Comparison of cooling rates for hot carriers in GaAs AlAs quantum wells based on macroscopic and microscopic phonon models

By using three analytical phonon models in quantum wells-the slab model, the guided-mode model, and the improved version of the Huang-Zhu model [Phys. Rev. B 38, 13 377 (1998)], -and the phonon modes in bulk, the energy-loss rates of hot carriers due to the Frohlich potential scattering in GaAs/AlAs multiple quantum wells (MQW's) are calculated and compared to those obtained based on a microscopic dipole superlattice model. In the study, a special emphasis is put on the effects of the phonon models on the hot-carrier relaxation process when taking the hot-phonon effect into account. Our numerical results show that, the calculated energy-loss rates based on the slab model and on the improved Huang-Zhu model are almost the same when ignoring the hot-phonon effect; however, with the hot phonon effect considered, the calculated cooling rate as well as the hot phonon occupation number do depend upon the phonon models to be adopted. Out of the four analytical phonon models investigated, the improved Huang-Zhu model gives the results most close to the microscopic calculation, while the guided-mode model presents the poorest results. For hot electrons with a sheet density around 10(12)/cm(2), the slab model has been found to overestimate the hot-phonon effect by more than 40% compared to the Huang-Zhu model, and about 75% compared to the microscopic calculation in which the phonon dispersion is fully included. Our calculation also indicates that Nash's improved version [J. Lumin. 44, 315 (1989)] is necessary for evaluating the energy-loss rates in quantum wells of wider well width, because Huang-Zhu's original analytical formulas an only approximately orthogonal for optical phonons associated with small in-plane wave numbers. [S0163-1829(99)08919-5].

Thermoelectric Cooling and Power Generation

In a typical thermoelectric device, a junction is formed from two different conducting materials, one containing positive charge carriers (holes) and the other negative charge carriers (electrons). When an electric current is passed in the appropriate direction through the junction, both types of charge carriers move away from the junction and convey heat away, thus cooling the junction. Similarly, a heat source at the junction causes carriers to flow away from the junction, making an electrical generator. Such devices have the advantage of containing no moving parts, but low efficiencies have limited their use to specialty applications, such as cooling laser diodes. The principles of thermoelectric devices are reviewed and strategies for increasing the efficiency of novel materials are explored. Improved materials would not only help to cool advanced electronics but could also provide energy benefits in refrigeration and when using waste heat to generate electrical power.

Measurement of respiratory acoustic impedance in children by a modified forced oscillation method

An introduction to a modified forced oscillation method, square-wave excitation technique, including fundamentals and methods, as used in respiratory function examination. On the basis of experimental results and theoretical predictions, we suggest that Respiratory Acoustic Impedance (RAI) measurement by spectral analysis can significantly improve estimation of contribution to RAI from different part of respiratory tract. The outcome is of considerable interest in the study of lung disease, such as COPD and asthma in young children.

Commissioning of electron cooling in CSRm

A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 108particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10−4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy,electron beam current, electron beam profile, expansion factor and injection interval have been performed.The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.

Circa AD 626 volcanic eruption；climatic cooling；and the collapse of the Eastern Turkic Empire

IEECAS SKLLQG

The influence and chronological uncertainties of the 8.2 ka cooling event on continental climate records in China

IEECAS SKLLQG

Primary design of stochastic cooling in CSRm

Based on several facts of CSRrn, such as the layout of the ring, the lattice parameters, exiting Schottky noise diagnosis equipment and fund, the primary stochastic cooling design of CSRm has been carried out. The optimum cooling time and the optimum cooling bandwidth axe obtained through simulation using the cooling function. The results indicate that the stochastic cooling is quite a powerful cooling method for CSRm. The comparison of the cooling effects of stochastic cooling and electron cooling in CSR are also presented. We can conclude that the combination of the two cooling methods on CSRrn will improve the beam cooling rate and quality beam greatly.

COD by magnetic field in electron-cooling section and correction at CSR

Application of electron-cooling upgrades the quality of ion beams in the storage rings and brings new problems. The transverse magnetic field distorts the ion orbit while guiding the intense electron beam. The closed-orbit distortion should be and can be localized and controlled well inside the ring acceptance. This paper deals with the field in the e-cool section and concomitant COD of ion orbit and shows the correction scheme.

兰州重离子加速器冷却储存环主环二极铁电源设计；Design of main ring dipole power supply for Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring

主环二极铁电源是兰州重离子加速器冷却储存环(HIRFL-CSR)工程的关键设备和指标要求最高的一台电源,采用了独特的拓扑和控制策略。为满足峰值功率3.15MW(3kA,1.45kV)的输出能力和快脉冲要求,采用了晶闸管整流并联脉宽调制补偿单元的主电路拓扑结构和特殊的控制方式,这套综合方案确保电源满足了全部技术指标。本文介绍了该拓扑结构的原理和优势,讨论了为满足±2×10-4的跟踪误差的要求而采用的控制拓扑和双基准给定的原理,并简介了调试过程和近年来的运行和改进情况。

基于P2P技术的CSRe冷却装置控制系统设计；Design of Control System for CSRe Cooling Equipment Based on P2P Technology

HIRFL-CSR工程对CSRe冷却装置电子冷却部分的控制系统在实时性和可靠性方面提出了非常高的要求。电子冷却工作环境复杂,各种干扰难以预测。从电子冷却的控制系统改进出发,以实现电子冷却的自动调束为目标,以高端FPGA和ARM嵌入式系统为基础,采用P2P通讯技术和神经元网络算法来实现对电子冷却的自动控制。该控制系统对电子冷却控制的完善提供了先进的硬件平台和软件实现方案。