Multi-connected Momentum Distribution and Fermion Condensation

The structure of the ground state beyond the instability point of the quasiparticle system with Fermi-step momentum distribution is studied within the model of a Fermi liquid with a strong repulsive interaction. A ground state rearrangement occurs as the interaction strength is increased beyond a definite critical value. Numerical investigation of the initial stage of this structural transition shows that there are two temperature regions, corresponding to different scenarios of the rearrangement. While for temperature T larger than some characteristic temperature T_0 the behaviour of the system is the same as that in the case of the fermion condensation, for T<T_0 the intermediate structure with multi-connected quasiparticle momentum distribution arises. The transition of this structure to the fermion condensate at increasing interaction strength is discussed.Comment: 10 pages, 8 postscript figure

Local Buckling Hysteretic Nonlinear Models for Cold-Formed Steel Axial Members

This paper studies the energy dissipation and damage in thin walled members that experience local buckling and presents an approach to model cold-formed steel (CFS) axial members that experience local buckling deformations. The model is implemented in OpenSees using hysteretic models for CFS axial members calibrated using experimental responses. Results from thin-shell element simulations using ABAQUS show that energy dissipation in thin plates dissipates through inelastic strains and yielding that concentrates in damaged zones that extent approximately the length of a buckled half-wave (Lcr). Generally damage accumulates in one zone but when more than one damaged zone occurred the energy dissipation increased proportionally. The results from the plate simulation and experimental results from cyclic tests on axially loaded CFS members (previously performed by the authors) support the assumptions for the modeling approach presented for CFS members governed by local buckling. Results demonstrate the capabilities of the modeling approach to efficiently and accurately simulate the response of the CFS axial members experiencing local buckling. The model presented can be used to facilitate the performance assessment of cold-formed steel lateral load resisting systems (e.g., shear walls) under different hazard/performance levels, a capability needed for the advance of performance-based earthquake engineering of cold-formed steel buildings

Towards Load-Deformation Models for Screw-Fastened Cold-Formed Steel-to-Steel Shear Connections

This paper summarizes results from an experimental program considering single-fastened cold-formed steel-to-steel shear connections. Fastener motion (displacement and tilting angle) and bearing deformation occurring on the connecting members at the fastener location were captured using an automated, optical non-contact measurement procedure. The results are used to relate cold-formed steel-to-steel shear connection load-deformation response to tilting and bearing response. A general steel-to-steel single shear fastener load-deformation equation is also proposed and demonstrated

Mechanisms driving alteration of the Landau state in the vicinity of a second-order phase transition

The rearrangement of the Fermi surface of a homogeneous Fermi system upon approach to a second-order phase transition is studied at zero temperature. The analysis begins with an investigation of solutions of the equation $\epsilon(p)=\mu$, a condition that ordinarily has the Fermi momentum $p_F$ as a single root. The emergence of a bifurcation point in this equation is found to trigger a qualitative alteration of the Landau state, well before the collapse of the collective degree of freedom that is responsible for the second-order transition. The competition between mechanisms that drive rearrangement of the Landau quasiparticle distribution is explored, taking into account the feedback of the rearrangement on the spectrum of critical fluctuations. It is demonstrated that the transformation of the Landau state to a new ground state may be viewed as a first-order phase transition.Comment: 16 pages, 10 figure

Improved Quantum Hard-Sphere Ground-State Equations of State

The London ground-state energy formula as a function of number density for a system of identical boson hard spheres, corrected for the reduced mass of a pair of particles in a sphere-of-influence picture, and generalized to fermion hard-sphere systems with two and four intrinsic degrees of freedom, has a double-pole at the ultimate \textit{regular} (or periodic, e.g., face-centered-cubic) close-packing density usually associated with a crystalline branch. Improved fluid branches are contructed based upon exact, field-theoretic perturbation-theory low-density expansions for many-boson and many-fermion systems, appropriately extrapolated to intermediate densities, but whose ultimate density is irregular or \textit{random} closest close-packing as suggested in studies of a classical system of hard spheres. Results show substantially improved agreement with the best available Green-function Monte Carlo and diffusion Monte Carlo simulations for bosons, as well as with ladder, variational Fermi hypernetted chain, and so-called L-expansion data for two-component fermions.Comment: 15 pages and 7 figure

Dimensional crossover of a boson gas in multilayers

We obtain the thermodynamic properties for a non-interacting Bose gas constrained on multilayers modeled by a periodic Kronig-Penney delta potential in one direction and allowed to be free in the other two directions. We report Bose-Einstein condensation (BEC) critical temperatures, chemical potential, internal energy, specific heat, and entropy for different values of a dimensionless impenetrability $P\geqslant 0$ between layers. The BEC critical temperature $T_{c}$ coincides with the ideal gas BEC critical temperature $T_{0}$ when $P=0$ and rapidly goes to zero as $P$ increases to infinity for any finite interlayer separation. The specific heat $C_{V}$ \textit{vs} $T$ for finite $P$ and plane separation $a$ exhibits one minimum and one or two maxima in addition to the BEC, for temperatures larger than $T_{c}$ which highlights the effects due to particle confinement. Then we discuss a distinctive dimensional crossover of the system through the specific heat behavior driven by the magnitude of $P$. For $T<T_{c}$ the crossover is revealed by the change in the slope of $\log C_{V}(T)$ and when $T>T_{c}$, it is evidenced by a broad minimum in $C_{V}(T)$.Comment: Ten pages, nine figure

Ground state instability in systems of strongly interacting fermions

We analyze stability of a fermion system with model repulsive pair interaction potential. The possibility for different types of restructuring of the Fermi ground state (at sufficiently great coupling constant) is related to the analytic properties of such potential. In particular, for the screened Coulomb law it is shown that the restructuring cannot be of the Fermi condensation type, known earlier for some exactly solvable models, and instead it belongs to the class of topological transitions (TT). For this model, a phase diagram has been built in the variables "screening parameter - coupling constant" which displays two kinds of TT: a 5/2-kind similar to the known Lifshitz transitions in metals, and a 2-kind characteristic for a uniform strongly interacting system.Comment: The article has 11 pages, in Latex 2e (from Lyx), 3 eps figures or a ps fil

Origen de las arterias testiculares en caninos

Ante las discrepancias existentes entre distintos autores de difundidos textos de anatomía animal, el propósito del trabajo fue investigar eventuales diferencias en el origen de las arterias testiculares del perro. Se emplearon 15 cadáveres de caninos de diferente raza, edad y talla. Tras ser inyectados con pasta de repleción (látex coloreado), se les practicaron las disecciones correspondientes. Los resultados obtenidos indicaron que en el 80% de los casos la arteria testicular derecha se originaba de la aorta abdominal, cranealmente con respecto a la arteria testicular izquierda. En el 20% restante se comprobó que ambas lo hacían a la misma altura. Además de enriquecer los conocimientos anatómicos acerca del patrón de irrigación testicular, el hallazgo es aplicable en las técnicas quirúrgicas que involucren la topografía regional estudiada

Síntese e caracterização de sistemas ácidos WO3/ZrO2 e WO3/TiO2 aplicados na hidratação do etileno em etanol

Este documento estuda a síntese e caracterização de ácidos dos sistemas obtidos pelo método de impregnação incipiente a partir de uma sal de tungsténio e usando TiO2, ZrO2 e os óxidos metálicos, tais como suportes. Os dois sistemas catalisadores de WO3/ZrO2 e WO3/TiO2 foram preparados com cargas de massa de tungsténio de 10, 30 e 40%. Para os dois tipos de catalisadores sintetizados forão determinadas as densidades superficiais, as transições de fase, a estrutura morfológica e a estabilidade térmica para cada uma das cargas de tungsténio empregue foram determinados. Além disso, a actividade catalítica destes catalisadores foi avaliada na hidratação do etileno em etanol, com uma mistura de fases gasosa e líquida, utilizando uma proporção equimolar de etileno de água a pressões de entre 30 e 40 bar. Os resultados revelaram que os sólidos que mostrarão um melhor desempenho melhor atingindo uma selectividade em relação ao etanol de 98% são aqueles com baixa carga de tungsténio (10% em peso) e a uma pressão de entre 30 e 40 bar.Este trabajo se enfoca en la síntesis y la caracterización de dos sistemas ácidos obtenidos por el método de impregnación húmeda incipiente, partiendo de una sal de tungsteno y empleando a los óxidos metálicos ZrO2 y TiO2 como soportes. Los dos sistemas de catalizadores WO3/ZrO2 y WO3/TiO2 se prepararon con cargas de tungsteno de 10, 30 y 40% en peso. Para los dos tipos de catalizadores se determinaron las densidades superficiales, transiciones de fase, estructura morfológica y estabilidad térmica para cada una de las cargas de tungsteno empleadas para preparar los catalizadores. Adicionalmente, se evaluó la actividad catalítica de estos catalizadores sólidos para la hidratación de etileno a etanol en presencia de una mezcla de fases líquida y gaseosa, empleando una relación equimolar de etileno a agua a presiones entre 30 y 40 bar. Los resultados revelaron que los catalizadores que presentaron un mejor desempeño alcanzando una selectividad hacia el etanol de 98%, fueron aquellos con una carga baja de tungsteno (10% en peso) y a una presión de trabajo entre 30 y 40 bar.This work focuses on the synthesis and characterization of two acid systems obtained by the incipient wetness impregnation method, starting from a tungsten salt and using the metal oxides TiO2 and ZrO2 as supports. The two catalyst systems WO3/ZrO2 and WO3/TiO2 were prepared with loads of tungsten of 10, 30 and 40%wt. Surface densities, phase transitions, morphological structure, and thermal stability were determined for each of the tungsten loads used to prepare the catalysts. Additionally, the catalytic activity of these catalysts was evaluated for the hydration of ethylene to ethanol in the presence of a mixture of liquid and gaseous phases, using an equimolar ratio of ethylene to water at pressures from 30 to 40 bar. The results revealed that the catalysts that showed a better performance, reaching a selectivity to ethanol of 98%, were those with a low load of tungsten (10%wt.) at a pressure in the range from 30 to 40 bar