液氮温区G-M制冷机的数值分析及新型结构制冷机的研制

G-M制冷机是回热式的小型低温制冷机，它利用绝热放气膨胀原理（又称为西蒙膨胀法）获得低温，具有振动小、运行稳定、寿命长、操作方便等特点，在对效率、重量、尺寸等没有太高要求的场合应用非常广泛。在八十年代末，G-M制冷机已经突破了液氦温度，非常适合在液氦温区为超导器件或电子元件提供冷量，在低温真空泵、MRI超导磁体冷却系统、SQUID再冷凝系统等方面有良好的应用前景，推广其应用已属当务之急。本文围绕着探索氦温区G-M制冷机工作机理、提高低温蓄冷器性能及新型结构G-M制冷机的研制等方面，进行了系统地理论分析和纳归纳，以及初步地实验研究：一. 首次比较完善地建立了液氦温区G-M型制冷机整机数值模拟方法，数值模拟方法给出了制冷机内工质参数瞬态分布及动态变化曲线，为分析制冷机独特的循环特性提供了直观的依据，为探讨运行及结构参数对制冷性能的影响机理提供了强有力的工具。模型中考虑了制冷机中的阻力、实际进排气角、物性变化及蓄冷器内空隙率的存在等多种实际因素：解决了一、二级耦合及部件交界处物性变化不连续对计算影响等问题；采取网格非均匀化、牛顿迭代法以及负反馈原理等措施，提高了计算精度和收敛性。在微机上成功地模拟了液氦温区G-M制冷机的工作过程，程序采用模块化编程，具有一定通用性。二. 运用液氦温区整套机数值模拟方法，计算了制冷机内工质参数（氦流温度、压力、流速等）周期性变化和空间分布，采用一级蓄冷器与低温蓄冷器工作特性对比法，从整机内工质参数动态变化规律分析的角度，验证了液氦温区G-M制冷机工质氦的循环主要分为两部分：常规循环、低温循环。并详细地讨论了运行参数（频率、工作压力）及一级制冷机结构参数对整机内工数动态变化的影响规律以及制冷机性能的影响机理。三. 首次建立了较完善的液氦温区多层混合填料型低温蓄冷器的数值模拟方法，运用数值模拟方法，首次详细地研究了常用填料的不同组合、一定组合下填料比例以及蓄冷器结构对制冷机性能的影响机理，提出了不同填料的最佳节组合及一定组合下填料最佳比例的确定和低温蓄冷器结构和填料优化的原则，为合理有效地设计高性能液氦温区低温蓄冷器提供了依据。四. 提出并设计、加工了一种新型结构的液氦温区双级G-M型制冷机，该机结构在国内外属于首创。其具有以下主要结构特点：一、二级分别独立驱动；一、二级之间通过热桥连接；二级蓄冷器外置于汽缸等。同时建立了新型结构液氦温区双级G-M型制冷机实验系统，为今后整机性能和内部动态过程的研究奠定了基础。五. 新型结构双级G-M型制冷机二级单机动转频率为0.6Hz时，制冷温度为13.6K，且在20K时有4.4W的制冷量；制冷机已达到液氦温区，f = 0.4Hz时，最低温度为4.6K；f = 1Hz，制冷温度为10K时，制冷量大于6W，上述结果目前均未见有文献报道。在新型G-M制冷机上，初步进行了低温蓄冷器性能测试实验及运行参数对制冷机性能影响的实验研究。

Synopse dos trabalhos da Camara dos Srs. Deputados : relativos ao anno de 1923 : acompanhados de differentes documentos : organizada na Secretaria da mesma Camara

Sinopse dos trabalhos na Câmara dos Deputados, em 1923.

La gestión de las actividades musicales del G-9 en contextos de educación fornal y no formal

479 p.

Las organizaciones juveniles del nacionalismo vasco: política, cultura y ocio (1893-1923)

909 p.

Modernización y Educación en Vitoria (1865-1931): Espacio escolar e Higienización

Historia de la influencia del higienismo en la evolución del espacio escolar de la ciudad de Vitoria entre 1865-1931.

Comparative growth and survival of fry of Clarias gariepinus (B), Clarias anguillaris (L), Heterobranchus bidorsalis (G), Heteroclarias, Clariabranchus and Clarias hybrids under outdoor nursery management system

Hybrids of Clariid catfishes; C. gariepinus (Netherlands), C. anguillaris, H. bidorsalis and their parental species were monitored for 8 weeks in 2 x 2 x 1m outdoor concrete tanks. The fry were fed NIFFR diet (40% crude protein) twice daily, 7 days of the week. Growth and survival records were taken weekly. The male HEB X female CLG hybrid showed an overall highest performance in growth rate while the lowest was recorded in male CLA X female CLG hybrid. The male HEB X female CLG hybrid grew at a faster rate than its reciprocal hybrid. In view or their growth rate, it is possible that the growth and survival rates or H. bidorsalis especially at the fry to fingerling stage could be improved through hybridization. The hybrid have potential as commercial food fish

On the determination of the properties of a medium from its reflection coefficient

This thesis demonstrates how the parameters of a slightly non-homogeneous medium can be derived approximately from the reflection coefficient.

Two types of media are investigated. The first is described by the one-dimensional wave equation, the second by the more complex Timoshenko beam equation. In both cases, the media are assumed to be infinite in extent, with the media parameters becoming homogeneous as the space variable approaches positive or negative infinity.

Much effort is placed in deriving properties of the reflection coefficient for both cases. The wave equation is considered primarily to introduce the techniques used to investigate the more complex Timoshenko equation. In both cases, an approximation is derived for one of the medium parameters involving the reflection coefficient.

Non-linear dispersive waves with a small dissipation

The general theory of Whitham for slowly-varying non-linear wavetrains is extended to the case where some of the defining partial differential equations cannot be put into conservation form. Typical examples are considered in plasma dynamics and water waves in which the lack of a conservation form is due to dissipation; an additional non-conservative element, the presence of an external force, is treated for the plasma dynamics example. Certain numerical solutions of the water waves problem (the Korteweg-de Vries equation with dissipation) are considered and compared with perturbation expansions about the linearized solution; it is found that the first correction term in the perturbation expansion is an excellent qualitative indicator of the deviation of the dissipative decay rate from linearity.

A method for deriving necessary and sufficient conditions for the existence of a general uniform wavetrain solution is presented and illustrated in the plasma dynamics problem. Peaking of the plasma wave is demonstrated, and it is shown that the necessary and sufficient existence conditions are essentially equivalent to the statement that no wave may have an amplitude larger than the peaked wave.

A new type of fully non-linear stability criterion is developed for the plasma uniform wavetrain. It is shown explicitly that this wavetrain is stable in the near-linear limit. The nature of this new type of stability is discussed.

Steady shock solutions are also considered. By a quite general method, it is demonstrated that the plasma equations studied here have no steady shock solutions whatsoever. A special type of steady shock is proposed, in which a uniform wavetrain joins across a jump discontinuity to a constant state. Such shocks may indeed exist for the Korteweg-de Vries equation, but are barred from the plasma problem because entropy would decrease across the shock front.

Finally, a way of including the Landau damping mechanism in the plasma equations is given. It involves putting in a dissipation term of convolution integral form, and parallels a similar approach of Whitham in water wave theory. An important application of this would be towards resolving long-standing difficulties about the "collisionless" shock.

Impact assessment of Niger State fisheries legislation on fisheries conservation in Edozhigi local government area (L.G.A.) of Niger State

A preliminary survey was conducted among the fishermen in five selected villages in Edozhigi L.G.A. of Niger State. One hundred and fifty fishermen were randomly selected and interviewed to find out the impact of Niger State fisheries legislation on fisheries conservation resources in the area. The analysis of data collected using descriptive statistics indicated that undersized mesh of gill nets, beach seines and traps are being used unabated. Also, fenced barriers across the entrance of flood plain ponds and Ex-bow lakes from the main stream are in the area. The fisheries rules and regulations implementers are rarely seen or not seen at all in the area. The decreasing nature of fish catches was detected. It is observed that government policy on fish conversation is neglected due to inadequate or lack of funding for meaningful extension and implementation of the fisheries rules and regulations

Chemical-scale studies of G protein-coupled receptors and ligand-gated ion channels

This dissertation describes studies of G protein-coupled receptors (GPCRs) and ligand-gated ion channels (LGICs) using unnatural amino acid mutagenesis to gain high precision insights into the function of these important membrane proteins.

Chapter 2 considers the functional role of highly conserved proline residues within the transmembrane helices of the D2 dopamine GPCR. Through mutagenesis employing unnatural α-hydroxy acids, proline analogs, and N-methyl amino acids, we find that lack of backbone hydrogen bond donor ability is important to proline function. At one proline site we additionally find that a substituent on the proline backbone N is important to receptor function.

In Chapter 3, side chain conformation is probed by mutagenesis of GPCRs and the muscle-type nAChR. Specific side chain rearrangements of highly conserved residues have been proposed to accompany activation of these receptors. These rearrangements were probed using conformationally-biased β-substituted analogs of Trp and Phe and unnatural stereoisomers of Thr and Ile. We also modeled the conformational bias of the unnatural Trp and Phe analogs employed.

Chapters 4 and 5 examine details of ligand binding to nAChRs. Chapter 4 describes a study investigating the importance of hydrogen bonds between ligands and the complementary face of muscle-type and α4β4 nAChRs. A hydrogen bond involving the agonist appears to be important for ligand binding in the muscle-type receptor but not the α4β4 receptor.

Chapter 5 describes a study characterizing the binding of varenicline, an actively prescribed smoking cessation therapeutic, to the α7 nAChR. Additionally, binding interactions to the complementary face of the α7 binding site were examined for a small panel of agonists. We identified side chains important for binding large agonists such as varenicline, but dispensable for binding the small agonist ACh.

Chapter 6 describes efforts to image nAChRs site-specifically modified with a fluorophore by unnatural amino acid mutagenesis. While progress was hampered by high levels of fluorescent background, improvements to sample preparation and alternative strategies for fluorophore incorporation are described.

Chapter 7 describes efforts toward a fluorescence assay for G protein association with a GPCR, with the ultimate goal of probing key protein-protein interactions along the G protein/receptor interface. A wide range of fluorescent protein fusions were generated, expressed in Xenopus oocytes, and evaluated for their ability to associate with each other.

Protein-protein recognition: The neonatal Fe receptor and immunoglobulin G

The neonatal Fe receptor (FeRn) binds the Fe portion of immunoglobulin G (IgG) at the acidic pH of endosomes or the gut and releases IgG at the alkaline pH of blood. FeRn is responsible for the maternofetal transfer of IgG and for rescuing endocytosed IgG from a default degradative pathway. We investigated how FeRn interacts with IgG by constructing a heterodimeric form of the Fe (hdFc) that contains one FeRn binding site. This molecule was used to characterize the interaction between one FeRn molecule and one Fe and to determine under what conditions FeRn forms a dimer. The hdFc binds one FeRn molecule at pH 6.0 with a K_d of 80 nM. In solution and with FeRn anchored to solid supports, the heterodimeric Fe does not induce a dimer of FeRn molecules. FcRnhdFc complex crystals were obtained and the complex structure was solved to 2.8 Å resolution. Analysis of this structure refined the understanding of the mechanism of the pH-dependent binding, shed light on the role played by carbohydrates in the Fe binding, and provided insights on how to design therapeutic IgG antibodies with longer serum half-lives. The FcRn-hdFc complex in the crystal did not contain the FeRn dimer. To characterize the tendency of FeRn to form a dimer in a membrane we analyzed the tendency of the hdFc to induce cross-phosphorylation of FeRn-tyrosine kinase chimeras. We also constructed FeRn-cyan and FeRn-yellow fluorescent proteins and have analyzed the tendency of these molecules to exhibit fluorescence resonance energy transfer. As of now, neither of these analyses have lead to conclusive results. In the process of acquiring the context to appreciate the structure of the FcRn-hdFc interface, we developed a study of 171 other nonobligate protein-protein interfaces that includes an original principal component analysis of the quantifiable aspects of these interfaces.

Diseño e implementación de un sistema para la validación de la recomendación G.1031 y P.1501 de la ITU-T

[ES]El objetivo principal de este trabajo es el diseño y desarrollo de un sistema para la validación de las metodolog��as propuestas en el borrador de recomendación P.STMWeb [1] “Metodolog��a para la evaluación subjetiva de la calidad percibida en la navegación web”. Como resultado de la validación realizada con el sistema han sido aprobadas las recomendaciones G.1031 [5] “Factores del QoE en web browsing��� y P.1501 [6] “Metodolog��a de prueba subjetiva para web browsing��� de la ITU-T. El sistema propuesto se ha diseñado en base a las especificaciones marcadas en el borrador de la recomendación en vías de estandarización [P.STMWeb].Estas especificaciones han servido de base para el diseño e implementación de un sistema que permite una navegación web interactiva, con control y actualización de páginas web en base a variaciones de parámetros de red, como el retardo en un entorno controlado. Así mismo siguiendo la metodolog��a establecida en el borrador de recomendación anteriormente mencionado se ha diseñado y desarrollado un sistema de encuestas para evaluar de forma subjetiva la calidad experimentada por los usuarios (QoE) en la navegación web. Para el diseño del sistema de encuestas, se analizaron y utilizaron como especificaciones los diferentes factores que se contemplan en el borrador de recomendación G.QoE-Web [2] “Factores relevantes y casos de uso para la QoE Web” de la ITU-T. En base al diseño realizado, se ha desarrollado un sistema que permite analizar la calidad experimentada por los usuarios en la navegación Web.

Quantum interference effects of two coherent population trapping states on the atomic spectral lines of a F-e=0 -> F-g=1 transition

We investigate the fluorescence spectrum in a nearly degenerate atomic system of a F-e = 0 -> F-g = 1 transition by analytically solving Schrodinger equations. An ultranarrow fluorescence spectral line in between the two coherent population trapping windows has been found. Our analytic solutions clearly show the origin of the ultranarrow spectral line. Due to quantum interference effects between two coherent population trapping states, the width and intensity of the central spectral line can be controlled by an external magnetic field. Such an effect may be used to detect a magnetic field.