冻干猪主动脉过程中升华界面移动特性实验研究

利用微CT扫描技术对猪主动脉在冷冻干燥保存中升华过程进行观察,分析升华界面移动特性,并使用质构仪对猪主动脉冻干前后力学性能进行检测。结果表明:干燥过程中对物料底部进行加热,升华是在外表面和内表面同时进行的。升华界面随干燥时间推移不断向壁面中心靠近。升华刚开始物料干燥速率比较快,界面移动明显,随着干燥层增厚,传质阻力增大,升华速率减慢,界面移动变化较小。质构实验对力学性能检测结果显示血管经冷冻干燥后其弹性和耐压性等与新鲜猪主动脉相比基本得到保持。     

粒状物料常压吸附流化床冷冻干燥的传热研究

以粒状马铃薯为研究对象,在常压吸附流化床冷冻干燥的实验基础上,建立了吸附流化床内对流边界条件下的球坐标冻干模型,并采用变时间步长的有限差分法,求解了物料内部温度分布及升华界面的移动速率,与实验结果吻合较好,分析了有关因素对于冻干过程中传热及干燥过程的影响。     

冻干过程中升华界面温度测量方法的研究

压力测温技术是基于在平衡状态下,冰晶温度与其饱和蒸汽压为单值函数这一基本规律,在升华干燥过程中,突然中断从冻干室流向冷阱的水蒸汽流,通过测量冻干室内压力回升情况去推算升华界面温度的一种非接触式测温方法。与热电偶或热敏电阻测温相比,压力测温技术即不破坏冻干样品的结构,又能够较为准确地反应出移动升华界面的温度,并能判断升华干燥过程终点。文中分析了升华界面温度测量的意义与困难,建立了压力测温技术的数学模型与分析方法,并通过实验研究了压力测温技术。     

冷冻干燥中升华过程界面的微CT观察及气固相变分析

采用微CT扫描成像、图像重构及灰度值分析技术对冷冻干燥中升华过程界面及气固相变进行实验观察与分析。采用高斯误差函数拟合,计算得到冰的平均灰度值为154。在后续灰度值比价分析中,固体物料苹果本身的灰度值高于冰的灰度值,从而可以分析冰晶的移动特性。从直接扫描图像和重构图像,均可看到升华界面的移动是一个立体的移动,由它所包裹的冻结区逐渐向物料几何中心收缩。对比冻结物料和冻干物料的灰度值曲线,可见刚开始灰度值较低的冰区,在冻干结束后变成灰度值相对较高的孔疏区。     

植物性材料红外辐射与对流脱水的非稳态实验研究

文中以木材红外干燥工程为背景,建立了红外辐射与对流脱水的物理模型,测量了木板的干燥速率、多点温度与湿度及干、湿球温度,研究了升速、恒速、降速三个干燥阶段的规律,推导了适于全干燥过程的非稳态干燥动力学方程,发现了升温速率对木材干燥的关键影响,并对辐射强化系数K_1、对流传质汽化系数K_t、对流放热系数H_c及总放热系数H_o进行了计算与分析。该理论对木板及难干物料的干燥,均有重要意义。     

加热方式对真空冷冻干燥热质传递机理的影响

1引言真空冷冻干燥（简称真空冻干）是多孔介质在低温低压下相变界面移动的耦合传热传质过程，其数学模型带有典型的非线性，难于精确求解［‘，2］。从应用上而言，真空冻干具有设备投资高，能耗大，干燥时间长的缺点。能量的供应即加热方式、升华水汽的流动条件、物料的输运性质是影响真空冻干性能的主要因素间。本文以牛肉的真空冷冻干燥过程为例，建立过程的非稳态数学模型，利用数值求解的结果，结合实验分析，研究了通过千层的辐射加热和通过冻结层的导热加热条件下真空冻干过程中传热传质的机理，分析了加热方式对缩短干燥时间的影响…     

菜豆种子薄层干燥物料内部水分扩散系数的确定

本文将数值方法应用于物性测试,用反问题的研究方法,通过建立物料的内部水分扩散模型及边界条件的处理,把反映物料干燥过程动态特性的实验含水率曲线与物料颗粒内部的水分扩散结合起来,确定物料颗粒在非稳态脱水过程中的内部水分扩散系数,并分析内部水分分布及其动态特性。计算结果与实验曲线拟合的分析表明,本文的方法是可行的,对于进一步分析干燥过程参数对种子劣变的影响及确定优化的干燥工艺从而达到干燥控制的目的有重要的意义。     

多孔介质干燥过程传热传质研究

一、过程分析及数学模型的建立 多孔介质的干燥过程一般可以分为三个阶段:预热阶段、恒速率干燥阶段和降速率干燥阶段.降速率干燥阶段通常又分为第一、第二降速率干燥阶段. 预热阶段一般很短,对过程影响不大,本文不考虑它的存在,只研究后面几个阶段. 根据本文的研究范围,对问题作如下简化: (1)被干燥材料存宏观结构上是统计均匀的,且在干燥过程中不发生体积变化.     

干燥物料水分状态研究

物料在太阳能干燥房中干燥以后 ,用水分测定仪测定其含水量进行再干燥。测定再干燥前后物料的红外光谱 ,研究其水分状态表明 ,在干燥过程后期 ,将干燥温度控制在结合水开始逸出的温度 ,可得到最好的干燥效果     

气固同轴撞击流干燥试验研究

撞击流干燥（Impinging Stream Drying，ISD）技术是强化相间传热传质和加快颗粒干燥过程的有效方法。通过在自行设计的同轴水平撞击流试验装置上对物料进行的一系列干燥试验，验证了空气温度、颗粒喂料速率、颗粒预热温度等操作参数和撞击距离、撞击室容积等结构参数对干燥性能的影响，获得了同轴撞击流干燥的一般规律...     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.