The influence of fluctuation fields on the force-free field .2. The local expansion

In Paper I (Hu, 1982), we discussed the the influence of fluctuation fields on the force-free field for the case of conventional turbulence and demonstrated the general relationships. In the present paper, by using the approach of local expansion, the equation of average force-free field is obtained as (1+b)×B 0=(#x002B;a)B 0#x002B;a (1)×B 0#x002B;K. The average coefficientsa,a (1),b, andK show the influence of the fluctuation fields in small scale on the configurations of magnetic field in large scale. As the average magnetic field is no longer parallel to the average electric current, the average configurations of force-free fields are more general and complex than the usual ones. From the view point of physics, the energy and momentum of the turbulent structures should have influence on the equilibrium of the average fields. Several examples are discussed, and they show the basic features of the fluctuation fields and the influence of fluctuation fields on the average configurations of magnetic fields. The astrophysical environments are often in the turbulent state, the results of the present paper may be applied to the turbulent plasma where the magnetic field is strong.

Influence of Water Depth on the Rate of Expansion of Giant Cutgrass Populations and Management Implications

Giant cutgrass ( Zizaniopsis miliacea (Michx.) Doell. & Asch.), a tall emergent grass native to the southeastern United States, was studied in Lake Seminole where it formed large expanding stands, and Lake Alice where it was confined to a stable narrow fringe.

Ancient DNA from Hunter-Gatherer and Farmer Groups from Northern Spain Supports a Random Dispersion Model for the Neolithic Expansion into Europe

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EQUIVALENT MODEL OF EXPANSION OF CEMENT MORTAR UNDER SULPHATE EROSION

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

Europäische Fischerei in afrikanischen Gewässern - Information über die Fischerei in Mauretanien

Die mauretanische Atlantikküste ist rund 700 km lang. Der Küste vorgelagert ist ein ca. 30 bis 120, im Mittel 50 km breiter Schelf, von insgesamt 34 000 km2, wenn man die 200-m-Tiefenlinie als Schelfgrenze zugrundelegt. Dieses Schelfgebiet liegt im Bereich des nordost-atlantischen Auftriebs. Aufsteigende, kalte und sauerstoffreiche Tiefenwasser führen dort zu einer hohen Primärproduktion. Das bedeutet gute Nahrungsbedingungen für eine vielfältige und reichhaltige Fauna mit hoher Reproduktionsfähigkeit. Das bedeutet gleichzeitig ideale Bedingungen für eine vielfältige und ertragreiche Fischerei. So ist die Fischerei auch neben dem Eisenerzabbau die wichtigste wirtschaftlichen Grundlage für das Land. Das Forschungsinstitut in Nouadhibou, der zweitgrößten Stadt des Landes, schätzt das Fischereipotential innerhalb der Wirtschaftszone auf über 1 Mill. Tonnen, wovon ca. 80 % auf pelagische Arten entfallen. Die unmittelbare Nutzung der Ressourcen durch die einheimische Fischerei spielte bisher nur eine kleine Rolle. Zwar ändert sich das in dem Maße wie die Bevölkerungszahl zunimmt, aber immer noch werden die größeren Anteile der fischbaren Reserven an ausländische Fischereien vergeben, gegen Lizenzgebühren, versteht sich. Einer der Vertragspartner Mauretaniens ist die Europäische Union. Seit dem 1. August 1996 ist ein Fischereiabkommen in Kraft, das der Union Fischereirechte an bestimmten Arten einräumt. Dieses Abkommen gilt zunächst für 5 Jahre, kann aber um jeweils den gleichen Zeitraum erweitert werden. Es soll hier umrissen werden, wie sich dieser Vertrag in die biologischen, fischereilichen, sozialen und politischen Bedingungen des Landes einfügt.

Size- And Temperature-Dependent Thermal Expansion Coefficient Of A Nanofilm

The thermal expansion coefficient (TEC) of an ideal crystal is derived by using a method of Boltzmann statistics. The Morse potential energy function is adopted to show the dependence of the TEC on the temperature. By taking the effects of the surface relaxation and the surface energy into consideration, the dimensionless TEC of a nanofilm is derived. It is shown that with decreasing thickness, the TEC can increase or decrease, depending on the surface relaxation of the nanofilm.

Thin metastructures with engineered thermal expansion

The geometry and constituent materials of metastructures can be used to engineer the thermal expansion coefficient. In this thesis, we design, fabricate, and test thin thermally stable metastructures consisting of bi-metallic unit cells and show how the coefficient of thermal expansion (CTE) of these metastructures can be finely and coarsely tuned by varying the CTE of the constituent materials and the unit cell geometry. Planar and three-dimensional finite element method modeling is used to drive the design and inform experiments, and predict the response of these metastructures. We demonstrate computationally the significance of out-of-plane effects in the metastructure response. We develop an experimental setup using digital image correlation and an infrared camera to experimentally measure full displacement and temperature fields during testing and accurately measure the metastructures’ CTE. We experimentally demonstrate high aspect ratio metastructures of Ti/Al and Kovar/Al which exhibit near-zero and negative CTE, respectively. We demonstrate robust fabrication procedures for thermally stable samples with high aspect ratios in thin foil and thin film scales. We investigate the lattice structure and mechanical properties of thin films comprising a near-zero CTE metastructure. The mechanics developed in this work can be used to engineer metastructures of arbitrary CTE and can be extended to three dimensions.

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the case of homonuclear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuclear clusters with larger sizes are required to achieve a greater neutron yield.

Functional evaluation of noncovalent interactions in neuroreceptors and progress toward the expansion of unnatural amino acid methodology

This dissertation primarily describes chemical-scale studies of G protein-coupled receptors and Cys-loop ligand-gated ion channels to better understand ligand binding interactions and the mechanism of channel activation using recently published crystal structures as a guide. These studies employ the use of unnatural amino acid mutagenesis and electrophysiology to measure subtle changes in receptor function.

In chapter 2, the role of a conserved aromatic microdomain predicted in the D3 dopamine receptor is probed in the closely related D2 and D4 dopamine receptors. This domain was found to act as a structural unit near the ligand binding site that is important for receptor function. The domain consists of several functionally important noncovalent interactions including hydrogen bond, aromatic-aromatic, and sulfur-π interactions that show strong couplings by mutant cycle analysis. We also assign an alternate interpretation for the linear fluorination plot observed at W6.48, a residue previously thought to participate in a cation-π interaction with dopamine.

Chapter 3 outlines attempts to incorporate chemically synthesized and in vitro acylated unnatural amino acids into mammalian cells. While our attempts were not successful, method optimizations and data for nonsense suppression with an in vivo acylated tRNA are included. This chapter is aimed to aid future researchers attempting unnatural amino acid mutagenesis in mammalian cells.

Chapter 4 identifies a cation-π interaction between glutamate and a tyrosine residue on loop C in the GluClβ receptor. Using the recently published crystal structure of the homologous GluClα receptor, other ligand-binding and protein-protein interactions are probed to determine the similarity between this invertebrate receptor and other more distantly related vertebrate Cys-loop receptors. We find that many of the interactions previously observed are conserved in the GluCl receptors, however care must be taken when extrapolating structural data.

Chapter 5 examines inherent properties of the GluClα receptor that are responsible for the observed glutamate insensitivity of the receptor. Chimera synthesis and mutagenesis reveal the C-terminal portion of the M4 helix and the C-terminus as contributing to formation of the decoupled state, where ligand binding is incapable of triggering channel gating. Receptor mutagenesis was unable to identify single residue mismatches or impaired protein-protein interactions within this domain. We conclude that M4 helix structure and/or membrane dynamics are likely the cause of ligand insensitivity in this receptor and that the M4 helix has an role important in the activation process.