Using a High-Quality Thermostated Acoustic Interferometer to Study Changes in the Structure of Human Serum Proteins

An acoustic interferometric technique for determining the protein in blood serum is presented. This acoustic approach is based on high-precision measurements of the temperature dependences of the velocity, frequency, and absorption of ultrasound. The acoustic characteristics of blood serum are measured by a constant-length interferometer in acoustic wells with volumes of around 80 μL in the temperature range of 28–40°C and the frequency range of 1.4–14 MHz.     

Specific features of the absorption and phase velocity of ultrasound near the low-temperature phase transition induced by 3<Emphasis Type="Italic">d</Emphasis> impurities in a ZnSe crystal

This paper reports on the results of temperature investigations into the absorption and velocity of ultrasound in ZnSe: Ni and ZnSe: Cr crystals in the frequency range 33–268 MHz. The frequency dependence of the absorption at the maximum is analyzed, and the energy of the excited state of the Ni²⁺ ions is calculated. The dynamic contribution to the effective elastic modulus is determined, and the results obtained are used to construct the temperature dependences of the relaxed and unrelaxed elastic moduli.     

A compact resonant Π-shaped photoacoustic cell with low window background for gas sensing

A resonant photoacoustic cell capable of detecting the traces of gases at an amplitude-modulation regime is represented. The cell is designed so as to minimize the window background for the cell operation at a selected acoustic resonance. A compact prototype cell (the volume of acoustic cavity of ~0.2 cm³, total cell weight of 3.5 g) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia traces in nitrogen flow with the help of a pigtailed DFB laser diode operated near a wavelength of 1.53 µm. The performance of absorption detection and gas-leak sensing for the prototype operated at the second longitudinal acoustic resonance (the resonance frequency of ~4.38 kHz, Q-factor of ~13.9) is estimated. The noise-equivalent absorption normalized to laser-beam power, and detection bandwidth is ~1.44 × 10^?9 cm^?1 W Hz^?1/2. The amplitude of the window-background signal is equivalent to an absorption coefficient of ~2.82 × 10^?7 cm^?1.     

Charge carrier mobility in crystals of the Pb<Subscript>0.67</Subscript>Cd<Subscript>0.33</Subscript>F<Subscript>2</Subscript> superionic conductor

The frequency (ν = 10^?1–10⁷ Hz) dependences σ(ν) of the conductivity of single crystals of the Pb_0.67Cd_0.33F₂ superionic conductor with the fluorite-type structure (CaF₂) in the temperature range of 132–395 K have been studied. The dependences σ(ν) have been discussed in the framework of the hopping relaxation of ionic carriers, which are mobile anions F^?. From experimental curves σ(ν), the direct-current (dc) conductivity σ_dc and the average charge carrier hopping frequency ν_h have been determined. This has made it possible to calculate the charge carrier mobility μ_mob and charge carrier concentration n _mob in these crystals. At room temperature (293 K), the electrical parameters are σ_dc = 1.6 × 10^?4 S/cm, ν_h = 2.7 × 10⁷ Hz, μ_mob = 2.0 × 10^?7 cm²/(s V), and n _mob = 5.1 × 10²¹ cm^?3.     

Attenuation of finite amplitude sound near the ferroelectric phase transition

The temperature dependences of the effective sound attenuation near the phase transition in the triglycine sulfate crystal are calculated for powerful acoustic waves with a strain of an order of 10^?5. It is demonstrated that the generation of harmonics and their absorption can appreciably contribute to the measured absorption coefficient at the basic frequency owing to a critical increase in the third-order elastic moduli. The calculated data are compared with the experiment.     

Acoustic anomalies and relaxation dynamics of relaxor ferroelectric Na1/2Bi1/2TiO3 single crystals studied by using Brillouin spectroscopy

Acoustic anomalies of relaxor ferroelectric Na_1/2Bi_1/2TiO₃ single crystals were investigated over a wide temperature range from −196 °C to 900 °C by using Brillouin spectroscopy. The longitudinal sound velocity, the acoustic absorption coefficient and the elastic constant C₁₁ were determined for the acoustic phonon mode propagating in the [100] direction. Two acoustic anomalies, weaker ones at the cubic-tetragonal phase transition temperature of ~540 °C and more pronounced ones at temperatures near 315 °C near the dielectric maximum temperature, were investigated and discussed in relation with the relevant order parameters coupled to the acoustic waves. The relaxation dynamics in the cubic phase were studied based on the flattening of the mode frequency and the half width, which was observed for the first time, and a modified Arrhenius law.     

Parametric excitation of helicon and acoustic waves in piezoelectric semiconductor-plasma

The parametric excitation of a helicon and an acoustic wave in a piezoelectric semiconductor-plasma in the presence of a strong magnetic field has been investigated using the coupled mode theory. The expressions for the threshold value of the electric field required for the onset of instability and for the growth rate well above the threshold have been obtained. It is observed that an acoustic wave of higher frequency and higher phase velocity than that of the pump wave cannot be excited. The analysis has been applied to the case of n type InSb sample where the threshold value of the electric field is found to be of the order 5.2 × 10³ Vm^?1 and the growth rate at an electric field 5.2 × 10⁴ Vm^?1 is of the order of 8.7 × 10¹⁰ sec^?1.     

Subterahertz electrodynamics of (TMTSF)2X (X = ClO4, PF6) salts

The terahertz-subterahertz spectra of the complex permittivity and dynamic conductivity of polycrystalline (TMTSF)₂ClO₄ and (TMTSF)₂PF₆ samples are measured quantitatively. The spectra of (TMTSF)₂ClO₄ have absorption lines at frequencies of 7 and 30 cm^?1. The obtained temperature dependences of the line parameters in the range 5–300 K cast some doubt on the earlier concept of their phonon origin. An excitation is detected at temperatures below 20 K in the frequency range near 30 cm^?1, and its nature is related to the activation of a transverse acoustic phonon caused by the folding of the Brillouin zone due to the ordering of noncentrosymmetrical anions below 20 K. An increase in the carrier relaxation rate is found in this temperature range, which indicates a close relation between the electron and phonon subsystems in (TMTSF)₂ClO₄. Sings of additional low-energy excitations that should manifest themselves at frequencies below 1–2 cm^?1 are detected. (TMTSF)₂PF₆ containing centrosymmetrical anions has no absorption lines in the frequency range 3–20 cm^?1 and the temperature range 5–300 K.     

Ultrasonic attenuation in a LiIO3 crystal

The temperature dependences of the attenuation of longitudinal acoustic waves along the x axis of a LiIO₃ crystal are studied experimentally by the method of Bragg diffraction of light by ultrasound. The measurements are performed in the temperature range from 215 to 335 K at frequencies of 400–690 MHz. Above 260 K, the attenuation is found to exhibit a frequency-independent growth of a relaxational character, which is used to calculate the enthalpy of the activation of ionic motion in the direction normal to the hexagonal axis. In addition, resonance attenuation peaks are observed; as the frequency increases, the peaks are shifted toward lower temperatures. A phenomenological model is proposed to explain the origin of the resonance absorption.     

A Novel Method for the Assessment of Cortisol Hormone in Different Body Fluids Using A New Photo Probe Thiazole Derivative

A low cost and accurate method for the detection and analytical determination of the cortisol in pharmaceutical preparation, blood serum and urine was developed. The method was based upon the enhancement of fluorescence intensity of the band at 424 nm of the photo probe by different cortisol concentrations in acetonitrile at (pH 5.7, λ_ex?=?320 nm). The influence of the different parameters, e.g. pH, solvent, cortisol concentration and foreign ions concentrations that control the enhancement process of fluorescence intensity of the band of photo probe was critically investigated. The remarkable enhancement of the fluorescence intensity at 424 nm in acetonitrile by various concentrations of cortisol was successfully used as a photo- probe for the assessment of cortisol concentration. The calibration plot was achieved over the concentration range 8.0?×?10^?6–5.5?×?10^?9 mol L^?1 cortisol with a correlation coefficient of 0.998 and a detection limit of 4.7?×?10^?9 mol L^?1. The developed method is simple and proceeds without practical artifacts compared to the other determination methods.     

Electromagnetic generation of ultrasound in metals at low temperatures

Excitation of longitudinal and transverse ultrasound by electromagnetic waves incident on the metal surface is the subject of the present work. This is a simple and convenient experimental technique. The reason for this approach is to overcome the primary difficulty during precise measurements of the frequency or temperature dependences of the velocity and attenuation of ultrasound in pure metals by the conventional methods where it is difficult to achieve reliable acoustic contact between the transducer and the sample. The reasons are (i) the creation of this contact unavoidably results in a deformation of a surface layer of the metal affecting the experimental results, (ii) as the temperature is varied over a broad range, the properties of the acoustic contact itself change resulting in non-reproducible experimental results.     

Absorption of Dy3+ and Nd3+ ions in BaR 2F8 single crystals

The Dy³⁺ absorption and excitation spectra of BaY₂F₈ and BaYb₂F₈ single crystals are investigated in the ultraviolet, vacuum ultraviolet, and visible ranges at a temperature of 300 K. These crystals exhibit intense broad absorption bands due to the spin-allowed 4f-5d transitions in the range (56–78) × 10^?3 cm^?1 and less intense absorption bands that correspond to the spin-forbidden transitions in the range (50–56) × 10^?3 cm^?1. The Nd³⁺ absorption spectra of BaY₂F₈ single crystals are studied in the range (34–82) × 10^?3 cm^?1 at 300 K for different crystal orientations.     

Thermal expansion and phase changes of 16Kh12V2FTaR steel in temperature range from 20 to 1000 °C

The article presents the results of investigation of thermal expansion of 16Kh12V2FTaR steel in the temperature range 20–1000 °C. Measurements were carried out by dilatometric method with the error (1.5–2)×10^?7 K^?1. The temperature dependences of thermal coefficient of linear expansion of steel have been obtained in ferrite-martensite and ferrite-perlite states, and reference tables have been calculated. Influence of samples cooling rate on martensite phase formation is shown.     

Ultrasound and Orientational Relaxation of Nematic Liquid Crystals at High Pressures

Acoustic properties of the anisotropic phase of N-96 nematic crystals and its solutions with benzene in a rotational magnetic field are investigated. Time dependences of the ultrasound absorption anisotropy on the concentration, temperature, pressure, and magnetic field rotation frequency are investigated. Values of the critical frequency and its dependence on the state parameters (P, T) are experimentally determined. The rotational viscosity ratios of the diamagnetic susceptibility anisotropy are calculated and the character of their temperature and pressure dependences is established. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 82–84, May, 2005.     

Precise Underwater Distance Measurement by Dual Acoustic Frequency Combs

Underwater acoustics is of fundamental importance for marine science and technology. However, acoustic waves transmitted by state‐of‐the‐art underwater acoustic systems are not inherently phase locked, which hinders the development of underwater acoustic technology. For example, the precision of underwater distance measurement can only achieve centimeter level. As a versatile tool, optical frequency combs have enabled revolutionary progress in optical metrology and precision measurement. In parallel with optical frequency combs, here, the generation of fully stabilized, underwater acoustic frequency combs is reported, in which equidistant acoustic modes are produced via a hydroacoustic transducer. The precision of each individual acoustic mode is measured to be 10^?9 at 1 s and 10^?12 at 1000 s averaging times. Underwater distance measurements are carried out in an anechoic pool using a dual‐comb scheme. Comparison with reference values shows consistency within 50 µm (7 × 10^?6 in relative). The relatively long‐duration experiments at 7 m distance yield an Allan deviation of 1.8 µm (2.6 × 10^?7 in relative) at 1 s and further 480 nm (6.8 × 10^?8 in relative) at 40 s averaging times. The approach to acoustic frequency comb generation offers a promising and powerful platform for future underwater distance measurement, positioning, and navigation.     

The impact of the Ramsauer effect on the frequency of elastic collisions in inductive RF discharges in inert gases

This paper presents the results of investigating the power absorption mechanism of an inductive RF discharge plasma. Dependences of the frequency of elastic electron collisions with inert gas atoms (helium, neon, argon, and krypton) on the pressure are given. In the frequency range of 3 × 10⁶–3 × 10⁷ s^?1, an equivalent plasma resistance and the power input into the plasma are determined by the values of collision frequency and electron density within a skin layer and do not depend on the type of gas within the limits of experimental error. Upon reaching the electron temperature of ～1 eV, the energy of the main part of electrons lies in the range of Ramsauer’s minimum for elastic cross section. This leads to a decreasing elastic-collision frequency in heavy inert gases as compared to helium.     

Optical properties of sapphire in its opacity range

We have studied the reflection spectrum of leucosapphire in the range of 2.5–25.0 μm. Based on the analysis of the known frequency and temperature dependences of the absorption coefficient in the range of 2.5–7.0 μm, its extrapolation to the range of 10.6 μm has been performed. We have shown that the absorption coefficient in the range of 10.6 μm and in the temperature interval 300–2300 K can be evaluated as β = (2–3) × 10⁴ cm^–1. It has also been shown that the value of this characteristic correlates with the results of investigations of the action of a powerful radiation pulse of a СО₂ laser on the surface of anodized aluminum. These data can be used in the development of technologies of laser processing of articles made of sapphire and ceramics based on aluminum oxide, as well as anodized articles made of aluminum alloys.     

Ultrasonic studies of structural transformations and phase transitions in liquid crystal emulsions

The propagation velocity and absorption coefficient of ultrasound in the range of 0.6–150 MHz in a series of liquid crystal emulsions prepared on the basis of thermotropic liquid crystals and isotropic liquids were studied. The dispersity parameters of emulsions were controlled by polarization microscopy and dynamic light scattering. Features of the temperature dependences of the acoustic parameters of emulsions due to the structural transformations and nematic-isotropic liquid transition in disperse and dispersion phases of liquid crystal emulsions were established.