An analytical model for evaporative cooling of atoms

Evaporative cooling of trapped atoms is described as a sequence of truncation of the high-energy tail of the thermal distribution followed by collisional relaxation. This model is solved analytically for arbitrary power-law potentials. The threshold density for accelerated evaporation is. found to be lowest in a three-dimensional linear potential.Dedicated to H. Walther on the occasion of his 60th birthday     

On the radiative cooling of a surface during dew formation

Summary From the energy balance of a radiant surface with zero mass and perfectly insulated from below, the equilibrium temperature is calculated as a function of both sensible and latent heat transfer resistance. Under the hypothesis of Robinson,r _L=r _H is the air in contact with the surface is saturated, the equilibrium temperature is estimated as a function of air temperature, dew temperature and wind speed. This result could be useful to calculate night-time temperature of passive solar collectors or the yield of dew collectors. Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Collision of cold CaF molecules: Towards evaporative cooling

Long range intermolecular interaction potential surface of CaF(~2∑~+) was simulated by employing the MOLPRO program and using the RCCSD(T)/def2-TZVP theory. The predicted data were further fitted to obtain the collision crosssection. The elastic collision cross-section of CaF at the temperature around 2 mK is as high as 6.5 × 10~(-9) cm~2 and the collision rate is over 4.1 × 10~6 Hz. Additionally, we found that an orientation electric field will simplify the intermolecular interaction potential function from quaternary into ternary and the collision cross-section will be raised by about three orders. All-optical evaporative cooling of cold CaF is discussed in the conclusion.     

The formation of rhombohedral phase during the slow cooling of the Al-Zn solid solutions

The decomposition of Al-Zn solid solutions (from 20 to 60 wt. % of zinc) during slow cooling was studied by differential thermal analysis. The X-ray diffraction and electron microscopic investigation of structural changes were carried out on samples heat-treated simultaneously with DTA-samples. The pronounced peaks on DTA-curves were explained by the formation of metastable rhombohedral α′ _R -phase. This decomposition of supercooled Al-Zn solid solution starts at temperatures corresponding to the nose of the C-shaped T-T-T curve for the beginning of transformation.     

Dynamics of antiproton cooling in a positron plasma during antihydrogen formation

We demonstrate cooling of 10⁴ antiprotons in a dense, cold plasma of 10⁸ positrons, confined in a nested cylindrical Penning trap at about 15 K. The time evolution of the cooling process has been studied in detail, and several distinct types of behavior identified. We propose explanations for these observations and discuss the consequences for antihydrogen production. We contrast these results with observations of interactions between antiprotons and “hot” positrons at about 3000 K, where antihydrogen production is strongly suppressed.     

Solitons as a model for the nuclear potential

Formal relations between the nonlinear Korteweg-de Vries (KdV) and the linear Schrödinger equations are discussed. Taking the one-soliton solution of the KdV as a model for the real central part of the nuclear potential quite realistic dependences on the mass numbers of projectile and target are obtained.     

Evanescent-wave trapping and evaporative cooling of an atomic gas at the crossover to two dimensions

A dense gas of cesium atoms at the crossover to two dimensions is prepared in a highly anisotropic surface trap that is realized with two evanescent light waves. Temperatures as low as 100 nK are reached with 20,000 atoms at a phase-space density close to 0.1. The lowest quantum state in the tightly confined direction is populated by more than 60%. The system provides atoms at a mean distance from the surface as low as 1 microm, and offers intriguing prospects for future experiments on degenerate quantum gases in two dimensions.     

Stark-potential evaporative cooling of polar molecules in a novel optical-access opened electrostatic trap

We propose a novel optical-access opened electrostatic trap to study the Stark-potential evaporative cooling of polar molecules by using two charged disk electrodes with a central hole of radius r0= 1.5 mm, and derive a set of new analytical equations to calculate the spatial distributions of the electrostatic field in the above charged-disk layout. Afterwards, we calculate the electric-field distributions of our electrostatic trap and the Stark potential for cold ND3 molecules, and analyze the dependences of both the electric field and the Stark potential on the geometric parameters of our charged-disk scheme,and find an optimal condition to form a desirable trap with the same trap depth in the x, y, and z directions. Also, we propose a desirable scheme to realize an efficient loading of cold polar molecules in the weak-field-seeking states, and investigate the dependences of the loading efficiency on both the initial forward velocity of the incident molecular beam and the loading time by Monte Carlo simulations. Our study shows that the maximal loading efficiency of our trap scheme can reach about 95%, and the corresponding temperature of the trapped cold molecules is about 28.8 m K. Finally, we study the Stark-potential evaporative cooling for cold polar molecules in our trap by the Monte Carlo method, and find that our simulated evaporative cooling results are consistent with our developed analytical model based on trapping-potential evaporative cooling.     

风力发电机自循环蒸发内冷系统稳定性的研究

自循环蒸发内冷系统的冷却效率高,可以实现无泵自循环,运行安全可靠,基本免维护,因此适合在大型风力发电机中使用.蒸发内冷系统的稳定性对风力发电机的安全运行十分重要,本文基于非线性分岔理论及其数值延拓法,对自循环蒸发内冷系统应用于风力发电机的的静态稳定性进行了深入研究.获得了系统静态分岔解图,分析了系统演化特性,同时分析了系统分岔现象的参数效应.搭建了实验平台,通过实验观测到了自循环蒸发内冷系统的静态分岔现象,验证了理论计算的正确性.     

VH-nuclei cosmic-ray tracks in chondrites as indicators for radiation-thermal history of the meteorite matter at the early stage of solar system primary body formation

VH-nuclei cosmic-ray track study in silicate mineral grains extracted from matrix and chondrules of no enriched by solar gas chondrites has been performed. A broad range of track densities, typical track density grouping and absence of track density gradients have been observed in these grains. The traces of low energy cosmic-ray VH-nuclei particles that were stored at the early pre-accretion history of the meteorite parent body formation have been established.     

Concurrent formation of two different type precipitation-free zones during the initial stage of homogenization

Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy were used to study the microstructure evolution of Al–Cu–Mg alloy during the initial stage of homogenization. It was found that two types of precipitation-free zones (PFZs) can form concurrently: one near grain boundaries and the other at the grain centres. Depth profile analyses of solute concentrations and dislocation-loop distributions strongly suggested that the formations of the two type of PFZs are different, due solely and exclusively to solute and vacancy depletion, respectively. A mechanism model was proposed to explain the concurrent formation of the two different type of PFZs during the initial stage of homogenization.     

Evaluation of liquid dessicant based evaporative cooling cycles for typical hot and humid climates

This communication presents an evaluation of various liquid dessicant cycles for air conditioning in hot and humid climates. Psychometric evaluation of seven potential cycles for achieving standard comfort conditions (25°C/10 g/kg) in rooms has been carried out for 16 typical Indian cities. A computer simulation model is based on the constant effectiveness of heat exchangers (HX)/evaporative coolers (EC) and wet surface heat exchangers (WSHE). The absorber-cum-dehumidifier is assumed to provide air at the specified humidity level, while the outlet air temperature is taken to be equal to the cooling water temperature. The effect of various outdoor conditions and the effectiveness of HXs/ECs on cooling COP and volumetric air flow rate per unit cooling capacity have been investigated. It was found that a combination of dehumidifier and WSHE is better, in terms of COP, for a wide range of outdoor conditions. The results should be useful in the design of liquid dessicant based air conditioning systems suitable for the monsoon season in tropical countries like India.     

Detection of early stage precursor during formation of plastic crystal ethanol from the supercooled liquid state: a simultaneous dielectric spectroscopy with neutron diffraction study

Transformation of deuterated ethanol from supercooled liquid into a plastic crystal or rotator phase is investigated by means of a particular experimental setup combining simultaneously dielectric spectroscopy with neutron diffraction techniques. We demonstrate that, previous to the growth of the bcc lattice of the plastic crystal phase, the formation of a precursor or intermediate phase through a liquid-liquid phase separation takes place. Once this precursor phase is formed, subsequent (plastic) crystalline nucleation and growth is expected to develop.     

RO处理早期垃圾渗滤液中DOM的荧光光谱分析

利用荧光检测技术对某垃圾填埋场渗滤液反渗透(RO)膜深度处理时的进水、出水、浓缩液、酸洗液以及酸洗后碱洗液中水溶性有机物(DOM)的组成变化进行了研究。同步荧光光谱显示,预处理后的渗滤液膜进水在波长280,340,370 nm出现三个较强的荧光峰,反渗透膜对此有效拦截,酸洗和碱洗的组合清洗方式有效去除了波长范围在300~420 nm的有机污染物。三维荧光光谱显示,进水含有2个类富里酸和3个类蛋白质荧光峰,RO膜出水仅含有2个类蛋白峰,浓缩液中出现其余3个高强度的荧光峰;酸洗和碱洗对膜上污染物质分子结构影响显著,存在着明显的荧光峰位移。结果表明,RO膜有效拦截了早期渗滤液中的类富里酸,而对膜的污染物除类富里酸外,还有类蛋白成分:主要为低激发类酪氨酸;为膜污染控制提供了理论支持。     

The formation of primary galactic nuclei during phase transitions in the early universe

A new mechanism describing the formation of protogalaxies is proposed, based on the second-order phase transition in the inflation stage and the domain wall formation upon the end of inflation. The presence of closed domain walls with the size markedly exceeding the cosmological horizon at the instant of their formation and the wall collapse in the postinflation epoch (when the wall size becomes comparable with the cosmological horizon) lead to the formation of massive black hole clusters that can serve as nuclei for the future galaxies. The black hole mass distributions obtained do not contradict the available experimental data. The number of black holes with M ～ 100 solar masses (M _⊙) and above is comparable with the number of galaxies in the visible Universe. Development of the proposed approach gives grounds for a principally new scenario of galaxy formation in the model of a hot Universe.     

Planckions and the early stage of the universe

It is shown that, due to Rosenfeld's inequality relations, there is no possibility of defining states of the Friedmann universe in a physically sensible manner when the world radius becomes equal to or smaller than Planck's length.     

Solitons as truncated asymptotic solutions of completely integrable models

The long time behaviour of solutions of soliton equations is considered. A method for finding the sets of scattering data associated with asymptotic solutions truncated on intervals with freely moving end points is presented. The method is applied to provide a simple proof of the solitonic properties of asymptotic solutions and to characterize the soliton-soliton, soliton-radiation and radiation-radiation collisions.     

真空冷却过程中实验条件对真空冷却速率的影响

以熟肉为实验材料,对实验条件对真空冷却速率的影响进行了理论分析和实验研究。实验结果表明:真空室有效容积越小、真空泵抽速越高,则真空冷却时间就会越短;冷阱温度对真空冷却速率有着明显的影响;当真空室内的最终压力在0.4～0.61kPa变化时,熟肉的表面温度一直在0℃以上,其真空冷却的时间随着真空室内压力的升高而增加。而真空室内的最终压力在0.3kPa左右时,熟肉的表面温度在真空冷却过程会低于0℃。