Application of formal optimization techniques in thermal/structural design of a heat-pipe-cooled panel for a hypersonic vehicle

Nonlinear mathematical programming methods are used to design a radiantly cooled and heat-pipe-cooled panel for a Mach 6.7 transport. The cooled portion of the panel is a hybrid heat-pipe/actively cooled design which uses heat pipes to transport the absorbed heat to the ends of the panel where it is removed by active cooling. The panels are optimized for minimum mass and to satisfy a set of heat-pipe, structural, geometric, and minimum-gage constraints. Two panel concepts are investigated: cylindrical heat pipes embedded in a honeycomb core and an integrated design which uses a web-core heat-pipe sandwich concept. The latter was lighter and resulted in a design which was less than 10 percent heavier than an all actively cooled concept. The heat-pipe concept, however, is redundant and can sustain a single-point failure, whereas the actively cooled concept cannot. An additional study was performed to determine the optimum number of coolant manifolds per panel for a minimum-mass design

An evaluation of higher-order model methods for calculating transient structural response

A higher-order modal method proposed by Leung for transient structural analysis entitled the force-derivative method is evaluated. This method repeatedly integrates by parts with respect to time the convolution-integral form of the structural response to produce successively better approximations to the contribution of the higher modes which are neglected in the modal summation. Comparisons are made of the force-derivative, the mode-displacement, and the mode-acceleration methods for several numerical example problems for various times, levels of damping, and forcing functions. The example problems include a tip-loaded cantilevered beam and a simply-supported multispan beam. The force-derivative method is shown to converge to an accurate solution in fewer modes than either the mode-displacement or the mode-acceleration methods. In addition, for problems in which there are a large number of closely-spaced frequencies whose mode shapes have a negligible contribution to the response, the force-derivative method is very effective in representing the effect of the important, but otherwise neglected, higher modes

A systematic review of neuropsychiatric symptoms in mild cognitive impairment

Mild cognitive impairment (MCI) is a clinical concept proposed as an intermediate state between normal aging and dementia. This condition has multiple heterogeneous sources, including clinical presentation, etiology, and prognosis. Recently, the prevalence and associated features of neuropsychiatric symptoms (NPS) in MCI have been described. We systematically searched the PubMed database (last accessed on August 31, 2008) for articles on NPS in MCI. Included articles used strict selection criteria, and outcome variables were extracted in duplicate; of the 27 articles included, 14 (52%) used prospective cohorts. The global prevalence of NPS in MCI ranged from 35% to 85%. The most common behavioral symptoms were depression, anxiety, and irritability. Hospital-based samples reported a higher global prevalence of NPS than population-based studies; this discrepancy probably reflected differences in demographics, study setting, MCI diagnostic criteria, and behavioral instruments used. Prospective studies showed that NPS, particularly depression, may represent risk factors for MCI or predictors for the conversion of MCI to Alzheimer's disease (AD). NPS are very prevalent in subjects with MCI, displaying a similar pattern of symptoms compared to dementia and AD. Large cohort studies using standardized MCI criteria and behavioral instruments are required to evaluate the prognostic role of NPS in MCI.Mild cognitive impairment (MCI) is a clinical concept proposed as an intermediate state between normal aging and dementia. This condition has multiple heterogeneous sources, including clinical presentation, etiology, and prognosis. Recently, the prevalence and associated features of neuropsychiatric symptoms (NPS) in MCI have been described. We systematically searched the PubMed database (last accessed on August 31, 2008) for articles on NPS in MCI. Included articles used strict selection criteria, and outcome variables were extracted in duplicate; of the 27 articles included, 14 (52%) used prospective cohorts. The global prevalence of NPS in MCI ranged from 35% to 85%. The most common behavioral symptoms were depression, anxiety, and irritability. Hospital-based samples reported a higher global prevalence of NPS than population-based studies; this discrepancy probably reflected differences in demographics, study setting, MCI diagnostic criteria, and behavioral instruments used. Prospective studies showed that NPS, particularly depression, may represent risk factors for MCI or predictors for the conversion of MCI to Alzheimer’s disease (AD). NPS are very prevalent in subjects with MCI, displaying a similar pattern of symptoms compared to dementia and AD. Large cohort studies using standardized MCI criteria and behavioral instruments are required to evaluate the prognostic role of NPS in MC

A variational method from the variance of energy

A variational method is studied based on the minimum of energy variance. The method is tested on exactly soluble problems in quantum mechanics, and is shown to be a useful tool whenever the properties of states are more relevant than the eigenvalues. In quantum field theory the method provides a consistent second order extension of the gaussian effective potential.Comment: 5 ps figure

Gaussian Effective Potential and superconductivity

The Gaussian Effective Potential in a fixed transverse unitarity gauge is studied for the static three-dimensional U(1) scalar electrodynamics (Ginzburg-Landau phenomenological theory of superconductivity). In the broken-symmetry phase the mass of the electromagnetic field (inverse penetration depth) and the mass of the scalar field (inverse correlation length) are both determined by solution of the coupled variational equations. At variance with previous calculations, the choice of a fixed unitarity gauge prevents from the occurrence of any unphysical degree of freedom. The theory provides a nice interpolation of the experimental data when approaching the critical region, where the standard mean-field method is doomed to failure

A general interpolation scheme for thermal fluctuations in superconductors

We present a general interpolation theory for the phenomenological effects of thermal fluctuations in superconductors. Fluctuations are described by a simple gauge invariant extension of the gaussian effective potential for the Ginzburg-Landau static model. The approach is shown to be a genuine variational method, and to be stationary for infinitesimal gauge variations around the Landau gauge. Correlation and penetration lengths are shown to depart from the mean field behaviour in a more or less wide range of temperature below the critical regime, depending on the class of material considered. The method is quite general and yields a very good interpolation of the experimental data for very different materials.Comment: some misprints have been corrected in Eq.(15),(19); more references and comments have been adde

Electron backscattering from stacking faults in SiC by means of \textit{ab initio} quantum transport calculations

We study coherent backscattering phenomena from single and multiple stacking faults (SFs) in 3C- and 4H-SiC within density functional theory quantum transport calculations. We show that SFs give rise to highly dispersive bands within both the valance and conduction bands that can be distinguished for their enhanced density of states at particular wave number subspaces. The consequent localized perturbation potential significantly scatters the propagating electron waves and strongly increases the resistance for $n$-doped systems. We argue that resonant scattering from SFs should be one of the principal degrading mechanisms for device operation in silicon carbide.Comment: 5 pages, 4 figure

Biomarkers of oxidative and nitrosative damage in Alzheimer's disease and mild cognitive impairment

Alzheimer's disease (AD) is the most common type of dementia in the elderly. Products of oxidative and nitrosative stress (OS and NS, respectively) accumulate with aging, which is the main risk factor for AD. This provides the basis for the involvement of OS and NS in AD pathogenesis. OS and NS occur in biological systems due to the dysregulation of the redox balance, caused by a deficiency of antioxidants and/or the overproduction of free radicals. Free radical attack against lipids, proteins, sugars and nucleic acids leads to the formation of bioproducts whose detection in fluids and tissues represents the currently available method for assessing oxidative/nitrosative damage. Post-mortem and in-vivo studies have demonstrated an accumulation of products of free radical damage in the central nervous system and in the peripheral tissues of subjects with AD or mild cognitive impairment (MCI). In addition to their individual role, biomarkers for OS and NS in AD are associated with altered bioenergetics and amyloid-beta (Aβ) metabolism. In this review we discuss the main results obtained in the field of biomarkers of oxidative/nitrosative stress in AD and MCI in humans, in addition to their potential role as a tool for diagnosis, prognosis and treatment efficacy in AD. © 2009 Elsevier Ireland Ltd. All rights reserved