Spectral methods in general relativistic astrophysics

We present spectral methods developed in our group to solve three-dimensional partial differential equations. The emphasis is put on equations arising from astrophysical problems in the framework of general relativity.Comment: 51 pages, elsart (Elsevier Preprint), 19 PostScript figures, submitted to Journal of Computational & Applied Mathematic

Gravitational signals due to tidal interactions between white dwarfs and black holes

In this paper we compute the gravitational signal emitted when a white dwarf moves around a black hole on a closed or open orbit using the affine model approach. We compare the orbital and the tidal contributions to the signal, assuming that the star moves in a safe region where, although very close to the black hole, the strength of the tidal interaction is insufficient to provoque the stellar disruption. We show that for all considered orbits the tidal signal presents sharp peaks corresponding to the excitation of the star non radial oscillation modes, the amplitude of which depends on how deep the star penetrates the black hole tidal radius and on the type of orbit. Further structure is added to the emitted signal by the coupling between the orbital and the tidal motion.Comment: 21 pages, 8 figres. Submitted to MNRA

Merger of black hole-neutron star binaries: nonspinning black hole case

We perform a simulation for merger of a black hole (BH)-neutron star (NS) binary in full general relativity preparing a quasicircular state as initial condition. The BH is modeled by a moving puncture with no spin and the NS by the $\Gamma$-law equation of state with $\Gamma=2$. Corotating velocity field is assumed for the NS. The mass of the BH and the rest-mass of the NS are chosen to be $\approx 3.2 M_{\odot}$ and $\approx 1.4 M_{\odot}$ with relatively large radius of the NS $\approx 14$ km. The NS is tidally disrupted near the innermost stable orbit but $\sim 80$ of the material is swallowed into the BH with small disk mass $\sim 0.3M_{\odot}$ even for such small BH mass $\sim 3M_{\odot}$. The result indicates that the system of a BH and a massive disk of $\sim M_{\odot}$ is not formed from nonspinning BH-NS binaries, although a disk of mass $\sim 0.1M_{\odot}$ is a possible outcome.Comment: 5 pages. Phys. Rev. D 74, 121503 (R) (2006

Darwin-Riemann problems in general relativity

A review is given of recent results about the computation of irrotational Darwin-Riemann configurations in general relativity. Such configurations are expected to represent fairly well the late stages of inspiralling binary neutron stars.Comment: 20 pages, 11 PostScript figures, uses PTPTeX, to appear in the Proceedings of Yukawa International Seminar 99 "Black Holes and Gravitational Waves", edited by T. Nakamura & H. Kodama, Prog. Theor. Phys. Supp

Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid, and L-aspartic acid esters

A series of copoly(α-amino acids) with varying percentages of hydrophilic (l-aspartic acid) and hydrophobic monomers (l-leucine, ß-methyl-l-aspartate, and ß-benzyl-l-aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A, B, C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr. \ud The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction

THE PERCEIVED IMPACT OF CLIMATE CHANGE ON A SELECTED MANILA BAY-AREA HOTEL

Climate change, an increasingly apparent phenomena, has the potential to affect the tourism industry. This exploratory paper was created to (1) look at the possible impacts of climate change, particularly sea-level rise, on a selected Manila-Bay area hotel; (2) explore possible changes in the operational systems of the selected hotel and propose changes into these systems; and (3) propose possible monitoring programs and policies aimed at mitigating the impact of climate change, particularly in the most vulnerable areas to climate change like the Philippines. The researcher employed a case-study method for this exploratory research. Data were then analyzed using the Climate Lens Model, in conjunction with the systems model. It was found out that storm surges, one of the indirect impacts of climate change caused by stronger typhoons, brought about changes in the operational system of the hotel. Yet, even if there were measures undertaken, these measures were only short-term, which in a climate change standpoint is inadequate due to the fact that climate change is very dynamic. It was recommended that the hotel establishment take into account a diverse range of technological, managerial, educational, policy and behavioral adaptations to deal with climate variability, based on the recommendation set by the Davos Declaration of the UNWTO