Temperature dependence of dc photoconductivity in CdTe thin films

The temperature dependence of dc photoconductivity in the measuring range 303–417 K has been studied in CdTe thin films having thicknesst < 4000 Å. The photoactivation energy decreases in dark which is explained on the basis of grain boundary (GB) effect. The current lost to recombination at GB space charge region causes a negative effect on the photosensitivity of the films. A decrease in photosensitivity with increase in temperature is attributed to the reduction of photoexcitation process. It is observed that the minority carrier lifetime varies inversely with light intensity which supports the sublinear relationship of photoconductivity with the intensity of light and thereby confirms the defect-controlled photoconductivity in CdTe thin films     

Impurity diffusion in a gas flow in a channel

The impurity concentration N in a gas flow in a channel is approximately calculated. In a number of cases, the wall losses of impurities in the channel can be taken into account by introducing an effective lifetime τ that describes the diffusion drift of the impurity from the flow toward the walls.     

Liquid entrainment by gas flow along the interface of a liquid bridge

We report the results of numerical and experimental studies of two-phase flows in an annulus. The geometry corresponds to a cylindrical liquid column co-axially placed into an outer cylinder with solid walls. Gas enters into the annular duct and entrains the initially quiescent liquid. The internal column consists of solid rods at the bottom and top, while the central part is a liquid bridge from a viscous liquid and kept in its position by surface tension. Silicone oil 5cSt was used as a test liquid and air and nitrogen as gases. An original numerical approach was developed to study the problem in complex geometry. The flow structure in the liquid is analyzed for a wide range of gas flow rates.     

Effect of catalysts on dc corona discharge poisoning

The processes of ozone generation in non-thermal plasma produced by an electrical discharge in air at atmospheric pressure are burdened by the presence of nitrogen oxides, which on the one hand contribute to ozone generation and on the other hand are responsible for unpleasant discharge poisoning. The term discharge poisoning refers to the situation when the discharge ozone formation completely breaks down. Discharge poisoning can be affected by placing a catalyst in the discharge chamber. For the dc hollow needle to mesh corona discharge enhanced by the flow of air through the needle electrode we studied the effect of titanium dioxide TiO₂, ZSM-5 zeolite or Cu⁺⁺ZSM-5 zeolite on discharge poisoning by monitoring the ozone, nitrogen monoxide and nitrogen dioxide discharge production. We found that placing globules of any of these catalysts on the mesh decreases the energy density of the onset of discharge poisoning, and this energy density is smallest for a discharge with globules of a TiO₂ on the mesh.     

Temperature of a thermally insulated surface in a gas flow

An equation is derived for determining the temperature of a thermally insulated surface in a gas flow. The equation does not contain any empirical coefficients. The derivation is based on allowance for the work done by a jet arrested at an obstructing surface on the surrounding flow layers. The application of the equation to subsonic and supersonic flows is discussed. Zh. Tekh. Fiz. 68, 134–135 (April 1998)     

Temperature dependence of the universal contact parameter in a unitary Fermi gas

The contact I, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter 1/(k(F)a), where k(F) is the Fermi wave vector and a is the s-wave scattering length, and the temperature T/T(F), where T(F) is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.     

Temperature dependence of intensities of laser-induced fluorescences of ethylbenzene and naphthalene seeded in gas flow at atmospheric pressure

The present study has been carried out with the aim of developing a technique for measuring two-dimensional gas temperature profiles based on two-color fluorescence induced by a one-color laser. The laser sheet of the fourth harmonic (266 nm) from a Nd:YAG laser induced fluorescence in species doped in a nitrogen gas flow. The LIF spectra of seven fluorescent species, namely acetone, methylethylketone, acetaldehyde ethylbenzene, anisole, aniline, and naphthalene, were measured to select the best prospective pair of fluorescent species for this technique. Ethylbenzene and naphthalene show relatively high LIF intensities and their LIF spectra overlap less with each other than with other species. Also, ethylbenzene has a high temperature dependence while naphthalene has a low temperature dependence. Thus by selecting one portion of wavelengths in the range where ethylbenzene or naphthalene is dominant, the temperature of the gas can be determined using the ratio of LIF intensities of the mixture at the two wavelengths with good temperature sensitivity. In addition, a general principle is presented for finding out an optimum pair of wavelengths to obtain a good temperature sensitivity in those LIF spectra.     

The power dependence of a carbon-dioxide laser on the gas flow

Summary The gas flow rate has resulted very important to get high power in a CO₂ diffusion-cooled laser. Some measurements suggest that the power dependence on the flow is connected with the chemical dissociation of the components of the gas mixture. Four different gas circuits have been experimented. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

An empirical model for ionic wind generation by a needle-to-cylinder dc corona discharge

We present the results of an experimental study on ionic wind generation by a needle-to-cylinder dc corona discharge. A strong electrical field in the air generates air flow driven by the motion of ionized gas molecules along electric field lines. We measured the ionic wind velocity and discharge current with respect to various electrode geometries, distances between electrodes, and applied voltages. Our measurements suggest an empirical model for the ionic wind velocity as a function of the geometric factors of the collector electrode and the applied electric potential, which is useful for designing ionic wind cooling systems for small electronics.     

Rarefied gas flow through a channel of finite length into a vacuum

A rarefied gas flow through a finite-length channel into a vacuum is studied by the direct simulation Monte Carlo method. The mass flow rate through the channel is calculated over the wide range of gas rarefactions. The analysis of the flow field, both within the channel and in upstream and downstream containers, is presented.     

Brownian deposition of nanoparticles from a laminar gas flow through a channel

Investigation of nanoparticle deposition by Brownian diffusion is conducted by mathematical simulation. The mobility of nanoparticles is calculated in the free-molecular approximation. The influence of the nanoparticle radius, flow parameters, and channel length on the process is studied. Variation of the distribution function and broadening of the nanoparticle beam as the particles move along the channel are calculated.     

气体的摩尔热容量随温度变化的实验研究

采用压力传感器和温度传感器,通过数据接口由计算机实时采集数据并进行处理,观察到气体的热力学过程的状态变化,测得了氧气的摩尔热容量CV随着温度的变化.结果表明氧气的CV随温度的变化有一突变,这与能量均分定理所描述的基本一致,氧气的振动自由度被冻结的温度在240K左右.     

Characteristics and underlying physics of ionic wind in dc corona discharge under different polarities

During a dc corona discharge, the ions' momentum will be transferred to the surrounding neutral molecules, inducing an ionic wind.The characteristics of corona discharge and the induced ionic wind are investigated experimentally and numerically under different polarities using a needle-to-ring electrode configuration.The morphology and mechanism of corona discharge, as well as the characteristics and mechanism of the ionic wind, are different when the needle serves as cathode or anode.Under the different polarities of the applied voltage, the ionic wind velocity has a linear relation with the overvoltage.The ionic wind is stronger but has a smaller active region for positive corona compared to that for negative corona under a similar condition.The involved physics are analyzed by theoretical deduction as well as simulation using a fluid model.The ionic wind of negative corona is mainly affected by negative ions.The discharge channel has a dispersed feature due to the dispersed field, and therefore the ionic wind has a larger active area.The ionic wind of positive corona is mainly affected by positive ions.The discharge develops in streamer mode, leading to a stronger ionic wind but a lower active area.     

Temperature and humidity behaviour of a corona based smoke sensor

Ionization smoke sensors are amongst the best smoke sensors; however, the little radioactive source that they include is no longer desirable since recycling gets more complicated. In this paper we discuss an electrostatic system in which corona phenomena is used to generate the ions needed to smoke detection. We show how the velocity of ions is reduced in our system for a better interaction between smoke and drifting ions. Influence of smoke, temperature and moisture is studied. It is shown that the proposed sensor has a good sensitivity compared with conventional ionic and optical smoke sensors.     

Grain-size dependence of superconductivity in dc sputtered Nb films

The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results show that the superconductivity is closely related to the grain size, rather than to the scattering strength of electrons or the surface layer proximity effect of the films. Supported by the National Basic Research Program of China (Grant No. 2006CB-91304), and the Knowledge Innovation Project of Chinese Academy of Sciences Contributed by ZHANG DianLin     

Temperature dependence of foreign gas broadening of HCl fundamental lines

A long-pathlength variable temperature cell has been used to study three hydrogen chloride 0–1 vibration-rotational lines, P(7), P(8), and P(9) which were broadened by He, Ar, N₂, O₂, and CO at room temperature and by Ar at low temperatures down to 190 K. The method employed to extract the linewidths is the equivalent width method. The temperature dependence of the resulting cross sections for the HClAr broadened lines is similar to that recently found for other argon broadened HCl infrared and microwave lines. The results reported here (for high J lines) complement the other results (for low J lines) and together seem to constitute enough new data for further theoretical attempts at describing the process of collisional broadening in general, and the broadening of HCl by argon in particular.     

Modeling of an EHD corona flow in nitrogen gas using an asymmetric capacitor for propulsion

The present work intends to identify the nature of the propulsive force that occurs during a positive corona discharge in nitrogen gas using an asymmetric capacitor geometry. We are going to apply the known theory of electrohydrodynamics (EHD) and electrostatics in order to compute all hydrodynamic and electrostatic forces that act on the considered geometry in an attempt to provide a physical insight on the force mechanism that acts on an asymmetrical capacitor.