Kinetic description of particle emission from expanding source

The freeze out of the expanding systems, created in relativistic heavy ion collisions, is discussed. We combine kinetic freeze out equations with Bjorken type system expansion into a unified model. The important feature of the proposed scenario is that physical freeze out is completely finished in a finite time, which can be varied from 0 (freeze out hypersurface) to ∞. The dependence of the post freeze out distribution function on the freeze out time will be studied. As an example, model is completely solved and analyzed for the gas of pions. We shall see that the basic freeze out features, pointed out in the earlier works, are not smeared out by the expansion of the system. The entropy evolution in such a scenario is also studied.     

冬小麦冻害胁迫高光谱分析与冻害严重度反演

对冬小麦冻害严重度的精确反演是及时采取补救措施降低损失的关键,同时及时预测产量损失对政府职能部门也具有积极意义。针对冬小麦冻害群体严重度评估方法在经典统计反演模型存在估算效果不理想的情况下,以冬小麦为试验对象,首先对冬小麦冠层光谱反射率数据进行重采样平滑处理,再用主成分分析(PCA)技术对高光谱数据进行分析,进一步实现综合原始光谱主成分信息作为自变量参与冬小麦冻害严重度反演过程,最后采用决定系数R2、均方根误差RMSE、准确度Accuracy三种模型精度验证方法对模型进行评价。结果显示,基于主成分分析法建立冬小麦冻害严重度模型精度分别达0.697 5,0.184 2和0.697 5;同时对反演模型进行验证,其精度也分别达到0.630 9,0.350 3和1.339 6。因此,该方法能有效地对冬小麦冻害严重度进行快速、精确的反演。     

加热方式对真空冷冻干燥过程的影响

以平板状饱和牛肉为对象，对不同供热方法下冷冻干燥过程的传热传质进行了数值计算与实验研究，分析比较了表面加热与微波加热两种供热方式对冻干过程的影响，为冻干过程中供热方式的选择提供了理论依据及分析方法。     

X‐ray tomography of morphological changes after freeze/thaw in gas diffusion layers

Liquid water produced in a polymer electrolyte membrane fuel cell experiences a freeze/thaw cycle when the cell is switched off and on while operating at ambient temperatures below freezing. This freeze/thaw cycle permanently deforms the polymer electrolyte membrane fuel cell capillary structures and reduces both the cell life and its ability to generate electric power. The X‐ray tomography facility at the Pohang Accelerator Laboratory was used to observe the freeze/thaw effects on the gas diffusion layer (GDL), which is the thickest capillary layer in the cell. Morphological changes in the GDL under a water freeze/thaw cycle were observed. A scenario in which freeze/thaw cycles affect fuel cell performance is suggested based on images from X‐ray tomography.     

流化床冷冻干燥气体制冷循环工质的比较研究

氩气、氮气来源于空气,都不与药品中热敏性成分起反应。吸附式流化床冷冻干燥设备简单、节能,而且冻干产品品质与真空冷冻干燥接近。分析了应用在流化床冷冻干燥装置上的制冷循环,对氩气、氮气作为工质应用于该系统的性能进行计算,在此基础上,进行了比较研究。     

Uniform Drug Loading into Prefabricated Microparticles by Freeze‐Drying

Microparticle‐based drug delivery is a promising technology for small volume bioassay platforms. The general utilization of the drug‐loaded microparticles in the in vitro bioassay platforms requires the drug loading method, which should impregnate the general drug types (e.g., water insoluble) with high payload into the variously designed microparticles. Loading the drug into the prefabricated microparticles using solvent evaporation satisfies the requirement. However, similar to the “coffee‐ring effect,” drugs are loaded in a seriously nonuniform manner, caused by the capillary flow during the evaporation process. Here, it is presented that the freeze‐drying is an efficient way to load uniform and high amount of the drug into the prefabricated microparticles. It is demonstrated that freezing solvent can block the capillary flow during the solvent removal process, improving the loading uniformity. The delivered amount of drugs is linearly proportional to the initial loading amount of drugs. Also, this drug loading method is shown to be applied to the various drug types and the prefabricated microparticles with different properties. Considering many challenges to suppress the “coffee‐ring effect” that induces nonuniform impregnation/deposition, the proposed concept can be applied not only for microparticle‐based drug delivery but also for uniform coating applications (e.g., thin‐film coating, DNA/protein microarray).     

Dual improvement in curcumin encapsulation efficiency and lyophilized complex dispersibility through ultrasound regulation of curcumin–protein assembly

Ultrasound has a recognized ability to modulate the structure and function of proteins. Discovering the influential mechanism of ultrasound on the intramolecular interactions of egg-white protein isolate–curcumin (EPI–Cur) nanoparticles and their intermolecular interaction during freeze drying and redispersion is meaningful. In this study, under the extension of pre-sonication time, the protein solubility, surface hydrophobicity, and curcumin encapsulation rate showed an increasing trend, reaching the highest value at 12 min of treatment. However, the values decreased under the followed extension of ultrasound time. After freeze drying and redispersion were applied, the EPI–Cur sample under 12 min of ultrasound treatment exhibited minimal aggregation degree and loss of curcumin. The retention and loading rates of curcumin in the lyophilized powder reached 96 % and 33.60 mg/g EPI, respectively. However, under excessive ultrasound of >12 min, scanning electron microscopy showed distinct blocky aggregates. Overexposure of the hydrophobic region of the protein triggered protein-mediated hydrophobic aggregation after freeze drying. X-ray diffraction patterns showed the highest crystallinity, indicating that the free curcumin-mediated hydrophobic aggregation during freeze drying was enhanced by the concentration effect and intensified the formation of larger aggregates. This work has practical significance for developing the delivery of hydrophobic active substances. It provides theoretical value for the dynamic dispersity change in protein-hydrophobic active substances during freeze drying and redissolving.     

Structural Relaxation of Polystyrene Glasses with Dis‐interpenetrated Chains Studied by Differential Scanning Calorimetry

The polystyrene (PS) samples were prepared by freeze‐drying solutions with different concentrations. The structural relaxation behaviors and the chain conformation were studied by differential scanning calorimetry and nonradiative energy transfer, respectively. The results showed that PS prepared by freeze‐drying from very dilute solution was in a disinterpenetrated state, and the structural relaxation was faster than that for interpenetrated coils and the cross‐linked samples.     

Quantitative visualization of a gas diffusion layer in a polymer electrolyte fuel cell using synchrotron X‐ray imaging techniques

A gas diffusion layer (GDL) in a polymer electrolyte fuel cell (PEFC) is quantitatively visualized using synchrotron X‐ray micro‐computed tomography. For three‐dimensional reconstruction, an adaptive threshold method is used. This method is compared with the conventional method, i.e. Otsu's method. Additionally, the spatial and temporal variations of the porosity distribution of the GDL under freeze‐and‐thaw cycles are investigated experimentally. The freeze‐and‐thaw cycles are established simply using a CRYO system and light source illumination, respectively. Structural defects are found to largely affect the porosity of the GDL. In addition, a cyclic porosity variation is observed in the GDL under freeze‐and‐thaw cycles. The heterogeneous porosity is irreversibly decreased with the progress of repetitive cycles.     

真空冷冻干燥机冷阱中的气体换热分析

从理论上分析了螺旋盘管式冻干机冷阱中气体的换热。对真空冷阱中处于滑流区的气体换热 ,应考虑温度跳跃和速度滑移对换热的影响。基于冷阱内表面定热流和恒壁温的假设 ,建立了相应的分析模型 ,导出了冻干机冷阱内处于滑流区的气体换热 Nusselt数表达式 ,认为随着冷阱压力的降低 ,换热 Nusselt数将不断减小     

Improvement of the properties of MnZn ferrite power cores through improvements on the microstructure of the compacts

In the present work freeze drying and wet-pressing technologies are applied and evaluated in the manufacturing process of functional ceramics such as MnZn power ferrites. In particular, the implementations of freeze drying instead of spray drying and the implementation of wet pressing instead of dry uniaxial pressing are investigated. It appeared that at high frequencies there is almost 25% power loss reduction by the implementation of freeze drying instead of spray drying. At low frequencies there is almost 23% power loss reduction by the implementation of wet pressing instead of dry pressing. By introducing wet pressing technology, MnZn ferrite materials exhibiting power losses of 210 mW cm⁻³ (100 kHz, 200 mT and 100 °C) could be synthesized. This is one of the lowest power loss values reported in the scientific or patented literature.     

A cryogenic scanning force microscope for the characterization of frozen biological samples

We present the design of a new scanning force microscope specially suited for the investigation of soft matter, particularly biological, in an ultrahigh vacuum. The key point is that the samples are immobilized by shock freezing in order to maintain their native structure before they are introduced into the vacuum system. The vacuum system itself consists of a transfer chamber, which allows an exchange of the cold sample with cryo-electron microscopes, a preparation chamber including a stage for in-situ freeze drying, freeze etching, or freeze fracturing, and the analysis chamber with the microscope. Sample cooling is maintained in all chambers. The microscope is mounted on a commercially available vibration isolation system; a flow cryostat cools the sample to the temperature of liquid nitrogen, while the tip is scanned. Besides measurements on test samples, which demonstrate the imaging capabilities of the instrument, first results on T4-bacteriophages (viruses) are shown. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-40/42838-6188, E-mail: wiesendanger@physnet.uni-hamburg.de     

A survey of dark matter and related topics in cosmology

This article presents an extensive review of the status of the search of the dark matter. The first eight sections are devoted to topics in dark matter and its experimental searches, and the rest to selected topics in astrophysics and cosmology, which are intended to supply some of the needed background for students in particle physics. Sections 9 and 13 are introductory cosmology. The three astrophysical topics, Big Bang nucleosynthesis Section 10, Boltzmann transport equation and freeze out of massive particles Section 11, and CMB anisotropy Section 12 can all be studied in analytical approaches when reasonable approximations are made. Their original analytically forms, to which this article follows very closely, were given by particle physicists. Dark matter is an evolving subject requiring timely update to stay current. Hence a review of such a subject matter would undoubtedly have something wanting when it appears in print. It is hoped that this review can form a humble basis for those graduate students who would like to pursue the subject of dark matter. The reader can use the extensive table of contents to see in some details the materials covered in the article.     

A comparision of four methods for cryopreservation of meristems in banana (Musa spp.)

To establish an improved protocol for the cryopreservation of banana (Musa spp.), a fast-freeze/fast-thaw method was applied and compared to three existing cryogenic procedures, namely, simple freezing, vitrification of proliferating meristems and vitrification of individual meristems. The average post-thaw shoot regeneration of the fast freeze/fast thaw protocol was 51.8 percent and was superior to the existing protocols which were 12.5 percent, 39.2 percent and 42.8 percent, respectively. Other factors such as time and ease of operation were considered for each method. It was found that the fast freeze and fast thaw technique was the best amongst all the four methods tested for the cryopreservation of in vitro banana meristems in the genotype Robusta (AAA).     

Spectrophotometric Determination of Enalapril Maleate and Ramipril in Dosage Forms

Three sensitive and accurate spectrophotometric methods have been developed for the assay of enalapril maleate and ramipril, each in its dosage forms. These methods depend on the reaction of the drugs with p-chloranilic acid, the reaction with picric acid, and the ion-pair salt formation with bromocresol green. The proposed methods have been applied to the analysis of these drugs in their commercial tablets. The results obtained were precise and accurate.     

The first second of the Universe

The history of the Universe after its first second is now tested by high quality observations of light element abundances and temperature anisotropies of the cosmic microwave background. The epoch of the first second itself has not been tested directly yet; however, it is constrained by experiments at particle and heavy ion accelerators. Here I attempt to describe the epoch between the electroweak transition and the primordial nucleosynthesis. The most dramatic event in that era is the quark‐hadron transition at 10 μs. Quarks and gluons condense to form a gas of nucleons and light mesons, the latter decay subsequently. At the end of the first second, neutrinos and neutrons decouple from the radiation fluid. The quark‐hadron transition and dissipative processes during the first second prepare the initial conditions for the synthesis of the first nuclei. As for the cold dark matter (CDM), WIMPs (weakly interacting massive particles) – the most popular candidates for the CDM – decouple from the presently known forms of matter, chemically (freeze‐out) at 10 ns and kinetically at 1 ms. The chemical decoupling fixes their present abundances and dissipative processes during and after thermal decoupling set the scale for the very first WIMP clouds.     

冷冻干燥法制备Li2O氚增殖剂陶瓷小球

以Li₂CO₃粉末为原料,采用一种冷冻干燥湿法工艺,制备出综合性能较好的Li₂O陶瓷小球。通过研究冷冻成形、煅烧、分解和烧结等工艺过程,优化了Li₂O陶瓷小球的制备工艺,并对获得的Li₂O陶瓷小球进行了性能表征。结果表明:冷冻成形制备的凝胶小球在650 ℃煅烧后可得到纯净的Li₂CO₃小球,再于真空条件下多步程序升温至720 ℃可制得主要相为Li₂O的小球,小球尺寸分布均匀,直径约为0.8 mm,平均晶粒尺寸为9 μm,于900 ℃高温烧结后小球的密度可达理论密度的69.5%。     

Metformin and glitazones: does similarity in biomolecular mechanism originate from tautomerism in these drugs?

This theoretical study attempts to find out similarity between metformin and glitazone class of antidiabetic drugs. It was found that some tautomeric forms of both metformin and thiazolidinedione ring of glitazones have similar molecular electrostatic potential (MESP) surface and may bind to a common complementary surface. Complexation and docking studies were also carried out in order to support this hypothesis. Copyright © 2007 John Wiley & Sons, Ltd.     

Terahertz absorption spectra of commonly used antimalarial drugs

Optical Review - Terahertz (THz) spectra from the pure forms [i.e. the active pharmaceutical ingredients (APIs)] of four commonly used antimalarial drugs are reported. The well-defined spectral...