. In order to interpret the meaning of both peaks, the hourly particle size, traffic and nitrogen oxide patterns are compared. The contribution of domestic heating, traffic exhaust emissions and the strong influence of the gas-to-particle conversion processes mainly within the 0.10–0.15 μm range, may be inferred.     

Vortex properties of the acoustic intensity vector in a shallow sea

We study the vortex properties of the field of the acoustic intensity vector as a function of distance and radiation frequency, determined using a combined acoustic system in Peter the Great Bay in the Sea of Japan. We present probability density histograms of the normalized intensity vector curl components at a frequency of 110 Hz for the distance interval between the source and receiver within the limits of 1200–1725 m. The vortex structure of the acoustic intensity vector was observed in the vertical plane at the full distance (4000 m) from the source to the receiver. The discovered vortex structures are of interest both for physical acoustics and for applied problems in underwater acoustics.     

Filtration of IR radiation by three-component polymer-crystalline systems

We have investigated the regularities in forming the spectral characteristic of three-component polymeric-crystalline polytetrafluorethylene-Ge-LiF interference systems in the wide IR spectral region 0.8–160 μm. The efficiency of suppressing short-wave radiation by structurally asymmetric imerference systems consisting of polytetrafluorethylene and quasihomogeneous layers with a high refractive index is shown. Two of this kind of three-layer systems are sufficient for suppressing background radiation within the wavelength interval from the visible range to ∼35 μm owing to multiple reflection at the boundaries of elementary Ge and LiF layers that form quasihomogeneous layers (λ ∼ 1.7–17.0 μm) and also due to absorption in the Ge (λ<1.7 μm) and Lif (λ ∼ 17–35 μm) layers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No_ 3, pp. 379–381, May–June, 2000.     

Excess noise in YBa2Cu3O7 epitaxial films and antenna-type microbolometers based on them

Monte Carlo modelled anneals of YBa₂Cu₃O₇ epitaxial films have been carried out, and the excess flicker noise in the operating frequency and temperature ranges were shown to be dominated by oxygen migration near small-angle block boundaries. Optimization of film and planar-microstructure fabrication permitted reaching a record-low Hooge noise parameter (1.8×10⁻⁴ at 93 K) for test structures, which can be used to prepare high-performance antenna-type strip microbolometers. Calculations show that the reduction of the microstrip size to 1×0.7 μm² and of the flicker noise made possible detection of radiation within the spectral range from 3 mm to 300 μm (100–1000 GHz) at 90 K, with a nanosecond response and a noise-equivalent power of 1.5×10⁻¹² W/Hz^1/2 at frequencies from 30 to 10⁷ Hz, which is close to the limitations imposed by phonon noise. Fiz. Tverd. Tela (St. Petersburg) 41, 1931–1935 (November 1999)     

Space-borne remote sensing of CO2, CH4, and N2O by integrated path differential absorption lidar: a sensitivity analysis

CO₂, CH₄, and N₂O are recognised as the most important greenhouse gases, the concentrations of which increase rapidly through human activities. Space-borne integrated path differential absorption lidar allows global observations at day and night over land and water surfaces in all climates. In this study we investigate potential sources of measurement errors and compare them with the scientific requirements. Our simulations reveal that moderate-size instruments in terms of telescope aperture (0.5–1.5 m) and laser average power (0.4–4 W) potentially have a low random error of the greenhouse gas column which is 0.2% for CO₂ and 0.4% for CH₄ for soundings at 1.6 μm, 0.4% for CO₂ at 2.1 μm, 0.6% for CH₄ at 2.3 μm, and 0.3% for N₂O at 3.9 μm. Coherent detection instruments are generally limited by speckle noise, while direct detection instruments suffer from high detector noise using current technology. The wavelength selection in the vicinity of the absorption line is critical as it controls the height region of highest sensitivity, the temperature cross-sensitivity, and the demands on frequency stability. For CO₂, an error budget of 0.08% is derived from our analysis of the sources of systematic errors. Among them, the frequency stability of ± 0.3 MHz for the laser transmitter and spectral purity of 99.9% in conjunction with a narrow-band spectral filter of 1 GHz (FWHM) are identified to be challenging instrument requirements for a direct detection CO₂ system operating at 1.6 μm. PACS 42.68.Wt; 95.75.Qr     

Evaluation of a PbTe detector for infrared imaging purposes

Summary An infra-red detector produced by the Elettronica SPA Company for the European Space Agency to be used in the Earth surface mapping from aircraft has been tested in our laboratory. We present the characteristics of the detector working in the spectral range (1÷2.5) μm. The acquisition system and the electronics are discussed and a detailed study of all the noise sources is presented; the measured NEP is 3.2·10⁻¹⁴W Hz^−1/2 at a temperature of 108 K. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Analysis of the Characteristics of Laser and Superluminescent Diodes

It is shown that superluminescent diodes rank below laser diodes in energy characteristics, but they have a wider emission spectrum and lower noise level. The amplitude-frequency and noise characteristics of the laser diode correlate with each other, whereas there is no such correlation for the superluminescent diode. The photon density distribution along the active area is more homogeneous for the laser diode than for the superluminescent one. Presented at the 5th International Scientific-Technical Conference “Quantum Electronics,” November 22–25, 2004, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 689–693. September–October, 2005.     

Study of the dielectric properties of water in the frequency range 75–120 GHz

We study experimentally the frequency dependences of the refractive index n and the absorption coefficient k of distilled, sea, and river water. The measurements were performed using a quasioptical device with a backward-wave oscillator as the radiation source and OAP-7 optical-acoustic receivers at a water temperature of 27°C in the cell. The quantities n and k were determined from the measured transmission and reflection coefficients of the cell with water by means of joint numerical solution of the equations for these quantities. For distilled water in the frequency range f = 75–120 GHz, we obtained n = 6.142–3.926 · 10–2f[GHz] + 1.307 · 10–4(f[GHz])² and k = 3.607–2.101 · 10⁻² f[GHz] + 5.252 · 10–5(f[GHz])². On the whole, these data are in good agreement with the measurement results obtained by other authors at several frequencies of the indicated range and coincide with the calculation data based on the models by Meissner and Wentz and by Liebe et al. within the limits of the rms determination errors 0.05 and 0.02 for the parameters n and k, respectively. The values of n and k for different seawater samples and river water containing insoluble admixtures coincide with the values of these quantities for distilled water within the limits of the experimental measurement errors 3–5% and 1–2%, respectively. The dependences n(f) and k(f) obtained experimentally for seawater are compared with those calculated on the basis of the developed models. Measurements of the transmission spectrum of a cell with double distilled water were performed for low power density of radiation (less than μW/cm²) to reproduce the effect of water resonant transparency reported many times in the literature. Our measurements did not reveal any resonant features in the spectral behavior of the refractive index n and the absorption coefficient k of water and gave the same result as for a power density exceeding the threshold of appearance of this effect. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 6, pp. 489–501, June 2006.     

On a mechanism forming a broadband maximum in the spectrum of background noise at frequencies 2–6 Hz

We study the properties of a broadband spectral maximum (BSM) of the background noise at frequencies 2–6 Hz using the data of mid-latitude observations. We find that the parameters of the maximum depend on the local ionosphere properties and that small scales (several tens of km) are absent in the field distribution at the BSM frequencies. We propose a mechanism forming the BSM, which is related to the large gradients of the refractive indices of normal ionospheric-plasma waves at altitudes from 70 to 300 km. The performed simulation of BSM spectra for a plane-stratified model of anisotropic inhomogeneous ionosphere allowed us to explain the main experimentally observed BSM properties. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 7, pp. 607–623, July 2007.     

320×256 HgCdTe IR FPA with a built-in shortwave cut-off filter

A photovoltaic detector design based on the graded band gap HgCdTe MBE structure with high conductivity layer (HCL) at interface, which provides photodiodes series resistance and a shortwave cut.off filter is developed. The optimal HCL parameters giving high quantum efficiency and minimal noise equivalent temperature difference were determined by calculations and experimentally confirmed. The hybrid 320×256 IR FPA operating in 8–12 μm spectral range was fabricated. The threshold power responsivity and minimal noise equivalent temperature difference values at wavelength maximum were 1.02×10⁻⁷ W/cm², 4.1×10⁸ V/W and 27 mK, respectively.     

Effect of the electron beam and ion flux parameters on the rate of plasma nitriding of an austenitic stainless steel

The method of nitriding of metals in an electron beam plasma is used to change the current density and energy of nitrogen ions by varying the electron beam parameters (5–20 A, 60–500 eV). An electron beam is generated by an electron source based on a self-heated hollow cathode discharge. Stainless steel 12Kh18N10T is saturated by nitrogen at 500°C for 1 h. The microhardness is measured on transverse polished sections to obtain the dependences of the nitrided layer thickness on the ion current density (1.6–6.2 mA/cm²), the ion energy (100–300 eV), and the nitrogen-argon mixture pressure (1–10 Pa). The layer thickness decreases by 4–5 μm when the ion energy increases by 100 V and increases from 19 to 33 μm when the ion current density increases. The pressure dependence of the layer thickness has a maximum. These results are in conflict with the conclusions of the theory of the limitation of the layer thickness by ion sputtering, and the effective diffusion coefficient significantly exceeds the well-known reported data.     

Structure and phase composition of a chromium-silicon system modified by high-current electron beams

The results of studies of the structure-phase state of a chromium-coated silicon substrate system’s subsurface layer treated with low-energy high-current electron beams, 50–200 μs in duration and with an energy density of 15 J/cm², are reported. The data of raster electron microscopy and X-ray structural and spectral microanalysis revealed the formation of a chromium-doped silicon layer with a thickness of 2–38 μm, chromium-enriched silicon dendrites, chromium disilicide CrSi₂, and an amorphous eutectic layer (the characteristic cross-section size of the chromium-enriched phase extrusions is ∼50 nm). The structure-phase transformations are discussed taking into account the peculiarities of the distribution of temperature, diffusion and convective mass-transfer in the modified layer.     

Formation of a plane layer of plasma under irradiation by a soft X-ray source

We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm³ and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident flux is assumed to have a Planck’s distribution over the spectrum with T _rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm³ causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm³ under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed.     

Estimation and interpolation of underwater low frequency ambient noise spectrum using artificial neural networks

In this work, estimation of ambient noise spectrum influenced by wind speed and wave height carried out for the frequency range of 500 Hz to 5 kHz using Feed forward Neural Network (FNN) is presented. Ocean ambient noise measurements were made in the shallow waters of Bay of Bengal using a portable data acquisition system with a high sensitivity hydrophone at a depth of 5 m from the surface.100 sets of data covering a rage of wind speeds from 2.5 m/s to 8.5 m/s with approximately 15 sets of data falling within 1 m/s over the range of wind speed were used for training the FNN. The parameter wave height which contributes to the noise producing mechanism is also used for training along with wind speed. The results revealed that the proposed method is useful in the estimation and interpolation of underwater noise spectrum level and hence in simulation for the considered frequency range. These were confirmed by calculating the Mean Squared Error (MSE) between the experimental data and the simulation. As the measurements of the underwater ambient noise level are very difficult in remote oceanic regions, where conditions are often inhospitable, these studies seem to be relevant.     

Solar and lunar tides in the geomagnetic field

Amplitudes of spectral geomagnetic field components and signal/noise ratios are estimated at frequencies of lunar and solar tides based on the data registered at the experimental site of Vladimir State University (VlSU) and Japanese geomagnetic stations Kakioka (1913–2006) and Memambetsu (1950–1999). The influence of thermal solar tides S1, S2, S3, and S4 and lunar gravitational tides O1, M2, and N2 on the geomagnetic field of the surface layer of the atmosphere is reliably distinguished.