Elevated-temperature application of the IITRI compression test fixture for graphite/polyimide filamentary composites

Seventy-nine graphite/polyimide compression specimens were tested to investigate experimentally the IITRI test method for determining compressive properties of composite materials at room and elevated temperatures (589 K (600 F)). Minor modifications were made to the standard IITRI fixture and a high degree of precision was maintained in specimen fabrication and load alignment. Specimens included four symmetric laminate orientations. Various widths were tested to evaluate the effect of width on measured modulus and strength. In most cases three specimens of each width were tested at room and elevated temperature and a polynomial regression analysis was used to reduce the data. Scatter of replicate tests and back-to-back strain variations were low, and no specimens failed by instability. Variation of specimen width had a negligible effect on the measured ultimate strengths and initial moduli of the specimens. Measured compressive strength and stiffness values were sufficiently high for the material to be considered a usable structural material at temperatures as high as 589 K (600 F)

Isolated, subtle, neurological abnormalities in neurologically and cognitively healthy aging subjects

The aim of this study is to describe the frequency of isolated, subtle, neurological abnormalities (ISNAs) in a large population of neurologically and cognitively healthy subjects and to compare ISNAs to various types of MRI-detected cerebrovascular lesions and subcortical brain atrophy in different age classes. 907 subjects were selected from a large, prospective hospital-based study. At baseline neurological examination, 17 ISNAs were selected. Primitive reflexes were the most common ISNAs (35.8 %), while dysphagia was the most rarely encountered (0.3 %). Measures of small vessel disease, i.e., deep and subcortical white matter hyperintensity and lacunar infarcts as well as subcortical atrophy, were variously associated with ISNAs. In the adult group, the ISNAs were associated with hypertriglyceridemia, TIA, and subcortical lacunar infarcts, while in the elderly-old group they were associated with arterial hypertension, subcortical white matter hyperintensity, and subcortical atrophy. An increased risk of ISNAs was associated with lacunae and white matter hyperintensity in the parietal region. This study shows that white matter hyperintensity, lacunae, and subcortical atrophy are associated with an increased risk of ISNAs in cognitively and neurologically healthy aging subjects. ISNAs are not benign signs. Therefore, adults and elderly people presenting with ISNAs should have access to accurate history and diagnosis to prevent progression of small vessel disease and future neurological and cognitive disabilities

Binary Black Hole Mergers in 3d Numerical Relativity

The standard approach to the numerical evolution of black hole data using the ADM formulation with maximal slicing and vanishing shift is extended to non-symmetric black hole data containing black holes with linear momentum and spin by using a time-independent conformal rescaling based on the puncture representation of the black holes. We give an example for a concrete three dimensional numerical implementation. The main result of the simulations is that this approach allows for the first time to evolve through a brief period of the merger phase of the black hole inspiral.Comment: 8 pages, 9 figures, REVTeX; expanded discussion, results unchange

Method for producing micro heat panels

Flat or curved micro heat pipe panels are fabricated by arranging essentially parallel filaments in the shape of the desired panel. The configuration of the filaments corresponds to the desired configuration of the tubes that will constitute the heat pipes. A thermally conductive material is then deposited on and around the filaments to fill in the desired shape of the panel. The filaments are then removed, leaving tubular passageways of the desired configuration and surface texture in the material. The tubes are then filled with a working fluid and sealed. Composite micro heat pipe laminates are formed by layering individual micro heat pipe panels and bonding them to each other to form a single structure. The layering sequence of the micro heat pipe panels can be tailored to transport heat preferentially in specific directions as desired for a particular application

Micro heat pipe panels and method for producing same

Flat or curved micro heat pipe panels are fabricated by arranging essentially parallel filaments in the shape of the desired panel. The configuration of the filaments corresponds to the desired configuration of the tubes that will constitute the heat pipes. A thermally conductive material is then deposited on and around the filaments to fill in the desired shape of the panel. The filaments are then removed, leaving tubular passageways of the desired configuration and surface texture in the material. The tubes are then filled with a working fluid and sealed. Composite micro heat pipe laminates are formed by layering individual micro heat pipe panels and bonding them to each other to form a single structure. The layering sequence of the micro heat pipe panels can be tailored to transport heat preferentially in specific directions as desired for a particular application

Dynamical Bar-Mode Instability in Differentially Rotating Magnetized Neutron Stars

This paper presents a numerical study over a wide parameter space of the likelihood of the dynamical bar-mode instability in differentially rotating magnetized neutron stars. The innovative aspect of this study is the incorporation of magnetic fields in such a context, which have thus far been neglected in the purely hydrodynamical simulations available in the literature. The investigation uses the Cosmos++ code which allows us to perform three dimensional simulations on a cylindrical grid at high resolution. A sample of Newtonian magneto-hydrodynamical simulations starting from a set of models previously analyzed by other authors without magnetic fields has been performed, providing estimates of the effects of magnetic fields on the dynamical bar-mode deformation of rotating neutron stars. Overall, our results suggest that the effect of magnetic fields are not likely to be very significant in realistic configurations. Only in the most extreme cases are the magnetic fields able to suppress growth of the bar mode.Comment: 12 pages, 16 figures. References added and minor edits made to match published versio

Symmetry without Symmetry: Numerical Simulation of Axisymmetric Systems using Cartesian Grids

We present a new technique for the numerical simulation of axisymmetric systems. This technique avoids the coordinate singularities which often arise when cylindrical or polar-spherical coordinate finite difference grids are used, particularly in simulating tensor partial differential equations like those of 3+1 numerical relativity. For a system axisymmetric about the z axis, the basic idea is to use a 3-dimensional Cartesian (x,y,z) coordinate grid which covers (say) the y=0 plane, but is only one finite-difference-molecule--width thick in the y direction. The field variables in the central y=0 grid plane can be updated using normal (x,y,z)--coordinate finite differencing, while those in the y \neq 0 grid planes can be computed from those in the central plane by using the axisymmetry assumption and interpolation. We demonstrate the effectiveness of the approach on a set of fully nonlinear test computations in 3+1 numerical general relativity, involving both black holes and collapsing gravitational waves.Comment: 17 pages, 4 figure

Detection of possible factors favouring the evolution of migraine without aura into chronic migraine

In a minority of cases, the natural history of migraine without aura (MO) is characterised over time by its evolution into a form of chronic migraine (CM). In order to detect the possible factors predicting this negative evolution of MO, we searched in our Headache Centre files for all clinical records that met the following criteria: (a) first visit between 1976 and 1998; (b) diagnosis of MO or of common migraine at the first observation, with or without association with other primary headache types; (c) <15 days per month of migraine at the first observation; and (d) at least one follow-up visit at least 10 years after the first visit. The patients thus identified were then divided into two groups based on a favourable/steady evolution (Group A: n = 243, 195 women and 48 men) or an unfavourable evolution (Group B: n = 72, 62 women and 10 men) of their migraine over time. In the two groups, we compared various clinical parameters that were present at the first observation or emerged at the subsequent follow-up visits. The parameters that were statistically significantly more frequent in Group B--and can therefore be considered possible negative prognostic factors--were: (a) ≥ 10 days per month of migraine at the first observation; (b) presence of depression at the first visit in males; and (c) onset of depression or arterial hypertension after the first observation but before transformation to CM in females. Based on these findings, in MO patients the high frequency of migraine attacks, comorbidity with depression, and the tendency to develop arterial hypertension should require particular attention and careful management to prevent evolution into CM

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