Connections of Trapezoidal Sheets under Fire

This paper describes two different experiments on connections of trapezoidal sheets under elevated temperatures. The first experiments were tensile tests carried out on four sets of tests with screwed connections under ambient and elevated temperatures. One diameter of self-drilling screws and three different thicknesses of trapezoidal sheets were used. The applied screws were without washers, or with sealed or steel washers. The second experiment was performed in a laboratory furnace to check the catenary action of a thin-walled trapezoidal sheet. The basic theory tested in this experiment was that in the first phase of the fire the sheet behaves as a simply supported beam, while in the second phase the load bearing is transferred by a tension membrane. These experiments will be used to develop a design model of connections at high temperatures. High fire resistance of the trapezoidal sheet, dependent on suitable design of the screwed connection to the bearing structure, was confirmed. The experiment with the simple beam also confirmed catenary action.

Coherent and Incoherent Dynamic Structure Function of the Free Fermi Gas

A detailed calculation of the coherent and incoherent dynamic structure functions of the free Fermi gas, starting from their expressions in terms of the one- and semi-diagonal two-body density matrices, is derived and discussed. Their behavior and evolution with the momentum transfer is analyzed, and particular attention is devoted to the contributions that both functions present at negative energies. Finally, an analysis of the energy weighted sum rules satisfied by both responses is also performed. Despite of the simplicity of the model, some of the conclusions can be extended to realistic systems.Comment: LaTeX, 3 figure

Inequalities of harmonic univalent functions with connections of hypergeometric functions

Let SH be the class of functions f = h + (g) over bar that are harmonic univalent and sense-preserving in the open unit disk U = {z : vertical bar z vertical bar < 1} for which f(0) = f'(0) - 1 = 0. In this paper, we introduce and study a subclass H(alpha, beta)of the class SH and the subclass NH(alpha, beta) with negative coefficients. We obtain basic results involving sufficient coefficient conditions for a function in the subclass H(alpha, beta) and we show that these conditions are also necessary for negative coefficients, distortion bounds, extreme points, convolution and convex combinations. In this paper an attempt has also been made to discuss some results that uncover some of the connections of hypergeometric functions with a subclass of harmonic univalent functions

Reciprocal regulation by the CepIR and CciIR quorum sensing systems in Burkholderia cenocepacia

<p>Abstract</p> <p>Background</p> <p><it>Burkholderia cenocepacia </it>belongs to a group of closely related organisms called the <it>B. cepacia </it>complex (Bcc) which are important opportunistic human pathogens. <it>B. cenocepacia </it>utilizes a mechanism of cell-cell communication called quorum sensing to control gene expression including genes involved in virulence. The <it>B. cenocepacia </it>quorum sensing network includes the CepIR and CciIR regulatory systems.</p> <p>Results</p> <p>Global gene expression profiles during growth in stationary phase were generated using microarrays of <it>B. cenocepacia cepR</it>, <it>cciR </it>and <it>cepRcciIR </it>mutants. This is the first time CciR was shown to be a global regulator of quorum sensing gene expression. CepR was primarily responsible for positive regulation of gene expression while CciR generally exerted negative gene regulation. Many of the genes that were regulated by both quorum sensing systems were reciprocally regulated by CepR and CciR. Microarray analysis of the <it>cepRcciIR </it>mutant suggested that CepR is positioned upstream of CciR in the quorum sensing hierarchy in <it>B. cenocepacia</it>. A comparison of CepIR-regulated genes identified in previous studies and in the current study showed a substantial amount of overlap validating the microarray approach. Several novel quorum sensing-controlled genes were confirmed using qRT-PCR or promoter::<it>lux </it>fusions. CepR and CciR inversely regulated flagellar-associated genes, the nematocidal protein AidA and a large gene cluster on Chromosome 3. CepR and CciR also regulated genes required for iron transport, synthesis of extracellular enzymes and surface appendages, resistance to oxidative stress, and phage-related genes.</p> <p>Conclusion</p> <p>For the first time, the influence of CciIR on global gene regulation in <it>B. cenocepacia </it>has been elucidated. Novel genes under the control of the CepIR and CciIR quorum sensing systems in <it>B. cenocepacia </it>have been identified. The two quorum sensing systems exert reciprocal regulation of many genes likely enabling fine-tuned control of quorum sensing gene expression in <it>B. cenocepacia </it>strains carrying the cenocepacia island.</p

Anomalous finite size spectrum in the S=1/2 two dimensional Heisenberg model

We study the low energy spectrum of the nearest neighbor Heisenberg model on a square lattice as a function of the total spin S. By quantum Monte Carlo simulation we compute this spectrum for the s=1/2, s=1 and s=3/2 Heisenberg models. We conclude that the nonlinear sigma model prediction for the low energy spectrum is always verified for large enough system size. However the crossover to the correct scaling regime is particularly slow just for the s=1/2 Heisenberg model. The possibility to detect this unexpected anomaly with finite temperature experiments on s=1/2 isotropic quantum antiferromagnets is also discussed.Comment: 4 pages, RevTeX + 5 encapsulated postscript figure

Exponential martingales and changes of measure for counting processes

We give sufficient criteria for the Dol\'eans-Dade exponential of a stochastic integral with respect to a counting process local martingale to be a true martingale. The criteria are adapted particularly to the case of counting processes and are sufficiently weak to be useful and verifiable, as we illustrate by several examples. In particular, the criteria allow for the construction of for example nonexplosive Hawkes processes as well as counting processes with stochastic intensities depending on diffusion processes

Quantum-Critical Behavior in a Two-Layer Antiferromagnet

We analyze quantum Monte Carlo data in the vicinity of the quantum transition between a Neel state and a quantum paramagnet in a two-layer, square lattice spin 1/2 Heisenberg antiferromagnet. The real-space correlation function and the universal amplitude ratio of the structure factor and the dynamic susceptibility show clear evidence of quantum critical behavior at low temperatures. The numerical results are in good quantitative agreement with $1/N$ calculations for the $O(N)$ non-linear sigma model. A discrepancy, reported earlier, between the critical properties of the antiferromagnet and the sigma model is resolved. We also discuss the values of prefactors of the dynamic susceptibility and the structure factor in a single layer antiferromagnet at low $T$.Comment: 11 pages, REVtex file, 5 figures in a uuencoded, gziped file. One citation added

Quasiparticle structure and coherent propagation in the t−Jz−J⊥t-J_{z}-J_{\perp} model

Numerical studies, from variational calculation to exact diagonalization, all indicate that the quasiparticle generated by introducing one hole into a two-dimensional quantum antiferromagnet has the same nature as a string state in the $t-J_{z}$ model. Based on this observation, we attempt to visualize the quasiparticle formation and subsequent coherent propagation at low energy by studying the generalized $t-J_{z}-J_{\perp}$ model in which we first diagonalize the $t-J_{z}$ model and then perform a {\em degenerate} perturbation in $J_{\perp}$. We construct the quasiparticle state and derive an effective Hamiltonian describing the coherent propagation of the quasiparticle and its interaction with the spin wave excitations in the presence of the N\'{e}el order. We expect that qualitative properties of the quasiparticle remain intact when analytically continuing $J_{\perp}$ from the anisotropic $J_{\perp} < J_{z}$ to the isotropic $J_{\perp} = J_{z}$ limit, despite the fact that the spin wave excitations change from gapful to gapless. Extrapolating to $J_{\perp}=J_{z}$, our quasiparticle dispersion and spectral weight compare well with the exact numerical results for small clusters.Comment: Revised with minor changes and references updated. To appear in Phys. Rev. B., Jan. 1996. 10 pages, The complete PostScript file including figures can be obtained via ftp at ftp://serval.berkeley.edu/tjzjp.ps . It is also posted in the WEB site of Niels Bohr Institute at http://roemer.fys.ku.dk/recent.ht

Spin Dynamics of La_2CuO_4 and the Two-Dimensional Heisenberg Model

The spin-lattice relaxation rate $1/T_1$ and the spin echo decay rate $1/T_{2G}$ for the 2D Heisenberg model are calculated using quantum Monte Carlo and maximum entropy analytic continuation. The results are compared to recent experiments on La$_2$CuO$_4$, as well as predictions based on the non-linear $\sigma$-model.Comment: Compressed & uuencoded Postscript file (4 pages with figures

Large-Scale Electron Microscopy Maps of Patient Skin and Mucosa Provide Insight into Pathogenesis of Blistering Diseases

Large-scale electron microscopy (“nanotomy”) allows straight forward ultrastructural examination of tissue, cells, organelles, and macromolecules in a single data set. Such data set equals thousands of conventional electron microscopy images and is freely accessible (www.nanotomy.org). The software allows zooming in and out of the image from total overview to nanometer scale resolution in a ‘Google Earth’ approach. We studied the life-threatening human autoimmune blistering disease pemphigus, using nanotomy. The pathomechanism of cell–cell separation (acantholysis) that underlies the blistering is poorly understood. Ultrastructural examination of pemphigus tissue revealed previously unreported findings: (i) the presence of double-membrane structures between cells in all pemphigus types; (ii) the absence of desmosomes around spontaneous blisters in pemphigus foliaceus (PF); (iii) lower level blistering in PF when force induced; and (iv) intercellular widening at non-acantholytic cell layers. Thus, nanotomy delivers open-source electron microscopic maps of patient tissue, which can be analyzed for additional anomalies from any computer by experts from different fields