Mechanisms of sibilant noise formation observed during forced exhalation of a healthy person

Wheezes of the forced exhalation (FEW) are important for the diagnostics of bronchial obstruction, however, mechanisms of FEW noise formation have not been clearly identified. The objective of the study is statistical modeling of mechanisms of FEW noise formation in the selected subset of health volunteers. FEW were identified by experts with the use of the spectrogram. The frequencies of FEW with maximal amplitudes were determined in four time fractions. In the assumption of air incompressibility for Weibel morphometry of the bronchial tree considering a decreased section of the respiratory tract at the forced exhalation, the average values of proportionality coefficients between the correlations of the linear velocity of air flow and the average diameters of the respiratory tract, and the maximal frequencies of FEW were calculated. Obtained values of the coefficients have been compared with predictable empirical models     

Study of plasma—solid interaction in electronegative gas mixtures

Low-temperature reactive plasmas employing electronegative gases are often used in modern technologies. Negative ions in such plasmas affect the transport of charged species and in this way influence the processes in the boundary layer between plasma and surface of metal substrate or probe. The contribution presents results of the computer experiment describing the interaction of electronegative plasma with immersed substrates. The method of solution was the particle simulation technique and several approximations were used; the most important was the simplified geometry of substrates. The simulation is based on experimental data obtained in a dc glow discharge in mixtures of oxygen with rare gases. This work is a part of the research plan MSM0021620834 that is financed by the Ministry of Education of Czech Republic.     

Fluctuations in the level density of a fermi gas

We present a theory that accurately describes the counting of excited states of a noninteracting fermionic gas. At high excitation energies the results reproduce Bethe's theory. At low energies oscillatory corrections to the many-body density of states, related to shell effects, are obtained. The fluctuations depend nontrivially on energy and particle number. Universality and connections with Poisson statistics and random matrix theory are established for regular and chaotic single-particle motion.     

Temporal damping of the axial breathing mode in a trapped unitary Fermi gas

The damping rate of the collective modes of the unitary Fermi gas is an important experimental observable. It varies with experimental conditions, and provides information about the viscosity. In this paper, we simulate the axial breathing modes basing on viscous hydrodynamics, and extract the concrete relation between the temporal damping rate and the experimental parameters: viscosity, atom number and the trap frequencies.     

Coherent spin dynamics of different density high mobility two-dimensional electron gas in a GaAs quantum well

We have addressed the dependence of quasi-two-dimensional electron spin dephasing time on the electron gas density in a 17-nm GaAs quantum well using the time-resolved magneto-optical Kerr effect. A superlinear increase in the electron dephasing time with decreasing electron density has been found. The degree of electron spin relaxation anisotropy has been measured and the dependence of spin-orbit splitting on electron gas density has been determined.     

Revealing of the simplest mechanisms of a structure formation

In this paper, results of investigations of the simplest mechanisms of a structure formation are presented. In frameworks of the suggested model the main attention was focused on such characteristics as wiring of the system, clusters formation, dynamics of the wiring. The idea to take into account an influence of the environment factor is employed in the proposed model. Investigations of systems with such principle of a structure formation reveal that the system's dynamics has typical features of self-organized criticality phenomenon. In the avalanche-like processes, which occur in the wiring dynamics, a power law was found with the index close to 1.4. It is independent on the environment factor (which in a sense can be considered as system parameter). The system wiring is approximated pretty well by the Gaussian distribution. The size of the system does not play any role in the dynamics of the model. Received 10 March 1999 and Received in final form 24 May 1999     

Degradation of ZnS:Cu,Al,Au phosphor powder in different gas mixtures

The ZnS:Cu,Al,Au (P22G) phosphor powder was bombarded by an electron beam in an O₂ ambient, Ar ambient and other mixture of gases. These gases consisted of mixtures of O₂ and CO_x, and O₂, CO_x and Ar gas. Auger electron spectroscopy (AES) was used to monitor changes in the surface composition of the P22G phosphor during electron bombardment. When the P22G phosphor powder was exposed to the electron beam in a water-rich O₂ ambient, a chemically limited ZnO layer was formed on the surface. The electron beam degradation of the P22G phosphor powder was also performed in a dry O₂ ambient and a layer of ZnSO₄ was formed on the surface. The ZnSO₄ formation decayed exponentially with time and it is postulated that this was due to the diffusion of the charge reactants through the ZnSO₄ film to the reaction interfaces. The P22G phosphor exposed to the electron beam in an Ar ambient and to the other gas mixtures degraded at a lower rate than in the case of the O₂ ambient. This suggests that Ar and CO_x may suppress the degradation of the P22G phosphor powder.     

Bose gas of small density in a random field

Bose gas in a random external field is considered. The effective action both for weak and strong random fields, compared with the interaction between particles, is derived in the framework of the path integral Keldysh-Schwinger technique. Using this effective action the properties of the system in strongly fluctuating random field are analyzed. Used approximation shows a gap in the chemical potential, when it flows from negative to positive values.     

喷气Z箍缩负载的质量线密度确定

 喷气Z箍缩的负载参数（如质量线密度及半径）必须和脉冲驱动源的电流（幅值和上升时间）相匹配。作者利用微型快速电离规测量了喷气Z箍缩中超音速喷嘴产生的气体负载的密度分布，并由此得到了负载质量线密度为43μg/cm，这符合原定的喷嘴设计指标。     

喷气Z箍缩负载的质量线密度确定

喷气Z箍缩的负载参数（如质量线密度及半径）必须和脉冲驱动源的电流（幅值和上升时间）相匹配。作者利用微型快速电离规测量了喷气Z箍缩中超音速喷嘴产生的气体负载的密度分布,并由此得到了负载质量线密度为43μg/cm,这符合原定的喷嘴设计指标。     

Nitriding of VT1-0 titanium in low-pressure non-self-maintained glow discharge with the use of different gas mixtures

The results of nitriding of VT1-0 titanium in the plasma of non-self-maintained glow discharge with a hollow cathode are presented. A nitriding process has been implemented in different gas mixtures at low pressure and temperatures less than 650°C. It is shown that two-hour nitriding in a helium-nitrogen mixture leads to formation of a nitrided layer on the specimen’s surface. The obtained layer hardness of 14.5 GPa exceeds the hardness corresponding to pure nitrogen and argon-nitrogen nitriding by a factor of 2 and 1.5, respectively.     

Relaxation of induced Compton scattering when a radiation flux propagates in a gas

The relaxation process by which the efficiency of induced Compton scattering is established is studied for the case when a powerful radiation flux is incident on an electron gas occupying a region of space. The temperature dependence of the scattering efficiency results in the scattering efficiency falling as time from the commencement of propagation increases. Possible manifestations of this effect in astrophysical applications are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 56–59, December, 1976.     

拉瓦尔喷嘴的气流线质量及密度分析

喷气负载是高功率Z箍缩的主要负载之一。应用一维等熵压缩气体动力学,分析了“强光一号”加速器拉瓦尔喷嘴的基本物理过程,获得了拉瓦尔喷嘴出口处气流的马赫数,Ma=4.6,并对其进行了修正,修正值为3.5。利用由雪耙模型导出的Z箍缩聚爆时间表达式,并结合“强光一号”Z箍缩实验结果,修正了由一维等熵气体动力学得到的喷嘴气流线质量表达式。最后根据已知气流的线质量40 μg/cm ,利用B-T模型初步估算了喷嘴的气流密度分布。估算结果为：在轴向2.5~40 mm,径向0~15 mm的区域内,气体分子密度基本在1016～1017/cm3,且在轴向2 cm内基本形成空心的气体壳层结构。     

Origin of density clustering in a freely evolving granular gas

The physical mechanisms leading to the development of density inhomogeneities in a freely evolving low density granular gas are investigated. By means of the direct simulation Monte Carlo method, numerical solutions of the inelastic Boltzmann equation are constructed for both a perturbed system and also for an initially homogeneous state. Analysis of the Fourier components of the fields indicates that the nonlinear coupling contributions of the transversal velocity play a crucial role in the initial setup of clustering. A simple hydrodynamic model is proposed to describe what is observed in the simulations. Finally, the nature of the inhomogeneous state is briefly discussed.     

Stimulated emission of inert gas mixtures in the VUV range

Amplification properties of continuous VUV emission of cooled discharge in mixtures of heavy inert gases are studied experimentally. The discharge current is 10–50 mA, the pressure is 100 GPa. Results pointing to amplification near the resonance line of xenon λ=146.96 nm are obtained. The amplification coefficient is measured to be κ=0.1 cm^?1. The problem of radiation outcoupling from the active medium remains to be solved for practical implementation of a VUV laser.     

Visual study of the microdrop component in sodium vapor-inert gas mixtures in a heat pipe

The parameters (size, density, and velocity) of the microdrop component in the cooling zone of a heat pipe in Na + He and Na + Kr mixtures have been determined by visualization. It is found that particles in helium have an average size of 14 μm and concentration of 1.6 × 10⁴ cm^?3, while the corresponding values for krypton are 42 μm and 3 × 10³ cm^?3. The effect of microdrops as causes of nonequilibrium enhanced concentration of sodium trimers is analyzed. Such a concentration of trimers can explain the high IR absorption coefficients (above 0.9 μm), which were previously observed in heat pipes.     

Spectral characteristics of a barrier discharge in cadmium dihalide vapor-inert gas mixtures

Spectral characteristics of a barrier-discharge plasma produced in atmospheric-pressure mixtures of cadmium diiodide and cadmium dibromide vapors with neon, krypton, and xenon at a repetition rate of sine voltage pulses up to 130 kHz are studied. The emission from the discharge is studied within the spectral range 200–900 nm with a resolution of 0.05 nm. Emission of exciplex molecules CdI(B → X) and CdBr(C, B → X), and cadmium and inert gas atoms is revealed, as well as emission of exciplex molecules XeI(B → X, A) and XeBr(B → X, A) in xenon-containing mixtures. The emission of xenon halides prevails in the spectra at a mixture temperature up to 200°C. With a further temperature increase, the emission of cadmium halides becomes dominating. It is ascertained that the most intense emissions of CdI(B → X) and CdI₂/CdBr₂/Xe/Kr and CdBr(B → X) molecules are observed, respectively, in CdI₂/CdBr₂/Xe/Kr and CdI₂/CdBr₂/Xe mixtures. The cadmium dihalide-inert gas mixtures are of interest for the use as a radiating gas in a multiwavelength and broadband excilamp emitting in the UV and visible spectral ranges.     

Numerical investigation of the influence of forced disturbances on jet flows in gas

The influence of forced disturbances in the velocity and pressure fields on stability loss, turbulization, and monodispersion of a capillary laminar jet of a viscous liquid in a gas is studied.