18,956 research outputs found
Sum rules for correlation functions of ionic mixtures in arbitrary dimension
The correlations in classical multi-component ionic mixtures with spatial
dimension are studied by using a restricted grand-canonical ensemble
and the associated hierarchy equations for the correlation functions. Sum rules
for the first few moments of the two-particle correlation function are derived
and their dependence on is established. By varying continuously near
it is shown how the sum rules for the two-dimensional mixture are related
to those for mixtures at higher .Comment: 19 page
Twisted Open Strings from Closed Strings: The WZW Orientation Orbifolds
Including {\it world-sheet orientation-reversing automorphisms}
in the orbifold program, we construct the operator
algebras and twisted KZ systems of the general WZW {\it orientation orbifold}
. We find that the orientation-orbifold sectors corresponding
to each are {\it twisted open} WZW strings, whose
properties are quite distinct from conventional open-string orientifold
sectors. As simple illustrations, we also discuss the classical (high-level)
limit of our construction and free-boson examples on abelian .Comment: 65 pages, typos correcte
Fluidized beds as turbulence promoters in the concentration of food liquids by reverse osmosis
Fluidized beds offer a potential improvement of reverse osmosis processes for food liquids, less fouling of the membrane, and reduced energy consumption. Our experiments were concerned with tubular systems in which fluidized beds of glass, steel, and lead beads were used. Glass beads appeared to be preferable, since they caused little damage to the membrane. Only with the larger glass beads (3 mm) did the membrane skin become corrugated, so that the rejection decreased. The permeate flux for Gouda cheese whey was almost equal to that of an empty tube for which the velocity was about thirty times higher. The erosive action of the glass beads on the fouling layer was partially responsible for this effect. For reverse osmosis of skim milk and potato fruit water the bed did not reduce the fouling layer to a sufficient extent and, therefore, had a lower permeate flux than an empty tube
High-pressure study of the non-Fermi liquid material U_2Pt_2In
The effect of hydrostatic pressure (p<= 1.8 GPa) on the non-Fermi liquid
state of U_2Pt_2In is investigated by electrical resistivity measurements in
the temperature interval 0.3-300 K. The experiments were carried out on
single-crystals with the current along (I||c) and perpendicular (I||a) to the
tetragonal axis. The pressure effect is strongly current-direction dependent.
For I||a we observe a rapid recovery of the Fermi-liquid T^2-term with
pressure. The low-temperature resistivity can be analysed satisfactorily within
the magnetotransport theory of Rosch, which provides strong evidence for the
location of U_2Pt_2In at an antiferromagnetic quantum critical point. For I||c
the resistivity increases under pressure, indicating the enhancement of an
additional scattering mechanism. In addition, we have measured the pressure
dependence of the antiferromagnetic ordering temperature (T_N= 37.6 K) of the
related compound U_2Pd_2In. A simple Doniach-type diagram for U_2Pt_2In and
U_2Pd_2In under pressure is presented.Comment: 21 pages (including 5 figures); pdf forma
The black silicon method: a universal method for determining the parameter setting of a fluorine-based reactive ion etcher in deep silicon trench etching with profile control
Very deep trenches (up to 200 µm) with high aspect ratios (up to 10) in silicon and polymers are etched using a fluorine-based plasma (SF6/O2/CHF3). Isotropic, positively and negatively (i.e. reverse) tapered as well as fully vertical walls with smooth surfaces are achieved by controlling the plasma chemistry. A convenient way to find the processing conditions needed for a vertical wall is described: the black silicon method. This new procedure is checked for three different reactive ion etchers (RIE), two parallel-plate reactors and a hexode. The influence of the RF power, pressure and gas mixture on the profile will be shown. Scanning electron microscope (SEM) photos are included to demonstrate the black silicon method, the influence of the gases on the profile, and the use of this method in fabricating microelectromechanical systems (MEMS)
Exact ground states of generalized Hubbard models
We present a simple method for the construction of exact ground states of
generalized Hubbard models in arbitrary dimensions. This method is used to
derive rigorous criteria for the stability of various ground state types, like
the -pairing state, or N\'eel and ferromagnetic states. Although the
approach presented here is much simpler than the ones commonly used, it yields
better bounds for the region of stability.Comment: Revtex, 8 page
HISTOLOGÍA DE HUESOS HUMANOS SECOS (UNA REVISIÓN)
Despite archaeological preservation conditions, the histomorphology of human dry bone still contains useful information on the physiological and pathological status of deceased individuals. Histology can therefore be a helpful addition to routine archaeological methods. But practice has shown that, for many archaeologists, unfamiliarity with this technique shaped a pointless obstacle to add it to their tool box. Thus, after having addressed the restrictions associated with histological analysis in general, we will show that the preparation of sections/slides does not need to be diff icult, expensive or time-consuming. Then we will provide an introduction to the histological application of assessing age at death of the deceased. It’s must be its theoretical basis, its value in comparison to other methods and its limits are discussed. Finally, we will elaborate on the effectiveness of histology as an indicator of pathological processes, and explain that only a small number of disorders have distinct ‘pathognonomic’ microscopic features. In all other cases, the histological findings must be combined with gross anatomical and radiological findings from the same individual to come to a conclusive diagnosis or to a shortened list of differential (alternative) diagnoses.Independientemente de las condiciones de conservación arqueológica, la histomorfología de hueso seco humano conserva información útil sobre el estado f isiológico y patológico de las personas fallecidas. Por lo tanto la utilización del análisis histológico puede ser una adición útil a los métodos arqueológicos de rutina. No obstante, en la práctica se ha demostrado, que para muchos arqueólogos la falta de familiaridad con esta técnica constituye un obstáculo para su utilización. Por lo tanto, después de haber abordado las restricciones asociadas al análisis histológico en general, vamos a demostrar que la preparación de secciones / diapositivas no tiene por qué ser difícil, costoso o requerir mucho tiempo para su utilización. En este trabajo se expone una intro- ducción a la aplicación de la evaluación histológica para poder determinar la edad de la persona fallecida. Se discute su base teórica, su valor en comparación con otros métodos y sus límites. Por último, vamos a tratar la ef icacia de la histología como indicador de procesos patológicos y mostrar que sólo un pequeño número de trastornos tienen características microscópicas ‘patognonomicas’ diferenciadas. En todos los demás casos los datos histológicos deben ser combinados con los resultados anatómicos macroscópicos y radiológicos del mismo individuo para obtener un diagnóstico concluyente o una lista abreviada de diferentes (alternativos) diagnósticos
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