Thermogravimetric analysis of aluminised E-glass fibre reinforced unsaturated polyester composites

Novel aluminised E-glass fibre reinforced unsaturated polyester composites, originally formulated for enhanced thermal and electrical shielding properties were evaluated in terms of their thermal performance. The thermal degradation of these specimens was analysed using a thermogravimetric analyser (TGA). The samples were heated from ambient temperature to 500 °C at a heating rate of 20 °C/min. All specimens were decomposed under dry nitrogen (N2) at a flow rate of 40 ml/min to yield gases and solid char. Aluminised E-glass composites were compared alongside the unmetallised E-glass and unreinforced composite. The major weight loss occurred between 200 and 400 °C. The unreinforced polyester had a maximum weight loss, 1.25%/°C, occurring at 360 °C. For the aluminised and unmetallised E-glass composites, the maximum rate of weight loss was 0.34 and 0.55%/°C, respectively. Experimental results show the degradation of the aluminised E-glass composites obtained from TGA tests is higher compared to those of unmetallised E-glass fibre and unreinforced polyester composite. This improvement is correlated to the aluminium coating.http://www.sciencedirect.com/science/article/B6TXX-4M2WP4H-2/1/bef16e64695f47cabc7a3f55ce5b745

X-ray emission from PSR B1800-21, its wind nebula, and similar systems

We detected X-ray emission from PSR B1800-21 and its synchrotron nebula with the Chandra X-ray Observatory. The pulsar's observed flux is (1.4+/-0.2) 10^{-14} ergs cm^{-2} s^{-1} in the 1-6 keV band. The spectrum can be described by a two-component PL+BB model, suggesting a mixture of thermal and magnetospheric emission. For a plausible hydrogen column density n_{H}=1.4 10^{22} cm^{-2}, the PL component has a slope Gamma=1.4+/-0.6 and a luminosity L_{psr}^{nonth}=4 10^{31}(d/4 kpc)^2 ergs s^{-1}. The properties of the thermal component (kT=0.1-0.3 keV, L^{bol}=10^{31}-10^{33} ergs s^{-1}) are very poorly constrained because of the strong interstellar absorption. The compact, 7''\times4'', inner pulsar-wind nebula (PWN), elongated perpendicular to the pulsar's proper motion, is immersed in a fainter asymmetric emission. The observed flux of the PWN is (5.5+/-0.6) 10^{-14} ergs cm^{-2} s^{-1} in the 1-8 keV band. The PWN spectrum fits by a PL model with Gamma=1.6+/-0.3, L=1.6 10^{32} (d/4 kpc})^2 ergs s^{-1}. The shape of the inner PWN suggests that the pulsar moves subsonically and X-ray emission emerges from a torus associated with the termination shock in the equatorial pulsar wind. The inferred PWN-pulsar properties (e.g., the PWN X-ray efficiency, L_{pwn}/\dot{E}~10^{-4}; the luminosity ratio, L_{pwn}/L_{psr}^{nonth}=4; the pulsar wind pressure at the termination shock, p_s=10^{-9} ergs cm^{-3}) are very similar to those of other subsonically moving Vela-like objects detected with Chandra (L_{pwn}/\dot{E}=10^{-4.5}-10^{-3.5}, L_{pwn}/L_{psr}^{nonth}~5, p_s=10^{-10}-10^{-8} ergs cm^{-1}).Comment: 11 pages, 10 figures, 2 tables; submitted to ApJ. Version with the high-resolution figures is available at http://www.astro.psu.edu/users/green/B1800/B1800_ApJ.pd

Perturbation theorems for Hele-Shaw flows and their applications

In this work, we give a perturbation theorem for strong polynomial solutions to the zero surface tension Hele-Shaw equation driven by injection or suction, so called the Polubarinova-Galin equation. This theorem enables us to explore properties of solutions with initial functions close to but are not polynomial. Applications of this theorem are given in the suction or injection case. In the former case, we show that if the initial domain is close to a disk, most of fluid will be sucked before the strong solution blows up. In the later case, we obtain precise large-time rescaling behaviors for large data to Hele-Shaw flows in terms of invariant Richardson complex moments. This rescaling behavior result generalizes a recent result regarding large-time rescaling behavior for small data in terms of moments. As a byproduct of a theorem in this paper, a short proof of existence and uniqueness of strong solutions to the Polubarinova-Galin equation is given.Comment: 25 page

The Distribution of Nearby Stars in Velocity Space Inferred from Hipparcos Data

(abridged) The velocity distribution f(v) of nearby stars is estimated, via a maximum- likelihood algorithm, from the positions and tangential velocities of a kinematically unbiased sample of 14369 stars observed by the HIPPARCOS satellite. f(v) shows rich structure in the radial and azimuthal motions, v_R and v_phi, but not in the vertical velocity, v_z: there are four prominent and many smaller maxima, many of which correspond to well known moving groups. While samples of early-type stars are dominated by these maxima, also up to 25% of red main-sequence stars are associated with them. These moving groups are responsible for the vertex deviation measured even for samples of late-type stars; they appear more frequently for ever redder samples; and as a whole they follow an asymmetric-drift relation, in the sense that those only present in red samples predominantly have large |v_R| and lag in v_phi w.r.t. the local standard of rest (LSR). The question arise, how these old moving groups got on their eccentric orbits. A plausible mechanism, known from solar system dynamics, which is able to manage a shift in orbit space involves locking into an orbital resonance. Apart from these moving groups, there is a smooth background distribution, akin to Schwarzschild's ellipsoidal model, with axis ratio of about 1:0.6:0.35 in v_R, v_phi, and v_z. The contours are aligned with the $v_r$ direction, but not w.r.t. the v_phi and v_z axes: the mean v_z increases for stars rotating faster than the LSR. This effect can be explained by the stellar warp of the Galactic disk. If this explanation is correct, the warp's inner edge must not be within the solar circle, while its pattern rotates with frequency of about 13 km/s/kpc or more retrograde w.r.t. the stellar orbits.Comment: 16 pages LaTeX (aas2pp4.sty), 6 figures, accepted by A

Fatigue behaviour of composite adhesive lap joints

http://www.sciencedirect.com/science/article/B6TWT-45YG5WP-1/1/d57bc6251d123772bfdb57edd6cc391

A New Approach to Large-Scale Nuclear Structure Calculations

A new approach to large-scale nuclear structure calculations, based on the Density Matrix Renormalization Group (DMRG), is described. The method is tested in the context of a problem involving many identical nucleons constrained to move in a single large-j shell and interacting via a pairing plus quadrupole interaction. In cases in which exact diagonalization of the hamiltonian is possible, the method is able to reproduce the exact results for the ground state energy and the energies of low-lying excited states with extreme precision. Results are also presented for a model problem in which exact solution is not feasible.Comment: 6 pages + 1 eps figur

Impact strength of composites with nano-enhanced resin after fire exposure

Composite materials have been widely used in several engineering applications. However, there are very few studies about the effects of nanoclays on the impact strength of laminates after exposure to the fire. Therefore, this paper intends to study this subject and the impact performance was analysed by low velocity impact tests carried out at different incident impact energy levels. For better dispersion and interface adhesion matrix/clay, nanoclays were previously subjected to a silane treatment appropriate to the epoxy resin. The exposure to the fire decreases the maximum load and increases the displacement in comparison with the respective values obtained at room temperature. Mathematical relationships are proposed to estimate the maximum impact force and displacement, based on the total impact energy and flexural stiffness. Finally, a decrease of the elastic recuperation can be found, independently of the benefits introduced by the nanoclays

Thermodynamic properties of a small superconducting grain

The reduced BCS Hamiltonian for a metallic grain with a finite number of electrons is considered. The crossover between the ultrasmall regime, in which the level spacing, $d$, is larger than the bulk superconducting gap, $\Delta$, and the small regime, where $\Delta \gtrsim d$, is investigated analytically and numerically. The condensation energy, spin magnetization and tunneling peak spectrum are calculated analytically in the ultrasmall regime, using an approximation controlled by $1/\ln N$ as small parameter, where $N$ is the number of interacting electron pairs. The condensation energy in this regime is perturbative in the coupling constant $\lambda$, and is proportional to $d N \lambda^2 = \lambda^2 \omega_D$. We find that also in a large regime with $\Delta>d$, in which pairing correlations are already rather well developed, the perturbative part of the condensation energy is larger than the singular, BCS, part. The condition for the condensation energy to be well approximated by the BCS result is found to be roughly $\Delta > \sqrt{d \omega_D}$. We show how the condensation energy can, in principle, be extracted from a measurement of the spin magnetization curve, and find a re-entrant susceptibility at zero temperature as a function of magnetic field, which can serve as a sensitive probe for the existence of superconducting correlations in ultrasmall grains. Numerical results are presented which suggest that in the large $N$ limit the 1/N correction to the BCS result for the condensation energy is larger than $\Delta$.Comment: 17 pages, 7 figures, Submitted to Phys. Rev.

Infrared Space Observatory Polarimetric Imaging of the Egg Nebula (RAFGL 2688)

We present polarimetric imaging of the protoplanetary nebula RAFGL 2688 obtained at 4.5 microns with the Infrared Space Observatory (ISO). We have deconvolved the images to remove the signature of the point spread function of the ISO telescope, to the extent possible. The deconvolved 4.5 micron image and polarimetric map reveal a bright point source with faint, surrounding reflection nebulosity. The reflection nebula is brightest to the north-northeast, in agreement with previous ground- and space-based infrared imaging. Comparison with previous near-infrared polarimetric imaging suggests that the polarization of starlight induced by the dust grains in RAFGL 2688 is more or less independent of wavelength between 2 microns and 4.5 microns. This, in turn, indicates that scattering dominates over thermal emission at wavelengths as long as ~5 microns, and that the dust grains have characteristic radii < 1 micron.Comment: 27 pages, 9 figures; to appear in the Astronomical Journal, May 2002 issu

Integrable model for interacting electrons in metallic grains

We find an integrable generalization of the BCS model with non-uniform Coulomb and pairing interaction. The Hamiltonian is integrable by construction since it is a functional of commuting operators; these operators, which therefore are constants of motion of the model, contain the anisotropic Gaudin Hamiltonians. The exact solution is obtained diagonalizing them by means of Bethe Ansatz. Uniform pairing and Coulomb interaction are obtained as the ``isotropic limit'' of the Gaudin Hamiltonians. We discuss possible applications of this model to a single grain and to a system of few interacting grains.Comment: 4 pages, revtex. Revised version to be published in Phys. Rev. Let