Abstract:
Ce texte, qui sera publié dans la revue Context (n°9) et que Mark Crispin Miller et l’éditeur nous ont généreusement permis de reproduire, est un papier d’humeur qui tente de relier deux aspects de la culture américaine, à savoir d’un c té la liberté de la parole démocratique auquel le médium d’internet a donné une nouvelle dimension, et de l’autre l’anti intellectualisme — vrai ou supposé — de cette même culture. En cela, il touche à un débat fondamental pour l’étude des Etats Unis. Ce premier numéro de TransatlanticA, du portrait de Tocqueville à la peinture américaine du XIXe siècle exposée à Giverny, lui fait une large place.

Abstract:
We investigate the dynamic stability of inspiraling neutron stars by performing multiple-orbit numerical relativity simulations of the binary neutron star inspiral process. By introducing eccentricities in the orbits of the neutron stars, significant changes in orbital separation are obtained within orbital timescales. We find that as the binary system evolves from apastron to periastron (as the binary separation decreases), the central rest mass density of each star decreases, thus stabilizing the stars against individual prompt collapse. As the binary system evolves from periastron to apastron, the central rest mass density increases; the neutron stars re-compress as the binary separation increases.

Abstract:
We present an algorithm for solving the general relativistic initial value equations for a corotating polytropic star in quasicircular orbit with a nonspinning black hole. The algorithm is used to obtain initial data for cases where the black hole mass is 1, 3, and 10 times larger than the mass of the star. By analyzing sequences of constant baryon mass, constant black hole mass initial data sets and carefully monitoring the numerical error, we find innermost stable circular orbit (ISCO) configuration for these cases. While these quasiequilibrium, conformally flat sequences of initial data sets are not true solutions of the Einstein equations (each set, however, solves the full initial value problem), and thus, we do not expect the ISCO configurations found here to be completely consistent with the Einstein equations, they will be used as convenient starting points for future numerical evolutions of the full 3+1 Einstein equations.

Abstract:
We perform a von Neumann stability analysis on a common discretization of the Einstein equations. The analysis is performed on two formulations of the Einstein equations, namely, the standard ADM formulation and the conformal-traceless (CT) formulation. The eigenvalues of the amplification matrix are computed for flat space as well as for a highly nonlinear plane wave exact solution. We find that for the flat space initial data, the condition for stability is simply $\frac {\Delta t}{\Delta z} \leq 1$. However, a von Neumann analysis for highly nonlinear plane wave initial data shows that the standard ADM formulation is unconditionally unstable, while the conformal-traceless (CT) formulation is stable for $0.25 \leq \frac {\Delta t}{\Delta z} < 1$.

Abstract:
One often-used approximation in the study of binary compact objects (i.e., black holes and neutron stars) in general relativity is the instantaneously circular orbit assumption. This approximation has been used extensively, from the calculation of innermost circular orbits to the construction of initial data for numerical relativity calculations. While this assumption is inconsistent with generic general relativistic astrophysical inspiral phenomena where the dissipative effects of gravitational radiation cause the separation of the compact objects to decrease in time, it is usually argued that the timescale of this dissipation is much longer than the orbital timescale so that the approximation of circular orbits is valid. Here, we quantitatively analyze this approximation using a post-Newtonian approach that includes terms up to order ({Gm/(rc^2)})^{9/2} for non-spinning particles. By calculating the evolution of equal mass black hole / black hole binary systems starting with circular orbit configurations and comparing them to the more astrophysically relevant quasicircular solutions, we show that a minimum initial separation corresponding to at least 6 (3.5) orbits before plunge is required in order to bound the detection event loss rate in gravitational wave detectors to < 5% (20%). In addition, we show that the detection event loss rate is > 95% for a range of initial separations that include all modern calculations of the innermost circular orbit (ICO).

Abstract:
I discuss the accuracy requirements on numerical relativity calculations of inspiraling compact object binaries whose extracted gravitational waveforms are to be used as templates for matched filtering signal extraction and physical parameter estimation in modern interferometric gravitational wave detectors. Using a post-Newtonian point particle model for the pre-merger phase of the binary inspiral, I calculate the maximum allowable errors for the mass and relative velocity and positions of the binary during numerical simulations of the binary inspiral. These maximum allowable errors are compared to the errors of state-of-the-art numerical simulations of multiple-orbit binary neutron star calculations in full general relativity, and are found to be smaller by several orders of magnitude. A post-Newtonian model for the error of these numerical simulations suggests that adaptive mesh refinement coupled with second order accurate finite difference codes will {\it not} be able to robustly obtain the accuracy required for reliable gravitational wave extraction on Terabyte-scale computers. I conclude that higher order methods (higher order finite difference methods and/or spectral methods) combined with adaptive mesh refinement and/or multipatch technology will be needed for robustly accurate gravitational wave extraction from numerical relativity calculations of binary coalescence scenarios.

Abstract:
A redox active medicinal plant and L-leucine mixture (HLM) was investigated in subjects with established osteoarthritis of the knee in a multi-center, rando- m-ized, placebo-controlled, double-blind clinical trial. A total of 96 subjects with osteoarthritis were enrolled and randomized to either placebo (n = 38) or HLM treatment group (n = 38). The HLM group re- ceived a combination of Uncaria tomentosa (300 mg), Boswellia serrata (200 mg), Lepidium meyenii (1000 mg) and L-Leucine (700 mg) given as 3 capsules once a day. The placebo group received matching capsules with carboxymethylcellulose. The treatment period was 8 weeks, with assessments made at days 7, 14, 28 and 56. The primary outcome was reduction in total WOMAC score. VAS pain, tolerability, investigator assessments, use of rescue medication (acetominophen), and safety assessments of vital signs and laboratory assessments were included. Subject randomization was effective for age, gender and disease severity. In the placebo group 32/38 subjects completed the trial and for HLM 35/38. WOMAC scores (pain, stiffness, physical performance and total) steadily declined over the course of the 8 week study in both groups, but the magnitude was significantly greater for HLM (P < 0.05). Total WOMAC was reduced 46.5% for HLM and 25.4 % for placebo. VAS pain was reduced 21.8% in the placebo group (p < 0.002) but the changes were significantly greater (37.8% p < 0.03) with HLM treatment. Investigator’s global assessment rating of good-excellent was 24/35 (69%) for HLM and 14/32 (44%) for placebo (P = 0.05). Rescue medication consumption and tolerability were comparable for HLM and placebo. No safety issues were evident with either group. As expected a placebo effect was observed, nevertheless HLM was clearly more effective in relieving the symptoms of osteoarthritis. This HLM represents a safe and effective new approach to the management of osteoarthritis symptoms.

Abstract:
The convergence properties of numerical Regge calculus as an approximation to continuum vacuum General Relativity is studied, both analytically and numerically. The Regge equations are evaluated on continuum spacetimes by assigning squared geodesic distances in the continuum manifold to the squared edge lengths in the simplicial manifold. It is found analytically that, individually, the Regge equations converge to zero as the second power of the lattice spacing, but that an average over local Regge equations converges to zero as (at the very least) the third power of the lattice spacing. Numerical studies using analytic solutions to the Einstein equations show that these averages actually converge to zero as the fourth power of the lattice spacing.

Abstract:
We present two Suzaku observations of the Galactic center microquasar 1E 1740.7-2942 separated by approximately 700 days. The source was observed on both occasions after a transition to the spectrally hard state. Significant emission from 1E 1740.7-2942 is detected out to an energy of 300 keV, with no spectral break or turnover evident in the data. We tentatively measure a lower limit to the cut-off energy of ~ 380 keV. The spectra are found to be consistent with a Comptonized corona on both occasions, where the high energy emission is consistent with a hard power-law (\Gamma ~ 1.8) with a significant contribution from an accretion disc with a temperature of ~ 0.4 keV at soft X-ray energies. The measured value for the inner radius of the accretion disc is found to be inconsistent with the picture whereby the disc is truncated at large radii in the low-hard state and instead favours a radius close to the ISCO (R_in ~ 10 - 20 R_g).

Abstract:
We present the results of a 40 ks Chandra observation of the quiescent stellar mass black hole GS 1354-64. A total of 266 net counts are detected at the position of this system. The resulting spectrum is found to be consistent with the spectra of previously observed quiescent black holes, i.e., a power-law with a photon index of \Gamma ~ 2. The inferred luminosity in the 0.5 -- 10 keV band is found to lie in the range 0.5 - 6.5 x 10^{34} erg/s, where the uncertainty in the distance is the dominant source of this large luminosity range. Nonetheless, this luminosity is over an order of magnitude greater than that expected from the known distribution of quiescent stellar mass black hole luminosities and makes GS 1354-64 the only known stellar mass black hole to disagree with this relation. This observation suggests the possibility of significant accretion persisting in the quiescent state.